JPH07155574A - Membrane for humidification and its production - Google Patents

Abstract

PURPOSE:To prepare a low-cost membrane for humidification not causing a water leak even after use over a long period of time and excellent in steam permeability by forming a polymer film by graft-polymerizing a monomer having a cation exchange group on a polymer base. CONSTITUTION:When a membrane for humidification made of a steam permeable polymer film is produced, the polymer film is formed by graft-polymerizing a monomer having a cation exchange group such as a carboxylate group, e.g. methacrylic acid on a polymer base such as polymethyl methacrylate. The objective low-cost membrane for humidification not causing a water leak even after use over a long period of time and excellent in steam permeability is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a humidifying membrane used in a natural evaporation humidifier and a method for producing the same.

[0002]

2. Description of the Related Art A method of humidifying air by using a humidifying film made of a water vapor permeable polymer film is widely used in a natural evaporation type humidifier because of its simple mechanism and high humidification efficiency. As the humidifying film, a hydrophobic porous polymer film made of a material such as polyethylene or polypropylene is generally used.

The principle of humidification using this humidifying membrane will be described with reference to FIG. 1. The humidifying membrane 1 is separated from the humidifying water 2, and the humidifying water 2 is stored on the primary side and the air 3 is kept constant on the secondary side. The water vapor 2a generated from the humidifying water 2 permeates the humidifying film 1 and moves to the air side. As a result, the dry air 3a is humidified as it moves in a certain direction to become wet air 3b. Next, as a specific configuration of a humidifier using this principle, for example, as shown in FIG. 2, a spiral tube 5 made of a humidifying film is arranged in a blower pipe 4, and in this, One example is that water for humidification is stored. By doing this, air 3 and water 2
It is possible to remarkably increase the contact area with, and as a result, a large amount of water vapor 2a can be supplied to the dry air 3a to efficiently generate the wet air 3b.

[0004]

As described above, the humidifier using the humidifying membrane has advantages in structure and humidifying efficiency, but on the other hand, when it is used for a long period of time, it is separated by the humidifying membrane. There is a problem that the existing water leaks to the air side. This is a problem caused by the above-mentioned hydrophobic porous polymer membrane. That is, this membrane has a large number of small holes, and water vapor is diffused from the small holes. Further, since it is hydrophobic, water does not pass through the small holes, and normally water leakage does not occur. However, generally, as water for humidification,
Tap water and well water are used. When the humidifier is used for a long period of time using this tap water, etc., impurities such as ions contained in tap water are concentrated, and this adheres to the hydrophobic porous polymer membrane and loses the hydrophobicity of the membrane. I will end up. as a result,
Water for humidification comes to leak from the hydrophobic porous polymer membrane.

As a means for solving this problem, there is a method of using a hydrophilic polymer film made of a material such as polyvinyl alcohol, polyether urethane, or cellulose acetate, instead of the hydrophobic porous polymer film. This hydrophilic polymer membrane has a mechanism of preventing water permeation and water vapor permeation, which is different from that of the hydrophobic porous polymer membrane, so that water leakage does not occur due to long-term use as described above. Is. However, this hydrophilic polymer membrane has a drawback that it has a low water vapor permeability and a low humidifying ability. Therefore, when this humidifying film is used, it is necessary to increase the evaporation area, which causes another problem that the humidifier becomes large.

On the other hand, in addition to the hydrophilic polymer membrane, there is a fluorine-based ion exchange membrane as a membrane having a function as a humidifying membrane. This membrane has excellent water vapor permeability and does not cause problems such as water leakage due to long-term use. However, this ion exchange membrane is higher in cost than the above-mentioned two types of humidifying membranes, and thus cannot be actually applied.

As described above, the conventional humidifying membrane has a problem of water leakage due to long-term use, a problem of water vapor permeability, and a problem of cost, and the advantages of the humidifier using the humidifying membrane can be fully utilized. Was not.

The present invention has been made in view of the above circumstances, and provides a low-cost humidifying membrane excellent in water vapor permeability, which does not cause water leakage even after long-term use, and a method for producing the same. Is its purpose.

[0009]

In order to achieve the above object, the present invention is a humidifying membrane comprising a water vapor permeable polymer membrane, wherein the polymer membrane has a cation exchange group in the molecule. A method for producing a moisturizing membrane comprising a water vapor permeable polymer membrane, wherein the moisturizing membrane having the first aspect is a method for producing a moisturizing membrane having a cation exchange group on a polymer base material. A method of manufacturing a moisturizing film for forming a molecular film is a second gist.

[0010]

In other words, the present inventor has conducted a series of studies centering on the application of ion exchange membranes other than fluorine in order to solve the above problems. As a result, when using a water vapor permeable polymer membrane having a cation exchange group in the molecule as a moisturizing membrane, it has excellent water vapor permeability as well as a fluorine-based ion exchange membrane, and tap water etc. We have found that water leakage does not occur even after long-term use. The present inventors have found that the polymer membrane having this cation exchange group in the molecule has a lower cost than that of a fluorine-based ion exchange membrane and can be put to practical use, and has reached the present invention. Furthermore, by applying an ordinary graft polymerization method to the production of the humidifying film of the present invention, it is possible to further reduce the cost of the humidifying film.

Next, the present invention will be described in detail.

The humidifying membrane of the present invention can be produced, for example, by graft-polymerizing a monomer having a cation exchange group in the molecule onto a polymer base material.

Examples of the polymer base material include polymethyl acrylate, polyethyl acrylate, polybutyl acrylate, polymethyl methacrylate, polybutyl methacrylate, polyacrylonitrile, polyethylene, polypropylene, polyisobutylene, polytetrafluoroethylene. , Polyvinyl chloride, polyvinyl alcohol, polyvinylpyrrolidone, cellulose, polydimethylsiloxane,
Polyamide etc. can be mentioned. Among these, it is preferable to use polyethylene which is inexpensive and has excellent moldability. In addition, these polymer base materials are
It may be crosslinked by addition of a crosslinking agent or the like.

The type of the cation exchange group is as follows:
Examples thereof include sulfonic acid and sulfonate group, carboxylic acid and carboxylate group, phosphoric acid and phosphate group, and acidic hydroxyl group and acidic hydroxyl group. Among these, the carboxylate groups represented by the following general formulas are preferable from the viewpoint of water vapor permeability, water absorption, moisture release and the like.

-COOM

In the above formula, M is an alkali metal. Among the carboxylate groups, the alkali metal is particularly preferably Na ⁺ or K ⁺ .

A monomer having a cation exchange group is used to introduce the cation exchange group into the polymer base material. For example, a vinyl monomer having a carboxyl group is used to introduce the carboxylate group into the polymer base material. Then, after the vinyl monomer is graft-polymerized on the polymer base material and neutralized with an aqueous solution of an alkali metal hydroxide, the carboxyl group becomes a carboxylate group. Methacrylic acid is preferably used as the vinyl monomer. Examples of alkali metal hydroxides include sodium hydroxide, potassium hydroxide, potassium chloride and the like.

Next, the graft polymerization using the monomer having a cation exchange group and the polymer base material is carried out, for example, as follows. That is, first, the polymer base material is formed into a film by hot pressing or the like. Then, the film-shaped polymer base material is irradiated with an electron beam using an electron accelerator under the conditions of 0.1 to 50 megarads, preferably 2 to 10 megarads. By this irradiation, radicals are generated in the polymer base material.

On the other hand, the above-mentioned monomer having a cation exchange group is dissolved in a solvent such as water or methanol to prepare a solution. The concentration at this time is appropriately determined depending on the kind of the monomer and the like, but is usually 10 to 80% by weight, preferably 20 to 40% by weight. Further, ferrous sulfate, ferrous chloride and the like can be added for the purpose of preventing homopolymerization.

Then, the polymer substrate irradiated with the electron beam is dipped in the above solution. By this immersion, the monomer having a cation exchange group is graft-polymerized on the polymer base material. Then, the produced graft polymer is washed with water, preferably distilled water, and then dried in air. The temperature of the water at this time is 15 ~ 90
C., preferably in the range of 25 to 70.degree. And it neutralizes using the aqueous solution of an alkali metal hydroxide. By doing so, a humidifying membrane having a cation exchange group in the molecule can be obtained.

In the humidifying membrane, the ratio of the monomers introduced by graft polymerization (grafting rate) is 10 to 1
The range of 00% is preferable, and the range of 20 to 80% is particularly preferable.
Is the range. That is, if it is less than 10%, the water vapor permeability tends to decrease, and conversely, if it exceeds 100%, the film strength tends to decrease when moisture is absorbed. This graft polymerization rate is calculated by the following formula (1). This graft ratio can be adjusted by changing the reaction time.

[0022]

[Equation 1]

As described above, the humidifying membrane composed of a polymer membrane having a cation exchange group in the molecule can be produced at a low cost by the graft polymerization method without using special equipment or equipment. This is one of the features of the present invention.

The thickness of the moisturizing film thus obtained is usually 0.1 to 500 μm, preferably 0.5 to 30.
It is set in the range of 0 μm. The water content (%) calculated by the following equation (2) is usually 10 to 250%, preferably 20 to 160%.

[0025]

[Equation 2]

The humidifying membrane of the present invention has a water vapor permeability coefficient of at least 5 to 200 g / m ² · hr · m.
Range of mHg, usually 10-180g / m ² · hr · mm
It is in the range of Hg. This range of water vapor permeability coefficient is a range sufficient for use as a humidifying membrane. The water vapor transmission coefficient is a value obtained by converting the amount of water vapor permeation of a membrane when pure water is used and a conditioned air is blown at a constant linear velocity into a unit membrane area, a unit time, and a unit vapor pressure. . Specifically, as shown in FIG. 1, pure water of 20 ° C. is supplied to the primary side and humidified air (20 ° C. x
10% RH) is blown at a linear velocity of 5 m / s, and it can be calculated by measuring the reduction amount of pure water on the primary side.

Although the graft polymerization method has been described as an example of the method for producing the polymer membrane having a cation exchange group in the molecule, the method is not limited to this but is shown below.
The manufacturing method of can also be applied to the manufacturing method of the humidifying membrane of the present invention. However, it is preferable to apply the graft polymerization method from the viewpoint of cost. An impregnation method in which a polymer substrate is impregnated with a substance having a cation exchange group. Soluble linear polymer electrolytes and binders are dissolved in a solvent and then the solvent is removed by evaporation. A polymerization method in which a vinyl monomer for introducing a cation exchange group, a cross-linking agent, a plasticizer, etc. are mixed and impregnated into a polymer base material to form a paste, which is then heated for polymerization. A method for polymerizing a vinyl polymer and a monomer having a cation exchange group.

When the humidifying membrane of the present invention is used in a humidifier, it is used as a membrane module having various shapes depending on the structure of the humidifier. For example, the spiral module, the flat membrane module, the hollow fiber module, the tubular module, and the plate type module which are formed in a spiral shape as described above can be mentioned.

Next, the humidifying membrane of the present invention can be used as a composite membrane by sticking a hydrophobic porous polymer membrane to the polymer membrane having the above cation exchange group. Examples of the hydrophobic porous polymer film include polyethylene,
Membranes made of polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polycarbonate, polyester, and fluororesin materials can be mentioned.

Examples of the attaching method at this time include a method of heating and melting the above-mentioned hydrophobic porous polymer film to fuse and a method of using an adhesive. From the viewpoint of water vapor permeability, it is preferable to use point bonding, which is not completely adhered and integrated, but is partially bonded at intervals of 5 to 10 mm.

Furthermore, the composite membrane and a material that allows water or water vapor to freely pass therethrough may be used in combination. Examples of such a material include woven fabrics and non-woven fabrics made of plant fibers, chemical fibers, metal fibers and the like. This compounding also includes methods such as fusion bonding and adhesion. In addition, as in the case of the sticking, as in the case of the above, the sticking is not complete sticking and integration, but point bonding, which partially joins at intervals of 5 to 10 mm, is preferable. By using such a composite film, the structural strength of the humidifying film is improved, the durability is excellent, and the life is long. Further, this composite membrane can also be used by molding it into the membrane module having various shapes as described above.

[0032]

INDUSTRIAL APPLICABILITY As described above, the humidifying membrane of the present invention is a humidifying membrane composed of a water vapor permeable polymer membrane having a cation exchange group in the molecule. Therefore, the cost of the membrane is lower than that of the fluorine-based ion exchange membrane, and the membrane has excellent water vapor permeability like the fluorine-based ion exchange membrane. Therefore, the humidifier in which this is incorporated can be reduced in cost, and at the same time, the humidifying ability can be improved. Further, even if the humidifier is operated for a long period of time using tap water or the like, water leakage does not occur, so that the life of the humidifier is extended. In addition, the graft polymerization method, which has a simple process and does not require a special device, can be applied to the production of the humidifying film of the present invention. Therefore, it is possible to further reduce the cost of the humidifier by using the humidifying film manufactured by this manufacturing method.

Next, examples will be described.

[0034]

[Examples 1 and 2] A polyethylene film having a thickness of 25 µm was prepared and irradiated with an electron beam of 10 megarads using an electron accelerator. On the other hand, 120 parts by weight of methacrylic acid (hereinafter abbreviated as "part") and 0.12 part of ferrous sulfate were dissolved in 160 parts of methanol. Then, this solution was heated to 73 ° C., and a polyethylene film irradiated with an electron beam was immersed in this heated solution for 15 minutes to perform graft polymerization. Then, this polyethylene film was washed with distilled water at 70 ° C. and then air-dried. The graft ratio at this time was 40%. Then, this film is divided into two, and Example 1 is used.
Was immersed in a potassium hydroxide solution (concentration: 30% by weight) and in Example 2 in a sodium hydroxide solution (concentration: 30% by weight) for 24 hours or more, respectively, to prepare a humidifying film.

[0035]

Example 3 A moisturizing film was prepared in the same manner as in Example 1. A 15 μm-thick polytetrafluoroethylene (average pore size: 5 μm) was fused to this film at 2 mm intervals to prepare a composite film.

[0036]

Example 4 A composite film was prepared in the same manner as in Example 3.
In addition to this, nylon mesh with a thickness of 200 μm (interval 1 m
m) was fused at 2 mm intervals to produce a composite film.

The moisture vapor transmission coefficients of the thus obtained humidifying membranes of Examples 1 to 4 were measured. That is, as shown in FIG. 1, humidifying water (distilled water at 20 ° C.) is supplied to the primary side, and humidified air (20 ° C. × 10%) is supplied to the secondary side across the humidifying membrane. RH) was blown. Then, the water vapor transmission coefficient when the linear velocity of the conditioned air was 5 m / s and 15 m / s was measured by the above-mentioned method. The results are shown in Table 1 below.

[0038]

[Table 1]

From Table 1 above, it can be seen that the humidifying membranes of Examples 1 to 4 have a high water vapor transmission coefficient. From this, it is clear that the humidifying membrane of the present invention has excellent water vapor permeability.

[0040]

[Embodiment 5] Using the humidifying membrane of Example 1 and tap water as the water for humidification, water vapor was added to the conditioned air at a linear velocity of 5 m / s for 1000 hours in the same manner as the above method. Supplied for hours. As a result, no adhesion of impurities was confirmed on the secondary side of the humidifying film, and no accident such as water leakage occurred.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a humidification principle of a humidifier using a humidifying film.

FIG. 2 is an explanatory diagram showing an example of a humidifier using a humidifying film.

Claims (4)

[Claims] 1. A humidifying film comprising a water vapor permeable polymer film, wherein the polymer film has a cation exchange group in the molecule. 2. The humidifying membrane according to claim 1, wherein the polymer membrane is a polymer membrane formed from a graft polymer of a monomer having a cation exchange group and a polymer base material. 3. The humidifying membrane according to claim 1, wherein the polymer membrane is a polymer membrane in which a polymer membrane having a cation exchange group in the molecule and a hydrophobic porous polymer membrane are adhered to each other. . 4. A method for producing a humidifying membrane comprising a water vapor permeable polymer membrane, wherein the polymer membrane is formed by graft polymerizing a monomer having a cation exchange group onto a polymer substrate. A method for producing a humidifying membrane, characterized by: