JPH09194609A - Ion-exchange membrane and its preparation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preparing an ion-exchange membrane which can prevent the ion-exchange membrane from breaking originated by change in repeating of operating condition during operation of an apparatus by using a specified method. SOLUTION: A drawn porous membrane is impregnated with a polymer dissolved in a solvent and, after the polymer is sticked on the porous membrane by drying it, an ion exchange group is introduced on the polymer. In another way, after the drawn porous membrane is impregnated with a polymer and a crosslinking agent dissolved in a solvent, the ion exchange group is introduced on the polymer. As the drawn porous membrane, a polytetrafluoroethylene membrane is cited. Pref. membrane thickness of the drawn porous membrane is 10-200μm and pref. mean pore diameter is 0.1-10μm and pref. porosity is 50-95%. As the polymer, e.g. a polystyrene resin, a polyimide resin and a polyamide resin are cited. This ion-exchange membrane is used in the fields of solid polymer type fuel cells, water electrolytic apparatus, etc.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an ion exchange membrane used in a polymer electrolyte fuel cell, a water electrolysis device, and the like.
The present invention relates to an ion exchange membrane that is free from damages due to repeated changes in the operating conditions of an apparatus and a method for producing the same.

[0002]

2. Description of the Related Art Ion exchange membranes used for polymer electrolyte fuel cells and water electrolysis devices are required to have improved energy efficiency, and for that purpose, it is necessary to reduce the membrane resistance of the ion exchange membrane. Therefore, while reducing the film thickness,
Attempts have been made to increase the number of ion exchange groups per gram of resin. However, as the film thickness becomes thinner, the strength will inevitably decrease.Therefore, when the ion-exchange membrane is installed in a polymer electrolyte fuel cell or a water electrolysis device, it breaks or the pressure difference between both sides of the film causes the film to burst. Or the sealing portion around the film may be torn. In order to prevent such damage, Japanese Patent Publication No.
57693 proposes a method of embedding an ion exchange resin in a woven fabric. Further, Japanese Patent Application Laid-Open No. 6-29032 proposes a method of using a stretched porous film such as a fluororesin as a reinforcing material as a film capable of expanding and contracting as the ion exchange resin swells and contracts.

[0003]

In the conventional ion exchange membrane using a woven cloth or the like as a reinforcing material, peeling may occur at the interface between the fiber of the woven cloth and the ion exchange resin, and as a result, the ion exchange resin. There was a problem that the ion-exchange membrane was punctured due to the falling off of. The cause is considered as follows. The ion exchange resin causes swelling and contraction depending on the change in water content. On the other hand, the woven fabric used as a reinforcing material for the ion-exchange membrane has a function of suppressing the swelling and shrinkage of the ion-exchange resin.
Stress is applied to the interface between the woven fabric fibers and the ion exchange resin. As a result, in a device such as a water electrolysis device and a polymer electrolyte fuel cell in which the operating conditions (output, etc.) repeatedly fluctuate, it is considered that the interface is separated due to the repeated generation of the stress. On the other hand, since the ion exchange resin has a hydrophilic group and the porous film such as a fluororesin is hydrophobic, it is difficult for the two to adhere to each other, which often causes defects such as pinholes. .

[0004]

The present inventors have found that even if the water content of the ion exchange resin is repeatedly changed, it is not damaged, and the ion exchange resin and the porous membrane such as a fluororesin adhere to each other, and The present invention has been completed as a result of continuing studies to develop an ion exchange membrane in which holes are less likely to be formed. The gist of the present invention is to impregnate at least the pores of a porous film such as a fluororesin produced by stretching with a polymer dissolved in a solvent and dry it to attach it to the porous film, and then introduce an ion exchange group. And a method for producing an ion exchange membrane, and an ion exchange membrane produced by the method.

An ion exchange membrane produced by the production method of the present invention comprising a porous membrane produced by stretching and an ion exchange resin contained in at least the pores of the porous membrane is a repetitive operating condition during the operation of the apparatus. It is possible to prevent the ion exchange membrane from being damaged due to a change or the like. The reason for this is not clear, but it is considered as follows. In the production method of the present invention, when a porous film produced by biaxial stretching is used as the porous film, the porous film has a three-dimensional network structure further developed, and therefore is included in the porous film and at least the pores thereof. The ion exchange membrane composed of the ion exchange resin thus formed can be expanded and contracted to a greater extent according to the swelling and contraction of the ion exchange resin. Therefore, it is considered that peeling at the interface between the ion exchange resin and the porous membrane is more difficult to occur, and the effect of preventing damage to the ion exchange membrane is increased.

Further, in the present invention, the use of a hydrophobic polymer as in the case of the porous film allows the polymer to sufficiently blend with the porous film, so that the polymer can be adhered to the pores of the porous film without gaps. . Further, thereafter, by introducing an ion exchange group into the polymer, it becomes possible to produce an ion exchange membrane with few pinholes.

In another embodiment of the present invention, a cross-linking agent is added to the polymer solution and impregnated into the porous membrane, and then the polymer is cross-linked in the pores of the porous membrane. By this method, it is considered that the polymer is densely fixed in the pores of the porous membrane, and therefore even if a large number of ion exchange groups are subsequently introduced, the polymer does not fall off.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The porous membrane used in the present invention is
It is produced as follows. A porous film used in the present invention having a three-dimensional network structure by stretching a fluororesin or other resin at least uniaxially at a temperature equal to or lower than its crystalline melting point, and then heating it to a crystalline melting point or higher in the stretched state. And Examples of the fluororesin include polytetrafluoroethylene and the like, and examples of the other resins include polypropylene and polyethylene. The above resin is
The molecular weight thereof is preferably in the range of 100,000 to 10,000,000. Porous membranes are generally hydrophobic. The temperature at which the above resin is stretched varies depending on the type of resin, but is generally preferably below the crystal melting point. The preferred thickness of the porous film stretched by the method of the present invention is 10 to 200 μm, the preferred average pore size is 0.1 to 10 μm, and the preferred porosity is 50 to 95%.

In the method of the present invention, at least the pores of the porous membrane are impregnated with a solution of a hydrophobic polymer similar to that of the porous membrane, and then ions such as --SO ₃ H, --N ⁺ H ₃ or --COOH are added. An ion exchange membrane can be prepared by introducing an exchange group and then removing the solvent by evaporation. An ion exchange group may be introduced after the solvent is removed by evaporation. Examples of the hydrophobic polymer include polystyrene resin, polyimide resin, and polyamide resin. Its molecular weight is preferably in the range of 10,000 to 5,000,000.

In the present invention, conventionally known solvents such as chloroform, benzene or pyrrolidone, and mixed solutions thereof can be used as the solvent for dissolving the hydrophobic polymer. The concentration of the polymer solution is
1-10% is desirable. The temperature at which the polymer solution is impregnated into the stretched porous membrane is preferably in the range of room temperature to 120 ° C, and the impregnation time is preferably 5 minutes to 7 days.

In the ion exchange membrane of the present invention, the amount of the polymer may be 100 to 900 parts by weight based on 100 parts by weight of the porous membrane.

The ion-exchange group is introduced, for example, as follows. The polymer solution is applied to the porous membrane, the solvent is evaporated, and the polymer is filled in the pores of the porous membrane. Next, this membrane is immersed in fuming sulfuric acid to sulfonate the -CH group. The amount of ion exchange groups is 0.5 to 5 per 1 g of ion exchange membrane.
may be meq. The temperature for drying the solvent in which the polymer is dissolved after the impregnation can be changed depending on the solvent used and the mixed solvent, but in general, room temperature (25 ° C) to 120 ° C is preferable, and the time is Generally, 10 minutes to 2 weeks is preferable. The pressure for drying the solvent can be normal pressure (atmospheric pressure) or reduced pressure (760 mmH
g-10 ⁻³ mmHg).

In another method of the present invention, a cross-linking agent is added to a solution of a polymer such as polystyrene resin, polyimide resin or polyamide resin to impregnate at least the pores of the porous membrane, and then heated. After promoting cross-linking of the polymer, the cross-linked polymer is treated with --SO ₃
H, can be introduced ion exchange group such as -N ⁺ H ₃ or -COOH. As the cross-linking agent, benzoyl peroxide, cumene hydroperoxide, ammonium persulfate,
A conventionally known cross-linking agent such as azobisisobutyronitrile can be used. The amount of the crosslinking agent added to the polymer solution is preferably in the range of 0.1 to 20 parts by weight based on 100 parts by weight of the polymer. The heating temperature for promoting the crosslinking of the polymer is preferably 50 to 100 ° C., and the heating time is preferably 1 hour to 7 days.

The ion exchange membrane produced by the method of the present invention is then preferably washed with pure water or the like to remove excess polymer.

Particularly when the polymer with which the porous membrane is impregnated is polystyrene, polyimide or polyamide, concentrated sulfuric acid or the like can be used in the step of introducing the ion exchange group,
Therefore, the —SO ₃ H group can be easily introduced.
In addition, when the stretched porous membrane is PTFE,
Since it is excellent in physical and chemical properties such as flexibility and chemical resistance, it is possible to prevent the deterioration of the porous membrane even when the ion exchange group is introduced.

[0016]

Example 1 A porous film (average pore size 1 μm, film thickness 50 μm, porosity 90%) produced by stretching polytetrafluoroethylene was added to a benzene solution of polystyrene (molecular weight: 250,000 to 300,000) (10 weight parts). %) (45 ° C., 10 minutes) and dried at room temperature (25 ° C.). Next, this film was immersed in fuming sulfuric acid at room temperature for 2 days to introduce —SO ₃ H groups into polystyrene. Then, the ion exchange membrane was washed with pure water to remove excess polymer.

Example 2 Polystyrene (Molecular weight: 250,000 to 300,000)
0.1 g of benzoyl peroxide was added to 20 mL of the benzene solution of (0) (10% by weight), and this was impregnated into the same porous membrane as in Example 1 (45 ° C., 10 minutes). After that, it was dried at room temperature and placed in a constant temperature bath at 100 ° C. for 1 hour to carry out a crosslinking reaction. Next, this film was immersed in fuming sulfuric acid at room temperature for 2 days to introduce —SO ₃ H groups into polystyrene. Then, it was washed with pure water to remove the excessively attached polymer.

Example 3 The same porous membrane as in Example 1 was impregnated with a polyvinyl alcohol solution, and then hydrophilized by irradiation with an electron beam of 6 Mrad. After air-drying it, a mixture of soluble polyimide (molecular weight: 20,000) N-methylpyrrolidone and water (N-methylpyrrolidone: water = 1: 1)
(10% by weight) was prepared and impregnated (100 ° C., 2 hours). Then, it was put in a constant temperature bath (100 ° C.) for 3 hours to evaporate the solvent. Next, this film was immersed in concentrated sulfuric acid at 80 ° C. for 2 days to introduce —SO ₃ H groups into the side chains of the polyimide.
Then, it was washed with pure water to remove excess resin (polyimide).

Example 4 The same porous membrane as in Example 1 was impregnated with a polyvinyl alcohol solution, hydrophilized by irradiation with an electron beam of 6 Mrad, and then naturally dried. Next, N of polyamic acid (molecular weight: 50,000-80,000)
-Methylpyrrolidone solution (10% by weight) was prepared, and 20 mL of the polyamic acid solution was added with 0.1% benzoyl peroxide.
After g was added and the porous membrane was impregnated (100 ° C., 2 hours), the solvent was evaporated and a crosslinking reaction was carried out by placing it in a thermostat at 80 ° C. for 1 day. Then, this membrane was immersed in concentrated sulfuric acid at 80 ° C. for 2 days to form side chains of polyamic acid.
An SO ₃ H group was introduced. Then, it was washed with pure water to remove excess polymer.

Example 5 Polystyrene (Molecular weight: 250,000 to 300,000)
0.1 g of benzoyl peroxide was added to 20 mL of the benzene solution of (0) (10% by weight), and the same porous membrane as in Example 1 was impregnated with it (45 ° C., 10 minutes). Then, it was dried at room temperature (25 ° C.). An aqueous solution of polyacrylic acid (10% by weight) was applied onto this film, and the mixture was placed in a thermostat bath at 100 ° C. for 2 hours to carry out a crosslinking reaction, and at the same time, a —COOH group was introduced into the polymer. Then, it was washed with pure water to remove excess resin.

Example 6 Polystyrene (molecular weight: 2) was added to the same porous membrane as in Example 1.
The solution was impregnated with a benzene solution (50,000 to 300,000) (10% by weight) (45 ° C., 10 minutes). The membrane was swollen by immersing it in chloroether (condition: 60 ° C., 1 hour), and then allowed to stand in vapor of trimethylamine for 1 hour,
A (CH ₃ ) ₃ N group was introduced into the polymer. Then, it was washed with pure water to remove excess resin.

COMPARATIVE EXAMPLE 1 As a reinforcing woven fabric, a weft-woven 200 denier polytetrafluoroethylene multifilament was used as a weft, and a 200 denier polytetrafluoroethylene multifilament was used as a warp to be woven and woven into 25 mesh. Polystyrene (molecular weight: 25
It was impregnated with a benzene solution (10 to 30% by weight) (45 to 10 minutes) and dried at room temperature (25 ° C). Next, this was immersed in fuming sulfuric acid at room temperature for 2 days, and an —SO ₃ H group was introduced into polystyrene to obtain an ion exchange membrane. Then, wash this ion exchange membrane with pure water,
Excess polymer was removed.

Comparative Example 2 Polystyrene (Molecular weight 250,000 to 300,000)
0.1 g of benzoyl peroxide was added to 20 mL of a benzene solution (10% by weight) of Example 1 and impregnated with the same reinforcing woven fabric as in Comparative Example 1 (45 ° C., 10 minutes). Then, it was dried at room temperature and further put in a constant temperature bath at 100 ° C. for 1 hour to carry out a crosslinking reaction. Next, this was immersed in fuming sulfuric acid at room temperature for 2 days to introduce —SO ₃ H groups into polystyrene to obtain an ion exchange membrane. Then, this ion exchange membrane was washed with pure water to remove the excessively attached polymer.

Comparative Example 3 The same reinforcing woven fabric as in Comparative Example 1 was used, impregnated with a polyvinyl alcohol solution, and then subjected to a hydrophilic treatment by irradiating with an electron beam of 6 Mrad. Then, the above hydrophilized woven fabric was impregnated with a mixed solution of N-methylpyrrolidone and water in which a soluble polyimide (molecular weight: 20,000) was dissolved (N-methylpyrrolidone: water = 1: 1) (10% by weight). After being allowed to stand (100 ° C., 2 hours), it was placed in a constant temperature bath (100 ° C.) for 3 hours to evaporate the solvent. next,
This was immersed in concentrated sulfuric acid at 80 ° C. for 2 days to introduce a —SO ₃ H group into the side chain of polyimide to obtain an ion exchange membrane.
Then, the ion exchange membrane was washed with pure water to remove excess resin.

Comparative Example 4 As the reinforcing woven fabric, the same one as in Comparative Example 1 was used. After impregnating it with a polyvinyl alcohol solution, it was hydrophilized by irradiating it with an electron beam of 6 Mrad, and thereafter,
Naturally dried. Next, polyamic acid (molecular weight: 5
2,000-80,000) N-methylpyrrolidone solution (10% by weight) was prepared, and this polyamic acid solution 20 m
0.1 g of benzoyl peroxide was added to L to impregnate the above hydrophilized woven fabric (100 ° C., 2 hours), and then
The solvent was evaporated and the crosslinking reaction was carried out by putting it in a thermostat at 80 ° C. for 1 day. Then, add this to concentrated sulfuric acid 80
Soak for 2 days at ℃ to the side chain of polyamic acid --SO ₃ H
A group was introduced to form an ion exchange membrane. Then, the ion exchange membrane was washed with pure water to remove excess polymer.

Comparative Example 5 Polystyrene (Molecular weight 250,000 to 300,000)
0.1 g of benzoyl peroxide was added to 20 mL of the benzene solution (10% by weight) and impregnated with the same reinforcing woven fabric as in Comparative Example 1 (45 ° C., 10 minutes). Then, this is dried at room temperature (25 ° C.), a polyacrylic acid aqueous solution (10% by weight) is applied onto this woven fabric, and the mixture is further placed in a 100 ° C. thermostat for 2 hours to carry out a crosslinking reaction. A COOH group was introduced into the polymer to give an ion exchange membrane. afterwards,
The ion exchange membrane was washed with pure water to remove excess resin.

Comparative Example 6 A reinforcing woven fabric similar to that of Comparative Example 1 was coated with a benzene solution (10) of polystyrene (molecular weight 250,000 to 300,000).
Wt%) (45 ° C., 10 minutes). This was immersed in chloroether (condition: 60 ° C., 1 hour) to swell, and then allowed to stand in vapor of triethylamine for 1 hour,
A (CH ₃ ) ₃ N group was introduced into the polymer to form an ion exchange membrane. Then, the ion exchange membrane was washed with pure water to remove excess resin.

The porous membranes obtained in Examples 1 to 6 and Comparative Examples 1 to 6 were each subjected to the "swelling cycle test". As a result, no pinholes were found in the porous films of Examples 1 to 6 after the test, but 20 to 30% of pinholes were generated in the porous films of Comparative Examples 1 to 6. Further, the ion exchange capacities of the porous membranes obtained in Examples 1 to 6 and Comparative Examples 1 to 6 were measured, and the results are shown in the table below.

[0029]

[Table 1]

The ion exchange capacity was measured by adding the porous membrane to a 2N NaCl aqueous solution, adding an indicator, and then titrating the cation exchange membrane with NaOH and the anion exchange membrane with HCl. I investigated by doing.

The "swelling cycle test" is performed as follows. Cut the ion exchange membrane into a circle with a diameter of 6 cm, put an O-ring on the outer periphery (diameter 5 cm), sandwich it with a donut-shaped retainer from the top and bottom, and fix the retainer at 6 points with bolts / nuts, 90 ° C. After being immersed in pure water for 5 minutes, it is taken out and dried at 100 ° C. for 5 minutes. After repeating this immersion drying step 10 times, the presence or absence of holes due to the dropping of the ion exchange resin is visually observed, and the presence or absence of air leakage to the other surface when pressure is applied from one surface of the membrane. Observe
Evaluate the presence of pinholes.

[0032]

The ion exchange membrane of the present invention has the effect of preventing damage to the ion exchange membrane due to repeated swelling and contraction of the ion exchange resin that occurs during the operation of the apparatus to which it is attached. Therefore, it is effective when used in the fields of polymer electrolyte fuel cells and water electrolysis devices. Further, when a resin such as styrene is fixed on the porous membrane and then the ion exchange membrane is introduced, the amount of ion exchange groups per unit area of the membrane can be increased as compared with fixing the ion exchange resin.

Claims (6)

[Claims] 1. An ion exchange membrane characterized in that a stretched porous membrane is impregnated with a polymer dissolved in a solvent, dried to adhere the polymer to the porous membrane, and then an ion exchange group is introduced into the polymer. Production method. 2. The method according to claim 1, wherein a polymer dissolved in a solvent and a crosslinking agent are impregnated in the stretched porous membrane to crosslink the polymer, and then an ion exchange group is introduced into the polymer. . 3. An ion exchange membrane produced by the method according to claim 1. 4. The ion exchange membrane according to claim 3, wherein the stretched porous membrane is PTFE. 5. The ion exchange membrane according to claim 3, wherein the polymer is styrene resin, polyimide or polyamide. 6. The ion exchange membrane according to claim 3, wherein the stretched porous membrane is PTFE and the polymer is styrene resin.