JP2008243393A - Forming method of solid polymer electrolyte membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a forming method a solid polymer electrolyte membrane for a fuel cell by radiation graft polymerization, wherein deterioration in the membrane is reduced, since a graft membrane having a high graft rate can be obtained only by radiating a small amount of radial rays. <P>SOLUTION: In the forming method of the solid polymer electrolyte membrane, when forming it by applying the graft polymerization of a radically reactive monomer to a fluororesin membrane irradiated with radial rays, the graft polymerization is carried out in an aprotic polar solvent. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a solid polymer electrolyte membrane, and more particularly to a solid polymer electrolyte membrane suitable for a fuel cell.

  A fuel cell using a solid polymer electrolyte type ion exchange membrane is expected to be widely put into practical use as a power source for electric vehicles or a simple auxiliary power source because of its low operating temperature of 100 ° C. or less and high energy density. In this fuel cell, there are important elemental technologies relating to a solid polymer electrolyte membrane, a platinum-based catalyst, a gas diffusion electrode, and a polymer electrolyte membrane-electrode assembly. However, among these, development of a solid polymer electrolyte membrane having good characteristics as a fuel cell is one of the most important technologies.

  In a solid polymer electrolyte membrane fuel cell, gas diffusion electrodes are combined on both surfaces of the electrolyte membrane, and the membrane and the electrode are substantially integrated. For this reason, the electrolyte membrane acts as an electrolyte for conducting protons, and also has a role as a diaphragm for preventing hydrogen or methanol as a fuel and an oxidizing agent from being directly mixed even under pressure. Such an electrolyte membrane is required to have a high proton transfer rate and high ion exchange capacity as an electrolyte, and a constant and high water retention in order to keep electric resistance low. On the other hand, because of its role as a diaphragm, the mechanical strength of the membrane is large, its dimensional stability is excellent, its chemical stability with respect to long-term use is excellent, and hydrogen gas or methanol as fuel In addition, it is required that the gas does not have excessive permeability to oxygen gas that is an oxidizing agent.

  In early solid polymer electrolyte membrane fuel cells, ion exchange membranes of hydrocarbon resins produced by copolymerization of styrene and divinylbenzene were used as electrolyte membranes. However, this electrolyte membrane is not very practical because of its very low durability. Therefore, the fluororesin-based perfluorosulfonic acid membrane “Nafion (registered trademark of DuPont)” developed by DuPont is generally used thereafter. Has been.

  However, conventional fluororesin-based electrolyte membranes such as “Nafion” are excellent in chemical durability and stability, but there are problems of many manufacturing processes and high cost, which is a major obstacle to practical use. It has become. For this reason, efforts have been made to develop low-cost electrolyte membranes that replace the “Nafion” and the like. For example, a method of producing a solid polymer electrolyte membrane by introducing a sulfone group into a fluororesin membrane by a radiation graft polymerization method has been proposed (Japanese Patent Laid-Open No. 2001-348439 (Patent Document 1)). JP 2002-313364 A (Patent Document 2), JP-A 2003-82129 (Patent Document 3)).

  By using radiation graft polymerization in this way, it is possible to obtain an electrolyte membrane having a proton conductivity equal to or exceeding that of “Nafion” and a methanol permeability of “Nafion” or less. However, in order to provide high ionic conductivity, it is essential to increase the number of ion exchange groups. For this reason, it is necessary to prepare a film having a high graft ratio by irradiating a large amount of radiation. However, as the dose increases, the film deteriorates and the mechanical strength decreases.

JP 2001-348439 A JP 2002-313364 A JP 2003-82129 A

  The present invention has been made in view of the above circumstances, and in the production of a solid polymer electrolyte membrane by a radiation graft polymerization method, the radiation dose to be irradiated can be reduced and a solid polymer electrolyte membrane having a high graft ratio can be produced. It aims to provide a possible method.

  As a result of intensive studies to achieve the above object, the present inventors have mixed an aprotic polar solvent with a radical reactive monomer at the time of radiation graft polymerization, and carried out graft polymerization in the aprotic polar solvent. Thus, since the graft ratio was remarkably improved, it was found that a solid polymer electrolyte membrane having a high graft ratio could be obtained even at a low dose, and the present invention was made.

Accordingly, the present invention provides the following method for producing a solid polymer electrolyte membrane.
Claim 1:
A method for producing a solid polymer electrolyte membrane by graft polymerization of a radical reactive monomer onto a fluororesin membrane irradiated with radiation, characterized in that the graft polymerization is carried out in an aprotic polar solvent. Manufacturing method.
Claim 2:
2. The method for producing a solid polymer electrolyte membrane according to claim 1, wherein the aprotic polar solvent is acetone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide or N-methylpyrrolidone. .
Claim 3:
The fluororesin is selected from a tetrafluoroethylene polymer, a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, an ethylene-tetrafluoroethylene copolymer, and a vinylidene fluoride polymer. The method for producing a solid polymer electrolyte membrane according to claim 1 or 2, wherein at least one kind is used.
Claim 4:
The method for producing a solid polymer electrolyte membrane according to any one of claims 1 to 3, wherein the radical-reactive monomer contains at least one selected from styrene, trifluorostyrene, and derivatives thereof.

  In the method for producing a solid polymer electrolyte membrane by radiation graft polymerization of the present invention, only a slight amount of radiation is irradiated. Since a graft membrane having a high graft ratio is obtained, it is suitable as a method for producing a solid polymer electrolyte membrane for a fuel cell with little membrane deterioration.

  In the present invention, the solid polymer electrolyte membrane is produced by graft polymerization of a radical reactive monomer to a fluororesin membrane irradiated with radiation, and this graft polymerization is performed in an aprotic polar solvent.

  Here, as the fluororesin used, tetrafluoroethylene polymer (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene -Fluororesin such as tetrafluoroethylene copolymer (ETFE) and vinylidene fluoride polymer (PVDF) is exemplified, and one of these can be used alone or in combination of two or more.

  In this case, the film thickness of the fluororesin film is not particularly limited, but is preferably 10 to 100 μm, particularly preferably 10 to 50 μm.

  The fluororesin film is irradiated with radiation in order to graft polymerize the radical reactive monomer. Examples of the radiation to be irradiated in the present invention include γ-rays, X-rays, electron beams, ion beams, ultraviolet rays and the like, but γ-rays and electron beams are preferable because of the ease of radical generation.

  The absorbed dose of radiation is preferably 1 kGy or more, particularly 1 to 100 kGy, particularly 1 to 50 kGy, and if it is less than 1 kGy, the amount of radical generation is small and grafting may be difficult. In some cases, the mechanical strength of the resulting electrolyte membrane may decrease.

  Further, the irradiation with radiation is preferably performed in an inert gas atmosphere such as helium, nitrogen, and argon gas, and the oxygen concentration in the gas is preferably 100 ppm or less, more preferably 50 ppm or less, but it is not necessarily in the absence of oxygen. There is no need to do it.

  A radical reactive monomer is graft-polymerized on the fluororesin film irradiated with radiation. Radiation graft polymerization is a method in which a radical is generated by irradiating a fluororesin film with radiation, and a radical reactive monomer is grafted using the radical as a grafting point. In this case, the grafting method using radiation includes a fluororesin. Radiation is applied to the main chain of the membrane in advance to generate radicals that will be the starting point of grafting, and then the pre-irradiation method in which the fluororesin film is brought into contact with the monomer to carry out the graft reaction, In the present invention, any method can be adopted.

  In the present invention, the radical-reactive monomer that is graft-polymerized by irradiating the fluororesin film with radiation contains at least one radical-reactive group such as alkenyl group (for example, vinyl group), acrylic group, and methacryl group in the molecule. Although it is a monomer which has, it is preferable to contain at least 1 sort (s) chosen from a styrene monofunctional monomer, especially styrene, trifluorostyrene, or derivatives thereof. Specific examples include substituted styrene derivatives such as styrene, α-methylstyrene, sodium styrenesulfonate, and trifluorostyrene. These radical reactive monomers may be used alone or in combination of two or more.

  Furthermore, in the present invention, an aprotic polar solvent is used during graft polymerization. As the aprotic polar solvent, those that uniformly dissolve the radical-reactive monomer are preferable, and examples thereof include acetone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and the like. . The aprotic polar solvent may be used alone or in combination of two or more. In addition, a solvent other than the aprotic polar solvent may be mixed and used as long as the effects of the present invention are not impaired. In addition, it is preferable that the usage-amount of a solvent is 50-900 mass parts with respect to 100 mass parts of radical reactive monomers, especially 100-300 mass parts.

  In the present invention, the graft polymerization is preferably performed in an inert gas atmosphere such as nitrogen or argon, and the oxygen concentration is preferably 5% by volume or less. The reaction conditions for graft polymerization are preferably 0 to 100 ° C., particularly 40 to 80 ° C., for 1 to 40 hours, particularly 4 to 20 hours.

  Here, the amount of the radical reactive monomer grafted onto the fluororesin film irradiated with radiation is 100 to 10,000 parts by mass, particularly 400 to 2,000 parts by mass of the radical reactive monomer with respect to 100 parts by mass of the fluororesin film. It is preferable to use parts by mass. If the amount of the radical reactive monomer is too small, the contact with the fluororesin film may be insufficient. If the amount is too large, the radical reactive monomer may not be used efficiently. Moreover, when graft-polymerizing a radical reactive monomer to a fluororesin film | membrane, you may use suitably initiators, such as azobisisobutyronitrile, in the range which does not impair the objective of this invention.

  As described above, an ion conductive group is usually introduced into a graft chain formed by grafting a radical reactive monomer onto a fluororesin film irradiated with radiation and then grafting the radical reactive monomer. . Examples of the ion conductive group include a sulfonic acid group and the like. Sulfonation for introducing the sulfonic acid group can be performed by a known method. For example, chlorosulfonic acid is immersed in chlorosulfonic acid-dichloroethane. A method of introducing a group and then sulfonating it by immersion in pure water and hydrolysis can be employed.

  The solid polymer electrolyte membrane thus obtained can be suitably used for a fuel cell.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example.

[Examples 1-3, Comparative Examples 1-3]
An ethylene-tetrafluoroethylene copolymer (ETFE, manufactured by Norton) having a length of 5 cm, a width of 6 cm, and a thickness of 25 μm was irradiated with an electron beam of 15 kGy at room temperature in a nitrogen atmosphere (acceleration voltage: 100 kV). In addition, N, N-dimethylformamide (DMF) [Example 1], acetone [Example 2], dimethyl sulfoxide (DMSO) [Example 3], toluene [Comparative Example 1], methanol [Comparative] Example 2] and hexane [Comparative Example 3] were added in a mass ratio of toluene: solvent = 1: 3 to obtain a reaction solution.

  The reaction solution was placed in a 60 ml test tube equipped with a three-way cock and nitrogen bubbling was performed for 15 min. Then, the irradiated film was immersed and graft polymerization was performed at room temperature for 16 hr. The extracted film was washed with xylene and then dried under reduced pressure at 100 ° C. for 2 hours.

From the change in the mass of the membrane before and after the graft polymerization, the graft ratio was determined by the following formula. Table 1 shows the graft ratio of the membrane obtained using each solvent.
Graft rate [%] = (Membrane mass after graft polymerization−Membrane mass before graft polymerization) / Membrane mass before graft polymerization × 100

Claims (4)

  A method for producing a solid polymer electrolyte membrane by graft polymerization of a radical reactive monomer onto a fluororesin membrane irradiated with radiation, characterized in that the graft polymerization is carried out in an aprotic polar solvent. Manufacturing method.   2. The method for producing a solid polymer electrolyte membrane according to claim 1, wherein the aprotic polar solvent is acetone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide or N-methylpyrrolidone. .   The fluororesin is selected from a tetrafluoroethylene polymer, a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, an ethylene-tetrafluoroethylene copolymer, and a vinylidene fluoride polymer. The method for producing a solid polymer electrolyte membrane according to claim 1 or 2, wherein at least one kind is used.   The method for producing a solid polymer electrolyte membrane according to any one of claims 1 to 3, wherein the radical-reactive monomer contains at least one selected from styrene, trifluorostyrene, and derivatives thereof.