JP2008127534A - Method for producing functional membrane and method for producing electrolyte membrane for fuel battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To remarkably shorten the production time (graft polymerization time) of functional membranes being used in various applications, having high functionality together with gas barrier characteristics inherent in the polymer film substrate and being excellent in the dimensional change in dry and moist conditions and in tensile strength. <P>SOLUTION: The method for producing the functional membrane comprises an ion-irradiating process of irradiating a polymer film substrate with high energy heavy ions, to produce active species in the film substrate and a graft polymerization process of graft-polymerizing the monomer to the film substrate, after the ion-irradiating process, by adding a protonic polar solvent solution of one or more species of monomers selected from a group A consisting of monomers having a functional group or monomers able to be introduced with the functional group in a succeeding process. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a novel functional membrane using latent tracks of high energy heavy ions or ion perforation, and a method for producing an electrolyte membrane for a fuel cell excellent in gas barrier properties.

  More specifically, the present invention relates to a bioreactor imitating a living body, a reactor for biomass conversion obtained by immobilizing an enzyme, an ion exchange membrane excellent in ion conductivity and selectivity, a secondary battery and a fuel. The present invention relates to a method for producing a functional membrane excellent in dry / wet dimensional change and tensile strength in a short reaction time, which is suitable for ion exchange membranes for batteries, selective amino acid separation membranes utilizing electrodialysis, and the like.

  Furthermore, the present invention relates to a method for producing a solid polymer electrolyte membrane which is a polymer ion exchange membrane suitable for use in a fuel cell. In particular, the present invention is a solid polymer membrane suitable for a fuel cell, and has an excellent gas barrier property and an excellent ion exchange capacity, and a solid polymer electrolyte membrane excellent in dry / wet dimensional change and tensile strength in a short reaction time. It relates to a method of manufacturing.

  A fuel cell is one that converts the chemical energy of fuel directly into electric energy by electrochemically oxidizing fuel such as hydrogen or methanol in the cell, and has recently attracted attention as a clean electric energy supply source. Has been. In particular, a polymer electrolyte fuel cell using a proton conductive membrane as an electrolyte is expected as a power source for an electric vehicle because it has a high output density and can be operated at a low temperature.

  The basic structure of such a polymer electrolyte fuel cell is composed of an electrolyte membrane and a pair of gas diffusion electrodes having a catalyst layer bonded to both surfaces thereof, and a structure in which current collectors are arranged on both sides thereof It is made up of. Then, hydrogen or methanol as fuel is supplied to one gas diffusion electrode (anode), oxygen or air as oxidant is supplied to the other gas diffusion electrode (cathode), and an external load is applied between both gas diffusion electrodes. By connecting the circuit, it operates as a fuel cell. At this time, protons generated at the anode move to the cathode side through the electrolyte membrane, and react with oxygen at the cathode to generate water. Here, the electrolyte membrane functions as a proton transfer medium and a hydrogen gas or oxygen gas diaphragm. Therefore, the polymer electrolyte membrane for a fuel cell is required to have high gas conductivity as well as high proton conductivity, strength, and chemical stability.

  By the way, what is called a conventional functional film is that the functional group is randomly distributed throughout the film, or in the case of a labyrinth structure or mesh structure film having a functional group, the spatial distribution of functional groups and the density of functional groups There was a problem that control was impossible.

  That is, a solid polymer electrolyte membrane manufactured using a commercially available electrolyte membrane such as Nafion (trade name) or radiation graft polymerization has a hydrophilic cation exchange group uniformly distributed inside the membrane. Swelling due to water content occurs, and excessive crossover of hydrogen and methanol occurs to weaken the interaction force between molecules. Furthermore, although Gore and Tokuyama have attempted to fill a porous membrane having three-dimensionally continuous pores with extremely high porosity with ion exchange resin, ion exchange that does not participate in cation exchange. The presence of the resin also causes excessive swelling. Furthermore, although the porous base material to be used is limited to polytetrafluoroethylene and polyethylene that can be made porous, since these are insufficient in gas barrier properties that are originally required as an electrolyte membrane for fuel cells, the resulting solid polymer The characteristics of the electrolyte membrane are not sufficient in view of the required characteristics of the fuel cell.

Therefore, the present inventors provide a functional membrane having both high functionality and a gas barrier property inherent in a polymer film substrate and mechanical strength in Patent Document 1, and in particular, a polymer electrolyte membrane for a fuel cell. 10 ⁴ to 10 ¹⁴ high-energy heavy ions on a polymer film substrate containing non-conductive inorganic particles, for the purpose of providing a polymer electrolyte membrane having high proton conductivity and excellent gas barrier properties / Cm ² irradiation and adding one or more monomers selected from the group A which is a monomer having a functional functional group after the ion irradiation step of generating active species on the film substrate and the ion irradiation step Thus, an application for a method for producing a functional film comprising the film substrate and a graft polymerization step for graft polymerization of the monomer was filed.

JP 2006-233086 A

  The method for producing a functional membrane and a polymer electrolyte membrane for a fuel cell disclosed in Patent Document 1 is excellent as a method for producing a polymer electrolyte membrane excellent in high proton conductivity and gas barrier properties. Accordingly, there has been a demand for shortening the reaction time of the graft polymerization step of graft polymerizing the film substrate and the monomer while maintaining the dry and wet dimensional changes and the tensile strength.

  That is, in order to reduce energy loss in the fuel cell, the fuel membrane electrolyte membrane is required to have high proton conductivity, that is, high proton conductivity. Similar to general proton conductive membranes, the electrolyte membrane realized in Patent Document 1 also has a higher dimensional change rate (dry / wet dimensional change rate) during drying and moisture content and higher tensile strength as the proton conducting ability is increased. There was a tendency to be smaller than the substrate. It has been desired to develop a technology that has sufficient proton conductivity as an electrolyte membrane for fuel cells, minimizes the wet / dry dimensional change rate, and maintains the tensile strength of the substrate.

  In the examination of Patent Document 1 and the like, it was necessary to lengthen the graft polymerization time in order to graft a sufficient amount of sulfonic acid for proton conduction. When the grafting time was lengthened, the graft chain grew to the outside of the existence region (phenambra region) of the active species generated in a columnar shape, which led to a decrease in wet / wet dimensional change and a decrease in tensile strength.

  The present invention is used in various applications and has both high functionality and gas barrier properties inherent to polymer film substrates, and greatly increases the production time (graft polymerization time) of functional membranes with excellent wet / dry dimensional changes and tensile strength. The purpose is to shorten. In particular, the polymer electrolyte membranes that are optimal as fuel cell polymer electrolyte membranes have excellent proton conductivity and gas barrier properties, and in particular, drastically reduce the production time (graft polymerization time) of polymer electrolyte membranes with excellent wet / dry dimensional change and tensile strength. For the purpose.

  The inventors of the present invention irradiate polymer ions such as polytetrafluoroethylene (PTFE) with heavy ions of elements such as C, K, N, and He under specific conditions. The present inventors have found that the above problems can be solved by using a specific monomer solution when an active species is generated and the monomer solution is graft-polymerized using the active species, and the present invention has been achieved.

  That is, first, the present invention is an invention of a method for producing a functional film, wherein a polymer film substrate is irradiated with high energy heavy ions, and an ion irradiation step for generating active species on the film substrate; After the ion irradiation step, a protic polar solvent solution of one or more monomers selected from Group A, which is a monomer having a functional functional group or capable of introducing a functional functional group in a subsequent step, is added, A graft polymerization step of graft polymerizing the monomer and the monomer.

  By including a graft polymerization step of graft-polymerizing the film substrate and the monomer, a functional film having a functional group introduced only in a latent track damaged by ion irradiation can be obtained, and a protic polar solvent can be used. By using it, the graft reaction time is greatly shortened as compared with the case of using no solvent or an aprotic polar solvent.

  According to the present invention, a functional group can be imparted only by introducing a functional group into a latent track portion having a diameter of several hundreds of nanometers damaged by irradiation with high-energy heavy ions. It is possible to maintain the physical properties of and to control the position / spatial distribution of functional groups and the density of functional groups. Here, the physical properties of the polymer film substrate include gas barrier properties and dimensional stability.

  In the present invention, the ratio of one or more monomers selected from Group A, which is a monomer having the functional functional group or capable of introducing a functional functional group in a later step, and the protic polar solvent is wide. Selected from a range. Specifically, the ratio of one or more monomers selected from Group A and the protic polar solvent is preferably 20 to 90:80 to 10.

The protic polar solvent used in the present invention is a polar solvent having a proton donating property that dissociates and easily releases protons (H +). Specific examples include alcohols and carboxylic acids. Many protic solvents have relatively highly acidic hydrogen bonded to oxygen or nitrogen atoms. At the same time, oxygen or nitrogen also has a property of accepting protons (Lewis basicity) because it also has an unshared electron pair. Due to this property, the protic polar solvent is also a solvent that forms hydrogen bonds between solvent molecules. More specifically, methanol (CH ₃ OH), ethanol (CH ₃ CH ₂ OH), isopropanol (CH ₃ CH ₃ CHOH), acetic acid (CH ₃ COOH), and the like can be given. Among these protic polar solvents, methanol and / or isopropanol are preferably exemplified.

  In the present invention, one or more monomers selected from Group A, which are monomers having functional functional groups or capable of introducing functional functional groups in a later step, may be used alone for graft polymerization reaction. The monomer may be subjected to a graft polymerization reaction as a monomer mixture obtained by adding a monomer of group B as a crosslinking agent to another group A monomer. When used as a monomer mixture, a group A monomer with respect to 20 to 99 mol% of one or more monomers selected from the group A which has a functional functional group or is capable of introducing a functional functional group in a later step It is preferable to use a protic polar solvent solution containing a monomer mixture obtained by adding 1 to 80 mol% of a monomer consisting of group B as a crosslinking agent.

  As will be described later, in the present invention, the one or more monomers selected from the group A, which is a monomer having a polymer film substrate and a functional functional group or capable of introducing a functional functional group in a later step, Various types are used. Among them, the polymer film substrate is made of a nonpolar polymer material and has one or more selected from group A which is a monomer having a functional functional group or capable of introducing a functional functional group in a later step. Combinations in which the monomers are nonpolar monomers are preferred.

  Non-polar substrates include ethylene tetrafluoroethylene copolymer (ETFE), polypropylene (PP), polyethylene (PE), tetrafluoroethylene / hexafluoropropylene copolymer (PFA), polytetrafluoroethylene (PTFE), Preferred examples include polyvinylidene fluoride (PVDF) and polychlorofluoroethylene (CTFE). Preferred examples of the nonpolar monomer include vinyl toluene, acenaphthylene, butyl vinyl ether, 2-chloroethyl vinyl ether, cyclohexyl vinyl ether, ethyl vinyl ether, and p-1-butoxystyrene.

In the present invention, it is also preferable that the polymer film substrate contains non-conductive inorganic particles.
In the present invention, in the ion irradiation step, it is preferable that a latent track damaged by high energy heavy ion irradiation penetrates the film and a proton conduction path or the like is sufficiently formed.

  The ion species of high-energy heavy ions irradiated in the ion irradiation step are not particularly limited, and various ion species accelerated by a cyclotron or the like are used. Among these, irradiation with one or more heavy ions selected from O, Fe, and Ar allows these heavy ions to reach the inside of the polymer film substrate having a large film thickness to generate radicals.

  By using O, Fe, or Ar as the ionic element to be irradiated, the range of ions in the polymer film is more than doubled as compared with other elements such as Xe. By using O, Fe, and Ar as the ionic elements to be irradiated, an electrolyte membrane having a uniform film quality can be obtained by ion irradiation from one side even if the polymer film is thick, for example, about 150 μm thick.

In the present invention, the graft polymerization temperature is preferably 10 to 80 ° C.
When the latent track damaged by high energy heavy ion irradiation does not penetrate the film, it is preferable to open a through hole by etching. In this case, the present invention provides an etching process for chemically or thermally etching the generated irradiation damage after the ion irradiation process to form a through-hole in the film base, and the perforated film base thus obtained. In addition, by using active species remaining in the latent track damaged by ion irradiation or active species newly generated by irradiation with either radiation or plasma in a vacuum or inert gas atmosphere, And a graft polymerization step of graft-polymerizing one or more types of monomers selected from the group A which is a monomer having a functional group or capable of introducing a functional functional group in a subsequent step.

  According to the present invention, after the irradiation damage is formed on the polymer film substrate by high energy heavy ion irradiation, the irradiation damage is chemically or thermally etched to form a through hole in the film substrate. Functionality can be imparted by introducing functional groups only on the surface and perforated wall of the perforated film substrate, so that the physical properties of individual polymer film substrates can be maintained, and the position / spatial distribution of functional groups, The base density can be controlled, and the cylindrical, conical, drum-shaped, and funnel-shaped cross-sectional shapes can be controlled.

  When the active species remaining in the latent track portion is used, it is preferable to graft-polymerize the monomer only on the hole wall of the through hole having a pore diameter in the range of 1 to 250 nm. In addition, when using active species newly generated by irradiation with any one of gamma rays, electron beams, and plasma in the vacuum or inert gas atmosphere, the hole wall of the through hole having a pore diameter in the range of 1 nm to 5 μm It is preferable to graft-polymerize the monomer only on the surface of the film substrate. Here, in the graft polymerization step, either radiation or plasma can be pre-irradiated to post-graft the monomer. Alternatively, in the graft polymerization step, after the monomer is introduced into the film substrate, either radiation or plasma can be irradiated for simultaneous graft polymerization.

As the polymer film substrate used in the present invention, those having an oxygen permeability coefficient at room temperature of 10.0 [cc * mm / (m ² * day * atm)] or less are excellent in gas barrier properties, and high It is preferable because the original performance of the molecular film substrate can be exhibited.

  When the polymer film substrate and at least one monomer selected from Group A are composed of the same element, the graft chain does not penetrate into the polymer film substrate during graft polymerization, which is preferable. For example, when the polymer film substrate is composed of a hydrocarbon polymer and one or more monomers selected from Group A are composed of a hydrocarbon monomer, or the polymer film substrate is composed of a fluorocarbon polymer. And one or more monomers selected from Group A include a fluorocarbon monomer.

  In the present invention, in the graft polymerization step, one or more monomers selected from Group C which is a functional monomer having a molecular weight of 200 or more can be added. A functional monomer having a molecular weight of 200 or more hardly penetrates into a polymer film substrate during graft polymerization, and a functional group can be introduced only into a latent track portion.

  In the present invention, in the graft polymerization step, one or more monomers selected from Group D, which is a monomer having a functional functional group that is difficult to graft polymerize, can be added.

  In the present invention, after the ion irradiation step, the film substrate is brought into contact with a gas such as methane or hydrogen to eliminate the active species, and then the film substrate is subjected to gamma rays, electrons, under a vacuum or an inert gas atmosphere. In carrying out the graft polymerization step, it is also preferable to generate active species again by irradiating either a line or plasma.

  In the present invention, after the ion irradiation step, the film base is brought into contact with a gas such as methane or hydrogen to disappear the active species, and then the gamma ray is applied to the film base in a vacuum or an inert gas atmosphere. It is also preferable to carry out the graft polymerization step by generating active species again by irradiating either electron beam or plasma.

  In the present invention, a polymer film substrate having a crosslinked structure can be used. However, when a polymer film substrate having a crosslinked structure is used, the polymer film substrate has a desired strength and physical / chemical stability. Can give sex. Various polymer materials can be used as the polymer film substrate. Of these, any of hydrocarbon-based, fluorine-based, and hydrocarbon / fluorine-based polymer films is preferable.

  Secondly, in the method for producing a functional film according to the present invention, one or more selected from the group A which is a monomer having a functional functional group or capable of introducing a functional functional group in a subsequent step. A method for producing an electrolyte membrane for a fuel cell, wherein the monomer is a monomer having a proton exchange group or a functional group that can be converted into a proton exchange group in a later step.

By the method for producing an electrolyte membrane for a fuel cell of the present invention, ion exchange ability is imparted by introducing a cation-exchange functional group only into an irradiation damage site penetrating in a film thickness direction by high energy heavy ion irradiation on a polymer film substrate. Because you can
(A) The physical properties of each polymer film substrate having a small porosity can be maintained.
(B) The position / spatial distribution of functional groups and the density of functional groups can be controlled.
(C) Since the filling amount of the ion exchange resin is small, swelling due to water content can be suppressed.
Furthermore, by using the ion irradiation method, it can be applied to all polymer materials that can be formed into a film without being bound by the existing porous substrate.
(D) It is easy to control the physical properties of the proton conductivity and gas barrier properties of the ion exchange membrane.
Etc.

By the method for producing an electrolyte membrane for a fuel cell of the present invention, for example, cation exchange is performed on a polymer film substrate having an oxygen permeability coefficient at room temperature of 10.0 [cc * mm / (m ² * day * atm)] or less. An electrolyte membrane for a fuel cell having a pore diameter of the group-containing path in the range of 1 nm to 5 μm, preferably 1 nm to 250 nm is produced in a short time.

  The functional film of the present invention can impart functionality by introducing a functional group only into the latent track portion damaged by high-energy heavy ion irradiation to the polymer film substrate. Can be maintained. In addition, the functional film of the present invention is formed by subjecting a polymer film substrate to irradiation damage by high-energy heavy ion irradiation, and then chemically or thermally etching the irradiation damage to the film substrate. Functionality can be imparted by introducing functional groups only on the surface of the perforated film substrate and the hole wall obtained by forming through-holes with columnar, conical, drum-shaped, and funnel-shaped cross-sections. The physical properties of the molecular film substrate can be maintained. In particular, in the graft polymerization step after ion irradiation, by using a monomer solution diluted with a protic polar solvent, the graft reaction rate is accelerated, the graft reaction time can be shortened, and the graft reaction time is short, which is a side reaction. Graft chain growth outside the fenambra region can be prevented, and changes in wet and dry dimensions can be suppressed and tensile strength can be increased. Thereby, it can be used for various applications, and has both high functionality and gas barrier properties inherent to the polymer film base material, and can greatly shorten the production time of a functional film excellent in dry / wet dimensional change and tensile strength. In particular, the production time of a polymer electrolyte membrane that is optimal as a polymer electrolyte membrane for fuel cells, excellent in high proton conductivity and gas barrier properties, and excellent in dry / wet dimensional change and tensile strength can be greatly reduced.

  The polymer film substrate that can be used in the present invention is not particularly limited. For example, a hydrocarbon polymer film having good penetrability of the monomer solution can be used. In addition, although the fluorine-based polymer film does not have good penetrability of the monomer solution, the monomer penetrates into the film by irradiating ions, and the graft reaction proceeds inside.

  Specifically, film bases such as ultra high molecular weight polyethylene, polypropylene, polystyrene, polyamide, aromatic polyamide, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyether ketone, polyether ether ketone, polyether sulfone, polyphenylene sulfide, polysulfone, etc. A material may be used.

  Further, polyimide, polyetherimide, polyamideimide, polybenzimidazole, or polyetheretherimide film base material which is a polyimide polymer film may be used.

  Furthermore, using polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, or tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer film substrate Also good.

  Among these film base materials, when a fluorinated film is cross-linked, a cross-linked structure is formed in the polymer structure to improve the grafting ratio of the monomer, and the heat resistance is further increased. Can be suppressed. Therefore, it is preferable to use a crosslinked film in order to produce a fuel cell that exhibits high performance in high temperature applications. For example, when styrene is used as the graft monomer, the graft ratio can be significantly increased with crosslinked polytetrafluoroethylene compared to uncrosslinked polytetrafluoroethylene, which is 2 to 10 times that of uncrosslinked polytetrafluoroethylene. The inventors have already found that sulfonic acid groups can be introduced into crosslinked polytetrafluoroethylene.

  Therefore, in the present invention, instead of the polyethylene terephthalate film substrate, ultrahigh molecular weight polyethylene having a crosslinked structure, polypropylene, polystyrene, polyamide / aromatic polyamide, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyether ketone It is preferred to use a polyetheretherketone, polyethersulfone, polyphenylene sulfide, or polysulfone film substrate.

  A polyimide, polyetherimide, polyamideimide, polybenzimidazole, or polyetheretherimide film substrate having a crosslinked structure is also suitable. Similarly, polyvinylidene fluoride having a crosslinked structure, ethylene-tetrafluoroethylene copolymer, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, or tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer film Substrates are also suitable.

  In the present invention, the polymer film substrate is irradiated with high energy heavy ions by a cyclotron accelerator or the like. Here, heavy ions refer to ions that are higher than carbon ions. Irradiation of these ions causes irradiation damage to the polymer film due to ion irradiation. The irradiation damage region depends on the mass and energy of irradiated ions, but is known to have a spread from about nanosize to several hundred nanosize per ion.

The number of ions to be irradiated is preferably 10 ⁴ to 10 ¹⁴ ions / cm ² so that irradiation damage areas by individual ions do not overlap. For irradiation, for example, a 10 cm × 10 cm film base is fixed to an irradiation stand in an irradiation chamber connected to a cyclone accelerator or the like, and the irradiation chamber is evacuated to 10 ⁻⁶ Torr or less with high energy ions. It is better to do this while scanning. The irradiation amount can be determined from the amount of ion current measured in advance with a high-precision ammeter and the irradiation time. As a kind of high energy heavy ions to be irradiated, ions having a mass greater than or equal to carbon ions, which can be actually accelerated by an accelerator, are preferable.

  Ion species such as carbon, nitrogen, oxygen, neon, argon, krypton, and xenon are more preferable from the viewpoint of easy generation of ions and easy handling of ions. Moreover, in order to enlarge the irradiation damage area | region of one ion, you may use large mass ions, such as a gold ion, a bismuth ion, or a uranium ion. Although the energy of ions depends on the ion species, it is sufficient if the energy is sufficient to penetrate the polymer film substrate in the thickness direction. For example, in a polyethylene terephthalate film substrate having a thickness of 50 μm, carbon ions are 40 MeV. As described above, neon ions are 80 MeV or more, and argon ions are 180 MeV or more. Similarly, at a thickness of 100 μm, carbon ions are 62 MeV or more, neon ions are 130 MeV or more, and argon ions are 300 MeV or more. In addition, a film substrate having a thickness of 40 μm can be penetrated by xenon ion 450 MeV, and a film substrate having a thickness of 120 μm by uranium ion 2.6 GeV.

  Even if the ion used for irradiation is about 1/2 the film thickness of the film substrate, the same or different ions are irradiated from both sides of the film while changing the irradiation amount. By irradiating from both sides of the film with a combination of heavier ions having a shorter range, it is possible to create different distributions of irradiation damage areas from the surface of the film toward the inside. This results in different amounts or lengths of graft chains in the film and also different forms of polymer structure in the grafting reaction described below. As a result, the distribution of moisture in the film substrate and the permeation of fuel gas in the film can be controlled using the change in the distribution of sulfonic acid groups in the graft chain of the film substrate.

  Moreover, in order to penetrate the film thickness of a heavy ion, the ion of very high energy as mentioned above is required. For example, the range of 22 MeV carbon ions in a polyethylene terephthalate film substrate is about 25 μm, and this film substrate having a thickness of 50 μm cannot be penetrated, and the 50 μm polyethylene terephthalate film substrate cannot be penetrated. Requires energy of about 40 MeV, but 22 MeV of carbon ions is sufficient when irradiated from both sides of the film. Generating higher energy ions requires a larger accelerator and is expensive to install. Also from this fact, ion irradiation from both sides is extremely effective for the production of the ion exchange membrane in the present invention.

  Here, by irradiating one or more heavy ions selected from O, Fe, and Ar, these heavy ions can reach the inside of the polymer film substrate having a large film thickness to generate radicals. By using O, Fe, or Ar as the ionic element to be irradiated, the range of ions in the polymer film is more than doubled as compared with other elements such as Xe. In order to obtain an electrolyte membrane having a uniform property in the thickness direction, a polymer film substrate having a thickness of about 30 μm or less is used. In the case of using a polymer film substrate having a film thickness larger than this, irradiation on both sides of the film was necessary in order to obtain a uniform electrolyte membrane. By using O, Fe, and Ar as the ionic elements to be irradiated, an electrolyte membrane having a uniform film quality can be obtained by ion irradiation from one side even if the polymer film is thick, for example, about 150 μm thick. Thereby, simplification of a manufacturing process and reduction of equipment cost can be achieved.

In order to obtain a film having high functionality such as ion exchange capacity, the ion irradiation amount may be increased. When the ion irradiation amount is large, the film base material is deteriorated, or the irradiation damage regions are overlapped, and the graft efficiency of the monomer described later is deteriorated. Further, when the irradiation amount is small, the amount of monomer grafting is small and a sufficient ion exchange capacity cannot be obtained. Accordingly, the ion irradiation density is preferably in the range of 10 ⁴ to 10 ¹⁴ ions / cm ² .

  The “one or more monomers selected from the group A that are functional monomers having functional functional groups or capable of introducing functional functional groups in a later step” used in the present invention refers to monomers having functional functional groups. It means not only the monomer itself but also a monomer having a group that can be converted into a functional functional group by a reaction in a later step.

In the present invention, a monomer exemplified below is added to a polymer film substrate irradiated with heavy ions, degassed and heated to graft polymerize the monomer on the film substrate, and further, a sulfonyl halide in the graft molecular chain. It is produced by converting a group [—SO ₂ X ¹ ], a sulfonate group [—SO ₃ R ¹ ], or a halogen group [—X ² ] into a sulfonate group [—SO ₃ H]. Further, phenyl groups, ketones, ether groups, etc. present in the hydrocarbon monomer units in the graft chain can be produced by introducing sulfonic acid groups with chlorosulfonic acid. In the present invention, the monomers shown in the following (1) to (6) are representative examples of the group A monomers that are graft-polymerized on the film substrate.
(1) One or more monomers selected from the group consisting of styrene, α-vinylstyrene, styrene derivative monomers 2,4-dimethylstyrene, vinyltoluene, and 4-tertbutylstyrene.
(2) CF ₂ ═CF (SO ₂ X ¹ ), which is a monomer having a sulfonyl halide group (wherein X ¹ is a halogen group —F or —Cl; the same shall apply hereinafter), CH ₂ ═CF ( SO ₂ X ¹ ), and CF ₂ ═CF (OCH ₂ (CF ₂ ) _m SO ₂ X ¹ ) (wherein, m is 1 to 4, the same shall apply hereinafter). Monomer.
(3) CF ₂ = CF (SO ₃ R ¹ ), which is a monomer having a sulfonic acid ester group (wherein R ¹ is an alkyl group, —CH ₃ , —C ₂ H ₅ or —C (CH ₃ ) ₃ The same shall apply hereinafter.), One or more monomers selected from the group consisting of CH ₂ = CF (SO ₃ R ¹ ) and CF ₂ = CF (OCH ₂ (CF ₂ ) _m SO ₃ R ¹ ).
(4) CF ₂ ═CF (O (CH ₂ ) _m X ² ) (wherein X ² is a halogen group —Br or —Cl; the same shall apply hereinafter), and CF ₂ ═CF (OCH ₂ (CF ₂ ) One or more monomers selected from the group consisting of _m X ² ).
(5) is an acrylic ^{_{monomer, CF 2 = CR 2 (COOR}} 3) ( wherein, ^{R 2} is -CH ₃ or -F, ^{R 3} is _{-H, -CH 3, -C 2 H} 5 or - And C (CH ₃ ) _{3. The} same shall apply hereinafter.), And one or more monomers selected from the group consisting of CH ₂ = CR ² (COOR ³ ).
(6) Acenaphthylene, vinyl ketone CH ₂ ═CH (COR ⁴ ) (wherein R ⁴ is —CH ₃ , —C ₂ H ₅ or a phenyl group (—C ₆ H ₅ )), and vinyl ether CH ₂ ═. CH (OR ⁵ ) (wherein R ⁵ is —C _n H _{2n + 1} (n = 1 to 5), —CH (CH ₃ ) ₂ , —C (CH ₃ ) ₃ , or a phenyl group). One or more monomers selected from the group consisting of:

  Specific examples of “monomers consisting of group B which is a crosslinking agent for group A monomers” used in the present invention include divinylbenzene, triallyl cyanurate, triallyl isocyanurate, and 3,5-bis (trifluorovinyl). Examples include phenol and 3,5-bis (trifluorovinyloxy) phenol. One or more kinds of these crosslinking agents are added in an amount of 30 mol% or less based on the total monomers, and graft polymerization is performed.

  The “one or more monomers selected from the group C which is a functional monomer having a molecular weight of 200 or more” used in the present invention is a monomer having a molecular weight of 200 or more among the monomers of the group A.

The “one or more monomers selected from group D which are monomers having a functional functional group that is difficult to graft polymerize” used in the present invention is shown in (1) to (3) in the monomers of group A above. Perfluorovinyl monomers are typical. The following is listed again.
(1) CF ₂ ═CF (SO ₂ X ¹ ), which is a monomer having a sulfonyl halide group (wherein X ¹ is a halogen group —F or —Cl; the same shall apply hereinafter), CH ₂ ═CF ( SO ₂ X ¹ ), and CF ₂ ═CF (OCH ₂ (CF ₂ ) _m SO ₂ X ¹ ) (wherein, m is 1 to 4, the same shall apply hereinafter). Monomer.
(2) CF ₂ ═CF (SO ₃ R ¹ ), which is a monomer having a sulfonate group (wherein R ¹ is an alkyl group, —CH ₃ , —C ₂ H ₅ or —C (CH ₃ ) ₃ The same shall apply hereinafter.), One or more monomers selected from the group consisting of CH ₂ = CF (SO ₃ R ¹ ) and CF ₂ = CF (OCH ₂ (CF ₂ ) _m SO ₃ R ¹ ).
_{(3) CF 2 = CF (} O (CH 2) m X 2) ( wherein, ^{X 2} is -Br or -Cl halogen group. Hereinafter the same.), And _{CF 2 = CF (OCH 2 (} CF ₂ ) One or more monomers selected from the group consisting of _m X ² ).

  Examples of the present invention and comparative examples are shown below.

[Examples 1 to 4]
As the substrate, ethylene-tetrafluoroethylene (ETFE) was used. The studied monomers and solvent compositions are as shown in Table 1 below.

The sample preparation process is as follows.
1) ETFE is used as a substrate (film).
2) The sample film was irradiated with Xe ions accelerated by a cyclotron at a density of 3 × 10 ⁸ ions / cm ² at 450 eV.
3) A sample was taken out from the irradiation chamber into the atmosphere, immersed in a styrene solution diluted with methanol or isopropanol, heated to 60 ° C., and polymerized.
4) A sample was taken out and washed with a toluene solution.
5) The sample was dried in a vacuum drying oven.
6) The sample was immersed in a 0.2 mol / l chlorosulfonic acid / 1,2-dichloroethane solution, and then immersed in water to sulfonate styrene.
7) The neutralization titration was performed, and the amount of sulfonic acid contained in the sample was determined.
8) AC impedance measurement was performed to determine proton conductivity.
9) Wet and dry dimension measurement and tensile strength measurement were performed.
The graft ratio (the amount of sulfonic acid contained in the sample) was changed with the length of the grafting time.

[Comparative Examples 1-4]
The above 3) step was carried out in the same manner as in Examples 1 to 4, except that a 100% styrene solution or an acetone solution of styrene was used. Similar to the example, the graft ratio (the amount of sulfonic acid contained in the sample) was changed with the length of the grafting time.
In Examples 1 to 4 and Comparative Examples 1 to 4, proton conductivity, wet and dry dimensions, and tensile strength were measured as follows.

[Measurement of conductivity]
A plurality of sample films are cut into a circle of 6 mmφ. Similarly, a commercially available electrolyte membrane having a known resistance value (this time Nafion N112 (trade name)) is sandwiched between them, and these are laminated. Using a 20 mm × 20 mm platinum electrode plate, these stacked samples are fastened with a constant load from above and below. This is placed in a thermostatic bath to create an environment of 80 ° C. and 90% RH. The AC impedance between the platinum electrodes is measured, and the resistance value of the sample is read from the measurement result. When the resistance value does not change over time, it is determined that the equilibrium in the environment has been reached. The proton conductivity is calculated from the resistance value.

[Measurement of wet and dry dimensions]
Samples are cut into 10 x 30 mm.
1) Immerse the membrane in 80 ° C. water for 30 minutes.
2) Immerse the membrane in room temperature water for 15 minutes.
3) Measure the dimensions (X, Y, l) of the membrane in water at room temperature.
4) Immerse the membrane in a vacuum at 80 ° C for 1 hour.
5) Measure the film dimensions (X, Y, l).
6) Repeat 1) to 5) any number of times.
7) Adopt stable change cycle data.

[Measurement of tensile strength]
Measurement environment: room temperature, in air atmosphere Sample shape: New JIS No. 7 tensile speed: 5 mm / min
Measurement: An SS curve of the sample is obtained by a tensile test. The maximum value in the SS curve is used as an index of sample strength.

  From the results of Table 1, the samples prepared in Examples 1 to 4 of the present invention using a monomeric protic polar solvent solution were compared with Comparative Examples 1 and 2 using a styrene bulk without solvent, and the graft reaction time. In spite of being significantly shortened, proton conductivity, wet and dry dimensions and tensile strength are comparable or rather superior. Moreover, compared with the comparative examples 3 and 4 which used acetone which is an aprotic polar solvent, the graft ratio is remarkably excellent, As a result, proton conductivity is excellent.

  In the present invention, by using a monomer solution diluted with a protic polar solvent in the graft polymerization step after ion irradiation, the graft reaction rate is accelerated and the graft reaction time can be shortened. It is possible to prevent the growth of graft chains outside the fenambra region, which can suppress changes in wet and dry dimensions and increase the tensile strength. Thereby, it can be used for various applications, and has both high functionality and gas barrier properties inherent to the polymer film base material, and can greatly shorten the production time of a functional film excellent in dry / wet dimensional change and tensile strength. In particular, the production time of a polymer electrolyte membrane that is optimal as a polymer electrolyte membrane for fuel cells, excellent in high proton conductivity and gas barrier properties, and excellent in dry / wet dimensional change and tensile strength can be greatly reduced.

  As a result, a polymer electrolyte membrane having high proton conductivity and excellent gas barrier properties, which is optimal for an electrolyte membrane for fuel cells, can be provided at low cost, contributing to the spread of fuel cells.

Claims (11)

  An ion irradiation step of irradiating a polymer film substrate with high-energy heavy ions to generate active species on the film substrate, and a functional functional group that has a functional functional group after or after the ion irradiation step A functional membrane comprising a graft polymerization step of adding a protic polar solvent solution of one or more monomers selected from Group A, which is a monomer capable of introducing a group, to graft polymerize the monomer Production method.   The ratio of one or more monomers selected from Group A, which is a monomer having the functional functional group or capable of introducing a functional functional group in a later step, and the protic polar solvent is 20 to 90: It is 80-10, The manufacturing method of the functional film of Claim 1 characterized by the above-mentioned.   The method for producing a functional film according to claim 1, wherein the protic polar solvent is methanol and / or isopropanol.   It is a crosslinking agent for the group A monomer with respect to 20 to 99 mol% of one or more monomers selected from the group A which has the functional functional group or can be introduced with a functional functional group in a later step. The method for producing a functional film according to any one of claims 1 to 3, wherein a protic polar solvent solution containing a monomer mixture to which 1 to 80 mol% of a monomer from Group B is added is used.   The polymer film substrate is made of a non-polar polymer material, and has one or more monomers selected from the group A which has the functional functional group or is a monomer capable of introducing a functional functional group in a later step. The method for producing a functional film according to claim 1, wherein the functional film is a nonpolar monomer.   The method for producing a functional film according to claim 1, wherein the polymer film substrate contains non-conductive inorganic particles.   The method for producing a functional film according to claim 1, wherein in the ion irradiation step, a latent track damaged by high energy heavy ion irradiation penetrates the film.   The method for producing a functional film according to claim 1, wherein in the ion irradiation step, one or more heavy ions selected from O, Fe, and Ar are irradiated.   After the ion irradiation step, the generated irradiation damage is chemically or thermally etched to form through holes in the film substrate, and the obtained perforated film substrate is damaged by ion irradiation. By using the active species remaining in the received latent track location or the active species newly generated by irradiation with either radiation or plasma in a vacuum or inert gas atmosphere, the functional functional group has The production of a functional film according to any one of claims 1 to 8, wherein one or more monomers selected from Group A, which are monomers capable of introducing a functional functional group in a subsequent step, are graft-polymerized. Method.   The method for producing a functional film according to any one of claims 1 to 9, wherein a temperature of the graft polymerization is 10 to 80 ° C.   The method for producing a functional film according to any one of claims 1 to 10, wherein the functional film has one of the functional functional groups or is selected from the group A which is a monomer capable of introducing a functional functional group in a subsequent step. A method for producing an electrolyte membrane for a fuel cell, wherein the monomer is a monomer having a proton exchange group or a functional group that can be converted into a proton exchange group in a later step.