JP2008138104A - Aromatic hydrocarbon-based ion exchange membrane and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ion exchange membrane which is improved in the bondability to a catalyst electrode, i.e., a problem in a conventional hydrocarbon-based solid polyelectrolyte membrane. <P>SOLUTION: Provided are an aromatic hydrocarbon-based ion exchange membrane characterized in that the difference between the surface orientation degree on one surface of the aromatic hydrocarbon-based ion exchange membrane and that on the other surface is 0.8 or smaller and a method for producing the aromatic hydrocarbon-based ion exchange membrane comprising casting an ionic-group-containing aromatic hydrocarbon polymer solvent solution onto a support, starting the evaporation of the solvent at a temperature lower than the boiling point of the solvent by at least 100°C, removing the solvent at a temperature lower than the boiling point of the solvent by at least 70°C to form a self-supporting membrane of the ionic-group-containing aromatic hydrocarbon-based polymer, and bringing the obtained membrane into contact with an acidic solution to convert its ionic groups into acidic groups. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polymer solid electrolyte membrane, and more particularly to an aromatic hydrocarbon ion exchange membrane and a method for producing the same.

  Examples of electrochemical devices that use polymer solid electrolytes as ion conductors include water electrolyzers and fuel cells. The polymer membranes used for these are required to have high ionic conductivity as a cation exchange membrane and to be chemically, thermally, electrochemically and mechanically stable. Sulfonic acid membranes have been used. However, at present, in the polymer electrolyte fuel cell field, since it contains fluorine, environmental pollution at the time of disposal, and hydrofluoric acid generated during power generation corrodes the fuel cell system. It has been pointed out. In addition, a fuel cell using an aqueous methanol solution has a problem of durability due to its large methanol swellability, which is an obstacle to practical use.

    On the other hand, as electrolyte membranes that replace perfluorocarbon sulfonic acid membranes, so-called hydrocarbon polymer solid electrolytes in which ionic groups such as sulfonic acid groups are introduced into polymers such as polyetheretherketone, polyethersulfone, and polysulfone have recently become popular. It is being considered. However, since the hydrocarbon-based polymer solid electrolyte generally has a higher elastic modulus than the perfluorocarbon sulfonic acid membrane, there is a problem that it is difficult to join the catalyst electrodes necessary for power generation as a fuel cell.

    With respect to the ionic conductivity of the polymer solid electrolyte membrane, the channel structure formed by the ion conductive component in the membrane is considered to be extremely important. In Non-Patent Document 1, ion conduction is described by percolation of a portion where ion dispersed in proton conductive membrane can diffuse (ion conduction portion). From the viewpoint that ions conduct through a channel, The spatial arrangement of ion conduction sites in the membrane is important. From such a viewpoint, as a method for improving the ionic conductivity of the polymer solid electrolyte membrane at the time of low humidification, increasing the sulfonic acid group concentration of the polymer solid electrolyte membrane and increasing the spatial arrangement of the ion conducting portion; It is conceivable to reduce the resistance by reducing the film thickness. However, a significant increase in the concentration of sulfonic acid groups reduces the mechanical strength and tear strength of the electrolyte membrane, causes dimensional changes during handling, and makes the electrolyte membrane creep easily during long-term operation, reducing durability. Problems occur. On the other hand, the reduction of the film thickness causes problems such as lowering the mechanical strength and tear strength of the electrolyte membrane, and further lowering workability and handleability when the membrane is joined to the gas diffusion electrode.

    There are various methods to improve the durability of polymer solid electrolyte membranes, such as improving the heat resistance and chemical stability of the polymer itself, improving the dimensional stability using a reinforcing membrane, and improving the bondability with the catalyst electrode. Many studies have been made. Among them, a polymer electrolyte membrane containing perfluorocarbon sulfonic acid or a proposed composite polymer solid electrolyte, for example, a perfluorocarbon sulfonic acid polymer which is an ion exchange resin in a void portion of an expanded porous polytetrafluoroethylene membrane. Composite polymer solid electrolyte membrane (see, for example, Patent Document 1) impregnated with polytetrafluoroethylene dispersed as a reinforcing material in a perfluorocarbon sulfonic acid polymer membrane Solid electrolyte membranes (for example, see Patent Document 2) are described respectively. Furthermore, a polymer solid electrolyte membrane in which perfluorocarbon sulfonic acid resin is applied to the interface between the hydrocarbon-based polymer solid electrolyte and the catalyst electrode to improve the bonding property has also been proposed. However, it still contains fluorine as an element, and the problems of environmental pollution during disposal and hydrofluoric acid generated during power generation have not been solved.

    On the other hand, as a polymer solid electrolyte reinforced with a hydrocarbon-based reinforcing material, a polymer solid electrolyte membrane (for example, see Patent Document 3) in which a polybenzoxazole porous membrane and a polymer solid electrolyte are combined is described. Yes. However, the composite membranes prepared by these methods are peeled off at the interface because the swelling properties of the porous membrane, which is a reinforcing material, and the solid polymer electrolyte in water and methanol differ when the power generation is actually repeated in the fuel cell. Durability is insufficient because there is an increase in the permeation amount of hydrogen gas and methanol estimated to have occurred.

    There is also an electrolyte membrane obtained by polymerizing a polymer having ion conductivity from a monomer permeated into a porous substrate (see, for example, Patent Document 4). However, in this method, it is difficult to completely fill the void with the polymer, the dimensional change between the filled portion and the unfilled portion is different, and defects etc. are formed, so hydrogen gas leak and methanol permeation cannot be sufficiently suppressed. There are problems such as lack of proton conduction at unfilled sites.

Edmondson, C.I. A: AD Report 2000, 18 JP-A-8-162132 JP 2001-35508 A International Publication No. WO00 / 22684 Pamphlet JP 2002-83612 A

  An object of the present invention is to improve the lack of bondability with a catalyst electrode, which has been a problem of aromatic hydrocarbon polymer solid electrolyte membranes, and to solve the lack of durability for fuel cells An object is to provide an ion exchange membrane and a method for producing the same.

  As a result of diligent research to solve the above problems, the inventors of the present invention have found that a membrane having poor adhesion to the catalyst electrode is curled and has surface orientation on the front and back surfaces of the aromatic hydrocarbon ion exchange membrane surface. It was found that there was a difference in the degree, and that the above object could be achieved by controlling the difference in the degree of orientation of the plane.

（ただし、Ａｒは２価の芳香族基、Ｙはスルホン基またはケトン基、ＸはＨ及び／または１価のカチオン種、Ｚはエーテル結合、チオエーテル結合及びアルキレン基から選ばれる少なくとも１種である。）

（ただし、Ａｒ’は２価の芳香族基、Ｚ’はエーテル結合チオエーテル結合及び２価の脂肪族基から選ばれる少なくとも１種である。）
６．イオン性基含有芳香族炭化水素系ポリマーを溶媒に溶かした溶液を、支持体上に流延した後、前記溶媒の沸点より１００℃以上低い温度で溶媒の蒸発除去を開始し、次いで溶媒の沸点より１００〜７０℃低い温度で溶媒の蒸発除去を行いイオン性基含有芳香族炭化水素系ポリマーの自己支持性膜とした後、得られた自己支持性膜のイオン性基を酸性液に接触させて酸型に変換することを特徴とする上記１に記載の芳香族炭化水素系イオン交換膜の製造方法。。 That is, the present invention is as follows.

1. The difference between the degree of orientation of the surface of one surface of the aromatic hydrocarbon ion exchange membrane and the degree of orientation of the surface of the other surface is 0.8 or less. .


2. 2. The aromatic hydrocarbon ion exchange membrane according to 1 above, wherein the surface orientation degree of the surface having the higher surface orientation degree is 2.0 or less.

3. 3. The aromatic hydrocarbon ion exchange membrane according to the above 1 or 2, having a curl degree of 5% or less.

4). The fragrance according to any one of the above 1 to 3, wherein the aromatic hydrocarbon ion exchange membrane has an ionic group-containing aromatic hydrocarbon polymer and has an ion exchange capacity of 0.3 to 3.5 meq / g. Group hydrocarbon ion exchange membrane.
5. 2. The aromatic hydrocarbon ion exchange membrane according to 1 above, wherein the ionic group-containing aromatic hydrocarbon polymer is a polyarylene ether compound containing structural units represented by general formula (1) and general formula (2). .

(However, Ar is a divalent aromatic group, Y is a sulfone group or ketone group, X is H and / or a monovalent cationic species, Z is at least one selected from an ether bond, a thioether bond and an alkylene group. .)

(However, Ar ′ is a divalent aromatic group, and Z ′ is at least one selected from an ether-linked thioether bond and a divalent aliphatic group.)
6). After casting a solution in which an ionic group-containing aromatic hydrocarbon polymer is dissolved in a solvent, the solvent is evaporated and removed at a temperature 100 ° C. or more lower than the boiling point of the solvent, and then the boiling point of the solvent After evaporating and removing the solvent at a temperature lower than 100 to 70 ° C. to obtain a self-supporting membrane of an ionic group-containing aromatic hydrocarbon polymer, the ionic groups of the obtained self-supporting membrane are brought into contact with an acidic liquid. 2. The method for producing an aromatic hydrocarbon-based ion exchange membrane as described in 1 above, which is converted to an acid form. .

    The curl degree of the membrane can be controlled to 5% or less by setting the difference in the degree of orientation of the surface surface between the front and back surfaces of the ion exchange membrane to 0.8 or less. As a result, the bondability with the catalyst electrode can be improved, and an aromatic hydrocarbon ion exchange membrane having excellent durability can be provided.

Hereinafter, the present invention will be described in detail. In the present invention, the weight means mass.
First, the aromatic hydrocarbon-based ionic group-containing polymer in the present invention will be described.
The aromatic hydrocarbon type ionic group-containing polymer in the present invention has an aromatic or aromatic ring and ether bond, sulfone bond, imide bond, ester bond, amide bond, urethane bond, sulfide bond, carbonate bond, and polymer main chain. A non-fluorine ion conductive polymer having a structure having at least one linking group selected from ketone bonds, such as polysulfone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyphenylene sulfide sulfone, polyparaphenylene , A polyarylene polymer, polyphenylquinoxaline, polyaryl ketone, polyether ketone, polybenzoxazole, polybenzthiazole, a polymer containing at least one component such as polyimide, Acid group, a phosphonic acid group, a carboxyl group, and at least one of those derivatives is a polymer which has been introduced.
In addition, the ionic conductivity of a polymer is expressed by including functional groups, such as a sulfonic acid group, a phosphonic acid group, and a carboxyl group, in a polymer. Among these, a functional group that acts particularly effectively is a sulfonic acid group. Polysulfone, polyethersulfone, polyetherketone, etc. as used herein are generic names for polymers having a sulfone bond, an ether bond, and a ketone bond in their molecular chains. Polyetherketoneketone, polyetheretherketone, It includes polyether ether ketone ketone, polyether ketone ether ketone ketone, polyether ketone sulfone and the like, and is not limited to a specific polymer structure.

    Among the polymers containing the functional group, a polymer having a sulfonic acid group on the aromatic ring can be obtained by reacting a polymer having a skeleton as in the above example with an appropriate sulfonating agent. Examples of such sulfonating agents include those using concentrated sulfuric acid or fuming sulfuric acid that have been reported as examples of introducing sulfonic acid groups into aromatic hydrocarbon polymers (for example, Solid State Ionics, 106, P.219 (1998)), those using chlorosulfuric acid (for example, J. Polym. Sci., Polym. Chem., 22, P.295 (1984)), those using anhydrous sulfuric acid complex (for example, J Polym. Sci., Polym. Chem., 22, P. 721 (1984), J. Polym. Sci., Polym. Chem., 23, P. 1231 (1985)) and the like are effective. In order to obtain the ionic group-containing polymer of the present invention, in particular, a polymer whose ion conductivity is a sulfonic acid group, it can be carried out by using these reagents and selecting reaction conditions according to each polymer. . Moreover, it is also possible to use the sulfonating agent described in Japanese Patent No. 2884189.

  The aromatic hydrocarbon ionic group-containing polymer can also be synthesized using a monomer containing an acidic group in at least one of the monomers used for polymerization. For example, in a polyimide synthesized from an aromatic diamine and an aromatic tetracarboxylic dianhydride, an acidic group-containing polyimide is obtained by using a diamine containing a sulfonic acid group or a phosphonic acid group as at least one of the aromatic diamines. I can do it. In the case of polybenzoxazole synthesized from aromatic diamine diol and aromatic dicarboxylic acid, and polybenzthiazole synthesized from aromatic diamine dithiol and aromatic dicarboxylic acid, at least one kind of aromatic dicarboxylic acid contains sulfonic acid group By using dicarboxylic acid or phosphonic acid group-containing dicarboxylic acid, an acidic group-containing polybenzoxazole or polybenzthiazole can be obtained. Polysulfone, polyethersulfone, polyetherketone, etc. synthesized from aromatic dihalide and aromatic diol are synthesized by using sulfonic acid group-containing aromatic dihalide or sulfonic acid group-containing aromatic diol as at least one monomer. I can do it. At this time, it is preferable to use a sulfonic acid group-containing dihalide rather than a sulfonic acid group-containing diol because the degree of polymerization tends to be high and the thermal stability of the obtained acidic group-containing polymer is high.

    The aromatic hydrocarbon-based ionic group-containing polymer in the present invention includes polyarylene ether compounds such as sulfonic acid group-containing polysulfone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyphenylene sulfide sulfone, polyether ketone-based polymer, and polyarylene. It is more preferable that it is a system compound.

一般式（１）中、Ａｒは２価の芳香族基、Ｙはスルホン基またはケトン基、ＸはＨ及び／または１価のカチオン種、Ｚは２価の脂肪族基、エーテル結合、チオエーテル結合など芳香環をつなぐ各種結合様式より選択されるが、エーテル結合または／及びチオエーテル結合（ＯまたはＳ）が好ましく、その中でもエーテル結合がより好ましい。 Furthermore, the polymer containing the structural unit shown by these following general formula (1) and general formula (2) is preferable.

In general formula (1), Ar is a divalent aromatic group, Y is a sulfone group or a ketone group, X is H and / or a monovalent cation species, Z is a divalent aliphatic group, an ether bond, a thioether bond Are selected from various bond modes for connecting aromatic rings, such as ether bond and / or thioether bond (O or S), and ether bond is more preferable.

一般式（２）中、Ａｒ’は２価の芳香族基、Ｚ’は２価の脂肪族基、エーテル結合、チオエーテル結合など芳香環をつなぐ各種結合様式より選択されるが、エーテル結合または／及びチオエーテル結合（ＯまたはＳ）が好ましく、その中でもエーテル結合がより好ましい。

In general formula (2), Ar ′ is a divalent aromatic group, Z ′ is selected from various bond modes connecting aromatic rings such as a divalent aliphatic group, an ether bond, and a thioether bond. And a thioether bond (O or S) is preferable, and an ether bond is more preferable among them.

  Furthermore, it is more preferable that the structural unit shown by General formula (4) is included with General formula (3).

ただし、Ａｒは２価の芳香族基、Ｙはスルホン基またはケトン基、ＸはＨまたは１価のカチオン種を示す。

Here, Ar represents a divalent aromatic group, Y represents a sulfone group or a ketone group, and X represents H or a monovalent cation species.

ただし、Ａｒ’は２価の芳香族基を示す。

However, Ar ′ represents a divalent aromatic group.

  The structural unit represented by the general formula (4) is preferably a structural unit represented by the following general formula (5).

ただし、Ａｒ’は２価の芳香族基を示す。

However, Ar ′ represents a divalent aromatic group.

In addition, as aromatic groups in general formulas (1) to (5), aromatic rings such as benzene rings and pyridine rings, condensed polycyclic aromatic groups such as naphthalene rings and anthracene rings, and aromatic rings are directly bonded. A group in which at least two aromatic rings are linked by an ether group or a thioether group, a group in which a plurality of aromatic rings are linked by an aliphatic group, a sulfide group, a perfluoroalkyl group, or the like; It is preferably at least one selected from groups linked by an electron-withdrawing group such as a group, a carbonyl group, and a sulfonyl group.
In addition, the aliphatic group in the general formulas (1) and (2) is at least selected from a —C (CH ₃ ) ₂ — group, a —C (CF ₃ ) ₂ — group, a —CH ₂ — group, and a cyclohexyl group. One type is preferable.

  The sulfonic acid group-containing polyarylene ether-based compound may contain a structural unit other than that represented by the general formula. At this time, it is preferable that the structural units other than those represented by the general formula are 50% by weight or less. By setting the content to 50% by weight or less, a composition utilizing the characteristics of the sulfonic acid group-containing polyarylene ether compound can be obtained.

   It is important that the ionic group of the aromatic hydrocarbon-based ionic group-containing polymer in the present invention contains at least one group selected from a sulfonic acid group, a phosphonic acid group, and a phosphoric acid group. A known method can be used for introducing an ionic group into the polymer. For example, the polymer may be polymerized from a monomer having a sulfonic acid group, a phosphonic acid group, or a phosphoric acid group. The sex group may be introduced by a known method.

    The molecular weight of the aromatic hydrocarbon-based polymer in the present invention is not particularly limited, but the logarithmic viscosity in an NMP solution having a concentration of 0.5 g / dl is 0.1 to 3.0. It is preferable. If it is less than 0.1, the membrane tends to become brittle when an ion exchange membrane is formed. The logarithmic viscosity is more preferably 0.3 or more. More preferably, it is 0.5 or more. On the other hand, when the logarithmic viscosity is more than 3.0, there are problems in processability such as difficulty in dissolving the polymer. The logarithmic viscosity is more preferably 2.0 or less.

In the aromatic hydrocarbon ion exchange membrane of the present invention, the difference in the degree of orientation of the surface between one surface and the other surface of the membrane surface, that is, the front and back surfaces of the membrane is 0.8 or less, preferably 0.6 or less, more preferably 0.4 or less. On the surface of the ion exchange membrane, if the surface orientation difference between the front and back surfaces of the membrane exceeds 0.8, the difference between the front and back of the stress (strain) in the membrane is large, so the membrane tends to curl and the membrane curls. The degree will exceed 5%. As a result, it is considered that the bondability between the membrane and the catalyst electrode deteriorates and the interface resistance during power generation increases.
In the present invention, the degree of curl of the aromatic hydrocarbon ion exchange membrane can be reduced to 5% or less by controlling the difference in degree of orientation between the front and back surfaces to 0.8 or less. Can be used in a fuel cell to greatly improve thermal deformation stability and swelling deformation stability during power generation.

In the present invention, the degree of orientation of the surface plane means the degree of orientation with respect to the membrane surface of the aromatic ring surface up to a depth of about 3 μm from the membrane surface. Specifically, polarization ATR measurement using a diamond crystal as an internal reflection element by FT-IR (measurement apparatus: manufactured by VARIAN, FTS-60A / 896, etc.), and once-reflection ATR attachment are set to golden gate Mkll (SPECAC). Ltd.), the absorption coefficient in each direction in 1490Cm ^-1 and 1456cm ^-1 when the film surface was measured under conditions of 45 ° angle of incidence, ^{4 cm -1} resolution, 128 cumulative (Kx, Ky and Kz ) Defined by the orientation factor (Kx + Ky) / (2 × Kz) (where Kx is the MD direction, Ky is the TD direction, and Kz is the absorption coefficient in the thickness direction).

    The difference between the degree of orientation of the surface of one surface of the membrane and the degree of orientation of the surface of the other surface is determined by measuring the degree of orientation of the surface of each surface of the aromatic hydrocarbon ion exchange membrane of the present invention. It is represented by the absolute value of.

    The surface orientation degree of the surface having the higher surface orientation degree is preferably 2.0 or less, more preferably 1.5 or less. More preferably, it is 1.0 or less. If the surface orientation degree of the higher surface orientation degree is larger than 2.0, it becomes difficult to control the difference in surface orientation degree of the film surface within a predetermined range, and it is easy to be deformed by heat and humidity. Become.

    The lower limit value of the surface plane orientation degree of the surface having the higher surface plane orientation degree is not particularly limited, but is preferably 0.2 or more, more preferably 0.3 or more, from the viewpoint of the flatness of the film. More preferably, it is 0.4 or more.

In the present invention, the curl degree of the film means the degree of deformation in the thickness direction with respect to the surface direction of the film after performing a predetermined treatment, and specifically, a test of 50 mm × 50 mm as shown in FIG. After the piece was treated with hot air at 100 ° C. for 10 minutes, the test piece was allowed to stand on a flat surface, and the average value of distances from the flat surfaces at four corners (h1, h2, h3, h4: unit mm) was the curl amount (mm) And a value expressed as a percentage (%) of the curl amount with respect to the distance (35.36 mm) from each vertex to the center of the test piece. Specifically, it is calculated by the following formula.
Curling amount (mm) = (h1 + h2 + h3 + h4) / 4
Curling degree (%) = 100 × (curl amount) /35.36

    In the method for producing an aromatic hydrocarbon ion exchange membrane of the present invention, a solution obtained by dissolving an ionic group-containing aromatic hydrocarbon polymer in a solvent is cast on a support, and then 100 ° C. or more from the boiling point of the solvent. The step of evaporating and removing the solvent at a low temperature, and then the step of obtaining the self-supporting membrane of the ionic group-containing aromatic hydrocarbon polymer by evaporating and removing the solvent at a temperature lower than the boiling point of the solvent by 100 to 70 ° C. The method includes a step of bringing a self-supporting membrane into contact with an acidic liquid to convert an ionic group into an acid form.

In the step of removing the solvent, the solvent can be removed, for example, by heating, drying under reduced pressure, or dipping in a polymer non-solvent that is miscible with the solvent that dissolves the polymer. It is preferable in that it can be easily obtained. More preferably, in order to avoid decomposition and deterioration of the polymer solvent and deterioration of the quality of the coating film, initial drying is performed at the lowest possible temperature under reduced pressure or normal pressure, and drying is performed with a temperature pattern that gradually shifts to a higher temperature side. is important. For this purpose, the solvent is finally removed at a temperature 100 to 70 ° C. lower than the boiling point of the solvent while starting to evaporate the solvent at a temperature lower than the boiling point of the solvent by 100 ° C. or more.
By performing initial drying at a temperature lower than the boiling point of the solvent by 100 ° C. or more, the orientation of molecules on the surface in contact with the support in the plane direction is suppressed, and the thickness from the support side of the membrane to the surface side of the membrane (thickness) It is considered that since the movement of the solvent (in the direction) is slow, the alignment in the thickness direction of the molecules is suppressed, and the orientation and strain during coating of the film surface are also reduced.
On the other hand, rapid drying at a high temperature promotes the orientation of molecules on the surface in contact with the support in the plane direction, and the movement of the solvent from the support side of the film to the surface side of the film (in the thickness direction) It is considered that the alignment in the thickness direction of the molecules occurs quickly, and the orientation and strain at the time of coating on the surface of the film are not relaxed, and the strain is stored in the film.

In the step of converting the ionic group into the acid form, the ionic group in the film may contain a metal salt, but using a suitable acidic solution, for example, sulfuric acid, hydrochloric acid, etc. It can convert into a free acidic group by acid treatment under heating or non-heating. Moreover, when converting into an acidic group, since it is common to process with an excess amount of acid, a polymer may contain an excess acid. Therefore, it is desirable to remove excess acid component by repeating washing with water after conversion to an acidic group. At this time, if the water used for washing contains a salt, the acidic group may be converted back to a metal salt, so use at least water that has been subjected to ion removal treatment, such as ion-exchanged water. Is desirable. Moreover, it is preferable that the ion conductivity of an ion exchange membrane is 1.0 * 10 ^<-2 > S / cm or more. When ion conductivity is 1.0 × ¹⁰ -2 S / cm or higher, tend to better output is obtained in the fuel cell using the ion-exchange membrane, 1.0 × ¹⁰ -2 S / When it is less than cm, the output of the fuel cell tends to decrease.

    As a solvent for dissolving the ionic group-containing aromatic hydrocarbon polymer in the present invention, N-methyl-2-pyrrolidone (boiling point: 202 ° C.), N, N-dimethyl is considered from the viewpoint of solubility, handleability and cost. Organic polar solvents such as acetamide (boiling point: 165 ° C.), N, N-dimethylformamide (boiling point: 153 ° C.), dimethyl sulfoxide (boiling point: 189 ° C.), tetramethylurea, dimethylimidazolidinone, hexamethylphosphonamide and the like are desirable. A plurality of these solvents may be used as a mixture within a possible range. The polymer concentration in the solution is preferably in the range of 0.1 to 50% by weight. If the polymer concentration in the solution is less than 0.1% by weight, it tends to be difficult to obtain a good molded product, and if it exceeds 50% by weight, the processability tends to deteriorate.

  As a method for casting from an ionic group-containing aromatic hydrocarbon polymer solvent solution, known methods such as a comma coater, a lip coater, a blade coater, a bar coater, a roll coater, and a knife coater can be used. As the support, an endless belt or drum made of a metal such as stainless steel, a film made of a resin such as polyethylene terephthalate, glass, or the like can be used, but is not limited thereto. The surface of the support may be modified by, for example, mirror-treating the surface of the support made of metal or corona treatment of the surface of the resin film. When the viscosity of the polymer solvent solution is high, when the substrate or the solution is heated and cast at a high temperature, the viscosity of the polymer solvent solution is lowered and can be easily cast.

The thickness of the polymer solvent solution at the time of casting is not particularly limited, but is preferably 10 to 1500 μm. If it is too thin, the shape of the film cannot be maintained, and if it is too thick, a non-uniform film tends to be easily formed. More preferably, it is 50-500 micrometers. If the thickness of the polymer solvent solution is less than 10 μm, the form as an ion exchange membrane tends to be not maintained, and if it is greater than 1500 μm, a non-uniform ion exchange membrane tends to be easily formed. As a method for controlling the cast thickness of the polymer solvent solution, a known method can be used. For example, the cast area can be made constant by using an applicator, a doctor blade or the like, or by using a glass petri dish or the like. The thickness can be controlled by the amount and concentration of the solution.
Also, a known method can be used to obtain a film from the cast polymer solvent solution. As described above, the cast polymer solvent solution can obtain a more uniform film by adjusting the drying temperature, drying conditions, etc., and adjusting the solvent removal rate. For example, in the case of heating, the evaporation rate can be lowered by lowering the temperature in the first stage. In addition, when immersed in a non-solvent such as water, the solidification rate of the polymer can be adjusted by leaving the solution in air or an inert gas for an appropriate time.

    The film of the present invention can have any film thickness depending on the purpose, but is preferably as thin as possible from the viewpoint of ion conductivity. Specifically, the thickness is preferably 5 to 200 μm, more preferably 5 to 50 μm, and most preferably 5 to 20 μm. If the thickness of the ion exchange membrane is less than 5 μm, the handling of the ion exchange membrane becomes difficult and a short circuit or the like tends to occur when a fuel cell is produced. If the thickness is greater than 200 μm, the electric resistance value of the ionic conductivity increases and the fuel cell increases. The power generation performance tends to decrease.

    The casting, drying, and acid treatment of the ionic group-containing aromatic hydrocarbon polymer solvent solution can be performed continuously or intermittently.

    EXAMPLES Hereinafter, although this invention is demonstrated concretely using an Example, this invention is not limited to these Examples. Various measurements were performed as follows.

<Ion exchange membrane evaluation method>
The ion exchange membrane evaluation method is shown below. In the evaluation, unless otherwise specified, the evaluation was performed in a measurement chamber in which the room temperature was 20 ° C. and the humidity was controlled to 30 ± 5 RH% for the purpose of accurately measuring the thickness and weight. In the measurement, a sample that was allowed to stand in a measurement chamber for 24 hours or more was used.

<Surface orientation degree>
The degree of surface orientation was measured using polarized light ATR at an incident angle of 45 °, a resolution of 4 cm ⁻¹ , and an integration count of 128 times. The absorption coefficient (Kx) in the MD direction, the absorption coefficient (Ky) in the TD direction, and the absorption coefficient (Kz) in the thickness direction at the peak (aromatic ring vibration) appearing in the vicinity of 1490 cm ⁻¹ are measured for the aromatic hydrocarbon ion exchange membrane. Obtained for each of the front and back surfaces, the surface orientation degree was calculated by the following formula.
Surface orientation degree = (Kx + Ky) / (2 × Kz)

<Difference in surface orientation>
In addition, the difference in the degree of surface plane orientation between the front and back surfaces of the aromatic hydrocarbon ion exchange membrane of the present invention is the difference in the degree of surface plane orientation between the air side (A side) and the support side (B side) as shown in the following equation. Calculated by the absolute value of the difference.
Difference in degree of orientation of surface plane = | degree of orientation of surface plane of plane A−degree of orientation of surface plane of plane B |
Device name: FT-IR (Varian, FTS-60A / 896)
Single reflection ATR attachment; golden gate MKII (manufactured by SPECAC)
IRE; Diamond incident angle; 45 °

<Curl degree>
The distance from the four corner ceramic plates after placing a 50 mm x 50 mm test piece on an alumina ceramic flat plate and treating with hot air at 100 ° C for 10 minutes (h ₁ , h ₂ , h ₃ , h ₄ : unit mm) Was the curl amount (mm), and the curl degree was calculated from the following equation. The curl amount of the used ceramic plate itself is 0.1 mm or less.
Curling amount (mm) = (h ₁ + h ₂ + h ₃ + h ₄ ) / 4
Curling degree (%) = 100 × (curling amount mm) /35.36 mm

<Ion exchange membrane thickness>
The thickness of the ion exchange membrane was determined by measurement using a micrometer (Mitutoyo DIGIMATIC MICROMETER minimum reading: 0.001 mm). Measurement was performed at 10 locations, and the average value was taken as the thickness.

<Polymer logarithmic viscosity>
The polymer powder was dissolved in N-methyl-2-pyrrolidone at a concentration of 0.5 g / dl, the viscosity was measured using a Ubbelohde viscometer in a thermostatic bath at 30 ° C., and the logarithmic viscosity ln [ta / tb] / Evaluation was made in c) (ta is the number of seconds that the sample solution was dropped, tb was the number of seconds that the solvent was dropped, and c was the polymer concentration).

<Ion exchange capacity (acid type)>
As the ion exchange capacity (IEC), the amount of acid type functional groups present in the ion exchange membrane was measured. First, as sample preparation, a sample piece (5 cm × 5 cm) was dried in an oven at 80 ° C. under a nitrogen stream for 2 hours, and further allowed to cool in a desiccator filled with silica gel for 30 minutes, and then the dry weight was measured (Ws). Next, 200 ml of a 1 mol / l sodium chloride-ultra pure aqueous solution and the weighed sample were placed in a 200 ml sealed glass bottle and stirred at room temperature for 24 hours while being sealed. Next, 30 ml of the solution was taken out, neutralized with a 10 mM aqueous sodium hydroxide solution (commercial standard solution), and IEC was determined from the titration (T) using the following formula.
IEC (meq / g) = 10 T / (30 Ws) × 0.2
(Unit of T: ml Unit of Ws: g)

<Ion conductivity>
The ion conductivity σ was measured as follows.
A platinum wire (diameter: 0.2 mm) is pressed against the surface of a strip-shaped film sample having a width of 10 mm on a self-made measurement probe (made of polytetrafluoroethylene) in a constant temperature and humidity chamber at 80 ° C. and a relative humidity of 95%. A sample was held on the substrate, and the AC impedance between the platinum wires was measured by SOLARTRON 1250 FREQUENCY RESPONSE ANALYSER. The distance between the electrodes is measured at 10 mm intervals from 10 mm to 40 mm, and the distance between the electrodes and the resistance measured value estimated from the C-C plot is plotted from the linear slope Dr [Ω / cm] according to the following formula. Calculation was made by canceling the contact resistance between the platinum wires.
σ [S / cm] = 1 / (film width [cm] × film thickness [cm] × Dr)

<Methanol permeation rate and methanol permeation coefficient>
The methanol permeation rate and methanol permeation coefficient of the proton exchange membrane were measured by the following methods.
It was immersed for 24 hours in an aqueous methanol solution with a concentration of 5 mol (5 mol / liter) adjusted to 25 ° C. (The methanol aqueous solution was prepared using commercially available reagent-grade methanol and ultrapure water (18 MΩ · cm)). A proton exchange membrane is sandwiched between H-type cells, 100 ml of a 5 molar aqueous methanol solution is injected into one side of the cell, and 100 ml of ultrapure water is injected into the other cell. The amount of methanol diffusing into the ultrapure water through the exchange membrane was calculated by measuring with a gas chromatograph (the area of the proton exchange membrane was 2.0 cm ² ). That is, it calculated using the following formula | equation from the methanol concentration change rate [Ct] (mmol / L / s) of the cell which put the ultrapure water.
Methanol permeation rate [mmol / m ² / s]
= (Ct [mmol / L / s] × 0.1 [L]) / 2 × 10 ⁻⁴ [m ² ]
Methanol permeability coefficient [mmol / m / s]
= Methanol permeation rate [mmol / m ² / s] × film thickness [m]

<Power generation characteristics>
After adding and dampening a small amount of ultrapure water and isopropyl alcohol to Pt / Ru catalyst-supporting carbon (Tanaka Kikinzoku Kogyo TEC61E54), a DuPont 20% Nafion (registered trademark) solution (product number: SE-20192) is used. The Pt / Ru catalyst-supported carbon and Nafion were added so that the weight ratio was 2.5: 1. Next, stirring was performed to prepare an anode catalyst paste. This catalyst paste is uniformly applied and dried using an applicator so that the amount of platinum deposited is 1.8 mg / cm ² on carbon paper (TGPH-060 manufactured by Toray Industries, Inc.) serving as a gas diffusion layer. Carbon paper with an electrode catalyst layer was produced. Moreover, after adding a small amount of ultrapure water and isopropyl alcohol to a Pt catalyst-supporting carbon (Tanaka Kikinzoku Kogyo Co., Ltd. TEC10V40E) and moistening, a 20% Nafion (registered trademark) solution (product number: SE-20192) manufactured by DuPont, A cathode catalyst paste was prepared by adding the Pt catalyst-carrying carbon and Nafion at a weight ratio of 2.5: 1 and stirring. This catalyst paste was applied and dried on carbon paper (TGPH-060 manufactured by Toray Industries, Inc.) that had been subjected to water repellent treatment so that the amount of platinum deposited was 1 mg / cm ^2. Produced. The membrane sample was sandwiched between the two types of carbon paper with the electrode catalyst layer so that the electrode catalyst layer was in contact with the membrane sample, and pressurized and heated by a hot press method to obtain a membrane-electrode assembly.

This joined body was incorporated into an evaluation fuel cell FC25-02SP manufactured by Electrochem, and a power generation test was performed using a fuel cell power generation tester (manufactured by Toyo Corporation). Power generation is performed while supplying a high-purity air gas (80 ml / min) adjusted to 40 ° C. and a 5 molar aqueous methanol solution (1.5 ml / min) at a cell temperature of 40 ° C. respectively. Aging was performed by generating electricity for hours. Next, the initial performance was evaluated by examining the open circuit voltage (V), the voltage (V) when the constant current discharge test was performed at 100 mA / cm ² , and the resistance (mΩ · cm ² ) determined by the current interruption method. .
In addition, a constant current continuous discharge test was conducted at 100 mA / cm ² for 300 hours, and a change with time in resistance value (mΩ · cm ² ) was investigated by a current interruption method. When the resistance value in the catalyst electrode and the electrolyte membrane assembly increases, it indicates that the connectivity between the catalyst electrode and the electrolyte membrane has decreased. The joining state was also confirmed from the appearance after power generation. When no peeling between the electrolyte membrane and the catalyst electrode was observed, “◯” was given, and when peeling occurred, “X” was given.

<Example 1>
72,6 g of 3,3′-disulfo-4,4′-dichlorodiphenylsulfone disodium salt, 585.9 g of 2,6-dichlorobenzonitrile, 885.0 g of 4,4′-biphenol, 754.8 g of potassium carbonate, N -5475.5 g of methyl-2-pyrrolidone was added and stirred at 150 ° C for 1 hour under a nitrogen atmosphere, and then the reaction was continued with the reaction temperature raised to 200 ° C and the viscosity of the system sufficiently increased. (About 8 hours). After cooling, it was precipitated in strands in water.
The obtained polymer was washed in water for 40 hours and then dried. The logarithmic viscosity of the polymer was 1.40. N-methyl-2-pyrrolidone (boiling point: 202 ° C.) was used as a solvent for the obtained polymer, and the solution was adjusted so that the polymer concentration was 26.0% by weight.
The prepared solution was cast on a stainless steel belt at a temperature of 25 ° C. so that the squeegee / belt gap was 300 μm, and in four hot-air drying zones, 80 ° C. × 10 minutes, 80 ° C. × 10 minutes, 80 ° C. It was dried for 10 minutes at 80 ° C. for 10 minutes. The film that became self-supporting after drying was peeled off from the support to obtain a gel film. Thereafter, in order to replace the metal salt of the ionic group with protons, it is immersed in sulfuric acid having a concentration of 2 mol (mol / liter) at 60 ° C. for 20 minutes, washed with water, dried at 80 ° C. for 12 hours, and ion exchange with a thickness of 55 μm. A membrane was obtained. The physical property values of the obtained ion exchange membrane are shown in Table 1.

<Examples 2 and 3 and Comparative Examples 1 to 3>
An ion exchange membrane was prepared in the same manner as in Example 1 except that the same solution as in Example 1 was cast on a stainless steel belt and then the temperature x time of the four hot air drying zones was changed as shown in Table 1. Obtained.

<Example 4, comparative example 4>
After casting the same solution as in Example 1 on a stainless steel belt at a temperature of 25 ° C. so that the squeegee / belt gap is 600 μm, the temperature x time of the four hot air drying zones is as shown in Table 1. Except that, an ion exchange membrane was obtained in the same manner as in Example 1.

Table 1 shows the production conditions of the ion exchange membranes obtained in Examples and Comparative Examples and the results of form evaluation, and Table 2 shows the results of performance evaluation.
From these evaluation results, in the comparative example, the initial drying temperature is drying from a high state of 120 ° C. As a result, the difference in the degree of orientation between the front and back surfaces is 0.8 or more, and the curl degree is also 5%. That's it. Although there is no significant difference in the single membrane characteristics in both the examples and the comparative examples, the membrane produced under the drying conditions of the comparative example is clearly inferior in terms of the power generation characteristics after joining with the catalyst electrode.
Therefore, according to the present invention, by making the degree of curl of the membrane less than 5%, the bondability with the catalyst electrode is improved, and excellent ion exchange that can avoid the deterioration of the performance of the fuel cell due to the separation between the membrane and the catalyst electrode It can be seen that a membrane can be provided.

  The aromatic hydrocarbon ion exchange membrane of the present invention is excellent in bondability with a catalyst electrode, and a fuel cell using this membrane / catalyst electrode assembly exhibits stable power generation characteristics over a long period of time. It is suitable for.

It is the schematic diagram which showed the measuring method of the curl degree of an aromatic hydrocarbon type | system | group ion exchange membrane. (A) is a schematic top view, (b) is a schematic cross-sectional view indicated by aa in (a) before hot air treatment, and (c) is aa in (a) after hot air treatment. It is a schematic cross section shown.

Explanation of symbols

A ... Test piece of aromatic hydrocarbon ion exchange membrane b ... Alumina / ceramic plate 1, 2, 3, 4 ... Four corners of test piece h ₁ ... Alumina at position 1 of membrane・ Distance from the ceramic plate h ₄・ ・ ・ Distance from the alumina ceramic plate at position 4 of the membrane

Claims (6)

  The difference between the degree of orientation of the surface of one surface of the aromatic hydrocarbon ion exchange membrane and the degree of orientation of the surface of the other surface is 0.8 or less. .   2. The aromatic hydrocarbon ion exchange membrane according to claim 1, wherein the surface having a higher surface orientation degree has a surface orientation degree of 2.0 or less.   The aromatic hydrocarbon ion exchange membrane according to claim 1 or 2, having a curl degree of 5% or less.   The aromatic hydrocarbon ion exchange membrane has an ionic group-containing aromatic hydrocarbon polymer, and has an ion exchange capacity of 0.3 to 3.5 meq / g. Aromatic hydrocarbon ion exchange membrane. An aromatic hydrocarbon-based ion exchange membrane, wherein the ionic group-containing aromatic hydrocarbon-based polymer is a polyarylene ether-based compound including the structural units represented by the general formula (1) and the general formula (2).

(However, Ar is a divalent aromatic group, Y is a sulfone group or a ketone group, X is H and / or a monovalent cation species, Z is selected from an ether bond, a thioether bond and a divalent aliphatic group. At least one).

(However, Ar ′ is a divalent aromatic group, and Z ′ is at least one selected from an ether bond, a thioether bond, and a divalent aliphatic group.)   After casting a solution in which an ionic group-containing aromatic hydrocarbon polymer is dissolved in a solvent, the solvent is evaporated and removed at a temperature 100 ° C. or more lower than the boiling point of the solvent, and then the boiling point of the solvent After evaporating and removing the solvent at a temperature lower than 100 to 70 ° C. to obtain a self-supporting membrane of an ionic group-containing aromatic hydrocarbon polymer, the ionic groups of the obtained self-supporting membrane are brought into contact with an acidic liquid. The method for producing an aromatic hydrocarbon ion exchange membrane according to claim 1, wherein the method is converted to an acid form.

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