JP2005171025A - Method of manufacturing proton conductive film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a proton conductive film which is used for a solid state polymer-type fuel cell, suitable to the use for electrolytes, and has a superior proton conductivity and mechanical strength. <P>SOLUTION: The method of manufacturing the proton conductive film is characterized in that a polymer having an acidic ion-conductive component and an additive which can perform an acid-base mutual action with respect to the ion conductive component are dispersed or dissolved in a solvent, the dispersion liquid or the dissolution liquid is cast to be formed in a film state, then the formed body is immersed in water to extract and remove the additive or residual components. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a proton conductive membrane having excellent proton conductivity and mechanical strength suitable for electrolyte applications, which is used in a polymer electrolyte fuel cell.

  A fuel cell basically comprises two catalyst electrodes and a solid electrolyte membrane sandwiched between the electrodes. Hydrogen as a fuel is ionized at one electrode, and this hydrogen ion diffuses through the solid electrolyte membrane and then combines with oxygen at the other electrode. At this time, if the two electrodes are connected by an external circuit, a current flows and power is supplied to the external circuit. Here, the solid electrolyte membrane has a function of diffusing hydrogen ions and at the same time physically separating hydrogen and oxygen of the fuel gas and blocking the flow of electrons.

  Examples of such a solid electrolyte membrane include polymers belonging to so-called cation exchange resins, such as sulfonated products of vinyl polymers such as polystyrene sulfonic acid, perfluoroalkyl sulfonic acid polymers, perfluoroalkyl carboxylic acid polymers, among others. A perfluoroalkylsulfonic acid proton conductive membrane represented by Nafion (trade name, manufactured by DuPont) has been widely used. However, while perfluoroalkylsulfonic acid polymers have high proton conductivity, they are very expensive, are cheaper, mechanically stable, and have a long-awaited material that exhibits excellent ionic conductivity as a solid electrolyte membrane. It was.

  Regarding ion conduction, the channel structure formed by ion conduction components in the membrane is considered to be extremely important. Edomondson, CA; ADReport 2000, 18 (Non-Patent Document 1) describes ion conduction by percolation of a site (ion conducting site) where hydrogen ions dispersed in a proton conducting membrane can diffuse. From the viewpoint that ions are conducted through, it is important to control the spatial arrangement of ion conduction sites in the membrane in order to obtain a solid electrolyte exhibiting excellent ion conductivity.

  Using a block copolymer in which two or more kinds of mutually incompatible polymers (block chains) are covalently bonded to form one polymer chain can control the arrangement of chemically different components on the nanometer scale. it can. In block copolymers, short-range interaction resulting from repulsion between chemically different block chains causes phase separation into regions (microdomains) consisting of the respective block chains, but the block chains are covalently bonded to each other. The effect of the long-range interaction that occurs causes each microdomain to be arranged in a specific order.

  A structure created by the assembly of microdomains made up of block chains is called a microphase separation structure. The microphase separation structure of the membrane shows a spherical micelle structure, a cylinder structure, a lamellar structure, etc. depending on the composition of the constituent components. Controlling the spatial arrangement of ion conduction sites in the membrane using these microphase separation structures is considered to be an element for obtaining a solid electrolyte exhibiting excellent ion conductivity.

  However, in systems using conventional block copolymers, the formation of microphase-separated structures is largely affected by thermodynamic control, and in many cases the shape is limited by the primary structure of the polymer and the film-forming conditions. It has been difficult to arbitrarily and in detail control the spatial arrangement of ion conduction sites required in the present invention.

A proton conductive solid polymer electrolyte using a block copolymer is disclosed in, for example, Japanese Patent Application Laid-Open No. H8-20704 (Patent Document 1). On the other hand, in Japanese Patent Application Laid-Open No. 10-503788 (Patent Document 2) and Japanese Patent Application Laid-Open No. 2003-142125 (Patent Document 3), an example of a solid electrolyte membrane obtained by sulfonating a triblock copolymer using an aliphatic vinyl compound as a raw material Is disclosed.
Edomondson, CA; ADReport 2000, 18 JP-A-8-20704 Japanese National Patent Publication No. 10-503788 JP 2003-142125 A

  Patent Document 1 discloses a combination of specific chemical structures as a block chain, and focuses on improving characteristics by controlling the spatial arrangement of ion-conducting sites in the film, which is the object of the present invention. The idea is different. Further, the one disclosed in Patent Document 1 has insufficient proton conductivity, and is not necessarily satisfactory in terms of heat resistance, oxidation resistance, and toughness.

  Patent Documents 2 and 3 focus on spatial arrangement control of ion conduction sites in the membrane, and have high proton conductivity by using a hydrophilic channel (ion conduction channel) as a continuous phase. The purpose is to ensure sex. However, block copolymers based on aliphatic skeletons are generally thermally unstable due to low glass point transfer, and the phase separation structure is deformed due to thermal history, resulting in a change in physical properties. is there.

  In view of such problems in the prior art, the present inventor has intensively studied a method for easily obtaining a proton conductive membrane having a thermally stable and high proton conductivity.

  As a result, a cast film is obtained by adding an ion-conductive component and an additive capable of acid-base interaction to a cast solution containing a block copolymer composed of a segment containing acidic ion conductivity and a segment not containing ion conductivity. It was found that high proton conductivity can be secured by arbitrarily controlling the microphase separation structure. Particularly, the gist of the present invention is characterized in that the microphase separation structure of the cast film can be controlled not by changing the primary structure of the polymer but by the effect of the kind or amount of the additive.

According to the present invention, the following method for producing a proton conducting membrane is provided.
(1) A polymer having an acidic ion conductive component and an additive capable of acid-base interaction with the ion conductive component are dispersed or dissolved in a solvent,
After casting the dispersion or solution into a film,
A method for producing a proton conductive membrane, wherein the molded body is immersed in water to extract and remove additives or residual components.
(2) It has the process of drying before a molded object is immersed in water.
(3) The additive is a compound that is soluble in water or a polar solvent and can form a salt with an acidic ion conducting component.
(4) The additive is added in an amount of 0.05 to 10.0 equivalents relative to the number of acidic ion conductive groups.
(5) A polymer having an acidic ion conductive component is
A block copolymer comprising a segment (A) containing ionic conductivity and a segment (B) not containing ionic conductivity,
The main chain skeleton forming the copolymer has a structure in which an aromatic ring is covalently bonded as a linking group, and a sulfonic acid group is contained in the polymer side chain as an ion conductive group.
(6) When extracting additives or residual components from the molded article, water having a high pH is used in stages, water having a pH of 1 to 4 is used in the former stage, and pH is 4 to 7 in the latter stage. Use water up to (but the latter pH is higher than the previous pH)
In the present invention as described above, the micro-phase separation structure of the membrane, particularly the spatial arrangement of the ion conduction site, can be controlled in more detail, so it has high proton conductivity, compared with the perfluoroalkylsulfonic acid system. It is possible to provide a proton conductive membrane that is inexpensive and has excellent mechanical strength and thermal stability.

  The proton conductive membrane obtained by the production method of the present invention exhibits excellent heat resistance, oxidation resistance, and toughness while maintaining high proton conductivity. Therefore, a fuel cell made of hydrogen or methanol, specifically, a fuel cell for household power supply, a fuel cell vehicle, a fuel cell for a mobile phone, a fuel cell for a personal computer, a fuel cell for a portable terminal, a fuel cell for a digital camera, It can be suitably used for applications such as portable CD, MD fuel cells, headphone stereo fuel cells, pet robot fuel cells, electrically assisted bicycle fuel cells, and electric scooter fuel cells.

Hereinafter, the method for producing a proton conductive membrane according to the present invention will be specifically described.
(Polymer having acidic ion conductive component)
As the polymer having an acidic ion conductive component used in the present invention, a polymer having an acidic ion conductive group is used. Examples of the acidic ion conductive group include a sulfonic acid group, a carboxylic acid group, and a sulfuric acid group.

  In the present invention, the polymer having an acidic ion conductive component is a block copolymer composed of a segment (A) containing ion conductivity and a segment (B) containing no ion conductivity, and forms a copolymer. It is preferable that the main chain skeleton has a structure in which an aromatic ring is covalently bonded with a linking group, and a sulfonic acid group is contained in the polymer side chain as an ion conductive group.

  Such a block copolymer can form a microphase separation structure. As a means for controlling the microphase separation structure as described above by defining the structure of the substrate, there is a use of a block copolymer in which incompatible polymers are covalently bonded to form one polymer chain. . When a copolymer comprising a polymer segment (A) having an ion conductive component and a polymer segment (B) having no ion conductive component is used as in the present invention, the hydrophilic-hydrophobic interaction is mainly driven. It is possible to form a micro phase separation structure with a force.

  As the main chain skeleton, a structure in which an aromatic ring is covalently bonded with a linking group in consideration of mechanical strength and heat resistance is preferable. The formation of the microphase separation structure is greatly affected by thermodynamic control, and it is known that the composition of the substrate and the thermal history after film formation are important for the phase separation structure. In particular, considering the stabilization of film properties after film formation, it is necessary to select a material that is not easily affected by thermal history, that is, a material having a high film softening point or glass transition point. It is preferable to select a block copolymer (polyarylene) containing a main chain skeleton. By introducing an aromatic unit into the basic skeleton of the main chain, the film softening point or glass transition point can be easily obtained at 100 ° C. or higher, and it has excellent thermal stability compared to aliphatic polymers. Has the advantage of being.

With respect to the ion conducting unit, a sulfonic acid group is preferred from the standpoint of substrate stability and conduction efficiency. Further, the introduction position is preferably introduced through a specific bonding group or atomic group as a side chain rather than directly introduced into the main chain from the viewpoint of formation of a microphase-separated structure and mechanical strength. . A polymer in which a sulfonic acid is directly introduced into the main chain has a low ability to form a microphase-separated structure and low mechanical strength, as well as required basic characteristics of a solid fuel cell electrolyte membrane, such as stability to water or hot water. There are drawbacks.

  In the present invention, as the polyarylene copolymer containing such a sulfonic acid group, those shown below are used.

  The polyarylene having a sulfonic acid group used in the present invention includes a repeating structural unit represented by the following general formula (A) and a repeating structural unit represented by the following general formula (B). It is a polymer represented by general formula (C).

In the formula, A represents a divalent electron-withdrawing group. Specifically, —CO—, —SO ₂ —, —SO—,
—CONH—, —COO—, — (CF ₂ ) ₁ — (wherein 1 is an integer of 1 to 10), —C (CF ₃ ) ₂ — and the like can be mentioned.

B represents a divalent electron donating group or a direct bond. Specific examples of the electron donating group include — (CH ₂ ) —, —C (CH ₃ ) ₂ —, —O—, —S—, —CH═CH—, —C≡C— and

Etc. The electron-withdrawing group means a group having a Hammett substituent constant of 0.06 or more when the phenyl group is in the m-position and 0.01 or more when the p-position is p-position.

Ar represents an aromatic group having a substituent represented by —SO ₃ H, and specific examples of the aromatic group include a phenyl group, a naphthyl group, an anthracenyl group, and a phenanthyl group. Of these groups, a phenyl group and a naphthyl group are preferable.
m represents an integer of 0 to 10, preferably 0 to 2, n represents an integer of 0 to 10, preferably 0 to 2, and k represents an integer of 1 to 4.

In formula (B), R ^{1 to} R ⁸ may be the same as or different from each other, and are selected from the group consisting of a hydrogen atom, a fluorine atom, an alkyl group, a fluorine-substituted alkyl group, an allyl group, an aryl group, and a cyano group. At least one atom or group is shown.

  Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, an amyl group, and a hexyl group, and a methyl group and an ethyl group are preferable.

  Examples of the fluorine-substituted alkyl group include trifluoromethyl group, perfluoroethyl group, perfluoropropyl group, perfluorobutyl group, perfluoropentyl group, perfluorohexyl group, trifluoromethyl group, pentafluoroethyl group, and the like. Etc. are preferable.

Examples of allyl groups include propenyl groups,
Examples of the aryl group include a phenyl group and a pentafluorophenyl group.

  W represents a single bond or a divalent electron-withdrawing group, and T represents a single bond or a divalent organic group.

  In the formula (B), p is 0 or a positive integer, and the upper limit is usually 100, preferably 10-80.

  The block copolymer is represented below.

(In the formula (D), W, T, A, B, Ar, m, n, k, p and R ^{1 to} R ⁸ are respectively W, T, A in the general formulas (A) and (B). , B, Ar, m, n, k, p, and R ^{1 to} R ⁸ .
The polyarylene having a sulfonic acid group used in the present invention contains 0.5 to 100 mol%, preferably 10 to 99.999 mol% of the repeating structural unit represented by the formula (A). ) Is contained in a proportion of 99.5 to 0 mol%, preferably 90 to 0.001 mol%.

  Such a block copolymer forms a monomer that forms the repeating unit (a) of the block represented by the general formula (A) and a repeating unit (b) of the block represented by the general formula (B). It can be synthesized by copolymerizing a monomer or oligomer.

  Further, a polymer having a block of the general formula (A) not containing a sulfonic acid group and a block represented by the general formula (B) can be synthesized in advance, and the polymer can be synthesized by sulfonation. .

  In addition, the block copolymer is prepared by previously polymerizing at least one of a monomer that forms a repeating unit and a monomer that forms a repeating unit to produce a precursor, and another copolymer component is reacted with the obtained precursor. Can be manufactured.

  Known reaction conditions and functional groups are selected as the reaction conditions for synthesizing the copolymer of the present invention and the functional groups of the monomer forming the repeating unit and the monomer forming the repeating unit.

  A monomer that can be a structural unit of the general formula (A) (for example, a monomer represented by the following general formula (D), also referred to as monomer (D)) and an oligomer that can be a structural unit of the general formula (B) (for example, In the case of synthesizing a polyarylene having a sulfonate group by copolymerizing with an oligomer represented by the following general formula (E) or oligomer (E), examples of the monomer (D) include A sulfonic acid ester represented by the general formula (D) is used.

In the formula (D), X represents a halogen atom other than fluorine (chlorine, bromine, iodine), —OSO ₂ Z (
Here, Z represents an alkyl group, a fluorine-substituted alkyl group or an aryl group. ), A, B, Ar, m, n and k have the same meanings as A, B, Ar, m, n and k in the above general formula (A), respectively. R ^a represents a hydrocarbon group having 1 to 20 carbon atoms, preferably 4 to 20 carbon atoms. Specifically, methyl group, ethyl group, n-propyl group, iso-propyl group, tert-butyl group, iso- Butyl group, n-butyl group, sec-butyl group, neopentyl group, cyclopentyl group, hexyl group, cyclohexyl group, cyclopentylmethyl group, cyclohexylmethyl group, adamantyl group, adamantanemethyl group, 2-ethylhexyl group, bicyclo [2.2 .1] heptyl group, bicyclo [2.2.1] heptylmethyl group, tetrahydrofurfuryl group, 2-methylbutyl group, 3,3-dimethyl-2,4-dioxolanemethyl group, cyclohexylmethyl group, adamantylmethyl group , Straight chain hydrocarbon group such as bicyclo [2.2.1] heptylmethyl group, branched hydrocarbon group, alicyclic hydrocarbon group, 5-membered And a hydrocarbon group having a heterocyclic ring. Among these, an n-butyl group, neopentyl group, tetrahydrofurfuryl group, cyclopentyl group, cyclohexyl group, cyclohexylmethyl group, adamantylmethyl group, and bicyclo [2.2.1] heptylmethyl group are preferable, and a neopentyl group is more preferable. .

Ar represents an aromatic group having a substituent represented by —SO ₃ R ^b , and specific examples of the aromatic group include a phenyl group, a naphthyl group, an anthracenyl group, and a phenanthyl group. Of these groups, a phenyl group and a naphthyl group are preferable.

The substituent —SO ₃ R ^b is substituted with one or more aromatic groups, and when two or more substituents —SO ₃ R ^b are substituted, these substituents are the same as each other. But it can be different.

Here, R ^b represents a hydrocarbon group having 1 to 20 carbon atoms, preferably 4 to 20 carbon atoms, and specific examples thereof include the hydrocarbon groups having 1 to 20 carbon atoms. Among these, n-butyl group, neopentyl group, tetrahydrofurfuryl group, cyclopentyl group, cyclohexyl group,
A cyclohexylmethyl group, an adamantylmethyl group, and a bicyclo [2.2.1] heptylmethyl group are preferable, and a neopentyl group is more preferable.

  m represents an integer of 0 to 10, preferably 0 to 2, n represents an integer of 0 to 10, preferably 0 to 2, and k represents an integer of 1 to 4.

  The monomer which introduce | transduces the block of the general formula (A) which does not contain a sulfonic acid group is exemplified by those having no sulfonic acid ester group in the formula (D).

  As the oligomer (E), for example, a compound represented by the following general formula (E) is used.

In the formula (E), R ′ and R ″ may be the same as or different from each other, and a halogen atom or —OSO ₂ Z excluding a fluorine atom (where Z is an alkyl group, a fluorine-substituted alkyl group or an aryl group) The group represented by this is shown. Examples of the alkyl group represented by Z include a methyl group and an ethyl group, examples of the fluorine-substituted alkyl group include a trifluoromethyl group, and examples of the aryl group include a phenyl group and a p-tolyl group.

R ^{1 to} R ⁸ , W, T, and p are the same as in the above formula (B).

  Such a block copolymer will be described by taking 4,4′-dihydroxybenzophenone and 4,4′-dichlorodiphenylsulfone as examples.

  By reacting 4,4′-dihydroxybenzophenone and 4,4′-dichlorodiphenylsulfone at a high temperature in the presence of a base, an oligomer having both ends of a chlorine atom is synthesized, and a polysiloxane constituting the block of the general formula (B) is synthesized. An ether ketone sulfone precursor is obtained. Next, coupling polymerization with 2,5-dichloro-4 ′-(4-phenoxy) phenoxybenzophenone is performed to synthesize a polyether ketone sulfone copolymer, and then the sulfone is synthesized to synthesize the copolymer of the present invention. can do.

  The amount of sulfonic acid groups in the block copolymer is 0.3 to 5 meq / g, preferably 0.5 to 3 meq / g, more preferably 0.8 to 2.8 meq / g. If it is less than 0.3 meq / g, the proton conductivity is low. On the other hand, if it exceeds 5 meq / g, the hydrophilicity is increased and the water resistance is greatly reduced, which is not preferable.

  The amount of the sulfonic acid group can be adjusted by changing the use ratio of the monomer that forms the repeating unit (a) and the monomer that forms the repeating unit (b), and the type and combination of the monomers.

The molecular weight of the block copolymer precursor containing the sulfonic acid group of the present invention, that is, the base polymer before sulfonic acid induction or introduction, is 10,000 to 1,000,000, preferably 20,000 to 80 in terms of polystyrene-converted weight average molecular weight. Ten thousand. If it is less than 10,000, the coating film properties are insufficient, such as cracks occurring in the molded film, and there are also problems with the strength properties. On the other hand, when it exceeds 1,000,000, there are problems such as insufficient solubility, high solution viscosity, and poor workability.
(Additive)
Additives added to a solution containing a polymer having an acidic ion-conducting component are capable of acid-base interaction, ie, salt formation, with respect to acidic ion-conducting groups in the polymer and are soluble in water or polar solvents. Organic or inorganic compounds are selected. By adding the above-mentioned additive to a solution containing a polymer having an acidic ion conductive component, the uniformity of cast film, control of microphase separation, and extraction after casting can be easily performed.

  As the classification of additives, inorganic substances and organic substances can be mentioned. Examples of inorganic substances include alkali metal salts, alkaline earth metal salts, sulfonic acid compound salts, and phosphoric acid salts. For example, barium chloride, barium bromide, barium iodide, barium oxide, barium hydroxide, calcium chloride, calcium bromide, calcium iodide, potassium chloride, potassium bromide, potassium iodide, potassium sulfate, potassium phosphate, water Potassium oxide, lithium chloride, lithium bromide, lithium iodide, lithium sulfate, lithium hydroxide, magnesium chloride, magnesium bromide, magnesium iodide, magnesium sulfate, ammonium chloride, ammonium bromide, ammonium iodide, ammonium sulfate, sodium chloride Sodium bromide, sodium iodide, sodium hydroxide, sodium sulfate, sodium phosphate, sodium phosphite, tin (II) chloride, tin (II) bromide, tin (II) iodide, tin sulfate, zinc chloride , Zinc bromide, zinc iodide, zinc sulfate, perchloric acid Magnesium, sodium perchlorate, lithium perchlorate, ammonium thiocyanate, sodium thiocyanate, and the like. These may be used alone or in plurality. Examples of organic substances include salts of carboxylic acid derivatives, salts of organic sulfonic acid derivatives, salts of organic phosphoric acid derivatives, salts of 1,3-diketones, primary, secondary and tertiary amines, or salts thereof. A quaternary ammonium salt etc. are mentioned. For example, lithium of various carboxylic acids such as succinic acid, maleic acid, oxalic acid, acetic acid, phthalic acid, benzoic acid, sodium, potassium salts, lithium of various sulfonic acids such as benzenesulfonic acid, p-toluenesulfonic acid, sodium, Lithium, sodium, potassium salt of various 1,3-diketones such as potassium salt, acetylacetone, ethyl acetoacetate, ammonia, methylamine, ethylamine, propylamine, butylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, trimethylamine , Amines such as triethylamine, tributylamine, hydroxides such as tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, fluoride, chloride, bromide De, iodide salts, and the like. Of the above compounds, lithium salts and fluoride salts are preferred from the viewpoint of solubility in a solvent.

  By changing the counter ion species that interacts with the acidic ion conductive group, the microphase separation structure can be arbitrarily controlled by the strength of the ionic interaction or the ionic radius.

The amount of additive added is preferably 0.05 to 10.0 equivalents relative to the number of acidic ion conductive groups. When the additive is in this range, the micro phase separation structure in the polymer having an acidic ion conductive component can be controlled, and the properties required for the electrolyte for a solid fuel cell can be secured while having high proton conductivity. . In other words, even if the same polymer is used without changing the primary structure of the polymer, the physical properties can be expressed by appropriately selecting the type and amount of the additive in consideration of the correlation with the polymer. There is.
(Proton conductive membrane production method)
The proton conductive membrane of the present invention is prepared by, for example, dissolving the above-described polymer having an acidic ion conductive component in a solvent to form a solution, adding an additive, mixing or dissolving, and then casting on a substrate by casting. Then, it is manufactured by being formed into a film by a method (casting method) or the like.

The substrate is not particularly limited as long as it is a substrate used in an ordinary solution casting method. For example, a substrate made of plastic or metal is used, and preferably a thermoplastic resin such as a polyethylene terephthalate (PET) film. A substrate is used.

  When preparing a proton conductive membrane, in addition to the polymer having an acidic ion conductive component and the above additives, an inorganic acid such as sulfuric acid and phosphoric acid, an organic acid containing a carboxylic acid, an appropriate amount of water, etc. may be used in combination. Good.

  The solvent for dissolving the polymer having an acidic ion conductive component is not particularly limited, but usually a solvent that easily volatilizes is preferably used. For example, when the polymer having an acidic ion conductive component is a polyarylene having a sulfonic acid group, specifically, N-methyl-2-pyrrolidone, N, N-dimethylformamide, γ-butyrolactone, N, N-dimethyl Examples include aprotic polar solvents such as acetamide, dimethyl sulfoxide, dimethylurea, dimethylimidazolidinone (DMI), and N-methyl-2-pyrrolidone is particularly preferred from the standpoint of solubility and solution viscosity. Aprotic polar solvents can be used alone or in combination of two or more. You may use the mixture of the said aprotic polar solvent and alcohol. Specific examples of the alcohol include methanol, ethanol, propyl alcohol, iso-propyl alcohol, sec-butyl alcohol, tert-butyl alcohol, etc. Methanol is particularly preferable because it has an effect of reducing the solution viscosity in a wide composition range. . Alcohol can be used individually or in combination of 2 or more types.

  When a mixture of an aprotic polar solvent and an alcohol is used as the solvent, the aprotic polar solvent is 25 to 95% by mass, preferably 25 to 90% by mass, and the alcohol is 5 to 75% by mass, preferably 10 to 10%. A mixture having a composition of 75% by weight is used. When the amount of alcohol is within the above range, the effect of lowering the solution viscosity is excellent.

  The polymer concentration in the solution in which the polymer having an acidic ion conductive component is dissolved is usually 5 to 40% by mass, preferably 7 to 25% by mass, although it depends on the polymer molecular weight. If it is less than 5% by mass, it is difficult to form a thick film, and pinholes are easily generated. On the other hand, if it exceeds 40% by weight, the solution viscosity is so high that it is difficult to form a film, and surface smoothness may be lacking.

The solution viscosity depends on the polymer molecular weight and the polymer concentration, but is usually from 2,000 to 2,000.
100,000 mPa · s, preferably 3,000 to 50,000 mPa · s. If it is less than 2,000 mPa · s, the retention of the solution during film formation is poor, and it may flow from the substrate. On the other hand, if it exceeds 100,000 mPa · s, the viscosity is too high to be extruded from the die and it may be difficult to form a film by the casting method.

  The polymer and additive having the acidic ion conductive component described above may not be completely dissolved in the solvent, but may be in a dispersed mixed state. Furthermore, it may be in a state where a part is dissolved and a part is dispersed.

  After forming the film as described above, by immersing the obtained undried film in water, the organic solvent in the undried film is replaced with water, and the residual solvent amount of the resulting proton conducting membrane is reduced. Can do. Also. The remaining additive is also removed at the same time.

  In addition, before immersing the undried film after film-forming in water, you may predry an undried film. The preliminary drying is performed by holding the undried film at a temperature of usually 50 to 150 ° C. for 0.1 to 10 hours.

When immersing an undried film in water, for example, a batch method in which a sheet is immersed in water is employed. Alternatively, a continuous method is adopted in which the laminated film is immersed in water in a state where the film is formed on a substrate film such as PET, or the film separated from the substrate is immersed in water and wound.

  In the case of the batch method, a method of fitting the treated film to the frame is preferable in that wrinkle formation on the surface of the treated film is suppressed.

  When immersing an undried film in water, it is preferable that water has a contact ratio of 10 parts by mass or more, preferably 30 parts by mass or more with respect to 1 part by mass of the undried film. In order to minimize the amount of residual solvent in the resulting proton conducting membrane, it is preferable to maintain a contact ratio as large as possible. In addition, it is effective in reducing the amount of residual solvent in the resulting proton conducting membrane by changing the water used for immersion or allowing it to overflow so that the organic solvent concentration in the water is always kept below a certain level. is there. In order to suppress the in-plane distribution of the amount of the organic solvent remaining in the proton conductive membrane, it is preferable to homogenize the concentration of the organic solvent in water by stirring or the like.

When the undried film is immersed in water, it is necessary to convert the sulfonate salt formed by salt formation with the additive into sulfonic acid. For this reason, when extracting additives or residual components from the molded body, water having a high pH is used stepwise, water having a pH of 1 to 4 is used in the former stage, and pH is 4 to 7 in the latter stage (however, It is preferable to use water up to the pH of the latter stage is higher than the pH of the former stage.

  The soaking has the role of first deriving the sulfonic acid with water having a pH of 1 to 4 and then soaking in the pH of 4 to 7 to remove the additive and its remaining components and return to neutrality. The immersion in acidic water having a pH of 1 to 4 is usually 10 minutes to 240 hours, preferably 30 minutes to 100 hours, depending on the treatment temperature. The number of immersions is usually 1 to 10 times, preferably 2 to 5 times, although it depends on the treatment temperature and the acidity of the aqueous solution.

  The pH may be adjusted using an acid such as hydrochloric acid, sulfuric acid, nitric acid or acetic acid, or an alkali such as ammonia, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogen carbonate or potassium hydrogen carbonate.

  The temperature of water when the undried film is immersed in water is preferably 5 to 90 ° C. The higher the temperature, the higher the rate of substitution between the organic solvent and water, but the greater the amount of water absorbed by the film, so the surface of the proton conducting membrane obtained after drying may become rough. Considering the replacement speed and ease of handling, a temperature range of 10 to 60 ° C. is more preferable.

  Thus, when the undried film is immersed in water and then dried, a proton conductive membrane with a reduced amount of residual solvent is obtained, and the amount of residual solvent and residual additive in the proton conductive membrane is usually 5% by mass. It is as follows.

  Further, for example, the contact ratio between the undried film and water is 50 parts by mass or more of water with respect to 1 part by mass of the undried film, the temperature of water at the time of immersion is 10 to 60 ° C., and the immersion time is 10 minutes. By setting it to 10 hours, the residual solvent amount of the proton conductive membrane obtained can be made 1 mass% or less.

  As described above, after immersing the undried film in water, the film is dried at 30 to 100 ° C., preferably 50 to 80 ° C., for 10 to 180 minutes, preferably 15 to 60 minutes, and then 50 to 150 ° C. Thus, a proton conducting membrane is obtained by drying for 0.5 to 24 hours.

  The proton conducting membrane thus obtained has a dry film thickness of usually 10 to 100 μm, preferably 20 to 80 μm.

  The proton conducting membrane of the present invention may contain an anti-aging agent, preferably a hindered phenol compound having a molecular weight of 500 or more. By containing an anti-aging agent, the durability of the proton conducting membrane is further improved. Can do.

As such a hindered phenol compound having a molecular weight of 500 or more, specifically, triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) proonate] (trade name: IRGANOX 245) 1,6-hexanediol-bis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] (trade name: IRGANOX 259), 2,4-bis- (n- Octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino) -3,5-triazine (trade name: IRGANOX 565), pentaerythrityl-tetrakis [3- (3,5-di-t -Butyl-4-hydroxyphenyl) propionate] (trade name: IRGANOX 1010), 2,2-thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] (trade) Product name: IRGANOX 1035), octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate) (trade name: IRGANOX 1076), N, N-hexamethylenebis (3,5-di-) t-butyl-4-hydroxy-hydrocinnamamide) (IRGAONOX 1098), 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene ( Trade name: IRGANOX 1330), tris- (3,5-di-t-butyl-4-hydroxybenzyl) -isocyanurate (trade name: IRGANOX 3114), 3,9-bis [2- [3- (3 -T-butyl-4-hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane (trade name: Sumilizer GA- 80).

These hindered phenol compounds are preferably used in an amount of 0.01 to 10 parts by mass with respect to 100 parts by mass of the polyarylene having a sulfonic acid group.
(Morphology)
The proton conductive membrane according to the present invention is a membrane comprising a polymer segment (A) having an ion conductive component and a polymer segment (B) having no ion conductive component. The type of polymer, the structure of each segment, and the solvent , And the type and amount of additives can be changed to control the microphase separation structure. The morphology of the proton conducting membrane can be observed with an electron microscope of the membrane cross section. The hydrophilic domain composed of A forming the microphase separation structure is a continuous layer, and the long period thereof is in the range of 1 to 300 nm, more preferably in the range of 10 to 100 nm.

EXAMPLES Hereinafter, the present invention will be described more specifically based on examples, but the present invention is not limited to these examples.

  In the examples, the sulfonic acid equivalent, molecular weight, and proton conductivity were obtained as follows.

1. Sulfonic acid equivalent The polymer having the sulfonic acid group was washed with water until the water was neutral, thoroughly washed with water except for free remaining acid, dried, weighed a predetermined amount, THF / Phenolphthalein dissolved in a mixed solvent of water was used as an indicator, titration was performed using a standard solution of NaOH, and the sulfonic acid equivalent was determined from the neutralization point.

2. Measurement of molecular weight The polyarylene weight-average molecular weight containing no sulfonic acid was determined by GPC using polystyrene (THF) as a solvent and the molecular weight in terms of polystyrene. The molecular weight of the polyarylene having a sulfonic acid group was determined by GPC using N-methyl-2-pyrrolidone (NMP) to which lithium bromide and phosphoric acid were added as a solvent as an eluent.

3. Measurement of proton conductivity AC resistance was measured by pressing a platinum wire (f = 0.5 mm) against the surface of a 5 mm wide strip-shaped proton conducting membrane sample, holding the sample in a constant temperature and humidity device, and between the platinum wires It was obtained from AC impedance measurement. That is, the impedance at an alternating current of 10 kHz was measured in an environment of 25 ° C., 60 ° C., and relative humidity 80%. A chemical impedance measurement system manufactured by NF Circuit Design Block Co., Ltd. was used as the resistance measurement device, and JW241 manufactured by Yamato Scientific Co., Ltd. was used as the constant temperature and humidity device. Five platinum wires were pressed at intervals of 5 mm, the distance between the wires was changed to 5 to 20 mm, and the AC resistance was measured. The specific resistance of the membrane was calculated from the line-to-line distance and the resistance gradient, and the proton conductivity was calculated from the reciprocal of the specific resistance.
Specific resistance R (Ω / cm) = 0.5 (cm) x film thickness (cm) x resistance line gradient (Ω / cm)
Synthesis example 1
Preparation of oligomer 4,4'-dihydroxybenzophenone (4,4'-DHBP) was added to a 2 L three-necked flask equipped with a stirrer, thermometer, condenser, Dean-Stark tube, and nitrogen-introduced three-way cock. 106.0 g (0.495 mol), 4,4′-dichlorodiphenyl sulfone (4,4′-DCDS) 148.2 g (0.516 mol), potassium carbonate 88.9 g (0.64 mol), 1,3-dimethyl -2-Imidazolidinone (DMI) (500 mL) and toluene (200 mL) were added, heated in an oil bath, and reacted at 150 ° C. with stirring in a nitrogen atmosphere. When water produced by the reaction was azeotroped with toluene and reacted while being removed from the system with a Dean-Stark tube, almost no water was produced in about 3 hours. Subsequently, most of the toluene was removed while gradually raising the reaction temperature to 180 ° C., and the reaction was continued at 180 ° C. for 8 hours. Then, 9.2 g (0.032 mol) of 4,4′-DCDS was added, and another 2 hours. Reacted.
After allowing the resulting reaction solution to cool, precipitates of inorganic compounds produced as a by-product were removed by filtration, and the filtrate was put into 4 L of methanol. The precipitated product was collected by filtration, dried, and then dissolved in 500 mL of DMI. This solution was added to 4 L of methanol and reprecipitated to obtain 185 g (yield 79%) of the target compound.

  The number average molecular weight in terms of polystyrene determined by GPC (THF solvent) of the obtained polymer was 2000. Further, the obtained polymer was soluble in NMP, DMAc, DMI and the like, Tg was 157 ° C., and thermal decomposition temperature was 500 ° C.

  The resulting polymer has the following formula (I):

It is presumed to have a structure represented by

Synthesis example 2
(Synthesis of polyarylene copolymer)
17.7 g (0.9 mmol) of the oligomer obtained in Synthesis Example 1, 25.7 g (59.1 mmol) of 2,5-dichloro-4 ′-(4-phenoxy) phenoxybenzophenone (DCPPB), bis (triphenylphosphine) ) 1.18 g (1.8 mmol) of nickel dichloride, 1.17 g (7.8 mmol) of sodium iodide, 6.30 g (24.0 mmol) of triphenylphosphine, and 9.41 g (144 mmol) of zinc dust are added to the flask. Replaced with dry nitrogen. Next, 100 ml of N-methyl-2-pyrrolidone was added to the flask, heated to 80 ° C., and polymerized for 4 hours with stirring.

  After the obtained polymerization solution was diluted with NMP, it was filtered using Celite as a filter aid, and the filtrate was poured into 1000 mL of a large excess of methanol to coagulate and precipitate. The coagulated product was collected by filtration, air-dried, redissolved in 200 mL of NMP, poured into 1500 mL of a large excess of methanol, and coagulated and precipitated. The coagulated product was collected by filtration and dried in vacuo to obtain 36.5 g (93%) of the desired copolymer. The number average molecular weight in terms of polystyrene determined by GPC (NMP) was 42300, and the weight average molecular weight was 161900.

Synthesis example 3
(Synthesis of polyarylene copolymer containing sulfonic acid group)
16 g of the copolymer obtained in Synthesis Example 2 was added to a 500 ml separable flask equipped with a stirrer and a thermometer, and then 160 ml of sulfuric acid having a concentration of 98% was added, and the temperature in the flask was kept at 25 ° C. under a nitrogen stream. For 24 hours. The obtained solution was poured into a large amount of ion exchange water to precipitate a polymer. Next, the polymer was repeatedly washed until the pH of the washing water reached 5, and then dried to obtain 17 g (yield 92%) of a sulfonic acid group-containing polymer. The number average molecular weight in terms of polystyrene determined by GPC (NMP) of this sulfonic acid group-containing polymer is 47700, the weight average molecular weight is 180,000, and the sulfonic acid equivalent is 2.1 meq / g.
(The sulfonic acid equivalent calculated from the monomer charge ratio was 2.3 meq / g).

Comparative Example 1
The conductivity of a cast film (film thickness: 180 μm) of perfluoroalkylsulfonic acid (trade name: Nafion117 (registered trademark), manufactured by DuPont) is 0.090 s / cm (60 ° C./80% RH), 0.049 s / cm (25 ° C./80% RH).

Comparative Example 2
5.0 g of the polymer containing a sulfonic acid group obtained in Synthesis Example 3 was added to 20.6 g of NMP and 10.3 g of methanol to a 50 cc screw tube, and the mixture was stirred for 24 hours with a wafer blower to obtain a uniform polymer solution. .

The above solution was cast on a PET film by a bar coder method and dried at 80 ° C. for 30 minutes and 150 ° C. for 60 minutes to obtain a uniform and transparent solid electrolyte film having a thickness of 50 μm. The film was washed by washing twice with a pH 1 hydrochloric acid solution and then 5 times with a pH 5 water, and the sample was air-dried for one day as a sample. (Ie without additives)
The conductivity of the produced film (film thickness 50 μm) was 0.065 s / cm (60 ° C./80% RH) and 0.019 s / cm (25 ° C./80% RH).

Example 1
5.0 g of NMP 20.6 g and 10.3 g of methanol obtained in Synthesis Example 3 were added to a 50 cc screw tube and dissolved, and then 0.45 g of lithium bromide (0 with respect to the sulfonic acid group). .5 equivalents) was added, and the mixture was stirred for 24 hours with a wafer blower to obtain a uniform polymer solution. Sample preparation was performed in the same manner as in Comparative Example 1.

  The conductivity of the produced film (film thickness 50 μm) was 0.108 s / cm (60 ° C./80% RH) and 0.046 s / cm (25 ° C./80% RH).

Example 2
After adding 5.0 g of NMP 20.6 g and 10.3 g of methanol obtained in Synthesis Example 3 to a 50 cc screw tube and dissolving, 1.37 g of lithium bromide (1 per sulfonic acid group) .5 equivalents) was added, and the mixture was stirred for 24 hours with a wafer blower to obtain a uniform polymer solution. Sample preparation was performed in the same manner as in Comparative Example 1.

  The conductivity of the produced film (film thickness 50 μm) was 0.144 s / cm (60 ° C./80% RH) and 0.050 s / cm (25 ° C./80% RH).

Example 3
After adding 5.0 g of NMP 20.6 g and 10.3 g of methanol obtained in Synthesis Example 3 to a 50 cc screw tube and dissolving it, 1.59 g of triethylamine (1. 5 equivalents) was added, and the mixture was stirred for 24 hours with a wafer blower to obtain a uniform polymer solution. Sample preparation was performed in the same manner as in Comparative Example 1.

  The conductivity of the produced film (film thickness 50 μm) was 0.113 s / cm (60 ° C./80% RH) and 0.053 s / cm (25 ° C./80% RH).

Claims (6)

A polymer having an acidic ion conductive component and an additive capable of acid-base interaction with the ion conductive component are dispersed or dissolved in a solvent,
After casting the dispersion or solution into a film,
A method for producing a proton conductive membrane, wherein the molded body is immersed in water to extract and remove additives or residual components.   2. The method for producing a proton conducting membrane according to claim 1, further comprising a step of drying the molded body before immersing it in water.   2. The method for producing a proton conducting membrane according to claim 1, wherein the additive is a compound that is soluble in water or a polar solvent and can form a salt with an acidic ion conducting component.   The method for producing a proton conducting membrane according to any one of claims 1 to 3, wherein the additive is added in an amount of 0.05 to 10.0 equivalents based on the number of acidic ion conductive groups. A polymer having an acidic ion conductive component is
A block copolymer comprising a segment (A) containing ionic conductivity and a segment (B) not containing ionic conductivity,
The main chain skeleton forming the copolymer has a structure in which an aromatic ring is covalently bonded as a linking group, and the polymer side chain contains a sulfonic acid group as an ion conductive group. 5. A method for producing a proton conducting membrane according to 4. When extracting an additive or a residual component from the said molded object, while using water whose pH is high stepwise, water from pH 1 to 4 is used in the former stage, and pH is 4 to 7 in the latter stage (however, Use water up to the pH of the latter stage)
The method for producing a proton conducting membrane according to claim 1, wherein the extraction temperature is 5 ° C. to 90 ° C.