WO2011136296A1

WO2011136296A1 - Anion exchange membrane and method for producing same

Info

Publication number: WO2011136296A1
Application number: PCT/JP2011/060314
Authority: WO
Inventors: 信義正司; 公平宮崎; 斎藤　恭一
Original assignee: Ａｇｃエンジニアリング株式会社; 国立大学法人千葉大学
Priority date: 2010-04-27
Filing date: 2011-04-27
Publication date: 2011-11-03
Also published as: JP5656201B2; JPWO2011136296A1

Abstract

Disclosed is an anion exchange membrane having heat resistance and alkali resistance, capable of controlling occurrences of pinholes and reduction in strength even with the formation of thin membranes, and having sufficiently low membrane resistance. Also disclosed is a method for producing the same. Specifically disclosed is a method for producing an anion exchange membrane wherein, after graft polymerization by radiation graft polymerization of a monomer component containing a monomer (1) to a membrane-shaped polymer in the presence of 0.005 - 3 parts by mass of a polymerization inhibitor per 100 parts by mass of the monomer component, a compound (2) is reacted. A is a C_3-8 alkylene group or the like; R¹ - R³ are H, C_1-6 alkyl groups or the like; and Z is Br or the like.

Description

Anion exchange membrane and method for producing the same

The present invention relates to an anion exchange membrane and a method for producing the same.

Anion exchange membranes are used as separators for fuel cells, secondary batteries, etc., in addition to seawater concentration by electrodialysis, brine desalination, acid concentration or recovery, and valuable metal recovery. In particular, alkaline solid polymer fuel cells using an anion exchange membrane that does not use noble metals such as platinum as an electrode catalyst have attracted attention, and there is a need for an anion exchange membrane having heat resistance and alkali resistance. Yes.

As an anion exchange membrane having heat resistance and alkali resistance and an intermediate thereof, for example, the following are proposed.
(1) A polyethylene cloth irradiated with an electron beam is impregnated with a viscous liquid in which a monomer component containing 4- (4-bromobutyl) styrene and a styrene thermoplastic elastomer are mixed, and the monomer component is polymerized in the cloth. Then, triethylamine is reacted to convert bromine into a trimethylammonium group, and the counter ion Br 2 ^— is exchanged with Cl 2 ^— (Patent Document 1).
(2) An anion exchange membrane obtained by impregnating a polyethylene-coated polypropylene nonwoven fabric irradiated with an electron beam with a solution containing 4- (4-bromobutyl) styrene and graft-polymerizing 4- (4-bromobutyl) styrene in the nonwoven fabric. Intermediate (Patent Document 2).

JP 2002-114854 A JP 2002-088132 A

Recently, an anion exchange membrane for an alkaline polymer electrolyte fuel cell is required to have a lower resistance, and accordingly, the anion exchange membrane is made thinner and the monomer graft ratio is improved. Is required.

However, when an anion exchange membrane based on cloth or nonwoven fabric is thinned, the following problems occur.
(I) Since the cloth and the nonwoven fabric are porous, when the cloth or the nonwoven fabric is thinned, pinholes are easily generated in the obtained anion exchange membrane. When many pinholes are generated, it cannot be used as an anion exchange membrane.
(Ii) Since the strength of the thin cloth or nonwoven fabric is low, the strength of the obtained anion exchange membrane is insufficient.

In addition, as a method of solving the problem of (i) and (ii), instead of cloth or non-woven cloth, it is not porous like cloth or non-woven cloth, and has higher strength than cloth or non-woven cloth even if it is thinned. It is conceivable to use a film-like polymer as a base. Patent Documents 1 and 2 also describe that a film-like material can be used.

However, when 4- (4-bromobutyl) styrene is graft polymerized to a film-like polymer by the method described in Patent Documents 1 and 2, oligomerization of 4- (4-bromobutyl) styrene is performed rather than graft polymerization. However, it is not possible to obtain an anion exchange membrane having a sufficiently high graft ratio, that is, a sufficiently low membrane resistance.

The present invention provides an anion exchange membrane having a heat resistance and an alkali resistance, capable of suppressing the occurrence of pinholes and a decrease in strength even when it is thinned, and a sufficiently low membrane resistance, and a method for producing the same.

The gist of the present invention is as follows.
(1) A monomer component containing a monomer represented by the following formula (1) is added to a film-like polymer in the presence of 0.005 to 3 parts by mass of a polymerization inhibitor with respect to 100 parts by mass of the monomer component. A method for producing an anion exchange membrane, wherein a compound of the following formula (2) is reacted after graft polymerization by a radiation graft polymerization method.

A is an alkylene group having 3 to 8 carbon atoms or an alkyleneoxymethylene group having 4 to 8 carbon atoms, and R ¹ to R ³ are each a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a carbon number 1 to 6 hydroxyalkyl groups, Z is a halogen atom, and the hydrogen atom of the benzene ring may be substituted with an alkyl group or a halogen atom.
(2) A monomer component containing the monomer represented by the following formula (31) or the monomer represented by the following formula (32) in the film-like polymer is added in an amount of 0.005 to 3 masses with respect to 100 mass parts of the monomer component. A method for producing an anion exchange membrane, wherein graft polymerization is carried out by radiation graft polymerization in the presence of a part of the polymerization inhibitor.

A is an alkylene group having 3 to 8 carbon atoms or an alkyleneoxymethylene group having 4 to 8 carbon atoms, and R ¹ to R ³ are each a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a carbon number 1 to 6 hydroxyalkyl groups, X 2 ^— is a counter ion of an ammonium group, and the hydrogen atom of the benzene ring may be substituted with an alkyl group or a halogen atom.
(3) The method for producing an anion exchange membrane according to the above (1) or (2), wherein the polymer is a polyolefin or a fluororesin.
(4) The method for producing an anion exchange membrane according to any one of (1) to (3), wherein the polymerization inhibitor is hydroquinone, p-methoxyphenol, cresol, or t-butylcatechol.
(5) The method for producing an anion exchange membrane according to any one of the above (1) to (4), wherein the thickness of the membrane polymer is 10 to 200 μm.
(6) An anion exchange membrane obtained by the production method according to any one of (1) to (5) above, wherein the graft ratio determined by the following formula (I) is 6 mol% or more. Anion exchange membrane.
dg = m _m / m _p × 100 (I).
However, dg is the graft rate [mol%], m _p is the number of moles of monomer units constituting the film-shaped polymer, m _m is moles of the monomer component is graft-polymerized to a membrane-like polymer Is a number.
(7) The anion exchange membrane according to the above (6), wherein the ion exchange capacity is 1.5 to 3 meq / g dry resin.

The anion exchange membrane of the present invention has heat resistance and alkali resistance, and even when it is thinned, generation of pinholes and a decrease in strength are suppressed, and membrane resistance is sufficiently low.
According to the method for producing an anion exchange membrane of the present invention, the anion exchange membrane has heat resistance and alkali resistance, the occurrence of pinholes and a decrease in strength can be suppressed even when the thickness is reduced, and the membrane resistance is sufficiently low. Can be manufactured.

In the present specification, the monomer means a compound having a radical polymerizable functional group.
In the present specification, the monomer unit means a unit derived from the monomer formed by polymerization of the monomer. The unit may be a unit directly formed by a polymerization reaction, or may be a unit in which a part of the unit is converted into another structure by treating the polymer.

In the present specification, a monomer represented by the formula (1) is referred to as a monomer (1). The same applies to compounds represented by other formulas.
In this specification, a compound represented by the formula (2) is referred to as a compound (2). The same applies to compounds represented by other formulas.

<Method for producing anion exchange membrane>
The anion exchange membrane of the present invention can be produced by the following method (α) or method (β).

(Α) A monomer component containing the monomer (1) is added to the film-like polymer by radiation graft polymerization in the presence of 0.005 to 3 parts by mass of a polymerization inhibitor with respect to 100 parts by mass of the monomer component. A method of reacting compound (2) after graft polymerization.

(Β) A monomer component containing monomer (31) or monomer (32) in a film-like polymer in the presence of 0.005 to 3 parts by mass of a polymerization inhibitor with respect to 100 parts by mass of the monomer component, A method of graft polymerization by radiation graft polymerization.

A is an alkylene group having 3 to 8 carbon atoms or an alkyleneoxymethylene group having 4 to 8 carbon atoms. The alkylene group may be linear or branched.
A is preferably an alkylene group having 3 to 7 carbon atoms, and more preferably an alkylene group having 3 to 5 carbon atoms.
When the number of carbon atoms is at least the lower limit, the positively charged ammonium group is hardly affected by the benzene ring through the alkylene group, and the heat resistance of the anion exchange group is improved. If the number of carbon atoms is not more than the upper limit value, the ion exchange capacity per mass becomes sufficiently high, and an increase in membrane resistance can be suppressed.

R ¹ to R ³ are each a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a hydroxyalkyl group having 1 to 6 carbon atoms. R ¹ to R ³ may be the same or one or more may be different.
As the alkyl group or hydroxyalkyl group, a methyl group, ethyl group, propyl group, butyl group, hydroxyethyl group or hydroxypropyl group is preferable.

Z is a halogen atom. The halogen atom is preferably bromine from the viewpoint of the stability of the monomer (1), polymerizability, and convertibility to an anion exchange group.
X ⁻ is a counter ion of an ammonium group. Examples of X ⁻ include halogen ions, HCO ₃ ⁻ , CO ₃ ²⁻ , acetate ions, NO ₃ ⁻ , OH ⁻ , p-toluenesulfonate ions, and the like. X ⁻ may be a polyvalent anion such as SO ₄ ²⁻ , in which case X ⁻ represents a polyvalent anion corresponding to a monovalent amount.

The hydrogen atom of the benzene ring may be substituted with an alkyl group or a halogen atom. The alkyl group is preferably a methyl group or an ethyl group, and the halogen atom is preferably chlorine or bromine.

(Film polymer)
A film-like polymer is obtained by forming a polymer into a film form (film, sheet, coating film, etc.).
Examples of the polymer include polyolefin, fluororesin, polyvinylidene chloride, polysulfone, nylon, polyester and the like. From the viewpoint of alkali resistance, polyolefin or fluororesin is preferable.

Polyolefins include high-pressure low-density polyethylene, linear low-density polyethylene, high-density polyethylene, polypropylene, propylene-ethylene block copolymers; polyolefin-based thermoplastics in which ethylene-propylene rubber, EPDM, etc. are dispersed in polyethylene, polypropylene, etc. An elastomer etc. are mentioned.

Fluororesin includes polytetrafluoroethylene, tetrafluoroethylene-perfluoro (alkyl vinyl ether) copolymer, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polychlorotrifluoroethylene, ethylene -Chlorotrifluoroethylene copolymer, polyvinylidene fluoride, polyvinyl fluoride and the like.

The thickness of the film-like polymer is preferably 10 to 200 μm, more preferably 15 to 150 μm. If the thickness of the film-like polymer is equal to or greater than the lower limit, the film-like polymer is easy to handle. If the thickness of the membranous polymer is below the upper limit, the monomer can be sufficiently graft polymerized near the center of the membranous polymer in the thickness direction, and the membrane resistance of the anion exchange membrane can be kept low. Can do.
The molecular weight of the film-like polymer is preferably about 10,000 to 1,000,000, more preferably about tens of thousands to hundreds of thousands in terms of number average molecular weight, but is not limited thereto.

(Monomer component)
The monomer component includes a component consisting only of monomer (1) or a mixture of monomers including monomer (1), or a component consisting only of monomer (31) or monomer (32) or monomer (31) or monomer (32). It is a mixture of monomers.

The monomer component may contain other monomers other than the monomer (1), the monomer (31), and the monomer (32) in order to adjust the ion selective permeability and strength of the obtained anion exchange membrane. Other monomers include styrene, vinyl toluene, ethylene, propylene, acrylonitrile, divinyl benzene, trivinyl benzene, divinyl toluene, divinyl naphthalene, ethylene glycol dimethacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, vinyl pyridine And chloromethylstyrene.
Among these, divinylbenzene, trivinylbenzene, divinyltoluene, or divinyl is used from the viewpoint of cross-linking an anion exchange membrane to increase strength and adjusting water and ion permeability by controlling the crosslink density. Naphthalene is preferred and divinylbenzene is particularly preferred.

The proportion of the other monomer is preferably 40% by mass or less and more preferably 30% by mass or less in the monomer component (100% by mass) from the viewpoint of heat resistance and alkali resistance of the obtained anion exchange membrane.
The monomer component may be diluted with a solvent and may not contain a solvent. When the monomer component is diluted with a solvent, the ratio of all monomer components to the total amount of all monomer components and the solvent is preferably 10% by mass or more.

(Polymerization inhibitor)
Polymerization inhibitors include hydroxyaromatics (hydroquinone, p-methoxyphenol, cresol, t-butylcatechol, 3,5-di-t-butyl-4-hydroxytoluene, 2,2′-methylenebis (4-methyl- 6-t-butylphenol), 2,2'-methylenebis (4-ethyl-6-butylphenol), 4,4'-thiobis (3-methyl-6-tert-butylphenol), thioethers (phenothiazine, distearylthiodipro) Pionate, etc.), amines (p-phenylenediamine, 4-aminodiphenylamine, N, N'-diphenyl-p-phenylenediamine, Ni-propyl-N'-phenyl-p-phenylenediamine, N- (1 , 3-Dimethylbutyl) -N′-phenyl-p-phenylenediamine, N, N′-di-2-naphthy Ru-p-phenylenediamine, diphenylamine, N-phenyl-β-naphthylamine, 4,4′-dicumyl-diphenylamine, 4,4′-dioctyl-diphenylamine, etc.), nitroso compound systems (N-nitrosodiphenylamine, N-nitrosophenyl) Naphthylamine, N-nitrosodinaphthylamine, p-nitrosophenol, nitrosobenzene, p-nitrosodiphenylamine, α-nitroso-β-naphthol, etc., and other nitrogen-containing compounds (piperidine-1-oxyl, pyrrolidine-1-oxyl, 2, 2,6,6-tetramethyl-4-oxopiperidine-1-oxyl, nitroxides such as 2,2,6,6-tetramethylpiperidine-1-oxyl, etc.), transition metal salts (copper dialkyldithiocarbamate, copper acetate) , Copper salicylate, thiocyan Copper salts of acid copper, copper nitrate, copper chloride, copper carbonate, copper hydroxide, copper acrylate, etc .; manganese dialkyldithiocarbamate, manganese diphenyldithiocarbamate, manganese formate, manganese acetate, manganese octoate, manganese naphthenate, permanganese Polymerization inhibitors such as manganese acid and manganese salt of ethylenediaminetetraacetic acid).
Among these, from the viewpoint of compatibility with monomers and solvents, hydroxyaromatic is preferable, more specifically, hydroquinone, p-methoxyphenol, cresol, or t-butylcatechol is preferable, and t-butylcatechol is more preferable. .

The amount of the polymerization inhibitor is 0.005 to 3 parts by mass, preferably 0.05 to 1.5 parts by mass with respect to 100 parts by mass of the monomer component. If the amount of the polymerization inhibitor is not less than the lower limit, oligomerization of the monomer (1), monomer (31) and monomer (32) is sufficiently suppressed, and the graft ratio is sufficiently high, that is, the membrane resistance is sufficiently low. An anion exchange membrane can be obtained. When the amount of the polymerization inhibitor is not more than the upper limit value, an anion exchange membrane having a sufficiently high graft ratio, that is, a sufficiently low membrane resistance can be obtained without inhibiting graft polymerization.

(Radiation graft polymerization method)
The radiation graft polymerization method is a method in which a radical is generated in the polymer by irradiating the polymer with radiation, and the monomer component is graft-polymerized using the radical as a starting point.
Examples of radiation include electron beams, ultraviolet rays, X-rays, α rays, β rays, γ rays and the like.

The irradiation with radiation is preferably performed in an atmosphere free of molecular oxygen, that is, in an atmosphere of an inert gas (such as nitrogen gas).
In the case of an electron beam, the radiation dose is preferably 5 to 300 kGy.

Graft polymerization may be performed in a state in which a film-like polymer is impregnated with a monomer component that is excessive or polymerized, or may be performed in a state in which a film-like polymer is immersed in the monomer component. The polymer may be immersed in a solution in which the monomer component is dissolved in a solvent.
Examples of the solvent include toluene, xylene, benzene, chlorobenzene, chlorobenzene derivatives, dimethyl sulfoxide, cyclohexane, hexane, various alcohols, various ketones, water and the like.
The temperature during graft polymerization is preferably 4 to 80 ° C.

Polymerization time affects the graft rate described later. The graft ratio increases as the polymerization time increases. However, if the content of the polymerization inhibitor in the monomer component is large or small, the graft ratio is not sufficiently high even if the polymerization time is lengthened, and the ion exchange capacity of the obtained anion exchange membrane is insufficient. Become. The polymerization time is preferably 60 minutes or longer, although it depends on the amount of monomer components, polymerization temperature, radiation dose, polymerization inhibitor amount and the like. If the polymerization time is too long, the productivity is lowered. Therefore, the polymerization time is preferably within 10 hours, more preferably within 8 hours, by appropriately adjusting the above conditions.

(Conversion of X group bonded to A group to anion exchange group)
In the method (α), for the graft polymerized membrane (anion exchange membrane intermediate) obtained after graft polymerization, the X group bonded to the A group is converted to an anion exchange group (amino group or ammonium group). There is a need.
Conversion of the X group bonded to the A group to an anion exchange group is performed by reacting the compound (2) with the X group bonded to the A group. Compound (2) may be in the form of a salt such as hydrochloride.

When the compound (2) is ammonia, a primary amine (such as methylamine), or a secondary amine (such as dimethylamine), a weakly basic anion exchange membrane can be obtained.
When compound (2) is a tertiary amine (trimethylamine, dimethylethanolamine, methyldiethanolamine, triethanolamine, etc.), a strongly basic anion exchange membrane is obtained.

(Exchange of counter ion)
When the anion exchange membrane obtained by the method (α) or the method (β) has an ammonium group, the counter ion of the ammonium group may be exchanged with another counter ion.
Counter ion exchange is performed by immersing the anion exchange membrane in an aqueous solution containing the converted counter ion.

(Function and effect)
In the method for producing an anion exchange membrane of the present invention described above, the monomer component containing monomer (1) or the monomer component containing monomer (31) or monomer (32) is grafted to the membrane polymer. Since it is polymerized, the obtained anion exchange membrane has heat resistance and alkali resistance.
In addition, since a film-like polymer is used as the base, even if the base is thinned, generation of pinholes and a decrease in strength can be suppressed even when the base is thinned.
In addition, since the monomer component is graft-polymerized by radiation graft polymerization in the presence of 0.005 to 3 parts by mass of a polymerization inhibitor with respect to 100 parts by mass of the monomer component, monomer (1), monomer Oligomerization of (31) and monomer (32) can be sufficiently suppressed, and an anion exchange membrane having a sufficiently high graft ratio, that is, a sufficiently low membrane resistance can be obtained.

Normally, when polymerizing monomers, it is common knowledge to purify the monomers and remove the polymerization inhibitor added for the storage stability of the monomers. In this method, even when 4- (4-bromobutyl) styrene purified to a film-like polymer is graft-polymerized, oligomerization of unstable 4- (4-bromobutyl) styrene proceeds preferentially, and graft polymerization It is probable that did not progress well. In addition, when the base is a cloth or a nonwoven fabric, the reason why the graft polymerization has proceeded well is that, after 4- (4-bromobutyl) styrene penetrates between the fibers of the cloth or the nonwoven fabric, oligomerization and graft polymerization occur between the fibers. Since the oligomers were confined between the fibers, it seemed that the graft polymerization seemed to proceed well.

<Anion exchange membrane>
The anion exchange membrane obtained by the production method of the present invention has a graft chain having a monomer unit represented by the following formula (41) or a monomer unit represented by the following formula (42).

A is an alkylene group having 3 to 8 carbon atoms or an alkyleneoxymethylene group having 4 to 8 carbon atoms, and R ¹ to R ³ are each a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a carbon number 1 to 6 hydroxyalkyl groups, X 2 ^— is a counter ion of an ammonium group, and the hydrogen atom of the benzene ring may be substituted with an alkyl group or a halogen atom. X ⁻ also includes Z ⁻ (halogen ion) derived from Z of the monomer (1).

(Graft rate)
In the anion exchange membrane of the present invention, the graft ratio (dg) determined by the following formula (I) is preferably 6 mol% or more, and more preferably 8 to 16 mol%.
dg = m _m / m _p × 100 (I).
However, dg is the graft rate [mol%], m _p is the number of moles of monomer units constituting the film-shaped polymer, m _m is moles of the monomer component is graft-polymerized to a membrane-like polymer Is a number.

When dg is less than 6 mol%, the ion exchange capacity of the anion exchange membrane becomes insufficient and the membrane resistance increases, so that the function as an anion exchange membrane cannot be fully exhibited. If dg is too high, the moisture content of the anion exchange membrane will increase, ion selective permeability will decrease, and current efficiency will also decrease.

m _p is the dry weight (W ₀ ) of the film-like polymer used in the radiation graft polymerization method, the molecular weight of the monomer unit constituting the polymer (M _p ) (in the case of a plurality of monomer units, the mole of each monomer unit) It is determined by dividing by the average molecular weight taking into account the fraction.
m _m is the mass (W ₁ −) obtained by subtracting the dry mass (W ₀ ) of the film-like polymer used in the radiation graft polymerization method from the dry mass (W ₁ ) of the graft polymer film obtained by the radiation graft polymerization method. W ₀ ), that is, the dry mass of the graft chain is divided by the molecular weight (M _m ) of the monomer units constituting the graft chain (in the case of a plurality of monomer units, the average molecular weight including the molar fraction of each monomer unit). Ask by.

(Ion exchange capacity)
The ion exchange capacity (Q) of the anion exchange membrane of the present invention is preferably 1 to 4 meq / g dry resin, more preferably 1.5 to 3 meq / g dry resin.
When Q is too small, the membrane resistance increases, and the function as an anion exchange membrane cannot be sufficiently exhibited. When Q is too large, the ion selective permeability decreases.

Q is obtained by the following formula (II).
Q = {(W ₁ −W ₀ ) / M _m } / W ₁ × 10 ³ (II).
However, W ₀ is the dry mass of the film-like polymer used in the radiation graft polymerization method, W ₁ is the dry mass of the graft polymer film obtained by the radiation graft polymerization method, and M _m is the graft chain. Is the molecular weight of the monomer unit that constitutes.
The anion exchange membrane obtained by the production method of the present invention preferably has a wet film thickness of 5 to 400 μm, more preferably 10 to 200 μm. Further, it is preferred membrane resistance is 0.05 ~ 4Ω · cm ² at 0.5 mol / l NaCL (25 ° C.), and more preferably 0.1 ~ 2Ω · cm ^2. Furthermore, the static transport number using 0.5 mol / liter NaCl and 1 mol / liter NaCl is preferably 0.90 or more, and more preferably 0.94 or more.

(X-ray intensity distribution of elements derived from the monomer units of the graft chain)
In the anion exchange membrane obtained by the production method of the present invention, the monomer component is preferentially graft-polymerized near both surfaces of the membrane-like polymer, and also in the vicinity of the central portion in the thickness direction of the membrane-like polymer. The monomer component is sufficiently graft polymerized.

In the anion exchange membrane of the present invention or an intermediate thereof (graft polymerized membrane), an element derived from a monomer unit of the graft chain in the thickness direction of the membrane measured using an X-ray element analyzer (for example, In the X-ray intensity distribution of the halogen element), the minimum value (X _min ) that appears near the center of the film in the thickness direction, the first maximum value (X _max1 ) that appears near one surface of the film, and the other of the film The ratio (X _min / X _max ) to the average value (X _max ) of the second maximum value (X _max2 ) appearing in the vicinity of the surface is preferably 0.6 or more, and more preferably 0.75 or more. Further, X _min / X _max is preferably 1.1 or less, and more preferably 1 or less.

If _Xmin / _Xmax is too small, the graft polymerization of the monomer in the vicinity of the center in the thickness direction of the membrane is insufficient, so that the ion exchange capacity of the anion exchange membrane becomes insufficient, and the membrane resistance increases. There is a possibility that the function as an anion exchange membrane cannot be sufficiently exhibited. If X _min / X _max is too large, the amount of ion exchange groups in the vicinity of the central portion in the thickness direction of the membrane increases, and the ion selective permeability may decrease.

An anion exchange membrane having an X _min / X _max of 0.6 to 1.1 is obtained by graft-polymerizing monomer components preferentially near both surfaces of a film-like polymer by a radiation graft polymerization method, and a dg of 6 to It can be obtained by adjusting to 16 mol%.

(Function and effect)
Since the anion exchange membrane of the present invention described above is an anion exchange membrane obtained by the production method of the present invention, the graft unit is represented by the monomer unit represented by the formula (41) or the formula (42). Having monomer units represented. As a result, it has heat resistance and alkali resistance.
In addition, since a film-like polymer is used as the base, generation of pinholes and a decrease in strength can be suppressed even if the base is made thinner than when the base is a cloth or a nonwoven fabric.
A graft ratio of 6 mol% or more is preferable because the membrane resistance is sufficiently low.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited by these examples.
Examples 1 to 6 are examples, and examples 7 and 8 are comparative examples.

(Abbreviation)
HDPE: high density polyethylene.
BBS: 4- (4-bromobutyl) styrene (the following formula (1-1)).
TBC: 4-t-butylcatechol.
TMA hydrochloride: trimethylammonium hydrochloride (N (CH ₃ ) ₃ .HCl).
DMF: N, N-dimethylformamide.

(Graft rate)
The graft ratio (dg) in the anion exchange membrane was determined by the following formula (I).
dg = m _m / m _p × 100
= {(W ₁ -W ₀ ) / M _m } / {W ₀ / M _p } × 100 (I).
However, dg is the graft rate [mol%], _{m p} is the number of moles of ethylene units constituting the HDPE film, _{m m} is the number of moles of BBS prepared by graft polymerizing a HDPE film, W ₀ is the dry mass of the HDPE film used in the radiation graft polymerization method, W ₁ is the dry mass of the graft polymer film obtained by the radiation graft polymerization method, and M _m is the BBS unit constituting the graft chain M _p is the molecular weight of the ethylene units that make up the HDPE film.

(Ion exchange capacity)
The ion exchange capacity (Q) of the anion exchange membrane was determined by the following formula (II).
Q = {(W ₁ −W ₀ ) / M _m } / W ₁ × 10 ³ (II).
However, W ₀ is the dry mass of the HDPE film used in the radiation graft polymerization method, W ₁ is the dry mass of the graft polymerized film obtained by the radiation graft polymerization method, and M _m constitutes the graft chain. The molecular weight of the BBS unit.

(X-ray intensity distribution of bromine element)
For the graft polymerized membrane (anion exchange membrane intermediate), a scanning electron microscope equipped with an energy dispersive X-ray element analyzer (SU6600, manufactured by Hitachi High-Technologies Corporation) was used to observe the cross section of the graft polymerized membrane and The X-ray intensity distribution of the bromine element in the thickness direction of the graft polymerized film was measured by a distributed X-ray element analyzer.

(thickness)
The thickness of the anion exchange membrane was determined by immersing the anion exchange membrane in a 0.5 mol / L sodium chloride aqueous solution for 6 hours, washing with pure water, and then using an electromagnetic membrane pressure gauge (LZ-, manufactured by Kent Science Laboratory Co., Ltd.). 200J) in a wet state.

(Moisture content)
The water content (H _w ) of the anion exchange membrane was determined by the following formula (III).
H _w = (W ₃ −W ₂ ) / W ₂ × 100 (III).
Where W ₂ is the dry mass of the anion exchange membrane, and W ₃ is the wet mass after the anion exchange membrane is immersed in a 0.5 mol / L sodium chloride aqueous solution for 6 hours and washed with pure water. It is.

(Membrane resistance)
An anion exchange membrane is sandwiched between membrane resistance measurement cells (effective membrane area: 1.77 cm ² ) having an inner diameter of 1.50 cm and a width of 5.5 cm, and platinum electrodes are placed at positions 1 cm on both sides of the anion exchange membrane. placed. Using an impedance meter (manufactured by Agilent Technologies, 433B), an AC resistance of 1 kHz in a 0.5 mol / L sodium chloride aqueous solution was measured. The measurement temperature was 25 ° C. After measuring the sum of the AC resistance of the anion exchange membrane and the aqueous solution, the anion exchange membrane was removed and the AC resistance of only the aqueous solution was measured. From these differences, the AC resistance R _m [Ω] of only the anion exchange membrane was calculated. The membrane resistance [Ω · cm ² ] was determined by the following formula (IV).
Membrane resistance = R _m × effective membrane area (IV).

(Static transportation rate)
The anion exchange membrane was sandwiched between measurement cells having an effective membrane area of 1.00 cm ² , and 1.0 mol / L sodium chloride aqueous solution and 0.50 mol / L sodium chloride aqueous solution were placed in the left and right cells, respectively. . The left and right cells were connected to saturated potassium chloride by a salt bridge, and a sweet potato electrode connected to a voltmeter (Texio, DL-2040) was installed. After the left and right cells were stirred and the potential difference was measured, the blank potential difference was measured. The measurement temperature was 25 ° C. From the measured potential difference and blank potential difference, the static transport number [−] was determined from the following formula (V).
Static transport number = 0.5− (E ₁ −E ₀ + E _L ) / [2RT / Fln (a ^{± 1.0} / a ^{± 0.5} )]
= 0.5- (E ₁ -E ₀ + E _L ) /33.7 (V).
However, E ₁ , E ₀ , E _L , R, T, F, a ^{± 1.0} and a ^{± 0.5} are the measured potential, 0.50 mol / L sodium chloride aqueous solution- ^1.0 mol / L, respectively. L potential between sodium chloride aqueous solution (4.4 mV), blank potential obtained by removing the anion exchange membrane from the transport number measuring device, gas constant (8.31 J / (K mol)), measurement temperature (298 K), Faraday constant (96485 C / mol), average activity of sodium chloride aqueous solution of 1.0 mol / L (0.657) and average activity of sodium chloride aqueous solution of 0.5 mol / L (0.341).

(Electroosmosis coefficient and alkali concentration of concentrate)
The anion exchange membrane was immersed in a 1.0 mol / L sodium hydroxide aqueous solution for 6 hours, so that the counter ion was OH ⁻ . The membrane resistance of the anion exchange membrane was measured using a 0.5 mol / L aqueous sodium hydroxide solution (25 ° C.).
Electrodialysis was performed using a 0.5 mol / L sodium hydroxide aqueous solution as a model alkaline solution. As a counter membrane at this time, a commercially available cation exchange membrane (manufactured by Asahi Glass Co., Ltd., SELEMION (registered trademark) CMV) was used. The effective membrane area and intermembrane distance during dialysis were 8.0 cm ² and 1.5 mm, respectively. A 0.50 mol / L sodium hydroxide aqueous solution was previously placed in the concentration chamber, and a 0.50 mol / L sodium hydroxide aqueous solution (25 ° C.) was circulated at 7.1 cm / s in the dilution chamber. . A direct current was applied at a current density of 30 mA / cm ² . After a steady operation for 200 minutes, the concentrated solution was collected for 100 minutes, and the alkali concentration (C _OH ⁻ ) of the concentrated solution was quantified by neutralization titration using 0.1 mol / L hydrochloric acid. The electroosmosis coefficient [−] was determined by the following formula (VI).
Electroosmosis coefficient = (permeation flux of water molecule) / (permeation flux of hydroxide ion) (VI).

[Examples 1 to 6]
An HDPE film (manufactured by Tamapoli Co., Ltd., thickness: 35 μm, density: 0.94 g / cm ³ ) was prepared. Further, BBS was used as it was without purifying a commercial product (purity: 97.5% by mass, TBC: 0.1% by mass = TBC with respect to 100 parts by mass of BBS: 0.1 part by mass).

The HDPE film was irradiated with an electron beam with a dose of 200 kGy in a nitrogen atmosphere to generate radicals. The HDPE film was immersed in a commercial product (unpurified) of BBS at 40 ° C., and BBS was graft-polymerized starting from a radical to obtain a graft-polymerized film. The graft ratio (dg) was adjusted by the graft polymerization time (0.25 to 4 hours).
The graft polymerized membrane was washed with DMF, methanol and pure water and then dried. Table 1 shows dg and ion exchange capacity (Q). Moreover, the X-ray intensity distribution of the bromine element in the thickness direction of the graft polymerization film was measured. Table 1 shows Br _min / Br _max obtained from the X-ray intensity distribution of bromine element.

The graft polymerized membrane was immersed in an aqueous 0.5 mol / L TMA hydrochloride solution (adjusted to pH 12) for 6 hours to convert bromine of BBS units into TMA groups to obtain an anion exchange membrane. The immersion temperature was 40 ° C.
The anion exchange membrane was washed with methanol and pure water. The anion exchange membrane was immersed in an aqueous 0.5 mol / L sodium bromide solution for 6 hours to make the counter ion Br 2 ^- and then dried.

The anion exchange membrane was immersed in a 0.5 mol / L sodium chloride aqueous solution for 6 hours, and the counter ion was Cl 2 ⁻ . After the anion exchange membrane was washed with pure water, the wet thickness was measured. Table 1 shows the thickness. Moreover, after measuring the wet mass of an anion exchange membrane, the anion exchange membrane was dried at 40 degreeC, and the dry mass was measured. The moisture content (H _w ) is shown in Table 1.
Table 1 shows the membrane resistance, static transport number, electroosmosis coefficient, and alkali concentration of the concentrate.

[Example 7]
As BBS, the polymerization inhibitor was removed from the commercial product (purity: 97.5 mass%, TBC: 0.1 mass%) by liquid-liquid extraction using a 5 mass% aqueous sodium hydroxide solution, and after the polymerization inhibitor was extracted The BBS was added with calcium chloride, dried and purified (TBC with respect to 100 parts by mass of BBS: 0 parts by mass).

The HDPE film was irradiated with an electron beam with a dose of 200 kGy in a nitrogen atmosphere to generate radicals. The HDPE film was immersed in a purified product of BBS at 40 ° C., and BBS was graft polymerized starting from radicals to obtain a graft polymerized film.
The graft polymerized membrane was washed with DMF, methanol and pure water and then dried. The dg is shown in Table 1.

The anion exchange membrane was immersed in a 0.5 mol / L sodium chloride aqueous solution for 6 hours, and the counter ion was Cl 2 ⁻ . After the anion exchange membrane was washed with pure water, the wet thickness was measured. Table 1 shows the thickness. Table 1 shows the membrane resistance.

[Example 8]
A commercially available anion exchange membrane (SELEMION (registered trademark) AHT, manufactured by Asahi Glass Co., Ltd.) was prepared. The anion exchange membrane was obtained by using HDPE cloth as a base, impregnating it with BBS and divinylbenzene, performing bulk polymerization, and then reacting with TMA hydrochloride.
Table 1 shows the Q, thickness, H _w , membrane resistance, static transport number, electroosmotic coefficient, and alkali concentration of the concentrate of the anion exchange membrane.

The anion exchange membrane of the present invention is useful as a separator for fuel cells, secondary batteries, etc. in addition to seawater concentration by electrodialysis, brine desalination, acid concentration or recovery, recovery of valuable metals, etc. In particular, it is useful as an anion exchange membrane for an alkaline solid polymer fuel cell.
The entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2010-102295 filed on April 27, 2010 are incorporated herein as the disclosure of the specification of the present invention. Is.

Claims

A monomer component containing a monomer represented by the following formula (1) is added to a film-like polymer in the presence of 0.005 to 3 parts by mass of a polymerization inhibitor with respect to 100 parts by mass of the monomer component. A method for producing an anion exchange membrane, in which a compound of the following formula (2) is reacted after graft polymerization by a legal method.

A is an alkylene group having 3 to 8 carbon atoms or an alkyleneoxymethylene group having 4 to 8 carbon atoms, and R 1 to R 3 are each a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a carbon number 1 to 6 hydroxyalkyl groups, Z is a halogen atom, and the hydrogen atom of the benzene ring may be substituted with an alkyl group or a halogen atom.
Polymerization of a monomer component containing the monomer represented by the following formula (31) or the monomer represented by the following formula (32) into the film-like polymer in an amount of 0.005 to 3 parts by mass with respect to 100 parts by mass of the monomer component A method for producing an anion exchange membrane, in which graft polymerization is carried out by radiation graft polymerization in the presence of an inhibitor.

A is an alkylene group having 3 to 8 carbon atoms or an alkyleneoxymethylene group having 4 to 8 carbon atoms, and R 1 to R 3 are each a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a carbon number 1 to 6 hydroxyalkyl groups, X 2 — is a counter ion of an ammonium group, and the hydrogen atom of the benzene ring may be substituted with an alkyl group or a halogen atom.
The method for producing an anion exchange membrane according to claim 1 or 2, wherein the polymer is a polyolefin or a fluororesin.
The method for producing an anion exchange membrane according to any one of claims 1 to 3, wherein the polymerization inhibitor is hydroquinone, p-methoxyphenol, cresol, or t-butylcatechol.
The method for producing an anion exchange membrane according to any one of claims 1 to 4, wherein the thickness of the membranous polymer is 10 to 200 µm.
6. The anion exchange membrane obtained by the production method according to claim 1, wherein the graft ratio determined by the following formula (I) is 6 mol% or more.
dg = m m / m p × 100 (I).
However, dg is the graft rate [mol%], m p is the number of moles of monomer units constituting the film-shaped polymer, m m is moles of the monomer component is graft-polymerized to a membrane-like polymer Is a number.
The anion exchange membrane according to claim 6, wherein the ion exchange capacity is 1.5 to 3 meq / g dry resin.