JP2015067770A - Anion exchange membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyvinyl alcohol-based anion exchange membrane which suppresses organic contamination and is excellent in basic properties, e.g. membrane strength, and also useful in electrodialysis.SOLUTION: An anion exchange membrane consists of a cationic vinyl alcohol-based copolymer (P) containing a vinyl alcohol-based polymer (A) and a polymer (B) having cationic groups, in a ratio of the vinyl alcohol-based polymer (A) to the polymer (B) having cationic groups of 97:3 to 60:40 mol%, subjected to a crosslinking treatment with a degree of crosslinking of 3.0-4.8.

Description

  The present invention relates to an anion exchange membrane useful for electrodialysis having excellent organic contamination resistance.

  Ion exchange membranes are currently used for a wide variety of applications such as seawater concentration, desalination of groundwater for drinking water and removal of nitrate nitrogen, salt removal in food manufacturing processes, and concentration of active pharmaceutical ingredients. It is used as a membrane in electrodialysis and diffusion dialysis. The useful ion exchange membranes used in these are mainly styrene-divinylbenzene-based homogeneous ion exchange membranes. Various ion exchange membranes such as monovalent and divalent ion selectivity, specific ion selectivity, low membrane resistance, etc. Technology has been developed and industrially useful separation has been achieved.

  In the process of synthesizing organic substances in the fields of foods, pharmaceuticals, agricultural chemicals and the like, salts are often produced as by-products. The salts contained in such organic substances are often separated by electrodialysis. In salt separation by electrodialysis, cation exchange membranes and anion exchange membranes are arranged alternately, and direct current is applied to cause cations to flow on the cathode side of the cation exchange membrane and on the anode side of the anion exchange membrane. Desalting is realized by removing the anion and thus removing the salt from the electrolyte solution supplied to the chamber formed by being sandwiched between the cation exchange membrane on the cathode side and the anion exchange membrane on the anode side. However, when desalting the treatment liquid by electrodialysis, organic pollutants in the liquid to be treated, especially macromolecules with a charge (hereinafter referred to as giant organic ions) adhere to the ion exchange membrane and degrade the performance of the membrane. The so-called organic contamination of the film occurs. In particular, the anion exchange membrane is likely to be organically contaminated, and the membrane performance gradually deteriorates with the progress of the dialysis cycle.

  Conventionally, as a method for suppressing organic contamination, an anion exchange membrane that prevents invasion of giant organic ions into the membrane is known. This is a film in which a thin layer having a charge opposite to neutral, amphoteric or ion exchange groups is formed on the membrane surface. The effect of the anion exchange membrane is more remarkable as the membrane structure is denser and the molecular weight of the giant organic ions is larger.

  Patent Document 1 discloses an anion exchange membrane in which an oppositely charged sulfonic acid group is introduced into the surface layer portion of a resin membrane having an anion exchange group to suppress the invasion of anionic giant organic ions into the membrane. Has been.

  Patent Document 2 discloses an anion exchange membrane having improved organic contamination by devising an anion pair structure of an anion exchange group.

Japanese Patent Publication No.51-40556 Japanese Patent Laid-Open No. 3-146525 JP 59-187003 A JP 59-189113 A

  However, the anion exchange membrane of Patent Document 1 that prevents the invasion of giant organic ions into the membrane can exhibit a certain degree of organic contamination resistance, but is opposite to the surface layer portion of the resin membrane. The formation of a charged layer has the disadvantage that the membrane resistance is remarkably increased. Further, the anion exchange membrane in which the structure of the anion pair of the anion exchange group disclosed in Patent Document 2 is not satisfactory in organic contamination resistance.

  Accordingly, an object of the present invention is to provide an anion exchange membrane that suppresses organic contamination, has excellent basic physical properties such as membrane strength, and is useful for electrodialysis.

The inventors of the present invention have arrived at the present invention as a result of intensive studies on the above problems.
That is, a cationic vinyl alcohol copolymer (P) containing a vinyl alcohol polymer (A) and a polymer (B) having a cationic group, the vinyl alcohol polymer (A) and a cation The ratio of the polymer (B) having a functional group is in the range of 97: 3 to 60:40 mol%, and is subjected to a crosslinking treatment, and the crosslinking degree is in the range of 3.0 to 4.8. It has been found that an anion exchange membrane characterized by being capable of suppressing contamination by organic substances, having excellent basic physical properties such as membrane strength, and allowing stable electrodialysis.

  The swelling degree of the anion exchange membrane is preferably in the range of 10-50.

  The saponification degree of the vinyl alcohol polymer (A) is preferably in the range of 70 to 99.9 mol%.

  The cationic vinyl alcohol copolymer (P) containing the vinyl alcohol polymer (A) and the polymer (B) having a cationic group is a block copolymer and / or a graft copolymer. preferable.

  The anion exchange membrane is preferably composed of a cationic vinyl alcohol copolymer (P) and a porous support.

  According to the anion exchange membrane of the present invention, contamination by organic substances can be suppressed, basic physical properties such as membrane strength can be excellent, and electrodialysis can be performed stably.

(Anion exchange membrane)
The anion exchange membrane of the present invention is a cationic vinyl alcohol copolymer (P) containing a vinyl alcohol polymer (A) and a polymer (B) having a cationic group, the vinyl alcohol The ratio of the polymer (A) and the polymer (B) having a cationic group is in the range of 97: 3 to 60:40 mol%, and is subjected to a crosslinking treatment, and the degree of crosslinking is 3.0 to It is characterized by being in the range of 4.8. That is, by adjusting the ratio of the vinyl alcohol polymer (A) and the polymer (B) having a cationic group, and controlling the degree of crosslinking, the original performance as an anion exchange membrane is maintained. There is an advantage that organic contamination resistance performance higher than ever can be exhibited.

(Cationic vinyl alcohol polymer (P))
The cationic vinyl alcohol copolymer (P) used in the present invention is a polyvinyl alcohol polymer having a cationic group, and is a vinyl alcohol polymer obtained by polymerizing the vinyl alcohol monomer (a). (A) and a copolymer composed of a polymer (B) having a cationic group obtained by polymerizing the cationic monomer (b), and the form of the copolymer is random polymer, block weight Any form of a polymer and a graft polymer may be used, but a block copolymer and / or a graft polymer is preferable.

  The cationic vinyl alcohol copolymer (P) used in the present invention is a polymer containing a cationic group in the molecular chain. The cationic group may be contained in any of the main chain, side chain, and terminal. Examples of the cationic group include an ammonium group, an iminium group, a sulfonium group, and a phosphonium group. In addition, a polymer having a functional group that can be converted into an ammonium group or an iminium group in water, such as an amino group or an imino group, is also included in the polymer having a cationic group of the present invention. Among these, an ammonium group is preferable from the viewpoint of industrial availability. As the ammonium group, any of primary ammonium group (ammonium salt), secondary ammonium group (ammonium salt), tertiary ammonium group (salt), and quaternary ammonium group (trialkylammonium group, etc.) can be used. A quaternary ammonium group (trialkylammonium group) is more preferable. The cationic polymer may contain only one kind of cationic group or may contain plural kinds of cationic groups. Further, the counter anion of the cation group is not particularly limited, and examples thereof include halide ions, hydroxide ions, phosphate ions, and carboxylate ions. Of these, halide ions are preferred and chloride ions are more preferred from the standpoint of availability. The cationic polymer may contain only one type of counter anion or may contain a plurality of types of counter anions.

  Examples of the cationic polymer include those having structural units of the following general formulas (1) to (8).

［式中、Ｒ^１は水素原子または炭素数１〜４のアルキル基を表す。Ｒ^２、Ｒ^３、Ｒ^４はそれぞれ独立に、水素原子、または、置換基を有していてもよい炭素数１〜１８のアルキル基、アリール基若しくはアラルキル基を表わす。Ｒ^２、Ｒ^３、Ｒ^４は、相互に連結して飽和若しくは不飽和環状構造を形成していてもよい。Ｚは−Ｏ−、−ＮＨ−、または−Ｎ（ＣＨ_３）−を表し、Ｙは酸素、窒素、硫黄またはリン原子を含んでもよい総炭素数１〜８の二価の連結基を表す。Ｘ⁻はアニオンを表す。］

[Wherein, R ¹ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. R ² , R ³ and R ⁴ each independently represents a hydrogen atom or an optionally substituted alkyl group, aryl group or aralkyl group having 1 to 18 carbon atoms. R ² , R ³ and R ⁴ may be connected to each other to form a saturated or unsaturated cyclic structure. Z represents —O—, —NH—, or —N (CH ₃ ) —, and Y represents a divalent linking group having 1 to 8 carbon atoms which may contain an oxygen, nitrogen, sulfur or phosphorus atom. X ⁻ represents an anion. ]

Examples of the counter anion X ⁻ in the general formula (1) include halide ions, hydroxide ions, phosphate ions, carboxylate ions, and the like. Examples of the cationic polymer containing the structural unit represented by the general formula (1) include 3- (meth) acrylamidopropyltrimethylammonium chloride and 3- (meth) acrylamide-3,3-dimethylpropyltrimethylammonium chloride. Examples include homopolymers or copolymers of-(meth) acrylamide-alkyltrialkylammonium salts.

［式中、Ｒ^５は水素原子またはメチル基を表わす。Ｒ^２、Ｒ^３、Ｒ^４、およびＸ⁻は一般式（１）と同義である。］

[Wherein R ⁵ represents a hydrogen atom or a methyl group. R ² , R ³ , R ⁴ , and X ⁻ are as defined in general formula (1). ]

  Examples of the cationic polymer containing the structural unit represented by the general formula (2) include homopolymers or copolymers of vinylbenzyltrialkylammonium salts such as vinylbenzyltrimethylammonium chloride.

［式中、Ｒ^２、Ｒ^３、およびＸ⁻は一般式（１）と同義である。］

[Wherein R ² , R ³ , and X ⁻ have the same meaning as in general formula (1). ]

［式中、Ｒ^２、Ｒ^３、およびＸ⁻は一般式（１）と同義である。］

[Wherein R ² , R ³ , and X ⁻ have the same meaning as in general formula (1). ]

  As the cationic polymer containing the structural unit represented by the general formula (3) and the general formula (4), a homopolymer or copolymer obtained by cyclopolymerizing a diallyldialkylammonium salt such as diallyldimethylammonium chloride. Is exemplified.

［式中、ｎは０または１を表わす。Ｒ^２およびＲ^３は一般式（１）と同義である。］

[Wherein n represents 0 or 1; R ² and R ³ have the same meaning as in the general formula (1). ]

  Examples of the cationic polymer containing the structural unit represented by the general formula (5) include an allylamine homopolymer or copolymer.

［式中、ｎは０または１を表わす。Ｒ^２、Ｒ^３、Ｒ^４、およびＸ⁻は一般式（１）と同義である。］

[Wherein n represents 0 or 1; R ² , R ³ , R ⁴ , and X ⁻ are as defined in general formula (1). ]

  Examples of the cationic polymer containing the structural unit represented by the general formula (6) include homopolymers or copolymers of allyl ammonium salts such as allylamine hydrochloride.

［式中、Ｒ^５は水素原子またはメチル基を表し、Ａは−ＣＨ（ＯＨ）ＣＨ_２−、−ＣＨ_２ＣＨ（ＯＨ）−、−Ｃ（ＣＨ_３）（ＯＨ）ＣＨ_２−、−ＣＨ_２Ｃ（ＣＨ_３）（ＯＨ）−、−ＣＨ（ＯＨ）ＣＨ_２ＣＨ_２−、または−ＣＨ_２ＣＨ_２ＣＨ（ＯＨ)−を表す。Ｅは−Ｎ（Ｒ^６）_２または−Ｎ^＋（Ｒ^６）_３・Ｘ⁻を表し、Ｒ^６は水素原子またはメチル基を表す。Ｘ⁻はアニオンを表す。］

[Wherein, R ⁵ represents a hydrogen atom or a methyl group, and A represents —CH (OH) CH ₂ —, —CH ₂ CH (OH) —, —C (CH ₃ ) (OH) CH ₂ —, —CH _{2 C (CH 3) (OH} ) -, - CH (OH) CH 2 CH 2 -, or _{-CH 2 CH 2 CH (OH)} - represents a. E is -N ^(R _{6) 2} or _{^{-N + (R 6) 3 ·}} X - represents, ^{R 6} represents a hydrogen atom or a methyl group. X ⁻ represents an anion. ]

  As a cationic polymer containing the structural unit represented by the general formula (7), a homopolymer or copolymer of N- (3-allyloxy-2-hydroxypropyl) dimethylamine or a quaternary ammonium salt thereof, N- A homopolymer or copolymer of (4-allyloxy-3-hydroxybutyl) diethylamine or a quaternary ammonium salt thereof is exemplified.

［式中、Ｒ^５は水素原子またはメチル基、Ｒ^７は水素原子、メチル基、エチル基、ｎ−プロピル基またはｉ−プロピル基、Ｒ^８は水素原子、メチル基、およびエチル基をそれぞれ表わす。］

[Wherein, R ⁵ represents a hydrogen atom or a methyl group, R ⁷ represents a hydrogen atom, a methyl group, an ethyl group, an n-propyl group or an i-propyl group, and R ⁸ represents a hydrogen atom, a methyl group or an ethyl group, respectively. . ]

  Examples of the cationic polymer containing the structural unit represented by the general formula (8) include (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide and the like. Is exemplified.

(Copolymer of monomer having cationic group and vinyl alcohol monomer)
As a vinyl alcohol copolymer having a cationic group, a copolymer of a methacrylamide alkyltrialkylammonium salt and a vinyl alcohol component, and a copolymer of a vinylbenzyl trialkylammonium salt and a vinyl alcohol component are easily available. Particularly preferred are copolymers and copolymers of diallyldialkylammonium salts and vinyl alcohol components.

(Ratio of vinyl alcohol polymer to cationic polymer)
The ratio of the vinyl alcohol polymer (A) of the cationic vinyl alcohol copolymer (P) of the present invention to the polymer (B) having a cationic group is in the range of 97: 3 to 60:40 mol%. And is preferably in the range of 95: 5 to 70:30 mol%, and more preferably in the range of 93: 7 to 80:20 mol%. When the ratio of the polymer (B) having a cationic group is less than 3 mol%, the effective charge density in the anion exchange membrane is lowered, and the counter ion selectivity of the membrane may be lowered. On the other hand, when the ratio of the cationic polymer exceeds 40 mol%, the degree of swelling of the anion exchange membrane is increased, and the mechanical strength may be lowered. Here, the ratio of the vinyl alcohol polymer (A) to the polymer (B) having a cationic group is the vinyl alcohol monomer unit (a) contained in the vinyl alcohol polymer (A) and the cation. It represents a molar ratio with the cationic monomer unit (b) contained in the polymer (B) having a functional group.

(Block or graft copolymer)
In the present invention, the cationic vinyl alcohol copolymer (P) is composed of a copolymer containing a monomer unit having a cationic group and a vinyl alcohol monomer unit. Among these, a block and / or graft copolymer containing a vinyl alcohol polymer (A) and a polymer (B) having a cationic group is preferably used. In particular, a block copolymer is more preferably used. By doing so, the cationic polymer is microphase-separated to polymerize the vinyl alcohol polymer component responsible for suppressing membrane swelling and maintaining shape, and the ion exchange unit responsible for permeating anions. The role of the polymer component formed can be shared, and the degree of swelling and dimensional stability of the anion exchange membrane can both be achieved. Examples of the monomer unit having a cationic group include those represented by the general formulas (1) to (8). Among these, as a cationic polymer, a block copolymer containing a polymer component obtained by polymerizing methacrylamide alkyltrialkylammonium salt and a vinyl alcohol polymer component, vinyl, A block copolymer containing a polymer component obtained by polymerizing a benzyltrialkylammonium salt and a vinyl alcohol polymer component, or a polymer component obtained by polymerizing a diallyldialkylammonium salt and a vinyl alcohol polymer component; A block copolymer containing is preferably used.
The graft copolymer includes a cationic polymer segment as a main chain and a vinyl alcohol polymer segment as a branched chain, and a vinyl alcohol polymer segment as a main chain and a cationic polymer segment as a branched chain. Sometimes it is a chain. Although it is not particularly limited in the present invention, a graft copolymer having vinyl alcohol as a main chain and a cationic polymer segment as a branch chain is preferable from the viewpoint of easily obtaining strength properties. A known method is applied as the graft copolymerization method.

(Production of random copolymer)
The cationic vinyl alcohol copolymer (P) used in the anion exchange membrane of the present invention is obtained by copolymerizing a cationic monomer and a vinyl ester monomer and saponifying this by a conventional method. It is done. The vinyl ester monomer can be used as long as it can be radically polymerized. For example, vinyl formate, vinyl acetate, vinyl propionate, vinyl valenate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl persate. Among these, vinyl acetate is preferable.

  Examples of a method for copolymerizing the cationic monomer and the vinyl ester monomer include known methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. Among these methods, a bulk polymerization method performed without a solvent or a solution polymerization performed using a solvent such as alcohol is usually employed. Examples of the alcohol used as a solvent when performing a copolymerization reaction by employing solution polymerization include lower alcohols such as methanol, ethanol, and propanol. Examples of the initiator used for the copolymerization reaction include 2,2′-azobis (2,4-dimethyl-valeronitrile), 1,1′-azobis (cyclohexane-1-carbonitrile), and 2,2′-azobis. Known initiators such as azo initiators such as (N-butyl-2-methylpropionamide) and peroxide initiators such as benzoyl peroxide and n-propyl peroxycarbonate can be used. Although there is no restriction | limiting in particular about the polymerization temperature at the time of performing a copolymerization reaction, The range of 5-180 degreeC is suitable.

  The vinyl ester polymer obtained by copolymerizing a cationic monomer and a vinyl ester monomer then contains a cationic group by saponification in a solvent according to a known method. A vinyl alcohol polymer can be obtained.

  Alkaline substances are usually used as the catalyst for the saponification reaction of vinyl ester polymers. Examples thereof include alkali metal hydroxides such as potassium hydroxide and sodium hydroxide, and alkali metal alkoxides such as sodium methoxide. It is done. The saponification catalyst may be added all at once in the early stage of the saponification reaction, or a part thereof may be added in the early stage of the saponification reaction, and the rest may be added and added during the saponification reaction. Examples of the solvent used for the saponification reaction include methanol, methyl acetate, dimethyl sulfoxide, dimethylformamide and the like. Of these, methanol is preferable. The saponification reaction can be carried out by either a batch method or a continuous method. After completion of the saponification reaction, the remaining saponification catalyst may be neutralized as necessary, and usable neutralizing agents include organic acids such as acetic acid and lactic acid, and ester compounds such as methyl acetate. .

  The degree of saponification of the cationic vinyl alcohol copolymer (P) is not particularly limited, but is preferably in the range of 70 to 99.9 mol%. If the degree of saponification is less than 70 mol%, the crystallinity is lowered, and the durability of the ion exchange membrane may be insufficient. The saponification degree is more preferably 75 mol% or more, and further preferably 80 mol% or more. Usually, the saponification degree is 99.9 mol% or less. At this time, the method for measuring the degree of saponification when the vinyl alcohol polymer is a mixture of a plurality of types of vinyl alcohol polymers is in accordance with JIS K6726.

  The viscosity average polymerization degree of the cationic vinyl alcohol copolymer (P) (hereinafter sometimes simply referred to as polymerization degree) is not particularly limited, but is preferably 50 to 10,000. If the degree of polymerization is less than 50, the ion exchange membrane may not be able to maintain sufficient durability in practical use. More preferably, the degree of polymerization is 100 or more. When the degree of polymerization exceeds 10,000, the viscosity may be too high when handled in an aqueous solution, which may be inconvenient to handle. The degree of polymerization is more preferably 8000 or less. At this time, the degree of polymerization when the vinyl alcohol copolymer is a mixture of a plurality of types of vinyl alcohol copolymers refers to the average degree of polymerization of the entire mixture. The viscosity average degree of polymerization of the vinyl alcohol polymer is a value measured according to JIS K6726.

(Manufacture of block copolymer)
The polymer production method used in the present invention in which a polymer component obtained by polymerizing a cationic monomer and a vinyl alcohol polymer component form a block copolymer is mainly divided into the following two methods. The (1) A method in which a desired block copolymer is produced and then a cationic group is bonded to a specific block; and (2) a desired block copolymer is polymerized by polymerizing at least one cationic monomer. It is a method of obtaining coalescence. Among these, for (1), one or more monomers are block copolymerized in the presence of a vinyl alcohol polymer having a mercapto group at the terminal, and then one or more monomers in the block copolymer are used. In the method of introducing a cationic group into a seed polymer component, (2), by radical polymerization of at least one cationic monomer in the presence of a vinyl alcohol polymer having a mercapto group at the terminal. A method for producing a block copolymer is preferred because of industrial ease. In particular, since the type and amount of each component in the block copolymer can be easily controlled, at least one cationic monomer is radically polymerized in the presence of a vinyl alcohol polymer having a mercapto group at the terminal. Thus, a method for producing a block copolymer is preferred.

  The vinyl alcohol polymer having a mercapto group at the end used for the production of these block copolymers can be obtained, for example, by the method described in Patent Document 3 and the like. That is, there is a method of saponifying a vinyl ester polymer obtained by radical polymerization of a vinyl ester monomer such as vinyl acetate in the presence of thiolic acid. Moreover, as a method of obtaining a block copolymer using the vinyl alcohol polymer which has a mercapto group at the terminal, and an ionic monomer, the method described in patent document 4 etc. is mentioned, for example. That is, a block copolymer can be obtained by radical polymerization of a cationic monomer using a polymerization initiator in the presence of a vinyl alcohol polymer having a mercapto group at the terminal. This radical polymerization can be carried out by a known method such as bulk polymerization, solution polymerization, pearl polymerization, emulsion polymerization, etc., but a solvent capable of dissolving a vinyl alcohol polymer containing a mercapto group at the terminal, such as water or dimethyl It is preferably carried out in a medium mainly composed of sulfoxide. As the polymerization process, any of a batch method, a semi-batch method, and a continuous method can be employed.

  The polymerization initiator is polymerized from ordinary radical polymerization initiators such as 2,2′-azobisisobutyronitrile, benzoyl peroxide, lauroyl peroxide, diisopropyl peroxycarbonate, potassium persulfate, ammonium persulfate, and the like. In the case of polymerization in water, the mercapto group at the end of the vinyl alcohol polymer and an oxidizing agent such as potassium bromate, potassium persulfate, ammonium persulfate, and hydrogen peroxide can be used. It is also possible to initiate the polymerization by means of a redox reaction.

  When copolymerizing a polymer having an anion exchange group in the presence of a vinyl alcohol polymer having a mercapto group at the terminal, the polymerization system is desirably acidic. This is because, under basic conditions, the mercapto group has a high rate of ionic addition to the double bond of the monomer and disappears, and the polymerization efficiency is significantly reduced. In the case of aqueous polymerization, it is preferable to carry out all polymerization operations at pH 4 or less.

(Manufacture of anion exchange membrane)
The production method relating to the anion exchange membrane of the present invention is:
Preparing a solution of the cationic vinyl alcohol copolymer (P);
Applying an aqueous solution of the cationic vinyl alcohol copolymer (P) on the release film to form a coating layer of the cationic vinyl alcohol copolymer (P);
Peeling the release film from the dried impregnated body.

In addition, the production method relating to the anion exchange membrane of the present invention,
Preparing a solution of the cationic vinyl alcohol copolymer (P);
Applying an aqueous solution of the cationic vinyl alcohol copolymer (P) on the release film to form a coating layer of the cationic vinyl alcohol copolymer (P);
A step of superposing a porous support on the coating layer and impregnating at least a part of the porous support with a cationic vinyl alcohol copolymer (P) to form an impregnated body;
A step of drying the impregnated body in a state where the coating layer and the porous support are superposed; and a step of peeling the release film from the dried impregnated body.

(Cationic vinyl alcohol copolymer (P) solution preparation process)
More specifically, the cationic vinyl alcohol copolymer (P) is dissolved in a solvent such as water or DMSO to prepare a solution (preferably an aqueous solution) of the cationic vinyl alcohol copolymer (P). To do.
From the viewpoint of satisfactorily forming a coating film on the release film, the obtained cationic vinyl alcohol copolymer (P) solution may have a viscosity of, for example, 300 to 5000 mPa, preferably 400 to 4000 mPa. More preferably, it may be 500 to 3000 mPa.
The concentration can be appropriately set according to the type of the cationic vinyl alcohol copolymer (P), but may be, for example, 1 to 50 wt%, preferably 2 to 45 wt%, more preferably 3-40 wt% may be sufficient.

(Coating layer forming process)
Then, the obtained cationic vinyl alcohol copolymer (P) solution (preferably an aqueous solution) is applied onto the release film using various coating means such as a bar coater, a gravure coater, a knife coater, and a blade coater. Coating is performed to form a coating layer (cast layer).
The release film is not particularly limited as long as it can form a uniform coating layer and can be finally peeled off. A known or commonly used release film or sheet (for example, PET film, polyethylene film, silicone sheet, etc.) is used. can do.
From the viewpoint of forming a good coating layer, the thickness of the coating layer may be, for example, about 300 μm to 1500 μm, preferably about 500 μm to 1400 μm, more preferably about 600 μm to 1300 μm. .

(Porous support impregnation step)
Prior to the drying process, this coating layer is formed by laminating a porous support to form an impregnated body in which at least a part of the porous support is impregnated with a solution of the cationic polyvinyl alcohol copolymer (P). It is also possible to make it.

  Although it does not specifically limit as a porous support body, a nonwoven fabric sheet and a synthetic resin fabric are preferable. The nonwoven fabric sheet may be a nonwoven fabric formed from continuous fibers, but a wet nonwoven fabric composed of short fibers is preferable because an impregnation layer of the cationic polyvinyl alcohol copolymer (P) can be easily formed. The polymer forming the nonwoven sheet is not particularly limited as long as the solution of the cationic vinyl alcohol copolymer (P) can be impregnated, and examples thereof include polyester fibers and polyvinyl alcohol fibers. Is preferred. The synthetic resin fabric is preferably a synthetic resin mesh in which a plurality of linear members are arranged so as to intersect at an angle of preferably 10 to 90 degrees and the intersections are melt-bonded. For example, it is manufactured by hot pressing a plurality of woven fabrics coarsely woven with synthetic resin yarns by a melt extrusion method. As the synthetic resin, polypropylene, polyethylene, polyester terephthalate, polyvinyl alcohol, or the like can be used.

From the viewpoint of forming the impregnated layer, the porous support may have, for example, a basis weight of about 10 to 90 g / m ² , preferably about 15 to 70 g / m ² , more preferably It may be about ²⁰ to 50 g / m ² .

  The porosity of the porous support is preferably 40 to 90%. When the porosity is in this range, the anion exchange membrane obtained has excellent mechanical strength and excellent durability. When the porosity of the porous support is less than 40%, the membrane resistance of the ion exchange membrane increases, which may make it difficult to transport ions and salts. The porosity is preferably 50% or more, and more preferably 55% or more. On the other hand, when the porosity of the porous support exceeds 90%, the mechanical strength of the resulting anion exchange membrane may be inferior, and there may be a problem in durability. The porosity is preferably 80% or less, and more preferably 75% or less.

(Drying process)
In the drying step, the impregnated body is dried in a state where the coating layer and the porous support are overlapped. The drying conditions may be room temperature drying or hot air drying, but it is preferable to use a hot air dryer in order to increase the working efficiency. When using a hot air dryer, as drying temperature, about 50-110 degreeC may be sufficient, for example, Preferably about 60-100 degreeC may be sufficient.

(Peeling process)
In the peeling step, the release film can be peeled from the dried impregnated body to obtain an ion exchange membrane on which an ion exchange layer is formed.

(Post-processing after ion exchange membrane formation)
In the present invention, it is preferable to perform heat treatment after forming the ion exchange layer. By performing the heat treatment, the degree of crystallinity of the vinyl alcohol polymer (A) increases, so that the number of physical crosslinking points increases and the mechanical strength of the resulting anion exchange membrane increases. Further, since the cationic group is concentrated in the amorphous part and the formation of the ion exchange path is promoted, the charge density is increased and the counter ion selectivity is improved. The method of heat treatment is not particularly limited, and a hot air dryer or the like is generally used. Although the temperature of heat processing is not specifically limited, It is preferable that it is 50-250 degreeC. If the temperature of the heat treatment is less than 50 ° C., the effect of increasing the mechanical strength of the obtained anion exchange membrane may not be sufficient. The temperature is more preferably 80 ° C. or higher, and further preferably 100 ° C. or higher. If the temperature of the heat treatment exceeds 250 ° C., the vinyl alcohol polymer may be melted. The temperature is more preferably 230 ° C. or less, and further preferably 200 ° C. or less. The heat treatment time is usually about 1 minute to 10 hours. The heat treatment is desirably performed in an inert gas (eg, nitrogen gas, argon gas, etc.) atmosphere.

  It is preferable to perform a crosslinking treatment after forming the ion exchange layer. By performing the crosslinking treatment, the mechanical strength of the obtained ion exchange layer is increased. Further, since the charge density is increased, the counter ion selectivity is improved. The method for the crosslinking treatment is not particularly limited as long as it is a method capable of bonding the molecular chains of the polymer by chemical bonding. Usually, a method of immersing the ion exchange layer in a solution containing a crosslinking agent is used. Examples of the crosslinking agent include glutaraldehyde, formaldehyde, glyoxal and the like. As for the density | concentration of this crosslinking agent, it is preferable that the volume concentration of the crosslinking agent with respect to a solution is 0.01 to 10 volume% normally. The crosslinking reaction can be performed by treating the vinyl aldehyde copolymer with the above aldehyde in water, alcohol or a mixed solvent thereof under acidic conditions to chemically introduce a crosslinking bond. . After the crosslinking reaction, it is preferable to remove unreacted aldehyde, acid and the like by washing with water.

  In the manufacturing method, both heat treatment and chemical crosslinking treatment may be performed, or only chemical crosslinking treatment may be performed. When both the heat treatment and the crosslinking treatment are performed, it is preferable to perform the crosslinking treatment after the heat treatment. In particular, after heat-treating a molded body obtained by removing a solvent from a coating layer obtained by coating a vinyl alcohol copolymer solution by drying at a temperature of 100 ° C. or higher, acidic conditions in water, alcohol, or a mixed solvent thereof An ion exchange membrane obtained by performing a crosslinking treatment with a dialdehyde compound is preferable from the viewpoint of mechanical strength.

(Film formation)
The above cationic vinyl alcohol copolymer (P) is dissolved in a solvent composed of water, a lower alcohol such as methanol, ethanol, 1-propanol, 2-propanol, or a mixed solvent thereof, and then from the die. A film having a predetermined thickness can be formed by extruding and forming into a film and removing the solvent by volatilization. The film forming temperature when the film is formed on a plate or a roller is not particularly limited, but a temperature range of about room temperature to about 100 ° C. is usually appropriate. Solvent removal can be performed by heating as appropriate.

(Film thickness)
The anion exchange membrane used in the present invention preferably has a thickness of about 1 to 1000 μm from the viewpoints of performance, mechanical strength, handling properties, etc. required as an electrolyte membrane for electrodialysis. When the film thickness is less than 1 μm, the mechanical strength of the film tends to be insufficient. On the other hand, when the film thickness exceeds 1000 μm, the membrane resistance increases and sufficient ion exchange properties are not exhibited, so that the electrodialysis efficiency tends to decrease. Preferably it is 5-500 micrometers, More preferably, it is 7-300 micrometers.

(Crosslinking degree)
In the present invention, it is necessary to introduce a crosslinking bond so that the degree of crosslinking of the cationic vinyl alcohol copolymer (P) is in the range of 3.0 to 4.8, and the range of 3.1 to 4.7. Is preferable, and the range of 3.2 to 4.6 is more preferable. For this reason, after the coating film of the cationic vinyl alcohol copolymer (P) is dried, a crosslinking treatment is applied to introduce a crosslinking bond. The degree of crosslinking is measured by the measurement method shown in the examples described later. By introducing cross-linking, swelling of the resulting anion exchange membrane is suppressed, a stable high current density is realized, ion exchange performance is improved, and mechanical strength and durability of the anion exchange membrane are improved. When the degree of crosslinking is less than 3.0, the organic contamination resistance performance of the anion exchange membrane decreases. On the other hand, when the degree of crosslinking exceeds 4.8, the strength of the anion exchange membrane decreases.

(Swelling degree)
In order to express sufficient workability for use as an anion exchange membrane for electrodialysis, the swelling degree of the obtained anion exchange membrane is preferably in the range of 10 to 50, and in the range of 12 to 48. Is more preferable, and the range of 15 to 45 is more preferable. When the degree of swelling is less than 10, the organic contamination resistance performance of the anion exchange membrane is lowered. On the other hand, when the degree of swelling exceeds 50, the strength of the anion exchange membrane decreases.

(Ion exchange capacity)
In order to develop sufficient ion exchange properties for use as an anion exchange membrane for electrodialysis, the obtained cationic vinyl alcohol copolymer (P) has an ion exchange capacity of 0.30 meq / g or more. It is preferable that it is 0.50 meq / g or more. The upper limit of the ion exchange capacity of the cationic vinyl alcohol copolymer (P) is 3.0 meq / g or less because if the ion exchange capacity becomes too large, hydrophilicity increases and it becomes difficult to suppress the degree of swelling. Is preferred.

(Anion exchange membrane used in electrodialysis treatment)
In the electrodialysis treatment, the cation exchange membrane used together with the anion exchange membrane of the present invention is not particularly limited, and a membrane made of a polymer having a sulfonate group, a carboxylate group, a phosphonate group or the like can be appropriately selected and used. . In addition, functional groups that can be converted at least partially into sulfonate groups, carboxylate groups, and phosphonate groups in water, such as sulfonic acid groups, carboxyl groups, and phosphonic acid groups are also included in the anionic groups.

(Electrodialysis)
In the electrodialysis using the anion exchange membrane of the present invention, at least one of the anode and the cathode is formed by arranging the cation exchange membrane and the anion exchange membrane using the anion membrane of the present invention. Any known electrodialysis tank can be used without particular limitation. For example, an anion exchange membrane and a cation exchange membrane are alternately arranged, such as a filter press type or unit cell type having a basic structure in which a desalination chamber and a concentration chamber are formed by the ion exchange membrane and a chamber frame. Such an electrodialysis tank can be preferably used. Note that the number of membranes used in the electrodialysis tank or the channel interval (membrane interval) between the desalting chamber and the concentrating chamber is appropriately selected depending on the type of liquid to be processed and the processing amount.

(Use of anion exchange membrane)
The anion exchange membrane of the present invention is excellent in organic contamination resistance, has a low membrane resistance, and can perform electrodialysis efficiently and stably over a long period of time. Therefore, such ion exchange membranes can be used for desalting organic substances (food, pharmaceutical raw materials, etc.), desalting whey, concentrating salts, desalting sugar solutions, desalting seawater and brine, and desalting tap water. Suitable for water softening. In general, it is particularly suitably used as an anion exchange membrane in which organic contamination is remarkable.

Hereinafter, examples will be given to describe the present invention in more detail, but the present invention is not limited to these examples. In the examples, “%” and “parts” are based on weight unless otherwise specified.

  The characteristics of the anion exchange membranes shown in Examples and Comparative Examples were measured by the following methods.

1) Measurement of film thickness After the anion exchange membrane was immersed in 25 ° C ion exchange water for 24 hours or more, the thickness was measured using a Digimatic Micrometer (manufactured by Mitutoyo Corporation).

2) was immersed for 24 hours or more in the swelling degree 25 ° C. in deionized water measured anion exchange membrane, thickness was measured using a Digimatic micrometer (manufactured by Mitutoyo Corporation) (H _2). Thereafter, 105 ° C. in a hot air drier DX60 (manufactured by Yamato Scientific), dried 4 hours, to measure the thickness with a Digimatic micrometer (manufactured by Mitutoyo Corporation) (H _1). The measurement of the film swelling degree was calculated by the following formula.
Swelling degree (%) = (H ₂ −H ₁ ) / H ₁ × 100

3) Measurement of the degree of cross-linking An anion exchange membrane was cut into a size of 2 × 3 cm, and the total reflection method (ATR method) using an infrared spectrophotometer JIR-5500 (manufactured by JEOL Ltd.), around 2920 cm ⁻¹ ( area of the peak (CH bond area of reference peak of the peak) derived from the stretching mode _{(I 1)} of 2770cm ^-1 ~2995cm ^-1), peak of 3380cm around ^{-1 (2995cm -1 ~3755cm -1) (} OH The area of the peak derived from the group was defined as the area of the target peak (I ₂ ), and I ₂ / I ₁ indicating the ratio was used as the degree of crosslinking of the ion exchange membrane.

4) Measurement of organic contamination resistance After immersing an anion exchange membrane in an aqueous solution of sodium chloride having a concentration of 0.05 mol / L for 24 hours, one ion exchange membrane is sandwiched between two chamber cells having a silver-silver chloride electrode. It is. Next, the anode chamber and the cathode chamber of the two-chamber cell were filled with a solution in which sodium chloride having a concentration of 0.05 mol / L as an electrolyte and 52 mg / L of sodium dodecylbenzenesulfonate as a contaminant were dissolved, and each 1.2 L / min. The electrodialysis was performed at a current density of 0.2 A / dm ² . At this time, a platinum wire was fixed in the vicinity of both membrane surfaces, and the transmembrane voltage was measured. When organic contamination occurs during energization, the transmembrane voltage increases. The voltage across the membrane 30 minutes after the start of energization was measured, and the voltage difference (ΔE) between when the organic contaminant was added and when it was not added was taken as a measure of the contamination of the membrane. During this test, the membrane could be measured without breakage.

5) Determination of membrane strength After measuring the organic contamination resistance using the above-described two-chamber cell for 6 hours, the anion exchange membrane was taken out of the cell and checked for damage. This evaluation was performed 5 times with the anion exchange membrane of the same lot, and the membrane strength was quantified and discriminated by the following equation.
Film strength = (total number of evaluated films−number of films damaged after evaluation) ÷ total number of evaluated films × 100
○: film strength 100%, Δ: film strength 60% to less than 100%, ×: film strength less than 60%

Reference Example (Synthesis of a polyvinyl alcohol polymer having a mercapto group at the molecular end)
Polyvinyl alcohol having a mercapto group at the molecular end shown in Table 1 was synthesized by the method described in Patent Document 3.

(Synthesis of P-1)
In a 6 L four-necked separable flask equipped with a reflux condenser and a stirring blade, 3299 g of water, 374 g of PVA-1 shown in Table 1 as a vinyl alcohol polymer having a mercapto group at the end, vinylbenzyltrimethylammonium chloride (VBTAC) ) 200 g was charged and heated to 90-95 ° C. with stirring to dissolve the vinyl alcohol polymer. Then, 3.64 g of 2,2′-azobisisobutyronitrile as a polymerization initiator was added to 121.3 g. An initiator aqueous solution dissolved in ion-exchanged water was sequentially added over 1.5 hours, and stirring was continued for 2 hours to proceed with copolymerization to obtain a vinyl alcohol copolymer containing a cationic group. A part of the obtained aqueous solution was dried, dissolved in heavy water, and subjected to ¹ H-NMR measurement at 400 MHz. As a result, the modified amount of VBTAC unit was 10 mol%.

(Synthesis of P-2 to 9)
By the same method as P-1 except that the polymerization conditions such as the type and addition amount of the vinyl alcohol polymer, the addition amount of the cationic group-containing monomer, and the addition amount of the initiator were changed to the contents shown in Table 2. , P-2 to 9 were obtained. Table 2 shows the modification amount and solid content concentration of the obtained cationic vinyl alcohol copolymer (P).

Example 1
The above P-1 aqueous solution is coated on a PET substrate having a film thickness of 200 μm using a YBA-type baker applicator, put in a dryer DX602 (manufactured by YAMATO) that has been heated to 80 ° C., and left for 60 minutes. Water was removed to obtain a P-1 molded body. After the PET base material was peeled from the P-1 molded body thus obtained, it was placed in a dryer that had been heated to 160 ° C. in advance, and allowed to stand for 30 minutes to cause physical crosslinking. To adjust the crosslinking bath, sulfuric acid was added to 1 L of ion-exchanged water to adjust the pH to 2.5, 400 g of sodium sulfate was dissolved in this bath, and then a glutaraldehyde solution (25% by volume) (Wako Pure) A cross-linking bath was prepared by adding 1% by volume of Yakuhin Kogyo Co., Ltd., and pre-warmed to 50 ° C. After the P-1 molded body was immersed in this crosslinking bath for 30 minutes, it was taken out from the crosslinking bath and washed with running water for 24 hours to obtain an anion exchange membrane of the P-1 crosslinked body.

(Evaluation of ion exchange membrane)
The anion exchange membrane thus produced was cut into a desired size to produce a measurement sample. Using the obtained measurement sample, according to the above method, the film swelling degree, the crosslinking degree, the organic contamination resistance, and the film strength were evaluated. The obtained results are shown in Table 3.

(Examples 2-5, 7-8)
An anion exchange membrane was prepared in the same manner as in Example 1 except that the composition ratio of the cationic vinyl alcohol copolymer (P), the type of polyvinyl alcohol, the pH of the crosslinking bath, etc. were changed to the contents shown in Table 3. And evaluated. The obtained results are shown in Table 3.

(Example 6)
An aqueous solution having a concentration of 12 wt% was prepared using the aforementioned P-4 aqueous solution. This P-4 aqueous solution was coated on a PET substrate using a baker applicator so that the film thickness of the coating solution was 800 μm. Next, on this coating film, vinylon paper (basis weight: 36 g / m ² , thickness: 90 μm, porosity: 67%) was superposed to impregnate the vinylon paper with P-4 aqueous solution. Then, after putting in hot air dryer DKM400 (product made from YAMATO), standing still at 60 degreeC for 60 minutes and removing a water | moisture content, PET base material was peeled and the P-4 molded object was obtained. The molded body thus obtained was heat-treated at 160 ° C. for 30 minutes to cause physical crosslinking. As the adjustment of the crosslinking bath, sulfuric acid was added to 1 L of ion exchange water to adjust the pH to 1.0, and 400 g of sodium sulfate was dissolved in this bath. Next, a glutaraldehyde solution (25% by volume) (manufactured by Wako Pure Chemical Industries, Ltd.) was added to 1% by volume to prepare a crosslinking bath, which was preheated to 50 ° C. After the P-4 molded body was immersed in this crosslinking bath for 30 minutes, it was taken out from the crosslinking bath and washed with running water for 24 hours to obtain a P-4 crosslinked anion exchange membrane.

(Evaluation of ion exchange membrane)
The anion exchange membrane thus produced was cut into a desired size to produce a measurement sample. Using the obtained measurement sample, according to the above method, the film swelling degree, the crosslinking degree, the organic contamination resistance, and the film strength were evaluated. The obtained results are shown in Table 3.

(Comparative Examples 1-5)
An anion exchange membrane was prepared in the same manner as in Example 1 except that the composition ratio of the cationic vinyl alcohol copolymer (P), presence or absence of crosslinking, pH of the crosslinking bath, etc. were changed to the contents shown in Table 3. Evaluation was performed. The obtained results are shown in Table 3.

  From the results shown in Table 3, a cationic vinyl alcohol copolymer (P) containing a vinyl alcohol polymer (A) and a polymer (B) having a cationic group, the vinyl alcohol polymer (P) The ratio of A) to the polymer (B) having a cationic group is in the range of 97: 3 to 60:40 mol%, and is subjected to crosslinking treatment, and the degree of crosslinking is 3.0 to 4. It can be seen that the anion exchange membrane in the range of 8 is excellent in organic contamination resistance and membrane strength (Examples 1 to 8). In particular, when the degree of swelling of the anion exchange membrane is in the range of 10 to 50, it can be seen that the organic contamination resistance and membrane strength are more excellent (Examples 1 to 6). On the other hand, if the crosslinking treatment was not performed, the ion exchange membrane was dissolved in the evaluation solution, and the membrane characteristics could not be measured (Comparative Example 1). The ratio of the vinyl alcohol polymer (A) and the polymer having a cationic group (B) contained in the cationic vinyl alcohol copolymer (P) is in the range of 97: 3 to 60:40 mol%. The organic contamination resistance or the film strength deteriorated when the value was removed (Comparative Examples 2-3). Furthermore, when the degree of crosslinking of the cationic vinyl alcohol copolymer (P) was outside the range of 3.0 to 4.8, the organic contamination resistance or film strength deteriorated (Comparative Examples 4 to 5).

  Since the anion exchange membrane of the present invention has excellent resistance to organic contamination and low membrane resistance, desalting of organic substances (food, pharmaceutical raw materials, etc.), desalting of whey, concentration of salt, desalting of sugar solution, seawater Since it can be widely used as an anion exchange membrane for electrodialysis used for desalting kettle water, demineralizing tap water, softening water, etc., it has industrial applicability.

  While the preferred embodiments of the present invention have been described above by way of example, those skilled in the art can make various modifications, additions and substitutions without departing from the spirit and spirit of the present invention disclosed in the claims. Is understandable.

Claims (6)

  A cationic vinyl alcohol copolymer (P) comprising a vinyl alcohol polymer (A) and a polymer (B) having a cationic group, the vinyl alcohol polymer (A) and the cationic group The ratio of the polymer (B) having a range of 97: 3 to 60:40 mol% and a crosslinking treatment, and the degree of crosslinking is in the range of 3.0 to 4.8. Anion exchange membrane characterized by   The anion exchange membrane according to claim 1, wherein the swelling degree of the anion exchange membrane is in the range of 10-50.   The anion exchange membrane according to claim 1 or 2, wherein the saponification degree of the cationic vinyl alcohol copolymer (P) is in the range of 70 to 99.9 mol%.   The cationic vinyl alcohol copolymer (P) contains a block copolymer of a vinyl alcohol polymer (A) and a polymer (B) having a cationic group. The anion exchange membrane of any one of -3.   2. The cationic vinyl alcohol copolymer (P) contains a graft copolymer of a vinyl alcohol polymer (A) and a polymer (B) having a cationic group. The anion exchange membrane of any one of -3.   The anion exchange membrane according to any one of claims 1 to 5, wherein the anion exchange membrane comprises a cationic vinyl alcohol copolymer (P) and a porous support.