JP6219755B2 - Ion exchange membrane and method for producing the same - Google Patents

Description

  The present invention relates to an ion exchange membrane comprising an ionic vinyl alcohol block copolymer having a cation exchange group or an anion exchange group.

  Ion exchange membranes are used as membranes for electrodialysis in desalination processes such as salt production, food, and underground brine. In general, ion exchange membranes exhibit ion selectivity by introducing ion exchange groups and crosslinks into a styrene / divinylbenzene polymer. However, since the film becomes brittle due to the introduction of crosslinking, a polymer mesh made of polyvinyl chloride or the like is used as the reinforcing material. For this reason, the manufacturing process becomes complicated and causes high costs. In the electrodialysis method, ions are moved by applying DC power to an electrodialysis tank in which an anion exchange membrane and a cation exchange membrane are alternately arranged between a cathode and an anode. Therefore, a desalination chamber in which the ion concentration decreases and a concentration chamber in which the ion concentration increases are alternately installed. As electrodialysis progresses and the concentration of sparingly soluble salts in the concentration chamber increases, scales are generated due to precipitation, so chemicals such as acids are added to the concentration chamber to prevent scale formation. There was a problem of increasing. Therefore, development of an ion exchange membrane that is inexpensive and has little membrane contamination is desired.

  Patent Document 1 includes a nonwoven fabric sheet and an ion exchange resin coating layer provided on one surface of the nonwoven fabric sheet, and the nonwoven fabric sheet has a long fiber layer with a fiber diameter of 8 to 30 μm on both sides. An ion exchange membrane having a fiber layer structure in which a fine fiber layer having a fiber diameter of 5 μm or less is formed by fusion of fibers as an intermediate layer between the long fiber layers is disclosed. The membrane can improve strength, dimensional stability, and shape stability even when using an inexpensive non-woven sheet, effectively suppresses undulation when in contact with the electrolyte, and has low membrane resistance. A membrane can be obtained.

  However, when the ion exchange membrane of Patent Document 1 is used for electrodialysis, the adhesion between the base sheet and the ion exchange resin is not sufficient, and the resin peels off from the base material during the long-term operation of electrodialysis. There was a problem that a blister occurred. Furthermore, when an ion exchange resin coating solution is applied in the process of providing an ion exchange resin coating layer on the surface of the nonwoven fabric sheet, it is difficult to replace the air inside the nonwoven fabric sheet with the coating solution, and foam defects due to residual air occur. There was an easy problem.

JP 2012-40508 A

  An object of the present invention is to provide an ion exchange membrane excellent in electrical characteristics and membrane strength and having few bubble defects inside and on the surface, and a method for producing the same.

  As a result of various studies on the above problems, the present inventors have found that when a specific ionic vinyl alcohol block copolymer is applied to a wet nonwoven fabric of vinylon short fibers by a specific manufacturing method, the wet nonwoven fabric has less bubble results. It was found that not only an impregnation layer can be formed, but also excellent electrical characteristics and film strength, and the present invention has been achieved.

[式中、０．５０００≦ｏ^１／（ｎ^１＋ｏ^１）≦０．９９９９であり、０．００１≦ｍ^１／（ｍ^１＋ｎ^１＋ｏ^１）≦０．５０であり、Ｘ^＋はＨ^＋またはアルカリ金属イオンまたは４級アンモニウムイオン等の１価のカチオンである。]

[式中、０．５０００≦ｏ²／（ｎ²＋ｏ²）≦０．９９９９であり、０．００１≦ｍ²／（ｍ²＋ｎ²＋ｏ²）≦０．５０であり、Ｙ⁻は、ＰＦ_６ ⁻、ＳｂＦ_６ ⁻、ＡｓＦ_６ ⁻等の５Ｂ族元素のハロゲン化アニオン、ＢＦ_４ ⁻等の３Ｂ族元素のハロゲン化アニオン、Ｉ⁻（Ｉ_３ ⁻）、Ｂｒ⁻、Ｃｌ⁻等のハロゲンアニオン、ＣｌＯ_４ ⁻等のハロゲン酸アニオン、ＡｌＣｌ_４ ⁻、ＦｅＣｌ_４ ⁻、ＳｎＣｌ_５ ⁻等の金属ハロゲン化物アニオン、ＮＯ_３ ⁻で示される硝酸アニオン、ｐ−トルエンスルホン酸アニオン、ナフタレンスルホン酸アニオン、ＣＨ_３ＳＯ_３ ⁻、ＣＦ_３ＳＯ_３ ⁻等の有機スルホン酸アニオン、ＣＦ_３ＣＯＯ⁻、Ｃ_６Ｈ_５ＣＯＯ⁻等のカルボン酸アニオン、ＯＨ⁻等の１価のアニオンである。］ That is, the ion exchange membrane of the present invention comprises a vinylon short fiber wet nonwoven fabric and an anionic vinyl alcohol block copolymer represented by the following general formula (1) or a cationic vinyl alcohol represented by the following general formula (2). An ion exchange membrane containing a system block copolymer,
The wet nonwoven fabric is provided with an impregnation layer impregnated with the ionic polymer at least partially in the thickness direction from one surface,
In the ion-exchange membrane, the main fiber of the wet nonwoven fabric has an average fiber diameter of 3 to 40 μm and a binder fiber content of 2 to 9% by mass.

[In the formula, 0.5000 ≦ o ¹ / (n ¹ + o ¹ ) ≦ 0.9999, 0.001 ≦ m ¹ / (m ¹ + n ¹ + o ¹ ) ≦ 0.50, and X ⁺ is H ⁺ Or a monovalent cation such as an alkali metal ion or a quaternary ammonium ion. ]

[In the formula, 0.5000 ≦ o ² / (n ² + o ² ) ≦ 0.9999, 0.001 ≦ m ² / (m ² + n ² + o ² ) ≦ 0.50, and Y ⁻ is Halogenated anions of group 5B elements such as PF ₆ ⁻ , SbF ₆ ⁻ , AsF ₆ ⁻ , halogenated anions of group 3B elements such as BF ₄ ⁻ , and halogens such as I ⁻ (I ₃ ⁻ ), Br ⁻ and Cl ^−. Anion, halogenate anion such as ClO ₄ ⁻ , metal halide anion such as AlCl ₄ ⁻ , FeCl ₄ ⁻ , SnCl ₅ ⁻ , nitrate anion represented by NO ₃ ⁻ , p-toluenesulfonate anion, naphthalenesulfonate anion, _{^{CH 3 SO 3 -, CF 3}} SO 3 - and the like organic sulfonic acid _{^{anion, CF 3 COO -, C 6}} H 5 COO - a carboxylic acid anion, OH ^- is a monovalent anion such as ]

  In the ion exchange membrane, it is desirable that the main fiber of the wet nonwoven fabric has an average fiber diameter of 8 to 20 μm and a binder fiber content of 3 to 8 mass%.

  In the ion exchange membrane, it is preferable that the ionic vinyl alcohol block copolymer is a crosslinked body that is crosslinked in a state where the ionic vinyl alcohol block copolymer is applied to a wet nonwoven fabric of vinylon short fibers.

The present invention also includes a method for producing an ion exchange membrane, the method comprising preparing an ionic vinyl alcohol block copolymer solution;
Applying an aqueous solution of the ionic vinyl alcohol block copolymer on the release sheet to form a coating layer of the ionic vinyl alcohol block copolymer;
A step of superposing a wet nonwoven fabric of vinylon short fibers on the coating layer and impregnating at least a part of the nonwoven fabric with an ionic vinyl alcohol block copolymer to form an impregnated body;
A step of drying the impregnated body in a state where the coating layer and the wet nonwoven fabric are overlaid; and a step of peeling the release sheet from the dried impregnated body;
Is included.

  In the manufacturing method, after the peeling step, the ionic vinyl alcohol block copolymer may be subjected to a heat treatment, and after the heat treatment step, the ionic vinyl alcohol block copolymer may be subjected to a crosslinking treatment. Good.

  In the present invention, impregnation means a state in which the ionic polyvinyl alcohol-based block copolymer substantially fills the voids and / or pores of the wet nonwoven fabric of vinylon short fibers.

According to the present invention, when a specific ionic vinyl alcohol block copolymer is applied to a wet nonwoven fabric of vinylon short fibers by a specific manufacturing method, an impregnation layer with few bubble defects can be formed on the wet nonwoven fabric. In addition, an ion exchange membrane having excellent electrical characteristics and membrane strength can be obtained.

It is the schematic of the membrane resistance test apparatus of an ion exchange membrane.

(Anionic vinyl alcohol block copolymer)
The anionic vinyl alcohol block copolymer used in the present invention is represented by the general formula (1).

In the general formula (1), o ¹ / (n ¹ + o ¹ ) represents a ratio other than vinyl acetate units contained in the vinyl alcohol copolymer component. About a minimum, it is 0.5000 or more, More preferably, it is 0.7000 or more, More preferably, it is 0.8000 or more. On the other hand, the upper limit is preferably 0.9999, more preferably 0.999 or less, and still more preferably 0.995 or less.

In the general formula (1), m ¹ / (m ¹ + n ¹ + o ¹ ) represents a ratio of a polymer component having an anion group contained in a vinyl alcohol copolymer component and a polymer component having an anion group. The lower limit is 0.001 or more, more preferably 0.003 or more, and further preferably 0.005 or more. The upper limit is 0.50 or less, more preferably 0.30 or less, and preferably 0.25 or less.

X ⁺ in the general formula (1) is preferably a quaternary ammonium ion or the like, and more preferably an alkali metal ion or a monovalent cation of H ⁺ ion.

(Cationic vinyl alcohol block copolymer)
The cationic vinyl alcohol block copolymer used in the present invention is represented by the general formula (2).

In the general formula (2), o ² / (n ² + o ² ) represents a ratio other than vinyl acetate units contained in the vinyl alcohol copolymer component. About a minimum, it is 0.5000 or more, More preferably, it is 0.7000 or more, More preferably, it is 0.8000 or more. On the other hand, the upper limit is preferably 0.9999, more preferably 0.999 or less, and still more preferably 0.995 or less.

In the general formula (2), m ² / (m ² + n ² + o ² ) represents the ratio of the polymer component having a cationic group contained in the vinyl alcohol polymer component and the polymer component having a cationic group. The lower limit is 0.001 or more, more preferably 0.003 or more, and further preferably 0.005 or more. The upper limit is 0.50 or less, more preferably 0.30 or less, and preferably 0.25 or less.

As Y- in the general formula (2), a halogenated anion of a group 5B element such as PF ₆ ⁻ , SbF ₆ ⁻ , AsF ₆ ^—, a halogenated anion of a group 3B element such as BF ₄ ^— , I ⁻ (I ^{_{3 -), Br - ,, ClO}} 4 - and halogen ^{_{anion, AlCl 4 -, FeCl 4 -}} , SnCl 5 - metal halide anions such as, NO ₃ ^- nitrate anion, p- toluenesulfonate anion represented by , Naphthalenesulfonate anion, organic sulfonate anions such as CH ₃ SO ₃ ⁻ and CF ₃ SO ₃ ^— , carboxylate anions such as CF ₃ COO ⁻ and C ₆ H ₅ COO ⁻ , and more preferably halogen anions such as Cl ⁻ , OH ^- 1 monovalent anion, and the like are preferable.

(Manufacture of block copolymer)
A method for producing a polymer in which a polymer component obtained by polymerizing the cation exchange monomer or anion exchange monomer of the present invention and a vinyl alcohol polymer component forms a block copolymer is mainly as follows. Broadly divided into two methods. (1) A method in which a desired block copolymer is produced and then a cationic group or an anionic group is bonded to a specific block, and (2) at least one cationic monomer or anionic monomer In this method, a desired block copolymer is obtained by polymerization. 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 or an anionic group into a polymer component of the kind, (2), at least one cationic monomer or anionic monomer in the presence of a vinyl alcohol polymer having a mercapto group at the terminal. A method for producing a block copolymer by radical polymerization of a monomer is preferred from the viewpoint of industrial ease. In particular, since the kind and amount of each component in the block copolymer can be easily controlled, at least one kind of cationic monomer or anionic monomer in the presence of a vinyl alcohol polymer having a mercapto group at the terminal. A method for producing a block copolymer by radical polymerization of a monomer is preferred.

  The vinyl alcohol polymer having a mercapto group at the terminal used for the production of these block copolymers can be obtained by, for example, a method described in JP-A-59-187003. 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. Examples of a method for obtaining a block copolymer using a vinyl alcohol polymer having a mercapto group at the terminal and an ionic monomer include the method described in JP-A-59-189113. It is done. That is, a block copolymer can be obtained by radical polymerization of an ionic monomer 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 ion exchange membrane of the present invention may contain a nonionic surfactant in the copolymer constituting the ionic vinyl alcohol block copolymer, if necessary.

(Production of ion exchange membrane)
The ion exchange membrane of the present invention is a step of preparing an ionic polyvinyl alcohol-based block copolymer solution;
Applying an aqueous solution of the ionic polyvinyl alcohol-based block copolymer on a release sheet to form a coating layer of the ionic polyvinyl alcohol-based block copolymer;
A step of superposing a vinylon nonwoven fabric on the coating layer and impregnating at least a part of the vinylon nonwoven fabric with an ionic polyvinyl alcohol-based block copolymer to form an impregnated body;
A step of drying the impregnated body in a state where the coating layer and the vinylon nonwoven fabric are overlaid;
And peeling the release sheet from the dried impregnated body.

(Ionic vinyl alcohol block copolymer solution preparation process)
More specifically, the above ionic vinyl alcohol block copolymer is dissolved in a solvent such as water or DMSO to prepare an ionic vinyl alcohol block copolymer solution (preferably an aqueous solution).
The obtained ionic vinyl alcohol block copolymer solution may have a viscosity of, for example, 300 to 5000 mPa · s, preferably 400 from the viewpoint of satisfactorily forming an impregnated layer with respect to the vinylon nonwoven fabric. It may be ˜4000 mPa · s, more preferably 500 to 3000 mPa · s. The concentration can be appropriately set according to the type of the ionic vinyl alcohol block copolymer, but may be, for example, 1 to 50 wt%, preferably 2 to 45 wt%, more preferably 3 It may be ˜40 wt%.

(Coating layer forming process)
Then, the obtained ionic vinyl alcohol block copolymer solution (preferably an aqueous solution) is applied to the release sheet using various application means such as a bar coater, a gravure coater, a knife coater, a blade coater, and the like. A layer (cast layer) is formed. The coating layer forms an appropriate coating surface according to the size of the vinylon nonwoven fabric to be overlaid next.
The release sheet 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.
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, from the viewpoint that it can be embedded and integrally formed with the vinylon nonwoven fabric. There may be. Without carrying out this coating layer and drying treatment, it is subsequently subjected to the next vinylon nonwoven fabric impregnation step.

(Vinylon nonwoven fabric impregnation process)
Before performing the drying step, the coating layer is overlapped with the vinylon nonwoven fabric, impregnated with the vinylon nonwoven fabric, impregnated with the ionic vinyl alcohol block copolymer solution, and buried and integrated with the vinylon nonwoven fabric.

The vinylon nonwoven fabric may have a basis weight of, for example, about 10 to 90 g / m ² , preferably about 15 to 70 g / m ² , more preferably from the viewpoint of being embedded and integrally formed. It may be about 25 to 50 g / m ² .
The vinylon nonwoven fabric may have a thickness of, for example, 50 μm to 150 μm, preferably 60 μm to 130 μm, more preferably 70 μm to 100 μm.

  The average fiber diameter of the main fibers of the vinylon nonwoven fabric is 3 to 40 μm. The average fiber diameter of the main fiber is preferably 8 to 20 μm. When the fiber diameter of the main fiber is within this range, the resulting ion exchange membrane has excellent mechanical strength and excellent durability. When the average fiber diameter of the main fiber is less than 3 μm, bubble defects may occur and durability may be reduced. On the other hand, when the average fiber diameter of the main fiber is more than 40 μm, the mechanical strength of the ion exchange membrane may be inferior.

  The binder fiber content of the vinylon nonwoven fabric is 2 to 9% by mass. It is preferable that the content rate of the said binder fiber is 3-8 mass%. When the binder fiber content is in this range, the resulting ion exchange membrane has excellent mechanical strength and excellent durability. When the binder fiber content of the vinylon nonwoven fabric is less than 2% by mass, the strength of the vinylon nonwoven fabric is weak and the handleability is poor. On the other hand, if the binder fiber content exceeds 9% by mass, the number of bubble defects may increase and the mechanical strength may also decrease.

(Drying process)
In the drying step, the impregnated body is dried in a state where the coating layer and the vinylon nonwoven fabric 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, there is no restriction | limiting in particular as drying temperature, For example, about 50-110 degreeC may be sufficient, Preferably it may be about 60-90 degreeC.

(Peeling process)
In the peeling step, the release sheet 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 crystallinity of the ionic vinyl alcohol block copolymer is increased, so that the number of physical crosslinking points is increased and the mechanical strength of the resulting ion exchange membrane is increased. In addition, since the cation group or anion 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 resulting ion 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 ionic vinyl alcohol block copolymer 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.

  In the present invention, 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 0.001-10 volume% normally.

  In the post-treatment, all of the heat treatment and the crosslinking treatment may be performed, two of them may be performed, or only one of them may be performed. The order of processing to be performed is not particularly limited. A plurality of treatments may be performed simultaneously, but it is preferable to perform a crosslinking treatment after the heat treatment. This is because a part that is difficult to be cross-linked is generated by performing heat treatment, and then a cross-linking part, in particular a chemical cross-linking part, is performed so that a cross-linked part and a non-cross-linked part coexist to increase the film strength. It is particularly preferable in the order of the heat treatment and the crosslinking treatment from the viewpoint of the mechanical strength of the resulting ion exchange membrane.

(Use of ion exchange membrane)
The ion exchange membrane of the present invention can be used for various applications. For example, the ion exchange membrane of the present invention having an ion exchange layer made of either a cationic vinyl alcohol block copolymer or an anionic vinyl alcohol block copolymer is excellent in organic contamination resistance and has a membrane resistance. Electrodialysis can be performed stably and efficiently over a long period of time. Therefore, such ion exchange membranes are used for desalting organic substances (food, pharmaceutical raw materials, etc.), desalting whey, concentrating salts, desalting sugar solutions, desalting seawater and brine, desalting tap water, Suitable for softening water. In general, it is particularly preferably used as an ion exchange membrane in which organic contamination is remarkable.

  Hereinafter, the present invention will be described in detail using examples. In the following examples and comparative examples, “%” and “parts” are based on mass unless otherwise specified. Analysis and evaluation in Examples and Comparative Examples were performed according to the following methods.

ここで、１．３は樹脂密度（ｇ／ｃｍ^３）、πは円周率３．１４である。 (1) Measurement of fiber diameter The weight I (g) of a single fiber having a length of 10 m was measured, the radius r of the main fiber was obtained from the following calculation formula, and the average fiber diameter (μm) of the main fiber was calculated.
Average fiber diameter of main fibers (μm) = 2r

Here, 1.3 is the resin density (g / cm ³ ), and π is the circumferential ratio of 3.14.

(2) Burst strength measurement The burst strength measurement was performed using a Murren low-pressure burst test (No. 305-YPL, Yasuda Seisakusho). The sample size was 60 × 60 mm or more, and was performed by the method specified in JIS-P8110.

(3) Bubble number measurement The obtained ion exchange membrane was observed with an optical microscope (ECLIPSE LV100, manufactured by Nikon) at a magnification of 5 times, and the number of bubbles having a size of 50 μm or more present in an area of 1 cm ² area was measured. I counted.

(4) Membrane resistance measurement Membrane resistance was measured by sandwiching an ion exchange membrane in a two-chamber cell having a platinum black electrode plate shown in FIG. 1 and filling a 0.5 mol / L-NaCl solution on both sides of the membrane. The resistance between the electrodes at 25 ° C. was measured at a frequency of 1000 cycles / second), and was obtained from the difference between the resistance between the electrodes and the resistance between the electrodes when no ion exchange membrane was installed. The membrane used for the above measurement was previously equilibrated in a 0.5 mol / L-NaCl solution.

(Synthesis of polyvinyl alcohol PVA having a mercapto group at the end)
Polyvinyl alcohol (PVA-1) having a mercapto group at the end was synthesized by the method described in JP-A-59-187003. The degree of polymerization of the obtained polyvinyl alcohol was 1550, and the degree of saponification was 99.9%.

(Synthesis of block copolymer P-1: PVA-b-PSS)
In a 500 mL four-necked separable flask equipped with a reflux condenser and a stirring blade, 117 g of water, 25.0 g of terminal mercapto group-containing polyvinyl alcohol (PVA-1) and sodium parastyrenesulfonate (PSS: manufactured by Aldrich) 12.6 g was charged, and heated to 90 ° C. with stirring to dissolve nitrogen while bubbling. After nitrogen substitution, 6.2 mL of a 2.0% aqueous solution of 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) -2-propionamide] was sequentially added to the above aqueous solution over 1.5 hours. The polymerization is started by adding to the polymer, and then allowed to proceed. Then, the system temperature is maintained at 90 ° C. for 24 hours to further promote the polymerization, and then cooled to block copolymer of polyvinyl alcohol and sodium parastyrenesulfonate. An aqueous solution P-1 of (PVA-b-PSS) was prepared. The pH of the aqueous solution was 6.5. A part of the aqueous solution P-1 was dried, dissolved in heavy water, and subjected to ¹ H-NMR measurement at 500 MHz. As a result, the amount of modification of the sodium parastyrenesulfonate unit was 10 mol%.

(Synthesis of block copolymer P-2: PVA-b-VBTAC)
In a 500 mL four-necked separable flask equipped with a reflux condenser and a stirring blade, 137 g of water, 25.0 g of polyvinyl alcohol (PVA) containing a terminal mercapto group and vinylbenzyltrimethylammonium chloride (VBTAC: manufactured by Aldrich) were added. 4 g was charged, heated to 90 ° C. with stirring, and dissolved while bubbling nitrogen. After nitrogen substitution, 12.2 mL of a 2.0% aqueous solution of 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) -2-propionamide] was sequentially added to the above aqueous solution over 1.5 hours. The polymerization is started and allowed to proceed, and then the system temperature is maintained at 90 ° C. for 4 hours to allow the polymerization to proceed further, followed by cooling to block copolymer of polyvinyl alcohol and vinylbenzyltrimethylammonium chloride. An aqueous solution P-2 of (PVA-b-VBTAC) was prepared. The pH of the aqueous solution was 8.0. A part of the aqueous solution P-2 was dried, dissolved in heavy water, and subjected to 1H-NMR measurement at 500 MHz. As a result, the modified amount of the vinylbenzyltrimethylammonium chloride unit was 10 mol%.

<Example 1>
(Preparation of cation exchange membrane CEM-1)
A P-1 aqueous solution having a concentration of 12 wt% was prepared using deionized water. This polymer aqueous solution was applied to a PET film to a thickness of 800 μm using a bar coater to form a coating layer (cast layer). Next, a vinylon nonwoven fabric (basis weight: 36 g / cm ² , average fiber system of main fibers: 3 μm, binder fiber content: 5 mass%) is superimposed on the cast layer surface of the PET film on which this cast layer is formed. -1 aqueous solution was impregnated into a vinylon nonwoven fabric. Then, after drying for 40 minutes at a temperature of 80 ° C. with a hot air dryer DKM400 (manufactured by YAMATO), the PET film was peeled off to prepare an impregnated coating film. The film thus obtained was heat treated at 160 ° C. for 30 minutes to cause physical crosslinking. Subsequently, the film was immersed in an aqueous electrolyte solution of 2 mol / L sodium sulfate for 24 hours. Concentrated sulfuric acid was added to the aqueous solution so that the pH was 1, and the film was immersed in a 1% by volume glutaraldehyde aqueous solution, followed by stirring with a stirrer at 25 ° C. for 24 hours for crosslinking. Here, as the glutaraldehyde aqueous solution, a product obtained by diluting “glutaraldehyde” (25% by volume) manufactured by Ishizu Pharmaceutical Co., Ltd. with water was used. After the cross-linking treatment, the film was immersed in deionized water, and while deionized water was exchanged several times in the middle, the film was immersed until the film reached a swelling equilibrium to obtain a cation exchange membrane CEM-1.

(Evaluation of ion exchange membrane)
The cation exchange membrane thus prepared was cut into a desired size to prepare a measurement sample. Using the obtained measurement sample, the number of bubbles, burst strength, and membrane resistance were measured by the methods described above according to the above methods. The results are shown in Table 1.

<Examples 2 to 10>
(Preparation of cation exchange membrane CEM-2 to 10)
Except that the average fiber diameter of the main fiber of the used vinylon nonwoven fabric and the content of the binder fiber were changed to the contents shown in Table 1, it was carried out in the same manner as in Example 1 to obtain CEM-2 to 10 .

(Evaluation of ion exchange membrane)
The cation exchange membrane thus prepared was cut into a desired size to prepare a measurement sample. Using the obtained measurement sample, the number of bubbles, burst strength, and membrane resistance were measured by the methods described above according to the above methods. The results are shown in Table 1.

<Comparative Examples 1-3>
(Preparation of cation exchange membranes CEM-11 to 13)
Except having changed the average fiber diameter of the main fiber of the used vinylon nonwoven fabric, and the content of binder fiber into the content shown in Table 1, it implemented by the method similar to Example 1, and obtained CEM-11-13 .

(Evaluation of ion exchange membrane)
The cation exchange membrane thus prepared was cut into a desired size to prepare a measurement sample. Using the obtained measurement sample, the number of bubbles, burst strength, and membrane resistance were measured by the methods described above according to the above methods. The results are shown in Table 1.

<Comparative Example 4>
(Preparation of cation exchange membrane CEM-14)
A P-1 aqueous solution having a concentration of 12 wt% was prepared using deionized water. This polymer aqueous solution was applied to a PET film to a thickness of 800 μm using a bar coater to form a coating layer (cast layer). Next, after drying for 40 minutes at a temperature of 80 ° C. with a hot air dryer DKM400 (manufactured by YAMATO), the PET film was peeled off to prepare an impregnated coating film. The film thus obtained was heat treated at 160 ° C. for 30 minutes to cause physical crosslinking. Subsequently, the film was immersed in an aqueous electrolyte solution of 2 mol / L sodium sulfate for 24 hours. Concentrated sulfuric acid was added to the aqueous solution so that the pH was 1, and the film was immersed in a 1% by volume glutaraldehyde aqueous solution, followed by stirring with a stirrer at 25 ° C. for 24 hours for crosslinking. Here, as the glutaraldehyde aqueous solution, a product obtained by diluting “glutaraldehyde” (25% by volume) manufactured by Ishizu Pharmaceutical Co., Ltd. with water was used. After the crosslinking treatment, the film was immersed in deionized water, and the film was immersed until the film reached the swelling equilibrium while exchanging the deionized water several times in the middle, to obtain a cation exchange membrane CEM-14.

(Evaluation of ion exchange membrane)
The cation exchange membrane thus prepared was cut into a desired size to prepare a measurement sample. Using the obtained measurement sample, the number of bubbles and the membrane resistance were measured by the above-described methods according to the above methods. Regarding the burst strength, the sample was too brittle and could not be measured. The results are shown in Table 1.

<Example 11>
(Preparation of anion exchange membrane AEM-1)
A P-2 aqueous solution having a concentration of 12 wt% was prepared using deionized water. This polymer aqueous solution was applied to a PET film to a thickness of 800 μm using a bar coater to form a coating layer (cast layer). Next, a vinylon nonwoven fabric (basis weight: 36 g / cm ² , average fiber system of main fibers: 3 μm, binder fiber content: 5 mass%) is superimposed on the cast layer surface of the PET film on which the cast layer is formed. -2 An aqueous solution of vinylon was impregnated with an aqueous solution. Then, after drying for 40 minutes at a temperature of 80 ° C. with a hot air dryer DKM400 (manufactured by YAMATO), the PET film was peeled off to prepare an impregnated coating film. The film thus obtained was heat treated at 160 ° C. for 30 minutes to cause physical crosslinking. Subsequently, the film was immersed in an aqueous electrolyte solution of 2 mol / L sodium sulfate for 24 hours. Concentrated sulfuric acid was added to the aqueous solution so that the pH was 1, and the film was immersed in a 1% by volume glutaraldehyde aqueous solution, followed by stirring with a stirrer at 25 ° C. for 24 hours for crosslinking. Here, as the glutaraldehyde aqueous solution, a product obtained by diluting “glutaraldehyde” (25% by volume) manufactured by Ishizu Pharmaceutical Co., Ltd. with water was used. After the cross-linking treatment, the film was immersed in deionized water, and while deionized water was exchanged several times in the middle, the film was immersed until the film reached a swelling equilibrium to obtain an 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, the number of bubbles, burst strength, and membrane resistance were measured by the methods described above according to the above methods. The results are shown in Table 2.

<Examples 12 to 20>
(Preparation of anion exchange membrane AEM-2 to 10)
Except having changed the average fiber diameter of the main fiber of the used vinylon nonwoven fabric, and the content of binder fiber into the content shown in Table 1, it implemented by the method similar to Example 11, and obtained AEM-2-10. .

(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, the number of bubbles, burst strength, and membrane resistance were measured by the methods described above according to the above methods. The results are shown in Table 2.

<Comparative Examples 5-7>
(Preparation of anion exchange membranes AEM-11-13)
Except having changed into the content shown in Table 2 the average fiber diameter of the main fiber of the used vinylon nonwoven fabric, and content of binder fiber, it implemented by the method similar to Example 1, and obtained AEM-11-13. .

(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, the number of bubbles, burst strength, and membrane resistance were measured by the methods described above according to the above methods. The results are shown in Table 1.

<Comparative Example 8>
(Preparation of anion exchange membrane AEM-14)
A P-2 aqueous solution having a concentration of 12 wt% was prepared using deionized water. This polymer aqueous solution was applied to a PET film to a thickness of 800 μm using a bar coater to form a coating layer (cast layer). Next, after drying for 40 minutes at a temperature of 80 ° C. with a hot air dryer DKM400 (manufactured by YAMATO), the PET film was peeled off to prepare an impregnated coating film. The film thus obtained was heat treated at 160 ° C. for 30 minutes to cause physical crosslinking. Subsequently, the film was immersed in an aqueous electrolyte solution of 2 mol / L sodium sulfate for 24 hours. Concentrated sulfuric acid was added to the aqueous solution so that the pH was 1, and the film was immersed in a 1% by volume glutaraldehyde aqueous solution, followed by stirring with a stirrer at 25 ° C. for 24 hours for crosslinking. Here, as the glutaraldehyde aqueous solution, a product obtained by diluting “glutaraldehyde” (25% by volume) manufactured by Ishizu Pharmaceutical Co., Ltd. with water was used. After the crosslinking treatment, the film was immersed in deionized water, and the film was immersed until the film reached the swelling equilibrium while exchanging the deionized water several times in the middle to obtain an anion exchange membrane AEM-14.

(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, the number of bubbles and the membrane resistance were measured by the above-described methods according to the above methods. Regarding the burst strength, the sample was too brittle and could not be measured. The results are shown in Table 2.

  As shown in Table 1, a cation exchange membrane using a wet nonwoven fabric of vinylon short fibers having a fiber diameter of 3 to 40 μm and a binder fiber content of 2 to 9% by mass is generated in the membrane. The number of bubble defects was small, the film strength was high, and the film resistance was low (Examples 1 to 10). In particular, a cation exchange membrane using a wet nonwoven fabric of vinylon short fibers having a fiber diameter of the main fiber of 8 to 20 μm and a binder fiber content of 3 to 8% by mass has fewer bubble defects. The film strength was higher (Examples 2-4, 7, 8). On the other hand, when the average fiber diameter of the main fiber was more than 40 μm, the film strength was inferior (Comparative Example 1). Further, when the average fiber diameter of the main fibers was less than 3 μm, there were many bubble defects (Comparative Example 2). Furthermore, the cation exchange membrane using the wet nonwoven fabric of vinylon short fibers having a binder fiber content of more than 9% by mass had many bubble defects (Comparative Example 3). When the substrate was used, the film was brittle and the burst strength could not be measured (Comparative Example 4).

  As shown in Table 2, an anion exchange membrane using a wet nonwoven fabric of vinylon short fibers having a fiber diameter of 3 to 40 μm and a binder fiber content of 2 to 9% by mass occurs in the membrane. The number of bubble defects was small, the film strength was high, and the film resistance was low (Examples 11 to 20). In particular, an anion exchange membrane using a wet nonwoven fabric of vinylon short fibers having a fiber diameter of 8 to 20 μm and a binder fiber content of 3 to 8% by mass has fewer bubble defects, The film strength was higher (Examples 12-14, 17, 18). On the other hand, when the average fiber diameter of the main fibers was more than 40 μm, the film strength was inferior (Comparative Example 5). Further, when the average fiber diameter of the main fibers was less than 3 μm, there were many bubble defects (Comparative Example 6). Furthermore, the ion exchange membrane using the wet nonwoven fabric of vinylon short fiber whose binder fiber content is more than 9% by mass had many bubble defects (Comparative Example 7). When the substrate was used, the film was brittle and the burst strength could not be measured (Comparative Example 8).

K: ion exchange membrane (effective area 1.0 cm2)
L: Platinum electrode M: NaCl aqueous solution N: Water bath O: LCR meter

Claims (5)

Ion exchange containing a wet non-woven fabric of vinylon short fibers and an anionic vinyl alcohol block copolymer represented by the following general formula (1) or a cationic vinyl alcohol block copolymer represented by the following general formula (2) A membrane,
The wet nonwoven fabric is provided with an impregnation layer impregnated with the ionic copolymer at least partially from one surface in the thickness direction,
An ion exchange membrane characterized in that an average fiber diameter of main fibers of the wet nonwoven fabric is 3 to 40 µm, and a binder fiber content is 2 to 9% by mass.

[In the formula, 0.5000 ≦ o ¹ / (n ¹ + o ¹ ) ≦ 0.9999, 0.001 ≦ m ¹ / (m ¹ + n ¹ + o ¹ ) ≦ 0.50, and X ⁺ is H ⁺ Or a monovalent cation such as an alkali metal ion or a quaternary ammonium ion. ]

[In the formula, 0.5000 ≦ o ² / (n ² + o ² ) ≦ 0.9999, 0.001 ≦ m ² / (m ² + n ² + o ² ) ≦ 0.50, and Y ⁻ is Halogenated anions of group 5B elements such as PF ₆ ⁻ , SbF ₆ ⁻ , AsF ₆ ⁻ , halogenated anions of group 3B elements such as BF ₄ ⁻ , and halogens such as I ⁻ (I ₃ ⁻ ), Br ⁻ and Cl ^−. Anion, halogenate anion such as ClO ₄ ⁻ , metal halide anion such as AlCl ₄ ⁻ , FeCl ₄ ⁻ , SnCl ₅ ⁻ , nitrate anion represented by NO ₃ ⁻ , p-toluenesulfonate anion, naphthalenesulfonate anion, _{^{CH 3 SO 3 -, CF 3}} SO 3 - and the like organic sulfonic acid _{^{anion, CF 3 COO -, C 6}} H 5 COO - a carboxylic acid anion, OH ^- is a monovalent anion such as ]   2. The ion exchange membrane according to claim 1, wherein the main fiber of the wet nonwoven fabric has an average fiber diameter of 8 to 20 μm and a binder fiber content of 3 to 8 mass%.   The ion exchange membrane according to claim 1 or 2, wherein the ionic vinyl alcohol block copolymer is a crosslinked product that is crosslinked in a state where the ionic vinyl alcohol block copolymer is applied to the nonwoven fabric. Preparing an ionic vinyl alcohol block copolymer solution;
Applying an aqueous solution of the ionic vinyl alcohol block copolymer on the release sheet to form a coating layer of the ionic vinyl alcohol block copolymer;
A step of superposing a wet nonwoven fabric of vinylon short fibers on the coating layer and impregnating at least a part of the nonwoven fabric with an ionic vinyl alcohol block copolymer to form an impregnated body;
A step of drying the impregnated body in a state where the coating layer and the wet nonwoven fabric are overlaid; and a step of peeling the release sheet from the dried impregnated body;
The manufacturing method of the ion exchange membrane containing this.   5. The method for producing an ion exchange membrane according to claim 4, wherein the ionic vinyl alcohol block copolymer is subjected to a heat treatment after the peeling step.

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