JP2007014958A - Ion-exchange membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ion-exchange membrane for electrodialysis capable of suppressing organic pollution, and excellent in fundamental characteristics such as the membrane resistance and ion selectivity. <P>SOLUTION: In the ion-exchange film, an ion-exchange resin is filled in pores 2 of a microporous membrane 1 with micro-pores 2 being penetrated therein. On the surface of the membrane, the diameter of the micro-pores 2 is ≤ 5 μm, the area occupied by the micro-pores 2 is 3-60% of the entire surface, and the thickness of the membrane is 15-120 μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ion exchange membrane using a microporous membrane as a base material, and more particularly to an ion exchange membrane for electrodialysis having a small thickness.

  In general, in the process of synthesizing organic substances in fields such as foods, pharmaceuticals, and agricultural chemicals, salts and the like are often produced as by-products. In order to separate salts contained in such organic substances, when desalting the liquid to be treated by ion exchange membrane electrodialysis, organic contaminants in the liquid to be treated, particularly macromolecules having a charge (hereinafter referred to as giant organic ions). )) Adheres to the ion exchange membrane and degrades the performance of the membrane, so-called organic contamination of the membrane occurs.

  Conventionally, as ion exchange membranes that suppress organic contamination, ion exchange membranes that prevent the entry of giant organic ions into the membrane at the membrane surface layer, and ion exchanges that allow giant organic ions to easily permeate the membrane Membranes have been proposed.

  The ion exchange membrane that prevents the invasion of the giant organic ions into the membrane is a membrane 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 this ion exchange membrane becomes more remarkable as the membrane structure is denser and the molecular weight of the giant organic ions is larger. As a representative example of the above-mentioned ion exchange membrane, an anion exchange membrane in which sulfonic acid groups having opposite charges are introduced into the surface layer portion of a resin membrane having an anion exchange group to suppress the penetration of organic anions into the membrane (patents) Reference 1).

On the other hand, the method of facilitating the permeation of giant organic ions is easily achieved by loosening the membrane structure.
Japanese Patent Publication No.51-40556

  However, the ion exchange membrane that prevents the invasion of the giant organic ions into the membrane can exhibit a certain degree of organic contamination resistance, but the formation of an oppositely charged layer provided on the surface layer portion of the resin membrane. As a result, the film resistance is remarkably increased.

  In addition, the method of facilitating the permeation of giant organic ions inevitably has a problem in that the ion selectivity is inevitably lowered, and as a result, the efficiency in electrodialysis or the like is lowered.

  Accordingly, an object of the present invention is to provide an ion exchange membrane for electrodialysis that suppresses organic contamination and is excellent in basic properties such as membrane resistance and ion selectivity.

  The inventors of the present invention have made extensive studies to achieve the above object. As a result, a thin ion exchange membrane with a microporous membrane filled with an ion exchange resin exhibits excellent organic contamination resistance without degrading basic properties such as membrane resistance and ion selectivity. It was found useful as an ion exchange membrane for electrodialysis, and the present invention was completed.

  According to the present invention, an ion exchange membrane is formed by filling an ion exchange resin into the pores of a microporous membrane through which fine pores pass, and the pore diameter of the micropores is on the membrane surface. There is provided an ion exchange membrane for electrodialysis characterized in that it is 5 μm or less and the area occupied by micropores is 3 to 60% of the total area and has a thickness of 15 to 120 μm.

In the ion exchange membrane for electrodialysis of the present invention,
(1) The ion exchange resin is an anion exchange resin,
(2) The microporous membrane is made of a stretched polyolefin film,
Is preferred.

  The ion exchange membrane for electrodialysis of the present invention has a high resistance to organic contamination and a relatively thin film thickness. Therefore, the membrane resistance is small, and electrodialysis can be performed efficiently and stably over a long period of time. In particular, it is known that organic contamination is remarkable when an anion exchange membrane is used. Therefore, the ion exchange membrane of the present invention is particularly preferably an anion exchange membrane.

FIG. 1 is a sectional view conceptually showing a typical embodiment of the ion exchange membrane of the present invention.
FIG. 2 is a view showing a state where the ion exchange membrane of the present invention is further subjected to a predetermined treatment to expose the ion exchange resin at a position depressed from the surface of the microporous membrane.

  In the ion exchange membrane of the present invention, as shown in FIG. 1, the ion exchange resin 3 is filled in fine pores 2 penetrating the microporous membrane 1. Exists so as to cover the entire surface of the microporous membrane 1. In general, in an ion exchange membrane in which the ion exchange resin is exposed on the membrane surface as described above, there is a strong interaction due to electrostatic attraction between the ion exchange group and a giant organic ion having an opposite charge. It occurs, and the organic surface is easily adsorbed on the membrane surface. As a result, so-called organic contamination occurs and the membrane resistance rapidly increases. In the present invention, the pores formed in the membrane 1 are fine. In addition, since the area occupied by the micropores is less than a certain ratio, the invasion of giant organic ions into the film is effectively suppressed, and as shown in the examples described later, high organic contamination resistance is achieved. Show.

  In general, the microporous membrane 1 has many fine pores 2 only on the surface layer. In this case, the space portion of the micropores 2 in the surface layer portion of the microporous membrane 1 is usually The space is narrower than the internal gap. And in the case of the conventional ion exchange resin filled with the ion exchange resin, the increase in the membrane resistance in the space portion due to the invasion of giant organic ions is remarkable, but the ion exchange membrane of the present invention has such a portion. Since there is little ion exchange resin present in the membrane, it is estimated that the rapid increase in the membrane resistance can also be prevented.

  Further, in the ion exchange membrane of the present invention, as shown in FIG. 2, at least one surface of the microporous membrane 1 is filled with the micropores 2 of the microporous membrane 1. It is also possible to treat the resin 3 so that it is exposed at a position recessed from the surface 4 of the microporous membrane, and the organic contamination resistance can be further improved by such treatment.

  Although the expression mechanism by the above treatment is not clear, the space portion of the micropores 2 (portion where the ion exchange resin 3 does not exist) between the ion exchange resin 3 and the microporous membrane surface 1 is huge. It has the effect of suppressing the penetration of organic ions into the membrane, and the interaction between the ion exchange groups and the giant organic ions is weakened, making the giant organic ions more difficult to adsorb on the membrane surface and further improving the organic contamination resistance. Estimated.

  Further, the ion exchange membrane of the present invention having the characteristic structure as shown in FIG. 1 (or FIG. 2) needs to be provided with an oppositely charged layer on the surface of the ion exchange membrane in order to exhibit organic contamination resistance. As a result, the ion exchange membrane has an extremely low resistance compared to the ion exchange membranes currently on the market.

  In particular, in the ion exchange membrane having the structure shown in FIG. 2, the space portion of the micropore 2 does not work as a migration inhibition layer for small ions such as salts and has low resistance. Therefore, the membrane resistance is low even with respect to an ion exchange membrane using a conventional porous membrane as a base material in which an ion exchange resin is present in the portion.

  Furthermore, since the ion exchange membrane of the present invention prevents organic contamination by preventing the invasion of giant organic ions, there is no need to loosen the above-mentioned ion exchange resin part, and as a result, good ion selectivity. Indicates.

  As described above, the ion exchange membrane of the present invention exhibits ideal characteristics with low membrane resistance and excellent ion selectivity.

  In the ion exchange membrane of the present invention, the pore diameter (maximum pore diameter) of the micropores 2 existing on the surface is 5 μm or less, particularly 1 μm or less on the surface of the membrane 1 to ensure the above-mentioned organic contamination resistance. Needed above. Moreover, the average pore diameter of the micropores 2 in the surface portion of the membrane 1 is preferably 0.005 to 4 μm, particularly preferably 0.01 to 0.8 μm. That is, depending on the type of organic pollutant to be used, when the maximum diameter of the micropores existing on the surface of the ion exchange membrane is larger than 5 μm, and further when the average pore diameter of the micropores exceeds 4 μm, the organic contamination Substances easily penetrate into the ion exchange resin, and the organic contamination resistance is reduced. On the other hand, when the average pore diameter of the micropores 2 is smaller than 0.005 μm, the membrane resistance increases, which is not preferable.

  Further, the area occupation ratio of the micropores 2 on the surface of the ion exchange membrane is 3 to 60%, particularly 20 to 50%. That is, when the area occupancy exceeds 60%, the mechanical strength of the film tends to decrease. Conversely, when the area occupancy is less than 3%, the film resistance increases.

  The area occupancy ratio of the fine holes is a value measured for holes having a hole diameter of 0.003 μm or more.

  Furthermore, the shape of the micropore 2 of the membrane 1 is not particularly limited, and any shape can be adopted. Usually, the shape is determined by a method for producing a microporous membrane as a base material, and takes a circular shape, an elliptical shape, a square shape, a rhombus shape, or any other irregular shape.

  In the present invention, the diameters of the fine holes other than circular are shown as equivalent circle diameters.

  In the present invention, the depth A of depression from the microporous membrane surface 4 to the exposed surface of the ion exchange resin 3 is not particularly limited in the ion exchange membrane having a structure shown in FIG. However, in order to impart effective organic contamination resistance and low membrane resistance to the ion exchange membrane, the depression depth is 0.01 μm to 10 μm, particularly 0. It is preferably in the range of 03 μm to 5 μm. That is, when the depression depth A is shallower than 0.01 μm, the effect of suppressing the adsorption of organic contaminants is reduced, and it is difficult to further improve the organic contamination resistance. Further, when the depression depth A is deeper than 10 μm, the anti-contamination effect reaches its peak. In addition, the packed bed of the ion exchange resin 3 may become thin as a result, resulting in a decrease in ion selectivity.

The membrane resistance of the ion exchange membrane of the present invention is a value obtained by converting the membrane resistance measured at 25 ° C. in 3 mol / l sulfuric acid at 25 ° C. per 10 μm thickness, and is 0.01 to 0.4 Ω · cm. A range of ² is preferable.

  The membrane resistance of the ion exchange membrane is somewhat different depending on the type of ion exchange resin filled in the microporous membrane as a base material, but mainly the porosity of the microporous membrane described later, the pore diameter of the micropores, and the micropores Therefore, the film resistance can be adjusted to an arbitrary film resistance by appropriately adjusting these conditions.

  In addition, the thickness of the ion exchange membrane of the present invention should be in the range of 15 to 120 μm from the viewpoint of reducing the membrane resistance in the total thickness and imparting the necessary mechanical strength. It can be executed efficiently and stably over a long period of time.

  When the ion exchange membrane of the present invention is used as a structure as shown in FIG. 2, the surface 4 of the microporous membrane 1 excluding the micropores 2 may be substantially free of ion exchange resin. preferable. That is, when an ion exchange resin is present on the surface 4 of the microporous membrane, the giant organic ions adsorbed and deposited on the ion exchange resin 3 on the surface protrude from the peripheral portion of the depressed portion toward the inside, and as a result, the membrane resistance is reduced. There is a risk that the effect of depression will be reduced.

  As described above, when the ion exchange resin 3 is not present on the microporous membrane surface 4, the thickness of the ion exchange membrane is substantially the thickness of the microporous membrane 1.

  As the microporous membrane 1 in the ion exchange membrane of the present invention, generally used is one made of a thermoplastic resin and having the micropores 2 communicating with the front and back surfaces in the aforementioned pore diameter and area ratio.

  As the thermoplastic resin, those having substantially no ion exchange group are suitable. For example, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-olefin. Polymers and other vinyl chloride resins; fluorine systems such as polytetrafluoroethylene, polytrifluoroethylene, polychlorotrifluoroethylene, poly (tetrafluoroethylene-hexafluoropropylene), poly (tetrafluoroethylene-perfluoroalkyl ether) Resin; What consists of polyamide resin, such as nylon 6 and nylon 66, is used without a restriction | limiting. It is particularly preferable to use a polyolefin resin because of its excellent mechanical strength, chemical stability, and chemical resistance. Examples of the polyolefin resin include α-olefins such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 4-methyl-1-pentene, and 5-methyl-1-heptene. A homopolymer or a copolymer is mentioned. Among these, in the present invention, polyethylene and polypropylene are preferable, and polyethylene is particularly preferable.

  The pore diameter of the micropores 2 existing on the surface of the ion exchange membrane, the area occupied by the micropores 2 and the like are almost determined by the properties of the microporous membrane 1 as a base material, and the properties are the pore diameters of the micropores 2. The area occupancy of the micropores 2 should be selected so as to be within the above-described range.

  The characteristics on the surface of the microporous membrane are mainly reflected in the air permeability. The air permeability is 20 to 1500 seconds / 100 ml, and preferably 100 to 1000 seconds / 100 ml.

  The microporous membrane 1 is preferably used with a porosity of 20 to 90%, preferably 30 to 70%, in order to achieve the above-mentioned suitable membrane resistance. That is, when the porosity is less than 20%, it is not easy to sufficiently fill the pores of the membrane with ion exchange resin, and furthermore, the amount of ion exchange resin per unit volume is reduced and sufficient ion exchange performance is exhibited. As a result, the film resistance increases. On the other hand, if it exceeds 90%, the amount of ion exchange resin per unit volume increases, and when used practically, the ion exchange resin swells and shrinks, so that dimensional stability is lost and mechanical strength is also lowered. The porosity is obtained by excluding the closed cells, and the microporous film obtained by the production method based on the stretching method described later has almost no closed cells.

  In the present invention, the microporous membrane 1 described above is manufactured by a so-called stretching method. Specifically, an additive that can be removed after stretching is dispersed in a thermoplastic resin, preferably a thermoplastic resin having crystallinity, and this is uniaxially or biaxially below the melting point of the thermoplastic resin. It is manufactured by removing the additive after stretching while heating.

  Examples of the additive include known additives such as paraffin and inorganic powder. Removal of the additive after stretching is performed by extraction with a solvent, dissolution with an acid, or the like.

  The microporous membrane 1 produced by such a stretching method can easily form a skin layer having a thickness of about 0.01 to 2 μm, generally 0.3 to 1.5 μm on the surface layer. As shown, a reasonably large porosity is achieved by the relatively large cavity existing inside, while having fine pores on the surface.

  Therefore, by using the microporous membrane 1 as a base material of the ion exchange membrane of the present invention, the effect of preventing contamination due to micropores on the surface is achieved. Further, by adjusting the depression depth of the exposed surface of the filled ion exchange resin so as to be in the vicinity of the thickness of the skin layer, the resistance of the micropores in the skin layer is eliminated, and the ion exchange is further reduced in resistance. It is possible to realize a membrane.

  In the present invention, the ion exchange resin 3 filled in the voids of the microporous membrane 1 is known per se, and is made of, for example, a hydrocarbon or fluorine material, and has a cation exchange function and / or It is a resin having anion exchange ability.

  Examples of the hydrocarbon material include styrene resins and acrylic resins, and examples of the fluorine material include perfluorocarbon resins.

  The ion exchange ability is expressed by the presence of an ion exchange group, and the ion exchange group is not particularly limited as long as it is a functional group that can be negatively or positively charged in an aqueous solution.

  Specifically, in the case of a cation exchange group, a sulfonic acid group, a carboxylic acid group, a phosphonic acid group and the like can be mentioned, and in general, a sulfonic acid group which is a strongly acidic group is preferably used.

  Moreover, in the case of an anion exchange group, a quaternary amino group, a quaternary ammonium group, a pyridyl group, an imidazole group, a quaternary pyridinium group, etc. are mentioned, and generally a quaternary which is a strongly basic group. An ammonium group or a quaternary pyridinium group is preferably used.

  Although the manufacturing method of the ion exchange membrane of this invention is not restrict | limited in particular, If the typical manufacturing method is illustrated, the following method will be mentioned.

  That is, after impregnating the monomer composition containing a monomer having an ion exchange group, a crosslinkable monomer, and a polymerization initiator in the voids of the microporous membrane 1, the monomer composition By polymerizing the product to produce an ion exchange resin, the ion exchange membrane of the present invention having the structure shown in FIG. 1 can be obtained. When a functional group capable of introducing an ion exchange group is used as the monomer, an ion exchange resin precursor is produced by polymerization in the same manner as described above, and the ion exchange group is introduced into the precursor. By doing so, an ion exchange membrane having the structure of FIG. 1 can be obtained.

  Moreover, after producing | generating an ion exchange resin or an ion exchange resin precursor as mentioned above, the ion exchange resin 3 or the ion exchange resin precursor which exists in the microporous 2 vicinity in the micropore 2 vicinity is further removed. Thus, an ion exchange membrane having the structure shown in FIG. 2 can be obtained.

  Since the monomer composition has a low molecular weight, it can be easily filled in the voids of the microporous membrane, and the ion exchange resin, which is a cured product thereof, is generated at a high density without any gaps in the voids.

  As the monomer having a functional group into which an ion exchange group can be introduced or the monomer having an ion exchange group, hydrocarbon monomers used in the production of conventionally known ion exchange resins are particularly limited. Used without. Specifically, examples of the monomer having a functional group into which a cation exchange group can be introduced include styrene, vinyl toluene, vinyl xylene, α-methyl styrene, vinyl naphthalene, and α-halogenated styrenes. Examples of the monomer having a cation exchange group include sulfonic acid monomers such as α-halogenated vinyl sulfonic acid, styrene sulfonic acid and vinyl sulfonic acid, and carboxylic acids such as methacrylic acid, acrylic acid and maleic anhydride. Acid monomers, phosphonic acid monomers such as vinyl phosphoric acid, salts and esters thereof, and the like are used.

  On the other hand, examples of the monomer having a functional group capable of introducing an anion exchange group include styrene, vinyl toluene, chloromethyl styrene, vinyl pyridine, vinyl imidazole, α-methyl styrene, vinyl naphthalene, and the like. Examples of the monomer having an anion exchange group include amine monomers such as vinylbenzyltrimethylamine and vinylbenzyltriethylamine, nitrogen-containing heterocyclic monomers such as vinylpyridine and vinylimidazole, salts and esters thereof. Etc. are used.

  In addition, the crosslinkable monomer is not particularly limited. A divinyl compound is used.

  In the present invention, in addition to the above-described monomer having a functional group into which an ion exchange group can be introduced, a monomer having an ion exchange group or a crosslinkable monomer, the monomer can be combined with these monomers as necessary. Other polymerizable monomers may be added. Examples of such other monomers include styrene, acrylonitrile, methylstyrene, acrolein, methyl vinyl ketone, and vinyl biphenyl.

  Further, conventionally known polymerization initiators are used without any particular limitation. Specific examples of such polymerization initiators include octanoyl peroxide, lauroyl peroxide, t-butylperoxy-2-ethylhexanoate, benzoyl peroxide, t-butylperoxyisobutyrate, t-butylperoxy Organic peroxides such as laurate, t-hexyl peroxybenzoate, and di-t-butyl peroxide are used.

  In the present invention, the mixing ratio of each component constituting the monomer composition is generally based on 100 parts by weight of the monomer having a functional group into which an ion exchange group can be introduced or the monomer having an ion exchange group. In addition, 0.1 to 50 parts by weight of a crosslinkable monomer, preferably 1 to 40 parts by weight, and 0 to 100 parts by weight of another monomer copolymerizable with these monomers are used. Is preferred. Further, the polymerization initiator is 0.1 to 20 parts by weight, preferably 0.5 to 100 parts by weight of the monomer having a functional group into which an ion exchange group can be introduced or the monomer having an ion exchange group. It is preferable to add 10 to 10 parts by weight.

  The method for filling the monomer composition in the voids of the microporous membrane 1 is not particularly limited, but in general, the method for immersing the microporous membrane in the monomer composition or the microporous composition is used. A method of applying and spraying on the conductive film is employed. At this time, if it is difficult to sufficiently fill the monomer composition into the voids of the microporous membrane due to properties such as viscosity, the microporous membrane is brought into contact with the monomer composition under reduced pressure. It is also possible to take a filling method.

  The method of polymerizing the monomer composition after filling the monomer composition in the microporous membrane as described above is generally preferably a method of raising the temperature from room temperature under pressure by sandwiching it between films of polyester or the like. Such polymerization conditions depend on the type of polymerization initiator involved, the composition of the monomer composition, and the like, and may be appropriately selected and determined from known conditions.

  The membrane-like material obtained by polymerization as described above may be converted into a known, for example, cation exchange membrane such as sulfonated, chlorosulfonated, phosphoniumated, hydrolyzed, or the like if necessary. If it is an ion exchange membrane, a desired ion exchange group can be introduced by a treatment such as amination or alkylation to obtain the ion exchange membrane of the present invention.

  Moreover, examples of the removal of the ion exchange resin existing near the surface of the microporous membrane in the micropores or the removal of the ion exchange resin precursor (that is, the depression process) include a corona discharge process and a plasma etching process.

  In the case of the plasma etching process, for example, the ion exchange resin can be removed by etching to a desired depth by performing a plasma process in an atmosphere of oxygen or an oxygen / argon mixture.

  In addition, by contacting the membrane surface with an oxidizing agent such as hydrogen peroxide, ozone, concentrated nitric acid, concentrated sulfuric acid, potassium dichromate, chlorine, iodine, sodium hypochlorite, etc. Can remove the ion exchange resin. In particular, the method using an oxidizing agent is simple and is preferably used.

  As a suitable method for easily obtaining the ion exchange membrane of the present invention, the monomer composition is obtained by further adding one or both of a solvent and a polymer having an average molecular weight of 500 to 10,000. An example is a method of filling the obtained composition into the voids of the microporous membrane, then curing the composition, and then introducing an ion exchange group as necessary.

  According to this manufacturing method, the ion exchange resin near the surface in the micropore 2 can be easily removed in the ion exchange group introduction step without employing a special removing means. In addition, when an ion exchange group introduction step is not necessary, the ion exchange resin in the vicinity of the surface of the microporous membrane in the micropores can be easily removed by contacting with a solvent, and ions can be introduced only into the micropore portions. An exchange resin 3 can be present.

  In such a production method, the solvent causes so-called microphase separation with the progress of the polymerization reaction of the monomer composition, so that the ion exchange resin near the surface of the microporous membrane in the micropores corresponding to the outermost surface portion is extremely It becomes a porous porous body. And since the mechanical strength resulting from this porous structure is low, it is easy to drop off by an ion exchange group introduction process or a simple solvent treatment, and this part can be easily removed.

  On the other hand, the polymer having an average molecular weight of 500 to 10000 is pushed out to the surface in the process of polymerization of the monomer because the molecules are large in the filling process of the monomer composition into the micropores 2 of the microporous film 1. It is unevenly distributed in the vicinity of the surface of the microporous membrane in the micropores, which corresponds to the outermost surface portion. These polymers can be extracted and removed by a solvent used in an ion exchange group introduction step and the like, and as a result, the ion exchange resin 3 existing in a portion other than the micropores 2 can be easily removed. Become.

  These actions become more effective when a solvent and a polymer having an average molecular weight of 500 to 10,000 are used in combination. That is, in order to completely remove the ion exchange resin other than the micropores 2 and the vicinity of the surface of the micropores 2 using only the solvent, it is necessary to add a large amount of solvent, and as a result, remain in the membrane. The ion exchange resin 3 to be made becomes more porous, and the ion selectivity is lowered. In addition, when only a polymer having an average molecular weight of 500 to 10000 is used, extraction and removal of the polymer is likely to be incomplete, and as a result, further improvement in the effect of preventing organic contamination cannot be expressed sufficiently.

  Therefore, when a solvent and a polymer having an average molecular weight of 500 to 10000 are used in combination, the polymer that is unevenly distributed in the vicinity of the membrane surface is easily extracted from the ion exchange resin that has become porous due to the removal of the solvent. Since the further improvement of the prevention effect is sufficiently exhibited and the amount of solvent added can be reduced, the ion exchange resin remaining inside the membrane is not excessively porous, and the decrease in ion selectivity can also be prevented.

  In such a production method, the solvent added to the monomer composition can be used without any limitation as long as the solvent does not participate in the polymerization reaction when the monomer composition is polymerized. is there. Specifically, alcohols such as methanol, ethanol, i-butanol and 2-ethoxyethanol, aliphatic hydrocarbons such as hexane, cyclohexane, heptane and i-octane, fatty acids such as octanoic acid, dimethyloctylamine and the like Amines, aromatic hydrocarbons such as toluene, xylene and naphthalene, ketones such as cyclohexanone and methyl ethyl ketone, ethers such as dibenzyl ether and diethylene glycol dimethyl ether, and halogenated hydrocarbons such as methylene chloride, chloroform and ethylene bromide Alcohols of aromatic and aliphatic acids such as dibutyl phthalate, dioctyl phthalate, dimethyl isophthalate, dibutyl adipate, triethyl citrate, acetyl tributyl citrate and dibutyl sebacate Ethers and alkyl phosphate and the like. These are appropriately selected in consideration of solubility with the monomer composition, polymerization temperature, etc., but i-butanol, 2-ethoxyethanol, dibenzyl ether, dioctyl phthalate, acetyl tributyl citrate and the like are particularly preferable. It is. These several types can also be used in combination.

  Next, specific examples of the polymer added to the monomer composition include styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, polybutadiene, polyethylene glycol, and polypropylene glycol.

These are also appropriately selected in consideration of solubility with the monomer composition, etc., but polybutadiene and polypropylene glycol are particularly preferable.
These polymers have an average molecular weight of 500 to 10,000, preferably 500 to 6,000. That is, when the average molecular weight is 500 or less, it is difficult to be unevenly distributed in the vicinity of the membrane surface, and the organic contamination prevention effect and ion selectivity become insufficient. On the other hand, when the average molecular weight is 10,000 or more, extraction removal becomes difficult, and further improvement of the organic contamination prevention effect becomes insufficient, which is not preferable. The mixing ratio of the above-mentioned solvent and polymer having an average molecular weight of 500 to 10,000 to the monomer composition is such that a monomer having a functional group capable of introducing an ion exchange group or an ion exchange group, a crosslinkable monomer, and polymerization initiation. A solvent is 15-150 weight part with respect to a total of 100 weight part of an agent, Preferably it is 20-120 weight part.
That is, when the amount of the solvent is less than 15 parts by weight, the effect of preventing organic contamination is not sufficient, and when it exceeds 150 parts by weight, the ion selectivity is lowered.

  The polymer having an average molecular weight of 500 to 10,000 is 5 to 100 with respect to a total of 100 parts by weight of the monomer having a functional group capable of introducing an ion exchange group or an ion exchange group, a crosslinkable monomer, and a polymerization initiator. Part by weight, preferably 10 to 70 parts by weight.

  That is, when the blending amount of the polymer having an average molecular weight of 500 to 10000 is less than 5 parts by weight, the organic contamination prevention effect is not sufficient, and when it exceeds 100 parts by weight, the monomer composition is filled into the microporous film. Becomes unsatisfactory, and the ion selectivity is further lowered.

  The monomer composition to which the solvent and the polymer having an average molecular weight of 500 to 10,000 are added as described above is filled into the microporous membrane by the method described in the description of the production method, and then cured. In the obtained film-like material, ion exchange groups are subsequently introduced as necessary by the above-described ion exchange group introduction method.

  When the ion exchange resin near the membrane surface in the micropores is removed in the ion exchange group introduction step, the ion exchange membrane of the present invention can be obtained without the need for a further removal step, and the membrane surface When the removal of the nearby ion exchange resin is not sufficient, the ion exchange resin is removed by performing an extraction step according to the nature of the added solvent and the polymer having an average molecular weight of 500 to 10,000, and the ion exchange membrane of the present invention Can be obtained.

  Also in this production method, the ion exchange resin or the ion exchange resin precursor may be removed before or after the introduction of the ion exchange group.

  As understood from the above description, the ion exchange membrane of the present invention is filled with an ion exchange resin in a microporous membrane having micropores with a predetermined pore diameter and area occupancy, and has excellent resistance to resistance. While having organic contamination, it has low membrane resistance, good ion selectivity, etc., has a relatively thin film thickness, and is excellent as an ion exchange membrane for electrodialysis. Moreover, in the case where the ion exchange resin has a structure exposed at a position depressed from the surface of the microporous membrane, the organic contamination resistance is further improved and the membrane resistance is further lowered.

  The ion exchange membrane of the present invention is particularly useful as a diaphragm for electrodialysis in the synthesis process of foods, pharmaceuticals, agricultural chemicals and the like. Especially when the present invention is applied to an anion exchange membrane, it is compared with a cation exchange membrane. Thus, the disadvantage of the anion exchange membrane that organic contamination easily occurs can be effectively improved.

Hereinafter, examples will be given to describe the present invention in more detail, but the present invention is not limited to these examples.
In addition, the characteristic of the ion exchange membrane shown to an Example and a comparative example was measured with the following method.

1) Depression depth from the surface of the microporous membrane to the exposed surface of the ion exchange resin;
After observing the surface of the ion exchange membrane with an electron microscope (SEM) and confirming that there is no ion exchange resin layer covering the entire surface of the microporous membrane, the surface roughness of the ion exchange membrane was measured with a scanning laser microscope (Lasertec Corporation). Manufactured, 1Lm21 type). In the obtained roughness distribution chart, the height difference between the deepest portion adjacent to the peak portion was measured, and the average value of the height difference measured over a length of 30 μm was taken as the depression depth.

2) ion exchange capacity and moisture content;
The ion exchange membrane is immersed in 1 mol / L-HCl for 10 hours or more.
Thereafter, in the case of a cation exchange membrane, the hydrogen ion type is replaced with the sodium ion type with 1 mol / L-NaCl, and the liberated hydrogen ions are quantified with a potentiometric titrator (COMMITE-900, manufactured by Hiranuma Sangyo Co., Ltd.). (Amol). On the other hand, in the case of an anion exchange membrane, 1 mol / L-NaNO3 is substituted for the chloride ion type to the nitrate ion type, and the liberated chlorine ion is quantified with a potentiometric titrator (COMMITE-900, manufactured by Hiranuma Sangyo Co., Ltd.). (Amol).

  Next, the same ion exchange membrane is immersed in 1 mol / L-HCl for 4 hours or more, washed thoroughly with ion exchange water, and then the membrane is taken out. The moisture on the surface is wiped off with tissue paper or the like, and the weight (Wg) when wet is obtained. It was measured. Next, the membrane was placed in a vacuum dryer and dried at 60 ° C. for 5 hours. The membrane was taken out and the weight (Dg) at the time of drying was measured.

The ion exchange capacity and water content were calculated by the following equations.
Ion exchange capacity = A × 1000 / W [mmol / g-dry membrane]
Water content = 100 × (WD) / D [%]

3) measurement of membrane resistance;
An ion exchange membrane is sandwiched in a two-chamber cell having a platinum black electrode plate, 3 mol / L-H2SO4 solution is filled on both sides of the ion exchange membrane, and the resistance between the electrodes at 25 ° C. is measured by an AC bridge (frequency 1000 cycles / second). Measured and determined by the difference between the interelectrode resistance and the interelectrode resistance when no ion exchange membrane was installed. The membrane used for the above measurement was previously equilibrated in a 3 mol / L-H2SO4 solution.

4) Measurement of organic contamination resistance;
In the anion exchange membrane, after conditioning the obtained anion exchange membrane, the ion exchange membrane is sandwiched between two-chamber cells having silver and silver chloride electrodes, and 0.05 mol / L-NaCl solution is placed in the anode chamber. In the cathode chamber, a mixed solution of 1000 ppm sodium dodecylbenzenesulfonate and 0.05 mol / L-NaCl was added. The liquid in both chambers was stirred at 1500rpm rotational speed, was electrodialysis 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.

  For the cation exchange membrane, the organic contaminant was changed from sodium dodecylbenzenesulfonate to polyethyleneimine having a molecular weight of 2000 in the above method, and the organic contamination resistance was measured in the same manner.

5) Permeation rate of acid and alkali;
In the anion exchange membrane, a two-chamber cell made of acrylic resin separated by an anion exchange membrane is used, and one chamber (stock solution chamber) contains 1 mol / L-sulfuric acid at 25 ° C. and 0.5 mol / L-magnesium sulfate. The other solution (dialysis solution chamber) was charged with ion exchange water at 25 ° C.

  Next, both chambers were stirred with a stirrer, and the liquid in the dialysate chamber was withdrawn after a certain time, and the permeation amount of sulfuric acid was measured by potentiometric titration, and the permeation amount of magnesium sulfate was measured by an atomic absorption photometer.

In the cation exchange membrane, the liquid containing 1 mol / L-sulfuric acid and 0.5 mol / L-magnesium sulfate in the above method is changed to the liquid containing 3 mol / L-sodium hydroxide and 0.5 mol / L-aluminum hydroxide. The same operation was performed while changing the permeation amount of sodium hydroxide and aluminum hydroxide. The permeation rate of each substance was determined by the following equation.
U = A / (T · S · ΔC)
U: Permeation rate of acid or alkali [mol / Hr · m ² · (mol / L)]
A: Permeation amount of acid or alkali [mol]
T: Stirring time [Hr]
S: Effective membrane area [m ² ]
ΔC: Difference in logarithmic average concentration of acid or alkali in both chambers before and after stirring [mol / L]

<Example 1>
The following prescription:
90 parts by weight divinylbenzene; 10 parts by weight benzoyl peroxide; 5 parts by weight styrene oxide; 3 parts by weight of a monomer composition was prepared.

  400 g of this monomer composition was placed in a 500 ml glass container, and a commercially available microporous membrane (20 cm × 20 cm) made of polyethylene having a thickness of 25 μm and a weight average molecular weight of 100,000 was obtained by immersion. Then, the monomer composition was filled in the voids of the microporous membrane.

  The microporous membrane used had a maximum micropore diameter of 1 μm on the surface, an average pore diameter of 0.04 μm, a porosity of 45%, an area occupation ratio of micropores of 15%, and an air permeability of 415 seconds / 100 ml.

  Subsequently, the porous membrane was taken out from the monomer composition, and both sides of the porous membrane were coated using a 100 μm polyester film as a release material, and then heated and polymerized at 80 ° C. for 8 hours under nitrogen pressure of 0.4 MPa. . The obtained film was reacted for 5 hours at room temperature in an amination bath consisting of 10 parts of 30% trimethylamine aqueous solution, 5 parts of water and 5 parts of acetone to obtain a quaternary ammonium type anion exchange membrane.

As a result of SEM observation of this ion exchange membrane, the microporous structure peculiar to the microporous membrane was not observed on the membrane surface. Further, the ion exchange membrane was immersed in a 1 wt% potassium permanganate aqueous solution, and MnO ₄ ⁻ As a result of ion exchange in the mold and analysis of the Mn element on the film surface with SEM-EDS, the presence of Mn element on the film surface of the film ion-exchanged into the MnO ₄ ⁻ type was confirmed. It was confirmed that the resin was exposed on the film surface.

  The depth of depression, ion exchange capacity, water content, membrane resistance, organic contamination resistance, and permeation rate of sulfuric acid and magnesium sulfate of the obtained anion exchange membrane were measured. These results are shown in Table 1.

<Reference Example 1>
The anion exchange membrane obtained in Example 1 was immersed in a 1 wt% aqueous sodium hypochlorite solution at room temperature for 24 hours to remove the ion exchange resin on the membrane surface.
When the surface of the obtained ion exchange membrane was observed with an SEM, a microporous structure peculiar to the surface of the microporous membrane was observed. Further, the ion exchange membrane was immersed in a 1 wt% potassium permanganate aqueous solution and MnO ₄ ⁻ As a result of ion-exchanged into a mold and performing a definite analysis of Mn element on the film surface with SEM-EDS, the peak attributed to Mn was not observed, so that the ion-exchange resin on the film surface was removed. confirmed.
The characteristics of the anion exchange membrane thus treated were measured in the same manner as in Example 1. The results are shown in Table 1. From this result, it can be seen that the organic contamination resistance is further improved by removing the ion exchange resin existing on the surface (that is, the depression process).

<Example 2>
The following prescription:
Styrene; 90 parts by weight Divinylbenzene; 10 parts by weight Benzoyl peroxide; 5 parts by weight Tributyl acetylcitrate; 10 parts by weight A monomer composition was prepared.

  This monomer composition was made of polyethylene having a thickness of 30 μm and a weight average molecular weight of 250,000 in the same manner as in Example 1, and was filled in the voids of a commercially available microporous membrane (20 cm × 20 cm) obtained by the stretching method. did.

  The microporous membrane used had a maximum micropore diameter of 1 μm, an average pore size of 0.02 μm, a porosity of 37%, a micropore area occupancy of 17%, and an air permeability of 600 seconds / 100 ml.

  Subsequently, the porous membrane was taken out from the monomer composition, and both sides of the porous membrane were coated using a 100 μm polyester film as a release material, and then heated and polymerized at 80 ° C. for 8 hours under nitrogen pressure of 0.4 MPa. . The obtained membrane was immersed in a 1: 1 (weight ratio) mixture of 98% concentrated sulfuric acid and chlorosulfonic acid having a purity of 90% or more at 40 ° C. for 45 hours to obtain a sulfonic acid type cation exchange membrane. It was.

As a result of SEM observation of this ion exchange membrane, the microporous structure peculiar to the microporous membrane was not observed on the membrane surface. Further, the ion exchange was carried out to Fe ²⁺ type, and the Fe element on the membrane surface was observed by SEM-EDS. As a result of conducting the steady state analysis, it was confirmed that the ion exchange resin was exposed on the film surface because the presence of Fe element was confirmed on the film surface.

  The depth of depression, ion exchange capacity, water content, membrane resistance, resistance to organic contamination, and permeation rate of sodium hydroxide and aluminum hydroxide of the obtained cation exchange membrane were measured. These results are shown in Table 2.

<Reference Example 2>
The cation exchange membrane obtained in Example 2 was immersed in a 1 wt% FeCl ₂ aqueous solution at room temperature for 24 hours to form a Fe ²⁺ type, and then immersed in a 2 wt% H ₂ O ₂ aqueous solution at room temperature for 30 minutes. The ion exchange resin on the membrane surface was removed.

When the surface of the cation exchange membrane thus treated was observed with an SEM, a microporous structure peculiar to the surface of the microporous membrane was observed, and further, a regular analysis of Fe elements on the membrane surface was performed with SEM-EDS. As a result, no peak attributed to Fe was observed, confirming that the ion exchange resin on the film surface was removed.
The depth of depression, ion exchange capacity, water content, membrane resistance, resistance to organic contamination, and permeation rate of sodium hydroxide and aluminum hydroxide of the obtained cation exchange membrane were measured. These results are shown in Table 2. From this result, it can be seen that the organic contamination resistance is further improved by removing the ion exchange resin on the surface (that is, the depression process).

Sectional drawing which shows notionally the ion exchange resin of this invention. The figure which shows the state which performed the predetermined depression process about the ion exchange membrane of this invention, and exposed the ion exchange resin in the position depressed from the microporous membrane surface.

Explanation of symbols

1: Microporous membrane 2: Micropores 3: Ion exchange resin 4: Microporous membrane surface A: Depression depth

Claims (3)

  An ion exchange membrane comprising a microporous membrane having fine pores penetrating therein and filled with an ion exchange resin, wherein the pore diameter of the micropores is 5 μm or less on the membrane surface, and An ion exchange membrane for electrodialysis characterized by having an area occupied by micropores of 3 to 60% of the total area and a thickness of 15 to 120 μm.   The ion exchange membrane for electrodialysis according to claim 1, wherein the ion exchange resin is an anion exchange resin.   The ion exchange membrane for electrodialysis according to claim 1, wherein the microporous membrane is made of a stretched polyolefin film.

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