JP4355557B2 - Method for producing anion exchange membrane - Google Patents

Description

  The present invention relates to a method for producing an ion exchange membrane. More specifically, the present invention relates to a method for producing an anion exchange membrane having good film forming properties and high production efficiency.

  As a method for producing an anion exchange membrane, a paste formed by adding a monomer having a functional group suitable for introduction of an anion exchange group, a crosslinking agent, and a thickener is used as a base membrane made of a woven fabric of polyvinyl chloride or the like. A paste method in which an anion exchange group is introduced after coating and polymerization is known (see Patent Document 1). In recent years, in order to simplify the film forming process, there are many examples of using haloalkylstyrene as a monomer having a functional group suitable for introduction of an anion exchange group. However, when the haloalkylstyrene is polymerized, hydrogen halide is generated, and due to the hydrogen halide, there is a problem of poor appearance such that white spots are generated on the surface of the film after polymerization.

  The generation mechanism of the white spots is considered as follows. That is, in the paste method, in order to prevent the substrates to which the polymer is attached from contacting each other, the polyester film and the like are polymerized by sandwiching the substrate on which the paste is applied. During this period, hydrogen halide accumulates, the surface of the polymer is depressed, and hydrogen halide is added to the double bond of the monomer.

  As a method for preventing the formation of white (whited-colored) spots, a method is proposed in which a low-molecular-weight or medium-molecular-weight epoxy compound is mixed into the paste, and the generated hydrogen halide is captured and removed. (See Patent Document 2). In this method, the formation of the white spots is suppressed based on the principle that the epoxy group contained in the epoxy compound reacts with the hydrogen halide to supplement the hydrogen halide.

JP 40-28951 A JP-A-56-36507

  However, low molecular weight epoxy compounds such as styrene oxide have a problem that they are mutagenic (carcinogenic) and difficult to use. In addition, medium molecular weight epoxy compounds such as epoxy soybean oil have poor compatibility with polymer components added to the paste as a thickener, and a uniform paste with excellent operability (applicability) when applied to a substrate is prepared. There is a problem that you can not. Therefore, an object of the present invention is to provide a method for preventing the formation of the vitiligo without using a low molecular weight or medium molecular weight epoxy compound.

As a result of diligent research to solve the above-mentioned problems, the present inventors have used a thermoplastic resin having an epoxy group as a thickener, so that an appropriate thickening can be achieved in the paste without using any other thickener. It has been found that a uniform paste without phase separation can be prepared and hydrogen halide generated during polymerization can be removed to prevent the occurrence of white spots.
That is, the present invention relates to a haloalkyl styrene, a monomer copolymerizable with haloalkyl styrene, a polymerization initiator and an epoxidized diene block copolymer having an epoxy equivalent of 100 to 5,000 and a weight average molecular weight of 5,000 to 200,000. A method for producing an anion exchange membrane, wherein an anion exchange group is introduced into an obtained polymer using an amine compound after polymerizing the composition comprising a base material on the base membrane It is.

Further, the present invention also relates to a haloalkylstyrene copolymer into which an anion exchange group is introduced, an epoxidized diene block copolymer, and / or an epoxidized diene block copolymer reacted with a hydrogen halide or an amine compound. It is an anion exchange membrane characterized by coat | covering a base film with the composite resin containing this. The anion exchange membrane of the present invention is an anion exchange membrane produced by the production method of the present invention, has membrane characteristics equivalent to those of a conventional haloalkylstyrene-based anion exchange membrane, and has no white spots on the surface. It has the characteristics.

  In the production method of the present invention, an anion exchange membrane free from vitiligo can be produced without using a low molecular weight epoxy compound which is difficult to use such as styrene oxide. Further, in the production method of the present invention, the thermoplastic resin having an epoxy group to be used also functions as a thickener, and it is not necessary to use other thickeners. Therefore, when a medium molecular weight epoxy compound is used. Thus, the applicability | paintability of a paste is also favorable, without impairing the property of a paste. For this reason, an anion exchange membrane free from vitiligo can be produced with excellent workability. Furthermore, when an epoxy compound as described in Patent Document 2 is used, the compound is eluted in the reaction solution in the reaction step after polymerization (anion exchange group introduction step). In the present invention, the thermoplastic resin having an epoxy group is physically fixed in the membrane, and another anion exchange group can be introduced using the remaining epoxy group.

  In the production method of the present invention, a composition comprising a haloalkyl styrene, a monomer copolymerizable with haloalkyl styrene, a polymerization initiator, and a thermoplastic resin having an epoxy group is first adhered to the substrate film.

  Here, the composition corresponds to a paste used in the conventional paste method using haloalkylstyrene (hereinafter also referred to as a conventional paste), and uses a thermoplastic resin having an epoxy group as a thickener. However, there is no particular difference from the conventional paste, and as the haloalkyl styrene, the monomer copolymerizable with haloalkyl styrene and the polymerization initiator, those conventionally used in the paste can be used without particular limitation.

  For example, as haloalkyl styrene, chloromethyl styrene, α-chloromethyl styrene, bromomethyl styrene, dichloromethyl styrene, chloroethyl styrene and the like, or a mixture thereof can be preferably used.

  Monomers that can be copolymerized with haloalkylstyrene include styrene, vinyltoluene, chlorostyrene, vinylnaphthalene, divinylbenzene, vinylethylbenzene, acrylic acid, methacrylic acid, acrylic acid chloride, methyl acrylate, ethyl acrylate, acrylic acid. Butyl, ethyl acrylate, propyl methacrylate, dodecyl methacrylate, allyl chloride, vinyl chloride, acrylamide, methyl vinyl ketone, 4-vinyl pyridine, vinyl sulfonyl chloride, styrene sulfonyl chloride and the like can be suitably used. These monomers may be used alone or as a mixture of a plurality of different types.

  Moreover, as a polymerization initiator, a well-known thing can be used without being specifically limited. For example, benzoyl peroxide, di-t-butyl peroxide lauroyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide, azobisisobutyronitrile, hydrogen peroxide, ammonium persulfide and the like can be suitably used. You may use these individually or in mixture of 2 or more types.

  The greatest feature of the present invention is that a thermoplastic resin having an epoxy group is blended in the paste. The thermoplastic resin functions as a scavenger for capturing hydrogen halide generated from haloalkylstyrene during the polymerization process, and also functions as a thickener for adjusting the viscosity of the paste. For this reason, it is not necessary to use a thickener conventionally used in the paste, that is, a thickener such as rubber or vinyl chloride powder, and the paste is not phase-separated.

  As the thermoplastic resin having an epoxy group, a known thermoplastic resin can be used as long as it is a thermoplastic resin having at least one epoxy group in the molecule. Examples of “thermoplastic resins having an epoxy group” that can be suitably used in the present invention include epoxy resins such as bisphenol A-based epoxy resins, novolac-based epoxy resins, brominated epoxy resins, and modified products thereof, glycidyl methacrylate resins, etc. A copolymer containing a polymerizable monomer having an epoxy group as a constituent, a diene system containing a conjugated diene compound as described in JP-B-40-23798, JP-B42-8704, etc. Examples include epoxidized diene block copolymers in which epoxy groups are introduced into the main chain by reacting block copolymers with peracids such as formic acid, peracetic acid, perbenzoic acid, and peroxides of hydride. it can.

  Among these thermoplastic resins having an epoxy group, the epoxy equivalent represented by the weight of the resin per 1 g equivalent of the epoxy group is 1 to 10 from the viewpoint of hydrogen halide scavenging effect and the chemical stability of the resin itself. It is preferably a thermoplastic resin of 1,000, especially 100 to 5,000. Further, from the viewpoint that the viscosity of the paste is easily adjusted to a range in which applicability is good, the weight average molecular weight of the thermoplastic resin is preferably 5,000 to 500,000, particularly 5,000 to 200,000. It is.

  The content of the haloalkyl styrene, the monomer copolymerizable with haloalkyl styrene, the polymerization initiator and the thermoplastic resin having an epoxy group in the composition used in the present invention is not particularly limited. The content of haloalkylstyrene is preferably 10% by weight or more, particularly 50% by weight or more of the total of both. Further, the viewpoint that the paste viscosity is in a suitable range, specifically, the viscosity at 20 ° C. is in the range of 0.1 to 100 poise, particularly 0.5 to 50 poise, and the electrochemical properties of the resulting anion exchange membrane. In view of the above, the content of the thermoplastic resin having an epoxy group is 0.1 to 50 parts by weight, particularly 1 to 30 parts by weight, based on 100 parts by weight of the total of haloalkylstyrene and monomers copolymerizable with haloalkylstyrene. Preferably there is. The blending amount of the polymerization initiator is preferably 0.1 to 20 parts by weight, particularly 0.1 to 10 parts by weight, based on a total of 100 parts by weight of haloalkylstyrene and monomers copolymerizable with haloalkylstyrene. It is.

  The composition to be a paste may contain components other than haloalkylstyrene, a monomer copolymerizable with haloalkylstyrene, and a polymerization initiator. For example, various crosslinking agents can be added for the purpose of suppressing swelling of the ion exchange membrane and imparting appropriate strength. Examples of such crosslinking agents include m-, p-, o-divinylbenzene, divinylsulfone, butadiene, chloroprene, isoprene, trivinylbenzenes, divinylnaphthalene, trivinylnaphthalene, diallylamine, triallylamine, divinylpyridines, and the like. Vinyl compounds can be used. The amount of these crosslinking agents to be used is not particularly limited, but it is 0.1 to 0.1 parts by weight based on a total of 100 parts by weight of haloalkylstyrene and monomers copolymerizable with haloalkylstyrene from the balance of crosslinking effect and electric resistance of the resulting ion exchange membrane. The amount is preferably 50 parts by weight, particularly 1 to 20 parts by weight. In addition, it is preferable not to include a thickener other than “a thermoplastic resin having an epoxy group” from the viewpoint that the paste is difficult to separate.

  In the method of the present invention, the composition (paste) containing each of the above components is attached to the substrate film, and then the composition is polymerized and cured. The base film is used for imparting appropriate strength to the ion exchange membrane and improving the durability. As the base film, a known base film used in the conventional paste method is used. Can be used without any particular restrictions. Specific examples of such a base film include woven fabrics, nonwoven fabrics and porous films made of hydrocarbon resins such as polyvinyl chloride and polyolefin, fluorine resins, and the like.

  A well-known technique can also be used for the method of polymerizing the paste by adhering the paste to the substrate film. For example, as a method for attaching the paste to the substrate, a known method such as a coating method, an impregnation method, or a coating method is appropriately employed. As the polymerization method, heat polymerization or photopolymerization is preferably employed. The polymerization conditions are selected appropriately according to the type of polymerization initiator, the type of monomer component, the type of substrate, etc., and further considering the electrochemical and mechanical properties of the desired ion exchange membrane. do it. In general, it is sufficient to polymerize at a polymerization temperature of 0 to 200 ° C., preferably 50 to 100 ° C. for a fixed time, for example, 4 to 48 hours. In the polymerization, from the viewpoint of workability and economy, it is preferable that the paste is attached to the base film and then sandwiched between the polyester films and then polymerized.

  In the method of the present invention, the paste adhering to the base material is polymerized in this way, and then an anion exchange group is introduced into the obtained polymer. The method of introducing an anion exchange group is not particularly different from the case of using a conventional paste, and can be suitably carried out by subjecting the haloalkyl group of the haloalkylstyrene copolymer to quaternary ammonium chloride using an amine compound. . At this time, as the amine compound, trimethylamine, dimethylethanolamine, methyldiethanolamine, triethylamine and the like can be suitably used.

  In the method of the present invention, for example, the polyester film is peeled off after polymerization, the obtained polymer is immersed in an aqueous trimethylamine solution, reacted at room temperature for 1 day, and the haloalkyl group is preferably quaternized to form an anion exchange group. Can be introduced.

  In addition, since the (paste) composition has an excessively large epoxy group to capture hydrogen halide that can usually be generated during polymerization, the polymer obtained after the polymerization (exactly haloalkylstyrene copolymer). A polymer and a thermoplastic resin having an epoxy group and / or a composite resin containing a thermoplastic resin having an epoxy group reacted with hydrochloric acid) on the surface and inside of the film, an epoxy group derived from the thermoplastic resin having an epoxy group Exists. When this remaining epoxy group is reacted with an amine or the like, an anion exchange group can be introduced by a ring-opening reaction. Therefore, it is possible to further increase the amount of ion-exchange groups in the membrane by using residual epoxy groups, and to further improve the electrochemical properties of the membrane, such as reducing the electrical resistance of the membrane and improving the ion selective permeability. Can do.

  Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. The characteristics of the ion exchange membranes shown in the following examples and comparative examples were measured by the following methods.

1) Evaluation of film surface condition The surface condition of the obtained film was visually observed, and “○” indicates that no white spots were observed on the film surface, and 10 or more white spots were observed per 10 cm ^2. Was evaluated as “×”.

2) Ion exchange capacity and water content First, the ion exchange membrane is immersed in a 0.5 (mol / l) HCl aqueous solution for 10 hours or longer, and then the amount of free ions { A (mol)} is measured. Chlorine ion type is substituted with nitrate ion type with 0.5 (mol / l) NaNO ₃ aqueous solution, and the liberated chlorine ion is quantified with a potentiometric titrator (COMTITE-900, manufactured by Hiranuma Sangyo Co., Ltd.). Next, the same ion exchange membrane is immersed in a 0.5 (mol / l) NaCl aqueous solution for 4 hours or more, washed thoroughly with ion exchange water, and then the membrane is taken out. The weight {W (g)} is measured, and then the membrane is put into a vacuum dryer and dried at 60 ° C. for 5 hours, and then the weight of the membrane taken out (weight when dried) {D (g)} is measured. Based on A, W, and D measured in this way, the ion exchange capacity and water content were determined by the following equations.

Ion exchange capacity = A × 1000 / W (mmol / g-dry membrane)
Moisture content = 100 × (WD) / D (%)
Examples 1-4
A paste-like mixture is obtained by adding 90 parts by weight of chloromethylstyrene, 10 parts by weight of 57% industrial divinylbenzene, 5 parts by weight of benzoyl peroxide, and an epoxidized polystyrene-polybutadiene copolymer in the amounts shown in Table 1. It was. The epoxidized polystyrene-polybutadiene copolymer used is a thermoplastic resin having a styrene / butadiene weight ratio of 40/60, an epoxy equivalent of 480 to 540, and a weight average molecular weight of 10,000 to 30,000.

  The obtained paste was adhered to a woven fabric of polyvinyl chloride, and both sides were coated with 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. Each membrane was then reacted in an amination bath consisting of 10 parts of 30% trimethylamine aqueous solution, 50 parts of water and 5 parts of acetone at room temperature for 24 hours to obtain a quaternary ammonium base type anion exchange membrane. The ion exchange membrane characteristics of the obtained anion exchange membrane were measured. These results are shown in Table 1. In addition, the thermoplastic resin in Table 1 means the epoxidized polystyrene-polybutadiene copolymer.

Comparative Example 1
In Example 1, the addition amount of the epoxidized polystyrene-polybutadiene copolymer was changed to 0%, but the viscosity of the paste at 20 ° C. was <0.1 poise, and the pasty material could not be uniformly applied to the substrate.

Comparative Example 2
As a conventional paste, 90 parts by weight of chloromethylstyrene, 10 parts by weight of 57% industrial divinylbenzene, 5 parts by weight of benzoyl peroxide, 5 parts by weight of styrene oxide, and 5 parts by weight of nitrile butadiene rubber are added to form a paste. A mixture was obtained. A quaternary ammonium base type anion exchange membrane was prepared from this paste by the same method as in Example 1, and the ion exchange membrane characteristics were measured. The results are shown in Table 2.

  When styrene oxide is added as a conventional low molecular weight epoxy compound as a method for capturing and removing the generated hydrogen halide, a thickener is required to uniformly apply the paste-like material to the substrate. Compared to Example 2, a decrease in exchange capacity was observed with the addition of the thickener.

Comparative Example 3
When an anion exchange membrane was prepared in the same manner except that the amount of styrene oxide added was changed to 0% in Comparative Example 2, white spots were generated on the membrane surface.

Claims (3)

A composition comprising a haloalkylstyrene, a monomer copolymerizable with haloalkylstyrene, a polymerization initiator, and an epoxidized diene block copolymer having an epoxy equivalent of 100 to 5,000 and a weight average molecular weight of 5,000 to 200,000 A method for producing an anion exchange membrane characterized in that an anion exchange group is introduced into an obtained polymer using an amine compound after the product is attached to a substrate membrane and polymerized. The content of the epoxidized diene-based block copolymer in the composition is 0. 0 parts by weight relative to 100 parts by weight of the total of haloalkylstyrene and monomers copolymerizable with haloalkylstyrene. The method for producing an anion exchange membrane according to claim 1, wherein the amount is 1 to 50 parts by weight. An anion exchange membrane obtained by the production method according to claim 1 , wherein the haloalkylstyrene copolymer and the epoxidized diene block copolymer and / or hydrogen halide or amine compound into which an anion exchange group is introduced An anion exchange membrane, wherein the base membrane is coated with a composite resin containing an epoxidized diene block copolymer reacted with.