Polyvinyl chloride fiber, fabric including said polyvinyl chloride fiber, method for producing polyvinyl chloride fiber, and ion exchange membrane

Abstract

The present invention addresses the problem of providing: a polyvinyl chloride fiber that has suitable adhesiveness to an ion exchange resin when used as a base material of an ion exchange membrane, has high strength, is not brittle when used in an ion exchange membrane, and in which shrinkage is minimized when immersed in a monomer; and a method for producing a polyvinyl chloride fiber in which there is no risk of fire due to vaporization of an organic solvent at a high temperature and no issues involving the leakage of harmful substances into the atmosphere.　The present invention is a polyvinyl chloride fiber having a crystallinity of 10%-60% and a styrene impregnation amount of 20-60 wt% when immersed in styrene and polymerized. The present invention is also a method for producing a polyvinyl chloride fiber comprising a discharge step in which a polyvinyl chloride solution is discharged into a coagulation bath, wherein the coagulation bath contains a solution that does not dissolve polyvinyl chloride and makes it possible to clean an organic solvent included in the polyvinyl chloride solution.

Description

Polyvinyl chloride fiber, fabric containing said polyvinyl chloride fiber, method for producing polyvinyl chloride fiber, and ion exchange membrane

[0001] The present invention relates to polyvinyl chloride fibers, fabrics containing the polyvinyl chloride fibers, a method for producing polyvinyl chloride fibers, and ion exchange membranes.

[0002] Ion exchange membranes are membranes that selectively allow cations or anions to pass through. They are used in a variety of applications, including producing salt by electrodialysis of seawater, recovering acid from acid wastewater containing metal ions after pickling by diffusion dialysis, and producing hydrogen by water electrolysis using anion exchange membranes.

[0003] Such ion exchange membranes have a structure in which a substrate sheet, which functions as a reinforcing material, is disposed as a core material in an ion exchange resin, thereby maintaining a certain level of strength. The substrate sheet may be a porous thin film made of polyolefin (Patent Document 1) or a nonwoven fabric made of polyolefin resin fibers (Patent Document 2).

[0004] JP 64-22932 A and WO 2012 / 23451 A

[0005] A substrate for ion exchange resins must not only fulfill its inherent role as a reinforcing material but also not impair the performance of the ion exchange resin. However, conventional substrates have problems such as poor adhesion to the ion exchange resin, low substrate strength, brittle ion exchange membranes, and shrinkage upon impregnation with monomers. Furthermore, the dry spinning method used to produce the fibers that make up the substrate involves vaporizing an organic solvent at high temperatures. However, this method poses problems such as the risk of fire due to the vaporization of the organic solvent at high temperatures and the release of hazardous substances into the atmosphere.

[0006] In view of the above circumstances, an object of the present invention is to provide a polyvinyl chloride fiber that, when used as a base material for an ion exchange membrane, has good adhesion to an ion exchange resin, has high strength, is not brittle when used as an ion exchange membrane, and is inhibited from shrinking when immersed in a monomer; and to provide a method for producing a polyvinyl chloride fiber that does not pose the risk of ignition due to evaporation of an organic solvent at high temperatures or the problem of leakage of harmful substances into the atmosphere.

[0007] As a result of extensive research, the present inventors have completed the following inventions: [1] A polyvinyl chloride fiber having a crystallinity of 10% to 60% and an impregnation amount of styrene of 20 wt% to 60 wt% when immersed in styrene and polymerized. [2] The polyvinyl chloride fiber according to [1], wherein the styrene shrinkage time when immersed in styrene is 5 minutes or longer.

[0008] [3] The polyvinyl chloride fiber according to [1] or [2], which has a breaking strength of 200 MPa or more and 800 MPa or less and a breaking elongation of 10% or more and 80% or less. [4] The polyvinyl chloride fiber according to any one of [1] to [3], which has a breaking elongation after polymerization of 5% or more.

[0009] [5] The polyvinyl chloride fiber according to any one of [1] to [4], which is a long fiber. [6] The polyvinyl chloride fiber according to any one of [1] to [5], which is a monofilament or multifilament.

[0010] [7] The polyvinyl chloride fiber according to any one of [1] to [6], wherein the degree of polymerization of the polyvinyl chloride fiber is from 1000 to 3000. [8] The polyvinyl chloride fiber according to any one of [1] to [7], wherein the polymer concentration used in producing the polyvinyl chloride fiber is from 15 wt % to 35 wt %.

[0011] [9] A fabric consisting of a woven fabric, a nonwoven fabric, or a knitted fabric, comprising the polyvinyl chloride fiber according to any one of [1] to [7].

[10] A method for producing polyvinyl chloride fiber, comprising a discharge step of discharging a polyvinyl chloride solution into a coagulation bath, the coagulation bath containing a solution that does not dissolve the polyvinyl chloride and can wash away the organic solvent.

[0012]

[11] The method for producing polyvinyl chloride fibers according to

[10] , wherein the organic solvent contained in the polyvinyl chloride solution is at least one selected from the group consisting of N,N-dimethylacetamide, cyclohexanone, N-methyl-2-pyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, and 1,3-dimethyl-2-imidazolidinone, and the coagulation bath is a mixed solvent of water and the organic solvent, or an alcoholic solvent.

[12] The method for producing polyvinyl chloride fibers according to

[10] or

[11] , wherein the coagulation bath is an alcoholic solvent.

[0013]

[13] The method for producing polyvinyl chloride fibers according to

[11] or

[12] , wherein in the discharging step according to

[10] , a distance between the discharging portion of the polyvinyl chloride solution and the coagulation bath is 0.1 cm or more.

[14] The method for producing polyvinyl chloride fibers according to any of

[10] to

[13] , further comprising a step of stretching the polyvinyl chloride fibers at 80 to 100°C after the discharging step.

[0014]

[15] The method for producing polyvinyl chloride fibers according to any one of

[10] to

[14] , further comprising, after the discharging step, a step of heat-treating the polyvinyl chloride fibers at 90 to 180° C.

[16] The fabric according to [9], wherein the woven fabric, nonwoven fabric, or knitted fabric is a substrate for an ion exchange membrane.

[0015]

[17] An ion exchange membrane comprising a fabric made of the woven fabric, nonwoven fabric, or knitted fabric according to

[16] , and an ion exchange resin supported on the fabric.

[0016] The polyvinyl chloride fiber of the present invention can provide a polyvinyl chloride fiber that, when used as a substrate for an ion exchange membrane, has good adhesion to an ion exchange resin, is high in strength, is not brittle when used as an ion exchange membrane, and is suppressed in shrinkage when immersed in a monomer. Furthermore, the method for producing a polyvinyl chloride fiber of the present invention can prevent the risk of ignition due to evaporation of organic solvents at high temperatures and the problem of atmospheric leakage of hazardous substances.

[0017] Fig. 1 is a conceptual diagram showing a method for producing polyvinyl chloride fibers of the present invention. Fig. 2 is a top view schematically showing an example of a woven fabric that is a fabric of the present invention. Fig. 3 is a cross-sectional view schematically showing an example of an ion exchange membrane of the present invention.

[0018] Next, the present invention will be described based on embodiments. However, the present invention is not limited to the embodiments described below. In the present invention, when it is stated that "X or more" (X is any number), it also means "preferably larger than X" unless otherwise specified, and when it is stated that "Y or less" (Y is any number), it also means "preferably smaller than Y" unless otherwise specified.

[0019] <Polyvinyl chloride fiber> Polyvinyl chloride fiber (PVC fiber) may be produced by a dry spinning method in which a polyvinyl chloride resin is swelled and dissolved in a mixed solvent of acetone, benzene, or the like, or an organic solvent such as tetrahydrofuran or cyclohexanone, and the solvent is evaporated in a spinning tube to form fibers, or may be produced by a wet or dry-wet spinning method described below. However, due to the harmfulness of the organic solvent used and the risk of ignition due to evaporation of the organic solvent at high temperatures, production by a wet or dry-wet spinning method is preferred. In wet or dry-wet production, it is also preferable from the viewpoints of safety and the environment to use water to wash off the organic solvent contained in the fiber after passing through a coagulation bath.

[0020] It should be noted that a structure similar to polyvinyl chloride fiber is flat yarn, which is made by thinly slitting a polyvinyl chloride film and stretching it, but this flat yarn is outside the scope of the polyvinyl chloride fiber of the present invention.

[0021] The average degree of polymerization of the polyvinyl chloride resin constituting the polyvinyl chloride fiber is, for example, from 600 to 3000, preferably from 1000 to 2500, and more preferably from 1500 to 2500. If the degree of polymerization of the polyvinyl chloride resin is too low outside the above range, the elongation of the fiber after polymerization decreases and mechanical strength cannot be obtained. On the other hand, if the degree of polymerization is too high outside the above range, the viscosity of the spinning solution increases, making it difficult to adjust the spinning solution.

[0022] (Crystallization degree) The crystallinity of the polyvinyl chloride fiber is preferably 10% to 60%, more preferably 15% to 50%, even more preferably 20% to 40%, and particularly preferably 25% to 40%. By setting the crystallinity of the polyvinyl chloride fiber to the above-mentioned lower limit or more, the strength of the polyvinyl chloride fiber can be improved, the amount of styrene impregnation can be limited, and shrinkage upon immersion in styrene can be suppressed. Furthermore, by setting the crystallinity of the polyvinyl chloride fiber to the upper limit or less, styrene impregnation can be tolerated to a certain extent, thereby improving adhesion to ion exchange resins. The crystallinity of the polyvinyl chloride fiber was measured by the method described in the following examples.

[0023] (Styrene Impregnation Amount) The styrene impregnation amount of polyvinyl chloride fiber when immersed in styrene and polymerized is preferably 20 wt% to 60 wt%, more preferably 25 wt% to 50 wt%, and even more preferably 30 wt% to 45 wt%. By setting the styrene impregnation amount of polyvinyl chloride fiber to the above-mentioned lower limit or more, it is possible to improve adhesion to ion exchange resins. Furthermore, by setting the styrene impregnation amount of polyvinyl chloride fiber to the above-mentioned upper limit or less, it is possible to suppress decreases in strength and brittleness. The styrene impregnation amount of polyvinyl chloride fiber was measured by the method described in the following examples.

[0024] Fabrics made from the polyvinyl chloride fibers of the present invention are suitable for use as substrates for ion exchange membranes. In ion exchange membranes produced by the paste method described below, the diffusion of ion exchange resin-forming monomer molecules into the fibers and the swelling of the fibers by the monomer are important (the degree of this diffusion and swelling is represented by the above-mentioned amount of styrene impregnation). Diffusion of the monomer into the fibers forms an ion conduction path within the fiber resin, which would otherwise serve as a resistance layer, and the resistance of the ion exchange membrane is reduced.

[0025] Furthermore, as the fibers swell, the fiber resin phase and the ion exchange resin phase penetrate each other, improving adhesion. However, if this diffusivity is too high, the mechanical strength of the ion exchange membrane may decrease. On the other hand, if the diffusivity is too low, the resistance of the ion exchange membrane increases. Furthermore, if the swelling rate is too low, adhesion decreases. By using a fabric made of the polyvinyl chloride fibers of the present invention, an ion exchange membrane with excellent resistance, adhesion, and mechanical strength can be achieved.

[0026] (Styrene Shrinkage Time) When polyvinyl chloride fibers are immersed in styrene at room temperature (25°C), the time required for the polyvinyl chloride fibers to shrink by 5% or more is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 20 minutes or more. In the present invention, the styrene shrinkage time is defined as the time required for the polyvinyl chloride fibers to shrink by 5% when immersed in styrene at room temperature (25°C). The styrene shrinkage time was measured by the method described in the following Examples. By setting the shrinkage time of the polyvinyl chloride fibers when immersed in styrene to the above-mentioned lower limit or more, defects in the ion exchange membrane production process can be avoided. Defects in the ion exchange membrane production process include, for example, premature shrinkage of the fabric before the voids in the fabric made of polyvinyl chloride fibers are filled with a monomer for forming an ion exchange resin, such as styrene, and the fabric is superimposed with a release sheet and wound into a roll, resulting in a reduction in the area of ​​the ion exchange membrane. A reduction in the area of ​​the ion exchange membrane causes poor appearance and increases in the thickness and resistance of the ion exchange membrane. The styrene shrinkage time when the polyvinyl chloride fiber was immersed in styrene was measured by the method described in the following examples.

[0027] (Breaking Strength, Breaking Elongation) The lower limit of the breaking strength of the polyvinyl chloride fiber is preferably 200 MPa or more, more preferably 300 MPa or more, and even more preferably 400 MPa or more. By setting the breaking strength to the above-mentioned lower limit or more, it is possible to increase the strength of the ion exchange membrane while reducing the thickness and resistance. The upper limit is not particularly specified, but is preferably 800 MPa or less. The lower limit of the breaking elongation of the polyvinyl chloride fiber is preferably 10% or more, more preferably 15% or more. The upper limit is preferably 80% or less, more preferably 60% or less. The breaking elongation of the polyvinyl chloride fiber after polymerization is preferably 5% or more, more preferably 10% or more, and even more preferably 20% or more. In the present invention, the "breaking elongation after polymerization" refers to the breaking elongation of a polymerized fiber obtained by impregnating the interior of the fiber with styrene and polymerizing it. By setting the breaking strength and breaking elongation of the polyvinyl chloride fiber and the breaking elongation of the polymerized fiber within the above ranges, it is possible to ensure strength and elongation suitable for use as a substrate for ion exchange membranes, which are the main application of the polyvinyl chloride fiber. The breaking strength and breaking elongation of the polyvinyl chloride fiber and the breaking elongation of the polymerized fiber were measured by the methods described in the following examples.

[0028] (Fineness) The lower limit of the fineness of polyvinyl chloride fiber (monofilament) is preferably 2 dtex or more and 80 dtex or less, more preferably 4 dtex or more and 60 dtex or less, and even more preferably 5 dtex or more and 50 dtex or less. The lower limit of the fineness of polyvinyl chloride fiber (multifilament) is preferably 20 dtex or more and 150 dtex or less, more preferably 30 dtex or more and 120 dtex or less, and even more preferably 40 dtex or more and 100 dtex or less. By setting the fineness of polyvinyl chloride fiber within the above range, strength can be ensured when used as a substrate for ion exchange membranes, which is a main application. The fineness of polyvinyl chloride fiber was measured by the method described in the following examples.

[0029] (Additives, etc.) It is preferable that the polyvinyl chloride fiber does not contain additives such as plasticizers. If a plasticizer is contained, crystallization of the polyvinyl chloride fiber is inhibited, making it difficult to achieve the above-mentioned preferred degree of crystallinity. When polyvinyl chloride fiber is produced by the above-mentioned dry spinning method or dry / wet spinning method, it is not necessary to use additives such as plasticizers in the production process, and therefore it is possible to produce polyvinyl chloride fiber that does not contain additives. However, in the case of flat yarns produced by slitting a film, additives such as plasticizers necessary for film formation are contained in the material itself, which inhibits crystallization.

[0030] (Filament and Staple Fiber) The polyvinyl chloride fiber of the present invention can be spun into either a filament or a staple fiber, but is preferably a filament from the viewpoint of being used as a woven fabric for a substrate of an ion exchange membrane. The filament may be used as a monofilament or a multifilament, and can be appropriately shaped in a suitable form depending on the intended use.

[0031] <Method for producing polyvinyl chloride fiber> The method for producing polyvinyl chloride fiber of the present invention includes a step of discharging a polyvinyl chloride solution into a coagulation bath, wherein the coagulation bath contains a solution that does not dissolve the polyvinyl chloride and can wash away the organic solvent.

[0032] The polyvinyl chloride fiber of the present invention is produced by wet and dry spinning methods, which are safer than dry spinning methods because they do not require evaporation of organic solvents.

[0033] (Polyvinyl chloride solution) The method for producing polyvinyl chloride fiber of the present invention includes a step of discharging a polyvinyl chloride solution into a coagulation bath. The organic solvent constituting the polyvinyl chloride solution can be at least one selected from the group consisting of N,N-dimethylacetamide, cyclohexanone, N-methyl-2-pyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, and 1,3-dimethyl-2-imidazolidinone. Dimethylacetamide is preferred because of its high solubility and from the viewpoint of practical solvent recycling.

[0034] In producing a polyvinyl chloride solution, it is preferable to disperse polyvinyl chloride in an organic solvent and then heat-melt the resulting polyvinyl chloride solution. From the viewpoint of achieving high dispersion, it is preferable to cool the organic solvent to a temperature below which swelling of the polyvinyl chloride powder is suppressed, for example, to a temperature of -10°C to 10°C, before adding polyvinyl chloride. The resulting solution is then heated, preferably at 50°C to 100°C, for 1 to 5 hours to form a polyvinyl chloride solution. Furthermore, it is preferable to subsequently remove bubbles from the solution by a standing step for 1 to 5 hours or by degassing under reduced pressure for 0.5 to 2 hours. Degassing under reduced pressure allows for a shorter degassing time.

[0035] The polyvinyl chloride concentration in the polyvinyl chloride solution is preferably 5 wt % to 70 wt %, more preferably 10 wt % to 50 wt %, even more preferably 15 wt % to 40 wt %, and particularly preferably 15 wt % to 35 wt %. By setting the polyvinyl chloride concentration in the polyvinyl chloride solution to the lower limit or more, excessive void formation and deterioration of mechanical properties in the resulting polyvinyl chloride fiber can be prevented, and by setting the polyvinyl chloride concentration in the polyvinyl chloride solution to the upper limit or less, the viscosity of the polyvinyl chloride solution can be prevented from becoming too high, thereby preventing deterioration of processability such as an extreme decrease in spinnability and secondary draw ratio, and ultimately preventing deterioration of the mechanical properties of the resulting polyvinyl chloride fiber.

[0036] (Coagulation Bath) The coagulation bath used in the present invention contains a solution that does not dissolve the polyvinyl chloride and can wash away the organic solvent. The solution constituting the coagulation bath can be a mixed solvent of water and the above-mentioned organic solvent, or an alcohol-based solvent. When a mixed solvent of water and the above-mentioned organic solvent is used as the coagulation bath, the mixing ratio (by volume) is preferably 10-80:20-90 (water:organic solvent), more preferably 15-80:20-85 (water:organic solvent), even more preferably 20-80:20-80 (water:organic solvent), and particularly preferably 40-80:20-60 (water:organic solvent). If the organic solvent concentration is too low, exceeding the above range, the coagulation rate increases, resulting in a fiber with many voids. Using an alcohol-based solvent as the coagulation bath is more effective for obtaining fibers with fewer voids than using a mixed solvent of water and the above-mentioned organic solvent. If voids exist within the fibers, a large amount of styrene will be impregnated into the voids, causing the polymerized fibers to become embrittled or to shrink prematurely when immersed in styrene. The temperature of the coagulation bath is set to preferably 20°C or less, more preferably 10°C or less, and even more preferably 5°C or less in order to solidify the discharged resin.

[0037] In the dry-wet spinning method, as shown in the schematic diagram of Figure 1, the polyvinyl chloride solution is filled into a cylinder 10 equipped with a nozzle at the tip of a syringe or the like, and the solution is discharged at a predetermined speed into the coagulation bath 20 to coagulate, and the resulting fibers are wound and recovered. The organic solvent in the polyvinyl chloride solution discharged into the coagulation bath 20 is extracted by the coagulation bath 20 and replaced by a non-solvent, causing the polyvinyl chloride to coagulate into fibers.

[0038] In the present invention, a distance (air gap) is provided between the coagulation bath 20 and the tip of the nozzle 10, and after the polyvinyl chloride solution is discharged from the nozzle 10, it travels through a gas before being introduced into the coagulation bath 20. The travel distance in the gas (air gap) is preferably 1 to 100 mm, more preferably 5 to 20 mm. In the dry-wet spinning method, an air gap is provided and a spinning step in a dry section is inserted, making it a method suitable for high-speed spinning. In addition, in the present invention, a wet spinning method without an air gap can also be used.

[0039] The polyvinyl chloride solution filled in a cylinder or the like is maintained at a temperature that provides good fluidity and prevents thermal degradation of the resin, preferably from 40°C to 100°C, more preferably from 50°C to 90°C, and even more preferably from 60°C to 80°C.

[0040] The nozzle to be used is not particularly limited as long as it can produce fibers of the desired fineness, but the inner diameter of the nozzle is preferably 0.05 mm or more and 0.50 mm or less, more preferably 0.08 mm or more and 0.30 mm or less.

[0041] The fiber obtained in the coagulation liquid is preferably wound up on a bobbin or the like. The winding speed is adjusted depending on the desired fineness, but is preferably 1 m / min or more, more preferably 100 m / min or more, and even more preferably 20 m / min or more. The fiber obtained by winding up on a bobbin is preferably washed with water or alcohol, and preferably dried in an oven at 20°C to 50°C. From the viewpoints of safety and the environment, it is more preferable to use water as the washing liquid.

[0042] (Drawing Step) The fiber obtained by the above step is preferably drawn at a predetermined draw ratio. The draw ratio is preferably 2 to 20 times, more preferably 3 to 10 times, and even more preferably 4 to 8 times. Drawing may be performed batchwise or continuously. In the case of continuous drawing, the draw ratio is set by adjusting the ratio between the fiber delivery speed and the take-up speed. The drawing temperature is preferably 80°C to 100°C, more preferably 90°C to 100°C. Examples of heat transfer media in the drawing treatment include hot air, hot rolls, steam, and hot water. From the viewpoint of efficient and uniform heat supply to the fiber, steam and hot water are preferred. By performing the above predetermined drawing treatment, the obtained fiber is more likely to have a desired crystallinity, which in turn makes it more likely to have a desired styrene impregnation rate and shrinkage rate.

[0043] (Heat Treatment Step) The fiber drawn in the drawing step is preferably heat-treated at a predetermined temperature in the heat treatment step. The heat treatment temperature is preferably 90°C or higher and 180°C or lower, more preferably 100°C or higher and 150°C or lower. Examples of heat media in the heat treatment step include hot air, hot rolls, steam, and hot water. By carrying out the predetermined heat treatment, the obtained fiber can easily maintain a desired crystallinity, which in turn makes it easier to maintain a desired styrene impregnation rate and shrinkage rate.

[0044] <Fabric (woven fabric, nonwoven fabric, textile)> (Uses) The polyvinyl chloride fiber of the present invention can be suitably used in the form of a fabric (woven fabric, nonwoven fabric, or knitted fabric) as a substrate for an ion exchange membrane. The polyvinyl chloride fiber of the present invention has a predetermined crystallinity, and therefore the styrene impregnation rate can be set within a predetermined range, which improves adhesion to ion exchange resins. Furthermore, shrinkage when immersed in styrene monomer is suppressed, so no problems occur during the production of ion exchange membranes. Furthermore, when used as a substrate, the fiber has sufficient strength and resistance to brittleness.

[0045] The weave of the woven fabric may be any of plain weave, twill weave, and satin weave, but plain weave is preferred from the viewpoint of mechanical strength. Each of the warp and weft of the woven fabric of the present invention contains the polyvinyl chloride fiber of the present invention. It is preferred that at least one of the warp and weft of the woven fabric is composed solely of the polyvinyl chloride fiber of the present invention, and it is more preferred that both the warp and weft are composed solely of the polyvinyl chloride fiber of the present invention.

[0046] The open area ratio of the woven fabric is, for example, 1% or more and 50% or less. This open area ratio can be calculated, for example, by observing the woven fabric from above, measuring the area of ​​the woven fabric portion and the area of ​​the void portion that is not woven fabric, and expressing it as a percentage by dividing the area of ​​the void portion by the area of ​​the fiber portion plus the area of ​​the void portion. FIG. 2 is a top view schematically illustrating an example of a woven fabric according to an embodiment. The woven fabric 30 shown in FIG. 2 is a plain weave fabric woven with warp yarns 32 and weft yarns 34. The woven fabric 30 according to the embodiment can be woven, for example, by using the polyvinyl chloride fibers of the present invention as the warp yarns 32 and weft yarns 34 and crossing them according to a specific weave.

[0047] The porosity of the woven fabric is, for example, 20% or more and 80% or less. This porosity is calculated by cutting out a rectangular sample of X cm x Y cm and using the following formula (1): Porosity (%) = {1 - (10000 x M / ρ) / (X x Y x T)} x 100 (1) In formula (1), T: sample thickness (μm), M: sample weight (g), and ρ: resin density (g / cm3).

[0048] The structure and manufacturing method of the nonwoven fabric are not particularly limited, and the nonwoven fabric can be manufactured by using the short fibers or long fibers of the present invention to form a web by a dry or wet method, and then bonding the fibers together by needle punching, thermal bonding, or spunlace.

[0049] The structure of the knitted fabric is not particularly limited, and includes flat knitting, circular knitting, and warp knitting using the filaments or spun yarns of the present invention.

[0050] <Ion Exchange Membrane> The ion exchange membrane of the present invention comprises a fabric made of the above-described woven fabric, nonwoven fabric, or knitted fabric, and an ion exchange resin supported on the fabric (substrate). The ion exchange membrane may be a cation exchange membrane or an anion exchange membrane. The ion exchange membrane according to the embodiment can be used in hydrogen production systems, water electrolysis systems, fuel cells, electrodialysis systems, diffusion dialysis systems, pure water production systems, ion-exchanged water production systems, etc.

[0051] (Ion Exchange Resin) The cation exchange group of the ion exchange resin may be a sulfonic acid group, a carboxylic acid group, a phosphonic acid group, a phenolic hydroxyl group, etc., and generally, a sulfonic acid group, which is a strongly acidic group, is preferred. The anion exchange group of the ion exchange resin may be a quaternary ammonium group, a pyridinium group, a triazolium group, an imidazolium group, a primary amino group, a secondary amino group, a tertiary amino group, etc., and generally, a quaternary ammonium group or a quaternary pyridinium group, which is a strongly basic group, is preferred.

[0052] As the ion exchange resin, at least one of a hydrocarbon-based resin and a fluorine-based resin can be used. As the hydrocarbon-based resin, a styrene-based resin, an acrylic-based resin, or the like can be used. As the fluorine-based resin, a resin having a perfluorocarbon skeleton can be used. As the ion exchange resin, a hydrocarbon-based resin is preferably used, and a styrene-based resin is more preferably used. The styrene-based resin includes a styrene resin, a copolymer of a styrene derivative and a comonomer, and the like.

[0053] The ion exchange resin may contain a resin of a type different from the above-described main component resin. Examples of such resins include at least one selected from the group consisting of chlorine-based resins and hydrocarbon-based resins. The proportion of such resins in the ion exchange resin is, for example, 1% by mass or more and 50% by mass or less. These other resins may be dispersed in the matrix of the ion exchange resin in the form of particles or islands.

[0054] The ion exchange resin may further contain an additive such as a plasticizer. Examples of the plasticizer include at least one selected from the group consisting of dibutyl phthalate, dioctyl phthalate, dibutyl phthalate, tributyl phosphate, and acetyl tributyl citrate. The proportion of the plasticizer in the ion exchange resin is, for example, 1% by mass or more and 20% by mass or less. The thickness of the ion exchange membrane is preferably 20 μm or more and 400 μm or less.

[0055] 3 is a cross-sectional view schematically illustrating an example of an ion exchange membrane according to an embodiment. The ion exchange membrane 50 shown in FIG. 3 includes the plain weave fabric 30 shown in FIG. 1 and an ion exchange resin 40 supported on the plain weave fabric 30.

[0056] (Method for Producing Ion Exchange Membrane) The ion exchange membrane according to the embodiment is produced, for example, by a paste method. The method for producing the ion exchange membrane according to the embodiment includes, for example, filling a substrate (fabric) with a polymerizable composition for forming an ion exchange resin to obtain a first composite membrane, polymerizing the first composite membrane to obtain a second composite membrane, and introducing ion exchange groups into the second composite membrane. Here, filling the substrate with the polymerizable composition means filling the voids between the fibers constituting the substrate with the polymerizable composition. The method for producing the ion exchange membrane according to the embodiment may include filling and dispersing a polymerizable composition for forming an ion exchange resin into a substrate (fabric) to obtain a first composite membrane, overlapping the first composite membrane and a release sheet and winding the resulting mixture into a roll to obtain a first wound body, polymerizing the first wound body to obtain a second composite membrane, peeling off the release sheet from the second composite membrane, and introducing ion exchange groups into the second composite membrane.

[0057] Examples of the release sheet include polyethylene terephthalate (PET) film, polyvinyl alcohol film, polycarbonate film, and polytetrafluoroethylene film. The polymerization method for the first composite membrane may be thermal polymerization, photopolymerization, or a combination of these. From the viewpoint of obtaining an ion exchange membrane with excellent adhesion, thermal polymerization is preferred. The thermal polymerization temperature for the first composite membrane is, for example, 50°C or higher and 140°C or lower, preferably 70°C or higher and 120°C or lower. The thermal polymerization time is, for example, 0.5 hours or higher and 10 hours or lower, preferably 1 hour or higher and 6 hours or lower, after reaching the maximum temperature.

[0058] The introduction of ion exchange groups is carried out, for example, by immersing the second composite membrane in a solution of a compound capable of introducing ion exchange groups. For example, an anion exchange membrane having quaternary ammonium groups introduced therein can be obtained by immersing a second composite membrane having chloromethylstyrene units in a trimethylamine solution for 12 hours or more. In another example, a cation exchange membrane having sulfonic acid groups introduced therein can be obtained by contacting a second composite membrane having styrene units with concentrated sulfuric acid.

[0059] The polymerizable composition for forming the ion exchange resin contains a monomer capable of introducing an ion exchange group. This polymerizable composition may further contain a crosslinking agent, a thickener, a plasticizer, a polymerization initiator, and other additives. The monomer capable of introducing an ion exchange group includes at least one selected from the group consisting of styrene, a styrene derivative, vinylpyridine, and a vinylpyridine derivative. The monomer capable of introducing an ion exchange group preferably includes at least one selected from the group consisting of styrene and a styrene derivative.

[0060] The styrene derivative may be at least one selected from the group consisting of chloromethylstyrene, vinyltoluene, vinylxylene, α-methylstyrene, vinylnaphthalene, and α-halogenated styrene. The proportion of the monomer capable of introducing an ion exchange group in the polymerizable composition is, for example, 10% by mass or more and 90% by mass or less, and preferably 30% by mass or more and 80% by mass or less. The pyridine derivative may be at least one selected from the group consisting of 4-vinylpyridine and 2-methyl-5-vinylpyridine.

[0061] As the crosslinking agent, a monomer having a difunctional or higher polymerizable group is used. As the crosslinking agent, at least one selected from the group consisting of divinylbenzene, divinyl sulfone, butadiene, chloroprene, divinylbiphenyl, divinylnaphthalene, diallylamine, divinylpyridine, and trivinylbenzene is preferably used, and divinylbenzene is preferred. The proportion of the crosslinking agent in the polymerizable composition is, for example, 30% by mass or less, and preferably 3% by mass or more and 20% by mass or less.

[0062] The thickener can be blended to increase the viscosity of the polymerizable composition and improve adhesion between the ion exchange resin and the substrate. For example, resin fine particles are used as the thickener. A chlorine-based resin is preferably used as the resin, and it is more preferable to use the same type of resin as the resin contained in the woven fabric substrate. The average particle size of the fine particles measured by the Coulter method is, for example, 0.1 μm to 20 μm. The proportion of the thickener in the polymerizable composition is, for example, 1% by mass to 50% by mass, preferably 3% by mass to 30% by mass.

[0063] Examples of the polymerization initiator include benzoyl peroxide, p-chlorobenzoyl peroxide, decanoyl peroxide, lauroyl peroxide, acetyl peroxide, tert-butyl (2-ethylhexanoyl) peroxide hexanoate, tert-butyl peroxyoctoate, and di-tert-butyl peroxide.

[0064] The plasticizer may be at least one selected from the group consisting of dibutyl phthalate, bis(2-ethylhexyl) phthalate, and acetyl tributyl citrate. The proportion of the plasticizer in the polymerizable composition is, for example, 1% by mass or more and 20% by mass or less. The proportion of the polymerization initiator in the polymerizable composition is, for example, 0.1% by mass or more and 15% by mass or less, and preferably 1% by mass or more and 10% by mass or less. Other additives contained in the polymerizable composition may include a polymerization inhibitor, a hydrochloric acid scavenger, etc.

[0065] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention.

[0066] [Production and Evaluation of Polyvinyl Chloride Fiber] <Evaluation (Fiber Properties)> (Crystallization) Calculating the crystallinity of polyvinyl chloride fiber (PVC fiber) requires amorphous scattering data for polyvinyl chloride (PVC). Therefore, an amorphous film was prepared. PVC (ZEST1300Z) was dissolved in tetrahydrofuran (THF) at room temperature to prepare a 10 wt% PVC / THF solution. This solution was heated in an oven at 55°C for 1 hour, and a glass slide was immersed in the solution. The solution was then immediately desolvated and solidified in a 10 wt% NaCl aqueous solution at 0°C to obtain a film. The resulting film was washed several times with water and then subjected to X-ray analysis. The X-ray scattering profile of the amorphous PVC film here was measured by wide-angle X-ray diffraction using the 2θ / θ method and the reflection method, and the same results as those described in the literature (E. V. Gouilock, Journal of Polymer Science: Polymer Physics Edition, Vol. 13, No. 5, p. 965 (1975)) were obtained.

[0067] The crystallinity of each fiber obtained in each example and comparative example was measured by wide-angle X-ray diffraction using a Rigaku MiniFlex 300 with a reflection method. To counteract the in-plane orientation of the fibers, the sample was placed on a rotating sample stage and rotated while measurements were taken. The prepared samples were measured at a scan speed of 2.0° / min and a step angle of 0.2°, and data was extracted from each diffraction angle 2θ range of 5 to 60° to plot profiles. The baseline was removed from each profile, and the height of the amorphous scattering profile was adjusted to distinguish between crystalline and amorphous scattering. The crystallinity was calculated from the scattering area and the following formula: Crystallinity (%) = crystalline scattering peak area / (crystalline scattering peak area + amorphous scattering peak area) × 100

[0068] (Fineness Measurement) To measure the mechanical properties of the produced fibers, the fineness of each fiber in the Examples and Comparative Examples was measured. A fineness measuring machine DENICON (DC-21 manufactured by Search Co., Ltd.) was used for the fineness measurement. This device can calculate the denier and tex values ​​from the inherent vibration frequency of the sample, a preset tension, and the sample length. The measurement was carried out at a measurement room temperature of 20°C, a humidity of 65%, and a test length of 2.5 cm.

[0069] (Tensile Test) To obtain the tensile mechanical properties of each fiber in the Examples and Comparative Examples, a tensile test was performed using a small benchtop testing machine, EZ-SX tensile tester, manufactured by Shimadzu Corporation. The breaking strength and breaking elongation were determined from the obtained stress-strain curve. The measurement was performed in a constant temperature and humidity room (20°C, 65%), using a 50 N load cell, an initial test length of 20 mm, and a tensile speed of 20 mm / min.

[0070] (Styrene shrinkage time) A styrene immersion test was conducted on each fiber of the Examples and Comparative Examples to determine the shrinkage time of the fiber when immersed in styrene. The fiber was cut to a length of 10 cm, clipped on only one side, and immersed in styrene at a liquid temperature of 25°C in a glass container, and the time until it shrunk by 5% was measured using the following shrinkage calculation formula. The time until it shrunk by 5% was taken as the styrene shrinkage time. Shrinkage rate (%) = {fiber length before immersion in styrene (cm) - fiber length after immersion in styrene (cm)} / fiber length before immersion in styrene (cm) × 100

[0071] <Evaluation (Polymerized Fiber Properties)> (Styrene Impregnation Amount) To measure the styrene impregnation amount for each fiber in the Examples and Comparative Examples, samples (referred to as polymerized fibers) were prepared by impregnating the interior of the fibers with styrene and polymerizing them. A PET film was placed on a stainless steel plate, and the fibers were arranged on top of it. A few drops of a paste consisting of 97.1 parts by mass of styrene and 2.9 parts by mass of the polymerization initiator t-butylperoxy-2-ethylhexanoate were then added. The top surface was covered with a PET film, and the upper surface was further pressed down with a stainless steel plate. The surface pressure of the PET film was 0.22 MPa. The SUS plate containing the PVC fibers and paste was held at 30°C for 10 minutes in a nitrogen atmosphere, then heated to 90°C at a heating rate of 1°C / min, and thermally polymerized at 90°C for 180 minutes to obtain polymerized fibers.

[0072] The obtained polymerized fiber was immersed in liquid nitrogen and freeze-fractured using a razor blade, and the Raman spectrum of the fiber cross section was obtained using a laser Raman spectrophotometer NRS-7100 manufactured by JASCO Corporation. To calculate the amount of styrene impregnated in the polymerized fiber, a standard sample was prepared by mixing and polymerizing known parts by mass of styrene and PVC powder, and a calibration curve was created from the Raman spectrum of this sample. The calibration curve was based on the peak (687 cm) derived from the PVC of the standard sample.－１ ) area and the styrene-derived peak (984 cm －１ The weight ratio (wt%) of styrene in the polymerized fiber was determined from the peak area ratio of PVC and styrene in the polymerized fiber and the calibration curve, and this was used as the styrene impregnation amount (wt%).

[0073] (Brittleness) To check the brittleness of the polymerized fibers obtained for measuring the amount of styrene impregnation, the polymerized fibers were bent by hand to check whether they broke. Polymerized fibers that did not break were rated as brittle "good", and polymerized fibers that broke were rated as brittle "poor".

[0074] (Breaking elongation of polymerized fiber) A tensile test was conducted on the polymerized fiber to quantitatively confirm the brittleness of the polymerized fiber obtained for measuring the amount of styrene impregnation. The measurement device used was an AGS-500NX manufactured by Shimadzu Corporation. The measurement conditions were a gripper distance of 300 mm and a tensile speed of 5 mm / min. The rate of change in breaking elongation when the fiber was converted to the polymerized fiber was calculated based on the following formula: Rate of change in breaking elongation (%) = {breaking elongation of polymerized fiber (%) - breaking elongation of fiber (%)} / breaking elongation of fiber (%) × 100

[0075] Example 1 A solution was prepared using polyvinyl chloride powder with a degree of polymerization of 1300 (PVC powder, manufactured by Shin-Dai-Ichi Vinyl, ZEST1300Z) and N,N-dimethylacetamide (DMAc) as a solvent according to the following procedure. The DMAc was cooled in an ice bath, and 25 wt % of PVC powder was added to the sufficiently cooled DMAc. The PVC powder was dispersed using a magnetic stirrer, and then heated, stirred, and dissolved at 70°C for 3 hours using a T.K. Hi-Bix 2P-03 kneader manufactured by Primix Corporation. The solution was allowed to stand in a 70°C oven for 3 hours to remove any air bubbles in the solution.

[0076] Fibers were produced by dry-wet spinning using a spinning apparatus manufactured by AIKI Liotech. A syringe filled with 25 wt% PVC / DMAc spinning solution was placed in the apparatus, which was maintained at a temperature (70°C) that ensured good fluidity and prevented thermal degradation. Pressure was applied to the solution from the top of the cylinder using an extrusion device, and the solution was extruded from a nozzle attached to the tip of the cylinder. The nozzle had an inner diameter of 0.21 mm, a nozzle length of 15 mm, and a single hole. An air gap of approximately 1 cm was used. The spinning solution was extruded from the nozzle at 0.1 mL / min into a coagulation bath (water:DMAc = 80:20) at approximately 0°C, coagulated, and wound onto a bobbin at a winding speed of 10 m / min. The wound fiber is referred to as as-spun fiber. The as-spun fiber was washed with water along with the bobbin for 24 hours and then dried overnight in a 30°C oven.

[0077] The as-span fiber was passed through a 30 cm long heating chamber (set temperature: 100°C) and subjected to continuous roll-to-roll heating and drawing in air. The draw ratio was defined as the ratio of the let-off speed and the take-up speed to achieve a 5x draw (DR5). The drawing conditions were room temperature 20°C, let-off speed 0.17 m / min, take-up speed 0.85 m / min, and a residence time in the chamber of approximately 35 seconds. The DR5 fiber obtained by the second drawing was fixed in a hand-crank drawing machine and placed in a 120°C oven for 10 minutes for constant length heat treatment to obtain a monofilament PVC long fiber.

[0078] Example 2 Using Alcosol NP-9 (manufactured by Amakasu Chemical Industries) in the coagulation bath, PVC fibers were produced in the same manner as in Example 1. Furthermore, monofilament PVC long fibers were obtained without heat treatment at 120°C.

[0079] Example 3 Monofilament PVC continuous fibers were obtained in the same manner as in Example 2, except that PVC powder with a degree of polymerization of 2500 (ZEST2500Z, manufactured by Shin-Daiichi Vinyl Corporation) was used and 20 wt % of the PVC powder was added to DMAc.

[0080] Example 4 In the same manner as in Example 3, the fiber was further left to stand in an oven at 120° C. for 10 minutes for a fixed length heat treatment, to obtain a monofilament PVC continuous fiber.

[0081] Example 5 A solution was prepared using PVC powder with a degree of polymerization of 2500 and DMAc according to the following procedure. Using an Aikosha kneader ACM-5LVT, 18 wt % PVC powder was added to DMAc cooled to 0°C in the kneader's jacket. The PVC powder was dispersed, and then heated, stirred, and dissolved at 80°C for 3 hours. The solution was allowed to stand at 60°C for 16 hours to remove air bubbles. Fiber production by wet spinning was carried out according to the following procedure. A jacket was attached to the spinning apparatus, and an 18 wt % PVC / DMAc spinning solution was maintained at 63°C. The pressure inside the jacket was set to 0.1 MPa, and the solution was discharged from the nozzle at the tip using a metering gear pump. A nozzle with an inner diameter of 0.1 mm, a nozzle length of 0.1 mm, and 25 holes was used. With the nozzle tip immersed in the coagulation bath, the spinning solution was extruded from the nozzle at 2.6 mL / min into an Alcosol NP-9 coagulation bath at approximately 0 °C and coagulated. The solution was then passed through a first roll with a take-up speed of 11.5 m / min, a 30 °C Alcosol washing bath, a second roll with a take-up speed of 16.8 m / min, a 55 °C hot air drying oven, and a 17.2 m / min winder onto a bobbin to obtain an as-span fiber stretched 1.5 times. This as-span fiber was then subjected to continuous hot water heat drawing using a hot water bath. Specifically, the fiber was passed through a first roll with a take-up speed of 21 m / min, a 98 °C hot water bath, a 70 m / min second roll, a 120 °C hot air bath, and a 70 m / min winder onto a bobbin to obtain a multifilament fiber with a total draw ratio of 5 times. This drawn fiber was then heat-treated to a fixed length using a hot roll. Specifically, the drawn fiber was passed through a first roll at a winding speed of 50 m / min, a second roll at 120°C and 50 m / min, and a winder at 50 m / min, and wound onto a bobbin. The contact time with the second roll at 120°C was 6 seconds.

[0082] Comparative Example 1: A uniaxially stretched PVC film (manufactured by Sun Plastics, 30 μm thick) containing a plasticizer and other additives was slit to a width of 1 mm, and the slit film was passed between two heated rollers (distance between rollers: 1.5 m) for continuous roll-to-roll heating and stretching. The stretch ratio was defined as the ratio of the let-off speed to the take-up speed to achieve 2x stretching (DR2). The stretching conditions were room temperature of 20°C, a let-off roller speed of 7 m / min at 70°C, and a take-up roller speed of 14 m / min at 70°C. The resulting DR2 fiber was subjected to a constant-length heat treatment at a let-off roller speed of 7 m / min at 90°C and a take-up roller speed of 7 m / min at 90°C to obtain a PVC flat yarn.

[0083] Comparative Example 2 A uniaxially stretched PVC film (manufactured by Sun Plastics Co., Ltd.) containing a plasticizer and the like was slit into a width of 1 mm to obtain a PVC flat yarn (unstretched).

[0084]

[0085] The drawn PVC flat yarn containing plasticizers (Comparative Example 1) had low crystallinity, making it difficult to achieve high breaking strength. Furthermore, when immersed in styrene, it shrunk within a short period of time. The undrawn PVC flat yarn containing plasticizers (Comparative Example 2) was not drawn, so it did not shrink with styrene. However, its low crystallinity and large amount of styrene impregnation resulted in a polymerized fiber with poor brittleness. The drawn PVC fiber of the present invention (Example 1) had high crystallinity, sufficient strength, and reduced styrene impregnation. Its shrinkage time when immersed in styrene was long and its brittleness was good. Furthermore, the PVC fiber (Example 2) using alcohol as a coagulation liquid reduced voids within the fiber, allowing for a longer styrene shrinkage time. Furthermore, the PVC fibers with increased molecular weight (Examples 3 to 5) had high breaking elongation, making them more suitable for the production of ion exchange membranes. Furthermore, Example 4, which was heat-treated, had a longer styrene shrinkage time than Example 3, which was not heat-treated, making the PVC fiber more suitable for producing an ion exchange membrane.

[0086] [Preparation and Evaluation of Cation Exchange Membrane] Example 6 A plain weave fabric (substrate) was prepared using the PVC fiber prepared in Example 5. The thickness of the woven fabric was 98 μm, the porosity was 60%, and the opening ratio was 5%.

[0087] The woven fabric was dipped in a paste-like polymerizable composition, both sides of the woven fabric were covered with 50 μm-thick PET films, and both sides of the woven fabric were sandwiched between iron plates with a surface pressure of 0.22 MPa on the PET films. The polymerizable composition was filled into the woven fabric to obtain a first composite membrane. The first composite membrane sandwiched between the iron plates was placed in an autoclave and held at 30° C. for 10 minutes under a nitrogen pressure of 0.3 MPa, then heated to 90° C. at a heating rate of 1° C. / min and thermally polymerized at 90° C. for 180 minutes to obtain a second composite membrane.

[0088] The polymerizable composition used was 58 parts by mass of styrene (Wako Special Grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 15 parts by mass of chloromethylstyrene (CMS-P, manufactured by AGC Seimi Chemical Co., Ltd.), 18 parts by mass of a 55% divinylbenzene isomer mixture (Practical Grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 9 parts by mass of acrylonitrile (Wako 1st Grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 7 parts by mass of dibutyl phthalate (Wako Special Grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 3 parts by mass of benzoyl peroxide (Niper BW, manufactured by NOF Corporation, containing 25% water), and 6 parts by mass of polyvinyl chloride resin (ZEST P22, manufactured by Shin-Dai-ichi Vinyl Corporation).

[0089] The second composite membrane was immersed in chlorosulfonic acid at 40° C. for 2 hours, and then immersed in a 3.5 N aqueous NaOH solution to obtain a cation exchange membrane into which sulfonic acid groups had been introduced.

[0090] Comparative Example 3 A plain weave fabric (substrate) was produced using the fibers produced in Comparative Example 1. The thickness of the fabric was 107 μm, the porosity was 53%, and the opening ratio was 14%. A second composite membrane and a cation exchange membrane were obtained in the same manner as in Example 1, except that this fabric was used instead.

[0091] <Evaluation (cation exchange membrane)> (Electrical resistance) The electrical resistance of the cation exchange membranes obtained in the examples and comparative examples was measured. The ion exchange membrane was sandwiched in a two-compartment cell having platinum black electrodes, and both sides of the ion exchange membrane were filled with a 0.5 mol / L NaCl aqueous solution. The resistance between the electrodes at 25°C was measured using an AC bridge (frequency 1000 cycles / second). The difference between the inter-electrode resistance and the inter-electrode resistance when no ion exchange membrane was installed was used to determine the membrane resistance (Ω cm ２ The ion exchange membrane used in the above measurement was previously equilibrated in a 0.5 mol / L NaCl aqueous solution.

[0092] (Membrane Thickness) The thickness of the woven fabrics and cation exchange membranes obtained in the Examples and Comparative Examples was measured using a Mitutoyo Digimatic Indicator ID-H0530 (flat probe φ5 mm, granite comparator stand).

[0093] (Ion Exchange Capacity and Water Content) The ion exchange capacity and water content of the cation exchange membranes obtained in the Examples and Comparative Examples were measured. The cation exchange membranes obtained in the Examples and Comparative Examples were immersed in a 1 mol / L HCl aqueous solution for 10 hours or more, and then the counter ions of the ion exchange groups were replaced with sodium ions from hydrogen ions using a 1 mol / L NaCl aqueous solution. The liberated hydrogen ions were quantified using a potentiometric titrator (COMTITE-900, manufactured by Hiranuma Sangyo Co., Ltd.) with a sodium hydroxide aqueous solution (Amol). Next, the same ion exchange membrane was immersed in a 0.5 mol / L NaCl aqueous solution for 4 hours or more and thoroughly rinsed with ion-exchanged water. The surface moisture was then wiped off with tissue paper, and the wet membrane mass (Wg) was measured. Furthermore, the membrane was dried under reduced pressure at 50°C for 12 hours, and the dry weight (Dg) was measured. Based on the above measurements, the ion exchange capacity and water content of the ion exchange membrane were calculated using the following equations. Ion exchange capacity [mmol / g - dry mass] = A x 1000 / D Water content [%] = 100 x (W - D) / D

[0094] (Fixed Ion Concentration) The fixed ion concentration of the cation exchange membranes obtained in the Examples and Comparative Examples was determined as follows: Fixed ion concentration [mmol / g-water]=ion exchange capacity [mmol / g-dry mass] / water content [%]×100

[0095]

[0096] (Tensile Test) The tensile stress at break and tensile elongation at break were measured for the substrate, second composite membrane, and cation exchange membrane using the following method. The substrate, second composite membrane, wet cation exchange membrane, and dry cation exchange membrane were punched out in the TD direction to a width of 1 cm and a length of 6 cm, and the membrane thickness was measured at three points to determine the average membrane thickness. The cross-sectional area [mm2] of the ion exchange membrane was calculated from the width and average membrane thickness. Next, tensile tests were performed on the substrate, second composite membrane, wet cation exchange membrane, and dry cation exchange membrane. The measurement device used was a Shimadzu AGS-500NX. The measurement conditions were a gripper distance of 300 mm and a tensile speed of 5 mm / min. For the wet cation exchange membrane, the membrane used to measure the wet membrane mass (Wg) was used when measuring the ion exchange capacity and water content. Pure water was sprayed on the membrane once every 10 seconds to prevent drying during the measurement. The dry cation exchange membrane was prepared by drying the above wet cation exchange membrane in a vacuum dryer at 50° C. overnight.

[0097]

[0098] In both the "rate of decrease in tensile breaking stress from the substrate" and the "rate of decrease in tensile breaking elongation from the substrate," the rate of decrease in Example 6 was suppressed compared to Comparative Example 3, and a high-strength ion exchange membrane was obtained.

Claims

1. Polyvinyl chloride fiber having a crystallinity of 10% or more and 60% or less, and having a styrene impregnation amount of 20% by weight or more and 60% by weight or less when immersed in styrene and polymerized.

2. The polyvinyl chloride fiber according to claim 1, wherein the styrene shrinkage time when immersed in styrene is 5 minutes or more.

3. Polyvinyl chloride fiber according to claim 1 or 2, having a breaking strength of 200 MPa or more and 800 MPa or less, and a breaking elongation of 10% or more and 80% or less.

4. Polyvinyl chloride fiber according to any one of claims 1 to 3, having a breaking elongation after polymerization of 5% or more.

5. The polyvinyl chloride fiber according to any one of claims 1 to 4, which is a long fiber.

6. The polyvinyl chloride fiber according to any one of claims 1 to 5, wherein the polyvinyl chloride fiber is a monofilament or a multifilament.

7. The polyvinyl chloride fiber according to any one of claims 1 to 6, wherein the degree of polymerization of the polyvinyl chloride fiber is 1,000 or more and 3,000 or less.

8. Polyvinyl chloride fiber according to any one of claims 1 to 7, wherein the polymer concentration used in producing the polyvinyl chloride fiber is 15 wt% or more and 35 wt% or less.

9. A fabric comprising a woven fabric, a nonwoven fabric, or a knitted fabric, which comprises the polyvinyl chloride fiber according to any one of claims 1 to 7.

10. A method for producing polyvinyl chloride fiber, comprising a step of discharging a polyvinyl chloride solution into a coagulation bath, wherein the coagulation bath contains a solution that does not dissolve the polyvinyl chloride but can wash away the organic solvent.

11. The method for producing polyvinyl chloride fiber according to claim 10, wherein the organic solvent contained in the polyvinyl chloride solution is at least one selected from the group consisting of N,N-dimethylacetamide, cyclohexanone, N-methyl-2-pyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, and 1,3-dimethyl-2-imidazolidinone, and the coagulation bath is a mixed solvent of water and the organic solvent, or an alcohol-based solvent.

12. The method for producing polyvinyl chloride fibers according to claim 10 or 11, characterized in that the coagulation bath is an alcohol-based solvent.

13. A method for producing polyvinyl chloride fiber according to claim 11 or 12, wherein in the discharge step according to claim 10, the distance between the discharge point of the polyvinyl chloride solution and the coagulation bath is 0.1 cm or more.

14. A method for producing polyvinyl chloride fibers according to any one of claims 10 to 13, further comprising a step of stretching the polyvinyl chloride fibers at 80 to 100°C after the discharging step.

15. A method for producing polyvinyl chloride fibers according to any one of claims 10 to 14, further comprising a step of heat treating the polyvinyl chloride fibers at 90 to 180°C after the discharging step.

16. The fabric of claim 9, wherein the woven, nonwoven, or knitted fabric is a substrate for an ion exchange membrane.

17. An ion exchange membrane comprising a fabric made of the woven fabric, nonwoven fabric, or knitted fabric according to claim 16, and an ion exchange resin supported on the fabric.

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