JP5868300B2 - Ion exchange membrane, method for producing ion exchange membrane, and electrolytic cell - Google Patents

Description

  The present invention relates to an ion exchange membrane, a method for producing the ion exchange membrane, and an electrolytic cell including the ion exchange membrane.

  Fluorine-containing cation exchange membranes are used as cation exchange membranes for electrolysis to produce chlorine and alkalis by electrolysis (electrolysis) such as alkali chlorides because of their excellent heat resistance and chemical resistance. Yes. In addition, it is used as various membranes for electrolysis such as ozone generating membranes, fuel cells, water electrolysis and hydrochloric acid electrolysis.

  Among them, in the electrolysis of alkali chloride, which electrolyzes salt water and the like to produce caustic soda, chlorine and hydrogen, a carboxylic acid layer having a high anion-exclusion carboxylic acid group as an ion exchange group and a low-resistance sulfonic acid group In general, a cation exchange membrane composed of at least two layers including a sulfonic acid layer having an ion exchange group as a cation exchange membrane is used. Since this cation exchange membrane is in direct contact with chlorine or caustic soda at 80 to 90 ° C. during electrolysis, a fluorine-containing polymer having high chemical resistance is used as a material for the cation exchange membrane.

  However, since such a fluorine-containing polymer alone does not have sufficient mechanical strength as a cation exchange membrane, it is reinforced by embedding a woven fabric made of polytetrafluoroethylene (PTFE) into the membrane as a reinforcing core material. That is being done.

  Further, with such a fluorine-containing polymer alone, gas such as chlorine or hydrogen generated by electrolysis of alkali chloride or the like adheres to the surface of the ion exchange membrane, and is made of inorganic fine particles or the like in order to significantly increase the electrolysis voltage. A coating is applied.

  For example, Patent Document 1 proposes an ion exchange membrane to which a coating containing an oxide, nitride, or carbide belonging to Group IV of the Periodic Table having an average primary particle size of 0.01 to 0.2 μm is proposed. Yes.

  In Patent Document 2, titanium, zirconium, niobium, tantalum, hafnium, tin, vanadium, manganese, molybdenum, tungsten, aluminum, chromium, gallium, cerium, thorium, selenium, iron, yttrium, rare earth, indium, nickel, silver, There has been proposed an ion exchange membrane provided with a gas- and liquid-permeable porous layer which does not have a cathode activity and is made of cobalt, beryllium oxide, nitride, carbide and a mixture thereof.

JP-A-3-137136 Japanese Patent Publication No.59-40231

  In general, impurities such as metals are present in the aqueous alkali chloride solution, and the electrolytic performance of the ion exchange membrane may be reduced by the impurities.

  Here, the electrolysis performance in electrolysis using an ion exchange membrane is high in production efficiency with respect to the current passed from the viewpoint of productivity, low in electrolysis voltage from the viewpoint of economy, and alkaline (from the viewpoint of product quality) The concentration of impurities (such as sodium chloride) in caustic soda) is low. Particularly in salt electrolysis, if electrolysis at an industrial level is performed, if the electrolysis voltage can be lowered even slightly and the current efficiency can be raised even slightly, thereby achieving significant energy savings. Can do.

And in order for an ion exchange membrane to continue exhibiting these high electrolytic performances, it is calculated | required that electrolytic performance does not fall with the impurity in the electrolyte solution used for electrolysis. Impurities such as Ca, Mg, Ba, Sr, I, SiO ₂ , Al, and Fe are present in the electrolyte, and when these impurities accumulate inside the cation exchange membrane, an increase in electrolytic voltage, current Reduced efficiency and increased impurity concentration in alkali. In particular, unlike cation impurities such as Ca and Mg, I is a cation exchange membrane that is difficult to be affected by I because it is an impurity that is difficult to reduce even if the electrolyte is treated in advance. It is required to be.

  However, the ion exchange membranes described in Patent Documents 1 and 2 are not yet sufficiently resistant to impurities, and the stability of the electrolytic performance of the ion exchange membrane against impurities is still insufficient.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an ion exchange membrane that exhibits little influence on the electrolytic performance due to impurities in the electrolytic solution and exhibits stable electrolytic performance.

As a result of intensive research in order to solve the above problems, the present inventors have conventionally identified a coating applied to an ion exchange membrane for the purpose of preventing adhesion of gas generated by electrolysis to the surface of the ion exchange membrane. The inventors have found that the above problems can be solved by using inorganic fine particles, and have completed the present invention. That is, the present invention is as follows.
[1] An ion exchange membrane having a membrane body containing a fluorine-containing polymer having an ion exchange group, and a coating layer provided on at least one surface of the membrane body,
The coating layer includes inorganic particles and a binder,
The ion exchange membrane whose specific surface area of the said coating layer is 0.1-10 m < ² > / g.
[2] The ion exchange membrane according to [1], wherein the inorganic particles have an average particle size of 0.90 to 2 μm.
[3] At least one inorganic material selected from the group consisting of oxides of Group IV elements of the periodic table, nitrides of Group IV elements of the periodic table, and carbides of Group IV elements of the periodic table. The ion exchange membrane according to [1] or [2], which is a particle containing
[4] The ion exchange membrane according to any one of [1] to [3], wherein the inorganic particles are zirconium oxide particles.
[5] The ion exchange membrane according to any one of [1] to [4], wherein the binder includes a fluorine-containing polymer.
[6] The ion exchange membrane according to any one of [1] to [5], wherein the coating layer contains 40 to 90% by mass of the inorganic particles and 10 to 60% by mass of the binder.
[7] The ion exchange membrane according to any one of [1] to [6], wherein the binder includes a fluorine-containing polymer having an ion exchange group derived from a carboxyl group or a sulfo group.
[8] The ion exchange membrane according to any one of [1] to [7], wherein the inorganic particles have an irregular shape.
[9] The ion exchange membrane according to any one of [1] to [8], wherein the inorganic particles are inorganic particles produced by pulverizing an inorganic material.
[10] The inorganic particles are selected from the group consisting of a ball mill, a bead mill, a colloid mill, a conical mill, a disk mill, an edge mill, a milling mill, a hammer mill, a pellet mill, a VSI mill, a Willy mill, a roller mill and a jet mill. The ion exchange membrane according to [9], which is an inorganic particle produced by pulverization by at least one method.
[11] A step of preparing a coating liquid containing inorganic particles obtained by pulverizing an inorganic material and a binder;
Applying the coating solution to the surface of the ion exchange membrane;
Drying the coating solution applied to the surface of the ion exchange membrane to form a coating layer;
A method for producing an ion exchange membrane.
[12] An electrolytic cell comprising the ion exchange membrane according to any one of [1] to [10].

  ADVANTAGE OF THE INVENTION According to this invention, the influence on the electrolysis performance by the impurity in electrolyte solution is little, and the ion exchange membrane which exhibits the stable electrolysis performance can be provided.

It is a cross-sectional schematic diagram which shows one Embodiment of an ion exchange membrane. It is the schematic for demonstrating the aperture ratio of the reinforcing core material which comprises an ion exchange membrane. It is a cross-sectional schematic diagram which shows one Embodiment of an electrolytic vessel. It is a schematic diagram for demonstrating the method of forming the communicating hole of an ion exchange membrane.

  Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. The present invention is not limited to the following embodiment, and can be implemented with various modifications within the scope of the gist. In the drawings, positional relationships such as up, down, left and right are based on the positional relationships shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

[Ion exchange membrane]
The ion exchange membrane of this embodiment has a membrane body containing a fluorine-containing polymer having an ion exchange group, and a coating layer provided on at least one surface of the membrane body. Moreover, in this embodiment, a coating layer contains an inorganic particle and a binder, and the specific surface area of a coating layer is 0.1-10 m < ² > / g. The ion exchange membrane having such a structure has little influence on the electrolytic performance due to impurities generated during electrolysis or contained in the electrolytic solution, and can exhibit stable electrolytic performance.

  FIG. 1 is a schematic cross-sectional view showing an embodiment of an ion exchange membrane. The ion exchange membrane 1 of the present embodiment includes a membrane body 10 including a fluorine-containing polymer having an ion exchange group, and coating layers 11 a and 11 b formed on both surfaces of the membrane body 10.

In the ion exchange membrane 1, the membrane body 10 includes a sulfonic acid layer 3 having a sulfo group-derived ion exchange group (a group represented by —SO ₃ ^— , hereinafter also referred to as “sulfonic acid group”), and a carboxyl group-derived. And a carboxylic acid layer 2 having an ion exchange group (a group represented by —CO ₂ ^— , hereinafter also referred to as “carboxylic acid group”), and the strength and dimensional stability are enhanced by the reinforcing core material 4. . Since the ion exchange membrane 1 includes the sulfonic acid layer 3 and the carboxylic acid layer 2, it is suitably used as a cation exchange membrane.

  In addition, the ion exchange membrane of this embodiment may have only one of a sulfonic acid layer and a carboxylic acid layer. Moreover, the ion exchange membrane of this embodiment does not necessarily need to be reinforced with the reinforcing core material, and the arrangement state of the reinforcing core material is not limited to the example of FIG.

(Membrane body)
First, the membrane body 10 constituting the ion exchange membrane 1 of the present embodiment will be described.
The membrane body 10 has a function of selectively permeating cations and may contain a fluorine-containing polymer having an ion exchange group. Can be selected.

  The fluorine-containing polymer having an ion exchange group in the membrane body 10 can be obtained from, for example, a fluorine-containing polymer having an ion exchange group precursor that can become an ion exchange group by hydrolysis or the like. Specifically, for example, the main chain is made of a fluorinated hydrocarbon, has a group (ion exchange group precursor) that can be converted into an ion exchange group by hydrolysis or the like as a pendant side chain, and can be melt processed. After preparing the precursor of the membrane body 10 using a polymer (hereinafter sometimes referred to as “fluorinated polymer (a)”), the membrane is obtained by converting the ion exchange group precursor into an ion exchange group. The main body 10 can be obtained.

  The fluorine-containing polymer (a) includes, for example, at least one monomer selected from the following first group and at least one monomer selected from the following second group and / or the following third group: It can be produced by copolymerization. Moreover, it can also manufacture by the homopolymerization of the monomer of 1 type chosen from either the following 1st group, the following 2nd group, and the following 3rd group.

  Examples of the first group of monomers include vinyl fluoride compounds. Examples of the vinyl fluoride compound include vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, perfluoro (alkyl vinyl ether) and the like. In particular, when the ion exchange membrane of the present embodiment is used as a membrane for alkaline electrolysis, the vinyl fluoride compound is preferably a perfluoromonomer, from tetrafluoroethylene, hexafluoropropylene, and perfluoro (alkyl vinyl ether). A perfluoromonomer selected from the group consisting of

Examples of the second group of monomers include vinyl compounds having a functional group that can be converted into a carboxylic acid type ion exchange group (carboxylic acid group). Examples of the vinyl compound having a functional group that can be converted into a carboxylic acid group include monomers represented by CF ₂ ═CF (OCF ₂ CYF) _s —O (CZF) _t —COOR (here, , S represents an integer of 0 to 2, t represents an integer of 1 to 12, Y and Z each independently represent F or CF ₃ , and R represents a lower alkyl group. , For example, an alkyl group having 1 to 3 carbon atoms.).

Among _{them, CF 2 = CF (OCF 2} CYF) n -O (CF 2) a compound represented by m -COOR are preferred. Here, n represents an integer of 0 to 2, m represents an integer of 1 to 4, Y represents F or CF ₃ , and R represents CH ₃ , C ₂ H ₅ , or C ₃ H ₇ .

  In addition, when using the ion exchange membrane of this embodiment as a cation exchange membrane for alkaline electrolysis, it is preferable to use at least a perfluoro compound as a monomer, but the alkyl group of the ester group (see R above) is hydrolyzed. The alkyl group (R) may not be a perfluoroalkyl group in which all of the hydrogen atoms are substituted with fluorine atoms.

As the second group of monomers, monomers shown below are more preferable among the above.
_{CF 2 = CFOCF 2 -CF (CF} 3) OCF 2 COOCH 3,
CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ COOCH ₃ ,
_{CF 2 = CF [OCF 2 -CF} (CF 3)] 2 O (CF 2) 2 COOCH 3,
CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₃ COOCH ₃ ,
CF ₂ = CFO (CF ₂ ) ₂ COOCH ₃ ,
_{CF 2 = CFO (CF 2)} 3 COOCH 3.

Examples of the third group of monomers include vinyl compounds having a functional group that can be converted into a sulfone-type ion exchange group (sulfonic acid group). The vinyl compound having a functional group that can be converted to sulfonic acid groups, _e.g., CF 2 = monomer represented by _{CFO-X-CF 2 -SO 2} F are preferred (wherein, X is perfluoroalkylene group Represents.) Specific examples thereof include the monomers shown below.
CF ₂ = CFOCF ₂ CF ₂ SO ₂ F,
CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ SO ₂ F,
CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ CF ₂ SO ₂ F,
CF ₂ = CF (CF ₂ ) ₂ SO ₂ F,
CF ₂ = CFO [CF ₂ CF (CF ₃ ) O] ₂ CF ₂ CF ₂ SO ₂ F,
_{CF 2 = CFOCF 2 CF (CF} 2 OCF 3) OCF 2 CF 2 SO 2 F.

Among _{them, CF 2 = CFOCF 2 CF (} CF 3) OCF 2 CF 2 CF 2 SO 2 F, and _{CF 2 = CFOCF 2 CF (CF} 3) OCF 2 CF 2 SO 2 F is more preferred.

  Copolymers obtained from these monomers can be produced by polymerization methods developed for homopolymerization and copolymerization of fluorinated ethylene, in particular, general polymerization methods used for tetrafluoroethylene. . For example, in the non-aqueous method, an inert solvent such as perfluorohydrocarbon or chlorofluorocarbon is used, and in the presence of a radical polymerization initiator such as perfluorocarbon peroxide or azo compound, the temperature is 0 to 200 ° C., the pressure is 0. The polymerization reaction can be performed under conditions of 1 to 20 MPa.

  In the copolymerization, the type of monomer combination and the ratio thereof are not particularly limited, and are selected and determined depending on the type and amount of functional groups to be imparted to the resulting fluorinated polymer. For example, when a fluorine-containing polymer containing only a carboxylic acid group is used, at least one monomer may be selected from the first group and the second group and copolymerized. Further, when a fluorine-containing polymer containing only a sulfonic acid group is used, at least one monomer may be selected from each of the first group and third group monomers and copolymerized. Further, when a fluorine-containing polymer having a carboxylic acid group and a sulfonic acid group is used, at least one monomer is selected from the monomers of the first group, the second group, and the third group, respectively. What is necessary is just to superpose | polymerize. In this case, the desired fluorine-containing system can also be obtained by separately polymerizing the copolymer consisting of the first group and the second group and the copolymer consisting of the first group and the third group and mixing them later. A polymer can be obtained. Further, the mixing ratio of each monomer is not particularly limited, but when increasing the amount of the functional group per unit polymer, if the ratio of the monomer selected from the second group and the third group is increased. Good.

  The total ion exchange capacity of the fluorine-containing copolymer is not particularly limited, but is preferably 0.5 to 2.0 mg equivalent / g, and more preferably 0.6 to 1.5 mg equivalent / g. Here, the total ion exchange capacity refers to the equivalent of exchange groups per unit weight of the dry resin, and can be measured by neutralization titration or the like.

  In the membrane body 10 of the ion exchange membrane 1, a sulfonic acid layer 3 containing a fluorinated polymer having a sulfonic acid group and a carboxylic acid layer 2 containing a fluorinated polymer having a carboxylic acid group are laminated. Yes. By setting it as the film | membrane main body 10 of such a layer structure, the selective permeability of cations, such as a sodium ion, can be improved further.

  When the ion exchange membrane 1 is arranged in the electrolytic cell, it is usually arranged so that the sulfonic acid layer 3 is located on the anode side of the electrolytic cell and the carboxylic acid layer 2 is located on the cathode side of the electrolytic cell.

  The sulfonic acid layer 3 is preferably made of a material having low electric resistance, and the film thickness is preferably thicker than that of the carboxylic acid layer 2 from the viewpoint of film strength. The film thickness of the sulfonic acid layer 3 is preferably 2 to 25 times that of the carboxylic acid layer 2, and more preferably 3 to 15 times.

  It is preferable that the carboxylic acid layer 2 has a high anion exclusion property even if the film thickness is thin. The term “anion-exclusion” as used herein refers to a property that tends to prevent the penetration and permeation of anions into the ion exchange membrane 1. In order to increase the anion exclusion property, it is effective to arrange a carboxylic acid layer having a small ion exchange capacity with respect to the sulfonic acid layer.

Examples of the fluorine-containing polymer used for the sulfonic acid layer 3 include polymers obtained using CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ SO ₂ F as a third group monomer. Is preferred.

As the fluorine-containing polymer used for the carboxylic acid layer 2, for example, a polymer obtained using CF ₂ = CFOCF ₂ CF (CF ₂ ) O (CF ₂ ) ₂ COOCH ₃ as the second group of monomers Is preferred.

(Coating layer)
The ion exchange membrane of this embodiment has a coating layer on at least one surface of the membrane body. As shown in FIG. 1, in the ion exchange membrane 1, coating layers 11 a and 11 b are formed on both surfaces of the membrane body 10, respectively.

The coating layer contains inorganic particles and a binder, and the specific surface area of the coating layer is 0.1 to 10 m ² / g. Here, the specific surface area of the coating layer indicates the value of the index S calculated by the following measurement method. When the index S is low, the influence on the electrolytic performance due to impurities in the electrolytic solution is reduced. Preferably, the specific surface area (index S) of the coating layer is 0.1 to ⁵ m ² / g, more preferably 0.1 to ³ m ² / g.

A specific method for measuring the specific surface area index S is as follows.
The specific surface area index S can be determined as follows. Prepare an ion exchange membrane (A) coated with a coating layer and an ion exchange membrane (B) removed by rubbing the coating from the ion exchange membrane (A) with a sponge. I do.

  A scattering intensity distribution derived from the coating layer is obtained from the small-angle X-ray scattering measurement results of the ion exchange membrane (A) and the ion exchange membrane (B), and absolute intensity correction is performed on the obtained scattering intensity distribution.

At this time, the unit is converted to e ² / nm ³ . In the absolute intensity correction, the thickness calculated from the transmittance of the coating layer is used as the sample thickness. In the scattering intensity distribution I thus obtained, a value of T is obtained by fitting with I = 2πΔρ ² Tq ⁻⁴ to a region where I is proportional to q ⁻⁴ . Here, the difference in electron density (1 / nm ³ ) between the inorganic particles and the binder in the coating layer is used as Δρ. In the small-angle X-ray scattering measurement, the q range is set so that a region where I is proportional to q ⁻⁴ is obtained (q is the absolute value of the scattering vector and the unit is nm ⁻¹ ). The index S of the specific surface area can be obtained from the following equation using this T.
S = T / ρ × 1000

Here, ρ is the density (g / cm ³ ) of the inorganic substance. In the case where the coating layer has no voids and all of the inorganic substance is covered with the binder and the inorganic surface has a sharp interface, the index S is a specific interface area between the inorganic particles and the binder (m ² / g).

  The average particle size of the inorganic particles is more preferably 0.90 μm or more. When the average particle size of the inorganic particles is 0.90 μm or more, the durability against impurities is extremely improved. That is, in the present embodiment, a particularly remarkable effect can be obtained by increasing the average particle diameter of the inorganic particles and satisfying the above-mentioned value of the specific surface area. In order to satisfy such an average particle size and specific surface area, irregular inorganic particles, preferably inorganic particles obtained by pulverizing raw stones can be suitably used in this embodiment.

  The average particle size of the inorganic particles can be 2 μm or less. If the average particle size of the inorganic particles is 2 μm or less, the membrane can be prevented from being damaged by the inorganic particles. The average particle diameter of the inorganic particles is more preferably 0.90 to 1.2 μm. More preferably, it is 1-1.2 micrometers.

  Here, the average particle diameter can be measured by a particle size distribution meter (“SALD2200”, Shimadzu Corporation).

  The shape of the inorganic particles is preferably an irregular shape. Thereby, the index S of the specific surface area becomes smaller, and the resistance to impurities is further improved. In addition, the particle size distribution of the inorganic particles is preferably varied and is preferably broad.

  The inorganic particles may include at least one inorganic material selected from the group consisting of oxides of Group IV elements of the periodic table, nitrides of Group IV elements of the periodic table, and carbides of Group IV elements of the periodic table. preferable. More preferred are zirconium oxide particles from the viewpoint of durability.

  The inorganic particles are preferably inorganic particles produced by pulverizing the raw particles of the inorganic particles. Conventionally, inorganic particles are produced by melting and refining the raw particles of inorganic particles, and spherical particles having a uniform particle diameter are used as inorganic particles in the coating layer. On the other hand, in the present embodiment, it has been found that the influence of the impurities on the electrolysis performance can be reduced by setting the specific surface area within the above range, and in order to increase the surface area of the inorganic particles and reduce the specific surface area, Inorganic particles obtained by pulverization can be used in the coating layer.

  The pulverization method is not particularly limited, and examples thereof include a ball mill, a bead mill, a colloid mill, a conical mill, a disk mill, an edge mill, a milling mill, a hammer mill, a pellet mill, a VSI mill, a Willy mill, a roller mill, and a jet mill. Moreover, it is preferable to wash | clean after grinding | pulverization, and it is preferable as an washing | cleaning method at that time to carry out an acid treatment. Thereby, impurities such as iron adhering to the surface of the inorganic particles can be reduced.

  In this embodiment, the coating layer includes a binder. The binder is a component that forms a coating layer by holding inorganic particles on the surface of the ion exchange membrane. The binder preferably contains a fluorine-containing polymer from the viewpoint of resistance to an electrolytic solution or a product by electrolysis.

  The binder is more preferably a fluorine-containing polymer having a carboxylic acid group or a sulfonic acid group from the viewpoint of resistance to an electrolytic solution or a product by electrolysis and adhesion to the surface of an ion exchange membrane. preferable. When a coating layer is provided on a layer containing a fluorinated polymer having a sulfonic acid group (sulfonic acid layer), it is more preferable to use a fluorinated polymer having a sulfonic acid group as a binder for the coating layer. . Moreover, when providing a coating layer on the layer (carboxylic acid layer) containing the fluorine-containing polymer which has a carboxylic acid group, it is using the fluorine-containing polymer which has a carboxylic acid group as a binder of the said coating layer. Further preferred.

  In the coating layer, the content of inorganic particles is preferably 40 to 90% by mass, and more preferably 50 to 90% by mass. Moreover, it is preferable that it is 10-60 mass%, and, as for content of a binder, it is more preferable that it is 10-50 mass%.

The distribution density of the coating layer in the ion exchange membrane is preferably 0.05 to ² mg per cm ² . Moreover, when the ion exchange membrane has an uneven shape on the surface, the distribution density of the coating layer is preferably 0.5 to ² mg per 1 cm ² .

  It does not specifically limit as a method of forming a coating layer, A well-known method can be used. For example, the method of apply | coating the coating liquid which disperse | distributed the inorganic substance particle | grains in the solution containing binder by spray etc. is mentioned.

(Reinforced core material)
The ion exchange membrane of this embodiment preferably has a reinforced core material arranged inside the membrane body.

  The reinforcing core material is a member that reinforces the strength and dimensional stability of the ion exchange membrane. By arranging the reinforcing core material inside the membrane body, in particular, the expansion and contraction of the ion exchange membrane can be controlled within a desired range. Such an ion exchange membrane does not expand and contract more than necessary during electrolysis and can maintain excellent dimensional stability over a long period of time.

  The configuration of the reinforcing core material is not particularly limited. For example, the reinforcing core material may be formed by spinning a yarn called a reinforcing yarn. The reinforcing yarn here is a member constituting a reinforcing core material, which can impart desired dimensional stability and mechanical strength to the ion exchange membrane, and can exist stably in the ion exchange membrane. It means a thread. By using a reinforcing core material obtained by spinning such reinforcing yarns, it is possible to impart more excellent dimensional stability and mechanical strength to the ion exchange membrane.

  The material of the reinforcing core material and the reinforcing yarn used therefor is not particularly limited, but is preferably a material resistant to acids, alkalis, etc., and needs long-term heat resistance and chemical resistance. A fiber made of a polymer is preferred.

  Examples of the fluorine-containing polymer used for the reinforcing core material include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and tetrafluoroethylene-ethylene copolymer (ETFE). , Tetrafluoroethylene-hexafluoropropylene copolymer, trifluorochloroethylene-ethylene copolymer, and vinylidene fluoride polymer (PVDF). Among these, it is preferable to use a fiber made of polytetrafluoroethylene particularly from the viewpoint of heat resistance and chemical resistance.

  The yarn diameter of the reinforcing yarn used for the reinforcing core material is not particularly limited, but is preferably 20 to 300 denier, more preferably 50 to 250 denier. The weaving density (the number of driving per unit length) is preferably 5 to 50 / inch. The form of the reinforcing core material is not particularly limited, and for example, a woven cloth, a non-woven cloth, a knitted cloth or the like is used, but a woven cloth form is preferable. The thickness of the woven fabric is preferably 30 to 250 μm, more preferably 30 to 150 μm.

  As the woven fabric or knitted fabric, monofilaments, multifilaments or yarns thereof, slit yarns or the like can be used, and various weaving methods such as plain weaving, entangled weaving, knitting weaving, cord weaving, shasatsuka and the like can be used.

  The weaving method and arrangement of the reinforcing core material in the membrane body are not particularly limited, and can be suitably arranged in consideration of the size and shape of the ion exchange membrane, the physical properties desired for the ion exchange membrane, the usage environment, and the like. .

  For example, the reinforcing core material may be disposed along a predetermined direction of the membrane body, but from the viewpoint of dimensional stability, the reinforcing core material is disposed along a predetermined first direction, and the first It is preferable to arrange another reinforcing core material along a second direction that is substantially perpendicular to the direction. By disposing a plurality of reinforcing cores so as to be substantially perpendicular to the inside of the membrane body in the longitudinal direction, more excellent dimensional stability and mechanical strength can be imparted in multiple directions. For example, an arrangement in which a reinforcing core material (warp yarn) arranged along the longitudinal direction and a reinforcing core material (weft yarn) arranged along the transverse direction is woven on the surface of the membrane body is preferable. A plain weave woven by weaving up and down alternately with warps and wefts, or a twine weaving with wefts while twisting two warps, and weaving the same number of wefts into two or several warp yarns arranged in a line. It is more preferable to use a diagonal weave from the viewpoint of dimensional stability, mechanical strength and manufacturability.

  In particular, it is preferable that the reinforcing core material is disposed along both the MD direction (Machine Direction direction) and the TD direction (Transverse Direction direction) of the ion exchange membrane. That is, it is preferable that plain weaving is performed in the MD direction and the TD direction. Here, the MD direction refers to the direction (flow direction) in which the membrane body and various core materials (for example, reinforcing core material, reinforcing yarn, sacrificial yarn described later, etc.) are transported in the ion exchange membrane manufacturing process described later. The TD direction is a direction substantially perpendicular to the MD direction. And the yarn woven along the MD direction is called MD yarn, and the yarn woven along the TD direction is called TD yarn. Usually, an ion exchange membrane used for electrolysis has a rectangular shape, and the longitudinal direction is often the MD direction and the width direction is often the TD direction. By weaving the reinforcing core material that is MD yarn and the reinforcing core material that is TD yarn, it is possible to impart more excellent dimensional stability and mechanical strength in multiple directions.

  The arrangement interval of the reinforcing core material is not particularly limited, and can be suitably arranged in consideration of the physical properties desired for the cation exchange membrane and the use environment.

  The aperture ratio of the reinforcing core material is not particularly limited, and is preferably 30% or more, more preferably 50% or more and 90% or less. The aperture ratio is preferably 30% or more from the viewpoint of the electrochemical properties of the ion exchange membrane, and preferably 90% or less from the viewpoint of the mechanical strength of the ion exchange membrane.

  The aperture ratio of the reinforcing core is the total surface through which substances such as ions (electrolyte and cations (for example, sodium ions)) such as ions in the area (A) of either surface of the membrane body can pass. The ratio (B / A) of area (B). The total surface area (B) through which substances such as ions can pass is the total area of the ion exchange membrane where cations, electrolytes, etc. are not blocked by the reinforcing core material contained in the ion exchange membrane. it can.

  FIG. 2 is a schematic view for explaining the aperture ratio of the reinforcing core material constituting the ion exchange membrane. FIG. 2 is an enlarged view of a part of the ion exchange membrane, showing only the arrangement of the reinforcing cores 21 and 22 in the region, and the other members are not shown.

From the area (A) of the region including the area of the reinforcing core material, which is surrounded by the reinforcing core material 21 arranged along the vertical direction and the reinforcing core material 22 arranged in the horizontal direction, the reinforcing core material By subtracting the total area (C), the total area (B) of the region through which substances such as ions in the area (A) of the region described above can pass can be obtained. That is, the aperture ratio can be obtained by the following formula (I).
Opening ratio = (B) / (A) = ((A) − (C)) / (A) (I)

  Among the reinforcing core materials, a particularly preferable form is a tape yarn containing PTFE or a highly oriented monofilament from the viewpoint of chemical resistance and heat resistance. Specifically, a tape yarn obtained by slitting a high-strength porous sheet made of PTFE into a tape shape, or a highly oriented monofilament made of PTFE of 50 to 300 denier, and a weave density of 10 to 50 / More preferably, the reinforcing core material is a plain weave that is inches, and has a thickness in the range of 50 to 100 μm. The aperture ratio of the ion exchange membrane containing such a reinforcing core is more preferably 60% or more.

  Examples of the shape of the reinforcing yarn include round yarn and tape-like yarn. A tape-like thread is preferable.

(Communication hole)
The ion exchange membrane of this embodiment preferably has a communication hole inside the membrane body.

  The communication hole refers to a hole that can serve as a flow path for cations generated during electrolysis or an electrolytic solution. The communication hole is a tubular hole formed inside the membrane body, and is formed by elution of a sacrificial core material (or sacrificial yarn) described later. The shape and diameter of the communication hole can be controlled by selecting the shape and diameter of the sacrificial core material (sacrificial yarn).

  By forming the communication holes in the ion exchange membrane, it is possible to ensure the mobility of alkali ions generated during electrolysis and the electrolytic solution. The shape of the communication hole is not particularly limited, but according to the manufacturing method described later, the shape of the sacrificial core material used for forming the communication hole can be obtained.

  In the present embodiment, the communication hole is preferably formed so as to alternately pass through the anode side (sulfonic acid layer side) and the cathode side (carboxylic acid layer side) of the reinforcing core material. With this structure, in the portion where the communication hole is formed on the cathode side of the reinforced core material, the cation (for example, sodium ion) transported through the electrolyte filled in the communication hole is reinforced core material. It can also flow to the cathode side. As a result, since the cation flow is not shielded, the electric resistance of the ion exchange membrane can be further reduced.

  The communication holes may be formed along only one predetermined direction of the membrane body constituting the ion exchange membrane of the present embodiment, but from the viewpoint of exhibiting more stable electrolysis performance, the longitudinal direction of the membrane body It is preferable that it is formed in both the horizontal direction and the horizontal direction.

〔Production method〕
As a suitable manufacturing method of the ion exchange membrane which concerns on this embodiment, the method which has the following (1) process-(6) processes is mentioned.
(1) Process: The process of manufacturing the fluorine-containing polymer which has an ion exchange group or the ion exchange group precursor which can become an ion exchange group by hydrolysis.
(2) Step: If necessary, by interweaving at least a plurality of reinforcing core materials and a sacrificial yarn having a property of dissolving in acid or alkali and forming a communicating hole, between adjacent reinforcing core materials A step of obtaining a reinforcing material having a sacrificial yarn disposed therebetween.
(3) Step: Step of forming a film of the fluorine-containing polymer having an ion exchange group or an ion exchange group precursor that can be converted into an ion exchange group by hydrolysis.
(4) Step: A step of embedding the reinforcing material in the film as necessary to obtain a membrane body in which the reinforcing material is disposed.
(5) Step: A step of hydrolyzing the membrane body obtained in the step (4) (hydrolysis step).
(6) Step: A step of providing a coating layer on the film body obtained in the step (5) (coating step).

  The manufacturing method of the ion exchange membrane of this embodiment is mainly characterized in that specific inorganic particles are used in the (6) coating step. Hereinafter, each process is explained in full detail.

(1) Step: Step of producing a fluorine-containing polymer In the step (1), a fluorine-containing polymer is produced using the raw material monomers described in the first group to the third group. In order to control the ion exchange capacity of the fluorine-containing polymer, the mixing ratio of raw material monomers may be adjusted in the production of the fluorine-containing polymer forming each layer.

(2) Process: Manufacturing process of a reinforcing material A reinforcing material is a woven fabric or the like woven with reinforcing yarn. The reinforcing core material is formed by embedding the reinforcing material in the film. When an ion exchange membrane having communication holes is used, the sacrificial yarn is also woven into the reinforcing material. In this case, the blended amount of the sacrificial yarn is preferably 10 to 80% by mass, more preferably 30 to 70% by mass, based on the entire reinforcing material. By weaving the sacrificial yarn, misalignment of the reinforcing core material can be prevented.

  The sacrificial yarn has solubility in the film production process or in an electrolytic environment, and rayon, polyethylene terephthalate (PET), cellulose, polyamide, or the like is used. Polyvinyl alcohol having a thickness of 20 to 50 denier and made of monofilament or multifilament is also preferable.

  In the step (2), by adjusting the arrangement of the reinforcing core material and the sacrificial yarn, the aperture ratio, the arrangement of the communication holes, and the like can be controlled.

(3) Step: Filming step In the (3) step, the fluorine-containing polymer obtained in the step (1) is formed into a film using an extruder. The film may have a single layer structure, as described above, may have a two-layer structure of a sulfonic acid layer and a carboxylic acid layer, or may have a multilayer structure of three or more layers.

Examples of the method for forming a film include the following.
A method in which a fluorine-containing polymer having a carboxylic acid group and a fluorine-containing polymer having a sulfonic acid group are separately formed into films.
A method of forming a composite film by coextrusion of a fluorinated polymer having a carboxylic acid group and a fluorinated polymer having a sulfonic acid group.

  A plurality of films may be used. Also, co-extrusion of different types of films is preferable because it contributes to increasing the adhesive strength at the interface.

(4) Step: Step of obtaining the membrane body In the step (4), in the step (2), the reinforcing material obtained in the step (2) is embedded in the film obtained in the step (3), so that the membrane body in which the reinforcing material is present is obtained. obtain.

  As a preferable method for forming the film body, (i) a fluorine-containing polymer having a carboxylic acid group precursor (for example, a carboxylic acid ester functional group) located on the cathode side (hereinafter, a layer formed thereof is referred to as a first layer). And a fluorine-containing polymer having a sulfonic acid group precursor (for example, a sulfonyl fluoride functional group) (hereinafter, a layer composed of the fluorine-containing polymer is referred to as a second layer) by coextrusion, and a heating source and Using a vacuum source, a reinforcing material and a second layer / first layer composite film are laminated in this order on a flat plate or drum having a large number of pores on the surface through a heat-resistant release paper having air permeability. And (ii) including a sulfonic acid group precursor separately from the second layer / first layer composite film, while removing the air between the layers by reducing the pressure at a temperature at which each polymer melts. Fluorine polymerization (Third layer) is made into a single film in advance, using a heat source and a vacuum source, if necessary, through a flat plate having a large number of pores on the surface or a heat-resistant release paper having air permeability on the drum. Then, the third layer film, the reinforcing core material, and the composite film composed of the second layer / first layer are laminated in this order, and are integrated while removing air between the layers by reducing the pressure at a temperature at which each polymer melts. A method is mentioned.

  Here, co-extrusion of the first layer and the second layer contributes to increasing the adhesive strength at the interface.

  Moreover, the method of integrating under reduced pressure has the characteristic that the thickness of the 3rd layer on a reinforcing material becomes large compared with the press-pressing method. Furthermore, since the reinforcing material is fixed to the inner surface of the membrane main body, it has a performance that can sufficiently maintain the mechanical strength of the ion exchange membrane.

  In addition, the variation of the lamination | stacking demonstrated here is an example, it considers the layer structure of a desired film | membrane main body, a physical property, etc., and after selecting a suitable lamination pattern (for example, combination of each layer etc.), it is coextrusion. can do.

  For the purpose of further improving the electrical performance of the ion exchange membrane, a second polymer comprising a fluorine-containing polymer having both a carboxylic acid group precursor and a sulfonic acid group precursor between the first layer and the second layer. It is also possible to further interpose four layers, or to use a fourth layer made of a fluorine-containing polymer having both a carboxylic acid group precursor and a sulfonic acid group precursor instead of the second layer.

  The method for forming the fourth layer may be a method in which a fluorine-containing polymer having a carboxylic acid group precursor and a fluorine-containing polymer having a sulfonic acid group precursor are separately produced and then mixed. A method using a copolymer of a monomer having a group precursor and a monomer having a sulfonic acid group precursor may also be used.

  When the fourth layer is configured as an ion exchange membrane, a coextruded film of the first layer and the fourth layer is formed, and the third layer and the second layer are separately formed into a film, It may be laminated by a method, or three layers of the first layer / fourth layer / second layer may be coextruded at a time to form a film.

  In this case, the direction in which the extruded film flows is the MD direction. In this way, a membrane body containing a fluorine-containing polymer having an ion exchange group can be formed on the reinforcing material.

  Moreover, it is preferable that the ion exchange membrane which concerns on this embodiment has the protruding part which consists of a fluoropolymer which has a sulfonic acid group, ie, a convex part, on the surface side which consists of a sulfonic acid layer. The method for forming such a convex portion is not particularly limited, and a known method for forming the convex portion on the resin surface can be employed. Specifically, for example, a method of embossing the surface of the film main body can be mentioned. For example, when the composite film and the reinforcing material are integrated with each other, the above-described convex portions can be formed by using a release paper that has been embossed in advance. When forming a convex part by embossing, control of the height and arrangement density of a convex part can be performed by controlling the emboss shape (shape of release paper) to transfer.

(5) Hydrolysis step In the step (5), the membrane body obtained in the step (4) is hydrolyzed to convert the ion exchange group precursor into an ion exchange group (hydrolysis step).

  In the step (5), elution holes can be formed in the membrane body by dissolving and removing the sacrificial yarn contained in the membrane body with acid or alkali. The sacrificial yarn may be left in the communication hole without being completely dissolved and removed. Further, the sacrificial yarn remaining in the communication hole may be dissolved and removed by the electrolytic solution when the ion exchange membrane is subjected to electrolysis.

  The sacrificial yarn is soluble in acid or alkali in the ion exchange membrane manufacturing process or in an electrolytic environment, and the sacrificial yarn is eluted to form a communication hole at the site.

  The step (5) can be performed by immersing the membrane body obtained in the step (4) in a hydrolysis solution containing an acid or an alkali. As the hydrolysis solution, for example, a mixed solution containing KOH and DMSO (dimethylsulfoxide) can be used.

  The mixed solution preferably contains 2.5 to 4.0 N of KOH and 25 to 35% by mass of DMSO.

  The hydrolysis temperature is preferably 70 to 100 ° C. The higher the temperature, the greater the apparent thickness. More preferably, it is 85-100 degreeC.

  The hydrolysis time is preferably 10 to 120 minutes. The longer the time, the thicker the apparent thickness. More preferably, it is 20 to 120 minutes.

  Here, the step of forming the communication hole by eluting the sacrificial yarn will be described in more detail. FIGS. 4A and 4B are schematic views for explaining a method of forming the communication hole of the ion exchange membrane in the present embodiment.

  4 (a) and 4 (b), only the communication hole 504 formed by the reinforcing yarn 52, the sacrificial yarn 504a, and the sacrificial yarn 504a is illustrated, and other members such as the membrane body are not illustrated. ing.

  First, the reinforcing yarn 52 that forms the reinforcing core material in the ion exchange membrane and the sacrificial yarn 504a for forming the communication hole 504 in the ion exchange membrane are used as a braided reinforcing material. Then, the communication hole 504 is formed by the elution of the sacrificial yarn 504a in the step (5).

  According to the above method, it is simple because the method of weaving the reinforcing yarn 52 and the sacrificial yarn 504a may be adjusted in accordance with the arrangement of the reinforcing core material and the communication hole in the membrane body of the cation exchange membrane. .

  FIG. 4A illustrates a plain weave reinforcing material in which reinforcing yarns 52 and sacrificial yarns 504a are woven in both the vertical and horizontal directions on the paper surface. However, the reinforcing yarns 52 in the reinforcing material are used as necessary. And the arrangement of the sacrificial yarn 504a can be changed.

(6) Coating step In the step (6), a coating solution containing inorganic particles obtained by crushing rough stones and a binder is prepared, and the coating solution is applied to the surface of the ion exchange membrane obtained in the step (5). And by drying, a coating layer can be formed.

As a binder, a fluorine-containing polymer having an ion exchange group precursor is hydrolyzed with an aqueous solution containing dimethyl sulfoxide (DMSO) and potassium hydroxide (KOH), and then immersed in hydrochloric acid to form a pair of ion exchange groups. A binder in which ions are substituted with H ⁺ (for example, a fluorine-containing polymer having a carboxyl group or a sulfo group) is preferable. This is preferable because it is easy to dissolve in water or ethanol described later.

  This binder is dissolved in a mixed solution of water and ethanol. In addition, the preferable volume ratio of water and ethanol is 10: 1 to 1:10, more preferably 5: 1 to 1: 5, and still more preferably 2: 1 to 1: 2. The inorganic particles are dispersed by a ball mill in the solution thus obtained to obtain a coating solution. At this time, the average particle diameter and the like of the particles can be adjusted by adjusting the time and the rotational speed at the time of dispersion. In addition, the preferable compounding quantity of an inorganic particle and a binder is as above-mentioned.

  The concentration of the inorganic particles and the binder in the coating solution is not particularly limited, but a thin coating solution is preferable. As a result, it is possible to uniformly coat the surface of the ion exchange membrane.

  Further, when dispersing the inorganic particles, a surfactant may be added to the dispersion. As the surfactant, a nonionic surfactant surfactant is preferable, and examples thereof include NOF Corporation HS-210, NS-210, P-210, E-212, and the like.

  An ion exchange membrane is obtained by apply | coating the obtained coating liquid on the surface of an ion exchange membrane by spray application or roll coating.

[Electrolysis tank]
The ion exchange membrane of this embodiment can be used as an electrolytic cell using this. FIG. 3 is a schematic view of an embodiment of the electrolytic cell according to the present embodiment.

  The electrolytic cell 100 of the present embodiment includes at least the anode 200, the cathode 300, and the cation exchange membrane 1 of the present embodiment disposed between the anode 200 and the cathode 300. Here, the electrolytic cell 100 provided with the cation exchange membrane 1 described above is described as an example. However, the present invention is not limited to this, and various configurations are modified within the scope of the effect of the present embodiment. can do.

  Although this electrolytic cell 100 can be used for various electrolysis, the case where it is used for electrolysis of an aqueous alkali chloride solution will be described below as a representative example.

  Electrolysis conditions are not particularly limited, and can be performed under known conditions. For example, an alkaline chloride aqueous solution of 2.5 to 5.5 N (N) is supplied to the anode chamber, and water or a diluted alkaline hydroxide aqueous solution is supplied to the cathode chamber, and electrolysis is performed with a direct current.

  The configuration of the electrolytic cell according to this embodiment is not particularly limited, and may be, for example, a monopolar type or a bipolar type. The material constituting the electrolytic cell 100 is not particularly limited. For example, the material of the anode chamber is preferably titanium or the like resistant to alkali chloride and chlorine, and the material of the cathode chamber is alkali hydroxide or hydrogen. Nickel or the like having resistance is preferable. The electrode may be arranged with an appropriate interval between the cation exchange membrane 1 and the anode 200, but there is no problem even if the anode 200 and the cation exchange membrane 1 are arranged in contact with each other. Can be used without In addition, the cathode is generally arranged at an appropriate distance from the cation exchange membrane, but even if it is a contact type electrolytic cell (zero gap type electrolytic cell) without this distance, it can be used without any problems. it can.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment.

  Hereinafter, the present invention will be described in detail by way of examples. In addition, this invention is not limited to a following example. In addition, the following units shall be based on a mass reference | standard unless there is particular notice.

[Impurity test]
When electrolysis was performed using the obtained ion exchange membrane, impurities were added to 5N (normality) salt water supplied as an electrolytic solution, and the change in performance as a cation exchange membrane was measured. As an electrolytic cell used for electrolysis, an ion exchange membrane is disposed between an anode and a cathode, and four electrolytic cells of a type (forced circulation type) in which an electrolytic solution is forcibly circulated are arranged in series. Was used.

  In the finite gap electrolysis evaluation, the distance between the anode and the cathode in the electrolytic cell was 1.5 mm. As the cathode, an electrode in which nickel expanded metal was applied as a catalyst to an expanded metal of nickel was used. As the anode, an electrode in which ruthenium, iridium and titanium were applied as catalysts to titanium expanded metal was used.

  In the zero gap electrolysis evaluation, both the cathode and the anode were in contact with the ion exchange membrane, and an electrode in which Ru and Ce were applied as a catalyst to a nickel mesh was used as the cathode. As the anode, an electrode in which ruthenium, iridium and titanium were applied as catalysts to titanium expanded metal was used.

Salt water was supplied to the anode side so as to maintain a concentration of 205 g / L, and water was supplied to the cathode side while maintaining the caustic soda concentration at 32% by mass. Then, using salt water containing 10 ppm of I and 0.03 ppm of Ba as impurities, the temperature of the salt water is set to 90 ° C., and the liquid pressure on the cathode side of the electrolytic cell is 6 kA / m ^2. Electrolysis was performed for 9 days under a condition 5.3 kPa higher than the fluid pressure on the anode side. Then, the increase / decrease in the value of the current efficiency on the ninth day after electrolysis was measured from the value of the current efficiency on the first day of electrolysis, and obtained as the rate of change per day. The current efficiency is the ratio of the amount of generated caustic soda to the flowed current. When the flow of current causes impurity ions and hydroxide ions to move through the cation exchange membrane instead of sodium ions, Efficiency is reduced.

  The current efficiency can be obtained by dividing the number of moles of caustic soda generated in a certain time by the number of moles of electrons of the current flowing during that time. The number of moles of caustic soda can be determined by collecting caustic soda generated by electrolysis in a plastic tank and measuring its mass.

[Example 1]
A reinforcing core material made of polytetrafluoroethylene (PTFE) and twisted at 900 times / m on a 100 denier tape yarn was used to form a yarn (hereinafter referred to as PTFE yarn). As a sacrificial yarn for warp, a yarn obtained by twisting 200 denier / m of 35 denier, 8-filament polyethylene terephthalate (PET) was used (hereinafter referred to as PET yarn). As a weft sacrificial yarn, a yarn of 35 denier, 8-filament polyethylene terephthalate (PET) twisted 200 times / m was used. First, plain weaving was performed so that 24 PTFE yarns / inch and two sacrificial yarns were arranged between adjacent PTFE yarns to obtain a woven fabric having a thickness of 100 μm.

Next, a polymer (A1) of a dry resin, which is a copolymer of CF ₂ = CF ₂ and CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ COOCH ₃ and has an ion exchange capacity of 0.84 mg equivalent / g , CF ₂ = CF ₂ and CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ SO ₂ F, a polymer (B1) of a dry resin having an ion exchange capacity of 0.98 mg equivalent / g Got ready. Using these polymers (A1) and (B1), a co-extrusion T die method is used to obtain a two-layer film X having a polymer (A1) layer thickness of 18 μm and a polymer (B1) layer thickness of 74 μm. It was. The ion exchange capacity of each polymer indicates the ion exchange capacity when the ion exchange group precursor of each polymer is hydrolyzed and converted to an ion exchange group.

Separately, a polymer of a dry resin (B2) having an ion exchange capacity of 1.05 mg equivalent / g, which is a copolymer of CF ₂ = CF ₂ and CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ SO ₂ F. ) Was prepared. This polymer was monolayer extruded to obtain a film Y of 20 μm.

  Subsequently, a release paper, a film Y, a reinforcing material and a film X, which are pre-embossed, are laminated in this order on a drum having a heating source and a vacuum source inside and having fine holes on the surface, and a drum temperature of 225 ° C., After heating and depressurizing for 2 minutes under the condition of a degree of vacuum of 0.067 MPa, the release paper was removed to obtain a composite film having an uneven shape. The obtained composite membrane was saponified by immersing in an aqueous solution containing 30% by mass of dimethyl sulfoxide (DMSO) and 15% by mass of potassium hydroxide (KOH) at 90 ° C., and then 0.5N of 90 ° C. It was immersed in NaOH for 1 hour to replace the ion attached to the ion exchange group with Na, followed by washing with water. Furthermore, it dried at 60 degreeC.

Further, a dry resin polymer (B3) which is a copolymer of CF ₂ ═CF ₂ and CF ₂ ═CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ SO ₂ F and has an ion exchange capacity of 1.05 mg equivalent / g Was hydrolyzed and acidified with hydrochloric acid. Zirconium oxide particles having a primary particle size of 1.15 μm are dissolved in a solution obtained by dissolving the acid type polymer (B3) in a 50/50 (mass ratio) mixture of water and ethanol at a ratio of 5 mass%. It added so that mass ratio of (B3) and a zirconium oxide particle might be 20/80. Thereafter, the suspension was obtained by dispersing with a ball mill until the average particle diameter of the zirconium oxide particles in the suspension became 0.94 μm. The zirconium oxide particles used were crushed raw stones.

  This suspension was applied to both surfaces of the ion exchange membrane by a spray method and dried to obtain an ion exchange membrane having a coating layer containing polymer (B3) and zirconium oxide particles.

When the coating layer after drying was measured by fluorescent X-ray measurement, the coating density was 0.5 mg per cm ² . Moreover, the specific surface area of the coating layer calculated | required from the scattering of a SAXS measurement was 2.2 m < ² > / g.

  After the ion exchange membrane having the dried coating layer was wetted with 2% by weight of sodium bicarbonate, the impurity resistance was measured by finite gap electrolysis using this ion exchange membrane. As a result, the current efficiency was reduced by 0.23%. / Day and high impurity durability. The results are shown in Table 1.

[Example 2]
Example 1 is the same as Example 1 except that the dispersion in the ball mill was adjusted so that the average particle diameter in the suspension of zirconium oxide particles was 1.12 μm to obtain a suspension. Similarly, an ion exchange membrane was produced.

When the coating layer after drying the ion exchange membrane was measured by fluorescent X-ray measurement, the coating density was 0.5 mg per cm ² . Moreover, the specific surface area of the coating layer calculated | required from scattering of SAXS measurement was 2.2 m < ² > / g.

  After the ion exchange membrane having a dried coating layer was moistened with 2% by weight of sodium bicarbonate, the impurity resistance was measured by finite gap electrolysis using this ion exchange membrane. As a result, the current efficiency was reduced by 0.27%. / Day and high impurity durability. The results are shown in Table 1.

[Example 3]
In Example 1, the zirconium oxide particles are changed to those having a primary particle size of 2.50 μm, and the dispersion in the ball mill is adjusted so that the average particle size in the suspension of zirconium oxide particles becomes 1.80 μm. An ion exchange membrane was prepared in the same manner as in Example 1 except that the suspension was obtained by dispersing the solution up to.

When the coating layer after drying the ion exchange membrane was measured by fluorescent X-ray measurement, the coating density was 0.5 mg per cm ² . Moreover, the specific surface area of the coating layer calculated | required from scattering of SAXS measurement was 1.8 m < ² > / g.

  After the ion exchange membrane having the dried coating layer was wetted with 2% by weight of sodium bicarbonate, the impurity resistance was measured by finite gap electrolysis using this ion exchange membrane. As a result, the decrease in current efficiency was 0.24%. / Day and high impurity durability. The results are shown in Table 1.

[Example 4]
Example 1 is the same as Example 1 except that the dispersion in the ball mill was adjusted and dispersed until the average particle size in the suspension of zirconium oxide particles became 0.89 μm. Similarly, an ion exchange membrane was produced.

When the coating layer after drying the ion exchange membrane was measured by fluorescent X-ray measurement, the coating density was 0.5 mg per cm ² . Moreover, the specific surface area of the coating layer calculated | required from the scattering of a SAXS measurement was 2.3 m < ² > / g.

  After wetting an ion exchange membrane having a dried coating layer with 2% by weight of sodium bicarbonate, the impurity resistance was measured by finite gap electrolysis using this ion exchange membrane. As a result, the decrease in current efficiency was 0.50%. / Day and high impurity durability. The results are shown in Table 1.

[Comparative Example 1]
In Example 1, the zirconium oxide particles were changed to those having a primary particle diameter of 0.04 μm, and the dispersion in the ball mill was adjusted until the average particle diameter in the zirconium oxide suspension became 1.64 μm. An ion exchange membrane was prepared in the same manner as in Example 1 except that a suspension was obtained by dispersion. The zirconium oxide particles used in Comparative Example 1 are particles produced by melting. The average particle size is considered to be the secondary particle size of the zirconium oxide particles.

When the coating layer after drying the ion exchange membrane was measured by fluorescent X-ray measurement, the coating density was 0.5 mg per cm ² . Moreover, the specific surface area of the coating layer calculated | required from the scattering of a SAXS measurement was 13.3 m < ² > / g. In addition, as observed by an electron microscope, the zirconium oxide particles having a primary particle size of 0.04 μm at the time of blending had a primary particle size of about 0.04 μm even in the coating layer.

  After the ion exchange membrane having a dried coating layer was moistened with 2% by weight of sodium bicarbonate, impurity resistance was measured by finite gap electrolysis using this cation exchange membrane. % / Day and strongly affected by impurities. The results are shown in Table 1.

  Since Comparative Example 1 is an inorganic particle obtained by melting, the index S of the specific surface area is high. In Example 3, which has an average particle diameter comparable to that of Comparative Example 1, the specific surface area index S is lower than that of Comparative Example 1, and the impurity resistance is high. From the above results, it can be seen that high impurity resistance can be achieved when the specific surface area index S is within the numerical range of the present invention.

  In addition, when Examples 1-3 are compared with Example 4, in Examples 1-3, the average particle diameter of inorganic particles is 0.90 μm or more, whereas in Example 4, the average particle diameter of inorganic particles is Is less than 0.90 μm. Therefore, compared with Example 4, Examples 1-3 have a result with higher impurity tolerance.

[Example 5]
As the reinforcing core material, a 90 denier monofilament made of polytetrafluoroethylene (PTFE) was used (hereinafter referred to as PTFE yarn). As the sacrificial yarn, a 40 denier, 6-filament polyethylene terephthalate (PET) twisted at 200 times / m was used (hereinafter referred to as PET yarn). First, plain weaving was performed so that 24 PTFE yarns / inch and two sacrificial yarns were arranged between adjacent PTFE yarns to obtain a woven fabric having a thickness of 100 μm.

Next, a polymer (A2) of a dry resin, which is a copolymer of CF ₂ = CF ₂ and CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ COOCH ₃ and has an ion exchange capacity of 0.87 mg equivalent / g , CF ₂ = CF ₂ and CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ SO ₂ F, a polymer (B4) of a dry resin having an ion exchange capacity of 1.03 mg equivalent / g Got ready. Using these polymers (A2) and (B4), a co-extrusion T die method is used to obtain a two-layer film X having a polymer (A2) layer thickness of 18 μm and a polymer (B4) layer thickness of 74 μm. It was.

  Subsequently, a release paper, a reinforcing material and a film X, which were previously embossed, were laminated in this order on a drum having a heating source and a vacuum source inside and having fine holes on the surface. After heating and depressurizing for 2 minutes under the condition of 0.067 MPa, the release paper was removed to obtain a composite film having an uneven shape. The obtained composite membrane was saponified by immersing in an aqueous solution containing 30 wt% of dimethyl sulfoxide (DMSO) and 15 wt% of potassium hydroxide (KOH) at 90 ° C for 1 hour, and then added to 0.5N NaOH at 90 ° C. After immersing for 1 hour, ions with ion exchange groups were replaced with Na, followed by washing with water. Furthermore, it dried at 60 degreeC.

A copolymer of CF ₂ ═CF ₂ and CF ₂ ═CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ SO ₂ F is used to hydrolyze a dry resin polymer (B5) having an ion exchange capacity of 1.05 mg equivalent / g. After decomposition, it was acidified with hydrochloric acid. Zirconium oxide particles having a primary particle size of 1.25 μm were dissolved in a solution obtained by dissolving 5% by mass of this acid-type polymer (B5) in a 50/50 (mass ratio) mixture of water and ethanol, and the polymer (B5). The zirconium oxide particles were added so that the weight ratio thereof was 50/50. Then, the suspension was obtained by dispersing with a ball mill until the average particle diameter in the suspension of zirconium oxide particles became 1.07 μm.

  This suspension was applied to both surfaces of the ion exchange membrane by a spray method and dried to obtain an ion exchange membrane having a coating layer containing the polymer (B5) and zirconium oxide particles.

When the coating layer after drying was measured by fluorescent X-ray measurement, the coating density was 0.5 mg per cm ² . Moreover, the specific surface area of the coating layer calculated | required from the scattering of a SAXS measurement was 0.6 m < ² > / g.

  After the ion exchange membrane having the dried coating layer was wetted with 2% by weight of sodium bicarbonate, the impurity resistance was measured by zero gap electrolysis using this ion exchange membrane. As a result, the reduction in current efficiency was 0.23% / High impurity durability with day. The results are shown in Table 2.

[Example 6]
In Example 5, the mass ratio of the polymer (B5) and zirconium oxide particles was changed to 40/60, and the suspension was dispersed by a ball mill until the average particle size in the suspension of zirconium oxide particles was 1.11 μm. An ion exchange membrane was prepared in the same manner as in Example 5 except that a turbid liquid was obtained.

When the coating layer after drying the ion exchange membrane was measured by fluorescent X-ray measurement, the coating density was 0.5 mg per cm ² . Moreover, the specific surface area of the coating layer calculated | required from the scattering of a SAXS measurement was 1.5 m < ² > / g.

  After the ion exchange membrane having the dried coating layer was wetted with 2% by weight of sodium bicarbonate, the impurity resistance was measured by zero gap electrolysis using this ion exchange membrane. As a result, the decrease in current efficiency was 0.14% / High impurity durability with day. The results are shown in Table 2.

[Example 7]
In Example 5, the mass ratio of the polymer (B5) and zirconium oxide particles was changed to 30/70, and the suspension was dispersed by a ball mill until the average particle size in the suspension of zirconium oxide particles was 1.10 μm. An ion exchange membrane was prepared in the same manner as in Example 5 except that a turbid liquid was obtained.

When the coating layer after drying the ion exchange membrane was measured by fluorescent X-ray measurement, the coating density was 0.5 mg per cm ² . Moreover, the specific surface area of the coating layer calculated | required from scattering of a SAXS measurement was 1.3 m < ² > / g.

  After the ion exchange membrane having the dried coating layer was moistened with 2% by weight of sodium bicarbonate, the impurity resistance was measured by zero gap electrolysis using this ion exchange membrane. As a result, the decrease in current efficiency was 0.34% / High impurity durability with day. The results are shown in Table 2.

  The ion exchange membrane of the present invention can be suitably used as a cation exchange membrane used for alkali chloride electrolysis or the like.

  DESCRIPTION OF SYMBOLS 1 ... Ion exchange membrane, 2 ... Carboxylic acid layer, 3 ... Sulphonic acid layer, 4 ... Reinforcement core material, 10 ... Membrane body, 11a, 11b ... Coating layer, 21, 22 ... Reinforcement core material, 100 ... Electrolytic cell, 200 ... Anode, 300 ... Cathode, 52 ... Reinforcement yarn, 504a ... Sacrificial yarn, 504 ... Communication hole 504.

Claims (10)

An ion exchange membrane having a membrane body containing a fluorine-containing polymer having an ion exchange group, and a coating layer provided on at least one surface of the membrane body,
The coating layer includes inorganic particles and a binder,
The inorganic particles are pulverized inorganic substance,
The average particle size of the inorganic particles is 0.90 to 2 μm,
The ion exchange membrane whose specific surface area of the said coating layer is 0.1-10 m < ² > / g.   Particles containing at least one inorganic substance selected from the group consisting of oxides of group IV elements of periodic table, nitrides of group IV elements of periodic table, and carbides of group IV elements of periodic table The ion exchange membrane according to claim 1, wherein   The ion exchange membrane according to claim 1 or 2, wherein the inorganic particles are zirconium oxide particles.   The ion exchange membrane according to any one of claims 1 to 3, wherein the binder comprises a fluorine-containing polymer.   5. The ion exchange membrane according to claim 1, wherein the coating layer contains 40 to 90% by mass of the inorganic particles and 10 to 60% by mass of the binder.   The ion exchange membrane according to any one of claims 1 to 5, wherein the binder comprises a fluorine-containing polymer having an ion exchange group derived from a carboxyl group or a sulfo group.   The ion exchange membrane according to any one of claims 1 to 6, wherein the inorganic particles have an irregular shape. A step of preparing a coating liquid containing inorganic particles having an average particle diameter of 0.90 to 2 μm obtained by pulverizing the inorganic substance and a binder;
Applying the coating solution to the surface of the ion exchange membrane;
Drying the coating solution applied to the surface of the ion exchange membrane to form a coating layer having a specific surface area of 0.1 to 10 m ² / g;
A method for producing an ion exchange membrane.   The inorganic particles are at least selected from the group consisting of a ball mill, a bead mill, a colloid mill, a conical mill, a disk mill, an edge mill, a milling mill, a hammer mill, a pellet mill, a VSI mill, a Willy mill, a roller mill, and a jet mill. The manufacturing method of Claim 8 which is the inorganic substance particle obtained by grind | pulverizing by one method. An electrolytic cell comprising the ion exchange membrane according to any one of claims 1 to 7 .

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