JP6927191B2 - Manufacture method of ion exchange membrane for alkali chloride electrolysis, ion exchange membrane for alkali chloride electrolysis and alkali chloride electrolyzer - Google Patents

Description

The present invention relates to an ion exchange membrane for alkali chloride electrolysis, a method for producing an ion exchange membrane for alkali chloride electrolysis, and an alkali chloride electrolyzer.

As an ion exchange membrane used in the alkali chloride electrolysis method for producing alkali hydroxide and chlorine by electrolyzing an alkaline chloride aqueous solution such as seawater, an electrolyte membrane made of a fluorine-containing polymer having an ion exchange group is known.
Patent Document 1 discloses an ion exchange membrane having a layer containing a fluoropolymer having a carboxylic acid type functional group and a layer containing a fluoropolymer having a sulfonic acid type functional group (paragraph 0074, etc.). ).

International Publication No. 2014/069165

In recent years, there has been a demand for further improvement in caustic quality of ion exchange membranes for alkali chloride electrolysis. Here, "excellent in caustic quality" means that the concentration of impurities (particularly sodium chloride) in the alkaline hydroxide aqueous solution (particularly sodium hydroxide aqueous solution) obtained by electrolysis of the alkaline chloride aqueous solution (particularly sodium chloride aqueous solution) It means a low state.
However, the alkaline chloride aqueous solution obtained by using the ion exchange membrane described in Patent Document 1 does not satisfy the level required in recent years with respect to caustic quality, and there is room for improvement.

In view of the above circumstances, an object of the present invention is to provide an ion exchange membrane for alkali chloride electrolysis capable of producing an alkaline chloride aqueous solution having excellent caustic quality, a method for producing the same, and an alkali chloride electrolyzer using the same.

As a result of diligent studies on the above problems, the present inventor has provided a layer (S) containing a fluoropolymer having a sulfonic acid type functional group and a layer (C) containing a fluoropolymer having a carboxylic acid type functional group. In the ion exchange membrane for alkali chloride electrolysis, at least one of the surface on the layer (S) side and the surface on the layer (C) side, which appears when the layer (C) is peeled from the layer (S), is roughened. We have found that a desired effect can be obtained if the (Ra) is within a predetermined range, and have arrived at the present invention.
That is, the present inventor has found that the above problem can be solved by the following configuration.

[1] An ion for alkali chloride electrolysis formed by laminating a layer (C) containing a fluoropolymer having a carboxylic acid type functional group and a layer (S) containing a fluoropolymer having a sulfonic acid type functional group. It is an exchange membrane
The layer (C) and the layer (S) are peeled off, and at least one of the surface roughness (Ra) on the layer (C) side and the surface on the layer (S) side that appears by the peeling is performed. ) Is 1 to 15 nm, an ion exchange membrane for alkali chloride electrolysis.
[2] The ion exchange membrane for alkali chloride electrolysis according to [1], wherein the surface roughness (Ra) is 1 to 10 nm.
[3] The ion exchange membrane for alkali chloride electrolysis according to [1] or [2], which comprises a reinforcing member including a reinforcing thread in the layer (S).
[4] The ion exchange for alkali chloride electrolysis according to any one of [1] to [3], wherein the alkali chloride ion exchange membrane has an inorganic particle layer containing inorganic particles and a binder on at least one outermost surface. film.
[5] A fluoropolymer (C') having a group capable of converting to a carboxylic acid type functional group and a fluoropolymer (S') having a group capable of converting to a sulfonic acid type functional group are pelleted, respectively.
Next, the pellets of the fluoropolymer (C') and the pellets of the fluoropolymer (S') are melt-extruded and molded to form a precursor layer (C') containing the fluoropolymer (C'). And the precursor layer (S') containing the fluoropolymer (S') are laminated to form a precursor film.
Next, the precursor film is brought into contact with the alkaline aqueous solution to convert a group that can be converted into the carboxylic acid type functional group in the precursor layer (C'), and the layer having the carboxylic acid type functional group ( A layer (S) having the sulfonic acid type functional group is formed by forming C) and converting a group capable of converting into the sulfonic acid type functional group in the precursor layer (S') [1]. ] To [4], the method for producing an ion exchange film for alkali chloride electrolysis.
A method for producing an ion exchange membrane for alkali chloride electrolysis, which satisfies at least one of the following requirements 1 and 2.
(Requirement 1) At the time of pelletization, at least one melt of the fluoropolymer (C') and the fluoropolymer (S') is filtered and then pelletized.
(Requirement 2) At the time of the melt extrusion molding, at least one melt of the fluoropolymer (C') pellet and the fluoropolymer (S') pellet is melt-extruded after passing through a filter. ..
[6] The method for producing an ion exchange membrane for alkali chloride electrolysis according to [5], wherein pelletization is performed while degassing in the above requirement 1, or melt extrusion molding is performed while degassing in the above requirement 2.
[7] The method for producing an ion exchange membrane for alkali chloride electrolysis according to [6], wherein the gauge pressure at the time of degassing is −0.1 to −0.02 MPa.
[8] The method for producing an ion exchange membrane for alkali chloride electrolysis according to [7], wherein the filter has a mesh size of 0.026 to 0.87 mm.
[9] The method for producing an ion exchange membrane for alkali chloride electrolysis according to any one of [5] to [8], wherein the filter has a mesh size of 0.026 to 0.32 mm.
[10] An electrolytic cell including a cathode and an anode,
It has the ion exchange membrane for alkali chloride electrolysis according to any one of [1] to [4].
The ion exchange membrane for alkali chloride electrolysis is arranged in the electrolytic cell so as to separate the cathode and the anode.
An alkali chloride electrolyzer in which the layer (C) is arranged on the cathode side and the layer (S) is arranged on the anode side.

According to the present invention, it is possible to provide an ion exchange membrane for alkali chloride electrolysis capable of producing an alkaline chloride aqueous solution having excellent caustic quality, a method for producing the same, and an alkali chloride electrolyzer using the same.

It is sectional drawing which shows an example of the ion exchange membrane for chlorinated alkali electrolysis of this invention. It is sectional drawing which shows an example of the ion exchange membrane for chlorinated alkali electrolysis of this invention. It is a schematic diagram which shows an example of the chlorinated alkali electrolyzer of this invention.

Unless otherwise noted, the definitions of the following terms apply throughout the specification and claims.
The "ion exchange membrane" is a membrane containing a polymer having an ion exchange group.
The "ion exchange group" is a group capable of exchanging at least a part of the ions contained in this group with another ion, and examples thereof include the following carboxylic acid type functional group and sulfonic acid type functional group.
The "carboxylic acid type functional group" means a carboxylic acid group (-COOH) or a carboxylic acid base (-COOM ¹ , where M ¹ is an alkali metal or a quaternary ammonium base).
"Sulfonic acid type functional group" means a sulfonic acid group (-SO ₃ H) or a sulfonic acid base (-SO ₃ M ² ; where M ² is an alkali metal or a quaternary ammonium base). do.
The "precursor layer" is a layer (membrane) containing a polymer having a group capable of converting into an ion exchange group.
The "group that can be converted into an ion-exchange group" means a group that can be converted into an ion-exchange group by a treatment such as a hydrolysis treatment or an acidification treatment.
The "group that can be converted into a carboxylic acid type functional group" means a group that can be converted into a carboxylic acid type functional group by a treatment such as a hydrolysis treatment or an acid type treatment.
The "group that can be converted into a sulfonic acid type functional group" means a group that can be converted into a sulfonic acid type functional group by a treatment such as a hydrolysis treatment or an acid type treatment.
"Milli equivalent / gram dry resin", which is a unit of ion exchange capacity, may be abbreviated as "mEq / g".

The "fluorine-containing polymer" means a polymer compound having a fluorine atom in the molecule.
"Perfluorocarbon polymer" means a polymer in which all hydrogen atoms bonded to carbon atoms in the polymer are replaced with fluorine atoms. Some of the fluorine atoms in the perfluorocarbon polymer may be replaced with one or both of chlorine and bromine atoms.
By "monomer" is meant a compound having a polymerization-reactive carbon-carbon unsaturated double bond.
The "fluorine-containing monomer" means a monomer having a fluorine atom in the molecule.
The "perfluoromonomer" means a monomer in which all the hydrogen atoms bonded to carbon atoms in the monomer are replaced with fluorine atoms.
"Constituent unit" means a monomer-derived polymerization unit that is present in the polymer and constitutes the polymer. For example, when the structural unit is generated by addition polymerization of a monomer having a carbon-carbon unsaturated double bond, the structural unit derived from this monomer is a divalent structural unit generated by cleavage of this unsaturated double bond. be. Further, the structural unit may be a structural unit obtained by chemically converting, for example, hydrolyzing, the structural unit after forming a polymer having the structure of a certain structural unit. In some cases, the structural unit derived from each monomer may be described by adding "unit" to the monomer name.

The "reinforcing member" means a member used to improve the strength of the ion exchange membrane. The reinforcing member is a member derived from the reinforcing cloth.
The "reinforcing cloth" means a cloth used as a raw material for a reinforcing member for improving the strength of the ion exchange membrane.
The "reinforcing thread" is a thread constituting the reinforcing cloth, and is a thread made of a material that does not elute even when the reinforcing cloth is immersed in an alkaline aqueous solution (for example, an aqueous solution of sodium hydroxide having a concentration of 32% by mass). be.
The "sacrificial thread" is a thread constituting the reinforcing cloth, and is a thread made of a material that elutes into the alkaline aqueous solution when the reinforcing cloth is immersed in the alkaline aqueous solution.
The "eluting hole" means a hole formed as a result of the sacrificial yarn being eluted into an alkaline aqueous solution.
"Reinforced precursor membrane" means a membrane containing a reinforcing cloth in the precursor layer.
The numerical range represented by "~" means a range including the numerical values before and after "~" as the lower limit value and the upper limit value.

The thickness of each layer when the ion exchange membrane is dried is determined by drying the ion exchange membrane at 90 ° C. for 2 hours, observing the cross section of the ion exchange membrane with an optical microscope, and using image software. When a reinforcing member is present between the layers, the thickness of the layer is measured at a position where neither the reinforcing thread nor the sacrificial thread constituting the reinforcing member is present.
The "TQ value" is a value related to the molecular weight of the polymer, and represents a temperature indicating ^{a volumetric flow velocity: 100 mm 3 / sec.} The volumetric flow velocity is a value indicating the amount of polymer that flows out when the polymer is melted and discharged from an orifice (diameter: 1 mm, length: 1 mm) at a constant temperature under a pressure of 3 MPa ^{in units of mm 3 / sec.} be. The higher the TQ value, the higher the molecular weight.
The "ion exchange capacity" is a value calculated as follows. First, about 0.5 mg of a fluoropolymer having a group that can be converted into an ion exchange group is flat-pressed at a temperature about 10 ° C. higher than its TQ value to form a film, and the obtained film-like sample is permeated. Analyze with an infrared spectrophotometer. _{Using the peak heights of CF 2} peak, CH ₃ peak, OH peak, CF peak, and SO ₂ F peak of the obtained spectrum, it can be converted into a group that can be converted into a carboxylic acid type functional group or a sulfonic acid type functional group. The ratio of the structural unit having a group was calculated, and this was used as the ratio of the structural unit having a carboxylic acid type functional group or a sulfonic acid type functional group in the fluorine-containing polymer obtained after the hydrolysis treatment, and a sample having a known ion exchange capacity was used. The ion exchange capacity is determined by using it as a calibration line. Similarly, the measurement can be performed on a film having an ion exchange group whose terminal group is an acid type, a potassium type or a sodium type.

[Ion exchange membrane]
The ion exchange membrane for alkali chloride electrolysis of the present invention (hereinafter, also referred to as “ion exchange membrane”) contains a layer (C) containing a fluorine-containing polymer having a carboxylic acid type functional group and a layer (C) containing a sulfonic acid type functional group. An ion exchange membrane in which a layer (S) containing a fluoropolymer is laminated, and the layer (C) and the layer (S) are peeled off, and the layer (S) side that appears by the peeling. The surface roughness (Ra) of at least one of the surface of the above and the surface on the layer (C) side is 1 to 15 nm.
By using the ion exchange membrane of the present invention, an alkaline chloride aqueous solution having excellent caustic quality can be produced. The reason for this is considered as follows.

In the electrolysis of an aqueous alkali chloride solution using an ion exchange membrane, chlorine ions generated on the anode side do not easily move to the cathode side due to electrical repulsion. However, if there is a peeled portion between the layer (S) and the layer (C), the peeled portion is less susceptible to electrical influence. Therefore, it is considered that the chloride ion easily moves to the cathode side through the peeled portion by using the concentration gradient between the anode side and the cathode side as a driving force, and the caustic quality deteriorates.
Further, the present inventors have found that such peeling is caused by a large surface roughness (Ra) of the peeled surface between the layer (S) and the layer (C). Further, it is presumed that such a large surface roughness is caused by impurities contained in the S layer and the C layer.
Therefore, when performing at least one of pelletization and film formation of the fluoropolymer constituting each layer, if the melt of the fluoropolymer for obtaining at least one of the layer (S) and the layer (C) is filtered. It is presumed that the above impurities were removed to obtain a predetermined surface roughness, and as a result, the number of peeled parts of the ion exchange membrane was reduced, and an alkaline chloride aqueous solution having excellent caustic quality could be produced.

Hereinafter, the ion exchange membrane of the present invention will be described with reference to FIGS. 1 and 2, but the present invention is not limited to the contents of FIGS. 1 and 2.
The ion exchange membrane 1 shown in FIG. 1 is formed by reinforcing an electrolyte membrane 10 made of a fluoropolymer having an ion exchange group with a reinforcing member 20.

The electrolyte membrane 10 is a laminate composed of the layer (C) 12 and the layer (S) 14. A reinforcing member 20 including a reinforcing thread is included in the layer (S) 14.

(Layer (C))
The layer (C) 12 may be a layer containing the fluoropolymer (C), but from the viewpoint of electrolytic performance, the layer (C) 12 is composed only of the fluoropolymer (C) containing no material other than the fluoropolymer (C). Is preferable. That is, the layer (C) 12 is preferably a layer made of a fluoropolymer having a carboxylic acid type functional group.
Although the layer (C) 12 is shown as a single layer in FIG. 1, it may be a layer formed from a plurality of layers. When the layer (C) 12 is formed from a plurality of layers, the type of the structural unit constituting the fluoropolymer (C) and the ratio of the structural unit having a carboxylic acid type functional group may be different in each layer.

The thickness of the layer (C) 12 at the time of drying (the total of the layers (C) 12 when it is formed from a plurality of layers) is preferably 1 to 50 μm, more preferably 5 to 50 μm, and 8 to 35 μm. It is particularly preferable, and 9 to 22 μm is most preferable. When the thickness of the layer (C) 12 at the time of drying is at least the above lower limit value, the caustic quality is more excellent. When the thickness of the layer (C) 12 at the time of drying is equal to or less than the above upper limit value, an increase in the electrolytic voltage can be suppressed.

The ion exchange capacity of the fluoropolymer (C) constituting the layer (C) 12 is preferably 0.5 to 2.0 mEq / g, more preferably 0.8 to 2.0 mEq / g, and 0.85-1. .10 mEq / g is particularly preferable, and 0.95 to 1.10 mEq / g is most preferable.
When the layer (C) 12 is formed of a plurality of layers, it is preferable that the ion exchange capacities of all the fluoropolymers (C) constituting the layer (C) 12 are in the above range.
When the ion exchange capacity of the fluoropolymer (C) is at least the above lower limit value, the electric resistance of the ion exchange membrane 1 when electrolyzing the alkaline chloride aqueous solution becomes low, and the ion exchange membrane 1 having a low electrolysis voltage can be obtained. When the ion exchange capacity of the fluoropolymer (C) is equal to or less than the above upper limit, it is easy to synthesize a polymer having a high molecular weight, excessive swelling of the polymer can be suppressed, and an ion exchange membrane whose current efficiency does not easily decrease. 1 is obtained.

The fluoropolymer (C) is obtained by converting a group that can be converted into a carboxylic acid type functional group of the fluoropolymer described later into a carboxylic acid type functional group by a method for producing an ion exchange membrane for alkali chloride electrolysis described later. Is preferable.
Specific examples of the fluoropolymer (C) include a monomer having a group capable of converting into a carboxylic acid type functional group and a fluorine atom (hereinafter, also referred to as "fluorine-containing monomer (C')"), a fluoroolefin. (Hereinafter, also referred to as "fluorine-containing polymer (C')") is hydrolyzed to convert a group capable of converting into a carboxylic acid type functional group into a carboxylic acid type functional group. Be done.

The fluorine-containing monomer (C') is a compound having one or more fluorine atoms in the molecule, having an ethylenic double bond, and having a group capable of converting into a carboxylic acid type functional group. The compound is not particularly limited, and conventionally known compounds are used.
The fluoropolymer (C') is preferably a monomer represented by the following formula (1) because it is excellent in the production cost of the monomer, the reactivity with other monomers, and the characteristics of the obtained fluoropolymer.

CF ₂ = CF- (O) _p- (CF ₂ ) _q- (CF ₂ CFX) _r- (O) _s- (CF ₂ ) _t- (CF ₂ CFX') _u- A ¹ ... (1)

In formula (1), X and X'are independent fluorine atoms or trifluoromethyl groups, respectively. A ¹ is a group that can be converted into a carboxylic acid type functional group. Specifically, -CN, -COF, -COOR ¹ (R ¹ is an alkyl group having 1 to 10 carbon atoms), -COONR ² R ³ (R ² and R ³ are independent hydrogen atoms, respectively). It is an atom or an alkyl group having 1 to 10 carbon atoms.). p is 0 or 1. q is an integer from 0 to 12. r is an integer from 0 to 3. s is 0 or 1. t is an integer from 0 to 12. u is an integer from 0 to 3. However, 1 ≦ p + s and 1 ≦ r + u.

Specific examples of the monomer represented by the formula (1) include the following compounds, and p = 1, q = 0, r = 1, s = 0 to 1, t = from the viewpoint of easy production. Compounds of 0 to 3 and u = 0 to 1 are preferable.
CF ₂ = CF-O-CF ₂ CF _2- COOCH ₃ ,
CF ₂ = CF-O-CF ₂ CF ₂ CF _2- COOCH ₃ ,
CF ₂ = CF-O-CF ₂ CF ₂ CF ₂ CF _2- COOCH ₃ ,
CF ₂ = CF-O-CF ₂ CF _2- O-CF ₂ CF _2- COOCH ₃ ,
CF ₂ = CF-O-CF ₂ CF _2- O-CF ₂ CF ₂ CF _2- COOCH ₃ ,
CF ₂ = CF-O-CF ₂ CF _2- O-CF ₂ CF ₂ CF ₂ CF _2- COOCH ₃ ,
CF ₂ = CF-O-CF ₂ CF ₂ CF _2- O-CF ₂ CF _2- COOCH ₃ ,
CF ₂ = CF-O-CF ₂ CF (CF ₃ ) -O-CF ₂ CF _2- COOCH ₃ ,
CF ₂ = CF-O-CF ₂ CF (CF ₃ ) -O-CF ₂ CF ₂ CF _2- COOCH ₃ .
The fluorine-containing monomer (C') may be used alone or in combination of two or more.

Examples of the fluorine-containing olefin include fluoroolefins having one or more fluorine atoms in the molecule and having 2 to 3 carbon atoms. Specific examples thereof include tetrafluoroethylene (TFE), chlorotrifluoroethylene, vinylidene fluoride, vinyl fluoride, and hexafluoropropylene. Of these, TFE is particularly preferable because it is excellent in the production cost of the monomer, the reactivity with other monomers, and the characteristics of the obtained fluoropolymer.
As the fluorine-containing olefin, one type may be used alone, or two or more types may be used in combination.

In addition to the fluorinated monomer (C') and the fluorinated olefin, other monomers may be used for producing the fluorinated polymer (C'). Specific examples of other monomers include CF ₂ = CFR ^f (R ^f is a perfluoroalkyl group having 2 to 10 carbon atoms), CF ₂ = CF-OR ^f1 (R ^f1 has 1 to 10 carbon atoms). Perfluoroalkyl groups), CF ₂ = CFO (CF ₂ ) _v CF = CF ₂ (v is an integer of 1-3). By copolymerizing other monomers, the flexibility and mechanical strength of the ion exchange membrane 1 can be improved.

The ion exchange capacity of the fluoropolymer (C) can be adjusted by changing the content of the structural unit derived from the fluoropolymer (C') in the fluoropolymer (C'). The content of the carboxylic acid type functional group in the fluoropolymer (C) is preferably the same as the content of the group that can be converted into the carboxylic acid functional group in the fluoropolymer (C').

The range of the TQ value of the fluoropolymer (C) is preferably 150 to 350 ° C., more preferably 170 to 300 ° C., and particularly preferably 200 to 250 ° C. from the viewpoint of mechanical strength and film forming property as an ion exchange membrane. preferable.

(Layer (S))
The layer (S) 14 may be a layer containing the fluoropolymer (S), but from the viewpoint of electrolytic performance, the layer (S) 14 is composed of only the fluoropolymer (S) containing no material other than the fluoropolymer (S). Layers are preferred. That is, the layer (S) 14 is preferably a layer made of a fluoropolymer having a sulfonic acid type functional group.
As shown in FIG. 1, the layer (S) 14 includes a reinforcing member 20 (described later) in order to increase the mechanical strength of the ion exchange membrane 1. Of the layers (S) 14, the layer (that is, the layer including the surface in contact with the layer (C) 12) located on the layer (C) 12 side (that is, the cathode side in the electrolytic apparatus) of the reinforcing member 20 is the layer (Sa). ) 14A, and the surface of the layer (that is, the surface opposite to the surface in contact with the layer (C) 12) located on the side opposite to the layer (C) 12 side of the reinforcing member 20 (that is, the anode side in the electrolytic apparatus). The containing layer) is the layer (Sb) 14B.
In FIG. 1, the layer (Sa) 14A and the layer (Sb) 14B are each shown as a single layer, but each may be a layer formed from a plurality of layers. When one or both of the layer (Sa) 14A and the layer (Sb) 14B are formed from a plurality of layers, in each layer, the type of the structural unit constituting the fluoropolymer (S) and the sulfonic acid type functional group are determined. The ratio of the constituent units to have may be different.

The thickness of the layer (S) 14 at the time of drying (the total of the layers (S) 14 formed from a plurality of layers) is preferably 30 to 200 μm, more preferably 55 to 200 μm, and 70 to 120 μm. Especially preferable. When the thickness of the layer (S) 14 at the time of drying is at least the above lower limit value, the mechanical strength of the ion exchange membrane 1 becomes sufficiently high. When the thickness of the layer (S) 14 at the time of drying is not more than the above upper limit value, the electric resistance of the ion exchange membrane 1 can be suppressed low.

The thickness of the layer (Sa) 14A at the time of drying (the total when the layer (Sa) 14A is formed from a plurality of layers) is preferably 30 to 140 μm, more preferably 40 to 140 μm, and 40 to 90 μm. Especially preferable. When the thickness of the layer (Sa) 14A at the time of drying is at least the above lower limit value, the mechanical strength of the ion exchange membrane 1 becomes sufficiently high. When the thickness of the layer (Sa) 14A at the time of drying is not more than the above upper limit value, the electric resistance of the ion exchange membrane 1 can be suppressed low.

The ion exchange capacity of the fluoropolymer (S) constituting the layer (Sa) 14A is preferably 0.6 to 2.5 mEq / g, particularly preferably 0.9 to 1.2 mEq / g.
When the layer (Sa) 14A is formed from a plurality of layers, it is preferable that the ion exchange capacities of all the fluoropolymers (S) constituting the layer (Sa) 14A are in the above range. Further, the layer (Sa) 14A is preferably composed of a plurality of layers, and more preferably composed of two layers. As another aspect, the layer (Sa) 14A is preferably a single layer.
When the ion exchange capacity of the fluoropolymer (S) constituting the layer (Sa) 14A is equal to or higher than the above lower limit, the electric resistance of the ion exchange membrane is lowered, and the electrolytic voltage when electrolyzing the alkaline chloride aqueous solution can be lowered. .. Further, in the fluoropolymer (S) having an ion exchange capacity of not more than the above upper limit value, it becomes easy to increase the molecular weight of the fluoropolymer (S) at the time of polymerization, and the fluoropolymer (S) having a high molecular weight is layered. When used for (Sa) 14A, the strength of layer (Sa) 14A becomes higher.

The thickness of the layer (Sb) 14B at the time of drying (the total when the layer (Sb) 14B is formed from a plurality of layers) is preferably 5 to 100 μm, more preferably 10 to 50 μm, and preferably 10 to 40 μm. Especially preferable. When the thickness of the layer (Sb) 14B at the time of drying is set to the above lower limit value or more, the reinforcing member 20 is included at an appropriate depth position from the surface of the electrolyte membrane 10, and the peeling resistance of the reinforcing member 20 is improved. Further, the surface of the electrolyte membrane 10 is less likely to be cracked, and as a result, a decrease in mechanical strength is suppressed. When the thickness of the layer (Sb) 14B at the time of drying is not more than the above upper limit value, the electric resistance of the ion exchange membrane 1 can be suppressed to a low level, and an increase in the electrolytic voltage can be suppressed.

The ion exchange capacity of the fluoropolymer (S) constituting the layer (Sb) 14B is preferably 0.5 to 2.5 mEq / g, more preferably 0.6 to 2.5 mEq / g, and 0.9 to 2 0.0 mEq / g is particularly preferable, and 1.05 to 2.00 mEq / g is most preferable.
When the layer (Sb) 14B is formed from a plurality of layers, it is preferable that the ion exchange capacity of the fluoropolymer (S) constituting the layer located at least on the anode side is in the above range, and the layer (Sb) 14B is formed. ) It is more preferable that the ion exchange capacities of all the fluoropolymers (S) constituting 14B are in the above range. In another aspect, it is preferable that the layer (Sb) 14B is composed of a single layer, and the ion exchange capacity of the fluoropolymer (S) constituting this layer is in the above range.
When the ion exchange capacity of the fluoropolymer (S) constituting the layer (Sb) 14B is at least the above lower limit value, the electric resistance of the ion exchange membrane is lowered, and the electrolytic voltage at the time of electrolysis can be lowered. When the ion exchange capacity of the fluoropolymer (S) constituting the layer (Sb) 14B is not more than the above upper limit value, the film strength can be maintained and the film tearing during the electrolytic operation or the film mounting can be suppressed.

At least a part of the fluoropolymer having a sulfonic acid type functional group constituting the layer (Sb) 14B is preferably a polymer having a structural unit based on a monomer having two or more sulfonic acid type functional groups, and a sulfonic acid type functional group. A polymer having a structural unit based on a monomer having two of is preferable. As a result, the concentration of ion exchange groups per unit weight can be increased at the same monomer concentration, so that the polymer has a higher ion exchange capacity even with a small amount of monomers as compared with a polymer having a structural unit having only one sulfonic acid type functional group. Layer (Sb) 14B is obtained.

The structural unit based on the monomer having two or more sulfonic acid type functional groups is preferably the structural unit represented by the following formula (U1).

In formula (U1), R ^f1 is a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, more preferably 2 or more, preferably 20 or less, and more preferably 10 or less.
R ^f2 is a perfluoroalkylene group that may contain an oxygen atom between a single bond or a carbon atom and a carbon atom. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, more preferably 2 or more, preferably 20 or less, and more preferably 10 or less.
r is 0 or 1.
M is a hydrogen atom, alkali metal or quaternary ammonium cation.
As the unit represented by the formula (U1), the unit represented by the formula (U1-1) is preferable.

R ^f3 is a linear perfluoroalkylene group having 1 to 6 carbon atoms, and R ^f4 is a linear chain having 1 to 6 carbon atoms which may contain an oxygen atom between a single bond or a carbon atom and a carbon atom. Perfluoroalkylene group. The definitions of r and M are as described above.

The fluoropolymer (S) is a group that can be converted into a sulfonic acid type functional group of a fluoropolymer having a group that can be converted into a sulfonic acid type functional group described later in the step of obtaining an ion exchange film for alkali chloride electrolysis described later. It is preferably obtained by converting to a sulfonic acid type functional group.
Specific examples of the fluoropolymer (S) include a monomer having a group capable of converting into a sulfonic acid type functional group and a fluorine atom (hereinafter, also referred to as “fluorine-containing monomer (S')”), a fluorine-containing olefin, and a fluorine-containing olefin. (Hereinafter, also referred to as "fluorine-containing polymer (S')") is hydrolyzed to convert a group capable of converting into a sulfonic acid type functional group into a sulfonic acid type functional group. Be done.

The fluorine-containing monomer (S') is a compound having one or more fluorine atoms in the molecule, having an ethylenic double bond, and having a group capable of converting into a sulfonic acid type functional group. The compound is not particularly limited, and conventionally known compounds are used.
The fluoropolymer (S') is a compound represented by the following formula (2) or the following formula (3) because it is excellent in the manufacturing cost of the monomer, the reactivity with other monomers, and the characteristics of the obtained fluoropolymer. ) Is preferable.

CF ₂ = CF- ^{OR f1-} A ² ... (2)
CF ₂ = CF-R ^f1- A ² ... (3)
In the formula (2) and ^(3), the definition of ^{R f1} is the same as ^{R f1} in formula (U1). A ² is a group that can be converted into a sulfonic acid type functional group, and specific examples thereof include -SO ₂ F, -SO ₂ Cl, and -SO ₂ Br.

Specific examples of the compound represented by the formula (2) include the following compounds. In the formula, w is an integer of 1 to 8 and x is an integer of 1 to 5.
CF ₂ = CF-O- (CF ₂ ) _w- SO ₂ F
CF ₂ = CF-O-CF ₂ CF (CF ₃ ) -O- (CF ₂ ) _w- SO ₂ F
CF ₂ = CF- [O-CF ₂ CF (CF ₃ )] _x- SO ₂ F

Specific examples of the compound represented by the formula (3) include CF ₂ = CF- (CF ₂ ) _w- SO ₂ F and CF ₂ = CF-CF _2- O- (CF ₂ ) _w- SO ₂ F. Can be mentioned. W in the formula is an integer of 1-8.

As the fluorine-containing monomer (S'), the following compounds are preferable from the viewpoint of easy industrial synthesis.
CF ₂ = CF-O-CF ₂ CF _2- SO ₂ F
CF ₂ = CF-O-CF ₂ CF ₂ CF _2- SO ₂ F
CF ₂ = CF-O-CF ₂ CF ₂ CF ₂ CF _2- SO ₂ F
CF ₂ = CF-O-CF ₂ CF (CF ₃ ) -O-CF ₂ CF _2- SO ₂ F
CF ₂ = CF-O-CF ₂ CF (CF ₃ ) -O-CF ₂ CF ₂ CF _2- SO ₂ F
CF ₂ = CF-O-CF ₂ CF (CF ₃ ) -SO ₂ F
CF ₂ = CF-CF ₂ CF _2- SO ₂ F
CF ₂ = CF-CF ₂ CF ₂ CF _2- SO ₂ F
CF ₂ = CF-CF _2- O-CF ₂ CF _2- SO ₂ F
The fluorine-containing monomer (S') may be used alone or in combination of two or more.

When the layer (Sb) 14B contains a polymer having a structural unit based on a monomer having two or more sulfonic acid type functional groups, the layer (Sb) has one or more fluorine atoms in the molecule as the fluorine-containing monomer (S'). However, a monomer having an ethylenic double bond and having two or more groups that can be converted into a sulfonic acid type functional group can be used. As such a monomer, a monomer from which the structural unit of the above formula (U1) can be obtained is preferable. As the monomer from which the structural unit of the formula (U1) can be obtained, the compound represented by the following formula (m1) is preferable.

Wherein ^(m1), each definition of R ^{f1, R f2,} r, is the same as ^{R f1, R f2,} r in the formula (U1), the definition of ^{A 2} in Formula (2) and (3 ) Is the same ^{as A 2.}

As the compound represented by the formula (m1), the compound represented by the formula (m1-1) is preferable.

Definition of ^{R f3, R f4,} r in the formula (m1-1) is the same as ^{R f3, R f4,} r of formula (U1-1), the definition of ^{A 2} in Formula (2) and It is the same ^{as A 2 in} (3).

Specific examples of the compound represented by the formula (m1-1) include the following.

By using a monomer having two or more sulfonic acid type functional groups, the ion exchange group concentration per unit weight can be increased at the same monomer concentration, so that the polymer constituting the layer (Sb) 14B without lowering the polymer molecular weight. Ion exchange capacity can be easily increased. As a result, a film having a high water permeability and a low electrolytic voltage can be obtained while maintaining excellent caustic quality.

Examples of the fluoropolymer include the compounds exemplified above, and TFE is particularly preferable because it is excellent in the production cost of the monomer, the reactivity with other monomers, and the characteristics of the obtained fluoropolymer.
As the fluorine-containing olefin, one type may be used alone, or two or more types may be used in combination.

In addition to the fluorinated monomer (S') and the fluorinated olefin, other monomers may be used for producing the fluorinated polymer (S'). Examples of other monomers include the compounds exemplified above. By copolymerizing other monomers, the flexibility and mechanical strength of the ion exchange membrane 1 can be improved. The proportion of the other monomer is preferably 30 mol% or less of the total constituent units (100 mol%) in the fluoropolymer (S') from the viewpoint of maintaining the ion exchange performance.

The ion exchange capacity of the fluoropolymer (S) can be adjusted by changing the content of the structural unit derived from the fluoropolymer (S') in the fluoropolymer (S'). The content of the sulfonic acid-type functional group in the fluoropolymer (S) is preferably the same as the content of the group that can be converted into the sulfonic acid-type functional group in the fluoropolymer (S').

The range of the TQ value of the fluoropolymer (S') is preferably 150 to 350 ° C., more preferably 170 to 300 ° C., and preferably 200 to 250 ° C. from the viewpoint of mechanical strength and film forming property as an ion exchange membrane. Especially preferable.

When the layer (Sa) 14A is composed of a plurality of layers, for example, when the layer (Sa) 14A is composed of two layers, as shown in FIG. 2, the layer in contact with the layer (C) 12 is the layer (Sa-1) 14Aa and the layer (Sb). ) The layer in contact with 14B is the layer (Sa-2) 14Ab. In this case, the layer (Sa-1) 14Aa has an ion exchange capacity of the fluoropolymer (S) constituting the layer (Sa-1) 14Aa from the viewpoint of adhesion to the layer (C) 12. -2) It is preferably lower than the ion exchange capacity of the fluoropolymer (S) constituting 14Ab, more preferably 0.01 to 0.5 mEq / g lower, and 0.03 to 0.3 mEq / g lower. Is particularly preferable.
The ion exchange capacity of the layer (Sa-1) 14Aa is preferably 0.5 to 2.5 mEq / g, more preferably 0.6 to 2.5 mEq / g, and particularly preferably 0.9 to 1.2 mEq / g. , 0.9 to 1.05 mEq / g is most preferable. The thickness of the layer (Sa-1) 14Aa at the time of drying may be an appropriate thickness that contributes to adhesiveness, preferably 1 to 100 μm, and particularly preferably 10 to 50 μm.

(Surface roughness (Ra))
In the ion exchange membrane 1, at least one of the surface on the layer (C) 12 side and the surface on the layer (S) 14 side that appears when the layer (C) 12 is peeled from the layer (S) 14 is roughened. The roughness (Ra) is 1 to 15 nm. As a result, the above-mentioned effect (obtaining an alkaline chloride aqueous solution having excellent caustic quality) is exhibited.
Of the surface on the layer (C) 12 side and the surface on the layer (S) 14 side, if the surface roughness of one of them is 1 to 15 nm, the above-mentioned effect is exhibited, but from the viewpoint that the effect is more exerted. , Both the surface on the layer (C) 12 side and the surface on the layer (S) 14 side preferably satisfy the surface roughness (Ra).
The surface roughness (Ra) is 1 to 15 nm, and is preferably 1 to 10 nm, particularly preferably 3 to 9 nm, from the viewpoint of more exerting the above-mentioned effects.
On the other hand, when the surface roughness (Ra) is less than 1 nm, the anchor effect between the layer (C) 12 and the layer (S) 14 becomes small, and the peeled portion (unbonded portion) at the interface between the two layers becomes small. It is estimated that there will be more. As a result, it is considered that the caustic quality of the alkaline chloride aqueous solution is lowered.
Further, when the surface roughness (Ra) exceeds 15 nm, it is presumed that the number of peeled parts (unbonded parts) at the interface between the two layers increases due to the surface roughness. As a result, it is considered that the caustic quality of the alkaline chloride aqueous solution is lowered.

The surface roughness (Ra) in the present invention is calculated based on the values measured as follows, and the details are as described in Examples described later.
First, the ion exchange membrane 1 is immersed in ion-exchanged water at 25 ° C., and then peeled at the interface between the layer (C) 12 and the layer (S) 14 using a peeling tester in a wet state. After measuring the surface roughness (Ra) of at least one surface of the layer (C) 12 side and the layer (S) 14 side after peeling at a plurality of places using an atomic force microscope (AFM), the surface roughness ( The arithmetic mean value of Ra) is calculated for each layer. The obtained arithmetic mean value is defined as the surface roughness (Ra) of the surface on the layer (C) 12 side or the surface on the layer (S) 14 side.

(Reinforcing member)
The reinforcing member 20 is included in the layer (S) 14. The reinforcing member 20 is a material that reinforces the electrolyte membrane 10, and is derived from the reinforcing cloth. The reinforcing cloth is composed of a warp and a weft, and it is preferable that the warp and the weft are orthogonal to each other. As shown in FIG. 1, the reinforcing cloth is preferably composed of the reinforcing thread 22 and the sacrificial thread 24.

The reinforcing thread 22 is a thread made of a material that does not elute even when the reinforcing precursor film (described later) is immersed in an alkaline aqueous solution. Even after the reinforced precursor membrane is immersed in an alkaline aqueous solution and the sacrificial yarn 24 is eluted from the reinforcing cloth, it remains undissolved as the yarn constituting the reinforcing member 20, and the mechanical strength and dimensional stability of the ion exchange membrane 1 are stable. Contributes to the maintenance of sex.
As the reinforcing thread 22, a thread containing a perfluorocarbon polymer is preferable, a thread containing PTFE is more preferable, and a PTFE thread composed of only PTFE is particularly preferable.

The sacrificial thread 24 is a thread in which at least a part thereof is eluted when the reinforced precursor film is immersed in an alkaline aqueous solution. The sacrificial yarn 24 may be monofilament or multifilament.
The sacrificial yarn 24 includes a PET yarn composed of PET only, a PET / PBT yarn composed of a mixture of PET and polybutylene terephthalate (hereinafter, also referred to as “PBT”), a PBT yarn composed of PBT only, or polytrimethylene terephthalate (hereinafter, also referred to as “PBT”). Hereinafter, a PTT yarn consisting of only "PTT") is preferable, and a PET yarn is particularly preferable.

In the ion exchange membrane 1, as shown in FIG. 1, a part of the sacrificial thread 24 remains, and an elution hole 28 is formed around the undissolved residue of the filament 26 of the sacrificial thread 24. As a result, the ion exchange membrane 1 is less likely to be damaged such as cracks during the handling of the ion exchange membrane 1 from the time of manufacture to before the conditioning operation of the alkali chloride electrolysis and the installation in the electrolytic cell during the conditioning operation. Become.

Even if a part of the sacrificial yarn 24 remains before the ion exchange membrane 1 is arranged in the electrolytic cell, the sacrificial yarn remaining during the conditioning operation of the alkali chloride electrolysis after the ion exchange membrane 1 is arranged in the electrolytic cell. 24 is eluted in an alkaline aqueous solution, most of which is preferably removed entirely. Therefore, at the time of the main operation of the alkali chloride electrolysis using the ion exchange membrane 1, the electric resistance is not affected. After the ion exchange membrane 1 is placed in the electrolytic cell, a large force does not act on the ion exchange membrane 1 from the outside. Therefore, even if the sacrificial yarn 24 is completely eluted in the alkaline aqueous solution and removed, the ion exchange membrane 1 cracks. Etc. are less likely to occur.
Although FIG. 1 shows a mode in which a part of the sacrificial thread 24 remains, all of the sacrificial thread 24 may be eluted.

(Inorganic particle layer)
The ion exchange membrane 1 preferably further has an inorganic particle layer (not shown) containing inorganic particles and a binder on at least one outermost surface. The inorganic particle layer is preferably provided on at least one surface of the outermost surface of the ion exchange membrane 1, and more preferably provided on both sides.
When the gas generated by the alkali chloride electrolysis adheres to the surface of the ion exchange membrane 1, the electrolysis voltage becomes high during the alkali chloride electrolysis. The inorganic particle layer is provided to suppress the adhesion of gas generated by alkali chloride electrolysis to the surface of the ion exchange membrane 1 and to suppress an increase in the electrolysis voltage.

The inorganic particles are preferably excellent in corrosion resistance to an aqueous alkali chloride solution and preferably have hydrophilicity. Specifically, at least one selected from the group consisting of oxides, nitrides and carbides of Group 4 or Group 14 elements is preferable, SiO ₂ , SiC, ZrO ₂ or ZrC is more preferable, and ZrO _{2 is more preferable.} Is particularly preferable.
The average particle size of the inorganic particles is preferably 0.01 to 10 μm, more preferably 0.01 to 1.5 μm, and particularly preferably 0.5 to 1.5 μm. When the average particle size is at least the above lower limit value, a high gas adhesion suppressing effect can be obtained. When the average particle size is equal to or less than the above upper limit value, the resistance to dropping of inorganic particles is excellent.

The binder is preferably excellent in corrosion resistance to an aqueous alkali chloride solution and has hydrophilicity, more preferably a fluorine-containing polymer having a carboxylic acid group or a sulfonic acid group, and particularly preferably a fluorine-containing polymer having a sulfonic acid group. The fluorine-containing polymer may be a homopolymer of a monomer having a carboxylic acid group or a sulfonic acid group, and is a copolymer of a monomer having a carboxylic acid group or a sulfonic acid group and a monomer copolymerizable with this monomer. May be good.

The mass ratio of the binder (hereinafter, also referred to as “binder ratio”) to the total mass of the inorganic particles and the binder in the inorganic particle layer is preferably 0.1 to 0.5. When the binder ratio is equal to or higher than the above lower limit value, the resistance to dropping of inorganic particles is excellent. When the binder ratio is not more than the above upper limit value, a high gas adhesion suppressing effect can be obtained.

[Manufacturing method of ion exchange membrane]
The method for producing an ion exchange membrane of the present invention (hereinafter, also referred to as "the present production method") is defined as a method for producing an ion exchange membrane.
A fluoropolymer (C') having a group that can be converted into a carboxylic acid type functional group and a fluoropolymer (S') having a group that can be converted into a sulfonic acid type functional group are pelleted, respectively.
Next, the pellet of the fluoropolymer (C') and the pellet of the fluoropolymer (S') are melt-extruded and molded to form a precursor layer (C') containing the fluoropolymer (C'). And the precursor layer (S') containing the fluoropolymer (S') are laminated to form a precursor film.
Next, the precursor film is brought into contact with the alkaline aqueous solution to convert a group that can be converted into the carboxylic acid type functional group in the precursor layer (C'), and the layer having the carboxylic acid type functional group ( Ion exchange that forms C) and converts a group that can be converted to a sulfonic acid type functional group in the precursor layer (S') to form a layer (S) having the sulfonic acid type functional group. It is a method of manufacturing a film.
At least one of the following requirements 1 and 2 is satisfied.
(Requirement 1) At the time of pelletization, at least one melt of the fluoropolymer (C') and the fluoropolymer (S') is filtered and then pelletized.
(Requirement 2) At the time of the melt extrusion molding, at least one melt of the fluoropolymer (C') pellet and the fluoropolymer (S') pellet is melt-extruded after passing through a filter. ..

According to the present production method, by satisfying the above requirement 1 or the above requirement 2, solid impurities (for example, dust, dust, etc.) contained in at least one of the fluoropolymer (C') and the fluoropolymer (S') are contained. Dust, polymer-derived by-products, process-derived metallic impurities, etc.) are removed. That is, since at least one of the fluoropolymer (C') and the fluoropolymer (S') is purified through melt filtration with a filter, an ion exchange membrane satisfying the above-mentioned predetermined surface roughness (Ra). Is obtained.

In the above requirement 1, it is preferable to pelletize while degassing. Further, in the above requirement 2, it is preferable to perform melt extrusion molding while degassing.
By carrying out degassing in Requirement 1 or Requirement 2, liquid impurities and gaseous impurities contained in at least one of the fluoropolymer (C') and the fluoropolymer (S') (for example, residual during polymerization) Monomers, water, etc.) are removed. That is, since liquid impurities and gas impurities are removed from at least one of the fluoropolymer (C') and the fluoropolymer (S') by degassing, ions satisfying the above-mentioned predetermined surface roughness (Ra). It becomes easier to obtain an exchange membrane.

(Manufacturing of pellets)
An example of the method for producing the fluoropolymer (C') pellet and the fluoropolymer (S') pellet is shown below.
First, a polymer (fluoropolymer (C') or fluoropolymer (S')) is supplied to a known melt extruder to obtain a melt of the polymer. Next, the melt of the polymer is extruded from a nozzle of an extruder and cooled to obtain strands, and then the obtained strands are cut to a predetermined size to obtain polymer pellets.
The melting temperature of the polymer is preferably 150 to 350 ° C, particularly preferably 200 to 300 ° C.
In the method for producing pellets, the case where the so-called strand cutting method is used is shown, but an underwater cutting method, a hot cutting method, or the like may be used.

Here, at the time of pelletization, it is preferable to pass at least one melt of the fluoropolymer (C') and the fluoropolymer (S') through a filter, and the effect of the present invention is more exhibited. Therefore, it is particularly preferable to pass the melt of both polymers through a filter.
The filter can be placed near the nozzle in, for example, a melt extruder for pellet production.
The opening (diameter) of the filter is preferably 0.026 to 0.87 mm, more preferably 0.026 to 0.32 mm, from the viewpoint that the surface roughness (Ra) can be easily set within a predetermined range. 0.026 to 0.132 mm is particularly preferable.
The filter is preferably a mesh filter of 20 to 500 mesh, preferably a mesh filter of 50 to 500 mesh, and a mesh filter of 120 to 500 mesh from the viewpoint that the surface roughness (Ra) can be easily set within a predetermined range. Is more preferable. Here, "mesh" means the number of mesh filters per inch.
The material of the filter is preferably metal from the viewpoint of heat resistance.

When the polymer (fluoropolymer (C') or fluoropolymer (S')) is supplied to a known melt extruder, it is preferable to degas at least one of the melts, and the effect of the present invention is more exhibited. It is particularly preferable to degas the melts of both polymers.
Degassing is performed, for example, by using a suction pump or the like connected to a vent hole of a melt extruder for producing pellets.
The gauge pressure at the time of degassing is preferably −0.1 to −0.02 MPa, more preferably −0.1 to −0.06 MPa from the viewpoint that it is easy to keep the surface roughness within a predetermined range. preferable.
When a filter having a mesh size in the range of 0.026 to 0.87 mm is used, the gauge pressure is −0.1 to −0. It is preferable to perform degassing within the range of 02 MPa (preferably −0.1 to −0.06 MPa).

(Manufacturing of precursor membrane)
Next, an example of a method for producing a precursor film in which a precursor layer (C') and a precursor layer (S') are laminated is shown below.
First, the fluoropolymer (C') pellets and the fluoropolymer (S') pellets are supplied to a known melt extruder for film production to melt the fluoropolymer (C') pellets. A product and a melt of fluoropolymer (S') pellets are obtained, respectively.
Next, the melt of each of the pellets is extruded from a nozzle (for example, T die) of a melt extruder (melt extrusion molding by a co-extrusion method), and a precursor layer (C') containing a fluoropolymer (C') is contained. And a laminated film having a precursor layer (S'a) containing a fluoropolymer (S'). Separately, a film made of a precursor layer (S'b) containing a fluoropolymer (S') is obtained by a single-layer extrusion method.
Next, the film composed of the precursor layer (S'b), the reinforcing member, and the laminated film are arranged in this order, and these are laminated using, for example, a laminated roll or a vacuum laminating device. At this time, the laminated film is arranged so that the precursor layer (S'a) side is in contact with the reinforcing member. In this way, a precursor film (reinforced precursor film) formed by laminating the precursor layer (S'b), the reinforcing member, the precursor layer (S'a), and the precursor layer (C') in this order is obtained. ..
The melting temperature of the pellets is preferably 150 to 350 ° C, particularly preferably 200 to 300 ° C.

When the number of layers (Sa) is two or more, a film made of a fluoropolymer having a group capable of converting into a sulfonic acid type functional group is separately obtained, and a layer (Sa) is obtained between the reinforcing member and the laminated film. ) May be laminated so as to be composed of a plurality of layers.

Here, at the time of the melt extrusion molding, it is preferable to pass at least one of the melt of the fluoropolymer (C') pellet and the melt of the fluoropolymer (S') pellet through a filter, and it is preferable to pass the melt of the pellet of the present invention. It is particularly preferable to pass the melt of both pellets through a filter because it is more effective.
The filter can be placed near a nozzle in, for example, a melt extruder for film production.
A preferred embodiment of the filter used in melt extrusion molding is the same as the above filter used in pellet production.
At least one of the filtering during pellet production (Requirement 1) and the filtering during melt extrusion (Requirement 2) may be performed, but it is preferable to carry out both from the viewpoint of more exerting the effect of the present invention. ..

At the time of the melt extrusion molding, it is preferable to degas at least one of the melt of the fluoropolymer (C') pellet and the melt of the fluoropolymer (S') pellet, and the effect of the present invention is more effective. It is particularly preferable to degas the melts of both pellets from the point of view of exertion.
Degassing is performed, for example, by using a suction pump or the like connected to a vent hole of a melt extruder for film production.
The gauge pressure at the time of degassing is preferably −0.1 to −0.02 MPa, more preferably −0.1 to −0.06 MPa from the viewpoint that it is easy to keep the surface roughness within a predetermined range. preferable.
When a filter having a mesh size in the range of 0.026 to 0.87 mm is used, the gauge pressure is −0.1 to −0. It is preferable to perform degassing within the range of 02 MPa (preferably −0.1 to −0.06 MPa).
At least one of degassing during pellet production and degassing during melt extrusion molding may be carried out, but it is preferable to carry out both from the viewpoint of more exerting the effects of the present invention.

(Contact with alkaline aqueous solution)
Next, an example of a method for producing an ion exchange membrane using the precursor membrane (reinforced precursor membrane) will be shown.
The reinforced precursor film and the alkaline aqueous solution are brought into contact with each other to convert a group that can be converted into a carboxylic acid type functional group in the precursor layer (C') to obtain a layer (C) having a carboxylic acid type functional group. A layer (S) having the sulfonic acid type functional group is formed by converting a group that can be formed and converted into a sulfonic acid type functional group in the precursor layer (S') to form an ion exchange film. obtain. At this time, at least a part of the sacrificial yarn contained in the reinforced precursor membrane is hydrolyzed by the action of the alkaline aqueous solution to elute.

Upon contact with the alkaline aqueous solution, the precursor layer (C') is converted into the layer (C) 12 shown in FIG. 1, and the precursor layer (S') is converted into the layer (S) 14 shown in FIG. As described above, when the precursor layer (S') has a precursor layer (S'a) and a precursor layer (S'b), the precursor layer (S'a) is shown in FIG. The layer (Sa) 14A and the precursor layer (S'b) are converted into the layer (Sb) 14B in FIG. 1, respectively.
When the layer (Sa) 14A is composed of a plurality of layers, for example, when the layer (Sa) 14A is composed of two layers, the layer (Sa-1) 14Aa and the layer (Sa-2) 14Ab are the layers (Sa) as shown in FIG. 14A is formed, and layer (S) 14 is formed together with layer (Sb) 14B.

Examples of the method of bringing the precursor membrane (reinforced precursor membrane) into contact with the alkaline aqueous solution include a method of immersing the precursor membrane in the alkaline aqueous solution, a method of spray-coating the surface of the precursor membrane with the alkaline aqueous solution, and the like.
The temperature of the alkaline aqueous solution is preferably 30 to 100 ° C, particularly preferably 40 to 100 ° C, and even more preferably 45 to 100 ° C. The contact time between the reinforced precursor membrane and the alkaline aqueous solution is preferably 3 to 100 minutes, particularly preferably 5 to 50 minutes.

The alkaline aqueous solution preferably contains an alkali metal hydroxide, a water-soluble organic solvent and water.
Examples of the alkali metal hydroxide include sodium hydroxide and potassium hydroxide.
In the present specification, the water-soluble organic solvent means an organic solvent that is easily dissolved in water, and specifically, an organic solvent having a solubility in 1000 ml (20 ° C.) of water of 0.1 g or more is preferable. , 0.5 g or more of organic solvent is particularly preferable. The water-soluble organic solvent preferably contains at least one selected from the group consisting of aprotic organic solvents, alcohols and amino alcohols, and particularly preferably contains an aprotic organic solvent. As the water-soluble organic solvent, one type may be used alone, or two or more types may be used in combination.

Specific examples of aprotonic organic solvents include dimethyl sulfoxide (DMSO), N, N-dimethylformamide (DMF), N, N-dimethylacetamide, N-methyl-2-pyrrolidone (NMP) and N-ethyl-2. -Pyrrolidone is mentioned, and among these, dimethyl sulfoxide is preferable.
Specific examples of alcohols include methanol, ethanol, isopropanol, butanol, methoxyethoxyethanol, butoxyethanol, butylcarbitol, hexyloxyethanol, octanol, 1-methoxy-2-propanol and ethylene glycol.
Specific examples of amino alcohols include ethanolamine, N-methylethanolamine, N-ethylethanolamine, 1-amino-2-propanol, 1-amino-3-propanol, 2-aminoethoxyethanol and 2-aminothio. Examples thereof include ethoxyethanol and 2-amino-2-methyl-1-propanol.

The concentration of the alkali metal hydroxide is preferably 1 to 60% by mass, more preferably 3 to 55% by mass, and particularly preferably 5 to 50% by mass in the alkaline aqueous solution (100% by mass).
The content of the water-soluble organic solvent is preferably 1 to 60% by mass, more preferably 3 to 55% by mass, and particularly preferably 4 to 50% by mass in the alkaline aqueous solution (100% by mass).
The concentration of water is preferably 39 to 80% by mass in the alkaline aqueous solution (100% by mass).

A group that can be converted into a carboxylic acid type functional group and a group that can be converted into a sulfonic acid type functional group by contact with an alkaline aqueous solution are referred to as a carboxylic acid type functional group and a sulfonic acid type functional group (hereinafter, also referred to as "ion exchange group", respectively. After conversion to.), If necessary, salt exchange may be carried out to exchange the counter cation of the ion exchange group. In salt exchange, for example, the counter cation of an ion exchange group is exchanged from potassium to sodium. A known method can be adopted for salt exchange.

After the contact between the precursor membrane (reinforced precursor membrane) and the alkaline aqueous solution, a treatment for removing the alkaline aqueous solution may be performed. Examples of the method for removing the alkaline aqueous solution include a method of washing the precursor membrane contacted with the alkaline aqueous solution with water.

[Electrolyzer]
The alkali chloride electrolyzer of the present invention has an electrolytic tank including a cathode and an anode, and an ion exchange film for alkali chloride electrolysis, and the ion exchange film for alkali chloride electrolysis has the cathode and the anode. The layer (C) of the ion exchange film for alkali chloride electrolysis is arranged on the cathode side and is arranged in the electrolytic tank so as to be separated, and the layer (S) of the ion exchange film for alkali chloride electrolysis is arranged. ) Is arranged on the anode side.
According to the alkali chloride electrolyzer of the present invention, since it has the above-mentioned ion exchange membrane for alkali chloride electrolysis, alkali hydroxide having excellent caustic quality can be obtained.

One aspect of the alkali chloride electrolyzer of the present invention will be described with reference to FIG. 3, which is a schematic diagram, as an example. The alkali chloride electrolyzer 100 includes an electrolytic cell 110 having a cathode 112 and an anode 114, and the inside of the electrolytic cell 110 so as to divide the inside of the electrolytic cell 110 into a cathode chamber 116 on the cathode 112 side and an anode chamber 118 on the anode 114 side. It has an ion exchange film 1 to be mounted.
As shown in FIG. 1, the ion exchange membrane 1 has an electrolyte membrane 10 composed of a layer (C) 12 and a layer (S) 14, and a reinforcing member 20 arranged in the layer (S). The ion exchange membrane 1 is mounted in the electrolytic cell 110 so that the layer (C) 12 is on the cathode 112 side and the layer (S) 14 is on the anode 114 side. The cathode 112 may be arranged in contact with the ion exchange membrane 1 or may be arranged at a distance from the ion exchange membrane 1.

The material constituting the cathode chamber 116 is preferably a material resistant to alkali hydroxide and hydrogen, and specific examples thereof include stainless steel and nickel. The material constituting the anode chamber 118 is preferably a material resistant to alkali chloride and chlorine, and specific examples thereof include titanium.

The material constituting the base material of the cathode is preferably stainless steel or nickel from the viewpoint of resistance to alkali hydroxide and hydrogen, processability, and the like. The surface of the cathode substrate is preferably coated with, for example, Raney nickel.
As the material constituting the base material of the anode, titanium is preferable from the viewpoint of resistance to alkali chloride and chlorine, processability, and the like. The surface of the base material of the anode is preferably coated with, for example, ruthenium oxide or iridium oxide.

[Manufacturing method of alkali hydroxide]
The method for producing alkali hydroxide of the present invention is carried out by electrolysis of alkali chloride using the alkali chloride electrolyzer of the present invention. A known embodiment can be adopted except that it is performed by the alkali chloride electrolyzer of the present invention.
For example, in the case of electrolyzing a sodium chloride aqueous solution to produce a sodium hydroxide aqueous solution, the sodium chloride aqueous solution is supplied to the anode chamber 118 of the alkali chloride electrolyzer 100, the sodium hydroxide aqueous solution is supplied to the cathode chamber 116, and the cathode chamber is used. The sodium chloride aqueous solution is electrolyzed while maintaining the concentration of the sodium hydroxide aqueous solution discharged from 116 at a predetermined concentration (for example, 32% by mass).

Hereinafter, the present invention will be described in detail with reference to examples. However, the present invention is not limited to these examples. The blending amount of each component in the table described later indicates a mass standard.

[Surface roughness]
Each ion exchange membrane of Examples and Comparative Examples described later was cut out to a size of 20 mm (TD direction) × 100 mm (MD direction). The MD direction (Machine Direction) is a direction in which the precursor membrane and the ion exchange membrane are conveyed in the production of the ion exchange membrane. The TD (Transverse Direction) is a direction perpendicular to the MD direction.
Next, the cut out ion exchange membrane was immersed in ion exchange water at 25 ° C.
Then, the ion exchange membrane was taken out from the above solution, and the layer (C) was peeled from the end of the ion exchange membrane to 30 mm in the MD direction using tweezers while the ion exchange membrane was in a wet state.
Then, using a peeling tester (product name "TENSILON RTC-120A", manufactured by Orientec Co., Ltd.), a layer (C) is applied to the upper chuck and a layer (S) is applied to the lower chuck so that the distance between the chucks is 20 mm. It was fixed and peeled by 50 mm in the vertical direction at a tensile speed of 50 mm / min. A 5 mm square was cut out from the layer (S) that appeared by peeling using a peeling tester to prepare a sample for surface roughness measurement.
The above sample was fixed on a metal sample disk of an atomic force microscope (AFM) with carbon tape, the surface roughness (Ra) of two different points was measured at a 10 μm square, and the arithmetic mean value of this was measured as the surface roughness of the sample. It was set to (Ra). The outline of the atomic force microscope and the measurement conditions is as follows.
Atomic force microscope: Product name "CyPher S", Oxford Instruments measurement mode: AC-air mode Probe: AC160TS-C3 (Olympus, radius of curvature: 7 nm, spring constant: 26 N / m)

[Caustic quality]
^{The ion exchange film is placed in a test electrolytic cell having an effective energization area of 1.5 dm 2} (electrolytic surface size: 150 mm in length × 100 mm in width) so that the layer (C) faces the cathode, and the anode is titanium. Punched metal (minor axis 4 mm, major axis 8 mm) coated with a solid solution of ruthenium oxide, iridium oxide, and titanium oxide was used. Was installed so that the electrode and the film were in direct contact with each other and no gap was formed.
After operating for one day under the conditions of ^{a temperature of 90 ° C. and a current density of 8 kA / m 2} while adjusting the concentration of sodium chloride supplied to the anode chamber to 40 to 50 g / L, the concentration of sodium chloride supplied to the anode chamber is adjusted. The sodium chloride aqueous solution was electrolyzed by operating for 7 days under the conditions of a temperature of 90 ° C. and a current density of 6 kA / m ^{2 while adjusting the concentration to 200 g / L.} The sodium chloride concentration (ppm) in the obtained aqueous sodium hydroxide solution was measured by the mercury (II) thiocyanate absorptiometry.
The lower the concentration of sodium chloride in the aqueous sodium hydroxide solution, the better the caustic quality.

[Example 1]
A fluoropolymer having a group capable of converting into a carboxylic acid type functional group by copolymerizing TFE with a fluoropolymer having a group capable of converting into a carboxylic acid type functional group represented by the following formula (X) (hydrolysis). Later ion exchange capacity: 1.08 mEq / g) (hereinafter, also referred to as “polymer C”) was synthesized.
CF ₂ = CF-O-CF ₂ CF ₂ CF _2- COOCH ₃ ... (X)
The obtained polymer C was supplied to a melt extruder for producing pellets, and the polymer C was melted while degassing at a gauge pressure of −0.1 MPa. Then, the melt of the polymer C is passed through a metal mesh filter (manufactured by Kansai Wire Mesh Co., Ltd., 500 mesh, opening 0.026 mm) provided in the melt extruder, and then extruded from the melt extruder and cooled. And got a strand. Subsequently, the strands were cut to obtain polymer C pellets.

A fluoropolymer having a group capable of converting into a sulfonic acid type functional group by copolymerizing TFE with a fluoropolymer having a group capable of converting into a sulfonic acid type functional group represented by the following formula (Y) (hydrolysis). Later ion exchange capacity: 1.10 mEq / g) (hereinafter, also referred to as “polymer S1”) was synthesized.
CF ₂ = CF-O-CF ₂ CF (CF ₃ ) -O-CF ₂ CF _2- SO ₂ F ... (Y)
The obtained polymer S1 was supplied to a melt extruder for producing pellets, and the polymer S1 was melted while being degassed at a gauge pressure of −0.1 MPa. Then, the melt of the polymer S1 is passed through a metal mesh filter (manufactured by Kansai Wire Mesh Co., Ltd., 500 mesh, opening 0.026 mm) provided in the melt extruder, and then extruded from the melt extruder and cooled. And got a strand. Subsequently, the strands were cut to obtain pellets of polymer S1.

Then, the pellets of polymer C and the pellets of polymer S1 were supplied to a melt extruder for film production, and the pellets of polymer C and the pellets of polymer S1 were melted while being degassed at a gauge pressure of −0.1 MPa. .. Then, after passing the melt of the pellet of the polymer C and the melt of the pellet of the polymer S1 through a metal mesh filter (manufactured by Kansai Wire Mesh Co., Ltd., 500 mesh, opening 0.026 mm) provided in the melt extruder, respectively. , Formed into a film by the co-extrusion method, and has two layers, a precursor layer (C') made of polymer C (thickness: 12 μm) and a precursor layer (S'a) made of polymer S1 (thickness: 68 μm). A film A having a composition was produced.

A fluoropolymer having a group that can be converted into a sulfonic acid type functional group by copolymerizing TFE with a fluoropolymer having a group that can be converted into a sulfonic acid type functional group represented by the formula (Y) (after hydrolysis). Ion exchange capacity: 1.10 mEq / g) (hereinafter, also referred to as “polymer S2”) was synthesized.
The polymer S2 was formed into a film by a melt extrusion method to obtain a film B of a precursor layer (S'b) (thickness: 30 μm) made of the polymer S2.

After the PTFE film was rapidly stretched, the monofilament obtained by slitting to a thickness of 100 denier was twisted 2000 times / m to obtain a PTFE yarn as a reinforcing yarn. The sacrificial yarn was a PET yarn made of a 30-denier multifilament in which six 5-denier PET filaments were drawn together. A plain weave was performed so that one reinforcing thread and two sacrificial threads were alternately arranged to obtain a reinforcing cloth (reinforcing thread density: 27 threads / inch, sacrificial thread density: 108 threads / inch).

Using the film A, the film B, and the reinforcing cloth obtained above, the ion exchange membrane 1 corresponding to the aspect of FIG. 1 was manufactured as follows.
The film B, the reinforcing cloth, the film A, and the PET film for mold release (thickness: 100 μm) are stacked in this order so that the precursor layer (C') of the film A is on the PET film side for mold release, and the rolls are rolled. Laminated using. The PET film for mold release was peeled off to obtain a reinforced precursor film. The thickness of each layer in the reinforced precursor film was 12 μm for the precursor layer (C'), 68 μm for the precursor layer (S'a), and 30 μm for the precursor layer (S'b). The precursor layer (S'a) and the precursor layer (S'b) constitute the precursor layer (S').

It consists of 29.0% by mass of zirconium oxide (average particle size: 1 μm), 1.3% by mass of methylcellulose, 4.6% by mass of cyclohexanol, 1.5% by mass of cyclohexane and 63.6% by mass of water. The paste was transferred by roll pressing to the upper layer side (that is, the precursor layer (S'b)) of the precursor layer (S') of the reinforced precursor film to form an inorganic particle layer. The amount of zirconium oxide adhered was 20 g / m ² .

The reinforced precursor membrane having an inorganic particle layer formed on one side was treated with an aqueous solution of 5% by mass of dimethyl sulfoxide and 30% by mass of potassium hydroxide at 95 ° C. for 15 minutes.
As a result, -COOCH _{3 of polymer C and -SO 2} F of polymer S1 and polymer S2 are hydrolyzed and converted into ion exchange groups, and the precursor layer (C') becomes the layer (C) and the precursor layer. A film having (S'a) as a layer (Sa) and a layer (S'b) as a layer (Sb) was obtained.

A salt exchange treatment for exchanging the counter cation of the ion exchange group from potassium to sodium was carried out using 10% by mass sodium hydroxide.

A dispersion was prepared by dispersing zirconium oxide (average particle size: 1 μm) at a concentration of 13% by mass in an ethanol solution containing 2.5% by mass of the acid polymer of the polymer S1. This dispersion was sprayed onto the layer (C) side of the film to form an inorganic particle layer. The amount of zirconium oxide adhered was 3 g / m ² .
In this way, the ion exchange membrane of Example 1 was obtained.

[Examples 2 to 7, Comparative Examples 1 to 4]
Examples 2 to 7 and Comparative Examples 1 to 4 are the same as in Example 1 except that the metal mesh film during pellet production and film production and the gauge pressure during degassing are shown in Table 1. Ion exchange membrane was obtained. In Comparative Example 3, the metal mesh film was not used and degassing was not performed during the pellet production and the film production. In Comparative Example 4, no metal mesh film was used during pellet production and film production.

Using the ion exchange membranes of Examples and Comparative Examples obtained as described above, the surface roughness (Ra) and caustic quality were measured according to the method described above. The results are shown in Table 1.

As shown in Table 1, the surface roughness (Ra) of at least one of the surface on the layer (S) side and the surface on the layer (C) side that appears when the layer (S) is peeled from the layer (C) is By using an ion exchange membrane having a diameter of 1 to 15 nm, an alkaline chloride aqueous solution having excellent caustic quality can be produced.
On the other hand, when an ion exchange membrane having a surface roughness (Ra) outside the above range was used, the caustic quality of the produced alkaline aqueous chloride solution was inferior.

1 Ion exchange membrane for alkali chloride electrolysis 10 Electrolyte membrane 12 layers (C)
14 layers (S)
14A layer (Sa)
14Aa layer (Sa-1)
14Ab layer (Sa-2)
14B layer (Sb)
20 Reinforcing member 22 Reinforcing thread 24 Sacrificial thread 26 Filament 28 Elution hole 100 Chloride alkali electrolyzer 110 Electrolytic cell 112 Cathode 114 Anode 116 Cathode chamber 118 Anode chamber

Claims (10)

An ion exchange membrane for alkali chloride electrolysis in which a layer (C) containing a fluoropolymer having a carboxylic acid type functional group and a layer (S) containing a fluoropolymer having a sulfonic acid type functional group are laminated. There,
The layer (C) and the layer (S) are peeled off, and at least one of the surface on the layer (C) side and the surface on the layer (S) side, which appears by the peeling, has a surface roughness (Ra). ) Is 1 to 15 nm, an ion exchange membrane for alkali chloride electrolysis. The ion exchange membrane for alkali chloride electrolysis according to claim 1, wherein the surface roughness (Ra) is 1 to 10 nm. The ion exchange membrane for alkali chloride electrolysis according to claim 1 or 2, which includes a reinforcing member including a reinforcing thread in the layer (S). The ion exchange membrane for alkali chloride electrolysis according to any one of claims 1 to 3, wherein the ion exchange membrane for alkali chloride electrolysis has an inorganic particle layer containing inorganic particles and a binder on at least one outermost surface. A fluoropolymer (C') having a group that can be converted into a carboxylic acid type functional group and a fluoropolymer (S') having a group that can be converted into a sulfonic acid type functional group are pelleted, respectively.
Next, the pellets of the fluoropolymer (C') and the pellets of the fluoropolymer (S') are melt-extruded, respectively, and the precursor layer containing the fluoropolymer (C') and the fluoropolymer (C') are contained. A precursor film in which a precursor layer containing a fluoropolymer (S') is laminated is formed.
Next, the precursor film and the alkaline aqueous solution are brought into contact with each other to convert a group that can be converted into the carboxylic acid type functional group in the precursor layer containing the fluorine-containing polymer (C') to convert the carboxylic acid type functional group. The sulfonic acid is formed by forming a layer (C) containing a fluorine-containing polymer having a group and converting a group capable of converting into a sulfonic acid type functional group in the precursor layer containing the fluorine-containing polymer (S'). The method for producing an ion exchange film for alkali chloride electrolysis according to any one of claims 1 to 4, wherein a layer (S) containing a fluorine-containing polymer having a type functional group is formed.
A method for producing an ion exchange membrane for alkali chloride electrolysis, which satisfies at least one of the following requirements 1 and 2.
(Requirement 1) At the time of pelletization, at least one melt of the fluoropolymer (C') and the fluoropolymer (S') is filtered and then pelletized.
(Requirement 2) At the time of the melt extrusion molding, at least one melt of the fluoropolymer (C') pellet and the fluoropolymer (S') pellet is melt-extruded after being filtered. .. The method for producing an ion exchange membrane for alkali chloride electrolysis according to claim 5, wherein pelletization is performed while degassing in the first requirement, or melt extrusion molding is performed while degassing in the second requirement. The method for producing an ion exchange membrane for alkali chloride electrolysis according to claim 6, wherein the gauge pressure at the time of degassing is −0.1 to −0.02 MPa. The method for producing an ion exchange membrane for alkali chloride electrolysis according to claim 7, wherein the filter has a mesh size of 0.026 to 0.87 mm. The method for producing an ion exchange membrane for alkali chloride electrolysis according to any one of claims 5 to 8, wherein the filter has a mesh size of 0.026 to 0.32 mm. An electrolytic cell including a cathode and an anode,
The ion exchange membrane for alkali chloride electrolysis according to any one of claims 1 to 4 is provided.
The ion exchange membrane for alkali chloride electrolysis is arranged in the electrolytic cell so as to separate the cathode and the anode.
An alkali chloride electrolyzer in which the layer (C) is arranged on the cathode side and the layer (S) is arranged on the anode side.

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