JP2001323084A - Ion exchanging membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ion exchanging membrane attaining a low electrolysis voltage in the electrolysis of table salt and reducing the table salt concentration in a product, caustic soda. SOLUTION: This ion exchanging membrane consisting of at least two layers of a layer having carboxylic acid and a layer having sulfonic acid, is provided by adjusting the cluster diameter and the number of the clusters of respective layers to meet the above purpose.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ion exchange membrane having high ion conductivity and useful for various applications. Particularly, the present invention relates to a useful ion exchange membrane capable of lowering the salt concentration in a product caustic soda in salt electrolysis.

[0002]

2. Description of the Related Art In a salt electrolysis application, a laminated film of a layer having a carboxylic acid and a layer having a sulfonic acid is used, and a device is designed by designing the exchange capacity of the polymer and the thickness of the layer. However, when the exchange capacity of the polymer is increased or the thickness of the layer is reduced in order to lower the electrolysis voltage, the salt concentration in the caustic soda as a product increases, and the quality of the product deteriorates. The salt concentration in 50% product caustic soda is generally limited to 50 ppm, and the target value is 35 ppm.
ppm. Therefore, an ion exchange membrane capable of achieving a salt concentration in a low electrolytic voltage and in caustic soda has been desired.

[0003]

SUMMARY OF THE INVENTION The present invention provides an ion-exchange membrane having high ionic conductivity, in particular, achieves a low electrolysis voltage in salt electrolysis applications, and reduces the salt concentration in the product caustic soda to 50% caustic soda. 35 ppm
An object of the present invention is to provide an ion exchange membrane having the following lower characteristics.

[0004]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, have found that the diameter of the ion cluster formed by collecting sulfonic acid or carboxylic acid formed in the ion exchange membrane is large. The present inventors have found that it is possible to lower the electrolysis voltage and to reduce the salt concentration in the product caustic soda by controlling the number and the number thereof, and have accomplished the present invention. That is, the present invention provides an ion exchange membrane comprising at least two layers of a fluorinated polymer layer A having a sulfonic acid group and a fluorinated polymer layer B having a carboxylic acid group. Ionic cluster diameter formed by aggregation of sulfonic acid groups is 3.5 to 150 μm.
4.5 nm, the number of ion clusters is 0.8 × 10 ¹⁹ to
1.5 × 10 ¹⁹ / cm ³ , the thickness of the fluoropolymer layer B is 5 to 20 μm, the ion cluster diameter formed by collecting carboxylic acid groups is 2.5 to 3.2 nm, The number of clusters is 1.7 × 10 ^{19 to} 3.0 × 10 ¹⁹ /
cm ³ , which relates to an ion-exchange membrane.
Hereinafter, the present invention will be described in detail.

There is no particular limitation on the fluoropolymer A or B according to the present invention, and a fluoropolymer having a wide range of sulfonic acid groups, carboxylic acid groups or precursors thereof can be used. As a typical example, a typical example of the fluoropolymer A is selected from one or more polymerizable monomers represented by the following formula (1) and a polymerizable monomer group described below. Copolymers composed of one or more polymerizable monomers are exemplified. (Wherein, -Y _{is, -SO 3 H, -SO 2 F} , -SO 3 N
_{a, -SO 3 K, -SO 2} NH 2, an -SO ₂ NH _4. a is an integer of 0 to 6, b is an integer of 0 to 6, c is 0 or 1, and a + b + c ≠ 0, and n is an integer of 0 to 6. X is any one of Cl, Br or F when n ≧ 1, or a combination of plural kinds thereof.

Rt and Rt ′ are F, Cl, 1 to
It is selected from perfluoroalkyl groups having 10 carbon atoms and fluorochloroalkyl groups having 1 to 10 carbon atoms. On the other hand, in the case of the fluoropolymer B, one or more polymerizable monomers represented by the following formula (2) and one or more polymerizable monomers selected from the polymerizable monomer group described below are added thereto. Copolymers comprising a polymerizable monomer are exemplified. (Wherein -Y is -COOH, -CN, -COOR. A is an integer of 0 to 6, b is an integer of 0 to 6, c is 0 or 1, and a + b + c ＋ 0, n is 0-6
Is an integer. X is Cl, Br or F when n ≧ 1
, Or a combination of two or more.

R is selected from alkyl groups having 1 to 10 carbons, and Rt and Rt 'are F, C
1, a perfluoroalkyl group having 1 to 10 carbon atoms and a fluorochloroalkyl group having 1 to 10 carbon atoms. The polymerizable monomers to be copolymerized with these are tetrafluoroethylene, trifluoromonochloroethylene,
Trifluoroethylene, vinylidene fluoride, 1,1-difluoro-2,2-dichloroethylene, 1,1-difluoro-2-chloroethylene, hexafluoropropylene, 1,1,1,3,3-pentafluoropropylene,
Octafluoroisobutylene, ethylene, vinyl chloride, alkyl vinyl ester and the like can be mentioned.

When a precursor of the fluoropolymer A or B is used, a sulfonic acid group precursor is converted into a sulfonic acid group and a carboxylic acid group precursor is converted into a carboxylic acid group after film formation by a method described later. Then, they are converted into the fluoropolymer A or B component, respectively. The fluoropolymer containing a sulfonic acid group or a carboxylic acid group has a structure in which a hydrophobic polymer main chain portion and a hydrophilic sulfonic acid group or a carboxylic acid group portion are microscopically separated. Alternatively, carboxylic acid groups are gathered to form an “ion cluster” (TD Gierke et al., ACS Symposium Series, 1982N18)
0, p283-307 (Reference 1)). When operating with salt electrolysis, Na ⁺ ions move from the anolyte side to the catholyte side through this ion cluster. Therefore, the ease of passing such cations depends on the diameter and number of ion clusters and the thickness of the layer having ion clusters. The ease with which the cations pass has a correlation with the electrolysis voltage during salt electrolysis, and the easier the cations pass, the lower the electrolysis voltage.

On the other hand, the salt concentration in the product caustic soda has a correlation with the amount of Cl ^- ions that diffuse from the anolyte side to the catholyte side through ion clusters in the membrane. The amount of salt increases and the quality of the product deteriorates. Further, the current efficiency is determined by the amount of OH ^- ions of the product caustic soda moving from the cathode side to the anolyte side through the ion cluster, and the smaller the amount of movement, the higher the current efficiency. Thus, it is no exaggeration to say that the ion exchange membrane performance in salt electrolysis is all determined by the ion cluster structure.

The measurement of the ion cluster diameter and the number of ion clusters is performed by a small-angle X-ray scattering method (see the above-mentioned document 1). The ion cluster diameter and the number of ion clusters in the present invention are defined as follows.
After immersion for 24 hours in an X-ray diffractometer (RINT2500, R-AXIS-II, manufactured by Rigaku Corporation), the angle at which the peak of the scattered light intensity is obtained, and the measurement of the water content of the ion exchange membrane described later It is calculated from the values. Regarding the method of small-angle X-ray scattering measurement, a wet ion-exchange membrane sample is sealed in a thin film bag (having no small-angle X-ray scattered light intensity peak) with a wet solvent and placed on a sample table. At room temperature, X-rays are irradiated at a power of 6 kW using a Cu target as a radiation source, and scattered light is reduced, for example, from about 0.1 ° to about 5 °.
Measure in the angle range of °. A pinhole slit and a graphite monochromator are used for the X-ray measuring device. Taking the angle dependence of the obtained scattered light intensity shows a scattered light intensity peak at a specific angle.

The presence of this peak indicates that there is structural regularity in the ion exchange membrane. This is an ion cluster. The angle indicating the peak of the scattered light intensity is a factor indicating the interval between ion clusters. Here, as the intensity correction, the obtained scattered light intensity multiplied by s ² in the following equation is plotted on the vertical axis, and s ² is plotted on the horizontal axis.
This made the peaks clearer. s ² = ( ² sin θ / λ) ² λ: wavelength of irradiated X-ray (n
m) This peak angle is defined as the angle 2θ indicating the peak of the scattered light intensity used in equation (4). On the other hand, the wet weight (Wwe) of the same ion exchange membrane sample whose small-angle X-ray scattering intensity was measured was measured.
The water content (W) is determined by the formula (3) from the measured values of t) and the weights in the dry state (Wdry1, Wdry2). The weight in the wet state (Wwet) is 2% sodium bicarbonate (NaHC) at 25 ° C.
O ₃ ) is the weight of the film after immersing the film in O ₃ ) and removing the liquid adhering to the surface.
Is a film weight measured after cooling in a desiccator to 25 ° C. for 16 hours, and a weight in a dry state (Wdry2).
Is the membrane weight measured after washing the membrane with deionized water at 90 ° C. to remove the Donan alkali, followed by vacuum drying at 90 ° C. for 16 hours and cooling to 25 ° C. in a desiccator.

W = (Wwet−Wdry1) / Wdry2 (3) From the angle (2θ) showing the peaks of the water content and the scattered light intensity, the ion cluster diameter P (n) is obtained by the formulas (4) and (5).
m) and the number of ion clusters Q (pieces / cm ³ ) are calculated. (Refer to Document 1) The density of the polymer in the dry state was 2.1 here. P = {[V / (1 + V) × d 3 × 6.02 × 10 23 + d 3 × 85.68 / ((1 + V) × EW)] × 6 / π} (1/3) × 10 7 (4) Q = 1 / d ³ (5) where d = λ / 2 sin θ (nm) V = W / dry polymer density EW: equivalent weight λ: wavelength of irradiated X-ray (nm) The present invention relates to a fluoropolymer A and a fluoropolymer. It is an ion exchange membrane composed of at least two layers of coalescing B. The basic idea of the present invention is to develop current efficiency in the fluoropolymer B layer, reduce the salt in caustic soda in the fluoropolymer A layer, and lower the electrolysis voltage by devising both A and B layers. is there.

The fluorinated polymer A having a sulfonic acid group which forms at least one layer of the ion exchange membrane of the present invention
Has an ion cluster diameter of 3.5 to 4.5 nm, and preferably 3.5 to 4.0 nm. If it is smaller than 3.5 nm, the ionic conductivity is small, and as a result, the cell voltage becomes high. If it is larger than 4.5 nm, diffusion of chloride ions in salt electrolysis increases, and as a result, the salt concentration in the product caustic soda increases. The number of ion clusters of the fluoropolymer A of the present invention is from 0.8 × 10 ^{19 to} 1.5 × 10 ¹⁹ / cm ³ . If it is less than 0.8 × 10 ¹⁹ / cm ³ , the ionic conductivity is reduced, and if it is more than 1.5 × 10 ¹⁹ / cm ³ , the mechanical strength of the layer itself is reduced, which is not practical. The thickness of the layer of the fluoropolymer A is 50 to 150 μm,
Preferably it is 70-100 μm. If the thickness is less than 50 μm, the mechanical strength decreases.

[0014] At least the ion exchange membrane of the present invention.
Fluoropolymer B having a carboxylic acid group forming one layer
Has an ion cluster diameter of 2.5 to 3.2 nm.
More preferably, it is 2.5 to 3.0 nm. Smaller than 2.5nm
Low ion conductivity, resulting in high cell voltage
It becomes. If it is larger than 3.5 nm, the current efficiency decreases.
This is OH^-Insufficient charge repulsion for ions
I guess. Ions of the fluoropolymer B of the present invention
The number of clusters is 1.7 × 10¹⁹~ 3.0 × 10 ¹⁹Pcs / c
m^ThreeIt is. 1.7 × 10¹⁹Pieces / cm^ThreeLess and Io
Conductivity is reduced to 3.0 × 10¹⁹Pieces / cm^Threeis more than
And the current efficiency decreases. The thickness of the layer of the fluoropolymer B is
5 to 30 μm, preferably 10 to 20 μm
You. If the thickness is less than 5 μm, the current efficiency is poor over time.
When the thickness is more than 30 μm, the ion conduction
And the voltage during electrolysis increases.

The ion cluster is formed during a hydrolysis reaction for converting a sulfonic acid group precursor or a carboxylic acid group precursor into a sulfonic acid group or a carboxylic acid group, respectively.
Therefore, the obtained ion cluster structure is different depending on the hydrolysis reaction conditions. Specifically, it is a liquid composition of a hydrolysis reaction, and the cluster diameter becomes larger as the liquid composition has higher affinity for the fluoropolymer. Alternatively, the ion cluster diameter increases as the reaction temperature increases. By changing these, the ion cluster structure can be controlled.

The obtained ion cluster structure differs depending on the primary structure of the fluoropolymer A or B.
Specifically, for example, in the case of a copolymer of the monomer of the formula (1) and tetrafluoroethylene, as the ratio of the monomer of the formula (1) increases, and n, a, b, and c in the formula (1) increase. The ion cluster diameter of the obtained layer is larger. Therefore, the ion cluster structure can be controlled by changing the ratio of the monomer of formula (1) or (2) to the copolymer of tetrafluoroethylene.

In the film of the present invention, a reinforcing material may be present in the film to impart strength and dimensional stability. Such a reinforcing material is preferably in the form of a woven fabric composed of fibers made of a fluoropolymer from the viewpoint of long-term heat resistance and chemical resistance, and a plain woven fabric made of polytetrafluoroethylene is particularly preferred. . Further, as a particularly preferred form, for example, a tape yarn obtained by slitting a high-strength porous sheet made of polytetrafluoroethylene disclosed in JP-B-56-17216 on a tape, or JP-A-2-127509 is disclosed. Using 50-300 denier of highly oriented non-porous monofilaments of the disclosed polytetrafluoroethylene,
A plain weave structure with a weave density of 10 to 50 yarns / inch,
Further, the thickness is preferably in the range of 50 to 100 μm, and the aperture ratio is preferably 65% or more.

Further, in order to prevent misalignment of the reinforcing fibers during the production process of the membrane, the production process of a membrane usually called a sacrificial yarn, as disclosed in US Pat. No. 4,213,327 and US Pat. It may contain auxiliary fibers that elute in the environment. This auxiliary fiber may be dissolved before being integrated with the film during the production process of the membrane, or may be integrated without being dissolved. The woven fabric is generally ion-impermeable, and its open area ratio (total area of the window (inter-fiber gap) with respect to the entire area of the woven fabric expressed as a percentage) greatly affects the electrolytic voltage. It is preferable that the aperture ratio is large. The opening ratio of the reinforcing material is determined by the thickness (strictly, the width of the fiber) and the weaving density of the reinforcing fibers (reinforcing yarns) to be used. If an attempt is made to increase the aperture ratio, the reinforcing effect becomes insufficient.
The opening ratio of only the reinforcing yarn used in the present invention is 65%.
In the following cases, of course, the electrolytic voltage of the membrane increases, but at the same time, the substantial current density of the window section separated by the reinforcing yarn increases, and depending on the impurity level of the anolyte, the current efficiency may decrease. There is not preferred. The upper limit of the opening ratio is about 85% in view of the reinforcing effect and the weaving property of the woven fabric.

The reinforcing material may be present at any position in the film. However, the reinforcing material is present on the surface on the side of the fluoropolymer layer A, and the reinforcing material protective layer made of the fluoropolymer A is provided outside the reinforcing material. Is preferably provided. In this layer, the same monomers as those constituting the fluoropolymer A can be used. By providing this layer, peeling of the reinforcing material is prevented, and in particular, the tear strength of the film is improved. The diameter and number of ion clusters in this layer may be the same as or different from those of the fluoropolymer A. In the same range, this layer functions as a part of the fluoropolymer A. The thickness of the reinforcing material protective layer is 5 to 30.
μ is preferred.

The film of the present invention can be produced by a known technique, for example, hot press molding, roll molding, extrusion molding and the like. As a particularly preferred method, the fluoropolymer layer B
The (first layer) and the fluoropolymer layer A (second layer) are formed into a film by a coextrusion method (hereinafter, composite film X). The reinforcing material protective layer (third layer) is formed into a film by a single-layer extrusion method. Next, for example, a heating source and a vacuum source disclosed in JP-A-56-99234, which are provided on a flat plate or a drum having a large number of pores on the surface thereof through a heat-resistant release paper having air permeability. The third layer film, the calendered reinforcing material woven fabric, and the composite film X with the second layer side facing the reinforcing material woven fabric are laminated in this order, and the air between the layers is depressurized at a temperature at which each polymer melts. It is a method of integrating while removing. Here, co-extrusion of the first layer and the second layer contributes to increasing the adhesive strength at the interface. Further, the method of integrating under reduced pressure has a feature that the thickness of the second layer on the reinforcing material is larger than that of the pressure pressing method.

The method of hydrolyzing the integrated laminate to form an ion-exchange membrane can be performed under known conditions. As an example of a preferred method, there is a hydrolysis method using a water-soluble organic compound and MOH (M = alkali metal) as disclosed in JP-A-1-140987. The electrolytic film obtained by the above method may have an inorganic coating layer on the cathode side surface and the anode side surface for preventing gas adhesion as required. The coating layer can be formed by a known method, for example, a method disclosed in JP-A-3-137136 in which fine inorganic oxide fine particles are dispersed in a binder polymer solution and applied by spraying. Is preferred.

The salt electrolysis process conditions using the membrane according to the present invention are as follows.
1, preferably 185 to 205 g / l, and the concentration of the catholyte is 28 to 35%, preferably 30 to 33%,
A current density of 1-6 kA / m ² and electrolysis conditions of 70-90 ° C. are employed. Although the type of electrolytic cell, the type of power supply, or the type of electrode can be applied to all disclosed and used today, the membrane of the present invention is particularly advantageously used widely from a fine gap to a zero gap electrode arrangement. .

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.

[0024]

Embodiment 1 CF ₂ = CF ₂ and CF ₂ = CFOCF ₂ CF
(CF ₃ ) OCF ₂ CF ₂ COOCH ₃ copolymer (C) having an equivalent weight of 1250, and CF ₂ = CF ₂ and CF
₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ SO ₂ F copolymer (D) having an equivalent weight of 1020, and polymer (E) having an equivalent weight of 950 having the same structure as polymer (D). The film was prepared, and a film having a thickness of 100 μm was obtained using an extruder and a single layer T-die.

These films were prepared by adding 30% by weight of dimethyl sulfoxide (DMSO) and 1% of potassium hydroxide (KOH).
It is hydrolyzed in an aqueous solution containing 5% by weight at a temperature of 75 ° C. for 45 minutes, washed with water, and washed with 0.5N sodium hydroxide at 85 ° C. (N
aOH) to convert the exchange group to the Na form,
An equilibrium treatment was performed with% sodium bicarbonate (NaHCO ₃ ). As a result of measuring the small-angle X-ray scattering and the water content of these films, the polymer (C) having an equivalent weight of 1250 and having a carboxylic acid group had a cluster diameter of 2.75 nm and a cluster number of 2.2 ×.
10 ¹⁹ pieces / cm ³ , equivalent weight with sulfonic acid group 10
The cluster diameter of the polymer (D) of No. 20 is 3.80 nm,
The cluster number of the polymer (E) having a cluster number of 1.25 × 10 ¹⁹ / cm ³ and an equivalent weight of 950 is 4.20 n.
m, and the number of clusters was 0.98 × 10 ¹⁹ / cm ³ .

Next, using the polymers (C) and (D),
By using two extruders and an apparatus equipped with a co-extrusion T-die, the thickness of the polymer (C) layer is 15 μm and the thickness of the (D) layer is 7
A 5 μm two-layer film (a) was obtained. Furthermore, using the polymer (E), a 20 μm film (b) was obtained by a single-layer T-die. 150 denier tape yarn made of polytetrafluoroethylene (PTFE) as reinforcing yarn, 30 denier 6 filament polyethylene terephthalate (PET) as sacrificial yarn, and 35 denier 8 as weft yarn
Filament made of polyethylene terephthalate (PE
T) Using a yarn, a plain woven woven fabric was woven so that the reinforcing yarn PTFE was 16 yarns / inch and the sacrificial yarn PET was 64 yarns / inch, four times the PTFE. After weaving, the thickness of the woven fabric was smoothed to 68μ by passing between two heated metal rolls. The opening ratio of only the PTFE reinforcing yarn of the woven fabric was 75%.

[0027] Air-permeable release paper, film (b), reinforced woven fabric, and polymer (D) are placed on the woven fabric side on a drum having a heating source and a vacuum source inside, and having a large number of fine holes on the surface thereof. The two-layer films (a) are sequentially laminated so as to face
The resultant was integrated at a temperature of 30 ° C. under reduced pressure to obtain a composite film. In a mixed solution of a 50/50 parts by weight of water and ethanol equal amounts by weight is 950 CF ₂ = CF ₂ and CF ₂ = CFOCF ₂ CF (CF
₃ ) 5 wt% of a fluorinated polymer having a sulfonic acid group obtained by hydrolyzing a copolymer of OCF ₂ CF ₂ SO ₂ F was dissolved. A suspension in which 20 wt% of zirconium oxide was added to the solution and uniformly dispersed was obtained. This suspension was applied to both surfaces of the composite film and dried to form a metal oxide layer.

This membrane is made of dimethyl sulfoxide (DMS)
O) 30 wt%, potassium hydroxide (KOH) 15 wt%
Is hydrolyzed at a temperature of 75 ° C. for 45 minutes in an aqueous solution containing
After washing with water 0.5N sodium hydroxide (NaOH) at 85 ° C
The exchange group was converted into Na type by means of, and finally an equilibrium treatment was carried out with 2% sodium bicarbonate (NaHCO ₃ ) at 25 ° C. Effective energizing area 1
Using an electrolytic cell having a dm ² of 1.5 mm between the electrodes, a cathode was placed on the carboxylic acid layer side of the ion exchange membrane coated with the metal oxide layer, an anode was placed on the sulfonic acid layer side, and chloride was placed on the anode side. A sodium aqueous solution was supplied while being adjusted to 205 g / l, and 40 A / A while maintaining the alkali concentration on the cathode side at 32%.
Electrolysis was performed at dm ² and a temperature of 90 ° C. As a result,
Ten days after the start of the electrolysis, the current efficiency was 98.0%, the voltage between electrodes was 2.96 V, and the salt concentration in the produced caustic soda was 20 ppm in terms of 50%, which was stable for 30 days. The membrane was observed after electrolysis, but no abnormality was observed.

[0029]

EXAMPLE 2 CF ₂ having a carboxylic acid group = CF ₂ and CF
₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ COOCH ₃
And a polymer (F) having an equivalent weight of 1320 and CF ₂ CF ₂ and CF ₂ ＣＦCFOCF ₂ CF (CF ₃ ) OC
A polymer (D) having an equivalent weight of 1020 as a copolymer of F ₂ CF ₂ SO ₂ F, and a polymer (E) having an equivalent weight of 950 having the same structure as the polymer (D) are prepared. Films each having a thickness of 100 μm were obtained by a T-die.

These films were prepared by adding 30% by weight of dimethyl sulfoxide (DMSO) and 1% of potassium hydroxide (KOH).
It is hydrolyzed in an aqueous solution containing 5 wt% at a temperature of 90 ° C. for 45 minutes, washed with water, and heated to 85 ° C. with 0.5N sodium hydroxide (N
aOH) to convert the exchange group to the Na form,
The equilibrium treatment at% sodium bicarbonate (NaHCO _3). As a result of measuring the small angle X-ray scattering and the water content of these films, the polymer (F) having a carboxylic acid group and having an equivalent weight of 1320 had a cluster diameter of 2.90 nm and a cluster number of 2.00.
× 10 ¹⁹ / cm ³ , equivalent weight 1 with sulfonic acid group
020 polymer (D) has a cluster diameter of 4.20 n
m, the number of clusters was 0.98 × 10 ¹⁹ / cm ³ , and the cluster diameter of the polymer (E) having an equivalent weight of 950 was 4.40.
nm, and the number of clusters was 0.84 × 10 ¹⁹ / cm ³ .

Next, using the polymers (F) and (D),
By using two extruders and an apparatus equipped with a co-extrusion T-die, the thickness of the polymer (F) layer was 15 μm and the thickness of the (D) layer was 7
A two-layer film (c) of 5 μm was obtained. Furthermore, using the polymer (E), a film (d) of 20 μm was obtained by a single-layer T-die. These films were combined with the reinforced woven fabric used in "Example 1" to obtain a composite film under the same conditions. Further, a metal oxide layer was formed on the surface as in "Example 1". This membrane is dimethylsulfoxide (DMSO) 30w
hydrolyzed at 90 ° C. for 45 minutes in an aqueous solution containing 0.1% by weight and 15% by weight of potassium hydroxide (KOH).
The exchange group was converted to Na form with 0.5N sodium hydroxide (NaOH) at 25 ° C, and finally 2% sodium bicarbonate (NaHCO) at 25 ° C.
_The equilibrium treatment was performed in ₃ ). When this film was electrolyzed under the same electrolysis cell and electrolysis conditions as in "Example 1," electrolysis was started.
After 9 days, the current efficiency is 98.0%, the voltage between contacts is 2.96V,
The salt concentration in the produced caustic soda is 20 ppm in 50% conversion.
And remained stable for 30 days. The membrane was observed after electrolysis, but no abnormality was observed.

[0032]

Embodiment 3 CF ₂ = CF ₂ and CF ₂ = CFOCF ₂ CF
(CF ₃ ) OCF ₂ CF ₂ COOCH ₃ copolymer (C) having an equivalent weight of 1250, and CF ₂ = CF ₂ and CF
₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ SO ₂ F copolymer (D) having an equivalent weight of 1020, and polymer (E) having an equivalent weight of 950 having the same structure as polymer (D). The film was prepared, and a film having a thickness of 100 μm was obtained using an extruder and a single-layer T-die.

These films were hydrolyzed under the same conditions as in "Example 2", and finally, 2% sodium bicarbonate (NaHC) at 25.degree.
Equilibration was performed with O ₃ ). Small angle X of these films
As a result of measuring the light scattering and the water content, the polymer (C) having an equivalent weight of 1250 having a carboxylic acid group has a cluster diameter of 3.05 nm and a number of clusters of 1.87 × 10 ¹⁹ / c.
Cluster of polymer (D) having an equivalent weight of 1020 having m ³ and a sulfonic acid group, a cluster diameter of 4.20 nm, a number of clusters of 0.98 × 10 ¹⁹ / cm ³ , and a cluster of polymer (E) having an equivalent weight of 950 The diameter was 4.40 nm, and the number of clusters was 0.84 × 10 ¹⁹ / cm ³ .

Next, using the polymers (C) and (D),
By using two extruders and an apparatus equipped with a co-extrusion T-die, the thickness of the polymer (C) layer is 15 μm and the thickness of the (D) layer is 7
A 5 μm two-layer film (e) was obtained. Further, using the polymer (E), a 20 μm film (f) was obtained by a single-layer T-die. These films were combined with the reinforced woven fabric used in "Example 1" to obtain a composite film under the same conditions. Further, a metal oxide layer was formed on the surface as in "Example 1". This membrane was hydrolyzed in the same manner as in "Example 2"
2% sodium bicarbonate (NaHCO ₃ ). When this film was electrolyzed under the same electrolysis cell and electrolysis conditions as those of “Example 1,” the current efficiency 10 days after the start of electrolysis was 97.5%,
The voltage between the electrodes was 2.93 V, and the sodium chloride concentration in the produced caustic soda was 30 ppm in terms of 50%, which was stable for 30 days. The membrane was observed after electrolysis, but no abnormality was observed.

[0035]

[Comparative Example] CF ₂ having a carboxylic acid group = CF ₂ and CF ₂
= CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ COOCH ₃
(G) having a copolymer weight of 1070 and CF ₂ = CF ₂ and CF ₂ = CFOCF ₂ CF (CF ₃ ) OC
A polymer (D) having an equivalent weight of 1020 as a copolymer of F ₂ CF ₂ SO ₂ F, and a polymer (E) having an equivalent weight of 950 having the same structure as the polymer (D) are prepared. Films each having a thickness of 100 μm were obtained by a T-die.

These films were hydrolyzed under the same conditions as in "Example 2", and finally, 2% sodium bicarbonate (NaHC) at 25.degree.
Equilibration was performed with O ₃ ). Small angle X of these films
As a result of measuring the line scattering and the water content, the polymer (G) having an equivalent weight of 1070 and having a carboxylic acid group had a cluster diameter of 3.70 nm and a number of clusters of 1.30 × 10 ¹⁹ / c.
Cluster of polymer (D) having an equivalent weight of 1020 having m ³ and a sulfonic acid group, a cluster diameter of 4.20 nm, a number of clusters of 0.98 × 10 ¹⁹ / cm ³ , and a cluster of polymer (E) having an equivalent weight of 950 The diameter was 4.40 nm, and the number of clusters was 0.84 × 10 ¹⁹ / cm ³ . Next, using the polymers (G) and (D), the thickness of the polymer (G) layer was 25 μm and the thickness of the (D) layer was 75 μm by an apparatus equipped with two extruders and a co-extrusion T-die. (G) was obtained. Further, using the polymer (E), a single layer T
A 20 μm film (h) was obtained by die. These films were combined with the reinforced woven fabric used in "Example 1" to obtain a composite film under the same conditions. Further, a metal oxide layer was formed on the surface as in "Example 1".

This membrane was hydrolyzed in the same manner as in "Example 2" and equilibrated with 2% sodium bicarbonate (NaHCO ₃ ) at 25 ° C. When this membrane was electrolyzed under the same electrolysis cell and electrolysis conditions as those in “Example 1,” the current efficiency 10 days after the start of electrolysis was 9
6.5%, the voltage between electrodes was 2.93 V, and the salt concentration in the produced caustic soda was 40 ppm in terms of 50%, which was stable for 30 days. The membrane was observed after electrolysis, but no abnormality was observed.

[0038]

As described above, according to the present invention, it is possible to obtain an ion exchange membrane which achieves a low electrolysis voltage in salt electrolysis and has a low salt concentration in the product caustic soda.

Claims (1)

[Claims] 1. An ion exchange membrane comprising at least two layers of a fluorinated polymer layer A having a sulfonic acid group and a fluorinated polymer layer B having a carboxylic acid group, wherein the thickness of the fluorinated polymer layer A is 50 １５０150 μm, the diameter of an ion cluster formed by collecting sulfonic acid groups is 3.5 to 4.5.
nm, the number of ion clusters is 0.8 × 10 ^{19 to} 1.5 ×
10 ¹⁹ particles / cm ³ , the thickness of the fluoropolymer layer B is 5 to 20 μm, the diameter of ion clusters formed by collecting carboxylic acid groups is 2.5 to 3.2 nm, and the number of ion clusters is 1 An ion-exchange membrane characterized by having a density of 0.7 × 10 ^{19 to} 3.0 × 10 ¹⁹ / cm ³ .