JP2002348389A - Fluoropolymer ion-exchange membrane having wide ion- exchange capacity and its production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluoropolymer ion-exchange membrane which is prepared at a low cost, has an ion-exchange capacity with a wide range and a high oxidation resistance, and is especially suitable for a fuel cell. SOLUTION: This fluoropolymer ion-exchange membrane mainly comprises a long-chain branched polytetrafluoroethylene structure and has oxyhydrofluorocarbon side chains having sulfo groups, represented by [-OCH2 CF2 CF2 SO3 H], and bonded thereto. The membrane is of a proton-exchange type and has an ion-exchange capacity of 0.5-2.0 meq/g, a tensile strength in the water-containing state of 5-25 MPa, and an electrical conductivity at 25 deg.C of 0.05-0.25 Ω<-1> .cm<-1> . The production method for the ion-exchange membrane is also provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluorine-containing polymer ion-exchange membrane having not only a solid polymer electrolyte membrane suitable for a fuel cell but also a membrane, and having excellent oxidation resistance. It relates to the manufacturing method.

[0002]

2. Description of the Related Art A fuel cell using a solid polymer electrolyte type ion exchange membrane has a low operating temperature of 100 ° C. or less and a high energy density, and is therefore expected to be used as a power source for electric vehicles and a simple auxiliary power source. In this fuel cell, an ion exchange membrane which is a solid polymer electrolyte, a platinum-based catalyst,
There are important element technologies such as gas diffusion electrodes and polymer electrolyte membrane-electrode assemblies. However, among these, the development of a polymer ion exchange membrane having good characteristics for use in fuel cells is one of the most important technologies.

[0003] In a polymer ion exchange membrane fuel cell, a gas diffusion electrode is bonded to both sides of the ion exchange membrane, and the membrane and the electrode have a substantially integral structure. For this reason, the ion exchange membrane acts as an electrolyte for conducting protons, and also has a role as a diaphragm for preventing the fuel or hydrogen or methanol from directly mixing with the oxidant even under pressure. Such an ion exchange membrane has a high proton exchange rate as an electrolyte, a high ion exchange capacity, and a large current flowing for a long period of time. It is required that resistance to radicals and the like (oxidation resistance) be excellent, and that water retention be constant and high in order to keep electric resistance low. On the other hand, from the role of the membrane, the membrane has high mechanical strength and excellent dimensional stability, and does not have excessive gas permeability for hydrogen gas or oxygen gas as a fuel. It is required to have long-term durability.

[0004] In the early polymer ion exchange membrane fuel cells, hydrocarbon polymer ion exchange membranes produced by copolymerization of styrene and divinylbenzene were used. However, this ion exchange membrane was poor in durability due to its extremely poor durability due to oxidation resistance, and was poor in practical use. Thereafter, a fluorocarbon (fluorine) polymer perfluorosulfonic acid membrane developed by DuPont, Inc. Nafion (registered trademark of DuPont) "and the like have been generally used.

However, conventional fluorine-based polymer ion-exchange membranes such as "Nafion" have excellent chemical durability and stability, but have a small ion exchange capacity of about 1 meq / g, which is insufficient. Electric output is not obtained, and the water retention is insufficient, drying of the ion exchange membrane occurs and proton conductivity decreases, and the reaction of fuel gas and oxidant gas at the electrode catalyst is inhibited. was there. Also, fluorine-based polymer ion-exchange membranes such as Nafion are difficult and complicated to synthesize monomers, and the process of polymerizing them to produce a polymer membrane is also complicated. This is a major obstacle to putting a fuel cell into a vehicle or the like for practical use. For this reason, efforts have been made to develop a low-cost, high-performance electrolyte membrane that replaces Nafion and the like.

In addition to the above, the conventional fluorine-based polymer ion-exchange membrane cannot introduce a cross-linked structure, so that the ion-exchange capacity cannot be increased. That is, if an attempt is made to increase the ion exchange capacity and to introduce a large amount of sulfonic acid groups, the membrane strength is remarkably reduced due to the absence of a crosslinked structure in the polymer chain, and the polymer is easily broken.
Therefore, in the conventional ion exchange membrane made of a fluorine-based polymer, the amount of sulfonic acid groups needs to be suppressed to such an extent that the membrane strength is maintained, so that only a relatively small ion exchange capacity can be obtained. This does not have the required performance as an ion exchange membrane for flowing a large current such as for a fuel cell.

Further, in the radiation graft polymerization method closely related to the present invention, an attempt has been made to produce a solid polymer electrolyte membrane by grafting a monomer capable of introducing a sulfonic acid group into a fluorine-based polymer membrane. ing. However, when irradiating radiation such as electron beam or γ-ray to perform a graft reaction in a fluoropolymer film, a significant decrease in film strength due to deterioration due to irradiation is observed, and the graft ratio is also extremely low. You can only get things. For this reason, when a fluorine-based ion-exchange membrane is produced by a radiation grafting method, the membrane is very fragile, and only a membrane having an extremely low ion-exchange capacity can be produced. In many cases, the membrane cannot be practically used as a battery membrane. there were.

For example, polytetrafluoroethylene (PT
FE) or PTFE-propylene hexafluoride copolymer (FE
In the case of P) or PTFE-perfluoroalkylvinyl ether copolymer (PFA) or the like, it is known that remarkable cleavage of the polymer main chain occurs upon irradiation with radiation. FEP
In a battery fabricated using a solid polymer electrolyte membrane in which styrene is radiation-grafted and sulfonic acid groups are introduced into the membrane, sulfonic acid groups are desorbed and the membrane swells due to decomposition of the membrane immediately after battery operation. It has been reported that as a result, the internal resistance of the battery increases, and the battery performance significantly decreases even in short-time operation for several tens of hours (Electr
ochimica Acta 40, 345 (1995)).

On the other hand, in the case of a fluorine-based polymer in which the main chain of the polymer partially contains an olefin hydrocarbon structure, the breakage of the main chain due to irradiation is greatly reduced. For example, an ion exchange membrane synthesized by introducing a styrene monomer into an ethylene-tetrafluoroethylene copolymer membrane containing a hydrocarbon structure by a radiation grafting reaction and then sulfonating it functions as an ion exchange membrane for a fuel cell. Kaihei 9-102322). However, as a drawback, the main chain and polystyrene graft chain of the polymer film are composed of hydrocarbons. Hydrocarbon radicals and polystyrene graft chains are generated by hydroxyl radicals generated when a large current is applied to the film for a long time. Of the membrane occurs, and the ion exchange capacity of the membrane is greatly reduced. Further, when the ion exchange membrane containing a large amount of the hydrocarbon structure is used for the solid electrolyte membrane, particularly when the catalyst layer of the gas diffusion electrode does not have sufficient water repellency, the positive electrode generates water in a fuel cell reaction. It has been pointed out that there is a problem that the output is reduced due to excessive wetness (Japanese Patent Laid-Open No. 11-11131).
0).

[0010]

SUMMARY OF THE INVENTION It has been difficult to introduce a crosslinked structure in a polymer having a fluorinated carbon skeleton main chain, particularly an ion exchange membrane mainly composed of polytetrafluoroethylene (PTFE). In fact, the ion exchange capacity could not be increased. In addition, when these films were irradiated with radiation such as γ-rays or electron beams in order to carry out a graft reaction, a significant decrease in the film strength was observed due to breakage of molecular chains, and further, only those having a low graft ratio were obtained. . For this reason, when a fluorine-based polymer membrane having ion conductivity is produced by radiation grafting, the membrane strength is low, and the ion exchange capacity is small, so that the membrane does not have sufficient performance as an electrolyte membrane or a diaphragm. Was. Furthermore, when a hydrocarbon-based monomer such as styrene is grafted to a fluorine-based polymer such as PTFE, the hydroxyl radicals generated when a large current flows degrade the styrene graft chain. It is known that the ion-exchange capacity of is lost. From these, the fluoropolymer by radiation grafting, especially,
Ion exchange membranes for fuel cells mainly composed of PTFE were not practically usable.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to overcome such problems of the prior art.
An object of the present invention is to provide a fluorine-based polymer ion-exchange membrane obtained by radiation grafting, which has excellent properties as a solid polymer electrolyte and has excellent oxidation resistance at low cost. That is, [—OCH ₂ CF ₂ CF ₂ SO _2] is an oxyhydrofluorocarbon side chain having a long chain branched polytetrafluoroethylene structure as a main component and having a sulfonic acid group.
₃ H] -bonded fluoropolymer ion exchange membrane, and the ion exchange capacity of the ion exchange membrane is 0.5.
２．０2.0 meq / g, tensile rupture strength of the ion exchange membrane in a water-containing state of 5-25 MPa, and electric conductivity at 25 ° C. of 0.05-0.25 Ω ⁻¹ · cm ^−1. To provide an excellent fluorine-based polymer ion-exchange membrane, and to graft a specific hydrofluorovinyl ether monomer onto a long-chain branched polytetrafluoroethylene membrane by a radiation grafting method and introduce sulfonic acid groups into the graft. To provide a method for producing a fluorinated polymer ion exchange membrane.

That is, polytetrafluoroethylene (PTF
E) is irradiated with high-temperature radiation to obtain a long-chain branched PTEF,
This was followed by irradiation to graft various monomers and further research into the introduction of sulfonic acid groups into the graft chains.As a result, the ion exchange capacity, the biggest drawback of fluorine-based polymer ion exchange membranes, was small. And, the capacity range is narrow, the oxidation resistance which is the biggest drawback of the PTFE ion exchange membrane grafted with hydrocarbon monomer is low, and the membrane strength seen in the radiation grafted PTFE membrane is greatly reduced. All of these problems could be solved. Further, they have invented a PTFE-based polymer ion-exchange membrane capable of appropriately controlling each property including the water content and the electric conductivity within a wide range.

The long-chain branched PTFE is represented by the following formula:

Embedded image and

A fluorine-containing polymer having a repeating unit represented by the following formula:

And

Refers to a mixture of fluoropolymers having a repeating unit as a bond.

[0014]

Embedded image

[0015]

Embedded image

[0016] Such a long-chain branched PTFE is obtained by adding PTFE to 30.
Under a temperature range of 0 to 365 ° C. and a reduced pressure of 10 ^{−3 to} 10 Torr,
Or γ in an inert gas at an oxygen partial pressure of 10 ^{−3 to 2} Torr
It can be manufactured by irradiating radiation of 5 rays or 500 kGy with an electron beam or an electron beam. Inert gases such as nitrogen, argon,
Helium gas or the like is used. A long-chain branched PTFE membrane can be produced by irradiating a PTFE membrane under the above conditions.However, a long-chain branched PTFE membrane can also be produced by irradiating a sintered block-shaped PTFE under the same conditions and shaving it. Obtainable.
The long-chain branched PTFE has many amorphous portions even in view of its molecular structure, and can solve the drawback of low graft ratio. For example, when styrene is used as a graft monomer,
Compared with normal PTFE, long-chain branched PTFE can significantly increase the graft ratio, and therefore has a 2-
Ten times as many sulfonic acid groups can be introduced into long-chain branched PTFE (Japanese Patent Application No. 2000-170450). The fluorine-based polymer ion exchange membrane according to the present invention is mainly composed of a long-chain branched polytetrafluoroethylene structure obtained by irradiating high-temperature radiation of PTFE,
It is composed of a fluorine-based polymer ion-exchange membrane to which [—OCH ₂ CF ₂ CF ₂ SO ₃ H] which is an oxyhydrofluorocarbon side chain having a sulfonic acid group is bonded. The above long-chain branched PTFE membrane is again exposed to an electron beam or γ-ray at a pressure of 10 ⁻³ torr or less or at room temperature in an inert gas at 5 to 500 kG.
After irradiating with y, CF ₂ ＣＦCFOCH ₂ CF ₂ which is a hydrofluorovinyl ether monomer from which oxygen gas has been removed
CF ₂ SR, CF ₂ = CFOCH ₂ CF ₂ CF ₂ SO ₂ R, C
F ₂ ＣＦCFOCH ₂ CF ₂ CF ₂ SX and / or CF
₂ = CFOCH ₂ CF ₂ CF ₂ SO ₂ X (where R: -CH
₃ or, -C (CH _{3) 3,} and,, X: -Cl, or, is reacted by addition of -F), grafting the monomer to the branched long chain PTFE film. At this time, the monomer may be diluted using a solvent such as 1,1,2-trichlorotrifluoroethane. Grafting temperature is -78 ° C under inert gas.
The reaction is carried out at a temperature of 100 ° C. or below the boiling point of the solvent in the monomer alone or in a solution obtained by diluting the monomer with the solvent. Since the presence of oxygen inhibits the grafting reaction, these series of operations are performed in an inert gas such as argon gas or nitrogen gas. Use with oxygen removed by bubbling. The radiation dose is proportional to the graft rate (see equation (1) in Example 2), and the higher the dose, the higher the graft rate, but the graft rate is 100% by weight.
(wt%), it gradually becomes saturated. The graft ratio is 5 to 200% by weight, more preferably 15 to 150% by weight, based on the long-chain branched PTFE. When performing radiation grafting on a long-chain branched PTFE, tetrafluoroethylene is used as a comonomer (comonomer) for the above hydrofluorovinyl ether monomer, and 2
A fluorine-based polymer ion-exchange membrane into which 3-80 wt% of tetrafluoroethylene units are introduced can be produced. This is because, when the graft chain is introduced, for example, 2 mol of tetrafluoroethylene comonomer equivalent to 1 mol of the above-mentioned hydrofluorovinyl ether monomer dissolved in a solvent is introduced into a reaction vessel and allowed to react, whereby high-resolution NMR is achieved. The analysis shows that the co-grafting was at a ratio of about 2: 3. Thus, by changing the charged composition ratio of the hydrofluorovinyl ether monomer and the tetrafluoroethylene comonomer, long-chain branched PTFE
It is preferable that 23 to 80% by weight of a tetrafluoroethylene unit is introduced into the graft chain of the membrane. A fluorine-based polymer ion-exchange membrane having a crosslinked structure can be further produced by copolymerization with divinylbenzene in the graft chain. This is when the above-mentioned long-chain branched PTFE is subjected to radiation grafting, the above-mentioned hydrofluorovinyl ether monomer, or 1 to 10% by weight of a crosslinking aid with respect to the total amount of the hydrofluorovinyl ether monomer and the tetrafluoroethylene comonomer. It is obtained by adding a certain divinylbenzene and performing a reaction. By introducing a crosslinked structure into the grafted chain of long-chain branched PTFE, the oxidation resistance of the present fluoropolymer ion exchange membrane can be improved.

Subsequently, the —SR group or —SO ₂ R group (R: —CH ₃ , R—CH ₃₎ in the graft chain of the obtained long-chain branched PTFE film is obtained.
Or —C (CH ₃ ) ₃ ) or —SX group or —SO ₂
X group (X: -Cl, or, -F) changed to a sulfonic acid group [-SO ₃ H], a oxyhydrofluorocarbon side chains having sulfonic acid groups [-OCH ₂ CF
_[2 CF ₂ SO ₃ H] is introduced.

For example, in the graft chain, -SCH_ThreeGroup or-
SC (CH_Three)_ThreeGrafted long-chain branched PTFE membranes
Is 85 to 1,1,2-trichlorotrifluoroethane solvent.
Reacted with chlorine gas at a temperature of 125 ° C. to form an —SCl group,
Subsequently, trifluoroacetic acid and water were allowed to exist in the same solvent.
-SO_TwoCl group. Add this to NaOH solution
And treated with sulfuric acid solution_TwoOH group. Also,-
SC (CH_Three)_ThreeGrafted long-chain branched PTFE membranes
Is oxidized with acetonitrile-HOF reagent and subsequently
Bromofluoride (BrF_Three) At -SO_TwoConvert to F group.
This is treated with a sulfuric acid solution followed by a NaOH solution to give -SO_Two
OH group. In addition, grafts having -SCl or -SF groups
Long chain branched PTFE membrane is oxidized with acetonitrile / HOF reagent
And -SO_TwoConverted to F group, followed by NaOH solution
And treated with sulfuric acid solution_TwoOH group. These methods
Is a graph of the long-chain branched PTFE film obtained above.
-SR group or -SO in the chain_TwoR group or -SX group or
-SO_TwoX group is a sulfonic acid group (—SO _TwoOH)
Oxyhydrofluorocarbon side with sulfonic acid group
A chain [-OCH_TwoCF_TwoCF_TwoSO_ThreeH]
An element-based polymer ion exchange membrane can be obtained.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The fluorine-based polymer ion-exchange membrane according to the present invention has an ion-exchange capacity (formula of Example 2) based on the graft amount of the above-mentioned hydrofluorovinyl ether monomer or hydrofluorovinyl ether monomer and tetrafluoroethylene comonomer. (See (2))
Can be changed.

In the case of a single graft of a hydrofluorovinyl ether monomer, for example, CF ₂ ＣＦCFOCH ₂ C
After grafting onto long-chain branched PTFE using F ₂ CF ₂ SF monomer and then introducing a sulfonic acid group, the graft ratio was 17%, the ion exchange capacity was about 0.5 meq / g, and the graft ratio was 50%. About 1.2 meq / g, about 1.8 meq / g at a graft rate of 100%, and about 2.2 meq at a graft rate of 150%.
/ G of film is obtained. Here, the ion exchange capacity of the ion exchange membrane is the amount of exchange groups (meq / g) per 1 g of the weight of the dry ion exchange membrane (see Example 2).

In the cografting of a hydrofluorovinyl ether monomer and a tetrafluoroethylene comonomer, when the charged monomer ratio is 1: 2, the graft ratio is 30%, the ion exchange capacity is about 0.5 meq / g, and the graft ratio is 80. % And about 1.4 meq / g at a graft ratio of 160%.

However, when the graft ratio is set to 150% or more,
Gradually, the mechanical strength of the film when hydrated begins to decrease. From these, the ion exchange capacity of the membrane of the present invention is 0.3 me.
q / g to 2.5 meq / g, preferably 0.5 to 0.5 meq / g in consideration of the graft ratio and membrane strength.
2.0 meq / g.

In the fluoropolymer ion exchange membrane of the present invention, the amount of the introduced sulfonic acid group, and

[Formula 1]

The double bond at the terminal of the molecule is a sulfonation reaction
Depending on the amount of -COOH groups that have been partially converted,
The water content of the polymer (see Example 2) can be controlled. This membrane
When used as an ion exchange membrane for fuel cells, the water content
If the pressure is too low, the oxygen or hydrogen
When using air, the output voltage drops and high current density and
High output cannot be maintained. Also, slight changes in operating conditions
The electrical conductivity and gas permeability coefficient change depending on
No. Therefore, the ion exchange membrane is less likely to dry.
The change in gas permeability and electrical conductivity is relatively small.
Is necessary. The water content of the ion exchange membrane of the present invention is 10
It can be controlled in the range of ~ 80 wt%. Generally ion exchange
As the exchange capacity increases, the water content also increases,
Can on-exchange membranes change moisture content?
The water content of the membrane is 10 to 100 wt%, preferably 10 to 100 wt%.
８０80 wt%. In the fluoropolymer according to the present invention
Despite high ion exchange capacity, long chain branched PTFE entanglement
Due to membrane swelling due to binding and binding at both ends of long chain branch
An increase in the water content is also suppressed, and an appropriate film strength can be maintained.
Here, the water-containing state of the membrane means that the
Ion-exchange membrane is stored and its moisture content is
(Refer to the formula (3) in Example 2)
Vacuum the weight of the ion exchange membrane at 60 ° C. for 16 hours.
It is the weight percentage of the membrane when dried. Conventionally, fluorine-based
For ion exchange membranes, from the viewpoint of mechanical strength and dimensional stability of the membrane
Only those with an ion exchange capacity of around 1 meq / g are available for practical use.
I couldn't. This is a fluorine-based polymer,
In general, it is difficult to introduce a crosslinked structure with PTFE.
For this reason, the PTFE crystal part is mainly used to strengthen the PTFE membrane.
Degree is maintained. Therefore, a large amount of graft chains and sulfo
When the acid group is introduced, the strength of the PTFE membrane drops sharply,
Become intolerable. In contrast, the long-chain branched PT of the present invention
Fluorine polymer with FE structure has long chain branch entanglement and long chain component
Ion exchange capacity of 2.0 meq due to the bond at both ends
/ G to introduce a large amount of graft chains and sulfonic acid groups
However, the mechanical properties and dimensional stability of the membrane are maintained,
(Examples 2, 3). Ion exchange
A film with a capacity of 2.0 meq / g or more can be produced
Of the film, and the dimensional stability of the film decreases. this
From these facts, the fluorinated polymer ion exchange in the present invention
The exchange membrane has an ion exchange capacity of 0.5 to 2.0 meq / g.
Tensile rupture strength of the membrane material in a water-containing state
Is 3 to 25 MPa, more preferably 5 to 25 MPa. This
, The tensile elongation of the film material is more than 15%, more preferable.
Or more than 30%. High ion exchange capacity and membrane power
A film having excellent chemical properties is a very important invention for practical use.
From the mechanical properties of the membrane, the graft ratio was 5 to 200 watts.
t%, more preferably 15 to 150 wt%. Fuel electricity
The higher the conductivity of a polymer ion exchange membrane for a pond, the more
Low air resistance and high performance as an electrolyte membrane. Soshi
The electrical conductivity of the ion exchange membrane at 25 ° C. (Example
Equation (4) of 2) is 0.05Ω^-1・ Cm^-1Is less than
And the output performance of the fuel cell
Therefore, the electrical conductivity of the ion exchange membrane is 0.05Ω^-1・ C
m^-1As described above, 0.10Ω is used for a higher performance ion exchange membrane.^-1
・ Cm ^-1It is necessary to be above. On the other hand,
In the case of a nitrogen-based ion exchange membrane,
Electric conductivity is 0.12Ω^-1・ Cm^-1Above is ion exchange
It is known that the strength of the film decreases. That is,
Increase the exchange capacity of the on-exchange membrane and reduce the electrical conductivity
If it is increased, the strength of the membrane will be reduced.
You. However, the ion exchange membrane according to the present invention has a temperature of 25 ° C.
Conductivity of ion exchange membrane is 0.11Ω^-1・ Cm^-1In
It is clear that high film strength is maintained even if
<Example 2>. This is the long-chain branched PTFE
Effects and effects of long chain branching and graphs
Entanglement of oxyhydrofluorocarbon side chains
It seems to be an effect that fits. From these facts, the present invention
Nitrogen-based polymer ion exchange membrane has electrical conductivity at 25 ° C.
0.03-0.25Ω^-1・ Cm^-1, Preferably 0.05
~ 0.25Ω^-1・ Cm^-1belongs to.

It is conceivable to reduce the thickness of the ion exchange membrane in order to improve the characteristics of the ion exchange membrane. However, at present, an extremely thin ion exchange membrane is easily damaged, and it is actually difficult to manufacture the ion exchange membrane itself. Also,
Since the absolute amount of water contained in the ion-exchange membrane is also reduced, the ion-exchange membrane is likely to dry, and it may not be possible to maintain high performance for a long time. Therefore, usually, an ion exchange membrane having a thickness in the range of 30 to 500 μm is used. In the case of the present invention, the film thickness is not particularly limited,
Those having a range of 50 μm to 300 μm are effective. After grafting hydrocarbon styrene to long-chain branched PTFE,
The oxidation resistance of a polymer ion exchange membrane obtained by sulfonating a polystyrene graft chain is extremely low. For example, a long-chain branched PTFE-grafted polystyrene polymer ion-exchange membrane obtained by grafting styrene to a long-chain branched PTFE at a graft ratio of 100%, and then sulfonating the same, in a 3% aqueous hydrogen peroxide solution at 100 ° C. for 5 to 15 In a minute, the ion exchange membrane deteriorates and the ion exchange capacity becomes almost zero. In contrast, the fluorinated polymer ion-exchange membrane according to the present invention has no hydrogen attached to tertiary carbon like a polystyrene graft chain, and has a fluorine atom bonded to carbon with a sulfone group, so it is oxidation-resistant. The ion exchange capacity hardly changes even when placed in a 3% hydrogen peroxide aqueous solution at 100 ° C for 24 hours.

As described above, the fluorinated polymer ion exchange membrane of the present invention has important characteristics as a membrane, that is, the ion exchange capacity is in a wide range of 0.5 to 2.0 meq /.
g, film strength is 5-25MPa, water content is 10-80wt
%, Electric conductivity at 25 ° C. is 0.05 to 0.25Ω.
It can be manufactured by controlling each numerical value range of ⁻¹ · cm ⁻¹ . It is also a feature of the present invention that the characteristics can be controlled within these limited ranges.

When grafting a hydrofluorovinyl ether monomer or this monomer with a tetrafluoroethylene monomer, helium,
Carbon, nitrogen, oxygen, neon, argon, krypton, xenon, or a heavy ion such as gold is irradiated with the ion beam having energy enough to penetrate the thickness of the long-chain branched polytetrafluoroethylene film, After grafting each of the above monomers, a sulfonated polymer ion-exchange membrane can be prepared by sulfonation. When a long-chain branched PTFE film irradiated with a heavy ion beam is used, radicals are generated along the tracks of heavy ions, and dense graft chains are generated there. Since these tracks penetrate the film, ions can move more effectively than when using the same dose of γ-rays or electron beams, and a film having high electric conductivity can be generated. If the film has a thickness of 50 μm, helium ions are 8 MeV or more, carbon ions are 40 MeV or more, neon ions are 80 MeV or more,
Argon ions are 180 MeV or more, and 10
For a 0 μm thick film, helium ions are 12 MeV or more, carbon ions are 62 MeV or more, and neon ions are 13 MeV or more.
Desirably, 0 MeV or more and argon ions are 300 MeV or more. The irradiation amount is preferably in the range of 1 × 10 ⁸ to 1 × 10 ¹³ / cm ² .

A fluorine-based polymer ion-exchange membrane according to the present invention is produced by the series of operations and reactions described above. Hereinafter, the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[0028]

EXAMPLES (Example 1) The following irradiation was performed to obtain a long-chain branched PTFE sheet. 50μm or 100μm thick
A 10 cm x 10 cm polytetrafluoroethylene (PTFE) sheet having a number average molecular weight of 1 x 10 ⁷ was applied to a SUS autoclave irradiation vessel equipped with a heater (inner diameter 7 cmφ x 30 cmH).
, And the inside of the vessel was degassed to about 10 ^-3 Torr and replaced with argon gas. Then, the temperature of the PTFE sheet is raised to 340 ° C. by heating with an electric heater, and the dose rate of ⁶⁰ Co-γ rays is 3 k.
A dose of 90 kGy (30 h) or a dose of 180 in Gy / h
Irradiated with kGy (60 h). After irradiation, the container was cooled and the high temperature irradiated PTFE sheet was taken out.

A polytetrafluoroethylene (PTF) having a thickness of 50 μm or 100 μm and a number average molecular weight of 1 × 10 ⁷ is used.
E) 10cm x 6cm of the sheet is fixed with a SUS frame, put into a heating type SUS irradiation container (inner diameter 8cm x 80cm x 10cmH) with a 50μm thick titanium foil window for electron beam incidence,
It was degassed to about 0 ^-3 Torr and replaced with argon gas. Then, heat with an electric heater to raise the temperature of the PTFE sheet to 335-350.
At 340 ° C., electron beam 2MV (current 0.5 mA (dose rate 0.5 kGy) while flowing argon gas slightly
/ S)) Irradiation. The dose was 100 kGy (200 s) or 200 kGy (400 s). After irradiation, the container was cooled and the high temperature irradiated PTFE sheet was taken out. Table 1 shows the properties of the obtained long-chain branched PTFE membrane.

The long-chain branched PTFE obtained by irradiation at a high temperature does not cause necking in a tensile test and shows a cutting behavior like an ordinary crosslinked rubber. In addition, since the transparency of the film has increased and the melting point of the film has decreased, the long-chain branched type
This shows that the crystal size in the PTFE is much smaller than the original PTFE. Also, the tensile strength was improved by increasing the dose. This is considered to be due to the fact that by increasing the dose, the bonds between the long-chain branched PTFE chains became denser, and the strength of the membrane was increased. In addition, it can be seen that the same long-chain branched PTFE is generated by γ-ray irradiation and electron beam irradiation.

(Comparative Example 1) Unirradiated thickness 100 μm
Table 1 shows the characteristics of the PTFE membrane.

[0032]

[Table 1]

(Embodiment 2) The γ-ray of Embodiment 1 was applied at 90 kGy.
The long-chain branched PTFE membrane (thickness: 50 μm)
In a glass separable container with a hole (inner diameter 3cmφ × 15cmH)
After being charged and degassed, the atmosphere was replaced with argon gas. Long chain in this state
Once again, γ-rays (dose rate 1 × 10 ^FourGy / h) 45
Irradiation at room temperature kGy. Successively, three freeze degassing
Therefore, the hydrofluoric acid was purged with argon gas except oxygen.
CF which is a vinyl ether monomer_Two= CFOCH_TwoC
F_TwoCF_TwoSCH_ThreeOf the long-chain branched PTFE membrane irradiated at 0 ° C
The glass container was introduced until the membrane was immersed. 0 ℃
And then allowed to react at room temperature for 24 hours.
After that, THF was added, washed with cold n-pentane, and dried.
Dried. The graft ratio determined by the following formula (1) is 65%
Met. The grafted long-chain branched PTFE membrane is 1,1,2-
At a temperature of 125 ° C in trichlorotrifluoroethane solvent
Reaction with chlorine gas, followed by trituration in the same solvent
React in the presence of fluoroacetic acid and water at 100 ° C for 6 hours
Was. The obtained membrane was washed with THF, dried, and then further dried at 60 ° C.
Was treated with a NaOH solution for 12 hours and then treated with a sulfuric acid solution. Book
The ion exchange capacity, water content, and electrical conductivity of the membrane obtained in the examples
Table 2 shows conductivity, tensile strength at break, and oxidation resistance.
You.

Assuming that the long-chain branched polytetrafluoroethylene is the main chain and the polymerized portion of hydrofluorovinyl ether is the graft chain, the weight ratio of the graft chain to the main chain is generally represented by the following formula: (X _dg (wt
%)).

X = 100 · (W _t −W ₀ ) / W ₀ (1) W ₀ : weight of PTFE membrane before graft (g) W _t : weight of PTFE membrane (dry state) after graft ( g) The ion exchange capacity (I _ex (meq / g)) of the membrane is expressed by the following equation.

I _ex = n (SO ₃ H) _obs / W _d (2) n (SO ₃ H) _obs : sulfonic acid group concentration of the ion exchange membrane (mM /
g) W _d : Dry weight of ion-exchange membrane (g) n (SO ₃ H) _obs was measured by _placing the membrane in a 1 M (1 mol) sulfuric acid solution.
It was immersed at 50 ° C. for 4 hours to make all the exchange groups —SO ₃ H type.
After that, it was immersed in a 3M NaCl aqueous solution at 50 ° C. for 4 hours to obtain —SO ₃
It was made into Na type, and the substituted proton (H ⁺ ) was neutralized and titrated with 0.2N NaOH to determine the sulfonic acid group concentration. Further, the weight of the membrane after taking out the SO ₃ H type ion exchange membrane stored in water at room temperature and gently wiping it was defined as W _s (g), and then the membrane was kept at 60 ° C. for 16 hours. The weight W _d (g) of the film after vacuum drying was defined as the dry weight. Also, the measured value W
_The water content is determined from _s and _Wd by the following equation.

Water content (%) = 100 · (Ws−W _d ) / W _d (3) The electric conductivity of the ion exchange membrane was measured by an AC method (New Experimental Chemistry Course 19, Polymer Chemistry <II>, p.992, Maruzen)
Normal membrane resistance measuring cell and LC made by Hewlett Packard
The film resistance (Rm) was measured using an R meter and E-4925A. The cell was filled with a 1 M sulfuric acid aqueous solution, and the resistance between the platinum electrodes (distance: 5 mm) was measured depending on the presence or absence of the membrane, and the electrical conductivity (specific conductivity) of the membrane was calculated using the following equation.

Κ = (1 / Rm) · (d / S) (Ω ⁻¹ cm ⁻¹ ) (4) κ: Electric conductivity of the membrane ((Ω− ¹ cm− ¹ ) d: Thickness of ion exchange membrane (Cm) S: Current-carrying area of ion exchange membrane (cm ² ) For comparison of measured values of electric conductivity, Mark W. Ver.
brugge, Robert F. Hill et al. (J. Electrochem. Soc.,. 137 ,
3770-3777 (1990)), a potentiostat, and a function generator. Good correlation was found between the measured values of the AC and DC methods. The values in Table 2 below are values measured by the AC method. The tensile test was performed at a pulling speed of 20.
At 0 mm / min, the size of the sample was equivalent to JIS-4 dumbbell (when wet). Further, the oxidation resistance was measured by placing the sample membrane in a 3% hydrogen peroxide solution at 100 ° C. and measuring the weight change and the ion exchange capacity after 24 hours.

Example 3 A long-chain branched PTFE membrane (thickness: 50 μm) obtained by irradiating 90 kGy with the γ-ray of Example 1 is a pressure-resistant glass separable container equipped with a cock (inner diameter: 3 cmφ × 15 cmH).
And then replaced with argon gas. In this state, the long-chain branched PTFE was again irradiated with γ-rays (dose rate: 10 kGy / h) at room temperature of 60 kGy. The tetrafluoroethylene gas from which the inhibitor was removed was introduced into the glass container containing the irradiated long-chain branched PTFE membrane, and the pressure was adjusted to 1 atm.

Subsequently, CF ₂ ＣＦCFOCH ₂ CF ₂ CF ₂ S, which is a hydrofluorovinyl ether monomer from which oxygen has been removed and the argon gas has been replaced by freezing and deaeration three times, is used.
A solution of O ₂ F and the solvent 1,1,2-trichlorotrifluoroethane (about 1: 1 by volume) was introduced into the glass container until the membrane was immersed. Stir the inside of the container, and keep the tetrafluoroethylene gas at about 1 atm.
Allowed to react for hours. Thereafter, the membrane was washed with acetone and dried. The graft ratio was 98%.

The grafted long-chain branched PTFE membrane is heated at 60 ° C.
For 12 hours and then with a sulfuric acid solution. Table 2 shows the ion exchange capacity, water content, electric conductivity, tensile strength at break, and oxidation resistance of the membrane obtained in this example.

The ion exchange capacity of the ion exchange membranes obtained in Examples 2 and 3 is 1 meq / g or more, which is higher than that of the conventional fluorine-based polymer ion exchange membrane. The membrane has a tensile strength of 10 MPa or more when containing water, and has a sufficient strength as a polymer ion exchange membrane.

(Comparative Examples 2 and 3) The ion exchange capacity, water content, electric conductivity, tensile breaking strength, and Nafion 115 and Nafion 117 shown in Table 2 were measured.
The results of the oxidation resistance are shown in Comparative Examples 2 and 3.

(Comparative Example 4) The gamma ray of Example 1 was applied at 90 kGy.
The long-chain branched PTFE membrane (thickness: 50 μm) obtained by irradiation was placed in a separable glass container (inner diameter: 3 cmφ × 15 cmH) equipped with a cock, degassed, and replaced with argon gas. In this state, γ-ray (dose rate 10 kGy / h) was again applied to the long-chain branched PTFE for 4 times.
Irradiation at 5 kGy room temperature. The styrene monomer, which had been purged with oxygen gas and purged with argon gas by bubbling with argon gas, was introduced into a glass container containing a long-chain branched PTFE membrane that had been irradiated until the membrane was immersed. Stir the inside of the container, 60 ℃
For 6 hours. Thereafter, the membrane was washed with toluene, followed by acetone and dried. The graft ratio was 93%. This graft membrane was treated with 0.5M chlorosulfonic acid (1,2-
(Dichloroethane solvent) and a sulfonation reaction was performed at 60 ° C. for 24 hours. Thereafter, the membrane was washed with water to obtain sulfonic acid groups. Table 2 shows the ion exchange capacity, water content, electric conductivity, tensile strength at break, and oxidation resistance of the membrane obtained in this comparative example.

[0045]

[Table 2]

[0046]

The fluororesin ion exchange membrane of the present invention has an ion exchange capacity of 0.5 to 2.0 meq / g and a tensile strength at break of 5 to 25 MPa, 25
The electric conductivity at ℃ is 0.05 to 0.25Ω ^-1 · cm
^-1 and very high oxidation resistance. It is a low cost fluoropolymer ion exchange membrane with a wide range of ion exchange capacity, high oxidation resistance and membrane strength. The ion exchange membrane of the present invention is particularly suitable for a fuel cell membrane. Further, it is useful as an inexpensive and durable electrolytic membrane or ion exchange membrane.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 27:22 C08L 27:22 (72) Inventor Hirota Morita 1233 Watanukicho, Takasaki-shi, Gunma Japan Atomic Energy Research Institute Inside the Takasaki Research Institute (72) Inventor Masaharu Asano 1233 Watanuki-cho, Takasaki City, Gunma Prefecture Japan Atomic Energy Research Institute Takasaki Research Institute F-term (reference) 4F071 AA27 AA77 AG05 AG14 FA02 FA05 FB01 FC01 FD02 4J026 AA26 BA16 DB02 DB06 DB09 DB36 FA05 FA08 GA02 GA08 5H026 AA06 BB00 BB01 BB10 CX05 EE19 HH00 HH05 HH08 HH09

Claims (6)

[Claims] 1. An oxyhydrofluorocarbon side chain mainly having a long-chain branched polytetrafluoroethylene structure and having a sulfonic acid group, [—OCH ₂ CF ₂ C]
F ₂ SO ₃ H] -bonded fluorine-based polymer ion-exchange membrane, and the ion-exchange membrane has an ion-exchange capacity of 0.5 to 2.0 meq / g and a tensile fracture of the ion-exchange membrane in a water-containing state. A fluorine-based polymer ion-exchange membrane having a strength of 5 to 25 MPa and an electric conductivity of 0.05 to 0.25 Ω ^-1 · cm ^-1 . 2. A polytetrafluoroethylene film having a thickness of 300
Temperature range of ~ 365 ° C, 10^-3Under reduced pressure of ~ 10 Torr,
Or, in an inert gas atmosphere,
Irradiation of 5-500 kGy for long-chain branched polytetrafluoro
A polyethylene film is prepared, and electron beams and gamma rays are applied to the film again.
Inert after irradiating 5-500 kGy in an inert gas at a temperature
Hydrophilic vinyl ether monomer under neutral gas
Some CF _Two= CFOCH_TwoCF_TwoCF_TwoSR, CF_Two= CF
OCH_TwoCF_TwoCF_TwoSO_TwoR, CF_Two= CFOCH_TwoCF_TwoC
F_TwoSX and / or CF_Two= CFOCH_TwoCF_TwoC
F _TwoSO_TwoX (where R: -CH_Three, Or -C (C
H_Three)_ThreeAnd X: -Cl or -F) by -78
C. to 100.degree. C. or below the boiling point of the solvent.
Nomer alone or in a solution obtained by diluting the monomer with a solvent
With a long chain branched polytetrafluoroethylene
A graft chain of the monomer is introduced into the ethylene film, and
Introducing a sulfonic acid group into this graft chain
Manufacture of a fluorinated polymer ion exchange membrane characterized by comprising
Construction method. 3. When introducing the graft chain into long-chain branched polytetrafluoroethylene, tetrafluoroethylene is used as a comonomer with respect to the hydrofluorovinyl ether monomer, and 2
3. The process according to claim 2, wherein from 3 to 80% by weight (wt%) of tetrafluoroethylene units are introduced. 4. The fluorinated polymer ion exchange membrane according to claim 1, wherein the graft chain of the long-chain branched polytetrafluoroethylene has a crosslinked structure by copolymerization with divinylbenzene. 5. When introducing the graft chain into the long-chain branched polytetrafluoroethylene, the amount of the hydrofluorovinyl ether monomer or the sum of the amount of the hydrofluorovinyl ether monomer and the tetrafluoroethylene comonomer is 1 to 5. The method for producing a fluorinated polymer ion-exchange membrane according to claim 2 or 3, wherein 10 wt% of a crosslinking aid, divinylbenzene, is used. 6. When introducing the graft chain into long-chain branched polytetrafluoroethylene, the weight of helium, carbon, nitrogen, oxygen, neon, argon, krypton, xenon, and gold is substituted for electron beam and γ-ray. The monomer or comonomer is grafted by irradiating an ion beam having energy enough to penetrate the thickness of the long-chain branched polytetrafluoroethylene film with ions to graft the monomer or comonomer. Production method.