JP5103024B2 - Stabilized fluoropolymer - Google Patents

Description

The present invention relates to a method for producing a stabilized fluoropolymer, a stabilized fluoropolymer obtained from the production method, and a polymer electrolyte membrane comprising a hydrolyzate of the stabilized fluoropolymer.

A sulfonic acid-derived group-containing fluoropolymer obtained by copolymerizing tetrafluoroethylene and perfluorovinyl ether having —SO ₂ F is an electrolyte such as a fuel cell or a chemical sensor obtained by hydrolyzing —SO ₂ F. Applications as membrane materials are known.

It has been reported that the hydrolyzate of the sulfonic acid-derived group-containing fluoropolymer deteriorates when used as a fuel cell electrolyte membrane for a long period of time, and the wastewater from the fuel cell contains HF.

This problem is caused by bringing a fluorine radical generating compound such as fluorine gas into contact with a solid sulfonic acid-derived group-containing fluoropolymer at 20 to 300 ° C. so that at least 40% of unstable groups at the end of the polymer chain are stable groups. It has been reported that it is improved by a stabilizing treatment that converts (see, for example, Patent Document 1).

Conventional stabilization treatment, especially when the sulfonic acid-derived group-containing fluoropolymer is obtained by emulsion polymerization, the conversion rate of unstable groups to stable groups becomes insufficient, and coloring, foaming, etc. occur during melt molding There was a problem to do.
Japanese Patent Publication No.46-23245

An object of the present invention includes a method for sufficiently stabilizing a sulfonic acid-derived group-containing fluoropolymer, a stabilized fluoropolymer obtained from the method, and a hydrolyzate of the stabilized fluoropolymer, in view of the above-described present situation. The object is to provide a highly durable fuel cell membrane.

The present invention relates to the following general formula (II)
^{_{CF 2 = CF-O- (CFY}} 2) m -A (II)
(In the formula, Y ² represents F, Cl, Br or I. m represents an integer of 1 to 5. When m is an integer of 2 to 5, m Y ^{2 s} were the same. A represents —SO ₂ X or —COZ, X represents F, Cl, Br, I, or —NR ⁵ R ⁶ , Z represents —NR ⁷ R ⁸ or ^.R 5 representing a -OR ^{9, R 6,} R ⁷ and ^{R 8} are the same or different, .R ⁹ representing H, an alkali metal element, an alkyl group or a sulfonyl-containing group, having 1 to 4 carbon atoms A stabilized fluoropolymer obtained by polymerization of an acid-derived group-containing perhalovinyl ether represented by (4) and tetrafluoroethylene, wherein the stabilized fluoropolymer is IR (infrared spectroscopic analysis). ) In the measurement, the peak [x] derived from the carboxyl group, CF 2 _- is a stabilized fluoropolymer, wherein the intensity ratio of the peak [y] derived from [x / y] is 0.05 or less in.
The present invention is a polymer electrolyte membrane containing a hydrolyzate of the above-mentioned stabilized fluoropolymer.
The present invention is described in detail below.

The method for producing a stabilized fluoropolymer of the present invention comprises producing a stabilized fluoropolymer by subjecting a treatment object containing a sulfonic acid-derived group-containing fluoropolymer to a fluorination treatment.

The sulfonic acid-derived group-containing fluoropolymer is a fluoropolymer having —SO ₃ M (M represents H, NR ¹ R ² R ³ R ⁴ or M ¹ _{1 / L} ).
R ¹ , R ² , R ³ and R ⁴ in the NR ¹ R ² R ³ R ⁴ are the same or different and represent H or an alkyl group having 1 to 4 carbon atoms.
Although it does not specifically limit as said C1-C4 alkyl group, It is preferable that it is a linear alkyl group, and it is more preferable that it is a methyl group.
M ¹ represents an L-valent metal. The L-valent metal is a metal belonging to Group 1, Group 2, Group 4, Group 8, Group 11, Group 12, or Group 13 of the Periodic Table.
The L-valent metal is not particularly limited, and examples thereof include Li, Na, K, Cs and the like as Group 1 of the periodic table, and Mg and Ca and the like as Group 2 of the periodic table. As the 4th group of the periodic table, Al and the like are listed. As the 8th group of the periodic table, Fe is listed. As the 11th group of the periodic table, Cu, Ag and the like are listed. As the 12th group of the periodic table, Zn is listed. Zr etc. are mentioned as group 13 of a periodic table.

The sulfonic acid-derived group-containing fluoropolymer is, in addition to the above -SO ₃ M, -SO ₂ X and / or -COZ (X represents F, Cl, Br, I or -NR ⁵ R ^6. Z represents —NR ⁷ R ⁸ or —OR ⁹ R ⁵ , R ⁶ , R ⁷ and R ⁸ are the same or different and represent H, an alkali metal element, an alkyl group or a sulfonyl-containing group, and R ⁹ is carbon. Represents an alkyl group of formulas 1 to 4).

X in the above -SO ₂ X is, F, Cl or Br, more preferably from F.
Z in the above -COZ is, -OR ⁹ are preferred.
The alkali metal element is not particularly limited, and examples thereof include Li, Na, K, and Cs.
It does not specifically limit as said alkyl group, For example, C1-C4 alkyl groups, such as a methyl group and an ethyl group, etc. are mentioned. The alkyl group may be substituted with a halogen atom.
The sulfonyl-containing group is a fluorine-containing alkyl group having a sulfonyl group, and examples thereof include a fluorine-containing alkylsulfonyl group which may have a substituent at the terminal. Examples of the fluorine-containing alkylsulfonyl group include , —SO ₂ R _f ¹ Z ¹ (R _f ¹ represents a fluorine-containing alkylene group, and Z ¹ represents an organic group).
As the organic group, for example, -SO ₂ F are ^{_{mentioned, -SO 2 (NR 5 SO 2}} R f 1 SO 2) k NR 5 SO 2 - (k represents an integer of 1 or _{more, R} ^{f 1} Represents an infinite fluorine group, such as —SO ₂ (NR ⁵ SO ₂ R _f ¹ SO ₂ ) _k NR ⁵ SO ₂ F (k is 1 or more, Represents an integer of 100 or less, and R ⁵ and Rf ¹ may be the same as above. When used in fuel cell applications, -COOH produced by hydrolysis has a problem in stability, and therefore preferably does not contain -COZ.

The sulfonic acid-derived group-containing fluoropolymer may further have —COOH at the end of the polymer chain.
The -COOH is introduced, for example, from the molecular structure of the polymerization initiator at the main chain terminal of the sulfonic acid-derived group-containing fluoropolymer.
The -COOH is formed at the end of the main chain of the sulfonic acid-derived group-containing fluoropolymer when, for example, peroxydicarbonate or the like is used as a polymerization initiator. When the sulfonic acid-derived group-containing fluoropolymer is obtained by emulsion polymerization, it usually has —COOH at the end of the polymer chain.
In addition, when perfluoroalkyldicarboxylic acid is used as a polymerization initiator and polymerized in a non-aqueous system, a part of the polymer chain terminal becomes a perfluoroalkyl group, but usually -COOH and -COF are formed. This is derived from β-cleavage of perhalovinyl ether.

The sulfonic acid-derived group-containing fluoropolymer is preferably a binary or higher copolymer composed of an acid-derived group-containing perhalovinyl ether and a monomer copolymerizable with the acid-derived group-containing perhalovinyl ether.

The acid-derived group-containing perhalovinyl ether has the following general formula (I)
^{_{CF 2 = CF-O- (CF}} 2 CFY 1 -O) n - (CFY 2) m -A (I)
It is preferable that it is a compound represented by these.

Y ¹ in the above general formula (I) represents F, Cl, Br, I or a perfluoroalkyl group, and among them, a perfluoroalkyl group is preferable, and a perfluoroalkyl group having 1 to 3 carbon atoms. More preferably, it is more preferably —CF ₃ .
N in the general formula (I) represents an integer of 0 to 3, and the n Y ¹ may be the same or different. N is preferably 0 or 1, more preferably 0.
Y ² in the general formula (I) represents F, Cl, Br or I, and among them, F is preferable.
M in the said general formula (I) represents the integer of 1-5. when m is integer from 2 to 5, m number of Y ² may be the same or different. The m is preferably 2.
In the general formula (I), Y ² is F and m is preferably ² , Y ² is F, m is 2 and n is 0.

A in the general formula (I) represents —SO ₂ X or —COZ (X and Z are as defined above) which is an acid-derived group.
The above-described —SO ₂ X and / or —COZ that the sulfonic acid-derived group-containing fluoropolymer may have is obtained by polymerizing the acid-derived group-containing perhalovinyl ether represented by the general formula (I). May be introduced.

The acid-derived group-containing perhalovinyl ether has the following general formula (II)
^{_{CF 2 = CF-O- (CFY}} 2) m -A (II)
(Wherein Y ² , m and A are the same as those in the above general formula (I)).
The said acid origin group containing perhalovinyl ether can be used 1 type or in combination of 2 or more types.

The monomer copolymerizable with the acid-derived group-containing perhalovinyl ether is preferably a vinyl ether other than the acid-derived group-containing perhalovinyl ether, or an ethylenic monomer. As the monomer copolymerizable with the acid-derived group-containing herhalovinyl ether, at least one selected from the group consisting of the above “other vinyl ethers other than the acid-derived group-containing perhalovinyl ether and the ethylenic monomer” is selected according to the purpose. can do.

The ethylenic monomer is a monomer having no ether oxygen and having a vinyl group, and the vinyl group may have a hydrogen atom partially or entirely substituted with a fluorine atom.

Examples of the ethylenic monomer include the following general formula CF ₂ = CF-Rf ²
(Wherein Rf ² represents F, Cl or a linear or branched fluoroalkyl group having 1 to 9 carbon atoms), a general formula CHY ³ = CFY ⁴ shown below
(Wherein Y ³ represents H or F, and Y ⁴ represents H, F, Cl, or a linear or branched fluoroalkyl group having 1 to 9 carbon atoms). Examples thereof include fluoroethylenic monomers.

The ethylenic monomer is selected from the group consisting of fluoro vinyl ethers represented by CF ₂ = CF ₂ , CH ₂ = CF ₂ , CF ₂ = CFCl, CF ₂ = CFH, CH ₂ = CFH, and CF ₂ = CFCF ₃ At least one selected from the above is preferable, and among them, a perhaloethylenic monomer is more preferable, a perfluoroethylenic monomer is further preferable, and tetrafluoroethylene is particularly preferable.
As said ethylenic monomer, 1 type (s) or 2 or more types can be used.

Other vinyl ethers other than the acid-derived group-containing perhalovinyl ether are not particularly limited as long as they do not contain the acid-derived group. For example, the following general formula CF ₂ = CF—O—Rf ³
(Wherein Rf ³ represents a fluoroalkyl group having 1 to 9 carbon atoms or a fluoropolyether group having 1 to 9 carbon atoms), the following general formula CHY ⁵ = CF—O— Rf ⁴
(Wherein Y ⁵ represents H or F, and Rf ⁴ represents a linear or branched fluoroalkyl group optionally having ether oxygen having 1 to 9 carbon atoms). And hydrogen-containing vinyl ether.
As said other vinyl ether, 1 type (s) or 2 or more types can be used.

The sulfonic acid-derived group-containing fluoropolymer is preferably a binary or higher copolymer obtained by copolymerizing at least one acid-derived group-containing perhalovinyl ether and at least one ethylenic monomer. A binary copolymer obtained by copolymerizing 1 type of perhalovinyl ether and 1 type of ethylenic monomer is more preferable, but if desired, in addition to acid-derived group-containing perhalovinyl ether and ethylenic monomer, it is derived from acid. A copolymer obtained by copolymerizing other vinyl ethers other than the group-containing perhalovinyl ether may also be used.

The sulfonic acid-derived group-containing fluoropolymer in the present invention is an acid-derived group-containing perhalovinyl ether unit derived from the acid-derived group-containing perhalovinyl ether in an amount of 5 to 40 mol%, an ethylenic monomer unit derived from the ethylenic monomer in an amount of 60 to It is preferably composed of 95 mol% and 0 to 5 mol% of other vinyl ether units derived from the other vinyl ethers.
The more preferable lower limit of the acid-derived group-containing perhalovinyl ether unit is 7 mol%, the more preferable lower limit is 10 mol%, the more preferable upper limit is 35 mol%, and the further preferable upper limit is 30 mol%.
The more preferable lower limit of the ethylenic monomer unit is 65 mol%, the still more preferable lower limit is 70 mol%, the more preferable upper limit is 90 mol%, and the still more preferable upper limit is 87 mol%.
The more preferable upper limit of the other vinyl ether units is 4 mol%, and the more preferable upper limit is 3 mol%.

The “ethylenic monomer unit” means a part of the molecular structure of the sulfonic acid-derived group-containing fluoropolymer and a part derived from the molecular structure of the ethylenic monomer. For example, the tetrafluoroethylene unit means a moiety [—CF ₂ —CF ₂ —] derived from tetrafluoroethylene [CF ₂ ═CF ₂ ].
The “acid-derived group-containing perhalovinyl ether unit” means a part of the molecular structure of the sulfonic acid-derived group-containing fluoropolymer and a part derived from the molecular structure of the acid-derived group-containing perhalovinyl ether.
The “other vinyl ether unit” means a part of the molecular structure of the sulfonic acid-derived group-containing fluoropolymer and a part derived from the molecular structure of the other vinyl ether.

In this specification, the content rate of the said acid origin group containing perhalo vinyl ether unit, an ethylenic monomer unit, and another vinyl ether unit is a value which made all the monomer units 100 mol%, respectively.
The “all monomer units” are all the portions derived from the monomers in the molecular structure of the sulfonic acid-derived group-containing fluoropolymer. Therefore, the monomer from which the “total monomer unit” is derived is the total amount of the monomer that has formed the sulfonic acid-derived group-containing fluoropolymer.
In the present specification, the content (mol%) of the “acid-derived group-containing perhalovinyl ether unit” is an acid occupying in the number of moles of monomers from which all monomer units in the sulfonic acid-derived group-containing fluoropolymer are derived. It is the ratio of the number of moles of the acid-derived group-containing perhalovinyl ether from which the derived group-containing perhalovinyl ether unit is derived. Similarly, the content (mol%) of the “ethylenic monomer unit” and the content (mol%) of the “other vinyl ether unit” are the ratio of the number of moles of the derived monomer. The content of these units is a value obtained by measuring without solvent at 300 ° C. using a high-temperature ¹⁹ F-nuclear magnetic resonance measuring apparatus (JNM-FX100 type, manufactured by JEOL, Japan). Hereinafter, this measurement is abbreviated as high temperature NMR.

The polymerization method of the sulfonic acid-derived group-containing fluoropolymer may be any of conventionally known methods such as solution polymerization, suspension polymerization, and emulsion polymerization. Emulsion polymerization is preferred because it is most effective.

For example, when the sulfonic acid-derived group-containing fluoropolymer is obtained by emulsion polymerization of a monomer having —SO ₂ F, in the polymerization process, a small part of —SO ₂ F is converted to —SO ₃ H. It is converted. The -SO ₃ H ^has to be converted to + ^NR 1 ^R 2 ^R 3 ^{R 4} or ^{M 1L +} easily _-SO 3 in the presence of ^NR 1 ^R 2 ^R 3 ^{R 4} or _-SO 3 ^M _{1 1 / L} (R ¹ , R ² , R ³ , R ⁴ and M ¹ are as defined above).
The monomer having a -SO 2 _F, but are not limited to, for example, A in the above general formula (I) may be mentioned acid-derived group-containing perhalo vinyl ether is a -SO 2 _F. Incidentally, -SO 3 M with the sulfonic acid-derived group-containing fluoropolymer of the present invention _(M is the same. As defined above) are limited to those derived from the -SO 2 _F with the monomers emulsion polymerization described above For example, it may be introduced by a known method.

The method for producing a stabilized fluoropolymer of the present invention comprises performing a fluorination treatment on a treatment object containing the sulfonic acid-derived group-containing fluoropolymer.
In the present specification, the “processing object” is an object to be subjected to the fluorination treatment.
The object to be treated may be in the form of a resin powder, a pellet, or a film obtained by molding. From the viewpoint of sufficiently performing the fluorination treatment described later, the treatment object is desirably in the form of a resin powder, but is desirably in the form of a pellet from the viewpoint of handleability.

The sulfonic acid-derived group-containing fluoropolymer has a problem that fluorination becomes insufficient when the fluorination treatment is performed by a conventional method. Possible reasons for insufficient fluorination are as follows. That is, even if the above sulfonic acid-derived group-containing fluoropolymer is dried and then prepared into a solid such as a powder, a pellet or a molded body, -SO ₃ M usually has high hygroscopicity. Will immediately absorb moisture in the air. High hygroscopicity of the -SO ₃ M, for example, -COOH, a salt thereof, -COZ, -SO ₂ X, such as (Z and X are the same. As defined above) much larger than the other functional groups . Due to the high hygroscopicity of -SO ₃ M, the solid having the sulfonic acid-derived group-containing fluoropolymer as a main component substantially depends on the humidity of the atmosphere in which it exists, but usually has a water content exceeding 500 ppm by mass. Contains. When a solid having a high water content and containing the sulfonic acid-derived group-containing fluoropolymer is subjected to a fluorination treatment by a conventional method, the following reaction formula (A)
2H ₂ O + 4 (F) → 4HF + O ₂ (A)
It is considered that the fluorine source (F) is consumed in the reaction (A) represented by the following formula, and as a result, the fluorination of the sulfonic acid-derived group-containing fluoropolymer is inhibited.

In the stabilized fluoropolymer production method of the present invention, the object to be treated has a water content of 500 ppm or less. If it exceeds 500 ppm, it is not preferable because it inhibits fluorination of the sulfonic acid-derived group-containing fluoropolymer. A preferable upper limit is 450 ppm, and a more preferable upper limit is 350 ppm. If the water | moisture content in the said process target object is in the said range, a minimum can be 0.01 ppm from a viewpoint of economical efficiency and productivity.
The amount of water in the treatment object is a value obtained by measurement using the Karl Fischer titration method.

The method for producing a stabilized fluoropolymer of the present invention suppresses the inhibition reaction of the fluorination treatment such as the above reaction (A) by performing the fluorination treatment under the condition that the water content of the treatment object falls within the above range. Thus, the sulfonic acid-derived group-containing fluoropolymer can be sufficiently fluorinated.

There is no particular limitation on the method of bringing the water content in the object to be processed into the above-mentioned range. For example, after performing centrifugal dehydration if necessary, the temperature is changed stepwise from 80 to 130 ° C. for 2 to 50 hours as desired. A conventionally known drying method such as a method of reducing pressure and heating if desired; a method of melting in a vent-type extruder and devolatilizing from a vent hole can be used. When the latter method is used, it is preferable in that a part of —SO ₃ M may be decomposed.
Since the sulfonic acid-derived group-containing fluoropolymer has a highly hygroscopic functional group, the steps from the drying to the fluorination treatment described later are preferably sealed or performed as quickly as possible.

The fluorination treatment in the method for producing a stabilized fluoropolymer of the present invention is performed using a fluorine source.
The fluorine source is preferably at least one selected from the group consisting of F ₂ , SF ₄ , IF ₅ , NF ₃ , PF ₅ , ClF and ClF ₃ , and more preferably F ₂ .
The fluorination treatment is preferably performed using a gaseous fluorinating agent comprising the fluorine source. In this case, the fluorine source is preferably 1% by volume or more of the gaseous fluorinating agent. A more preferred lower limit is 10% by volume.
The gaseous fluorinating agent comprises the fluorine source and a gas inert to fluorination.
The gas inert to the fluorination is not particularly limited, and examples thereof include nitrogen gas and argon gas.

The fluorination treatment is preferably carried out below the melting point of the fluoropolymer, usually 250 ° C. or less, more preferably from room temperature to 150 ° C.
The fluorination treatment can be performed continuously or batchwise.
The apparatus used in the above fluorination treatment includes a stationary reactor such as a shelf reactor, a cylindrical reactor, a reactor equipped with a stirring blade, a rotary kiln, a W cone reactor, a V blender, etc. It is appropriately selected from a container rotating (tumbling) reactor; a vibrating reactor; various fluidized bed reactors such as a stirred fluidized bed;
In the fluorination treatment, in order to keep the reaction temperature homogeneous, a solvent inert to a fluorine source such as fluorocarbons can be used. Further, when the object to be treated is in the form of a resin powder or a pellet, it is preferable to perform the fluorination treatment in a container rotating reactor or a vibrating reactor because it is easy to keep the reaction temperature homogeneous.

The fluorination treatment is a treatment for converting a sulfonic acid-derived group-containing fluoropolymer before fluorination treatment into a stable group that is difficult to thermally decompose by fluorinating unstable groups that are easily thermally decomposed. is there.
In the fluorination treatment, preferably, —CF ₂ SO ₃ M (M is the same as the above definition) contained in the sulfonic acid-derived group-containing fluoropolymer is changed to —CF ₂ H, —CF ₃ or the like. Further, it is considered that the sulfonic acid-derived group-containing fluoropolymer further converts —COOH at the chain end to —CF ₃ and —SO ₂ NH ₂ to —SO ₂ F, respectively, as desired.
In the fluorination treatment, by these conversions, unstable groups such as —SO ₃ M are thermally decomposed and colored during melt molding using the sulfonic acid-derived group-containing fluoropolymer, or unstable groups such as —COOH. Can be prevented from being decomposed and foamed.
By the fluorination treatment, impurities such as low molecular weight substances such as oligomers, unreacted monomers, and by-products contained in the object to be treated can be removed.

In addition, —SO ₃ M (M is the same as the above definition) included in the sulfonic acid-derived group-containing fluoropolymer is converted into —CF ₂ H, —CF _3, or the like that does not have ion exchange ability by fluorination treatment. While being converted, if the -SO ₃ M is what -SO ₂ F with the monomers described above was converted by emulsion polymerization, since the conversion of -SO ₂ F into -SO ₃ M is a trace amount Even when the molded membrane or the like is used for ion exchange after the fluorination treatment, the ion exchange equivalent weight [Ew] can be maintained without greatly increasing.

The method for producing a stabilized fluoropolymer of the present invention comprises producing a stabilized fluoropolymer by performing the above fluorination treatment.
In the present specification, the “stabilized fluoropolymer” is a fluoropolymer obtained by performing the fluorination treatment from a sulfonic acid-derived group-containing fluoropolymer, and the sulfonic acid-derived group-containing fluoropolymer has In addition, unstable groups such as —COOH, —CF ₂ SO ₃ M, —SO ₂ NH _{2 and the} like that are easily decomposed by heat are converted into stable groups such as —CF ₂ H, —CF ₃ , and —SO ₂ F that are difficult to thermally decompose. It is a thing.
Since the stabilized fluoropolymer may coexist with a volatile component such as HF after the fluorination treatment, it is preferably removed.
The removal of the volatile component is preferably performed using an extruder having a devolatilization mechanism, and more preferably performed using a vent type extruder having at least one vent hole.

Although it has been described above that a resin powder is desirable as an object to be fluorinated, when a resin powder is used as an object to be treated, the object to be treated is melt-kneaded in a vent-type extruder after the fluorination treatment. It is preferable to remove the volatile component and subsequently pelletize, more preferably to perform the fluorination treatment in the above-described vent type extruder, and subsequently to remove and pelletize the volatile component in the same extruder. .

The fluorination treatment can be similarly stabilized even when the object to be treated is a film.
Performing the above fluorination treatment on the film-like body means that when the film-like body is used as an electrolyte membrane, there is no significant thermal damage after the stabilization treatment, and unstable groups are generated due to the breakage of the polymer chain. It is preferable in that there is no point.
As the fluorination treatment when the object to be treated is in the form of a film, for example, pellets formed by the method of melting in the vent type extruder and devolatilizing from the vent hole are used, and subsequently melt extrusion film formation Then, it is preferable to perform fluorination treatment using a reactor equipped with a cylindrical reactor or a winder.

When the drying treatment is performed prior to the fluorination treatment using the above various reactors, it is preferable to perform vacuum evacuation or to distribute a dry gas.
In addition, when the sulfonic acid-derived group-containing fluoropolymer in the object to be treated has -COF as an unstable group, a relatively high temperature is required to stabilize it. After conversion to —COOH, the moisture content can be adjusted to 500 ppm or less and subjected to fluorination treatment.

In the present invention, as described above, the stabilized fluoropolymer has a —COOH at the end of the polymer chain, which was usually held before the fluorination treatment, converted into a stable group such as —CF ₂ H or —CF ₃ by the fluorination treatment. It has been converted. This conversion rate is extremely high in the method for producing a stabilized fluoropolymer of the present invention. In infrared spectroscopic analysis [IR] measurement, a peak derived from a carboxyl group [x] and a peak derived from —CF ₂ — [y] Strength ratio [x / y] can be 0.05 or less. A preferable upper limit of the intensity ratio [x / y] is 0.04, and a more preferable upper limit is 0.03.
The stabilized fluoropolymer obtained by the method for producing a stabilized fluoropolymer (hereinafter sometimes referred to as “stabilized fluoropolymer (A)”) is also one aspect of the present invention.
In the present invention, the stabilized fluoropolymer has the characteristics of the stabilized fluoropolymer (A) and the characteristics of the stabilized fluoropolymer (B) described later, and the characteristics of the stabilized fluoropolymer (A). And having the characteristics of the stabilized fluoropolymer (C) described later, or having the characteristics of the stabilized fluoropolymer (A) and having the characteristics of the stabilized fluoropolymer (B) and the stabilized fluoropolymer It is preferable that it also has the characteristic of (C).

The stabilized fluoropolymer of the present invention (hereinafter sometimes referred to as “stabilized fluoropolymer (B)”) includes an acid-derived group-containing perhalovinyl ether represented by the general formula (II), tetrafluoroethylene, In the IR measurement, the stabilized fluoropolymer has an intensity of a peak [x] derived from a carboxyl group and a peak [y] derived from —CF ₂ — in IR measurement. The ratio [x / y] is 0.05 or less.
The polymerization of the acid-derived group-containing perhalovinyl ether and tetrafluoroethylene is preferably emulsion polymerization.

In the stabilized fluoropolymer (B), the carboxyl group [—COOH] is mainly formed as a polymer chain end group, and the —CF ₂ — is mainly present in the polymer main chain. is there.
In the stabilized fluoropolymer (B), a preferable upper limit of the strength ratio [x / y] is 0.04, and a more preferable upper limit is 0.03.
The production method of the stabilized fluoropolymer (B) is not particularly limited as long as it has an intensity ratio [x / y] within the above range, but the production method of the stabilized fluoropolymer of the present invention is used. Thus, it can be easily obtained.

The stabilized fluoropolymer (B) can be efficiently obtained by the above-described stabilized fluoropolymer production method of the present invention, but is not necessarily limited to that obtained by the above-described stabilized fluoropolymer production method of the present invention. Thus, the concept is different from the above-mentioned stabilized fluoropolymer (A).
In the present specification, without referring to (A), (B) or (C) described later, when simply referred to as “stabilized fluoropolymer”, the stabilized fluoropolymer (A), the stabilized fluoropolymer (B) and A high-level concept that can include the stabilized fluoropolymer (A), the stabilized fluoropolymer (B), and / or the stabilized fluoropolymer (C) without distinguishing between the stabilized fluoropolymer (C) described below. It is.

The stabilized fluoropolymer has an intensity ratio [x / y] in the above-mentioned range in infrared spectroscopic analysis [IR] measurement, so that foaming hardly occurs during melt molding.
In the present invention, the intensity ratio [x / y] is calculated from the intensity of each peak obtained by measurement using an infrared spectrophotometer.
Peak [x] derived from the carboxyl group, and the absorption peak intensity derived from the aggregate of the carboxyl groups to be observed near 1776 cm ^-1, the absorption peak intensity derived from non-aggregate observed near 1807cm ^-1 And the sum.
The peak [y] derived from —CF ₂ — is an absorption peak derived from the overtone of —CF ₂ —.

The stabilized fluoropolymer preferably has an amount of sulfonyl groups of 200 ppm or less. A more preferable upper limit is 50 ppm.
The stabilized fluoropolymer preferably has a carboxyl group content of 100 ppm or less. A more preferable upper limit is 30 ppm.

In the present specification, the amount of the sulfonyl group and the amount of the carboxyl group are determined by FT-IR spectroscopy by heat-pressing the stabilized fluoropolymer at 270 ° C. and 10 MPa for 20 minutes to form a measurement film having a thickness of 150 to 200 μm. This is a value obtained by measuring the spectrum using a container and by the following procedure.
First, a standard sample in which unstable groups are completely stabilized by performing fluorination treatment at 150 ° C. for 20 hours is prepared separately, and the difference spectrum between the IR spectrum and the IR spectrum of the measurement film is expressed as C−F. derived normalized by the absorption peak of the harmonics, from the resulting difference spectrum, the absorption peak derived from a sulfonic acid group is observed near 1056cm ^-1, the aggregate of the carboxyl groups to be observed near 1776 cm ^-1 The absorption peak intensity Abs is obtained by reading the intensity of the absorption peak and the absorption peak derived from the non-aggregate observed in the vicinity of 1807 cm ⁻¹ and normalizing with the peak intensity of the C—F overtone.
The amount of each functional group is determined based on the absorption coefficient ε (cm ³ / mol · cm) of the absorption peak of each functional group, the specific gravity d (g / cm ³ ) of the sample, and the intensity of the CF overtone being 1. Using the Lambert-Beer rule (Abs = εcl, c is the concentration) from the sample film thickness l (cm), the following formula functional group amount (ppm) = {Abs × (molecular weight of each functional group)} × 10 ¹¹ / εdl
Is calculated based on
In the present specification, the amount of the carboxyl group is the sum of the amount of association of the carboxyl group and the amount of non-association.

A fluoropolymer obtained by polymerizing an acid-derived group-containing perhalovinyl ether represented by the general formula (II) and tetrafluoroethylene, wherein the hydrolyzate is compared with the hydrolyzate of the fluoropolymer. The integral strength of the main chain end-CF ₃ group of the hydrolyzate obtained by swelling with an oxygen-containing hydrocarbon compound having a dielectric constant of 5.0 or more and performing ¹⁹ F solid-state nuclear magnetic resonance measurement, and branching from the main chain Per 100,000 carbon atoms constituting the main chain of the hydrolyzate calculated using the integrated intensity of the side chain -CF _2- adjacent to the ether bond and the ion exchange equivalent weight Ew value determined by the titration method there stabilized fluoropolymer, wherein (hereinafter, also referred to as "stabilized fluoropolymer (C)" that the number of main chain terminal -CF ₃ group present (X) is 10 or more in It is also one of the present invention.

In the stabilized fluoropolymer (C), the number (X) of the main chain terminal —CF ₃ groups is 10 or more, so that the main chain terminal group is sufficiently stabilized.
The lower limit of the number (X) of the main chain terminal —CF ₃ groups is more preferably 15.

The number of the main chain terminal -CF ₃ group (X) is the integrated intensity of main chain terminal -CF ₃ groups obtained by carrying out the ^{19 F} solid state nuclear magnetic resonance measurement, adjacent to the branched ether bonds from the main chain It can be calculated from the integrated intensity of —CF ₂ — and the ion exchange equivalent weight Ew of the sample obtained by the titration method.
In the ¹⁹ F solid nuclear magnetic resonance measurement, an oxygen-containing hydrocarbon compound having a relative dielectric constant of 5.0 or more can be used as a swelling solvent. The oxygen-containing hydrocarbon compound having a relative dielectric constant of 5.0 or more is not particularly limited, and examples thereof include N-methylacetamide.
In the present invention, the ¹⁹ F solid-state nuclear magnetic resonance measurement was carried out using a MAS (Magic Angle Spinning) rotation speed of 4.8 kHz, a measurement frequency of 376.5 MHz, a chemical shift reference CF ₃ for a fluoropolymer swollen with N-methylacetamide. The measurement is performed using DSX400 (manufactured by Bruker Biospin, Germany) as a measuring instrument at COOH (−77 ppm) and a measurement temperature of 473 K.
In the ¹⁹ F solid state nuclear magnetic resonance measurement, the integrated intensity (A) of the main chain terminal —CF ₃ group is a side chain adjacent to the ether bond of the side chain branched from the main chain from a signal having a peak at −79.7 ppm. The integrated intensity (B) of —CF ₂ — can be measured from a signal having a peak at −76.4 ppm.
The number (X) of the main chain terminal —CF ₃ groups is represented by the following formula (III) from the integral intensity (A) and integral intensity (B), and the ion exchange equivalent weight Ew of the sample obtained by the titration method.
X = 100000 / [{(B / A) × 3/2} × {2 × (Ew−178−50 × m) / 100} +2] (III)
Can be used to calculate. Here, m follows the value of m in the general formula (II).

In the IR measurement described above, the stabilized fluoropolymer (C) has an intensity ratio [x / y] of a peak [x] derived from a carboxyl group and a peak [y] derived from —CF ₂ — of 0. It is preferable that it is 05 or less.
In the stabilized fluoropolymer (C), the preferred range of the strength ratio [x / y] is the same as the range described for the stabilized fluoropolymer (B).

If the stabilized fluoropolymer (C) is obtained through polymerization of the acid-derived group-containing perhalovinyl ether represented by the general formula (II) and tetrafluoroethylene, the production method thereof is particularly Although not limited, the polymerization is preferably emulsion polymerization.
The stabilized fluoropolymer (C) can be efficiently obtained by the above-described method for producing a stabilized fluoropolymer of the present invention. The stabilized fluoropolymer (C) is different in concept from the above-mentioned stabilized fluoropolymer (A) in that it is not necessarily limited to that obtained by the method for producing a stabilized fluoropolymer of the present invention.
As is clear from the general formula (II), the stabilized fluoropolymer (B) and the stabilized fluoropolymer (C) of the present invention have side chains such that n in the general formula (I) is 0. It is short.
As is apparent from the results of Fenton treatment 1 described later, the present inventors have found that a polymer having a short side chain is superior in chemical stability, and the stabilized fluoropolymer (B) of the present invention and the stable Fluoropolymer (C) was completed.

The stabilized fluoropolymer of the present invention preferably has a melt index of 0.1 to 20 g / 10 min measured under conditions of 270 ° C. and a load of 2.16 kg according to JIS K 7210. The melt index [MI] here may be expressed as melt mass flow rate [MFR].
In the stabilized fluoropolymer of the present invention, when the melt index [MI] is less than 0.1 (g / 10 minutes), melt molding tends to be difficult, and when it exceeds 20 (g / 10 minutes). When the polymer electrolyte membrane is used for a fuel cell, the durability tends to deteriorate.
A more preferable lower limit of the MI is 0.5 (g / 10 minutes), and a more preferable upper limit is 10 (g / 10 minutes).
In the present specification, MI represents the weight of a polymer extruded from an orifice having a specific shape and size when a load of 2.16 kg is applied at 270 ° C. according to JIS K 7210 in grams per 10 minutes. It is a thing.
In addition, the stabilized fluoropolymer of the present invention is less likely to foam even when melt-molded, compared to unstabilized ones.

The polymer electrolyte membrane of the present invention contains the hydrolyzate of the above-described stabilized fluoropolymer of the present invention.
The “hydrolyzed product of the stabilized fluoropolymer” is a fluoropolymer obtained by hydrolyzing the stabilized fluoropolymer.
As the hydrolyzate of the above-mentioned stabilized fluoropolymer, for example, the acid-derived group —SO ₂ F possessed by the stabilized fluoropolymer of the present invention is saponified and converted into a salt group such as —SO ₃ Na or —SO ₃ K. Sulfonic acid type fluoropolymer converted to —SO ₃ H by reacting with acid, etc., or —COOCH ₃ is saponified and converted to salt type groups such as —COONa, —COOK, etc., and then the acid is allowed to act Examples thereof include carboxylic acid type fluoropolymers converted into —COOH.
Since the polymer electrolyte membrane of the present invention contains a hydrolyzate of the above-mentioned stabilized fluoropolymer, when used as an electrolyte membrane material in fuel cells, chemical sensors, etc., it does not deteriorate even when used for a long period of time. It is possible to avoid a situation in which the drainage of water will contain HF.
The polymer electrolyte membrane of the present invention is different as the hydrolyzate of the above-mentioned stabilized fluoropolymer due to, for example, different m and / or A in the above general formula (II), different copolymerization ratio with TFE, etc. 1 type or 2 types or more may be included.

The polymer electrolyte membrane of the present invention has a ratio of b / w of polymer electrolyte membrane to a liter of aqueous hydrogen peroxide solution having an initial concentration of iron (II) cation of 2 ppm and an initial concentration of hydrogen peroxide of 1% by mass. [B / a] The amount of fluoride ions eluted by Fenton treatment consisting of immersion in 3.2 and holding at 80 ° C. for 2 hours is 11 × 10 ^{−4 with respect} to 100 parts by mass of the polymer electrolyte membrane. What is below a mass part is preferable.
The polymer electrolyte membrane of the present invention has a sufficiently high degree of stabilization of the stabilized fluoropolymer as long as the amount of fluoride ions is within the above range.
The amount of fluoride ions eluted by the Fenton treatment is more preferably 8.0 × 10 ⁻⁴ parts by mass or less, and 5.0 × 10 ⁻⁴ parts by mass or less with respect to 100 parts by mass of the polymer electrolyte membrane. Is more preferred. If the amount of fluoride ions eluted by the Fenton treatment is within the above range, it is industrially acceptable even if it is, for example, 1.0 × 10 ⁻⁴ parts by mass or more with respect to 100 parts by mass of the polymer electrolyte membrane. Can do.
In the present specification, the amount of fluoride ions is described later by an ion chromatography method (IC-2001 manufactured by Tosoh Corporation, Japan, and TSKgel SuperIC-Anion manufactured by Tosoh Corporation, Japan as an anion analysis column). It is measured by the method of “Fenton treatment 2”.

The polymer electrolyte membrane of the present invention preferably has a thickness of 5 to 100 μm. When it is less than 5 μm, when used in a fuel cell, the mechanical strength tends to decrease during the fuel cell operation process, and the membrane tends to break. When it exceeds 100 μm, when used in a fuel cell, the membrane resistance is large and sufficient initial characteristics cannot be exhibited.
In the present specification, the above-mentioned “initial characteristics” means that the fuel cell operation is performed using the polymer electrolyte membrane of the present invention, the current density-voltage curve is measured, and the power generation performance with a large voltage value and a wide current density. Etc.
The more preferable lower limit of the film thickness of the polymer electrolyte membrane is 10 μm, and the more preferable upper limit is 75 μm.

The polymer electrolyte membrane of the present invention can be obtained by molding and hydrolysis.
The molding may be (1) the stabilized fluoropolymer of the present invention may be molded into a film (film), or (2) a sulfonic acid-derived group-containing fluoropolymer that has not undergone the fluorination treatment described above. May be formed into a film shape (film shape). When the molding (2) is performed, the fluorination treatment can be performed after the molding.
The molding can be performed by a melt molding method such as a molding method using a T die, an inflation molding method, or a calendar molding method.
In the molding, a third component may be mixed as necessary with the stabilized fluoropolymer in the molding of (1) or the sulfonic acid-derived group-containing fluoropolymer in the molding of (2).
The molding conditions can be appropriately set according to the molding method to be performed. For example, in the case of a melt molding method using a T-die, the molten resin temperature is preferably 100 to 400 ° C, more preferably 200 to 300 ° C. is there.

The hydrolysis may be performed before molding or may be performed after molding as long as the fluorination treatment is performed.
The above hydrolysis, by contacting the strong base, such as stabilized fluoropolymer and aqueous NaOH or KOH aqueous solution of the present invention, for example, the _{-SO 2} F -SO 3 Na, a metal salt such as -SO ₃ K, also Saponification such as conversion of —COOCH ₃ to a metal salt such as —COONa, —COOK, etc. is performed, and after washing with water, the mixture is further reacted with an acidic solution such as nitric acid, sulfuric acid, hydrochloric acid, etc. (for example, —SO ₃ Na Are converted into —SO ₃ H and —COONa into —COOH), and further washed with water, whereby the acid-derived group represented by A in the above general formula (I) or general formula (II), particularly —SO ₂ X can be converted into a sulfonic acid group, and a polymer electrolyte membrane can be obtained by the above method.

(1) As a method for forming the stabilized fluoropolymer of the present invention into a film (film), the film casting solution is cast on a support, and a liquid coating film is formed on the support. And the method (cast method) which removes a liquid medium from a liquid coating film can also be mentioned.
The membrane casting solution is prepared by bringing the fluorinated sulfonic acid-derived group-containing fluoropolymer into contact with a strong base such as an aqueous NaOH solution or an aqueous KOH solution, saponifying it, washing it with water, and further adding it to an acidic solution such as nitric acid, sulfuric acid, hydrochloric acid, etc. The step of making it act and further washing with water to convert the acid-derived group at the end of the side chain into a sulfonic acid group and the polymer obtained thereby into an appropriate solvent using water, alcohol, organic solvent, etc., if necessary, autoclave, etc. Obtained by dispersing or dissolving at 80 to 300 ° C. In addition, when the polymer is dispersed or solution, a third component other than the polymer may be mixed as necessary.
As a method for casting on a support, known coating methods such as a gravure roll coater, a natural roll coater, a reverse roll coater, a knife coater, a dip coater, and a pipe doctor coater can be used.
Although the support body used for casting is not limited, a general polymer film, a metal foil, a substrate made of alumina, Si, or the like can be suitably used. Such a support can be removed from the polymer electrolyte membrane as desired when forming a membrane / electrode assembly (described later).

Further, a porous film obtained by stretching a polytetrafluoroethylene [PTFE] film described in Japanese Patent Publication No. 5-75835 is impregnated with a film casting solution, and then the liquid medium is removed, whereby a reinforcing body (the porous film) is obtained. It is also possible to produce a polymer electrolyte membrane including a membrane. Further, by adding a fibrillated fiber made of PTFE or the like to the membrane casting solution and casting it, and then removing the liquid medium, as shown in Japanese Patent Laid-Open No. 53-149881 and Japanese Patent Publication No. 63-61337. A polymer electrolyte membrane reinforced with fibrillated fibers can also be produced.

The polymer electrolyte membrane of the present invention may be obtained by subjecting to a heat treatment (annealing) at 40 to 300 ° C., preferably 80 to 220 ° C., if desired. Furthermore, acid treatment may be performed with hydrochloric acid, nitric acid or the like, if desired, in order to fully exhibit the original ion exchange capacity. Further, stretch orientation can be imparted by using a horizontal uniaxial tenter or a sequential or simultaneous biaxial tenter.

The hydrolyzate of the stabilized fluoropolymer can be used as a membrane and / or an electrode constituting a membrane / electrode assembly in a solid polymer electrolyte fuel cell described later.
The hydrolyzate of the above-mentioned stabilized fluoropolymer may be a membrane / electrode assembly constituting a solid polymer electrolyte fuel cell, which constitutes a membrane and does not constitute an electrode, or does not constitute a membrane. It may constitute, or it may constitute a membrane and an electrode.

The active substance fixed body of the present invention comprises the hydrolyzate of the stabilized fluoropolymer and an active substance.
The active substance fixed body is usually obtained by coating a substrate with a liquid composition in which the hydrolyzate of the stabilized fluoropolymer and the active substance are dispersed in a liquid medium. When a liquid composition comprising a fluoropolymer and an active substance is coated on a substrate, it can usually be obtained by hydrolyzing the stabilized fluoropolymer after the coating.
The active substance is not particularly limited as long as it can have activity in the active substance immobilization body, and is appropriately selected according to the purpose of the active substance immobilization body of the present invention. May be used. The active substance fixed body of the present invention using a catalyst as the active substance can be suitably used as an electrode constituting a membrane / electrode assembly in a fuel cell.
As said catalyst, an electrode catalyst is preferable and it is more preferable that it is a metal containing platinum.
The catalyst is not particularly limited as long as it is usually used as an electrode catalyst. For example, a metal containing platinum, ruthenium or the like; an organometallic complex having a central metal usually composed of one or more metals. And organometallic complexes in which at least one of the central metals is platinum or ruthenium.
The metal containing platinum, ruthenium or the like may be a metal containing ruthenium, such as ruthenium alone, but a metal containing platinum is preferable. The metal containing platinum is not particularly limited, and examples thereof include platinum alone (platinum black); platinum-ruthenium alloy and the like.
The catalyst is usually used by being supported on a carrier such as silica, alumina, carbon or the like.

As the liquid medium, in the case where good dispersibility of particles or solution comprising the stabilized fluoropolymer hydrolyzate is desired, in addition to water, alcohols such as methanol; N-methylpyrrolidone [NMP] Examples include nitrogen-containing solvents such as acetone; ketones such as acetone; esters such as ethyl acetate; polar ethers such as diglyme and tetrahydrofuran [THF]; and polar organic solvents such as carbonates such as diethylene carbonate. Among them, one kind or a mixture of two or more kinds can be used.

The liquid composition comprises at least the stabilized fluoropolymer or a hydrolyzate thereof and the active substance, and may contain other components as necessary.
Examples of the other components include, for the purpose of forming a film by casting, impregnation and the like, alcohols for improving leveling properties, polyoxyethylenes for improving film forming properties, and the like. It is done.

The substrate is not particularly limited, and examples thereof include a porous support, a resin molded body, a metal plate, and the like, and an electrolyte membrane, a porous carbon electrode, and the like used for a fuel cell are preferable.
The electrolyte membrane is preferably made of a fluororesin in the usual sense, and may be made of a hydrolyzate of the stabilized fluoropolymer of the present invention. The electrolyte membrane may contain substances other than the fluororesin and hydrolyzate of the stabilized fluoropolymer in a normal sense as long as the properties of the active substance fixed body are not hindered.

The above-mentioned “coating the liquid composition on the substrate” means that the liquid composition is applied to the substrate, dried as necessary, and further converted into a hydrolyzate as necessary, usually further stabilized. It consists of heating at a temperature above the melting point of the hydrolyzate of fluoropolymer.
The heating conditions are not particularly limited as long as the hydrolyzate of the stabilized fluoropolymer and the active substance can be fixed on the base material. For example, the heating conditions are 200 to 350 ° C. for several minutes, for example, 2 to 2 It is preferable to heat for 30 minutes.
The active substance fixed body of the present invention, when used as a solid polymer fuel cell, is an electrode (also referred to as “catalyst layer”) comprising the hydrolyzate of the above-mentioned stabilized fluoropolymer, carbon and catalyst (Pt or the like). Is preferred.

The membrane / electrode assembly of the present invention is a membrane / electrode assembly comprising a polymer electrolyte membrane and an electrode, and satisfies at least one selected from the group consisting of the following conditions (1) and (2). is there.
(1) The polymer electrolyte membrane is the polymer electrolyte membrane of the present invention described above (2) The electrode is the above-mentioned active substance fixed body of the present invention. The membrane / electrode assembly of the present invention is, for example, It can be used for a polymer electrolyte fuel cell.

When the polymer electrolyte membrane of the present invention is used in a solid polymer fuel cell, a membrane / electrode assembly (membrane / electrode assembly) in which the polymer electrolyte membrane of the present invention is held tightly between an anode and a cathode ( (Hereinafter often referred to as “MEA”). Here, the anode is composed of an anode catalyst layer and has proton conductivity, and the cathode is composed of a cathode catalyst layer and has proton conductivity. Further, a gas diffusion layer (described later) joined to the outer surface of each of the anode catalyst layer and the cathode catalyst layer is also referred to as MEA.

The anode catalyst layer includes a catalyst that easily oxidizes fuel (for example, hydrogen) to easily generate protons, and the cathode catalyst layer generates water by reacting protons and electrons with an oxidant (for example, oxygen or air). Including the catalyst to be produced. For both the anode and the cathode, platinum or an alloy made of platinum and ruthenium is preferably used as the catalyst, and the catalyst particles are preferably 10 to 1000 angstroms or less. Such catalyst particles are preferably supported on conductive particles having a size of about 0.01 to 10 μm such as furnace black, channel black, acetylene black, carbon black, activated carbon, and graphite. The amount of catalyst particles supported relative to the projected area of the catalyst layer is preferably 0.001 mg / cm ² or more and 10 mg / cm ² or less.
Further, the anode catalyst layer and the cathode catalyst layer may contain a hydrolyzate of a fluoropolymer obtained by polymerization of an acid-derived group-containing perhalovinyl ether represented by the general formula (II) and tetrafluoroethylene. preferable. The supported amount of the hydrolyzed perfluorocarbonsulfonic acid polymer relative to the projected area of the catalyst layer is preferably 0.001 mg / cm ^{2 to} 10 mg / cm ² or less.

As a method for manufacturing the MEA, for example, the following method can be given. First, a commercially available platinum-supported carbon (for example, TEC10E40E manufactured by Kunitaka Tanaka Metal Co., Ltd., Japan) is used as a catalyst in a hydrolyzate of a stabilized fluoropolymer dissolved in a mixed solution of alcohol and water to form a paste. To. A certain amount of this is applied to one side of each of the two PTFE sheets and dried to form a catalyst layer. Next, the coated surfaces of the PTFE sheets are faced to each other, the polymer electrolyte membrane of the present invention is sandwiched between them, transferred and bonded by hot pressing at 100 to 200 ° C., and then the PTFE sheet is removed to remove the MEA. Obtainable. A person skilled in the art knows how to make MEAs. The method for producing MEA is described in, for example, JOURNAL OF APPLIED ELECTROCHEMISTRY, 22 (1992) p. 1-7.
As the gas diffusion layer, commercially available carbon cloth or carbon paper can be used. Representative examples of the former include carbon cloth E-tek, B-1 manufactured by DE NORA NORTH AMERICA, USA. Representative examples of the latter include CARBEL (registered trademark, Japan Gore-Tex, Japan), Japan. Examples thereof include TGP-H manufactured by Kunito Toray and carbon paper 2050 manufactured by SPCTRACORP.
A structure in which the electrode catalyst layer and the gas diffusion layer are integrated is called a “gas diffusion electrode”. MEA can also be obtained by joining the gas diffusion electrode to the polymer electrolyte membrane of the present invention. A typical example of a commercially available gas diffusion electrode is a gas diffusion electrode ELAT (registered trademark) manufactured by DE NORA NORTH AMERICA (using carbon cloth as a gas diffusion layer).

The polymer electrolyte fuel cell of the present invention has the above membrane / electrode assembly.
The solid polymer electrolyte fuel cell is not particularly limited as long as it has the membrane / electrode assembly, and usually contains components such as electrodes and gas constituting the solid polymer electrolyte fuel cell. It may be.

Since the stabilized fluoropolymer of the present invention and the hydrolyzate thereof are excellent in chemical stability as described above, as an electrolyte membrane and a material thereof for a fuel cell such as a solid polymer electrolyte fuel cell whose use conditions are usually severe. Can also be suitably used for a long time.

Any of the membranes obtained by performing the cast membrane described above, the membrane formed on the porous support, the active substance immobilization body, the polymer electrolyte membrane, or the solid polymer electrolyte fuel cell are all stabilized fluorocarbons. A polymer hydrolyzate is used. The liquid composition described above is preferably composed of a hydrolyzate of a stabilized fluoropolymer.

The polymer electrolyte membrane of the present invention is used, for example, as a membrane material for the solid polymer electrolyte fuel cell, for example, a lithium battery membrane, a salt electrolysis membrane, a water electrolysis membrane, a hydrohalic acid electrolysis It can be used as a membrane material for electrolyte membranes or ion exchange membranes such as membranes for use, membranes for oxygen concentrators, membranes for humidity sensors, membranes for gas sensors, and separation membranes.

The method for producing a stabilized fluoropolymer of the present invention can sufficiently fluorinate unstable groups of a sulfonic acid-derived group-containing fluoropolymer.
Since the stabilized fluoropolymer of the present invention is excellent in chemical stability as described above, the hydrolyzate thereof is a membrane such as an electrolyte membrane of a fuel cell such as a solid polymer electrolyte fuel cell in which use conditions are usually severe. A highly durable fuel cell membrane or electrode that can be suitably used for a material or an electrode and has a small amount of fluorine ions in waste water can be obtained.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited only to these examples.

Measuring method 1. Moisture content measurement method Using a moisture vaporizer (trade name: ADP-351, manufactured by Kyoto Electronics Industry Co., Ltd.), dry nitrogen was used as a carrier gas, and the moisture vaporized by heating the sample was captured by a Karl Fischer moisture meter. Collected and coulometrically titrated to determine moisture content.
The sample amount was 1 g, and the measurement temperature was 150 ° C.

2. Functional group quantification by IR A polymer sample was heat-pressed at 270 ° C. and 10 MPa for 20 minutes to form a film having a thickness of 150 to 200 μm, and the spectrum was measured using an FT-IR spectrometer.

3. Stability test with Fenton reagent (1) Fenton treatment 1
The polymer sample was heat-pressed at 270 ° C. and 10 MPa for 20 minutes, and then the terminal group of the polymer side chain was converted to a sulfonic acid group to obtain a stability test membrane.
In a bottle made of a tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer, 1 mg of FeSO ₄ · 7H ₂ O is dissolved in 20 ml of a 30% by mass hydrogen peroxide aqueous solution, and 3 g of a stability test film is immersed therein. Hold at 85 ° C. for 20 hours. Then, it cooled to room temperature, the film | membrane for stability tests was taken out, and the fluorine ion concentration of the liquid phase was measured using the fluorine ion meter (Expandable Analyzer Analyzer EA940 by ORION).
(2) Fenton treatment 2
The polymer electrolyte membrane b gram is set to a membrane liquid ratio [b / a] of 3.2 to a liter of aqueous hydrogen peroxide solution having an initial concentration of iron (II) cation of 2 ppm and an initial concentration of hydrogen peroxide of 1% by mass. After immersion and holding at 80 ° C. for 2 hours, the sample polymer (the polymer electrolyte membrane) is removed, and after measuring the liquid volume, it is diluted appropriately with distilled water for ion chromatography, and fluoride ions are obtained by ion chromatography. The F ^- amount was measured. The measuring apparatus used was IC-2001 manufactured by Tosoh Corporation of Japan, and TSKgel SuperIC-Anion manufactured by Tosoh Corporation of Japan as the anion analysis column.
The amount of eluted fluoride ions was expressed as the mass of eluted fluoride ions per 100 parts by mass of the sample polymer mass.

4). Measurement Method of Ion Exchange Equivalent Weight Ew A polymer electrolyte membrane cut into 0.1 g was immersed in 30 ml of saturated NaCl aqueous solution at a temperature of 25 ° C. and allowed to stand for 30 minutes with stirring. Neutralization titration using 0.01N aqueous sodium hydroxide solution, with the point of the meter (made by Toko Chemical Laboratories, Japan: TPX-90) showing the value in the range of 6.95 to 7.05 as the equivalence point did. The Na-type electrolyte membrane obtained after neutralization was rinsed pure, then vacuum dried and weighed. The equivalent amount of sodium hydroxide required for neutralization was M (mmol), the weight of the Na-type electrolyte membrane was W (mg), and the ion exchange equivalent weight Ew (g / eq) was determined by the following formula.
Ew = (W / M) −22

5. ¹⁹ F solid state nuclear magnetic resonance measurement method
¹⁹ F solid state NMR measurement was performed under the following conditions. The sample is subjected to NMR measurement while being immersed in a swelling solvent in an NMR test tube.
・ Device: DSX400 manufactured by Bruker Biospin, Germany
-MAS rotation speed: 4.8 kHz
・ Observation frequency: 376.5 MHz
And chemical shift _standard: CF 3 COOH _(-77ppm)
Swelling solvent: N-methylacetamide Measurement temperature: 473K
The calculation method is shown below. The main chain terminal —CF ₃ group (a in FIG. 1) is detected at −79.7 ppm. Let this integrated intensity be A. On the other hand, a signal of —CF ₂ — (b in FIG. 2) adjacent to the side chain ether is observed at −76.4 ppm. Let this integrated intensity be B. The number (X) of main chain terminal CF ₃ groups present per 100,000 carbon atoms constituting the main chain is represented by A and B and 4. It can calculate using the following formula (III) from Ew of the sample calculated | required by the measuring method of the ion exchange equivalent weight Ew of description.
X = 100000 / [{(B / A) × 3/2} × {2 × (Ew−178−50 × m) / 100} +2] (III)
Here, m follows the value of m described in the general formula (II).

6). Fuel cell evaluation The fuel cell evaluation of the polymer electrolyte membrane was performed as follows. First, an electrode catalyst layer is prepared as follows. With respect to 1.00 g of Pt-supported carbon (TEC10E40E, Pt 36.4 wt%, manufactured by Nippon Kuninaka Naka Kikinzoku Co., Ltd.), a 5 mass% fluoropolymer was used as a solvent composition (mass ratio: ethanol / water = 50/50). Further, 3.31 g of a polymer solution concentrated to 11% by mass was added, and further 3.24 g of ethanol was added, and then mixed well with a homogenizer to obtain an electrode ink. This electrode ink was applied on a PTFE sheet by a screen printing method. There were two types of coating amounts: a coating amount in which both the Pt loading amount and the polymer loading amount were 0.15 mg / cm ^2, and a coating amount in which both the Pt loading amount and the polymer loading amount were 0.30 mg / cm ² . After coating, the electrode catalyst layer having a thickness of about 10 μm was obtained by drying at room temperature for 1 hour and in air at 120 ° C. for 1 hour. Of these electrode catalyst layers, those having both Pt loading and polymer loading of 0.15 mg / cm ² are anode catalyst layers, and those having both Pt loading and polymer loading of 0.30 mg / cm ² are cathodes. A catalyst layer was obtained.
The anode catalyst layer and the cathode catalyst layer thus obtained are faced to each other, a polymer electrolyte membrane is sandwiched between them, and hot pressing is performed at 160 ° C. and a surface pressure of 0.1 MPa. An MEA was produced by transferring and joining to a polymer electrolyte membrane.

A carbon cloth (ELAT (registered trademark) B-1 manufactured by DE NORA NORTH AMERICA, USA) was set as a gas diffusion layer on both sides of the MEA (the outer surfaces of the anode catalyst layer and the cathode catalyst layer) and incorporated in the evaluation cell. . This evaluation cell was set in an evaluation device (Fuel Cell Evaluation System 890CL manufactured by Toyo Technica Co., Ltd., Japan) and heated to 80 ° C., then hydrogen gas at 150 cc / min on the anode side and air gas on the cathode side At 400 cc / min. A water bubbling system was used for gas humidification, and the initial characteristics were examined by measuring a current density-voltage curve in a state where the gas was humidified at 80 ° C. and the air gas was humidified at 50 ° C. and supplied to the cell.

After examining the initial characteristics, a durability test was performed at a cell temperature of 100 ° C. In either case, the gas humidification temperature was 60 ° C. for both the anode and the cathode. When the cell temperature is 100 ° C., hydrogen gas is flowed at 74 cc / min on the anode side and air gas is flowed at 102 cc / min on the cathode side, 0.30 MPa (absolute pressure) on the anode side, and 0.15 MPa (absolute pressure) on the cathode side. ) Was pressed at a current density of 0.3 A / cm ² . At this time, if the polymer in the membrane or the electrode deteriorates, the fluorine ion concentration in the drainage on the anode side and the cathode side increases. Therefore, the fluorine ion concentration in the drainage is changed to the model 9609BNionplus fluorine composite electrode of the bench top type pH ion meter model 920Aplus ( (Manufactured by Japan Medical Company)).
In the durability test, when a pinhole is generated in the polymer electrolyte membrane, a phenomenon called cross leak occurs in which a large amount of hydrogen gas leaks to the cathode side. In order to investigate the amount of cross leak, the hydrogen concentration in the cathode side exhaust gas was measured with a micro GC (CP4900 manufactured by Varian, the Netherlands), and the test was terminated when the measured value was 10 times or more of the initial value. .
7). Melt Index [MI] Measurement Method MI was measured using a MELT INDEXER TYPE C-5059D manufactured by Toyo Seiki Co., Ltd. under conditions of 270 ° C. and a load of 2.16 kg according to JIS K 7210. . The weight of the extruded polymer was expressed in grams per 10 minutes.

Example 1
(1) Polymer synthesis
A stainless steel stirring autoclave with a capacity of 3000 ml was charged with 300 g of a 10% aqueous solution of C ₇ F ₁₅ COONH ₄ and 1170 g of pure water, and sufficiently subjected to vacuum and nitrogen substitution. After the autoclave was fully evacuated, tetrafluoroethylene [TFE] gas was introduced to a gauge pressure of 0.2 MPa, and the temperature was raised to 50 ° C. Thereafter, 100 g of CF ₂ = CFOCF ₂ CF ₂ SO ₂ F was injected, and TFE gas was introduced to increase the pressure to 0.7 MPa with a gauge pressure. Subsequently, an aqueous solution in which 0.5 g of ammonium persulfate [APS] was dissolved in 60 g of pure water was injected to initiate polymerization.
In order to replenish TFE consumed by the polymerization, TFE was continuously supplied to keep the pressure of the autoclave at 0.7 MPa. Furthermore, the amount of CF ₂ = CFOCF ₂ CF ₂ SO ₂ F corresponding to 0.53 times the mass ratio was continuously supplied to the supplied TFE to continue the polymerization.
When the supplied TFE reached 522 g, the pressure in the autoclave was released and the polymerization was stopped. Thereafter, the mixture was cooled to room temperature to obtain 2450 g of a slightly cloudy aqueous dispersion containing about 33% by mass of a perfluorinated polymer containing SO ₂ F.
The aqueous dispersion was coagulated with nitric acid, washed with water, dried at 90 ° C. for 24 hours, and further dried at 120 ° C. for 12 hours to obtain fluorinated polymer A 800 g.
Next, 1 g of the obtained fluorinated polymer A was immediately put into a tube furnace heated to 150 ° C. to evaporate the moisture, and dry nitrogen was introduced as a carrier gas into a Karl Fischer moisture measuring device to measure the amount of moisture. However, the mass was 200 ppm.
As a result of high-temperature NMR measurement at 300 ° C., the content of CF ₂ ═CFOCF ₂ CF ₂ SO ₂ F units in the fluoropolymer A was 19 mol%.
The fluoropolymer A was heat pressed at 270 ° C. and 10 MPa for 20 minutes to obtain a transparent film having a thickness of 170 μm.
As a result of IR measurement, no peak derived from sulfonic acid was observed. In addition, the intensity ratio [x / y] between the peak [x] derived from the carboxyl group and the peak [y] derived from —CF ₂ — was 0.23.

(2) 200 g of the above-mentioned fluorinated polymer A having a water content of 200 ppm was placed in an autoclave (manufactured by Hastelloy) having a fluorination volume of 1000 ml, and the temperature was raised to 120 ° C. while vacuum degassing. After repeating vacuum and nitrogen replacement three times, nitrogen was introduced to a gauge pressure of 0 MPa. Subsequently, a gaseous fluorinating agent obtained by diluting fluorine gas with nitrogen gas to 20% by volume was introduced until the gauge pressure became 0.1 MPa, and held for 30 minutes.
Next, after exhausting the fluorine in the autoclave and evacuating, a gaseous fluorinating agent obtained by diluting the fluorine gas with nitrogen gas to 20% by volume was introduced until the gauge pressure became 0.1 MPa, Hold for 3 hours.
Then, it cooled to room temperature, the fluorine in an autoclave was exhausted, and after repeating vacuum and nitrogen substitution 3 times, the autoclave was open | released and the stabilized fluoropolymer B was obtained.
The stabilized fluoropolymer B was heat-pressed at 270 ° C. and 10 MPa for 20 minutes to obtain a transparent film having a thickness of 170 μm.
As a result of IR measurement, no peak derived from sulfonic acid was observed. Further, the intensity ratio [x / y] between the peak [x] derived from the carboxyl group and the peak [y] derived from —CF ₂ — was 0.03.
The obtained stabilized fluoropolymer was extruded with a melt index meter (MI meter) at a load of 270 ° C. and 5 kg to obtain an extruded strand. The strand after the operation of extruding the obtained strand again with the MI meter was repeated twice was hardly colored.

Comparative Example 1
The fluorine-containing polymer A obtained in Example 1 was left in the air for 2 days, and the water content was measured and found to be 700 ppm.
This polymer was fluorinated in the same manner as in Example 1 to obtain fluorinated polymer C. The upper part of the autoclave from which the fluoropolymer C was obtained was discolored in green, indicating that the corrosion was progressing.
The obtained fluoropolymer C was heat-pressed at 270 ° C. and 10 MPa for 20 minutes to obtain a transparent film having a thickness of 160 μm.
As a result of IR measurement, the intensity ratio [z / y] between the peak [z] derived from sulfonic acid and the peak [y] derived from —CF ₂ — was 0.03. Further, the intensity ratio [x / y] between the peak [x] derived from the carboxyl group and the peak [y] derived from —CF ₂ — was 0.14.
The obtained fluoropolymer C was extruded with an MI meter at a load of 270 ° C. and 5 kg to obtain an extruded strand. The strand after the operation of extruding the obtained strand again with the MI meter was repeated twice was colored dark brown.
From the above results, Example 1 in which the fluorinated polymer A having a water content of 500 ppm or less was fluorinated was able to stabilize the terminal as compared with Comparative Example 1 having a water content of 700 ppm. Moreover, it turned out that coloring of a fluorine-containing polymer is suppressed.

Example 2
The membrane obtained in Example 1 (2) was treated in a 20% aqueous sodium hydroxide solution at 90 ° C. for 24 hours and then washed with water. Subsequently, it was treated in 6N sulfuric acid at 60 ° C. for 24 hours. Thereafter, the membrane was washed with water until the washing solution became neutral to obtain a sulfonic acid type membrane.
This film was sufficiently dried at 110 ° C., and 3 g was collected and subjected to a stability test by Fenton treatment 1. As a result, the fluorine ion concentration was 5 ppm.

Comparative Example 2
Using a polymer film (trade name: Nafion 117, manufactured by DuPont) obtained by polymerizing CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ SO ₂ F as a sulfonic acid-derived group-containing fluoropolymer, Example 2 Similarly, when the stability test by Fenton treatment 1 was performed, the fluorine ion concentration was 20 ppm.
From the results of the above stability test, a polymer obtained by copolymerizing CF ₂ = CFOCF ₂ CF ₂ SO ₂ F and TFE and further stabilizing the terminal is CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ It was found that the polymer using CF ₂ SO ₂ F is excellent in stability.

Example 3
(1) A stainless steel stirred autoclave with a polymer synthesis volume of 3000 ml was sufficiently vacuumed and replaced with nitrogen, and then the autoclave was fully evacuated. Then, 1530 g of perfluorohexane and CF ₂ = CFOCF ₂ CF ₂ SO ₂ F were added. 990 g was charged and the temperature was adjusted to 25 ° C. Tetrafluoroethylene [TFE] gas was introduced here to a gauge pressure of 0.30 MPa, and then 13.14 g of a 10 mass% perfluorohexane solution of a polymerization initiator (C ₃ F ₇ COO) ₂ was injected to carry out the polymerization reaction. Started.
In order to replenish the TFE consumed by the polymerization, TFE was continuously supplied to keep the pressure of the autoclave at 0.30 MPa. CF ₂ = CFOCF a ₂ CF ₂ SO ₂ F was intermittently meter 47g supply was continued polymerization.
When the supplied TFE reached 73 g, the pressure in the autoclave was released and the polymerization was stopped.
After completion of the polymerization reaction, 1500 ml of chloroform was added and stirred for 10 minutes. Next, solid-liquid separation was performed using a centrifuge, and 1500 ml of chloroform was added to the solid content and stirred for 10 minutes. This operation was performed three times to wash the polymer. Next, residual chloroform was removed from the washed polymer under vacuum at 120 ° C. to obtain 128 g of fluorinated polymer D.

Next, 1 g of the obtained fluoropolymer D was immediately put into a tube furnace heated to 150 ° C. to volatilize water, and dry nitrogen was introduced as a carrier gas into a Karl Fischer moisture measuring device to measure the amount of moisture. However, the mass was 50 ppm.
As a result of high-temperature NMR measurement at 300 ° C., the content of CF ₂ ═CFOCF ₂ CF ₂ SO ₂ F units in the fluoropolymer D was 18 mol%.
The fluoropolymer D was heat pressed at 270 ° C. and 10 MPa for 20 minutes to obtain a transparent film having a thickness of 160 μm.
As a result of IR measurement, no peak derived from sulfonic acid was observed. Further, the intensity ratio [x / y] between the peak [x] derived from the carboxyl group and the peak [y] derived from —CF ₂ — was 0.08.

(2) A fluorinated fluoropolymer D (100 g) was treated in the same manner as in Example 1 to obtain a stabilized fluoropolymer E.
As a result of performing heat press in the same manner as in Example 1 to prepare a thin film and performing IR measurement, a peak derived from a sulfonic acid and a peak derived from a carboxyl group were not observed.

Example 4
The thin film of stabilized fluoropolymer E was treated in the same manner as in Example 2 to obtain a sulfonic acid type film.
After the membrane was sufficiently dried at 110 ° C., 3 g was collected and subjected to the Fenton treatment 1. As a result, the fluorine ion concentration was 5 ppm.

Example 5
(1) A stainless steel stirring autoclave having a polymer synthesis volume of 6 L was charged with 150 g of a 10% aqueous solution of C ₇ F ₁₅ COONH ₄ and 2840 g of pure water, and sufficiently subjected to vacuum and nitrogen substitution. After the autoclave was fully evacuated, tetrafluoroethylene [TFE] gas was introduced to a gauge pressure of 0.2 MPa, and the temperature was raised to 50 ° C. Thereafter, 180 g of CF ₂ = CFOCF ₂ CF ₂ SO ₂ F was injected, TFE gas was introduced, and the pressure was increased to 0.7 MPa with a gauge pressure. Subsequently, an aqueous solution in which 1.5 g of ammonium persulfate [APS] was dissolved in 20 g of pure water was injected to initiate polymerization.
In order to replenish TFE consumed by the polymerization, TFE was continuously supplied to keep the pressure of the autoclave at 0.7 MPa. Against further supplied to the TFE, the polymerization was continued by continuously supplying the amount of _{CF 2 = CFOCF 2 CF 2 SO} 2 F , which corresponds to 0.70 times by mass ratio.
When the supplied TFE reached 920 g, the pressure in the autoclave was released and the polymerization was stopped. Thereafter, the mixture was cooled to room temperature to obtain 4650 g of a slightly cloudy aqueous dispersion containing about 32% by mass of a perfluorinated polymer containing SO ₂ F.
The aqueous dispersion was coagulated with nitric acid, washed with water, dried at 90 ° C. for 24 hours, and further dried at 120 ° C. for 12 hours to obtain 1500 g of a fluoropolymer F.

Next, 1 g of the obtained fluoropolymer F was immediately put into a tubular furnace heated to 150 ° C. to volatilize water, and dry nitrogen was introduced as a carrier gas into a Karl Fischer moisture measuring device to measure the amount of water. However, the mass was 150 ppm.
As a result of high-temperature NMR measurement at 300 ° C., the content of CF ₂ ═CFOCF ₂ CF ₂ SO ₂ F units in the fluoropolymer F was 18.6 mol%.
The fluoropolymer F was heat-pressed at 270 ° C. and 10 MPa for 20 minutes to obtain a transparent film having a thickness of 170 μm. As a result of IR measurement, the intensity ratio [z / y] between the peak [z] derived from sulfonic acid and the peak [y] derived from —CF ₂ — was 0.05. Further, the intensity ratio [x / y] between the peak [x] derived from the carboxyl group and the peak [y] derived from —CF ₂ — was 0.20.

(2) Fluorination Subsequently, 700 g of the above-mentioned fluoropolymer F was put into a 3 L Hastelloy autoclave and heated to 120 ° C. while vacuum degassing. After repeating vacuum and nitrogen substitution three times, nitrogen was introduced to a gauge pressure of -0.5 MPa. Subsequently, a gaseous fluorinating agent obtained by diluting the fluorine gas with nitrogen gas to 20% by volume was introduced until the gauge pressure reached 0 MPa and held for 30 minutes.
Next, after the fluorine in the autoclave is evacuated and evacuated, a gaseous fluorinating agent obtained by diluting the fluorine gas to 20% by volume with nitrogen gas is introduced until the gauge pressure becomes 0 MPa, and 3 hours Retained.
Then, it cooled to room temperature, the fluorine in an autoclave was exhausted, and after repeating vacuum and nitrogen substitution 3 times, the autoclave was open | released and the stabilized fluoropolymer G was obtained.
The stabilized fluoropolymer G was heat-pressed at 270 ° C. and 10 MPa for 20 minutes to obtain a transparent film having a thickness of 170 μm.
As a result of IR measurement, neither a peak derived from sulfonic acid nor a peak derived from a carboxyl group was observed.

The MI of this stabilizing polymer G was 3.5 (g / 10 minutes). The stabilized fluoropolymer G was extruded and melt molded at 280 ° C. with a T die to obtain a thin film having a thickness of 50 μm. This thin film was treated in the same manner as in Example 2 to obtain a sulfonic acid type membrane. The Ew of this sulfonic acid type membrane was measured according to the above-described method for measuring the ion exchange equivalent weight Ew. As a result, it was 720 (g / eq). Moreover, as a result of measuring according to the ¹⁹ F solid nuclear magnetic resonance measuring method, it was B / A = 302.1, X = 20.4 (m = 2 in the said general formula (II)).
Furthermore, as a result of performing the Fenton treatment 2 on this sulfonic acid type membrane, the fluoride ion was 3.1 × 10 ⁻⁴ parts by mass with ^respect to 100 parts by mass of the membrane.
Next, using this electrolyte membrane, a membrane / electrode assembly (MEA) was produced according to the method described above. At this time, the fluoropolymer used for the electrode was a polymer obtained by treating the same stabilized fluoropolymer G as the electrolyte membrane into a sulfonic acid type.
When this MEA was incorporated into an evaluation cell and the initial characteristics at a cell temperature of 80 ° C. were measured according to the method described above, the relationship between voltage (V) and current density (A / cm ² ) was 0 at 0.5 A / cm ² . A very high cell performance of 0.68 V at .77 V, 1.0 A / cm ² and 0.55 V at 1.5 A / cm ² was obtained.
Further, in the durability test at 100 ° C., the operation for 550 hours was possible, and high durability was obtained. The concentration of fluorine ions in the waste water after 50 hours was 0.16 ppm on the cathode side and 0.23 ppm on the anode side. The fluorine ion concentration in the waste water after 400 hours was 0.22 ppm on the cathode side and 0.48 ppm on the anode side.

Comparative Example 3
A polymer produced in exactly the same manner as the fluorinated polymer F except that it was untreated with fluorination was subjected to extrusion melt molding at 280 ° C. with a T die in the same manner as in Example 5 to obtain a thin film having a thickness of 50 μm. The MI of this fluoropolymer F was 3.5 (g / 10 min). This thin film was treated in the same manner as in Example 2 to obtain a sulfonic acid type membrane.
The Ew of this sulfonic acid type membrane was measured according to the above-described method for measuring the ion exchange equivalent weight Ew. As a result, it was 720 (g / eq). Moreover, as a result of measuring according to the ¹⁹ F solid state nuclear magnetic resonance measuring method, it was B / A = ∞ and X = 0 (m = 2 in the general formula (II)). Furthermore, as a result of performing the Fenton treatment 2 on the sulfonic acid type membrane, the fluoride ion was 13.3 × 10 ⁻⁴ parts by mass with respect to 100 parts by mass of the membrane.
Next, using this electrolyte membrane, a membrane / electrode assembly (MEA) was produced according to the method described above. At this time, the fluoropolymer used for the electrode was a polymer obtained by treating the fluorinated polymer F, which is the same as the electrolyte membrane and not treated with fluorination, into a sulfonic acid type.
When this MEA was incorporated into an evaluation cell and the initial characteristics at a cell temperature of 80 ° C. were measured according to the method described above, the relationship between voltage (V) and current density (A / cm ² ) was 0 at 0.5 A / cm ² . .72V, with 1.0A / cm ² 0.44V, was inoperable at 1.5A / cm ^2.
Further, in the durability test at 100 ° C., the operation was terminated by a cross leak after 85 hours of operation. After 50 hours, the fluorine ion concentration in the wastewater was 2.8 ppm on the cathode side and 6.1 ppm on the anode side.

Comparative Example 4
The fluorinated fluoropolymer C obtained in Comparative Example 1 was extruded and melt molded at 280 ° C. with a T die in the same manner as in Example 5 to obtain a thin film having a thickness of 50 μm. The MI of this fluoropolymer C was 3.2 (g / 10 min). This thin film was treated in the same manner as in Example 2 to obtain a sulfonic acid type membrane. The Ew of this sulfonic acid type membrane was measured according to the above-described method for measuring the ion exchange equivalent weight Ew. As a result, it was 720 (g / eq). Moreover, as a result of measuring according to the ¹⁹ F solid nuclear magnetic resonance measuring method, they were B / A = 921 and X = 6.7 (m = 2 in the general formula (II)). Furthermore, as a result of performing the Fenton treatment 2 on this sulfonic acid type membrane, the fluoride ion was 12.8 × 10 ⁻⁴ parts by mass with respect to 100 parts by mass of the membrane.
Next, using this electrolyte membrane, a membrane / electrode assembly (MEA) was produced according to the method described above. At this time, the fluoropolymer used for the electrode was also a polymer obtained by treating the same fluoropolymer C as the electrolyte membrane into a sulfonic acid type.
When this MEA was incorporated into an evaluation cell and the initial characteristics at a cell temperature of 80 ° C. were measured according to the method described above, the relationship between voltage (V) and current density (A / cm ² ) was 0 at 0.5 A / cm ² . It was 0.52 V at .75 V, 1.0 A / cm ² and 0.18 V at 1.5 A / cm ² .
Further, in the durability test at 100 ° C., the operation was terminated due to a cross leak after 120 hours of operation. The fluorine ion concentration in the waste water after 50 hours was 1.18 ppm on the cathode side and 2.5 ppm on the anode side.

The method for producing a stabilized fluoropolymer of the present invention can be used for producing a raw material suitable for a membrane material used under severe conditions such as a fuel cell electrolyte membrane.
Since the stabilized fluoropolymer of the present invention is excellent in chemical stability as described above, the hydrolyzate is used as a membrane material or an electrode of a fuel cell such as a solid polymer electrolyte fuel cell whose use conditions are usually severe. A highly durable fuel cell membrane or electrode that can be suitably used and has a small amount of fluorine ions in the waste water can be obtained.

It is a NMR chart obtained by measuring ¹⁹ F solid state nuclear magnetic resonance of the stabilized fluoropolymer G obtained in Example 5 (the vertical axis is enlarged 13 times that of FIG. 2). 6 is an NMR chart obtained by ¹⁹ F solid state nuclear magnetic resonance measurement of the stabilized fluoropolymer G obtained in Example 5.

Claims (5)

An active substance fixed body comprising a hydrolyzate of a stabilized fluoropolymer and an active substance,
The active substance fixed body is obtained by coating a substrate with a liquid composition in which the hydrolyzate of the stabilized fluoropolymer and the active substance are dispersed in a liquid medium, or the stable substance Obtained by hydrolyzing the stabilized fluoropolymer after coating a liquid composition comprising a stabilized fluoropolymer and the active substance on a substrate,
The stabilized fluoropolymer has the following general formula (II)
^{_{CF 2 = CF-O- (CFY}} 2) m -A (II)
(In the formula, Y ² represents F, Cl, Br or I. m represents an integer of 1 to 5. When m is an integer of 2 to 5, m Y ^{2 s} were the same. A represents —SO ₂ X or —COZ, X represents F, Cl, Br, I, or —NR ⁵ R ⁶ , Z represents —NR ⁷ R ⁸ or ^.R 5 representing a -OR ^{9, R 6,} R ⁷ and ^{R 8} are the same or different, .R ⁹ representing H, an alkali metal element, an alkyl group or a sulfonyl-containing group, having 1 to 4 carbon atoms A stabilized fluoropolymer obtained by polymerization of tetrafluoroethylene with an acid-derived group-containing perhalovinyl ether represented by the following formula:
The stabilized fluoropolymer has been fluorinated.
In the IR measurement, the stabilized fluoropolymer has an intensity ratio [x / y] of a peak [x] derived from a carboxyl group and a peak [y] derived from —CF ₂ — of 0.05 or less,
The substrate is a porous support, a resin molded body, or a metal plate,
The active substance fixed body, wherein the active substance is a catalyst, and the catalyst is a metal containing platinum. The active substance fixed body according to claim 1, wherein the polymerization of the acid-derived group-containing perhalovinyl ether and tetrafluoroethylene is emulsion polymerization. The active substance immobilization body according to claim 1 or 2, wherein the stabilized fluoropolymer has a melt index of 0.1 to 20 g / 10 min measured under conditions of 270 ° C and a load of 2.16 kg in accordance with JIS K 7210. A membrane / electrode assembly comprising a polymer electrolyte membrane and an electrode,
4. The membrane / electrode assembly according to claim 1, wherein the electrode is the active substance immobilization body according to claim 1. A solid polymer fuel cell comprising the membrane / electrode assembly according to claim 4.

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