JP5978762B2 - Method for producing fluoropolymer aqueous dispersion and purified fluoropolymer aqueous dispersion - Google Patents

Description

The present invention relates to a method for producing a fluoropolymer aqueous dispersion and a purified fluoropolymer aqueous dispersion.

In recent years, fluorine-containing polymers having sulfonic acid groups and carboxyl groups have attracted attention as materials for electrolyte membranes such as fuel cells and chemical sensors, and fluorine-containing polymers having sulfonate-type groups such as —SO ₃ Na. The polymer is used as an ion exchange membrane for salt electrolysis.

As a medium for fixing a catalyst on the surface of an electrolyte membrane in the production of an electrolyte membrane or the like, an aqueous dispersion of a fluorine-containing polymer is required from the viewpoint of workability and the like instead of a conventional medium mainly composed of an organic solvent. Since the aqueous dispersion of the fluorine-containing polymer can be used as a coating composition itself, it can be suitably used for cast film formation, impregnation and the like, and has a wide range of uses.

When such an aqueous dispersion is used, for example, in an electrochemical device such as a fuel cell, impurities contained in the aqueous dispersion may adversely affect an electrochemical reaction. A method of removing is desired.

For example, an ultrapurified aqueous dispersion containing a fluorine-containing polymer having an acid salt group can be ultrafiltered and then subjected to a cation exchange treatment to efficiently produce a high-purity fluorine-containing polymer dispersion. It is disclosed that it can be performed (for example, refer patent document 1). In Examples of Patent Document 1, ultrafiltration and cation exchange treatment were performed in this order on an aqueous dispersion of a fluorine-containing polymer having a —SO ₃ Na group, and the sodium content in the dispersion was reduced to 100 ppm. Is described.

JP 2009-102490 A

The method described in Patent Document 1 is intended to remove impurity cations that cannot be removed only by ultrafiltration by using a cation exchange treatment in combination. Can be manufactured. However, even the dispersion purified by the method described in Patent Document 1 still has about 100 ppm of impurity cations remaining, and there is room for further reduction.

The present invention has been made in view of the above situation, and a method for producing an aqueous fluoropolymer dispersion capable of efficiently removing impurity cations from an aqueous fluoropolymer dispersion and a purified fluoropolymer aqueous dispersion The purpose is to provide a body.

The inventor of the present invention uses —SO ₃ X, —SO ₂ NR ¹ ₂ and —COOX (X represents M _{1 / L} or NR ¹ _4. M represents a hydrogen atom or an 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, and each R ¹ independently represents a hydrogen atom or an alkyl having 1 to 4 carbon atoms. Various methods for efficiently removing impurity cations from a fluoropolymer aqueous dispersion containing a fluoropolymer having at least one group selected from the group consisting of: a fluoropolymer aqueous dispersion It has been found that the efficiency of cation exchange treatment in the body depends on the amount of carrier in the aqueous dispersion. The carrier here is a water-soluble electrolyte. Conventionally, a cation exchange treatment has been performed on a dispersion whose electrical conductivity is as low as possible by ultrafiltration or the like. However, in this method, there are few ions serving as carriers in water as a dispersion medium, and the fluoropolymer It is considered that the impurity cations cannot be sufficiently removed because the cation exchange between the ion exchange resin and the ion exchange resin does not proceed sufficiently. In the method of performing cation exchange subsequent to ultrafiltration, the present inventor is sufficient in the dispersion if the electrical conductivity at 25 ° C. of the fluoropolymer aqueous dispersion subjected to cation exchange treatment is greater than 1 mS / cm. Thus, the present inventors have found that a large amount of carriers are present, and that impurity cations in the dispersion, particularly alkali metal ions, can be significantly reduced as compared with the conventional art.

That is, the present invention relates to —SO ₃ X, —SO ₂ NR ¹ ₂ and —COOX (X represents M _{1 / L} or NR ¹ _4. M represents a hydrogen atom or an L-valent metal; A 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, and each R ¹ is independently a hydrogen atom or a group having 1 to 4 carbon atoms. Step (A) of preparing a fluoropolymer aqueous dispersion containing a fluoropolymer having at least one group selected from the group consisting of an alkyl group.), And subjecting the fluoropolymer aqueous dispersion to ultrafiltration Step (B) to be performed and Step (C) after obtaining the purified fluoropolymer aqueous dispersion by bringing the fluoropolymer aqueous dispersion into contact with the cation exchange ion exchange resin after the step (B). Including cation exchange type a in step (C) A method for producing an aqueous fluoropolymer dispersion, wherein the electrical conductivity at 25 ° C. of the aqueous fluoropolymer dispersion to be contacted with an on-exchange resin is greater than 1 mS / cm.

The present invention is also a purified fluoropolymer aqueous dispersion obtained by the above-described method for producing a fluoropolymer aqueous dispersion.
The present invention is described in detail below.

Method for producing a fluoropolymer aqueous dispersion of the present ^{_{invention, -SO 3 X, -SO 2 NR}} 1 2 and -COOX (X _is .M representing the _{M 1 / L} or ^NR _{1 4} is hydrogen atom or L -valent metal, said L-valent metal, group 1 of the periodic table, group 2, group 4, group 8, group 11, it .R ¹ are each independently a metal belonging to group 12 or group 13, hydrogen (A) represents a fluorine-containing polymer aqueous dispersion containing a fluorine-containing polymer having at least one group selected from the group consisting of an atom or an alkyl group having 1 to 4 carbon atoms.

Examples of the fluorine-containing polymer include the following general formula (I):
^{_{CF 2 = CF- (O) n1}} - (CF 2 CFY 1 -O) n2 - (CFY 2) n3 -A (I)
(Wherein, ^{Y 1} is, .n2 .n1 represents a halogen atom or a perfluoroalkyl group represents an integer of 0 or 1, .N2 amino ^{Y 1} represents an integer of 0 to 3, and the same good .Y ² be different also may, .N3 represents a halogen atom, .N3 one Y ² representing a 1-8 integer may be different or may be the same .A ^{_{is, -SO 3 X, -SO 2 NR}} 1 2 or -COOX (X _is .M representing the _{M 1 / L} or ^NR _{1 4} represents a hydrogen atom or a metal whose valence is L, 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, and each R ¹ independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. .)) Having a structural unit derived from a fluoromonomer represented by

The aqueous fluoropolymer dispersion can be produced by a known method. For example, in Japanese translations of PCT publication No. 2001-504872, an unpurified aqueous dispersion containing a fluoropolymer precursor is obtained by putting a fluoropolymer precursor into a pressure vessel together with a medium and heating it with stirring. In addition, in International Publication No. 2004/018527, -SO ₃ X and / or -COOX (X is the same as defined above) or a monomer having a precursor thereof and a monomer having an ethylenic double bond. After copolymerization in an aqueous medium, an unrefined aqueous dispersion containing a fluorine-containing polymer or a precursor thereof is obtained by adding alkali hydroxide or the like as necessary.

The fluorine-containing polymer has the following general formula (III):
^{_{CF 2 = CF- (O) n1}} - (CF 2 CFY 1 -O) n2 - (CFY 2) n3 -A 2 (III)
(In the formula, Y ¹ , Y ² , n ¹ , n 2 and n 3 are the same as defined in the general formula (I). A ² represents —SO ₂ Y ³ , —SO ₂ NR ¹ ₂ , — SO ₃ M _{1 / L} , —SO ₃ NR ¹ ₄ , —COONR ¹ ₄ , —COOM _{1 / L} or —COOR ² (Y ³ represents a halogen atom. M represents hydrogen or 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, and R ¹ is the same or different and is a hydrogen atom or a carbon number. Represents an alkyl group having 1 to 4. R ² represents an alkyl group having 1 to 4 carbon atoms.)) Or a polymer obtained by polymerizing the fluoromonomer represented by It is preferable that it is obtained by hydrolyzing.

N1 in the said general formula (III) represents the integer of 0-1. N1 is preferably 1. N2 represents an integer of 0 to 3. N2 is preferably 0 or 1. N3 represents an integer of 1 to 8. N3 is preferably 2, 3 or 4, and more preferably 2.

Y ¹ in the general formula (III) represents a halogen atom or a perfluoroalkyl group, and n2 Y ^{1 s} may be the same or different. Y ² in the general formula (III) represents a halogen atom, and n3 Y ^{2 s} may be the same or different. The halogen atom for Y ¹ and Y ² is not particularly limited, and may be any of a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and is preferably a fluorine atom. The perfluoroalkyl group is not particularly limited, and examples thereof include a trifluoromethyl group and a pentafluoroethyl group. In the general formula (III), Y ¹ is preferably a trifluoromethyl group, and Y ² is preferably a fluorine atom.

As the fluoromonomer represented by the general formula (III), Y ¹ in the general formula (I) is a trifluoromethyl group, Y ² is a fluorine atom, n1 is 1, n2 is 0 or 1, and n3 is Those of 2 are preferred.

From the group consisting of at least one or more of —SO ₂ Y ³ and —COOR ² (Y ³ represents a halogen atom, R ² represents an alkyl group having 1 to 4 carbon atoms). It is preferably obtained by hydrolyzing a fluoropolymer precursor having a structural unit derived from a fluoromonomer having at least one selected group. What is obtained by such a production method is more effective when the treatment by the production method of the present invention is performed because a large amount of ionic impurities are likely to be mixed into the system in the hydrolysis step and the neutralization step. It will be remarkable.

The fluoropolymer precursor is preferably subjected to acid treatment after the hydrolysis. That is, since hydrolysis is often performed in a basic manner, the fluoropolymer after hydrolysis has a salt structure. For this reason, it is preferable to perform an acid treatment in order to substitute for H. By further carrying out the alkaline step after the acid treatment _step, -SO ³ _{M 2 1 / L} or ^{_{-SO 3 NR 3 R 4 R 5}} R 6, and / or, -COOM ² _{1 / L} or -COONR ³ R ⁴ R ⁵ R ⁶ (M ² represents an L-valent metal, and 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. R ³ , R ⁴ , R ⁵ , and R ⁶ may be the same or different and each represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

The fluoropolymer is a copolymer of two or more having a structural unit derived from the fluoromonomer represented by the general formula (I) and a structural unit derived from another fluorine-containing ethylenic monomer. Is preferred. The fluorine-containing ethylenic monomer is a monomer copolymerizable with the fluoromonomer represented by the general formula (I), and is not particularly limited as long as it has a vinyl group. The general formula (I) Is different from the fluoromonomer represented by

Examples of the fluorine-containing ethylenic monomer include the following general formula (II):
^{_{CF 2 = CF-R f 1}} (II)
(In the formula, R _f ¹ represents a fluorine atom, a chlorine atom, R _f ² or OR _f ² , and R _f ² is linear or branched which may have an ether bond having 1 to 9 carbon atoms. It is preferably at least one monomer represented by the following formula: The monomer represented by the general formula (II) is more preferably partly or wholly tetrafluoroethylene.

The fluorine-containing ethylenic monomer is represented by the following general formula (IV)
CHY ³ = CFY ⁴ (IV)
(Wherein, ^{Y 3} represents a hydrogen atom or a fluorine atom, ^{Y 4} is a hydrogen atom, a fluorine atom, a chlorine _{atom, .R} ^{f 3} representing a _R ^{f 3} or _-OR ^{f 3} is 1 to 9 carbon atoms And a hydrogen-containing fluoroethylenic monomer represented by a linear or branched fluoroalkyl group optionally having an ether bond.

The fluorine-containing ethylenic monomer is CF ₂ = CF ₂ , CH ₂ = CF ₂ , CF ₂ = CFCl, CF ₂ = CFH, CH ₂ = CFH, CF ₂ = CFCF ₃ , and CF ₂ = CF- _{(wherein, R} ^{f 4} represents. fluoropolyether group having 1 to 9 fluoroalkyl group or a carbon number of 1 to 9 carbon atoms) _O-R ^{f 4} is selected from the group consisting of fluorovinyl ethers represented by At least one is preferred. The fluorovinyl ether is preferably a perfluoroalkyl group having 1 to 3 carbon atoms in R _f ⁴ .

The fluorine-containing ethylenic monomer is particularly preferably a perfluoroethylenic monomer, and more preferably CF ₂ = CF ₂ . As said fluorine-containing ethylenic monomer, 1 type (s) or 2 or more types can be used.

In addition to the above-mentioned fluorine-containing ethylenic monomer, other copolymerizable monomers may be used as long as the basic performance of the fluorine-containing polymer is not impaired in order to impart various functions to the fluorine-containing polymer. A monomer may be added. The other copolymerizable monomers are not particularly limited, and can be copolymerized according to the purpose such as control of polymerization rate, control of polymer composition, control of mechanical properties such as elastic modulus, introduction of cross-linking sites, etc. be chosen from among the monomers, monomers having an unsaturated bond such as perfluoro divinyl ether two or more monomers containing CF 2 ₌ CFOCF 2 _CF 2 _CN cyano group and the like.

The fluoropolymer preferably has a fluoromonomer unit content of 5 to 40 mol%. If it is less than 5 mol%, the performance as an electrolyte of the fluoropolymer obtained through the acid treatment step described later or the acid treatment step and the alkali treatment step described later may be reduced, and 40 mol% If it exceeds 1, the mechanical strength of the film obtained using the above-mentioned fluoropolymer may be insufficient. When the content ratio of the fluoromonomer unit is larger in the particle surface than in the particles of the fluorine-containing polymer, the ratio of A in the general formula (I) is larger on the particle surface of the particles of the fluorine-containing polymer. It is preferable that it is the said range.
The “inside of the particle” means a portion occupying 50% by mass of the center of the total mass of the particle. The “particle surface” means a portion of the particle excluding the inside of the particle.

In the present specification, the “fluoromonomer unit” means a part of the molecular structure of the fluoropolymer and derived from the fluoromonomer represented by the general formula (I).
The “content ratio of the fluoromonomer unit” is a ratio of the number of moles of the fluoromonomer derived from the fluoromonomer unit to the number of moles of the monomer derived from all the monomer units in the molecule of the fluoropolymer. The “all monomer units” are all of the portions derived from the monomers in the molecular structure of the fluoropolymer. The “monomer from which all monomer units are derived” refers to the total amount of monomers that have formed the fluoropolymer.
The content of the fluoromonomer unit is a value obtained using infrared absorption spectrum analysis [IR] or melting NMR at 300 ° C.

The polymerization reaction for obtaining a fluoropolymer having a structural unit derived from the fluoromonomer or a precursor thereof is preferably emulsion polymerization. In the present specification, “emulsion polymerization” for the method for producing an aqueous fluoropolymer dispersion of the present invention means polymerization carried out using an emulsifier and / or an emulsifying agent in an aqueous reaction medium. The emulsifier may be an emulsifier usually used in conventional emulsion polymerization or a different one from the existing emulsifier, or both an existing emulsifier and a new emulsifier may be used.

As the emulsifier, a compound composed of a fluoroalkyl group having 4 to 12 carbon atoms which may contain oxygen and a dissociative polar group can be used. For example, ammonium perfluorooctanoate [C ₇ F ₁₅ COONH ₄ ], Examples include fluorohexanoic acid [C ₅ F ₁₁ COONH ₄ ], CF ₃ OCF (CF ₃ ) CF ₂ OCF (CF ₃ ) COONH _{4, and the} like. In general, the emulsifier used in the emulsion polymerization can be used in an amount of 0.01 to 10% by mass of the aqueous reaction medium.

As the emulsifying agent, among the fluoromonomers represented by the above general formula (III), A is —SO ₃ M _{1 / L} , —SO ₃ NR ¹ ₄ , —COONR ¹ ₄ or —COOM _{1 / L.} can be used fluoromonomer, in particular _{CF 2 = CFOCF 2 CF 2 SO} 3 Na, CF 2 = CFOCF 2 CF (CF 3) OCF 2 CF 2 SO 3 Na, CF 2 = CFOCF 2 CF (CF 3) OCF 2 A fluoromonomer that can participate in a polymerization reaction such as CF ₂ CO ₂ Na and give a polymer emulsifier is preferred. Since the fluoromonomer has an emulsifying effect in emulsion polymerization and is an ethylenic compound, it can be added as a monomer in the polymerization reaction and polymerized so as to be at least part of the molecular structure of the fluoropolymer. it can.

When the above-mentioned emulsifying agent is used, the aqueous reaction medium can be emulsified without having an existing emulsifier, so that emulsion polymerization can be performed without using an emulsifier.

In the above emulsion polymerization, depending on the polymerization conditions, the number of particles of the resulting fluoropolymer may be reduced and the particle size may be increased, and the ultrafiltration membrane may be loaded in the ultrafiltration described later. In this case, since the film may be inhomogeneous, it may be preferable to use the emulsifier in the emulsion polymerization. In order to increase the number of particles, so-called “seed polymerization” can be performed in which a dispersion obtained by polymerization using a large amount of emulsifier is diluted and polymerization is continued.

In the present specification, the “aqueous reaction medium” refers to a medium composed of water used in the polymerization, and water or a medium obtained by dissolving or dispersing an organic medium in water. The aqueous reaction medium preferably does not contain the organic medium, and even if it contains the organic medium, a very small amount is preferable.

The polymerization reaction may be performed using a polymerization initiator. The polymerization initiator is not particularly limited as long as it is usually used for polymerization of fluoropolymers, and examples thereof include organic peroxides, inorganic peroxides, and azo compounds. In particular, it is preferable to use ammonium persulfate [APS]. The addition amount of the polymerization initiator is preferably 0.01 to 1% by mass of the total of all monomers used in the polymerization reaction.

The pH of the aqueous reaction medium in the polymerization reaction is preferably 4-7. When the pH is within the above range, the polymerization reaction proceeds smoothly, and —SO ₂ Y ³ and / or —COOR ² (Y ³ , R ^{2) of the} fluoromonomer and / or fluoropolymer in the polymerization reaction. Is the same as defined above)).

The reaction conditions such as the reaction temperature in the polymerization reaction are not particularly limited and can be performed according to a usual method.

When A ² in the general formula (III) is —SO ₂ Y ³ or —COOR ² , a target fluoropolymer is obtained by performing a hydrolysis reaction of the fluoropolymer precursor obtained by polymerization. Can do. The hydrolysis can be carried out under the conditions of pH 8 to 14 while adding an aqueous solution of a basic compound such as sodium hydroxide or potassium hydroxide at 0 to 100 ° C.

The aqueous fluoropolymer dispersion obtained in the step (A) is obtained by dispersing particles comprising the above-mentioned fluoropolymer in an aqueous medium. The aqueous fluoropolymer dispersion preferably includes spherical particles having an average particle diameter of 10 nm or more made of the fluoropolymer. In the fluoropolymer aqueous dispersion containing spherical particles as described above, the fluoropolymer aqueous dispersion is composed of a fluoropolymer under conditions where the electrical conductivity of the aqueous dispersion is low, that is, under conditions where the amount of carrier in water as a dispersion medium is small. The tendency that the cation exchange between the particles and the ion exchange resin does not sufficiently proceed and the impurity cations cannot be removed sufficiently appears more remarkably. For this reason, the effects of the present invention are more remarkable by performing the following steps (B) and (C) on the fluoropolymer aqueous dispersion containing spherical particles having an average particle diameter of 10 nm or more and comprising the above fluoropolymer. Will be demonstrated.

The spherical particles refer to particles that are substantially spherical among the particles made of the fluorine-containing polymer. In the present specification, the term “substantially spherical” means that the aspect ratio is 3 or less. Usually, the closer the aspect ratio is to 1, the closer to a spherical shape. The aspect ratio of the spherical particles is preferably 3 or less. A more preferred upper limit is 2, and a more preferred upper limit is 1.5.

It is preferable that 25% by mass or more of the particles made of the fluoropolymer are the spherical particles. More preferably, it is 50 mass% or more. From the dispersion obtained by emulsion polymerization, spherical particles made of a fluorine-containing polymer having 90% by mass or more can be obtained.

If the average particle diameter is within the above range, the upper limit can be set to, for example, 300 nm from the viewpoint of stability of the fluoropolymer aqueous dispersion and ease of making the fluoropolymer, but it exceeds 300 nm. There may be. A more preferable lower limit of the average particle diameter is 30 nm, and a more preferable upper limit is 160 nm.

The above aspect ratio and average particle diameter are obtained by applying the above fluoropolymer aqueous dispersion to a glass plate with a scanning or transmission electron microscope, atomic force microscope, etc., and then removing the aqueous dispersion medium. In addition, the aggregate of the particles made of the fluoropolymer was observed, and the ratio of the major axis to the minor axis length (major axis / minor axis) measured for 20 or more particles on the obtained image was the aspect ratio. The average value of the lengths of the major axis and the minor axis can be obtained as the average particle diameter described later.

The aqueous fluoropolymer dispersion preferably contains 25% by mass or more of spherical particles having an average particle diameter of 10 nm or more among particles made of the fluoropolymer. The aqueous fluoropolymer dispersion is more preferably 25% by mass or more of spherical particles having an average particle diameter of 10 to 300 nm among the particles made of the fluoropolymer. Moreover, it is more preferable that the aqueous fluoropolymer dispersion contains 25% by mass or more of spherical particles having an average particle diameter of 30 to 160 nm among particles made of the fluoropolymer.

The manufacturing method of the fluoropolymer aqueous dispersion of this invention includes the process (B) which performs ultrafiltration on the said fluoropolymer aqueous dispersion.

The ultrafiltration is not particularly limited as long as it is a method of removing low molecular weight impurities using an ultrafiltration device having an ultrafiltration membrane. For example, centrifugal ultrafiltration, batch ultrafiltration, circulation, etc. Formula ultrafiltration method and the like can be mentioned. The ultrafiltration device having the ultrafiltration membrane and the ultrafiltration membrane is appropriately selected depending on the molecular weight and type of the low molecular weight impurities to be removed, the type of the aqueous medium, the molecular weight and type of the fluoropolymer. Examples of the low molecular weight impurities include surfactants such as fluorine-containing anionic surfactants. As the ultrafiltration apparatus having the ultrafiltration membrane, a commercially available apparatus can be suitably used. For testing, for example, Centriprep (trade name, manufactured by Amicon), Millitan (trade name, Millipore) Manufactured) and the like. By the ultrafiltration, the salt generated during hydrolysis can be removed. Moreover, the obtained fluorine-containing polymer can also be concentrated.

In the method for producing a fluoropolymer aqueous dispersion of the present invention, an operation of adding purified water to the fluoropolymer aqueous dispersion, which is a treatment target, while performing ultrafiltration, You may perform operation which makes pH of a fluorine-containing polymer aqueous dispersion 3 or less. Specifically, after performing the treatment by the centrifugal ultrafiltration method and the batch ultrafiltration method, the process of adding purified water or acid to the treated liquid and performing the ultrafiltration treatment again may be repeated. it can. Further, in the circulation ultrafiltration method, purified water or acid may be appropriately added to the treatment liquid tank.

It is appropriate to determine the end point of the ultrafiltration based on the amount of impurities contained in the filtrate. As a simple method, in the method of adding purified water, it can be determined based on the electrical conductivity of the filtrate. In addition, the method of adding an acid includes a method of quantifying alkali metals or the like by ICP analysis or atomic absorption analysis, and a method of titrating the filtrate with acid / base titration to a point when the acid is no longer consumed. Therefore, the latter method is preferable.

The ultrafiltration in the step (B) is preferably performed while adding purified water corresponding to the amount discharged out of the system as a filtrate. The end point of the ultrafiltration is preferably determined based on the electrical conductivity of the filtrate. The electrical conductivity can be easily measured using, for example, a Twincond B-173 electrical conductivity meter manufactured by HORIBA, Ltd.

The end point of the ultrafiltration is that the electrical conductivity at 25 ° C. of the fluoropolymer aqueous dispersion (liquid to be treated) brought into contact with the cation exchange type ion exchange resin in the cation exchange treatment in the step (C) described later is 1 mS / It is preferable to determine so that it can be over cm. As a method of setting the electric conductivity at 25 ° C. of the liquid to be treated in the step (C) to be over 1 mS / cm, (i) electric conduction at 25 ° C. of the fluoropolymer aqueous dispersion by ultrafiltration in the step (B) Adjusting the electrical conductivity at 25 ° C. of the aqueous dispersion to more than 1 mS / cm by adding a substance (electrolyte) that ionizes into a cation and an anion in the aqueous dispersion after the degree is 1 mS / cm or less. And (ii) a method in which the time when the electrical conductivity of the fluoropolymer aqueous dispersion at 25 ° C. exceeds 1 mS / cm is used as the end point of the ultrafiltration in step (B).

In step (B), the electrical conductivity of the fluoropolymer aqueous dispersion after ultrafiltration can be measured as the electrical conductivity of the filtrate of ultrafiltration, and the electrical conductivity of the filtrate is the end point described above. By determining whether or not the above criteria are satisfied, it can be determined whether or not the ultrafiltration has reached the end point.

In the method (i), the end point of the ultrafiltration is the time when the electrical conductivity becomes 1 mS / cm or less. The time is preferably 100 μS / cm or less, more preferably 10 μS / cm or less. Moreover, it is preferable that the minimum of the said electrical conductivity in the end point of the said ultrafiltration is 0.1 microsiemens / cm. A more preferred lower limit is 1 μS / cm.

In the method (ii), the end point of the ultrafiltration is not limited as long as the electrical conductivity at 25 ° C. of the fluoropolymer aqueous dispersion is more than 1 mS / cm, From the viewpoint of increasing the amount of carriers and improving the efficiency of the cation exchange treatment, it is preferable that the end point of the ultrafiltration is preferably a time point at which the electrical conductivity at 25 ° C. is 2 mS / cm or more. Is more preferable. In the method (ii), the electrical conductivity that is the end point of the ultrafiltration is preferably 20 mS / cm or less, more preferably 10 mS / cm or less, from the viewpoint of utilization efficiency of the cation type ion exchange resin to be used.

In step (B), when the ultrafiltration end point is the time when the electrical conductivity of the fluoropolymer aqueous dispersion at 25 ° C. is 1 mS / cm or less (when the method (i) above is employed) Is followed by the step (B-1) of adjusting the electrical conductivity of the aqueous dispersion at 25 ° C. to more than 1 mS / cm by adding an electrolyte to the fluoropolymer aqueous dispersion after the step (B). is necessary. The electrical conductivity at 25 ° C. of the aqueous fluoropolymer dispersion after the treatment in the step (B-1) is preferably 2 mS / cm or more, and more preferably 5 mS / cm or more. Moreover, it is preferable to set it as 20 mS / cm or less from a viewpoint of the utilization efficiency of the cation type ion exchange resin to be used, and it is more preferable to set it as 10 mS / cm or less.

Examples of the electrolyte added in the step (B-1) include acids such as hydrogen chloride, nitric acid, and sulfuric acid, and salts of the acids. Of these, nitric acid and nitrate are preferable. The electrolyte may be added to the fluoropolymer aqueous dispersion as it is, or may be added as a solution after being dissolved in an appropriate medium such as water.

In the step (B), when the ultrafiltration end point is the time when the electrical conductivity of the fluoropolymer aqueous dispersion at 25 ° C. exceeds 1 mS / cm (when the method (ii) is adopted) The fluoropolymer aqueous dispersion obtained in the step (B) can be directly used in the step (C).

In the method for producing an aqueous fluoropolymer dispersion of the present invention, after the step (B), the aqueous fluoropolymer dispersion and the cation exchange ion exchange resin are brought into contact with each other to obtain a purified fluoropolymer aqueous dispersion. Obtaining step (C).
The treatment in which the fluoropolymer aqueous dispersion is contacted with a cation exchange ion exchange resin (hereinafter also referred to as cation exchange resin), that is, as the cation exchange treatment, a column filled with the cation exchange resin is used in an aqueous fluoropolymer dispersion. There are a method of circulating the body, a method of dispersing the cation exchange resin in an aqueous fluoropolymer dispersion and performing ion exchange, and then separating the cation exchange resin by filtration or the like.

The electrical conductivity at 25 ° C. of the fluoropolymer aqueous dispersion (liquid to be treated) brought into contact with the cation exchange ion exchange resin in the step (C) is larger than 1 mS / cm. Thereby, a sufficient amount of carriers are present in the liquid to be treated, and impurity cations, particularly alkali metal ions, in the liquid to be treated can be sufficiently removed by the cation exchange treatment. The electrical conductivity is preferably 2 mS / cm or more, and more preferably 5 mS / cm or more. Moreover, 20 mS / cm or less is preferable from a viewpoint of the utilization efficiency of the cation type ion exchange resin to be used, and 10 mS / cm or less is more preferable.

Examples of the method for setting the electric conductivity at 25 ° C. of the liquid to be treated in the step (C) to exceed 1 mS / cm include the above-described methods (i) and (ii).

The degree of ion exchange is determined based on the amount of impurity cations contained in the purified fluoropolymer aqueous dispersion (treated fluoropolymer aqueous dispersion after treatment), in particular, alkali metal ions such as sodium ions and potassium ions. It is preferable that the point that satisfies the above is the end point. In order not to adversely affect the film forming property and the performance and durability of the fuel cell, the content of alkali metal ions in the purified fluoropolymer aqueous dispersion is preferably less than 100 ppm, and is preferably 50 ppm or less. More preferably, it is more preferably 10 ppm or less. The amount of the alkali metal ion can be measured by atomic absorption spectrophotometry.

Examples of the cation exchange resin include a cation exchange resin in which an acidic functional group is introduced into an organic polymer molecule.

The acidity of the cation exchange resin to be used can be set variously depending on the type of polymer skeleton and functional group. Generally, sulfonic acid functional group introduced into styrene skeleton, acrylic resin, methacrylic resin, perfluoro Those obtained by introducing sulfonic acid or carboxylic acid into the polymer skeleton can be used. In this application, the intended purpose can be achieved regardless of the acidity, and it is not particularly limited, but it is preferable to use a commercially available one because it is easily available. Such a cation exchange resin is usually used by conditioning a resin commercially available in Na type with mineral acid to prepare H type, but a resin commercially available in H type may be used. Specifically, Amberlite IR120B, Amberlite IR124, Amberlite FPC3500 manufactured by Rohm & Haas, Diaion SK1B, SK110, SK112, Diaion WK10, WK11, WK11, WK100, and WK40 manufactured by Mitsubishi Chemical Corporation Etc. can be selected.

It is preferable that the manufacturing method of the fluoropolymer aqueous dispersion of this invention further includes the process (D) which performs ultrafiltration after a process (C). In the step (C) described above, in order to increase the efficiency of the cation exchange treatment, the step (C) is performed because the fluoropolymer aqueous dispersion having a high electrical conductivity (a large amount of ions) is used as the liquid to be treated. Thereafter, the aqueous fluoropolymer dispersion contains a large amount of anions that cannot be removed by cation exchange. By performing ultrafiltration again after the step (C), anionic impurities and the like can be removed, and a fluoropolymer aqueous dispersion with higher purity can be produced.

The ultrafiltration in the step (D) can be performed by the same apparatus and method as the ultrafiltration in the step (B). The end point of the ultrafiltration in the step (D) can be determined by an electric conductivity of the filtrate or an ion meter that measures anion species. The electrical conductivity of the filtrate serving as the end point is preferably 100 μS / cm or less, more preferably 10 μS / cm or less, and still more preferably 1 μS / cm or less.

The present invention also provides a purified fluoropolymer aqueous dispersion obtained by the above-described method for producing a fluoropolymer aqueous dispersion.

The purified fluoropolymer aqueous dispersion is obtained by dispersing particles composed of the above-mentioned fluoropolymer in an aqueous dispersion medium, and the impurity cation content is sufficiently reduced.
The aqueous dispersion medium may be made of water or water and a water-soluble organic solvent. The aqueous dispersion medium may have additives such as surfactants and stabilizers that are usually used in aqueous dispersions.
The aqueous dispersion medium preferably has a water content of 10 to 100% by mass. If it is less than 10% by mass, the dispersibility tends to deteriorate, which is not preferable from the viewpoint of environment and human body. A more preferred lower limit is 40% by mass.

The solid content mass of the particles made of the fluoropolymer contained in the purified fluoropolymer aqueous dispersion is preferably 2 to 80% by mass of the total mass of the purified fluoropolymer aqueous dispersion. The amount of particles comprising the fluoropolymer in the purified fluoropolymer aqueous dispersion usually corresponds to the solid content mass in the purified fluoropolymer aqueous dispersion. When the content of the particles composed of the fluoropolymer in the fluoropolymer dispersion is less than 2% by mass, the amount of the aqueous dispersion medium increases, and when used for film formation, the productivity may decrease. On the other hand, if it exceeds 80% by mass, the viscosity tends to be high and handling tends to be difficult. A more preferable lower limit is 5% by mass, and a more preferable upper limit is 60% by mass.

The particles made of the fluoropolymer preferably contain 25% by mass or more of fluoropolymer spherical particles that are substantially spherical. In the present specification, the phrase “containing 25 mass% or more of fluorine-containing polymer spherical particles” means that 25 mass% or more of the particles made of the fluorine-containing polymer are fluorine-containing polymer spherical particles.

An aspect ratio can be used as a guide for the shape of the particles made of the fluoropolymer. In the present specification, the term “substantially spherical” means that the aspect ratio is 3 or less. Usually, the closer the aspect ratio is to 1, the closer to a spherical shape. The aspect ratio of the particles made of the fluoropolymer is preferably 3 or less. A more preferred upper limit is 2, and a more preferred upper limit is 1.5.
In general, when the shape of the polymer particles is anisotropic, the dispersion of the polymer particles tends to be highly viscous, and when the dispersion of the polymer particles is high, the concentration of the polymer particles in the dispersion is increased. It is not preferable because it becomes difficult to do.

When the particle comprising the fluoropolymer contains 25% by mass or more of the fluoropolymer spherical particles that are substantially spherical, the viscosity of the purified fluoropolymer aqueous dispersion is, for example, the viscosity of the particle comprising the fluoropolymer. Compared to the case where the shape is not substantially spherical, it is possible to reduce the shape, and the solid content concentration of the purified fluoropolymer aqueous dispersion can be increased. As a result, when forming a film by a method such as cast film formation. It is possible to achieve high productivity.

More preferably, the particles made of the fluoropolymer contain 50 mass% or more of fluoropolymer spherical particles.
A purified fluoropolymer aqueous dispersion having a fluoropolymer spherical particle content in the above range can be obtained by preparing from a dispersion obtained by emulsion polymerization. A dispersion containing 90% by mass or more of fluorine-containing polymer spherical particles can be obtained from the dispersion obtained by emulsion polymerization. The purified fluoropolymer aqueous dispersion of the present invention is prepared by blending particles having a relatively high content of fluoropolymer spherical particles with particles that are not substantially spherical out of the fluoropolymer particles. It is also possible to adjust so as to exhibit the performance according to.
Particles made of a fluorine-containing polymer containing 50% by mass or more of the spherical particles can be produced, for example, by emulsion polymerization of a fluoromonomer having —SO ₂ F, followed by hydrolysis.

The particles made of the fluoropolymer preferably have an average particle size of 10 nm or more. When the thickness is less than 10 nm, when used as an electrode material, active points may be covered and good battery characteristics may not be obtained.
If the average particle diameter is within the above range, the upper limit can be set to, for example, 300 nm from the viewpoint of the stability of the purified fluoropolymer aqueous dispersion and the ease of producing the fluoropolymer, but it exceeds 300 nm. However, it does not greatly affect the battery characteristics.
As for the particle | grains which consist of the said fluoropolymer, what has an average particle diameter of 10-300 nm is more preferable. A more preferable lower limit of the average particle diameter is 30 nm, and a more preferable upper limit is 160 nm.

The above aspect ratio and average particle diameter are obtained by applying the purified fluoropolymer aqueous dispersion to a glass plate with a scanning or transmission electron microscope, atomic force microscope, etc., and then removing the aqueous dispersion medium. The aggregate of particles made of the obtained fluoropolymer was observed, and the ratio of the major axis to minor axis length (major axis / minor axis) measured for 20 or more particles on the obtained image was measured according to the aspect. The average value of the ratio, the length of the long axis and the length of the short axis can be obtained as the average particle diameter described later.

The purified fluorine-containing polymer aqueous dispersion preferably contains 25% by mass or more of fluorine-containing spherical particles having an average particle diameter of 10 nm or more among particles made of a fluorine-containing polymer.
More preferably, the purified fluoropolymer aqueous dispersion contains 25 mass% or more of fluorine-containing spherical particles having an average particle diameter of 10 to 300 nm among particles made of the fluorine-containing polymer.
It is more preferable that the purified fluoropolymer aqueous dispersion contains 25 mass% or more of fluorine-containing spherical particles having an average particle diameter of 30 to 160 nm among particles made of the fluoropolymer.

Since the purified fluoropolymer aqueous dispersion of the present invention is obtained by the above-described production method, the content of impurity cations, particularly alkali metal ions, is sufficiently reduced. The alkali metal ion contained in the purified fluoropolymer aqueous dispersion is preferably less than 100 ppm, more preferably 50 ppm or less, still more preferably 10 ppm or less, based on the aqueous dispersion.

The purified fluoropolymer aqueous dispersion of the present invention may be prepared by adding an additive, if necessary, in addition to the particles made of the fluoropolymer. The additive is not particularly limited. For example, polytetrafluoroethylene [PTFE], tetrafluoroethylene / hexafluoropropylene copolymer [FEP], tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer [PFA]. Fluorine resin such as polyethylene, polypropylene, polyethylene terephthalate [PET], etc .; Thermosetting resin such as polyamide, polyimide, etc .; Fine powder such as other ion exchange resin; Alumina, silica, zirconia, carbon, etc. Examples thereof include fine powders of inorganic materials.

The purified fluoropolymer aqueous dispersion of the present invention is formed into a film-forming dispersion composition by blending a liquid medium different from the above-mentioned aqueous dispersion medium as necessary, and impregnating the porous support to form a film. Or cast into a film and can be suitably used for film formation. The purified fluoropolymer aqueous dispersion of the present invention can also be used for the purpose of forming a thick film by blending polyethylene glycol or the like as required.
The liquid medium is a liquid that can wet the particles made of the fluoropolymer. The liquid medium is preferably a liquid at room temperature.
As the liquid medium, when good dispersibility of the particles made of the fluorine-containing polymer is desired, for example, alcohols; nitrogen-containing solvents such as N-methylpyrrolidone [NMP]; ketones such as acetone; acetic acid Examples include esters such as ethyl; polar ethers such as diglyme and tetrahydrofuran [THF]; carbonates such as diethylene carbonate; and polar organic solvents such as sulfones such as dimethyl sulfoxide [DMSO]. 1 type (s) or 2 or more types can be mixed and used. The liquid medium is a concept that may contain a water-soluble organic solvent in the aqueous dispersion medium.

The film-forming dispersion composition contains other components other than the purified fluoropolymer aqueous dispersion and the liquid medium as long as the properties such as film forming properties of the film-forming dispersion composition are not impaired. You may do it. Examples of the other components include a film-forming auxiliary and an active substance.

The purified fluoropolymer aqueous dispersion or the film-forming dispersion composition can be suitably used for film formation. The film forming method is not particularly limited, and examples thereof include cast film formation and film formation by impregnating a porous support. The cast film is usually formed by applying the purified fluoropolymer aqueous dispersion or the film-forming dispersion composition to the surface of a substrate such as glass and drying at room temperature and / or heating. The thin film is obtained by immersing in water and peeling off from the surface of the substrate. The film formation by impregnating the porous support is performed by impregnating the porous support with the purified fluoropolymer aqueous dispersion or the film-forming dispersion composition, and then removing the liquid medium. It refers to obtaining a film. The liquid medium can be usually removed by drying at room temperature and / or heating.

The membrane thus obtained can be particularly suitably used for an active substance fixed body and a membrane electrode assembly in a solid polymer electrolyte fuel cell.

Since the method for producing an aqueous fluoropolymer dispersion according to the present invention has the above-described configuration, impurity cations, particularly alkali metal ions, can be efficiently removed from the aqueous fluoropolymer dispersion. The purified fluoropolymer aqueous dispersion obtained by the production method of the present invention is suitably used in a dispersion composition for film formation, a membrane, an active substance fixed body, a membrane electrode assembly, and a solid polymer electrolyte fuel cell. be able to.

FIG. 1 is a diagram showing the relationship between the electrical conductivity at 25 ° C. of the liquid to be treated in the cation exchange treatment and the amount of ions (cation amount) in the obtained purified fluoropolymer aqueous dispersion. The horizontal axis indicates the electrical conductivity measured before ion exchange, and the vertical axis indicates the amount of ions contained in the aqueous fluoropolymer dispersion after ion exchange.

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

The circulation type ultrafiltration unit used in the following examples and comparative examples is an ultrafiltration device manufactured by Millipore, and an ultrafiltration membrane having a fractional molecular weight of 10,000 (Pelicon2 Filter manufactured by Millipore) It is sandwiched between stainless steel holders. In supplying the fluoropolymer aqueous dispersion to the circulation ultrafiltration unit, a liquid feed pump (easy-load MasterFlex 1 / P manufactured by Millipore) was used.

The cation exchange resin beads used in the following Examples and Comparative Examples are those obtained by converting Amberlite IR120B manufactured by Rohm & Haas Co., Ltd. into acid form by treating with hydrochloric acid.

The apparatus used for the electrical conductivity measurement in the following examples and comparative examples is a Twincond B-173 electrical conductivity meter manufactured by HORIBA, Ltd.

In the following examples and comparative examples, the apparatus used for measuring sodium ion and potassium ion amounts by atomic absorption spectrophotometry is Z8000 manufactured by Hitachi, Ltd., and the detection lower limit is 1 ppb.

Example 1
(1) Synthesis of fluoropolymer aqueous dispersion A stainless steel stirred autoclave with a synthetic volume of 6000 ml was charged with 150 g of a 20 mass% aqueous solution of CF ₃ (CF ₂ ) ₆ CO ₂ NH ₄ and 2850 g of pure water, and was sufficiently vacuum and nitrogen Replacement was performed. 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 30 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 0.65 times by mass ratio.

When the supplied TFE reached 780 g, the pressure in the autoclave was released and the polymerization was stopped. Thereafter, the mixture was cooled to room temperature to obtain 4450 g of a slightly cloudy fluoropolymer aqueous dispersion containing about 28% by mass of a fluoropolymer containing SO ₂ F.

(2) Hydrolysis of fluorinated polymer aqueous dispersion To 3500 g of the fluorinated polymer aqueous dispersion obtained in (1), 650 g of 48 wt% KOH and 4500 g of pure water were added and heated at 80 ° C. for 20 hours. And allowed to cool to room temperature. 1400 g of 10% by weight of nitric acid is added to the cooled fluoropolymer aqueous dispersion, and the pH of the liquid is adjusted to 8 to 9, thereby containing a fluoropolymer aqueous solution containing about 11% by mass of the fluoropolymer. 10050 g of dispersion was obtained.

(3) Purification of fluorinated polymer aqueous dispersion 10050 g of the fluorinated polymer aqueous dispersion prepared as in (2) was supplied to a circulation type ultrafiltration unit for purification. Specifically, the low molecular weight component contained in the fluoropolymer aqueous dispersion was discharged out of the system as a filtrate, and the fluoropolymer component was circulated through a circulating ultrafiltration unit. After treating for a certain period of time, purification was performed by repeatedly supplying pure water corresponding to the removed water amount into the system. The purification was completed when the electrical conductivity at 25 ° C. of the filtrate discharged out of the system reached 1 μS / cm.

Water was removed from the aqueous fluoropolymer dispersion after purification using a circulating ultrafiltration unit to obtain a concentrated fluoropolymer aqueous dispersion. The fluorine-containing polymer aqueous dispersion that had been concentrated was changed to 4000 g of a cloudy fluorine-containing polymer aqueous dispersion containing about 25% by mass of the fluorine-containing polymer. When the amount of cation contained therein was measured by an atomic absorption photometry, potassium ion was 13500 ppm and sodium ion was 10 ppm with respect to the fluoropolymer aqueous dispersion.

(4) Adjustment of electric conductivity of fluoropolymer aqueous dispersion 30 wt. Of 10% nitric acid aqueous solution is added to 0.1 wt% of fluoropolymer aqueous dispersion which has been purified and concentrated in (3). 4030 g of a fluorine-containing polymer aqueous dispersion containing about 25% by weight of a fluorine-containing polymer in a nitric acid aqueous solution. The electrical conductivity of this aqueous fluoropolymer dispersion at 25 ° C. was measured and found to be about 7 mS / cm.

(5) Ion Exchange of Fluoropolymer Aqueous Dispersion A glass column having a diameter of 10 cm and a height of 50 cm filled with a 0.1% by weight nitric acid aqueous solution and a cation exchange resin bead was prepared. 4030 g of a fluoropolymer aqueous dispersion with adjusted conductivity was circulated. The distribution speed was such that 60 g of the fluoropolymer aqueous dispersion was distributed per minute. After distribution, 4300 g of a fluoropolymer aqueous dispersion containing about 23% of a fluoropolymer was obtained. The nitrate ion concentration of the obtained fluoropolymer aqueous dispersion was measured with a nitrate ion meter and found to be 900 ppm.

(6) Repurification of fluoropolymer aqueous dispersion 4300 g of the fluoropolymer aqueous dispersion subjected to ion exchange was supplied to a circulating ultrafiltration unit for purification. Specifically, the nitric acid component added to the fluoropolymer aqueous dispersion in the step (4) was discharged out of the system as a filtrate, and the fluoropolymer component was circulated through a circulating ultrafiltration unit. After treating for a certain period of time, purification was performed by repeatedly supplying pure water corresponding to the removed water amount into the system. The end point of the purification was the time when the electrical conductivity of the filtrate at 25 ° C. reached 1 μS / cm. Further, the fluoropolymer aqueous dispersion was concentrated by the same procedure as in (4) to obtain 3800 g of a cloudy fluoropolymer aqueous dispersion containing about 25% by mass of the fluoropolymer.

When the amount of cation contained in the aqueous fluoropolymer dispersion was measured by atomic absorption photometry, potassium ion was 2 ppm with respect to the aqueous fluoropolymer dispersion, and no sodium ion was detected. The nitrate ion concentration of the fluoropolymer aqueous dispersion measured with a nitrate ion meter was 1 ppm.

Example 2
(1) Synthesis of fluoropolymer aqueous dispersion In a stainless steel stirred autoclave having a volume of 6000 ml, 100 g of a 20% by mass aqueous solution of CF ₃ (CF ₂ ) ₄ CO ₂ NH ₄ and CF ₂ = CFOCF ₂ CF ₂ SO ₂ Na 10 g and 2850 g of pure water were charged, and vacuum and nitrogen substitution were sufficiently performed. 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 30 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 0.65 times by mass ratio.

When the supplied TFE reached 780 g, the pressure in the autoclave was released and the polymerization was stopped. Thereafter, the mixture was cooled to room temperature to obtain 4450 g of a slightly cloudy fluoropolymer aqueous dispersion containing about 28% by mass of a fluoropolymer containing SO ₂ F.

The same steps as (2) to (3) of Example 1 were carried out to obtain 4000 g of a fluoropolymer aqueous dispersion containing about 25% by mass of a fluoropolymer and purified by ultrafiltration.

Fluorine polymer aqueous dispersion containing approximately 23% by weight of a fluoropolymer in 3% by weight of nitric acid aqueous solution by adding 330 g of 30% by weight of nitric acid aqueous solution to the fluoropolymer aqueous dispersion having been purified and concentrated. The body was 4330 g. The electrical conductivity of this fluoropolymer aqueous dispersion at 25 ° C. was measured and found to be about 200 mS / cm.

By carrying out ion exchange and repurification of the fluoropolymer aqueous dispersion in the same procedure as in (5) to (6) of Example 1, a white turbid fluoropolymer aqueous solution containing about 25% by mass of the fluoropolymer is obtained. 3800 g of dispersion was obtained. The end point of repurification was the time when the electrical conductivity of the filtrate at 25 ° C. reached 1 μS / cm.

When the amount of cation contained in the aqueous fluoropolymer dispersion was measured by atomic absorption photometry, potassium ion was 2 ppm with respect to the aqueous fluoropolymer dispersion, and no sodium ion was detected. The nitrate ion concentration of the obtained fluoropolymer aqueous dispersion was measured with a nitrate ion meter and found to be 1 ppm.

Example 3
The same steps as (1) to (3) of Example 1 were performed to obtain 4000 g of an aqueous fluoropolymer dispersion containing about 25% by mass of the fluoropolymer and purified by ultrafiltration.

Fluorine-containing polymer containing about 25% by weight of fluorine-containing polymer in 0.1% by weight of potassium nitrate aqueous solution by adding 30 g of 10% by weight of potassium nitrate aqueous solution to the aqueous dispersion of fluorine-containing polymer that has been purified and concentrated An aqueous dispersion was 4030 g. The electrical conductivity of this fluoropolymer aqueous dispersion at 25 ° C. was measured and found to be about 5 mS / cm.

By carrying out ion exchange and repurification of the fluoropolymer aqueous dispersion in the same procedure as in (5) to (6) of Example 1, a white turbid fluoropolymer aqueous solution containing about 25% by mass of the fluoropolymer is obtained. 3800 g of dispersion was obtained. The end point of repurification was the time when the electrical conductivity of the filtrate at 25 ° C. reached 1 μS / cm.

When the amount of cation contained in the aqueous fluoropolymer dispersion was measured by atomic absorption photometry, potassium ion was 2 ppm with respect to the aqueous fluoropolymer dispersion, and no sodium ion was detected.

Example 4
The same steps as (1) and (2) of Example 1 were performed to obtain 10050 g of a fluoropolymer aqueous dispersion containing about 11% by mass of a fluoropolymer.

10050 g of the fluoropolymer aqueous dispersion prepared as described above was supplied to a circulating ultrafiltration unit, and low molecular weight components were removed in the same procedure as in (1) of Example 1. Addition of pure water was stopped when the electrical conductivity at 25 ° C. of the filtrate discharged out of the system reached 3 mS / cm, and the ultrafiltration machine was stopped when the treatment liquid reached 4000 g, and fluorine-containing 4000 g of an aqueous polymer dispersion was obtained. When the fluorine ion concentration of the fluoropolymer aqueous dispersion was measured with a fluorine ion meter, it was 700 ppm.

By carrying out the ion exchange and repurification of the fluoropolymer aqueous dispersion in the same procedure as in (5) to (6) of Example 1, the cloudy fluoropolymer aqueous solution containing about 25% by mass of the fluoropolymer is contained. 3800 g of dispersion was obtained. The end point of repurification was the time when the electrical conductivity of the filtrate at 25 ° C. reached 1 μS / cm.

When the amount of cation contained in the aqueous fluoropolymer dispersion was measured by atomic absorption spectrophotometry, potassium ion was 7 ppm with respect to the aqueous fluoropolymer dispersion, and no sodium ion was detected. When the fluorine ion concentration of the fluoropolymer aqueous dispersion was measured with a fluorine ion meter, it was 1 ppm.

Example 5
The same steps as (1) and (2) of Example 1 were performed to obtain 10000 g of a fluoropolymer aqueous dispersion containing about 11% by mass of a fluoropolymer.

10000 g of the fluoropolymer aqueous dispersion prepared as described above was supplied to a circulating ultrafiltration unit, and low molecular weight components were removed in the same procedure as (3) of Example 1. The addition of pure water was stopped when the electrical conductivity of the filtrate at 25 ° C. discharged to the outside of the system reached 1.5 mS / cm, and the ultrafilter was stopped when the treatment liquid reached 4000 g. 4000 g of a fluoropolymer aqueous dispersion was obtained. When the fluorine ion concentration of the fluoropolymer aqueous dispersion was measured with a fluorine ion meter, it was 200 ppm.

By carrying out the ion exchange and repurification of the fluoropolymer aqueous dispersion in the same procedure as in (5) to (6) of Example 1, the cloudy fluoropolymer aqueous solution containing about 25% by mass of the fluoropolymer is contained. 3800 g of dispersion was obtained. The end point of repurification was the time when the electrical conductivity of the filtrate at 25 ° C. reached 1 μS / cm.

When the amount of cation contained in the aqueous fluoropolymer dispersion was measured by atomic absorption spectrophotometry, potassium ion was 18 ppm with respect to the aqueous fluoropolymer dispersion, and no sodium ion was detected. When the fluorine ion concentration of the fluoropolymer aqueous dispersion was measured with a fluorine ion meter, it was 1 ppm.

Comparative Example 1
The same steps as (1) to (3) of Example 1 were performed to obtain 4000 g of an aqueous fluoropolymer dispersion containing about 25% by mass of the fluoropolymer and purified by ultrafiltration. The end point of the purification was the time when the electrical conductivity of the filtrate at 25 ° C. reached 1 μS / cm.

A glass column having a diameter of 10 cm and a height of 50 cm filled with cation exchange resin beads filled with pure water was prepared, and 4000 g of the fluoropolymer aqueous dispersion prepared above was circulated. The distribution speed was such that 60 g of the fluoropolymer aqueous dispersion was distributed per minute. After distribution, 4300 g of a fluoropolymer aqueous dispersion containing about 23% of a fluoropolymer was obtained.

When the amount of cation contained in the aqueous fluoropolymer dispersion was measured by atomic absorption spectrophotometry, the potassium ion was 700 ppm and the sodium ion was 5 ppm with respect to the aqueous fluoropolymer dispersion.

Comparative Example 2
The same steps as (1) and (2) of Example 1 were performed to obtain 10050 g of a fluoropolymer aqueous dispersion containing about 11% by mass of a fluoropolymer.

10050 g of the fluoropolymer aqueous dispersion prepared as described above was supplied to a circulating ultrafiltration unit, and low molecular weight components were removed in the same procedure as in (1) of Example 1. The addition of pure water was stopped when the electrical conductivity of the filtrate at 25 ° C. discharged to the outside of the system reached 10 μS / cm, and the ultrafilter was stopped when the treatment liquid reached 4000 g. 4000 g of an aqueous fluoropolymer dispersion was obtained.

By carrying out the ion exchange and repurification of the fluoropolymer aqueous dispersion in the same procedure as in (5) to (6) of Example 1, the cloudy fluoropolymer aqueous solution containing about 25% by mass of the fluoropolymer is contained. 3800 g of dispersion was obtained. The end point of repurification was the time when the electrical conductivity of the filtrate at 25 ° C. reached 1 μS / cm.

When the amount of cation contained in the aqueous fluoropolymer dispersion was measured by atomic absorption spectrophotometry, potassium ions were 200 ppm with respect to the aqueous fluoropolymer dispersion, and no sodium ion was detected.

About the said Example and comparative example, the relationship between the electrical conductivity in 25 degreeC of the to-be-processed liquid in a cation exchange process and the ion amount (cation amount) in the obtained refinement | purification fluoropolymer aqueous dispersion is shown in FIG. It was. The horizontal axis indicates the electrical conductivity measured before ion exchange, and the vertical axis indicates the amount of ions contained in the aqueous fluoropolymer dispersion after ion exchange.

Claims (9)

^{_{-SO 3 X, -SO 2 NR 1}} 2 and -COOX (X _is .M representing the _{M 1 / L} or ^NR _{1 4} represents a hydrogen atom or a metal whose valence is L, the L-valent metal is periodically (It is a metal belonging to Group 1, Group 2, Group 4, Group 8, Group 11, Group 12 or Group 13. R ¹ represents each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.) A step (A) of preparing a fluoropolymer aqueous dispersion containing a fluoropolymer having at least one group selected from the group consisting of:
(B) performing ultrafiltration on the fluoropolymer aqueous dispersion, and
After the step (B), the method includes a step (C) of obtaining a purified fluoropolymer aqueous dispersion by bringing the fluoropolymer aqueous dispersion into contact with a cation exchange ion exchange resin.
A method for producing an aqueous fluoropolymer dispersion, wherein the fluoropolymer aqueous dispersion to be contacted with a cation exchange ion exchange resin in step (C) has an electrical conductivity at 25 ° C. of greater than 1 mS / cm. Furthermore, the manufacturing method of the fluoropolymer aqueous dispersion of Claim 1 including the process (D) which performs ultrafiltration after a process (C). The method for producing an aqueous fluoropolymer dispersion according to claim 1 or 2, wherein the content of alkali metal ions in the purified fluoropolymer aqueous dispersion obtained in step (C) is less than 100 ppm. The fluorine-containing polymer has the following general formula (I):
^{_{CF 2 = CF- (O) n1}} - (CF 2 CFY 1 -O) n2 - (CFY 2) n3 -A (I)
(Wherein, ^{Y 1} is, .n2 .n1 represents a halogen atom or a perfluoroalkyl group represents an integer of 0 or 1, .N2 amino ^{Y 1} represents an integer of 0 to 3, and the same good .Y ² be different also may, .N3 represents a halogen atom, .N3 one Y ² representing a 1-8 integer may be different or may be the same .A ^{_{is, -SO 3 X, -SO 2 NR}} 1 2 or -COOX (X _is .M representing the _{M 1 / L} or ^NR _{1 4} represents a hydrogen atom or a metal whose valence is L, 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, and each R ¹ independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. 4. The fluorine-containing polymer according to claim 1, which has a structural unit derived from a fluoromonomer represented by Method of manufacturing a mer aqueous dispersion. The fluorine-containing polymer is selected from the group consisting of at least one kind of —SO ₂ Y ³ and —COOR ² (Y ³ represents a halogen atom. R ² represents an alkyl group having 1 to 4 carbon atoms). The method for producing an aqueous fluoropolymer dispersion according to claim 1, 2, 3, or 4 obtained by hydrolyzing the fluoropolymer precursor having at least one kind of group. The fluorine-containing polymer is a binary or higher copolymer having a structural unit derived from the fluoromonomer represented by the general formula (I) and a structural unit derived from another fluorine-containing ethylenic monomer. A method for producing an aqueous fluoropolymer dispersion according to claim 4 or 5. The fluorine-containing ethylenic monomer has the following general formula (II):
^{_{CF 2 = CF-R f 1}} (II)
(In the formula, R _f ¹ represents a fluorine atom, a chlorine atom, R _f ² or OR _f ^2. R _f ² is a linear or branched chain having 1 to 9 carbon atoms which may have an ether bond. The method for producing an aqueous fluoropolymer dispersion according to claim 6, which is at least one monomer represented by: The method for producing an aqueous fluoropolymer dispersion according to claim 7, wherein a part or all of the monomer represented by the general formula (II) is tetrafluoroethylene. Y ¹ in the general formula (I) is a trifluoromethyl group, Y ² is a fluorine atom, n1 is 1, n2 is 0 or 1, and n3 is 2. Or the manufacturing method of the fluorine-containing polymer aqueous dispersion of 8.

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