Particle, and method for producing fluorine-containing polymer

Abstract

Provided are: a particle containing a fluorine-containing polymer with suppressed agglomeration during storage; and a method for producing a fluorine-containing polymer produced using said particle.　This particle comprises a core part and a shell part covering the core part, wherein: the core part contains a first fluorine-containing polymer having a group represented by –SO2X; the shell part contains a second fluorine-containing polymer having a group represented by -SO3M; and in the formulae, X represents a halogen atom and M represents an alkali metal, a hydrogen atom, or a quaternary ammonium cation.

Description

Method for producing particles and fluorine-containing polymer

[0001] The present invention relates to a method for producing particles and a fluorine-containing polymer.

[0002] The ion exchange membrane (electrolyte membrane) of a polymer electrolyte fuel cell or a water electrolysis device is obtained by forming a membrane from a fluoropolymer having an ion exchange group such as a sulfonic acid group. Here, the fluoropolymer having an ion exchange group such as a sulfonic acid group is produced by converting the fluorosulfonyl group of a fluoropolymer having a group that can be converted to an ion exchange group such as a fluorosulfonyl group into a salt form by hydrolysis, and then converting it into an acid form. Example 1 of Patent Document 1 describes a method for producing such a fluoropolymer having a group that can be converted to an ion exchange group, using tetrafluoroethylene and CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ SO ２ F is copolymerized with a monomer represented by F to form a fluorosulfonyl group (-SO ２ A method for obtaining particles of a fluoropolymer having F) is disclosed.

[0003] Patent No. 6642452

[0004] The present inventors have investigated the use of a fluorosulfonyl group (—SO ) as described in Patent Document 1. ２ It has been found that when particles of a fluoropolymer having ion-exchange groups (F) are stored for a predetermined period of time, the particles of the fluoropolymer may fuse together and form agglomerates. When the particles of the fluoropolymer are agglomerated in this way, a step of pulverizing the fluoropolymer becomes necessary before the subsequent hydrolysis treatment or acid-form treatment, which may complicate the production of a fluoropolymer having ion-exchange groups.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide particles containing a fluoropolymer that are inhibited from agglomerating during storage, and a method for producing a fluoropolymer using these particles.

[0006] As a result of extensive research into the above-mentioned problems, the present inventors have discovered a particle comprising a core portion and a shell portion covering the core portion, the particle having the following structure: -SO ２ a core part containing a first fluorine-containing polymer having a group represented by X (X represents a halogen atom), and a polymer having a group represented by —SO ３ and a shell portion containing a second fluorine-containing polymer having a group represented by M (M represents an alkali metal, a hydrogen atom or a quaternary ammonium cation), and the use of such particles can suppress agglomeration during storage, leading to the present invention.

[0007] That is, the inventors have found that the above-mentioned problems can be solved by the following configuration: [1] A particle including a core portion and a shell portion covering the core portion, wherein the core portion is -SO ２ a first fluorine-containing polymer having a group represented by X, and the shell portion is -SO ３ Particles comprising a second fluoropolymer having a group represented by M. In the formula, X represents a halogen atom, and M represents an alkali metal, a hydrogen atom, or a quaternary ammonium cation. [2] The particle according to [1], wherein the thickness of the shell part is 0.01 μm or more. [3] The particle according to [1] or [2], wherein both the first fluoropolymer and the second fluoropolymer contain units based on a fluorine-containing olefin. [4] The particle according to any one of [1] to [3], wherein the ion exchange capacity of the second fluoropolymer is 0.90 meq / g dry resin or more. [5] -SO ２ Step 1: Polymerizing a monomer containing a fluorine-containing monomer having a group represented by X to obtain particles of a first fluorine-containing polymer; Step 2: Performing a first treatment of hydrolysis on the surfaces of the particles obtained in Step 1, or a second treatment of hydrolysis and acid-form conversion to obtain particles according to any one of [1] to [4]; Step 3: Storing the particles obtained in Step 2; and Step 3: Performing a third treatment of hydrolysis and acid-form conversion to the particles after storage to remove -SO ２ The group represented by X is -SO ３and step 4 of converting the group represented by formula (I) into a group represented by formula (I), thereby obtaining a fluoropolymer. In the formula, X represents a halogen atom, and M represents an alkali metal, a hydrogen atom, or a quaternary ammonium cation.

[0008] According to the present invention, it is possible to provide particles containing a fluoropolymer that are inhibited from agglomerating during storage, and a method for producing a fluoropolymer using these particles.

[0009] The definitions of the following terms apply throughout the present specification and claims unless otherwise specified. An "ion exchange group" is a group that can exchange at least a portion of the ions contained in this group with other ions, and examples thereof include the sulfonic acid functional group and carboxylic acid functional group shown below. A "sulfonic acid functional group" is a sulfonic acid group (-SO ３ Here, the form of the sulfonate group is, for example, (—SO ３ － ) Ma ＋ , (-SO ３ － ) ２ Mb ２＋ , and (-SO ３ － ) ３ Mc ３＋ (However, Ma ＋ is an alkali metal ion or a quaternary ammonium cation, and Mb ２＋ is a divalent metal ion, Mc ３＋ is a trivalent metal ion.) When there are two ligands, the number of ion exchange groups is counted as two, and when there are three ligands, the number of ion exchange groups is counted as three. "Carboxylic acid type functional group" means a carboxylic acid group (-COOH) or a carboxylic acid salt group. Here, the form of the carboxylic acid salt group can be, for example, (-COO － ) Ma ＋ , (-COO － ) ２ Mb ２＋ , and (-COO － ) ３ Mc ３＋ (However, Ma ＋is an alkali metal ion or a quaternary ammonium cation, and Mb ２＋ is a divalent metal ion, Mc ３＋ is a trivalent metal ion.) When there are two ligands, the number of ion exchange groups is counted as two, and when there are three ligands, the number of ion exchange groups is counted as three. "Groups that can be converted into ion exchange groups" means groups that can be converted into ion exchange groups by treatment such as hydrolysis treatment or acidification treatment. "Groups that can be converted into sulfonic acid functional groups" means groups that can be converted into sulfonic acid functional groups by treatment such as hydrolysis treatment or acidification treatment. "Groups that can be converted into carboxylic acid functional groups" means groups that can be converted into carboxylic acid functional groups by known treatment such as hydrolysis treatment or acidification treatment.

[0010] A "unit" in a polymer refers to an atomic group derived from one molecule of a monomer formed by polymerization of the monomer. The unit may be an atomic group formed directly by the polymerization reaction, or may be an atomic group in which part of the atomic group is converted into a different structure by treating the polymer obtained by the polymerization reaction. In the following, units derived from individual monomers may be referred to by the name of the monomer followed by "unit" in some cases.

[0011] A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the upper and lower limits. In the numerical ranges described in stages in this specification, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the examples.

[0012] [Particles] The particles of the present invention (hereinafter also referred to as "specific particles") are particles including a core portion and a shell portion covering the core portion, and the core portion is -SO ２ The polymer contains a first fluorine-containing polymer having a group represented by X, and the shell portion is -SO ３The specific particles contain a second fluorine-containing polymer having a group represented by M. In the formula, X represents a halogen atom, and M represents an alkali metal, a hydrogen atom, or a quaternary ammonium cation. The specific particles are less likely to agglomerate even when stored for a predetermined period of time. Although the details of this are not yet fully understood, it is presumed to be due to the following reasons. That is, -SO ３ The second fluorine-containing polymer having a group represented by M is —SO ２ It has a higher modulus of elasticity than the first fluoropolymer having a group represented by X. Since the shell part of the specific particle is composed of the second fluoropolymer having a higher modulus of elasticity, it is presumed that fusion of particles to each other during storage was suppressed, thereby suppressing particle agglomeration.

[0013] The specific particles may be in the form of powder or pellets. From the viewpoint of ease of handling during production, the average particle size of the specific particles is preferably 0.1 mm or more, more preferably 1 mm or more, and is preferably 50 mm or less, more preferably 10 mm or less, and even more preferably 3 mm or less. The average particle size of the specific particles is a value (D50) calculated from the particle size distribution measured by mechanical sieving using a stainless steel test sieve (JIS-Z8801).

[0014] The total content of the first fluoropolymer and the second fluoropolymer is preferably at least 50% by mass, more preferably at least 75% by mass, and even more preferably 100% by mass, relative to the total mass of the specific particles, in order to obtain better effects of the present invention.

[0015] The specific particles are preferably used for producing a fluoropolymer having sulfonic acid groups. Furthermore, the fluoropolymer having sulfonic acid groups obtained using the specific particles is preferably used for forming an electrolyte membrane or a catalyst layer of a polymer electrolyte fuel cell or a water electrolysis device.

[0016] [Core portion] The core portion of the specific particle contains a first fluoropolymer. It is preferable that the core portion does not contain a second fluoropolymer, which will be described later. The core portion corresponds to the portion of the specific particle excluding the shell portion. Since the shell portion covers the surface of the specific particle with an extremely thin thickness, the core portion occupies the majority of the specific particle and has approximately the same size and shape as the specific particle.

[0017] <First Fluorine-Containing Polymer> The first fluorine-containing polymer has fluorine atoms and is —SO ２ There are no particular limitations on the polymer as long as it has a group represented by X, but in terms of achieving better effects of the present invention, the following polymer F-1 or polymer F-2 is preferred. ２ X in the group represented by X represents a halogen atom, preferably a fluorine atom, a chlorine atom or a bromine atom, more preferably a fluorine atom. ３ It is preferred that the group represented by M is not present.

[0018] (Polymer F-1) Polymer F-1 is a polymer having a unit based on a fluorine-containing olefin and a unit of —SO ２ X, and a unit based on a fluorine-containing olefin and a group represented by -SO ２ and a copolymer containing units based on a fluorine-containing monomer having a group represented by X. Polymer F-1 preferably does not have a cyclic ether structure.

[0019] Examples of fluorine-containing olefins include fluoroolefins having 2 to 3 carbon atoms and one or more fluorine atoms in the molecule. Specific examples of fluoroolefins include tetrafluoroethylene (hereinafter also referred to as "TFE"), chlorotrifluoroethylene, vinylidene fluoride, vinyl fluoride, and hexafluoropropylene. Among these, TFE is preferred in terms of the production cost of the monomer, reactivity with other monomers, and excellent properties of the resulting polymer F-1. One type of fluorine-containing olefin may be used alone, or two or more types may be used in combination.

[0020] The content of units based on fluorine-containing olefin is preferably 11% by mass or more, more preferably 38% by mass or more, and preferably 59% by mass or less, more preferably 55% by mass or less, based on all units in polymer F-1.

[0021] -SO ２ The fluorine-containing monomer having a group represented by X is a monomer having one or more fluorine atoms in the molecule, an ethylenic double bond, and a —SO ２ Examples of the compound include compounds having a group represented by X. ２ As the fluorine-containing monomer having a group represented by X, a compound represented by formula (1) is preferred in terms of the production cost of the monomer, reactivity with other monomers, and excellent properties of the resulting polymer F-1. ２ =CF-L-(A) ｎ

[0022] L is an (n+1)-valent perfluorohydrocarbon group which may contain an etheric oxygen atom. The etheric oxygen atom may be located at the terminal of the perfluorohydrocarbon group or between carbon atoms. The number of carbon atoms in the (n+1)-valent perfluorohydrocarbon group is preferably 1 or more, more preferably 2 or more, and preferably 20 or less, more preferably 10 or less. L is preferably an (n+1)-valent perfluoroaliphatic hydrocarbon group which may contain an etheric oxygen atom, and more preferably a divalent perfluoroalkylene group which may contain an etheric oxygen atom in the embodiment where n = 1, or a trivalent perfluoroaliphatic hydrocarbon group which may contain an etheric oxygen atom in the embodiment where n = 2. The divalent perfluoroalkylene group may be either linear or branched.

[0023] A is -SO ２ It is a group represented by X. ２ The group represented by X is preferably a functional group that can be converted into a sulfonic acid functional group by hydrolysis. ２ Specific examples of the group represented by X include -SO ２ F, -SO ２ Cl, —SO ２ Br, among others, —SO ２F is preferred.

[0024] n is 1 or 2.

[0025] The compound represented by formula (1) is preferably a compound represented by formula (1-1), a compound represented by formula (1-2), a compound represented by formula (1-3), or a compound represented by formula (1-4). ２ =CF-O-R ｆ１ -A Formula (1-2) CF ２ =CF-R ｆ１ -A

[0026]

[0027]

[0028] R ｆ１ is a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, more preferably 2 or more, and is preferably 20 or less, more preferably 10 or less.

[0029] R ｆ２ is a single bond or a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, more preferably 2 or more, and is preferably 20 or less, more preferably 10 or less.

[0030] R ｆ３ is a single bond or a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, more preferably 2 or more, and is preferably 20 or less, more preferably 10 or less.

[0031] r is 0 or 1. m is 0 or 1.

[0032] The definition of A in the formula is as described above. In formula (1-3) and formula (1-4), two As may be the same or different.

[0033] As the compound represented by formula (1-1) and the compound represented by formula (1-2), a compound represented by formula (1-5) is preferred. ２ =CF-(CF ２ ) ｘ -(OCF ２ CFY) ｙ -O-(CF ２ ) ｚ -SO ２ F x is 0 or 1, y is an integer from 0 to 2, z is an integer from 1 to 4, and Y is F or CF ３ is.

[0034] Specific examples of the compound represented by formula (1-1) include the following compounds. In the formula, w is an integer of 1 to 8, and x is an integer of 1 to 5. CF ２ =CF-O-(CF ２ ) ｗ -SO ２ FCF ２ =CF-O-CF ２ CF (CF ３ )-O-(CF ２ ) ｗ -SO ２ FCF ２ =CF-[O-CF ２ CF (CF ３ )] ｘ -SO ２ F

[0035] Specific examples of the compound represented by formula (1-2) include the following compounds: In the formula, w is an integer of 1 to 8. CF ２ =CF-(CF ２ ) ｗ -SO ２ FCF ２ =CF-CF ２ -O-(CF ２ ) ｗ -SO ２ F

[0036] The compound represented by formula (1-3) is preferably a compound represented by formula (1-3-1).

[0037]

[0038] R ｆ４is a linear perfluoroalkylene group having 1 to 6 carbon atoms, and R ｆ５ represents a single bond or a linear perfluoroalkylene group having 1 to 6 carbon atoms which may contain an oxygen atom between the carbon atoms. The definitions of r and A are as described above.

[0039] Specific examples of the compound represented by formula (1-3-1) include the following.

[0040]

[0041] The compound represented by formula (1-4) is preferably a compound represented by formula (1-4-1).

[0042]

[0043] R in the formula ｆ１ , R ｆ２ and A are defined as above.

[0044] Specific examples of the compound represented by formula (1-4-1) include the following.

[0045]

[0046] -SO ２ The fluorine-containing monomer having a group represented by X may be used alone or in combination of two or more.

[0047] -SO ２ The content of units based on a fluorine-containing monomer having a group represented by X is preferably 41% by mass or more, more preferably 45% by mass or more, and is preferably 89% by mass or less, more preferably 62% by mass or less, based on all units of polymer F-1.

[0048] Polymer F-1 may be produced using monomers other than the above monomers (hereinafter also referred to as "other monomers"). Specific examples of other monomers include CF ２ = CFR ｆ６ (However, R ｆ６ is a perfluoroalkyl group having 2 to 10 carbon atoms, CF ２ =CF-OR ｆ７ (However, R ｆ７is a perfluoroalkyl group having 1 to 10 carbon atoms, CF ２ = CFO (CF ２ ) ｖ CF = CF ２ (wherein v is an integer of 1 to 3.) The content of units based on other monomers is preferably 30% by mass or less based on the total units of polymer F-1, in order to maintain ion exchange performance.

[0049] (Polymer F-2) Polymer F-2 has units based on a monomer having a cyclic ether structure, and —SO ２ X, and a unit based on a monomer having a cyclic ether structure and a group represented by -SO ２ and a copolymer having a unit based on a fluorine-containing monomer having a group represented by X. Specific examples of the monomer having a cyclic ether structure include monomer m11, monomer m12, monomer m21, and monomer m22.

[0050] Monomer m11 is a monomer represented by formula (m11), and preferred embodiments of monomer m11 include formulae (m11-1) to (m11-4).

[0051]

[0052] R １１ is a divalent perfluoroalkylene group which may have an ether-bonded oxygen atom. When the perfluoroalkylene group has an ether-bonded oxygen atom, the number of oxygen atoms may be one or two or more. The oxygen atom may be located between the carbon-carbon bonds of the perfluoroalkylene group, or at the carbon atom bond terminal. The perfluoroalkylene group may be linear or branched, but is preferably linear. R １２ , R １３ , R １５ and R １６ R each independently represents a monovalent perfluoroalkyl group which may have an ether-bonded oxygen atom or a fluorine atom. １５ and R １６In view of high polymerization reactivity, it is preferable that at least one of R is a fluorine atom, and it is more preferable that both of R are fluorine atoms. １４ represents a monovalent perfluoroalkyl group which may have an ether-bonded oxygen atom, a fluorine atom, or R １１ SO ２ It is a group represented by F. When the perfluoroalkyl group has an ether-bonded oxygen atom, the number of oxygen atoms may be one or two or more. In addition, the oxygen atom may be located between the carbon-carbon bonds of the perfluoroalkyl group, or may be located at the carbon atom bond terminal. The perfluoroalkyl group may be linear or branched, but is preferably linear. In formula (m11), two R １１ If it contains two R １１ may be the same or different from each other.

[0053] Monomer m12 is a monomer represented by formula (m12), and preferred embodiments of monomer m12 include formulae (m12-1) to (m12-2).

[0054]

[0055] R ２１ is a perfluoroalkylene group having 1 to 6 carbon atoms or a perfluoroalkylene group having 2 to 6 carbon atoms and having an ether-bonding oxygen atom between the carbon-carbon bond. When the perfluoroalkylene group has an ether-bonding oxygen atom, the number of oxygen atoms may be one or more. The perfluoroalkylene group may be linear or branched, but is preferably linear. R ２２ is a fluorine atom, a perfluoroalkyl group having 1 to 6 carbon atoms, a perfluoroalkyl group having 2 to 6 carbon atoms and an ether-bonded oxygen atom between the carbon-carbon bonds, or R ２１ SO ２ It is a group represented by F. When the perfluoroalkyl group has an ether-bonded oxygen atom, the number of oxygen atoms may be one or two or more. The perfluoroalkyl group may be linear or branched, but is preferably linear. In formula (m12), two R ２１If it contains two R ２１ may be the same or different from each other.

[0056] Monomer m21 is a monomer represented by formula (m21), and preferred embodiments of monomer m21 include formulae (m21-1) to (m21-2).

[0057]

[0058] R ４１ , R ４２ , R ４３ , R ４４ , R ４５ and R ４６ are each independently a monovalent perfluoroalkyl group which may have an ether-bonded oxygen atom or a fluorine atom. When the perfluoroalkyl group has an ether-bonded oxygen atom, the number of oxygen atoms may be one or two or more. The oxygen atom may be located between the carbon-carbon bonds of the perfluoroalkyl group, or at the carbon atom bond terminal. The perfluoroalkyl group may be linear or branched, but is preferably linear. R ４５ and R ４６ In view of high polymerization reactivity, it is preferable that at least one of the groups is a fluorine atom, and it is more preferable that both of the groups are fluorine atoms.

[0059] Monomer m22 is a monomer represented by formula (m22), and preferred embodiments of monomer m22 include formulae (m22-1) to (m22-11).

[0060]

[0061] s is 0 or 1, and is preferably 0. ５１ and R ５２ are each independently a fluorine atom, a perfluoroalkyl group having 1 to 5 carbon atoms, or a spiro ring formed by linking together (when s is 0). ５３ and R ５４ are each independently a fluorine atom or a perfluoroalkyl group having 1 to 5 carbon atoms. ５５is a fluorine atom, a perfluoroalkyl group having 1 to 5 carbon atoms, or a perfluoroalkoxy group having 1 to 5 carbon atoms. ５５ is preferably a fluorine atom from the viewpoint of high polymerization reactivity. The perfluoroalkyl group and perfluoroalkoxy group may be linear or branched, but are preferably linear.

[0062] The content of units based on a monomer having a cyclic ether structure is preferably 30% by mass or more, more preferably 48% by mass or more, and is preferably 70% by mass or less, more preferably 63% by mass or less, based on the total units of polymer F-2.

[0063] -SO ２ Specific examples of the fluorine-containing monomer having a group represented by X include —SO ２ The same applies to the fluorine-containing monomer having a group represented by X. ２ The content of units based on a fluorine-containing monomer having a group represented by X is preferably 20% by mass or more, more preferably 28% by mass or more, and is preferably 60% by mass or less, more preferably 50% by mass or less, based on all units of polymer F-2.

[0064] Polymer F-2 may have units based on a fluorine-containing olefin. Specific examples of the fluorine-containing olefin are the same as those for Polymer F-1. The content of units based on a fluorine-containing olefin (particularly TFE) is preferably 0% by mass or more, more preferably 1% by mass or more, and preferably 20% by mass or less, more preferably 10% by mass or less, based on all units of Polymer F-2.

[0065] (Physical properties of first fluoropolymer) The TQ value of the first fluoropolymer is preferably 150° C. or higher, more preferably 170° C. or higher, and even more preferably 200° C. or higher, and is preferably 350° C. or lower, more preferably 340° C. or lower, and even more preferably 300° C. or lower. The TQ value is a value related to the molecular weight of the polymer, and is ３The first fluoropolymer was vacuum-dried at 240°C for 16 hours, and then the vacuum-dried first fluoropolymer was melt-extruded using a flow tester (Shimadzu Corporation, CFT-500D) equipped with a nozzle having a length of 1 mm and an inner diameter of 1 mm, while changing the temperature under the condition of an extrusion pressure of 2.94 MPa (gauge pressure), until the extrusion amount of the first fluoropolymer reached 100 mm. ３ The temperature at which the temperature reaches 1 / second is defined as the TQ value.

[0066] -SO of the first fluorine-containing polymer ２ The group represented by X can be converted to —SO ３ When converted to a group represented by M (M represents an alkali metal, a hydrogen atom, or a quaternary ammonium cation), -SO ３ A fluoropolymer having a group represented by M (hereinafter also referred to as "polymer H") is obtained. Polymer H corresponds to the second fluoropolymer described below. The ion exchange capacity of polymer H is preferably 0.90 milliequivalents / g dry resin or more, more preferably 1.20 milliequivalents / g dry resin or more, and even more preferably 1.30 milliequivalents / g dry resin or more, and preferably 2.30 milliequivalents / g dry resin or less, more preferably 2.00 milliequivalents / g dry resin or less, and even more preferably 1.50 milliequivalents / g dry resin or less. The ion exchange capacity of polymer H can be determined by the method described in the Examples section below.

[0067] [Shell Portion] The shell portion of the specific particle covers the core portion. The shell portion may cover the entire surface of the core portion, or may cover only a portion of the surface of the core portion. A high coverage of the surface of the core portion is preferred, preferably 90% or more, more preferably 95% or more, even more preferably 98% or more, and most preferably completely covered. Here, whether or not a shell portion is present on the surface of the specific particle can be determined based on a composition analysis of the particle surface by energy dispersive X-ray spectroscopy (SEM-EDX) or X-ray photoelectron spectroscopy (XPS) of the specific particle. Specifically, in the composition analysis, -SO ３When sulfur atoms derived from the group represented by M and atoms represented by M are detected, it can be said that a shell portion is present on the surface of the specific particle. ３ The ratio of the atomic composition percentage (at %) of M in the group represented by M (atomic composition percentage of M / atomic composition percentage of sulfur atoms) is preferably 0.50 or more.

[0068] The thickness of the shell portion is preferably 0.01 μm or more, more preferably 0.2 μm or more, even more preferably 0.3 μm or more, and is preferably 10 μm or less, in order to obtain better effects of the present invention. The thickness of the shell portion is determined by the method described in the Examples section below.

[0069] <Second Fluorine-Containing Polymer> The second fluorine-containing polymer has fluorine atoms and is —SO ３ M, and the first fluorine-containing polymer is a polymer having a group represented by —SO ２ The group represented by X is subjected to hydrolysis treatment or hydrolysis treatment and acidification treatment to form -SO ３ It is preferably a polymer converted into a group represented by M. The second fluorine-containing polymer is preferably Polymer H-1 or Polymer H-2 shown below, in terms of achieving better effects of the present invention. ３ In the group represented by M, M represents an alkali metal, a hydrogen atom, or a quaternary ammonium cation.

[0070] (Polymer H-1) Polymer H-1 is a polymer having the same structure as the —SO 3 group in the above-mentioned polymer F-1. ２ The group represented by X is -SO ３ The polymer H-1 is preferably a polymer having a unit based on a fluorine-containing olefin and a group represented by —SO ３ A polymer having a group represented by M, and a unit based on a fluorine-containing olefin and —SO ３ and a copolymer containing units based on a fluorine-containing monomer having a group represented by M. Polymer H-1 preferably does not have a cyclic ether structure.

[0071] Specific examples of units based on fluorine-containing olefin are the same as the specific examples of units based on fluorine-containing olefin in polymer F-1. The content of units based on fluorine-containing olefin relative to all units of polymer H-1 is the same as the content of units based on fluorine-containing olefin relative to all units of polymer F-1.

[0072] -SO ３ The unit based on a fluorine-containing monomer having a group represented by M is preferably a unit represented by formula (2): Formula (2) -[CF ２ -CF(-L-(SO ３ M) ｎ )]-

[0073] In formula (2), L and n are defined as the same as in formula (1), and M is a hydrogen atom, an alkali metal, or a quaternary ammonium cation.

[0074] The unit represented by formula (2) is preferably a unit represented by formula (2-1), a unit represented by formula (2-2), a unit represented by formula (2-3), or a unit represented by formula (2-4). ２ -CF(-O-R ｆ１ -SO ３ M)] - Formula (2-2) - [CF ２ -CF(-R ｆ１ -SO ３ M) ]-

[0075]

[0076]

[0077] R in formula (2-1) to formula (2-4) ｆ１ , R ｆ２ , R ｆ３ The definitions of r and m are as follows: ｆ１ , R ｆ２ , R ｆ３ , r, and m are defined in the same way. The definition of M in the formula is as described above. In formula (2-3) and formula (2-4), two Ms may be the same or different.

[0078] As the unit represented by formula (2-1) and the unit represented by formula (2-2), a unit represented by formula (2-5) is more preferred. ２ -CF(-(CF ２ ) ｘ -(OCF ２ CFY) ｙ -O-(CF ２ ) ｚ -SO ３ M)]— The definitions of x, y, z, and Y in formula (2-5) are the same as those of x, y, z, and Y in formula (1-5) above. M is as defined above.

[0079] Specific examples of the unit represented by formula (2-1) include the following units. In the formula, w is an integer of 1 to 8, and x is an integer of 1 to 5. The definition of M in the formula is as described above. -[CF ２ -CF(-O-(CF ２ ) ｗ -SO ３ M)]- -[CF ２ -CF(-O-CF ２ CF (CF ３ )-O-(CF ２ ) ｗ -SO ３ M)]- -[CF ２ -CF(-(O-CF ２ CF (CF ３ )) ｘ -SO ３ M) ]-

[0080] Specific examples of the unit represented by formula (2-2) include the following units. In the formula, w is an integer of 1 to 8. The definition of M in the formula is as described above. -[CF ２ -CF(-(CF ２ ) ｗ -SO ３ M)]- -[CF ２ -CF (-CF ２ -O-(CF ２ ) ｗ -SO ３ M) ]-

[0081] The unit represented by formula (2-3) is preferably a unit represented by formula (2-3-1), where M is defined as above.

[0082]

[0083] R in formula (2-3-1) ｆ４ and R ｆ５ The definition of is R in formula (1-3-1). ｆ４ and R ｆ５ The definitions of r and M are as described above.

[0084] Specific examples of the unit represented by formula (2-3-1) include the following.

[0085]

[0086] As the unit represented by formula (2-4), a unit represented by formula (2-4-1) is preferred. ｆ１ , R ｆ２ and M are defined as above.

[0087]

[0088] Specific examples of the unit represented by formula (2-4-1) include the following.

[0089]

[0090] -SO ３ The units based on a fluorine-containing monomer having a group represented by M may be used alone or in combination of two or more.

[0091] -SO in polymer H-1 ３ The content of units based on a fluorine-containing monomer having a group represented by M is -SO ２ The content is the same as the content of units based on a fluorine-containing monomer having a group represented by X.

[0092] Polymer H-1 may contain units based on other monomers described above for Polymer F-1. The content of units based on other monomers in Polymer H-1 is the same as the content of units based on other monomers in Polymer F-1.

[0093] (Polymer H-2) Polymer H-2 is the same as —SO 3 in the above-mentioned polymer F-2. ２ The group represented by X is -SO ３ The polymer H-2 preferably has a unit based on a monomer having a cyclic ether structure, and is a polymer in which the unit is converted into a group represented by —SO ３ M, and a unit based on a monomer having a cyclic ether structure and a group represented by —SO ３ and a copolymer having a unit based on a fluorine-containing monomer having a group represented by M.

[0094] Specific examples of units based on a monomer having a cyclic ether structure include the unit (u11), unit (u12), unit (u21), and unit (u22). The unit (u11) is a unit based on the above-mentioned monomer m11, and a preferred embodiment thereof is the unit (u11-1). The unit (u12) is a unit based on the above-mentioned monomer m12, and a preferred embodiment thereof is the unit (u12-1) to unit (u12-2). The unit (u21) is a unit based on the above-mentioned monomer m21, and a preferred embodiment thereof is the unit (u21-1). The unit (u22) is a unit based on the above-mentioned monomer m22, and a preferred embodiment thereof is the unit (u22-1). The definitions of each group in the formula are as described above.

[0095]

[0096]

[0097]

[0098]

[0099] The content of units based on monomers having a cyclic ether structure relative to all units of polymer H-2 is similar to the content of units based on monomers having a cyclic ether structure relative to all units of polymer F-2.

[0100] -SO ３ Specific examples of units based on a fluorine-containing monomer having a group represented by M include —SO２ The same applies to the fluorine-containing monomer having a group represented by X. The ratio of —SO 3 to all units of polymer H-2 is ３ The content of units based on a fluorine-containing monomer having a group represented by M is -SO ２ The content is the same as the content of units based on a fluorine-containing monomer having a group represented by X.

[0101] Polymer H-2 may have units based on a fluorine-containing olefin. Specific examples of the fluorine-containing olefin are the same as those for Polymer H-1. The content of units based on a fluorine-containing olefin (particularly, TFE) relative to all units of Polymer H-2 is the same as the content of units based on a fluorine-containing olefin (particularly, TFE) relative to all units of Polymer F-2.

[0102] (Physical properties of second fluoropolymer) The ion exchange capacity of the second fluoropolymer is preferably 0.90 milliequivalent / g dry resin or more, more preferably 1.20 milliequivalent / g dry resin or more, even more preferably 1.30 milliequivalent / g dry resin or more, and preferably 2.30 milliequivalent / g dry resin or less, more preferably 2.00 milliequivalent / g dry resin or less, even more preferably 1.50 milliequivalent / g dry resin or less. Here, when the ion exchange capacity of the fluoropolymer present on the surface of the particles containing the fluoropolymer is high (specifically, 1.20 milliequivalent / g dry resin or more), the particles are likely to be agglomerated during storage. However, the second fluoropolymer present on the surface of the specific particles is -SO ３ Since the second fluoropolymer has a group represented by M, even if the ion exchange capacity of the second fluoropolymer is high, the specific particles are less likely to agglomerate during storage. Therefore, when the ion exchange capacity of the second fluoropolymer is 1.20 meq / g dry resin or more, the effects of the present invention are more significantly exhibited. The ion exchange capacity of the second fluoropolymer can be determined by the method described in the Examples section below.

[0103] The elastic modulus of the second fluoropolymer is preferably at least 10 times, more preferably at least 50 times, and even more preferably at least 100 times, the elastic modulus of the first fluoropolymer. The magnitude of the elastic modulus of the second fluoropolymer relative to the elastic modulus of the first fluoropolymer can be determined by the method described in the Examples section below.

[0104] [Method for producing fluoropolymer] The method for producing a fluoropolymer of the present invention comprises the steps of: ２ Step 1: obtaining particles of a first fluoropolymer by polymerizing a monomer containing a fluoromonomer having a group represented by X; Step 2: obtaining the specific particles by carrying out a first treatment of hydrolysis or a second treatment of hydrolysis and acid-form conversion on the surfaces of the particles obtained in Step 1; Step 3: storing the particles obtained in Step 2; and Step 3: performing a third treatment of hydrolysis and acid-form conversion on the particles after storage to remove -SO ２ The group represented by X is -SO ３ and step 4 of converting X to a group represented by M to obtain a fluoropolymer. In the formula, X represents a halogen atom, and M represents an alkali metal, a hydrogen atom, or a quaternary ammonium cation. The fluoropolymer obtained by this production method is suitably used for forming an electrolyte membrane or a catalyst layer of a polymer electrolyte fuel cell or a water electrolysis device.

[0105] [Step 1] Step 1 is -SO ２ This is a step of polymerizing monomers including a fluorine-containing monomer having a group represented by X to obtain particles of a first fluorine-containing polymer (hereinafter also referred to as "first particles").

[0106] Specific examples of the monomer are as shown in the description of polymer F-1 and polymer F-2 above.

[0107] As the polymerization method, known polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization can be used. Polymerization may also be carried out in liquid or supercritical carbon dioxide. Polymerization is carried out under conditions that generate radicals. Methods for generating radicals include irradiation with radiation such as ultraviolet rays, gamma rays, and electron beams, and addition of a radical initiator.

[0108] In step 1, the first particles are preferably recovered while being separated from the unreacted monomer, the polymerization solvent, etc. The first particles may be heat-treated at 200°C to 300°C for 3 to 40 hours. This makes it possible to remove the unreacted monomer, the polymerization solvent, etc.

[0109] The first fluoropolymer contained in the first particles is the same as the first fluoropolymer contained in the core portion of the above-mentioned specific particles. The first particles may be in the form of powder or pellets. The average particle size of the first particles is the same as that of the above-mentioned specific particles, including preferred embodiments.

[0110] [Step 2] Step 2 is a step of performing a first treatment of hydrolysis treatment on the surface of the first particle, or a second treatment of hydrolysis treatment and acidification treatment on the surface of the first particle, to obtain the above-mentioned specific particle.

[0111] <First Treatment (Hydrolysis Treatment)> The first treatment is a treatment in which the surfaces of the first particles are subjected to hydrolysis treatment. As a result, —SO of the first fluoropolymer present on the surfaces of the first particles is ２ The group represented by X is —SO ３ M １ (In the formula, M １ represents an alkali metal or quaternary ammonium cation. In this way, the above-mentioned specific particles are obtained.

[0112] The hydrolysis treatment is carried out, for example, by bringing the first particles into contact with an alkaline aqueous solution. The alkaline aqueous solution preferably contains a solvent and a basic compound. Examples of the solvent contained in the alkaline aqueous solution include water and a mixed solvent of water and a polar solvent. Specific examples of polar solvents include alcohols (methanol, ethanol, etc.) and dimethyl sulfoxide. Among these, the -SO present in the vicinity of the surface of the first particles is preferably used. ２ Only the group represented by X is -SO ３ M １ In order to efficiently obtain specific particles, the solvent in the alkaline aqueous solution preferably does not substantially contain a polar solvent and preferably consists of only water. Here, "substantially does not contain a polar solvent" means that the content of the polar solvent is 1% by mass or less, and preferably 0% by mass, relative to the total mass of the solvent contained in the alkaline aqueous solution.

[0113] Specific examples of the basic compound include sodium hydroxide, potassium hydroxide, and ammonia. The content of the basic compound is preferably 10% by mass or more, more preferably 20% by mass or more, based on the total mass of the alkaline aqueous solution, in order to improve the reaction rate. ２ Only the group represented by X is -SO ３ M １ In view of the ease of conversion into the above, the content is preferably 50% by mass or less, and more preferably 40% by mass or less.

[0114] The amount of the alkaline aqueous solution used relative to the amount of the first particles used (100 parts by mass) is preferably 200 parts by mass or more, and more preferably 300 parts by mass or more, from the viewpoint of reaction efficiency, and is preferably 1,000 parts by mass or less, and more preferably 500 parts by mass or less, from the viewpoint of reducing the amount of waste liquid.

[0115] The temperature of the alkaline aqueous solution is preferably 5° C. or higher, more preferably 30° C. or higher, in order to improve the reaction rate. ２ Only the group represented by X is -SO ３ M １ The temperature is preferably 100°C or lower, more preferably 80°C or lower, in that case the conversion into

[0116] The time for the hydrolysis treatment (specifically, the contact time between the first particles and the alkaline aqueous solution) is preferably 1 minute or more, more preferably 15 minutes or more, because the thickness of the shell portion can be increased as the time increases. ２ Only the group represented by X is -SO ３ M １ The time is preferably 10 hours or less, more preferably 2 hours or less, in that case the conversion into

[0117] <Second Treatment (Hydrolysis Treatment and Acid Form Conversion Treatment)> The second treatment is a treatment of carrying out a hydrolysis treatment and an acid form conversion treatment. By this, —SO 3 of the first fluoropolymer present on the surface of the first particles is converted to an acid form. ２ The group represented by X is —SO ３ M ２ (In the formula, M ２ represents a hydrogen atom.) In this way, the above-mentioned specific particles are obtained.

[0118] The hydrolysis treatment in the second treatment is the same as the hydrolysis treatment in the first treatment.

[0119] The acidification treatment in the second treatment is carried out by removing -SO generated on the surface of the particles by the hydrolysis treatment. ３ M １ The group represented by -SO ３ M ２ In this way, the above-mentioned specific particles are obtained.

[0120] The acid-form treatment is carried out, for example, by bringing the hydrolyzed particles into contact with an acidic aqueous solution, which preferably contains an acid component and water.

[0121] Specific examples of the acid component include sulfuric acid and hydrochloric acid. The content of the acid component is preferably 5% by mass or more, more preferably 8% by mass or more, relative to the total mass of the acidic aqueous solution, from the viewpoint of improving the reaction rate, and is preferably 30% by mass or less, more preferably 25% by mass or less, from the viewpoint of ease of handling the acidic aqueous solution.

[0122] The amount of the acidic aqueous solution used is preferably 100 parts by mass or more, and more preferably 200 parts by mass or more, relative to the amount of particles used after hydrolysis (100 parts by mass) from the viewpoint of reaction efficiency, and is preferably 1,000 parts by mass or less, and more preferably 500 parts by mass or less, from the viewpoint of reducing the amount of waste liquid.

[0123] The temperature of the acidic aqueous solution is preferably 40°C or higher, more preferably 50°C or higher, from the viewpoint of allowing the reaction to proceed sufficiently, and is preferably 100°C or lower, more preferably 80°C or lower, from the viewpoint of suppressing elution of the polymer.

[0124] The time for the acid-formation treatment (specifically, the contact time (reaction time) between the particles after hydrolysis treatment and the acidic aqueous solution) is preferably 10 minutes or more, more preferably 30 minutes or more, from the viewpoint of allowing the reaction to proceed sufficiently, and is preferably 120 minutes or less, more preferably 90 minutes or less, from the viewpoint of suppressing elution of the polymer.

[0125] Step 2 may include a water washing treatment in which the particles after the hydrolysis treatment and / or the particles after the acid-formation treatment are washed with water.

[0126] [Step 3] Step 3 is a step of storing the specific particles obtained through Step 2. As described above, the specific particles are less likely to fuse together after storage. Therefore, the specific particles after storage have excellent handleability when used in Step 4 described below. Another advantage is that when the specific particles after storage are used in Step 4 described below, steps such as pulverization can be omitted.

[0127] The specific particles are preferably stored by being filled in a storage member such as a bag, a container, etc. Materials constituting the storage member include paper, resin (e.g., acrylic resin, polyolefin, polyester, vinyl chloride), metal, etc.

[0128] The storage temperature of the specific particles is preferably 0° C. or higher, more preferably 20° C. or higher, from the viewpoint of equipment constraints, and is preferably 100° C. or lower, more preferably 60° C. or lower, and even more preferably 40° C. or lower, from the viewpoint of further suppressing agglomeration of the specific particles during storage. The storage period of the specific particles is preferably 180 days or shorter, more preferably 90 days or shorter, and even more preferably 10 days or shorter, from the viewpoint of further suppressing agglomeration of the specific particles during storage.

[0129] [Step 4] In step 4, the specific particles after storage are subjected to a third treatment, which involves hydrolysis and acidification, to remove -SO in the specific particles. ２ The group represented by X is -SO ３ This is a step of converting the —SO 2 —SO 3 —SO 4 —SO 5 —SO 6 —SO 7 —SO 8 —SO 9 —SO 10 —SO 11 —SO 12 —SO 13 —SO 14 —SO 15 —SO 16 —SO 17 —SO 18 —SO 19 —SO 20 —SO 21 —SO 32 —SO 16 —SO 17 —SO 24 —SO 35 —SO 18 —SO 19 —SO 25 —SO 36 —SO 19 —SO 26 —SO 37 —SO 40 —SO 19 —SO 21 —SO 38 —SO 41 —SO 19 —SO 24 —SO 39 —SO 40 —SO 19 —SO 25 —SO 36 —SO 41 —SO 26 —SO 37 —SO 40 —SO 19 —SO 24 —SO 38 ２ The group represented by X is —SO ３ It is converted into a group represented by M. Therefore, it can be said that the particles containing the fluoropolymer obtained through step 4 are particles made of the above-mentioned second fluoropolymer.

[0130] <Hydrolysis Treatment> The hydrolysis treatment in step 4 is a treatment in which the specific particles after storage are subjected to hydrolysis treatment. As a result, -SO of the first fluorine-containing polymer present in the specific particles (particularly in the core portion) after storage is hydrolyzed. ２ The group represented by X is —SO ３ M １ (In the formula, M １ represents an alkali metal or quaternary ammonium cation.

[0131] The hydrolysis treatment in step 4 is carried out, for example, by bringing the specific particles after storage into contact with an alkaline aqueous solution. The alkaline aqueous solution preferably contains a solvent and a basic compound. Examples of the solvent contained in the alkaline aqueous solution include water and a mixed solvent of water and a polar solvent. Specific examples of the polar solvent are as described in step 2 above. In particular, the solvent contained in the alkaline aqueous solution used in the hydrolysis treatment in step 4 is preferably a mixed solvent of water and a polar solvent. In the hydrolysis treatment in step 4, when the solvent contained in the alkaline aqueous solution is the above-mentioned mixed solvent, the content of the polar solvent is preferably 10% by mass or more, more preferably 15% by mass or more, relative to the total mass of the mixed solvent, from the viewpoint of improving the reaction rate, and is preferably 50% by mass or less, more preferably 40% by mass or less, from the viewpoint of suppressing elution of the polymer.

[0132] Specific examples of the basic compound are as described above in Step 2. The content of the basic compound is preferably 10% by mass or more, more preferably 15% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, based on the total mass of the alkaline aqueous solution, from the viewpoint of improving the reaction rate.

[0133] In the hydrolysis treatment in step 4, the amount of the alkaline aqueous solution used relative to the amount (100 parts by mass) of the specific particles after storage is preferably 200 parts by mass or more, and more preferably 300 parts by mass or more, from the viewpoint of reaction efficiency, and is preferably 1,000 parts by mass or less, and more preferably 500 parts by mass or less, from the viewpoint of reducing the amount of waste liquid.

[0134] In the hydrolysis treatment in step 4, the temperature of the alkaline aqueous solution is preferably 60°C or higher, more preferably 80°C or higher, from the viewpoint of improving the reaction rate, and is preferably 120°C or lower, more preferably 100°C or lower, from the viewpoint of suppressing elution of the polymer.

[0135] In the hydrolysis treatment in step 4, the contact time (reaction time) between the specific particles after storage and the alkaline aqueous solution is preferably 12 hours or more, more preferably 16 hours or more, from the viewpoint of allowing the reaction to proceed sufficiently, and is preferably 200 hours or less, more preferably 100 hours or less, from the viewpoint of suppressing elution of the polymer.

[0136] <Acid Forming Treatment> The acid form forming treatment in step 4 is carried out to remove —SO ３ M １ The group represented by -SO ３ M ２ This is a process for converting a group represented by the formula:

[0137] The acid-form treatment in step 4 is carried out, for example, by bringing the particles after the hydrolysis treatment in step 4 into contact with an acidic aqueous solution. The acidic aqueous solution preferably contains an acid component and water.

[0138] Specific examples of the acid component are as described above in Step 2. In the acid-form conversion treatment in Step 4, the content of the acid component is preferably 5% by mass or more, and more preferably 8% by mass or more, relative to the total mass of the acidic aqueous solution, from the viewpoint of improving the reaction rate, and is preferably 30% by mass or less, and more preferably 25% by mass or less, from the viewpoint of the handleability of the acidic aqueous solution.

[0139] In the acid-form treatment in step 4, the amount of the acidic aqueous solution used relative to the amount of particles used after the hydrolysis treatment (100 parts by mass) is preferably 100 parts by mass or more, and more preferably 200 parts by mass or more, from the viewpoint of reaction efficiency, and is preferably 1,000 parts by mass or less, and more preferably 500 parts by mass or less, from the viewpoint of reducing the amount of waste liquid.

[0140] In the acidification treatment in step 4, the temperature of the acidic aqueous solution is preferably 40°C or higher, more preferably 50°C or higher, from the viewpoint of improving the reaction rate, and is preferably 100°C or lower, more preferably 80°C or lower, from the viewpoint of suppressing elution of the polymer.

[0141] In the acid-form conversion treatment in step 4, the time for the acid-form conversion treatment (specifically, the contact time (reaction time) between the particles after hydrolysis treatment and the acidic aqueous solution) is preferably 10 minutes or more, more preferably 30 minutes or more, from the viewpoint of allowing the reaction to proceed sufficiently, and is preferably 120 minutes or less, more preferably 90 minutes or less, from the viewpoint of suppressing elution of the polymer. The acid-form conversion treatment in step 4 may be carried out multiple times. In this case, the above-mentioned contact time is the contact time per one time.

[0142] Step 4 may include a water washing treatment in which the particles after the hydrolysis treatment and / or the particles after the acid-formation treatment are washed with water.

[0143] The present invention will be described in detail below with reference to examples. Examples 1 to 4 are working examples, and Examples 5 and 6 are comparative examples. However, the present invention is not limited to these examples.

[0144] [Abbreviation] TFE:CF ２ =CF ２ Monomer (m1): CF ２ = CFOCF ２ CF (CF ３ ) OCF ２CF ２ SO ２ F

[0145] [Ion Exchange Capacity] Particles containing polymer F-1A (corresponding to the first fluoropolymer described above) were vacuum dried for 16 hours at 240° C. The dried polymer F-1A was weighed and placed in a polycarbonate container. The dried polymer F-1A was then dissolved in a 0.7 N NaOH solution (solvent: H ２ O / CH ３ The polymer F-1A was immersed in a solution of 100% hydroxybenzoates (OH=10 / 90 (mass ratio)) at 60°C for 72 hours or more to obtain -SO ２ The F groups were completely converted to the Na salt form. The NaOH solution in which the dried polymer F-1A had been immersed was back-titrated with 0.1 mol / L HCl using phenolphthalein as an indicator to determine the amount of NaOH in the solution, thereby calculating the ion exchange capacity (meq / g dry resin). Note that "meq / g" means "meq / g dry resin," which is the unit of ion exchange capacity.

[0146] [Elastic Modulus Ratio] The elastic modulus of the surface of the hydrolyzed particles obtained in each example was measured using an atomic force microscope (AFM Cypher S, manufactured by Oxford Instruments). An AC-240TS probe (spring constant: 2 N / m, resonance frequency: 70 kHz, tip R<7 nm) was used. Specifically, the probe was brought into contact with the surface of the hydrolyzed particles obtained in each example, and force mapping measurement was performed at 25°C to measure the elastic modulus of the surface of the hydrolyzed particles. All measured elastic modulus values ​​that were 10 to 80% of the maximum measured value were considered valid measurement results, and their average value was considered to be the elastic modulus of the shell portion of the particle. Furthermore, the elastic modulus of the surface of the pre-hydrolyzed particles was measured in the same manner as described above, except that the pre-hydrolyzed particles obtained in each example were used instead of the pre-hydrolyzed particles obtained in each example. All measured values ​​of elastic modulus were considered to be valid when the magnitude of the measured value was 10 to 80% of the maximum measured value, and the average value was considered to be the elastic modulus of the core portion of the particle. From the values ​​of the elastic modulus of the core portion and the elastic modulus of the shell portion thus obtained, the ratio of the elastic modulus of the shell portion to the elastic modulus of the core portion (shell portion / core portion) was calculated.

[0147] [Average Particle Diameter] The average particle diameter (D50) of the particles obtained in each example was calculated from the particle size distribution measured by mechanical sieving using a stainless steel test sieve (JIS-Z8801).

[0148] [Analysis of Shell Portion] Whether or not a shell portion was present on the surface of the hydrolyzed particles obtained in each example was determined by the following method. The hydrolyzed particles obtained in each example were subjected to particle surface composition analysis by energy dispersive X-ray spectroscopy (SEM-EDX). As a result, all of the hydrolyzed particles obtained in Examples 1 to 4 were found to have a shell portion containing -SO ３ Since sulfur atoms derived from the group represented by M and atoms represented by M were detected, it was confirmed that a shell portion was present on the surface. In addition, based on the results of the composition analysis, the ratio of -SO to the atomic composition percentage (at%) of sulfur atoms was ３The ratio of the atomic composition percentage (at %) of M in the group represented by M (atomic composition percentage of M / atomic composition percentage of sulfur atoms) was determined. As a result, the above ratio was 0.5 or more for all of the particles after hydrolysis obtained in Examples 1 to 4. <Measurement conditions> Apparatus: "SU6600" manufactured by Hitachi High-Technologies Corporation and "Noran System 6" manufactured by Thermo Electronics Corporation Acceleration voltage: 10 kV WD (working distance): 15 mm Probe current: medium Detector: SE (secondary electrons)

[0149] [Shell Thickness] The particles after hydrolysis in each example were cut with a cutter to expose the central part of the particle, thereby exposing the cross section. The cutting was carried out so that the central part of the particle was exposed. The composition of the exposed cross section was analyzed by SEM-EDX. As a result, the particles after hydrolysis in each of Examples 1 to 4 had a thickness of -SO ３ There were sites where sulfur atoms derived from the group represented by M and atoms represented by M were detected. Based on the results of the composition analysis, the atomic composition percentage (at%) of sulfur atoms was ３ The ratio of the atomic composition percentage (at %) of M in the group represented by M (atomic composition percentage of M / atomic composition percentage of sulfur atoms) was calculated. The portion where this ratio was 0.5 or more was considered to be the shell portion, and the thicknesses of three different points in the portion considered to be the shell portion were calculated based on the SEM image, and the arithmetic average value thereof was defined as the thickness of the shell portion.

[0150] [Evaluation of Agglomeration] 100 g of the particles obtained in each example were packed into an acrylic cylinder with an inner diameter of 56 mm, and a metal cylinder with an inner diameter of 55 mm and a weight of 1.6 kg was placed on top of the particles to apply a predetermined load to the polymer. The particles in the acrylic cylinder were stored at 40°C for a certain period (1 week). Thereafter, the particles were removed from the cylinder, observed visually, and evaluated according to the following criteria: ◎: No adhesion (fusion) between particles at all. ○: Slight adhesion (fusion) between particles was observed, but no overall agglomeration was observed. ×: Overall agglomeration occurred due to adhesion (fusion) between particles.

[0151] [Example 1] Polymer F-1A containing units based on monomer (m1) and units based on TFE was obtained by referring to the method described in paragraph 0200 of JP 2015-99772 A before the hydrolysis treatment. The ion exchange capacity measured using the polymer F-1A by the above-mentioned method was 1.39 meq / g. Polymer F-1A was placed in a pulverizer with a 2 mm mesh screen, and the polymer F-1A was pulverized to obtain powdered particles 1-1 (average particle diameter 2.0 mm). 10 g of particles 1-1 were placed in 900 g of a 48% by mass aqueous KOH solution (25°C) and immersed for 2 hours (hydrolysis treatment). After immersion, the KOH aqueous solution adhering to the particle surface was washed away with water (water washing treatment). In this way, particles 2-1 (average particle diameter 2.0 mm) in Example 1 were obtained.

[0152] [Example 2] Polymer F-1A obtained in the same manner as in Example 1 was fed into a melt extruder to obtain strands of polymer F-1A, which were then cut to obtain pellet-shaped particles 1-2 (average particle diameter 2.0 mm). Hydrolysis treatment and water washing treatment were carried out under the same conditions as in Example 1, except that particles 1-2 were used instead of particles 1-1, to obtain particles 2-2 in Example 2 (average particle diameter 2.0 mm).

[0153] [Example 3] Particles 2-3 (average particle diameter 2.0 mm) in Example 3 were obtained in the same manner as in Example 1, except that the concentration of the KOH aqueous solution used in the hydrolysis treatment was changed to 10 mass % and the immersion time was changed to 1 minute.

[0154] [Example 4] Particles 2-4 (average particle diameter 2.0 mm) in Example 4 were obtained in the same manner as in Example 1, except that the concentration of the KOH aqueous solution used in the hydrolysis treatment was changed to 10 mass % and the immersion time was changed to 1 hour.

[0155] Example 5 Particles 1-1 obtained in Example 1 were used as particles in Example 5.

[0156] Example 6 Particles 1-2 obtained in Example 1 were used as particles in Example 6.

[0157]

[0158] As shown in Table 1, it was shown that when the above-mentioned specific particles were used, the occurrence of agglomeration could be suppressed (Examples 1 to 4).

[0159] 100 g of particles 2-1 before the agglomeration evaluation test was immersed for 24 hours in 900 g of an aqueous solution (80°C) containing 20% ​​by mass of KOH and 16% by mass of methanol. After immersion, the KOH aqueous solution adhering to the particle surface was washed away with water. Next, 100 g of the washed particles 2-1 were immersed for 30 minutes in 900 g of a 3.0 N aqueous sulfuric acid solution (60°C). After immersion, the sulfuric acid aqueous solution adhering to the particle surface was washed away with water (washing treatment). The acid treatment and washing treatment were repeated 15 times in this order. In this way, particles 3-1 were obtained. Particles 3-1 were analyzed by IR analysis and ICP emission spectroscopy, and it was found that the -SO ２ F and -SO ３ K is all -SO ３ It was confirmed that it was converted to H.

[0160] Particles 3-2 to 3-4 were obtained in the same manner as in the production method of Particle 3-1, except that Particles 2-2 to 2-4 before the agglomeration evaluation test were used instead of Particles 2-1 before the agglomeration evaluation test. Particles 3-2 to 3-4 were analyzed in the same manner as in Particle 3-1, and the -SO ２ F and -SO ３ K is all -SO ３ It was confirmed that the compound was converted to H. The entire contents of the specification, claims and abstract of Japanese Patent Application No. 2024-090121, filed on June 3, 2024, are incorporated herein by reference as the disclosure of the present invention.

Claims

1. A particle comprising a core portion and a shell portion covering the core portion, wherein the core portion is -SO ２ The polymer contains a first fluorine-containing polymer having a group represented by X, and the shell portion is -SO ３ A particle comprising a second fluorine-containing polymer having a group represented by M. In the formula, X represents a halogen atom, and M represents an alkali metal, a hydrogen atom, or a quaternary ammonium cation.

2. The particle according to claim 1, wherein the thickness of the shell portion is 0.01 μm or more.

3. The particle according to claim 1, wherein the first fluorine-containing polymer and the second fluorine-containing polymer both contain units based on a fluorine-containing olefin.

4. The particles according to claim 1, wherein the ion exchange capacity of said second fluorine-containing polymer is 0.90 meq / g dry resin or more.

5. -SO ２ Step 1: Polymerizing a monomer containing a fluorine-containing monomer having a group represented by X to obtain particles of a first fluorine-containing polymer; Step 2: Performing a first treatment of hydrolysis on the surfaces of the particles obtained in Step 1, or a second treatment of hydrolysis and acid-form conversion to obtain particles according to any one of claims 1 to 4; Step 3: Storing the particles obtained in Step 2; and Step 3: Performing a third treatment of hydrolysis and acid-form conversion to the particles after storage to remove -SO ２ The group represented by X is -SO ３ and step 4 of converting the group represented by formula (I) into a group represented by formula (I), to obtain a fluoropolymer. In the formula, X represents a halogen atom, and M represents an alkali metal, a hydrogen atom, or a quaternary ammonium cation.

Images