Powder containing fluoropolymer particles and manufacturing method therefor, powder coating, and liquid coating composition

Abstract

Provided is a powder containing fluoropolymer particles, wherein: the powder contains a fluorine-containing compound having a hydrophilic group; the content of the fluorine-containing compound having the hydrophilic group relative to the powder is 250 ppb by mass or less; the average secondary particle diameter of the fluoropolymer particles is 0.5-10 μm; and the fluoropolymer is at least one selected from the group consisting of a tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer, a tetrafluoroethylene / hexafluoropropylene copolymer, and a tetrafluoroethylene / perfluoro (alkyl vinyl ether) / hexafluoropropylene copolymer.

Description

Powder containing fluoropolymer particles and its manufacturing method, powder coating and liquid coating composition

[0001] The present disclosure relates to a powder containing fluoropolymer particles and a method for producing the same, a powder coating, and a liquid coating composition.

[0002] Patent Document 1 describes a TFE thermally processable perfluoropolymer containing the following amounts of perfluoroalkyl vinyl ethers, expressed as weight percents relative to the total of the monomers: a) 0.2 to 5.5% perfluoromethyl vinyl ether (PMVE); b) 0.4 to 4.5% perfluoroethyl vinyl ether (PEVE) and / or perfluoropropyl vinyl ether (PFVE); c) 0.5 to 6% hexafluoropropene (HFP); the amount of perfluoroalkyl vinyl ethers a) + b) is in the range of 1.5 to 5.5% by weight relative to the total of the monomers; and the amount of TFE is an amount that adds up to 100% by weight.

[0003] Patent Document 2 discloses a mixture of thermoplastic fluoropolymers essentially comprising 0.5 to 10 mol % of tetrafluoroethylene units and one or more perfluoroalkyl vinyl ether units having 1 to 4 carbon atoms in the perfluoroalkyl group, wherein: at least 10% by weight, but not more than 90% by weight, of a MFI of 30 or more. Ａ and - a proportion by weight of not more than 90% but at least 10% of an MFI of not more than 15 Ｂ wherein each component comprises at least one component B) having an MFI of component B). Ｂ MFI of component A) Ａ The above mixture is described, wherein the ratio of

[0004] Patent Document 3 describes a compound of formula (1) CF ３ CF ２ OCF ２ CF ２ OCF ２ COONH ４a method for producing a melt-moldable fluororesin by emulsion polymerizing a fluorine-containing monomer or a fluorine-containing monomer and an olefin in an aqueous medium containing a fluorine-containing emulsifier represented by the formula (I), wherein the melt-moldable fluororesin is selected from the group consisting of a tetrafluoroethylene / hexafluoropropylene copolymer having a tetrafluoroethylene / hexafluoropropylene molar ratio of 95 / 5 to 90 / 10, a tetrafluoroethylene / perfluoro(propyl vinyl ether) copolymer having a tetrafluoroethylene / perfluoro(propyl vinyl ether) molar ratio of 99.7 / 0.3 to 97 / 3, a tetrafluoroethylene / ethylene copolymer having a tetrafluoroethylene / ethylene molar ratio of 65 / 35 to 50 / 50, a chlorotrifluoroethylene / ethylene copolymer having a chlorotrifluoroethylene / ethylene molar ratio of 65 / 35 to 50 / 50, The document describes a method for producing a melt-moldable fluororesin, characterized in that the melt-moldable fluororesin is selected from the group consisting of a tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride copolymer having a tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride molar ratio of 35 to 75 / 5 to 15 / 20 to 50, a tetrafluoroethylene / hexafluoropropylene / ethylene copolymer having a tetrafluoroethylene / hexafluoropropylene / ethylene molar ratio of 35 to 65 / 5 to 15 / 30 to 50, a tetrafluoroethylene / hexafluoropropylene / perfluoro(alkyl vinyl ether) copolymer having a tetrafluoroethylene / hexafluoropropylene / perfluoro(alkyl vinyl ether) molar ratio of 88 to 94.8 / 5 to 10 / 0.2 to 2, and polyvinylidene fluoride.

[0005] International Publication No. 2007 / 96347 JP 2002-503744 A JP 2013-100532 A

[0006] An object of the present disclosure is to provide a powder containing fluoropolymer particles with a reduced content of fluorine-containing compounds having hydrophilic groups. Another object of the present disclosure is to provide a method for producing a powder containing fluoropolymer particles with a reduced content of fluorine-containing compounds having hydrophilic groups.

[0007] According to the present disclosure, there is provided a powder containing fluoropolymer particles, which contains a fluorine-containing compound having a hydrophilic group, the content of the fluorine-containing compound having a hydrophilic group being 250 mass ppb or less relative to the powder, the fluoropolymer particles having an average secondary particle size of 0.5 to 10 μm, and the fluoropolymer being at least one selected from the group consisting of a tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer, a tetrafluoroethylene / hexafluoropropylene copolymer, and a tetrafluoroethylene / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymer.

[0008] According to the present disclosure, it is possible to provide a powder containing fluoropolymer particles with a reduced content of fluorine-containing compounds having hydrophilic groups. Also, according to the present disclosure, it is possible to provide a method for producing a powder containing fluoropolymer particles with a reduced content of fluorine-containing compounds having hydrophilic groups.

[0009] Before specifically describing the present disclosure, some terms used in the present disclosure will be defined or explained.

[0010] In the present disclosure, fluororesins are partially crystalline fluoropolymers, or fluoroplastics. Fluororesins have a melting point and are thermoplastic, but may be melt-processable or non-melt-processable.

[0011] In the present disclosure, melt-processable means that the polymer can be melted and processed using conventional processing equipment such as an extruder, an injection molding machine, etc. Therefore, melt-processable fluororesins usually have a melt flow rate of 0.01 to 500 g / 10 min, as measured by the measurement method described below.

[0012] In the present disclosure, the fluororesin (excluding polytetrafluoroethylene) is preferably a fluoropolymer having a content of tetrafluoroethylene units relative to all polymerized units of less than 99 mol%.

[0013] In the present disclosure, the content of each monomer constituting the fluoropolymer can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and X-ray fluorescence analysis depending on the type of monomer.

[0014] In the present disclosure, the term "organic group" refers to a group containing one or more carbon atoms or a group formed by removing one hydrogen atom from an organic compound. Examples of the "organic group" include an alkyl group which may have one or more substituents, an alkenyl group which may have one or more substituents, an alkynyl group which may have one or more substituents, a cycloalkyl group which may have one or more substituents, a cycloalkenyl group which may have one or more substituents, a cycloalkadienyl group which may have one or more substituents, an aryl group which may have one or more substituents, an aralkyl group which may have one or more substituents, a non-aromatic heterocyclic group which may have one or more substituents, a heteroaryl group which may have one or more substituents, a cyano group, a formyl group, RaO-, RaCO-, and RaSO. ２ -, RaCOO-, RaNRaCO-, RaCONRa-, RaOCO-, RaOSO ２ -, and RaNRbSO ２ - (In these formulas, Ra is independently an alkyl group which may have one or more substituents, an alkenyl group which may have one or more substituents, an alkynyl group which may have one or more substituents, a cycloalkyl group which may have one or more substituents, a cycloalkenyl group which may have one or more substituents, a cycloalkadienyl group which may have one or more substituents, an aryl group which may have one or more substituents, an aralkyl group which may have one or more substituents, a non-aromatic heterocyclic group which may have one or more substituents, or a heteroaryl group which may have one or more substituents; and Rb is independently H or an alkyl group which may have one or more substituents). As the organic group, an alkyl group which may have one or more substituents is preferred.

[0015] In the present disclosure, the term "substituent" refers to a substitutable group. Examples of the "substituent" include an aliphatic group, an aromatic group, a heterocyclic group, an acyl group, an acyloxy group, an acylamino group, an aliphatic oxy group, an aromatic oxy group, a heterocyclic oxy group, an aliphatic oxycarbonyl group, an aromatic oxycarbonyl group, a heterocyclic oxycarbonyl group, a carbamoyl group, an aliphatic sulfonyl group, an aromatic sulfonyl group, a heterocyclic sulfonyl group, an aliphatic sulfonyloxy group, an aromatic sulfonyloxy group, a heterocyclic sulfonyloxy group, a sulfamoyl group, an aliphatic sulfonamido group, an aromatic sulfonamido group, a heterocyclic sulfonamido group, an amino group, and an aliphatic amino group. groups, aromatic amino groups, heterocyclic amino groups, aliphatic oxycarbonylamino groups, aromatic oxycarbonylamino groups, heterocyclic oxycarbonylamino groups, aliphatic sulfinyl groups, aromatic sulfinyl groups, aliphatic thio groups, aromatic thio groups, hydroxy groups, cyano groups, sulfo groups, carboxy groups, aliphatic oxyamino groups, aromatic oxyamino groups, carbamoylamino groups, sulfamoylamino groups, halogen atoms, sulfamoylcarbamoyl groups, carbamoylsulfamoyl groups, dialiphatic oxyphosphinyl groups, and diaromatic oxyphosphinyl groups.

[0016] The aliphatic group may be saturated or unsaturated and may have a hydroxy group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aliphatic group include alkyl groups having a total of 1 to 8, preferably 1 to 4, carbon atoms, such as a methyl group, an ethyl group, a vinyl group, a cyclohexyl group, and a carbamoylmethyl group.

[0017] The aromatic group may have, for example, a nitro group, a halogen atom, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aromatic group include aryl groups having 6 to 12 carbon atoms, preferably 6 to 10 carbon atoms in total, such as a phenyl group, a 4-nitrophenyl group, a 4-acetylaminophenyl group, and a 4-methanesulfonylphenyl group.

[0018] The heterocyclic group may have a halogen atom, a hydroxy group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the heterocyclic group include 5- or 6-membered heterocycles having a total of 2 to 12, preferably 2 to 10, carbon atoms, such as a 2-tetrahydrofuryl group and a 2-pyrimidyl group.

[0019] The acyl group may have an aliphatic carbonyl group, an arylcarbonyl group, a heterocyclic carbonyl group, a hydroxy group, a halogen atom, an aromatic group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the acyl group include acyl groups having a total of 2 to 8, preferably 2 to 4, carbon atoms, such as an acetyl group, a propanoyl group, a benzoyl group, and a 3-pyridinecarbonyl group.

[0020] The acylamino group may have an aliphatic group, an aromatic group, a heterocyclic group, etc., such as an acetylamino group, a benzoylamino group, a 2-pyridinecarbonylamino group, a propanoylamino group, etc. Examples of the acylamino group include acylamino groups having a total of 2 to 12 carbon atoms, preferably 2 to 8 carbon atoms, and alkylcarbonylamino groups having a total of 2 to 8 carbon atoms, such as an acetylamino group, a benzoylamino group, a 2-pyridinecarbonylamino group, a propanoylamino group, etc.

[0021] The aliphatic oxycarbonyl group may be saturated or unsaturated and may have a hydroxy group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aliphatic oxycarbonyl group include alkoxycarbonyl groups having a total of 2 to 8, preferably 2 to 4, carbon atoms, such as a methoxycarbonyl group, an ethoxycarbonyl group, and a (t)-butoxycarbonyl group.

[0022] The carbamoyl group may have an aliphatic group, an aromatic group, a heterocyclic group, etc. Examples of the carbamoyl group include an unsubstituted carbamoyl group, an alkylcarbamoyl group having a total of 2 to 9 carbon atoms, preferably an unsubstituted carbamoyl group, or an alkylcarbamoyl group having a total of 2 to 5 carbon atoms, such as an N-methylcarbamoyl group, an N,N-dimethylcarbamoyl group, or an N-phenylcarbamoyl group.

[0023] The aliphatic sulfonyl group may be saturated or unsaturated and may have a hydroxy group, an aromatic group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aliphatic sulfonyl group include alkylsulfonyl groups having a total of 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms, such as a methanesulfonyl group.

[0024] The aromatic sulfonyl group may have a hydroxy group, an aliphatic group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aromatic sulfonyl group include arylsulfonyl groups having a total of 6 to 10 carbon atoms, such as a benzenesulfonyl group.

[0025] The amino group may have an aliphatic group, an aromatic group, a heterocyclic group, or the like.

[0026] The acylamino group may have, for example, an acetylamino group, a benzoylamino group, a 2-pyridinecarbonylamino group, a propanoylamino group, etc. Examples of the acylamino group include acylamino groups having a total of 2 to 12 carbon atoms, preferably 2 to 8 carbon atoms, and more preferably alkylcarbonylamino groups having a total of 2 to 8 carbon atoms, such as an acetylamino group, a benzoylamino group, a 2-pyridinecarbonylamino group, a propanoylamino group, etc.

[0027] The aliphatic sulfonamide group, aromatic sulfonamide group, and heterocyclic sulfonamide group may be, for example, a methanesulfonamide group, a benzenesulfonamide group, or a 2-pyridinesulfonamide group.

[0028] The sulfamoyl group may have an aliphatic group, an aromatic group, a heterocyclic group, etc. Examples of the sulfamoyl group include a sulfamoyl group, an alkylsulfamoyl group having 1 to 9 carbon atoms in total, a dialkylsulfamoyl group having 2 to 10 carbon atoms in total, an arylsulfamoyl group having 7 to 13 carbon atoms in total, and a heterocyclic sulfamoyl group having 2 to 12 carbon atoms in total, more preferably a sulfamoyl group, an alkylsulfamoyl group having 1 to 7 carbon atoms in total, a dialkylsulfamoyl group having 3 to 6 carbon atoms in total, an arylsulfamoyl group having 6 to 11 carbon atoms in total, and a heterocyclic sulfamoyl group having 2 to 10 carbon atoms in total, such as a sulfamoyl group, a methylsulfamoyl group, an N,N-dimethylsulfamoyl group, a phenylsulfamoyl group, and a 4-pyridine sulfamoyl group.

[0029] The aliphatic oxy group may be saturated or unsaturated and may have a methoxy group, an ethoxy group, an i-propyloxy group, a cyclohexyloxy group, a methoxyethoxy group, etc. Examples of the aliphatic oxy group include alkoxy groups having a total of 1 to 8, preferably 1 to 6, carbon atoms, such as a methoxy group, an ethoxy group, an i-propyloxy group, a cyclohexyloxy group, and a methoxyethoxy group.

[0030] The aromatic amino group and heterocyclic amino group may have an aliphatic group, an aliphatic oxy group, a halogen atom, a carbamoyl group, a heterocyclic group fused with the aryl group, or an aliphatic oxycarbonyl group, preferably an aliphatic group having 1 to 4 carbon atoms in total, an aliphatic oxy group having 1 to 4 carbon atoms in total, a halogen atom, a carbamoyl group having 1 to 4 carbon atoms in total, a nitro group, or an aliphatic oxycarbonyl group having 2 to 4 carbon atoms in total.

[0031] The aliphatic thio group may be saturated or unsaturated and includes alkylthio groups having a total of 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms, such as a methylthio group, an ethylthio group, a carbamoylmethylthio group, and a t-butylthio group.

[0032] The carbamoylamino group may have an aliphatic group, an aryl group, a heterocyclic group, etc. Examples of the carbamoylamino group include a carbamoylamino group, an alkylcarbamoylamino group having a total of 2 to 9 carbon atoms, a dialkylcarbamoylamino group having a total of 3 to 10 carbon atoms, an arylcarbamoylamino group having a total of 7 to 13 carbon atoms, and a heterocyclic carbamoylamino group having a total of 3 to 12 carbon atoms, preferably a carbamoylamino group, an alkylcarbamoylamino group having a total of 2 to 7 carbon atoms, a dialkylcarbamoylamino group having a total of 3 to 6 carbon atoms, an arylcarbamoylamino group having a total of 7 to 11 carbon atoms, and a heterocyclic carbamoylamino group having a total of 3 to 10 carbon atoms, such as a carbamoylamino group, a methylcarbamoylamino group, an N,N-dimethylcarbamoylamino group, a phenylcarbamoylamino group, and a 4-pyridinecarbamoylamino group.

[0033] In this disclosure, ranges expressed by endpoints include all numbers subsumed within that range (eg, 1 to 10 includes 1.4, 1.9, 2.33, 5.75, 9.98, etc.).

[0034] In this disclosure, the term "at least 1" includes all numbers greater than or equal to 1 (e.g., at least 2, at least 4, at least 6, at least 8, at least 10, at least 25, at least 50, at least 100, etc.).

[0035] Specific embodiments of the present disclosure will be described in detail below, but the present disclosure is not limited to the following embodiments.

[0036] The present disclosure relates to a powder containing fluoropolymer particles, which contains a fluorine-containing compound having a hydrophilic group, the content of the fluorine-containing compound having a hydrophilic group being 250 mass ppb or less relative to the powder, and the fluoropolymer being at least one selected from the group consisting of a tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer, a tetrafluoroethylene / hexafluoropropylene copolymer, and a tetrafluoroethylene / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymer.

[0037] Fluoropolymers are produced by emulsion polymerization of a fluorine-containing monomer or a fluorine-containing monomer and an olefin in an aqueous medium containing a fluorine-containing emulsifier, as described in Patent Document 3, for example. Example 1 of Patent Document 3 also describes that the aqueous emulsion obtained by emulsion polymerization is frozen to precipitate a copolymer, which is then dried at 150° C. for 12 hours to obtain a tetrafluoroethylene / perfluoro(propyl vinyl ether) copolymer. The copolymer powder thus obtained contains the fluorine-containing emulsifier used in the polymerization.

[0038] Such fluorine-containing compounds having a hydrophilic group, such as fluorine-containing emulsifiers, are unnecessary compounds when the copolymer is used for various applications, and therefore it is preferable to remove them from the copolymer.

[0039] The powder of the present disclosure contains a fluorine-containing compound having a hydrophilic group, but the content of the fluorine-containing compound is reduced to 250 mass ppb or less relative to the powder. Therefore, for example, when a molded body or a coating film is obtained using the powder of the present disclosure, the obtained molded body or coating film fully exhibits the excellent properties of the fluoropolymer constituting the molded body, i.e., tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer, tetrafluoroethylene / hexafluoropropylene copolymer, or tetrafluoroethylene / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymer.

[0040] In one embodiment, there is provided a powder containing fluoropolymer particles, which contains a fluorine-containing compound having a hydrophilic group, wherein the content of the fluorine-containing compound having a hydrophilic group is 250 mass ppb or less relative to the powder, the fluoropolymer particles have an average secondary particle diameter of 0.5 to 10 μm, and the fluoropolymer is at least one selected from the group consisting of a tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer, a tetrafluoroethylene / hexafluoropropylene copolymer, and a tetrafluoroethylene / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymer (sometimes referred to as a "first powder" in the present disclosure).

[0041] The first powder has a reduced content of the fluorine-containing compound having a hydrophilic group and an average secondary particle diameter of 0.5 to 10 μm, and therefore is easy to handle and mold. Furthermore, by powder coating using the powder of the present disclosure, it is easy to form a coating film.

[0042] In one embodiment, a powder containing fluoropolymer particles is provided, the powder containing a fluorine-containing compound having a hydrophilic group, the content of the fluorine-containing compound having a hydrophilic group being 250 ppb by mass or less relative to the powder, the fluoropolymer being at least one selected from the group consisting of tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer, tetrafluoroethylene / hexafluoropropylene copolymer, and tetrafluoroethylene / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymer, and a raw powder containing the fluoropolymer is densified using a roll under conditions that result in a specific gravity of 90% or more of the true specific gravity, pulverized, and then air-classified to remove fine particles in the range of 3 to 40% by mass of the entire particle size distribution of the pulverized product, and further to remove coarse particles in the range of 1 to 20% by mass of the entire particle size distribution of the pulverized product by classification (sometimes referred to as a "second powder" in the present disclosure).

[0043] The second powder has a reduced content of fluorine-containing compounds having hydrophilic groups, and is obtained by densifying and pulverizing a raw powder containing a fluoropolymer using a roll under conditions that result in a specific gravity of 90% or more of the true specific gravity, followed by air classification to remove fine particles in the range of 3 to 40% by mass of the entire particle size distribution of the pulverized product, and then further removing coarse particles in the range of 1 to 20% by mass of the entire particle size distribution of the pulverized product by classification, and therefore has a uniform particle shape, a narrow particle size distribution, and excellent fluidity. Powder coating using the second powder also makes it easy to form a thin coating film with a uniform surface.

[0044] Next, the powder and the method for producing the powder according to the present disclosure will be described in detail.

[0045] 1. Powder (First Powder) The first powder of the present disclosure is a powder containing fluoropolymer particles, and the average secondary particle size of the fluoropolymer particles is 0.5 to 10 μm. In the present disclosure, the powder is an aggregate of fluoropolymer particles. When a fluoropolymer is produced by emulsion polymerization, the fluoropolymer particles are secondary particles formed by agglomeration of primary particles obtained by polymerization. Emulsion polymerization of a fluoromonomer usually produces an aqueous dispersion in which primary particles of the fluoropolymer are dispersed in an aqueous medium. The fluoropolymer particles are formed by agglomerating the primary particles in the aqueous dispersion. The formed aggregates are collected and dried to obtain a powder (aggregate) of fluoropolymer particles.

[0046] The fluoropolymer particles constituting the first powder of the present disclosure have an average secondary particle size of 0.5 to 10 μm. This average secondary particle size is different from the average particle size of the primary particles dispersed in the aqueous dispersion (average primary particle size), and is the average particle size of the secondary particles formed by aggregation of the primary particles.

[0047] The average secondary particle size of the fluoropolymer particles contained in the first powder is 0.5 to 10 μm, preferably 1 μm or more, preferably 5 μm or less, and more preferably 3 μm or less. When the average secondary particle size of the fluoropolymer particles is within the above range, a coating film with a uniform thickness can be easily obtained without impairing handleability.

[0048] The average secondary particle diameter of the fluoropolymer particles contained in the first powder can be adjusted, for example, by polymerizing a fluoromonomer in the presence of a fluorine-containing surfactant, a polymerization initiator and an aqueous medium to prepare primary particles of the fluoropolymer, and then coagulating the primary particles of the fluoropolymer obtained by polymerization, and drying them at an appropriate temperature.The powder obtained in this way is not formed by the fusion of fluoropolymer particles (secondary particles), but by the simple aggregation of fluoropolymer particles.Therefore, the average secondary particle diameter of the fluoropolymer particles in the powder can be set within the above range.

[0049] The average secondary particle size of the fluoropolymer particles is the volume-based average particle size (50% cumulative particle size) d50, which can be determined by laser diffraction.

[0050] The average primary particle size of the fluoropolymer particles contained in the first powder is preferably less than 0.5 μm, and preferably 0.01 μm or more. The average primary particle size of the fluoropolymer particles can be measured by dynamic light scattering. First, an aqueous fluoropolymer dispersion is prepared in which the polymer solids concentration is adjusted to about 1.0 mass%, and the average primary particle size can be measured using dynamic light scattering at a measurement temperature of 25°C, a refractive index of the solvent (water) of 1.3328, a viscosity of the solvent (water) of 0.8878 mPa·s, and an accumulation number of 70. For example, an ELSZ-1000S (manufactured by Otsuka Electronics Co., Ltd.) can be used for the dynamic light scattering method.

[0051] The specific surface area of ​​the first powder is preferably 8 m ２ / g or more, and more preferably 10m ２ / g or more, preferably 100m ２ / g or less, more preferably 50m ２ When the specific surface area of ​​the powder is within the above range, a smooth coating film with excellent appearance can be obtained more easily.

[0052] The specific surface area of ​​the powder containing the fluoropolymer particles contained in the first powder can be adjusted, for example, by polymerizing a fluoromonomer in the presence of a fluorine-containing surfactant, a polymerization initiator, and an aqueous medium to prepare primary particles of the fluoropolymer, coagulating the primary particles of the fluoropolymer obtained by polymerization, and drying them at an appropriate temperature.The primary particles obtained in this way have a relatively small specific surface area.Furthermore, the fluoropolymer particles (secondary particles) constituting the powder obtained in this way are not formed by the fusion of the primary particles of the fluoropolymer, but are formed by the simple aggregation of the primary particles of the fluoropolymer.Therefore, the specific surface area of ​​the powder can be made to reflect the specific surface area of ​​the primary particles of the fluoropolymer, and a relatively large specific surface area can be obtained.

[0053] The specific surface area of ​​the powder is a value obtained by measurement using a surface analyzer according to the BET method.

[0054] (Second Powder) The second powder of the present disclosure is a powder containing fluoropolymer particles, and is obtained by a manufacturing method in which raw powder containing fluoropolymer is densified using a roll under conditions that result in a specific gravity of 90% or more of the true specific gravity, pulverized, and then air-classified to remove fine particles in the range of 3 to 40% by mass of the entire particle size distribution of the pulverized product, and further classified to remove coarse particles in the range of 1 to 20% by mass of the entire particle size distribution of the pulverized product.

[0055] The second powder is obtained by the above-mentioned manufacturing method, and therefore has a high apparent density and the fluoropolymer particles constituting the powder have a uniform shape. Furthermore, the second powder has a uniform particle shape and a narrow particle size distribution. Therefore, the second powder has excellent flowability.

[0056] The average secondary particle size of the fluoropolymer particles constituting the second powder is preferably 5 to 100 μm, more preferably 15 μm or more, even more preferably 30 μm or more, and more preferably 80 μm or less. When the average secondary particle size of the fluoropolymer particles is within the above range, a thick coating film with a uniform thickness can be easily obtained without impairing the flowability.

[0057] The apparent density of the second powder is preferably 0.60 to 1.00 g / mL. The apparent density of the powder can be measured in accordance with JIS K 6891-5.3.

[0058] (Fluorine-containing compound having a hydrophilic group) The first powder and the second powder (both of which may be referred to as "powder of the present disclosure" in the present disclosure) contain a fluorine-containing compound having a hydrophilic group. The fluorine-containing compound having a hydrophilic group includes a fluorine-containing surfactant added during polymerization and a fluorine-containing compound having a hydrophilic group produced by polymerization of a fluoromonomer.

[0059] In the present disclosure, the hydrophilic group possessed by the fluorine-containing compound is preferably an anionic group such as an acid group, for example, —NH ２ , -PO ３ M, -OPO ３ M, -SO ３ M, -OSO ３ Examples of the hydrophilic group include -M and -COOM (in each formula, M represents a cation). ３ M or -COOM is preferred, and -COOM is more preferred.

[0060] The content of the fluorine-containing compound having a hydrophilic group in the powder is 250 ppb by mass or less, preferably 100 ppb by mass or less, more preferably 50 ppb by mass or less, even more preferably 25 ppb by mass or less, still more preferably 10 ppb by mass or less, particularly preferably 5 ppb by mass or less, and preferably more than 0 ppb by mass, relative to the powder.

[0061] The content of the fluorine-containing compound having a hydrophilic group in the powder can be adjusted, for example, by polymerizing a fluoromonomer in the presence of a fluorine-containing surfactant, a polymerization initiator and an aqueous medium to prepare an aqueous dispersion containing primary particles of a fluoropolymer, and then adding a relatively large amount of a radical generator to the aqueous dispersion and subjecting it to heat treatment.

[0062] The content of the fluorine-containing compound having a hydrophilic group in the powder can be quantified by known methods. For example, it can be quantified by LC / MS analysis. First, methanol is added to the powder to perform extraction, and the resulting extract is analyzed by LC / MS. To further improve the extraction efficiency, treatments such as Soxhlet extraction and ultrasonic treatment may be performed. The resulting extract is concentrated using an appropriate nitrogen purge, and the fluorine-containing compound in the concentrated extract is measured by LC / MS. Molecular weight information is extracted from the obtained LC / MS spectrum, and a match with the structural formula of the candidate fluorine-containing compound having a hydrophilic group is confirmed. Then, aqueous solutions containing five or more levels of the confirmed fluorine-containing compound having a hydrophilic group are prepared, and LC / MS analysis is performed on each aqueous solution. The relationship between the content and the area area relative to the content is plotted, and a calibration curve is drawn. Then, using the calibration curve, the area area of ​​the LC / MS chromatogram of the fluorine-containing compound having a hydrophilic group in the extract can be converted to the content of the fluorine-containing compound having a hydrophilic group. Note that the resulting extract can be concentrated by nitrogen purging, which lowers the lower limit of quantitation of the measurement method.

[0063] In one embodiment of the powder, the fluorine-containing compound having a hydrophilic group contains at least a fluorine-containing surfactant. The fluorine-containing surfactant may be a fluorine-containing surfactant that is commonly used in the polymerization of a fluoromonomer. Typical compounds of the fluorine-containing surfactant are fluorine-containing surfactants having a molecular weight of 1000 g / mol or less, preferably 800 g / mol or less.

[0064] The fluorine-containing surfactant is not particularly limited as long as it is a surfactant containing at least one fluorine atom, and any conventionally known fluorine-containing surfactant can be used.

[0065] Examples of the fluorine-containing surfactant include anionic fluorine-containing surfactants, etc. The anionic fluorine-containing surfactant may be, for example, a surfactant containing fluorine atoms and having a total carbon number of 20 or less excluding the anionic group.

[0066] The fluorine-containing surfactant may also be a surfactant containing fluorine, the molecular weight of the anionic moiety of which is 1,000 or less. The "anionic moiety" means the part of the fluorine-containing surfactant excluding the cation. For example, F(CF) represented by the formula (I) below may be used. ２ ) ｎ１ In the case of COOM, "F(CF ２ ) ｎ１ This is the "COO" part.

[0067] The fluorine-containing surfactant also includes a fluorine-containing surfactant having a Log POW of 3.5 or less. The Log POW is the partition coefficient between 1-octanol and water, and is expressed as Log P [where P represents the ratio of the fluorine-containing surfactant concentration in octanol to the fluorine-containing surfactant concentration in water when a 1:1 octanol / water mixture containing the fluorine-containing surfactant undergoes phase separation]. The Log POW can be measured using a column: TOSOH ODS-120T column (φ4.6 mm×250 mm, manufactured by Tosoh Corporation), an eluent: acetonitrile / 0.6% by mass HClO ４ HPLC is performed on standard substances (heptanoic acid, octanoic acid, nonanoic acid, and decanoic acid) with known octanol / water partition coefficients under conditions of water=1 / 1 (vol / vol %), flow rate: 1.0 ml / min, sample amount: 300 μL, column temperature: 40°C, and detection light: UV 210 nm. A calibration curve is prepared between each elution time and the known octanol / water partition coefficient, and the elution time is calculated from the HPLC elution time of the sample solution based on this calibration curve.

[0068] Specific examples of the fluorine-containing surfactants include those described in U.S. Patent Application Publication Nos. 2007 / 0015864, 2007 / 0015865, 2007 / 0015866, 2007 / 0276103, 2007 / 0117914, 2007 / 142541, 2008 / 0015319, and U.S. Pat. No. 3,250,808. , U.S. Patent No. 3,271,341, JP 2003-119204 A, WO 2005 / 042593, WO 2008 / 060461, WO 2007 / 046377, JP 2007-119526 A, WO 2007 / 046482, WO 2007 / 046345, U.S. Patent Application Publication No. 2014 / 0228531, WO 2013 / 189824, and those described in WO 2013 / 189826, and the like.

[0069] The anionic fluorine-containing surfactant may be a compound represented by the following general formula (N ０ ): X ｎ０ -Rf ｎ０ -Y ０ (N ０ ) (wherein, X ｎ０ is H, Cl or F. ｎ０ is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which some or all of the H atoms are substituted with F, and the alkylene group may contain one or more ether bonds, and some of the H atoms may be substituted with Cl. ０ is an anionic group. ０ The anionic group is -COOM, -SO ２ M or -SO ３ M, -COOM or -SO ３ M. M may be H, a metal atom, NR ７ ４ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium, and R ７is H or an organic group. The metal atom includes alkali metals (Group 1), alkaline earth metals (Group 2), etc., such as Na, K, or Li. ７ As the group, H or C １－１０ and may be an organic group of the formula: １－４ and may be an organic group of the formula: １－４ M may be H, a metal atom, or an alkyl group of the formula NR ７ ４ may be H, an alkali metal (Group 1), an alkaline earth metal (Group 2), or NR ７ ４ may be H, Na, K, Li or NH ４ The above Rf ｎ０ may be one in which 50% or more of H is substituted with fluorine.

[0070] The general formula (N ０ The compound represented by the following general formula (N １ ): X ｎ０ -(CF ２ ) ｍ１ -Y ０ (N １ ) (wherein, X ｎ０ is H, Cl, and F, m1 is an integer from 3 to 15, and Y ０ is as defined above), a compound represented by the following general formula (N ２ ): Rf ｎ１ -O-(CF(CF ３ )CF ２ O) ｍ２ CFX ｎ１ -Y ０ (N ２ ) (wherein, Rf ｎ１ is a perfluoroalkyl group having 1 to 5 carbon atoms, m2 is an integer of 0 to 3, and X ｎ１ is F or CF ３ and Y ０ is as defined above), a compound represented by the following general formula (N ３ ): Rf ｎ２ (CH ２ ) ｍ３ -(Rf ｎ３ ) ｑ-Y ０ (N ３ ) (wherein, Rf ｎ２ is a partially or fully fluorinated alkyl group having 1 to 13 carbon atoms, which may contain an ether bond and / or a chlorine atom, m3 is an integer of 1 to 3, and Rf ｎ３ is a linear or branched perfluoroalkylene group having 1 to 3 carbon atoms, q is 0 or 1, and Y ０ is as defined above), a compound represented by the following general formula (N ４ ): Rf ｎ４ -O-(CY ｎ１ Y ｎ２ ) ｐ CF ２ -Y ０ (N ４ ) (wherein, Rf ｎ４ is a linear or branched partially or fully fluorinated alkyl group having 1 to 12 carbon atoms, which may contain an ether bond; Y ｎ１ and Y ｎ２ are the same or different and are H or F, p is 0 or 1, and Y ０ is as defined above.) and a compound represented by the general formula (N ５ ): (In the formula, X ｎ２ , X ｎ３ and X ｎ４ Rf may be the same or different and are H, F, or a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms, which may contain an ether linkage. ｎ５ is a linear or branched partially or fully fluorinated alkylene group having 1 to 3 carbon atoms, which may contain an ether bond; L is a linking group; Y ０ is as defined above, where X ｎ２ , X ｎ３ , X ｎ４ and Rf ｎ５ wherein the total number of carbon atoms is 18 or less.

[0071] The general formula (N ０) More specifically, the compounds represented by the formula (I) below include perfluorocarboxylic acids (I), ω-H perfluorocarboxylic acids (II), perfluoroether carboxylic acids (III), perfluoroalkyl alkylene carboxylic acids (IV), perfluoroalkoxy fluorocarboxylic acids (V), perfluoroalkyl sulfonic acids (VI), ω-H perfluoro sulfonic acids (VII), perfluoroalkyl alkylene sulfonic acids (VIII), alkyl alkylene carboxylic acids (IX), fluorocarboxylic acids (X), alkoxy fluorosulfonic acids (XI), alkoxy fluorosulfonic acids (XI), and the like.

[0072] The perfluorocarboxylic acid (I) is represented by the following general formula (I): F(CF ２ ) ｎ１ COOM (I) (wherein n1 is an integer of 3 to 13, and M is H, a metal atom, NR ７ ４ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium, and R ７ is H or an organic group.

[0073] The ω-H perfluorocarboxylic acid (II) is represented by the following general formula (II): H(CF ２ ) ｎ２ COOM (II) (wherein n2 is an integer of 4 to 15, and M is as defined above).

[0074] The perfluoroethercarboxylic acid (III) is a compound represented by the following general formula (III): １ -O-(CF(CF ３ )CF ２ O) ｎ３CF (CF ３ ) COOM (III) (wherein, Rf １ is a perfluoroalkyl group having 1 to 5 carbon atoms, n3 is an integer of 0 to 3, and M is as defined above.

[0075] The perfluoroalkyl alkylene carboxylic acid (IV) is represented by the following general formula (IV): ２ (CH ２ ) ｎ４ Rf ３ COOM (IV) (wherein, Rf ２ is a perfluoroalkyl group having 1 to 5 carbon atoms, and Rf ３ is a linear or branched perfluoroalkylene group having 1 to 3 carbon atoms, n4 is an integer of 1 to 3, and M is as defined above.

[0076] The alkoxyfluorocarboxylic acid (V) is represented by the following general formula (V): Rf ４ -O-CY １ Y ２ CF ２ -COOM (V) (wherein, Rf ４ is a linear or branched partially or fully fluorinated alkyl group having 1 to 12 carbon atoms, which may contain ether bonds and / or chlorine atoms; Y １ and Y ２ are the same or different and are H or F, and M is as defined above.

[0077] The perfluoroalkylsulfonic acid (VI) is represented by the following general formula (VI): F(CF ２ ) ｎ５ SO ３ M (VI) (wherein n5 is an integer of 3 to 14, and M is as defined above).

[0078] The ω-H perfluorosulfonic acid (VII) is represented by the following general formula (VII): H(CF ２ ) ｎ６ SO ３M (VII) (wherein n6 is an integer of 4 to 14, and M is as defined above).

[0079] The perfluoroalkyl alkylene sulfonic acid (VIII) is a compound represented by the following general formula (VIII): ５ (CH ２ ) ｎ７ SO ３ M (VIII) (wherein, Rf ５ is a perfluoroalkyl group having 1 to 13 carbon atoms, n7 is an integer of 1 to 3, and M is as defined above.

[0080] The alkyl alkylene carboxylic acid (IX) is represented by the following general formula (IX): ６ (CH ２ ) ｎ８ COOM (IX) (wherein, Rf ６ is a linear or branched partially or fully fluorinated alkyl group having 1 to 13 carbon atoms which may contain an ether bond, n8 is an integer from 1 to 3, and M is as defined above.

[0081] The fluorocarboxylic acid (X) is represented by the following general formula (X): ７ -O-Rf ８ -O-CF ２ -COOM (X) (wherein, Rf ７ is a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms, which may contain an ether bond and / or a chlorine atom, and Rf ８ is a linear or branched, partially or fully fluorinated alkyl group having 1 to 6 carbon atoms, and M is as defined above.

[0082] The alkoxyfluorosulfonic acid (XI) is represented by the following general formula (XI): Rf ９ -O-CY １ Y ２ CF ２ -SO ３ M (XI) (wherein, Rf ９is a linear or branched alkyl group having 1 to 12 carbon atoms, which may contain an ether bond, and which may contain chlorine, and which is partially or completely fluorinated; Y １ and Y ２ are the same or different and are H or F, and M is as defined above.

[0083] The compound (XII) is represented by the following general formula (XII): (In the formula, X １ , X ２ and X ３ Rf may be the same or different and are H, F and linear or branched partially or fully fluorinated alkyl groups having 1 to 6 carbon atoms, which may contain ether bonds; １０ is a perfluoroalkylene group having 1 to 3 carbon atoms, L is a linking group, and Y ０ is an anionic group. ０ is -COOM, -SO ２ M or -SO ３ M, and -SO ３ M or COOM (wherein M is as defined above). Examples of L include a single bond, a partially or fully fluorinated alkylene group having 1 to 10 carbon atoms which may contain an ether bond.

[0084] The compound (XIII) has the following general formula (XIII): １１ -O-(CF ２ CF (CF ３ ) O) ｎ９ (CF ２ O) ｎ１０ CF ２ COOM (XIII) (wherein, Rf １１ is a fluoroalkyl group containing chlorine and having 1 to 5 carbon atoms, n9 is an integer of 0 to 3, n10 is an integer of 0 to 3, and M is as defined above. ２ ClO(CF ２ CF (CF ３ ) O) ｎ９ (CF ２ O) ｎ１０CF ２ COONH ４ (a mixture having an average molecular weight of 750, wherein n9 and n10 are defined above).

[0085] As mentioned above, examples of the anionic fluorine-containing surfactant include carboxylic acid surfactants and sulfonic acid surfactants.

[0086] The fluorine-containing surfactant may be one type of fluorine-containing surfactant or a mixture containing two or more types of fluorine-containing surfactants.

[0087] The fluorine-containing surfactant preferably has a methylene group (—CH ２ -), and more preferably, does not have a C-H bond. ２ By using a fluorine-containing surfactant having no - or C--H bond, the polymerization of the fluoromonomer can be smoothly carried out in the presence of an aqueous medium.

[0088] The number of H atoms in the hydrophobic group of the fluorine-containing surfactant is preferably 0 or 1, more preferably 0. By using a fluorine-containing surfactant having a small number of H atoms bonded to the carbon atoms constituting the hydrophobic group, the polymerization of the fluoromonomer can be smoothly carried out in the presence of an aqueous medium. The number of carbon atoms in the hydrophobic group of the fluorine-containing surfactant having a hydrophobic group and a hydrophilic group is preferably 1 to 50, more preferably 3 to 20, and even more preferably 6 to 12. The hydrophobic group usually constitutes the above-mentioned "portion excluding the anionic group" of the molecular structure of the fluorine-containing surfactant. As the hydrophilic group, Y ０ Examples of the anionic group include the groups exemplified above for the anionic group of the formula (I). The fluorine-containing surfactant may be a saturated fluorinated surfactant in which all of the carbon atoms bonded to the hydrophobic group have been substituted with fluorine atoms.

[0089] As the fluorine-containing surfactant, among the above-mentioned anionic fluorine-containing surfactants, those represented by the general formula (N １ ), a compound represented by the general formula (N ２ ), a compound represented by the general formula (N ４ ): Rf ｎ４ -O-(CY ｎ１F) ｐ CF ２ -Y ０ (N ４ ) (wherein, Rf ｎ４ is a linear or branched or fully fluorinated alkyl group having 1 to 12 carbon atoms, which may contain an ether linkage (provided that -CH ２ -), and Y ｎ１ is H or F, p is 0 or 1, and Y ０ is as defined above.) and a compound represented by the general formula (N ５ ): (In the formula, X ｎ２ , X ｎ３ and X ｎ４ may be the same or different and are H, F, or a linear or branched alkyl group having 1 to 6 carbon atoms, which may contain an ether bond, or a fully fluorinated alkyl group (provided that -CH ２ -), except that X ｎ３ and X ｎ４ Both of Rf cannot be H. ｎ５ is a linear or branched or fully fluorinated alkylene group having 1 to 3 carbon atoms, which may contain an ether bond (provided that -CH ２ -), L is a linking group, and Y ０ is as defined above, where X ｎ２ , X ｎ３ , X ｎ４ and Rf ｎ５ wherein the total number of carbon atoms is 18 or less.

[0090] As the fluorine-containing surfactant, among the above-mentioned anionic fluorine-containing surfactants, perfluorocarboxylic acid (I) represented by general formula (I), ω-H perfluorocarboxylic acid (II) represented by general formula (II), perfluoroether carboxylic acid (III) represented by general formula (III), perfluoroalkyl alkylene carboxylic acid (IV) represented by general formula (IV), perfluoroalkoxy fluorocarboxylic acid (V) represented by general formula (V), perfluoroalkyl sulfonic acid (VI) represented by general formula (VII), ω-H perfluoro sulfonic acid (VII) represented by general formula (VII), perfluoroalkyl alkylene sulfonic acid (VIII) represented by general formula (VIII), general formula (X): Rf ７ -O-Rf ８ -O-CF ２ -COOM (wherein, Rf ７ is a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms, which may contain ether bonds and / or chlorine atoms (provided that -CH ２ -), and Rf ８ is a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms (provided that -CH ２ Fluorocarboxylic acid (X) represented by general formula (XI): Rf ９ -O-CY １ FCF ２ -SO ３ M (wherein, Rf ９ is a linear or branched alkyl group having 1 to 12 carbon atoms, which may contain an ether bond, and which may contain chlorine, and which is partially or completely fluorinated (provided that -CH ２ -), and Y １ is H or F, and M is as defined above.) an alkoxyfluorosulfonic acid (XI) represented by the general formula (XII): (In the formula, X １ , X ２ and X ３may be the same or different and are H, F and straight or branched chain alkyl groups having 1 to 6 carbon atoms which may contain ether bonds or fully fluorinated alkyl groups (provided that -CH ２ -), except that X ２ and X ３ Both of Rf １０ is a perfluoroalkylene group having 1 to 3 carbon atoms, L is a linking group, and Y ０ is an anionic group.) and a compound (XII) represented by the general formula (XIII): Rf １１ -O-(CF ２ CF (CF ３ ) O) ｎ９ (CF ２ O) ｎ１０ CF ２ COOM (where Rf １１ represents a fluoroalkyl group having 1 to 5 carbon atoms and containing chlorine (wherein -CH ２ n9 is an integer of 0 to 3, n10 is an integer of 0 to 3, and M is as defined above. The use of these fluorine-containing surfactants allows the polymerization of fluoromonomers to proceed smoothly in the presence of an aqueous medium.

[0091] Examples of the fluorine-containing surfactant include compounds represented by the following formula: F(CF ２ ) ７ COOM, F(CF ２ ) ５ COOM, H(CF ２ ) ６ COOM, H(CF ２ ) ７ COOM, C.F. ３ O (CF ２ ) ３ OCHFCF ２ COOM, C. ３ F ７ OCF (CF ３ )CF ２ OCF (CF ３ ) COOM, C.F.３ CF ２ CF ２ OCF (CF ３ ) COOM, C.F. ３ CF ２ OCF ２ CF ２ OCF ２ COOM, C. ２ F ５ OCF (CF ３ )CF ２ OCF (CF ３ ) COOM, C.F. ３ OCF (CF ３ )CF ２ OCF (CF ３ ) COOM, C.F. ２ ClCF ２ CF ２ OCF (CF ３ )CF ２ OCF ２ COOM, C.F. ２ ClCF ２ CF ２ OCF ２ CF (CF ３ ) OCF ２ COOM, C.F. ２ ClCF(CF ３ ) OCF (CF ３ )CF ２ OCF ２ COOM, C.F. ２ ClCF(CF ３ ) OCF ２ CF (CF ３ ) OCF ２ COOM, (In each formula, M is H, metal atom, NR ７ ４ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium. ７ is H or an organic group.

[0092] When the powder contains at least a fluorine-containing surfactant as the fluorine-containing compound having a hydrophilic group, the content of the fluorine-containing surfactant in the powder is preferably 250 ppb by mass or less, more preferably 100 ppb by mass or less, even more preferably 50 ppb by mass or less, still more preferably 25 ppb by mass or less, and preferably more than 0 ppb by mass, relative to the powder.

[0093] In one embodiment of the powder, the fluorine-containing compound having a hydrophilic group contains a perfluoroethercarboxylic acid. The perfluoroethercarboxylic acid is preferably a compound (III) represented by the following general formula (III): General formula (III): Rf １ -O-(CF(CF ３ )CF ２ O) ｎ３ CF (CF ３ ) COOM (wherein, Rf １ is a perfluoroalkyl group having 1 to 5 carbon atoms, n3 is an integer of 0 to 3, M is H, a metal atom, or NR ７ ４ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium, and R ７ is H or an organic group.

[0094] When the powder contains at least a perfluoroethercarboxylic acid as the fluorine-containing compound having a hydrophilic group, the content of the perfluoroethercarboxylic acid in the powder is preferably 250 mass ppb or less, more preferably 100 mass ppb or less, even more preferably 50 mass ppb or less, still more preferably 25 mass ppb or less, particularly preferably 10 mass ppb or less, and most preferably 5 mass ppb or less, and preferably more than 0 mass ppb, based on the powder.

[0095] In one embodiment of the powder, the powder contains a compound represented by the following general formula (H1) as the fluorine-containing compound having a hydrophilic group: － ] ｉ M ｉ＋(Wherein, X represents H, Cl, Br, F or I; Rf represents a linear or branched partially or fully fluorinated aliphatic group, or a linear or branched partially or fully fluorinated aliphatic group interrupted by at least one oxygen atom; A － is an acid group, M ｉ＋ represents a cation having a valence i, where i is an integer from 1 to 3.

[0096] In one embodiment of the powder, the powder contains a compound represented by the following general formula (H2) as the fluorine-containing compound having a hydrophilic group. ｎ－１ F ２ｎ－１ COO － ]M ＋ (wherein n is an integer of 4 to 14, M ＋ represents a cation.)

[0097] It is known that the compound represented by general formula (H2) (perfluoroalkanoic acid) is formed during polymerization when perfluoroalkyl vinyl ether or the like is used as a modified monomer (see WO 2019 / 161153).

[0098] When the powder contains at least a compound represented by general formula (H2) as a fluorine-containing compound having a hydrophilic group, the content of the compound represented by general formula (H2) in the powder is preferably 25 ppb by mass or less, more preferably 10 ppb by mass or less, even more preferably 5 ppb by mass or less, still more preferably 1 ppb by mass or less, and preferably more than 0 ppb by mass, relative to the powder.

[0099] In one embodiment of the powder, the powder contains a compound represented by the following general formula (H3) as the fluorine-containing compound having a hydrophilic group. General formula (H3): [R １ -O-L-CO ２ － ]M ＋ (In the formula, R １represents a linear or branched partially or fully fluorinated aliphatic group, or a linear or branched partially or fully fluorinated aliphatic group interrupted by at least one oxygen atom; L represents a linear or branched non-fluorinated, partially fluorinated or fully fluorinated alkylene group; M represents a linear or branched non-fluorinated, partially fluorinated or fully fluorinated alkylene group; ＋ represents a cation.)

[0100] When the powder contains at least a compound represented by general formula (H3) as a fluorine-containing compound having a hydrophilic group, the content of the compound represented by general formula (H3) in the powder is preferably 250 ppb by mass or less, more preferably 100 ppb by mass or less, even more preferably 50 ppb by mass or less, still more preferably 25 ppb by mass or less, and preferably more than 0 ppb by mass, relative to the powder.

[0101] In one embodiment of the powder, the powder contains a compound represented by general formula (H4) as the fluorine-containing compound having a hydrophilic group. General formula (H4): H-Rf ｎ０ -Y ０ (wherein, Rf ｎ０ is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which some or all of the H atoms are substituted with F, and the alkylene group may contain one or more ether bonds, and some of the H atoms may be substituted with Cl. ０ is an anionic group.)

[0102] The compound represented by general formula (H4) includes compounds represented by any of the following general formulas: General formula: [H—(CF ２ ) ｍ CO ２ － ]M ＋ (wherein m is an integer of 3 to 19, M ＋ represents a cation.) General formula: [H-(CF ２ ) ｍ２ -(CF(CF ３ )) ｍ３ -CO ２ － ]M ＋ (wherein m2 is an integer of 1 to 17, m3 is an integer of 1 to 9, M ＋represents a cation, provided that m2 and m3 are selected so as to satisfy the relationship 3≦(m2+2×m3)≦19, and the order of occurrence of each repeating unit in the formula is arbitrary.

[0103] When the powder contains at least a compound represented by general formula (H4) as a fluorine-containing compound having a hydrophilic group, the content of the compound represented by general formula (H4) in the powder is preferably 250 ppb by mass or less, more preferably 100 ppb by mass or less, even more preferably 50 ppb by mass or less, still more preferably 25 ppb by mass or less, particularly preferably 10 ppb by mass or less, and most preferably 5 ppb by mass or less, and preferably more than 0 ppb by mass, relative to the powder.

[0104] Fluoropolymer The powder of the present disclosure contains particles of at least one fluoropolymer selected from the group consisting of tetrafluoroethylene (TFE) / perfluoro(alkyl vinyl ether) copolymer, TFE / hexafluoropropylene copolymer, and TFE / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymer.

[0105] The fluoropolymer is preferably a fluororesin, more preferably a melt-processable fluororesin.

[0106] The perfluoro(alkyl vinyl ether) may be a compound represented by the general formula: CF ２ ═CF—ORf (wherein Rf represents a perfluoroalkyl group having 1 to 10 carbon atoms). When the perfluoroalkyl group has 2 or more carbon atoms, it may have an ether oxygen inserted between the two carbon atoms.

[0107] The perfluoroalkyl group preferably has 1 to 5 carbon atoms, and more preferably 1 to 3 carbon atoms.

[0108] Examples of the perfluoroalkyl group include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group.

[0109] The perfluoro(alkyl vinyl ether) is preferably at least one selected from the group consisting of perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether) and perfluoro(propyl vinyl ether), more preferably at least one selected from the group consisting of perfluoro(methyl vinyl ether) and perfluoro(propyl vinyl ether), and even more preferably perfluoro(propyl vinyl ether).

[0110] The TFE / perfluoro(alkyl vinyl ether) copolymer is a copolymer containing at least TFE units and perfluoro(alkyl vinyl ether) units. The preferred monomer composition (mol %) of the TFE / perfluoro(alkyl vinyl ether) copolymer is TFE:perfluoro(alkyl vinyl ether)=(90-99.7):(0.3-10), more preferably (97-99):(1-3).

[0111] The TFE / perfluoro(alkyl vinyl ether) copolymer may contain, in addition to TFE units and perfluoro(alkyl vinyl ether) units, other monomer units copolymerizable with TFE and perfluoro(alkyl vinyl ether). As the other monomer, fluoromonomers (excluding TFE and perfluoro(alkyl vinyl ether)) are preferred.

[0112] Fluoromonomers (excluding TFE and perfluoro(alkyl vinyl ether)) include hexafluoropropylene, chlorotrifluoroethylene, vinyl fluoride, vinylidene fluoride, trifluoroethylene, fluoroalkyl ethylene, fluoroalkyl allyl ether, trifluoropropylene, pentafluoropropylene, trifluorobutene, tetrafluoroisobutene, hexafluoroisobutene, and fluoroalkyl ethers represented by the general formula: CHX １０１ =CX １０２ Rf １０１ (In the formula, X １０１ and X １０２ is H on one side and F on the other side, and Rf １０１is a straight-chain or branched fluoroalkyl group having 1 to 12 carbon atoms), fluorinated vinyl heterocyclic compounds, and monomers that provide crosslinking sites.

[0113] Of the fluoromonomers (excluding TFE and perfluoro(alkyl vinyl ether)), hexafluoropropylene is particularly preferred.

[0114] The content of other monomer units in the TFE / perfluoro(alkyl vinyl ether) copolymer may be 0.1 to 2% by mass based on the total monomer units.

[0115] The TFE / hexafluoropropylene copolymer is a copolymer containing at least TFE units and hexafluoropropylene units. The monomer composition (mass%) of the TFE / hexafluoropropylene copolymer is preferably TFE:hexafluoropropylene=(60-95):(5-40), more preferably (85-92):(8-15).

[0116] The TFE / hexafluoropropylene copolymer may contain, in addition to TFE units and hexafluoropropylene units, other monomer units copolymerizable with TFE and hexafluoropropylene. As the other monomer, fluoromonomers (excluding TFE and hexafluoropropylene) are preferred.

[0117] Fluoromonomers (excluding TFE and hexafluoropropylene) include chlorotrifluoroethylene, vinyl fluoride, vinylidene fluoride, trifluoroethylene, perfluoro(alkyl vinyl ether), fluoroalkyl ethylene, fluoroalkyl allyl ether, trifluoropropylene, pentafluoropropylene, trifluorobutene, tetrafluoroisobutene, hexafluoroisobutene, and fluorocarbons represented by the general formula: CHX １０１ =CX １０２ Rf １０１ (In the formula, X １０１ and X １０２ is H on one side and F on the other side, and Rf １０１is a straight-chain or branched fluoroalkyl group having 1 to 12 carbon atoms), fluorinated vinyl heterocyclic compounds, and monomers that provide crosslinking sites.

[0118] Of the fluoromonomers (excluding TFE and hexafluoropropylene), perfluoro(alkyl vinyl ether) is preferred.

[0119] Among these, the fluoropolymer is preferably at least one selected from the group consisting of tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer, tetrafluoroethylene / hexafluoropropylene copolymer, and tetrafluoroethylene / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymer.

[0120] The melt flow rate of the fluoropolymer at 372° C. may be 0.1 to 500 g / 10 min, preferably 20 g / 10 min or more, more preferably 25 g / 10 min, and preferably 80 g / 10 min or less.

[0121] In the present disclosure, MFR is a value obtained in accordance with ASTM D1238 using a melt indexer, as the mass of polymer flowing out per 10 minutes from a nozzle having an inner diameter of 2.1 mm and a length of 8 mm under a load of 5 kg at 372°C (g / 10 min).

[0122] The melting point of the fluoropolymer may be 180 to 324°C. The melting point of the tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer may be 180 to 324°C, preferably 220°C or higher, more preferably 240°C or higher, even more preferably 260°C or higher, still more preferably 280°C or higher, particularly preferably 300°C or higher, preferably 320°C or lower, and more preferably 315°C or lower. The melting points of the tetrafluoroethylene / hexafluoropropylene copolymer and the tetrafluoroethylene / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymer may be 180 to 320°C, preferably 220°C or higher, more preferably 240°C or higher, and preferably 300°C or lower, more preferably 280°C or lower.

[0123] The melting point can be measured using a differential scanning calorimeter (DSC).

[0124] The fluoropolymer may have a functional group. The functional group is introduced into the fluoropolymer by, for example, a chain transfer agent or a polymerization initiator used in producing the fluoropolymer. For example, an alcohol is used as a chain transfer agent, or a —CH ２ When a peroxide having an OH structure is used, a —CH ２ Furthermore, by polymerizing a monomer having a functional group, the functional group is introduced into the side chain terminal of the fluoropolymer.

[0125] Fluoropolymer main chain carbon number 10 ６ The number of functional groups per unit is preferably more than 50. ６ The number of functional groups per unit is preferably 100 or more, more preferably 150 or more, even more preferably 200 or more, and preferably 1200 or less, more preferably 1000 or less, even more preferably 800 or less. When a fluoropolymer is subjected to a stabilization treatment such as a treatment of contacting the fluoropolymer with fluorine gas, the number of functional groups of the fluoropolymer is usually reduced, and the number of functional groups of the fluoropolymer having 10 main chain carbon atoms is reduced.６ It is not possible to obtain a fluoropolymer having a number of functional groups per unit within the above range.

[0126] Infrared spectroscopy can be used to identify the type of functional group and measure the number of functional groups.

[0127] The number of functional groups is specifically measured by the following method. First, a fluoropolymer is molded by cold pressing to produce a film with a thickness of 0.25 to 0.30 mm. This film is analyzed by Fourier transform infrared spectroscopy to obtain an infrared absorption spectrum of the fluoropolymer, and a difference spectrum is obtained from the base spectrum, which is completely fluorinated and has no functional groups. From the absorption peaks of specific functional groups that appear in this difference spectrum, the number of carbon atoms in the fluoropolymer is calculated according to the following formula (A): ６ The number of functional groups per molecule, N, is calculated.

[0128] N = I x K / t (A) I: absorbance K: correction coefficient t: film thickness (mm)

[0129] For reference, the absorption frequencies, molar absorption coefficients, and correction factors for several functional groups are shown in Table 1. The molar absorption coefficients were determined from FT-IR measurement data of low-molecular-weight model compounds.

[0130] -CH ２ CF ２ H, —CH ２ COF, -CH ２ COOH, -CH ２ COOCH ３ , -CH ２ CONH ２ The absorption frequencies of -CF are shown in the table. ２ H, -COF, -COOH free and -COOH bonded, -COOCH ３ , -CONH ２ absorption frequency from tens of Kaiser (cm －１ ) becomes lower.

[0131] For example, the number of functional groups of -COF is -CF ２ Absorption frequency due to COF: 1883 cm－１ The number of functional groups determined from the absorption peak of -CH ２ Absorption frequency due to COF: 1840 cm －１ The number of functional groups is the sum of the number of functional groups determined from the absorption peaks of the compounds.

[0132] The functional groups are those present at the ends of the main chain or side chains of the fluoropolymer, and those present in the main chain or side chains. The number of functional groups is -CF=CF ２ , -CF ２ H, -COF, -COOH, -COOCH ３ , -CONH ２ and -CH ２ It may be the total number of OH.

[0133] The powder of the present disclosure may contain other components in addition to the fluoropolymer, such as fillers, plasticizers, processing aids, mold release agents, pigments, flame retardants, lubricants, light stabilizers, weather stabilizers, conductive agents, antistatic agents, UV absorbers, antioxidants, foaming agents, fragrances, oils, softening agents, and dehydrofluorination agents.

[0134] The other component may contain a polymer other than the above-mentioned copolymer, such as a fluororesin other than the above-mentioned fluoropolymer, a fluororubber, or a non-fluorinated polymer.

[0135] The powder of the present disclosure can be suitably used as a powder coating. The powder coating is usually applied to an object to be coated, and then heated and baked to form a film. The coating film obtained in this manner can be used for various purposes, such as a corrosion-resistant lining.

[0136] The method for applying the powder coating is not particularly limited, and examples thereof include spraying, electrostatic spraying, electrostatic spray coating, fluidized bed dip coating, electrostatic fluidized bed dip coating, and roto-lining.

[0137] A coating film formed from a powder paint is usually formed by applying the powder paint to an object to be coated, followed by heating and baking to form a film. The temperature at which the powder paint applied to the object to be coated is heated and baked is, for example, 295 to 400°C. The heating and baking time is, for example, 20 to 180 minutes. When the powder paint is applied and baked multiple times, the heating and baking time indicates the time for one baking session.

[0138] The thickness of the coating film formed from the powder coating material may be appropriately determined depending on the application, and may be, for example, 20 to 10,000 μm. The thickness is the thickness after heating and baking, and may be the thickness of the coating film obtained by one application or two or more applications.

[0139] The object to be coated is not particularly limited, and examples thereof include those to which corrosion resistance is desired, such as tanks, vessels, towers, valves, pumps, joints, and other piping materials that are to be provided with corrosion-resistant linings, and chemical and medical instruments, wafer baskets, coil bobbin tower packings, chemical valves, and pump impellers that are to be provided with other corrosion-resistant treatments.

[0140] The object to be coated may be subjected to surface treatment such as cleaning or sandblasting, or may be coated with a primer, if necessary.

[0141] The powders of the present disclosure can also be used as processing aids, molding materials, and the like.

[0142] The powder of the present disclosure can be used, for example, in the following applications: Fluid transfer components for food manufacturing equipment, such as food packaging films, lining materials for fluid transfer lines used in food manufacturing processes, packings, sealing materials, and sheets; Chemical liquid transfer components, such as chemical stoppers, packaging films, lining materials for fluid transfer lines used in chemical manufacturing processes, packings, sealing materials, and sheets; Inner surface lining components for chemical liquid tanks and piping in chemical plants and semiconductor factories; Fuel transfer components, such as O-rings, tubes, packings, valve core materials, hoses, and sealing materials used in automobile fuel systems and peripheral devices, and hoses and sealing materials used in automobile automatic transmissions; Other automobile components, such as carburetor flange gaskets, shaft seals, valve stem seals, sealing materials, and hoses used in automobile engines and peripheral devices, automobile brake hoses, air conditioner hoses, radiator hoses, and electrical wire coating materials; Chemical liquid transfer components for semiconductor manufacturing equipment, such as O-rings, tubes, packings, valve core materials, hoses, sealing materials, rolls, gaskets, diaphragms, and fittings; coating and ink components such as paint rolls, hoses, tubes, ink containers, etc. for coating equipment; food and beverage transport components such as tubes, hoses, belts, packing, joints, etc., such as tubes and hoses for food and beverages, food packaging materials, and glass cooking equipment; waste liquid transport components such as tubes and hoses for transporting waste liquids; high-temperature liquid transport components such as tubes and hoses for transporting high-temperature liquids; steam piping components such as tubes and hoses for steam piping; anti-corrosion tapes for piping, such as tapes wrapped around piping on ship decks, etc.; various coating materials, such as electrical wire coating materials, optical fiber coating materials, and transparent surface coating materials and backing agents applied to the light-incident surface of photovoltaic elements in solar cells; sliding components such as diaphragms and various packings for diaphragm pumps; agricultural films, weather-resistant covers for various roofing materials and side walls, etc.; interior materials used in the construction field, and glass coating materials such as non-flammable fire-resistant safety glass; lining materials, such as laminated steel sheets, used in home appliances, etc.

[0143] The powder of the present disclosure can be suitably produced by the production method of the present disclosure. Next, the production method of the present disclosure will be described in detail.

[0144] 2. Powder manufacturing method In one embodiment, a method for manufacturing a powder containing fluoropolymer particles comprises polymerizing a fluoromonomer in a reactor in the presence of a fluorine-containing surfactant, a polymerization initiator, and an aqueous medium to prepare an aqueous dispersion containing primary particles of at least one fluoropolymer selected from the group consisting of tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer, tetrafluoroethylene / hexafluoropropylene copolymer, and tetrafluoroethylene / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymer, after preparing the aqueous dispersion, performing at least one of the following operations: removing the fluoromonomer remaining in the reactor from the reactor, and recovering the aqueous dispersion in the reactor and storing it in a container different from the reactor, adding a radical generator to the aqueous dispersion in an amount equivalent to 5 molar times or more the molar amount of the fluorine-containing surfactant used in the polymerization, heat-treating the aqueous dispersion containing the radical generator, and coagulating the fluoropolymer in the heat-treated aqueous dispersion to prepare a wet powder containing fluoropolymer particles, The wet powder is dried at a temperature not exceeding 50°C lower than the melting point of the fluoropolymer to produce the powder (sometimes referred to as the "first production method" in the present disclosure).

[0145] In the first production method of the present disclosure, after preparing an aqueous dispersion, a relatively large amount of a radical generator is added to the obtained aqueous dispersion, the aqueous dispersion containing the radical generator is heat-treated, and the fluoropolymer in the heat-treated aqueous dispersion is recovered and dried at a relatively low temperature. By using such a production method, it is possible to produce a powder containing fluoropolymer particles that is easy to handle and has a reduced content of a fluorine-containing compound having a hydrophilic group.

[0146] That is, by using the first production method of the present disclosure, it is possible to produce a powder having a content of fluorine-containing compounds having hydrophilic groups of 250 mass ppb or less.Furthermore, by using the first production method of the present disclosure, it is possible to produce a powder containing fluoropolymer particles having an average secondary particle diameter of 0.5 to 10 μm.

[0147] In one embodiment, a method for producing a powder containing fluoropolymer particles comprises polymerizing a fluoromonomer in a reactor in the presence of a fluorine-containing surfactant, a polymerization initiator, and an aqueous medium to produce an aqueous dispersion containing primary particles of at least one fluoropolymer selected from the group consisting of tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer, tetrafluoroethylene / hexafluoropropylene copolymer, and tetrafluoroethylene / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymer; after producing the aqueous dispersion, at least one of removing the fluoromonomer remaining in the reactor from the reactor and recovering the aqueous dispersion in the reactor and storing it in a container different from the reactor is performed; adding a radical generator to the aqueous dispersion in an amount equivalent to 5 molar times or more the molar amount of the fluorine-containing surfactant used in the polymerization, heat-treating the aqueous dispersion containing the radical generator, and coagulating the fluoropolymer in the heat-treated aqueous dispersion to produce a wet powder containing fluoropolymer particles, and drying the wet powder to produce a bulk powder containing the fluoropolymer, The powder is produced by densifying and pulverizing the raw powder containing the fluoropolymer using a roll under conditions that result in a specific gravity of 90% or more of the true specific gravity, followed by air classification to remove fine particles that account for 3 to 40% by mass of the entire particle size distribution of the pulverized product, and further removing coarse particles that account for 1 to 20% by mass of the entire particle size distribution of the pulverized product by classification (sometimes referred to as the "second production method" in the present disclosure).

[0148] In the second production method of the present disclosure, after preparing an aqueous dispersion, a relatively large amount of a radical generator is added to the obtained aqueous dispersion, the aqueous dispersion containing the radical generator is heat-treated, the fluoropolymer in the heat-treated aqueous dispersion is recovered, the fluoropolymer is dried, the obtained dried product is compressed, the obtained compressed product is pulverized, and the obtained pulverized product is classified. By using such a production method, it is possible to produce a powder containing fluoropolymer particles that has excellent flowability and has a reduced content of a fluorine-containing compound having a hydrophilic group.

[0149] That is, by using the second production method of the present disclosure, it is possible to produce a powder having a content of a fluorine-containing compound having a hydrophilic group of 250 ppb by mass or less. Furthermore, by using the second production method of the present disclosure, it is possible to produce a powder having a uniform particle morphology, a narrow particle size distribution, and excellent flowability.

[0150] Each step and the materials used in each step will be described in detail below.

[0151] (Fluoromonomer Polymerization) In the production method of the present disclosure, first, a fluoromonomer is polymerized in a reactor in the presence of a fluorine-containing surfactant, a polymerization initiator, and an aqueous medium to prepare an aqueous dispersion containing a fluoropolymer.

[0152] The polymerization of fluoromonomer can be carried out by charging a reactor with fluoromonomer, fluorine-containing surfactant, polymerization initiator, aqueous medium and other additives as required, stirring the contents of the reactor, and maintaining the reactor at a predetermined polymerization temperature, and then adding a predetermined amount of polymerization initiator to start the polymerization reaction.After the start of the polymerization reaction, fluoromonomer, polymerization initiator, fluorine-containing surfactant, chain transfer agent, etc. may be added additionally depending on the purpose.The polymerization method of fluoromonomer is not particularly limited, but emulsion polymerization method is preferred.

[0153] (Fluorine-containing surfactant) As the fluorine-containing surfactant used in the polymerization of the fluoromonomer, the fluorine-containing surfactant that can be contained in the powder of the present disclosure can be mentioned, and the same ones are preferably used.

[0154] The amount of the fluorine-containing surfactant added is preferably 10 ppm by mass to 10% by mass, more preferably 100 ppm by mass or more, even more preferably 300 ppm by mass or more, and more preferably 5% by mass or less, and even more preferably 1% by mass or less, relative to the aqueous medium.

[0155] (Fluoromonomer) In the manufacturing method of the present disclosure, at least TFE and at least one selected from the group consisting of perfluoro(alkyl vinyl ether) and hexafluoropropylene are polymerized as fluoromonomers, thereby making it possible to prepare an aqueous dispersion containing primary particles of at least one fluoropolymer selected from the group consisting of TFE / perfluoro(alkyl vinyl ether) copolymer, TFE / hexafluoropropylene copolymer and tetrafluoroethylene / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymer.

[0156] As the fluoromonomer for preparing these copolymers, the fluoromonomers constituting the fluoropolymer contained in the powder of the present disclosure can be mentioned, and the same ones are preferably used.

[0157] In addition, as fluoromonomer, other monomer that can be copolymerized with TFE and perfluoro(alkyl vinyl ether), or other monomer that can be copolymerized with TFE and hexafluoropropylene can also be polymerized.As these other monomers, the fluoromonomer that constitutes the fluoropolymer that the powder of the present disclosure contains can also be mentioned, and the same one is preferably used.

[0158] The amount of each fluoromonomer used is preferably such that the fluoropolymer contained in the powder of the present disclosure is obtained.

[0159] (Polymerization initiator) The polymerization initiator used for the polymerization of fluoromonomer is not particularly limited as long as it can generate radicals within the polymerization temperature range, and known oil-soluble and / or water-soluble polymerization initiators can be used. Furthermore, it can also be combined with a reducing agent or the like to initiate polymerization as a redox. The concentration of the polymerization initiator is appropriately determined depending on the type of monomer, the molecular weight of the target fluoropolymer, and the reaction rate.

[0160] As the polymerization initiator, an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator can be used.

[0161] The oil-soluble radical polymerization initiator may be a known oil-soluble peroxide, for example, dialkyl peroxycarbonates such as diisopropyl peroxydicarbonate and disec-butyl peroxydicarbonate, peroxyesters such as t-butyl peroxyisobutyrate and t-butyl peroxypivalate, dialkyl peroxides such as di-t-butyl peroxide, and the like. Also usable are di(ω-hydro-dodecafluoroheptanoyl) peroxide, di(ω-hydro-tetradecafluorooctanoyl) peroxide, di(ω-hydro-hexadecafluorononanoyl) peroxide, di(perfluorobutyryl) peroxide, di(perfluorovaleryl) peroxide, di(perfluorohexanoyl) peroxide, di(perfluoroheptanoyl) peroxide, di(perfluorooctanoyl) peroxide, di(perfluorononanoyl) peroxide, di(ω-chloro Representative examples include di[perfluoro(or fluorochloro)acyl]peroxides such as di(ω-chlorohexafluorobutyryl)peroxide, di(ω-chlorodecafluorohexanoyl)peroxide, di(ω-chlorotetradecafluorooctanoyl)peroxide, ω-hydro-dodecafluoroheptanoyl-ω-hydrohexadecafluorononanoyl-peroxide, ω-chloro-hexafluorobutyryl-ω-chloro-decafluorohexanoyl-peroxide, ω-hydrododecafluoroheptanoyl-perfluorobutyryl-peroxide, di(dichloropentafluorobutanoyl)peroxide, di(trichlorooctafluorohexanoyl)peroxide, di(tetrachloroundecafluorooctanoyl)peroxide, di(pentachlorotetradecafluorodecanoyl)peroxide, and di(undecachlorodotriacontafluorodocosanoyl)peroxide.

[0162] The water-soluble radical polymerization initiator may be a known water-soluble peroxide, such as ammonium salts, potassium salts, or sodium salts of persulfuric acid, perboric acid, perchloric acid, perphosphoric acid, or percarbonate; organic peroxides such as disuccinic acid peroxide or diglutaric acid peroxide; t-butyl permaleate; t-butyl hydroperoxide; etc. A reducing agent such as a sulfite may also be contained, and the amount used may be 0.1 to 20 times the amount of the peroxide.

[0163] (Aqueous medium) The aqueous medium used for the polymerization of the fluoromonomer is a reaction medium for polymerization, and refers to a liquid containing water. The aqueous medium is not particularly limited as long as it contains water, and may contain water and, for example, a fluorine-free organic solvent such as an ether or a ketone, and / or a fluorine-containing organic solvent having a boiling point of 40° C. or less.

[0164] As the aqueous medium, an aqueous medium containing only water or an aqueous medium containing only water and a fluorine-free organic solvent is preferred, and an aqueous medium containing only water is more preferred, because it allows the polymerization of the fluoromonomer to proceed smoothly and also prevents a decrease in the efficiency of removing the fluorine-containing compound having a hydrophilic group.

[0165] The content of water in the aqueous medium is preferably 90% or more, more preferably 95% or more, even more preferably 99.0% or more, still more preferably 99.5% or more, particularly preferably 99.9% or more, and may be 100%, based on the mass of the aqueous medium, because this allows the polymerization of the fluoromonomer to proceed smoothly and also prevents a decrease in the efficiency of removing the fluorine-containing compound having a hydrophilic group.

[0166] (Chain Transfer Agent) In the production method of the present disclosure, the fluoromonomer can be polymerized in the presence of a chain transfer agent. The use of a chain transfer agent can adjust the polymerization rate and molecular weight. Examples of the chain transfer agent include esters such as dimethyl malonate, diethyl malonate, methyl acetate, ethyl acetate, butyl acetate, and dimethyl succinate, as well as isopentane, methane, ethane, propane, methanol, isopropanol, acetone, various mercaptans, various halogenated hydrocarbons such as carbon tetrachloride, and cyclohexane.

[0167] The amount of chain transfer agent used is usually 1 to 50,000 mass ppm, preferably 1 to 20,000 mass ppm, based on the total amount of fluoromonomer supplied. The amount of chain transfer agent used is preferably an amount that is completely consumed during the polymerization of the fluoromonomer and does not remain in the aqueous dispersion containing the fluoropolymer, so as not to reduce the removal efficiency of the fluorine-containing compound having a hydrophilic group as much as possible. Therefore, the amount of chain transfer agent used is more preferably 10,000 mass ppm or less, even more preferably 5,000 mass ppm or less, still more preferably 1,000 mass ppm or less, particularly preferably 500 mass ppm or less, and most preferably 200 mass ppm or less, based on the total amount of fluoromonomer supplied.

[0168] The chain transfer agent may be added all at once to the reaction vessel before the initiation of polymerization, may be added all at once after the initiation of polymerization, may be added in multiple divided portions during the polymerization, or may be added continuously during the polymerization.

[0169] (Other Additives) In the polymerization of fluoromonomers, additives such as buffers, pH adjusters, stabilizing aids, and dispersion stabilizers can be used. In addition, in the polymerization of fluoromonomers, radical scavengers and decomposers can be added to adjust the polymerization rate and molecular weight. In addition, in the polymerization of fluoromonomers, fluorine-free anionic surfactants, fluorine-free nonionic surfactants, fluorine-free cationic surfactants, etc. may be used.

[0170] Preferred stabilizing aids include paraffin wax, fluorine-based oil, fluorine-based solvent, and silicone oil. The stabilizing aids may be used alone or in combination of two or more. Paraffin wax is more preferred as the stabilizing aid. Paraffin wax may be liquid, semi-solid, or solid at room temperature, but saturated hydrocarbons having 12 or more carbon atoms are preferred. The melting point of the paraffin wax is generally preferably 40 to 65°C, more preferably 50 to 65°C.

[0171] The amount of the stabilizing aid used is preferably 0.1 to 12% by mass, more preferably 0.1 to 8% by mass, based on the mass of the aqueous medium used. It is desirable that the stabilizing aid is sufficiently hydrophobic so that it is completely separated from the aqueous dispersion after polymerization and does not become a contaminating component.

[0172] (Polymerization conditions) Polymerization of fluoromonomers can be carried out under normal pressure and temperature. Usually, the polymerization temperature is 5 to 120°C, and the polymerization pressure is 0.05 to 10 MPaG. The polymerization temperature and polymerization pressure are appropriately determined depending on the type of monomer, the molecular weight of the target fluoropolymer, the reaction rate, etc.

[0173] (Aqueous dispersion obtained by polymerization) An aqueous dispersion containing a fluoropolymer is obtained by polymerization of a fluoromonomer. The content of the fluoropolymer in the aqueous dispersion after polymerization is usually 8 to 50 mass % based on the aqueous dispersion.

[0174] The aqueous dispersion obtained by polymerizing a fluoromonomer usually contains, in addition to the fluoropolymer, a fluorine-containing surfactant used in polymerizing the fluoromonomer as a fluorine-containing compound having a hydrophilic group. Furthermore, the aqueous dispersion obtained by polymerizing a fluoromonomer may contain, in addition to the fluoropolymer, a fluorine-containing compound having a hydrophilic group produced by polymerization of the fluoromonomer.

[0175] A typical compound as the fluorine-containing compound having a hydrophilic group in the aqueous dispersion obtained by polymerization is a fluorine-containing compound having a hydrophilic group with a molecular weight of 1000 g / mol or less. According to the production method of the present disclosure, it is possible to finally produce a powder in which the content of the fluorine-containing compound having a hydrophilic group with a molecular weight of 1000 g / mol or less is reduced.

[0176] In one embodiment of the aqueous dispersion obtained by polymerization, the fluorine-containing compound having a hydrophilic group contains a fluorine-containing surfactant added during polymerization. The fluorine-containing surfactant added during polymerization is as described above for the fluorine-containing surfactant used in polymerization of a fluoromonomer.

[0177] The content of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion obtained by polymerization may be 200 ppb by mass or more, 300 ppb by mass or more, or 400 ppb by mass or more, and may be 10% by mass or less, 1% by mass or less, or 0.5% by mass or less, relative to the aqueous dispersion.

[0178] The content of the fluorine-containing surfactant used when polymerizing the fluoromonomer in the aqueous dispersion obtained by polymerization may be 200 mass ppb or more, 300 mass ppb or more, or 400 mass ppb or more, and may be 10 mass % or less, 1 mass % or less, or 0.5 mass % or less, relative to the aqueous dispersion.

[0179] In one embodiment of the aqueous dispersion obtained by polymerization, the fluorine-containing compound having a hydrophilic group contains a perfluoroethercarboxylic acid. As the perfluoroethercarboxylic acid, a compound (III) represented by the following general formula (III) is preferred. General formula (III): Rf １ -O-(CF(CF ３ )CF ２ O) ｎ３ CF (CF ３ ) COOM (wherein, Rf １ is a perfluoroalkyl group having 1 to 5 carbon atoms, n3 is an integer of 0 to 3, M is H, a metal atom, or NR ７ ４, optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium, and R ７ is H or an organic group.

[0180] When the aqueous dispersion obtained by polymerization contains at least a perfluoroethercarboxylic acid as a fluorine-containing compound having a hydrophilic group, the content of the perfluoroethercarboxylic acid in the aqueous dispersion obtained by polymerization may be 200 ppb by mass or more, 300 ppb by mass or more, or 400 ppb by mass or more, and may be 10% by mass or less, 1% by mass or less, or 0.5% by mass or less, relative to the aqueous dispersion.

[0181] In one embodiment of the aqueous dispersion obtained by polymerization, the aqueous dispersion contains a compound represented by the following general formula (H1) as a fluorine-containing compound having a hydrophilic group. － ] ｉ M ｉ＋ (Wherein, X represents H, Cl, Br, F or I; Rf represents a linear or branched partially or fully fluorinated aliphatic group, or a linear or branched partially or fully fluorinated aliphatic group interrupted by at least one oxygen atom; A － is an acid group, M ｉ＋ represents a cation having a valence i, where i is an integer from 1 to 3.

[0182] In one embodiment of the aqueous dispersion obtained by polymerization, the aqueous dispersion contains a compound represented by the following general formula (H2) as the fluorine-containing compound having a hydrophilic group. ｎ－１ F ２ｎ－１ COO － ]M ＋ (wherein n is an integer of 4 to 14, M ＋ represents a cation.)

[0183] It is known that compounds represented by general formula (2) (perfluoroalkanoic acids) are formed during polymerization when perfluoro(alkyl vinyl ether) or the like is used as a fluoromonomer (see WO 2019 / 161153).

[0184] In one embodiment of the aqueous dispersion obtained by polymerization, the aqueous dispersion contains a compound represented by the following general formula (H3) as the fluorine-containing compound having a hydrophilic group. １ -O-L-CO ２ － ]M ＋ (In the formula, R １ represents a linear or branched partially or fully fluorinated aliphatic group, or a linear or branched partially or fully fluorinated aliphatic group interrupted by at least one oxygen atom; L represents a linear or branched non-fluorinated, partially fluorinated or fully fluorinated alkylene group; M represents a linear or branched non-fluorinated, partially fluorinated or fully fluorinated alkylene group; ＋ represents a cation.)

[0185] In one embodiment of the aqueous dispersion obtained by polymerization, the fluorine-containing compound having a hydrophilic group contains a compound represented by general formula (H4). General formula (H4): H-Rf ｎ０ -Y ０ (wherein, Rf ｎ０ is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which some or all of the H atoms are substituted with F, and the alkylene group may contain one or more ether bonds, and some of the H atoms may be substituted with Cl. ０ is an anionic group.)

[0186] The compound represented by general formula (H4) includes compounds represented by any of the following general formulas: General formula: [H—(CF ２ ) ｍ CO ２ － ]M ＋ (wherein m is an integer of 3 to 19, M ＋ represents a cation.) General formula: [H-(CF ２ ) ｍ２ -(CF(CF ３ )) ｍ３ -CO ２ － ]M ＋ (wherein m2 is an integer of 1 to 17, m3 is an integer of 1 to 9, M ＋represents a cation, provided that m2 and m3 are selected so as to satisfy the relationship 3≦(m2+2×m3)≦19, and the order of occurrence of each repeating unit in the formula is arbitrary.

[0187] (Removal of fluoromonomer or recovery of aqueous dispersion) In the manufacturing method of the present disclosure, after preparing aqueous dispersion by polymerization, before adding radical generator to aqueous dispersion, (a) can carry out at least one of the following operations: (a) remove the fluoromonomer remaining in reactor from reactor, and (b) recover the aqueous dispersion in reactor and store it in a container different from reactor.In particular, if the method of removing fluoromonomer in reactor is used, subsequent steps can be carried out in the same reactor that is used in polymerization, and the productivity of powder is improved, so it is preferred.

[0188] After preparing the aqueous dispersion, it is preferable to stop stirring the contents of the reactor before removing the fluoromonomer or recovering the aqueous dispersion, since this makes the subsequent operations easier and allows the polymerization of the fluoromonomer to be stopped smoothly.

[0189] The method for removing the fluoromonomer from the reactor is not particularly limited. After preparing the aqueous dispersion, if desired, the stirring of the contents of the reactor may be stopped, and the fluoromonomer may be removed from the reactor by venting until the pressure in the reactor reaches normal pressure, or the fluoromonomer may be removed from the reactor by reducing the pressure in the reactor to less than 0.0 MPaG, or the fluoromonomer in the reactor may be replaced with an inert gas such as nitrogen gas by supplying an inert gas into the reactor. Alternatively, the entire amount of the fluoromonomer in the reactor may be reacted and converted into a fluoropolymer, thereby removing the fluoromonomer from the reactor. The removal of the fluoromonomer remaining in the reactor from the reactor can be carried out to the extent that the polymerization reaction of the fluoromonomer is sufficiently stopped, so that a small amount of the fluoromonomer may remain in the reactor. The removed fluoromonomer can be recovered by known means. The recovered fluoromonomer may be reused to produce a fluoropolymer.

[0190] As a method for removing the fluoromonomer from the reactor, a method is also suitable in which, after preparing the aqueous dispersion, stirring of the contents of the reactor is stopped if desired, the pressure in the reactor is reduced to less than 0.0 MPaG, and then an inert gas is supplied into the reactor. The reduction in pressure in the reactor and the supply of the inert gas may be repeated several times.

[0191] When the polymerization of fluoromonomer is carried out at a temperature higher than room temperature, the reactor may be cooled before or after removing the fluoromonomer from the reactor.When removing the fluoromonomer from the reactor by means of evacuation or nitrogen substitution, there is a possibility that unreacted fluoromonomer, particularly in liquid form, remains in the reactor, but by cooling the reactor, the progress of the reaction of the unreacted fluoromonomer can be sufficiently suppressed.

[0192] The method for recovering the aqueous dispersion in the reactor and storing it in a container different from the reactor used for polymerization is not particularly limited. For example, after preparing the aqueous dispersion, stirring of the content of the reactor may be stopped if desired, the reactor may be opened, and the aqueous dispersion in the reactor may be poured into another container, or after preparing the aqueous dispersion, stirring of the content of the reactor may be stopped if desired, and the aqueous dispersion may be supplied from the reactor to another container via a pipe connecting the reactor and another container.

[0193] To terminate the polymerization reaction of the fluoromonomer, a polymerization terminator (radical scavenger) may be added.

[0194] As the polymerization terminator, a compound that does not have the ability to re-initiate after addition or chain transfer to a free radical in the polymerization system is used. Specifically, a compound that easily undergoes a chain transfer reaction with a primary radical or a propagating radical to generate a stable radical that does not subsequently react with a monomer, or a compound that easily undergoes an addition reaction with a primary radical or a propagating radical to generate a stable radical, is used. The activity of what is generally called a chain transfer agent is characterized by the chain transfer constant and the re-initiation efficiency, and among chain transfer agents, those with a re-initiation efficiency of almost 0% are called polymerization terminators. Examples of polymerization terminators include aromatic hydroxy compounds, aromatic amines, N,N-diethylhydroxylamine, quinone compounds, terpenes, thiocyanates, and cupric chloride (CuCl ２ ) is preferred. Examples of aromatic hydroxy compounds include unsubstituted phenol, polyhydric phenol, salicylic acid, m- or p-salicylic acid, gallic acid, naphthol, etc. Examples of the unsubstituted phenol include o-, m-, or p-nitrophenol, o-, m-, or p-aminophenol, p-nitrosophenol, etc. Examples of polyhydric phenols include catechol, resorcinol, hydroquinone, pyrogallol, phloroglucinol, naphthresorcinol, etc. Examples of aromatic amines include o-, m-, or p-phenylenediamine, benzidine, etc. Examples of the quinone compounds include hydroquinone, o-, m-, or p-benzoquinone, 1,4-naphthoquinone, alizarin, etc. Examples of thiocyanates include ammonium thiocyanate (NH ４ Examples of the polymerization terminator include potassium thiocyanate (KSCN), sodium thiocyanate (NaSCN), etc. Among these, quinone compounds are preferred, and hydroquinone is more preferred.

[0195] (Radical Generator) In the production method of the present disclosure, after carrying out at least one of the operations (a) and (b), and before subjecting the aqueous dispersion to heat treatment, a radical generator is added to the aqueous dispersion in an amount equivalent to 5 or more times the molar amount of the fluorine-containing surfactant used in polymerization. By adding a relatively large amount of radical generator, the content of the fluorine-containing compound having a hydrophilic group can be sufficiently reduced.

[0196] The aqueous dispersion to which the radical generator is added may be the aqueous dispersion remaining in the reactor, or may be the aqueous dispersion recovered from the reactor and stored in a separate container.

[0197] The radical generator is not particularly limited as long as it is a compound that can decompose at the temperature during heat treatment to generate radicals. As the radical generator, a water-soluble radical generator is preferred because it can easily diffuse radicals in the aqueous dispersion.

[0198] Examples of the radical generator include organic peroxides, inorganic peroxides, organic azo compounds, and combinations of oxidizing agents and reducing agents. At least one selected from the group consisting of inorganic peroxides, organic peroxides, and combinations of oxidizing agents and reducing agents is preferred.

[0199] The inorganic peroxide is preferably a water-soluble inorganic peroxide. Examples of the inorganic peroxide include hydrogen peroxide, perchlorates, perborates, perphosphates, percarbonates, and persulfates, with persulfates being preferred. The persulfates are preferably at least one selected from the group consisting of ammonium persulfate, sodium persulfate, and potassium persulfate, with ammonium persulfate being more preferred.

[0200] The organic peroxide is preferably a water-soluble organic peroxide, and examples of the organic peroxide include peroxydicarbonates such as disuccinic acid peroxide and diglutaric acid peroxide.

[0201] The radical generator may be a combination of an oxidizing agent and a reducing agent. By using a combination of an oxidizing agent and a reducing agent, radicals can be generated from the radical generator by a redox reaction between the oxidizing agent and the reducing agent, so that the temperature during heat treatment can be lowered.

[0202] Examples of oxidizing agents include persulfates, organic peroxides, potassium permanganate, manganese triacetate, and cerium ammonium nitrate. Examples of reducing agents include sulfites, bisulfites, bromates, diimines, and oxalic acid. Examples of persulfates include ammonium persulfate and potassium persulfate. Examples of sulfites include sodium sulfite and ammonium sulfite. It is also preferable to add a copper salt or an iron salt to increase the decomposition rate of the oxidizing agent. Examples of copper salts include copper(II) sulfate, and examples of iron salts include iron(II) sulfate.

[0203] Examples of combinations of oxidizing agents and reducing agents include potassium permanganate / oxalic acid, ammonium persulfate / bisulfite / iron sulfate, manganese triacetate / oxalic acid, cerium ammonium nitrate / oxalic acid, and bromate / bisulfite, with potassium permanganate / oxalic acid being preferred. When using a combination of an oxidizing agent and a reducing agent, either the oxidizing agent or the reducing agent may be added to the aqueous dispersion in advance, and then the other may be added continuously or intermittently.

[0204] The amount of radical generator added is preferably 5 times or more by mole, more preferably 10 times or more by mole, and preferably 1000 times or less by mole, more preferably 500 times or less by mole, and even more preferably 100 times or less by mole, relative to the molar amount of the fluorine-containing surfactant used in the polymerization, since this can further improve the removal efficiency of the fluorine-containing compound having a hydrophilic group. Since the production method of the present disclosure is for producing a powder, it does not matter if a relatively large amount of radical generator is added, even if the fluoropolymer in the aqueous dispersion precipitates.

[0205] The method for adding the radical generator is not particularly limited. The radical generator may be added directly to the aqueous dispersion, or a solution containing the radical generator may be prepared and added to the aqueous dispersion. The radical generator may be added while stirring the aqueous dispersion, or the aqueous dispersion may be stirred after adding the radical generator.

[0206] The temperature of the aqueous dispersion to which the radical generator is added is not particularly limited, and may be the temperature of the aqueous dispersion after polymerizing the fluoromonomer, the temperature reached by cooling the aqueous dispersion after polymerizing the fluoromonomer, or the temperature of the heat treatment. That is, after adding the radical generator to the aqueous dispersion, the aqueous dispersion may be heated for the heat treatment, or the aqueous dispersion may be heated to a temperature for the heat treatment and then the radical generator may be added to the aqueous dispersion.

[0207] (Heat Treatment) In the production method of the present disclosure, the aqueous dispersion to which the radical generator has been added (aqueous dispersion containing a radical generator) is subjected to heat treatment. By subjecting the aqueous dispersion containing a relatively large amount of the radical generator to heat treatment, the content of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion can be surprisingly reduced.

[0208] Before the heat treatment, the content of the fluoropolymer in the aqueous dispersion may be adjusted by a known method such as concentration or dilution.

[0209] The content of the fluoropolymer in the aqueous dispersion to be subjected to the heat treatment is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, based on the mass of the aqueous dispersion, since the aqueous fluoropolymer dispersion can be produced with high productivity without impairing the removal efficiency of the fluorine-containing compound having a hydrophilic group. The upper limit of the fluoropolymer content is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less.

[0210] The content of the fluorine-containing surfactant added during polymerization in the aqueous dispersion to be subjected to heat treatment is preferably 500 ppm by mass or more, more preferably 1000 ppm by mass or more, and preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less, based on the mass of the fluoropolymer in the aqueous dispersion.

[0211] The content of the fluorine-containing compound having a hydrophilic group produced by polymerization of a fluoromonomer in the aqueous dispersion to be subjected to heat treatment is preferably 500 ppb by mass or more, more preferably 1000 ppb by mass or more, and preferably 1.0% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0.01% by mass or less, relative to the mass of the fluoropolymer in the aqueous dispersion.

[0212] The content of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion to be subjected to heat treatment (the total content of the fluorine-containing surfactant added during polymerization and the content of the fluorine-containing compound having a hydrophilic group produced by polymerization of the fluoromonomer) is preferably 500 ppm by mass or more, more preferably 1000 ppm by mass or more, and preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less, based on the fluoropolymer in the aqueous dispersion.

[0213] The temperature of the heat treatment is preferably 35°C or higher, more preferably 40°C or higher, even more preferably 45°C or higher, particularly preferably 50°C or higher, and preferably 120°C or lower, more preferably 110°C or lower, even more preferably 100°C or lower, and particularly preferably 90°C or lower, since this can further improve the removal efficiency of fluorine-containing compounds having hydrophilic groups. When heat treating an aqueous dispersion containing an added radical generator, the heat treatment temperature is preferably equal to or higher than the temperature at which the radical generator decomposes to generate radicals (decomposition temperature). Since the production method of the present disclosure is for producing a powder, it does not matter if the fluoropolymer in the aqueous dispersion precipitates by heat treatment at a relatively high temperature.

[0214] In the heat treatment of aqueous dispersion, if aqueous dispersion can be maintained at a desired temperature or higher, it is not necessary to heat aqueous dispersion.For example, when the temperature of fluoromonomer polymerization is sufficiently high, and the temperature of the resulting aqueous dispersion is also sufficiently high, heat treatment can be started before the resulting aqueous dispersion is cooled.However, since it is easier to control the temperature of heat treatment, it is preferable to cool the aqueous dispersion before and after removing fluoromonomer from reactor or recovering the aqueous dispersion in reactor, heat the aqueous dispersion to the above-mentioned temperature range, and maintain this temperature for a certain period of time.The temperature of the aqueous dispersion to be subjected to heat treatment can be, for example, 30 ° C or less.

[0215] The heating means when the heat treatment is performed while heating the aqueous dispersion is not particularly limited. For example, the aqueous dispersion may be heated by placing a container containing the aqueous dispersion in a thermostatic bath, or the aqueous dispersion may be placed in a container equipped with a heater and heated by the heater.

[0216] The pressure of the heat treatment is not particularly limited and may be atmospheric pressure. For example, when the temperature of the heat treatment is relatively high and it is necessary to suppress boiling of the aqueous dispersion, the pressure of the heat treatment may be a pressure higher than atmospheric pressure.

[0217] The heat treatment time is preferably 15 minutes or more, more preferably 30 minutes or more, even more preferably 60 minutes or more, and is preferably 1200 minutes or less, more preferably 900 minutes or less, even more preferably 600 minutes or less, since this can further improve the efficiency of removing the fluorine-containing compound having a hydrophilic group.

[0218] The heat treatment may be carried out while stirring the aqueous dispersion.

[0219] (Preparation of Wet Powder and Drying of Wet Powder) In the first production method of the present disclosure, a wet powder containing fluoropolymer particles is prepared by coagulating the fluoropolymer in a heat-treated aqueous dispersion, and the wet powder is dried at a temperature not exceeding 50°C lower than the melting point of the fluoropolymer to prepare a powder containing fluoropolymer particles.

[0220] In the second production method of the present disclosure, a bulk powder containing a fluoropolymer is produced in the same manner as in the first production method of the present disclosure, except that the wet powder is dried at an arbitrary temperature. In the second production method of the present disclosure, drying can be carried out at an arbitrary temperature, but drying may also be carried out at a low temperature, as in the first production method of the present disclosure.

[0221] In the first and second production methods of the present disclosure, the method for coagulating the fluoropolymer is not particularly limited. For example, the aqueous dispersion is diluted with water to a polymer concentration of 5 to 20% by mass, and the pH is adjusted to neutral or alkaline in some cases, followed by stirring more vigorously than during the polymerization of the fluoromonomer in a container equipped with a stirrer. The fluoropolymer may be coagulated by adding a water-soluble organic compound such as methanol or acetone; an inorganic salt such as potassium nitrate or ammonium carbonate; or an inorganic acid such as hydrochloric acid, sulfuric acid, or nitric acid to the aqueous dispersion as a coagulant, followed by stirring. After coagulating the fluoropolymer, a wet powder containing fluoropolymer particles can be recovered. The wet powder may include a fluoropolymer precipitate precipitated by adding a radical generator or a fluoropolymer precipitate precipitated by heat treatment.

[0222] Before drying the wet powder, the wet powder may be washed. Water or an organic solvent can be used to wash the wet powder. Washing may be performed once or multiple times. Examples of organic solvents used for washing include ethers, halogenated hydrocarbons, aromatic hydrocarbons, pyridine, nitriles, nitrogen-containing polar organic compounds, dimethyl sulfoxide, and alcohols.

[0223] In the first production method of the present disclosure, the wet powder is dried at a temperature equal to or lower than the melting point of the fluoropolymer by 50° C. Drying the wet powder at a relatively low temperature makes it possible to obtain a powder that is easy to handle.

[0224] In the first production method of the present disclosure, the drying temperature of the wet powder is not more than a temperature 50°C lower than the melting point of the fluoropolymer, more preferably not more than a temperature 70°C lower than the melting point of the fluoropolymer, and even more preferably not more than a temperature 100°C lower than the melting point of the fluoropolymer.

[0225] In the first production method of the present disclosure, the drying temperature of the wet powder is preferably 250°C or less, more preferably 230°C or less, even more preferably 200°C or less, and still more preferably 180°C or less.

[0226] In the first production method of the present disclosure, the drying temperature of the wet powder is preferably 80° C. or higher, more preferably 100° C. or higher, even more preferably 120° C. or higher, and still more preferably 140° C. or higher. If the drying temperature is too low, drying takes a long time, which may result in a decrease in productivity.

[0227] In the first manufacturing method of the present disclosure, the obtained powder may be classified or granulated. The obtained powder may also be formed into pellets. In the manufacturing method of the present disclosure, since a powder that is easy to handle after drying is directly obtained, it is also a preferred embodiment that the dried powder is not subjected to any post-treatment.

[0228] In the second production method of the present disclosure, a raw powder containing a fluoropolymer obtained by drying a wet powder is densified using a roll under conditions such that a specific gravity of 90% or more of the true specific gravity is obtained, and then pulverized. After that, fine particles in the range of 3 to 40% by mass of the entire particle size distribution of the pulverized product are removed by air classification, and coarse particles in the range of 1 to 20% by mass of the entire particle size distribution of the pulverized product are further removed by classification.

[0229] A sheet containing a fluoropolymer is usually obtained by compressing the bulk powder using a roll. In the second production method of the present disclosure, the bulk powder is formed into a sheet using a roll, and the sheet is compressed under conditions such that the specific gravity of the sheet is 90% or more of the true specific gravity (the specific gravity of a melt-molded product of the fluoropolymer). The specific gravity after compression is preferably 95% to 99% of the true specific gravity. If the compressed specific gravity is less than 90% of the true specific gravity, the powder particles obtained after pulverization are similar to the agglomerated fine powder obtained after polymerization and drying, resulting in a low apparent density and poor powder flowability. If the compressed specific gravity exceeds 99% of the true specific gravity, it becomes difficult to obtain a powder with excellent flowability.

[0230] The sheeting with rolls is carried out so that the sheet thickness is 0.05 to 5 mm, preferably 0.1 to 3 mm. As the rolls, those having two or more rolls arranged in a vertical, inverted L, Z or other configuration are preferred, and specific examples include calendar rolls, mixing rolls, and roll compactors. When forming the fluoropolymer into a sheet with rolls, a strong shear force is applied to the fluoropolymer during sheeting, which expels air present in the particles of the bulk powder and produces a homogeneous sheet.

[0231] The temperature at which the bulk powder is compressed is preferably 0 to 250°C, more preferably 5 to 150°C.

[0232] The densified bulk powder (sheet) is then pulverized. After the sheet is pulverized to obtain pulverized particles of 0.1 to 10 mm, the pulverized particles may be further pulverized.

[0233] The pulverization is preferably carried out by a mechanical pulverizer, such as an impact pulverizer such as a cutter mill, hammer mill, pin mill, or jet mill, or an attrition pulverizer that pulverizes by shear force.

[0234] The grinding temperature is preferably −200° C. to 100° C., more preferably 20° C. or higher, and more preferably 50° C. or lower.

[0235] The resulting pulverized material is then classified. Classification of the pulverized material can be carried out by air classification to remove fine particles, followed by air classification using a mesh or a vibrating sieve to remove coarse particles. By removing fine particles first, it is possible to carry out classification with high efficiency while suppressing clogging of the mesh or sieve.

[0236] In air classification, the ground raw material is sent to a cylindrical classification chamber by reduced pressure air (blower), dispersed by a swirling air current at room temperature, and the fine particles are classified by centrifugal force. A rotating body such as a cone or rotor is installed in the classification chamber to ensure uniform swirling motion of the raw material and air. In the case of a classification cone, the classification point is adjusted by adjusting the air volume by secondary air and the gap between the classification cones. In the case of a rotor, the air volume in the classification chamber is adjusted by the rotor rotation speed. The blower air pressure is 1 to 10 kg / cm. ２ , preferably 3 to 6 kg / cm ２ is.

[0237] By air classification, fine particles in the range of 3 to 40 mass %, preferably 5 to 30 mass %, of the entire particle size distribution of the pulverized material are removed. If the amount of fine particles removed is too small, the fluidity of the resulting powder cannot be sufficiently improved, whereas if the amount of fine particles removed is too large, it is economically disadvantageous.

[0238] Next, coarse particles in the range of 1 to 20 mass %, preferably 2 to 10 mass %, of the entire particle size distribution of the pulverized product are removed by classification. If the amount of coarse particles removed is too small, the fluidity of the resulting powder cannot be sufficiently improved, whereas if the amount of coarse particles removed is too large, it is economically disadvantageous.

[0239] The removed fine and coarse particles can be reused as raw material for powder.

[0240] The powder of the present disclosure can be used to prepare a liquid coating composition.The liquid coating composition of the present disclosure contains a powder with a reduced content of fluorine-containing compounds having hydrophilic groups, and therefore provides a film with a large contact angle and a small coefficient of friction.The reason for this is not clear, but it is presumed that the dispersion stability of the fluoropolymer powder in the liquid coating composition is moderately low due to the powder containing a reduced content of fluorine-containing compounds having hydrophilic groups, and therefore, when forming a film, the fluoropolymer powder is more likely to float to the surface of the film than other components, resulting in a high content of fluoropolymer on the film surface.

[0241] The liquid coating composition of the present disclosure can be prepared by mixing the powder of the present disclosure and a solvent. Before or during mixing with the solvent, the powder of the present disclosure may be pulverized using a pulverizer such as a ball mill to adjust the particle size of the powder. The liquid coating composition of the present disclosure is prepared using a powder that is easy to handle, and therefore is easy to prepare.

[0242] Examples of the solvent include water and organic solvents such as N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-butyl-2-pyrrolidone, 3-methoxy-N,N-dimethylpropanamide, N,N-dimethylacetamide, N,N-dimethylformamide, cresol, methyl isobutyl ketone, and xylene.

[0243] The content of the fluoropolymer powder in the liquid coating composition is preferably 1 to 90% by weight, more preferably 5% by weight or more, and more preferably 80% by weight or less, based on the mass of the liquid coating composition.

[0244] The liquid coating composition may further contain a polymer compound other than the fluoropolymer. Examples of the polymer compound include polyamideimide (PAI), polyimide (PI), polyethersulfone (PES), polyarylene sulfide (PAS), polyetherimide, polyetheretherketone, and aromatic polyester. The polymer compounds may be used alone or in combination of two or more.

[0245] PAI is a resin made of a polymer having an amide bond and an imide bond in its molecular structure. There are no particular limitations on the PAI. Examples of PAI include, but are not limited to, resins made of high-molecular-weight polymers obtained by various reactions, such as the reaction of an aromatic diamine having an amide bond in the molecule with an aromatic tetracarboxylic acid such as pyromellitic acid; the reaction of an aromatic tricarboxylic acid such as trimellitic anhydride with a diamine such as 4,4-diaminophenyl ether or a diisocyanate such as diphenylmethane diisocyanate; and the reaction of a dibasic acid having an aromatic imide ring in the molecule with a diamine. As PAI, those made of a polymer having an aromatic ring in the main chain are preferred because of their excellent heat resistance.

[0246] PI is a resin made of a polymer having an imide bond in its molecular structure. There are no particular limitations on the PI, but examples include resins made of high-molecular-weight polymers obtained by the reaction of aromatic tetracarboxylic anhydrides such as pyromellitic anhydride. As PI, those made of polymers having an aromatic ring in the main chain are preferred because of their excellent heat resistance.

[0247] PES is represented by the following general formula:

[0248]

[0249] The PES is not particularly limited, but examples thereof include a resin made of a polymer obtained by polycondensation of dichlorodiphenyl sulfone and bisphenol.

[0250] PAS is a resin made of a polymer having a repeating unit represented by the general formula -[Ar-S]- (wherein Ar represents an arylene group). The PAS is not particularly limited, but examples thereof include polyphenylene sulfide (PPS).

[0251] As the polymer compound, at least one selected from the group consisting of PAI, PI, PES, and PPS is preferred, with PAI being more preferred, as it can provide a coating that has even better adhesion to the substrate. Furthermore, PES is preferred as the polymer compound, as it can suppress coloration during baking and increase the degree of freedom in the color tone of the coating. Using a combination of PAI and PES as the polymer compound is also a preferred embodiment.

[0252] The content of the polymer compound is preferably 1% by mass or more, more preferably 3% by mass or more, and preferably 15% by mass or less, more preferably 12% by mass or less, based on the liquid coating composition.

[0253] In the liquid coating composition, the volume ratio of the fluoropolymer (fluoropolymer powder) to the polymer compound is preferably 10 / 90 to 90 / 10, more preferably 15 / 85 or more, and more preferably 85 / 15 or less.

[0254] The content of the fluoropolymer (fluoropolymer powder) and the polymer compound in the liquid coating composition is preferably 1 to 90% by weight, more preferably 10% by weight or more, and more preferably 80% by weight or less, based on the mass of the liquid coating composition.

[0255] The liquid coating composition may contain other components as needed, such as crosslinking agents, antistatic agents, heat stabilizers, foaming agents, foam nucleating agents, antioxidants, surfactants, photopolymerization initiators, anti-wear agents, surface modifiers, various organic and inorganic pigments, copper inhibitors, anti-foaming agents, adhesion promoters, lubricants, processing aids, colorants, phosphorus-based stabilizers, lubricants, release agents, sliding materials, ultraviolet absorbers, dyes and pigments, reinforcing materials, anti-drip agents, fillers, curing agents, ultraviolet curing agents, and flame retardants.

[0256] The content of other components in the liquid coating composition is preferably less than 30% by weight, more preferably less than 10% by weight, and even more preferably 5% by weight or less, relative to the mass of the fluoropolymer (fluoropolymer powder) and polymer compound in the liquid coating composition, and although there is no particular lower limit, it may be 0% by weight or more. In other words, the liquid coating composition does not need to contain other components.

[0257] By using the liquid coating composition of the present disclosure, a film can be obtained. The film obtained from the liquid coating composition of the present disclosure has excellent water and oil repellency and low friction.

[0258] Although the embodiments have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the claims.

[0259] <1> According to a first aspect of the present disclosure, there is provided a powder containing fluoropolymer particles, the powder containing a fluorine-containing compound having a hydrophilic group, the content of the fluorine-containing compound having a hydrophilic group being 250 mass ppb or less relative to the powder, the fluoropolymer particles having an average secondary particle size of 0.5 to 10 μm, and the fluoropolymer being at least one selected from the group consisting of a tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer, a tetrafluoroethylene / hexafluoropropylene copolymer, and a tetrafluoroethylene / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymer. <2> According to a second aspect of the present disclosure, there is provided a powder having a specific surface area of ​​8 m ２ / g or more. <3> According to a third aspect of the present disclosure, there is provided a powder according to the first or second aspect, wherein the average primary particle size of the fluoropolymer particles is less than 0.5 μm. <4> According to a fourth aspect of the present disclosure, there is provided a powder according to any one of the first to third aspects, wherein the perfluoro(alkyl vinyl ether) is perfluoro(propyl vinyl ether). <5> According to a fifth aspect of the present disclosure, there is provided a powder according to any one of the first to fourth aspects, wherein the fluoropolymer has a melt flow rate at 372°C of 10 g / 10 min or more. <6> According to a sixth aspect of the present disclosure, there is provided a powder according to any one of the first to fifth aspects, wherein the fluoropolymer has a melting point of 220°C or more. <7> According to a seventh aspect of the present disclosure, there is provided a powder according to any one of the first to fifth aspects, wherein the fluoropolymer has functional groups, and the number of the functional groups is 10 or more. ６ <8> According to an eighth aspect of the present disclosure, there is provided a powder according to any one of the first to sixth aspects, wherein the fluorine-containing compound having a hydrophilic group is represented by the following general formula (N ０ According to any one of the first to seventh aspects, there is provided a powder which is a compound represented by the general formula (N ０ ): X ｎ０ -Rf ｎ０ -Y ０ (In the formula, X ｎ０ is H, Cl or F. ｎ０ is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which some or all of the H atoms are substituted with F, and the alkylene group may contain one or more ether bonds, and some of the H atoms may be substituted with Cl. ０ is an anionic group.) <9> According to a ninth aspect of the present disclosure, there is provided a powder according to any one of the first to eighth aspects, wherein the fluorine-containing compound having a hydrophilic group contains at least a compound (H2) represented by general formula (H2), and the content of the compound (H2) is 25 ppb by mass or less relative to the powder. General formula (H2): [C ｎ－１ F ２ｎ－１ COO － ]M ＋(wherein n is an integer of 4 to 14, M ＋represents a cation.) <10> According to a tenth aspect of the present disclosure, there is provided a powder according to any one of the first to ninth aspects, wherein the fluorine-containing compound having a hydrophilic group contains at least a perfluoroether carboxylic acid. <11> According to an eleventh aspect of the present disclosure, there is provided a powder coating material containing the powder according to any one of the first to tenth aspects. <12> According to a twelfth aspect of the present disclosure, there is provided a method for producing a powder containing fluoropolymer particles, comprising: polymerizing a fluoromonomer in a reactor in the presence of a fluorinated surfactant, a polymerization initiator, and an aqueous medium to produce an aqueous dispersion containing primary particles of at least one fluoropolymer selected from the group consisting of a tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer, a tetrafluoroethylene / hexafluoropropylene copolymer, and a tetrafluoroethylene / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymer; after producing the aqueous dispersion, performing at least one of removing the fluoromonomer remaining in the reactor from the reactor and recovering the aqueous dispersion in the reactor and storing it in a container different from the reactor; adding a radical generator to the aqueous dispersion in an amount equivalent to 5 molar times or more the molar amount of the fluorinated surfactant used in the polymerization; heat-treating the aqueous dispersion containing the radical generator; and coagulating the fluoropolymer in the heat-treated aqueous dispersion to produce a wet powder containing fluoropolymer particles; and drying the wet powder at a temperature equal to or lower than the melting point of the fluoropolymer by 50° C. to produce the powder. <13> According to a thirteenth aspect of the present disclosure, there is provided a liquid coating composition containing the powder according to any one of the first to tenth aspects.<14> According to a fourteenth aspect of the present disclosure, there is provided a powder containing fluoropolymer particles, comprising a fluorine-containing compound having a hydrophilic group, the content of the fluorine-containing compound having a hydrophilic group being 250 ppb by mass or less relative to the powder, the fluoropolymer being at least one selected from the group consisting of tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer, tetrafluoroethylene / hexafluoropropylene copolymer, and tetrafluoroethylene / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymer, and the powder is obtained by densifying a raw powder containing the fluoropolymer using a roll under conditions such that a specific gravity of 90% or more of the true specific gravity is obtained, pulverizing the densified raw powder, and then removing fine particles in a range of 3 to 40% by mass of the entire particle size distribution of the pulverized product by air classification, and further removing coarse particles in a range of 1 to 20% by mass of the entire particle size distribution of the pulverized product by classification. <15> According to a fifteenth aspect of the present disclosure, there is provided a powder obtained by: ０ According to a fourteenth aspect, there is provided a powder which is a compound represented by the general formula (N ０ ): X ｎ０ -Rf ｎ０ -Y ０ (In the formula, X ｎ０ is H, Cl or F. ｎ０ is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which some or all of the H atoms are substituted with F, and the alkylene group may contain one or more ether bonds, and some of the H atoms may be substituted with Cl. ０is an anionic group.) <16> According to a sixteenth aspect of the present disclosure, there is provided a powder according to the fourteenth or fifteenth aspect, wherein the fluoropolymer particles have an average secondary particle size of 5 to 100 μm. <17> According to a seventeenth aspect of the present disclosure, there is provided a powder according to any one of the fourteenth to sixteenth aspects, wherein pulverization of a densified bulk powder is carried out at 20 to 100° C. <18> According to an eighteenth aspect of the present disclosure, there is provided a method for producing a powder containing fluoropolymer particles, comprising: polymerizing a fluoromonomer in a reactor in the presence of a fluorinated surfactant, a polymerization initiator, and an aqueous medium to produce an aqueous dispersion containing primary particles of at least one fluoropolymer selected from the group consisting of a tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer, a tetrafluoroethylene / hexafluoropropylene copolymer, and a tetrafluoroethylene / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymer; after producing the aqueous dispersion, performing at least one of removing the fluoromonomer remaining in the reactor from the reactor and recovering the aqueous dispersion in the reactor and storing it in a container different from the reactor; adding a radical generator to the aqueous dispersion in an amount equivalent to 5 molar times or more the molar amount of the fluorinated surfactant used in the polymerization; heat-treating the aqueous dispersion containing the radical generator; and coagulating the fluoropolymer in the heat-treated aqueous dispersion to produce a wet powder containing fluoropolymer particles; The wet powder is dried to produce a bulk powder containing the fluoropolymer, the bulk powder containing the fluoropolymer is densified using a roll under conditions to obtain a specific gravity of 90% or more of the true specific gravity, and pulverized, followed by air classification to remove fine particles in a range of 3 to 40% by mass of the entire particle size distribution of the pulverized product, and further by classification to remove coarse particles in a range of 1 to 20% by mass of the entire particle size distribution of the pulverized product, thereby producing the powder.

[0260] Next, embodiments of the present disclosure will be described with reference to examples, but the present disclosure is not limited to these examples.

[0261] Each value in the examples was measured by the following method: <Solid content concentration of aqueous dispersion> 1 g of the aqueous dispersion was dried in a blower dryer at 150°C for 60 minutes, and the ratio of the mass of the heating residue to the mass (1 g) of the aqueous dispersion, expressed as a percentage, was used.

[0262] <Average primary particle diameter> A PTFE aqueous dispersion with a solid content adjusted to approximately 1.0% by mass was prepared, and the average primary particle diameter was measured at 25°C and 70 times cumulatively using an ELSZ-1000S (manufactured by Otsuka Electronics Co., Ltd.) The refractive index of the solvent (water) was 1.3328, and the viscosity of the solvent (water) was 0.8878 mPa s.

[0263] <Average secondary particle diameter> The particle size distribution was measured using a laser diffraction particle size distribution analyzer (manufactured by JEOL Ltd.) without using a cascade, at a pressure of 0.1 MPa, for a measurement time of 3 seconds, and the average secondary particle diameter was set to be equal to the value corresponding to 50% of the integrated particle size distribution obtained.

[0264] <PPVE Unit Content> The content of perfluoro(propyl vinyl ether) (PPVE) units in the copolymer is １９ It was determined by F-NMR analysis.

[0265] <Melting point> Measurement was carried out using a DSC (differential scanning calorimeter). 10 mg of a sample was weighed, heated from 140°C to 360°C at a rate of 10°C / min, held at 360°C for 1 minute, cooled to 140°C at a rate of 10°C / min, held at 140°C for 1 minute, and then heated again to 380°C at a rate of 10°C / min. The melting peak temperature (Tm) from the melting curve obtained during the second heating was taken as the melting point.

[0266] <Melt Flow Rate (MFR)> Using a melt indexer (manufactured by Toyo Seiki Seisakusho) equipped with a corrosion-resistant cylinder, die, and piston conforming to ASTM D1238-95, 5 g of a sample was filled into a cylinder maintained at 372±1°C, maintained for 5 minutes, and then extruded through a die orifice under a 5 kg load (piston and weight), and the extrusion rate (g / 10 min) of the molten material at this time was determined as MFR.

[0267] <Specific Surface Area> Measured by the BET method using a surface analyzer (product name: MONOSORB, manufactured by QUANTA CHLROME). A mixed gas of 30% nitrogen and 70% helium was used as the carrier gas, and cooling was performed using liquid nitrogen.

[0268] <Number of Functional Groups> Copolymer pellets were molded by cold pressing to prepare a film with a thickness of 0.25 to 0.30 mm. This film was scanned 40 times using a Fourier transform infrared spectrometer [FT-IR (Spectrum One, manufactured by PerkinElmer)] to obtain an infrared absorption spectrum, and a difference spectrum was obtained from a base spectrum where the sample was completely fluorinated and no functional groups were present. From the absorption peaks of specific functional groups appearing in this difference spectrum, the number of carbon atoms in the sample (1 × 10) was calculated according to the following formula (A): ６ The number of functional groups per molecule, N, was calculated. N = I × K / t (A) where I: absorbance, K: correction coefficient, t: film thickness (mm). For reference, the absorption frequencies, molar absorption coefficients, and correction coefficients for the functional groups in this disclosure are shown in Table 2. The molar absorption coefficients were determined from FT-IR measurement data of low molecular weight model compounds.

[0269]

[0270] <Measurement of Fluorine-Containing Compound Having Hydrophilic Group> The content of the fluorine-containing compound having a hydrophilic group contained in the powder was determined as the content of the fluorine-containing compound having a hydrophilic group extracted from the powder.

[0271] 0. Extraction of fluorine-containing compounds having hydrophilic groups from powder 10 g (12.6 mL) of methanol was added to 1 g of powder, and the mixture was subjected to ultrasonic treatment for 2 hours at 60° C. After allowing to stand at room temperature, the solid content was removed to obtain an extract.

[0272] <Measurement of perfluoroethercarboxylic acid A> 1. Calibration curve of perfluoroethercarboxylic acid A Five levels of methanol standard solutions of perfluoroethercarboxylic acid A with known concentrations were prepared and measured using a liquid chromatograph mass spectrometer (Agilent, Ultivo triple quadrupole LC-MS). A calibration curve was created for each concentration range using a first-order approximation from the methanol standard solution concentration and the peak integral value.

[0273] Measurement equipment configuration and LC-MS measurement conditions

[0274] MRM measurement parameters

[0275] 2. Content of perfluoroethercarboxylic acid A contained in powder Using a liquid chromatograph mass spectrometer, the content of perfluoroethercarboxylic acid A contained in the extract was measured from a calibration curve. The content of perfluoroethercarboxylic acid A contained in the powder was calculated using the following relational formula (1). Y Ａ =X Ａ ×12.6 (1) Y Ａ X: content of perfluoroethercarboxylic acid A contained in powder (mass ppb / powder) Ａ : Content of perfluorocarboxylic acid A contained in extract (ng / mL) The lower limit of determination for the content of perfluoroethercarboxylic acid A contained in the powder is 1 ppb by mass / powder.

[0276] <Content of Compound Represented by General Formula (H2)> The content of the compound represented by general formula (H2) was determined using a calibration curve of a linear perfluorocarboxylic acid having the same number of carbon atoms.

[0277] 1. Calibration curve of perfluorocarboxylic acid Five levels of methanol standard solutions of known concentrations of perfluorobutanoic acid, perfluoropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid, perfluoroundecanoic acid, perfluorododecanoic acid, perfluorotridecanoic acid, and perfluorotetradecanoic acid were prepared, and measurements were performed using a liquid chromatograph mass spectrometer (Agilent, Ultivo triple quadrupole LC-MS). A calibration curve was created for each concentration range using a first-order approximation from the methanol standard solution concentration and the peak integral value.

[0278] Measurement equipment configuration and LC-MS measurement conditions

[0279] MRM measurement parameters

[0280] 2. Content of Compound Represented by General Formula (H2) in Powder Using a liquid chromatograph mass spectrometer, the content of the compound represented by general formula (H2) and having n carbon atoms contained in the extract was measured from a calibration curve. The content of the compound represented by general formula (H2) and having n carbon atoms contained in the powder was determined using the following relational expression (2): Yn = Xn × 12.6 (2) Yn: content of the compound represented by general formula (H2) and having n carbon atoms contained in the powder (mass ppb / powder) Xn: content of the compound represented by general formula (H2) and having n carbon atoms contained in the extract (ng / mL) The lower limit of quantitation for the content of the compound represented by general formula (H2) and having n carbon atoms contained in the powder is 1 mass ppb / powder.

[0281] MRM measurement parameters

[0282] Synthesis Example 1 By the method described in Synthesis Example 1 of WO 2021 / 045228, a white solid A of perfluoroethercarboxylic acid A having a molecular weight of 1,000 or less was obtained.

[0283] Production Example 1: 3,750 g of deionized water and 5.49 g of the white solid A obtained in Synthesis Example 1 as a fluorine-containing surfactant were placed in a 6 L stainless steel reactor equipped with a stirrer. The contents of the reactor were then heated to 60°C, while simultaneously suctioning and purging with TFE to remove oxygen from the reactor, and the contents were stirred. 6.9 g of methylene chloride and 27 g of perfluoro(propyl vinyl ether) (PPVE) were added to the reactor, followed by the addition of TFE until the pressure reached 1.3 MPaG. 990 mg of ammonium persulfate (APS) initiator dissolved in 20 g of deionized water was injected into the reactor. After the initiator was injected, a pressure drop occurred and the initiation of polymerization was observed. TFE was added to the reactor to maintain a constant pressure of 1.3 MPaG. After the initiation of polymerization, 4 g of PPVE was continuously added per 100 g of TFE. When the TFE consumed in reaction reaches about 1080g, stop supplying TFE, stop stirring, and finish reaction.Then, the pressure in reactor is exhausted until normal pressure, obtain tetrafluoroethylene / perfluoro(propyl vinyl ether) copolymer (PFA) aqueous dispersion.The solid content concentration of the obtained PFA aqueous dispersion is 22.8 mass%, and the average primary particle size is 0.26 μm.

[0284] Comparative Example 1 Nitric acid was added to the PFA aqueous dispersion obtained in Production Example 1, and coagulation was carried out by applying intense mechanical shearing force. The obtained wet powder was then filtered and repeatedly washed with fresh deionized water. The obtained wet powder was dried for 6 hours in a hot air circulation dryer at 180°C to obtain a PFA powder. The obtained PFA powder had a PPVE content of 3.9% by mass, an MFR of 40 g / 10 min, a melting point of 310°C, an average secondary particle diameter of 1.5 μm, and a specific surface area of ​​16.0 m. ２ / g.

[0285] Example 1 The PFA aqueous dispersion obtained in Production Example 1 was placed in another reactor, the contents of the reactor were heated to 80 ° C, and 30.3 g of ammonium persulfate (10 times the molar amount of the fluorine-containing surfactant used in polymerization) was added as a radical generator. Thereafter, the temperature was maintained at 80 ° C for 3 hours to obtain a heat-treated PFA aqueous dispersion. Nitric acid was added to the obtained heat-treated PFA aqueous dispersion, and the mixture was stirred and coagulated to obtain a wet powder, which was then dried at 180 ° C for 6 hours. The PPVE content of the obtained PFA powder was 3.9 mass%, MFR was 40 g / 10 min, the melting point was 310 ° C, the average secondary particle diameter was 1.6 μ m, and the specific surface area was 15.6 m ２ / g, the number of functional groups is 10 main chain carbon atoms ６ There were 286 per piece.

[0286] The content of perfluoroethercarboxylic acid contained in the obtained powder is shown in Table 8.

[0287] The obtained powder contains a compound of general formula (H2): [C ｎ－１ F ２ｎ－１ COO － ]M ＋ The contents of the compounds represented by the formula are shown in Table 9.

[0288] Next, embodiments of liquid coating compositions containing the PFA powder obtained in the above examples and comparative examples will be described with reference to examples.

[0289] The values ​​in the examples were measured by the following methods: <Contact angle> The contact angles with water and n-cetane were measured using a contact angle meter CA-DT model manufactured by Kyowa Interface Science Co., Ltd.

[0290] <Coefficient of Friction> Using a surface property tester HEIDON Type 38 manufactured by Shinto Scientific Co., Ltd., the static and dynamic coefficients of friction were measured when a ball indenter was pressed against the surface with a load (1 kg) and moved at a speed of 600 mm / min. The results are shown in Table 10.

[0291] Comparative Example 2 10 g of the PFA powder obtained in Comparative Example 1 and 10 g of polyethersulfonic acid resin (PES5003P manufactured by Sumitomo Chemical Co., Ltd.) were added to a mixed solvent of 50 g of 3-methoxy-N,N-dimethylpropanamide, 15 g of methyl isobutyl ketone, and 15 g of xylene, and dissolved and dispersed using a ball mill to obtain a PFA powder dispersion composition. Next, this dispersion composition was applied to a 0.5 mm thick stainless steel plate that had been treated with paint-type chromate using a bar coater so that the dry film thickness was 10 μm, and the plate was baked at 400 ° C for 90 seconds to obtain a coating. The contact angle and friction coefficient of this coating were measured.

[0292] Example 2 A coating was obtained in the same manner as in Comparative Example 3, except that the PFA powder obtained in Example 1 was used instead of the PFA powder obtained in Comparative Example 1. The contact angle and friction coefficient of this coating were measured. The results are shown in Table 10.

[0293]

[0294] Production Example 2 According to the production method described in Example 1 of JP 2010-235667 A, the reaction scale, reaction pressure, TFE charge amount, HFP charge amount, PPVE charge amount, ammonium persulfate charge amount, etc. were appropriately adjusted to obtain an aqueous dispersion of TFE / HFP / PPVE copolymer (FEP). The solid content concentration of the obtained FEP aqueous dispersion was 20.1 mass%.

[0295] The obtained polymer had an MFR of 35.7 g / 10 min, a composition ratio (mass %) of TFE / HFP / PPVE=87.6 / 11.5 / 0.9, and a melting point of 257°C.

[0296] Preparation Example 3: The FEP aqueous dispersion obtained in Preparation Example 2 was placed in another reactor, and the contents of the reactor were heated to 80°C. As a radical generator, ammonium persulfate was added in an amount of 10 times the molar amount of the fluorine-containing surfactant used in polymerization. Then, the temperature was kept at 80°C for 3 hours to obtain a heat-treated FEP aqueous dispersion. Nitric acid was added to the obtained heat-treated FEP aqueous dispersion, and the mixture was stirred and coagulated to obtain a wet powder, which was then dried at 180°C for 6 hours. The obtained FEP powder had an MFR of 35.5g / 10min, a composition ratio (mass%) of TFE / HFP / PPVE=87.6 / 11.5 / 0.9, and a melting point of 256°C.

[0297] Example 3: A pulverized powder was obtained in accordance with the method described in Example 1 of International Publication No. 97 / 040089, except that the powder compressed into a sheet was changed to the powder obtained in Production Example 3. The specific gravity of the obtained sheet was measured using a hydrometer to be 2.04, confirming that the density had been increased to 95% of the direct specific gravity. The fine particle removal rate was 16% by mass, and the coarse particle removal rate was 4% by mass.

[0298] The obtained powder after pulverization had an average secondary particle size of 60 μm and an apparent density of 0.88 g / mL, as measured in accordance with JIS K 6891-5.3.

[0299] The obtained powder contains a compound of general formula (H2): [C ｎ－１ F ２ｎ－１ COO － ]M ＋ The contents of the compounds represented by the formula are shown in Table 11.

Claims

1. A powder containing particles of a fluoropolymer, The powder contains a fluorine-containing compound having a hydrophilic group, and the content of the fluorine-containing compound having a hydrophilic group is 250 ppb by mass or less relative to the powder, The average secondary particle size of the fluoropolymer particles is 0.5 to 10 μm; The fluoropolymer is at least one selected from the group consisting of tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer, tetrafluoroethylene / hexafluoropropylene copolymer, and tetrafluoroethylene / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymer. powder.

2. Specific surface area is 8m ２ The powder according to claim 1, wherein the molecular weight is 1 / g or more.

3. 3. The powder according to claim 1, wherein the average primary particle size of the fluoropolymer particles is less than 0.5 μm.

4. 3. The powder according to claim 1, wherein the perfluoro(alkyl vinyl ether) is perfluoro(propyl vinyl ether).

5. 3. The powder according to claim 1, wherein the fluoropolymer has a melt flow rate at 372°C of 10 g / 10 min or more.

6. 3. The powder according to claim 1, wherein the melting point of the fluoropolymer is 220° C. or higher.

7. The fluoropolymer has a functional group, and the number of the functional groups is 10 or less. ６ The powder according to claim 1 or 2, wherein each particle has more than 50 particles.

8. The fluorine-containing compound having a hydrophilic group is represented by the following general formula (N ０ 3. The powder according to claim 1 or 2, which is a compound represented by the formula: General formula (N ０ ):X ｎ０ -Rf ｎ０ -Y ０ (In the formula, X ｎ０ is H, Cl or F. ｎ０ is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, some or all of the H's being replaced by F, and the alkylene group may contain one or more ether bonds, and some of the H's may be replaced by Cl. Y ０ is an anionic group.)

9. 3. The powder according to claim 1, wherein the fluorine-containing compound having a hydrophilic group contains at least a compound (H2) represented by general formula (H2), and the content of compound (H2) is 25 ppb by mass or less relative to the powder. General formula (H2): [C ｎ－１ F ２ｎ－１ COO － ] ＋ (wherein n is an integer from 4 to 14; M ＋ represents a cation.)

10. 3. The powder according to claim 1, wherein the fluorine-containing compound having a hydrophilic group contains at least a perfluoroether carboxylic acid.

11. A powder coating comprising the powder according to claim 1 or 2.

12. 1. A method for producing a powder containing particles of a fluoropolymer, comprising the steps of: A fluoromonomer is polymerized in a reactor in the presence of a fluorine-containing surfactant, a polymerization initiator and an aqueous medium to prepare an aqueous dispersion containing primary particles of at least one fluoropolymer selected from the group consisting of a tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer, a tetrafluoroethylene / hexafluoropropylene copolymer and a tetrafluoroethylene / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymer; After preparing the aqueous dispersion, at least one of the following operations is carried out: removing the fluoromonomer remaining in the reactor from the reactor; and recovering the aqueous dispersion in the reactor and storing it in a container different from the reactor; a radical generator is added to the aqueous dispersion in an amount equivalent to 5 molar times or more the molar amount of the fluorine-containing surfactant used in the polymerization; The aqueous dispersion containing the radical generator is subjected to a heat treatment, coagulating the fluoropolymer in the heat-treated aqueous dispersion to produce a wet powder containing particles of fluoropolymer; The wet powder is dried at a temperature not exceeding 50° C. below the melting point of the fluoropolymer to produce the powder. Manufacturing method.

13. A liquid coating composition comprising the powder according to claim 1 or 2.

14. A powder containing particles of a fluoropolymer, The powder contains a fluorine-containing compound having a hydrophilic group, and the content of the fluorine-containing compound having a hydrophilic group is 250 ppb by mass or less relative to the powder, the fluoropolymer is at least one selected from the group consisting of tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymers, tetrafluoroethylene / hexafluoropropylene copolymers, and tetrafluoroethylene / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymers; The raw powder containing the fluoropolymer is densified by a roll under conditions where a specific gravity of 90% or more of the true specific gravity is obtained, and then pulverized, and fine particles in the range of 3 to 40% by mass of the whole particle size distribution of the pulverized product are removed by air classification, and coarse particles in the range of 1 to 20% by mass of the whole particle size distribution of the pulverized product are further removed by classification to obtain the above-mentioned powder. powder.

15. The fluorine-containing compound having a hydrophilic group is represented by the following general formula (N ０ 15. The powder according to claim 14, which is a compound represented by the formula: General formula (N ０ ):X ｎ０ -Rf ｎ０ -Y ０ (In the formula, X ｎ０ is H, Cl or F. ｎ０ is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, some or all of the H's being replaced by F, and the alkylene group may contain one or more ether bonds, and some of the H's may be replaced by Cl. Y ０ is an anionic group.)

16. The powder according to claim 14 or 15, wherein the average secondary particle size of the fluoropolymer particles is 5 to 100 μm.

17. The powder according to claim 14 or 15, wherein the pulverization of the densified raw powder is carried out at a temperature of 20 to 100°C.

18. 1. A method for producing a powder containing particles of a fluoropolymer, comprising the steps of: A fluoromonomer is polymerized in a reactor in the presence of a fluorine-containing surfactant, a polymerization initiator and an aqueous medium to prepare an aqueous dispersion containing primary particles of at least one fluoropolymer selected from the group consisting of a tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer, a tetrafluoroethylene / hexafluoropropylene copolymer and a tetrafluoroethylene / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymer; After preparing the aqueous dispersion, at least one of the following operations is carried out: removing the fluoromonomer remaining in the reactor from the reactor; and recovering the aqueous dispersion in the reactor and storing it in a container different from the reactor; a radical generator is added to the aqueous dispersion in an amount equivalent to 5 molar times or more the molar amount of the fluorine-containing surfactant used in the polymerization; The aqueous dispersion containing the radical generator is subjected to a heat treatment, coagulating the fluoropolymer in the heat-treated aqueous dispersion to produce a wet powder containing particles of fluoropolymer; The wet powder is dried to prepare a raw powder containing the fluoropolymer; The raw powder containing the fluoropolymer is densified and pulverized under conditions in which a specific gravity of 90% or more of the true specific gravity is obtained using a roll, and then the powder is produced by removing fine particles within a range of 3 to 40% by mass of the entire particle size distribution of the pulverized product using air classification, and further removing coarse particles within a range of 1 to 20% by mass of the entire particle size distribution of the pulverized product using classification. Manufacturing method.