Powder containing particles of fluorine-containing polymer, method for producing same, powder coating material, and liquid coating material composition

Abstract

Provided is a powder containing particles of a fluorine-containing polymer, 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 particles of the fluorine-containing polymer having an average secondary particle diameter of 0.5 [mu] m to 10 [mu] m, and the particles of the fluorine-containing polymer having an average secondary particle diameter of 0.5 [mu] m to 10 [mu] m. The fluorine-containing polymer is at least one type 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

Technical Field

[0001] The present invention relates to a powder containing fluorine-containing polymer particles, a method for producing the powder, a powder coating and a liquid coating composition. Background Art

[0002] Patent Document 1 describes a TFE hot-processable perfluoropolymer containing the following amount of perfluoroalkyl vinyl ether in terms of weight percentage relative to the total amount of monomers.

[0003] a) 0.2% to 5.5% perfluoromethyl vinyl ether (PMVE);

[0004] b) 0.4% to 4.5% of perfluoroethyl vinyl ether (PEVE) and / or perfluoropropyl vinyl ether (PFVE);

[0005] c) 0.5% to 6% hexafluoropropylene (HFP);

[0006] The amount of perfluoroalkyl vinyl ether a) + b) is in the range of 1.5 wt% to 5.5 wt% based on the total amount of monomers;

[0007] The amount of TFE adds up to 100% by weight.

[0008] Patent Document 2 describes a mixture of a thermoplastic fluorinated polymer, which essentially comprises units of tetrafluoroethylene and 0.5 mol% to 10 mol% of units of one or more perfluoroalkyl vinyl ethers having 1 to 4 carbon atoms in the perfluoroalkyl group, wherein:

[0009] Include:

[0010] - at least 10% by weight but less than 90% by weight of a proportion having an MFI of 30 or more A at least one component A), and

[0011] - less than 90% by weight but at least 10% by weight of a proportion having an MFI of less than 15 B at least one component B),

[0012] At this time, each component is based on the MFI of component A). A MFI relative to component B) B The ratio is selected in the range of 80 to 2500.

[0013] Patent document 3 describes a method for producing a melt-moldable fluororesin, which is a method for producing a melt-moldable fluororesin by emulsion polymerization of a fluorinated monomer or a fluorinated monomer and an olefin in an aqueous medium containing a fluorinated emulsifier represented by the formula (1): CF3CF2OCF2CF2OCF2COONH4, characterized in that the melt-moldable fluororesin is selected from 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 / ethylene molar ratio of 65 / 35 to 50 / 50 A melt-moldable fluororesin comprising a tetrafluoroethylene / ethylene copolymer having a molar ratio of tetrafluoroethylene / ethylene of 65 / 35 to 50 / 50, a chlorotrifluoroethylene / ethylene copolymer having a molar ratio of chlorotrifluoroethylene / ethylene of 65 / 35 to 50 / 50, a tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride copolymer having a molar ratio of tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride of 35 to 75 / 5 to 15 / 20 to 50, a tetrafluoroethylene / hexafluoropropylene / ethylene copolymer having a molar ratio of tetrafluoroethylene / hexafluoropropylene / ethylene of 35 to 65 / 5 to 15 / 30 to 50, a tetrafluoroethylene / hexafluoropropylene / perfluoro(alkyl vinyl ether) copolymer having a molar ratio of tetrafluoroethylene / hexafluoropropylene / perfluoro(alkyl vinyl ether) of 88 to 94.8 / 5 to 10 / 0.2 to 2, and polyvinylidene fluoride.

[0014] Prior art literature

[0015] Patent Literature

[0016] Patent Document 1: International Publication No. 2007 / 96347

[0017] Patent Document 2: Japanese Patent Application No. 2002-503744

[0018] Patent Document 3: Japanese Patent Application Publication No. 2013-100532 Summary of the invention

[0019] Problems to be solved by the invention

[0020] An object of the present invention is to provide a powder containing fluorinated polymer particles in which the content of a fluorinated compound having a hydrophilic group is reduced.

[0021] Another object of the present invention is to provide a method for producing a powder containing fluorinated polymer particles in which the content of a fluorinated compound having a hydrophilic group is reduced.

[0022] Means for solving problems

[0023] According to the present invention, there is provided a powder, which is a powder containing particles of a fluorine-containing polymer, wherein the powder contains a fluorine-containing compound having a hydrophilic group, the content of the fluorine-containing compound having a hydrophilic group is 250 mass ppb or less relative to the powder, the average secondary particle size of the particles of the fluorine-containing polymer is 0.5 μm to 10 μm, and the fluorine-containing polymer 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.

[0024] Effects of the Invention

[0025] According to the present invention, there can be provided a powder containing fluorine-containing polymer particles in which the content of a fluorine-containing compound having a hydrophilic group is reduced.

[0026] Furthermore, according to the present invention, there can be provided a method for producing a powder containing fluorinated polymer particles in which the content of the fluorinated compound having a hydrophilic group is reduced. DETAILED DESCRIPTION

[0027] Before describing the present invention in detail, some terms used in the present invention are defined or described.

[0028] In the present invention, fluororesin refers to a partially crystalline fluorine-containing polymer, which is a fluoroplastic. Fluororesin has a melting point, is thermoplastic, and can be melt-processable or non-melt-processable.

[0029] In the present invention, melt processability means that the polymer can be melted and processed using existing processing equipment such as extruders and injection molding machines. Therefore, melt-processable fluororesins generally have a melt flow rate of 0.01 g / 10 min to 500 g / 10 min as measured by the measurement method described below.

[0030] In the present invention, the fluororesin (excluding polytetrafluoroethylene) is preferably a fluorine-containing polymer having a tetrafluoroethylene unit content of less than 99 mol % based on all polymer units.

[0031] In the present invention, the content of each monomer constituting the fluorine-containing polymer can be calculated by appropriately combining NMR, FT-IR, elemental analysis and fluorescent X-ray analysis according to the type of the monomer.

[0032] In the present invention, the "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.

[0033] Examples of the "organic group" include:

[0034] an alkyl group which may have one or more substituents,

[0035] an alkenyl group which may have one or more substituents,

[0036] an alkynyl group which may have one or more substituents,

[0037] a cycloalkyl group which may have one or more substituents,

[0038] a cycloalkenyl group which may have one or more substituents,

[0039] a cycloalkadienyl group which may have one or more substituents,

[0040] an aryl group which may have one or more substituents,

[0041] an aralkyl group which may have one or more substituents,

[0042] a non-aromatic heterocyclic group which may have one or more substituents,

[0043] a heteroaryl group which may have one or more substituents,

[0044] Cyano,

[0045] Formyl,

[0046] RaO-,

[0047] RaCO-,

[0048] RaSO2-,

[0049] RaCOO-

[0050] RaNRaCO-,

[0051] RaCONRa-

[0052] RaOCO-,

[0053] RaOSO2-, and

[0054] RaNRbSO2-

[0055] (In these formulas, Ra is independently

[0056] an alkyl group which may have one or more substituents,

[0057] an alkenyl group which may have one or more substituents,

[0058] an alkynyl group which may have one or more substituents,

[0059] a cycloalkyl group which may have one or more substituents,

[0060] a cycloalkenyl group which may have one or more substituents,

[0061] a cycloalkadienyl group which may have one or more substituents,

[0062] an aryl group which may have one or more substituents,

[0063] an aralkyl group which may have one or more substituents,

[0064] A non-aromatic heterocyclic group which may have one or more substituents, or

[0065] a heteroaryl group which may have one or more substituents,

[0066] Rb is independently H or an alkyl group which may have one or more substituents).

[0067] As the organic group, an alkyl group which may have one or more substituents is preferred.

[0068] In the present invention, a "substituent" refers to a group that can be substituted. 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 sulfonamide group, an aromatic sulfonamide group, a heterocyclic sulfonamide group, an amino group, an aliphatic an aliphatic amino group, an aromatic amino group, a heterocyclic amino group, an aliphatic oxycarbonylamino group, an aromatic oxycarbonylamino group, a heterocyclic oxycarbonylamino group, an aliphatic sulfinyl group, an aromatic sulfinyl group, an aliphatic thiol group, an aromatic thiol group, a hydroxyl group, a cyano group, a sulfo group, a carboxyl group, an aliphatic oxyamino group, an aromatic oxyamino group, a carbamoylamino group, a sulfamoylamino group, a halogen atom, a sulfamoylcarbamoyl group, a carbamoylsulfamoyl group, a dialiphatic oxyphosphinyl group, and a diaromatic oxyphosphinyl group.

[0069] The aliphatic group may be saturated or unsaturated, and may have a hydroxyl group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thiol group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aliphatic group include an alkyl group having a total carbon number of 1 to 8, preferably 1 to 4, such as a methyl group, an ethyl group, a vinyl group, a cyclohexyl group, a carbamoylmethyl group, etc.

[0070] 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 thiol group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aromatic group include an aryl group 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-methylsulfonylphenyl group.

[0071] The heterocyclic group may have a halogen atom, a hydroxyl group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thiol group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the heterocyclic group include a 5- to 6-membered heterocyclic ring having a total carbon number of 2 to 12, preferably 2 to 10, such as a 2-tetrahydrofuranyl group and a 2-pyrimidinyl group.

[0072] The acyl group may have an aliphatic carbonyl group, an arylcarbonyl group, a heterocyclic carbonyl group, a hydroxyl group, a halogen atom, an aromatic group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thiol group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the acyl group include an acyl group having a total carbon number of 2 to 8, preferably 2 to 4, such as an acetyl group, a propionyl group, a benzoyl group, a 3-pyridinecarbonyl group, etc.

[0073] The acylamino group may have an aliphatic group, an aromatic group, a heterocyclic group, etc., and may have, for example, an acetylamino group, a benzoylamino group, a 2-pyridinecarbonylamino group, a propionylamino group, etc. Examples of the acylamino group include acylamino groups having a total carbon number of 2 to 12, preferably 2 to 8, and alkylcarbonylamino groups having a total carbon number of 2 to 8, such as acetylamino groups, benzoylamino groups, 2-pyridinecarbonylamino groups, and propionylamino groups.

[0074] The aliphatic oxycarbonyl group may be saturated or unsaturated, and may have a hydroxyl group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thiol group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aliphatic oxycarbonyl group include an alkoxycarbonyl group having a total carbon number of 2 to 8, preferably 2 to 4, such as a methoxycarbonyl group, an ethoxycarbonyl group, a tert-butoxycarbonyl group, etc.

[0075] 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 and an alkyl carbamoyl group having 2 to 9 carbon atoms in total, preferably an unsubstituted carbamoyl group and an alkyl carbamoyl group having 2 to 5 carbon atoms in total, such as N-methyl carbamoyl group, N,N-dimethyl carbamoyl group, N-phenyl carbamoyl group, etc.

[0076] The aliphatic sulfonyl group may be saturated or unsaturated, and may have a hydroxyl group, an aromatic group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thiol group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aliphatic sulfonyl group include an alkylsulfonyl group having a total carbon number of 1 to 6, preferably a total carbon number of 1 to 4, such as a methylsulfonyl group.

[0077] The aromatic sulfonyl group may have a hydroxyl group, an aliphatic group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thiol group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aromatic sulfonyl group include an arylsulfonyl group having a total carbon number of 6 to 10, such as a benzenesulfonyl group.

[0078] The amino group may have an aliphatic group, an aromatic group, a heterocyclic group or the like.

[0079] The acylamino group may include, for example, acetylamino, benzoylamino, 2-pyridinecarbonylamino, propionylamino, etc. Examples of the acylamino group include acylamino groups having a total carbon number of 2 to 12, preferably acylamino groups having a total carbon number of 2 to 8, and more preferably alkylcarbonylamino groups having a total carbon number of 2 to 8, such as acetylamino, benzoylamino, 2-pyridinecarbonylamino, propionylamino, etc.

[0080] The aliphatic sulfonamide group, aromatic sulfonamide group, and heterocyclic sulfonamide group may be, for example, a methanesulfonamide group, a benzenesulfonamide group, a 2-pyridinesulfonamide group, or the like.

[0081] 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 total carbon atoms, a dialkylsulfamoyl group having 2 to 10 total carbon atoms, an arylsulfamoyl group having 7 to 13 total carbon atoms, and a heterocyclic sulfamoyl group having 2 to 12 total carbon atoms. More preferred examples include a sulfamoyl group, an alkylsulfamoyl group having 1 to 7 total carbon atoms, a dialkylsulfamoyl group having 3 to 6 total carbon atoms, an arylsulfamoyl group having 6 to 11 total carbon atoms, and a heterocyclic sulfamoyl group having 2 to 10 total carbon atoms, such as a sulfamoyl group, a methylsulfamoyl group, an N,N-dimethylsulfamoyl group, a phenylsulfamoyl group, and a 4-pyridylsulfamoyl group.

[0082] The aliphatic oxy group may be saturated or unsaturated, and may include methoxy, ethoxy, isopropoxy, cyclohexyloxy, methoxyethoxy, etc. Examples of the aliphatic oxy group include alkoxy groups having a total carbon number of 1 to 8, preferably 1 to 6, such as methoxy, ethoxy, isopropoxy, cyclohexyloxy, methoxyethoxy, etc.

[0083] 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 condensed with the aromatic group, or an aliphatic oxycarbonyl group, and preferably may have an aliphatic group having a total carbon number of 1 to 4, an aliphatic oxy group having a total carbon number of 1 to 4, a halogen atom, a carbamoyl group having a total carbon number of 1 to 4, a nitro group, or an aliphatic oxycarbonyl group having a total carbon number of 2 to 4.

[0084] The aliphatic thiol group may be saturated or unsaturated, and examples thereof include alkylthio groups having 1 to 8 total carbon atoms, more preferably 1 to 6 total carbon atoms, such as methylthio, ethylthio, carbamoylmethylthio, tert-butylthio and the like.

[0085] The carbamoylamino group may have an aliphatic group, an aryl group, a heterocyclic group, etc. Examples of the carbamoylamino group include carbamoylamino groups, alkylcarbamoylamino groups having 2 to 9 total carbon atoms, dialkylcarbamoylamino groups having 3 to 10 total carbon atoms, arylcarbamoylamino groups having 7 to 13 total carbon atoms, and heterocycliccarbamoylamino groups having 3 to 12 total carbon atoms. Carbamoylamino groups, alkylcarbamoylamino groups having 2 to 7 total carbon atoms, dialkylcarbamoylamino groups having 3 to 6 total carbon atoms, arylcarbamoylamino groups having 7 to 11 total carbon atoms, and heterocycliccarbamoylamino groups having 3 to 10 total carbon atoms are preferred, such as carbamoylamino groups, methylcarbamoylamino groups, N,N-dimethylcarbamoylamino groups, phenylcarbamoylamino groups, and 4-pyridylcarbamoylamino groups.

[0086] In the present invention, the range represented by endpoints includes all the numerical values ​​included in the range (for example, 1 to 10 includes 1.4, 1.9, 2.33, 5.75, 9.98, etc.).

[0087] In the present invention, the term "at least 1" includes all numerical values ​​greater than or equal to 1 (for example, 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.).

[0088] Hereinafter, specific embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments.

[0089] The present invention relates to a powder containing particles of a fluorinated polymer. The powder of the present invention is a powder containing particles of a fluorinated polymer, wherein the powder contains a fluorinated compound having a hydrophilic group, the content of the fluorinated compound having a hydrophilic group is 250 ppb or less relative to the powder, and the fluorinated polymer 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.

[0090] Fluorine-containing polymers are produced by emulsion polymerization of fluorine-containing monomers or fluorine-containing monomers and olefins in an aqueous medium containing a fluorine-containing emulsifier, as described in Patent Document 3. In addition, Example 1 of Patent Document 3 describes that the aqueous emulsion obtained by emulsion polymerization is frozen to precipitate the copolymer, which is then dried at 150° C. for 12 hours to obtain a tetrafluoroethylene / perfluoro(propyl vinyl ether) copolymer. The powder of the copolymer obtained in this way contains the fluorine-containing emulsifier used in the polymerization.

[0091] Such a fluorinated compound having a hydrophilic group, such as a fluorinated emulsifier, is an unnecessary compound when the copolymer is used for various purposes, and therefore, it is preferably removed from the copolymer.

[0092] The powder of the present invention contains a fluorine-containing compound having a hydrophilic group, and the content thereof is reduced to 250 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 invention, the obtained molded body or coating film fully demonstrates the excellent properties of the fluorine-containing polymer constituting the molded body, that is, the tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer, the tetrafluoroethylene / hexafluoropropylene copolymer, or the tetrafluoroethylene / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymer.

[0093] In one embodiment, a powder (sometimes referred to as "first powder" in the present invention) is provided, which is a powder containing particles of a fluorinated polymer, wherein the powder contains a fluorinated compound having a hydrophilic group, the content of the fluorinated compound having a hydrophilic group is 250 mass ppb or less relative to the powder, the average secondary particle size of the particles of the fluorinated polymer is 0.5 μm to 10 μm, and the fluorinated polymer 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.

[0094] The first powder has a reduced content of the fluorine-containing compound having a hydrophilic group and an average secondary particle size of 0.5 μm to 10 μm, so it is easy to handle and mold. In addition, by using the powder of the present invention for powder coating, a coating film can be easily formed.

[0095] In one embodiment, a powder (sometimes referred to as "second powder" in the present invention) is provided, which is a powder containing particles of a fluorine-containing polymer, wherein the powder contains a fluorine-containing compound having a hydrophilic group, the content of the fluorine-containing compound having a hydrophilic group is 250 ppb or less relative to the powder, and the fluorine-containing polymer 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, and the raw material powder containing the fluorine-containing polymer is densified using a roller under conditions such that a specific gravity of 90% or more of the true specific gravity is obtained, and after pulverization, fine particles in the range of 3% to 40% by mass of the overall particle size distribution of the pulverized product are removed by air flow classification, and coarse particles in the range of 1% to 20% by mass of the overall particle size distribution of the pulverized product are further removed by classification, thereby obtaining the powder.

[0096] In addition to reducing the content of the fluorine-containing compound having a hydrophilic group, the second powder is obtained by using a roller to obtain a high density of the raw material powder containing the fluorine-containing polymer under the condition of obtaining a specific gravity of 90% or more of the true specific gravity, and then removing 3% to 40% of the particles in the range of the particle size distribution of the crushed product by air flow classification, and then removing 1% to 20% of the coarse particles in the overall particle size distribution of the crushed product by classification, so that it is a uniform particle form, a narrow particle size distribution, and excellent fluidity. By using the second powder for powder coating, it is also easy to form a uniform and thin coating film on the surface.

[0097] Next, the powder and the method for producing the powder of the present invention are described in detail.

[0098] 1. Powder

[0099] (1st powder)

[0100] The first powder of the present invention is a powder containing particles of a fluorinated polymer, wherein the average secondary particle size of the particles of the fluorinated polymer is 0.5 μm to 10 μm. In the present invention, the powder is an aggregate of particles of a fluorinated polymer. When a fluorinated polymer is produced by emulsion polymerization, the particles of the fluorinated polymer are secondary particles formed by agglomeration of primary particles obtained by polymerization. An aqueous dispersion in which primary particles of a fluorinated polymer are dispersed in an aqueous medium is usually obtained by emulsion polymerization of a fluorinated monomer. The particles of the fluorinated polymer are formed by agglomerating primary particles in an aqueous dispersion. The formed agglomerates are recovered and dried to obtain a powder (aggregate) of particles of the fluorinated polymer.

[0101] The fluorinated polymer particles constituting the first powder of the present invention 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 primary particles dispersed in the aqueous dispersion (average primary particle size) and is the average particle size of secondary particles formed by agglomeration of primary particles.

[0102] The average secondary particle size of the fluorinated polymer particles contained in the first powder is 0.5 μm to 10 μm, preferably 1 μm or more, preferably 5 μm or less, and more preferably 3 μm or less. By making the average secondary particle size of the fluorinated polymer particles within the above range, a coating film with uniform thickness can be easily obtained without impairing workability.

[0103] The average secondary particle size of the particles of the fluoropolymer contained in the first powder can be adjusted as follows: the primary particles of the fluoropolymer are prepared by polymerizing the fluoromonomer in the presence of a fluorosurfactant, a polymerization initiator and an aqueous medium, and the primary particles of the fluoropolymer obtained by polymerization are precipitated and dried at an appropriate temperature, thereby adjusting. The powder thus obtained is not formed by the fusion of the particles (secondary particles) of the fluoropolymer, but is formed by the aggregation of the particles of the fluoropolymer. Therefore, the average secondary particle size of the particles of the fluoropolymer in the powder can be within the above range.

[0104] The average secondary particle size of the fluorinated polymer particles is a volume-based average particle size (50% cumulative particle size) d50, which can be determined by a laser diffraction method.

[0105] The average primary particle size of the particles of the fluorinated polymer contained in the first powder is preferably less than 0.5 μm, preferably 0.01 μm or more. The average particle size of the average primary particle size of the particles of the fluorinated polymer can be measured by a dynamic light scattering method. First, an aqueous dispersion of a fluorinated polymer in which the polymer solid content concentration is adjusted to about 1.0% by mass is prepared, and the dynamic light scattering method is used, the measurement temperature is set to 25°C, the refractive index of the solvent (water) is set to 1.3328, the viscosity of the solvent (water) is set to 0.8878 mPa·s, and the cumulative number of times is set to 70 times, and the measurement can be performed. In the dynamic light scattering method, for example, ELSZ-1000S (manufactured by Otsuka Electronics Co., Ltd.) can be used.

[0106] The specific surface area of ​​the first powder is preferably 8 m 2 / g or more, 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 having an excellent appearance can be obtained more easily.

[0107] The specific surface area of ​​the powder containing the particles of the fluoropolymer contained in the first powder can be adjusted, for example, as follows: primary particles of the fluoropolymer are prepared by polymerizing the fluoromonomer in the presence of a fluorosurfactant, a polymerization initiator and an aqueous medium, and the primary particles of the fluoropolymer obtained by polymerization are precipitated and dried at an appropriate temperature, thereby adjusting. The specific surface area of ​​the primary particles thus obtained is relatively small. Furthermore, the particles (secondary particles) of the fluoropolymer constituting the powder thus obtained are not formed by the fusion of the primary particles of the fluoropolymer, but are formed by the only agglomeration of the primary particles of the fluoropolymer. Therefore, the specific surface area of ​​the powder can reflect the specific surface area of ​​the primary particles of the fluoropolymer, and a relatively large specific surface area can be obtained.

[0108] The specific surface area of ​​the powder is a value measured using a surface analyzer according to the BET method.

[0109] (Second powder)

[0110] The second powder of the present invention is a powder containing particles of a fluorine-containing polymer, which is obtained by the following manufacturing method: a raw material powder containing a fluorine-containing polymer is densified using a roller under conditions where a specific gravity of 90% or more of the true specific gravity is obtained, and after pulverization, fine particles in the range of 3% to 40% by mass of the overall particle size distribution of the pulverized material are removed by air flow classification, and coarse particles in the range of 1% to 20% by mass of the overall particle size distribution of the pulverized material are further removed by classification.

[0111] The second powder is obtained by the above-mentioned manufacturing method, so the apparent density is large, and the shape of the particles of the fluorine-containing polymer constituting the powder is uniform. In addition, the second powder is a uniform particle form with a narrow particle size distribution. Therefore, the second powder is excellent in fluidity.

[0112] The average secondary particle size of the fluorinated polymer particles constituting the second powder is preferably 5 μm to 100 μm, more preferably 15 μm or more, further preferably 30 μm or more, and more preferably 80 μm or less. By making the average secondary particle size of the fluorinated polymer particles within the above range, a thick coating film with uniform thickness can be easily obtained without impairing fluidity.

[0113] The apparent density of the second powder is preferably 0.60 g / mL to 1.00 g / mL. The apparent density of the powder can be measured in accordance with JIS K6891-5.3.

[0114] (Fluorine-containing compound having a hydrophilic group)

[0115] The first powder and the second powder (in the present invention, both are sometimes referred to as "powders of the present invention") 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 generated by polymerization of a fluorine-containing monomer.

[0116] In the present invention, as the hydrophilic group possessed by the fluorine-containing compound, anionic groups such as acid groups are preferred, for example, -NH2, -PO3M, -OPO3M, -SO3M, -OSO3M, -COOM (in each formula, M represents a cation). As the above-mentioned hydrophilic group, -SO3M or -COOM is preferred, and -COOM is more preferred.

[0117] 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, further preferably 25 ppb by mass or less, further preferably 10 ppb by mass or less, particularly preferably 5 ppb by mass or less, and preferably more than 0 ppb by mass.

[0118] The content of the fluorinated compound having a hydrophilic group in the powder can be adjusted, for example, as follows: by polymerizing the fluorinated monomer in the presence of a fluorinated surfactant, a polymerization initiator and an aqueous medium to prepare an aqueous dispersion of primary particles containing the fluorinated polymer, and by adding a relatively large amount of a free radical generator to the aqueous dispersion and performing a heat treatment to thereby adjust the content.

[0119] The content of the fluorine-containing compound having a hydrophilic group in the powder can be quantified by a known method, for example, by LC / MS analysis.

[0120] First, methanol is added to the powder for extraction, and the obtained extract is analyzed by LC / MS. In order to further improve the extraction efficiency, Soxhlet extraction, ultrasonic treatment, etc. can be used for treatment. The obtained extract is appropriately purged with nitrogen for concentration, and the fluorinated compounds in the concentrated extract are determined by LC / MS.

[0121] Molecular weight information was extracted from the obtained LC / MS spectrum, and it was confirmed that the molecular weight matched the structural formula of a candidate fluorine-containing compound having a hydrophilic group.

[0122] Then, aqueous solutions having five or more levels of the confirmed fluorinated compound having a hydrophilic group are prepared, and the aqueous solutions having each content are analyzed by LC / MS. The relationship between the content and the area of ​​the region relative to the content is plotted to create a calibration curve.

[0123] Then, using the calibration curve, the area of ​​the LC / MS chromatogram of the fluorine-containing compound having a hydrophilic group in the extract can be converted into the content of the fluorine-containing compound having a hydrophilic group.

[0124] It should be noted that the obtained extract can be concentrated by purging with nitrogen, so that the quantitative lower limit of the measurement method can be reduced.

[0125] In one embodiment of the powder, as a fluorinated compound having a hydrophilic group, at least a fluorinated surfactant is contained. The fluorinated surfactant may be a fluorinated surfactant commonly used in the polymerization of a fluorinated monomer. As the fluorinated surfactant, a typical compound is a fluorinated surfactant having a molecular weight of 1000 g / mol or less, preferably 800 g / mol or less.

[0126] The fluorinated surfactant is not particularly limited as long as it is a surfactant containing at least one fluorine atom, and a conventionally known fluorinated surfactant can be used.

[0127] Examples of the fluorinated surfactant include anionic fluorinated surfactants, etc. The anionic fluorinated surfactant may be, for example, a surfactant containing fluorine atoms and having a total carbon number of 20 or less in the moiety excluding the anionic group.

[0128] Furthermore, the fluorine-containing surfactant may be a surfactant containing fluorine whose anionic part has a molecular weight of 1,000 or less.

[0129] It should be noted that the above-mentioned "anionic part" refers to the part of the above-mentioned fluorinated surfactant other than the cation. For example, in the F(CF2) shown in the formula (I) described below n1 In the case of COOM, it is "F(CF2) n1 COO” section.

[0130] In addition, as the above-mentioned fluorinated surfactant, a fluorinated surfactant having a LogPOW of 3.5 or less can be cited. The above-mentioned LogPOW is the partition coefficient between 1-octanol and water, and is represented by LogP [wherein P represents the ratio of the fluorinated surfactant concentration in octanol to the fluorinated surfactant concentration in water when a fluorinated surfactant-containing octanol / water (1:1) mixed solution undergoes phase separation].

[0131] The above LogPOW is calculated as follows: On column: TOSOH ODS-120T column ( HPLC was performed on standard substances (heptanoic acid, octanoic acid, nonanoic acid and decanoic acid) with known octanol / water partition coefficients under the following conditions: (a) elution solvent: acetonitrile / 0.6 mass% HClO4 water = 1 / 1 (vol / vol%), flow rate: 1.0 ml / min, sample amount: 300 μL, column temperature: 40°C, detection light: UV210 nm, and a calibration curve of each elution time and the known octanol / water partition coefficient was prepared. Based on the calibration curve, the elution time of HPLC in the sample solution was calculated.

[0132] Specific examples of the fluorinated surfactant include U.S. Patent Application Publication No. 2007 / 0015864, U.S. Patent Application Publication No. 2007 / 0015865, U.S. Patent Application Publication No. 2007 / 0015866, U.S. Patent Application Publication No. 2007 / 0276103, U.S. Patent Application Publication No. 2007 / 0117914, U.S. Patent Application Publication No. 2007 / 142541, U.S. Patent Application Publication No. 2008 / 0015319, and U.S. Patent No. 3250808. Fluorinated surfactants described in Japanese Unexamined Patent Application No. 3,271,341, Japanese Unexamined Patent Application No. 2003-119204, International Publication No. 2005 / 042593, International Publication No. 2008 / 060461, International Publication No. 2007 / 046377, Japanese Unexamined Patent Application No. 2007-119526, International Publication No. 2007 / 046482, International Publication No. 2007 / 046345, U.S. Patent Application Publication No. 2014 / 0228531, International Publication No. 2013 / 189824, and International Publication No. 2013 / 189826.

[0133] Examples of the anionic fluorinated surfactant include the following general formula (N 0 ):

[0134] X n0 -Rf n0 -Y 0 (N 0 )

[0135] (Where X n0 is H, Cl or F. Rf n0 It is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms in which some or all of the H groups are substituted with F. The alkylene group may contain one or more ether bonds, and some of the H groups may be substituted with Cl. 0 is an anionic group).

[0136] Y 0The anionic group may be -COOM, -SO2M or -SO3M, or may be -COOM or -SO3M.

[0137] M is H, metal atom, NR 7 4. an imidazolium which may be substituted, a pyridinium which may be substituted, or a phosphonium which may be substituted, R 7 is H or an organic group.

[0138] Examples of the metal atom include alkali metals (Group 1) and alkaline earth metals (Group 2), such as Na, K, or Li.

[0139] As R 7 , can be H or C 1-10 The organic group can also be H or C 1-4 The organic group can also be H or C 1-4 of alkyl.

[0140] M can be H, metal atom or NR 7 4, may also be H, alkali metal (Group 1), alkaline earth metal (Group 2) or NR 7 4, and can also be H, Na, K, Li or NH4.

[0141] The above Rf n0 In the above formula (A), more than 50% of the H can be replaced by fluorine.

[0142] As the above general formula (N 0 ) can include:

[0143] The following general formula (N 1 ):

[0144] X n0 -(CF2) m1 -Y 0 (N 1 )

[0145] (Where X n0 is H, Cl and F, m1 is an integer from 3 to 15, Y 0 The compound represented by the following general formula (N 2 ):

[0146] R n1 -O-(CF(CF3)CF2O) m2 CFX n1 -Y 0 (N 2 )

[0147] (Where Rf n1is a perfluoroalkyl group having 1 to 5 carbon atoms, m2 is an integer of 0 to 3, and X n1 F or CF3, Y 0 The compound represented by the following general formula (N 3 ):

[0148] R n2 (CH2) m3 -(Rf n3 ) q -Y 0 (N 3 )

[0149] (Where Rf n2 is a partially or completely 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, Rf n3 is a linear or branched perfluoroalkylene group having 1 to 3 carbon atoms, q is 0 or 1, and Y 0 The compound represented by the following general formula (N 4 ):

[0150] R n4 -O-(CY n1 Y n2 ) p CF2-Y 0 (N 4 )

[0151] (Where Rf n4 is a linear or branched partially or completely fluorinated alkyl group having 1 to 12 carbon atoms which may contain an ether bond, n1 and Y n2 The same or different, H or F, p is 0 or 1, Y 0 The compound represented by the above-defined substance); and the general formula (N 5 ):

[0152] [Chemistry 1]

[0153]

[0154] (Where X n2 , X n3 and X n4 Rf may be the same or different and is H, F, or a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms which may contain an ether bond. n5 is a linear or branched partially or completely fluorinated alkylene group having 1 to 3 carbon atoms and may contain an ether bond, L is a connecting group, Y 0 is the substance defined above. n2 , Xn3 , X n4 and Rf n5 The total number of carbon atoms is 18 or less).

[0155] As the above general formula (N 0 ), more specifically, a perfluorocarboxylic acid (I) represented by the following general formula (I), an ω-H perfluorocarboxylic acid (II) represented by the following general formula (II), a perfluoroether carboxylic acid (III) represented by the following general formula (III), a perfluoroalkyl alkylene carboxylic acid (IV) represented by the following general formula (IV), a perfluoroalkoxy fluorocarboxylic acid (V) represented by the following general formula (V), a perfluoroalkyl sulfonic acid (VI) represented by the following general formula (VI), an ω-H perfluorosulfonic acid (VII) represented by the following general formula (VII), a perfluoroalkyl alkylene sulfonic acid (VIII) represented by the following general formula (VIII), an alkyl alkylene carboxylic acid (IX) represented by the following general formula (IX), a fluorocarboxylic acid (X) represented by the following general formula (X), an alkoxy fluorosulfonic acid (XI) represented by the following general formula (XI), a compound (XII) represented by the following general formula (XII), a compound (XIII) represented by the following general formula (XIII), and the like.

[0156] The above perfluorocarboxylic acid (I) is represented by the following general formula (I):

[0157] F(CF2) n1 COOM(I)

[0158] (where n1 is an integer from 3 to 13, M is H, a metal atom, NR 7 4. an imidazolium which may be substituted, a pyridinium which may be substituted, or a phosphonium which may be substituted, R 7 is H or an organic group).

[0159] The above-mentioned ω-H perfluorocarboxylic acid (II) is represented by the following general formula (II):

[0160] H(CF2) n2 COOM(II)

[0161] (wherein n2 is an integer of 4 to 15, and M is the substance defined above).

[0162] The above perfluoroether carboxylic acid (III) is represented by the following general formula (III):

[0163] R 1 -O-(CF(CF3)CF2O) n3 CF(CF3)COOM(III)

[0164] (Where Rf 1is a perfluoroalkyl group having 1 to 5 carbon atoms, n3 is an integer of 0 to 3, and M is the substance defined above).

[0165] The above perfluoroalkyl alkylene carboxylic acid (IV) is represented by the following general formula (IV):

[0166] R 2 (CH2) n4 R 3 COOM(IV)

[0167] (Where Rf 2 is a perfluoroalkyl group having 1 to 5 carbon atoms, 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 the substance defined above).

[0168] The above alkoxy fluorocarboxylic acid (V) is represented by the following general formula (V):

[0169] R 4 -O-CY 1 Y 2 CF2-COOM(V)

[0170] (Where Rf 4 is a linear or branched partially or completely fluorinated alkyl group having 1 to 12 carbon atoms which may contain an ether bond and / or a chlorine atom, 1 and Y 2 are the same or different, are H or F, and M is the substance defined above).

[0171] The above perfluoroalkylsulfonic acid (VI) is represented by the following general formula (VI):

[0172] F(CF2) n5 SO3M(VI)

[0173] (wherein n5 is an integer of 3 to 14, and M is the substance defined above).

[0174] The above-mentioned ω-H perfluorosulfonic acid (VII) is represented by the following general formula (VII):

[0175] H(CF2) n6 SO3M(VII)

[0176] (wherein n6 is an integer of 4 to 14, and M is the substance defined above).

[0177] The above perfluoroalkyl alkylene sulfonic acid (VIII) is represented by the following general formula (VIII):

[0178] R 5 (CH2) n7SO3M(VIII)

[0179] (Where Rf 5 is a perfluoroalkyl group having 1 to 13 carbon atoms, n7 is an integer of 1 to 3, and M is the substance defined above).

[0180] The above alkyl alkylene carboxylic acid (IX) is represented by the following general formula (IX):

[0181] R 6 (CH2) n8 COOM(IX)

[0182] (Where Rf 6 It is a linear or branched partially or completely fluorinated alkyl group having 1 to 13 carbon atoms which may contain an ether bond, n8 is an integer of 1 to 3, and M is the substance defined above).

[0183] The above fluorocarboxylic acid (X) is represented by the following general formula (X):

[0184] R 7 -O-Rf 8 -O-CF2-COOM(X)

[0185] (Where Rf 7 is a linear or branched partially or completely fluorinated alkyl group having 1 to 6 carbon atoms and which may contain an ether bond and / or a chlorine atom, Rf 8 is a linear or branched partially or completely fluorinated alkyl group having 1 to 6 carbon atoms, and M is the substance defined above).

[0186] The above alkoxy fluorosulfonic acid (XI) is represented by the following general formula (XI):

[0187] R 9 -O-CY 1 Y 2 CF2-SO3M(XI)

[0188] (Where 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, which may be partially or completely fluorinated, 1 and Y 2 are the same or different, are H or F, and M is the substance defined above).

[0189] The above compound (XII) is represented by the following general formula (XII):

[0190] [Chemistry 2]

[0191]

[0192] (Where X1 , X 2 and X 3 Rf may be the same or different and is H, F and a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms and may contain an ether bond. 10 is a perfluoroalkylene group having 1 to 3 carbon atoms, L is a connecting group, Y 0 is an anionic group).

[0193] Y 0 It can be -COOM, -SO2M or -SO3M, or -SO3M or COOM (wherein M is the substance defined above).

[0194] Examples of L include a single bond and a partially or completely fluorinated alkylene group having 1 to 10 carbon atoms which may include an ether bond.

[0195] The above compound (XIII) is represented by the following general formula (XIII):

[0196] R 11 -O-(CF2CF(CF3)O) n9 (CF2O) n10 CF2COOM(XIII)

[0197] (Where Rf 11 is a fluorinated alkyl group having 1 to 5 carbon atoms and containing chlorine, n9 is an integer of 0 to 3, n10 is an integer of 0 to 3, and M is the substance defined above). Examples of compound (XIII) include CF2ClO(CF2CF(CF3)O) n9 (CF2O) n10 CF2COONH4 (mixture with an average molecular weight of 750, wherein n9 and n10 are the numbers defined above).

[0198] As described above, examples of the anionic fluorinated surfactant include carboxylic acid-based surfactants and sulfonic acid-based surfactants.

[0199] The fluorinated surfactant may be a single type of fluorinated surfactant or a mixture containing two or more types of fluorinated surfactants.

[0200] The fluorinated surfactant preferably has no methylene group (-CH2), and more preferably has no CH bond. By using a fluorinated surfactant having no methylene group (-CH2) or CH bond in the molecule, polymerization of the fluorinated monomer in the presence of an aqueous medium can be smoothly performed.

[0201] The number of H atoms possessed by the hydrophobic group of the fluorinated surfactant is preferably 0 or 1, more preferably 0. By using a fluorinated surfactant having a small number of H atoms bonded to the carbon atoms constituting the hydrophobic group, the polymerization of the fluorinated monomer in the presence of an aqueous medium can be smoothly carried out. The number of carbon atoms in the hydrophobic group of the fluorinated surfactant having a hydrophobic group and a hydrophilic group is preferably 1 to 50, more preferably 3 to 20, and further preferably 6 to 12. The hydrophobic group usually constitutes the above-mentioned "portion other than the anionic group" in the molecular structure of the fluorinated surfactant. Examples of the hydrophilic group include Y 0 The fluorinated surfactant may be a saturated fluorinated surfactant in which all carbon atoms bonded to the hydrophobic group are substituted with fluorine atoms.

[0202] As the fluorinated surfactant, among the above anionic fluorinated surfactants, there can be mentioned the general formula (N 1 ) represented by the general formula (N 2 ) represented by the general formula (N 4 ):

[0203] R n4 -O-(CY n1 F) p CF2-Y 0 (N 4 )

[0204] (Where Rf n4 is a linear or branched partially or completely fluorinated alkyl group having 1 to 12 carbon atoms which may contain an ether bond (excluding alkyl groups having -CH2-), n1 is H or F, p is 0 or 1, Y 0 As defined above), and the compound represented by the general formula (N 5 ):

[0205] [Chemistry 3]

[0206]

[0207] (Where X n2 , X n3 and X n4 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 and which may contain an ether bond (excluding an alkyl group having -CH2-), wherein X n3 and X n4 Neither of them is H. Rf n5is a linear or branched partially or completely fluorinated alkylene group having 1 to 3 carbon atoms and which may contain an ether bond (excluding alkylene groups having -CH2-), L is a connecting group, and Y 0 As defined above. Where X n2 , X n3 , X n4 and Rf n5 The total number of carbon atoms is 18 or less).

[0208] As the fluorinated surfactant, among the above-mentioned anionic fluorinated surfactants, at least one selected from the group consisting of the following substances is more preferred, the substance being a perfluorocarboxylic acid (I) represented by the general formula (I), an ω-H perfluorocarboxylic acid (II) represented by the general formula (II), a perfluoroether carboxylic acid (III) represented by the general formula (III), a perfluoroalkyl alkylene carboxylic acid (IV) represented by the general formula (IV), a perfluoroalkoxy fluorocarboxylic acid (V) represented by the general formula (V), a perfluoroalkyl sulfonic acid (VI) represented by the general formula (VI), an ω-H perfluorosulfonic acid (VII) represented by the general formula (VII), a perfluoroalkyl alkylene sulfonic acid (VIII) represented by the general formula (VIII), and a general formula (X): Rf 7 -O-Rf 8 -O-CF2-COOM

[0209] (Where Rf 7 is a linear or branched partially or completely fluorinated alkyl group having 1 to 6 carbon atoms and which may contain an ether bond and / or a chlorine atom (excluding an alkyl group having -CH2-), Rf 8 is a linear or branched partially or completely fluorinated alkyl group having 1 to 6 carbon atoms (excluding alkyl groups having -CH2-), and M is as defined above. ) is a fluorinated carboxylic acid (X) represented by the general formula (XI): Rf 9 -O-CY 1 FCF2-SO3M

[0210] (Where Rf 9 is a linear or branched, partially or fully fluorinated alkyl group having 1 to 12 carbon atoms, which may contain an ether bond, and may contain chlorine (excluding alkyl groups having -CH2-), 1 is H or F, and M is as defined above. ) represented by an alkoxy fluorosulfonic acid (XI), general formula (XII):

[0211] [Chemistry 4]

[0212]

[0213] (Where X 1 , X 2 and X 3may be the same or different and are H, F and a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms and which may contain an ether bond (excluding an alkyl group having -CH2-), wherein X 2 and X 3 Neither of them is H, Rf 10 is a perfluoroalkylene group having 1 to 3 carbon atoms, L is a connecting group, Y 0 is an anionic group. ) and the compound (XII) represented by the general formula (XIII):

[0214] R 11 -O-(CF2CF(CF3)O) n9 (CF2O) n10 CF2COOM

[0215] (Where Rf 11 The compound (XIII) is a fluorinated alkyl group having 1 to 5 carbon atoms containing chlorine (excluding fluorinated alkyl groups having -CH2-), n9 is an integer of 0 to 3, n10 is an integer of 0 to 3, and M is as defined above. By using these fluorinated surfactants, the polymerization of fluorinated monomers in the presence of an aqueous medium can be smoothly carried out.

[0216] Examples of the fluorinated surfactant include compounds represented by the following formula: The fluorinated surfactant may be a mixture of these compounds.

[0217] F(CF2)7COOM,

[0218] F(CF2)5COOM,

[0219] H(CF2)6COOM,

[0220] H(CF2)7COOM,

[0221] CF3O(CF2)3OCHFCF2COOM,

[0222] C3F7OCF(CF3)CF2OCF(CF3)COOM,

[0223] CF3CF2CF2OCF(CF3)COOM,

[0224] CF3CF2OCF2CF2OCF2COOM,

[0225] C2F5OCF(CF3)CF2OCF(CF3)COOM,

[0226] CF3OCF(CF3)CF2OCF(CF3)COOM,

[0227] CF2ClCF2CF2OCF(CF3)CF2OCF2COOM,

[0228] CF2ClCF2CF2OCF2CF(CF3)OCF2COOM,

[0229] CF2ClCF(CF3)OCF(CF3)CF2OCF2COOM,

[0230] CF2ClCF(CF3)OCF2CF(CF3)OCF2COOM,

[0231] [Chemistry 5]

[0232]

[0233] (In each formula, M is H, metal atom, NR 7 4. An imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent. 7 is H or an organic group. )

[0234] In the case where the powder contains at least a fluorinated surfactant as a fluorinated compound having a hydrophilic group, the content of the fluorinated surfactant in the powder is preferably 250 ppb by mass or less, more preferably 100 ppb by mass or less, further preferably 50 ppb by mass or less, further preferably 25 ppb by mass or less, and preferably more than 0 ppb by mass, relative to the powder.

[0235] In one embodiment of the powder, the fluorine-containing compound having a hydrophilic group contains a perfluoroether carboxylic acid. As the perfluoroether carboxylic acid, a compound (III) represented by the following general formula (III) is preferred.

[0236] General formula (III): Rf 1 -O-(CF(CF3)CF2O) n3 CF(CF3)COOM

[0237] (Where 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, NR 7 4. an imidazolium which may be substituted, a pyridinium which may be substituted, or a phosphonium which may be substituted, R 7 is H or an organic group. )

[0238] When the powder contains at least a perfluoroether carboxylic acid as the fluorine-containing compound having a hydrophilic group, the content of the perfluoroether carboxylic acid in the powder is preferably 250 mass ppb or less, more preferably 100 mass ppb or less, further preferably 50 mass ppb or less, further preferably 25 mass ppb or less, particularly preferably 10 mass ppb or less, most preferably 5 mass ppb or less, and preferably more than 0 mass ppb.

[0239] 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.

[0240] General formula (H1): [X-Rf-A - ] i M i+

[0241] (wherein X represents H, Cl, Br, F or I, Rf represents a linear or branched partially fluorinated or fully fluorinated aliphatic group, or a linear or branched partially fluorinated or fully fluorinated aliphatic group interrupted by at least one oxygen atom, A - Represents acid group, M i+ represents a cation having a valence number i, where i represents an integer from 1 to 3)

[0242] In one embodiment of the powder, a compound represented by the following general formula (H2) is contained as the fluorine-containing compound having a hydrophilic group.

[0243] General formula (H2): [C n-1 F 2n-1 COO - ]M +

[0244] (where n represents an integer from 4 to 14, M + represents a cation.)

[0245] It is known that when perfluoroalkyl vinyl ether or the like is used as a modifying monomer, a compound represented by the general formula (H2) (perfluoroalkanoic acid) is formed during polymerization (see International Publication No. 2019 / 161153).

[0246] In the case where the powder contains at least a compound represented by the general formula (H2) as a fluorine-containing compound having a hydrophilic group, the content of the compound represented by the general formula (H2) in the powder is preferably 25 mass ppb or less, more preferably 10 mass ppb or less, further preferably 5 mass ppb or less, further preferably 1 mass ppb or less, and preferably more than 0 mass ppb.

[0247] In one embodiment of the powder, a compound represented by the following general formula (H3) is contained as the fluorine-containing compound having a hydrophilic group.

[0248] General formula (H3): [R 1 -OL-CO2 - ]M +

[0249] (Where R 1 represents a linear or branched partially fluorinated or fully fluorinated aliphatic group, or a linear or branched partially fluorinated 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 cation.)

[0250] In the case where the powder contains at least a compound represented by the general formula (H3) as a fluorine-containing compound having a hydrophilic group, the content of the compound represented by the general formula (H3) in the powder is preferably 250 mass ppb or less, more preferably 100 mass ppb or less, further preferably 50 mass ppb or less, further preferably 25 mass ppb or less, and preferably more than 0 mass ppb.

[0251] In one embodiment of the powder, the powder contains a compound represented by the general formula (H4) as the fluorine-containing compound having a hydrophilic group.

[0252] General formula (H4): H-Rf n0 -Y 0

[0253] (Where Rf n0 It is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which a part or all of the H groups are replaced by F, the alkylene group may or may not contain one or more ether bonds, and a part of the H groups may or may not be replaced by Cl. 0 is an anionic group.)

[0254] Examples of the compound represented by the general formula (H4) include compounds represented by any of the following general formulae.

[0255] General formula: [H-(CF2) m CO2 - ]M +

[0256] (wherein, m represents an integer from 3 to 19, M + represents a cation.)

[0257] General formula: [H-(CF2) m2 -(CF(CF3)) m3 -CO2 -]M +

[0258] (wherein, m2 represents an integer of 1 to 17, m3 represents an integer of 1 to 9, and M + represents a cation. Wherein, m2 and m3 are selected in a manner to satisfy 3≤(m2+2×m3)≤19, and the order of existence of each repeating unit in the formula is arbitrary. )

[0259] In the case where the powder contains at least a compound represented by the general formula (H4) as a fluorine-containing compound having a hydrophilic group, the content of the compound represented by the general formula (H4) in the powder is preferably 250 mass ppb or less, more preferably 100 mass ppb or less, further preferably 50 mass ppb or less, further preferably 25 mass ppb or less, particularly preferably 10 mass ppb or less, most preferably 5 mass ppb or less, and preferably more than 0 mass ppb.

[0260] (Fluoropolymer)

[0261] The powder of the present invention contains particles of at least one fluorine-containing polymer selected from the group consisting of tetrafluoroethylene (TFE) / perfluoro(alkyl vinyl ether) copolymers, TFE / hexafluoropropylene copolymers, and TFE / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymers.

[0262] The fluorine-containing polymer is preferably a fluororesin, more preferably a melt-processable fluororesin.

[0263] Examples of perfluoro(alkyl vinyl ether) include those of the general formula:

[0264] CF2=CF-ORf

[0265] (wherein Rf represents a perfluoroalkyl group having 1 to 10 carbon atoms.) The perfluoroalkyl group may have an ether oxygen inserted between two carbon atoms when the perfluoroalkyl group has 2 or more carbon atoms.

[0266] The perfluoroalkyl group preferably has 1 to 5 carbon atoms, more preferably 1 to 3 carbon atoms.

[0267] 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.

[0268] As the perfluoro(alkyl vinyl ether), at least one selected from the group consisting of perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether) and perfluoro(propyl vinyl ether) is preferred, at least one selected from the group consisting of perfluoro(methyl vinyl ether) and perfluoro(propyl vinyl ether) is more preferred, and perfluoro(propyl vinyl ether) is further preferred.

[0269] 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), and more preferably (97-99):(1-3).

[0270] The TFE / perfluoro(alkyl vinyl ether) copolymer may contain other monomer units copolymerizable with TFE and perfluoro(alkyl vinyl ether) in addition to TFE units and perfluoro(alkyl vinyl ether) units. As other monomers, fluorine-containing monomers (excluding TFE and perfluoro(alkyl vinyl ether)) are preferred.

[0271] Examples of fluorinated monomers (excluding TFE and perfluoro(alkyl vinyl ether)) include hexafluoropropylene, chlorotrifluoroethylene, vinyl fluoride, vinylidene fluoride, trifluoroethylene, fluoroalkylethylene, fluoroalkyl allyl ether, trifluoropropylene, pentafluoropropylene, trifluorobutylene, tetrafluoroisobutylene, hexafluoroisobutylene, and the general formula: CHX 101 =CX 102 R 101 (Where X 101 and X 102 One of them is H and the other is F, Rf 101 is a fluorinated monomer represented by a linear or branched fluorinated alkyl group having 1 to 12 carbon atoms, a fluorinated vinyl heterocyclic body, a monomer providing a crosslinking site, and the like.

[0272] As the fluorine-containing monomer (excluding TFE and perfluoro(alkyl vinyl ether)), hexafluoropropylene is preferred among them.

[0273] The content of other monomer units in the TFE / perfluoro(alkyl vinyl ether) copolymer may be 0.1% by mass to 2% by mass based on the total monomer units.

[0274] The TFE / hexafluoropropylene copolymer is a copolymer containing at least TFE units and hexafluoropropylene units. The preferred monomer composition (mass %) of the TFE / hexafluoropropylene copolymer is TFE:hexafluoropropylene=(60-95):(5-40), more preferably (85-92):(8-15).

[0275] The TFE / hexafluoropropylene copolymer may contain other monomer units copolymerizable with TFE and hexafluoropropylene in addition to the TFE units and the hexafluoropropylene units. As the other monomer, a fluorine-containing monomer (excluding TFE and hexafluoropropylene) is preferred.

[0276] Examples of fluorinated monomers (excluding TFE and hexafluoropropylene) include chlorotrifluoroethylene, vinyl fluoride, vinylidene fluoride, trifluoroethylene, perfluoro(alkyl vinyl ether), fluoroalkylethylene, fluoroalkyl allyl ether, trifluoropropylene, pentafluoropropylene, trifluorobutylene, tetrafluoroisobutylene, hexafluoroisobutylene, and the general formula: CHX 101 =CX 102 R 101 (Where X 101 and X 102 One of them is H and the other is F, Rf 101 is a fluorinated monomer represented by a linear or branched fluorinated alkyl group having 1 to 12 carbon atoms, a fluorinated vinyl heterocyclic body, a monomer providing a crosslinking site, and the like.

[0277] As the fluorine-containing monomer (excluding TFE and hexafluoropropylene), perfluoro(alkyl vinyl ether) is preferred.

[0278] Among them, the fluorinated polymer is preferably 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.

[0279] The melt flow rate of the fluorine-containing polymer at 372° C. may be 0.1 g / 10 min 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.

[0280] In the present invention, MFR is a value obtained as the mass (g / 10 minutes) of a polymer flowing out from a nozzle having an inner diameter of 2.1 mm and a length of 8 mm at 372° C. and a load of 5 kg per 10 minutes using a melt indexer in accordance with ASTM D1238.

[0281] The melting point of the fluorine-containing polymer may be 180°C to 324°C.

[0282] The melting point of the tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer can be 180°C to 324°C, preferably above 220°C, more preferably above 240°C, further preferably above 260°C, further preferably above 280°C, particularly preferably above 300°C, preferably below 320°C, more preferably below 315°C.

[0283] The melting points of tetrafluoroethylene / hexafluoropropylene copolymer and tetrafluoroethylene / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymer may be 180°C to 320°C, preferably 220°C or higher, more preferably 240°C or higher, preferably 300°C or lower, more preferably 280°C or lower.

[0284] The melting point can be determined using a differential scanning calorimeter [DSC].

[0285] The fluorinated polymer may have a functional group. The functional group is introduced into the fluorinated polymer, for example, by a chain transfer agent or a polymerization initiator used when manufacturing the fluorinated polymer. For example, when an alcohol is used as a chain transfer agent, or a peroxide having a structure of -CH2OH is used as a polymerization initiator, -CH2OH is introduced into the main chain end of the fluorinated polymer. In addition, by polymerizing a monomer having a functional group, the functional group is introduced into the side chain end of the fluorinated polymer.

[0286] Fluorine-containing polymers per 10 6 The number of functional groups per 10 carbon atoms in the main chain is preferably more than 50. 6 The number of functional groups per 10 carbon atoms in the main chain is preferably 100 or more, more preferably 150 or more, and even more preferably 200 or more, and is preferably 1200 or less, more preferably 1000 or less, and even more preferably 800 or less. In the case of a stabilization treatment of the fluorinated polymer such as a treatment of contacting the fluorinated polymer with fluorine gas, the number of functional groups of the fluorinated polymer is usually reduced, and it is not possible to obtain a fluorinated polymer having a functional group of 10 carbon atoms per 10 carbon atoms. 6 A fluorine-containing polymer having a main chain carbon atom number and a functional group number within the above range.

[0287] The identification of the types of the functional groups and the measurement of the number of the functional groups can be performed using infrared spectroscopy.

[0288] The number of functional groups is specifically determined by the following method. First, the fluorinated polymer is formed by cold pressing to produce a film with a thickness of 0.25 mm to 0.30 mm. The film is analyzed by Fourier transform infrared spectroscopy to obtain an infrared absorption spectrum of the fluorinated polymer and a differential spectrum from a background spectrum of a fully fluorinated polymer without functional groups. The number of functional groups in the fluorinated polymer relative to each 1×10 6 The number of functional groups N per carbon atom.

[0289] N=I×K / t(A)

[0290] I: Absorbance

[0291] K: Correction coefficient

[0292] t: film thickness (mm)

[0293] For reference, absorption frequencies, molar absorption coefficients, and correction coefficients for some functional groups are shown in Table 1. The molar absorption coefficients were determined from FT-IR measurement data of low-molecular model compounds.

[0294] [Table 1]

[0295] Table 1

[0296]

[0297] The absorption frequencies of -CH2CF2H, -CH2COF, -CH2COOH, -CH2COOCH3, and -CH2CONH2 are several tens of kaise (cm2) lower than the absorption frequencies of -CF2H, -COF, free -COOH, and bound -COOH, -COOCH3, and -CONH2 shown in the table, respectively. -1 ).

[0298] For example, the functional group number of -COF is the absorption frequency 1883 cm due to -CF2COF. -1 The number of functional groups obtained from the absorption peak at 1840 cm-1 due to -CH2COF -1 The total number of functional groups found from the absorption peak at .

[0299] The functional group is a functional group present at the main chain terminal or side chain terminal of the fluorine-containing polymer, as well as a functional group present in the main chain or side chain. The number of functional groups can be the total number of -CF=CF2, -CF2H, -COF, -COOH, -COOCH3, -CONH2 and -CH2OH.

[0300] The powder of the present invention may contain other components besides the fluorinated polymer. Examples of other components include fillers, plasticizers, processing aids, mold release agents, pigments, flame retardants, lubricants, light stabilizers, weather stabilizers, conductive agents, antistatic agents, ultraviolet absorbers, antioxidants, foaming agents, fragrances, oils, softeners, dehydrofluorination agents, and the like.

[0301] As the other components, other polymers other than the above copolymers may be contained. Examples of the other polymers include fluororesins, fluororubbers, and non-fluorinated polymers other than the above fluorinated polymers.

[0302] The powder of the present invention can be suitably used as a powder coating. Powder coatings are usually applied to a coating object and then heated and fired to form a film. The coating film thus applied can be used for various purposes such as corrosion-resistant lining.

[0303] The method for applying the powder coating material is not particularly limited, and examples thereof include spraying, electrostatic spraying, electrostatic spraying, fluidized dip coating, electrostatic fluidized dip coating, and spin lining.

[0304] The coating film formed by the powder coating is usually formed by applying the powder coating to the object to be coated and then heating and firing it to form a film. The temperature for heating and firing the powder coating applied to the object to be coated is, for example, 295°C to 400°C. The heating and firing time is, for example, 20 minutes to 180 minutes. In the case of applying and firing the powder coating multiple times, the heating and firing time represents the firing time for one time.

[0305] The film thickness of the coating formed by the powder coating can be appropriately determined according to the application, and can be, for example, 20 μm to 10000 μm. The film thickness is the film thickness after heating and firing, and can be the film thickness of the coating obtained by one coating or by two or more coatings.

[0306] The object to be coated is not particularly limited, and any object to which corrosion resistance is desired can be cited. Examples of such objects to be coated include tanks, containers, towers, valves, pumps, joints, other piping materials, etc., which are coated with corrosion-resistant linings; chemical and medical instruments, wafer baskets, coil shaft tower liners, valves for pharmaceuticals, pump impellers, etc., which are coated with other corrosion-resistant processes.

[0307] The object to be coated can be cleaned, surface treated by sandblasting, or primed as needed.

[0308] The powder of the present invention can also be used as a processing aid, molding material, etc.

[0309] The powder of the present invention can be used, for example, in the following applications.

[0310] Films for food packaging, lining materials for fluid delivery pipelines used in food manufacturing processes, gaskets, sealing materials, sheets and other fluid delivery components for food manufacturing equipment;

[0311] Chemical plugs, packaging films, lining materials, gaskets, sealing materials, thin plates and other reagent delivery components for fluid delivery pipelines used in chemical manufacturing processes;

[0312] Lining components for the inner surface of liquid tanks and piping in chemical equipment and semiconductor factories;

[0313] O (square) rings / tubes / gaskets, valve core materials, hoses, sealing materials, etc. used in automobile fuel systems and peripheral devices; fuel delivery components such as hoses and sealing materials used in automobile AT devices;

[0314] Flange gaskets, shaft seals, valve stem seals, sealing materials, hoses, etc. used in car engines and peripheral devices of automobiles; other automobile components such as automobile brake hoses, air conditioning hoses, radiator hoses, wire covering materials, etc.;

[0315] Semiconductor manufacturing equipment O (square) rings, tubes, gaskets, valve core materials, hoses, sealing materials, rollers, gaskets, diaphragms, joints and other semiconductor device liquid delivery components;

[0316] Coating rollers, hoses, tubes, ink containers and other coating and ink components for coating equipment;

[0317] Food and beverage conveying components such as tubes or hoses for food and beverages, tubes, hoses, belts, gaskets, joints, etc., food packaging materials, and glass cooking equipment;

[0318] Waste liquid transmission components such as pipes and hoses used for waste liquid transmission;

[0319] Components for high-temperature liquid transmission such as pipes and hoses used for high-temperature liquid transmission;

[0320] Steam piping components such as pipes and hoses used for steam piping;

[0321] Pipe corrosion protection tapes such as tapes wrapped around pipes on ship decks, etc.

[0322] Various covering materials such as wire covering materials, optical fiber covering materials, transparent surface covering materials and back-side agents provided on the light incident side surface of photovoltaic elements of solar cells;

[0323] Diaphragms of diaphragm pumps and sliding components such as various sealing gaskets;

[0324] Weather-resistant covers for agricultural films, various roofing materials, sidewalls, etc.;

[0325] Interior materials used in the construction field, non-combustible fireproof safety glass and other glass covering materials;

[0326] Lining materials for laminated steel sheets used in the home appliance field, etc.

[0327] The powder of the present invention can be suitably produced by the production method of the present invention. Next, the production method of the present invention will be described in detail.

[0328] 2. Powder manufacturing method

[0329] In one embodiment, there is provided a method for producing a powder (sometimes referred to as "first production method" in the present invention), which is a method for producing a powder containing particles of a fluorinated polymer, wherein:

[0330] In a reactor, a fluorinated monomer is polymerized in the presence of a fluorinated surfactant, a polymerization initiator and an aqueous medium, thereby preparing an aqueous dispersion of primary particles containing a fluorinated polymer, wherein the fluorinated polymer 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,

[0331] After the aqueous dispersion is prepared, at least one of the following operations is performed: removing the fluorinated monomer 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.

[0332] Adding a radical generator in an amount equivalent to 5 times or more the molar amount of the fluorinated surfactant used in the polymerization to the aqueous dispersion,

[0333] The aqueous dispersion containing the free radical generator is subjected to heat treatment.

[0334] The fluorinated polymer in the heat-treated aqueous dispersion is precipitated to prepare a wet powder containing particles of the fluorinated polymer.

[0335] The wet powder is dried at a temperature that is 50° C. or lower than the melting point of the fluorinated polymer, thereby producing the powder.

[0336] In the first production method of the present invention, after preparing an aqueous dispersion, a relatively large amount of a free radical generator is added to the obtained aqueous dispersion, the aqueous dispersion containing the free radical generator is heat-treated, and the fluorinated polymer in the heat-treated aqueous dispersion is recovered and dried at a relatively low temperature. By using such a production method, a powder containing particles of a fluorinated polymer with excellent operability and a reduced content of a fluorinated compound having a hydrophilic group can be produced.

[0337] That is, by using the first production method of the present invention, a powder having a hydrophilic group-containing fluorine-containing compound content of 250 mass ppb or less can be produced. Furthermore, by using the first production method of the present invention, a powder containing particles of a fluorine-containing polymer having an average secondary particle size of 0.5 μm to 10 μm can be produced.

[0338] In one embodiment, there is provided a method for producing a powder (sometimes referred to as "second production method" in the present invention), which is a method for producing a powder containing particles of a fluorinated polymer, wherein:

[0339] In a reactor, a fluorinated monomer is polymerized in the presence of a fluorinated surfactant, a polymerization initiator and an aqueous medium, thereby preparing an aqueous dispersion of primary particles containing a fluorinated polymer, wherein the fluorinated polymer 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,

[0340] After the aqueous dispersion is prepared, at least one of the following operations is performed: removing the fluorinated monomer 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.

[0341] Adding a radical generator in an amount equivalent to 5 times or more the molar amount of the fluorinated surfactant used in the polymerization to the aqueous dispersion,

[0342] The aqueous dispersion containing the free radical generator is subjected to heat treatment.

[0343] The fluorinated polymer in the heat-treated aqueous dispersion is precipitated to prepare a wet powder containing particles of the fluorinated polymer.

[0344] drying the wet powder to prepare a raw material powder containing the fluorine-containing polymer;

[0345] The raw material powder containing the above-mentioned fluorine-containing polymer is densified using a roller under conditions where a specific gravity of 90% or more of the true specific gravity is obtained, and after pulverization, fine particles in the range of 3% to 40% by mass of the overall particle size distribution of the pulverized material are removed by air flow classification, and coarse particles in the range of 1% to 20% by mass of the overall particle size distribution of the pulverized material are further removed by classification, thereby producing the above-mentioned powder.

[0346] In the second production method of the present invention, after preparing an aqueous dispersion, a relatively large amount of a free radical generator is added to the obtained aqueous dispersion, the aqueous dispersion containing the free radical generator is heat-treated, the fluorinated polymer in the heat-treated aqueous dispersion is recovered, the fluorinated polymer 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, a powder containing particles of a fluorinated polymer having excellent fluidity and a reduced content of a fluorinated compound having a hydrophilic group can be produced.

[0347] That is, by using the second production method of the present invention, a powder having a hydrophilic group-containing fluorine-containing compound content of 250 mass ppb or less can be produced. Furthermore, by using the second production method of the present invention, a powder having a uniform particle morphology, a narrow particle size distribution, and excellent fluidity can be produced.

[0348] Each process and the materials used in each process are described in detail below.

[0349] (Polymerization of fluorinated monomers)

[0350] In the production method of the present invention, first, a fluorinated monomer is polymerized in a reactor in the presence of a fluorinated surfactant, a polymerization initiator and an aqueous medium to prepare an aqueous dispersion containing a fluorinated polymer.

[0351] The polymerization of fluorinated monomers can be carried out as follows: fluorinated monomers, fluorinated surfactants, polymerization initiators, aqueous media and other additives as needed are added to a reactor, the contents of the reactor are stirred, and the reactor is then maintained at a specified polymerization temperature, followed by adding a specified amount of polymerization initiator to initiate the polymerization reaction, thereby carrying out the polymerization. After the polymerization reaction begins, fluorinated monomers, polymerization initiators, fluorinated surfactants, chain transfer agents, etc. may be added according to the purpose. The polymerization method of fluorinated monomers is not particularly limited, and emulsion polymerization is preferred.

[0352] (Fluorinated surfactant)

[0353] As the fluorinated surfactant used for the polymerization of the fluorinated monomer, there may be mentioned the fluorinated surfactant which the powder of the present invention may contain, and it is preferred to use the same fluorinated surfactant.

[0354] The amount of the fluorinated surfactant added is preferably 10 to 10 mass ppm, more preferably 100 mass ppm or more, further preferably 300 mass ppm or more, more preferably 5 mass % or less, further preferably 1 mass % or less, relative to the aqueous medium.

[0355] (Fluorinated monomers)

[0356] In the production method of the present invention, at least one selected from the group consisting of TFE, perfluoro(alkyl vinyl ether) and hexafluoropropylene is polymerized as a fluorinated monomer, thereby making it possible to prepare an aqueous dispersion of primary particles containing a fluorinated polymer, wherein the fluorinated polymer is at least one selected from the group consisting of TFE / perfluoro(alkyl vinyl ether) copolymers, TFE / hexafluoropropylene copolymers and tetrafluoroethylene / perfluoro(alkyl vinyl ether) / hexafluoropropylene copolymers.

[0357] The fluorinated monomers used for preparing these copolymers include the fluorinated monomers constituting the fluorinated polymer contained in the powder of the present invention, and it is preferred to use the same fluorinated monomers.

[0358] In addition, as the fluorine-containing monomer, other monomers copolymerizable with TFE and perfluoro(alkyl vinyl ether) or other monomers copolymerizable with TFE and hexafluoropropylene can be further polymerized. Regarding these other monomers, the fluorine-containing monomers constituting the fluorine-containing polymer contained in the powder of the present invention can also be cited, and the same fluorine-containing monomers are preferably used.

[0359] The amount of each fluorinated monomer used is preferably an amount by which the fluorinated polymer contained in the powder of the present invention can be obtained.

[0360] (Polymerization initiator)

[0361] The polymerization initiator used in the polymerization of the fluorinated monomer is not particularly limited as long as it is a polymerization initiator that can generate free radicals within the polymerization temperature range, and a known oil-soluble and / or water-soluble polymerization initiator can be used. Furthermore, it can also be combined with a reducing agent to initiate polymerization in a redox form. The concentration of the above-mentioned polymerization initiator is appropriately determined according to the type of monomer, the molecular weight of the target fluorinated polymer, and the reaction rate.

[0362] As the polymerization initiator, an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator can be used.

[0363] The oil-soluble free radical polymerization initiator may be a known oil-soluble peroxide, and for example, the following peroxides may be cited as representative substances: dialkyl peroxycarbonates such as diisopropyl peroxydicarbonate and di-sec-butyl peroxydicarbonate; peroxyesters such as tert-butyl peroxyisobutyrate and tert-butyl peroxypivalate; dialkyl peroxides such as di-tert-butyl peroxide; and di(ω-hydro-dodecafluoroheptanoyl) peroxide, di(ω-hydro-tetrafluorooctanoyl) peroxide, di(ω-hydro-hexafluorononanoyl) peroxide, di(perfluorobutyryl) peroxide, di(perfluorovaleranoyl) peroxide, di(perfluorohexanoyl) peroxide, di(perfluoroheptanoyl) peroxide, di(perfluorooctanoyl) peroxide, peroxide, di(perfluorononanoyl)peroxide, di(ω-chloro-hexafluorobutyryl)peroxide, di(ω-chloro-decafluorohexanoyl)peroxide, di(ω-chloro-tetrafluorooctanoyl)peroxide, ω-hydro-dodecafluoroheptanoyl-ω-hydrohexafluorononanoyl-peroxide, ω-chloro-hexafluorobutyryl-ω-chloro-decafluorohexanoyl-peroxide, ω-hydro-dodecafluoroheptanoyl-perfluorobutyryl-peroxide, di(dichloropentafluorobutyryl)peroxide, di(trichlorooctafluorohexanoyl)peroxide, di(tetrachloroundecanoyl)peroxide, di(pentachlorotetrafluorodecanoyl)peroxide, di(undecanotridodecanoyl)peroxide and the like di[perfluoro(or fluorochloro)acyl]peroxides; and the like.

[0364] As the water-soluble free radical polymerization initiator, it can be a known water-soluble peroxide, for example, ammonium salts, potassium salts, sodium salts of persulfuric acid, perboric acid, perchloric acid, perphosphoric acid, percarbonic acid, etc., organic peroxides such as disuccinic acid peroxide and diglutaric acid peroxide, tert-butyl peroxymaleate, tert-butyl hydroperoxide, etc. It can also contain a reducing agent such as sulfites, and its use amount can be 0.1 to 20 times that of the peroxide.

[0365] (Aqueous medium)

[0366] The aqueous medium used in the polymerization of the fluorinated monomer refers to the reaction medium for the polymerization, which is a liquid containing water. The aqueous medium is not particularly limited as long as it contains water, and may contain water and a non-fluorinated organic solvent such as alcohol, ether, ketone, and / or a fluorinated organic solvent having a boiling point of 40° C. or less.

[0367] As the aqueous medium, from the perspective of being able to smoothly carry out the polymerization of the fluorinated monomer and also being able to suppress the reduction in the removal efficiency of the fluorinated compound having a hydrophilic group, an aqueous medium containing only water, or an aqueous medium containing only water and a non-fluorinated organic solvent is preferred, and an aqueous medium containing only water is more preferred.

[0368] From the perspective of being able to smoothly carry out the polymerization of the fluorinated monomer and also being able to suppress the reduction in the removal efficiency of the fluorinated compound having a hydrophilic group, the content of water in the aqueous medium is preferably 90% or more, more preferably 95% or more, further preferably 99.0% or more, further preferably 99.5% or more, particularly preferably 99.9% or more, and may also be 100%, relative to the mass of the aqueous medium.

[0369] (Chain transfer agent)

[0370] In the production method of the present invention, the fluorinated monomer can also be polymerized in the presence of a chain transfer agent. By using a chain transfer agent, the polymerization rate and molecular weight can be adjusted. As the chain transfer agent, for example, in addition to esters such as dimethyl malonate, diethyl malonate, methyl acetate, ethyl acetate, butyl acetate, and dimethyl succinate, various halogenated hydrocarbons such as isopentane, methane, ethane, propane, methanol, isopropanol, acetone, various mercaptans, and carbon tetrachloride, cyclohexane, etc. can also be cited.

[0371] The amount of chain transfer agent used is usually 1 mass ppm to 50,000 mass ppm, preferably 1 mass ppm to 20,000 mass ppm, relative to the total amount of fluorinated monomers supplied. In order not to reduce the removal efficiency of fluorinated compounds having hydrophilic groups as much as possible, the amount of chain transfer agent used is preferably an amount that is completely consumed in the polymerization of fluorinated monomers and does not remain in the aqueous dispersion containing fluorinated polymers. Therefore, the amount of chain transfer agent used is more preferably 10,000 mass ppm or less, further preferably 5,000 mass ppm or less, further preferably 1,000 mass ppm or less, particularly preferably 500 mass ppm or less, and most preferably 200 mass ppm or less, relative to the total amount of fluorinated monomers supplied.

[0372] The chain transfer agent may be added to the reaction vessel all at once before the start of polymerization, may be added all at once after the start of polymerization, may be added in divided portions during polymerization, or may be added continuously during polymerization.

[0373] (Other additives)

[0374] In the polymerization of fluorinated monomers, additives such as buffers, pH regulators, stabilizing aids, and dispersion stabilizers may be used. In addition, in the polymerization of fluorinated monomers, free radical scavengers and decomposers may be added to adjust the polymerization rate and molecular weight. In addition, in the polymerization of fluorinated monomers, non-fluorinated anionic surfactants, non-fluorinated nonionic surfactants, non-fluorinated cationic surfactants, etc. may also be used.

[0375] As the stabilizing aid, paraffin, fluorine oil, fluorine solvent, silicone oil and the like are preferred. The stabilizing aid can be used alone or in combination of two or more. As the stabilizing aid, paraffin is more preferred. Paraffin can be liquid, semi-solid or solid at room temperature, but preferably a saturated hydrocarbon having 12 or more carbon atoms. The melting point of paraffin is usually preferably 40°C to 65°C, more preferably 50°C to 65°C.

[0376] The amount of the stabilizing agent 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. The stabilizing agent is preferably sufficiently hydrophobic to be completely separated and removed from the aqueous dispersion after polymerization and not to become a contaminating component.

[0377] (Polymerization conditions)

[0378] The polymerization of fluorinated monomers can be carried out at normal pressure and temperature. Usually, the polymerization temperature is 5°C to 120°C and the polymerization pressure is 0.05 MPaG to 10 MPaG. The polymerization temperature and polymerization pressure are appropriately determined according to the type of monomer, the molecular weight of the target fluorinated polymer, the reaction rate, etc.

[0379] (Aqueous dispersion obtained by polymerization)

[0380] The fluorinated monomer is polymerized to obtain an aqueous dispersion containing a fluorinated polymer. The content of the fluorinated polymer in the aqueous dispersion after the polymerization is usually 8 to 50% by mass based on the aqueous dispersion.

[0381] In the aqueous dispersion obtained by polymerizing the fluorinated monomer, in addition to the fluorinated polymer, as a fluorinated compound having a hydrophilic group, a fluorinated surfactant used when polymerizing the fluorinated monomer is usually contained. In addition, in the aqueous dispersion obtained by polymerizing the fluorinated monomer, in addition to the fluorinated polymer, a fluorinated compound having a hydrophilic group generated by the polymerization of the fluorinated monomer is sometimes contained.

[0382] As the fluorinated compound having a hydrophilic group in the aqueous dispersion obtained by polymerization, a typical compound is a fluorinated compound having a hydrophilic group with a molecular weight of 1000 g / mol or less. According to the manufacturing method of the present invention, a powder having a reduced content of the fluorinated compound having a hydrophilic group with a molecular weight of 1000 g / mol or less can be manufactured in the end.

[0383] In one embodiment of the aqueous dispersion obtained by polymerization, a fluorinated surfactant added during polymerization is contained as a fluorinated compound having a hydrophilic group. The fluorinated surfactant added during polymerization is as described above as the fluorinated surfactant used for polymerization of the fluorinated monomer.

[0384] The content of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion obtained by polymerization may be 200 ppb or more, 300 ppb or more, 400 ppb or more, 10% or less, 1% or less, or 0.5% or less by mass relative to the aqueous dispersion.

[0385] The content of the fluorinated surfactant used when polymerizing the fluorinated monomer in the aqueous dispersion obtained by polymerization can be 200 mass ppb or more, 300 mass ppb or more, 400 mass ppb or more, 10 mass % or less, 1 mass % or less, or 0.5 mass % or less relative to the aqueous dispersion.

[0386] In one embodiment of the aqueous dispersion obtained by polymerization, the fluorine-containing compound having a hydrophilic group contains a perfluoroether carboxylic acid. As the perfluoroether carboxylic acid, a compound (III) represented by the following general formula (III) is preferred.

[0387] General formula (III): Rf 1 -O-(CF(CF3)CF2O)n3 CF(CF3)COOM

[0388] (Where 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, NR 7 4. an imidazolium which may be substituted, a pyridinium which may be substituted, or a phosphonium which may be substituted, R 7 is H or an organic group. )

[0389] When the aqueous dispersion obtained by polymerization contains at least perfluoroether carboxylic acid as the fluorine-containing compound having a hydrophilic group, the content of perfluoroether carboxylic acid in the aqueous dispersion obtained by polymerization may be 200 mass ppb or more, 300 mass ppb or more, 400 mass ppb or more, 10 mass % or less, 1 mass % or less, or 0.5 mass % or less relative to the aqueous dispersion.

[0390] In one embodiment of the aqueous dispersion obtained by the polymerization, the compound represented by the following general formula (H1) is contained as the fluorine-containing compound having a hydrophilic group.

[0391] General formula (H1): [X-Rf-A - ] i M i+

[0392] (wherein X represents H, Cl, Br, F or I, Rf represents a linear or branched partially fluorinated or fully fluorinated aliphatic group, or a linear or branched partially fluorinated or fully fluorinated aliphatic group interrupted by at least one oxygen atom, A - Represents acid group, M i+ represents a cation having a valence number i, where i represents an integer from 1 to 3)

[0393] In one embodiment of the aqueous dispersion obtained by the polymerization, the compound represented by the following general formula (H2) is contained as the fluorine-containing compound having a hydrophilic group.

[0394] General formula (H2): [C n-1 F 2n-1 COO - ]M +

[0395] (where n represents an integer of 4 to 14, M + represents a cation.)

[0396] It is known that the compound represented by the general formula (2) (perfluoroalkanoic acid) is formed during polymerization when perfluoro(alkyl vinyl ether) or the like is used as a fluorine-containing monomer (see International Publication No. 2019 / 161153).

[0397] In one embodiment of the aqueous dispersion obtained by the polymerization, the compound represented by the following general formula (H3) is contained as the fluorine-containing compound having a hydrophilic group.

[0398] General formula (H3): [R 1 -OL-CO2 - ]M +

[0399] (Where R 1 represents a linear or branched partially fluorinated or fully fluorinated aliphatic group, or a linear or branched partially fluorinated 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 cation.)

[0400] In one embodiment of the aqueous dispersion obtained by the polymerization, the compound represented by the general formula (H4) is contained as the fluorine-containing compound having a hydrophilic group.

[0401] General formula (H4): H-Rf n0 -Y 0

[0402] (Where Rf n0 It is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which a part or all of the H groups are replaced by F, the alkylene group may or may not contain one or more ether bonds, and a part of the H groups may or may not be replaced by Cl. 0 is an anionic group.)

[0403] Examples of the compound represented by the general formula (H4) include compounds represented by any of the following general formulae.

[0404] General formula: [H-(CF2) m CO2 - ]M +

[0405] (wherein, m represents an integer from 3 to 19, M + represents a cation.)

[0406] General formula: [H-(CF2) m2 -(CF(CF3)) m3 -CO2 - ]M +

[0407] (wherein, m2 represents an integer of 1 to 17, m3 represents an integer of 1 to 9, and M + represents a cation. Wherein, m2 and m3 are selected in a manner to satisfy 3≤(m2+2×m3)≤19, and the order of existence of each repeating unit in the formula is arbitrary. )

[0408] (Removal of fluorinated monomers or recovery of aqueous dispersions)

[0409] In the production method of the present invention, after the aqueous dispersion is prepared by polymerization and before the free radical generator is added to the aqueous dispersion, at least one of (a) removing the fluorinated monomer remaining in the reactor from the reactor and (b) recovering the aqueous dispersion in the reactor and storing it in a container different from the reactor can be performed. In particular, when the method of removing the fluorinated monomer in the reactor is used, the subsequent steps can be carried out in the same reactor used in the polymerization, and the productivity of the powder is improved, which is preferred.

[0410] After the aqueous dispersion is prepared, it is preferred to remove the fluorinated monomer or recover the aqueous dispersion after stopping the stirring of the contents of the reactor, because the subsequent operations become easy and the polymerization of the fluorinated monomer can be stopped smoothly.

[0411] The method for removing the fluorinated monomer from the reactor is not particularly limited. After the aqueous dispersion is prepared, the stirring of the contents of the reactor can be stopped as needed, and the pressure in the reactor can be exhausted to reach normal pressure, thereby removing the fluorinated monomer from the reactor. The pressure in the reactor can also be reduced to less than 0.0MPaG, thereby removing the fluorinated monomer from the reactor. Inert gas can also be supplied to the reactor, thereby replacing the fluorinated monomer in the reactor with inert gases such as nitrogen. In addition, the entire amount of the fluorinated monomer in the reactor can be reacted and converted into a fluorinated polymer, resulting in the removal of the fluorinated monomer from the reactor. As long as the removal of the fluorinated monomer remaining in the reactor can be carried out to the extent that the polymerization reaction of the fluorinated monomer is fully stopped, a small amount of fluorinated monomer can also remain in the reactor. The removed fluorinated monomer can be recovered by known means. The recovered fluorinated monomer can also be reused in the manufacture of fluorinated polymers.

[0412] As a method for removing the fluorinated monomer from the reactor, the following method is also preferred: after preparing the aqueous dispersion, the stirring of the contents of the reactor is stopped as needed to reduce the pressure in the reactor to less than 0.0 MPaG, and then an inert gas is supplied to the reactor. The decompression in the reactor and the supply of the inert gas may be repeated multiple times.

[0413] When the polymerization of the fluorinated monomer is carried out at a temperature exceeding room temperature, the reactor may be cooled before or after the fluorinated monomer is removed from the reactor. When the fluorinated monomer is removed from the reactor by exhaust gas, nitrogen substitution, etc., unreacted fluorinated monomer, especially liquid, may remain in the reactor, but by cooling the reactor, the reaction of the unreacted fluorinated monomer can be sufficiently suppressed.

[0414] The method of recovering the aqueous dispersion in the reactor and containing it in a container different from the reactor used for polymerization is not particularly limited. For example, after preparing the aqueous dispersion, the stirring of the contents of the reactor may be stopped as needed, the reactor may be opened, and the aqueous dispersion in the reactor may be injected into another container. Alternatively, after preparing the aqueous dispersion, the stirring of the contents of the reactor may be stopped as needed, and the aqueous dispersion may be supplied from the reactor to the other container via a pipe connecting the reactor and the other container.

[0415] In order to stop the polymerization reaction of the fluorinated monomer, a polymerization inhibitor (radical scavenger) may be added.

[0416] As a polymerization inhibitor, a compound that is added to the free radical in the polymerization system or has no reinitiation ability after chain transfer is used. Specifically, a compound having the following functions is used: it is easy to undergo a chain transfer reaction with a primary free radical or a growing free radical, and then generate a stable free radical that does not react with the monomer, or it is easy to undergo an addition reaction with a primary free radical or a growing free radical to generate a stable free radical. The activity of a substance generally referred to as a chain transfer agent is characterized by a chain transfer constant and a reinitiation efficiency. Among chain transfer agents, a substance with a reinitiation efficiency of substantially 0% is referred to as a polymerization inhibitor. As a polymerization inhibitor, it is preferred that at least one of the group consisting of, for example, aromatic hydroxy compounds, aromatic amines, N,N-diethylhydroxylamine, quinone compounds, terpenes, thiocyanates, and copper chloride (CuCl2) be selected. As aromatic hydroxy compounds, non-substituted phenols, polyphenols, salicylic acid, m-salicylic acid or p-salicylic acid, gallic acid, naphthol, etc. can be cited. As the above-mentioned unsubstituted phenol, o-nitrophenol, m-nitrophenol or p-nitrophenol, o-aminophenol, m-aminophenol or p-aminophenol, p-nitrosophenol, etc. can be mentioned. As the polyphenol, catechol, resorcinol, hydroquinone, pyrogallol, pyrogallol, naphthol resorcinol, etc. can be mentioned. As aromatic amines, o-phenylenediamine, m-phenylenediamine or p-phenylenediamine, benzidine, etc. can be mentioned. As the above-mentioned quinone compound, hydroquinone, o-benzoquinone, m-benzoquinone or p-benzoquinone, 1,4-naphthoquinone, alizarin, etc. can be mentioned. As thiocyanate, ammonium thiocyanate (NH4SCN), potassium thiocyanate (KSCN), sodium thiocyanate (NaSCN), etc. can be mentioned. As the above-mentioned inhibitor, quinone compounds are preferred, and hydroquinone is more preferred.

[0417] (Free Radical Generator)

[0418] In the production method of the present invention, after performing at least one of the operations (a) and (b) and before heat-treating the aqueous dispersion, a free radical generator in an amount equivalent to 5 times or more the molar amount of the fluorinated surfactant used in the polymerization is added to the aqueous dispersion. By adding a relatively large amount of the free radical generator, the content of the fluorinated compound having a hydrophilic group can be sufficiently reduced.

[0419] 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 contained in another container.

[0420] The radical generator is not particularly limited as long as it is a compound that can decompose at the temperature during the heat treatment to generate radicals. As the radical generator, a water-soluble radical generator is preferred because it can easily diffuse radicals into the aqueous dispersion.

[0421] Examples of the radical generator include organic peroxides, inorganic peroxides, organic azo compounds, and combinations of oxidants and reducing agents. Preferably, the radical generator is at least one selected from the group consisting of inorganic peroxides, organic peroxides, and combinations of oxidants and reducing agents.

[0422] As the inorganic peroxide, a water-soluble inorganic peroxide is preferred. As the inorganic peroxide, hydrogen peroxide, perchlorate, perborate, perphosphate, percarbonate, persulfate, etc. can be cited, and persulfate is preferred. As the persulfate, at least one selected from the group consisting of ammonium persulfate, sodium persulfate and potassium persulfate is preferred, and ammonium persulfate is more preferred.

[0423] As the organic peroxide, a water-soluble organic peroxide is preferred. As the organic peroxide, peroxydicarbonates such as disuccinic acid peroxide and diglutaric acid peroxide can be mentioned.

[0424] As the free radical generator, an oxidizing agent and a reducing agent may be used in combination. By using the oxidizing agent and the reducing agent in combination, free radicals can be generated from the free radical generator by a redox reaction between the oxidizing agent and the reducing agent, so that the temperature during the heat treatment can be lowered.

[0425] As the oxidizing agent, persulfate, organic peroxide, potassium permanganate, manganese triacetate, ammonium cerium nitrate, etc. can be mentioned. As the reducing agent, sulfite, bisulfite, bromate, diimide, oxalic acid, etc. can be mentioned. As the persulfate, ammonium persulfate and potassium persulfate can be mentioned. As the sulfite, sodium sulfite and ammonium sulfite can be mentioned. In order to increase the decomposition rate of the oxidizing agent, it is also preferred to add copper salts and iron salts. As the copper salt, copper (II) sulfate can be mentioned, and as the iron salt, iron (II) sulfate can be mentioned.

[0426] As a combination of an oxidizing agent and a reducing agent, for example, potassium permanganate / oxalic acid, ammonium persulfate / bisulfite / ferric sulfate, manganese triacetate / oxalic acid, cerium ammonium nitrate / oxalic acid, bromate / bisulfite, etc. can be mentioned, preferably potassium permanganate / oxalic acid. When a combination of an oxidizing agent and a reducing agent is used, either the oxidizing agent or the reducing agent can be added to the aqueous dispersion in advance, and then the other can be added continuously or intermittently.

[0427] From the aspect of being able to further improve the removal efficiency of the fluorinated compound having a hydrophilic group, the amount of the free radical generator added is preferably 5 mole times or more, more preferably 10 mole times or more, preferably 1000 mole times or less, more preferably 500 mole times or less, and further preferably 100 mole times or less relative to the mole amount of the fluorinated surfactant used in the polymerization. The production method of the present invention is a method for producing a powder, so by adding a relatively large amount of free radical generator, the fluorinated polymer in the aqueous dispersion can also be precipitated.

[0428] The method for adding the free radical generator is not particularly limited. The free radical generator may be added directly to the aqueous dispersion, or a solution containing the free radical generator may be prepared and added to the aqueous dispersion. In addition, the free radical generator may be added while stirring the aqueous dispersion, or the aqueous dispersion may be stirred after the free radical generator is added.

[0429] The temperature of the aqueous dispersion to which the free radical generator is added is not particularly limited, and may be the temperature of the aqueous dispersion after the fluorinated monomer is polymerized, may be the temperature reached by cooling the aqueous dispersion after the fluorinated monomer is polymerized, or may be the temperature of the heat treatment. That is, after adding the free radical generator to the aqueous dispersion, the aqueous dispersion may be heated for the heat treatment, or after heating the aqueous dispersion to the temperature for the heat treatment, the free radical generator may be added to the aqueous dispersion.

[0430] (Heat Treatment)

[0431] In the production method of the present invention, the aqueous dispersion to which the free radical generator is added (the aqueous dispersion containing the free radical generator) is subjected to heat treatment. By heat treating the aqueous dispersion containing a relatively large amount of the free radical generator, the content of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion can be surprisingly reduced.

[0432] Before the heat treatment, the content of the fluorinated polymer in the aqueous dispersion may be adjusted. The content of the fluorinated polymer may be adjusted by a known method such as concentration or dilution.

[0433] From the aspect of being able to produce the fluoropolymer aqueous dispersion with high productivity without damaging the removal efficiency of the fluorochemical having a hydrophilic group, the content of the fluoropolymer in the aqueous dispersion for heat treatment is preferably 1% by mass or more, more preferably 5% by mass or more, and further preferably 10% by mass or more relative to the mass of the aqueous dispersion. The upper limit of the content of the fluoropolymer is preferably 60% by mass or less, more preferably 55% by mass or less, and further preferably 50% by mass or less.

[0434] The content of the fluorinated surfactant added during the polymerization in the aqueous dispersion subjected to the heat treatment is preferably 500 mass ppm or more, more preferably 1000 mass ppm or more, and is preferably 10 mass % or less, more preferably 5 mass % or less, and further preferably 1 mass % or less, relative to the mass of the fluorinated polymer in the aqueous dispersion.

[0435] The content of the fluorinated compound having a hydrophilic group generated by polymerization of the fluorinated monomer in the aqueous dispersion subjected to the heat treatment is preferably 500 ppb by mass or more, more preferably 1000 ppb by mass or more, and is preferably 1.0% by mass or less, more preferably 0.1% by mass or less, and further preferably 0.01% by mass or less, relative to the mass of the fluorinated polymer in the aqueous dispersion.

[0436] The content of the fluorinated compound having a hydrophilic group in the aqueous dispersion subjected to the heat treatment (the total amount of the content of the fluorinated surfactant added during the polymerization and the content of the fluorinated compound having a hydrophilic group generated by the polymerization of the fluorinated monomer) is preferably 500 mass ppm or more, more preferably 1000 mass ppm or more, preferably 10 mass % or less, more preferably 5 mass % or less, and further preferably 1 mass % or less, relative to the fluorinated polymer in the aqueous dispersion.

[0437] From the perspective of being able to further improve the removal efficiency of the fluorinated compound having a hydrophilic group, the temperature of the heat treatment is preferably 35°C or more, more preferably 40°C or more, further preferably 45°C or more, particularly preferably 50°C or more, preferably 120°C or less, more preferably 110°C or less, further preferably 100°C or less, and particularly preferably 90°C or less. In the case of heat-treating an aqueous dispersion to which a free radical generator is added, the temperature of the heat treatment is preferably above the temperature (decomposition temperature) at which the free radical generator decomposes to generate free radicals. The manufacturing method of the present invention is a method for manufacturing a powder, so by heat-treating at a relatively high temperature, the fluorinated polymer in the aqueous dispersion can also be precipitated.

[0438] In the heat treatment of the aqueous dispersion, it is not necessary to heat the aqueous dispersion as long as the aqueous dispersion can be maintained at a temperature above the desired temperature. For example, when the temperature for polymerizing the fluorinated monomer is sufficiently high and the temperature of the obtained aqueous dispersion is also sufficiently high, the heat treatment can be started before the obtained aqueous dispersion is cooled. However, since the control of the temperature of the heat treatment becomes easy, it is preferred to cool the aqueous dispersion before and after removing the fluorinated monomer from the reactor or recovering the aqueous dispersion in the reactor, heat the aqueous dispersion to the above temperature range, and maintain the temperature for a certain period of time. The temperature of the aqueous dispersion provided for the heat treatment can be, for example, below 30°C.

[0439] The heating means for heat treatment while heating the aqueous dispersion is not particularly limited. For example, the container containing the aqueous dispersion may be placed in a thermostatic bath for heating, or the aqueous dispersion may be contained in a container equipped with a heater and heated by the heater.

[0440] The pressure of the heat treatment is not particularly limited and may be normal pressure. For example, when the temperature of the heat treatment is relatively high and boiling of the aqueous dispersion needs to be suppressed, the pressure of the heat treatment may be a pressure exceeding normal pressure.

[0441] From the perspective of being able to further improve the removal efficiency of fluorine-containing compounds having hydrophilic groups, the heat treatment time is preferably 15 minutes or more, more preferably 30 minutes or more, further preferably 60 minutes or more, preferably 1200 minutes or less, more preferably 900 minutes or less, further preferably 600 minutes or less.

[0442] The heat treatment may be performed while stirring the aqueous dispersion.

[0443] (Preparation of wet powder and drying of wet powder)

[0444] In the first manufacturing method of the present invention, a wet powder containing particles of a fluorinated polymer is prepared by precipitating a fluorinated polymer in a heat-treated aqueous dispersion, and a powder containing particles of a fluorinated polymer is prepared by drying the wet powder at a temperature 50° C. or less lower than the melting point of the fluorinated polymer.

[0445] In the second production method of the present invention, a raw material powder containing a fluorine-containing polymer is prepared in the same manner as in the first production method of the present invention, except that the wet powder is dried at an arbitrary temperature. In the second production method of the present invention, the drying may be performed at an arbitrary temperature, but the drying may also be performed at a low temperature as in the first production method of the present invention.

[0446] In the first and second manufacturing methods of the present invention, the precipitation method of the fluoropolymer is not particularly limited. For example, the aqueous dispersion is diluted with water in a manner to achieve a polymer concentration of 5% to 20% by mass, and the pH is adjusted to neutral or alkaline according to the situation, and then the polymerization is carried out in a container with a stirrer more vigorously than the stirring in the polymerization of the fluoromonomer. Water-soluble organic compounds such as methanol and acetone; inorganic salts such as potassium nitrate and ammonium carbonate; inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, etc. can be added to the aqueous dispersion as a precipitating agent and stirred to precipitate the fluoropolymer. After the fluoropolymer is precipitated, the wet powder containing the particles of the fluoropolymer can be recovered. The wet powder may include a precipitate of the fluoropolymer precipitated by adding a free radical generator and a precipitate of the fluoropolymer precipitated by heat treatment.

[0447] The wet powder may be washed before drying. The wet powder may be washed with water or an organic solvent. The washing may be performed once or multiple times. Examples of the organic solvent used for washing include ethers, halogenated hydrocarbons, aromatic hydrocarbons, pyridine, nitrile, nitrogen-containing polar organic compounds, dimethyl sulfoxide, alcohols, and the like.

[0448] In the first production method of the present invention, the wet powder is dried at a temperature 50° C. or lower than the melting point of the fluorinated polymer. By drying the wet powder at a relatively low temperature, a powder having excellent handleability can be obtained.

[0449] In the first production method of the present invention, the drying temperature of the wet powder is 50°C lower than the melting point of the fluorinated polymer, more preferably 70°C lower than the melting point of the fluorinated polymer, and further preferably 100°C lower than the melting point of the fluorinated polymer.

[0450] In the first production method of the present invention, the drying temperature of the wet powder is preferably 250° C. or lower, more preferably 230° C. or lower, further preferably 200° C. or lower, and further preferably 180° C. or lower.

[0451] In the first production method of the present invention, 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 further preferably 140° C. or higher. If the drying temperature is too low, drying takes time and productivity may decrease.

[0452] In the first manufacturing method of the present invention, the obtained powder can be classified or granulated. In addition, the obtained powder can also be formed into pellets. In the manufacturing method of the present invention, since a powder with excellent operability can be directly obtained after drying, it is also one of the preferred modes not to perform any post-treatment on the dried powder.

[0453] In the second manufacturing method of the present invention, the raw material powder containing the fluorine-containing polymer obtained by drying the wet powder is densified using a roller under conditions where a specific gravity of 90% or more of the true specific gravity is obtained, and after pulverization, fine particles in the range of 3% to 40% by mass of the overall particle size distribution of the pulverized material are removed by air flow classification, and coarse particles in the range of 1% to 20% by mass of the overall particle size distribution of the pulverized material are further removed by classification.

[0454] By compressing the raw powder using rollers, a sheet containing a fluorine-containing polymer is usually obtained. In the second manufacturing method of the present invention, the raw powder is rolled into a sheet and compressed under conditions such that the specific gravity of the sheet is 90% or more of the true specific gravity (specific gravity of a melt-molded product of a fluorine-containing polymer). The specific gravity after compression is preferably 95% to 99% of the true specific gravity. When the compressed specific gravity is less than 90% of the true specific gravity, the powder particles obtained after pulverization are close to agglomerated fine powders after polymerization and drying, and the apparent density is small, and the fluidity of the powder is poor. In addition, when the compressed specific gravity exceeds 99% of the true specific gravity, it is difficult to obtain a powder with excellent fluidity.

[0455] The sheeting by rollers is made into sheets with a thickness of 0.05 mm to 5 mm, preferably 0.1 mm to 3 mm. As rollers, preferably two or more rollers are arranged in a vertical type, an inverted L-type, a Z-type, etc. Specifically, calendering rollers, mixing rollers, roller pressing rollers, etc. can be cited. In the sheeting by rollers, a strong shear force is applied to the fluoropolymer during the sheeting, and the air in the particles in the raw material powder is discharged to obtain a homogeneous sheet.

[0456] The temperature when the raw material powder is compressed is preferably 0°C to 250°C, more preferably 5°C to 150°C.

[0457] Next, the high-density raw material powder (sheet) is crushed. After the sheet is crushed to obtain a crushed product with a size of 0.1 mm to 10 mm, the crushed product can be further crushed.

[0458] The pulverization is preferably performed by a mechanical pulverizer. Examples of the mechanical pulverizer include impact pulverizers such as a cutter mill, a hammer mill, a pin mill, and a jet mill, and an attrition pulverizer that pulverizes using shear force.

[0459] The pulverization temperature is preferably -200°C to 100°C, more preferably 20°C or higher, and more preferably 50°C or lower.

[0460] Next, the obtained pulverized material is classified. The classification of the pulverized material can be performed by the following method: after removing fine particles by air flow classification, coarse particles are removed by air flow classification using a screen or a vibrating screen. By removing coarse particles after removing fine particles, classification can be performed efficiently while suppressing clogging of the screen or sieve.

[0461] In air flow classification, the crushed raw material is sent to a cylindrical classification chamber by reduced pressure air (blower), dispersed by the swirling airflow at room temperature, and the particles are classified by centrifugal force. In the classification chamber, a rotating body such as a conical cone or a rotor is set to make the raw material and air swirl evenly. In the case of a classification cone, the classification point is adjusted by adjusting the air volume of the 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 rotation speed of the rotor. The air pressure of the blower is 1kg / cm 2 ~10kg / cm 2 , preferably 3kg / cm 2 ~6kg / cm 2 .

[0462] By air flow classification, 3% to 40% by mass, preferably 5% to 30% by mass of the total particle size distribution of the pulverized product is removed. If the amount of removed particles is too small, the fluidity of the obtained powder cannot be fully improved, and if the amount of removed particles is too large, it is economically disadvantageous.

[0463] Next, the pulverized product is classified to remove coarse particles in the range of 1% to 20% by mass, preferably 2% to 10% by mass, of the overall particle size distribution of the pulverized product. If the amount of coarse particles removed is too small, the fluidity of the obtained powder cannot be fully improved, and if the amount of coarse particles removed is too large, it is economically disadvantageous.

[0464] The removed fine particles and coarse particles can be reused as raw materials for powders.

[0465] The powder of the present invention can be used to prepare a liquid coating composition. The liquid coating composition of the present invention contains a powder having a reduced content of a fluorinated compound with a hydrophilic group, thereby providing a film having a large contact angle and a small friction coefficient. The reason is not clear, but it is speculated that the dispersion stability of the fluoropolymer powder in the liquid coating composition is moderately low due to the powder containing the fluorinated compound with a hydrophilic group, so when the film is formed, the fluoropolymer powder is more likely to float on the surface of the film than other components, and as a result, the content ratio of the fluoropolymer on the surface of the film becomes higher.

[0466] The liquid coating composition of the present invention can be prepared by mixing the powder of the present invention with a solvent. Before or during mixing with the solvent, the powder of the present invention can be crushed using a pulverizer such as a ball mill to adjust the particle size of the powder. The liquid coating composition of the present invention is prepared using a powder with excellent operability and is therefore easy to prepare.

[0467] Examples of the solvent include water and organic solvents. Examples of the organic solvent include N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-butyl-2-pyrrolidone, 3-methoxy-N,N-dimethylpropionamide, N,N-dimethylacetamide, N,N-dimethylformamide, cresol, methyl isobutyl ketone, and xylene.

[0468] The content of the fluorinated polymer 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.

[0469] The liquid coating composition may further contain a polymer compound different from the fluorinated polymer. Examples of the polymer compound include polyamideimide (PAI), polyimide (PI), polyethersulfone (PES), polyarylether sulfide (PAS), polyetherimide, polyetheretherketone, aromatic polyester, etc. The polymer compound may be used alone or in combination of two or more.

[0470] PAI is a resin composed of a polymer having an amide bond and an imide bond in the molecular structure. PAI is not particularly limited, and examples thereof include: a resin formed by a high molecular weight polymer obtained by the reaction of an aromatic diamine having an amide bond in the molecule with an aromatic tetracarboxylic acid such as pyromellitic acid; a 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; a reaction of a dibasic acid having an aromatic imide ring in the molecule with a diamine, etc. As PAI, it is preferably composed of a polymer having an aromatic ring in the main chain from the perspective of excellent heat resistance.

[0471] PI is a resin composed of a polymer having an imide bond in its molecular structure. PI is not particularly limited, and examples thereof include resins composed of high molecular weight polymers obtained by reaction of aromatic tetracarboxylic anhydrides such as pyromellitic anhydride, etc. PI is preferably composed of a polymer having an aromatic ring in its main chain from the perspective of excellent heat resistance.

[0472] PES is a resin composed of a polymer having a repeating unit represented by the following general formula.

[0473] [Chemistry 6]

[0474]

[0475] The PES is not particularly limited, and examples thereof include resins composed of a polymer obtained by polycondensation of dichlorodiphenyl sulfone and bisphenol.

[0476] PAS is a resin composed 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, and examples thereof include polyphenylene sulfide (PPS) and the like.

[0477] As the polymer compound, from the aspect of being able to provide a film with better adhesion to the substrate, it is preferably at least one selected from the group consisting of PAI, PI, PES and PPS, and more preferably PAI. In addition, from the viewpoint of being able to suppress coloration during firing and being able to increase the degree of freedom of the color tone of the film, as the polymer compound, PES is preferred. As the polymer compound, using PAI and PES in combination is also one of the preferred modes.

[0478] The content of the polymer compound is preferably 1% by mass or more, more preferably 3% by mass or more, and is preferably 15% by mass or less, more preferably 12% by mass or less, based on the liquid coating composition.

[0479] In the liquid coating composition, the volume ratio of the fluorinated polymer (fluorinated polymer powder) to the high molecular compound is preferably 10 / 90 to 90 / 10, more preferably 15 / 85 or more, and more preferably 85 / 15 or less.

[0480] The content of the fluorinated polymer (fluorinated polymer powder) and the high molecular compound in the liquid coating composition is preferably 1 to 90 wt %, more preferably 10 wt % or more, and more preferably 80 wt % or less, based on the mass of the liquid coating composition.

[0481] The liquid coating composition may contain other components as required. Other components include crosslinking agents, antistatic agents, heat stabilizers, foaming agents, foaming nucleating agents, antioxidants, surfactants, photopolymerization initiators, anti-wear agents, surface modifiers, various pigments of organic and inorganic systems, copper damage prevention agents, bubble prevention agents, adhesion imparting agents, lubricants, processing aids, colorants, phosphorus stabilizers, lubricants, mold release agents, sliding materials, ultraviolet absorbers, dyes and pigments, reinforcing materials, anti-drip agents, fillers, curing agents, ultraviolet curing agents, flame retardants and other additives.

[0482] 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 further preferably less than 5% by weight, relative to the mass of the fluorinated polymer (fluorinated polymer powder) and the polymer compound in the liquid coating composition. The lower limit is not particularly limited and may be 0% by weight or more. That is, the liquid coating composition may not contain other components.

[0483] By using the liquid coating composition of the present invention, a coating film can be obtained. The coating film obtained from the liquid coating composition of the present invention has excellent water- and oil-repellency and low friction.

[0484] Although the embodiments have been described above, it should be understood that various modifications may be made to the embodiments and details without departing from the spirit and scope of the claims.

[0485] <1> According to a first aspect of the present invention, there is provided a powder comprising particles of a fluorinated polymer, wherein:

[0486] The powder contains a fluorine-containing compound having a hydrophilic group, wherein the content of the fluorine-containing compound having a hydrophilic group is 250 ppb or less relative to the powder.

[0487] The average secondary particle size of the fluorinated polymer particles is 0.5 μm to 10 μm.

[0488] The fluorine-containing polymer 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.

[0489] <2> According to a second aspect of the present invention, there is provided a powder according to the first aspect, wherein the specific surface area is 8 m 2 / g or above.

[0490] <3> According to a third aspect of the present invention, there is provided the powder according to the first aspect or the second aspect, wherein the average primary particle size of the particles of the fluorinated polymer is less than 0.5 μm.

[0491] <4> According to a fourth aspect of the present invention, there is provided the powder according to any one of the first to third aspects, wherein the perfluoro(alkyl vinyl ether) is perfluoro(propyl vinyl ether).

[0492] <5> According to a fifth aspect of the present invention, there is provided the powder according to any one of the first to fourth aspects, wherein the fluorinated polymer has a melt flow rate of 10 g / 10 min or more at 372°C.

[0493] <6> According to a sixth aspect of the present invention, there is provided the powder according to any one of the first to fifth aspects, wherein the fluorinated polymer has a melting point of 220° C. or higher.

[0494] <7> According to a seventh aspect of the present invention, there is provided a powder according to any one of the first to sixth aspects, wherein the fluorinated polymer has functional groups, and the number of the functional groups is 6 The number of carbon atoms exceeds 50.

[0495] <8> According to an eighth aspect of the present invention, there is provided a powder according to any one of the first to seventh aspects, wherein the fluorine-containing compound having a hydrophilic group is of the following general formula (N 0 ) shown in the compound.

[0496] General formula (N 0 ):X n0 -Rf n0 -Y 0

[0497] (Where X n0 is H, Cl or F; Rf n0 It is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which a part or all of the H groups are replaced by F, the alkylene group may or may not contain one or more ether bonds, and a part of the H groups may or may not be replaced by Cl. 0 is an anionic group.)

[0498] <9> According to the 9th aspect of the present invention, a powder based on any one of the 1st to 8th aspects is provided, wherein the fluorine-containing compound having a hydrophilic group contains at least a compound (H2) represented by the general formula (H2), and the content of the compound (H2) is less than 25 mass ppb relative to the powder.

[0499] General formula (H2): [C n-1 F 2n-1 COO - ]M +

[0500] (where n represents an integer of 4 to 14, M +represents a cation.)

[0501] <10> According to a tenth aspect of the present invention, there is provided the 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.

[0502] <11> According to an eleventh aspect of the present invention, there is provided a powder coating material comprising the powder according to any one of the first to tenth aspects.

[0503] <12> According to a twelfth aspect of the present invention, there is provided a method for producing a powder, which is a method for producing a powder containing particles of a fluorinated polymer, wherein:

[0504] In a reactor, a fluorinated monomer is polymerized in the presence of a fluorinated surfactant, a polymerization initiator and an aqueous medium, thereby preparing an aqueous dispersion of primary particles containing a fluorinated polymer, wherein the fluorinated polymer 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,

[0505] After the aqueous dispersion is prepared, at least one of removing the fluorinated monomer 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.

[0506] Adding a radical generator in an amount equivalent to 5 times or more the molar amount of the fluorinated surfactant used in the polymerization to the aqueous dispersion,

[0507] heat-treating the aqueous dispersion containing the free radical generator,

[0508] The fluorinated polymer in the heat-treated aqueous dispersion is precipitated to prepare a wet powder containing particles of the fluorinated polymer.

[0509] The wet powder is dried at a temperature that is 50° C. or lower than the melting point of the fluorinated polymer, thereby producing the powder.

[0510] <13> According to a thirteenth aspect of the present invention, there is provided a liquid coating composition comprising the powder according to any one of the first to tenth aspects.

[0511] <14> According to a fourteenth aspect of the present invention, there is provided a powder comprising particles of a fluorine-containing polymer, wherein:

[0512] The powder contains a fluorine-containing compound having a hydrophilic group, wherein the content of the fluorine-containing compound having a hydrophilic group is 250 ppb or less relative to the powder.

[0513] The fluorine-containing polymer 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,

[0514] The raw material powder containing the fluorine-containing polymer is densified using a roller under conditions where a specific gravity of 90% or more of the true specific gravity is obtained, and after pulverization, fine particles in the range of 3% to 40% by mass of the overall particle size distribution of the pulverized product are removed by air flow classification, and coarse particles in the range of 1% to 20% by mass of the overall particle size distribution of the pulverized product are further removed by classification, thereby obtaining the powder.

[0515] <15> According to a fifteenth aspect of the present invention, there is provided a powder according to the fourteenth aspect, wherein the fluorine-containing compound having a hydrophilic group is of the following general formula (N 0 ) shown in the compound.

[0516] General formula (N 0 ):X n0 -Rf n0 -Y 0

[0517] (Where X n0 is H, Cl or F; Rf n0 Y is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which a part or all of the H is substituted by F, the alkylene group may or may not contain one or more ether bonds, and a part of the H is substituted by Cl or is unsubstituted; 0 is an anionic group.)

[0518] <16> According to a sixteenth aspect of the present invention, there is provided the powder according to the fourteenth aspect or the fifteenth aspect, wherein the average secondary particle size of the particles of the fluorinated polymer is 5 μm to 100 μm.

[0519] <17> According to a seventeenth aspect of the present invention, there is provided the powder according to any one of the fourteenth to sixteenth aspects, wherein the raw material powder to be densified is pulverized at 20°C to 100°C.

[0520] <18> According to an eighteenth aspect of the present invention, there is provided a method for producing a powder, which is a method for producing a powder containing particles of a fluorine-containing polymer, wherein:

[0521] In a reactor, a fluorinated monomer is polymerized in the presence of a fluorinated surfactant, a polymerization initiator and an aqueous medium, thereby preparing an aqueous dispersion of primary particles containing a fluorinated polymer, wherein the fluorinated polymer 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,

[0522] After the aqueous dispersion is prepared, at least one of removing the fluorinated monomer 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.

[0523] Adding a radical generator in an amount equivalent to 5 times or more the molar amount of the fluorinated surfactant used in the polymerization to the aqueous dispersion,

[0524] heat-treating the aqueous dispersion containing the free radical generator,

[0525] The fluorinated polymer in the heat-treated aqueous dispersion is precipitated to prepare a wet powder containing particles of the fluorinated polymer.

[0526] drying the wet powder to prepare a raw material powder containing the fluorine-containing polymer,

[0527] The raw material powder containing the fluorine-containing polymer is densified using a roller under conditions where a specific gravity of 90% or more of the true specific gravity is obtained, and after pulverization, fine particles in the range of 3% to 40% by mass of the overall particle size distribution of the pulverized product are removed by air flow classification, and coarse particles in the range of 1% to 20% by mass of the overall particle size distribution of the pulverized product are further removed by classification, thereby producing the powder.

[0528] Example

[0529] Next, embodiments of the present invention will be described with reference to examples, but the present invention is not limited to these examples.

[0530] Each numerical value in the examples was measured by the following method.

[0531] <Solid Content Concentration of Aqueous Dispersion>

[0532] 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 was expressed as a percentage.

[0533] <Average primary particle size>

[0534] A PTFE aqueous dispersion with the solid component concentration adjusted to approximately 1.0 mass% was prepared and measured 70 times at 25 °C 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.

[0535] <Average secondary particle size>

[0536] Using a laser diffraction particle size distribution analyzer (manufactured by JEOL Ltd.), without using a cascade, the particle size distribution was measured at a pressure of 0.1 MPa for 3 seconds. It is the value corresponding to 50% of the cumulative particle size distribution obtained.

[0537] <Content of PPVE units>

[0538] The content of perfluoro(propyl vinyl ether) (PPVE) units in the copolymer was determined by 19 F-NMR analysis.

[0539] <Melting point>

[0540] Measurement was carried out using a DSC (differential scanning calorimeter). 10 mg of the sample was weighed, heated from 140 °C to 360 °C at a rate of 10 °C / min, held at 360 °C for 1 minute, then cooled to 140 °C at a rate of 10 °C / min, held at 140 °C for 1 minute, and further heated to 380 °C at a rate of 10 °C / min again. From the melting curve obtained during the second heating, the melting peak temperature (Tm) was taken as the melting point.

[0541] <Melt flow rate (MFR)>

[0542] Using a melt indexer (manufactured by Toyo Seiki) with a corrosion-resistant barrel, die, and piston in accordance with ASTM D1238-95, 5 g of the sample was filled into the barrel maintained at 372 ± 1 °C and held for 5 minutes, then extruded through the die hole under a load of 5 kg (piston and weight), and the extrusion speed (g / 10 min) of the melt at this time was determined as the MFR.

[0543] <Specific surface area>

[0544] Measurement was carried out by the BET method using a surface analyzer (trade name: MONOSORB, manufactured by QUANTA CHLROME). In addition, as the carrier gas, a mixed gas of 30% nitrogen and 70% helium was used, and cooling was carried out using liquid nitrogen.

[0545] <Number of functional groups>

[0546] The pellets of the copolymer were formed by cold pressing to produce a film with a thickness of 0.25 mm to 0.3 mm. The 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 the basic spectrum that was completely fluorinated and had no functional groups. From the absorption peaks of specific functional groups appearing in the difference spectrum, the following formula (A) was used to calculate the absorption peaks of each 1×10 6 The number of functional groups N per carbon atom.

[0547] N=I×K / t(A)

[0548] I: Absorbance

[0549] K: Correction coefficient

[0550] t: film thickness (mm)

[0551] For reference, regarding the functional groups in the present invention, the absorption frequency, molar absorption coefficient and correction coefficient are shown in Table 2. The molar absorption coefficient was determined from the FT-IR measurement data of a low molecular model compound.

[0552] [Table 2]

[0553] Table 2

[0554]

[0555] <Determination of Fluorinated Compounds Having Hydrophilic Groups>

[0556] The content of the fluorine-containing compound having a hydrophilic group contained in the powder is determined as the content of the fluorine-containing compound having a hydrophilic group extracted from the powder.

[0557] 0. Extraction of fluorinated compounds with hydrophilic groups from powders

[0558] To 1 g of the powder was added 10 g (12.6 mL) of methanol, and ultrasonic treatment was performed at 60° C. for 2 hours. After the mixture was allowed to stand at room temperature, the solid content was removed to obtain an extract.

[0559] <Determination of Perfluoroether Carboxylic A>

[0560] 1. Calibration curve of perfluoroether carboxylic acid A

[0561] Five methanol standard solutions of perfluoroethercarboxylic acid A with known concentrations were prepared and measured using a liquid chromatography mass spectrometer (Agilent, Ultivo triple quadrupole LC-MS). Within each concentration range, a calibration curve was prepared using the first order approximation from the methanol standard solution concentration and the peak integral value.

[0562] Measurement equipment structure and LC-MS measurement conditions

[0563]

[0564] MRM assay parameters

[0565] [Table 4]

[0566] Table 4 MRM assay parameters

[0567]

[0568] 2. Content of perfluoroether carboxylic acid A in the powder

[0569] The content of perfluoroether carboxylic acid A contained in the extract was measured from the calibration curve using a liquid chromatography-mass spectrometer. The content of perfluoroether carboxylic acid A contained in the powder was determined from the following relational formula (1).

[0570] Y A =X A ×12.6 (1)

[0571] Y A : Content of perfluoroether carboxylic acid A contained in powder (mass ppb / powder)

[0572] X A : Content of perfluorocarboxylic acid A in the extract (ng / mL)

[0573] The quantitative lower limit of the content of the perfluoroether carboxylic acid A contained in the powder is 1 mass ppb / powder.

[0574] <Content of the compound represented by the general formula (H2)>

[0575] The content of the compound represented by the general formula (H2) is determined using a calibration curve of straight-chain perfluorocarboxylic acids having the same number of carbon atoms.

[0576] 1. Calibration curve of perfluorocarboxylic acid

[0577] Five levels of methanol standard solutions of perfluorobutyric acid, perfluoropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid, perfluoroundecanoic acid, perfluorododecanoic acid, perfluorotridecanoic acid, and perfluorotetradecanoic acid with known concentrations were prepared and measured using a liquid chromatography mass spectrometer (Agilent, Ultivo triple quadrupole LC-MS). Within each concentration range, a calibration curve was prepared using a first order approximation from the concentration of the methanol standard solution and the integral value of the peak.

[0578] Measurement equipment structure and LC-MS measurement conditions

[0579]

[0580] MRM assay parameters

[0581] [Table 6]

[0582] Table 6 MRM assay parameters

[0583]

[0584] 2. Content of the compound represented by the general formula (H2) contained in the powder

[0585] The content of the compound represented by the general formula (H2) with carbon number n contained in the extract was determined from the calibration curve using a liquid chromatography mass spectrometer. The content of the compound represented by the general formula (H2) with carbon number n contained in the powder was calculated using the following relationship (2).

[0586] Yn=Xn×12.6 (2)

[0587] Yn: The content of the compound represented by the general formula (H2) with carbon number n contained in the powder (mass ppb / powder)

[0588] Xn: The content of the compound represented by the general formula (H2) with carbon number n contained in the extract (ng / mL)

[0589] The quantitative lower limit of the content of the compound represented by the general formula (H2) having a carbon number n contained in the powder is 1 mass ppb / powder.

[0590] MRM assay parameters

[0591] [Table 7]

[0592] Table 7 MRM assay parameters

[0593]

[0594] Synthesis example 1

[0595] By the method described in Synthesis Example 1 of International Publication No. 2021 / 045228, a white solid A of a perfluoroether carboxylic acid A having a molecular weight of 1000 or less was obtained.

[0596] Production Example 1

[0597] 3750 g of deionized water and 5.49 g of the white solid A obtained in Synthesis Example 1 as a fluorinated surfactant were added to a SUS reactor with a content of 6 L and equipped with a stirrer. Next, the contents of the reactor were heated to 60°C while being sucked and purged with TFE to remove oxygen in the reactor and stir the contents. After adding 6.9 g of dichloromethane and 27 g of perfluoro(propyl vinyl ether) (PPVE) to the reactor, TFE was added until a pressure of 1.3 MPaG was reached. 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 decrease in pressure occurred and the start of polymerization was observed. TFE was added to the reactor and the pressure was kept constant at 1.3 MPaG. After the polymerization started, 4 g of PPVE was added continuously relative to 100 g of TFE. When the TFE consumed in the reaction reached about 1080 g, the supply of TFE was stopped, stirring was stopped, and the reaction was terminated. Then, the reactor was vented until the pressure inside reached normal pressure, thereby obtaining an aqueous dispersion of tetrafluoroethylene / perfluoro(propyl vinyl ether) copolymer (PFA).

[0598] The obtained PFA aqueous dispersion had a solid content concentration of 22.8% by mass and an average primary particle size of 0.26 μm.

[0599] Comparative Example 1

[0600] Nitric acid was added to the PFA aqueous dispersion obtained in Preparation Example 1, and precipitated by applying a severe mechanical shear force. The obtained wet powder was further filtered out and repeatedly washed with deionized water. The obtained wet powder was dried in a hot air circulation dryer at 180° C. for 6 hours to obtain PFA powder.

[0601] 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 size of 1.5 μm, and a specific surface area of ​​16.0 m 2 / g.

[0602] Example 1

[0603] The PFA aqueous dispersion obtained in Manufacturing Example 1 is placed in another reactor, the contents of the reactor are heated to 80°C, and 30.3g of ammonium persulfate (10 molar times the molar amount of the fluorinated surfactant used in the polymerization) is added as a free radical generator. Then, it is kept at 80°C for 3 hours to obtain a heat-treated PFA aqueous dispersion. Nitric acid is added to the obtained heat-treated PFA aqueous dispersion, stirred and precipitated to obtain a wet powder, and then dried at 180°C for 6 hours. The obtained PFA powder has a PPVE content of 3.9% by mass, an MFR of 40g / 10 minutes, a melting point of 310°C, an average secondary particle size of 1.6μm, and a specific surface area of ​​15.6m 2 / g, the number of functional groups is relative to every 10 6 The number of carbon atoms in the main chain is 286.

[0604] Table 8 shows the content of perfluoroether carboxylic acid contained in the obtained powder.

[0605] [Table 8]

[0606] Table 8

[0607] Comparative Example 1 Example 1 Perfluoroether carboxylic acid A 504 21

[0608] Unit: mass ppb / powder

[0609] The obtained powder contains the general formula (H2): [C n-1 F 2n-1 COO - ]M + The contents of the compounds shown are shown in Table 9.

[0610] [Table 9]

[0611] Table 9

[0612] n Comparative Example 1 Example 1 4 <1 <1 5 6 <1 6 <1 <1 7 <1 <1 8 <1 <1 9 <1 <1 10 <1 <1 11 1 <1 12 <1 <1 13 6 <1 14 <1 <1

[0613] Unit: mass ppb / powder

[0614] Next, embodiments of the liquid coating compositions containing PFA powder obtained in the above-mentioned Examples and Comparative Examples will be described with reference to Examples.

[0615] Each numerical value in the examples was measured by the following method.

[0616] <Contact Angle>

[0617] The contact angles with respect to water and n-hexadecane were measured using a contact angle meter CA-DT manufactured by Kyowa Interface Science Co., Ltd.

[0618] <Friction coefficient>

[0619] Using a surface property tester HEIDON Type 38 manufactured by Shinto Scientific Co., Ltd., the static friction coefficient and the dynamic friction coefficient were measured while being pressed (ball indenter) with a load (1 kg) and moving at a speed of 600 mm / min. The results are shown in Table 10.

[0620] Comparative Example 2

[0621] 10 g of the PFA powder obtained in Comparative Example 1 and 10 g of a polyether sulfonic acid resin (PES5003P manufactured by Sumitomo Chemical Co., Ltd.) were added to a mixed solvent of 50 g of 3-methoxy-N,N-dimethylpropionamide, 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, the dispersion composition was applied to a 0.5 mm thick stainless steel plate treated with a coating type chromate using a rod coater in a manner such that the dry film thickness became 10 μm, and calcined at 400° C. for 90 seconds to obtain a film. For the film, the contact angle and friction coefficient were measured.

[0622] Example 2

[0623] A film was obtained by the same procedure 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 the film were measured. The results are shown in Table 10.

[0624] [Table 10]

[0625] Table 10

[0626] unit Comparative Example 2 Example 2 Contact angle (relative to water) Spend 95 103 Contact angle (relative to n-hexadecane) Spend 33 39 Static friction coefficient － 0.19 0.13 Dynamic friction coefficient － 0.10 0.06

[0627] Production Example 2

[0628] According to the production method described in Example 1 of Japanese Patent Application Laid-Open No. 2010-235667, the reaction scale, reaction pressure, TFE input amount, HFP input amount, PPVE input amount, ammonium persulfate input 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% by mass.

[0629] The obtained polymer had an MFR of 35.7 g / 10 minutes, a composition ratio (mass %) of TFE / HFP / PPVE=87.6 / 11.5 / 0.9, and a melting point of 257°C.

[0630] Production Example 3

[0631] The FEP aqueous dispersion obtained in Preparation Example 2 was placed in another reactor, the contents of the reactor were heated to 80°C, and ammonium persulfate was added as a free radical generator in an amount 10 times the molar amount of the fluorinated surfactant used in the polymerization. Then, it was kept at 80°C for 3 hours to obtain a heat-treated FEP aqueous dispersion. Nitric acid was added to the heat-treated FEP aqueous dispersion obtained, stirred and precipitated to obtain a wet powder, which was then dried at 180°C for 6 hours. The MFR of the obtained FEP powder was 35.5 g / 10 minutes, the composition ratio (mass %) was TFE / HFP / PPVE=87.6 / 11.5 / 0.9, and the melting point was 256°C.

[0632] Example 3

[0633] The powder after pulverization was obtained according to the method described in Example 1 of International Publication No. 97 / 040089, except that the powder compressed into a sheet shape was changed to the powder obtained in Production Example 3. The specific gravity of the obtained sheet was measured using a hydrometer, and the result was 2.04, confirming that the specific gravity was high-densified to 95% of the true specific gravity. In addition, the removal rate of fine particles was 16% by mass, and the removal rate of coarse particles was 4% by mass.

[0634] The average secondary particle size of the obtained pulverized powder was 60 μm, and the apparent density was 0.88 g / mL. The apparent density was measured in accordance with JIS K 6891-5.3.

[0635] The obtained powder contains the general formula (H2): [C n-1 F 2n-1 COO - ]M + The contents of the compounds shown are shown in Table 11.

[0636] [Table 11]

[0637] Table 11

[0638] n Example 3 4 <1 5 <1 6 <1 7 <1 8 <1 9 <1 10 <1 11 <1 12 <1 13 <1 14 <1

[0639] Unit: mass ppb / powder

Claims

1. A powder comprising particles of a fluorine-containing polymer, wherein: The powder contains a fluorine-containing compound having a hydrophilic group, wherein the content of the fluorine-containing compound having a hydrophilic group is 250 ppb or less relative to the powder. The average secondary particle size of the fluorinated polymer particles is 0.5 μm to 10 μm. The fluorine-containing polymer 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.

2. The powder according to claim 1, having a specific surface area of ​​8 m 2 / g or above.

3. The powder according to claim 1 or 2, wherein The average primary particle size of the fluorine-containing polymer particles is less than 0.5 μm.

4. The powder according to any one of claims 1 to 3, wherein The perfluoro(alkyl vinyl ether) is perfluoro(propyl vinyl ether).

5. The powder according to any one of claims 1 to 4, wherein The fluorine-containing polymer has a melt flow rate of 10 g / 10 min or more at 372° C.

6. The powder according to any one of claims 1 to 5, wherein The melting point of the fluorine-containing polymer is 220° C. or higher.

7. The powder according to any one of claims 1 to 6, wherein The fluorine-containing polymer has functional groups, the number of which is relative to every 10 6 The number of carbon atoms exceeds 50.

8. The powder according to any one of claims 1 to 7, wherein The fluorine-containing compound having a hydrophilic group is of the following general formula (N 0 ), General formula (N 0 ):X n0 -Rf n0 -Y 0 Where, X n0 is H, Cl or F; Rf n0 Y is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which a part or all of the H is substituted by F, the alkylene group may or may not contain one or more ether bonds, and a part of the H is substituted by Cl or is unsubstituted; 0 It is an anionic group.

9. The powder according to any one of claims 1 to 8, wherein The fluorine-containing compound having a hydrophilic group contains at least a compound (H2) represented by the general formula (H2), and the content of the compound (H2) is 25 ppb or less relative to the powder. General formula (H2): [C n-1 F 2n-1 COO - ]M + In the formula, n represents an integer of 4 to 14, M + Represents a cation.

10. The powder according to any one of claims 1 to 9, wherein The fluorine-containing compound having a hydrophilic group contains at least a perfluoroether carboxylic acid.

11. A powder coating material comprising the powder according to any one of claims 1 to 10.

12. A method for producing a powder, which is a method for producing a powder containing particles of a fluorine-containing polymer, wherein: In a reactor, a fluorinated monomer is polymerized in the presence of a fluorinated surfactant, a polymerization initiator and an aqueous medium, thereby preparing an aqueous dispersion of primary particles containing a fluorinated polymer, wherein the fluorinated polymer 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, After the aqueous dispersion is prepared, at least one of removing the fluorinated monomer 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 in an amount equivalent to 5 times or more the molar amount of the fluorinated surfactant used in the polymerization to the aqueous dispersion, heat-treating the aqueous dispersion containing the free radical generator, The fluorinated polymer in the heat-treated aqueous dispersion is precipitated to prepare a wet powder containing particles of the fluorinated polymer. The wet powder is dried at a temperature that is 50° C. or lower than the melting point of the fluorinated polymer, thereby producing the powder.

13. A liquid coating composition comprising the powder according to any one of claims 1 to 10.

14. A powder comprising particles of a fluorine-containing polymer, wherein: The powder contains a fluorine-containing compound having a hydrophilic group, wherein the content of the fluorine-containing compound having a hydrophilic group is 250 ppb or less relative to the powder. The fluorine-containing polymer 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 material powder containing the fluorine-containing polymer is densified using a roller under conditions where a specific gravity of 90% or more of the true specific gravity is obtained, and after pulverization, fine particles in the range of 3% to 40% by mass of the overall particle size distribution of the pulverized product are removed by air flow classification, and coarse particles in the range of 1% to 20% by mass of the overall particle size distribution of the pulverized product are further removed by classification, thereby obtaining the powder.

15. The powder according to claim 14, wherein The fluorine-containing compound having a hydrophilic group is of the following general formula (N 0 ), General formula (N 0 ):X n0 -Rf n0 -Y 0 Where, X n0 is H, Cl or F; Rf n0 Y is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which a part or all of the H is substituted by F, the alkylene group may or may not contain one or more ether bonds, and a part of the H is substituted by Cl or is unsubstituted; 0 It is an anionic group.

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

17. The powder according to any one of claims 14 to 16, wherein The raw material powder is pulverized at 20°C to 100°C to obtain a high density.

18. A method for producing a powder, which is a method for producing a powder containing particles of a fluorine-containing polymer, wherein: In a reactor, a fluorinated monomer is polymerized in the presence of a fluorinated surfactant, a polymerization initiator and an aqueous medium, thereby preparing an aqueous dispersion of primary particles containing a fluorinated polymer, wherein the fluorinated polymer 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, After the aqueous dispersion is prepared, at least one of removing the fluorinated monomer 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 in an amount equivalent to 5 times or more the molar amount of the fluorinated surfactant used in the polymerization to the aqueous dispersion, heat-treating the aqueous dispersion containing the free radical generator, The fluorinated polymer in the heat-treated aqueous dispersion is precipitated to prepare a wet powder containing particles of the fluorinated polymer. drying the wet powder to prepare a raw material powder containing the fluorine-containing polymer, The raw material powder containing the fluorine-containing polymer is densified using a roller under conditions where a specific gravity of 90% or more of the true specific gravity is obtained, and after pulverization, fine particles in the range of 3% to 40% by mass of the overall particle size distribution of the pulverized product are removed by air flow classification, and coarse particles in the range of 1% to 20% by mass of the overall particle size distribution of the pulverized product are further removed by classification, thereby producing the powder.

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