Powder containing particles of low molecular weight polytetrafluoroethylene and method for producing same

Abstract

Provided is a powder containing particles of a low molecular weight polytetrafluoroethylene, 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, and the specific surface area being 7 m2 / g to 50 m2 / g.

Description

Technical Field

[0001] The present invention relates to a powder containing particles of low molecular weight polytetrafluoroethylene and a method for producing the same. Background Art

[0002] Patent Document 1 describes a polytetrafluoroethylene fine powder containing up to about 3 wt% of a monomer copolymerizable with tetrafluoroethylene, and having a polydispersity Mw / Mn of 1.5 to 2.5, a 7m 2 / g~13m 2 / g specific surface area (BET) and a primary particle size of 150nm to 250nm.

[0003] Patent Document 2 describes a low molecular weight polytetrafluoroethylene granulated powder characterized by being obtained by granulation from low molecular weight polytetrafluoroethylene particles containing low molecular weight polytetrafluoroethylene having a number average molecular weight of 600,000 or less.

[0004] Patent Document 3 describes a polytetrafluoroethylene powder characterized by having a number average molecular weight of 40,000 to 600,000, a 2 / g~20m 2 / g specific surface area, an average particle size of 1 μm to 30 μm, and a water contact angle of 110° to 125°.

[0005] Patent Document 4 discloses a low molecular weight polytetrafluoroethylene powder, which is a powder of low molecular weight polytetrafluoroethylene containing tetrafluoroethylene units, or tetrafluoroethylene units and modified monomer units copolymerizable with the tetrafluoroethylene units, wherein:

[0006] The content of the fluorine-containing compound represented by the following general formula (1) is 100 ppm or less relative to the low molecular weight polytetrafluoroethylene powder.

[0007] X-(CF2) m -Y(1)

[0008] (In the formula, X represents H or F, m represents an integer of 3 to 5, and Y represents -SO3M, -SO4M, -SO3R, -SO4R, -COOM, -PO3M2, -PO4M2 (M represents H, NH4 or an alkali metal, and R represents an alkyl group having 1 to 12 carbon atoms).)

[0009] does not contain a fluorine-containing compound represented by the following general formula (3),

[0010] X-(CF2) m -Y(3)

[0011] (In the formula, X represents H or F, m represents an integer greater than 6, and Y represents -SO3M, -SO4M, -SO3R, -SO4R, -COOM, -PO3M2, -PO4M2 (M represents H, NH4 or an alkali metal, and R represents an alkyl group having 1 to 12 carbon atoms).)

[0012] Prior art literature

[0013] Patent Literature

[0014] Patent Document 1: Japanese Patent Application Laid-Open No. 07-165828

[0015] Patent Document 2: Japanese Patent Application Publication No. 2005-2322

[0016] Patent Document 3: Japanese Patent Application Laid-Open No. 10-147617

[0017] Patent Document 4: International Publication No. 2009 / 020187 Summary of the invention

[0018] Problems to be solved by the invention

[0019] An object of the present invention is to provide a powder containing particles of low molecular weight polytetrafluoroethylene which is excellent in fine dispersibility in other materials and has a reduced content of a fluorine-containing compound having a hydrophilic group.

[0020] Another object of the present invention is to provide a method for producing a powder containing particles of low molecular weight polytetrafluoroethylene which has excellent fine dispersibility in other materials and has a reduced content of a fluorine-containing compound having a hydrophilic group.

[0021] Means for solving problems

[0022] According to the present invention, there is provided a powder containing particles of low molecular weight polytetrafluoroethylene, 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 specific surface area is 7 m 2 / g~50m 2 / g.

[0023] Effects of the Invention

[0024] According to the present invention, it is possible to provide a powder containing particles of low molecular weight polytetrafluoroethylene which is excellent in fine dispersibility in other materials and has a reduced content of a fluorine-containing compound having a hydrophilic group.

[0025] Furthermore, according to the present invention, it is possible to provide a method for producing a powder containing particles of low molecular weight polytetrafluoroethylene which is excellent in fine dispersibility in other materials and has a reduced content of a fluorine-containing compound having a hydrophilic group. DETAILED DESCRIPTION

[0026] Before describing the present invention in detail, some terms used in the present invention are defined or described.

[0027] 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.

[0028] In the present invention, the polytetrafluoroethylene [PTFE] is preferably a fluorine-containing polymer having a tetrafluoroethylene unit content of 99 mol % or more based on all polymer units.

[0029] 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 types of monomers.

[0030] 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.

[0031] Examples of the "organic group" include:

[0032] an alkyl group which may have one or more substituents,

[0033] an alkenyl group which may have one or more substituents,

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

[0035] a cycloalkyl group which may have one or more substituents,

[0036] a cycloalkenyl group which may have one or more substituents,

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

[0038] an aryl group which may have one or more substituents,

[0039] an aralkyl group which may have one or more substituents,

[0040] a non-aromatic heterocyclic group which may have one or more substituents,

[0041] a heteroaryl group which may have one or more substituents,

[0042] Cyano,

[0043] Formyl,

[0044] RaO-,

[0045] RaCO-,

[0046] RaSO2-,

[0047] RaCOO-

[0048] RaNRaCO-,

[0049] RaCONRa-

[0050] RaOCO-,

[0051] RaOSO2-, and

[0052] RaNRbSO2-

[0053] (In these formulas, Ra is independently

[0054] an alkyl group which may have one or more substituents,

[0055] an alkenyl group which may have one or more substituents,

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

[0057] a cycloalkyl group which may have one or more substituents,

[0058] a cycloalkenyl group which may have one or more substituents,

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

[0060] an aryl group which may have one or more substituents,

[0061] an aralkyl group which may have one or more substituents,

[0062] A non-aromatic heterocyclic group which may have one or more substituents, or

[0063] a heteroaryl group which may have one or more substituents,

[0064] Rb is independently H or an alkyl group which may have one or more substituents).

[0065] As the organic group, an alkyl group which may have one or more substituents is preferred.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] The amino group may have an aliphatic group, an aromatic group, a heterocyclic group or the like.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.).

[0085] 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.).

[0086] Hereinafter, specific embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments.

[0087] The present invention relates to a powder containing particles of low molecular weight polytetrafluoroethylene. The powder of the present invention is a powder containing particles of low molecular weight polytetrafluoroethylene, 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 specific surface area is 7 m 2 / g~50m 2 / g.

[0088] As a method for producing low molecular weight polytetrafluoroethylene, for example, as described in Patent Document 4, there is known a method as follows: in the presence of a chain transfer agent, tetrafluoroethylene or a modified monomer copolymerizable with tetrafluoroethylene is emulsion polymerized in an aqueous medium, and the emulsion polymerization is carried out in the presence of a fluorine-containing compound represented by the following general formula:

[0089] X-(CF2) m -Y

[0090] (In the formula, X represents H or F, m represents an integer of 3 to 5, and Y represents -SO3M, -SO4M, -SO3R, -SO4R, -COOM, -PO3M2, -PO4M2 (M represents H, NH4 or an alkali metal, and R represents an alkyl group having 1 to 12 carbon atoms).) In addition, Patent Document 4 describes that a low molecular weight polytetrafluoroethylene powder can be produced by precipitating and drying an aqueous dispersion of low molecular weight polytetrafluoroethylene obtained by emulsion polymerization. The powder of the copolymer thus obtained contains the fluorine-containing compound used in the polymerization.

[0091] Patent Document 4 records that by improving the removal efficiency in the cleaning and drying process, the content of the fluorinated compound can be easily reduced to less than 1 ppm, but it is required to further reduce the content of the fluorinated compound. Furthermore, Patent Document 4 only records the reduction of the content of the fluorinated compound used during polymerization, but the fluorinated compound with a hydrophilic group generated by the polymerization of tetrafluoroethylene is also preferably removed from the powder.

[0092] In addition, as a method for producing low molecular weight polytetrafluoroethylene, a method of producing by suspension polymerization is also known, as described in Patent Document 2. As described in Patent Document 2, when low molecular weight polytetrafluoroethylene is produced by suspension polymerization, the specific surface area of ​​the powder containing particles of low molecular weight polytetrafluoroethylene becomes small.

[0093] The powder of the present invention contains a fluorine-containing compound having a hydrophilic group, and its content is reduced to less than 250 mass ppb relative to the powder. Therefore, for example, when the powder of the present invention is added to other materials, there is no influence caused by the residual fluorine-containing compound having a hydrophilic group, and the originally expected properties of low molecular weight polytetrafluoroethylene can be fully exerted. Furthermore, in addition to the reduced content of the fluorine-containing compound having a hydrophilic group, the powder of the present invention has a specific surface area of ​​7m 2 / g~50m 2 / g, so when added to other materials, it can be easily finely dispersed in other materials, and the effect of adding the powder of the present invention can be fully exerted.

[0094] Next, the powder and the method for producing the powder of the present invention are described in detail.

[0095] 1. Powder

[0096] The powder of the present invention is a powder containing particles of low molecular weight polytetrafluoroethylene, wherein the specific surface area of ​​the powder is 7 m 2 / g~50m 2 / g. In the present invention, powder refers to an aggregate of particles of low molecular weight polytetrafluoroethylene. In the case of manufacturing low molecular weight polytetrafluoroethylene by emulsion polymerization, the particles of low molecular weight polytetrafluoroethylene are secondary particles formed by agglomeration of primary particles obtained by polymerization. By emulsion polymerization of low molecular weight polytetrafluoroethylene, an aqueous dispersion in which primary particles of low molecular weight polytetrafluoroethylene are dispersed in an aqueous medium can usually be obtained. The particles of low molecular weight polytetrafluoroethylene are formed by agglomerating primary particles in an aqueous dispersion. By recovering the formed agglomerates and drying them, a powder (aggregate) of particles of low molecular weight polytetrafluoroethylene can be obtained.

[0097] The specific surface area of ​​the powder is 7m 2 / g~50m 2 / g, more preferably 8m 2 / g or more, more preferably 9m 2 / g or more, more preferably 35m 2 / g or less, more preferably 20m 2 / g or less. By making the specific surface area of ​​the powder within the above range, excellent microdispersibility relative to other materials can be obtained. If the specific surface area is too small, the microdispersibility relative to other materials is poor, and if the specific surface area is too large, the time required for dispersion in other materials becomes longer, or the viscosity increases excessively when added to coatings, etc.

[0098] The specific surface area of ​​the powder containing the particles of low molecular weight polytetrafluoroethylene can be adjusted as follows, for example: tetrafluoroethylene is polymerized in the presence of a fluorinated surfactant, a polymerization initiator and an aqueous medium, thus making the primary particles of low molecular weight polytetrafluoroethylene, and the primary particles of the low molecular weight polytetrafluoroethylene obtained by polymerization are precipitated, dried at an appropriate temperature, and thus adjusted. The specific surface area of ​​the primary particles obtained in this way is relatively small. And then, the particles (secondary particles) of the low molecular weight polytetrafluoroethylene constituting the powder obtained in this way are not formed by the primary particle fusion of low molecular weight polytetrafluoroethylene, but are formed by the primary particles of low molecular weight polytetrafluoroethylene only condensing. Therefore, the specific surface area of ​​the powder can be made to reflect the specific surface area of ​​the primary particles of low molecular weight polytetrafluoroethylene, and a relatively large specific surface area can be obtained.

[0099] The specific surface area of ​​the powder was measured by the BET method using a surface analyzer (trade name: MONOSORB, manufactured by QUANTA CHLROME) using a mixed gas of 30% nitrogen and 70% helium as a carrier gas and liquid nitrogen for cooling.

[0100] The melt viscosity of the low molecular weight polytetrafluoroethylene constituting the powder of the present invention at 380°C is preferably 1×10 2 Pa·s~7×10 5Pa·s. In the present invention, "low molecular weight" means that the melt viscosity is within the above range. Compared with low molecular weight polytetrafluoroethylene, the melt viscosity of high molecular weight polytetrafluoroethylene is extremely high, and it is difficult to measure its exact melt viscosity. The melt viscosity is measured according to ASTM D 1238 using a flow tester (manufactured by Shimadzu Corporation) and The value is measured by using a die head and holding a 2 g sample heated in advance at 380° C. for 5 minutes at the above temperature under a load of 0.7 MPa.

[0101] Low molecular weight polytetrafluoroethylene is polytetrafluoroethylene that has melt processability and does not have fibrillation properties. On the other hand, high molecular weight polytetrafluoroethylene is polytetrafluoroethylene that has neither melt processability nor fibrillation properties.

[0102] Non-melt processability refers to the property that the melt flow rate cannot be determined at a temperature above the crystallization melting point according to ASTM D 1238 and D 2116.

[0103] The presence or absence of fibrillation can be determined by "paste extrusion", a representative method for molding a powder made of a tetrafluoroethylene polymer, namely "high molecular weight polytetrafluoroethylene powder". Generally, paste extrusion is possible because high molecular weight polytetrafluoroethylene has fibrillation. In the case where the unburned molded product obtained by paste extrusion has no substantial strength or elongation, for example, in the case where it breaks when stretched at an elongation of 0%, it can be considered that it does not have fibrillation.

[0104] The average particle size of the low molecular weight polytetrafluoroethylene particles contained in the powder of the present invention is preferably 1.0 μm to 30 μm, more preferably 2.0 μm or more, and more preferably 20 μm or less. By setting the average particle size of the low molecular weight polytetrafluoroethylene particles within the above range, excellent microdispersibility relative to other materials can be obtained.

[0105] The average particle size of the low molecular weight polytetrafluoroethylene particles is a volume-based average particle size (50% cumulative particle size) d50, which can be determined by a laser diffraction method.

[0106] The melting point of the low molecular weight polytetrafluoroethylene is preferably 322° C. to 333° C., more preferably 323° C. or higher, further preferably 324° C. or higher, and more preferably 332° C. or lower.

[0107] The melting point can be determined by using a differential scanning calorimeter (DSC) to draw a DSC curve by heating low molecular weight polytetrafluoroethylene that has not been heated to a temperature of 300°C or higher at 10°C / min, and determining the temperature corresponding to the minimum point of the heat of fusion in the temperature range of 250°C to 380°C of the DSC curve.

[0108] (Fluorine-containing compound having a hydrophilic group)

[0109] The powder of the present invention contains 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 monomer.

[0110] 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.

[0111] 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.

[0112] The content of the fluorine-containing compound having a hydrophilic group in the powder can be adjusted, for example, by polymerizing tetrafluoroethylene in the presence of a fluorine-containing surfactant, a polymerization initiator and an aqueous medium to prepare an aqueous dispersion of primary particles containing low molecular weight polytetrafluoroethylene, adding a relatively large amount of a free radical generator to the aqueous dispersion, and performing a heat treatment.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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 tetrafluoroethylene. 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.

[0120] 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.

[0121] 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.

[0122] Furthermore, the fluorine-containing surfactant may be a surfactant containing fluorine whose anionic part has a molecular weight of 1,000 or less.

[0123] 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” part.

[0124] 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].

[0125] 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.

[0126] 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.

[0127] Examples of the anionic fluorinated surfactant include the following general formula (N 0 ):

[0128] X n0 -Rf n0 -Y 0 (N 0 )

[0129] (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 replaced by F. The alkylene group may contain one or more ether bonds, and some of the H groups may be replaced by Cl. 0 is an anionic group).

[0130] Y 0The anionic group may be -COOM, -SO2M or -SO3M, or may be -COOM or -SO3M.

[0131] 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.

[0132] Examples of the metal atom include alkali metals (Group 1) and alkaline earth metals (Group 2), such as Na, K, or Li.

[0133] 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.

[0134] 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.

[0135] The above Rf n0 In the above formula (A), more than 50% of the H can be replaced by fluorine.

[0136] As the above general formula (N 0 ) can include:

[0137] The following general formula (N 1 ):

[0138] X n0 -(CF2) m1 -Y 0 (N 1 )

[0139] (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 ):

[0140] R n1 -O-(CF(CF3)CF2O) m2 CFX n1 -Y 0 (N 2 )

[0141] (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 ):

[0142] R n2 (CH2) m3 -(Rf n3 ) q -Y 0 (N 3 )

[0143] (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 ):

[0144] R n4 -O-(CY n1 Y n2 ) p CF2-Y 0 (N 4 )

[0145] (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 ):

[0146] [Chemistry 1]

[0147]

[0148] (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).

[0149] 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.

[0150] The above perfluorocarboxylic acid (I) is represented by the following general formula (I):

[0151] F(CF2) n1 COOM (I)

[0152] (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).

[0153] The above-mentioned ω-H perfluorocarboxylic acid (II) is represented by the following general formula (II):

[0154] H(CF2) n2 COOM (II)

[0155] (wherein n2 is an integer of 4 to 15, and M is the substance defined above).

[0156] The above perfluoroether carboxylic acid (III) is represented by the following general formula (III):

[0157] R 1 -O-(CF(CF3)CF2O) n3 CF(CF3)COOM(III)

[0158] (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).

[0159] The above perfluoroalkyl alkylene carboxylic acid (IV) is represented by the following general formula (IV):

[0160] R 2 (CH2) n4 R 3 COOM (IV)

[0161] (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).

[0162] The above alkoxy fluorocarboxylic acid (V) is represented by the following general formula (V):

[0163] R 4 -O-CY 1 Y 2 CF2-COOM (V)

[0164] (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).

[0165] The above perfluoroalkylsulfonic acid (VI) is represented by the following general formula (VI):

[0166] F(CF2) n5 SO3M (VI)

[0167] (wherein n5 is an integer of 3 to 14, and M is the substance defined above).

[0168] The above-mentioned ω-H perfluorosulfonic acid (VII) is represented by the following general formula (VII):

[0169] H(CF2) n6 SO3M (VII)

[0170] (wherein n6 is an integer of 4 to 14, and M is the substance defined above).

[0171] The above perfluoroalkyl alkylene sulfonic acid (VIII) is represented by the following general formula (VIII):

[0172] R 5 (CH2) n7SO3M (VIII)

[0173] (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).

[0174] The above alkyl alkylene carboxylic acid (IX) is represented by the following general formula (IX):

[0175] R 6 (CH2) n8 COOM (IX)

[0176] (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).

[0177] The above fluorocarboxylic acid (X) is represented by the following general formula (X):

[0178] R 7 -O-Rf 8 -O-CF2-COOM (X)

[0179] (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).

[0180] The above alkoxy fluorosulfonic acid (XI) is represented by the following general formula (XI):

[0181] R 9 -O-CY 1 Y 2 CF2-SO3M (XI)

[0182] (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).

[0183] The above compound (XII) is represented by the following general formula (XII):

[0184] [Chemistry 2]

[0185]

[0186] (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).

[0187] Y 0 It can be -COOM, -SO2M or -SO3M, or -SO3M or COOM (wherein M is the substance defined above).

[0188] 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.

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

[0190] R 11 -O-(CF2CF(CF3)O) n9 (CF2O) n10 CF2COOM (XIII)

[0191] (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).

[0192] As described above, examples of the anionic fluorinated surfactant include carboxylic acid-based surfactants and sulfonic acid-based surfactants.

[0193] The fluorinated surfactant may be a single type of fluorinated surfactant or a mixture containing two or more types of fluorinated surfactants.

[0194] 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 tetrafluoroethylene in the presence of an aqueous medium can be smoothly performed.

[0195] 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 tetrafluoroethylene 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.

[0196] 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 ):

[0197] R n4 -O-(CY n1 F) p CF2-Y 0 (N 4 )

[0198] (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 an alkyl group 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 ):

[0199] [Chemistry 3]

[0200]

[0201] (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).

[0202] 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

[0203] (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

[0204] (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):

[0205] [Chemistry 4]

[0206]

[0207] (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):

[0208] R 11 -O-(CF2CF(CF3)O) n9 (CF2O) n10 CF2COOM

[0209] (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 tetrafluoroethylene in the presence of an aqueous medium can be smoothly carried out.

[0210] Examples of the fluorinated surfactant include compounds represented by the following formula: The fluorinated surfactant may be a mixture of these compounds.

[0211] F(CF2)7COOM,

[0212] F(CF2)5COOM,

[0213] H(CF2)6COOM,

[0214] H(CF2)7COOM,

[0215] CF3O(CF2)3OCHFCF2COOM,

[0216] C3F7OCF(CF3)CF2OCF(CF3)COOM,

[0217] CF3CF2CF2OCF(CF3)COOM,

[0218] CF3CF2OCF2CF2OCF2COOM,

[0219] C2F5OCF(CF3)CF2OCF(CF3)COOM,

[0220] CF3OCF(CF3)CF2OCF(CF3)COOM,

[0221] CF2ClCF2CF2OCF(CF3)CF2OCF2COOM,

[0222] CF2ClCF2CF2OCF2CF(CF3)OCF2COOM,

[0223] CF2ClCF(CF3)OCF(CF3)CF2OCF2COOM,

[0224] CF2ClCF(CF3)OCF2CF(CF3)OCF2COOM,

[0225] [Chemistry 5]

[0226]

[0227] (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. )

[0228] 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 25 ppb by mass or less, more preferably 10 ppb by mass or less, further preferably 5 ppb by mass or less, further preferably 1 ppb by mass or less, and preferably more than 0 ppb by mass, relative to the powder.

[0229] In one embodiment of the powder, the powder contains a compound (I) represented by the following general formula (I) as the fluorine-containing compound having a hydrophilic group.

[0230] General formula (I): F(CF2) n1 COOM

[0231] (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. )

[0232] In the case where the powder contains at least a compound (I) represented by the general formula (I) as a fluorine-containing compound having a hydrophilic group, the content of the compound represented by the general formula (I) 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, relative to the powder.

[0233] In one embodiment of the powder, the compound represented by the following general formula (H1) is contained as the fluorine-containing compound having a hydrophilic group.

[0234] General formula (H1): [X-Rf-A - ] i M i+

[0235] (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 - Indicates acid group, M i+ represents a cation having a valence number i, where i represents an integer from 1 to 3)

[0236] In the case where the powder contains at least a compound represented by the general formula (H1) as a fluorine-containing compound having a hydrophilic group, the content of the compound represented by the general formula (H1) 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.

[0237] 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.

[0238] General formula (H2): [C n-1 F 2n-1 COO - ]M +

[0239] (where n represents an integer from 9 to 14, M + represents a cation.)

[0240] It is known that when perfluoroalkyl vinyl ether or the like is used as a monomer, a compound represented by the general formula (H2) (perfluoroalkanoic acid) is formed during polymerization (see International Publication No. 2019 / 161153).

[0241] 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.

[0242] 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.

[0243] General formula (H3): [R 1 -OL-CO2 - ]M +

[0244] (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.)

[0245] 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 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.

[0246] 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.

[0247] General formula (H4): H-Rf n0 -Y 0

[0248] (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.)

[0249] Examples of the compound represented by the general formula (H4) include compounds represented by any of the following general formulae.

[0250] General formula (H4-1): [H-(CF2) m1 CO2 - ]M +

[0251] (In the formula, m1 represents an integer from 3 to 19, M + represents a cation.)

[0252] General formula (H4-2): [H-(CF2) m2 -(CF(CF3)) m3 -CO2- ]M +

[0253] (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. )

[0254] 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, and preferably more than 0 mass ppb.

[0255] (Low molecular weight polytetrafluoroethylene)

[0256] The low molecular weight polytetrafluoroethylene (low molecular weight PTFE) may be a tetrafluoroethylene (TFE) homopolymer containing only TFE units, or may be a modified polytetrafluoroethylene containing TFE units and modifying monomer units.

[0257] The modifying monomer is not particularly limited as long as it is copolymerizable with TFE, and examples thereof include fluorine-containing monomers and non-fluorine-containing monomers. The modifying monomer used may be one kind or two or more kinds.

[0258] The non-fluorine-containing monomer is not particularly limited, and examples thereof include the following:

[0259] CH2=CR Q1 -LR Q2

[0260] (Where R Q1 represents a hydrogen atom or an alkyl group. L represents a single bond, -CO-O-*, -O-CO-* or -O-. * represents the same Q2 The bonding position of R Q2 represents a hydrogen atom, an alkyl group or a nitrile group).

[0261] Examples of the non-fluorine-containing monomer include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, vinyl methacrylate, vinyl acetate, acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, ethyl vinyl ether, and cyclohexyl vinyl ether. Among the non-fluorine-containing monomer, butyl methacrylate, vinyl acetate, and acrylic acid are preferred.

[0262] Examples of the fluorine-containing monomer include perfluoroolefins such as hexafluoropropylene [HFP]; hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride [VDF]; perhaloolefins such as chlorotrifluoroethylene; perfluorovinyl ether; (perfluoroalkyl)ethylene; and perfluoroallyl ether.

[0263] The perfluorovinyl ether is not particularly limited, and examples thereof include those of the general formula (A):

[0264] CF2=CF-ORf(A)

[0265] (wherein Rf represents a perfluoro organic group) and the like. In the present invention, the above-mentioned "perfluoro organic group" refers to an organic group in which all hydrogen atoms bonded to carbon atoms are replaced by fluorine atoms. The above-mentioned perfluoro organic group may have an ether oxygen.

[0266] Examples of the perfluorovinyl ether include perfluoro(alkyl vinyl ether) [PAVE] wherein Rf in the general formula (A) is a perfluoroalkyl group having 1 to 10 carbon atoms. The perfluoroalkyl group preferably has 1 to 5 carbon atoms.

[0267] Examples of the perfluoroalkyl group in PAVE include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group.

[0268] As the perfluorovinyl ether, further examples include monomers wherein Rf in the general formula (A) is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, and Rf is the following formula:

[0269] [Chemistry 6]

[0270]

[0271] (wherein m represents 0 or an integer of 1 to 4) and Rf is the following formula:

[0272] CF3CF2CF2-(O-CF(CF3)-CF2) n -

[0273] (wherein n represents an integer of 1 to 4) and the like.

[0274] Examples of hydrogen-containing fluoroolefins include CH2=CF2, CFH=CH2, CFH=CF2, CH2=CFCF3, CH2=CHCF3, CHF=CHCF3 (E form), and CHF=CHCF3 (Z form).

[0275] The (perfluoroalkyl)ethylene (PFAE) is not particularly limited, and examples thereof include (perfluorobutyl)ethylene (PFBE) and (perfluorohexyl)ethylene.

[0276] Examples of the perfluoroallyl ether include

[0277] General formula: CF2=CF-CF2-ORf

[0278] (wherein Rf represents a perfluoro organic group).

[0279] Rf in the above general formula is the same as Rf in general formula (A). As Rf, a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoroalkoxyalkyl group having 1 to 10 carbon atoms is preferred. As the perfluoroallyl ether, at least one selected from the group consisting of CF2=CF-CF2-O-CF3, CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7 and CF2=CF-CF2-O-C4F9 is preferred, at least one selected from the group consisting of CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7 and CF2=CF-CF2-O-C4F9 is more preferred, and CF2=CF-CF2-O-CF2CF3 is further preferred.

[0280] Preferred examples of the modified monomer include a modified monomer (3) having a monomer reactivity ratio of 0.1 to 8. The presence of the modified monomer (3) can provide PTFE particles having a small particle size and an aqueous dispersion having high dispersion stability.

[0281] Here, the monomer reactivity ratio in the copolymerization with TFE is a value obtained as follows: when the growth free radical is smaller than the repeating unit based on TFE, the rate constant when the growth free radical reacts with TFE is divided by the rate constant when the growth free radical reacts with the modified monomer, and the obtained value is the above-mentioned monomer reactivity ratio. The lower the value, the higher the reactivity of the modified monomer with TFE. The monomer reactivity ratio can be calculated as follows: copolymerize TFE and the modified monomer, find the composition of the generated polymer immediately after the start, and calculate it by the Fineman-Ross formula.

[0282] The copolymerization is carried out in a stainless steel autoclave with an internal volume of 6.0 L using 3600 g of deionized degassed water, 1000 mass ppm of ammonium perfluorooctanoate relative to the water, and 100 g of paraffin wax at a pressure of 0.78 MPaG and a temperature of 70°C. 0.05 g, 0.1 g, 0.2 g, 0.5 g, and 1.0 g of the modified monomer are added to the reactor respectively, and 0.072 g of ammonium persulfate (20 mass ppm relative to water) is added. In order to maintain a polymerization pressure of 0.78 MPaG, TFE is continuously supplied. When the TFE feed reaches 1000 g, stirring is stopped and depressurization is performed until the reactor reaches atmospheric pressure. After cooling, paraffin wax is separated to obtain an aqueous dispersion containing the generated polymer. The aqueous dispersion is stirred to precipitate the generated polymer and dried at 150°C. The composition of the resulting polymer is calculated by appropriately combining NMR, FT-IR, elemental analysis, and fluorescent X-ray analysis depending on the type of monomer.

[0283] The modified monomer (3) having a monomer reactivity ratio of 0.1 to 8 is preferably at least one selected from the group consisting of modified monomers represented by formulas (3a) to (3d).

[0284] CH2=CH-Rf 1 (3a)

[0285] (Where Rf 1 It is a perfluoroalkyl group having 1 to 10 carbon atoms. )

[0286] CF2=CF-O-Rf 2 (3b)

[0287] (Where Rf 2 It is a perfluoroalkyl group having 1 to 2 carbon atoms. )

[0288] CF2=CF-O-(CF2) n CF=CF2 (3c)

[0289] (In the formula, n is 1 or 2.)

[0290] [Chemistry 7]

[0291]

[0292] (Where X 3 and X 4 is F, Cl or methoxy, and Y is of the formula Y1 or Y2.)

[0293] [Chemistry 8]

[0294]

[0295] (In formula Y2, Z and Z' are F or a fluorinated alkyl group having 1 to 3 carbon atoms.)

[0296] The content of the modified monomer (3) unit is preferably in the range of 0.00001% by mass to 1.0% by mass relative to the total polymerized units of PTFE. As the lower limit, it is more preferably 0.0001% by mass, more preferably 0.0005% by mass, further preferably 0.001% by mass, and further more preferably 0.005% by mass. As the upper limit, it is 0.90% by mass, 0.50% by mass, 0.40% by mass, 0.30% by mass, 0.20% by mass, 0.15% by mass, 0.10% by mass, 0.08% by mass, 0.05% by mass, 0.01% by mass in a preferred order.

[0297] As above-mentioned modified monomer, owing to can obtain the aqueous dispersion liquid of the average primary particle diameter of primary particle little, the aspect ratio of primary particle little, excellent stability, thus preferably selected from at least one in the group of the modified monomer composition of hexafluoropropylene, trifluorochloroethylene, vinylidene fluoride, perfluor (alkyl vinyl ether), (perfluoroalkyl) ethylene, ethylene and the functional group that can pass through free radical polymerization and hydrophilic group.By using above-mentioned modified monomer, can obtain the aqueous dispersion liquid of the PTFE of average primary particle diameter little, the aspect ratio of primary particle little, excellent dispersion stability.In addition, can obtain the aqueous dispersion liquid of the few unprecipitated polymer.

[0298] From the viewpoint of reactivity with TFE, the modifying monomer preferably contains at least one selected from the group consisting of hexafluoropropylene, perfluoro(alkyl vinyl ether) and (perfluoroalkyl)ethylene.

[0299] More preferably, it contains at least one selected from the group consisting of hexafluoropropylene, perfluoro(methyl vinyl ether), perfluoro(propyl vinyl ether), (perfluorobutyl)ethylene, (perfluorohexyl)ethylene, and (perfluorooctyl)ethylene.

[0300] The total amount of the above-mentioned hexafluoropropylene unit, perfluoro (alkyl vinyl ether) unit and (perfluoroalkyl) ethylene unit is preferably in the range of 0.00001 mass % to 1 mass % relative to the total polymerized units of PTFE. As the lower limit of the above-mentioned total amount, it is more preferably 0.0001 mass %, more preferably 0.0005 mass %, further preferably 0.001 mass %, further preferably 0.005 mass %. As the upper limit, it is 0.80 mass %, 0.70 mass %, 0.50 mass %, 0.40 mass %, 0.30 mass %, 0.20 mass %, 0.15 mass %, 0.10 mass %, 0.08 mass %, 0.05 mass %, 0.01 mass %.

[0301] The above-mentioned modified monomer also preferably includes a modified monomer having a functional group capable of a radical polymerization reaction and a hydrophilic group (hereinafter referred to as "modified monomer (A)").

[0302] The presence of the modified monomer (A) can provide PTFE particles with a small primary particle size, and an aqueous dispersion with high dispersion stability. In addition, the amount of unprecipitated polymer can be reduced. Furthermore, the aspect ratio of the primary particles can be reduced.

[0303] The amount of the modified monomer (A) is preferably an amount exceeding an amount equivalent to 0.1 mass ppm of the aqueous medium, more preferably an amount exceeding 0.5 mass ppm, further preferably an amount exceeding 1.0 mass ppm, and further more preferably 5 mass ppm or more, particularly preferably 10 mass ppm or more. If the amount of the modified monomer (A) is too little, the average primary particle size of the obtained PTFE may not be reduced.

[0304] The amount of the modified monomer (A) may be within the above range, and the upper limit may be 5000 ppm by mass, for example. In addition, in the above production method, in order to improve the stability of the aqueous dispersion during or after the reaction, the modified monomer (A) may be added to the system during the reaction.

[0305] The modified monomer (A) has high water solubility. Therefore, even if unreacted modified monomer (A) remains in the aqueous dispersion, it can be easily removed in the concentration step or the precipitation / washing step.

[0306] The modified monomer (A) is introduced into the resulting polymer during the polymerization process. However, since the concentration of the modified monomer (A) in the polymerization system is low and the amount introduced into the polymer is small, there is no problem of reduced heat resistance of PTFE or coloration after firing.

[0307] Examples of the hydrophilic group in the modified monomer (A) include -NH2, -PO3M, -OPO3M, -SO3M, -OSO3M, -COOM (wherein M is H, a metal atom, NR 7y 4. an imidazolium which may be substituted, a pyridinium which may be substituted, or a phosphonium which may be substituted, R 7y R is H or an organic group, which may be the same or different. Any two of them may be bonded to each other to form a ring). As the above-mentioned hydrophilic group, -SO3M or -COOM is preferred. 7y The organic group in is preferably an alkyl group. 7y , preferably H or C 1-10 An organic group, more preferably H or C 1-4 The organic group is preferably H or C 1-4 of alkyl.

[0308] Examples of the metal atom include monovalent and divalent metal atoms, such as alkali metals (Group 1) and alkaline earth metals (Group 2), and Na, K or Li is preferred.

[0309] Examples of the "functional group capable of free radical polymerization" in the modified monomer (A) include groups having ethylenically unsaturated bonds such as vinyl and allyl groups. The group having ethylenically unsaturated bonds can be represented by the following formula:

[0310] CX e X g =CX f R-

[0311] (Where X e , X f and X g Each independently represents F, Cl, H, CF3, CF2H, CFH2 or CH3; R represents a linking group). Examples of the linking group of R include the following R a Preferred examples include groups having unsaturated bonds such as -CH=CH2, -CF=CH2, -CH=CF2, -CF=CF2, -CH2-CH=CH2, -CF2-CF=CH2, -CF2-CF=CF2, -(C=O)-CH=CH2, -(C=O)-CF=CH2, -(C=O)-CH=CF2, -(C=O)-CF=CF2, -(C=O)-C(CH3)=CH2, -(C=O)-C(CF3)=CH2, -(C=O)-C(CH3)=CF2, -(C=O)-C(CF3)=CF2, -O-CH2-CH=CH2, -O-CF2-CF=CH2, -O-CH2-CH=CF2, and -O-CF2-CF=CF2.

[0312] Since the modified monomer (A) has a functional group capable of free radical polymerization, if used in the polymerization, it reacts with the fluorinated monomer in the initial stage of the polymerization reaction, and it is presumed that the hydrophilic group derived from the modified monomer (A) can form particles with high stability. Therefore, if the polymerization is carried out in the presence of the modified monomer (A), it is believed that the number of particles increases.

[0313] In the above polymerization, the above-mentioned modified monomer (A) may be present alone or in combination of two or more.

[0314] In the above-mentioned polymerization, a compound having an unsaturated bond can be used as the above-mentioned modified monomer (A).

[0315] The modified monomer (A) is preferably of the general formula (4):

[0316] CX i X k =CX j R a -(CZ 1 Z 2 ) k -Y 3 (4)

[0317] (Where X i , X j and X k Each independently represents F, Cl, H or CF3; Y 3 is a hydrophilic group; R a is a connecting group; Z 1 and Z 2 Each independently represents H, F or CF3, and k represents 0 or 1).

[0318] Examples of the hydrophilic group include -NH2, -PO3M, -OPO3M, -SO3M, -OSO3M, -COOM (wherein M is H, a metal atom, NR 7y 4. an imidazolium which may be substituted, a pyridinium which may be substituted, or a phosphonium which may be substituted, R 7y R is H or an organic group, which may be the same or different. Any two of them may be bonded to each other to form a ring). As the above-mentioned hydrophilic group, -SO3M or -COOM is preferred. 7y The organic group in is preferably an alkyl group. 7y , preferably H or C 1-10 An organic group, more preferably H or C 1-4 The organic group is preferably H or C 1-4 The metal atom may be a monovalent or divalent metal atom, and may be an alkali metal (Group 1) or an alkaline earth metal (Group 2). Preferably, Na, K or Li is used.

[0319] By using the modified monomer (A), an aqueous dispersion having a smaller average primary particle size and better stability can be obtained, and the aspect ratio of the primary particles can be further reduced.

[0320] The above R a is a linking group. In the present invention, "linking group" refers to a divalent linking group. The linking group may be a single bond, preferably contains at least one carbon atom, and the number of carbon atoms may be 2 or more, 4 or more, 8 or more, 10 or more, or 20 or more. The upper limit is not limited, for example, it may be 100 or less, or 50 or less.

[0321] The linking group may be linear or branched, cyclic or acyclic, saturated or unsaturated, substituted or unsubstituted, and may contain one or more heteroatoms selected from the group consisting of sulfur, oxygen and nitrogen as desired, and may contain one or more functional groups selected from the group consisting of ester, amide, sulfonamide, carbonyl, carbonate, carbamate, urea and carbamate as desired. The linking group does not contain carbon atoms and may be chain heteroatoms such as oxygen, sulfur or nitrogen.

[0322] The above R a Preferred are, for example, chain heteroatoms such as oxygen, sulfur, and nitrogen, or divalent organic groups.

[0323] R a In the case of a divalent organic group, the hydrogen atom bonded to the carbon atom may be replaced by a halogen other than fluorine, such as chlorine, and may or may not contain a double bond. a It may be either a linear or branched chain, or a cyclic or acyclic chain. a Functional groups (eg, ester, ether, ketone, amine, halide, etc.) may be included.

[0324] In addition, R a It may be a non-fluorinated divalent organic group or a partially fluorinated or perfluorinated divalent organic group.

[0325] As R a , and can be, for example: a hydrocarbon group in which no fluorine atoms are bonded to the carbon atom; a hydrocarbon group in which a part of the hydrogen atoms bonded to the carbon atom are substituted by fluorine atoms; a hydrocarbon group in which all the hydrogen atoms bonded to the carbon atom are substituted by fluorine atoms; a hydrocarbon group containing -(C=O)-, -(C=O)-O- or -(C=O)-, which may contain oxygen atoms, double bonds, and functional groups.

[0326] R a Preferably, it is a hydrocarbon group having 1 to 100 carbon atoms which may contain -(C=O)-, -(C=O)-O- or an ether bond and may contain a carbonyl group, and a part or all of the hydrogen atoms bonded to the carbon atoms in the hydrocarbon group may be substituted with fluorine.

[0327] As R a , preferably selected from -(CH2) a -、-(CF2) a -、-O-(CF2) a -、-(CF2) a -O-(CF2) b -、-O(CF2) a -O-(CF2) b -、-(CF2) a -[O-(CF2) b] c -、-O(CF2) a -[O-(CF2) b ] c -、-[(CF2) a -O] b -[(CF2) c -O] d -、-O[(CF2) a -O] b -[(CF2) c -O] d -、-O-[CF2CF(CF3)O] a -(CF2) b -, -(C=O)-, -(C=O)-O-, -(C=O)-(CH2) a -、-(C=O)-(CF2) a -、-(C=O)-O-(CH2) a -、-(C=O)-O-(CF2) a -、-(C=O)-[(CH2) a -O] b -、-(C=O)-[(CF2) a -O] b -、-(C=O)-O[(CH2) a -O] b -、-(C=O)-O[(CF2) a -O] b -、-(C=O)-O[(CH2) a -O] b -(CH2) c -、-(C=O)-O[(CF2) a -O] b -(CF2) c -、-(C=O)-(CH2) a -O-(CH2) b -、-(C=O)-(CF2) a -O-(CF2) b -、-(C=O)-O-(CH2) a -O-(CH2) b -、-(C=O)-O-(CF2) a -O-(CF2) b At least one of -, -(C=O)-O-C6H4- and combinations thereof.

[0328] In the formula, a, b, c and d are independently at least 1. a, b, c and d can independently be 2 or more, 3 or more, 4 or more, 10 or more, or 20 or more. The upper limit of a, b, c and d is, for example, 100.

[0329] As R a Preferred specific examples include -CF2-O-, -CF2-O-CF2-, -CF2-O-CH2-, -CF2-O-CH2CF2-, -CF2-O-CF2CF2-, -CF2-O-CF2CH2-, -CF2-O-CF2CF2CH2-, -CF2-O-CF(CF3)-, -CF2-O-CF(CF3)CF2-, -CF2-O-CF(CF3)CF2-, -CF2-O-CF(CF3)CF2-O-, -CF2-O-CF(CF3)CH2-, -(C=O)-, -(C=O)-O-, -(C=O)-(CH2)-, -(C=O)-(CF2)-, -(C=O)-O-(CH2)-, -(C=O)-O-(CF2)-, -(C=O)-[(CH2)2-O] n -、-(C=O)-[(CF2)2-O] n -、-(C=O)-O[(CH2)2-O] n -、-(C=O)-O[(CF2)2-O] n -、-(C=O)-O[(CH2)2-O] n -(CH2)-, -(C=O)-O[(CF2)2-O] n -(CF2)-, -(C=O)-(CH2)2-O-(CH2)-, -(C=O)-(CF2)2-O-(CF2)-, -(C=O)-O-(CH2)2-O-(CH2)-, -(C=O)-O-(CF2)2-O-(CF2)-, -(C=O)-O-C6H4-, etc. Specifically, the above R a Preferably -CF2-O-, -CF2-O-CF2-, -CF2-O-CF2CF2-, -CF2-O-CF(CF3)-, -CF2-O-CF(CF3)CF2-, -CF2-O- CF(CF3)CF2-O-, -(C=O)-, -(C=O)-O-, -(C=O)-(CH2)-, -(C=O)-O-(CH2)-, -(C=O)-O[(CH2)2-O] n -、-(C=O)-O[(CH2)2-O] n -(CH2)-, -(C=O)-(CH2)2-O-(CH2)-, or -(C=O)-O-C6H4-.

[0330] In the above formula, n is an integer from 1 to 10.

[0331] As -R in the general formula (4) a -(CZ 1 Z 2 ) k -, preferably -CF2-O-CF2-, -CF2-O-CF(CF3)-, -CF2-O-C(CF3)2-, -CF2-O-CF2-CF2-, -CF2-O-CF2-CF(CF3)-, -CF2-O-CF2-C(CF3)2-, -CF2-O-CF2CF2-CF2-, -CF2-O-CF2CF2-CF(CF3)-, -CF2-O-CF2CF2-C(CF3)2-, -CF2-O-CF(CF3)-CF2-, -CF2-O-CF(CF3)-CF(CF3)-, -CF2-O-CF(CF3)-C(CF3)2-, -CF2-O-CF(CF3)CF2-CF2-, -CF2-O-CF(CF3)CF2-CF(CF3)-, -CF2-O-CF(CF3)CF2-C(CF3)2-, -CF2-O-CF(CF3)CF2-O-CF2-, -CF2-O-CF(CF3)CF2-O-CF(CF3)-, -CF2-O-CF(CF3)CF2-O-C(CF3)2-, -(C=O)-, -(C=O)-O-, -(C=O)-(CH2)-, -(C=O)-(CF2)-, -(C=O)-O-(CH2)-, -(C=O)-O-(CF2)-, -(C=O)-[(CH2)2-O] n -(CH2)-, -(C=O)-[(CF2)2-O] n -(CF2)-, -(C=O)-[(CH2)2-O] n -(CH2)-(CH2)-, -(C=O)-[(CF2)2-O] n -(CF2)-(CF2)-, -(C=O)-O[(CH2)2-O] n -(CF2)-, -(C=O)-O[(CH2)2-O] n -(CH2)-(CH2)-, -(C=O)-O[(CF2)2-O] n -(CF2)-, -(C=O)-O[(CF2)2-O] n-(CF2)-(CF2)-, -(C=O)-(CH2)2-O-(CH2)-(CH2)-, -(C=O)-(CF2)2-O-(CF2)-(CF2)-, -(C=O)-O-(CH2)2-O-(CH2)-(CH2)-, -(C= O)-O-(CF2)2-O-(CF2)-(CF2)-, -(C=O)-O-(CH2)2-O-(CH2)-C(CF3)2-, -(C=O)-O-(CF2)2-O-(CF2)-C(CF3)2-, or -(C=O)-O-C6H4 -C(CF3)2-, more preferably -CF2-O-CF(CF3)-, -CF2-O-CF2-CF(CF3)-, -CF2-O-CF2CF2-CF(CF3)-, -CF2-O-CF(CF3)-CF(CF3)-, -CF2-O-CF(CF 3)CF2-CF(CF3)-, -CF2-O-CF(CF3)CF2-O-CF(CF3)-, -(C=O)-, -(C=O)-O-(CH2)-, -(C=O)-O-(CH2)-(CH2)-, -(C=O)-O[(CH2)2-O] n -(CH2)-(CH2)-, -(C=O)-O-(CH2)2-O-(CH2)-C(CF3)2-, or -(C=O)-O-C6H4-C(CF3)2-.

[0332] In the above formula, n is an integer of 1-10.

[0333] Specific examples of the compound represented by the general formula (4) include:

[0334] [Chemistry 9]

[0335]

[0336] (Where X j and Y 3 Same as above. n is an integer from 1 to 10) and the like.

[0337] As R a , preferably general formula (r1):

[0338] -(C=O) h -(O) i -CF2-O-(CX 6 2) e -{O-CF(CF3)} f -(O) g - (r1)

[0339] (Where X 6Each independently represents H, F or CF3, e represents an integer of 0 to 3, f represents an integer of 0 to 3, g represents 0 or 1, h represents 0 or 1, and i represents 0 or 1), and the general formula (r2) is also preferred:

[0340] -(C=O) h -(O) i -CF2-O-(CX 7 2) e -(O) g - (r2)

[0341] (Where X 7 Each independently represents H, F or CF3, e is an integer of 0 to 3, g is 0 or 1, h is 0 or 1, and i is 0 or 1).

[0342] As -R in the general formula (4) a -(CZ 1 Z 2 ) k -, the following formula (t1) is also preferred:

[0343] -(C=O) h -(O) i -CF2-O-(CX 6 2) e -{O-CF(CF3)} f -(O) g -CZ 1 Z 2 - (t1)

[0344] (Where X 6 Each independently represents H, F or CF3, e represents an integer of 0 to 3, f represents an integer of 0 to 3, g represents 0 or 1, h represents 0 or 1, i represents 0 or 1, Z 1 and Z 2 Each independently represents a divalent group represented by F or CF3, wherein Z 1 and Z 2 More preferably, one is F and the other is CF3.

[0345] In the general formula (4), -R a -(CZ 1 Z 2 ) k -, the following formula (t2) is also preferred:

[0346] -(C=O) h -(O) i -CF2-O-(CX 7 2) e -(O) g -CZ1 Z 2 - (t2)

[0347] (Where X 7 Each independently represents H, F or CF3, e represents an integer from 0 to 3, g represents 0 or 1, h represents 0 or 1, i represents 0 or 1, Z 1 and Z 2 Each independently represents a divalent group represented by F or CF3, wherein Z 1 and Z 2 More preferably, one is F and the other is CF3.

[0348] The compound represented by the general formula (4) also preferably has a hydrophilic group (Y 3 ) has a CF bond and does not have a CH bond. That is, in the general formula (4), preferably X i , X j and X k All are F, R a The perfluoroalkylene group may have 1 or more carbon atoms, and the perfluoroalkylene group may be any one of a linear or branched chain, cyclic or acyclic, and may contain at least one chain heteroatom. The perfluoroalkylene group may have 2 to 20 carbon atoms, or 4 to 18 carbon atoms.

[0349] The compound represented by the general formula (4) may also be partially fluorinated. That is, the compound represented by the general formula (4) also preferably has, in addition to the hydrophilic group (Y 3 ) has at least one hydrogen atom bonded to a carbon atom and at least one fluorine atom bonded to a carbon atom.

[0350] The compound represented by the general formula (4) is also preferably a compound represented by the following formula (4a).

[0351] CF2=CF-O-Rf 0 -Y 3 (4a)

[0352] (Where Y 3 is a hydrophilic group, Rf 0 It is perfluorinated and may be linear or branched, cyclic or acyclic, saturated or unsaturated, substituted or unsubstituted, and is a perfluorinated divalent linking group that optionally contains one or more heteroatoms selected from the group consisting of sulfur, oxygen and nitrogen.

[0353] The compound represented by the general formula (4) is also preferably a compound represented by the following formula (4b).

[0354] CH2=CH-O-Rf 0 -Y 3 (4b)

[0355] (Where Y 3 is a hydrophilic group, Rf 0 is a perfluorinated divalent linking group defined by formula (4a).

[0356] In the general formula (4), Y 3 -OSO3M is one of the preferred methods. 3 In the case of -OSO3M, examples of the compound represented by the general formula (4) include CF2=CF(OCF2CF2CH2OSO3M), CF2=CF(O(CF2)4CH2OSO3M), CF2=CF(OCF2CF(CF3)CH2OSO3M), CF2=CF(OCF2CF(CF3)OCF2CF2CH2OSO3M), CH2=CH((CF2)4CH2OSO3M), CF2=CF(OCF2CF2SO2N(CH3)CH2CH2OSO3M), CH2=CH(CF2CF2CH2OSO3M), CF2=CF(OCF2CF2CF2CF2SO2N(CH3)CH2CH2OSO3M). In the above formula, M is the same as above.

[0357] In the general formula (4), Y 3 -SO3M is also one of the preferred forms. 3 In the case of -SO3M, examples of the compound represented by the general formula (4) include CF2=CF(OCF2CF2SO3M), CF2=CF(O(CF2)4SO3M), CF2=CF(OCF2CF(CF3)SO3M), CF2=CF(OCF2CF(CF3)OCF2CF2SO3M), CH2=CH(CF2CF2SO3M), CF2=CF(OCF2CF(CF3)OCF2CF2CF2CF2SO3M), CH2=CH((CF2)4SO3M), and CH2=CH((CF2)3SO3M). In the above formula, M is the same as above.

[0358] In the general formula (4), Y 3 -COOM is also one of the preferred methods. 3 In the case of -COOM, examples of the compound represented by the general formula (4) include CF2=CF(OCF2CF2COOM), CF2=CF(OCF2CF2CF2COOM), CF2=CF(O(CF2)5COOM), CF2=CF(OCF2CF(CF3)COOM), CF2=CF(OCF2CF(CF3)O(CF2) nCOOM) (n is greater than 1), CH2=CH(CF2CF2COOM), CH2=CH((CF2)4COOM), CH2=CH((CF2)3COOM), CF2=CF(OCF2CF2SO2NR'CH2COOM), CF2=CF(O(CF2)4SO2NR'CH2COOM), CF2=CF(OCF2CF(CF3)SO2NR'CH2COOM), CF2=CF(OCF2CF(CF3)OCF2CF2SO2NR'CH2COOM), CH2=CH(CF2CF2SO2NR'CH2COOM), CF2=CF(OCF2CF(CF3)OCF2CF2CF2SO2NR'CH2COOM), CH2=CH((CF2)4SO2NR'CH2COOM), CH2=CH((CF2)3SO2NR'CH2COOM), etc. In the above formula, R' is H or C 1-4 The alkyl group and M are the same as described above.

[0359] In the general formula (4), Y 3 It is also one of the preferred embodiments to be -OPO3M or -OP(O)(OM)2. 3 In the case of -OPO3M or -OP(O)(OM)2, examples of the compound represented by the general formula (4) include CF2=CF(OCF2CF2CH2OP(O)(OM)2), CF2=CF(O(CF2)4CH2OP(O)(OM)2), CF2=CF(OCF2CF(CF3)CH2OP(O)(OM)2), CF2=CF(OCF2CF(CF3)OCF2CF2CH2OP(O)(OM)2), and CF2=C F(OCF2CF2SO2N(CH3)CH2CH2OP(O)(OM)2), CF2=CF(OCF2CF2CF2CF2SO2N(CH3)CH2CH2OP(O)(OM)2), CH2=CH(CF2CF2CH2OP(O)(OM)2, CH2=CH((CF2)4CH2OP(O)(OM)2), CH2=CH((CF2)3CH2OP(O)(OM)2), etc. In the above formula, M is the same as above.

[0360] In the general formula (4), Y 3 It is also one of the preferred forms to be -PO3M or -P(O)(OM)2. 3In the case of -PO3M or -P(O)(OM)2, the compound represented by the general formula (4) may include CF2=CF(OCF2CF2P(O)(OM)2), CF2=CF(O(CF2)4P(O)(OM)2), CF2=CF(OCF2CF(CF3)P(O)(OM)2), CF2=CF(OCF2CF(CF3)OCF2CF2P(O)(OM)2), CH2=CH(CF2CF2P(O)(OM)2), CH2=CH((CF2)4P(O)(OM)2), CH2=CH((CF2)3P(O)(OM)2), etc., wherein M is the same as above.

[0361] The compound represented by the general formula (4) is preferably at least one selected from the group consisting of the following compounds, wherein the compound is represented by the general formula (5):

[0362] CX2=CY(-CZ2-O-Rf-Y 3 ) (5)

[0363] (wherein, X is the same or different and is -H or -F, Y is -H, -F, an alkyl group or a fluorinated alkyl group, and Z is the same or different and is -H, -F, an alkyl group or a fluorinated alkyl group. Rf is a fluorinated alkylene group having 1 to 40 carbon atoms, or a fluorinated alkylene group having 2 to 100 carbon atoms and having an ether bond. Y 3 Same as above) and the compound represented by the general formula (6):

[0364] CX2=CY(-O-Rf-Y 3 ) (6)

[0365] (wherein, X is the same or different and is -H or -F, Y is -H, -F, an alkyl group or a fluorinated alkyl group, and Rf is a fluorinated alkylene group having 1 to 40 carbon atoms or a fluorinated alkylene group having an ether bond and having 2 to 100 carbon atoms. 3 Same as above);And general formula (7):

[0366] CX2=CY(-Rf-Y 3 ) (7)

[0367] (wherein, X is the same or different and is -H or -F, Y is -H, -F, an alkyl group or a fluorinated alkyl group, and Rf is a fluorinated alkylene group having 1 to 40 carbon atoms or a fluorinated alkylene group having an ether bond and having 2 to 100 carbon atoms. 3 Same as above).

[0368] The fluorine-containing alkylene group having 2 to 100 carbon atoms and having an ether bond is an alkylene group having no structure with an oxygen atom at the end and having an ether bond between carbon atoms.

[0369] In the general formula (5), X is -H or -F. Both Xs may be -F, or at least one of them may be -H. For example, one may be -F and the other may be -H, or both may be -H.

[0370] In the general formula (5), Y is -H, -F, an alkyl group or a fluorine-containing alkyl group.

[0371] The alkyl group is an alkyl group not containing fluorine atoms and may have at least 1 carbon atom. The alkyl group may have preferably 6 or less carbon atoms, more preferably 4 or less carbon atoms, and even more preferably 3 or less carbon atoms.

[0372] The fluorine-containing alkyl group is an alkyl group containing at least one fluorine atom, and the number of carbon atoms may be 1 or more. The number of carbon atoms in the fluorine-containing alkyl group is preferably 6 or less, more preferably 4 or less, and even more preferably 3 or less.

[0373] As the above-mentioned Y, -H, -F or -CF3 is preferred, and -F is more preferred.

[0374] In the general formula (5), Z is the same or different and is -H, -F, alkyl or fluoroalkyl.

[0375] The alkyl group is an alkyl group not containing fluorine atoms and may have at least 1 carbon atom. The alkyl group may have preferably 6 or less carbon atoms, more preferably 4 or less carbon atoms, and even more preferably 3 or less carbon atoms.

[0376] The fluorine-containing alkyl group is an alkyl group containing at least one fluorine atom, and the number of carbon atoms may be 1 or more. The number of carbon atoms in the fluorine-containing alkyl group is preferably 6 or less, more preferably 4 or less, and even more preferably 3 or less.

[0377] As the above-mentioned Z, -H, -F or -CF3 is preferred, and -F is more preferred.

[0378] In the general formula (5), at least one of X, Y and Z preferably contains a fluorine atom. For example, X may be -H, and Y and Z may be -F.

[0379] In the general formula (5), Rf is a fluorinated alkylene group having 1 to 40 carbon atoms or a fluorinated alkylene group having 2 to 100 carbon atoms and having an ether bond.

[0380] The number of carbon atoms of the fluorinated alkylene group is preferably 2 or more. In addition, it is preferably 30 or less, more preferably 20 or less, and further preferably 10 or less. Examples of the fluorinated alkylene group include -CF2-, -CH2CF2-, -CF2CF2-, -CF2CH2-, -CF2CF2CH2-, -CF(CF3)-, -CF(CF3)CF2-, -CF(CF3)CH2-, etc. The fluorinated alkylene group is preferably a perfluoroalkylene group.

[0381] The number of carbon atoms in the fluorinated alkylene group having an ether bond is preferably 3 or more. The number of carbon atoms in the fluorinated alkylene group having an ether bond is preferably 60 or less, more preferably 30 or less, and further preferably 12 or less.

[0382] As the fluorine-containing alkylene group having an ether bond, for example, the following formula is also preferred:

[0383] [Chemistry 10]

[0384]

[0385] (Where Z 1 F or CF3; Z 2 and Z 3 H or F; Z 4 is a divalent group represented by H, F or CF3; p1+q1+r1 is an integer from 1 to 10; s1 is 0 or 1; t1 is an integer from 0 to 5).

[0386] Specific examples of the fluorinated alkylene group having an ether bond include -CF(CF3)CF2-O-CF(CF3)-, -(CF(CF3)CF2-O) n -CF(CF3)- (wherein n is an integer from 1 to 10), -CF(CF3)CF2-O-CF(CF3)CH2-, -(CF(CF3)CF2-O) n -CF(CF3)CH2- (wherein n is an integer of 1 to 10), -CH2CF2CF2O-CH2CF2CH2-, -CF2CF2CF2O-CF2CF2-, -CF2CF2CF2O-CF2CF2CH2-, -CF2CF2O-CF2-, -CF2CF2O-CF2CH2-, etc. The fluorine-containing alkylene group having an ether bond is preferably a perfluoroalkylene group.

[0387] In the general formula (5), Y 3 Preferably -COOM, -SO3M or -OSO3M (M is H, metal atom, NR 7y 4. an imidazolium which may be substituted, a pyridinium which may be substituted, or a phosphonium which may be substituted, R 7y is H or an organic group, which may be the same or different. Any two of them may be bonded to each other to form a ring).

[0388] As R 7y The organic group in is preferably an alkyl group.

[0389] As R 7y , preferably H or C 1-10 An organic group, more preferably H or C 1-4The organic group is preferably H or C 1-4 of alkyl.

[0390] Examples of the metal atom include alkali metals (Group 1) and alkaline earth metals (Group 2), and Na, K, or Li is preferred.

[0391] As M, -H, a metal atom or NR 7 4, more preferably -H, alkali metal (Group 1), alkaline earth metal (Group 2) or NR 7 4, further preferably -H, -Na, -K, -Li or NH4, still more preferably -H, -Na, -K or NH4, particularly preferably -H, -Na or NH4, most preferably -H or -NH4.

[0392] As the above Y 3 , preferably -COOM or -SO3M, more preferably -COOM.

[0393] The compound represented by the general formula (5) is preferably a compound (5a) represented by the general formula (5a).

[0394] CH2=CF(-CF2-O-Rf-Y 3 ) (5a)

[0395] (In the formula, Rf and Y 3 Same as above.)

[0396] Specific examples of the compound represented by the general formula (5a) include the following:

[0397] [Chemistry 11]

[0398]

[0399] (Where Z 1 F or CF3; Z 2 and Z 3 H or F; Z 4 is H, F or CF3; p1+q1+r1 is an integer from 0 to 10; s1 is 0 or 1; t1 is an integer from 0 to 5, Y 3 Same as above. Where Z 3 and Z 4 When all are H, p1+q1+r1+s1 is not 0). More specifically, preferably,

[0400] [Chemistry 12]

[0401]

[0402] CH2=CFCF2OCH2CF2-Y 3, CH2=CFCF2O(CH2CF2CF2O)CH2CF2-Y 3 ,

[0403] CH2=CFCF2OCH2CF2CH2-Y 3 ,

[0404] CH2=CFCF2O(CH2CF2CF2O)CH2CF2CH2-Y 3 ,

[0405] CH2--CFCF2OCF2CF2-Y 3 , CH2=CFCF2O(CF2CF2CF2O)CF2CF2-Y 3 ,

[0406] CH2=CFCF2OCF2CF2CH2-Y 3 ,

[0407] CH2=CFCF2O(CF2CF2CF2O)CF2CF2CH2-Y 3 ,

[0408] CH2=CFCF2OCF2-Y 3 , CH2=CFCF2O(CF2CF2O)CF2-Y 3 ,

[0409] CH2=CFCF2OCF2CH2-Y 3 ,

[0410] CH2=CFCF2O(CF2CF2O)CF2CH2-Y 3 ,

[0411] etc., among which preferably

[0412] [Chemistry 13]

[0413]

[0414] As the compound represented by the general formula (5a), Y in the formula (5a) is preferably 3 It is -COOM, and is particularly preferably at least one selected from the group consisting of CH2=CFCF2OCF(CF3)COOM and CH2=CFCF2OCF(CF3)CF2OCF(CF3)COOM (wherein M has the same meaning as above), and more preferably CH2=CFCF2OCF(CF3)COOM.

[0415] The compound represented by the general formula (5) is preferably a compound (5b) represented by the general formula (5b).

[0416] CX 2 2=CFCF2-O-(CF(CF3)CF2O) n5 -CF(CF3)-Y 3 (5b)

[0417] (In the formula, each X 2 The same, represents F or H. n5 represents 0 or an integer from 1 to 10, Y 3 Same as the above definition.)

[0418] In the above formula (5b), from the perspective of stability of the obtained aqueous dispersion, the above n5 is preferably 0 or an integer of 1 to 5, more preferably 0, 1 or 2, and even more preferably 0 or 1. From the perspective of obtaining appropriate water solubility and stability of the aqueous dispersion, the above Y 3 -COOM is preferred, and M is preferably H or NH 4 because it is less likely to remain as an impurity and the heat resistance of the obtained molded body is improved.

[0419] Examples of the compound represented by the above formula (5b) include CH2=CFCF2OCF(CF3)COOM and CH2=CFCF2OCF(CF3)CF2OCF(CF3)COOM (wherein M has the same meaning as defined above).

[0420] In addition, examples of the compound represented by the general formula (5) include compounds represented by the general formula (5c) and the like.

[0421] CF2=CFCF2-O-Rf-Y 3 (5c)

[0422] (In the formula, Rf and Y 3 Same as above.)

[0423] More specifically, we can cite

[0424] [Chemistry 14]

[0425] CF2=CFCF2OCF2CF2CF2-Y 3 ,

[0426]

[0427] CF2=CFCF2OCF2CF2CF2CH2-Y 3 ,

[0428] wait.

[0429] In the general formula (6), X is -H or -F. Both Xs may be -F, or at least one of them may be -H. For example, one may be -F and the other may be -H, or both may be -H.

[0430] In the general formula (6), Y is -H, -F, an alkyl group or a fluorine-containing alkyl group.

[0431] The alkyl group is an alkyl group not containing fluorine atoms and may have at least 1 carbon atom. The alkyl group may have preferably 6 or less carbon atoms, more preferably 4 or less carbon atoms, and even more preferably 3 or less carbon atoms.

[0432] The fluorine-containing alkyl group is an alkyl group containing at least one fluorine atom, and the number of carbon atoms may be 1 or more. The number of carbon atoms in the fluorine-containing alkyl group is preferably 6 or less, more preferably 4 or less, and even more preferably 3 or less.

[0433] As the above-mentioned Y, -H, -F or -CF3 is preferred, and -F is more preferred.

[0434] In the general formula (6), at least one of X and Y preferably contains a fluorine atom. For example, X may be -H, and Y and Z may be -F.

[0435] In the general formula (6), Rf is a fluorinated alkylene group having 1 to 40 carbon atoms or a fluorinated alkylene group having 2 to 100 carbon atoms and having an ether bond.

[0436] The number of carbon atoms of the fluorinated alkylene group is preferably 2 or more. In addition, the number of carbon atoms of the fluorinated alkylene group is preferably 30 or less, more preferably 20 or less, and further preferably 10 or less. Examples of the fluorinated alkylene group include -CF2-, -CH2CF2-, -CF2CF2-, -CF2CH2-, -CF2CF2CH2-, -CF(CF3)-, -CF(CF3)CF2-, -CF(CF3)CH2-, etc. The fluorinated alkylene group is preferably a perfluoroalkylene group.

[0437] In the above general formula (6), Y 3 Preferably -COOM, -SO3M or -OSO3M (M is H, metal atom, NR 7y 4. an imidazolium with or without a substituent, a pyridinium with or without a substituent, or a phosphonium with or without a substituent, R 7y is H or an organic group, which may be the same or different. Any two of them may be bonded to each other to form a ring).

[0438] As R 7y As R 7y , preferably H or C 1-10 An organic group, more preferably H or C 1-4 The organic group is preferably H or C1-4 of alkyl.

[0439] Examples of the metal atom include alkali metals (Group 1) and alkaline earth metals (Group 2), and Na, K, or Li is preferred.

[0440] As M, -H, a metal atom or NR 7 4, more preferably -H, alkali metal (Group 1), alkaline earth metal (Group 2) or NR 7 4, further preferably -H, -Na, -K, -Li or NH4, still more preferably -H, -Na, -K or NH4, particularly preferably -H, -Na or NH4, most preferably -H or -NH4.

[0441] As the above Y 3 , preferably -COOM or -SO3M, more preferably -COOM.

[0442] The compound represented by the general formula (6) is preferably at least one selected from the group consisting of compounds represented by the general formulae (6a), (6b), (6c), (6d) and (6e).

[0443] CF2=CF-O-(CF2) n1 -Y 3 (6a)

[0444] (where n1 represents an integer from 1 to 10, Y 3 Same as the above definition.)

[0445] CF2=CF-O-(CF2C(CF3)F) n2 -Y 3 (6b)

[0446] (where n2 represents an integer from 1 to 5, Y 3 Same as the above definition.)

[0447] CF2=CF-O-(CFX 1 ) n3 -Y 3 (6c)

[0448] (Where X 1 represents F or CF3, n3 represents an integer from 1 to 10, Y 3 Same as the above definition.)

[0449] CF2=CF-O-(CF2CFX 1 O) n4 -(CF2) n6 -Y 3 (6d)

[0450] (wherein, n4 represents an integer of 1 to 10, n6 represents an integer of 1 to 3, and Y 3 and X 1 Same as the above definition.)

[0451] CF2=CF-O-(CF2CF2CFX 1 O) n5 -CF2CF2CF2-Y 3 (6e)

[0452] (where n5 represents an integer from 0 to 10, Y 3 and X 1 Same as the above definition.)

[0453] In the above formula (6a), the above n1 is preferably an integer of 5 or less, and more preferably an integer of 2 or less. From the perspective of obtaining appropriate water solubility and stability of the aqueous dispersion, the above Y 3 -COOM or -SO3M is preferred, and M is preferably H or NH4 because it is less likely to remain as an impurity and the heat resistance of the obtained molded body is improved.

[0454] As the compound represented by the above formula (6a), for example, CF2=CF-O-CF2COOM, CF2=CF(OCF2CF2COOM), CF2=CF(OCF2CF2CF2COOM), CF2=CF-O-CF2SO3M, CF2=CF(OCF2CF2SO3M), CF2=CF(OCF2CF2CF2SO3M) (wherein M has the same definition as above).

[0455] In the above formula (6b), from the perspective of the stability of the obtained aqueous dispersion, the above n2 is preferably an integer of 3 or less, and from the perspective of obtaining appropriate water solubility and stability of the aqueous dispersion, Y 3 -COOM or -SO3M is preferred, and M is preferably H or NH4 because it is less likely to remain as an impurity and the heat resistance of the obtained molded body is improved.

[0456] In the above formula (6c), from the viewpoint of water solubility, the above n3 is preferably an integer of 5 or less, and from the viewpoint of obtaining appropriate water solubility and stability of the aqueous dispersion, the above Y 3 It is preferably -COOM or -SO3M, and from the viewpoint of improving dispersion stability, the above-mentioned M is preferably H or NH4.

[0457] In the above formula (6d), from the perspective of the stability of the aqueous dispersion, the above X 1Preferably -CF3, from the perspective of water solubility, the above n4 is preferably an integer of 5 or less, from the perspective of obtaining appropriate water solubility and stability of the aqueous dispersion, the above Y 3 It is preferably -COOM or -SO3M, and the above M is preferably H or NH4.

[0458] As the compound represented by the above formula (6d), for example, CF2=CFOCF2CF(CF3)OCF2CF2COOM, CF2=CFOCF2CF(CF3)OCF2COOM, CF2=CFOCF2CF(CF3)OCF2CF2CF2COOM, CF2=CFOCF2CF(CF3)OCF2CF2CF2COOM, CF2=CFOCF2CF(CF3)OCF2CF2SO3M, CF2=CFOCF2CF(CF3)OCF2SO3M, CF2=CFOCF2CF(CF3)OCF2CF2CF2SO3M (wherein M represents H, NH4 or an alkali metal).

[0459] In the general formula (6e), from the viewpoint of water solubility, the above n5 is preferably an integer of 5 or less, and from the viewpoint of obtaining appropriate water solubility and stability of the aqueous dispersion, the above Y 3 It is preferably -COOM or -SO3M, and the above M is preferably H or NH4.

[0460] Examples of the compound represented by the general formula (6e) include CF2=CFOCF2CF2CF2COOM and CF2=CFOCF2CF2CF2SO3M (wherein M represents H, NH4 or an alkali metal).

[0461] In the general formula (7), Rf is preferably a fluorine-containing alkylene group having 1 to 40 carbon atoms. In the general formula (7), at least one of X and Y preferably contains a fluorine atom.

[0462] The compound represented by the general formula (7) is preferably selected from the general formula (7a):

[0463] CF2=CF-(CF2) n1 -Y 3 (7a)

[0464] (where n1 represents an integer from 1 to 10, Y 3 The compound represented by the following formula (7b):

[0465] CF2=CF-(CF2C(CF3)F) n2 -Y 3 (7b)

[0466] (where n2 represents an integer from 1 to 5, Y 3At least one of the group consisting of compounds represented by (same as defined above).

[0467] The above Y 3 Preferably -SO3M or -COOM, M is preferably H, metal atom, NR 7y 4. An imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent. 7y represents H or an organic group.

[0468] In the above formula (7a), the above n1 is preferably an integer of 5 or less, and more preferably an integer of 2 or less. From the perspective of obtaining appropriate water solubility and stability of the aqueous dispersion, the above Y 3 -COOM or -SO3M is preferred, and M is preferably H or NH4 because it is less likely to remain as an impurity and the heat resistance of the obtained molded body is improved.

[0469] Examples of the compound represented by the above formula (7a) include CF2=CFCF2COOM and CF2=CFCF2SO3M (wherein M has the same meaning as defined above).

[0470] In the above formula (7b), from the perspective of the stability of the obtained aqueous dispersion, the above n2 is preferably an integer of 3 or less, and from the perspective of obtaining appropriate water solubility and stability of the aqueous dispersion, Y 3 -COOM or -SO3M is preferred, and M is preferably H or NH4 because it is less likely to remain as an impurity and the heat resistance of the obtained molded body is improved.

[0471] The above-mentioned modified monomer preferably includes a modified monomer (A), preferably includes at least one selected from the group consisting of compounds represented by general formula (5a), general formula (5c), general formula (6a), general formula (6b), general formula (6c) and general formula (6d), and more preferably includes a compound represented by general formula (5a) or general formula (5c).

[0472] When using modified monomer (A) as modified monomer, the content of modified monomer (A) unit is preferably in the range of 0.00001 mass % to 1.0 mass % relative to the total polymerized units of the above-mentioned TFE polymer (PTFE). As the lower limit, it is more preferably 0.0001 mass %, more preferably 0.0005 mass %, further preferably 0.001 mass %, and further more preferably 0.005 mass %. As the upper limit, it is 0.90 mass %, 0.50 mass %, 0.40 mass %, 0.30 mass %, 0.20 mass %, 0.15 mass %, 0.10 mass %, 0.08 mass %, 0.05 mass %, 0.01 mass % in the preferred order.

[0473] Low molecular weight PTFE can have a carboxyl group. For example, when TFE is polymerized, by using water-soluble free radical polymerization initiators such as water-soluble peroxides as polymerization initiators, carboxyl groups are imported into the molecular chain ends. On the other hand, in suspension polymerization etc., oil-soluble free radical polymerization initiators are mostly used, and when using oil-soluble free radical polymerization initiators, carboxyl groups are not imported into the molecular chain. Low molecular weight PTFE preferably has a carboxyl group at the molecular end. Having a carboxyl group by low molecular weight PTFE further improves the dispersibility of powder relative to other materials.

[0474] Low molecular weight PTFE relative to each 10 6 The number of carboxyl groups per main chain carbon atom is preferably 29 or less. 6 The number of functional groups is preferably 25 or less per the number of carbon atoms in the main chain.

[0475] The number of carboxyl groups can be measured according to the analytical method of the terminal group recorded in Japanese Patent Laid-Open No. 4-20507 Gazette. Specifically, the powder containing the particles of low molecular weight PTFE is preformed using a hand press to make a film of about 0.1 mm thickness. The produced film is subjected to infrared absorption spectrum analysis. The infrared absorption spectrum analysis of the terminal fully fluorinated PTFE produced by contacting PTFE with fluorine gas is also carried out, and the number of terminal carboxyl groups is calculated by the following formula by the differential spectrum of the two.

[0476] Number of carboxyl groups (relative to every 10 6 carbon atoms) = (l×K) / t

[0477] l: absorbance

[0478] K: Correction coefficient

[0479] t: film thickness (mm)

[0480] The absorption frequency of carboxyl group is 3560 cm -1 , the correction factor is 440.

[0481] The powder of the present invention can be suitably used as molding materials, inks, cosmetics, coatings, greases, parts for office automation equipment, additives for modifying toners, additives in plating solutions, etc. Examples of the above-mentioned molding materials include engineering plastics such as polyoxybenzoyl polyester, polyimide, polyamide, polyamideimide, polyacetal, polycarbonate, and polyphenylene sulfide. The powder of the present invention is particularly suitable as a thickener for grease.

[0482] The powder of the present invention can be used as an additive for molding materials, for example, to improve the non-stickiness and sliding properties of copy rollers, to improve the texture of engineering plastic molded products such as the surface sheets of furniture, the dashboards of automobiles, and the covers of household appliances; and to improve the sliding properties and wear resistance of mechanical parts that generate mechanical friction, such as light-load bearings, gears, cams, buttons of push-button telephones, projectors, camera parts, and sliding materials.

[0483] The powder of the present invention can be used as an additive for coatings to improve the slip of varnishes or paints. The powder of the present invention can be used as an additive for cosmetics to improve the slip of foundation and other cosmetics.

[0484] The powder of the present invention is also suitable for improving the oil repellency or water repellency of wax or the like, and for improving the sliding properties of grease or toner.

[0485] The powder of the present invention can also be used as an electrode binder for secondary batteries or fuel cells, a hardness adjuster for electrode binders, a water-repellent treatment agent for electrode surfaces, and the like.

[0486] The powder of the present invention and lubricating oil can also be used to prepare grease. The grease is characterized by containing the powder of the present invention and lubricating oil, so that the powder of the present invention is uniformly and stably dispersed in the lubricating oil, and has excellent properties such as load resistance, electrical insulation, and low hygroscopicity.

[0487] The lubricating oil (base oil) may be a mineral oil or a synthetic oil. Examples of the lubricating oil (base oil) include paraffinic and cycloparaffinic mineral oils, synthetic hydrocarbon oils, ester oils, fluorinated oils, synthetic oils such as silicone oils, and the like. Fluorinated oils are preferred from the perspective of heat resistance. Examples of the fluorinated oil include perfluoropolyether oils, oligomers of trifluoroethylene chloride, and the like. The weight average molecular weight of the oligomers of trifluoroethylene chloride may be 500 to 1200.

[0488] The grease may further contain a thickener. Examples of the thickener include metal soaps, composite metal soaps, bentonite, phthalocyanine, silica gel, urea compounds, urea-urethane compounds, urethane compounds, and imide compounds. Examples of the metal soaps include sodium soaps, calcium soaps, aluminum soaps, and lithium soaps. Examples of the urea compounds, urea-urethane compounds, and urethane compounds include diurea compounds, triurea compounds, tetraurea compounds, other polyurea compounds, urea-urethane compounds, diurea compounds, or mixtures thereof.

[0489] The grease preferably contains 0.1% to 50% by mass of the powder of the present invention, more preferably 0.5% by mass or more, and more preferably 30% by mass or less. If the amount of the powder is too much, the grease becomes too hard and may not exhibit sufficient lubricity, and if the amount of the powder is too little, the sealing property may not be exhibited.

[0490] The above-mentioned grease may also contain a solid lubricant, an extreme pressure agent, an antioxidant, an oiliness agent, a rust inhibitor, a viscosity index improver, a detergent dispersant, and the like.

[0491] 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.

[0492] 2. Powder manufacturing method

[0493] In the 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 low molecular weight polytetrafluoroethylene 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 low molecular weight polytetrafluoroethylene having excellent microdispersibility in other materials and a reduced content of a fluorine-containing compound having a hydrophilic group can be produced.

[0494] That is, by using the production method of the present invention, a powder having a content of a fluorine-containing compound having a hydrophilic group of 250 ppb or less can be produced. Furthermore, by using the production method of the present invention, a powder having a specific surface area of ​​7 m 2 / g~50m 2 / g of powder.

[0495] Each process and the materials used in each process are described in detail below.

[0496] (Polymerization of Tetrafluoroethylene)

[0497] In the production method of the present invention, first, tetrafluoroethylene 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 primary particles of low molecular weight polytetrafluoroethylene.

[0498] The polymerization of tetrafluoroethylene can be carried out as follows: tetrafluoroethylene, fluorinated surfactant, polymerization initiator, aqueous medium and other additives as needed are added into a reactor, the contents of the reactor are stirred, and then the reactor is maintained at a specified polymerization temperature, followed by adding a specified amount of polymerization initiator to initiate a polymerization reaction. After the polymerization reaction begins, tetrafluoroethylene, polymerization initiator, fluorinated surfactant, chain transfer agent, etc. can be added according to the purpose. The polymerization method of tetrafluoroethylene is not particularly limited, and an emulsion polymerization method is preferred.

[0499] The above-mentioned modifying monomer may be polymerized together with tetrafluoroethylene. The amount of tetrafluoroethylene and the optional modifying monomer used is preferably an amount that can obtain the modified polytetrafluoroethylene contained in the powder of the present invention.

[0500] (Fluorinated surfactant)

[0501] As the fluorinated surfactant used for the polymerization of tetrafluoroethylene, there can be mentioned the fluorinated surfactants which the powder of the present invention can contain, and it is preferred to use the same fluorinated surfactants.

[0502] 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.

[0503] (Polymerization initiator)

[0504] The polymerization initiator used in the polymerization of tetrafluoroethylene is not particularly limited as long as it can generate free radicals within the polymerization temperature range, and known oil-soluble and / or water-soluble polymerization initiators can be used. Furthermore, it can also be combined with a reducing agent 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 low molecular weight polytetrafluoroethylene, and the reaction rate.

[0505] As the polymerization initiator, an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator can be used.

[0506] 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.

[0507] 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.

[0508] For example, in the case of implementing polymerization at a low temperature below 30°C, etc., as a polymerization initiator, it is preferred to use a redox initiator composed of an oxidant and a reducing agent. As the oxidant, 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 persulfate, ammonium persulfate and potassium persulfate can be mentioned. As sulfite, sodium sulfite and ammonium sulfite can be mentioned. In order to increase the decomposition rate of the initiator, it is also preferred to add copper salts and iron salts to the combination of redox initiators. As the copper salt, copper (II) sulfate can be mentioned, and as the iron salt, iron (II) sulfate can be mentioned.

[0509] As the above-mentioned redox initiator, for example, potassium permanganate / oxalic acid, potassium permanganate / ammonium oxalate, ammonium persulfate / bisulfite / ferric sulfate, manganese triacetate / oxalic acid, cerium ammonium nitrate / oxalic acid, bromate / bisulfite, etc. can be cited, preferably potassium permanganate / oxalic acid. In the case of using a redox initiator, either the oxidant or the reductant can be put into a polymerization kettle in advance, and then the other can be added continuously or intermittently to initiate polymerization. For example, in the case of using potassium permanganate / oxalic acid, it is preferred to put oxalic acid into the polymerization kettle and continuously add potassium permanganate thereto.

[0510] The amount of polymerization initiator added is not particularly limited, and may be added once, sequentially, or continuously at the initial stage of polymerization in an amount that does not significantly reduce the polymerization rate (e.g., a concentration of several ppm relative to water). The upper limit is a range in which the heat of polymerization reaction can be used to remove heat from the device surface and the reaction temperature can be increased, and a more preferred upper limit is a range in which the heat of polymerization reaction can be removed from the device surface.

[0511] During the polymerization of tetrafluoroethylene, the free radical concentration in the polymerization can be adjusted by adding a decomposition agent. As decomposition agents, sulfites, bisulfites, bromates, diimides, oxalic acid, copper salts, iron salts, etc. can be mentioned. As sulfites, sodium sulfite and ammonium sulfite can be mentioned. As copper salts, copper sulfate (II) can be mentioned, and as iron salts, iron sulfate (II) can be mentioned. The amount of the decomposition agent added is in the range of 25 mass % to 300 mass % relative to the amount of the oxidant combined as a polymerization initiator (redox initiator). As the amount of the decomposition agent added, it is preferably 25 mass % to 150 mass %, and more preferably 50 mass % to 100 mass %. In addition, it is preferred to add the decomposition agent after 5 mass % of all tetrafluoroethylene consumed in the polymerization reaction is polymerized, and more preferably after 10 mass % is polymerized. The amount of the decomposition agent added is preferably an amount equivalent to 0.1 mass ppm to 20 mass ppm of the mass of the aqueous medium used, and more preferably an amount equivalent to 3 mass ppm to 10 mass ppm.

[0512] (Aqueous medium)

[0513] The aqueous medium used in the polymerization of tetrafluoroethylene 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.

[0514] As the aqueous medium, 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, since the polymerization of tetrafluoroethylene can be smoothly carried out and the removal efficiency of the fluorinated compound having a hydrophilic group can be suppressed.

[0515] Since the polymerization of tetrafluoroethylene can be smoothly carried out and the reduction in the removal efficiency of the fluorinated compound having a hydrophilic group can be suppressed, the mass of 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%.

[0516] (Chain transfer agent)

[0517] In the production method of the present invention, tetrafluoroethylene can be further 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 chain transfer agents, esters such as dimethyl malonate, diethyl malonate, methyl acetate, ethyl acetate, butyl acetate, dimethyl succinate, and isopentane, methane, ethane, propane, methanol, isopropanol, acetone, various mercaptans, various halogenated hydrocarbons such as carbon tetrachloride, cyclohexane, etc. can be cited.

[0518] The amount of the 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 tetrafluoroethylene supplied. The amount of the chain transfer agent used is preferably an amount that is completely consumed in the polymerization of tetrafluoroethylene and does not remain in the aqueous dispersion containing low molecular weight polytetrafluoroethylene, so that the removal efficiency of the fluorine-containing compound having a hydrophilic group is minimized. Therefore, the amount of the 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 tetrafluoroethylene supplied.

[0519] 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 several portions during polymerization, or may be added continuously during polymerization.

[0520] (Other additives)

[0521] In the polymerization of tetrafluoroethylene, additives such as buffers, pH regulators, stabilizing aids, and dispersion stabilizers may be used. In addition, in the polymerization of tetrafluoroethylene, free radical scavengers and decomposers may be added to adjust the polymerization rate and molecular weight. In addition, in the polymerization of tetrafluoroethylene, non-fluorinated anionic surfactants, non-fluorinated nonionic surfactants, non-fluorinated cationic surfactants, etc. may also be used.

[0522] 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.

[0523] 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.

[0524] (Polymerization conditions)

[0525] The polymerization of tetrafluoroethylene can be carried out under 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 low molecular weight polytetrafluoroethylene, the reaction rate, etc.

[0526] (Aqueous dispersion obtained by polymerization)

[0527] The polymerization of tetrafluoroethylene produces an aqueous dispersion of primary particles containing low molecular weight polytetrafluoroethylene. The content of the low molecular weight polytetrafluoroethylene in the aqueous dispersion after polymerization is usually 8 to 50% by mass based on the aqueous dispersion.

[0528] In the aqueous dispersion obtained by polymerizing tetrafluoroethylene, in addition to low molecular weight polytetrafluoroethylene, as a fluorinated compound having a hydrophilic group, a fluorinated surfactant used when polymerizing tetrafluoroethylene is generally included. In addition, in the aqueous dispersion obtained by polymerizing tetrafluoroethylene, in addition to low molecular weight polytetrafluoroethylene, a fluorinated compound having a hydrophilic group generated by polymerization of a monomer is sometimes included.

[0529] As the fluorinated compound with a hydrophilic group in the aqueous dispersion obtained by polymerization, a typical compound is a fluorinated compound with a hydrophilic group having 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 with a hydrophilic group having a molecular weight of 1000 g / mol or less can be manufactured.

[0530] 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 tetrafluoroethylene.

[0531] 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, or 400 ppb or more, or may be 10% or less, 1% or less, or 0.5% or less by mass relative to the aqueous dispersion.

[0532] The content of the fluorinated surfactant used when polymerizing tetrafluoroethylene in the aqueous dispersion obtained by polymerization may be 200 ppb by mass or more, 300 ppb by mass or more, or 400 ppb by mass or more, and may be 10% by mass or less, 1% by mass or less, or 0.5% by mass or less, relative to the aqueous dispersion.

[0533] In one embodiment of the aqueous dispersion obtained by polymerization, the fluorine-containing compound having a hydrophilic group contains a compound (I) represented by the following general formula (I).

[0534] General formula (I): F(CF2) n1 COOM(I)

[0535] (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. )

[0536] When the aqueous dispersion obtained by polymerization contains at least the compound (I) represented by the general formula (I) as the fluorine-containing compound having a hydrophilic group, the content of the compound (I) in the aqueous dispersion obtained by polymerization may be 200 ppb or more, 300 ppb or more, or 400 ppb or more, or may be 10% or less, or 1% or less, or 0.5% or less, relative to the aqueous dispersion.

[0537] 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.

[0538] General formula (H1): [X-Rf-A - ] i M i+

[0539] (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)

[0540] 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.

[0541] General formula (H2): [C n-1 F 2n-1 COO - ]M +

[0542] (where n represents an integer from 9 to 14, M + represents a cation.)

[0543] It is known that when perfluoro(alkyl vinyl ether) or the like is used as a monomer, a compound represented by the general formula (H2) (perfluoroalkanoic acid) is formed during polymerization (see International Publication No. 2019 / 161153).

[0544] 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.

[0545] General formula (H3): [R 1 -OL-CO2 - ]M +

[0546] (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.)

[0547] 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.

[0548] General formula (H4): H-Rf n0 -Y 0

[0549] (Where Rf n0It 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.)

[0550] Examples of the compound represented by the general formula (H4) include compounds represented by any of the following general formulae.

[0551] General formula (H4-1): [H-(CF2) m1 CO2 - ]M +

[0552] (In the formula, m1 represents an integer from 3 to 19, M + represents a cation.)

[0553] General formula (H4-2): [H-(CF2) m2 -(CF(CF3)) m3 -CO2 - ]M +

[0554] (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. )

[0555] (Removal of tetrafluoroethylene or recovery of aqueous dispersion)

[0556] In the manufacturing method of the present invention, after the aqueous dispersion is prepared by polymerization, before the free radical generator is added to the aqueous dispersion, at least one of (a) removing the tetrafluoroethylene remaining in the reactor from the reactor and (b) recovering the aqueous dispersion in the reactor and containing it in a container different from the reactor can be performed. In particular, when the method of removing the tetrafluoroethylene 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, so it is preferred. In the case of polymerizing the modified monomer together with the tetrafluoroethylene, the modified monomer is also removed from the reactor together with the tetrafluoroethylene.

[0557] After the aqueous dispersion is prepared, it is preferred to remove tetrafluoroethylene or recover the aqueous dispersion after stopping stirring of the contents of the reactor, because this facilitates subsequent operations and enables smooth termination of tetrafluoroethylene polymerization.

[0558] The method of removing tetrafluoroethylene 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 tetrafluoroethylene from the reactor, or the pressure in the reactor can be reduced to less than 0.0MPaG, thereby removing tetrafluoroethylene from the reactor, and an inert gas can also be supplied to the reactor, thereby replacing the tetrafluoroethylene in the reactor with inert gases such as nitrogen. In addition, it is also possible to react the entire amount of tetrafluoroethylene in the reactor and convert it into low molecular weight polytetrafluoroethylene, and as a result, tetrafluoroethylene is removed from the reactor. The removal of the tetrafluoroethylene remaining in the reactor from the reactor can be carried out to the extent that the polymerization reaction of tetrafluoroethylene is fully stopped, and a small amount of tetrafluoroethylene can also remain in the reactor. The removed tetrafluoroethylene can be recovered by known means. The recovered tetrafluoroethylene can be reused in the manufacture of low molecular weight polytetrafluoroethylene.

[0559] As a method for removing tetrafluoroethylene 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.

[0560] When tetrafluoroethylene is polymerized at a temperature exceeding room temperature, the reactor may be cooled before or after tetrafluoroethylene is removed from the reactor. When tetrafluoroethylene is removed from the reactor by exhaust gas, nitrogen replacement, or the like, unreacted modifying monomers, particularly liquid ones, may remain in the reactor, but by cooling the reactor, the reaction of the unreacted modifying monomers can be sufficiently suppressed.

[0561] 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.

[0562] In order to stop the polymerization reaction of tetrafluoroethylene, a polymerization inhibitor (radical scavenger) may be added.

[0563] 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.

[0564] (Free Radical Generator)

[0565] In the production method of the present invention, after performing at least one of the operations (a) and (b), 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.

[0566] 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.

[0567] 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.

[0568] 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.

[0569] 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.

[0570] 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.

[0571] 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.

[0572] 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.

[0573] 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.

[0574] 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 8 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 more 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, low molecular weight polytetrafluoroethylene in the aqueous dispersion can also be precipitated.

[0575] 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.

[0576] 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 tetrafluoroethylene polymerization, the temperature reached by cooling the aqueous dispersion after tetrafluoroethylene polymerization, or the temperature of heat treatment. That is, the aqueous dispersion may be heated for heat treatment after the free radical generator is added to the aqueous dispersion, or the free radical generator may be added to the aqueous dispersion after the aqueous dispersion is heated to a temperature for heat treatment.

[0577] (Heat Treatment)

[0578] 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.

[0579] Before the heat treatment, the content of low molecular weight polytetrafluoroethylene in the aqueous dispersion may be adjusted. The content of low molecular weight polytetrafluoroethylene may be adjusted by a known method such as concentration or dilution.

[0580] From the aspect of being able to produce a low molecular weight polytetrafluoroethylene aqueous dispersion with high productivity without damaging the removal efficiency of the fluorinated compound having a hydrophilic group, the content of the low molecular weight polytetrafluoroethylene 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 low molecular weight polytetrafluoroethylene is preferably 60% by mass or less, more preferably 55% by mass or less, and further preferably 50% by mass or less.

[0581] 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 preferably 10 mass % or less, more preferably 5 mass % or less, and further preferably 1 mass % or less, relative to the mass of the low molecular weight polytetrafluoroethylene in the aqueous dispersion.

[0582] The content of the fluorinated compound having a hydrophilic group generated by polymerization of tetrafluoroethylene in the aqueous dispersion subjected to 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 low molecular weight polytetrafluoroethylene in the aqueous dispersion.

[0583] The content of the fluorinated compound having a hydrophilic group in the aqueous dispersion subjected to the heat treatment (the total 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 tetrafluoroethylene) 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 low molecular weight polytetrafluoroethylene in the aqueous dispersion.

[0584] From the perspective of being able to further improve the removal efficiency of the fluorine-containing 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 production method of the present invention is a method for producing a powder, so low molecular weight polytetrafluoroethylene in the aqueous dispersion can also be precipitated by heat treatment at a relatively high temperature.

[0585] In the heat treatment of the aqueous dispersion, as long as the aqueous dispersion can be maintained at a desired temperature or above, it is not necessary to heat the aqueous dispersion. For example, when the temperature of tetrafluoroethylene polymerization is high enough and the temperature of the obtained aqueous dispersion is also high enough, 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 tetrafluoroethylene from the reactor or recovering the aqueous dispersion in the reactor, heat the aqueous dispersion to the above-mentioned 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.

[0586] 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.

[0587] 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.

[0588] 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.

[0589] The heat treatment may be performed while stirring the aqueous dispersion.

[0590] (Preparation of wet powder and drying of wet powder)

[0591] In the production method of the present invention, a wet powder containing particles of low molecular weight polytetrafluoroethylene is prepared by precipitating low molecular weight polytetrafluoroethylene in an aqueous dispersion liquid that has been subjected to heat treatment, and a powder containing particles of low molecular weight polytetrafluoroethylene is prepared by drying the wet powder at a temperature that is 70° C. or less lower than the melting point of the low molecular weight polytetrafluoroethylene.

[0592] The precipitation method of low molecular weight polytetrafluoroethylene is not particularly limited. For example, the aqueous dispersion is diluted with water to a polymer concentration of 5% to 20% by mass, and the pH is adjusted to neutral or alkaline according to the situation, and then stirred more vigorously than the stirring in the polymerization of tetrafluoroethylene in a container with a stirrer. 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 also be added to the aqueous dispersion as a precipitating agent and stirred to precipitate the low molecular weight polytetrafluoroethylene. After the low molecular weight polytetrafluoroethylene is precipitated, a wet powder containing particles of low molecular weight polytetrafluoroethylene can be recovered. The wet powder may contain a precipitate of low molecular weight polytetrafluoroethylene precipitated by adding a free radical generator and a precipitate of low molecular weight polytetrafluoroethylene precipitated by heat treatment.

[0593] 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.

[0594] In the production method of the present invention, the wet powder is dried at a temperature 70° C. or lower than the melting point of low molecular weight polytetrafluoroethylene. By drying the wet powder at a relatively low temperature, a powder having excellent fine dispersibility in other materials can be obtained.

[0595] The drying temperature of the wet powder is preferably a temperature 80° C. or lower than the melting point of the low molecular weight polytetrafluoroethylene, and more preferably a temperature 100° C. or lower than the melting point of the low molecular weight polytetrafluoroethylene.

[0596] The drying temperature of the wet powder is preferably 250°C or lower, more preferably 230°C or lower, and further preferably 220°C or lower.

[0597] The drying temperature of the wet powder is preferably 100° C. or higher, more preferably 120° C. or higher, further preferably 140° C. or higher, and further preferably 160° C. or higher. When the drying temperature is too low, drying takes time and productivity may decrease.

[0598] The obtained powder can be classified or granulated. In addition, the obtained powder can be formed into pellets. In the production method of the present invention, since a powder with excellent microdispersibility in other materials can be directly obtained after drying, it is also one of the preferred modes not to perform any post-treatment on the dried powder.

[0599] 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.

[0600] <1> According to a first aspect of the present invention, there is provided a powder comprising particles of low molecular weight polytetrafluoroethylene, wherein:

[0601] 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.

[0602] The specific surface area is 7m 2 / g~50m 2 / g.

[0603] <2> According to a second aspect of the present invention, there is provided the powder according to the first aspect, wherein the low molecular weight polytetrafluoroethylene has a melting point of 322°C to 333°C.

[0604] <3> According to a third aspect of the present invention, there is provided a powder according to the first aspect or the second aspect, wherein the melt viscosity of the low molecular weight polytetrafluoroethylene at 380° C. is 1×10 2 Pa·s~7×10 5 Pa·s.

[0605] <4> According to a fourth aspect of the present invention, there is provided a powder according to any one of the first to third aspects, wherein the low molecular weight polytetrafluoroethylene has carboxyl groups, and the number of carboxyl groups is 6 The number of carbon atoms is 29 or less.

[0606] <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 average particle size of the low molecular weight polytetrafluoroethylene particles is 1.0 μm to 30 μm.

[0607] <6> According to a sixth aspect of the present invention, there is provided a powder according to any one of the first to fifth aspects, wherein the fluorine-containing compound having a hydrophilic group is of the following general formula (N 0 ) shown in the compound.

[0608] General formula (N 0 ):X n0 -Rf n0 -Y 0

[0609] (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.)

[0610] <7> According to the seventh aspect of the present invention, there is provided a powder based on any one of the first aspect to the sixth aspect, wherein the fluorine-containing compound having a hydrophilic group contains at least a compound represented by the general formula (I) (I).

[0611] General formula (I): F(CF2) n1 COOM

[0612] (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. )

[0613] <8> According to an eighth aspect of the present invention, there is provided the powder according to the seventh aspect, wherein the content of the compound (I) is 25 ppb by mass or less based on the powder.

[0614] <9> According to a ninth aspect of the present invention, there is provided the powder according to the seventh aspect, wherein the content of the compound (I) is 5 ppb by mass or less based on the powder.

[0615] <10> According to a tenth 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 low molecular weight polytetrafluoroethylene, wherein:

[0616] In a reactor, tetrafluoroethylene is polymerized in the presence of a fluorinated surfactant, a polymerization initiator and an aqueous medium, thereby preparing an aqueous dispersion containing primary particles of the low molecular weight polytetrafluoroethylene.

[0617] After the aqueous dispersion is prepared, at least one of removing tetrafluoroethylene 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.

[0618] Adding a free 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,

[0619] heat-treating the aqueous dispersion containing the free radical generator,

[0620] The low molecular weight polytetrafluoroethylene in the aqueous dispersion subjected to the heat treatment is precipitated to prepare a wet powder containing particles of the low molecular weight polytetrafluoroethylene.

[0621] The wet powder is dried at a temperature that is 70° C. or lower than the melting point of the low-molecular-weight polytetrafluoroethylene, thereby producing the powder.

[0622] Example

[0623] Next, embodiments of the present invention will be described with reference to examples, but the present invention is not limited to these examples.

[0624] Each numerical value in the examples was measured by the following method.

[0625] <Content of Fluorine-Containing Compound Having Hydrophilic Group>

[0626] 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.

[0627] 0. Extraction of fluorinated compounds with hydrophilic groups from powders

[0628] To 1 g of the powder was added 10 g (12.6 mL) of methanol, and the mixture was ultrasonically treated 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.

[0629] <Content of the compound represented by general formula (I)>

[0630] The content of the compound represented by the general formula (I) is determined using a calibration curve of straight-chain perfluorocarboxylic acids having the same number of carbon atoms.

[0631] 1. Calibration curve of linear perfluorocarboxylic acids

[0632] 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.

[0633] Measurement equipment structure and LC-MS measurement conditions

[0634]

[0635] MRM assay parameters

[0636] [Table 2]

[0637] Table 2 MRM assay parameters

[0638]

[0639] 2. Content of the compound represented by general formula (I) contained in the powder

[0640] The content of the compound represented by the general formula (I) with a carbon number (n1+1) contained in the extract was determined by a calibration curve using a liquid chromatography-mass spectrometer. The content of the compound represented by the general formula (I) with a carbon number (n1+1) contained in the powder was calculated using the following relationship (2).

[0641] Yn=Xn×12.6 (2)

[0642] Yn: The content of the compound represented by the general formula (I) with the carbon number (n1+1) contained in the powder (mass ppb / powder)

[0643] Xn: The content of the compound represented by the general formula (I) with the carbon number (n1+1) contained in the extract (ng / mL)

[0644] The quantitative lower limit of the content of the compound represented by the general formula (I) having a carbon number (n1+1) contained in the powder is 1 mass ppb / powder.

[0645] MRM assay parameters

[0646] [Table 3]

[0647] Table 3 MRM assay parameters

[0648]

[0649]

[0650] <Measurement of Compound Represented by General Formula (H4-1)>

[0651] The content of the compound represented by the general formula (H4-1) was calculated by converting it into perfluorooctanoic acid.

[0652] 1. Calibration curve of the compound represented by general formula (H4-1)

[0653] Five levels of methanol standard solutions of perfluorooctanoic 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 the first order approximation from the methanol standard solution concentration and the peak integral value.

[0654] Measurement equipment structure and LC-MS measurement conditions

[0655]

[0656] MRM assay parameters

[0657] [Table 5]

[0658] Table 5 MRM assay parameters

[0659]

[0660] 2. Content of the compound represented by the general formula (H4-1) contained in the powder

[0661] The content of the compound represented by the general formula (H4-1) having the carbon number (m1+1) contained in the extract was measured from the calibration curve using a liquid chromatography-mass spectrometer.

[0662] The content of the compound represented by the general formula (H4-1) having the carbon number (m1+1) contained in the powder is calculated from the following relational formula (5).

[0663] Ym=Xm×12.6 (5)

[0664] Ym: The content of the compound represented by the general formula (H4-1) with the number of carbon atoms (m1+1) contained in the powder (mass ppb / powder)

[0665] Xm: The content of the compound represented by the general formula (H4-1) with the carbon number (m1+1) contained in the extract (ng / mL)

[0666] The quantitative lower limit of the content of the compound represented by the general formula (H4-1) having a carbon number (m1+1) contained in the powder is 1 mass ppb / powder.

[0667] MRM assay parameters

[0668] [Table 6]

[0669] Table 6 MRM assay parameters

[0670]

[0671] <Solid content concentration>

[0672] About 1 g (Xg) of the sample was taken into an aluminum cup with a diameter of 5 cm, heated at 110°C for 30 minutes, and further heated at 300°C for 30 minutes. The heating residual component (Zg) was determined by the formula: P = Z / X×100 (mass %).

[0673] <Specific surface area>

[0674] The measurement was performed by the BET method using a surface analyzer (trade name: MONQSORB, manufactured by QUANTA CHLROME Co., Ltd.) A mixed gas of 30% nitrogen and 70% helium was used as a carrier gas, and cooling was performed using liquid nitrogen.

[0675] <Melting point>

[0676] A differential scanning calorimeter (DSC) RDC220 manufactured by SII NanoTechnology was used. Indium and lead were used as standard samples for temperature calibration in advance. Then, about 3 mg of low molecular weight PTFE powder was placed in an aluminum pan (sealed container). The temperature was raised at a rate of 10°C / min in a temperature range of 250°C to 380°C under an air flow of 200 ml / min. The minimum point of the heat of fusion in the above range was taken as the melting point.

[0677] <Melt Viscosity>

[0678] According to ASTM D 1238, a flow tester (manufactured by Shimadzu Corporation) and A die of 100 mm was used, and a 2 g sample that had been heated in advance at a measurement temperature (380° C.) for 5 minutes was maintained at the above temperature under a load of 0.7 MPa for measurement.

[0679] <Number of carboxyl groups>

[0680] The following measurement was performed according to the terminal group analysis method described in Japanese Patent Application Laid-Open No. 4-20507.

[0681] The low molecular weight PTFE powder was preformed using a hand press to produce a film of about 0.1 mm thickness. The produced film was subjected to infrared absorption spectroscopy analysis. The infrared absorption spectroscopy analysis of the terminal fully fluorinated PTFE produced by contacting PTFE with fluorine gas was also performed, and the number of terminal carboxyl groups was calculated by the following formula from the difference spectrum of the two.

[0682] The number of terminal carboxyl groups (relative to the number of carbon atoms 10 6 )=(l×K) / t

[0683] l: absorbance

[0684] K: Correction coefficient

[0685] t: film thickness (mm)

[0686] The absorption frequency of carboxyl group is 3560 cm -1 , the correction factor is 440.

[0687] <Average particle size>

[0688] The particle size distribution was measured using a laser diffraction particle size distribution analyzer (manufactured by JEOL Ltd.) without using a cascade, at a pressure of 0.1 MPa and a measurement time of 3 seconds, and the value corresponding to 50% of the cumulative particle size distribution obtained was equal.

[0689] Production Example 1

[0690] The input amount of ammonium perfluorohexanoate was changed from 1.7 g to 2.0 g. In addition, the polymerization reaction of TFE was carried out in the same manner as the method described in Example 7 of International Publication No. 2009 / 020187, and the reaction was terminated. Then, the pressure in the reactor was vented to atmospheric pressure, and the contents were recovered from the reactor to obtain a low molecular weight PTFE aqueous dispersion. The solid content concentration of the aqueous dispersion was 20.4% by mass.

[0691] Comparative Example 1

[0692] Nitric acid was added to the low molecular weight PTFE aqueous dispersion obtained in Preparation Example 1, and precipitated by applying a severe mechanical shear force. The obtained wet powder was dried in a hot air circulation dryer at 160° C. for 18 hours, thereby obtaining a low molecular weight PTFE powder. The melt viscosity of the obtained low molecular weight PTFE powder was 1.6×10 4 Pa·s, melting point 329°C, specific surface area 11.1m 2 / g, and the average particle size is 4.3μm.

[0693] Example 1

[0694] The low molecular weight PTFE aqueous dispersion obtained in Manufacturing Example 1 is placed in another reactor, the contents of the reactor are heated to 80°C, and 13.8 g 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 low molecular weight PTFE aqueous dispersion. Nitric acid is added to the obtained heat-treated low molecular weight PTFE aqueous dispersion, and precipitated by applying severe mechanical shear force. The obtained wet powder is dried in a hot air circulation dryer at 160°C for 18 hours to obtain a low molecular weight PTFE powder. The melt viscosity of the obtained low molecular weight PTFE powder is 1.6×10 4 Pa·s, melting point 329°C, specific surface area 11.0m 2 / g, average particle size 4.2μm, number of carboxyl groups per 10 6 The number of carbon atoms is 12.

[0695] The obtained powder contains the general formula (I): F(CF2) n1 COOM and general formula (H4-1): [H-(CF2) m1 CO2 - ]M + The contents of the compounds shown are shown in Tables 7 and 8.

[0696] Production Example 2

[0697] In a stainless steel autoclave with an internal volume of 6 L equipped with a stainless steel anchor-type stirring blade and a temperature regulating jacket, 3.6 L of deionized water and 7.2 g of ammonium perfluorohexanoate as a fluorine-based surfactant were added and sealed. After removing oxygen in the system by repeatedly injecting nitrogen and degassing, 820 mg of ethane as a chain transfer agent was injected with tetrafluoroethylene [TFE]. The temperature in the tank was raised under stirring, and after the temperature in the tank reached 70°C, TFE was injected again.

[0698] As a polymerization initiator, an aqueous solution prepared by dissolving 460 mg of ammonium persulfate [APS] in 20 ml of deionized water was pressed into the tank with TFE to a pressure of 0.74 MPa. Due to the decomposition of the polymerization initiator, the pressure in the tank decreased, so TFE was continuously supplied to maintain the pressure in the tank at 0.74 MPa. The temperature in the tank was always adjusted to 70°C during the reaction. Stirring was stopped when the consumption of TFE was 1100 g, the pressure in the tank was opened to normal pressure, and then the gas phase was replaced with nitrogen to obtain an aqueous dispersion of low molecular weight PTFE.

[0699] Example 2

[0700] The low molecular weight PTFE aqueous dispersion obtained in Preparation Example 2 is placed in another reactor, the contents of the reactor are heated to 80°C, and 29.7 g of ammonium persulfate (6 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 low molecular weight PTFE aqueous dispersion. Nitric acid is added to the obtained heat-treated low molecular weight PTFE aqueous dispersion, and it is precipitated by applying severe mechanical shear force. The obtained wet powder is dried in a hot air circulation dryer at 160°C for 18 hours to obtain a low molecular weight PTFE powder. The melt viscosity of the obtained low molecular weight PTFE powder is 4.9×10 3 Pa·s, melting point 328°C, specific surface area 19.0m 2 / g, average particle size 5.2μm, number of carboxyl groups per 10 6 The number of carbon atoms is 24.

[0701] [Table 7]

[0702] Table 7

[0703] n1 Comparative Example 1 Example 1 Example 2 3 <1 <1 <1 4 <1 <1 <1 5 2 <1 <1 6 <1 <1 <1 7 <1 <1 <1 8 <1 <1 <1 9 <1 <1 <1 10 <1 <1 <1 11 <1 <1 <1 12 <1 <1 <1 13 <1 <1 <1

[0704] Unit: mass ppb / powder

[0705] [Table 8]

[0706] Table 8

[0707] m1 Comparative Example 1 Example 1 Example 2 9 2 1 <1 11 1 <1 <1 13 5 <1 <1 15 75 <1 <1 17 230 <1 <1

[0708] Unit: mass ppb / powder.

Claims

1. A powder comprising particles of low molecular weight polytetrafluoroethylene, 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 specific surface area is 7m 2 / g~50m 2 / g.

2. The powder according to claim 1, wherein The melting point of the low molecular weight polytetrafluoroethylene is 322°C to 333°C.

3. The powder according to claim 1 or 2, wherein The melt viscosity of the low molecular weight polytetrafluoroethylene at 380°C is 1×10 2 Pa·s~7×10 5 Pa·s.

4. The powder according to any one of claims 1 to 3, wherein The low molecular weight polytetrafluoroethylene has carboxyl groups, the number of which is relative to every 10 6 The number of carbon atoms is 29 or less.

5. The powder according to any one of claims 1 to 4, wherein The average particle size of the low molecular weight polytetrafluoroethylene particles is 1.0 μm to 30 μm.

6. The powder according to any one of claims 1 to 5, 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.

7. The powder according to any one of claims 1 to 6, wherein The fluorine-containing compound having a hydrophilic group contains at least a compound (I) represented by the general formula (I), General formula (I): F(CF2) n1 COOM In the formula, 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.

8. The powder according to claim 7, wherein The content of the compound (I) is 25 ppb by mass or less based on the powder.

9. The powder according to claim 7, wherein The content of the compound (I) is 5 ppb by mass or less based on the powder.

10. A method for producing a powder, which is a method for producing a powder containing particles of low molecular weight polytetrafluoroethylene, wherein: In a reactor, tetrafluoroethylene is polymerized in the presence of a fluorinated surfactant, a polymerization initiator, and an aqueous medium, thereby preparing an aqueous dispersion containing primary particles of the low molecular weight polytetrafluoroethylene. After the aqueous dispersion is prepared, at least one of removing tetrafluoroethylene 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 low molecular weight polytetrafluoroethylene in the aqueous dispersion subjected to the heat treatment is precipitated to prepare a wet powder containing particles of the low molecular weight polytetrafluoroethylene. The wet powder is dried at a temperature that is 70° C. or lower than the melting point of the low-molecular-weight polytetrafluoroethylene, thereby producing the powder.

Images