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

Abstract

Provided is a powder containing particles of low-molecular-weight polytetrafluoroethylene, the powder containing a fluorine-containing compound having hydrophilic groups. The content of fluorine-containing compound having hydrophilic groups is 250 ppb by mass or less with respect to the powder. The powder has a specific surface area of 7 to 50 m2 / g.

Description

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

[0001] The present disclosure relates to powders containing particles of low molecular weight polytetrafluoroethylene and methods for producing the same.

[0002] Patent Document 1 describes a polytetrafluoroethylene micropowder containing up to about 3% by weight of a monomer copolymerizable with tetrafluoroethylene, which has a polydispersity Mw / Mn of 1.5 to 2.5 and a molecular weight of 7 to 13 m. ２ The polytetrafluoroethylene micropowder is described as having a specific surface area (BET) of 150 to 250 nm / g and a primary particle size of 150 to 250 nm.

[0003] Patent Document 2 describes a low-molecular-weight polytetrafluoroethylene granulated powder characterized by being obtained by a granulation process from low-molecular-weight polytetrafluoroethylene particles made of 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 specific surface area of ​​7 to 20 m / g, an average particle size of 1 to 30 μm, and a water contact angle of 110 to 125°.

[0005] Patent Document 4 discloses a powder of low-molecular-weight polytetrafluoroethylene containing tetrafluoroethylene units or tetrafluoroethylene units and modified monomer units copolymerizable with the tetrafluoroethylene units, which is represented by the following general formula (1): X-(CF ２ ) ｍ -Y (1) (wherein X represents H or F, m represents an integer of 3 to 5, and Y represents -SO ３ M, -SO ４ M, -SO ３ R, -SO ４ R, -COOM, -PO ３ M ２ , -PO ４ M ２ (M is H, NH ４or an alkali metal, and R represents an alkyl group having 1 to 12 carbon atoms. The content of the fluorine-containing compound represented by the following general formula (3): X-(CF ２ ) ｍ -Y (3) (wherein X represents H or F, m represents an integer of 6 or more, and Y represents -SO ３ M, -SO ４ M, -SO ３ R, -SO ４ R, -COOM, -PO ３ M ２ , -PO ４ M ２ (M is H, NH ４ or an alkali metal, and R represents an alkyl group having 1 to 12 carbon atoms.) ). A low-molecular-weight polytetrafluoroethylene powder is disclosed, which is free of a fluorine-containing compound represented by the formula (I).

[0006] Japanese Patent Application Laid-Open No. 07-165828 Japanese Patent Application Laid-Open No. 2005-2322 Japanese Patent Application Laid-Open No. 10-147617 International Publication No. 2009 / 020187

[0007] An object of the present disclosure is to provide a powder containing particles of low-molecular-weight polytetrafluoroethylene that has excellent fine dispersibility in other materials and a reduced content of fluorine-containing compounds having hydrophilic groups. Another object of the present disclosure is to provide a method for producing a powder containing particles of low-molecular-weight polytetrafluoroethylene that has excellent fine dispersibility in other materials and a reduced content of fluorine-containing compounds having hydrophilic groups.

[0008] According to the present disclosure, there is provided a powder containing particles of low-molecular-weight polytetrafluoroethylene, which contains a fluorine-containing compound having a hydrophilic group, the content of the fluorine-containing compound having a hydrophilic group being 250 mass ppb or less relative to the powder, and the specific surface area being 7 to 50 m ２ / g powder is provided.

[0009] According to the present disclosure, it is possible to provide a powder containing particles of low-molecular-weight polytetrafluoroethylene that has excellent fine dispersibility in other materials and has a reduced content of fluorine-containing compounds having hydrophilic groups. Also, according to the present disclosure, it is possible to provide a method for producing a powder containing particles of low-molecular-weight polytetrafluoroethylene that has excellent fine dispersibility in other materials and has a reduced content of fluorine-containing compounds having hydrophilic groups.

[0010] Before specifically describing the present disclosure, some terms used in the present disclosure will be defined or explained.

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

[0012] In the present disclosure, polytetrafluoroethylene [PTFE] is preferably a fluoropolymer having a content of tetrafluoroethylene units relative to all polymer units of 99 mol % or more.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0036] The present disclosure relates to a powder containing particles of low-molecular-weight polytetrafluoroethylene. The powder of the present disclosure contains particles of low-molecular-weight polytetrafluoroethylene, and contains a fluorine-containing compound having a hydrophilic group, the content of the fluorine-containing compound having a hydrophilic group being 250 mass ppb or less relative to the powder, and the powder has a specific surface area of ​​7 to 50 m. ２ / g.

[0037] As a method for producing low-molecular-weight polytetrafluoroethylene, for example, as described in Patent Document 4, emulsion polymerization of tetrafluoroethylene or a modified monomer copolymerizable with tetrafluoroethylene is carried out in an aqueous medium in the presence of a chain transfer agent, and the emulsion polymerization is carried out by polymerizing a copolymer represented by the following general formula X-(CF ２ ) ｍ -Y (wherein X represents H or F, m represents an integer of 3 to 5, and Y is -SO ３ M, -SO ４ M, -SO ３ R, -SO ４ R, -COOM, -PO ３ M ２ , -PO ４ M ２ (M is H, NH ４ or an alkali metal, and R represents an alkyl group having 1 to 12 carbon atoms. ) is known. A production method is known in which a low-molecular-weight polytetrafluoroethylene powder is produced by coagulating and drying an aqueous dispersion of low-molecular-weight polytetrafluoroethylene obtained by emulsion polymerization. The copolymer powder thus obtained contains the fluorine-containing compound used in the polymerization.

[0038] Although Patent Document 4 describes that the content of fluorine-containing compounds can be easily reduced to 1 ppm or less by increasing the removal efficiency in the washing and drying steps, a further reduction in the content of fluorine-containing compounds is desired. Furthermore, Patent Document 4 only describes reducing the content of fluorine-containing compounds used in polymerization, but it is preferable to also remove from the powder fluorine-containing compounds having hydrophilic groups that are produced by polymerization of tetrafluoroethylene.

[0039] Also known as a method for producing low-molecular-weight polytetrafluoroethylene is a method of production by suspension polymerization, 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 low-molecular-weight polytetrafluoroethylene particles becomes small.

[0040] The powder of the present disclosure contains a fluorine-containing compound having a hydrophilic group, but the content of the fluorine-containing compound is reduced to 250 mass ppb or less relative to the powder. Therefore, for example, when the powder of the present disclosure is added to another material, there is no effect due to the residual fluorine-containing compound having a hydrophilic group, and the properties originally expected of low-molecular-weight polytetrafluoroethylene can be fully exhibited. Furthermore, in addition to the reduced content of the fluorine-containing compound having a hydrophilic group, the powder of the present disclosure has a specific surface area of ​​7 to 50 m ２ / g, when added to other materials, the powder of the present disclosure can be easily finely dispersed in the other materials, and the effect of adding the powder of the present disclosure can be fully exerted.

[0041] Next, the powder and the method for producing the powder according to the present disclosure will be described in detail.

[0042] 1. Powder The powder of the present disclosure is a powder containing particles of low-molecular-weight polytetrafluoroethylene, and the specific surface area of ​​the powder is 7 to 50 m ２ / g. In the present disclosure, the powder refers to an aggregate of low-molecular-weight polytetrafluoroethylene particles. When low-molecular-weight polytetrafluoroethylene is produced by emulsion polymerization, the low-molecular-weight polytetrafluoroethylene particles are secondary particles formed by agglomeration of primary particles obtained by polymerization. Emulsion polymerization of low-molecular-weight polytetrafluoroethylene usually produces an aqueous dispersion in which primary particles of low-molecular-weight polytetrafluoroethylene are dispersed in an aqueous medium. The low-molecular-weight polytetrafluoroethylene particles are formed by agglomerating the primary particles in the aqueous dispersion. The formed aggregates are collected and dried to produce a powder (aggregate) of low-molecular-weight polytetrafluoroethylene particles.

[0043] The specific surface area of ​​the powder is 7 to 50 m ２ / g, more preferably 8m ２ / g or more, and more preferably 9m ２ / g or more, more preferably 35m ２ / g or less, and more preferably 20m ２ / g or less. When the specific surface area of ​​the powder is within the above range, excellent fine dispersibility in other materials can be obtained. If the specific surface area is too small, the fine dispersibility in other materials will be poor, and if the specific surface area is too large, it will take a long time to disperse the powder in other materials or the viscosity will increase too much when added to paints, etc.

[0044] The specific surface area of ​​the powder containing low molecular weight polytetrafluoroethylene particles can be adjusted by, for example, polymerizing tetrafluoroethylene in the presence of a fluorine-containing surfactant, a polymerization initiator and an aqueous medium to prepare the primary particles of low molecular weight polytetrafluoroethylene, and then coagulating the primary particles of low molecular weight polytetrafluoroethylene obtained by polymerization, and drying at an appropriate temperature.The primary particles thus obtained have a relatively small specific surface area.Furthermore, the particles (secondary particles) of low molecular weight polytetrafluoroethylene that constitute the powder thus obtained are not formed by the fusion of the primary particles of low molecular weight polytetrafluoroethylene, but are formed by the simple aggregation of the primary particles of low molecular weight polytetrafluoroethylene.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 can obtain a relatively large specific surface area.

[0045] The specific surface area of ​​the powder is measured by the BET method using a surface analyzer (trade name: MONOSORB, manufactured by QUANTA CHLROME) with a mixed gas of 30% nitrogen and 70% helium as the carrier gas and liquid nitrogen for cooling.

[0046] The melt viscosity at 380°C of the low molecular weight polytetrafluoroethylene constituting the powder of the present disclosure is preferably 1 x 10 ２ ~7 x 10 ５ The viscosity is Pa·s. In the present disclosure, "low molecular weight" means that the melt viscosity is within the above range. High molecular weight polytetrafluoroethylene has a much higher melt viscosity than low molecular weight polytetrafluoroethylene, and it is difficult to measure its melt viscosity accurately. The melt viscosity is measured in accordance with ASTM D 1238 using a flow tester (manufactured by Shimadzu Corporation) and a 2φ-8L die, with a 2g sample preheated at 380°C for 5 minutes, and maintained at the above temperature under a load of 0.7 MPa.

[0047] Low molecular weight polytetrafluoroethylene is melt-processible, non-fibrillating polytetrafluoroethylene, while high molecular weight polytetrafluoroethylene is non-melt-processible, non-fibrillating polytetrafluoroethylene.

[0048] By non-melt processable is meant that the melt flow rate cannot be measured at a temperature higher than the crystallization melting point according to ASTM D 1238 and D 2116.

[0049] The presence or absence of fibrillating properties can be determined by "paste extrusion," a typical method for molding "high molecular weight polytetrafluoroethylene powder," which is a powder made from a polymer of tetrafluoroethylene. Paste extrusion is usually possible because high molecular weight polytetrafluoroethylene has fibrillating properties. If the unsintered molded product obtained by paste extrusion has no substantial strength or elongation, for example, if it breaks when pulled at 0% elongation, it can be considered to have no fibrillating properties.

[0050] The average particle size of the low-molecular-weight polytetrafluoroethylene particles contained in the powder of the present disclosure is preferably 1.0 to 30 μm, more preferably 2.0 μm or more, and more preferably 20 μm or less. When the average particle size of the low-molecular-weight polytetrafluoroethylene particles is within the above range, excellent fine dispersibility in other materials can be obtained.

[0051] The average particle size of the particles of low-molecular-weight polytetrafluoroethylene is the volume-based average particle size (50% cumulative particle size) d50, which can be determined by laser diffraction.

[0052] The melting point of the low-molecular-weight polytetrafluoroethylene is preferably 322 to 333°C, more preferably 323°C or higher, even more preferably 324°C or higher, and more preferably 332°C or lower.

[0053] The melting point can be determined by using a differential scanning calorimeter (DSC) to draw a DSC curve by raising the temperature of low-molecular-weight polytetrafluoroethylene that has not been heated to a temperature of 300°C or higher at a rate of 10°C / min, and identifying the temperature corresponding to the minimum point of the heat of fusion in the temperature range of 250 to 380°C on the DSC curve.

[0054] (Fluorine-containing compound having a hydrophilic group) The powder of the present disclosure 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 produced by polymerization of a monomer.

[0055] In the present disclosure, the hydrophilic group possessed by the fluorine-containing compound is preferably an anionic group such as an acid group, for example, —NH ２ , -PO ３ M, -OPO ３ M, -SO ３ M, -OSO ３ Examples of the hydrophilic group include -M and -COOM (in each formula, M represents a cation). ３ M or -COOM is preferred, and -COOM is more preferred.

[0056] The content of the fluorine-containing compound having a hydrophilic group in the powder is 250 ppb by mass or less, preferably 100 ppb by mass or less, more preferably 50 ppb by mass or less, even more preferably 25 ppb by mass or less, still more preferably 10 ppb by mass or less, particularly preferably 5 ppb by mass or less, and preferably more than 0 ppb by mass, relative to the powder.

[0057] 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 containing primary particles of low-molecular-weight polytetrafluoroethylene, and then adding a relatively large amount of a radical generator to the aqueous dispersion and subjecting it to heat treatment.

[0058] The content of the fluorine-containing compound having a hydrophilic group in the powder can be quantified by known methods. For example, it can be quantified by LC / MS analysis. First, methanol is added to the powder to perform extraction, and the resulting extract is analyzed by LC / MS. To further improve the extraction efficiency, treatments such as Soxhlet extraction and ultrasonic treatment may be performed. The resulting extract is concentrated using an appropriate nitrogen purge, and the fluorine-containing compound in the concentrated extract is measured by LC / MS. Molecular weight information is extracted from the obtained LC / MS spectrum, and a match with the structural formula of the candidate fluorine-containing compound having a hydrophilic group is confirmed. Then, aqueous solutions containing five or more levels of the confirmed fluorine-containing compound having a hydrophilic group are prepared, and LC / MS analysis is performed on each aqueous solution. The relationship between the content and the area area relative to the content is plotted, and a calibration curve is drawn. Then, using the calibration curve, the area area of ​​the LC / MS chromatogram of the fluorine-containing compound having a hydrophilic group in the extract can be converted to the content of the fluorine-containing compound having a hydrophilic group. Note that the resulting extract can be concentrated by nitrogen purging, which lowers the lower limit of quantitation of the measurement method.

[0059] In one embodiment of the powder, the fluorine-containing compound having a hydrophilic group contains at least a fluorine-containing surfactant. The fluorine-containing surfactant may be a fluorine-containing surfactant commonly used in the polymerization of tetrafluoroethylene. Typical compounds of the fluorine-containing surfactant are fluorine-containing surfactants having a molecular weight of 1000 g / mol or less, preferably 800 g / mol or less.

[0060] The fluorine-containing surfactant is not particularly limited as long as it is a surfactant containing at least one fluorine atom, and any conventionally known fluorine-containing surfactant can be used.

[0061] Examples of the fluorine-containing surfactant include anionic fluorine-containing surfactants, etc. The anionic fluorine-containing surfactant may be, for example, a surfactant containing fluorine atoms and having a total carbon number of 20 or less excluding the anionic group.

[0062] The fluorine-containing surfactant may also be a surfactant containing fluorine, the molecular weight of the anionic moiety of which is 1,000 or less. The "anionic moiety" means the part of the fluorine-containing surfactant excluding the cation. For example, F(CF) represented by the formula (I) below may be used. ２ ) ｎ１ In the case of COOM, "F(CF ２ ) ｎ１ This is the "COO" part.

[0063] The fluorine-containing surfactant also includes a fluorine-containing surfactant having a Log POW of 3.5 or less. The Log POW is the partition coefficient between 1-octanol and water, and is expressed as Log P [where P represents the ratio of the fluorine-containing surfactant concentration in octanol to the fluorine-containing surfactant concentration in water when a 1:1 octanol / water mixture containing the fluorine-containing surfactant undergoes phase separation]. The Log POW can be measured using a column: TOSOH ODS-120T column (φ4.6 mm×250 mm, manufactured by Tosoh Corporation), an eluent: acetonitrile / 0.6% by mass HClO ４ HPLC is performed on standard substances (heptanoic acid, octanoic acid, nonanoic acid, and decanoic acid) with known octanol / water partition coefficients under conditions of water=1 / 1 (vol / vol %), flow rate: 1.0 ml / min, sample amount: 300 μL, column temperature: 40°C, and detection light: UV 210 nm. A calibration curve is prepared between each elution time and the known octanol / water partition coefficient, and the elution time is calculated from the HPLC elution time of the sample solution based on this calibration curve.

[0064] Specific examples of the fluorine-containing surfactants include those described in U.S. Patent Application Publication Nos. 2007 / 0015864, 2007 / 0015865, 2007 / 0015866, 2007 / 0276103, 2007 / 0117914, 2007 / 142541, 2008 / 0015319, and U.S. Pat. No. 3,250,808. , U.S. Patent No. 3,271,341, JP 2003-119204 A, WO 2005 / 042593, WO 2008 / 060461, WO 2007 / 046377, JP 2007-119526 A, WO 2007 / 046482, WO 2007 / 046345, U.S. Patent Application Publication No. 2014 / 0228531, WO 2013 / 189824, and those described in WO 2013 / 189826, and the like.

[0065] The anionic fluorine-containing surfactant may be a compound represented by the following general formula (N ０ ): X ｎ０ -Rf ｎ０ -Y ０ (N ０ ) (wherein, X ｎ０ is H, Cl or F. ｎ０ is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which some or all of the H atoms are substituted with F, and the alkylene group may contain one or more ether bonds, and some of the H atoms may be substituted with Cl. Y ０ is an anionic group. ０ The anionic group is -COOM, -SO ２ M or -SO ３ M, -COOM or -SO ３ M. M may be H, a metal atom, NR ７ ４ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium, and R ７is H or an organic group. The metal atom includes alkali metals (Group 1), alkaline earth metals (Group 2), etc., such as Na, K, or Li. ７ As the group, H or C １－１０ and may be an organic group of the formula: １－４ and may be an organic group of the formula: １－４ M may be H, a metal atom, or an alkyl group of the formula NR ７ ４ may be H, an alkali metal (Group 1), an alkaline earth metal (Group 2), or NR ７ ４ may be H, Na, K, Li or NH ４ The above Rf ｎ０ may be one in which 50% or more of H is substituted with fluorine.

[0066] The general formula (N ０ The compound represented by the following general formula (N １ ): X ｎ０ -(CF ２ ) ｍ１ -Y ０ (N １ ) (wherein, X ｎ０ is H, Cl, and F, m1 is an integer from 3 to 15, and Y ０ is as defined above), a compound represented by the following general formula (N ２ ): Rf ｎ１ -O-(CF(CF ３ )CF ２ O) ｍ２ CFX ｎ１ -Y ０ (N ２ ) (wherein, Rf ｎ１ is a perfluoroalkyl group having 1 to 5 carbon atoms, m2 is an integer of 0 to 3, and X ｎ１ is F or CF ３ and Y ０ is as defined above), a compound represented by the following general formula (N ３ ): Rf ｎ２ (CH ２ ) ｍ３ -(Rf ｎ３ ) ｑ-Y ０ (N ３ ) (wherein, Rf ｎ２ is a partially or fully fluorinated alkyl group having 1 to 13 carbon atoms, which may contain an ether bond and / or a chlorine atom, m3 is an integer of 1 to 3, and Rf ｎ３ is a linear or branched perfluoroalkylene group having 1 to 3 carbon atoms, q is 0 or 1, and Y ０ is as defined above), a compound represented by the following general formula (N ４ ): Rf ｎ４ -O-(CY ｎ１ Y ｎ２ ) ｐ CF ２ -Y ０ (N ４ ) (wherein, Rf ｎ４ is a linear or branched partially or fully fluorinated alkyl group having 1 to 12 carbon atoms, which may contain an ether bond; Y ｎ１ and Y ｎ２ are the same or different and are H or F, p is 0 or 1, and Y ０ is as defined above.) and a compound represented by the general formula (N ５ ): (In the formula, X ｎ２ , X ｎ３ and X ｎ４ Rf may be the same or different and are H, F, or a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms, which may contain an ether linkage. ｎ５ is a linear or branched partially or fully fluorinated alkylene group having 1 to 3 carbon atoms, which may contain an ether bond; L is a linking group; Y ０ is as defined above, where X ｎ２ , X ｎ３ , X ｎ４ and Rf ｎ５ wherein the total number of carbon atoms is 18 or less.

[0067] The general formula (N ０) More specifically, the compounds represented by the formula (I) below include perfluorocarboxylic acids (I), ω-H perfluorocarboxylic acids (II), perfluoroether carboxylic acids (III), perfluoroalkyl alkylene carboxylic acids (IV), perfluoroalkoxy fluorocarboxylic acids (V), perfluoroalkyl sulfonic acids (VI), ω-H perfluoro sulfonic acids (VII), perfluoroalkyl alkylene sulfonic acids (VIII), alkyl alkylene carboxylic acids (IX), fluorocarboxylic acids (X), alkoxy fluorosulfonic acids (XI), alkoxy fluorosulfonic acids (XI), and the like.

[0068] The perfluorocarboxylic acid (I) is represented by the following general formula (I): F(CF ２ ) ｎ１ COOM (I) (wherein n1 is an integer of 3 to 13, and M is H, a metal atom, NR ７ ４ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium, and R ７ is H or an organic group.

[0069] The ω-H perfluorocarboxylic acid (II) is represented by the following general formula (II): H(CF ２ ) ｎ２ COOM (II) (wherein n2 is an integer of 4 to 15, and M is as defined above).

[0070] The perfluoroethercarboxylic acid (III) is a compound represented by the following general formula (III): １ -O-(CF(CF ３ )CF ２ O) ｎ３CF (CF ３ ) COOM (III) (wherein, Rf １ is a perfluoroalkyl group having 1 to 5 carbon atoms, n3 is an integer of 0 to 3, and M is as defined above.

[0071] The perfluoroalkyl alkylene carboxylic acid (IV) is represented by the following general formula (IV): ２ (CH ２ ) ｎ４ Rf ３ COOM (IV) (wherein, Rf ２ is a perfluoroalkyl group having 1 to 5 carbon atoms, and Rf ３ is a linear or branched perfluoroalkylene group having 1 to 3 carbon atoms, n4 is an integer of 1 to 3, and M is as defined above.

[0072] The alkoxyfluorocarboxylic acid (V) is represented by the following general formula (V): Rf ４ -O-CY １ Y ２ CF ２ -COOM (V) (wherein, Rf ４ is a linear or branched partially or fully fluorinated alkyl group having 1 to 12 carbon atoms, which may contain ether bonds and / or chlorine atoms; Y １ and Y ２ are the same or different and are H or F, and M is as defined above.

[0073] The perfluoroalkylsulfonic acid (VI) is represented by the following general formula (VI): F(CF ２ ) ｎ５ SO ３ M (VI) (wherein n5 is an integer of 3 to 14, and M is as defined above).

[0074] The ω-H perfluorosulfonic acid (VII) is represented by the following general formula (VII): H(CF ２ ) ｎ６ SO ３M (VII) (wherein n6 is an integer of 4 to 14, and M is as defined above).

[0075] The perfluoroalkyl alkylene sulfonic acid (VIII) is a compound represented by the following general formula (VIII): ５ (CH ２ ) ｎ７ SO ３ M (VIII) (wherein, Rf ５ is a perfluoroalkyl group having 1 to 13 carbon atoms, n7 is an integer of 1 to 3, and M is as defined above.

[0076] The alkyl alkylene carboxylic acid (IX) is represented by the following general formula (IX): ６ (CH ２ ) ｎ８ COOM (IX) (wherein, Rf ６ is a linear or branched partially or fully fluorinated alkyl group having 1 to 13 carbon atoms which may contain an ether bond, n8 is an integer from 1 to 3, and M is as defined above.

[0077] The fluorocarboxylic acid (X) is represented by the following general formula (X): ７ -O-Rf ８ -O-CF ２ -COOM (X) (wherein, Rf ７ is a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms, which may contain an ether bond and / or a chlorine atom, and Rf ８ is a linear or branched, partially or fully fluorinated alkyl group having 1 to 6 carbon atoms, and M is as defined above.

[0078] The alkoxyfluorosulfonic acid (XI) is represented by the following general formula (XI): Rf ９ -O-CY １ Y ２ CF ２ -SO ３ M (XI) (wherein, Rf ９is a linear or branched alkyl group having 1 to 12 carbon atoms, which may contain an ether bond, and which may contain chlorine, and which is partially or completely fluorinated; Y １ and Y ２ are the same or different and are H or F, and M is as defined above.

[0079] The compound (XII) is represented by the following general formula (XII): (In the formula, X １ , X ２ and X ３ Rf may be the same or different and are H, F and linear or branched partially or fully fluorinated alkyl groups having 1 to 6 carbon atoms, which may contain ether bonds; １０ is a perfluoroalkylene group having 1 to 3 carbon atoms, L is a linking group, and Y ０ is an anionic group. ０ is -COOM, -SO ２ M or -SO ３ M, and -SO ３ M or COOM (wherein M is as defined above). Examples of L include a single bond, a partially or fully fluorinated alkylene group having 1 to 10 carbon atoms which may contain an ether bond.

[0080] The compound (XIII) has the following general formula (XIII): １１ -O-(CF ２ CF (CF ３ ) O) ｎ９ (CF ２ O) ｎ１０ CF ２ COOM (XIII) (wherein, Rf １１ is a fluoroalkyl group containing chlorine and having 1 to 5 carbon atoms, n9 is an integer of 0 to 3, n10 is an integer of 0 to 3, and M is as defined above. ２ ClO(CF ２ CF (CF ３ ) O) ｎ９ (CF ２ O) ｎ１０CF ２ COONH ４ (a mixture having an average molecular weight of 750, wherein n9 and n10 are defined above).

[0081] As mentioned above, examples of the anionic fluorine-containing surfactant include carboxylic acid surfactants and sulfonic acid surfactants.

[0082] The fluorine-containing surfactant may be one type of fluorine-containing surfactant or a mixture containing two or more types of fluorine-containing surfactants.

[0083] The fluorine-containing surfactant preferably has a methylene group (—CH ２ -), and more preferably, does not have a C-H bond. ２ By using a fluorine-containing surfactant having no - or C--H bond, the polymerization of tetrafluoroethylene in the presence of an aqueous medium can be smoothly carried out.

[0084] The number of H atoms in the hydrophobic group of the fluorine-containing surfactant is preferably 0 or 1, more preferably 0. By using a fluorine-containing surfactant having a small number of H atoms bonded to the carbon atoms constituting the hydrophobic group, the polymerization of tetrafluoroethylene in the presence of an aqueous medium can be smoothly carried out. The number of carbon atoms in the hydrophobic group of a fluorine-containing surfactant having a hydrophobic group and a hydrophilic group is preferably 1 to 50, more preferably 3 to 20, and even more preferably 6 to 12. The hydrophobic group usually constitutes the above-mentioned "portion excluding the anionic group" of the molecular structure of the fluorine-containing surfactant. As the hydrophilic group, Y ０ Examples of the anionic group include the groups exemplified above for the anionic group of the formula (I). The fluorine-containing surfactant may be a saturated fluorinated surfactant in which all of the carbon atoms bonded to the hydrophobic group have been substituted with fluorine atoms.

[0085] As the fluorine-containing surfactant, among the above-mentioned anionic fluorine-containing surfactants, those represented by the general formula (N １ ), a compound represented by the general formula (N ２ ), a compound represented by the general formula (N ４ ): Rf ｎ４ -O-(CYｎ１ F) ｐ CF ２ -Y ０ (N ４ ) (wherein, Rf ｎ４ is a linear or branched or fully fluorinated alkyl group having 1 to 12 carbon atoms, which may contain an ether linkage (provided that -CH ２ -), and Y ｎ１ is H or F, p is 0 or 1, and Y ０ is as defined above.) and a compound represented by the general formula (N ５ ): (In the formula, X ｎ２ , X ｎ３ and X ｎ４ may be the same or different and are H, F, or a linear or branched alkyl group having 1 to 6 carbon atoms, which may contain an ether bond, or a fully fluorinated alkyl group (provided that -CH ２ -), except that X ｎ３ and X ｎ４ Both of Rf cannot be H. ｎ５ is a linear or branched or fully fluorinated alkylene group having 1 to 3 carbon atoms, which may contain an ether bond (provided that -CH ２ -), L is a linking group, and Y ０ is as defined above, where X ｎ２ , X ｎ３ , X ｎ４ and Rf ｎ５ wherein the total number of carbon atoms is 18 or less.

[0086] As the fluorine-containing surfactant, among the above-mentioned anionic fluorine-containing surfactants, perfluorocarboxylic acid (I) represented by general formula (I), ω-H perfluorocarboxylic acid (II) represented by general formula (II), perfluoroether carboxylic acid (III) represented by general formula (III), perfluoroalkyl alkylene carboxylic acid (IV) represented by general formula (IV), perfluoroalkoxy fluorocarboxylic acid (V) represented by general formula (V), perfluoroalkyl sulfonic acid (VI) represented by general formula (VII), ω-H perfluoro sulfonic acid (VII) represented by general formula (VII), perfluoroalkyl alkylene sulfonic acid (VIII) represented by general formula (VIII), general formula (X): Rf ７ -O-Rf ８ -O-CF ２ -COOM (wherein, Rf ７ is a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms, which may contain ether bonds and / or chlorine atoms (provided that -CH ２ -), and Rf ８ is a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms (provided that -CH ２ Fluorocarboxylic acid (X) represented by general formula (XI): Rf ９ -O-CY １ FCF ２ -SO ３ M (wherein, Rf ９ is a linear or branched alkyl group having 1 to 12 carbon atoms, which may contain an ether bond, and which may contain chlorine, and which is partially or completely fluorinated (provided that -CH ２ -), and Y １ is H or F, and M is as defined above.), an alkoxyfluorosulfonic acid (XI) represented by the general formula (XII): (In the formula, X １ , X ２ and X ３may be the same or different and are H, F and straight or branched chain alkyl groups having 1 to 6 carbon atoms which may contain ether bonds or fully fluorinated alkyl groups (provided that -CH ２ -), except that X ２ and X ３ Both of Rf １０ is a perfluoroalkylene group having 1 to 3 carbon atoms, L is a linking group, and Y ０ is an anionic group.) and a compound (XII) represented by the general formula (XIII): Rf １１ -O-(CF ２ CF (CF ３ ) O) ｎ９ (CF ２ O) ｎ１０ CF ２ COOM (where Rf １１ represents a fluoroalkyl group having 1 to 5 carbon atoms and containing chlorine (wherein -CH ２ n9 is an integer of 0 to 3, n10 is an integer of 0 to 3, and M is as defined above. The use of these fluorine-containing surfactants allows the polymerization of tetrafluoroethylene to proceed smoothly in the presence of an aqueous medium.

[0087] Examples of the fluorine-containing surfactant include compounds represented by the following formula: F(CF ２ ) ７ COOM, F(CF ２ ) ５ COOM, H(CF ２ ) ６ COOM, H(CF ２ ) ７ COOM, C.F. ３ O (CF ２ ) ３ OCHFCF ２ COOM, C. ３ F ７ OCF (CF ３ )CF ２ OCF (CF ３) COOM, C.F. ３ CF ２ CF ２ OCF (CF ３ ) COOM, C.F. ３ CF ２ OCF ２ CF ２ OCF ２ COOM, C. ２ F ５ OCF (CF ３ )CF ２ OCF (CF ３ ) COOM, C.F. ３ OCF (CF ３ )CF ２ OCF (CF ３ ) COOM, C.F. ２ ClCF ２ CF ２ OCF (CF ３ )CF ２ OCF ２ COOM, C.F. ２ ClCF ２ CF ２ OCF ２ CF (CF ３ ) OCF ２ COOM, C.F. ２ ClCF(CF ３ ) OCF (CF ３ )CF ２ OCF ２ COOM, C.F. ２ ClCF(CF ３ ) OCF ２ CF (CF ３ ) OCF ２ COOM, (In each formula, M is H, metal atom, NR ７ ４ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium. ７ is H or an organic group.

[0088] When the powder contains at least a fluorine-containing surfactant as the fluorine-containing compound having a hydrophilic group, the content of the fluorine-containing surfactant in the powder is preferably 25 ppb by mass or less, more preferably 10 ppb by mass or less, even more preferably 5 ppb by mass or less, still more preferably 1 ppb by mass or less, and preferably more than 0 ppb by mass, relative to the powder.

[0089] In one embodiment of the powder, the powder contains a compound (I) represented by the following general formula (I) as a fluorine-containing compound having a hydrophilic group. General formula (I): F(CF ２ ) ｎ１ COOM (wherein n1 is an integer of 3 to 13, and M is H, a metal atom, or NR ７ ４ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium, and R ７ is H or an organic group.

[0090] When the powder contains at least compound (I) represented by general formula (I) as a fluorine-containing compound having a hydrophilic group, the content of the compound represented by general formula (I) in the powder is preferably 25 ppb by mass or less, more preferably 10 ppb by mass or less, even more preferably 5 ppb by mass or less, still more preferably 1 ppb by mass or less, and preferably more than 0 ppb by mass, relative to the powder.

[0091] In one embodiment of the powder, the fluorine-containing compound having a hydrophilic group contains a compound represented by the following general formula (H1): General formula (H1): [X-Rf-A － ] ｉ M ｉ＋ (Wherein, X represents H, Cl, Br, F or I; Rf represents a linear or branched partially or fully fluorinated aliphatic group, or a linear or branched partially or fully fluorinated aliphatic group interrupted by at least one oxygen atom; A － is an acid group, M ｉ＋ represents a cation having a valence i, where i is an integer from 1 to 3.

[0092] When the powder contains at least a compound represented by general formula (H1) as a fluorine-containing compound having a hydrophilic group, the content of the compound represented by general formula (H1) in the powder is preferably 250 ppb by mass or less, more preferably 100 ppb by mass or less, even more preferably 50 ppb by mass or less, still more preferably 25 ppb by mass or less, particularly preferably 10 ppb by mass or less, and most preferably 5 ppb by mass or less, and preferably more than 0 ppb by mass, relative to the powder.

[0093] In one embodiment of the powder, the fluorine-containing compound having a hydrophilic group contains a compound represented by the following general formula (H2): General formula (H2): [C ｎ－１ F ２ｎ－１ COO － ]M ＋ (wherein n is an integer of 9 to 14, M ＋ represents a cation.)

[0094] It is known that the compound represented by general formula (H2) (perfluoroalkanoic acid) is formed during polymerization when perfluoroalkyl vinyl ether or the like is used as a monomer (see WO 2019 / 161153).

[0095] When the powder contains at least a compound represented by general formula (H2) as a fluorine-containing compound having a hydrophilic group, the content of the compound represented by general formula (H2) in the powder is preferably 25 ppb by mass or less, more preferably 10 ppb by mass or less, even more preferably 5 ppb by mass or less, still more preferably 1 ppb by mass or less, and preferably more than 0 ppb by mass, relative to the powder.

[0096] In one embodiment of the powder, the powder contains a compound represented by the following general formula (H3) as the fluorine-containing compound having a hydrophilic group. General formula (H3): [R １ -O-L-CO ２ － ]M ＋ (In the formula, R １represents a linear or branched partially or fully fluorinated aliphatic group, or a linear or branched partially or fully fluorinated aliphatic group interrupted by at least one oxygen atom; L represents a linear or branched non-fluorinated, partially fluorinated or fully fluorinated alkylene group; M represents a linear or branched non-fluorinated, partially fluorinated or fully fluorinated alkylene group; ＋ represents a cation.)

[0097] When the powder contains at least a compound represented by general formula (H3) as a fluorine-containing compound having a hydrophilic group, the content of the compound represented by general formula (H3) in the powder is preferably 25 ppb by mass or less, more preferably 10 ppb by mass or less, even more preferably 5 ppb by mass or less, still more preferably 1 ppb by mass or less, and preferably more than 0 ppb by mass, relative to the powder.

[0098] In one embodiment of the powder, the powder contains a compound represented by general formula (H4) as the fluorine-containing compound having a hydrophilic group. General formula (H4): H-Rf ｎ０ -Y ０ (wherein, Rf ｎ０ is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which some or all of the H atoms are substituted with F, and the alkylene group may contain one or more ether bonds, and some of the H atoms may be substituted with Cl. Y ０ is an anionic group.)

[0099] The compound represented by the general formula (H4) includes compounds represented by any of the following general formulas: General formula (H4-1): [H—(CF ２ ) ｍ１ CO ２ － ]M ＋ (wherein m1 is an integer of 3 to 19, M ＋ represents a cation.) General formula (H4-2): [H—(CF ２ ) ｍ２ -(CF(CF ３ )) ｍ３ -CO ２ － ]M ＋ (wherein m2 is an integer of 1 to 17, m3 is an integer of 1 to 9, M ＋represents a cation, provided that m2 and m3 are selected so as to satisfy the relationship 3≦(m2+2×m3)≦19, and the order of occurrence of each repeating unit in the formula is arbitrary.

[0100] When the powder contains at least a compound represented by general formula (H4) as a fluorine-containing compound having a hydrophilic group, the content of the compound represented by general formula (H4) in the powder is preferably 250 ppb by mass or less, more preferably 100 ppb by mass or less, even more preferably 50 ppb by mass or less, still more preferably 25 ppb by mass or less, and preferably more than 0 ppb by mass, relative to the powder.

[0101] (Low-molecular-weight polytetrafluoroethylene) Low-molecular-weight polytetrafluoroethylene (low-molecular-weight PTFE) may be a TFE homopolymer containing only tetrafluoroethylene (TFE) units, or may be a modified polytetrafluoroethylene containing TFE units and modified monomer units.

[0102] The modifying monomer is not particularly limited as long as it can be copolymerized with TFE, and includes fluoromonomers and non-fluoromonomers. The modifying monomer used may be one type or multiple types.

[0103] The non-fluoromonomer is not particularly limited and may be a monomer represented by the general formula: ２ =CR Ｑ１ -LR Ｑ２ (In the formula, R Ｑ１ represents a hydrogen atom or an alkyl group. L represents a single bond, -CO-O-*, -O-CO-* or -O-. * represents R Ｑ２ represents the bonding position with Ｑ２ represents a hydrogen atom, an alkyl group or a nitrile group.

[0104] Examples of non-fluoromonomers 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, cyclohexyl vinyl ether, etc. Of these, butyl methacrylate, vinyl acetate, and acrylic acid are preferred as non-fluoromonomers.

[0105] Examples of fluoromonomers include perfluoroolefins such as hexafluoropropylene (HFP); hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride (VDF); perhaloolefins such as chlorotrifluoroethylene; perfluorovinyl ethers; (perfluoroalkyl)ethylenes; and perfluoroallyl ethers.

[0106] The perfluorovinyl ether is not particularly limited, and examples thereof include perfluorovinyl ethers represented by the general formula (A): CF ２ ═CF-ORf (A) (wherein Rf represents a perfluoroorganic group). In the present disclosure, the term "perfluoroorganic group" refers to an organic group in which all hydrogen atoms bonded to carbon atoms are substituted with fluorine atoms. The perfluoroorganic group may have an ether oxygen.

[0107] Examples of the perfluorovinyl ether include perfluoro(alkyl vinyl ether) [PAVE], which is represented by general formula (A) and in which Rf is a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5.

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

[0109] The perfluorovinyl ether further includes those in which Rf in the general formula (A) is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, and those in which Rf ... the following formula:

[0110]

[0111] (wherein m represents 0 or an integer of 1 to 4), and Rf is a group represented by the following formula:

[0112] CF ３ CF ２ CF ２ -(O-CF(CF ３ )-CF ２ ) ｎ - (wherein n represents an integer of 1 to 4).

[0113] Hydrogen-containing fluoroolefins include CH ２ =CF ２ , CFH=CH ２ , CFH=CF ２ , C.H. ２ =CFCF ３ , C.H. ２ = CHCF ３ , CHF=CHCF ３ (E form), CHF=CHCF ３ (Z-isomer), etc.

[0114] The (perfluoroalkyl)ethylene (PFAE) is not particularly limited, and examples thereof include (perfluorobutyl)ethylene (PFBE) and (perfluorohexyl)ethylene.

[0115] Examples of perfluoroallyl ethers include those represented by the general formula: CF ２ =CF-CF ２ Examples of the fluoromonomer include those represented by —ORf (wherein Rf represents a perfluoroorganic group).

[0116] Rf in the above general formula is the same as Rf in general formula (A). Rf is preferably a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoroalkoxyalkyl group having 1 to 10 carbon atoms. Examples of perfluoroallyl ethers include CF ２ =CF-CF２ -O-CF ３ , C.F. ２ =CF-CF ２ -O-C ２ F ５ , C.F. ２ =CF-CF ２ -O-C ３ F ７ , and CF ２ =CF-CF ２ -O-C ４ F ９ At least one selected from the group consisting of CF ２ =CF-CF ２ -O-C ２ F ５ , C.F. ２ =CF-CF ２ -O-C ３ F ７ , and CF ２ =CF-CF ２ -O-C ４ F ９ More preferably, at least one selected from the group consisting of CF ２ =CF-CF ２ -O-CF ２ CF ２ CF ３ is more preferable.

[0117] A preferred example of the modifying monomer is the modified monomer (3) having a monomer reactivity ratio of 0.1 to 8. The presence of the modified monomer (3) makes it possible to obtain PTFE particles having a small particle size and an aqueous dispersion having high dispersion stability.

[0118] Here, the monomer reactivity ratio in copolymerization with TFE is the value obtained by dividing the rate constant of the reaction of the growing radical with TFE when the growing radical is less than the repeating unit based on TFE by the rate constant of the reaction of the growing radical with modified monomer.The lower this value, the higher the reactivity of the modified monomer with TFE.The monomer reactivity ratio can be calculated by copolymerizing TFE with modified monomer, determining the composition in the produced polymer immediately after the start, and using the Feynman-Ross equation.

[0119] The copolymerization was carried out in a 6.0L stainless steel autoclave using 3600g of deionized and degassed water, 1000 mass ppm of ammonium perfluorooctanoate relative to the water, and 100g of paraffin wax at a pressure of 0.78 MPaG and a temperature of 70 ° C. 0.05g, 0.1g, 0.2g, 0.5g, and 1.0g of modified monomer were added to the reactor, respectively, and 0.072g of ammonium persulfate (20 mass ppm relative to water) was added. TFE was continuously supplied to maintain the polymerization pressure at 0.78 MPaG. When the amount of TFE charged reached 1000g, stirring was stopped and the reactor was depressurized until atmospheric pressure was reached. After cooling, the paraffin wax was separated to obtain an aqueous dispersion containing the resulting polymer. The aqueous dispersion was stirred to coagulate the resulting polymer, and then dried at 150 ° C. The composition of the resulting polymer is calculated by appropriately combining NMR, FT-IR, elemental analysis, and X-ray fluorescence analysis depending on the type of monomer.

[0120] 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): CH ２ =CH-Rf １ (3a) (wherein, Rf １ is a perfluoroalkyl group having 1 to 10 carbon atoms.) CF ２ ═CF—O—Rf ２ (3b) (wherein, Rf ２ is a perfluoroalkyl group having 1 to 2 carbon atoms.) CF ２ =CF-O-(CF ２ ) ｎ CF = CF ２ (3c) (Wherein, n is 1 or 2.)

[0121] (In the formula, X ３ and X ４ is F, Cl or a methoxy group, and Y is of formula Y1 or Y2.

[0122] (In formula Y2, Z and Z′ are F or a fluorinated alkyl group having 1 to 3 carbon atoms.)

[0123] The content of the modified monomer (3) unit is preferably in the range of 0.00001 to 1.0% by mass relative to the total polymerized units of PTFE. The lower limit is more preferably 0.0001% by mass, more preferably 0.0005% by mass, even more preferably 0.001% by mass, and even more preferably 0.005% by mass. The upper limit is, in order of preference, 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, and 0.01% by mass.

[0124] As the above-mentioned modified monomer, because it can obtain the aqueous dispersion of the average primary particle diameter of primary particle is small, the aspect ratio of primary particle is small, and excellent stability, it is preferred to be selected from the group consisting of hexafluoropropylene, chlorotrifluoroethylene, vinylidene fluoride, perfluoro(alkyl vinyl ether), (perfluoroalkyl)ethylene, ethylene, and the modified monomer of the functional group and hydrophilic group that can react by radical polymerization.By using the above-mentioned modified monomer, it can obtain the aqueous dispersion of PTFE that has the average primary particle diameter smaller, the aspect ratio of primary particle is small, and excellent dispersion stability.In addition, it can obtain the aqueous dispersion of less uncoagulated polymer.

[0125] From the viewpoint of reactivity with TFE, the modified monomer preferably contains at least one selected from the group consisting of hexafluoropropylene, perfluoro(alkyl vinyl ether), and (perfluoroalkyl)ethylene. 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. The total amount of the hexafluoropropylene unit, perfluoro(alkyl vinyl ether) unit, and (perfluoroalkyl)ethylene unit is preferably in the range of 0.00001 to 1% by mass relative to the total polymerization units of PTFE. The lower limit of the total amount is more preferably 0.0001% by mass, more preferably 0.0005% by mass, even more preferably 0.001% by mass, and even more preferably 0.005% by mass. The upper limits are, in order of preference, 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%, and 0.01 mass%.

[0126] The modified monomer preferably includes a modified monomer having a functional group capable of reacting by radical polymerization and a hydrophilic group (hereinafter referred to as "modified monomer (A)").

[0127] By making the above-mentioned modified monomer (A) exist, it is possible to obtain PTFE particles with small primary particle diameter, and obtain the aqueous dispersion with high dispersion stability.In addition, it is also possible to reduce the amount of uncoagulated polymer.Furthermore, it is possible to reduce the aspect ratio of primary particle.

[0128] The amount of the modified monomer (A) used is preferably more than the amount corresponding to 0.1 ppm by mass of the aqueous medium, more preferably more than 0.5 ppm by mass, even more preferably more than 1.0 ppm by mass, even more preferably 5 ppm by mass or more, and particularly preferably 10 ppm by mass or more. If the amount of the modified monomer (A) used is too small, the average primary particle diameter of the resulting PTFE may not be small. The amount of the modified monomer (A) used may be within the above range, but the upper limit can be, for example, 5000 ppm by mass. In addition, in the above production method, the modified monomer (A) may be added to the system during the reaction to improve the stability of the aqueous dispersion during or after the reaction.

[0129] The modified monomer (A) is highly water-soluble, so even if unreacted modified monomer (A) remains in the aqueous dispersion, it can be easily removed in the concentration step or the coagulation and washing steps.

[0130] The above-mentioned modified monomer (A) is incorporated into the produced polymer during the polymerization process, but since the concentration of the modified monomer (A) itself in the polymerization system is low and the amount incorporated into the polymer is small, there are no problems such as a decrease in the heat resistance of PTFE or coloration after baking.

[0131] The hydrophilic group in the modified monomer (A) is, for example, —NH ２ , -PO ３ M, -OPO ３ M, -SO ３ M, -OSO ３ M, -COOM (in each formula, M is H, a metal atom, NR ７ｙ ４ , optionally substituted imidazolium, optionally substituted pyridinium or optionally substituted phosphonium, R ７ｙ are H or organic groups and may be the same or different. Any two of them may be bonded to each other to form a ring.) Among the above hydrophilic groups, -SO ３ M or -COOM is preferred. ７ｙ The organic group in R is preferably an alkyl group. ７ｙAs the group, H or C １－１０ is preferably an organic group represented by the formula: １－４ More preferred are organic groups represented by the formula: １－４ The metal atom is preferably a monovalent or divalent metal atom, such as an alkali metal (Group 1) or an alkaline earth metal (Group 2), and is preferably Na, K, or Li.

[0132] Examples of the "functional group capable of reacting by radical polymerization" in the modifying monomer (A) include groups having an ethylenically unsaturated bond, such as a vinyl group and an allyl group. The group having an ethylenically unsaturated bond is a group represented by the following formula: CX ｅ X ｇ =CX ｆ R- (wherein, X ｅ , X ｆ and X ｇ are each independently F, Cl, H, or CF ３ , C.F. ２ H, C.F.H. ２ , or CH ３ and R is a linking group. The linking group of R can be represented by the formula: ａ Preferably, the linking group is -CH=CH ２ , -CF=CH ２、 -CH=CF ２、 -CF = CF ２ , -CH ２ -CH=CH ２ , -CF ２ -CF=CH ２ , -CF ２ -CF = CF ２ , -(C=O)-CH=CH ２ , -(C=O)-CF=CH ２ , -(C=O)-CH=CF ２ , -(C=O)-CF=CF ２ , -(C=O)-C(CH ３ ) = CH ２ , -(C=O)-C(CF ３ ) = CH ２ , -(C=O)-C(CH ３ ) = CF ２ , -(C=O)-C(CF ３ ) = CF ２, —O—CH ２ -CH=CH ２ , —O—CF ２ -CF=CH ２ , —O—CH ２ -CH=CF ２ , —O—CF ２ -CF = CF ２ Examples of groups having an unsaturated bond include the following.

[0133] The modified monomer (A) has a functional group that can react by radical polymerization, so when used in the polymerization, it is assumed that it will react with the fluorine-containing monomer at the initial stage of the polymerization reaction, and form particles that have hydrophilic groups derived from the modified monomer (A) and have high stability.Therefore, it is thought that when polymerization is carried out in the presence of the modified monomer (A), the number of particles will increase.

[0134] The polymerization may be carried out in the presence of one type of the modifying monomer (A), or in the presence of two or more types thereof.

[0135] In the polymerization, a compound having an unsaturated bond can be used as the modifying monomer (A).

[0136] The modifying monomer (A) is a compound represented by the general formula (4): ｉ X ｋ =CX ｊ R ａ - (CZ １ Z ２ ) ｋ -Y ３ (4) (wherein, X ｉ , X ｊ and X ｋ are each independently F, Cl, H or CF ３ and Y ３ is a hydrophilic group; R ａ is a linking group; Z １ and Z ２ are each independently H, F or CF ３ and k is 0 or 1. Examples of the hydrophilic group include —NH ２ , -PO ３ M, -OPO ３ M, -SO ３ M, -OSO３ M, -COOM (in each formula, M is H, a metal atom, NR ７ｙ ４ , optionally substituted imidazolium, optionally substituted pyridinium or optionally substituted phosphonium, R ７ｙ are H or organic groups and may be the same or different. Any two of them may be bonded to each other to form a ring.) Among the above hydrophilic groups, -SO ３ M or -COOM is preferred. ７ｙ The organic group in R is preferably an alkyl group. ７ｙ As the group, H or C １－１０ is preferably an organic group represented by the formula: １－４ More preferred are organic groups represented by the formula: １－４ The alkyl group represented by the formula (I) is more preferred. Examples of the metal atom include monovalent and divalent metal atoms, such as alkali metals (Group 1) and alkaline earth metals (Group 2), with Na, K, or Li being preferred. By using the modified monomer (A), an aqueous dispersion having a smaller average primary particle size and better stability can be obtained. Furthermore, the aspect ratio of the primary particles can be made smaller.

[0137] The above R ａ is a linking group. In the present disclosure, a "linking group" refers to a divalent linking group. The linking group may be a single bond and preferably contains at least one carbon atom. The number of carbon atoms may be 2 or more, 4 or more, 8 or more, 10 or more, or 20 or more. There is no upper limit, but it may be, for example, 100 or less, or 50 or less. The linking group may have a linear or branched, cyclic or acyclic structure, saturated or unsaturated, substituted or unsubstituted, and may optionally contain one or more heteroatoms selected from the group consisting of sulfur, oxygen, and nitrogen, and may optionally contain one or more functional groups selected from the group consisting of ester, amide, sulfonamide, carbonyl, carbonate, urethane, urea, and carbamate. The linking group may not contain carbon atoms, but may contain a catenary heteroatom such as oxygen, sulfur, or nitrogen.

[0138] The above R ａ is preferably a catenary heteroatom such as oxygen, sulfur, or nitrogen, or a divalent organic group. ａ When R is a divalent organic group, the hydrogen atom bonded to the carbon atom may be replaced with a halogen other than fluorine, such as chlorine, and the group may or may not contain a double bond. ａ may be either linear or branched, and may be either cyclic or acyclic. ａ R may contain functional groups (e.g., esters, ethers, ketones, amines, halides, etc.). ａ R may also be a non-fluorinated divalent organic group, or a partially fluorinated or perfluorinated divalent organic group. ａ Examples of the hydrocarbon group include a hydrocarbon group in which no fluorine atoms are bonded to a carbon atom, a hydrocarbon group in which some of the hydrogen atoms bonded to a carbon atom are substituted with fluorine atoms, a hydrocarbon group in which all of the hydrogen atoms bonded to a carbon atom are substituted with fluorine atoms, -(C=O)-, -(C=O)-O-, or a hydrocarbon group containing an ether bond, which may contain an oxygen atom, a double bond, or a functional group.

[0139] R ａ is preferably -(C=O)-, -(C=O)-O-, or a hydrocarbon group having 1 to 100 carbon atoms which may contain an ether bond and may contain a carbonyl group, and in the hydrocarbon group, some or all of the hydrogen atoms bonded to the carbon atoms may be substituted with fluorine. ａ is preferably —(CH ２ ) ａ -, - (CF ２ ) ａ -, -O-(CF ２ ) ａ -, - (CF ２ ) ａ -O-(CF ２ ) ｂ -, -O(CF ２ ) ａ -O-(CF ２ ) ｂ -, - (CF ２ ) ａ-[O-(CF ２ ) ｂ ] ｃ -、-O(CF ２ ) ａ -[O-(CF ２ ) ｂ ] ｃ -、-[(CF ２ ) ａ -O] ｂ -[(CF ２ ) ｃ -O] ｄ -、-O[(CF ２ ) ａ -O] ｂ -[(CF ２ ) ｃ -O] ｄ -、-O-[CF ２ CF(CF ３ )O] ａ -(CF ２ ) ｂ -、-(C=O)-、-(C=O)-O-、-(C=O)-(CH ２ ) ａ -、-(C=O)-(CF ２ ) ａ -、-(C=O)-O-(CH ２ ) ａ -、-(C=O)-O-(CF ２ ) ａ -、-(C=O)-[(CH ２ ) ａ -O] ｂ -、-(C=O)-[(CF ２ ) ａ -O] ｂ -、-(C=O)-O[(CH ２ ) ａ -O] ｂ -、-(C=O)-O[(CF ２ ) ａ -O] ｂ -、-(C=O)-O[(CH ２ ) ａ -O] ｂ -(CH ２ ) ｃ -、-(C=O)-O[(CF ２ ) ａ -O] ｂ -(CF ２ ) ｃ-, -(C=O)-(CH ２ ) ａ -O-(CH ２ ) ｂ -, -(C=O)-(CF ２ ) ａ -O-(CF ２ ) ｂ -, -(C=O)-O-(CH ２ ) ａ -O-(CH ２ ) ｂ -, -(C=O)-O-(CF ２ ) ａ -O-(CF ２ ) ｂ -, -(C=O)-OC ６ H ４ - and at least one selected from combinations thereof. In the formula, a, b, c, and d are independently at least 1. a, b, c, and d may independently be 2 or more, 3 or more, 4 or more, 10 or more, or 20 or more. The upper limits of a, b, c, and d are, for example, 100.

[0140] R ａ A specific example of a suitable group is —CF ２ —O—, —CF ２ -O-CF ２ -, -CF ２ -O-CH ２ -, -CF ２ -O-CH ２ CF ２ -, -CF ２ -O-CF ２ CF ２ -, -CF ２ -O-CF ２ CH ２ -, -CF ２ -O-CF ２ CF ２ CH ２ -, -CF ２ -O-CF(CF ３ ) -, -CF ２ -O-CF(CF ３ )CF ２ -, -CF ２ -O-CF(CF ３ )CF ２-O-, -CF ２ -O-CF(CF ３ )CH ２ -, -(C=O)-, -(C=O)-O-, -(C=O)-(CH ２ )-, -(C=O)-(CF ２ )-, -(C=O)-O-(CH ２ )-, -(C=O)-O-(CF ２ )-, -(C=O)-[(CH ２ ) ２ -O] ｎ -, -(C=O)-[(CF ２ ) ２ -O] ｎ -, -(C=O)-O[(CH ２ ) ２ -O] ｎ -, -(C=O)-O[(CF ２ ) ２ -O] ｎ -, -(C=O)-O[(CH ２ ) ２ -O] ｎ -(CH ２ )-, -(C=O)-O[(CF ２ ) ２ -O] ｎ -(CF ２ )-, -(C=O)-(CH ２ ) ２ -O-(CH ２ )-, -(C=O)-(CF ２ ) ２ -O-(CF ２ )-, -(C=O)-O-(CH ２ ) ２ -O-(CH ２ )-, -(C=O)-O-(CF ２ ) ２ -O-(CF ２ )-, -(C=O)-O-C ６ H ４ - etc. are included. Among them, the above R ａ is specifically, -CF ２ -O-, -CF ２ -O-CF ２ -, -CF ２ -O-CF ２ CF ２ -, -CF ２-O-CF(CF ３ ) -, -CF ２ -O-CF(CF ３ )CF ２ -, -CF ２ -O-CF(CF ３ )CF ２ -O-, -(C=O)-, -(C=O)-O-, -(C=O)-(CH ２ )-,-(C=O)-O-(CH ２ )-,-(C=O)-O[(CH ２ ) ２ -O] ｎ -, -(C=O)-O[(CH ２ ) ２ -O] ｎ - (CH ２ )-,-(C=O)-(CH ２ ) ２ -O-(CH ２ )-, or -(C=O)-O-C ６ H ４ In the above formula, n is an integer of 1 to 10.

[0141] -R in general formula (4) ａ - (CZ １ Z ２ ) ｋ - is -CF ２ -O-CF ２ -, -CF ２ -O-CF(CF ３ ) -, -CF ２ -O-C(CF ３ ) ２ -, -CF ２ -O-CF ２ -CF ２ -, -CF ２ -O-CF ２ -CF (CF ３ ) -, -CF ２ -O-CF ２ -C(CF ３ ) ２ -, -CF ２ -O-CF ２ CF ２ -CF ２ -, -CF ２ -O-CF ２ CF ２ -CF (CF３ )-、-CF ２ -O-CF ２ CF ２ -C(CF ３ ) ２ -、-CF ２ -O-CF(CF ３ )-CF ２ -、-CF ２ -O-CF(CF ３ )-CF(CF ３ )-、-CF ２ -O-CF(CF ３ )-C(CF ３ ) ２ -、-CF ２ -O-CF(CF ３ )CF ２ -CF ２ -、-CF ２ -O-CF(CF ３ )CF ２ -CF(CF ３ )-、-CF ２ -O-CF(CF ３ )CF ２ -C(CF ３ ) ２ -、-CF ２ -O-CF(CF ３ )CF ２ -O-CF ２ -、-CF ２ -O-CF(CF ３ )CF ２ -O-CF(CF ３ )-、-CF ２ -O-CF(CF ３ )CF ２ -O-C(CF ３ ) ２ -、-(C=O)-、-(C=O)-O-、-(C=O)-(CH ２ )-、-(C=O)-(CF ２ )-、-(C=O)-O-(CH ２ )-、-(C=O)-O-(CF ２ )-、-(C=O)-[(CH ２ ) ２ -O] ｎ -(CH ２ )-、-(C=O)-[(CF ２ ) ２ -O]ｎ -(CF ２ )-、-(C=O)-[(CH ２ ) ２ -O] ｎ -(CH ２ )-(CH ２ )-、-(C=O)-[(CF ２ ) ２ -O] ｎ -(CF ２ )-(CF ２ )-、-(C=O)-O[(CH ２ ) ２ -O] ｎ -(CF ２ )-、-(C=O)-O[(CH ２ ) ２ -O] ｎ -(CH ２ )-(CH ２ )-、-(C=O)-O[(CF ２ ) ２ -O] ｎ -(CF ２ )-、-(C=O)-O[(CF ２ ) ２ -O] ｎ -(CF ２ )-(CF ２ )-、-(C=O)-(CH ２ ) ２ -O-(CH ２ )-(CH ２ )-、-(C=O)-(CF ２ ) ２ -O-(CF ２ )-(CF ２ )-、-(C=O)-O-(CH ２ ) ２ -O-(CH ２ )-(CH ２ )-、-(C=O)-O-(CF ２ ) ２ -O-(CF ２ )-(CF ２ )-、-(C=O)-O-(CH ２ ) ２ -O-(CH ２ )-C(CF ３ ) ２ -、-(C=O)-O-(CF ２ ) ２ -O-(CF２ )-C(CF ３ ) ２ - or -(C=O)-O-C ６ H ４ -C(CF ３ ) ２ - is preferred, and -CF ２ -O-CF(CF ３ ) -, -CF ２ -O-CF ２ -CF (CF ３ ) -, -CF ２ -O-CF ２ CF ２ -CF (CF ３ ) -, -CF ２ -O-CF(CF ３ )-CF(CF ３ ) -, -CF ２ -O-CF(CF ３ )CF ２ -CF (CF ３ ) -, -CF ２ -O-CF(CF ３ )CF ２ -O-CF(CF ３ )-, -(C=O)-, -(C=O)-O-(CH ２ )-,-(C=O)-O-(CH ２ )-(CH ２ )-,-(C=O)-O[(CH ２ ) ２ -O] ｎ - (CH ２ )-(CH ２ )-,-(C=O)-O-(CH ２ ) ２ -O-(CH ２ )-C(CF ３ ) ２ - or -(C=O)-O-C ６ H ４ -C(CF ３ ) ２ In the above formula, n is an integer of 1 to 10.

[0142] Specific examples of the compound represented by formula (4) include: (In the formula, X ｊ and Y ３ is the same as above. n is an integer of 1 to 10.

[0143] R ａ As the general formula (r1): -(C=O) ｈ -(O) ｉ -CF ２ -O-(CX ６ ２ ) ｅ -{O-CF(CF ３ ) ｆ -(O) ｇ - (r1) (wherein, X ６ are each independently H, F or CF ３ wherein e is an integer of 0 to 3, f is an integer of 0 to 3, g is 0 or 1, h is 0 or 1, and i is 0 or 1), and a divalent group represented by the general formula (r2): -(C=O) ｈ -(O) ｉ -CF ２ -O-(CX ７ ２ ) ｅ -(O) ｇ - (r2) (wherein, X ７ are each independently H, F or CF ３ wherein e is an integer of 0 to 3, g is 0 or 1, h is 0 or 1, and i is 0 or 1.) is also preferred.

[0144] -R in general formula (4) ａ - (CZ １ Z ２ ) ｋ - may also be represented by the following formula (t1): -(C=O) ｈ -(O) ｉ -CF ２ -O-(CX ６ ２ ) ｅ -{O-CF(CF ３ ) ｆ -(O) ｇ -CZ １ Z ２ - (t1) (wherein, X ６ are each independently H, F or CF ３ wherein e is an integer of 0 to 3, f is an integer of 0 to 3, g is 0 or 1, h is 0 or 1, i is 0 or 1, and Z １and Z ２ are each independently F or CF ３ In formula (t1), a divalent group represented by １ and Z ２ is one F and the other CF ３ In addition, in the general formula (4), -R ａ - (CZ １ Z ２ ) ｋ - is the following formula (t2): -(C=O) ｈ -(O) ｉ -CF ２ -O-(CX ７ ２ ) ｅ -(O) ｇ -CZ １ Z ２ - (t2) (wherein, X ７ are each independently H, F or CF ３ wherein e is an integer of 0 to 3, g is 0 or 1, h is 0 or 1, i is 0 or 1, and Z １ and Z ２ are each independently F or CF ３ In formula (t2), a divalent group represented by １ and Z ２ is one F and the other CF ３ It is more preferable that:

[0145] The compound represented by the general formula (4) is a compound having a hydrophilic group (Y ３ ) except for the above, it is also preferable that the compound has a C—F bond and does not have a C—H bond. ｉ , X ｊ , and X ｋ All of the are F and R ａ is preferably a perfluoroalkylene group having one or more carbon atoms, and the perfluoroalkylene group may be either linear or branched, may be either cyclic or acyclic, and may contain at least one catenary heteroatom. The number of carbon atoms in the perfluoroalkylene group may be 2 to 20, or may be 4 to 18.

[0146] The compound represented by the general formula (4) may be partially fluorinated. That is, the compound represented by the general formula (4) may have a hydrophilic group (Y ３ ), it is also preferred that the alkyl group has at least one hydrogen atom bonded to a carbon atom and at least one fluorine atom bonded to a carbon atom.

[0147] The compound represented by general formula (4) is also preferably a compound represented by the following formula (4a): CF ２ ═CF—O—Rf ０ -Y ３ (4a) (wherein, Y ３ is a hydrophilic group, and Rf ０ is a perfluorinated divalent linking group which may be linear or branched, cyclic or acyclic in structure, saturated or unsaturated, substituted or unsubstituted, and which optionally contains one or more heteroatoms selected from the group consisting of sulfur, oxygen, and nitrogen.

[0148] The compound represented by general formula (4) is also preferably a compound represented by the following formula (4b): CH ２ =CH-O-Rf ０ -Y ３ (4b) (wherein, Y ３ is a hydrophilic group, and Rf ０ is a perfluorinated divalent linking group defined by formula (4a).

[0149] In the general formula (4), Y ３ Ha-OSO ３ One of the preferred embodiments is Y. ３ Ga-OSO ３ When M is a compound represented by general formula (4), CF ２ =CF(OCF ２ CF ２ CH ２ OSO ３ M), CF ２ =CF(O(CF ２ ) ４ CH ２ OSO ３ M), CF ２ =CF(OCF ２ CF (CF ３ ) CH２ OSO ３ M), CF ２ =CF(OCF ２ CF (CF ３ ) OCF ２ CF ２ CH ２ OSO ３ M), CH ２ =CH((CF ２ ) ４ CH ２ OSO ３ M), CF ２ =CF(OCF ２ CF ２ SO ２ N (CH ３ ) CH ２ CH ２ OSO ３ M), CH ２ =CH(CF ２ CF ２ CH ２ OSO ３ M), CF ２ =CF(OCF ２ CF ２ CF ２ CF ２ SO ２ N (CH ３ ) CH ２ CH ２ OSO ３ In the above formula, M is the same as above.

[0150] In the general formula (4), Y ３ Ha-SO ３ M is also a preferred embodiment. ３ Ga-SO ３ When M is a compound represented by general formula (4), CF ２ =CF(OCF ２ CF ２ SO ３ M), CF ２ =CF(O(CF ２ ) ４ SO ３ M), CF ２ =CF(OCF ２ CF (CF ３ ) SO ３ M), CF ２=CF(OCF ２ CF (CF ３ ) OCF ２ CF ２ SO ３ M), CH ２ =CH(CF ２ CF ２ SO ３ M), CF ２ =CF(OCF ２ CF (CF ３ ) OCF ２ CF ２ CF ２ CF ２ SO ３ M), CH ２ =CH((CF ２ ) ４ SO ３ M), CH ２ =CH((CF ２ ) ３ SO ３ In the above formula, M is the same as above.

[0151] In the general formula (4), Y ３ It is also a preferred embodiment that Y is -COOM. ３ is -COOM, the compound represented by general formula (4) is CF ２ =CF(OCF ２ CF ２ COOM), C.F. ２ =CF(OCF ２ CF ２ CF ２ COOM), C.F. ２ =CF(O(CF ２ ) ５ COOM), C.F. ２ =CF(OCF ２ CF (CF ３ ) COOM), CF ２ =CF(OCF ２ CF (CF ３ ) O(CF ２ ) ｎ COOM) (n is greater than 1), CH ２ =CH(CF ２ CF ２ COOM), CH ２ =CH((CF ２) ４ COOM), CH ２ =CH((CF ２ ) ３ COOM), C.F. ２ =CF(OCF ２ CF ２ SO ２ NR'CH ２ COOM), C.F. ２ =CF(O(CF ２ ) ４ SO ２ NR'CH ２ COOM), C.F. ２ =CF(OCF ２ CF (CF ３ ) SO ２ NR'CH ２ COOM), C.F. ２ =CF(OCF ２ CF (CF ３ ) OCF ２ CF ２ SO ２ NR'CH ２ COOM), CH ２ =CH(CF ２ CF ２ SO ２ NR'CH ２ COOM), C.F. ２ =CF(OCF ２ CF (CF ３ ) OCF ２ CF ２ CF ２ CF ２ SO ２ NR'CH ２ COOM), CH ２ =CH((CF ２ ) ４ SO ２ NR'CH ２ COOM), CH ２ =CH((CF ２ ) ３ SO ２ NR'CH ２ In the above formula, R' is H or C １－４ is an alkyl group, and M is the same as above.

[0152] In the general formula (4), Y ３ Ha-OPO３ M or -OP(O)(OM) ２ It is also a preferred embodiment that ３ Ga-OPO ３ M or -OP(O)(OM) ２ In this case, the compound represented by the general formula (4) is CF ２ =CF(OCF ２ CF ２ CH ２ OP (O) (OM) ２ ), CF ２ =CF(O(CF ２ ) ４ CH ２ OP (O) (OM) ２ ), CF ２ =CF(OCF ２ CF (CF ３ ) CH ２ OP (O) (OM) ２ ), CF ２ =CF(OCF ２ CF (CF ３ ) OCF ２ CF ２ CH ２ OP (O) (OM) ２ ), CF ２ =CF(OCF ２ CF ２ SO ２ N (CH ３ ) CH ２ CH ２ OP (O) (OM) ２ ), CF ２ =CF(OCF ２ CF ２ CF ２ CF ２ SO ２ N (CH ３ ) CH ２ CH ２ OP (O) (OM) ２ ), C.H. ２ =CH(CF ２ CF ２ CH ２ OP (O) (OM) ２ , C.H. ２ =CH((CF ２ ) ４ CH ２ OP (O) (OM)２ ), C.H. ２ =CH((CF ２ ) ３ CH ２ OP (O) (OM) ２ In the above formula, M is the same as above.

[0153] In the general formula (4), Y ３ Ha-PO ３ M or -P(O)(OM) ２ It is also a preferred embodiment that ３ Ga-PO ３ M or -P(O)(OM) ２ In this case, the compound represented by the general formula (4) is CF ２ =CF(OCF ２ CF ２ P(O)(OM) ２ ), CF ２ =CF(O(CF ２ ) ４ P(O)(OM) ２ ), CF ２ =CF(OCF ２ CF (CF ３ ) P (O) (OM) ２ ), CF ２ =CF(OCF ２ CF (CF ３ ) OCF ２ CF ２ P(O)(OM) ２ ), C.H. ２ =CH(CF ２ CF ２ P(O)(OM) ２ ), C.H. ２ =CH((CF ２ ) ４ P(O)(OM) ２ ), C.H. ２ =CH((CF ２ ) ３ P(O)(OM) ２ ) and the like, in which M is the same as above.

[0154] The compound represented by the general formula (4) includes a compound represented by the general formula (5): CX ２ =CY(-CZ ２ -O-Rf-Y ３) (5) (In the formula, X is the same or different and is -H or -F; Y is -H, -F, an alkyl group or a fluorine-containing alkyl group; Z is the same or different and is -H, -F, an alkyl group or a fluorine-containing alkyl group. Rf is a fluorine-containing alkylene group having 1 to 40 carbon atoms or a fluorine-containing alkylene group having 2 to 100 carbon atoms and an ether bond. Y ３ is the same as above.), a compound represented by general formula (6): CX ２ =CY(-O-Rf-Y ３ ) (6) (In the formula, X is the same or different and is -H or -F, Y is -H, -F, an alkyl group or a fluorine-containing alkyl group, and Rf is a fluorine-containing alkylene group having 1 to 40 carbon atoms or a fluorine-containing alkylene group having an ether bond and having 2 to 100 carbon atoms. Y ３ is the same as above.) and a compound represented by general formula (7): CX ２ =CY(-Rf-Y ３ ) (7) (In the formula, X is the same or different and is -H or -F, Y is -H, -F, an alkyl group or a fluorine-containing alkyl group, and Rf is a fluorine-containing alkylene group having 1 to 40 carbon atoms or a fluorine-containing alkylene group having an ether bond and having 2 to 100 carbon atoms. Y ３ is the same as above.) The fluorine-containing alkylene group having 2 to 100 carbon atoms and an ether bond is an alkylene group that does not contain a structure in which an oxygen atom is at the terminal and contains an ether bond between carbon atoms.

[0155] In general formula (5), X is -H or -F. Both Xs may be -F, or at least one X may be -H. For example, one X may be -F and the other may be -H, or both Xs may be -H.

[0156] In general formula (5), Y is -H, -F, an alkyl group or a fluorine-containing alkyl group. The alkyl group is an alkyl group that does not contain a fluorine atom, and may have one or more carbon atoms. The alkyl group preferably has six or fewer carbon atoms, more preferably four or fewer carbon atoms, and even more preferably three or fewer carbon atoms. The fluorine-containing alkyl group is an alkyl group that contains at least one fluorine atom, and may have one or more carbon atoms. The fluorine-containing alkyl group preferably has six or fewer carbon atoms, more preferably four or fewer carbon atoms, and even more preferably three or fewer carbon atoms. Y may be -H, -F or -CF ３ is preferred, and —F is more preferred.

[0157] In general formula (5), Z's may be the same or different and are -H, -F, an alkyl group, or a fluoroalkyl group. The alkyl group is an alkyl group that does not contain a fluorine atom, and may have one or more carbon atoms. The alkyl group preferably has six or fewer carbon atoms, more preferably four or fewer carbon atoms, and even more preferably three or fewer carbon atoms. The fluorine-containing alkyl group is an alkyl group that contains at least one fluorine atom, and may have one or more carbon atoms. The fluorine-containing alkyl group preferably has six or fewer carbon atoms, more preferably four or fewer carbon atoms, and even more preferably three or fewer carbon atoms. The Z's may be -H, -F, or -CF ３ is preferred, and —F is more preferred.

[0158] In general formula (5), it is preferable that at least one of X, Y, and Z contains a fluorine atom. For example, X may be —H, and Y and Z may be —F.

[0159] In general formula (5), Rf is a fluorine-containing alkylene group having 1 to 40 carbon atoms, or a fluorine-containing alkylene group having 2 to 100 carbon atoms and an ether bond. The number of carbon atoms in the fluorine-containing alkylene group is preferably 2 or more. Also, the number of carbon atoms is preferably 30 or less, more preferably 20 or less, and even more preferably 10 or less. Examples of the fluorine-containing alkylene group include -CF ２ -, -CH ２ CF ２ -, -CF ２ CF ２ -, -CF ２ CH ２ -, -CF２ CF ２ CH ２ -, -CF(CF ３ ) -, -CF(CF ３ )CF ２ -, -CF(CF ３ ) CH ２ The fluorine-containing alkylene group is preferably a perfluoroalkylene group.

[0160] The number of carbon atoms of the fluorine-containing alkylene group having an ether bond is preferably 3 or more. The number of carbon atoms of the fluorine-containing alkylene group having an ether bond is preferably 60 or less, more preferably 30 or less, and even more preferably 12 or less. Examples of the fluorine-containing alkylene group having an ether bond include those represented by the following formula: (In the formula, Z １ is F or CF ３ ;Z ２ and Z ３ are H or F; Z ４ is H, F or CF ３ ; p1+q1+r1 is an integer of 1 to 10; s1 is 0 or 1; t1 is an integer of 0 to 5). Specific examples of the fluorine-containing alkylene group having an ether bond include -CF(CF ３ )CF ２ -O-CF(CF ３ )-,-(CF(CF ３ )CF ２ -O) ｎ -CF (CF ３ )-(wherein n is an integer from 1 to 10), -CF(CF ３ )CF ２ -O-CF(CF ３ ) CH ２ -, -(CF(CF ３ )CF ２ -O) ｎ -CF (CF ３ ) CH ２ - (wherein n is an integer of 1 to 10), -CH ２ CF ２ CF ２ O-CH ２ CF ２ CH ２ -, -CF ２CF ２ CF ２ O-CF ２ CF ２ -, -CF ２ CF ２ CF ２ O-CF ２ CF ２ CH ２ -, -CF ２ CF ２ O-CF ２ -, -CF ２ CF ２ O-CF ２ CH ２ The fluorine-containing alkylene group having an ether bond is preferably a perfluoroalkylene group.

[0161] In the general formula (5), Y ３ is -COOM, -SO ３ M or -OSO ３ M (M is H, metal atom, NR ７ｙ ４ , optionally substituted imidazolium, optionally substituted pyridinium or optionally substituted phosphonium, R ７ｙ are H or organic groups, and may be the same or different. Any two of them may be bonded to each other to form a ring. ７ｙ The organic group in R is preferably an alkyl group. ７ｙ As the group, H or C １－１０ is preferably an organic group represented by the formula: １－４ More preferred are organic groups represented by the formula: １－４ The metal atom includes alkali metals (Group 1) and alkaline earth metals (Group 2), and Na, K, or Li is preferred. M represents —H, a metal atom, or NR ７ ４ is preferred, and —H, an alkali metal (Group 1), an alkaline earth metal (Group 2), or NR ７ ４ is more preferred, and —H, —Na, —K, —Li or NH ４ is more preferred, and —H, —Na, —K or NH ４is even more preferred, and —H, —Na or NH ４ is particularly preferred, and —H or —NH ４ The most preferred is the above Y ３ As the group, -COOM or -SO ３ M is preferred, and —COOM is more preferred.

[0162] The compound represented by general formula (5) is preferably a compound (5a) represented by general formula (5a): CH ２ =CF(-CF ２ -O-Rf-Y ３ ) (5a) (wherein Rf and Y ３ is the same as above.)

[0163] Specific examples of the compound represented by general formula (5a) include compounds represented by the following formula:

[0164]

[0165] (In the formula, Z １ is F or CF ３ ;Z ２ and Z ３ are H or F; Z ４ is H, F or CF ３ p1+q1+r1 are an integer of 0 to 10; s1 is 0 or 1; t1 is an integer of 0 to 5; Y ３ is the same as above. However, Z ３ and Z ４ are both H, then p1+q1+r1+s1 is not 0). More specifically, compounds represented by the following formula are exemplified:

[0166]

[0167] Among them,

[0168]

[0169] It is preferable that:

[0170] The compound represented by general formula (5a) includes compounds represented by formula (5a) ３ is preferably -COOM, and in particular CH ２ =CFCF ２ OCF (CF ３ ) COOM, and CH２ =CFCF ２ OCF (CF ３ )CF ２ OCF (CF ３ )COOM (wherein M is as defined above), and CH ２ =CFCF ２ OCF (CF ３ ) COOM is more preferred.

[0171] The compound represented by general formula (5) is preferably a compound (5b) represented by general formula (5b): CX ２ ２ =CFCF ２ -O-(CF(CF ３ )CF ２ O) ｎ５ -CF (CF ３ )-Y ３ (5b) (where each X ２ are the same and represent F or H. n5 represents 0 or an integer of 1 to 10, Y ３ is the same as the above definition.)

[0172] In the formula (5b), n5 is preferably 0 or an integer of 1 to 5, more preferably 0, 1 or 2, and even more preferably 0 or 1, in terms of the stability of the resulting aqueous dispersion. ３ is preferably -COOM in that it provides adequate water solubility and stability of the aqueous dispersion, and M is preferably H or NH in that it is less likely to remain as an impurity and the heat resistance of the resulting molded article is improved. ４ It is preferable that:

[0173] Examples of the compound represented by the formula (5b) include CH ２ =CFCF ２ OCF (CF ３ ) COOM, C.H. ２ =CFCF ２ OCF (CF ３ )CF ２ OCF (CF ３ ) COOM (wherein M is as defined above).

[0174] Further, examples of the compound represented by the general formula (5) include a compound represented by the general formula (5c).

[0175] CF ２ =CFCF ２ -O-Rf-Y ３ (5c) (wherein Rf and Y ３ is the same as above)

[0176] More specifically, etc.

[0177] In general formula (6), X is -H or -F. Both Xs may be -F, or at least one X may be -H. For example, one X may be -F and the other may be -H, or both Xs may be -H.

[0178] In general formula (6), Y is -H, -F, an alkyl group or a fluorine-containing alkyl group. The alkyl group is an alkyl group that does not contain a fluorine atom, and may have one or more carbon atoms. The alkyl group preferably has six or fewer carbon atoms, more preferably four or fewer carbon atoms, and even more preferably three or fewer carbon atoms. The fluorine-containing alkyl group is an alkyl group that contains at least one fluorine atom, and may have one or more carbon atoms. The fluorine-containing alkyl group preferably has six or fewer carbon atoms, more preferably four or fewer carbon atoms, and even more preferably three or fewer carbon atoms. The Y may be -H, -F or -CF ３ is preferred, and —F is more preferred.

[0179] In general formula (6), it is preferable that at least one of X and Y contains a fluorine atom. For example, X may be —H, and Y and Z may be —F.

[0180] In general formula (6), Rf is a fluorine-containing alkylene group having 1 to 40 carbon atoms, or a fluorine-containing alkylene group having 2 to 100 carbon atoms and an ether bond. The number of carbon atoms in the fluorine-containing alkylene group is preferably 2 or more. The number of carbon atoms in the fluorine-containing alkylene group is preferably 30 or less, more preferably 20 or less, and even more preferably 10 or less. Examples of the fluorine-containing alkylene group include -CF ２ -, -CH ２ CF ２ -, -CF２ CF ２ -, -CF ２ CH ２ -, -CF ２ CF ２ CH ２ -, -CF(CF ３ ) -, -CF(CF ３ )CF ２ -, -CF(CF ３ ) CH ２ The fluorine-containing alkylene group is preferably a perfluoroalkylene group.

[0181] In the above general formula (6), Y ３ is -COOM, -SO ３ M or -OSO ３ M (M is H, metal atom, NR ７ｙ ４ , optionally substituted imidazolium, optionally substituted pyridinium or optionally substituted phosphonium, R ７ｙ are H or organic groups, and may be the same or different. Any two of them may be bonded to each other to form a ring. ７ｙ The organic group in R is preferably an alkyl group. ７ｙ As the group, H or C １－１０ is preferably an organic group represented by the formula: １－４ More preferred are organic groups represented by the formula: １－４ The metal atom includes alkali metals (Group 1) and alkaline earth metals (Group 2), and Na, K, or Li is preferred. M represents —H, a metal atom, or NR ７ ４ is preferred, and —H, an alkali metal (Group 1), an alkaline earth metal (Group 2), or NR ７ ４ is more preferred, and —H, —Na, —K, —Li or NH ４ is more preferred, and —H, —Na, —K or NH ４ is even more preferred, and —H, —Na or NH ４ is particularly preferred, and —H or —NH ４ The most preferred is the above Y ３As the group, -COOM or -SO ３ M is preferred, and —COOM is more preferred.

[0182] The compound represented by general formula (6) is preferably at least one selected from the group consisting of compounds represented by general formulas (6a), (6b), (6c), (6d), and (6e). ２ =CF-O-(CF ２ ) ｎ１ -Y ３ (6a) (wherein n1 represents an integer of 1 to 10, and Y ３ is the same as the definition above.) CF ２ =CF-O-(CF ２ C (CF ３ ) F) ｎ２ -Y ３ (6b) (wherein n2 represents an integer of 1 to 5, and Y ３ is the same as the definition above.) CF ２ =CF-O-(CFX １ ) ｎ３ -Y ３ (6c) (wherein, X １ is F or CF ３ n3 represents an integer of 1 to 10; Y ３ is the same as the definition above.) CF ２ =CF-O-(CF ２ CFX １ O) ｎ４ -(CF ２ ) ｎ６ -Y ３ (6d) (wherein n4 represents an integer of 1 to 10, n6 represents an integer of 1 to 3, and Y ３ and X １ is the same as the definition above.) CF ２ =CF-O-(CF ２ CF ２ CFX １ O) ｎ５ -CF ２ CF ２ CF ２ -Y ３ (6e) (wherein n5 represents an integer of 0 to 10, and Y ３ and X １ is the same as the above definition.)

[0183] In the formula (6a), n1 is preferably an integer of 5 or less, and more preferably an integer of 2 or less. ３ is preferable in that it can provide a suitable water solubility and stability of the aqueous dispersion. ３ M is preferably H or NH, in that M is unlikely to remain as an impurity and the heat resistance of the resulting molded article is improved. ４ It is preferable that:

[0184] Examples of the compound represented by the formula (6a) include CF ２ =CF-O-CF ２ COOM, C.F. ２ =CF(OCF ２ CF ２ COOM), C.F. ２ =CF(OCF ２ CF ２ CF ２ COOM), C.F. ２ =CF-O-CF ２ SO ３ M., C.F. ２ =CF(OCF ２ CF ２ SO ３ M), CF ２ =CF(OCF ２ CF ２ CF ２ SO ３ M) (wherein M is as defined above).

[0185] In the formula (6b), n2 is preferably an integer of 3 or less in terms of the stability of the resulting aqueous dispersion, and Y ３ is preferable in that it provides suitable water solubility and stability of the aqueous dispersion. ３ M is preferably H or NH, in that M is unlikely to remain as an impurity and the heat resistance of the resulting molded article is improved. ４ It is preferable that:

[0186] In the formula (6c), n3 is preferably an integer of 5 or less in terms of water solubility, and Y ３ is preferable in that it provides suitable water solubility and stability of the aqueous dispersion.３ M is preferably H or NH in that dispersion stability is improved. ４ It is preferable that:

[0187] In the formula (6d), the X １ In terms of the stability of the aqueous dispersion, -CF ３ In terms of water solubility, n4 is preferably an integer of 5 or less, and Y ３ is preferable to -COOM or -SO in that it provides suitable water solubility and stability of the aqueous dispersion. ３ Preferably, M is H or NH. ４ It is preferable that:

[0188] Examples of the compound represented by the formula (6d) include CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ COOM, C.F. ２ = CFOCF ２ CF (CF ３ ) OCF ２ COOM, C.F. ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ CF ２ COOM, C.F. ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ SO ３ M., C.F. ２ = CFOCF ２ CF (CF ３ ) OCF ２ SO ３ M., C.F. ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ CF ２ SO ３ M (wherein M is H, NH ４ or an alkali metal.

[0189] In the general formula (6e), n5 is preferably an integer of 5 or less in terms of water solubility, and Y ３ is preferable to -COOM or -SO in that it provides suitable water solubility and stability of the aqueous dispersion. ３ Preferably, M is H or NH. ４ It is preferable that:

[0190] Examples of the compound represented by general formula (6e) include CF ２ = CFOCF ２ CF ２ CF ２ COOM, C.F. ２ = CFOCF ２ CF ２ CF ２ SO ３ M (wherein M is H, NH ４ or an alkali metal.

[0191] In general formula (7), Rf is preferably a fluorine-containing alkylene group having 1 to 40 carbon atoms. In general formula (7), at least one of X and Y preferably contains a fluorine atom.

[0192] The compound represented by general formula (7) is represented by general formula (7a): CF ２ =CF-(CF ２ ) ｎ１ -Y ３ (7a) (wherein n1 represents an integer of 1 to 10, and Y ３ is the same as defined above.) and a compound represented by general formula (7b): CF ２ =CF-(CF ２ C (CF ３ ) F) ｎ２ -Y ３ (7b) (wherein n2 represents an integer of 1 to 5, and Y ３ is as defined above. ３ is -SO ３ M or -COOM is preferred, where M is H, a metal atom, NR ７ｙ ４, optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium. ７ｙ represents H or an organic group.

[0193] In the formula (7a), n1 is preferably an integer of 5 or less, and more preferably an integer of 2 or less. ３ is preferable in that it can provide a suitable water solubility and stability of the aqueous dispersion. ３ M is preferably H or NH, in that M is unlikely to remain as an impurity and the heat resistance of the resulting molded article is improved. ４ The compound represented by the formula (7a) is preferably, for example, CF ２ =CFCF ２ COOM, C.F. ２ =CFCF ２ SO ３ M (wherein M is as defined above).

[0194] In the formula (7b), n2 is preferably an integer of 3 or less in terms of the stability of the resulting aqueous dispersion, and Y ３ is preferable in that it provides suitable water solubility and stability of the aqueous dispersion. ３ M is preferably H or NH, in that M is unlikely to remain as an impurity and the heat resistance of the resulting molded article is improved. ４ It is preferable that:

[0195] The modified monomer preferably contains modified monomer (A), and preferably contains 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 contains a compound represented by general formula (5a) or general formula (5c).

[0196] When using a modified monomer (A) as the modified monomer, the content of the modified monomer (A) unit is preferably in the range of 0.00001 to 1.0 mass% relative to the total polymerized units of the TFE polymer (PTFE).The lower limit is more preferably 0.0001 mass%, more preferably 0.0005 mass%, even more preferably 0.001 mass%, and even more preferably 0.005 mass%.The upper limit is, in order of preference, 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%, and 0.01 mass%.

[0197] The low-molecular-weight PTFE may have a carboxyl group. For example, when polymerizing TFE, the carboxyl group is introduced to the molecular chain end by using a water-soluble radical polymerization initiator such as a water-soluble peroxide as a polymerization initiator. On the other hand, in suspension polymerization, an oil-soluble radical polymerization initiator is often used, and when an oil-soluble radical polymerization initiator is used, a carboxyl group is not introduced to the molecular chain. The low-molecular-weight PTFE preferably has a carboxyl group at the molecular end. The presence of a carboxyl group in the low-molecular-weight PTFE further improves the dispersibility of the powder in other materials.

[0198] Low molecular weight PTFE main chain carbon number 10 ６ The number of carboxyl groups per unit is preferably 29 or less. ６ The number of functional groups per unit is preferably 25 or less.

[0199] The number of carboxyl groups can be measured in accordance with the method for analyzing terminal groups described in Japanese Patent Laid-Open No. 4-20507. Specifically, a powder containing particles of low molecular weight PTFE is preformed by hand pressing to prepare a film of approximately 0.1 mm thickness. The prepared film is subjected to infrared absorption spectroscopy. Perfluorinated terminal PTFE prepared by bringing PTFE into contact with fluorine gas is also subjected to infrared absorption spectroscopy, and the number of terminal carboxyl groups is calculated from the difference spectrum between the two using the following formula: Number of carboxyl groups (number of carbon atoms: 10 ６(per particle) = (l × K) / t, l: absorbance, K: correction coefficient, t: film thickness (mm), the absorption frequency of the carboxyl group is 3560 cm －１ , the correction coefficient is set to 440.

[0200] The powder of the present disclosure can be suitably used as a molding material, ink, cosmetics, paint, grease, office automation equipment components, a toner modifying additive, an additive for plating solutions, etc. Examples of the molding material include engineering plastics such as polyoxybenzoyl polyester, polyimide, polyamide, polyamideimide, polyacetal, polycarbonate, and polyphenylene sulfide. The powder of the present disclosure is particularly suitable as a thickening agent for grease.

[0201] The powder of the present disclosure can be used as an additive to molding materials, for example, to improve the non-stickiness and sliding properties of copy rolls, to improve the texture of engineering plastic molded products such as furniture surface sheets, automobile dashboards, and home appliance covers, and to improve the slip properties and wear resistance of machine parts that generate mechanical friction, such as light-load bearings, gears, cams, push-button phone buttons, projectors, camera parts, and sliding materials.

[0202] The powder of the present disclosure can be used as a paint additive to improve the slipperiness of varnishes and paints.The powder of the present disclosure can be used as a cosmetic additive to improve the slipperiness of cosmetics such as foundations.

[0203] The powder of the present disclosure is also suitable for applications such as improving the oil repellency or water repellency of waxes and the like, and for improving the slipperiness of greases and toners.

[0204] The powder of the present disclosure can also be used as an electrode binder for secondary batteries and fuel cells, a hardness adjuster for electrode binders, a water-repellent treatment agent for electrode surfaces, and the like.

[0205] The powder of the present disclosure and a lubricating oil can also be used to prepare a grease. The grease is characterized by containing the powder of the present disclosure and a lubricating oil, and therefore the powder of the present disclosure is uniformly and stably dispersed in the lubricating oil, resulting in excellent properties such as load-bearing capacity, electrical insulation, and low moisture absorption.

[0206] The lubricating oil (base oil) may be a mineral oil or a synthetic oil. Examples of the lubricating oil (base oil) include paraffinic and naphthenic mineral oils, synthetic hydrocarbon oils, ester oils, fluorinated oils, and synthetic oils such as silicone oils. From the viewpoint of heat resistance, fluorinated oils are preferred. Examples of the fluorinated oil include perfluoropolyether oils and oligomers of trifluorochloroethylene. The oligomers of trifluorochloroethylene may have a weight average molecular weight of 500 to 1,200.

[0207] 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, diurethane compounds, and mixtures thereof.

[0208] The grease preferably contains 0.1 to 50 mass %, more preferably 0.5 mass % or more, and even more preferably 30 mass % or less of the powder of the present disclosure. If the amount of powder is too large, the grease may become too hard and may not exhibit sufficient lubrication, whereas if the amount of powder is too small, the grease may not exhibit sufficient sealing properties.

[0209] The grease may also contain solid lubricants, extreme pressure agents, antioxidants, oiliness agents, rust inhibitors, viscosity index improvers, detergents and dispersants, and the like.

[0210] The powder of the present disclosure can be suitably produced by the production method of the present disclosure. Next, the production method of the present disclosure will be described in detail.

[0211] 2. Powder Manufacturing Method In the manufacturing method of the present disclosure, after preparing an aqueous dispersion, a relatively large amount of a radical generator is added to the obtained aqueous dispersion, the aqueous dispersion containing the radical generator is heat-treated, and the low-molecular-weight polytetrafluoroethylene in the heat-treated aqueous dispersion is recovered and dried at a relatively low temperature. By using such a manufacturing method, it is possible to manufacture a powder containing low-molecular-weight polytetrafluoroethylene particles that has excellent fine dispersibility in other materials and has a reduced content of fluorine-containing compounds having hydrophilic groups.

[0212] That is, by using the production method of the present disclosure, it is possible to produce a powder having a content of a fluorine-containing compound having a hydrophilic group of 250 mass ppb or less. Furthermore, by using the production method of the present disclosure, it is possible to produce a powder having a specific surface area of ​​7 to 50 m ２ / g of powder can be produced.

[0213] Each step and the materials used in each step will be described in detail below.

[0214] (Polymerization of Tetrafluoroethylene) In the production method of the present disclosure, first, tetrafluoroethylene is polymerized in a reactor in the presence of a fluorine-containing surfactant, a polymerization initiator, and an aqueous medium to prepare an aqueous dispersion containing primary particles of low-molecular-weight polytetrafluoroethylene.

[0215] The polymerization of tetrafluoroethylene can be carried out by charging a reactor with tetrafluoroethylene, a fluorine-containing surfactant, a polymerization initiator, an aqueous medium, and, if necessary, other additives, stirring the contents of the reactor, maintaining the reactor at a predetermined polymerization temperature, and then adding a predetermined amount of polymerization initiator to initiate the polymerization reaction. After the start of the polymerization reaction, tetrafluoroethylene, a polymerization initiator, a fluorine-containing surfactant, a chain transfer agent, etc. may be added additionally depending on the purpose. The polymerization method of tetrafluoroethylene is not particularly limited, but an emulsion polymerization method is preferred.

[0216] The above-mentioned modifying monomer may be polymerized together with tetrafluoroethylene. The amounts of tetrafluoroethylene and the optional modifying monomer used are preferably such that the modified polytetrafluoroethylene contained in the powder of the present disclosure is obtained.

[0217] (Fluorine-containing surfactant) As the fluorine-containing surfactant used in the polymerization of tetrafluoroethylene, the fluorine-containing surfactants that can be contained in the powder of the present disclosure can be mentioned, and the same ones are preferably used.

[0218] The amount of the fluorine-containing surfactant added is preferably 10 ppm by mass to 10% by mass, more preferably 100 ppm by mass or more, even more preferably 300 ppm by mass or more, and more preferably 5% by mass or less, and even more preferably 1% by mass or less, relative to the aqueous medium.

[0219] (Polymerization initiator) The polymerization initiator used for the polymerization of tetrafluoroethylene is not particularly limited as long as it can generate radicals within the polymerization temperature range, and known oil-soluble and / or water-soluble polymerization initiators can be used. Furthermore, it can also be combined with a reducing agent or the like to initiate polymerization as a redox. The concentration of the polymerization initiator is appropriately determined depending on the type of monomer, the molecular weight of the desired low-molecular-weight polytetrafluoroethylene, and the reaction rate.

[0220] As the polymerization initiator, an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator can be used.

[0221] The oil-soluble radical polymerization initiator may be a known oil-soluble peroxide, for example, dialkyl peroxycarbonates such as diisopropyl peroxydicarbonate and disec-butyl peroxydicarbonate, peroxyesters such as t-butyl peroxyisobutyrate and t-butyl peroxypivalate, dialkyl peroxides such as di-t-butyl peroxide, and the like. Also usable are di(ω-hydro-dodecafluoroheptanoyl) peroxide, di(ω-hydro-tetradecafluorooctanoyl) peroxide, di(ω-hydro-hexadecafluorononanoyl) peroxide, di(perfluorobutyryl) peroxide, di(perfluorovaleryl) peroxide, di(perfluorohexanoyl) peroxide, di(perfluoroheptanoyl) peroxide, di(perfluorooctanoyl) peroxide, di(perfluorononanoyl) peroxide, di(ω-chloro Representative examples include di[perfluoro(or fluorochloro)acyl]peroxides such as di(ω-chlorohexafluorobutyryl)peroxide, di(ω-chlorodecafluorohexanoyl)peroxide, di(ω-chlorotetradecafluorooctanoyl)peroxide, ω-hydro-dodecafluoroheptanoyl-ω-hydrohexadecafluorononanoyl-peroxide, ω-chloro-hexafluorobutyryl-ω-chloro-decafluorohexanoyl-peroxide, ω-hydrododecafluoroheptanoyl-perfluorobutyryl-peroxide, di(dichloropentafluorobutanoyl)peroxide, di(trichlorooctafluorohexanoyl)peroxide, di(tetrachloroundecafluorooctanoyl)peroxide, di(pentachlorotetradecafluorodecanoyl)peroxide, and di(undecachlorodotriacontafluorodocosanoyl)peroxide.

[0222] The water-soluble radical polymerization initiator may be a known water-soluble peroxide, such as ammonium salts, potassium salts, or sodium salts of persulfuric acid, perboric acid, perchloric acid, perphosphoric acid, or percarbonate; organic peroxides such as disuccinic acid peroxide or diglutaric acid peroxide; t-butyl permaleate; t-butyl hydroperoxide; etc. A reducing agent such as a sulfite may also be contained, and the amount used may be 0.1 to 20 times the amount of the peroxide.

[0223] For example, when polymerization is carried out at a low temperature of 30°C or less, it is preferable to use a redox initiator that combines an oxidizing agent and a reducing agent as the polymerization initiator. Examples of oxidizing agents include persulfates, organic peroxides, potassium permanganate, manganese triacetate, and cerium ammonium nitrate. Examples of reducing agents include sulfites, bisulfites, bromates, diimines, and oxalic acid. Examples of persulfates include ammonium persulfate and potassium persulfate. Examples of sulfites include sodium sulfite and ammonium sulfite. In order to increase the decomposition rate of the initiator, it is also preferable to add a copper salt or an iron salt to the redox initiator combination. Examples of copper salts include copper(II) sulfate, and examples of iron salts include iron(II) sulfate.

[0224] Examples of the redox initiator include potassium permanganate / oxalic acid, potassium permanganate / ammonium oxalate, ammonium persulfate / bisulfite / iron sulfate, manganese triacetate / oxalic acid, cerium ammonium nitrate / oxalic acid, and bromate / bisulfite, with potassium permanganate / oxalic acid being preferred. When using a redox initiator, either an oxidizing agent or a reducing agent may be charged into a polymerization vessel in advance, and then the other may be added continuously or intermittently to initiate polymerization. For example, when potassium permanganate / oxalic acid is used, it is preferred to charge oxalic acid into a polymerization vessel and then continuously add potassium permanganate thereto.

[0225] The amount of polymerization initiator to be added is not particularly limited, but may be added all at once, stepwise, or continuously at the beginning of polymerization in an amount (for example, several ppm relative to water concentration) that does not significantly decrease the polymerization rate. The upper limit is a range in which the reaction temperature can be increased while removing heat from the equipment using the heat of polymerization reaction, and a more preferred upper limit is a range in which the heat of polymerization reaction can be removed from the equipment.

[0226] During the polymerization of tetrafluoroethylene, the radical concentration during polymerization can be adjusted by adding a decomposing agent. Examples of decomposing agents include sulfites, bisulfites, bromates, diimines, oxalic acid, copper salts, and iron salts. Examples of sulfites include sodium sulfite and ammonium sulfite. Examples of copper salts include copper(II) sulfate, and examples of iron salts include iron(II) sulfate. The amount of decomposing agent added is in the range of 25 to 300% by mass relative to the amount of oxidizing agent combined as a polymerization initiator (redox initiator). The amount of decomposing agent added is preferably 25 to 150% by mass, more preferably 50 to 100% by mass. Furthermore, the decomposing agent is preferably added after 5% by mass of the total tetrafluoroethylene consumed in the polymerization reaction has been polymerized, and more preferably after 10% by mass has been polymerized. The amount of decomposing agent added is preferably an amount equivalent to 0.1 to 20 ppm by mass of the aqueous medium used, and more preferably an amount equivalent to 3 to 10 ppm by mass.

[0227] (Aqueous Medium) The aqueous medium used in the polymerization of tetrafluoroethylene is a reaction medium for polymerization, and refers to a liquid containing water. The aqueous medium is not particularly limited as long as it contains water, and may contain water and, for example, a fluorine-free organic solvent such as an ether or a ketone, and / or a fluorine-containing organic solvent having a boiling point of 40° C. or less.

[0228] As the aqueous medium, an aqueous medium containing only water or an aqueous medium containing only water and a fluorine-free organic solvent is preferred, and an aqueous medium containing only water is more preferred, because it allows the polymerization of tetrafluoroethylene to proceed smoothly and also prevents a decrease in the efficiency of removing the fluorine-containing compound having a hydrophilic group.

[0229] The content of water in the aqueous medium is preferably 90% or more, more preferably 95% or more, even more preferably 99.0% or more, still more preferably 99.5% or more, particularly preferably 99.9% or more, and may be 100%, based on the mass of the aqueous medium, in order to smoothly proceed with the polymerization of tetrafluoroethylene and to suppress a decrease in the efficiency of removing the fluorine-containing compound having a hydrophilic group.

[0230] (Chain Transfer Agent) In the production method of the present disclosure, tetrafluoroethylene can be polymerized in the presence of a chain transfer agent. The use of a chain transfer agent can adjust the polymerization rate and molecular weight. Examples of chain transfer agents include esters such as dimethyl malonate, diethyl malonate, methyl acetate, ethyl acetate, butyl acetate, and dimethyl succinate, as well as isopentane, methane, ethane, propane, methanol, isopropanol, acetone, various mercaptans, various halogenated hydrocarbons such as carbon tetrachloride, and cyclohexane.

[0231] The amount of chain transfer agent used is usually 1 to 50,000 ppm by mass, preferably 1 to 20,000 ppm by mass, relative to the total amount of tetrafluoroethylene supplied. The amount of chain transfer agent used is preferably an amount that is completely consumed during the polymerization of tetrafluoroethylene and does not remain in the aqueous dispersion containing low-molecular-weight polytetrafluoroethylene, so as not to reduce the removal efficiency of the fluorine-containing compound having a hydrophilic group as much as possible. Therefore, the amount of chain transfer agent used is more preferably 10,000 ppm by mass or less, even more preferably 5,000 ppm by mass or less, still more preferably 1,000 ppm by mass or less, particularly preferably 500 ppm by mass or less, and most preferably 200 ppm by mass or less, relative to the total amount of tetrafluoroethylene supplied.

[0232] The chain transfer agent may be added all at once to the reaction vessel before the initiation of polymerization, may be added all at once after the initiation of polymerization, may be added in multiple divided portions during the polymerization, or may be added continuously during the polymerization.

[0233] (Other Additives) In the polymerization of tetrafluoroethylene, additives such as a buffer, a pH adjuster, a stabilizing aid, and a dispersion stabilizer can be used. In addition, in the polymerization of tetrafluoroethylene, a radical scavenger or a decomposing agent can be added to adjust the polymerization rate and molecular weight. In addition, in the polymerization of tetrafluoroethylene, a fluorine-free anionic surfactant, a fluorine-free nonionic surfactant, a fluorine-free cationic surfactant, and the like can be used.

[0234] Preferred stabilizing aids include paraffin wax, fluorine-based oil, fluorine-based solvent, and silicone oil. The stabilizing aids may be used alone or in combination of two or more. Paraffin wax is more preferred as the stabilizing aid. Paraffin wax may be liquid, semi-solid, or solid at room temperature, but saturated hydrocarbons having 12 or more carbon atoms are preferred. The melting point of the paraffin wax is generally preferably 40 to 65°C, more preferably 50 to 65°C.

[0235] The amount of the stabilizing aid used is preferably 0.1 to 12% by mass, more preferably 0.1 to 8% by mass, based on the mass of the aqueous medium used. It is desirable that the stabilizing aid is sufficiently hydrophobic so that it is completely separated from the aqueous dispersion after polymerization and does not become a contaminating component.

[0236] (Polymerization Conditions) The polymerization of tetrafluoroethylene can be carried out under ordinary pressure and temperature. Usually, the polymerization temperature is 5 to 120°C, and the polymerization pressure is 0.05 to 10 MPaG. The polymerization temperature and polymerization pressure are appropriately determined depending on the type of monomer, the molecular weight of the desired low-molecular-weight polytetrafluoroethylene, the reaction rate, etc.

[0237] (Aqueous dispersion obtained by polymerization) By polymerization of tetrafluoroethylene, an aqueous dispersion containing primary particles of low-molecular-weight polytetrafluoroethylene is obtained. The content of low-molecular-weight polytetrafluoroethylene in the aqueous dispersion after polymerization is usually 8 to 50 mass% based on the aqueous dispersion.

[0238] The aqueous dispersion obtained by polymerizing tetrafluoroethylene usually contains, in addition to low-molecular-weight polytetrafluoroethylene, the fluorine-containing surfactant used in polymerizing tetrafluoroethylene as a fluorine-containing compound having a hydrophilic group. Furthermore, the aqueous dispersion obtained by polymerizing tetrafluoroethylene may contain, in addition to low-molecular-weight polytetrafluoroethylene, a fluorine-containing compound having a hydrophilic group produced by polymerization of a monomer.

[0239] A typical compound as the fluorine-containing compound having a hydrophilic group in the aqueous dispersion obtained by polymerization is a fluorine-containing compound having a hydrophilic group with a molecular weight of 1000 g / mol or less. According to the production method of the present disclosure, it is possible to finally produce a powder in which the content of the fluorine-containing compound having a hydrophilic group with a molecular weight of 1000 g / mol or less is reduced.

[0240] In one embodiment of the aqueous dispersion obtained by polymerization, the fluorine-containing compound having a hydrophilic group contains a fluorine-containing surfactant added during polymerization. The fluorine-containing surfactant added during polymerization is as described above for the fluorine-containing surfactant used in the polymerization of tetrafluoroethylene.

[0241] The content of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion obtained by polymerization may be 200 ppb by mass or more, 300 ppb by mass or more, or 400 ppb by mass or more, and may be 10% by mass or less, 1% by mass or less, or 0.5% by mass or less, relative to the aqueous dispersion.

[0242] The content of the fluorine-containing 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.

[0243] 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): General formula (I): F(CF ２ ) ｎ１ COOM (I) (wherein n1 is an integer of 3 to 13, and M is H, a metal atom, NR ７ ４ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium, and R ７ is H or an organic group.

[0244] When the aqueous dispersion obtained by polymerization contains at least compound (I) represented by general formula (I) as a fluorine-containing compound having a hydrophilic group, the content of compound (I) 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.

[0245] In one embodiment of the aqueous dispersion obtained by polymerization, the fluorine-containing compound having a hydrophilic group contains a compound represented by the following general formula (H1): General formula (H1): [X-Rf-A － ] ｉ M ｉ＋ (Wherein, X represents H, Cl, Br, F or I; Rf represents a linear or branched partially or fully fluorinated aliphatic group, or a linear or branched partially or fully fluorinated aliphatic group interrupted by at least one oxygen atom; A － is an acid group, M ｉ＋ represents a cation having a valence i, where i is an integer from 1 to 3.

[0246] In one embodiment of the aqueous dispersion obtained by polymerization, the aqueous dispersion contains a compound represented by the following general formula (H2) as the fluorine-containing compound having a hydrophilic group. ｎ－１ F ２ｎ－１ COO － ]M ＋(wherein n is an integer of 9 to 14, M ＋ represents a cation.)

[0247] It is known that compounds represented by general formula (H2) (perfluoroalkanoic acids) are formed during polymerization when perfluoro(alkyl vinyl ether) or the like is used as a monomer (see WO 2019 / 161153).

[0248] In one embodiment of the aqueous dispersion obtained by polymerization, the aqueous dispersion contains a compound represented by the following general formula (H3) as the fluorine-containing compound having a hydrophilic group. １ -O-L-CO ２ － ]M ＋ (In the formula, R １ represents a linear or branched partially or fully fluorinated aliphatic group, or a linear or branched partially or fully fluorinated aliphatic group interrupted by at least one oxygen atom; L represents a linear or branched non-fluorinated, partially fluorinated or fully fluorinated alkylene group; M represents a linear or branched non-fluorinated, partially fluorinated or fully fluorinated alkylene group; ＋ represents a cation.)

[0249] In one embodiment of the aqueous dispersion obtained by polymerization, the fluorine-containing compound having a hydrophilic group contains a compound represented by general formula (H4). General formula (H4): H-Rf ｎ０ -Y ０ (wherein, Rf ｎ０ is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which some or all of the H atoms are substituted with F, and the alkylene group may contain one or more ether bonds, and some of the H atoms may be substituted with Cl. Y ０ is an anionic group.)

[0250] The compound represented by the general formula (H4) includes compounds represented by any of the following general formulas: General formula (H4-1): [H—(CF ２ ) ｍ１ CO ２ － ]M ＋ (wherein m1 is an integer of 3 to 19, M ＋represents a cation.) General formula (H4-2): [H—(CF ２ ) ｍ２ -(CF(CF ３ )) ｍ３ -CO ２ － ]M ＋ (wherein m2 is an integer of 1 to 17, m3 is an integer of 1 to 9, M ＋ represents a cation, provided that m2 and m3 are selected so as to satisfy the relationship 3≦(m2+2×m3)≦19, and the order of occurrence of each repeating unit in the formula is arbitrary.

[0251] (Removal of tetrafluoroethylene or recovery of aqueous dispersion) In the production method of the present disclosure, after preparing an aqueous dispersion by polymerization, and before adding a radical generator to the aqueous dispersion, at least one of the following operations can be carried out: (a) removing the tetrafluoroethylene remaining in the reactor from the reactor, and (b) recovering the aqueous dispersion in the reactor and storing it in a container different from the reactor. In particular, using a method of removing tetrafluoroethylene from the reactor is preferred because subsequent steps can be carried out in the same reactor used in polymerization, thereby improving powder productivity. When a modified monomer is polymerized together with tetrafluoroethylene, the modified monomer is also removed from the reactor together with tetrafluoroethylene.

[0252] After preparing the aqueous dispersion, it is preferable to stop stirring the contents of the reactor before removing tetrafluoroethylene or recovering the aqueous dispersion, since this makes the subsequent operations easier and enables the polymerization of tetrafluoroethylene to be stopped smoothly.

[0253] The method for removing tetrafluoroethylene from the reactor is not particularly limited. After preparing the aqueous dispersion, if desired, stirring of the reactor contents may be stopped and tetrafluoroethylene may be removed from the reactor by venting until the pressure inside the reactor reaches normal pressure, or by reducing the pressure inside the reactor to less than 0.0 MPaG, or by supplying an inert gas into the reactor to replace the tetrafluoroethylene in the reactor with an inert gas such as nitrogen gas. Alternatively, the entire amount of tetrafluoroethylene in the reactor may be reacted and converted into low-molecular-weight polytetrafluoroethylene, thereby removing tetrafluoroethylene from the reactor. The removal of tetrafluoroethylene remaining in the reactor from the reactor can be carried out to an extent that the polymerization reaction of tetrafluoroethylene is sufficiently stopped, so long as a small amount of tetrafluoroethylene remains in the reactor. The removed tetrafluoroethylene can be recovered by known means. The recovered tetrafluoroethylene may be reused to produce low-molecular-weight polytetrafluoroethylene.

[0254] As a method for removing tetrafluoroethylene from the reactor, a method is also suitable in which, after preparing the aqueous dispersion, stirring of the contents of the reactor is stopped if desired, the pressure in the reactor is reduced to less than 0.0 MPaG, and then an inert gas is supplied into the reactor. The reduction in pressure in the reactor and the supply of the inert gas may be repeated several times.

[0255] When tetrafluoroethylene polymerization is carried out at a temperature above room temperature, the reactor may be cooled before or after removing tetrafluoroethylene from the reactor. When tetrafluoroethylene is removed from the reactor by means of evacuation or nitrogen substitution, there is a possibility that unreacted modified monomer, particularly in liquid form, may remain in the reactor, but by cooling the reactor, the progress of the reaction of the unreacted modified monomer can be sufficiently suppressed.

[0256] The method for recovering the aqueous dispersion in the reactor and storing it in a container different from the reactor used for polymerization is not particularly limited. For example, after preparing the aqueous dispersion, stirring of the content of the reactor may be stopped if desired, the reactor may be opened, and the aqueous dispersion in the reactor may be poured into another container, or after preparing the aqueous dispersion, stirring of the content of the reactor may be stopped if desired, and the aqueous dispersion may be supplied from the reactor to another container via a pipe connecting the reactor and another container.

[0257] In order to terminate the polymerization reaction of tetrafluoroethylene, a polymerization terminator (radical scavenger) may be added.

[0258] As the polymerization terminator, a compound that does not have the ability to re-initiate after addition or chain transfer to a free radical in the polymerization system is used. Specifically, a compound that easily undergoes a chain transfer reaction with a primary radical or a propagating radical to generate a stable radical that does not subsequently react with a monomer, or a compound that easily undergoes an addition reaction with a primary radical or a propagating radical to generate a stable radical, is used. The activity of what is generally called a chain transfer agent is characterized by the chain transfer constant and the re-initiation efficiency, and among chain transfer agents, those with a re-initiation efficiency of almost 0% are called polymerization terminators. Examples of polymerization terminators include aromatic hydroxy compounds, aromatic amines, N,N-diethylhydroxylamine, quinone compounds, terpenes, thiocyanates, and cupric chloride (CuCl ２) is preferred. Examples of aromatic hydroxy compounds include unsubstituted phenol, polyhydric phenol, salicylic acid, m- or p-salicylic acid, gallic acid, naphthol, etc. Examples of the unsubstituted phenol include o-, m-, or p-nitrophenol, o-, m-, or p-aminophenol, p-nitrosophenol, etc. Examples of polyhydric phenols include catechol, resorcinol, hydroquinone, pyrogallol, phloroglucinol, naphthresorcinol, etc. Examples of aromatic amines include o-, m-, or p-phenylenediamine, benzidine, etc. Examples of the quinone compounds include hydroquinone, o-, m-, or p-benzoquinone, 1,4-naphthoquinone, alizarin, etc. Examples of thiocyanates include ammonium thiocyanate (NH ４ Examples of the polymerization terminator include potassium thiocyanate (KSCN), sodium thiocyanate (NaSCN), etc. Among these, quinone compounds are preferred, and hydroquinone is more preferred.

[0259] (Radical Generator) In the production method of the present disclosure, after carrying out at least one of the operations (a) and (b), and before subjecting the aqueous dispersion to heat treatment, a radical generator is added to the aqueous dispersion in an amount equivalent to 5 molar times or more the molar amount of the fluorine-containing surfactant used in polymerization. By adding a relatively large amount of radical generator, the content of the fluorine-containing compound having a hydrophilic group can be sufficiently reduced.

[0260] The aqueous dispersion to which the radical generator is added may be the aqueous dispersion remaining in the reactor, or may be the aqueous dispersion recovered from the reactor and stored in a separate container.

[0261] The radical generator is not particularly limited as long as it is a compound that can decompose at the temperature during heat treatment to generate radicals. As the radical generator, a water-soluble radical generator is preferred because it can easily diffuse radicals in the aqueous dispersion.

[0262] Examples of the radical generator include organic peroxides, inorganic peroxides, organic azo compounds, and combinations of oxidizing agents and reducing agents. At least one selected from the group consisting of inorganic peroxides, organic peroxides, and combinations of oxidizing agents and reducing agents is preferred.

[0263] The inorganic peroxide is preferably a water-soluble inorganic peroxide. Examples of the inorganic peroxide include hydrogen peroxide, perchlorates, perborates, perphosphates, percarbonates, and persulfates, with persulfates being preferred. The persulfates are preferably at least one selected from the group consisting of ammonium persulfate, sodium persulfate, and potassium persulfate, with ammonium persulfate being more preferred.

[0264] The organic peroxide is preferably a water-soluble organic peroxide, and examples of the organic peroxide include peroxydicarbonates such as disuccinic acid peroxide and diglutaric acid peroxide.

[0265] The radical generator may be a combination of an oxidizing agent and a reducing agent. By using a combination of an oxidizing agent and a reducing agent, radicals can be generated from the radical generator by a redox reaction between the oxidizing agent and the reducing agent, so that the temperature during heat treatment can be lowered.

[0266] Examples of oxidizing agents include persulfates, organic peroxides, potassium permanganate, manganese triacetate, and cerium ammonium nitrate. Examples of reducing agents include sulfites, bisulfites, bromates, diimines, and oxalic acid. Examples of persulfates include ammonium persulfate and potassium persulfate. Examples of sulfites include sodium sulfite and ammonium sulfite. It is also preferable to add a copper salt or an iron salt to increase the decomposition rate of the oxidizing agent. Examples of copper salts include copper(II) sulfate, and examples of iron salts include iron(II) sulfate.

[0267] Examples of combinations of oxidizing agents and reducing agents include potassium permanganate / oxalic acid, ammonium persulfate / bisulfite / iron sulfate, manganese triacetate / oxalic acid, cerium ammonium nitrate / oxalic acid, and bromate / bisulfite, with potassium permanganate / oxalic acid being preferred. When using a combination of an oxidizing agent and a reducing agent, either the oxidizing agent or the reducing agent may be added to the aqueous dispersion in advance, and then the other may be added continuously or intermittently.

[0268] The amount of radical generator added is preferably 5 times or more by mole, more preferably 8 times or more by mole, even more preferably 10 times or more by mole, and preferably 1000 times or less by mole, more preferably 500 times or less by mole, and even more preferably 100 times or less by mole, relative to the molar amount of the fluorine-containing surfactant used in the polymerization, since this can further improve the removal efficiency of the fluorine-containing compound having a hydrophilic group. Since the production method of the present disclosure is for producing a powder, it does not matter if a relatively large amount of radical generator is added, even if low-molecular-weight polytetrafluoroethylene in the aqueous dispersion precipitates.

[0269] The method for adding the radical generator is not particularly limited. The radical generator may be added directly to the aqueous dispersion, or a solution containing the radical generator may be prepared and added to the aqueous dispersion. The radical generator may be added while stirring the aqueous dispersion, or the aqueous dispersion may be stirred after adding the radical generator.

[0270] The temperature of the aqueous dispersion to which the radical generator is added is not particularly limited, and may be the temperature of the aqueous dispersion after polymerization of tetrafluoroethylene, a temperature reached by cooling the aqueous dispersion after polymerization of tetrafluoroethylene, or the temperature of heat treatment. That is, the radical generator may be added to the aqueous dispersion, and then the aqueous dispersion may be heated for heat treatment, or the aqueous dispersion may be heated to a temperature for heat treatment, and then the radical generator may be added to the aqueous dispersion.

[0271] (Heat Treatment) In the production method of the present disclosure, the aqueous dispersion to which the radical generator has been added (aqueous dispersion containing a radical generator) is subjected to heat treatment. By subjecting the aqueous dispersion containing a relatively large amount of the radical generator to heat treatment, the content of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion can be surprisingly reduced.

[0272] Before the heat treatment, the content of low-molecular-weight polytetrafluoroethylene in the aqueous dispersion may be adjusted by a known method such as concentration or dilution.

[0273] The content of low-molecular-weight polytetrafluoroethylene in the aqueous dispersion to be subjected to heat treatment is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, based on the mass of the aqueous dispersion, since the aqueous dispersion of low-molecular-weight polytetrafluoroethylene can be produced with high productivity without impairing the removal efficiency of fluorine-containing compounds having hydrophilic groups. The upper limit of the content of low-molecular-weight polytetrafluoroethylene is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less.

[0274] The content of the fluorine-containing surfactant added during polymerization in the aqueous dispersion to be subjected to heat treatment is preferably 500 ppm by mass or more, more preferably 1000 ppm by mass or more, and preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less, relative to the mass of low-molecular-weight polytetrafluoroethylene in the aqueous dispersion.

[0275] The content of the fluorine-containing compound having a hydrophilic group produced by polymerization of tetrafluoroethylene in the aqueous dispersion to be subjected to heat treatment is preferably 500 ppb by mass or more, more preferably 1000 ppb by mass or more, and preferably 1.0% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0.01% by mass or less, relative to the mass of low-molecular-weight polytetrafluoroethylene in the aqueous dispersion.

[0276] The content of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion to be subjected to heat treatment (the total content of the fluorine-containing surfactant added during polymerization and the content of the fluorine-containing compound having a hydrophilic group produced by polymerization of tetrafluoroethylene) is preferably 500 ppm by mass or more, more preferably 1000 ppm by mass or more, and preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less, based on the low-molecular-weight polytetrafluoroethylene in the aqueous dispersion.

[0277] The temperature of the heat treatment is preferably 35°C or higher, more preferably 40°C or higher, even more preferably 45°C or higher, particularly preferably 50°C or higher, and preferably 120°C or lower, more preferably 110°C or lower, even more preferably 100°C or lower, and particularly preferably 90°C or lower, since this can further improve the removal efficiency of fluorine-containing compounds having hydrophilic groups. When heat-treating an aqueous dispersion containing an added radical generator, the heat treatment temperature is preferably equal to or higher than the temperature at which the radical generator decomposes to generate radicals (decomposition temperature). Since the production method of the present disclosure is for producing a powder, it does not matter if low-molecular-weight polytetrafluoroethylene in the aqueous dispersion precipitates by heat-treating at a relatively high temperature.

[0278] In the heat treatment of the aqueous dispersion, as long as the aqueous dispersion can be maintained at a desired temperature or higher, it is not necessary to heat the aqueous dispersion.For example, if the temperature at which tetrafluoroethylene is polymerized is sufficiently high and the temperature of the resulting aqueous dispersion is also sufficiently high, the heat treatment can be started before the resulting aqueous dispersion is cooled.However, since this makes it easier to control the temperature of the heat treatment, it is preferable 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 temperature range, and maintain that temperature for a certain period of time.The temperature of the aqueous dispersion to be subjected to the heat treatment may be, for example, 30°C or less.

[0279] When the heat treatment is performed while heating the aqueous dispersion, the heating means is not particularly limited. For example, the aqueous dispersion may be heated by placing a container containing the aqueous dispersion in a thermostatic bath, or the aqueous dispersion may be placed in a container equipped with a heater and heated by the heater.

[0280] The pressure of the heat treatment is not particularly limited and may be atmospheric pressure. For example, when the temperature of the heat treatment is relatively high and it is necessary to suppress boiling of the aqueous dispersion, the pressure of the heat treatment may be a pressure higher than atmospheric pressure.

[0281] The heat treatment time is preferably 15 minutes or more, more preferably 30 minutes or more, even more preferably 60 minutes or more, and is preferably 1200 minutes or less, more preferably 900 minutes or less, even more preferably 600 minutes or less, since this can further improve the efficiency of removing the fluorine-containing compound having a hydrophilic group.

[0282] The heat treatment may be carried out while stirring the aqueous dispersion.

[0283] (Preparation of Wet Powder and Drying of Wet Powder) In the manufacturing method of the present disclosure, a wet powder containing low-molecular-weight polytetrafluoroethylene particles is prepared by coagulating low-molecular-weight polytetrafluoroethylene in a heat-treated aqueous dispersion, and the wet powder is dried at a temperature not exceeding 70°C lower than the melting point of the low-molecular-weight polytetrafluoroethylene to prepare a powder containing low-molecular-weight polytetrafluoroethylene particles.

[0284] The method for coagulating 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, as needed, followed by stirring more vigorously than during the polymerization of tetrafluoroethylene in a container equipped with a stirrer. The low-molecular-weight polytetrafluoroethylene may be coagulated by adding a water-soluble organic compound such as methanol or acetone; an inorganic salt such as potassium nitrate or ammonium carbonate; or an inorganic acid such as hydrochloric acid, sulfuric acid, or nitric acid to the aqueous dispersion as a coagulant, followed by stirring. After coagulating the low-molecular-weight polytetrafluoroethylene, a wet powder containing low-molecular-weight polytetrafluoroethylene particles can be recovered. The wet powder may include a precipitate of low-molecular-weight polytetrafluoroethylene precipitated by adding a radical generator and a precipitate of low-molecular-weight polytetrafluoroethylene precipitated by heat treatment.

[0285] Before drying the wet powder, the wet powder may be washed. Water or an organic solvent can be used to wash the wet powder. Washing may be performed once or multiple times. Examples of organic solvents used for washing include ethers, halogenated hydrocarbons, aromatic hydrocarbons, pyridine, nitriles, nitrogen-containing polar organic compounds, dimethyl sulfoxide, and alcohols.

[0286] In the manufacturing method of the present disclosure, the wet powder is dried at a temperature equal to or lower than the melting point of the low-molecular-weight polytetrafluoroethylene by 70° C. Drying the wet powder at a relatively low temperature makes it possible to obtain a powder that has excellent fine dispersibility in other materials.

[0287] The drying temperature of the wet powder is preferably not more than 80° C. lower than the melting point of the low-molecular-weight polytetrafluoroethylene, and more preferably not more than 100° C. lower than the melting point of the low-molecular-weight polytetrafluoroethylene.

[0288] The drying temperature for the wet powder is preferably 250° C. or lower, more preferably 230° C. or lower, and even more preferably 220° C. or lower. The drying temperature for the wet powder is preferably 100° C. or higher, more preferably 120° C. or higher, even more preferably 140° C. or higher, and even more preferably 160° C. or higher. If the drying temperature is too low, drying takes a long time, which may result in a decrease in productivity.

[0289] The obtained powder may be classified or granulated. The obtained powder may also be formed into pellets. In the manufacturing method of the present disclosure, since a powder having excellent fine dispersibility in other materials after drying is directly obtained, it is also a preferred embodiment that the dried powder is not subjected to any post-treatment.

[0290] Although the embodiments have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the claims.

[0291] <1> According to a first aspect of the present disclosure, there is provided a powder containing particles of 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 powder having a specific surface area of ​​7 to 50 m ２ / g. <2> According to a second aspect of the present disclosure, there is provided the powder according to the first aspect, in which the melting point of the low-molecular-weight polytetrafluoroethylene is 322 to 333°C. <3> According to a third aspect of the present disclosure, there is provided the powder according to the first aspect, in which the melting viscosity of the low-molecular-weight polytetrafluoroethylene at 380°C is 1 x 10 ２ ~7 x 10 ５ <4> According to a fourth aspect of the present disclosure, there is provided a powder according to the first or second aspect, wherein the low-molecular-weight polytetrafluoroethylene has carboxyl groups, and the number of the carboxyl groups is 10 or less. ６<5> According to a fifth aspect of the present disclosure, there is provided a powder according to any one of the first to fourth aspects, wherein the low-molecular-weight polytetrafluoroethylene particles have an average particle size of 1.0 to 30 μm. <6> According to a sixth aspect of the present disclosure, there is provided a powder according to any one of the first to fourth aspects, wherein the low-molecular-weight polytetrafluoroethylene particles have an average particle size of 1.0 to 30 μm. <7> According to a sixth aspect of the present disclosure, there is provided a powder according to any one of the first to fourth aspects, wherein the low-molecular-weight polytetrafluoroethylene particles have an average particle size of 1.0 to 30 μm. ０ According to any one of the first to fifth aspects, there is provided a powder which is a compound represented by the general formula (N ０ ): X ｎ０ -Rf ｎ０ -Y ０ (In the formula, X ｎ０ is H, Cl or F. ｎ０ is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which some or all of the H atoms are substituted with F, and the alkylene group may contain one or more ether bonds, and some of the H atoms may be substituted with Cl. Y ０ is an anionic group.) <7> According to a seventh aspect of the present disclosure, there is provided a powder according to any one of the first to sixth aspects, in which the fluorine-containing compound having a hydrophilic group contains at least a compound (I) represented by general formula (I): General formula (I): F(CF ２ ) ｎ１ COOM (wherein n1 is an integer of 3 to 13, and M is H, a metal atom, or NR ７ ４ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium, and R ７is H or an organic group.) <8> According to an eighth aspect of the present disclosure, there is provided the powder according to the seventh aspect, wherein the content of compound (I) is 25 ppb by mass or less relative to the powder. <9> According to a ninth aspect of the present disclosure, there is provided the powder according to the seventh aspect, wherein the content of compound (I) is 5 ppb by mass or less relative to the powder. <10> According to a tenth aspect of the present disclosure, there is provided a method for producing a powder containing low-molecular-weight polytetrafluoroethylene particles, comprising: polymerizing tetrafluoroethylene in a reactor in the presence of a fluorine-containing surfactant, a polymerization initiator, and an aqueous medium to produce an aqueous dispersion containing primary particles of the low-molecular-weight polytetrafluoroethylene; after producing the aqueous dispersion, performing 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; adding a radical generator to the aqueous dispersion in an amount equivalent to 5 molar times or more the molar amount of the fluorine-containing surfactant used in the polymerization; heat-treating the aqueous dispersion containing the radical generator; coagulating the low-molecular-weight polytetrafluoroethylene in the heat-treated aqueous dispersion to produce a wet powder containing the low-molecular-weight polytetrafluoroethylene particles; and drying the wet powder at a temperature not exceeding 70°C lower than the melting point of the low-molecular-weight polytetrafluoroethylene to produce the powder.

[0292] Next, embodiments of the present disclosure will be described with reference to examples, but the present disclosure is not limited to these examples.

[0293] The values ​​in the examples were measured by the following methods.

[0294] <Content of Fluorine-Containing Compound Having Hydrophilic Group> The content of the fluorine-containing compound having a hydrophilic group contained in the powder was determined as the content of the fluorine-containing compound having a hydrophilic group extracted from the powder.

[0295] 0. Extraction of fluorine-containing compounds having hydrophilic groups from powder 10 g (12.6 mL) of methanol was added to 1 g of powder, and the mixture was subjected to ultrasonic treatment for 2 hours at 60° C. After allowing to stand at room temperature, the solid content was removed to obtain an extract.

[0296] <Content of Compound Represented by General Formula (I)> The content of the compound represented by general formula (I) was determined using a calibration curve for a linear perfluorocarboxylic acid having the same number of carbon atoms. 1. Calibration Curve for Linear Perfluorocarboxylic Acid Five levels of methanol standard solutions of known concentrations of perfluorobutanoic acid, perfluoropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid, perfluoroundecanoic acid, perfluorododecanoic acid, perfluorotridecanoic acid, and perfluorotetradecanoic acid were prepared, and measurements were performed using a liquid chromatograph mass spectrometer (Agilent, Ultivo triple quadrupole LC-MS). Within each concentration range, a calibration curve was created using a first-order approximation from the methanol standard solution concentration and the peak integral value.

[0297] Measurement equipment configuration and LC-MS measurement conditions

[0298] MRM measurement parameters

[0299] 2. Content of Compound Represented by General Formula (I) in Powder Using a liquid chromatograph mass spectrometer, the content of the compound represented by general formula (I) having the number of carbon atoms (n1+1) contained in the extract was measured from a calibration curve. The content of the compound represented by general formula (I) having the number of carbon atoms (n1+1) contained in the powder was calculated using the following relational expression (2): Yn = Xn × 12.6 (2) Yn: Content (mass ppb / powder) of the compound represented by general formula (I) having the number of carbon atoms (n1+1) contained in the powder Xn: Content (ng / mL) of the compound represented by general formula (I) having the number of carbon atoms (n1+1) contained in the extract The lower limit of quantitation for the content of the compound represented by general formula (I) having the number of carbon atoms (n1+1) contained in the powder is 1 mass ppb / powder.

[0300] MRM measurement parameters

[0301] <Measurement of Compound Represented by General Formula (H4-1)> The content of the compound represented by general formula (H4-1) was determined by converting it into perfluorooctanoic acid.

[0302] 1. Calibration curve for the compound represented by general formula (H4-1) Five levels of methanol standard solutions of perfluorooctanoic acid with known concentrations were prepared and measured using a liquid chromatograph mass spectrometer (Agilent, Ultivo triple quadrupole LC-MS). A calibration curve was created for each concentration range using a first-order approximation based on the concentration of the methanol standard solution and the peak integral value.

[0303] Measurement equipment configuration and LC-MS measurement conditions

[0304] MRM measurement parameters

[0305] 2. Content of Compound Represented by General Formula (H4-1) in Powder Using a liquid chromatograph mass spectrometer, the content of the compound represented by general formula (H4-1) and having the number of carbon atoms (m1+1) contained in the extract was measured from a calibration curve. The content of the compound represented by general formula (H4-1) and having the number of carbon atoms (m1+1) contained in the powder was calculated using the following relational expression (5): Ym = Xm × 12.6 (5) Ym: content (mass ppb / powder) of the compound represented by general formula (H4-1) and having the number of carbon atoms (m1+1) contained in the powder Xm: content (ng / mL) of the compound represented by general formula (H4-1) and having the number of carbon atoms (m1+1) contained in the extract The lower limit of quantitation for the content of the compound represented by general formula (H4-1) and having the number of carbon atoms (m1+1) contained in the powder is 1 mass ppb / powder.

[0306] MRM measurement parameters

[0307] <Solid content concentration> Approximately 1 g (X g) of a sample was placed in 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. Based on the heating residue (Z g), the solid content was determined using the formula: P = Z / X × 100 (mass%).

[0308] <Specific Surface Area> Measured by the BET method using a surface analyzer (product name: MONQSORB, manufactured by QUANTA CHLROME Inc.) A mixed gas of 30% nitrogen and 70% helium was used as the carrier gas, and cooling was performed using liquid nitrogen.

[0309] <Melting point> Using a differential scanning calorimeter RDC220 (DSC) manufactured by SII Nanotechnology Inc., after temperature calibration was performed in advance using indium and lead as standard samples, about 3 mg of low molecular weight PTFE powder was placed in an aluminum pan (crimp container), and the temperature was raised at 10°C / min in a temperature range of 250 to 380°C under an air flow of 200 ml / min, and the minimum point of the heat of fusion in the above range was taken as the melting point.

[0310] <Melt Viscosity> According to ASTM D 1238, using a flow tester (manufactured by Shimadzu Corporation) and a 2φ-8L die, measurement was carried out on a 2 g sample that had been preheated at the measurement temperature (380°C) for 5 minutes, while maintaining the temperature under a load of 0.7 MPa.

[0311] <Number of carboxyl groups> The following measurement was carried out in accordance with the method for analyzing terminal groups described in JP-A-4-20507. Low-molecular-weight PTFE powder was preformed by hand pressing to prepare a film approximately 0.1 mm thick. The prepared film was subjected to infrared absorption spectroscopy. Perfluorinated terminal PTFE prepared by bringing PTFE into contact with fluorine gas was also subjected to infrared absorption spectroscopy, and the number of terminal carboxyl groups was calculated from the difference spectrum between the two using the following formula: Number of terminal carboxyl groups (10 carbon atoms) ６ (per particle) = (l × K) / t, l: absorbance, K: correction coefficient, t: film thickness (mm), the absorption frequency of the carboxyl group is 3560 cm －１ , the correction coefficient is set to 440.

[0312] <Average particle diameter> The particle size distribution was measured using a laser diffraction particle size distribution analyzer (manufactured by JEOL Ltd.) without using a cascade, at a pressure of 0.1 MPa, for a measurement time of 3 seconds, and the average particle diameter was set to be equal to the value corresponding to 50% of the integrated particle size distribution obtained.

[0313] Preparation example 1: Except that the amount of charged ammonium perfluorohexanoate is changed from 1.7g to 2.0g, carry out the polymerization reaction of TFE in the same manner as the method described in embodiment 7 of WO2009 / 020187, and finish the reaction.Then, the pressure in reactor is exhausted until atmospheric pressure, and the content is recovered from reactor, and obtain low molecular weight PTFE aqueous dispersion.The solid content concentration of aqueous dispersion is 20.4 mass%.

[0314] Comparative Example 1 Nitric acid was added to the aqueous dispersion of low-molecular-weight PTFE obtained in Production Example 1, and coagulation was caused by applying a strong mechanical shearing force. The obtained wet powder was dried for 18 hours in a hot air circulation dryer at 160°C, thereby obtaining a powder of low-molecular-weight PTFE. The melt viscosity of the obtained powder of low-molecular-weight PTFE was 1.6 x 10 ４ Pa·s, melting point is 329°C, specific surface area is 11.1 m ２ / g, and the average particle size was 4.3 μm.

[0315] Example 1 The low molecular weight PTFE aqueous dispersion obtained in Preparation Example 1 is placed in another reactor, the reactor contents are heated to 80 ° C, and 13.8 g of ammonium persulfate (10 times the molar amount of the fluorine-containing surfactant used in polymerization) is added as a radical generator.Then, the temperature is kept at 80 ° C for 3 hours, and a heat-treated low molecular weight PTFE aqueous dispersion is obtained.Nitric acid is added to the obtained heat-treated low molecular weight PTFE aqueous dispersion, and coagulation is carried out by applying a strong mechanical shearing force.The obtained wet powder is dried in a hot air circulation dryer at 160 ° C for 18 hours, and a low molecular weight PTFE powder is obtained.The melt viscosity of the obtained low molecular weight PTFE powder is 1.6 × 10 ４ Pa·s, melting point is 329°C, specific surface area is 11.0 m ２ / g, average particle size is 4.2 μm, number of carboxyl groups is 10 ６ There were 12 per piece.

[0316] The powder thus obtained contains a compound of general formula (I): F(CF ２ ) ｎ１ COOM and general formula (H4-1): [H—(CF ２ ) ｍ１ CO ２ － ]M＋ The contents of the compounds represented by the formula (I) are shown in Tables 7 and 8.

[0317] Production Example 2: A 6 L stainless steel autoclave equipped with a stainless steel anchor-type stirring blade and a temperature-controlling jacket was charged with 3.6 L of deionized water and 7.2 g of ammonium perfluorohexanoate as a fluorine-based surfactant, and then sealed. After repeatedly injecting nitrogen gas and degassing the system to remove oxygen, 820 mg of ethane as a chain transfer agent was injected in the form of tetrafluoroethylene (TFE). The temperature inside the vessel was increased with stirring, and when the temperature inside the vessel reached 70°C, TFE was again injected.

[0318] As a polymerization initiator, the aqueous solution of ammonium persulfate (APS) 460 mg dissolved in 20 ml of deionized water is introduced into the tank by TFE pressure, and the tank pressure is set to 0.74 MPa.Since the tank pressure decreases due to the decomposition of the polymerization initiator, TFE is continuously supplied, and the tank pressure is maintained at 0.74 MPa.During the reaction, the tank temperature is always adjusted to 70 ° C.When the consumption amount of TFE reaches 1100 g, stirring is stopped, the tank pressure is released to normal pressure, and then the gas phase is replaced with nitrogen, and an aqueous dispersion of low molecular weight PTFE is obtained.

[0319] Example 2 The low molecular weight PTFE aqueous dispersion obtained in Preparation Example 2 is placed in another reactor, the reactor contents are heated to 80 ° C, and 29.7 g of ammonium persulfate (6 times the molar amount of the fluorine-containing surfactant used in polymerization) is added as a radical generator.Then, the temperature is kept at 80 ° C for 3 hours, and a heat-treated low molecular weight PTFE aqueous dispersion is obtained.Nitric acid is added to the obtained heat-treated low molecular weight PTFE aqueous dispersion, and coagulation is carried out by applying a strong mechanical shearing force.The obtained wet powder is dried in a hot air circulation dryer at 160 ° C for 18 hours, and a low molecular weight PTFE powder is obtained.The melt viscosity of the obtained low molecular weight PTFE powder is 4.9 × 10 ３ Pa·s, melting point is 328°C, specific surface area is 19.0 m ２ / g, average particle size is 5.2 μm, number of carboxyl groups is 10 ６ There were 24 per piece.

[0320]

[0321]

Claims

1. A powder containing particles of low molecular weight polytetrafluoroethylene, The powder contains a fluorine-containing compound having a hydrophilic group, and the content of the fluorine-containing compound having a hydrophilic group is 250 ppb by mass or less relative to the powder, Specific surface area: 7 to 50 m ２ / g powder.

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

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

4. The low-molecular-weight polytetrafluoroethylene has a carboxyl group, and the number of the carboxyl groups is 10 or less. ６ 3. The powder according to claim 1 or 2, wherein each particle has 29 or less particles.

5. 3. The powder according to claim 1, wherein the average particle size of the low-molecular-weight polytetrafluoroethylene particles is 1.0 to 30 μm.

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

7. 3. The powder according to claim 1, wherein the fluorine-containing compound having a hydrophilic group contains at least a compound (I) represented by general formula (I). General formula (I): F (CF ２ ) ｎ１ COM (wherein n1 is an integer from 3 to 13, M is H, a metal atom, NR ７ ４ , optionally substituted imidazolium, optionally substituted pyridinium or optionally substituted phosphonium; R ７ is H or an organic group.

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

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

10. A method for producing a powder containing particles of low molecular weight polytetrafluoroethylene, comprising the steps of: preparing an aqueous dispersion containing primary particles of the low-molecular-weight polytetrafluoroethylene by polymerizing tetrafluoroethylene in a reactor in the presence of a fluorine-containing surfactant, a polymerization initiator and an aqueous medium; After preparing the aqueous dispersion, at least one of the following operations is carried out: 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; a radical generator is added to the aqueous dispersion in an amount equivalent to 5 molar times or more the molar amount of the fluorine-containing surfactant used in the polymerization; The aqueous dispersion containing the radical generator is subjected to a heat treatment, preparing a wet powder containing particles of the low-molecular-weight polytetrafluoroethylene by coagulating the low-molecular-weight polytetrafluoroethylene in the heat-treated aqueous dispersion; The wet powder is dried at a temperature equal to or lower than 70° C. below the melting point of the low-molecular-weight polytetrafluoroethylene to produce the powder. Manufacturing method.