Method for producing polytetrafluoroethylene

Abstract

Provided is a method for producing a non-melt-processable polytetrafluoroethylene, the method involving preparing a composition containing an aqueous medium and a non-melt-processable polytetrafluoroethylene by subjecting tetrafluoroethylene to suspension polymerization in the presence of a polymerization initiator and an aqueous medium in a reactor, wherein a polymerization inhibitor for inhibiting polymerization of residual radicals is supplied into the reactor after a polymerization terminator is supplied into the reactor or after the tetrafluoroethylene remaining in the reactor is removed from the reactor.

Description

Polytetrafluoroethylene manufacturing method

[0001] The present disclosure relates to a method for producing polytetrafluoroethylene.

[0002] Patent Document 1 describes a method for producing polytetrafluoroethylene, which comprises bringing tetrafluoroethylene into contact with an aqueous medium containing a water-soluble polymerization initiator to carry out a polymerization reaction, recovering unreacted tetrafluoroethylene after the polymerization reaction, and then washing the contents with an inert gas.

[0003] Special Publication No. 48-034399

[0004] An object of the present disclosure is to provide a method for producing non-melt-processible polytetrafluoroethylene, in which a polytetrafluoroethylene composition obtained by polymerization is treated by a novel method.

[0005] According to the present disclosure, there is provided a method for producing non-melt-processible polytetrafluoroethylene, in which a composition containing an aqueous medium and non-melt-processible polytetrafluoroethylene is prepared by suspension polymerizing tetrafluoroethylene in a reactor in the presence of a polymerization initiator and an aqueous medium, wherein a polymerization inhibitor is supplied into the reactor to inhibit polymerization of residual radicals after supplying a polymerization terminator into the reactor or after removing tetrafluoroethylene remaining in the reactor from the reactor.

[0006] According to the present disclosure, it is possible to provide a method for producing non-melt-processible polytetrafluoroethylene, in which a polytetrafluoroethylene composition obtained by polymerization is treated by a novel method.

[0007] Before specifically describing the present disclosure, some terms used in the present disclosure will be defined or explained.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] 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. The organic group is preferably an alkyl group which may have one or more substituents.

[0012] 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.).

[0013] 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.).

[0014] Specific embodiments of the present disclosure will be described in detail below, but the present disclosure is not limited to the following embodiments.

[0015] A composition obtained by suspension polymerization of tetrafluoroethylene may contain a fluorine-containing compound having a hydrophilic group in addition to non-melt-processable polytetrafluoroethylene.

[0016] In the production method of the present disclosure, tetrafluoroethylene is suspension polymerized in a reactor to produce non-melt-processable polytetrafluoroethylene, a polymerization terminator is supplied into the reactor, or the tetrafluoroethylene remaining in the reactor is removed from the reactor, and then a polymerization inhibitor is supplied into the reactor to inhibit the polymerization of the residual radicals. By using such a production method, polytetrafluoroethylene with a low content of fluorine-containing compounds having hydrophilic groups can be produced.

[0017] That is, the present disclosure relates to a method for producing non-melt-processible polytetrafluoroethylene, in which a composition containing an aqueous medium and non-melt-processible polytetrafluoroethylene is prepared by suspension polymerizing tetrafluoroethylene in a reactor in the presence of a polymerization initiator and an aqueous medium, wherein a polymerization inhibitor is supplied into the reactor to inhibit polymerization of residual radicals after supplying a polymerization terminator into the reactor or after removing tetrafluoroethylene remaining in the reactor from the reactor.

[0018] Each step and the materials used in each step will be described in detail below.

[0019] (Polymerization of Tetrafluoroethylene) In the production method of the present disclosure, non-melt-processible polytetrafluoroethylene is prepared by suspension polymerization of tetrafluoroethylene (TFE) in a reactor in the presence of a polymerization initiator and an aqueous medium.

[0020] By carrying out suspension polymerization of TFE, obtain suspension polymerization particles of polytetrafluoroethylene.Suspension polymerization particles cannot exist in the state of being dispersed in aqueous medium.On the other hand, when TFE is carried out emulsion polymerization to prepare polytetrafluoroethylene, obtain polytetrafluoroethylene in the form of primary particles (emulsion polymerization particles) dispersed in aqueous medium.

[0021] Suspension-polymerized particles typically have a larger average particle size than emulsion-polymerized particles, and the average particle size of suspension-polymerized particles is preferably 200 μm or more, more preferably 400 μm or more, even more preferably 800 μm or more, particularly preferably 1 mm or more, and preferably 100 mm or less.

[0022] In the production method of the present disclosure, the polytetrafluoroethylene obtained by suspension polymerization is a high-molecular-weight polytetrafluoroethylene that is non-melt-processable. Non-melt-processable means that the melt flow rate cannot be measured at a temperature higher than the crystallization melting point in accordance with ASTM D 1238 and D 2116.

[0023] The polytetrafluoroethylene preferably has a standard specific gravity (SSG) of 2.130 to 2.280. The standard specific gravity can be measured in accordance with ASTM D4894. In the present disclosure, when the standard specific gravity (SSG) of polytetrafluoroethylene is within the above range, it means that the polytetrafluoroethylene is high-molecular-weight polytetrafluoroethylene.

[0024] The polytetrafluoroethylene preferably has a peak temperature of 333 to 347°C, more preferably 335 to 347°C. The peak temperature can be specified as the temperature corresponding to the maximum value appearing on a differential thermal (DTA) curve obtained by using a TG / DTA (thermogravimetric / differential thermal analyzer) to raise the temperature of polytetrafluoroethylene that has not been heated to a temperature of 300°C or higher at a rate of 10°C / min. In the present disclosure, when the peak temperature of polytetrafluoroethylene is within the above range, it means that the polytetrafluoroethylene is high-molecular-weight polytetrafluoroethylene.

[0025] Preferably, polytetrafluoroethylene that has not been heated to a temperature of 300°C or higher has at least one endothermic peak in the range of 333 to 347°C in the heat of fusion curve when the temperature is raised at a rate of 10°C / min using a differential scanning calorimeter (DSC), and the heat of fusion between 290 and 350°C calculated from the heat of fusion curve is 52 mJ / mg or more. The heat of fusion of polytetrafluoroethylene is more preferably 55 mJ / mg or more, and even more preferably 58 mJ / mg or more.

[0026] Suspension polymerization can be carried out, for example, by charging a reactor with a monomer such as TFE, an aqueous medium, and other additives as necessary, 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, additional monomers such as TFE, polymerization initiators, chain transfer agents, etc. may be added depending on the purpose.

[0027] (Polymerization initiator) Suspension polymerization can be carried out in the presence of a polymerization initiator. The polymerization initiator 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, polymerization can also be initiated as a redox reaction in combination with a reducing agent or the like. The concentration of the polymerization initiator is appropriately determined depending on the type of monomer, the molecular weight of the target polytetrafluoroethylene, and the reaction rate.

[0028] As the polymerization initiator, an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator can be used.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] During the polymerization of TFE, 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 TFE 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 mass of the aqueous medium used, and more preferably an amount equivalent to 3 to 10 ppm by mass.

[0035] (Aqueous medium) Suspension polymerization is carried out by polymerizing TFE in an aqueous medium under stirring. The aqueous medium 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 ether or ketone, and / or a fluorine-containing organic solvent having a boiling point of 40° C. or less.

[0036] 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, as it allows the polymerization of TFE to proceed smoothly, and an aqueous medium containing only water is more preferred.

[0037] 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, since this allows the polymerization of TFE to proceed smoothly.

[0038] (modified monomer) In the manufacturing method of the present disclosure, it is also preferred to carry out suspension polymerization of TFE and modified monomer.That is, polytetrafluoroethylene can be the homopolytetrafluoroethylene that only contains TFE unit, or can be the modified polytetrafluoroethylene that contains TFE unit and the modified monomer unit that is based on the modified monomer that can copolymerize with TFE.

[0039] The amount of the modified monomer that is added when polymerizing TFE is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, even more preferably 0.03% by mass or more, particularly preferably 0.05% by mass or more, preferably 1.0% by mass or less, more preferably 0.8% by mass or less, even more preferably 0.5% by mass or less, particularly preferably 0.3% by mass or less, based on the amount of the polytetrafluoroethylene obtained.

[0040] The modifying monomer is not particularly limited as long as it can be copolymerized with TFE, and examples thereof include fluoromonomers and non-fluoromonomers. The modifying monomer used may be one type or multiple types.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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:

[0048]

[0049] (wherein m represents 0 or an integer of 1 to 4), and Rf is a group represented by the following formula: CF ３ CF ２ CF ２ -(O-CF(CF ３ )-CF ２ ) ｎ - (wherein n represents an integer of 1 to 4).

[0050] Hydrogen-containing fluoroolefins include CH ２ =CF ２ , CHF=CH ２ , CHF=CF ２ , C.H. ２ =CFCF ３ , C.H. ２ = CHCF ３ , CHF=CHCF ３ (E form), CHF=CHCF ３ (Z-isomer), etc.

[0051] The (perfluoroalkyl)ethylene (PFAE) is not particularly limited, and examples thereof include (perfluorobutyl)ethylene (PFBE) and (perfluorohexyl)ethylene.

[0052] 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).

[0053] 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-CF ２ -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.

[0054] As the modified monomer, from the viewpoint of reactivity with TFE, at least one selected from the group consisting of hexafluoropropylene, perfluoro(alkyl vinyl ether) and (perfluoroalkyl)ethylene is preferred, 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 is more preferred, and at least one selected from the group consisting of perfluoro(methyl vinyl ether) and perfluoro(propyl vinyl ether) is even more preferred.

[0055] (Chain Transfer Agent) In the production method of the present disclosure, TFE can be polymerized in the presence of a chain transfer agent. By using a chain transfer agent, the polymerization rate and molecular weight can be adjusted. Examples of the chain transfer agent include esters such as dimethyl malonate, diethyl malonate, methyl acetate, ethyl acetate, butyl acetate, and dimethyl succinate, as well as isopentane, methane, ethane, propane, methanol, isopropanol, acetone, various mercaptans, various halogenated hydrocarbons such as carbon tetrachloride, and cyclohexane.

[0056] The amount of chain transfer agent used is usually 1 to 50,000 mass ppm, preferably 1 to 20,000 mass ppm, based on the total amount of TFE supplied.The amount of chain transfer agent used is preferably an amount that is completely consumed during the polymerization of TFE and does not remain in the composition containing polytetrafluoroethylene.Therefore, the amount of chain transfer agent used is more preferably 10,000 mass ppm or less, even more preferably 5,000 mass ppm or less, still more preferably 1,000 mass ppm or less, particularly preferably 500 mass ppm or less, and most preferably 200 mass ppm or less, based on the total amount of TFE supplied.

[0057] The chain transfer agent may be added to the reactor all at once before the start of polymerization, may be added all at once after the start of polymerization, may be added in multiple divided portions during polymerization, or may be added continuously during polymerization.

[0058] (Fluorine-containing surfactant) The suspension polymerization can be carried out in the presence or absence of a fluorine-containing surfactant. 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] The anionic fluorine-containing surfactant may be a compound represented by the following general formula (N ０ ): X ｎ０ -Rf ｎ０ -Y ０ (N ０ ) (wherein, X ｎ０ is H, Cl or F. ｎ０ is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which some or all of the H atoms are substituted with F, and the alkylene group may contain one or more ether bonds, and some of the H atoms may be substituted with Cl. ０ is an anionic group. ０ The anionic group is -COOM, -SO ２ M or -SO ３ M, -COOM or -SO ３ M. M may be H, a metal atom, NR ７ ４ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium, and R ７is H or an organic group. The metal atom includes alkali metals (Group 1), alkaline earth metals (Group 2), etc., such as Na, K, or Li. ７ As the group, H or C １－１０ and may be an organic group of the formula: １－４ and may be an organic group of the formula: １－４ M may be H, a metal atom, or an alkyl group of the formula NR ７ ４ may be H, an alkali metal (Group 1), an alkaline earth metal (Group 2), or NR ７ ４ may be H, Na, K, Li or NH ４ The above Rf ｎ０ may be one in which 50% or more of H is substituted with fluorine.

[0064] 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.

[0065] 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.

[0066] 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 14, 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.

[0067] 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).

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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).

[0072] 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).

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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).

[0079] As mentioned above, examples of the anionic fluorine-containing surfactant include carboxylic acid surfactants and sulfonic acid surfactants.

[0080] The fluorine-containing surfactant may be one type of fluorine-containing surfactant or a mixture containing two or more types of fluorine-containing surfactants.

[0081] 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 C—H bond, the polymerization of TFE in the presence of an aqueous medium can be smoothly carried out.

[0082] 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 carbon atoms constituting the hydrophobic group, the polymerization of TFE in the presence of an aqueous medium can be smoothly carried out. The number of carbon atoms in the hydrophobic group of the fluorine-containing surfactant having a hydrophobic group and a hydrophilic group is preferably 1 to 50, more preferably 3 to 20, and even more preferably 6 to 12. The hydrophobic group usually constitutes the above-mentioned "portion excluding the anionic group" of the molecular structure of the fluorine-containing surfactant. As the hydrophilic group, Y ０ Examples of the anionic group include the groups exemplified above for the anionic group of the formula (I). The fluorine-containing surfactant may be a saturated fluorinated surfactant in which all of the carbon atoms bonded to the hydrophobic group have been substituted with fluorine atoms.

[0083] As the fluorine-containing surfactant, among the above-mentioned anionic fluorine-containing surfactants, those represented by the general formula (N １ ), a compound represented by the general formula (N ２ ), a compound represented by the general formula (N ４ ): Rf ｎ４ -O-(CY ｎ１ 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.

[0084] 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 TFE to proceed smoothly in the presence of an aqueous medium.

[0085] 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.

[0086] 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.

[0087] Suspension polymerization can be carried out in the presence or absence of a fluorine-containing surfactant. The amount of fluorine-containing surfactant added in the suspension polymerization method is preferably 2000 mass ppm or less, more preferably 1000 mass ppm or less, still more preferably 500 mass ppm or less, particularly preferably 200 mass ppm or less, and most preferably 100 mass ppm or less, relative to the aqueous medium. The amount of fluorine-containing surfactant may be 0 mass ppm.

[0088] (Polymerization Conditions) TFE polymerization can be carried out under normal pressure and temperature. Usually, the polymerization temperature is 5 to 120°C, and the polymerization pressure is 0.05 to 10 MPaG. The polymerization temperature and polymerization pressure are appropriately determined depending on the type of monomer, the molecular weight of the target polytetrafluoroethylene, the reaction rate, etc.

[0089] (Termination of polymerization) In the manufacturing method of the present disclosure, after the polymerization of TFE produces non-melt-processable polytetrafluoroethylene, by feeding polymerization terminator into reactor, or removing the TFE remaining in reactor and possibly modified monomer from reactor.By these operations, can terminate the polymerization of TFE.

[0090] As a polymerization terminator (radical scavenger), a compound that does not have the ability to reinitiate after addition or chain transfer to a free radical in a 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 reinitiating efficiency, and among chain transfer agents, those with a reinitiating 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.

[0091] The method for removing the TFE remaining in the reactor from the reactor is not particularly limited.After producing polytetrafluoroethylene, if desired, stopping the stirring of the contents of the reactor, and venting the TFE until the pressure in the reactor reaches normal pressure, can be used to remove the TFE from the reactor, or the pressure in the reactor can be reduced to less than 0.0 MPaG, can be used to remove the TFE from the reactor, or an inert gas such as nitrogen gas can be supplied into the reactor to replace the TFE in the reactor with an inert gas.In addition, the total amount of TFE in the reactor can be reacted and converted into polytetrafluoroethylene, so that the TFE can be removed from the reactor.The removal of the TFE remaining in the reactor from the reactor can be carried out to the extent that the polymerization reaction of TFE can be sufficiently stopped, so that a small amount of TFE can remain in the reactor.The removed TFE can be recovered by known means.The recovered TFE can be reused to produce polytetrafluoroethylene.

[0092] As a method for removing TFE from the reactor, after producing polytetrafluoroethylene, if desired, stopping stirring of the contents of the reactor, reducing the pressure in the reactor to less than 0.0 MPaG, and then supplying an inert gas into the reactor is also suitable. The reduction in pressure in the reactor and the supply of an inert gas may be repeated several times.

[0093] When TFE polymerization is carried out at the temperature exceeding normal temperature, before removing TFE from reactor, or after removing TFE from reactor, reactor can be cooled.When removing TFE from reactor by means such as exhaust or nitrogen substitution, there is a possibility that the unreacted fluoromonomer in liquid form remains in reactor, but by cooling reactor, it can sufficiently suppress the progress of the reaction of unreacted fluoromonomer.

[0094] (Composition Obtained by Polymerization) Suspension polymerization of TFE typically results in a composition containing an aqueous medium and non-melt-processible polytetrafluoroethylene.

[0095] When using fluorine-containing surfactant in the polymerization of TFE, in addition to polytetrafluoroethylene, the composition obtained usually contains the fluorine-containing surfactant that is used when polymerizing TFE.In addition to polytetrafluoroethylene, the composition obtained by the polymerization of TFE may contain the fluorine-containing compound that has hydrophilic group and is produced by the polymerization of TFE and sometimes modified monomer.

[0096] 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.

[0097] The fluorine-containing compound having a hydrophilic group in the composition obtained by polymerization is typically 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, polytetrafluoroethylene can be produced with a low content of the fluorine-containing compound having a hydrophilic group with a molecular weight of 1000 g / mol or less.

[0098] In one embodiment of the composition 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 the same as the fluorine-containing surfactant used in the polymerization of TFE described above.

[0099] The content of the fluorine-containing surfactant in the composition obtained by polymerization may be 10 ppm by mass or more, 100 ppm by mass or more, or 1,000 ppm by mass or more, and may be 10% by mass or less, 5% by mass or less, or 1% by mass or less, relative to the polytetrafluoroethylene in the composition.

[0100] The content of the fluorine-containing compound having a hydrophilic group in the composition obtained by polymerization (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 TFE and, if necessary, the modified monomer) may be 10 ppm by mass or more, 100 ppm by mass or more, or 1000 ppm by mass or more, or 10% by mass or less, 5% by mass or less, or 1% by mass or less, relative to the polytetrafluoroethylene in the composition.

[0101] In one embodiment of the composition obtained by polymerization, the fluorine-containing compound having a hydrophilic group contains a compound represented by the following general formula (1): General formula (1): [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.

[0102] In one embodiment of the composition obtained by polymerization, the fluorine-containing compound having a hydrophilic group contains a compound represented by the following general formula (2): General formula (2): [C ｎ－１ F ２ｎ－１ COO － ]M ＋ (wherein n is an integer of 9 to 14, M ＋ represents a cation.)

[0103] It is known that compounds represented by general formula (2) (perfluoroalkanoic acids) are formed during polymerization when perfluoro(alkyl vinyl ether) or the like is used as a fluoromonomer (see WO 2019 / 161153).

[0104] In one embodiment of the composition obtained by polymerization, the fluorine-containing compound having a hydrophilic group contains a compound represented by the following general formula (3): General formula (3): [R１ -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.)

[0105] In one embodiment of the composition obtained by polymerization, the fluorine-containing compound having a hydrophilic group contains a compound represented by general formula (4). General formula (4): [H—(CF ２ ) ｍ CO ２ － ]M ＋ (wherein m is an integer of 3 to 19, M ＋ represents a cation.)

[0106] (Supply of polymerization inhibitor after polymerization) In the present disclosure, after supplying a polymerization terminator into the reactor or after removing TFE remaining in the reactor from the reactor, a polymerization inhibitor is supplied into the reactor to inhibit polymerization of residual radicals.

[0107] By supplying a polymerization inhibitor into the reactor or by removing the TFE remaining in the reactor from the reactor, the polymerization of TFE is usually terminated.In the production method of the present disclosure, after the polymerization of TFE is terminated, a polymerization inhibitor for inhibiting the polymerization of residual radicals is supplied into the reactor, and the composition in the reactor is brought into contact with the newly supplied polymerization inhibitor.When a polymerization terminator is supplied into the reactor before terminating suspension polymerization, that is, during suspension polymerization, the polymerization terminator may remain after the termination of polymerization.The polymerization inhibitor for inhibiting the polymerization of residual radicals is supplied into the reactor after the termination of polymerization, and is distinguished from the polymerization terminator that is supplied into the reactor before the termination of polymerization and remains after the termination of polymerization.

[0108] It has been found that, unexpectedly, by further supplying a polymerization inhibitor after terminating the polymerization of TFE and, if necessary, modified monomer, it is possible to produce polytetrafluoroethylene with a low content of fluorine-containing compounds with hydrophilic groups.At the time of filing this application, there is no data available on the radicals remaining in the reactor after terminating polymerization.However, from the data showing that by adding a polymerization inhibitor, it is possible to produce polytetrafluoroethylene with a low content of fluorine-containing compounds with hydrophilic groups, it is presumed that there are residual radicals in the composition after terminating polymerization, and that the polymerization inhibitor supplied after terminating polymerization inhibits the polymerization of the residual radicals.

[0109] Examples of polymerization inhibitors for inhibiting the polymerization of residual radicals include alcohols, fatty acid esters, alkanes, halogenated hydrocarbons, cycloalkanes, ketones, mercaptans, sulfur, aromatic hydroxy compounds, aromatic amines, aliphatic amines, quinone compounds, hydroquinone compounds, polyoxy compounds, nitro compounds, nitroso compounds, terpenes, thiocyanates, and cupric chloride (CuCl ２ ) At least one selected from the group consisting of

[0110] Examples of alcohols include alcohols having 1 to 5 carbon atoms, such as methanol and isopropanol. Examples of fatty acid esters include dimethyl malonate, diethyl malonate, methyl acetate, ethyl acetate, butyl acetate, and dimethyl succinate. Examples of alkanes include isopentane, methane, ethane, and propane. Examples of halogenated hydrocarbons include carbon tetrachloride. Examples of cycloalkanes include cyclohexane. Examples of ketones include acetone. Examples of mercaptans include methyl mercaptan. Examples of aromatic hydroxy compounds include unsubstituted phenol, polyhydric phenol, salicylic acid, m- or p-salicylic acid, gallic acid, and naphthol. Examples of aromatic amines include o-, m-, or p-phenylenediamine, and benzidine. Examples of aliphatic amines include N,N-dimethylhydroxyamine. Examples of quinone compounds include hydroquinone, o-, m-, or p-benzoquinone, 1,4-naphthoquinone, and alizarin. Examples of polyoxy compounds include polyoxyethylene and polyoxypropylene. Examples of nitro and nitroso compounds include o-, m-, or p-nitrophenol, o-, m-, or p-aminophenol, and p-nitrosophenol. Examples of terpenes include monoterpenes, sesquiterpenes, diterpenes, sesterterpenes, triterpenes, and tetraterpenes. Examples of thiocyanates include ammonium thiocyanate (NH ４ Examples of suitable thiocyanates include potassium thiocyanate (KSCN), potassium thiocyanate (KSCN), and sodium thiocyanate (NaSCN).

[0111] As the polymerization inhibitor for inhibiting the polymerization of residual radicals, alcohols having 1 to 5 carbon atoms are preferred, and at least one selected from the group consisting of methanol and isopropanol is more preferred.

[0112] The polymerization and termination of TFE and the treatment with a polymerization inhibitor for inhibiting the polymerization of residual radicals are usually carried out in the same reactor.In one embodiment, the TFE remaining in the reactor is removed, and then a polymerization inhibitor for inhibiting the polymerization of residual radicals is supplied into the same reactor.In one embodiment, after preparing the composition, a part of the TFE in the pressurized reactor is released from the reactor, thereby reducing the pressure in the reactor to normal pressure, and a polymerization inhibitor for inhibiting the polymerization of residual radicals is supplied into the reactor.

[0113] The supply of a polymerization inhibitor to inhibit the polymerization of residual radicals into the reactor is preferably carried out promptly after the preparation of a composition containing an aqueous medium and polytetrafluoroethylene. By treating the composition obtained by polymerization with a polymerization inhibitor at an early stage, without leaving it to stand, polytetrafluoroethylene having an even lower content of fluorine-containing compounds having hydrophilic groups can be obtained.

[0114] For example, it is preferred to supply a polymerization inhibitor for inhibiting polymerization of residual radicals into the reactor preferably within 10 minutes, more preferably within 5 minutes, from the time when the polymerization terminator is supplied into the reactor or when TFE remaining in the reactor is removed from the reactor.

[0115] The method of supplying the polymerization inhibitor to inhibit the polymerization of residual radicals is not particularly limited. The polymerization inhibitor may be supplied directly to the reactor, or a solution containing the polymerization inhibitor may be prepared and supplied to the reactor. The polymerization inhibitor may be supplied while stirring the composition in the reactor, or the composition in the reactor may be stirred after supplying the polymerization inhibitor.

[0116] The polytetrafluoroethylene content in the composition to be treated with a polymerization inhibitor to inhibit polymerization of residual radicals may be, for example, 5 to 75% by mass. The polytetrafluoroethylene content in the composition is a value obtained by drying 1 g of the composition in a blower dryer at 150°C for 60 minutes, measuring the mass of the heating residue, and calculating the ratio of the mass of the heating residue to the mass (1 g) of the polymer dispersion as a percentage.

[0117] The amount of the polymerization inhibitor supplied to inhibit polymerization of residual radicals is preferably 0.001 to 10% by mass, more preferably 0.005% by mass or more, even more preferably 0.01% by mass or more, still more preferably 0.05% by mass or more, particularly preferably 0.10% by mass or more, more preferably 5.0% by mass or less, and even more preferably 1.0% by mass or less, based on the amount of the aqueous medium.

[0118] In the production method of the present disclosure, it is preferable to supply a polymerization inhibitor to the reactor to inhibit polymerization of residual radicals, and to bring the composition in the reactor into sufficient contact with the polymerization inhibitor.

[0119] The temperature of the composition when it is brought into contact with a polymerization inhibitor for inhibiting polymerization of residual radicals is preferably 5°C or higher, more preferably 15°C or higher, even more preferably 30°C or higher, still more preferably 35°C or higher, and preferably 85°C or lower, more preferably 75°C or lower, still more preferably 65°C or lower, and still more preferably 55°C or lower.

[0120] The time for contacting the composition with the polymerization inhibitor for inhibiting polymerization of residual radicals is preferably 1 minute or more, more preferably 5 minutes or more, even more preferably 10 minutes or more, still more preferably 30 minutes or more, and preferably 24 hours or less, more preferably 12 hours or less, even more preferably 6 hours or less.

[0121] The contact of the composition with the polymerization inhibitor can be carried out while stirring the composition in the reactor. The stirring is preferably carried out with a stirring force sufficient to bring the composition into sufficient contact with the polymerization inhibitor while suppressing aggregation and fibrillation of polytetrafluoroethylene in the composition.

[0122] In one embodiment, by polymerizing TFE while stirring an aqueous medium to prepare a composition, and then, while stirring at a stirring speed of -80% or more and +50% or less compared to the stirring speed during polymerization, the composition and a polymerization inhibitor are contacted.The lower limit of the stirring speed is, in order of preference, -75% or more, -50% or more, -25% or more, and -10% or more, and the upper limit of the stirring speed is preferably +25% or less, more preferably +0% or less.In this way, by carrying out the contact of the composition and the polymerization inhibitor while stirring the composition with the stirring force that is adopted when polymerizing TFE, the composition can be sufficiently contacted with the polymerization inhibitor while suppressing the aggregation and fibrillation of polytetrafluoroethylene in the composition, and therefore, polytetrafluoroethylene with a lower content of fluorine-containing compounds having hydrophilic groups can be obtained.

[0123] (Washing, drying, pulverization, molding) The composition obtained by polymerization can be treated with a polymerization inhibitor to inhibit polymerization of residual radicals, and then the polytetrafluoroethylene in the composition can be washed or dried.

[0124] In the manufacturing method of the present disclosure, TFE is polymerized by suspension polymerization, so polytetrafluoroethylene can be recovered from composition as wet suspension polymerization particles.Therefore, the composition obtained by polymerization is treated with polymerization inhibitor to inhibit the polymerization of residual radical, and then the polytetrafluoroethylene (suspension polymerization particles) in composition can be recovered, and then washed or dried.

[0125] In one embodiment of the production method of the present disclosure, a polymerization inhibitor is supplied into the reactor to inhibit polymerization of residual radicals, and after the composition in the reactor is brought into contact with the polymerization inhibitor, the polytetrafluoroethylene is washed. Water or an organic solvent can be used to wash the polytetrafluoroethylene. Washing may be performed once or multiple times.

[0126] Examples of organic solvents used for washing include ethers, halogenated hydrocarbons, aromatic hydrocarbons, pyridine, nitriles, nitrogen-containing polar organic compounds, dimethyl sulfoxide, and alcohols.

[0127] In one embodiment of the production method of the present disclosure, a polymerization inhibitor is supplied into the reactor to inhibit polymerization of residual radicals, and after the composition in the reactor is brought into contact with the polymerization inhibitor, the polytetrafluoroethylene is dried.

[0128] Examples of methods for drying polytetrafluoroethylene include methods using a dryer, such as a hot air dryer, box dryer, band dryer, tunnel dryer, jet flow dryer, moving bed dryer, rotary dryer, fluidized bed dryer, flash dryer, disk dryer, cylindrical agitator dryer, inverted cone agitator dryer, microwave device, vacuum heat treatment device, box-type electric furnace, flash dryer, vibration dryer, belt dryer, extrusion dryer, and spray dryer.

[0129] The temperature at which polytetrafluoroethylene is dried is preferably less than 300°C, more preferably 280°C or less, even more preferably 250°C or less, preferably 50°C or more, more preferably 100°C or more, even more preferably 120°C or more, and particularly preferably 140°C or more. The drying temperature is the temperature of the atmosphere surrounding the polytetrafluoroethylene, and when hot air is used for drying, it can be specified by measuring the temperature of the hot air. The temperature of the hot air can be measured at the supply port that supplies hot air to the dryer or the exhaust port that exhausts hot air from the dryer, but is preferably measured at the exhaust port.

[0130] Before drying, the polytetrafluoroethylene may be dehydrated. Examples of methods for dehydrating wet polytetrafluoroethylene include a method using a dehydrator. Examples of dehydrators include a vibration dehydrator, a filtration dehydrator, and a centrifugal dehydrator.

[0131] In one embodiment of the manufacturing method of the present disclosure, a polymerization inhibitor for inhibiting polymerization of residual radicals is supplied into a reactor, and the composition in the reactor is contacted with the polymerization inhibitor, and then the polytetrafluoroethylene is pulverized. The pulverization may be performed after drying the polytetrafluoroethylene, after washing the polytetrafluoroethylene, or while washing the polytetrafluoroethylene. In one embodiment, pulverized polytetrafluoroethylene is produced by pulverizing the polytetrafluoroethylene, the pulverized polytetrafluoroethylene is washed, and the washed polytetrafluoroethylene is dried. In another embodiment, coarsely pulverized polytetrafluoroethylene is produced by coarsely pulverizing the polytetrafluoroethylene, and the coarsely pulverized polytetrafluoroethylene is finely pulverized while washing to produce finely pulverized polytetrafluoroethylene, the finely pulverized polytetrafluoroethylene is further washed, and the washed polytetrafluoroethylene is dried.

[0132] The pulverization may be wet pulverization or dry pulverization. Examples of methods for pulverizing polytetrafluoroethylene include pulverization using a pulverizer. Examples of pulverizers include impact pulverizers such as hammer mills, pin mills, high-speed rotary mills, and jet mills, and attrition pulverizers such as cutter mills, feather mills, and colloid mills that pulverize by shearing forces generated by rotary blades and peripheral stators (fixed blades). For pulverization, a combination of multiple pulverizers may be used.

[0133] The temperature at which the grinding treatment is carried out is preferably −200 to 50° C., more preferably 1° C. or higher, more preferably 40° C. or lower, and even more preferably 30° C. or lower.

[0134] The method of pulverizing polytetrafluoroethylene while washing it includes a method of pulverizing polytetrafluoroethylene in water or an organic solvent.For example, water or an organic solvent and polytetrafluoroethylene may be simultaneously supplied to a grinding type grinder such as a cutter mill to pulverize the polytetrafluoroethylene, or water or an organic solvent and polytetrafluoroethylene may be mixed in advance, and the mixture may be supplied to a grinder to pulverize the polytetrafluoroethylene.

[0135] The pulverization may be carried out once, or may be carried out repeatedly until pulverized particles having a desired average particle size or a desired particle size distribution are produced.

[0136] After pulverizing the polytetrafluoroethylene, the obtained pulverized particles may be classified by a known method such as air classification, etc. By classifying, it is possible to remove fine particles with very small particle diameters and coarse particles with very large particle diameters, thereby obtaining polytetrafluoroethylene having a desired average particle diameter or a desired particle size distribution.

[0137] (Polytetrafluoroethylene) By using the production method of the present disclosure, polytetrafluoroethylene with a low content of fluorine-containing compounds having hydrophilic groups can be obtained. The form of polytetrafluoroethylene obtained by the production method of the present disclosure is not particularly limited, and may be, for example, powder.

[0138] The content of the fluorine-containing compound having a hydrophilic group in the polytetrafluoroethylene may be more than 0 mass ppb and less than 300 mass ppb, relative to the polytetrafluoroethylene. A preferred upper limit of the content of the fluorine-containing compound having a hydrophilic group in the polytetrafluoroethylene is 280 mass ppb or less, 260 mass ppb or less, 240 mass ppb or less, 220 mass ppb or less, 200 mass ppb or less, 180 mass ppb or less, 160 mass ppb or less, or 140 mass ppb or less.

[0139] Examples of the fluorine-containing compound having a hydrophilic group include the fluorine-containing surfactants described above for use in the polymerization of polytetrafluoroethylene. Typical fluorine-containing surfactants are those having a molecular weight of 1,000 g / mol or less, preferably 800 g / mol or less.

[0140] In one embodiment of the polytetrafluoroethylene, the compound represented by the following general formula (1) is substantially not contained as a fluorine-containing compound having a hydrophilic group. － ] ｉ M ｉ＋ (Wherein, X represents H, Cl, Br, F or I; Rf represents a linear or branched partially or fully fluorinated aliphatic group, or a linear or branched partially or fully fluorinated aliphatic group interrupted by at least one oxygen atom; A － is an acid group, M ｉ＋ represents a cation having a valence i, where i is an integer from 1 to 3.

[0141] In one embodiment of the polytetrafluoroethylene, the compound represented by the following general formula (2) is substantially not contained as a 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.)

[0142] The compound represented by general formula (2) (perfluoroalkanoic acid) is known to be formed during polymerization when perfluoroalkyl vinyl ether or the like is used as a modified monomer (see WO 2019 / 161153).

[0143] In one embodiment of the polytetrafluoroethylene, the compound represented by the following general formula (3) is substantially not contained as a fluorine-containing compound having a hydrophilic group. 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.)

[0144] In one embodiment of the polytetrafluoroethylene, the compound represented by general formula (4) is substantially not contained as a fluorine-containing compound having a hydrophilic group. ２ ) ｍ CO ２ － ]M ＋ (wherein m is an integer of 3 to 19, M ＋ represents a cation.)

[0145] In the present disclosure, "substantially free of any of the compounds represented by general formulas (1) to (4)" means that the content of any of the compounds represented by general formulas (1) to (4) in the polytetrafluoroethylene is 100 ppb by mass or less. The content of any of the compounds represented by general formulas (1) to (4) in the fluoropolymer is preferably 80 ppb by mass or less, more preferably 60 ppb by mass or less, even more preferably 30 ppb by mass or less, still more preferably 15 ppb by mass or less, particularly preferably 1 ppb by mass or less, and most preferably below the detection limit of the fluorine-containing surfactant as measured by liquid chromatography mass spectrometry (LC / MS).

[0146] The content of the fluorine-containing compound having a hydrophilic group in polytetrafluoroethylene can be quantified by known methods. For example, it can be quantified by LC / MS analysis. First, methanol is added to polytetrafluoroethylene, extraction is performed, and the obtained extract is analyzed by LC / MS. To further improve the extraction efficiency, treatments such as Soxhlet extraction and ultrasonic treatment may be performed. The obtained extract is appropriately concentrated with a nitrogen purge, and the fluorine-containing compound having a hydrophilic group in the concentrated extract is measured by LC / MS. Molecular weight information is extracted from the obtained LC / MS spectrum, and its agreement with the structural formula of the candidate fluorine-containing compound having a hydrophilic group is confirmed. Thereafter, 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 the aqueous solutions containing each level. 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. The resulting extract can be concentrated by purging with nitrogen, which allows the lower limit of quantitation of the measurement method to be lowered.

[0147] Polytetrafluoroethylene obtained by the production method of the present disclosure can be molded to obtain a polytetrafluoroethylene molded article.

[0148] Methods for molding polytetrafluoroethylene include, for example, compression molding, ram extrusion molding, and isostatic compression molding. Of these, compression molding is preferred as a molding method. By compression molding polytetrafluoroethylene, a polytetrafluoroethylene compression-molded product can be obtained.

[0149] In compression molding, a mold is generally filled with polytetrafluoroethylene and compressed to produce a preform, which is then placed in a furnace to be sintered and cooled to produce a compression-molded product.

[0150] Compression molding can be performed, for example, by filling a mold with polytetrafluoroethylene, compressing the polytetrafluoroethylene at 1 to 100 MPa, and heating the preform obtained by compression to 345 to 400°C for sintering.

[0151] The polytetrafluoroethylene molded article may be processed by machining such as cutting to produce a molded article having a desired shape. For example, a polytetrafluoroethylene sheet can be obtained by cutting the polytetrafluoroethylene molded article. The obtained polytetrafluoroethylene sheet can be used as a lining sheet, packing, gasket, or diaphragm valve. The obtained polytetrafluoroethylene sheet can also be used as a heat-resistant electric wire, heat-resistant insulating tape for vehicle motors and generators, or a release sheet.

[0152] Polytetrafluoroethylene molded articles can also be used for sealing materials, casings, sleeves, bellows, hoses, piston rings, butterfly valves, square tanks, wafer carriers, and the like.

[0153] Furthermore, polytetrafluoroethylene obtained by the manufacturing method of the present disclosure can also be used as a raw material for granulation or compounding. The polytetrafluoroethylene obtained by the manufacturing method of the present disclosure may be granulated by a known granulation method. A filler may also be appropriately blended with the polytetrafluoroethylene obtained by the manufacturing method of the present disclosure. Furthermore, molding powder blended with the filler may be granulated by a known granulation method. The resulting granules or molding material can be molded in the same manner as the method for molding polytetrafluoroethylene.

[0154] 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.

[0155] <1> According to a first aspect of the present disclosure, there is provided a method for producing non-melt-processible polytetrafluoroethylene, which comprises suspension polymerizing tetrafluoroethylene in a reactor in the presence of a polymerization initiator and an aqueous medium to prepare a composition containing an aqueous medium and non-melt-processible polytetrafluoroethylene, wherein a polymerization inhibitor for inhibiting polymerization of residual radicals is supplied into the reactor after supplying a polymerization terminator into the reactor or after removing tetrafluoroethylene remaining in the reactor from the reactor. <2> According to a second aspect of the present disclosure, there is provided a method for producing non-melt-processible polytetrafluoroethylene, which comprises supplying a polymerization inhibitor for inhibiting polymerization of residual radicals into the reactor after supplying a polymerization terminator into the reactor or after removing tetrafluoroethylene remaining in the reactor from the reactor. <2> According to a second aspect of the present disclosure, there is provided a method for producing non-melt-processible polytetrafluoroethylene, which comprises supplying a polymerization inhibitor for inhibiting polymerization of residual radicals into the reactor ２) is at least one selected from the group consisting of: <3> According to a third aspect of the present disclosure, there is provided a production method according to the first or second aspect, in which the polymerization inhibitor for inhibiting polymerization of residual radicals is an alcohol having 1 to 5 carbon atoms. <4> According to a fourth aspect of the present disclosure, there is provided a production method according to any one of the first to third aspects, in which the amount of the polymerization inhibitor for inhibiting polymerization of residual radicals supplied is 0.001 to 10 mass% with respect to the aqueous medium. <5> According to a fifth aspect of the present disclosure, there is provided a production method according to any one of the first to fourth aspects, in which the composition is brought into contact with the polymerization inhibitor for inhibiting polymerization of residual radicals while stirring the composition. <6> According to a sixth aspect of the present disclosure, there is provided a production method according to any one of the first to fifth aspects, in which the temperature of the composition when the composition is brought into contact with the polymerization inhibitor for inhibiting polymerization of residual radicals is 30°C or higher. <7> According to a seventh aspect of the present disclosure, there is provided a production method according to any one of the first to sixth aspects, in which the contact time between the composition and the polymerization inhibitor for inhibiting polymerization of residual radicals is 1 minute or longer. <8> According to an eighth aspect of the present disclosure, there is provided a production method according to any one of the first to seventh aspects, in which tetrafluoroethylene remaining in the reactor is removed from the reactor by evacuating the reactor or by replacing the tetrafluoroethylene remaining in the reactor with an inert gas. <9> According to a ninth aspect of the present disclosure, there is provided a production method according to any one of the first to eighth aspects, in which tetrafluoroethylene remaining in the reactor is removed from the reactor by reacting the entire amount of tetrafluoroethylene supplied to the reactor. <10> According to a tenth aspect of the present disclosure, there is provided a production method according to any one of the first to ninth aspects, in which perfluoro(alkyl vinyl ether) is suspension polymerized in addition to tetrafluoroethylene.<11> According to an eleventh aspect of the present disclosure, there is provided the production method according to any one of the first to tenth aspects, wherein the polymerization inhibitor for inhibiting polymerization of residual radicals is supplied into the reactor, and then the polytetrafluoroethylene is washed. <12> According to a twelfth aspect of the present disclosure, there is provided the production method according to any one of the first to eleventh aspects, wherein the polymerization inhibitor for inhibiting polymerization of residual radicals is supplied into the reactor, and then the polytetrafluoroethylene is dried. <13> According to a thirteenth aspect of the present disclosure, there is provided the production method according to any one of the first to twelfth aspects, wherein the polymerization inhibitor for inhibiting polymerization of residual radicals is supplied into the reactor, and then the polytetrafluoroethylene is pulverized. <14> According to a fourteenth aspect of the present disclosure, there is provided the production method according to any one of the first to thirteenth aspects, wherein the standard specific gravity of the polytetrafluoroethylene is 2.130 to 2.280. <15> According to a fifteenth aspect of the present disclosure, a method for producing a polymerizable composition comprising the steps of: carrying out suspension polymerization of tetrafluoroethylene in the presence or absence of 100 ppm by mass or less of a fluorine-containing surfactant relative to an aqueous medium; the polymerization initiator is a persulfate; suspension polymerizing a perfluoro(alkyl vinyl ether) in addition to tetrafluoroethylene; the polytetrafluoroethylene being a modified polytetrafluoroethylene; the amount of perfluoro(alkyl vinyl ether) added being 0.001 to 1.0% by mass relative to the modified polytetrafluoroethylene obtained; removing the tetrafluoroethylene remaining in the reactor from the reactor by replacing it with an inert gas; supplying an alcohol having 1 to 5 carbon atoms into the reactor in an amount of 0.10 to 1.0% by mass relative to the aqueous medium as the polymerization inhibitor for inhibiting polymerization of residual radicals; and contacting the composition with the polymerization inhibitor for inhibiting polymerization of residual radicals at 30 to 55°C for 30 minutes or more while stirring the composition; Next, the polytetrafluoroethylene is washed, and the washed polytetrafluoroethylene is dried to obtain polytetrafluoroethylene powder.

[0156] Next, embodiments of the present disclosure will be described with reference to examples, but the present disclosure is not limited to these examples.

[0157] The values ​​in the examples were measured by the following methods.

[0158] <Apparent Density> Measured in accordance with JIS K6892.

[0159] <Standard Specific Gravity (SSG)> Using a sample molded in accordance with ASTM D4894, the standard specific gravity was measured by the water displacement method in accordance with ASTM D792.

[0160] <Average particle size (50% cumulative particle size)> The average particle size was determined by the following laser diffraction method. A dry method was performed using a HELOS & RODOS system (product name, manufactured by SYMPATEC). The powder to be measured was dispersed with compressed air at a dispersion pressure of 2 bar, and the measurement sensor detected the shadow of the powder projected by a laser. The particle size distribution of the powder to be measured was calculated, and the average particle size (50% cumulative particle size) d50 value was determined on a volume basis. d50 was defined as the particle size corresponding to 50% of the cumulative particle size distribution.

[0161] <PPVE Content> The perfluoro(propyl vinyl ether) (PPVE) content was determined by press-molding PTFE powder to prepare a thin film disk, measuring the infrared absorbance of the thin film disk by FT-IR, and calculating the ratio (995 cm －１ Absorbance at / 935 cm －１ The absorbance at 1000 nm was calculated and multiplied by 0.14.

[0162] <ΔPPVE Measurement> The PTFE thin film disk prepared above was heated at 220°C for 3 hours. After cooling the heated thin film disk to room temperature, it was again subjected to FT-IR to measure the PPVE composition. ΔPPVE was calculated by subtracting the PPVE content after heating from the PPVE content before heating. The magnitude of ΔPPVE of PTFE is an indicator of the amount of PPVE that did not fully copolymerize with TFE and remained in the PTFE in the form of a monomer or oligomer. The ΔPPVE of PTFE obtained when almost all of the PPVE used in polymerization is copolymerized with TFE becomes small. Furthermore, the ΔPPVE of PTFE heat-treated at high temperatures and fluorinated PTFE is 0.000% by mass or close to 0.000% by mass.

[0163] <Measurement of fluorine-containing compounds having hydrophilic groups> The content of fluorine-containing compounds having hydrophilic groups contained in the powder was determined as the content of fluorine-containing compounds having hydrophilic groups extracted from the powder. 1. Extraction of fluorine-containing compounds having hydrophilic groups from powder 10 g (12.6 mL) of methanol was added to 1 g of PTFE powder, and ultrasonic treatment was carried out for 120 minutes while heating to 60°C. After leaving to stand at room temperature, the solid content was removed to obtain an extract.

[0164] Five levels of methanol standard solutions of known concentrations of perfluorononanoic acid, perfluorodecanoic acid, perfluoroundecanoic acid, perfluorododecanoic acid, perfluorotridecanoic acid, and perfluorotetradecanoic acid were prepared, and measurements were performed using a liquid chromatograph mass spectrometer (Agilent, Ultivo triple quadrupole LC-MS). A calibration curve was created for each concentration range by first-order approximation based on the concentration of the methanol standard solution and the peak integral value.

[0165] Measurement equipment configuration and LC-MS measurement conditions

[0166]

[0167] MRM measurement parameters

[0168]

[0169] 3. Content of Compound Represented by General Formula (2) in Powder Using a liquid chromatograph mass spectrometer, the content of the compound represented by general formula (2) and having carbon number n contained in the extract was measured from a calibration curve. The content of the compound represented by general formula (2) and having carbon number n contained in the powder was calculated using the following relational expression (2): Yn = Xn × 12.6 (2) Yn: content of the compound represented by general formula (2) and having carbon number n contained in the powder (mass ppb / powder) Xn: content of the compound represented by general formula (2) and having carbon number n contained in the extract (ng / mL) The lower limit of quantitation for the content of the compound represented by general formula (2) and having carbon number n contained in the powder is 1 mass ppb / powder.

[0170] MRM measurement parameters

[0171]

[0172] (Production Example) 1.9 L of deionized water and 0.12 g of ammonium carbonate were charged into a 6 L autoclave equipped with a stainless steel stirring blade and a temperature-controlling jacket, and the autoclave was sealed. The contents were stirred while heated to 70 ° C., and the inside of the autoclave was substituted with nitrogen, and the oxygen concentration inside the autoclave was 10 ppm. The pressure was reduced to remove nitrogen, and 3 g of perfluoro(propyl vinyl ether) was injected with tetrafluoroethylene, and the pressure was increased with tetrafluoroethylene to a pressure of 0.8 MPaG. Polymerization was initiated by adding ammonium persulfate as a polymerization initiator. The polymerization was carried out by continuously adding tetrafluoroethylene to maintain the pressure at 0.8 MPaG, and was continued until 22.5% by mass of tetrafluoroethylene was consumed relative to the weight of the aqueous medium, after which the monomer was released without stopping the stirring.

[0173] Example 1 After releasing the monomer, the autoclave was quickly purged with nitrogen gas to reduce the pressure, and an aqueous methanol solution was added. Nitrogen gas was then introduced under pressure from the reduced pressure state to 0.01 MPaG. The methanol content in the aqueous medium was 0.24% by mass. The mixture was stirred at 40°C for 3 hours.

[0174] The stirring was stopped, the autoclave was opened, and the aqueous medium containing the resulting polytetrafluoroethylene suspension polymerized particles was removed, drained, and washed twice with pure water. Simultaneously with washing, the mixture was pulverized in a high-speed mill to obtain pulverized particles. The mixture was dried to obtain a PTFE molding powder. The results of the physical property evaluation are shown in Tables 4 and 5.

[0175] Comparative Example 1 The autoclave was purged with nitrogen gas, and then nitrogen gas alone was introduced from a reduced pressure state until the pressure reached 0.01 MPaG, in the same manner as in Example 1, to obtain a PTFE molding powder. The results of the physical property evaluation are shown in Tables 4 and 5.

[0176]

[0177]

[0178] Example 2 A PTFE molding powder was obtained in the same manner as in Example 1, except that the amount of methanol charged in the aqueous medium was changed from 0.24% by mass to 0.13% by mass. The evaluation results of the physical properties are shown in Tables 6 and 7.

[0179] Example 3 A PTFE molding powder was obtained in the same manner as in Example 1, except that isopropanol was used instead of methanol. The evaluation results of the physical properties are shown in Tables 6 and 7.

[0180]

[0181]

Claims

1. A method for producing non-melt-processable polytetrafluoroethylene, comprising suspension polymerizing tetrafluoroethylene in a reactor in the presence of a polymerization initiator and an aqueous medium to prepare a composition containing an aqueous medium and non-melt-processable polytetrafluoroethylene, the method comprising: supplying a polymerization inhibitor into the reactor to inhibit polymerization of residual radicals after supplying a polymerization terminator into the reactor or after removing tetrafluoroethylene remaining in the reactor from the reactor.

2. The polymerization inhibitor for inhibiting the polymerization of residual radicals is selected from the group consisting of alcohols, fatty acid esters, alkanes, halogenated hydrocarbons, cycloalkanes, ketones, mercaptans, sulfur, aromatic hydroxy compounds, aromatic amines, aliphatic amines, quinone compounds, hydroquinone compounds, polyoxy compounds, nitro compounds, nitroso compounds, terpenes, thiocyanates, and cupric chloride (CuCl ２ 2. The method according to claim 1, wherein the at least one selected from the group consisting of:

3. The method according to claim 1 or 2, wherein the polymerization inhibitor for inhibiting polymerization of residual radicals is an alcohol having 1 to 5 carbon atoms.

4. The method according to any one of claims 1 to 3, wherein the amount of the polymerization inhibitor fed to inhibit polymerization of the residual radicals is 0.001 to 10% by mass relative to the aqueous medium.

5. The method according to any one of claims 1 to 4, wherein the composition is contacted with the polymerization inhibitor for inhibiting polymerization of residual radicals while stirring the composition.

6. The method according to any one of claims 1 to 5, wherein the temperature of the composition when it comes into contact with the polymerization inhibitor for inhibiting polymerization of residual radicals is 30°C or higher.

7. The method according to any one of claims 1 to 6, wherein the contact time between the composition and the polymerization inhibitor for inhibiting polymerization of residual radicals is 1 minute or longer.

8. The process according to any one of claims 1 to 7, wherein the tetrafluoroethylene remaining in the reactor is removed from the reactor by evacuating the reactor or by replacing the tetrafluoroethylene remaining in the reactor with an inert gas.

9. The process according to any one of claims 1 to 8, wherein the entire amount of tetrafluoroethylene supplied to the reactor is reacted, thereby removing tetrafluoroethylene remaining in the reactor from the reactor.

10. The process according to any one of claims 1 to 9, wherein in addition to tetrafluoroethylene, perfluoro(alkyl vinyl ether) is suspension polymerized.

11. The method according to any one of claims 1 to 10, wherein the polytetrafluoroethylene is washed after the polymerization inhibitor for inhibiting polymerization of residual radicals is supplied into the reactor.

12. The method according to any one of claims 1 to 11, wherein the polymerization inhibitor for inhibiting polymerization of residual radicals is supplied into the reactor, and then the polytetrafluoroethylene is dried.

13. The method according to any one of claims 1 to 12, wherein the polytetrafluoroethylene is pulverized after the polymerization inhibitor for inhibiting polymerization of residual radicals is supplied into the reactor.

14. The method according to any one of claims 1 to 13, wherein the standard specific gravity of the polytetrafluoroethylene is 2.130 to 2.

280.

15. A method for producing a polymerizable composition comprising the steps of: carrying out suspension polymerization of tetrafluoroethylene in the presence or absence of a fluorine-containing surfactant of 100 ppm by mass or less relative to an aqueous medium; the polymerization initiator is a persulfate; in addition to tetrafluoroethylene, perfluoro(alkyl vinyl ether) is suspension polymerized; the polytetrafluoroethylene is modified polytetrafluoroethylene; the amount of perfluoro(alkyl vinyl ether) added is 0.001 to 1.0% by mass relative to the modified polytetrafluoroethylene obtained; after removing the tetrafluoroethylene remaining in the reactor from the reactor by replacing the tetrafluoroethylene remaining in the reactor with an inert gas, supplying an alcohol having 1 to 5 carbon atoms in an amount of 0.10 to 1.0% by mass relative to the aqueous medium as the polymerization inhibitor for inhibiting polymerization of residual radicals into the reactor; and contacting the composition with the polymerization inhibitor for inhibiting polymerization of residual radicals at 30 to 55°C for 30 minutes or more while stirring the composition; The method according to claim 1 , further comprising washing the polytetrafluoroethylene and drying the washed polytetrafluoroethylene to obtain a polytetrafluoroethylene powder.

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