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  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F6/00—Post-polymerisation treatments
  • C08F6/14—Treatment of polymer emulsions
  • C08F6/16—Purification
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F14/00—Homopolymers and copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen
  • C08F14/18—Monomers containing fluorine
  • C08F14/26—Tetrafluoroethene
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  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2/00—Processes of polymerisation
  • C08F2/12—Polymerisation in non-solvents
  • C08F2/16—Aqueous medium
  • C08F2/22—Emulsion polymerisation
  • C08F2/24—Emulsion polymerisation with the aid of emulsifying agents
  • C08F2/26—Emulsion polymerisation with the aid of emulsifying agents anionic
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  • C08F2/00—Processes of polymerisation
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  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F6/00—Post-polymerisation treatments
  • C08F6/14—Treatment of polymer emulsions
  • C08F6/22—Coagulation
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  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F8/00—Chemical modification by after-treatment
  • C08F8/06—Oxidation
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  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
  • C08K3/20—Oxides; Hydroxides
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  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/30—Sulfur-, selenium- or tellurium-containing compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F214/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen
  • C08F214/18—Monomers containing fluorine
  • C08F214/26—Tetrafluoroethene
  • C08F214/262—Tetrafluoroethene with fluorinated vinyl ethers
• • C—CHEMISTRY; METALLURGY
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  • C08F2400/00—Characteristics for processes of polymerization
  • C08F2400/02—Control or adjustment of polymerization parameters

Definitions

• This disclosure relates to a method for producing an aqueous dispersion of low molecular weight polytetrafluoroethylene.
• Patent Document 1 describes a method for producing a fluoropolymer composition that contains a fluoropolymer, in which a fluoromonomer is polymerized in a reactor in the presence of a fluorine-containing surfactant, a polymerization initiator, and an aqueous medium to prepare an aqueous dispersion containing a fluoropolymer, and after preparing the aqueous dispersion, either removes the fluoromonomer remaining in the reactor from the reactor or recovers the aqueous dispersion in the reactor and stores it in a container different from the reactor, adds a radical generator to the aqueous dispersion, and heat-treats the aqueous dispersion containing the radical generator to obtain a fluoropolymer composition.
• Patent Document 2 describes a method for producing a fluoropolymer composition containing a fluoropolymer, in which a fluoromonomer is polymerized in a reactor in the presence of a fluorine-containing surfactant, a polymerization initiator, and an aqueous medium to prepare an aqueous dispersion containing a fluoropolymer, and an inert gas is supplied into the reactor, and the aqueous dispersion in the reactor is subjected to a heat treatment to obtain a fluoropolymer composition.
• the present disclosure aims to provide a method for producing an aqueous dispersion of low molecular weight polytetrafluoroethylene in which the content of fluorine-containing compounds having hydrophilic groups is reduced.
• a method for producing an aqueous dispersion of low molecular weight polytetrafluoroethylene which comprises polymerizing tetrafluoroethylene in the presence of a fluorine-containing surfactant, a polymerization initiator, a hydrocarbon chain transfer agent, and an aqueous medium to prepare an aqueous dispersion containing low molecular weight polytetrafluoroethylene, pretreating the aqueous dispersion obtained, adding a radical generator to the pretreated aqueous dispersion, and subjecting the aqueous dispersion containing the radical generator to a heat treatment, thereby obtaining an aqueous dispersion of low molecular weight polytetrafluoroethylene.
• the present disclosure provides a method for producing an aqueous dispersion of low molecular weight polytetrafluoroethylene with a reduced content of fluorine-containing compounds having hydrophilic groups.
• FIG. 1 shows first differential spectra obtained by analyzing the aqueous dispersions obtained in Examples 1, 9, 11, 15 and 16 using an electron spin resonance method.
• melt processable means that the polymer can be melted and processed using conventional processing equipment such as extruders and injection molding machines. Therefore, melt processable fluororesin typically has a melt flow rate of 0.01 to 500 g/10 min, as measured by the measurement method described below.
• polytetrafluoroethylene is preferably a fluoropolymer in which the content of tetrafluoroethylene units relative to the total polymerized units is 99 mol % or more.
• 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.
• organic group means 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.
• ranges represented by endpoints include all numbers within that range (e.g., 1 to 10 includes 1.4, 1.9, 2.33, 5.75, 9.98, etc.).
• At least 1 includes all numbers equal to or greater than 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.).
• Patent Document 1 and Patent Document 2 propose the above-mentioned production method as a production method capable of producing a fluoropolymer composition in which the content of the fluorine-containing surfactant used in polymerizing the fluoromonomer and the content of the fluorine-containing compound generated by the polymerization of the fluoromonomer are reduced.
• an aqueous dispersion containing low molecular weight polytetrafluoroethylene is prepared by polymerizing tetrafluoroethylene in the presence of a fluorine-containing surfactant, a polymerization initiator, a hydrocarbon chain transfer agent, and an aqueous medium.
• a fluorine-containing surfactant e.g., a fluorine-containing surfactant, a polymerization initiator, a hydrocarbon chain transfer agent, and an aqueous medium.
• the aqueous dispersion is pretreated, a radical generator is added to the pretreated aqueous dispersion, and the aqueous dispersion containing the radical generator is heat-treated to obtain an aqueous dispersion of low molecular weight polytetrafluoroethylene.
• tetrafluoroethylene is polymerized in the presence of a fluorine-containing surfactant, a polymerization initiator, a hydrocarbon-based chain transfer agent, and an aqueous medium to prepare an aqueous dispersion containing low-molecular-weight polytetrafluoroethylene.
• the polymerization of tetrafluoroethylene can be carried out in a reactor.
• the polymerization of tetrafluoroethylene is carried out by charging a reactor with tetrafluoroethylene, a fluorine-containing surfactant, a polymerization initiator, an aqueous medium, and other additives as necessary, stirring the contents of the reactor, and maintaining the reactor at a predetermined polymerization temperature, and then adding a predetermined amount of polymerization initiator to start the polymerization reaction.
• tetrafluoroethylene, a polymerization initiator, a fluorine-containing surfactant, a chain transfer agent, and the like may be added additionally depending on the purpose.
• the polymerization method of tetrafluoroethylene is not particularly limited, but an emulsion polymerization method is preferred.
• the fluorine-containing surfactant used in the polymerization of tetrafluoroethylene may be a fluorine-containing surfactant that is commonly used in the polymerization of tetrafluoroethylene.
• a typical compound is a fluorine-containing surfactant having a molecular weight of 1000 g/mol or less, preferably 800 g/mol or less.
• 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.
• fluorine-containing surfactants examples include anionic fluorine-containing surfactants.
• Anionic fluorine-containing surfactants may be, for example, surfactants containing fluorine atoms with a total carbon number of 20 or less excluding the anionic group.
• the fluorine-containing surfactant may also be a surfactant containing fluorine in the anionic moiety having a molecular weight of 1,000 or less.
• anionic portion refers to the portion of the above fluorine-containing surfactant excluding the cation.
• F(CF 2 ) n1 COOM represented by formula (I) described below, it is the portion "F(CF 2 ) n1 COO”.
• the above-mentioned fluorosurfactant also includes a fluorosurfactant having a LogPOW of 3.5 or less.
• the LogPOW is a partition coefficient between 1-octanol and water, and is expressed as LogP [wherein P represents the ratio of the fluorosurfactant concentration in octanol to the fluorosurfactant concentration in water when a 1:1 octanol/water mixture containing the fluorosurfactant undergoes phase separation].
• a standard substance heptanoic acid, octanoic acid, nonanoic acid, and decanoic acid
• fluorine-containing surfactants include those described in U.S. Patent Application Publication No. 2007/0015864, U.S. Patent Application Publication No. 2007/0015865, U.S. Patent Application Publication No. 2007/0015866, U.S. Patent Application Publication No. 2007/0276103, U.S. Patent Application Publication No. 2007/0117914, U.S. Patent Application Publication No. 2007/142541, U.S. Patent Application Publication No. 2008/0015319, and U.S. Patent No. 3,250,808. Examples of such compounds include those described in U.S. Pat. No.
• 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 ) (In the formula, X n0 is H, Cl or F. Rf n0 is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms in which some or all of the H's are substituted with F, and the alkylene group may contain one or more ether bonds, and some of the H's may be substituted with Cl. Y 0 is an anionic group.
• the anionic group of Y 0 may be -COOM, -SO 2 M or -SO 3 M, and may be -COOM or -SO 3 M.
• M is H, a metal atom, NR 7 4 , an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent
• R 7 is H or an organic group.
• the metal atom includes alkali metals (group 1) and alkaline earth metals (group 2), such as Na, K, or Li.
• R 7 may be H or a C 1-10 organic group, may be H or a C 1-4 organic group, or may be H or a C 1-4 alkyl group.
• M may be H, a metal atom or NR 7 4 , which may be H, an alkali metal (group 1), an alkaline earth metal (group 2) or NR 7 4 , which may be H, Na, K, Li or NH 4 .
• Rf n0 may be one in which 50% or more of H is substituted with fluorine.
• the compound represented by the above general formula (N 0 ) includes a compound represented by the following general formula (N 1 ): X n0 - (CF 2 ) m1 - Y 0 (N 1 ) (wherein X n0 is H, Cl or F, m1 is an integer of 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, 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 (
• the compound represented by the above general formula (N 0 ) includes perfluorocarboxylic acid (I) represented by the following general formula (I), ⁇ -H perfluorocarboxylic acid (II) represented by the following general formula (II), perfluoroether carboxylic acid (III) represented by the following general formula (III), perfluoroalkyl alkylene carboxylic acid (IV) represented by the following general formula (IV), perfluoroalkoxy fluorocarboxylic acid (V) represented by the following general formula (V), perfluoroalkyl sulfonic acid (VI) represented by the following general formula (VII), ⁇ -H perfluoro sulfonic acid (VII) represented by the following general formula (VII), perfluoroalkyl alkylene sulfonic acid (VIII) represented by the following general formula (VIII), alkyl alkylene carboxylic acid (IX) represented by the following general formula (IX), fluorocarboxylic acid (
• the perfluorocarboxylic acid (I) is represented by the following general formula (I): F (CF 2 ) n1 COOM (I) (wherein n1 is an integer of 3 to 13, M is H, a metal atom, NR 7 4 , an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent, and R 7 is H or an organic group).
• ⁇ -H perfluorocarboxylic acid (II) is represented by the following general formula (II): H(CF 2 ) n2 COOM (II) (wherein n2 is an integer from 4 to 15, and M is as defined above).
• the perfluoroether carboxylic acid (III) is represented by the following general formula (III): Rf 1 -O-(CF(CF 3 )CF 2 O) n3 CF(CF 3 )COOM (III) (wherein Rf1 is a perfluoroalkyl group having 1 to 5 carbon atoms, n3 is an integer of 0 to 3, and M is as defined above).
• the perfluoroalkyl alkylene carboxylic acid (IV) is represented by the following general formula (IV): Rf 2 (CH 2 ) n4 Rf 3 COOM (IV) (In the formula, Rf 2 is a perfluoroalkyl group having 1 to 5 carbon atoms, Rf 3 is a linear or branched perfluoroalkylene group having 1 to 3 carbon atoms, n4 is an integer of 1 to 3, and M is as defined above.)
• 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 completely fluorinated alkyl group having 1 to 12 carbon atoms which may contain an ether bond and/or a chlorine atom, Y 1 and Y 2 are the same or different and are H or F, and M is as defined above).
• 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 from 3 to 14, and M is as defined above).
• the ⁇ -H perfluorosulfonic acid (VII) is represented by the following general formula (VII): H(CF 2 ) n6 SO 3 M (VII) (wherein n6 is an integer from 4 to 14, and M is as defined above).
• the perfluoroalkyl alkylene sulfonic acid (VIII) is represented by the following general formula (VIII): Rf5 ( CH2 ) n7SO3M (VIII ) (wherein Rf5 is a perfluoroalkyl group having 1 to 13 carbon atoms, n7 is an integer of 1 to 3, and M is as defined above).
• the alkyl alkylene carboxylic acid (IX) is represented by the following general formula (IX): Rf 6 (CH 2 ) n8 COOM (IX) (wherein Rf6 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).
• the fluorocarboxylic acid (X) is represented by the following general formula (X): Rf 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 linkage and/or a chlorine atom; 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).
• 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) (In the formula, Rf 9 is a linear or branched alkyl group having 1 to 12 carbon atoms which may contain an ether bond and which is partially or completely fluorinated and may contain chlorine; Y 1 and Y 2 are the same or different and are H or F; and M is as defined above.)
• the compound (XII) is represented by the following general formula (XII): (wherein X 1 , X 2 and X 3 may be the same or different and are H, F and a linear or branched partially or completely fluorinated alkyl group having 1 to 6 carbon atoms which may contain an ether bond, Rf 10 is a perfluoroalkylene group having 1 to 3 carbon atoms, L is a linking group, and Y 0 is an anionic group). Y 0 may be -COOM, -SO 2 M or -SO 3 M, and may be -SO 3 M or COOM, where M is as defined above. Examples of L include a single bond, and a partially or fully fluorinated alkylene group having 1 to 10 carbon atoms which may contain an ether bond.
• the compound (XIII) is represented by the following general formula (XIII): Rf 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 from 0 to 3, n10 is an integer from 0 to 3, and M is as defined above).
• Compound (XIII) is represented by CF 2 ClO(CF 2 CF(CF 3 )O) n9 (CF 2 O) n10 CF 2 COONH 4 (a mixture having an average molecular weight of 750, wherein n9 and n10 are as defined above).
• anionic fluorine-containing surfactant examples include carboxylic acid surfactants and sulfonic acid surfactants.
• the fluorine-containing surfactant may be one type of fluorine-containing surfactant or a mixture containing two or more types of fluorine-containing surfactants.
• the fluorine-containing surfactant preferably has no methylene group (-CH 2 -), and more preferably has no C-H bond.
• a fluorine-containing surfactant that has no methylene group (-CH 2 -) or no C-H bond in the molecule the polymerization of tetrafluoroethylene in the presence of an aqueous medium can be smoothly carried out.
• the number of H atoms in the hydrophobic group of the fluorine-containing surfactant is preferably 0 or 1, more preferably 0.
• a fluorine-containing surfactant having a small number of H atoms bonded to the carbon atom constituting the hydrophobic group the polymerization of tetrafluoroethylene in the presence of an aqueous medium can be smoothly carried out.
• the number of carbon atoms in the hydrophobic group of the 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 "part other than the anionic group" in the molecular structure of the fluorine-containing surfactant.
• the hydrophilic group include the groups exemplified as the anionic group of Y 0.
• the fluorine-containing surfactant may be a saturated fluorinated surfactant in which all the carbon atoms bonded to the hydrophobic group are substituted with fluorine atoms.
• fluorine-containing surfactant examples include, among the above-mentioned anionic fluorine-containing surfactants, perfluorocarboxylic acid (I) represented by general formula (I), ⁇ -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), ⁇ -H perfluoro sulfonic acid (VII) represented by general formula (VII), perfluoroalkyl alkylene sulfonic acid (VIII) represented by general formula (VIII), and perfluoroalkyl alkylene sulfonic acid (VIII) represented by general formula (X): Rf 7
• fluorine-containing surfactant examples include compounds represented by the following formula:
• the fluorine-containing surfactant may be a mixture of these compounds.
• 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, more preferably 5% by mass or less, and even more preferably 1% by mass or less, relative to the aqueous medium.
• the polymerization initiator used for the polymerization of tetrafluoroethylene is not particularly limited as long as it can generate radicals within the polymerization temperature range, and known oil-soluble and/or water-soluble polymerization initiators can be used. Furthermore, it can also be combined with a reducing agent or the like to initiate polymerization as a redox.
• concentration of the polymerization initiator is appropriately determined depending on the type of monomer, the molecular weight of the desired low-molecular-weight polytetrafluoroethylene, and the reaction rate.
• an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator can be used as the polymerization initiator.
• 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 also di( ⁇ -hydro-dodecafluoroheptanoyl) peroxide, di( ⁇ -hydro-tetradecafluorooctanoyl) peroxide, di( ⁇ -hydro-hexadecafluorononanoyl) peroxide, di(perfluorobutyryl) peroxide, di(perfluorovaleryl) peroxide, di(perfluorohexanoyl) peroxide, di(perfluoroheptanoyl) peroxide, di(per
• Representative examples include di[perfluoro(or fluorochloro)acyl]peroxides such as di( ⁇ -hexafluorobutyryl) peroxide, di( ⁇ -chloro-decafluorohexanoyl) peroxide, di( ⁇ -chloro-tetradecafluorooctanoyl) peroxide, ⁇ -hydro-dodecafluoroheptanoyl- ⁇ -hydrohexadecafluorononanoyl-peroxide, ⁇ -chloro-hexafluorobutyryl- ⁇ -chloro-decafluorohexanoyl-peroxide, ⁇ -hydrododecafluoroheptanoyl-perfluorobutyryl-peroxide, di(dichloropentafluorobutanoyl) peroxide, di(trichlorooctafluorohexanoyl) peroxide, di(
• the water-soluble radical polymerization initiator may be a known water-soluble peroxide, such as ammonium, potassium, or sodium salts of persulfuric acid, perboric acid, perchloric acid, perphosphoric acid, or percarbonic acid; organic peroxides such as disuccinic acid peroxide or diglutaric acid peroxide; t-butyl permaleate; or t-butyl hydroperoxide.
• a reducing agent such as sulfites may also be included, and the amount used may be 0.1 to 20 times the amount of the peroxide.
• a redox initiator that combines an oxidizing agent and a reducing agent as the polymerization initiator.
• oxidizing agents include persulfates, organic peroxides, potassium permanganate, manganese triacetate, and cerium ammonium nitrate.
• reducing agents include sulfites, bisulfites, bromates, diimines, and oxalic acid.
• persulfates include ammonium persulfate and potassium persulfate.
• sulfites include sodium sulfite and ammonium sulfite.
• a copper salt or an iron salt to the combination of redox initiators.
• copper salts include copper (II) sulfate
• iron salts include iron (II) sulfate.
• the redox initiator may be, for example, potassium permanganate/oxalic acid, ammonium persulfate/bisulfite/ferrous sulfate, manganese triacetate/oxalic acid, cerium ammonium nitrate/oxalic acid, bromate/bisulfite, etc., with potassium permanganate/oxalic acid being preferred.
• potassium permanganate/oxalic acid either the oxidizing agent or the reducing agent may be charged in advance into the polymerization tank, and then the other may be added continuously or intermittently to initiate polymerization.
• potassium permanganate/oxalic acid it is preferred to charge oxalic acid into the polymerization tank and continuously add potassium permanganate thereto.
• the amount of polymerization initiator to be added is not particularly limited, but it is sufficient to add an amount at least to the extent that the polymerization rate does not decrease significantly (for example, a few ppm relative to the water concentration) all at once at the beginning of the polymerization, or gradually, or continuously.
• the upper limit is the range in which the reaction temperature can be increased while removing heat from the equipment surface using the heat of polymerization reaction, and a more preferable upper limit is the range in which the heat of polymerization reaction can be removed from the equipment surface.
• the radical concentration during polymerization can be adjusted by adding a decomposition agent.
• decomposition agents include sulfites, bisulfites, bromates, diimines, oxalic acid, copper salts, and iron salts.
• sulfites include sodium sulfite and ammonium sulfite.
• copper salts include copper (II) sulfate
• iron salts include iron (II) sulfate.
• the amount of decomposition agent added is in the range of 25 to 300 mass% based on the amount of oxidizing agent combined as a polymerization initiator (redox initiator).
• the amount of decomposition agent added is preferably 25 to 150 mass%, more preferably 50 to 100 mass%. In addition, it is preferable to add the decomposition agent after 5 mass% of the total tetrafluoroethylene consumed in the polymerization reaction has been polymerized, and more preferably after 10 mass% has been polymerized.
• the amount of decomposition agent added is preferably an amount equivalent to 0.1 to 20 mass ppm of the mass of the aqueous medium used, and more preferably an amount equivalent to 3 to 10 mass ppm.
• a hydrocarbon chain transfer agent is used as the chain transfer agent used in the polymerization of tetrafluoroethylene.
• the hydrocarbon chain transfer agent is not particularly limited as long as it contains only carbon atoms and hydrogen atoms, but is preferably an alkane having 1 to 5 carbon atoms, and more preferably at least one selected from the group consisting of isopentane, methane, ethane, and propane.
• the amount of chain transfer agent used is usually 1 to 50,000 ppm by mass, and preferably 1 to 20,000 ppm by mass, based on the total amount of tetrafluoroethylene supplied.
• the amount of chain transfer agent used is preferably an amount that is completely consumed during the polymerization of tetrafluoroethylene and does not remain in the aqueous dispersion containing low-molecular-weight polytetrafluoroethylene, so as not to reduce the efficiency of removing fluorine-containing compounds having hydrophilic groups as much as possible.
• the amount of chain transfer agent used is more preferably 10,000 ppm by mass or less, even more preferably 5,000 ppm by mass or less, still more preferably 1,000 ppm by mass or less, particularly preferably 500 ppm by mass or less, and most preferably 200 ppm by mass or less, based on the total amount of tetrafluoroethylene supplied.
• the chain transfer agent may be added to the reaction vessel all at once before the start of polymerization, may be added all at once after the start of polymerization, may be added in multiple divided doses during polymerization, or may be added continuously during polymerization.
• the aqueous medium used in the polymerization of tetrafluoroethylene is a reaction medium in which polymerization is carried out, 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.
• an aqueous medium containing only water or an aqueous medium containing only water and a non-fluorine-containing organic solvent is preferred, since it allows the polymerization of tetrafluoroethylene to proceed smoothly and also suppresses a decrease in the efficiency of removing fluorine-containing compounds having hydrophilic groups, and an aqueous medium containing only water is more preferred.
• the water content 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 tetrafluoroethylene to proceed smoothly and also prevents a decrease in the efficiency of removing fluorine-containing compounds having hydrophilic groups.
• additives such as a buffer, a pH adjuster, a stabilizing aid, and a dispersion stabilizer can be used.
• a radical scavenger and a decomposer can be added to adjust the polymerization rate and molecular weight.
• a fluorine-free anionic surfactant, a fluorine-free nonionic surfactant, a fluorine-free cationic surfactant, and the like can be used.
• the stabilizing aid is preferably paraffin wax, fluorine-based oil, fluorine-based solvent, silicone oil, etc.
• the stabilizing aid may be used alone or in combination of two or more.
• the stabilizing aid is more preferably paraffin wax.
• Paraffin wax may be liquid, semi-solid, or solid at room temperature, but is preferably a saturated hydrocarbon having 12 or more carbon atoms.
• the melting point of paraffin wax is usually preferably 40 to 65°C, more preferably 50 to 65°C.
• the amount of the stabilizing aid used is preferably 0.1 to 12 mass % based on the mass of the aqueous medium used, and more preferably 0.1 to 8 mass %. It is desirable that the stabilizing aid is sufficiently hydrophobic and completely separates from the aqueous dispersion after polymerization so as not to become a contaminating component.
• Modified monomer may be polymerized together with tetrafluoroethylene.
• the modified monomer is not particularly limited as long as it can be copolymerized with tetrafluoroethylene (TFE), and includes fluoromonomer and non-fluoromonomer.
• TFE tetrafluoroethylene
• the modified monomer used may be one type or multiple types.
• non-fluoromonomers examples include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, vinyl methacrylate, vinyl acetate, acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, ethyl vinyl ether, and cyclohexyl vinyl ether. Of these, butyl methacrylate, vinyl acetate, and acrylic acid are preferred as non-fluoromonomers.
• fluoromonomers examples 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.
• HFP hexafluoropropylene
• VDF vinylidene fluoride
• perhaloolefins such as chlorotrifluoroethylene
• perfluorovinyl ethers perfluorovinyl ethers
• (perfluoroalkyl)ethylenes examples of fluoroallyl ethers.
• the "perfluoro organic group” refers to an organic group in which all hydrogen atoms bonded to carbon atoms are replaced with fluorine atoms.
• the perfluoro organic group may have an ether oxygen.
• perfluorovinyl ethers include, for example, perfluoro(alkyl vinyl ether)s [PAVE], in which Rf is a perfluoroalkyl group having 1 to 10 carbon atoms in general formula (A).
• the number of carbon atoms in the above-mentioned perfluoroalkyl group is preferably 1 to 5.
• Examples of the perfluoroalkyl group in the above PAVE include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, a perfluorohexyl group, and the like.
• perfluorovinyl ether further includes those in which Rf in general formula (A) is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, and those in which Rf is the following formula:
• Rf is a group represented by the following formula: CF 3 CF 2 CF 2 -(O-CF(CF 3 )-CF 2 ) n - (wherein n is an integer of 1 to 4).
• the (perfluoroalkyl)ethylene (PFAE) is not particularly limited, and examples include (perfluorobutyl)ethylene (PFBE) and (perfluorohexyl)ethylene.
• 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.
• the perfluoroallyl ether is preferably at least one selected from the group consisting of CF 2 ⁇ CF-CF 2 -O-CF 3 , CF 2 ⁇ CF-CF 2 -O-C 2 F 5 , CF 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-C 2 F 5 , CF 2 ⁇ CF-CF 2 -O-C 3 F 7 , and CF 2 ⁇ CF-CF 2 -O-C 4 F 9 , and even more preferably CF 2 ⁇ CF-CF 2 -O-CF 2 CF 2 CF 3 .
• modified monomer (3) having a monomer reactivity ratio of 0.1 to 8.
• modified monomer (3) makes it possible to obtain PTFE particles with a small particle size, and an aqueous dispersion with high dispersion stability.
• the monomer reactivity ratio in copolymerization with TFE is the rate constant when a growing radical reacts with TFE when the growing radical is less than a repeating unit based on TFE, divided by the rate constant when the growing radical reacts with a modified monomer.
• the lower this value the higher the reactivity of the modified monomer with TFE.
• the monomer reactivity ratio can be calculated from the composition in the resulting polymer immediately after the start of copolymerization of TFE with the modified monomer, using the Feynman-Ross equation.
• the copolymerization is carried out in a 6.0 L stainless steel autoclave using 3600 g of deionized degassed water, 1000 ppm by mass of ammonium perfluorooctanoate relative to the water, and 100 g of paraffin wax at a pressure of 0.78 MPaG and a temperature of 70°C.
• 0.05 g, 0.1 g, 0.2 g, 0.5 g, and 1.0 g of modified monomer are added to the reactor, respectively, and 0.072 g of ammonium persulfate (20 ppm by mass relative to water) is added, and TFE is continuously fed to maintain the polymerization pressure of 0.78 MPaG.
• the amount of TFE charged reaches 1000 g, stirring is stopped and the reactor is depressurized until atmospheric pressure is reached. After cooling, the paraffin wax is separated to obtain an aqueous dispersion containing the produced polymer. The aqueous dispersion is stirred to coagulate the produced polymer, and then dried at 150°C.
• the composition of the resulting polymer is calculated by appropriately combining NMR, FT-IR, elemental analysis, and X-ray fluorescence analysis depending on the type of monomer.
• the modified monomer (3) having a monomer reactivity ratio of 0.1 to 8 is preferably at least one selected from the group consisting of modified monomers represented by formulas (3a) to (3d).
• CH 2 CH-Rf 1 (3a) (In the formula, Rf1 is a perfluoroalkyl group having 1 to 10 carbon atoms.)
• CF 2 CF-O-Rf 2 (3b) (In the formula, Rf2 is a perfluoroalkyl group having 1 to 2 carbon atoms.)
• Z and Z' are F or a fluorinated alkyl group having 1 to 3 carbon atoms.
• the content of modified monomer (3) units is preferably in the range of 0.00001 to 1.0 mass% relative to the total polymerized units of PTFE.
• the lower limit is more preferably 0.0001 mass%, more preferably 0.0005 mass%, even more preferably 0.001 mass%, and even more preferably 0.005 mass%.
• the upper limits are 0.90 mass%, 0.50 mass%, 0.40 mass%, 0.30 mass%, 0.20 mass%, 0.15 mass%, 0.10 mass%, 0.08 mass%, 0.05 mass%, and 0.01 mass%.
• the modified monomer is preferably at least one selected from the group consisting of hexafluoropropylene, chlorotrifluoroethylene, vinylidene fluoride, perfluoro(alkyl vinyl ether), (perfluoroalkyl)ethylene, ethylene, and modified monomers having a functional group capable of reacting by radical polymerization and a hydrophilic group, because it is possible to obtain an aqueous dispersion having a small average primary particle size, a small aspect ratio of the primary particles, and excellent stability.
• modified monomer it is possible to obtain an aqueous dispersion of PTFE having a smaller average primary particle size, a small aspect ratio of the primary particles, and excellent dispersion stability.
• the modifying monomer preferably contains at least one selected from the group consisting of hexafluoropropylene, perfluoro(alkyl vinyl ether) and (perfluoroalkyl)ethylene. More preferably, it contains at least one selected from the group consisting of hexafluoropropylene, perfluoro(methyl vinyl ether), perfluoro(propyl vinyl ether), (perfluorobutyl)ethylene, (perfluorohexyl)ethylene, and (perfluorooctyl)ethylene.
• the total amount of the hexafluoropropylene unit, the perfluoro(alkyl vinyl ether) unit and the (perfluoroalkyl)ethylene unit is preferably in the range of 0.00001 to 1 mass% based on the total polymerization units of PTFE.
• the lower limit of the total amount is more preferably 0.0001 mass%, more preferably 0.0005 mass%, even more preferably 0.001 mass%, and even more preferably 0.005 mass%.
• the upper limit is, in order of preference, 0.80 mass%, 0.70 mass%, 0.50 mass%, 0.40 mass%, 0.30 mass%, 0.20 mass%, 0.15 mass%, 0.10 mass%, 0.08 mass%, 0.05 mass%, and 0.01 mass%.
• the modified monomer preferably includes a modified monomer having a functional group capable of reacting by radical polymerization and a hydrophilic group (hereinafter referred to as "modified monomer (A)").
• modified monomer (A) By adding the modified monomer (A), it is possible to obtain PTFE particles with a small primary particle size, and an aqueous dispersion with high dispersion stability can be obtained. It is also possible to reduce the amount of uncoagulated polymer. Furthermore, it is possible to reduce the aspect ratio of the primary particles.
• the amount of the modified monomer (A) used is preferably more than the amount corresponding to 0.1 mass ppm of aqueous medium, more preferably more than 0.5 mass ppm, even more preferably more than 1.0 mass ppm, even more preferably more than 5 mass ppm, and particularly preferably more than 10 mass ppm. If the amount of the modified monomer (A) used is too small, the average primary particle diameter of the PTFE obtained may not be small.
• the amount of the modified monomer (A) used may be within the above range, but the upper limit can be, for example, 5000 ppm by mass. In the above production method, the modified monomer (A) may be added to the system during the reaction in order to improve the stability of the aqueous dispersion during or after the reaction.
• the modified monomer (A) is highly water-soluble, so even if unreacted modified monomer (A) remains in the aqueous dispersion, it can be easily removed in the concentration process or the coagulation/washing process.
• the modified monomer (A) is incorporated into the resulting polymer during the polymerization process, but because the concentration of the modified monomer (A) itself in the polymerization system is low and the amount incorporated into the polymer is small, there is no problem with the heat resistance of the PTFE decreasing or discoloration after baking.
• hydrophilic group in the modified monomer (A) examples include -NH 2 , -PO 3 M, -OPO 3 M, -SO 3 M, -OSO 3 M, and -COOM (in each formula, M is H, a metal atom, NR 7y 4 , an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent, and R 7y is H or an organic group, which may be the same or different. Any two of them may be bonded to each other to form a ring).
• the hydrophilic group is preferably -SO 3 M or -COOM.
• the organic group in R 7y is preferably an alkyl group.
• R 7y is preferably H or a C 1-10 organic group, more preferably H or a C 1-4 organic group, and even more preferably H or a C 1-4 alkyl group.
• the metal atom may be a monovalent or divalent metal atom, such as an alkali metal (group 1) or an alkaline earth metal (group 2), with Na, K or Li being preferred.
• Examples of the "functional group capable of reacting by radical polymerization" in the modified monomer (A) include groups having an ethylenically unsaturated bond, such as a vinyl group and an allyl group.
• Examples of the linking group for R include the linking group as Ra described below.
• the modified monomer (A) has a functional group that can react by radical polymerization, so when used in the above polymerization, it is presumed to react with the fluorine-containing monomer at the beginning of the polymerization reaction, forming highly stable particles that have hydrophilic groups derived from the modified monomer (A). For this reason, it is believed that the number of particles will increase if polymerization is carried out in the presence of the modified monomer (A).
• the polymerization may involve the presence of one type of the modified monomer (A) or two or more types.
• a compound having an unsaturated bond can be used as the modified monomer (A).
• hydrophilic group examples include -NH 2 , -PO 3 M, -OPO 3 M, -SO 3 M, -OSO 3 M, and -COOM (in each formula, M is H, a metal atom, NR 7y 4 , an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent, and R 7y is H or an organic group which may be the same or different. Any two of them may be bonded to each other to form a ring).
• the hydrophilic group is preferably -SO 3 M or -COOM.
• the organic group in R 7y is preferably an alkyl group.
• R 7y is preferably H or a C 1-10 organic group, more preferably H or a C 1-4 organic group, and even more preferably H or a C 1-4 alkyl group.
• the metal atom may be a monovalent or divalent metal atom, such as an alkali metal (group 1) or an alkaline earth metal (group 2), with Na, K or Li being preferred.
• R a is a linking group.
• the "linking group” refers to a divalent linking group.
• the linking group may be a single bond, and preferably contains at least one carbon atom, and the number of carbon atoms may be 2 or more, 4 or more, 8 or more, 10 or more, or 20 or more. There is no upper limit, but it may be, for example, 100 or less, or 50 or less.
• the linking group may be linear or branched, cyclic or acyclic in structure, saturated or unsaturated, substituted or unsubstituted, and may optionally contain one or more heteroatoms selected from the group consisting of sulfur, oxygen, and nitrogen, and may optionally contain one or more functional groups selected from the group consisting of esters, amides, sulfonamides, carbonyls, carbonates, urethanes, ureas, and carbamates.
• the linking group may not contain carbon atoms, but may be a catenary heteroatom such as oxygen, sulfur, or nitrogen.
• R a is preferably, for example, a catenary heteroatom such as oxygen, sulfur or nitrogen, or a divalent organic group.
• R a is a divalent organic group
• the hydrogen atom bonded to the carbon atom may be replaced with a halogen other than fluorine, such as chlorine, and may or may not contain a double bond.
• R a may be either linear or branched, and may be either cyclic or acyclic.
• R a may contain a functional group (e.g., ester, ether, ketone, amine, halide, etc.).
• R a may also be a non-fluorinated divalent organic group, or a partially fluorinated or perfluorinated divalent organic group.
• R a is preferably -(CH 2 ) a -, -(CF 2 ) a -, -O-(CF 2 ) a -, -(CF 2 ) a -O-(CF 2 ) b -, -O(CF 2 ) a -O-(CF 2 ) b -, -(CF 2 ) a -[O-(CF 2 ) b ] c -, -O(CF 2 ) a -[O-(CF 2 ) b ] c -, -[(CF 2 ) a -O] b -[(CF 2 ) c -O] d -, -O[(CF 2 ) a -O] b -[(CF 2 ) c -O] d -, -O[(CF 2 ) a -O] b -[(CF 2 ) c -O] d -
• a, b, c, and d are independently at least 1.
• a, b, c, and d may be independently 2 or more, 3 or more, 4 or more, 10 or more, or 20 or more.
• the upper limit of a, b, c, and d is, for example, 100.
• -R a -(CZ 1 Z 2 ) k - in general formula (4) is -CF 2 -O-CF 2 -, -CF 2 -O-CF(CF 3 )-, -CF 2 -O- C(CF 3 ) 2 -, -CF 2 -O-CF 2 -CF 2 -, -CF 2 -O-CF 2 -CF(CF 3 )-, -CF 2 -O-CF 2 -C(CF 3 ) 2 -, -CF 2 -O-CF 2 CF 2 -CF 2 -, -CF 2 -O-CF 2 CF 2 -CF (CF 3 )-, -CF 2 -O-CF 2 CF 2 -C ( C.F.
• the compound represented by the general formula (4) has a C-F bond and does not have a C-H bond, except for the hydrophilic group (Y 3 ). That is, in the general formula (4), it is preferable that all of X i , X j , and X k are F, and R a is a perfluoroalkylene group having one or more carbon atoms, and the perfluoroalkylene group may be either linear or branched, may be either cyclic or acyclic, and may contain at least one catenary heteroatom. The number of carbon atoms of the perfluoroalkylene group may be 2 to 20, or may be 4 to 18.
• the compound represented by the general formula (4) may be partially fluorinated, i.e., the compound represented by the general formula (4) preferably has at least one hydrogen atom bonded to a carbon atom, except for the hydrophilic group (Y 3 ), and also preferably has at least one fluorine atom bonded to a carbon atom.
• Y 3 is preferably —OSO 3 M.
• Y3 is --SO.sub.3M .
• M is the same as above.
• Y3 is -COOM.
• Y 3 is --OPO 3 M or --OP(O)(OM) 2 .
• examples of the compound represented by the general formula (4) include CF 2 ⁇ CF(OCF 2 CF 2 CH 2 OP(O)(OM) 2 ), CF 2 ⁇ CF(O(CF 2 ) 4 CH 2 OP(O)(OM) 2 ), CF 2 ⁇ CF(OCF 2 CF(CF 3 )CH 2 OP(O)(OM) 2 ), CF 2 ⁇ CF(OCF 2 CF(CF 3 )OCF 2 CF 2 CH 2 OP( O )(OM ) 2 ), and CF 2 ⁇ CF(OCF 2 CF(CF 3 )OCF 2 CF 2 CH 2 OP (O)(OM) 2 .
• M is the same as above.
• Y3 is -PO3M or -P(O)(OM) 2 .
• examples of the compound represented by the general formula (4) include CF 2 ⁇ CF(OCF 2 CF 2 P(O)(OM) 2 ), CF 2 ⁇ CF(O(CF 2 ) 4 P(O)(OM) 2 ), CF 2 ⁇ CF(OCF 2 CF(CF 3 )P(O)(OM) 2 ), CF 2 ⁇ CF(OCF 2 CF(CF 3 )OCF 2 CF 2 P(O)(OM) 2 ), CH 2 ⁇ CH(CF 2 CF 2 P(O)(OM) 2 ), CH 2 ⁇ CH((CF 2 ) 4 P(O)(OM) 2 ), and CH 2 ⁇ CH((CF 2 ) 3 P(O)(OM) 2 ), and the like, in which M is the same
• the above-mentioned fluorine-containing alkylene group having 2 to 100 carbon atoms and an ether bond is an alkylene group that does not include a structure in which an oxygen atom is at the terminal and that contains an ether bond between carbon atoms.
• X is -H or -F. Both X's may be -F, or at least one X may be -H. For example, one X may be -F and the other -H, or both X's may be -H.
• Y is -H, -F, an alkyl group or a fluorine-containing alkyl group.
• the alkyl group is an alkyl group containing no fluorine atom, and may have a carbon number of at least 1.
• the alkyl group preferably has a carbon number of at most 6, more preferably at most 4, and even more preferably at most 3.
• the fluorine-containing alkyl group is an alkyl group containing at least one fluorine atom, and may have a carbon number of at least 1.
• the fluorine-containing alkyl group preferably has a carbon number of at most 6, more preferably at most 4, and even more preferably at most 3.
• the above Y is preferably -H, -F or -CF3 , and more preferably -F.
• Z may be the same or different and is -H, -F, an alkyl group or a fluoroalkyl group.
• the alkyl group is an alkyl group containing no fluorine atom, and may have a carbon number of at least 1.
• the alkyl group preferably has a carbon number of at most 6, more preferably at most 4, and even more preferably at most 3.
• the fluorine-containing alkyl group is an alkyl group containing at least one fluorine atom, and may have a carbon number of at least 1.
• the fluorine-containing alkyl group preferably has a carbon number of at most 6, more preferably at most 4, and even more preferably at most 3.
• the above Z is preferably -H, -F or -CF3 , and more preferably -F.
• X may be -H
• Y and Z may be -F.
• Rf is a fluorine-containing alkylene group having 1 to 40 carbon atoms, or a fluorine-containing alkylene group having 2 to 100 carbon atoms and an ether bond.
• the number of carbon atoms in the fluorine-containing alkylene group is preferably 2 or more. Also, it is preferably 30 or less , more preferably 20 or less, and even more preferably 10 or less.
• fluorine-containing alkylene group examples include -CF2- , -CH2CF2- , -CF2CF2- , -CF2CH2- , -CF2CF2CH2-, -CF( CF3 )-, -CF( CF3 ) CF2- , -CF( CF3 ) CH2- , and the like.
• the fluorine-containing alkylene group is preferably a perfluoroalkylene group.
• the carbon number of the fluorine-containing alkylene group having an ether bond is preferably 3 or more.
• the carbon number of the fluorine-containing alkylene group having an ether bond is preferably 60 or less, more preferably 30 or less, and even more preferably 12 or less.
• Examples of the fluorine-containing alkylene group having an ether bond include a group represented by the following formula: (wherein Z1 is F or CF3 ; Z2 and Z3 are each H or F; Z4 is H, F or CF3 ; p1+q1+r1 is an integer of 1 to 10; s1 is 0 or 1; and t1 is an integer of 0 to 5) is also preferred.
• fluorine-containing alkylene group having an ether bond examples include, -CF( CF3 ) CF2 -O-CF( CF3 )-, -(CF( CF3 ) CF2 -O) n -CF( CF3 )- (wherein n is an integer from 1 to 10), -CF( CF3 ) CF2 -O-CF( CF3 ) CH2- , -(CF( CF3 ) CF2 - O ) n -CF ( CF3 ) CH2- (wherein n is an integer from 1 to 10), -CH2CF2CF2O - CH2CF2CH2- , -CF2CF2CF2O - CF2CF2- , -CF2CF2 Examples thereof include CF 2 O-CF 2 CF 2 CH 2 -, -CF 2 CF 2 O-CF 2 -, -CF 2 CF 2 O-CF 2 CH 2 -, etc.
• Y 3 is preferably -COOM, -SO 3 M or -OSO 3 M
• M is H, a metal atom, NR 7y 4 , an imidazolium which may have a substituent, a pyridinium which may have a substituent or a phosphonium which may have a substituent
• R 7y is H or an organic group which may be the same or different, and any two of them may be bonded to each other to form a ring).
• the organic group for R 7y is preferably an alkyl group.
• R 7y is preferably H or a C 1-10 organic group, more preferably H or a C 1-4 organic group, and even more preferably H or a C 1-4 alkyl group.
• the metal atom includes alkali metals (Group 1) and alkaline earth metals (Group 2), and is preferably Na, K or Li.
• a metal atom or NR 7 4 is preferable, -H, an alkali metal (group 1), an alkaline earth metal (group 2) or NR 7 4 is more preferable, -H, -Na, -K, -Li or NH 4 is even more preferable, -H, -Na, -K or NH 4 is even more preferable, -H, -Na or NH 4 is particularly preferable, and -H or -NH 4 is most preferable.
• the above Y3 is preferably --COOM or --SO.sub.3M , and more preferably --COOM.
• the compound represented by the general formula (5) is preferably a compound (5a) represented by the general formula (5a).
• CH 2 CF(-CF 2 -O-Rf-Y 3 ) (5a) (In the formula, Rf and Y3 are the same as above.)
• Z1 is F or CF3 ; Z2 and Z3 are each H or F; Z4 is H, F or CF3 ; p1+q1+r1 is an integer from 0 to 10; s1 is 0 or 1; t1 is an integer from 0 to 5; and Y3 is the same as above, provided that when Z3 and Z4 are both H, p1+q1+r1+s1 is not 0). More specifically,
• Y 3 in formula (5a) is -COOM, and in particular, at least one selected from the group consisting of CH 2 ⁇ CFCF 2 OCF(CF 3 )COOM and CH 2 ⁇ CFCF 2 OCF(CF 3 )CF 2 OCF(CF 3 )COOM (wherein M is as defined above) is preferable, and CH 2 ⁇ CFCF 2 OCF(CF 3 )COOM is more preferable.
• the compound represented by the general formula (5) is preferably a compound (5b) represented by the general formula (5b).
• CX 2 2 CFCF 2 -O-(CF(CF 3 )CF 2 O) n5 -CF(CF 3 )-Y 3 (5b)
• each X2 is the same and represents F or H
• n5 represents 0 or an integer of 1 to 10
• Y3 is as defined above.
• n5 is preferably 0 or an integer from 1 to 5 in terms of the stability of the resulting aqueous dispersion, more preferably 0, 1 or 2, and even more preferably 0 or 1.
• Y3 is preferably -COOM in terms of obtaining appropriate water solubility and stability of the aqueous dispersion, and M is preferably H or NH4 in terms of being less likely to remain as an impurity and improving the heat resistance of the resulting molded article.
• Examples of the compound represented by formula (5b) include CH 2 ⁇ CFCF 2 OCF(CF 3 )COOM and CH 2 ⁇ CFCF 2 OCF(CF 3 )CF 2 OCF(CF 3 )COOM (wherein M is as defined above).
• examples of compounds represented by general formula (5) include compounds represented by general formula (5c).
• CF 2 CFCF 2 -O-Rf-Y 3 (5c) (Wherein, Rf and Y3 are the same as above.)
• X is -H or -F. Both Xs may be -F, or at least one X may be -H. For example, one X may be -F and the other -H, or both Xs may be -H.
• Y is -H, -F, an alkyl group or a fluorine-containing alkyl group.
• the alkyl group is an alkyl group containing no fluorine atom, and may have a carbon number of at least 1.
• the alkyl group preferably has a carbon number of at most 6, more preferably at most 4, and even more preferably at most 3.
• the fluorine-containing alkyl group is an alkyl group containing at least one fluorine atom, and may have a carbon number of at least 1.
• the fluorine-containing alkyl group preferably has a carbon number of at most 6, more preferably at most 4, and even more preferably at most 3.
• the above Y is preferably -H, -F or -CF3 , and more preferably -F.
• X and Y contains a fluorine atom.
• X may be -H
• Y and Z may be -F.
• Rf is a fluorine-containing alkylene group having 1 to 40 carbon atoms, or a fluorine-containing alkylene group having 2 to 100 carbon atoms and an ether bond.
• the number of carbon atoms in the fluorine-containing alkylene group is preferably 2 or more.
• the number of carbon atoms in the fluorine-containing alkylene group is preferably 30 or less , more preferably 20 or less, and even more preferably 10 or less.
• fluorine-containing alkylene group examples include -CF2- , -CH2CF2- , -CF2CF2- , -CF2CH2- , -CF2CF2CH2- , -CF( CF3 )-, -CF( CF3 ) CF2- , -CF( CF3 ) CH2- , and the like.
• the fluorine-containing alkylene group is preferably a perfluoroalkylene group.
• Y 3 is preferably -COOM, -SO 3 M or -OSO 3 M
• M is H, a metal atom, NR 7y 4 , an imidazolium which may have a substituent, a pyridinium which may have a substituent or a phosphonium which may have a substituent
• R 7y is H or an organic group which may be the same or different, and any two of them may be bonded to each other to form a ring).
• the organic group of R 7y is preferably an alkyl group.
• R 7y is preferably H or a C 1-10 organic group, more preferably H or a C 1-4 organic group, and even more preferably H or a C 1-4 alkyl group.
• the metal atom includes alkali metals (Group 1) and alkaline earth metals (Group 2), and is preferably Na, K or Li.
• a metal atom or NR 7 4 is preferable, -H, an alkali metal (group 1), an alkaline earth metal (group 2) or NR 7 4 is more preferable, -H, -Na, -K, -Li or NH 4 is even more preferable, -H, -Na, -K or NH 4 is even more preferable, -H, -Na or NH 4 is particularly preferable, and -H or -NH 4 is most preferable.
• the above Y3 is preferably --COOM or --SO.sub.3M , and more preferably --COOM.
• the compound represented by formula (6) is preferably at least one selected from the group consisting of compounds represented by formulae (6a), (6b), (6c), (6d) and (6e).
• CF 2 CF-O-(CF 2 ) n1 -Y 3 (6a) (In the formula, n1 represents an integer of 1 to 10, and Y3 is as defined above.)
• CF 2 CF-O-(CF 2 C(CF 3 )F) n2 -Y 3 (6b) (In the formula, n2 represents an integer of 1 to 5, and Y3 is as defined above.)
• CF 2 CF-O-(CFX 1 ) n3 -Y 3 (6c) (In the formula, X1 represents F or CF3 , n3 represents an integer of 1 to 10, and Y3 is as defined above.)
• CF 2 CF-O-(CF 2 CFX 1 O) n4 -(CF 2 ) n6 -Y 3 (6d) (In the formula, n4 represents an
• n1 is preferably an integer of 5 or less, and more preferably an integer of 2 or less.
• Y3 is preferably -COOM or -SO3M in order to obtain appropriate water solubility and stability of the aqueous dispersion, and M is preferably H or NH4 in order to prevent it from remaining as an impurity and to improve the heat resistance of the obtained molded article.
• Examples of compounds represented by formula (6a) include CF 2 ⁇ CF-O-CF 2 COOM, CF 2 ⁇ CF(OCF 2 CF 2 COOM), CF 2 ⁇ CF(OCF 2 CF 2 CF 2 COOM), CF 2 ⁇ CF-O-CF 2 SO 3 M, CF 2 ⁇ CF(OCF 2 CF 2 SO 3 M), and CF 2 ⁇ CF(OCF 2 CF 2 CF 2 SO 3 M) (wherein M is as defined above).
• n2 is preferably an integer of 3 or less from the viewpoint of the stability of the resulting aqueous dispersion
• Y3 is preferably -COOM or -SO3M from the viewpoint of obtaining appropriate water solubility and stability of the aqueous dispersion
• M is preferably H or NH4 from the viewpoint of being less likely to remain as an impurity and improving the heat resistance of the resulting molded article.
• n3 is preferably an integer of 5 or less in terms of water solubility
• Y3 is preferably -COOM or -SO3M in terms of obtaining appropriate water solubility and stability of the aqueous dispersion
• M is preferably H or NH4 in terms of improving dispersion stability.
• X1 is preferably -CF3 from the viewpoint of stability of the aqueous dispersion
• n4 is preferably an integer of 5 or less from the viewpoint of water solubility
• Y3 is preferably -COOM or -SO3M from the viewpoint of obtaining appropriate water solubility and stability of the aqueous dispersion
• M is preferably H or NH4 .
• n5 is preferably an integer of 5 or less from the viewpoint of water solubility
• Y3 is preferably -COOM or -SO3M from the viewpoint of obtaining appropriate water solubility and stability of the aqueous dispersion
• M is preferably H or NH4 .
• Examples of the compound represented by general formula (6e) include CF 2 ⁇ CFOCF 2 CF 2 CF 2 COOM and CF 2 ⁇ CFOCF 2 CF 2 CF 2 SO 3 M (wherein M represents H, NH 4 or an alkali metal).
• Rf is preferably a fluorine-containing alkylene group having 1 to 40 carbon atoms.
• at least one of X and Y preferably contains a fluorine atom.
• Y3 is preferably -SO3M or -COOM
• M is preferably H, a metal atom, NR7y4 , an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent.
• R7y represents H or an organic group.
• n1 is preferably an integer of 5 or less, and more preferably an integer of 2 or less.
• Y3 is preferably -COOM or -SO3M in order to obtain appropriate water solubility and stability of the aqueous dispersion, and M is preferably H or NH4 in order to prevent it from remaining as an impurity and to improve the heat resistance of the obtained molded article.
• M is preferably H or NH4 in order to prevent it from remaining as an impurity and to improve the heat resistance of the obtained molded article.
• Examples of the compound represented by formula (7a) include CF 2 ⁇ CFCF 2 COOM and CF 2 ⁇ CFCF 2 SO 3 M (wherein M is as defined above).
• n2 is preferably an integer of 3 or less from the viewpoint of the stability of the resulting aqueous dispersion
• Y3 is preferably -COOM or -SO3M from the viewpoint of obtaining appropriate water solubility and stability of the aqueous dispersion
• M is preferably H or NH4 from the viewpoint of being less likely to remain as an impurity and improving the heat resistance of the resulting molded article.
• the modified monomer preferably includes modified monomer (A), and preferably includes at least one selected from the group consisting of compounds represented by general formula (5a), general formula (5c), general formula (6a), general formula (6b), general formula (6c), and general formula (6d), and more preferably includes a compound represented by general formula (5a) or general formula (5c).
• the content of modified monomer (A) units is preferably in the range of 0.00001 to 1.0 mass% based on the total polymerized units of polytetrafluoroethylene.
• the lower limit is more preferably 0.0001 mass%, more preferably 0.0005 mass%, even more preferably 0.001 mass%, and even more preferably 0.005 mass%.
• the upper limits are 0.90 mass%, 0.50 mass%, 0.40 mass%, 0.30 mass%, 0.20 mass%, 0.15 mass%, 0.10 mass%, 0.08 mass%, 0.05 mass%, and 0.01 mass%.
• the polymerization of tetrafluoroethylene can be carried out under normal pressure and temperature.
• the polymerization temperature is 5 to 120° C.
• the polymerization pressure is 0.05 to 10 MPaG.
• the polymerization temperature and polymerization pressure are appropriately determined depending on the type of monomer, the molecular weight of the desired low-molecular-weight polytetrafluoroethylene, the reaction rate, and the like.
• the polymerization of tetrafluoroethylene can be stopped, if desired, by stopping the stirring of the reactor contents and venting the reactor until the pressure inside the reactor is normal.
• a polymerization terminator may be added to stop the polymerization reaction of tetrafluoroethylene.
• a compound that does not have the ability to restart after addition or chain transfer to the free radical in the polymerization system is used.
• a compound that easily undergoes a chain transfer reaction with a primary radical or a growing radical, and then generates a stable radical that does not react with a monomer, or a compound that easily undergoes an addition reaction with a primary radical or a growing radical to generate a stable radical is used.
• the activity of a chain transfer agent is generally characterized by a chain transfer constant and a restart efficiency, and among chain transfer agents, a chain transfer agent with a restart efficiency of almost 0% is called a polymerization terminator.
• the polymerization terminator for example, at least one selected from the group consisting of aromatic hydroxy compounds, aromatic amines, N,N-diethylhydroxylamine, quinone compounds, terpenes, thiocyanates, and cupric chloride (CuCl 2 ) is preferable.
• aromatic hydroxy compound unsubstituted phenol, polyhydric phenol, salicylic acid, m- or p-salicylic acid, gallic acid, naphthol, etc. can be mentioned.
• the unsubstituted phenol include o-, m-, or p-nitrophenol, o-, m-, or p-aminophenol, and p-nitrosophenol.
• polyhydric phenol examples include catechol, resorcin, hydroquinone, pyrogallol, phloroglucin, and naphthresorcinol.
• aromatic amine examples include o-, m-, or p-phenylenediamine, and benzidine.
• quinone compound examples include hydroquinone, o-, m-, or p-benzoquinone, 1,4-naphthoquinone, and alizarin.
• thiocyanate examples include ammonium thiocyanate (NH 4 SCN), potassium thiocyanate (KSCN), and sodium thiocyanate (NaSCN).
• the polymerization terminator is preferably a quinone compound, and more preferably hydroquinone.
• aqueous Dispersion Obtained by Polymerization By polymerization of tetrafluoroethylene, an aqueous dispersion containing primary particles of low-molecular-weight polytetrafluoroethylene is obtained.
• the content of low-molecular-weight polytetrafluoroethylene in the aqueous dispersion after polymerization is usually 8 to 50 mass % based on the aqueous dispersion.
• the aqueous dispersion obtained by polymerizing tetrafluoroethylene may contain fluorine-containing compounds with hydrophilic groups that are produced by polymerization of monomers.
• fluorine-containing compounds with hydrophilic groups tend to be produced.
• a typical example of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion obtained by polymerization is a fluorine-containing compound having a hydrophilic group with a molecular weight of 1000 g/mol or less. According to the manufacturing method disclosed herein, it is possible to ultimately manufacture an aqueous dispersion in which the content of the fluorine-containing compound having a hydrophilic group with a molecular weight of 1000 g/mol or less is reduced.
• the fluorine-containing compound having a hydrophilic group contains a fluorine-containing surfactant added during polymerization.
• the fluorine-containing surfactant added during polymerization is as described above for the fluorine-containing surfactant used in the polymerization of tetrafluoroethylene.
• the content of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion obtained by polymerization may be 200 ppb by mass or more, 300 ppb by mass or more, or 400 ppb by mass or more, or 10% by mass or less, 1% by mass or less, or 0.5% by mass or less, based on the aqueous dispersion.
• the content of the fluorine-containing surfactant used in polymerizing tetrafluoroethylene in the aqueous dispersion obtained by polymerization may be 200 ppb by mass or more, 300 ppb by mass or more, or 400 ppb by mass or more, or 10% by mass or less, 1% by mass or less, or 0.5% by mass or less, based on the aqueous dispersion.
• the aqueous dispersion contains a compound (I) represented by the following general formula (I) as a fluorine-containing compound having a hydrophilic group:
• n1 is an integer of 3 to 13
• M is H, a metal atom, NR 7 4 , an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent
• R 7 is H or an organic group.
• the content of compound (I) in the aqueous dispersion obtained by polymerization may be 200 ppb by mass or more, 300 ppb by mass or more, or 400 ppb by mass or more, or 10% by mass or less, 1% by mass or less, or 0.5% by mass or less, relative to the aqueous dispersion.
• the aqueous dispersion contains a compound represented by the following general formula (H1) as a fluorine-containing compound having a hydrophilic group.
• the aqueous dispersion contains a compound represented by the following general formula (H2) as a fluorine-containing compound having a hydrophilic group.
• General formula (H2) [C n-1 F 2n-1 COO ⁇ ]M + (In the formula, n is an integer of 9 to 14, and M + represents a cation.)
• the compound represented by the general formula (H2) (perfluoroalkanoic acid) is known to be formed during polymerization when perfluoro(alkyl vinyl ether) or the like is used as a monomer (see WO 2019/161153).
• the aqueous dispersion contains a compound represented by the following general formula (H3) as a fluorine-containing compound having a hydrophilic group.
• the aqueous dispersion contains a compound represented by general formula (H4) as the fluorine-containing compound having a hydrophilic group.
• General formula (H4) H-Rf n0 -Y 0 (In the formula, Rf n0 is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which some or all of H are substituted with F, and the alkylene group may contain one or more ether bonds, and some of H may be substituted with Cl.
• Y 0 is an anionic group.
• Examples of the compound represented by general formula (H4) include compounds represented by any of the following general formulas.
• General formula (H4-1) [H-(CF 2 ) m1 CO 2 - ]M + (In the formula, m1 is an integer of 3 to 20, and M + represents a cation.)
• an aqueous dispersion containing low-molecular-weight polytetrafluoroethylene is prepared by polymerizing tetrafluoroethylene, and then the aqueous dispersion is pretreated before a radical generator is added to the aqueous dispersion.
• any one of the following methods (1) to (4) is preferable. These methods can be carried out alone or in combination.
• the method (1) for example, a method of polymerizing tetrafluoroethylene and then supplying an oxygen-containing gas into a reactor to contact the aqueous dispersion with the oxygen-containing gas; a method in which after polymerizing tetrafluoroethylene, the aqueous dispersion in the reactor is recovered and stored in a container separate from the reactor, and the aqueous dispersion is brought into contact with an oxygen-containing gas (air); A method in which an oxygen-containing gas is blown into an aqueous dispersion to generate bubbles, thereby bringing the aqueous dispersion into contact with the oxygen-containing gas (bubbling method); and a method of stirring in air.
• method (1) a method in which an oxygen-containing gas is blown into the aqueous dispersion to generate bubbles and bring the aqueous dispersion into contact with the oxygen-containing gas (bubbling method), or a method in which the aqueous dispersion is stirred in the atmosphere is preferred.
• the flow rate of the gas is, for example, 1 to 30 L/min.
• the aqueous dispersion may be stirred (aeration stirring) while blowing the oxygen-containing gas into the aqueous dispersion.
• oxygen-containing gases examples include oxygen gas and air.
• the oxygen content of the oxygen-containing gas may be 20 to 100% by volume.
• the temperature at which the aqueous dispersion is brought into contact with the oxygen-containing gas is preferably 5 to 99°C, more preferably 15°C or higher, and more preferably less than 35°C.
• the pressure when the aqueous dispersion is brought into contact with the oxygen-containing gas may be normal pressure.
• the time for contacting the aqueous dispersion with the oxygen-containing gas is preferably 1 minute or more, more preferably 5 minutes or more, even more preferably 10 minutes or more, particularly preferably 30 minutes or more, preferably 48 hours or less, more preferably 24 hours or less, and even more preferably 12 hours or less.
• the time for contacting the aqueous dispersion with the oxygen-containing gas may be the time for carrying out the bubbling method.
• the time for contacting the aqueous dispersion with the oxygen-containing gas may be the stirring time for stirring in the atmosphere.
• an aqueous dispersion having an oxygen saturation of 50.0% or more by performing pretreatment of the aqueous dispersion using method (1).By sufficiently increasing the dissolved oxygen amount of the aqueous dispersion before adding the radical generator to the aqueous dispersion, the content of the fluorine-containing compound in the aqueous dispersion can be more efficiently reduced.
• the oxygen saturation of the aqueous dispersion is preferably 60.0% or more, more preferably 70.0% or more, and even more preferably 80.0% or more.
• the oxygen saturation of the aqueous dispersion may be 99% or less.
• the oxygen saturation of the aqueous dispersion is increased to 50.0 to 70.0% by pretreating the aqueous dispersion using method (1), and then the oxygen saturation of the aqueous dispersion is increased to 80.0% or more using any one of methods (1) to (4).
• oxygen saturation is the ratio of the actual amount of dissolved oxygen to the saturated amount of dissolved oxygen in water at 1 atmosphere. Oxygen saturation can be measured with an optical dissolved oxygen meter.
• an aqueous dispersion in which the content of the polymerization radical represented by the general formula (1) is 0 g ⁇ 1 or less and the content of the oxidation radical represented by the general formula (2) is 0.1 g ⁇ 1 or more by performing pretreatment of the aqueous dispersion using the method (1).
• the content of the oxidation radical may be 9.0 g ⁇ 1 or less.
• the aqueous dispersion obtained by polymerizing tetrafluoroethylene or tetrafluoroethylene and a modified monomer contains the polymerization radical represented by the general formula (1).
• the content of the fluorine-containing compound in the aqueous dispersion can be more efficiently reduced by converting the polymerization radical in the aqueous dispersion to an oxidation radical before adding a radical generator to the aqueous dispersion.
• the content of the polymerization radical does not fall below 0 g ⁇ 1 in theory, but a measured value below 0 g ⁇ 1 may be obtained.
• R is a monovalent group.
• R is preferably COOH, OH, SO 3 H, CF 3 , CH 3 , or R 11 -R 12 - (wherein R 11 represents COOH, OH, SO 3 H, CF 3 , or CH 3 , and R 12 represents a chain formed by polymerization of tetrafluoroethylene and a modifying monomer).
• An example of method (2) is a method in which an oxidizing agent is added to the aqueous dispersion, thereby bringing the aqueous dispersion into contact with the oxidizing agent.
• Oxidizing agents include gaseous oxidizing agents such as ozone gas, fluorine gas, chlorine gas, bromine gas, and iodine gas; inorganic acids and inorganic acid salts such as nitric acid, nitric acid, sulfurous acid, sulfuric acid, persulfuric acid, hydrochloric acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, hydrofluoric acid, bromic acid, iodic acid, phosphoric acid, boric acid, chromic acid, dichromate, and permanganic acid; and peroxides such as hydrogen peroxide. Of these, hydrogen peroxide is the most preferable oxidizing agent.
• the amount of oxidizing agent to be brought into contact with the aqueous dispersion is preferably 1 to 500 ppm by mass, more preferably 3 ppm by mass or more, and more preferably 200 ppm by mass or less, relative to the mass of the aqueous dispersion.
• the temperature at which the aqueous dispersion is brought into contact with the oxidizing agent is preferably 5 to 99°C, more preferably 15°C or higher, and more preferably less than 35°C.
• the pressure when contacting the aqueous dispersion with the oxidizing agent may be normal pressure.
• the time for contacting the aqueous dispersion with the oxidizing agent is preferably 1 minute or more, more preferably 5 minutes or more, even more preferably 10 minutes or more, particularly preferably 30 minutes or more, and is preferably 48 hours or less, more preferably 24 hours or less, even more preferably 12 hours or less.
• an aqueous dispersion having an oxygen saturation of 50.0% or more by pretreating the aqueous dispersion using method (2).
• the oxygen saturation of the aqueous dispersion is preferably 60.0% or more, more preferably 70.0% or more, and even more preferably 80.0% or more.
• the oxygen saturation of the aqueous dispersion may be 99% or less.
• an aqueous dispersion in which the content of the polymerization radical represented by the general formula (1) is 0 g ⁇ 1 or less and the content of the oxidation radical represented by the general formula (2) is 0.1 g ⁇ 1 or more by performing pretreatment of the aqueous dispersion using the method (2).
• the content of the oxidation radical may be 9.0 g ⁇ 1 or less.
• the aqueous dispersion obtained by polymerizing tetrafluoroethylene or tetrafluoroethylene and a modified monomer contains the polymerization radical represented by the general formula (1).
• the content of the fluorine-containing compound in the aqueous dispersion can be more efficiently reduced by converting the polymerization radical in the aqueous dispersion into the oxidation radical before adding the radical generator to the aqueous dispersion.
• the polymerization radical and the oxidation radical are as described above.
• Method (3) can be, for example, a method in which an alcohol is added to the aqueous dispersion to bring the aqueous dispersion into contact with the alcohol.
• An aqueous dispersion obtained by polymerizing tetrafluoroethylene or tetrafluoroethylene and a modified monomer contains a polymerization radical represented by general formula (1).
• the polymerization radical contained in the aqueous dispersion extracts H from the C-H bond of the alcohol, and the polymerization radical is deactivated.
• the content of the fluorine-containing compound in the aqueous dispersion can be reduced more efficiently.
• the alcohol is preferably an alcohol having 1 to 10 carbon atoms, more preferably at least one selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol and 2-butanol, and even more preferably at least one selected from the group consisting of methanol and ethanol.
• the amount of alcohol brought into contact with the aqueous dispersion is preferably 1 to 500 ppm by mass, more preferably 3 ppm by mass or more, and more preferably 200 ppm by mass or less, relative to the mass of the aqueous dispersion.
• the temperature at which the aqueous dispersion is brought into contact with the alcohol is preferably 5 to 99°C, more preferably 15°C or higher, and more preferably less than 35°C.
• the pressure when contacting the aqueous dispersion with the alcohol may be normal pressure.
• the time for contacting the aqueous dispersion with the alcohol is preferably 1 minute or more, more preferably 5 minutes or more, even more preferably 10 minutes or more, particularly preferably 30 minutes or more, and is preferably 48 hours or less, more preferably 24 hours or less, even more preferably 12 hours or less.
• an aqueous dispersion having an oxygen saturation of 50.0% or more by pretreating the aqueous dispersion using method (3).
• the oxygen saturation of the aqueous dispersion is preferably 60.0% or more, more preferably 70.0% or more, and even more preferably 80.0% or more.
• the oxygen saturation of the aqueous dispersion may be 99% or less.
• Method (4) includes a method of adjusting the pH of the aqueous dispersion to 4.0 or more by adding an alkali such as ammonia to the aqueous dispersion.
• the aqueous dispersion obtained by polymerizing tetrafluoroethylene or tetrafluoroethylene and a modified monomer contains a polymerization radical represented by general formula (1). Adjusting the pH of the aqueous dispersion to 4.0 or more improves the reactivity of the polymerization radical contained in the aqueous dispersion, and also makes it easier for radicals to be generated from the radical generator during heat treatment.
• the content of the fluorine-containing compound in the aqueous dispersion can be reduced more efficiently.
• the pH of the aqueous dispersion obtained by polymerization is usually less than 4.0, so in method (4), the pH of the aqueous dispersion is usually increased by adding an alkali.
• the pH of the aqueous dispersion can be adjusted to preferably 5.0 or higher, more preferably 6.0 or higher, and even more preferably 7.0 or higher.
• a radical generator is added to the aqueous dispersion.
• the radical generator is not particularly limited as long as it is a compound that can decompose at the temperature during heat treatment to generate radicals.
• a water-soluble radical generator is preferable because it can easily diffuse radicals in the aqueous dispersion.
• the radical generator may be an organic peroxide, an inorganic peroxide, an organic azo compound, or a combination of an oxidizing agent and a reducing agent. At least one selected from the group consisting of inorganic peroxides, organic peroxides, and a combination of an oxidizing agent and a reducing agent is preferred, and inorganic peroxides are more preferred.
• the inorganic peroxide a water-soluble inorganic peroxide is preferable.
• the inorganic peroxide include hydrogen peroxide, perchlorates, perborates, perphosphates, percarbonates, and persulfates, with persulfates being preferable.
• the persulfate at least one selected from the group consisting of ammonium persulfate, sodium persulfate, and potassium persulfate is preferable, with ammonium persulfate being more preferable.
• the organic peroxide is preferably a water-soluble organic peroxide.
• examples of the organic peroxide include peroxydicarbonates such as disuccinic acid peroxide and diglutaric acid peroxide.
• a combination of an oxidizing agent and a reducing agent can be used as a radical generator.
• radicals can be generated from the radical generator through a redox reaction between the oxidizing agent and the reducing agent, making it possible to lower the temperature during heat treatment.
• Oxidizing agents include persulfates, organic peroxides, potassium permanganate, manganese triacetate, and cerium ammonium nitrate.
• Reducing agents include sulfites, bisulfites, bromates, diimines, and oxalic acid.
• Persulfates include ammonium persulfate and potassium persulfate.
• Sulfites include sodium sulfite and ammonium sulfite. It is also preferable to add copper salts and iron salts to increase the decomposition rate of the oxidizing agent. Copper salts include copper (II) sulfate, and iron salts include iron (II) sulfate.
• Combinations of oxidizing agents and reducing agents include, for example, potassium permanganate/oxalic acid, ammonium persulfate/bisulfite/ferrous sulfate, manganese triacetate/oxalic acid, cerium ammonium nitrate/oxalic acid, bromate/bisulfite, etc., with potassium permanganate/oxalic acid being preferred.
• potassium permanganate/oxalic acid is preferred.
• either the oxidizing agent or the reducing agent may be added to the aqueous dispersion in advance, and then the other may be added continuously or intermittently.
• the amount of the radical generator added is preferably 0.0001 molar or more, more preferably 0.001 molar or more, even more preferably 0.01 molar or more, and preferably 1000 molar or less, more preferably 500 molar or less, and even more preferably 100 molar or less, relative to the number of moles of the fluorine-containing surfactant in the aqueous dispersion, from the viewpoint of improving the efficiency of removing the fluorine-containing compound having a hydrophilic group.
• the fluoropolymer in the aqueous dispersion may partially or entirely precipitate due to the heat treatment. Therefore, in order to obtain an aqueous dispersion of low molecular weight polytetrafluoroethylene in which primary particles of low molecular weight polytetrafluoroethylene are stably dispersed in an aqueous medium, it is preferable to select an upper limit for the amount of radical generator added.
• the amount of radical generator added is preferably 50 molar times or less, more preferably 25 molar times or less, even more preferably less than 10 molar times, and particularly preferably less than 5 molar times, relative to the number of moles of fluorine-containing surfactant in the aqueous dispersion, since this can suppress the precipitation of low molecular weight polytetrafluoroethylene without impairing the removal efficiency of fluorine-containing compounds having hydrophilic groups.
• the method of adding the radical generator is not particularly limited.
• the radical generator may be added directly to the aqueous dispersion, or a solution containing the radical generator may be prepared and added to the aqueous dispersion.
• the radical generator may be added while stirring the aqueous dispersion, or the aqueous dispersion may be stirred after adding the radical generator.
• the temperature of the aqueous dispersion to which the radical generator is added is not particularly limited. After the radical generator is added to the aqueous dispersion, the aqueous dispersion may be heated for the heat treatment, or the aqueous dispersion may be heated to a temperature for the heat treatment and then the radical generator is added to the aqueous dispersion.
• the heat treatment may be carried out while stirring the aqueous dispersion.
• a radical generator is added to an aqueous dispersion to prepare an aqueous dispersion containing the radical generator, and then the aqueous dispersion containing the radical generator is subjected to a heat treatment.
• the temperature of the heat treatment is not particularly limited as long as it is equal to or higher than the temperature at which the radical generator decomposes to generate radicals (decomposition temperature), but is preferably 35°C or higher, more preferably 40°C or higher, even more preferably 45°C or higher, particularly preferably 50°C or higher, preferably 120°C or lower, more preferably 110°C or lower, even more preferably 100°C or lower, and particularly preferably 90°C or lower.
• the heat treatment temperature When the heat treatment temperature is relatively high, the heat treatment may cause partial or complete precipitation of the fluoropolymer in the aqueous dispersion. Therefore, in order to obtain an aqueous dispersion of low-molecular-weight polytetrafluoroethylene in which primary particles of low-molecular-weight polytetrafluoroethylene are stably dispersed in an aqueous medium, it is preferable to select an upper limit for the heat treatment temperature.
• the heat treatment temperature is preferably 95°C or lower, more preferably 90°C or lower, and even more preferably 85°C or lower, since this can suppress precipitation of low-molecular-weight polytetrafluoroethylene without impairing the efficiency of removing fluorine-containing compounds having hydrophilic groups.
• the heating means is not particularly limited.
• a container containing the aqueous dispersion may be placed in a thermostatic bath and heated, or the aqueous dispersion may be placed in a container equipped with a heater and the aqueous dispersion may be heated by the heater.
• the pressure of the heat treatment is not particularly limited and may be normal pressure.
• the pressure of the heat treatment may be a pressure exceeding normal pressure.
• the duration of the heat treatment is not particularly limited as long as it is a time that allows the generated radicals to act sufficiently on the components contained in the aqueous dispersion, but is preferably 15 minutes or more, more preferably 30 minutes or more, even more preferably 60 minutes or more, and is preferably 1200 minutes or less, more preferably 900 minutes or less, and even more preferably 600 minutes or less.
• the heat treatment may be carried out while stirring the aqueous dispersion. Radicals are generated by the decomposition of the radical generator by the heat treatment, but when a combination of an oxidizing agent and a reducing agent is used as the radical generator, radicals are generated by the thermal decomposition of the radical generator as well as by a redox reaction.
• Low molecular weight polytetrafluoroethylene aqueous dispersion can be obtained.
• Low molecular weight polytetrafluoroethylene can be the TFE homopolymer that contains only tetrafluoroethylene unit, or can be the modified polytetrafluoroethylene that contains TFE unit and modified monomer unit.
• the low molecular weight polytetrafluoroethylene contained in the aqueous dispersion is polytetrafluoroethylene that is melt processable but not fibrillable.
• the high molecular weight polytetrafluoroethylene is polytetrafluoroethylene that is not melt processable and has fibrillable properties.
• Non-melt processable means that the melt flow rate cannot be measured at temperatures above the crystallization melting point in accordance with ASTM D 1238 and D 2116.
• the presence or absence of fibrillation properties can be determined by "paste extrusion," a typical method for molding "high molecular weight polytetrafluoroethylene powder," a powder made from a polymer of tetrafluoroethylene. Normally, paste extrusion is possible because high molecular weight polytetrafluoroethylene has fibrillation properties. If the unsintered molded product obtained by paste extrusion has no substantial strength or elongation, for example if it has an elongation of 0% and breaks when pulled, it can be considered to have no fibrillation properties.
• the melt viscosity of the low molecular weight polytetrafluoroethylene at 380°C is preferably 1 x 102 to 7 x 105 Pa ⁇ s.
• low molecular weight means that the melt viscosity is within the above range.
• High molecular weight polytetrafluoroethylene has a much higher melt viscosity than low molecular weight polytetrafluoroethylene, and it is difficult to measure its melt viscosity accurately.
• the melt viscosity is measured in accordance with ASTM D 1238 using a flow tester (manufactured by Shimadzu Corporation) and a 2 ⁇ -8L die, with a 2g sample that has been heated at 380°C for 5 minutes in advance, and maintained at the above temperature under a load of 0.7 MPa.
• the peak temperature of the low molecular weight polytetrafluoroethylene is preferably 322 to 333°C, more preferably 323°C or higher, even more preferably 324°C or higher, and more preferably 332°C or lower.
• the peak temperature can be determined by using a differential scanning calorimeter (DSC) to draw a DSC curve by heating low-molecular-weight polytetrafluoroethylene that has not been heated to a temperature of 300°C or higher at a rate of 10°C/min, and identifying the temperature on the DSC curve that corresponds to the minimum point of the heat of fusion in the temperature range of 250 to 380°C.
• DSC differential scanning calorimeter
• the aqueous dispersion contains a fluorine-containing compound having a hydrophilic group, and the content thereof is preferably 25 ppb by mass or less, more preferably 10 ppb by mass or less, even more preferably 5 ppb by mass or less, still more preferably less than 1 ppb by mass, and preferably more than 0 ppb by mass, relative to the mass of low-molecular-weight polytetrafluoroethylene in the aqueous dispersion.
• the aqueous dispersion contains a compound represented by the following general formula (H1) as a fluorine-containing compound having a hydrophilic group.
• the aqueous dispersion contains a compound represented by the following general formula (H2) as a fluorine-containing compound having a hydrophilic group.
• General formula (H2) [C n-1 F 2n-1 COO ⁇ ]M + (In the formula, n is an integer of 9 to 14, and M + represents a cation.)
• the compound represented by the general formula (H2) (perfluoroalkanoic acid) is known to be formed during polymerization when perfluoro(alkyl vinyl ether) or the like is used as a monomer (see WO 2019/161153).
• the aqueous dispersion contains a compound represented by the following general formula (H3) as a fluorine-containing compound having a hydrophilic group.
• the aqueous dispersion contains a compound represented by general formula (H4) as a fluorine-containing compound having a hydrophilic group.
• Y 0 is an anionic group.
• Examples of the compound represented by general formula (H4) include compounds represented by any of the following general formulas.
• General formula (H4-1) [H-(CF 2 ) m1 CO 2 - ]M + (In the formula, m1 is an integer of 3 to 20, and M + represents a cation.)
• the content of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion or powder can be quantified by a known method, for example, LC/MS analysis.
• methanol is added to the aqueous dispersion or powder to perform extraction, and the resulting extract is analyzed by LC/MS.
• Soxhlet extraction, ultrasonic treatment, etc. may be performed.
• the resulting extract is appropriately concentrated with nitrogen purging, and the fluorine-containing compounds in the concentrated extract are measured by LC/MS.
• Molecular weight information is extracted from the obtained LC/MS spectrum, and its agreement with the structural formula of a candidate fluorine-containing compound having a hydrophilic group is confirmed.
• aqueous solutions having five or more levels of the content of the confirmed fluorine-containing compound having a hydrophilic group are prepared, and the aqueous solutions having the respective contents are subjected to LC/MS analysis.
• the relationship between the content and the area for each content is plotted to draw a calibration curve.
• the area of the LC/MS chromatogram of the fluorine-containing compound having a hydrophilic group in the extract can be converted into the content of the fluorine-containing compound having a hydrophilic group.
• the obtained extract can be concentrated by purging with nitrogen, which makes it possible to lower the lower limit of quantification of the measurement method.
• the manufacturing method of the present disclosure after obtaining an aqueous dispersion of low-molecular-weight polytetrafluoroethylene by the above-mentioned manufacturing method, the low-molecular-weight polytetrafluoroethylene in the aqueous dispersion is coagulated to produce a wet powder containing particles of low-molecular-weight polytetrafluoroethylene, and the wet powder is dried to produce a powder.
• the method for coagulating low-molecular-weight polytetrafluoroethylene is not particularly limited.
• the aqueous dispersion is diluted with water to a polymer concentration of 5 to 20% by mass, and in some cases, the pH is adjusted to neutral or alkaline, and then the mixture is stirred in a container equipped with a stirrer with more vigor than during polymerization of tetrafluoroethylene.
• the low-molecular-weight polytetrafluoroethylene may be coagulated by adding water-soluble organic compounds such as methanol and acetone; inorganic salts such as potassium nitrate and ammonium carbonate; or inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid as coagulants to the aqueous dispersion and stirring. After coagulating the low-molecular-weight polytetrafluoroethylene, a wet powder containing particles of low-molecular-weight polytetrafluoroethylene can be collected.
• water-soluble organic compounds such as methanol and acetone
• inorganic salts such as potassium nitrate and ammonium carbonate
• inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid
• the wet powder Before drying the wet powder, the wet powder may be washed. Water or an organic solvent may be used to wash the wet powder. Washing may be performed once or multiple times.
• Organic solvents used for washing include ethers, halogenated hydrocarbons, aromatic hydrocarbons, pyridine, nitriles, nitrogen-containing polar organic compounds, dimethyl sulfoxide, alcohols, etc.
• the wet powder can be dried at a relatively low temperature.
• a powder with a small particle size and excellent fine dispersibility in other materials can be obtained.
• the drying temperature of the wet powder is preferably not more than 70°C lower than the peak temperature of the low molecular weight polytetrafluoroethylene, and more preferably not more than 100°C lower than the peak temperature of the low molecular weight polytetrafluoroethylene.
• the drying temperature of the wet powder is preferably 250° C. or less, more preferably 230° C. or less, and further preferably 220° C. or less.
• the drying temperature of the wet powder is preferably 100° C. or higher, more preferably 120° C. or higher, even more preferably 140° C. or higher, and even more preferably 160° C. or higher. If the drying temperature is too low, it takes a long time to dry, which may result in a decrease in productivity.
• the obtained powder may be classified or granulated.
• the obtained powder may also be formed into pellets.
• a powder that has excellent fine dispersibility in other materials after drying is directly obtained, so it is also a preferred embodiment not to subject the dried powder to any post-treatment.
• the aqueous dispersion and powder obtained by the manufacturing method of the present disclosure can be suitably used as molding materials, inks, cosmetics, paints, greases, office automation equipment components, additives for modifying toners, additives for plating solutions, etc.
• the molding materials include engineering plastics such as polyoxybenzoyl polyester, polyimide, polyamide, polyamideimide, polyacetal, polycarbonate, and polyphenylene sulfide.
• the powder is particularly suitable as a thickening agent for grease.
• the aqueous dispersions and powders can be used as additives to molding materials, for example to improve the non-stickiness and sliding properties of copy rolls, to improve the texture of engineering plastic molded products such as furniture surface sheets, automobile dashboards and home appliance covers, and to improve the slipperiness and abrasion resistance of machine parts that generate mechanical friction, such as light-load bearings, gears, cams, push-button phone buttons, projectors, camera parts and sliding materials.
• the aqueous dispersions and powders can be used as additives to paints to improve the slipperiness of varnishes and paints.
• the aqueous dispersions and powders can be used as additives to cosmetics to improve the slipperiness of cosmetics such as foundations.
• the powder is also suitable for applications such as improving the oil or water repellency of waxes and the like, and for improving the slipperiness of greases and toners.
• aqueous dispersions and powders can also be used as electrode binders for secondary batteries and fuel cells, hardness adjusters for electrode binders, water-repellent treatment agents for electrode surfaces, etc.
• Grease can also be prepared using powder and lubricating oil.
• the grease is characterized by containing powder and lubricating oil, so the powder is uniformly and stably dispersed in the lubricating oil, and the grease has excellent properties such as load-bearing capacity, electrical insulation, and low moisture absorption.
• the lubricating oil (base oil) may be a mineral oil or a synthetic oil.
• examples of the lubricating oil (base oil) include paraffinic or naphthenic mineral oils, synthetic hydrocarbon oils, ester oils, fluorine oils, and synthetic oils such as silicone oils. From the viewpoint of heat resistance, fluorine oils are preferred.
• examples of the fluorine oils include perfluoropolyether oils and oligomers of trifluorochloroethylene.
• the oligomers of trifluorochloroethylene may have a weight average molecular weight of 500 to 1200.
• the grease may further contain a thickener.
• the thickener include metal soaps, composite metal soaps, bentonite, phthalocyanine, silica gel, urea compounds, urea-urethane compounds, urethane compounds, and imide compounds.
• the metal soaps include sodium soaps, calcium soaps, aluminum soaps, and lithium soaps.
• the urea compounds, urea-urethane compounds, and urethane compounds include diurea compounds, triurea compounds, tetraurea compounds, other polyurea compounds, urea-urethane compounds, diurethane compounds, and mixtures thereof.
• the grease preferably contains 0.1 to 50% by mass of powder, more preferably 0.5% by mass or more, and even more preferably 30% by mass or less. If the amount of powder is too much, the grease may become too hard and may not be able to exhibit sufficient lubrication, and if the amount of powder is too little, it may not be able to exhibit sealing properties.
• the above grease may also contain solid lubricants, extreme pressure agents, antioxidants, oiliness agents, rust inhibitors, viscosity index improvers, detergents and dispersants, etc.
• a method for producing an aqueous dispersion of low molecular weight polytetrafluoroethylene comprising the steps of: preparing an aqueous dispersion containing low-molecular-weight polytetrafluoroethylene by polymerizing tetrafluoroethylene in the presence of a fluorine-containing surfactant, a polymerization initiator, a hydrocarbon-based chain transfer agent, and an aqueous medium; The resulting aqueous dispersion is pretreated,
• the present invention provides a production method for obtaining an aqueous dispersion of low-molecular-weight polytetrafluoroethylene by adding a radical generator to a pretreated aqueous dispersion and then subjecting the aqueous dispersion containing the radical generator to a heat treatment.
• a production method in which the aqueous dispersion is pretreated by at least one of the following methods.
• aqueous dispersion is pretreated using a method of contacting the aqueous dispersion with a gas containing oxygen to obtain an aqueous dispersion having an oxygen saturation of 50.0% or more.
• a production method according to any one of the first to third aspects, in which the aqueous dispersion is pretreated by contacting the aqueous dispersion with an oxygen-containing gas by blowing an oxygen-containing gas into the aqueous dispersion or by stirring the aqueous dispersion in the atmosphere.
• aqueous dispersion is pretreated using a method of contacting the aqueous dispersion with a gas containing oxygen, thereby obtaining an aqueous dispersion having a content of a polymerization radical represented by general formula (1) of 0 g -1 or less and a content of an oxidation radical represented by general formula (2) of 0.1 g -1 or more.
• aqueous dispersion is pretreated using a method in which the aqueous dispersion is brought into contact with an oxidizing agent to obtain an aqueous dispersion having a content of a polymerization radical represented by general formula (1) of 0 g ⁇ 1 or less and a content of an oxidation radical represented by general formula (2) of 0.1 g ⁇ 1 or more.
• General formula (1) R-(CF 2 -CF 2 ) n ⁇ (wherein R is a monovalent group, n is an integer of 1 or more, and ⁇ represents an unpaired electron).
• the production method according to the first or second aspect provides a method of pretreating the aqueous dispersion by contacting the aqueous dispersion with an alcohol to obtain an aqueous dispersion having an oxygen saturation level of 50.0% or higher.
• a process according to the second or ninth aspect wherein the alcohol is at least one selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol and 2-butanol.
• the polymerization initiator is a water-soluble radical polymerization initiator.
• a production method according to any one of the first to eleventh aspects, wherein the temperature of the heat treatment is equal to or higher than the decomposition temperature of the radical generator. ⁇ 13> According to a thirteenth aspect of the present disclosure, there is provided a production method according to any one of the first to twelfth aspects, wherein the radical generator is an inorganic peroxide. ⁇ 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 low-molecular-weight polytetrafluoroethylene has a peak temperature of 322 to 333° C.
• the production method according to any one of the first to fourteenth aspects wherein the low-molecular-weight polytetrafluoroethylene has a melt viscosity at 380° C. of 1 ⁇ 10 2 to 7 ⁇ 10 5 Pa ⁇ s.
• a sixteenth aspect of the present disclosure The method according to any one of the first to fifteenth aspects is provided, wherein the polymerization initiator is a persulfate, the hydrocarbon chain transfer agent is an alkane having 1 to 5 carbon atoms, and (1) a pretreatment is carried out by a method of contacting the aqueous dispersion with a gas containing oxygen to obtain an aqueous dispersion having an oxygen saturation of 50.0% or more.
• the polymerization initiator is a persulfate
• the hydrocarbon chain transfer agent is an alkane having 1 to 5 carbon atoms
• aqueous dispersion is pretreated to obtain an aqueous dispersion having an oxygen saturation level of 80% or more.
• a persulfate is added to the pretreated aqueous dispersion in an amount of 0.01 to 5 times the molar amount of the fluorosurfactant in the aqueous dispersion, and the aqueous dispersion containing the persulfate is heat-treated at 35 to 95° C.
• a method for producing a powder of low molecular weight polytetrafluoroethylene comprising the steps of: After obtaining an aqueous dispersion of low-molecular-weight polytetrafluoroethylene by the production method according to any one of the first to seventeenth aspects, preparing a wet powder containing particles of the low-molecular-weight polytetrafluoroethylene by coagulating the low-molecular-weight polytetrafluoroethylene in the aqueous dispersion; The method for producing the powder includes drying the wet powder to produce the powder.
• ⁇ Amount of Radicals in Aqueous Dispersion The contents of polymerization radicals and oxidation radicals in the aqueous dispersion were determined by electron spin resonance (ESR) method.
• Polymerization radical HOOC-(CF 2 -CF 2 ) n ⁇ (wherein n is an integer of 1 or more, ⁇ represents an unpaired electron).
• Oxidizing radical HOOC-(CF 2 -CF 2 ) n O-O. (wherein n is an integer of 1 or more, and . represents an unpaired electron.)
• DTA differential thermal
• the content of the compound represented by general formula (H4-1) was calculated by converting it to perfluorooctanoic acid.
• Ym Xm ⁇ 12.6 (1)
• Ym the content (mass ppb/resin) of the compound represented by the general formula (H4-1) having the carbon number (m1+1) contained in the powder
• Xm content (ng/mL) of the compound represented by general formula (H4-1) having the carbon number (m1+1) contained in the extract
• the content of the compound represented by general formula (H4-1) having the carbon number (m1+1) contained in the aqueous dispersion was calculated using the following relational formula (2).
• Ym Xm ⁇ (1.26+(100-P)/100)/(P/100) (1)
• Ym the content (mass ppb/resin) of the compound represented by general formula (H4-1) having the carbon number (m1+1) contained in the aqueous dispersion
• Xm content (ng/mL) of the compound represented by general formula (H4-1) having the carbon number (m1+1) contained in the extract
• P solids concentration (mass%) of the aqueous dispersion
• the lower limit of quantification for the content of the compound represented by general formula (H4-1) with carbon number (m1+1) contained in the aqueous dispersion is 1.26 + (100-P)/100)/(P/100) mass ppb/resin.
• the lower limit of quantification for the content of the compound represented by the general formula (H4-1) with the carbon number (m1+1) contained in the powder is 13 ppb by mass/resin.
• Comparative Example 1 A polymerization reaction of TFE was carried out according to a method similar to Example 7 of WO 2009/020187 to obtain PTFE aqueous dispersion 1. 4 kg of PTFE aqueous dispersion 1 was obtained. The oxygen saturation was 0%.
• Comparative Example 2 PTFE aqueous dispersion 1 was polymerized in the same manner as in Comparative Example 1. The oxygen saturation was 0%.
• Example 1 In the same manner as in Comparative Example 1, PTFE aqueous dispersion 1 was polymerized. The pH of PTFE aqueous dispersion 1 was 3.4. After that, the autoclave was opened, and 4 kg of the obtained PTFE aqueous dispersion 1 was transferred to another container. The oxygen saturation was 53.4%, the amount of polymerization radicals was 0 g -1 , and the amount of oxidation radicals was 4.0 g -1 .
• the temperature in the tank was raised under stirring, and when the temperature in the tank reached 80°C, an aqueous solution in which 1.2 g of ammonium persulfate [APS] was dissolved was injected into the tank with nitrogen, the pressure in the tank was set to 0.60 MPa, and the mixture was stirred for 3 hours to perform heat treatment, thereby obtaining PTFE aqueous dispersion 3.
• the solid content concentration was 15.9% by mass.
• Example 2 The same procedure as in Example 1 was carried out, except that the amount of ammonium persulfate [APS] added in the heat treatment was 11.7 g.
• the oxygen saturation of the aqueous dispersion after transferring to the container was 53.4%, the amount of polymerization radicals was 0 g -1 , and the amount of oxidation radicals was 4.0 g -1 .
• the PTFE contained in the aqueous dispersion after polymerization was partially coagulated by the heat treatment, and a PTFE aqueous dispersion and a PTFE wet powder 1 were obtained.
• the solid content concentration of the PTFE aqueous dispersion was 0.1 mass%.
• Comparative Example 3 85.8g of 10% by weight nitric acid aqueous solution was added to 4kg of the above PTFE aqueous dispersion liquid 1, and coagulated by applying strong mechanical shearing force, and then 12.6g of 24% by weight sodium hydroxide aqueous solution was added to neutralize.
• the obtained wet powder was filtered and washed with 4200g of pure water. After repeating this washing operation six times, the powder was dried for 18 hours in a hot air circulation dryer at 100°C to obtain PTFE powder.
• Various physical properties of the obtained PTFE powder were measured. The melt viscosity of the PTFE powder was 2.2 ⁇ 10 4 Pa ⁇ s, and the peak temperature was 329°C. This shows that the obtained PTFE powder is low molecular weight PTFE.
• Comparative Example 4 A PTFE powder was obtained in the same manner as in Comparative Example 3, except that the PTFE aqueous dispersion 2 was used. Various physical properties of the obtained PTFE powder were measured. The melt viscosity of the PTFE powder was 2.2 x 104 Pa ⁇ s, and the peak temperature was 329°C. This shows that the obtained PTFE powder is low molecular weight PTFE.
• Example 3 A PTFE powder was obtained in the same manner as in Comparative Example 3, except that the above PTFE aqueous dispersion 3 was used. Various physical properties of the obtained PTFE powder were measured. The melt viscosity of the PTFE powder was 2.2 x 104 Pa ⁇ s, and the peak temperature was 329°C. This shows that the obtained PTFE powder is low molecular weight PTFE.
• Example 4 The above PTFE wet powder 1 was washed with 4200 g of pure water. This washing operation was repeated six times, and then the powder was dried in a hot air circulation dryer at 100°C for 18 hours to obtain a PTFE powder. Various physical properties of the obtained PTFE powder were measured. The melt viscosity of the PTFE powder was 2.2 x 104 Pa ⁇ s, and the peak temperature was 329°C. This shows that the obtained PTFE powder is low molecular weight PTFE.
• Example 5 Except for changing the heat treatment time to 1 hour, a PTFE aqueous dispersion was obtained in the same manner as in Example 1. After transferring to a container, the oxygen saturation of the aqueous dispersion was 53.4%, the amount of polymerization radicals was 0 g -1 , and the amount of oxidation radicals was 4.0 g -1 . The solid content concentration was 14.7 mass%.
• Example 6 Except for changing the heat treatment time to 0.5 hours, the same procedure as in Example 1 was followed to obtain an aqueous PTFE dispersion. After transferring to a container, the aqueous dispersion had an oxygen saturation of 53.4%, a polymerization radical amount of 0 g -1 , and an oxidation radical amount of 4.0 g -1 . The solid content was 15.5% by mass.
• Example 7 PTFE aqueous dispersion 1 was polymerized in the same manner as in Comparative Example 1. The autoclave was opened, and 4 kg of the obtained PTFE aqueous dispersion 1 was transferred to another container, and air was blown in at a flow rate of 2 L/min for 1 hour for bubbling. The oxygen saturation of the aqueous dispersion was 97.3%, the amount of polymerization radicals was 0 g -1 , and the amount of oxidation radicals was 7.0 g -1 .
• Example 8 A PTFE aqueous dispersion was obtained in the same manner as in Example 7, except that the heat treatment time was changed to 1 hour.
• the oxygen saturation of the aqueous dispersion after bubbling was 97.3%, the amount of polymerization radicals was 0 g -1 , and the amount of oxidation radicals was 7.0 g -1 .
• the solid content concentration was 15.4 mass%.
• Reference Example 5 A PTFE aqueous dispersion was obtained in the same manner as in Example 7, except that the gas used for bubbling was nitrogen and the flow rate was 5 L/min.
• the oxygen saturation of the aqueous dispersion after bubbling was 87.4%
• the amount of polymerization radicals was 0 g -1
• the amount of oxidation radicals was 6.4 g -1 .
• the solid content concentration was 15.4 mass%.
• Example 9 A PTFE aqueous dispersion was obtained in the same manner as in Example 7, except that the air flow rate was 5 L/min, the bubbling time was 0.1 hours, and the heat treatment time was 0.5 hours.
• the oxygen saturation of the aqueous dispersion after bubbling was 88.5%, the amount of polymerization radicals was 0 g -1 , and the amount of oxidation radicals was 6.5 g -1 .
• the solid content concentration was 15.9 mass%.
• Example 10 A PTFE aqueous dispersion was obtained in the same manner as in Example 9, except that the bubbling time was changed to 0.5 hours.
• the oxygen saturation of the aqueous dispersion after bubbling was 97.4%
• the amount of polymerization radicals was 0 g -1
• the amount of oxidation radicals was 7.0 g -1 .
• the solid content concentration was 15.8 mass%.
• Example 11 A PTFE aqueous dispersion was obtained in the same manner as in Example 9, except that the bubbling time was changed to 1 hour.
• the oxygen saturation of the aqueous dispersion after bubbling was 97.4%
• the amount of polymerization radicals was 0 g -1
• the amount of oxidation radicals was 7.2 g -1 .
• the solid content concentration was 15.9 mass%.
• Example 12 A PTFE aqueous dispersion was obtained in the same manner as in Example 9, except that the bubbling time was changed to 2 hours.
• the oxygen saturation of the aqueous dispersion after bubbling was 97.4%
• the amount of polymerization radicals was 0 g -1
• the amount of oxidation radicals was 7.0 g -1 .
• the solid content concentration was 15.9 mass%.
• Example 13 In the same manner as in Comparative Example 1, PTFE aqueous dispersion 1 was polymerized. The autoclave was opened, and 4 kg of the obtained PTFE aqueous dispersion 1 was transferred to another container. The temperature in the tank was raised under stirring, and when the temperature in the tank reached 80°C, an aqueous solution in which 3.5 g of hydrogen peroxide [H 2 O 2 ] was dissolved in 10 ml of deionized water as an oxidizing agent was added, and the mixture was stirred for 10 minutes under an air atmosphere.
• H 2 O 2 hydrogen peroxide
• the oxygen saturation of the aqueous dispersion was 90.0%, the amount of polymerization radicals was 0 g -1 , and the amount of oxidation radicals was 7.0 g -1 .
• the oxygen in the system was removed by repeatedly injecting nitrogen gas and degassing it several times, and then an aqueous solution in which 1.2 g of ammonium persulfate [APS] was dissolved was injected into the tank with nitrogen, the pressure in the tank was set to 0.60 MPa, and the mixture was stirred for 0.5 hours to perform heat treatment, thereby obtaining a PTFE aqueous dispersion.
• the solid content concentration was 15.0% by mass.
• Example 14 A PTFE aqueous dispersion was obtained in the same manner as in Example 13, except that the amount of H 2 O 2 added was 35.4 g. The oxygen saturation of the aqueous dispersion after H 2 O 2 addition and stirring was 93.0%, the amount of polymerization radicals was 0 g -1 , and the amount of oxidation radicals was 7.2 g -1 . The solid content concentration was 14.7 mass%.
• Example 15 A PTFE aqueous dispersion was obtained in the same manner as in Example 13, except that the aqueous solution of hydrogen peroxide was changed to 1.7 g of methanol [MeOH].
• the oxygen saturation of the aqueous dispersion after addition of MeOH and stirring was 88.0%, the amount of polymerization radicals was 0 g -1 , and the amount of oxidation radicals was 3.9 g -1 .
• the solid content concentration was 15.4 mass%.
• Example 16 A PTFE aqueous dispersion was obtained in the same manner as in Example 15, except that the amount of MeOH added was 16.8 g. The oxygen saturation of the aqueous dispersion after the addition of MeOH and stirring was 88.0%, the amount of polymerization radicals was 0 g , and the amount of oxidation radicals was 2.6 g . The solid content concentration was 15.3 mass%.
• Example 17 The PTFE aqueous dispersion 1 was polymerized in the same manner as in Comparative Example 1. After that, the autoclave was opened, and 4 kg of the obtained PTFE aqueous dispersion 1 was transferred to another container, and a 0.2% aqueous solution of Na 2 CO 3 was added, and the pH was adjusted to 5.6.
• the temperature in the tank was raised under stirring, and when the temperature in the tank reached 80°C, an aqueous solution in which 1.2 g of ammonium persulfate [APS] was dissolved was injected into the tank with nitrogen, and the tank pressure was set to 0.60 MPa, and the heat treatment was performed by stirring for 0.5 hours, to obtain a PTFE aqueous dispersion.
• the solid content concentration was 14.6% by mass.
• Example 18 A PTFE aqueous dispersion was obtained in the same manner as in Example 17, except that the pH was adjusted to 7.0. The solid content concentration was 14.5% by mass.
• Example 19 A PTFE aqueous dispersion was obtained in the same manner as in Example 17, except that the pH was adjusted to 9.0. The solid content concentration was 14.4% by mass.
• Example 20 PTFE Aqueous Dispersion 1 was polymerized in the same manner as in Comparative Example 1. The autoclave was opened, and 4 kg of the obtained PTFE Aqueous Dispersion 1 was transferred to another container, and air was blown in at a flow rate of 5 L/min for 1 hour for bubbling.
• FIG. 1 shows the first differential spectra (horizontal axis: g value (-), vertical axis: Int. [PTFE]/Int. [Mn 2+ ]/sample weight (g -1 )) of the aqueous dispersions obtained in Examples 1, 9, 11, 15 and 16. From the results shown in FIG. 1, no triplets are observed in the first differential spectra of the aqueous dispersions obtained by the production method of the present disclosure, and only singlets appear. This result indicates that no polymerization radicals are present in the aqueous dispersions, and only oxidation radicals are present.

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