Method for producing fluoropolymer and fluoropolymer

Abstract

Provided is a production method for producing a fluoropolymer by polymerizing a fluoromonomer in the presence of an aqueous medium, a chain-transfer agent, and a polymerization initiator and substantially in the absence of a surfactant in a reaction vessel, in which the chain-transfer agent in an amount of 10.0 mol% or more relative to the total amount of aqueous medium, fluoromonomer, and monomer and chain-transfer agent in the gas phase within the reaction vessel is supplied to the reaction vessel, and polymerization of the fluoromonomer is then initiated by supplying the polymerization initiator to the reaction vessel.

Description

Fluoropolymer manufacturing method and fluoropolymer

[0001] The present disclosure relates to methods for making fluoropolymers and to fluoropolymers.

[0002] Patent Document 1 describes a method for producing an aqueous dispersion of low-molecular-weight polytetrafluoroethylene [PTFE], which comprises carrying out emulsion polymerization of tetrafluoroethylene [TFE] or a monomer copolymerizable with TFE and TFE in an aqueous medium containing a polymerization initiator in the presence of a chain transfer agent without adding a fluorinated surfactant, wherein the chain transfer agent is at least one compound selected from the group consisting of hydrogen, hydrocarbons having 1 to 3 carbon atoms and halogenated hydrocarbons having 1 to 3 carbon atoms, and the polymerization initiator is a water-soluble peroxide.

[0003] JP 2009-001745 A

[0004] An object of the present disclosure is to provide a novel method for producing a fluoropolymer by polymerization substantially in the absence of surfactants.

[0005] According to the present disclosure, there is provided a method for producing a fluoropolymer by polymerizing a fluoromonomer in a reaction vessel in the presence of an aqueous medium, a chain transfer agent and a polymerization initiator in the substantial absence of a surfactant, the method comprising supplying into the reaction vessel an amount of chain transfer agent of 10.0 mol % or more relative to the total amount of the aqueous medium, the fluoromonomer, and the monomer and chain transfer agent in the gas phase in the reaction vessel, and then supplying a polymerization initiator into the reaction vessel to initiate polymerization of the fluoromonomer.

[0006] According to the present disclosure, a novel method for producing a fluoropolymer by polymerization substantially in the absence of a surfactant can be provided.

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

[0008] In the present disclosure, fluororesins are partially crystalline fluoropolymers, or fluoroplastics. Fluororesins have a melting point and are thermoplastic, but may be melt-processable or non-melt-processable.

[0009] In the present disclosure, melt-processable means that the polymer can be melted and processed using conventional processing equipment such as an extruder, an injection molding machine, etc. Therefore, melt-processable fluororesins usually have a melt flow rate of 0.01 to 500 g / 10 min, as measured by the measurement method described below.

[0010] In the present disclosure, polytetrafluoroethylene [PTFE] is preferably a fluoropolymer having a content of tetrafluoroethylene units relative to all polymer units of 99 mol % or more.

[0011] In the present disclosure, the fluororesin (excluding polytetrafluoroethylene) is preferably a fluoropolymer having a tetrafluoroethylene content of less than 99 mol% relative to all polymerized units.

[0012] In the present disclosure, the content of each monomer constituting the fluoropolymer can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and X-ray fluorescence analysis depending on the type of monomer.

[0013] In the present disclosure, the term "organic group" refers to a group containing one or more carbon atoms or a group formed by removing one hydrogen atom from an organic compound. The organic group is preferably an alkyl group which may have one or more substituents.

[0014] In this disclosure, ranges expressed by endpoints include all numbers subsumed within that range (eg, 1 to 10 includes 1.4, 1.9, 2.33, 5.75, 9.98, etc.).

[0015] In this disclosure, the term "at least 1" includes all numbers greater than or equal to 1 (e.g., at least 2, at least 4, at least 6, at least 8, at least 10, at least 25, at least 50, at least 100, etc.).

[0016] Specific embodiments of the present disclosure will be described in detail below, but the present disclosure is not limited to the following embodiments.

[0017] Patent Document 1 describes that by using the above-mentioned production method, the polymerization reaction can be maintained in an emulsified state in the reaction system without adding a fluorine-containing surfactant, and that low-molecular-weight PTFE can ultimately be obtained in the form of a stable aqueous dispersion with a solid content of about 12% by mass. Patent Document 1 also describes that the emulsified particles preferably have an average primary particle size of 50 to 300 nm in terms of dispersion stability, and that the low-molecular-weight PTFE powder obtained by emulsion polymerization is formed by agglomeration of emulsified particles, and therefore its specific surface area is larger than that of the low-molecular-weight PTFE powder obtained directly by suspension polymerization, generally 7 to 15 m. ２ It is stated that the saturation energy is / g.

[0018] However, there is a demand for a new production method that allows the polymerization reaction to proceed in the same manner as or more smoothly than conventional production methods without using a surfactant.

[0019] According to the production method of the present disclosure, the polymerization reaction can proceed in the same manner as or more smoothly than conventional production methods without using a surfactant. Therefore, the production method of the present disclosure can produce fluoropolymer particles with a small average primary particle size and a fluoropolymer powder with a large specific surface area. Furthermore, the production method of the present disclosure can produce an aqueous fluoropolymer dispersion with a higher solids concentration than conventional production methods.

[0020] 1. Production Method In the production method of the present disclosure, a fluoropolymer is produced by polymerizing a fluoromonomer in a reaction vessel in the presence of an aqueous medium, a chain transfer agent, and a polymerization initiator, substantially in the absence of a surfactant.

[0021] Furthermore, in the production method of the present disclosure, when initiating polymerization of the fluoromonomer, a chain transfer agent is supplied into the reaction vessel in an amount of 10.0 mol % or more relative to the total amount of the aqueous medium, the fluoromonomer, and the monomer and chain transfer agent in the gas phase in the reaction vessel, and then a polymerization initiator is supplied into the reaction vessel to initiate polymerization of the fluoromonomer.

[0022] Although the detailed cause is unknown, adding a relatively large amount of chain transfer agent before supplying the polymerization initiator, i.e., before starting the polymerization reaction of the fluoromonomer, allows an aqueous dispersion with a high solids content to be obtained without the use of a surfactant, thereby allowing the polymerization reaction to proceed smoothly. Furthermore, in the production method of the present disclosure, the polymerization reaction usually proceeds in a state in which the fluoromonomer is emulsified in the aqueous medium, so fluoropolymer particles with a small average primary particle size can be obtained, and a fluoropolymer powder with a large specific surface area can be obtained. Furthermore, the production method of the present disclosure usually produces an aqueous dispersion containing fluoropolymer particles. The production method of the present disclosure also makes it possible to obtain an aqueous dispersion with a higher solids concentration than conventional production methods. Furthermore, when polymerization is carried out in the presence of a hydrocarbon surfactant, the resulting fluoropolymer may become discolored. However, in the production method of the present disclosure, polymerization is carried out substantially in the absence of a surfactant, so the problem of discoloration of the resulting fluoropolymer is less likely to occur.

[0023] In the production method of the present disclosure, before supplying the polymerization initiator into the reaction vessel, the aqueous medium, the fluoromonomer, and the chain transfer agent are supplied into the reaction vessel.

[0024] From the viewpoint of polymerization efficiency, the supply ratio of the chain transfer agent is 10.0 mol% or more, preferably 12.0 mol% or more, more preferably 14.0 mol% or more, even more preferably 15.0 mol% or more, and preferably 70.0 mol% or less, more preferably 60.0 mol% or less, even more preferably 50.0 mol% or less, based on the total amount of the monomer and the chain transfer agent in the gas phase in the reaction vessel.

[0025] The supply ratio (mol %) of the chain transfer agent to the total amount of the monomer and chain transfer agent in the gas phase in the reaction vessel can be calculated by the following formula: Supply ratio (mol %) of chain transfer agent = Supply amount of chain transfer agent (mol) / Total amount of monomer and chain transfer agent (mol) × 100 Total amount of monomer and chain transfer agent (mol) = [(Pressure in reaction vessel (PaG)) × (Volume of gas phase in reaction vessel (L))] / [8.314 × 10 ３ (Pa·L / (mol·K))×(temperature in reaction vessel (K))]

[0026] The total amount of monomer and chain transfer agent is the total amount of monomer and chain transfer agent present in the gas phase in the reaction vessel at the time when the polymerization initiator is supplied into the reaction vessel.The total amount of monomer and chain transfer agent does not include the amount of monomer and chain transfer agent dissolved in the aqueous medium and not present in the gas phase.In addition, the amount of monomer includes not only the amount of fluoromonomer but also the amount of fluorine-free monomer when fluorine-free monomer is supplied into the reaction vessel.

[0027] After the aqueous medium, the fluoromonomer and the chain transfer agent are fed into a reaction vessel, a polymerization initiator is fed into the reaction vessel to initiate polymerization of the fluoromonomer.

[0028] The supply ratio of the polymerization initiator relative to the total amount of the monomer and chain transfer agent in the gas phase in the reaction vessel is preferably 1.0 mol% or more, more preferably 1.5 mol% or more, even more preferably 2.0 mol% or more, still more preferably 2.5 mol% or more, and is preferably 25.0 mol% or less, more preferably 20.0 mol% or less, and even more preferably 15.0 mol% or less.

[0029] By adding a relatively large amount of polymerization initiator in this way, the polymerization reaction can proceed more smoothly without using a surfactant.

[0030] The supply ratio (mol %) of the polymerization initiator to the total amount of the monomer and chain transfer agent in the gas phase in the reaction vessel can be calculated by the following formula: Supply ratio (mol %) of polymerization initiator = Supply amount of polymerization initiator (mol) / Total amount of monomer and chain transfer agent (mol) × 100 Total amount of monomer and chain transfer agent (mol) = [(Pressure in reaction vessel (PaG)) × (Volume of gas phase in reaction vessel (L))] / [8.314 × 10 ３ (Pa·L / (mol·K)×(temperature in reaction vessel (K))]

[0031] When the polymerization initiator is a redox initiator, the supply amount of the polymerization initiator is the total supply amount of the oxidizing agent and the reducing agent. The supply amount of the polymerization initiator is also the total supply amount of the polymerization initiator used in the polymerization. For example, when the polymerization initiator is supplied continuously or intermittently during the polymerization, the supply amount of the polymerization initiator is the total amount of the polymerization initiator supplied.

[0032] The pressure inside the reaction vessel when starting polymerization of the fluoromonomer is preferably 0.01 MPaG or more, more preferably 0.05 MPaG or more, even more preferably 0.10 MPaG or more, and preferably 10.00 MPaG or less, more preferably 1.00 MPaG or less, even more preferably 0.30 MPaG or less.

[0033] The polymerization of the fluoromonomer can be carried out while stirring the contents of the reaction vessel.

[0034] The pressure in the reaction vessel can be adjusted mainly by the amount of monomer fed into the reaction vessel. By feeding a sufficient amount of monomer into the reaction vessel when starting the polymerization of the fluoromonomer, the polymerization reaction can proceed more smoothly without using a surfactant.

[0035] The polymerization pressure after the initiation of polymerization of the fluoromonomer may be, for example, 0.05 to 10 MPaG. Usually, the polymerization temperature is 5 to 120° C. The polymerization temperature and polymerization pressure are appropriately determined depending on the type of monomer used, the molecular weight of the target fluoropolymer, and the reaction rate.

[0036] After starting the polymerization of fluoromonomer, part or all of the chain transfer agent can be removed from the reaction vessel.Furthermore, after removing part or all of the chain transfer agent from the reaction vessel, the chain transfer agent can be supplied again into the reaction vessel.By adjusting the amount of chain transfer agent present in the reaction vessel in this way, the polymerization reaction can proceed smoothly, the molecular weight of the fluoropolymer can be appropriately adjusted, and a high solid content can be achieved.

[0037] The removal of the chain transfer agent is preferably carried out before the amount of fluoropolymer produced reaches 10% by mass relative to the mass of the fluoropolymer finally obtained.By removing the chain transfer agent at a relatively early stage, the polymerization reaction can proceed smoothly, and the molecular weight of the fluoropolymer can be more appropriately adjusted, and further, a higher solid content can be achieved.

[0038] The chain transfer agent is preferably removed after the amount of fluoropolymer produced reaches 0.3 mass % relative to the mass of the finally obtained fluoropolymer, and more preferably after it reaches 0.5 mass %. If the chain transfer agent is removed too early, the polymerization reaction may not proceed smoothly.

[0039] In one embodiment, the pressure in the reaction vessel is adjusted to 0.30 MPaG or less to initiate polymerization of the fluoromonomer, and during polymerization, the pressure in the reaction vessel can be adjusted to more than 0.30 MPaG to continue polymerization of the fluoromonomer. Also, in one embodiment, the pressure in the reaction vessel is adjusted to 0.30 MPaG or less to initiate polymerization of the fluoromonomer, and then part or all of the chain transfer agent is removed from the reaction vessel, and the pressure in the reaction vessel is adjusted to more than 0.30 MPaG to continue polymerization of the fluoromonomer. In this way, by starting the polymerization reaction at a low pressure and then continuing the polymerization reaction at a high pressure, the polymerization reaction can proceed smoothly, the molecular weight of the fluoropolymer can be more appropriately adjusted, and a higher solids concentration can be achieved. After adjusting the pressure in the reaction vessel to more than 0.30 MPaG, the pressure in the reaction vessel can be reduced to 0.30 MPaG or less.

[0040] (Chain Transfer Agent) Examples of chain transfer agents include esters such as dimethyl malonate, diethyl malonate, methyl acetate, ethyl acetate, butyl acetate, and dimethyl succinate, as well as isopentane, methane, ethane, propane, methanol, isopropanol, acetone, various mercaptans, various halogenated hydrocarbons such as carbon tetrachloride, and cyclohexane.

[0041] The chain transfer agent is preferably a compound that is gaseous at room temperature (15 to 25°C), and preferably a compound with a normal boiling point of 20°C or less. By using a chain transfer agent that is gaseous at room temperature, the polymerization reaction can proceed more smoothly and the amount of chain transfer agent in the reaction vessel can be easily adjusted. For example, the amount of chain transfer agent in the reaction vessel can be easily adjusted by releasing the chain transfer agent from the reaction vessel during the polymerization.

[0042] The chain transfer agent is preferably a compound containing one or more hydrogen atoms, and particularly preferably a non-halogenated alkane having 2 to 4 carbon atoms. Specifically, at least one selected from the group consisting of methane, ethane, propane, butane, and isobutane is more preferred, and at least one selected from the group consisting of ethane and propane is even more preferred.

[0043] (Polymerization Initiator) As the polymerization initiator, at least one selected from the group consisting of water-soluble radical polymerization initiators and redox initiators can be suitably used. As the water-soluble radical polymerization initiator, known water-soluble peroxides are preferred, such as ammonium salts, potassium salts, and sodium salts of persulfuric acid, perborate, perchloric acid, perphosphoric acid, and percarbonate; organic peroxides such as disuccinic acid peroxide and diglutaric acid peroxide; t-butyl permaleate; and t-butyl hydroperoxide. A reducing agent such as a sulfite may also be contained, and the amount used may be 0.1 to 20 times the amount of the peroxide. Among these, persulfates are preferred because they can more smoothly promote the polymerization reaction.

[0044] It is also preferable to use a redox initiator, which combines an oxidizing agent and a reducing agent, as the polymerization initiator. Examples of oxidizing agents include persulfates, organic peroxides, potassium permanganate, manganese triacetate, and cerium ammonium nitrate. Examples of reducing agents include sulfites, bisulfites, bromates, diimines, and oxalic acid. Examples of persulfates include ammonium persulfate and potassium persulfate. Examples of sulfites include sodium sulfite and ammonium sulfite. In order to increase the decomposition rate of the initiator, it is also preferable to add a copper salt or an iron salt to the combination of redox initiators. Examples of copper salts include copper(II) sulfate, and examples of iron salts include iron(II) sulfate.

[0045] Examples of the redox initiator include potassium permanganate / oxalic acid, potassium permanganate / ammonium oxalate, ammonium persulfate / bisulfite / iron sulfate, ammonium persulfate / ammonium sulfite, manganese triacetate / oxalic acid, cerium ammonium nitrate / oxalic acid, and bromate / bisulfite, with potassium permanganate / oxalic acid and ammonium persulfate / bisulfite / iron sulfate being preferred. When using a redox initiator, either an oxidizing agent or a reducing agent may be charged into a polymerization vessel in advance, and then the other may be added continuously or intermittently to initiate polymerization. For example, when using potassium permanganate / oxalic acid, it is preferred to charge oxalic acid into a polymerization vessel and then continuously add potassium permanganate thereto.

[0046] (Aqueous Medium) The aqueous medium is a reaction medium for polymerization and refers to a liquid containing water. The aqueous medium is not particularly limited as long as it contains water, and may contain water and, for example, a fluorine-free organic solvent such as an ether or a ketone, and / or a fluorine-containing organic solvent having a boiling point of 40° C. or lower.

[0047] As the aqueous medium, an aqueous medium containing only water or an aqueous medium containing only water and a fluorine-free organic solvent is preferred, as it allows the polymerization to proceed smoothly, and an aqueous medium containing only water is more preferred.

[0048] The content of water in the aqueous medium is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99.0% by mass or more, still more preferably 99.5% by mass or more, particularly preferably 99.9% by mass or more, and may be 100% by mass, based on the mass of the aqueous medium, in order to allow the polymerization to proceed smoothly.

[0049] In the production method of the present disclosure, it is preferable to use an aqueous medium in an amount that occupies 20.0 to 80.0 volume % of the internal volume of the reaction vessel. The amount of aqueous medium in the reaction vessel is preferably an amount that occupies 75.0 volume % or less of the internal volume of the reaction vessel, and more preferably an amount that occupies 70.0 volume % or less of the internal volume of the reaction vessel. By forming a gas phase portion of an appropriate size in the reaction vessel, the polymerization reaction can proceed more smoothly. The formed gas phase portion is filled with monomer, or monomer and chain transfer agent, when polymerization of the fluoromonomer begins.

[0050] (Surfactant) In the production method of the present disclosure, polymerization of fluoromonomers is carried out substantially in the absence of surfactants. In the present disclosure, "substantially in the absence of surfactants" means that the amount of surfactant relative to the aqueous medium is 10 mass ppm or less. The amount of surfactant relative to the aqueous medium is preferably 1 mass ppm or less, more preferably 100 mass ppb or less, even more preferably 10 mass ppb or less, and still more preferably 1 mass ppb or less. "Polymerization carried out in the absence of surfactants" includes polymerization carried out without intentionally adding a surfactant.

[0051] Examples of the surfactant include anionic surfactants, nonionic surfactants, cationic surfactants, etc. Examples of the surfactant include fluorine-containing surfactants, hydrocarbon-containing surfactants (fluorine-free surfactants), reactive surfactants, etc.

[0052] (Additives) In the polymerization, additives may be used, such as a buffer, a pH adjuster, a stabilizing aid, and a dispersion stabilizer.

[0053] Preferred stabilizing aids include paraffin wax, fluorine-based oil, fluorine-based solvent, and silicone oil. The stabilizing aids may be used alone or in combination of two or more. Paraffin wax is more preferred as the stabilizing aid. Paraffin wax may be liquid, semi-solid, or solid at room temperature, but saturated hydrocarbons having 12 or more carbon atoms are preferred. The melting point of the paraffin wax is generally preferably 40 to 65°C, more preferably 50 to 65°C.

[0054] The amount of the stabilizing aid used is preferably 0.1 to 12% by mass, more preferably 0.1 to 8% by mass, based on the mass of the aqueous medium used. It is desirable that the stabilizing aid is sufficiently hydrophobic so that it is completely separated from the aqueous dispersion after polymerization and does not become a contaminating component.

[0055] The polymerization is carried out by charging an aqueous medium, a monomer, a chain transfer agent, and, if necessary, additives into a polymerization reactor, stirring the contents of the reactor, maintaining the reactor at a predetermined polymerization temperature, and then adding a predetermined amount of a polymerization initiator to initiate the polymerization reaction. After the start of the polymerization reaction, additional monomers, polymerization initiators, chain transfer agents, etc. may be added depending on the purpose.

[0056] (Fluoromonomer) As the fluoromonomer, it is preferable that it has at least one double bond.As the fluoromonomer, tetrafluoroethylene [TFE], hexafluoropropylene [HFP], chlorotrifluoroethylene [CTFE], vinyl fluoride, vinylidene fluoride [VDF], trifluoroethylene, fluoroalkyl vinyl ether, fluoroalkyl ethylene, fluoroalkyl allyl ether, trifluoropropylene, pentafluoropropylene, trifluorobutene, tetrafluoroisobutene, hexafluoroisobutene, general formula (100): CHX １０１ =CX １０２ Rf １０１ (In the formula, X １０１ and X １０２ is H on one side and F on the other side, and Rf １０１is a linear or branched fluoroalkyl group having 1 to 12 carbon atoms), a fluorinated vinyl heterocycle, and a monomer that provides a crosslinking site.

[0057] Examples of the fluoroalkyl vinyl ether include those represented by the general formula (110): CF ２ =CF-ORf １１１ (wherein, Rf １１１ represents a perfluoroorganic group.) A fluoromonomer represented by general formula (120): CF ２ =CF-OCH ２ -Rf １２１ (wherein, Rf １２１ is a perfluoroalkyl group having 1 to 5 carbon atoms), a fluoromonomer represented by the general formula (130): CF ２ = CFOCF ２ ORf １３１ (wherein, Rf １３１ is a linear or branched perfluoroalkyl group having 1 to 6 carbon atoms, a cyclic perfluoroalkyl group having 5 to 6 carbon atoms, or a linear or branched perfluorooxyalkyl group having 2 to 6 carbon atoms and containing 1 to 3 oxygen atoms.) Fluoromonomers represented by general formula (140): CF ２ = CFO (CF ２ CF (Y １４１ ) O) ｍ (CF ２ ) ｎ F (wherein, Y １４１ represents a fluorine atom or a trifluoromethyl group, m is an integer of 1 to 4, and n is an integer of 1 to 4.) and a fluoromonomer represented by the general formula (150): CF ２ =CF-O-(CF ２ CFY １５１ -O) ｎ -(CFY １５２ ) ｍ -A １５１ (In the formula, Y １５１ represents a fluorine atom, a chlorine atom, -SO ２ It represents a F group or a perfluoroalkyl group. The perfluoroalkyl group is an etheric oxygen and -SO ２The group n may contain an F group. n represents an integer of 0 to 3. １５１ may be the same or different. １５２ represents a fluorine atom, a chlorine atom, or —SO ２ represents an F group, and m represents an integer of 1 to 5. １５２ may be the same or different. １５１ is -SO ２ X １５１ , -COZ １５１ or -POZ １５２ Z １５３ represents. １５１ is F, Cl, Br, I, -OR １５１ or -NR １５２ R １５３ Represents Z. １５１ , Z １５２ and Z １５３ are the same or different and represent -NR １５４ R １５５ Or -OR １５６ Represents R １５１ , R １５２ , R １５３ , R １５４ , R １５５ and R １５６ are the same or different and represent H, ammonium, an alkali metal, an alkyl group which may contain a fluorine atom, an aryl group, or a sulfonyl-containing group.

[0058] In the present disclosure, the term "perfluoroorganic group" refers to an organic group in which all hydrogen atoms bonded to carbon atoms are substituted with fluorine atoms. The perfluoroorganic group may have an ether oxygen atom.

[0059] The fluoromonomer represented by the general formula (110) is Rf １１１ is a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5.

[0060] Examples of the perfluoroorganic group in the general formula (110) include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group. The fluoromonomer represented by the general formula (110) further includes a fluoromonomer represented by the general formula (110) in which Rf １１１ is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, Rf １１１ is of the following formula:

[0061]

[0062] (wherein m represents 0 or an integer of 1 to 4), and Rf is a group represented by the following formula:

[0063] CF ３ CF ２ CF ２ -(O-CF(CF ３ )-CF ２ ) ｎ - (wherein n represents an integer of 1 to 4).

[0064] Among the fluoromonomers represented by the general formula (110), those represented by the general formula (160): CF ２ =CF-ORf １６１ (wherein, Rf １６１ Rf represents a perfluoroalkyl group having 1 to 10 carbon atoms. １６１ is preferably a perfluoroalkyl group having 1 to 5 carbon atoms.

[0065] The fluoroalkyl vinyl ether is preferably at least one selected from the group consisting of fluoromonomers represented by the general formulas (160), (130) and (140).

[0066] The fluoromonomer represented by general formula (160) is preferably at least one selected from the group consisting of perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), and perfluoro(propyl vinyl ether), and more preferably at least one selected from the group consisting of perfluoro(methyl vinyl ether) and perfluoro(propyl vinyl ether).

[0067] The fluoromonomer represented by the general formula (130) is CF ２ = CFOCF ２ OCF ３ , C.F. ２ = CFOCF ２ OCF ２ CF ３ , and CF ２ = CFOCF ２ OCF ２ CF ２ OCF ３ It is preferable that the polymer is at least one selected from the group consisting of:

[0068] The fluoromonomer represented by the general formula (140) is CF ２ = CFOCF ２ CF (CF ３ ) O(CF ２ ) ３ F, CF ２ = CFO (CF ２ CF (CF ３ ) O) ２ (CF ２ ) ３ F and CF ２ = CFO (CF ２ CF (CF ３ ) O) ２ (CF ２ ) ２ It is preferable that the compound is at least one selected from the group consisting of F.

[0069] The fluoromonomer represented by the general formula (150) is CF ２ = CFOCF ２ CF ２ SO ２ F, CF ２ = CFOCF ２ CF (CF３ ) OCF ２ CF ２ SO ２ F, CF ２ = CFOCF ２ CF (CF ２ CF ２ SO ２ F) OCF ２ CF ２ SO ２ F and CF ２ = CFOCF ２ CF (SO ２ F) ２ At least one selected from the group consisting of:

[0070] The fluoromonomer represented by the general formula (100) is Rf １０１ is a linear fluoroalkyl group, and Rf １０１ More preferred is a fluoromonomer in which Rf is a linear perfluoroalkyl group. １０１ The number of carbon atoms of the fluoromonomer represented by the general formula (100) is preferably 1 to 6. ２ =CFCF ３ , C.H. ２ =CFCF ２ CF ３ , C.H. ２ =CFCF ２ CF ２ CF ３ , C.H. ２ =CFCF ２ CF ２ CF ２ H, CH ２ =CFCF ２ CF ２ CF ２ CF ３ , CHF=CHCF ３ (E form), CHF=CHCF ３ (Z-isomer), among which CH ２ =CFCF ３ Preferred is 2,3,3,3-tetrafluoropropylene represented by the following formula:

[0071] The fluoroalkylethylene includes fluoroalkyl ethylenes represented by the general formula (170): CH ２ =CH-(CF２ ) ｎ -X １７１ (In the formula, X １７１ is H or F, and n is an integer of 3 to 10.) is preferred, and CH ２ =CH-C ４ F ９ , and C.H. ２ =CH-C ６ F １３ It is more preferable that the polymer is at least one selected from the group consisting of:

[0072] Examples of the fluoroalkyl allyl ether include those represented by the general formula (180): CF ２ =CF-CF ２ -ORf １１１ (wherein, Rf １１１ represents a perfluoroorganic group.

[0073] Rf of general formula (180) １１１ is Rf in general formula (110). １１１ Rf is the same as １１１ As the fluoroalkyl aryl ether represented by the general formula (180), a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoroalkoxyalkyl group having 1 to 10 carbon atoms is preferred. ２ =CF-CF ２ -O-CF ３ , C.F. ２ =CF-CF ２ -O-C ２ F ５ , C.F. ２ =CF-CF ２ -O-C ３ F ７ , and CF ２ =CF-CF ２ -O-C ４ F ９ At least one selected from the group consisting of CF ２ =CF-CF ２ -O-C ２ F ５ , C.F. ２ =CF-CF ２ -O-C ３ F７ , and CF ２ =CF-CF ２ -O-C ４ F ９ More preferably, at least one selected from the group consisting of CF ２ =CF-CF ２ -O-CF ２ CF ２ CF ３ is more preferable.

[0074] The fluorinated vinyl heterocycle may be a heterocyclic compound represented by the general formula (230): (In the formula, X ２３１ and X ２３２ are independently F, Cl, a methoxy group, or a fluorinated methoxy group; Y ２３１ is the formula Y ２３２ or formula Y ２３３ is.

[0075] (In the formula, Z ２３１ and Z ２３２ are independently F or a fluorinated alkyl group having 1 to 3 carbon atoms.

[0076] The monomer that provides the crosslinking site is CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ C.N., C.F. ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ COOH, C.F. ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ CH ２ I, CF ２ = CFOCF ２ CF ２ CH ２ I, CH ２ =CFCF ２ OCF (CF ３ )CF ２ OCF (CF ３ ) CN, CH２ =CFCF ２ OCF (CF ３ )CF ２ OCF (CF ３ ) COOH, CH ２ =CFCF ２ OCF (CF ３ )CF ２ OCF (CF ３ ) CH ２ OH, CH ２ = CHCF ２ CF ２ I, CH ２ =CH(CF ２ ) ２ CH=CH ２ , C.H. ２ =CH(CF ２ ) ６ CH=CH ２ , and CF ２ = CFO (CF ２ ) ５ CN, and CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ CN and CF ２ = CFOCF ２ CF ２ CH ２ It is more preferable that the compound is at least one selected from the group consisting of I.

[0077] In the polymerization, the fluoromonomer may be polymerized with a non-fluorine-containing monomer, such as a hydrocarbon-based monomer reactive with the fluoromonomer.

[0078] Examples of the hydrocarbon monomers include alkenes such as ethylene, propylene, butylene, and isobutylene; alkyl vinyl ethers such as ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, isobutyl vinyl ether, and cyclohexyl vinyl ether; vinyl acetate, vinyl propionate, vinyl n-butyrate, vinyl isobutyrate, vinyl valerate, vinyl pivalate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl versatate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl benzoate, vinyl para-t-butylbenzoate, vinyl cyclohexanecarboxylate, vinyl monochloroacetate, vinyl adipate, vinyl acrylate, vinyl methacrylate, vinyl crotonate, vinyl sorbate, vinyl cinnamate, vinyl undecylenate, vinyl hydroxyacetate, and vinyl hydroxybenzoates. vinyl esters such as vinyl hydroxypropionate, vinyl hydroxybutyrate, vinyl hydroxyvalerate, vinyl hydroxyisobutyrate, and vinyl hydroxycyclohexanecarboxylate; alkyl allyl ethers such as ethyl allyl ether, propyl allyl ether, butyl allyl ether, isobutyl allyl ether, and cyclohexyl allyl ether; alkyl allyl esters such as ethyl allyl ester, propyl allyl ester, butyl allyl ester, isobutyl allyl ester, and cyclohexyl allyl ester; and (meth)acrylic acid esters such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, and vinyl methacrylate.

[0079] The above-mentioned fluorine-free monomer may also be a functional group-containing hydrocarbon monomer (however, excluding the monomer that provides crosslinking site).The above-mentioned functional group-containing hydrocarbon monomer may be, for example, hydroxyalkyl vinyl ethers such as hydroxyethyl vinyl ether, hydroxypropyl vinyl ether, hydroxybutyl vinyl ether, hydroxyisobutyl vinyl ether, hydroxycyclohexyl vinyl ether, etc.; fluorine-free monomers having carboxyl groups such as acrylic acid, methacrylic acid, itaconic acid, succinic acid, succinic anhydride, fumaric acid, fumaric anhydride, crotonic acid, maleic acid, maleic anhydride, perfluorobutenoic acid, etc.; fluorine-free monomers having sulfo groups such as vinyl sulfonic acid, etc.; fluorine-free monomers having glycidyl groups such as glycidyl vinyl ether, glycidyl allyl ether, etc.; fluorine-free monomers having amino groups such as aminoalkyl vinyl ether, aminoalkyl allyl ether, etc.; fluorine-free monomers having amide groups such as (meth)acrylamide, methylol acrylamide, etc.; fluorine-free monomers having nitrile groups such as acrylonitrile, methacrylonitrile, etc.

[0080] In the manufacturing method of the present disclosure, it is preferable to use at least TFE as the fluoromonomer.In one embodiment, TFE or a combination of TFE and a fluoromonomer other than TFE is used as the fluoromonomer.Before starting the polymerization reaction of the fluoromonomer, by supplying an aqueous medium, TFE and a chain transfer agent into a reaction vessel, the polymerization reaction can proceed more smoothly.In one embodiment of the manufacturing method of the present disclosure, VDF is not used in polymerization.

[0081] In the above polymerization, the desired fluoropolymer can be obtained by polymerizing one or more of the above fluoromonomers.

[0082] The polymerization can produce an aqueous dispersion containing the fluoropolymer. The fluoropolymer typically has a concentration of 8 to 50 mass% in the aqueous dispersion obtained by the polymerization. In the aqueous dispersion, the lower limit of the fluoropolymer concentration is preferably 10 mass%, more preferably 15 mass%, and the upper limit is preferably 40 mass%, more preferably 35 mass%. By using the production method of the present disclosure, an aqueous dispersion having a fluoropolymer concentration of 16 mass% or more can be produced without using a surfactant.

[0083] The fluoropolymer content in the aqueous dispersion is a value obtained by drying 1 g of the aqueous dispersion in a blower dryer at 150°C for 60 minutes, measuring the mass of the heating residue, and calculating the percentage of the mass of the heating residue relative to the mass (1 g) of the aqueous dispersion.

[0084] In one embodiment of the production method, polytetrafluoroethylene (PTFE) is produced using at least TFE as the fluoromonomer. In one embodiment of the production method, polytetrafluoroethylene (PTFE) is produced using TFE alone, a mixture of TFE and HFP, or a mixture of TFE and a fluoroalkyl vinyl ether as the fluoromonomer. Upon completion of the polymerization of TFE, a polymer dispersion having a solids concentration of 1.0 to 50 mass% and an average primary particle size of 50 to 500 nm can be obtained. The lower limit of the solids concentration is preferably 5 mass%, more preferably 8 mass%. The upper limit is not particularly limited, but may be 40 mass% or 35 mass%. The lower limit of the average primary particle size is preferably 100 nm, more preferably 150 nm. The upper limit is preferably 400 nm, more preferably 350 nm. By using the manufacturing method of the present disclosure, a dispersion containing PTFE particles having a larger average primary particle diameter can be obtained compared to the aqueous dispersion obtained by the manufacturing method described in Patent Document 1, and further, despite the larger average primary particle diameter of the PTFE particles, a dispersion having a high solids concentration can be obtained.

[0085] Alternatively, the fluoropolymer powder can be obtained by coagulating the fluoropolymer in the aqueous dispersion and drying the coagulated product. The coagulated product may be washed before being dried.

[0086] (Fluoropolymer) By the manufacturing method of the present disclosure, fluoropolymer can be obtained. Examples of fluoropolymer include TFE polymer in which the monomer with the highest molar fraction of the monomer in the polymer (hereinafter referred to as "most abundant monomer") is TFE, VDF polymer in which the most abundant monomer is VDF, CTFE polymer in which the most abundant monomer is CTFE, etc.

[0087] Preferably, the fluoropolymer has an ion exchange ratio (IXR) greater than 53. Preferred fluoropolymers have no ionic groups or a limited number of ionic groups resulting in an ion exchange ratio greater than about 100. Preferred fluoropolymers have an ion exchange ratio of 1000 or greater, more preferably 2000 or greater, and even more preferably 5000 or greater.

[0088] The TFE polymer may suitably be a TFE homopolymer or a copolymer comprising (1) TFE, (2) one or more fluorine-containing monomers other than TFE having 2 to 8 carbon atoms, particularly VDF, HFP, or CTFE, and (3) other monomers. Examples of the (3) other monomers include fluoro(alkyl vinyl ethers) having an alkyl group having 1 to 5 carbon atoms, particularly 1 to 3 carbon atoms; fluorodioxole; perfluoroalkylethylene; ω-hydroperfluoroolefin, etc.

[0089] The TFE polymer may also be a copolymer of TFE and one or more fluorine-free monomers. Examples of the fluorine-free monomers include alkenes such as ethylene and propylene; vinyl esters; and vinyl ethers. The TFE polymer may also be a copolymer of TFE and one or more fluorine-containing monomers having 2 to 8 carbon atoms and one or more fluorine-free monomers.

[0090] The VDF polymer may suitably be a VDF homopolymer [PVDF] or a copolymer of (1) VDF, (2) one or more fluoroolefins other than VDF having 2 to 8 carbon atoms, particularly TFE, HFP, or CTFE, and (3) a perfluoro(alkyl vinyl ether) having an alkyl group having 1 to 5 carbon atoms, particularly 1 to 3 carbon atoms.

[0091] The CTFE polymer may suitably be a CTFE homopolymer or a copolymer consisting of (1) CTFE, (2) one or more fluoroolefins other than CTFE having 2 to 8 carbon atoms, particularly TFE or HFP, and (3) a perfluoro(alkyl vinyl ether) having an alkyl group having 1 to 5 carbon atoms, particularly 1 to 3 carbon atoms.

[0092] The CTFE polymer may also be a copolymer of CTFE with one or more non-fluorine-containing monomers, and the non-fluorine-containing monomers include alkenes such as ethylene and propylene; vinyl esters; and vinyl ethers.

[0093] In the production method of the present disclosure, for example, (I) tetrafluoroethylene polymer [TFE polymer (PTFE)] can be suitably produced as a non-melt-processable fluororesin, and (II) ethylene / TFE copolymer [ETFE], TFE / HFP copolymer [FEP], TFE / perfluoro(alkyl vinyl ether) copolymer [PFA, MFA, etc.], TFE / perfluoroallyl ether copolymer, TFE / VDF copolymer, electrolyte polymer precursor, etc. can be suitably produced as a melt-processable fluororesin.

[0094] The fluorine substitution rate of the fluoropolymer, calculated by the following formula, is preferably 50% or more, more preferably 55% or more, even more preferably 60% or more, still more preferably 75% or more, and particularly preferably 80% or more. The fluorine substitution rate of the fluoropolymer is most preferably 90 to 100%.

[0095] The fluoropolymer is preferably a fluororesin, and particularly, a fluororesin having a fluorine substitution rate of 50% or more, as calculated by the following formula, is more preferred, a fluororesin having a fluorine substitution rate of more than 50% is even more preferred, a fluororesin having a fluorine substitution rate of 55% or more is even more preferred, a fluororesin having a fluorine substitution rate of 60% or more is even more preferred, a fluororesin having a fluorine substitution rate of 75% or more is even more preferred, a fluororesin having a fluorine substitution rate of 80% or more is particularly preferred, and a fluororesin having a fluorine substitution rate of 90 to 100%, i.e., a perfluororesin, is most preferred.

[0096] (Formula) Fluorine substitution rate (%) = (number of fluorine atoms bonded to carbon atoms constituting the fluoropolymer) / ((number of hydrogen atoms bonded to carbon atoms constituting the fluoropolymer) + (number of fluorine atoms and chlorine atoms bonded to carbon atoms constituting the fluoropolymer)) × 100

[0097] As the perfluororesin, a fluororesin having a fluorine substitution rate of 95 to 100% is more preferred, PTFE, FEP or PFA is even more preferred, and PTFE is even more preferred.

[0098] The fluoropolymer may have a core-shell structure. Examples of fluoropolymers having a core-shell structure include modified PTFE particles containing a core of high molecular weight PTFE and a shell of lower molecular weight PTFE or modified PTFE. Examples of such modified PTFE include the PTFE described in JP-A-2005-527652.

[0099] The core-shell structure may have the following structures: Core: TFE homopolymer Shell: TFE homopolymer Core: Modified PTFE Shell: TFE homopolymer Core: Modified PTFE Shell: Modified PTFE Core: TFE homopolymer Shell: Modified PTFE Core: Low molecular weight PTFE Shell: High molecular weight PTFE Core: High molecular weight PTFE Shell: Low molecular weight PTFE

[0100] In the fluoropolymer having the core-shell structure, the lower limit of the core ratio is preferably 0.5% by mass, more preferably 1.0% by mass, even more preferably 2.0% by mass, even more preferably 3.0% by mass, particularly preferably 5.0% by mass, and most preferably 10.0% by mass. The upper limit of the core ratio is preferably 99.5% by mass, more preferably 99.0% by mass, even more preferably 98.0% by mass, even more preferably 97.0% by mass, particularly preferably 95.0% by mass, and most preferably 90.0% by mass.

[0101] In the fluoropolymer having the core-shell structure, the lower limit of the shell ratio is preferably 0.5% by mass, more preferably 1.0% by mass, even more preferably 2.0% by mass, even more preferably 3.0% by mass, particularly preferably 5.0% by mass, and most preferably 10.0% by mass. The upper limit of the shell ratio is preferably 99.5% by mass, more preferably 99.0% by mass, even more preferably 98.0% by mass, even more preferably 97.0% by mass, particularly preferably 95.0% by mass, and most preferably 90.0% by mass.

[0102] PTFE can be produced by polymerizing at least TFE as a fluoromonomer. In the production of PTFE, various known modified monomers can also be used in combination. In this disclosure, PTFE is a concept that includes not only TFE homopolymer but also the copolymer of TFE and modified monomer (hereinafter referred to as "modified PTFE").

[0103] The modifying monomer is not particularly limited as long as it can be copolymerized with TFE, and includes fluoromonomers and non-fluoromonomers. The modifying monomer used may be one type or multiple types.

[0104] The non-fluoromonomer is not particularly limited and may be a monomer represented by the general formula: ２ =CR Ｑ１ -LR Ｑ２ (In the formula, R Ｑ１ represents a hydrogen atom or an alkyl group. L represents a single bond, -CO-O-*, -O-CO-* or -O-. * represents R Ｑ２ represents the bonding position withＱ２ represents a hydrogen atom, an alkyl group or a nitrile group.

[0105] Examples of non-fluoromonomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, vinyl methacrylate, vinyl acetate, acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, ethyl vinyl ether, cyclohexyl vinyl ether, etc. Of these, butyl methacrylate, vinyl acetate, and acrylic acid are preferred as non-fluoromonomers.

[0106] Examples of fluoromonomers include perfluoroolefins such as hexafluoropropylene (HFP); hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride (VDF); perhaloolefins such as chlorotrifluoroethylene; perfluorovinyl ethers; (perfluoroalkyl)ethylenes; and perfluoroallyl ethers.

[0107] From the viewpoint of reactivity with TFE, the modified monomer preferably comprises at least one selected from the group consisting of hexafluoropropylene, perfluoro(alkyl vinyl ether) and (perfluoroalkyl)ethylene.More preferably, it comprises 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.

[0108] In the production of the above-mentioned TFE polymer, as the polymerization initiator, persulfates (e.g., ammonium persulfate), organic peroxides such as disuccinic acid peroxide and diglutaric acid peroxide can be used alone or in the form of a mixture thereof. They may also be used in combination with a reducing agent such as sodium sulfite to form a redox system. Furthermore, during polymerization, a radical scavenger such as hydroquinone or catechol, or a peroxide decomposer such as ammonium sulfite, can be added to adjust the radical concentration in the system.

[0109] As the redox polymerization initiator, it is preferable to use a redox initiator that combines an oxidizing agent and a reducing agent. Examples of oxidizing agents include persulfates, organic peroxides, potassium permanganate, manganese triacetate, and cerium ammonium nitrate. Examples of reducing agents include sulfites, bisulfites, bromates, diimines, and oxalic acid. Examples of persulfates include ammonium persulfate and potassium persulfate. Examples of sulfites include sodium sulfite and ammonium sulfite. In order to increase the decomposition rate of the initiator, it is also preferable to add a copper salt or an iron salt to the combination of redox initiators. Examples of copper salts include copper(II) sulfate, and examples of iron salts include iron(II) sulfate.

[0110] Examples of the redox initiator include potassium permanganate / oxalic acid, potassium permanganate / ammonium oxalate, ammonium persulfate / bisulfite / iron sulfate, manganese triacetate / oxalic acid, cerium ammonium nitrate / oxalic acid, and bromate / bisulfite, with potassium permanganate / oxalic acid being preferred. When using a redox initiator, either an oxidizing agent or a reducing agent may be charged into a polymerization vessel in advance, and then the other may be added continuously or intermittently to initiate polymerization. For example, when potassium permanganate / oxalic acid is used, it is preferred to charge oxalic acid into a polymerization vessel and then continuously add potassium permanganate thereto.

[0111] In the production of the TFE polymer, known chain transfer agents can be used, including, for example, saturated hydrocarbons such as methane, ethane, propane, and butane; halogenated hydrocarbons such as chloromethane, dichloromethane, and difluoroethane; alcohols such as methanol, ethanol, and isopropanol; and hydrogen. However, those that are in a gaseous state at normal temperature and pressure are preferred.

[0112] In the production of the TFE polymer, a saturated hydrocarbon having 12 or more carbon atoms, which is substantially inert to the reaction and becomes liquid under the above reaction conditions, can also be used as a dispersion stabilizer for the reaction system in an amount of 2 to 10 parts by mass per 100 parts by mass of the aqueous medium. Furthermore, ammonium carbonate, ammonium phosphate, etc. can be added as a buffer for adjusting the pH during the reaction.

[0113] At the time when the polymerization of TFE is completed, a polymerized dispersion having a solid content concentration of 1.0 to 50 mass% and an average primary particle size of 50 to 500 nm can be obtained. The lower limit of the solid content concentration is preferably 5 mass%, more preferably 8 mass%. The upper limit is not particularly limited, but may be 40 mass% or 35 mass%. The lower limit of the average primary particle size is preferably 100 nm, more preferably 150 nm. The upper limit is preferably 400 nm, more preferably 350 nm. By using the manufacturing method of the present disclosure, a dispersion containing PTFE particles having a larger average primary particle size can be obtained compared to the aqueous dispersion obtained by the manufacturing method described in Patent Document 1, and further, a dispersion having a high solid content concentration can be obtained despite the larger average primary particle size of the PTFE particles.

[0114] Fine powders can be produced by coagulating aqueous dispersions of TFE polymers. The aqueous dispersions of TFE polymers can be used for various applications as fine powders after coagulation, washing, and drying. When coagulating the aqueous dispersions of TFE polymers, the aqueous dispersion obtained by polymerization of a polymer latex or the like is usually diluted with water to a polymer concentration of 5 to 20% by mass, and the pH is adjusted to neutral or alkaline, as needed, followed by stirring more vigorously than during the reaction in a vessel equipped with a stirrer. The coagulation may be carried out while stirring while adding a coagulant such as a water-soluble organic compound (e.g., methanol or acetone), an inorganic salt (e.g., potassium nitrate or ammonium carbonate), or an inorganic acid (e.g., hydrochloric acid, sulfuric acid, or nitric acid). The coagulation may also be carried out continuously using an in-line mixer or the like.

[0115] The concentration of the unaggregated TFE polymer in the wastewater resulting from the aggregation is preferably low from the viewpoint of productivity, more preferably less than 0.4% by mass, particularly preferably less than 0.3% by mass.

[0116] According to the production method of the present disclosure, low-molecular-weight PTFE can also be produced as PTFE.

[0117] Low-molecular-weight PTFE (also called PTFE micropowder) having a molecular weight of 600,000 or less has excellent chemical stability, extremely low surface energy, and is resistant to fibrillation. Therefore, it is suitable as an additive for improving the slipperiness and texture of coating surfaces in the production of plastics, inks, cosmetics, paints, greases, office automation equipment components, toners, etc. (see, for example, JP-A-10-147617).

[0118] When the low-molecular-weight PTFE obtained by the above polymerization is used as a powder, the aqueous dispersion can be coagulated to form powder particles.

[0119] The manufacturing method of the present disclosure can also produce high-molecular-weight PTFE as PTFE. In the present disclosure, high-molecular-weight PTFE refers to PTFE that is not melt-processable. In one embodiment, high-molecular-weight PTFE is non-melt-processable and fibrillating. On the other hand, low-molecular-weight PTFE refers to PTFE that is melt-processable. In one embodiment, low-molecular-weight PTFE is melt-processable and not fibrillating.

[0120] The term "non-melt processable" means that the melt flow rate cannot be measured at a temperature higher than the crystallization melting point in accordance with ASTM D 1238 and D 2116.

[0121] The presence or absence of fibrillation properties can be determined by "paste extrusion," a typical method for molding "high molecular weight PTFE powder," which is a powder made from a TFE polymer. Paste extrusion is usually possible because high molecular weight PTFE has fibrillation properties. If the unsintered molded product obtained by paste extrusion has no substantial strength or elongation, for example, if it breaks when pulled at 0% elongation, it can be considered to have no fibrillation properties.

[0122] The high-molecular-weight PTFE preferably has a standard specific gravity (SSG) of 2.130 to 2.280. The standard specific gravity is measured by the water displacement method in accordance with ASTM D 792 using a sample molded in accordance with ASTM D 4895-89. In this disclosure, "high molecular weight" means that the standard specific gravity is within the above range.

[0123] The low-molecular-weight PTFE has a melt viscosity of 1×10 at 380° C. ２ ~7 x 10 ５ In the present disclosure, "low molecular weight" means that the melt viscosity is within the above range. The melt viscosity is measured in accordance with ASTM D 1238 using a flow tester (manufactured by Shimadzu Corporation) and a 2φ-8L die, with a 2 g sample preheated at 380°C for 5 minutes, and maintained at the above temperature under a load of 0.7 MPa.

[0124] The melt viscosity of the high molecular weight PTFE is much higher than that of the low molecular weight PTFE, making it difficult to measure its melt viscosity accurately. On the other hand, although the melt viscosity of the low molecular weight PTFE can be measured, it is difficult to obtain a molded product from the low molecular weight PTFE that can be used to measure its standard gravity, making it difficult to measure its accurate standard gravity. Therefore, in this disclosure, standard specific gravity is used as an indicator of the molecular weight of the high molecular weight PTFE, and melt viscosity is used as an indicator of the molecular weight of the low molecular weight PTFE. Note that no measurement method is known that can directly determine the molecular weight of either the high molecular weight PTFE or the low molecular weight PTFE.

[0125] The high-molecular-weight PTFE preferably has a peak temperature of 333 to 347° C., more preferably 335 to 345° C. The low-molecular-weight PTFE preferably has a peak temperature of 322 to 333° C., more preferably 324 to 332° C. The peak temperature can be specified as the temperature corresponding to the maximum value that appears on a differential thermal (DTA) curve obtained by using a TG / DTA (thermogravimetric / differential thermal analyzer) to raise the temperature of PTFE that has not been heated to a temperature of 300° C. or higher at a rate of 10° C. / min.

[0126] The peak temperature of PTFE may be 322 to 347°C. When PTFE is high molecular weight PTFE, the upper limit of the peak temperature of PTFE may be 347°C or lower, 346°C or lower, 345°C or lower, 344°C or lower, 343°C or lower, 342°C or lower, 341°C or lower, or 340°C or lower. When PTFE is high molecular weight PTFE, the lower limit of the peak temperature of PTFE may be 333°C or higher or 335°C or higher. When PTFE is low molecular weight PTFE, the upper limit of the peak temperature of PTFE may be 333°C or lower or 332°C or lower. When PTFE is low molecular weight PTFE, the lower limit of the peak temperature of PTFE may be 322°C or higher or 324°C or higher.

[0127] The average primary particle size of the primary particles of the low-molecular-weight PTFE is preferably 10 to 350 nm, more preferably 100 nm or more, even more preferably 150 nm or more, more preferably 400 nm or less, and even more preferably 350 nm or less.

[0128] The high-molecular-weight PTFE preferably exhibits at least one endothermic peak in the range of 333 to 347°C in a heat of fusion curve when PTFE that has not been heated to a temperature of 300°C or higher is heated at a rate of 10°C / min using a differential scanning calorimeter (DSC), and the heat of fusion between 290 and 350°C calculated from the heat of fusion curve is 52mJ / mg or more. The heat of fusion of PTFE is more preferably 55mJ / mg or more, and even more preferably 58mJ / mg or more.

[0129] The manufacturing method of the present disclosure can also be used to manufacture a TFE / HFP copolymer (FEP). The monomer composition (mass%) of FEP is preferably TFE:HFP=(60-95):(5-40), more preferably (85-92):(8-15).

[0130] In addition to TFE and HFP, other monomers copolymerizable with these monomers may be polymerized to obtain a copolymer of TFE, HFP, and other monomers as FEP. Examples of the other monomers include the above-mentioned fluorine-containing monomers (excluding TFE and HFP) and non-fluorine-containing monomers. One or more types of other monomers may be used. Perfluoro(alkyl vinyl ether) is preferred as the other monomer. The content of the other monomer units in FEP may be 0.1 to 2% by mass based on the total monomer units.

[0131] The manufacturing method of the present disclosure can also be used to manufacture a TFE / perfluoro(alkyl vinyl ether) copolymer (PFA). The preferred monomer composition (mol %) of the TFE / perfluoro(alkyl vinyl ether) copolymer is TFE:perfluoro(alkyl vinyl ether)=(90-99.7):(0.3-10), more preferably (97-99):(1-3). The perfluoro(alkyl vinyl ether) is a compound represented by the formula: CF２ =CFORf ４ (wherein, Rf ４ is a perfluoroalkyl group having 1 to 6 carbon atoms).

[0132] In addition to TFE and perfluoro(alkyl vinyl ether), other monomers copolymerizable with these monomers may be polymerized to obtain a copolymer of TFE, perfluoro(alkyl vinyl ether), and other monomers as a TFE / perfluoro(alkyl vinyl ether) copolymer. Examples of the other monomers include the above-mentioned fluorine-containing monomers (excluding TFE and perfluoro(alkyl vinyl ether)) and fluorine-free monomers. One or more types of other monomers may be used. The content of the other monomer units in the TFE / perfluoro(alkyl vinyl ether) copolymer may be 0.1 to 2 mass% based on the total monomer units.

[0133] 2. Fluoropolymer The present disclosure also provides a fluoropolymer having an average primary particle size of 500 nm or less, a carboxylic acid group having 10 carbon atoms, and ６ The present invention also relates to fluoropolymers having 30 or more per unit area.

[0134] The average primary particle size of the fluoropolymer is 500 nm or less, preferably 450 nm or less, more preferably 400 nm or less, even more preferably 350 nm or less, still more preferably 300 nm or less, particularly preferably 250 nm or less, preferably 10 nm or more, more preferably 100 nm or more, and even more preferably 150 nm or more.

[0135] By producing a fluoropolymer using the production method of the present disclosure, the average primary particle size of the fluoropolymer can be adjusted to fall within the above-mentioned range. The reason for this is presumably because the polymerization reaction proceeds in a state where the fluoromonomer is emulsified in an aqueous medium. On the other hand, when a fluoropolymer is produced by a conventional suspension polymerization method, it is difficult to generate primary particles of the fluoropolymer, and a fluoropolymer having an average primary particle size within the above-mentioned range cannot be obtained.

[0136] The average primary particle size is the average particle size of primary particles dispersed in an aqueous dispersion, and is different from the average particle size of secondary particles (powder) formed by aggregation of primary particles. The average primary particle size can be measured by dynamic light scattering. First, an aqueous dispersion is prepared in which the polymer solids concentration is adjusted to about 1.0 mass %, and the average primary particle size can be measured using dynamic light scattering at a measurement temperature of 25°C, a refractive index of the solvent (water) of 1.3328, a viscosity of the solvent (water) of 0.8878 mPa s, and an accumulation number of 70. For example, an ELSZ-1000S (manufactured by Otsuka Electronics Co., Ltd.) can be used for dynamic light scattering.

[0137] The average primary particle diameter can also be measured by the following method. The dispersion is diluted with water to a solid content of 0.15% by mass, and the transmittance of 550 nm incident light per unit length of the diluted latex obtained and the number-average particle diameter determined by measuring the unidirectional diameter using a transmission electron microscope photograph are measured to prepare a calibration curve. Using this calibration curve, the average particle diameter can be calculated from the measured transmittance of 550 nm incident light of each sample.

[0138] The number of carboxylic acid groups (—COOH groups) in the fluoropolymer is 10 ６ The number of carboxylic acid groups (—COOH groups) per unit area is 30 or more, preferably 50 or more, more preferably 100 or more, even more preferably 150 or more, and still more preferably 200 or more. When the fluoropolymer is high-molecular-weight PTFE, the number of carboxylic acid groups (—COOH groups) of the high-molecular-weight PTFE is 10 or more. ６ When the fluoropolymer is a low-molecular-weight PTFE, the number of carboxylic acid groups (—COOH groups) of the low-molecular-weight PTFE is 10 or more, and preferably 40 or more. ６ The upper limit of the number of carboxylic acid groups (—COOH groups) in the fluoropolymer varies depending on the molecular weight of the fluoropolymer, but for example, ６ There may be 500 or less per piece.

[0139] When the fluoropolymer of the present disclosure is a powder of low-molecular-weight PTFE, the dispersibility of the powder in other materials is further improved by the low-molecular-weight PTFE having a carboxylic acid group.

[0140] By using the manufacturing method of the present disclosure and by using a polymerization initiator in a supply amount within the above-mentioned range to produce a fluoropolymer, a large number of carboxylic acid groups are introduced into the fluoropolymer, and the number of carboxylic acid groups in the fluoropolymer can be adjusted within the above-mentioned range. Furthermore, by using a water-soluble radical polymerization initiator such as a persulfate as the polymerization initiator, or a redox initiator using a persulfate as an oxidizing agent, the number of carboxylic acid groups in the fluoropolymer can be more easily adjusted within the above-mentioned range. On the other hand, in suspension polymerization, etc., an oil-soluble radical polymerization initiator is often used, and when an oil-soluble radical polymerization initiator is used, carboxylic acid groups are not introduced into the fluoropolymer.

[0141] The number of fluorocarbonyl groups (-COF groups) in the fluoropolymer is 10 ６ The number of molecules per molecule is preferably less than 30, more preferably 20 or less, and even more preferably 10 or less.

[0142] By using the production method of the present disclosure and by using a polymerization initiator in a supply amount within the above-mentioned range to produce a fluoropolymer, many carboxylic acids are introduced into the fluoropolymer, but almost no -COF groups are produced, so the number of -COF groups in the fluoropolymer can be adjusted to within the above-mentioned range. On the other hand, when the fluoropolymer is irradiated with radiation to adjust the molecular weight of the fluoropolymer, -COF groups are likely to be produced at the terminals of the fluoropolymer, and a fluoropolymer having the number of -COF groups within the above-mentioned range cannot be obtained.

[0143] The number of carboxylic acid groups and the number of fluorocarbonyl groups can be measured in accordance with the method for analyzing terminal groups described in JP-A-4-20507. Specifically, a fluoropolymer powder is preformed by hand pressing to prepare a film approximately 0.1 mm thick. The prepared film is subjected to infrared absorption spectroscopy. An infrared absorption spectroscopy of a fluoropolymer prepared by contacting the fluoropolymer with fluorine gas and completely fluorinating the terminals is also performed, and the number of carboxylic acid groups or fluorocarbonyl groups is calculated from the difference spectrum between the two using the following formula: The number of carboxylic acid groups or fluorocarbonyl groups (10 carbon atoms) is calculated by the following formula: ６ (per unit) = (l × K) / t, l: absorbance, K: correction coefficient, t: film thickness (mm), the absorption frequency of the carboxylic acid group is 3560 cm －１ The correction factor is 440. The absorption frequency of the fluorocarbonyl group is 1883 cm －１ , the correction coefficient is set to 440.

[0144] The specific surface area of ​​the fluoropolymer is preferably 8.0 m ２ / g or more, more preferably 10m ２ / g or more, preferably 100m ２ / g or less, more preferably 50m ２ The specific surface area can be measured by the BET method.

[0145] In particular, when the fluoropolymer of the present disclosure is a fluoropolymer powder such as a powder of polytetrafluoroethylene, it is preferable that the specific surface area is within the above-mentioned range.When the fluoropolymer of the present disclosure is a powder of low molecular weight PTFE, if the low molecular weight PTFE has a specific surface area within the above-mentioned range, excellent fine dispersion in other materials can be obtained.

[0146] By producing a fluoropolymer using the production method of the present disclosure, the specific surface area of ​​the fluoropolymer can be adjusted to fall within the above-mentioned range. The reason for this is presumably because the polymerization reaction proceeds in a state in which the fluoromonomer is emulsified in an aqueous medium. On the other hand, when a fluoropolymer is produced by a conventional suspension polymerization method, the specific surface area of ​​the fluoropolymer becomes small, and a fluoropolymer having a specific surface area within the above-mentioned range cannot be obtained.

[0147] The fluoropolymer of the present disclosure can be suitably produced by the production method of the present disclosure.

[0148] The present disclosure also relates to a composition containing the fluoropolymer of the present disclosure. The form of the fluoropolymer of the present disclosure and the composition of the present disclosure is not particularly limited, and may be, for example, an aqueous dispersion, a coagulate, a dried product, a powder, a pellet, or the like. An aqueous dispersion is a dispersion system in which an aqueous medium is the dispersion medium and a fluoropolymer is the dispersoid. The aqueous medium is not particularly limited as long as it is a liquid containing water, and may contain, in addition to water, an organic solvent such as alcohol, ether, ketone, or paraffin wax.

[0149] The fluoropolymer and composition of the present disclosure may be an aqueous fluoropolymer dispersion in which primary particles of the fluoropolymer are dispersed in an aqueous medium. The aqueous dispersion may be any of the aqueous dispersions obtained by carrying out the polymerization described above, dispersions obtained by concentrating or subjecting the aqueous dispersion to a dispersion stabilization treatment, and those in which a powder of the fluoropolymer is dispersed in an aqueous medium. The fluoropolymer and composition of the present disclosure may also be a fluoropolymer powder. The fluoropolymer powder can be obtained, for example, by coagulating the fluoropolymer in the aqueous fluoropolymer dispersion using a known method.

[0150] The fluoropolymer of the present disclosure and the fluoropolymer in the composition may have the same structure as the fluoropolymer obtained by the manufacturing method of the present disclosure. Therefore, the fluoropolymer may include tetrafluoroethylene polymer [TFE polymer (PTFE)], melt-processable fluororesin, etc.

[0151] The fluoropolymer may be a polymer that is not melt-processable or a polymer that is melt-processable, and the fluoropolymer is preferably a non-melt-processable fluororesin or a melt-processable fluororesin.

[0152] The fluorine substitution rate of the fluoropolymer is preferably 50% or more, more preferably 55% or more, even more preferably 60% or more, still more preferably 75% or more, and particularly preferably 80% or more. The fluorine substitution rate of the fluoropolymer is most preferably 90 to 100%.

[0153] The fluoropolymer is preferably a fluororesin, and particularly, a fluororesin having a fluorine substitution rate of 50% or more, as calculated by the following formula, is more preferred, a fluororesin having a fluorine substitution rate of more than 50% is even more preferred, a fluororesin having a fluorine substitution rate of 55% or more is even more preferred, a fluororesin having a fluorine substitution rate of 60% or more is even more preferred, a fluororesin having a fluorine substitution rate of 75% or more is even more preferred, a fluororesin having a fluorine substitution rate of 80% or more is particularly preferred, and a fluororesin having a fluorine substitution rate of 90 to 100%, i.e., a perfluororesin, is most preferred.

[0154] (Formula) Fluorine substitution rate (%) = (number of fluorine atoms bonded to carbon atoms constituting the fluoropolymer) / ((number of hydrogen atoms bonded to carbon atoms constituting the fluoropolymer) + (number of fluorine atoms and chlorine atoms bonded to carbon atoms constituting the fluoropolymer)) × 100

[0155] The perfluororesin is more preferably a fluororesin having a fluorine substitution rate of 95 to 100%, and is further preferably PTFE, FEP, or PFA, and even more preferably PTFE. In one embodiment of the fluoropolymer, the fluoropolymer does not contain VDF units.

[0156] In one embodiment of the fluoropolymer and the composition containing the fluoropolymer of the present disclosure, the fluoropolymer and the composition containing the fluoropolymer are substantially free of surfactants. The fluoropolymer and the composition containing the fluoropolymer that are substantially free of surfactants have the advantage of being less likely to discolor.

[0157] In the present disclosure, "substantially free of surfactant" means that the content of surfactant in the fluoropolymer or composition is 10 ppm by mass or less, preferably 1 ppm by mass or less, more preferably 100 ppb by mass or less, even more preferably 10 ppb by mass or less, still more preferably 1 ppb by mass or less, and particularly preferably below the detection limit of surfactant as measured by liquid chromatography-mass spectrometry (LC / MS).

[0158] In one embodiment of the fluoropolymer and the composition containing the fluoropolymer of the present disclosure, the composition is substantially free of a fluorine-containing surfactant.

[0159] In the present disclosure, "substantially free of fluorine-containing surfactant" means that the content of fluorine-containing surfactant in the fluoropolymer or composition is 10 ppm by mass or less, preferably 1 ppm by mass or less, more preferably 100 ppb by mass or less, even more preferably 10 ppb by mass or less, still more preferably 1 ppb by mass or less, and particularly preferably below the detection limit of the fluorine-containing surfactant as measured by liquid chromatography-mass spectrometry (LC / MS).

[0160] The content of surfactants such as fluorine-containing surfactants can be quantified by known methods. For example, it can be quantified by LC / MS analysis. First, methanol is added to the fluoropolymer or composition, extraction is performed, and the resulting extract is analyzed by LC / MS. To further improve the extraction efficiency, treatments such as Soxhlet extraction and ultrasonic treatment may be performed. Molecular weight information is extracted from the obtained LC / MS spectrum, and a match with the structural formula of the candidate surfactant is confirmed. Then, aqueous solutions containing five or more levels of the confirmed surfactant are prepared, and LC / MS analysis is performed on each of the aqueous solutions. The relationship between the content and the area relative to the content is plotted, and a calibration curve is drawn. Then, using the calibration curve, the area of ​​the LC / MS chromatogram of the surfactant in the extract can be converted to the surfactant content.

[0161] Specific examples of the fluorine-containing surfactant include compounds represented by the following formulas: F(CF ２ ) ７ COOM, F(CF ２ ) ５ COOM, C.F. ３ O (CF ２ ) ３ OCHFCF ２ COOM, C. ３ F ７ OCF (CF ３ )CF ２ OCF (CF ３ ) COOM, C.F. ３ CF ２ CF ２ OCF (CF ３ ) COOM, C.F. ３ CF ２ OCF ２ CF ２ OCF ２ COOM, C. ２ F ５ OCF (CF ３ )CF ２ OCF (CF ３ ) COOM, C.F. ３ OCF (CF ３ )CF ２OCF (CF ３ ) COOM, C.F. ２ ClCF ２ CF ２ OCF (CF ３ )CF ２ OCF ２ COOM, C.F. ２ ClCF ２ CF ２ OCF ２ CF (CF ３ ) OCF ２ COOM, C.F. ２ ClCF(CF ３ ) OCF (CF ３ )CF ２ OCF ２ COOM, C.F. ２ ClCF(CF ３ ) OCF ２ CF (CF ３ ) OCF ２ COOM, and (In each formula, M is H, metal atom, NR １ ４ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium. １ is H or an organic group.

[0162] The fluoropolymers and compositions of the present disclosure can be suitably used in the applications described above.

[0163] Although the embodiments have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the claims.

[0164] <1> According to a first aspect of the present disclosure, there is provided a method for producing a fluoropolymer by polymerizing a fluoromonomer in a reaction vessel in the presence of an aqueous medium, a chain transfer agent, and a polymerization initiator in the substantial absence of a surfactant, the method comprising supplying into the reaction vessel a chain transfer agent in an amount of 10.0 mol % or more relative to the total amount of the aqueous medium, the fluoromonomer, and the monomer and chain transfer agent in the gas phase in the reaction vessel, and then supplying a polymerization initiator into the reaction vessel to initiate polymerization of the fluoromonomer. <2> According to a second aspect of the present disclosure, there is provided a production method according to the first aspect, in which the fluoromonomer contains at least tetrafluoroethylene. <3> According to a third aspect of the present disclosure, there is provided a production method according to the first or second aspect, in which the chain transfer agent is a compound that is gaseous at room temperature. <4> According to a fourth aspect of the present disclosure, there is provided a production method according to any of the first to third aspects, in which the chain transfer agent is a non-halogenated alkane having 2 to 4 carbon atoms. <5> According to a fifth aspect of the present disclosure, there is provided a production method according to any one of the first to fourth aspects, in which the polymerization initiator is at least one selected from the group consisting of a water-soluble radical polymerization initiator and a redox initiator. <6> According to a sixth aspect of the present disclosure, there is provided a production method according to any one of the first to fifth aspects, in which polymerization of a fluoromonomer is initiated by supplying into the reaction vessel a polymerization initiator in an amount of 1.0 mol % or more relative to the total amount of the monomer and chain transfer agent in the gas phase in the reaction vessel. <7> According to a seventh aspect of the present disclosure, there is provided a production method according to any one of the first to sixth aspects, in which the pressure in the reaction vessel when polymerization of the fluoromonomer is initiated is 0.30 MPaG or less. <8> According to an eighth aspect of the present disclosure, there is provided a production method according to any one of the first to seventh aspects, in which after polymerization of the fluoromonomer is initiated, part or all of the chain transfer agent is removed from the reaction vessel. <9> According to a ninth aspect of the present disclosure, there is provided a production method according to any one of the first to eighth aspects, in which the pressure in the reaction vessel is adjusted to 0.30 MPaG or less to initiate polymerization of the fluoromonomer, and the pressure in the reaction vessel is adjusted to more than 0.30 MPaG during the polymerization to continue polymerization of the fluoromonomer.<10> According to a tenth aspect of the present disclosure, there is provided the production method according to any one of the first to ninth aspects, wherein the fluorine substitution rate of the fluoropolymer is 50% or more. <11> According to an eleventh aspect of the present disclosure, there is provided the production method according to any one of the first to tenth aspects, for producing an aqueous dispersion containing a fluoropolymer. <12> According to a twelfth aspect of the present disclosure, there is provided the production method according to any one of the first to eleventh aspects, for producing an aqueous dispersion containing polytetrafluoroethylene, wherein the fluoromonomer is tetrafluoroethylene alone or a mixture of tetrafluoroethylene and hexafluoropropylene, the chain transfer agent is propane, and the polymerization initiator is a persulfate. <13> According to a thirteenth aspect of the present disclosure, there is provided the production method according to any one of the first to eleventh aspects, for producing an aqueous dispersion containing polytetrafluoroethylene, wherein the average primary particle size is 500 nm or less, and the number of carboxylic acid groups is 10 carbon atoms. ６ <14> According to a fourteenth aspect of the present disclosure, there is provided a fluoropolymer according to the thirteenth aspect, wherein the fluorine substitution rate is 50% or more. <15> According to a fifteenth aspect of the present disclosure, there is provided a fluoropolymer according to the thirteenth aspect, wherein the number of —COF groups is 10 or more carbon atoms. ６ <16> According to a sixteenth aspect of the present disclosure, there is provided a fluoropolymer according to any one of the thirteenth to fifteenth aspects which is polytetrafluoroethylene. <17> According to a seventeenth aspect of the present disclosure, there is provided a fluoropolymer according to any one of the thirteenth to fifteenth aspects which is high molecular weight polytetrafluoroethylene. <18> According to an eighteenth aspect of the present disclosure, there is provided a low molecular weight polytetrafluoroethylene, ６ <19> According to the 19th aspect of the present disclosure, there is provided a fluoropolymer having a specific surface area of ​​8.0 m or more, wherein the number of particles per particle is 50 or more. ２ / g or more.

[0165] Next, embodiments of the present disclosure will be described with reference to examples, but the present disclosure is not limited to these examples.

[0166] The values ​​in the examples were measured by the following methods.

[0167] <Solids concentration in aqueous dispersion> 1 g of the aqueous fluoropolymer dispersion is dried in a blower dryer at 150°C for 60 minutes, and the ratio of the mass of the heating residue to the mass (1 g) of the aqueous dispersion is expressed as a percentage.

[0168] <Average primary particle diameter> The average primary particle diameter of particles in the PTFE aqueous dispersions prepared in Examples 1 to 3 was measured by the following method. The fluoropolymer aqueous dispersions were diluted with water to a solid content of 0.15% by mass, and the transmittance of 550 nm projected light per unit length of the resulting diluted latex and the number-based length average primary particle diameter determined by measuring the unidirectional diameter using a transmission electron microscope photograph were measured to create a calibration curve. Using this calibration curve, the average primary particle diameter was determined from the measured transmittance of 550 nm projected light for each sample.

[0169] <Specific Surface Area> Measured by the BET method using a surface analyzer (product name: MONOSORB, manufactured by QUANTA CHLROME). A mixed gas of 30% nitrogen and 70% helium was used as the carrier gas, and cooling was performed using liquid nitrogen.

[0170] <Number of Terminal Groups> The fluoropolymer powder was preformed by hand pressing to prepare a film approximately 0.1 mm thick. The prepared film was subjected to infrared absorption spectroscopy. A fully fluorinated terminal fluoropolymer prepared by contacting the fluoropolymer with fluorine gas was also subjected to infrared absorption spectroscopy, and the number of carboxylic acid groups or fluorocarbonyl groups (-COF groups) was calculated from the difference spectrum between the two using the following formula. The number of carboxylic acid groups or fluorocarbonyl groups (number of carbon atoms: 10 ６ (per unit) = (l × K) / t, l: absorbance, K: correction coefficient, t: film thickness (mm), the absorption frequency of the carboxylic acid group is 3560 cm －１ The correction factor is 440. The absorption frequency of the fluorocarbonyl group is 1883 cm－１ , the correction coefficient is set to 440.

[0171] <Peak Temperature> Approximately 10 mg of powder that has not been heated to a temperature of 300° C. or higher is precisely weighed, placed in a dedicated aluminum pan, and measured using a TG / DTA (thermogravimetric / differential thermal analyzer). The peak temperature is determined as the temperature corresponding to the maximum value of the differential thermal (DTA) curve when the aluminum pan is heated in an air atmosphere in the temperature range from 25° C. to 600° C. at a rate of 10° C. / min.

[0172] <Melt Viscosity> In accordance with ASTM D 1238, a flow tester (manufactured by Shimadzu Corporation) and a 2φ-8L die were used to measure the melt viscosity of a 2 g sample that had been preheated at 380°C for 5 minutes under a load of 0.7 MPa while maintaining the same temperature.

[0173] <Average primary particle size> The average primary particle size of the particles in the PTFE aqueous dispersion prepared in Example 4 was measured by the following method. It was measured by dynamic light scattering. An aqueous fluoropolymer dispersion adjusted to a fluoropolymer solids concentration of 1.0 mass% was prepared, and measurements were taken at 25°C using an ELSZ-1000S (manufactured by Otsuka Electronics Co., Ltd.) for a total of 70 measurements. The refractive index of the solvent (water) was 1.3328, and the viscosity of the solvent (water) was 0.8878 mPa s.

[0174] Example 1: A 6-L stainless steel reactor equipped with a stirrer was charged with 3.2 L of deionized water and sealed. The reactor contents were then heated to 70°C while simultaneously evacuating and purging with TFE to remove oxygen from the reactor, and the contents were stirred. 1.5 g of propane was injected into the reactor with TFE until the pressure reached 0.10 MPaG. 1.65 g of ammonium persulfate (APS) dissolved in 20 g of deionized water was added to bring the reactor pressure to 0.20 MPaG. The total amount of water added to the reactor was 3,300 g, and the amount of chain transfer agent immediately after the initiator injection was 12.0 mol% relative to the total amount of monomer and chain transfer agent in the gas phase of the reactor. After the initiator injection, a pressure drop occurred, and the initiation of polymerization was observed. When the pressure reached 0.16 MPaG, stirring was stopped. The gas in the reactor was then slowly released until the reactor pressure reached 0.02 MPaG. Thereafter, 0.07 g of propane was injected using TFE, and TFE was supplied until the pressure reached 0.83 MPaG. A decrease in pressure was confirmed again, and thereafter TFE was added to the reactor to maintain the pressure at a constant 0.78 MPaG. When the amount of TFE consumed in the reaction reached 660 g, the supply of TFE was stopped, stirring was stopped, and the reaction was terminated. Thereafter, the pressure in the reactor was vented until it reached normal pressure, and the contents were removed from the reactor and cooled, yielding an aqueous PTFE dispersion. In the obtained aqueous dispersion, almost no polymer particles were generated on the gas-liquid interface.

[0175] The solids concentration of the PTFE aqueous dispersion was 15.1% by mass, and the average primary particle size was 258 nm. The resulting PTFE aqueous dispersion was stirred in a vessel equipped with a stirrer in the presence of nitric acid to coagulate the PTFE. The coagulated PTFE was separated and dried at 160°C for 18 hours. The PTFE powder at this stage had a specific surface area of ​​8.7 m ２ / g, has melt processability, and has 249 carboxylic acid groups / 10 carbon atoms. ６ 0 -COF groups / 10 carbon atoms ６ The peak temperature by TG / DTA was 324.5°C, and it was confirmed that the polymer was low-molecular-weight PTFE.

[0176] Example 2: A 6-L stainless steel reactor equipped with a stirrer was charged with 3.2 L of deionized water and sealed. The reactor contents were then heated to 70°C while simultaneously evacuating and purging with TFE to remove oxygen from the reactor, and the contents were stirred. 1.5 g of propane was injected into the reactor with TFE until the pressure reached 0.10 MPaG. 1.65 g of APS dissolved in 20 g of deionized water was added to bring the pressure inside the reactor to 0.20 MPaG. The total amount of water added to the reactor was 3,300 g, and the amount of chain transfer agent immediately after the initiator was added was 12.0 mol% relative to the total amount of monomer and chain transfer agent in the gas phase inside the reactor. After the initiator was added, a pressure drop occurred, and the initiation of polymerization was observed. When the pressure reached 0.16 MPaG, TFE was added until the pressure reached 0.83 MPaG. A decrease in pressure was confirmed again, and thereafter TFE was added to the reactor to maintain a constant pressure of 0.78 MPaG. When the amount of TFE consumed in the reaction reached 660 g, the supply of TFE was stopped, stirring was stopped, and the reaction was terminated. Thereafter, the pressure inside the reactor was vented to normal pressure, and the contents were removed from the reactor and cooled, yielding an aqueous PTFE dispersion. In the obtained aqueous dispersion, almost no polymer particles were generated on the gas-liquid interface.

[0177] The resulting PTFE aqueous dispersion had a solids concentration of 17.1% by mass and an average primary particle size of 246 nm. The resulting PTFE aqueous dispersion was gently stirred in a container equipped with a stirrer in the presence of nitric acid to coagulate the PTFE. The coagulated PTFE was separated and dried at 160°C for 18 hours. The PTFE powder at this stage had melt processability and contained 150 carboxylic acid groups per 10 carbon atoms. ６ 0 -COF groups / 10 carbon atoms ６ There were 100 pieces.

[0178] Example 3 Polymerization was carried out in the same manner as in Example 1, except that the amount of propane was changed from 1.5 g to 3.0 g. In the obtained aqueous dispersion, almost no polymer particles were generated on the gas-liquid interface. The amount of chain transfer agent immediately after the introduction of the initiator was 24.0 mol % relative to the total amount of monomer and chain transfer agent in the gas phase in the reaction vessel.

[0179] The resulting PTFE aqueous dispersion had a solids concentration of 15.2% by mass and an average primary particle size of 237 nm. The resulting PTFE aqueous dispersion was gently stirred in a container equipped with a stirrer in the presence of nitric acid to coagulate the PTFE. The coagulated PTFE was separated and dried at 160°C for 18 hours. The PTFE powder at this stage had melt processability and contained 120 carboxylic acid groups per 10 carbon atoms. ６ 0 -COF groups / 10 carbon atoms ６ There were 100 pieces.

[0180] Example 4: A 1 L glass reactor equipped with a stirrer was charged with 27.5 g of paraffin and 530 g of deionized water and sealed. The contents of the reactor were then heated to 90°C while being aspirated and simultaneously purged with TFE to remove oxygen from the reactor, and the contents were stirred. 0.5 g of propane and 0.5 g of HFP were charged into the reactor, and TFE was introduced to a pressure of 0.10 MPaG. The reactor was maintained at 90°C, and 275 mg of ammonium persulfate (APS) dissolved in 20 g of deionized water was added, followed by the addition of TFE to adjust the pressure inside the reactor to 0.20 MPaG. The total amount of water added to the reactor was 550 g, and the amount of chain transfer agent immediately after the initiator was added was 24.0 mol% relative to the total amount of monomer and chain transfer agent in the gas phase inside the reactor.

[0181] After the initiator was injected, a pressure drop occurred, and the initiation of polymerization was observed. When the pressure reached 0.16 MPaG, TFE was charged and the pressure was adjusted to 0.20 MPaG. This operation was repeated twice. Then, stirring was stopped, the reactor was cooled to 70 ° C., and the reactor was evacuated to remove propane. The pressure was again increased to 0.83 MPaG with TFE, and 16.5 mg of APS dissolved in deionized water was charged. A pressure drop was again observed, and then TFE was added to the reactor to maintain a constant pressure of 0.78 MPaG. When 82 g of TFE was consumed in the reaction, 2.8 mg of hydroquinone dissolved in deionized water was charged, and when 175 g of TFE was consumed in the reaction, the supply of TFE was stopped, stirring was stopped, and the reaction was terminated. Thereafter, the pressure in the reactor was discharged until it reached atmospheric pressure, and the contents were removed from the reactor and cooled, and the paraffin was separated to obtain an aqueous PTFE dispersion.

[0182] The solids concentration of the resulting PTFE aqueous dispersion was 23.1% by mass, and the average primary particle diameter was 212 nm. The resulting PTFE aqueous dispersion was diluted with deionized water to a solids concentration of 15% by mass, and coagulated by high-speed stirring to obtain a wet polymer. The resulting wet polymer was dried at 150°C for 18 hours to obtain a PTFE powder. The melt viscosity of the resulting PTFE powder was measured, but it did not melt, indicating non-melt processability. The PTFE powder at this time had a carboxylic acid group ratio of 46 / 10 carbon atoms. ６ 0 -COF groups / 10 carbon atoms ６ There were 100 pieces.

[0183] Comparative Example 1: A 6-L stainless steel reactor equipped with a stirrer was charged with 3.2 L of deionized water and sealed. The reactor contents were then heated to 70°C while simultaneously evacuating and purging with TFE to remove oxygen from the reactor, and the contents were stirred. 1.5 g of propane was injected into the reactor with TFE until the pressure reached 0.68 MPaG. 1.65 g of APS dissolved in 20 g of deionized water was added to bring the reactor pressure to 0.83 MPaG. The total amount of water added to the reactor was 3,300 g, and the amount of chain transfer agent immediately after the initiator was added was 4.3 mol% relative to the total amount of monomer and chain transfer agent in the gas phase within the reactor. After the initiator was added, a pressure drop occurred and the initiation of polymerization was observed. TFE was added to the reactor to maintain a constant pressure of 0.78 MPaG. When 660 g of TFE had been consumed in the reaction, the TFE supply was stopped, stirring was stopped, and the reaction was terminated. Thereafter, the pressure in the reactor was vented to atmospheric pressure. The entire contents were solidified, and an aqueous dispersion could not be obtained.

[0184] Comparative Example 2: A 6-L stainless steel reactor equipped with a stirrer was charged with 3.2 L of deionized water and sealed. The reactor contents were then heated to 70°C while being aspirated and simultaneously purged with TFE to remove oxygen from the reactor, and the contents were stirred. 2.6 g of propane was injected into the reactor with TFE until a pressure of 0.68 MPaG was reached. 1.65 g of APS dissolved in 20 g of deionized water was added, and the reactor pressure was adjusted to 0.83 MPaG. The total amount of water added to the reactor was 3,300 g, and the amount of chain transfer agent immediately after the initiator was added was 7.3 mol% relative to the total amount of monomer and chain transfer agent in the gas phase within the reactor. After the initiator was added, a pressure drop occurred and the initiation of polymerization was observed. TFE was added to the reactor to maintain a constant pressure of 0.78 MPaG. When 660 g of TFE had been consumed in the reaction, the TFE supply was stopped, stirring was stopped, and the reaction was terminated. Thereafter, the pressure in the reactor was vented to atmospheric pressure. The entire contents were solidified, and an aqueous dispersion could not be obtained.

[0185] As the above results show, according to the production method of the present disclosure, the polymerization reaction can proceed in the same manner as or more smoothly than conventional production methods without using a surfactant. Therefore, according to the production method of the present disclosure, fluoropolymer particles having a small average primary particle size can be obtained, and a fluoropolymer powder having a large specific surface area can be obtained. Furthermore, according to the production method of the present disclosure, an aqueous dispersion of a fluoropolymer having a higher solid content concentration than conventional production methods can be produced.

Claims

1. A method for producing a fluoropolymer by polymerizing a fluoromonomer in a reaction vessel in the substantial absence of a surfactant and in the presence of an aqueous medium, a chain transfer agent and a polymerization initiator, comprising: supplying into the reaction vessel an amount of chain transfer agent in an amount of 10.0 mol % or more based on the total amount of the aqueous medium, the fluoromonomer, and the monomer and the chain transfer agent in the gas phase in the reaction vessel; and then supplying a polymerization initiator into the reaction vessel to initiate polymerization of the fluoromonomer.

2. The method according to claim 1, wherein the fluoromonomer contains at least tetrafluoroethylene.

3. The process according to claim 1 or 2, wherein the chain transfer agent is a gaseous compound at room temperature.

4. The process according to any one of claims 1 to 3, wherein the chain transfer agent is a non-halogenated alkane having 2 to 4 carbon atoms.

5. The method according to any one of claims 1 to 4, wherein the polymerization initiator is at least one selected from the group consisting of water-soluble radical polymerization initiators and redox initiators.

6. The method according to any one of claims 1 to 5, wherein polymerization of the fluoromonomer is initiated by supplying into the reaction vessel a polymerization initiator in an amount of 1.0 mol % or more based on the total amount of the monomer and the chain transfer agent in the gas phase in the reaction vessel.

7. The process according to any one of claims 1 to 6, wherein the pressure inside the reaction vessel when the polymerization of the fluoromonomer is started is 0.30 MPaG or less.

8. The process according to any one of claims 1 to 7, wherein after the polymerization of the fluoromonomer is initiated, a part or all of the chain transfer agent is removed from the reaction vessel.

9. The method according to any one of claims 1 to 8, wherein the pressure in the reaction vessel is adjusted to 0.30 MPaG or less to initiate polymerization of the fluoromonomer, and the pressure in the reaction vessel is adjusted to more than 0.30 MPaG during polymerization to continue polymerization of the fluoromonomer.

10. The method according to any one of claims 1 to 9, wherein the fluorine substitution rate of the fluoropolymer is 50% or more.

11. The method according to any one of claims 1 to 10, for producing an aqueous dispersion containing a fluoropolymer.

12. The method according to any one of claims 1 to 11, which produces an aqueous dispersion containing polytetrafluoroethylene, wherein the fluoromonomer is tetrafluoroethylene alone or a mixture of tetrafluoroethylene and hexafluoropropylene, the chain transfer agent is propane, and the polymerization initiator is a persulfate.

13. The average primary particle size is 500 nm or less, and the number of carboxylic acid groups is 10 or less. ６ Fluoropolymer having 30 or more per unit.

14. The fluoropolymer according to claim 13, having a fluorine substitution rate of 50% or more.

15. The number of -COF groups is 10 carbon atoms. ６ The fluoropolymer according to claim 13 or 14, wherein the number of molecules per molecule is less than 30.

16. The fluoropolymer according to any one of claims 13 to 15 which is polytetrafluoroethylene.

17. The fluoropolymer of any one of claims 13 to 15 which is a high molecular weight polytetrafluoroethylene.

18. Low molecular weight polytetrafluoroethylene, the number of carboxylic acid groups is 10 carbon atoms. ６ The fluoropolymer according to any one of claims 13 to 15, wherein the number of molecules per molecule is 50 or more.

19. The specific surface area is 8.0 m ２ The fluoropolymer according to any one of claims 13 to 18, wherein the fluoropolymer has a molecular weight of 1 / g or more.

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