Fluorine-containing polymer production method, aqueous dispersion, and composition

Abstract

This fluorine-containing polymer production method involves polymerizing monomers including a fluorine-containing monomer in a first aqueous dispersion that contains an aqueous medium and first particles containing a first fluorine-containing polymer that includes a unit based on a compound represented by formula (1) and that has a glass transition temperature of 10°C or lower, to produce a second fluorine-containing polymer that is different from the first fluorine-containing polymer. Before starting the polymerizing of the monomers, the percentage content of the first fluorine-containing polymer is 0.01-4.0 mass% with respect to the total mass of the first aqueous dispersion. (1): CX1X2=CX3-CF2-O-Rf In formula (1), X1, X2, and X3 each independently represent a hydrogen atom or a fluorine atom, and Rf represents a perfluoroalkyl group having 1-10 carbon atoms and optionally has an ethereal oxygen atom between carbon atoms in the perfluoroalkyl group.

Description

Method for producing fluorine-containing polymer, aqueous dispersion, and composition

[0001] The present disclosure relates to a method for producing a fluoropolymer, an aqueous dispersion, and a composition.

[0002] Fluorine-containing polymers such as tetrafluoroethylene copolymers are used in various industrial fields because of their excellent heat resistance, chemical resistance, flame retardancy, weather resistance, etc. As a method for producing a fluorine-containing polymer, for example, Patent Document 1 discloses a method for polymerizing a fluorine-containing monomer in an aqueous medium in the presence of a methacrylate polymer such as polymethyl methacrylate, a radical initiator, a reducing agent, and an acid substance.

[0003] International Publication No. 2022 / 265048

[0004] In a method of polymerizing a fluorine-containing monomer in an aqueous medium in the presence of polymethyl methacrylate, the productivity of the fluorine-containing polymer is low, and the obtained fluorine-containing polymer may be discolored during heating due to its low heat resistance. In the production of a fluorine-containing polymer, it is required to obtain a polymer with high heat resistance and to have high productivity.

[0005] The present disclosure has been made in view of these circumstances, and the problem to be solved by one embodiment of the present invention is to provide a method for producing a fluoropolymer which can give a fluoropolymer having excellent heat resistance and which is highly productive. Another problem to be solved by one embodiment of the present invention is to provide an aqueous dispersion containing a fluoropolymer having excellent heat resistance. A further problem to be solved by one embodiment of the present invention is to provide a composition containing a fluoropolymer having excellent heat resistance.

[0006] The present disclosure includes the following aspects: [1] A method for producing a fluoropolymer, comprising polymerizing a monomer containing a fluorine-containing monomer in a first aqueous dispersion comprising first particles containing a first fluoropolymer which contains units based on a compound represented by the following formula (1) and has a glass transition temperature of 10°C or lower, and producing a second fluoropolymer different from the first fluoropolymer, wherein the content of the first fluoropolymer is 0.01 to 4.0% by mass relative to the total mass of the first aqueous dispersion before the start of polymerization of the monomer: CX １ X ２ =CX ３ -CF ２ -O-Rf...(1) In formula (1), X １ , X ２ , and X ３are each independently a hydrogen atom or a fluorine atom, and Rf is a perfluoroalkyl group having 1 to 10 carbon atoms, which may have an etheric oxygen atom between carbon atoms in the perfluoroalkyl group. [2] The method for producing a fluoropolymer according to [1], wherein the fluorine-containing monomer comprises at least one selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, and vinylidene fluoride. [3] The method for producing a fluoropolymer according to [1] or [2], wherein the content of units based on the compound represented by formula (1) is 5 to 70 mol % based on all units contained in the first fluoropolymer. [4] The method for producing a fluoropolymer according to any one of [1] to [3], wherein the first fluoropolymer further comprises units based on tetrafluoroethylene. [5] The method for producing a fluoropolymer according to any one of [1] to [4], wherein the first fluoropolymer does not have a melting point. [6] The method for producing a fluoropolymer according to any one of [1] to [5], wherein the volume average particle diameter of the first particles is 200 nm or less. [7] The method for producing a fluoropolymer according to any one of [1] to [6], wherein the content of the fluorinated emulsifier in the first aqueous dispersion is 100 ppm by mass or less relative to the total mass of the aqueous medium contained in the first aqueous dispersion. [8] An aqueous dispersion comprising second particles containing a fluoropolymer containing units based on a compound represented by the following formula (1), and an aqueous medium, wherein the volume average particle diameter of the second particles is 500 nm or less, and the content of the units based on the compound represented by formula (1) is 0.05 to 5.0 mol % relative to the total units contained in the fluoropolymer contained in the second particles: CX １ X ２ =CX ３ -CF ２ -O-Rf...(1) In formula (1), X １ , X ２ , and X ３are each independently a hydrogen atom or a fluorine atom, and Rf is a perfluoroalkyl group having 1 to 10 carbon atoms, and the perfluoroalkyl group may have an etheric oxygen atom between carbon atoms. [9] The aqueous dispersion according to [8], wherein the second particles contain a fluorine-containing polymer including units based on at least one selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, and vinylidene fluoride.

[10] The aqueous dispersion according to [8] or [9], wherein the second particles contain a fluorine-containing polymer including units based on tetrafluoroethylene.

[11] The aqueous dispersion according to any one of [8] to

[10] , wherein the content of the fluorine-containing emulsifier in the aqueous dispersion is 100 ppm by mass or less relative to the total mass of the aqueous medium contained in the aqueous dispersion.

[12] A composition containing a fluoropolymer containing units based on a compound represented by the following formula (1), wherein the content of units based on the compound represented by formula (1) is 0.05 to 5.0 mol % based on all units contained in the fluoropolymer contained in the composition, and the composition is solid at 25°C. CX １ X ２ =CX ３ -CF ２ -O-Rf...(1) In formula (1), X １ , X ２ , and X ３ are each independently a hydrogen atom or a fluorine atom, and Rf is a perfluoroalkyl group having 1 to 10 carbon atoms, which may have an etheric oxygen atom between carbon atoms.

[13] The composition according to

[12] , which contains a fluorine-containing polymer containing at least one selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, and vinylidene fluoride.

[14] The composition according to

[12] or

[13] , which contains a fluorine-containing polymer containing units based on tetrafluoroethylene.

[15] The composition according to any one of

[12] to

[14] , which contains a fluorine-containing emulsifier in an amount of 100 ppm by mass or less based on the total mass of the fluorine-containing polymer.

[0007] According to one embodiment of the present invention, a method for producing a fluoropolymer with high productivity is provided, which allows a fluoropolymer having excellent heat resistance to be obtained. Also, according to one embodiment of the present invention, an aqueous dispersion containing a fluoropolymer having excellent heat resistance is provided. Furthermore, according to one embodiment of the present invention, a composition containing a fluoropolymer having excellent heat resistance is provided.

[0008] In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in the present disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another staged numerical range. Furthermore, in numerical ranges described in this specification, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In the present disclosure, when multiple substances corresponding to each component are present in the composition, the amount of each component in the composition means the total amount of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the present disclosure, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0009] [Method for producing a fluoropolymer] The method for producing a fluoropolymer of the present disclosure (hereinafter also referred to as "the present production method") is a method for producing a second fluoropolymer different from the first fluoropolymer by polymerizing a monomer containing a fluorine-containing monomer in a first aqueous dispersion containing first particles containing a first fluoropolymer which contains units based on a compound represented by the following formula (1) and has a glass transition temperature of 10°C or lower, and an aqueous medium, wherein the content of the first fluoropolymer is 0.01 to 4.0% by mass relative to the total mass of the first aqueous dispersion before the start of polymerization of the monomer: CX １ X ２ =CX ３ -CF ２ -O-Rf...(1) In formula (1), X １ , X２ , and X ３ are each independently a hydrogen atom or a fluorine atom, and Rf is a perfluoroalkyl group having 1 to 10 carbon atoms, which may have an etheric oxygen atom between carbon atoms. Hereinafter, the compound represented by formula (1) will also be referred to as "compound (1)", a unit based on compound (1) as "compound (1) unit", the glass transition temperature as "Tg", a monomer used in production of the second fluorine-containing polymer as "specific monomer", and the content of the first fluorine-containing polymer relative to the total mass of the first aqueous dispersion before initiation of polymerization of the specific monomer as "first polymer content".

[0010] In this production method, since the specific monomer is polymerized in a first aqueous dispersion containing the first fluoropolymer and having a first polymer content within the above range, a second fluoropolymer having excellent heat resistance is obtained, and the productivity of the second fluoropolymer is high. The reason for this is unclear, but it is presumed to be because the first fluoropolymer has a low Tg and contains fluorine atoms. Specifically, it is thought that the low Tg of the first fluoropolymer makes it easier for the molecular structure of the first fluoropolymer to deform at the temperature at which the specific monomer is polymerized, and hydrophilic groups are more likely to be oriented toward the surface side of the first particles, thereby increasing the dispersion stability of the first particles in the first aqueous dispersion. It is also presumed that the high dispersion stability of the first particles facilitates contact between the first particles and the specific monomer, thereby increasing the productivity of the second fluoropolymer. It is also presumed that the first fluoropolymer contains fluorine atoms, which makes it more chemically stable to heat due to the high bond energy between the fluorine atoms and carbon atoms, thereby resulting in a second fluoropolymer having high heat resistance and less likely to be discolored by heating.

[0011] <First Aqueous Dispersion> The first aqueous dispersion contains at least first particles containing a first fluoropolymer and an aqueous medium, and may contain other components such as additives as necessary.

[0012] (First Particle) The first particle contains a first fluorine-containing polymer which contains a compound (1) unit and has a Tg of 10° C. or less. １ X ２ =CX ３ -CF ２-O-Rf...(1) In formula (1), X １ , X ２ , and X ３ are each independently a hydrogen atom or a fluorine atom, and Rf is a perfluoroalkyl group having 1 to 10 carbon atoms, which may have an etheric oxygen atom between carbon atoms.

[0013] X １ , X ２ , and X ３ may all be hydrogen atoms, and X １ , X ２ , and X ３ may be partly or entirely fluorine atoms. １ , X ２ , and X ３ Among these, it is preferred that one or more of them are fluorine atoms, more preferred that two or more of them are fluorine atoms, and even more preferred that all three of them are fluorine atoms. ２ =CF-CF ２ —O—Rf and CH ２ =CF-CF ２ -O-Rf is preferred, and CF ２ =CF-CF ２ --O--Rf is more preferred.

[0014] The carbon number of Rf is preferably 1 to 8, more preferably 1 to 5. When the carbon number of Rf is 3 or more, Rf may be linear, branched, or may contain a ring structure, but is preferably linear. Examples of Rf include -(CF ２ ) ｍ CF ３ , and −(CF ２ ) ｒ１ -O-(CF ２ ) ｒ２ CF ３ From the viewpoint of improving the crystallinity of the copolymer, -(CF ２ ) ｍ CF ３ Preferably, m is an integer of 0 to 9. r1 is an integer of 1 to 9, r2 is an integer of 0 to 8, and r1+r2 is an integer of 1 to 9.

[0015] Among these, m is preferably an integer of 0 to 7, more preferably an integer of 0 to 5. r1 is preferably an integer of 1 to 6, more preferably an integer of 1 to 4. r2 is preferably an integer of 0 to 6, more preferably an integer of 0 to 4.

[0016] In particular, compound (1) is CF ２ =CF-CF ２ -OCF ３ (hereinafter also referred to as "PMAE"), CF ２ =CF-CF ２ -OCF ２ CF ３ (hereinafter also referred to as "PEAE"), and CF ２ =CF-CF ２ -OCF ２ CF ２ CF ３ (hereinafter also referred to as "PPAE") is preferred, PMAE and PPAE are more preferred, and PMAE is even more preferred.

[0017] The first fluorine-containing polymer solubilizes the specific monomer by adsorbing and incorporating the specific monomer at the hydrophobic portion during polymerization of the specific monomer. It is presumed that the specific monomer is polymerized within the first particles by adding a polymerization initiator thereto. It is also presumed that the first fluorine-containing polymer contributes to stabilizing the dispersion of the first particles and the specific monomer in the aqueous medium.

[0018] The first fluorine-containing polymer may contain units other than compound (1) units. The content of compound (1) units is preferably 5 to 70 mol%, more preferably 20 to 70 mol%, still more preferably 25 to 65 mol%, particularly preferably 30 to 60 mol%, based on all units contained in the first fluorine-containing polymer. When the content of compound (1) units is at least the above lower limit, the Tg of the first fluorine-containing polymer is likely to be 10°C or less, and the productivity of the second fluorine-containing polymer is likely to be high. In addition, when the content of compound (1) units is at most the above upper limit, there is an advantage that a second fluorine-containing polymer having excellent heat resistance can be obtained. The content of each unit contained in the polymer is, １９ Calculated by F-NMR analysis.

[0019] The first fluoropolymer preferably further contains units based on tetrafluoroethylene as units other than compound (1) units, from the viewpoint of ease of adjusting Tg within the above range and of better heat resistance. Hereinafter, tetrafluoroethylene will also be referred to as "TFE," and units based on TFE will also be referred to as "TFE units." The content of TFE units is preferably 30 to 80 mol%, more preferably 35 to 75 mol%, and even more preferably 40 to 70 mol%, based on all units contained in the first fluoropolymer, from the viewpoint of improving the productivity and heat resistance of the second fluoropolymer. When the first fluoropolymer contains compound (1) units and TFE units, the content of compound (1) units relative to the total content of TFE units and compound (1) units is preferably 20 to 70 mol%, more preferably 25 to 65 mol%, and even more preferably 30 to 60 mol%, from the viewpoint of ease of adjusting Tg within the above range.

[0020] The first fluorine-containing polymer may further contain units based on perfluoro(alkyl vinyl ether). Hereinafter, perfluoro(alkyl vinyl ether) will also be referred to as "PAVE", and units based on PAVE will also be referred to as "PAVE units". That is, the first fluorine-containing polymer may be a fluorine-containing polymer containing compound (1) units and PAVE units. When the first fluorine-containing polymer contains PAVE units, it preferably contains compound (1) units, PAVE units and TFE units. Examples of PAVE include perfluoro(methyl vinyl ether) (hereinafter also referred to as "PMVE"), perfluoro(ethyl vinyl ether) (hereinafter also referred to as "PEVE"), and perfluoro(propyl vinyl ether) (hereinafter also referred to as "PPVE"). Preferred PAVEs are PMVE, PEVE, and PPVE, more preferably PMVE and PPVE, and even more preferably PMVE.

[0021] When the first fluorinated polymer contains PAVE units, the combination of compound (1) units and PAVE units is preferably a combination of at least one selected from the group consisting of PMAE, PEAE, and PPAE with at least one selected from the group consisting of PMVE, PEVE, and PPVE. The combination of compound (1) units and PAVE units is more preferably a combination of at least one selected from the group consisting of PMAE and PPAE with at least one selected from the group consisting of PMVE and PPVE. The combination of compound (1) units and PAVE units is even more preferably a combination of PPAE and PMVE.

[0022] When the first fluorine-containing polymer contains PAVE units, the content of PAVE units is preferably 1 to 30 mol%, more preferably 3 to 25 mol%, and even more preferably 5 to 20 mol%, based on all units contained in the first fluorine-containing polymer, from the viewpoint of lowering the glass transition temperature of the first polymer. When the first fluorine-containing polymer contains compound (1) units, TFE units, and PAVE units, the content of compound (1) units relative to the total content of compound (1) units, TFE units, and PAVE units is preferably 1 to 30 mol%, more preferably 3 to 25 mol%, and even more preferably 5 to 20 mol%, from the viewpoint of facilitating adjustment of Tg within the above range. When the first fluorinated polymer contains compound (1) units, TFE units and PAVE units, the content of TFE units relative to the total content of compound (1) units, TFE units and PAVE units is preferably from 30 to 90 mol %, more preferably from 35 to 85 mol %, and even more preferably from 40 to 80 mol %, from the viewpoint of improving heat resistance.

[0023] The first fluorine-containing polymer is preferably a fluorine-containing polymer containing compound (1) units and TFE units, or a fluorine-containing polymer containing compound (1) units, PAVE units, and TFE units. From the viewpoint of improving the heat resistance of the first polymer, the first fluorine-containing polymer is more preferably a fluorine-containing polymer containing compound (1) units and TFE units and substantially free of PAVE units. "Substantially free of PAVE units" means that the content of PAVE units is 0.01 mol% or less, more preferably 0.00 mol%, based on the total structural units of the first fluorine-containing polymer.

[0024] The first fluorine-containing polymer may contain structural units based on other monomers other than TFE units, PAVE units, and compound (1) units. When the first fluorine-containing polymer contains structural units based on other monomers, examples of the other monomers include fluoroolefins (excluding TFE, PAVE, and compound (1)); acid anhydrides such as itaconic anhydride, citraconic anhydride, and 5-norbornene-2,3-dicarboxylic anhydride; and allyl ethers other than compound (1). Furthermore, examples of other monomers similar to PAVE include CX １１ X １２ ═CF—O—Rf １ -A １ (X １１ and X １２ are each independently H or F, Rf １ is a perfluoroalkylene group having 1 to 6 carbon atoms, A １ is COOM １ or SO ３ M １ , M １ is H, Na, K, or NH ４ Examples of allyl ethers other than compound (1) include CX ２１ X ２２ =CF-CF ２ -O-Rf ２ -A ２ (X ２１ and X ２２ are each independently H or F, Rf ２ is a perfluoroalkylene group having 1 to 6 carbon atoms, A ２ is COOM ２ or SO ３ M ２ , M ２ is H, Na, K, or NH ４In order to produce the second fluorine-containing polymer more efficiently, the content of the structural units based on the other monomers is preferably 30 mol % or less, more preferably 25 mol % or less, even more preferably 20 mol % or less, and particularly preferably 15 mol % or less, relative to all the structural units of the first fluorine-containing polymer. It is more preferable that the first fluorine-containing polymer is substantially free of structural units based on other monomers. "Substantially free of units based on other monomers" means that the content of units based on other monomers is 0.01 mol % or less, more preferably 0.00 mol %, relative to all the structural units of the first fluorine-containing polymer.

[0025] The Tg of the first fluoropolymer is 10° C. or lower, and from the viewpoint of efficient adsorption of a specific monomer described below, it is preferably 5° C. or lower, more preferably 3° C. or lower, and even more preferably 0° C. or lower. From the viewpoint of thermal stability after molding, the Tg of the first fluoropolymer is preferably −50° C. or higher, more preferably −45° C. or higher, and even more preferably −40° C. or higher.

[0026] The Tg of the first fluoropolymer is measured by differential scanning calorimetry (DSC). For example, Tg is measured using a NEXTA DSC600 manufactured by Hitachi High-Technologies Corporation. Specifically, 5 mg of a sample for measurement is weighed into an aluminum sample pan, and the sample is heated to 100°C at a heating rate of 10°C / min under a nitrogen atmosphere. Thereafter, the sample is cooled to -60°C at a rate of 10°C / min. Once the predetermined temperature is reached, the temperature is again raised to 100°C at 10°C / min. The Tg is estimated from the inflection point confirmed in this second heating operation.

[0027] As a method for adjusting the Tg of the first fluoropolymer within the above range, for example, a method of adjusting the type and amount of the monomer used in producing the first fluoropolymer can be mentioned.

[0028] From the viewpoint of improving the productivity of the second fluoropolymer, it is preferable that the first fluoropolymer does not have a melting point. Examples of methods for obtaining a first fluoropolymer that does not have a melting point include a method of adjusting the type and amount of monomers used in producing the first fluoropolymer. "Having no melting point" means that no melting peak is observed when the melting point of the first fluoropolymer is measured using a differential scanning calorimeter, and specifically means that no melting peak is observed in a temperature range of 150°C or higher (preferably a temperature range of 150 to 330°C). Note that a glass transition peak does not fall under the category of the above-mentioned melting peak. Specific methods for measuring the melting point include the measurement methods shown in the Examples section.

[0029] The first polymer content, i.e., the content of the first fluoropolymer relative to the total mass of the first aqueous dispersion before the start of polymerization of the specific monomer, is 0.01 to 4.0 mass%, preferably 0.05 to 3.5 mass%, more preferably 0.1 to 3.0 mass%. When the first polymer content is not less than the above lower limit, the productivity of the second fluoropolymer becomes high, and when the first polymer content is not more than the above upper limit, the second fluoropolymer is more likely to have the desired performance.

[0030] In the present disclosure, "before initiating polymerization of the specific monomer" means immediately before the initiation of polymerization of the specific monomer. Here, examples of "initiation of polymerization" include the time when the specific monomer and the polymerization initiator are allowed to coexist in the reactor after the reactor is heated to a polymerization temperature or higher, and the time when the reactor is heated to a polymerization temperature or higher after the specific monomer and the polymerization initiator are allowed to coexist in the reactor. The term "first aqueous dispersion" does not include the specific monomer and the polymerization initiator used in the polymerization of the specific monomer. Meanwhile, the polymerization initiator used in the production of the first particles may be contained in the first aqueous dispersion.

[0031] The first particles are obtained by dispersing the first fluoropolymer in a particulate form. The first particles contain at least the first fluoropolymer and may or may not contain components other than the first fluoropolymer. From the viewpoint of improving the productivity of the second fluoropolymer, the content of the first fluoropolymer in the entire first particles is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0032] From the viewpoint of improving the productivity of the second fluorinated polymer, the volume average particle diameter of the first particles is preferably 200 nm or less, more preferably 1 to 200 nm, even more preferably 10 to 150 nm, even more preferably 50 to 120 nm, and particularly preferably 50 to 85 nm. The volume average particle diameter of the first particles is a particle diameter calculated by analyzing an autocorrelation function obtained by dynamic light scattering using the monodisperse cumulant method. When the volume average particle diameter of the first particles is within this range, it is thought that the specific monomer is likely to polymerize within the first particles, and polymerization is likely to proceed stably even in the substantial absence of an emulsifier.

[0033] A preferred method for producing the first particles involves polymerizing a monomer containing compound (1) in an aqueous medium in the presence of a polymerization initiator. This results in first particles, which are first fluorine-containing polymers dispersed in the aqueous medium in a particulate form. The polymerization initiator used in producing the first particles is preferably a water-soluble polymerization initiator, more preferably persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate, or organic polymerization initiators such as disuccinic acid peroxide and azobisisobutylamidine dihydrochloride, with persulfates being even more preferred, and ammonium persulfate being particularly preferred. Examples of the aqueous medium used in producing the first particles include water or a mixed solvent of water and a water-soluble organic solvent. Specific examples of the water-soluble organic solvent include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol. In producing the first particles, a dispersion of the first particles dispersed in the aqueous medium may be heated after the dispersion is obtained.

[0034] The dispersion thus obtained, in which the first particles are dispersed in an aqueous medium, may be used as the first aqueous dispersion as is, or another aqueous medium may be added and the resulting dispersion may be used as the first aqueous dispersion. Alternatively, the first particles may be dispersed in another aqueous medium after solvent substitution and the resulting dispersion may be used as the first aqueous dispersion. As described below, the first aqueous dispersion may have sulfate ions removed by a sulfate ion removal means such as an anion exchange resin, or may have ammonium ions removed by an ammonium ion removal means such as a cation exchange resin.

[0035] (Aqueous medium) The first aqueous dispersion used in the present production method contains an aqueous medium. The aqueous medium contained in the first aqueous dispersion may be the polymerization solvent used in the production of the first particles, as described above. Specific examples of the aqueous medium contained in the first aqueous dispersion are the same as the specific examples of the aqueous medium used in the production of the first particles described above. Before starting polymerization of the specific monomer used in the polymerization of the second fluorine-containing polymer, the content of the aqueous medium is preferably 60 to 99.9 mass%, more preferably 96 to 99.9 mass%, and even more preferably 98 to 99.9 mass%, based on the total mass of the first aqueous dispersion.

[0036] (Other Components) The first aqueous dispersion may contain other components in addition to the first particles and the aqueous medium. Specific examples of other components that the first aqueous dispersion may contain include a chain transfer agent, a fluorinated emulsifier, an emulsifier other than a fluorinated emulsifier, a pH adjuster, and a wax.

[0037] The first aqueous dispersion may contain a fluorine-containing emulsifier as another component, but preferably does not contain a fluorine-containing emulsifier. The fluorine-containing emulsifier is an emulsifier having a fluorine atom. The first aqueous dispersion preferably does not contain a fluorine-containing emulsifier, or contains a fluorine-containing emulsifier in a range of 100 mass ppm or less relative to the total mass of the aqueous medium contained in the first aqueous dispersion. The content of the fluorine-containing emulsifier in the first aqueous dispersion is preferably 100 mass ppm or less, more preferably 10 mass ppm or less, still more preferably 5 mass ppm or less, particularly preferably less than 1 mass ppm, extremely preferably less than 250 mass ppb, and most preferably 0 mass ppm, relative to the total mass of the aqueous medium contained in the first aqueous dispersion. The content of the fluorine-containing emulsifier relative to the total mass of the aqueous medium is determined by the method described in the Examples.

[0038] In the present disclosure, an emulsifier is a compound that has a hydrophilic portion and a hydrophobic portion.

[0039] Examples of emulsifiers include hydrocarbon-containing surfactants, fluorine-containing emulsifiers, and polymer emulsifiers. The first fluorine-containing polymer is water-insoluble and therefore does not qualify as an emulsifier. A solubility of 10 mg / mL or more in water at room temperature (25°C) is defined as water-soluble. The emulsifier may be either ionic or nonionic.

[0040] The hydrocarbon-containing surfactant is a surfactant that contains a hydrocarbon group. More specifically, as long as the hydrocarbon-containing surfactant contains a hydrocarbon group, it may contain substitution with halogen atoms such as fluorine atoms and chlorine atoms. In the hydrocarbon-containing surfactant, it is preferred that 75% or more of the atoms or monovalent groups bonded to the carbon atoms of the hydrocarbon group are hydrogen atoms, more preferably 85% or more, and even more preferably 95% or more.

[0041] The hydrocarbon-containing surfactant can be exemplified by hydrocarbon surfactant and siloxane surfactant.Hydrocarbon-containing surfactant means the surfactant that does not contain silicon atom, and 100% of the atoms or monovalent groups that bond to the carbon atom of hydrocarbon group are hydrogen atoms, so it does not contain halogen atoms such as chlorine atom and fluorine atom.Siloxane surfactant means the hydrocarbon-containing surfactant that has a hydrophobic group and contains a siloxane skeleton that contains many siloxane units.

[0042] Examples of hydrocarbon-containing surfactants include anionic hydrocarbon surfactants. Anionic hydrocarbon surfactants refer to hydrocarbon-containing surfactants having a negatively charged hydrophilic moiety such as a carboxylic acid group, sulfonic acid group, sulfate group, phosphonic acid group, or phosphate group, and a hydrocarbon moiety such as an alkyl group as a hydrophobic moiety. An example of an anionic hydrocarbon surfactant is the highly branched C10 tertiary carboxylic acid supplied by Resolution Performance Products as Versatic® 10. Another example of an anionic hydrocarbon surfactant is the linear alkyl polyethersulfonate sodium supplied by BASF as part of the Avanel® S series.

[0043] Anionic hydrocarbon surfactants also include sodium dodecyl sulfate.

[0044] Another example of an anionic hydrocarbon surfactant is the sulfosuccinate surfactant Lankropol® K8300, available from Akzo Nobel Surface Chemistry LLC.

[0045] Hydrocarbon-containing surfactants also include nonionic hydrocarbon surfactants.Nonionic hydrocarbon surfactants do not have charged groups, but have hydrophobic moieties that are often long-chain hydrocarbons.The hydrophilic moieties of nonionic hydrocarbon surfactants include water-soluble functional groups such as polyethylene oxide chains obtained from the polymerization of ethylene oxide.Nonionic hydrocarbon surfactants include block copolymers with various types of polyalkylene oxide blocks, for example, polyethylene oxide and polypropylene oxide.

[0046] Examples of nonionic hydrocarbon surfactants include surfactants described in paragraphs

[0043] to

[0052] of JP-A No. 2016-537499.

[0047] Siloxane surfactants include those described in US Pat. Nos. 6,841,616 (Wille et al.) and 7,977,438 (Brothers et al.).

[0048] The fluorine-containing emulsifier may be an anionic fluorine-containing surfactant. Examples of the anionic fluorine-containing surfactant include surfactants containing fluorine atoms whose total carbon number excluding the anionic group is 20 or less, and surfactants containing fluorine atoms whose anionic moiety has a molecular weight of 800 or less. The "anionic moiety" refers to the moiety excluding the cation of the fluorine-containing surfactant.

[0049] The polymer emulsifier is water-soluble and includes a polymer having a hydrophilic group in the side chain. Such a polymer emulsifier includes, for example, a polymer containing a structural unit based on a compound having a site capable of polymerization reaction and a hydrophilic group. Also included are polymers obtained by subjecting a polymer containing a structural unit based on a compound having a group that can become a hydrophilic group to post-treatment such as hydrolysis. The polymer emulsifier is a hydrocarbon-containing surfactant or a fluorine-containing emulsifier, and refers to a polymer of these.

[0050] Specific examples of chain transfer agents include ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane.

[0051] Specific examples of pH adjusters include inorganic salts. Specific examples of inorganic salts include phosphates such as disodium hydrogen phosphate and sodium dihydrogen phosphate; and carbonates such as sodium bicarbonate and sodium carbonate. More preferred specific examples of phosphates include disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate.

[0052] Specific examples of wax include Paraffin Wax-155 and Paraffin Wax-150 (both manufactured by Nippon Seiro Co., Ltd.).

[0053] When the first aqueous dispersion contains a chain transfer agent, the content of the chain transfer agent is preferably 0.1 to 5.0 parts by mass relative to 100 parts by mass of the aqueous medium. The amount of the chain transfer agent used is preferably 0.1 to 20.0 parts by mass, more preferably 0.1 to 15.0 parts by mass, and even more preferably 0.1 to 10.0 parts by mass, relative to 100 parts by mass of the specific monomer described below.

[0054] When the first aqueous dispersion contains an emulsifier other than the fluorine-containing emulsifier, the content of the emulsifier other than the fluorine-containing emulsifier is preferably 0.01 to 5.0 parts by mass relative to 100 parts by mass of the aqueous medium. It is preferable that the first aqueous dispersion is substantially free of an emulsifier. "Substantially free of an emulsifier" means that the content of the emulsifier is less than 1 ppm by mass relative to the total mass of the aqueous medium contained in the first aqueous dispersion, preferably 0.03 ppm by mass or less, more preferably 0.02 ppm by mass or less, and even more preferably 0 ppm by mass. It is also preferable that the first aqueous dispersion is substantially free of any emulsifier other than the fluorine-containing emulsifier. "Substantially free of emulsifiers other than fluorine-containing emulsifiers" means that the content of emulsifiers other than fluorine-containing emulsifiers is less than 1 ppm by mass relative to the total mass of the aqueous medium contained in the first aqueous dispersion, preferably 0.75 ppm by mass or less, more preferably 0.03 ppm by mass or less, even more preferably 0.02 ppm by mass or less, and particularly preferably 0 ppm by mass. The content of emulsifiers relative to the total mass of the aqueous medium and the content of emulsifiers other than fluorine-containing emulsifiers relative to the total mass of the aqueous medium can be measured by the method described in the Examples.

[0055] When the first aqueous dispersion contains a pH adjuster, the content of the pH adjuster is preferably 0.01 to 3.0 parts by mass relative to 100 parts by mass of the aqueous medium. When the first aqueous dispersion contains a wax, the content of the wax is preferably 1 to 10 parts by mass relative to 100 parts by mass of the aqueous medium.

[0056] Before starting polymerization of the specific monomer, the concentration of fluoride ions is preferably 100 ppm by mass or less, more preferably 50 ppm by mass or less, relative to the total mass of the first aqueous dispersion, from the viewpoint of polymerization stability. The lower limit can be 0 ppm by mass. One example of a method for adjusting the fluoride ion concentration to the above value is a method of removing fluoride ions using an anion exchange resin during the production of the first particles. Here, fluoride ions may be generated by the reaction between a polymerization initiator (e.g., ammonium persulfate) and a fluorine-containing monomer and contained in the aqueous dispersion.

[0057] Before starting polymerization of the specific monomer, the sulfate ion concentration is preferably 10 ppm by mass or less, more preferably 5 ppm by mass or less, relative to the total mass of the aqueous medium in the first aqueous dispersion, from the viewpoint of suppressing discoloration of the second fluoropolymer. The lower limit can be 0 ppm by mass. One example of a method for adjusting the sulfate ion concentration to the above value is a method of removing sulfate ions using an anion exchange resin during the production of the first particles. Here, the sulfate ions are derived, for example, from the polymerization initiator (particularly ammonium persulfate) used during the production of the first particles, and may be contained in the first aqueous dispersion containing the first particles. It is presumed that by having the sulfate ion content be 10 ppm by mass or less (particularly 5 ppm by mass or less), it is possible to suppress the formation of terminal groups with low heat resistance in the second fluoropolymer, thereby suppressing discoloration of the second fluoropolymer.

[0058] Before the start of polymerization of the specific monomer, the concentration of ammonium ions is preferably 20 ppm by mass or less, more preferably 10 ppm by mass or less, relative to the total mass of the aqueous medium in the first aqueous dispersion, from the viewpoint of suppressing aggregation of the second fluorinated polymer. The lower limit may be 0 ppm by mass.

[0059] An example of a method for adjusting the ammonium ion concentration to the above value is a method of removing ammonium ions using a cation exchange resin during the production of the first particles.Here, the ammonium ions are derived, for example, from the initiator (particularly ammonium persulfate) used during the production of the first particles, and may be contained in the first aqueous dispersion containing the first particles.It is presumed that when the ammonium ion content is 20 mass ppm or less, the ionic strength in the aqueous medium decreases, thereby improving the production efficiency of the second fluorine-containing polymer.The contents of fluoride ions, sulfate ions, and ammonium ions can be measured by ion chromatography.

[0060] <Specific Monomer> The specific monomer includes a fluorine-containing monomer. The fluorine-containing monomer preferably includes at least one selected from the group consisting of TFE, chlorotrifluoroethylene (hereinafter also referred to as "CTFE"), and vinylidene fluoride (hereinafter also referred to as "VdF") (hereinafter also referred to as "specific fluorine-containing monomer"), more preferably includes TFE, and even more preferably is TFE. Two or more types of fluorine-containing monomers may be used in combination. The amount of the fluorine-containing monomer used is preferably 10.0 to 100.0 mol%, more preferably 30.0 to 100.0 mol%, and even more preferably 40.0 to 100.0 mol%, based on the amount of the specific monomer used. Furthermore, a fluorine-containing monomer other than the specific fluorine-containing monomer (hereinafter also referred to as "other fluorine-containing monomer") may be included. Specific examples of the other fluorine-containing monomer include fluoroalkylethylene (hereinafter also referred to as "FAE"), compound (1), PAVE, and hexafluoropropylene. Two or more of the other fluorine-containing monomers may be used in combination. Specific examples of FAE include CH ２ =CH(CF ２ ) ２ F, CH ２ =CH(CF ２ ) ３ F, CH ２ =CH(CF ２ ) ４ F (hereinafter also referred to as "C4OLF"), CH ２ =CF(CF ２ ) ３ H, and CH２ =CF(CF ２ ) ４ H is exemplified, with C4OLF being preferred. Specific examples and preferred ranges of compound (1) and PAVE are as described above. When another fluorine-containing monomer is used, the amount of the other fluorine-containing monomer used is preferably 0.1 to 30.0 mol %, more preferably 0.1 to 10.0 mol %, and even more preferably 0.5 to 5.0 mol %, relative to the amount of the specific monomer used.

[0061] The specific monomer may contain a monomer other than the fluorine-containing monomer (hereinafter also referred to as "other monomer"). Specific examples of the other monomer include ethylene, propylene, vinyl chloride, and vinylidene chloride. Among them, the other monomer preferably contains ethylene, and more preferably is ethylene. Two or more types of other monomers may be used in combination. When the other fluorine-containing monomer is used, the amount of the other monomer used is preferably 10.0 to 70.0 mol%, more preferably 20.0 to 60.0 mol%, and even more preferably 30.0 to 50.0 mol%, relative to the amount of the specific monomer used. The specific monomer may contain the specific fluorine-containing monomer, another fluorine-containing monomer, and another monomer.

[0062] The amount of the specific monomer used is preferably 1 to 50 parts by mass, more preferably 1 to 40 parts by mass, and even more preferably 1 to 30 parts by mass, per 100 parts by mass of the aqueous medium contained in the first aqueous dispersion.

[0063] <Polymerization Initiator> In the present production method, the specific monomer is preferably polymerized in the presence of a polymerization initiator. Examples of the polymerization initiator include an oil-soluble radical initiator, a water-soluble radical initiator, and a water-soluble redox catalyst. Specific examples of the oil-soluble radical initiator include oil-soluble organic peroxides such as tert-butyl peroxypivalate (hereinafter also referred to as "PBPV") and diisopropyl peroxydicarbonate (hereinafter also referred to as "IPP"). Specific examples of the water-soluble radical initiator include persulfates such as ammonium persulfate and potassium persulfate, and water-soluble organic peroxides such as disuccinic acid peroxide, bisglutaric acid peroxide, and tert-butyl hydroperoxide (hereinafter also referred to as "TBHP"). The water-soluble redox catalyst is preferably a combination of an oxidizing agent such as bromic acid or a salt thereof, chloric acid or a salt thereof, persulfuric acid or a salt thereof, permanganic acid or a salt thereof, or hydrogen peroxide, and a reducing agent such as sulfurous acid or a salt thereof, hydrogen sulfite or a salt thereof, thiosulfuric acid or a salt thereof, organic acid, or inorganic salt. Potassium persulfate and ammonium persulfate are preferred as persulfates. Sodium sulfite is preferred as sulfites. Inorganic salts include combinations of sulfate anions, sulfite anions, and chloride anions with metal ions. Transition metal ions are preferred, including manganese, iron, cobalt, nickel, copper, zinc, cerium, and silver ions, with iron ions being preferred. Iron (II) sulfate is preferred as an inorganic salt. The polymerization initiator is preferably an oil-soluble radical initiator or a water-soluble radical initiator. From the viewpoint of more efficient production of fluoropolymers, oil-soluble radical initiators are more preferred, and oil-soluble organic peroxides are even more preferred. Two or more polymerization initiators may be used in combination.

[0064] The amount of the polymerization initiator used is preferably 0.001 to 5 parts by mass, more preferably 0.001 to 3 parts by mass, and even more preferably 0.01 to 2 parts by mass, per 100 parts by mass of the specific monomer used.

[0065] <Other Components> When polymerizing the specific monomer, components other than those described above (hereinafter also referred to as "other components") may be further used. A specific example of the other component is a reducing agent. The amount of the other component used is preferably 0.1 to 2 parts by mass per 100 parts by mass of the specific monomer used.

[0066] <Steps> In the present production method, the specific monomer is polymerized in the first aqueous dispersion to produce a second fluorine-containing polymer different from the first fluorine-containing polymer.

[0067] The specific monomer is added to the reaction system (i.e., polymerization reaction vessel) by a conventional method. For example, the specific monomer may be added to the reaction system continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. Alternatively, the specific monomer may be dissolved in an aqueous medium, and the resulting solution may be added to the reaction system continuously or intermittently. When a polymerization initiator is used, the polymerization initiator may be added to the reaction system all at once or in portions.

[0068] The polymerization temperature is preferably 10 to 95° C., more preferably 15 to 90° C. The polymerization pressure is preferably 0.5 to 4.0 MPaG, more preferably 0.6 to 3.5 MPaG. In the case of batch processing, the polymerization time is preferably 90 to 1,000 minutes, more preferably 90 to 700 minutes.

[0069] The polymerization of the specific monomer is preferably carried out in an environment in which the content of the fluorine-containing emulsifier is 100 ppm by mass or less, more preferably 10 ppm by mass or less, still more preferably 5 ppm by mass or less, particularly preferably less than 1 ppm by mass, extremely preferably less than 250 ppb by mass, and most preferably 0 ppm by mass, relative to the total mass of the aqueous medium contained in the first aqueous dispersion. The content of the fluorine-containing emulsifier relative to the total mass of the aqueous medium is determined by the method described in the Examples.

[0070] The polymerization of the specific monomer is preferably carried out in the substantial absence of an emulsifier. Examples of the emulsifier include known emulsifiers, including common surfactants. "In the substantial absence of an emulsifier" refers to an environment in which the content of the emulsifier is less than 1 mass ppm relative to the total mass of the aqueous medium contained in the first aqueous dispersion, preferably 0.03 mass ppm or less, more preferably 0.02 mass ppm or less, and even more preferably 0 mass ppm. The polymerization of the specific monomer is particularly preferably carried out in the substantial absence of any emulsifier other than the fluorine-containing emulsifier. "In the substantial absence of any emulsifier other than the fluorine-containing emulsifier" refers to an environment in which the content of the emulsifier other than the fluorine-containing emulsifier is less than 1 mass ppm relative to the total mass of the aqueous medium contained in the first aqueous dispersion, preferably 0.75 mass ppm or less, more preferably 0.03 mass ppm or less, even more preferably 0.02 mass ppm or less, and particularly preferably 0 mass ppm. The content of the emulsifier relative to the total mass of the aqueous medium and the content of the emulsifier other than the fluorine-containing emulsifier relative to the total mass of the aqueous medium can be measured by the method described in the Examples.

[0071] As mentioned above, it is presumed that the specific monomer polymerizes within the first particles during polymerization of the specific monomer, and therefore, in the present production method, second particles containing the first fluorine-containing polymer and the second fluorine-containing polymer are presumed to be produced. That is, it is presumed that, according to the present production method, the second fluorine-containing polymer is obtained in the form of particles containing the first fluorine-containing polymer and the second fluorine-containing polymer. In this case, the present production method provides a second aqueous dispersion in which second particles containing the first fluorine-containing polymer and the second fluorine-containing polymer are dispersed in the aqueous medium.

[0072] The polymerization of the specific monomer is preferably carried out by emulsion polymerization. As described above, it is presumed that the specific monomer is polymerized within the first particles during polymerization of the specific monomer, and therefore, in the present production method, emulsion polymerization is likely to proceed stably even when the content of the fluorine-containing emulsifier and the content of the emulsifier are within the above-mentioned ranges.

[0073] <Second Fluorine-Containing Polymer> The second fluorine-containing polymer obtained by the present production method is a fluorine-containing polymer containing at least units based on the above-mentioned fluorine-containing monomer (hereinafter also referred to as "fluorine-containing units"). The second fluorine-containing polymer may contain fluorine-containing units and units based on the above-mentioned other monomers (hereinafter also referred to as "other units"). The second fluorine-containing polymer preferably contains at least one selected from the group consisting of TFE units, units based on CTFE, and units based on VdF, and more preferably contains TFE units. The second fluorine-containing polymer preferably comprises at least one selected from the group consisting of a polymer of TFE (hereinafter also referred to as "PTFE"), a copolymer of TFE and ethylene (hereinafter also referred to as "ETFE"), a copolymer of TFE and compound (1), a copolymer of TFE and PAVE (hereinafter also referred to as "PFA"), a copolymer of TFE, compound (1) and PAVE, a copolymer of TFE and HFP, and a copolymer of TFE and propylene, and more preferably comprises at least one selected from the group consisting of PTFE and ETFE. The first fluorine-containing polymer and the second fluorine-containing polymer are different. "The first fluorine-containing polymer and the second fluorine-containing polymer are different" means that the types of units constituting the first fluorine-containing polymer and the second fluorine-containing polymer are different, or that the types of units constituting the first fluorine-containing polymer and the second fluorine-containing polymer are the same but the contents of each unit are different.

[0074] When the second fluorine-containing polymer contains PTFE, the proportion of TFE units relative to all units constituting PTFE is preferably 97 to 100% by mass, more preferably 98 to 100% by mass, and even more preferably 99 to 100% by mass. Also, it is preferably 95.0 to 100.0 mol%, more preferably 99 to 100.0 mol%, and even more preferably 99.5 to 100.0 mol%. When the second polymer contains ETFE, the proportion of E units relative to the total of E units and TFE units in ETFE is preferably 20 to 70 mol%, more preferably 25 to 60 mol%, and even more preferably 35 to 55 mol%. When the second fluorine-containing polymer contains ETFE, the total proportion of E units and TFE units relative to all units constituting ETFE is preferably 80 mol% or more, more preferably 85 mol% or more, still more preferably 90 mol% or more, and is preferably 100 mol% or less, more preferably 99.5 mol% or less, still more preferably 99 mol% or less.

[0075] [Aqueous Dispersion] The aqueous dispersion of the present disclosure (hereinafter also referred to as "the present aqueous dispersion") is an aqueous dispersion comprising second particles containing a fluoropolymer containing compound (1) units, and an aqueous medium. In the present aqueous dispersion, the volume average particle diameter of the second particles is 500 nm or less. Furthermore, in the present aqueous dispersion, the second particles contain compound (1) units, and the content of the compound (1) units is 0.05 to 5.0 mol % based on the total units of the fluoropolymer contained in the second particles. The present aqueous dispersion is preferably the second aqueous dispersion obtained by the above-mentioned present production method.

[0076] <Second Particles> The second particles contain one or more types of fluoropolymers, and may contain two or more types of fluoropolymers. The second particles may have a plurality of Tg's, and preferably have a plurality of Tg's. Having a plurality of Tg's means that the second particles contain two or more types of fluoropolymers. The Tg's of the second particles can be measured in the same manner as the Tg's of the first fluoropolymer.

[0077] The second particles contain a fluorine-containing polymer containing compound (1) units. When the second particles contain two or more types of fluorine-containing polymers, the second particles only need to contain a fluorine-containing polymer containing compound (1) units, and may contain a fluorine-containing polymer that does not fall under the category of a fluorine-containing polymer containing compound (1) units. Details of the compound (1) units are the same as those of the compound (1) units contained in the above-mentioned first fluorine-containing polymer, and preferred embodiments are also the same.

[0078] The content of compound (1) units contained in the fluoropolymer contained in the second particles is 0.05 to 5.0 mol % relative to all units of the fluoropolymer contained in the second particles. The content of compound (1) units is preferably 0.1 mol % or more. The content of compound (1) units is preferably 1.0 mol % or less, more preferably 0.9 mol % or less, and even more preferably 0.8 mol % or less. When the content of compound (1) units is equal to or greater than the above lower limit, the second particles tend to have excellent stability. Furthermore, when the content of compound (1) units is equal to or less than the above upper limit, the mechanical properties of the second particles are superior.

[0079] In the present disclosure, when the second particles contain only one type of fluoropolymer, "all units of the fluoropolymer" means all units contained in that one type of fluoropolymer. When the second particles contain two or more types of fluoropolymer, "all units of the fluoropolymer" means all units contained in the two or more types of fluoropolymer.

[0080] The fluorine-containing polymer contained in the second particles preferably contains compound (1) units and units based on the above-mentioned fluorine-containing monomer other than compound (1) units (i.e., the above-mentioned fluorine-containing units), more preferably compound (1) units and at least one unit selected from the group consisting of TFE units, CTFE units, and VdF units, and even more preferably compound (1) units and TFE units. The fluorine-containing polymer contained in the second particles may contain PAVE units as units based on a fluorine-containing monomer other than compound (1) units, or may contain compound (1) units, PAVE units, and at least one unit selected from the group consisting of TFE units, CTFE units, and VdF units, or may contain compound (1) units, PAVE units, and TFE units.

[0081] When the fluorine-containing polymer contained in the second particles contains fluorine-containing units other than compound (1) units, the content of the fluorine-containing units other than compound (1) units is preferably 30 to 99.9 mol%, more preferably 40 to 99.8 mol%, and even more preferably 45 to 99.7 mol%, based on all units of the fluorine-containing polymer contained in the second particles. When the fluorine-containing polymer contained in the second particles contains PAVE units as fluorine-containing units other than compound (1) units, the content of PAVE units is preferably 0.01 to 0.50 mol%, more preferably 0.02 to 0.45 mol%, and even more preferably 0.03 to 0.40 mol%, based on all units of the fluorine-containing polymer contained in the second particles.

[0082] The fluorine-containing polymer contained in the second particles may contain units based on the other monomers described above (i.e., the other units described above). When the fluorine-containing polymer contained in the second particles contains other units, it is preferable that the fluorine-containing polymer contained in the second particles contain the E units described above. When the fluorine-containing polymer contained in the second particles contains other units, the content of the other units is preferably 30 to 70 mol%, more preferably 40 to 60 mol%, and even more preferably 40 to 55 mol%, based on the total units of the fluorine-containing polymer contained in the second particles.

[0083] The preferred embodiment of the fluorine-containing polymer contained in the second particle is the embodiment comprising compound (1) unit and fluorine-containing unit other than compound (1) unit, and the embodiment comprising compound (1) unit, fluorine-containing unit other than compound (1) unit, and other unit.The preferred embodiment of the fluorine-containing polymer contained in the second particle is, among others, the embodiment comprising compound (1) unit and TFE unit; the embodiment comprising compound (1) unit, PAVE unit, and TFE unit; the embodiment comprising compound (1) unit, TFE unit, and E unit; and the embodiment comprising compound (1) unit, PAVE unit, TFE unit, and E unit are more preferred, and the embodiment comprising compound (1) unit and TFE unit; the embodiment comprising compound (1) unit, PAVE unit, and TFE unit; and the embodiment comprising compound (1) unit, TFE unit, and E unit are even more preferred. The fluorine-containing polymer contained in the second particles is particularly preferably an embodiment containing compound (1) units and TFE units and substantially not containing PAVE units; and an embodiment containing compound (1) units, TFE units, and E units and substantially not containing PAVE units. "Substantially not containing PAVE units" means that the content of PAVE units is 0.01 mol% or less, with 0.00 mol% being extremely preferred, based on the total structural units of the fluorine-containing polymer contained in the second particles.

[0084] When the fluorine-containing polymer contained in the second particles contains compound (1) units, TFE units, and PAVE units, the content of compound (1) units contained in the fluorine-containing polymer is preferably 0.01 to 0.50 mol%, more preferably 0.02 to 0.45 mol%, and even more preferably 0.03 to 0.40 mol%. The content of TFE units contained in the fluorine-containing polymer is preferably 98 to 99.98 mol%, more preferably 98.50 to 99.95 mol%, and even more preferably 99.00 to 99.90 mol%. The content of PAVE units is preferably 0.01 to 0.50 mol%, more preferably 0.02 to 0.45 mol%, and even more preferably 0.03 to 0.40 mol%.

[0085] When the fluorine-containing polymer contained in the second particles contains compound (1) units and TFE units but does not substantially contain PAVE units, the content of compound (1) units contained in the fluorine-containing polymer is preferably 0.02 to 0.50 mol%, more preferably 0.03 to 0.45 mol%, and even more preferably 0.05 to 0.45 mol%. The content of TFE units contained in the fluorine-containing polymer is preferably 98.00 to 99.98 mol%, more preferably 98.50 to 99.97 mol%, and even more preferably 99.00 to 99.95 mol%.

[0086] When the fluorine-containing polymer contained in the second particles contains compound (1) units, TFE units, and E units, the content of compound (1) units contained in the fluorine-containing polymer is preferably 0.01 to 1.00 mol%, more preferably 0.03 to 0.80 mol%, and even more preferably 0.05 to 0.75 mol%. The content of TFE units contained in the fluorine-containing polymer is preferably 45 to 75 mol%, more preferably 47 to 73 mol%, and even more preferably 50 to 70 mol%. The content of E units is preferably 25 to 55 mol%, more preferably 27 to 53 mol%, and even more preferably 30 to 50 mol%.

[0087] The melting point of the second particles is preferably from 200 to 350°C, more preferably from 210 to 347°C, and even more preferably from 220 to 345°C.

[0088] The second particles may be melt-formable. When the second particles are melt-formable, the MFR (melt flow rate) of the second particles is preferably 0.1 to 100 g / 10 min, more preferably 1 to 80 g / 10 min.

[0089] From the viewpoint of heat resistance, it is preferable that the second particles cannot be melt-molded. The standard specific gravity of the second particles is preferably less than 2.30, more preferably less than 2.25. The standard specific gravity is preferably 2.10 or more, more preferably 2.11 or more. The second particles are obtained by dispersing a fluoropolymer in a particulate form. The second particles contain at least a fluoropolymer, and may or may not contain components other than the fluoropolymer. The content of the fluoropolymer relative to the entire second particles is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0090] The present aqueous dispersion can be easily obtained by the above-mentioned present production method. Therefore, the second particles contained in the present aqueous dispersion are preferably second particles obtained by the above-mentioned present production method, that is, particles containing the above-mentioned first fluorine-containing polymer and the above-mentioned second fluorine-containing polymer. In this case, the fluorine-containing polymer contained in the second particles contains two types of fluorine-containing polymers, the first fluorine-containing polymer and the second fluorine-containing polymer. Furthermore, the second particles may contain a copolymer of the first fluorine-containing polymer and the second fluorine-containing polymer. Note that the second particles are different from the above-mentioned first particles, and the present aqueous dispersion is different from the above-mentioned first aqueous dispersion.

[0091] The content of the second particles is preferably 1 to 50 mass %, more preferably 1 to 40 mass %, and even more preferably 1 to 30 mass %, relative to the total mass of the aqueous dispersion, from the viewpoint of dispersion stability of the second particles.

[0092] The volume average particle diameter of the second particles is 500 nm or less. From the viewpoint of dispersion stability of the second particles, it is preferably 400 nm or less, more preferably 300 nm or less, and even more preferably 275 nm or less. From the viewpoint of aggregation, the volume average particle diameter of the second particles is preferably 50 nm or more, more preferably 70 nm or more, and even more preferably 100 nm or more. The volume average particle diameter of the second particles is a particle diameter calculated by analyzing the autocorrelation function obtained by dynamic light scattering using the monodisperse cumulant method. When the present aqueous dispersion is obtained using the above-mentioned production method, second particles with a small volume average particle diameter are easily obtained. This is thought to be because, as described above, in this production method, it is assumed that the specific monomer polymerizes within the first particles during polymerization of the specific monomer, so polymerization proceeds stably even in the substantial absence of an emulsifier, and polymers are less likely to aggregate. It is preferable that the second particles are solid at 25°C.

[0093] <Aqueous medium> Specific examples of the aqueous medium contained in the present aqueous dispersion are the same as the specific examples of the aqueous medium used in producing the first fluoropolymer described above. The content of the aqueous medium is preferably 50 to 99 mass%, more preferably 60 to 99 mass%, and even more preferably 70 to 99 mass%, based on the total mass of the present aqueous dispersion, from the viewpoint of dispersion stability of the second particles.

[0094] <Others> The present aqueous dispersion preferably does not contain a fluorine-containing emulsifier, or contains a fluorine-containing emulsifier in an amount of 100 mass ppm or less relative to the total mass of the aqueous medium contained in the first aqueous dispersion. The content of the fluorine-containing emulsifier in the present aqueous dispersion is preferably 100 mass ppm or less, more preferably 10 mass ppm or less, still more preferably 5 mass ppm or less, particularly preferably less than 1 mass ppm, extremely preferably less than 250 mass ppb, and most preferably 0 mass ppm, relative to the total mass of the aqueous medium contained in the present aqueous dispersion. The content of the fluorine-containing emulsifier relative to the total mass of the aqueous medium can be determined by the method described in the Examples.

[0095] The present aqueous dispersion preferably contains substantially no emulsifier. "Substantially free of emulsifier" in the present aqueous dispersion means that the content of emulsifier is less than 1 ppm by mass, preferably 0.03 ppm by mass or less, more preferably 0.02 ppm by mass or less, and even more preferably 0 ppm by mass, relative to the total mass of the aqueous medium contained in the present aqueous dispersion. It is particularly preferred that the present aqueous dispersion contains substantially no emulsifiers other than fluorine-containing emulsifiers. "Substantially free of emulsifiers other than fluorine-containing emulsifiers" means that the content of emulsifiers other than fluorine-containing emulsifiers is less than 1 ppm by mass, preferably 0.75 ppm by mass or less, more preferably 0.03 ppm by mass or less, even more preferably 0.02 ppm by mass or less, and particularly preferably 0 ppm by mass. The content of emulsifier relative to the total mass of the aqueous medium and the content of emulsifiers other than fluorine-containing emulsifiers relative to the total mass of the aqueous medium can be measured by the method described in the Examples.

[0096] <Uses> As described above, the present aqueous dispersion does not require an emulsifier, and therefore can be easily converted into a dispersion in an organic solvent such as N-methylpyrrolidone, acetone, etc. by solvent substitution. For example, the present aqueous dispersion can be converted into a dispersion in an organic solvent by mixing the present aqueous dispersion with an organic solvent and dehydrating it by evaporation or using anhydrous sodium sulfate, etc.

[0097] The aqueous dispersion of the present invention stably disperses the fluoropolymer even without the addition of an emulsifier, and is therefore suitable for use in coating applications, binders, etc.

[0098] Furthermore, by aggregating the second particles from the aqueous dispersion, a powder of the second particles can be obtained. Furthermore, the powder of the second particles obtained by aggregating can be homogenized by melt kneading or the like to form a molding material in the form of pellets, granules, or the like, and the powder of the second particles obtained by aggregating can also be formed into a molded product by melt molding or the like.

[0099] Aggregation methods include, but are not limited to, freeze aggregation, acid aggregation, base aggregation, and aggregation using a coagulant. In the case of freeze aggregation, the aggregation temperature is preferably -20 to 0°C. The aggregation time is preferably 1 hour or more, more preferably 2 hours or more. In the case of acid aggregation, a method in which an acid-containing solution is added to the present aqueous dispersion is preferred. Examples of acids to be added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, and hydrofluoric acid, with hydrochloric acid being preferred. The acid concentration in the acid-containing solution is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. In the case of base aggregation, a method in which a base-containing solution is added to the present aqueous dispersion is preferred. Examples of bases to be added include sodium hydroxide, potassium hydroxide, and ammonium carbonate, with sodium hydroxide being preferred. The base concentration in the base-containing solution is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. For aggregation using a coagulant, known coagulants can be used. Known coagulants include aluminum salts, calcium salts, and magnesium salts. Specific examples include aluminum sulfate, a compound of the general formula M'Al(SO ４ ) ２ ・12H ２Examples of the coagulation method include alum represented by the formula: O (wherein M' is a monovalent cation other than lithium), calcium nitrate, and magnesium sulfate, of which alum is preferred, and potassium alum, in which M is potassium, is more preferred. As the coagulation method, base coagulation is preferred because coagulation proceeds particularly easily.

[0100] [Composition] The composition of the present disclosure (hereinafter also referred to as "the composition") is a composition containing a fluoropolymer containing compound (1) units. Furthermore, the content of compound (1) units in the composition is 0.05 to 5.0 mol % based on all units of the fluoropolymer contained in the composition, and the composition is solid at 25°C. The composition is preferably a composition obtained by the aggregation method using the aqueous dispersion of the present invention described above. The content of the fluoroemulsifier in the composition is preferably 100 ppm by mass or less, more preferably 10 ppm by mass or less, even more preferably 5 ppm by mass or less, particularly preferably less than 1 ppm by mass, extremely preferably less than 250 ppb by mass, more extremely preferably 25 ppb by mass or less, and most preferably 0 ppm by mass, based on the total mass of the fluoropolymer contained in the composition. The content of the fluoroemulsifier relative to the total mass of the fluoropolymer is determined by the method described in the Examples.

[0101] The present composition is preferably substantially free of emulsifiers. "Substantially free" means that the content of emulsifiers is less than 1 ppm by mass, more preferably 0.25 ppm by mass or less, more preferably 0.03 ppm by mass or less, more preferably 0.02 ppm by mass or less, and even more preferably 0 ppm by mass. The present composition is particularly preferably substantially free of emulsifiers other than fluorinated emulsifiers. "Substantially free" means that the content of emulsifiers other than fluorinated emulsifiers is less than 1 ppm by mass, based on the total mass of the fluorinated polymer contained in the present composition, preferably 0.75 ppm by mass or less, more preferably 0.25 ppm by mass or less, even more preferably 0.03 ppm by mass or less, particularly preferably 0.02 ppm by mass or less, and extremely preferably 0 ppm by mass. The content of the emulsifier relative to the total mass of the fluoropolymer and the content of the emulsifier other than the fluorinated emulsifier relative to the total mass of the fluoropolymer can be determined by the method described in Examples. Other preferred aspects of the composition of the present invention are the same as the preferred aspects of the second particles contained in the aqueous dispersion of the present invention described above, and therefore description thereof will be omitted.

[0102] The present invention will be described in detail below with reference to examples. Examples 1, 2 and 5 are working examples, and Examples 3 and 4 are comparative examples. However, the present invention is not limited to these examples.

[0103] [Measurement Methods] Various measurement methods are as follows.

[0104] <Glass transition temperature (Tg)> Tg was measured using a NEXTA DSC600 manufactured by Hitachi High-Technologies Corporation. Specifically, 5 mg of a sample for measurement was weighed into an aluminum sample pan, and the sample was heated to 100°C at a heating rate of 10°C / min under a nitrogen atmosphere. Thereafter, the sample was cooled to -60°C at a rate of 10°C / min. Once the predetermined temperature was reached, the temperature was again raised to 100°C at 10°C / min. Tg was estimated from the inflection point observed in this second heating operation.

[0105] <Melting Point> The first aqueous dispersion or the second aqueous dispersion of each example described below was freeze-aggregated and then filtered to obtain first particles or second particles. A 5 mg sample of the obtained first particles or second particles was weighed out and placed in an aluminum pan. Using a Hitachi DSC600, the sample was heated from 20°C to 360°C at a heating rate of 10°C / min in an air atmosphere, and a melting peak was confirmed in the temperature range of 150 to 330°C.

[0106] <MFR> Measurement was carried out in accordance with ASTM D3307 under conditions of a temperature of 372°C and a load of 49 N, and the MFR was calculated as the mass flowing out of an orifice having a diameter of 2 mm and a length of 8 mm in 10 minutes.

[0107] <Standard Specific Gravity> Measured in accordance with ASTM D4895-04. Specifically, 12.0 g of sample (modified PTFE powder) was weighed and compression molded in a cylindrical mold with an inner diameter of 28.6 mm to obtain a pellet sample. This was placed in an oven at 290°C and heated at a rate of 120°C / hour. After holding at 380°C for 30 minutes, the temperature was lowered at a rate of 60°C / hour and held at 294°C for 24 minutes. The sample was held in a desiccator at 23°C for 12 hours, and then the specific gravity of the sample relative to water at 23°C was measured, and this was taken as the standard specific gravity. The smaller the standard specific gravity value, the larger the molecular weight.

[0108] <Volume average particle diameter of particles in liquid> The dispersion to be measured was degassed for 5 minutes at room temperature (25°C), pressurized with nitrogen to 0.2 MPaG, and then purged to atmospheric pressure to obtain a sample for measurement. The particle diameter of the obtained sample was calculated by analyzing the autocorrelation function obtained by dynamic light scattering using a laser diffraction / scattering particle size distribution analyzer (Otsuka Electronics Co., Ltd., ELSZ) with an accumulation number set to 100, using the monodisperse cumulant method. This was taken as the volume average particle diameter of the particles in the dispersion.

[0109] <Proportion of each structural unit in the polymer> The proportion of each structural unit in the polymer is １９ It was determined by F-NMR analysis.

[0110] <Solid content concentration of second aqueous dispersion> 2.0 g of the second aqueous dispersion of each example described below was heated at 170°C for 20 minutes, and then the mass (g) of the residue was weighed and the solid content concentration was calculated using the following formula: Solid content concentration of second aqueous dispersion (mass%) = 100 × (mass of residue) / (mass of second aqueous dispersion (2.0 g))

[0111] <Method for measuring the content of emulsifier contained in aqueous dispersion> The first and second aqueous dispersions of each example described below were freeze-aggregated at -20°C. When thawed at room temperature (25°C), polymer precipitated, so this was filtered off and the aqueous phase was recovered. The amounts of fluorine-containing emulsifier and hydrocarbon-containing surfactant contained in the obtained aqueous phase were calculated by the following method. Specifically, five levels of methanol standard solutions of fluorine-containing emulsifier and hydrocarbon-containing surfactant with known concentrations of 1 to 180 ng / g were first prepared and measured by LC / MS / MS. The LC / MS / MS measurement conditions were the same as those in Table 1 below, and the MRM parameters used and the method for calculating the MRM parameters were also the same as those described in the "Method for measuring the content of emulsifier contained in a composition" below. Using a first-order approximation from the concentration of each sample and the integral value of the peak, a was calculated according to the following formula (A1): A = a × X (A1), where A: emulsifier peak area, X: emulsifier concentration (ng / g).

[0112] Next, the contents of the fluorine-containing emulsifier and hydrocarbon-containing surfactant contained in the aqueous medium were each calculated using the following formula (A2). In formula (A2), a means the a calculated by the above formula (A1). XCm = ACm / a (A2), where XCm is the content (ng / g) of the emulsifier in the aqueous phase and ACm is the peak area of ​​the emulsifier in the aqueous phase.

[0113] <Method for Measuring the Emulsifier Content in the Composition> (Preparation of Measurement Sample) The compositions obtained in each example described below were freeze-pulverized using a freeze-pulverizer Freezer Mill 6775 (manufactured by SPEX) under the following conditions. Before freeze-pulverization, 10% by mass of dibutylhydroxytoluene (BHT) based on the total mass of the composition was added to obtain a pulverized powder. The freeze-pulverization conditions were: composition: 3 g, BHT: 0.3 g, run time: 5 minutes, rate: 15 cps, cycle: 3. 5 mL of methanol was added to 0.25 g of the obtained pulverized powder, and the mixture was subjected to ultrasonic treatment at 50°C for 2 hours and centrifuged (5000 rpm, 5 minutes) to precipitate each fluoropolymer. The supernatant was used as an extract. The obtained extract was subjected to LC / MS / MS analysis. The fluorine-containing emulsifier and hydrocarbon-containing surfactant in the extract were measured using a liquid chromatograph mass spectrometer. The configuration of the measuring equipment and the LC-MS measurement conditions are shown in Table 1. Using aqueous solutions of fluorine-containing emulsifier and hydrocarbon-containing surfactant with known concentrations, methanol solutions with five or more levels of content were prepared, and LC / MS analysis of the methanol solutions with each content was performed. The relationship between the content and the area relative to the content was plotted to draw a calibration curve. Using the calibration curve, the area of ​​the LC / MS chromatogram of the fluorine-containing emulsifier and hydrocarbon-containing surfactant in the extract was converted into the content of the fluorine-containing emulsifier and hydrocarbon-containing surfactant.

[0114]

[0115] The MRM measurement parameters are appropriately selected depending on the structures of the fluorine-containing emulsifier and hydrocarbon-containing surfactant to be measured. Literature values ​​can be used for the MRM parameters, or they can be calculated using an LC-MS device. The specific procedure for determining the MRM parameters using an LC-MS device is as follows. Using an LC / MS device (Shimadzu Corporation, LCMS-8060NX), a search for product ions is selected, the molecular weights of the fluorine-containing emulsifier and hydrocarbon-containing surfactant to be measured are input, and precursor ions, precursor adjustment, voltage optimization, and product m / z optimization are performed. The calculated MRM measurement parameters are used. As an example, the MRM measurement parameters for compounds (S1) and (S2), which are fluorine-containing emulsifiers, are shown in Tables 2 and 3, respectively. In formulas (S1) and (S2), M Ｓ represents a hydrogen atom, a metal atom, or NR ４ (R may be the same or different and represents a hydrogen atom or an organic group having 1 to 10 carbon atoms), an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent. F-(CF ２ ) ｎ１ -COOM Ｓ (S1) F-(CF ２ ) ｎ２ -SO ３ M Ｓ (S2)

[0116]

[0117]

[0118] (Quantitative Determination of Fluorine-Containing Emulsifier and Hydrocarbon-Containing Surfactant Contained in Composition) Specifically, five levels of methanol standard solutions of the fluorine-containing emulsifier and hydrocarbon-containing surfactant, each with known concentrations of 1 to 180 ng / g, were first prepared, and a was calculated from the sample concentration and peak integral value of each sample using a first-order approximation according to formula (A1): A = a × X (A1), where A is the peak area of ​​each emulsifier, and X is the concentration (ng / g) of each emulsifier.

[0119] Next, the amount of emulsifier contained in the extract was calculated using formula (A2). Note that a in formula (A2) means a calculated using formula (A1) above. XCm = ACm / a (A2) XCm: content (ng / g) of emulsifier in each extract ACm: peak area of ​​emulsifier in each extract The quantitation limit in this measurement is 25 ng / g.

[0120] The content of the emulsifier in the composition relative to the total mass of the composition (ZCm) was calculated using the following formula (A3): ZCm = XCm × ρ1 × La / W1 (A3), where ZCm is the content of the emulsifier in the composition, ρ1 is the density of the extraction solvent (methanol), La is the volume of the extraction solvent (5 mL), and W1 is the mass of the sample used for extraction (2.5 g of composition).

[0121] <Concentration of sulfate ions and fluoride ions> The concentrations of sulfate ions and fluoride ions relative to the total mass of the aqueous medium in the aqueous dispersion were determined based on a calibration curve by freeze-flocculating the aqueous dispersion, filtering the resultant aqueous medium, and analyzing the resulting aqueous medium by ion chromatography. The ion chromatography analysis was performed using an ion chromatograph (Thermo Fisher Scientific, ICS-5000). AS-19 was used as the separation column, and an aqueous potassium hydroxide solution was used as the eluent.

[0122] (Creation of calibration curves for sulfate ions and fluoride ions) Four levels of aqueous solutions with known concentrations of 0.01 to 1 mass ppm were prepared for each of sulfate ions and fluoride ions, and measurements were performed using an ion chromatograph. Using a linear approximation from the concentration of each sample and the integral value of the peak, a was calculated using the following relational expression (1). The lower limit of quantitation was 0.01 mass ppm. Y1 = a × X1 (1) Y1: peak area of ​​each anion X1: concentration of each anion (mass ppm)

[0123] <Ammonium ion concentration> The concentration of ammonium ions relative to the total mass of the aqueous medium in the aqueous dispersion was determined by freeze-flocculating the aqueous dispersion, filtering the resulting aqueous medium, and analyzing the resulting aqueous medium by ion chromatography based on a calibration curve. The ion chromatography analysis was performed using an ion chromatograph (Shimadzu Corporation, HIC-SP). A Shim-pack IC-C4 was used as the separation column, and an aqueous solution of oxalic acid was used as the eluent.

[0124] (Calibration curve for ammonium ions) Four levels of aqueous solutions containing known concentrations of ammonium ions ranging from 0.1 to 10 ppm by mass were prepared and measured by ion chromatography. Using a linear approximation from the concentration of each sample and the integral value of the peak, c was calculated using the following relational expression (3). The lower limit of quantitation was 0.1 ppm by mass. Y3 = c × X3 (3) Y3: ammonium ion peak area X3: ammonium ion concentration (ppm by mass)

[0125] [Production of Raw Material Solution A] Ultrapure water (717 g) was charged into a 1.3 L stainless steel pressure reactor and heated to 90° C. while stirring at 500 rpm. ２ =CFCF ２ OCF ３ A mixed gas (18 / 82 molar ratio) of ammonium persulfate (PMAE) was injected up to 1.5 MPaG. Next, an aqueous ammonium persulfate solution (3.6 mass%, 5 mL) was added to initiate polymerization. As the polymerization started, the pressure inside the reactor decreased, so TFE was added to keep the pressure constant. When 2 g of TFE had been injected, the reactor was cooled to terminate the polymerization reaction. After recovering the gas remaining in the reactor, nitrogen was injected up to 0.2 MPaG and the temperature was raised to 90°C. After heating the reactor for 3 hours, it was cooled and the liquid was extracted. This liquid was used as raw material liquid A. Raw material liquid A was freeze-aggregated and then filtered to obtain fluoropolymer 1A, which was the first fluoropolymer contained in the first particles. １９ F-NMR analysis revealed that the molar ratio of TFE units to PMAE units was 55 / 45, the Tg was 0° C., and the polymer had no melting point.

[0126] [Production of Raw Material Solution B] Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 40 g) was added to the above raw material solution A (1000 g). 60 minutes after the start of stirring, the raw material solution and the ion exchange resin were separated by filtration. Diaion SA10AOH (manufactured by Mitsubishi Chemical Corporation, anion exchange resin, 40 g) was added to the filtered raw material solution. 60 minutes after the start of stirring, the raw material solution and the ion exchange resin were separated by filtration to obtain raw material solution B. Raw material solution B is a dispersion of first particles containing a first fluorine-containing polymer in an aqueous medium. The volume average particle diameter of the first particles in raw material solution B was 70 nm.

[0127] [Example 1] Ultrapure water (121 g), raw material liquid B (475 g), and wax (28 g) were charged into a 1.0 L stainless steel pressure reactor to obtain aqueous dispersion A, which is a first aqueous dispersion. The emulsifier content of aqueous dispersion A was less than 1 ppm by mass relative to the total mass of the aqueous medium, the fluorine-containing emulsifier content was less than 250 ppb by mass relative to the total mass of the aqueous medium, and the content of emulsifiers other than the fluorine-containing emulsifier was 0.75 ppm by mass or less relative to the total mass of the aqueous medium. The first polymer content in aqueous dispersion A, i.e., the content of the first fluorine-containing polymer relative to the total mass of aqueous dispersion A before the start of polymerization of the specific monomer, is shown in Table 4. The amount of wax added per 100 parts by mass of the aqueous medium contained in aqueous dispersion A was 4.7 parts by mass. In addition, the aqueous dispersion A had a fluoride ion concentration of less than 0.1 ppm by mass, a sulfate ion concentration of less than 0.1 ppm by mass, and an ammonium ion concentration of less than 0.1 ppm by mass.

[0128] The aqueous dispersion A was heated to 70°C while stirring at 260 rpm. TFE was injected into the reactor until the pressure reached 1.4 MPaG, and an aqueous disuccinic acid peroxide (DSAP) solution (0.45% by mass, 3 ml) was added to initiate polymerization. As the polymerization began, the pressure in the reactor decreased, so TFE was added to maintain the pressure constant. When 170 g of TFE had been injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 450 minutes. The amount of TFE used per 100 parts by mass of the aqueous medium contained in the aqueous dispersion A was 20 parts by mass, and the amount of DSAP used per 100 parts by mass of TFE was 0.004 parts by mass.

[0129] After recovering the gas remaining in the reactor, the liquid was extracted. This liquid was designated as aqueous dispersion 1. Aqueous dispersion 1 was a second aqueous dispersion in which second particles (volume average particle diameter 270 nm, solid at 25 ° C) containing a fluorine-containing polymer were dispersed in an aqueous medium, and the solid content was 20.0 mass%, the content of the emulsifier was less than 1 mass ppm relative to the total mass of the aqueous medium, the content of the fluorine-containing emulsifier was less than 250 mass ppb relative to the total mass of the aqueous medium, and the content of emulsifiers other than the fluorine-containing emulsifier was 0.75 mass ppm or less relative to the total mass of the aqueous medium. The second particles in the obtained aqueous dispersion 1 were agglomerated and filtered to obtain a composition containing PTFE. The composition dried at 150 ° C had a melting point of 345 ° C, a crystallization energy of 16.5 J / g, and a standard specific gravity of 2.17. Regarding the composition after drying, １９ The composition was calculated using F-NMR, and as a result, the molar ratio of TFE units to PMAE units was 99.6 / 0.4. In the dried composition, the emulsifier content was 250 ppb by mass or less relative to the total mass of the fluoropolymer, the fluorinated emulsifier content was 25 ppb by mass or less relative to the total mass of the fluoropolymer, and the emulsifier content other than the fluorinated emulsifier was 225 ppb by mass or less relative to the total mass of the fluoropolymer.

[0130] [Example 2] Ultrapure water (343 g) and raw material liquid B (370 mL) were charged into a 1.2 L stainless steel pressure reactor to obtain aqueous dispersion B, which was a first aqueous dispersion. The emulsifier content of aqueous dispersion B was less than 1 ppm by mass relative to the total mass of the aqueous medium, the fluorinated emulsifier content was less than 250 ppb by mass relative to the total mass of the aqueous medium, and the content of emulsifiers other than the fluorinated emulsifier was 0.75 ppm by mass or less relative to the total mass of the aqueous medium. The first polymer content in aqueous dispersion B, i.e., the content of the first fluorinated polymer relative to the total mass of aqueous dispersion B before the start of polymerization of the specific monomer, is shown in Table 4. The fluoride ion concentration in aqueous dispersion B was less than 0.1 ppm by mass, the sulfate ion concentration was less than 0.1 ppm by mass, and the ammonium ion concentration was less than 0.1 ppm by mass.

[0131] C4OLF (0.3 g) and tert-butyl methyl ether (1.0 g) were added to aqueous dispersion B, and the temperature was raised to 60 ° C. while stirring at 260 rpm. A mixed gas (TFE / ethylene = 86 / 14 (molar ratio)) was injected until the pressure in the reactor reached 2.6 MPaG, and an isododecane solution of perbutyl PV (PBPV) (40 mass%, 4 cc) was added to initiate polymerization. As the pressure in the reactor decreased with the start of polymerization, a mixed CG gas (TFE / ethylene = 54 / 46 (mol%)) was added to maintain the pressure constant. C4OLF was continuously added so that the amount was 1 mol % relative to the amount of mixed CG gas being added. When 160 g of mixed CG gas had been injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 370 minutes. The total amount of the specific monomers (i.e., TFE, ethylene, and C4OLF) used per 100 parts by mass of the aqueous medium contained in aqueous dispersion B was 20 parts by mass, and the amount of PBPV used per 100 parts by mass of the total of the specific monomers (i.e., TFE, ethylene, and C4OLF) was 0.97 parts by mass.

[0132] After recovering the gas remaining in the reactor, the liquid was extracted. This liquid was designated as aqueous dispersion 2. Aqueous dispersion 2 was a second aqueous dispersion in which second particles (volume average particle diameter 256 nm, solid at 25°C) containing a fluorinated polymer were dispersed in an aqueous medium, and the solid concentration was 20.0 mass%, the emulsifier content was less than 1 mass ppm relative to the total mass of the aqueous medium, the fluorinated emulsifier content was less than 250 mass ppb relative to the total mass of the aqueous medium, and the content of emulsifiers other than the fluorinated emulsifier was 0.75 mass ppm or less relative to the total mass of the aqueous medium. The second particles in the obtained aqueous dispersion 2 were aggregated and dried, and then １９ The composition was calculated using F-NMR, and the molar ratio was TFE unit / E unit / COLF unit / PMAE unit=53.4 / 45 / 1 / 0.6. The melting point of the dried composition was 267°C, the MFR was 2.5 g / 10 min, the content of emulsifier in the composition was 250 ppb by mass or less relative to the total mass of the fluoropolymer, the content of fluorinated emulsifier was 25 ppb by mass or less relative to the total mass of the fluoropolymer, and the content of emulsifiers other than the fluorinated emulsifier was 225 ppb by mass or less relative to the total mass of the fluoropolymer.

[0133] [Production of Raw Material Solution C] Ultrapure water (740 g), sodium sulfite (88 mg), methyl methacrylate (MMA, 330 mg), iron(II) sulfate heptahydrate (11 mg), and Chelate HC (17 mg) were charged into a 1.2 L stainless steel pressure reactor, and the temperature was raised to 60°C while stirring at 500 rpm. Next, an aqueous potassium persulfate solution (5.0 mass%, 3.8 mL) was added, and polymerization was carried out for 60 minutes. After completion of the polymerization reaction, the liquid was extracted. This liquid was used as Raw Material Solution C. Raw Material Solution C was heated to remove water, and the residue was then dried by heating to obtain Methacrylate Polymer 1C (PMMA). The Tg of Methacrylate Polymer 1C was 105°C.

[0134] [Production of Raw Material Solution D] Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 20 g) was added to the raw material solution C (490 g). 60 minutes after the start of stirring, the raw material solution and the ion exchange resin were separated by filtration. Purolite A300 (manufactured by Purolite, anion exchange resin, 20 g) was added to the filtered raw material solution. 60 minutes after the start of stirring, the raw material solution and the ion exchange resin were separated by filtration to obtain raw material solution D. Raw material solution D contained particles of methacrylate polymer 1C (volume average particle diameter 89 nm) dispersed in an aqueous medium, and the content of methacrylate polymer 1C calculated from the amount of MMA charged was 0.044 mass% relative to the total mass of raw material solution D.

[0135] [Example 3] Ultrapure water (428 g) and raw material solution D (185 mL) were charged into a 1.2 L stainless steel pressure reactor to obtain aqueous dispersion C. C4OLF (0.3 g) and tert-butyl methyl ether (0.2 g) were added to aqueous dispersion C, and the temperature was raised to 60 ° C while stirring at 320 rpm. A mixed gas (TFE / ethylene = 86 / 14 (molar ratio)) was injected until the pressure in the reactor reached 2.6 MPaG, and an aqueous potassium persulfate (KPS) solution (5 mass%, 10 cc) was added to initiate polymerization. As the pressure in the reactor decreased with the start of polymerization, a mixed CG gas (TFE / ethylene = 54 / 46 (mol%)) was added to maintain the pressure constant. C4OLF was continuously added so that the amount was 1 mol % relative to the amount of mixed CG gas being added. When 80 g of mixed CG gas had been injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 190 minutes. The total amount of the specific monomers (i.e., TFE, ethylene, and C4OLF) used per 100 parts by mass of the aqueous medium contained in aqueous dispersion C was 10 parts by mass, and the amount of KPS used per 100 parts by mass of the total of the specific monomers (i.e., TFE, ethylene, and C4OLF) was 0.6 parts by mass.

[0136] After recovering the gas remaining in the reactor, the liquid was extracted. This liquid was designated as aqueous dispersion 3. Aqueous dispersion 3 was a dispersion in which particles containing a fluorinated polymer (volume average particle diameter 240 nm, solid at 25°C) were dispersed in an aqueous medium, and the solid content concentration was 10 mass%. The particles in the obtained aqueous dispersion 3 were aggregated and dried, and then １９ The composition was calculated using F-NMR to find that the molar ratio of TFE units / E units / C4OLF units was 54.1 / 45 / 0.9. The melting point of the dried composition was 267°C, and the MFR was 7.5 g / 10 min.

[0137] [Production of Raw Material Solution E] Ultrapure water (740 g), sodium sulfite (88 mg), methyl acrylate (MA, 330 mg), iron(II) sulfate heptahydrate (11 mg), and Chelate HC (17 mg) were charged into a 1.2 L stainless steel pressure reactor, and the temperature was raised to 60°C while stirring at 500 rpm. Next, an aqueous potassium persulfate solution (5.0 mass%, 3.8 mL) was added, and polymerization was carried out for 60 minutes. After completion of the polymerization reaction, the liquid was extracted. This liquid was used as Raw Material Solution E. Raw Material Solution E was heated to remove water, and the residue was then dried by heating to obtain Acrylate Polymer 1D (PMA). The Tg of Acrylate Polymer 1D was 8°C.

[0138] [Production of Raw Material Solution F] Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 20 g) was added to the raw material solution E (490 g). 60 minutes after the start of stirring, the raw material solution and the ion exchange resin were separated by filtration. Purolite A300 (manufactured by Purolite, anion exchange resin, 20 g) was added to the filtered raw material solution. 60 minutes after the start of stirring, the raw material solution and the ion exchange resin were separated by filtration to obtain raw material solution F. Raw material solution F contained particles of acrylate polymer 1D (volume average particle diameter 107 nm) dispersed in an aqueous medium, and the content of acrylate polymer 1D calculated from the amount of MA charged was 0.044 mass% relative to the total mass of raw material solution F.

[0139] [Example 4] Ultrapure water (428 g) and raw material solution F (185 mL) were charged into a 1.2 L stainless steel pressure reactor to obtain aqueous dispersion D. C4OLF (0.3 g) and tert-butyl methyl ether (0.1 g) were added to aqueous dispersion D, and the temperature was raised to 60 ° C while stirring at 320 rpm. A mixed gas (TFE / ethylene = 86 / 14 (molar ratio)) was injected until the pressure in the reactor reached 2.6 MPaG, and an aqueous potassium persulfate (KPS) solution (5 mass%, 10 cc) was added to initiate polymerization. As the pressure in the reactor decreased with the start of polymerization, a mixed CG gas (TFE / ethylene = 54 / 46 (mol%)) was added to maintain the pressure constant. C4OLF was continuously added so that the amount was 1 mol % relative to the amount of mixed CG gas being added. When 80 g of mixed CG gas had been injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 230 minutes. The total amount of the specific monomers (i.e., TFE, ethylene, and C4OLF) used per 100 parts by mass of the aqueous medium contained in aqueous dispersion D was 10 parts by mass, and the amount of KPS used per 100 parts by mass of the total of the specific monomers (i.e., TFE, ethylene, and C4OLF) was 0.6 parts by mass.

[0140] After recovering the gas remaining in the reactor, the liquid was extracted. This liquid was designated as aqueous dispersion 4. Aqueous dispersion 4 was a dispersion in which particles containing a fluorinated polymer (volume average particle diameter 310 nm, solid at 25°C) were dispersed in an aqueous medium, and had a solid content concentration of 10 mass%. The particles in the obtained aqueous dispersion 4 were aggregated and dried, and then １９ The composition was calculated using F-NMR to find that the molar ratio of TFE units / E units / COLF units was 54.2 / 44.9 / 0.9. The melting point of the dried composition was 267° C., and the MFR was 10.4 g / 10 min.

[0141] [Production of Raw Material Solution G] Ultrapure water (702 g), CF ２ =CFCF ２ OCF ２ CF ２ CF ３(PPAE, 20 g), TFE (3 g), and perfluoro(methyl vinyl ether) (PMVE, 9 g) were charged, and the temperature was raised to 90°C while stirring at 500 rpm. Next, an aqueous ammonium persulfate solution (1.8 mass%, 20 mL) was added to initiate polymerization. As the polymerization started, the pressure in the reactor decreased, so TFE was added to keep the pressure constant. When 3 g of TFE had been injected, the reactor was cooled to terminate the polymerization reaction. After recovering the gas remaining in the reactor, it was cooled and the liquid was extracted. This liquid was used as raw material liquid G. Raw material liquid G was freeze-aggregated and then filtered, and fluoropolymer 1E, the first fluoropolymer contained in the resulting first particles, was obtained. １９ F-NMR analysis revealed that the molar ratio of TFE units / PPAE units / PMVE units was 72.5 / 9.2 / 18.3, the Tg was −5° C., and the polymer had no melting point.

[0142] [Production of Raw Material Solution H] Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 27 g) was added to the above raw material solution G (330 g). 60 minutes after the start of stirring, the raw material solution and the ion exchange resin were separated by filtration. Diaion SA10AOH (manufactured by Mitsubishi Chemical Corporation, anion exchange resin, 27 g) was added to the filtered raw material solution. 60 minutes after the start of stirring, the raw material solution and the ion exchange resin were separated by filtration to obtain raw material solution H. Note that raw material solution H is a dispersion of first particles containing a first fluorine-containing polymer in an aqueous medium. The volume average particle diameter of the first particles in raw material solution H was 73 nm.

[0143] [Example 5] Ultrapure water (121 g), raw material liquid H (475 g), and wax (28 g) were charged into a 1.0 L stainless steel pressure reactor to obtain aqueous dispersion E, which was a first aqueous dispersion. The emulsifier content of aqueous dispersion E was less than 1 ppm by mass relative to the total mass of the aqueous medium, the fluorine-containing emulsifier content was less than 250 ppb by mass relative to the total mass of the aqueous medium, and the content of emulsifiers other than the fluorine-containing emulsifier was 0.75 ppm by mass or less relative to the total mass of the aqueous medium. The first polymer content in aqueous dispersion E, i.e., the content of the first fluorine-containing polymer relative to the total mass of aqueous dispersion E before the start of polymerization of the specific monomer, is shown in Table 4. The amount of wax added per 100 parts by mass of the aqueous medium contained in aqueous dispersion E was 4.7 parts by mass. In addition, the concentration of fluoride ions in aqueous dispersion E was less than 0.1 ppm by mass, the concentration of sulfate ions was less than 0.1 ppm by mass, and the concentration of ammonium ions was less than 0.1 ppm by mass.

[0144] Aqueous Dispersion E was heated to 70°C while stirring at 260 rpm. TFE was injected into the reactor until the pressure reached 1.4 MPaG, and an aqueous disuccinic acid peroxide (DSAP) solution (0.45% by mass, 3 ml) was added to initiate polymerization. As the polymerization began, the pressure in the reactor decreased, so TFE was added to maintain the pressure constant. When 170 g of TFE had been injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 476 minutes. The amount of TFE used per 100 parts by mass of the aqueous medium contained in Aqueous Dispersion E was 20 parts by mass, and the amount of DSAP used per 100 parts by mass of TFE was 0.004 parts by mass.

[0145] After recovering the gas remaining in the reactor, the liquid was extracted. This liquid was designated as aqueous dispersion 5. Aqueous dispersion 5 was a second aqueous dispersion in which second particles (volume average particle diameter 280 nm, solid at 25 ° C) containing a fluorine-containing polymer were dispersed in an aqueous medium, the solid content was 20.0 mass%, the content of the emulsifier was less than 1 mass ppm relative to the total mass of the aqueous medium, the content of the fluorine-containing emulsifier was less than 250 mass ppm relative to the total mass of the aqueous medium, and the content of emulsifiers other than the fluorine-containing emulsifier was 0.75 mass ppm or less relative to the total mass of the aqueous medium. The second particles in the obtained aqueous dispersion 5 were agglomerated and filtered to obtain a composition containing PTFE. The melting point of the composition dried at 150 ° C was 345 ° C, the crystallization energy was 16.1 J / g, and the standard specific gravity was 2.17. Regarding the composition after drying, １９ The composition was calculated using F-NMR, and the molar ratio was TFE unit / PPAE unit / PMVE unit=99.8 / 0.07 / 0.13. After drying, the emulsifier content in the composition was 250 ppb by mass or less relative to the total mass of the fluoropolymer, the fluorinated emulsifier content was 25 ppb by mass or less relative to the total mass of the fluoropolymer, and the emulsifier content other than the fluorinated emulsifier was 225 ppb by mass or less relative to the total mass of the fluoropolymer.

[0146] [Evaluation] <Productivity evaluation> The productivity of the second fluorine-containing polymer was evaluated based on the solids concentration of the second aqueous dispersion after the polymerization reaction was completed. The higher the solids concentration of the second aqueous dispersion, the more the second fluorine-containing polymer was produced, which means higher productivity. The solids concentration in each example is shown in Table 4.

[0147] <Evaluation of Heat Resistance> The particles contained in each of the aqueous dispersions 1 to 5 of each example were aggregated and dried to obtain an aggregate corresponding to each example. A 200 μm-thick sheet was prepared from the obtained aggregate by the following method, and the Y.I. was measured by transmittance using a color meter (SM Color Meter, manufactured by Suga Test Instruments Co., Ltd.). The Y.I. values ​​are shown in Table 1. "Y.I." is an index representing yellowness, and the higher this value, the more yellowish the sample. In other words, a smaller Y.I. value is preferable. Furthermore, the 200 μm-thick sheet was obtained by heating 0.5 g of the aggregate at each temperature (300°C for Examples 2 to 4, 340°C for Examples 1 and 5) for 10 minutes, press-molding at each temperature (300°C for Examples 2 to 4, 340°C for Examples 1 and 5) for 5 minutes under conditions of 10 MPa, and then cooling.

[0148]

[0149] As shown in Table 1, in Examples 1 to 2 and 5, the solids concentration was higher and the Y.I. value was lower than in Examples 3 to 4, and it is therefore clear that a second fluorine-containing polymer excellent in heat resistance was obtained and the productivity of the second fluorine-containing polymer was high.

[0150] The disclosure of Japanese Patent Application No. 2024-099118, filed on June 19, 2024, is incorporated herein by reference in its entirety. In addition, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A method for producing a fluoropolymer, comprising polymerizing a monomer containing a fluorine-containing monomer in a first aqueous dispersion comprising first particles containing a first fluoropolymer which contains units based on a compound represented by the following formula (1) and has a glass transition temperature of 10°C or lower, and producing a second fluoropolymer different from the first fluoropolymer, wherein the content of the first fluoropolymer is 0.01 to 4.0% by mass relative to the total mass of the first aqueous dispersion before the start of polymerization of the monomer: CX １ X ２ =CX ３ -CF ２ -O-Rf...(1) In formula (1), X １ , X ２ , and X ３ are each independently a hydrogen atom or a fluorine atom, and Rf is a perfluoroalkyl group having 1 to 10 carbon atoms, which may have an etheric oxygen atom between carbon atoms.

2. The method for producing a fluorine-containing polymer according to claim 1, wherein the fluorine-containing monomer comprises at least one member selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, and vinylidene fluoride.

3. The method for producing a fluorinated polymer according to claim 1 or 2, wherein the content of units based on the compound represented by formula (1) is 5 to 70 mol % based on all units contained in said first fluorinated polymer.

4. The method for producing a fluorine-containing polymer according to claim 1 or 2, wherein the first fluorine-containing polymer further contains units based on tetrafluoroethylene.

5. The method for producing a fluorine-containing polymer according to claim 1 or 2, wherein the first fluorine-containing polymer has no melting point.

6. A method for producing a fluoropolymer according to claim 1 or 2, wherein the volume average particle diameter of the first particles is 200 nm or less.

7. A method for producing a fluorine-containing polymer according to claim 1 or 2, wherein the content of the fluorine-containing emulsifier in the first aqueous dispersion is 100 ppm by mass or less relative to the total mass of the aqueous medium contained in the first aqueous dispersion.

8. An aqueous dispersion comprising second particles containing a fluoropolymer containing units based on a compound represented by the following formula (1) and an aqueous medium, wherein the volume average particle diameter of the second particles is 500 nm or less, and the content of the units based on the compound represented by formula (1) is 0.05 to 5.0 mol % based on all units contained in the fluoropolymer contained in the second particles: CX １ X ２ =CX ３ -CF ２ -O-Rf...(1) In formula (1), X １ , X ２ , and X ３ are each independently a hydrogen atom or a fluorine atom, and Rf is a perfluoroalkyl group having 1 to 10 carbon atoms, which may have an etheric oxygen atom between carbon atoms.

9. The aqueous dispersion according to claim 8, wherein the second particles contain a fluorine-containing polymer containing units based on at least one selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, and vinylidene fluoride.

10. The aqueous dispersion according to claim 8 or 9, wherein the second particles contain a fluorine-containing polymer containing units based on tetrafluoroethylene.

11. The aqueous dispersion according to claim 8 or 9, wherein the content of the fluorine-containing emulsifier in the aqueous dispersion is 100 ppm by mass or less based on the total mass of the aqueous medium contained in the aqueous dispersion.

12. A composition containing a fluoropolymer containing units based on a compound represented by the following formula (1), wherein the content of units based on the compound represented by formula (1) is 0.05 to 5.0 mol % based on all units contained in the fluoropolymer contained in the composition, and the composition is solid at 25°C. CX １ X ２ =CX ３ -CF ２ -O-Rf...(1) In formula (1), X １ , X ２ , and X ３ are each independently a hydrogen atom or a fluorine atom, and Rf is a perfluoroalkyl group having 1 to 10 carbon atoms, which may have an etheric oxygen atom between carbon atoms.

13. The composition according to claim 12, wherein the composition contains a fluorine-containing polymer containing units based on at least one selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, and vinylidene fluoride.

14. The composition according to claim 12 or 13, wherein the composition contains a fluorine-containing polymer containing units based on tetrafluoroethylene.

15. The composition according to claim 12 or 13, wherein the content of the fluorine-containing emulsifier in the composition is 100 ppm by mass or less based on the total mass of the fluorine-containing polymer.

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