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

Abstract

A composition comprising a first perfluoro polymer having a glass transition temperature of 10°C or less, and a second fluoro polymer different from the first perfluoro polymer and containing a structural unit based on tetrafluoroethylene and a structural unit based on perfluoro (alkyl vinyl ether). The content of the structural unit based on perfluoro (alkyl vinyl ether) with respect to the total content of all structural units of the first perfluoro polymer and the second fluoro polymer is 0.1-10.0 mol %.

Description

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

[0001] The present invention relates to a method for producing a fluorine-containing polymer, an aqueous dispersion, particles 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. Examples of methods for producing fluorine-containing polymers include a method of emulsion polymerization of fluorine-containing monomers in an aqueous medium using a fluorine-containing emulsifier (see Patent Document 1).

[0003] International Publication No. 2007 / 046377

[0004] The method for producing a fluorinated polymer disclosed in Patent Document 1 uses an aqueous medium and therefore has a small environmental impact, but when a large amount of a fluorinated emulsifier, which is an essential component, remains in the aqueous dispersion obtained by polymerization, it becomes necessary to remove the fluorinated emulsifier depending on the application. Moreover, in recent years, there has been a trend toward restricting the use of fluorinated emulsifiers.

[0005] The present disclosure has been made in view of these circumstances, and a problem to be solved by one embodiment of the present invention is to provide a composition containing a fluorinated polymer having excellent heat resistance without requiring a fluorinated emulsifier. Another problem to be solved by one embodiment of the present invention is to provide a method for producing a fluorinated polymer that can produce a fluorinated polymer having excellent heat resistance without requiring a fluorinated emulsifier. A further problem to be solved by one embodiment of the present invention is to provide an aqueous dispersion containing a fluorinated polymer having excellent heat resistance. A further problem to be solved by one embodiment of the present invention is to provide particles containing a fluorinated polymer having excellent heat resistance.

[0006] The present disclosure includes the following aspects: [1] A composition comprising a first perfluoropolymer having a glass transition temperature of 10°C or less, and a second fluoropolymer which contains structural units based on tetrafluoroethylene and structural units based on perfluoro(alkyl vinyl ether) and is different from the first perfluoropolymer, wherein the content of structural units based on perfluoro(alkyl vinyl ether) is 0.1 to 10.0 mol% relative to the total content of all structural units of the first perfluoropolymer and the second fluoropolymer. [2] A composition wherein neither the first perfluoropolymer nor the second fluoropolymer contains a functional group, or the first perfluoropolymer and the second fluoropolymer each contain a main chain having 10 carbon atoms. ６The composition according to [1], wherein the total number of functional groups per unit is less than 100. [3] The composition according to [1] or [2], wherein the first perfluoropolymer contains structural units based on tetrafluoroethylene and structural units based on perfluoro(alkyl vinyl ether). [4] The composition according to [3], wherein the structural units based on perfluoro(alkyl vinyl ether) account for 20 to 70 mol % of the total of the structural units based on tetrafluoroethylene and the structural units based on perfluoro(alkyl vinyl ether) in the first perfluoropolymer. [5] A method for producing a fluoropolymer, comprising the steps of preparing an aqueous dispersion A containing a first perfluoropolymer having a glass transition temperature of 10°C or lower and an aqueous medium, and polymerizing a monomer containing tetrafluoroethylene and perfluoro(alkyl vinyl ether) in the aqueous dispersion A to produce a second fluoropolymer different from the first perfluoropolymer, wherein, before the start of monomer polymerization, the content of the first perfluoropolymer is 0.01 to 4.0% by mass relative to the total mass of aqueous dispersion A, and before the start of monomer polymerization, aqueous dispersion A does not contain a fluorinated emulsifier or the content of the fluorinated emulsifier is 100 ppm by mass or less relative to the total mass of aqueous dispersion A. [6] A method for producing a fluoropolymer according to [5], wherein the amount of monomer used is 1 to 50 parts by mass relative to 100 parts by mass of the aqueous medium used. [7] The method for producing a fluoropolymer according to [5] or [6], wherein the step of preparing aqueous dispersion A is a step of preparing aqueous dispersion A containing particles of a first perfluoropolymer and an aqueous medium, and the step of producing a second fluoropolymer is a step of polymerizing a monomer to produce a second fluoropolymer different from the first perfluoropolymer, thereby producing particles containing the first perfluoropolymer and the second fluoropolymer, and the ratio of the average particle size of the particles containing the first perfluoropolymer and the second fluoropolymer to the average particle size of the particles of the first perfluoropolymer is at least 2. [8] The method for producing a fluoropolymer according to any one of [5] to [7], wherein the viscosity of aqueous dispersion A is 2.0 mPa s or less.[9] The method for producing a fluoropolymer according to any one of [5] to [8], wherein the thixotropy ratio of the aqueous dispersion A is 0.9 to 1.2.

[10] The method for producing a fluoropolymer according to any one of [5] to [9], wherein the monomers are polymerized in the presence of a polymerization initiator.

[11] The method for producing a fluoropolymer according to any one of [5] to

[10] , further comprising a step of subjecting the first perfluoropolymer and the second fluoropolymer to a fluorination treatment.

[12] An aqueous dispersion comprising an aqueous medium and melt-moldable particles, wherein the particles have an average particle size of 1 μm or less, the particles comprise one or more fluorine-containing polymers, the fluorine-containing polymers comprise units based on tetrafluoroethylene and structural units based on perfluoro(alkyl vinyl ether), the content of the structural units based on perfluoro(alkyl vinyl ether) being 0.1 to 10.0 mol % relative to all structural units of the fluorine-containing polymer, the particle content being 1 to 50 mass % relative to the total mass of the aqueous dispersion, and the aqueous dispersion does not contain a fluorine-containing emulsifier, or the content of the fluorine-containing emulsifier is 100 ppm by mass or less relative to the content of the fluorine-containing polymer.

[13] The aqueous dispersion according to

[12] , which has a viscosity of 0.8 to 2.0 mPa s.

[14] Melt-moldable particles, the particles having an average particle size of 1 μm or less, the particles comprising one or more types of fluorine-containing polymer, the fluorine-containing polymer comprising structural units based on tetrafluoroethylene and structural units based on perfluoro(alkyl vinyl ether), the content of structural units based on perfluoro(alkyl vinyl ether) being 0.1 to 10.0 mol% based on all structural units of the fluorine-containing polymer, the particles containing no fluorine-containing emulsifier or the content of the fluorine-containing emulsifier being 100 ppm by mass or less based on the content of the fluorine-containing polymer, the content of the compound represented by formula (S1) being 1 to 10,000 ppb by mass and the content of the compound represented by formula (S2) being 100 ppb by mass or less based on the fluorine-containing polymer. Formula (S1): H-(CF). ２ ) ｎ -COOM Formula (S2): H-(CF ２ ) ｍ -SO ３M In formula (S1) and formula (S2), M each independently represents a hydrogen atom, Na, K, or NH ４ wherein n is 7 to 11, and m is 8 to 12.

[0007] According to one embodiment of the present invention, there is provided a composition comprising a fluoropolymer having excellent heat resistance, without requiring a fluorinated emulsifier. Also, according to one embodiment of the present invention, there is provided a method for producing a fluoropolymer, which can produce a fluoropolymer having excellent heat resistance, without requiring a fluorinated emulsifier. Furthermore, according to one embodiment of the present invention, there is provided an aqueous dispersion comprising a fluoropolymer having excellent heat resistance. Furthermore, according to one embodiment of the present invention, there is provided particles comprising a fluoropolymer having excellent heat resistance.

[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] [Composition] The composition of the present disclosure contains a first perfluoropolymer having a glass transition temperature of 10°C or lower, and a second fluoropolymer that contains structural units based on tetrafluoroethylene (hereinafter also referred to as "TFE") (hereinafter also referred to as "TFE units") and structural units based on perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE") (hereinafter also referred to as "PAVE units") and is different from the first perfluoropolymer, and the content of PAVE units is 0.1 to 10.0 mol% relative to the total content of all structural units of the first perfluoropolymer and the second fluoropolymer.

[0010] The composition of the present disclosure contains a first perfluoropolymer and a second fluoropolymer, and has excellent heat resistance because the content of PAVE units is 0.1 to 10.0 mol% relative to the total content of all structural units of the first perfluoropolymer and the second fluoropolymer.

[0011] In contrast, Patent Document 1 does not mention a composition containing two or more types of fluorine-containing copolymers.

[0012] (First Perfluoropolymer) The first perfluoropolymer is a perfluoropolymer having a glass transition temperature of 10° C. or lower. In the present disclosure, "perfluoropolymer" means a polymer in which all hydrogen atoms bonded to carbon atoms in the structural units of the polymer have been substituted with fluorine atoms. "Fluoropolymer" means a polymer in which some or all of the hydrogen atoms bonded to carbon atoms in the structural units of the polymer have been substituted with fluorine atoms.

[0013] The glass transition temperature (hereinafter also referred to as "Tg") of the first perfluoropolymer is 10°C or lower. From the viewpoint of efficient adsorption of a specific monomer described below, the Tg of the first perfluoropolymer 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 perfluoropolymer is preferably -50°C or higher, more preferably -45°C or higher, and even more preferably -40°C or higher.

[0014] The Tg of the first perfluoropolymer 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.

[0015] As a method for adjusting the Tg of the first perfluoropolymer within the above range, for example, a method of adjusting the type and amount of the monomer used in producing the first perfluoropolymer can be mentioned.

[0016] The first perfluoropolymer preferably contains TFE units and PAVE units, since this makes it easier to adjust the Tg to the above range and provides better heat resistance.

[0017] The PAVE is preferably a monomer represented by formula (1) because it has excellent polymerization reactivity when producing the first perfluoropolymer. ２ =CF-O-R ｆ１ ...(1) In formula (1), R ｆ１ represents a perfluoroalkyl group having 1 to 10 carbon atoms. ｆ１ From the viewpoint of better polymerization reactivity, the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 8, more preferably 1 to 6, still more preferably 1 to 5, and particularly preferably 1 to 3. The perfluoroalkyl group may be linear or branched.

[0018] Specific 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").

[0019] Among them, the PAVE is preferably PMVE or PPVE, more preferably PMVE, from the viewpoint of more efficient production of the second fluoropolymer.

[0020] When the first perfluoropolymer contains TFE units and PAVE units, the content of PAVE units relative to the total content of TFE units and PAVE units in the first perfluoropolymer is preferably 20.0 to 70.0 mol%, more preferably 25.0 to 65.0 mol%, and even more preferably 30.0 to 60.0 mol%, from the viewpoint of ease of adjusting Tg within the above range.

[0021] The first perfluoropolymer may contain structural units based on other monomers other than TFE and PAVE. From the viewpoint of more efficient production of the second fluoropolymer, the structural units based on other monomers are preferably 20.0 mol% or less, more preferably 15.0 mol% or less, based on the total structural units of the first perfluoropolymer. It is more preferable that the first perfluoropolymer 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%, based on the total structural units of the first perfluoropolymer. When structural units based on other monomers are contained, hexafluoropropylene is preferred as the other monomer.

[0022] (Second Fluoropolymer) The second fluoropolymer is a fluoropolymer different from the first perfluoropolymer. The second fluoropolymer contains TFE units and PAVE units.

[0023] When the first perfluoropolymer comprises TFE unit and PAVE unit, the type of PAVE unit that the second fluoropolymer contains can be the same as the type of PAVE unit that the first perfluoropolymer contains, or can be different.When the type of PAVE unit is the same, for example, the molar ratio of the TFE unit and PAVE unit that the second fluoropolymer contains is different from the molar ratio of the TFE unit and PAVE unit that the first perfluoropolymer contains.In addition, when the type of PAVE unit is the same, for example, the type or content of other structural units other than TFE unit and PAVE unit between the second fluoropolymer and the first perfluoropolymer is different.

[0024] In the PAVE units contained in the second fluoropolymer, the PAVE is preferably a monomer represented by the above formula (1).

[0025] Among them, PMVE or PPVE is preferred as PAVE, and PPVE is more preferred, in terms of superior heat resistance.

[0026] In the second fluoropolymer, the content of PAVE units relative to the total content of TFE units and PAVE units is preferably 0.1 to 10.0 mol%, more preferably 0.5 to 7.0 mol%, and even more preferably 1.0 to 5.0 mol%, from the viewpoint of heat resistance.

[0027] The second fluoropolymer may contain structural units based on monomers other than TFE and PAVE. However, from the viewpoint of heat resistance, the structural units based on other monomers are preferably 10.0 mol% or less, more preferably 5.0 mol% or less, based on the total structural units of the second fluoropolymer. It is even more preferable that the second fluoropolymer 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%, based on the total structural units of the second fluoropolymer. When structural units based on other monomers are contained, examples of the other monomers include fluoroolefins such as hexafluoropropylene (excluding TFE and PAVE); and acid anhydrides such as itaconic anhydride, citraconic anhydride, and 5-norbornene-2,3-dicarboxylic anhydride.

[0028] In the composition of the present disclosure, the content of PAVE units relative to the total content of all structural units of the first perfluoropolymer and the second fluoropolymer is 0.1 to 10.0 mol%, preferably 0.5 to 7.0 mol%, and more preferably 1.0 to 5.0 mol%. Since the content of PAVE units is 0.1 to 10.0 mol%, the composition has excellent heat resistance.

[0029] The content of the first perfluoropolymer in the solid content of the composition of the present disclosure is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and is preferably 10% by mass or less, more preferably 5% by mass or less.

[0030] The content of the second fluoropolymer in the solid content of the composition of the present disclosure is preferably 90% by mass or more, more preferably 95% by mass or more, and is preferably 99.99% by mass or less, more preferably 99.9% by mass or less.

[0031] In the composition of the present disclosure, the ratio of the content of the first perfluoropolymer to the total content of the first perfluoropolymer and the second fluoropolymer is preferably 0.2% by mass or more, more preferably 0.5% by mass or more, from the viewpoint of polymerization stability. The ratio of the content of the first perfluoropolymer to the total content of the first perfluoropolymer and the second fluoropolymer is preferably 10% by mass or less, more preferably 5% by mass or less, from the viewpoint of heat resistance.

[0032] In order to obtain a more excellent heat resistance, the first perfluoropolymer and the second fluoropolymer do not contain any functional group, or the first perfluoropolymer and the second fluoropolymer have a main chain carbon number of 10 or less. ６ The total number of functional groups per unit is preferably less than 100, more preferably 50 or less, and even more preferably 30 or less.

[0033] Infrared spectroscopy can be used to identify the type of functional group and measure the number of functional groups.

[0034] The number of functional groups is measured by the following method. A first perfluoropolymer and a second fluoropolymer are press-molded at 340°C to produce a film with a thickness of 200 μm. This film is scanned 16 times with a Fourier transform infrared spectrometer and analyzed to obtain an infrared absorption spectrum. The first perfluoropolymer and the second fluoropolymer are subjected to a fluorination treatment for a long period of time in the fluorination step described below to obtain a fully fluorinated first perfluoropolymer and a fully fluorinated second fluoropolymer. The fully fluorinated first perfluoropolymer and the second fluoropolymer are press-molded at 340°C to produce a fully fluorinated film with a thickness of 200 μm. The fully fluorinated film is scanned 16 times with a Fourier transform infrared spectrometer and analyzed to obtain a base spectrum. From the absorption peaks of specific functional groups that appear in the difference spectrum between the obtained infrared absorption spectrum and the base spectrum, the number of main chain carbon atoms of 10 is determined according to the following formula (A): ６ The number of functional groups per particle, N, is calculated as follows: N = I x K / t (A) where I: absorbance, K: correction coefficient, and t: film thickness (mm).

[0035] Table 1 shows -CF ２ The absorption frequency, molar absorption coefficient, and correction factor are shown for specific functional groups such as H. The molar absorption coefficient of a specific functional group is determined from FT-IR measurement data of a low molecular weight model compound.

[0036]

[0037] In the copolymer, -CH ２ CF ２ H, —CH ２ COF, -CH ２ COOH, -CH ２ COOCH ３ , and -CH ２ CONH ２ The absorption frequency of -CF is shown in the table. ２ H, -COF, -COOH (free and bonded), -COOCH ３ and -CONH ２ From each absorption frequency, several tens of Kaiser (cm －１ ) becomes lower. For example, the number of -COF becomes lower.２ Absorption frequency due to COF: 1883 cm －１ The number of functional groups determined from the absorption peak of -CH ２ Absorption frequency due to COF: 1840 cm －１ The number of functional groups is the sum of the number of functional groups determined from the absorption peaks of the

[0038] The functional groups in the first perfluoropolymer and the second fluoropolymer are functional groups present at the ends of the main chain or side chains of each polymer, and functional groups present in the main chain or side chain. ２ , -CF ２ H, -COF, -COOH, -COOCH ３ , -CONH ２ , and -CH ２ Examples include OH.

[0039] The number of functional groups is -CF=CF ２ , -CF ２ H, -COF, -COOH, -COOCH ３ , -CONH ２ , and -CH ２ It may be the total number of OH.

[0040] The functional group is introduced, for example, by a chain transfer agent or a polymerization initiator used in producing the first perfluoropolymer and the second fluoropolymer, or by polymerizing a monomer having a functional group, the functional group is introduced into the side chain terminal of the polymer.

[0041] By subjecting the polymer having a functional group to a fluorination treatment, the first perfluoropolymer and the second fluoropolymer each having 10 carbon atoms in the main chain can be ６ The total number of functional groups per polymer can be less than 100. That is, the composition of the present disclosure is preferably a composition containing a polymer that has been subjected to a fluorination treatment.

[0042] The composition of the present disclosure may be in the form of particles, a powder composition containing a plurality of particles, or a liquid composition. Furthermore, when the composition of the present disclosure is a liquid composition, the composition of the present disclosure may be a dispersion in which particles are dispersed in water or an organic solvent. When the composition of the present disclosure is in the form of particles, the composition is preferably a particle (hereinafter also referred to as "the present particle") that contains a first perfluoropolymer and a second fluoropolymer and has a PAVE unit content of 0.1 to 10.0 mol% relative to the total content of all structural units of the first perfluoropolymer and the second fluoropolymer.

[0043] When the composition of the present disclosure is a powder composition or a liquid composition, it preferably contains the present particles. The average particle size of the present particles is preferably 1 μm or less, more preferably 700 nm or less, and even more preferably 500 nm or less. From the viewpoint of aggregability, the lower limit of the average particle size of the present particles is preferably 30 nm. Furthermore, the composition of the present disclosure may be in the form of pellets or molded articles such as films and tubes.

[0044] When the composition of the present disclosure is a particle or powder composition, the average particle size of the present particles means the arithmetic mean value of particle sizes determined from five different particles photographed by a scanning electron microscope in an SEM image. When the composition of the present disclosure is a liquid composition, the average particle size of the present particles is the particle size (D50) at the point on the cumulative curve where the cumulative volume is 50% when the particle size distribution is measured by a laser diffraction / scattering method and the total volume of the particle group is taken as 100%.

[0045] When the composition of the present disclosure is a dispersion, from the viewpoint of ease of handling, the viscosity of the dispersion is preferably 0.8 to 2.0 mPa·s, and more preferably 1.0 to 1.5 mPa·s. The viscosity of the dispersion is a value measured using a Brookfield viscometer at room temperature (25°C) and a rotation speed of 30 rpm. The measurement is repeated three times, and the average value of the three measured values ​​is used.

[0046] The composition of the present disclosure preferably does not substantially contain a fluorine-containing emulsifier. Details of the fluorine-containing emulsifier will be described later. The composition of the present disclosure preferably does not contain a fluorine-containing emulsifier, or the content of the fluorine-containing emulsifier is preferably 100 mass ppm or less, more preferably 10 mass ppm or less, even more preferably 5 mass ppm or less, and particularly preferably 1 mass ppm or less, relative to the total content of the first perfluoropolymer and the second fluoropolymer.

[0047] The content of the fluorine-containing emulsifier relative to the total content of the first perfluoropolymer and the second fluoropolymer can be determined by a method similar to the method for measuring the content of a fluorine-containing surfactant by liquid chromatography-mass spectrometry described in paragraphs

[0364] to

[0369] of WO 2021 / 045227.

[0048] In the composition of the present disclosure, the content of the compound represented by the following formula (S1) relative to the total content of the first perfluoropolymer and the second fluoropolymer is preferably 1 ppb by mass or more, and more preferably 10 ppb by mass or more, relative to the fluoropolymer, from the viewpoint of processability.

[0049] In the composition of the present disclosure, the content of the compound represented by the following formula (S1) relative to the total content of the first perfluoropolymer and the second fluoropolymer is preferably 10,000 ppb by mass or less, more preferably 1,000 ppb by mass or less, and even more preferably 100 ppb by mass or less, from the viewpoint of suppressing deterioration of the physical properties such as heat resistance of the composition of the present disclosure.

[0050] In the composition of the present disclosure, the content of the compound represented by the following formula (S2) relative to the total content of the first perfluoropolymer and the second fluoropolymer is preferably 0.1 ppb by mass or more, and more preferably 1 ppb by mass or more, relative to the fluoropolymer, from the viewpoint of processability.

[0051] The content of the compound represented by the following formula (S2) in the composition of the present disclosure relative to the total content of the first perfluoropolymer and the second fluoropolymer is preferably 50 ppb by mass or less, and more preferably 25 ppb by mass or less, from the viewpoint of suppressing deterioration of the physical properties such as heat resistance of the composition of the present disclosure. ２ )ｎ -COOM Formula (S2): H-(CF ２ ) ｍ -SO ３ M In formula (S1) and formula (S2), M each independently represents a hydrogen atom, Na, K, or NH ４ wherein n is 7 to 11, and m is 8 to 12.

[0052] The content of the compound represented by formula (S1) relative to the total content of the first perfluoropolymer and the second fluoropolymer can be calculated by a method using an aqueous dispersion, among the measurement methods using a liquid chromatograph mass spectrometer described in paragraphs

[0710] to

[0720] of WO 2018 / 181904.

[0053] The content of the compound represented by formula (S2) relative to the total content of the first perfluoropolymer and the second fluoropolymer can be calculated by a method using an aqueous dispersion, among the measurement methods using a liquid chromatograph mass spectrometer described in paragraphs

[0721] to

[0732] of WO 2018 / 181904.

[0054] The composition of the present disclosure may be subjected to a fluorination treatment to adjust the content of the compound represented by formula (S1). Fluorination treatment methods include the methods described below. Fluorinating the composition of the present disclosure can reduce the content of the compound represented by formula (S1) in the particles of the present disclosure.

[0055] [Method for producing a fluoropolymer] The method for producing a fluoropolymer of the present disclosure comprises the steps of preparing an aqueous dispersion A containing a first perfluoropolymer having a Tg of 10°C or less and an aqueous medium, and polymerizing a monomer containing TFE and PAVE (hereinafter also referred to as a "specific monomer") in the aqueous dispersion A to produce a second fluoropolymer different from the first perfluoropolymer. Before starting polymerization of the specific monomer, the content of the first perfluoropolymer is 0.01 to 4.0% by mass relative to the total mass of the aqueous dispersion A, and before starting polymerization of the specific monomer, the aqueous dispersion A does not contain a fluorinated emulsifier, or the content of the fluorinated emulsifier is 100 ppm by mass or less relative to the total mass of the aqueous dispersion A.

[0056] 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 brought into the reactor after the temperature inside the reactor is raised to the polymerization temperature or higher, and the time when the temperature inside the reactor is raised to the polymerization temperature or higher after the temperature inside the reactor is raised to the polymerization temperature or higher.

[0057] In the method for producing a fluoropolymer of the present disclosure, by polymerizing a monomer containing TFE and PAVE in an aqueous dispersion A containing a first perfluoropolymer having a Tg of 10°C or less and an aqueous medium, a second fluoropolymer can be produced efficiently even when the content of the fluorinated emulsifier is 100 ppm by mass or less relative to the total mass of the aqueous dispersion A.

[0058] The method for producing a fluoropolymer of the present disclosure preferably comprises, in this order, a step of preparing aqueous dispersion A and a step of producing a second fluoropolymer different from the first perfluoropolymer.

[0059] <Step of preparing aqueous dispersion A> The method for producing a fluoropolymer of the present disclosure includes a step of preparing an aqueous dispersion A containing a first perfluoropolymer having a Tg of 10°C or less and an aqueous medium (hereinafter also referred to as the "step of preparing aqueous dispersion A").

[0060] (First Perfluoropolymer) Details of the first perfluoropolymer having a Tg of 10° C. or less, which is contained in the aqueous dispersion A prepared in the aqueous dispersion A preparation step, are as described above.

[0061] The first perfluoropolymer is preferably dispersed in the aqueous medium in the form of particles. The average particle size of the first perfluoropolymer is preferably 1 to 200 nm, more preferably 10 to 150 nm, and even more preferably 30 to 120 nm, from the viewpoint of more efficiently producing the second fluoropolymer.

[0062] The average particle diameter of the first perfluoropolymer is determined by measuring the particle size distribution by a laser diffraction / scattering method, determining a cumulative curve with the total volume of the particle population set to 100%, and measuring the particle diameter (D50) at the point on the cumulative curve where the cumulative volume is 50%.

[0063] The first perfluoropolymer can be produced, for example, by polymerizing a monomer (preferably a mixture of monomers containing TFE and PAVE) in a polymerization solvent in the presence of a polymerization initiator, thereby obtaining a dispersion of the first perfluoropolymer dispersed in particulate form in the polymerization solvent.

[0064] When polymerizing a monomer to obtain the first perfluoropolymer, the pH of the reaction system containing the monomer and the polymerization solvent before starting polymerization is preferably 6.5 or more, more preferably 7.0 or more, from the viewpoint of efficiently proceeding polymerization.The pH of the reaction system is preferably 10.5 or less, more preferably 10 or less, from the viewpoint of improving the stability of the first perfluoropolymer.The pH of the reaction system can be adjusted using a pH adjuster.As the pH adjuster, the pH adjuster that may be contained in the aqueous dispersion A described later and ammonia can be mentioned, and ammonia is preferred.

[0065] The dispersion of the first perfluoropolymer thus obtained may be used as is as the aqueous dispersion A. Another aqueous medium may be added to the dispersion of the first perfluoropolymer, and the resulting mixture may be used as the aqueous dispersion. Alternatively, the first perfluoropolymer may be dispersed in another aqueous medium by solvent substitution, and the resulting mixture may be used as the aqueous dispersion A.

[0066] The polymerization initiator used in producing the first perfluoropolymer is preferably a water-soluble polymerization initiator, more preferably a persulfate such as ammonium persulfate, sodium persulfate, or potassium persulfate; a peroxide such as disuccinic acid peroxide; or an azo compound such as azobisisobutylamidine dihydrochloride, still more preferably a persulfate, and particularly preferably ammonium persulfate.

[0067] The polymerization solvent may be water or a mixed solvent of water and a water-soluble organic solvent, such as tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, or tripropylene glycol.

[0068] The method for producing the first perfluoropolymer may include a heating step of heating the dispersion liquid in which the first perfluoropolymer is dispersed after the dispersion liquid is obtained.

[0069] (Aqueous medium) The aqueous medium contained in the aqueous dispersion A prepared in the aqueous dispersion A preparation step may be the polymerization solvent used in producing the first perfluoropolymer. Specific examples of the aqueous medium contained in the aqueous dispersion A are the same as the specific examples of the polymerization solvent used in producing the first perfluoropolymer. Before starting polymerization of the monomers used in polymerizing the second perfluoropolymer, the content of the aqueous medium is preferably 60.0 to 99.9 mass%, more preferably 96.0 to 99.9 mass%, and even more preferably 98.0 to 99.9 mass%, based on the total mass of the aqueous dispersion A.

[0070] (Other Components) The aqueous dispersion A may contain other components in addition to the first perfluoropolymer and the aqueous medium. Specific examples of other components that the aqueous dispersion A may contain include a chain transfer agent, an emulsifier other than the fluorine-containing emulsifier, a pH adjuster, and a wax.

[0071] In the present disclosure, an emulsifier is a compound that has a hydrophilic portion and a hydrophobic portion.

[0072] Examples of emulsifiers include hydrocarbon-containing surfactants, fluorine-containing emulsifiers, and polymer emulsifiers. Neither the first perfluoropolymer nor the second fluoropolymer is an emulsifier. The emulsifier may be either ionic or nonionic.

[0073] 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.

[0074] The hydrocarbon-containing surfactant can be exemplified by hydrocarbon surfactant and siloxane surfactant.Hydrocarbon 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.

[0075] Examples of hydrocarbon surfactants include anionic hydrocarbon surfactants. Anionic hydrocarbon surfactants refer to hydrocarbon surfactants having a negatively charged hydrophilic portion such as a carboxylic acid group, sulfonic acid group, sulfate group, phosphonic acid group, or phosphate group, and a hydrocarbon portion such as an alkyl group as a hydrophobic portion. 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 salt supplied by BASF as part of the Avanel® S series.

[0076] Anionic hydrocarbon surfactants also include sodium dodecyl sulfate.

[0077] Another example of an anionic hydrocarbon surfactant is the sulfosuccinate surfactant Lankropol® K8300, available from Akzo Nobel Surface Chemistry LLC.

[0078] Hydrocarbon surfactants also include nonionic hydrocarbon surfactants.Nonionic hydrocarbon surfactants do not have charged groups, but have a hydrophobic portion that is often a long-chain hydrocarbon.The hydrophilic portion of nonionic hydrocarbon surfactants includes 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.

[0079] Examples of nonionic hydrocarbon surfactants include surfactants described in paragraphs

[0043] to

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

[0080] Siloxane surfactants include those described in US Pat. Nos. 6,841,616 (Wille et al.) and 7,977,438 (Brothers et al.).

[0081] 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.

[0082] The polymer emulsifier may be a water-soluble polymer having a hydrophilic group in its side chain. Such a polymer emulsifier may be, for example, a polymer containing a structural unit based on a compound having a site capable of polymerization reaction and a hydrophilic group. Further, a polymer 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 may also be used.

[0083] Specific examples of the chain transfer agent include ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane. From the viewpoint of being able to control the molecular weight with a small amount, the chain transfer agent is preferably t-butyl methyl ether or methane, and more preferably t-butyl methyl ether.

[0084] 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.

[0085] Specific examples of wax include Paraffin Wax-155 and Paraffin Wax-150 (both manufactured by Nippon Seiro Co., Ltd.).

[0086] When aqueous dispersion A 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. Furthermore, 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. When aqueous dispersion A contains an emulsifier other than the fluorinated emulsifier, the content of the emulsifier other than the fluorinated emulsifier is preferably 0.01 to 5.0 parts by mass relative to 100 parts by mass of the aqueous medium.

[0087] When the aqueous dispersion A contains a pH adjuster, the content of the pH adjuster is preferably 0.01 to 3.0 parts by mass per 100 parts by mass of the aqueous medium.

[0088] From the viewpoint of stably polymerizing the second fluoropolymer, the pH of aqueous dispersion A is preferably 1.0 or higher, more preferably 2.0 or higher. From the viewpoint of stably polymerizing the second fluoropolymer, the pH of aqueous dispersion A is preferably 11 or lower, more preferably 10.5 or lower. When aqueous dispersion A contains a wax, the content of the wax is preferably 1 to 10 parts by mass per 100 parts by mass of the aqueous medium.

[0089] From the viewpoint of stable polymerization of the second fluoropolymer, the viscosity of aqueous dispersion A is preferably 2.0 mPa s or less, more preferably 1.9 mPa s or less, and even more preferably 1.7 mPa s or less. From the viewpoint of stable polymerization of the second fluoropolymer, the viscosity of aqueous dispersion A is preferably 0.85 mPa s or more, and more preferably 0.9 mPa s or more.

[0090] The thixotropy ratio of aqueous dispersion A is preferably 0.9 or more, more preferably 0.95 or more, from the viewpoint of stable polymerization of the second fluoropolymer. The thixotropy ratio of aqueous dispersion A is preferably 1.2 or less, more preferably 1.1 or less, from the viewpoint of stable polymerization of the second fluoropolymer. The viscosity of aqueous dispersion A is measured using a B-type viscometer at room temperature (25 ° C) and a rotation speed of 30 rpm. The measurement is repeated three times, and the average value of the three measured values ​​is taken. The thixotropy ratio of aqueous dispersion A is the viscosity of aqueous dispersion A measured at a rotation speed of 30 rpm divided by the viscosity of aqueous dispersion A measured at a rotation speed of 60 rpm.

[0091] <Second fluoropolymer production step> The method for producing a fluoropolymer of the present disclosure includes a step of polymerizing a specific monomer in aqueous dispersion A to produce a second fluoropolymer different from the first perfluoropolymer (hereinafter also referred to as the "second fluoropolymer production step").

[0092] Details of the second fluoropolymer are as described above.

[0093] Before the start of polymerization of the specific monomer, the content of the first perfluoropolymer is 0.01 to 4.0% by mass, preferably 0.05 to 3.0% by mass, and more preferably 0.1 to 2.0% by mass, relative to the total mass of the aqueous dispersion A. When the content of the first perfluoropolymer is 0.01% by mass or more, the polymerization stability (productivity) is excellent, and when the content of the first perfluoropolymer is 4.0% by mass or less, the polymer obtained by polymerization (i.e., the mixture of the first perfluoropolymer and the second fluoropolymer) has excellent heat resistance.

[0094] Before starting polymerization of the specific monomer, the aqueous dispersion A does not contain a fluorine-containing emulsifier, or the content of the fluorine-containing emulsifier is 100 mass ppm or less, preferably 50 mass ppm or less, more preferably 25 mass ppm or less, and even more preferably 5 mass ppm or less, relative to the total mass of the aqueous dispersion A. The lower limit may be 0 mass ppm. In the method for producing a fluorine-containing polymer of the present disclosure, the second fluoropolymer can be produced efficiently even if the content of the fluorine-containing emulsifier is 100 mass ppm or less.

[0095] Before starting polymerization of specific monomer, the concentration of fluoride ion is preferably 100 mass ppm or less, more preferably 50 mass ppm or less, based on the total mass of aqueous dispersion A, from the viewpoint of polymerization stability.The lower limit can be 0 mass ppm.An example of a method for adjusting the concentration of fluoride ion to the above value can be a method of removing sulfate ion using an anion exchange resin during the production of the first perfluoropolymer.Here, fluoride ion may be generated by the reaction between a polymerization initiator (e.g., ammonium persulfate) and the monomer used in the production of the first fluorine-containing polymer, and may be contained in the aqueous dispersion.

[0096] Before the start of polymerization of the specific monomer, the concentration of sulfate ions 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 aqueous dispersion, from the viewpoint of suppressing discoloration of the second fluorinated polymer. The lower limit may be 0 ppm by mass.

[0097] An example of a method for adjusting the sulfate ion concentration to the above range is to remove sulfate ions using an anion exchange resin during production of the first perfluoropolymer.

[0098] Here, the sulfate ions are derived from, for example, the polymerization initiator (particularly ammonium persulfate) used in the production of the first perfluoropolymer, and may be contained in the aqueous dispersion containing the first perfluoropolymer. It is presumed that by making the content of sulfate ions 10 ppm by mass or less (particularly 5 ppm by mass or less), it is possible to prevent the formation of terminal groups with low heat resistance in the second fluoropolymer, thereby preventing the discoloration of the second fluoropolymer.

[0099] Before starting 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 aqueous dispersion, from the viewpoint of suppressing aggregation of the second fluoropolymer. The lower limit is 0 ppm by mass.

[0100] As an example of the method for making the concentration of ammonium ion the above value, there can be mentioned a method of removing ammonium ion using cation exchange resin during the production of the first perfluoropolymer.Here, ammonium ion, for example, originates from the initiator (particularly ammonium persulfate) used during the production of the first perfluoropolymer, and may be contained in the aqueous dispersion containing the first perfluoropolymer.It is presumed that the content of ammonium ion is 20 mass ppm or less, so that the ionic strength in the aqueous medium is reduced, and the production efficiency of the second fluoropolymer is improved.

[0101] (Specific Monomer) The specific monomer includes TFE and PAVE.

[0102] The PAVE is preferably a monomer represented by the above formula (1).

[0103] Among them, PMVE or PPVE is preferred as PAVE, and PPVE is more preferred, in terms of superior heat resistance.

[0104] The amount of PAVE used relative to the total amount of TFE and PAVE used is preferably 0.1 to 10.0 mol %, more preferably 0.5 to 7.0 mol %, and even more preferably 1.0 to 5.0 mol %, from the viewpoint of heat resistance.

[0105] The specific monomer may contain other monomers in addition to TFE and PAVE. From the viewpoint of heat resistance, the amount of other monomers used is preferably 10.0 mol % or less, more preferably 5.0 mol % or less, based on the total amount of the specific monomers used. It is even more preferable that the specific monomer is substantially free of other monomers. "Substantially free of other monomers" means that the amount of other monomers used is 0.01 mol % or less, based on the total amount of the specific monomers used, and may be 0.00 mol %. Examples of other monomers include fluoroolefins such as hexafluoropropylene (excluding TFE and PAVE); and acid anhydrides such as itaconic anhydride, citraconic anhydride, and 5-norbornene-2,3-dicarboxylic anhydride.

[0106] 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 aqueous dispersion A.

[0107] (Polymerization initiator) In the second fluoropolymer production step, it is preferable to polymerize the specific monomer in the presence of a polymerization initiator.

[0108] The polymerization initiator is preferably an oil-soluble radical initiator, a water-soluble radical initiator, or a water-soluble oxidation-reduction catalyst.

[0109] Examples of oil-soluble radical initiators 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").

[0110] 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").

[0111] As the water-soluble oxidation-reduction catalyst, a combination of an oxidizing agent such as bromic acid or its salts, chloric acid or its salts, persulfuric acid or its salts, permanganic acid or its salts, or hydrogen peroxide, and a reducing agent such as sulfurous acid or its salts, hydrogen sulfite or its salts, thiosulfuric acid or its salts, organic acids, or inorganic salts is preferred. Potassium persulfate and ammonium persulfate are preferred as persulfates. Sodium sulfite is preferred as sulfites. Examples of inorganic salts include combinations of sulfate anions, sulfite anions, and chloride anions with metal ions. Examples of metal ions include transition metal ions, such as manganese, iron, cobalt, nickel, copper, zinc, cerium, and silver ions, with iron ions being preferred. Examples of inorganic salts include iron(II) sulfate.

[0112] The polymerization initiator is preferably an oil-soluble radical initiator or a water-soluble radical initiator, more preferably an oil-soluble radical initiator from the viewpoint of more efficiently producing a fluorine-containing polymer, and even more preferably an oil-soluble organic peroxide. One type of polymerization initiator may be used alone, or two or more types may be used in combination.

[0113] The amount of the polymerization initiator used is preferably 1 to 1,000 ppm by mass, more preferably 5 to 750 ppm, and even more preferably 10 to 500 ppm, relative to the amount of the specific monomer used.

[0114] (Other Components) When polymerizing the specific monomer, components other than those described above (hereinafter also referred to as "other components") may be further used. Specific examples of other components include a reducing agent. The amount of other components used is preferably 1 to 2000 ppm by mass relative to the amount of the specific monomer used.

[0115] (Production Method) The second fluoropolymer obtained in the second fluoropolymer production step may be copolymerized with the first perfluoropolymer.

[0116] 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. 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.

[0117] 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.

[0118] When the first perfluoropolymer is particulate, it is presumed that the specific monomer polymerizes in or near the particles of the first perfluoropolymer during polymerization of the specific monomer, and therefore, in the method for producing a fluorine-containing polymer of the present disclosure, particles containing the first perfluoropolymer and the second fluoropolymer are presumed to be produced. That is, it is presumed that the second fluoropolymer is obtained in the form of particles containing the first perfluoropolymer and the second fluoropolymer. In this case, an aqueous dispersion is obtained in which particles containing the first perfluoropolymer and the second fluoropolymer are dispersed in the above-mentioned aqueous medium.

[0119] In the method for producing a fluoropolymer of the present disclosure, it is preferable to obtain particles containing a first perfluoropolymer and a second fluoropolymer. That is, the method for producing a fluoropolymer of the present disclosure comprises the steps of: preparing an aqueous dispersion A containing particles of a first perfluoropolymer having a glass transition temperature of 10°C or less and an aqueous medium; and polymerizing a monomer containing tetrafluoroethylene and perfluoro(alkyl vinyl ether) in the aqueous dispersion A to produce particles containing the first perfluoropolymer and a second fluoropolymer different from the first perfluoropolymer. Preferably, the method for producing a fluoropolymer is such that, before the start of monomer polymerization, the content of the first perfluoropolymer is 0.01 to 4.0 mass% relative to the total mass of the aqueous dispersion A, and, before the start of monomer polymerization, the aqueous dispersion A does not contain a fluorinated emulsifier or the content of the fluorinated emulsifier is 100 ppm by mass or less relative to the total mass of the aqueous dispersion A. From the viewpoint of polymerization stability, the average particle size of the particles containing the first perfluoropolymer and the second fluoropolymer is preferably 1 μm or less, more preferably 700 nm or less, and more preferably 500 nm or less. From the viewpoint of aggregation, the lower limit of the average particle size of the particles containing the first perfluoropolymer and the second fluoropolymer is preferably 30 nm.

[0120] In the production method for a fluoropolymer of the present disclosure, the average particle size of the particles is determined by measuring the particle size distribution by a laser diffraction / scattering method, determining a cumulative curve with the total volume of the particle population set to 100%, and determining the particle size at the point on the cumulative curve where the cumulative volume is 50%.

[0121] When the first perfluoropolymer is particulate and particles containing the first perfluoropolymer and the second fluoropolymer are obtained by the method for producing a fluoropolymer of the present disclosure, the ratio of the average particle size of the particles containing the first perfluoropolymer and the second fluoropolymer to the average particle size of the particles of the first perfluoropolymer is preferably at least 2, more preferably at least 3. From the viewpoint of polymerization stability, the ratio of the average particle sizes is preferably at most 10, more preferably at most 8. When the ratio is at least 2, particles having excellent heat resistance that reflect the physical properties of the second fluoropolymer can be obtained.

[0122] <Fluorination Step> The method for producing a fluoropolymer according to the present disclosure preferably further comprises a step of subjecting the first perfluoropolymer and the second fluoropolymer to a fluorination treatment (hereinafter also referred to as the "fluorination step").

[0123] The method of fluorination treatment is not particularly limited, and can be carried out by a conventionally known method. For example, fluorination can be carried out by contacting the first perfluoropolymer and the second fluoropolymer with fluorine gas. The fluorine gas may be diluted with an inert gas before use. Examples of the inert gas include rare gases such as helium gas, neon gas, and argon gas, and nitrogen gas. Nitrogen gas or helium gas is preferred, and nitrogen gas is more preferred from the viewpoint of economical advantage. The proportion of fluorine gas is preferably 10 to 60% by volume, based on 100% by volume of the total of fluorine gas and inert gas.

[0124] The temperature of the fluorination treatment is, for example, 100 to 250° C. The time of the fluorination treatment is, for example, 1 to 15 hours.

[0125] By carrying out the fluorination step, the functional groups contained in the first perfluoropolymer and the second fluoropolymer are fluorinated. Fluorination improves heat resistance. ６ The total number of functional groups per unit is preferably less than 100, more preferably 50 or less, and even more preferably 30 or less. The lower limit of the number of functional groups is 0.

[0126] [Aqueous Dispersion] The aqueous dispersion of the present disclosure is an aqueous dispersion comprising an aqueous medium and melt-moldable particles, wherein the particles have an average particle size of 1 μm or less, the particles comprise one or more types of fluoropolymer, the fluoropolymer comprises TFE units and PAVE units, the content of PAVE units is 0.1 to 10.0 mol% based on all constitutional units of the fluoropolymer, the content of particles is 1 to 50 mass% based on the total mass of the aqueous dispersion, and the aqueous dispersion does not contain a fluorinated emulsifier or the content of the fluorinated emulsifier is 100 ppm by mass or less based on the content of the fluoropolymer.

[0127] The aqueous dispersion of the present disclosure can be obtained, for example, by the method for producing a fluoropolymer of the present disclosure. The aqueous dispersion A is an aqueous dispersion obtained during the method for producing a fluoropolymer of the present disclosure, and is different from the aqueous dispersion of the present disclosure.

[0128] Melt-Formable Particles The aqueous dispersions of the present disclosure include melt-formable particles.

[0129] In the present disclosure, "melt-formable" means that the melt flow rate (MFR) is 0.1 to 1000 g / 10 min. The MFR of the particles is preferably 0.1 to 100 g / 10 min, more preferably 1 to 80 g / 10 min. In the present disclosure, the MFR is measured in accordance with ASTM D3307 under conditions of a temperature of 372°C and a load of 49 N, and is measured as the mass flowing out of an orifice having a diameter of 2 mm and a length of 8 mm in 10 minutes.

[0130] The average particle size of the particles is 1 μm or less, and from the viewpoint of dispersibility, it is preferably 700 nm or less, more preferably 500 nm or less. From the viewpoint of aggregation, the lower limit of the average particle size of the particles is preferably 30 nm.

[0131] In the present disclosure, the average particle diameter of particles is the particle diameter at the point on the cumulative curve where the cumulative volume is 50% when the particle size distribution is measured by a laser diffraction / scattering method and the total volume of the particle group is set to 100%.

[0132] From the viewpoint of dispersion stability, the content of the particles is 1 to 50% by mass, preferably 2 to 45% by mass, and more preferably 3 to 40% by mass, relative to the total mass of the aqueous dispersion of the present disclosure.

[0133] The particles contained in the aqueous dispersion of the present disclosure contain one or more fluoropolymers. The fluoropolymers contain TFE units and PAVE units.

[0134] When the particles contain two or more types of fluoropolymers, the particles are only required to contain a fluoropolymer containing TFE units and PAVE units, and may also contain a fluoropolymer that does not fall under the category of a fluoropolymer containing TFE units and PAVE units.

[0135] In addition, when the particles contain two or more kinds of fluoropolymers, any one of the fluoropolymers contained in the particles may not be melt-formable, so long as the particles are melt-formable.

[0136] The content of PAVE units is 0.1 to 10.0 mol %, preferably 0.5 to 7.0 mol %, and more preferably 1.0 to 5.0 mol %, based on all constitutional units of the fluoropolymer. Since the content of PAVE units is 0.1 to 10.0 mol %, the fluoropolymer has excellent heat resistance.

[0137] When the particles contain two or more types of fluorine-containing polymers, "all structural units of the fluorine-containing polymer" means all structural units in the two or more types of fluorine-containing polymers.

[0138] In the PAVE unit, the PAVE is preferably a monomer represented by the above formula (1).

[0139] Among them, from the viewpoint of superior heat resistance, the PAVE is preferably at least one selected from the group consisting of PMVE and PPVE, and more preferably a combination of PMVE and PPVE.

[0140] The particles preferably contain the first perfluoropolymer and the second fluoropolymer, the details of which are as described above.

[0141] The content of the first perfluoropolymer in the particles is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and preferably 10% by mass or less, more preferably 5% by mass or less.

[0142] The content of the second fluoropolymer in the particles is preferably 90% by mass or more, more preferably 95% by mass or more, and is preferably 99.99% by mass or less, more preferably 99.9% by mass or less.

[0143] The ratio of the content of the first perfluoropolymer in the particles to the total content of the first perfluoropolymer and the second fluoropolymer is preferably 0.01% by mass or more, and more preferably 0.1% by mass or more, from the viewpoint of improving physical properties such as heat resistance, etc. The ratio of the content of the first perfluoropolymer in the particles to the total content of the first perfluoropolymer and the second fluoropolymer is preferably 10% by mass or less, and more preferably 5% by mass or less, from the viewpoint of improving physical properties such as heat resistance, etc.

[0144] <Aqueous Medium> Specific examples of the aqueous medium contained in the aqueous dispersion of the present disclosure are the same as the specific examples of the aqueous medium used in producing the first perfluoropolymer described above.

[0145] 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 aqueous dispersion of the present disclosure.

[0146] <Others> The aqueous dispersion of the present disclosure preferably does not substantially contain a fluorine-containing emulsifier. Details of the fluorine-containing emulsifier are as described above. The aqueous dispersion of the present disclosure does not contain a fluorine-containing emulsifier, or the content of the fluorine-containing emulsifier is 100 ppm by mass or less, preferably 10 ppm by mass or less, more preferably 5 ppm by mass or less, and even more preferably 1 ppm by mass or less, relative to the content of the fluorine-containing polymer. The content of the fluorine-containing emulsifier relative to the content of the fluorine-containing polymer is determined by a method similar to the method for measuring the content of a fluorine-containing surfactant by liquid chromatography-mass spectrometry described in paragraphs

[0364] to

[0369] of WO 2021 / 045227.

[0147] From the viewpoint of processability, the viscosity of the aqueous dispersion of the present disclosure is preferably 0.8 to 2.0 mPa·s, and more preferably 1.0 to 1.5 mPa·s. The viscosity of the aqueous dispersion is a value measured using a Brookfield viscometer at room temperature (25°C) and a rotation speed of 30 rpm. The measurement is repeated three times, and the average value of the three measured values ​​is used.

[0148] The content of the compound represented by the following formula (S1) relative to the fluoropolymer in the aqueous dispersion of the present disclosure is preferably 1 ppb by mass or more, and more preferably 10 ppb by mass or more, relative to the fluoropolymer, from the viewpoint of stabilizing the fluoropolymer in the aqueous dispersion. The content of the compound represented by the following formula (S1) relative to the fluoropolymer in the aqueous dispersion of the present disclosure is preferably 10,000 ppb by mass or less, more preferably 1,000 ppb by mass or less, and even more preferably 100 ppb by mass or less, from the viewpoint of preventing deterioration in physical properties.

[0149] The content of the compound represented by the following formula (S2) relative to the fluoropolymer in the aqueous dispersion of the present disclosure is preferably 0.1 ppb by mass or more, and more preferably 1 ppb by mass or more, relative to the fluoropolymer, from the viewpoint of stabilizing the fluoropolymer in the aqueous dispersion. The content of the compound represented by the following formula (S2) relative to the fluoropolymer in the aqueous dispersion of the present disclosure is preferably 50 ppb by mass or less, and more preferably 25 ppb by mass or less, from the viewpoint of preventing deterioration of physical properties. Formula (S1): H—(CF ２ ) ｎ -COOM Formula (S2): H-(CF ２ ) ｍ -SO ３ M In formula (S1) and formula (S2), M each independently represents a hydrogen atom, Na, K, or NH ４ wherein n is 7 to 11, and m is 8 to 12.

[0150] The content of the compound represented by formula (S1) relative to the fluoropolymer can be calculated by a method using an aqueous dispersion, among the measurement methods using a liquid chromatograph mass spectrometer described in paragraphs

[0710] to

[0720] of WO 2018 / 181904.

[0151] The content of the compound represented by formula (S2) relative to the fluoropolymer can be calculated by a method using an aqueous dispersion, among the measurement methods using a liquid chromatograph mass spectrometer described in paragraphs

[0721] to

[0732] of WO 2018 / 181904.

[0152] The compound represented by formula (S1) and the compound represented by formula (S2) are components that can be generated when the above-mentioned specific monomer (particularly TFE) is polymerized in the presence of a polymerization initiator, a chain transfer agent and a fluorine-containing emulsifier.Therefore, in the production method of the fluorine-containing polymer of the present disclosure, when no fluorine-containing emulsifier is used, the generated amounts of the compound represented by formula (S1) and the compound represented by formula (S2) can be suppressed, and it is easy to make the contents of these compounds fall within the above-mentioned ranges.

[0153] <Uses> As described above, the aqueous dispersion of the present disclosure does not necessarily require a fluorinated emulsifier, and therefore can easily be converted by solvent substitution into a dispersion in an organic solvent such as N-methylpyrrolidone, acetone, etc. For example, the aqueous dispersion of the present disclosure can be mixed with an organic solvent and dehydrated by evaporation or with anhydrous sodium sulfate, etc., to form a dispersion in an organic solvent.

[0154] In the aqueous dispersion of the present disclosure, the fluorine-containing polymer is stably dispersed even without containing a fluorine-containing emulsifier, and therefore, it can be suitably used for coating applications, binders, etc.

[0155] Additionally, powders can be obtained by agglomerating particles from the aqueous dispersion of the present disclosure.

[0156] Aggregation methods include, but are not limited to, freeze aggregation, acid aggregation, base aggregation, and aggregation using a coagulation agent. 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 aqueous dispersion of the present disclosure is preferred. Examples of acids to be added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, hydrofluoric acid, etc., 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 aqueous dispersion of the present disclosure is preferred. Examples of bases to be added include sodium hydroxide, potassium hydroxide, ammonium carbonate, etc., 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 coagulation agent, known coagulation agents 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 ２ Examples 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.

[0157] [Particles] The particles of the present disclosure are melt-moldable particles, wherein the average particle size of the particles is 1 μm or less, the particles comprise one or more types of fluoropolymer, the fluoropolymer comprises TFE units and PAVE units, the content of PAVE units is 0.1 to 10.0 mol% based on all constitutional units of the fluoropolymer, the particles do not contain a fluorinated emulsifier or the content of the fluorinated emulsifier is 100 ppm by mass or less based on the content of the fluoropolymer, and the content of the compound represented by formula (S1) is 1 to 10,000 ppb by mass and the content of the compound represented by formula (S2) is 100 ppb by mass or less based on the fluoropolymer. Formula (S1): H-(CF２ ) ｎ -COOM Formula (S2): H-(CF ２ ) ｍ -SO ３ M In formula (S1) and formula (S2), M each independently represents a hydrogen atom, Na, K, or NH ４ where n represents 7 to 11, and m represents 8 to 12. The particles of the present disclosure can be obtained, for example, by the method for producing a fluoropolymer of the present disclosure. Alternatively, the particles of the present disclosure may be obtained by aggregating particles from the aqueous dispersion of the present disclosure.

[0158] <Melt-formable particles> The definition of the melt-formable particles in the particles of the present disclosure, including preferred embodiments and ranges thereof, is the same as that in the aqueous dispersion of the present disclosure. However, in the particles of the present disclosure, the average particle size of the particles means the arithmetic average of the particle sizes of five different particles obtained from SEM images of the particles photographed by a scanning electron microscope.

[0159] <Others> The particles of the present disclosure preferably do not substantially contain a fluorine-containing emulsifier. Details of the fluorine-containing emulsifier are as described above. The particles of the present disclosure do not contain a fluorine-containing emulsifier, or the content of the fluorine-containing emulsifier is 100 ppm by mass or less, preferably 10 ppm by mass or less, more preferably 5 ppm by mass or less, and even more preferably 1 ppm by mass or less, relative to the content of the fluorine-containing polymer. The content of the fluorine-containing emulsifier relative to the content of the fluorine-containing polymer is determined by a method similar to the method for measuring the content of a fluorine-containing surfactant by liquid chromatography-mass spectrometry described in paragraphs

[0364] to

[0369] of WO 2021 / 045227.

[0160] The particles of the present disclosure have a content of the compound represented by formula (S1) of 1 to 10,000 ppb by mass, and a content of the compound represented by formula (S2) of 100 ppb by mass or less, relative to the fluoropolymer. The compound represented by formula (S1) and the compound represented by formula (S2) are components that can be generated when the above-mentioned specific monomer (particularly TFE) is polymerized in the presence of a polymerization initiator, a chain transfer agent, and an emulsifier. Therefore, in the method for producing a fluoropolymer of the present disclosure, when no emulsifier is used, the amounts of the compound represented by formula (S1) and the compound represented by formula (S2) generated can be suppressed, and it is easy to keep the contents of these compounds within the above ranges.

[0161] The content of the compound represented by formula (S1) relative to the fluoropolymer in the particles of the present disclosure is preferably 10 ppb by mass or more relative to the fluoropolymer from the viewpoint of processability. The content of the compound represented by formula (S1) relative to the fluoropolymer in the particles of the present disclosure is preferably 1000 ppb by mass or less, more preferably 100 ppb by mass or less, from the viewpoint of suppressing deterioration of physical properties such as heat resistance.

[0162] The content of the compound represented by formula (S2) relative to the fluoropolymer in the particles of the present disclosure is preferably 0.1 ppb by mass or more, more preferably 1 ppb by mass or more, relative to the fluoropolymer from the viewpoint of processability. The content of the compound represented by formula (S2) relative to the fluoropolymer in the particles of the present disclosure is preferably 50 ppb by mass or less, more preferably 25 ppb by mass or less, from the viewpoint of suppressing deterioration of physical properties such as heat resistance.

[0163] The content of the compound represented by formula (S1) relative to the fluoropolymer can be calculated by a method using a powder, among the measurement methods using a liquid chromatograph mass spectrometer described in paragraphs

[0710] to

[0720] of WO 2018 / 181904.

[0164] The content of the compound represented by formula (S2) relative to the fluoropolymer can be calculated by a method using a powder, among the measurement methods using a liquid chromatograph mass spectrometer described in paragraphs

[0721] to

[0732] of WO 2018 / 181904.

[0165] The particles of the present disclosure may be further subjected to a fluorination treatment to adjust the content of the compound represented by formula (S1). Fluorination treatment methods include the methods described above. Fluorination of the particles of the present disclosure can reduce the content of the compound represented by formula (S1) in the particles of the present disclosure.

[0166] In addition, the fluorine-containing polymer of the particles of the present disclosure has a main chain carbon number of 10 ６ The total number of functional groups per unit is preferably less than 100, more preferably 50 or less, and even more preferably 30 or less. The lower limit of the number of functional groups is 0. Examples of functional groups include those described above, and the method for measuring the number of functional groups is also as described above.

[0167] <Uses> Because the particles of the present disclosure are substantially free of emulsifiers, they can easily be made into a dispersion in an organic solvent such as N-methylpyrrolidone, acetone, etc. The particles of the present disclosure may also be used as a powder composition.

[0168] The present invention will be described in detail below with reference to examples. Examples 1 and 4 are working examples, and Examples 2 and 3 are comparative examples. However, the present invention is not limited to these examples.

[0169] [Measurement and Evaluation Methods] Various measurement and evaluation methods are as follows.

[0170] <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.

[0171] <Average Particle Diameter of Particles in Liquid> The stock solution 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 size of the obtained sample was measured using a laser diffraction / scattering particle size distribution analyzer (Otsuka Electronics Co., Ltd., ELSZ) with an accumulation number set to 100, and measurement was initiated. D50 was calculated from particle diameters measured in the range of 1 to 300 nm, and this was used as the average particle diameter of the particles in the stock solution. When the average particle diameter of particles in an aqueous dispersion corresponding to the stock solution was measured using the same method as for the stock solution, it was found to be identical to the average particle diameter of the particles in the stock solution. Here, the aqueous dispersion corresponding to the stock solution refers to aqueous dispersion A1 corresponding to stock solution T2 in Example 1 described below. In Example 4 described below, it refers to aqueous dispersion A2 corresponding to stock solution T2. The average particle size (D50) of particles in each aqueous dispersion obtained using an aqueous dispersion corresponding to the raw material liquid was measured using a laser diffraction / scattering particle size distribution analyzer (ELSZ, Otsuka Electronics Co., Ltd.). However, the range of particle sizes to be measured was not limited, unlike the method for measuring the average particle size of particles in the raw material liquid. Here, the aqueous dispersion obtained using an aqueous dispersion corresponding to the raw material liquid in each example means aqueous dispersion 1 obtained using aqueous dispersion A1 in Example 1 described below, and aqueous dispersion 4 obtained using aqueous dispersion A2 in Example 4.

[0172] <Average particle size of particles after drying> The aqueous dispersion containing the second fluoropolymer obtained in each example was coagulated, filtered, and then dried to obtain particles, which were then photographed with a scanning electron microscope (for example, JSM-IT700HR InTouchScope, manufactured by JEOL Ltd.) The particle sizes of five different particles measured from the obtained SEM image were determined, and the particle sizes were then arithmetically averaged.

[0173] <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 and infrared absorption spectrum analysis.

[0174] <Content of Fluorinated Emulsifier> The content of the fluorinated emulsifier relative to the content of the fluorinated polymer was determined by a method similar to the method for measuring the content of a fluorinated surfactant by liquid chromatography-mass spectrometry described in paragraphs

[0364] to

[0369] of WO 2021 / 045227.

[0175] <Content of compound represented by formula (S1)> The content of the compound represented by formula (S1) relative to the content of the fluoropolymer was calculated by a method using an aqueous dispersion or a powder composition, among the measurement methods using a liquid chromatograph mass spectrometer described in paragraphs

[0710] to

[0720] of WO 2018 / 181904. The apparatus used was an Agilent 1260 series HPLC / 6460S, and the column used was a Cadenza CD-C18 manufactured by Imtakt.

[0176] <Content of compound represented by formula (S2)> The content of the compound represented by formula (S2) relative to the content of the fluoropolymer was calculated by a method using an aqueous dispersion or a powder composition, among the measurement methods using a liquid chromatograph mass spectrometer described in paragraphs

[0721] to

[0732] of WO 2018 / 181904. The apparatus used was an Agilent 1260 series HPLC / 6460S, and the column used was a Cadenza CD-C18 manufactured by Imtakt.

[0177] [Production of Raw Material Solution T1] Ultrapure water (717 g), PMVE (50 g), and TFE (8 g) were charged into a 1.3 L stainless steel pressure reactor, and the temperature was raised to 90°C while stirring at 500 rpm. Next, an aqueous ammonium persulfate solution (3.6 mass%, 5 mL) was added to initiate polymerization. As the polymerization started, the pressure in the reactor decreased, so TFE was added to maintain the pressure constant. When 1 g of TFE had been injected, the reactor was cooled to terminate the polymerization reaction. The gas remaining in the reactor was recovered, and the liquid was then extracted. This liquid was used as raw material solution T1. Raw material solution T1 was freeze-coagulated and then filtered. The resulting fluoropolymer 1A was analyzed by NMR, and the ratio of TFE units to PMVE units was 52 / 48 (molar ratio), and the Tg was -5.9°C.

[0178] [Production of Raw Material Solution T2] To the above raw material solution T1 (490 g) was added Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 20 g). 60 minutes after the start of stirring, the raw material solution was separated from the ion exchange resin by filtration. To the filtered raw material solution was added Purolite A300 (manufactured by Purolite, anion exchange resin, 20 g). 60 minutes after the start of stirring, the raw material solution was separated from the ion exchange resin by filtration to obtain raw material solution T2. ​​In raw material solution T2, particles of fluoropolymer 1A (average particle size 52 nm) were dispersed in an aqueous medium, and the content of fluoropolymer 1A was 0.4 mass% based on the total mass of raw material solution T2.

[0179] Example 1: Ultrapure water (121 g), raw material solution T2 (475 g), and t-BuOMe (0.5 g) were charged into a 1.0 L stainless steel pressure reactor to obtain aqueous dispersion A1. Aqueous dispersion A1 had a pH of 4.7, a viscosity of 1.1 mPa·s, and a thixotropic ratio of 1.0. PPVE (20 g) was added to aqueous dispersion A1, and the mixture was heated to 70°C while stirring at 260 rpm. TFE was injected into the reactor until the pressure reached 1.0 MPaG, and an aqueous solution of ammonium persulfate (APS) (1.9 wt%, 4 mL) was added to initiate polymerization. As polymerization began, the pressure in the reactor decreased, so TFE was added to maintain the pressure constant. When 60 g of TFE had been injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 238 minutes. The gas remaining in the reactor was recovered, and the liquid was then withdrawn. This liquid was designated as aqueous dispersion 1. Aqueous dispersion 1 was a dispersion in which particles containing fluoropolymer 1A (average particle diameter 165 nm) were dispersed in an aqueous medium, and had a solids concentration of 7.0% by mass, a pH of 2.0, and a viscosity of 1.4 mPa s. The obtained particles contained a first perfluoropolymer containing TFE units and PMVE units, and a second fluoropolymer containing TFE units and PPVE units, within the same particles. The ratio of the average particle diameter of the obtained particles to the average particle diameter of the particles of fluoropolymer 1A contained in raw material liquid T2 was 3.2. In aqueous dispersion 1, the content of the fluorine-containing emulsifier relative to the total content of the first perfluoropolymer and the second fluoropolymer was less than 25 ppb by mass. The obtained particles were aggregated and dried to obtain particles 1 (average particle diameter 160 nm). The composition of Particle 1 was calculated using NMR, and the molar ratio of TFE unit / PPVE unit / PMVE unit was 97.5 / 1 / 1.5. The MFR was 6.5 g / 10 min.

[0180] Particle 1 contains a first perfluoropolymer containing TFE units and PMVE units and a second fluoropolymer containing TFE units and PPVE units within the same particle, and the content of the first perfluoropolymer was 96.1% by mass, and the content of the second fluoropolymer was 3.9% by mass.

[0181] In Particle 1, the content of the fluorine-containing emulsifier was less than 25 ppb by mass relative to the total content of the first perfluoropolymer and the second fluoropolymer.

[0182] In particle 1, the content of the compound represented by the above formula (S1) was 250 ppb by mass, and the content of the compound represented by the above formula (S2) was less than 25 ppb by mass, relative to the total content of the first perfluoropolymer and the second fluoropolymer.

[0183] Example 2 Ultrapure water (596 g), PPVE (20 g), and t-BuOMe (0.5 g) were charged into a 1.0 L stainless steel pressure reactor to obtain aqueous dispersion C. Aqueous dispersion C was heated to 70°C while stirring at 260 rpm. TFE was injected into the reactor until the pressure reached 1.0 MPaG, and an aqueous APS solution (1.9 mass%, 4 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 70 g of TFE had been injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 277 minutes. After recovering the gas remaining in the reactor, the liquid was withdrawn, but all of it had aggregated, and it was not possible to obtain an aqueous dispersion in which fluoropolymer particles were dispersed in an aqueous medium.

[0184] <Example 3> Ultrapure water (770 g), PPVE (30 g), and a fluorine-containing emulsifier (C ２ F ５ OCF ２ CF ２ OCF ２Aqueous dispersion D was obtained by charging aqueous dispersion D with ammonium salt of COOH (30% by mass, 16 g) and t-BuOMe (1.2 g). Aqueous dispersion D was heated to 70°C while stirring at 400 rpm. TFE was injected into the reactor until the pressure reached 1.5 MPaG, and an aqueous APS solution (10% by mass, 5 mL) was added to initiate polymerization. As the pressure in the reactor decreased with the initiation of polymerization, TFE was added to maintain the pressure constant. When 120 g of TFE had been injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 54 minutes. The gas remaining in the reactor was recovered, and the liquid was withdrawn. This liquid was designated aqueous dispersion 3. Aqueous dispersion 3 had a solids concentration of 16.0% by mass. The obtained particles were aggregated and dried to obtain particles 3. The composition of particles 3 was calculated using NMR, and the ratio of TFE units to PPVE units was 99 / 1 (molar ratio). The MFR was 2.8 g / 10 min.

[0185] In particles 3, the content of the fluorine-containing emulsifier was 2000 ppb by mass relative to the content of the fluorine-containing polymer having TFE units and PPVE units.

[0186] In particles 3, the content of the compound represented by the above formula (S1) was 1,200 ppb by mass, and the content of the compound represented by the above formula (S2) was less than 25 ppb by mass, relative to the content of the fluoropolymer having TFE units and PPVE units.

[0187] Example 4: Ultrapure water (121 g), raw material solution T2 (475 g), and t-BuOMe (0.5 g) were charged into a 1.0 L stainless steel pressure reactor to obtain aqueous dispersion A2. The aqueous dispersion A2 had a pH of 4.0, a viscosity of 1.1 mPa·s, and a thixotropic ratio of 1.0. PPVE (20 g), PMVE (10 g), and TFE (27 g) were added to aqueous dispersion A2, and the mixture was heated to 70°C while stirring at 260 rpm. An aqueous solution of ammonium persulfate (APS) (1.9% by mass, 4 mL) was added to initiate polymerization. As the pressure in the reactor decreased with the initiation of polymerization, TFE was added to maintain the pressure constant. When 120 g of TFE had been injected, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 380 minutes. The gas remaining in the reactor was recovered, and the liquid was then withdrawn. This liquid was designated as aqueous dispersion 4. Aqueous dispersion 4 was a dispersion in which particles containing fluoropolymer 2A (average particle diameter 220 nm) were dispersed in an aqueous medium, and had a solids concentration of 18% by mass and a viscosity of 1.4 mPa s. The obtained particles contained a first perfluoropolymer containing TFE units and PMVE units and a second fluoropolymer containing TFE units and PPVE units within the same particle. The ratio of the average particle diameter of the obtained particles to the average particle diameter of the fluoropolymer 1A particles contained in the raw material liquid T2 was 4.2. In aqueous dispersion 4, the content of the fluorine-containing emulsifier relative to the total content of the first perfluoropolymer and the second fluoropolymer was less than 25 ppb by mass. The obtained particles were aggregated and dried to obtain particles 4 (average particle diameter 210 nm). The composition of Particle 4 was calculated using NMR, and the molar ratio of TFE unit / PPVE unit / PMVE unit was 97 / 1 / 2.0. The MFR was 12.3 g / 10 min.

[0188] Particle 4 contains a first perfluoropolymer containing TFE units and PMVE units and a second fluoropolymer containing TFE units, PPVE units and PMVE units within the same particle, and the content of the first perfluoropolymer was 98.6% by mass, and the content of the second fluoropolymer was 1.4% by mass.

[0189] Particles 4 had a fluorine-containing emulsifier content of less than 25 ppb by mass based on the total content of the first perfluoropolymer and the second fluoropolymer.

[0190] In particle 4, the content of the compound represented by the above formula (S1) was 98 mass ppb, and the content of the compound represented by the above formula (S2) was less than 25 mass ppb, relative to the total content of the first perfluoropolymer and the second fluoropolymer.

[0191] [Evaluation] (Fluorination Treatment) Particles 1, 3, and 4 were placed in a vacuum oscillatory reactor and heated to 210°C. After evacuation, fluorine gas diluted to 20% by volume with nitrogen gas was introduced. After 2 hours, the atmosphere inside the reactor was thoroughly replaced with nitrogen gas to terminate the fluorination reaction. The fluorinated particles were analyzed, and the number of terminal functional groups was calculated.

[0192] (Main chain carbon number 10 ６ (Number of functional groups per particle) Fluorinated particles 1, 3, and 4 were each press-molded at 340°C to produce a film with a thickness of 200 μm. This film was scanned 16 times using a Fourier transform infrared spectrometer and analyzed to obtain an infrared absorption spectrum. Fluorinated particles 1, 3, and 4 were placed in a vacuum oscillatory reactor and heated to 210°C. After evacuation, fluorine gas diluted to 20% by volume with nitrogen gas was introduced. After 10 hours, the atmosphere inside the reactor was thoroughly replaced with nitrogen gas to terminate the fluorination reaction, and completely fluorinated particles 1, 3, and 4 were obtained. Completely fluorinated particles 1, 3, and 4 were each press-molded at 340°C to produce a completely fluorinated film with a thickness of 200 μm. The completely fluorinated film was scanned 16 times using a Fourier transform infrared spectrometer and analyzed to obtain a base spectrum. From the absorption peaks of specific functional groups appearing in the difference spectrum between the obtained infrared absorption spectrum and the base spectrum, the fluorinated particles 1, 3, and 4 having a main chain carbon number of 10 were identified according to the following formula (A). ６ The number of functional groups per particle, N, was calculated as follows: N = I × K / t (A), where I is absorbance, K is correction coefficient, and t is film thickness (mm).

[0193] Table 2 shows -CF ２The absorption frequency, molar absorption coefficient, and correction factor are shown for specific functional groups such as H. The molar absorption coefficient of a specific functional group is determined from FT-IR measurement data of a low molecular weight model compound.

[0194]

[0195] In the copolymer, -CH ２ CF ２ H, —CH ２ COF, -CH ２ COOH, -CH ２ COOCH ３ and -CH ２ CONH ２ The absorption frequency of -CF is shown in the table. ２ H, -COF, -COOH (free and bonded), -COOCH ３ and -CONH ２ From each absorption frequency, several tens of Kaiser (cm －１ ) becomes lower. For example, the number of -COF becomes lower. ２ Absorption frequency due to COF: 1883 cm －１ The number of functional groups determined from the absorption peak of -CH ２ Absorption frequency due to COF: 1840 cm －１ The number of functional groups is the sum of the number of functional groups determined from the absorption peaks of the

[0196] Both the fluorinated particles 1 and 4 have a main chain carbon number of 10 in the first perfluoropolymer and the second fluoropolymer. ６ The number of functional groups per particle was less than 10. The fluorinated particles 3 were made of a fluorine-containing polymer having a main chain carbon number of 10 and a fluorine-containing polymer having a TFE unit and a PPVE unit. ６ The number of functional groups per molecule was less than 10.

[0197] (Heat Resistance) 2 g of each of the fluorinated particles 1, 3, and 4 was weighed out and heated at 340° C. for 2 hours. The degree of foaming of the sample after heating was visually observed. It was found that all of the fluorinated particles 1, 3, and 4 did not foam upon heating and had excellent heat resistance.

[0198] From the above, it was found that in Examples 1 and 4, a fluorinated copolymer having excellent heat resistance equivalent to that of Example 3 could be obtained without using a fluorinated emulsifier. In Example 2, a fluorinated polymer could not be obtained without using a fluorinated emulsifier.

[0199] The composition of the present disclosure can be obtained without using a fluorine-containing emulsifier, and is extremely useful in cases where the use of a fluorine-containing emulsifier is restricted.

[0200] The disclosures of Japanese Patent Application No. 2023-129555, filed on August 8, 2023, and Japanese Patent Application No. 2024-099098, filed on June 19, 2024, are incorporated herein by reference in their 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 were specifically and individually indicated to be incorporated by reference.

Claims

1. A composition comprising: a first perfluoropolymer having a glass transition temperature of 10°C or lower; and a second fluoropolymer which contains structural units based on tetrafluoroethylene and structural units based on perfluoro(alkyl vinyl ether) and is different from the first perfluoropolymer, wherein the content of structural units based on perfluoro(alkyl vinyl ether) is 0.1 to 10.0 mol% relative to the total content of all structural units of the first perfluoropolymer and the second fluoropolymer.

2. Neither the first perfluoropolymer nor the second fluoropolymer contains a functional group, or the first perfluoropolymer and the second fluoropolymer each have a main chain carbon number of 10 or less. ６ The composition according to claim 1 , wherein the total number of functional groups per unit is less than 100.

3. The composition according to claim 1 or 2, wherein the first perfluoropolymer comprises constitutional units based on tetrafluoroethylene and constitutional units based on perfluoro(alkyl vinyl ether).

4. The composition according to claim 3, wherein in the first perfluoropolymer, the constituent units based on perfluoro(alkyl vinyl ether) account for 20 to 70 mol % of the constituent units based on perfluoro(alkyl vinyl ether) relative to the total of the constituent units based on tetrafluoroethylene and the constituent units based on perfluoro(alkyl vinyl ether).

5. A method for producing a fluoropolymer, comprising the steps of: preparing an aqueous dispersion A containing a first perfluoropolymer having a glass transition temperature of 10°C or lower, and an aqueous medium; and polymerizing a monomer containing tetrafluoroethylene and perfluoro(alkyl vinyl ether) in said aqueous dispersion A to produce a second fluoropolymer different from said first perfluoropolymer, wherein, before polymerization of the monomers is started, the content of said first perfluoropolymer is 0.01 to 4.0 mass% based on the total mass of said aqueous dispersion A; and, before polymerization of the monomers is started, said aqueous dispersion A does not contain a fluorine-containing emulsifier, or the content of said fluorine-containing emulsifier is 100 ppm by mass or less based on the total mass of said aqueous dispersion A.

6. The process for producing a fluorine-containing polymer according to claim 5, wherein the amount of said monomer used is 1 to 50 parts by mass per 100 parts by mass of said aqueous medium used.

7. A method for producing a fluoropolymer according to claim 5 or 6, wherein the step of preparing the aqueous dispersion A is a step of preparing an aqueous dispersion A containing particles of the first perfluoropolymer and an aqueous medium, the step of producing the second fluoropolymer is a step of polymerizing the monomer to produce a second fluoropolymer different from the first perfluoropolymer and producing particles containing the first perfluoropolymer and the second fluoropolymer, and the ratio of the average particle size of the particles containing the first perfluoropolymer and the second fluoropolymer to the average particle size of the particles of the first perfluoropolymer is 2 or more.

8. The process for producing a fluorine-containing polymer according to claim 5 or 6, wherein the viscosity of the aqueous dispersion A is 2.0 mPa·s or less.

9. The process for producing a fluorine-containing polymer according to claim 5 or 6, wherein the thixotropy ratio of said aqueous dispersion A is from 0.9 to 1.

2.

10. The process for producing a fluorine-containing polymer according to claim 5 or 6, wherein the monomers are polymerized in the presence of a polymerization initiator.

11. The method for producing a fluorine-containing polymer according to claim 5 or 6, further comprising a step of subjecting said first perfluoropolymer and said second fluoropolymer to a fluorination treatment.

12. An aqueous dispersion comprising an aqueous medium and melt-formable particles, wherein the average particle size of the particles is 1 μm or less, the particles comprise one or more types of fluorine-containing polymer, the fluorine-containing polymer comprises units based on tetrafluoroethylene and structural units based on perfluoro(alkyl vinyl ether), the content of the structural units based on perfluoro(alkyl vinyl ether) is 0.1 to 10.0 mol % based on all structural units of the fluorine-containing polymer, the content of the particles is 1 to 50 mass % based on the total mass of the aqueous dispersion, and the aqueous dispersion does not contain a fluorine-containing emulsifier or the content of the fluorine-containing emulsifier is 100 ppm by mass or less based on the content of the fluorine-containing polymer.

13. The aqueous dispersion according to claim 12, having a viscosity of 0.8 to 2.0 mPa·s.

14. A melt-moldable particle, the average particle size of the particle being 1 μm or less, the particle comprising one or more kinds of fluorine-containing polymer, the fluorine-containing polymer comprising structural units based on tetrafluoroethylene and structural units based on perfluoro(alkyl vinyl ether), the content of the structural units based on perfluoro(alkyl vinyl ether) being 0.1 to 10.0 mol % based on all structural units of the fluorine-containing polymer, the particle comprising no fluorine-containing emulsifier or the content of the fluorine-containing emulsifier being 100 ppm by mass or less based on the content of the fluorine-containing polymer, the content of the compound represented by formula (S1) being 1 to 10,000 ppb by mass and the content of the compound represented by formula (S2) being 100 ppb by mass or less based on the fluorine-containing polymer. Formula (S1): H-(CF ２ ) ｎ -COOM Formula (S2): H-(CF ２ ) ｍ -SO ３ In formula (S1) and formula (S2), M is independently a hydrogen atom, Na, K, or NH ４ wherein n is an integer of 7 to 11, and m is an integer of 8 to 12.

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