Method for producing aqueous dispersion

Abstract

A method for producing an aqueous dispersion, wherein a first monomer, which includes at least one selected from the group consisting of tetrafluoroethylene and hexafluoropropylene, is polymerized in the presence of a compound represented by formula (X) and a polymerization initiator under conditions in which an aqueous medium is present and an emulsifier having a fluorine atom is substantially absent, to produce a first aqueous dispersion containing particles of a first fluorine-containing polymer, and a second monomer including tetrafluoroethylene is polymerized in the first aqueous dispersion to produce a second aqueous dispersion containing particles of a second fluorine-containing polymer different from the first fluorine-containing polymer.　(X): C(X1)(X2)=C(X3)CONH-R-Z

Description

Method for producing aqueous dispersion

[0001] The present disclosure relates to a method for making an aqueous dispersion.

[0002] Fluorine-containing polymers are used in various industrial fields due to their excellent heat resistance, chemical resistance, flame retardancy, weather resistance, etc. When producing such fluorine-containing polymers, an aqueous dispersion containing fluorine-containing polymer particles may be used. As a method for producing an aqueous dispersion, Patent Document 1 discloses a method of polymerizing a fluorine-containing monomer in the presence of a specific compound.

[0003] International Publication No. 2022 / 019241

[0004] It has been found that the number of particles of the fluoropolymer produced by the method for producing an aqueous dispersion of Patent Document 1 is small, and there is room for improvement. Furthermore, from the viewpoint of reducing the environmental load, it is desirable to substantially not use an emulsifier having a fluorine atom.

[0005] An object of the present disclosure is to provide a method for producing an aqueous dispersion that can produce an aqueous dispersion containing a large number of fluorine-containing polymer particles without substantially using an emulsifier having fluorine atoms.

[0006] As a result of intensive research into the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by the following configuration: [1] A method for producing an aqueous dispersion, comprising: polymerizing a first monomer containing at least one selected from the group consisting of tetrafluoroethylene and hexafluoropropylene in the presence of a compound represented by formula (X) described below and a polymerization initiator in the presence of an aqueous medium and substantially in the absence of an emulsifier having a fluorine atom, to produce a first aqueous dispersion containing particles of a first fluorine-containing polymer; and polymerizing a second monomer containing tetrafluoroethylene in the first aqueous dispersion to produce a second aqueous dispersion containing particles of a second fluorine-containing polymer different from the first fluorine-containing polymer. [2] A method for producing an aqueous dispersion, comprising: polymerizing a first monomer containing at least one selected from the group consisting of tetrafluoroethylene and hexafluoropropylene in the presence of an aqueous medium and substantially in the absence of an emulsifier having a fluorine atom, to produce a first aqueous dispersion containing particles of a first fluorine-containing polymer; and polymerizing a second monomer containing tetrafluoroethylene in the first aqueous dispersion. ３[3] The method for producing an aqueous dispersion according to [1], wherein the compound represented by formula (X) is 1.0 to 1000 ppm by mass relative to the total mass of the aqueous medium. [4] The method for producing an aqueous dispersion according to any one of [1] to [3], wherein the first monomer comprises perfluoro(alkyl vinyl ether). [5] The method for producing an aqueous dispersion according to any one of [1] to [4], wherein the first monomer comprises at least one selected from the group consisting of propylene and vinylidene fluoride. [6] The method for producing an aqueous dispersion according to any one of [1] to [4], wherein the number of particles of the first fluorine-containing polymer is 2.0 × 10 １３ [7] The method for producing an aqueous dispersion according to any one of [1] to [5], wherein the number of particles of the second fluorine-containing polymer is 2.0 × 10 particles / mL or more. １３ [8] The method for producing an aqueous dispersion according to any one of [1] to [7], wherein the polymerization rate of the second monomer is 29 g / L / h or more.

[0007] According to the present disclosure, it is possible to provide a method for producing an aqueous dispersion, which can produce an aqueous dispersion having a large number of fluorine-containing polymer particles without substantially using an emulsifier having a fluorine atom.

[0008] The meanings of terms used in this disclosure are as follows. A numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the upper and lower limits. In numerical ranges described in this specification in stages, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another staged numerical range. Furthermore, in numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the Examples. In this specification, each component may be used alone or in combination with two or more substances corresponding to the component. Herein, when two or more substances are used in combination for each component, the content of that component refers to the total content of the substances used in combination, unless otherwise specified. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment. A "unit" is a collective term for an atomic group derived from one molecule of the monomer that is formed directly by polymerization of the monomer, and an atomic group obtained by chemically converting a portion of the atomic group. Hereinafter, a "unit based on a monomer" will also be simply referred to as a "unit." The content (mass % or mol %) of each unit relative to all units contained in the polymer is determined by analyzing the polymer by solid-state nuclear magnetic resonance spectroscopy (NMR), and usually, the content of each unit calculated from the amount of each monomer added substantially coincides with the actual content of each unit.

[0009] [Method for producing aqueous dispersion] The method for producing an aqueous dispersion of the present disclosure (hereinafter also referred to as "the present production method") is a method for producing an aqueous dispersion, comprising polymerizing a first monomer containing at least one selected from the group consisting of tetrafluoroethylene and hexafluoropropylene in the presence of a compound represented by formula (X) described below and a polymerization initiator in the presence of an aqueous medium and in the substantial absence of an emulsifier having a fluorine atom, to produce a first aqueous dispersion containing particles of a first fluorine-containing polymer, and polymerizing a second monomer containing tetrafluoroethylene in the first aqueous dispersion to produce a second aqueous dispersion containing particles of a second fluorine-containing polymer different from the first fluorine-containing polymer. Hereinafter, the step of polymerizing a first monomer containing tetrafluoroethylene in the presence of a compound represented by formula (X) described below and a polymerization initiator in the presence of an aqueous medium and substantially no emulsifier having a fluorine atom to produce a first aqueous dispersion containing particles of a first fluorine-containing polymer will be referred to as "step 1," and the step of polymerizing a second monomer containing tetrafluoroethylene in the first aqueous dispersion obtained in step 1 to produce a second aqueous dispersion containing particles of a second fluorine-containing polymer different from the first fluorine-containing polymer will be referred to as "step 2."

[0010] The present production method can provide an aqueous dispersion containing a large number of fluoropolymer particles. The reason why the present production method can provide a large number of fluoropolymer particles without requiring an emulsifier containing fluorine atoms is that the use of compound X improves the dispersibility of the first fluoropolymer particles, thereby increasing the number of first fluoropolymer particles that can function as polymerization sites for the second monomer. One factor contributing to the improved dispersibility is thought to be the improvement in the zeta potential of the first fluoropolymer caused by compound X. Another factor considered to be the improvement in dispersibility is that polymerizing the second fluoropolymer using particles polymerized in the presence of compound X also improves the dispersibility of the second fluoropolymer particles. It has also been found that, when the second monomer is polymerized using an aqueous dispersion containing particles of a first fluoropolymer having a large particle number, the greater the number of first fluoropolymer particles, the faster the polymerization rate of the second monomer tends to be. Therefore, it is desirable to increase the number of particles of the first fluoropolymer. Hereinafter, an increase in the number of particles of the resulting fluoropolymer will also be referred to as the "effect of the present disclosure."

[0011] [Step 1] <Emulsifier> Step 1 of the present production method is carried out under conditions in which an emulsifier having a fluorine atom is substantially absent. "Substantially absent" means that, in the production of the first aqueous dispersion, the content of the emulsifier having a fluorine atom is 10 ppm by mass or less, preferably 150 ppb by mass or less, more preferably 50 ppb by mass or less, relative to the total mass of the aqueous medium, and the lower limit is 0 ppb by mass. The present production method is preferably carried out under conditions in which an emulsifier having a fluorine atom and an emulsifier not having a fluorine atom are substantially absent, in order to prevent a decrease in the molecular weight of the produced fluoropolymer. "Substantially absent" means that, in the production of the first aqueous dispersion, the content of the emulsifier is 10 ppm by mass or less, preferably 150 ppb by mass or less, more preferably 50 ppb by mass or less, relative to the total mass of the aqueous medium, and the lower limit is 0 ppb by mass. The lower limit is 0 ppb by mass. The content of various emulsifiers can be measured using a liquid chromatograph mass spectrometer. Specifically, the measurement method described in paragraphs

[0721] to

[0732] of WO 2018 / 181904 can be used.

[0012] Examples of the emulsifier having a fluorine atom and the emulsifier not having a fluorine atom include water-soluble emulsifiers. A water-soluble emulsifier means an emulsifier having a solubility of 100 mg or more in 1000 g of water at 25°C, and a water-insoluble emulsifier means an emulsifier other than the above-mentioned water-soluble emulsifiers. The water-soluble emulsifier may be either ionic or non-ionic. Examples of the emulsifier having a fluorine atom and the emulsifier not having a fluorine atom include those not having a carbon-carbon double bond. The first fluorine-containing polymer described below and the second fluorine-containing polymer described below are both water-insoluble. Furthermore, compound X described below, the first fluorine-containing polymer described below, and the second fluorine-containing polymer described below do not all fall under the category of emulsifiers.

[0013] Examples of emulsifiers having fluorine atoms include anionic fluorine-containing emulsifiers. Examples of anionic fluorine-containing emulsifiers include emulsifiers containing fluorine atoms whose total carbon number excluding anionic groups is 20 or less, and emulsifiers containing fluorine atoms whose anionic moiety has a molecular weight of 800 or less. The above-mentioned "anionic moiety" means the moiety excluding the cation of the fluorine-containing emulsifier.

[0014] The fluorine-free emulsifier is an emulsifier that does not contain fluorine atoms and has a hydrocarbon group such as an alkyl group as a hydrophobic moiety. It is also possible to substitute a hydrogen atom of the hydrocarbon group of the fluorine-free emulsifier with a halogen atom other than a fluorine atom.

[0015] The emulsifiers having no fluorine atoms include anionic hydrocarbon emulsifiers and nonionic hydrocarbon emulsifiers.

[0016] Anionic hydrocarbon emulsifiers refer to emulsifiers having a negatively charged hydrophilic moiety, such as a carboxylic acid group, a sulfonic acid group, a sulfate group, a phosphonic acid group, or a phosphate group, and a hydrocarbon group, such as an alkyl group, as a hydrophobic moiety. Specific examples of anionic hydrocarbon emulsifiers include sodium dodecyl sulfate, highly branched C10 tertiary carboxylic acid supplied by Resolution Performance Products as Versatic® 10, linear alkyl polyethersulfonate sodium supplied by BASF as the Avanel® S series, and sulfosuccinate emulsifier Lankropol® K8300 available from AkzoNobelSurfaceChemistry LLC.

[0017] Nonionic hydrocarbon emulsifiers are emulsifiers that exhibit surface activity in water without dissociating into ions and have hydrocarbon groups such as alkyl groups as their hydrophobic moieties. The hydrophilic moieties of nonionic hydrocarbon emulsifiers include water-soluble functional groups such as polyethylene oxide chains obtained from the polymerization of ethylene oxide. Nonionic hydrocarbon emulsifiers include polyalkylene oxide block copolymers, such as block copolymers having polyethylene oxide and polypropylene oxide.

[0018] Further, other nonionic hydrocarbon emulsifiers include those described in paragraphs

[0043] to

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

[0019] The emulsifier with fluorine atom and the emulsifier without fluorine atom can contain silicon atom.The emulsifier with silicon atom can include siloxane emulsifier.Siloxane emulsifier is a hydrocarbon-containing emulsifier with siloxane skeleton.The siloxane emulsifier can include the emulsifier described in U.S. Patent No. 6,841,616 (Wille et al.) and U.S. Patent No. 7,977,438 (Brothers et al.).

[0020] The emulsifier having a fluorine atom and the emulsifier not having a fluorine atom may be a polymer emulsifier. Examples of the polymer emulsifier include a polymer having a hydrophilic group in a side chain. Examples of such a polymer emulsifier include a polymer containing a unit based on a compound having a site capable of polymerization reaction and a hydrophilic group. Further, even if the polymer does not originally have a hydrophilic group, a polymer containing a unit based on a compound having a group that can become a hydrophilic group and subjected to post-treatment such as hydrolysis may also be used.

[0021] When the first monomer is polymerized in the presence of an emulsifier having no fluorine atoms, typically, 0.1 to 15 parts by mass of the emulsifier having no fluorine atoms is used per 100 parts by mass of the aqueous medium.

[0022] <Aqueous Medium> The present production method is carried out in the presence of an aqueous medium. Specific examples of the aqueous medium include water and a mixed solvent of water and a water-soluble organic solvent. Specific examples of the water-soluble organic solvent include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol.

[0023] Before the polymerization of the first monomer is initiated, the content of the aqueous medium is preferably 20 to 80% by volume, and more preferably 40 to 70% by volume, relative to the volume of the reactor. In this specification, "before the polymerization of the first monomer is initiated" means immediately before the initiation of polymerization. Here, examples of the "initiation of polymerization" include the time when the first monomer is placed in the reactor and the temperature is raised to or above the polymerization temperature, the time when the first monomer and the polymerization initiator are allowed to coexist in the reactor after the reactor is heated to or above the polymerization temperature, and the time when the temperature of the reactor is raised to or above the polymerization temperature after the first monomer and the polymerization initiator are allowed to coexist in the reactor.

[0024] <Compound X> Compound X is used in the present production method. Compound X can be polymerized together with a first monomer described below. By using compound X having --CONH--, the dispersibility of the first fluoropolymer particles and the second fluoropolymer particles is improved as described above, and the number of first fluoropolymer particles and second fluoropolymer particles increases. Compound X is a compound represented by formula (X).

[0025] C(X １ ) (X ２ ) = C(X ３ ) CONH-R-Z (X) In formula (X), １ , X ２ and X ３ are each independently a hydrogen atom, a fluorine atom, a perfluoromethyl group or an alkyl group, R is an alkylene group having 1 to 6 carbon atoms or a fluoroalkylene group having 1 to 6 carbon atoms, Z is -SO ３ M, -OSO ３ M, -P (=O) (OM) ２ , -OP(=O)(OM) ２ or -COOM, where M is a hydrogen atom, a metal atom, N(RＭ１ ) ４ or P(R Ｍ２ ) ４ When a plurality of M's are present, the plurality of M's may be the same or different from each other, R Ｍ１ and R Ｍ２ are each independently a hydrogen atom or a substituent, and R Ｍ１ Any two of R may be bonded to each other to form a ring, and multiple R Ｍ１ may be the same or different from each other, R Ｍ２ Any two of R may be bonded to each other to form a ring, and multiple R Ｍ２ may be the same or different from each other.

[0026] X １ , X ２ and X ３ are each independently a fluorine atom, a perfluoromethyl group, a hydrogen atom, or an alkyl group. The alkyl group may be linear, branched, or cyclic. The alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 3 carbon atoms, and even more preferably 1. X １ , X ２ and X ３ As the alkyl group, a fluorine atom or a hydrogen atom is preferred, and a hydrogen atom is preferred in terms of excellent polymerization reactivity.

[0027] R is an alkylene group having 1 to 6 carbon atoms or a fluoroalkylene group having 1 to 6 carbon atoms. The alkylene group or the fluoroalkylene group may be linear, branched, or cyclic, and is preferably branched. The alkylene group or the fluoroalkylene group has 1 to 6 carbon atoms, preferably 2 to 4 carbon atoms, and more preferably 4 carbon atoms. R is preferably an alkylene group having 1 to 6 carbon atoms.

[0028] Z is -SO ３ M, -OSO ３ M, -P (=O) (OM) ２ , -OP(=O)(OM) ２ or -COOM. Z is -SO ３ M is preferred, and —SO ３ Na is more preferred.３ When it is M, the latex tends to be more stable and the number of particles of the first fluorine-containing polymer increases.

[0029] M is a hydrogen atom, a metal atom, N(R Ｍ１ ) ４ or P(R Ｍ２ ) ４ and R Ｍ１ and R Ｍ２ are each independently a hydrogen atom or a substituent. The metal atom represented by M is preferably a metal atom of Group 1, more preferably Li, Na or K. Ｍ１ and R Ｍ２ The substituent represented by the formula (I) is preferably a monovalent organic group, more preferably a monovalent hydrocarbon group, and even more preferably an alkyl group or an aromatic hydrocarbon group. The substituent preferably has 1 to 10 carbon atoms. The alkyl group may be linear, branched, or cyclic. The aromatic hydrocarbon group may be monocyclic or polycyclic. The aromatic hydrocarbon group is preferably a phenyl group.

[0030] Specific examples of compound X include 2-acrylamido-2-methyl-1-propanesulfonic acid, N-tigloylglycine, 6-acrylamidohexanoic acid, 1,1-difluoro-2-methyl-2-[(1-oxo-2-propen-1-yl)amino]-1-propanesulfonic acid, 3-methyl-3-[(2-methyl-1-oxo-2-propen-1-yl)amino]-2-butanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, 2,3-dimethyl-3-[(1-oxo-2-propen-1-yl)amino]-2-butanesulfonic acid, and metal salts thereof. Examples of the metal salts include metal salts of the metal atom represented by M. As compound X, (meth)acrylamides having a sulfonic acid group and metal salts thereof are preferred, and 2-acrylamido-2-methyl-1-propanesulfonic acid, sodium 2-acrylamido-2-methyl-1-propanesulfonate (hereinafter also referred to as NaAAMPS), 2-methacrylamido-2-methyl-1-propanesulfonic acid, or sodium 2-methacrylamido-2-methyl-1-propanesulfonate are preferred. Note that the above-mentioned "(meth)acrylamide" is a concept that encompasses both acrylamide and methacrylamide.

[0031] Before starting polymerization of the first monomer, the content of compound X is preferably 1.0 to 1000 ppm by mass, and in terms of achieving better effects of the present disclosure, is more preferably 1.0 to 800 ppm by mass, even more preferably 3.0 to 500 ppm by mass, and particularly preferably 5.0 to 300 ppm by mass, relative to the total mass of the aqueous medium.

[0032] <Polymerization initiator> The polymerization initiator used in the present production method is preferably a water-soluble polymerization initiator, and more preferably an organic polymerization initiator such as a persulfate such as ammonium persulfate, sodium persulfate, or potassium persulfate, disuccinic acid peroxide, or azobisisobutylamidine dihydrochloride.

[0033] The amount of the polymerization initiator used is preferably 0.01 to 10 parts by mass, more preferably 0.01 to 8 parts by mass, and even more preferably 0.01 to 5 parts by mass, relative to 100 parts by mass of the first monomer used.

[0034] <First Monomer> The first monomer used in the present production method includes at least one selected from the group consisting of tetrafluoroethylene (hereinafter also referred to as "TFE") and hexafluoropropylene (hereinafter also referred to as "HFP"). The first monomer may include a monomer other than TFE and HFP, and preferably includes a monomer other than TFE and HFP. Examples of the monomer other than TFE and HFP include perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE"), propylene, vinylidene fluoride (hereinafter also referred to as "VdF"), CH ２ =CF-CF ２ -O-Rf-COOH, CH ２ =CF-CF ２ —O—Rf—SO ３ H, C.F. ２ =CF-CF ２ -O-Rf-COOH, CF ２ =CF-CF ２ —O—Rf—SO ３ H, CH ２ =CF-O-Rf-COOH, CH ２ =CF-O-Rf-SO ３ H, C.F. ２ ═CF—O—Rf-COOH and CF ２ =CF-O-Rf-SO ３ H (Rf represents a perfluoroalkyl group having 1 to 10 carbon atoms, and the perfluoroalkyl group may have an etheric oxygen atom between the carbon atoms). When the first monomer contains TFE, the amount of TFE used is preferably 10 to 90 mol%, more preferably 30 to 85 mol%, and even more preferably 40 to 80 mol%, relative to the amount of the first monomer used. When the first monomer contains HFP, the amount of HFP used is preferably 30 to 95 mol%, more preferably 40 to 90 mol%, and even more preferably 50 to 85 mol%, relative to the amount of the first monomer used.

[0035] From the viewpoint of excellent polymerization reactivity of the first fluoropolymer and of more excellent effects of the present disclosure, the first monomer preferably contains PAVE. PAVE is preferably a monomer represented by formula (1) from the viewpoint of excellent polymerization reactivity in producing the first fluoropolymer and of more efficiently producing the second fluoropolymer.

[0036] CF ２ =CF-O-R ｆ１ (1) In formula (1), R ｆ１ is 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.

[0037] 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"), and from the viewpoint of enabling more efficient production of the second fluorinated polymer, PMVE or PPVE is preferred, and PMVE is more preferred.

[0038] When the first monomer contains PAVE, the amount of PAVE used is preferably 15 to 95 mol %, more preferably 20 to 80 mol %, and even more preferably 25 to 60 mol %, based on the amount of the first monomer used. The suitable amount is the same whether the PAVE is PMVE, PEVE, or PPVE, or a mixture of two or more of these.

[0039] In view of the excellent polymerization reactivity of the first fluoropolymer and the excellent effects of the present disclosure, it is also preferable that the first monomer contains at least one selected from the group consisting of propylene and VdF.

[0040] When the first monomer contains propylene, the amount of propylene used is preferably 5 to 90 mol %, more preferably 8 to 70 mol %, and even more preferably 10 to 60 mol %, relative to the amount of the first monomer used. When the first monomer contains VdF, the amount of VdF used is preferably 5 to 90 mol %, more preferably 8 to 80 mol %, and even more preferably 10 to 70 mol %, relative to the amount of the first monomer used.

[0041] The first monomer preferably includes any combination of TFE and PAVE, TFE and propylene, or HFP and VdF. When the first monomer includes TFE and PAVE, the amount of PAVE used is preferably 20 to 95 mol%, more preferably 25 to 80 mol%, and even more preferably 30 to 60 mol%, based on the total amount of TFE and PAVE used. When the first monomer includes TFE and PAVE, the total amount of TFE and PAVE used is preferably 99.0 to 100.0 mol%, more preferably 99.5 to 100.0 mol%, and even more preferably 99.9 to 100.0 mol%, based on the total amount of the first monomer used. When the first monomer includes TFE and propylene, the amount of propylene used is preferably 5 to 90 mol%, more preferably 8 to 70 mol%, and even more preferably 10 to 60 mol%, based on the total amount of TFE and propylene used. When the first monomer comprises TFE and propylene, the total amount of TFE and propylene used is preferably 99.0 to 100.0 mol%, more preferably 99.5 to 100.0 mol%, and even more preferably 99.9 to 100.0 mol%, based on the amount of the first monomer used. When the first monomer comprises HFP and VdF, the total amount of VdF used is preferably 5 to 90 mol%, more preferably 8 to 80 mol%, and even more preferably 10 to 70 mol%, based on the total amount of HFP and VdF used. When the first monomer comprises HFP and VdF, the total amount of HFP and VdF used is preferably 99.0 to 100.0 mol%, more preferably 99.5 to 100.0 mol%, and even more preferably 99.9 to 100.0 mol%, based on the amount of the first monomer used.

[0042] The first monomer may contain other monomers than those mentioned above, or may be substantially free of other monomers from the viewpoint of more efficiently producing the second fluorine-containing polymer. "Substantially free of other monomers" means that the amount of other monomers used is 0.01 mol % or less, preferably 0 mol %, based on the amount of the first monomer used.

[0043] <Step> The method for producing the first aqueous dispersion is not particularly limited, as long as it is a method of polymerizing a first monomer containing at least one selected from the group consisting of TFE and HFP using compound X and a polymerization initiator under conditions in which an aqueous medium is present and an emulsifier having a fluorine atom is substantially absent. Examples of the method include a method in which a solution containing an aqueous medium and compound X is prepared, and the first monomer is polymerized using this solution and a polymerization initiator. More specifically, a method in which the solution and the first monomer are added to a reactor, the reactor is heated, and a polymerization initiator is added to the reactor to polymerize the first monomer is exemplified. Polymerization of the first monomer results in a first fluorine-containing polymer dispersed in the aqueous medium in the form of particles. The aqueous dispersion thus obtained in which particles of the first fluorine-containing polymer are dispersed may be used as the first aqueous dispersion, or another aqueous medium or the like may be added to make this the first aqueous dispersion. Alternatively, solvent substitution may be performed to disperse particles of the first fluorine-containing polymer in another aqueous medium, and this may be used as the first aqueous dispersion.

[0044] The first monomer is charged into the reactor by a conventional method. For example, the first monomer may be charged into the reactor continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. Alternatively, the first monomer may be dispersed in an aqueous medium, and the resulting solution may be charged into the reactor continuously or intermittently. When a polymerization initiator is used, the polymerization initiator may be added to the reactor all at once or in portions.

[0045] The polymerization temperature is preferably 10 to 95° C., more preferably 15 to 90° C. The polymerization pressure is preferably 0.1 to 4.0 MPaG, more preferably 0.2 to 3.5 MPaG. The polymerization time is preferably 10 to 1,000 minutes, more preferably 30 to 700 minutes.

[0046] (First aqueous dispersion) Step 1 provides a first aqueous dispersion in which a first fluorine-containing polymer is dispersed in an aqueous medium. The first aqueous dispersion preferably does not substantially contain a water-soluble emulsifier. The water-soluble emulsifier is as described above. "Substantially not containing a water-soluble emulsifier" means that the content of the water-soluble emulsifier is 10 mass ppm or less, more preferably 150 mass ppb or less, and even more preferably 50 mass ppb or less, relative to the total mass of the first aqueous dispersion. The lower limit is 0 mass ppb.

[0047] Furthermore, it is preferable that the first aqueous dispersion is substantially free of a compound represented by any one of formulas (S1) to (S4). "Substantially free of a compound represented by any one of formulas (S1) to (S4)" means that the content of each of the compounds represented by formulas (S1) to (S4) is 10 ppm by mass or less, preferably 5 ppm by mass or less, more preferably 150 ppb by mass or less, and even more preferably 50 ppb by mass or less, relative to the total mass of the aqueous dispersion. The lower limit is 0 ppb by mass. When no emulsifier is used during the production of the first fluorinated polymer contained in the first aqueous dispersion, the amount of the compound represented by any one of formulas (S1) to (S4) generated can be suppressed, making it easier to adjust the content of these compounds.

[0048] H-(CF ２ ) ｎ１ -COOM Ｓ (S1) H-(CF ２ ) ｎ２ -SO ３ M Ｓ (S2) F-(CF ２ ) ｎ１ -COOM Ｓ (S3) F-(CF ２ ) ｎ２ -SO ３ M Ｓ (S4) In the formulas (S1) to (S4), n1 is an integer of 3 to 13, 15, or 17, n2 is an integer of 4 to 10, or 12, and M Ｓ is a hydrogen atom, Na, K, or NH ４ is.

[0049] The solid content concentration of the first aqueous dispersion is preferably 0.01 to 30% by mass, and more preferably 0.01 to 20% by mass. The solid content concentration of the first aqueous dispersion can be measured, for example, by the following method. The solid content concentration of the first aqueous dispersion is calculated by heating 2.0 g of the first aqueous dispersion at 170°C for 20 minutes, weighing the mass of the residue, and determining the solid content concentration using the following formula: "Solid content concentration (mass %) = 100 × heating residue of first aqueous dispersion (g) / mass of first aqueous dispersion (2.0 g)"

[0050] (First fluorine-containing polymer) By polymerization of the first monomer, a first fluorine-containing polymer dispersed in the form of particles in an aqueous medium is obtained.It is presumed that the particles of the first fluorine-containing polymer adsorb and incorporate the second monomer at the hydrophobic part during polymerization of the second monomer described below, thereby solubilizing the second monomer and facilitating polymerization of the second monomer even when the particles do not substantially contain an emulsifier having a fluorine atom.It should be noted that the first fluorine-containing polymer is a polymer different from the second fluorine-containing polymer described below.

[0051] The average particle size of the particles of the first fluorine-containing polymer is preferably 500 nm or less, and from the viewpoint of particle dispersion stability, more preferably 300 nm or less, even more preferably 200 nm or less, particularly preferably 150 nm or less. The lower limit is preferably 2 nm or more, more preferably 5 nm or more, and even more preferably 10 nm or more. As the average particle size of the particles of the first fluorine-containing polymer, a particle size calculated by analyzing the autocorrelation function obtained by dynamic light scattering using the monodisperse cumulant method or D50 (median diameter) can be used. The above D50 is the particle size at the point on the cumulative curve where the cumulative volume is 50% when the particle size distribution is measured by laser diffraction / scattering and the total volume of the particle group is taken as 100%. As a specific method for measuring the average particle size, the method described in the Examples below can be used.

[0052] The number of particles of the first fluorine-containing polymer is 2.0 × 10 １３ Preferably, the number of particles / mL or more is 1.0 x 10 １４ 2.0 × 10 １４ The upper limit is preferably 10.0 × 10 １５In many cases, the particle number of the first fluoropolymer is the number of particles per mL of the first aqueous dispersion. Examples of a method for measuring the particle number include the measurement methods shown in the Examples section.

[0053] The first fluorine-containing polymer has units based on a first monomer. The first fluorine-containing polymer contains at least one unit selected from the group consisting of units based on TFE (hereinafter also referred to as "TFE units") and units based on HFP (hereinafter "HFP units").

[0054] The first fluorine-containing polymer preferably contains units other than TFE units and HFP units. Examples of the units other than TFE units and HFP units include units based on monomers other than TFE and HFP exemplified as the first monomer, and preferred are units based on PAVE (hereinafter also referred to as "PAVE units"), units based on propylene (hereinafter also referred to as "P units"), or units based on VdF (hereinafter also referred to as "VdF units"). When TFE units are contained, the content of TFE units is preferably 10 to 80 mol%, more preferably 30 to 70 mol%, and even more preferably 40 to 60 mol%, based on all units of the first fluorine-containing polymer. When HFP units are contained, the content of HFP units is preferably 10 to 80 mol%, more preferably 15 to 70 mol%, and even more preferably 20 to 60 mol%, based on all units of the first fluorine-containing polymer.

[0055] In this specification, when there is only one type of first fluorine-containing polymer, "all units of the first fluorine-containing polymer" means all units contained in that one type of first fluorine-containing polymer. When there are two or more types of first fluorine-containing polymers, "all units of the first fluorine-containing polymer" means all units contained in the two or more types of first fluorine-containing polymers. The above also applies to other fluorine-containing polymers.

[0056] The first fluoropolymer preferably contains PAVE units. Details of the PAVE from which the PAVE units are derived are the same as those of the PAVE in the production method of the present invention described above, and preferred embodiments are also the same. When the first fluoropolymer contains PAVE units, the content of PAVE units is preferably 15 to 95 mol%, more preferably 20 to 80 mol%, and even more preferably 25 to 60 mol%, based on the total units of the first fluoropolymer. When the PAVE is PMVE, PEVE or PPVE, or when a mixture of two or more of these is used, the preferred amount used is the same.

[0057] It is also preferable that the first fluorine-containing polymer contains at least one selected from the group consisting of P units and VdF units. When the first fluorine-containing polymer contains P units, the content of P units is preferably 20 to 90 mol%, more preferably 25 to 80 mol%, and even more preferably 30 to 70 mol%, based on all units of the first fluorine-containing polymer. When the first fluorine-containing polymer contains VdF units, the content of VdF units is preferably 20 to 90 mol%, more preferably 25 to 80 mol%, and even more preferably 30 to 70 mol%, based on all units of the first fluorine-containing polymer.

[0058] The first fluorine-containing polymer preferably contains any combination of TFE units and PAVE units, TFE units and P units, and HFP units and VdF units. When the first fluorine-containing polymer contains TFE units and PAVE units, the content of PAVE units is preferably 20 to 95 mol%, more preferably 25 to 80 mol%, and even more preferably 30 to 60 mol%, based on the total amount of TFE units and PAVE units used. When the first fluorine-containing polymer contains TFE units and PAVE units, the total content of TFE units and PAVE units is preferably 99.0 to 100.0 mol%, more preferably 99.5 to 100.0 mol%, and even more preferably 99.9 to 100.0 mol%, based on all units of the first fluorine-containing polymer. When the first fluorine-containing polymer contains TFE units and P units, the content of P units is preferably 20 to 90 mol%, more preferably 25 to 80 mol%, and even more preferably 30 to 70 mol%, based on the total content of TFE units and P units. When the first fluorine-containing polymer contains TFE units and P units, the total content of TFE units and P units is preferably 99.0 to 100.0 mol%, more preferably 99.5 to 100.0 mol%, and even more preferably 99.9 to 100.0 mol%, based on all units of the first fluorine-containing polymer. When the first fluorine-containing polymer contains HFP units and VdF units, the content of VdF units is preferably 20 to 90 mol%, more preferably 25 to 80 mol%, and even more preferably 30 to 70 mol%, based on the total content of HFP units and VdF units. When the first fluorinated polymer contains HFP units and VdF units, the total content of HFP units and VdF units is preferably from 99.0 to 100.0 mol%, more preferably from 99.5 to 100.0 mol%, and still more preferably from 99.9 to 100.0 mol%, based on all units of the first fluorinated polymer.

[0059] The first fluorine-containing polymer may contain units other than those described above, but from the viewpoint of more efficiently producing the second fluorine-containing polymer, it may be substantially free of other units. "Substantially free of other units" means that the content of other units is 0.01 mol % or less, preferably 0 mol %, based on the total units of the first fluorine-containing polymer.

[0060] The first fluorine-containing polymer preferably does not have a melting point. "Doing not have a melting point" means that when the melting point of the first fluorine-containing polymer is measured using a differential scanning calorimeter, no melting peak is observed, specifically, no melting peak is observed in a temperature range of 150°C or higher (preferably a temperature range of 150 to 330°C). Note that a glass transition peak does not fall under the category of the above-mentioned melting peak. Specific methods for measuring the melting point include the measurement methods shown in the Examples section.

[0061] [Step 2] <First aqueous dispersion> The first aqueous dispersion in Step 2 contains an aqueous medium and a first fluoropolymer dispersed in the aqueous medium. Preferred embodiments of the aqueous medium and the first fluoropolymer are as described above. In terms of facilitating the production of a second fluoropolymer having desired physical properties, it is preferred to use the aqueous dispersion obtained in Step 3 described below as the first aqueous dispersion in Step 2.

[0062] The number of particles of the first fluorine-containing polymer is 2.0 × 10 １３ Preferably, the number of particles / mL or more is 1.0 x 10 １４ 2.0 × 10 １４ The upper limit is preferably 10.0 × 10 １５ In many cases, the particle concentration is less than 1 / mL. In particular, it is preferable to satisfy the above range before the start of polymerization of the second monomer. The particle number of the first fluoropolymer is the number of particles per mL of the first aqueous dispersion. Examples of a method for measuring the particle number include the measurement methods shown in the Examples section. In this specification, "before the start of polymerization of the second monomer" means immediately before the start of polymerization of the second monomer. Here, "the start of polymerization" includes the time when the second monomer is placed in the reactor and the temperature is raised to the polymerization temperature or higher, the time when the second monomer and the polymerization initiator are made to coexist in the reactor after the reactor is heated to the polymerization temperature or higher, and the time when the second monomer and the polymerization initiator are made to coexist in the reactor after the reactor is heated to the polymerization temperature or higher. Note that the first aqueous dispersion before the start of polymerization of the second monomer does not contain the second monomer and the polymerization initiator used in the polymerization of the second fluoropolymer.

[0063] The content of the particles of the first fluoropolymer is preferably 0.01 to 10.0% by mass, and from the viewpoint of more efficient production of the second fluoropolymer, more preferably 0.01 to 5.0% by mass, relative to the total mass of the first aqueous dispersion. In particular, it is preferable that the above range is satisfied before the start of polymerization of the second monomer.

[0064] Before the polymerization of the second monomer is initiated, the first aqueous dispersion may contain components other than the various components described above. Specific examples of other components that the first aqueous dispersion may contain include a chain transfer agent, a reducing agent, a wax, and a pH adjuster. Specific examples of chain transfer agents include ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane. Specific examples of waxes include paraffin wax. Specific examples of paraffin waxes that can be used include Paraffin Wax-155 and Paraffin Wax-150 (both manufactured by Nippon Seiro). Specific examples of pH adjusters include inorganic salts and ammonia. 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. Specific examples of more preferred phosphates include disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate.

[0065] When the first aqueous dispersion contains a chain transfer agent, the content of the chain transfer agent is preferably 0.1 to 5 parts by mass per 100 parts by mass of the aqueous medium. When the aqueous dispersion 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. When the first aqueous dispersion contains a pH adjuster, the content of the pH adjuster is preferably 0.01 to 3.0 parts by mass per 100 parts by mass of the aqueous medium.

[0066] <Second Monomer> The second monomer includes TFE. The second monomer preferably has a different composition from the first monomer described above. The second monomer may include units other than TFE. The amount of TFE used is preferably 99.0 mol% or more, more preferably 99.5 mol% or more, and even more preferably 99.9 mol% or more, relative to the amount of the second monomer used. The upper limit is 100 mol%. It is also preferable that the second monomer does not substantially contain any monomer other than TFE. "Substantially not containing any monomer other than TFE" means that the amount of monomers other than TFE used is 0.01 mol% or less, preferably 0 mol%, relative to the total amount of the second monomer used. The amount of TFE used may be 10.0 to 100.0 mol% relative to the amount of the second monomer used, and in this case, it is more preferably 30.0 to 70.0 mol%, and even more preferably 40.0 to 60.0 mol%.

[0067] The monomer other than TFE may be a fluorine-containing monomer other than TFE. Examples of the fluorine-containing monomer other than TFE include PAVE, VdF, HFP, chlorotrifluoroethylene (hereinafter also referred to as "CTFE"), perfluoroalkylethylene, and fluoroalkylethylene. Specific examples of fluoroalkylethylene include CH ２ =CH(CF ２ ) ２ F, CH ２ =CH(CF ２ ) ３ F, CH ２ =CH(CF ２ ) ４ F (hereinafter also referred to as "C4OLF"), CH ２ =CF(CF ２ ) ３ H and CH ２ =CF(CF ２ ) ４H is an example, with C4OLF being preferred. The total amount of TFE and the fluorine-containing monomer other than TFE used is preferably 10.0 to 100.0 mol%, more preferably 30.0 to 70.0 mol%, and even more preferably 40.0 to 60.0 mol%, relative to the amount of the second monomer used. The monomer other than TFE also includes a monomer other than the fluorine-containing monomer. Examples of the monomer other than the fluorine-containing monomer include ethylene, propylene, vinyl chloride, and vinylidene chloride, with ethylene being preferred. The amount of the monomer other than TFE used is preferably 10.0 to 70.0 mol%, more preferably 20.0 to 60.0 mol%, and even more preferably 30.0 to 50.0 mol%, relative to the amount of the second monomer used.

[0068] The amount of the second monomer used is preferably 1 to 60 parts by mass, more preferably 5 to 50 parts by mass, and even more preferably 10 to 40 parts by mass, relative to 100 parts by mass of the aqueous medium contained in the first aqueous dispersion.

[0069] <Polymerization Initiator> The second monomer is preferably polymerized using a polymerization initiator. The polymerization initiator is preferably an oil-soluble radical initiator, a water-soluble radical initiator, or a water-soluble redox catalyst. Specific 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"). Specific examples of water-soluble radical initiators include persulfates such as ammonium persulfate and potassium persulfate, disuccinic acid peroxide, bisglutaric acid peroxide, and water-soluble organic peroxides such as tert-butyl hydroperoxide (hereinafter also referred to as "TBHP"). The water-soluble redox catalyst is preferably a combination of an oxidizing agent such as bromic acid or a salt thereof, chloric acid or a salt thereof, persulfuric acid or a salt thereof, permanganic acid or a salt thereof, or hydrogen peroxide, and a reducing agent such as sulfurous acid or a salt thereof, hydrogen sulfite or a salt thereof, thiosulfuric acid or a salt thereof, an organic acid, or an inorganic salt. The persulfate is preferably potassium persulfate or ammonium persulfate. The sulfite is preferably sodium sulfite. The inorganic salt may be a combination of a sulfate anion, a sulfite anion, or a chloride anion with a metal ion. The metal ion is preferably a transition metal, such as manganese, iron, cobalt, nickel, copper, zinc, cerium, or silver ion, with iron ion being preferred. The inorganic salt is preferably iron(II) sulfate. The polymerization initiator is preferably an oil-soluble radical initiator or a water-soluble radical initiator. From the viewpoint of more efficient production of a fluorine-containing polymer, a water-soluble radical initiator is more preferred, a water-soluble organic peroxide is even more preferred, and disuccinic acid peroxide is particularly preferred.

[0070] The amount of the polymerization initiator used is preferably 0.1 to 10,000 ppm by mass, more preferably 1 to 5,000 ppm by mass, and even more preferably 10 to 2,000 ppm by mass, relative to 100 parts by mass of the second monomer used.

[0071] <Step> The method for producing the second aqueous dispersion in Step 2 is not particularly limited as long as it is a method for polymerizing the second monomer in the first aqueous dispersion. Examples of the method for polymerizing the second monomer include the same methods as the method for polymerizing the first monomer described above.

[0072] The polymerization of the second monomer is preferably carried out under conditions in which an emulsifier having a fluorine atom is substantially absent. The polymerization of the second monomer is more preferably carried out under conditions in which an emulsifier having a fluorine atom and an emulsifier not having a fluorine atom are substantially absent. Examples of the emulsifier include the emulsifiers described above. "Substantially absent" means that the content of the emulsifier is 10 mass ppm or less, preferably 150 mass ppb or less, and more preferably 50 mass ppb or less, relative to the total mass of the first aqueous dispersion before the polymerization of the second monomer. The lower limit is 0 mass ppb.

[0073] As mentioned above, the greater the particle number of the first fluoropolymer, the faster the polymerization rate of the second monomer tends to be. The polymerization rate of the second monomer is preferably 29 g / L / h or more, more preferably 29 to 400 g / L / h, still more preferably 30 to 350 g / L / h, and particularly preferably 31 to 300 g / L / h. The polymerization rate can be converted from the consumption amount of the second monomer.

[0074] <Second aqueous dispersion> Particles of the second fluorine-containing polymer are produced in step 2, and a second aqueous dispersion in which the particles of the second fluorine-containing polymer are dispersed in the aqueous medium is obtained. The second aqueous dispersion is preferably an aqueous dispersion containing an aqueous medium, the first fluorine-containing polymer, and the second fluorine-containing polymer.

[0075] It is preferable that the second aqueous dispersion is substantially free of a water-soluble emulsifier having a fluorine atom. "Substantially free of a water-soluble emulsifier having a fluorine atom" means that the content of the water-soluble emulsifier having a fluorine atom is 10 mass ppm or less, preferably 150 mass ppb or less, and more preferably 50 mass ppb or less, relative to the total mass of the second aqueous dispersion. The lower limit is 0 mass ppb. It is also preferable that the second aqueous dispersion is substantially free of a water-soluble emulsifier having no fluorine atoms. Examples of the water-soluble emulsifier having no fluorine atoms include the water-soluble emulsifier having no fluorine atoms in the production method described above. "Substantially free of a water-soluble emulsifier having no fluorine atoms" means that the content of the water-soluble emulsifier having no fluorine atoms is 10 mass ppm or less, preferably 150 mass ppb or less, and more preferably 50 mass ppb or less, relative to the total mass of the second aqueous dispersion. The lower limit is 0 mass ppb. Furthermore, it is preferable that the second aqueous dispersion is substantially free of a compound represented by any one of the above formulas (S1) to (S4). "Substantially free of a compound represented by any one of formulas (S1) to (S4)" means that the content of each of the compounds represented by formulas (S1) to (S4) is 10 mass ppm or less, preferably 5 mass ppm or less, more preferably 150 mass ppb or less, and even more preferably 50 mass ppb or less, relative to the total mass of the second aqueous dispersion. The lower limit is 0 mass ppb.

[0076] The aqueous medium contained in the second aqueous dispersion is the same as the specific example of the aqueous medium in the above-mentioned step 1. The content of the aqueous medium is preferably 50 to 99 mass %, more preferably 60 to 99 mass %, and still more preferably 70 to 99 mass %, relative to the total mass of the second aqueous dispersion.

[0077] In the second aqueous dispersion, the definition and preferred embodiments of the first fluorine-containing polymer are as described above.

[0078] (Second Fluorine-Containing Polymer) A second fluorine-containing polymer dispersed in the form of particles in an aqueous medium is obtained by polymerization of the second monomer. The second fluorine-containing polymer is a fluorine-containing polymer different from the above-mentioned first fluorine-containing polymer.

[0079] The second fluorine-containing polymer contains units based on a second monomer. The second fluorine-containing polymer contains TFE units. The second fluorine-containing polymer may contain units other than TFE units. The content of TFE units is preferably 99.0 to 100 mol%, more preferably 99.5 to 100 mol%, and even more preferably 99.9 to 100 mol%, based on all units of the second fluorine-containing polymer. It is also preferable that the second fluorine-containing polymer does not substantially contain units other than TFE units. In other words, it is also preferable that the second fluorine-containing polymer is a TFE homopolymer (polytetrafluoroethylene). "Substantially not containing units other than TFE units" means that the content of units other than TFE units is 0.01 mol% or less, based on all units of the second fluorine-containing polymer, and is preferably 0 mol%. The content of TFE units may be 10.0 to 100.0 mol % based on all units of the second fluorine-containing polymer, and in this case, it is more preferably 30.0 to 70.0 mol %, and even more preferably 40.0 to 60.0 mol %.

[0080] Examples of units other than TFE units include units based on fluorine-containing monomers such as PAVE units, VdF units, HFP units, CTFE units, perfluoroalkylethylene units, and fluoroalkylethylene units, as well as units based on monomers other than fluorine-containing monomers such as P units, ethylene units, vinyl chloride units, and vinylidene chloride units. When the second fluorine-containing polymer contains other units, the content of the other units is preferably 10.0 to 70.0 mol%, more preferably 20.0 to 60.0 mol%, and still more preferably 30.0 to 50.0 mol%, based on the total units of the second fluorine-containing polymer.

[0081] It is also preferable that the second fluorine-containing polymer has a melting point. The melting point of the second fluorine-containing polymer is preferably 320 to 380°C, more preferably 325 to 370°C, and even more preferably 330 to 360°C. When it contains units other than TFE units, the melting point of the second fluorine-containing polymer is preferably 130 to 350°C, more preferably 150 to 330°C, and even more preferably 180 to 320°C. The melting point can be measured using a differential scanning calorimeter. Specific methods for measuring the melting point include the measurement methods shown in the Examples section.

[0082] In the second aqueous dispersion, the first fluorine-containing polymer and the second fluorine-containing polymer are preferably present in the form of particles. The first fluorine-containing polymer and the second fluorine-containing polymer may be present separately in the second aqueous dispersion, but are preferably present in the form of particles comprising the first fluorine-containing polymer and the second fluorine-containing polymer (preferably particles consisting of the first fluorine-containing polymer and the second fluorine-containing polymer).

[0083] In this case, the average particle size of the fluoropolymer particles contained in the second aqueous dispersion is more preferably 400 nm or less, even more preferably 350 nm or less, and particularly preferably 300 nm or less. The lower limit is preferably 10 nm or more, more preferably 30 nm or more, and even more preferably 50 nm or more. The average particle size of the particles can be measured in the same manner as for the average particle size of the first fluoropolymer particles.

[0084] The number of particles of the second fluorine-containing polymer is 2.0 × 10 １３ Preferably, the number of particles / mL or more is 3.0 × 10 １３ More preferably, 1.0 x 10 １４ More preferably, 2.0 × 10 １４ The upper limit is 10.0 × 10 １５ The particle number of the second fluoropolymer is the number of particles per mL of the second aqueous dispersion. Examples of a method for measuring the particle number include the measurement methods shown in the Examples section.

[0085] The content of the first fluorine-containing polymer is preferably 0.01 to 10% by mass, more preferably 0.01 to 7% by mass, and even more preferably 0.1 to 5% by mass, relative to the total mass of the second aqueous dispersion. The content of the second fluorine-containing polymer is preferably 5.0 to 80% by mass, more preferably 8.0 to 50% by mass, and even more preferably 10 to 40% by mass, relative to the total mass of the second aqueous dispersion. In the second aqueous dispersion, the total content of the first fluorine-containing polymer and the second fluorine-containing polymer is preferably 5.0 to 80% by mass, more preferably 8.0 to 55% by mass, and even more preferably 10 to 50% by mass, relative to the total mass of the second aqueous dispersion. Furthermore, the content of the first fluorine-containing polymer is preferably 0.01 to 50% by mass, more preferably 0.1 to 30% by mass, and even more preferably 0.5 to 25% by mass, relative to the total content of the second fluorine-containing polymer and the first fluorine-containing polymer.

[0086] The content of TFE units relative to the total of all units of the first and second fluorine-containing polymers is preferably from 80 to 99.8 mol %, more preferably from 85 to 99.5 mol %, and even more preferably from 90 to 99 mol %.

[0087] [Step 3] In order to easily obtain a second fluorine-containing polymer having desired physical properties, the present production method preferably includes step 3 of subjecting an aqueous dispersion containing the first fluorine-containing polymer obtained by polymerizing the first monomer to a purification treatment. In other words, it is preferable to polymerize the second monomer in step 2 using the aqueous dispersion after the purification treatment in step 3. This makes it possible to remove impurities such as the polymerization initiator and its decomposition products, making it easier to obtain a fluorine-containing polymer with desired physical properties. Examples of purification methods include heat treatment and a method of removal using an ion exchange resin, and a method of contacting the aqueous dispersion with an ion exchange resin is preferred.

[0088] The ion exchange resin is preferably a cation exchange resin or an anion exchange resin. The amount of the ion exchange resin used is preferably 1 to 100 parts by mass, more preferably 1 to 50 parts by mass, per 100 parts by mass of the specific aqueous dispersion used. Specific examples of methods for contacting the aqueous dispersion with the ion exchange resin include a method of mixing the aqueous dispersion with the ion exchange resin and a method of passing the aqueous dispersion through a column packed with the ion exchange resin.

[0089] The purification may be carried out multiple times.

[0090] [Uses] As described above, the second aqueous dispersion obtained by the present production method does not necessarily require an emulsifier such as an emulsifier having a fluorine atom, and therefore can easily be converted into a dispersion in an organic solvent such as N-methylpyrrolidone, acetone, etc. by solvent substitution. For example, the second aqueous dispersion can be converted into a dispersion in an organic solvent by mixing it with an organic solvent and dehydrating it using evaporation or anhydrous sodium sulfate, etc.

[0091] The second aqueous dispersion has a large number of particles and the fluoropolymer is stably dispersed even without containing an emulsifier, and is therefore suitable for use in coating applications, binders, etc.

[0092] Furthermore, a solid of fluoropolymer particles can be obtained by aggregating the fluoropolymer particles from the second aqueous dispersion. The fluoropolymer particles contain particles of the second fluoropolymer and may further contain particles of the first fluoropolymer. Furthermore, the solid obtained by aggregating can be appropriately molded by a known method. Examples of the molding method include injection molding, extrusion molding, coextrusion molding, blow molding, compression molding, inflation molding, transfer molding, and calender molding.

[0093] Examples of aggregation methods include, but are not limited to, freeze aggregation, acid aggregation, base aggregation, mechanical aggregation, and aggregation using a coagulant. A specific example of mechanical aggregation is a method in which the aqueous dispersion is diluted with water to a concentration of the first fluoropolymer and the second fluoropolymer of 8 to 20% by mass, and then the aqueous dispersion is vigorously stirred to apply shear force to aggregate the primary particles of the first fluoropolymer and the second fluoropolymer. If necessary, the pH of the aqueous dispersion may be adjusted, and aggregation aids such as electrolytes and water-soluble organic solvents may be added. Examples of pH adjusters include sodium carbonate and sodium bicarbonate. Mechanical aggregation can also be performed in the presence of one or more compounds selected from the group consisting of ammonia, ammonium salts, and urea. Examples of electrolytes include inorganic salts such as potassium nitrate, sodium nitrate, sodium carbonate, and sodium bicarbonate. Examples of water-soluble organic solvents include alcohols and acetone. 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 second aqueous dispersion is preferred. Examples of the acid to be added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, and hydrofluoric acid, with nitric acid being preferred. The concentration of the acid 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. For base coagulation, a method in which a solution containing a base is added to the second aqueous dispersion is preferred. Examples of the base to be added include sodium hydroxide, potassium hydroxide, and ammonium carbonate, with sodium hydroxide being preferred. The concentration of the base 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 coagulation using a coagulant, known coagulants can be used. Known coagulants include aluminum salts, calcium salts, and magnesium salts. Specifically, aluminum sulfate, ammonium hydroxide represented by the general formula M'Al(SO ４ ) ２ ・12H ２0 (wherein M' is a monovalent cation other than lithium), calcium nitrate, and magnesium sulfate are exemplified, with alum being preferred, and potassium alum, where M' is potassium, being more preferred.

[0094] In the solid of the fluoropolymer particles, the content of the fluorine atom-containing emulsifier is preferably 150 ppb by mass or less, more preferably less than 100 ppb by mass, and even more preferably 50 ppb by mass or less, relative to the total mass of the solid of the fluoropolymer particles. The lower limit is 0 ppb by mass. Furthermore, in the solid of the fluoropolymer particles, the content of each of the compounds represented by any of the above formulas (S1) to (S4) is preferably 150 ppb by mass or less, more preferably less than 100 ppb by mass, and even more preferably 50 ppb by mass or less, relative to the solid of the fluoropolymer particles. The lower limit is 0 ppb by mass. In particular, the total content of the compounds represented by formulas (S1) to (S4) is preferably 150 ppb by mass or less, more preferably less than 100 ppb by mass, and even more preferably 50 ppb by mass or less, relative to the solid of the fluoropolymer particles. The lower limit is 0 ppb by mass. In the present production method, the aqueous dispersion containing a fluorine-containing polymer is produced in the substantial absence of an emulsifier having a fluorine atom, and therefore the above requirements can be easily achieved.

[0095] The present disclosure will be described in detail below with reference to examples. Examples 1 to 4 are working examples, and Examples 5 and 6 are comparative examples. However, the present disclosure is not limited to these examples.

[0096] [Measurement and Evaluation Methods] Various measurement and evaluation methods are as follows.

[0097] [Proportion of each unit in the polymer] The proportion of each unit in the polymer is １９ It was determined by F-NMR analysis.

[0098] [Solid content concentration in aqueous dispersion] 2.0 g of the aqueous dispersion was heated at 170°C for 20 minutes, and then the mass (g) of the residue was weighed and the solid content concentration was calculated using the following formula: Solid content concentration of aqueous dispersion (mass%) = 100 × (mass of residue) / (mass of aqueous dispersion (2.0 g))

[0099] [Average particle size of particles in aqueous dispersion] Measurement was performed using dynamic light scattering. The solid content of the aqueous dispersion to be measured was adjusted to 5.0% by mass using water as the solvent to prepare a sample solution. However, when the solid content of the aqueous dispersion to be measured (stock solution) was less than 5%, the stock solution with a solid content of less than 5% was used as the sample solution as is. Measurements were performed at 23°C with a total of 125 measurements using a particle size measurement system (Otsuka Electronics Co., Ltd., product name "ELSZ-neo"), and the average particle size determined by the cumulant method was used as the average particle size (unit: nm) of primary particles. When a stock solution with a solid content of less than 5% was used as the sample solution, D50 (median diameter) was used. The refractive index of the solvent (water) was 1.333, and the viscosity of the solvent (water) was 0.93 mPa·s.

[0100] [Number of Particles in Aqueous Dispersion] Using the relational equation, solid concentration of aqueous dispersion x = number of primary particles N × primary particle volume V × primary particle specific gravity ρ1 / specific gravity of aqueous dispersion ρ2, the number of primary particles per mL of aqueous dispersion was calculated using the following formula. Primary particles were considered to be true spheres. N = x ρ2 / (V ρ1), N (unit: particles / mL): number of primary particles per mL, x (unit: g / g): solid concentration of aqueous dispersion, V (unit: mL / particle): volume of primary particles, V = 4 / 3 π (r / 2 × 10 －７ ) ３ r (unit: nm): primary particle diameter; ρ1 (unit: g / mL): density of primary particles. In the second aqueous dispersion, the value of SSG was set as ρ1, and in the first aqueous dispersion, ρ1 = 2.2; ρ2 (unit: g / mL): specific gravity of the aqueous dispersion. The empirically obtained value was ρ2 = 0.492x ２ +0.5319x +0.09992 was used, where x represents the solid content concentration.

[0101] <SSG> Standard specific gravity (SSG) was measured in accordance with ASTM D4895-04. 12.0 g of sample was weighed and held in a cylindrical mold with an inner diameter of 28.6 mm at 34.5 MPa for 2 minutes. This was placed in a 290 ° C. oven and heated at 120 ° C. / hr. After holding at 380 ° C. for 30 minutes, the temperature was lowered at 60 ° C. / hr and held at 294 ° C. for 24 minutes. The sample was held in a desiccator at 23 ° C. for 12 hours, and then the specific gravity value of the sample relative to water at 23 ° C. was measured, and this was taken as SSG. A smaller SSG value indicates a larger molecular weight.

[0102] [Melting point] Using a differential scanning calorimeter (DSC7200, manufactured by SII), the melting point was determined from the endothermic peak when the sample was heated to 300° C. at a rate of 10° C. / min in an air atmosphere. When there were multiple endothermic peaks, the peak temperature of the largest endothermic peak was used.

[0103] [Total Content of Compounds Represented by Formulae (S1) to (S4)] The content of the compounds represented by the above formulae (S1) to (S4) relative to the total mass of the fluoropolymer in the dry powder (hereinafter also referred to as "content M") was measured using a liquid chromatograph mass spectrometer as follows. 5 mL of methanol was added to 2.5 g of the dry powder obtained in each example described below, and the mixture was subjected to ultrasonic treatment at 50°C for 2 hours and centrifuged (5000 rpm, 5 minutes) to precipitate the fluoropolymer, and the supernatant was extracted as an extract. The extract was diluted with water or methanol as necessary and used for measurement. In this way, extract M to be used for measuring content M was obtained.

[0104] For extract M, the peak areas of the compounds represented by formulas (S1) to (S4) with each carbon number were determined using the MRM method. Compounds in formula (S1) where n1 is 3 to 13, 15, and 17 were determined by converting them into perfluorocarboxylic acids with the same carbon number (compound (S3)). Compounds in formula (S2) where n2 is 4 to 10, and 12 were determined by converting them into perfluorosulfonic acids with the same carbon number (compound (S4)). The measuring equipment and conditions are shown in Table 1 below.

[0105]

[0106] The MRM measurement parameters are shown in Tables 2 to 5 below.

[0107]

[0108]

[0109]

[0110]

[0111] Specifically, five levels of methanol standard solutions of each compound with known concentrations ranging from 1 to 180 ng / g were prepared, and a was calculated from the sample concentration and peak integral value of each compound using a first-order approximation according to the following formula (A1): A = a × X (A1), where A is the peak area of ​​the compound and X is the concentration of the compound (ng / g).

[0112] Next, the content of each compound in extract M was calculated using the following formula (A2), where a in formula (A2) means a calculated using formula (A1) above: XCm=ACm / a×ρ1 / ρ2 (A2) XCm: content (ng / g) of compound in extract M ACm: peak area of ​​compound in extract M ρ1: density of methanol ρ2: density of extract The quantitation limit in this measurement is 1 ng / g.

[0113] The content (ZCm) of each compound relative to the content of fluoropolymer in the dry powder, which will be described later, was calculated by the following formula (A3) based on the XCm value of each compound obtained using extract M. ZCm = XCm × dilution ratio × W2a / W2b (A3) ZCm: content of compound contained in powder (relative to fluoropolymer) W2a: mass (g) of extract M W2b: mass (g) of dry powder used to prepare a sample of extract M The dilution ratio indicates the mass ratio at which the extract was diluted with water or methanol so that XCm was 180 ng / g or less. The ZCm values ​​of each compound were summed up to obtain the content M.

[0114] [Example 1] [Production of Raw Material Solution A-1] Ultrapure water (1689 g) and a 50% by weight aqueous solution of sodium 2-acrylamido-2-methyl-1-propanesulfonate (NaAAMPS, corresponding to Compound X) (360 μL, 180 mg of NaAAMPS) were charged into a 3.3 L stainless steel pressure reactor, and the pressure was increased to 2.5 MPaG at 75°C while stirring at 300 rpm. Next, a TFE / propylene mixed gas (TFE / P=88 / 12) (molar ratio) was added to adjust the pressure to 2.5 MPa. An aqueous ammonium persulfate solution (14% by weight, 24 g) was added to initiate polymerization. As the pressure in the reactor decreased with the initiation of polymerization, a TFE / propylene mixed gas (TFE / P=56 / 44) (molar ratio) was added to maintain the pressure constant. When 100 g of the TFE / propylene mixed gas had been injected, the reactor was cooled to terminate the polymerization reaction. This liquid was designated as raw material liquid A-1. In raw material liquid A-1, the first fluoropolymer P1-A was dispersed in an aqueous medium.

[0115] To the above raw material liquid A-1 (330 g) was added a cation exchange resin, DIAION SK1BH (26.4 g) manufactured by Mitsubishi Chemical Corporation. 60 minutes after the start of stirring, the raw material liquid and the ion exchange resin were separated by filtration. To the filtered raw material liquid was added an anion exchange resin, DIAION SA10AOH (26.4 g) manufactured by Mitsubishi Chemical Corporation. 60 minutes after the start of stirring, the raw material liquid and the ion exchange resin were separated by filtration to obtain raw material liquid A-2. In raw material liquid A-2, particles of the first fluorine-containing polymer P1-A were dispersed in an aqueous medium, and the content of the first fluorine-containing polymer P1-A was 4.6 mass% relative to the total mass of raw material liquid A-2.

[0116] [Production of Aqueous Dispersion A-4] A 1.3 L stainless steel pressure reactor was charged with paraffin wax (36 g), ultrapure water (633 g), and raw material liquid A-2 (141 g), to obtain aqueous dispersion A-3 (corresponding to the first aqueous dispersion). Using the methods described above, the solids concentration (content of the first fluoropolymer) of aqueous dispersion A-3, the average particle size of primary particles in aqueous dispersion A-3, and the number of particles in aqueous dispersion A-3 were determined. The results are shown in Table 6 (the same applies hereinafter). The temperature was raised to 70°C, and aqueous dispersion A-3 was stirred at 260 rpm. TFE was injected until the pressure in the reactor reached 1.4 MPaG, and disuccinic acid peroxide (1.3 mmol) was added to initiate polymerization. Since the pressure in the reactor decreased with the initiation of polymerization, TFE was added to maintain the pressure constant. When 170 g of TFE had been injected, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 411 minutes, and the polymerization rate calculated from the amount of TFE consumed was 32 g / L / h. After recovering the gas remaining in the reactor, the liquid was withdrawn. This liquid was designated as aqueous dispersion A-4 (corresponding to the second aqueous dispersion). Aqueous dispersion A-4 was a dispersion in which particles containing the first fluoropolymer P1-A and the second fluoropolymer P2-A were dispersed in an aqueous medium. Using the methods described above, the solids concentration of aqueous dispersion A-4, the average particle size of the primary particles in aqueous dispersion A-4, and the number of particles in aqueous dispersion A-4 were determined. The results are shown in Table 6 (the same applies hereinafter). The particles in the obtained aqueous dispersion A-4 were agglomerated and filtered to obtain PTFE. The melting point of PTFE dried at 200°C was 343°C. In the obtained dry powder, the content of the first fluoropolymer relative to the total mass of the first fluoropolymer (P1) and the second fluoropolymer (P2) (indicated as "P1 / (P1+P2)" in the tables) was 3.50 mass%. The total content of the compounds represented by formulae (S1) to (S4) in the obtained dry powder was less than 100 ppb by mass.

[0117] [Example 2] [Production of Raw Material Solution B-1] Ultrapure water (713 g), PMVE (55 g), and a 0.5 mass% aqueous solution of sodium 2-acrylamido-2-methyl-1-propanesulfonate (NaAAMPS, corresponding to Compound X) (3.6 g, NaAAMPS was 18 mg) were charged into a 1.3 L stainless steel pressure reactor, and the temperature was raised to 80°C while stirring at 500 rpm. Next, TFE (9 g) and an aqueous solution of ammonium persulfate (3.6 mass%, 5 mL) were 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 24 g of TFE had been injected, the reactor was cooled and the polymerization reaction was terminated. This liquid was designated raw material solution B-1. In raw material solution B-1, the first fluoropolymer P1-B was dispersed in an aqueous medium. The raw material liquid B-1 was freeze-coagulated and then filtered to obtain a first fluoropolymer P1-B, which was analyzed by NMR and found to have a TFE unit / PMVE unit ratio of 60 / 40.

[0118] Except for changing the raw material liquid to the above raw material liquid B-1, raw material liquid B-2 was obtained in the same manner as in Example 1. In raw material liquid B-2, particles of the first fluoropolymer P1-B were dispersed in an aqueous medium, and the content of the first fluoropolymer P1-B was 5.05% by mass relative to the total mass of raw material liquid B-2.

[0119] [Production of Aqueous Dispersion B-4] A 1.3 L stainless steel pressure reactor was charged with paraffin wax (36 g), ultrapure water (157 g), and raw material solution B-2 (617 g), to obtain aqueous dispersion B-3 (corresponding to the first aqueous dispersion). The temperature was raised to 70°C, and aqueous dispersion B-3 was stirred at 260 rpm. TFE was injected until the pressure in the reactor reached 1.4 MPaG, and disuccinic acid peroxide (0.11 mmol) 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 90 g of TFE had been injected, the reactor was cooled, and the polymerization reaction was terminated. The polymerization time was 222 minutes, and the polymerization rate calculated from the TFE consumption was 31 g / L / h. After the gas remaining in the reactor was recovered, the liquid was withdrawn. This liquid was named aqueous dispersion B-4 (corresponding to the second aqueous dispersion). Aqueous dispersion B-4 was a dispersion in which particles containing the first fluoropolymer P1-B and the second fluoropolymer P2-B were dispersed in an aqueous medium. The particles in the obtained aqueous dispersion B-4 were coagulated and separated by filtration to obtain PTFE. The melting point of PTFE dried at 200°C was 338°C. In the obtained dry powder, the content of the first fluoropolymer relative to the total mass of the first fluoropolymer and the second fluoropolymer (represented as "P1 / (P1+P2)" in the tables) was 23.7% by mass. The total content of the compounds represented by formulae (S1) to (S4) in the obtained dry powder was less than 100 ppb by mass. The obtained dry powder was brought into contact with fluorine gas to fluorinate the terminal groups. [Example 3] [Production of Raw Material Solution C-1] Ultrapure water (1766 g), PMVE (67 g), and a 0.5% by mass aqueous solution of NaAAMPS (8.8 g, NaAAMPS was 44 mg) were added to a 3.2 L stainless steel pressure reactor, and the temperature was raised to 90°C while stirring at 250 rpm. Next, TFE (11 g) and an aqueous solution of ammonium persulfate (14.8% by mass, 6 mL) were 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 58 g of TFE had been injected, the reactor was cooled and the polymerization reaction was terminated. This liquid was designated raw material solution C-1. In raw material solution C-1, the first fluoropolymer P1-C was dispersed in an aqueous medium.The raw material liquid C-1 was freeze-coagulated and then filtered to obtain a first fluoropolymer P1-C, which was analyzed by NMR and found to have a TFE unit / PMVE unit ratio of 71 / 29 (molar ratio).

[0120] Except for changing the raw material liquid to the above raw material liquid C-1, raw material liquid C-2 was obtained in the same manner as in Example 1. In raw material liquid C-2, particles of the first fluoropolymer P1-C were dispersed in an aqueous medium, and the content of the first fluoropolymer P1-C was 4.66 mass% relative to the total mass of raw material liquid C-2.

[0121] [Production of Aqueous Dispersion C-4] A 1.3 L stainless steel pressure reactor was charged with paraffin wax (36 g), ultrapure water (668 g), and raw material liquid C-2 (106 g), to obtain aqueous dispersion C-3 (corresponding to the first aqueous dispersion). The temperature was raised to 70°C, and aqueous dispersion C-3 was stirred at 260 rpm. TFE was injected until the pressure in the reactor reached 1.4 MPaG, and disuccinic acid peroxide (0.11 mmol) 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 130 g of TFE had been injected, the reactor was cooled, and the polymerization reaction was terminated. The polymerization time was 320 minutes, and the polymerization rate calculated from the TFE consumption was 31 g / L / h. After the gas remaining in the reactor was recovered, the liquid was withdrawn. This liquid was designated aqueous dispersion C-4 (corresponding to the second aqueous dispersion). Aqueous dispersion C-4 was a dispersion in which particles containing the first fluoropolymer P1-C and the second fluoropolymer P2-C were dispersed in an aqueous medium. The particles in the obtained aqueous dispersion C-4 were agglomerated and separated by filtration to obtain PTFE. The melting point of PTFE dried at 200°C was 338°C. In the obtained dry powder, the content of the first fluoropolymer relative to the total mass of the first fluoropolymer and the second fluoropolymer (represented as "P1 / (P1+P2)" in the tables) was 3.63% by mass. The total content of the compounds represented by formulae (S1) to (S4) in the obtained dry powder was less than 100 ppb by mass.

[0122] [Example 4] [Production of Raw Material Solution D-1] Ultrapure water (1874 g) and a 50% by weight aqueous solution of NaAAMPS (360 μL, 180 mg of NaAAMPS) were added to a 3.2 L stainless steel pressure reactor. After degassing under reduced pressure, a mixed gas (VdF / HFP = 20 / 80) (molar ratio) was injected under reduced pressure, and the pressure was increased to 2.0 MPaG at 75 ° C. while stirring at 300 rpm. Next, an aqueous ammonium persulfate solution (14% by weight, 3 mL) was added to initiate polymerization. Since the pressure in the reactor decreased with the initiation of polymerization, a VdF / HFP mixed gas was added to maintain a constant pressure. After the addition of the initiator, an aqueous ammonium persulfate solution (14% by weight, 3 mL) was added every 15 minutes. When the amount of the mixed gas added reached 100 g, the addition of the mixed gas to be injected after polymerization was stopped, the temperature inside the reactor was cooled to 15° C. to terminate the polymerization reaction, and the gas remaining in the reactor was recovered, and then the liquid was withdrawn and this liquid was designated as raw material liquid D-1. In raw material liquid D-1, the first fluoropolymer P1-D was dispersed in an aqueous medium.

[0123] Except for changing the raw material liquid to the above raw material liquid D-1, raw material liquid D-2 was obtained in the same manner as in Example 1. In raw material liquid D-2, particles of the first fluoropolymer P1-D were dispersed in an aqueous medium, and the content of the first fluoropolymer P1-D was 5.0 mass % relative to the total mass of raw material liquid D-2.

[0124] [Production of Raw Material Liquid D-4] A 1.3 L stainless steel pressure reactor was charged with paraffin wax (36 g), ultrapure water (633 g), and raw material liquid D-2 (141 g), to obtain aqueous dispersion D-3 (corresponding to the first aqueous dispersion). The temperature was raised to 70°C, and aqueous dispersion D-3 was stirred at 260 rpm. TFE was injected until the pressure in the reactor reached 1.4 MPaG, and disuccinic acid peroxide (1.3 mmol) was added to initiate polymerization. As the polymerization began, the pressure in the reactor decreased, so TFE was added to maintain the pressure constant. When 170 g of TFE had been injected, the reactor was cooled, and the polymerization reaction was terminated. The polymerization time was 420 minutes, and the polymerization rate calculated from the TFE consumption was 31 g / L / h. After the gas remaining in the reactor was recovered, the liquid was withdrawn. This liquid was designated aqueous dispersion D-4 (corresponding to the second aqueous dispersion). Aqueous dispersion D-4 was a dispersion in which particles containing the first fluoropolymer P1-D and the second fluoropolymer P2-D were dispersed in an aqueous medium. The particles in the obtained aqueous dispersion D-4 were agglomerated and separated by filtration to obtain PTFE. The melting point of PTFE dried at 200°C was 343°C. In the obtained dry powder, the content of the first fluoropolymer relative to the total mass of the first fluoropolymer and the second fluoropolymer (represented as "P1 / (P1+P2)" in the tables) was 3.88% by mass. The total content of the compounds represented by formulae (S1) to (S4) in the obtained dry powder was less than 100 ppb by mass.

[0125] [Example 5] [Production of Raw Material Solution E-1] Ultrapure water (1689 g) and sodium lauryl sulfate (8.9 g) were charged into a 3.3 L stainless steel pressure reactor, and the temperature was raised to 75°C while stirring at 300 rpm. Next, a TFE / propylene mixed gas (TFE / P = 88 / 12) (molar ratio) was added, and the pressure was adjusted to 2.5 MPa. An aqueous ammonium persulfate solution (14 mass%, 24 g) was added to initiate polymerization. As the pressure in the reactor decreased with the start of polymerization, a TFE / propylene mixed gas (TFE / P = 56 / 44) (molar ratio) was added to maintain the pressure constant. When 100 g of a TFE / propylene mixed gas had been injected, the reactor was cooled and the polymerization reaction was terminated. This liquid was designated raw material solution E-1. In raw material solution E-1, the first fluoropolymer P1-E was dispersed in an aqueous medium.

[0126] Except for changing the raw material liquid to the above raw material liquid E-1, raw material liquid E-2 was obtained in the same manner as in Example 1. In raw material liquid E-2, particles of the first fluoropolymer P1-E were dispersed in an aqueous medium, and the content of the first fluoropolymer P1-E was 4.8% by mass relative to the total mass of raw material liquid E-2.

[0127] [Production of Aqueous Dispersion E-4] A 1.3 L stainless steel pressure reactor was charged with paraffin wax (36 g), ultrapure water (157 g), and raw material liquid E-2 (617 g), to obtain aqueous dispersion E-3. The temperature was raised to 70°C, and aqueous dispersion E-3 was stirred at 260 rpm. TFE was injected until the pressure inside the reactor reached 1.4 MPaG, and disuccinic acid peroxide (1.13 mmol) was added, but polymerization did not proceed, and aqueous dispersion E-4 in which particles of the second fluorinated polymer were dispersed in an aqueous medium was not obtained.

[0128] [Example 6] [Production of Raw Material Liquid F-1] Ultrapure water (717 g) and PMVE (50 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, TFE (8 g) and an aqueous ammonium persulfate solution (3.6 mass%, 5 g) were added to initiate polymerization. As the polymerization started, the pressure inside the reactor decreased, so TFE was added to maintain the pressure constant. When 2 g of TFE had been injected, the reactor was cooled and the polymerization reaction was terminated. This liquid was designated raw material liquid F-1. In raw material liquid F-1, the first fluoropolymer P1-F was dispersed in an aqueous medium. Raw material liquid F-1 was freeze-coagulated and then filtered, and the obtained first fluoropolymer P1-F was analyzed by NMR, and the ratio of TFE units to PMVE units was 52 / 48 (molar ratio).

[0129] Except for changing the raw material liquid to the above raw material liquid F-1, raw material liquid F-2 was obtained in the same manner as in Example 1. In raw material liquid F-2, particles of the first fluoropolymer P1-F were dispersed in an aqueous medium, and the content of the first fluoropolymer P1-F was 0.5% by mass relative to the total mass of raw material liquid F-2.

[0130] [Production of Aqueous Dispersion F-4] A 1.3 L stainless steel pressure reactor was charged with paraffin wax (36 g), ultrapure water (157 g), and raw material solution F-2 (617 g), to obtain aqueous dispersion F-3. The temperature was raised to 70°C, and aqueous dispersion F-3 was stirred at 260 rpm. TFE was injected until the pressure inside the reactor reached 1.4 MPaG, and disuccinic acid peroxide (0.11 mmol) was added to initiate polymerization. As the polymerization began, the pressure inside the reactor decreased, so TFE was added to maintain the pressure constant. When 90 g of TFE had been injected, the reactor was cooled, and the polymerization reaction was terminated. The polymerization time was 250 minutes, and the polymerization rate calculated from the TFE consumption was 28 g / L / h. After the gas remaining in the reactor was recovered, the liquid was withdrawn. This liquid was designated aqueous dispersion F-4. Aqueous dispersion F-4 was a dispersion in which particles containing a first fluoropolymer P1-F and a second fluoropolymer P2-F were dispersed in an aqueous medium. The particles in the obtained aqueous dispersion F-4 were coagulated and filtered off to obtain PTFE. The melting point of PTFE dried at 200°C was 338°C. In the obtained dry powder, the content of the first fluoropolymer relative to the total mass of the first fluoropolymer and the second fluoropolymer (represented as "P1 / (P1+P2)" in the tables) was 2.26% by mass. The total content of the compounds represented by formulae (S1) to (S4) in the obtained dry powder was less than 100 ppb by mass.

[0131] In producing the aqueous dispersions of Examples 1 to 4, the polymerization of the first fluorine-containing polymer was carried out under conditions substantially absent of an emulsifier having a fluorine atom and an emulsifier not having a fluorine atom.

[0132] In Table 6 below, the first aqueous dispersion represents the aqueous dispersion A-3, B-3, C-3, D-3, E-3, or F-3 in each of the above-mentioned examples. In Table 6 below, the second aqueous dispersion represents the aqueous dispersion A-4, B-4, C-4, D-4, E-4, or F-4 in each of the above-mentioned examples.

[0133]

[0134] From the evaluation results of Examples 1 to 6, it was confirmed that according to the present production method for producing a second fluoropolymer in an aqueous dispersion containing a first fluoropolymer produced in the presence of compound X, an aqueous dispersion having a large number of fluoropolymer particles can be produced without substantially using an emulsifier having a fluorine atom.

[0135] The disclosure of Japanese Patent Application No. 2024-098701, filed on June 19, 2024, is incorporated herein by reference in its entirety. In addition, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually indicated to be incorporated by reference.

Claims

a compound represented by formula (X) and a polymerization initiator are polymerized in the presence of an aqueous medium and in the substantial absence of an emulsifier having a fluorine atom, to produce a first aqueous dispersion containing particles of a first fluorine-containing polymer; A method for producing an aqueous dispersion, comprising polymerizing a second monomer containing tetrafluoroethylene in the first aqueous dispersion to produce a second aqueous dispersion containing particles of a second fluoropolymer different from the first fluoropolymer. C(X １ )(X ２ )=C(X ３ )CONH-R-Z (X) In formula (X), X １ , X ２ and X ３ each independently represents a hydrogen atom, a fluorine atom, a perfluoromethyl group, or an alkyl group, R is an alkylene group having 1 to 6 carbon atoms or a fluoroalkylene group having 1 to 6 carbon atoms, Z is -SO ３ M, -OSO ３ M, -P (=O) (OM) ２ , -OP(=O)(OM) ２ or -COOM, M is a hydrogen atom, a metal atom, N(R Ｍ１ ) ４ or P(R Ｍ２ ) ４ When a plurality of M's are present, the plurality of M's may be the same or different from one another; R Ｍ１ and R Ｍ２ are each independently a hydrogen atom or a substituent, and R Ｍ１ Any two of R may be bonded to each other to form a ring, and multiple R Ｍ１ may be the same or different from each other, R Ｍ２ Any two of R may be bonded to each other to form a ring, and multiple R Ｍ２ may be the same or different from each other. Z is -SO ３ The method for producing the aqueous dispersion according to claim 1, wherein M is M.

3. The method for producing an aqueous dispersion according to claim 1, wherein the content of the compound represented by formula (X) is 1.0 to 1000 ppm by mass with respect to the total mass of the aqueous medium. 　 The method for producing an aqueous dispersion according to claim 1 or 2, wherein the first monomer comprises a perfluoro(alkyl vinyl ether). 　 The method for producing an aqueous dispersion according to claim 1 or 2, wherein the first monomer comprises at least one selected from the group consisting of propylene and vinylidene fluoride. 　 The number of particles of the first fluorine-containing polymer is 2.0 × 10 １３ The method for producing an aqueous dispersion according to claim 1 or 2, wherein the concentration of the aqueous dispersion is 1 / mL or more. 　 The number of particles of the second fluorine-containing polymer is 2.0 × 10 １３ The method for producing an aqueous dispersion according to claim 1 or 2, wherein the concentration of the aqueous dispersion is 1 / mL or more. 　 The method for producing an aqueous dispersion according to claim 1 or 2, wherein the polymerization rate of the second monomer is 29 g / L / h or more.

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