Method for producing aqueous dispersion

Abstract

A method for producing an aqueous dispersion, comprising forming a reaction system containing fluoroolefin-based polymer particles and water but not containing a fluorine-based emulsifier, and polymerizing at least gaseous perfluoroolefin in the reaction system to obtain an aqueous dispersion containing fluoropolymer particles, wherein the ratio of the specific gravity of the fluoropolymer to the specific gravity of the fluoroolefin-based polymer is 0.80 to 1.20, the ratio of the average particle size of the fluoropolymer particles contained in the aqueous dispersion to the average particle size of the fluoroolefin-based polymer particles is greater than 1, and the ratio of the content of fluoropolymer particles in the aqueous dispersion to the content of fluoroolefin-based polymer particles in the reaction system is 2 or more.

Description

[Technical Field]

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

[0002] Fluoropolymers containing units based on fluoroolefins are used in various industrial fields due to their excellent heat resistance, chemical resistance, flame retardancy, weather resistance, and the like.

[0003] As a method for producing a fluoropolymer, there is a method in which a fluoroolefin is emulsion-polymerized in water using a fluorine-based emulsifier (see Patent Document 1, etc.). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2007 / 046377 Summary of the Invention [Problem to be solved by the invention]

[0005] The method of Patent Document 1 can obtain an aqueous dispersion containing fluoropolymer particles, which has a small environmental impact. However, depending on the content of the fluorine-based emulsifier, which is an essential component, or depending on the intended use or in some cases, it may be necessary to remove the fluorine-based emulsifier.

[0006] In recent years, further improvements in the dispersibility of fluoropolymer particles in such aqueous dispersions have also been required.

[0007] An object of the present disclosure is to provide a method for efficiently producing an aqueous dispersion containing fluoropolymer particles, which does not require a fluorine-based emulsifier, has a small environmental impact, and has excellent dispersibility in liquid. [Means for solving the problem]

[0008] The present disclosure provides the following inventions. [1] A method for producing an aqueous dispersion, comprising forming a reaction system containing fluoroolefin-based polymer particles and water but not containing a fluorine-based emulsifier, and polymerizing at least gaseous perfluoroolefin in the reaction system to obtain an aqueous dispersion containing fluoropolymer particles, the ratio of the specific gravity of the fluoropolymer to the specific gravity of the fluoroolefin-based polymer is 0.80 to 1.20, and the ratio of the average particle size of the fluoropolymer particles contained in the aqueous dispersion to the average particle size of the fluoroolefin-based polymer particles in the reaction system is greater than 1; A method for producing an aqueous dispersion, wherein the ratio of the content of fluoropolymer particles in the aqueous dispersion to the content of fluoroolefin polymer particles in the reaction system is 2 or more. [2] The method for producing an aqueous dispersion according to [1], wherein the specific gravity of the fluoroolefin polymer and the specific gravity of the fluoropolymer are each independently 1.60 to 2.20. [3] The method for producing an aqueous dispersion according to [1] or [2], wherein the specific gravity of the fluoropolymer is greater than the specific gravity of the fluoroolefin-based polymer. [4] The method for producing an aqueous dispersion according to any one of [1] to [3], wherein the liquid viscosity of the reaction system is less than 2 mPa·s. [5] The method for producing an aqueous dispersion according to any one of [1] to [4], wherein the aqueous dispersion has a liquid viscosity of less than 10 mPa·s. [6] The method for producing an aqueous dispersion according to any one of [1] to [5], wherein the gaseous perfluoroolefin is tetrafluoroethylene or hexafluoropropylene. [7] The method for producing an aqueous dispersion according to any one of [1] to [6], wherein the polymerization is carried out by copolymerizing a gaseous perfluoroolefin with a monomer other than the gaseous perfluoroolefin. [8] The method for producing an aqueous dispersion according to [7], wherein the monomer other than the gaseous perfluoroolefin is ethylene, chlorotrifluoroethylene, vinylidene fluoride, propylene, a fluoroalkylethylene, a perfluoroalkyl vinyl ether, a perfluoroalkyl allyl ether, or a fluoromonomer having a fluorosulfonyl group, a carboxy group, or an alkoxycarbonyl group. [9] The method for producing an aqueous dispersion according to any one of [1] to [8], wherein the fluoroolefin polymer particles have an average particle size of 10 nm or more and less than 150 nm.

[10] The method for producing an aqueous dispersion according to any one of [1] to [9], wherein the average particle size of the fluoropolymer particles is more than 50 nm and not more than 1000 nm.

[11] The method for producing an aqueous dispersion according to any one of [1] to

[10] , wherein the particle size distribution of the fluoropolymer particles is monomodal and the polydispersity index of the particle sizes of the fluoropolymer particles is 0.5 or less.

[12] The method for producing an aqueous dispersion according to any one of [1] to

[11] , wherein the content of the fluoroolefin polymer in the reaction system is 0.01% by mass or more and 4.0% by mass or less.

[13] The method for producing an aqueous dispersion according to any one of [1] to

[12] , wherein the reaction system is formed by polymerizing at least a gaseous fluoroolefin in the presence of water and a polymerization initiator, without using a fluorine-based emulsifier.

[14] The method for producing an aqueous dispersion according to

[13] , wherein the gaseous fluoroolefin is vinyl fluoride, vinylidene fluoride, tetrafluoroethylene or hexafluoropropylene.

[15] The method for producing an aqueous dispersion according to

[14] , wherein the polymerization is carried out by copolymerizing the gaseous fluoroolefin with ethylene, chlorotrifluoroethylene, propylene, a perfluoroalkyl vinyl ether, or a perfluoroalkyl allyl ether. [Effects of the Invention]

[0009] According to the present disclosure, an aqueous dispersion in which fluoropolymer particles are stably dispersed can be efficiently produced without requiring a fluorine-based emulsifier. DETAILED DESCRIPTION OF THE INVENTION

[0010] In this disclosure, the terms have the following meanings: A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the upper and lower limits. In the numerical ranges described in stages in this specification, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the 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.

[0011] In this specification, each component may be a single substance corresponding to the component, or two or more substances may be used in combination. When two or more substances are used in combination for each component, the content of the component refers to the total content of the substances used in combination, unless otherwise specified.

[0012] As used herein, a combination of two or more preferred embodiments is a more preferred embodiment.

[0013] The term "unit" refers collectively to an atomic group derived from one molecule of the monomer, which is formed directly by polymerizing the monomer, and an atomic group obtained by chemically converting a part of the atomic group. Hereinafter, a "unit based on a monomer" will also be referred to simply as a "unit," and a "unit based on monomer A" will also be referred to simply as a "monomer A unit."

[0014] In this specification, 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 charged substantially coincides with the actual content of each unit.

[0015] In this specification, "gaseous compound" refers to a compound whose boiling point at atmospheric pressure (1013 hPa) is less than 25°C, and "liquid compound" refers to a compound whose boiling point at atmospheric pressure (1013 hPa) is 25°C or higher.

[0016] The manufacturing method of the present disclosure (hereinafter also referred to as "this method") is a method for manufacturing an aqueous dispersion, which comprises forming a reaction system containing fluoroolefin polymer (hereinafter also referred to as "FO polymer") particles (hereinafter also referred to as "FO particles") and water but not containing a fluorine-based emulsifier, and polymerizing at least a gaseous perfluoroolefin in the reaction system to obtain an aqueous dispersion containing fluoropolymer (hereinafter also referred to as "F polymer") particles (hereinafter also referred to as "F particles"). This method is for manufacturing an aqueous dispersion in which the ratio of the specific gravity of the F polymer to the specific gravity of the FO polymer (hereinafter also referred to as "specific gravity ratio") is 0.80 to 1.20, the ratio of the average particle size of the F particles to the average particle size of the FO particles (hereinafter also referred to as "particle size ratio") is greater than 1, and the ratio of the content of the F particles to the content of the FO particles (hereinafter also referred to as "content ratio") is 2 or greater. The content ratio is a value calculated from the respective contents (% by mass).

[0017] The reason why this method can efficiently produce an aqueous dispersion containing dense fluoropolymer particles with excellent dispersibility in liquid in the absence of a fluorine-based emulsifier is not entirely clear, but the following reasons may be cited.

[0018] In a liquid medium containing water, which has a specific gravity of 1, polymer particles that contain fluorine atoms and are generally hydrophobic and have a high specific gravity tend to become unstable in the liquid. When gaseous perfluoroolefin is polymerized in a reaction system in such a state, the resulting polymer particles also tend to disproportionate, making the dispersion state in the liquid even more unstable.

[0019] In this method, the specific gravities of the polymer (FO polymer) already present in the reaction system and the polymer (F polymer) formed in the reaction system are balanced within a predetermined range. In the polymerization process of this method, the gaseous perfluoroolefin introduced into the reaction system is easily adsorbed by the FO polymer, which contains fluorine atoms and has a high affinity for it. In other words, it is believed that the FO particles function highly as a polymerization site. In this process, the specific gravities of the particles are balanced within a predetermined range, which is thought to facilitate homogenization of the overall particle dispersion state in the liquid and facilitate uniform and dense polymerization. As a result, it is thought that this method can efficiently produce an aqueous dispersion containing F particles with excellent dispersibility in the liquid while increasing both the particle size ratio and content ratio, even without the presence of a fluorine-based emulsifier. This mechanism of action is more easily manifested by the preferred embodiment of this method, which will be described later.

[0020] The reaction system in this method does not contain a fluorine-based emulsifier, in other words, the reaction system in this method is preferably formed without using a fluorine-based emulsifier.

[0021] The fluorine-based emulsifier is an emulsifier containing fluorine atoms that is different from FO polymers, and specifically refers to a water-soluble fluorine-containing compound or salt thereof having a fluorine-containing organic group (such as a perfluoroalkyl group) and a hydrophilic functional group (such as a carboxy group, sulfonic acid group, or phosphonic acid group), more specifically perfluoroalkylcarboxylic acid, perfluoroalkylsulfonic acid, or a salt thereof. Etheric oxygen atoms may be present between carbon atoms in the molecules of these compounds.

[0022] The reaction system in this method is preferably formed without using a fluorine-containing emulsifier (an emulsifier having a fluorine atom) or an emulsifier not having a fluorine atom. Hereinafter, emulsifiers having fluorine atoms and emulsifiers having no fluorine atoms will also be collectively referred to as "emulsifiers." The content of various emulsifiers can be measured using a liquid chromatograph mass spectrometer.

[0023] The emulsifier may be a water-soluble emulsifier. The water-soluble emulsifier refers to an emulsifier having a solubility of 100 mg or more in 1000 g of water at 25°C, and the water-insoluble emulsifier refers to an emulsifier other than the water-soluble emulsifiers described above. The water-soluble emulsifier may be either ionic or nonionic. Emulsifiers include those that do not have a carbon-carbon double bond.

[0024] 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. The emulsifiers having no fluorine atoms include ionic hydrocarbon emulsifiers and nonionic hydrocarbon emulsifiers.

[0025] Examples of ionic hydrocarbon emulsifiers include anionic hydrocarbon emulsifiers, which 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, a highly branched C10 tertiary carboxylic acid supplied by Resolution Performance Products as Versatic® 10, sodium linear alkyl polyether sulfonates supplied by BASF as the Avanel® S series, and the sulfosuccinate emulsifier Lankropol® K8300 available from AkzoNobel Surface Chemistry LLC.

[0026] A nonionic hydrocarbon emulsifier is an emulsifier that exhibits surface activity in water without dissociating into ions and has a hydrocarbon group such as an alkyl group as a hydrophobic portion. The hydrophilic portion of the nonionic hydrocarbon emulsifier includes a water-soluble functional group such as a polyethylene oxide chain 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.

[0027] Further, other nonionic hydrocarbon emulsifiers include those described in paragraphs

[0043] to

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

[0028] The emulsifier having a fluorine atom and the emulsifier not having a fluorine atom may contain a silicon atom. Examples of the emulsifier containing a silicon atom include a siloxane emulsifier. The siloxane emulsifier is a hydrocarbon-containing emulsifier having a siloxane skeleton. Siloxane emulsifiers include those described in US Pat. Nos. 6,841,616 (Wille et al.) and 7,977,438 (Brothers et al.).

[0029] 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 its side chain. Examples of such polymer emulsifiers include polymers containing units based on a compound having a site capable of polymerization reaction and a hydrophilic group. Furthermore, even if the polymer does not originally have a hydrophilic group, a polymer obtained by subjecting a polymer containing units based on a compound having a group that can become a hydrophilic group to post-treatment such as hydrolysis may also be used. Specific examples of polymer emulsifiers include polymethyl methacrylate, which is an emulsifier not having a fluorine atom.

[0030] In this method, the water content of the reaction system is preferably 60% by mass or more, more preferably 90% by mass or more, and even more preferably 96% by mass or more, based on the total mass of the reaction system. The water content is preferably 100% by mass or less, and more preferably 99.9% by mass or less. Even when the liquid component in the reaction system is comprised of water in this range, in other words, when the liquid component in the reaction system is essentially water, an aqueous dispersion with excellent sub-liquid dispersibility and a high content of F particles can be directly obtained by the above-described mechanism of action without using a fluorine-based emulsifier.

[0031] The specific gravity ratio in this method is 0.80 to 1.20. The ratio may be 0.90 or more, or 0.95 or more. The specific gravity ratio may be 1.10 or less, or 1.05 or less.

[0032] The specific gravity of the FO polymer and the F polymer is preferably independently 1.60 to 2.20, and more preferably 1.65 or more, more preferably 1.70 or more.

[0033] The specific gravity of the F polymer may be smaller than that of the FO polymer, or may be larger than that of the FO polymer. In particular, in the latter case, the above-mentioned mechanism of action is more likely to be realized. Alternatively, the specific gravity of the F polymer may be the same as that of the FO polymer.

[0034] A specific example of an F polymer having a larger specific gravity than an FO polymer is PTFE, which will be described later, and the FO polymer is any one of PFA, FEP, ETFE, FKM, FEPM, and FFKM, which will be described later.

[0035] When the polymer is an elastomer, the specific gravity is a value measured in accordance with JIS K 6268. Specifically, the masticated polymer is placed in a plastic bag, a weight is placed on top, and the bag is left to stand for 10 minutes or more, and the specific gravity is measured using an automatic hydrometer (device name: DSG-1, manufactured by Toyo Seiki Seisaku-sho).

[0036] When the polymer is PTFE, the specific gravity is a value measured in accordance with ASTM D4985-04. Specifically, the specific gravity is measured by placing 12.0 g of the polymer in a cylindrical mold (inner diameter: 28.6 mm) at 34.5 MPa for 2 minutes, heating the polymer at 120°C / hr, holding it at 380°C for 30 minutes, lowering the temperature at 60°C / hr, holding it at 294°C for 24 minutes, and then storing it in a desiccator at 23°C for 12 hours, and then measuring the specific gravity of the polymer sample relative to water at 23°C.

[0037] When the polymer is a resin other than PTFE, the specific gravity is a value measured in accordance with ASTM D-792 using an automatic hydrometer (device name: DSG-1, manufactured by Toyo Seiki).

[0038] In this method, the liquid viscosity of the reaction system is preferably less than 2 mPa·s, more preferably 1.8 mPa·s or less, and even more preferably 1.6 mPa·s or less. Furthermore, the liquid viscosity of the reaction system is preferably 0.8 mPa·s or more, and more preferably 1.0 mPa·s or more. In this case, the above-mentioned mechanism of action is more likely to occur.

[0039] The liquid viscosity in this specification is a value determined by measuring the liquid viscosity of the reaction system using a Brookfield viscometer at 25° C. and a rotation speed of 30 rpm. The viscosity measurement is repeated three times, and the average value of the three measurements is used.

[0040] In this method, the ratio of the liquid viscosity of the aqueous dispersion to the liquid viscosity of the reaction system is preferably greater than 1. Furthermore, the viscosity ratio is preferably less than 5. In this case, the above-mentioned mechanism of action is more likely to occur.

[0041] The thixotropy ratio of the liquid in the reaction system in this method is preferably 0.95 or more, more preferably 0.98 or more. The thixotropy ratio of the liquid is preferably 1.05 or less, more preferably 1.02 or less. The reaction system in this method preferably does not have thixotropy, in other words, the thixotropy ratio is preferably 1. In this case, the above-mentioned mechanism of action is more likely to occur.

[0042] In this specification, the thixotropy ratio of a liquid is measured using a Brookfield viscometer, and is calculated from the viscosity of the target liquid measured at 25°C and a rotation speed of 30 rpm and the viscosity of the target liquid measured at 60 rpm, and is the value obtained by dividing the former viscosity by the latter viscosity.

[0043] These liquid properties can be controlled by adjusting the type of FO polymer in the reaction system, the particle size of the FO particles, and the contents of the FO particles, water, or other components.

[0044] The FO polymer in this method is a polymer containing units based on a fluoroolefin, preferably a polymer containing units based on a gaseous fluoroolefin.

[0045] The fluoroolefin may be one type or a plurality of types.

[0046] The fluoroolefin is preferably vinyl fluoride, vinylidene fluoride (hereinafter also referred to as "VdF"), tetrafluoroethylene (hereinafter also referred to as "TFE"), or hexafluoropropylene (hereinafter also referred to as "HFP"), and more preferably contains at least TFE.

[0047] The FO polymer may contain units based on a monomer other than a fluoroolefin. The monomer is preferably a gaseous monomer other than a fluoroolefin. The monomer may be one type or multiple types.

[0048] Examples of the monomer include ethylene (hereinafter also referred to as "Et"), propylene (hereinafter also referred to as "Pp"), vinyl chloride, vinylidene chloride, chlorotrifluoroethylene (hereinafter also referred to as "CTFE"), perfluoroalkyl vinyl ether (hereinafter also referred to as "PAVE"), perfluoroalkyl allyl ether (hereinafter also referred to as "PAAE"), perfluoro-2-methylene-4-methyl-1,3-dioxolane, perfluoro-2,2-dimethyl-1,3-dioxole, perfluorobutenyl vinyl ether, and perfluoroallyl vinyl ether.

[0049] Examples of PAVE include CF2=CFOCF3 (hereinafter also referred to as "PMVE"), CF2=CFOCF2CF3 (hereinafter also referred to as "PEVE"), and CF2=CFOCF2CF2CF3 (hereinafter also referred to as "PPVE").

[0050] Examples of PAAE include CF2=CFCF2OCF3 (hereinafter also referred to as "PMAE") and CF2=CFCF2CF2OCF3 (hereinafter also referred to as "PEAE").

[0051] The monomer is preferably Et, Pp, vinyl chloride, vinylidene chloride, CTFE, PAVE, or PAAE, more preferably PAVE or PAAE, and even more preferably PMVE, PEVE, or PAAE, which increases the conformational freedom of the FO polymer and makes it easier to exhibit the above-mentioned mechanism of action.

[0052] The FO polymer preferably contains a monomer unit having a side chain, and is preferably FKM, FFKM, FEPM, or FEP, as described below, and more preferably FKM, FFKM, or FEPM, which increases the degree of conformational freedom of the FO polymer and makes it easier to exhibit the above-mentioned mechanism of action.

[0053] The glass transition temperature (hereinafter also referred to as "Tg") of the FO polymer is preferably from -50 to +10° C., more preferably from -45 to +5° C., even more preferably from -40 to +3° C., and particularly preferably from -35 to 0° C. In this case, the above-mentioned mechanism of action is more likely to be exhibited.

[0054] The FO polymer is preferably a polymer obtained by the method described below.

[0055] In this method, FO particles are dispersed in the liquid in the reaction system.

[0056] The average particle size of the FO particles is preferably 1 nm or more, more preferably 10 nm or more, even more preferably 25 nm or more, and particularly preferably 30 nm or more. The average particle size of the FO particles is preferably less than 150 nm, more preferably 120 nm or less. In this case, the above-mentioned mechanism of action is more likely to be realized.

[0057] The average particle size of particles in this specification is a particle size calculated by analyzing an autocorrelation function obtained by dynamic light scattering using a monodisperse cumulant method.

[0058] The content of FO particles in the reaction system of this method is preferably 0.01% by mass or more, based on the total mass of the reaction system. The content is preferably 4.0% by mass or less, more preferably 2.0% by mass or less, even more preferably 1.0% by mass or less, and particularly preferably 0.8% by mass or less. In this case, the above-mentioned mechanism of action is more easily manifested, and the content ratio in the resulting aqueous dispersion is particularly easily increased.

[0059] The method for forming the reaction system in this method is not particularly limited, but it is preferably formed by a method in which at least gaseous fluoroolefin is polymerized in the presence of water and a polymerization initiator without using a fluorine-based emulsifier. This method makes it easy to form a reaction system containing FO particles and water but not containing a fluorine-based emulsifier.

[0060] The gaseous fluoroolefin is preferably vinyl fluoride, VdF, TFE or HFP, and more preferably contains at least TFE.

[0061] The polymerization is preferably carried out by copolymerizing a gaseous fluoroolefin with a monomer other than the gaseous fluoroolefin.

[0062] Examples of the monomer other than the fluoroolefin include the monomers that form the monomer units that can be contained in the FO polymer described above.

[0063] The polymerization initiator used in the polymerization is preferably a water-soluble polymerization initiator, more preferably a persulfate, an organic peroxide, or an oxidation-reduction catalyst, and even more preferably a persulfate.

[0064] Examples of persulfates include ammonium persulfate (hereinafter also referred to as "APS") and potassium persulfate.

[0065] Examples of organic peroxides include disuccinic acid peroxide, bisglutaric acid peroxide, and tert-butyl hydroperoxide.

[0066] Examples of the oxidation-reduction catalyst include catalysts containing 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.

[0067] Oxidizing agents include potassium persulfate, APS, and sodium sulfite.

[0068] Inorganic salts include salts containing sulfate, sulfite or chloride anions and metal ions such as manganese, iron, cobalt, nickel, copper, zinc, cerium and silver, particularly iron(II) sulfate.

[0069] The polymerization initiator may be used alone or in combination with a plurality of types.

[0070] The amount of the polymerization initiator in the polymerization is preferably 0.01 to 5 mass%, more preferably 0.01 to 3 mass%, and even more preferably 0.01 to 2 mass%, based on the total mass of all monomers to be polymerized, including gaseous fluoroolefin.

[0071] The polymerization is carried out by maintaining the temperature above the half-life temperature of the polymerization initiator or by maintaining the pressure at 0.8 MPaG or higher. The polymerization is preferably carried out by maintaining the temperature above the half-life temperature of the polymerization initiator and the pressure at 0.8 MPaG or higher.

[0072] The half-life temperature of a polymerization initiator is usually a 10-hour half-life temperature, but when the polymerization initiator is a persulfate, it is set to 55°C. Typically, persulfates have a half-life at 55°C of 18 to 120 hours, and are polymerization initiators with high activity at 55°C. The polymerization initiator may be present in the reaction system by a conventional method, and may be added to the reaction system all at once, added in portions, or added continuously to the reaction system.

[0073] The temperature during the polymerization is preferably above 55° C., more preferably at least 60° C., and even more preferably at least 65° C. The temperature during the polymerization is preferably below 100° C. In this case, the above-mentioned mechanism of action is more likely to occur.

[0074] The pressure during the polymerization is preferably 0.9 MPaG or more, more preferably 1.0 MPaG or more. The pressure during the polymerization is preferably 4.0 MPaG or less, more preferably 3.5 MPaG or less. In this case, the above-mentioned mechanism of action is more likely to occur.

[0075] In this specification, "MPaG" refers to gauge pressure, which is the pressure obtained by subtracting atmospheric pressure (0.1013 MPa) from absolute pressure.

[0076] The pressure in the polymerization can be adjusted by introducing gaseous fluoroolefin into the reaction system by a conventional method. Specifically, the pressure in the polymerization can be adjusted by continuously or intermittently introducing gaseous fluoroolefin into the reaction system so that the pressure is a predetermined pressure. In addition, the pressure can be adjusted by using a gaseous monomer other than the gaseous fluoroolefin in combination.

[0077] In the polymerization, the polymerization time is preferably from 90 to 1000 minutes, more preferably from 90 to 700 minutes, in the case of batch processing.

[0078] The product liquid obtained by such a method may be used as a reaction system as it is, or may be used as a reaction system after adjusting the component types and contents in the product liquid, or may be used as a reaction system after the formation of a product liquid is confirmed in such a method.

[0079] Specific embodiments of preparing the product liquid obtained by the above-described method and then using it as a reaction system include adding water to the product liquid to adjust the FO particle content before using it as a reaction system, adding other components described below to the product liquid to adjust the liquid properties before using it as a reaction system, and treating the product liquid with an ion exchange resin to remove salts derived from the polymerization initiator and the like before using it as a reaction system. Alternatively, a reaction system may be formed by polymerizing at least gaseous fluoroolefin in the presence of a solvent other than water and a polymerization initiator without using a fluorine-based emulsifier, and then adding water. In this case, the liquid components of the reaction system may be substantially replaced with water by a solvent substitution method.

[0080] The reaction system in this method may contain components other than FO particles and water.

[0081] Specific examples of other components include chain transfer agents, emulsifiers other than fluorine-based emulsifiers, pH adjusters, and reducing agents.

[0082] Specific examples of chain transfer agents include ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane.

[0083] Specific examples of emulsifiers include sodium lauryl sulfate, Perex SS-H manufactured by Kao Chemical Corporation, and Newcol 1305-SN manufactured by Nippon Nyukazai Co., Ltd.

[0084] Specific examples of pH adjusters include phosphates such as disodium hydrogen phosphate and sodium dihydrogen phosphate, and carbonates such as sodium bicarbonate and sodium carbonate. The phosphate may be a hydrate such as disodium hydrogen phosphate dihydrate or disodium hydrogen phosphate dodecahydrate.

[0085] When the reaction system contains a chain transfer agent, its content is preferably 0.1 to 5 mass% relative to the total mass of the reaction system. The amount of the chain transfer agent used is preferably 0.1 to 20 mass%, more preferably 0.1 to 15 mass%, and even more preferably 0.1 to 10 mass%, relative to the amount of gaseous perfluoroolefin used.

[0086] When the reaction system contains an emulsifier other than a fluorine-containing emulsifier, the content thereof is preferably 5% by mass or less, more preferably 1% by mass or less, relative to the total mass of the reaction system. The content is preferably 0% by mass or more.

[0087] When the reaction system contains a pH adjuster, the content thereof is preferably 0.01 to 3.0% by mass relative to the total mass of the reaction system.

[0088] When the reaction system contains a reducing agent, the content thereof is preferably 0.1 to 2% by mass relative to the total mass of the reaction system.

[0089] In this method, the reaction system preferably contains 10 ppm by mass or less of persulfate ions or sulfate ions, preferably 5 ppm by mass or less. The lower limit of the content is preferably 0 ppm. When the content is within this range, coloration of the F polymer is suppressed, and the physical properties of the aqueous dispersion tend to improve. Specific examples of cases in which these ions are contained in the reaction system include cases in which the polymerization initiator in the above-mentioned method is a persulfate. In this case, it is preferable to treat the product solution obtained by the above-mentioned method with an ion exchange resin to remove these ions.

[0090] In this method, the reaction system preferably has a fluoride ion concentration of 100 mass ppm or less, more preferably 50 mass ppm or less. The lower limit of the fluoride ion content is preferably 0 mass ppm. Specific examples of fluoride ions contained in the reaction system include by-products containing fluoride ions produced by the reaction of a polymerization initiator (e.g., APS) with a fluoroolefin.

[0091] Polymerization in the reaction system in this method (hereinafter also referred to as "main polymerization") is carried out by polymerizing gaseous perfluoroolefin. The gaseous perfluoroolefin may be one type or multiple types.

[0092] The gaseous perfluoroolefin is preferably TFE or HFP, and more preferably contains at least TFE.

[0093] The main polymerization may be carried out in the presence of a monomer other than the gaseous perfluoroolefin, and it is preferable to copolymerize the gaseous perfluoroolefin with the monomer.

[0094] The monomer may be a gaseous monomer or a liquid monomer, and the number of types of the monomer may be one or more.

[0095] Examples of the monomer include Et, Pp, vinyl chloride, vinylidene chloride, VdF, CTFE, fluoroalkylethylene (hereinafter also referred to as "FAE"), PAVE, PAAE, fluoromonomers having a fluorosulfonyl group, a carboxy group, or an alkoxycarbonyl group, perfluoro-2-methylene-4-methyl-1,3-dioxolane, perfluoro-2,2-dimethyl-1,3-dioxole, perfluorobutenyl vinyl ether, and perfluoroallyl vinyl ether.

[0096] FAEs include CH2=CH(CF2)2F, CH2=CH(CF2)3F, CH2=CH(CF2)4F, CH2=CF(CF2)3H, and CH2=CF(CF2)4H.

[0097] Examples of fluoromonomers having a fluorosulfonyl group, a carboxy group, or an alkoxycarbonyl group include CF2=CFSO2F, CF2=CFO(CFCF(CF3))OCF2CF2SO2F, and CF2=CFO(CF2)3COOCH3.

[0098] In this polymerization, the amount of gaseous perfluoroolefin used is preferably 10 mol% or more, more preferably 30 mol% or more, and preferably 40 mol% or more, based on the total amount of monomers used in the polymerization. The amount of gaseous perfluoroolefin used is preferably 100 mol% or less.

[0099] In addition, when a monomer other than gaseous perfluoroolefin is used in this polymerization, the amount of gaseous perfluoroolefin used is preferably 90 mol% or less, more preferably 70 mol% or less, and preferably 60 mol% or less, based on the total amount of monomers used in the polymerization. In this case, the amount of gaseous perfluoroolefin used is preferably more than 0 mol%.

[0100] In this polymerization, the amount of gaseous perfluoroolefin used is preferably 1 to 60 mass%, more preferably 1 to 50 mass%, and even more preferably 1 to 40 mass%, relative to the content of the liquid components in the reaction system. When a monomer other than gaseous perfluoroolefin is used, the total amount of gaseous perfluoroolefin and the monomer used is preferably within this range.

[0101] The polymerization is preferably carried out in the presence of a polymerization initiator, in other words, the reaction system in the present method preferably contains a polymerization initiator.

[0102] Examples of the polymerization initiator include an oil-soluble radical initiator, a water-soluble polymerization initiator, and a water-soluble oxidation-reduction catalyst.

[0103] Examples of the water-soluble polymerization initiator and the water-soluble redox catalyst include the agents described above.

[0104] Examples of the oil-soluble radical initiator include tert-butyl peroxypivalate and diisopropyl peroxydicarbonate. One or more polymerization initiators may be used.

[0105] The polymerization initiator is preferably an oil-soluble polymerization initiator or a water-soluble radical initiator, and can be selected depending on the type of the target F polymer.

[0106] The amount of the polymerization initiator used is preferably 0.01 to 5 mass %, more preferably 0.01 to 3 mass %, and even more preferably 0.01 to 2 mass %, based on the total mass of the monomers to be polymerized.

[0107] In this polymerization, the gaseous perfluoroolefin may be introduced into the reaction system by a conventional method. Specifically, the gaseous perfluoroolefin may be continuously or intermittently introduced into the reaction system so that the polymerization pressure reaches a predetermined pressure. The polymerization initiator may also be present in the reaction system by a conventional method, and may be added to the reaction system all at once, may be added in portions to the reaction system, or may be added continuously to the reaction system.

[0108] The temperature in the main polymerization is preferably 10 to 95°C, more preferably 15 to 90°C.

[0109] The pressure in the main polymerization is preferably 0.5 to 4.0 MPaG, more preferably 0.6 to 3.5 MPaG.

[0110] In the main polymerization, the polymerization time is preferably from 90 to 1000 minutes, more preferably from 90 to 700 minutes, in the case of batch treatment.

[0111] The aqueous dispersion obtained by this method (hereinafter also referred to as "this dispersion") contains particles of the F polymer (F particles) dispersed in the liquid.

[0112] The F polymer as a whole is preferably a polymer containing VdF units and TFE units or HFP units, a polymer containing TFE units and Pp units, a polymer containing TFE units and PAVE units or PAAE units, a polymer consisting of TFE units, a polymer containing TFE units and HFP units, or a polymer containing TFE units and Et units.

[0113] The polymer containing VdF units and TFE units or HFP units is preferably a fluoroelastomer FKM containing 20 to 60 mol% of VdF units and 40 to 80 mol% of TFE units or HFP units. The FKM may further contain other units such as PAVE units and Pp units.

[0114] The polymer containing TFE units and Pp units is preferably FEPM, which is a fluoroelastomer containing 30 to 70 mol % of TFE units and 30 to 70 mol % of Pp units. FEPM may further contain other units such as VdF units.

[0115] The polymer containing TFE units and PAVE units or PAAE units is preferably FFKM, a fluoroelastomer containing 40 to 85 mol% of TFE units and 15 to 60 mol% of PAVE units, or PFA, a fluororesin containing 90 to 99.5 mol% of TFE units and 0.5 to 10 mol% of PAVE units. The PAVE units in FFKM are preferably PMVE units or PEVE units, more preferably PMVE units. The PAVE units in PFA are preferably PEVE units or PPVE units, more preferably PPVE units. PFA may further contain other units such as HFP units and FAE units.

[0116] The polymer consisting of TFE units is preferably PTFE, which is a fluororesin consisting only of TFE units, or modified PTFE, which is a fluororesin consisting of TFE units and trace amounts of other monomer units. The content of other monomer units in the modified PTFE is preferably less than 0.1 mol%. Examples of other monomer units contained in the modified PTFE include PAVE units, HFP units, FAE units, and CTFE units.

[0117] The polymer containing TFE units and HFP units is preferably FEP, which is a fluororesin containing 55 to 97 mol% of TFE units and 3 to 45 mol% of HFP units. FEP may further contain other units such as PAVE units and FAE units.

[0118] The polymer containing TFE units and Et units is preferably ETFE, which is a fluororesin containing 35 to 65 mol% of TFE units and 35 to 65 mol% of Et units. ETFE may further contain other units such as PAVE units, HFP units, and FAE units.

[0119] The fluoroelastomer may further contain a monomer unit having a functional group that forms a crosslinking site, such as an iodine atom, a bromine atom, or a nitrile group (such as a fluorovinyl ether monomer unit having the functional group).

[0120] The F polymer and the FO polymer may be polymers composed of the same monomer units and having the same content of the monomer units, and may be the same polymer as a whole. Alternatively, the F polymer and the FO polymer may be polymers composed of the same monomer units but having different content of the monomer units, or may be polymers composed of different monomer units.

[0121] The viscosity of the dispersion is preferably less than 10 mPa·s, more preferably 5 mPa·s or less, and even more preferably 2 mPa·s or less.

[0122] The thixotropy ratio of the dispersion is preferably 0.95 or more, more preferably 0.98 or more. The thixotropy ratio of the dispersion is preferably 1.05 or less, more preferably 1.02 or less. The dispersion is preferably non-thixotropic, i.e., has a thixotropy ratio of 1.

[0123] According to this method, a dispersion having such excellent liquid physical properties can be easily obtained directly due to the above-mentioned mechanism of action.

[0124] The average particle size of the F particles in the present dispersion is preferably more than 50 nm, more preferably 70 nm or more, and even more preferably 100 nm or more. The average particle size of the F particles is preferably 1000 nm or less, more preferably 500 nm or less, and even more preferably 400 nm or less.

[0125] The particle size distribution of the F particles in this dispersion is preferably unimodal. Furthermore, the polydispersity index of the particle sizes of the F particles is preferably 0.5 or less, more preferably 0.25 or less. According to this method, a dispersion with excellent particle properties can be easily obtained due to the above-mentioned mechanism of action.

[0126] The polydispersity index is the width of the particle size distribution determined by analyzing the autocorrelation function obtained by dynamic light scattering using the cumulant method. A smaller value indicates a narrower particle size distribution of the F particles dispersed in a liquid.

[0127] The content of F particles in the dispersion is preferably more than 4.0% by mass, more preferably 5% by mass or more, and even more preferably 10% by mass or more, based on the total mass of the dispersion. The content of F particles is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less.

[0128] The water content in the dispersion is preferably less than 96.0% by mass, more preferably 95% by mass or less, and even more preferably 90% by mass or less, based on the total mass of the dispersion. The water content is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more.

[0129] Furthermore, the sum of the F particle content and the water content in the dispersion is preferably 90% by mass or more, more preferably 96% by mass or more, based on the total mass. The upper limit of this sum is 100% by mass. Due to the above-mentioned mechanism, this method can efficiently produce an aqueous dispersion containing a high content of dense F particles with excellent dispersibility in liquid, essentially using water as the liquid medium.

[0130] The particle size ratio in this method is the value obtained by dividing the average particle size of F particles in the dispersion by the average particle size of FO particles in the reaction system, and is greater than 1, may be 1.1 or greater, may be 1.2 or greater, may be 1.5 or greater, or may be greater than 2. The particle size ratio may be 10 or less, may be 5 or less, or may be 2 or less.

[0131] The content ratio in this method is the value obtained by dividing the content of F particles in the dispersion by the content of FO particles in the reaction system, and is 2 or more, optionally 5 or more, optionally 7 or more, or optionally 10 or more. The content ratio may be 500 or less, optionally 250 or less, optionally 100 or less, optionally 50 or less, or optionally 25 or less. The content ratio is a value calculated from the respective contents (% by mass).

[0132] Due to the above-mentioned mechanism of action, this method allows the production of an aqueous dispersion by selecting the desired particle size ratio and content ratio. The particle size ratio and content ratio in this method can be appropriately determined depending on the physical properties of the target F polymer, the physical properties of the target aqueous dispersion, and the intended use.

[0133] For example, when a fluoroelastomer is used as the FO polymer to produce the present dispersion containing particles of an F polymer with excellent fluoroelastomer properties, the particle size ratio and content ratio are preferably 1.2 to 5 and 2 to 100, respectively, and the average particle sizes of the FO particles and F particles are preferably 25 to 150 nm and 30 to 400 nm, respectively.

[0134] For example, when a fluoroelastomer is used as the FO polymer to produce the present dispersion containing particles of an F polymer with excellent fluororesin properties, the particle size ratio and content ratio are preferably 1.2 to 5 and 2 to 50, respectively, and the average particle sizes of the FO particles and F particles are preferably 25 to 150 nm and 30 to 300 nm, respectively.

[0135] For example, when using a fluororesin as the FO polymer to produce the present dispersion containing particles of an F polymer with excellent fluororesin properties, the particle size ratio and content ratio are preferably 1.5 to 10 and 2 to 100, respectively, and the average particle size of the FO particles and the average particle size of the F particles are preferably 50 to 200 nm and 100 to 400 nm, respectively.

[0136] Fluororesins include PTFE, modified PTFE, ETFE, PFA, and FEP.

[0137] Fluoroelastomers include FKM, FEPM, and FFKM.

[0138] According to this method, the polymerization of gaseous perfluoroolefin proceeds precisely due to the above-mentioned mechanism of action, so that the by-production of low molecular weight substances derived from the gaseous perfluoroolefin contained in the dispersion can be suppressed, and in particular, when the gaseous perfluoroolefin contains tetrafluoroethylene, the generation amounts of the compound represented by the following formula (S1) and the compound represented by the formula (S2) can be suppressed.

[0139] Formula (S1): H-(CF2) n -COO - M + Formula (S2): H-(CF2) n -SO3 - M +

[0140] In the formula, M each independently represents H, Na, K, or NH4, n in the compound represented by formula (S1) represents an integer of 7 to 11, and n in the compound represented by formula (S2) represents an integer of 8 to 12.

[0141] In the aqueous dispersion in this method (hereinafter also referred to as "the dispersion"), the content of the compound represented by formula (S1) and the content of the compound represented by formula (S2) are preferably 100 mass ppb or less, more preferably 50 mass ppb or less, and even more preferably 25 mass ppb or less, relative to the total mass of the F particles. The lower limit of the content is preferably 0 mass ppb. In other words, the aqueous dispersion in this method preferably does not contain these compounds.

[0142] This dispersion is an aqueous dispersion in which F particles with high dispersion stability are dispersed, and can be suitably used as a coating agent, binder agent, etc.

[0143] Alternatively, the water contained in the dispersion may be replaced with an organic solvent such as N-methylpyrrolidone or acetone to prepare a dispersion containing F particles using such an organic solvent as a liquid dispersion medium.

[0144] Alternatively, the F particles may be aggregated from the dispersion to obtain a powder of F particles. The powder of F particles obtained by aggregation may be directly processed into a molded product by melt molding or the like. Furthermore, the powder of F particles obtained by aggregation may be homogenized by melt kneading or the like and processed into a molding base material in the form of pellets, granules, or the like.

[0145] Examples of the flocculation method include mechanical flocculation, freeze flocculation, acid flocculation, base flocculation, and flocculation using a flocculant, and mechanical flocculation, acid flocculation, and flocculation using a flocculant are preferred.

[0146] The aggregation temperature in the freeze aggregation is preferably −20 to 0° C. The aggregation time is preferably 1 hour or more, more preferably 2 hours or more.

[0147] In the case of acid coagulation, a method of adding an acid-containing solution to the dispersion is preferred. Examples of acids include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, and hydrofluoric acid. The acid concentration of the acid-containing solution is preferably 1 to 10% by mass.

[0148] In the case of base coagulation, a method in which a solution containing a base is added to the dispersion is preferred. Examples of the base include sodium hydroxide, potassium hydroxide, ammonium carbonate, etc. The concentration of the base in the solution containing the base is preferably 1 to 10% by mass.

[0149] In the case of using a coagulant, it is preferable to add the coagulant to the dispersion, and examples of the coagulant include aluminum sulfate, alum, calcium nitrate, magnesium sulfate, and ammonium carbonate. [Example]

[0150] The present disclosure will be described in detail below using examples, but the present disclosure is not limited thereto. The abbreviations in the examples have the following meanings.

[0151] APS: Ammonium persulfate TFE: Tetrafluoroethylene (CF2=CF2) VdF: Vinylidene fluoride (CH2=CF2) HFP: hexafluoropropylene (CF2=CFCF3) PMVE: Perfluoromethyl vinyl ether (CF2=CFOCF3) PMAE: Perfluoromethyl allyl ether (CF2 = CFCF2OCF3) Et: Ethylene (CH2=CH2)

[0152] The average particle size of the particles in the dispersion was measured using a laser diffraction / scattering particle size distribution analyzer (Otsuka Electronics Co., Ltd., ELSZ).

[0153] The content of the compound represented by (S1) and the content of the compound represented by (S2) in the dispersion were each calculated using an aqueous dispersion, among the measurement methods using a liquid chromatograph mass spectrometer described in paragraphs

[0710] to

[0732] of WO 2018 / 181904. The instrument used was an Agilent 1260 Series HPLC / 6460S, and the column used was an Imtakt Cadenza CD-C18.

[0154] The sulfate ion concentration in the dispersion was determined by freeze-flocculating the aqueous dispersion, filtering the collected liquid, and analyzing it with ion chromatography. The ion chromatograph ICS-5000 (Thermo Fisher Scientific) was used for the ion chromatography analysis. A Dionex IonPac AS-19 separation column and a Dionex IonPac AG-19 guard column were used, and KOH was used as the eluent.

[0155] All reactors used were made of stainless steel.

[0156] [Example 1] Example of producing aqueous dispersion A pressure-resistant reactor (internal volume 2.2 L) was charged with ultrapure water (1130 g), 30% by mass aqueous ammonia solution (30 mg), PMVE (72 g), and TFE (14 g). The mixture was heated to 90 °C while stirring at 600 rpm. Next, an APS aqueous solution (5.0% by mass, 30 mL) was added to initiate polymerization. TFE was added to compensate for the decrease in reactor pressure associated with polymerization, maintaining the pressure at 0.8 MPaG or higher. After 4 g of TFE had been injected, the reactor was cooled to terminate the polymerization reaction. The gas remaining in the reactor was recovered, and the liquid was withdrawn to obtain a mother liquor. The mother liquor was a dispersion of FO polymer particles (specific gravity: 2.04) containing 34 mol% PMVE units and 66 mol% TFE units.

[0157] Ultrapure water and ion exchange resin were added to the mother liquor, and the mixture was stirred and filtered to obtain a treated liquid. This treated liquid was a dispersion of the FO polymer particles (average particle diameter: 98 nm). The content of the particles in the liquid was 0.6% by mass.

[0158] A pressure-resistant reactor (internal volume 1.2 L) was charged with ultrapure water (175 g) and the treatment liquid (1000 mL) to form a reaction system (liquid viscosity: 1.0 mPa·s, thixotropy ratio: 1.00) containing 0.5% by mass of the particles. PMVE (72 g) and TFE (14 g) were charged into the reactor, and the temperature was raised to 80 °C while stirring at 600 rpm. TFE and PMVE were injected until the reactor pressure reached 1.2 MPaG, and an APS aqueous solution (2.5% by mass, 7 mL) was added to initiate polymerization. As the pressure in the reactor decreased during polymerization, TFE and PMVE were alternately injected to maintain a constant pressure. When 80 g of TFE and 63 g of PMVE had been injected, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 138 minutes.

[0159] After the gas remaining in the reactor was collected, the liquid content was extracted to obtain an aqueous dispersion.

[0160] The aqueous dispersion contained 11.5 mass% of fluoropolymer particles (average particle size: 141.1 nm) with a specific gravity of 2.04 and a total of 66 mol% TFE units and 34 mol% PMVE units (liquid viscosity: 1.1 mPa·s, thixotropic ratio: 1.00). The specific gravity ratio was 1.00. The aqueous dispersion exhibited excellent liquid properties, such as dispersion stability, and ease of handling. The fluoropolymer exhibited excellent physical properties in relation to the fluoroelastomer FFKM. The particle size distribution was monomodal, with a polydispersity index of less than 0.5.

[0161] The contents of the compounds represented by the formula (S1) and the formula (S2) contained in the aqueous dispersion relative to the total mass of the particles in the aqueous dispersion were both 100 ppb by mass or less.

[0162] [Example 2] Example of production of aqueous dispersion A pressure-resistant reactor (internal volume 2.1 L) was charged with ultrapure water (1162 g), 28% NH3 aqueous solution (1 drop), PMVE (70 g), and TFE (14 g), and the internal temperature was raised to 80 °C while stirring at 600 rpm. An aqueous solution of APS (5.9 mass%, 5 mL) was added to initiate polymerization. TFE was injected to compensate for the decrease in pressure inside the reactor due to polymerization, and the pressure was maintained at 0.8 MPaG or higher. When 24 g of TFE had been injected, the reactor was cooled to terminate the polymerization reaction. After recovering the gas remaining in the reactor, the solution inside the reactor was withdrawn to obtain a mother liquor.

[0163] The mother liquor was a dispersion of particles (average particle size: 110 nm) of an FO polymer (specific gravity: 2.04) containing 34.4 mol % of PMVE units and 65.6 mol % of TFE units. The content of the particles in the liquid was 3.0 mass %.

[0164] Ultrapure water (520.5 g), mother liquor (92.5 ml), disodium hydrogen phosphate dodecahydrate (0.5 g), and t-BuOH (16.5 g) were charged into a pressure reactor (internal volume 1.2 L) to form a reaction system (liquid viscosity: 1.1 mPa s, thixotropy ratio: 1.00) containing 0.22 mass% of the particles.

[0165] The reaction system was stirred at 320 rpm while the internal temperature was raised to 60°C. A mixed gas (a gas containing 86 mol% and 14 mol% of TFE and Et, respectively; the same applies below) was injected into the reactor until the pressure inside the reactor reached 2.6 MPaG. An aqueous solution of tert-butyl hydroperoxide (0.2 mass%, 2 mL) and a reducing agent (BRUGGOLITE® FF6M, 0.396 mass%, 2 mL) were added to the reactor to initiate polymerization. The pressure inside the reactor was maintained constant by adding the mixed gas to compensate for the decrease in pressure caused by polymerization. An aqueous solution of tert-butyl hydroperoxide (0.2 mass%, 1 mL) and the reducing agent (1 mL) were added every 5 minutes after the start of polymerization. When the amount of injected mixed gas reached 80 g, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 181 minutes.

[0166] After the gas remaining in the reactor was collected, the liquid content was extracted to obtain an aqueous dispersion.

[0167] The aqueous dispersion contained 10.2 mass% of fluoropolymer particles (average particle size: 182 nm) with a specific gravity of 1.73 and a total of 56.9 mol% TFE units, 42.4 mol% Et units, and 0.7 mol% PMVE units (liquid viscosity: 1.3 mPa·s, thixotropy ratio: 1.00). The specific gravity ratio was 0.85. The aqueous dispersion exhibited excellent liquid properties, including dispersion stability, and ease of handling. The fluoropolymer exhibited excellent physical properties compared to the fluororesin ETFE. The particle size distribution was monomodal, with a polydispersity index of less than 0.5.

[0168] The contents of the compounds represented by the formula (S1) and the formula (S2) contained in the aqueous dispersion relative to the total mass of the particles in the aqueous dispersion were both 100 ppb by mass or less.

[0169] [Example 3] Example of production of aqueous dispersion Ultrapure water and ion exchange resin were added to the mother liquor obtained in Example 1, and the mixture was stirred and filtered to obtain a treated liquid. This treated liquid was a dispersion of particles (average particle size: 110 nm) of an FO polymer (specific gravity: 2.04) containing 34.4 mol% of PMVE units and 65.6 mol% of TFE units. The content of the particles in the liquid was 1.5 mass%.

[0170] Ultrapure water (428 g), treatment solution (185 ml), disodium hydrogen phosphate dodecahydrate (0.5 g), and t-BuOH (16.5 g) were charged into a pressure reactor (internal volume 1.2 L) to form a reaction system containing 0.44 mass% of the particles (liquid viscosity: 1.3 mPa·s, thixotropy ratio: 1.00).

[0171] The reaction system was stirred at 320 rpm, and the internal temperature was raised to 60°C. A mixed gas (a gas containing 86 mol% and 14 mol% of TFE and Et, respectively; the same applies below) was injected into the reactor until the pressure inside the reactor reached 2.6 MPaG, and an aqueous solution of tert-butyl hydroperoxide (0.2 mass%, 2 mL) and the reducing agent were added to the reactor to initiate polymerization. The pressure inside the reactor decreased with polymerization, and the mixed gas was added to maintain a constant pressure. An aqueous solution of tert-butyl hydroperoxide (0.2 mass%, 1 mL) and the reducing agent (1 mL) were added every 5 minutes after the start of polymerization. When the amount of injected mixed gas reached 80 g, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 167 minutes.

[0172] After the gas remaining in the reactor was collected, the liquid content was extracted to obtain an aqueous dispersion.

[0173] The aqueous dispersion contained 10.6 mass% of fluoropolymer particles (average particle size: 156 nm) with a specific gravity of 1.73 and a total of 56.3 mol% TFE units, 43.1 mol% Et units, and 0.6 mol% PMVE units (liquid viscosity: 1.4 mPa·s, thixotropy ratio: 1.00). The specific gravity ratio was 0.85. The aqueous dispersion exhibited excellent liquid properties, including dispersion stability, and ease of handling. The fluoropolymer exhibited excellent physical properties compared to the fluororesin ETFE. The particle size distribution was monomodal, with a polydispersity index of less than 0.5.

[0174] The content of the compounds represented by formula (S1) and formula (S2) contained in the aqueous dispersion relative to the total mass of the particles in the aqueous dispersion was 100 ppb by mass or less, and the sulfate ion concentration in the aqueous dispersion was less than 0.1 ppm by mass.

[0175] [Example 4] Example of production of aqueous dispersion Ultrapure water (717 g), PMVE (50 g), and TFE (8 g) were charged into a pressure-resistant reactor (internal volume 1.3 L) and heated to 90°C while stirring at 500 rpm. An aqueous solution of APS (3.6 mass%, 5 mL) was added to initiate polymerization. TFE was injected to compensate for the decrease in pressure inside the reactor due to polymerization, and the pressure was maintained at 1.4 MPaG. When 2 g of TFE had been injected, the reactor was cooled to terminate the polymerization reaction. The gas remaining in the reactor was recovered, and the solution in the reactor was withdrawn to obtain a mother liquor.

[0176] The mother liquor was a dispersion of particles of an FO polymer (specific gravity: 2.04) containing 48 mol % of PMVE units and 52 mol % of TFE units.

[0177] An ion exchange resin was added to the mother liquor, and the mixture was stirred and filtered to obtain a treated liquid containing FO polymer particles (average particle size: 87 nm) at a content of 0.6% by mass.

[0178] Ultrapure water (121 g), treatment liquid (475 g), and wax (28 g) were charged into a pressure-resistant reactor (internal volume 1.0 L) to form a reaction system (liquid viscosity: 1.3 mPa·s, thixotropy ratio: 1.00) containing 0.48 mass% of the particles.

[0179] The reaction system was stirred at 260 rpm while the internal temperature was raised to 70°C. TFE was injected into the reactor until the pressure inside the reactor reached 1.4 MPaG, and an aqueous solution of APS (0.2 mass%, 5 mL) was added to the reactor to initiate polymerization. TFE was added to compensate for the decrease in the internal pressure of the reactor that occurred during polymerization, and the pressure was maintained constant. When the amount of injected TFE reached 110 g, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 220 minutes.

[0180] After the gas remaining in the reactor was collected, the liquid content was extracted to obtain an aqueous dispersion.

[0181] The aqueous dispersion contained 16.0 mass% fluoropolymer particles (average particle size: 228 nm) containing 99.1 mol% TFE units and 0.9 mol% PMVE units (liquid viscosity: 1.5 mPa·s, thixotropy ratio: 1.00). The specific gravity ratio was 1.07. The aqueous dispersion exhibited excellent liquid properties, such as dispersion stability, and ease of handling. The fluoropolymer exhibited excellent physical properties compared to PTFE, a fluororesin (specific gravity: 2.18). Specifically, the melting point of the fluoropolymer was 338°C, and its crystallization energy was -35 J / g. The particle size distribution was monomodal, with a polydispersity index of less than 0.5.

[0182] The contents of the compounds represented by the formula (S1) and the formula (S2) contained in the aqueous dispersion relative to the total mass of the particles in the aqueous dispersion were both 100 ppb by mass or less.

[0183] [Example 5] Example of production of aqueous dispersion Distilled water (717 g), 28% by mass ammonia water (one drop), and a mixed gas of TFE and HFP were charged into a pressure-resistant reactor (internal volume 1.0 L) and heated to 90°C while stirring at 500 rpm. The internal pressure of the reactor after reaching 90°C was 1.64 MPaG. Next, an aqueous solution of APS (3.6% by mass, 5 mL) was added to initiate polymerization. TFE was injected to compensate for the decrease in internal pressure of the reactor due to polymerization, and the pressure was maintained constant. 3 g of TFE was injected, and 72 minutes later, the reactor was cooled to terminate the polymerization reaction. The gas remaining in the reactor was recovered, and the solution in the reactor was withdrawn to obtain a mother liquor.

[0184] The mother liquor was added with ion exchange resin, stirred, and filtered to obtain a treated solution, which was a dispersion of particles (average particle size: 103 nm) of FO polymer (specific gravity: 2.12) containing 83 mol % of TFE units and 17 mol % of HFP units.

[0185] A pressure-resistant reactor (internal volume 1.0 L) was charged with the treatment liquid (600.0 g) and wax (28 g) to form a reaction system (liquid viscosity: 1.2 mPa·s, thixotropy ratio: 1.00) containing 0.72 mass % of the particles.

[0186] The reaction system was stirred at 260 rpm, and the internal temperature was raised to 70°C. TFE was injected into the reactor until the pressure inside the reactor reached 1.4 MPaG, and an aqueous solution of disuccinic acid peroxide (0.56 mass%, 11 mL) was added to the reactor to initiate polymerization. TFE was added to compensate for the decrease in the internal pressure of the reactor due to polymerization, and the pressure was kept constant. After 216 minutes, when the amount of TFE consumed reached 50 g, the reactor was cooled to terminate the polymerization reaction.

[0187] After the gas remaining in the reactor was collected, the liquid content was extracted to obtain an aqueous dispersion.

[0188] The aqueous dispersion contained 7.7 mass% of fluoropolymer particles (average particle size: 301 nm) with a specific gravity of 2.18 and a total of 99.1 mol% TFE units and 0.9 mol% HFP units (liquid viscosity: 1.4 mPa·s, thixotropy ratio: 1.00). The specific gravity ratio was 1.03. The aqueous dispersion exhibited excellent liquid properties, including dispersion stability, and ease of handling. The fluoropolymer exhibited excellent physical properties compared to PTFE, a fluororesin. Specifically, the melting point of the fluoropolymer was 338°C, and its DSC heat of fusion was 64 J / g. The particle size distribution was monomodal, with a polydispersity index of less than 0.5.

[0189] Furthermore, the contents of the compounds represented by the formula (S1) and the formula (S2) contained in the aqueous dispersion relative to the total mass of the particles in the aqueous dispersion were both 100 ppb by mass or less.

[0190] [Example 6] Example of production of aqueous dispersion Distilled water (717 g), 28% by mass ammonia water (one drop), and a mixed gas of TFE and HFP were charged into a pressure-resistant reactor (internal volume 1.0 L) and heated to 90°C while stirring at 500 rpm. The pressure inside the reactor after reaching 90°C was 1.94 MPaG. Next, an aqueous solution of APS (3.6% by mass, 5 mL) was added to initiate polymerization. After 97 minutes, the polymerization was terminated when the pressure inside the reactor reached 1.78 MPaG. After recovering the gas remaining in the reactor, the solution inside the reactor was removed to obtain a mother liquor.

[0191] The mother liquor was added with ion exchange resin, stirred, and filtered to obtain a treated solution, which was a dispersion of particles (average particle size: 97 nm) of FO polymer (specific gravity: 2.12) containing 77 mol % of TFE units and 23 mol % of HFP units.

[0192] A pressure-resistant reactor (internal volume 1.0 L) was charged with the treatment liquid (600.0 g), CH2=CH(CF2)4F (0.73 g), and t-butyl methyl ether (0.51 g), forming a reaction system (liquid viscosity: 1.0 mPa s, thixotropy ratio: 1.00) containing 0.77 mass% of the particles.

[0193] The reaction system was stirred at 260 rpm while the internal temperature was raised to 70°C. TFE was injected into the reactor until the pressure inside the reactor reached 1.8 MPaG, and an isododecane solution of tert-butyl peroxypivalate (40% by mass, 2 mL) was added to the reactor to initiate polymerization. The pressure inside the reactor decreased with the polymerization, so the pressure was maintained constant by adding a mixed gas (a gas containing TFE and Et, in that order, 86 mol% and 14 mol%, respectively; the same applies below). An additional 1.6 g of the isododecane solution was also added. When the amount of injected mixed gas reached 50 g, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 170 minutes.

[0194] After the gas remaining in the reactor was collected, the liquid content was extracted to obtain an aqueous dispersion.

[0195] The aqueous dispersion contained 7.2 mass% of fluoropolymer particles (average particle size: 155 nm) with a specific gravity of 1.74 and a total of 55.0 mol% TFE units, 43.8 mol% Et units, 0.8 mol% PFBE units, and 0.4 mol% HFP units (liquid viscosity: 1.2 mPa·s, thixotropic ratio: 1.00). The specific gravity ratio was 0.82. The aqueous dispersion exhibited excellent liquid properties, including dispersion stability, and ease of handling. The fluoropolymer exhibited excellent physical properties compared with the fluororesin ETFE. Specifically, the melting point of the fluoropolymer was 244°C, and its DSC heat of fusion was 43 J / g. The particle size distribution was monomodal, with a polydispersity index of less than 0.5.

[0196] The contents of the compounds represented by the formula (S1) and the formula (S2) contained in the aqueous dispersion relative to the total mass of the particles in the aqueous dispersion were both 100 ppb by mass or less.

[0197] [Example 7] Example of production of aqueous dispersion Ultrapure water (717 g) was charged into a pressure-resistant reactor (internal volume 1.3 L) and heated to 90 °C while stirring at 500 rpm. A mixed gas containing 18 mol% TFE and 82 mol% PMAE, in that order, was injected until the reactor pressure reached 1.5 MPaG. Next, an aqueous solution of APS (3.6 mass%, 5 mL) was added to initiate polymerization. After 180 minutes, the reactor was cooled to terminate the polymerization. The gas remaining in the reactor was recovered, and the solution in the reactor was removed to obtain a mother liquor.

[0198] The mother liquor was added with ion exchange resin, stirred, and filtered to obtain a treated liquid. This treated liquid was a dispersion of particles (average particle size: 70 nm) of FO polymer (specific gravity: 2.04) containing 69 mol% TFE units and 31 mol% PMAE units. The content of the particles in the treated liquid was 0.94 mass%.

[0199] Ultrapure water (121 g), treatment liquid (475 g), and wax (28 g) were charged into a pressure-resistant reactor (internal volume 1.0 L) to form a reaction system (liquid viscosity: 1.2 mPa·s, thixotropy ratio: 1.00) containing 0.75 mass% of the particles.

[0200] The reaction system was stirred at 260 rpm, and the internal temperature was raised to 70°C. TFE was injected into the reactor until the pressure inside the reactor reached 1.4 MPaG, and an aqueous solution of disuccinic acid peroxide (0.45% by mass, 3 mL) was added to the reactor to initiate polymerization. TFE was added to compensate for the decrease in the internal pressure of the reactor due to polymerization, and the pressure was kept constant. After 450 minutes, when the amount of injected TFE reached 170 g, the reactor was cooled to terminate the polymerization reaction.

[0201] After the gas remaining in the reactor was collected, the liquid content was extracted to obtain an aqueous dispersion.

[0202] The aqueous dispersion contained 20.0 mass% of fluoropolymer particles (average particle size: 270 nm) with a specific gravity of 2.18 and a total of 99.6 mol% TFE units and 0.4 mol% PMAE units (liquid viscosity: 1.4 mPa·s, thixotropic ratio: 1.00). The specific gravity ratio was 1.07. The aqueous dispersion exhibited excellent liquid properties, including dispersion stability, and ease of handling. The fluoropolymer exhibited excellent physical properties compared with PTFE, a fluororesin. Specifically, the melting point of the fluoropolymer was 345°C, and its DSC heat of fusion was 16.5 J / g. The particle size distribution was monomodal, with a polydispersity index of less than 0.5.

[0203] The contents of the compounds represented by the formula (S1) and the formula (S2) contained in the aqueous dispersion relative to the total mass of the particles in the aqueous dispersion were both 100 ppb by mass or less.

[0204] The sulfate ion concentration in the aqueous dispersion was less than 0.1 ppm by mass.

[0205] [Example 8] Example of production of aqueous dispersion Ultrapure water (717 g) was charged into a pressure-resistant reactor (internal volume 1.0 L) and heated to 90 °C while stirring at 500 rpm. A mixed gas of TFE and VdF was then injected until the reactor pressure reached 1.98 MPaG. Next, an aqueous solution of APS (3.6 mass%, 5 mL) was added to initiate polymerization. After 96 minutes, when the reactor pressure dropped to 1.81 MPaG, the reactor was cooled to terminate the polymerization. The gas remaining in the reactor was recovered, and the solution in the reactor was removed to obtain a mother liquor.

[0206] The mother liquor was added with ion exchange resin, stirred, and filtered to obtain a treated solution, which was a dispersion of particles (average particle size: 114 nm) of FO polymer (specific gravity: 1.81) containing 57 mol % of HFP units and 43 mol % of VdF units.

[0207] A pressure-resistant reactor (internal volume 1.0 L) was charged with the treatment liquid (600 g) and wax (28 g) to form a reaction system (liquid viscosity: 1.2 mPa·s, thixotropy ratio: 1.00) containing 0.75 mass % of the particles.

[0208] The reaction system was stirred at 260 rpm, and the internal temperature was raised to 70°C. TFE was injected into the reactor until the pressure inside the reactor reached 1.4 MPaG, and an aqueous solution of disuccinic acid peroxide (0.56 mass%, 11 mL) was added to the reactor to initiate polymerization. TFE was added to compensate for the decrease in the internal pressure of the reactor due to polymerization, and the pressure was kept constant. After 292 minutes, when the amount of injected TFE reached 80 g, the reactor was cooled to terminate the polymerization reaction.

[0209] After the gas remaining in the reactor was collected, the liquid content was extracted to obtain an aqueous dispersion.

[0210] The aqueous dispersion contained 10.1 mass% of fluoropolymer particles (average particle size: 301 nm) (specific gravity: 2.17) containing 99.3 mol% TFE units, 0.4 mol% HFP units, and 0.3 mol% VdF units (liquid viscosity: 1.5 mPa·s, thixotropy ratio: 1.00). The specific gravity ratio was 1.20. The aqueous dispersion exhibited excellent liquid properties, such as dispersion stability, and ease of handling. The fluoropolymer exhibited excellent physical properties compared to the fluororesin PTFE. The particle size distribution was monomodal, with a polydispersity index of less than 0.5.

[0211] The contents of the compounds represented by the formula (S1) and the formula (S2) contained in the aqueous dispersion relative to the total mass of the particles in the aqueous dispersion were both 100 ppb by mass or less.

[0212] The disclosure of Japanese Patent Application No. 2024-099104, 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

1. A method for producing an aqueous dispersion, comprising forming a reaction system containing fluoroolefin-based polymer particles and water but not containing a fluorine-based emulsifier, and polymerizing at least gaseous perfluoroolefin in the reaction system to obtain an aqueous dispersion containing fluoropolymer particles, comprising: the ratio of the specific gravity of the fluoropolymer to the specific gravity of the fluoroolefin-based polymer is 0.80 to 1.20; the ratio of the average particle size of the fluoroolefin-based polymer particles in the reaction system to the average particle size of the fluoropolymer particles contained in the aqueous dispersion is greater than 1; the ratio of the content of fluoropolymer particles in the aqueous dispersion to the content of fluoroolefin-based polymer particles in the reaction system is 2 or more; Method for producing aqueous dispersion.

2. 2. The method for producing an aqueous dispersion according to claim 1, wherein the specific gravity of the fluoroolefin polymer and the specific gravity of the fluoropolymer are each independently 1.60 to 2.

20.

3. The method for producing an aqueous dispersion according to claim 1 , wherein the specific gravity of the fluoropolymer is greater than the specific gravity of the fluoroolefin-based polymer.

4. 2. The method for producing an aqueous dispersion according to claim 1, wherein the liquid viscosity of the reaction system is less than 2 mPa·s as measured using a Brookfield viscometer at 25°C and a rotation speed of 30 rpm.

5. 2. The method for producing an aqueous dispersion according to claim 1, wherein the liquid viscosity of the aqueous dispersion is less than 10 mPa·s as measured using a Brookfield viscometer at 25°C and a rotation speed of 30 rpm.

6. The method for producing an aqueous dispersion according to claim 1, wherein the gaseous perfluoroolefin is tetrafluoroethylene or hexafluoropropylene.

7. The method for producing an aqueous dispersion according to claim 1 , wherein the polymerization is carried out by copolymerizing a gaseous perfluoroolefin with a monomer other than the gaseous perfluoroolefin.

8. 8. The method for producing an aqueous dispersion according to claim 7, wherein the gaseous monomer other than perfluoroolefin is ethylene, chlorotrifluoroethylene, vinylidene fluoride, propylene, fluoroalkylethylene, perfluoroalkyl vinyl ether, perfluoroalkyl allyl ether, or a fluoromonomer having a fluorosulfonyl group, a carboxy group, or an alkoxycarbonyl group.

9. The method for producing an aqueous dispersion according to claim 1, wherein the average particle size of the fluoroolefin polymer particles is 10 nm or more and less than 150 nm.

10. The method for producing an aqueous dispersion according to claim 1, wherein the average particle size of the fluoropolymer particles is more than 50 nm and not more than 1000 nm.

11. 2. The method for producing an aqueous dispersion according to claim 1, wherein the particle size distribution of the fluoropolymer particles is unimodal, and the polydispersity index of particle size, which is the width of the particle size distribution determined by analyzing the autocorrelation function obtained by dynamic light scattering of the fluoropolymer particles using the cumulant method, is 0.5 or less.

12. The method for producing an aqueous dispersion according to claim 1, wherein the content of the fluoroolefin polymer in the reaction system is 0.01% by mass or more and 4.0% by mass or less.

13. The method for producing an aqueous dispersion according to claim 1, wherein the reaction system is formed by polymerizing at least a gaseous fluoroolefin in the presence of water and a polymerization initiator without using a fluorine-containing emulsifier.

14. 14. The method for producing an aqueous dispersion according to claim 13, wherein the gaseous fluoroolefin is vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, or hexafluoropropylene.

15. The method for producing an aqueous dispersion according to claim 14, wherein the polymerization is carried out by copolymerizing the gaseous fluoroolefin with ethylene, chlorotrifluoroethylene, propylene, a perfluoroalkyl vinyl ether, or a perfluoroalkyl allyl ether.