Method for producing aqueous dispersion

Abstract

Provided is a method for producing an aqueous dispersion containing particles of a fluoropolymer by forming a fluorine-based emulsifier-free reaction system containing particles of a fluoroolefin polymer and water and polymerizing at least a gaseous perfluoroolefin in the reaction system. The fluoroolefin polymer has a hydrophilic group and does not contain a unit based on a monomer having a hydrophilic group. The ratio of the average particle size of the particles of the fluoropolymer contained in the aqueous dispersion to the average particle size of the particles of the fluoroolefin polymer is more than 1, and the ratio of the content of particles of the fluoropolymer in the aqueous dispersion to the content of particles of the fluoroolefin polymer in the reaction system is 2 or more.

Description

Method for producing aqueous dispersion

[0001] The present invention relates to a method for producing an aqueous dispersion.

[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, etc. Examples of methods for producing fluoropolymers include a method of emulsion polymerization of fluoroolefins in water using a fluorine-based emulsifier (see Patent Document 1, etc.).

[0003] International Publication No. 2007 / 046377

[0004] The method of Patent Document 1 produces an aqueous dispersion containing fluoropolymer particles that has a low environmental impact, but depending on the content of the fluorine-based emulsifier, which is an essential component, or depending on the intended use or circumstances, it may be necessary to remove the fluorine-based emulsifier. Furthermore, in recent years, such aqueous dispersions have been required to further improve the dispersibility of the fluoropolymer particles in the liquid. An object of the present invention is to provide a method for efficiently producing an aqueous dispersion containing fluoropolymer particles that does not require a fluorine-based emulsifier, has a low environmental impact, and has excellent dispersibility in the liquid.

[0005] The present invention 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 a gaseous perfluoroolefin in the reaction system to obtain an aqueous dispersion containing fluoropolymer particles, wherein the fluoroolefin-based polymer is a fluoroolefin-based polymer having a hydrophilic group but not containing units derived from a monomer having a hydrophilic group, 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 being 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 being 2 or more. [2] The production method of [1], wherein the hydrophilic group is a carbonyl group-containing group, a sulfonic acid group-containing group, or a phosphonic acid group-containing group. [3] The production method of [1] or [2], wherein the liquid viscosity of the reaction system is less than 2 mPa s. [4] The manufacturing method of any one of [1] to [3], wherein the gaseous perfluoroolefin is tetrafluoroethylene or hexafluoropropylene. [5] The manufacturing method of any one of [1] to [4], wherein the polymerization is carried out by copolymerizing the gaseous perfluoroolefin with a monomer other than the gaseous perfluoroolefin. [6] The manufacturing method of [5], wherein the monomer other than the gaseous perfluoroolefin is ethylene, chlorotrifluoroethylene, propylene, fluoroalkylethylene, perfluoroalkyl vinyl ether, perfluoroalkyl allyl ether, or a fluoromonomer having a fluorosulfonyl group, a carboxy group, or an alkoxycarbonyl group. [7] The manufacturing method of any one of [1] to [6], wherein the average particle size of the fluoroolefin-based polymer particles is 10 nm or more and less than 150 nm. [8] The manufacturing method of any one of [1] to [7], wherein the average particle size of the fluoropolymer particles is more than 50 nm and 1,000 nm or less. [9] The manufacturing method of any one of [1] to [8], wherein the content of the fluoroolefin-based polymer in the reaction system is 0.01 mass% or more and 4.0 mass% or less.

[10] The manufacturing method of any one of [1] to [9], wherein the particle size distribution of the fluoropolymer particles is unimodal and the polydispersity index of the particle sizes of the fluoropolymer particles is 0.5 or less.

[11] The manufacturing method of any one of [1] to

[10] , 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.

[12] The manufacturing method of

[11] , wherein the polymerization initiator is a water-soluble polymerization initiator.

[13] The manufacturing method of

[11] or

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

[14] The manufacturing method of any one of

[11] to

[13] , wherein the polymerization is carried out by copolymerizing a gaseous fluoroolefin with a monomer other than the gaseous fluoroolefin.

[15] The production method according to

[14] , wherein the gaseous monomer other than the fluoroolefin is ethylene, chlorotrifluoroethylene, propylene, perfluoroalkyl vinyl ether, or perfluoroalkyl allyl ether.

[0006] According to the present invention, an aqueous dispersion in which fluoropolymer particles are stably dispersed can be efficiently produced without requiring a fluorine-based emulsifier.

[0007] The meanings of terms used in the present invention 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 the 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 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. In this specification, each component may be used alone or in combination with two or more substances corresponding to the component. Here, 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.

[0008] "Unit" is a general term for an atomic group derived from one molecule of the monomer formed directly by polymerization of a monomer, and an atomic group obtained by chemically converting a portion of the atomic group. "Units based on a monomer" will hereinafter be simply referred to as "units", and "units based on monomer A" will hereinafter be simply referred to as "monomer A units". In this specification, the content (mass% or mol%) of each unit relative to the total units contained in a polymer is determined by analyzing the polymer using solid-state nuclear magnetic resonance spectroscopy (NMR). Usually, the content of each unit calculated from the amount of each monomer charged is approximately the same as the actual content of each unit. In this specification, "gaseous compound" refers to a compound having a boiling point of less than 25°C at atmospheric pressure (1013 hPa), and "liquid compound" refers to a compound having a boiling point of 25°C or higher at atmospheric pressure (1013 hPa).

[0009] The production method of the present invention (hereinafter also referred to as "this method") is a method for producing an aqueous dispersion that includes a reaction system containing particles (hereinafter also referred to as "FO particles") of a fluoroolefin polymer (hereinafter also referred to as "FO polymer") and water, but does not contain a fluorine-based emulsifier, and polymerizes at least a gaseous perfluoroolefin in the reaction system to obtain an aqueous dispersion containing particles (hereinafter also referred to as "F particles") of a fluoropolymer (hereinafter also referred to as "F polymer"). The FO polymer is a fluoroolefin polymer that has a hydrophilic group and does not contain units derived from a monomer having a hydrophilic group, and 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).

[0010] 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 necessarily clear, but the following reasons can be cited. The FO polymer used in this method does not contain hydrophilic groups in the monomer units forming the main backbone of the polymer molecule, but has other hydrophilic groups. The FO polymer can also be considered to be a polymer having a hydrophilic portion composed of such hydrophilic groups and a hydrophobic portion composed of units based on fluoroolefin, in other words, a hydrophobic portion composed of the main chain of the polymer. FO particles, which are particles of such polymers, are thought to be highly dispersed in liquid in a reaction system containing water due to the action of the hydrophilic portion. The gaseous perfluoroolefin introduced into such a reaction system contains fluorine atoms and is easily adsorbed by the FO polymer, which has a high affinity for it. In other words, it is thought that the FO particles function highly as a polymerization site for the perfluoroolefin. This makes it easier for polymerization to proceed uniformly and densely, and also improves the heat transfer properties associated with polymerization. As a result, it is believed that this method can efficiently produce an aqueous dispersion containing F particles with excellent dispersibility in liquid while increasing both the particle size ratio and the content ratio, even without the presence of a fluorine-based emulsifier. Note that this mechanism of action is more easily realized by the preferred embodiment of this method described below.

[0011] 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. The fluorine-based emulsifier is an emulsifier having fluorine atoms that is different from FO polymers, specifically a water-soluble fluorine-containing compound or its salt having a fluorine-containing organic group (such as a perfluoroalkyl group) and a hydrophilic functional group (such as a carboxy group, a sulfonic acid group, a phosphonic acid group), more specifically a perfluoroalkylcarboxylic acid, a perfluoroalkylsulfonic acid, or a salt thereof. An ethereal oxygen atom may be present between the carbon atoms in the molecules of these compounds.

[0012] 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, even 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.

[0013] 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 easily manifested. Note that the liquid viscosity in this specification is a value obtained 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. 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 easily manifested.

[0014] The thixotropic ratio of the liquid in the reaction system in this method is preferably 0.95 or more, more preferably 0.98 or more. The thixotropic 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 thixotropic ratio is preferably 1. In this case, the above-mentioned mechanism of action is more likely to occur. Note that the thixotropic ratio of the liquid in this specification is a value obtained by measuring the viscosity of the target liquid measured using a Brookfield viscometer at 25°C and a rotation speed of 30 rpm and the viscosity of the target liquid measured at a rotation speed of 60 rpm, and dividing the former viscosity by the latter viscosity.

[0015] These liquid properties may 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.

[0016] The hydrophilic group in the FO polymer of this method is preferably a carbonyl group-containing group, a sulfonic acid group-containing group, or a phosphonic acid group-containing group, and more preferably a carbonyl group-containing group. Examples of the carbonyl group-containing group include a carboxy group, an acid anhydride group, a carbonate group, an alkoxycarbonyl group, and an amide group, and a carboxy group is preferred. The carboxy group has a counter cation of sodium ion (Na ＋ ), potassium ions (K ＋ ), ammonium ion (NH ４ ＋ ) and the like, carboxylate (—COO － The sulfonic acid-containing group may be a sulfonic acid group. The sulfonic acid group may have a counter cation of sodium ion (Na ＋ ), potassium ions (K ＋ ), ammonium ion (NH ４ ＋ ) and the like, sulfonates (—SO ３ － The phosphonic acid-containing group may be a phosphonic acid group. The phosphonic acid group may have a counter cation of sodium ion (Na ＋ ), potassium ions (K ＋ ), ammonium ion (NH ４ ＋ ) and the like, phosphonates (-PO ３ － ) may be formed.

[0017] The content of hydrophilic groups in the FO polymer is 10 carbon atoms in the main chain of the polymer. ６ It is preferable that the number of hydrophilic groups per unit is 100 to 10,000. In this case, the above-mentioned mechanism of action is more easily manifested. The content of hydrophilic groups in the FO polymer is a value measured by infrared spectroscopy of a film formed from the FO polymer, specifically, a value measured by the method described in JP 2022-50435 A.

[0018] The FO polymer in this method is a polymer having a hydrophilic group that does not contain units based on a monomer having a hydrophilic group but contains units based on a fluoroolefin, and is preferably a polymer having a hydrophilic group at the polymer terminal that does not contain units based on a monomer having a hydrophilic group but contains units based on a fluoroolefin.

[0019] The fluoroolefin may be one type or multiple types. 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.

[0020] 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. 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.

[0021] As for PAVE, CF ２ = CFOCF ３ (hereinafter also referred to as "PMVE"), CF ２ = CFOCF ２ CF ３ (hereinafter also referred to as "PEVE"), CF ２ = CFOCF ２ CF ２ CF ３ (hereinafter also referred to as "PPVE"). PAAEs include CF２ =CFCF ２ OCF ３ (hereinafter also referred to as "PMAE"), CF ２ =CFCF ２ CF ２ OCF ３ (hereinafter also referred to as "PEAE").

[0022] 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 improves the conformational freedom of the FO polymer and makes it easier to exhibit the above-mentioned mechanism of action.

[0023] The FO polymer preferably contains a monomer unit having a side chain, preferably FKM, FFKM, FEPM, or FEP, as described below, and more preferably FKM, FFKM, or FEPM. In this case, the conformational freedom of the FO polymer is improved, making it easier to realize the above-mentioned mechanism of action. Furthermore, the glass transition temperature (hereinafter also referred to as "Tg") of the FO polymer is preferably -50 to +10°C, more preferably -45 to +5°C, even more preferably -40 to +3°C, and particularly preferably -35 to 0°C. In this case, the above-mentioned mechanism of action is easier to realize. The FO polymer is preferably a polymer obtained by the method described below.

[0024] In this method, the FO particles are dispersed in the liquid in the reaction system. 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 exhibited. Note that the average particle size of the particles in this specification is the particle size calculated by analyzing the autocorrelation function obtained by dynamic light scattering using the monodisperse cumulant method.

[0025] The content of FO particles in the reaction system of this method is preferably 0.01% by mass or more relative to the total mass. 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 of the resulting aqueous dispersion is particularly easily increased.

[0026] The formation of the reaction system in this method is not particularly limited, and it is preferably formed by a method in which at least a gaseous fluoroolefin is polymerized in the presence of water and a polymerization initiator without using a fluorine-based emulsifier. Such a method not only makes it easy to form a reaction system containing the desired FO polymer particles (FO particles) and water but not containing a fluorine-based emulsifier, but also makes it easier to realize the above-mentioned mechanism of action.

[0027] The gaseous fluoroolefin is preferably vinyl fluoride, VdF, TFE or HFP, and more preferably contains at least TFE.

[0028] The polymerization is preferably carried out by copolymerizing a gaseous fluoroolefin with a monomer other than the gaseous fluoroolefin, such as a monomer that forms the monomer unit that can be contained in the FO polymer.

[0029] The polymerization initiator used in the polymerization is preferably a water-soluble polymerization initiator, more preferably a persulfate, an organic peroxide, or a redox catalyst, and even more preferably a persulfate. Examples of persulfates include ammonium persulfate (hereinafter also referred to as "APS") and potassium persulfate. Examples of organic peroxides include disuccinic acid peroxide, bisglutaric acid peroxide, and tert-butyl hydroperoxide. Examples of redox catalysts 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.

[0030] Examples of the oxidizing agent include potassium persulfate, APS, and sodium sulfite. Examples of the inorganic salt include salts containing sulfate anions, sulfite anions, or chloride anions and metal ions such as manganese, iron, cobalt, nickel, copper, zinc, cerium, and silver, particularly iron (II) sulfate. One or more polymerization initiators may be used.

[0031] 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 the gaseous fluoroolefin.

[0032] 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 maintaining the pressure at 0.8 MPaG or higher. The half-life temperature of the 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.

[0033] The temperature during the polymerization is preferably higher than 55° C., more preferably equal to or higher than 60° C., and even more preferably equal to or higher than 65° C. The temperature during the polymerization is preferably lower than 100° C. In this case, the above-described mechanism of action is more likely to be exhibited.

[0034] The pressure in the polymerization is preferably 0.9 MPaG or more, more preferably 1.0 MPaG or more. The pressure in 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 be exhibited. In this specification, "MPaG" refers to gauge pressure, and is the pressure obtained by subtracting atmospheric pressure (0.1013 MPa) from absolute pressure. The pressure in the polymerization may be adjusted by introducing a gaseous fluoroolefin into the reaction system in a conventional manner. Specifically, the pressure in the polymerization may be adjusted by continuously or intermittently introducing the gaseous fluoroolefin into the reaction system so that the pressure in the polymerization reaches a predetermined pressure. The pressure may also be adjusted by using a gaseous monomer other than the gaseous fluoroolefin in combination.

[0035] In the polymerization, the polymerization time is preferably 90 to 1000 minutes, more preferably 90 to 700 minutes, in the case of batch processing.

[0036] The product liquid obtained by such a method may be used as a reaction system as is, or may be used as a reaction system after adjusting the component types and their contents in the product liquid. Furthermore, the reaction system may be used when the formation of the product liquid is confirmed in such a method. Specific embodiments of preparing the product liquid obtained by the above method and then using it as a reaction system include adding water to the product liquid to adjust the content of FO particles before using it as a reaction system, adding other components described below to the product liquid to adjust the liquid properties of the reaction system 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, etc., 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.

[0037] The reaction system in this method may contain components other than FO particles and water. Specific examples of other components include chain transfer agents, emulsifiers other than fluorine-based emulsifiers, pH adjusters, and reducing agents. 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 emulsifiers include sodium lauryl sulfate, Perex SS-H manufactured by Kao Chemical Corporation, and Newcol 1305-SN manufactured by Nippon Nyukazai Co., Ltd. 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.

[0038] 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. Furthermore, the amount of chain transfer agent used is preferably 0.1 to 20 mass% relative to the amount of gaseous perfluoroolefin used, more preferably 0.1 to 15 mass%, and even more preferably 0.1 to 10 mass%. When the reaction system contains an emulsifier other than a fluorine-based emulsifier, its content is preferably 5 mass% or less, more preferably 1 mass% or less, relative to the total mass of the reaction system. The content is preferably 0 mass% or more. When the reaction system contains a pH adjuster, its content is preferably 0.01 to 3.0 mass% relative to the total mass of the reaction system. When the reaction system contains a reducing agent, its content is preferably 0.1 to 2 mass% relative to the total mass of the reaction system.

[0039] 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.

[0040] In the reaction system of this method, the fluoride ion concentration is preferably 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.

[0041] The polymerization in the reaction system of this method (hereinafter also referred to as "main polymerization") is carried out by polymerizing gaseous perfluoroolefin. The gaseous perfluoroolefin may be one kind or a plurality of kinds. The gaseous perfluoroolefin is preferably TFE or HFP, and more preferably contains at least TFE.

[0042] 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. The monomer may be a gaseous monomer or a liquid monomer. The monomer may be one type or multiple types.

[0043] 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.

[0044] As a FAE, CH ２ =CH(CF ２ ) ２ F, CH ２ =CH(CF ２ ) ３ F, CH ２ =CH(CF ２ ) ４ F, CH ２ =CF(CF ２ ) ３ H and CH ２ =CF(CF ２ ) ４ Examples of fluoromonomers having a fluorosulfonyl group, a carboxy group, or an alkoxycarbonyl group include CF ２ =CFSO ２ F, CF ２ =CFO(CFCF(CF ３ ))OCF ２ CF ２ SO ２ F, CF ２ = CFO (CF ２ ) ３ COOCH ３ Examples include:

[0045] In this polymerization, the amount of gaseous perfluoroolefin used is preferably 10 mol% or more, more preferably 30 mol% or more, and more 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.

[0046] Furthermore, when a monomer other than gaseous perfluoroolefin is used in the main 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%.

[0047] In this polymerization, the amount of gaseous perfluoroolefin used is preferably 1 to 60% by mass, more preferably 1 to 50% by mass, and even more preferably 1 to 40% by 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.

[0048] This polymerization is preferably carried out in the presence of a polymerization initiator. In other words, the reaction system in this method preferably contains a polymerization initiator. Examples of polymerization initiators include oil-soluble radical initiators, water-soluble polymerization initiators, and water-soluble redox catalysts. Examples of water-soluble polymerization initiators and water-soluble redox catalysts include those described above. Examples of oil-soluble radical initiators include tert-butyl peroxypivalate and diisopropyl peroxydicarbonate. One or more polymerization initiators may be used. The polymerization initiator is preferably an oil-soluble polymerization initiator or a water-soluble radical initiator, and can be selected based on the type of target F polymer. The amount of polymerization initiator used is preferably 0.01 to 5% by mass, more preferably 0.01 to 3% by mass, and even more preferably 0.01 to 2% by mass, based on the total mass of monomers used in the polymerization.

[0049] 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.

[0050] The temperature in the main polymerization is preferably 10 to 95° C., more preferably 15 to 90° C. The pressure in the main polymerization is preferably 0.5 to 4.0 MPaG, more preferably 0.6 to 3.5 MPaG. In the main polymerization, the polymerization time in the case of batch treatment is preferably 90 to 1,000 minutes, more preferably 90 to 700 minutes.

[0051] 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.

[0052] 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. As a polymer containing VdF units and TFE units or HFP units, FKM, which is a fluoroelastomer containing 20 to 60 mol% of VdF units and 40 to 80 mol% of TFE units or HFP units, is preferred. FKM may further contain other units such as PAVE units and Pp units. As a polymer containing TFE units and Pp units, FEPM, which is a fluoroelastomer containing 30 to 70 mol% of TFE units and 30 to 70 mol% of Pp units, is preferred. FEPM may further contain other units such as VdF units.

[0053] 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. Furthermore, PFA may further contain other units such as HFP units and FAE units.

[0054] As a polymer comprising TFE units, PTFE, a fluororesin comprising only TFE units, or modified PTFE, a fluororesin comprising TFE units and trace amounts of other monomer units, is preferred. The content of other monomer units in modified PTFE is preferably less than 0.1 mol%. Examples of other monomer units contained in modified PTFE include PAVE units, HFP units, FAE units, and CTFE units. As a polymer comprising TFE units and HFP units, FEP, a fluororesin comprising 55 to 97 mol% of TFE units and 3 to 45 mol% of HFP units, is preferred. FEP may further comprise other units such as PAVE units and FAE units. As a polymer comprising TFE units and Et units, ETFE, a fluororesin comprising 35 to 65 mol% of TFE units and 35 to 65 mol% of Et units, is preferred. ETFE may further contain other units such as PAVE units, HFP units, and FAE units.

[0055] 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).

[0056] 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.

[0057] 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. 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 preferably does not have thixotropy, in other words, the thixotropy ratio is preferably 1.

[0058] 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.

[0059] 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.

[0060] 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, due to the above-mentioned mechanism of action, a dispersion having such excellent particle properties is easily obtained. 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 the liquid.

[0061] The content of F particles in the present dispersion is preferably greater than 4.0% by mass, more preferably 5% by mass or greater, and even more preferably 10% by mass or greater, relative to the total mass of the present dispersion. The content of F particles is preferably 40% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less. The content of water in the present 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, relative to the total mass of the present dispersion. The content of water is preferably 60% by mass or more, more preferably 50% by mass or greater, and even more preferably 60% by mass or greater. Furthermore, the sum of the content of F particles and the content of water in the present dispersion is preferably 90% by mass or greater, more preferably 96% by mass or greater, relative to the total mass. The upper limit of this sum is 100% by mass. Due to the above-mentioned mechanism of action, this method allows for efficient production of a dense aqueous dispersion containing a high content of F particles with excellent dispersibility in liquid, in which water is essentially the liquid medium.

[0062] 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 may be 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.

[0063] The content ratio in this method is the value obtained by dividing the content of F particles in the dispersion liquid by the content of FO particles in the reaction system, and is 2 or more, or may be 5 or more, 7 or more, or 10 or more. The content ratio may be 500 or less, 250 or less, 100 or less, 50 or less, or 25 or less. The content ratio is a value calculated from the respective contents (% by mass).

[0064] 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 may 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.

[0065] For example, when a fluoroelastomer is used as the FO polymer to produce the present dispersion containing F polymer particles with excellent fluororesin 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. For example, when a fluoroelastomer is used as the FO polymer to produce the present dispersion containing F polymer particles 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. For example, when a fluororesin is used as the FO polymer to produce a 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. Examples of fluororesins include PTFE, modified PTFE, ETFE, PFA, and FEP. Examples of fluoroelastomers include FKM, FEPM, and FFKM.

[0066] 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 compounds derived from the gaseous perfluoroolefin contained in the dispersion can be suppressed, and in particular, when the gaseous perfluoroolefin contains tetrafluoroethylene, the amount of the compound represented by the following formula (S1) and the compound represented by the formula (S2) can be suppressed. Formula (S1): H—(CF ２ ) ｎ -COO － M ＋ Formula (S2): H-(CF ２ ) ｎ -SO ３ － M ＋ In the formula, each M is independently H, Na, K, or NH ４ In the compound represented by formula (S1), n ​​represents an integer of 7 to 11, and in the compound represented by formula (S2), n represents an integer of 8 to 12.

[0067] 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 each 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.

[0068] This dispersion is an aqueous dispersion in which F particles have high dispersion stability and can be suitably used as a coating agent, a binder, etc. Alternatively, the water contained in this 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. Alternatively, the F particles may be aggregated from this 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.

[0069] Examples of aggregation methods include mechanical aggregation, freeze aggregation, acid aggregation, base aggregation, and aggregation using a coagulant. Mechanical aggregation, acid aggregation, and aggregation using a coagulant are preferred. The aggregation temperature for freeze aggregation is preferably -20 to 0°C. The aggregation time is preferably 1 hour or more, more preferably 2 hours or more. In the case of acid aggregation, a method in which an acid-containing solution is added to the present 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. In the case of base aggregation, a method in which a base-containing solution is added to the present dispersion is preferred. Examples of bases include sodium hydroxide, potassium hydroxide, and ammonium carbonate. The base concentration in the base-containing solution is preferably 1 to 10% by mass. In the case of aggregation using a coagulant, a method in which the coagulant is added to the present dispersion is preferred. Examples of coagulants include aluminum sulfate, alum, calcium nitrate, magnesium sulfate, and ammonium carbonate.

[0070] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. The abbreviations in the examples have the following meanings: APS: ammonium persulfate TFE: tetrafluoroethylene (CF ２ =CF ２ ) VdF: vinylidene fluoride (CH ２ =CF ２ ) HFP: hexafluoropropylene (CF ２ =CFCF ３ ) PMVE: Perfluoromethyl vinyl ether (CF ２ = CFOCF ３ ) PMAE: Perfluoromethyl allyl ether (CF ２ =CFCF ２ OCF ３ ) Et: ethylene (CH ２ =CH ２ )

[0071] A laser diffraction / scattering particle size distribution analyzer (Otsuka Electronics Co., Ltd., ELSZ) was used to measure the average particle size of the particles in the dispersion. The content of the compound represented by (S1) and the content of the compound represented by (S2) in the dispersion were each calculated by a method using an aqueous dispersion, among the measurement methods using a liquid chromatograph mass spectrometer described in paragraphs

[0710] to

[0732] of International Publication No. 2018 / 181904. The apparatus used was an Agilent 1260 series HPLC / 6460S, and the column used was an Imtakt Cadenza CD-C18. The concentration of sulfate ions in the dispersion was determined by freeze-flocculating the aqueous dispersion, and then analyzing the liquid recovered by filtration using ion chromatography. For the ion chromatography analysis, an ion chromatograph ICS-5000 (manufactured by Thermo Fisher Scientific) was used. The separation column used was Dionex IonPac AS-19, the guard column used was Dionex IonPac AG-19, and the eluent used was KOH.

[0072] All reactors used were made of stainless steel.

[0073] [Example 1] Example of producing an aqueous dispersion Ultrapure water (1130 g), 30 mass% aqueous ammonia solution (30 mg), PMVE (72 g), and TFE (14 g) were charged into a pressure-resistant reactor (internal volume 2.2 L), and the temperature was raised to 90 ° C. while stirring at 600 rpm. Next, an aqueous APS solution (5.0 mass%, 30 mL) was added to initiate polymerization. TFE was added 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 4 g of TFE had been injected, the reactor was cooled and the polymerization reaction was terminated. After recovering the gas remaining in the reactor, the liquid was withdrawn to obtain a mother liquor. The mother liquor was a dispersion of FO polymer particles containing 34 mol% PMVE units and 66 mol% TFE units and having carboxy groups at the polymer terminals.

[0074] Ultrapure water and an 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 size: 98 nm). The content of the particles in the liquid was 0.6% by mass.

[0075] Ultrapure water (175 g) and a treatment liquid (1000 ml) were charged into a pressure-resistant reactor (internal volume 1.2 L), and a reaction system containing 0.5% by mass of the particles (liquid viscosity: 1.0 mPa s, thixotropy ratio: 1.00) was formed. 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 pressure in the reactor reached 1.2 MPaG, and an aqueous APS solution (2.5% by mass, 7 mL) was added to initiate polymerization. TFE and PMVE were alternately injected to compensate for the decrease in pressure inside the reactor due to polymerization, and the pressure was maintained constant. When 80 g of TFE and 63 g of PMVE were injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 138 minutes.

[0076] After recovering the gas remaining in the reactor, the liquid content was extracted to obtain an aqueous dispersion. The aqueous dispersion was a dispersion (liquid viscosity: 1.1 mPa s, thixotropy ratio: 1.00) containing 11.5 mass% of fluoropolymer particles (average particle size: 141.1 nm) having 66 mol% TFE units and 34 mol% PMVE units as a whole. The aqueous dispersion was excellent in liquid physical properties, such as dispersion stability, and handleability, and the fluoropolymer had excellent FFKM physical properties as a fluoroelastomer. The particle size distribution of the particles was unimodal, and the polydispersity index was 0.5 or less. 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 mass ppb or less.

[0077] [Example 2] Example of producing aqueous dispersion Ultrapure water (1162 g), 28% NH ３ An aqueous solution (1 drop), PMVE (70 g), and TFE (14 g) were charged, and the internal temperature was raised to 80°C while stirring at 600 rpm. An aqueous solution of APS (5.9% by mass, 5 mL) was added to initiate polymerization. TFE was injected to compensate for the decrease in reactor internal pressure associated with the polymerization, maintaining the pressure 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 in the reactor was withdrawn to obtain a mother liquor. The mother liquor was a dispersion of FO polymer particles (average particle size: 110 nm) containing 34.4 mol% PMVE units and 65.6 mol% TFE units and having carboxy groups at the polymer terminals. The content of the particles in the liquid was 3.0% by mass.

[0078] A pressure-resistant reactor (internal volume 1.2 L) was charged with ultrapure water (520.5 g), mother liquor (92.5 ml), disodium hydrogen phosphate dodecahydrate (0.5 g), and t-BuOH (16.5 g), and a reaction system (liquid viscosity: 1.1 mPa s, thixotropy ratio: 1.00) containing 0.22% by mass of the particles was formed. The reaction system was stirred at 320 rpm, and the internal temperature was raised to 60 ° C. A mixed gas (a gas containing TFE and Et, in that order, 86 mol% and 14 mol%, respectively; the same applies below) was pressurized into the reactor until the pressure inside the reactor reached 2.6 MPaG, and an aqueous solution of tert-butyl hydroperoxide (0.2% by mass, 2 mL) and a reducing agent (BRUGGOLITE (registered trademark) FF6M, 0.396% by 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 the polymerization. An aqueous solution of tert-butyl hydroperoxide (0.2% by mass, 1 mL) and the reducing agent (1 mL) were added every 5 minutes from the start of the polymerization. When the amount of the injected mixed gas reached 80 g, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 181 minutes.

[0079] After recovering the gas remaining in the reactor, the liquid content was extracted to obtain an aqueous dispersion. The aqueous dispersion was a dispersion (liquid viscosity: 1.3 mPa s, thixotropy ratio: 1.00) containing 10.2 mass% of fluoropolymer particles (average particle size: 182 nm) having 56.9 mol% of TFE units, 42.4 mol% of Et units, and 0.7 mol% of PMVE units as a whole. The aqueous dispersion was excellent in liquid physical properties, represented by dispersion stability, and handleability, and the fluoropolymer was excellent in the physical properties of ETFE, a fluororesin. In addition, the particle size distribution of the particles was unimodal, and the polydispersity index was 0.5 or less. 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 mass ppb or less.

[0080] [Example 3] Example of producing an aqueous dispersion Ultrapure water and an 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 FO polymer particles (average particle size: 110 nm) containing 34.4 mol% PMVE units and 65.6 mol% TFE units and having carboxy groups at the polymer terminals. The content of the particles in the liquid was 1.5% by mass.

[0081] A pressure-resistant reactor (internal volume 1.2 L) was charged with ultrapure water (428 g), treatment liquid (185 ml), disodium hydrogen phosphate dodecahydrate (0.5 g), and t-BuOH (16.5 g), forming a reaction system containing 0.44 mass% of the particles (liquid viscosity: 1.3 mPa s, thixotropy ratio: 1.00). 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 mixed gas was added to compensate for the decrease in pressure inside the reactor due to polymerization, maintaining the pressure constant. An aqueous solution of tert-butyl hydroperoxide (0.2% by mass, 1 mL) and the reducing agent (1 mL) were added every 5 minutes from 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.

[0082] After recovering the gas remaining in the reactor, extract the liquid content to obtain an aqueous dispersion.The aqueous dispersion is a dispersion (liquid viscosity: 1.4 mPa s, thixotropy ratio: 1.00) containing 10.6 mass% of fluoropolymer particles (average particle size: 156 nm) having 56.3 mol% of TFE unit, 43.1 mol% of Et unit, and 0.6 mol% of PMVE unit.The aqueous dispersion is excellent in liquid physical properties represented by dispersion stability and handling properties, and the fluoropolymer is excellent in the physical properties of ETFE, which is a fluororesin.In addition, the particle size distribution of the particles is unimodal, and its polydispersity index is 0.5 or less.

[0083] 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.

[0084] [Example 4] Example of producing an 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, maintaining the pressure at 1.4 MPaG. When 2 g of TFE had been injected, the reactor was cooled and the polymerization reaction was terminated. After recovering the gas remaining in the reactor, the solution in the reactor was extracted to obtain a mother liquor. The mother liquor was a dispersion of FO polymer particles containing 48 mol% PMVE units and 52 mol% TFE units and having carboxy groups at the polymer terminals. An ion exchange resin was added to the mother liquor, which was stirred and filtered to obtain a treated liquid. This treatment liquid contained FO polymer particles (average particle size: 87 nm), and the content was 0.6% by mass.

[0085] Ultrapure water (121 g), treatment liquid (475 g), and wax (28 g) were charged into a pressure-resistant reactor (internal volume 1.0 L), and a reaction system containing 0.48% by mass of the particles (liquid viscosity: 1.3 mPa s, thixotropy ratio: 1.00) was formed. 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 APS (0.2% by mass, 5 mL) was added to the reactor to initiate polymerization. TFE was added to compensate for the decrease in pressure inside the reactor due to polymerization, and the pressure was kept 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.

[0086] After recovering the gas remaining in the reactor, the liquid content was extracted to obtain an aqueous dispersion. The aqueous dispersion was a dispersion (liquid viscosity: 1.5 mPa s, thixotropy ratio: 1.00) containing 16.0 mass% of fluoropolymer particles (average particle size: 228 nm) having 99.1 mol% TFE units and 0.9 mol% PMVE units overall. The aqueous dispersion was excellent in liquid physical properties, typified by dispersion stability, and handleability, and the fluoropolymer had excellent physical properties relative to PTFE, a fluororesin. Specifically, the melting point of the fluoropolymer was 338°C, and its crystallization energy was -35 J / g. The particle size distribution was unimodal, and its polydispersity index was 0.5 or less. The contents 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 were both 100 ppb by mass or less.

[0087] [Example 5] Example of production of aqueous dispersion Distilled water (717 g), 28 mass% aqueous ammonia (one drop), and a mixed gas of TFE and HFP were charged into a pressure-resistant reactor (internal volume 1.0 L), and the temperature was raised to 90 ° C. while stirring at 500 rpm. The pressure inside the reactor after reaching 90 ° C. was 1.64 MPaG. Next, an aqueous solution of APS (3.6 mass%, 5 mL) was added to initiate polymerization. TFE was injected to compensate for the decrease in the pressure inside the reactor due to polymerization, and the pressure was maintained constant. 3 g of TFE was injected, and after 72 minutes, the reactor was cooled to terminate the polymerization reaction. After recovering the gas remaining in the reactor, the solution inside the reactor was extracted to obtain a mother liquor. An ion exchange resin was added to the mother liquor, and the mixture was stirred and filtered to obtain a treated liquid. This treatment liquid was a dispersion of FO polymer particles (average particle size: 103 nm) containing 83 mol % of TFE units and 17 mol % of HFP units and having carboxy groups at the polymer terminals.

[0088] A pressure-resistant reactor (internal volume 1.0 L) was charged with the treatment liquid (600.0 g) and wax (28 g), and a reaction system containing 0.72% by mass of the particles (liquid viscosity: 1.2 mPa s, thixotropy ratio: 1.00) was formed. 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% by mass, 11 mL) was added to the reactor to initiate polymerization. TFE was added to compensate for the decrease in the pressure inside the reactor due to polymerization, and the pressure was kept constant. After 216 minutes, when the consumption amount of TFE reached 50 g, the reactor was cooled to terminate the polymerization reaction.

[0089] After recovering the gas remaining in the reactor, the liquid was extracted to obtain an aqueous dispersion. The aqueous dispersion was a dispersion (liquid viscosity: 1.4 mPa s, thixotropy ratio: 1.00) containing 7.7 mass% of fluoropolymer particles (average particle size: 301 nm) having 99.1 mol% TFE units and 0.9 mol% HFP units overall. The aqueous dispersion had excellent liquid properties, such as dispersion stability, and handleability, and the fluoropolymer had excellent physical properties relative 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, and its polydispersity index was 0.5 or less. The contents 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 were both 100 mass ppb or less.

[0090] [Example 6] Example of production of aqueous dispersion Distilled water (717 g), 28 mass% aqueous ammonia (one drop), and a mixed gas of TFE and HFP were charged into a pressure-resistant reactor (internal volume 1.0 L), and the temperature was raised 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 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 extracted to obtain a mother liquor. An ion exchange resin was added to the mother liquor, which was then stirred and filtered to obtain a treated liquid. This treated liquid was a dispersion of FO polymer particles (average particle size: 97 nm) containing 77 mol% TFE units and 23 mol% HFP units and having carboxy groups at the polymer terminals.

[0091] A pressure-resistant reactor (inner volume 1.0 L) was charged with the treatment liquid (600.0 g), CH ２ =CH(CF ２ ) ４ F (0.73 g) and t-butyl methyl ether (0.51 g) were charged to form a reaction system containing 0.77% by mass of the particles (liquid viscosity: 1.0 mPa·s, thixotropy ratio: 1.00). While stirring the reaction system at 260 rpm, 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 during polymerization, and a mixed gas (a gas containing 86 mol% and 14 mol% of TFE and Et, respectively; the same applies below) was added to maintain a constant pressure. Furthermore, 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.

[0092] After recovering the gas remaining in the reactor, the liquid content was extracted to obtain an aqueous dispersion. The aqueous dispersion was a dispersion (liquid viscosity: 1.2 mPa s, thixotropy ratio: 1.00) containing 7.2 mass% of fluoropolymer particles (average particle size: 155 nm) having 55.0 mol% of TFE units, 43.8 mol% of Et units, 0.8 mol% of PFBE units, and 0.4 mol% of HFP units. The aqueous dispersion was excellent in liquid physical properties, represented by dispersion stability, and handleability, and the fluoropolymer was excellent in the physical properties of ETFE, a fluororesin. Specifically, the melting point of the fluoropolymer was 244 ° C, and its DSC heat of fusion was 43 J / g. In addition, the particle size distribution of the particles was monomodal, and its polydispersity index was 0.5 or less. 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.

[0093] [Example 7] Example of Preparation 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 % and 82 mol % of TFE and PMAE, respectively, was injected until the pressure inside the reactor 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. After recovering the gas remaining in the reactor, the solution in the reactor was extracted to obtain a mother liquor. An ion exchange resin was added to the mother liquor, which was then stirred and filtered to obtain a treatment liquid. This treatment liquid was a dispersion of FO polymer particles (average particle size: 70 nm) containing 69 mol % of TFE units and 31 mol % of PMAE units and having carboxy groups at the polymer terminals. The content of the particles in the treatment liquid was % by mass.

[0094] Ultrapure water (121 g), treatment liquid (475 g), and wax (28 g) were charged into a pressure-resistant reactor (internal volume 1.0 L), and a reaction system containing 0.75% by mass of the particles (liquid viscosity: 1.2 mPa s, thixotropy ratio: 1.00) was formed. While stirring the reaction system at 260 rpm, 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 pressure inside 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.

[0095] After recovering the gas remaining in the reactor, the liquid was extracted to obtain an aqueous dispersion. The aqueous dispersion was a dispersion (liquid viscosity: 1.4 mPa s, thixotropy ratio: 1.00) containing 20.0 mass% of fluoropolymer particles (average particle size: 270 nm) having 99.6 mol% TFE units and 0.4 mol% PMAE units overall. The aqueous dispersion had excellent liquid properties, such as dispersion stability, and handleability, and the fluoropolymer had excellent physical properties relative to 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, and its polydispersity index was 0.5 or less. The contents 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 were both 100 mass ppb or less. The sulfate ion concentration of the aqueous dispersion was less than 0.1 ppm by mass.

[0096] [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 the temperature was raised to 90 ° C. while stirring at 500 rpm. A mixed gas of TFE and VdF was then injected until the reactor internal 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 internal pressure dropped to 1.81 MPaG, the reactor was cooled to terminate the polymerization. After recovering the gas remaining in the reactor, the solution in the reactor was extracted to obtain a mother liquor. An ion exchange resin was added to the mother liquor, which was then stirred and filtered to obtain a treated liquid. This treated liquid was a dispersion of FO polymer particles (average particle size: 114 nm) containing 57 mol% HFP units and 43 mol% VdF units and having carboxy groups at the polymer terminals.

[0097] A pressure-resistant reactor (internal volume 1.0 L) was charged with the treatment liquid (600 g) and wax (28 g), and a reaction system containing 0.75% by mass of the particles (liquid viscosity: 1.2 mPa s, thixotropy ratio: 1.00) was formed. 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% by mass, 11 mL) was added to the reactor to initiate polymerization. TFE was added to compensate for the decrease in pressure inside 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.

[0098] After recovering the gas remaining in the reactor, the liquid was extracted to obtain an aqueous dispersion. The aqueous dispersion was a dispersion (liquid viscosity: 1.5 mPa s, thixotropy ratio: 1.00) containing 10.1 mass% of fluoropolymer particles (average particle size: 301 nm) having 99.3 mol% TFE units, 0.4 mol% HFP units, and 0.3 mol% VdF units as a whole. The aqueous dispersion had excellent liquid properties, such as dispersion stability, and handleability, and the fluoropolymer had excellent physical properties relative to the fluororesin PTFE. The particle size distribution was monomodal, and the polydispersity index was 0.5 or less. The contents of the compounds represented by the formulas (S1) and (S2) contained in the aqueous dispersion relative to the total mass of the particles in the aqueous dispersion were both 100 mass ppb or less.

[0099] The disclosure of Japanese Patent Application No. 2024-099119, filed on June 19, 2024, is incorporated herein by reference in its entirety. In addition, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A method for producing an aqueous dispersion, comprising forming a reaction system containing fluoroolefin 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 fluoroolefin polymer is a fluoroolefin polymer having a hydrophilic group but not containing units derived from a monomer having a hydrophilic group, the ratio of the average particle size of the fluoropolymer particles contained in the aqueous dispersion to the average particle size of the fluoroolefin polymer particles in the reaction system is greater than 1, and 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 according to claim 1, wherein the hydrophilic group is a carbonyl group-containing group, a sulfonic acid group-containing group, or a phosphonic acid group-containing group.

3. The method according to claim 1, wherein the liquid viscosity of the reaction system is less than 2 mPa·s.

4. The process according to claim 1, wherein the gaseous perfluoroolefin is tetrafluoroethylene or hexafluoropropylene.

5. The method according to claim 1, wherein the polymerization is carried out by copolymerizing a gaseous perfluoroolefin with a monomer other than the gaseous perfluoroolefin.

6. The production method according to claim 5, wherein the gaseous monomer other than perfluoroolefin is ethylene, chlorotrifluoroethylene, propylene, fluoroalkylethylene, perfluoroalkyl vinyl ether, perfluoroalkyl allyl ether, or a fluoromonomer having a fluorosulfonyl group, a carboxy group, or an alkoxycarbonyl group.

7. The method according to claim 1, wherein the average particle size of the fluoroolefin polymer particles is 10 nm or more and less than 150 nm.

8. The method according to claim 1, wherein the average particle size of the fluoropolymer particles is more than 50 nm and not more than 1000 nm.

9. The method 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.

10. The process of claim 1, 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.

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

12. The method according to claim 11, wherein the polymerization initiator is a water-soluble polymerization initiator.

13. The process according to claim 11, wherein the gaseous fluoroolefin is vinyl fluoride, vinylidene fluoride, tetrafluoroethylene or hexafluoropropylene.

14. The production method according to claim 11, wherein the polymerization is carried out by copolymerizing a gaseous fluoroolefin with a monomer other than the gaseous fluoroolefin.

15. The process according to claim 14, wherein the gaseous non-fluoroolefin monomer is ethylene, chlorotrifluoroethylene, propylene, a perfluoroalkyl vinyl ether, or a perfluoroalkyl allyl ether.