Method for producing an aqueous dispersion

Abstract

To provide a method for efficiently producing an aqueous dispersion containing fluoropolymer particles with excellent dispersibility in liquid, without requiring a fluorine-based emulsifier. [Solution] A method for producing an aqueous dispersion containing fluoropolymer particles, comprising forming a reaction system comprising particles of a fluoroolefin polymer and water, and not comprising a fluorine-based emulsifier, and polymerizing at least gaseous perfluoroolefin in the reaction system, wherein the fluoroolefin polymer is a hydrophilic fluoroolefin polymer that does not contain units based on a monomer having a hydrophilic group, the ratio of the average particle diameter of the fluoropolymer particles contained in the aqueous dispersion to the average particle diameter of the fluoroolefin polymer particles 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.

Description

[Technical Field]

[0001] This invention relates to a method for producing an aqueous dispersion. [Background technology]

[0002] Fluoropolymers, which contain units based on fluoroolefins, are used in various industrial fields because they have excellent heat resistance, chemical resistance, flame retardancy, weather resistance, and other properties. One method for producing fluoropolymers is to use a fluorine-based emulsifier and emulsion polymerization of fluoroolefins in water (see Patent Document 1, etc.). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2007 / 046377 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The method described in Patent Document 1 yields an aqueous dispersion containing fluoropolymer particles with low environmental impact; however, depending on the content of the essential component, the fluorine-based emulsifier, or depending on the application and circumstances, it may be necessary to remove the fluorine-based emulsifier. Furthermore, in recent years, there has been a demand for further improvement in the dispersibility of fluoropolymer particles in aqueous dispersions. The present invention aims 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 exhibits excellent dispersibility in liquid. [Means for solving the problem]

[0005] This invention provides the following: [1] A method for producing an aqueous dispersion, comprising forming a reaction system comprising particles of a fluoroolefin polymer 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 hydrophilic fluoroolefin polymer having hydrophilic groups and not containing units based on monomers having hydrophilic groups, the ratio of the average particle diameter of fluoropolymer particles contained in the aqueous dispersion to the average particle diameter of 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 for producing [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] A method for producing [1] or [2], wherein the liquid viscosity of the reaction system is less than 2 mPa·s. [4] A method for producing any of [1] to [3], wherein the gaseous perfluoroolefin is tetrafluoroethylene or hexafluoropropylene. [5] A method of production according to any of [1] to [4], wherein the polymerization is carried out by copolymerizing a gaseous perfluoroolefin with a monomer other than the gaseous perfluoroolefin. [6] A method for producing [5] in which 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 carboxyl group or an alkoxycarbonyl group. [7] A method for producing the fluoroolefin polymer, wherein the average particle size of the particles is 10 nm or more and less than 150 nm, according to any of [1] to [6]. [8] A method for producing the fluoropolymer whose average particle size is greater than 50 nm and less than or equal to 1000 nm, according to any of [1] to [7]. [9] A method for producing the product according to any one of [1] to [8], 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] A method for producing the fluoropolymer particles, wherein the particle size distribution of the fluoropolymer particles is unimodal and the polydispersity index of the particle size of the fluoropolymer particles is 0.5 or less, according to any of [1] to [9].

[11] A method of production according to 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 method for producing

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

[13] A method for producing

[11] or

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

[14] A method of production according to any 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 method for producing

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

[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. [Modes for carrying out the invention]

[0007] The meanings of the terms used in this invention are as follows: Numerical ranges expressed using "~" represent a range that includes the numbers before and after "~" as the lower and upper limits, respectively. In numerical ranges described stepwise in this specification, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described stepwise. Furthermore, in numerical ranges described in this specification, the upper or lower limit stated in one numerical range may be replaced with the values ​​shown in the examples. In this specification, each component may be represented by a single substance or by a combination of two or more substances. When two or more substances are used in combination for each component, the content of that component refers to the total content of the combined substances unless otherwise specified. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment.

[0008] A "unit" is a general term for an atomic group derived from one monomer molecule directly formed by the polymerization of monomers, and an atomic group obtained by chemically transforming a part of the above atomic group. A "monomer-based unit" will also be simply referred to as a "unit" below, and a "monomer A-based unit" will also be simply referred to as a "monomer A unit" below. In this specification, the content (mass %) or molar %) of each unit relative to the total units contained in the polymer is determined by analyzing the polymer using solid-state nuclear magnetic resonance (NMR) spectroscopy. However, the content of each unit calculated from the amount of each monomer used usually closely matches the actual content of each unit. 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.

[0009] The production method of the present invention (hereinafter also referred to as "this method") forms a reaction system containing particles of a fluoroolefin-based polymer (hereinafter also referred to as "FO polymer") (hereinafter also referred to as "FO particles") and water and not containing a fluorine-based emulsifier, and polymerizes at least gaseous perfluoroolefin in the reaction system to obtain an aqueous dispersion containing particles of a fluoropolymer (hereinafter also referred to as "F polymer") (hereinafter also referred to as "F particles"). It is a method for producing an aqueous dispersion, wherein the FO polymer is a fluoroolefin-based polymer having no unit based on a monomer having a hydrophilic group, the ratio of the average particle diameter of the F particles to the average particle diameter of the FO particles (hereinafter also referred to as "particle size ratio") is more 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 more. The content ratio is a value calculated from the respective contents (mass%).

[0010] The reason why an aqueous dispersion containing particles of a dense fluoropolymer with excellent in-liquid dispersibility can be efficiently produced by this method in the absence of a fluorine-based emulsifier is not necessarily clear, but the following reasons can be cited. In this method, the FO polymer has no hydrophilic group in the monomer units forming the main skeleton of the polymer molecule, but has other hydrophilic groups. The FO polymer can also be regarded as a polymer having a hydrophilic part composed of such hydrophilic groups and a hydrophobic part composed of units based on fluoroolefins, that is, a hydrophobic part composed of the main chain of the polymer. It is considered that the FO particles, which are particles of such a polymer, are highly dispersed in the liquid phase due to the action of the hydrophilic part in a reaction system containing water. The gaseous perfluoroolefin introduced into such a reaction system has fluorine atoms and is likely to be adsorbed by the FO polymer with high affinity for it. In other words, it is considered that the FO particles function highly as a polymerization field for perfluoroolefin. As a result, it is considered that the polymerization tends to proceed uniformly and densely, and the heat transfer property associated with the polymerization is also likely to be improved. As a result, according to this method, it is considered that an aqueous dispersion containing F particles excellent in liquid-phase dispersibility can be efficiently produced while increasing each of the particle size ratio and the content ratio without the presence of a fluorine-based emulsifier. Note that such an action mechanism is more likely to be expressed by the preferred embodiment of this method described later.

[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. A fluorine-based emulsifier is an emulsifier having fluorine atoms, different from the FO polymer. Specifically, it is 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, etc.). More specifically, it is perfluoroalkyl carboxylic acid, perfluoroalkyl sulfonic acid, or their salts. An etheric oxygen atom may be present between 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 its total mass. Furthermore, the water content is preferably 100% by mass or less, and more preferably 99.9% by mass or less. When water occupies the liquid component of the reaction system within this range, in other words, even when the liquid component of the reaction system is substantially water, an aqueous dispersion with excellent dispersibility in liquid and a high content of F particles can be directly obtained without using a fluorine-based emulsifier, through the mechanism of action described above.

[0013] In this method, the 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 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-described mechanism of action is more likely to manifest. In this specification, the liquid viscosity is determined by measuring the viscosity of the reaction system using a B-type viscometer at 25°C and a rotation speed of 30 rpm. The viscosity measurement is repeated three times, and the average of the three measurements is used. In this method, the ratio of the viscosity of the aqueous dispersion to the viscosity of the reaction system is preferably greater than 1. Furthermore, the viscosity ratio is preferably less than 5. In this case, the aforementioned mechanism of action is more likely to manifest.

[0014] In this method, the thixotropic ratio of the reaction system liquid is preferably 0.95 or higher, and more preferably 0.98 or higher. The thixotropic ratio of the liquid is preferably 1.05 or lower, and more preferably 1.02 or lower. In this method, the reaction system is preferably thixotropic, in other words, the thixotropic ratio is preferably 1. In this case, the above-described mechanism of action is more likely to manifest. In this specification, the thixotropy ratio of a liquid is determined using a B-type viscometer, comparing the viscosity of the liquid measured at 25°C and a rotation speed of 30 rpm with the viscosity of the liquid measured at 60 rpm, and is the value obtained by dividing the former viscosity by the latter viscosity.

[0015] These liquid physical properties may be controlled by adjusting the type of FO polymer, the particle size of FO particles, and the content of FO particles, water, or other components in the reaction system.

[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 may be carboxylated with a counter cation such as sodium ion (Na + ), potassium ion (K + ), ammonium ion (NH4 + ), etc., to form a carboxylate (-COO - ). Examples of the sulfonic acid-containing group include a sulfonic acid group. The sulfonic acid group may be sulfonated with a counter cation such as sodium ion (Na + ), potassium ion (K + ), ammonium ion (NH4 + ), etc., to form a sulfonate (-SO3 - ). Examples of the phosphonic acid-containing group include a phosphonic acid group. The phosphonic acid group may be phosphonated with a counter cation such as sodium ion (Na + ), potassium ion (K + ), ammonium ion (NH4 + ), etc., to form a phosphonate (-PO3 - ).

[0017] The content of the hydrophilic group possessed by the FO polymer is preferably 100 to 10,000 per 10 6 main chain carbon atoms of the polymer. In this case, the above-described mechanism of action is more likely to be exhibited. The hydrophilic group content of the FO polymer is a value measured by infrared spectroscopy of a film molded from the FO polymer, specifically the value measured by the method described in Japanese Patent Application Publication No. 2022-50435.

[0018] In this Act, the FO polymer is a hydrophilic polymer that contains units based on fluoroolefins but does not contain units based on monomers having hydrophilic groups, and preferably a polymer that contains units based on fluoroolefins but does not contain units based on monomers having hydrophilic groups, and has hydrophilic groups at its polymer ends.

[0019] 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 monomers other than fluoroolefins. Preferably, the monomer is a gaseous monomer other than a fluoroolefin. The monomer may be one type or multiple types. Examples of the monomers mentioned above 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-dioxol, perfluorobutenyl vinyl ether, and perfluoroallyl vinyl ether.

[0021] 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"). Examples of PAAEs include CF2=CFCF2OCF3 (hereinafter also referred to as "PMAE") and CF2=CFCF2CF2OCF3 (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. In this case, the degree of conformational freedom of the FO polymer is improved, and the above-described mechanism of action is more easily expressed.

[0023] The FO polymer preferably contains monomer units having side chains, and is preferably FKM, FFKM, FEPM, or FEP, as described later, and more preferably FKM, FFKM, or FEPM. In this case, the conformational freedom of the FO polymer is improved, and the above-mentioned mechanism of action is more easily expressed. 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 mechanism of action described above is more likely to be expressed. The FO polymer is preferably a polymer obtained by the method described later.

[0024] In this method, the FO particles are dispersed in liquid within the reaction system. The average particle diameter 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 diameter of the FO particles is preferably less than 150 nm, and more preferably 120 nm or less. In this case, the above-described mechanism of action is more likely to be expressed. In this specification, the average particle diameter is the particle diameter 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-described mechanism of action is more easily expressed, and the content ratio of the resulting aqueous dispersion is particularly easy to increase.

[0026] The formation of the reaction system in this method is not particularly limited, but it is preferable to form it by polymerizing at least a gaseous fluoroolefin in the presence of water and a polymerization initiator without using a fluorine-based emulsifier. This method not only makes it easier to form a reaction system containing the desired FO polymer particles (FO particles) and water, but without a fluorine-based emulsifier, but also makes the above-described mechanism of action more readily apparent.

[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. Examples of monomers other than the aforementioned fluoroolefins include monomers that form monomer units that can be included in the FO polymer described above.

[0029] The polymerization initiator in the above 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 bromate or its salt, chloric acid or its salt, persulfuric acid or its salt, permanganic acid or its salt, or hydrogen peroxide, and a reducing agent such as sulfurous acid or its salt, bisulfite or its salt, thiosulfuric acid or its salt, organic acids, or inorganic salts.

[0030] Examples of oxidizing agents include potassium persulfate, APS, and sodium sulfite. Examples of inorganic salts include salts containing sulfate anions, sulfite anions, or chloride anions and metal ions such as manganese, iron, cobalt, nickel, copper, zinc, cerium, and silver, with iron(II) sulfate being a particularly notable example. The polymerization initiator may be one type or multiple types.

[0031] The amount of polymerization initiator in the above polymerization is preferably 0.01 to 5% by mass, more preferably 0.01 to 3% by mass, and even more preferably 0.01 to 2 parts by mass, based on the total mass of all monomers subjected to polymerization, including gaseous fluoroolefins.

[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. It is preferable to carry out the polymerization 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 a polymerization initiator is usually 10 hours, but if the polymerization initiator is a persulfate, it is set to 55°C. Typically, persulfates have a half-life of 18 to 120 hours at 55°C and are polymerization initiators with high activity at 55°C. The polymerization initiator can be introduced into the reaction system by conventional methods, and may be added to the reaction system all at once, in portions, or continuously.

[0033] The polymerization temperature is preferably above 55°C, more preferably above 60°C, and even more preferably above 65°C. Furthermore, the polymerization temperature is preferably below 100°C. In this case, the above-described mechanism of action is more likely to manifest.

[0034] The pressure during polymerization is preferably 0.9 MPaG or higher, and more preferably 1.0 MPaG or higher. Furthermore, the pressure during polymerization is preferably 4.0 MPaG or lower, and more preferably 3.5 MPaG or lower. In this case, the above-described mechanism of action is more likely to manifest. In this specification, "MPaG" refers to gauge pressure, which is the pressure obtained by subtracting atmospheric pressure (0.1013 MPa) from absolute pressure. The pressure during polymerization can be adjusted by introducing gaseous fluoroolefin into the reaction system using a conventional method. Specifically, the pressure during polymerization can be adjusted by continuously or intermittently introducing gaseous fluoroolefin into the reaction system so that it reaches a predetermined pressure. Alternatively, gaseous monomers other than gaseous fluoroolefin may be used in combination to adjust the pressure.

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

[0036] The product obtained by this method may be used as a reaction system as is, or the types of components in the product and their content may be adjusted before it is used as a reaction system. Alternatively, the product may be used as a reaction system at the stage when its formation is confirmed in this method. Furthermore, specific embodiments of preparing the product solution obtained by the above method before forming the reaction system include: adjusting the FO particle content by adding water to the product solution before forming the reaction system; adjusting the liquid properties of the reaction system by adding other components, as described later, to the product solution before forming the reaction system; and treating the product solution with an ion exchange resin to remove salts derived from polymerization initiators before forming the reaction system. Alternatively, without using a fluorine-based emulsifier, at least gaseous fluoroolefins may be polymerized in the presence of a solvent other than water and a polymerization initiator, and then water may be added to form the reaction system. 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 Act may contain components other than FO particles and water. Other specific examples of ingredients include chain transfer agents, emulsifiers other than fluorinated 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 Emulsifier 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 phosphates may also be hydrates such as disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate.

[0038] If the reaction system contains a chain transfer agent, its content is preferably 0.1 to 5% by mass relative to the total mass of the reaction system. Furthermore, the amount of chain transfer agent used is preferably 0.1 to 20% by mass, more preferably 0.1 to 15% by mass, and even more preferably 0.1 to 10% by mass, relative to the amount of gaseous perfluoroolefin used. If the reaction system contains emulsifiers other than fluorinated emulsifiers, their content is preferably 5% by mass or less, and more preferably 1% by mass or less, relative to the total mass of the reaction system. The aforementioned content is preferably 0% by mass or more. If the reaction system contains a pH adjusting agent, its content is preferably 0.01 to 3.0% by mass relative to the total mass of the reaction system. If the reaction system contains a reducing agent, its content is preferably 0.1 to 2% by mass relative to the total mass of the reaction system.

[0039] In this method, the reaction system preferably contains persulfate ions or sulfate ions in a concentration of 10 ppm by mass or less, and more preferably 5 ppm by mass or less. The lower limit of the concentration is preferably 0 ppm. When the concentration is within this range, the coloration of the F polymer is suppressed, and the physical properties of the aqueous dispersion tend to improve. A specific example of a reaction system containing these ions is when the polymerization initiator in the above method is persulfates. In this case, it is preferable to treat the resulting solution obtained by the above method with an ion exchange resin to remove these ions.

[0040] In this method, the fluoride ion concentration in the reaction system is preferably 100 ppm by mass or less, and more preferably 50 ppm by mass or less. The lower limit of the fluoride ion content is preferably 0 ppm by mass. A specific example of a reaction system containing fluoride ions is a by-product containing fluoride ions produced by the reaction of a polymerization initiator (e.g., APS) with a fluoroolefin.

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

[0042] This polymerization may be carried out in the presence of monomers other than gaseous perfluoroolefins, and copolymerization of gaseous perfluoroolefins and the monomers is preferred. The monomer may be a gaseous monomer or a liquid monomer. The monomer may be one type or multiple types.

[0043] Examples of the monomers mentioned above include Et, Pp, vinyl chloride, vinylidene chloride, VdF, CTFE, fluoroalkylethylene (hereinafter also referred to as "FAE"), PAVE, PAAE, fluoromonomers having a fluorosulfonyl group, a carboxyl group or an alkoxycarbonyl group, perfluoro-2-methylene-4-methyl-1,3-dioxolane, perfluoro-2,2-dimethyl-1,3-dioxol, perfluorobutenyl vinyl ether, and perfluoroallyl vinyl ether.

[0044] Examples of FAEs include CH2=CH(CF2)2F, CH2=CH(CF2)3F, CH2=CH(CF2)4F, CH2=CF(CF2)3H, and CH2=CF(CF2)4H. Examples of fluoromonomers having a fluorosulfonyl group, a carboxyl group, or an alkoxycarbonyl group include CF2=CFSO2F, CF2=CFO(CFCF(CF3))OCF2CF2SO2F, and CF2=CFO(CF2)3COOCH3.

[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, relative to the total amount of monomers used for polymerization. The amount of gaseous perfluoroolefin used is preferably 100 mol% or less.

[0046] Furthermore, when monomers other than gaseous perfluoroolefins are 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, relative to the total amount of monomers used in polymerization. In this case, it is preferable that the amount of gaseous perfluoroolefin used is greater 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 of the reaction system. When monomers other than gaseous perfluoroolefins are used, it is preferable that the total amount of gaseous perfluoroolefin and the monomers used is 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. 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 the agents mentioned above. Examples of oil-soluble radical initiators include tert-butyl peroxypivalate and diisopropyl peroxydicarbonate. One polymerization initiator may be used, or multiple 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 from the type of F polymer to be used. 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 parts by mass, relative to the total mass of monomers subjected to polymerization.

[0049] In this polymerization, the gaseous perfluoroolefin can be introduced into the reaction system by conventional methods. Specifically, the gaseous perfluoroolefin can be introduced into the reaction system continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. The polymerization initiator can also be introduced into the reaction system by conventional methods, and may be added to the reaction system all at once, in portions, or continuously.

[0050] The polymerization temperature is preferably 10 to 95°C, and more preferably 15 to 90°C. The pressure used in this polymerization is preferably 0.5 to 4.0 MPaG, and more preferably 0.6 to 3.5 MPaG. In this polymerization process, the polymerization time is preferably 90 to 1000 minutes, and more preferably 90 to 700 minutes, in the case of batch processing.

[0051] The aqueous dispersion obtained by this method (hereinafter also referred to as "this dispersion") contains particles of F polymer (F particles) dispersed in the liquid.

[0052] The F polymer is preferably, as a whole, 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. A preferred polymer containing VdF units and TFE units or HFP units is FKM, which is a fluoroelastomer containing 20 to 60 mol% of VdF units and 40 to 80 mol% of TFE units or HFP units. 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 or PAAE units is preferably FFKM, which is a fluoroelastomer containing 40-85 mol% of TFE units and 15-60 mol% of PAVE units, or PFA, which is a fluororesin containing 90-99.5 mol% of TFE units and 0.5-10 mol% of PAVE units. In FFKM, the PAVE units are preferably PMVE units or PEVE units, and more preferably PMVE units. In PFA, the PAVE units are preferably PEVE units or PPVE units, and more preferably PPVE units. Furthermore, PFA may also contain other units such as HFP units and FAE units.

[0054] Preferred polymers consisting of TFE units include PTFE, which is a fluororesin consisting solely of TFE units, or modified PTFE, which is a fluororesin consisting of TFE units and trace amounts of other monomer units. The other monomer units in modified PTFE are preferably less than 0.1 mol%. Examples of other monomer units included in modified PTFE include PAVE units, HFP units, FAE units, and CTFE units. As a polymer containing TFE units and HFP units, FEP, which is a fluororesin containing 55 to 97 mol% of TFE units and 3 to 45 mol% of HFP units, is preferred. FEP may further contain other units such as PAVE units and FAE units. As a polymer containing TFE units and Et units, ETFE, which is a fluororesin containing 35-65 mol% TFE units and 35-65 mol% Et units, is preferred. ETFE may further contain other units such as PAVE units, HFP units, and FAE units.

[0055] Furthermore, the fluoroelastomer may further contain monomer units having functional groups that form crosslinking sites, such as iodine atoms, bromine atoms, and nitrile groups (such as fluorovinyl ether monomer units having the aforementioned functional groups).

[0056] The F polymer is a polymer in which the F polymer and the FO polymer consist of the same monomer units and have the same monomer unit content, and may be the same polymer as a whole. Alternatively, the F polymer and the FO polymer may consist of the same monomer units but have different monomer unit content, or they may be polymers composed of different monomer units.

[0057] The viscosity of this 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 of the dispersion is preferably 0.95 or higher, and more preferably 0.98 or higher. The thixotropy of the liquid is preferably 1.05 or lower, and more preferably 1.02 or lower. The dispersion is preferably thixotropic, in other words, it is preferable that the thixotropy is 1.

[0058] According to this method, a dispersion with such excellent liquid properties can be easily obtained directly through the mechanism of action described above.

[0059] The average particle size of F particles in this dispersion is preferably greater than 50 nm, more preferably 70 nm or greater, and even more preferably 100 nm or greater. The average particle size of F particles is preferably 1000 nm or less, more preferably 500 nm or less, and even more preferably 400 nm or less.

[0060] In this dispersion, the particle size distribution of F particles is preferably unimodal. Furthermore, the polydispersity index of the particle size of F particles is preferably 0.5 or less, and more preferably 0.25 or less. According to this method, a dispersion with such excellent particle properties can be easily obtained due to the mechanism of action described above. The polydispersion index is the width of the particle size distribution obtained by analyzing the autocorrelation function obtained from dynamic light scattering using the cumulant method. A smaller value indicates a narrower particle size distribution of F particles dispersed in a liquid.

[0061] The content of F particles in this 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 40% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less. The water content in this 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 60% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more. Furthermore, the sum of the F particle content and water content in this dispersion is preferably 90% by mass or more, and more preferably 96% by mass or more, relative to the total mass. The upper limit of the sum is 100% by mass. Due to the mechanism of action described above, this method allows for the efficient production of a dense aqueous dispersion with a high content of F particles, which is substantially composed of water as the liquid medium and exhibits excellent dispersibility in liquid.

[0062] In this method, the particle size ratio is the value obtained by dividing the average particle diameter of F particles in the dispersion by the average particle diameter 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, and may be greater than 2. The particle size ratio may be 10 or less, may be 5 or less, and may be 2 or less.

[0063] In this method, the content ratio 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 greater, may be 5 or greater, may be 7 or greater, or may be 10 or greater. The content ratio may be 500 or less, may be 250 or less, may be 100 or less, may be 50 or less, or may be 25 or less. The content ratio is a value calculated from the respective content (mass%).

[0064] Due to the mechanism of action described above, this method allows for the production of aqueous dispersions by selecting the desired particle size ratio and content ratio. The respective values ​​of the particle size ratio and content ratio in this method should be appropriately determined depending on the physical properties of the target F polymer, the physical properties of the target aqueous dispersion, and the intended application.

[0065] For example, when using a fluoroelastomer as the FO polymer and producing this dispersion containing F polymer particles 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 diameters of the FO particles and F particles are preferably 25 to 150 nm and 30 to 400 nm, respectively. For example, when producing this dispersion using a fluoroelastomer as the FO polymer and containing particles of 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 diameters of the FO particles and F particles are preferably 25 to 150 nm and 30 to 300 nm, respectively. For example, when using fluororesin as the FO polymer and producing this dispersion containing particles of 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 diameter of the FO particles and the average particle diameter 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 perfluoroolefins proceeds densely due to the mechanism of action described above, thereby suppressing the generation of low-molecular-weight by-products derived from gaseous perfluoroolefins in the dispersion. In particular, when tetrafluoroethylene is included in the gaseous perfluoroolefin, the amount of compounds represented by formula (S1) and formula (S2) below can be suppressed. Formula (S1): H-(CF2) n -COO - M + Formula (S2): H-(CF2) n -SO3 - M + In the formulas, M independently represents H, Na, K, or NH4, n in the compound represented by formula (S1) represents an integer from 7 to 11, and n in the compound represented by formula (S2) represents an integer from 8 to 12.

[0067] In this method, the aqueous dispersion (hereinafter also referred to as "this dispersion") preferably contains 100 ppb by mass or less of the compound represented by formula (S1) and 50 ppb by mass or less, and even more preferably 25 ppb by mass or less, relative to the total mass of F particles. The lower limit of the above content is preferably 0 ppb by mass. In other words, it is preferable that the aqueous dispersion in this method does not contain these compounds.

[0068] This dispersion is an aqueous dispersion containing highly dispersion-stable F particles, and can be suitably used as a coating agent, binder, etc. Alternatively, a dispersion containing F particles may be prepared by replacing the water in this dispersion with an organic solvent such as N-methylpyrrolidone or acetone, using such an organic solvent as the liquid dispersion medium. Alternatively, F particles may be agglomerated from this dispersion to obtain F particle powder. The F particle powder obtained by agglomeration may be directly processed into molded products by melt molding or the like. Furthermore, the F particle powder obtained by agglomeration may be homogenized by melt kneading or the like to be processed into molded base materials such as pellets or granules.

[0069] Methods of agglutination include mechanical agglutination, freeze agglutination, acid agglutination, base agglutination, and agglutination using a coagulant, with mechanical agglutination, acid agglutination, or agglutination using a coagulant being preferred. The preferred coagulation temperature for freeze-coagulation is -20 to 0°C. The coagulation time is preferably 1 hour or more, and more preferably 2 hours or more. In the case of acid agglutination, it is preferable to add an acid-containing solution to the dispersion. 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 agglutination, it is preferable to add a solution containing the base to the dispersion. Examples of bases include sodium hydroxide, potassium hydroxide, and ammonium carbonate. The base concentration in the solution containing the base is preferably 1 to 10% by mass. In the case of coagulation using a coagulant, it is preferable to add the coagulant to the dispersion. Examples of coagulants include aluminum sulfate, alum, calcium nitrate, magnesium sulfate, and ammonium carbonate. [Examples]

[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 (CF2 = CF2) VdF: Vinylidene fluoride (CH2=CF2) HFP: Hexafluoropropylene (CF2=CFCF3) PMVE: Perfluoromethyl vinyl ether (CF2=CFOCF3) PMAE: Perfluoromethylallyl ether (CF2=CFCF2OCF3) Et: Ethylene (CH2=CH2)

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

[0710] to

[0732] of International Publication No. 2018 / 181904. The instrument 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 freezing and condensing the aqueous dispersion, then filtering and analyzing the recovered liquid using ion chromatography. An ion chromatograph ICS-5000 (Thermo Fisher Scientific) was used for the ion chromatography analysis. A Dionex IonPac AS-19 column was used for separation, a Dionex IonPac AG-19 column for guarding, and KOH was used as the eluent.

[0072] The reactors used were all made of stainless steel.

[0073] [Example 1] Example of manufacturing an aqueous dispersion Ultrapure water (1130 g), 30% by mass ammonia aqueous solution (30 mg), PMVE (72 g), and TFE (14 g) were charged into a pressure reactor (internal volume 2.2 L), and the temperature was raised to 90°C while stirring at 600 rpm. Next, 5.0% by mass APS aqueous solution (30 mL) was added, and polymerization was started. TFE was added to compensate for the decrease in reactor pressure due to polymerization, and the pressure was maintained at 0.8 MPaG or higher. After adding 4 g of TFE under pressure, the reactor was cooled, and the polymerization reaction was terminated. After recovering the remaining gas in the reactor, the liquid was withdrawn to obtain the mother liquor. The mother liquor was a dispersion of FO polymer particles having carboxyl groups at the polymer ends, containing 34 mol% PMVE units and 66 mol% TFE units.

[0074] Ultrapure water and ion exchange resin were added to the mother liquor, stirred, and filtered to obtain a treated solution. This treated solution was a dispersion of the FO polymer particles (average particle size: 98 nm). The particle content in the solution was 0.6% by mass.

[0075] Ultrapure water (175g) and processing solution (1000ml) were charged into a pressure-resistant reactor (internal volume 1.2L) to form a reaction system containing 0.5% by mass of the aforementioned particles (liquid viscosity: 1.0 mPa·s, thixotropy ratio: 1.00). PMVE (72g) and TFE (14g) were charged into the reactor and the temperature was raised to 80°C while stirring at 600 rpm. TFE and PMVE were injected under pressure until the reactor pressure reached 1.2 MPaG, and an aqueous solution of APS (2.5% by mass, 7mL) was added to start polymerization. As the reactor pressure decreased due to polymerization, TFE and PMVE were alternately injected under pressure to maintain a constant pressure. When 80g of TFE and 63g of PMVE had been injected under pressure, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 138 minutes.

[0076] After recovering the remaining gas in the reactor, the liquid contents were removed to obtain an aqueous dispersion. The aqueous dispersion contained 11.5% by mass of fluoropolymer particles (average particle size: 141.1 nm) with an overall TFE unit content of 66 mol% and PMVE unit content of 34 mol% (liquid viscosity: 1.1 mPa·s, thixotropy: 1.00). The aqueous dispersion exhibited excellent liquid properties, such as dispersion stability, and handling properties, and the fluoropolymer exhibited excellent properties as a fluoroelastomer (FFKM). Furthermore, the particle size distribution was unimodal, and its polydispersity index was 0.5 or less. The content of the compounds represented by formulas (S1) and (S2) in the aqueous dispersion, relative to the total mass of the particles in the aqueous dispersion, was 100 ppb by mass or less in both cases.

[0077] [Example 2] Example of manufacturing an aqueous dispersion Ultrapure water (1162g), 28% NH3 aqueous solution (1 drop), PMVE (70g), and TFE (14g) were charged into a pressure reactor (internal volume 2.1L), and the internal temperature was raised to 80°C while stirring at 600rpm. Polymerization was started by adding an aqueous solution of APS (5.9% by mass, 5mL). To compensate for the decrease in reactor pressure due to polymerization, TFE was injected under pressure to maintain a pressure of 0.8MPaG or higher. The reactor was cooled and the polymerization reaction was terminated when 24g of TFE had been injected under pressure. After recovering the remaining gas in the reactor, the solution in the reactor was drained to obtain the mother liquor. The mother liquor was a dispersion of FO polymer particles (average particle size: 110 nm) having carboxyl groups at the polymer ends, containing 34.4 mol% PMVE units and 65.6 mol% TFE units. The content of these particles in the solution was 3.0% by mass.

[0078] 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-resistant reactor (internal volume 1.2 L) to form a reaction system (liquid viscosity: 1.1 mPa·s, thixotropic ratio: 1.00) containing 0.22 mass% of the aforementioned particles. The reaction system was stirred at 320 rpm while the internal temperature was raised to 60°C. A mixed gas (containing 86 mol% TFE and 14 mol% Et, in that order; the same applies hereafter) was injected into the reactor under pressure until the pressure reached 2.6 MPaG. An aqueous solution of tert-butyl hydroperoxide (0.2% by mass, 2 mL) and a reducing agent (BRUGGOLITE® FF6M, 0.396% by mass, 2 mL) were added to the reactor to start polymerization. The pressure inside the reactor was kept constant by adding the mixed gas to compensate for the decrease in pressure due to polymerization. An aqueous solution of tert-butyl hydroperoxide (0.2% by mass, 1 mL) and the aforementioned reducing agent (1 mL) were added every 5 minutes from the start of polymerization. When the amount of mixed gas injected reached 80 g, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 181 minutes.

[0079] After recovering the remaining gas in the reactor, the liquid contents were removed to obtain an aqueous dispersion. The aqueous dispersion contained 10.2% by mass of fluoropolymer particles (average particle size: 182 nm) with an overall content of 56.9 mol% TFE units, 42.4 mol% Et units, and 0.7 mol% PMVE units (liquid viscosity: 1.3 mPa·s, thixotropy: 1.00). The aqueous dispersion exhibited excellent liquid properties, particularly dispersion stability, and handling properties, while the fluoropolymer, specifically ETFE (fluororesin), demonstrated superior properties. Furthermore, the particle size distribution was unimodal, and its polydispersity index was 0.5 or less. The content of the compounds represented by formulas (S1) and (S2) in the aqueous dispersion, relative to the total mass of the particles in the aqueous dispersion, was 100 ppb by mass or less in both cases.

[0080] [Example 3] Example of manufacturing aqueous dispersion Ultrapure water and ion exchange resin were added to the mother liquor obtained in Example 1, stirred, and filtered to obtain a treated solution. This treated solution was a dispersion of FO polymer particles (average particle size: 110 nm) having carboxyl groups at the polymer ends, containing 34.4 mol% PMVE units and 65.6 mol% TFE units. The content of these particles in the solution was 1.5% by mass.

[0081] Ultrapure water (428 g), processing 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 aforementioned particles (liquid viscosity: 1.3 mPa·s, thixotropic ratio: 1.00). The reaction system was stirred at 320 rpm while the internal temperature was raised to 60°C. A mixed gas (containing 86 mol% TFE and 14 mol% Et, in that order; the same applies hereafter) was injected into the reactor under pressure until the pressure reached 2.6 MPaG. An aqueous solution of tert-butyl hydroperoxide (0.2% by mass, 2 mL) and the reducing agent were added to the reactor to start polymerization. The pressure inside the reactor was kept constant by adding the mixed gas to compensate for the decrease in pressure due to 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 polymerization. When the amount of mixed gas injected reached 80 g, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 167 minutes.

[0082] After recovering the remaining gas in the reactor, the liquid contents were removed to obtain an aqueous dispersion. The aqueous dispersion contained 10.6% by mass of fluoropolymer particles (average particle size: 156 nm) with an overall composition of 56.3 mol% TFE units, 43.1 mol% Et units, and 0.6 mol% PMVE units (liquid viscosity: 1.4 mPa·s, thixotropy: 1.00). The aqueous dispersion exhibited excellent liquid properties, particularly dispersion stability, and handling properties, while the fluoropolymer, specifically ETFE (fluororesin), demonstrated superior properties. Furthermore, the particle size distribution was unimodal, and its polydispersity index was 0.5 or less.

[0083] The content of the compounds represented by formulas (S1) and (S2) in the aqueous dispersion, relative to the total mass of the particles in the aqueous dispersion, was 100 ppb by mass or less in both cases. The sulfate ion concentration in the aqueous dispersion was less than 0.1 ppm by mass.

[0084] [Example 4] Example of production of aqueous dispersion In a pressure reactor (internal volume 1.3 L), ultrapure water (717 g), PMVE (50 g), and TFE (8 g) were charged, and the temperature was raised to 90°C while stirring at 500 rpm. Polymerization was started by adding an aqueous solution of APS (3.6 mass%, 5 mL). As the reactor pressure decreased due to polymerization, TFE was injected under pressure to maintain a pressure of 1.4 MPaG. The reactor was cooled and the polymerization reaction was terminated when 2 g of TFE had been injected under pressure. After recovering the remaining gas in the reactor, the solution in the reactor was removed to obtain the mother liquor. The mother liquor was a dispersion of FO polymer particles having carboxyl groups at the polymer ends, containing 48 mol% PMVE units and 52 mol% TFE units. An ion exchange resin was added to the mother liquor, stirred, and filtered to obtain a treated solution. This treated solution contained FO polymer particles (average particle size: 87 nm), with a content of 0.6% by mass.

[0085] In a pressure-resistant reactor (internal volume 1.0 L), ultrapure water (121 g), processing solution (475 g), and wax (28 g) were charged to form a reaction system containing 0.48% by mass of the aforementioned particles (liquid viscosity: 1.3 mPa·s, thixotropic ratio: 1.00). The reaction system was stirred at 260 rpm while the internal temperature was raised to 70°C. TFE was injected into the reactor under pressure until the pressure reached 1.4 MPaG, and an aqueous solution of APS (0.2% by mass, 5 mL) was added to the reactor to start polymerization. As the reactor pressure decreased due to polymerization, TFE was added to maintain a constant pressure. When the amount of TFE injected reached 110 g, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 220 minutes.

[0086] After recovering the remaining gas in the reactor, the liquid contents were removed to obtain an aqueous dispersion. The aqueous dispersion contained 16.0% by mass of fluoropolymer particles (average particle size: 228 nm) with an overall TFE unit content of 99.1 mol% and PMVE unit content of 0.9 mol% (liquid viscosity: 1.5 mPa·s, thixotropy: 1.00). The aqueous dispersion exhibited excellent liquid properties, such as dispersion stability, and handling properties, and the fluoropolymer exhibited excellent properties as PTFE, a fluororesin. Specifically, the melting point of the fluoropolymer was 338°C, and its crystallization energy was -35 J / g. Furthermore, the particle size distribution was unimodal, and its polydispersity index was 0.5 or less. The content of the compounds represented by formulas (S1) and (S2) in the aqueous dispersion, relative to the total mass of the particles in the aqueous dispersion, was 100 ppb by mass or less in both cases.

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

[0088] A pressure-resistant reactor (internal volume 1.0 L) was charged with a processing liquid (600.0 g) and wax (28 g) to form a reaction system containing 0.72% by mass of the aforementioned particles (liquid viscosity: 1.2 mPa·s, thixotropic ratio: 1.00). The reaction system was stirred at 260 rpm while the internal temperature was raised to 70°C. TFE was injected into the reactor under pressure until the pressure reached 1.4 MPaG, and an aqueous solution of disuccinic acid peroxide (0.56% by mass, 11 mL) was added to the reactor to start polymerization. As the reactor pressure decreased due to polymerization, TFE was added to maintain a constant pressure. After 216 minutes, when the consumption of TFE reached 50 g, the reactor was cooled to terminate the polymerization reaction.

[0089] After recovering the remaining gas in the reactor, the liquid contents were removed to obtain an aqueous dispersion. The aqueous dispersion contained 7.7% by mass of fluoropolymer particles (average particle size: 301 nm) with an overall composition of 99.1 mol% TFE units and 0.9 mol% HFP units (liquid viscosity: 1.4 mPa·s, thixotropy: 1.00). The aqueous dispersion exhibited excellent liquid properties, particularly dispersion stability, and handling properties, while the fluoropolymer, a fluororesin (PTFE), exhibited superior properties. Specifically, the melting point of the fluoropolymer was 338°C, and its DSC heat of fusion was 64 J / g. Furthermore, the particle size distribution was unimodal, and its polydispersity index was 0.5 or less. Furthermore, the content of the compounds represented by formulas (S1) and (S2) in the aqueous dispersion, relative to the total mass of the particles in the aqueous dispersion, was 100 ppb by mass or less in both cases.

[0090] [Example 6] Example of manufacturing aqueous dispersion In a pressure reactor (internal volume 1.0 L), distilled water (717 g), 28% by mass aqueous ammonia (one drop), and a mixed gas of TFE and HFP were charged, and the temperature was raised to 90°C while stirring at 500 rpm. The reactor pressure after reaching 90°C was 1.94 MPaG. Next, an aqueous solution of APS (3.6% by mass, 5 mL) was added, and polymerization was started. Polymerization was stopped after 97 minutes when the reactor pressure reached 1.78 MPaG. After recovering the remaining gas in the reactor, the solution in the reactor was removed to obtain the mother liquor. An ion exchange resin was added to the mother liquor, stirred, and filtered to obtain a treated solution. This treated solution was a dispersion of FO polymer particles (average particle size: 97 nm) having carboxyl groups at the polymer ends, containing 77 mol% TFE units and 23 mol% HFP units.

[0091] A pressure-resistant reactor (internal volume 1.0 L) was charged with a processing liquid (600.0 g), CH2=CH(CF2)4F (0.73 g), and t-butyl methyl ether (0.51 g) to form a reaction system containing 0.77 mass% of the aforementioned particles (liquid viscosity: 1.0 mPa·s, thixotropic ratio: 1.00). The reaction system was stirred at 260 rpm while the internal temperature was raised to 70°C. TFE was injected into the reactor under pressure until the pressure reached 1.8 MPaG, and a solution of tert-butyl peroxypivalate in isododecane (40% by mass, 2 mL) was added to the reactor to start polymerization. To maintain a constant pressure, a mixed gas (containing 86 mol% TFE and 14 mol% Et, in that order; the same applies hereafter) was added to compensate for the decrease in reactor pressure due to polymerization. An additional 1.6 g of the isododecane solution was also added. When the amount of mixed gas injected reached 50 g, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 170 minutes.

[0092] After recovering the remaining gas in the reactor, the liquid contents were removed to obtain an aqueous dispersion. The aqueous dispersion contained 7.2% by mass of fluoropolymer particles (average particle size: 155 nm) with an overall content 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, thixotropy: 1.00). The aqueous dispersion exhibited excellent liquid properties, particularly dispersion stability, and handling properties, while the fluoropolymer, being a fluororesin (ETFE), demonstrated superior properties. Specifically, the melting point of the fluoropolymer was 244°C, and its DSC heat of fusion was 43 J / g. Furthermore, the particle size distribution was unimodal, and its polydispersity index was 0.5 or less. The content of the compounds represented by formulas (S1) and (S2) in the aqueous dispersion, relative to the total mass of the particles in the aqueous dispersion, was 100 ppb by mass or less in both cases.

[0093] [Example 7] Example of production of aqueous dispersion Ultrapure water (717g) was charged into a pressure reactor (internal volume 1.3L), and the temperature was raised to 90°C while stirring at 500 rpm. A mixed gas containing TFE and PMAE in 18 mol% and 82 mol% concentrations, in that order, was then injected under pressure until the reactor pressure reached 1.5 MPaG. Next, an aqueous solution of APS (3.6% by mass, 5 mL) was added to start polymerization. After 180 minutes, the reactor was cooled to terminate polymerization. After recovering the remaining gas in the reactor, the solution was removed from the reactor to obtain the mother liquor. An ion exchange resin was added to the mother liquor, stirred, and filtered to obtain a treated solution. This treated solution was a dispersion of FO polymer particles (average particle size: 70 nm) having carboxyl groups at the polymer ends, containing 69 mol% TFE units and 31 mol% PMAE units. The content of the particles in the treated solution was expressed in mass%.

[0094] A pressure-resistant reactor (internal volume 1.0 L) was charged with ultrapure water (121 g), processing solution (475 g), and wax (28 g) to form a reaction system containing 0.75% by mass of the aforementioned particles (liquid viscosity: 1.2 mPa·s, thixotropic ratio: 1.00). The reaction system was stirred at 260 rpm while the internal temperature was raised to 70°C. TFE was injected into the reactor under pressure until the pressure reached 1.4 MPaG, and an aqueous solution of disuccinic acid peroxide (0.45% by mass, 3 mL) was added to the reactor to start polymerization. As the reactor pressure decreased due to polymerization, TFE was added to maintain a constant pressure. After 450 minutes, when the amount of TFE injected reached 170 g, the reactor was cooled to terminate the polymerization reaction.

[0095] After recovering the remaining gas in the reactor, the liquid contents were removed to obtain an aqueous dispersion. The aqueous dispersion contained 20.0% by mass of fluoropolymer particles (average particle size: 270 nm) with an overall content of 99.6 mol% TFE units and 0.4 mol% PMAE units (liquid viscosity: 1.4 mPa·s, thixotropy: 1.00). The aqueous dispersion exhibited excellent liquid properties, such as dispersion stability, and handling properties, and the fluoropolymer exhibited excellent properties as PTFE, a fluororesin. Specifically, the melting point of the fluoropolymer was 345°C, and its DSC heat of fusion was 16.5 J / g. Furthermore, the particle size distribution was unimodal, and its polydispersity index was 0.5 or less. The content of the compounds represented by formulas (S1) and (S2) in the aqueous dispersion, relative to the total mass of the particles in the aqueous dispersion, was 100 ppb by mass or less in both cases. Furthermore, the sulfate ion concentration in the aqueous dispersion was less than 0.1 ppm by mass.

[0096] [Example 8] Example of manufacturing an aqueous dispersion Ultrapure water (717g) was charged into a pressure reactor (internal volume 1.0L), and the temperature was raised to 90°C while stirring at 500 rpm. A mixed gas of TFE and VdF was then injected into the reactor until the internal pressure reached 1.98 MPaG. Next, an aqueous solution of APS (3.6% by mass, 5 mL) was added, and polymerization was started. After 96 minutes, when the internal pressure of the reactor had decreased to 1.81 MPaG, the reactor was cooled to terminate the polymerization. After recovering the remaining gas in the reactor, the solution in the reactor was removed to obtain the mother liquor. An ion exchange resin was added to the mother liquor, stirred, and filtered to obtain the treated solution. This treated solution was a dispersion of FO polymer particles (average particle size: 114 nm) having carboxyl groups at the polymer ends, containing 57 mol% HFP units and 43 mol% VdF units.

[0097] A pressure-resistant reactor (internal volume 1.0 L) was charged with a processing liquid (600 g) and wax (28 g) to form a reaction system containing 0.75% by mass of the aforementioned particles (liquid viscosity: 1.2 mPa·s, thixotropic ratio: 1.00). The reaction system was stirred at 260 rpm while the internal temperature was raised to 70°C. TFE was injected into the reactor under pressure until the pressure reached 1.4 MPaG, and an aqueous solution of disuccinic acid peroxide (0.56% by mass, 11 mL) was added to the reactor to start polymerization. As the reactor pressure decreased due to polymerization, TFE was added to maintain a constant pressure. After 292 minutes, when the amount of TFE injected reached 80 g, the reactor was cooled to terminate the polymerization reaction.

[0098] After recovering the remaining gas in the reactor, the liquid contents were removed to obtain an aqueous dispersion. The aqueous dispersion contained 10.1% by mass of fluoropolymer particles (average particle size: 301 nm) with an overall composition of 99.3 mol% TFE units, 0.4 mol% HFP units, and 0.3 mol% VdF units (liquid viscosity: 1.5 mPa·s, thixotropy: 1.00). The aqueous dispersion exhibited excellent liquid properties, particularly dispersion stability, and handling properties, and the fluoropolymer, being a fluororesin (PTFE), demonstrated superior properties. Furthermore, the particle size distribution was unimodal, and its polydispersity index was 0.5 or less. The content of the compounds represented by formulas (S1) and (S2) in the aqueous dispersion, relative to the total mass of the particles in the aqueous dispersion, was 100 ppb by mass or less in both cases.

[0099] The disclosure of Japanese Patent Application No. 2024-099119, filed on 19 June 2024, is incorporated herein by reference in its entirety. Furthermore, 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 as being incorporated by reference.

Claims

1. A method for producing an aqueous dispersion, comprising forming a reaction system containing particles of a fluoroolefin polymer and water, but without a fluorine-based emulsifier, and polymerizing at least gaseous perfluoroolefin in the reaction system to obtain an aqueous dispersion containing fluoropolymer particles, The fluoroolefin polymer is a hydrophilic fluoroolefin polymer that does not contain units based on a monomer having a hydrophilic group, The ratio of the average particle diameter of the fluoropolymer particles in the aqueous dispersion to the average particle diameter of the fluoroolefin polymer particles in the reaction system is greater than 1. 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. A method for producing an aqueous dispersion.

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

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

5. The manufacturing 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 manufacturing method according to claim 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 carboxyl group, or an alkoxycarbonyl group.

7. The manufacturing 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 manufacturing method according to claim 1, wherein the average particle size of the fluoropolymer particles is greater than 50 nm and less than or equal to 1000 nm.

9. The manufacturing 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 manufacturing method according to claim 1, wherein the particle size distribution of the fluoropolymer particles is unimodal, and the polydispersity index of the particle size of the fluoropolymer particles is 0.5 or less.

11. The manufacturing method according to claim 1, wherein the formation of the reaction system is carried out 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 according to claim 11, wherein the polymerization initiator is a water-soluble polymerization initiator.

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

14. The manufacturing 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 manufacturing method according to claim 14, wherein the monomer other than the gaseous fluoroolefin is ethylene, chlorotrifluoroethylene, propylene, perfluoroalkyl vinyl ether, or perfluoroalkyl allyl ether.