Method for producing dispersion and method for producing aqueous dispersion

Abstract

A method for producing a dispersion, comprising: polymerizing a gaseous fluoroolefin in a reaction system containing water and a water-soluble polymerization initiator but not a fluorine-based emulsifier, by maintaining the temperature above the half-life temperature of the polymerization initiator or maintaining a pressure of 0.8 MPaG or higher, to obtain a dispersion containing polymer particles having units based on the fluoroolefin and having an average particle size of 1 to 150 nm in an amount of less than 10 mass% relative to the total mass.

Description

[Technical Field]

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

[0002] Fluoropolymers containing units based on fluoroolefins are used in various industrial fields due to their excellent heat resistance, chemical resistance, flame retardancy, weather resistance, and the like. As a method for producing a fluoropolymer, there is a method in which a fluoroolefin is emulsion-polymerized in water using a fluorine-based emulsifier (see Patent Document 1, etc.). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2007 / 046377 Summary of the Invention [Problem to be solved by the invention]

[0004] The method of Patent Document 1 can obtain an aqueous dispersion containing fluoropolymer particles, which has a small environmental impact. However, depending on the content of the fluorine-based emulsifier, which is an essential component, or depending on the intended use or in some cases, it may be necessary to remove the fluorine-based emulsifier. In recent years, further improvements in the dispersibility of fluoropolymer particles in such aqueous dispersions have also been required. An object of the present invention is to provide a method for efficiently producing an aqueous dispersion containing fluoropolymer particles, which does not require a fluorine-based emulsifier, has a small environmental impact, and has excellent dispersibility in liquid. [Means for solving the problem]

[0005] The present invention provides the following inventions. [1] A method for producing a dispersion, comprising: polymerizing a gaseous fluoroolefin in a reaction system containing water and a water-soluble polymerization initiator but not a fluorine-based emulsifier, by maintaining the temperature above the half-life temperature of the polymerization initiator or maintaining a pressure of 0.8 MPaG or higher, to obtain a dispersion containing polymer particles having units based on the fluoroolefin and having an average particle size of 1 to 150 nm in an amount of less than 10 mass% based on the total mass. [2] The method of producing according to [1], wherein the polymerization initiator is a persulfate and the temperature is higher than 55°C and lower than 100°C. [3] The manufacturing method of [1] or [2], wherein the pressure is 0.9 MPaG or more and 4.0 MPaG or less. [4] The production method according to any one of [1] to [3], wherein the gaseous fluoroolefin is vinyl fluoride, vinylidene fluoride, tetrafluoroethylene or hexafluoropropylene. [5] The production method according to any one of [1] to [4], wherein the polymerization is carried out by copolymerizing the gaseous fluoroolefin with ethylene, chlorotrifluoroethylene, propylene, a perfluoroalkyl vinyl ether, or a perfluoroalkyl allyl ether. [6] The production method according to any one of [1] to [5], wherein the dispersion contains water in an amount of 80 mass % or more based on the total mass. [7] A method for producing an aqueous dispersion, which is prepared from a dispersion obtained by any of the production methods of [1] to [6], by polymerizing gaseous perfluoroolefin in the presence of a polymerization initiator in a reaction system not containing a fluorine-based emulsifier to obtain an aqueous dispersion containing fluoropolymer particles, wherein the ratio of the average particle size of the fluoropolymer particles to the average particle size of the polymer containing units based on the fluoroolefin is greater than 1, and the ratio of the particle content in the aqueous dispersion to the particle content in the reaction system is 2 or more. [8] The method according to [7], wherein the polymerization is carried out at a temperature of 20°C or higher but lower than 100°C and at a pressure of 0.8 MPaG or higher but 4.0 MPaG or lower. [9] The method according to [7] or [8], wherein the liquid viscosity of the reaction system is less than 2 mPa·s.

[10] The production method according to any one of [7] to [9], wherein the gaseous perfluoroolefin is tetrafluoroethylene or hexafluoropropylene.

[11] The production method according to any one of [7] to

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

[12] The production method of

[11] , wherein the gaseous monomer other than perfluoroolefin is ethylene, vinyl fluoride, vinylidene fluoride, chlorotrifluoroethylene, propylene, fluoroalkylethylene, perfluoroalkyl vinyl ether, perfluoroalkyl allyl ether, or a fluoromonomer having a fluorosulfonyl group, a carboxy group, or an alkoxycarbonyl group.

[13] The method according to any one of [7] to

[12] , wherein the average particle size of the fluoropolymer particles is more than 50 nm and not more than 1000 nm.

[14] The method according to any one of [7] to

[13] , 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.

[15] The method according to any one of [7] to

[14] , wherein the fluoropolymer particles comprise 5 to 50% by mass of the total mass. [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. DETAILED DESCRIPTION OF THE INVENTION

[0007] The terms used in the present invention have the following meanings. A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the upper and lower limits. In the numerical ranges described in stages in this specification, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the examples. In this specification, each component may be a single substance corresponding to the component, or two or more substances may be used in combination. When two or more substances are used in combination for each component, the content of the component refers to the total content of the substances used in combination, unless otherwise specified. As used herein, a combination of two or more preferred embodiments is a more preferred embodiment.

[0008] The term "unit" refers collectively to an atomic group derived from one molecule of the monomer, which is formed directly by polymerizing the monomer, and an atomic group obtained by chemically converting a part of the atomic group. Hereinafter, a "unit based on a monomer" will also be referred to simply as a "unit," and a "unit based on monomer A" will also be referred to simply as a "monomer A unit." In this specification, the content (mass % or mol %) of each unit relative to all units contained in the polymer is determined by analyzing the polymer by solid-state nuclear magnetic resonance spectroscopy (NMR), and usually, the content of each unit calculated from the amount of each monomer charged substantially coincides with the actual content of each unit. 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 is a method for producing a dispersion (hereinafter also referred to as "aqueous dispersion 1") (hereinafter also referred to as "this method 1") containing particles (hereinafter also referred to as "FO particles") of a polymer containing units based on the fluoroolefin (hereinafter also referred to as "FO polymer") having an average particle size of 1 to 150 nm, in an amount of less than 10 mass% based on the total mass, by polymerizing gaseous fluoroolefin in a reaction system containing water and a water-soluble polymerization initiator but not a fluorine-based emulsifier, while maintaining the temperature above the half-life temperature of the polymerization initiator or maintaining a pressure of 0.8 MPaG or higher.

[0010] The production method of the present invention is a method for producing an aqueous dispersion containing fluoropolymer (hereinafter also referred to as "F polymer") particles (hereinafter also referred to as "F particles") prepared from aqueous dispersion 1 by polymerizing gaseous perfluoroolefin in the presence of a polymerization initiator in a reaction system containing no fluorine-based emulsifier, wherein 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 F particles in aqueous dispersion 2 to the content of FO particles in the reaction system prepared from aqueous dispersion 1 (hereinafter also referred to as "content ratio") is 2 or greater (hereinafter also referred to as "this method 2"). The content ratio is a value calculated from the respective contents (% by mass). Note that, hereinafter, this method 1 and this method 2 may be collectively referred to as "this method."

[0011] According to Method 1, in the absence of a fluorine-based emulsifier, an aqueous dispersion (aqueous dispersion 1) with excellent dispersibility can be obtained, which contains a predetermined amount of ultrafine particles of a fluoropolymer with excellent dispersibility in liquid. In reaction systems containing water but no fluorine-based emulsifier, gaseous fluoroolefins with low affinity for water generally do not polymerize densely, and polymer particles themselves do not form, or even if they do form, they tend to be heterogeneous and have extremely low dispersibility in liquid. After extensive research, the present inventors have found that using a water-soluble polymerization initiator and polymerizing gaseous fluoroolefins at high temperatures to enhance its activity or under high pressure to enhance the water dispersibility or solubility of the fluoroolefin promotes the production of ultrafine polymer particles (FO particles), and when the content is within a predetermined range, these particles form an aqueous dispersion (aqueous dispersion 1) with excellent dispersibility in liquid. In particular, the present inventors have found that this tendency is more pronounced when the water-soluble polymerization initiator is a persulfate whose half-life at 55°C is 18 to 120 hours.

[0012] The present inventors further discovered that when a gaseous perfluoroolefin is polymerized in a reaction system prepared from Aqueous Dispersion 1, an aqueous dispersion (Aqueous Dispersion 2) containing particles (F particles) of a fluoropolymer (F polymer) with excellent dispersibility in liquid can be efficiently produced even in the absence of a fluorine-based emulsifier. The reasons for this are not necessarily clear, but include the following:

[0013] The FO polymer formed under the above-described high activity conditions can be considered to be a polymer in which the proportion of polymer end groups derived from the polymerization initiator in the polymer molecules is relatively high. In a reaction system containing water, these end groups are likely to form hydrophilic groups such as carboxyl groups. In other words, the FO polymer can be considered to be a polymer having hydrophilic portions composed of these hydrophilic groups and hydrophobic portions composed of the polymer main chain. FO particles, which are particles of such polymers, are thought to be highly dispersed in a reaction system containing water due to the action of the hydrophilic portions. Gaseous perfluoroolefins introduced into such a reaction system are easily adsorbed by the FO polymer, which has a high affinity for fluorine atoms, and polymerize there. In other words, the FO particles are thought to function highly as a polymerization site for the perfluoroolefin. This is thought to facilitate uniform and dense polymerization and improve the heat transfer associated with polymerization. As a result, it is believed that this method made it possible to directly produce an aqueous dispersion (aqueous dispersion 2) containing F particles with excellent dispersibility in liquid while increasing both the particle size ratio and content ratio, even without the presence of a fluorine-based emulsifier. This mechanism of action is more likely to be exhibited significantly by a preferred embodiment of the present method, which will be described later.

[0014] The water-soluble polymerization initiator in Method 1 is preferably a persulfate, an organic peroxide, or an oxidation-reduction catalyst, and 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 the oxidation-reduction catalyst include catalysts containing an oxidizing agent such as bromic acid or a salt thereof, chloric acid or a salt thereof, persulfuric acid or a salt thereof, permanganic acid or a salt thereof, or hydrogen peroxide, and a reducing agent such as sulfurous acid or a salt thereof, hydrogen sulfite or a salt thereof, thiosulfuric acid or a salt thereof, an organic acid, or an inorganic salt.

[0015] Oxidizing agents include potassium persulfate, APS, and sodium sulfite. Inorganic salts include salts containing sulfate, sulfite or chloride anions and metal ions such as manganese, iron, cobalt, nickel, copper, zinc, cerium and silver, particularly iron(II) sulfate. The polymerization initiator may be used alone or in combination with a plurality of types.

[0016] The amount of the polymerization initiator in the polymerization of Method 1 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.

[0017] The polymerization in Method 1 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 a polymerization initiator is usually a 10-hour half-life temperature, but when the polymerization initiator is a persulfate, it is set to 55°C. Typically, persulfates have a half-life at 55°C of 18 to 120 hours, and are polymerization initiators with high activity at 55°C. The polymerization initiator may be present in the reaction system by a conventional method, and may be added to the reaction system all at once, added in portions, or added continuously to the reaction system.

[0018] The polymerization temperature in Method 1 is preferably above 55° C., more preferably at least 60° C., and even more preferably at least 65° C. The polymerization temperature is preferably below 100° C. In this case, the above-described mechanism of action of Method 1 is more likely to be realized.

[0019] The polymerization pressure in Method 1 is preferably 0.9 MPaG or higher, more preferably 1.0 MPaG or higher. The polymerization pressure is preferably 4.0 MPaG or lower, more preferably 3.5 MPaG or lower. In this case, the above-mentioned mechanism of action of Method 1 is more likely to be realized. 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 in the polymerization of Method 1 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 is a predetermined pressure. The pressure may also be adjusted by using a gaseous monomer other than the gaseous fluoroolefin in combination.

[0020] The polymerization time in Method 1 is preferably 90 to 1000 minutes, more preferably 90 to 700 minutes, in the case of batch processing.

[0021] The reaction system of Method 1 does not contain a fluorine-based emulsifier. In other words, the reaction system of Method 1 is preferably formed without using a fluorine-based emulsifier. The fluorine-based emulsifier is an emulsifier containing fluorine atoms that is different from FO polymers, and specifically refers to a water-soluble fluorine-containing compound or salt thereof having a fluorine-containing organic group (such as a perfluoroalkyl group) and a hydrophilic functional group (such as a carboxy group, sulfonic group, or phosphonic acid group), more specifically perfluoroalkylcarboxylic acid, perfluoroalkylsulfonic acid, or a salt thereof. Ethereal oxygen atoms may be present between carbon atoms in the molecules of these compounds.

[0022] The water content in the reaction system of Method 1 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 water content in the reaction system is within this range, in other words, even when the liquid component in the reaction system is essentially water, an aqueous dispersion of FO particles with excellent dispersibility in liquid can be directly obtained due to the above-described mechanism of action without using a fluorine-based emulsifier.

[0023] The gaseous fluoroolefin in Method 1 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.

[0024] The polymerization in Method 1 is preferably carried out by copolymerizing a gaseous fluoroolefin with a monomer other than the gaseous fluoroolefin. Examples of the monomer other than the fluoroolefin 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.

[0025] 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 PAAE include CF2=CFCF2OCF3 (hereinafter also referred to as "PMAE") and CF2=CFCF2CF2OCF3 (hereinafter also referred to as "PEAE").

[0026] The monomer is preferably Et, Pp, vinyl chloride, vinylidene chloride, CTFE, PAVE, or PAAE, more preferably PAVE or PAAE, and even more preferably PMVE, PEVE, or PAAE, which increases the conformational freedom of the FO polymer and makes it easier to exhibit the above-mentioned mechanism of action.

[0027] The FO polymer in Method 1 is a polymer containing units based on a fluoroolefin, and is preferably a polymer containing units based on a gaseous fluoroolefin. The fluoroolefins include the fluoroolefins described above, and the preferred ranges are also the same. 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. The monomer may be the fluoroolefin described above, and the preferred ranges are the same.

[0028] The glass transition temperature (hereinafter also referred to as "Tg") of the FO polymer is preferably from -50 to +10° C., more preferably from -45 to +5° C., even more preferably from -40 to +3° C., and particularly preferably from -35 to 0° C. In this case, the above-mentioned mechanism of action is more likely to be exhibited.

[0029] The FO polymer is preferably FEP, FKM, FEPM or FFKM, as described below, and more preferably FKM, FEPM or FFKM, as described below, in which case the above-mentioned mechanism of action is more likely to be exhibited.

[0030] The FO polymer in Method 1 is preferably a polymer having a hydrophilic group containing a unit based on a fluoroolefin, more preferably a polymer having a hydrophilic group but not containing a unit based on a monomer having a hydrophilic group and containing a unit based on a fluoroolefin, and even more preferably a polymer having a hydrophilic group at the polymer end but not containing a unit based on a monomer having a hydrophilic group and containing a unit based on a fluoroolefin. In this case, the above-mentioned mechanism of action is more easily manifested. Furthermore, due to the above-mentioned mechanism of action, Method 1 makes it easy to form a dispersion containing particles of such a polymer.

[0031] The hydrophilic group 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 (NH4 + ) and carboxylates (-COO - ) may be used. The sulfonic acid-containing group includes a sulfonic acid group. The sulfonic acid group has a counter cation of sodium ion (Na + ), potassium ions (K + ), ammonium ion (NH4 + ) and sulfonates (-SO3 - ) may be used. The phosphonic acid-containing group includes a phosphonic acid group. The phosphonic acid group has a counter cation of sodium ion (Na + ), potassium ions (K + ), ammonium ion (NH4 + ) and the like, phosphonates (-PO3 - ) may be used.

[0032] The content of hydrophilic groups in the FO polymer is 6 The number of molecules per molecule is preferably 100 to 10,000. In this case, the above-mentioned mechanism of action is more likely to be exhibited. 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.

[0033] The FO particles in aqueous dispersion 1 are dispersed in the liquid. The average particle size of the FO particles is 1 nm or more, preferably 10 nm or more, more preferably 25 nm or more, and particularly preferably 30 nm or more. The average particle size of the FO particles is less than 150 nm, more preferably 120 nm or less. Due to the above-mentioned mechanism of action, Method 1 makes it easy to form a dispersion with such particle sizes. The average particle size of particles in this specification is a particle size calculated by analyzing an autocorrelation function obtained by dynamic light scattering using a monodisperse cumulant method.

[0034] The content of FO particles in aqueous dispersion 1 is less than 10% by mass relative to the total mass. The content is preferably 8.0% by mass or less, more preferably 6.0% by mass or less, and even more preferably 5.0% by mass or less. The content is preferably 0.01% by mass or more. Due to the above-mentioned mechanism of action, method 1 makes it easy to form a dispersion with such a content.

[0035] The water content in aqueous dispersion 1 is preferably 80% by mass or more, more preferably more than 90% by mass, based on the total mass. The water content is 99.99% by mass or less, more preferably 95.0% by mass or less. According to Method 1, the above-mentioned mechanism of action makes it easy to form such an aqueous dispersion in which water is essentially the aqueous medium. Furthermore, the sum of the F particle content and the water content in aqueous dispersion 1 is preferably 96% by mass or more, more preferably 98% by mass or more, and even more preferably 99% by mass or more, based on the total mass. The upper limit of this sum is 100% by mass. Due to the above-mentioned mechanism of action, this method can produce a dense aqueous dispersion of F particles with excellent dispersibility in liquid, in which water is essentially the liquid medium.

[0036] The liquid viscosity of the aqueous dispersion 1 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. The liquid viscosity of the reaction system is preferably 0.8 mPa·s or more, and more preferably 1.0 mPa·s or more. The liquid viscosity in this specification is a value determined by measuring the liquid viscosity of the reaction system using a Brookfield viscometer at 25° C. and a rotation speed of 30 rpm. The viscosity measurement is repeated three times, and the average value of the three measurements is used.

[0037] The thixotropy ratio of the aqueous dispersion 1 is preferably 0.95 or more, more preferably 0.98 or more. The thixotropy ratio of the aqueous dispersion 1 is preferably 1.05 or less, more preferably 1.02 or less. The reaction system in this method preferably does not have thixotropy, in other words, the thixotropy ratio is preferably 1. In this specification, the thixotropy ratio of a liquid is measured using a Brookfield viscometer, and is calculated from the viscosity of the target liquid measured at 25°C and a rotation speed of 30 rpm and the viscosity of the target liquid measured at 60 rpm, and is the value obtained by dividing the former viscosity by the latter viscosity.

[0038] Due to the above-mentioned mechanism of action, the present method makes it easy to obtain an aqueous dispersion having such liquid properties.

[0039] A preferred embodiment of aqueous dispersion 1 is an aqueous dispersion containing no fluorine-based emulsifier, which contains particles of at least one fluoroolefin polymer selected from the group consisting of 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, and a polymer containing TFE units and Et units, wherein the content of the particles relative to the total mass is less than 10 mass% and the content of the water is 80 mass% or more, and the particles are dispersed in the liquid with an average particle diameter of 1 to 150 nm.

[0040] The polymer containing TFE or HFP units and VdF units is preferably a fluoroelastomer FKM containing 20 to 60 mol% of VdF units and 40 to 80 mol% of TFE units or HFP units. The FKM may further contain other units such as PAVE units and Pp units. The polymer containing TFE units and Pp units is preferably FEPM, which is a fluoroelastomer containing 30 to 70 mol % of TFE units and 30 to 70 mol % of Pp units. FEPM may further contain other units such as VdF units.

[0041] The polymer containing TFE units and PAVE 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 or PAAE units in FFKM are preferably PMVE units, PEVE units, or PAAE units, and more preferably PMVE units. The PAVE units in PFA are preferably PEVE units or PPVE units, and more preferably PPVE units. PFA may further contain other units such as HFP units and fluoroalkylethylene (hereinafter also referred to as "FAE") units.

[0042] The polymer consisting of TFE units is preferably PTFE, which is a fluororesin consisting only of TFE units, or modified PTFE, which is a fluororesin consisting of TFE units and trace amounts of other monomer units. The content of other monomer units in the modified PTFE is preferably less than 0.1 mol%. Examples of other monomer units contained in the modified PTFE include PAVE units, HFP units, FAE units, and CTFE units. The polymer containing TFE units and HFP units is preferably FEP, which is a fluororesin containing 55 to 97 mol% of TFE units and 3 to 45 mol% of HFP units. FEP may further contain other units such as PAVE units and FAE units. The polymer containing TFE units and Et units is preferably ETFE, which is a fluororesin containing 35 to 65 mol% of TFE units and 35 to 65 mol% of Et units. ETFE may further contain other units such as PAVE units, HFP units, and FAE units.

[0043] In the preferred embodiment, the Tg of the fluoroolefin polymer is preferably in the same range as the Tg of the FO polymer in the aqueous dispersion 1 described above, including the preferred range. In the preferred embodiment, the fluoroolefin polymer is preferably FKM, FEPM or FFKM. In the preferred embodiment, the fluoroolefin polymer preferably has a hydrophilic group. In this case, the embodiment, including the preferred embodiment, is the same as the embodiment of the FO polymer in the aqueous dispersion 1 described above. In addition, in the preferred embodiment, the average particle size of the fluoroolefin polymer particles, the content of the particles, the content of water, the range of the sum of the content of the particles and the content of the water relative to the total mass, the liquid viscosity of the aqueous dispersion, and the thixotropy ratio of the aqueous dispersion are the same as those in the above-mentioned aqueous dispersion 1, including the preferred embodiment.

[0044] Due to the above-mentioned mechanism of action, this method can obtain such a preferred embodiment of aqueous dispersion 1. Such a preferred embodiment of aqueous dispersion 1 is preferably used as a polymerization medium for gaseous perfluoroolefins, and more preferably used for preparing a reaction system in this method 2.

[0045] In Method 2, gaseous perfluoroolefin is polymerized in the presence of a polymerization initiator in a reaction system prepared from Aqueous Dispersion 1 that does not contain a fluorine-based emulsifier, to obtain Aqueous Dispersion 2 containing particles of an F polymer (F particles). When preparing the reaction system, the dispersion obtained by Method 1 (aqueous dispersion 1) may be used as the reaction system as is, or the component types and contents in aqueous dispersion 1 may be adjusted before use as the reaction system. Specific examples of the latter adjustment include adding water to aqueous dispersion 1 to adjust the content of FO particles before using it as a reaction system, adding other components described below to aqueous dispersion 1 to adjust the liquid properties of the reaction system before using it as a reaction system, and treating aqueous dispersion 1 with an ion exchange resin to remove salts derived from the polymerization initiator and the like before using it as a reaction system.

[0046] The content of persulfate ions or sulfate ions in the reaction system in Method 2 is preferably 10 ppm by mass or less, and more 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 aqueous dispersion 2 tend to improve. A specific example of a case in which these ions are contained in the reaction system is a case in which the polymerization initiator in Method 1 is a persulfate. In this case, it is preferable to treat aqueous dispersion 1 with an ion exchange resin to remove these ions.

[0047] In Method 2, the fluoride ion concentration in the reaction system is preferably 100 ppm by mass or less, 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 when aqueous dispersion 1 contains a by-product containing fluoride ions produced by the reaction of a polymerization initiator (e.g., APS) with a fluoroolefin.

[0048] The polymerization of Method 2 (hereinafter also referred to as "main polymerization") is carried out by polymerizing gaseous perfluoroolefin. The gaseous perfluoroolefin may be one type or multiple types. The gaseous perfluoroolefin is preferably TFE or HFP, and more preferably contains at least TFE.

[0049] 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, and the number of types of the monomer may be one or more. Examples of the monomer include Et, Pp, vinyl chloride, vinylidene chloride, VdF, CTFE, 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.

[0050] 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 carboxy group, or an alkoxycarbonyl group include CF2=CFSO2F, CF2=CFO(CFCF(CF3))OCF2CF2SO2F, and CF2=CFO(CF2)3COOCH3.

[0051] In this polymerization, the amount of gaseous perfluoroolefin used is preferably 10 mol% or more, more preferably 30 mol% or more, and preferably 40 mol% or more, based on the total amount of monomers used in the polymerization. The amount of gaseous perfluoroolefin used is preferably 100 mol% or less.

[0052] In addition, when a monomer other than gaseous perfluoroolefin is used in this polymerization, the amount of gaseous perfluoroolefin used is preferably 90 mol% or less, more preferably 70 mol% or less, and preferably 60 mol% or less, based on the total amount of monomers used in the polymerization. In this case, the amount of gaseous perfluoroolefin used is preferably more than 0 mol%.

[0053] In this polymerization, the amount of gaseous perfluoroolefin used is preferably 1 to 60 mass%, more preferably 1 to 50 mass%, and even more preferably 1 to 40 mass%, relative to the content of the liquid components in the reaction system. When a monomer other than gaseous perfluoroolefin is used, the total amount of gaseous perfluoroolefin and the monomer used is preferably within this range.

[0054] The polymerization is preferably carried out in the presence of a polymerization initiator, in other words, the reaction system in the present method preferably contains a polymerization initiator. Examples of the polymerization initiator include an oil-soluble radical initiator, a water-soluble polymerization initiator, and a water-soluble oxidation-reduction catalyst. Examples of the water-soluble polymerization initiator and the water-soluble redox catalyst include the agents described above. Examples of the oil-soluble radical initiator 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 depending on the type of the target F polymer. The amount of the polymerization initiator used is preferably 0.01 to 5 mass %, more preferably 0.01 to 3 mass %, and even more preferably 0.01 to 2 mass %, based on the total mass of the monomers to be polymerized.

[0055] 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.

[0056] The temperature in the main polymerization is preferably 20°C or higher. The temperature is preferably less than 100°C, more preferably 90°C or lower. The temperature in the main polymerization is preferably lower than the polymerization temperature in Method 1. In this case, an F polymer having better fluoropolymer physical properties is more likely to be formed. The pressure in the main polymerization is preferably 0.8 MPaG or more, more preferably 0.9 MPaG or more, and is preferably 4.0 MPaG or less, more preferably 0.6 to 3.5 MPaG. In the main polymerization, the polymerization time is preferably from 90 to 1000 minutes, more preferably from 90 to 700 minutes, in the case of batch treatment.

[0057] In the reaction of Method 2, 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 realized. The average particle size of FO particles in this specification is a particle size calculated by analyzing the autocorrelation function obtained by dynamic light scattering using the monodisperse cumulant method.

[0058] In Method 2, the FO particle content in the reaction system is preferably 0.01% by mass or more, based on 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 in the resulting aqueous dispersion is particularly easily increased.

[0059] The water content in the reaction system of Method 2 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 water content in the reaction system is within this range, in other words, even when the liquid component in the reaction system is essentially water, an aqueous dispersion of F particles with excellent dispersibility in liquid can be directly obtained due to the above-described mechanism of action without using a fluorine-based emulsifier.

[0060] The reaction system of Method 2 does not contain a fluorine-based emulsifier. In other words, the reaction system of Method 2 is preferably formed without using a fluorine-based emulsifier. The definition of the fluorine-based emulsifier, including specific examples, is the same as that of Method 1.

[0061] The liquid viscosity of the reaction system in Method 2 is preferably less than 2 mPa·s, more preferably 1.8 mPa·s or less, and even more preferably 1.6 mPa·s or less. Furthermore, the liquid viscosity of the reaction system is preferably 0.8 mPa·s or more, and more preferably 1.0 mPa·s or more. In this case, the above-mentioned mechanism of action is more likely to occur. In Method 2, the ratio of the liquid viscosity of Aqueous Dispersion 2 to the liquid viscosity of Aqueous Dispersion 1 in the reaction system is preferably greater than 1. Furthermore, the viscosity ratio is preferably less than 5. In this case, the above-mentioned mechanism of action is more likely to occur.

[0062] The thixotropy ratio of the liquid in the reaction system of Method 2 is preferably 0.95 or more, more preferably 0.98 or more. The thixotropy ratio of the liquid is preferably 1.05 or less, more preferably 1.02 or less. The reaction system in Method 2 preferably does not have thixotropy, in other words, the thixotropy ratio is preferably 1. In this case, the above-mentioned mechanism of action is more likely to occur.

[0063] The liquid properties of the reaction system in Method 2 can be controlled by preparing Aqueous Dispersion 1.

[0064] The aqueous dispersion obtained by Method 2 (aqueous dispersion 2) contains particles of the F polymer (F particles) dispersed in the liquid. The F polymer as a whole is preferably PTFE, modified PTFE, ETFE, PFA, FEP, FKM, FEPM, or FFKM. The fluoroelastomers FKM, FEPM, and FFKM 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 (e.g., a fluorovinyl ether monomer unit having the functional group). 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.

[0065] The viscosity of the aqueous dispersion 2 is preferably less than 10 mPa·s, more preferably 5 mPa·s or less, and even more preferably 2 mPa·s or less.

[0066] The thixotropy ratio of the aqueous dispersion 2 is preferably 0.95 or more, more preferably 0.98 or more. The thixotropy ratio of the liquid is preferably 1.05 or less, more preferably 1.02 or less. The reaction system in this method preferably does not have thixotropy, in other words, the thixotropy ratio is preferably 1.

[0067] According to this method, due to the above-mentioned mechanism of action, it is easy to directly obtain such an aqueous dispersion having excellent liquid physical properties.

[0068] The average particle size of the F particles in the aqueous dispersion 2 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. Furthermore, the particle size distribution of the F particles in the aqueous dispersion 2 is preferably unimodal. The polydispersity index of the particle sizes of the F particles is preferably 0.5 or less, and more preferably 0.25 or less. According to this method, a dispersion having such excellent particle properties can be easily obtained due to the above-mentioned mechanism of action. 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, and the smaller the value, the narrower the particle size distribution of the F particles.

[0069] The content of F particles in aqueous dispersion 2 is preferably more than 4.0% by mass, more preferably 5% by mass or more, and even more preferably 10% by mass or more, relative to the total mass of aqueous dispersion 2. 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 aqueous dispersion 2 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 aqueous dispersion 2. 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 the water content in aqueous dispersion 2 is preferably 90% by mass or more, more preferably 96% by mass or more, based on the total mass. The upper limit of this sum is 100% by mass. Due to the above-mentioned mechanism, this method can efficiently obtain an aqueous dispersion containing a high content of dense F particles with excellent dispersibility in liquid, essentially using water as the liquid medium.

[0070] The particle size ratio in Method 2 is the value obtained by dividing the average particle size of F particles in Aqueous Dispersion 2 by the average particle size of FO particles in the reaction system, and is greater than 1, may be 1.1 or greater, may be 1.2 or greater, may be 1.5 or greater, or may be greater than 2. The particle size ratio may be 10 or less, may be 5 or less, or may be 2 or less.

[0071] The content ratio in Method 2 is the value obtained by dividing the content of F particles in Aqueous Dispersion 2 by the content of FO particles in the reaction system of Method 2, and is 2 or more, optionally 5 or more, optionally 7 or more, or optionally 10 or more. The content ratio may be 500 or less, optionally 250 or less, optionally 100 or less, optionally 50 or less, or optionally 25 or less. The content ratio is a value calculated from the respective contents (% by mass).

[0072] Due to the above-mentioned mechanism of action, an aqueous dispersion can be produced by selecting the desired particle size ratio and content ratio according to Method 2. The respective values ​​of the particle size ratio and content ratio in Method 2 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.

[0073] For example, when a fluoroelastomer is used as the FO polymer to produce the present dispersion containing particles of an F polymer with excellent fluoroelastomer properties, the particle size ratio and content ratio are preferably 1.2 to 5 and 2 to 100, respectively, and the average particle sizes of the FO particles and F particles are preferably 25 to 150 nm and 30 to 400 nm, respectively. For example, when a fluoroelastomer is used as the FO polymer to produce the present dispersion containing particles of an F polymer with excellent fluororesin properties, the particle size ratio and content ratio are preferably 1.2 to 5 and 2 to 50, respectively, and the average particle sizes of the FO particles and F particles are preferably 25 to 150 nm and 30 to 300 nm, respectively. For example, when using a fluororesin as the FO polymer to produce the present dispersion containing particles of an F polymer with excellent fluororesin properties, the particle size ratio and content ratio are preferably 1.5 to 10 and 2 to 100, respectively, and the average particle size of the FO particles and the average particle size of the F particles are preferably 50 to 200 nm and 100 to 400 nm, respectively. Fluororesins include PTFE, modified PTFE, ETFE, PFA, and FEP. Fluoroelastomers include FKM, FEPM, and FFKM.

[0074] According to Method 2, the polymerization of gaseous perfluoroolefin proceeds precisely due to the above-mentioned mechanism of action, so that the by-production of low molecular weight substances derived from the gaseous perfluoroolefin contained in the dispersion can be suppressed, and in particular, when the gaseous perfluoroolefin contains tetrafluoroethylene, the generation amounts of the compound represented by the following formula (S1) and the compound represented by the formula (S2) can be suppressed. Formula (S1): H-(CF2) n -COO - M + Formula (S2): H-(CF2) n -SO3 - M + In the formula, M each independently represents H, Na, K, or NH4, n in the compound represented by formula (S1) represents an integer of 7 to 11, and n in the compound represented by formula (S2) represents an integer of 8 to 12.

[0075] In the aqueous dispersion 2 in the present method 2, 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 the present method preferably does not contain these compounds.

[0076] Aqueous dispersion 2 is an aqueous dispersion in which F particles with high dispersion stability are dispersed, and can be suitably used as a coating agent, binder agent, etc. Alternatively, the water contained in the aqueous dispersion 2 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, a powder of F particles may be obtained by aggregating the F particles from the aqueous dispersion 2. The powder of F particles obtained by aggregating may be directly processed into a molded product by melt molding or the like. Furthermore, the powder of F particles obtained by aggregating 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.

[0077] Examples of the flocculation method include mechanical flocculation, freeze flocculation, acid flocculation, base flocculation, and flocculation using a flocculant, and mechanical flocculation, acid flocculation, and flocculation using a flocculant are preferred. The aggregation temperature in the freeze aggregation is preferably −20 to 0° C. The aggregation time is preferably 1 hour or more, more preferably 2 hours or more. In the case of acid coagulation, a method of adding an acid-containing solution to the dispersion is preferred. Examples of acids include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, and hydrofluoric acid. The acid concentration of the acid-containing solution is preferably 1 to 10% by mass. In the case of base coagulation, a method in which a solution containing a base is added to the dispersion is preferred. Examples of the base include sodium hydroxide, potassium hydroxide, ammonium carbonate, etc. The concentration of the base in the solution containing the base is preferably 1 to 10% by mass. In the case of aggregation using a coagulant, it is preferable to add the coagulant to the dispersion, and examples of the coagulant include aluminum sulfate, alum, calcium nitrate, magnesium sulfate, and ammonium carbonate. [Example]

[0078] 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: Perfluoromethyl allyl ether (CF2 = CFCF2OCF3) Et: Ethylene (CH2=CH2)

[0079] The average particle size of the particles in the dispersion was measured using a laser diffraction / scattering particle size distribution analyzer (Otsuka Electronics Co., Ltd., ELSZ). The content of the compound represented by (S1) and the content of the compound represented by (S2) in the dispersion were each calculated using an aqueous dispersion, among the measurement methods using a liquid chromatograph mass spectrometer described in paragraphs

[0710] to

[0732] of WO 2018 / 181904. The instrument used was an Agilent 1260 Series HPLC / 6460S, and the column used was an Imtakt Cadenza CD-C18. The sulfate ion concentration in the dispersion was determined by freeze-flocculating the aqueous dispersion, filtering the collected liquid, and analyzing it with ion chromatography. The ion chromatograph ICS-5000 (Thermo Fisher Scientific) was used for the ion chromatography analysis. A Dionex IonPac AS-19 separation column and a Dionex IonPac AG-19 guard column were used, and KOH was used as the eluent.

[0080] All reactors used were made of stainless steel.

[0081] [Example 1] Example of producing aqueous dispersion A pressure-resistant reactor (internal volume 2.2 L) was charged with ultrapure water (1130 g), 30% by weight aqueous ammonia solution (30 mg), PMVE (72 g), and TFE (14 g). The mixture was heated to 90 °C while stirring at 600 rpm. Next, an aqueous APS solution (5.0% by weight, 30 mL) was added to initiate polymerization. TFE was added to compensate for the decrease in reactor pressure associated with polymerization, maintaining the pressure at 0.8 MPaG or higher. After 4 g of TFE had been injected, the reactor was cooled to terminate the polymerization reaction. The remaining gas in the reactor was recovered, and the liquid was withdrawn to obtain a mother liquor. The mother liquor was a dispersion of FO polymer particles containing 34 mol% PMVE units and 66 mol% TFE units and bearing carboxyl groups at the polymer terminals. Ultrapure water and ion exchange resin were added to the mother liquor, and the mixture was stirred and filtered to obtain a treated liquid. This treated liquid was a dispersion of the FO polymer particles (average particle diameter: 98 nm). The content of the particles in the liquid was 0.6% by mass.

[0082] A pressure-resistant reactor (internal volume 1.2 L) was charged with ultrapure water (175 g) and the treatment liquid (1000 mL) to form a reaction system (liquid viscosity: 1.0 mPa·s, thixotropy ratio: 1.00) containing 0.5% by mass of the particles. PMVE (72 g) and TFE (14 g) were charged into the reactor, and the temperature was raised to 80 °C while stirring at 600 rpm. TFE and PMVE were injected until the reactor pressure reached 1.2 MPaG, and an APS aqueous solution (2.5% by mass, 7 mL) was added to initiate polymerization. As the pressure in the reactor decreased during polymerization, TFE and PMVE were alternately injected to maintain a constant pressure. When 80 g of TFE and 63 g of PMVE had been injected, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 138 minutes.

[0083] After the gas remaining in the reactor was collected, the liquid content was extracted to obtain an aqueous dispersion. The aqueous dispersion contained 11.5 mass% of fluoropolymer particles (average particle size: 141.1 nm) containing 66 mol% TFE units and 34 mol% PMVE units (liquid viscosity: 1.1 mPa·s, thixotropy ratio: 1.00). The aqueous dispersion exhibited excellent liquid properties, such as dispersion stability, and ease of handling. The fluoropolymer exhibited excellent physical properties compared to the fluoroelastomer FFKM. The particle size distribution was monomodal, with a polydispersity index of less than 0.5. 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.

[0084] [Example 2] Example of producing aqueous dispersion A pressure-resistant reactor (internal volume 2.1 L) was charged with ultrapure water (1162 g), 28% NH3 aqueous solution (1 drop), PMVE (70 g), and TFE (14 g), and the internal temperature was raised to 80 °C while stirring at 600 rpm. An aqueous solution of APS (5.9 mass%, 5 mL) was added to initiate polymerization. TFE was injected to compensate for the decrease in pressure inside the reactor due to polymerization, and the pressure was maintained at 0.8 MPaG or higher. When 24 g of TFE had been injected, the reactor was cooled to terminate the polymerization reaction. After recovering the gas remaining in the reactor, the solution inside the reactor was withdrawn to obtain a mother liquor. 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 mass %.

[0085] Ultrapure water (520.5 g), mother liquor (92.5 ml), disodium hydrogen phosphate dodecahydrate (0.5 g), and t-BuOH (16.5 g) were charged into a pressure reactor (internal volume 1.2 L) to form a reaction system (liquid viscosity: 1.1 mPa s, thixotropy ratio: 1.00) containing 0.22 mass% of the particles. The reaction system was stirred at 320 rpm while the internal temperature was raised to 60°C. A mixed gas (a gas containing 86 mol% and 14 mol% of TFE and Et, respectively; the same applies below) was injected into the reactor until the pressure inside the reactor reached 2.6 MPaG. An aqueous solution of tert-butyl hydroperoxide (0.2 mass%, 2 mL) and a reducing agent (BRUGGOLITE® FF6M, 0.396 mass%, 2 mL) were added to the reactor to initiate polymerization. The pressure inside the reactor was maintained constant by adding the mixed gas to compensate for the decrease in pressure caused by polymerization. An aqueous solution of tert-butyl hydroperoxide (0.2 mass%, 1 mL) and the reducing agent (1 mL) were added every 5 minutes after the start of polymerization. When the amount of injected mixed gas reached 80 g, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 181 minutes.

[0086] After the gas remaining in the reactor was collected, the liquid content was extracted to obtain an aqueous dispersion. The aqueous dispersion contained 10.2 mass% of fluoropolymer particles (average particle size: 182 nm) with an overall composition of 56.9 mol% TFE units, 42.4 mol% Et units, and 0.7 mol% PMVE units (liquid viscosity: 1.3 mPa·s, thixotropy ratio: 1.00). The aqueous dispersion exhibited excellent liquid properties, such as dispersion stability, and ease of handling. The fluoropolymer exhibited excellent physical properties compared to the fluororesin ETFE. The particle size distribution was monomodal, with a polydispersity index of less than 0.5. 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.

[0087] [Example 3] Example of production of aqueous dispersion Ultrapure water and ion exchange resin were added to the mother liquor obtained in Example 1, and the mixture was stirred and filtered to obtain a treated liquid. This treated liquid was a dispersion of 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 mass %.

[0088] Ultrapure water (428 g), treatment solution (185 ml), disodium hydrogen phosphate dodecahydrate (0.5 g), and t-BuOH (16.5 g) were charged into a pressure reactor (internal volume 1.2 L) to form a reaction system containing 0.44 mass% of the particles (liquid viscosity: 1.3 mPa·s, thixotropy ratio: 1.00).

[0089] The reaction system was stirred at 320 rpm, and the internal temperature was raised to 60°C. A mixed gas (a gas containing 86 mol% and 14 mol% of TFE and Et, respectively; the same applies below) was injected into the reactor until the pressure inside the reactor reached 2.6 MPaG, and an aqueous solution of tert-butyl hydroperoxide (0.2 mass%, 2 mL) and the reducing agent were added to the reactor to initiate polymerization. The pressure inside the reactor decreased with polymerization, and the mixed gas was added to maintain a constant pressure. An aqueous solution of tert-butyl hydroperoxide (0.2 mass%, 1 mL) and the reducing agent (1 mL) were added every 5 minutes after the start of polymerization. When the amount of injected mixed gas reached 80 g, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 167 minutes.

[0090] After the gas remaining in the reactor was collected, the liquid content was extracted to obtain an aqueous dispersion. The aqueous dispersion contained 10.6 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 ratio: 1.00). The aqueous dispersion exhibited excellent liquid properties, such as dispersion stability, and ease of handling. The fluoropolymer exhibited excellent physical properties compared to the fluororesin ETFE. The particle size distribution was monomodal, with a polydispersity index of less than 0.5. 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.

[0091] [Example 4] Example of production of aqueous dispersion Ultrapure water (717 g), PMVE (50 g), and TFE (8 g) were charged into a pressure-resistant reactor (internal volume 1.3 L) and heated to 90°C while stirring at 500 rpm. An aqueous solution of APS (3.6 mass%, 5 mL) was added to initiate polymerization. TFE was injected to compensate for the decrease in pressure inside the reactor due to polymerization, and the pressure was maintained at 1.4 MPaG. When 2 g of TFE had been injected, the reactor was cooled to terminate the polymerization reaction. The gas remaining in the reactor was recovered, and the solution in the reactor was withdrawn to obtain a mother liquor. The mother liquor was a dispersion of particles of an FO polymer containing 48 mol % of PMVE units and 52 mol % of TFE units and having carboxy groups at the polymer terminals. An ion exchange resin was added to the mother liquor, which was then stirred and filtered to obtain a treated liquid containing FO polymer particles (average particle size: 87 nm) at a content of 0.6% by mass.

[0092] Ultrapure water (121 g), treatment liquid (475 g), and wax (28 g) were charged into a pressure-resistant reactor (internal volume 1.0 L) to form a reaction system (liquid viscosity: 1.3 mPa·s, thixotropy ratio: 1.00) containing 0.48 mass% of the particles. The reaction system was stirred at 260 rpm while the internal temperature was raised to 70°C. TFE was injected into the reactor until the pressure inside the reactor reached 1.4 MPaG, and an aqueous solution of APS (0.2 mass%, 5 mL) was added to the reactor to initiate polymerization. TFE was added to compensate for the decrease in the internal pressure of the reactor that occurred during polymerization, and the pressure was maintained constant. When the amount of injected TFE reached 110 g, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 220 minutes.

[0093] After the gas remaining in the reactor was collected, the liquid content was extracted to obtain an aqueous dispersion. The aqueous dispersion contained 16.0 mass% of fluoropolymer particles (average particle size: 228 nm) containing 99.1 mol% TFE units and 0.9 mol% PMVE units (liquid viscosity: 1.5 mPa·s, thixotropy ratio: 1.00). The aqueous dispersion exhibited excellent liquid properties, such as dispersion stability, and ease of handling. The fluoropolymer exhibited excellent physical properties compared to PTFE, a fluororesin. Specifically, the melting point of the fluoropolymer was 338°C, and its crystallization energy was -35 J / g. The particle size distribution was monomodal, with a polydispersity index of less than 0.5. 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.

[0094] [Example 5] Example of production of aqueous dispersion Distilled water (717 g), 28% by mass ammonia water (one drop), and a mixed gas of TFE and HFP were charged into a pressure-resistant reactor (internal volume 1.0 L) and heated to 90°C while stirring at 500 rpm. The internal pressure of the reactor after reaching 90°C was 1.64 MPaG. Next, an aqueous solution of APS (3.6% by mass, 5 mL) was added to initiate polymerization. TFE was injected to compensate for the decrease in internal pressure of the reactor due to polymerization, and the pressure was maintained constant. 3 g of TFE was injected, and 72 minutes later, the reactor was cooled to terminate the polymerization reaction. The gas remaining in the reactor was recovered, and the solution in the reactor was withdrawn to obtain a mother liquor. The mother liquor was added with ion exchange resin, stirred, and filtered to obtain a treated solution, which was a dispersion of FO polymer particles (average particle size: 103 nm) containing 83 mol % TFE units and 17 mol % HFP units and having carboxy groups at the polymer terminals.

[0095] A pressure-resistant reactor (internal volume 1.0 L) was charged with the treatment liquid (600.0 g) and wax (28 g) to form a reaction system (liquid viscosity: 1.2 mPa·s, thixotropy ratio: 1.00) containing 0.72 mass % of the particles. The reaction system was stirred at 260 rpm, and the internal temperature was raised to 70°C. TFE was injected into the reactor until the pressure inside the reactor reached 1.4 MPaG, and an aqueous solution of disuccinic acid peroxide (0.56 mass%, 11 mL) was added to the reactor to initiate polymerization. TFE was added to compensate for the decrease in the internal pressure of the reactor due to polymerization, and the pressure was kept constant. After 216 minutes, when the amount of TFE consumed reached 50 g, the reactor was cooled to terminate the polymerization reaction.

[0096] After the gas remaining in the reactor was collected, the liquid content was extracted to obtain an aqueous dispersion. The aqueous dispersion contained 7.7 mass% of fluoropolymer particles (average particle size: 301 nm) containing 99.1 mol% TFE units and 0.9 mol% HFP units (liquid viscosity: 1.4 mPa·s, thixotropy ratio: 1.00). The aqueous dispersion exhibited excellent liquid properties, such as dispersion stability, and ease of handling. The fluoropolymer exhibited excellent physical properties compared to PTFE, a fluororesin. Specifically, the melting point of the fluoropolymer was 338°C, and its DSC heat of fusion was 64 J / g. The particle size distribution was monomodal, with a polydispersity index of less than 0.5. Furthermore, the contents of the compounds represented by the formula (S1) and the formula (S2) contained in the aqueous dispersion relative to the total mass of the particles in the aqueous dispersion were both 100 ppb by mass or less.

[0097] [Example 6] Example of production of aqueous dispersion Distilled water (717 g), 28% by mass ammonia water (one drop), and a mixed gas of TFE and HFP were charged into a pressure-resistant reactor (internal volume 1.0 L) and heated to 90°C while stirring at 500 rpm. The pressure inside the reactor after reaching 90°C was 1.94 MPaG. Next, an aqueous solution of APS (3.6% by mass, 5 mL) was added to initiate polymerization. After 97 minutes, the polymerization was terminated when the pressure inside the reactor reached 1.78 MPaG. After recovering the gas remaining in the reactor, the solution inside the reactor was removed to obtain a mother liquor. The mother liquor was added with ion exchange resin, stirred, and filtered to obtain a treated solution, which 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.

[0098] A pressure-resistant reactor (internal volume 1.0 L) was charged with the treatment liquid (600.0 g), CH2=CH(CF2)4F (0.73 g), and t-butyl methyl ether (0.51 g), forming a reaction system (liquid viscosity: 1.0 mPa s, thixotropy ratio: 1.00) containing 0.77 mass% of the particles. The reaction system was stirred at 260 rpm while the internal temperature was raised to 70°C. TFE was injected into the reactor until the pressure inside the reactor reached 1.8 MPaG, and an isododecane solution of tert-butyl peroxypivalate (40% by mass, 2 mL) was added to the reactor to initiate polymerization. The pressure inside the reactor decreased with the polymerization, so the pressure was maintained constant by adding a mixed gas (a gas containing TFE and Et, in that order, 86 mol% and 14 mol%, respectively; the same applies below). An additional 1.6 g of the isododecane solution was also added. When the amount of injected mixed gas reached 50 g, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 170 minutes.

[0099] After the gas remaining in the reactor was collected, the liquid content was extracted to obtain an aqueous dispersion. The aqueous dispersion contained 7.2 mass% of fluoropolymer particles (average particle size: 155 nm) with an overall composition 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 ratio: 1.00). The aqueous dispersion exhibited excellent liquid properties, including dispersion stability, and ease of handling. The fluoropolymer exhibited excellent physical properties compared with the fluororesin ETFE. Specifically, the melting point of the fluoropolymer was 244°C, and its DSC heat of fusion was 43 J / g. The particle size distribution was monomodal, with a polydispersity index of less than 0.5. 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.

[0100] [Example 7] Example of production of aqueous dispersion Ultrapure water (717 g) was charged into a pressure-resistant reactor (internal volume 1.3 L) and heated to 90 °C while stirring at 500 rpm. A mixed gas containing 18 mol% TFE and 82 mol% PMAE, in that order, was injected until the reactor pressure reached 1.5 MPaG. Next, an aqueous solution of APS (3.6 mass%, 5 mL) was added to initiate polymerization. After 180 minutes, the reactor was cooled to terminate the polymerization. The gas remaining in the reactor was recovered, and the solution in the reactor was removed to obtain a mother liquor. The mother liquor was added with ion exchange resin, stirred, and filtered to obtain a treated liquid. This treated liquid was a dispersion of FO polymer particles (average particle diameter: 70 nm) containing 69 mol% TFE units and 31 mol% PMAE units and having carboxy groups at the polymer terminals. The content of the particles in the treated liquid was % by mass.

[0101] Ultrapure water (121 g), treatment liquid (475 g), and wax (28 g) were charged into a pressure-resistant reactor (internal volume 1.0 L) to form a reaction system (liquid viscosity: 1.2 mPa·s, thixotropy ratio: 1.00) containing 0.75 mass% of the particles. The reaction system was stirred at 260 rpm, and the internal temperature was raised to 70°C. TFE was injected into the reactor until the pressure inside the reactor reached 1.4 MPaG, and an aqueous solution of disuccinic acid peroxide (0.45% by mass, 3 mL) was added to the reactor to initiate polymerization. TFE was added to compensate for the decrease in the internal pressure of the reactor due to polymerization, and the pressure was kept constant. After 450 minutes, when the amount of injected TFE reached 170 g, the reactor was cooled to terminate the polymerization reaction.

[0102] After the gas remaining in the reactor was collected, the liquid content was extracted to obtain an aqueous dispersion. The aqueous dispersion contained 20.0 mass% of fluoropolymer particles (average particle size: 270 nm) containing 99.6 mol% TFE units and 0.4 mol% PMAE units (liquid viscosity: 1.4 mPa·s, thixotropy ratio: 1.00). The aqueous dispersion exhibited excellent liquid properties, such as dispersion stability, and ease of handling. The fluoropolymer exhibited excellent physical properties compared to PTFE, a fluororesin. Specifically, the melting point of the fluoropolymer was 345°C, and its DSC heat of fusion was 16.5 J / g. The particle size distribution was monomodal, with a polydispersity index of less than 0.5. 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. The sulfate ion concentration in the aqueous dispersion was less than 0.1 ppm by mass.

[0103] [Example 8] Example of production of aqueous dispersion Ultrapure water (717 g) was charged into a pressure-resistant reactor (internal volume 1.0 L) and heated to 90 °C while stirring at 500 rpm. A mixed gas of TFE and VdF was then injected until the reactor pressure reached 1.98 MPaG. Next, an aqueous solution of APS (3.6 mass%, 5 mL) was added to initiate polymerization. After 96 minutes, when the reactor pressure dropped to 1.81 MPaG, the reactor was cooled to terminate the polymerization. The gas remaining in the reactor was recovered, and the solution in the reactor was removed to obtain a mother liquor. The mother liquor was added with ion exchange resin, stirred, and filtered to obtain a treated solution, which 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.

[0104] A pressure-resistant reactor (internal volume 1.0 L) was charged with the treatment liquid (600 g) and wax (28 g) to form a reaction system (liquid viscosity: 1.2 mPa·s, thixotropy ratio: 1.00) containing 0.75 mass % of the particles. The reaction system was stirred at 260 rpm, and the internal temperature was raised to 70°C. TFE was injected into the reactor until the pressure inside the reactor reached 1.4 MPaG, and an aqueous solution of disuccinic acid peroxide (0.56 mass%, 11 mL) was added to the reactor to initiate polymerization. TFE was added to compensate for the decrease in the internal pressure of the reactor due to polymerization, and the pressure was kept constant. After 292 minutes, when the amount of injected TFE reached 80 g, the reactor was cooled to terminate the polymerization reaction.

[0105] After the gas remaining in the reactor was collected, the liquid content was extracted to obtain an aqueous dispersion. The aqueous dispersion contained 10.1 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 ratio: 1.00). The aqueous dispersion exhibited excellent liquid properties, such as dispersion stability, and ease of handling. The fluoropolymer exhibited excellent physical properties compared to the fluororesin PTFE. The particle size distribution was monomodal, with a polydispersity index of less than 0.5. 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.

[0106] The disclosure of Japanese Patent Application No. 2024-099120, 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. In a first reaction system comprising water and a water-soluble polymerization initiator, but without a fluorine-based emulsifier, the temperature is maintained above the half-life temperature of the polymerization initiator, or the pressure is maintained at 0.8 MPaG or higher to polymerize a gaseous fluoroolefin, and a dispersion is obtained containing less than 10% by mass of polymer particles, which have an average particle size of 1 to 150 nm and include units based on the fluoroolefin, relative to the total mass. A method for producing an aqueous dispersion, comprising polymerizing gaseous perfluoroolefin in a second reaction system, which is prepared from the obtained dispersion and does not contain a fluorine-based emulsifier, in the presence of a polymerization initiator to obtain an aqueous dispersion containing fluoropolymer particles, The ratio of the average particle diameter of the fluoropolymer particles to the average particle diameter of the polymer particles containing the fluoroolefin units is greater than 1. The ratio of the particle content in the aqueous dispersion to the particle content in the second reaction system is 2 or more. A method for producing an aqueous dispersion.

2. The manufacturing method according to claim 1, wherein the polymerization initiator contained in the first reaction system is a persulfate, and the temperature is greater than 55°C and less than 100°C.

3. The manufacturing method according to claim 1, wherein the pressure during polymerization of the gaseous fluoroolefin is 0.9 MPaG or more and 4.0 MPaG or less.

4. The manufacturing method according to claim 1, wherein the gaseous fluoroolefin is vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, or hexafluoropropylene.

5. The manufacturing method according to claim 1, wherein the polymerization of the gaseous fluoroolefin is carried out by copolymerizing the gaseous fluoroolefin with ethylene, chlorotrifluoroethylene, propylene, perfluoroalkyl vinyl ether, or perfluoroalkyl allyl ether.

6. The manufacturing method according to claim 1, wherein the dispersion contains 80% by mass or more of water based on the total mass.

7. The manufacturing method according to claim 1, wherein the polymerization of the gaseous perfluoroolefin is carried out at a temperature of 20°C or more and less than 100°C, and at a pressure of 0.8 MPaG or more and 4.0 MPaG or less.

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

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

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

11. The manufacturing method according to claim 10, wherein the monomer other than the gaseous perfluoroolefin is ethylene, vinyl fluoride, vinylidene fluoride, chlorotrifluoroethylene, propylene, fluoroalkylethylene, perfluoroalkyl vinyl ether, perfluoroalkyl allyl ether, or a fluoromonomer having a fluorosulfonyl group, a carboxyl group, or an alkoxycarbonyl group.

12. 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.

13. 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.

14. The manufacturing method according to claim 1, wherein the fluoropolymer particles are present in an amount of 5 to 50% by mass relative to the total mass.