Method for producing a dispersion, and method for producing an aqueous dispersion

Abstract

A method for producing a dispersion containing less than 10% by mass of particles of a polymer containing units based on the fluoroolefin, with an average particle size of 1 to 150 nm, obtained by polymerizing a gaseous fluoroolefin in a reaction system comprising water, a monomer having an -SO3X group, -PO3X group, -P(OR)O2X group, or -COOX group (wherein X represents H, K, Na, or NH4, and R represents an alkyl group) and not having a fluorine atom, or a polymer of the monomer, and a polymerization initiator, and without a fluorine-based emulsifier.

Description

[Technical Field]

[0001] This disclosure 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 because they have excellent heat resistance, chemical resistance, flame retardancy, weather resistance, and other properties.

[0003] 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]

[0004] [Patent Document 1] International Publication No. 2007 / 046377 [Overview of the project] [Problems that the invention aims to solve]

[0005] 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.

[0006] Furthermore, in recent years, there has been a demand for further improvement in the dispersibility of fluoropolymer particles in such aqueous dispersions.

[0007] This disclosure 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]

[0008] [1] A method for producing a dispersion, comprising water, a monomer having a -SO3X group, -PO3X group, -P(OR)O2X group, or -COOX group (wherein X is H, K, Na, or NH4, and R is an alkyl group) and not having a fluorine atom, or a polymer of the monomer, and a polymerization initiator, wherein a fluorine-based emulsifier is not used to polymerize a gaseous fluoroolefin, and a dispersion is obtained in which particles of the polymer containing the fluoroolefin-based unit, having an average particle diameter of 1 to 150 nm, are present in less than 10% by mass of the total mass. [2] A method for producing [1], wherein the monomer is vinyl monomers having a -SO3X group, a -PO3X group, a -P(OR)O2X group or a -COOX group, allyl monomers having a -SO3X group, a -PO3X group, a -P(OR)O2X group or a -COOX group, (meth)acrylic acid, (meth)acrylates having a -SO3X group, a -PO3X group, a -P(OR)O2X group or a -COOX group, or (meth)acrylamides having a -SO3X group, a -PO3X group, a -P(OR)O2X group or a -COOX group. [3] The method for producing [1] or [2], wherein the content of the monomer or polymer of the monomer in the reaction system is 1.0 ppm by mass or more and 1000 ppm by mass or less. [4] A method for producing any of [1] to [3], wherein the gaseous fluoroolefin is vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, or hexafluoropropylene. [5] A method of production according to any one of [1] to [4], wherein the polymerization is carried out by copolymerizing the gaseous fluoroolefin with ethylene, chlorotrifluoroethylene, propylene, perfluoroalkyl vinyl ether, or perfluoroalkyl allyl ether. [6] A method of production according to any of [1] to [5], wherein the polymerization is carried out while maintaining a temperature greater than 55°C and less than 100°C, and a pressure of 0.8 MPaG or more and 2.0 MPaG or less. [7] A method of manufacturing the dispersion, wherein the dispersion contains 80% by mass or more of water based on the total mass, as described in any of [1] to [6]. A method for producing an aqueous dispersion, comprising polymerizing a gaseous perfluoroolefin in the presence of a polymerization initiator in a reaction system free of a fluorine-based emulsifier, prepared from a dispersion obtained by the production method of [8][1], to obtain an aqueous dispersion containing fluoropolymer particles, wherein the ratio of the average particle diameter of the fluoropolymer particles to the average particle diameter of the polymer particles 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. [9] The method for producing [8], wherein the viscosity of the reaction system is less than 2 mPa·s.

[10] A method for producing [8] or [9], wherein the gaseous perfluoroolefin is tetrafluoroethylene or hexafluoropropylene.

[11] A method of production according to any of [8] to

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

[12] A method for producing

[11] , 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.

[13] A method for producing the fluoropolymer whose average particle size is greater than 50 nm and less than or equal to 1000 nm, as described in any of [8] to

[12] .

[14] 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 the methods described in [8] to

[13] .

[15] A method of producing the fluoropolymer particles in any of the methods described in [8] to

[14] , comprising 5 to 50% by mass relative to the total mass. [Effects of the Invention]

[0009] According to the present disclosure, an aqueous dispersion in which fluoropolymer particles are stably dispersed can be efficiently produced without using a fluorine-based emulsifier as an essential component.

Embodiments for Carrying Out the Invention

[0010] The meanings of the terms in the present disclosure are as follows.

[0011] A numerical range represented using “~” means a range including the numerical values described before and after “~” as the lower limit value and the upper limit value. In the numerical ranges described stepwise in this specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other stepwise descriptions. Also, in the numerical ranges described in this specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples.

[0012] In this specification, each component may be used alone as one kind of substance corresponding to each component, or two or more kinds may be used in combination. Here, when two or more kinds of substances are used in combination for each component, the content of that component refers to the total content of the substances used in combination, unless otherwise specified.

[0013] In this specification, a combination of two or more preferred embodiments is a more preferred embodiment.

[0014] “Unit” is a general term for an atomic group directly formed by polymerization of monomers and derived from one molecule of the above monomer, and an atomic group obtained by chemically converting a part of the above atomic group. “Unit based on a monomer” is hereinafter simply referred to as “unit”, and “unit based on monomer A” is hereinafter simply referred to as “monomer A unit”.

[0015] In this specification, the content (% by mass or mol%) of each unit with respect to all the units contained in the polymer is determined by analyzing the polymer by solid-state nuclear magnetic resonance spectroscopy (NMR) method. Usually, the content of each unit calculated from the charged amount of each monomer substantially coincides with the actual content of each unit.

[0016] 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.

[0017] The present disclosure is a method for producing a dispersion (hereinafter also referred to as "aqueous dispersion 1") (hereinafter also referred to as "this method 1") in which gaseous fluoroolefin is polymerized in a reaction system (hereinafter also referred to as "reaction system 1") comprising water, a monomer having a -SO3X group, -PO3X group, -P(OR)O2X group, or -COOX group (wherein X represents H, K, Na, or NH4, and R represents an alkyl group) and not having a fluorine atom (hereinafter also referred to as "hydrophilic monomer") or a polymer of a hydrophilic monomer (hereinafter collectively referred to as "hydrophilic compound"), and a polymerization initiator, and no fluorine-based emulsifier, thereby polymerizing a polymer (hereinafter also referred to as "FO polymer") having an average particle size of 1 to 150 nm and containing units based on fluoroolefins (hereinafter also referred to as "FO particles"), in an amount of less than 10% by mass of the total mass.

[0018] Furthermore, the present disclosure relates to a method for producing an aqueous dispersion containing particles of a fluoropolymer (hereinafter also referred to as "F polymer") (hereinafter also referred to as "F particles") by polymerizing a gaseous perfluoroolefin in a reaction system free of a fluorine-based emulsifier, prepared from an aqueous dispersion 1, in the presence of a polymerization initiator, wherein 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 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 more. The content ratio is a value calculated from the respective content (mass%). In the following, Method 1 and Method 2 may be collectively referred to as "the present method".

[0019] According to this method, a highly dispersible aqueous dispersion (aqueous dispersion 1) can be obtained containing a predetermined amount of extremely fine particles of a fluoropolymer with excellent dispersibility in liquid, in the absence of a fluorine-based emulsifier.

[0020] In a reaction system containing water and without a fluorine-based emulsifier, gaseous fluoroolefins, which have low affinity for water, generally do not polymerize densely. As a result, polymer particles are either not formed at all, or if they are formed, they are non-uniform, and their dispersibility in liquid tends to be extremely low. As a result of diligent research, the present inventors have found that when a certain hydrophilic compound that does not contain fluorine atoms is included in the reaction system, and gaseous fluoroolefins are polymerized there, extremely fine polymer particles (FO particles) are generated, and when the content is within a predetermined range, an aqueous dispersion (aqueous dispersion 1) in which these particles are extremely well dispersed in liquid can be obtained.

[0021] Furthermore, the inventors have discovered that by further preparing a reaction system from such aqueous dispersion and polymerizing gaseous perfluoroolefin therein, an aqueous dispersion (aqueous dispersion 2) containing particles (F particles) of a fluoropolymer (F polymer) with excellent dispersibility in liquid can be obtained, even without the presence of a fluorine-based emulsifier.

[0022] The reason is not always clear, but the following reasons can be cited.

[0023] In a reaction system prepared from an aqueous dispersion 1 in which FO particles are highly dispersed in liquid, the introduced gaseous perfluoroolefin is readily adsorbed onto the FO polymer, which has a fluorine atom and a high affinity for it. In other words, the FO particles are thought to function highly as a polymerization site. As a result, this method allows for the direct production of an aqueous dispersion (aqueous dispersion 2) containing F particles with excellent dispersibility in liquid, while increasing both the particle size ratio and content ratio, without the presence of a fluorine-based emulsifier. This mechanism of action is more pronounced in preferred embodiments of this method, which will be described later.

[0024] The hydrophilic compound in this Law 1 is a monomer having a -SO3X group, -PO3X group, -P(OR)O2X group or -COOX group and not having a fluorine atom, or a polymer of the monomer. Here, X represents H, K, Na or NH4, and R represents an alkyl group. The polymer of the monomer means a polymer having units based on a monomer having a -SO3X group, -PO3X group, -P(OR)O2X group or -COOX group and not having a fluorine atom.

[0025] The -SO3X group, in other words, is a sulfonic acid group or a sulfonated (-SO3 + ) sulfonic acid group having a counter cation of sodium ion (Na + ), potassium ion (K + ) or ammonium ion (NH4 - ).

[0026] Also, the -PO3X group, in other words, is a phosphonic acid group or a phosphonated (-PO3 + ) phosphonic acid group having a counter cation of sodium ion (Na + ), potassium ion (K + ) or ammonium ion (NH4 - ).

[0027] Also, the -P(OR)O2X group, in other words, is an alkyl phosphate group. R is preferably an alkyl group having 1 to 6 carbon atoms, and more preferably a methyl group or an ethyl group.

[0028] Also, the -COOX group, in other words, is a carboxy group or a carboxylated (-COO + ) carboxy group having a counter cation of sodium ion (Na + ), potassium ion (K + ) or ammonium ion (NH4 - ).

[0029] The monomers include vinyl monomers having a -SO3X group, -PO3X group, -P(OR)O2X group or -COOX group, allyl monomers having a -SO3X group, -PO3X group, -P(OR)O2X group or -COOX group, (meth)acrylic acid, (meth)acrylates having a -SO3X group, -PO3X group, -P(OR)O2X group or -COOX group, or having a -SO3X group, -PO3X group, -P(OR)O2X group or -COOX group. It is preferable that the (meth)acrylamide is a vinyl monomer having a -SO3X group, -PO3X group, -P(OR)O2X group, or -COOX group, (meth)acrylic acid, (meth)acrylates having a -SO3X group or -COOX group, or (meth)acrylamide having a -SO3X group or -COOX group, and even more preferable that the (meth)acrylamide has a -SO3X group or -COOX group. In this case, the above-described mechanism of action is more likely to be expressed.

[0030] Note that (meth)acrylic acid is a general term for acrylic acid and methacrylic acid, (meth)acrylates are a general term for acrylates and methacrylates, and (meth)acrylamide is a general term for acrylamides and methacrylateamides.

[0031] Specific examples of the monomers mentioned above include vinyl sulfonic acid, vinyl phosphonic acid, acrylic acid, methacrylic acid, itaconic acid, maleic acid, crotonic acid, fumaric acid, vinyl acetic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid, 2-sulfoethylmethacrylic acid, 4-vinylbenzenesulfonic acid, N-tigroylglycine, 6-acrylamidohexanoic acid, 2-methacrylamido-2-methylpropylsulfonic acid, their sodium salts, and their ammonium salts.

[0032] In the reaction system of Method 1, the hydrophilic compound may consist only of the monomer, only of the polymer of the monomer, or both of the monomer and the polymer of the monomer.

[0033] The hydrophilic compound content in the reaction system of Method 1 is preferably 1.0 ppm by mass or more, more preferably 3 ppm by mass or more, and even more preferably 5 ppm by mass or more. Furthermore, the content is preferably 1000 ppm by mass or less, more preferably 500 ppm by mass or less, even more preferably 100 ppm by mass or less, and particularly preferably 60 ppm by mass or less.

[0034] The polymerization initiator in Method 1 is preferably a water-soluble polymerization initiator, more preferably a persulfate, an organic peroxide, or a redox catalyst, and even more preferably a persulfate. In this case, the mechanism of action described above is more likely to be expressed.

[0035] Examples of persulfates include ammonium persulfate (hereinafter also referred to as "APS") and potassium persulfate.

[0036] Examples of organic peroxides include disuccinic acid peroxide, bisglutaric acid peroxide, and tert-butyl hydroperoxide.

[0037] 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.

[0038] Examples of oxidizing agents include potassium persulfate, APS, and sodium sulfite.

[0039] 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.

[0040] The polymerization initiator may be one type or multiple types.

[0041] The amount of polymerization initiator in the polymerization of Method 1 is preferably 0.01 to 5% by mass, more preferably 0.01 to 3% by mass, and even more preferably 0.01 to 2% by mass, based on the total mass of all monomers subjected to polymerization, including gaseous fluoroolefins.

[0042] Polymerization in Method 1 is preferably 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. Polymerization is more 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.

[0043] 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 a conventional method, and may be added to the reaction system all at once, in installments, or continuously.

[0044] The polymerization temperature in Method 1 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 mechanism of action of Method 1 described above is more likely to manifest.

[0045] The polymerization pressure in Method 1 is preferably 0.9 MPaG or higher, and more preferably 1.0 MPaG or higher. Furthermore, the polymerization pressure is preferably 4.0 MPa or lower, and more preferably 3.5 MPaG or lower. In this case, the mechanism of action of Method 1 described above is more likely to manifest.

[0046] In this specification, "MPaG" refers to gauge pressure, which is the pressure obtained by subtracting atmospheric pressure (0.1013 MPa) from absolute pressure.

[0047] The pressure during polymerization in Method 1 can be prepared by introducing gaseous fluoroolefin into the reaction system by conventional methods. 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.

[0048] In the polymerization process of Method 1, the polymerization time is preferably 90 to 1000 minutes, and more preferably 90 to 700 minutes, in the case of batch processing.

[0049] The reaction system of Method 1 does not contain a fluorine-based emulsifier. In other words, it is preferable that the reaction system of Method 1 be formed without the use of a fluorine-based emulsifier.

[0050] Fluorine-based emulsifiers are emulsifiers containing fluorine atoms, distinct from FO polymers. Specifically, they are water-soluble fluorine-containing compounds or salts thereof that have a fluorine-containing organic group (such as a perfluoroalkyl group) and a hydrophilic functional group (such as a carboxyl group, sulfonic acid group, or phosphonic acid group). More specifically, they are perfluoroalkyl carboxylic acids, perfluoroalkyl sulfonic acids, and their salts. Etheric oxygen atoms may be present between carbon atoms in the molecules of these compounds.

[0051] In Method 1, it is preferable that the reaction system be formed without using fluorine-based emulsifiers (emulsifiers containing fluorine atoms) and emulsifiers that do not contain fluorine atoms. Emulsifiers containing fluorine atoms and emulsifiers not containing fluorine atoms will collectively be referred to as "emulsifiers" below. The content of various emulsifiers can be measured using a liquid chromatograph-mass spectrometer.

[0052] Examples of emulsifiers include water-soluble emulsifiers. A water-soluble emulsifier is defined as an emulsifier whose solubility in 1000g of water at 25°C is 100mg or more, while a non-water-soluble emulsifier is defined as an emulsifier other than the water-soluble emulsifiers mentioned above. Water-soluble emulsifiers may be either ionic or nonionic. Examples of emulsifiers include those that do not contain a carbon-carbon double bond.

[0053] A fluorine-free emulsifier is an emulsifier that does not contain fluorine atoms and has hydrocarbon groups such as alkyl groups as its hydrophobic portion. It is also possible to substitute the hydrogen atoms of the hydrocarbon groups in a fluorine-free emulsifier with halogen atoms other than fluorine atoms. Examples of emulsifiers that do not contain fluorine atoms include ionic hydrocarbon emulsifiers and nonionic hydrocarbon emulsifiers.

[0054] An example of an ionic hydrocarbon emulsifier is an anionic hydrocarbon emulsifier. An anionic hydrocarbon emulsifier refers to an emulsifier having a negatively charged hydrophilic portion such as a carboxylic acid group, sulfonic acid group, sulfate group, phosphonic acid group, and phosphate group, and a hydrocarbon group such as an alkyl group as a hydrophobic portion. Specific examples of anionic hydrocarbon emulsifiers include sodium dodecyl sulfate, highly branched C10 tertiary carboxylic acids supplied by Resolution Performance Products as Versatic® 10, sodium linear alkyl polyethersulfonate supplied by BASF as the Avane® S series, and the sulfosuccinate emulsifier Lankropol® K8300 available from AkzoNobelSurfaceChemistryLLC.

[0055] Nonionic hydrocarbon emulsifiers are emulsifiers that exhibit surface activity without dissociating into ions in water and have hydrocarbon groups such as alkyl groups as their hydrophobic portion. Examples of hydrophilic portions of nonionic hydrocarbon emulsifiers include water-soluble functional groups such as polyethylene oxide chains obtained from the polymerization of ethylene oxide. Examples of nonionic hydrocarbon emulsifiers include polyalkylene oxide block copolymers, such as block copolymers having polyethylene oxide and polypropylene oxide.

[0056] Another example of a nonionic hydrocarbon emulsifier is the emulsifier described in paragraphs

[0043] to

[0052] of Japanese Patent Publication No. 2016-537499.

[0057] Emulsifiers containing fluorine atoms and emulsifiers not containing fluorine atoms may also contain silicon atoms. Examples of emulsifiers containing silicon atoms include siloxane emulsifiers. Siloxane emulsifiers are hydrocarbon-containing emulsifiers having a siloxane skeleton. Examples of siloxane emulsifiers include those described in U.S. Patent No. 6,841,616 (Wille et al.) and No. 7,977,438 (Brothers et al.).

[0058] Emulsifiers containing fluorine atoms and emulsifiers not containing fluorine atoms may be polymer emulsifiers. Examples of polymer emulsifiers include polymers having hydrophilic groups in their side chains. Such polymer emulsifiers include polymers containing units based on compounds having both a polymerizable site and a hydrophilic group. Also included are polymers obtained by post-treatment such as hydrolysis of polymers containing units based on compounds that have a group that can become a hydrophilic group, even if they do not initially have a hydrophilic group. Specific examples of polymer emulsifiers include polymethyl methacrylate, which is an emulsifier not containing fluorine atoms.

[0059] 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. Furthermore, the water content is preferably 100% by mass or less, and more preferably 99.9% by mass or less. When the water content in the reaction system falls within this range, in other words, even when the liquid component in the reaction system is substantially water, an aqueous dispersion of FO particles with excellent dispersibility in liquid can be directly obtained without using a fluorine-based emulsifier, through the mechanism of action described above.

[0060] The gaseous fluoroolefin in this Act 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.

[0061] In Method 1, polymerization is preferably carried out by copolymerizing a gaseous fluoroolefin with a monomer other than the gaseous fluoroolefin.

[0062] Other monomers besides the aforementioned fluoroolefins 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.

[0063] 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").

[0064] Examples of PAAEs include CF2=CFCF2OCF3 (hereinafter also referred to as "PMAE") and CF2=CFCF2CF2OCF3 (hereinafter also referred to as "PEAE").

[0065] 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.

[0066] In this method 1, the FO polymer is a polymer containing units based on fluoroolefins, and preferably a polymer containing units based on gaseous fluoroolefins.

[0067] Examples of fluoroolefins include the fluoroolefins mentioned above, and the preferred range is the same.

[0068] 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.

[0069] Examples of the monomers mentioned above include the fluoroolefins described above, and the preferred range is the same.

[0070] Furthermore, the glass transition temperature (Tg) of the FO polymer (hereinafter also referred to as "Tg") is preferably -50 to +10°C, more preferably -45 to +5°C, even more preferably -40 to +3°C, and particularly preferably -35 to 0°C. In this case, the above-described mechanism of action is more likely to be expressed.

[0071] The FO polymer is preferably FEP, FKM, FEPM, or FFKM, as described later, and more preferably FKM, FEPM, or FFKM. In this case, the mechanism of action described above is more likely to be expressed.

[0072] The FO polymer is preferably a polymer obtained by the method described later.

[0073] In aqueous dispersion 1, the FO particles are dispersed in the liquid.

[0074] The average particle diameter of the FO particles is 1 nm or more, more preferably 10 nm or more, more preferably 25 nm or more, and particularly preferably 30 nm or more. The average particle diameter of the FO particles is less than 150 nm, and more preferably 120 nm or less. Due to the mechanism of action described above, a dispersion with such particle diameters is easily formed according to Method 1.

[0075] 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.

[0076] The content of FO particles in aqueous dispersion 1 is less than 10% by mass of the total mass. Preferably, the content is 8.0% by mass or less, more preferably 6.0% by mass or less, and even more preferably 5.0% by mass or less. Furthermore, it is preferable that the content is 0.01% by mass or more. Due to the mechanism of action described above, dispersions with such content are easily formed according to this method 1.

[0077] The water content in aqueous dispersion 1 is preferably 80% by mass or more, and more preferably over 90% by mass, based on the total mass. The content is 99.99% by mass or less, and more preferably 95.0% by mass or less. According to this method 1, such an aqueous dispersion with substantially water as the aqueous medium is easily formed by the mechanism of action described above.

[0078] Furthermore, the sum of the content of F particles and water in the 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 the sum is 100% by mass. According to the above-described mechanism of action, this method yields a dense aqueous dispersion of F particles with excellent dispersibility in liquid, with water being substantially the liquid medium.

[0079] The viscosity of 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 viscosity of the reaction system is preferably 0.8 mPa·s or more, and more preferably 1.0 mPa·s or more.

[0080] 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.

[0081] The thixotropy of the aqueous dispersion 1 is preferably 0.95 or higher, and more preferably 0.98 or higher. The thixotropy of the aforementioned solution is preferably 1.05 or lower, and more preferably 1.02 or lower. The reaction system in this method is preferably non-thixotropic, in other words, it is preferable that the thixotropy is 1.

[0082] 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.

[0083] Due to the mechanism of action described above, this method makes it easy to obtain an aqueous dispersion with the aforementioned liquid properties.

[0084] A preferred embodiment of the aqueous dispersion 1 is an aqueous dispersion that does not contain a fluorine-based emulsifier, comprising 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, and water, wherein the content of the particles in the total mass is less than 10% by mass, and the water content is 80% by mass or more, and the particles are dispersed in the liquid with an average particle diameter of 1 to 150 nm.

[0085] A preferred polymer containing TFE units or HFP units and VdF units is FKM, which is a fluoroelastomer containing 20-60 mol% of VdF units and 40-80 mol% of TFE units or HFP units. FKM may further contain other units such as PAVE units and Pp units.

[0086] 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.

[0087] 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 or PAAE units are preferably PMVE units, PEVE units, or PAAE 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 fluoroalkylethylene (hereinafter also referred to as "FAE") units.

[0088] 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.

[0089] 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.

[0090] As a polymer containing TFE units and Et units, ETFE, which is a fluororesin containing 35 to 65 mol% of TFE units and 35 to 65 mol% of Et units, is preferred. ETFE may further contain other units such as PAVE units, HFP units, and FAE units.

[0091] In the above preferred embodiment, the Tg of the fluoroolefin polymer is preferably the same as the Tg range of the FO polymer in the aqueous dispersion 1 described above, including the preferred range.

[0092] In the above preferred embodiment, the fluoroolefin polymer is preferably FKM, FEPM, or FFKM.

[0093] Furthermore, in the preferred embodiment, the average particle size of the fluoroolefin polymer particles, the content of the particles, the water content, the range of the sum of the content of the particles and the water content relative to the total mass, the viscosity of the aqueous dispersion, and the thixotropy of the aqueous dispersion are the same as those in the aqueous dispersion 1 described above, including the preferred embodiment.

[0094] According to the mechanism of action described above, the present method yields the aqueous dispersion 1 in the preferred form. The aqueous dispersion 1 in the preferred form is preferably used as a polymerization medium for gaseous perfluoroolefins, and more preferably used in the preparation of the reaction system in the present method 2.

[0095] Method 2 involves polymerizing gaseous perfluoroolefin in a reaction system free of fluorine-based emulsifiers, prepared from aqueous dispersion 1, in the presence of a polymerization initiator, to obtain aqueous dispersion 2 containing F polymer particles (F particles).

[0096] When preparing the reaction system, the dispersion obtained by Method 1 (aqueous dispersion 1) may be used as is, or the types of components in aqueous dispersion 1 and their content may be adjusted before using it as the reaction system.

[0097] Furthermore, specific methods of the latter adjustment include adding water to the aqueous dispersion 1 to adjust the FO particle content before forming the reaction system, adding other components described later to the aqueous dispersion 1 to adjust the liquid properties of the reaction system before forming the reaction system, and treating the aqueous dispersion 1 with an ion exchange resin to remove salts derived from polymerization initiators before forming the reaction system.

[0098] The reaction system of Method 2 may or may not contain a hydrophilic compound. In the former case, the hydrophilic compound content in the aqueous dispersion 1 of the reaction system of Method 2 is preferably 30 ppm by mass or less, and more preferably 10 ppm by mass or less. The hydrophilic compound content can be prepared according to the embodiments described above.

[0099] In the reaction system of Method 2, the content of persulfate ions or sulfate ions 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, the coloration of the F polymer is suppressed, and the physical properties of the aqueous dispersion 2 tend to improve. A specific example of a reaction system containing these ions is the case in Method 1 where the polymerization initiator is persulfates. In this case, it is preferable to treat the aqueous dispersion 1 with an ion exchange resin to remove these ions.

[0100] In the reaction system of Method 2, the concentration of fluoride ions in the aqueous dispersion 1 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 an example in which the aqueous dispersion 1 contains a by-product containing fluoride ions produced by the reaction of a polymerization initiator (e.g., APS) with a fluoroolefin.

[0101] The polymerization described in Method 2 (hereinafter also referred to as "this polymerization") is carried out by polymerizing gaseous perfluoroolefins. The gaseous perfluoroolefins may be one type or multiple types.

[0102] The gaseous perfluoroolefin is preferably TFE or HFP, and more preferably contains at least TFE.

[0103] 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.

[0104] The monomer may be a gaseous monomer or a liquid monomer. The monomer may be one type or multiple types.

[0105] Examples of the monomers include Et, Pp, vinyl chloride, vinylidene chloride, VdF, CTFE, 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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%.

[0110] Furthermore, 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.

[0111] 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.

[0112] Polymerization initiators include oil-soluble radical initiators, water-soluble polymerization initiators, and water-soluble redox catalysts.

[0113] Examples of water-soluble polymerization initiators and water-soluble redox catalysts include the agents mentioned above.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] The polymerization temperature is preferably 20°C or higher. The temperature is preferably less than 100°C, and more preferably 90°C or lower. The polymerization temperature is preferably lower than the polymerization temperature in Method 1. In this case, an F polymer with superior fluoropolymer properties is more likely to be formed.

[0119] The pressure in this polymerization is preferably 0.8 MPaG or higher, more preferably 0.9 MPaG or higher. The pressure is preferably 4.0 MPaG or lower, more preferably 0.6 to 3.5 MPaG or lower.

[0120] 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.

[0121] In the reaction of Method 2, the FO particles are dispersed in liquid within the reaction system.

[0122] 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.

[0123] In this specification, the average particle diameter of FO particles is the particle diameter calculated by analyzing the autocorrelation function obtained by dynamic light scattering using the monodisperse cumulant method.

[0124] The content of FO particles in the reaction system of Method 2 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.

[0125] 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. Furthermore, the water content is preferably 100% by mass or less, and more preferably 99.9% by mass or less. When the water content in the reaction system falls within this range, in other words, even when the liquid component of the reaction system is substantially water, an aqueous dispersion of F particles with excellent dispersibility in liquid can be directly obtained without using a fluorine-based emulsifier, through the mechanism of action described above.

[0126] The reaction system of Method 2 does not contain a fluorine-based emulsifier. In other words, it is preferable that the reaction system of Method 2 be formed without the use of a fluorine-based emulsifier. The definition of a fluorine-based emulsifier, including specific examples, is the same as that of Method 1.

[0127] In Method 2, it is preferable that the reaction system be formed without using fluorine-based emulsifiers (emulsifiers containing fluorine atoms) and emulsifiers that do not contain fluorine atoms.

[0128] The 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 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.

[0129] In the reaction system of Method 2, it is preferable that the ratio of the viscosity of aqueous dispersion 2 to the viscosity of aqueous dispersion 1 is greater than 1. Furthermore, it is preferable that the viscosity ratio is less than or equal to 5. In this case, the above-described mechanism of action is more likely to manifest.

[0130] The thixotropic ratio of the reaction system liquid in Method 2 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. The reaction system in this method is preferably non-thixotropic, in other words, it is preferable that the thixotropic ratio is 1. In this case, the mechanism of action described above is more likely to manifest.

[0131] The liquid properties of the reaction system in Method 2 can be controlled by adjusting the aqueous dispersion 1.

[0132] The aqueous dispersion obtained by this method (aqueous dispersion 2) contains particles of F polymer dispersed in the liquid (F particles).

[0133] The F polymer is preferably PTFE, modified PTFE, ETFE, PFA, FEP, FKM, FEPM, or FFKM overall. Furthermore, the fluoroelastomers FKM, FEPM, and FFKM 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).

[0134] 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.

[0135] The thixotropy of aqueous dispersion 2 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 reaction system in this method is preferably not thixotropic, in other words, it is preferable that the thixotropy is 1.

[0136] According to this method, an aqueous dispersion with such excellent liquid properties can be easily obtained directly through the mechanism of action described above.

[0137] In aqueous dispersion 2, the average particle size of F particles 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.

[0138] Furthermore, the particle size distribution of F particles in aqueous dispersion 2 is preferably unimodal. 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.

[0139] 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.

[0140] The content of F particles in the 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, based on the total mass of the aqueous dispersion 2. The content of F particles is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less.

[0141] 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 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more.

[0142] Furthermore, the sum of the content of F particles and water in the aqueous dispersion 2 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 efficiently yields an aqueous dispersion with a high content of dense F particles, which has excellent dispersibility in liquid, and is substantially composed of water as the liquid medium.

[0143] In this method 2, the particle size ratio is the value obtained by dividing the average particle diameter of F particles in aqueous dispersion 2 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.

[0144] 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 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%).

[0145] According to the mechanism of action described above, Method 2 allows for the production of an aqueous dispersion by selecting the desired particle size ratio and content ratio. The respective values ​​of the particle size ratio and content ratio in Method 2 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] Examples of fluororesins include PTFE, modified PTFE, ETFE, PFA, and FEP.

[0150] Examples of fluoroelastomers include FKM, FEPM, and FFKM.

[0151] According to Method 2, 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 contained 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.

[0152] Formula (S1): H-(CF2) n -COO - M + Formula (S2): H-(CF2) n -SO3 - M +

[0153] 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.

[0154] In the aqueous dispersion 2 of this method 2, the content of the compound represented by formula (S1) and the compound represented by formula (S2) is preferably 100 ppb by mass or less, more preferably 50 ppb by mass or less, and even more preferably 25 ppb by mass or less, based on 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.

[0155] Aqueous dispersion 2 is an aqueous dispersion in which highly dispersion-stable F particles are dispersed, and can be suitably used as a coating agent, binder, etc.

[0156] Alternatively, a dispersion containing F particles may be prepared by replacing the water in aqueous dispersion 2 with an organic solvent such as N-methylpyrrolidone or acetone, using such an organic solvent as the liquid dispersion medium.

[0157] Alternatively, F particles may be agglomerated from the aqueous dispersion 2 to obtain F particle powder. The F particle powder obtained by agglomeration may be directly processed into a molded product 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 a molded base material such as pellets or granules.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] 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.

[0162] In the case of 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]

[0163] The following examples illustrate the disclosure in detail, but the disclosure is not limited thereto. The abbreviations in the examples have the following meanings.

[0164] NaAAMPS: Sodium 2-acrylamido-2-methyl-1-propanesulfonate TFE: Tetrafluoroethylene PMVE: Perfluoromethyl vinyl ether

[0165] 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.

[0166] 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.

[0167] 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.

[0168] The reactors used were all made of stainless steel.

[0169] [Example 1] Example of manufacturing an aqueous dispersion In a pressure-resistant reactor (internal volume: 1.3 L), ultrapure water (713 g), PMVE (55 g), and an aqueous solution containing 0.5% by mass of NaAAMPS (3.6 g) were charged. The temperature was raised to 80°C while stirring, and an aqueous solution of ammonium persulfate (3.6% by mass, 5 mL) and TFE (9 g) were added to form the reaction system and start polymerization. As the pressure dropped due to polymerization, TFE was injected under pressure to maintain a constant pressure of 0.8 MPaG or higher. When 24 g of TFE had been injected under pressure, the reactor was cooled to terminate polymerization. After recovering the remaining gas in the reactor, the contents were withdrawn and the resulting solution was a dispersion containing 5.1% by mass of FO polymer particles (average particle size: 102 nm) containing 40 mol% PMVE units and 60 mol% TFE units. This liquid was treated with a cation exchange resin (Diaion SK1BH, manufactured by Mitsubishi Chemical Corporation) and then with an anion exchange resin (Diaion SA10AOH, manufactured by Mitsubishi Chemical Corporation) to obtain a dispersion containing 5.1% by mass of the aforementioned particles.

[0170] In a pressure-resistant reactor (internal volume: 1.3 L), the dispersion (617 g), ultrapure water (157 g), and paraffin wax (36 g) were added to form a reaction system containing 4.0 mass% of the particles. The temperature was raised to 70°C, and while stirring at 260 rpm, TFE was injected under pressure until the pressure reached 1.4 MPaG. Disuccinate peroxide (0.11 mmol) was added, and polymerization was started. As the pressure dropped due to polymerization, TFE was injected under pressure to maintain the pressure at 1.4 MPa. When 90 g of TFE had been injected under pressure, the reactor was cooled to terminate the polymerization. The polymerization time was 222 minutes, and the polymerization rate, calculated from the amount of TFE consumed, was 31 g / L / h.

[0171] After recovering the remaining gas in the reactor, the liquid contents were removed to obtain an aqueous dispersion.

[0172] The aqueous dispersion contained 23.8% by mass of fluoropolymer particles (average particle size: 298 nm) with an overall composition of 99.3 mol% TFE units and 0.7 mol% PMVE units. The aqueous dispersion exhibited excellent liquid properties, such as dispersion stability, and handling properties, while the fluoropolymer exhibited excellent properties as PTFE, a fluororesin. Specifically, the melting point of the fluoropolymer was 338°C. Furthermore, the particle size distribution was unimodal, and its polydispersity index was 0.5 or less.

[0173] 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.

[0174] Furthermore, the disclosure of Japanese Patent Application No. 2024-099106, filed on 19 June 2024, is incorporated herein by reference in its entirety. In addition, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

Claims

1. Water and -SO ３ X group, -PO ３ X group, -P(OR)O ２ X group or -COOX group (where X is H, K, Na, or NH) ４ A method for producing a dispersion, comprising a reaction system comprising a monomer having (where R represents an alkyl group) and not having a fluorine atom, and a polymerization initiator, and not containing a fluorine-based emulsifier, wherein a gaseous fluoroolefin is polymerized to obtain a dispersion containing less than 10% by mass of polymer particles having the fluoroolefin-based unit and having an average particle diameter of 1 to 150 nm, based on the total mass.

2. where the monomer has a -SO ３ X group, -PO ３ X group, -P(OR)O ２ vinyl monomers having an X group or -COOX group, -SO ３ X group, -PO ３ X group, -P(OR)O ２ allyl monomers having an X group or -COOX group, (meth)acrylic acid, -SO ３ X group, -PO ３ X group, -P(OR)O ２ (meth)acrylates having an X group or -COOX group, or -SO ３ X group, -PO ３ X group, -P(OR)O ２ The method for producing a dispersion according to claim 1, which is (meth)acrylamides having an X group or -COOX group.

3. The method for producing a dispersion according to claim 1, wherein the monomer content in the reaction system is 1.0 ppm by mass or more and 1000 ppm by mass or less.

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

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

6. The method for producing a dispersion according to claim 1, wherein the polymerization is carried out while maintaining a temperature of more than 55°C and less than 100°C, and a pressure of 0.8 MPaG or more and 2.0 MPaG or less.

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

8. A method for producing an aqueous dispersion, comprising polymerizing gaseous perfluoroolefin in a reaction system free of fluorine-based emulsifiers, prepared from a dispersion obtained by the production method described in claim 1, 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 reaction system is 2 or more. A method for producing an aqueous dispersion.

9. The method for producing an aqueous dispersion according to claim 8, wherein the viscosity of the reaction system is less than 2 mPa·s.

10. The method for producing an aqueous dispersion according to claim 8, wherein the gaseous perfluoroolefin is tetrafluoroethylene or hexafluoropropylene.

11. The method for producing an aqueous dispersion according to claim 8, wherein the polymerization is carried out by copolymerizing the gaseous perfluoroolefin with a monomer other than the gaseous perfluoroolefin.

12. The method for producing an aqueous dispersion according to claim 11, 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.

13. The method for producing an aqueous dispersion according to claim 8, wherein the average particle size of the fluoropolymer particles is greater than 50 nm and less than or equal to 1000 nm.

14. A method for producing an aqueous dispersion according to claim 8, 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.

15. A method for producing an aqueous dispersion according to claim 8, comprising 5 to 50% by mass of the fluoropolymer particles based on the total mass.