Aqueous dispersion, method for producing aqueous dispersion, and method for producing polymer-containing substrate

Abstract

Provided are: an aqueous dispersion capable of forming a coating film with suppressed coloration; a method for producing an aqueous dispersion; and a method for producing a polymer-containing substrate.　This aqueous dispersion comprises: a first fluorine-containing polymer which has at most 1,000 ionic functional groups per 106 main-chain carbon atoms of the polymer, has a glass transition temperature of at most 10ºC, and contains a fluorine atom; a second fluorine-containing polymer which is polytetrafluoroethylene; a surfactant which includes a nonionic surfactant; and an aqueous medium, wherein said aqueous dispersion is substantially free of a fluorine-containing polymer which is different from the first fluorine-containing polymer and which has an ionic functional group.

Description

Aqueous dispersion, method for producing aqueous dispersion, and method for producing polymer-containing substrate

[0001] The present invention relates to aqueous dispersions, methods for making aqueous dispersions, and methods for making polymer-containing substrates.

[0002] Polytetrafluoroethylene is used in various industrial fields due to its excellent heat resistance, chemical resistance, flame retardancy, weather resistance, etc. Polytetrafluoroethylene is sometimes used in the form of an aqueous dispersion in which polytetrafluoroethylene is dispersed in an aqueous medium, for reasons such as ease of handling. As a method for producing such an aqueous dispersion, Patent Document 1 discloses a method in which tetrafluoroethylene is polymerized in the presence of a fluorine-containing polymer having anionic groups in its side chains and an aqueous medium to obtain an aqueous dispersion containing polytetrafluoroethylene, and then a surfactant is added to the obtained aqueous dispersion in order to improve the dispersion stability of polytetrafluoroethylene.

[0003] International Publication No. 2022 / 191286

[0004] In recent years, further improvements in the performance of coating films obtained using aqueous dispersions containing polytetrafluoroethylene have been demanded, for example, coating films with reduced coloration. The present inventors evaluated coating films obtained using aqueous dispersions such as those described in Patent Document 1 and found that there is room for improvement in the coloration of the coating films.

[0005] An object of the present invention is to provide an aqueous dispersion capable of forming a coating film with suppressed coloration. Another object of the present invention is to provide a method for producing the aqueous dispersion, and a polymer-containing substrate.

[0006] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by the following constitution, and have arrived at the present invention. [1] The main chain of the polymer has 10 carbon atoms. ６An aqueous dispersion comprising: a first fluorine-containing polymer containing fluorine atoms, having 1,000 or less ionic functional groups per polymer and a glass transition temperature of 10°C or less; a second fluorine-containing polymer which is polytetrafluoroethylene; a surfactant including a nonionic surfactant; and an aqueous medium, wherein the aqueous dispersion is substantially free of a fluorine-containing polymer having ionic functional groups other than a fluorine-containing polymer different from the first fluorine-containing polymer. [2] The aqueous dispersion according to [1], wherein the first fluorine-containing polymer has units based on a monomer having a vinyl group optionally substituted with a fluorine atom. [3] The aqueous dispersion according to [1] or [2], wherein the first fluorine-containing polymer has units based on tetrafluoroethylene. [4] The aqueous dispersion according to any of [1] to [3], wherein the total content of the first fluorine-containing polymer and the second fluorine-containing polymer is 10 to 80% by mass based on the total mass of the aqueous dispersion. [5] The aqueous dispersion according to any one of [1] to [4], wherein the content of the surfactant is 1.1 to 19.8% by mass relative to the total mass of the first fluoropolymer and the second fluoropolymer in the aqueous dispersion. [6] The aqueous dispersion according to any one of [1] to [5], wherein the nonionic surfactant comprises at least one selected from the group consisting of a compound represented by formula (S-1), a compound represented by formula (S-2), and a compound represented by formula (S-3). Formula (S-1) R Ｓ１ -O-L Ｓ１ -H Formula (S-2) R Ｓ２ -C ６ H ４ -O-L Ｓ２ -H Formula (S-3) R Ｓ３ -O-L Ｓ３ -H In the above formula (S-1), R Ｓ１ represents an alkyl group having 8 to 18 carbon atoms, and L Ｓ１ represents a polyoxyalkylene chain composed of oxyethylene groups having an average number of added moles of 5 to 20 and oxypropylene groups having an average number of added moles of 0 to 2. In the above formula (S-2), R Ｓ２ represents an alkyl group having 4 to 12 carbon atoms, and L Ｓ２represents a polyoxyethylene chain composed of oxyethylene groups with an average number of added moles of 5 to 20. Ｓ３ represents an alkyl group having 8 to 18 carbon atoms, and L Ｓ３ represents a polyoxyalkylene chain composed of an oxyethylene group having an average number of added moles of 5 to 20 and an oxybutylene group having an average number of added moles of 0.1 to 3. [7] The main chain carbon number of the polymer is 10 ６ a first aqueous dispersion comprising a first fluorine-containing polymer having 1,000 or less ionic functional groups per monomer, a glass transition temperature of 10°C or less, and containing fluorine atoms, and a first aqueous medium, by polymerizing a monomer containing tetrafluoroethylene in the first aqueous dispersion to produce a second fluorine-containing polymer which is polytetrafluoroethylene and is different from the first fluorine-containing polymer, thereby producing a second aqueous dispersion comprising the first fluorine-containing polymer, the second fluorine-containing polymer, and a second aqueous medium; and a second aqueous dispersion comprising the first fluorine-containing polymer, the second fluorine-containing polymer, and a second aqueous medium, by polymerizing a monomer containing tetrafluoroethylene in the first aqueous dispersion to produce a second aqueous dispersion comprising the first fluorine-containing polymer, the second fluorine-containing polymer, and a second aqueous medium; and a second aqueous dispersion comprising the first fluorine-containing polymer and a second aqueous medium by adding a surfactant containing a nonionic surfactant to the second aqueous dispersion to obtain an aqueous dispersion, wherein the content of the first fluorine-containing polymer is 0.01 to 4.0% by mass relative to the total mass of the first aqueous dispersion before the start of polymerization of the monomers, and the concentration of the fluorine-containing emulsifier is 100 ppm by mass or less relative to the total mass of the first fluorine-containing polymer in the first aqueous dispersion before the start of polymerization of the monomers. [8] A method for producing the aqueous dispersion according to [7], comprising a step of contacting the aqueous dispersion with an ion exchange resin. [9] A method for producing a polymer-containing substrate, comprising contacting the aqueous dispersion according to any one of [1] to [6] with a substrate made of glass fiber to obtain a polymer-containing substrate.

[0007] According to the present invention, an aqueous dispersion capable of forming a coating film with suppressed coloration can be provided. The present invention also provides a method for producing the aqueous dispersion and a polymer-containing substrate.

[0008] The meanings of terms used in the present invention are as follows. A numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the upper and lower limits. In the numerical ranges described in this specification in stages, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another staged numerical range. Furthermore, in the numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the Examples. In this specification, each component may be used alone or in combination with two or more substances corresponding to the component. Herein, when two or more substances are used in combination for each component, the content of that component refers to the total content of the substances used in combination, unless otherwise specified. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment. A "unit" is a collective term for an atomic group derived from one molecule of the above-mentioned monomer, formed directly by polymerization of the monomer, and an atomic group obtained by chemically converting a portion of the above-mentioned atomic group. Hereinafter, a "unit based on a monomer" will also be simply referred to as a "unit." 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.

[0009] [Aqueous Dispersion] The aqueous dispersion of the present invention (hereinafter also referred to as "the present aqueous dispersion") is a polymer having 10 carbon atoms in its main chain. ６ The present invention relates to a fluoropolymer having 1,000 or less ionic functional groups per polymer and a glass transition temperature (hereinafter also referred to as "Tg") of 10°C or less, and containing fluorine atoms; a second fluoropolymer which is polytetrafluoroethylene (hereinafter also referred to as "PTFE"); a surfactant which contains a nonionic surfactant; and an aqueous medium, wherein the second fluoropolymer is a fluoropolymer different from the first fluoropolymer and is substantially free of a fluoropolymer having ionic functional groups.

[0010] The coating film formed using this aqueous dispersion is inhibited from discoloring. Although the details of the reason for this are not clear, it is presumed to be due to the following reasons. When a fluorine-containing polymer having an ionic functional group is used, the fluorine-containing polymer having an ionic functional group remains in the aqueous dispersion. When the aqueous dispersion containing the residue is used to apply to a substrate, dried, and baked, the residue decomposes upon heating, causing discoloration. In response to this problem, it is presumed that the aqueous dispersion is substantially free of a fluorine-containing polymer having an ionic functional group, and therefore discoloration of the coating film formed using this dispersion is inhibited.

[0011] [First fluorine-containing polymer] The first fluorine-containing polymer is a polymer having a main chain carbon number of 10 ６ The number of ionic functional groups per polymer is 1,000 or less, and the number of carbon atoms in the main chain of the polymer is 10 ６ The number of ionic functional groups per unit is preferably 1 or more. When the amount of ionic functional groups is within this range, production stability during production of the second fluorine-containing polymer is improved. ６ The number of ionic functional groups per molecule can be determined by a known method such as Fourier transform infrared spectroscopy (FT-IR). Examples of the ionic functional groups include cationic functional groups and anionic functional groups. Specific examples of the ionic functional groups include carboxylic acid groups (-COO － ), sulfonic acid group (—SO ３ － ), sulfate group (-SO ４ ２－ ), a phosphonic acid group (—PO ３ ２－ ) and a phosphate group (-PO ４ ３－ ) and other anionic functional groups.

[0012] The Tg of the first fluoropolymer is 10°C or lower. When the first fluoropolymer is used to produce the second fluoropolymer, the Tg of the first fluoropolymer is preferably 5°C or lower, more preferably 3°C or lower, and even more preferably 0°C or lower, from the viewpoint of efficient adsorption of the tetrafluoroethylene-containing monomer used in the production of the second fluoropolymer. The Tg of the first fluoropolymer is preferably -50°C or higher, more preferably -45°C or higher, and even more preferably -40°C or higher, from the viewpoint of thermal stability after molding. The Tg of the first fluoropolymer is measured by differential scanning calorimetry (DSC), and detailed measurement conditions are as described in the Examples section below. Examples of a method for adjusting the Tg of the first fluoropolymer within the above range include, for example, adjusting the type and amount of monomer used in the production of the first fluoropolymer.

[0013] In view of better effects of the present invention, the first fluorine-containing polymer preferably has units based on a monomer having a vinyl group which may be substituted with a fluorine atom, and more preferably has units based on a monomer having a vinyl group substituted with a fluorine atom.

[0014] The unit based on a monomer having a vinyl group substituted with a fluorine atom is preferably a unit based on perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE") (hereinafter also referred to as "PAVE unit"). As PAVE, a monomer represented by formula (1) is preferred from the viewpoints of excellent polymerization reactivity in producing the first fluorine-containing polymer and of enabling more efficient production of the second fluorine-containing polymer. CF ２ =CF-O-R ｆ１ (1) In formula (1), R ｆ１ represents a perfluoroalkyl group having 1 to 10 carbon atoms. ｆ１ From the viewpoint of better polymerization reactivity, the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 8, more preferably 1 to 6, still more preferably 1 to 5, and particularly preferably 1 to 3. The perfluoroalkyl group may be linear or branched.

[0015] Specific examples of PAVE include perfluoro(methyl vinyl ether) (hereinafter also referred to as "PMVE"), perfluoro(ethyl vinyl ether) (hereinafter also referred to as "PEVE"), and perfluoro(propyl vinyl ether) (hereinafter also referred to as "PPVE"), and among these, PMVE and PPVE are preferred, with PMVE being more preferred, from the viewpoint of enabling more efficient production of the second fluorinated polymer.

[0016] When the first fluorine-containing polymer has units based on a monomer having a vinyl group optionally substituted with a fluorine atom, the content of the units based on a monomer having a vinyl group optionally substituted with a fluorine atom is preferably from 20 to 60 mol %, more preferably from 25 to 60 mol %, and still more preferably from 30 to 55 mol %, based on all units of the first fluorine-containing polymer.

[0017] The first fluorine-containing polymer preferably has units based on tetrafluoroethylene (hereinafter also referred to as "TFE") (hereinafter also referred to as "TFE units"), in view of better effects of the present invention. When the first fluorine-containing polymer has TFE units, the content of TFE units is preferably 30 to 90 mol%, more preferably 40 to 80 mol%, and even more preferably 45 to 70 mol%, based on all units of the first fluorine-containing polymer.

[0018] The first fluoropolymer preferably contains TFE units and PAVE units, from the viewpoint of ease of adjusting the Tg within the above range and of more excellent effects of the present invention. When the first fluoropolymer contains TFE units and PAVE units, the content of PAVE units relative to the total of TFE units and PAVE units in the first fluoropolymer is preferably 20 to 60 mol%, more preferably 25 to 60 mol%, and even more preferably 30 to 55 mol%, from the viewpoint of ease of adjusting the Tg within the above range and of more efficiently producing the second fluoropolymer. The preferred amount used is the same whether the PAVE units are PMVE units, PEVE units or PPVE units, or a mixture of two or more of these is used.

[0019] The first fluorine-containing polymer may contain units based on monomers other than the above-mentioned monomers, but from the viewpoint of more efficient production of the second fluorine-containing polymer when the first fluorine-containing polymer is used to produce the second fluorine-containing polymer, it is preferable that the first fluorine-containing polymer is substantially free of units based on other monomers. "Substantially free of units based on other monomers" means that the content of units based on other monomers is 0.01 mol% or less, more preferably 0 mol%, based on the total units of the first fluorine-containing polymer. When units based on other monomers are contained, the other monomer is preferably hexafluoropropylene.

[0020] The content of the first fluoropolymer is preferably from 0.10 to 2.0 mass%, more preferably from 0.15 to 1.5 mass%, and even more preferably from 0.2 to 0.8 mass%, relative to the total mass of the aqueous dispersion, from the viewpoint of better dispersion stability of the second fluoropolymer in the aqueous dispersion.

[0021] [Second fluorine-containing polymer] The second fluorine-containing polymer, PTFE, may be a homopolymer of TFE or may be modified PTFE. The second fluorine-containing polymer is a fluorine-containing polymer different from the first fluorine-containing polymer. The first fluorine-containing polymer and the second fluorine-containing polymer may be copolymerized.

[0022] The modified PTFE preferably contains TFE units and units based on a modified monomer copolymerizable with the TFE units (hereinafter also referred to as "modified monomer units"). The content of the modified monomer units in the modified PTFE is preferably 0.0001 to 1 mass %, more preferably 0.0005 to 0.50 mass %, and even more preferably 0.001 to 0.40 mass %, relative to the total units of the modified PTFE. The modified monomer units refer to a portion of the molecular structure of the modified PTFE that is derived from the modified monomer, and the total units of the modified PTFE refer to portions derived from all monomers in the molecular structure of the modified PTFE. The content of the modified monomer units can be determined by known methods such as Fourier transform infrared spectroscopy (FT-IR). Modified monomer can be any monomer that can be copolymerized with TFE, and can be exemplified by perfluoroolefin such as hexafluoropropylene; chlorofluoroolefin such as chlorotrifluoroethylene; hydrogen-containing fluoroolefin such as trifluoroethylene, vinylidene fluoride; perfluorovinyl ether; perfluoroalkylethylene; ethylene.Modified monomer can be used alone or in combination of two or more kinds.

[0023] The content of the second fluorine-containing polymer is preferably from 10 to 80% by mass, more preferably from 20 to 75% by mass, and even more preferably from 25 to 70% by mass, based on the total mass of the aqueous dispersion, depending on the intended use of the aqueous dispersion (such as impregnating cloth or string woven from fibers such as glass fiber, mixing with inorganic powder or plastic powder, adding a small amount to paint, or coating).

[0024] In the present aqueous dispersion, the first fluorine-containing polymer and the second fluorine-containing polymer may be present in the form of particles containing the first fluorine-containing polymer and the second fluorine-containing polymer (preferably particles consisting of the first fluorine-containing polymer and the second fluorine-containing polymer). In this case, from the viewpoint of dispersion stability, the average particle size of the particles is preferably 500 μm or less, more preferably 450 μm or less, and even more preferably 400 μm or less. Furthermore, from the viewpoint of aggregation, the average particle size of the particles is preferably 50 nm or more, more preferably 80 nm or more, and even more preferably 100 nm or more. The average particle size of the particles is determined by measuring the particle size distribution by a laser diffraction / scattering method, determining a cumulative curve with the total volume of the particle population as 100%, and the particle size on the cumulative curve is the particle size at the point where the cumulative volume is 50%. Furthermore, the first fluorine-containing polymer and the second fluorine-containing polymer may be copolymerized.

[0025] The total content of the first fluoropolymer and the second fluoropolymer is preferably from 10 to 80 mass%, more preferably from 15 to 80 mass%, and even more preferably from 20 to 75 mass%, based on the total mass of the aqueous dispersion, from the viewpoint of better dispersion stability of the second fluoropolymer in the aqueous dispersion.

[0026] [Surfactant] The surfactant contained in the present aqueous dispersion includes a nonionic surfactant. When the surfactant includes a nonionic surfactant, the dispersion stability of the present aqueous dispersion is improved. The surfactant may further include a surfactant other than the nonionic surfactant (hereinafter also referred to as "other surfactant").

[0027] The content of the surfactant is preferably 1.1 to 19.8% by mass, more preferably 1.2 to 16.5% by mass, and even more preferably 1.4 to 15.4% by mass, relative to the total mass of the first fluoropolymer and the second fluoropolymer in the aqueous dispersion. When the content of the surfactant is 1.1% by mass or more, the storage stability of the aqueous dispersion is superior. Furthermore, when the content of the surfactant is 19.8% by mass or less, microcracks are less likely to occur when the aqueous dispersion is formed into a coating film.

[0028] <Nonionic Surfactant> From the viewpoint of further improving the stability of the present aqueous dispersion, the nonionic surfactant preferably contains at least one selected from the group consisting of a compound represented by formula (S-1), a compound represented by formula (S-2), and a compound represented by formula (S-3).

[0029] Formula (S-1) R Ｓ１ -O-L Ｓ１ -H Formula (S-2) R Ｓ２ -C ６ H ４ -O-L Ｓ２ -H Formula (S-3) R Ｓ３ -O-L Ｓ３ -H

[0030] In the above formula (S-1), R Ｓ１ represents an alkyl group having 8 to 18 carbon atoms. Ｓ１ The alkyl group in R may be linear or branched. Ｓ１ The number of carbon atoms in the alkyl group in the formula (I) is 8 to 18, preferably 10 to 16, and more preferably 12 to 16. When the alkyl group has 8 or more carbon atoms, the surface tension of the present aqueous dispersion is low, and the permeability and wettability are excellent. When the alkyl group has 18 or less carbon atoms, the particles of the second fluorine-containing polymer are less likely to settle even when the present aqueous dispersion is left to stand for a long period of time, and the storage stability is excellent. Ｓ１ represents a polyoxyalkylene chain composed of oxyethylene groups having an average number of added moles of 5 to 20 (preferably 7 to 12) and oxypropylene groups having an average number of added moles of 0 to 2 (preferably 0.5 to 1.5). Ｓ１ When the average number of moles of oxypropylene groups added is 0.5 to 1.5, good defoaming properties are obtained, which is preferred.

[0031] In the above formula (S-2), R Ｓ２ represents an alkyl group having 4 to 12 carbon atoms. Ｓ２ The alkyl group in R may be linear or branched. Ｓ２The number of carbon atoms in the alkyl group in the formula (I) is 4 to 12, preferably 6 to 10, and more preferably 8 to 9. When the number of carbon atoms in the alkyl group is 4 or more, the surface tension of the aqueous PTFE dispersion is low, and the permeability and wettability are excellent. When the number of carbon atoms in the alkyl group is 12 or less, the particles of the second fluoropolymer are less likely to settle even when the aqueous dispersion is left to stand for a long period of time, and the storage stability is excellent. Ｓ２ represents a polyoxyethylene chain composed of oxyethylene groups having an average added mole number of 5 to 20 (preferably 6 to 16, more preferably 7 to 12).

[0032] In the above formula (S-3), R Ｓ３ represents an alkyl group having 8 to 18 carbon atoms. Ｓ３ The alkyl group in R may be linear or branched. Ｓ３ The number of carbon atoms in the alkyl group in the formula (I) is 8 to 18, preferably 10 to 16, and more preferably 12 to 16. When the number of carbon atoms in the alkyl group is 8 or more, the surface tension of the aqueous PTFE dispersion is low, and the permeability and wettability are excellent. When the number of carbon atoms in the alkyl group is 18 or less, the particles of the second fluoropolymer are less likely to settle even when the aqueous dispersion is left to stand for a long period of time, and the storage stability is excellent. Ｓ３ represents a polyoxyalkylene chain composed of oxyethylene groups having an average number of added moles of 5 to 20 (preferably 6 to 15, more preferably 7 to 12) and oxybutylene groups having an average number of added moles of 0.1 to 3 (preferably 0.5 to 2, more preferably 0.7 to 1.7, and even more preferably 0.9 to 1.5). Among these, when the number of oxybutylene groups is 0.5 to 2, good defoaming properties are obtained and this is preferred.

[0033] The average molecular weight of the compound represented by formula (S-1), the average molecular weight of the compound represented by formula (S-2), and the average molecular weight of the compound represented by formula (S-3) are each preferably 450 to 800, more preferably 500 to 750, and even more preferably 550 to 700.

[0034] Examples of the compound represented by formula (S-1) include C 13 H 27 —O—(C2H4O) 10 -H, C 12 H 25—O—(C2H4O) 10 -H, C 10 H 21 CH(CH3)CH2-O-(C2H4O)9-H, C 13 H 27 -O-(C2H4O)9-CH(CH3)CH2-OH, C 16 H 33 —O—(C2H4O) 10 -H, HC(CH 11 ) (C7H 15 )-O-(C2H4O)9-H. Commercially available products include the Tergitol (registered trademark) 15S series manufactured by Dow and the Lionol (registered trademark) TD series manufactured by Lion Corporation. Examples of compounds represented by formula (S-2) include C8H 17 -C6H4-O-(C2H4O) 10 -H, CH 19 -C6H4-O-(C2H4O) 10 Commercially available products include the Triton (registered trademark) X series manufactured by Dow Chemicals and the Nikkol (registered trademark) OP series or NP series manufactured by Nikko Chemicals. Examples of the compound represented by formula (S-3) include C 13 H 27 OCH2CH(C2H5)O(C2H4O)8H,C 10 H 21 CH(CH3)CH2OCH2CH(C2H5)O(C2H4O)8H,C 12 H 25 OCH2CH(C2H5)O(C2H4O)8H, C8H 17 OCH2CH(C2H5)O(C2H4O) 10 H, C 13 H 27 OCH2CH2OCH2CH(C2H5)O(C2H4O)8H,C 10 H 21 CH(CH3)CH2O(C2H4O)9CH2CH(C2H5)OH,C 16 H 33 OC2H4OCH(C2H5)CH2O(C2H4O)9H,C 12 H 25 OCH2CH(C2H5)O(C2H4O)8CH2CH(C2H5)OH,C 13 H27 OCH(CH3)CH(CH3)O(C2H4O)8H,C 12 H 25 OCH(CH3)CH(CH3)O(C2H4O)8H,C 13 H 27 O(CH2)4O(C2H4O)8H,C 12 H 25 O(CH2)2CH(CH3)O(C2H4O)8H.

[0035] The compound represented by formula (S-1), the compound represented by formula (S-2), and the compound represented by formula (S-3) may each be used alone or in combination of two or more. The nonionic surfactant is a mixture of multiple substances with different molecular structures, and the number of carbon atoms in the alkyl group in the nonionic surfactant, and the number of oxyethylene groups, oxypropylene groups, and oxybutylene groups in the polyoxyalkylene chain are treated as average values. Each numerical value is not limited to an integer.

[0036] The content of the nonionic surfactant is preferably 1.0 to 12% by mass, more preferably 1.1 to 8.0% by mass, and even more preferably 1.3 to 5.0% by mass, relative to the total mass of the first fluoropolymer and the second fluoropolymer in the aqueous dispersion. When the content of the nonionic surfactant is 1.0% by mass or more, the storage stability of the aqueous dispersion is superior. Furthermore, when the content of the nonionic surfactant is 12% by mass or less, microcracks are less likely to occur when the aqueous dispersion is formed into a coating film.

[0037] The content of the nonionic surfactant is preferably 85 to 99.9% by mass, more preferably 90 to 99% by mass, and even more preferably 92 to 98% by mass, relative to the content of the surfactant in the aqueous dispersion. When the content of the nonionic surfactant is 85% by mass or more, the storage stability of the aqueous dispersion is superior. Furthermore, when the content of the nonionic surfactant is 99.9% by mass or less, microcracks are less likely to occur when the aqueous dispersion is formed into a coating film.

[0038] <Other Surfactants> The type of other surfactant is not particularly limited, but anionic surfactants are preferred. The anionic surfactant is preferably an anionic surfactant that does not contain a fluorine atom, and specific examples thereof include ammonium laurate, triethanolamine laurate, sodium lauryl sulfate, ammonium lauryl sulfate, and triethanolamine lauryl sulfate.

[0039] [Aqueous medium] Examples of the aqueous medium include water and a mixed solvent of water and a water-soluble organic solvent. Specific examples of the water-soluble organic solvent include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol. The aqueous medium contained in the aqueous dispersion may be the polymerization solvent used in producing the first fluorine-containing polymer and the second fluorine-containing polymer.

[0040] The content of the aqueous medium is preferably from 20 to 90% by mass, more preferably from 22 to 88% by mass, and even more preferably from 25 to 80% by mass, based on the total mass of the aqueous dispersion.

[0041] [Other Components] The present aqueous dispersion may contain other components in addition to those described above. Specific examples of other components that the present aqueous dispersion may contain include chain transfer agents, pH adjusters, waxes, various leveling agents, preservatives, fillers, and viscosity adjusters (e.g., polyethylene oxide, polyurethane-based viscosity adjusters). When the present aqueous dispersion contains other components, the content of the other components is preferably 0.01 to 2.0% by mass, more preferably 0.01 to 1.8% by mass, and even more preferably 0.01 to 1.5% by mass, relative to the total mass of the present aqueous dispersion.

[0042] [Fluoropolymer having ionic functional group] The present aqueous dispersion is substantially free of a fluorine-containing polymer having an ionic functional group other than the first fluorine-containing polymer. A fluorine-containing polymer having an ionic functional group is a polymer having an ionic functional group and a fluorine atom. Specific examples of the ionic functional group are as described above. A fluorine-containing polymer having an ionic functional group acts like a fluorine-containing emulsifier in water. For example, when a vinyl group-containing fluorine-containing emulsifier represented by the following general formulae (A-I) to (A-VII) is used, a fluorine-containing polymer having an ionic functional group remains in the aqueous dispersion, and when the aqueous dispersion containing the residue is applied to a substrate, dried and baked, the residue decomposes upon heating, causing coloration. General formula (A-I) CF ２ =CF-(CF ２ ) ａ１ -Y (AI) [wherein a1 represents an integer of 1 to 10, and Y represents -SO ３ M or -COOM, where M is H, NH ４ or an alkali metal, a vinyl group-containing fluorine-containing compound (AI) represented by the general formula (A-II): CF ２ =CF-(CF ２ C (CF ３ ) F) ｂ１ -Y (A-II) [wherein b1 represents an integer of 1 to 5, and Y represents -SO ３ M or -COOM, where M is H, NH ４ or an alkali metal, a vinyl group-containing fluorine-containing compound (A-II) represented by the general formula (A-III): CF ２ =CFO-(CFX) ｃ１ -Y [wherein X is -F or -CF ３ c1 represents an integer of 1 to 10, and Y represents -SO ３ M or -COOM, where M is H, NH ４ or an alkali metal, a vinyl group-containing fluorine-containing compound (A-III) represented by the general formula (A-IV): CF ２ = CFO-(CF ２ CFXO) ｄ１ -(CF ２ ) ｅ１-Y (A-IV) [wherein X represents -F or -CF3, d1 represents an integer of 1 to 10, e1 represents an integer of 1 to 3, and Y represents -SO ３ M or -COOM, where M is H, NH ４ or an alkali metal, a fluorine-containing vinyl group-containing compound (A-IV) represented by the general formula (AV): CH ２ =CFCF ２ O-(CF(CF ３ )CF ２ O) ｆ１ -CF (CF ３ )-Y (AV) [wherein f1 represents an integer of 0 to 10, and Y represents -SO ３ M or -COOM, where M is H, NH ４ or an alkali metal, a fluorine-containing compound (AV) having a vinyl group represented by the general formula (A-VI): CF ２ =CFCF ２ O-(CF(CF ３ )CF ２ O) ｇ１ -CF (CF ３ )-Y (A-VI) [wherein g1 represents an integer of 1 to 10, and Y represents -SO ３ M or -COOM, where M is H, NH ４ or an alkali metal.], and / or a fluorine-containing compound (A-VI) having a vinyl group represented by the general formula (A-VII): CF ２ ═CF—(OZ)—Y (A-VII) [wherein Z represents a perfluoroalkylene group having 1 to 6 carbon atoms, and Y represents —SO ３ M or -COOM, where M is H, NH ４ or an alkali metal.] The phrase "substantially free of a fluorine-containing polymer having an ionic functional group" means that the content of the fluorine-containing polymer having an ionic functional group is 0.01% by mass or less, and may be 0% by mass, based on the total mass of the aqueous dispersion.

[0043] [Physical Properties] The pH of the present aqueous dispersion is preferably 7.0 to 11.0, more preferably 8.0 to 11.0. The surface tension of the present aqueous dispersion is preferably 24 to 40 mN / m, more preferably 25 to 35 mN / m. The viscosity (23°C) of the present aqueous dispersion is more preferably 3 to 400 mPa s, more preferably 5 to 100 mPa s. The methods for measuring pH, surface tension, and viscosity are as described in the Examples section below.

[0044] [Method for producing aqueous dispersion] The method for producing an aqueous dispersion of the present invention (hereinafter also referred to as "the present production method") is a method for producing an aqueous dispersion of a polymer having 10 carbon atoms in its main chain. ６ the first aqueous dispersion containing a first fluorine-containing polymer having 1,000 or less ionic functional groups per monomer and a glass transition temperature of 10°C or less and containing fluorine atoms, and a first aqueous medium, by polymerizing a monomer containing tetrafluoroethylene (hereinafter also referred to as "specific monomer") in the first aqueous dispersion to produce a second fluorine-containing polymer which is polytetrafluoroethylene and is different from the first fluorine-containing polymer, thereby producing a second aqueous dispersion containing the first fluorine-containing polymer, the second fluorine-containing polymer, and a second aqueous medium; and step 2 adding a surfactant containing a nonionic surfactant to the second aqueous dispersion to obtain an aqueous dispersion (hereinafter also referred to as "specific aqueous dispersion"), Before starting polymerization of the monomers, the concentration of the fluorine-containing emulsifier is 100 mass ppm or less relative to the total mass of the first fluorine-containing polymer in the first aqueous dispersion. Also, the concentration of the fluorine-containing emulsifier is preferably 10 mass ppm or less, more preferably 150 mass ppb or less, more preferably 50 mass ppb or less, particularly preferably 25 mass ppb or less relative to the total mass of the first fluorine-containing polymer in the first aqueous dispersion. The lower limit is 0 mass ppb.

[0045] In the present production method, when producing the first fluorinated polymer, compound (2) may be used in addition to the monomer represented by the above formula (1).

[0046] <Compound (2)> Compound (2) is a compound represented by the following formula (2): CX １ X ２ =CX ３ -L-Z...(2) In formula (2), X １ and X ２ are each independently a hydrogen atom or an alkyl group, ３ represents a hydrogen atom, a fluorine atom, or an alkyl group; L represents a single bond or a divalent linking group; Z represents -SO ３ M １ , -OSO ３ M １ , -P(=O)(OM １ ) ２ , -OP(=O)(OM １ ) ２ , or -COOM １ and M １ represents a hydrogen atom, a metal atom, N(R Ｍ１１ ) ４ or P(R Ｍ１２ ) ４ and M １ If there are multiple M １ may be the same or different from each other, R Ｍ１１ and R Ｍ１２ are each independently a hydrogen atom or a substituent, and R Ｍ１１ Any two of R may be bonded to each other to form a ring, and multiple R Ｍ１１ may be the same or different from each other, R Ｍ１２ Any two of R may be bonded to each other to form a ring, and multiple R Ｍ１２ may be the same or different from each other.

[0047] The alkyl group may be linear, branched, or cyclic. The alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 3 carbon atoms, and even more preferably 1 carbon atom. X １ and X ２ In terms of increasing the number of particles of the first polymer, it is preferable that each of X is a hydrogen atom. ３is a hydrogen atom, a fluorine atom, or an alkyl group. Specific examples and preferred embodiments of the alkyl group are １ and X ２ The specific examples and preferred embodiments of the alkyl group in X are the same as those in X. ３ is preferably a fluorine atom or a hydrogen atom, more preferably a hydrogen atom, from the viewpoint of increasing the number of particles of the first polymer.

[0048] In formula (2), L is a single bond or a divalent linking group. Examples of the divalent linking group include an alkylene group, a carbonyl group, an ether bond, a thioether bond, a sulfonyl group, —NH—, and —SiH ２ -, phenylene group, -CF ２ -, and groups combining two or more of these. Examples of the above groups combining two or more of these include an ester bond, a thioester bond, an amide bond, a sulfonamide bond, a combination of an alkylene group and an ether bond, a combination of an alkylene group and an ester bond, and a combination of an alkylene group and an amide bond. The alkylene group may be linear, branched, or cyclic, and is preferably linear or branched, and more preferably branched. The number of carbon atoms in the alkylene group may be, for example, 1 to 6, and preferably 1 to 4.

[0049] Specific examples of L include a single bond, an alkylene group, an ether bond, an ester bond, * Ｃ -CO-NH-R-* Ｚ and the like, and examples thereof include a single bond, an alkylene group having 1 to 6 carbon atoms, and * Ｃ -CO-NH-R-* Ｚ are preferred, and particularly preferred are a single bond, an alkylene group having 1 to 2 carbon atoms, and * Ｃ -CO-NH-R-* Ｚ is more preferable. Ｃ is the bonding site to the carbon atom in formula (2), and * Ｚ is the bonding site to Z in formula (2), and R is an alkylene group having 1 to 6 carbon atoms.

[0050] In formula (2), Z is —SO ３ M １ , -OSO ３ M １, -P(=O)(OM １ ) ２ , -OP(=O)(OM １ ) ２ or -COOM １ From the viewpoint of stabilizing the dispersion and increasing the number of particles of the first polymer, Z is -SO ３ M １ and -COOM １ is preferred, and —SO ３ Na and —COONa are more preferred, and —SO ３ Na is more preferred.

[0051] M １ represents a hydrogen atom, a metal atom, N(R Ｍ１１ ) ４ or P(R Ｍ１２ ) ４ and R Ｍ１１ and R Ｍ１２ are each independently a hydrogen atom or a substituent. １ The metal atom represented by R is preferably a metal atom of Group 1, more preferably Li, Na, or K. Ｍ１１ and R Ｍ１２ The substituent represented by the formula (I) is preferably a monovalent organic group, more preferably a monovalent hydrocarbon group, and even more preferably an alkyl group or an aromatic hydrocarbon group. The substituent preferably has 1 to 10 carbon atoms. The alkyl group may be linear, branched, or cyclic. The aromatic hydrocarbon group may be monocyclic or polycyclic. The aromatic hydrocarbon group is preferably a phenyl group.

[0052] The molecular weight of the compound (2) is, for example, 70 to 500, preferably 70 to 450, more preferably 100 to 300, from the viewpoint of dispersion stability.

[0053] Specific examples of compound (2) include vinyl sulfonic acid, vinyl phosphonic acid, (meth)acrylic acid, allyl sulfonic acid, allyl phosphonic acid, butenoic acid, crotonic acid, vinyl acetic acid, 2-sulfoethyl methacrylic acid, 4-vinyl benzene sulfonic acid, 2-acrylamido-2-methyl-1-propane sulfonic acid, N-tigloyl glycine, 6-acrylamido hexanoic acid, 1,1-difluoro-2-methyl-2-[(1-oxo-2-propen-1-yl)amino]-1-propanesulfonic acid, and 3-methyl-3-[(2-methyl-1-oxo-2-propen-1-yl)amino]-2-butanesulfonic acid. acid, 2-methacrylamido-2-methylpropanesulfonic acid, 2,3-dimethyl-3-[(1-oxo-2-propen-1-yl)amino]-2-butanesulfonic acid, and metal salts thereof. １ Examples of the metal salt include a metal salt of a metal atom represented by the following formula:

[0054] As compound (2), vinyl compounds having a sulfonic acid group, phosphonic acid group, or carboxy group, allyl compounds having a sulfonic acid group, phosphonic acid group, or carboxy group, (meth)acrylic acid, (meth)acrylamides having a sulfonic acid group, phosphonic acid group, or carboxy group, and metal salts thereof are preferred, and vinyl sulfonic acid, sodium vinyl sulfonate, allyl sulfonic acid, sodium allyl sulfonate, 2-acrylamido-2-methyl-1-propanesulfonic acid, sodium 2-acrylamido-2-methyl-1-propanesulfonate, 2-methacrylamido-2-methyl-1-propanesulfonic acid, or sodium 2-methacrylamido-2-methyl-1-propanesulfonate are preferred. Note that the term "(meth)acrylic acid" encompasses both acrylic acid and methacrylic acid, and the term "(meth)acrylamide" encompasses both acrylamide and methacrylamide.

[0055] According to the present production method, an aqueous dispersion capable of forming a coating film with suppressed coloration can be provided. The present production method is suitable as a production method for obtaining the above-mentioned present aqueous dispersion.

[0056] [Step 1] Step 1 is a step of polymerizing a specific monomer in a first aqueous dispersion to produce a second aqueous dispersion. According to Step 1, the second fluorine-containing polymer can be produced efficiently using an aqueous medium with a small environmental load and without requiring an emulsifier. The reason for this is presumably that the use of a first aqueous dispersion containing a predetermined amount of the first fluorine-containing polymer allows the first fluorine-containing polymer to function as a good polymerization site for the second fluorine-containing polymer.

[0057] From the viewpoint of suppressing a decrease in molecular weight of the fluorine-containing polymer, step 1 is preferably carried out under conditions in which fluorine-based emulsifiers (emulsifiers having fluorine atoms) and emulsifiers not having fluorine atoms are substantially absent. In other words, it is preferable that the aqueous dispersion is substantially free of fluorine-based emulsifiers and emulsifiers not having fluorine atoms. "Substantially free of fluorine-based emulsifiers and emulsifiers not having fluorine atoms" (hereinafter collectively referred to as "emulsifiers") means that the content of emulsifiers is 10 mass ppm or less, preferably 150 mass ppb or less, more preferably 50 mass ppb or less, and particularly preferably 25 mass ppb or less, relative to the total mass of the first aqueous dispersion. The lower limit is 0 mass ppb. The content of various emulsifiers can be measured using a liquid chromatograph mass spectrometer. Specifically, the measurement methods described in paragraphs

[0721] to

[0732] of WO 2018 / 181904 can be mentioned.

[0058] Examples of fluorine-containing emulsifiers and emulsifiers having no fluorine atoms include water-soluble emulsifiers. A water-soluble emulsifier means an emulsifier having a solubility of 100 mg or more in 1000 g of water at 25°C, and a water-insoluble emulsifier means an emulsifier other than the above-mentioned water-soluble emulsifiers. The water-soluble emulsifier may be either ionic or nonionic. Examples of fluorine-containing emulsifiers and emulsifiers having no fluorine atoms include those having no carbon-carbon double bonds. Note that the above compound (2), the first fluorine-containing polymer, and the second fluorine-containing polymer do not fall under the category of emulsifiers.

[0059] The fluorine-containing emulsifier may be an anionic fluorine-containing emulsifier. Examples of the anionic fluorine-containing emulsifier include emulsifiers containing fluorine atoms whose total carbon number excluding anionic groups is 20 or less, and emulsifiers containing fluorine atoms whose anionic moiety has a molecular weight of 800 or less. The "anionic moiety" refers to the moiety excluding the cation of the fluorine-containing emulsifier.

[0060] The fluorine-free emulsifier is an emulsifier that does not contain fluorine atoms and has a hydrocarbon group such as an alkyl group as a hydrophobic moiety. It is also possible to replace the hydrogen atom of the hydrocarbon group of the fluorine-free emulsifier with a halogen atom other than a fluorine atom.

[0061] The emulsifiers having no fluorine atoms include anionic hydrocarbon emulsifiers and nonionic hydrocarbon emulsifiers.

[0062] Anionic hydrocarbon emulsifiers refer to emulsifiers having a negatively charged hydrophilic moiety, such as a carboxylic acid group, a sulfonic acid group, a sulfate group, a phosphonic acid group, or a phosphate group, and a hydrocarbon group, such as an alkyl group, as a hydrophobic moiety. Specific examples of anionic hydrocarbon emulsifiers include sodium dodecyl sulfate, highly branched C10 tertiary carboxylic acid supplied by Resolution Performance Products as Versatic® 10, linear alkyl polyethersulfonate sodium supplied by BASF as the Avanel® S series, and sulfosuccinate emulsifier Lankropol® K8300 available from AkzoNobelSurfaceChemistry LLC.

[0063] Nonionic hydrocarbon emulsifiers are emulsifiers that exhibit surface activity in water without dissociating into ions and have hydrocarbon groups such as alkyl groups as their hydrophobic moieties. The hydrophilic moieties of nonionic hydrocarbon emulsifiers include water-soluble functional groups such as polyethylene oxide chains obtained from the polymerization of ethylene oxide. Nonionic hydrocarbon emulsifiers include polyalkylene oxide block copolymers, such as block copolymers having polyethylene oxide and polypropylene oxide.

[0064] Further, other nonionic hydrocarbon emulsifiers include those described in paragraphs

[0043] to

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

[0065] Fluorine-based emulsifier and emulsifier without fluorine atom may contain silicon atom.The emulsifier containing silicon atom can include siloxane emulsifier.Siloxane emulsifier is a hydrocarbon-containing emulsifier with siloxane skeleton.The siloxane emulsifier can include the emulsifier described in U.S. Patent No. 6,841,616 (Wille et al.) and U.S. Patent No. 7,977,438 (Brothers et al.).

[0066] The fluorine-based emulsifier and the fluorine-free emulsifier may be a polymer emulsifier. Examples of the polymer emulsifier include a polymer having a hydrophilic group in its side chain. Examples of such polymer emulsifiers include polymers containing units based on a compound having a polymerization-reactive site and a hydrophilic group. Furthermore, examples of such polymer emulsifiers include polymers that do not originally have a hydrophilic group but that have been subjected to post-treatment such as hydrolysis of a polymer containing units based on a compound having a group that can become a hydrophilic group. When polymerization is carried out under conditions in which an emulsifier not containing a fluorine atom is present, typically 0.1 to 15 parts by mass of the emulsifier not containing a fluorine atom is used per 100 parts by mass of the aqueous medium.

[0067] The following will first describe in detail the materials used in step 1, and then the procedure of step 1. <First aqueous dispersion> In step 1, a first aqueous dispersion containing a first fluoropolymer and an aqueous medium is used.

[0068] (First Fluorine-Containing Polymer) The first fluorine-containing polymer contained in the first aqueous dispersion is the same as the first fluorine-containing polymer contained in the present aqueous dispersion described above, including preferred embodiments, and therefore description thereof will be omitted. When compound (2) is used in producing the first fluorine-containing polymer, the content of compound (2) is preferably 1.0 to 1000 ppm by mass, based on the entire aqueous dispersion before the start of polymerization, and from the viewpoint of better effects of the present invention, is more preferably 1.0 to 800 ppm by mass, still more preferably 3.0 to 500 ppm by mass, and particularly preferably 5.0 to 300 ppm by mass.

[0069] Before the start of polymerization of the monomers to be used in polymerization of the second fluoropolymer, the content of the first fluoropolymer is 0.01 to 4.0 mass% relative to the total mass of the first aqueous dispersion, and from the viewpoint of enabling the second fluoropolymer to be produced more efficiently, it is preferably 0.01 to 2.0 mass%, more preferably 0.01 to 1.5 mass%.

[0070] In this specification, "before initiating polymerization of the monomers used in the polymerization of the second fluoropolymer" means immediately before the initiation of polymerization. Here, "the initiation of polymerization" includes the time when the monomers and the polymerization initiator are brought into the reactor together after the temperature inside the reactor is raised to the polymerization temperature or higher, and the time when the temperature inside the reactor is raised to the polymerization temperature or higher after the monomers and the polymerization initiator are brought into the reactor together.

[0071] Before starting polymerization of the monomers used in the polymerization of the second fluoropolymer, the sulfate ion concentration is preferably 10 ppm by mass or less, more preferably 5 ppm by mass or less, relative to the total mass of the aqueous medium in the first aqueous dispersion, from the viewpoint of suppressing discoloration of the second fluoropolymer. An example of the lower limit is 0 ppm by mass. One example of a method for adjusting the sulfate ion concentration to the above value is a method of removing sulfate ions using an anion exchange resin during the production of the first fluoropolymer. Here, the sulfate ions are derived, for example, from the polymerization initiator (particularly ammonium persulfate) used during the production of the first fluoropolymer, and may be contained in the first aqueous dispersion containing the first fluoropolymer. It is presumed that by keeping the sulfate ion content at 10 ppm by mass or less (particularly 5 ppm by mass or less), it is possible to suppress the formation of terminal groups with low heat resistance, such as carboxylic acid groups and sulfonic acid groups, in the second fluoropolymer, thereby suppressing discoloration of the second fluoropolymer.

[0072] Before starting polymerization of the monomers used in the polymerization of the second fluoropolymer, the concentration of ammonium ions is preferably 20 ppm by mass or less, more preferably 10 ppm by mass or less, relative to the total mass of the aqueous medium in the first aqueous dispersion, from the viewpoint of suppressing aggregation of the second fluoropolymer.The lower limit can be 0 ppm by mass.One example of a method for adjusting the ammonium ion concentration to the above value is a method of removing ammonium ions using a cation exchange resin during the production of the first fluoropolymer.Here, the ammonium ions are derived, for example, from the initiator (particularly ammonium persulfate) used during the production of the first fluoropolymer, and may be contained in the first aqueous dispersion containing the first fluoropolymer.It is presumed that when the content of ammonium ions is 20 ppm by mass or less, the ionic strength in the aqueous medium is reduced, resulting in improved production efficiency of the second fluoropolymer.

[0073] The first fluorine-containing polymer is preferably dispersed in the first aqueous medium in the form of particles. In this case, the average particle size of the first fluorine-containing polymer is preferably 1 to 150 nm, more preferably 10 to 120 nm, and even more preferably 50 to 120 nm, from the viewpoint of more efficient production of the second fluorine-containing polymer. The average particle size of the first fluorine-containing polymer is determined by measuring the particle size distribution by a laser diffraction / scattering method, determining a cumulative curve with the total volume of the particle population as 100%, and measuring the particle size (D50) at the point on the cumulative curve where the cumulative volume is 50%, with detailed measurement conditions being as described in the Examples section.

[0074] The method for producing the first fluorine-containing polymer is preferably a method of polymerizing a monomer (preferably a monomer mixture containing TFE and PAVE) in an aqueous medium in the presence of a polymerization initiator.This gives the first fluorine-containing polymer dispersed in the form of particles in the aqueous medium.The aqueous medium thus obtained in which the particles of the first fluorine-containing polymer are dispersed may be used as the first aqueous dispersion as is, or another aqueous medium may be added and the resulting mixture may be used as the first aqueous dispersion.Furthermore, the first fluorine-containing polymer may be dispersed in another aqueous medium by solvent substitution, and the resulting mixture may be used as the first aqueous dispersion.

[0075] The polymerization initiator used in the production of the first fluorine-containing polymer is preferably a water-soluble polymerization initiator, more preferably a persulfate such as ammonium persulfate, sodium persulfate or potassium persulfate, or an organic polymerization initiator such as disuccinic acid peroxide or azobisisobutylamidine dihydrochloride, still more preferably a persulfate, and particularly preferably ammonium persulfate.

[0076] The aqueous medium used in producing the first fluorine-containing polymer may be water or a mixed solvent of water and a water-soluble organic solvent. Specific examples of the water-soluble organic solvent include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether and tripropylene glycol.

[0077] The method for producing the first fluoropolymer preferably includes a heating step of heating the aqueous medium having the first fluoropolymer dispersed therein after obtaining the aqueous medium. This deactivates the polymerization initiator present in the system, so that the polymerization of the second fluoropolymer is less susceptible to the influence of the polymerization initiator used in producing the first fluoropolymer. As a result, a second fluoropolymer having a high molecular weight is more likely to be obtained. The heating temperature in the heating step is preferably 70 to 100°C, more preferably 80 to 98°C, and even more preferably 85 to 95°C, from the viewpoint of further accelerating the deactivation of the polymerization initiator in the aqueous medium.

[0078] (First aqueous medium) The first aqueous dispersion used in step 1 contains a first aqueous medium. As described above, the first aqueous medium contained in the first aqueous dispersion may be the polymerization solvent used in producing the first fluoropolymer. Specific examples of the first aqueous medium contained in the first aqueous dispersion are the same as the specific examples of the aqueous medium used in producing the first fluoropolymer described above. Before starting polymerization of the monomers used in polymerizing the second fluoropolymer, the content of the first aqueous medium is preferably 60 to 99.9 mass%, more preferably 96 to 99.9 mass%, and even more preferably 98 to 99.9 mass%, based on the total mass of the first aqueous dispersion.

[0079] (Other Components) The first aqueous dispersion used in step 1 may contain other components in addition to the first fluorine-containing polymer and the aqueous medium. Specific examples of other components that the first aqueous dispersion may contain include a chain transfer agent, an emulsifier other than a fluorine-containing emulsifier, a pH adjuster, and a wax. Details of the other components are as described above, so their explanation will be omitted.

[0080] When the first aqueous dispersion contains a chain transfer agent, the content of the chain transfer agent is preferably 0.1 to 5 parts by mass per 100 parts by mass of the aqueous medium. Furthermore, the amount of the chain transfer agent used is preferably 0.1 to 20 parts by mass, more preferably 0.1 to 15 parts by mass, and even more preferably 0.1 to 10 parts by mass per 100 parts by mass of the specific monomer described below. When the first aqueous dispersion contains an emulsifier other than a fluorine-based emulsifier, the content of the emulsifier other than a fluorine-based emulsifier is preferably 0.01 to 5 parts by mass per 100 parts by mass of the aqueous medium. When the first aqueous dispersion contains a pH adjuster, the content of the pH adjuster is preferably 0.01 to 3.0 parts by mass per 100 parts by mass of the aqueous medium. When the first aqueous dispersion contains a wax, the content of the wax is preferably 1 to 10 parts by mass per 100 parts by mass of the aqueous medium.

[0081] Before starting polymerization of the monomers used in the polymerization of the second fluorine-containing polymer, the concentration of the fluorine-containing emulsifier is 100 ppm by mass or less relative to the total mass of the first fluorine-containing polymer in the first aqueous dispersion, and from the viewpoint of better effects of the present invention, it is preferably 50 ppm by mass or less, more preferably 25 ppm by mass or less, and even more preferably 5 ppm by mass or less. The lower limit can be 0 ppm by mass. The fluorine-containing emulsifier means an emulsifier in which the hydrophobic moiety contains a fluorine atom in the hydrophilic moiety and the hydrophobic moiety possessed by the emulsifier. Specific examples of the fluorine-containing emulsifier include fluorine-containing alkanoate salts and fluorine-containing ether carboxylic acid compounds. One example of a method for adjusting the concentration of the fluorine-containing emulsifier to the above-mentioned range is a method for producing an aqueous dispersion without using a fluorine-containing emulsifier. Before the start of polymerization of the monomers to be used in polymerization of the second fluoropolymer, the concentration of the emulsifier is 100 ppm by mass or less, based on the total mass of the first fluoropolymer in the first aqueous dispersion, and from the viewpoint of better effects of the present invention, it is preferably 50 ppm by mass or less, more preferably 25 ppm by mass, and even more preferably 5 ppm by mass or less. The lower limit may be 0 ppm by mass.

[0082] Before starting polymerization of the monomers used in the polymerization of the second fluorine-containing polymer, the concentration of fluoride ions is preferably 100 mass ppm or less, more preferably 50 mass ppm or less, relative to the total mass of the first aqueous dispersion, from the viewpoint of polymerization stability.The lower limit can be 0 mass ppm.One example of a method for adjusting the fluoride ion concentration to the above value is a method of removing sulfate ions using an anion exchange resin during the production of the first fluorine-containing polymer.Here, fluoride ions may be generated by the reaction between a polymerization initiator (e.g., ammonium persulfate) and the monomers used in the production of the first fluorine-containing polymer, and may be contained in the first aqueous dispersion.

[0083] <Specific Monomer> A specific monomer including TFE is used in step 1. The amount of TFE used is preferably 97 to 100 mass%, more preferably 98 to 100 mass%, and even more preferably 99 to 100 mass%, based on the amount of the specific monomer used.

[0084] Specific monomer may contain fluorine-containing monomer other than TFE, but may not substantially contain fluorine-containing monomer other than TFE.Not substantially contain fluorine-containing monomer other than TFE means that the amount of fluorine-containing monomer other than TFE used is less than 0.0001 mass% with respect to the amount of specific monomer used, and may be 0 mass%.As fluorine-containing monomer other than TFE, among the monomers exemplified in the above-mentioned modified monomer, the monomer containing fluorine atom can be enumerated.As fluorine-containing monomer other than TFE, two or more kinds can be used in combination.

[0085] The specific monomer may contain a monomer other than the fluorine-containing monomer (hereinafter also referred to as "other monomer"), but preferably does not contain any other monomer. "Substantially free of other monomers" means that the amount of other monomers used is less than 0.0001% by mass, more preferably 0% by mass, relative to the amount of the specific monomer used. Examples of other monomers include monomers that do not contain fluorine atoms, among the monomers exemplified as the modified monomers described above. Two or more types of other monomers may be used in combination.

[0086] The amount of the specific monomer used is preferably 1 to 50 parts by mass, more preferably 1 to 40 parts by mass, and even more preferably 1 to 30 parts by mass, per 100 parts by mass of the aqueous medium contained in the first aqueous dispersion.

[0087] <Polymerization Initiator> In step 1, the specific monomer is preferably polymerized in the presence of a polymerization initiator. The polymerization initiator is preferably an oil-soluble radical initiator, a water-soluble radical initiator, or a water-soluble redox catalyst. Specific examples of oil-soluble radical initiators include oil-soluble organic peroxides such as tert-butyl peroxypivalate (hereinafter also referred to as "PBPV") and diisopropyl peroxydicarbonate (hereinafter also referred to as "IPP"). Specific examples of water-soluble radical initiators include persulfates such as ammonium persulfate and potassium persulfate, and water-soluble organic peroxides such as disuccinic acid peroxide, bisglutaric acid peroxide, and tert-butyl hydroperoxide (hereinafter also referred to as "TBHP"). The water-soluble redox catalyst is preferably a combination of 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, organic acid, or inorganic salt. Potassium persulfate and ammonium persulfate are preferred as persulfates. Sodium sulfite is preferred as sulfites. Inorganic salts include combinations of sulfate anions, sulfite anions, and chloride anions with metal ions. Transition metal ions are preferred, including manganese, iron, cobalt, nickel, copper, zinc, cerium, and silver ions, with iron ions being preferred. Iron (II) sulfate is preferred as an inorganic salt. The polymerization initiator is preferably an oil-soluble radical initiator or a water-soluble radical initiator. From the viewpoint of more efficient production of fluoropolymers, oil-soluble radical initiators are more preferred, and oil-soluble organic peroxides are even more preferred. Two or more polymerization initiators may be used in combination.

[0088] The amount of the polymerization initiator used is preferably 1 to 1,000 ppm, more preferably 5 to 750 ppm, and even more preferably 10 to 500 ppm, relative to 100 parts by mass of the amount of the specific monomer used.

[0089] <Other Components> When polymerizing the specific monomer, components other than those described above (hereinafter also referred to as "other components") may be further used. A specific example of the other component is a reducing agent. The amount of the other component used is preferably 1 to 2000 ppm relative to 100 parts by mass of the specific monomer used.

[0090] <Procedure of Step 1> In step 1, a specific monomer is polymerized in a first aqueous dispersion to produce a second aqueous dispersion.

[0091] The specific monomer is added to the reaction system (i.e., polymerization reaction vessel) by a conventional method. For example, the specific monomer may be added to the reaction system continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. Alternatively, the specific monomer may be dissolved in an aqueous medium, and the resulting solution may be added to the reaction system continuously or intermittently. When a polymerization initiator is used, the polymerization initiator may be added to the reaction system all at once or in portions.

[0092] The polymerization temperature is preferably 10 to 95° C., more preferably 15 to 90° C. The polymerization pressure is preferably 0.5 to 4.0 MPaG, more preferably 0.6 to 3.5 MPaG. In the case of batch processing, the polymerization time is preferably 90 to 1,000 minutes, more preferably 90 to 700 minutes.

[0093] The polymerization of the specific monomer is preferably carried out in the substantial absence of an emulsifier. Examples of the emulsifier include known emulsifiers, such as common surfactants. The substantial absence of an emulsifier refers to an environment in which the content of the emulsifier is 0.03 mass ppm or less, preferably 0.02 mass ppm or less, and more preferably 0 mass ppm, relative to the total mass of the aqueous medium contained in the first aqueous dispersion.

[0094] (Second Aqueous Dispersion) By carrying out step 1, a second aqueous dispersion containing the first fluoropolymer, the second fluoropolymer, and the second aqueous medium is obtained.

[0095] First Fluorine-Containing Polymer and Second Fluorine-Containing Polymer The first fluorine-containing polymer and second fluorine-containing polymer contained in the second aqueous dispersion are similar to the first fluorine-containing polymer and second fluorine-containing polymer contained in the present aqueous dispersion described above, including preferred embodiments, and therefore description thereof will be omitted.

[0096] It is presumed that the specific monomer is polymerized within the particles of the first fluorine-containing polymer during polymerization of the specific monomer.Therefore, it is considered that particles containing the first fluorine-containing polymer and the second fluorine-containing polymer are produced by carrying out step 1.That is, it is presumed that the second fluorine-containing polymer is obtained in the form of particles containing the first fluorine-containing polymer and the second fluorine-containing polymer according to step 1.In this case, a second aqueous dispersion in which particles containing the first fluorine-containing polymer and the second fluorine-containing polymer are dispersed in the aqueous medium is obtained by step 1.In addition, the first fluorine-containing polymer and the second fluorine-containing polymer may be copolymerized.

[0097] The content of the first fluorine-containing polymer is preferably from 0.10 to 3.0 mass %, more preferably from 0.15 to 2.0 mass %, and even more preferably from 0.20 to 1.5 mass %, relative to the total mass of the second aqueous dispersion.

[0098] The content of the second fluorine-containing polymer is preferably from 10 to 40 mass %, more preferably from 12 to 35 mass %, and even more preferably from 15 to 30 mass %, based on the total mass of the second aqueous dispersion.

[0099] In the second aqueous dispersion, the content of PAVE units relative to the total of all units of the first fluoropolymer and the second fluoropolymer is preferably 0.1 to 5.0 mol%, more preferably 0.2 to 3.0 mol%, and even more preferably 0.3 to 2.5 mol%. When the PAVE units are PMVE units, PEVE units or PPVE units, or when a mixture of two or more of these is used, the suitable content is the same. It is preferable that the PAVE units are contained in the first fluoropolymer.

[0100] In the second aqueous dispersion, the content of TFE units relative to the total of all units of the first fluoropolymer and the second fluoropolymer is preferably from 90 to 99.8 mol%, more preferably from 93 to 99.5 mol%, and even more preferably from 95 to 99.0 mol%. It is sufficient that the TFE units are contained in at least the second fluoropolymer, but it is preferable that they are contained in both the first fluoropolymer and the second fluoropolymer.

[0101] In the second aqueous dispersion, the total content of the first fluoropolymer and the second fluoropolymer is preferably from 10 to 40 mass%, more preferably from 12 to 35 mass%, and even more preferably from 15 to 35 mass%, relative to the total mass of the second aqueous dispersion.

[0102] The first fluorine-containing polymer and the second fluorine-containing polymer may be present separately in the second aqueous dispersion, but are preferably present in the form of particles containing the first fluorine-containing polymer and the above-mentioned second fluorine-containing polymer (preferably particles consisting of the first fluorine-containing polymer and the second fluorine-containing polymer). In this case, the average particle size of the particles is preferably 500 μm or less, more preferably 450 μm or less, and even more preferably 400 μm or less, from the viewpoint of dispersion stability. Furthermore, the average particle size of the particles is preferably 50 nm or more, more preferably 80 nm or more, and even more preferably 100 nm or more, from the viewpoint of aggregation. The average particle size of the particles is determined by measuring particle size distribution by laser diffraction / scattering method, determining a cumulative curve with the total volume of the particle population as 100%, and the particle size on the cumulative curve is the particle size at the point where the cumulative volume is 50%.

[0103] Second Aqueous Medium Specific examples of the second aqueous medium contained in the second aqueous dispersion are the same as the specific examples of the aqueous medium used in producing the first fluorine-containing polymer described above. The second aqueous medium may be the first aqueous medium contained in the first aqueous dispersion itself, or may contain the first aqueous medium contained in the first aqueous dispersion and an aqueous medium added separately.

[0104] The content of the second aqueous medium is preferably from 50 to 99 mass%, more preferably from 60 to 99 mass%, and even more preferably from 70 to 99 mass%, based on the total mass of the second aqueous dispersion, from the viewpoint of dispersion stability of the first fluorinated polymer and the second fluorinated polymer.

[0105] The compound represented by formula (S1) and the compound represented by formula (S2) In second aqueous dispersion, the content of the compound represented by formula (S1) and the content of the compound represented by formula (S2) are preferably 100 mass ppb or less, respectively, relative to the total mass of the first fluorine-containing polymer and the second fluorine-containing polymer.The compound represented by formula (S1) and the compound represented by formula (S2) are the components that can be generated when TFE is polymerized in the presence of polymerization initiator, chain transfer agent and emulsifier (particularly hydrocarbon-based emulsifier).Therefore, when no emulsifier is used during the production of second aqueous dispersion, the amount of the compound represented by formula (S1) and the compound represented by formula (S2) can be suppressed, so that the content of these compounds can be easily made into the range described below.

[0106] Formula (S1): H-(CF ２ ) ｎ -COOM Formula (S2): H-(CF ２ ) ｎ -SO ３ In formula (S1) and formula (S2), M each independently represents a hydrogen atom, Na, K, or NH ４ and n's each independently represent 8 or 10.

[0107] In the second aqueous dispersion, the content of the compound represented by formula (S1) and the content of the compound represented by formula (S2) are each preferably 100 ppb by mass or less, more preferably 50 ppb by mass or less, still more preferably 25 ppb by mass or less, and particularly preferably 0 ppb by mass (i.e., no compound represented by formula (S1) or no compound represented by formula (S2)) relative to the total mass of the first fluorinated polymer and the second fluorinated polymer.

[0108] Others It is preferable that the second aqueous dispersion is substantially free of an emulsifier. The emulsifier is as described above, and therefore its description will be omitted. "Substantially free of an emulsifier" in the second aqueous dispersion means that the content of the emulsifier is 0.03 mass ppm or less, preferably 0.02 mass ppm or less, more preferably 0 mass ppm, relative to the total mass of the second aqueous dispersion. In step 1, the second aqueous dispersion may be subjected to a heat treatment. When the heat treatment is performed, the second aqueous dispersion obtained in step 1 may be heated as is, or may be heated after adding a radical generator, or may be heated after adjusting the contents of the first fluorine-containing polymer and the second fluorine-containing polymer contained in the second aqueous dispersion by concentration, dilution, etc.

[0109] [Step 2] Step 2 is a step of adding a surfactant containing a nonionic surfactant to the second aqueous dispersion to obtain a specific aqueous dispersion. Hereinafter, first, the materials used in Step 2 will be described in detail, and then the procedure of Step 2 will be described in detail.

[0110] <Second Aqueous Dispersion> The second aqueous dispersion used in step 2 is as described above, and therefore a description thereof will be omitted.

[0111] <Surfactant> The surfactant used in step 2 includes a nonionic surfactant. The surfactant may further include a surfactant other than a nonionic surfactant (hereinafter also referred to as "other surfactant"). The amount of surfactant used is preferably 0.10 to 19.8 mass%, more preferably 0.15 to 16.5 mass%, still more preferably 0.20 to 15.4 mass%, and particularly preferably 0.20 to 12.0 mass%, relative to the total mass of the first fluoropolymer and the second fluoropolymer contained in the second aqueous dispersion to be subjected to step 2. When the amount of surfactant used is 0.1 mass% or more, the dispersion stability of the specific aqueous dispersion is more excellent. When the amount of surfactant used is 19.8 mass% or less, aggregation during subsequent steps can be suppressed, and production stability is more excellent.

[0112] (Nonionic Surfactant) The nonionic surfactant used in Step 2 is similar to the nonionic surfactant contained in the present aqueous dispersion described above, including preferred embodiments, and therefore description thereof will be omitted. The amount of nonionic surfactant used is preferably 0.10 to 5.0 mass%, more preferably 0.15 to 4.0 mass%, and even more preferably 0.20 to 3.5 mass%, relative to the total mass of the first fluoropolymer and the second fluoropolymer contained in the second aqueous dispersion used in Step 2. When the amount of nonionic surfactant used is 0.1 mass% or more, the dispersion stability of the specific aqueous dispersion is superior. When the amount of nonionic surfactant used is 5.0 mass% or less, aggregation during subsequent steps can be suppressed, resulting in superior production stability. The amount of nonionic surfactant used is preferably 85 to 99.9 mass%, more preferably 90 to 99 mass%, and even more preferably 92 to 98 mass%, relative to the amount of surfactant used in Step 2. When the amount of nonionic surfactant used is 85 mass% or more, the dispersion stability of the specific aqueous dispersion is superior. When the amount of the nonionic surfactant used is 99.9% by mass or less, aggregation during the subsequent steps can be suppressed, resulting in superior production stability.

[0113] (Other Surfactants) In step 2, other surfactants may be further added, which can improve the concentration rate in step 4 described below.

[0114] The type of other surfactant is not particularly limited, but an anionic surfactant is preferred. The anionic surfactant is similar to the anionic surfactant that can be contained in the aqueous dispersion described above, including preferred embodiments, and therefore a description thereof will be omitted.

[0115] The amount of the other surfactant (particularly, anionic surfactant) used is preferably 100 to 3000 ppm by mass, more preferably 150 to 2500 ppm by mass, and even more preferably 150 to 2000 ppm by mass, relative to the total mass of the first fluoropolymer and the second fluoropolymer contained in the second aqueous dispersion to be subjected to step 2. When the amount of the other surfactant (particularly, anionic surfactant) used is 100 ppm by mass or more, the concentration rate in step 4 described below can be improved. When the amount of the other surfactant (particularly, anionic surfactant) used is 3000 ppm by mass or less, the generation of aggregates during concentration in step 4 described below can be further suppressed.

[0116] <Procedure of Step 2> In Step 2, a surfactant including a nonionic surfactant is added to the second aqueous dispersion to produce a specific aqueous dispersion.

[0117] (Specific aqueous dispersion) A specific aqueous dispersion containing a surfactant containing the nonionic surfactant, and the first fluorine-containing polymer, the second fluorine-containing polymer, and the second aqueous medium contained in the second aqueous dispersion is obtained by carrying out step 2. The specific aqueous dispersion may contain other components that can be contained in the present aqueous dispersion.

[0118] [Step 3] The present production method preferably includes Step 3 of contacting the specific aqueous dispersion with an ion exchange resin to obtain a purified specific aqueous dispersion, which makes it possible to remove impurities such as components derived from the polymerization initiator and fluorine-containing polymers having ionic functional groups, thereby further suppressing coloration of the coating film.

[0119] The ion exchange resin used in step 3 may be either an anion exchange resin or a cation exchange resin, but an anion exchange resin is preferred because it can more effectively remove components that cause coloration of the coating film.

[0120] The amount of the anion exchange resin used is preferably 1 to 100 parts by mass, more preferably 1 to 50 parts by mass, per 100 parts by mass of the specific aqueous dispersion used.

[0121] Specific examples of methods for contacting the specific aqueous dispersion with the anion exchange resin include mixing the specific aqueous dispersion with the anion exchange resin and passing the specific aqueous dispersion through a column packed with the anion exchange resin. When contacting the anion exchange resin with the specific aqueous dispersion, the temperature of the specific aqueous dispersion is preferably 10 to 50°C, more preferably 15 to 40°C. The contact time between the anion exchange resin and the specific aqueous dispersion is preferably 10 to 360 minutes, more preferably 10 to 240 minutes. When contacting the anion exchange resin with the specific aqueous dispersion, the pH of the specific aqueous dispersion is not limited. The pH may be less than 7 or may be 7 or greater.

[0122] Step 3 preferably includes a treatment of contacting the specific aqueous dispersion with an ion exchange resin and then adding at least one of the nonionic surfactant and the anionic surfactant to the purified specific aqueous dispersion. The amount of the nonionic surfactant used in Step 3 is preferably 0.1 to 7.0 mass%, more preferably 0.2 to 6.5 mass%, relative to the total mass of the first fluoropolymer and the second fluoropolymer contained in the specific aqueous dispersion obtained in Step 2. The amount of the anionic surfactant used in Step 3 is preferably 200 to 3000 mass%, more preferably 250 to 2500 mass%, relative to the total mass of the first fluoropolymer and the second fluoropolymer contained in the specific aqueous dispersion obtained in Step 2.

[0123] [Step 4] The present production method may include Step 4, in which the purified specific aqueous dispersion obtained in Step 3 is concentrated. This gives the above-mentioned present aqueous dispersion. The concentration of the second fluoropolymer in the present aqueous dispersion obtained in Step 4 is higher than the concentration of the second fluoropolymer in the specific aqueous dispersion obtained in Step 2.

[0124] The purified specific aqueous dispersion obtained in step 3 can be concentrated by a known concentration method, such as centrifugal sedimentation, electrophoresis, or phase separation.

[0125] Step 4 may include concentrating the purified specific aqueous dispersion obtained in Step 3, and then adding at least one selected from the group consisting of a nonionic surfactant, aqueous ammonia, and a viscosity modifier (e.g., polyethylene oxide) to the concentrated purified specific aqueous dispersion. The amount of the nonionic surfactant used in Step 4 is preferably 1.0 to 18% by mass, more preferably 1.1 to 15% by mass, based on the total mass of the first fluoropolymer and the second fluoropolymer contained in the purified specific aqueous dispersion obtained in Step 3. The concentration of ammonia contained in the aqueous ammonia is preferably 1 to 40% by mass, more preferably 5 to 40% by mass, and more preferably 10 to 35% by mass. The amount of aqueous ammonia used in Step 4 is preferably 0.001 to 1.0% by mass, more preferably 0.005 to 0.5% by mass, based on the total mass of the first fluoropolymer and the second fluoropolymer contained in the purified specific aqueous dispersion obtained in Step 3. The amount of viscosity modifier used is preferably from 0 to 3.0 mass %, more preferably from 0.01 to 2.5 mass %, relative to the total mass of the first fluoropolymer and the second fluoropolymer contained in the purified specific aqueous dispersion obtained in step 3.

[0126] The present aqueous dispersion obtained in step 4 contains a surfactant including a nonionic surfactant, a first fluoropolymer, a second fluoropolymer, and a second aqueous medium, and may further contain an anionic surfactant. The content of the surfactant is preferably 1.1 to 19.8 mass%, more preferably 1.2 to 16.5 mass%, and even more preferably 1.4 to 15.4 mass%, relative to the total mass of the first fluoropolymer and the second fluoropolymer contained in the present aqueous dispersion obtained in step 4. The content of the nonionic surfactant is preferably 1.0 to 12 mass%, more preferably 1.1 to 8.0 mass%, and even more preferably 1.3 to 5.0 mass%, relative to the total mass of the first fluoropolymer and the second fluoropolymer contained in the present aqueous dispersion obtained in step 4. The content of the first fluoropolymer is preferably 0.1 to 7.5 mass%, more preferably 0.5 to 7.0 mass%, and even more preferably 0.8 to 6.5 mass%, relative to the total mass of the specific aqueous dispersion obtained in step 4. The content of the second fluorine-containing polymer is preferably 20 to 85% by mass, more preferably 30 to 80% by mass, and even more preferably 40 to 75% by mass, relative to the total mass of the specific aqueous dispersion obtained in step 4. The content of the second aqueous medium is preferably 15 to 80% by mass, more preferably 20 to 70% by mass, and even more preferably 25 to 60% by mass, relative to the total mass of the specific aqueous dispersion obtained in step 4. When the present aqueous dispersion obtained in step 4 contains a viscosity modifier, the content of the viscosity modifier is preferably 0.05 to 3.0% by mass, more preferably 0.08 to 2.5% by mass, and even more preferably 0.1 to 2.0% by mass, relative to the total mass of the specific aqueous dispersion obtained in step 4.

[0127] [Method for producing polymer-containing substrate] The method for producing a polymer-containing substrate of the present invention is a method for obtaining a polymer-containing substrate by contacting the above-mentioned aqueous dispersion with a substrate made of glass fiber (hereinafter also referred to as "glass fiber substrate"). Examples of the glass fiber substrate include glass fiber woven fabric and string. The method for contacting the aqueous dispersion with the glass fiber substrate can be a known method, and examples thereof include a method of immersing the glass fiber substrate in the aqueous dispersion, a method of spray-coating the aqueous dispersion, and a method of coating the aqueous dispersion with a roller or a brush.

[0128] The present invention will be described in detail below with reference to examples. Examples 1 to 4 and 7 to 10 are working examples, and Examples 5 and 6 are comparative examples. However, the present invention is not limited to these examples. The blending amounts of each component in the tables below are based on mass.

[0129] [Measurement and Evaluation Methods] <Average Primary Particle Diameter of PTFE Particles> Using an aqueous PTFE dispersion as a sample, the average primary particle diameter of the PTFE particles was measured using a laser diffraction / scattering particle size distribution analyzer (ELSZ, Otsuka Electronics Co., Ltd.).

[0130] <Standard Specific Gravity of PTFE Powder> The standard specific gravity was measured in accordance with ASTM D4895-04. 12.0 g of sample (PTFE powder) was weighed and held in a cylindrical mold with an inner diameter of 28.6 mm at 34.5 MPa for 2 minutes. This was placed in a 290°C oven and heated at 120°C / hr. After holding at 380°C for 30 minutes, the temperature was lowered at 60°C / hr and held at 294°C for 24 minutes. The sample was held in a desiccator at 23°C for 12 hours, and then the specific gravity of the sample relative to water at 23°C was measured, and this was taken as the standard specific gravity (hereinafter also referred to as "SSG"). The smaller the SSG value, the larger the molecular weight.

[0131] <PTFE Concentration and Surfactant Concentration> Approximately 7 g of the PTFE aqueous dispersion was placed in an aluminum dish (mass W0) and weighed (mass W1), and the PTFE concentration and surfactant concentration (ratio of surfactant to PTFE mass) were calculated using the following formulas from the mass (mass W2) after drying at 120°C for 1 hour and the mass (mass W3) after drying at 380°C for 35 minutes. PTFE concentration (mass %) = [(W3 - W0) / (W1 - W0)] x 100 Surfactant concentration (mass % / PTFE) = [(W2 - W3) / (W3 - W0)] x 100

[0132] <Viscosity> The viscosity of the aqueous PTFE dispersion was measured using a Brookfield viscometer with a #1 spindle at a liquid temperature of 23°C and 60 rpm.

[0133] <pH> The pH of the aqueous PTFE dispersion was measured by the glass electrode method.

[0134] <Surface Tension> The surface tension of the aqueous PTFE dispersion was measured by the ring method using a platinum wire ring.

[0135] <Glass transition temperature Tg and melting point Tm> Tg was measured using a NEXTA DSC600 manufactured by Hitachi High-Technologies Corporation. Specifically, 5 mg of a sample for measurement was weighed into an aluminum sample pan, and the sample was heated to 100°C at a heating rate of 10°C / min under a nitrogen atmosphere. Thereafter, the sample was cooled to -60°C at a rate of 10°C / min. Once the predetermined temperature was reached, the temperature was again raised to 100°C at 10°C / min. Tg was estimated from the inflection point confirmed in this second heating operation. Tm was measured using a DSC8500 manufactured by PerkinElmer, which had been temperature-calibrated in advance using indium and zinc as standard samples. Specifically, 10 mg of a sample for measurement was weighed into an aluminum sample pan, and the sample was heated to 380°C at a heating rate of 10°C / min under an air atmosphere, and the endothermic peak was determined.

[0136] <Coloration Evaluation> A coating film obtained using an aqueous PTFE dispersion was baked and evaluated for coloration. Specifically, 7 g of the aqueous PTFE dispersion was added to an aluminum dish with an inner diameter of 6 cm, and dried at 120°C for 60 minutes to obtain a PTFE coating film. The obtained PTFE coating film was baked at 380°C for 35 minutes, and the color of the obtained baked PTFE coating film was visually confirmed, and coloration was evaluated according to the following criteria. The closer the color is to milky white, the more the coloration of the coating film is suppressed. ○: The color of the baked PTFE coating film is milky white to yellow. ×: The color of the baked PTFE coating film is black to brownish-red.

[0137] [Production of Raw Material Solution A1] Ultrapure water (33.0 kg) and PMVE (2.28 kg) were charged into a 50 L stainless steel pressure reactor equipped with a stirring blade and baffles, and the temperature was raised to 90 ° C. while stirring at 170 rpm. TFE was injected into the reactor until the pressure reached 1.30 MPaG, and an aqueous solution of ammonium persulfate (APS) (5.57 mass%, 150 g) was added to initiate the reaction. As the reaction began, the pressure in the reactor decreased, so TFE was added to maintain the pressure constant. When 120 g of TFE had been injected, the rotation speed was changed to 40 rpm, the reactor was cooled, and the polymerization reaction was terminated. After recovering the gas remaining in the reactor, nitrogen was injected up to 0.10 MPaG while stirring at 20 rpm, and the temperature was raised to 90 ° C. The reactor was heated for 3 hours, cooled, and the liquid was withdrawn. This liquid was designated as raw material solution A1. After freeze-coagulating the raw material liquid A, it was filtered off, and the resulting fluoropolymer A1 was analyzed by NMR, and as a result, it was found that the TFE unit / PMVE unit ratio was 51 / 49 (molar ratio) and the Tg was -5.5°C.

[0138] [Production of Raw Material Solution B1] Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 20 g) was added to raw material solution A1 (490 g). 60 minutes after the start of stirring, the raw material solution and the ion exchange resin were separated by filtration. SA10AOH (manufactured by Mitsubishi Chemical Corporation, anion exchange resin, 20 g) was added to the filtered raw material solution. 60 minutes after the start of stirring, the raw material solution and the ion exchange resin were separated by filtration to obtain raw material solution B1. The content of the fluoropolymer A1 was 0.8 mass% based on the total mass of raw material solution B1.

[0139] Example 1 Ultrapure water (37 g), raw material liquid B1 (475 g), and paraffin wax (28 g) were charged into a 1.0 L stainless steel pressure reactor equipped with a stirring blade and a baffle, to obtain aqueous dispersion B1-1 (corresponding to the first aqueous dispersion). The content of fluoropolymer A1 was 0.7 mass% based on the total mass of aqueous dispersion B1-1. The concentration of the fluorine-containing emulsifier was 0 ppm by mass based on the total mass of fluoropolymer A1 in aqueous dispersion B1-1. The content of fluoropolymer A1 in aqueous dispersion B1-1 (solids concentration) was calculated by the following formula after heating 2.0 g of aqueous dispersion B at 170°C for 20 minutes and then weighing the mass of the residue. The solids concentration was calculated. For each example described below, calculations were performed in the same manner, except that the type of aqueous dispersion was changed to that used in each example. "Solid content concentration (mass%) = 100 × heating residue of aqueous dispersion B1-1 (g) / mass of aqueous dispersion B1-1 (2 g)" A press sheet of the obtained fluoropolymer A1 was prepared and analyzed using a Fourier transform infrared spectrophotometer (Nicolet iS50, manufactured by Thermofisher Scientific) in accordance with the method described in JP 2022-50435 A. As a result, it was found that the fluoropolymer A1 had a main chain carbon number of 10. ６ The number of ionic functional groups per particle was 1,000 or less.

[0140] The obtained aqueous dispersion B1-1 was heated to 70 ° C. while stirring at 260 rpm. TFE was injected until the pressure in the reactor reached 1.40 MPaG, and an aqueous APS solution (0.436% by mass, 5 ml) was added to initiate polymerization. As the polymerization began, the pressure in the reactor decreased, so TFE was added to maintain the pressure constant. When 80 g of TFE had been injected, an aqueous hydroquinone (HQ) solution (0.349% by mass, 5 ml) was added. When 120 g of TFE had been injected, the reactor was cooled, the polymerization reaction was terminated, and aqueous dispersion C1-1 (corresponding to the second aqueous dispersion) was obtained. The aqueous dispersion C1-1 was a dispersion in which PTFE particles (average primary particle diameter 249 nm) containing fluoropolymer A1 and fluoropolymer A2 were dispersed in an aqueous medium, and had a solids concentration of 15.5% by mass. A portion of the obtained aqueous dispersion C1-1 was adjusted to 20°C and stirred to aggregate the PTFE particles, thereby obtaining a PTFE powder. Next, this PTFE powder was dried at 200°C. The obtained PTFE powder had an SSG of 2.22 and a melting point of 339°C. Furthermore, no by-product fluorine oligomers were confirmed in the obtained PTFE powder.

[0141] The ratio of the mass of the nonionic surfactant (a) (Newcol 1308FA, manufactured by Nippon Nyukazai Co., Ltd.) to the mass of the PTFE particles in the aqueous dispersion C1-1 was １３ H ２７ - (OC ２ H ４ ) ８ -OCH(CH ３ ) CH ２Each component was added to aqueous dispersion C1-1 so that the content of ammonium laurate (-OH) was 2.7 mass%, the content of ammonium laurate was 560 mass ppm, and the content of triethanolamine lauryl sulfate was 210 mass ppm, to obtain aqueous dispersion C2-1 (corresponding to a specific aqueous dispersion). The pH of aqueous dispersion C2-1 was 2.2. MP62WS (manufactured by Lewatit, anion exchange resin, 623 g) was added to aqueous dispersion C2-1 and stirred for 60 minutes, and then filtered to separate the aqueous dispersion and the ion exchange resin, to obtain aqueous dispersion C3-1 (corresponding to a purified specific aqueous dispersion). The pH of aqueous dispersion C3-1 was 3.7. The components were added to aqueous dispersion C3-1 so that the content of nonionic surfactant (a) was 4.0 mass%, the content of ammonium laurate was 1680 mass ppm, and the content of triethanolamine lauryl sulfate was 630 mass ppm relative to the mass of PTFE particles in aqueous dispersion C3-1, and then the mixture was concentrated by electrophoresis. The supernatant was removed to obtain aqueous dispersion C4-1. In aqueous dispersion C4-1, the concentration (content) of PTFE particles was 65.9 mass%, and the concentration of nonionic surfactant (a) was 2.46 mass% relative to the mass of PTFE particles. The content of polyethylene oxide relative to the mass of PTFE particles in this aqueous dispersion C4-1 was 0.1 mass%, the content of nonionic surfactant (a) was 2.2 mass%, and the content of nonionic surfactant (b) (Newcol FAA-09601, manufactured by Nippon Nyukazai Co., Ltd.) was 0.1 mass%. １３ H ２７ -OCH ２ CH(C ２ H ５ ) O(C ２ H ４ O) ８ H) content was 1.3 mass %, and nonionic surfactant (c) (Newcol G1301-H, manufactured by Nippon Nyukazai Co., Ltd.) １３ H ２７ -OCH ２ CH(C ２ H ５ ) O(C ２ H ４ O) １２Each component was added to aqueous dispersion C4-1 so that the content of surfactant H) was 1.3% by mass, and water and aqueous ammonia were also added to obtain PTFE aqueous dispersion C5-1 (corresponding to the present aqueous dispersion). PTFE aqueous dispersion C5-1 had a PTFE particle concentration (content) of 60.6% by mass, a surfactant concentration (total content) of 5.1% by mass relative to the mass of the PTFE particles, and a pH of 10.4. The average primary particle size of the PTFE particles in aqueous dispersion C5-1 was the same as the average primary particle size of the PTFE particles in aqueous dispersion C1-1. The obtained PTFE aqueous dispersion C5-1 was used to carry out the above-mentioned measurements and evaluations. The results are shown in Table 1. The PTFE aqueous dispersion C5-1 did not substantially contain a fluoropolymer having an ionic functional group.

[0142] [Example 2] Aqueous dispersion C1-2 (corresponding to the second aqueous dispersion) was obtained in the same manner as the production method of aqueous dispersion C1-1 in Example 1, except that a disuccinic acid peroxide aqueous solution (0.45% by mass, 25 ml) was used instead of the APS aqueous solution, and HQ was not added during the reaction. Aqueous dispersion C1-2 was a dispersion in which PTFE particles (average primary particle diameter 205 nm) containing fluoropolymer A1 and fluoropolymer A3 were dispersed in an aqueous medium, and had a solids concentration of 19.6% by mass. A portion of the obtained aqueous dispersion C1-2 was adjusted to 20°C and stirred to aggregate the PTFE particles, thereby obtaining a PTFE powder. Next, this PTFE powder was dried at 200°C. The obtained PTFE powder had an SSG of 2.20 and a melting point of 340°C. Furthermore, no by-product fluorine oligomers were confirmed in the obtained PTFE powder.

[0143] Using the aqueous dispersion C1-2, a nonionic surfactant (d) (Tergitol TMN100X, manufactured by DOW Corporation) was used in place of the nonionic surfactant (a). １２ H ２５ - (OC ２ H ４ ) １０Aqueous dispersion C4-2 was obtained following the same procedures as aqueous dispersions C2-1 to C4-1 in Example 1, except that a polyethylene oxide (PEG-14-1) containing 0.1% by mass of polyethylene oxide and a nonionic surfactant (d) containing 4.8% by mass of nonionic surfactant (d) were used. The components were added to aqueous dispersion C4-2 so that the polyethylene oxide content was 0.1% by mass and the nonionic surfactant (d) content was 4.8% by mass relative to the mass of the PTFE particles in this aqueous dispersion C4-2, and water and aqueous ammonia were also added to obtain PTFE aqueous dispersion C5-2 (corresponding to this aqueous dispersion). PTFE aqueous dispersion C5-2 had a PTFE particle concentration (content) of 60.5% by mass, a surfactant concentration (total content) of 5.0% by mass relative to the mass of the PTFE particles, and a pH of 10.0. Furthermore, the average primary particle diameter of the PTFE particles in PTFE aqueous dispersion C5-2 was the same as the average primary particle diameter of the PTFE particles in the above aqueous dispersion C1-2. The above-mentioned measurements and evaluations were carried out using the obtained PTFE aqueous dispersion C5-2. The results are shown in Table 1. Note that the PTFE aqueous dispersion C5-2 did not substantially contain a fluorine-containing polymer having an ionic functional group.

[0144] [Example 3] Ultrapure water (11 L), raw material liquid B1 (48 L), and paraffin wax (1.5 kg) were charged into a 100 L stainless steel pressure reactor equipped with a stirring blade and a baffle, to obtain aqueous dispersion B1-2 (corresponding to the first aqueous dispersion). The content of fluoropolymer A1 was 0.7% by mass relative to the total mass of aqueous dispersion B1-2. The concentration of the fluorine-containing emulsifier was 0 ppm by mass relative to the total mass of fluoropolymer A1 in aqueous dispersion B1-2. The obtained aqueous dispersion B1-2 was heated to 70°C while stirring at 100 rpm. TFE was injected until the pressure in the reactor reached 1.86 MPaG, and a solution obtained by dissolving 3.4 g of disuccinic acid peroxide (concentration 80% by mass, remainder water) in 1 L of warm water was injected into the reactor to initiate polymerization. As the pressure in the reactor decreased with the initiation of polymerization, TFE was added to maintain the pressure constant. When 13 kg of TFE was injected, the reactor was cooled, the polymerization reaction was terminated, and an aqueous dispersion C1-3 was obtained. The aqueous dispersion C1-3 was a dispersion in which PTFE particles (average primary particle diameter 200 nm) containing fluoropolymer A1 and fluoropolymer A4 were dispersed in an aqueous medium, and the solids concentration was 16.7% by mass. A portion of the obtained aqueous dispersion C1-3 was adjusted to 20 ° C and stirred to aggregate the PTFE particles, thereby obtaining a PTFE powder. Next, this PTFE powder was dried at 200 ° C. The obtained PTFE powder had an SSG of 2.14 and a melting point of 343 ° C. Furthermore, no by-product fluorine oligomers were confirmed in the obtained PTFE powder.

[0145] Aqueous dispersion C4-3 was obtained following the same procedure as for aqueous dispersions C2-1 to C4-1 in Example 1, except that aqueous dispersion C1-3 was used. Nonionic surfactant (a) was added to aqueous dispersion C4-5 so that the content of nonionic surfactant (a) relative to the mass of PTFE particles in this aqueous dispersion C4-3 was 14.0 mass%, and water and aqueous ammonia were also added to obtain PTFE aqueous dispersion C5-3 (corresponding to this aqueous dispersion). PTFE aqueous dispersion C5-3 had a PTFE particle concentration (content) of 57.6 mass%, a surfactant concentration (total content) of 14.1 mass% relative to the mass of PTFE particles, and a pH of 10.2. Furthermore, the average primary particle diameter of the PTFE particles in PTFE aqueous dispersion C5-3 was the same as the average primary particle diameter of the PTFE particles in the above aqueous dispersion C1-3. The above-mentioned measurements and evaluations were carried out using the obtained aqueous PTFE dispersion C5-3. The results are shown in Table 1. Note that the aqueous PTFE dispersion C5-3 did not substantially contain a fluorine-containing polymer having an ionic functional group.

[0146] Example 4 Aqueous dispersion C4-3 was obtained according to the procedure of Example 3. Nonionic surfactant (a) was added to aqueous dispersion C4-3 so that the content of nonionic surfactant (a) relative to the mass of PTFE particles in this aqueous dispersion C4-3 was 10.0 mass%, and water and aqueous ammonia were also added to obtain PTFE aqueous dispersion C5-4 (corresponding to this aqueous dispersion). PTFE aqueous dispersion C5-4 had a PTFE particle concentration (content) of 59.0 mass%, a surfactant concentration (total content) of 10.1 mass% relative to the mass of PTFE particles, and a pH of 10.2. The average primary particle diameter of the PTFE particles in PTFE aqueous dispersion C5-4 was the same as the average primary particle diameter of the PTFE particles in the above-mentioned aqueous dispersion C1-3. The obtained PTFE aqueous dispersion C5-4 was used to perform the above-mentioned measurements and evaluations. The results are shown in Table 1. The aqueous PTFE dispersion C5-4 did not substantially contain a fluorine-containing polymer having an ionic functional group.

[0147] [Example 5] A PTFE aqueous dispersion produced according to Example 1 of WO2021 / 085470 was designated PTFE aqueous dispersion C5-5. The PTFE aqueous dispersion C5-5 is a dispersion in which PTFE particles are dispersed in an aqueous medium, and does not contain a fluoropolymer corresponding to the first fluoropolymer described above. The obtained PTFE aqueous dispersion C5-5 was used to carry out the above-mentioned measurements and evaluations. The results are shown in Table 1.

[0148] [Example 6] A 100 L stainless steel pressure reactor equipped with a stirring blade and a baffle was charged with ultrapure water (60 L), CF ２ = CFOCF ２ CF ２ CF ２ CO ２ A homopolymer of H (weight average molecular weight 4500, 18 g) and paraffin wax (1.5 kg) were charged and heated to 75 ° C. while stirring at 100 rpm. TFE was injected until the pressure in the reactor reached 1.86 MPaG, and a solution of 1.08 g of APS and 106 g of disuccinic acid peroxide (concentration 80%, remaining water) dissolved in 1 L of warm water was injected into the reactor to initiate polymerization. Since the pressure in the reactor decreased with the start of polymerization, TFE was added to maintain the pressure constant. When 9 kg of TFE had been injected, the reactor was cooled, the polymerization reaction was terminated, and an aqueous dispersion C1-6 was obtained. The aqueous dispersion C1-6 was a dispersion in which PTFE particles (average primary particle size 200 nm) were dispersed in an aqueous medium, and the solids concentration was 12.1% by mass. A portion of the obtained aqueous dispersion C1-6 was adjusted to 20°C and stirred to aggregate the PTFE particles, thereby obtaining a PTFE powder. This PTFE powder was then dried at 200°C. The obtained PTFE powder had an SSG of 2.18 and a melting point of 337°C.

[0149] A PTFE aqueous dispersion C5-6 was obtained according to the same procedures as for the aqueous dispersions C2-1 to C4-1 and the PTFE aqueous dispersion C5-1 in Example 1, except that the aqueous dispersion C1-6 was used. The PTFE aqueous dispersion C5-6 had a PTFE particle concentration (content) of 60.8% by mass, a surfactant concentration (total content) of 5.0% by mass relative to the mass of the PTFE particles, and a pH of 10.0. The average primary particle size of the PTFE particles in the PTFE aqueous dispersion C5-6 was the same as that of the aqueous dispersion C1-6. The PTFE aqueous dispersion C5-6 did not contain a fluoropolymer corresponding to the first fluoropolymer described above. The obtained PTFE aqueous dispersion C5-6 was used to carry out the above-mentioned measurements and evaluations. The results are shown in Table 1.

[0150] [Production of Raw Material Solution A5] 320 kg of deionized water was charged into a 430 L stainless steel autoclave equipped with a baffle and a stirrer. The autoclave was then purged with nitrogen, reduced pressure, and 6010 g of PMVE (perfluoromethyl vinyl ether) was charged. The temperature was raised to 90 ° C. with stirring, and 985 g of TFE was charged and pressurized to 1.36 MPa. 1000 g of an 8.09 wt % aqueous solution of APS was injected to initiate polymerization. Polymerization was also allowed to proceed while adding TFE to maintain the autoclave internal pressure at 1.36 MPa. The polymerization reaction was terminated when the amount of TFE added after the start of polymerization reached 1200 g. The autoclave was cooled, and the TFE in the autoclave was released into the atmosphere. Nitrogen was injected to 0.2 MPa, and the temperature was raised to 90 ° C. The autoclave was heated for 3 hours, cooled, and reaction solution A5 was extracted. The reaction liquid A5 was freeze-coagulated and then filtered. The resulting fluoropolymer A5 was analyzed by NMR, and as a result, it was found that the ratio of TFE units to PMVE units was 52 / 48 (molar ratio) and that Tg was -5°C.

[0151] [Production of Raw Material Solution B2] Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 20 g) was added to raw material solution A5 (X g). 60 minutes after the start of stirring, the raw material solution and the ion exchange resin were separated by filtration. SA10AOH (manufactured by Mitsubishi Chemical Corporation, anion exchange resin, 20 g) was added to the filtered raw material solution. 60 minutes after the start of stirring, the raw material solution and the ion exchange resin were separated by filtration to obtain raw material solution B2. The content of fluoropolymer A5 was 0.7 mass% based on the total mass of raw material solution B2.

[0152] [Example 7] Ultrapure water (6.6 L), raw material liquid B2 (52 L), and paraffin wax (1.5 kg) were charged into a 100 L stainless steel pressure reactor equipped with a stirring blade and a baffle, to obtain aqueous dispersion B1-7 (corresponding to the first aqueous dispersion). The content of fluoropolymer A5 was 0.6 mass% relative to the total mass of aqueous dispersion B1-7. The concentration of the fluorine-containing emulsifier was 0 mass ppm relative to the total mass of fluoropolymer A1 in aqueous dispersion B1-7. The obtained aqueous dispersion B1-7 was heated to 65°C while stirring at 95 rpm. TFE was injected until the pressure in the reactor reached 1.40 MPaG, and a solution obtained by dissolving 7.0 g of disuccinic acid peroxide (concentration 80 mass%, remainder water) in 1 L of warm water was injected into the reactor to initiate polymerization. As the pressure in the reactor decreased with the initiation of polymerization, TFE was added to maintain the pressure constant. When 15.8 kg of TFE was injected, the reactor was cooled, the polymerization reaction was terminated, and an aqueous dispersion C1-7 was obtained. The aqueous dispersion C1-7 was a dispersion in which PTFE particles (average primary particle diameter 172 nm) containing fluoropolymer A5 and fluoropolymer A6 were dispersed in an aqueous medium, and the solids concentration was 20.3% by mass. A portion of the obtained aqueous dispersion C1-7 was adjusted to 20 ° C and stirred to aggregate the PTFE particles, thereby obtaining a PTFE powder. Next, this PTFE powder was dried at 200 ° C. The obtained PTFE powder had an SSG of 2.15 and a melting point of 343 ° C. Furthermore, no by-product fluorine oligomers were confirmed in the obtained PTFE powder. The content of nonionic surfactant (a) relative to the mass of the PTFE particles in the aqueous dispersion C1-7 was added to the aqueous dispersion C1-7 so as to be 2.7% by mass, to obtain aqueous dispersion C2-7 (corresponding to a specific aqueous dispersion). The pH of the aqueous dispersion C2-7 was 3.0. SA10AOH (manufactured by Lewatit, anion exchange resin, 623 g) was added to the aqueous dispersion C2-7 and stirred for 60 minutes, and then filtered to separate the aqueous dispersion and the ion exchange resin, to obtain aqueous dispersion C3-7 (corresponding to a purified specific aqueous dispersion). The pH of the aqueous dispersion C3-7 was 3.7.The components were added to aqueous dispersion C3-7 so that the content of nonionic surfactant (a) was 10% by mass, the content of ammonium laurate was 1680 ppm by mass, and the content of triethanolamine lauryl sulfate was 630 ppm by mass relative to the mass of PTFE particles in aqueous dispersion C3-7, and then concentrated by electrophoresis. The supernatant was removed to obtain aqueous dispersion C4-7. In aqueous dispersion C4-7, the concentration (content) of PTFE particles was 66.0% by mass, and the concentration of nonionic surfactant (a) was 3.47% by mass relative to the mass of PTFE particles. This aqueous dispersion C4-7 was added to aqueous dispersion C4-7 so that the content of nonionic surfactant (a) was 10.0% by mass relative to the mass of PTFE particles in this aqueous dispersion C4-7, and water and aqueous ammonia were also added to obtain PTFE aqueous dispersion C5-7 (corresponding to this aqueous dispersion). The PTFE aqueous dispersion C5-7 had a PTFE particle concentration (content) of 60.9% by mass, a surfactant concentration (total content) of 10.0% by mass relative to the mass of the PTFE particles, and a pH of 10.3. The average primary particle size of the PTFE particles in the aqueous dispersion C5-7 was the same as the average primary particle size of the PTFE particles in the aqueous dispersion C1-7. The above-mentioned measurements and evaluations were carried out using the obtained PTFE aqueous dispersion C5-7. The results are shown in Table 1. The PTFE aqueous dispersion C5-7 did not substantially contain a fluorine-containing polymer having an ionic functional group.

[0153] Example 8 Aqueous dispersion C4-7 was obtained according to the procedure of Example 7. Nonionic surfactant (a) was added to aqueous dispersion C4-7 so that the content of nonionic surfactant (a) relative to the mass of PTFE particles in this aqueous dispersion C4-7 was 14.0 mass%, and water and aqueous ammonia were also added to obtain PTFE aqueous dispersion C5-8 (corresponding to this aqueous dispersion). PTFE aqueous dispersion C5-8 had a PTFE particle concentration (content) of 60.5 mass%, a surfactant concentration (total content) of 14.0 mass% relative to the mass of PTFE particles, and a pH of 10.4. Furthermore, the average primary particle diameter of the PTFE particles in PTFE aqueous dispersion C5-8 was the same as the average primary particle diameter of the PTFE particles in the above-mentioned aqueous dispersion C1-7. The obtained PTFE aqueous dispersion C5-8 was used to perform the above-mentioned measurements and evaluations. The results are shown in Table 1. The aqueous PTFE dispersion C5-8 did not substantially contain a fluorine-containing polymer having an ionic functional group.

[0154] [Production of Raw Material Solution A7] Ultrapure water (33.0 kg) and 1.66 g of a 50 mass% aqueous solution of sodium 2-acrylamido-2-methyl-1-propanesulfonate (hereinafter also referred to as "NaAAMPS") were charged into a 50 L stainless steel pressure reactor equipped with a stirring blade and a baffle, and then PMVE (2.44 kg) was charged and the temperature was raised to 90 °C while stirring at 170 rpm. TFE was injected until the pressure in the reactor reached 1.49 MPaG, and an aqueous solution of ammonium persulfate (APS) (21.07 mass%, 400 g) was added to initiate the reaction. As the reaction began, the pressure in the reactor decreased, so TFE was added to maintain the pressure constant. When 1200 g of TFE had been injected, the rotation speed was changed to 40 rpm, and the reactor was cooled to terminate the polymerization reaction. After recovering the gas remaining in the reactor, nitrogen was injected up to 0.10 MPaG while stirring at 20 rpm, and the temperature was raised to 90°C. The reactor was heated for 3 hours, then cooled, and the liquid was withdrawn. This liquid was designated as raw material liquid A7. Raw material liquid A was freeze-coagulated and then filtered. The obtained fluoropolymer A7 was analyzed by NMR, and the results showed that the TFE unit / PMVE unit ratio was 68 / 37 (molar ratio) and the Tg was -5.5°C. [Production of raw material liquid B3] Raw material liquid B3 was obtained according to the procedure for raw material liquid B2, except that raw material liquid A7 was diluted 5 times. The content of fluoropolymer A7 was 1.1% by mass based on the total mass of raw material liquid B3.

[0155] [Example 9] Ultrapure water (26.6 L), raw material liquid B3 (32.1 L), and paraffin wax (1.5 kg) were charged into a 100 L stainless steel pressure reactor equipped with a stirring blade and a baffle, to obtain aqueous dispersion B1-9 (corresponding to the first aqueous dispersion). The content of fluoropolymer A7 was 0.6 mass% relative to the total mass of aqueous dispersion B1-9. The concentration of the fluorine-containing emulsifier was 0 ppm by mass relative to the total mass of fluoropolymer A7 in aqueous dispersion B1-9. The obtained aqueous dispersion B1-9 was heated to 65°C while stirring at 95 rpm. TFE was injected until the pressure in the reactor reached 1.40 MPaG, and a solution obtained by dissolving 7.0 g of disuccinic acid peroxide (concentration 80 mass%, remainder water) in 1 L of warm water was injected into the reactor to initiate polymerization. As the polymerization began, the pressure inside the reactor decreased, so TFE was added to maintain the pressure constant. When 15.8 kg of TFE had been injected, the reactor was cooled, the polymerization reaction was terminated, and aqueous dispersion C1-9 was obtained. Aqueous dispersion C1-9 was a dispersion in which PTFE particles (average primary particle diameter 156 nm) containing fluoropolymer A7 and fluoropolymer A8 were dispersed in an aqueous medium, and the solids concentration was 20.5% by volume. A portion of the obtained aqueous dispersion C1-9 was adjusted to 20°C and stirred to aggregate the PTFE particles, thereby obtaining a PTFE powder. Next, this PTFE powder was dried at 200°C. The obtained PTFE powder had an SSG of 2.15 and a melting point of 343°C. Furthermore, no by-product fluorine oligomers were confirmed in the obtained PTFE powder. Following the procedure of Example 7, aqueous dispersion C4-9 was obtained. In aqueous dispersion C4-9, the concentration (content) of PTFE particles was 65.3% by mass, and the concentration of nonionic surfactant (a) was 3.59% by mass relative to the mass of the PTFE particles. The nonionic surfactant (a) was added to aqueous dispersion C4-9 so that the content relative to the mass of the PTFE particles in this aqueous dispersion C4-9 was 14.0% by mass, and water and aqueous ammonia were also added to obtain PTFE aqueous dispersion C5-9 (corresponding to the present aqueous dispersion). The PTFE aqueous dispersion C5-9 had a PTFE particle concentration (content) of 60.6% by mass, a surfactant concentration (total content) of 14.0% by mass relative to the mass of the PTFE particles, and a pH of 10.4.The average primary particle size of the PTFE particles in aqueous dispersion C5-9 was the same as the average primary particle size of the PTFE particles in aqueous dispersion C1-9. The above-mentioned measurements and evaluations were carried out using the obtained PTFE aqueous dispersion C5-9. The results are shown in Table 1. The PTFE aqueous dispersion C5-9 did not substantially contain a fluorine-containing polymer having an ionic functional group.

[0156] Example 10 Aqueous dispersion C1-9 was obtained according to the procedure of Example 9. Aqueous dispersion C4-10 was obtained using aqueous dispersion C1-9 according to the same procedure as in Example 9, except that nonionic surfactant (d) was used instead of nonionic surfactant (a). Nonionic surfactant (d) was added to aqueous dispersion C4-10 so that the content of nonionic surfactant (d) relative to the mass of PTFE particles in this aqueous dispersion C4-10 was 14.0 mass%, and water and aqueous ammonia were also added to obtain PTFE aqueous dispersion C5-10 (corresponding to this aqueous dispersion). PTFE aqueous dispersion C5-10 had a PTFE particle concentration (content) of 60.5 mass%, a surfactant concentration (total content) of 14.1 mass% relative to the mass of PTFE particles, and a pH of 10.6. The average primary particle size of the PTFE particles in the PTFE aqueous dispersion C5-10 was the same as that of the PTFE particles in the aqueous dispersion C1-9. The above-mentioned measurements and evaluations were carried out using the obtained PTFE aqueous dispersion C5-10. The results are shown in Table 1. The PTFE aqueous dispersion C5-10 did not substantially contain a fluorine-containing polymer having an ionic functional group.

[0157]

[0158] As shown in Table 1, it was confirmed that the use of the aqueous dispersion of the present invention allowed the formation of a coating film with suppressed coloration (Examples 1 to 4, Examples 7 to 10). The entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2024-056669, filed on March 29, 2024, are incorporated herein by reference as part of the disclosure of the present invention.

Claims

1. The main chain of the polymer has 10 carbon atoms ６ 1. An aqueous dispersion comprising: a first fluorine-containing polymer which contains fluorine atoms and has 1,000 or less ionic functional groups per polymer and a glass transition temperature of 10°C or less; a second fluorine-containing polymer which is polytetrafluoroethylene; a surfactant which contains a nonionic surfactant; and an aqueous medium, wherein the aqueous dispersion is substantially free of any other fluorine-containing polymer having ionic functional groups other than the first fluorine-containing polymer.

2. The aqueous dispersion according to claim 1, wherein the first fluorine-containing polymer has units based on a monomer having a vinyl group optionally substituted with a fluorine atom.

3. The aqueous dispersion according to claim 1, wherein the first fluorine-containing polymer has units based on tetrafluoroethylene.

4. The aqueous dispersion according to claim 1, wherein the total content of said first fluoropolymer and said second fluoropolymer is 10 to 80% by mass based on the total mass of said aqueous dispersion.

5. The aqueous dispersion according to claim 1, wherein the content of said surfactant is 1.1 to 19.8 mass % based on the total mass of said first fluoropolymer and said second fluoropolymer in said aqueous dispersion.

6. The aqueous dispersion according to claim 1, wherein the nonionic surfactant comprises at least one selected from the group consisting of a compound represented by formula (S-1), a compound represented by formula (S-2), and a compound represented by formula (S-3). Ｓ１ -O-L Ｓ１ -H Formula (S-2) R Ｓ２ -C ６ H ４ -O-L Ｓ２ -H Formula (S-3) R Ｓ３ -O-L Ｓ３ -H In the formula (S-1), R Ｓ１ represents an alkyl group having 8 to 18 carbon atoms, and L Ｓ１ represents a polyoxyalkylene chain composed of oxyethylene groups having an average number of added moles of 5 to 20 and oxypropylene groups having an average number of added moles of 0 to 2. In the formula (S-2), R Ｓ２ represents an alkyl group having 4 to 12 carbon atoms, and L Ｓ２ represents a polyoxyethylene chain composed of oxyethylene groups having an average added mole number of 5 to 20. Ｓ３ represents an alkyl group having 8 to 18 carbon atoms, and L Ｓ３ represents a polyoxyalkylene chain composed of oxyethylene groups having an average number of added moles of 5 to 20 and oxybutylene groups having an average number of added moles of 0.1 to 3.

7. Polymer main chain carbon number: 10 ６ a first aqueous dispersion comprising a first fluorine-containing polymer having 1,000 or less ionic functional groups per monomer, a glass transition temperature of 10°C or less, and containing fluorine atoms, and a first aqueous medium, by polymerizing a monomer containing tetrafluoroethylene in the first aqueous dispersion to produce a second fluorine-containing polymer which is polytetrafluoroethylene and is different from the first fluorine-containing polymer, thereby producing a second aqueous dispersion comprising the first fluorine-containing polymer, the second fluorine-containing polymer, and a second aqueous medium; and a second aqueous dispersion comprising the first fluorine-containing polymer, the second fluorine-containing polymer, and a second aqueous medium; and a second aqueous dispersion comprising the first fluorine-containing polymer and a second aqueous medium by adding a surfactant containing a nonionic surfactant to the second aqueous dispersion, wherein the content of the first fluorine-containing polymer is 0.01 to 4.0% by mass relative to the total mass of the first aqueous dispersion before the start of polymerization of the monomers, and the concentration of the fluorine-containing emulsifier is 100 ppm by mass or less relative to the total mass of the first fluorine-containing polymer in the first aqueous dispersion before the start of polymerization of the monomers.

8. A method for producing the aqueous dispersion according to claim 7, comprising the step of contacting the aqueous dispersion with an ion exchange resin.

9. A method for producing a polymer-containing substrate, comprising contacting the aqueous dispersion according to any one of claims 1 to 6 with a substrate made of glass fibers to obtain a polymer-containing substrate.

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