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 the aqueous dispersion, and a polymer-containing substrate. The aqueous dispersion of the present invention is a polymer having a main chain carbon number of 10 6 The polymer composition comprises a first fluorine-containing polymer having 1,000 or less ionic functional groups per polymer and a glass transition temperature of 10°C or less and containing fluorine atoms; a second fluorine-containing polymer which is polytetrafluoroethylene; a surfactant containing a nonionic surfactant; and an aqueous medium, and is a fluorine-containing polymer different from the first fluorine-containing polymer and is substantially free of a fluorine-containing polymer having ionic functional groups.

Description

[Technical Field]

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

[0002] Polytetrafluoroethylene is used in various industrial fields due to its excellent heat resistance, chemical resistance, flame retardancy, weather resistance, and the like. 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 fluoropolymer 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 the polytetrafluoroethylene. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2022 / 191286 Summary of the Invention [Problem to be solved by the invention]

[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 an aqueous dispersion and a polymer-containing substrate. [Means for solving the problem]

[0006] As a result of extensive research, the present inventors have found that the above problems can be solved by the following configuration, and have arrived at the present invention. [1] Polymer main chain carbon number: 10 6 a first fluorine-containing polymer having 1,000 or less ionic functional groups per polymer and a glass transition temperature of 10°C or less, and containing fluorine atoms; a second fluorine-containing polymer which is polytetrafluoroethylene; and a surfactant including a nonionic surfactant; an aqueous medium; An aqueous dispersion that is substantially free of a fluorine-containing polymer having an ionic functional group 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 which may be 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 one of [1] to [3], wherein the total content of the first fluorine-containing polymer and the second fluorine-containing polymer is 10 to 80 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 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 -OL S1 -H Formula (S-2) R S2 -C6H4-OL S2 -H Formula (S-3) R S3 -OL 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 S2 represents a polyoxyethylene chain composed of oxyethylene groups with an average number of added moles of 5 to 20. In the above formula (S-3), R S3 represents an alkyl group having 8 to 18 carbon atoms, and L S3 represents a polyoxyalkylene chain composed of oxyethylene groups with an average number of moles added of 5 to 20 and oxybutylene groups with an average number of moles added of 0.1 to 3. [7] Polymer main chain carbon number: 10 6 a step 1 of polymerizing a monomer containing tetrafluoroethylene in a 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, to produce a second fluorine-containing polymer which is polytetrafluoroethylene and is different from the first fluorine-containing polymer, and producing a second aqueous dispersion containing the first fluorine-containing polymer, the second fluorine-containing polymer, and a second aqueous medium; and step 2 of adding a surfactant containing a nonionic surfactant to the second aqueous dispersion to obtain an aqueous dispersion, before the start of polymerization of the monomers, 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, A method for producing an aqueous dispersion, wherein the concentration of the fluorine-containing emulsifier is 100 ppm by mass or less based on the total mass of the first fluorine-containing polymer in the first aqueous dispersion before the start of polymerization of the monomers. [8] [7] 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 fibers to obtain the polymer-containing substrate. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an aqueous dispersion capable of forming a coating film with suppressed coloration. The present invention also provides a method for producing an aqueous dispersion and a polymer-containing substrate. DETAILED DESCRIPTION OF THE INVENTION

[0008] The terms used in the present invention have the following meanings. A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the upper and lower limits. In the numerical ranges described in 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 a single substance corresponding to the component, or two or more substances may be used in combination. Here, when two or more substances are used in combination for each component, the content of that component refers to the total content of the substances used in combination, unless otherwise specified. As used herein, a combination of two or more preferred embodiments is a more preferred embodiment. The term "unit" refers collectively to an atomic group derived from one molecule of the monomer formed directly by polymerization of the monomer, and an atomic group obtained by chemically converting a part of the atomic group. Hereinafter, a "unit based on a monomer" will also be 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 a main chain carbon number of 10 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, and the second fluoropolymer is 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 exhibits reduced coloration. Although the details of the reason for this are not clear, it is presumed that the following reasons are the main cause. When a fluoropolymer having an ionic functional group is used, the fluoropolymer having an ionic functional group remains in the aqueous dispersion. When the aqueous dispersion containing the residue is applied to a substrate, dried, and baked, the residue decomposes upon heating and becomes discolored. It is presumed that this problem is solved by the fact that the present aqueous dispersion is substantially free of a fluorine-containing polymer having an ionic functional group, and therefore coloration of the coating film formed using this dispersion is suppressed.

[0011] [First fluoropolymer] The first fluorine-containing polymer has 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 106 The number of ionic functional groups per unit is preferably at least 1. When the amount of ionic functional groups is within this range, production stability during production of the second fluorine-containing polymer is improved. Polymer main chain carbon number: 10 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 group include a cationic functional group and an anionic functional group. Specific examples of the ionic functional group include a carboxylic acid group (-COO - ), sulfonic acid group (-SO3 - ), sulfate group (-SO4 2- ), phosphonic acid group (-PO3 2- ) and phosphate group (-PO4 3- ) and other anionic functional groups.

[0012] The first fluorine-containing polymer has a Tg of 10°C or lower. When a second fluoropolymer is produced using the first 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 efficiently adsorbing a monomer containing tetrafluoroethylene 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 the detailed measurement conditions are as described in the Examples section below. As a method for adjusting the Tg of the first fluoropolymer within the above range, for example, a method of adjusting the type and amount of the monomer used in producing the first fluoropolymer can be mentioned.

[0013] In view of achieving 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"). The PAVE is preferably a monomer represented by formula (1) from the viewpoint of excellent polymerization reactivity in producing the first fluoropolymer and of enabling more efficient production of the second fluoropolymer. CF2=CF-OR f1 (1) In formula (1), R f1 represents a perfluoroalkyl group having 1 to 10 carbon atoms. f1 The number of carbon atoms in the alkyl group is preferably 1 to 8, more preferably 1 to 6, still more preferably 1 to 5, and particularly preferably 1 to 3, in terms of better polymerization reactivity. 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 fluorine-containing polymer.

[0016] When the first fluorine-containing polymer has units based on a monomer having a vinyl group which may be substituted with a fluorine atom, the content of the units based on a monomer having a vinyl group which may be substituted with a fluorine atom is preferably from 20 to 60 mol%, more preferably from 25 to 60 mol%, and even 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 achieving better effects of the present invention. When the first fluorine-containing polymer has TFE units, the content of TFE units is preferably from 30 to 90 mol %, more preferably from 40 to 80 mol %, and even more preferably from 45 to 70 mol %, based on all units of the first fluorine-containing polymer.

[0018] The first fluorine-containing polymer preferably contains TFE units and PAVE units, since this makes it easier to adjust the Tg within the above range and the effects of the present invention are more excellent. When the first fluorine-containing polymer contains TFE units and PAVE units, the amount of PAVE units in the first fluorine-containing polymer relative to the total amount of TFE units and PAVE units is preferably 20 to 60 mol%, more preferably 25 to 60 mol%, and even more preferably 30 to 55 mol%, from the viewpoints of easily adjusting Tg within the above range and of more efficiently producing the second fluorine-containing polymer. 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 amount used is the same.

[0019] The first fluorine-containing polymer may contain units based on monomers other than the above-mentioned monomers, but in producing a second fluorine-containing polymer using the first fluorine-containing polymer, it is preferable that the first fluorine-containing polymer is substantially free of units based on other monomers, since this enables the second fluorine-containing polymer to be produced more efficiently. Substantially free of units derived from other monomers means that the content of units derived from 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 another monomer are contained, the other monomer is preferably hexafluoropropylene.

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

[0021] [Second fluoropolymer] The second fluoropolymer, PTFE, may be a homopolymer of TFE or a modified PTFE. The second fluoropolymer is a fluoropolymer different from the first fluoropolymer. 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 modifying monomer copolymerizable with the TFE units (hereinafter also referred to as "modifying monomer units"). The content of the modifying 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 %, based on the total units of the modified PTFE. The modified monomer unit means a portion of the molecular structure of the modified PTFE that is derived from the modified monomer, and the entire unit of the modified PTFE means portions derived from all monomers in the molecular structure of the modified PTFE. The content of the modified monomer unit can be determined by a known method such as Fourier transform infrared spectroscopy (FT-IR). The modifying monomer may be any monomer that can be copolymerized with TFE, and examples thereof include perfluoroolefins such as hexafluoropropylene; chlorofluoroolefins such as chlorotrifluoroethylene; hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride; perfluorovinyl ethers; perfluoroalkylethylenes; and ethylene. The modifying monomer may be used alone or in combination of two or more kinds.

[0023] The content of the second fluorine-containing polymer is preferably 10 to 80 mass%, more preferably 20 to 75 mass%, and even more preferably 25 to 70 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 made 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 particles is determined by measuring the particle size distribution using a laser diffraction / scattering method, calculating a cumulative curve with the total volume of the particle group as 100%, and determining the particle size at the point on the cumulative curve where the cumulative volume is 50%. 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, since this provides 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 "another 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 surfactants> In order to further improve the stability of the aqueous dispersion, it is preferable that the nonionic surfactant 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 -OL S1 -H Formula (S-2) R S2 -C6H4-OL S2 -H Formula (S-3) R S3 -OL 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 may be linear or branched. R S1 The alkyl group has 8 to 18 carbon atoms, 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 aqueous dispersion is low and the penetration 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 aqueous dispersion is left to stand for a long period of time, and the storage stability is excellent. L S1represents 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 preferable.

[0031] In the above formula (S-2), R S2 represents an alkyl group having 4 to 12 carbon atoms. S2 The alkyl group in may be linear or branched. R S2 The number of carbon atoms in the alkyl group 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 fluorine-containing polymer 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. L S2 represents a polyoxyethylene chain composed of oxyethylene groups with an average number of added moles 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 may be linear or branched. R S3 The alkyl group has 8 to 18 carbon atoms, 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 aqueous PTFE dispersion is low, and the permeability and wettability are excellent. When the alkyl group has 18 or less carbon atoms, the second fluorine-containing polymer particles 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. L S3represents 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 Tergitol (registered trademark) 15S series manufactured by Dow and Lionol (registered trademark) TD series manufactured by Lion Corporation. The compound represented by formula (S-2) is, for example, CH 17 -C6H4-O-(C2H4O) 10 -H, C9H 19 -C6H4-O-(C2H4O) 10 -H. Commercially available products include the Triton (registered trademark) X series manufactured by Dow and the Nikkor (registered trademark) OP series or NP series manufactured by Nikko Chemical Co., Ltd. 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 H 27 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 Examples include 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. Note that a 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, and each 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, based on the total surfactant content 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] The aqueous medium may be water or a mixture of water and a water-soluble organic solvent, such as tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, or tripropylene glycol. The aqueous medium contained in the present 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 ingredients] The aqueous dispersion may contain other components in addition to those described above. Specific examples of other components that may be contained in the aqueous dispersion 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 mass %, more preferably 0.01 to 1.8 mass %, and even more preferably 0.01 to 1.5 mass %, relative to the total mass of the present aqueous dispersion.

[0042] [Fluoropolymer having ionic functional group] The present aqueous dispersion does not substantially contain any 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 formulas (AI) to (A-VII) is used, the fluorine-containing polymer having the 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 (AI) CF2=CF-(CF2) a1 -Y (AI) a fluorine-containing compound (AI) having a vinyl group, represented by the formula: [wherein a1 represents an integer of 1 to 10, Y represents -SO3M or -COOM, and M represents H, NH4 or an alkali metal]; General formula (A-II) CF2=CF-(CF2C(CF3)F) b1 -Y (A-II) [wherein b1 represents an integer of 1 to 5, Y represents -SO3M or -COOM, and M represents H, NH4 or an alkali metal], General formula (A-III) CF2=CFO-(CFX) c1 -Y a fluorine-containing compound (A-III) having a vinyl group, represented by the formula: [wherein X represents -F or -CF3, c1 represents an integer of 1 to 10, Y represents -SO3M or -COOM, and M represents H, NH4, or an alkali metal]; General formula (A-IV) CF2=CFO-(CF2CFXO) d1 -(CF2) e1 -Y (A-IV) a fluorine-containing vinyl group-containing compound (A-IV) represented by the formula: [wherein X represents -F or -CF3, d1 represents an integer of 1 to 10, e1 represents an integer of 1 to 3, Y represents -SO3M or -COOM, and M represents H, NH4, or an alkali metal]; General formula (AV) CH2=CFCF2O-(CF(CF3)CF2O) f1 -CF(CF3)-Y (AV) a fluorine-containing compound (AV) having a vinyl group, represented by the formula: [wherein f1 represents an integer of 0 to 10, Y represents -SO3M or -COOM, and M represents H, NH4 or an alkali metal]; General formula (A-VI) CF2=CFCF2O-(CF(CF3)CF2O) g1 -CF(CF3)-Y (A-VI) [wherein g1 represents an integer of 1 to 10, Y represents -SO3M or -COOM, and M represents H, NH4 or an alkali metal], and / or General formula (A-VII) CF2=CF-(OZ)-Y (A-VII) A fluorine-containing compound (A-VII) having a vinyl group, represented by the formula: wherein Z represents a perfluoroalkylene group having 1 to 6 carbon atoms, Y represents -SO3M or -COOM, and M represents H, NH4 or an alkali metal. "Substantially free of fluorine-containing polymers having ionic functional groups" means that the content of fluorine-containing polymers having ionic functional groups is 0.01% by mass or less, and may be 0% by mass, relative to 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 from 3 to 400 mPa·s, and more preferably from 5 to 100 mPa·s. The methods for measuring pH, surface tension, and viscosity are as described in the Examples section below.

[0044] [Method of producing aqueous dispersion] The method for producing the aqueous dispersion of the present invention (hereinafter also referred to as "the present production method") includes the steps of: Polymer main chain carbon number: 10 6 a step 1 of polymerizing a monomer containing tetrafluoroethylene (hereinafter also referred to as "specific monomer") in a first aqueous dispersion containing a first fluorine-containing polymer having 1,000 or less ionic functional groups per polymer and a glass transition temperature of 10°C or less and containing fluorine atoms, and a first aqueous medium, to produce a second fluorine-containing polymer which is polytetrafluoroethylene and is different from the first fluorine-containing polymer, and to produce a second aqueous dispersion containing the first fluorine-containing polymer, the second fluorine-containing polymer, and a second aqueous medium; and step 2 of 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 the start of polymerization of the monomers, 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 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. Furthermore, 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, and 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 fluorine-containing polymer, compound (2) may be used in addition to the monomer represented by the above formula (1).

[0046] <Compound (2)> The compound (2) is a compound represented by the following formula (2). CX 1 X 2 =CX 3 -LZ …(2) In formula (2), X 1 and X 2 are each independently a hydrogen atom or an alkyl group, X 3 is a hydrogen atom, a fluorine atom, or an alkyl group, L is a single bond or a divalent linking group, Z is -SO3M 1 , -OSO3M 1 , -P(=O)(OM 1 )2, -OP(=O)(OM 1 )2, or -COOM 1 and M 1 is 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 M11Any 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 are preferably all hydrogen atoms, from the viewpoint of increasing the number of particles of the first polymer. In formula (2), X 3 is a hydrogen atom, a fluorine atom, or an alkyl group. Specific examples and preferred embodiments of the alkyl group are: X 1 and X 2 The specific examples and preferred embodiments of the alkyl group are the same as those in the above. 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-, -SiH2-, a phenylene group, -CF2-, and a group combining two or more of these. Examples of the group 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, preferably linear or branched, and more preferably branched. The alkylene group may have 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms.

[0049] Specific examples of L include a single bond, an alkylene group, an ether bond, an ester bond, and 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 preferred, where * 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 -SO3M 1 , -OSO3M 1 , -P(=O)(OM 1 )2, -OP(=O)(OM 1 )2 or -COOM 1 is. As Z, from the viewpoint of stabilizing the dispersion and increasing the number of particles of the first polymer, -SO3M 1 and -COOM 1 is preferred, -SO3Na and -COONa are more preferred, and -SO3Na is even more preferred.

[0051] M 1 is 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. M 1 The metal atom represented by the formula (I) is preferably a metal atom of Group 1, and more preferably Li, Na, or K. R M11 and R M12 The substituent represented by the formula (I) is preferably a monovalent organic group, more preferably a monovalent hydrocarbon group, and further 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 either monocyclic or polycyclic, and is preferably a phenyl group.

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

[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-propanesulfonic acid, N-tigloylglycine, 6-acrylamidohexanoic acid, 1,1-difluoro-2-methyl-2-[(1-oxo-2-propen-1-yl)amino]-1-propanesulfonic acid, 3-methyl-3-[(2-methyl-1-oxo-2-propen-1-yl)amino]-2-butanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, 2,3-dimethyl-3-[(1-oxo-2-propen-1-yl)amino]-2-butanesulfonic acid, and metal salts thereof. The metal salts include M 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, a phosphonic acid group, or a carboxy group, allyl compounds having a sulfonic acid group, a phosphonic acid group, or a carboxy group, (meth)acrylic acid, (meth)acrylamides having a sulfonic acid group, a phosphonic acid group, or a 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 this production method, it is possible to provide an aqueous dispersion that can form a coating film with reduced coloration. This production method is suitable for producing the above-mentioned aqueous dispersion.

[0056] [Process 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 fluoropolymer can be produced efficiently without the need for an emulsifier, while using an aqueous medium with a small environmental impact. The reason for this is presumably that the use of the first aqueous dispersion containing a predetermined amount of the first fluoropolymer allows the first fluoropolymer to function as a good polymerization site for the second fluoropolymer.

[0057] From the viewpoint of suppressing a decrease in the molecular weight of the fluoropolymer, step 1 is preferably carried out under conditions in which a fluorine-containing emulsifier (an emulsifier having a fluorine atom) and an emulsifier not having a fluorine atom are substantially absent. In other words, it is preferable that the aqueous dispersion does not substantially contain a fluorine-containing emulsifier and an emulsifier not having a fluorine atom. Being substantially free of fluorine-based emulsifiers and emulsifiers not having fluorine atoms (hereinafter also 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 method described in paragraphs

[0721] to

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

[0058] Examples of fluorine-based emulsifiers and emulsifiers that do not contain fluorine atoms include water-soluble emulsifiers. A water-soluble emulsifier refers to an emulsifier that has a solubility of 100 mg or more in 1000 g of water at 25°C, and a water-insoluble emulsifier refers to an emulsifier other than the water-soluble emulsifiers described above. The water-soluble emulsifier may be either ionic or nonionic. Fluorine-based emulsifiers and emulsifiers that do not have fluorine atoms include those that do not have a carbon-carbon double bond. It should be noted 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 includes anionic fluorine-containing emulsifiers. Examples of the anionic fluorine-containing emulsifier include emulsifiers containing fluorine atoms whose total carbon number excluding the anionic group is 20 or less, and emulsifiers containing fluorine atoms whose anionic moiety has a molecular weight of 800 or less. The "anionic moiety" means 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 substitute a 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 portion 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 portion. Specific examples of anionic hydrocarbon emulsifiers include sodium dodecyl sulfate, a highly branched C10 tertiary carboxylic acid supplied by Resolution Performance Products as Versatic® 10, sodium linear alkyl polyether sulfonates supplied by BASF as the Avanel® S series, and the sulfosuccinate emulsifier Lankropol® K8300 available from AkzoNobel Surface Chemistry LLC.

[0063] A nonionic hydrocarbon emulsifier is an emulsifier that exhibits surface activity in water without dissociating into ions and has a hydrocarbon group such as an alkyl group as the hydrophobic portion. The hydrophilic portion of the nonionic hydrocarbon emulsifier includes a water-soluble functional group such as a polyethylene oxide chain 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] The fluorine-based emulsifier and the emulsifier not containing a fluorine atom may contain a silicon atom. Examples of the emulsifier containing a silicon atom include a siloxane emulsifier. The siloxane emulsifier is a hydrocarbon-containing emulsifier having a siloxane skeleton. Siloxane emulsifiers include those described in US Pat. Nos. 6,841,616 (Wille et al.) and 7,977,438 (Brothers et al.).

[0066] The fluorine-based emulsifier and the emulsifier not having a fluorine atom may be a polymer emulsifier. Examples of the polymer emulsifier include a polymer having a hydrophilic group in a side chain. Examples of such a polymer emulsifier include a polymer containing a unit based on a compound having a site capable of polymerization reaction and a hydrophilic group. Further, even if the polymer does not originally have a hydrophilic group, a polymer containing a unit based on a compound having a group that can become a hydrophilic group may be subjected to post-treatment such as hydrolysis. When polymerization is carried out in the presence of an emulsifier having no fluorine atoms, typically 0.1 to 15 parts by mass of the emulsifier having no fluorine atoms is used per 100 parts by mass of the aqueous medium.

[0067] In the following, first, the materials used in step 1 will be described in detail, and then the procedure for step 1 will be described in detail. <First aqueous dispersion> In step 1, a first aqueous dispersion containing a first fluorine-containing polymer and an aqueous medium is used.

[0068] (First fluoropolymer) 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 fluorinated polymer, the content of compound (2) before the start of polymerization is preferably from 1.0 to 1000 ppm by mass based on the total amount of the aqueous dispersion, and in terms of better effects of the present invention, is more preferably from 1.0 to 800 ppm by mass, still more preferably from 3.0 to 500 ppm by mass, particularly preferably from 5.0 to 300 ppm by mass.

[0069] Before starting 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 more efficient production of the second fluoropolymer, 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 fluorine-containing polymer" 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 concentration of sulfate ions 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 coloration of the second fluoropolymer. The lower limit is 0 ppm by mass. An example of a method for adjusting the sulfate ion concentration to the above range is to remove sulfate ions using an anion exchange resin during production of the first fluorine-containing polymer. Here, the sulfate ions are derived, for example, from the polymerization initiator (particularly ammonium persulfate) used in producing the first fluoropolymer, and may be contained in the first aqueous dispersion containing the first fluoropolymer. It is presumed that by keeping the content of sulfate ions at 10 ppm by mass or less (particularly 5 ppm by mass or less), it is possible to prevent terminal groups with low heat resistance, such as carboxylic acid groups and sulfonic acid groups, from being formed in the second fluoropolymer, thereby preventing 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 is 0 ppm by mass. An example of a method for adjusting the ammonium ion concentration to the above range is to remove ammonium ions using a cation exchange resin during the production of the first fluorinated polymer. Here, the ammonium ions are derived, for example, from the initiator (particularly ammonium persulfate) used in producing the first fluoropolymer, and may be contained in the first aqueous dispersion containing the first fluoropolymer. It is presumed that the ammonium ion content of 20 ppm by mass or less reduces the ionic strength in the aqueous medium, resulting in improved production efficiency of the second fluoropolymer.

[0073] The first fluoropolymer is preferably dispersed in the first aqueous medium in the form of particles, and in this case, the average particle size of the first fluoropolymer 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 fluoropolymer. The average particle size of the first fluoropolymer 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 set to 100%, and measuring the particle size (D50) at the point on the cumulative curve where the cumulative volume is 50%; detailed measurement conditions are as described in the Examples section.

[0074] The method for producing the first fluorine-containing polymer is preferably a method in which a monomer (preferably a monomer mixture containing TFE and PAVE) is polymerized in an aqueous medium in the presence of a polymerization initiator, thereby obtaining the first fluorine-containing polymer dispersed in the aqueous medium in the form of particles. 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 it is, or another aqueous medium may be added thereto and the resulting mixture may be used as the first aqueous dispersion. Alternatively, 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, further 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, making the second fluoropolymer less susceptible to the influence of the polymerization initiator used in producing the first fluoropolymer during polymerization. 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, since this can further promote the deactivation of the polymerization initiator in the aqueous medium.

[0078] (1st 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 fluorine-containing polymer described above. Before starting polymerization of the monomers to be used in polymerization of the second fluorine-containing polymer, the content of the first aqueous medium is preferably from 60 to 99.9 mass%, more preferably from 96 to 99.9 mass%, and even more preferably from 98 to 99.9 mass%, based on the total mass of the first aqueous dispersion.

[0079] (Other ingredients) The first aqueous dispersion used in step 1 may contain other components in addition to the first fluorinated polymer and the aqueous medium. Specific examples of other components that may be contained in the first aqueous dispersion include a chain transfer agent, an emulsifier other than a fluorine-based emulsifier, a pH adjuster, and a wax. Details of the other components are as described above, so further description thereof 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 relative to 100 parts by mass of the aqueous medium, and 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, relative to 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 relative to 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 relative to 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 relative to 100 parts by mass of the aqueous medium.

[0081] Before starting polymerization of the monomers used in polymerization of the second fluoropolymer, the concentration of the fluorine-containing 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 achieving better effects of the present invention, 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 is 0 ppm by mass. The fluorine-containing emulsifier refers to an emulsifier in which the hydrophobic moiety contains a fluorine atom, and specific examples of the fluorine-containing emulsifier include fluorine-containing alkanoates and fluorine-containing ether carboxylic acid compounds. One example of a method for adjusting the concentration of the fluorine-containing emulsifier to fall within the above range is to produce an aqueous dispersion without using a fluorine-containing emulsifier. Before starting 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 relative to 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 or less, and even more preferably 5 ppm by mass or less. The lower limit is 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 ppm by mass or less, more preferably 50 ppm by mass or less, relative to the total mass of the first aqueous dispersion, from the viewpoint of polymerization stability. The lower limit is 0 ppm by mass. An example of a method for adjusting the fluoride ion concentration to the above range is to remove sulfate ions using an anion exchange resin during the production of the first fluorine-containing polymer. Here, the fluoride ions may be generated by the reaction between a polymerization initiator (for example, ammonium persulfate) and a monomer used in producing the first fluorine-containing polymer, and may be contained in the first aqueous dispersion.

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

[0084] The specific monomer may contain a fluorine-containing monomer other than TFE, but may not substantially contain a fluorine-containing monomer other than TFE. "Substantially free of fluorine-containing monomers other than TFE" means that the amount of fluorine-containing monomers other than TFE used is less than 0.0001% by mass, or may be 0% by mass, based on the amount of the specific monomer used. Examples of the fluorine-containing monomer other than TFE include fluorine atom-containing monomers among the monomers exemplified above as the modified monomers. Two or more kinds of the fluorine-containing monomer other than TFE may 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 it is preferable that it 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 the other monomer include the monomers exemplified above as the modified monomers that do not contain a fluorine atom. Two or more of the 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, relative to 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. As the polymerization initiator, an oil-soluble radical initiator, a water-soluble radical initiator, or a water-soluble oxidation-reduction catalyst is preferred. 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"). Preferred water-soluble redox catalysts are combinations of oxidizing agents such as bromic acid or its salts, chloric acid or its salts, persulfuric acid or its salts, permanganic acid or its salts, and hydrogen peroxide with reducing agents such as sulfurous acid or its salts, hydrogen sulfite or its salts, thiosulfuric acid or its salts, organic acids, and inorganic salts. Preferred persulfates are potassium persulfate and ammonium persulfate. Preferred sulfites are sodium sulfite. Examples of inorganic salts include combinations of sulfate anions, sulfite anions, and chloride anions with metal ions. Preferred metal ions are transition metals, including manganese, iron, cobalt, nickel, copper, zinc, cerium, and silver ions, with iron ions being preferred. Preferred inorganic salts are iron(II) sulfate. The polymerization initiator is preferably an oil-soluble radical initiator or a water-soluble radical initiator, more preferably an oil-soluble radical initiator from the viewpoint of more efficient production of the fluorine-containing polymer, and further preferably an oil-soluble organic peroxide. Two or more types of polymerization initiators may be used in combination.

[0088] The amount of the polymerization initiator used is preferably 1 to 1000 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 ingredients> 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 components is a reducing agent. The amount of the other components used is preferably 1 to 2000 ppm relative to 100 parts by mass of the specific monomer used.

[0090] <Step 1 Procedure> 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 from 10 to 95°C, more preferably from 15 to 90°C. The polymerization pressure is preferably from 0.5 to 4.0 MPaG, more preferably from 0.6 to 3.5 MPaG. In the case of batch processing, the polymerization time is preferably from 90 to 1000 minutes, more preferably from 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. "Substantially free of emulsifier" means an environment in which the content of emulsifier is 0.03 mass ppm or less relative to the total mass of the aqueous medium contained in the first aqueous dispersion, preferably 0.02 mass ppm or less, and more preferably 0 mass ppm.

[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 the second fluorine-containing polymer contained in the second aqueous dispersion are respectively similar to the first fluorine-containing polymer and the second fluorine-containing polymer contained in the above-mentioned present aqueous dispersion, including preferred embodiments, and therefore description thereof will be omitted.

[0096] It is presumed that the specific monomer polymerizes within particles of the first fluoropolymer during polymerization of the specific monomer. Therefore, it is considered that particles containing the first fluoropolymer and the second fluoropolymer are produced by carrying out step 1. That is, it is presumed that the second fluoropolymer is obtained in the form of particles containing the first fluoropolymer and the second fluoropolymer by step 1. In this case, a second aqueous dispersion in which particles containing the first fluoropolymer and the second fluoropolymer are dispersed in the aqueous medium is obtained by step 1. 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 and second fluoropolymers is preferably 0.1 to 5.0 mol%, more preferably 0.2 to 3.0 mol%, even more preferably 0.3 to 2.5 mol%. The suitable content is the same whether the PAVE units are PMVE units, PEVE units or PPVE units, or whether a mixture of two or more of these is used. The PAVE unit is preferably contained in the first fluorine-containing polymer.

[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%. The TFE units may be contained in at least the second fluorine-containing polymer, but are preferably contained in both the first and second fluorine-containing polymers.

[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 particles is determined by measuring the particle size distribution using a laser diffraction / scattering method, calculating a cumulative curve with the total volume of the particle group as 100%, and determining the particle size at the point on the cumulative curve 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 fluoropolymer and the second fluoropolymer.

[0105] A compound represented by formula (S1) and a compound represented by formula (S2) 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 relative to the total mass of the first fluorinated polymer and the second fluorinated polymer. The compound represented by formula (S1) and the compound represented by formula (S2) are components that can be generated when TFE is polymerized in the presence of a polymerization initiator, a chain transfer agent, and an emulsifier (particularly, a hydrocarbon-based emulsifier). Therefore, when no emulsifier is used in producing the second aqueous dispersion, the amounts of the compound represented by formula (S1) and the compound represented by formula (S2) generated can be suppressed, making it easy to keep the contents of these compounds within the ranges described below.

[0106] Formula (S1): H-(CF2) n -COOM Formula (S2): H-(CF2) n -SO3M In formula (S1) and formula (S2), M each independently represents a hydrogen atom, Na, K, or NH 4 , and n each independently represents 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 The second aqueous dispersion preferably does not substantially contain an emulsifier. As the emulsifier is as described above, its description will be omitted. The second aqueous dispersion being substantially free of emulsifier means that the content of 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 second aqueous dispersion. The second aqueous dispersion may be heat-treated in step 1. When the heat treatment is carried out, the second aqueous dispersion obtained in step 1 may be heated as it is, or may be heated after adding a radical generator, or may be heated after adjusting the contents of the first fluoropolymer and the second fluoropolymer contained in the second aqueous dispersion by concentration, dilution, etc.

[0109] [Process 2] Step 2 is a step of adding a surfactant including a nonionic surfactant to the second aqueous dispersion to obtain a specific aqueous dispersion. Below, first, the materials used in step 2 will be described in detail, and then the procedure for 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 its description will be omitted.

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

[0112] (nonionic surfactants) The nonionic surfactant used in step 2 is the same as the nonionic surfactant contained in the present aqueous dispersion described above, including preferred embodiments, and therefore a description thereof will be omitted. The amount of the nonionic surfactant used is preferably 0.10 to 5.0% by mass, more preferably 0.15 to 4.0% by mass, and even more preferably 0.20 to 3.5% 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 nonionic surfactant used is 0.1% by mass or more, the dispersion stability of the specific aqueous dispersion is superior. When the amount of the nonionic surfactant used is 5.0% by mass or less, aggregation during the subsequent steps can be suppressed, and production stability is superior. The amount of the nonionic surfactant used 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 amount of the surfactant used in step 2. When the amount of the nonionic surfactant used is 85% by 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 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 anionic surfactants are preferred. The anionic surfactant is similar to the anionic surfactant that can be contained in the present 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] <Step 2 Procedure> In step 2, a surfactant including a nonionic surfactant is added to the second aqueous dispersion to produce a specific aqueous dispersion.

[0117] (Specified aqueous dispersion) By carrying out step 2, a specific aqueous dispersion is obtained which contains a surfactant including 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. The specific aqueous dispersion may contain other components that can be contained in the present aqueous dispersion described above.

[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 a method of mixing the specific aqueous dispersion with the anion exchange resin, and a method of passing the specific aqueous dispersion through a column packed with the anion exchange resin. When the anion exchange resin is brought into contact with the specific aqueous dispersion, the temperature of the specific aqueous dispersion is preferably from 10 to 50°C, more preferably from 15 to 40°C. The contact time between the anion exchange resin and the specific aqueous dispersion is preferably from 10 to 360 minutes, more preferably from 10 to 240 minutes. When the anion exchange resin is brought into contact with the specific aqueous dispersion, the pH of the specific aqueous dispersion is not limited and may be less than 7 or 7 or higher.

[0122] Step 3 preferably includes a treatment in which, after contacting the specific aqueous dispersion with an ion exchange resin, at least one of the nonionic surfactant and the anionic surfactant is added to the purified specific aqueous dispersion. The amount of the nonionic surfactant used in step 3 is preferably from 0.1 to 7.0 mass %, more preferably from 0.2 to 6.5 mass %, based on 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 from 200 to 3,000 mass %, more preferably from 250 to 2,500 mass %, based on 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 a step 4 of concentrating the purified specific aqueous dispersion obtained in the step 3. This results in the present aqueous dispersion described above. The concentration of the second fluorine-containing polymer in the present aqueous dispersion obtained in step 4 is higher than the concentration of the second fluorine-containing polymer 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 adjuster (e.g., polyethylene oxide) to the concentrated purified specific aqueous dispersion. The amount of the nonionic surfactant used in step 4 is preferably from 1.0 to 18 mass %, more preferably from 1.1 to 15 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 ammonia water is preferably from 1 to 40% by mass, more preferably from 5 to 40% by mass, and more preferably from 10 to 35% by mass. The amount of aqueous ammonia used in step 4 is preferably from 0.001 to 1.0 mass %, more preferably from 0.005 to 0.5 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 %, based on 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 containing a nonionic surfactant, a first fluorinated polymer, a second fluorinated polymer, and a second aqueous medium, and may further contain an anionic surfactant. The content of the surfactant is preferably from 1.1 to 19.8 mass%, more preferably from 1.2 to 16.5 mass%, and even more preferably from 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 from 1.0 to 12 mass%, more preferably from 1.1 to 8.0 mass%, and even more preferably from 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 from 0.1 to 7.5 mass %, more preferably from 0.5 to 7.0 mass %, and even more preferably from 0.8 to 6.5 mass %, based on the total mass of the specific aqueous dispersion obtained in step 4. The content of the second fluorine-containing polymer is preferably from 20 to 85 mass %, more preferably from 30 to 80 mass %, and even more preferably from 40 to 75 mass %, based on the total mass of the specific aqueous dispersion obtained in step 4. The content of the second aqueous medium is preferably 15 to 80 mass %, more preferably 20 to 70 mass %, and even more preferably 25 to 60 mass %, based on 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 mass%, more preferably 0.08 to 2.5 mass%, and even more preferably 0.1 to 2.0 mass%, relative to the total mass of the specific aqueous dispersion obtained in step 4.

[0127] [Method of manufacturing 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 fibers (hereinafter also referred to as a "glass fiber substrate"). Examples of the glass fiber substrate include glass fiber woven fabric and string. The method for contacting the present aqueous dispersion with a glass fiber substrate can be a known method, and examples thereof include a method of immersing the glass fiber substrate in the present aqueous dispersion, a method of spraying the present aqueous dispersion, and a method of applying the present aqueous dispersion with a roller or a brush.

Example

[0128] Hereinafter, the present invention will be described in detail with examples. Examples 1 to 4 and Examples 7 to 10 are examples, and Examples 5 to 6 are comparative examples. However, the present invention is not limited to these examples. The compounding amounts of each component in the tables described later are shown on a mass basis.

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

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

[0131] <PTFE Concentration and Surfactant Concentration> Put about 7 g of the PTFE aqueous dispersion into an aluminum dish (mass W0) and weighed it (mass W1). From the mass after drying at 120 °C for hour (mass W2) and the mass after drying at 380 °C for 35 minutes (mass W3), the PTFE concentration and the surfactant concentration (the ratio of the surfactant to the PTFE mass) were determined by the following formula. PTFE Concentration (mass %) = [(W3 - W0) / (W1 - W0)] × 100 Surfactant Concentration (mass % / PTFE) = [(W2 - W3) / (W3 - W0)] × 100

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

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

[0134] <Surface tension> The surface tension of the PTFE aqueous 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 the 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. It was then cooled to -60°C at a rate of 10°C / min. Once the specified temperature was reached, the temperature was again raised to 100°C at 10°C / min. Tg was estimated from the inflection point observed during this second heating operation. Tm was measured using a PerkinElmer DSC8500 that had been temperature-calibrated in advance using indium and zinc standard samples. Specifically, 10 mg of the 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 in an air atmosphere, and the Tm was determined from the endothermic peak.

[0136] <Coloring evaluation> The coating film obtained using the PTFE aqueous dispersion was baked and subjected to coloring evaluation. 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 then baked at 380°C for 35 minutes, and the color of the baked PTFE coating film was visually confirmed and evaluated for coloration 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 dark brown.

[0137] [Production of raw material solution A1] A 50 L stainless steel pressure reactor equipped with a stirring blade and baffles was charged with ultrapure water (33.0 kg) and PMVE (2.28 kg) and heated 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 wt%, 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, and the reactor was cooled to terminate the polymerization reaction. After recovering the remaining gas 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 molar ratio of TFE units / PMVE units was 51 / 49 and that Tg was -5.5°C.

[0138] [Production of raw material solution B1] To raw material liquid A1 (490 g) was added Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 20 g). 60 minutes after starting stirring, the raw material liquid and the ion exchange resin were separated by filtration. To the separated raw material liquid was added SA10AOH (manufactured by Mitsubishi Chemical Corporation, anion exchange resin, 20 g). 60 minutes after starting stirring, the raw material liquid and the ion exchange resin were separated by filtration to obtain raw material liquid B1. The content of fluoropolymer A1 was 0.8 mass% based on the total mass of raw material liquid 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 baffles 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 (solids concentration) of the fluoropolymer A1 in aqueous dispersion B1-1 was determined by heating 2.0 g of aqueous dispersion B at 170°C for 20 minutes, weighing the mass of the residue, and calculating the solids concentration using the following formula. The solids concentration was calculated in the same manner for each example described below, 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) according to the method described in Japanese Patent Application Laid-Open No. 2022-50435. As a result, 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 resulting aqueous dispersion B1-1 was heated to 70°C while stirring at 260 rpm. TFE was injected until the reactor pressure reached 1.40 MPaG, and an APS aqueous solution (0.436 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 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. 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 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 The components were added to aqueous dispersion C1-1 so that the content of -(OC2H4)8-OCH(CH3)CH2-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, thereby obtaining aqueous dispersion C2-1 (corresponding to the specific aqueous dispersion). The pH of aqueous dispersion C2-1 was 2.2. MP62WS (anion exchange resin, manufactured by Lewatit, 623 g) was added to the aqueous dispersion C2-1, and the mixture was stirred for 60 minutes. The aqueous dispersion was then filtered to separate the ion exchange resin, yielding aqueous dispersion C3-1 (corresponding to the purified specific aqueous dispersion). The pH of the 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 the 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 1.0 mass%. 13 H 27 -OCH2CH(C2H5)O(C2H4O)8H) content of 1.3 mass%, nonionic surfactant (c) (Newcol G1301-H, manufactured by Nippon Nyukazai Co., Ltd., C 13 H 27 -OCH2CH(C2H5)O(C2H4O) 12 Each component was added to aqueous dispersion C4-1 so that the content of surfactant H) was 1.3 mass%, and water and aqueous ammonia were also added to obtain PTFE aqueous dispersion C5-1 (corresponding to this aqueous dispersion). PTFE aqueous dispersion C5-1 had a PTFE particle concentration (content) of 60.6 mass%, a surfactant concentration (total content) of 5.1 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 above-mentioned measurements and evaluations were carried out using the obtained PTFE aqueous dispersion C5-1. The results are shown in Table 1. The aqueous PTFE dispersion C5-1 did not substantially contain a fluorine-containing polymer 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 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 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 Co.) was used in place of the nonionic surfactant (a). 12 H 25 -(OC2H4) 10 Aqueous dispersion C4-2 was obtained in the same manner as for aqueous dispersions C2-1 to C4-1 in Example 1, except that a hydroxy group containing 1-methyl-4-hydroxybenzoyl group (—OH) was used instead. 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. The average primary particle size of the PTFE particles in the PTFE aqueous dispersion C5-2 was the same as the average primary particle size 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. The aqueous PTFE 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 baffles to obtain aqueous dispersion B1-2 (corresponding to the first aqueous dispersion). The content of fluoropolymer A1 was 0.7 mass% relative to the total mass of aqueous dispersion B1-2. The concentration of the fluorine-containing emulsifier was 0 mass ppm 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 of 3.4 g of disuccinic acid peroxide (concentration 80% by mass, remainder water) dissolved in 1 L of warm water was injected into the reactor to initiate polymerization. As the polymerization started, the pressure in the reactor decreased, so TFE was added to maintain the pressure constant. When 13 kg of TFE had been injected, the reactor was cooled, the polymerization reaction was terminated, and aqueous dispersion C1-3 was obtained. 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 had a solids concentration of 16.7 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. This PTFE powder was then 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 in the same manner as for aqueous dispersions C2-1 to C4-1 in Example 1, except that aqueous dispersion C1-3 was used. The nonionic surfactant (a) was added to the aqueous dispersion C4-5 so that the content of the nonionic surfactant (a) relative to the mass of the PTFE particles in this aqueous dispersion C4-3 was 14.0 mass%, and water and aqueous ammonia were also added to obtain the PTFE aqueous dispersion C5-3 (corresponding to the present aqueous dispersion). The 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 the PTFE particles, and a pH of 10.2. The average primary particle size of the PTFE particles in the PTFE aqueous dispersion C5-3 was the same as the average primary particle size of the PTFE particles in the above aqueous dispersion C1-3. The above-mentioned measurements and evaluations were carried out using the obtained PTFE aqueous dispersion C5-3. The results are shown in Table 1. 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 size of the PTFE particles in the PTFE aqueous dispersion C5-4 was the same as the average primary particle size of the PTFE particles in the above aqueous dispersion C1-3. The above-mentioned measurements and evaluations were carried out using the obtained PTFE aqueous dispersion C5-4. 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] The PTFE aqueous dispersion produced according to Example 1 of WO2021 / 085470 was designated PTFE aqueous dispersion C5-5. Note that 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 above-mentioned first fluoropolymer. The above-mentioned measurements and evaluations were carried out using the obtained PTFE aqueous dispersion C5-5. The results are shown in Table 1.

[0148] [Example 6] A 100 L stainless steel pressure reactor equipped with a stirring blade and baffles was charged with ultrapure water (60 L), a homopolymer of CF₂=CFOCF₂CF₂CO₂H (weight average molecular weight 4500, 18 g), and paraffin wax (1.5 kg). The mixture was stirred at 100 rpm and heated to 75 °C. TFE was then added until the reactor pressure reached 1.86 MPaG, and a solution of 1.08 g of APS and 106 g of disuccinic acid peroxide (80% concentration, remaining water) dissolved in 1 L of warm water was added to the reactor to initiate polymerization. As the polymerization began, the pressure in the reactor decreased, so TFE was added to maintain the pressure constant. When 9 kg of TFE had been added, the reactor was cooled, and the polymerization reaction was terminated, yielding aqueous dispersion C1-6. Aqueous dispersion C1-6 was a dispersion in which PTFE particles (average primary particle diameter: 200 nm) were dispersed in an aqueous medium, and had a solids concentration of 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, 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] Except for using aqueous dispersion C1-6, aqueous PTFE dispersion C5-6 was obtained according to the same procedures as for aqueous dispersions C2-1 to C4-1 and aqueous PTFE dispersion C5-1 in Example 1. Aqueous PTFE dispersion C5-6 had a PTFE particle concentration (content) of 60.8 mass%, a surfactant concentration (total content) of 5.0 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 the average primary particle size of the PTFE particles in the aqueous dispersion C1-6. Incidentally, the aqueous PTFE dispersion C5-6 does not contain a fluoropolymer that corresponds to the above-mentioned first fluoropolymer. The above-mentioned measurements and evaluations were carried out using the obtained PTFE aqueous dispersion C5-6. The results are shown in Table 1.

[0150] [Production of raw material solution A5] A 430L stainless steel autoclave equipped with a baffle and a stirrer was charged with 320 kg of deionized water, and the autoclave was then purged with nitrogen. The autoclave was then depressurized and charged with 6010 g of PMVE (perfluoromethyl vinyl ether). The temperature was raised to 90°C with stirring, and 985 g of TFE was charged, pressurizing the autoclave to 1.36 MPa. 1000 g of an 8.09 wt% aqueous solution of APS was then injected to initiate polymerization. Polymerization was allowed to proceed while TFE was added to maintain the internal pressure of the autoclave at 1.36 MPa. The polymerization reaction was terminated when the amount of TFE added after the start of polymerization reached 1,200 g. The autoclave was cooled, and the TFE in the autoclave was then released into the atmosphere. Nitrogen was introduced under pressure up to 0.2 MPa, and the temperature was raised to 90°C. The autoclave was heated for 3 hours, cooled, and reaction liquid A5 was extracted. The reaction liquid A5 was freeze-aggregated and then filtered. The resulting fluoropolymer A5 was analyzed by NMR, and it was found that the molar ratio of TFE units / PMVE units was 52 / 48 and the Tg was -5°C.

[0151] [Production of raw material solution B2] To raw material liquid A5 (X g) was added Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 20 g). 60 minutes after starting stirring, the raw material liquid and the ion exchange resin were separated by filtration. To the filtered raw material liquid was added SA10AOH (manufactured by Mitsubishi Chemical Corporation, anion exchange resin, 20 g). 60 minutes after starting stirring, the raw material liquid and the ion exchange resin were separated by filtration to obtain raw material liquid B2. The content of fluoropolymer A5 was 0.7 mass% based on the total mass of raw material liquid 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 baffles 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 ppm by mass relative to the total mass of fluoropolymer A1 in aqueous dispersion B1-7. The resulting 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 of 7.0 g of disuccinic acid peroxide (concentration 80% by mass, remainder water) dissolved in 1 L of warm water was injected into the reactor to initiate polymerization. As the polymerization began, the pressure in 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 C1-7 was obtained. 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 had a solids concentration of 20.3 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 2.7 mass% to obtain aqueous dispersion C2-7 (corresponding to the specific aqueous dispersion). The pH of the aqueous dispersion C2-7 was 3.0. SA10AOH (anion exchange resin, manufactured by Lewatit, 623 g) was added to the aqueous dispersion C2-7, and the mixture was stirred for 60 minutes. The aqueous dispersion was then filtered to separate the ion exchange resin, yielding aqueous dispersion C3-7 (corresponding to the 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 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 C3-7, and then the mixture was 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 mass%, and the concentration of nonionic surfactant (a) was 3.47 mass% relative to the mass of PTFE particles. A nonionic surfactant (a) was added to aqueous dispersion C4-7 so that the content relative to the mass of the PTFE particles in this aqueous dispersion C4-7 was 10.0 mass%, and water and aqueous ammonia were also added to obtain PTFE aqueous dispersion C5-7 (corresponding to this aqueous dispersion). PTFE aqueous dispersion C5-7 had a PTFE particle concentration (content) of 60.9 mass%, a surfactant concentration (total content) of 10.0 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 aqueous dispersion C5-7 was the same as the average primary particle size of the PTFE particles in 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 aqueous PTFE 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. The average primary particle size of the PTFE particles in the PTFE aqueous dispersion C5-8 was the same as the average primary particle size of the PTFE particles in the above aqueous dispersion C1-7. The above-mentioned measurements and evaluations were carried out using the obtained PTFE aqueous dispersion C5-8. 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] A 50 L stainless steel pressure reactor equipped with a stirring blade and baffles was charged with ultrapure water (33.0 kg) and 1.66 g of a 50 wt% aqueous solution of sodium 2-acrylamido-2-methyl-1-propanesulfonate (hereinafter also referred to as "NaAAMPS"), followed by PMVE (2.44 kg). The temperature was raised to 90 °C while stirring at 170 rpm. TFE was injected into the reactor until the pressure reached 1.49 MPaG, and ammonium persulfate (APS) aqueous solution (21.07 wt%, 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, the reactor was cooled, and the polymerization reaction was terminated. After recovering the remaining gas in the reactor, nitrogen was injected until 0.10 MPaG while stirring at 20 rpm, and the temperature was raised to 90 °C. After heating the reactor for 3 hours, the reactor was cooled and the liquid was withdrawn, which was designated as raw material liquid A7. After freeze-coagulating the raw material liquid A, it was filtered off, and the resulting fluoropolymer A7 was analyzed by NMR, and as a result, it was found that the molar ratio of TFE units / PMVE units was 68 / 37 and that Tg was -5.5°C. [Production of raw material solution B3] Raw material solution B3 was obtained according to the procedure for raw material solution B2, except that raw material solution A7 was diluted by a factor of 5. The content of fluoropolymer A7 was 1.1 mass % relative to the total mass of raw material solution 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 baffles 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 resulting 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 of 7.0 g of disuccinic acid peroxide (concentration 80% by mass, remainder water) dissolved in 1 L of warm water was injected into the reactor to initiate polymerization. As the polymerization began, the pressure in 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 mass. 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. An aqueous dispersion C4-9 was obtained according to the procedure of Example 7. In the aqueous dispersion C4-9, the concentration (content) of the PTFE particles was 65.3 mass%, and the concentration of the nonionic surfactant (a) was 3.59 mass% relative to the mass of the PTFE particles. A nonionic surfactant (a) was added to this aqueous dispersion C4-9 so that the content relative to the mass of the PTFE particles in the aqueous dispersion C4-9 was 14.0 mass%, and water and aqueous ammonia were also added to obtain PTFE aqueous dispersion C5-9 (corresponding to the present aqueous dispersion). PTFE aqueous dispersion C5-9 had a PTFE particle concentration (content) of 60.6 mass%, a surfactant concentration (total content) of 14.0 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 aqueous PTFE 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). The 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 the average primary particle size of the PTFE particles in the above 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 aqueous PTFE dispersion C5-10 did not substantially contain a fluorine-containing polymer having an ionic functional group.

[0157] [Table 1]

[0158] As shown in Table 1, it was confirmed that the use of the aqueous dispersion of the present invention made it possible to form a coating film with reduced 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 hereby incorporated by reference as the disclosure of the specification of the present invention.< / ph>

Claims

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

2. 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 the first fluoropolymer and the second fluoropolymer is 10 to 80 mass % relative to the total mass of the aqueous dispersion.

5. The aqueous dispersion according to claim 1, wherein the content of the surfactant is 1.1 to 19.8 mass% based on the total mass of the first fluoropolymer and the second fluoropolymer in the 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). Equation (S-1) R Ｓ１ -O-L Ｓ１ -H Equation (S-2) R Ｓ２ -C ６ H ４ -O-L Ｓ２ -H Equation (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 with an average added mole number of 5 to 20. In the formula (S-3), R 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 step 1 of polymerizing a monomer containing tetrafluoroethylene in a 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, to produce a second fluorine-containing polymer which is polytetrafluoroethylene and is different from the first fluorine-containing polymer, and to produce a second aqueous dispersion containing the first fluorine-containing polymer, the second fluorine-containing polymer, and a second aqueous medium; and step 2 of adding a surfactant including a nonionic surfactant to the second aqueous dispersion to obtain an aqueous dispersion, before the start of polymerization of the monomers, the content of the first fluorinated polymer is 0.01 to 4.0% by mass relative to the total mass of the first aqueous dispersion, a concentration of the fluorine-containing emulsifier in the first aqueous dispersion is 100 ppm by mass or less based on the total mass of the first fluorine-containing polymer in the first aqueous dispersion before starting polymerization of the monomers.

8. The method for producing the aqueous dispersion according to claim 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 claims 1 to 6 with a substrate made of glass fibers to obtain a polymer-containing substrate.