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

Abstract

The present invention provides an aqueous dispersion capable of forming a coating film in which coloring is inhibited, a method for producing the aqueous dispersion, and a polymer-containing substrate. The aqueous dispersion of the present invention contains a first fluorine-containing polymer, a second fluorine-containing polymer that is polytetrafluoroethylene, a surfactant containing a nonionic surfactant, and an aqueous medium, the first fluorine-containing polymer being a fluorine-containing polymer having an ionic functional group of 1000 or less per 10 6 main chain carbons, a glass transition temperature of 10°C or less, and a fluorine atom, the aqueous dispersion substantially not containing a fluorine-containing polymer that is different from the first fluorine-containing polymer and has an ionic functional group.

Description

Technical Field

[0001] This invention relates to aqueous dispersions, methods for manufacturing aqueous dispersions, and methods for manufacturing polymer-containing substrates. Background Technology

[0002] Polytetrafluoroethylene (PTFE) is used in various industrial fields due to its excellent heat resistance, chemical resistance, flame retardancy, and weather resistance.

[0003] Considering ease of operation, polytetrafluoroethylene (PTFE) is sometimes used in the form of an aqueous dispersion in an aqueous medium.

[0004] As a method for manufacturing such an aqueous dispersion, Patent Document 1 discloses a method in which tetrafluoroethylene is polymerized in the presence of a fluoropolymer with anionic side chains and an aqueous medium to obtain an aqueous dispersion containing polytetrafluoroethylene, and then, from the perspective of improving the dispersion stability of polytetrafluoroethylene, a surfactant is added to the obtained aqueous dispersion.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 2022 / 191286 Summary of the Invention

[0008] The technical problem that the invention aims to solve

[0009] In recent years, there has been a demand for improved performance of coatings obtained using aqueous dispersions containing polytetrafluoroethylene, for example, coatings that suppress coloration.

[0010] The inventors evaluated the coating obtained using the aqueous dispersion described in Patent Document 1 and found that there is room for improvement in the coloring of the coating.

[0011] The technical problem to be solved by the present invention is to provide an aqueous dispersion that can form a coating film with suppressed coloration.

[0012] Furthermore, the technical problem to be solved by the present invention is to provide a method for manufacturing an aqueous dispersion and a polymer-containing substrate.

[0013] means of solving technical problems

[0014] The inventors conducted in-depth research and found that the above-mentioned technical problems could be solved by the following configuration, thereby completing the present invention. [1]

[0016] An aqueous dispersion comprises a first fluoropolymer, a second fluoropolymer being polytetrafluoroethylene, a surfactant containing a nonionic surfactant, and an aqueous medium. The first fluoropolymer is per 10 of the polymer 6 Fluoropolymers containing fluorine atoms, with fewer than 1000 ionic functional groups in the main chain, a glass transition temperature below 10°C, and fluorine atoms. The aqueous dispersion does not substantially contain any fluorinated polymers with ionic functional groups other than the first fluorinated polymer.

[0017] [2] The aqueous dispersion as described in [1], wherein the first fluoropolymer contains units based on monomers having vinyl groups that can be substituted with fluorine atoms.

[0018] [3] An aqueous dispersion as described in [1] or [2], wherein the first fluoropolymer contains tetrafluoroethylene-based units.

[0019] [4] The aqueous dispersion as described in any one of [1] to [3], wherein the total content of the first fluoropolymer and the second fluoropolymer is 10 to 80% by mass relative to the total mass of the aqueous dispersion.

[0020] [5] The aqueous dispersion as described in any one of [1] to [4], wherein the content of the surfactant is 1.1 to 19.8% of the total mass of the first fluoropolymer and the second fluoropolymer in the aqueous dispersion.

[0021] [6] An aqueous dispersion as described in any one of [1] to [5], wherein the nonionic surfactant comprises at least one selected from the compounds represented by formula (S-1), the compounds represented by formula (S-2), and the compounds represented by formula (S-3). Equation (S-1) R S1 -OL S1 -H Equation (S-2) R S2 -C6H4-OL S2 -H Formula (S-3) R S3 -OL S3 -H In the above formula (S-1), R S1 L represents an alkyl group having 8 to 18 carbon atoms. S1 It represents a polyoxyalkylene chain composed of oxyethylene with an average addition molar number of 5 to 20 and oxypropylene with an average addition molar number of 0 to 2.

[0022] In the above formula (S-2), R S2L represents an alkyl group having 4 to 12 carbon atoms. S2 It represents a polyoxyethylene chain composed of oxyethylene with an average addition molar number of 5 to 20.

[0023] In the above formula (S-3), R S3 L represents an alkyl group having 8 to 18 carbon atoms. S3 It represents a polyoxyalkylene chain composed of oxyethylene with an average addition molar number of 5 to 20 and oxybutylene with an average addition molar number of 0.1 to 3.

[0024] [7] A method for manufacturing an aqueous dispersion, comprising step 1 and step 2, Step 1: A monomer containing tetrafluoroethylene is polymerized in a first aqueous dispersion containing a first fluoropolymer and a first aqueous medium to produce a second fluoropolymer, which is polytetrafluoroethylene and is different from the first fluoropolymer. A second aqueous dispersion containing the first fluoropolymer, the second fluoropolymer, and a second aqueous medium is then produced, wherein the first fluoropolymer is a polymer comprising 10... 6 Fluoropolymers containing fluorine atoms, with fewer than 1000 ionic functional groups in the main chain, a glass transition temperature below 10°C, and fluorine atoms. Step 2: Add a surfactant containing a nonionic surfactant to the second aqueous dispersion to obtain an aqueous dispersion. Prior to the start of polymerization of the monomer, the content of the first fluoropolymer is 0.01 to 4.0% by mass relative to the total mass of the first aqueous dispersion. Prior to the start of polymerization of the monomer, the concentration of the fluorinated emulsifier is less than 100 ppm by mass relative to the total mass of the first fluoropolymer in the first aqueous dispersion.

[0025] [8] The method for manufacturing an aqueous dispersion as described in [7] includes a step of contacting the aqueous dispersion with an ion exchange resin.

[0026] [9] A method for manufacturing a polymer-containing substrate, wherein an aqueous dispersion as described in any one of [1] to [6] is contacted with a substrate made of glass fiber to obtain a polymer-containing substrate.

[0027] Invention Effects

[0028] According to the present invention, an aqueous dispersion capable of forming a coating film with suppressed coloration can be provided.

[0029] In addition, according to the present invention, a method for manufacturing an aqueous dispersion and a polymer-containing substrate can also be provided. Detailed Implementation

[0030] The meanings of the terms used in this invention are as follows.

[0031] The numerical range indicated by "~" includes the values ​​before and after "~" as both the lower and upper limits. In this disclosure, the upper or lower limit of a numerical range can be replaced by the upper or lower limit of another numerical range. Furthermore, the upper or lower limit of a numerical range described in this specification can be replaced by the values ​​shown in the embodiments.

[0032] In this specification, each component may be used alone with one corresponding substance, or with two or more substances used in combination. When two or more corresponding substances are used in combination, unless otherwise specified, the content of the component refers to the total content of the substances used in combination.

[0033] In this specification, a combination of two or more preferred methods is a more preferred method.

[0034] "Unit" is a general term for atomic groups directly formed by the polymerization of monomers, derived from one molecule of the monomer, and atomic groups obtained by chemically transforming a portion of the atomic group. "Monomer-based unit" is hereinafter referred to as "unit".

[0035] The content (mass % or molar %) of each unit relative to all units in the polymer can be determined by analyzing the polymer using solid-state nuclear magnetic resonance (NMR) or estimated from the amount of each monomer added. Typically, the content of each unit calculated from the amount of each monomer added is approximately the same as the actual content of each unit.

[0036] [Aqueous dispersion]

[0037] The aqueous dispersion of the present invention (hereinafter also referred to as "the aqueous dispersion") comprises a first fluoropolymer, a second fluoropolymer being polytetrafluoroethylene (hereinafter also referred to as "PTFE"), a surfactant containing a nonionic surfactant, and an aqueous medium, wherein the first fluoropolymer is present in 10% of the polymer. 6 The aqueous dispersion contains fluorinated polymers with fewer than 1000 ionic functional groups in the main chain, a glass transition temperature (hereinafter also referred to as "Tg") below 10°C, and containing fluorine atoms. The aqueous dispersion does not substantially contain fluorinated polymers that are different from the first fluorinated polymer and have ionic functional groups.

[0038] Coloration of the coating film formed using this aqueous dispersion is suppressed. Although the details of the reason are not clear, it is speculated that it is due to the following reasons.

[0039] When using fluoropolymers with ionic functional groups, the fluoropolymers with ionic functional groups remain in the aqueous dispersion. If the aqueous dispersion containing the residue is coated onto a substrate, dried, and fired, the residue will decompose and become colored during heating.

[0040] Regarding this issue, it is speculated that since this aqueous dispersion does not actually contain fluorinated polymers with ionic functional groups, the coloring of the coating film formed using this polymer is suppressed.

[0041] [First Fluoropolymer]

[0042] In the first fluoropolymer, every 10 of the polymer 6 The number of ionic functional groups per carbon atom in the main chain is less than 1000, and the polymer has 10 6 The number of ionic functional groups per carbon atom in the main chain is preferably one or more. If the amount of ionic functional groups is within this range, the production stability during the manufacture of the second fluoropolymer is improved.

[0043] Polymer per 10 6 The number of ionic functional groups with a main chain carbon number can be determined using known methods such as Fourier transform infrared spectroscopy (FT-IR).

[0044] Examples of ionic functional groups include cationic and anionic functional groups. Specific examples of ionic functional groups include carboxylic acid groups (-COO-) and sulfonic acid groups (-SO3-). - ), sulfate group (-SO4) 2- ), phosphonic acid group (-PO3) 2- ) and phosphate group (-PO4) 3- (Anionic functional groups)

[0045] The first fluoropolymer has a Tg below 10°C.

[0046] From the perspective of effectively adsorbing the tetrafluoroethylene-containing monomer used in the manufacture of the second fluoropolymer when using the first fluoropolymer to manufacture the second fluoropolymer, the Tg of the first fluoropolymer is preferably below 5°C, more preferably below 3°C, and even more preferably below 0°C.

[0047] From the perspective of thermal stability after molding and processing, the Tg of the first fluoropolymer is preferably above -50°C, more preferably above -45°C, and even more preferably above -40°C.

[0048] The Tg of the first fluoropolymer was determined by differential scanning calorimetry (DSC), with detailed determination conditions as described in the Examples section below.

[0049] As a method to bring the Tg of the first fluoropolymer within the above-mentioned range, for example, methods can be used to adjust the type and amount of monomers used in the manufacture of the first fluoropolymer.

[0050] From the perspective of achieving better results from the present invention, the first fluoropolymer preferably contains units based on monomers having vinyl groups that can be substituted with fluorine atoms, and more preferably contains units based on monomers having vinyl groups that can be substituted with fluorine atoms.

[0051] The unit based on the monomer having vinyl groups substituted with fluorine atoms is preferably based on the unit based on perfluorinated (alkyl vinyl ether) (hereinafter also referred to as "PAVE unit").

[0052] From the perspective of excellent polymerization reactivity when manufacturing the first fluoropolymer and the ability to manufacture the second fluoropolymer more efficiently, the monomer represented by formula (1) is preferred by PAVE.

[0053] CF2 = CF - OR f1 (1)

[0054] In equation (1), R f1 This refers to perfluoroalkyl groups with 1 to 10 carbon atoms. From the perspective of superior polymerization reactivity, R... f1 The carbon number is preferably 1 to 8, more preferably 1 to 6, even more preferably 1 to 5, and particularly preferably 1 to 3.

[0055] Perfluoroalkyl groups can be either linear or branched.

[0056] 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"). Among these, from the perspective of being able to manufacture the second fluoropolymer more efficiently, PMVE and PPVE are preferred, and PMVE is more preferred.

[0057] When the first fluoropolymer contains units based on monomers having vinyl groups that can be substituted with fluorine atoms, the content of units based on monomers having vinyl groups that can be substituted with fluorine atoms relative to all units of the first fluoropolymer is preferably 20 to 60 mol%, more preferably 25 to 60 mol%, and even more preferably 30 to 55 mol%.

[0058] From the perspective of achieving better results from the present invention, the first fluoropolymer preferably contains a unit based on tetrafluoroethylene (hereinafter also referred to as "TFE unit").

[0059] When the first fluoropolymer contains TFE units, the content of TFE units relative to all units of the first fluoropolymer is preferably 30 to 90 mol%, more preferably 40 to 80 mol%, and even more preferably 45 to 70 mol%.

[0060] From the perspective of easily adjusting Tg to the above range and from the perspective of better performance of the present invention, the first fluoropolymer preferably contains TFE unit and PAVE unit.

[0061] When the first fluoropolymer contains TFE units and PAVE units, from the perspective of easily adjusting Tg to the above-mentioned range and being able to manufacture the second fluoropolymer more efficiently, the proportion of PAVE units in the first fluoropolymer relative to the total 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%. When the PAVE units are PMVE units, PEVE units, or PPVE units, or when using a mixture of two or more of them, the amount used is preferably the same.

[0062] The first fluoropolymer may also contain units based on monomers other than those mentioned above, but from the perspective of being able to manufacture the second fluoropolymer more efficiently when the first fluoropolymer has been used to manufacture the second fluoropolymer, it is preferable that it does not contain units based on other monomers.

[0063] "Substantively free of units based on other monomers" means that the content of units based on other monomers relative to all units of the first fluoropolymer is less than 0.01 mol%, more preferably 0 mol%.

[0064] In the case of units based on other monomers, hexafluoropropylene is preferred as the other monomer.

[0065] From the perspective of the superior dispersion stability of the second fluoropolymer in the aqueous dispersion, the content of the first fluoropolymer relative to the total mass of the aqueous dispersion is preferably 0.10 to 2.0% by mass, more preferably 0.15 to 1.5% by mass, and even more preferably 0.2 to 0.8% by mass.

[0066] [Second Fluoropolymer]

[0067] The PTFE used as the second fluoropolymer can be a homopolymer of TFE or a modified PTFE. The second fluoropolymer is a different fluoropolymer from the first fluoropolymer described above.

[0068] In addition, the first fluoropolymer and the second fluoropolymer can be copolymerized.

[0069] Modified PTFE preferably contains TFE units and units based on modified monomers that can copolymerize with the TFE units (hereinafter also referred to as "modified monomer units").

[0070] The content of modified monomer units in modified PTFE relative to all units of modified PTFE is preferably 0.0001 to 1% by mass, more preferably 0.0005 to 0.50% by mass, and even more preferably 0.001 to 0.40% by mass.

[0071] Modified monomer units refer to the portions of the modified PTFE molecular structure that originate from the modified monomer. All units of modified PTFE refer to all portions of the modified PTFE molecular structure that originate from the monomer.

[0072] The content of modified monomer units can be determined by known methods such as Fourier transform infrared spectroscopy (FT-IR).

[0073] The modified monomer can be any monomer that can copolymerize with TFE. Examples include: perfluoroolefins such as hexafluoropropylene; chlorofluoroolefins such as trifluorochloroethylene; hydrofluoroolefins such as trifluoroethylene and vinylidene fluoride; perfluorovinyl ethers; perfluoroalkyl ethylene; and ethylene.

[0074] Modified monomers can be used alone or in combination with two or more.

[0075] Considering the intended use of this aqueous dispersion (uses for impregnating fibers such as glass fibers in fabrics or ropes, uses for mixing with inorganic or plastic powders, uses for adding small amounts to coatings, uses for coating, etc.), the content of the second fluoropolymer relative to the total mass of this aqueous dispersion is preferably 10 to 80% by mass, more preferably 20 to 75% by mass, and even more preferably 25 to 70% by mass.

[0076] In this aqueous dispersion, the first fluoropolymer and the second fluoropolymer can exist in the form of particles containing the first fluoropolymer and the second fluoropolymer (preferably particles composed of the first fluoropolymer and the second fluoropolymer).

[0077] In this case, from the perspective of dispersion stability, the average particle size is preferably below 500 μm, more preferably below 450 μm, and even more preferably below 400 μm.

[0078] In addition, from the perspective of cohesion, the average particle size is preferably above 50 nm, more preferably above 80 nm, and even more preferably above 100 nm.

[0079] The average particle size is determined by measuring the particle size distribution using laser diffraction and scattering. The cumulative curve is calculated with the total volume of the particle group as 100%, and the particle size is the point on the cumulative curve where the cumulative volume reaches 50%.

[0080] In addition, the first fluoropolymer and the second fluoropolymer can be copolymerized.

[0081] From the perspective of the superior dispersion stability of the second fluoropolymer in the aqueous dispersion, the total content of the first fluoropolymer and the second fluoropolymer relative to the total mass of the aqueous dispersion is preferably 10 to 80% by mass, more preferably 15 to 80% by mass, and even more preferably 20 to 75% by mass.

[0082] [surfactant]

[0083] The surfactant contained in this aqueous dispersion is a nonionic surfactant. Because the surfactant is nonionic, the dispersion stability of this aqueous dispersion is improved.

[0084] Surfactants may also include surfactants other than nonionic surfactants (hereinafter also referred to as "other surfactants").

[0085] The surfactant content relative to the total mass of the first and second fluoropolymers in the aqueous dispersion 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. If the surfactant content is 1.1% by mass or higher, the aqueous dispersion exhibits superior storage stability. If the surfactant content is 19.8% by mass or lower, microcracks are less likely to form when the aqueous dispersion is used to make a coating film.

[0086] <Nonionic surfactants>

[0087] From the perspective of further improving the stability of this aqueous dispersion, the nonionic surfactant preferably contains at least one selected from the compounds represented by formula (S-1), the compounds represented by formula (S-2), and the compounds represented by formula (S-3).

[0088] Equation (S-1) R S1 -OL S1 -H

[0089] Equation (S-2) R S2 -C6H4-OL S2 -H

[0090] Formula (S-3) R S3 -OL S3 -H

[0091] In the above equation (S-1), R S1 R indicates an alkyl group having 8 to 18 carbon atoms. S1 The alkyl group can be either straight-chain or branched.

[0092] 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 reduced, resulting in excellent permeability or wettability. When the alkyl group has 18 or fewer carbon atoms, even when the aqueous dispersion is left to stand for a long time, the particles of the second fluoropolymer are not prone to sedimentation, resulting in excellent storage stability.

[0093] L S1 This refers to a polyoxyalkylene chain composed of an average addition molar number of 5–20 (preferably 7–12) oxyethylidene and an average addition molar number of 0–2 (preferably 0.5–1.5) oxypropylene. L S1 When the average molar number of oxypropylidene addition is 0.5 to 1.5, the defoaming properties are good, making it the preferred choice.

[0094] In the above formula (S-2), R S2 R indicates an alkyl group having 4 to 12 carbon atoms. S2 The alkyl group can be straight-chain or branched.

[0095] R S2 The alkyl group has 4 to 12 carbon atoms, preferably 6 to 10, and more preferably 8 to 9. When the alkyl group has 4 or more carbon atoms, the surface tension of the PTFE aqueous dispersion decreases, resulting in excellent permeability or wettability. When the alkyl group has 12 or fewer carbon atoms, even if the aqueous dispersion is left to stand for a long time, the particles of the second fluoropolymer are not prone to sedimentation, resulting in excellent storage stability.

[0096] L S2 It refers to an oxoethylene chain composed of oxoethylene with an average addition molar number of 5 to 20 (preferably 6 to 16, more preferably 7 to 12).

[0097] In the above formula (S-3), R S3 R indicates an alkyl group having 8 to 18 carbon atoms. S3 The alkyl group can be either straight-chain or branched.

[0098] R S3 The alkyl carbon number is 8 to 18, preferably 10 to 16, and more preferably 12 to 16. When the alkyl carbon number is 8 or more, the surface tension of the PTFE aqueous dispersion is reduced, resulting in excellent permeability or wettability. When the alkyl carbon number is 18 or less, even if the aqueous dispersion is left for a long time, the particles of the second fluoropolymer are not easily settled, resulting in excellent storage stability.

[0099] L S3This refers to a polyoxyalkylene chain composed of an average addition molar number of 5–20 (preferably 6–15, more preferably 7–12) oxyethylidene and an average addition molar number of 0.1–3 (preferably 0.5–2, more preferably 0.7–1.7, even more preferably 0.9–1.5) oxybutylidene. A number of 0.5–2 oxybutylidene groups indicates good defoaming properties and is preferred.

[0100] 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 preferably 450 to 800, more preferably 500 to 750, and even more preferably 550 to 700.

[0101] Examples of compounds 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(C5H) 11 (C7H) 11 ) -O-(C2H4O)9-H. As commercially available products, examples include the TERGITOL (registered trademark) 15S series manufactured by Dow Chemical and the LIONOL (registered trademark) TD series manufactured by Lion Corporation.

[0102] As a compound represented by formula (S-2), C8H can be cited as an example. 17 -C6H4-O-(C2H4O) 10 -H, C9H 19 -C6H4-O-(C2H4O) 10 -H. Examples of commercially available products include the TRITON (registered trademark) X series manufactured by Dow Chemical Company, and the NIKKOL (registered trademark) OP or NP series manufactured by Nikko Chemical Co., Ltd.

[0103] As a compound represented by formula (S-3), C can be cited as an example. 13 H 27 OCH2CH(C2H5)O(C2H4O)8H、C 10 H21 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 O(CH2)2CH(CH3)O(C2H4O)8H.

[0104] The compound represented by formula (S-1), the compound represented by formula (S-2), and the compound represented by formula (S-3) can be used individually or in combination of two or more.

[0105] Furthermore, nonionic surfactants are mixtures of various substances with different molecular structures. The average values ​​are used to represent the number of alkyl carbons in the nonionic surfactant and the number of oxyethylidene, oxypropylene, and oxybutylidene groups in the polyoxyalkylene chain. These values ​​are not limited to integers.

[0106] The content of the nonionic surfactant relative to the total mass of the first and second fluoropolymers in the aqueous dispersion 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. If the content of the nonionic surfactant is 1.0% by mass or more, the storage stability of the aqueous dispersion is better. If the content of the nonionic surfactant is 12% by mass or less, micro-cracks are less likely to occur when the aqueous dispersion is formed into a coating film.

[0107] The content of the nonionic surfactant relative to the surfactant content in this aqueous dispersion is preferably 85-99.9% by mass, more preferably 90-99% by mass, and even more preferably 92-98% by mass. If the content of the nonionic surfactant is 85% by mass or more, the storage stability of this aqueous dispersion is better. If the content of the nonionic surfactant is 99.9% by mass or less, micro-cracks are less likely to occur when this aqueous dispersion is made into a coating film.

[0108] <Other Surfactants>

[0109] There are no particular restrictions on the types of other surfactants, but anionic surfactants are preferred.

[0110] The anionic surfactant is preferably an anionic surfactant that does not contain fluorine atoms. Specifically, examples include ammonium laurate, triethanolamine laurate, sodium lauryl sulfate, ammonium lauryl sulfate, and triethanolamine lauryl sulfate.

[0111] [Aqueous media]

[0112] Examples of aqueous media include water, or mixtures of water and water-soluble organic solvents. Specific examples of water-soluble organic solvents include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol.

[0113] The aqueous medium contained in this aqueous dispersion may also be the polymerization solvent used in the manufacture of the first fluoropolymer or the second fluoropolymer.

[0114] The content of the aqueous medium relative to the total mass of the aqueous dispersion is preferably 20-90% by mass, more preferably 22-88% by mass, and even more preferably 25-80% by mass.

[0115] (Other ingredients)

[0116] This aqueous dispersion may also contain other components besides those mentioned above.

[0117] Other components that may be included in this aqueous dispersion include chain transfer agents, pH adjusters, waxes, various leveling agents, preservatives, fillers, and viscosity modifiers (e.g., polyethylene oxide and polyurethane-based viscosity modifiers).

[0118] When the aqueous dispersion contains other components, the content of the other components relative to the total mass of the aqueous dispersion is preferably 0.01 to 2.0% by mass, more preferably 0.01 to 1.8% by mass, and even more preferably 0.01 to 1.5% by mass.

[0119] Fluoropolymers with ionic functional groups

[0120] This aqueous dispersion does not actually contain any fluorinated polymers with ionic functional groups, except for the first fluorinated polymer mentioned above.

[0121] Fluoropolymers with ionic functional groups are polymers possessing both ionic functional groups and fluorine atoms. Specific examples of ionic functional groups are described above. Fluoropolymers with ionic functional groups act as fluorinated emulsifiers in water. For example, when using vinyl-containing fluorinated emulsifiers represented by the following general formulas (A1) to (A-VII), fluoropolymers with ionic functional groups remain in the aqueous dispersion. If an aqueous dispersion containing the residue is applied to a substrate, dried, and fired, the residue decomposes and becomes colored upon heating.

[0122] General formula (AI)

[0123] CF2 = CF - (CF2) a1 -Y (AI)

[0124] [In the formula, a1 represents an integer from 1 to 10, Y represents -SO3M or -COOM, and M represents H, NH4 or an alkali metal] represents a vinyl-containing fluorine compound (AI). General Formula (A-II) CF2 = CF - (CF2)C(CF3)F) b1 -Y (A-II) [In the formula, b1 represents an integer from 1 to 5, Y represents -SO3M or -COOM, and M represents H, NH4 or an alkali metal] represents the vinyl-containing fluorine compound (A-II). General Formula (A-III) CF2 = CFO - (CFX) c1 -Y [In the formula, X represents -F or -CF3, c1 represents an integer from 1 to 10, Y represents -SO3M or -COOM, and M represents H, NH4 or an alkali metal] represents the vinyl-containing fluorine compound (A-III). General formula (A-IV) CF2 = CFO - (CF2CFXO) d1 -(CF2) e1 -Y (A-IV) [In the formula, X represents -F or -CF3, d1 represents an integer from 1 to 10, e1 represents an integer from 1 to 3, Y represents -SO3M or -COOM, and M represents H, NH4 or an alkali metal] represents fluorinated vinyl compounds (A-IV). General formula (AV) CH2=CFCF2O-(CF(CF3)CF2O) f1-CF(CF3) -Y (AV) [In the formula, f1 represents an integer from 0 to 10, Y represents -SO3M or -COOM, and M represents H, NH4 or an alkali metal] represents the vinyl-containing fluorine compound (AV). General formulas (A-VI) CF2=CFCF2O-(CF(CF3)CF2O) g1 -CF(CF3)-Y (A-VI) [In the formula, g1 represents an integer from 1 to 10, Y represents -SO3M or -COOM, and M represents H, NH4 or an alkali metal] represents the vinyl-containing fluorinated compound (A-VI), and / or General formulas (A-VII) CF2 = CF - (OZ) - Y (A-VII) [In the formula, 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] represents vinyl-containing fluorinated compounds (A-VII).

[0125] Essentially, the absence of fluoropolymers with ionic functional groups means that the content of fluoropolymers with ionic functional groups is less than 0.01% by mass relative to the total mass of the aqueous dispersion, which can be 0% by mass.

[0126] [physical properties]

[0127] The pH value of this aqueous dispersion is preferably 7.0 to 11.0, more preferably 8.0 to 11.0.

[0128] The surface tension of this aqueous dispersion is preferably 24–40 mN / m, more preferably 25–35 mN / m.

[0129] The viscosity (at 23°C) of this aqueous dispersion is preferably 3 to 400 mPa·s, more preferably 5 to 100 mPa·s.

[0130] The methods for determining pH, surface tension, and viscosity are described in the Examples section below.

[0131] [Method for manufacturing aqueous dispersions]

[0132] The method for manufacturing the aqueous dispersion of the present invention (hereinafter also referred to as "the manufacturing method") includes step 1 and step 2. Step 1: A monomer containing tetrafluoroethylene is polymerized in a first aqueous dispersion containing a first fluoropolymer and a first aqueous medium to produce a second fluoropolymer, which is polytetrafluoroethylene and is different from the first fluoropolymer. A second aqueous dispersion containing the first fluoropolymer, the second fluoropolymer, and a second aqueous medium is then produced, wherein the first fluoropolymer is a polymer comprising 10... 6 Fluoropolymers containing fluorine atoms, with fewer than 1000 ionic functional groups in the main chain, a glass transition temperature below 10°C, and fluorine atoms. Step 2: Add a surfactant containing a nonionic surfactant to the second aqueous dispersion to obtain an aqueous dispersion. Prior to the start of polymerization of the monomer, the content of the first fluoropolymer is 0.01 to 4.0% by mass relative to the total mass of the first aqueous dispersion. Before the polymerization of the monomer begins, the concentration of the fluorinated emulsifier is 100 ppm by mass or less relative to the total mass of the first fluoropolymer in the first aqueous dispersion. Furthermore, the concentration of the fluorinated emulsifier relative to the total mass of the first fluoropolymer in the first aqueous dispersion is preferably 10 ppm by mass or less, more preferably 150 ppb by mass or less, more preferably 50 ppb by mass or less, and particularly preferably 25 ppb by mass or less. The lower limit is 0 ppb by mass.

[0133] In this manufacturing method, in manufacturing the first fluoropolymer, in addition to the monomer represented by formula (1) above, compound (2) may also be used.

[0134] <Compound(2)>

[0135] Compound (2) is a compound represented by the following formula (2).

[0136] CX 1 X 2 =CX 3 -LZ …(2)

[0137] In equation (2), X 1 and X 2 Each is independently a hydrogen atom or an alkyl group. X 3 It can be a hydrogen atom, a fluorine atom, or an alkyl group. L is a single bond or a divalent linker. Z is -SO3M 1 -OSO3M 1 -P(=O)(OM) 1 )2、-OP(=O)(OM 1 )2 or -COOM 1 , M 1 For hydrogen atoms, metal atoms, N(RM) 11 )4 or P(RM 12 4. When there are multiple M 1 In the case of multiple M 1 They can be the same, or they can be different. RM 11 and RM 12 Each is an independent hydrogen atom or substituent, RM 11 Any two of them can bond together to form a ring, and multiple RM 11 They can be the same, or they can be different from each other, RM 12 Any two of them can bond together to form a ring, and multiple RM 12 They can be the same, or they can be different from each other.

[0138] The alkyl group can be any of the following: straight-chain, branched, or cyclic.

[0139] The number of carbon atoms in the alkyl group is preferably 1 to 10, more preferably 1 to 3, and even more preferably 1.

[0140] Considering the increase in the number of particles in the first fluoropolymer, X 1 and X 2 All are preferably hydrogen atoms.

[0141] In equation (2), X 3 It can be a hydrogen atom, a fluorine atom, or an alkyl group.

[0142] Specific examples and preferred embodiments of the above-mentioned alkyl groups are the same as those of X. 1 and X 2 The specific examples and preferred methods of the alkyl groups are the same.

[0143] Considering the increase in the number of particles in the first fluoropolymer, X 3 Fluorine atoms or hydrogen atoms are preferred, with hydrogen atoms being more preferred.

[0144] In formula (2), L is a single bond or a divalent linker.

[0145] Examples of divalent linking groups include alkylene groups, carbonyl groups, ether bonds, thioether bonds, sulfonyl groups, -NH-, -SiH2-, phenylene groups, -CF2-, and groups formed by combinations of two or more of these groups. Examples of groups formed by combinations of two or more of these groups include ester bonds, thioester bonds, amide bonds, sulfonamide bonds, combinations of alkylene and ether bonds, combinations of alkylene and ester bonds, and combinations of alkylene and amide bonds.

[0146] The aforementioned alkylene group can be any of straight-chain, branched, or cyclic, preferably straight-chain or branched, and more preferably branched. Examples of the number of carbon atoms in the alkylene group include 1 to 6, preferably 1 to 4.

[0147] Specific examples of L include single bonds, alkylene bonds, ether bonds, ester bonds, etc. C -CO-NH-R- Z And so on, preferably single bonds, alkylene groups having 1 to 6 carbon atoms, and C -CO-NH-R- Z Especially preferred are single bonds, alkylene groups with 1 to 2 carbon atoms, and... C -CO-NH-R- Z .in, C For the bonding sites with carbon atoms in equation (2), Z R is the bonding site with Z in formula (2), and R is an alkylene group with 1 to 6 carbon atoms.

[0148] In equation (2), Z is -SO3M 1 -OSO3M 1 -P(=O)(OM) 1 )2、-OP(=O)(OM 1 )2 or -COOM 1 .

[0149] From the perspective of stabilizing the dispersion and increasing the number of particles of the first fluoropolymer, Z is preferred. 1 and -COOM 1 More preferably -SO3Na and -COONa, and even more preferably -SO3Na.

[0150] M 1 For hydrogen atoms, metal atoms, N(RM) 11 )4 or P(RM 12 )4,RM 11 and RM 12 Each can be a hydrogen atom or a substituent, independently.

[0151] M 1 The metal atom represented is preferably a group 1 metal atom, more preferably Li, Na or K.

[0152] RM 11 and RM 12 The substituents indicated are preferably monovalent organic groups, more preferably monovalent hydrocarbon groups, and even more preferably alkyl or aromatic hydrocarbon groups.

[0153] The number of carbon atoms in the above-mentioned substituents is preferably 1 to 10.

[0154] The alkyl group can be any of the following: straight-chain, branched, or cyclic.

[0155] The aforementioned aromatic hydrocarbon group can be either monocyclic or polycyclic. Phenyl is preferred as the aforementioned aromatic hydrocarbon group.

[0156] The molecular weight of compound (2) can be 70 to 500, for example, but from the perspective of dispersion stability, 70 to 450 is preferred, and 100 to 300 is more preferred.

[0157] 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-vinylbenzene sulfonic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid, N-tyrosine, 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 their metal salts.

[0158] As an example of the aforementioned metal salts, M can be cited. 1 Metal salts representing metal atoms.

[0159] As compound (2), preferably, it is a vinyl compound having a sulfonic acid group, a phosphonic acid group, or a carboxyl group; an allyl compound having a sulfonic acid group, a phosphonic acid group, or a carboxyl group; (meth)acrylic acid; (meth)acrylamide having a sulfonic acid group, a phosphonic acid group, or a carboxyl group; and its metal salt, preferably 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-propanesulfonic acid, 2-methacrylamido-2-methyl-1-propanesulfonic acid, or sodium 2-methacrylamido-2-methyl-1-propanesulfonic acid. Furthermore, the term "(meth)acrylic acid" above encompasses both acrylic acid and methacrylic acid, and the term "(meth)acrylamide" above encompasses both acrylamide and methacrylamide.

[0160] According to this manufacturing method, an aqueous dispersion capable of forming a coating film with suppressed coloration can be provided.

[0161] This manufacturing method is suitable for producing the above-described aqueous dispersion.

[0162] [Process 1]

[0163] Step 1 is a step of producing a second aqueous dispersion by polymerizing a specific monomer in a first aqueous dispersion.

[0164] Through step 1, even when using an aqueous medium with low environmental impact, a second fluoropolymer can be efficiently manufactured without an emulsifier. The reason for this is presumably because, by using a first aqueous dispersion containing a specified amount of a first fluoropolymer, the first fluoropolymer acts as a favorable polymerization field for the second fluoropolymer.

[0165] From the perspective of suppressing the decrease in molecular weight of fluoropolymers, step 1 is preferably carried out under conditions where there are substantially no fluorinated emulsifiers (emulsifiers with fluorine atoms) and emulsifiers without fluorine atoms. That is, the aqueous dispersion is preferably substantially free of fluorinated emulsifiers and emulsifiers without fluorine atoms.

[0166] Essentially, the absence of fluorinated emulsifiers and fluorine-free emulsifiers (hereinafter collectively referred to as "emulsifiers") means that the content of the emulsifier relative to the total mass of the first aqueous dispersion is 10 ppm by mass or less, preferably 150 ppb by mass or less, more preferably 50 ppb by mass or less, and particularly preferably 25 ppb by mass or less. The lower limit is 0 ppb by mass.

[0167] The content of various emulsifiers can be determined using liquid chromatography-mass spectrometry. Specifically, the determination method described in paragraphs

[0721] to

[0732] of International Publication No. 2018 / 181904 can be cited as an example.

[0168] Examples of fluorinated and fluorine-free emulsifiers include water-soluble emulsifiers. A water-soluble emulsifier is defined as one with a solubility of 100 mg or more in 1000 g of water at 25°C. A non-water-soluble emulsifier is any emulsifier other than the water-soluble type mentioned above. Water-soluble emulsifiers can be either ionic or non-ionic.

[0169] Fluorinated emulsifiers and fluorine-free emulsifiers include those that do not contain carbon-carbon double bonds.

[0170] In addition, the above-mentioned compound (2), the first fluoropolymer and the second fluoropolymer are not emulsifiers.

[0171] Anionic fluorinated emulsifiers can be cited as examples of fluorinated emulsifiers.

[0172] Examples of anionic fluorinated emulsifiers include emulsifiers containing fluorine atoms with a total carbon number of 20 or less in the portion excluding the anionic group, and emulsifiers containing fluorine atoms with a molecular weight of 800 or less in the anionic portion. Furthermore, the term "anionic portion" refers to the portion of the fluorinated emulsifier that has been stripped of its cationic components.

[0173] Fluorine-free emulsifiers are emulsifiers that do not contain fluorine atoms and have alkyl or other hydrocarbon groups as hydrophobic moieties. The hydrogen atoms in the hydrocarbon groups of fluorine-free emulsifiers can be replaced by halogen atoms other than fluorine atoms.

[0174] Examples of emulsifiers that are free of fluorine atoms include anionic hydrocarbon emulsifiers and nonionic hydrocarbon emulsifiers.

[0175] Anionic hydrocarbon emulsifiers are emulsifiers that have negatively charged hydrophilic parts such as carboxylic acid groups, sulfonic acid groups, sulfuric acid groups, phosphonic acid groups and phosphate groups, and hydrocarbon groups such as alkyl groups as hydrophobic parts.

[0176] Specific examples of anionic hydrocarbon emulsifiers include sodium dodecyl sulfate, highly branched C10 tertiary carboxylic acids supplied by Resolution Performance Products under the trademark Versatic 10, linear alkyl polyether sulfonates supplied by BASF under the trademark Avanel S series, and sulfosuccinic acid emulsifier Lankropol K8300 available from Akzo Nobel Surface Chemistry LLC.

[0177] Nonionic hydrocarbon emulsifiers are emulsifiers that do not dissociate into ions in water and exhibit surface activity, having alkyl or other hydrocarbon groups as hydrophobic parts.

[0178] Examples of water-soluble functional groups, such as polyoxyethylene chains obtained by polymerization of ethylene oxide, can be cited as the hydrophilic portion of nonionic hydrocarbon emulsifiers. Nonionic emulsifiers include polyoxyalkylene block copolymers, such as block copolymers having polyoxyethylene and polyoxypropylene groups.

[0179] In addition, as other nonionic hydrocarbon emulsifiers, the emulsifiers described in paragraphs

[0043] to

[0052] of Japanese Patent Publication No. 2016-537499 can be cited as examples.

[0180] Fluorinated emulsifiers and fluorine-free emulsifiers can contain silicon atoms. Examples of silicon-containing emulsifiers include siloxane emulsifiers. Siloxane emulsifiers are hydrocarbon-containing emulsifiers with a siloxane backbone.

[0181] Examples of siloxane emulsifiers include those described in U.S. Patent No. 6,841,616 (Wille et al.) and U.S. Patent No. 7,977,438 (Brothers et al.).

[0182] Fluorinated emulsifiers and fluorine-free emulsifiers can also be polymeric emulsifiers. Examples of polymeric emulsifiers include polymers with hydrophilic side chains. Examples of such polymeric emulsifiers include polymers containing units based on compounds having sites that can react with polymerization and hydrophilic groups. Additionally, examples can be polymers obtained through post-treatment such as hydrolysis from polymers containing units based on compounds that initially lack hydrophilic groups but have groups that can become hydrophilic.

[0183] In the case of polymerization in the presence of a fluorine-free emulsifier, a fluorine-free emulsifier is typically used in an amount of 0.1 to 15 parts by mass relative to 100 parts by mass of the aqueous medium.

[0184] The following sections will first describe in detail the materials used in process 1, and then describe in detail the steps of process 1.

[0185] <First Aqueous Dispersion>

[0186] In step 1, a first aqueous dispersion containing a first fluoropolymer and a first aqueous medium is used.

[0187] (First fluoropolymer)

[0188] The first fluoropolymer contained in the first aqueous dispersion is the same as the first fluoropolymer contained in the above-described aqueous dispersion, including its preferred form, therefore its description is omitted.

[0189] In addition, when compound (2) is used in the manufacture of the first fluoropolymer, the content of compound (2) is preferably 1.0 to 1000 ppm by mass relative to the total aqueous dispersion before the start of polymerization. From the viewpoint of further improving the effect of the present invention, it is more preferably 1.0 to 800 ppm by mass, even more preferably 3.0 to 500 ppm by mass, and particularly preferably 5.0 to 300 ppm by mass.

[0190] Before the polymerization of the monomers used in the manufacture of the second fluoropolymer begins, the content of the first fluoropolymer relative to the total mass of the first aqueous dispersion is 0.01 to 4.0% by mass, preferably 0.01 to 2.0% by mass, and more preferably 0.01 to 1.5% by mass, from the perspective of being able to manufacture the second fluoropolymer more efficiently.

[0191] In this specification, "before the polymerization of the monomer used in the manufacture of the second fluoropolymer" refers to the point immediately preceding the start of polymerization. Here, "the point at which polymerization begins" refers to the point in time when the monomer and polymerization initiator are coexisting in the reactor after the reactor has reached a point above the polymerization temperature, and the point in time when the reactor has reached a point above the polymerization temperature after the monomer and polymerization initiator are coexisting in the reactor.

[0192] Before the polymerization of the monomers used in the manufacture of the second fluoropolymer begins, from the perspective of suppressing coloration of the second fluoropolymer, the concentration of sulfate ions relative to the total mass of the aqueous medium in the first aqueous dispersion is preferably 10 ppm by mass or less, more preferably 5 ppm by mass or less. As a lower limit, 0 ppm by mass can be cited as an example.

[0193] As an example of a method to achieve the above-mentioned concentration of sulfate ions, a method of removing sulfate ions using an anion exchange resin during the manufacture of the first fluoropolymer can be cited.

[0194] Here, sulfate ions are derived, for example, from the polymerization initiator (especially ammonium persulfate) used in the manufacture of the first fluoropolymer, and are sometimes contained in the first aqueous dispersion containing the first fluoropolymer. By keeping the sulfate ion content below 10 ppm by mass (especially below 5 ppm by mass), it is presumed that the formation of heat-sensitive end groups such as carboxylic acid groups and sulfonic acid groups on the second fluoropolymer can be suppressed, resulting in suppressed coloring of the second fluoropolymer.

[0195] Before the polymerization of the monomers used in the manufacture of the second fluoropolymer begins, from the perspective of suppressing the aggregation of the second fluoropolymer, the concentration of ammonium ions relative to the total mass of the aqueous medium in the first aqueous dispersion is preferably 20 ppm by mass or less, more preferably 10 ppm by mass or less. As a lower limit, 0 ppm by mass can be cited as an example.

[0196] As an example of a method to achieve the above-mentioned concentration of ammonium ions, a method of removing ammonium ions using an anion exchange resin during the manufacture of the first fluoropolymer can be cited.

[0197] Here, ammonium ions, for example, originate from the initiator (especially ammonium persulfate) used in the manufacture of the first fluoropolymer, and are sometimes contained in the first aqueous dispersion containing the first fluoropolymer. By keeping the ammonium ion content below 20 ppm by mass, it is presumed that the ionic strength in the aqueous medium will decrease, resulting in an increase in the manufacturing efficiency of the second fluoropolymer.

[0198] The first fluoropolymer is preferably dispersed in the form of particles in the first aqueous medium.

[0199] In this case, from the perspective of being able to manufacture the second fluoropolymer more efficiently, 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.

[0200] The average particle size of the first fluoropolymer was determined by laser diffraction and scattering. A cumulative curve was calculated with the total volume of the particle clusters as 100%. The particle size (D) at the point where the cumulative volume reaches 50% on this cumulative curve was then calculated.50 The detailed measurement conditions are as described in the Examples section.

[0201] The preferred method for manufacturing the first fluoropolymer is to polymerize monomers (preferably a mixture of monomers including TFE and PAVE) in an aqueous medium in the presence of a polymerization initiator. This yields a first fluoropolymer dispersed in particulate form in the aqueous medium.

[0202] The aqueous medium thus obtained, in which the first fluoropolymer particles are dispersed, can be used directly as the first aqueous dispersion, or it can be used as the first aqueous dispersion after further addition of other aqueous media. Alternatively, the first fluoropolymer can be dispersed in another aqueous medium after solvent replacement and used as the first aqueous dispersion.

[0203] As the polymerization initiator used in the manufacture of the first fluoropolymer, a water-soluble polymerization initiator is preferred, more preferably a persulfate such as ammonium persulfate, sodium persulfate, or potassium persulfate, or an organic polymerization initiator such as bis(2-di ...

[0204] Examples of aqueous media used in the manufacture of the first fluoropolymer include water, or a mixture of water and a water-soluble organic solvent. Specific examples of water-soluble organic solvents include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol.

[0205] The method for manufacturing the first fluoropolymer preferably includes a heating step that involves heating the aqueous medium in which the first fluoropolymer is dispersed. This deactivates the polymerization initiator present in the system, thus reducing the influence of the polymerization initiator used in the manufacturing of the first fluoropolymer during the production of the second fluoropolymer. As a result, a second fluoropolymer with a high molecular weight is readily obtained.

[0206] From the perspective of further promoting the deactivation of polymerization initiators in aqueous media, the heating temperature of the heating process is preferably 70-100°C, more preferably 80-98°C, and even more preferably 85-95°C.

[0207] (First aqueous medium)

[0208] The first aqueous dispersion used in step 1 contains a first aqueous medium. As mentioned above, the first aqueous medium contained in the first aqueous dispersion may also be a polymerization solvent used in the manufacture of the first fluoropolymer.

[0209] A specific example of the first aqueous medium contained in the first aqueous dispersion is the same as a specific example of the aqueous medium used in the manufacture of the first fluoropolymer.

[0210] Before the polymerization of the monomers used in the manufacture of the second fluoropolymer begins, the content of the first aqueous medium relative to the total mass of the first aqueous dispersion is preferably 60 to 99.9% by mass, more preferably 96 to 99.9% by mass, and even more preferably 98 to 99.9% by mass.

[0211] (Other ingredients)

[0212] The first aqueous dispersion used in step 1 may also contain other components besides the first fluoropolymer and the aqueous medium.

[0213] Specific examples of other components that may be included in the first aqueous dispersion include chain transfer agents, emulsifiers other than fluorinated emulsifiers, pH adjusters, and waxes. Details of other components are as described above and therefore omitted.

[0214] 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 first aqueous medium. Furthermore, the amount of chain transfer agent used is preferably 0.1 to 20 parts by mass relative to 100 parts by mass of the specific monomer described later, more preferably 0.1 to 15 parts by mass, and even more preferably 0.1 to 10 parts by mass.

[0215] When the first aqueous dispersion contains an emulsifier other than a fluorinated emulsifier, the content of the emulsifier other than a fluorinated emulsifier is preferably 0.01 to 5 parts by mass relative to 100 parts by mass of the first aqueous medium.

[0216] 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 first aqueous medium.

[0217] When the first aqueous dispersion contains wax, the wax content is preferably 1 to 10 parts by mass relative to 100 parts by mass of the first aqueous medium.

[0218] Before the polymerization of the monomers used in the manufacture of the second fluoropolymer begins, the concentration of the fluorinated emulsifier is 100 ppm by mass or less relative to the total mass of the first fluoropolymer in the first aqueous dispersion. For better results from the present invention, it is preferably 50 ppm by mass or less, more preferably 25 ppm by mass, and even more preferably 5 ppm by mass or less. As a lower limit, 0 ppm by mass can be cited as an example.

[0219] Fluorinated emulsifiers are emulsifiers in which fluorine atoms are present in the hydrophobic portion of the hydrophilic or hydrophobic site. Specific examples of fluorinated emulsifiers include fluoroalkyl salts and fluorinated ether carboxylic acids.

[0220] As an example of a method to bring the concentration of fluorinated emulsifier within the above-mentioned range, a method for producing an aqueous dispersion without using fluorinated emulsifiers can be cited.

[0221] Before the polymerization of the monomers used in the manufacture of the second fluoropolymer begins, 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. For better results from the present invention, it is preferably 50 ppm by mass or less, more preferably 25 ppm by mass, and even more preferably 5 ppm by mass or less. As a lower limit, 0 ppm by mass can be cited as an example.

[0222] Before the polymerization of the monomers used in the manufacture of the second fluoropolymer begins, from the perspective of polymerization stability, the concentration of fluoride ions relative to the total mass of the first aqueous dispersion is preferably 100 ppm by mass or less, more preferably 50 ppm by mass or less. As a lower limit, 0 ppm by mass can be cited as an example.

[0223] As an example of a method to achieve the above-mentioned concentration of fluoride ions, one can exemplify the method of removing fluoride ions using an anion exchange resin during the manufacture of the first fluoropolymer.

[0224] Here, fluoride ions are generated by the reaction of a polymerization initiator (e.g., ammonium persulfate) with the monomers used in the manufacture of the first fluoropolymer and are sometimes contained in the first aqueous dispersion.

[0225] <Specific monomer>

[0226] In step 1, a specific monomer containing TFE is used.

[0227] The amount of TFE used relative to the amount of a specific monomer is preferably 97-100% by mass, more preferably 98-100% by mass, and even more preferably 99-100% by mass.

[0228] A particular monomer may contain fluorinated monomers other than TFE, but may also substantially not contain fluorinated monomers other than TFE.

[0229] Essentially, "excluding fluorinated monomers other than TFE" means that the amount of fluorinated monomers other than TFE used is less than 0.0001% by mass relative to the amount of a specific monomer used, and can be 0 by mass.

[0230] Other fluorinated monomers besides TFE include those monomers containing fluorine atoms as exemplified above as modified monomers. Two or more fluorinated monomers other than TFE may be used in combination.

[0231] A particular monomer may also contain monomers other than fluorinated monomers (hereinafter also referred to as "other monomers"), but preferably does not contain other monomers.

[0232] "Substantially free of other monomers" means that the amount of other monomers used is less than 0.0001% by mass relative to the amount of a specific monomer used, more preferably 0% by mass.

[0233] Other monomers can be listed as examples of monomers that do not contain fluorine atoms, as exemplified above as modified monomers. Two or more other monomers may also be used in combination.

[0234] The amount of the specific monomer used is preferably 1 to 50 parts by mass relative to 100 parts by mass of the aqueous medium contained in the first aqueous dispersion, more preferably 1 to 40 parts by mass, and even more preferably 1 to 30 parts by mass.

[0235] <Polymerization Initiator>

[0236] In step 1, a specific monomer is preferably polymerized in the presence of a polymerization initiator.

[0237] Oil-soluble free radical initiators, water-soluble free radical initiators, and water-soluble redox catalysts are preferred as polymerization initiators.

[0238] Specific examples of oil-soluble free radical initiators include oil-soluble organic peroxides such as tert-butyl peroxypentanoate (hereinafter also referred to as "PBPV") and diisopropyl peroxydicarbonate (hereinafter also referred to as "IPP").

[0239] Specific examples of water-soluble free radical initiators include persulfates such as ammonium persulfate and potassium persulfate, and water-soluble organic peroxides such as bis(butyl) peroxide, bis(glutar) peroxide, and tert-butyl hydroperoxide (hereinafter also referred to as "TBHP").

[0240] As a water-soluble redox catalyst, a combination of oxidants such as bromic acid or its salts, chloric acid or its salts, persulfate or its salts, permanganate or its salts, and hydrogen peroxide with reducing agents such as sulfites or their salts, bisulfite or its salts, thiosulfate or its salts, organic acids, and inorganic salts is preferred. Potassium persulfate and ammonium persulfate are preferred as persulfates. Sodium sulfite is preferred as a sulfite. Combinations of sulfate anions, sulfite anions, chloride anions, and metal ions can be included as inorganic salts. Transition metal ions are preferred, including ions of manganese, iron, cobalt, nickel, copper, zinc, cerium, and silver, with iron ions being the most preferred. Ferrous sulfate is preferred as an inorganic salt.

[0241] The preferred polymerization initiators are oil-soluble free radical initiators and water-soluble free radical initiators. From the perspective of being able to manufacture fluoropolymers more effectively, oil-soluble free radical initiators are preferred, and oil-soluble organic peroxides are even more preferred.

[0242] Two or more polymerization initiators can be used together.

[0243] The amount of polymerization initiator used relative to 100 parts by weight of a specific monomer is preferably 1 to 1000 ppm, more preferably 5 to 750 ppm, and even more preferably 10 to 500 ppm.

[0244] <Other Ingredients>

[0245] During the polymerization of a particular monomer, components other than those mentioned above (hereinafter also referred to as "other components") may be used. A specific example of an other component is a reducing agent.

[0246] The amount of other components used is preferably 1 to 2000 ppm relative to 100 parts by weight of a specific monomer.

[0247] <Steps of Process 1>

[0248] In step 1, a specific monomer is polymerized in a first aqueous dispersion to produce a second aqueous dispersion.

[0249] Specific monomers are added to the reaction system (i.e., the polymerization reactor) using conventional methods. For example, specific monomers can be added to the reaction system continuously or intermittently to bring the polymerization pressure to a specified level. Alternatively, specific monomers can be dissolved in an aqueous medium, and the resulting solution can be added to the reaction system continuously or intermittently.

[0250] When using a polymerization initiator, the initiator can be added to the reaction system all at once or in batches.

[0251] The polymerization temperature is preferably 10–95°C, more preferably 15–90°C.

[0252] The polymerization pressure is preferably 0.5 to 4.0 MPaG, more preferably 0.6 to 3.5 MPaG.

[0253] In the case of batch processing, the polymerization time is preferably 90 to 1000 minutes, more preferably 90 to 700 minutes.

[0254] The polymerization of a particular monomer is preferably carried out in the absence of a substantially emulsifier.

[0255] As emulsifiers, well-known emulsifiers and conventional surfactants can be cited as examples.

[0256] The absence of emulsifiers refers to an environment where the content of emulsifiers relative to the total mass of the aqueous medium contained in the first aqueous dispersion is 0.03 ppm by mass or less, preferably 0.02 ppm by mass or less, and more preferably 0 ppm by mass.

[0257] (Second aqueous dispersion)

[0258] By implementing step 1, a second aqueous dispersion containing the first fluoropolymer, the second fluoropolymer, and the second aqueous medium is obtained.

[0259] First fluoropolymer and second fluoropolymer

[0260] The first and second fluoropolymers contained in the second aqueous dispersion are the same as those contained in the above-mentioned aqueous dispersion, including their preferred embodiments, and therefore their descriptions are omitted.

[0261] It is presumed that during the polymerization of a specific monomer, the specific monomer polymerizes within the particles of the first fluoropolymer. Therefore, by performing step 1, particles containing both the first and second fluoropolymers can be generated. That is, according to step 1, it is presumed that the second fluoropolymer is obtained in the form of particles containing both the first and second fluoropolymers. In this case, by performing step 1, a second aqueous dispersion containing particles of both the first and second fluoropolymers dispersed in the aforementioned aqueous medium can be obtained.

[0262] In addition, the first fluoropolymer and the second fluoropolymer can be copolymerized.

[0263] The content of the first fluoropolymer relative to the total mass of the second aqueous dispersion is preferably 0.10 to 3.0 by mass, more preferably 0.15 to 2.0 by mass, and even more preferably 0.20 to 1.5 by mass.

[0264] The content of the second fluoropolymer relative to the total mass of the second aqueous dispersion is preferably 10 to 40% by mass, more preferably 12 to 35% by mass, and even more preferably 15 to 30% by mass.

[0265] 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%, and even more preferably 0.3 to 2.5 mol%. When the PAVE units are PMVE, PEVE, or PPVE units, or when a mixture of two or more of these units is used, the content is preferably the same.

[0266] The PAVE unit is preferably contained in the first fluoropolymer.

[0267] In the second aqueous dispersion, the content of TFE units relative to the total of all units of the first and second fluoropolymers is preferably 90 to 99.8 mol%, more preferably 93 to 99.5 mol%, and even more preferably 95 to 99.0 mol%.

[0268] The TFE unit only needs to be contained in at least the second fluoropolymer, but preferably in both the first and second fluoropolymers.

[0269] In the second aqueous dispersion, the total content of the first fluoropolymer and the second fluoropolymer relative to the total mass of the second aqueous dispersion is preferably 10 to 40% by mass, more preferably 12 to 35% by mass, and even more preferably 15 to 35% by mass.

[0270] The first fluoropolymer and the second fluoropolymer may exist separately in the second aqueous dispersion, but preferably in the form of particles containing the first fluoropolymer and the second fluoropolymer (preferably particles composed of the first fluoropolymer and the second fluoropolymer).

[0271] In this case, from the perspective of dispersion stability, the average particle size is preferably below 500 μm, more preferably below 450 μm, and even more preferably below 400 μm.

[0272] In addition, from the perspective of cohesion, the average particle size is preferably above 50 nm, more preferably above 80 nm, and even more preferably above 100 nm.

[0273] The average particle size is determined by laser diffraction and scattering to measure the particle size distribution. The cumulative curve is calculated with the total volume of the particle group as 100%, and the particle size is the point on the cumulative curve where the cumulative volume reaches 50%.

[0274] Second water-based medium

[0275] The specific example of the second aqueous medium contained in the second aqueous dispersion is the same as the specific example of the aqueous medium used in the manufacture of the first fluoropolymer.

[0276] The second aqueous medium can be the first aqueous medium itself contained in the first aqueous dispersion, or it can include the first aqueous medium contained in the first aqueous dispersion and additionally added aqueous media.

[0277] From the perspective of the dispersion stability of the first fluoropolymer and the second fluoropolymer, the content of the second aqueous medium relative to the total mass of the second aqueous dispersion is preferably 50-99% by mass, more preferably 60-99% by mass, and even more preferably 70-99% by mass.

[0278] The compounds represented by formula (S1) and formula (S2)

[0279] 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 preferably 100 ppb or less relative to the total mass of the first fluoropolymer and the second fluoropolymer.

[0280] The compounds represented by formula (S1) and formula (S2) are components produced during the polymerization of TFE in the presence of a polymerization initiator, a chain transfer agent, and an emulsifier (especially a hydrocarbon emulsifier). Therefore, when an emulsifier is not used in the manufacture of the second aqueous dispersion, the amount of compounds represented by formula (S1) and formula (S2) generated can be suppressed, making it easy to keep the content of these compounds within the range described later.

[0281] Formula (S1): H-(CF2) n -COOM

[0282] Formula (S2): H-(CF2) n -SO3M

[0283] In formulas (S1) and (S2), M independently represents a hydrogen atom, Na, K, or NH4, and n independently represents 8 or 10.

[0284] In the second aqueous dispersion, the content of the compound represented by formula (S1) and the content of the compound represented by formula (S2) relative to the total mass of the first fluoropolymer and the second fluoropolymer are preferably 100 ppb or less by mass, more preferably 50 ppb or less by mass, even more preferably 25 ppb or less by mass, and particularly preferably 0 ppb by mass (i.e., free of the compound represented by formula (S1) and the compound represented by formula (S2)).

[0285] other

[0286] The second aqueous dispersion preferably contains substantially no emulsifier. As mentioned above, the emulsifier is an example of an emulsifier, and therefore its description is omitted.

[0287] The second aqueous dispersion is substantially free of emulsifiers, meaning that the content of emulsifiers relative to the total mass of the second aqueous dispersion is 0.03 ppm by mass or less, preferably 0.02 ppm by mass or less, and more preferably 0 ppm by mass.

[0288] In step 1, the second aqueous dispersion can be heat-treated. During heat treatment, the second aqueous dispersion obtained in step 1 can be heated directly, or it can be heated after adding a free radical initiator, or it can be heated after adjusting the content of the first and second fluoropolymers in the second aqueous dispersion through concentration, dilution, etc.

[0289] [Process 2]

[0290] Step 2 is the process of adding a surfactant containing a nonionic surfactant to the above-mentioned second aqueous dispersion to obtain a specific aqueous dispersion.

[0291] The following sections will first provide a detailed description of the materials used in process 2, and then provide a detailed description of the steps in process 2.

[0292] <Second Aqueous Dispersion>

[0293] The second aqueous dispersion used in step 2 is as described above, so its description is omitted.

[0294] <surfactants>

[0295] The surfactant used in step 2 includes a nonionic surfactant. The surfactant may also include surfactants other than nonionic surfactants (hereinafter also referred to as "other surfactants").

[0296] The amount of surfactant used relative to the total mass of the first and second fluoropolymers contained in the second aqueous dispersion supplied to step 2 is preferably 0.10 to 19.8% by mass, more preferably 0.15 to 16.5% by mass, even more preferably 0.20 to 15.4% by mass, and particularly preferably 0.20 to 12.0% by mass. If the amount of surfactant used is 0.1% by mass or more, the dispersion stability of the specific aqueous dispersion is better. If the amount of surfactant used is 19.8% by mass or less, aggregation during subsequent processes can be suppressed, resulting in better manufacturing stability.

[0297] (Nonionic surfactant)

[0298] The nonionic surfactant used in step 2 is the same as the nonionic surfactant contained in the above-mentioned aqueous dispersion, including its preferred form, so its description is omitted.

[0299] The amount of nonionic surfactant used relative to the total mass of the first and second fluoropolymers contained in the second aqueous dispersion supplied to step 2 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. If the amount of nonionic surfactant used is 0.1% by mass or more, the dispersion stability of the specific aqueous dispersion is better. If the amount of nonionic surfactant used is 5.0% by mass or less, aggregation in subsequent processes can be suppressed, resulting in better manufacturing stability.

[0300] The amount of nonionic surfactant used is preferably 85–99.9% by mass, more preferably 90–99% by mass, and even more preferably 92–98% by mass, relative to the amount of surfactant used in step 2. If the amount of nonionic surfactant used is 85% by mass or more, the dispersion stability of the specific aqueous dispersion is better. If the amount of nonionic surfactant used is 99.9% by mass or less, aggregation during subsequent processes can be suppressed, resulting in better manufacturing stability.

[0301] (Other surfactants)

[0302] In step 2, other surfactants can also be added. This can increase the concentration rate in step 4, which will be described later.

[0303] There are no particular restrictions on the types of other surfactants, but anionic surfactants are preferred.

[0304] The anionic surfactants are the same as the anionic surfactants that may be contained in the above-mentioned aqueous dispersion, including their preferred forms, so their description is omitted.

[0305] The amount of other surfactants (especially anionic surfactants) used relative to the total mass of the first and second fluoropolymers contained in the second aqueous dispersion supplied to step 2 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. If the amount of other surfactants (especially anionic surfactants) used is 100 ppm by mass or more, the concentration rate in step 4 described later can be increased. If the amount of other surfactants (especially anionic surfactants) used is 3000 ppm by mass or less, the formation of aggregates during the concentration in step 4 described later can be further suppressed.

[0306] <Steps of Process 2>

[0307] In step 2, a surfactant containing a nonionic surfactant is added to the second aqueous dispersion to produce a specific aqueous dispersion.

[0308] (Specific aqueous dispersion)

[0309] By implementing step 2, a specific aqueous dispersion is obtained, comprising a surfactant containing the nonionic surfactant, and a first fluoropolymer, a second fluoropolymer, and a second aqueous medium contained in the second aqueous dispersion.

[0310] A particular aqueous dispersion may also contain other components that may be included in the aqueous dispersion.

[0311] [Process 3]

[0312] In this manufacturing method, step 3 is preferably included, in which a specific aqueous dispersion is contacted with an ion exchange resin to obtain a purified specific aqueous dispersion. This removes impurities such as components from the polymerization initiator and fluoropolymers with ionic functional groups, thereby further suppressing coloration of the coating film.

[0313] The ion exchange resin used in step 3 can be either anion exchange resin or cation exchange resin. From the perspective of further removing the components that cause the coating to become colored, anion exchange resin is preferred.

[0314] The amount of anion exchange resin used is preferably 1 to 100 parts by weight relative to 100 parts by weight of a specific aqueous dispersion, more preferably 1 to 50 parts by weight.

[0315] As a specific example of a method for contacting a particular aqueous dispersion with an anion exchange resin, examples include mixing the particular aqueous dispersion with an anion exchange resin, or passing the particular aqueous dispersion through a column packed with anion exchange resin.

[0316] When the anion exchange resin is brought into contact with a specific aqueous dispersion, the temperature of the specific aqueous dispersion is preferably 10–50°C, more preferably 15–40°C.

[0317] The contact time between the anion exchange resin and the specific aqueous dispersion is preferably 10 to 360 minutes, more preferably 10 to 240 minutes.

[0318] When contacting anion exchange resin with a specific aqueous dispersion, the pH value of the specific aqueous dispersion is not limited. The pH value can be less than 7 or higher than 7.

[0319] Step 3 preferably includes a treatment of adding at least one of the nonionic surfactant and the anionic surfactant to the purified specific aqueous dispersion after contacting the specific aqueous dispersion with the ion exchange resin.

[0320] In step 3, the amount of nonionic surfactant used is preferably 0.1 to 7.0% by mass relative to the total mass of the first fluoropolymer and the second fluoropolymer contained in the specific aqueous dispersion obtained in step 2, more preferably 0.2 to 6.5% by mass.

[0321] In step 3, the amount of anionic surfactant used is preferably 200 to 3000% by mass relative to the total mass of the first fluoropolymer and the second fluoropolymer contained in the specific aqueous dispersion obtained in step 2, more preferably 250 to 2500% by mass.

[0322] [Process 4]

[0323] This manufacturing method may further include a step 4, which involves concentrating the purified specific aqueous dispersion obtained in step 3. Thus, the aforementioned aqueous dispersion is obtained.

[0324] The concentration of the second fluoropolymer in the aqueous dispersion obtained in step 4 is higher than the concentration of the second fluoropolymer in the specific aqueous dispersion obtained in step 2.

[0325] The concentration method for the purified specific aqueous dispersion obtained in step 3 can be a known concentration method, such as centrifugation, electrophoresis, or phase separation.

[0326] Step 4 may include adding at least one of nonionic surfactants, ammonia, and viscosity modifiers (e.g., polyethylene oxide) to the concentrated purified specific aqueous dispersion after concentrating the purified specific aqueous dispersion obtained in step 3.

[0327] The amount of nonionic surfactant used in step 4 is preferably 1.0 to 18% by mass relative to the total mass of the first fluoropolymer and the second fluoropolymer contained in the purified specific aqueous dispersion obtained in step 3, more preferably 1.1 to 15% by mass.

[0328] The concentration of ammonia in the ammonia solution is preferably 1-40% by mass, more preferably 5-40% by mass, and even more preferably 10-35% by mass.

[0329] The amount of ammonia used in step 4 is preferably 0.001 to 1.0% by mass relative to the total mass of the first fluoropolymer and the second fluoropolymer contained in the purified specific aqueous dispersion obtained in step 3, more preferably 0.005 to 0.5% by mass.

[0330] The amount of viscosity modifier used is preferably 0 to 3.0% by mass relative to the total mass of the first fluoropolymer and the second fluoropolymer contained in the purified specific aqueous dispersion obtained in step 3, more preferably 0.01 to 2.5% by mass.

[0331] The aqueous dispersion obtained in step 4 contains a surfactant containing a nonionic surfactant, a first fluoropolymer, a second fluoropolymer, and a second aqueous medium, and may also contain anionic surfactants.

[0332] The content of surfactant relative to the total mass of the first fluoropolymer and the second fluoropolymer contained in the aqueous dispersion obtained in step 4 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.

[0333] The content of the nonionic surfactant relative to the total mass of the first fluoropolymer and the second fluoropolymer contained in the aqueous dispersion obtained in step 4 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.

[0334] The content of the first fluoropolymer relative to the total mass of the aqueous dispersion obtained in step 4 is preferably 0.1 to 7.5% by mass, more preferably 0.5 to 7.0% by mass, and even more preferably 0.8 to 6.5% by mass.

[0335] The content of the second fluoropolymer relative to the total mass of the aqueous dispersion obtained in step 4 is preferably 20-85% by mass, more preferably 30-80% by mass, and even more preferably 40-75% by mass.

[0336] The content of the second aqueous medium relative to the total mass of the aqueous dispersion obtained in step 4 is preferably 15 to 80% by mass, more preferably 20 to 70% by mass, and even more preferably 25 to 60% by mass.

[0337] When the aqueous dispersion obtained in step 4 contains a viscosity modifier, the content of the viscosity modifier relative to the total mass of the aqueous dispersion obtained in step 4 is preferably 0.05 to 3.0% by mass, more preferably 0.08 to 2.5% by mass, and even more preferably 0.1 to 2.0% by mass.

[0338] [Manufacturing method containing polymer substrate]

[0339] The method for manufacturing the polymer-containing substrate of the present invention is a method of obtaining the polymer-containing substrate by contacting the above-mentioned aqueous dispersion with a substrate made of glass fiber (hereinafter also referred to as "glass fiber substrate").

[0340] Examples of glass fiber substrates include woven glass fiber fabrics or ropes.

[0341] The method of contacting the aqueous dispersion with the glass fiber substrate can be a known method, such as immersing the glass fiber substrate in the aqueous dispersion, spraying the aqueous dispersion, or applying the aqueous dispersion with a roller or brush.

[0342] Example

[0343] The present invention will be described in detail below with examples. Examples 1 to 4 and 7 to 10 are exemplary embodiments, and examples 5 to 6 are comparative examples. However, the present invention is not limited to these examples. In addition, the mixing amounts of each component in the tables described below are shown on a mass basis.

[0344] [Measurement and Evaluation Methods]

[0345] <Average primary particle size of PTFE particles>

[0346] Using an aqueous dispersion of PTFE as the sample, the average primary particle size of PTFE particles was determined using a laser diffraction-scattering particle size distribution measuring device (Otsuka Electronics Co., Ltd., ELSZ).

[0347] <Standard specific gravity of PTFE powder>

[0348] Specific gravity is measured according to ASTM D4895-04 standard.

[0349] Weigh 12.0 g of the sample (PTFE powder) and hold it in a cylindrical mold with an inner diameter of 28.6 mm at 34.5 MPa for 2 minutes. Place it in an oven at 290 °C and heat at 120 °C / hour. Then, hold it at 380 °C for 30 minutes, cool it at 60 °C / hour, and hold it at 294 °C for 24 minutes. After holding the sample in a desiccator at 23 °C for 12 hours, determine the specific gravity of the sample relative to water at 23 °C, and use this as the standard specific gravity (hereinafter also referred to as "SSG"). The smaller the SSG value, the larger the molecular weight.

[0350] <PTFE concentration and surfactant concentration>

[0351] Approximately 7g of PTFE aqueous dispersion was placed in an aluminum pan (mass W0) and weighed (mass W1). Based on the mass after drying at 120℃ for 1 hour (mass W2) and the mass after drying at 380℃ for 35 minutes (mass W3), the PTFE concentration and surfactant concentration (the ratio of surfactant to PTFE mass) were calculated using the following formula.

[0352] PTFE concentration (mass%) = [(W3-W0) / (W1-W0)] × 100

[0353] Surfactant concentration (mass% / PTFE) = [(W2-W3) / (W3-W0)] × 100

[0354] <Viscosity>

[0355] The viscosity of the PTFE aqueous dispersion was measured using a Brookfield viscometer with a #1 rotor at a liquid temperature of 23°C and a rotation speed of 60 rpm.

[0356] <pH value>

[0357] The pH value of an aqueous PTFE dispersion was determined by the glass electrode method.

[0358] <Surface tension>

[0359] The surface tension of aqueous PTFE dispersions was determined using a platinum wire ring method.

[0360] <Glass transition temperature Tg and melting point Tm>

[0361] Tg was measured using a NEXTA DSC 600 manufactured by Hitachi Advanced Technology Co., Ltd. Specifically, 5 mg of the sample was measured in an aluminum sample pan, and the sample was heated to 100°C at a rate of 10°C / min under a nitrogen atmosphere. Then, it was cooled to -60°C at a rate of 10°C / min. When the specified temperature was reached, it was heated again to 100°C at a rate of 10°C / min. Tg was estimated from the inflection point confirmed by the second heating operation.

[0362] Tm was determined using a DSC 8500 manufactured by PerkinElmer, which was pre-calibrated for temperature using indium and zinc as standard samples. Specifically, 10 mg of the test sample was measured in an aluminum sample pan, and the sample was heated to 380 °C at a rate of 10 °C / min in air. The endothermic peak at this point was then used to determine the temperature.

[0363] <Coloring Evaluation>

[0364] The coating obtained using an aqueous PTFE dispersion was fired, and a color evaluation was performed.

[0365] Specifically, 7g of PTFE aqueous dispersion was added to an aluminum pan with an inner diameter of 6cm, and dried at 120℃ for 60 minutes to obtain a PTFE coating. The resulting PTFE coating was then fired at 380℃ for 35 minutes, and the hue of the fired PTFE coating was visually confirmed. Color evaluation was performed according to the following criteria: It can be said that the closer the color is to milky white, the more suppressed the coloration of the coating.

[0366] ○: The PTFE coating after firing is milky white to yellow in color.

[0367] ×: The PTFE coating after firing is black to brownish-black.

[0368] [Preparation of raw material solution A1]

[0369] Ultrapure water (33.0 kg) and PMVE (2.28 kg) were added to a 50 L stainless steel pressure reactor equipped with stirring blades and baffles. The reactor was heated to 90 °C while stirring at 170 rpm. TFE was added until the reactor pressure reached 1.30 MPaG, and then 150 g of ammonium persulfate (APS) aqueous solution (5.57% by mass) was added to initiate the reaction. As the reaction started, the pressure inside the reactor decreased, so TFE was added to maintain a constant pressure. After adding 120 g of TFE, the stirring speed was reduced to 40 rpm, the reactor was cooled, and the polymerization reaction was stopped. After recovering the residual gas in the reactor, nitrogen was introduced to 0.10 MPaG while stirring at 20 rpm, and the temperature was raised to 90 °C. The reactor was heated for 3 hours, then cooled and the liquid was extracted. This liquid was used as feedstock A1.

[0370] After freezing and coagulating the raw material liquid A, it was filtered and the fluoropolymer A1 was analyzed by NMR. The results showed that the TFE unit / PMVE unit ratio was 51 / 49 (molar ratio) and the Tg was -5.5℃.

[0371] [Preparation of Raw Material Solution B1]

[0372] Add 20g of Dowex Monosphere 650C (DuPont, cation exchange resin) to feed solution A1 (490g). After stirring for 60 minutes, separate the feed solution from the ion exchange resin by filtration. Add 20g of SA10AOH (Mitsubishi Chemical Corporation, anion exchange resin) to the filtered feed solution. After stirring for 60 minutes, separate the feed solution from the ion exchange resin by filtration to obtain feed solution B1. The content of fluoropolymer A1 is 0.8% of the total mass of feed solution B1.

[0373] [Example 1]

[0374] Ultrapure water (37 g), feed solution B1 (475 g), and paraffin wax (28 g) were added to a 1.0 L stainless steel pressure reactor equipped with stirring blades and baffles to obtain aqueous dispersion B1-1 (equivalent to the first aqueous dispersion). The content of fluoropolymer A1 was 0.7% by mass relative to the total mass of aqueous dispersion B1-1. Furthermore, the concentration of the fluorinated emulsifier was 0 ppm by mass relative to the total mass of fluoropolymer A1 in aqueous dispersion B1-1.

[0375] The content (solid component concentration) of fluoropolymer A1 in aqueous dispersion B1-1 is calculated by weighing the residue after heating 2.0g of aqueous dispersion B at 170°C for 20 minutes and then using the following formula. The solid component concentration is then calculated. For the examples described later, the same method is used, except that the type of aqueous dispersion is changed to the dispersion used in each example.

[0376] "Solid component concentration (mass %) = 100 × heating residue of aqueous dispersion B1-1 (g) / mass of aqueous dispersion B1-1 (2g)"

[0377] The prepared tablets of fluoropolymer A1 were analyzed using a Fourier transform infrared spectrophotometer (Nicoleti S50, Thermo Fisher Scientific) according to the method described in Japanese Patent Application Publication No. 2022-50435. The results showed that per 10... 6 The number of ionic functional groups per carbon atom in the main chain is less than 1000.

[0378] The resulting aqueous dispersion B1-1 was heated to 70°C while being stirred at 260 rpm. TFE was added until the reactor pressure reached 1.40 MPaG, and then 5 ml of APS aqueous solution (0.436% by mass) was added to initiate polymerization. As polymerization began, the pressure inside the reactor decreased, so TFE was added to maintain a constant pressure. After adding 80 g of TFE, 5 ml of hydroquinone (HQ) aqueous solution (0.349% by mass) was added. After adding 120 g of TFE, the reactor was cooled, and the polymerization reaction was terminated, yielding aqueous dispersion C1-1 (equivalent to the second aqueous dispersion).

[0379] Aqueous dispersion C1-1 is a dispersion containing PTFE particles (average primary particle size 249 nm) of fluoropolymer A1 and fluoropolymer A2 dispersed in an aqueous medium, with a solid content concentration of 15.5% by mass.

[0380] A portion of the obtained aqueous dispersion C1-1 was adjusted to 20°C and stirred to agglomerate the PTFE particles, obtaining PTFE powder. The PTFE powder was then dried at 200°C. The resulting PTFE powder had an SSG of 2.22 and a melting point of 339°C. Furthermore, no byproduct fluorinated oligomers were identified in the obtained PTFE powder.

[0381] Add the various components to the aqueous dispersion C1-1 to achieve the desired effect. This results in the addition of nonionic surfactant (a) (NEWCOL 1308FA manufactured by Nippon Emulsifier Co., Ltd., C...). 13 H 27 The content of -(OC2H4)8-OCH(CH3)CH2-OH) is 2.7% by mass, the content of ammonium laurate is 560 ppm by mass, and the content of triethanolamine lauryl sulfate is 210 ppm by mass, thus obtaining an aqueous dispersion C2-1 (specific aqueous dispersion) equivalent to aqueous dispersion C2-1. The pH value of aqueous dispersion C2-1 is 2.2.

[0382] MP62WS (Lanxess, anion exchange resin, 623g) was added to aqueous dispersion C2-1, and the mixture was stirred for 60 minutes. The mixture was then filtered to separate the aqueous dispersion from the ion exchange resin, yielding aqueous dispersion C3-1 (equivalent to purifying a specific aqueous dispersion). The pH of aqueous dispersion C3-1 was 3.7.

[0383] The components were added to aqueous dispersion C3-1 such that, relative to the mass of PTFE particles in aqueous dispersion C3-1, the content of nonionic surfactant (a) was 4.0% by mass, the content of ammonium laurate was 1680 ppm by mass, and the content of triethanolamine lauryl sulfate was 630 ppm by mass. The dispersion was then 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% by mass, and the concentration of nonionic surfactant (a) relative to the mass of PTFE particles was 2.46% by mass.

[0384] The components were added to aqueous dispersion C4-1 such that, relative to the mass of PTFE particles in aqueous dispersion C4-1, the content of polyethylene oxide was 0.1% by mass, the content of nonionic surfactant (a) was 2.2% by mass, and the content of nonionic surfactant (b) (NEWCOL FAA-09601, C) was [missing information - likely a brand name or product name]. 13 H 27 The content of -OCH2CH(C2H5)O(C2H4O)8H is 1.3% by mass, and the nonionic surfactant (c) is (NEWCOL G1301-H, C manufactured by Japan Emulsifiers Co., Ltd.) 13 H 27 -OCH2CH(C2H5)O (C2H4O) 12 The content of H) is 1.3% by mass. Water and ammonia are then added to obtain PTFE aqueous dispersion C5-1 (equivalent to this aqueous dispersion). The concentration (content) of PTFE particles in PTFE aqueous dispersion C5-1 is 60.6% by mass, the concentration (total content) of surfactant relative to the mass of PTFE particles is 5.1% by mass, and the pH value is 10.4.

[0385] In addition, the average primary particle size of PTFE particles in aqueous dispersion C5-1 is the same as that in aqueous dispersion C1-1.

[0386] The above determinations and evaluations were performed using the obtained PTFE aqueous dispersion C5-1. The results are shown in Table 1.

[0387] In addition, the PTFE aqueous dispersion C5-1 does not substantially contain fluoropolymers with ionic functional groups.

[0388] [Example 2]

[0389] Except that an aqueous solution of disuccinic acid peroxide (0.45% by mass, 25 ml) was used instead of an aqueous solution of APS and no HQ was added during the reaction, an aqueous dispersion C1-2 (equivalent to a second aqueous dispersion) was obtained in the same manner as the preparation method of aqueous dispersion C1-1 in Example 1.

[0390] Aqueous dispersion C1-2 is a dispersion containing PTFE particles (average primary particle size 205 nm) of fluoropolymer A1 and fluoropolymer A3 dispersed in an aqueous medium, with a solid content concentration of 19.6% by mass.

[0391] A portion of the obtained aqueous dispersion C1-2 was adjusted to 20°C and stirred to agglomerate the PTFE particles, obtaining PTFE powder. The PTFE powder was then dried at 200°C. The resulting PTFE powder had an SSG of 2.20 and a melting point of 340°C. Furthermore, no byproduct fluorinated oligomers were identified in the obtained PTFE powder.

[0392] In addition to using aqueous dispersion C1-2, nonionic surfactant (d) (Tergitol TMN100X, C manufactured by Dow Chemical) was also used. 12 H 25 -(OC2H4) 10 Except for replacing the nonionic surfactant (a) with -OH), aqueous dispersion C4-2 was obtained by following the same steps as aqueous dispersions C2-1 to C4-1 in Example 1.

[0393] The components were added to aqueous dispersion C4-2 such that, relative to the mass of PTFE particles in aqueous dispersion C4-2, the content of polyethylene oxide was 0.1% by mass and the content of nonionic surfactant (d) was 4.8% by mass. Water and ammonia were also added to obtain PTFE aqueous dispersion C5-2 (equivalent to this aqueous dispersion). The concentration (content) of PTFE particles in PTFE aqueous dispersion C5-2 was 60.5% by mass, the concentration (total content) of surfactant relative to the mass of PTFE particles was 5.0% by mass, and the pH value was 10.0.

[0394] In addition, the average primary particle size of PTFE particles in the aqueous PTFE dispersion C5-2 is the same as that of PTFE particles in the aqueous dispersion C1-2.

[0395] The above determinations and evaluations were performed using the obtained PTFE aqueous dispersion C5-2. The results are shown in Table 1.

[0396] In addition, the PTFE aqueous dispersion C5-2 does not substantially contain fluoropolymers with ionic functional groups.

[0397] [Example 3]

[0398] Ultrapure water (11L), feed solution B1 (48L), and paraffin wax (1.5kg) were added to a 100L stainless steel pressure reactor equipped with stirring blades and baffles to obtain aqueous dispersion B1-2 (equivalent to the first aqueous dispersion). The content of fluoropolymer A1 was 0.7% by mass relative to the total mass of aqueous dispersion B1-2. Furthermore, the concentration of the fluorinated emulsifier was 0 ppm by mass relative to the total mass of fluoropolymer A1 in aqueous dispersion B1-2.

[0399] The obtained aqueous dispersion B1-2 was heated to 70°C while being stirred at 100 rpm. TFE was injected into the reactor until the reactor pressure reached 1.86 MPaG. A solution of 3.4 g of bis(butanoic acid) peroxide (80% by mass, the remainder being water) dissolved in 1 L of warm water was injected into the reactor to begin polymerization. As polymerization began, the pressure inside the reactor decreased, so TFE was added to maintain a constant pressure. After injecting 13 kg of TFE, the reactor was cooled, and the polymerization reaction was terminated, yielding aqueous dispersion C1-3.

[0400] Aqueous dispersion C1-3 is a dispersion containing PTFE particles (average primary particle size 200 nm) of fluoropolymer A1 and fluoropolymer A4 dispersed in an aqueous medium, with a solid content concentration of 16.7% by mass.

[0401] A portion of the obtained aqueous dispersion C1-3 was adjusted to 20°C and stirred to agglomerate the PTFE particles, obtaining PTFE powder. This PTFE powder was then dried at 200°C. The resulting PTFE powder had an SSG of 2.14 and a melting point of 343°C. Furthermore, no byproduct fluorinated oligomers were identified in the obtained PTFE powder.

[0402] Except for using aqueous dispersion C1-3, aqueous dispersion C4-3 was obtained by following the same steps as aqueous dispersions C2-1 to C4-1 in Example 1.

[0403] Nonionic surfactant (a) was added to aqueous dispersion C4-3, such that the content of nonionic surfactant (a) was 14.0% by mass relative to the mass of PTFE particles in aqueous dispersion C4-3. Water and ammonia were then added to obtain PTFE aqueous dispersion C5-3 (equivalent to this aqueous dispersion). The concentration (content) of PTFE particles in PTFE aqueous dispersion C5-3 was 57.6% by mass, the concentration (total content) of surfactants relative to the mass of PTFE particles was 14.1% by mass, and the pH value was 10.2.

[0404] In addition, the average primary particle size of PTFE particles in the aqueous PTFE dispersion C5-3 is the same as that of PTFE particles in the aqueous dispersion C1-3.

[0405] The above determinations and evaluations were performed using the obtained PTFE aqueous dispersion C5-3. The results are shown in Table 1.

[0406] In addition, the PTFE aqueous dispersion C5-3 does not actually contain fluoropolymers with ionic functional groups.

[0407] [Example 4]

[0408] Following the steps in Example 3, aqueous dispersion C4-3 was obtained. A nonionic surfactant (a) was added to aqueous dispersion C4-3 so that the content of nonionic surfactant (a) was 10.0% by mass relative to the mass of PTFE particles in aqueous dispersion C4-3. Water and ammonia were then added to obtain PTFE aqueous dispersion C5-4 (equivalent to this aqueous dispersion). The concentration (content) of PTFE particles in PTFE aqueous dispersion C5-4 was 59.0% by mass, the concentration (total content) of surfactants relative to the mass of PTFE particles was 10.1% by mass, and the pH value was 10.2.

[0409] In addition, the average primary particle size of PTFE particles in the aqueous PTFE dispersion C5-4 is the same as that of PTFE particles in the aqueous dispersion C1-3.

[0410] The above determinations and evaluations were performed using the obtained PTFE aqueous dispersion C5-4. The results are shown in Table 1.

[0411] In addition, the PTFE aqueous dispersion C5-4 does not actually contain fluoropolymers with ionic functional groups.

[0412] [Example 5]

[0413] The PTFE aqueous dispersion manufactured according to Example 1 of WO2021 / 085470 is PTFE aqueous dispersion C5-5. In addition, PTFE aqueous dispersion C5-5 is a dispersion in which PTFE particles are dispersed in an aqueous medium and does not contain fluoropolymers equivalent to the first fluoropolymer described above.

[0414] The above determinations and evaluations were performed using the obtained PTFE aqueous dispersion C5-5. The results are shown in Table 1.

[0415] [Example 6]

[0416] In a 100L stainless steel pressure reactor equipped with stirring blades and baffles, 60L of ultrapure water, 18g of homopolymer of CF2=CFOCF2CF2CF2CO2H (weight average molecular weight 4500), and 1.5kg of paraffin wax were added. The mixture was stirred at 100rpm while the temperature was raised to 75°C. TFE was injected into the reactor until the pressure reached 1.86MPaG. A solution of 1.08g APS and 106g disuccinic acid peroxide (80% concentration, the remainder being water) dissolved in 1L of warm water was then injected into the reactor to begin polymerization. As polymerization began, the pressure inside the reactor decreased; therefore, TFE was added to maintain a constant pressure. After injecting 9kg of TFE, the reactor was cooled to terminate the polymerization reaction, yielding an aqueous dispersion C1-6.

[0417] Aqueous dispersion C1-6 is a dispersion of PTFE particles (average primary particle size 200 nm) in an aqueous medium, with a solid content concentration of 12.1% by mass.

[0418] A portion of the obtained aqueous dispersion C1-6 was adjusted to 20°C and stirred to agglomerate the PTFE particles, obtaining PTFE powder. The PTFE powder was then dried at 200°C. The resulting PTFE powder had an SSG of 2.18 and a melting point of 337°C.

[0419] Except for using aqueous dispersion C1-6, PTFE aqueous dispersion C5-6 was obtained by following the same steps as in Examples 1 for aqueous dispersions C2-1 to C4-1 and PTFE aqueous dispersion C5-1. The concentration (content) of PTFE particles in PTFE aqueous dispersion C5-6 was 60.8% by mass, the concentration (total content) of surfactant relative to the mass of PTFE particles was 5.0% by mass, and the pH value was 10.0.

[0420] In addition, the average primary particle size of PTFE particles in the aqueous PTFE dispersion C5-6 is the same as that of PTFE particles in the aqueous dispersion C1-6.

[0421] In addition, PTFE aqueous dispersion C5-6 does not contain fluoropolymers equivalent to the first fluoropolymer mentioned above.

[0422] The above determinations and evaluations were performed using the obtained PTFE aqueous dispersion C5-6. The results are shown in Table 1.

[0423] [Preparation of raw material solution A5]

[0424] After adding 320 kg of deionized water to a 430 L stainless steel autoclave equipped with baffles and a stirrer, the autoclave was purged with nitrogen and the pressure reduced. Then, 6010 g of PMVE (perfluoromethyl vinyl ether) was added. While stirring, the temperature was raised to 90 °C, 985 g of TFE was added, and the pressure was increased to 1.36 MPa. Then, 1000 g of an 8.09 wt% aqueous solution of APS was forced in to initiate polymerization. Simultaneously, TFE was added while polymerization continued, maintaining the pressure inside the autoclave at 1.36 MPa.

[0425] The polymerization reaction was terminated when the amount of TFE added reached 1200g. After cooling the autoclave, the TFE inside was released into the atmosphere. Nitrogen gas was introduced to 0.2MPa, and the temperature was raised to 90℃. After heating the autoclave for 3 hours, it was cooled, and reaction solution A5 was extracted.

[0426] After the reaction solution A5 was frozen and condensed, it was filtered and separated. The obtained fluoropolymer A5 was analyzed by NMR. The results showed that the TFE unit / PMVE unit ratio was 52 / 48 (molar ratio) and the Tg was -5℃.

[0427] [Preparation of raw material solution B2]

[0428] Add 20g of Dowex Monosphere 650C (DuPont, cation exchange resin) to feed solution A5 (Xg). After stirring for 60 minutes, separate the feed solution from the ion exchange resin by filtration. Add 20g of SA10AOH (Mitsubishi Chemical Corporation, anion exchange resin) to the filtered feed solution. After stirring for 60 minutes, separate the feed solution from the ion exchange resin by filtration to obtain feed solution B2. The content of fluoropolymer A5 is 0.7% of the total mass of feed solution B2.

[0429] [Example 7]

[0430] Ultrapure water (6.6 L), feed solution B2 (52 L), and paraffin wax (1.5 kg) were added to a 100 L stainless steel pressure reactor equipped with stirring blades and baffles to obtain aqueous dispersion B1-7 (equivalent to the first aqueous dispersion). The content of fluoropolymer A5 was 0.6% by mass relative to the total mass of aqueous dispersion B1-7. Furthermore, the concentration of the fluorinated emulsifier was 0 ppm by mass relative to the total mass of fluoropolymer A5 in aqueous dispersion B1-7.

[0431] The obtained aqueous dispersion B1-7 was heated to 65°C while stirring at 95 rpm. TFE was injected into the reactor until the reactor pressure reached 1.40 MPaG. A solution of 7.0 g of bis(butanoic acid) peroxide (80% by mass, the remainder being water) dissolved in 1 L of warm water was injected into the reactor to begin polymerization. As polymerization began, the pressure inside the reactor decreased, so TFE was added to maintain a constant pressure. After injecting 15.8 kg of TFE, the reactor was cooled, and the polymerization reaction was terminated, yielding aqueous dispersion C1-7.

[0432] Aqueous dispersion C1-7 is a dispersion containing PTFE particles (average primary particle size 172 nm) of fluoropolymer A5 and fluoropolymer A6 dispersed in an aqueous medium, with a solid content concentration of 20.3% by mass.

[0433] A portion of the obtained aqueous dispersion C1-7 was adjusted to 20°C and stirred to agglomerate the PTFE particles, obtaining PTFE powder. The PTFE powder was then dried at 200°C. The resulting PTFE powder had an SSG of 2.15 and a melting point of 343°C. Furthermore, no byproduct fluorinated oligomers were identified in the obtained PTFE powder.

[0434] A nonionic surfactant (a) was added to aqueous dispersion C1-7, such that its content was 2.7% by mass relative to the mass of PTFE particles in aqueous dispersion C1-7, to obtain aqueous dispersion C2-7 (equivalent to a specific aqueous dispersion). The pH value of aqueous dispersion C2-7 was 3.0.

[0435] SA10AOH (Lanxess, anion exchange resin, 623g) was added to aqueous dispersion C2-7. After stirring for 60 minutes, the aqueous dispersion and the ion exchange resin were separated by filtration to obtain aqueous dispersion C3-7 (equivalent to purifying a specific aqueous dispersion). The pH value of aqueous dispersion C3-7 is 3.7.

[0436] The components were added to aqueous dispersion C3-7 such that, relative to the mass of PTFE particles in aqueous dispersion C3-7, the content of nonionic surfactant (a) was 10% by mass, the content of ammonium laurate was 1680 ppm by mass, and the content of triethanolamine lauryl sulfate was 630 ppm by mass. The dispersion was then concentrated by electrophoresis. The supernatant was removed to obtain aqueous dispersion C4-7. In aqueous dispersion C4-7, the concentration (content) of PTFE particles was 66.0% by mass, and the concentration of nonionic surfactant (a) relative to the mass of PTFE particles was 3.47% by mass.

[0437] A nonionic surfactant (a) was added to aqueous dispersion C4-7, such that its content was 10.0% by mass relative to the mass of PTFE particles in aqueous dispersion C4-7. Water and ammonia were then added to obtain PTFE aqueous dispersion C5-7 (equivalent to this aqueous dispersion). The concentration (content) of PTFE particles in PTFE aqueous dispersion C5-7 was 60.9% by mass, the concentration (total content) of surfactants was 10.0% by mass relative to the mass of PTFE particles, and the pH value was 10.3.

[0438] In addition, the average primary particle size of PTFE particles in aqueous dispersion C5-7 is the same as that in aqueous dispersion C1-7.

[0439] The above determinations and evaluations were performed using the obtained PTFE aqueous dispersion C5-7. The results are shown in Table 1.

[0440] In addition, the PTFE aqueous dispersion C5-7 does not substantially contain fluoropolymers with ionic functional groups.

[0441] [Example 8]

[0442] Following the steps in Example 7, aqueous dispersion C4-7 was obtained. A nonionic surfactant (a) was added to aqueous dispersion C4-7 such that the content of nonionic surfactant (a) was 14.0% by mass relative to the mass of PTFE particles in aqueous dispersion C4-7. Water and ammonia were then added to obtain PTFE aqueous dispersion C5-8 (equivalent to this aqueous dispersion). The concentration (content) of PTFE particles in PTFE aqueous dispersion C5-8 was 60.5% by mass, the concentration (total content) of surfactants relative to the mass of PTFE particles was 14.0% by mass, and the pH value was 10.4.

[0443] In addition, the average primary particle size of PTFE particles in the aqueous PTFE dispersion C5-8 is the same as that of PTFE particles in the aqueous dispersion C1-7.

[0444] The above determinations and evaluations were performed using the obtained PTFE aqueous dispersion C5-8. The results are shown in Table 1.

[0445] In addition, the PTFE aqueous dispersion C5-8 does not actually contain fluoropolymers with ionic functional groups.

[0446] [Manufacturing of Raw Material Solution A7]

[0447] In a 50L stainless steel pressure reactor equipped with stirring blades and baffles, 33.0 kg of ultrapure water and 1.66 g of a 50% by mass aqueous solution of sodium 2-acrylamido-2-methyl-1-propanesulfonate (hereinafter also referred to as "NaAAMPS") were added, followed by 2.44 kg of PMVE. The reactor was heated to 90°C while stirring at 170 rpm. TFE was added until the reactor pressure reached 1.49 MPaG, and then 400 g of an aqueous solution of ammonium persulfate (APS) (21.07% by mass) was added to initiate the reaction. As the reaction began, the pressure inside the reactor decreased, so TFE was added to maintain a constant pressure. After adding 1200 g of TFE, the reactor was cooled at 40 rpm to end the polymerization reaction. After recovering the residual gas in the reactor, nitrogen was introduced to 0.10 MPaG while stirring at 20 rpm, and the temperature was raised to 90°C. After heating the reactor for 3 hours, it was cooled and the liquid was extracted. This liquid was used as feedstock A7.

[0448] After freezing and coagulating the raw material liquid A, it was filtered and the fluoropolymer A7 was analyzed by NMR. The results showed that the TFE unit / PMVE unit ratio was 68 / 37 (molar ratio) and the Tg was -5.5℃.

[0449] [Preparation of raw material solution B3]

[0450] Except for diluting feedstock A7 by 5 times, feedstock B3 is obtained by following the same steps as feedstock B2. The content of fluoropolymer A7 is 1.1% of the total mass of feedstock B3.

[0451] [Example 9]

[0452] Ultrapure water (26.6 L), feed solution B3 (32.1 L), and paraffin wax (1.5 kg) were added to a 100 L stainless steel pressure reactor equipped with stirring blades and baffles to obtain aqueous dispersion B1-9 (equivalent to the first aqueous dispersion). The content of fluoropolymer A7 was 0.6% by mass relative to the total mass of aqueous dispersion B1-9. Furthermore, the concentration of the fluorinated emulsifier was 0 ppm by mass relative to the total mass of fluoropolymer A7 in aqueous dispersion B1-9.

[0453] The obtained aqueous dispersion B1-9 was heated to 65°C while stirring at 95 rpm. TFE was injected into the reactor until the reactor pressure reached 1.40 MPaG. A solution of 7.0 g of bis(butanoic acid) peroxide (80% by mass, the remainder being water) dissolved in 1 L of warm water was injected into the reactor to begin polymerization. As polymerization began, the pressure inside the reactor decreased, so TFE was added to maintain a constant pressure. After injecting 15.8 kg of TFE, the reactor was cooled, and the polymerization reaction was terminated, yielding aqueous dispersion C1-9. Aqueous dispersion C1-9 is a dispersion containing PTFE particles (average primary particle size 156 nm) of fluoropolymers A7 and A8 dispersed in an aqueous medium, with a solids concentration of 20.5% by mass.

[0454] A portion of the obtained aqueous dispersion C1-9 was adjusted to 20°C and stirred to agglomerate the PTFE particles, obtaining PTFE powder. The PTFE powder was then dried at 200°C. The resulting PTFE powder had an SSG of 2.15 and a melting point of 343°C. Furthermore, no byproduct fluorinated oligomers were identified in the obtained PTFE powder.

[0455] Following the steps in Example 7, aqueous dispersion C4-9 was obtained. In aqueous dispersion C4-9, the concentration (content) of PTFE particles was 65.3% by mass, and the concentration of nonionic surfactant (a) relative to the mass of PTFE particles was 3.59% by mass.

[0456] Nonionic surfactant (a) was added to aqueous dispersion C4-9, such that its content was 14.0% by mass relative to the mass of PTFE particles in aqueous dispersion C4-9. Water and ammonia were then added to obtain PTFE aqueous dispersion C5-9 (equivalent to this aqueous dispersion). The concentration (content) of PTFE particles in PTFE aqueous dispersion C5-9 was 60.6% by mass, the concentration (total content) of surfactants was 14.0% by mass relative to the mass of PTFE particles, and the pH value was 10.4.

[0457] In addition, the average primary particle size of PTFE particles in aqueous dispersion C5-9 is the same as that in aqueous dispersion C1-9.

[0458] The above determinations and evaluations were performed using the obtained PTFE aqueous dispersion C5-9. The results are shown in Table 1.

[0459] In addition, the PTFE aqueous dispersion C5-9 does not actually contain fluoropolymers with ionic functional groups.

[0460] [Example 10]

[0461] Following the steps of Example 9, aqueous dispersion C1-9 was obtained. Aqueous dispersion C4-10 was obtained following the same steps as in Example 9, except that aqueous dispersion C1-9 was used and nonionic surfactant (d) was used instead of nonionic surfactant (a). Nonionic surfactant (d) was added to aqueous dispersion C4-10 such that the content of nonionic surfactant (d) was 14.0% by mass relative to the mass of PTFE particles in aqueous dispersion C4-10. Water and ammonia were then added to obtain PTFE aqueous dispersion C5-10 (equivalent to this aqueous dispersion). The concentration (content) of PTFE particles in PTFE aqueous dispersion C5-10 was 60.5% by mass, the concentration (total content) of surfactants relative to the mass of PTFE particles was 14.1% by mass, and the pH value was 10.6.

[0462] In addition, the average primary particle size of PTFE particles in the aqueous PTFE dispersion C5-10 is the same as that of PTFE particles in the aqueous dispersion C1-9 mentioned above.

[0463] The above determinations and evaluations were performed using the obtained PTFE aqueous dispersion C5-10. The results are shown in Table 1.

[0464] In addition, the PTFE aqueous dispersion C5-10 does not actually contain fluorinated polymers with ionic functional groups.

[0465] [Table 1]

[0466] As shown in Table 1, it was confirmed that if the aqueous dispersion of the present invention is used, a coating film with suppressed coloring can be formed (Examples 1 to 4, Examples 7 to 10).

[0467] Furthermore, the entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2024-056669, filed on March 29, 2024, are incorporated herein as a disclosure of this invention.

Claims

1. An aqueous dispersion comprising a first fluoropolymer, a second fluoropolymer being polytetrafluoroethylene, a surfactant containing a nonionic surfactant, and an aqueous medium. The first fluoropolymer is per 10 of the polymer 6 Fluoropolymers containing fluorine atoms, with fewer than 1000 ionic functional groups in the main chain, a glass transition temperature below 10°C, and fluorine atoms. The aqueous dispersion does not substantially contain any fluorinated polymers with ionic functional groups other than the first fluorinated polymer.

2. The aqueous dispersion as described in claim 1, wherein, The first fluoropolymer contains units based on monomers having vinyl groups that can be substituted with fluorine atoms.

3. The aqueous dispersion as described in claim 1, wherein, The first fluoropolymer contains tetrafluoroethylene-based units.

4. The aqueous dispersion as described in claim 1, wherein, The total content of the first fluoropolymer and the second fluoropolymer is 10 to 80% of the total mass of the aqueous dispersion.

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

6. The aqueous dispersion as described in claim 1, wherein, The nonionic surfactant comprises at least one selected from the compounds represented by formula (S-1), the compounds represented by formula (S-2), and the compounds represented by formula (S-3). Equation (S-1) R S1 -OL S1 -H Equation (S-2) R S2 -C6H4-OL S2 -H Formula (S-3) R S3 -OL S3 -H In the formula (S-1), R S1 L represents an alkyl group having 8 to 18 carbon atoms. S1 It represents a polyoxyalkylene chain composed of oxyethylene with an average addition molar number of 5 to 20 and oxypropylene with an average addition molar number of 0 to 2; In the formula (S-2), R S2 L represents an alkyl group having 4 to 12 carbon atoms. S2 It represents a polyoxyethylene chain composed of oxyethylene with an average addition molar number of 5 to 20; In the aforementioned formula (S-3), R S3 L represents an alkyl group having 8 to 18 carbon atoms. S3 It represents a polyoxyalkylene chain composed of oxyethylene with an average addition molar number of 5 to 20 and oxybutylene with an average addition molar number of 0.1 to 3.

7. A method for manufacturing an aqueous dispersion, comprising step 1 and step 2, Step 1: A monomer containing tetrafluoroethylene is polymerized in a first aqueous dispersion containing a first fluoropolymer and a first aqueous medium to produce a second fluoropolymer, which is polytetrafluoroethylene and is different from the first fluoropolymer. A second aqueous dispersion containing the first fluoropolymer, the second fluoropolymer, and a second aqueous medium is then produced, wherein the first fluoropolymer is a polymer comprising 10... 6 Fluoropolymers containing fluorine atoms, with fewer than 1000 ionic functional groups in the main chain, a glass transition temperature below 10°C, and fluorine atoms. Step 2: Add a surfactant containing a nonionic surfactant to the second aqueous dispersion to obtain an aqueous dispersion. Prior to the start of polymerization of the monomer, the content of the first fluoropolymer is 0.01 to 4.0% by mass relative to the total mass of the first aqueous dispersion. Prior to the start of polymerization of the monomer, the concentration of the fluorinated emulsifier is less than 100 ppm by mass relative to the total mass of the first fluoropolymer in the first aqueous dispersion.

8. The method for manufacturing the aqueous dispersion as described in claim 7, wherein, This includes the process of contacting the aqueous dispersion with the ion exchange resin.

9. A method for manufacturing a polymer-containing substrate, wherein, A polymer-containing substrate is obtained by contacting the aqueous dispersion of any one of claims 1 to 6 with a substrate made of glass fiber.

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