Polytetrafluoroethylene aqueous dispersion

Abstract

To provide a PTFE aqueous dispersion having low viscosity at high temperature.SOLUTION: A PTFE aqueous dispersion contains PTFE and a nonionic surfactant, has a PTFE solid concentration of 50 to 70 mass%, is substantially free from a fluorine-containing surfactant, and has a viscosity at 55°C of 50 mPa s or lower.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to aqueous polytetrafluoroethylene dispersions. [Background technology]

[0002] Generally, polytetrafluoroethylene (hereinafter referred to as "PTFE") is produced by emulsion polymerization of tetrafluoroethylene (hereinafter referred to as "TFE") in an aqueous medium using a surfactant. The emulsion polymerization method produces an aqueous dispersion in which PTFE particles are dispersed in an aqueous medium. It is known that this aqueous dispersion can be stabilized by adding a nonionic surfactant as a dispersant.

[0003] For example, Patent Document 1 describes an aqueous PTFE dispersion containing 15 to 70 mass% of PTFE particles having an average primary particle size of 0.1 to 0.5 μm, 0.1 to 20,000 ppm, relative to the mass of the PTFE particles, of a fluorine-containing surfactant selected from the group consisting of fluorine-containing carboxylic acids having 4 to 7 carbon atoms and optionally having an etheric oxygen atom and salts thereof, 1 to 20 parts by mass, relative to 100 parts by mass of the PTFE particles, of a nonionic surfactant having a specific structure, 0.01 to 3.0 parts by mass, relative to 100 parts by mass of the PTFE particles, of a compound having a specific structure, and water.

[0004] Patent Document 2 discloses a tetrafluoroethylene core-shell polymer and a polymer having the general formula: R1O-[CH2CH2O] n -[R2O] m R3(I) wherein R1 represents a linear or branched aliphatic hydrocarbon group having at least 6 carbon atoms, preferably 8 to 18 carbon atoms; R2 represents an alkylene unit having 3 or 4 carbon atoms; R3 represents hydrogen, a C1-C3 alkyl group, or a C1-C3 hydroxyalkyl group; n has a value from 0 to 40; m has a value from 0 to 40; and the sum of n+m is at least 2, wherein the core-shell polymer contains an outer shell having a larger molecular weight than the core, and the dispersion is YR f -ZM [wherein Y represents hydrogen, Cl, or F; R f represents a straight-chain or branched-chain fully or partially fluorinated alkylene, the alkylene chain may be interrupted one or more times by an oxygen atom, Z represents one or more kinds of acid anions, and M represents one or more kinds of counter cations], where essentially free means an amount of less than 50 ppm, including 0 ppm, based on the weight of the dispersion.

[0005] Patent Document 3 describes an aqueous dispersion of a fluoropolymer, which contains: (a) 45 to 70% by weight of PTFE particles relative to the total weight of the dispersion, the PTFE particles being non-melt-processable; (b) 1 to 15% by weight of a nonionic surfactant; and (c) 1 to 10% by weight of a water-soluble alkaline earth metal salt, or 0.1 to 10% by weight of colloidal silica, wherein the weight percentage of component (b) or (c) is the percentage relative to the weight of the PTFE particles. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2017 / 094798 [Patent Document 2] Special Publication No. 2017-511394 [Patent Document 3] Special Publication No. 2014-508193 Summary of the Invention [Problem to be solved by the invention]

[0007] The present disclosure provides an aqueous PTFE dispersion that has low viscosity at high temperatures and preferably also has excellent mechanical stability. [Means for solving the problem]

[0008] The present disclosure provides an aqueous PTFE dispersion comprising PTFE and a nonionic surfactant, having a PTFE solids concentration of 50 to 70 mass %, being substantially free of a fluorinated surfactant, and having a viscosity at 55°C of 50 mPa s or less.

[0009] The content of the fluorine-containing surfactant is preferably 100 ppb or more and 1.0 ppm or less.

[0010] The aqueous dispersion of the present disclosure preferably has a ratio [viscosity at 55°C / viscosity at 25°C] of 4.00 or less.

[0011] The content of the nonionic surfactant is preferably 4% by mass or more and 12% by mass or less relative to the PTFE.

[0012] The aqueous dispersion of the present disclosure preferably has a stability retention time at 60°C of 30 minutes or more.

[0013] The aqueous dispersion of the present disclosure also preferably has a stability retention time at 60°C of 40 minutes or more.

[0014] The nonionic surfactant is represented by the following general formula (i): R 3 -OA 1 -H(i) (In the formula, R 3 is an alkyl group having 8 to 18 carbon atoms, and A 1is a polyoxyalkylene chain consisting of oxyethylene units or oxypropylene units.

[0015] R 3 is represented by the following general formula (i-1): CHR 31 R 32 - (i-1) (In the formula, R 31 represents a hydrogen atom or an alkyl group having 1 to 16 carbon atoms, and R 32 represents an alkyl group having 1 to 17 carbon atoms, and R 31 and R 32 and the total number of carbon atoms is 7 to 17).

[0016] R 3 is preferably an alkyl group having 8 to 18 carbon atoms and an average number of methyl groups of 2.0 or more.

[0017] In formula (i), R 3 is preferably a 2,6,8-trimethyl-4-nonyl group.

[0018] In formula (i), A 1 is preferably a polyoxyethylene chain having an average number of oxyethylene units of 10.1 to 10.8.

[0019] The nonionic surfactant preferably has an HLB of 14.00 or more.

[0020] Nonionic surfactants are 1 It is preferable that the compound is a mixture of compounds represented by formula (i) having different average numbers of oxyethylene units.

[0021] The nonionic surfactant is R 3 is a 2,6,8-trimethyl-4-nonyl group, and A 1 is a polyoxyethylene chain having an average number of oxyethylene units of 7.0 to 9.0, and R 3is a 2,6,8-trimethyl-4-nonyl group, and A 1 is preferably a mixture with a compound in which the average number of oxyethylene units is 10.0 to 12.0.

[0022] The nonionic surfactant is R 3 is a 2,6,8-trimethyl-4-nonyl group, and A 1 is a polyoxyethylene chain having an average number of oxyethylene units of 7.0 to 9.0 (first component), and R 3 is a 2,6,8-trimethyl-4-nonyl group, and A 1 and a compound (second component) which is a polyoxyethylene chain having an average number of oxyethylene units of 10.0 to 12.0, and preferably contains 5% by mass or more and 25% by mass or less of the first component and 75% by mass or more and 95% by mass or less of the second component.

[0023] The present disclosure also provides a method for producing an aqueous PTFE dispersion, comprising: Step A: Emulsion polymerizing TFE in the presence of a fluorine-containing anionic surfactant to obtain a dispersion containing PTFE; Step B of adding a nonionic surfactant (1) to the dispersion obtained in Step A; Step C is a step of removing the fluorine-containing anionic surfactant from the dispersion obtained in Step B and further concentrating the dispersion, or a step of concentrating the dispersion obtained in Step B and further removing the fluorine-containing anionic surfactant; and Step D of adding a nonionic surfactant (2) and a fluorine-free anionic surfactant to the dispersion obtained in Step C; The present invention provides a method for producing an aqueous PTFE dispersion, comprising:

[0024] Step A is preferably a step of polymerizing TFE and at least one monomer selected from the group consisting of perfluoro(alkyl vinyl ether) (hereinafter referred to as "PAVE"), (perfluoroalkyl)ethylene, and cyclic monomers.

[0025] Step A is a step of obtaining a dispersion of modified polytetrafluoroethylene having a core-shell structure, It is preferable that the method comprises: Step A-1 of polymerizing TFE and at least one modified monomer selected from the group consisting of perfluoro(alkyl vinyl ether), (perfluoroalkyl)ethylene, and a cyclic monomer to produce the core; and Step A-2 of polymerizing TFE, the modified monomer, and at least one selected from the group consisting of hexafluoropropylene and a chain transfer agent to produce the shell.

[0026] The nonionic surfactant (1) is represented by the following formula (1): R 4 -OA 2 -H (1) (In the formula, R 4 is a linear or branched primary or secondary alkyl group having 8 to 18 carbon atoms and an average number of methyl groups per molecule of 4.0 or more, and A 2 is a polyoxyalkylene chain having an average number of oxyethylene units of 7.0 to 12.0 and an average number of oxypropylene units of 0.0 to 2.0.

[0027] In formula (1), R 4 is preferably a 2,6,8-trimethyl-4-nonyl group.

[0028] The nonionic surfactant (2) is represented by the following formula (2): R 5 -OA 3 -H (2) (In the formula, R 5 is a linear or branched primary or secondary alkyl group having 8 to 18 carbon atoms and an average number of methyl groups per molecule of 4.0 or more, and A 3 is a polyoxyalkylene chain having an average number of oxyethylene units of 10.0 to 12.0.

[0029] In formula (2), R 5is preferably a 2,6,8-trimethyl-4-nonyl group.

[0030] Step D is preferably a step of adding the nonionic surfactant (2) so that the concentration of the nonionic surfactant in the dispersion is 4% by mass or more and 12% by mass or less relative to the PTFE.

[0031] In the PTFE aqueous dispersion, the cloud point of the nonionic surfactant is preferably 60 to 80°C.

[0032] In the PTFE aqueous dispersion, the nonionic surfactant preferably has an HLB of 14.00 or more.

[0033] The removal of the fluorine-containing anionic surfactant in step C is preferably carried out by contacting the aqueous dispersion with an anion exchange resin.

[0034] The PTFE aqueous dispersion preferably has a fluorine-containing anionic surfactant content of 1.0 ppm or less relative to the aqueous dispersion.

[0035] The fluorine-containing anionic surfactant is preferably a fluorine-containing anionic surfactant having a LogPOW of 3.5 or less.

[0036] The fluorine-containing anionic surfactant is preferably a fluorine-containing anionic surfactant having a LogPOW of 3.4 or less.

[0037] The fluorine-free anionic surfactant is preferably at least one selected from the group consisting of alkyl sulfates and salts thereof, and fatty acids and salts thereof.

[0038] The PTFE aqueous dispersion preferably contains the fluorine-free anionic surfactant in an amount of 50 to 5000 ppm relative to the PTFE.

[0039] The manufacturing method of the present disclosure preferably further comprises the step of adding a preservative to the aqueous dispersion.

[0040] The preservative is preferably an organic iodine compound or an organic nitrogen-sulfur compound.

[0041] The manufacturing method of the present disclosure preferably further includes a step of adding coating raw materials.

[0042] The present disclosure also provides an aqueous PTFE dispersion obtained by the above production method.

[0043] The aqueous dispersion of the present disclosure is preferably a water-based paint.

[0044] The present disclosure also provides a coating film obtained by applying the aqueous dispersion.

[0045] The present disclosure also provides an impregnated membrane obtained by impregnating with the aqueous dispersion.

[0046] The present disclosure also provides a depolymerizable acrylic resin particle composition comprising: (A) polytetrafluoroethylene resin particles; (B) a high-boiling polyhydric alcohol containing no nitrogen atoms, having a boiling point of 100°C or higher, and having two or more hydroxyl groups; (C) depolymerizable acrylic resin particles whose decomposition and vaporization temperature is within a temperature range up to the decomposition temperature of the PTFE resin; (D) a nonionic surfactant; and (E) an aqueous medium; The polytetrafluoroethylene aqueous dispersion contains the high-boiling polyhydric alcohol (B) and the depolymerizable acrylic resin particles (C) in amounts of 5 to 18 parts by mass and 5 to 25 parts by mass, respectively, per 100 parts by mass of polytetrafluoroethylene (A), and is free of oxidizing agents and amine-based solvents.

[0047] The present disclosure also provides an aqueous polytetrafluoroethylene dispersion comprising polytetrafluoroethylene resin particles, depolymerizable acrylic resin particles, and water, wherein the dispersion contains a nonionic surfactant in an amount that occupies 75 to 95% of the theoretical void ratio of 26% between the resin particles when the resin particles are arranged in a close-packed structure, assuming that the primary average particles of each resin particle are replaced with true spheres of the same volume, and the nonionic surfactant is a solvent that is substantially non-volatile in a temperature range up to 100°C and that volatilizes or thermally decomposes at a temperature lower than the thermal decomposition temperature of the resin particles.

[0048] The present disclosure further provides a coated article having a coating film obtained by applying the above aqueous polytetrafluoroethylene dispersion.

[0049] The coated article is preferably at least one selected from the group consisting of metal cooking utensils, bearings, valves, electric wires, metal foils, boilers, pipes, ship bottoms, oven linings, iron bottom plates, bread pans, rice cookers, grill pans, electric kettles, ice trays, snow shovels, plows, tools, knives, scissors, hoppers, industrial containers, and molds. [Effects of the Invention]

[0050] The aqueous PTFE dispersion of the present disclosure has low viscosity at high temperatures. [Brief explanation of the drawings]

[0051] [Figure 1] The stirring blade used to evaluate mechanical stability is shown. (a) is a plan view from above, and (b) is a side view. DETAILED DESCRIPTION OF THE INVENTION

[0052] The aqueous PTFE dispersion of the present disclosure (hereinafter also referred to as the "first aqueous PTFE dispersion of the present disclosure") contains PTFE (or PTFE resin particles) and a nonionic surfactant, has a PTFE solids concentration of 50 to 70 mass%, is substantially free of a fluorine-containing surfactant, and has a viscosity at 55°C of 50 mPa s or less.

[0053] The first aqueous PTFE dispersion of the present disclosure has a viscosity of 50 mPa·s or less at 55°C. Because the first aqueous PTFE dispersion of the present disclosure has a viscosity of 50 mPa·s or less at 55°C, it is particularly suitable for applications requiring high temperatures, such as impregnation of fiber substrates. Impregnation requires a baking step, which tends to result in high temperatures. The first aqueous PTFE dispersion of the present disclosure has good penetration into fiber substrates and can be uniformly impregnated even in high-temperature environments. The viscosity at 55°C is preferably 45 mPa·s or less, more preferably 40 mPa·s or less, and even more preferably 35 mPa·s or less. The lower limit of the viscosity at 55°C is not particularly limited, but may be, for example, 10 mPa·s or more.

[0054] The first aqueous PTFE dispersion of the present disclosure preferably has a ratio [viscosity at 55°C / viscosity at 25°C] of 4.00 or less. The first aqueous PTFE dispersion of the present disclosure is particularly suitable for use in impregnation of fiber substrates. The impregnation process involves a baking step, which tends to result in high environmental temperatures. Since the amount of PTFE adhered to the fiber substrate during impregnation is easily affected by the viscosity of the aqueous dispersion, an aqueous dispersion with low viscosity-temperature dependency is required. The first aqueous PTFE dispersion of the present disclosure is excellent in that, by having the ratio of 4.00 or less, it has low viscosity-temperature dependency and is stable in quality. From the above viewpoint, the ratio [viscosity at 55°C / viscosity at 25°C] is more preferably 3.00 or less, even more preferably 2.00 or less, even more preferably 1.50 or less, especially preferably 1.20 or less, particularly preferably 1.10 or less, and especially especially preferably 1.00 or less.

[0055] The viscosity at 25°C was measured using a B-type rotational viscometer under the conditions shown in the Examples section below. The viscosity at 55°C was measured under the same conditions as the viscosity at 25°C after the liquid temperature was raised to 55°C and held for 60 minutes. Note that for viscosity values ​​of 80 mPa·s or higher, the viscosity increases over time, so the viscosity is measured 5 and 10 minutes after the start of measurement, and the average value is used.

[0056] The first aqueous PTFE dispersion of the present disclosure preferably has a viscosity temperature transition [VTT] of more than 55° C., more preferably 60° C. or more. A VTT of more than 55° C. has the technical significance of eliminating the need to change the processing conditions at 25° C. and 55° C. VTT represents the viscosity-temperature dependency of an aqueous PTFE dispersion. VTT can be obtained by raising the temperature of an aqueous PTFE dispersion to 25°C, 35°C, 45°C, and 55°C, holding the temperature for 60 minutes, and then measuring using a B-type rotational viscometer under the conditions shown in the Examples below. The VTT point is the temperature at which the viscosity once again reaches the same value as measured at 25°C. Note that for viscosity values ​​of 80 mPa·s or higher, the viscosity increases over time, so the viscosity is measured 5 and 10 minutes after the start of measurement, and the average value is used.

[0057] The first PTFE aqueous dispersion of the present disclosure has a PTFE solids concentration of 50 to 70% by mass. The solids concentration is preferably 55% by mass or more, more preferably 57% by mass or more. Furthermore, the solids concentration is preferably 65% ​​by mass or less, more preferably 60% by mass or less. Even if the PTFE solids concentration is within the above range, the aqueous dispersion of the present disclosure can have a viscosity of 50 mPa·s or less at 55°C.

[0058] In the first PTFE aqueous dispersion of the present disclosure, the content of the nonionic surfactant relative to the PTFE is preferably 4% by mass or more, more preferably 5% by mass or more, and even more preferably 5.5% by mass or more, and is preferably 12% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less, and especially preferably 7% by mass or less. If the amount of nonionic surfactant is too large, the viscosity may become too high, whereas if the amount is too small, the storage stability and mechanical stability may decrease.

[0059] The nonionic surfactant is preferably a nonionic surfactant that does not contain fluorine, for example, a surfactant represented by the following general formula (i): R 3 -OA 1 -H(i) (In the formula, R 3 is a linear or branched primary or secondary alkyl group having 8 to 18 carbon atoms, and A 1 is a polyoxyalkylene chain. R 3 The number of carbon atoms in R is preferably 8 to 16, and more preferably 10 to 14. 3 When the number of carbon atoms is within the above range, the affinity with PTFE in the aqueous dispersion is high, and a lower viscosity at 55°C and excellent mechanical stability can be achieved. Above R 3 is represented by the following general formula (i-1): CH2R 31 R 32 - (i-1) (In the formula, R 31 represents a hydrogen atom or an alkyl group having 1 to 16 carbon atoms, and R 32 represents an alkyl group having 1 to 17 carbon atoms, and R 31 and R 32 The total number of carbon atoms in R is preferably 7 to 17. 31 is more preferably a hydrogen atom or an alkyl group having 1 to 15 carbon atoms, even more preferably a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, and even more preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. 32 As the alkyl group, an alkyl group having 1 to 15 carbon atoms is more preferable, an alkyl group having 1 to 14 carbon atoms is even more preferable, and an alkyl group having 1 to 13 carbon atoms is even more preferable. Above R 3 is preferably an alkyl group having 8 to 18 carbon atoms and an average number of methyl groups of 2.0 or more. 3The average number of methyl groups in R is more preferably 2.5 or more, even more preferably 3.0 or more, even more preferably 3.5 or more, and particularly preferably 4.0 or more. 3 The upper limit of the average number of methyl groups is preferably 12 or less, more preferably 10 or less, and even more preferably 8 or less. Also, the above R 3 The average number of methyl groups per molecule is preferably 4.0 or more, more preferably 4.3 or more, even more preferably 4.7 or more, and most preferably 5.0 or more. 3 Particularly preferred is a 2,6,8-trimethyl-4-nonyl group. In this specification, the average number of methyl groups is determined by adding methanol to a sample, performing Soxhlet extraction, and then 1 This value is determined by measuring with H-NMR.

[0060] Commercially available examples of the nonionic surfactant include Genapol X080 (product name, manufactured by Clariant), the Noigen TDS series (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) such as Noigen TDS-80 (trade name) and Noigen TDS-100 (trade name), the Leocol TD series (manufactured by Lion Chemicals) such as Leocol TD-90 (trade name), the Lionol (registered trademark) TD series (manufactured by Lion Chemicals), the T-Det A series (manufactured by Harcros Chemicals) such as T-Det A138 (trade name), the Tergitol (registered trademark) 15S series (manufactured by Dow Chemicals), and Dispanol TOC (trade name, manufactured by NOF Corporation).

[0061] The nonionic surfactant may be a mixture of two different nonionic surfactants, for example, A of the general formula (i) 1 and a compound having a polyoxyalkylene chain with an average number of oxyethylene units of 7.0 to 12.0 and an average number of oxypropylene units of 0.0 to 2.0, and A 1 It may also be a mixture with a compound which is a polyoxyalkylene chain having an average number of oxyethylene units of 10.0 to 12.0. In addition, for example, A in the above general formula (i)1 and a compound having an average number of oxyethylene units of 7.0 or more and less than 10.0, and A 1 The compound may be a mixture of the above with a compound having a polyoxyalkylene chain with an average number of oxyethylene units of 10.0 or more and 12.0 or less.

[0062] The nonionic surfactant is preferably poly(oxyethylene) 2,6,8-trimethyl-4-nonyl ether having an average number of oxyethylene units of 4.0 to 18.0, poly(oxyethylene) 2,6,8-trimethyl-4-nonyl ether having an average number of oxyethylene units of 6.0 to 12.0, or a mixture thereof. Nonionic surfactants of this type are also commercially available, for example, as TERGITOL TMN-6, TERGITOL TMN-10, and TERGITOL TMN-100X (all product names, manufactured by The Dow Chemical Company).

[0063] A in the above formula (i) 1 The average number of oxyalkylene units is preferably 5.0 to 20.0, more preferably 8.0 to 15.0, and even more preferably 10.0 to 12.0. In particular, it is preferable that the sample contains oxyethylene units, and the average number of oxyethylene units is preferably 10.1 or more, more preferably 10.2 or more, preferably 10.8 or less, more preferably 10.7 or less, even more preferably 10.6 or less, and even more preferably 10.5 or less. In this specification, the average number of oxyalkylene units is determined by adding methanol to a sample, performing Soxhlet extraction, and then extracting the extract. 1 This value is determined by measuring with H-NMR.

[0064] A in the above formula (i) 1may be composed of oxyethylene units and oxypropylene units. For example, it may be a polyoxyalkylene chain having an average number of oxyethylene units of 5.0 to 20.0 and an average number of oxypropylene units of 0.0 to 2.0. The number of oxyethylene units may include either a broad or narrow unimodal distribution, which is typically provided, or a broader or bimodal distribution obtained by blending. When the average number of oxypropylene units is greater than 0.0, the oxyethylene units and oxypropylene units in the polyoxyalkylene chain may be arranged in a block or random configuration. From the viewpoint of the viscosity and mechanical stability of the aqueous PTFE dispersion, a polyoxyalkylene chain having an average number of oxyethylene units of 7.0 to 12.0 and an average number of oxypropylene units of 0.0 to 2.0 is preferred. 1 However, if the average number of propylene units is 0.5 to 1.5, it is preferable in terms of low foaming properties.

[0065] The nonionic surfactant preferably has an HLB of 13.00 or more, more preferably 13.20 or more, even more preferably 14.00 or more, even more preferably 14.05 or more, and particularly preferably 14.10 or more. It is also preferably 14.50 or less, more preferably 14.40 or less, even more preferably 14.30 or less, even more preferably 14.20 or less, and particularly preferably 14.15 or less. By keeping the HLB within the above range, it is possible to reduce the viscosity at high temperatures while maintaining mechanical stability. The HLB value is calculated using the Griffin formula [HLB=E / 5 (wherein E is the weight percent of ethylene oxide in the molecule); HLB=(E+P) / 5 (wherein E is as defined above and P is the weight percent of polyhydric alcohol in the molecule); and HLB=20(1-S / N) / 5 (wherein S is the saponification value of the ester and N is the neutralization value of the fatty acid that constitutes the ester)]. When two or more nonionic surfactants are used, the HLB is calculated from the HLB of each nonionic surfactant and its mass ratio. For example, if the nonionic surfactant with an HLB of 14.00 accounts for 60 mass% of the total content of nonionic surfactants and the nonionic surfactant with an HLB of 15.00 accounts for 40 mass%, the HLB is 14.00 × 0.6 + 15.00 × 0.4 = 14.40.

[0066] To obtain the aqueous dispersion of the present disclosure, it is preferable to add two types of nonionic surfactants with different hydrophilicities. The HLB index can be used to indicate the difference in hydrophilicity. For example, the aqueous dispersion of the present disclosure preferably contains a nonionic surfactant with an HLB of 13.00 or more and less than 14.10, and a nonionic surfactant with an HLB of 14.10 or more and 15.00 or less. Adding nonionic surfactants with different HLB values ​​can also suppress foaming without adding an antifoaming agent. Furthermore, for example, the aqueous dispersion of the present disclosure preferably contains a nonionic surfactant having an HLB of 13.00 or more and less than 13.50, and a nonionic surfactant having an HLB of 13.50 or more and 15.00 or less (preferably 14.50 or less, more preferably 14.00 or less).

[0067] The cloud point of a nonionic surfactant is a measure of the solubility of the surfactant in water. The surfactant used in the aqueous dispersion of the present disclosure has a cloud point of 30 to 90°C, preferably 35 to 85°C, more preferably 40 to 80°C, and even more preferably 45 to 75°C.

[0068] To obtain the aqueous dispersion of the present disclosure, it is preferable to add two types of nonionic surfactants with different cloud points. For example, the aqueous dispersion of the present disclosure preferably contains a nonionic surfactant with a cloud point of 30°C or higher and 60°C or lower and a nonionic surfactant with a cloud point of more than 60°C and 90°C or lower, and more preferably contains a nonionic surfactant with a cloud point of 35 to 60°C and a nonionic surfactant with a cloud point of 65 to 80°C. The use of a nonionic surfactant with a high cloud point can improve mechanical stability. Furthermore, the addition of nonionic surfactants with different cloud points can suppress foaming without the addition of an antifoaming agent. Furthermore, for example, the aqueous dispersion of the present disclosure preferably contains a nonionic surfactant having a cloud point of 30°C or higher and 60°C or lower, and a nonionic surfactant having a cloud point of more than 60°C and 90°C or lower, and more preferably contains a nonionic surfactant having a cloud point of 35 to 60°C, and a nonionic surfactant having a cloud point of 65 to 80°C.

[0069] The viscosity of 50 mPa· or less at 55°C can be achieved by appropriately adjusting the HLB and average number of oxyalkylene units of the nonionic surfactant. For example, it is preferable that the HLB of the nonionic surfactant is 14.05 to 14.35 and the average number of oxyalkylene units is 10.2 to 10.9. In a more specific configuration, the nonionic surfactant is R 3 is a 2,6,8-trimethyl-4-nonyl group, and A 1 is a polyoxyethylene chain having an average number of oxyethylene units of 7.0 to 9.0 (first component), and R 3 is a 2,6,8-trimethyl-4-nonyl group, and A 1 and a compound (second component) in which the first component is a polyoxyethylene chain having an average number of oxyethylene units of 10.0 to 12.0, and the first component is preferably 5% by mass to 25% by mass and the second component is preferably 75% by mass to 95% by mass. The nonionic surfactant more preferably contains 10% by mass or more, and more preferably 15% by mass or less, of the first component, and more preferably 85% by mass or more, and more preferably 90% by mass or less of the second component.

[0070] The viscosity of 50 mPa· or less at 55°C can be achieved by appropriately adjusting the HLB and average number of oxyalkylene units of the nonionic surfactant. For example, it is preferable that the HLB of the nonionic surfactant is 13.00 to 13.50 and the average number of oxyalkylene units is 7.0 to 12.0. More specifically, the nonionic surfactant is A of formula (i): 1 is a polyoxyethylene chain having an average number of oxyethylene units of 7.0 to 9.5 (first component), and A 1 and a compound (second component) in which the first component is a polyoxyethylene chain having an average number of oxyethylene units of 10.0 to 12.0, and the first component is preferably 40% by mass to 70% by mass and the second component is 30% by mass to 60% by mass. The nonionic surfactant more preferably contains 45% by mass or more, and more preferably 65% ​​by mass or less, of the first component, and more preferably contains 35% by mass or more, and more preferably 55% by mass or less of the second component.

[0071] The PTFE may be a homopolymer of TFE, or a modified PTFE containing 99.0% by mass or more of polymerized units based on TFE and 1.0% by mass or less of polymerized units based on a modifying monomer. Modified PTFE is preferred from the viewpoint of further improving mechanical stability at high temperatures.

[0072] The modified PTFE preferably contains polymerized units based on a modified monomer (hereinafter also referred to as "modified monomer units") in the range of 0.00001 to 1.0% by mass. The lower limit of the modified monomer units is more preferably 0.0001% by mass, even more preferably 0.001% by mass, even more preferably 0.005% by mass, especially preferably 0.010% by mass, and even especially preferably 0.030% by mass. The upper limit of the modified monomer units is preferably 0.90% by mass, more preferably 0.50% by mass, even more preferably 0.40% by mass, and even more preferably 0.30% by mass. In this specification, the modified monomer unit means a part of the molecular structure of PTFE that is derived from the modified monomer.

[0073] In this specification, the content of each monomer constituting PTFE can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and X-ray fluorescence analysis depending on the type of monomer.

[0074] The modifying monomer is not particularly limited as long as it is copolymerizable with TFE, and examples thereof include perfluoroolefins such as hexafluoropropylene (HFP), hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride (VDF), perhaloolefins such as chlorotrifluoroethylene, perfluorovinyl ether, perfluoroallyl ether, (perfluoroalkyl)ethylene, ethylene, etc. The modifying monomer used may be one type or multiple types.

[0075] The perfluorovinyl ether is not particularly limited, and examples thereof include perfluorovinyl ethers represented by the following general formula (A): CF2=CF-ORf (A) (wherein Rf represents a perfluoroorganic group). In this specification, the "perfluoroorganic group" refers to an organic group in which all hydrogen atoms bonded to carbon atoms are substituted with fluorine atoms. The perfluoroorganic group may have an ether oxygen.

[0076] An example of the perfluorovinyl ether is perfluoro(alkyl vinyl ether) [PAVE], where Rf in the general formula (A) is a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5.

[0077] Examples of the perfluoroalkyl group in the PAVE include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group.

[0078] The perfluorovinyl ether further includes those in which Rf in the general formula (A) is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, and those in which Rf ...

[0079] [ka]

[0080] (wherein m represents 0 or an integer of 1 to 4), and Rf is a group represented by the following formula:

[0081] [ka]

[0082] (wherein n represents an integer of 1 to 4).

[0083] The (perfluoroalkyl)ethylene (PFAE) is not particularly limited, and examples thereof include (perfluorobutyl)ethylene (PFBE) and (perfluorohexyl)ethylene.

[0084] Examples of perfluoroallyl ethers include: General formula: CF2=CF-CF2-ORf 11 (In the formula, Rf 11 represents a perfluoroorganic group.

[0085] Above Rf 11is preferably a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoroalkoxyalkyl group having 1 to 10 carbon atoms. The perfluoroallyl ether is preferably at least one selected from the group consisting of CF2=CF-CF2-O-CF3, CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7, and CF2=CF-CF2-O-C4F9, more preferably at least one selected from the group consisting of CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7, and CF2=CF-CF2-O-C4F9, and even more preferably CF2=CF-CF2-O-CF2CF2CF3.

[0086] The modifying monomer also includes a cyclic monomer. The cyclic monomer is represented by the following general formula (ii): [ka] (In the formula, X 2 and X 3 are the same or different and represent a hydrogen atom or a fluorine atom, and Y is -CR 1 R 2 - represents R 1 and R 2 are the same or different and represent a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms.) Preferred vinyl heterocycles represented by the above general formula (ii) include, for example, vinyl heterocycles represented by X 2 and X 3 is preferably a fluorine atom, and R 1 and R 2 is preferably a fluoroalkyl group having 1 to 6 carbon atoms. The vinyl heterocyclic compound represented by the general formula (ii) includes X 2 and X 3 is a fluorine atom, R 1 and R 2 is a perfluoromethyl group, perfluoro-2,2-dimethyl-1,3-dioxole [PDD] is preferred.

[0087] From the viewpoint of the transparency of the coating film, the modifying monomer is preferably at least one selected from the group consisting of PAVE, PFAE, and the cyclic monomers.

[0088] A preferred example of the modifying monomer is the modifying monomer (3) having a monomer reactivity ratio of 0.1 to 8. The presence of the modifying monomer (3) makes it possible to obtain PTFE particles having a small particle size and an aqueous dispersion with high dispersion stability.

[0089] Here, the monomer reactivity ratio in copolymerization with TFE is the value obtained by dividing the rate constant when the propagating radical reacts with TFE when the propagating radical is less than a repeating unit based on TFE by the rate constant when the propagating radical reacts with the modified monomer. The lower this value, the higher the reactivity of the modified monomer with TFE. The monomer reactivity ratio can be calculated by copolymerizing TFE and the modified monomer, determining the composition in the resulting polymer immediately after the start of copolymerization, and using the Feynman-Ross equation.

[0090] The copolymerization was carried out in a 6.0 L stainless steel autoclave using 3600 g of deionized, degassed water, 1000 ppm ammonium perfluorooctanoate relative to the water, and 100 g of paraffin wax at a pressure of 0.78 MPa and a temperature of 70°C. 0.05 g, 0.1 g, 0.2 g, 0.5 g, and 1.0 g of the modified monomer were added to the reactor, respectively, and 0.072 g of ammonium persulfate (20 ppm relative to the water) was added. TFE was continuously fed to maintain the polymerization pressure at 0.78 MPa. When the TFE charge reached 1000 g, stirring was stopped and the reactor was depressurized until atmospheric pressure was reached. After cooling, the paraffin wax was separated to obtain an aqueous dispersion containing the resulting polymer. The aqueous dispersion was stirred to coagulate the resulting polymer, which was then dried at 150°C. The composition of the resulting polymer is calculated by appropriately combining NMR, FT-IR, elemental analysis, and X-ray fluorescence analysis depending on the type of monomer.

[0091] The modified monomer (3) having a monomer reactivity ratio of 0.1 to 8 is preferably at least one selected from the group consisting of modified monomers represented by formulas (3a) to (3d). CH2=CH-Rf 1 (3a) (In the formula, Rf 1 is a perfluoroalkyl group having 1 to 10 carbon atoms. CF2=CF-O-Rf 2 (3b) (In the formula, Rf 2 is a perfluoroalkyl group having 1 to 2 carbon atoms. CF2=CF-O-(CF2) n CF=CF2(3c) (wherein n is 1 or 2).

[0092] [ka] (In the formula, X 3 and X 4 is F, Cl or a methoxy group, and Y is of formula Y1 or Y2.

[0093] [ka] (In formula Y2, Z and Z′ are F or a fluorinated alkyl group having 1 to 3 carbon atoms.)

[0094] The content of the modifying monomer (3) is preferably in the range of 0.00001 to 1.0% by mass relative to PTFE. The lower limit is more preferably 0.0001% by mass, even more preferably 0.001% by mass, even more preferably 0.005% by mass, particularly preferably 0.010% by mass, and even more particularly preferably 0.030% by mass. The upper limit is preferably 0.90% by mass, more preferably 0.50% by mass, even more preferably 0.40% by mass, and even more preferably 0.30% by mass.

[0095] The modified monomer preferably contains at least one selected from the group consisting of hexafluoropropylene, vinylidene fluoride, fluoro(alkyl vinyl ether), perfluoroallyl ether, (perfluoroalkyl)ethylene, ethylene, and a modified monomer having a functional group reactive by radical polymerization and a hydrophilic group, because the modified monomer has low viscosity at high temperatures and excellent mechanical stability at high temperatures. Furthermore, the modified monomer preferably contains at least one selected from the group consisting of hexafluoropropylene, perfluoro(alkyl vinyl ether), and (perfluoroalkyl)ethylene, more preferably perfluoro(alkyl vinyl ether), and even more preferably perfluoro(propyl vinyl ether) (hereinafter also referred to as PPVE). The total amount of the hexafluoropropylene units, perfluoro(alkyl vinyl ether) units, and (perfluoroalkyl)ethylene units is preferably in the range of 0.00001 to 1% by mass relative to PTFE. The lower limit of the total amount is more preferably 0.0001% by mass, even more preferably 0.001% by mass, even more preferably 0.005% by mass, particularly preferably 0.010% by mass, and even more particularly preferably 0.030% by mass. The upper limit is more preferably 0.50% by mass, even more preferably 0.40% by mass, and even more preferably 0.30% by mass.

[0096] The modified monomer is preferably a modified monomer having a functional group capable of reacting by radical polymerization and a hydrophilic group (hereinafter referred to as "modified monomer (4)"). By including polymerized units based on modified monomer (4), PTFE particles having a small particle size can be obtained, and an aqueous dispersion with high dispersion stability can be obtained.

[0097] In the polymerization for producing PTFE, the amount of the modified monomer (4) is preferably more than the amount corresponding to 0.1 ppm of the aqueous medium, more preferably 5 ppm or more, and even more preferably 10 ppm or more. If the amount of the modified monomer (4) is too small, the particle size of the resulting PTFE may be large. The amount of the modified monomer (4) may be within the above range, but the upper limit can be set to, for example, 5000 ppm. In addition, in the above production method, the modified monomer (4) may be added to the system during the reaction to improve the stability of the aqueous dispersion during or after the reaction.

[0098] Since the above-mentioned modified monomer (4) is highly water-soluble, even if unreacted modified monomer (4) remains in the aqueous dispersion, it can be easily removed in the concentration step or the coagulation and washing step, as with the fluorine-containing compound described below.

[0099] The above-mentioned modifying monomer (4) is incorporated into the produced polymer during the polymerization process. However, since the concentration of the modifying monomer (4) itself in the polymerization system is low and the amount incorporated into the polymer is small, there are no problems such as a decrease in the heat resistance of PTFE or coloration after baking.

[0100] The modified monomer (4) has a functional group capable of reacting by radical polymerization and a hydrophilic group. Examples of the hydrophilic group in the modified monomer (4) include -NH2, -PO3M, -OPO3M, -SO3M, -OSO3M, and -COOM (in each formula, M represents H, a metal atom, or NR 7 4. An imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent, R 7 are H or organic groups and may be the same or different. Any two of them may be bonded to each other to form a ring.) Among them, -SO3M and -COOM are preferred as the hydrophilic group. As the metal atom, alkali metals are preferred, and examples of alkali metals include Na and K.

[0101] Examples of the "functional group capable of reacting by radical polymerization" in the modified monomer (4) include groups having an unsaturated bond, such as a vinyl group and an allyl group.

[0102] Since the modified monomer (4) has a functional group capable of reacting by radical polymerization, it is presumed that when used in the polymerization, it reacts with the fluorine-containing monomer in the early stage of the polymerization reaction to form highly stable particles having hydrophilic groups derived from the modified monomer (4).For this reason, it is considered that the number of emulsified particles increases when polymerization is carried out in the presence of the modified monomer (4).

[0103] The polymerization may be carried out in the presence of one type of the modifying monomer (4), or in the presence of two or more types.

[0104] In the polymerization, a compound having an unsaturated bond can be used as the modifying monomer (4).

[0105] The modified monomer (4) is represented by the general formula (4): CX i X k =CX j R a -(CZ 1 Z 2 ) k -Y 3 (4) (In the formula, X i , X j and X k are each independently F, Cl, H, or CF; Y 3 is a hydrophilic group; R a is a linking group; Z 1 and Z 2 are each independently H, F or CF3, and k is 0 or 1). Examples of the hydrophilic group include -NH2, -PO3M, -OPO3M, -SO3M, -OSO3M, and -COOM (in each formula, M represents H, a metal atom, or NR 74. An imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent, R 7 are H or organic groups and may be the same or different. Any two of them may be bonded to each other to form a ring. ) are examples of the hydrophilic group. Of these, -SO3M or -COOM is preferred. R 7 As for H or C 1-10 is preferably an organic group represented by the formula: 1-4 The organic group is more preferably H or C 1-4 More preferred are alkyl groups of the formula: The metal atom may be a monovalent or divalent metal atom, such as an alkali metal (Group 1) or an alkaline earth metal (Group 2), with Na, K, or Li being preferred.

[0106] Above R a is a linking group. In this specification, the term "linking group" refers to a divalent linking group. The linking group may be a single bond and preferably contains at least one carbon atom, and the number of carbon atoms may be 2 or more, 4 or more, 8 or more, 10 or more, or 20 or more. There is no upper limit, but it may be, for example, 100 or less, or 50 or less. The linking group may be linear or branched, cyclic or acyclic, saturated or unsaturated, substituted or unsubstituted, and may optionally contain one or more heteroatoms selected from the group consisting of sulfur, oxygen, and nitrogen, and may optionally contain one or more functional groups selected from the group consisting of ester, amide, sulfonamide, carbonyl, carbonate, urethane, urea, and carbamate. The linking group may not contain carbon atoms but may be a catenary heteroatom such as oxygen, sulfur, or nitrogen.

[0107] Above R a is preferably a catenary heteroatom such as oxygen, sulfur, or nitrogen, or a divalent organic group. R aWhen R is a divalent organic group, the hydrogen atom bonded to the carbon atom may be replaced with a halogen other than fluorine, such as chlorine, and may or may not contain a double bond. a may be either linear or branched, and may be either cyclic or acyclic. a may contain functional groups (e.g., esters, ethers, ketones, amines, halides, etc.). R a may also be a non-fluorinated divalent organic group, or a partially fluorinated or perfluorinated divalent organic group. R a Examples of the hydrocarbon group include a hydrocarbon group in which no fluorine atoms are bonded to a carbon atom, a hydrocarbon group in which some of the hydrogen atoms bonded to a carbon atom are substituted with fluorine atoms, a hydrocarbon group in which all of the hydrogen atoms bonded to a carbon atom are substituted with fluorine atoms, -(C=O)-, -(C=O)-O-, or a hydrocarbon group containing -(C=O)-, which may contain an oxygen atom, a double bond, or a functional group.

[0108] The modifying monomer (4) is preferably at least one selected from the group consisting of compounds represented by the following formulas (4a) to (4e). CF2=CF-(CF2) n1 -Y 3 (4a) (wherein n1 represents an integer of 1 to 10, and Y 3 -SO3M 1 or -COOM 1 represents M 1 represents H, NH4 or an alkali metal. CF2=CF-(CF2C(CF3)F) n2 -Y 3 (4b) (wherein n2 represents an integer of 1 to 5, and Y 3 is the same as the definition above.) CF2=CF-O-(CFX 1 ) n3 -Y 3 (4c) (In the formula, X 1represents F or CF3, n3 represents an integer of 1 to 10, and Y 3 is the same as the definition above.) CF2=CF-O-(CF2CFX 1 O) n4 -CF2CF2-Y 3 (4d) (wherein n4 represents an integer of 1 to 10, and Y 3 and X 1 is the same as the definition above.) CX 2 2=CFCF2-O-(CF(CF3)CF2O) n5 -CF(CF3)-Y 3 (4e) (In the formula, each 2 are the same and represent F or H. n5 represents 0 or an integer of 1 to 10, and Y 3 is the same as the definition above.) The alkali metals include Na, K, and the like.

[0109] In the formula (4a), n1 is preferably an integer of 5 or less, and more preferably an integer of 2 or less. 3 -COOM is advantageous in that it provides adequate water solubility and surface activity. 1 Preferably, M 1 is preferably H or NH4, since it is unlikely to remain as an impurity and the heat resistance of the resulting molded article is improved.

[0110] The perfluorovinyl alkyl compound represented by the above formula (4a) is, for example, CF2=CFCF2COOM 1 (In the formula, M 1 is the same as the definition above.

[0111] In the formula (4b), n2 is preferably an integer of 3 or less in terms of emulsifying ability, and Y 3 -COOM is advantageous in that it provides adequate water solubility and surface activity. 1 Preferably, M 1is preferably H or NH4, since it is unlikely to remain as an impurity and the heat resistance of the resulting molded article is improved. In the formula (4c), n3 is preferably an integer of 5 or less in terms of water solubility, and Y 3 -COOM is advantageous in that it provides adequate water solubility and surface activity. 1 It is preferable that the above M 1 is preferably H or NH4 in terms of improving dispersion stability.

[0112] In the above formula (4d), the above X 1 is preferably -CF3 from the viewpoint of surface activity, n4 is preferably an integer of 5 or less from the viewpoint of water solubility, and Y 3 COOM has the advantage of providing moderate water solubility and surface activity. 1 It is preferable that the above M 1 is preferably H or NH4.

[0113] Examples of the perfluorovinyl ether compound represented by the above formula (4d) include CF2=CFOCF2CF(CF3)OCF2CF2COOM 1 (In the formula, M 1 represents H, NH4 or an alkali metal.

[0114] In the formula (4e), n5 is preferably 0 or an integer of 1 to 5, more preferably 0, 1 or 2, and even more preferably 0 or 1, in terms of emulsifying ability. 3 COOM has the advantage of providing moderate water solubility and surface activity. 1 It is preferable that the above M 1 is preferably H or NH4, since it is unlikely to remain as an impurity and the heat resistance of the resulting molded article is improved.

[0115] Examples of the perfluorovinyl alkyl compound represented by the formula (4e) include CH2=CFCF2OCF(CF3)COOM 1 , CH2=CFCF2OCF(CF3)CF2OCF(CF3)COOM1 (In the formula, M 1 is the same as the definition above.

[0116] The PTFE preferably has a core-shell structure. Examples of fluoropolymers having a core-shell structure include modified PTFE particles containing a core of high molecular weight PTFE and a shell of lower molecular weight PTFE or modified PTFE. Examples of such modified PTFE include the PTFE described in JP-A-2005-527652.

[0117] The core-shell structure may have the following structure. Core: TFE homopolymer Shell: TFE homopolymer Core: Modified PTFE Shell: TFE homopolymer Core: Modified PTFE Shell: Modified PTFE Core: TFE homopolymer Shell: Modified PTFE The above structures may each have a high molecular weight or a low molecular weight. For example, they may have a structure of a high molecular weight TFE homopolymer core and a low molecular weight TFE homopolymer shell, a structure of a high molecular weight modified PTFE core and a low molecular weight TFE homopolymer shell, a structure of a high molecular weight modified PTFE core and a low molecular weight modified PTFE shell, a structure of a high molecular weight TFE homopolymer core and a low molecular weight modified PTFE shell, a structure of a low molecular weight TFE homopolymer core and a high molecular weight TFE homopolymer shell, a structure of a low molecular weight modified PTFE core and a high molecular weight modified PTFE shell, or a structure of a low molecular weight TFE homopolymer core and a high molecular weight modified PTFE shell.

[0118] The PTFE is particularly preferably a core-shell structure having a modified PTFE core and a low-molecular-weight PTFE shell. By polymerizing a monomer composition containing TFE in the presence of a chain transfer agent, the shell can be made into low-molecular-weight PTFE, which significantly improves mechanical stability. The TFE-containing monomer composition may contain only TFE, or may contain TFE and a modified monomer.

[0119] The modified monomer of the modified PTFE constituting the core is preferably at least one selected from the group consisting of PAVE, PFAE, and the above-mentioned cyclic monomers. Examples of PAVE include PPVE, PEVE, and PMVE, with PPVE being preferred. Examples of PFAE include PFBE and (perfluorohexyl)ethylene, with PFBE being preferred. The cyclic monomer may be a vinyl heterocyclic compound represented by the above general formula (ii), with perfluoro-2,2-dimethyl-1,3-dioxole [PDD] being preferred.

[0120] In the modified PTFE constituting the core, the content of polymerized units based on the modifying monomer is preferably in the range of 0.00001 to 1.0% by mass relative to the PTFE. The lower limit is preferably 0.0001% by mass, more preferably 0.001% by mass, even more preferably 0.005% by mass, particularly preferably 0.010% by mass, and even more particularly preferably 0.030% by mass. The upper limit is preferably 0.90% by mass, more preferably 0.50% by mass, even more preferably 0.40% by mass, and even more preferably 0.30% by mass.

[0121] The low-molecular-weight PTFE in the shell can be obtained by polymerizing a monomer composition containing TFE in the presence of a chain transfer agent. The chain transfer agent is not particularly limited as long as it reduces the molecular weight of the PTFE that constitutes the shell, and examples include non-peroxide organic compounds such as water-soluble alcohols, hydrocarbons, and fluorohydrocarbons; water-soluble organic peroxides such as disuccinic acid peroxide (DSP); and persulfates such as ammonium persulfate (APS) and potassium persulfate (KPS). In the polymerization to form the shell, it is preferable to use at least one of the non-peroxide organic compounds, water-soluble organic peroxides, and persulfates as the chain transfer agent. In the chain transfer agent, one or more of each of the non-peroxide organic compound, the water-soluble organic peroxide, and the persulfate can be used.

[0122] The chain transfer agent is preferably at least one selected from the group consisting of water-soluble alcohols having 1 to 4 carbon atoms, hydrocarbons having 1 to 4 carbon atoms, and fluorohydrocarbons having 1 to 4 carbon atoms, from the viewpoint of good dispersibility and uniformity in the reaction system, more preferably at least one selected from the group consisting of methane, ethane, n-butane, isobutane, methanol, and isopropanol, and even more preferably at least one selected from the group consisting of methanol and isobutane.

[0123] The polymerization is usually carried out in an aqueous medium. The amount of the chain transfer agent is preferably 0.001 to 10,000 ppm relative to the aqueous medium. The amount of the chain transfer agent is more preferably 0.01 ppm or more relative to the aqueous medium, even more preferably 0.05 ppm or more, and particularly preferably 0.1 ppm or more. The amount is more preferably 1,000 ppm or less relative to the aqueous medium, even more preferably 750 ppm or less, and particularly preferably 500 ppm or less.

[0124] In the PTFE having the core-shell structure, the upper limit of the core ratio is preferably 99.5% by mass, more preferably 99.0% by mass, even more preferably 98.0% by mass, still more preferably 97.0% by mass, particularly preferably 95.0% by mass, and most preferably 90.0% by mass.

[0125] In the PTFE having the core-shell structure, the lower limit of the shell ratio is preferably 0.5 mass%, more preferably 1.0 mass%, even more preferably 3.0 mass%, particularly preferably 5.0 mass%, and most preferably 10.0 mass%.

[0126] In the PTFE having the core-shell structure, the core or the shell may be configured to have two or more layers, for example, a three-layer structure having a core center portion of modified PTFE, a core outer layer portion of TFE homopolymer, and a shell of low-molecular-weight PTFE.

[0127] The PTFE having the core-shell structure has an extrusion pressure of preferably 80 MPa or less, more preferably 70 MPa or less, and even more preferably 60 MPa or less at a reduction ratio of 1500. An extrusion pressure within the above range at a reduction ratio of 1500 can be achieved by the first method for producing an aqueous PTFE dispersion of the present disclosure, which will be described later. In this specification, the "extrusion pressure at a reduction ratio of 1500" is measured according to the following procedure. The first PTFE aqueous dispersion of the present disclosure is coagulated with methanol, and the resulting wet PTFE powder is further subjected to Soxhlet extraction with methanol to remove additives including nonionic surfactants. The wet PTFE powder from which the additives are removed is then dried at 150°C for 18 hours to obtain a PTFE powder. Alternatively, the aqueous PTFE dispersion after polymerization, i.e., before the addition of the nonionic surfactant, is diluted with deionized water to a PTFE concentration of 10 to 15% by mass, and then subjected to mechanical shearing to obtain wet PTFE powder, which is then dried at 150°C for 18 hours to obtain PTFE powder. 20.5 parts by mass (12.3 g) of hydrocarbon oil (trade name: Isopar G, manufactured by Exxon Chemical Co.) was added as an extrusion aid to 100 parts by mass (60 g) of PTFE powder, and the mixture was aged for 1 hour at room temperature (25±1°C), after which paste extrusion molding was carried out using an extrusion die equipped with a cylinder having an inner diameter of 25.4 mm (reduction ratio 1500). In the latter half of the extrusion, the pressure at the point where the pressure reached equilibrium was divided by the cross-sectional area of ​​the cylinder, and this value was taken as the extrusion pressure at a reduction ratio of 1500.

[0128] The PTFE preferably has an average primary particle diameter of 500 nm or less, more preferably 400 nm or less, and even more preferably 350 nm or less. The lower limit of the average primary particle diameter is not particularly limited, but may be, for example, 100 nm. From the viewpoint of molecular weight, for example, in the case of high molecular weight PTFE, it is preferably 150 nm or more, and more preferably 200 nm or more. The average primary particle diameter was determined from the transmittance based on a calibration curve of the transmittance of 550 nm projected light per unit length of an aqueous dispersion in which the resin solid content concentration was adjusted to 0.15% by mass, and the number-based length average primary particle diameter determined by measuring the unidirectional diameter in a transmission electron microscope photograph.

[0129] In the aqueous dispersion of the present disclosure, the content of PTFE particles having an aspect ratio of 5 or more is preferably less than 1.5 mass % based on the total content of PTFE particles. The aspect ratio is determined by observing an aqueous PTFE dispersion diluted to a solids concentration of approximately 1% by mass with a scanning electron microscope (SEM), processing the images of 200 or more randomly selected particles, and averaging the ratio of their major axis to their minor axis.

[0130] The standard specific gravity (SSG) of the PTFE is preferably 2.220 or less, more preferably 2.190 or less, and is preferably 2.140 or more, more preferably 2.150 or more. The SSG is measured by the water displacement method according to ASTM D-792 using a sample molded according to ASTM D 4895-89.

[0131] The PTFE generally has extensibility, fibrillation properties, and non-melt fabricability. The non-melt processability means that the melt flow rate cannot be measured at a temperature higher than the crystallization melting point in accordance with ASTM D-1238 and D-2116, i.e., the polymer does not flow easily even in the melting temperature range.

[0132] The first aqueous PTFE dispersion of the present disclosure is substantially free of a fluorine-containing surfactant. In the composition of the present disclosure, the phrase "substantially free of a fluorine-containing surfactant" means that the content of the fluorine-containing surfactant in the aqueous PTFE dispersion is 1.0 ppm or less. The first aqueous PTFE dispersion of the present disclosure is substantially free of a fluorine-containing surfactant, yet can have a low viscosity at high temperatures and excellent mechanical stability at high temperatures. The content of the fluorine-containing surfactant may be equal to or higher than the lower limit of detection, may be equal to or higher than the lower limit of quantitation, or may be 100 ppb or higher, preferably 700 ppb or lower, more preferably 600 ppb or lower, and even more preferably 500 ppb or lower. In the composition of the present disclosure, the content of the fluorine-containing surfactant is a value measured by liquid chromatography mass spectrometry, as described in the examples below. Specifically, it can be measured by the following method. [Method for measuring fluorine-containing surfactant content] The solids content of the aqueous dispersion was measured, and an amount of the aqueous dispersion equivalent to 1.5 g of PTFE solids was weighed into a 100 mL screw tube. The mixture was then combined with the water contained in the aqueous dispersion, and water and methanol were added so that the extraction solvent was 37 g of water / methanol = 10 / 90 mass%, and the mixture was shaken vigorously until coagulation occurred. The liquid phase was removed and centrifuged at 4000 rpm for 1 hour to extract the supernatant. Alternatively, a Soxhlet extraction method using methanol added to the aqueous dispersion may be used instead. The fluorine-containing surfactant in the extract obtained above is measured using a liquid chromatograph mass spectrometer.

[0133] When the first aqueous PTFE dispersion of the present disclosure is obtained by polymerization using a fluorine-containing surfactant, the amount of the fluorine-containing surfactant can be adjusted to the above range by adding a nonionic surfactant to the aqueous PTFE dispersion after polymerization, concentrating the dispersion, or the like.

[0134] Examples of the fluorine-containing surfactant include anionic fluorine-containing surfactants. The fluorine-containing anionic surfactant may be, for example, a compound represented by the following general formula (N 0 ) anionic group Y 0 The surfactant may be a fluorine atom-containing surfactant having a total carbon number of 20 or less excluding the carbon atoms in the moiety.

[0135] The fluorine-containing surfactant may also be a surfactant containing fluorine in the anionic moiety having a molecular weight of 800 or less. The "anionic portion" refers to the portion of the fluorine-containing surfactant excluding the cation. For example, F(CF2) represented by the formula (I) below n1 In the case of COOM, "F(CF2) n1 The "COO" part.

[0136] The above-mentioned fluorine-containing surfactant also includes a fluorine-containing surfactant having a LogPOW of 3.5 or less, preferably 3.4 or less. The LogPOW is a partition coefficient between 1-octanol and water, and is expressed as LogP (where P represents the ratio of the fluorine-containing surfactant concentration in octanol to the fluorine-containing surfactant concentration in water when a 1:1 octanol / water mixture containing the fluorine-containing surfactant undergoes phase separation). The LogPOW is calculated from the HPLC elution time of the sample solution using standard substances (heptanoic acid, octanoic acid, nonanoic acid, and decanoic acid) with known octanol / water partition coefficients under the following conditions: column: TOSOH ODS-120T column (φ4.6 mm×250 mm, manufactured by Tosoh Corporation), eluent: acetonitrile / 0.6% by mass HClO₄ / water=1 / 1 (vol / vol%), flow rate: 1.0 mL / min, sample amount: 300 μL, column temperature: 40°C, detection light: UV 210 nm. A calibration curve between each elution time and the known octanol / water partition coefficient is then prepared, and the LogPOW is calculated from the HPLC elution time of the sample solution based on this calibration curve.

[0137] Specific examples of the fluorine-containing surfactants include those described in U.S. Patent Application Publication Nos. 2007 / 0015864, 2007 / 0015865, 2007 / 0015866, 2007 / 0276103, 2007 / 0117914, 2007 / 142541, 2008 / 0015319, and U.S. Pat. No. 3,250,808. , U.S. Pat. No. 3,271,341, JP 2003-119204 A, WO 2005 / 042593, WO 2008 / 060461, WO 2007 / 046377, WO 2007 / 119526, WO 2007 / 046482, WO 2007 / 046345, U.S. Patent Application Publication No. 2014 / 0228531, WO 2013 / 189824, and WO 2013 / 189826.

[0138] The fluorine-containing anionic surfactant is a surfactant represented by the following general formula (N 0 ): X n0 -Rf n0 -Y 0 (N 0 ) (In the formula, X n0 is H, Cl or F. n0 is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which some or all of the H's are substituted with F, and the alkylene group may contain one or more ether bonds, and some of the H's may be substituted with Cl. Y 0 is an anionic group. Y 0 The anionic group may be -COOM, -SO2M, or -SO3M, and may be -COOM or -SO3M. M is H, metal atom, NR 7 4. An optionally substituted imidazolium, an optionally substituted pyridinium, or an optionally substituted phosphonium, wherein R 7is H or an organic group. The metal atom includes alkali metals (Group 1) and alkaline earth metals (Group 2), such as Na, K, or Li. R 7 As for H or C 1-10 may be an organic group of H or C 1-4 may be an organic group of H or C 1-4 The alkyl group may be: M is H, a metal atom, or NR 7 4, and may be H, an alkali metal (Group 1), an alkaline earth metal (Group 2), or NR 7 4, which may be H, Na, K, Li, or NH4. Above Rf n0 may be one in which 50% or more of H is substituted with fluorine.

[0139] The general formula (N 0 ) as a compound represented by The following general formula (N 1 ): X n0 -Rf m -Y 0 (N 1 ) (In the formula, X n0 are H, Cl and F, and Rf m is a linear or branched perfluoroalkylene group having 3 to 15 carbon atoms, and Y 0 is as defined above) (more specifically, a compound represented by the following general formula (N 1a ): X n0 -(CF2) m1 -Y 0 (N 1a ) (In the formula, X n0 is H, Cl, or F, m1 is an integer of 3 to 15, and Y 0 is as defined above), a compound represented by the following general formula (N 2 ): Rf n1 -O-(CF(CF3)CF2O) m2 CFX n1 -Y0 (N 2 ) (In the formula, Rf n1 is a perfluoroalkyl group having 1 to 5 carbon atoms, m2 is an integer of 0 to 3, and X n1 is F or CF3, and Y 0 is as defined above, a compound represented by the following general formula (N 3 ): Rf n2 (CH2) m3 -(Rf n3 ) q -Y 0 (N 3 ) (In the formula, Rf n2 is a partially or fully fluorinated alkyl group having 1 to 13 carbon atoms which may contain an ether bond, m3 is an integer of 1 to 3, and Rf n3 is a linear or branched perfluoroalkylene group having 1 to 3 carbon atoms, q is 0 or 1, and Y 0 is as defined above, a compound represented by the following general formula (N 4 ): Rf m4 -OL 4 -Y 0 (N 4 ) (In the formula, Rf m4 represents a linear or branched, partially or fully fluorinated aliphatic group which may contain an ether bond and / or chlorine; L represents a partially or fully fluorinated linear alkylene group or an aliphatic hydrocarbon group; Y 0 is as defined above) (more specifically, a compound represented by the following general formula (N 4a ): Rf n4 -O-(CY n1 Y n2 ) p CF2-Y 0 (N 4a ) (In the formula, Rf n4 is a linear or branched partially or fully fluorinated alkyl group having 1 to 12 carbon atoms, which may contain an ether bond and / or chlorine; Y n1 and Yn2 are the same or different and are H or F, p is 0 or 1, and Y 0 is as defined above, and a compound represented by the following general formula (N 5 ): [ka] (In the formula, X n2 , X n3 and X n4 Rf may be the same or different and are H, F, or a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms, which may contain an ether bond. n5 is a linear or branched partially or fully fluorinated alkylene group having 1 to 3 carbon atoms, which may contain an ether bond; L is a linking group; Y 0 is as defined above, where X n2 , X n3 , X n4 and Rf n5 The total number of carbon atoms is 18 or less.

[0140] The general formula (N 0 ) More specifically, the compounds represented by the formula (I) include perfluorocarboxylic acids (I) represented by the following general formula (I), ω-H perfluorocarboxylic acids (II) represented by the following general formula (II), perfluoropolyether carboxylic acids (III) represented by the following general formula (III), perfluoroalkyl alkylene carboxylic acids (IV) represented by the following general formula (IV), perfluoroalkoxy fluorocarboxylic acids (V) represented by the following general formula (V), perfluoroalkyl sulfonic acids (VI) represented by the following general formula (VII), ω-H perfluoro sulfonic acids (VII) represented by the following general formula (VII), perfluoroalkyl alkylene sulfonic acids (VIII) represented by the following general formula (VIII), alkyl alkylene carboxylic acids (IX) represented by the following general formula (IX), fluorocarboxylic acids (X) represented by the following general formula (X), alkoxy fluoro sulfonic acids (XI) represented by the following general formula (XI), and compounds (XII) represented by the following general formula (XII).

[0141] The perfluorocarboxylic acid (I) is represented by the following general formula (I): F(CF2) n1 COOM (I) (wherein n1 is an integer of 3 to 14, and M is H, a metal atom, or NR 7 4. An optionally substituted imidazolium, an optionally substituted pyridinium, or an optionally substituted phosphonium, wherein R 7 is H or an organic group.

[0142] The ω-H perfluorocarboxylic acid (II) is represented by the following general formula (II): H(CF2) n2 COOM (II) (wherein n2 is an integer of 4 to 15, and M is as defined above).

[0143] The perfluoropolyether carboxylic acid (III) is represented by the following general formula (III): Rf 1 -O-(CF(CF3)CF2O) n3 CF(CF3)COOM (III) (In the formula, Rf 1 is a perfluoroalkyl group having 1 to 5 carbon atoms, n3 is an integer of 0 to 3, and M is as defined above. The perfluoropolyether carboxylic acid (III) is preferably a perfluoropolyether carboxylic acid having a total carbon number of 7 or less and a LogPOW of 3.5 or less. The total carbon number is particularly preferably 5 to 7. The LogPOW is more preferably 3.4 or less.

[0144] The perfluoroalkyl alkylene carboxylic acid (IV) is represented by the following general formula (IV): Rf 2 (CH2) n4 Rf 3 COOM (IV) (In the formula, Rf 2is a perfluoroalkyl group having 1 to 5 carbon atoms, and Rf 3 is a linear or branched perfluoroalkylene group having 1 to 3 carbon atoms, n4 is an integer of 1 to 3, and M is as defined above.

[0145] The alkoxyfluorocarboxylic acid (V) is represented by the following general formula (V): Rf 4 -O-CY 1 Y 2 CF2-COOM (V) (In the formula, Rf 4 is a linear or branched partially or fully fluorinated alkyl group having 1 to 12 carbon atoms, which may contain an ether bond and / or chlorine; Y 1 and Y 2 are the same or different and are H or F, and M is as defined above.

[0146] The perfluoroalkylsulfonic acid (VI) is represented by the following general formula (VI): F(CF2) n5 SO3M (VI) (wherein n5 is an integer of 3 to 14, and M is as defined above).

[0147] The ω-H perfluorosulfonic acid (VII) is represented by the following general formula (VII): H(CF2) n6 SO3M (VII) (wherein n6 is an integer of 4 to 14, and M is as defined above).

[0148] The perfluoroalkyl alkylene sulfonic acid (VIII) is represented by the following general formula (VIII): Rf 5 (CH2) n7 SO3M (VIII) (In the formula, Rf 5is a perfluoroalkyl group having 1 to 13 carbon atoms, n7 is an integer of 1 to 3, and M is as defined above.

[0149] The alkyl alkylene carboxylic acid (IX) is represented by the following general formula (IX): Rf 6 (CH2) n8 COOM (IX) (In the formula, Rf 6 is a linear or branched partially or fully fluorinated alkyl group having 1 to 13 carbon atoms which may contain an ether bond, n8 is an integer of 1 to 3, and M is as defined above.

[0150] The fluorocarboxylic acid (X) is represented by the following general formula (X): Rf 7 -O-Rf 8 -O-CF2-COOM (X) (In the formula, Rf 7 is a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms, which may contain an ether bond and / or chlorine; Rf 8 is a linear or branched, partially or fully fluorinated alkyl group having 1 to 6 carbon atoms, and M is as defined above.

[0151] The alkoxyfluorosulfonic acid (XI) is represented by the following general formula (XI): Rf 9 -O-CY 1 Y 2 CF2-SO3M (XI) (In the formula, Rf 9 is a linear or branched alkyl group having 1 to 12 carbon atoms, which may contain an ether bond, and which may contain chlorine, and which is partially or completely fluorinated; Y 1 and Y 2 are the same or different and are H or F, and M is as defined above.

[0152] The compound (XII) is represented by the following general formula (XII): [ka] In the formula, X 1 , X 2 and X 3 may be the same or different and are H, F and linear or branched partially or fully fluorinated alkyl groups having 1 to 6 carbon atoms which may contain ether bonds; Rf 10 is a perfluoroalkylene group having 1 to 3 carbon atoms, L is a linking group, and Y 0 is an anionic group. Y 0 may be -COOM, -SO2M, or -SO3M, and may be -SO3M or COOM (wherein M is as defined above). Examples of L include a single bond and a partially or fully fluorinated alkylene group having 1 to 10 carbon atoms which may contain an ether bond.

[0153] As described above, examples of the fluorine-containing anionic surfactant include carboxylic acid surfactants and sulfonic acid surfactants.

[0154] In the above-mentioned fluorine-containing anionic surfactant, 1 When a compound represented by the formula (N 1 ) Rf m The number of carbon atoms in the formula (N) is preferably an integer of 3 to 6. 1a In general formula (I), m1 is preferably an integer of 3 to 6. When perfluorocarboxylic acid (I) is used, n1 in general formula (I) is preferably an integer of 3 to 6.

[0155] As the fluorine-containing anionic surfactant, particularly preferred is a compound selected from the group consisting of fluorine-containing carboxylic acids and salts thereof, which have 4 to 9 carbon atoms, preferably 4 to 7 carbon atoms, and which may have etheric oxygen and / or chlorine. Here, the carbon number means the total number of carbon atoms in one molecule. Two or more of the above fluorine-containing anionic surfactants may be used in combination.

[0156] The fluorine-containing anionic surfactant is preferably a compound selected from the group consisting of fluorine-containing carboxylic acids and salts thereof, which have 4 to 9, preferably 4 to 7, carbon atoms and have etheric oxygen and / or chlorine. The fluorine-containing carboxylic acid having etheric oxygen is a compound having 4 to 9, preferably 4 to 7, carbon atoms, which has etheric oxygen in the middle of the main carbon chain, and which has -COOH at the terminal. The -COOH at the terminal may form a salt. The number of etheric oxygen atoms present in the main chain is one or more, preferably 1 to 4, and more preferably 1 or 2. The number of carbon atoms is preferably 5 to 7.

[0157] The fluorine-containing anionic surfactant is particularly preferably a partially or fully fluorinated carboxylic acid or a salt thereof whose main chain has 6 to 7 carbon atoms, 1 to 4 etheric oxygen atoms, and is linear, branched, or cyclic. Here, the term "main chain" means a continuous chain with the maximum number of carbon atoms.

[0158] Examples of the fluorine-containing surfactants include F(CF2)7COOM, F(CF2)5COOM, H(CF2)6COOM, CF3O(CF2)3OCHFCF2COOM, C3F7OCF(CF3)CF2OCF(CF3)COOM, CF3CF2CF2OCF(CF3)COOM, CF3CF2CF2OCF(CF3)COOM, CF3CF2OCF2CF2OCF2COOM, C2F5OCF(CF3)CF2OCF(CF3)COOM, CF3OCF(CF3)CF2OCF(CF3)COOM, CF2ClCF2CF2OCF(CF3)CF2OCF2COOM, CF2ClCF2CF2OCF2CF(CF3)OCF2COOM, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOM, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOM, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOM, CF2ClCF(CF3)OCF2CF(CF3)OCF2COOM, The following formula: [ka] (wherein M is as defined above.) Furthermore, the anionic fluorine-containing surfactant may not be a single composition, but may be a mixture of two or more kinds.

[0159] The first aqueous PTFE dispersion of the present disclosure preferably contains an anionic surfactant for the purpose of adjusting viscosity or improving miscibility with pigments, fillers, etc. The anionic surfactant can be added as appropriate within an economically and environmentally acceptable range.

[0160] The anionic surfactant may be a fluorine-free anionic surfactant or a fluorine-containing anionic surfactant, with a fluorine-free anionic surfactant (i.e., a hydrocarbon-based anionic surfactant) being preferred.

[0161] For the purpose of viscosity adjustment, the type of anionic surfactant is not particularly limited as long as it is a known anionic surfactant. For example, the fluorine-free anionic surfactants described in WO 2013 / 146950 and WO 2013 / 146947 can be used. Examples include those having a saturated or unsaturated aliphatic chain with 6 to 40 carbon atoms, preferably 8 to 20 carbon atoms, and more preferably 9 to 13 carbon atoms. The saturated or unsaturated aliphatic chain may be either a linear or branched chain, or may have a cyclic structure. The hydrocarbon may be aromatic or may have an aromatic group. The hydrocarbon may have a heteroatom such as oxygen, nitrogen, or sulfur. Examples of the fluorine-free anionic surfactant include alkyl sulfonates, alkyl sulfates, alkylaryl sulfates, and salts thereof; fatty acids (aliphatic carboxylic acids) and salts thereof; alkyl phosphates, alkylaryl phosphates, and salts thereof; and among these, alkyl sulfonates, alkyl sulfates, aliphatic carboxylic acids, and salts thereof are preferred. The alkyl sulfate or its salt is preferably ammonium lauryl sulfate or sodium lauryl sulfate. As the fatty acid (aliphatic carboxylic acid) or a salt thereof, succinic acid, decanoic acid, undecanoic acid, undecenoic acid, lauric acid, hydrododecanoic acid, or a salt thereof is preferred. The fluorine-free anionic surfactant is preferably at least one selected from the group consisting of alkyl sulfates and salts thereof, and fatty acids and salts thereof.

[0162] The content of the fluorine-free anionic surfactant varies depending on the type of the fluorine-free anionic surfactant and other compounding ingredients, but is preferably 10 ppm to 5000 ppm relative to the solid mass of PTFE. The lower limit of the amount of the fluorine-free anionic surfactant added is more preferably 50 ppm or more, and even more preferably 100 ppm or more. If the amount added is too small, the viscosity adjusting effect is poor. The upper limit of the amount of the fluorine-free anionic surfactant to be added is preferably 4000 ppm or less, and more preferably 3000 ppm or less. If the amount is too large, the viscosity may increase, particularly at high temperatures. In addition, there is a risk of excessive foaming.

[0163] For the purpose of adjusting the viscosity of the first aqueous PTFE dispersion of the present disclosure, in addition to the fluorine-free anionic surfactant, for example, methyl cellulose, alumina sol, polyvinyl alcohol, carboxylated vinyl polymer, etc. may also be blended. For the purpose of adjusting the pH of the aqueous dispersion, a pH adjuster such as aqueous ammonia may be added. The first aqueous PTFE dispersion of the present disclosure preferably has a pH of 8 to 13, more preferably 9 to 12, and even more preferably 9 to 11. The pH value is measured at 25°C in accordance with JIS K6893.

[0164] The first aqueous PTFE dispersion of the present disclosure may contain other water-soluble polymer compounds as needed, provided that the characteristics of the aqueous dispersion are not impaired. The other water-soluble polymer compounds are not particularly limited and include, for example, polyethylene oxide (dispersion stabilizer), polyethylene glycol (dispersion stabilizer), polyvinylpyrrolidone (dispersion stabilizer), phenol resin, urea resin, epoxy resin, melamine resin, polyester resin, polyether resin, acrylic silicone resin, silicone resin, silicone polyester resin, polyurethane resin, etc. Furthermore, preservatives such as isothiazolones, azoles, pronopol, chlorothalonil, methylsulfonyltetrachloropyrrolidone, carbentazim, fluorophorbet, sodium diacetate, and diiodomethyl-paratolyl sulfone may be contained.

[0165] The first aqueous PTFE dispersion of the present disclosure may contain an antifoaming agent. The antifoaming agent can be added appropriately within an economical and environmentally friendly range. Various aqueous defoaming agents can be used, including lower alcohols such as methanol, ethanol, and butanol; higher alcohols such as amyl alcohol, polypropylene glycol, and its derivatives; oils and fats such as oleic acid, tall oil, mineral oil, and soap; surfactants such as sorbitan fatty acid esters, polyethylene glycol fatty acid esters, and Pluronic nonionic surfactants; and silicone surfactants such as siloxanes and silicone resins, which can be used alone or in combination. Representative commercially available defoaming agents include the B-series (manufactured by Asahi Denka Kogyo Co., Ltd.) such as Adekanate B and Adekanate B1068; the SN Deformer series (manufactured by Formaster DL, Nopco NXZ, and SN Deformer 113, 325, 308, and 368); Dehydran 1293 and Dehydran 1513 (manufactured by San Nopco Co., Ltd.); Flonone SB-110N, SB-210, 510, and 551; Aqualene 800 and 805. , Aqualene 1488 (manufactured by Kyoeisha Chemical Co., Ltd.); Surfynol 104E and 440 (acetylene-based defoamers manufactured by Air Products Co., Ltd.); KS-607A (manufactured by Shin-Etsu Chemical Co., Ltd.); FS Antifoam (manufactured by Dow Corning Corporation); BYK-020, 031, 073, and W (manufactured by Big Chemie); Dehydran 981 (manufactured by Henkel Hakusui Chemical Co., Ltd.); Epan-410, 710, and 720 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.); Tego Foamex series (manufactured by Tego Goldschmidt); and Foamrex-747, TY-10, and EP series (manufactured by Nicca Chemical Co., Ltd.). The content of the defoaming agent is preferably 0.01 to 10% by mass, and particularly preferably 0.05 to 5% by mass, of the PTFE aqueous dispersion. The first aqueous PTFE dispersion of the present disclosure may contain an antifoaming agent, but preferably does not contain an antifoaming agent. Not containing an antifoaming agent is advantageous in terms of cost. Furthermore, if an antifoaming agent is contained, the aqueous PTFE dispersion may be colored when it is formed into a coating film.

[0166] The first PTFE aqueous dispersion of the present disclosure usually contains an aqueous medium. The aqueous medium means a liquid containing water. The aqueous medium is not particularly limited as long as it contains water, and may contain water and, for example, a fluorine-free organic solvent such as an alcohol, ether, or ketone, and / or a fluorine-containing organic solvent having a boiling point of 40°C or lower. The aqueous medium preferably contains 90% by mass or more, more preferably 95% by mass or more, of water.

[0167] The first aqueous PTFE dispersion of the present disclosure preferably has a stability retention time at 60°C of 30 minutes or more, more preferably 40 minutes or more, even more preferably 50 minutes or more, still more preferably 55 minutes or more, particularly preferably 60 minutes or more, and particularly preferably 65 minutes or more. There is no particular upper limit to the stability retention time. The stability retention time is a value measured by the following method. A plastic cup with a diameter of 67 mm and a capacity of 300 ml was placed in 100 g of PTFE aqueous dispersion and immersed in a water bath at 60°C. A stirring blade with a diameter of 50 mm (Fig. 1) was set so that the height from the bottom of the plastic cup to the center of the stirring blade (6 mm from the bottom end of the stirring blade in the axial direction of Fig. 1(b)) was 20 mm, and the cup was rotated at 3000 rpm. The stability retention time was the time until the PTFE aqueous dispersion aggregated or solidified and scattered. did.

[0168] The first PTFE aqueous dispersion of the present disclosure may contain other additives, for example, coating materials. Examples of coating materials include pigments (extender pigments, scaly pigments, etc.), pigment dispersants, thickeners, leveling agents, film-forming aids, solid lubricants, anti-settling agents, moisture absorbers, surface conditioners, thixotropic agents, viscosity modifiers, anti-gelling agents, UV absorbers, HALS (light stabilizers), matting agents, plasticizers, color separation inhibitors, anti-skinning agents, anti-scratch agents, rust inhibitors, mildew inhibitors, antibacterial agents, antioxidants, flame retardants, anti-sagging agents, anti-static agents, silane coupling agents, and flame retardants. Examples of the additives include ordinary paint additives such as filler, carbon black, clay, talc, diamond, fluorinated diamond, tourmaline, jade, germanium, extender pigment, corundum, silica stone, chrysoberyl, topaz, beryl, garnet, quartz, garnet, zirconium oxide, zirconium carbide, barium sulfate, glass, various reinforcing materials, various extenders, conductive filler, colloidal silica, and metal powders such as gold, silver, copper, platinum, and stainless steel. More preferably, the first aqueous PTFE dispersion of the present disclosure does not contain colloidal silica.

[0169] The first aqueous PTFE dispersion of the present disclosure also preferably contains a preservative. Examples of the preservative include hydrogen peroxide, organic bromine compounds, organic nitrogen-sulfur compounds, organic iodine compounds, organic sulfur compounds, and triazine compounds. From the viewpoint of preservative performance, organic iodine compounds or organic nitrogen-sulfur compounds are preferred. Specific examples of organic iodine compounds and organic nitrogen-sulfur compounds include the Deltop series manufactured by Osaka Gas Chemicals Co., Ltd. The amount of the preservative added is preferably 0.01% by mass or more, and more preferably 0.05% by mass or more, based on the PTFE aqueous dispersion.

[0170] The first aqueous PTFE dispersion of the present disclosure can be obtained, for example, by adding a nonionic surfactant to an aqueous PTFE dispersion immediately after polymerization, or by adjusting the solid content concentration of PTFE by concentration, dilution, or the like. More specifically, the aqueous PTFE dispersion of the present disclosure can be produced by the following production method.

[0171] A first method for producing an aqueous PTFE dispersion according to the present disclosure is a method for producing an aqueous PTFE dispersion, comprising the steps of: Step A: Emulsion polymerizing TFE in the presence of a fluorine-containing anionic surfactant to obtain a dispersion containing PTFE; Step B of adding a nonionic surfactant (1) to the dispersion obtained in Step A; The method includes step C of removing the fluorine-containing anionic surfactant from the dispersion obtained in step B and further concentrating the dispersion, or step C of concentrating the dispersion obtained in step B and further removing the fluorine-containing anionic surfactant, and step D of adding a nonionic surfactant (2) and a fluorine-free anionic surfactant to the dispersion obtained in step C. In this specification, the phrase "dispersion obtained in step A" may refer to a dispersion that has undergone step A, or may refer to a dispersion that has undergone other treatments after step A. The same applies to steps B to D.

[0172] The emulsion polymerization can be carried out, for example, by charging a reaction apparatus with an aqueous medium, a fluorine-containing anionic surfactant, a monomer, and, if necessary, other additives, stirring the contents of the reaction apparatus, maintaining the reaction apparatus at a predetermined polymerization temperature, and then adding a predetermined amount of polymerization initiator to initiate the polymerization reaction. After the polymerization reaction has started, additional monomers, polymerization initiators, chain transfer agents, the surfactants, and the like may be added depending on the purpose. The surfactant may also be added after the polymerization reaction has started.

[0173] The polymerization temperature and polymerization pressure in the emulsion polymerization are appropriately determined depending on the type of monomer used, the desired molecular weight of PTFE, and the reaction rate. For example, the polymerization temperature is preferably 10 to 150° C. The polymerization temperature is more preferably 30° C. or higher, and even more preferably 50° C. or higher. The polymerization temperature is more preferably 120° C. or lower, and even more preferably 100° C. or lower. The polymerization pressure is preferably 0.05 to 10 MPa, more preferably 0.3 MPa or more, and even more preferably 0.5 MPa or more, and more preferably 5.0 MPa or less, and even more preferably 3.0 MPa or less.

[0174] The polymerization initiator is not particularly limited as long as it can generate radicals within the polymerization temperature range, and known oil-soluble and / or water-soluble polymerization initiators can be used. Furthermore, it can also be combined with a reducing agent or the like to initiate polymerization as a redox. The concentration of the polymerization initiator is determined appropriately depending on the type of monomer, the molecular weight of the target PTFE, and the reaction rate.

[0175] As the polymerization initiator, an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator can be used.

[0176] The oil-soluble radical polymerization initiator may be a known oil-soluble peroxide, for example, dialkyl peroxycarbonates such as diisopropyl peroxydicarbonate and di-sec-butyl peroxydicarbonate, peroxyesters such as t-butyl peroxyisobutyrate and t-butyl peroxypivalate, dialkyl peroxides such as di-t-butyl peroxide, and also di(ω-hydro-dodecafluoroheptanoyl) peroxide, di(ω-hydro-tetradecafluoroheptanoyl) peroxide, di(ω-hydro-hexadecafluorononanoyl) peroxide, di(perfluorobutyryl) peroxide, di(perfluorovaleryl) peroxide, di(perfluorohexanoyl) peroxide, di(perfluoroheptanoyl) peroxide, di(perfluorooctanoyl) peroxide, di(perfluorononanoyl) peroxide, di(ω-chloro Representative examples include di[perfluoro(or fluorochloro)acyl]peroxides such as di(ω-chlorohexafluorobutanoyl)peroxide, di(ω-chloro-decafluorohexanoyl)peroxide, di(ω-chloro-tetradecafluorooctanoyl)peroxide, ω-hydro-dodecafluoroheptanoyl-ω-hydrohexadecafluorononanoyl-peroxide, ω-chloro-hexafluorobutyryl-ω-chloro-decafluorohexanoyl-peroxide, ω-hydrododecafluoroheptanoyl-perfluorobutyryl-peroxide, di(dichloropentafluorobutanoyl)peroxide, di(trichlorooctafluorohexanoyl)peroxide, di(tetrachloroundecafluorooctanoyl)peroxide, di(pentachlorotetradecafluorodecanoyl)peroxide, and di(undecachlorodotriacontafluorodocosanoyl)peroxide.

[0177] The water-soluble radical polymerization initiator may be a known water-soluble peroxide, such as ammonium salts, potassium salts, or sodium salts of persulfuric acid, perborate, perchloric acid, perphosphoric acid, or percarbonate, t-butyl permaleate, or t-butyl hydroperoxide. A reducing agent such as sulfites or sulfites may also be contained, and the amount used may be 0.1 to 20 times the amount of the peroxide.

[0178] For example, when polymerization is carried out at low temperatures below 30°C, it is preferable to use a redox initiator, which combines an oxidizing agent and a reducing agent, as the polymerization initiator. Examples of oxidizing agents include persulfates, organic peroxides, potassium permanganate, manganese triacetate, cerium ammonium nitrate, and bromates. Examples of reducing agents include sulfites, bisulfites, bromates, diimines, and oxalic acid. Examples of persulfates include ammonium persulfate and potassium persulfate. Examples of sulfites include sodium sulfite and ammonium sulfite. To increase the decomposition rate of the initiator, it is also preferable to add a copper salt or an iron salt to the redox initiator combination. Examples of copper salts include copper(II) sulfate, and examples of iron salts include iron(II) sulfate.

[0179] Examples of the redox initiator include potassium permanganate / oxalic acid, ammonium persulfate / bisulfite / iron(II) sulfate, ammonium persulfate / sulfite / iron(II) sulfate, ammonium persulfate / sulfite, ammonium persulfate / iron(II) sulfate, manganese triacetate / oxalic acid, cerium ammonium nitrate / oxalic acid, bromate / sulfite, and bromate / bisulfite. Potassium permanganate / oxalic acid and ammonium persulfate / sulfite / iron(II) sulfate are preferred. When using a redox initiator, either the oxidizing agent or the reducing agent may be pre-charged into a polymerization vessel, followed by continuous or intermittent addition of the other agent to initiate polymerization. For example, when using potassium permanganate / oxalic acid, it is preferred to charge oxalic acid into a polymerization vessel and then continuously add potassium permanganate thereto.

[0180] The amount of polymerization initiator to be added is not particularly limited, but may be added all at once, stepwise, or continuously at the beginning of polymerization in an amount (for example, several ppm relative to the water concentration) that does not significantly decrease the polymerization rate. The upper limit is a range in which the reaction temperature can be increased while removing heat from the equipment using the heat of polymerization reaction, and a more preferred upper limit is a range in which the heat of polymerization reaction can be removed from the equipment.

[0181] A radical polymerization initiator can also be used as the polymerization initiator. A peroxide is preferred as the radical polymerization initiator. Examples of the radical polymerization initiator include the oil-soluble radical polymerization initiator and the water-soluble radical polymerization initiator described above, with the water-soluble radical polymerization initiator being preferred. A more preferred water-soluble radical polymerization initiator is a peroxide, and even more preferred are persulfates, organic peroxides, or mixtures thereof. Examples of persulfates include ammonium persulfate and potassium persulfate. Examples of organic peroxides include disuccinic acid peroxide and diglutaric acid peroxide. Even more preferred are ammonium persulfate and disuccinic acid peroxide. In the emulsion polymerization, the water-soluble radical polymerization initiator is preferably used in an amount of 500 ppm or less relative to the aqueous medium, more preferably 400 ppm or less, even more preferably 300 ppm or less, particularly preferably 200 ppm or less, and is preferably 5 ppm or more, more preferably 10 ppm or more, and even more preferably 20 ppm or more. For example, the water-soluble radical polymerization initiator is preferably ammonium persulfate at a concentration of preferably 0.1 ppm or more, more preferably 1.0 ppm or more, even more preferably 1.5 ppm or more, still more preferably 2.0 ppm or more, and particularly preferably 2.5 ppm or more relative to the aqueous medium, and is preferably ammonium sulfate at a concentration of preferably 50 ppm or less, more preferably 40 ppm or less, and even more preferably 30 ppm or less relative to the aqueous medium. The water-soluble radical polymerization initiator is preferably disuccinic acid peroxide in an amount of 10 ppm or more, more preferably 30 ppm or more, and even more preferably 50 ppm or more relative to the aqueous medium, and preferably 500 ppm or less, more preferably 300 ppm or less, and even more preferably 200 ppm or less relative to the aqueous medium. In the above emulsion polymerization, it is particularly preferable to use ammonium persulfate and disuccinic acid peroxide in combination. When used in combination, the amounts of ammonium persulfate and disuccinic acid peroxide can be the same as those of the ammonium persulfate and disuccinic acid peroxide described above. In the emulsion polymerization, after the polymerization is initiated, a radical polymerization initiator may be added continuously or intermittently.

[0182] Examples of the chain transfer agent include esters such as dimethyl malonate, diethyl malonate, methyl acetate, ethyl acetate, butyl acetate, and dimethyl succinate, as well as isopentane, methane, ethane, propane, isobutane, methanol, ethanol, isopropanol, acetone, various mercaptans, various halogenated hydrocarbons such as carbon tetrachloride, and cyclohexane.

[0183] Among these, at least one selected from the group consisting of alkanes and alcohols is preferred from the viewpoints of polymerization reactivity, crosslinking reactivity, availability, etc. The number of carbon atoms in the alkanes is preferably 1 to 6, more preferably 1 to 5. The number of carbon atoms in the alcohols is preferably 1 to 5, more preferably 1 to 4. The chain transfer agent is particularly preferably at least one selected from the group consisting of methane, ethane, propane, isobutane, methanol, ethanol, and isopropanol.

[0184] The amount of the chain transfer agent is preferably 0.001 to 10,000 ppm relative to the aqueous medium. The amount of the chain transfer agent is more preferably 0.01 ppm or more relative to the aqueous medium, even more preferably 0.05 ppm or more, and particularly preferably 0.1 ppm or more. The amount is more preferably 1,000 ppm or less relative to the aqueous medium, even more preferably 500 ppm or less.

[0185] The chain transfer agent may be added to the reaction vessel all at once before the start of polymerization, may be added all at once after the start of polymerization, may be added in multiple divided portions during polymerization, or may be added continuously during polymerization.

[0186] Step (A) is preferably a step of polymerizing TFE and a monomer copolymerizable with TFE. Examples of the monomer copolymerizable with TFE include the modified monomers described above, but in particular, at least one monomer selected from the group consisting of PAVE, PFAE, perfluoroallyl ether, and cyclic monomers is preferred, with PAVE being more preferred.

[0187] Examples of the PAVE include perfluoro(alkyl vinyl ether), such as perfluoro(methyl vinyl ether) [PMVE], perfluoro(ethyl vinyl ether) [PEVE], perfluoro(propyl vinyl ether) [PPVE], and perfluoro(butyl vinyl ether) [PBVE]. At least one selected from the group consisting of PMVE, PEVE, and PPVE is preferred, with PPVE being more preferred.

[0188] The PFAE is not particularly limited, and examples thereof include (perfluorobutyl)ethylene (PFBE) and (perfluorohexyl)ethylene.

[0189] Examples of perfluoroallyl ethers include: General formula: CF2=CF-CF2-ORf 12 (In the formula, Rf 12represents a perfluoroorganic group.

[0190] Above Rf 12 is preferably a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoroalkoxyalkyl group having 1 to 10 carbon atoms. The perfluoroallyl ether is preferably at least one selected from the group consisting of CF2=CF-CF2-O-CF3, CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7, and CF2=CF-CF2-O-C4F9, more preferably at least one selected from the group consisting of CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7, and CF2=CF-CF2-O-C4F9, and even more preferably CF2=CF-CF2-O-CF2CF2CF3.

[0191] The cyclic monomer is a monomer represented by the general formula (ii): [ka] (In the formula, X 2 and X 3 are the same or different and represent a hydrogen atom or a fluorine atom, and Y is -CR 1 R 2 - represents R 1 and R 2 are the same or different and represent a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms.) Preferred vinyl heterocycles represented by the above general formula (ii) include, for example, vinyl heterocycles represented by X 2 and X 3 is preferably a fluorine atom, and R 1 and R 2 is preferably a fluoroalkyl group having 1 to 6 carbon atoms. The vinyl heterocyclic compound represented by the general formula (ii) includes X 2 and X 3 is a fluorine atom, R 1 and R 2is a perfluoromethyl group, perfluoro-2,2-dimethyl-1,3-dioxole [PDD] is preferred.

[0192] In step A, the fluorine-containing anionic surfactant may be any of the fluorine-containing anionic surfactants described in the first aqueous PTFE dispersion of the present disclosure, and for example, a fluorine-containing anionic surfactant having a LogPOW of 3.5 or less, preferably a fluorine-containing anionic surfactant having a LogPOW of 3.4 or less may be used.

[0193] The above step A is preferably a step of obtaining a dispersion of PTFE having a core-shell structure. For example, it can be obtained by first polymerizing TFE and, if necessary, a modified monomer to produce a core (PTFE or modified PTFE), and then polymerizing TFE and, if necessary, a modified monomer to produce a shell (PTFE or modified PTFE). Step A is a step of obtaining a dispersion of modified polytetrafluoroethylene having a core-shell structure, and preferably includes Step A-1 of polymerizing TFE and at least one modifying monomer selected from the group consisting of perfluoro(alkyl vinyl ether), (perfluoroalkyl)ethylene, and a cyclic monomer to produce the core, and Step A-2 of polymerizing TFE, the modifying monomer, and at least one selected from the group consisting of hexafluoropropylene and a chain transfer agent to produce the shell. The above step A-2 is more preferably a step of polymerizing TFE and a chain transfer agent.

[0194] The shell may be obtained by copolymerizing TFE with a modifying monomer that is a copolymerizable monomer, or by adding a chain transfer agent during polymerization, or by performing both of these methods.

[0195] The shelling is carried out by using a chain transfer agent and / or a compound represented by the following general formula (iii): F2C=CFO(CF2) n1X 1 (iii) (In the formula, X 1 represents a hydrogen atom or a fluorine atom, and n1 represents an integer of 1 to 6.) or a fluoro(alkyl vinyl ether) represented by the following general formula (iv): CX 4 X 5 =CX 6 (CF2) n2 F(iv) (In the formula, X 4 , X 5 and X 6 represents a hydrogen atom or a fluorine atom, and at least one represents a fluorine atom. n2 represents an integer of 1 to 5. Preferably, the copolymerization is carried out by copolymerizing a fluoroolefin represented by the following formula:

[0196] The chain transfer agent used in producing the shell is not particularly limited as long as it reduces the molecular weight of the PTFE that constitutes the shell, and examples thereof include non-peroxide organic compounds such as water-soluble alcohols, hydrocarbons, and fluorohydrocarbons, water-soluble organic peroxides such as disuccinic acid peroxide (DSP), and / or persulfates such as ammonium persulfate (APS) and potassium persulfate (KPS). The chain transfer agent may contain at least one of a non-peroxide organic compound, a water-soluble organic peroxide, and a persulfate. The chain transfer agent may contain one or more of each of a non-peroxide organic compound, a water-soluble organic peroxide, and a persulfate.

[0197] The chain transfer agent is preferably at least one selected from the group consisting of water-soluble alcohols having 1 to 4 carbon atoms, hydrocarbons having 1 to 4 carbon atoms, and fluorohydrocarbons having 1 to 4 carbon atoms, in view of good dispersibility and uniformity in the reaction system, more preferably at least one selected from the group consisting of methane, ethane, n-butane, isobutane, methanol, isopropanol, DSP, APS, and KPS, and even more preferably methanol and / or isobutane.

[0198] The modifying monomer used in the production of the shell is preferably a fluoroolefin represented by the general formula (iv) above. Examples of the fluoroolefin include perfluoroolefins having 2 to 4 carbon atoms and hydrogen-containing fluoroolefins having 2 to 4 carbon atoms. The fluoroolefin is preferably a perfluoroolefin, and among these, hexafluoropropylene [HFP] is preferred.

[0199] In the shell, the amount of the modifying agent units derived from the modifying monomer depends on the type of the modifying monomer used, but from the viewpoint of the stability of the PTFE dispersion, it is preferably 0.001 to 0.5 mass% of the total primary particles constituting the PTFE, with a more preferred lower limit of 0.005 mass%, a more preferred upper limit of 0.2 mass%, and an even more preferred upper limit of 0.10 mass%. When HFP is used as the modifying monomer in the shell, it is preferably 0.001 to 0.3 mass% of the total primary particles constituting the PTFE, with a more preferred lower limit of 0.005 mass%, and a more preferred upper limit of 0.15 mass%.

[0200] The PTFE may be prepared by either using a chain transfer agent or copolymerizing a modifying agent, or by both copolymerizing a modifying monomer and using a chain transfer agent. When the fluoro(alkyl vinyl ether) represented by the general formula (iii), particularly PPVE, is used as the modifying monomer in the PTFE constituting the core, the PTFE is preferably obtained by using methanol, isobutane, DSP and / or APS as a chain transfer agent, or by copolymerizing HFP and / or PPVE as a modifying agent, more preferably by using methanol or HFP.

[0201] The step A is preferably a step of polymerizing TFE and a modifying monomer to produce a core, and then polymerizing a monomer composition containing TFE in the presence of a chain transfer agent to produce a shell. The modifying monomer and / or chain transfer agent may be the same as those described above for the PTFE having a core-shell structure.

[0202] The core-shell structure may be any of the structures described above, but a core-shell structure having a core of modified PTFE and a shell of low-molecular-weight PTFE obtained by polymerizing a monomer composition containing TFE in the presence of a chain transfer agent is particularly preferred. As described above, the shell of low-molecular-weight PTFE can be obtained by polymerizing a monomer composition containing TFE in the presence of a chain transfer agent.

[0203] The above step A preferably includes step 1 of charging a reaction apparatus with deionized water, a fluorine-containing anionic surfactant (excluding PFOA or a salt thereof), and a stabilizing aid, removing oxygen, and then adding TFE and a polymerization initiator; step 2 of adding a monomer copolymerizable with TFE; step 3 of adding a chain transfer agent; and step 4 of cooling and removing the stabilizing aid after the completion of polymerization.

[0204] In the above step 1, the fluorine-containing anionic surfactant (excluding PFOA or a salt thereof) may be any fluorine-containing anionic surfactant other than PFOA or a salt thereof among the above-mentioned fluorine-containing surfactants. For example, a fluorine-containing anionic surfactant having a LogPOW of less than 3.5 is preferred, and a fluorine-containing anionic surfactant having a LogPOW of 3.4 or less is preferred. More specifically, the above general formula (N 1 ) (excluding PFOA or its salts), 2 ), a compound represented by the above general formula (N 3 ), a compound represented by the above general formula (N 4 ) and a compound represented by the above general formula (N 5 and n is 0 or 1. The compound of formula (I) is at least one compound selected from the group consisting of compounds represented by the formula (II) (excluding PFOA and salts thereof). More specifically, the perfluorocarboxylic acid (I) represented by the general formula (I) (excluding PFOA or a salt thereof), the ω-H perfluorocarboxylic acid (II) represented by the general formula (II), the perfluoropolyether carboxylic acid (III) represented by the general formula (III), the perfluoroalkyl alkylene carboxylic acid (IV) represented by the general formula (IV), the perfluoroalkoxy fluorocarboxylic acid (V) represented by the general formula (V), the perfluoroalkyl sulfonic acid (VI) represented by the general formula (VII), the ω-H perfluorosulfonic acid (VII) represented by the general formula (VII), the perfluoroalkyl alkylene sulfonic acid (VIII) represented by the general formula (VIII), the alkyl alkylene carboxylic acid (IX) represented by the general formula (IX), the fluorocarboxylic acid (X) represented by the general formula (X), the alkoxy fluorosulfonic acid (XI) represented by the general formula (XI), and at least one selected from the group consisting of the compound (XII) represented by the following general formula (XII). In the above step 1, the fluorine-containing anionic surfactant is a surfactant represented by the general formula (N 1 When a compound represented by the formula (N 1 ) Rf m The number of carbon atoms in the formula (N) is preferably an integer of 3 to 6. 1a In general formula (I), m1 is preferably an integer of 3 to 6. When perfluorocarboxylic acid (I) is used, n1 in general formula (I) is preferably an integer of 3 to 6.

[0205] As the fluorine-containing anionic surfactant, a compound selected from the group consisting of fluorine-containing carboxylic acids and salts thereof, which have 4 to 7 carbon atoms and may have an etheric oxygen atom, is particularly preferred. Here, the carbon number means the total number of carbon atoms in one molecule. Two or more of the fluorine-containing anionic surfactants may be used in combination.

[0206] The fluorine-containing anionic surfactant is preferably a compound selected from the group consisting of a fluorine-containing carboxylic acid having 4 to 7 carbon atoms and having an etheric oxygen and a salt thereof. The fluorine-containing carboxylic acid having an etheric oxygen is a compound having 4 to 7 carbon atoms, having an etheric oxygen in the middle of the carbon chain of the main chain, and having a -COOH group at the terminal. The -COOH group at the terminal may form a salt. The number of etheric oxygen atoms present in the main chain is one or more, preferably 1 to 4, and more preferably 1 or 2. The number of carbon atoms is preferably 5 to 7.

[0207] The fluorine-containing anionic surfactant is particularly preferably a partially or fully fluorinated carboxylic acid or a salt thereof whose main chain has 6 to 7 carbon atoms, 1 to 4 etheric oxygen atoms, and is linear, branched, or cyclic. Here, the term "main chain" means a continuous chain with the maximum number of carbon atoms.

[0208] Examples of the fluorine-containing surfactants include F(CF2)7COOM, F(CF2)5COOM, H(CF2)6COOM, CF3O(CF2)3OCHFCF2COOM, C3F7-O-CF(CF3)CF2-O-CF(CF3)COOM, CF3CF2CF2OCF(CF3)COOM, CF3CF2OCF2CF2CF2OCF2COOM, C2F5-O-CF(CF3)CF2-O-CF(CF3)COOM, CF3OCF(CF3)CF2OCF(CF3)COOM, CF2ClCF2CF2OCF(CF3)CF2OCF2COOM, CF2ClCF2CF2OCF2CF(CF3)OCF2COOM, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOM, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOM, CF2ClCF(CF3)OCF2CF(CF3)OCF2COOM, CF2ClCF(CF3)OCF2CF(CF3)OCF2COOM, The following formula: [ka] (wherein M is as defined above.) Furthermore, the anionic fluorine-containing surfactant may not be a single composition, but may be a mixture of two or more kinds.

[0209] In the above step 1, examples of the stabilizing aid include those mentioned above, with paraffin wax being particularly preferred. Paraffin wax may be liquid, semi-solid, or solid at room temperature, but is preferably a saturated hydrocarbon having 12 or more carbon atoms. The melting point of the paraffin wax is generally preferably 40 to 65°C, more preferably 50 to 65°C.

[0210] In the above step 1, the polymerization initiator that can be used is the same as that described in step A, and the amount added is not particularly limited.

[0211] In the above step 2, the monomer copolymerizable with TFE can be the modified monomer described above, and preferably at least one monomer selected from the group consisting of PAVE, PFAE, and cyclic monomers. The PAVE is preferably at least one selected from the group consisting of PMVE, PEVE, and PPVE. The cyclic monomer is preferably a vinyl heterocycle represented by the above general formula (II). Examples of the PFAE include (perfluorobutyl)ethylene (PFBE) and (perfluorohexyl)ethylene.

[0212] In the above step 2, the monomer copolymerizable with TFE is preferably added before the start of polymerization or after the start of polymerization when the solid content of PTFE is less than 5 mass %, thereby obtaining a dispersion of PTFE having a core of modified PTFE.

[0213] In the above step 2, the method for removing oxygen is not particularly limited, and any conventionally known method can be used.

[0214] In the above step 3, the amount of chain transfer agent added may be the same as that described in the above step A.

[0215] In the above step 3, p1 / p2 is preferably 0.60 or more. p1 / p2 is more preferably 0.70 or more, even more preferably 0.80 or more, and particularly preferably 0.90 or more. The upper limit of p1 / p2 is not particularly limited, but may be, for example, 0.98. The above p1 / p2 indicates the ratio of the core to the entire PTFE, and indicates the ratio of the amount of TFE charged when a modified monomer or a chain transfer agent is charged during polymerization to the total amount of TFE charged in PTFE polymerization. The above p1 is the amount of TFE charged when the shell is charged, and p2 indicates the total amount of TFE charged.

[0216] In the above step 4, the method for removing the cooling and stabilizing aid is not particularly limited, and any conventionally known method can be used.

[0217] In the emulsion polymerization, in addition to the surfactant and, if desired, other surface-active compounds, additives for stabilizing each compound can be used, such as buffers, pH adjusters, stabilizing aids, and dispersion stabilizers.

[0218] The stabilizing aid is preferably paraffin wax, fluorine-based oil, fluorine-based solvent, silicone oil, etc. The stabilizing aid may be used alone or in combination of two or more. The stabilizing aid is more preferably paraffin wax. The paraffin wax may be liquid, semi-solid, or solid at room temperature, but is preferably a saturated hydrocarbon having 12 or more carbon atoms. The melting point of the paraffin wax is usually preferably 40 to 65°C, more preferably 50 to 65°C.

[0219] The amount of the stabilizing aid used is preferably 0.1 to 12 mass % and more preferably 0.1 to 8 mass % based on the mass of the aqueous medium (e.g., deionized water) used. It is desirable that the stabilizing aid is sufficiently hydrophobic so that it is completely separated from the aqueous PTFE emulsion after emulsion polymerization of TFE and does not become a contaminating component.

[0220] The aqueous medium is a reaction medium for polymerization and refers to a liquid containing water. The aqueous medium is not particularly limited as long as it contains water, and may contain water and, for example, a fluorine-free organic solvent such as an alcohol, ether, or ketone, and / or a fluorine-containing organic solvent having a boiling point of 40° C. or lower.

[0221] As the nonionic surfactant (1) added in step B, the nonionic surfactant represented by the above formula (i) can be used. The nonionic surfactant (1) may be: The following formula (1): R 4 -OA 2 -H (1) (In the formula, R 4 is a linear or branched primary or secondary alkyl group having 8 to 18 carbon atoms and an average number of methyl groups per molecule of 2.0 or more, and A 2 is a polyoxyalkylene chain having an average number of oxyethylene units of 7.0 to 12.0 and an average number of oxypropylene units of 0.0 to 2.0. Above R 4 is represented by the following general formula (1-1): CHR 41 R 42 - (1-1) (In the formula, R 41 represents a hydrogen atom or an alkyl group having 1 to 16 carbon atoms, and R 42 represents an alkyl group having 1 to 17 carbon atoms, and R 41 and R 42 The total number of carbon atoms in R is preferably 7 to 17. 41 is more preferably a hydrogen atom or an alkyl group having 1 to 15 carbon atoms, even more preferably a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, and even more preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. 42 As the alkyl group, an alkyl group having 1 to 15 carbon atoms is more preferable, an alkyl group having 1 to 14 carbon atoms is even more preferable, and an alkyl group having 1 to 13 carbon atoms is even more preferable. Above R 4is preferably an alkyl group having 8 to 18 carbon atoms and an average number of methyl groups of 2.5 or more. 4 The average number of methyl groups in R is more preferably 3.0 or more, even more preferably 3.5 or more, and even more preferably 4.0 or more. 4 The upper limit of the average number of methyl groups is preferably 12 or less, more preferably 10 or less, and even more preferably 8 or less. In formula (1), R 4 is preferably a 2,6,8-trimethyl-4-nonyl group. R 4 When the oxyethylene group is a 2,6,8-trimethyl-4-nonyl group, the average number of oxyethylene units is preferably 10.0 to 10.5. In this case, the average number of oxypropylene units is 0.0.

[0222] The removal of the fluorine-containing anionic surfactant in step C is preferably carried out by contacting the aqueous dispersion with an anion exchange resin.

[0223] The anion exchange resin in step C is not particularly limited, and known resins can be used. In addition, known methods can be used for contacting with the anion exchange resin. The anion exchange resin may, for example, have a functional group of -N + X - A strongly basic anion exchange resin having (CH3)3 groups (X represents Cl or OH), -N + X - Examples of suitable resins include well-known strong basic anion exchange resins having a (CH)(CHOH) group (X is the same as above). Specific examples include those described in WO 99 / 62858, WO 03 / 020836, WO 2004 / 078836, WO 2013 / 027850, and WO 2014 / 084399.

[0224] The cation exchange resin is not particularly limited, and may be, for example, a resin having a functional group of -SO3 - Strongly acidic cation exchange resin with -COO functional group -Examples of suitable ion exchange resins include well-known weakly acidic cation exchange resins having a hydroxyl group, but among these, strongly acidic cation exchange resins are preferred from the viewpoint of removal efficiency. + Strongly acidic cation exchange resins of the type are more preferred.

[0225] The above-mentioned "mixed bed consisting of a cation exchange resin and an anion exchange resin" is not particularly limited, and includes cases where both are packed in the same column, where both are packed in different columns, where both are dispersed in an aqueous dispersion, etc.

[0226] The removal of the fluorine-containing anionic surfactant in step C may be carried out by concentration. As described in WO 2005 / 042593, the concentration step may be carried out two or more times. Therefore, step C may involve concentrating the dispersion obtained in step B two or more times. Step C is preferably carried out by contacting the aqueous dispersion with an anion exchange resin.

[0227] Known methods can be used for the concentration in step C. Specific examples include those described in WO 2007 / 046482 and WO 2014 / 084399. Examples of such methods include phase separation, centrifugal sedimentation, cloud point concentration, electroconcentration, electrophoresis, filtration using ultrafiltration, filtration using a reverse osmosis membrane (RO membrane), and nanofiltration. The above concentration can be performed to a PTFE concentration of 50 to 70 mass % depending on the application. Because concentration can impair the stability of the dispersion, a nonionic surfactant may be further added in step C. The nonionic surfactant in step C is the same as that in the first aqueous PTFE dispersion of the present disclosure. Furthermore, dispersion stabilizers other than nonionic surfactants may be used as needed. The total amount of the dispersion stabilizers is a concentration of 0.5 to 20% by mass relative to the solid mass of PTFE. If it is less than 0.5% by mass, the dispersion stability may be poor, and if it exceeds 20% by mass, the dispersion effect will not be commensurate with the amount present, making it impractical. The lower limit of the dispersion stabilizer is more preferably 2% by mass, and the upper limit is more preferably 12% by mass. By the above concentration operation, even when a fluorine-containing surfactant is used in the polymerization, the fluorine-containing surfactant can be removed from the aqueous dispersion.

[0228] The concentration is preferably cloud point concentration. Cloud point concentration is preferably carried out by, for example, heating at a temperature that is at least 5°C lower than the cloud point of the nonionic surfactant. More specifically, it is preferable to heat the solution at a temperature that is at least 5°C lower than the cloud point of the nonionic surfactant, and then allow it to stand, causing separation into an upper supernatant phase and a concentrated phase.

[0229] The above concentration may be carried out only once or may be carried out two or more times.

[0230] Step D is a step of adding a nonionic surfactant (2) and a fluorine-free anionic surfactant to the dispersion liquid obtained in step C. The order in which the nonionic surfactant (2) and the fluorine-free anionic surfactant are added is not particularly limited. The nonionic surfactant (2) may be added first, followed by the fluorine-free anionic surfactant; the fluorine-free anionic surfactant may be added first, followed by the nonionic surfactant (2); or the fluorine-containing anionic surfactant and the nonionic surfactant may be added simultaneously. The addition of the nonionic surfactant (2) and the non-fluorine-containing anionic surfactant may each be carried out multiple times, or the addition of the nonionic surfactant (2) and the non-fluorine-containing anionic surfactant may be carried out alternately multiple times.

[0231] The nonionic surfactant (2) added in step D may be a nonionic surfactant represented by the above formula (i). The nonionic surfactant (2) may be a nonionic surfactant represented by the following formula (2): R 5 -OA 3 -H (2) (In the formula, R 5 is a linear or branched primary or secondary alkyl group having 8 to 18 carbon atoms and an average number of methyl groups per molecule of 2.0 or more, and A 3 is a polyoxyalkylene chain having an average number of oxyethylene units of 10.0 to 12.0.

[0232] R 5 is represented by the following general formula (2-1): CHR 51 R 52 - (2-1) (In the formula, R 51 represents a hydrogen atom or an alkyl group having 1 to 16 carbon atoms, and R 52 represents an alkyl group having 1 to 17 carbon atoms, and R 51 and R 52 The total number of carbon atoms in R is preferably 7 to 17. 51 is more preferably a hydrogen atom or an alkyl group having 1 to 15 carbon atoms, even more preferably a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, and even more preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. 52 As the alkyl group, an alkyl group having 1 to 15 carbon atoms is more preferable, an alkyl group having 1 to 14 carbon atoms is even more preferable, and an alkyl group having 1 to 13 carbon atoms is even more preferable. Above R 5 is preferably an alkyl group having 8 to 18 carbon atoms and an average number of methyl groups of 2.5 or more. 5 The average number of methyl groups in R is more preferably 3.0 or more, even more preferably 3.5 or more, and even more preferably 4.0 or more. 5 The upper limit of the average number of methyl groups is preferably 12 or less, more preferably 10 or less, and even more preferably 8 or less. In formula (2), R 5is preferably a 2,6,8-trimethyl-4-nonyl group. R 5 When the oxyethylene group is a 2,6,8-trimethyl-4-nonyl group, the average number of oxyethylene units is preferably 10.1 to 11.0. In this case, the average number of oxypropylene units is 0.0.

[0233] The step D is preferably a step of adding the nonionic surfactant (2) so that the concentration of the nonionic surfactant in the dispersion is 4 to 12% by mass relative to the polytetrafluoroethylene, more preferably 5% by mass or more, more preferably 10% by mass or less, and even more preferably 8% by mass or less.

[0234] Examples of the fluorine-free anionic surfactant added in step D include alkyl sulfonates, alkyl sulfates, alkylaryl sulfates, and salts thereof; fatty acids (aliphatic carboxylic acids) and salts thereof; alkyl phosphates, alkylaryl phosphates, and salts thereof; and among these, alkyl sulfonates, alkyl sulfates, aliphatic carboxylic acids, and salts thereof are preferred. Among these, at least one selected from the group consisting of alkyl sulfates and salts thereof, and fatty acids and salts thereof is more preferred. As the alkyl sulfate and its salt, ammonium lauryl sulfate, sodium lauryl sulfate, etc. are preferred. As the fatty acid and its salt, succinic acid, decanoic acid, undecanoic acid, undecenoic acid, lauric acid, hydrododecanoic acid, and salts thereof are preferred.

[0235] The content of the fluorine-free anionic surfactant is preferably 50 to 5000 ppm relative to the PTFE. The lower limit of the amount of the fluorine-free anionic surfactant added is more preferably 50 ppm, even more preferably 100 ppm, and even more preferably 200 ppm. If the amount added is too small, the viscosity adjusting effect is poor. The upper limit of the amount of the fluorine-free anionic surfactant to be added is more preferably 4000 ppm, even more preferably 3000 ppm, even more preferably 2000 ppm, and particularly preferably 1000 ppm. If the amount is too large, the viscosity may increase, particularly at high temperatures. In addition, there is a risk of excessive foaming.

[0236] The manufacturing method of the present disclosure preferably further comprises the step of adding a preservative to the aqueous dispersion. Preservatives include those described above for the aqueous dispersion of the present disclosure.

[0237] The manufacturing method of the present disclosure preferably further includes a step of adding coating materials. Examples of coating materials include additives that can be added to coating materials. Specific examples include typical coating additives such as pigments (extender pigments, scale-like pigments, etc.), pigment dispersants, thickeners, leveling agents, film-forming aids, solid lubricants, anti-settling agents, moisture absorbers, surface conditioners, thixotropic agents, viscosity modifiers, anti-gelling agents, UV absorbers, HALS (light stabilizers), matting agents, plasticizers, anti-color separation agents, anti-skinning agents, anti-scratch agents, rust inhibitors, mildew inhibitors, antibacterial agents, antioxidants, flame retardants, anti-sagging agents, antistatic agents, silane coupling agents, fillers, carbon black, clay, barium sulfate, glass, various reinforcing materials, various extenders, conductive fillers, colloidal silica, and metal powders such as gold, silver, copper, platinum, and stainless steel. The additive may be an additive other than colloidal silica. The content of the coating material is not particularly limited and may be appropriately determined depending on the application.

[0238] The above production method may also include a step of recovering the aqueous PTFE dispersion obtained by polymerization.

[0239] The present disclosure also provides an aqueous PTFE dispersion obtained by the production method of the present disclosure. The aqueous PTFE dispersion obtained by the production method of the present disclosure can appropriately adopt the characteristics described for the first aqueous PTFE dispersion of the present disclosure. Furthermore, the PTFE aqueous dispersion obtained by the production method of the present disclosure preferably has a nonionic surfactant concentration of 4% by mass or more, more preferably 5% by mass or more, and preferably 12% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less, and even more preferably 7% by mass or less, based on the PTFE. In the aqueous PTFE dispersion obtained by the production method of the present disclosure, the cloud point of the nonionic surfactant is preferably 60° C. or higher, more preferably 63° C. or higher, and even more preferably 65° C. or higher. It is preferably 80° C. or lower, more preferably 76° C. or lower, and even more preferably 73° C. or lower. In the aqueous PTFE dispersion obtained by the production method of the present disclosure, the HLB of the nonionic surfactant is preferably 13.00 to 15.00, more preferably 13.30 or higher, and even more preferably 13.50 or higher. The aqueous PTFE dispersion obtained by the production method of the present disclosure preferably has a fluorine-containing anionic surfactant content of 1.0 ppm or less based on the aqueous dispersion.

[0240] The PTFE aqueous dispersion obtained by the production method of the present disclosure can be used as is, or after adding additives as necessary, to produce coated articles such as those exemplified below. Examples of the coated articles include cooking utensils such as frying pans, grills, pressure cookers, other various pots, rice cookers, rice cake makers, ovens, hot plates, bread molds, knives, and gas stoves; food and beverage containers such as electric kettles and ice trays; food industry parts such as kneading rolls, rolling rolls, conveyers, and hoppers; industrial products such as office automation equipment (OA) rolls, OA belts, OA separation claws, papermaking rolls, and film manufacturing calendar rolls; mold release tools for molding polystyrene foam, such as molds, casting molds, and release plates for manufacturing plywood and decorative panels; kitchen supplies such as range hoods; frozen food manufacturing equipment such as conveyor belts; tools such as saws, files, dies, and drills; household products such as irons, scissors, and knives; metal foils, electric wires; plain bearings for food processing machines, packaging machines, and textile machines; sliding parts for cameras and watches; automotive parts such as pipes, valves, and bearings; snow shovels, plows, chutes, ship bottoms, boilers, and industrial containers (particularly for the semiconductor industry).

[0241] The uses of the first aqueous PTFE dispersion of the present disclosure and the aqueous PTFE dispersion obtained by the production method of the present disclosure (hereinafter, when the term "aqueous dispersion of the present disclosure" is used without any particular indication, it will encompass both the first aqueous PTFE dispersion of the present disclosure and the aqueous PTFE dispersion obtained by the production method of the present disclosure) are not particularly limited, and examples of applications of the aqueous dispersion as is include coating, which involves applying the dispersion to a substrate, drying, and optionally firing; impregnation, which involves impregnating a porous support such as a nonwoven fabric or a molded resin product, drying, and preferably firing; and cast film formation, which involves applying the dispersion to a substrate such as glass, drying, and optionally immersing the substrate in water, and peeling off the substrate to obtain a thin film. Examples of these applications include water-based paints, tent membranes, conveyor belts, printed circuit boards (CCL), electrode binders, and electrode water repellents.

[0242] The first aqueous PTFE dispersion of the present disclosure is preferably an aqueous paint. The first aqueous PTFE dispersion of the present disclosure has low viscosity at high temperatures, making it particularly suitable as an aqueous paint. The aqueous paint contains PTFE, an aqueous medium, and a nonionic surfactant, and may also contain the above-mentioned preservatives and paint raw materials, as necessary.

[0243] The first aqueous PTFE dispersion of the present disclosure can be used as an aqueous coating material by blending it with known compounding agents such as pigments, thickeners, dispersants, antifoaming agents, antifreezing agents, and film-forming aids, or by further combining it with other polymer compounds.

[0244] The present disclosure also relates to a coating film obtained by applying the first aqueous dispersion of the present disclosure. The coating film of the present disclosure can be produced by a conventionally known method except for using the aqueous dispersion of the present disclosure. The coating film of the present disclosure can be obtained by applying the aqueous dispersion of the present disclosure to a substrate. The material of the substrate is not particularly limited, and examples thereof include metals such as iron, aluminum, stainless steel, copper, and other simple metals and alloys thereof; and non-metallic inorganic materials such as enamel, glass, and ceramics. Examples of the alloys include stainless steel. The material of the substrate is preferably a metal, and more preferably aluminum or stainless steel.

[0245] The first aqueous PTFE dispersion of the present disclosure is particularly suitable as an aqueous coating material for impregnation. Impregnation processing requires a baking step, which tends to result in high temperatures. However, the aqueous PTFE dispersion of the present disclosure has good permeability into fiber substrates even in high-temperature environments, allowing for uniform impregnation. The present disclosure also relates to an impregnated membrane obtained by impregnating the aqueous dispersion of the present disclosure. The impregnated membrane of the present disclosure can be produced by a conventionally known method except for using the aqueous dispersion of the present disclosure. For example, the impregnated membrane of the present disclosure can be obtained by impregnating a porous support with the first aqueous PTFE dispersion of the present disclosure and then removing the aqueous medium. The aqueous medium can usually be removed by drying at room temperature and / or under heat. The impregnated membrane obtained by impregnation with the first aqueous PTFE dispersion of the present disclosure is preferably one that has been dried at least under heat. The "drying under heat" in the above impregnation can be carried out, for example, at 80 to 400°C. The porous support is not particularly limited as long as it has a porous structure, and may be made of either an organic or inorganic material, such as glass wool, ceramic, alumina, a PTFE porous film, carbon, nonwoven fabric, or various polymers.

[0246] The first aqueous PTFE dispersion of the present disclosure can also be used as an additive, for example, as a binder or adhesive that prevents the active material of an electrode from falling off, as a compound such as an anti-drip agent, or as a dust suppression treatment that prevents soil, dust, and the like from flying up.

[0247] The first PTFE aqueous dispersion of the present disclosure is also preferably used as a dust-suppressing treatment agent. The dust-suppressing treatment agent can be used in a method of mixing the agent with a dust-generating substance and subjecting the mixture to a compression-shear action at a temperature of 20 to 200°C to fibrillate the PTFE and suppress dust from the dust-generating substance, such as the methods described in Japanese Patent No. 2827152 and Japanese Patent No. 2538783. The above-mentioned PTFE aqueous dispersion can be suitably used, for example, in the dust suppression treatment composition described in WO 2007 / 004250, and can also be suitably used in the dust suppression treatment method described in WO 2007 / 000812.

[0248] The dust suppression treatment agent is suitable for use in the fields of building materials, soil stabilization materials, solidification materials, fertilizers, landfill disposal of incineration ash and hazardous substances, explosion prevention, cosmetics, and dust suppression treatment of sand for pet excretion, such as cat litter.

[0249] The present inventors conducted extensive research to find a composition that simultaneously prevents mud cracking and prevents discoloration during baking. Conventional methods for preventing mud cracking include adding a high-boiling solvent, such as triethanolamine or diethanolamine, and a long-chain fatty acid, such as caprylic acid, capric acid, or oleic acid, which is liquid at room temperature and nonvolatile. However, adding high-boiling solvents or long-chain fatty acids in amounts sufficient to prevent mud cracking would cause them to react during baking and turn into substances that discolor the coating film, necessitating the addition of an oxidizing agent. However, adding an oxidizing agent decomposes most of the high-boiling solvents and long-chain fatty acids below the melting point of the fluororesin, reducing the amount of discoloring substances, but making it impossible to prevent shrinkage cracks that occur during baking.

[0250] Another possible method is to add a water-soluble high-boiling point solvent such as butyl diglycol or dipropylene glycol methyl ether, which dissolves the acrylic resin particles, and dissolves them during drying, thereby simultaneously preventing mud cracking and thermal shrinkage.However, this water-soluble high-boiling point solvent reduces the emulsifying power of the nonionic surfactant added as a dispersant, so the fluororesin emulsion is destroyed by shear during spray coating, resulting in uneven coating films and the occurrence of paint bumps.

[0251] The present inventors have investigated blending a high-boiling polyhydric alcohol and depolymerizable acrylic resin particles in a specific ratio with an aqueous PTFE dispersion in which PTFE resin particles are dispersed with a nonionic surfactant, and have found that while mud cracking can be prevented with the use of a high-boiling polyhydric alcohol alone, cracking due to thermal shrinkage cannot be prevented without an acrylic resin binder, and that mud cracking cannot be prevented with the use of depolymerizable acrylic resin particles alone, but that the desired effect can be achieved only when the two are combined in a specific blending ratio. Furthermore, they have found that it is possible to simultaneously prevent mud cracking and discoloration during baking without adding an oxidizing agent, and that it is possible to give a molten coating film with excellent appearance, and have thereby completed the second and third aqueous PTFE dispersions described below.

[0252] The present disclosure also provides a depolymerizable acrylic resin particle composition comprising: (A) PTFE resin particles; (B) a high-boiling polyhydric alcohol containing no nitrogen atoms, having a boiling point of 100°C or higher, and having two or more hydroxyl groups; (C) depolymerizable acrylic resin particles whose decomposition and vaporization temperature is within a temperature range up to the decomposition temperature of the PTFE resin; (D) a nonionic surfactant; and (E) an aqueous medium; The present disclosure also relates to an aqueous PTFE dispersion (hereinafter also referred to as a second aqueous PTFE dispersion of the present disclosure), in which the blending amounts of the high-boiling point polyhydric alcohol (B) and the depolymerizable acrylic resin particles (C) are 5 to 18 parts by mass and 5 to 25 parts by mass, respectively, per 100 parts by mass of the PTFE resin (A), and which does not contain an oxidizing agent or an amine-based solvent.

[0253] (A)PTFE resin particles The PTFE resin particles used in the second PTFE aqueous dispersion of the present disclosure may be the same PTFE as in the first PTFE aqueous dispersion of the present disclosure, or may be a TFE homopolymer. However, a modified PTFE containing 99.0% by mass or more of polymerization units based on TFE and 1.0% by mass or less of polymerization units based on a modifying monomer is preferred. The content of the modifying monomer constituting the modified PTFE is preferably in the range of 0.00001 to 1.0% by mass relative to the PTFE. The lower limit is preferably 0.0001% by mass, more preferably 0.001% by mass, even more preferably 0.005% by mass, even more preferably 0.010% by mass, and even more preferably 0.030% by mass. The upper limit is preferably 0.90% by mass, more preferably 0.50% by mass, even more preferably 0.40% by mass, and even more preferably 0.30% by mass. When the modified PTFE contains PPVE as the modifying monomer, the lower limit of the amount of polymerization units based on PPVE in the modified PTFE is preferably 0.17% by mass. It is also more preferable that the modified PTFE has a core-shell structure.

[0254] (B) Polyhydric alcohol The function of the high-boiling polyhydric alcohol used in the second aqueous PTFE dispersion of the present disclosure is to prevent the occurrence of mud cracks when the aqueous dispersion is applied and then dried. The applied aqueous dispersion composition is usually dried at room temperature to 150°C. During this drying, water evaporates first, but unless a high-boiling polyhydric alcohol that does not evaporate at the drying temperature or has an evaporation rate slower than that of water is used in combination, the water will evaporate before the decomposable acrylic resin particles soften, resulting in gaps between the resin particles and causing mud cracks.

[0255] As a result, depending on the drying temperature and the type of high-boiling-point polyhydric alcohol (especially its boiling point), the dried coating film may be in a state where (1) high-boiling-point polyhydric alcohol and depolymerizable acrylic resin particles coexist, (2) almost no high-boiling-point polyhydric alcohol remains and the depolymerizable acrylic resin has melted and fixed the PTFE resin particles, or (3) a mixture of both of these states.

[0256] The polyhydric alcohol used in the second aqueous PTFE dispersion of the present disclosure is a nitrogen-free polyhydric alcohol having two or more hydroxyl groups and a boiling point of 100°C or higher (however, higher than the thermal melting onset temperature (softening temperature) of the depolymerizable acrylic resin). Polyhydric alcohols containing nitrogen atoms are undesirable because they cause coloration due to thermal decomposition during baking. The reason for the boiling point being 100°C or higher (however, higher than the thermal melting onset temperature (softening temperature) of the depolymerizable acrylic resin) is that they must not evaporate faster than water during drying, and are intended to remain in the coating film after drying. Preferably, the boiling point is higher than the drying temperature, more preferably 150°C or higher, and even more preferably 200°C or higher. Furthermore, they must have two or more hydroxyl groups. Substances with one or no hydroxyl groups have poor hydrophilicity and are difficult to mix uniformly with a substance having a boiling point of 100°C or higher. The preferred number of hydroxyl groups is 2 to 3. Many of the compounds with four or more hydroxyl groups are solid at room temperature, making it difficult to expect them to prevent mud cracking.

[0257] The polyhydric alcohol used in the second aqueous PTFE dispersion of the present disclosure must be completely evaporated or decomposed and vaporized by heating during the baking process described below. Therefore, it is preferable that the boiling point or thermal decomposition temperature is equal to or lower than the melting temperature of the PTFE resin, preferably 340°C or lower.

[0258] Suitable polyhydric alcohols include, for example, one or more of ethylene glycol (boiling point: 198°C), 1,2-propanediol (188°C), 1,3-propanediol (214°C), 1,2-butanediol (190°C), 1,3-butanediol (208°C), 1,4-butanediol (229°C), 1,5-pentanediol (242°C), 2-butene-1,4-diol (235°C), glycerin (290°C), 2-ethyl-2-hydroxymethyl-1,3-propanediol (295°C), and 1,2,6-hexanetriol (178°C / 5mmHg). Among these, glycerin is advantageous in terms of price and safety.

[0259] If necessary, organic solvents other than polyhydric alcohols may be used in combination within a range that does not impair the effects of the second aqueous PTFE dispersion of the present disclosure. Examples of such organic solvents include aromatic hydrocarbon solvents such as toluene and xylene, and aliphatic hydrocarbon solvents having 9 to 11 carbon atoms.

[0260] The amount of polyhydric alcohol (B) to be blended is 5 to 18 parts, preferably 7 to 15 parts, and particularly preferably 7 to 12 parts, per 100 parts of PTFE resin particles (solid content). If it is less than 5 parts, the effect of preventing mud cracks will be weak, and if it exceeds 18 parts, the coating film may become cloudy.

[0261] (C) Depolymerizable acrylic resin particles The depolymerizable acrylic resin particles used in the second aqueous PTFE dispersion of the present disclosure gradually decompose while maintaining their binder effect on the PTFE resin particles when the second aqueous PTFE dispersion of the present disclosure is applied, dried, and then baked, thereby preventing the occurrence of shrinkage cracks. Therefore, it is necessary that the depolymerizable acrylic resin particles are melted at a temperature equal to or lower than the melting temperature of the PTFE resin and depolymerization has begun, that at least a portion of the depolymerizable acrylic resin particles remain at the melting temperature of the PTFE resin particles, and that most of the particles are decomposed and volatilized at the baking temperature.

[0262] When the dried coating is heated, the remaining polyhydric alcohol first evaporates or decomposes and vaporizes, and the depolymerizable acrylic resin particles begin to melt. The polyhydric alcohol must remain until the depolymerizable acrylic resin particles are completely melted. As the temperature rises further, the evaporation or decomposition of the remaining polyhydric alcohol is completed, and the depolymerization of the molten depolymerizable acrylic resin begins. The depolymerization of the depolymerizable acrylic resin begins gradually below the melting temperature of the PTFE resin, but is not complete at the temperature at which the PTFE resin particles begin to melt. It is completed at the baking temperature, which exceeds the melting temperature of the PTFE resin. This prevents large amounts of depolymerizable acrylic resin from remaining in the resulting PTFE resin coating. Because this depolymerizable acrylic resin is viscous when melted, and depolymerization proceeds gradually, sudden shrinkage does not occur even when the PTFE resin particles melt and fuse, suppressing the occurrence of thermal shrinkage cracks.

[0263] Therefore, even if depolymerization begins below the melting point of the PTFE resin, the depolymerizable acrylic resin particles preferably remain until the temperature at which the PTFE resin particles begin to melt (the melting temperature), and then decompose and volatilize at the baking (processing) temperature. For example, at the melting temperature of the PTFE resin (usually 240-345°C), 5% or more, particularly 10% or more, at least 50%, and preferably at least 20%, remain. At the baking (processing) temperature (usually a temperature above the melting temperature of the PTFE resin and up to 415°C, preferably 360-400°C), only 10% or less, particularly 5% or less, and essentially none remain at the completion of baking, are preferred. From this perspective, the depolymerization (decomposition) temperature of the depolymerizable acrylic resin particles is preferably above about 200°C but below the baking (processing) temperature of the PTFE resin, particularly below the melting temperature of the PTFE resin. Note that acrylic resin particles whose depolymerization (thermal decomposition) temperature exceeds the melting temperature of the PTFE resin and generate a large amount of decomposition gas are prone to coating defects such as pinholes in the resulting coating. In particular, regardless of the type of resin, depolymerizable acrylic resins that remain at approximately 25 to 50% in the temperature range of 300 to 320°C and approximately 20 to 10% in the temperature range of 330 to 345°C are suitable in terms of the balance between the effect of preventing shrinkage cracking and the effect of preventing discoloration, and any depolymerizable acrylic resin particles that satisfy this condition can be used.

[0264] As described in "Polym. Eng. Soi., Vol. 6, p. 273 (1966)," "Plast. Massy., Vol. 75, p. 48 (1971)," and "Deterioration of Polymer Materials," Corona Publishing, p. 144 (1958), the more branches there are in the polymer chain, the weaker the C—C bonds and C—H bonds become, and the easier it is to undergo oxidative decomposition and depolymerization. Therefore, the depolymerizable acrylic resin particles in the second aqueous PTFE dispersion of the present disclosure include methacrylate resins, and specifically, for example, those represented by the formula (5): CH2=C(CH3)COOR (5) Preferred examples include methacrylate homopolymers or copolymers essentially containing a methacrylate monomer represented by the formula (wherein R is an alkyl or hydroxyalkyl group having 1 to 5 carbon atoms). Specific examples of methacrylate monomers that are preferably used include methyl methacrylate, ethyl methacrylate, propyl methacrylate, dimethylpropyl methacrylate, butyl methacrylate, and pentyl methacrylate. Among these, depolymerizable acrylic resins containing butyl methacrylate as a monomer are preferred because of their low glass transition temperature and good depolymerizability (decomposability).

[0265] Furthermore, there is no problem if a stable emulsion can be formed using a homopolymer, but from the viewpoint of stabilizing the emulsion, a monomer having a carboxyl group or a hydroxyl group may be used as a comonomer as appropriate.

[0266] The depolymerizable acrylic resin particles can be, for example, fine particles (depolymerizable acrylic resin emulsion) produced by a method such as emulsion polymerization, and the average particle size is preferably 0.1 to 100 μm, particularly 0.2 to 1 μm. Particles with an average particle size of less than 0.1 μm tend to easily cause mud cracks, while particles with an average particle size of more than 100 μm tend to make coating difficult.

[0267] The amount of depolymerizable acrylic resin particles (C) to be blended is 5 to 25 parts, preferably 7 to 20 parts, and particularly preferably 10 to 15 parts, per 100 parts of PTFE resin particles (solid content). If the amount is less than 5 parts, it becomes difficult to form a PTFE resin film, and if the amount exceeds 25 parts, the coating film may become discolored.

[0268] The depolymerizable acrylic resin particles are preferably mixed with other ingredients in the form of an emulsion.

[0269] (D) Nonionic surfactants The nonionic surfactant used in the second PTFE aqueous dispersion of the present disclosure can be the same as the nonionic surfactant described in the first PTFE aqueous dispersion of the present disclosure, and the content thereof is preferably 4% by mass or more, more preferably 5% by mass or more, and even more preferably 5.5% by mass or more, and is preferably 12% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less, and especially preferably 7% by mass or less, relative to the PTFE. If the amount of nonionic surfactant is too large, the viscosity may become too high, whereas if the amount is too small, the storage stability and mechanical stability may decrease.

[0270] Other nonionic surfactants that can be used include those having the general formula: R1O-[CH2CH2O] n -[R2O] m R3(6) [wherein R1 represents a linear or branched aliphatic hydrocarbon group having at least 6 carbon atoms, preferably 8 to 18 carbon atoms, R2 represents an alkylene unit having 3 or 4 carbon atoms, R3 represents hydrogen, a C1-C3 alkyl group, or a C1-C3 hydroxyalkyl group, n has a value of 0 to 40, m has a value of 0 to 40, and the sum of n and m is at least 2]. Specific examples include polyoxyalkylene alkyl ether nonionic surfactants represented by the above formula (6), and particularly preferred non-phenol type nonionic surfactants are those represented by the formula (7): C x H 2x+1 CH(C y H 2y+1 )C z H 2z O(C2H4O) n H (7) (wherein x is an integer of 1 or more, y is an integer of 1 or more, z is 0 or 1, provided that x+y+z is an integer of 8 to 18, and n is an integer of 4 to 20) and has an HLB value of 9.50 to 16.00, and / or a nonionic surfactant represented by formula (8):

[0271] CX H 2X+1 -OAH (8) (wherein x is an integer of 8 to 18, and A is a polyoxyalkylene chain having 5 to 20 oxyethylene units and 1 or 2 oxypropylene units). The HLB value of these surfactants is preferably 9.50 to 16.00, more preferably 12.00 to 15.00, and even more preferably 12.00 to 14.00, which is preferred from the viewpoint of stably dispersing the PTFE resin.

[0272] (E) Aqueous solvent It is used as a liquid medium for the aqueous dispersion composition for coating to adjust the solids concentration of the composition. Water may be used alone, or may be used in combination with a water-soluble compound to form an aqueous mixed solvent. If necessary, other additives may be further added. (F) Inorganic materials Examples of inorganic materials include pigments, mica particles, mica particles coated with pigments, metal flakes, or two or more of these inorganic fillers, which are blended in an amount that does not impair the effects of the second aqueous PTFE dispersion of the present disclosure.

[0273] As the pigment, various conventionally known pigments can be used, such as titanium oxide, carbon black, red iron oxide, etc. Among these, the present disclosure is advantageous in that carbon black, which has traditionally been subject to discoloration due to the influence of oxidizing agents, can also be used safely.

[0274] Inorganic fillers improve abrasion resistance, and mica is preferred for its aesthetic appeal. The particle size of mica particles is 10 to 100 μm, preferably 15 to 50 μm. Particle sizes less than 10 μm tend to result in reduced abrasion resistance and glitter, while particles greater than 100 μm tend to result in reduced non-stick properties. Pigment-coated mica particles can be obtained by attaching a pigment such as TiO2·Fe2O3 to the mica particles using a sintering deposition method or similar. Metal flakes include flakes of titanium, zirconium, aluminum, zinc, antimony, tin, iron, and nickel, with titanium and zirconium being preferred for their rust resistance. Sizes within the range typically used in paints can be used.

[0275] In addition, various known additives can be added as long as they do not impair the effects of the second aqueous PTFE dispersion of the present disclosure, such as antifoaming agents, drying agents, thickening agents, leveling agents, and anti-cracking agents. Examples of the antifoaming agent include non-polar solvents such as toluene, xylene, hydrocarbons having 9 to 11 carbon atoms, and silicone oil. The drying agent may be, for example, cobalt oxide. Examples of the thickener include methyl cellulose, polyvinyl alcohol, carboxylated vinyl polymers, and aqueous sodium lauryl sulfate solutions.

[0276] The second aqueous PTFE dispersion of the present disclosure preferably has a viscosity of 50 mPa·s or less at 55°C. Because the second aqueous PTFE dispersion of the present disclosure has a viscosity of 50 mPa·s or less at 55°C, it is particularly suitable for applications requiring high temperatures, such as impregnation of fiber substrates. Impregnation requires a baking step, which can easily result in high temperatures. The second aqueous PTFE dispersion of the present disclosure has good penetration into fiber substrates and can be uniformly impregnated even in high-temperature environments. The viscosity at 55°C is more preferably 45 mPa·s or less, even more preferably 40 mPa·s or less, and even more preferably 35 mPa·s or less. The lower limit of the viscosity at 55°C is not particularly limited, but may be, for example, 10 mPa·s or more.

[0277] The second aqueous PTFE dispersion of the present disclosure preferably has a ratio [viscosity at 55°C / viscosity at 25°C] of 4.00 or less. The second aqueous PTFE dispersion of the present disclosure is particularly suitable for use in impregnation of fiber substrates. The impregnation process involves a baking step, which tends to result in high environmental temperatures. Since the amount of PTFE adhered to the fiber substrate during impregnation is easily affected by the viscosity of the aqueous dispersion, an aqueous dispersion with low viscosity-temperature dependency is required. The first aqueous PTFE dispersion of the present disclosure is excellent in that, by having the above ratio of 4.00 or less, it has low viscosity-temperature dependency and is stable in quality. From the above viewpoint, the ratio [viscosity at 55°C / viscosity at 25°C] is more preferably 3.00 or less, even more preferably 2.00 or less, even more preferably 1.50 or less, especially preferably 1.20 or less, particularly preferably 1.10 or less, and especially especially preferably 1.00 or less.

[0278] The viscosity at 25°C was measured using a B-type rotational viscometer under the conditions shown in the Examples section below. The viscosity at 55°C was measured under the same conditions as the viscosity at 25°C after the liquid temperature was raised to 55°C and held for 60 minutes. Note that for viscosity values ​​of 80 mPa·s or higher, the viscosity increases over time, so the viscosity is measured 5 and 10 minutes after the start of measurement, and the average value is used.

[0279] The second aqueous PTFE dispersion of the present disclosure preferably has a viscosity temperature transition [VTT] of more than 55° C., more preferably 60° C. or more. Having a VTT of more than 55° C. has the technical significance of eliminating the need to change the processing conditions at 25° C. and 55° C. VTT represents the viscosity-temperature dependency of an aqueous PTFE dispersion. VTT can be obtained by raising the temperature of an aqueous PTFE dispersion to 25°C, 35°C, 45°C, and 55°C, holding the temperature for 60 minutes, and then measuring using a B-type rotational viscometer under the conditions shown in the Examples below. The VTT point is the temperature at which the viscosity once again reaches the same value as measured at 25°C. Note that for viscosity values ​​of 80 mPa·s or higher, the viscosity increases over time, so the viscosity is measured 5 and 10 minutes after the start of measurement, and the average value is used.

[0280] The second aqueous PTFE dispersion of the present disclosure has a PTFE resin solids concentration of 50 to 70% by mass. The solids concentration is preferably 55% by mass or more, more preferably 57% by mass or more. Furthermore, the solids concentration is preferably 65% ​​by mass or less, more preferably 60% by mass or less. Even if the solids concentration of the PTFE resin is within the above range, the second aqueous dispersion of the present disclosure can have a viscosity of 50 mPa·s or less at 55°C.

[0281] Furthermore, the second aqueous PTFE dispersion of the present disclosure is preferably substantially free of a fluorine-containing surfactant. In the composition of the present disclosure, "substantially free of a fluorine-containing surfactant" means that the content of the fluorine-containing surfactant in the aqueous PTFE dispersion is 1.0 ppm or less. The second aqueous PTFE dispersion of the present disclosure is substantially free of a fluorine-containing surfactant, yet can have a low viscosity at high temperatures and excellent mechanical stability at high temperatures. The content of the fluorine-containing surfactant is preferably 700 ppb or less, more preferably 600 ppb or less, and even more preferably 500 ppb or less. The content of the fluorine-containing surfactant in the second aqueous PTFE dispersion of the present disclosure can be measured by the same method as described for the first aqueous PTFE dispersion of the present disclosure.

[0282] When the second aqueous PTFE dispersion of the present disclosure is obtained by polymerization using a fluorine-containing surfactant, the amount of the fluorine-containing surfactant can be adjusted to the above range by adding a nonionic surfactant to the aqueous PTFE dispersion after polymerization, concentrating the dispersion, etc. Examples of the fluorine-containing surfactant include the fluorine-containing anionic surfactants described for the first aqueous PTFE dispersion of the present disclosure.

[0283] The second aqueous PTFE dispersion of the present disclosure can be prepared according to the method described above. Alternatively, it can be prepared by a conventional method. For example, the second aqueous PTFE dispersion can be prepared by adding a polyhydric alcohol (B), a depolymerizable acrylic resin particle emulsion (C), an inorganic material (F) if necessary, and other additives to an aqueous PTFE resin dispersion in which PTFE resin particles (A) are dispersed in an aqueous medium (E) using a nonionic surfactant (D), and mixing the mixture with stirring at 5 to 30°C for 10 to 40 minutes. Furthermore, the solids concentration may be adjusted by adding more aqueous medium (E), for example.

[0284] The second aqueous PTFE dispersion of the present disclosure is useful as a coating material, particularly as a topcoat coating material. Conventional coating methods can be used, including dipping, spraying, roll coating, doctor blade coating, and flow coating.

[0285] The second aqueous PTFE dispersion of the present disclosure may be directly applied to a substrate, but in order to improve adhesion, it is desirable to form a primer layer and then form the second aqueous PTFE dispersion as a topcoat layer. The substrate is not particularly limited, but examples thereof include various metals, enamel, glass, and various ceramics. In addition, in order to improve adhesion, it is desirable to roughen the surface by sandblasting or the like.

[0286] The coating composition applied to the substrate is then dried. The second aqueous PTFE dispersion of the present disclosure is characterized in that it does not produce mud cracks during this drying stage. Drying can be carried out under normal conditions, and varies depending on the boiling point of the polyhydric alcohol used. For example, drying can be carried out at room temperature to 150°C, preferably 80 to 150°C, for 5 to 20 minutes to achieve touch-dryness.

[0287] The dried coating film is then baked (processed). According to the second PTFE aqueous dispersion of the present disclosure, the depolymerizable acrylic resin functions as a binder until the PTFE resin particles melt and fuse together, preventing cracks from occurring due to thermal shrinkage during this baking step. The baking (processing) temperature and time vary depending on the type and melting temperature of the PTFE resin, but are typically performed at a temperature above the melting temperature of the PTFE resin, typically 360 to 415°C, for 5 to 30 minutes. Preferably, baking is performed at 360 to 380°C for 10 to 30 minutes.

[0288] When a primer layer is provided, a method in which a primer layer is applied, dried, and baked, and then the second aqueous PTFE dispersion of the present disclosure is applied, dried, and baked (two-coat, two-bake method) may be used, or a method in which a primer layer is applied and dried, and then the second aqueous PTFE dispersion of the present disclosure is applied and dried, and then both are baked simultaneously (two-coat, one-bake method) may be used.

[0289] According to the second aqueous PTFE dispersion of the present disclosure, a thick coating film having a thickness of 30 μm or more can be obtained by a single coating. Although there is no particular upper limit, if the thickness is too thick, various decomposition residues remain in the coating film, causing discoloration, so it is preferably 100 μm or less.

[0290] Although the second aqueous PTFE dispersion of the present disclosure is most useful for coating metal cookware, particularly frying pans, the aqueous PTFE dispersion can also be used to coat other products requiring corrosion resistance, such as bearings, valves, electrical wires, metal foil, boilers, pipes, boat bottoms, oven linings, ironing boards, bread pans, rice cookers, grill pans, electric kettles, ice trays, snow shovels, plows, chutes, conveyors, rolls, molds, dies, tools such as saws, files, and drills, knives, scissors, hoppers, other industrial containers (particularly for the semiconductor industry), and molds.

[0291] The present disclosure also relates to a coated article having a coating film obtained by applying the second aqueous PTFE dispersion of the present disclosure. The coating film can be produced by a conventionally known method and can be obtained by applying the aqueous dispersion of the present disclosure to a substrate. The material of the substrate is not particularly limited, and examples include metals such as simple metals such as iron, aluminum, stainless steel, and copper, and alloys thereof; and non-metallic inorganic materials such as enamel, glass, and ceramic. Examples of the alloys include stainless steel. The material of the substrate is preferably a metal, and more preferably aluminum or stainless steel. The thickness of the coating film is preferably 30 μm or more, and is preferably 100 μm or less, since if the coating film is too thick, various decomposition residues will remain in the coating film, causing discoloration.

[0292] The coated article may be provided with a primer layer.

[0293] Applications of the above-mentioned coated articles include metal cooking utensils (especially frying pans), bearings, valves, electric wires, metal foils, boilers, pipes, ship bottoms, oven linings, iron bottom plates, bread pans, rice cookers, grill pans, electric kettles, ice trays, snow shovels, plows, chutes, conveyors, rolls, molds, dies, tools such as saws, files and drills, knives, scissors, hoppers, other industrial containers (especially for the semiconductor industry), and molds.

[0294] The present disclosure also relates to a PTFE aqueous dispersion (hereinafter also referred to as the third PTFE aqueous dispersion of the present disclosure) comprising PTFE resin particles, depolymerizable acrylic resin particles, and water, characterized in that the nonionic surfactant is present in an amount that occupies 75 to 95% of the theoretical void ratio of 26% between the resin particles when the resin particles are arranged in a close-packed structure, assuming that the primary average particles of each resin particle are replaced with true spheres having the same volume, and the nonionic surfactant is a solvent that is substantially non-volatile in a temperature range up to 100°C and that volatilizes or thermally decomposes at a temperature lower than the thermal decomposition temperature of the resin particles.

[0295] The third PTFE aqueous dispersion of the present disclosure contains PTFE resin particles, depolymerizable acrylic resin particles, and water, with a nonionic surfactant present in the voids between the resin particles.

[0296] As the nonionic surfactant, the same nonionic surfactant as described in the first PTFE aqueous dispersion of the present disclosure can be used, and the content thereof is preferably 4.0 mass% or more, more preferably 5.0 mass% or more, and even more preferably 5.5 mass% or more, based on the PTFE, and is preferably 12.0 mass% or less, more preferably 10.0 mass% or less, even more preferably 8.0 mass% or less, and especially preferably 7.0 mass% or less. If the amount of nonionic surfactant is too large, the viscosity may become too high, whereas if the amount is too small, the storage stability and mechanical stability may decrease.

[0297] In the third aqueous PTFE dispersion of the present disclosure, (1) Assuming that each resin particle is a perfect sphere, the amount of nonionic surfactant present is such that it occupies 75 to 95% of the theoretical void ratio of 26% between the resin particles when the resin particles are arranged in a close-packed structure (hereinafter referred to as "occupancy ratio"; this is based on the theoretical void ratio). (2) The nonionic surfactant must be a solvent that is nonvolatile up to a temperature of 100° C. and that vaporizes or thermally decomposes at a temperature lower than the thermal decomposition temperature of the resin particles.

[0298] These features (1) and (2) mean that when the aqueous PTFE dispersion is applied and dried, the water evaporates, but the aqueous PTFE dispersion is prepared in advance so that 75 to 95% of the voids in the dried coating film, which no longer contain water, are occupied by the nonionic surfactant of feature (2).

[0299] That is, when considering a system in which no nonionic surfactant is present, water occupies the spaces between the resin particles when the PTFE aqueous dispersion is first applied, but as it dries (evaporates water), voids form between the resin particles, causing mud cracks. Therefore, if nonionic surfactants remain between the resin particles even after the water has evaporated, mud cracks can be prevented. On the other hand, while mud cracks do not occur when a large amount of nonionic surfactants such as nonionic surfactants are present, excessive amounts can also be problematic, as they cause significant shrinkage during the baking process and poor film-forming properties. However, the percentage of liquid required to effectively prevent mud cracks cannot be determined without repeated experiments.

[0300] When a nonionic surfactant having the thermal properties of characteristic (2) is present in an aqueous dispersion composition under the conditions of characteristic (1), the necessary amount of nonionic surfactant remains interposed between the resin particles even after the water evaporates and the coating dries. This nonionic surfactant functions as a binder, effectively preventing mud cracks. If the content of this nonionic surfactant is too low, the movement of resin particles due to water evaporation becomes significant, making it impossible to effectively prevent mud cracks. On the other hand, if the content is too high, excessive shrinkage occurs when the nonionic surfactant is decomposed and evaporated by heating, resulting in cracks. The preferred coverage is 76 to 94%, and even 77 to 93%.

[0301] The resin particles are assumed to be spherical because, even if they are usually particulate, they are not spherical, and because they must be spherical in order to be arranged in a close-packed structure. However, particles arranged in a close-packed structure have a theoretical void ratio of 26% regardless of particle diameter (the proportion occupied by resin particles is 74%). Therefore, the void ratio can be calculated using the following formula.

[0302]

number

[0303] The volume of the resin particles is calculated from the weight and specific gravity of the resin particles.

[0304] The above characteristic (2) defines the thermal properties of nonionic surfactants. The need for non-volatile surfactants in the temperature range up to 100°C means that if they evaporate with water, mud cracking cannot be prevented. Furthermore, even if a solvent has a high boiling point, there is no guarantee that it will not evaporate in this temperature range. Mud cracking occurs if evaporation occurs. Furthermore, the need for nonionic surfactants that volatilize or thermally decompose at temperatures lower than the thermal decomposition temperature of resin particles is due to the fact that the objective is to form a resin coating, and if any surfactant remains even at the temperature at which the resin thermally decomposes, it will interfere with the formation of the resin coating.

[0305] It should be noted here that the occupancy rate of the nonionic surfactant is based on the state after water has evaporated. In other words, the state in which the resin particles are arranged in a close-packed structure is not the state of the aqueous dispersion composition, but the state in which the resin particles move and become close-packed after water has evaporated. Therefore, if other nonionic surfactants are present, these other nonionic surfactants may evaporate along with the water by heating (drying, etc.), but the key is that the nonionic surfactant is present in the coating film at the above-mentioned occupancy rate when drying is complete. If the occupancy rate exceeds a certain level, the final process involves a baking step to volatilize the nonionic surfactant. For example, when a fluororesin is used, the shrinkage associated with the decomposition and volatilization of the organic matter is too great, causing cracks.

[0306] The particle size of the resin particles is not limited. This is because the theoretical porosity in a close-packed structure is a constant value of 26%, independent of the type of resin or particle size. When particles of different particle sizes are mixed, the theoretical porosity can be calculated by considering the packed structure for each particle separately, and then calculating the total void volume. This is because the third PTFE aqueous dispersion of the present disclosure is a coating composition, and therefore typically contains two or more types of particles, with the ratio being unspecified. Furthermore, since a thickener is typically added as needed, small particles do not infiltrate the gaps between larger particles.

[0307] In short, even when two or more types of resin particles are packed in a closest packed structure, it is sufficient that the nonionic surfactant occupies 75 to 95% of the voids (theoretical voids) generated between the resin particles.

[0308] In the third PTFE aqueous dispersion of the present disclosure, the same PTFE resin particles (or aqueous dispersion) as those in the first PTFE aqueous dispersion of the present disclosure can be used as is, and the average particle size is preferably 0.01 to 100 μm, particularly 0.1 to 5 μm. Average particle sizes less than 0.01 μm tend to reduce film-forming properties, while average particle sizes greater than 100 μm tend to clog gun nozzles used for coating. The PTFE may be a TFE homopolymer, but modified PTFE containing 99.0% by mass or more of polymerization units based on TFE and 1.0% by mass or less of polymerization units based on a modifying monomer is preferred. The content of the modifying monomer constituting the modified PTFE is preferably in the range of 0.00001 to 1.0% by mass relative to the PTFE. The lower limit is more preferably 0.0001% by mass, even more preferably 0.001% by mass, even more preferably 0.005% by mass, even more preferably 0.010% by mass, even more preferably 0.05% by mass, even more preferably 0.10% by mass, and most preferably 0.15% by mass. The upper limit is preferably 0.90% by mass, more preferably 0.50% by mass, even more preferably 0.40% by mass, and even more preferably 0.30% by mass. When the modified PTFE contains PPVE as a modifying monomer, the lower limit of the amount of polymerized units based on PPVE in the modified PTFE is preferably 0.17% by mass. It is also more preferable that the modified PTFE has a core-shell structure.

[0309] Alternatively, an aqueous dispersion of PTFE resin particles obtained by emulsion polymerization or powdery particles obtained from this aqueous dispersion can be used. However, in the case of powder, handling may be impaired due to electrical repulsion of the particles, so it is preferable to use it in the form of an aqueous dispersion.

[0310] The standard specific gravity (SSG) of the PTFE is preferably 2.220 or less, more preferably 2.190 or less, and is preferably 2.140 or more, more preferably 2.150 or more. If the SSG exceeds 2.220, the coating film tends to become brittle, and if it is less than 2.140, the melt viscosity tends to be too high, making it difficult for the particles to fuse together.

[0311] As described above, when the aqueous dispersion composition is applied, dried, and then baked, the depolymerizable acrylic resin particles gradually decompose while maintaining their binder effect on the PTFE resin particles, thereby preventing the occurrence of shrinkage cracks. Therefore, it is necessary that the depolymerizable acrylic resin particles are melted at a temperature equal to or lower than the melting temperature of the PTFE resin and depolymerization has begun, that at least a portion of the depolymerizable acrylic resin particles remain at the melting temperature of the PTFE resin particles, and that most of the particles are decomposed and volatilized at the baking temperature.

[0312] When the dried coating is heated, the remaining nonionic surfactant first evaporates or decomposes and volatilizes, and the depolymerizable acrylic resin particles begin to melt. The nonionic surfactant must remain at least until the thermal melting of the depolymerizable acrylic resin particles is complete. As the temperature rises further, the evaporation or decomposition of the remaining nonionic surfactant is complete, and the depolymerization of the thermally molten depolymerizable acrylic resin begins. The depolymerization of the depolymerizable acrylic resin begins gradually below the melting temperature of the PTFE resin, but is not complete at the temperature at which the PTFE resin particles begin to melt. It is completed at the baking temperature, which exceeds the melting temperature of the PTFE resin. This prevents large amounts of depolymerizable acrylic resin from remaining in the resulting PTFE resin coating. Because this depolymerizable acrylic resin is viscous when thermally molten and depolymerization proceeds gradually, sudden shrinkage does not occur even when the PTFE resin particles melt and fuse, suppressing the occurrence of thermal shrinkage cracks.

[0313] Therefore, even if depolymerization begins below the melting point of the PTFE resin, the depolymerizable acrylic resin particles preferably remain until the temperature at which the PTFE resin particles begin to melt (the melting temperature), and then decompose and volatilize at the baking (processing) temperature. For example, at the melting temperature of the PTFE resin, 5% or more, particularly 10% or more, at least 50%, and preferably at least 20%, remain. At the baking (processing) temperature (usually a temperature above the melting temperature of the PTFE resin and up to 415°C, preferably 360-400°C), only 10% or less, particularly 5% or less, remain, and essentially none remain at the completion of baking. From this perspective, the depolymerization (decomposition) temperature of the depolymerizable acrylic resin particles is preferably above about 200°C but below the baking (processing) temperature of the PTFE resin, particularly below the melting temperature of the PTFE resin. Note that acrylic resin particles whose depolymerization (thermal decomposition) temperature exceeds the melting temperature of the PTFE resin and generate a large amount of decomposition gas are prone to coating defects such as pinholes in the resulting coating.

[0314] In particular, regardless of the type of resin, depolymerizable acrylic resins that remain at approximately 25 to 50% in the temperature range of 300 to 320°C and approximately 20 to 10% in the temperature range of 330 to 345°C are suitable in terms of the balance between the effect of preventing shrinkage cracking and the effect of preventing discoloration, and any depolymerizable acrylic resin particles that satisfy this condition can be used.

[0315] As described in "Polym. Eng. Sci.", Vol. 6, p. 273 (1966), "Plast. Massy.", Vol. 75, p. 48 (1971), and "Degradation of Polymer Materials," Corona Publishing, p. 144 (1958), generally, the more branches there are in the polymer chain, the weaker the C-C and C-H bonds become, making them more susceptible to oxidative decomposition and depolymerization. Therefore, the depolymerizable acrylic resin particles of the present disclosure include methacrylate resins. Specific examples include methacrylate homopolymers or copolymers containing a methacrylate monomer represented by the formula (9): CH═C(CH)COOR (9) (where R is an alkyl or hydroxyalkyl group having 1 to 5 carbon atoms). Specific examples of preferred methacrylate monomers include methyl methacrylate, ethyl methacrylate, propyl methacrylate, dimethylpropyl methacrylate, butyl methacrylate, and pentyl methacrylate. Among these, depolymerizable acrylic resins containing butyl methacrylate as a monomer are preferred because they have a low glass transition temperature and good depolymerization (decomposability).

[0316] Furthermore, there is no problem if a stable emulsion can be formed using a homopolymer, but from the viewpoint of stabilizing the emulsion, a monomer having a carboxyl group or a hydroxyl group may be used as a comonomer as appropriate.

[0317] The depolymerizable acrylic resin particles can be, for example, fine particles (depolymerizable acrylic resin emulsion) produced by a method such as emulsion polymerization, and the average particle size is preferably 0.1 to 100 μm, particularly 0.2 to 1 μm. Particles with an average particle size of less than 0.1 μm tend to easily cause mud cracks, while particles with an average particle size of more than 100 μm tend to make coating difficult.

[0318] The amount of depolymerizable acrylic resin particles to be blended is 5 to 25 parts, preferably 7 to 20 parts, and particularly preferably 10 to 15 parts, per 100 parts of PTFE resin particles (solid content). If the amount is less than 5 parts, it becomes difficult to form a PTFE resin film, and if the amount exceeds 25 parts, the coating film may become discolored.

[0319] The depolymerizable acrylic resin particles are preferably mixed with other ingredients in the form of an emulsion.

[0320] In addition, elastomers, if in particulate form, are also included within the scope of the present disclosure, just like resin particles.

[0321] The particle size can be selected from a wide range, but for normal coating applications, a range of 0.1 to 10 μm is appropriate, and one or more types of resin particles within this range are used.

[0322] In addition to the above-mentioned PTFE resin particles and depolymerizable acrylic resin, particles of acrylic resins such as butyl methacrylate-based urethane emulsions; polyurethane resins such as urethane emulsions; polyester resins such as polyester emulsions; polyolefin resins such as polyethylene emulsions; and other particles of PPS, PAI, PES, PEEK, etc. can also be used.

[0323] In the present disclosure, in addition to the nonionic surfactant, other liquid organic compounds having hydrophilic groups may be used in combination in order to improve the affinity with water and the dispersion stability of the aqueous dispersion composition. As such hydrophilic group-containing organic compounds, high-boiling polyhydric alcohols are preferred.

[0324] As the high-boiling polyhydric alcohol, a polyhydric alcohol containing no nitrogen atoms is preferred because it is less likely to cause coloration due to thermal decomposition during baking. The preferred number of hydroxyl groups is 2 to 3. Many polyhydric alcohols with 4 or more hydroxyl groups are solid at room temperature.

[0325] Suitable polyhydric alcohols include, for example, one or more of ethylene glycol (boiling point: 198°C), 1,2-propanediol (188°C), 1,3-propanediol (214°C), 1,2-butanediol (190°C), 1,3-butanediol (208°C), 1,4-butanediol (229°C), 1,5-pentanediol (242°C), 2-butene-1,4-diol (235°C), glycerin (290°C), 2-ethyl-2-hydroxymethyl-1,3-propanediol (295°C), and 1,2,6-hexanetriol (178°C / 5mmHg).

[0326] If necessary, organic solvents other than the high-boiling polyhydric alcohols may be used in combination within a range that does not impair the effects of the present disclosure. Examples of such organic solvents include aromatic hydrocarbon solvents such as toluene and xylene, and aliphatic hydrocarbon solvents having 9 to 11 carbon atoms.

[0327] The amount of polyhydric alcohol to be added is 5 to 18 parts, preferably 7 to 15 parts, and particularly preferably 7 to 12 parts, per 100 parts of PTFE resin particles (solid content). If the amount is less than 5 parts, the effect of preventing mud cracks will be weak, and if the amount is more than 18 parts, the coating film may become cloudy.

[0328] Water is used as a liquid medium for the third aqueous PTFE dispersion of the present disclosure to adjust the solid content concentration of the aqueous dispersion. Water may be used alone, or may be used in combination with a water-soluble compound to form an aqueous mixed solvent.

[0329] In the present disclosure, other additives such as inorganic materials may be further blended as needed.

[0330] Examples of inorganic materials include pigments, mica particles, mica particles coated with pigments, metal flakes, or inorganic fillers of two or more of these, which are blended in amounts that do not impair the effects of the present disclosure.

[0331] As the pigment, various known pigments can be used, such as titanium oxide, carbon black, and red iron oxide.

[0332] Inorganic fillers improve abrasion resistance, and mica is preferred for its aesthetic appeal. The particle size of mica particles is 10 to 100 μm, preferably 15 to 50 μm. Particle sizes less than 10 μm tend to result in reduced abrasion resistance and glitter, while particles greater than 100 μm tend to result in reduced non-stick properties. Pigment-coated mica particles can be obtained by attaching a pigment such as TiO2·Fe2O3 to the mica particles using a sintering deposition method or similar. Metal flakes include flakes of titanium, zirconium, aluminum, zinc, antimony, tin, iron, and nickel, with titanium and zirconium being preferred for their rust resistance. Sizes within the range typically used in paints can be used.

[0333] In addition, various known additives can be added as long as they do not impair the effects of the third aqueous dispersion of the present disclosure, such as antifoaming agents, drying agents, thickening agents, leveling agents, and anti-cracking agents.

[0334] Examples of the antifoaming agent include non-polar solvents such as toluene, xylene, hydrocarbons having 9 to 11 carbon atoms, and silicone oil.

[0335] The drying agent may be, for example, cobalt oxide.

[0336] Examples of the thickener include methyl cellulose, polyvinyl alcohol, and carboxylated vinyl polymers.

[0337] The third aqueous PTFE dispersion of the present disclosure preferably has a viscosity of 50 mPa·s or less at 55°C. Because the third aqueous PTFE dispersion of the present disclosure has a viscosity of 50 mPa·s or less at 55°C, it is particularly suitable for applications requiring high temperatures, such as impregnation of fiber substrates. Impregnation requires a baking step, which tends to result in high temperatures. The second aqueous PTFE dispersion of the present disclosure has good penetration into fiber substrates and can be uniformly impregnated even in high-temperature environments. The viscosity at 55°C is more preferably 45 mPa·s or less, even more preferably 40 mPa·s or less, and even more preferably 35 mPa·s or less. The lower limit of the viscosity at 55°C is not particularly limited, but may be, for example, 10 mPa·s or more.

[0338] The third PTFE aqueous dispersion of the present disclosure preferably has a ratio [viscosity at 55°C / viscosity at 25°C] of 4.00 or less. The second PTFE aqueous dispersion of the present disclosure is particularly suitable for use in impregnation of fiber substrates. The impregnation process involves a baking step, which tends to result in high environmental temperatures. Since the amount of PTFE adhered to the fiber substrate during impregnation is easily affected by the viscosity of the aqueous dispersion, an aqueous dispersion with low viscosity-temperature dependency is required. The first PTFE aqueous dispersion of the present disclosure is excellent in that, by having the ratio of 4.00 or less, it has low viscosity-temperature dependency and is stable in quality. From the above viewpoint, the ratio [viscosity at 55°C / viscosity at 25°C] is more preferably 3.00 or less, even more preferably 2.00 or less, even more preferably 1.50 or less, especially preferably 1.20 or less, particularly preferably 1.10 or less, and especially especially preferably 1.00 or less.

[0339] The viscosity at 25°C was measured using a B-type rotational viscometer under the conditions shown in the Examples section below. The viscosity at 55°C was measured under the same conditions as the viscosity at 25°C after the liquid temperature was raised to 55°C and held for 60 minutes. Note that for viscosity values ​​of 80 mPa·s or higher, the viscosity increases over time, so the viscosity is measured 5 and 10 minutes after the start of measurement, and the average value is used.

[0340] The third aqueous PTFE dispersion of the present disclosure preferably has a viscosity temperature transition [VTT] of more than 55° C., more preferably 60° C. or more. A VTT of more than 55° C. has the technical significance of eliminating the need to change the processing conditions at 25° C. and 55° C. VTT represents the viscosity-temperature dependency of an aqueous PTFE dispersion. VTT can be obtained by raising the temperature of an aqueous PTFE dispersion to 25°C, 35°C, 45°C, and 55°C, holding the temperature for 60 minutes, and then measuring using a B-type rotational viscometer under the conditions shown in the Examples below. The VTT point is the temperature at which the viscosity once again reaches the same value as measured at 25°C. Note that for viscosity values ​​of 80 mPa·s or higher, the viscosity increases over time, so the viscosity is measured 5 and 10 minutes after the start of measurement, and the average value is used.

[0341] The third aqueous PTFE dispersion of the present disclosure preferably has a PTFE solids concentration of 50 to 70% by mass. The solids concentration is more preferably 55% by mass or more, and even more preferably 57% by mass or more. Furthermore, the solids concentration is more preferably 65% ​​by mass or less, and even more preferably 60% by mass or less. Even if the PTFE solids concentration is within the above range, the third aqueous dispersion of the present disclosure can have a viscosity of 50 mPa·s or less at 55°C.

[0342] Furthermore, the third aqueous PTFE dispersion of the present disclosure is preferably substantially free of a fluorine-containing surfactant. In the composition of the present disclosure, "substantially free of a fluorine-containing surfactant" means that the content of the fluorine-containing surfactant in the aqueous PTFE dispersion is 1.0 ppm or less. The third aqueous PTFE dispersion of the present disclosure is substantially free of a fluorine-containing surfactant, yet can have a low viscosity at high temperatures and excellent mechanical stability at high temperatures. The content of the fluorine-containing surfactant is preferably 700 ppb or less, more preferably 600 ppb or less, and even more preferably 500 ppb or less. The content of the fluorine-containing surfactant in the third aqueous PTFE dispersion of the present disclosure can be measured by the same method as described for the first aqueous PTFE dispersion of the present disclosure.

[0343] When the third aqueous PTFE dispersion of the present disclosure is obtained by polymerization using a fluorine-containing surfactant, the amount of the fluorine-containing surfactant can be adjusted to the above range by adding a nonionic surfactant to the aqueous PTFE dispersion after polymerization, concentrating the dispersion, etc. Examples of the fluorine-containing surfactant include the fluorine-containing anionic surfactants described for the first aqueous PTFE dispersion of the present disclosure.

[0344] The third aqueous PTFE dispersion of the present disclosure can be prepared by the method described for the first aqueous PTFE dispersion of the present disclosure.

[0345] The third aqueous PTFE dispersion of the present disclosure is useful for coatings, such as various paints, particularly topcoats. Conventional coating methods can be used for coating, such as dipping, spraying, roll coating, doctor blade coating, and flow coating.

[0346] The third aqueous PTFE dispersion of the present disclosure may be directly applied to a substrate, but in order to improve adhesion, it is desirable to form a topcoat layer on a primer layer. The substrate is not particularly limited, but examples thereof include various metals, enamel, glass, and various ceramics. In addition, in order to improve adhesion, it is desirable to roughen the surface by sandblasting or the like.

[0347] The composition applied to the substrate is then dried. The third PTFE aqueous dispersion of the present disclosure is characterized in that it does not produce mud cracks during this drying stage. Drying can be carried out under normal conditions, for example, at room temperature to 80°C, preferably 80 to 100°C, for 5 minutes to 1 hour, until the composition is dry to the touch.

[0348] In the case of baked paints, such as fluororesin paints, the dried coating is baked (processed). When a depolymerizable acrylic resin is added, it functions as a binder until the fluororesin particles melt and fuse, preventing cracks from occurring due to thermal shrinkage during this baking stage. The baking (processing) temperature and time vary depending on the type and melting temperature of the PTFE resin, but are typically performed at a temperature above the melting temperature of the PTFE resin, typically 360-415°C, for 5-30 minutes. 10-30 minutes at 360-380°C is preferred.

[0349] When a primer layer is provided, a method in which a primer layer is applied, dried, and baked, and then the composition of the present disclosure is applied, dried, and baked (two-coat, two-bake method) may be used, or a method in which a primer layer is applied and dried, then the composition of the present disclosure is applied and dried, and then both are baked simultaneously (two-coat, one-bake method) may be used.

[0350] According to the third aqueous PTFE dispersion of the present disclosure, a thick coating film having a thickness of 30 μm or more can be obtained by a single coating. Although there is no particular upper limit, if the thickness is too thick, various decomposition residues remain in the coating film, causing discoloration, so the upper limit is 100 μm or less.

[0351] Although the third aqueous PTFE dispersion of the present disclosure is most useful for coating metal cookware, particularly frying pans, the composition can also be used to coat other products requiring corrosion resistance, such as bearings, valves, electrical wires, metal foil, boilers, pipes, boat bottoms, oven liners, ironing boards, bread pans, rice cookers, grill pans, electric kettles, ice trays, snow shovels, plows, chutes, conveyors, rolls, molds, dies, tools such as saws, files, and drills, knives, scissors, hoppers, other industrial containers (particularly for the semiconductor industry), and molds.

[0352] The present disclosure also relates to a coated article having a coating film obtained by applying the third aqueous PTFE dispersion of the present disclosure. The coating film can be produced by a conventionally known method and can be obtained by applying the aqueous dispersion of the present disclosure to a substrate. The material of the substrate is not particularly limited, and examples include metals such as simple metals such as iron, aluminum, stainless steel, and copper, and alloys thereof; and non-metallic inorganic materials such as enamel, glass, and ceramic. Examples of the alloys include stainless steel. The material of the substrate is preferably a metal, and more preferably aluminum or stainless steel. The thickness of the coating film is preferably 30 μm or more, and is preferably 100 μm or less, since if the coating film is too thick, various decomposition residues will remain in the coating film, causing discoloration.

[0353] The coated article may be provided with a primer layer.

[0354] Applications of the above-mentioned coated articles include metal cooking utensils (especially frying pans), bearings, valves, electric wires, metal foils, boilers, pipes, ship bottoms, oven linings, iron bottom plates, bread pans, rice cookers, grill pans, electric kettles, ice trays, snow shovels, plows, chutes, conveyors, rolls, molds, dies, tools such as saws, files and drills, knives, scissors, hoppers, other industrial containers (especially for the semiconductor industry), and molds. [Example]

[0355] Next, the present disclosure will be described with reference to examples, but the present disclosure is not limited to these examples.

[0356] The values ​​in the examples were measured by the following methods. (1) Average primary particle size The PTFE aqueous dispersion was diluted with water to a solids concentration of 0.15% by mass, and the transmittance of the resulting diluted aqueous dispersion to a 550 nm incident light per unit length and the number-based average primary particle diameter determined by measuring the unidirectional diameter using a transmission electron microscope photograph were measured to create a calibration curve. Using this calibration curve, the average primary particle diameter was determined from the measured transmittance of the 550 nm incident light for each sample.

[0357] (2) Solid content concentration (P) Approximately 1 g (X g) of sample was placed in a 5 cm diameter aluminum cup, dried at 110°C for 30 minutes, and then further dried at 300°C for 30 minutes. Based on the heating residue (Z g), P was determined using the formula: P = Z / X × 100 (mass%).

[0358] (3) Standard specific gravity (SSG) Using samples molded in accordance with ASTM D4895-89, measurements were made by the water displacement method in accordance with ASTM D-792.

[0359] (4) Content of modified monomer The HFP content was determined by press-molding PTFE powder to create a thin film disk, and measuring the infrared absorbance of the thin film disk by FT-IR. -1 Absorbance at / 935cm -1 The absorbance ratio was calculated by multiplying the absorbance ratio by 0.3. The PPVE content was determined by press-molding PTFE powder to create a thin film disk, measuring the infrared absorbance of the thin film disk by FT-IR at 995 cm -1 Absorbance at / 935cm -1 The absorbance ratio was calculated by multiplying the absorbance ratio by 0.14.

[0360] (5) Fluorine-containing surfactant concentration The solid content of the aqueous dispersion was measured, and an amount of the aqueous dispersion equivalent to 1.5 g of PTFE solids was weighed into a 100 mL screw tube. The mixture was then combined with the water contained in the aqueous dispersion, and water and methanol were added so that the extraction solvent was 37 g of water / methanol = 10 / 90 mass%, and the mixture was shaken vigorously until coagulation occurred. The liquid phase was removed and centrifuged at 4000 rpm for 1 hour, and the supernatant was extracted. The fluorine-containing surfactants in the extract were measured using a liquid chromatograph mass spectrometer (Waters, LC-MS ACQUITY UPLC / TQD). The measurement equipment configuration and LC-MS measurement conditions are shown in Table 1.

[0361] [Table 1]

[0362] The calibration curve used to calculate the concentration of the fluorine-containing surfactant was obtained under the following conditions. Five standard methanol solutions of fluorine-containing surfactants with known concentrations ranging from 1 ng / mL to 100 ng / mL were prepared and measured using a liquid chromatograph mass spectrometer (Waters, LC-MS ACQUITY UPLC / TQD). Using a first-order approximation from the respective sample concentrations and peak integral values, a and b were calculated using the following relational equation (3). A=a×X+b (3) A: Peak area of ​​fluorine-containing surfactant X: Concentration of fluorine-containing surfactant (ng / mL) The lower limit of quantification is 100 ppb.

[0363] (6) Nonionic surfactant content (N) Approximately 1 g (X g) of sample was placed in a 5 cm diameter aluminum cup and heated at 110°C for 30 minutes to obtain the heating residue (Y g). The heating residue (Y g) was then heated at 300°C for 30 minutes to obtain the heating residue (Z g). The amount calculated from the formula: N = [(YZ) / X] x 100 (mass%) minus the amount of stabilizer was used to determine the content of nonionic surfactant. The stabilizer was calculated based on the amount added during preparation.

[0364] (7) Mechanical stability A plastic cup with a diameter of 67 mm and a capacity of 300 ml was placed in 100 g of aqueous PTFE dispersion and immersed in a water bath at 60°C. A stirring blade with a diameter of 50 mm (Fig. 1) was set so that the height from the bottom of the plastic cup to the center of the stirring blade (6 mm from the bottom end of the stirring blade in the axial direction of Fig. 1(b)) was 20 mm, and the cup was rotated at 3000 rpm. The time until the aqueous PTFE dispersion aggregated or solidified and scattered was measured as the stability retention time.

[0365] (8) Viscosity The viscosity at 25°C was measured using a B-type rotational viscometer (Tohki Sangyo Co., Ltd., rotor No. 2) at a rotation speed of 60 rpm for a measurement time of 120 seconds. The viscosity at 55°C was measured under the same conditions as the viscosity measurement at 25°C after the liquid temperature was raised to 55°C and held for 60 minutes. Note that for viscosity values ​​of 80 mPa·s or higher, the viscosity increases over time, so the viscosity was measured 5 and 10 minutes after the start of measurement and the average value was used.

[0366] (9) pH The pH was measured at 25°C using a glass electrode (manufactured by Horiba Ltd.) in accordance with JIS K6893. (10) Viscosity temperature transition (VTT) VTT was obtained by heating the aqueous PTFE dispersion to 25°C, 35°C, 45°C, and 55°C, holding the temperature for 60 minutes, and then measuring the viscosity using a B-type rotational viscometer (Tohki Sangyo Co., Ltd., rotor No. 2) at 60 rpm for a measurement time of 120 seconds. The VTT point is the temperature at which the viscosity again reaches the same value as measured at 25°C. Note that for viscosity values ​​above 80 mPa·s, a viscosity increase occurs over time, so the viscosity was measured 5 and 10 minutes after the start of measurement, and the average value was used. (11) Average number of methyl groups per molecule An equal amount of methanol was added to the PTFE aqueous dispersion and subjected to Soxhlet extraction. 1 It was determined by H-NMR measurement. (12) Extrusion pressure at reduction ratio 1500 20.5 parts by mass (12.3 g) of hydrocarbon oil (trade name: Isopar G, manufactured by Exxon Chemical Co.) was added as an extrusion aid to 100 parts by mass (60 g) of PTFE powder, and the mixture was aged for 1 hour at room temperature (25±1°C), after which paste extrusion molding was carried out using an extrusion die equipped with a cylinder having an inner diameter of 25.4 mm (reduction ratio 1500). In the latter half of the extrusion, the pressure at the point where the pressure reached equilibrium was divided by the cross-sectional area of ​​the cylinder, and this value was taken as the extrusion pressure at a reduction ratio of 1500.

[0367] The average molecular structures of the surfactants used in the examples and comparative examples are shown below. Surfactant (a): Tergitol TMN-100X C 12 H 25 O(CH2CH2O) 10 H (average number of methyl groups per molecule: 5.0), HLB: 14.00, cloud point: 65°C Surfactant (b): Tergitol TMN-10 C 12 H 25 O(CH2CH2O) 11 H (average number of methyl groups per molecule: 5.0), HLB 14.40, cloud point 76℃ Tergitol TMN-100X is a mixture of Tergitol TMN-6 and Tergitol TMN-10, and the composition ratio is as follows: TMN-6:TMN-10=30:70 (weight ratio) Structural formula of TMN-6 C 12 H 25 O(CH2CH2O)8H (average number of methyl groups per molecule: 5.0), HLB: 13.10, cloud point: 36°C Surfactant (c): C 13 H 27 O(CH2CH2O)8H (average number of methyl groups per molecule: 4.0), HLB: 13.30, cloud point: 60°C Surfactant (d): C 13 H 27 O(CH2CH2O) 10H (average number of methyl groups per molecule: 4.0), HLB 13.80, cloud point 71℃

[0368] Synthesis Example 1 After purging a 1L autoclave with nitrogen, 16.5g of dehydrated tetramethylurea and 220g of diethylene glycol dimethyl ether were charged and cooled. 38.5g of carbonyl fluoride was charged, followed by 100g of hexafluoropropylene oxide, which was then stirred. 38.5g of carbonyl fluoride and 100g of hexafluoropropylene oxide were then charged. Then, equal amounts of carbonyl fluoride and hexafluoropropylene oxide were added. After the reaction was complete, the reaction mixture was removed and separated to obtain the lower layer reaction product.

[0369] A 6-L autoclave was charged with 1,000 ml of tetraglyme and 75 g of CsF, and the atmosphere inside the autoclave was replaced with nitrogen. The autoclave was then cooled, and 2,100 g of the reaction product obtained above was charged, and hexafluoropropylene oxide was introduced into the autoclave to initiate the reaction. Finally, 1,510 g of hexafluoropropylene oxide was charged. The contents were then removed, and the upper and lower layers were separated using a separatory funnel. The upper layer weighed 1,320 g, and the lower layer weighed 3,290 g. The lower layer was subjected to rectification.

[0370] Next, 1000 g of pure water was added to 1000 g of the product obtained by rectification of the lower layer, and hydrolysis was carried out. The organic layer (lower layer) was then separated using a separatory funnel and recovered. The recovered organic layer (lower layer) was washed with sulfuric acid water. The washed organic layer was subjected to simple distillation to obtain a distillate. 500 g of the distillate obtained above was then added dropwise to an aqueous solution prepared by mixing 76 g of 28 wt % aqueous ammonia solution and 600 g of pure water. After the dropwise addition was completed, 28 wt % aqueous ammonia solution was added to adjust the pH to 7. This was then freeze-dried to obtain a white solid.

[0371] Manufacturing Example 1 A 6-L stainless steel reactor equipped with a stirrer was charged with 3540 g of deionized water, 94 g of paraffin wax, and 5.4 g of the white solid obtained in Synthesis Example 1 as a fluorine-containing surfactant. The contents of the reactor were then heated to 70°C while being aspirated and simultaneously purged with TFE to remove oxygen from the reactor, and the contents were stirred. 0.78 g of perfluoropropyl vinyl ether (PPVE) was injected into the reactor using TFE. 250.6 mg of disuccinic acid peroxide (DSP) dissolved in 20 g of deionized water and 10.7 mg of ammonium persulfate (APS) dissolved in 20 g of deionized water were injected into the reactor as initiators, and the pressure in the reactor was adjusted to 0.90 MPaG. After the initiator injection, a pressure drop occurred and the initiation of polymerization was observed. TFE was added to the reactor to maintain a constant pressure of 0.90 MPaG. When the amount of TFE consumed in the reaction reached 1,380 g, 1.0 g of methanol was added to the reactor, and the reaction was continued. When the amount of TFE consumed in the reaction reached 1,534 g, the supply of TFE was stopped, stirring was stopped, and the reaction was terminated. The pressure in the reactor was then vented to atmospheric pressure, and the contents were removed from the reactor and cooled. The paraffin wax was removed, yielding PTFE aqueous dispersion 1-1.

[0372] The resulting aqueous dispersion 1-1 had a solids concentration of 30.0% by mass and an average primary particle size of 254 nm. The resulting PTFE aqueous dispersion 1-1 was diluted with deionized water to a solids concentration of approximately 13% by mass, coagulated under high-speed stirring conditions, and the coagulated wet powder was dried at 150°C for 18 hours to obtain a PTFE powder. The standard specific gravity of the resulting PTFE powder was 2.174 and the PPVE content was 0.046% by mass. The extrusion pressure at a reduction ratio of 1500 was 42.1 MPa.

[0373] A nonionic surfactant, surfactant (a), was added to aqueous dispersion 1-1 to prepare a dispersion with a nonionic surfactant concentration of 10 parts by mass per 100 parts by mass of PTFE. Subsequently, a 20 mm diameter column was filled with 250 ml of OH-type anion exchange resin (trade name Amberjet AMJ4002, manufactured by Rohm and Haas) and the dispersion was passed through at SV=1. Furthermore, surfactant (a) was added to the aqueous dispersion obtained after passing through the column so that the concentration was 20 parts by mass per 100 parts by mass of PTFE, and the mixture was maintained at 65°C for 3 hours, resulting in separation into a supernatant phase and a concentrated phase. The concentrated phase was recovered to obtain aqueous PTFE dispersion 1-2.

[0374] The resulting PTFE aqueous dispersion 1-2 had a solids concentration of 71.5 mass %, a nonionic surfactant content of 2.7 mass % relative to the PTFE, and a fluorine-containing surfactant concentration of 480 ppb relative to the PTFE aqueous dispersion.

[0375] Manufacturing Example 2 Polymerization was performed in accordance with Example 2 of WO 2015 / 116754, except that CF3OCF2CF2CF2OCHFCF2COOH was replaced with the white solid obtained in Synthesis Example 1, to obtain PTFE aqueous dispersion 2-1. The average primary particle size of the obtained PTFE aqueous dispersion 2-1 was 250 nm. The obtained PTFE aqueous dispersion 2-1 was diluted with deionized water to a solids concentration of approximately 10%, coagulated under high-speed stirring conditions, and the coagulated wet powder was dried at 150°C for 18 hours to obtain PTFE powder. The standard specific gravity of the obtained PTFE powder was 2.205, and the HFP content was 0.010% by mass.

[0376] The obtained PTFE aqueous dispersion 2-1 was subjected to ion exchange treatment and concentration in the same manner as in Production Example 1 to obtain a PTFE aqueous dispersion 2-2. The obtained PTFE aqueous dispersion 2-2 had a solids concentration of 69.5 mass % and a nonionic surfactant content of 2.9 mass % relative to PTFE.

[0377] Manufacturing Example 3 Polymerization was carried out in accordance with Example 1 of WO 2006 / 127317 to obtain PTFE aqueous dispersion 3-1, with the following changes: The fluorine-containing surfactant was changed from 3.24 parts of ammonium perfluorooctanoate to 2.03 parts of the white solid obtained in Synthesis Example 1. No additional fluorine-containing surfactant was added during the polymerization. In addition, the timing of adding the APS and methanol solution was changed from the TFE charging amount of 88.1 parts to 62.4 parts. Furthermore, the timing for stopping the feeding of TFE was changed from 96.9 parts to 69.4 parts. The average primary particle diameter of the PTFE aqueous dispersion 3-1 was 285 nm. Furthermore, the PTFE aqueous dispersion 3-1 was diluted with deionized water to a solids concentration of approximately 10%, coagulated under high-speed stirring conditions, and the coagulated wet powder was dried at 150°C for 18 hours to obtain a PTFE powder. The standard specific gravity of the obtained PTFE powder was 2.241.

[0378] The obtained PTFE aqueous dispersion 3-1 was subjected to ion exchange treatment and concentration in the same manner as in Production Example 1 to obtain a PTFE aqueous dispersion 3-2. The obtained PTFE aqueous dispersion 3-2 had a solids concentration of 70.9 mass % and a nonionic surfactant content of 2.9 mass % relative to PTFE.

[0379] Example 1 To the PTFE aqueous dispersion 1-2 obtained in Production Example 1, surfactant (a) was added so that the concentration was 4.0 mass% relative to PTFE, and then surfactant (b) was added at 2.0 mass% relative to PTFE, and ammonium lauryl sulfate was added at 500 ppm relative to PTFE, and deionized water and aqueous ammonia were then added. The solids concentration (mass%) of the resulting PTFE aqueous dispersion 1-3 and the content (mass%) of each component relative to PTFE are shown in Table 2. The pH and viscosity of this PTFE aqueous dispersion 1-3 were measured by the above-mentioned method, and a mechanical stability test was carried out. The results are shown in Table 2. Furthermore, an equal volume of methanol was added to the obtained PTFE aqueous dispersion 1-3, and Soxhlet extraction was carried out. The extract was then measured by 1H-NMR, and the average number of oxyalkylene units was found to be 10.4.

[0380] Examples 2 to 7 Aqueous PTFE dispersions were obtained and evaluated in the same manner as in Example 1, except that the compounds added to the aqueous PTFE dispersion 1-2 were changed as shown in Table 2. The results are shown in Table 2.

[0381] Comparative Example 1 To the PTFE aqueous dispersion 1-2 obtained in Production Example 1, surfactant (a) was added so that the amount was 5.5 mass % relative to the PTFE, ammonium lauryl sulfate was added in an amount of 1000 ppm relative to the PTFE, and an acetylene-based antifoaming agent (trade name Surfynol 440, manufactured by Air Products Co., Ltd.) was added as an antifoaming agent so that the amount was 0.5 mass % relative to the PTFE. Otherwise, an aqueous PTFE dispersion was obtained in the same manner as in Example 1 and evaluated in the same manner. The results are shown in Table 3.

[0382] Comparative Example 2 To the PTFE aqueous dispersion 2-2 obtained in Production Example 2, surfactant (a) was added so that the concentration was 6.0 mass % relative to the PTFE, ammonium lauryl sulfate was added in an amount of 1000 ppm relative to the PTFE, and deionized water and aqueous ammonia were further added. Except for this, an aqueous PTFE dispersion was obtained in the same manner as in Example 1 and evaluated in the same manner. The results are shown in Table 3.

[0383] Comparative Example 3 The PTFE aqueous dispersion 3-2 obtained in Production Example 3 was used to carry out the same treatment as in Comparative Example 2. The results are shown in Table 3.

[0384] Comparative Example 4 The PTFE aqueous dispersion 1-2 obtained in Production Example 1 was used to carry out the same treatment as in Comparative Example 2. The results are shown in Table 3. [Table 2] [Table 3]

[0385] Compared with Comparative Examples 1 to 4, Examples 1 to 7 had significantly lower viscosities at 55°C, and VTT exceeded 55°C, so that the increase in viscosity at high temperatures was suppressed. Furthermore, the stability retention time at 60°C in Examples 1 to 7 was significantly longer than that in Comparative Examples 1 to 4, and therefore mechanical stability was improved.

[0386] Production Example 4 A 6-L stainless steel reactor equipped with a stirrer was charged with 3580 g of deionized water, 160 g of paraffin wax, and 4.7 g of the white solid obtained in Synthesis Example 1 as a fluorinated surfactant. The contents of the reactor were then heated to 70°C while being aspirated and simultaneously purged with TFE to remove oxygen from the reactor, and the contents were stirred. 6.5 g of PPVE was then injected into the reactor using TFE. 50 mg of APS dissolved in 20 g of deionized water was injected into the reactor as an initiator, and the pressure was adjusted to 1.5 MPaG. TFE was added to maintain a constant pressure of 1.5 MPaG. When the amount of TFE consumed in the reaction reached 1466 g, 0.5 g of methanol was injected into the reactor, and the reaction continued. When the amount of TFE consumed in the reaction reached 1543 g, the TFE supply was stopped, stirring was stopped, and the reaction was terminated. The reactor was then vented to atmospheric pressure, and the contents were removed from the reactor and cooled. The paraffin wax was removed to obtain PTFE aqueous dispersion 4-1.

[0387] The resulting aqueous dispersion 4-1 had a solids concentration of 30.0% by mass and an average primary particle size of 272 nm. The resulting PTFE aqueous dispersion 4-1 was diluted with deionized water to a solids concentration of approximately 10% by mass, coagulated under high-speed stirring conditions, and the coagulated wet powder was dried at 150°C for 18 hours to obtain a PTFE powder. The standard specific gravity of the resulting PTFE powder was 2.167 and the PPVE content was 0.28% by mass. The extrusion pressure at a reduction ratio of 1500 was 58.9 MPa.

[0388] Production Example 5 A PTFE aqueous dispersion 5-1 was obtained in the same manner as in Production Example 4, except that the reaction was continued without injecting methanol into the reactor when the amount of TFE consumed in the reaction reached 1,466 g.

[0389] The resulting PTFE aqueous dispersion 5-1 had a solids concentration of 30.0% by mass and an average primary particle diameter of 270 nm. PTFE powder was obtained from the resulting PTFE aqueous dispersion 5-1 in the same manner as in Production Example 4. The resulting PTFE powder had a standard specific gravity of 2.163 and a PPVE content of 0.28% by mass. The extrusion pressure at a reduction ratio of 1500 exceeded 100 MPa, so measurement was discontinued.

[0390] Example 8 A nonionic surfactant, surfactant (c), was added to aqueous dispersion 4-1 to prepare a dispersion with a nonionic surfactant concentration of 10 parts by mass per 100 parts by mass of PTFE. Subsequently, a 20 mm diameter column was filled with 250 ml of OH-type anion exchange resin (trade name Amberjet AMJ4002, manufactured by Rohm and Haas) and the dispersion was passed through at SV=1. Further, surfactant (c) was added to the aqueous dispersion obtained after passing through the column so that the concentration was 16 parts by mass per 100 parts by mass of PTFE, and the mixture was maintained at 65°C for 3 hours, resulting in separation into a supernatant phase and a concentrated phase. The concentrated phase was recovered to obtain aqueous PTFE dispersion 4-2.

[0391] The resulting PTFE aqueous dispersion 4-2 had a solids concentration of 68.3 mass %, a nonionic surfactant content of 2.7 mass % relative to the PTFE, and a fluorine-containing surfactant concentration of 420 ppb relative to the PTFE aqueous dispersion. To the obtained PTFE aqueous dispersion 4-2, surfactant (d) was added so that the amount was 5.0 mass % relative to PTFE, ammonium lauryl sulfate was added in an amount of 500 ppm relative to PTFE, and deionized water and aqueous ammonia were further added to obtain PTFE aqueous dispersion 4-3. The resulting PTFE aqueous dispersion 4-3 had a solids concentration of 62.9% by mass and a nonionic surfactant content of 5.0% by mass relative to PTFE. Evaluation was performed in the same manner as in Example 1. However, the stability retention time was measured after diluting the solids concentration to 60.0% by mass. The results are shown in Table 4.

[0392] Comparative Example 5 Aqueous PTFE dispersions 5-2 and 5-3 were obtained in the same manner as in Example 8, except that aqueous PTFE dispersion 4-1 was replaced with aqueous PTFE dispersion 5-1.

[0393] The resulting PTFE aqueous dispersion 5-2 had a solids concentration of 68.3 mass %, a nonionic surfactant content of 2.7 mass % relative to the PTFE, and a fluorine-containing surfactant concentration of 430 ppb relative to the PTFE aqueous dispersion. The resulting PTFE aqueous dispersion 5-3 had a solids concentration of 62.9% by mass and a nonionic surfactant content of 5.0% by mass relative to PTFE. Evaluation was performed in the same manner as in Example 1. However, the stability retention time was measured after diluting the solids concentration to 60.0% by mass. The results are shown in Table 4.

[0394] [Table 4]

[0395] The viscosity at 55°C in Example 8 was significantly lower than that in Comparative Example 5, and the VTT was 55°C or higher, so that the increase in viscosity at high temperatures was suppressed. Furthermore, the stability retention time at 60°C in Example 8 was significantly longer than that in Comparative Example 5, indicating that the mechanical stability was improved.

[0396] Example 9 The following ingredients were mixed in the order listed: (A) 80.7 parts of PTFE aqueous dispersion 1-3 obtained in Example 1 (B) Glycerin 4.7 parts (C) Depolymerizable acrylic resin particle emulsion (butyl methacrylate resin, average particle size 0.3 μm, solid content 40%) 11.7 parts (D) Nonionic surfactant (polyoxyethylene tridecyl ether, Dispanol TOC (50% aqueous solution) manufactured by Nippon Oil & Fats Co., Ltd.) 4.7 parts (Other) Thickener (25% aqueous solution of sodium lauryl sulfate) 1.9 parts (E) 0.5 part of water The following properties of the obtained aqueous dispersion composition for coating were investigated, and the results are shown in Table 5.

[0397] (Storage stability) 500 g of the aqueous dispersion composition for coating was placed in a polyethylene bottle and left in a thermostatic chamber at 40°C for one month. The redispersibility was evaluated. A 150-mesh wire screen was used for evaluation; a mark indicating that all the particles passed through was marked ○, and a mark indicating that some particles remained on the screen was marked ×. The resulting aqueous dispersion composition for coating was then sprayed onto a non-blasted aluminum plate and dried at 80°C for 15 minutes. The surface of the resulting dried coating film was observed under an optical microscope to check for the presence or absence of mud cracks. No mud cracks were found. The dried coating film was then baked at 380°C for 20 minutes to form a fused coating film. The following physical properties of this coating film were examined. (Coating appearance) The coating surface was observed under an optical microscope. (Pencil hardness) The evaluation was carried out at 25°C according to the method described in JIS K5600. (Crack limit film thickness) The film thickness was varied, and the film thickness at which cracks began to occur was determined as the crack limit film thickness. (Coloring) The coating was visually inspected. (Alkylphenol content) The sample was analyzed by liquid chromatography (column: ASAHIPAC GS-310, eluent: acetonitrile / water = 50 / 50 volume ratio, flow rate: 1.2 ml / min, column temperature: 25-28°C, detection: UV (230 nm)). ○ indicates no detection, × indicates detection. (Gun jammed) Using an Iwata spray gun W88 (nozzle diameter 1.5mm), we set the pressure to 9.8N (5kgf), turned the paint output valve back one turn, and fully closed the pattern valve, and then opened and closed the trigger intermittently to paint, and counted the number of times paint stopped coming out of the gun. (Vitiligo) Using an Iwata Spray Gun W88 (nozzle diameter 1.5mm), with the pressure set to 9.8N (5kgf), the paint output valve turned back one turn, and the pattern valve fully closed, 10 sheets of 20cm x 60cm black kraft paper were sprayed by opening and closing the trigger intermittently, and the number of shots until white spots appeared was visually counted.

[0398] Example 10 In Example 9, the PTFE aqueous dispersion 1-3 of Example 1 was replaced with the PTFE aqueous dispersion 4-3 obtained in Example 8, and mixed in the composition shown in Table 5 to obtain an aqueous dispersion composition for coating. Measurements were carried out in the same manner as in Example 9. The results are shown in Table 5.

[0399] Comparative Example 6 In Example 9, the PTFE aqueous dispersion 1-3 of Example 1 was replaced with the PTFE aqueous dispersion 5-3 obtained in Comparative Example 5, and mixed in the composition shown in Table 5 to obtain an aqueous dispersion composition for coating. Measurements were carried out in the same manner as in Example 9. The results are shown in Table 5. [Table 5]

[0400] In comparison with Comparative Example 6, Examples 9 and 10 showed a significant increase in the number of shots required to cause gun clogging and the number of shots required to cause white spots, indicating that mechanical stability was improved.

[0401] Example 11 The following ingredients were mixed in the order listed: (A) 80.6 parts of the PTFE aqueous dispersion 1-3 obtained in Example 1 (B) Depolymerizable acrylic resin particle emulsion (specific gravity approximately 1.1, butyl methacrylate resin, average particle size 0.6 μm, solid content concentration 40%) 14.1 parts (C) Nonionic surfactant (specific gravity approximately 1.0) Nonionic surfactant (polyoxyethylene tridecyl ether, Dispanol TOC (50% aqueous solution) manufactured by Nippon Oil & Fats Co., Ltd.) 8.8 parts (D) Other additives 3.5 parts glycerin Hydrocarbon solvent 1.4 parts 3.2 parts water The properties of the resulting aqueous resin dispersion composition were examined, and the results are shown in Table 6.

[0402] Example 12 In Example 11, the PTFE aqueous dispersion 1-3 of Example 1 was replaced with the PTFE aqueous dispersion 4-3 obtained in Example 8, and the components were mixed according to the composition shown in Table 6. The properties of the obtained resin aqueous dispersion composition were investigated. The results are shown in Table 6.

[0403] Comparative Example 7 In Example 11, the PTFE aqueous dispersion 1-3 of Example 1 was replaced with the PTFE aqueous dispersion 5-3 obtained in Comparative Example 5, and the components were mixed according to the composition shown in Table 6. The properties of the obtained resin aqueous dispersion composition were investigated. The results are shown in Table 6. [Table 6]

[0404] In comparison with Comparative Example 7, Examples 11 and 12 showed a significant increase in the number of shots required until gun clogging occurred and the number of shots required until white spots appeared, indicating that mechanical stability was improved.

Claims

1. Polytetrafluoroethylene and a nonionic surfactant are included, The solid content concentration of polytetrafluoroethylene is 50 to 70 mass %, Substantially free of fluorine-containing surfactants, The viscosity at 55°C is 50 mPa s or less, The nonionic surfactant is a mixture of two different nonionic surfactants.

1. A polytetrafluoroethylene aqueous dispersion comprising:

2. 2. The aqueous polytetrafluoroethylene dispersion according to claim 1, wherein the content of the fluorine-containing surfactant is 100 ppb or more and 1.0 ppm or less.

3. 3. The aqueous dispersion according to claim 1, wherein the ratio [viscosity at 55°C / viscosity at 25°C] is 4.00 or less.

4. 4. The aqueous dispersion according to claim 1, wherein the content of the nonionic surfactant is 4% by mass or more and 12% by mass or less based on the polytetrafluoroethylene.

5. 5. The aqueous dispersion according to claim 1, wherein the stability retention time at 60° C. is 30 minutes or more.

6. 5. The aqueous dispersion according to claim 1, wherein the stability retention time at 60° C. is 40 minutes or more.

7. The nonionic surfactant is represented by the following general formula (i): R ３ -O-A １ -H (i) (In the formula, R ３ is an alkyl group having 8 to 18 carbon atoms, and A １ The aqueous dispersion according to any one of claims 1 to 6, comprising a compound represented by the formula:

8. R ３ is represented by the following general formula (i-1): CHR ３１ R ３２ - (i-1) (In the formula, R ３１ represents a hydrogen atom or an alkyl group having 1 to 16 carbon atoms, R ３２ represents an alkyl group having 1 to 17 carbon atoms, and R ３１ and R ３２ The aqueous dispersion according to claim 7, wherein the alkyl group is an alkyl group represented by the formula (I) and the total number of carbon atoms is 7 to 17.

9. R ３ The aqueous dispersion according to claim 7 or 8, wherein is an alkyl group having 8 to 18 carbon atoms and an average number of methyl groups of 2.0 or more.

10. In formula (i), R ３ The aqueous dispersion according to claim 7, 8 or 9, wherein is a 2,6,8-trimethyl-4-nonyl group.

11. In formula (i), A １ The aqueous dispersion according to claim 10, wherein is a polyoxyethylene chain having an average number of oxyethylene units of 10.1 to 10.

8.

12. 12. The aqueous dispersion according to claim 10, wherein the nonionic surfactant has an HLB of 14.00 or more.

13. A method for producing an aqueous polytetrafluoroethylene dispersion, comprising the steps of: Step A: emulsion-polymerizing tetrafluoroethylene in the presence of a fluorine-containing anionic surfactant to obtain a dispersion containing polytetrafluoroethylene; Step B of adding a nonionic surfactant (1) to the dispersion obtained in Step A; Step C is a step of removing the fluorine-containing anionic surfactant from the dispersion obtained in Step B and further concentrating the dispersion, or a step of concentrating the dispersion obtained in Step B and further removing the fluorine-containing anionic surfactant; and Step D of adding a nonionic surfactant (2) and a fluorine-free anionic surfactant to the dispersion obtained in Step C; Including, The pressure in the emulsion polymerization is 0.05 to 10 MPa, The nonionic surfactant (1) is represented by the following formula (1): R 4 -O-A 2 -H (1) (wherein R 4 is a 2,6,8-trimethyl-4-nonyl group, and A 2 is a polyoxyalkylene chain having an average number of oxyethylene units of 7.0 to 12.0 and an average number of oxypropylene units of 0.0 to 2.0).

1. A method for producing an aqueous polytetrafluoroethylene dispersion, comprising:

14. The method according to claim 13, wherein step A is a step of polymerizing tetrafluoroethylene with at least one monomer selected from the group consisting of perfluoro(alkyl vinyl ether), (perfluoroalkyl)ethylene, and cyclic monomers.

15. Step A is a step of obtaining a dispersion of modified polytetrafluoroethylene having a core-shell structure, The production method according to claim 13 or 14, comprising: Step A-1 of polymerizing tetrafluoroethylene and at least one modified monomer selected from the group consisting of perfluoro(alkyl vinyl ether), (perfluoroalkyl)ethylene, and a cyclic monomer to produce the core; and Step A-2 of polymerizing tetrafluoroethylene, the modified monomer, and at least one selected from the group consisting of hexafluoropropylene and a chain transfer agent to produce the shell.

16. The nonionic surfactant (2) is represented by the following formula (2): R ５ -O-A ３ -H (2) (In the formula, R ５ is a linear or branched primary or secondary alkyl group having 8 to 18 carbon atoms and an average number of methyl groups per molecule of 4.0 or more, and A ３ is a polyoxyalkylene chain having an average number of oxyethylene units of 10.0 to 12.

0.

17. In formula (2), R ５ The method according to claim 16, wherein is a 2,6,8-trimethyl-4-nonyl group.

18. The method according to any one of claims 13 to 17, wherein step D is a step of adding the nonionic surfactant (2) so that the concentration of the nonionic surfactant in the dispersion is 4% by mass or more and 12% by mass or less relative to the polytetrafluoroethylene.

19. The method according to any one of claims 13 to 18, wherein the polytetrafluoroethylene aqueous dispersion contains a nonionic surfactant having a cloud point of 60 to 80°C.

20. The method according to any one of claims 13 to 19, wherein the polytetrafluoroethylene aqueous dispersion contains a nonionic surfactant having an HLB of 14.00 or more.

21. The process according to any one of claims 13 to 20, wherein the removal of the fluorine-containing anionic surfactant in step C is carried out by contacting the aqueous dispersion with an anion exchange resin.

22. The method according to any one of claims 13 to 21, wherein the polytetrafluoroethylene aqueous dispersion has a fluorine-containing anionic surfactant content of 1.0 ppm or less based on the aqueous dispersion.

23. The method according to any one of claims 13 to 22, wherein the fluorine-containing anionic surfactant has a Log POW of 3.5 or less.

24. The method according to any one of claims 13 to 23, wherein the fluorine-containing anionic surfactant is a fluorine-containing anionic surfactant having a Log POW of 3.4 or less.

25. The method according to any one of claims 13 to 24, wherein the fluorine-free anionic surfactant is at least one selected from the group consisting of alkyl sulfates and salts thereof, and fatty acids and salts thereof.

26. The method according to any one of claims 13 to 25, wherein the content of the fluorine-free anionic surfactant in the aqueous polytetrafluoroethylene dispersion is 50 to 5000 ppm relative to the polytetrafluoroethylene.

27. The method according to any one of claims 13 to 26, further comprising the step of adding a preservative to the aqueous dispersion.

28. 28. The method according to claim 27, wherein the preservative is an organic iodine compound or an organic nitrogen-sulfur compound.

29. The method according to any one of claims 13 to 28, further comprising the step of adding a coating material.

30. The aqueous dispersion according to any one of claims 1 to 12, which is an aqueous paint.

31. A coating film obtained by applying the aqueous dispersion according to any one of claims 1 to 12 and 30.

32. An impregnated membrane obtained by impregnating with the aqueous dispersion according to any one of claims 1 to 12 and 30.

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