Aqueous dispersions, paints, coatings, and coated articles

Abstract

The present invention provides an aqueous dispersion that exhibits excellent effects in terms of paintability and film appearance when used in the field of coatings. [Solution] An aqueous dispersion containing a perfluoropolymer, wherein the perfluoropolymer has a melt flow rate of 1 to 50 g / 10 min and a viscosity change of 15% or less after standing at 40°C for 90 days.

Description

Technical Field

[0001] The present disclosure relates to an aqueous dispersion, a paint, a coating film, and a coated article.

Background Art

[0002] Aqueous dispersions containing perfluoropolymers have been widely used in the field of various paints. Regarding such aqueous dispersions, attempts have been continuously made to enhance stability and improve the coating film performance when used as a paint. Such attempts have also been made in Patent Documents 1 to 3, but there is still a demand for further performance improvement.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present disclosure is to provide an aqueous dispersion that has excellent effects on coating properties and coating film appearance when used in the field of paints.

Means for Solving the Problems

[0005] The present disclosure is an aqueous dispersion containing a perfluoropolymer, where the perfluoropolymer has a melt flow rate of 1 to 50 g / 10 min, and is characterized in that the viscosity change after standing at 40°C for 90 days is 15% or less.

[0006] The above aqueous dispersion is an aqueous dispersion containing a perfluoropolymer, and preferably contains an electrolyte in an amount of 0.001% by mass or more and less than 10.0% by mass relative to the perfluoropolymer. The electrolyte is preferably at least one selected from the group consisting of ammonium sulfate, hydroxymonocarboxylic acid, hydroxydicarboxylic acid, tricarboxylic acid, and amino acids. The electrolyte is preferably ammonium sulfate.

[0007] The above-mentioned perfluoropolymer is preferably at least one selected from the group consisting of tetrafluoroethylene / hexafluoropropylene copolymer, tetrafluoroethylene / hexafluoropropylene / perfluoro(alkyl vinyl ether) copolymer, and tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer. The above aqueous dispersion preferably contains 0.005 to 9% by mass of ammonium sulfate relative to the perfluoropolymer, and the above perfluoropolymer is preferably at least one selected from the group consisting of tetrafluoroethylene / hexafluoropropylene copolymer, tetrafluoroethylene / hexafluoropropylene / perfluoro(alkyl vinyl ether) copolymer, and tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer.

[0008] This disclosure also relates to a paint characterized by containing the aqueous dispersion described above. This disclosure also relates to a coating film obtained by applying the above-mentioned paint. This disclosure also relates to a painted article having a coating film obtained by applying the above-mentioned paint. [Effects of the Invention]

[0009] The aqueous dispersion of this disclosure exhibits excellent effects in terms of paintability and film appearance when used in the field of coatings. [Modes for carrying out the invention]

[0010] The details of this disclosure are described below. The aqueous dispersion of this disclosure contains a perfluoropolymer, the perfluoropolymer having a melt flow rate of 1 to 50 g / 10 min, and satisfying the performance of having a viscosity change of 15% or less after standing at 40°C for 90 days. The aqueous dispersion of this disclosure contains a specific perfluoropolymer and has the characteristic of having little viscosity change during storage.

[0011] The aqueous dispersion of this disclosure maintains stable performance even during long-term storage, and when used as a paint, it exhibits minimal viscosity reduction during storage, thus reducing the likelihood of dripping during painting.

[0012] In the viscosity change described above, the viscosity was measured using a Type B rotational viscometer under the conditions of rotor No. 2, rotation speed of 60 rpm, and measurement time of 120 seconds. The viscosity change described above is 15% or less, and more preferably 10% or less.

[0013] The aqueous dispersion of this disclosure is in which resin particles containing a perfluoropolymer are dispersed in water. The perfluoropolymer will be described in detail below.

[0014] (Perfluoropolymer) In this disclosure, the perfluoropolymer in the aqueous dispersion is a melt-mold perfluoropolymer having a melt flow rate (MFR) of 1 to 50 g / 10 min. The aqueous dispersion of this disclosure contains such a melt-mold perfluoropolymer.

[0015] The meltability of the above perfluoropolymer is generally expressed as MFR, which is an indicator of flowability. MFR is determined according to ASTM D1238-95, using a melt indexer, and is the weight extruded from a nozzle with a diameter of 2.1 mm and a length of 8 mm under a load of 5 kg for 10 minutes. MFR is measured at 372°C.

[0016] The lower limit of the MFR of the above perfluoropolymer is 1 g / 10 min, and more preferably 2 g / 10 min. The upper limit of the MFR of the above perfluoropolymer is 50 g / 10 min, and more preferably 30 g / 10 min.

[0017] The above perfluoropolymer essentially contains tetrafluoroethylene, and further contains hexafluoropropylene [HFP], CF2=CF-ORf 1 (wherein, Rf <s 1 represents a perfluoroalkyl group having 1 to 8 carbon atoms). It preferably has a repeating unit derived from at least one perfluoroethylene monomer selected from the group consisting of perfluoro(alkyl vinyl ether) [PAVE] as a copolymer component.

[0018] The above perfluoropolymer is preferably at least one selected from the group consisting of TFE / HFP copolymer [FEP], TFE / PAVE copolymer [PFA], and TFE / HFP / PAVE copolymer.

[0019] The above perfluoropolymer preferably has a melting point of 100 to 347 °C, and more preferably 150 to 347 °C. The above melting point can be determined, for example, as the temperature corresponding to the maximum value in the melting heat curve when the temperature is raised at a rate of 10 °C / min using a differential scanning calorimeter [DSC].

[0020] The above perfluoropolymer is in particle form. Hereinafter, the particulate perfluoropolymer is referred to as perfluoropolymer particles. The average particle diameter of the above perfluoropolymer particles is preferably 0.01 to 1.0 μm, and more preferably 0.02 to 0.3 μm. The above average particle diameter is the volume-based average particle diameter (50% integrated particle diameter) d50, and can be measured by the dynamic light scattering method. For example, it can be measured by Microtrac MT-3000EXII type manufactured by Microtrac Bell Co., Ltd.

[0021] Examples of the above-mentioned PAVE include perfluoro(methyl vinyl ether) [PMVE], perfluoro(ethyl vinyl ether) [PEVE], perfluoro(propyl vinyl ether) [PPVE], and perfluoro(butyl vinyl ether), with PMVE, PEVE, or PPVE being more preferred.

[0022] While not particularly limited, FEP is preferably a copolymer containing 70-99 mol% TFE units and 1-30 mol% HFP units, and more preferably a copolymer containing 80-97 mol% TFE units and 3-20 mol% HFP units. If the TFE unit content is less than 70 mol%, the mechanical properties tend to decrease, and if it exceeds 99 mol%, the melting point becomes too high and moldability tends to decrease. It is also preferable that the FEP is a copolymer in which monomer units derived from monomers copolymerizable with TFE and HFP amount to 0.1-10 mol%, and the total of TFE units and HFP units is 90-99.9 mol%. Examples of monomers copolymerizable with TFE and HFP include PAVE and alkyl perfluorovinyl ether derivatives.

[0023] While there are no particular limitations on the PFA, copolymers with a molar ratio of TFE units to PAVE units (TFE units / PAVE units) of 70 / 30 or more and less than 99 / 1 are preferred. A more preferred molar ratio is 70 / 30 or more and 98.9 / 1.1 or less, and an even more preferred molar ratio is 80 / 20 or more and 98.9 / 1.1 or less. Too few TFE units tend to reduce mechanical properties, while too many tend to raise the melting point too much and reduce moldability. The above PFA is also preferably a copolymer in which monomer units derived from monomers copolymerizable with TFE and PAVE are 0.1 to 10 mol%, and the total of TFE units and PAVE units is 90 to 99.9 mol%.

[0024] The content of each monomer in the copolymer described above can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and X-ray fluorescence analysis depending on the type of monomer.

[0025] The aqueous dispersion of the present disclosure preferably has a solid content concentration of 35 to 75% by mass of the perfluoropolymer, a more preferable lower limit of 40% by mass, an even more preferable lower limit of 45% by mass, and a more preferable upper limit of 70% by mass. The aqueous dispersion of the present disclosure exhibits high dispersion stability even when it contains a high concentration of the perfluoropolymer.

[0026] The solid content concentration of the above perfluoropolymer can be determined by the formula: P = Z / X × 100 (%) based on the heat residue (Zg) obtained by taking approximately 1g (Xg) of the sample in a 5cm diameter aluminum cup, drying it at 110°C for 30 minutes, and then drying it again at 300°C for 30 minutes.

[0027] The above-mentioned perfluoropolymer can be made to have a melt flow rate within the above-mentioned range by adjusting its molecular weight.

[0028] (electrolyte) The aqueous dispersion of this disclosure contains an electrolyte. It is known that the inclusion of an electrolyte suppresses the decrease in pH of an aqueous dispersion containing a perfluoropolymer. In this disclosure, by adjusting the type and amount of such electrolyte to keep it within the viscosity change range described above, the paintability is improved, and the properties of the coating film are further improved.

[0029] The electrolyte is preferably at least one selected from the group consisting of ammonium sulfate, hydroxymonocarboxylic acid, hydroxydicarboxylic acid, tricarboxylic acid, and amino acids. Each of these has at least one carboxyl group in one molecule, and a total of two or more carboxyl groups, hydroxyl groups, and amino groups. The electrolyte is preferably free of fluorine atoms.

[0030] Examples of the above-mentioned hydroxy monocarboxylic acids include lactic acid, glyceric acid, glycolic acid, and hydroxybutyric acid. Examples of the above-mentioned hydroxydicarboxylic acids include malic acid and tartaric acid. Examples of the above-mentioned tricarboxylic acids include citric acid and isocitric acid. Examples of the above-mentioned amino acids include glycine.

[0031] To obtain an aqueous dispersion with minimal viscosity change, it is preferable to use ammonium sulfate as the electrolyte. It is presumed that using ammonium sulfate is particularly advantageous because the sulfate and ammonium ions maintain structural viscosity and suppress viscosity reduction.

[0032] The aqueous dispersion of this disclosure preferably contains the electrolyte in an amount of 0.001% by mass or more and less than 10% by mass relative to the perfluoropolymer. The lower limit is more preferably 0.005% by mass, and even more preferably 0.01% by mass. The upper limit is more preferably 7.0% by mass, and even more preferably 5.0% by mass. It is preferable to have an electrolyte content of less than 10% by mass in order to reduce separation during storage, and it is preferable to have an electrolyte content of 0.001% by mass or more in order to suppress pH changes during storage.

[0033] The aqueous dispersion of this disclosure does not exhibit a decrease in pH. The reason for the decrease in pH of conventional aqueous dispersions is not clear, but it is presumed that factors such as the evaporation of ammonia used for neutralization, the dissolution of carbon dioxide from the air, and the decomposition of polymerization initiator residues are influencing the process. In this disclosure, by adjusting the type and amount of electrolyte used, the viscosity change after standing at 40°C for 90 days can be reduced to 15% or less.

[0034] The aqueous dispersion of this disclosure may contain resin particles and other components of the electrolyte. Such components include surfactants. Preferably, the surfactant is a fluorine-free surfactant.

[0035] The fluorine-free surfactant mentioned above may be a nonionic surfactant or anionic surfactant, as long as it contains a compound that does not contain fluorine. Nonionic surfactants and anionic surfactants may also be used in combination, but a fluorine-free nonionic surfactant is preferred.

[0036] Examples of the fluorine-free anionic surfactants mentioned above include alkyl sulfonic acid and its salts, alkyl sulfate esters and their salts, alkyl sulfosuccinate esters and their salts, oxyalkylated sulfonic acid and its salts, etc. By using nonionic surfactants and anionic surfactants in combination as the fluorine-free surfactants mentioned above, the storage stability of the resulting aqueous dispersion can be efficiently improved and the viscosity increase associated with rising liquid temperature can be suppressed.

[0037] The above nonionic surfactant is not particularly limited as long as it contains a nonionic compound that does not contain fluorine (fluorine-free nonionic surfactant), and known ones can be used. Examples of the above fluorine-free nonionic surfactant include ether-type nonionic surfactants such as polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ether, and polyoxyethylene alkylene alkyl ether; polyoxyethylene derivatives such as ethylene oxide / propylene oxide block copolymer; ester-type nonionic surfactants such as sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, and polyoxyethylene fatty acid ester; and amine-type nonionic surfactants such as polyoxyethylene alkylamine and alkyl alkanolamide.

[0038] In the compounds constituting the nonionic surfactant described above, the hydrophobic group may be an alkylphenol group, a linear alkyl group, or a branched alkyl group, but it is preferable that the compound does not have an alkylphenol group in its structure, or does not have a benzene ring.

[0039] The aqueous dispersion of this disclosure preferably has a concentration of fluorine-free surfactant of 0.1 to 30% by mass, more preferably 0.2% by mass or more, and more preferably 10% by mass or less, based on the mass of the solids content of the perfluoropolymer. Lowering the concentration of fluorine-free surfactant is preferable from an economic standpoint, and setting it above a certain amount may improve the dispersion stability of the aqueous dispersion.

[0040] In this specification, the concentration (N) of the fluorine-free surfactant is calculated using the formula: N = [(YZ) / Z] × 100 (%) from the heating residue (Yg) obtained by placing approximately 1g of the sample in an aluminum cup with a diameter of 5cm and heating it at 110°C for 30 minutes, and then heating the obtained heating residue (Yg) at 300°C for 30 minutes and obtaining the heating residue (Zg).

[0041] The aqueous dispersion of this disclosure can be produced, for example, by a production method characterized by comprising the steps of: (1) emulsion polymerization of a fluoromonomer in an aqueous medium; (2) adding a fluorine-free surfactant to the aqueous dispersion obtained in step (1); (3) adding an electrolyte to the aqueous dispersion obtained in step (2); and (4) adjusting the pH of the aqueous dispersion to 8 to 10. The above production method may also include a step of concentrating the aqueous dispersion. It is also preferable that step (2) is a step of concentrating the aqueous dispersion.

[0042] It is preferable to add 0.001% by mass or more and less than 10% by mass of the electrolyte to the perfluoropolymer in the aqueous dispersion obtained in step (2), and more preferably 0.005 to 7% by mass.

[0043] After concentration, a fluorine-free surfactant may be added to the aqueous dispersion, or the concentration of the perfluoropolymer may be adjusted. The pH of the aqueous dispersion can be adjusted by adding alkaline compounds such as ammonia, sodium hydroxide, or calcium hydroxide.

[0044] The aqueous dispersions of this disclosure can be used as is or with the addition of various additives to be processed into coatings, cast films, impregnated bodies, etc. They may also be used diluted or mixed with other dispersions or compounds as needed. A paint containing the above aqueous dispersion is also one of the disclosures.

[0045] Applications of the aqueous dispersions of this disclosure include, for example, kitchen and cooking utensils such as frying pans, pressure cookers, pots, grill pans, rice cookers, hot plates, bread molds, knives, gas stoves, electric kettles, molds, range hoods, oven linings, and ice trays; food industry parts such as kneading rolls, rolling rolls, conveyors, hoppers, food processing machines, and packaging machines; industrial products such as rolls for office automation (OA), OA belts, OA separation claws, papermaking rolls, and calender rolls for film manufacturing; and polystyrene foam molding. Examples of applications include molds and castings for various uses; release plates for molds used in the manufacture of plywood and decorative panels; industrial containers (especially for the semiconductor industry); medical guide wires, catheters, sheaths, sheath introducers, etc.; tools such as saws, files, and scissors; electric wires, pipes, valves, bearings, ship hulls, high-frequency printed circuit boards, conveyor belts, knives, metal foils, snow shovels, plows, chutes, and covering materials for iron bottom plates; fibrous substrates, woven and nonwoven fabrics, fuel sealing valves for automobiles, bearings, sliding members for cameras, watches, etc. The fibrous substrate is not particularly limited and can be processed into impregnated materials such as glass fibers, carbon fibers, and aramid fibers (Kevlar® fibers, etc.). Furthermore, it can also be used as a binder for active materials in batteries. The processing of the aqueous dispersion can be carried out by conventionally known methods.

[0046] A coating obtained using the paint described above, and a coated article, are also part of this disclosure.

[0047] While embodiments of this disclosure have been described above, it will be understood that a variety of modifications to the form and details are possible without departing from the spirit and scope of the claims. [Examples]

[0048] The present disclosure will be described below in detail based on the following examples. In the following examples, unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass," respectively. The present disclosure is not limited to the contents of the following examples.

[0049] Example 1 (FEP aqueous dispersion 1) An aqueous dispersion containing tetrafluoroethylene / hexafluoropropylene copolymer (FEP) (solids content 23% by mass) was treated with polyoxyethylene alkyl ether (HLB=13) as a nonionic surfactant at room temperature, in an amount equivalent to 21% by mass relative to the FEP. When the mixture was allowed to stand at 65°C for 14 hours, it separated into two phases: a phase substantially free of FEP (supernatant phase) and a concentrated phase. The pH of the concentrated phase was 2.0. The supernatant phase was removed, and the concentrated phase was recovered. The resulting aqueous dispersion had an FEP concentration of 62% by mass and a nonionic surfactant amount equivalent to 6.0% by mass relative to the FEP. To the obtained aqueous dispersion, an amount of ammonium sulfate equivalent to 0.100% by mass relative to FEP was added and stirred to obtain a homogeneous solution. Ammonia water (28% by mass) and citric acid were added to adjust the pH to 4.0. The amount of ammonium sulfate added is as shown in Table 7. The composition of Example 1 is shown in Table 1.

[0050] [Table 1]

[0051] Examples 2-5 were prepared in the same manner as in Example 1, except that the amount of ammonium sulfate was changed as shown in Table 7.

[0052] Examples 6-7 were prepared in the same manner as in Example 1, except that the tetrafluoroethylene / hexafluoropropylene copolymer (FEP) having the MFRs shown in Table 7 was changed.

[0053] Example 11 (FEP aqueous dispersion 2) Polyoxyethylene alkyl ether (HLB=13) was added to the aqueous dispersion obtained in Example 11 to adjust the concentration of FEP to 53.5% by mass and the nonionic surfactant to 7.5% by mass of FEP. Then, sodium dodecyl sulfate equivalent to 0.5% by mass of FEP was added, and aqueous ammonia (28% by mass) was added to adjust the pH to 8.8. The composition of Example 11 is shown in Table 2, and the evaluation results are shown in Table 7.

[0054] [Table 2]

[0055] Examples 8 and 9 (FEP aqueous dispersions 3 and 4) A film-forming agent and other components were added to the aqueous dispersion prepared in Example 1 and stirred to produce the compositions shown in the table. The composition of Example 8 is shown in Table 3, and the composition of Example 9 is shown in Table 4.

[0056] [Table 3]

[0057] [Table 4]

[0058] Example 10 (Aqueous dispersion of TFE / HFP / PAVE copolymer) An aqueous dispersion was prepared in the same manner as in Example 1, except that a tetrafluoroethylene / hexafluoropropylene / perfluoropropyl vinyl ether copolymer was used instead of FEP. The composition of Example 10 is shown in Table 5.

[0059] [Table 5]

[0060] Example 12 (PFA aqueous dispersion) An aqueous dispersion was prepared in the same manner as in Example 1, except that a tetrafluoroethylene / perfluoropropyl vinyl ether copolymer was used instead of FEP, and ethylene glycol and the like were added. The amount of ammonium sulfate shown in Table 8 was added. The composition of Example 12 is shown in Table 6.

[0061] [Table 6]

[0062] Examples 13-16 were prepared in the same manner as Example 12, except that the amount of ammonium sulfate was changed as shown in Table 8.

[0063] Examples 17-18 were prepared in the same manner as Example 12, except that the tetrafluoroethylene / perfluoropropyl vinyl ether copolymer (PFA) having the MFRs shown in Table 8 was used instead.

[0064] (Evaluation method) (Melt flow rate) For each example, a melt indexer (manufactured by Toyo Seiki) equipped with a corrosion-resistant cylinder, die, and piston conforming to ASTM D1238-95 was used to measure the perfluoropolymer contained in the aqueous dispersion used as the raw material. 5 g of the sample was filled into a cylinder maintained at 372°C ± 1°C and held for 5 minutes. Then, under a load of 5 kg (piston and weight), it was extruded through the die orifice, and the extrusion rate of the molten material (g / 10 min) was determined as the MFR.

[0065] (viscosity) A Type B rotational viscometer (manufactured by Toki Sangyo Co., Ltd.) was used to measure viscosity at 25°C under the following conditions: rotor No. 2, rotation speed 60 rpm, and measurement time 120 seconds. Two measurements were taken, and the average of the two viscosity measurements was used as the measured value.

[0066] (Viscosity after 90 days) The aqueous dispersion was left to stand at 40°C for 90 days. After 90 days, the aqueous dispersion was removed, the liquid temperature was lowered to 25°C, and the viscosity was measured under the same conditions as above.

[0067] (pH) Using a glass electrode (manufactured by Horiba, Ltd.), the pH at 25°C was measured in accordance with JIS K6893.

[0068] (Solid content) Approximately 1 g (X g) of the sample was placed in a 5 cm diameter aluminum cup, dried at 110°C for 30 minutes, and then dried again at 300°C for 30 minutes. Based on the residual amount (Z g), P was calculated using the formula: P = Z / X × 100 (%).

[0069] (Painability) After degreasing the surface of a 1.5mm thick, 5 x 20cm aluminum plate (A-1050) with acetone, the aluminum plate was fixed vertically and spray-coated with a gravity-feed spray gun W-101 (product name, manufactured by Anest Iwata Corporation, nozzle diameter 1.0mm) at a spraying pressure of 0.2MPa to achieve a dry film thickness of 10-15μm. If a smooth coating surface was obtained without paint dripping, the paintability was considered good.

[0070] (Appearance of the coating) The coating film obtained by the above painting method was dried at 80-100°C for 15 minutes, baked at 380°C for 20 minutes, and then allowed to cool naturally to produce a coating film, thereby obtaining a coating panel for evaluation. A coating film was considered to have a good appearance if it was smooth and free from abnormalities such as cracks, bumps, and surface roughness.

[0071] (Pencil hardness) The surface of an aluminum plate (A-1050) with a thickness of 1.5 mm and dimensions of 5 x 10 cm was degreased with acetone, and then sandblasted to roughen the surface, with a surface roughness Ra value of 2.5 to 3.5 μm measured in accordance with JIS B 1982. As a primer, Daikin Industries, Ltd.'s Polyflon PTFE EK-1909S21R was spray-painted under the above conditions, dried at 80 to 100°C for 15 minutes, and then cooled to room temperature. An aqueous dispersion was spray-painted onto the resulting coating film, dried at 80 to 100°C for 15 minutes, and then baked at 380°C for 20 minutes. After cooling, the resulting coated plate was evaluated at 25°C according to the method described in JIS K5600.

[0072] Examples 1-11 and Comparative Examples 1-5 are shown in Table 7, and Examples 12-18 and Comparative Examples 6-10 are shown in Table 8.

[0073] [Table 7]

[0074] [Table 8]

[0075] The results in Tables 7 and 8 clearly show that the aqueous dispersions disclosed herein have excellent effects in terms of coating appearance and hardness. [Industrial applicability]

[0076] The aqueous dispersion of this disclosure exhibits minimal viscosity reduction during storage, making it suitable for use as a paint, impregnation material, and the like.

Claims

1. an aqueous dispersion containing a perfluoropolymer, The perfluoropolymer has a melt flow rate of 1 to 50 g / 10 min. An aqueous dispersion characterized by a viscosity change of 15% or less after standing at 40°C for 90 days.

2. The aqueous dispersion according to claim 1, comprising a perfluoropolymer, wherein the electrolyte is contained in an amount of 0.001% by mass or more and less than 10% by mass relative to the perfluoropolymer.

3. The aqueous dispersion according to claim 2, wherein the electrolyte is at least one selected from the group consisting of ammonium sulfate, hydroxymonocarboxylic acid, hydroxydicarboxylic acid, tricarboxylic acid, and amino acids.

4. The aqueous dispersion according to claim 3, wherein the electrolyte is ammonium sulfate.

5. The aqueous dispersion according to any one of claims 1 to 4, wherein the perfluoropolymer is at least one selected from the group consisting of tetrafluoroethylene / hexafluoropropylene copolymer, tetrafluoroethylene / hexafluoropropylene / perfluoro(alkyl vinyl ether) copolymer, and tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer.

6. The perfluoropolymer contains 0.005 to 9% by mass of ammonium sulfate. The perfluoropolymer is at least one selected from the group consisting of tetrafluoroethylene / hexafluoropropylene copolymer, tetrafluoroethylene / hexafluoropropylene / perfluoro(alkyl vinyl ether) copolymer, and tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer. The aqueous dispersion according to claim 3 or 4.

7. A paint characterized by containing an aqueous dispersion according to any one of claims 1 to 4.

8. A coating film characterized by being obtained by applying the paint described in claim 7.

9. A painted article characterized by having a coating film obtained by applying the paint described in claim 7.

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