Method for producing an aqueous dispersion of fluoropolymer, method for producing a fluoropolymer, and method for reducing the concentration of a fluorine-containing emulsifier in an aqueous dispersion of fluoropolymer containing a fluorine-containing emulsifier.

Abstract

To propose a method for effectively reducing the amount of fluorine-containing emulsifiers that may remain in aqueous emulsion polymerization solutions of fluoropolymers, including fluoroelastomers and perfluoroelastomers. [Solution] The following steps: A process of preconditioning a strongly basic anion exchange resin using an aqueous solution of polyoxyethylene alkyl ether carboxylic acid. A step of obtaining a fluoropolymer aqueous dispersion by passing a fluoropolymer aqueous dispersion containing a fluorine-containing emulsifier through the pre-conditioned strongly basic anion exchange resin, A method for producing an aqueous dispersion of a fluoropolymer containing at least [a certain substance] is provided. Furthermore, a method for producing a fluoropolymer is provided for obtaining a fluoropolymer from the obtained aqueous dispersion of a fluoropolymer.

Description

Technical Field

[0001] The present invention relates to a method for producing an aqueous dispersion of a fluoropolymer. Further, the present invention relates to a method for producing a fluoropolymer. Further, the present invention relates to a method for reducing the concentration of a fluorinated emulsifier in an aqueous dispersion of a fluoropolymer containing a fluorinated emulsifier.

Background Art

[0002] Fluoroelastomers (FKM) and perfluoroelastomers (FFKM) are known to have extremely excellent heat resistance, chemical resistance, weather resistance, low friction, non-stickiness, and plasma resistance at the same level as fluoropolymers. Fluoropolymers (fluorinated polymers) including FKM and FFKM are usually produced by emulsion polymerization of fluoromonomers using a fluorinated compound as an emulsifier (fluorinated emulsifier). However, in the chemical substance regulation by the European Chemicals Agency (ECHA), or the comprehensive registration, evaluation, authorization, and restriction system for chemical substances in Europe known as the REACH regulation, it is required to reduce the fluorinated emulsifier contained in fluoropolymers.

[0003] As a method for reducing the amount of the fluorinated emulsifier contained in an aqueous dispersion of a fluoropolymer, a method has been proposed in which an aqueous dispersion of a fluoropolymer is brought into contact with a basic anion exchange resin to adsorb the fluorinated emulsifier to the basic anion exchange resin. For example, it has been proposed to add a nonionic surfactant to an aqueous emulsion polymerization liquid of a fluoropolymer to produce an aqueous dispersion of a fluoropolymer, and then bring the aqueous dispersion of the fluoropolymer into contact with a basic anion exchange resin to produce an aqueous dispersion of a fluoropolymer having a low content of the fluorinated emulsifier (Patent Document 1, Patent Document 2).

[0004] Patent Document 1 discloses the use of Triton X100, TergitolTMN100X, Antarox863, Rodasurf870, and GenapolX080 as nonionic surfactants, and Patent Document 2 discloses the use of TergitolTMN-6, TergitolTMN-10, and Tergitol100X as nonionic surfactants. However, when these nonionic surfactants are added to an aqueous emulsion polymerization solution of a fluoropolymer, the fluoropolymer is stabilized in the aqueous dispersion, making it difficult to coagulate using conventional methods such as salts or acids, thus making it difficult to obtain a fluoropolymer as a product.

[0005] Patent Document 3 is the only reported example in which a fluoropolymer was obtained by adding a nonionic surfactant to an aqueous emulsion polymerization solution of a fluoropolymer, then contacting it with a basic anion exchange resin, and finally coagulating it. However, this example proposes the use of an organic solvent and a forced stirrer during coagulation, which makes it impractical from the standpoint of commercializing fluoropolymers.

[0006] On the other hand, fluoroelastomers are known that have nitrile groups in the polymer molecular chain, which are substituents for crosslinking in subsequent processes. However, when an aqueous emulsion polymerization solution of such a fluoroelastomer is brought into contact with an anion exchange resin preconditioned with potassium hydroxide (strongly basic), the nitrile moieties in the fluoroelastomer molecular chain decompose because the inside of the anion exchange resin column becomes basic. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 4494932 [Patent Document 2] Patent No. 5364576 [Patent Document 3] International Publication No. 2008 / 134138 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The present invention aims to propose a method for effectively reducing the amount of fluorine-containing emulsifier that may remain in aqueous emulsion polymerization solutions of fluoropolymers containing FKM and FFKM. [Means for solving the problem]

[0009] One aspect of the present invention involves the following steps: A process of preconditioning a strongly basic anion exchange resin using an aqueous solution of polyoxyethylene alkyl ether carboxylic acid. A step of obtaining a fluoropolymer aqueous dispersion by passing a fluoropolymer aqueous dispersion containing a fluorine-containing emulsifier through the pre-conditioned strongly basic anion exchange resin, This is a method for producing an aqueous dispersion of a fluoropolymer containing at least [a specific ingredient].

[0010] In one embodiment, it is preferable that the polyoxyethylene alkyl ether carboxylic acid is selected from the group consisting of polyoxyethylene octyl ether acetate, polyoxyethylene heptyl ether acetate, polyoxyethylene hexyl ether acetate, and mixtures of two or more of these.

[0011] A second aspect of the present invention involves the following steps: A process of preconditioning a strongly basic anion exchange resin using an aqueous solution of polyoxyethylene alkyl ether carboxylic acid. A step of obtaining a fluoropolymer aqueous dispersion by passing a fluoropolymer aqueous dispersion containing a fluorine-containing emulsifier through the pre-conditioned strongly basic anion exchange resin, The process of evaporating the water from the aqueous dispersion of the fluoropolymer to obtain the fluoropolymer. This is a method for producing fluoropolymers, which include [the specified element].

[0012] In the second embodiment, it is preferable that the polyoxyethylene alkyl ether carboxylic acid is selected from the group consisting of polyoxyethylene octyl ether acetate, polyoxyethylene heptyl ether acetate, polyoxyethylene hexyl ether acetate, and mixtures of two or more of these.

[0013] A third aspect of the present invention involves the following steps: A process of preconditioning a strongly basic anion exchange resin using an aqueous solution of polyoxyethylene alkyl ether carboxylic acid. A step of passing a fluoropolymer aqueous dispersion containing a fluorine-containing emulsifier through the pre-conditioned strongly basic anion exchange resin, This is a method for reducing the concentration of a fluorine-containing emulsifier in an aqueous dispersion of a fluoropolymer containing a fluorine-containing emulsifier, which contains at least [specific element].

[0014] In the third embodiment, it is preferable that the polyoxyethylene alkyl ether carboxylic acid is selected from the group consisting of polyoxyethylene octyl ether acetate, polyoxyethylene heptyl ether acetate, polyoxyethylene hexyl ether acetate, and mixtures of two or more of these. [Effects of the Invention]

[0015] The method of the present invention removes fluorine-containing emulsifiers contained in aqueous fluoropolymer dispersions without hindering the coagulation of fluoropolymers in the aqueous fluoropolymer dispersions, thus enabling the provision of high-quality fluoropolymers without impeding the commercialization of fluoropolymers. When removing fluorine-containing emulsifiers from aqueous dispersions of fluoroelastomers containing polymerizable substituents such as nitrile groups or substituents that act as crosslinking points in the molecular chains using the method of the present invention, the polymerizable substituents or substituents that act as crosslinking points in the fluoroelastomer molecular chains do not decompose, thus enabling the efficient provision of high-quality fluoroelastomers with the intended structure. [Modes for carrying out the invention]

[0016] Embodiments of the present invention will be explained in more detail, but the present invention is not limited only to the following embodiments.

[0017] One embodiment includes the following steps: A step of preconditioning a strongly basic anion exchange resin using an aqueous solution of polyoxyethylene alkyl ether carboxylic acid; A step of passing a fluoropolymer aqueous dispersion containing a fluorinated emulsifier through the preconditioned strongly basic anion exchange resin to obtain a fluoropolymer aqueous dispersion; A method for producing a fluoropolymer aqueous dispersion that includes at least these steps.

[0018] In one embodiment, a fluoropolymer, also called a fluorinated polymer, etc., has been conventionally used in a wide range of applications such as the chemical industry, the electric and electronic fields, the automotive and aerospace industries, household goods, the medical and bio fields, etc. General fluoropolymers include thermoplastic or thermosetting fluororesins such as polytetrafluoroethylene (PTFE), tetrafluoroethylene - hexafluoropropene copolymer (FEP), tetrafluoroethylene - ethylene copolymer (ETFE), etc., and fluorine elastomers (FKM), perfluoroelastomers (FFKM), etc. having substituents capable of polymerization or crosslinking in the polymer molecular chain. In one embodiment, the term fluoropolymer is intended to include all polymers containing fluorine atoms in the polymer molecular chain.

[0019] A fluoropolymer is obtained by polymerizing a fluoromonomer. Here, a fluoromonomer is a compound having at least one polymerizable substituent in the molecule, and refers to a partially fluorinated or perfluorinated compound. In this specification, a fluoromonomer may be referred to as a fluorinated monomer, and these may be considered synonymous. Examples of fluoromonomers include tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE), hexafluoropropene (HFP), perfluoro(2-phenoxypropyl) vinyl ether (PVE), vinylidene fluoride (VDF), trifluoroethylene (TrFE), perfluoroalkyl vinyl ethers such as perfluoromethyl vinyl ether, and perfluoroalkoxyalkyl vinyl ethers (PAAVE) such as perfluoromethyl-oligo(isopropoxy) vinyl ether.

[0020] A fluoropolymer aqueous dispersion produced according to one embodiment is an aqueous liquid in which the above-mentioned fluoropolymer is emulsified or dispersed. When referring to a fluoropolymer aqueous dispersion in this specification, it shall also include an aqueous emulsion of the fluoropolymer. That is, when referring to a fluoropolymer aqueous dispersion in this specification, it shall also include a fluoropolymer aqueous emulsion polymerization liquid obtained by aqueous emulsion polymerization of a fluoromonomer.

[0021] One embodiment is a method for producing an aqueous fluoropolymer dispersion by removing a fluorine-containing emulsifier from an aqueous fluoropolymer dispersion containing a fluorine-containing emulsifier. Here, a fluorine-containing emulsifier refers to any emulsifier that has a fluorine atom in its molecule. When obtaining an aqueous fluoropolymer dispersion by aqueous emulsion polymerization of fluoromonomers, it is necessary to first emulsify the fluoromonomers in water, and therefore an emulsifier must be added. Conventionally, fluorine-containing emulsifiers have been used in this process. Examples of fluorine-containing emulsifiers include perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), fluorine telomer alcohols (FTOHs), and PFOA substitute compounds such as hexafluoropropylene oxide dimer carboxylic acid (HFPO-DA), hexafluoropropylene oxide trimer carboxylic acid (HFPO-TA), or 3H-perfluoro-3-(3-methoxypropyl)-propanoic acid (ADONA).

[0022] As described above, generally, the polymerization of fluoromonomers is carried out by emulsion polymerization of fluoromonomers in an aqueous dispersion, so the resulting aqueous fluoropolymer dispersion contains a fluorine-containing emulsifier. However, in recent years, many countries have imposed regulations on the use of fluorine-containing compounds such as PFOA and PFOS, and it is required to reduce the amount of these compounds contained in products as much as possible. For this reason, one embodiment attempts to remove the fluorine-containing emulsifier from the aqueous fluoropolymer dispersion by adsorbing it onto a strongly basic anion exchange resin. In one embodiment, first, a step is performed to precondition the strongly basic anion exchange resin using an aqueous solution of polyoxyethylene alkyl ether carboxylic acid.

[0023] Anion exchange resins are ion exchange resins that can exchange anions in a substance. Anion exchange resins contain a fixed ion with a positive charge bonded to a negatively charged ion, and these negative ions exchange with other anions. Anion exchange resins include strongly basic anion exchange resins, consisting of strongly basic anion exchange resin type I or strongly basic anion exchange resin type II, and weakly basic anion exchange resins. In one embodiment, strongly basic anion exchange resins are preferably used. As strongly basic anion exchange resins, those made of resins such as styrene-divinylbenzene copolymers, acrylics, and polyvinylbenzylamines can be used. As strongly basic anion exchange resins, commercially available strongly basic anion exchange resins such as the DIANON® series from Mitsubishi Chemical Corporation, AMBERLITE® IRA400JCl, IRA402BL CL, IRA900J CL, etc. from DuPont, DOWEX 1X8 from Dow Chemical, and LEWATIT MP 500 from Lanxess are available.

[0024] In one embodiment, preconditioning of a strongly basic anion exchange resin refers to the treatment performed before using the strongly basic anion exchange resin. Specifically, preconditioning includes initial adjustment and activation treatment performed before using the strongly basic anion exchange resin. In one embodiment, first, the strongly basic anion exchange resin is preconditioned using an aqueous solution of polyoxyethylene alkyl ether carboxylic acid. This step includes washing the strongly basic anion exchange resin with water to remove any fine particles, impurities, suspended matter, etc. that may be contained in the strongly basic anion exchange resin. If necessary, the strongly basic anion exchange resin is washed and then contacted with an aqueous solution of polyoxyethylene alkyl ether carboxylic acid to activate it. If necessary, the strongly basic anion exchange resin may be washed again with water to stabilize the pH of the activated resin, and this subsequent washing is also included in the preconditioning step.

[0025] It is preferable to use a polyoxyethylene alkyl ether carboxylic acid selected from the group consisting of polyoxyethylene octyl ether acetate, polyoxyethylene heptyl ether acetate, polyoxyethylene hexyl ether acetate, and mixtures of two or more of these. Commercially available products such as Akipo LS-F4 (Kao Corporation) and Akipo LS-F2 (Kao Corporation) can be used as these polyoxyethylene alkyl ether carboxylic acids.

[0026] Next, a fluoropolymer aqueous dispersion containing a fluorine-containing emulsifier is brought into contact with a strongly basic anion exchange resin. As described above, fluoropolymers are produced by emulsion polymerization in an aqueous dispersion of fluoromonomers, but fluorine-containing emulsifiers such as PFOA and PFOS are used during the emulsification of fluoromonomers in water. Therefore, fluorine-containing emulsifiers remain in the fluoropolymer aqueous dispersion obtained by emulsion polymerization of the aqueous dispersion of fluoromonomers. In order to commercialize the fluoropolymer aqueous dispersion and fluoropolymer, it is necessary to remove the fluorine-containing emulsifier as much as possible. Therefore, the fluoropolymer aqueous dispersion containing a fluorine-containing emulsifier is brought into contact with a strongly basic anion exchange resin to adsorb the fluorine-containing emulsifier onto the ion exchange resin and remove it from the fluoropolymer aqueous dispersion.

[0027] Prior to contacting the aqueous fluoropolymer dispersion containing a fluorine-containing emulsifier with a strongly basic anion exchange resin, polyoxyethylene alkyl ether carboxylic acid may be added to the aqueous fluoropolymer dispersion containing the fluorine-containing emulsifier. The polyoxyethylene alkyl ether carboxylic acid used here is preferably selected from the group consisting of polyoxyethylene octyl ether acetate, polyoxyethylene heptyl ether acetate, polyoxyethylene hexyl ether acetate, and mixtures of two or more of these. Commercially available products such as Akipo LS-F4 (Kao Corporation) and Akipo LS-F2 (Kao Corporation) can be used as these polyoxyethylene alkyl ether carboxylic acids. Adding polyoxyethylene alkyl ether carboxylic acid to the aqueous fluoropolymer dispersion containing a fluorine-containing emulsifier stabilizes the aqueous fluoropolymer dispersion containing the fluorine-containing emulsifier. However, while conventionally used nonionic surfactants such as Triton X100 and Tergitol TMN-6 stabilize the aqueous fluoropolymer dispersion to such an extent that it makes coagulation of the fluoropolymer difficult, it was found that when polyoxyethylene alkyl ether carboxylic acid is added to the aqueous fluoropolymer dispersion, the dispersion does not stabilize to such an extent that coagulation of the fluoropolymer becomes difficult.

[0028] Thus, after appropriately stabilizing the aqueous fluoropolymer dispersion containing a fluorine-containing emulsifier as needed, the aqueous fluoropolymer dispersion containing the fluorine-containing emulsifier (and, in some cases, polyoxyethylene alkyl ether carboxylic acid) is passed through a pre-conditioned strongly basic anion exchange resin to obtain an aqueous fluoropolymer dispersion. In this step, the fluorine-containing emulsifier is adsorbed by the strongly basic anion exchange resin, so that an aqueous fluoropolymer dispersion with a reduced fluorine-containing emulsifier content, preferably one containing almost no fluorine-containing emulsifier, can be obtained. The strongly basic anion exchange resin pre-conditioned with an aqueous solution of polyoxyethylene alkyl ether carboxylic acid does not decompose polymerization substituents such as FKM or FFKM or substituents that act as crosslinking points (e.g., nitrile groups) in the aqueous fluoropolymer dispersion. Therefore, it is possible to effectively remove the fluorine-containing emulsifier from the aqueous fluoropolymer dispersion containing the fluorine-containing emulsifier and obtain an aqueous fluoropolymer dispersion while maintaining the intended structure.

[0029] A second embodiment of the present invention involves the following steps: A process of preconditioning a strongly basic anion exchange resin using an aqueous solution of polyoxyethylene alkyl ether carboxylic acid. A step of obtaining a fluoropolymer aqueous dispersion by passing a fluoropolymer aqueous dispersion containing a fluorine-containing emulsifier through the pre-conditioned strongly basic anion exchange resin, The process of evaporating the water from the aqueous dispersion of the fluoropolymer to obtain the fluoropolymer. This is a method for producing fluoropolymers, which include [the specified element].

[0030] The second embodiment is a method for obtaining a fluoropolymer by first removing the fluorine-containing emulsifier from an aqueous fluoropolymer dispersion containing the fluorine-containing emulsifier according to the first embodiment of this specification, thereby obtaining an aqueous fluoropolymer dispersion that is substantially free of the fluorine-containing emulsifier, and then further evaporating the water from the aqueous fluoropolymer dispersion to obtain the fluoropolymer. The evaporation of the water from the aqueous fluoropolymer dispersion can be carried out by conventional methods. For example, the water can be evaporated by drying in a dryer, evaporation, freeze-drying, etc., to obtain the fluoropolymer. The resulting fluoropolymer is substantially free of the fluorine-containing emulsifier, and the fluoropolymer maintains its intended structure.

[0031] The third embodiment involves the following steps: A process of preconditioning a strongly basic anion exchange resin using an aqueous solution of polyoxyethylene alkyl ether carboxylic acid. A step of passing a fluoropolymer aqueous dispersion containing a fluorine-containing emulsifier through the pre-conditioned strongly basic anion exchange resin, This is a method for reducing the concentration of a fluorine-containing emulsifier in an aqueous dispersion of a fluoropolymer containing a fluorine-containing emulsifier, which contains at least [specific element].

[0032] The third embodiment is a method for reducing the concentration of a fluorine-containing emulsifier in an aqueous dispersion of a fluoropolymer containing a fluorine-containing emulsifier by performing the same steps as in the first embodiment of this specification. In this specification, "reducing the concentration of the fluorine-containing emulsifier" means making the concentration of the fluorine-containing emulsifier smaller, and also includes making the concentration of the fluorine-containing emulsifier 0% by mass, that is, completely removing the fluorine-containing emulsifier. Furthermore, "removing the fluorine-containing emulsifier" generally means making the concentration of the fluorine-containing emulsifier 0% by mass, but also includes making the concentration of the fluorine-containing emulsifier approximately 0% by mass, that is, not completely 0% by mass, but at a concentration that is almost undetectable.

[0033] According to the three embodiments, the concentration of the fluorine-containing emulsifier in an aqueous dispersion of fluoropolymer containing the fluorine-containing emulsifier can be reduced, and from the aqueous dispersion of fluoropolymer with reduced fluorine-containing emulsifier concentration, a fluoropolymer can be obtained that has reduced fluorine-containing emulsifier concentration while maintaining the originally intended structure. [Examples]

[0034] The embodiments of the present invention will be described in detail below. The present invention is not limited to the following embodiments.

[0035] [Example 1] An aqueous perfluoroelastomer dispersion was obtained by emulsion polymerization. In a 500-liter autoclave, 6.1 kg of tetrafluoroethylene (TFE), 5.7 kg of perfluoromethyl vinyl ether (FMVE), 431.6 g of perfluorocyanopentyl vinyl ether (CPeVE), 3870 g of hexafluoropropylene oxide trimer acid (HFPO-TA) (pre-neutralized with 9700 g of 1.4% aqueous ammonia), 3480 g of potassium dihydrogen phosphate, and 243.8 kg of deionized water were added, and the temperature was raised to 60°C. 623 g of ammonium peroxodisulfate, a polymerization initiator, was added, and polymerization was carried out under a pressure of 0.80 MPa. 39.8 kg of TFE, 39.8 kg of FMVE, and 2954.6 g of CPeVE were added in stages while maintaining a pressure of 0.80 MPa in the autoclave. After polymerization, the mixture was aged for 1 hour to obtain an aqueous perfluoroelastomer dispersion. To 1050 g of the obtained aqueous dispersion, 210 g of Akipo LF-F2 (polyoxyethylene octyl ether acetate, Kao Corporation) and 450 g of water were added to obtain an aqueous dispersion of perfluoroelastomer.

[0036] The strongly basic anion exchange resin AmberliteIRA900OH (DuPont) was preconditioned with a 20 wt% Akipo LF-F2 aqueous solution at a water flow rate (BV) of 6 and a space velocity (SV) of 5. Then, it was extruded with water at a BV of 1.5 and an SV of 4, and further washed with water at a BV of 10 and an SV of 20.

[0037] The aqueous dispersion of the previously obtained perfluoroelastomer containing polyoxyethylene alkyl ether carboxylic acid was passed through the strongly basic anion exchange resin prepared in this manner using BV5 and SV1. NMR measurements were performed on the liquids before and after passage, using sodium hexafluorophosphate as the internal standard. The concentrations of HFPO-TA were 7181 ppm and below the limit of quantification (10 ppm), respectively. Furthermore, the pH of the liquids before and after passage remained below 7 in both cases.

[0038] Next, the aqueous dispersion of perfluoroelastomer obtained after the liquid was passed through was dried overnight at 120°C to obtain a white solid (polymer).

[0039] [Reference example] 0.316g each of Akipo RO50VG (polyoxyethylene oleyl ether acetate, Kao Corporation), Akipo RLM-45 (polyoxyethylene lauryl ether acetate, Kao Corporation), Akipo RLM-100 (polyoxyethylene (10) lauryl ether acetate, Kao Corporation), Akipo LS-O90 (polyoxyethylene oleyl ether acetate, Kao Corporation), Akipo LS-F4 (polyoxyethylene hexyl / octyl ether acetate, Kao Corporation), and Akipo LS-F2 (polyoxyethylene octyl ether acetate, Kao Corporation) were prepared and dissolved in 6g of water. 14 g of an aqueous dispersion of perfluoroelastomer, obtained in the same manner as in Example 1, was slowly added dropwise to each aqueous solution.

[0040] Perfluoroelastomers did not precipitate in aqueous solutions of Akipo LS-F4 and Akipo LS-F2. On the other hand, in aqueous solutions of Akipo RO50VG, Akipo RLM-45, Akipo RLM-100, and Akipo LS-O90, a white solid, believed to be a perfluoroelastomer, precipitated. In other words, it is thought that if these aqueous solutions are used as preconditioning for a strongly basic anion exchange resin, the fluoropolymer will solidify in the strongly basic anion exchange resin column, making it impossible to obtain an aqueous dispersion of the fluoropolymer.

[0041] The method of the present invention made it possible to reduce the amount of fluorine-containing emulsifier in an aqueous dispersion of a fluoropolymer containing a fluorine-containing emulsifier. Furthermore, the method of the present invention made it possible to obtain a fluoropolymer that contains almost no fluorine-containing emulsifier.

Claims

1. The following steps: A step of preconditioning a strongly basic anion exchange resin using an aqueous solution of a polyoxyethylene alkyl ether carboxylic acid selected from the group consisting of polyoxyethylene octyl ether acetate, polyoxyethylene hexyl ether acetate, and mixtures thereof. A step to obtain an aqueous dispersion of a fluoropolymer obtained by polymerizing a fluoromonomer mixture containing a fluorine-containing emulsifier and one or more fluoromonomers selected from the group consisting of perfluoro(2-phenoxypropyl) vinyl ether, perfluoroalkyl vinyl ether, perfluorocyanopentyl vinyl ether, and perfluoroalkoxyalkyl vinyl ether, by passing the aqueous dispersion of the fluoropolymer through the pre-conditioned strongly basic anion exchange resin. A method for producing an aqueous dispersion of a fluoropolymer containing at least [a certain substance].

2. The following steps: A step of preconditioning a strongly basic anion exchange resin using an aqueous solution of a polyoxyethylene alkyl ether carboxylic acid selected from the group consisting of polyoxyethylene octyl ether acetate, polyoxyethylene hexyl ether acetate, and mixtures thereof. A step to obtain an aqueous dispersion of a fluoropolymer obtained by polymerizing a fluoromonomer mixture containing a fluorine-containing emulsifier and one or more fluoromonomers selected from the group consisting of perfluoro(2-phenoxypropyl) vinyl ether, perfluoroalkyl vinyl ether, perfluorocyanopentyl vinyl ether, and perfluoroalkoxyalkyl vinyl ether, by passing the aqueous dispersion of the fluoropolymer through the pre-conditioned strongly basic anion exchange resin. The process of evaporating the water from the aqueous dispersion of the fluoropolymer to obtain the fluoropolymer. A method for producing fluoropolymers, including the following:

3. The following steps: A step of preconditioning a strongly basic anion exchange resin using an aqueous solution of a polyoxyethylene alkyl ether carboxylic acid selected from the group consisting of polyoxyethylene octyl ether acetate, polyoxyethylene hexyl ether acetate, and mixtures thereof. A step of passing an aqueous dispersion of a fluoropolymer obtained by polymerizing a fluoromonomer mixture containing a fluorine-containing emulsifier and one or more fluoromonomers selected from the group consisting of perfluoro(2-phenoxypropyl) vinyl ether, perfluoroalkyl vinyl ether, perfluorocyanopentyl vinyl ether, and perfluoroalkoxyalkyl vinyl ether through the pre-conditioned strongly basic anion exchange resin. A method for reducing the concentration of a fluorine-containing emulsifier in an aqueous dispersion of a fluoropolymer containing at least the fluorine-containing emulsifier.