Aqueous dispersions of fluoroolefins and aqueous dispersions of fluoroolefin copolymers, and methods for producing the same.

Abstract

To provide a water dispersion of fluoroolefin and the like by a copolymer with high conversion rate and high productivity from fluoroolefin as a raw material monomer without corrosion of a container.SOLUTION: A water dispersion includes: fluoroolefin (a) represented by a general formula (1); a surface active agent (c) represented by a general formula (2); and a dispersant containing water, where the cumulant diameter of the water dispersion is 250-2,000 nm, and pH of the water dispersion is 2.0-7.0. CF2=CF-[O-CF2-CF(CF3)]n-O-[CF2]m-Z (1), where n is an integer of 0 or larger and 2 or smaller, m is an integer of 2 or larger and 4 or smaller, and Z is CF3, SO2F, or COOCH3. CF3-[CF2]m-O-[CF(CF3)-CF2-O]n-CF(CF3)-Z (2), where m is an integer of 0-2, n is an integer of 0-6, Z is COOM, M is H, Li, Na, K or NR4, and R is H or a 1-4C straight chain alkyl group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to aqueous dispersions of fluoroolefins and aqueous dispersions of fluoroolefin copolymers, as well as methods for producing the same. [Background technology]

[0002] Functional group-containing perfluorocarbon copolymers are widely used as substrates for cation exchange membranes in salt electrolysis and diaphragms in fuel cells. Among functional group-containing perfluorocarbon copolymers, sulfonic acid-type functional group-containing perfluorocarbon copolymers are particularly useful. For example, in a cation exchange membrane electrolysis method for sodium chloride, it is known that providing a layer with carboxylic acid-type cation exchange groups, formed by converting the functional groups of a carboxylic acid-type functional group-containing perfluorocarbon copolymer into cation exchange groups, on the cathode chamber side of the membrane, and providing a layer with sulfonic acid-type cation exchange groups, formed by converting the functional groups of a sulfonic acid-type functional group-containing perfluorocarbon copolymer into cation exchange groups, on the anode chamber side of the membrane, is effective in producing high-purity caustic soda and yields high current efficiency and low electrolysis voltage. The manufacturing technology for this sulfonic acid-type functional group-containing perfluorocarbon copolymer has been clarified for both aqueous and non-aqueous systems.

[0003] Regarding manufacturing technologies in non-aqueous systems, see, for example, Patent Documents 1 to 5, and regarding methods for manufacturing sulfonic acid-type functional group-containing fluoroolefin copolymers in aqueous systems, see, for example, Patent Documents 6 to 9. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 57-92026 [Patent Document 2] U.S. Patent No. 3528954 [Patent Document 3] U.S. Patent No. 362742 [Patent Document 4] U.S. Patent No. 4138426 [Patent Document 5] U.S. Patent No. 4,267,364 [Patent Document 6] Patent No. 5075307 [Patent Document 7] Japanese Patent Application Publication No. 62-288615 [Patent Document 8] Japanese Patent Application Publication No. 62-288617 [Patent Document 9] Patent No. 5332617 [Overview of the project] [Problems that the invention aims to solve]

[0005] In the methods described in Patent Documents 1 to 5, the viscosity of the system increases rapidly as polymerization progresses, making it difficult to achieve a high conversion rate on an industrial scale from the standpoint of heat removal. In the method described in Patent Document 6, the sulfonic acid type functional group is prone to hydrolysis, and the resulting sulfonic acid type functional group-containing fluoroolefin copolymer has low melt moldability, resulting in foaming and other issues with conventionally known methods, making it impossible to produce a uniform and good film, which is particularly problematic when creating thin films useful for industrial applications. In the methods described in Patent Documents 7 and 8, in addition to the problem of hydrolysis of the sulfonic acid type functional group, it is difficult to achieve a high conversion rate while maintaining a constant copolymer composition ratio of the raw material fluoroolefin, and it is difficult to increase the copolymer concentration in the aqueous dispersion. In the method described in Patent Document 9, although hydrolysis of the sulfonic acid type functional group is suppressed, the equipment must be made of highly corrosion-resistant Hastelloy or glass lining from the standpoint of container corrosion, and C8F is used as an emulsifier. 17 COONH4 is undesirable for environmental reasons.

[0006] The present invention has been made in view of the above problems, and an object thereof is to provide an aqueous dispersion of fluoroolefin or the like that can obtain a copolymer from fluoroolefin as a raw material monomer with high conversion rate and high productivity without corrosion of the container. **Means for Solving the Problems**

[0007] As a result of intensive studies, the present inventors have found that an aqueous dispersion having a predetermined composition or physical properties can solve the above problems, and have completed the present invention.

[0008] That is, the present invention includes the following aspects. [1] A fluoroolefin (a) represented by the following general formula (1), A surfactant (c) represented by the following general formula (2), A dispersion medium containing water, An aqueous dispersion comprising: The cumulant diameter of the aqueous dispersion is 250 to 2000 nm, The pH of the aqueous dispersion is 2.0 to 7.0. CF2=CF-[O-CF2-CF(CF3)] n -O-[CF2] m -Z···(1) (In the above general formula (1), n represents an integer of 0 or more and 2 or less, m represents an integer of 2 or more and 4 or less, and Z represents CF3, SO2F or COOCH3.) CF3-[CF2] m -O-[CF(CF3)-CF2-O] n -CF(CF3)-Z···(2) (In the above general formula (2), m represents an integer of 0 to 2, n represents an integer of 0 to 6, Z represents COOM, where M represents H, Li, Na, K or NR4, where R represents H or a linear alkyl group having 1 to 4 carbon atoms.) [2] The aqueous dispersion according to [1], wherein the GWP of the dispersion medium is less than 1000. [3] The fluoroolefin (a) includes at least one fluoroolefin (a') selected from CF2=CF-O-CF2-CF2-SO2F, CF2=CF-O-CF2-CF2-CF2-CF2-SO2F, CF2=CF-O-CF2-CF(CF3)-O-CF2-CF2-SO2F, CF2=CF-O-CF2-CF(CF3)-O-CF2-CF2-CF3, and CF2=CF-O-CF2-CF(CF3)-O-CF2-CF2-COOCH3, The aqueous dispersion according to [1] or [2], wherein the content of the fluoroolefin (a') is 15 to 40% by mass. [4] The aqueous dispersion according to any one of [1] to [3], wherein the surfactant (c) comprises CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COOM or CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COOM (wherein M represents H, Li, Na, K, or NR4, and wherein R represents H or a linear alkyl group having 1 to 4 carbon atoms). [5] The aqueous dispersion according to any one of [1] to [4], wherein the content of M1OOCCF2SO3M2 (wherein M1 and M2 each independently represent H, Li, Na, K, or NR4, where R represents H or a linear alkyl group having 1 to 4 carbon atoms) in the aqueous dispersion is 100 ppm or less. [6] Fe in the aqueous dispersion 2+ and Fe 3+ The total amount is 1 ppm or less. The aqueous dispersion according to any one of [1] to [5], wherein the amount of dissolved oxygen in the aqueous dispersion is 1 ppm or less. [7] The aqueous dispersion according to any one of [1] to [6], wherein the value obtained by dividing the volume-average particle size of the aqueous dispersion by the number-average particle size is 2.0 or less. [8] A copolymer of fluoroolefin (a) represented by the following general formula (1) and fluoroolefin (b) represented by the following general formula (3), A surfactant (c) represented by the following general formula (2), A dispersion medium containing water, A water dispersion containing The content of the surfactant (c) with respect to the copolymer is 0.5% or more and 5.0% or less, A water dispersion having a solid content concentration exceeding 18% by mass. CF2=CF-[O-CF2-CF(CF3)] n -O-[CF2] m -Z···(1) (In the above general formula (1), n represents an integer of 0 or more and 2 or less, m represents an integer of 2 or more and 4 or less, and Z represents CF3, SO2F, or COOCH3.) CF3-[CF2] m -O-[CF(CF3)-CF2-O] n -CF(CF3)-Z···(2) (In the above general formula (2), m represents an integer of 0 to 2, n represents an integer of 0 to 6, Z represents COOM, where M represents H, Li, Na, K, or NR4, and here R represents H or a linear alkyl group having 1 to 4 carbon atoms.) CX1X2=CX3X4···(3) (In the above general formula (3), X1, X2, X3, and X4 each represent H, F, or CF3.) [9] The water dispersion according to [8], wherein the absolute value of the zeta potential measured for the water dispersion exceeds 25 mV.

[10] The water dispersion according to [8] or [9], wherein the cumulative diameter of the water dispersion is 10 to 300 nm.

[11] The water dispersion according to any one of [8] to

[10] , wherein the pH of the water dispersion is 2.0 to 7.0.

[12] The water dispersion according to any one of [8] to

[11] , wherein the GWP of the dispersion medium is less than 1000.

[13] The water dispersion according to any one of [8] to

[12] , wherein the fluoroolefin (b) contains tetrafluoroethylene.

[14] A method for producing an aqueous dispersion according to any one of [1] to [7], A manufacturing method comprising an emulsification step of shearing a mixture containing water, the surfactant (c), and the fluoroolefin (a) at a peripheral speed of 20 to 50 m / s.

[15] The manufacturing method according to

[14] , wherein in the emulsification step, the oxygen concentration in the atmosphere is 0.1% or less, and the temperature of the mixed liquid is 20°C or less.

[16] A method for producing a second aqueous dispersion, as described in any of [8] to

[13] , from an aqueous dispersion, as described in any of [1] to [7], as a first aqueous dispersion, A method for producing a second aqueous dispersion, comprising a polymerization step of polymerizing a polymerization initiator, the first aqueous dispersion, and the fluoroolefin (b) to obtain the second aqueous dispersion.

[17] The manufacturing method according to

[16] , wherein in the polymerization step, the pH of the emulsion solution containing the polymerization initiator and the first aqueous dispersion is 2.0 to 7.0, the polymerization temperature is 0 to 90°C, and the polymerization pressure is 0.0 to 2.0 MPaG. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide aqueous dispersions of fluoroolefins, etc., that do not corrode the container and that allow copolymers to be obtained from fluoroolefins as raw material monomers with a high conversion rate and high productivity. [Modes for carrying out the invention]

[0010] The embodiments for carrying out the present invention will be described in detail below. However, the present invention is not limited to the following embodiments and can be implemented in various modifications within the scope of its gist. In this specification, unless otherwise specified, "~" means that the numerical values ​​at both ends are included as the upper and lower limits.

[0011] [Water dispersion] (First aqueous dispersion) The aqueous dispersion according to the first aspect of this embodiment (hereinafter also referred to as the "first aqueous dispersion") is an aqueous dispersion comprising a fluoroolefin (a) represented by the following general formula (1), a surfactant (c) represented by the following general formula (2), and a dispersion medium containing water, wherein the cumulant diameter of the aqueous dispersion is 250 to 2000 nm, and the pH of the aqueous dispersion is 2.0 to 7.0. CF2 = CF - [O - CF2 - CF(CF3)] n -O-[CF2] m -Z···(1) (In the general formula (1) above, n represents an integer between 0 and 2, m represents an integer between 2 and 4, and Z represents CF3, SO2F, or COOCH3.) CF3-[CF2] m -O-[CF(CF3)-CF2-O] n -CF(CF3)-Z···(2) (In the above general formula (2), m represents an integer from 0 to 2, n represents an integer from 0 to 6, Z represents COOM, where M represents H, Li, Na, K, or NR4, and R represents H or a linear alkyl group having 1 to 4 carbon atoms.) Since the first aqueous dispersion is constructed as described above, there is no corrosion of the container, and a polymer can be obtained from fluoroolefin as the raw material monomer with a high conversion rate.

[0012] In the first aqueous dispersion, fluoroolefin (a) is granulated by a surfactant (c). That is, the first aqueous dispersion has a structure in which fine particles (dispersed phase) derived from fluoroolefin (a) are dispersed in a dispersion medium containing water. The particle size of the first aqueous dispersion is expressed as the cumulant diameter. The cumulant diameter of the first aqueous dispersion is 250 to 2000 nm, and preferably 250 to 1500 nm. Because fluoroolefin (a) has a large difference in specific gravity with water and is extremely prone to settling, if the cumulant diameter exceeds 2000 nm, oil droplets derived from fluoroolefin (a) will settle and coalesce, causing two-layer separation. If the cumulant diameter is less than 250 nm, the total surface area of ​​fluoroolefin (a) increases, increasing the opportunities for contact with water, and there is a risk of hydrolysis of fluoroolefin (a). The above cumulant diameter can be measured by the method described in the examples below. Furthermore, the cumulant diameter can be kept within the above range, for example, by performing the emulsification process described later.

[0013] In the first aqueous dispersion, the pH is set to 2.0 to 7.0, more preferably 2.0 to 6.9, and even more preferably 2.2 to 6.7. If the pH is greater than 7.0, hydrolysis of fluoroolefin (a) occurs, and if the pH is less than 2.0, the stability of particles derived from fluoroolefin (a) decreases, causing sedimentation and coalescence of these particles, or metal ions such as iron ions to leach from the reaction vessel, promoting the decomposition of the polymerization initiator, which can make it difficult to control the copolymerization reaction. A pH adjusting agent may be used to adjust the pH of the first aqueous dispersion. A wide range of conventionally known and publicly available pH adjusting agents may be optionally included in the first aqueous dispersion. For example, inorganic acids such as nitric acid, sulfuric acid, and phosphoric acid; organic acids such as trifluoromethanesulfonic acid and trifluoroacetic acid; or buffering agents such as phosphoric acid / sodium dihydrogen phosphate or sodium dihydrogen phosphate / disodium hydrogen phosphate may be used.

[0014] The content of the pH adjusting agent in the first aqueous dispersion is not particularly limited, but can be 0.01 to 150 mM, and preferably used in the range of 0.01 to 50 mM. When the content of the pH adjusting agent is 150 mM or less, the oil droplets derived from the finely granulated and dispersed fluoroolefin (a) are stabilized, and coalescence and sedimentation of the oil droplets tend to be preferably prevented. It is preferable to add the pH adjusting agent before the fine granulation and dispersion of the fluoroolefin (a).

[0015] In this specification, GWP refers to the global warming potential, and the values ​​for each substance can be identified by referring to Federal Register / Vol. 78, No. 66. In this embodiment, from the viewpoint of impact on the global environment, it is preferable that the GWP of the dispersion medium in the first aqueous dispersion is less than 1000. Such dispersion mediums are not particularly limited, but examples include water and methanol. If substances other than water are included as dispersion mediums in the first aqueous dispersion, it is preferable that the GWP of each dispersion medium is less than 1000. Furthermore, it is preferable that the first aqueous dispersion substantially does not contain any components with a GWP of 1000 or more. Substantially not containing any components means that the content of components with a GWP of 1000 or more in the first aqueous dispersion is less than 100 ppm.

[0016] As the fluoroolefin (a) in the first aqueous dispersion, any known and publicly available compound can be used as long as it satisfies the above general formula (1). However, from the viewpoint of industrial productivity, CF2=CF-O-CF2-CF2-SO2F, CF2=CF-O-CF2-CF2-CF2-CF2-SO2F, CF2=CF-O-CF2-CF(CF3)-O-CF2-CF2-SO2F, CF2=CF-O-CF2-CF(CF3)-O-CF2- Preferably, the product contains at least one fluoroolefin (a') selected from CF(CF3)-O-CF2-CF2-SO2F, CF2=CF-O-CF2-CF(CF3)-O-CF2-CF2-CF3, CF2=CF-O-CF2-CF2-COOCH3, CF2=CF-O-CF2-CF2-CF2-COOCH3, and CF2=CF-O-CF2-CF(CF3)-O-CF2-CF2-COOCH3. As for fluoroolefin (a), one type from the above-mentioned list can be used alone, or two or more types can be used in combination.

[0017] In the first aqueous dispersion, the content of fluoroolefin (a) is preferably 5% to 40% by mass, more preferably 15% to 40% by mass, and even more preferably 15% to 33% by mass, based on 100% by mass of the first aqueous dispersion. If the proportion of fluoroolefin (a) is 40% by mass or less, the oil droplets of the monomer tend to settle and coalesce, making separation from water less likely, and hydrolysis of fluoroolefin (1) during emulsification treatment is less likely. If the proportion of fluoroolefin (a) is 5% by mass or more, the reaction apparatus and copolymer separation and recovery equipment can be miniaturized, which tends to be advantageous in terms of operation. In this embodiment, from the same viewpoint as above, the content of fluoroolefin (a') is preferably 5% to 40% by mass, more preferably 15% to 40% by mass, and even more preferably 15% to 33% by mass, based on 100% by mass of the first aqueous dispersion.

[0018] As the surfactant (c) in the first aqueous dispersion, any known or publicly used compound can be used as long as it satisfies the above general formula (2). However, from the viewpoint of affinity with the monomer in the first aqueous dispersion and suppression of chain transfer reactions that are side reactions during polymerization, CF3-O-CF(CF3)-CF2-O-CF(CF3)-COOM, CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COOM, CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-CF2-O-CF(CF3)-CF2-O-CF(CF3)-CF2-O-CF Perfluorosurfactants such as (CF3)-COOM (wherein M represents H, Li, Na, K, or NR4, and R represents H or a linear alkyl group having 1 to 4 carbon atoms) are preferred, and perfluoroether carboxylic acid derivatives such as CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COOM or CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-CF2-O-CF(CF3)-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COOM (wherein M represents H, Li, Na, K, or NR4, and R represents H or a linear alkyl group having 1 to 4 carbon atoms) are more preferred from the viewpoint of impact on the global environment and industrial productivity. In this embodiment, one of the surfactants (c) described above may be used alone, or two or more may be used in combination. For example, C8F 19 -COOM (M is the same as above) and others can also be used in combination with the surfactant (c) in this embodiment for emulsification.

[0019] In this embodiment, the content of surfactant (c) is preferably adjusted in relation to the amount of dispersion medium in the first aqueous dispersion. Specifically, it is preferably 0.01% to 5.0% by mass, and more preferably 0.1% to 4.0% by mass, based on 100% by mass of the dispersion medium in the first aqueous dispersion. If the surfactant content is 0.01% by mass or more, the finely granulated and dispersed fluoroolefin (a) oil droplets are stabilized, and sedimentation and coalescence of the oil droplets tend to be less likely. If the surfactant content is 5.0% by mass or less, foaming of the liquid is reduced during polymerization, and the dissolution and diffusion of fluoroolefin (b), described later, into the aqueous layer is not inhibited, and the formation of heterogeneous polymers tends to decrease. Furthermore, it is preferable that the content of surfactant (c) be at a concentration such that micelles do not form after the fluoroolefin (a) is granulated and dispersed. From this viewpoint as well, it is preferable to adjust the content of surfactant (c) to the range described above. Furthermore, while it is preferable to add the entire amount of surfactant (c) to the fluoroolefin (a) before pulverization and dispersion, it is also possible to add a portion of the surfactant (c) to the fluoroolefin (a) before pulverization and dispersion, and then add the remainder after the desired pulverization and dispersion. The amount of dispersion medium contained in the first aqueous dispersion can be approximately 50% to 95% by mass, or 50% to 90% by mass, relative to 100% by mass of the first aqueous dispersion.

[0020] The content of M1OOCCF2SO3M2 (where M1 and M2 represent H, Li, Na, K, or NR4, respectively, and R represents H or a linear alkyl group having 1 to 4 carbon atoms) in the first aqueous dispersion is preferably 100 ppm or less, and more preferably 20 ppm or less. M1OOCCF2SO3M2 can be considered a typical impurity in the first aqueous dispersion, and when its content is 100 ppm or less, the subsequent copolymerization reaction tends to be easier to control. The above content can be measured by the method described in the examples below. Furthermore, the above content can be kept within the above range by, for example, thoroughly purifying the raw material fluoroolefin (a) by washing with water or distillation.

[0021] Fe in the first aqueous dispersion 2+ and Fe 3+ The total amount of Fe is preferably 1 ppm or less, and more preferably 0.1 ppm or less. 2+ and Fe 3+ This can be considered a typical impurity in the first aqueous dispersion, and when its content is 0.1 ppm or less, it tends to be less likely to promote the decomposition of the polymerization initiator, making it easier to control the subsequent copolymerization reaction. The above content can be measured by the method described in the examples below. Furthermore, the above content can be kept within the above range by, for example, carrying out the emulsification process described later under conditions of pH 2.0 to 7.0.

[0022] The dissolved oxygen content in the first aqueous dispersion is preferably 1 ppm or less, and more preferably 0.5 ppm or less. Dissolved oxygen can be considered a typical impurity in the first aqueous dispersion, and when its content is 1 ppm or less, it tends to inactivate the growth species having radicals during the polymerization reaction, cause less chain transfer reactions, and suppress the formation of so-called oligomers with small molecular weights. Since these oligomers can cause uneven flow and foaming during melt film formation, it is preferable to reduce their amount. The above dissolved oxygen amount can be measured by the method described in the examples below. Furthermore, the amount of dissolved oxygen can be kept within the above range by, for example, carrying out the emulsification process described later in an atmosphere with an oxygen concentration of 0.1% or less.

[0023] In this embodiment, from the above-mentioned viewpoint, in particular, Fe in the first aqueous dispersion 2+ and Fe 3+ It is preferable that the total amount of [the substance] is 1 ppm or less, and the amount of dissolved oxygen in the first aqueous dispersion is 1 ppm or less.

[0024] The value obtained by dividing the volume-average particle size of the first aqueous dispersion by the number-average particle size is preferably 2.0 or less, and more preferably 1.6 or less. When the above value is 2.0 or less, the movement of fluoroolefin (a) from the oil droplets to the reaction field during polymerization becomes uniform, and the copolymerization reaction can be easily controlled. The volume-average particle size and number-average particle size can be measured by the method described in the examples below. Furthermore, the above values ​​can be kept within the above range by, for example, properly stirring the entire system in the emulsification process described later.

[0025] (Second aqueous dispersion) The aqueous dispersion according to the second aspect of this embodiment (also referred to as the "second aqueous dispersion" in this specification) is an aqueous dispersion comprising a copolymer of a fluoroolefin (a) represented by the above general formula (1) and a fluoroolefin (b) represented by the following general formula (3), a surfactant (c) represented by the above general formula (2), and a dispersion medium containing water, wherein the content of the surfactant (c) relative to the copolymer is 0.5% or more and 5.0% or less, and the solid content concentration is greater than 18% by mass. CX1 x 2 = CX3 x 4 ... (3) (In the above general formula (3), X1, X2, X3, and X4 represent H, F, or CF3, respectively.) The second aqueous dispersion is not particularly limited as long as it is configured as described above, but is typically preferably obtained from the first aqueous dispersion. That is, by using the first aqueous dispersion as a raw material, polymerization of fluoroolefin (a) and fluoroolefin (b) in an aqueous system can proceed smoothly under mild conditions, and a second aqueous dispersion containing these copolymers can be obtained. In other words, the second aqueous dispersion contains fluoroolefin (b), a copolymer of fluoroolefin (a) contained in the first aqueous dispersion, and water.

[0026] The fluoroolefin (b) in the second aqueous dispersion is not particularly limited as long as it satisfies the above general formula (3), but tetrafluoroethylene and hexafluoropropylene are preferred, and tetrafluoroethylene is more preferred.

[0027] The solid content concentration of the second aqueous dispersion is greater than 18% by mass, preferably 20% by mass or more, and more preferably 22% by mass or more. There is no particular upper limit to the above solid content concentration, but it is preferably 45% by mass or less. When the above solid content concentration is greater than 18% by mass, productivity is improved. Also, when the above solid content concentration is 45% by mass or less, the dispersion state of the second aqueous dispersion becomes stable and tends to be less prone to aggregation.

[0028] As the surfactant (c) in the second aqueous dispersion, any known or publicly used compound can be used as long as it satisfies the above general formula (2). However, from the viewpoint of affinity with the copolymer in the second aqueous dispersion, CF3-O-CF(CF3)-CF2-O-CF(CF3)-COOM, CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COOM, CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-CF2-O-CF(CF3)-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COOM Perfluorosurfactants such as (wherein M represents H, Li, Na, K, or NR4, and R represents H or a linear alkyl group having 1 to 4 carbon atoms) are preferred, and perfluoroether carboxylic acid derivatives such as CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COOM or CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-CF2-O-CF(CF3)-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COOM (wherein M represents H, Li, Na, K, or NR4, and R represents H or a linear alkyl group having 1 to 4 carbon atoms) are more preferred from the viewpoint of impact on the global environment and industrial productivity. As the surfactant (c) in the second aqueous dispersion, one type from the above-mentioned group may be used alone, or two or more types may be used in combination. For example, C8F 19 -COOM (where M is the same as above) and others can also be used in combination with surfactant (c) in this embodiment.

[0029] In the second aqueous dispersion, the content of surfactant (c) relative to the copolymer is 0.5% by mass or more and 5.0% by mass or less, preferably 1.0% by mass or more and 5.0% by mass or less, and more preferably 1.0% by mass or more and less than 4.0% by mass. When the above content is 0.5% by mass or more, the dispersion state of the second aqueous dispersion becomes stable and less prone to aggregation, and the portion derived from fluoroolefin (a) in the copolymer is less susceptible to hydrolysis. When the above content is 5.0% by mass or less, it becomes easier to remove when isolating the copolymer. The above content can be measured based on the method described in the examples below. Furthermore, the above content can be kept within the above range, for example, by carrying out the polymerization process described later.

[0030] The cumulant diameter of the second aqueous dispersion is preferably 10 nm to 300 nm, and more preferably 30 nm to 250 nm. Since copolymers tend to settle easily due to a large difference in specific gravity with water, when the cumulant diameter is 300 nm or less, it tends to prevent the settling of copolymer particles. Furthermore, when the cumulant diameter is 10 nm or more, it tends to prevent an excessive increase in contact with water due to the large total surface area of ​​the copolymer, thereby preventing hydrolysis of the portion derived from fluoroolefin (a) in the copolymer. The above cumulant diameter can be measured based on the method described in the examples below. Furthermore, the cumulant diameter can be kept within the above range, for example, by carrying out the polymerization process described later.

[0031] The absolute value of the zeta potential of the second aqueous dispersion is preferably 25 mV or higher, more preferably 30 mV or higher, even more preferably 35 mV or higher, and even more preferably 40 mV or higher. When it is 25 mV or higher, the dispersion state of the second aqueous dispersion tends to be stable and less prone to aggregation. The absolute value of the zeta potential can be measured based on the method described in the examples below. Furthermore, the absolute value of the zeta potential can be kept within the above range, for example, by performing the polymerization process described later.

[0032] The pH of the second aqueous dispersion is preferably 2.0 to 7.0, more preferably 2.0 to 6.9, and even more preferably 2.2 to 6.7. When the pH is 7.0 or lower, hydrolysis of the fluoroolefin (a) portion in the copolymer tends to be prevented, and when the pH is 2.0 or higher, metal ions such as iron ions tend to leach from the reaction vessel during further processing of the second aqueous dispersion, which tends to affect the physical properties of the aqueous dispersion. A pH adjusting agent may be used to adjust the pH of the second aqueous dispersion, and the type and amount used are as described above for the first aqueous dispersion.

[0033] In this embodiment, from the viewpoint of impact on the global environment, it is preferable that the GWP of the dispersion medium in the second aqueous dispersion is less than 1000. If the second aqueous dispersion contains substances other than water as dispersion mediums, it is preferable that the GWP of each dispersion medium is less than 1000. Furthermore, it is preferable that the second aqueous dispersion substantially does not contain any components that have a GWP of 1000 or more. Substantially not containing any components means that the content of components that have a GWP of 1000 or more in the second aqueous dispersion is less than 100 ppm.

[0034] The second aqueous dispersion has no particular applications, but examples include cation exchange membranes for salt electrolysis and diaphragms for fuel cells. The ion exchange capacity of the ion exchange membrane is preferably 0.83 meq. / g or more and 2.08 meq. / g or less. When the above ion exchange capacity is 0.83 meq. / g or more, a thin film as a self-supporting membrane tends to be obtained, and when it is 2.08 meq. / g or less, sufficient ion exchange performance is ensured and the electrolysis voltage tends to be lower (energy loss is reduced). The above ion exchange capacity can be measured based on the method described in the examples below. Furthermore, the above-mentioned ion exchange capacity can be kept within the above range by, for example, manufacturing an ion exchange membrane using a known method with a second aqueous dispersion as a raw material.

[0035] [Method for producing aqueous dispersions] (Method for producing the first aqueous dispersion) The method for producing the first aqueous dispersion is not particularly limited as long as the first aqueous dispersion having the configuration described above can be obtained. However, from the viewpoint of obtaining the first aqueous dispersion more reliably and efficiently, the method for producing the first aqueous dispersion preferably includes an emulsification step in which a mixture containing water, the surfactant (c), and the fluoroolefin (a) is sheared at a peripheral speed of 10 to 50 m / s, and more preferably the peripheral speed is 20 to 50 m / s.

[0036] (emulsification process) In the emulsification step of this embodiment, it is preferable to shear the mixture containing water, the surfactant (c), and the fluoroolefin (a) at a peripheral speed of 10 to 50 m / s, and more preferably at 20 to 50 m / s. The mixture may optionally contain the aforementioned pH adjusting agent from the viewpoint of adjusting the pH of the obtained first aqueous dispersion. The shearing means can be any known or publicly available dispersers or emulsifiers that can be used in a wide range of applications without particular limitation. For example, an ultrasonic crusher, homogenizer, or colloid mill mixer can be used, but it is preferable to use a homogenizer to suppress the hydrolysis of fluoroolefin (a). As a homogenizer, for example, a BioMixer ABM-4 manufactured by Nippon Seiki can be used.

[0037] From the viewpoint of suppressing the hydrolysis of fluoroolefin (a), it is preferable to keep the temperature of the above mixture below 20°C, and more preferably below 12°C, during the emulsification process.

[0038] In this embodiment, from the viewpoint of obtaining the desired grain size, the peripheral speed in shearing is preferably 10 m / s or more and 50 m / s or less, more preferably 20 m / s or more and 50 m / s or less, even more preferably 24 m / s or more and 50 m / s or less, and even more preferably 24 m / s or more and 48 m / s or less.

[0039] Furthermore, from the viewpoint of preventing oxidative decomposition of fluoroolefin (a) by dissolved oxygen and radical deactivation during polymerization, it is preferable to keep the oxygen concentration in the atmosphere at 1% or less, and more preferably at 0.1% or less, during the emulsification process.

[0040] In this embodiment, from the above-mentioned viewpoint, it is particularly preferable to keep the oxygen concentration in the atmosphere at 0.1% or less and the temperature of the mixed liquid at 20°C or less during the emulsification process.

[0041] (Method for producing the second aqueous dispersion) The method for producing the second aqueous dispersion is not particularly limited as long as a second aqueous dispersion having the above-described configuration can be obtained. However, from the viewpoint of obtaining the second aqueous dispersion more reliably and efficiently, the method for producing the second aqueous dispersion preferably includes a polymerization step of polymerizing a polymerization initiator, the first aqueous dispersion, and fluoroolefin (b) to obtain the second aqueous dispersion.

[0042] (Polymerization process) In this embodiment, polymerization is carried out using a first aqueous dispersion obtained by granulating and dispersing fluoroolefin (a) as described above. The conditions for the copolymerization reaction with fluoroolefin (b) can be broadly adopted from known and commonly used general conditions used for the homopolymerization or copolymerization of fluorinated ethylene.

[0043] In the polymerization process, the pH of the emulsion solution containing the polymerization initiator and the first aqueous dispersion is preferably 2.0 to 7.0, more preferably 2.0 to 6.9, even more preferably 2.2 to 3.9, and even more preferably 2.2 to 3.9. If the pH is 7.0 or lower, hydrolysis of fluoroolefin (a) tends to be prevented. If the pH is 2.0 or higher, the stability of the dispersed particles is reduced, making particle sedimentation and coalescence less likely, metal ions such as iron ions are less likely to leach from the reaction vessel, and the decomposition of the polymerization initiator is suppressed, thus making it easier to control the copolymerization reaction.

[0044] The polymerization temperature in the polymerization process is preferably 0 to 90°C, and more preferably 20 to 60°C, as the liquid temperature of the emulsion solution. If the polymerization temperature is 0°C or higher, the possibility of the system solidifying during polymerization is low, and if it is 90°C or lower, the possibility of hydrolysis of fluoroolefin (a) or fluoroolefin (b) is low.

[0045] The polymerization pressure in the polymerization process is preferably 0.0 to 2.0 MPaG, and more preferably 0.1 to 0.7 MPaG. If the polymerization pressure is 0.1 MPaG or higher, the polymerization rate will be faster, allowing for miniaturization of the reaction apparatus and copolymer separation and recovery equipment, which is advantageous in terms of operation. If the polymerization pressure is 2.0 MPaG or lower, homopolymerization of fluoroolefin (b) in the gas phase is less likely to occur, which is preferable from both a production and safety standpoint.

[0046] The polymerization initiator used in this embodiment is not particularly limited, and examples of water-soluble polymerization initiators include inorganic peroxides such as sodium persulfate, potassium persulfate, and ammonium persulfate; redox initiators such as ammonium persulfate-ferrous sulfate and ammonium persulfate-ammonium bisulfite; and hydroperoxides such as t-butyl hydroperoxide. Other polymerization initiators that can be used, but are not limited to the following, include azo compounds such as azobisisobutyronitrile, diacyl peroxides such as benzoyl peroxide and pentafluoropropionyl peroxide, and peroxides such as di-t-butyl peroxide. Among the above, it is preferable to use a water-soluble polymerization initiator. When a water-soluble polymerization initiator is used, it is easy to distribute it evenly even when added after the granulation and dispersion of fluoroolefin (a), and it tends to have excellent operability.

[0047] The polymerization initiator is preferably one that exhibits high activity at the polymerization temperature described above, and its concentration is used in a range of 0.001 to 5 mol% of fluoroolefin (a) per hour, preferably in the range of 0.01 to 1 mol%, and particularly preferably in the range of 0.02 to 0.8 mol%. If the initiator concentration is 0.001 mol% or higher, the polymerization rate increases, and the reaction apparatus and copolymer separation and recovery equipment can be made smaller, which is advantageous in terms of operation. If the initiator concentration is 5 mol% or lower, the tendency for the molecular weight to decrease decreases, so sufficient strength can be imparted, and polymers with sufficiently high molecular weight tend to be obtained. In addition to considering the above-mentioned activity, inorganic peroxides such as sodium sulfate, potassium persulfate, and ammonium persulfate, and redox initiators such as ammonium persulfate-ferrous sulfate and ammonium persulfate-ammonium bisulfite are particularly preferred as polymerization initiators from the viewpoint of suppressing chain transfer reactions, which are side reactions during polymerization.

[0048] The inventors have found that copolymers with a wide range of compositions can be obtained by copolymerizing fluoroolefin (a) and fluoroolefin (b) in a manner in which fluoroolefin (a) and fluoroolefin (b) are continuously or intermittently supplied into the reaction system during the polymerization process. This is achieved by arbitrarily changing the supply ratio of fluoroolefin (a) and fluoroolefin (b) into the system. It is also possible to change the composition over time by changing the ratio during the reaction. In the case of batch charging, due to pressure constraints, the amount of fluoroolefin (b) that can exist in the system is small, and the corresponding amount of fluoroolefin (a) is also small, which tends to be disadvantageous in terms of operational aspects such as the need for a larger reaction apparatus. Furthermore, in the method of continuously or intermittently supplying only fluoroolefin (b), only copolymers with a high proportion of fluoroolefin (a) can be obtained, which tends to be disadvantageous from the viewpoint of obtaining copolymers with a wide range of compositions. For this reason, it is preferable to continuously or intermittently supply fluoroolefin (b) or to continuously or intermittently supply fluoroolefin (b) and the first aqueous dispersion during the polymerization process. In this embodiment, from the viewpoint described above, it is particularly preferable that in the polymerization step, the pH of the emulsion solution is 2.0 to 7.0, the polymerization temperature is 0 to 90°C, and the polymerization pressure is 0.0 to 2.0 MPaG, and more preferably, in the polymerization step, the pH of the emulsion solution is 2.0 to 7.0, the polymerization temperature is 30 to 90°C, and the polymerization pressure is 0.5 to 2.0 MPaG, and under these conditions, it is further preferable to continuously or intermittently supply fluoroolefin (b), or to continuously or intermittently supply fluoroolefin (b) and the first aqueous dispersion. [Examples]

[0049] The embodiment will be described in detail below with reference to examples and comparative examples, but the embodiment is not limited in any way by these examples.

[0050] The evaluation methods used in the examples and comparative examples were as follows.

[0051] [pH] 50 mL of either the first or second aqueous dispersion was placed in a PP sample cup and stirred using a magnetic stirrer. A probe from a HORIBA Scientific pH METER D-71 was then inserted, and the pH value was taken once it stabilized.

[0052] [Amount of oxygen in the system] The oxygen concentration in the atmosphere during the emulsification process was measured by installing an OXY-1 oxygen concentration meter manufactured by Ichinen Jiko in the system.

[0053] [Dissolved oxygen level] As a sample, 400 mL of the first aqueous dispersion was placed in a PP sample cup and stirred using a magnetic stirrer. A probe from a HORIBA Scientific DO METER OM-71 was then inserted, and the value was taken as the dissolved oxygen level once it stabilized. To avoid disturbances, the measurement was performed under the same atmosphere as the emulsification process.

[0054] [M1OOCCF2 SO3M2, Fe 2+ and Fe 3+ [Content] M1OOCCF2SO3M2, Fe in the first aqueous dispersion 2+ and Fe 3+ The content was determined by diluting the sample to an appropriate concentration with distilled water and then filtering it through a polytetrafluoroethylene membrane filter with a pore size of 200 nm. The filtrate was subjected to measurement using a Tosoh IC-2010 ion chromatograph, and various quantifications were performed using the absolute calibration curve method.

[0055] [Particle size] The first or second aqueous dispersion was used as a sample and diluted with distilled water to obtain an appropriate scattered light intensity. The scattered light of the diluted solution was measured using an Otsuka Electronics ELSZ-2000ZS, and the cumulant diameter, volume-average particle size, and number-average particle size were determined by the CONTIN method. This was repeated three times, and the arithmetic mean values ​​were taken as the cumulant diameter, volume-average particle size, and number-average particle size, respectively.

[0056] [Solid content concentration] A second aqueous dispersion with mass w2 [g] was placed in an aluminum dish with mass w1 [g], and heated at 200°C for 1 hour to remove volatile components. The total mass of the aluminum dish and non-volatile components after heating was taken as w3 [g], and the value calculated by the following formula was defined as the solid content concentration. Solid concentration [%]=(w3-w1) / w2*100

[0057] [Melt Flow Rate] The melt flow rate was measured in accordance with JIS K7210. Specifically, 5g of the sample was placed in a Toyo Seiki Manufacturing Co., Ltd. melt indexer F-F01, preheated to 270°C, and heated for 5 minutes. A load of 2.16 kg was applied to the molten sample, and the mass of resin that dissolved from a 2.095 mm vertical hole in 10 minutes was measured and defined as the melt flow rate.

[0058] [Conversion rate of fluoroolefin (a) after polymerization] 5 g of tetrahydrofuran was added to 1 g of an aqueous dispersion and vigorously mixed for 10 minutes to separate and precipitate the copolymer and extract fluoroolefin (a). The extract was filtered through a polytetrafluoroethylene membrane filter with a pore size of 200 nm, and 1,2-dimethoxyethane was added as an internal standard. The concentration of fluoroolefin (a) in the extract was then quantified using the internal calibration curve method with a Shimadzu GC-2014 gas chromatograph. The mass w4 [g] of fluoroolefin (a) in the aqueous dispersion was calculated from the concentration of fluoroolefin (a) in the extract, and the conversion rate was calculated using the following equation (2) with the mass w5 [g] of fluoroolefin (a) introduced into the polymerization system. Conversion rate [%] = (w5 - w4) / w5 * 100 ... (2)

[0059] [Ion exchange capacity of copolymers] The second aqueous dispersion obtained in the polymerization process described later was thoroughly purified and dried in the same manner as the measurement of [surfactant (c) content relative to copolymer] below to obtain a copolymer powder, which was then press-molded into a film with a thickness of approximately 130 μm. The infrared transmission spectrum of this film was measured using a JASCO FT / IR-4200 at 29.5 ± 1.5 °C under a nitrogen atmosphere. The proportion A [mass %] of SO2F groups in the copolymer was determined from the intensity ratio of the absorption peaks derived from SO2F groups and CF2 groups in the obtained spectrum. Using this, the ion exchange capacity was calculated from the following formula. Ion exchange capacity [meq.] = 1000 / (81.1 / A) (In the formula, 81.1 is the molecular weight of the SO3H group obtained by hydrolysis of the SO2F group.)

[0060] [Content of surfactant (c) relative to copolymer] The second aqueous dispersion obtained in the polymerization process described later was treated as follows: The second aqueous dispersion was frozen at -35°C and then thawed at room temperature to obtain copolymer aggregates. This operation confirmed that more than 99% of the copolymer in the second aqueous dispersion aggregated. The obtained aggregates were thoroughly washed with a mixture of water, methanol, and methanol / CF3CF2CHFCFHCF3 to remove inorganic salts, surfactants, and unreacted fluoroolefins. The resulting copolymer-containing solution was thoroughly vacuum-dried at 110°C to obtain copolymer powder. The mass (g) of the copolymer obtained in this way was measured. Furthermore, as described later, the surface tension of the second aqueous dispersion was measured and compared with the surface tension of the surfactant aqueous solution of known concentration to determine the concentration of free surfactant present in the water of the second aqueous dispersion. Subtracting this from the amount of surfactant added allowed us to determine the mass (g) of surfactant (c) adhering to the surface of the copolymer particles. From the masses obtained as described above, the surfactant (c) content in the copolymer was calculated using the following formula. The amount of surfactant (c) in the copolymer = 100 × mass of surfactant (c) / mass of copolymer [Surface tension measurement] The sample (second aqueous dispersion or aqueous solution of surfactant of known concentration) was placed in a glass petri dish to a liquid height of 15 mm, and the surface tension was measured using the Dunouy method with a Dunouy surface tensioner type D manufactured by Ito Seisakusho. This was repeated three times, and the average value was taken as the surface tension.

[0061] [Zeta potential of copolymers] The second aqueous dispersion obtained in the polymerization process described later was diluted with a 10 mM KCl aqueous solution to a solid content concentration of 1%. The zeta potential of the diluted solution was determined by electrophoretic light scattering using an Otsuka Electronics ELSZ-2000ZS. This was repeated three times, and the arithmetic mean was taken as the zeta potential.

[0062] [Example 1] (emulsification process) 481g of distilled water was dissolved with 0.914g of CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COONH, 2.27g of Na2HPO4·12H2O, and 1.35g of NaH2PO4·2H2O. Furthermore, 120g of CF2=CF-O-CF2-CF2-SO2F was added. The mixture was stirred at a peripheral speed of 40m / s for 15 minutes using a Nippon Seiki ABM-4 biomixer while maintaining the temperature at 12°C to obtain an aqueous dispersion as an emulsion (first aqueous dispersion). Specifically, during the emulsification process, the oxygen concentration in the atmosphere was 20.9%, and the temperature of the emulsion was 12°C. (Polymerization process) Next, 102 g of water, 1.90 g of CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COONH4, 0.266 g of Na2HPO4·12H2O, and 0.158 g of NaH2PO4·2H2O were added to a 1 L stainless steel pressure-resistant reaction vessel. After thoroughly replacing the inside of the vessel with tetrafluoroethylene, the temperature was raised to 50°C, and 71.0 g of the above emulsion was added. A solution of (NH4OSO2O) 20.328 g dissolved in 25.0 g of water was then injected under pressure as a polymerization initiator to start the polymerization of the resulting emulsion. During the reaction, tetrafluoroethylene was intermittently introduced from outside the system, and the pressure was maintained at 0.5 MPaG. Tetrafluoroethylene and the emulsion were continuously injected under pressure so that the molar ratio of consumed tetrafluoroethylene to CF2=CF-O-CF2-CF2-SO2F in the emulsion was 5.00. After injecting 186g of the emulsion, the unreacted tetrafluoroethylene was purged to terminate the polymerization, and an aqueous dispersion containing the copolymer (second aqueous dispersion) was obtained. The pH of the emulsion solution was measured by removing the emulsion solution used for polymerization from the system during the reaction, and it was found to be pH 6.5. (evaluation) The first and second aqueous dispersions obtained above were subjected to the aforementioned physical property evaluations. The cumulant diameter of the second aqueous dispersion was 111 nm. Furthermore, no corrosion was observed in the reaction vessel after polymerization, and almost no polytetrafluoroethylene residue was found. In addition, the second aqueous dispersion was left to stand at 5°C for one week, and its appearance was visually inspected. No sedimentation was observed, and the second aqueous dispersion was evaluated as being in a stable dispersion state. The ion exchange capacity of the obtained copolymer was 1.46 meq. / g, and the conversion rate of CF2=CF-O-CF2-CF2-SO2F was 77%. The results of the various evaluations are shown in Table 1.

[0063] [Comparative Example 1] Emulsification and polymerization were carried out in the same manner as in Example 1, except that emulsification treatment using a biomixer was not performed. (Preparation of mixed solution) Specifically, 0.914 g of CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COONH, 2.27 g of Na2HPO4·12H2O, and 1.35 g of NaH2PO4·2H2O were dissolved in 481 g of distilled water, and then 120 g of CF2=CF-O-CF2-CF2-SO2F was added to obtain a mixture. The oxygen concentration in the atmosphere during the preparation of the above mixture was 20.9%, and the temperature of the mixture was 12°C. Because the monomer droplets in the above mixture settled rapidly without dispersing, particle size measurement was practically impossible, but they were estimated to be on the order of microns or larger (at least over 2000 nm). (polymerization) Next, 102 g of water, 1.90 g of CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COONH4, 0.266 g of Na2HPO4·12H2O, and 0.158 g of NaH2PO4·2H2O were added to a 1 L stainless steel pressure-resistant reaction vessel. After thoroughly replacing the inside of the vessel with tetrafluoroethylene, the temperature was raised to 50°C, and 71.0 g of the above mixture was added. A solution of (NH4OSO2O) 20.328 g dissolved in 25.0 g of water was then injected under pressure as a polymerization initiator to start the polymerization of the resulting solution. During the reaction, tetrafluoroethylene was intermittently introduced from outside the system, and the pressure was maintained at 0.5 MPaG. Tetrafluoroethylene and the mixture were continuously injected under pressure so that the molar ratio of tetrafluoroethylene consumed to CF2=CF-O-CF2-CF2-SO2F in the emulsion was 5.00. After injecting 186g of the mixture under pressure, the unreacted tetrafluoroethylene was purged to terminate the polymerization and obtain an aqueous dispersion. The solution used for polymerization was removed from the system during the reaction and measured to have a pH of 6.5. (evaluation) The mixture obtained in the above preparation and the aqueous dispersion obtained in the polymerization operation were subjected to the aforementioned physical property evaluations, corresponding to the first and second aqueous dispersions, respectively. The cumulant diameter of the aqueous dispersion obtained in the polymerization operation was 99 nm. Partial corrosion was observed in the reaction vessel after polymerization. Almost no polytetrafluoroethylene residue was observed. The ion exchange capacity of the obtained copolymer was 1.23 meq. / g, and the conversion rate of CF2=CF-O-CF2-CF2-SO2F was 60%. The results of the various evaluations are shown in Table 1.

[0064] [Example 2] (emulsification process) Under a nitrogen atmosphere, CF2=CF-O-CF2-CF2-SO2F and distilled water from which dissolved oxygen had been removed by nitrogen bubbling were mixed in a mass ratio of 2:1. After vigorous stirring for 2 minutes, the mixture was allowed to stand, and the settled CF2=CF-O-CF2-CF2-SO2F was collected. The above washing procedure was repeated until the HOOCCF2SO3H in the washing water was 100 ppm or less. CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COONH4 30.0 g, 85% H3PO4(aq.) 3.54 g, and NaH2PO4·2H2O 33.9 g were dissolved in 6000 g of distilled water, and then 2000 g of the washed CF2=CF-O-CF2-CF2-SO2F was added. Under a nitrogen atmosphere with an oxygen concentration of 0.1% or less, the above mixture was stirred for 30 minutes at a peripheral speed of 40 m / s using a Nippon Seiki Bio Mixer ABM-4 while maintaining the temperature at 12°C. To this, a solution of 490.0 g of CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COONH dissolved in 2000 g of distilled water was added to obtain an aqueous dispersion as an emulsion (first aqueous dispersion). That is, the oxygen concentration in the atmosphere was 0.1% or less, and the temperature of the emulsion was 12°C. (Polymerization process) In a 22L stainless steel pressure-resistant reaction vessel, 2300g of water, 24.3g of CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COONH4, 1.15g of 85% H3PO4(aq.), and 9.81g of NaH2PO4·2H2O were added. After thoroughly replacing the inside of the vessel with tetrafluoroethylene, the temperature was raised to 50°C, and 762g of the above emulsion was added. A solution of (NH4OSO2O) 21.83g dissolved in 200g of distilled water was then injected under pressure as a polymerization initiator to start the polymerization of the resulting emulsion. During the reaction, tetrafluoroethylene was intermittently introduced from outside the system, and the pressure was maintained at 0.5 MPaG. After consuming 80 g of tetrafluoroethylene, a solution of 23.65 g of (NH4OSO2O) dissolved in 200 g of distilled water was injected under pressure. The injection of tetrafluoroethylene and emulsion continued until the molar ratio of tetrafluoroethylene consumed to monomer in the emulsion was 2.65. After injecting 8800 g of emulsion, the unreacted tetrafluoroethylene was purged to terminate the polymerization, and an aqueous dispersion containing the copolymer (second aqueous dispersion) was obtained. The pH of the emulsion solution was measured by removing the emulsion solution used for polymerization from the system during the reaction, and it was found to be pH 3.5. (Rating 1) The first and second aqueous dispersions obtained above were subjected to the physical property evaluations described above. The cumulant diameter of the second aqueous dispersion was 102 nm. Furthermore, no corrosion was observed in the reaction vessel after polymerization, and almost no polytetrafluoroethylene residue was observed. In addition, the second aqueous dispersion was left to stand at 5°C for one week, and its appearance was visually inspected. No sedimentation was observed, and the second aqueous dispersion was evaluated to be in a stable dispersion state. The ion exchange capacity of the obtained copolymer was 1.41 meq. / g, and the conversion rate of CF2=CF-O-CF2-CF2-SO2F was 77%. The results of the various evaluations are shown in Table 1. (Evaluation 2: Impurity levels and reproducibility) Polymerization was carried out three times under the same conditions as in Example 2, and the ion exchange capacity and melt flow index were measured for each. The standard error of the ion exchange capacity calculated from the measured values ​​was 0.4%, and the standard error of the melt flow index was 4.3%. In addition, polymerization was carried out three times in the same manner as in Example 2, except that the water washing procedure in Example 2 was not performed. The ion exchange capacity and melt flow index were measured, and the standard errors were calculated. The standard error for the ion exchange capacity was 5.4%, and the standard error for the melt flow index was 18.9%, respectively. As a result of not performing the water washing procedure, the MOOCCF2SO3M content exceeded 100 ppm, and the dissolved oxygen concentration increased to 4.6 ppm. As described above, it can be seen that reducing the amount of various impurities improves the reproducibility of the performance of the resulting copolymer.

[0065] [Example 3] (emulsification process) 431 g of distilled water was dissolved with 40.952 g of CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COONH, 2.27 g of Na2HPO4·12H2O, and 1.37 g of NaH2PO4·2H2O. Then, 120 g of CF2=CF-O-CF2-CF(CF3)-O-CF2-CF2-SO2F, which had been thoroughly washed with water (as in Example 2), was added. The above mixture was stirred for 15 minutes at a peripheral speed of 40 m / s using a Nippon Seiki Bio Mixer ABM-4 while maintaining the temperature at 12°C to obtain an aqueous dispersion as an emulsion (first aqueous dispersion). In other words, during the emulsification process, the oxygen concentration in the atmosphere was 20.9%, and the temperature of the emulsion was 12°C. (Polymerization process) The above emulsion and CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COONH42.41g were added to a 1L stainless steel pressure-resistant reaction vessel. After thoroughly substituting the vessel with tetrafluoroethylene, the temperature was raised to 50°C. A solution of (NH4OSO2O)20.710g dissolved in 50.0g of water was then injected under pressure as a polymerization initiator to start the polymerization of the resulting emulsion. During the reaction, tetrafluoroethylene was intermittently introduced from outside the system, and the pressure was maintained at 0.5 MPaG. 260 minutes after the start of polymerization, unreacted tetrafluoroethylene was purged to terminate the polymerization, and an aqueous dispersion containing the copolymer (second aqueous dispersion) was obtained. The pH of the emulsion was measured by removing the emulsion from the system during the polymerization reaction and found to be pH 6.7. (evaluation) The first and second aqueous dispersions obtained above were subjected to the physical property evaluations described above. Furthermore, no corrosion was observed in the reaction vessel after polymerization, and almost no polytetrafluoroethylene residue was found. In addition, the second aqueous dispersion was left to stand at 5°C for one week, and its appearance was visually inspected. No sedimentation was observed, indicating that the second aqueous dispersion was in a stable dispersion state. The ion exchange capacity of the obtained copolymer was 1.62 meq. / g, and the conversion rate of CF2=CF-O-CF2-CF(CF3)-O-CF2-CF2-SO2F was 91%. The results of the various evaluations are shown in Table 1.

[0066] [Comparative Example 2] Emulsification and polymerization were carried out in the same manner as in Example 3, except that emulsification treatment using a biomixer was not performed. (Preparation of mixed solution) 431 g of distilled water was dissolved with 0.952 g of CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COONH, 2.27 g of Na2HPO4·12H2O, and 1.37 g of NaH2PO4·2H2O. Then, 120 g of CF2=CF-O-CF2-CF(CF3)-O-CF2-CF2-SO2F, which had been thoroughly washed with water (as in Example 2), was added to obtain a mixture. That is, the oxygen concentration in the atmosphere during the preparation of the above mixture was 20.9%, and the temperature of the mixture was 12°C. Because the monomer droplets in the above mixture settled rapidly without dispersing, particle size measurement was practically impossible, but they were estimated to be on the order of microns or larger (at least over 2000 nm). (polymerization) The above mixture and CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COONH42.41g were added to a 1L stainless steel pressure-resistant reaction vessel. After thoroughly substituting the vessel with tetrafluoroethylene, the temperature was raised to 50°C. A solution of (NH4OSO2O)20.710g dissolved in 50.0g of water was then injected under pressure as a polymerization initiator to start the polymerization of the resulting solution. During the reaction, tetrafluoroethylene was intermittently introduced from outside the system to maintain the pressure at 0.5 MPaG. After 260 minutes from the start of polymerization, unreacted tetrafluoroethylene was purged to terminate the polymerization and obtain an aqueous dispersion. The solution subjected to polymerization was removed from the system during the reaction and measured, and the pH was 6.7. (evaluation) The mixture obtained in the above preparation and the aqueous dispersion obtained in the polymerization operation were subjected to the aforementioned physical property evaluations, corresponding to the first and second aqueous dispersions, respectively. The cumulant diameter of the aqueous dispersion obtained in the polymerization operation was 35 nm. Although no corrosion was observed in the reaction vessel after polymerization, a large amount of polytetrafluoroethylene residue was found. The obtained copolymer did not melt when heated, making film formation impossible, and therefore the ion exchange capacity could not be measured. The conversion rate of CF2=CF-O-CF2-CF(CF3)-O-CF2-CF2-SO2F was only 6%. The results of various evaluations are shown in Table 1.

[0067] [Example 4] (emulsification process) 40.503g of CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COONH, 1.39g of Na2HPO4·12H2O, and 0.827g of NaH2PO4·2H2O were dissolved in 294g of distilled water, and then 147g of CF2=CF-O-CF2-CF(CF3)-O-CF2-CF2-SO2F, which had been thoroughly washed with water (as in Example 2), was added. The above mixture was stirred for 15 minutes at a peripheral speed of 40m / s using a Nippon Seiki Bio Mixer ABM-4 while maintaining the temperature at 12°C to obtain an aqueous dispersion as an emulsion (first aqueous dispersion). That is, during the emulsification process, the oxygen concentration in the atmosphere was 20.9%, and the temperature of the emulsion was 12°C. (Polymerization process) In a 1L stainless steel pressure-resistant reaction vessel, 92g of water, 1.41g of CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COONH4, 0.525g of Na2HPO4·12H2O, and 0.312g of NaH2PO4·2H2O were added. After thoroughly replacing the inside of the vessel with tetrafluoroethylene, the temperature was raised to 50°C, and 21.2g of the above emulsion was added. A solution of (NH4OSO2O) 21.13g dissolved in 25g of water was then injected under pressure as a polymerization initiator to start the polymerization of the resulting emulsion. During the reaction, tetrafluoroethylene was intermittently introduced from outside the system, and the pressure was maintained at 0.2 MPaG. Tetrafluoroethylene and emulsion were continuously injected under pressure so that the molar ratio of tetrafluoroethylene consumed to monomers in the emulsion was 4.06. After injecting 420g of the emulsion under pressure, unreacted tetrafluoroethylene was purged to terminate the polymerization, and an aqueous dispersion containing the copolymer (second aqueous dispersion) was obtained. The pH of the emulsion solution was measured by removing the emulsion solution used for polymerization from the system during the reaction, and it was found to be pH 6.7. (evaluation) The first and second aqueous dispersions obtained above were subjected to the physical property evaluations described above. Furthermore, no corrosion was observed in the reaction vessel after polymerization, and almost no polytetrafluoroethylene residue was found. In addition, the second aqueous dispersion was left to stand at 5°C for one week, and its appearance was visually inspected. No sedimentation was observed, indicating that the second aqueous dispersion was in a stable dispersion state. The ion exchange capacity of the obtained copolymer was 1.13 meq. / g, the conversion rate of CF2=CF-O-CF2-CF(CF3)-O-CF2-CF2-SO2F was 90%, and the solid content concentration in the polymerization solution was 38%. The results of the various evaluations are shown in Table 1.

[0068] [Comparative Example 3] In the emulsification step of Example 1, sulfuric acid was used instead of Na2HPO4·12H2O and NaH2PO4·2H2O, and the pH of the resulting mixture was adjusted to 1.7. As a result, two-phase separation, which is thought to be due to the protonation of the surfactant, was observed, and fluoroolefin (a) was not emulsified. Therefore, polymerization using this mixture was evaluated as difficult.

[0069] [Example 5] (emulsification process) 2500g of CF2=CF-O-CF2-CF(CF3)-O-CF(CF3)-COONH4, 112.5g of CF3-CF2-CF2-O-CF(CF3)-COONH4, 4.45g of 85% H3PO4(aq.), and 42.4g of NaH2PO4·2H2O were dissolved in 8400g of distilled water, and then 2500g of CF2=CF-O-CF2-CF(CF3)-O-CF2-CF2-SO2F, which had been thoroughly washed with water (as in Example 2), was added. Under a nitrogen atmosphere with an oxygen concentration of 0.1% or less, the above mixture was stirred for 60 minutes at a peripheral speed of 40 m / s using a Nippon Seiki Bio Mixer ABM-4 while maintaining the temperature at 12°C. To this, a solution of CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COONH4 112.5g dissolved in 1600g of distilled water was added to obtain an aqueous dispersion as an emulsion (first aqueous dispersion). In other words, during the emulsification process, the oxygen concentration in the atmosphere was 0.1% or less, and the temperature of the emulsion was 12°C. (Polymerization process) In a 22L stainless steel pressure-resistant reaction vessel, 2700g of water, 15.1g of CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COONH4, 1.31g of 85% H3PO4(aq.), and 11.1g of NaH2PO4·2H2O were added. After thoroughly replacing the inside of the vessel with tetrafluoroethylene, the temperature was raised to 50°C, and 381g of the above emulsion was added. A solution of (NH4OSO2O) 23.65g dissolved in 100g of distilled water was then injected under pressure as a polymerization initiator to start the polymerization of the resulting emulsion. During the reaction, tetrafluoroethylene was intermittently introduced from outside the system, and the pressure was maintained at 0.2 MPaG. After consuming 84 g of tetrafluoroethylene, a solution of 23.65 g of (NH4OSO2O) dissolved in 100 g of distilled water was injected under pressure. The injection of tetrafluoroethylene and emulsion continued until the molar ratio of tetrafluoroethylene consumed to monomer in the emulsion was 4.74. After injecting 10747 g of emulsion, the unreacted tetrafluoroethylene was purged to terminate the polymerization, and an aqueous dispersion containing the copolymer (second aqueous dispersion) was obtained. The pH of the emulsion solution was measured by removing the emulsion solution used for polymerization from the system during the reaction, and it was found to be pH 3.3. (evaluation) The first and second aqueous dispersions obtained above were subjected to the physical property evaluations described above. The cumulant diameter of the second aqueous dispersion was 106 nm. Furthermore, no corrosion was observed in the reaction vessel after polymerization, and almost no polytetrafluoroethylene residue was observed. In addition, the second aqueous dispersion was left to stand at 5°C for one week, and its appearance was visually inspected. No sedimentation was observed, and the second aqueous dispersion was evaluated to be in a stable dispersion state. The ion exchange capacity of the obtained copolymer was 1.03 meq. / g, and the conversion rate of CF2=CF-O-CF2-CF(CF3)-O-CF2-CF2-SO2F was 94%. The results of the various evaluations are shown in Table 1.

[0070] [Example 6] (emulsification process) 30.0g of CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COONH4, 3.55g of 85% H3PO4(aq.), and 33.9g of NaH2PO4·2H2O were dissolved in 6000g of distilled water, and then 2000g of CF2=CF-O-CF2-CF2-SO2F, which had been thoroughly washed with water (as in Example 2), was added. Under a nitrogen atmosphere with an oxygen concentration of 0.1% or less, the above mixture was stirred for 30 minutes at a peripheral speed of 40m / s using a Nippon Seiki Bio Mixer ABM-4 while maintaining the temperature at 12°C. To this, a solution of 90.1g of CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COONH4 dissolved in 2000g of distilled water was added to obtain an aqueous dispersion as an emulsion (first aqueous dispersion). In other words, during the emulsification process, the oxygen concentration in the atmosphere was 0.1% or less, and the temperature of the emulsified liquid was 12°C. (Polymerization process) In a 22L stainless steel pressure-resistant reaction vessel, 2300g of water, 24.3g of CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COONH4, 1.15g of 85% H3PO4(aq.), and 9.82g of NaH2PO4·2H2O were added. After thoroughly replacing the inside of the vessel with tetrafluoroethylene, the temperature was raised to 50°C, and 762g of the above emulsion was added. A solution of (NH4OSO2O) 21.83g dissolved in 200g of distilled water was then injected under pressure as a polymerization initiator to start the polymerization of the resulting emulsion. During the reaction, tetrafluoroethylene was intermittently introduced from outside the system, and the pressure was maintained at 0.5 MPaG. After consuming 79 g of tetrafluoroethylene, a solution of 23.65 g of (NH4OSO2O) dissolved in 200 g of distilled water was injected under pressure. The injection of tetrafluoroethylene and emulsion continued until the molar ratio of tetrafluoroethylene consumed to monomer in the emulsion was 2.65. After injecting 8790 g of emulsion, the supply of emulsion and tetrafluoroethylene was stopped, and the reaction was continued for another 90 minutes. Unreacted tetrafluoroethylene was purged to terminate the polymerization, and an aqueous dispersion containing the copolymer (second aqueous dispersion) was obtained. The pH of the emulsion solution was measured by removing the emulsion solution used for polymerization from the system during the reaction, and it was found to be pH 3.7. (Rating 1) The first and second aqueous dispersions obtained above were subjected to the physical property evaluations described above. The cumulant diameter of the second aqueous dispersion was 113 nm. Furthermore, no corrosion was observed in the reaction vessel after polymerization, and almost no polytetrafluoroethylene residue was observed. In addition, the second aqueous dispersion was left to stand at 5°C for one week, and its appearance was visually inspected. No sedimentation was observed, and the second aqueous dispersion was evaluated to be in a stable dispersion state. The ion exchange capacity of the obtained copolymer was 1.25 meq. / g, the conversion rate of CF2=CF-O-CF2-CF2-SO2F was 94%, the solid content concentration in the polymerization solution was 32%, and the zeta potential of the fluoropolymer was -66 mV. The results of the various evaluations are shown in Table 1.

[0071] [Example 7] (emulsification process) 47.20g of CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COONH, 0.213g of 85% H3PO4(aq.), and 2.03g of NaH2PO4·2H2O were dissolved in 480g of distilled water, and then 240g of CF2=CF-O-CF2-CF(CF3)-O-CF2-CF2-SO2F, which had been thoroughly washed with water (as in Example 2), was added. Under a nitrogen atmosphere with an oxygen concentration of 0.1% or less, the above mixture was stirred for 10 minutes at a peripheral speed of 40m / s using a Nippon Seiki Bio Mixer ABM-4 while maintaining the temperature at 12°C to obtain an aqueous dispersion as an emulsion (first aqueous dispersion). That is, during the emulsification process, the oxygen concentration in the atmosphere was 0.1% or less, and the temperature of the emulsion was 12°C. (Polymerization process) In a 1L stainless steel pressure-resistant reaction vessel, 99.0g of water, 0.518g of CF3-CF2-CF2-O-CF(CF3)-CF2-O-CF(CF3)-COONH4, 0.044g of 85% H3PO4(aq.), and 0.420g of NaH2PO4·2H2O were added. After thoroughly replacing the inside of the vessel with tetrafluoroethylene, the temperature was raised to 50°C, and 13.6g of the above emulsion was added. A solution of (NH4OSO2O)20.123g dissolved in 6g of distilled water was then injected under pressure as a polymerization initiator to start the polymerization of the resulting emulsion. During the reaction, tetrafluoroethylene was intermittently introduced from outside the system, and the pressure was maintained at 0.2 MPaG. After consuming 3.1 g of tetrafluoroethylene, a solution of 20.246 g of (NH4OSO2O) dissolved in 6 g of distilled water was injected under pressure. The injection of tetrafluoroethylene and emulsion continued until the molar ratio of tetrafluoroethylene consumed to monomer in the emulsion was 6.48. After injecting 428 g of emulsion, the unreacted tetrafluoroethylene was purged to terminate the polymerization, and an aqueous dispersion containing the copolymer (second aqueous dispersion) was obtained. The pH of the emulsion solution was measured by removing the emulsion solution used for polymerization from the system during the reaction, and it was found to be pH 3.3. (evaluation) The first and second aqueous dispersions obtained above were subjected to the aforementioned physical property evaluations. The cumulant diameter of the second aqueous dispersion was 136 nm. Furthermore, no corrosion was observed in the reaction vessel after polymerization, and almost no polytetrafluoroethylene residue was found. In addition, the second aqueous dispersion was left to stand at 5°C for one week, and its appearance was visually inspected. No sedimentation was observed, and the second aqueous dispersion was evaluated to be in a stable dispersion state. The ion exchange capacity of the obtained copolymer was 1.05 meq. / g, the conversion rate of CF2=CF-O-CF2-CF(CF3)-O-CF2-CF2-SO2F was 92%, the solid content concentration in the polymerization solution was 39%, and the zeta potential of the fluoropolymer was -59 mV. The results of the various evaluations are shown in Table 1.

[0072] [Table 1] [Industrial applicability]

[0073] The aqueous dispersion of fluoroolefin (first aqueous dispersion) and the aqueous dispersion of fluoroolefin copolymer (second aqueous dispersion) of the present invention can be suitably used for ion exchange membrane applications.

Claims

1. A fluoroolefin (a) represented by the following general formula (1), A surfactant (c) represented by the following general formula (2), A dispersion medium containing water, an aqueous dispersion containing, The cumulant diameter of the aqueous dispersion is 250 to 2000 nm. An aqueous dispersion having a pH of 2.0 to 7.

0. CF 2 =CF-[O-CF 2 -CF(CF 3 )] n -O-[CF 2 ] m -Z・・・(1) (In the above general formula (1), n represents an integer of 0 or more and 2 or less, m represents an integer of 2 or more and 4 or less, and Z is CF 3 , SO 2 F or COOCH 3 .) CF 3 -[CF 2 ] m -O-[CF(CF 3 )-CF 2 -O] n -CF(CF 3 )-Z・・・(2) (In the above general formula (2), m represents an integer from 0 to 2, n represents an integer from 0 to 6, Z represents COOM, where M is H, Li, Na, K or NR) 4 This represents a linear alkyl group, where R represents hydrogen (H) or a linear alkyl group having 1 to 4 carbon atoms.

2. The fluoroolefin (a) is CF 2 = CF - O - CF 2 -CF 2 -SO 2 F, CF 2 = CF - O - CF 2 -CF 2 -CF 2 -CF 2 -SO 2 F, CF 2 = CF - O - CF 2 -CF (CF 3 )-O-CF 2 -CF 2 -SO 2 F, CF 2 = CF - O - CF 2 -CF (CF 3 )-O-CF 2 -CF 2 -CF 3 , and CF 2 = CF - O - CF 2 -CF (CF 3 )-O-CF 2 -CF 2 - COOCH 3 It comprises at least one fluoroolefin (a') selected from, The aqueous dispersion according to claim 1, wherein the content of the fluoroolefin (a') is 15 to 40% by mass.

3. The surfactant (c) is CF 3 -CF 2 -CF 2 -O-CF(CF 3 ) - CF 2 -O-CF(CF 3 ) - COOM or CF 3 -CF 2 -CF 2 -O-CF(CF 3 ) - CF 2 -O-CF(CF 3 ) - CF 2 -O-CF(CF 3 ) - CF 2 -O-CF(CF 3 ) - CF 2 -O-CF(CF 3 )-COOM (where M is H, Li, Na, K or NR) 4 The aqueous dispersion according to claim 1 or 2, comprising (where R represents H or a linear alkyl group having 1 to 4 carbon atoms).

4. M in the aqueous dispersion 1 OOCCF 2 SO 3 M 2 (M here) 1 and M 2 Each of these is independently H, Li, Na, K, or NR 4 The aqueous dispersion according to any one of claims 1 to 3, wherein the content of (where R represents H or a linear alkyl group having 1 to 4 carbon atoms) is 100 ppm or less.

5. Fe in the aqueous dispersion 2+ and Fe 3+ The total amount is 1 ppm or less. The aqueous dispersion according to any one of claims 1 to 4, wherein the amount of dissolved oxygen in the aqueous dispersion is 1 ppm or less.

6. The aqueous dispersion according to any one of claims 1 to 5, wherein the value obtained by dividing the volume-average particle size of the aqueous dispersion by the number-average particle size is 2.0 or less.

7. A copolymer of a fluoroolefin (a) represented by the following general formula (1) and a fluoroolefin (b) represented by the following general formula (3), A surfactant (c) represented by the following general formula (2), A dispersion medium containing water, an aqueous dispersion containing, The content of the surfactant (c) in the copolymer is 0.5% or more and 5.0% or less. An aqueous dispersion having a solid content concentration of more than 18% by mass. CF 2 =CF-[O-CF 2 -CF(CF 3 )] n -O-[CF 2 ] m -Z・・・(1) (In the above general formula (1), n ​​represents an integer between 0 and 2, m represents an integer between 2 and 4, and Z represents CF) 3 SO 2 F or COOCH 3 (This represents...) CF 3 -[CF 2 ] m -O-[CF(CF 3 )-CF 2 -O] n -CF(CF 3 )-Z・・・(2) (In the above general formula (2), m represents an integer of 0 to 2, n represents an integer of 0 to 6, Z represents COOM, where M is H, Li, Na, K or NR 4 represents, where R represents H or a linear alkyl group having 1 to 4 carbon atoms.) CX1X2=CX3X4...(3) (In the above general formula (3), X1, X2, X3, and X4 represent H, F, or CF3, respectively.)

8. The aqueous dispersion according to claim 7, wherein the absolute value of the zeta potential measured for the aqueous dispersion is greater than 25 mV.

9. The aqueous dispersion according to claim 7 or 8, wherein the cumulant diameter of the aqueous dispersion is 10 to 300 nm.

10. The aqueous dispersion according to any one of claims 7 to 9, wherein the pH of the aqueous dispersion is 2.0 to 7.

0.

11. The aqueous dispersion according to any one of claims 7 to 10, wherein the fluoroolefin (b) comprises tetrafluoroethylene.

12. A method for producing an aqueous dispersion according to any one of claims 1 to 6, A manufacturing method comprising an emulsification step of shearing a mixture containing water, the surfactant (c), and the fluoroolefin (a) at a peripheral speed of 20 to 50 m / s.

13. The manufacturing method according to claim 12, wherein in the emulsification step, the oxygen concentration in the atmosphere is 0.1% or less, and the temperature of the mixed liquid is 20°C or less.

14. A method for producing a second aqueous dispersion, as described in any one of claims 7 to 11, from an aqueous dispersion, as described in any one of claims 1 to 6, as a first aqueous dispersion, A manufacturing method comprising a polymerization step of polymerizing a polymerization initiator, the first aqueous dispersion, and the fluoroolefin (b) to obtain the second aqueous dispersion.

15. The manufacturing method according to claim 14, wherein in the polymerization step, the pH of the emulsion solution containing the polymerization initiator and the first aqueous dispersion is 2.0 to 7.0, the polymerization temperature is 0 to 90°C, and the polymerization pressure is 0.0 to 2.0 MPaG.

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