Fluorine-containing polymer production method, aqueous dispersion, and solid composition

Abstract

To provide a fluorine-containing polymer production method by which a fluorine-containing polymer can be efficiently produced without requiring an emulsifier, while using an environmentally friendly aqueous medium; an aqueous dispersion; and a solid composition.SOLUTION: A method for producing a fluorine-containing polymer according to the present invention includes a step in which a monomer containing tetrafluoroethylene is polymerized in an aqueous dispersion containing a first fluorine-containing polymer having a glass transition temperature of 10°C or lower and an aqueous medium, thereby producing a second fluorine-containing polymer different from the first fluorine-containing polymer, where before starting polymerization of the monomer, the content of the first fluorine-containing polymer is 0.01 to 4.0 mass% relative to the total mass of the aqueous dispersion, and before starting polymerization of the monomer, the concentration of a fluorine-based emulsifier is 100 mass ppm or less relative to the total mass of the first fluorine-containing polymer in the aqueous dispersion.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing a fluorine-containing polymer, an aqueous dispersion, and a solid composition.

Background Art

[0002] Fluorine-containing polymers such as tetrafluoroethylene-based copolymers are used in various industrial fields because they are excellent in heat resistance, chemical resistance, flame retardancy, weather resistance, etc. As a method for producing a fluorine-containing polymer, a method of emulsion-polymerizing a fluorine-containing monomer in an aqueous medium using a fluorine-containing emulsifier can be mentioned (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the method for producing a fluorine-containing polymer of Patent Document 1, since an aqueous medium is used, the environmental load is small. However, when a large amount of the emulsifier, which is an essential component, remains in the aqueous dispersion obtained by polymerization, removal of the emulsifier is required depending on the application.

[0005] An object of the present invention is to provide a method for producing a fluorine-containing polymer that can efficiently produce a fluorine-containing polymer without using an emulsifier as an essential component while using an aqueous medium with a small environmental load. Another object of the present invention is to provide an aqueous dispersion and a solid composition.

Means for Solving the Problems

[0006] As a result of intensive studies, the present inventors have found that the above problems can be solved by the following configuration. [1] A method for producing a fluorine-containing polymer, which polymerizes a monomer containing tetrafluoroethylene in an aqueous dispersion containing a first fluorine-containing polymer having a glass transition temperature of 10°C or lower and an aqueous medium to produce a second fluorine-containing polymer different from the first fluorine-containing polymer. Before starting the polymerization of the monomer, the content of the first fluorine-containing polymer is 0.01 to 4.0% by mass based on the total mass of the aqueous dispersion. A method for producing a fluorine-containing polymer, wherein before starting the polymerization of the monomer, the concentration of the fluorine-based emulsifier is 100 ppm by mass or less based on the total mass of the first fluorine-containing polymer in the aqueous dispersion. [2] The method for producing a fluorine-containing polymer according to [1], wherein the first fluorine-containing polymer contains units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether). [3] The method for producing a fluorine-containing polymer according to [2], wherein the units based on perfluoro(alkyl vinyl ether) are 20 to 60 mol% based on the total of the units based on tetrafluoroethylene and the units based on perfluoro(alkyl vinyl ether) in the first fluorine-containing polymer. [4] The method for producing a fluorine-containing polymer according to any one of [1] to [3], wherein the amount of the monomer used is 1 to 50 parts by mass with respect to 100 parts by mass of the amount of the aqueous medium used. [5] The method for producing a fluorine-containing polymer according to any one of [1] to [4], wherein the monomer is polymerized in the presence of a polymerization initiator. [6] An aqueous dispersion containing an aqueous medium, a first fluorine-containing polymer having a glass transition temperature of 10°C or lower, and a second fluorine-containing polymer containing units based on tetrafluoroethylene and different from the first fluorine-containing polymer. The temperature T showing the maximum endothermic amount in the range of 10 to 35°C of the solid composition obtained by aggregating the aqueous dispersion, measured by the following method, is 19°C or lower. Measurement method of temperature T: A solid composition having no heating history at a temperature of 300°C or higher is measured with a differential scanning calorimeter at a heating rate of 10°C / min. [7] A solid composition comprising a first fluorine-containing polymer having a glass transition temperature of 10 °C or lower and a second fluorine-containing polymer different from the first fluorine-containing polymer and containing units based on tetrafluoroethylene, wherein the temperature T indicating the maximum endothermic amount in the range of 10 to 35 °C of the solid composition, measured by the following method, is 19 °C or lower. Method for measuring temperature T: Measure a solid composition without a heating history at a temperature of 300 °C or higher using a differential scanning calorimeter at a heating rate of 10 °C / min. [8] A solid composition obtained by aggregating the aqueous dispersion according to [6], wherein the temperature T indicating the maximum endothermic amount in the range of 10 to 35 °C is 19 °C or lower. Method for measuring temperature T: Measure a solid composition without a heating history at a temperature of 300 °C or higher using a differential scanning calorimeter at a heating rate of 10 °C / min. [9] The content of units based on perfluoro(alkyl vinyl ether) with respect to the total of all units of the first fluorine-containing polymer and the second fluorine-containing polymer is 0.1 to 5.0 mol%, and the content of the compound represented by formula (S1) and the content of the compound represented by formula (S2) are each 100 mass ppb or less with respect to the total mass of the first fluorine-containing polymer and the second fluorine-containing polymer. The aqueous dispersion according to [6]. Formula (S1): H-(CF2) n―1 -COOM Formula (S2): H-(CF2) n -SO3M In formula (S1) and formula (S2), M each independently represents a hydrogen atom, Na, K, or NH4, and n each independently represents 8 or 10.

[10] The content of units based on perfluoro(alkyl vinyl ether) with respect to the total of all units of the first fluorine-containing polymer and the second fluorine-containing polymer is 0.1 to 5.0 mol%, and the content of the compound represented by formula (S1) and the content of the compound represented by formula (S2) are each 100 mass ppb or less with respect to the total mass of the first fluorine-containing polymer and the second fluorine-containing polymer. The solid composition according to [7]. Formula (S1): H-(CF2) n―1 -COOM Formula (S2): H-(CF2) n -SO3M In Formula (S1) and Formula (S2), M each independently represents a hydrogen atom, Na, K, or NH4, and n each independently represents 8 or 10.

Advantages of the Invention

[0007] According to the present invention, it is possible to provide a method for producing a fluorine-containing polymer that can efficiently produce a fluorine-containing polymer without requiring an emulsifier while using an aqueous medium with a small environmental load. Further, according to the present invention, an aqueous dispersion and a solid composition can also be provided.

Modes for Carrying Out the Invention

[0008] The meanings of the terms in the present invention are as follows. The numerical range represented by “~” means a range including the numerical values described before and after “~” as the lower limit value and the upper limit value. In the numerical ranges described stepwise in this specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of another stepwise numerical range. Also, in the numerical ranges described in this specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples. In this specification, each component may be used alone as one kind of substance corresponding to each component, or two or more kinds may be used in combination. Here, when two or more kinds of substances are used in combination for each component, the content of that component refers to the total content of the combined substances, unless otherwise specified. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment. “Unit” is a general term for an atomic group directly formed by polymerization of a monomer and derived from one molecule of the above monomer, and an atomic group obtained by chemically converting a part of the above atomic group. “Unit based on a monomer” is hereinafter also simply referred to as “unit”. The content (mass % or mol %) of each unit in the polymer relative to all the units contained in the polymer is determined by analyzing the polymer by solid-state nuclear magnetic resonance spectroscopy (NMR). Usually, the content of each unit calculated from the charged amount of each monomer is substantially the same as the actual content of each unit.

[0009] [Method for producing fluoropolymer] The method for producing a fluoropolymer of the present invention (hereinafter also referred to as "this production method") is a method for polymerizing a monomer containing tetrafluoroethylene (hereinafter also referred to as "specific monomer") in a first fluoropolymer having a glass transition temperature of 10 °C or lower and an aqueous dispersion containing an aqueous medium to produce a second fluoropolymer different from the first fluoropolymer. In this production method, before starting the polymerization of the monomer, the content of the first fluoropolymer is 0.01 to 4.0% by mass based on the total mass of the aqueous dispersion. Further, in this production method, before starting the polymerization of the monomer, the concentration of the fluorine-based emulsifier is 100 mass ppm or less based on the total mass of the first fluoropolymer in the aqueous dispersion.

[0010] The reason why the second fluoropolymer can be efficiently produced without using an emulsifier as an essential component by this production method is presumably that, by using an aqueous dispersion containing a predetermined amount of the first fluoropolymer having a glass transition temperature of 10 °C or lower, the first fluoropolymer functioned as a good polymerization field for the second fluoropolymer.

[0011] [Aqueous dispersion] In this production method, an aqueous dispersion containing a first fluoropolymer and an aqueous medium is used.

[0012] [First fluoropolymer] When the first fluorine-containing polymer polymerizes a specific monomer, it adsorbs and incorporates the specific monomer in the hydrophobic part to solubilize the specific monomer, and it is presumed that the specific monomer polymerizes inside the particles of the first fluorine-containing polymer by adding a polymerization initiator thereto. Further, it is presumed that the first fluorine-containing polymer contributes to the dispersion stabilization in an aqueous medium.

[0013] The glass transition temperature (hereinafter also referred to as "Tg") of the first fluorine-containing polymer is 10 ° C or lower. From the viewpoint of efficiently adsorbing the specific monomer, the Tg of the first fluorine-containing polymer is preferably 5 ° C or lower, more preferably 3 ° C or lower, and still more preferably 0 ° C or lower. From the viewpoint of the thermal stability after molding processing, the Tg of the first fluorine-containing polymer is preferably -50 ° C or higher, more preferably -45 ° C or higher, and still more preferably -40 ° C or higher. The Tg of the first fluorine-containing polymer is measured by a differential scanning calorimetry (DSC) method, and the detailed measurement conditions are as described in the Examples section below. Examples of the method for setting the Tg of the first fluorine-containing polymer within the above range include a method of adjusting the type and amount of monomers used in the production of the first fluorine-containing polymer.

[0014] The first fluorine-containing polymer preferably contains a unit based on tetrafluoroethylene (hereinafter also referred to as "TFE") (hereinafter also referred to as "TFE unit") and a unit based on perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE") (hereinafter also referred to as "PAVE unit") from the viewpoints of being easily adjusted to the above range of Tg and the effects of the present invention being more excellent.

[0015] PAVE is preferably a monomer represented by the formula (1) from the viewpoints of excellent polymerization reactivity in the production of the first fluorine-containing polymer and the ability to more efficiently produce the second fluorine-containing polymer. CF2=CF-O-R f1 (1) In the formula (1), R f1 represents a perfluoroalkyl group having 1 to 10 carbon atoms. R f1The number of carbon atoms is preferably 1 to 8, more preferably 1 to 6, still more preferably 1 to 5, and particularly preferably 1 to 3, from the viewpoint of more excellent polymerization reactivity. The perfluoroalkyl group may be linear or branched.

[0016] Specific examples of PAVE include perfluoro(methyl vinyl ether) (hereinafter also referred to as "PMVE"), perfluoro(ethyl vinyl ether) (hereinafter also referred to as "PEVE"), and perfluoro(propyl vinyl ether) (hereinafter also referred to as "PPVE"). Among these, PMVE and PPVE are preferred, and PMVE is more preferred, from the viewpoint of being able to produce the second fluorine-containing polymer more efficiently.

[0017] When the first fluorine-containing polymer contains TFE units and PAVE units, in the first fluorine-containing polymer, the PAVE units are preferably 20 to 60 mol%, more preferably 25 to 60 mol%, and still more preferably 30 to 55 mol%, based on the total of the TFE units and PAVE units, from the viewpoints of easily adjusting the Tg within the above range and being able to produce the second fluorine-containing polymer more efficiently.

[0018] The first fluorine-containing polymer may contain units based on monomers other than TFE and PAVE, but it is preferably substantially free of units based on other monomers, from the viewpoint of being able to produce the second fluorine-containing polymer more efficiently. Substantially free of units based on other monomers means that the content of units based on other monomers is 0.01 mol% or less based on all the units of the first fluorine-containing polymer, and 0 mol% is more preferred. When containing units based on other monomers, hexafluoropropylene is preferred as the other monomer.

[0019] Before starting the polymerization of the monomer used for the polymerization of the second fluorine-containing polymer, the content of the first fluorine-containing polymer is 0.01 to 4.0% by mass, preferably 0.01 to 0.6% by mass, and more preferably 0.01 to 0.5% by mass, based on the total mass of the aqueous medium in the aqueous dispersion, from the viewpoint of more efficiently producing the second fluorine-containing polymer.

[0020] In this specification, "before starting the polymerization of the monomer used for the polymerization of the second fluorine-containing polymer" means immediately before the polymerization start point. Here, the "polymerization start point" includes the point in time when the monomer and the polymerization initiator coexist in the reactor after raising the temperature in the reactor to the polymerization temperature or higher, and the point in time when the temperature in the reactor is raised to the polymerization temperature or higher after the monomer and the polymerization initiator coexist in the reactor.

[0021] Before starting the polymerization of the monomer used for the polymerization of the second fluorine-containing polymer, the concentration of sulfate ions is preferably 10 ppm by mass or less, more preferably 5 ppm by mass or less, based on the total mass of the aqueous medium in the aqueous dispersion, from the viewpoint of suppressing the coloring of the second fluorine-containing polymer. The lower limit is 0 ppm by mass. As an example of a method for setting the concentration of sulfate ions to the above value, a method of removing sulfate ions using an anion exchange resin during the production of the first fluorine-containing polymer can be mentioned. Here, sulfate ions are derived from, for example, a polymerization initiator (especially ammonium persulfate) used during the production of the first fluorine-containing polymer and may be contained in the aqueous dispersion containing the first fluorine-containing polymer. When the content of sulfate ions is 10 ppm by mass or less (especially 5 ppm by mass or less), it is presumed that the formation of end groups with low heat resistance in the second fluorine-containing polymer is suppressed, and as a result, the coloring of the second fluorine-containing polymer is suppressed.

[0022] Before starting the polymerization of the monomer used for the polymerization of the second fluorine-containing polymer, the concentration of ammonium ions is preferably 20 ppm by mass or less, more preferably 10 ppm by mass or less, based on the total mass of the aqueous medium in the aqueous dispersion, from the viewpoint of suppressing the aggregation of the second fluorine-containing polymer. The lower limit is 0 ppm by mass. As an example of a method for setting the ammonium ion concentration to the above value, a method of removing ammonium ions using a cation exchange resin during the production of the first fluorine-containing polymer can be mentioned. Here, the ammonium ions are derived from, for example, an initiator (particularly ammonium persulfate) used during the production of the first fluorine-containing polymer, and may be contained in the aqueous dispersion containing the first fluorine-containing polymer. It is presumed that when the ammonium ion content is 20 mass ppm or less, the ionic strength in the aqueous medium decreases, resulting in an improvement in the production efficiency of the second fluorine-containing polymer.

[0023] The first fluorine-containing polymer is preferably dispersed in the aqueous medium in the form of particles. In this case, from the viewpoint of being able to produce the second fluorine-containing polymer more efficiently, the average particle diameter of the first fluorine-containing polymer is preferably 1 to 150 nm, more preferably 10 to 120 nm, and still more preferably 50 to 120 nm. The average particle diameter of the first fluorine-containing polymer is the particle diameter (D50) at the point where the cumulative volume becomes 50% on the cumulative curve obtained by measuring the particle size distribution by the laser diffraction / scattering method with the total volume of the particle population as 100%. The detailed measurement conditions are as described in the Examples section.

[0024] As a method for producing the first fluorine-containing polymer, a method of polymerizing a monomer (preferably a monomer mixture containing TFE and PAVE) in an aqueous medium in the presence of a polymerization initiator is preferable. Thereby, a first fluorine-containing polymer dispersed in the form of particles in the aqueous medium can be obtained. The aqueous medium in which the particles of the first fluorine-containing polymer thus obtained are dispersed may be used as it is as the above aqueous dispersion, or another aqueous medium may be further added and used as the above aqueous dispersion. Alternatively, the solvent may be replaced to disperse the first fluorine-containing polymer in another aqueous medium and used as the above aqueous dispersion.

[0025] As the polymerization initiator used in the production of the first fluorine-containing polymer, a water-soluble polymerization initiator is preferred. Among them, persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate, organic polymerization initiators such as disuccinic peroxide and azobisisobutylamidine dihydrochloride are more preferred, persulfates are even more preferred, and ammonium persulfate is particularly preferred.

[0026] As the aqueous medium used in the production of the first fluorine-containing polymer, water or a mixed solvent of water and a water-soluble organic solvent can be mentioned. Specific examples of the water-soluble organic solvent include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol.

[0027] The production method of the first fluorine-containing polymer preferably has a heating step of heating the aqueous medium in which the first fluorine-containing polymer is dispersed. Thereby, the polymerization initiator present in the system is deactivated, so that during the polymerization of the second fluorine-containing polymer, it is less likely to be affected by the polymerization initiator used in the production of the first fluorine-containing polymer. As a result, it is easy to obtain a second fluorine-containing polymer with a high molecular weight. From the viewpoint of further promoting the deactivation of the polymerization initiator in the aqueous medium, the heating temperature in the heating step is preferably 70 to 100 °C, more preferably 80 to 98 °C, and even more preferably 85 to 95 °C.

[0028] (Aqueous medium) The aqueous dispersion used in this production method contains an aqueous medium. The aqueous medium contained in the aqueous dispersion may be the polymerization solvent used in the production of the first fluorine-containing polymer as described above. Specific examples of the aqueous medium contained in the aqueous dispersion are the same as those of the aqueous medium used in the production of the first fluorine-containing polymer described above. Before starting the polymerization of the monomer used in the polymerization of the second fluorine-containing polymer, the content of the aqueous medium is preferably 60 to 99.9% by mass, more preferably 96 to 99.9% by mass, and even more preferably 98 to 99.9% by mass based on the total mass of the aqueous dispersion.

[0029] (Other components) The aqueous dispersion used in this manufacturing method may contain components other than the first fluorine-containing polymer and the aqueous medium. Specific examples of other components that the aqueous dispersion may contain include a chain transfer agent, an emulsifier other than a fluorine-based emulsifier, a pH adjuster, and a wax.

[0030] Specific examples of the chain transfer agent include ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane.

[0031] Specific examples of the emulsifier other than the fluorine-based emulsifier include sodium lauryl sulfate, Perex SS-H manufactured by Kao Chemical Co., Ltd., Newcol 1305-SN manufactured by Nippon Emulsifier Co., Ltd., and the like.

[0032] Specific examples of the pH adjuster include inorganic salts. Specific examples of the inorganic salts include phosphates such as disodium hydrogen phosphate and sodium dihydrogen phosphate, carbonates such as sodium hydrogen carbonate and sodium carbonate, and the like. More preferred specific examples of the phosphate include disodium hydrogen phosphate dihydrate, disodium hydrogen phosphate dodecahydrate, and the like.

[0033] Specific examples of the wax include Parafffin Wax-155 and Parafffin Wax-150 (both manufactured by Nippon Seiro Co., Ltd.).

[0034] When the aqueous dispersion contains a chain transfer agent, the content of the chain transfer agent is preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the aqueous medium. Further, the amount of the chain transfer agent used is preferably 0.1 to 20 parts by mass, more preferably 0.1 to 15 parts by mass, and still more preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the amount of the specific monomer described later. When the aqueous dispersion contains an emulsifier other than the fluorine-based emulsifier, the content of the emulsifier other than the fluorine-based emulsifier is preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of the aqueous medium. When the aqueous dispersion contains a pH adjuster, the content of the pH adjuster is preferably 0.01 to 3.0 parts by mass with respect to 100 parts by mass of the aqueous medium. When the aqueous dispersion contains wax, the content of the wax is preferably 1 to 10 parts by mass with respect to 100 parts by mass of the aqueous medium.

[0035] Before starting the polymerization of the monomer used for the polymerization of the second fluorine-containing polymer, the concentration of the fluorine-based emulsifier is 100 mass ppm or less with respect to the total mass of the first fluorine-containing polymer in the aqueous dispersion. From the viewpoint of more excellent effects of the present invention, it is preferably 50 mass ppm or less, more preferably 25 mass ppm, and still more preferably 5 mass ppm or less. The lower limit may be 0 mass ppm. The fluorine-based emulsifier means an emulsifier in which the hydrophobic part contains a fluorine atom at the hydrophilic part and the hydrophobic part of the emulsifier. Specific examples of the fluorine-based emulsifier include fluorinated alkanoate and fluorinated ether carboxylic acid compounds. As an example of a method for making the concentration of the fluorine-based emulsifier within the above range, a method of producing an aqueous dispersion without using a fluorine-based emulsifier can be mentioned.

[0036] Before starting the polymerization of the monomer used for the polymerization of the second fluorine-containing polymer, the concentration of fluoride ions is preferably 100 mass ppm or less, more preferably 50 mass ppm or less, from the viewpoint of polymerization stability, with respect to the total mass of the aqueous dispersion. The lower limit may be 0 mass ppm. As an example of a method for making the concentration of fluoride ions to the above value, a method of removing sulfate ions using an anion exchange resin during the production of the first fluorine-containing polymer can be mentioned. Here, fluoride ions may be generated by the reaction of a polymerization initiator (for example, ammonium persulfate) and a monomer used for the production of the first fluorine-containing polymer, and may be contained in the aqueous dispersion.

[0037] <Specific monomer> The specific monomer contains TFE. The amount of TFE used is preferably 97 to 100% by mass, more preferably 98 to 100% by mass, and still more preferably 99 to 100% by mass, based on the amount of the specific monomer used.

[0038] The specific monomer may contain a fluorine-containing monomer other than TFE, but may not substantially contain a fluorine-containing monomer other than TFE. Not substantially containing a fluorine-containing monomer other than TFE means that the amount of the fluorine-containing monomer other than TFE is 0.0001% by mass or less based on the amount of the specific monomer used, and it may be 0% by mass. Examples of the fluorine-containing monomer other than TFE include chlorotrifluoroethylene (hereinafter also referred to as "CTFE"), vinylidene fluoride (hereinafter also referred to as "VdF"), fluoroalkyl ethylene, PAVE, and hexafluoropropylene. Two or more of the fluorine-containing monomers other than TFE may be used in combination.

[0039] The specific monomer may contain a monomer other than the fluorine-containing monomer (hereinafter also referred to as "other monomer"), but preferably does not contain other monomers. Not substantially containing other monomers means that the amount of other monomers is 0.0001% by mass or less based on the amount of the specific monomer used, and 0% by mass is more preferable. Specific examples of other monomers include ethylene, propylene, vinyl chloride, and vinylidene chloride. Two or more of other monomers may be used in combination.

[0040] The amount of the specific monomer used is preferably 1 to 50 parts by mass, more preferably 1 to 40 parts by mass, and still more preferably 1 to 30 parts by mass, based on 100 parts by mass of the aqueous medium contained in the above aqueous dispersion.

[0041] <Polymerization initiator> In this production method, the specific monomer is preferably polymerized in the presence of a polymerization initiator. As the polymerization initiator, an oil-soluble radical initiator, a water-soluble radical initiator, or a water-soluble redox catalyst is preferable. Specific examples of the oil-soluble radical initiator include oil-soluble organic peroxides such as tert-butyl peroxypivalate (hereinafter also referred to as "PBPV"), diisopropyl peroxydicarbonate (hereinafter also referred to as "IPP"), and the like. Specific examples of the water-soluble radical initiator include persulfates such as ammonium persulfate and potassium persulfate, water-soluble organic peroxides such as disuccinic peroxide, bisglutaric peroxide, and tert-butyl hydroperoxide (hereinafter also referred to as "TBHP"), and the like. As the water-soluble redox catalyst, a combination of an oxidizing agent such as bromic acid or its salt, chloric acid or its salt, persulfuric acid or its salt, permanganic acid or its salt, hydrogen peroxide, and a reducing agent such as sulfurous acid or its salt, bisulfite or its salt, thiosulfuric acid or its salt, organic acid, inorganic salt, etc. is preferable. As the persulfate, potassium persulfate and ammonium persulfate are preferable. As the sulfite, sodium sulfite is preferable. As the inorganic salt, a combination of a sulfate anion, a sulfite anion, and a chloride anion with a metal ion can be mentioned. As the metal ion, a transition metal is preferable, and ions of manganese, iron, cobalt, nickel, copper, zinc, cerium, and silver can be mentioned. Among them, iron ions are preferable. As the inorganic salt, iron(II) sulfate is preferable. The polymerization initiator is preferably an oil-soluble radical initiator or a water-soluble radical initiator, and from the viewpoint of more efficiently producing a fluorine-containing polymer, an oil-soluble radical initiator is more preferable, and an oil-soluble organic peroxide is even more preferable. Two or more polymerization initiators may be used in combination.

[0042] The amount of the polymerization initiator used is preferably 1 to 1000 ppm, more preferably 5 to 750 ppm, and even more preferably 10 to 500 ppm with respect to 100 parts by mass of the amount of the specific monomer used.

[0043] <Other Components> When polymerizing the specific monomer, components other than the above (hereinafter also referred to as "other components") may be further used. Specific examples of the other components include reducing agents. The amount of the other components used is preferably 1 to 2000 ppm with respect to 100 parts by mass of the amount of the specific monomer used.

[0044] <Engineering> In this production method, the above-mentioned specific monomer is polymerized in the above-mentioned aqueous dispersion to produce a second fluorine-containing polymer.

[0045] The second fluorine-containing polymer obtained by this production method preferably contains units based on TFE (hereinafter also referred to as "TFE units") and is a homopolymer of TFE (hereinafter also referred to as "PTFE"). Note that the first fluorine-containing polymer and the second fluorine-containing polymer may be copolymerized.

[0046] The content of TFE units contained in the second fluorine-containing polymer is preferably 99.0 to 100.0 mol%, more preferably 99.5 to 100.0 mol%, and still more preferably 99.9 to 100.0 mol% based on all the units constituting the second fluorine-containing polymer.

[0047] The specific monomer is charged into the reaction system (i.e., the polymerization reaction vessel) by a conventional method. For example, the specific monomer may be continuously or intermittently charged into the reaction system so that the polymerization pressure becomes a predetermined pressure. Alternatively, the specific monomer may be dissolved in an aqueous medium, and the resulting solution may be continuously or intermittently charged into the reaction system. When a polymerization initiator is used, the polymerization initiator may be added to the reaction system all at once or in portions.

[0048] The polymerization temperature is preferably 10 to 95 °C, more preferably 15 to 90 °C. The polymerization pressure is preferably 0.5 to 4.0 MPaG, more preferably 0.6 to 3.5 MPaG. The polymerization time is preferably 90 to 1000 minutes, more preferably 90 to 700 minutes in the case of batch processing.

[0049] The polymerization of the specific monomer is preferably carried out in the substantial absence of an emulsifier. Examples of the emulsifier include known emulsifiers and common surfactants. The phrase "substantially free of an emulsifier" means an environment where the content of the emulsifier is 0.03 mass ppm or less, preferably 0.02 mass ppm or less, and more preferably 0 mass ppm, based on the total mass of the aqueous medium contained in the above aqueous dispersion.

[0050] As described above, it is presumed that the specific monomer polymerizes within the particles of the first fluorine-containing polymer during the polymerization of the specific monomer. Therefore, in this production method, it is considered that particles containing the first fluorine-containing polymer and the second fluorine-containing polymer are generated. That is, according to this production method, it is estimated that the second fluorine-containing polymer is obtained in the form of particles containing the first fluorine-containing polymer and the second fluorine-containing polymer. In this case, an aqueous dispersion in which particles containing the first fluorine-containing polymer and the second fluorine-containing polymer are dispersed in the above aqueous medium is obtained by this production method.

[0051] [Aqueous dispersion] The aqueous dispersion of the present invention (hereinafter also referred to as "this aqueous dispersion") is an aqueous dispersion containing an aqueous medium, a first fluorine-containing polymer having a Tg of 10°C or lower, and a second fluorine-containing polymer containing a TFE unit and different from the above first fluorine-containing polymer. In this aqueous dispersion, the content of the PAVE unit relative to the total of all units of the above first fluorine-containing polymer and the above second fluorine-containing polymer is 0.1 to 5.0 mol%. Further, in this aqueous dispersion, the content of the compound represented by the following formula (S1) and the content of the compound represented by the following formula (S2) are each 100 mass ppb or less based on the total mass of the above first fluorine-containing polymer and the above second fluorine-containing polymer.

[0052] This aqueous dispersion can be obtained, for example, by the above-described production method of the present invention.

[0053] <The first fluorine-containing polymer and the second fluorine-containing polymer> The first fluorine-containing polymer is the same as the first fluorine-containing polymer in the above-described production method of the present invention, and the preferred embodiments are also the same. A preferred embodiment of the first fluorine-containing polymer contained in this aqueous dispersion is an embodiment containing a TFE unit and a PAVE unit. When the first fluorine-containing polymer contains TFE units and PAVE units, in the first fluorine-containing polymer, the PAVE units are preferably 20 to 60 mol%, more preferably 25 to 60 mol%, and still more preferably 30 to 55 mol% based on the total of the TFE units and the PAVE units.

[0054] The content of the first fluorine-containing polymer is preferably 0.10 to 1.0% by mass, more preferably 0.15 to 0.80% by mass, and still more preferably 0.20 to 0.60% by mass based on the total mass of the aqueous dispersion.

[0055] The second fluorine-containing polymer is the same as the second fluorine-containing polymer in the above-described production method, and the preferred embodiments are also the same. The second fluorine-containing polymer contained in the aqueous dispersion contains TFE units. The content of the TFE units contained in the second fluorine-containing polymer is preferably 99.0 to 100.0 mol%, more preferably 99.5 to 100.0 mol%, and still more preferably 99.9 to 100.0 mol% based on all the units constituting the second fluorine-containing polymer.

[0056] The content of the second fluorine-containing polymer is preferably 10 to 40% by mass, more preferably 12 to 35% by mass, and still more preferably 15 to 30% by mass based on the total mass of the aqueous dispersion.

[0057] In the aqueous dispersion, the content of the PAVE units based on the total of all the units of the first fluorine-containing polymer and the second fluorine-containing polymer is 0.1 to 5.0 mol%, preferably 0.2 to 3.0 mol%, and more preferably 0.3 to 2.0 mol%. The PAVE units may be contained in at least one of the first fluorine-containing polymer and the second fluorine-containing polymer, but are preferably contained in the first fluorine-containing polymer.

[0058] In the aqueous dispersion, the content of the TFE units based on the total of all the units of the first fluorine-containing polymer and the second fluorine-containing polymer is preferably 90 to 99.8 mol%, more preferably 93 to 99.5 mol%, and still more preferably 95 to 99.0 mol%. The TFE units may be contained in at least the second fluorine-containing polymer, but are preferably contained in both the first fluorine-containing polymer and the second fluorine-containing polymer.

[0059] In this aqueous dispersion, the total content of the first fluorine-containing polymer and the second fluorine-containing polymer is preferably 10 to 40% by mass, more preferably 12 to 35% by mass, and still more preferably 15 to 35% by mass with respect to the total mass of the aqueous dispersion.

[0060] The first fluorine-containing polymer and the second fluorine-containing polymer may be present separately in the aqueous dispersion, but are preferably present in the form of particles containing the first fluorine-containing polymer and the above-mentioned second fluorine-containing polymer. In this case, from the viewpoint of dispersion stability, the average particle diameter of the particles is preferably 500 μm or less, more preferably 450 μm or less, and still more preferably 400 μm or less. Also, from the viewpoint of cohesiveness, the average particle diameter of the particles is preferably 50 nm or more, more preferably 80 nm or more, and still more preferably 100 nm or more. The average particle diameter of the particles is the particle diameter at the point where the cumulative volume becomes 50% on the cumulative curve obtained by measuring the particle size distribution by the laser diffraction / scattering method and setting the total volume of the particle population to 100%.

[0061] <aqueous medium> Specific examples of the aqueous medium contained in this aqueous dispersion are the same as the specific examples of the aqueous medium used in the production of the above-mentioned first fluorine-containing polymer. The content of the aqueous medium is preferably 50 to 99% by mass, more preferably 60 to 99% by mass, and still more preferably 70 to 99% by mass with respect to the total mass of the aqueous dispersion from the viewpoint of the dispersion stability of the first fluorine-containing polymer and the second fluorine-containing polymer.

[0062] <Compound represented by formula (S1) and compound represented by formula (S2)> The compound represented by formula (S1) and the compound represented by formula (S2) are components that can be generated when polymerizing TFE in the presence of a polymerization initiator, a chain transfer agent, and an emulsifier (especially a hydrocarbon-based emulsifier). Therefore, when no emulsifier is used in the production of the second fluorine-containing polymer contained in this aqueous dispersion, the generation amounts of the compound represented by formula (S1) and the compound represented by formula (S2) can be suppressed, making it easy to keep the contents of these compounds within the ranges described below.

[0063] Formula (S1): H-(CF2) n―1 -COOM Formula (S2): H-(CF2) n -SO3M In formula (S1) and formula (S2), M each independently represents a hydrogen atom, Na, K, or NH4, and n each independently represents 8 or 10.

[0064] In this aqueous dispersion, the content of the compound represented by formula (S1) and the content of the compound represented by formula (S2) are each 100 mass ppb or less, preferably 50 mass ppb or less, more preferably 25 mass ppb or less, and still more preferably 0 mass ppb (that is, not containing the compound represented by formula (S1) and the compound represented by formula (S2)), based on the total mass of the first fluorine-containing polymer and the second fluorine-containing polymer.

[0065] <Others> This aqueous dispersion preferably contains substantially no emulsifier. Examples of the emulsifier include the above-mentioned fluorine-based emulsifier and emulsifiers other than the fluorine-based emulsifier. Substantially not containing an emulsifier in this aqueous dispersion means that the content of the emulsifier is 0.03 mass ppm or less, preferably 0.02 mass ppm or less, and more preferably 0 mass ppm, based on the total mass of this aqueous dispersion.

[0066] <Use> As described above, since this aqueous dispersion does not require an emulsifier, it is also easy to obtain a dispersion in an organic solvent such as N-methylpyrrolidone or acetone by solvent substitution. For example, the present aqueous dispersion can be mixed with an organic solvent and dehydrated by evaporation or using anhydrous sodium sulfate or the like to obtain a dispersion of the organic solvent.

[0067] The present aqueous dispersion enables the fluorine-containing polymer to be stably dispersed even without containing an emulsifier. Therefore, it can be suitably used for coating applications, binders, etc.

[0068] Further, by aggregating the first fluorine-containing polymer and the second fluorine-containing polymer (preferably, particles containing the first fluorine-containing polymer and the second fluorine-containing polymer) from the present aqueous dispersion, powders of the first fluorine-containing polymer and the second fluorine-containing polymer can be obtained.

[0069] Examples of the aggregation method include, but are not limited to, freeze aggregation, acid aggregation, base aggregation, and aggregation using a coagulant. In the case of freeze aggregation, the aggregation temperature is preferably -20 to 0°C. The aggregation time is preferably 1 hour or more, more preferably 2 hours or more. In the case of acid aggregation, a method of adding a solution containing an acid to the present aqueous dispersion is preferred. Examples of the acid to be added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, hydrofluoric acid, etc., and hydrochloric acid is preferred. The concentration of the acid in the solution containing the acid is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and still more preferably 1 to 10% by mass. As base aggregation, a method of adding a solution containing a base to the present aqueous dispersion is preferred. Examples of the base to be added include sodium hydroxide, potassium hydroxide, ammonium carbonate, etc., and sodium hydroxide is preferred. The concentration of the base in the solution containing the base is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and still more preferably 1 to 10% by mass. As for aggregation by a coagulant, known coagulants can be used. Examples of known coagulants include aluminum salts, calcium salts, and magnesium salts. Specifically, aluminum sulfate, alum represented by the general formula M’Al(SO4)2·12H2O [wherein M’ is a monovalent cation other than lithium], calcium nitrate, and magnesium sulfate can be mentioned. Alum is preferred, and potassium alum where M is potassium is more preferred. As the aggregation method, base aggregation is preferred because aggregation particularly easily proceeds.

[0070] [Solid composition] The solid composition of the present invention (hereinafter, also referred to as "the present solid composition") is a solid composition containing a first fluorine-containing polymer having a glass transition temperature of 10°C or lower and a second fluorine-containing polymer containing a TFE unit and different from the first fluorine-containing polymer. In the present solid composition, the content of the PAVE unit is 0.1 to 5.0 mol% with respect to the total of all units of the first fluorine-containing polymer and the second fluorine-containing polymer. Further, in the present solid composition, the content of the compound represented by the above formula (S1) and the content of the compound represented by the above formula (S2) are each 100 mass ppb or less with respect to the total mass of the first fluorine-containing polymer and the second fluorine-containing polymer.

[0071] In the present specification, the solid composition means a composition having a solid content mass of 99 mass% or more. Here, the solid content mass is calculated by the following method based on the mass before and after heating. After heating 2.0 g of the solid composition at 170°C for 20 minutes, the mass of the residue is weighed, and the solid content mass is calculated by the following formula. Solid content mass (mass%) = 100 × (mass of residue) / (mass of solid composition)

[0072] This solid composition is preferably obtained by the aggregation method using the above-described aqueous dispersion. Since the preferred embodiments of this solid composition are the same as those of the first fluorine-containing polymer and the second fluorine-containing polymer contained in the above-described aqueous dispersion, the description thereof will be omitted. The first fluorine-containing polymer and the second fluorine-containing polymer may be present separately in the solid composition, but are preferably present in the form of particles containing the first fluorine-containing polymer and the above-described second fluorine-containing polymer.

[0073] The content of the first fluorine-containing polymer is preferably 0.1 to 5% by mass, more preferably 0.2 to 4% by mass, and still more preferably 0.3 to 3% by mass based on the total mass of the solid composition. The content of the second fluorine-containing polymer is preferably 95 to 99.9% by mass, more preferably 96 to 99.8% by mass, and still more preferably 97 to 99.7% by mass based on the total mass of the solid composition. The total content of the first fluorine-containing polymer and the second fluorine-containing polymer is preferably 99.0 to 100% by mass, more preferably 99.5 to 100% by mass, and still more preferably 99.8 to 100% by mass based on the total mass of the solid composition.

[0074] <Temperature T> For the solid composition obtained by aggregating the aqueous dispersion of the present invention, or the solid composition of the present invention, the temperature T showing the maximum endothermic amount in the range of 10 to 35°C, measured by the method shown below, is preferably 19°C or lower. The temperature T is more preferably 18°C or lower, and still more preferably 17.5°C or lower. The lower limit of the temperature T is 10°C. By including the first fluorine-containing polymer and the second fluorine-containing polymer (preferably, particles containing the first fluorine-containing polymer and the second fluorine-containing polymer) in the aqueous dispersion, the temperature T can be adjusted within the above range.

Examples

[0075] Hereinafter, the present invention will be described in detail with examples. Examples 1, 2, 5, and 6 are examples, and Examples 3, 4, and 7 are comparative examples. However, the present invention is not limited to these examples. Note that the blending amounts of the respective components in the tables described later are based on mass.

[0076] [Measurement and Evaluation Methods] The various measurement methods and evaluation methods are as follows.

[0077] <Glass Transition Temperature (Tg)> Tg was measured using a NEXTA DSC600 manufactured by Hitachi High-Tech Corporation. Specifically, 5 mg of the sample for measurement was weighed into an aluminum sample pan, and the sample was heated to 100 °C at a heating rate of 10 °C / min under a nitrogen atmosphere. Then, it was cooled to -60 °C at a rate of 10 °C / min. When the predetermined temperature was reached, it was heated again to 100 °C at 10 °C / min. Tg was estimated from the inflection point confirmed in this second heating operation.

[0078] <Average Particle Diameter of Particles in Liquid> The raw material liquid was degassed at room temperature (25 °C) for 5 minutes, pressurized with nitrogen to 0.2 MPaG, then purged, and made into atmospheric pressure to obtain a sample for measurement. The particle size of the obtained sample was set to 100 times of integrated count using a laser diffraction / scattering particle size distribution measuring apparatus (Otsuka Electronics Co., Ltd., ELSZ), and the measurement was started. D50 was calculated from the particle diameters measured in the range of 1 to 300 nm, and this was taken as the average particle diameter of the particles in the raw material liquid. Note that when the average particle diameter of the particles in the aqueous dispersion corresponding to the raw material liquid was measured in the same manner as the raw material liquid, it was the same as the average particle diameter of the particles in the raw material liquid. Here, the aqueous dispersion corresponding to the raw material liquid means the aqueous dispersion B corresponding to the raw material liquid B in the case of Example 1 described later. Also, regarding the average particle diameter (D50) of the particles in each aqueous dispersion obtained using the aqueous dispersion corresponding to the raw material liquid, it was measured using a laser diffraction / scattering particle size distribution analyzer (Otsuka Electronics Co., Ltd., ELSZ). However, the range of particle diameters to be measured was not limited, unlike the measurement method for the average particle diameter of the particles in the raw material liquid. Here, each aqueous dispersion obtained using the aqueous dispersion corresponding to the raw material liquid means, in the case of Example 1 described later, the aqueous dispersion 1 obtained using the aqueous dispersion B.

[0079] <Average particle diameter of the dried particles> After drying and aggregating the particles obtained in each example, they were photographed using a scanning electron microscope (for example, JSM-IT700HR InTouchScope manufactured by JEOL Ltd.). The particle diameters of five different particles measured from the obtained SEM images were determined and their arithmetic mean was calculated.

[0080] <Ratio of each unit in the polymer> The ratio of each unit in the polymer was determined from 19 19F-NMR analysis and infrared absorption spectrum analysis.

[0081] <Content of the compound represented by formula (S1)> Regarding the content of the compound represented by the above formula (S1) with respect to the total mass of the particles in the aqueous dispersion obtained in each example described later, it was calculated by the method using the aqueous dispersion among the measurement methods described in paragraphs

[0710] to

[0720] of WO 2018 / 181904 using a liquid chromatography-mass spectrometer. The apparatus used was an Agilent 1260 series HPLC / 6460S, and the column used was cadenza CD-C18 manufactured by Imtakt.

[0082] <Content of the compound represented by formula (S2)> The content of the compound represented by the above formula (S2) with respect to the total mass of the particles in the aqueous dispersion obtained in each of the following examples was calculated by the method using the aqueous dispersion among the measurement methods using the liquid chromatograph mass spectrometer described in paragraphs

[0721] to

[0732] of WO 2018 / 181904. The apparatus used was an Agilent 1260 series HPLC / 6460S, and the column used was a cadenza CD-C18 manufactured by Imtakt.

[0083] <Concentration of fluorinated emulsifier in the raw material liquid> The concentration of the fluorinated emulsifier in the raw material liquid with respect to the total mass of the fluorine-containing polymer was calculated from the charged amount.

[0084] <Crystallization energy> The melting point and the crystallization energy were measured using a DSC8500 manufactured by Perkin Elmer. Specifically, 5 mg of the sample for measurement was weighed into an aluminum sample pan, and the temperature was raised to 200 °C at a rate of 10 °C / min under an air atmosphere and held for 1 minute. Then, the sample was heated to 380 °C at a rate of 10 °C / min. The sample was held at 380 °C for 1 minute and cooled to 200 °C at 10 °C / min. The peak top temperature derived from the thermal melting of the sample confirmed in the heating operation from 200 °C to 380 °C was defined as the melting point, and the crystallization energy was calculated from the peak area confirmed in the cooling operation from 380 °C to 200 °C. It can be said that the smaller the absolute value of the crystallization energy, the higher the molecular weight.

[0085] <Temperature T> The temperature T was measured using a DSC8500 manufactured by Perkin Elmer as a differential scanning calorimeter. Specifically, 10 mg of the sample for measurement was weighed into an aluminum sample pan, and the temperature was raised from -20 °C to 370 °C at a rate of 10 °C / min under an air atmosphere. Among these, the temperature showing the maximum endothermic amount in the range of 10 to 35 °C was defined as the temperature T.

[0086] [Production of raw material liquid A] Into a 1.3 L stainless steel pressure reactor, 717 g of ultrapure water, 50 g of PMVE, and 8 g of TFE were charged, and the temperature was raised to 90 °C while stirring at 500 rpm. Next, an aqueous ammonium persulfate solution (3.6 mass%, 5 cc) was added to initiate polymerization. Since the pressure inside the reactor decreased with the start of polymerization, TFE was added to keep the pressure constant. When 2 g of TFE was injected, the reactor was cooled to terminate the polymerization reaction. After collecting the gas remaining in the reactor, the liquid was withdrawn. This liquid was designated as raw material liquid A. After freeze-aggregating raw material liquid A and then filtering it, the resulting fluoropolymer 1A was analyzed by NMR. As a result, the TFE unit / PMVE unit = 52 / 48 (molar ratio), and the Tg was -5.9 °C.

[0087] [Production of Raw Material Liquid B] To 490 g of the above raw material liquid A, 20 g of Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin) was added. Sixty minutes after starting stirring, the raw material liquid and the ion exchange resin were separated by filtration. To the filtered raw material liquid, 20 g of Purolite A300 (manufactured by Purolite, anion exchange resin) was added. Sixty minutes after starting stirring, the raw material liquid and the ion exchange resin were separated by filtration to obtain raw material liquid B. In raw material liquid B, particles of fluoropolymer 1A (average particle diameter 87 nm) were dispersed in an aqueous medium, and the content of fluoropolymer 1A was 0.6 mass% based on the total mass of raw material liquid B.

[0088] [Production of Raw Material Liquid C] Into a 1.3 L stainless steel pressure reactor, 717 g of ultrapure water, 55 g of PMVE, 9 g of TFE, and 1 drop of an aqueous ammonia solution (30 mass%) were charged, and the temperature was raised to 90 °C while stirring at 500 rpm. Next, an aqueous ammonium persulfate solution (3.6 mass%, 5 cc) was added to initiate polymerization. Since the pressure inside the reactor decreased with the start of polymerization, TFE was added to keep the pressure constant. When 2 g of TFE was injected, the reactor was cooled to terminate the polymerization reaction. After collecting the gas remaining in the reactor, the liquid was withdrawn. This liquid was designated as raw material liquid C. After freezing and aggregating the raw material liquid C, it was filtered, and the obtained fluoropolymer 1C was analyzed by NMR. As a result, the TFE unit / PMVE unit = 52.4 / 47.6 (molar ratio), and the Tg was -5.3 °C.

[0089] [Production of Raw Material Liquid D] To the above raw material liquid C (490 g), Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 20 g) was added. Sixty minutes after starting stirring, the raw material liquid and the ion exchange resin were filtered off by filtration. To the filtered raw material liquid, Purolite A300 (manufactured by Purolite, anion exchange resin, 20 g) was added. Sixty minutes after starting stirring, the raw material liquid and the ion exchange resin were filtered off by filtration to obtain raw material liquid D. In raw material liquid D, particles of fluoropolymer 1C (average particle diameter 23 nm) were dispersed in the aqueous medium, and the content of fluoropolymer 1C was 0.7% by mass based on the total mass of raw material liquid D.

[0090] [Production of Raw Material Liquid E] Ultra-pure water (717 g) and TFE (43 g) were charged into a 1.3 L stainless steel pressure reactor, and the temperature was raised to 90 °C while stirring at 500 rpm. Next, an aqueous ammonium persulfate solution (3.6% by mass, 5 cc) was added to initiate polymerization. Since the pressure in the reactor decreased with the start of polymerization, TFE was added to keep the pressure constant. When 2 g of TFE was injected, the reactor was cooled to terminate the polymerization reaction. After collecting the gas remaining in the reactor, the liquid was withdrawn. This liquid was used as raw material liquid E. After freezing and aggregating raw material liquid E, it was filtered to obtain fluoropolymer 1E. The Tg of fluoropolymer 1E was 110 °C.

[0091] [Production of Raw Material Liquid F] To the above raw material liquid E (490 g), Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 20 g) was added. Sixty minutes after starting stirring, the raw material liquid and the ion exchange resin were separated by filtration. To the filtered raw material liquid, Purolite A300 (manufactured by Purolite, anion exchange resin, 20 g) was added. Sixty minutes after starting stirring, the raw material liquid and the ion exchange resin were separated by filtration to obtain raw material liquid F. Raw material liquid F had particles of fluorine-containing polymer 1E (average particle diameter 80 nm) dispersed in an aqueous medium, and the content of fluorine-containing polymer 1E was 0.48% by mass based on the total mass of raw material liquid F.

[0092] [Production of Raw Material Liquid G] Ultra-pure water (740 g), sodium sulfite (88 mg), n-BMA (n-butyl methacrylate, 330 mg), iron(II) sulfate heptahydrate (11 mg), and Kresto HC (17 mg) were charged into a 1.2 L stainless steel pressure reactor, and the temperature was raised to 60 °C while stirring at 500 rpm. Next, an aqueous potassium persulfate solution (5.0% by mass, 3.8 cc) was added, and polymerization was carried out for 60 minutes. After the polymerization reaction was completed, the liquid was withdrawn. This liquid was used as raw material liquid G. After heating raw material liquid G to remove water, the residue was heated and dried to obtain hydrocarbon polymer 1G (poly(n-BMA)). The Tg of hydrocarbon polymer 1G was 20 °C.

[0093] [Production of Raw Material Liquid H] To the above raw material liquid G (490 g), Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 20 g) was added. Sixty minutes after starting stirring, the raw material liquid and the ion exchange resin were separated by filtration. To the filtered raw material liquid, Purolite A300 (manufactured by Purolite, anion exchange resin, 20 g) was added. Sixty minutes after starting stirring, the raw material liquid and the ion exchange resin were separated by filtration to obtain raw material liquid H. Raw material liquid H had particles of hydrocarbon polymer 1G (average particle diameter 89 nm) dispersed in an aqueous medium, and based on the charged amount of n-BMA, the content of hydrocarbon polymer 1G was 0.044% by mass based on the total mass of raw material liquid H.

[0094] [Production of Feed Liquid I] Into a 1.3 L stainless steel pressure reactor, ultrapure water (717 g), PMVE (55 g), TFE (9 g), and an aqueous ammonia solution (30% by mass, 1 drop) were charged, and the temperature was raised to 90°C while stirring at 500 rpm. Next, an aqueous ammonium persulfate solution (3.6% by mass, 5 cc) was added to initiate polymerization. Since the pressure in the reactor decreased with the start of polymerization, TFE was added to keep the pressure constant. When 1 g of TFE was injected, the reactor was cooled to 20°C to terminate the polymerization reaction. After recovering the gas remaining in the reactor, nitrogen was injected up to 0.2 MPaG and the temperature was raised to 90°C. After heating the reactor for 3 h, it was cooled and the liquid was withdrawn. This liquid was used as Feed Liquid I. After freeze-aggregating Feed Liquid I and then filtering it, the resulting fluoropolymer 1I was analyzed by NMR. As a result, the TFE unit / PMVE unit = 52 / 48 (molar ratio), and the Tg was -5.5°C.

[0095] [Production of Feed Liquid J] Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 20 g) was added to the above Feed Liquid I (490 g). Sixty minutes after starting stirring, the feed liquid and the ion exchange resin were separated by filtration. To the filtered feed liquid, Purolite A300 (manufactured by Purolite, anion exchange resin, 20 g) was added. Sixty minutes after starting stirring, the feed liquid and the ion exchange resin were separated by filtration to obtain Feed J. Feed Liquid J has particles of fluoropolymer 1I (average particle diameter 28 nm) dispersed in an aqueous medium, and the content of fluoropolymer 1I is 0.36% by mass based on the total mass of Feed Liquid J.

[0096] [Production of Feed Liquid K] Into a 60.5 L stainless steel pressure reactor equipped with a baffle plate and a stirrer, ultrapure water (45.4 kg) and PMVE (1.1 kg) were charged, and the temperature was raised to 90 °C while stirring at 170 rpm. Next, TFE (72 g) and an aqueous ammonium persulfate solution (7.7 mass%, 150 g) were added to initiate polymerization. Since the pressure inside the reactor decreased with the start of polymerization, TFE was added to keep the pressure constant. When 165 g of TFE was injected, the reactor was cooled to terminate the polymerization reaction. This liquid was designated as raw material liquid K. Raw material liquid K contains a fluorine-containing polymer 1K. After freeze-aggregating raw material liquid K and then filtering it, the resulting fluorine-containing polymer 1K was analyzed by NMR. As a result, the TFE unit / PMVE unit = 43 / 57 (molar ratio), and the Tg was -5 °C.

[0097] [Production of Raw Material Liquid L] Two ion-exchange resin-packed columns filled with Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 843 mL) and Purolite A300 (manufactured by Purolite, anion exchange resin, 843 mL) were prepared, and raw material liquid K was passed through them to obtain raw material liquid L. In raw material liquid L, particles of fluorine-containing polymer 1K (average particle diameter 50 nm) are dispersed in an aqueous medium, and the content of fluorine-containing polymer 1K is 0.77 mass% based on the total mass of raw material liquid L.

[0098] [Example 1] Into a 1.0 L stainless steel pressure reactor, ultrapure water (121 g), raw material liquid B (475 g), and WAX (28 g) were charged to obtain an aqueous dispersion B. Aqueous dispersion B was heated to 70 °C while stirring at 260 rpm. TFE was injected until the pressure in the reactor reached 1.4 MPaG, and an aqueous APS (ammonium persulfate) solution (0.2 mass%, 5 ml) was added to initiate polymerization. Since the pressure inside the reactor decreased with the start of polymerization, TFE was added to keep the pressure constant. When 110 g of TFE was injected, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 220 minutes. The content of fluorine-containing polymer 1A was 0.48 mass% based on the total mass of aqueous dispersion B. The content (solid content concentration) of the fluoropolymer 1A in the aqueous dispersion B was determined by weighing the mass of the residue after heating 2.0 g of the aqueous dispersion B at 170 °C for 20 minutes, and using the following formula. The solid content concentration was calculated. For each of the examples described later, the calculation was performed in the same manner except that the type of the aqueous dispersion was changed to that used in each example. "Solid content concentration (mass %) = 100 × (residue of the aqueous dispersion B after heating (g)) / (mass of the aqueous dispersion B (2 g))" Also, the concentration of the fluorine-based emulsifier was 0 mass ppm with respect to the total mass of the fluoropolymer 1A in the aqueous dispersion B. Moreover, when the amount of the aqueous medium used in the aqueous dispersion B used for the polymerization was 100 parts by mass, the amount of the monomer (TFE) used for the polymerization was 18.5 parts by mass. After collecting the gas remaining in the reactor, the liquid was withdrawn. This liquid was designated as the aqueous dispersion 1. The aqueous dispersion 1 was a dispersion in which particles (average particle diameter: 228 nm) containing the fluoropolymer 1A and the fluoropolymer 2A were dispersed in the aqueous medium, and the solid content concentration was 16.0 mass %. The particles in the obtained aqueous dispersion 1 were aggregated and filtered to obtain PTFE. The melting point of the PTFE dried at 150 °C was 338 °C, and the crystallization energy was -35 J / g. The temperature T was 15 °C. After drying, the composition was calculated using NMR, and as a result, the TFE unit / PMVE unit = 99.1 / 0.9 (molar ratio). Also, in the aqueous dispersion 1, the content of the compound represented by the above formula (S1) and the compound represented by the above formula (S2) with respect to the total mass of the above particles in the aqueous dispersion 1 was 100 mass ppb or less in each case.

[0099] [Example 2] Into a 1.0 L pressure-resistant stainless steel reactor, ultrapure water (121 g), raw material liquid D (475 g), and WAX (28 g) were charged to obtain an aqueous dispersion D. The aqueous dispersion D was heated to 70°C while stirring at 260 rpm. TFE was pressured into the reactor until the pressure reached 1.4 MPaG, and an aqueous APS solution (0.2 mass%, 5 ml) was added to initiate polymerization. Since the pressure in the reactor decreased with the start of polymerization, TFE was added to keep the pressure constant. When 170 g of TFE was pressured in, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 282 minutes. The content of the fluorine-containing polymer 1C was 0.56 mass% based on the total mass of the aqueous dispersion D. Also, the concentration of the fluorine-based emulsifier was 0 mass ppm based on the total mass of the fluorine-containing polymer 1C in the aqueous dispersion D. When the amount of the aqueous medium used in the aqueous dispersion D used for polymerization was 100 parts by mass, the amount of the monomer (TFE) used for polymerization was 28.5 parts by mass. After recovering the gas remaining in the reactor, the liquid was withdrawn. This liquid was designated as aqueous dispersion 2. Aqueous dispersion 2 was a dispersion in which particles (average particle diameter 258 nm) containing a fluorine-containing polymer 1C and a fluorine-containing polymer 2C were dispersed in an aqueous medium, and the solid content concentration was 22.3 mass%. The particles in the obtained aqueous dispersion 2 were aggregated and filtered to obtain PTFE. The melting point of the PTFE dried at 150°C was 338°C, and the crystallization energy was -33 J / g. The temperature T was 17°C. After drying, the composition was calculated using NMR, and as a result, the TFE unit / PMVE unit = 99.3 / 0.7 (molar ratio). Also, in the aqueous dispersion 2, the content of the compound represented by the above formula (S1) and the compound represented by the above formula (S2) with respect to the total mass of the above particles in the aqueous dispersion 2 was 100 mass ppb or less in each case.

[0100] [Example 3] Into a 1.0 L stainless steel pressure reactor, ultrapure water (121 g), raw material liquid F (475 g), and WAX (28 g) were charged to obtain an aqueous dispersion F. The aqueous dispersion F was heated to 70°C while stirring at 260 rpm. TFE was pressured in until the pressure in the reactor reached 1.4 MPaG, and an aqueous APS solution (0.2 mass%, 5 ml) was added to initiate polymerization. Since the pressure in the reactor decreased with the start of polymerization, TFE was added to keep the pressure constant. When 70 g of TFE was pressured in, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 185 minutes. After collecting the gas remaining in the reactor, the liquid was drained, but the entire amount had aggregated, and an aqueous dispersion in which particles of the fluorine-containing polymer were dispersed in an aqueous medium could not be obtained.

[0101] [Example 4] Into a 1.0 L stainless steel pressure reactor, raw material liquid H (596 g) and WAX (28 g) were charged and heated to 70°C while stirring at 260 rpm. TFE was pressured in until the pressure in the reactor reached 1.4 MPaG, and an aqueous APS solution (0.2 mass%, 5 ml) was added to initiate polymerization. Since the pressure in the reactor decreased with the start of polymerization, TFE was added to keep the pressure constant. When 70 g of TFE was pressured in, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 470 minutes. After collecting the gas remaining in the reactor, the liquid was drained. This liquid was designated as aqueous dispersion 4. Aqueous dispersion 4 was a dispersion in which particles (average particle diameter 278 nm) containing hydrocarbon polymer 1G and fluorine-containing polymer 2G were dispersed in an aqueous medium, and the solid content concentration was 10.2 mass%. Since the solid content concentration of aqueous dispersion 4 was low, it can be said that the fluorine-containing polymer was not efficiently produced. The particles in the obtained aqueous dispersion 4 were aggregated and filtered to obtain PTFE. The melting point of the PTFE dried at 150°C was 338°C, and the crystallization energy was -27 J / g. The temperature T was 20°C. Also, in aqueous dispersion 4, the content of the compound represented by the above formula (S1) and the compound represented by the above formula (S2) with respect to the total mass of the above particles in aqueous dispersion 4 was each 100 mass ppb or less.

[0102] [Example 5] 121 g of ultrapure water, 475 g of raw material liquid J, and 28 g of WAX were charged into a 1.0 L stainless steel pressure reactor to obtain an aqueous dispersion J. The aqueous dispersion J was heated to 70°C while stirring at 260 rpm. TFE was pressured in until the pressure in the reactor reached 1.4 MPaG, and an aqueous solution of DSAP (disebacic acid peroxide) (0.45 mass%, 3 ml) was added to initiate polymerization. Since the pressure in the reactor decreased with the start of polymerization, TFE was added to keep the pressure constant. When 170 g of TFE was pressured in, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 426 minutes. The content of the fluoropolymer 1I was 0.29 mass% based on the total mass of the aqueous dispersion J. Also, the concentration of the fluorinated emulsifier was 0 mass ppm based on the total mass of the fluoropolymer 1I in the aqueous dispersion J. Also, when the amount of the aqueous medium used in the aqueous dispersion J used for polymerization was 100 parts by mass, the amount of the monomer (TFE) used for polymerization was 28.5 parts by mass. After recovering the gas remaining in the reactor, the liquid was withdrawn. This liquid was designated as aqueous dispersion 5. Aqueous dispersion 5 is a dispersion in which particles (average particle diameter 262 nm) containing fluoropolymer 1I and fluoropolymer 2I are dispersed in an aqueous medium, and the solid content concentration was 21.3 mass%. The particles in the obtained aqueous dispersion 5 were aggregated and filtered to obtain PTFE. The melting point of the PTFE dried at 150°C was 345°C, and the crystallization energy was -17.5 J / g. The temperature T was 17°C. After drying, the composition was calculated using NMR, and as a result, the TFE unit / PMVE unit = 99.6 / 0.4 (molar ratio). Also, in the aqueous dispersion 5, the content of the compound represented by the above formula (S1) and the compound represented by the above formula (S2) with respect to the total mass of the above particles in the aqueous dispersion 5 was 100 mass ppb or less in each case.

[0103] [Example 6] Into a 100 L stainless steel pressure reactor, ultrapure water (9.64 kg), raw material liquid L (42.0 kg), and WAX (1324 g) were charged to obtain an aqueous dispersion L. The aqueous dispersion L was heated to 70 °C and stirring was started. TFE was pressured in until the pressure in the reactor reached 1.76 MPaG, and an aqueous DSAP solution (0.2 mass%, 1 L) was added to initiate polymerization. Since the pressure in the reactor decreased with the start of polymerization, TFE was added to keep the pressure constant. When 14.0 kg of TFE was pressured in, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 154 minutes. The content of the fluoropolymer 1K was 0.62 mass% based on the total mass of the aqueous dispersion L. Also, the concentration of the fluorine-based emulsifier was 0 mass ppm based on the total mass of the fluoropolymer 1K in the aqueous dispersion L. When the amount of the aqueous medium used in the aqueous dispersion L used for polymerization was 100 parts by mass, the amount of the monomer (TFE) used for polymerization was 27.1 parts by mass. After recovering the gas remaining in the reactor, the liquid was withdrawn. This liquid was designated as aqueous dispersion 6. Aqueous dispersion 6 is a dispersion in which particles (average particle diameter 200 nm) containing fluoropolymer 1K and fluoropolymer 2K are dispersed in an aqueous medium, and the solid content concentration was 21 mass%. The particles in the obtained aqueous dispersion 6 were aggregated and filtered to obtain PTFE. The melting point of the PTFE dried at 150 °C was 344 °C, and the crystallization energy was -16 J / g. The temperature T was 17 °C. After drying, as a result of calculating the composition using NMR, the TFE unit / PMVE unit = 99.1 / 0.9 (molar ratio). Also, in the aqueous dispersion 7, the contents of the compound represented by the above formula (S1) and the compound represented by the above formula (S2) with respect to the total mass of the above particles in the aqueous dispersion 2 were both 100 mass ppb or less.

[0104] [Example 7] After the raw material liquid B was frozen and aggregated, it was filtered, and the obtained fluoropolymer 1B (0.2 g) was mixed with PTFE powder (manufactured by AGC, Fluon (registered trademark) PTFE CD145E, 9.8 g) to obtain a solid composition 7. The temperature T was 22.1 °C.

[0105] [Evaluation] [Colorability] 12 g of the dried particles obtained in each example were weighed, pressed at a pressure of 0.78 MPaG for 2 minutes, and molded into a columnar shape with a diameter of 26 mm and a height of 8 mm. The obtained molded body (pellet) was heated at 380 °C in the atmosphere for 30 minutes and cooled to room temperature (25 °C). Then, the number of black foreign matters on the pellet surface was counted visually, and the colorability was evaluated according to the following criteria. The results are shown in Table 1. In the table, "-" indicates that the evaluation of colorability was not carried out. A: 0 to 4 black foreign matters B: 5 or more black foreign matters

[0106] [Table 1]

[0107] According to the method for producing a fluorine-containing polymer of the present invention, it has been shown that a fluorine-containing polymer can be efficiently produced without using an emulsifier while using an aqueous medium with a small environmental load (Examples 1, 2, 5, and 6). Further, from the comparison of Examples 1, 2, and 5, it has been shown that if there is a heating step of heating the aqueous medium in which the first fluorine-containing polymer is dispersed after obtaining the first fluorine-containing polymer, high-molecular-weight PTFE can be obtained (Example 5). On the other hand, in Examples 3 and 4, the fluorine-containing polymer could not be efficiently produced.

[0108] The entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2023-063511 filed on April 10, 2023 are hereby incorporated herein by reference and made a part of the disclosure of the present invention.

Claims

1. A method for producing a fluoropolymer, comprising polymerizing a monomer containing tetrafluoroethylene in an aqueous dispersion containing a first fluoropolymer having a glass transition temperature of 10° C. or lower and an aqueous medium to produce a second fluoropolymer different from the first fluoropolymer, comprising: before the start of polymerization of the monomers, the content of the first fluorinated polymer is 0.01 to 4.0% by mass based on the total mass of the aqueous dispersion, The method for producing a fluorine-containing polymer, wherein the concentration of the fluorine-containing emulsifier is 100 ppm by mass or less based on the total mass of the first fluorine-containing polymer in the aqueous dispersion before initiation of polymerization of the monomers.

2. The method for producing a fluorine-containing polymer according to claim 1, wherein the first fluorine-containing polymer contains units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether).

3. The method for producing a fluorine-containing polymer according to claim 2, wherein the first fluorine-containing polymer contains 20 to 60 mol% of units based on perfluoro(alkyl vinyl ether) relative to the total of the units based on tetrafluoroethylene and the units based on perfluoro(alkyl vinyl ether).

4. The process for producing a fluorine-containing polymer according to claim 1 or 2, wherein the amount of the monomer used is 1 to 50 parts by mass per 100 parts by mass of the aqueous medium used.

5. The process for producing a fluorine-containing polymer according to claim 1 or 2, wherein the monomers are polymerized in the presence of a polymerization initiator.

6. The aqueous dispersion comprises an aqueous medium, a first fluoropolymer having a glass transition temperature of 10°C or lower, and a second fluoropolymer which contains a unit based on tetrafluoroethylene and is different from the first fluoropolymer, wherein a temperature T showing a maximum endothermic amount in the range of 10 to 35°C of a solid composition obtained by aggregating the aqueous dispersion, as measured by the following method, is 19°C or lower. How to measure temperature T: A solid composition that has not been heated to a temperature of 300° C. or higher is measured by a differential scanning calorimeter at a heating rate of 10° C. / min.

7. A solid composition comprising a first fluoropolymer having a glass transition temperature of 10°C or lower, and a second fluoropolymer which contains units based on tetrafluoroethylene and is different from the first fluoropolymer, wherein the temperature T showing the maximum endothermic amount of the solid composition in the range of 10 to 35°C, as measured by the following method, is 19°C or lower. How to measure temperature T: A solid composition that has not been heated to a temperature of 300° C. or higher is measured by a differential scanning calorimeter at a heating rate of 10° C. / min.

8. A solid composition obtained by agglomerating the aqueous dispersion according to claim 6, which has a maximum endothermic temperature T of 19°C or lower in the range of 10 to 35°C. How to measure temperature T: A solid composition that has not been heated to a temperature of 300° C. or higher is measured by a differential scanning calorimeter at a heating rate of 10° C. / min.

9. The aqueous dispersion according to claim 6, wherein a content of units based on perfluoro(alkyl vinyl ether) is 0.1 to 5.0 mol% relative to the total of all units of the first fluorine-containing polymer and the second fluorine-containing polymer, and each of the content of the compound represented by formula (S1) and the content of the compound represented by formula (S2) is 100 ppb by mass or less relative to the total mass of the first fluorine-containing polymer and the second fluorine-containing polymer. Formula (S1): H-(CF ２ ) ｎ―１ -COOM Formula (S2): H-(CF ２ ) ｎ -SO ３ M In formula (S1) and formula (S2), M is independently a hydrogen atom, Na, K, or NH ４ and each n independently represents 8 or 10.

10. A solid composition comprising a first fluorine-containing polymer having a glass transition temperature of 10° C. or lower, and a second fluorine-containing polymer which contains a unit based on tetrafluoroethylene and is different from the first fluorine-containing polymer, The solid composition according to claim 7, wherein a content of units based on perfluoro(alkyl vinyl ether) is 0.1 to 5.0 mol% relative to the total of all units in the first fluorine-containing polymer and the second fluorine-containing polymer, and each of the content of the compound represented by formula (S1) and the content of the compound represented by formula (S2) is 100 ppb by mass or less relative to the total mass of the first fluorine-containing polymer and the second fluorine-containing polymer. Formula (S1): H-(CF ２ ) ｎ―１ -COOM Formula (S2): H-(CF ２ ) ｎ -SO ３ M In formula (S1) and formula (S2), M is independently a hydrogen atom, Na, K, or NH ４ and each n independently represents 8 or 10.

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