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

Abstract

Provided are: a fluorine-containing polymer production method by which a fluorine-containing polymer can be efficiently produced without requiring an emulsifier, while using an aqueous medium which is environmentally friendly; an aqueous dispersion; and a solid composition.　The fluorine-containing polymer production method according to the present invention includes polymerizing a monomer that contains tetrafluoroethylene in an aqueous dispersion containing an aqueous medium and a first fluorine-containing polymer having a glass transition temperature of 10°C or lower, to produce a second fluorine-containing polymer different from the first fluorine-containing polymer. The content of the first fluorine-containing polymer is 0.01-4.0 mass% relative to the total mass of the aqueous dispersion before starting the polymerization of the monomer, and the concentration of the fluorine-based emulsifier is 100 mass ppm or less relative to the total mass of the first fluorine-containing polymer in the aqueous dispersion before starting the polymerization of the monomer.

Description

Method for producing fluorine-containing polymer, aqueous dispersion and solid composition

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

[0002] Fluorine-containing polymers such as tetrafluoroethylene copolymers are used in various industrial fields because of their excellent heat resistance, chemical resistance, flame retardancy, weather resistance, etc. Examples of methods for producing fluorine-containing polymers include a method of emulsion polymerization of fluorine-containing monomers in an aqueous medium using a fluorine-containing emulsifier (see Patent Document 1).

[0003] International Publication No. 2007 / 046377

[0004] The process for producing a fluoropolymer disclosed in Patent Document 1 uses an aqueous medium and therefore has a small environmental impact. However, when a large amount of an emulsifier, which is an essential component, remains in the aqueous dispersion obtained by polymerization, it may be necessary to remove the emulsifier depending on the application.

[0005] An object of the present invention is to provide a method for producing a fluoropolymer, which can efficiently produce a fluoropolymer using an aqueous medium that has a small environmental impact and does not require an emulsifier. Another object of the present invention is to provide an aqueous dispersion and a solid composition.

[0006] As a result of intensive investigations, the present inventors have found that the above-mentioned problems can be solved by the following configuration. [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, wherein the content of the first fluoropolymer is 0.01 to 4.0% by mass relative to the total mass of the aqueous dispersion before polymerization of the monomers is started, and the concentration of the fluorine-containing emulsifier is 100 ppm by mass or less relative to the total mass of the first fluoropolymer in the aqueous dispersion before polymerization of the monomers is started. [2] The method for producing a fluoropolymer according to [1], wherein the first fluoropolymer contains units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether). [3] The method for producing a fluoropolymer according to [2], wherein the first fluoropolymer contains 20 to 60 mol% of the 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 method for producing a fluoropolymer according to any of [1] to [3], 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 method for producing a fluoropolymer according to any of [1] to [4], wherein the monomer is polymerized in the presence of a polymerization initiator. [6] An aqueous dispersion comprising an aqueous medium, 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, which shows the maximum endothermic amount in the range of 10 to 35°C, of ​​a solid composition obtained by aggregating the aqueous dispersion, is 19°C or lower, as measured by the following method. Method for measuring temperature T: A solid composition that has not been heated to a temperature of 300° C. or higher is measured using a differential scanning calorimeter at a temperature rise 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 at which the solid composition shows the maximum endothermic heat in the range of 10 to 35°C, as measured by the following method, is 19°C or lower. Method for measuring temperature T: A solid composition which has no history of being 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 which is obtained by aggregating the aqueous dispersion described in [6], and which has a temperature T at which the maximum endothermic heat in the range of 10 to 35°C is 19°C or lower. Method for measuring temperature T: A solid composition which has no history of being 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 [6], wherein the 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 the content of the compound represented by formula (S1) and the content of the compound represented by formula (S2) are each 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 each independently represents a hydrogen atom, Na, K, or NH ４ and n each independently represents 8 or 10.

[10] The solid composition according to [7], wherein the 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 the content of the compound represented by formula (S1) and the content of the compound represented by formula (S2) are each 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 each independently represents a hydrogen atom, Na, K, or NH ４ and n's each independently represent 8 or 10.

[0007] According to the present invention, there is provided a method for producing a fluoropolymer, which can efficiently produce a fluoropolymer using an aqueous medium which has a small environmental load and does not necessarily require an emulsifier. Furthermore, according to the present invention, there is also provided an aqueous dispersion and a solid composition.

[0008] The meanings of terms used in the present invention are as follows. A numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the upper and lower limits. In the numerical ranges described in this specification in stages, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another staged numerical range. Furthermore, in the numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the Examples. In this specification, each component may be used alone or in combination with two or more substances corresponding to the component. Herein, when two or more substances are used in combination for each component, the content of that component refers to the total content of the substances used in combination, unless otherwise specified. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment. A "unit" is a collective term for an atomic group derived from one molecule of the above-mentioned monomer, formed directly by polymerization of the monomer, and an atomic group obtained by chemically converting a portion of the above-mentioned atomic group. Hereinafter, a "unit based on a monomer" will also be simply referred to as a "unit." The content (mass % or mol %) of each unit relative to all units contained in the polymer is determined by analyzing the polymer by solid-state nuclear magnetic resonance spectroscopy (NMR), and usually, the content of each unit calculated from the amount of each monomer charged substantially coincides with the actual content of each unit.

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

[0010] The reason why the second fluorine-containing polymer was efficiently produced by this production method without the essential use of an emulsifier is presumably because the use of an aqueous dispersion containing a predetermined amount of the first fluorine-containing polymer having a glass transition temperature of 10°C or lower allowed the first fluorine-containing polymer to function as a good polymerization site for the second fluorine-containing polymer.

[0011] <Aqueous Dispersion> In the present production method, an aqueous dispersion containing a first fluorinated polymer and an aqueous medium is used.

[0012] (First Fluorine-Containing Polymer) It is presumed that the first fluorine-containing polymer solubilizes the specific monomer by adsorbing and incorporating the specific monomer at the hydrophobic part during polymerization of the specific monomer, and that by adding a polymerization initiator thereto, the specific monomer is polymerized within the particles of the first fluorine-containing polymer. It is also presumed that the first fluorine-containing polymer contributes to dispersion stabilization in an aqueous medium.

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

[0014] The first fluorine-containing polymer preferably contains units based on tetrafluoroethylene (hereinafter also referred to as "TFE") (hereinafter also referred to as "TFE units") and units based on perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE") (hereinafter also referred to as "PAVE units"), since this makes it easier to adjust the Tg within the above range and the effects of the present invention are more excellent.

[0015] The PAVE is preferably a monomer represented by formula (1) from the viewpoint of excellent polymerization reactivity in producing the first fluoropolymer and enabling more efficient production of the second fluoropolymer. ２ =CF-O-R ｆ１ (1) In formula (1), R ｆ１ represents a perfluoroalkyl group having 1 to 10 carbon atoms. ｆ１ From the viewpoint of better polymerization reactivity, the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 8, more preferably 1 to 6, still more preferably 1 to 5, and particularly preferably 1 to 3. 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"), and among these, PMVE and PPVE are preferred, with PMVE being more preferred, from the viewpoint of enabling more efficient production of the second fluorinated polymer.

[0017] When the first fluorine-containing polymer contains TFE units and PAVE units, the content of PAVE units in the first fluorine-containing polymer relative to the total of TFE units and PAVE units is preferably 20 to 60 mol %, more preferably 25 to 60 mol %, still more preferably 30 to 55 mol %, from the viewpoints that Tg can be easily adjusted to within the above range and that the second fluorine-containing polymer can be produced more efficiently.

[0018] The first fluorine-containing polymer may contain units based on other monomers other than TFE and PAVE, but preferably does not substantially contain units based on other monomers, from the viewpoint of more efficient production of the second fluorine-containing polymer. "Substantially does not contain units based on other monomers" means that the content of units based on other monomers is 0.01 mol% or less, more preferably 0 mol%, based on the total units of the first fluorine-containing polymer. When units based on other monomers are contained, the other monomer is preferably hexafluoropropylene.

[0019] Before the start of polymerization of the monomers to be used in polymerization of the second fluorine-containing polymer, the content of the first fluorine-containing polymer is 0.01 to 4.0 mass% relative to the total mass of the aqueous medium in the aqueous dispersion, and from the viewpoint of enabling more efficient production of the second fluorine-containing polymer, it is preferably 0.01 to 0.6 mass%, more preferably 0.01 to 0.5 mass%.

[0020] In this specification, "before initiating polymerization of the monomers used in the polymerization of the second fluoropolymer" means immediately before the initiation of polymerization. Here, "the initiation of polymerization" includes the time when the monomers and the polymerization initiator are brought into the reactor together after the temperature inside the reactor is raised to the polymerization temperature or higher, and the time when the temperature inside the reactor is raised to the polymerization temperature or higher after the monomers and the polymerization initiator are brought into the reactor together.

[0021] Before starting polymerization of the monomers used in the polymerization of the second fluoropolymer, the sulfate ion concentration is preferably 10 ppm by mass or less, more preferably 5 ppm by mass or less, relative to the total mass of the aqueous medium in the aqueous dispersion, from the viewpoint of suppressing discoloration of the second fluoropolymer. An example of the lower limit is 0 ppm by mass. One example of a method for adjusting the sulfate ion concentration to the above value is a method of removing sulfate ions using an anion exchange resin during the production of the first fluoropolymer. Here, the sulfate ions are derived, for example, from the polymerization initiator (particularly ammonium persulfate) used during the production of the first fluoropolymer, and may be contained in the aqueous dispersion containing the first fluoropolymer. It is presumed that by keeping the content of sulfate ions at 10 ppm by mass or less (particularly 5 ppm by mass or less), it is possible to suppress the formation of terminal groups with low heat resistance in the second fluoropolymer, thereby suppressing discoloration of the second fluoropolymer.

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

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

[0024] The method for producing the first fluorine-containing polymer is preferably 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.This gives the first fluorine-containing polymer dispersed in the form of particles in the aqueous medium.The aqueous medium thus obtained in which the particles of the first fluorine-containing polymer are dispersed may be used as the aqueous dispersion as is, or another aqueous medium may be added and used as the aqueous dispersion.Furthermore, the first fluorine-containing polymer may be dispersed in another aqueous medium by solvent substitution, and this may be used as the aqueous dispersion.

[0025] The polymerization initiator used in the production of the first fluorine-containing polymer is preferably a water-soluble polymerization initiator, more preferably a persulfate such as ammonium persulfate, sodium persulfate or potassium persulfate, or an organic polymerization initiator such as disuccinic acid peroxide or azobisisobutylamidine dihydrochloride, still more preferably a persulfate, and particularly preferably ammonium persulfate.

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

[0027] The method for producing the first fluoropolymer preferably includes a heating step of heating the aqueous medium having the first fluoropolymer dispersed therein after obtaining the aqueous medium. This deactivates the polymerization initiator present in the system, so that the polymerization of the second fluoropolymer is less susceptible to the influence of the polymerization initiator used in producing the first fluoropolymer. As a result, a second fluoropolymer having a high molecular weight is more likely to be obtained. 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, from the viewpoint of further accelerating the deactivation of the polymerization initiator in the aqueous medium.

[0028] (Aqueous medium) The aqueous dispersion used in the present production method contains an aqueous medium. The aqueous medium contained in the aqueous dispersion may be the polymerization solvent used in producing the first fluoropolymer, as described above. Specific examples of the aqueous medium contained in the aqueous dispersion are the same as the specific examples of the aqueous medium used in producing the first fluoropolymer described above. Before starting polymerization of the monomers used in polymerizing the second fluoropolymer, the content of the aqueous medium is preferably 60 to 99.9 mass%, more preferably 96 to 99.9 mass%, and even more preferably 98 to 99.9 mass%, based on the total mass of the aqueous dispersion.

[0029] (Other Components) The aqueous dispersion used in the present production method may contain other components in addition to the first fluorinated 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 fluorinated emulsifier, a pH adjuster, and a wax.

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

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

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

[0033] Specific examples of wax include Paraffin Wax-155 and Paraffin Wax-150 (both manufactured by Nippon Seiro).

[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 per 100 parts by mass of the aqueous medium. Furthermore, 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 even more preferably 0.1 to 10 parts by mass per 100 parts by mass of the specific monomer described below. When the aqueous dispersion contains an emulsifier other than a fluorine-based emulsifier, the content of the emulsifier other than a fluorine-based emulsifier is preferably 0.01 to 5 parts by mass per 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 per 100 parts by mass of the aqueous medium. When the aqueous dispersion contains a wax, the content of the wax is preferably 1 to 10 parts by mass per 100 parts by mass of the aqueous medium.

[0035] Before starting polymerization of the monomers used in the polymerization of the second fluorine-containing polymer, the concentration of the fluorine-containing emulsifier is 100 ppm by mass or less relative to the total mass of the first fluorine-containing polymer in the aqueous dispersion, and from the viewpoint of better effects of the present invention, it is preferably 50 ppm by mass or less, more preferably 25 ppm by mass or less, and even more preferably 5 ppm by mass or less. The lower limit can be 0 ppm by mass. The fluorine-containing emulsifier means an emulsifier in which the hydrophobic moiety contains a fluorine atom in the hydrophilic moiety and the hydrophobic moiety possessed by the emulsifier. Specific examples of the fluorine-containing emulsifier include fluorine-containing alkanoate salts and fluorine-containing ether carboxylic acid compounds. One example of a method for adjusting the concentration of the fluorine-containing emulsifier to the above-mentioned range can be a method for producing an aqueous dispersion without using a fluorine-containing emulsifier.

[0036] Before starting polymerization of the monomers used in 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, based on the total mass of the aqueous dispersion, from the viewpoint of polymerization stability.The lower limit can be 0 mass ppm.An example of a method for adjusting the fluoride ion concentration to the above value can be a method of removing sulfate ions using an anion exchange resin during the production of the first fluorine-containing polymer.Here, fluoride ions may be generated by the reaction between a polymerization initiator (e.g., ammonium persulfate) and the monomers used in the production of the first fluorine-containing polymer, and may be contained in the aqueous dispersion.

[0037] <Specific Monomer> The specific monomer includes TFE. The amount of TFE used is preferably 97 to 100 mass %, more preferably 98 to 100 mass %, and even more preferably 99 to 100 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. "Substantially not containing a fluorine-containing monomer other than TFE" means that the amount of the fluorine-containing monomer other than TFE used is 0.0001 mass% or less, or may be 0 mass%, relative to the amount of the specific monomer used. 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"), fluoroalkylethylene, PAVE, and hexafluoropropylene. Two or more types of 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 any other monomer. "Substantially free of other monomers" means that the amount of other monomers used is 0.0001% by mass or less, more preferably 0% by mass, relative to the amount of the specific monomer used. Specific examples of other monomers include ethylene, propylene, vinyl chloride, and vinylidene chloride. Two or more types 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 even more preferably 1 to 30 parts by mass, per 100 parts by mass of the aqueous medium contained in the aqueous dispersion.

[0041] <Polymerization Initiator> In the present production method, the specific monomer is preferably polymerized in the presence of a polymerization initiator. Examples of the polymerization initiator include an oil-soluble radical initiator, a water-soluble radical initiator, and a water-soluble redox catalyst. Specific examples of the oil-soluble radical initiator include oil-soluble organic peroxides such as tert-butyl peroxypivalate (hereinafter also referred to as "PBPV") and diisopropyl peroxydicarbonate (hereinafter also referred to as "IPP"). Specific examples of the water-soluble radical initiator include persulfates such as ammonium persulfate and potassium persulfate, and water-soluble organic peroxides such as disuccinic acid peroxide, bisglutaric acid peroxide, and tert-butyl hydroperoxide (hereinafter also referred to as "TBHP"). The water-soluble redox catalyst is preferably a combination of an oxidizing agent such as bromic acid or a salt thereof, chloric acid or a salt thereof, persulfuric acid or a salt thereof, permanganic acid or a salt thereof, or hydrogen peroxide, and a reducing agent such as sulfurous acid or a salt thereof, hydrogen sulfite or a salt thereof, thiosulfuric acid or a salt thereof, organic acid, or inorganic salt. Potassium persulfate and ammonium persulfate are preferred as persulfates. Sodium sulfite is preferred as sulfites. Inorganic salts include combinations of sulfate anions, sulfite anions, and chloride anions with metal ions. Transition metal ions are preferred, including manganese, iron, cobalt, nickel, copper, zinc, cerium, and silver ions, with iron ions being preferred. Iron (II) sulfate is preferred as an inorganic salt. The polymerization initiator is preferably an oil-soluble radical initiator or a water-soluble radical initiator. From the viewpoint of more efficient production of fluoropolymers, oil-soluble radical initiators are more preferred, and oil-soluble organic peroxides are even more preferred. Two or more polymerization initiators may be used in combination.

[0042] The amount of the polymerization initiator used is preferably 1 to 1,000 ppm, more preferably 5 to 750 ppm, and even more preferably 10 to 500 ppm, relative to 100 parts by mass of the amount of the specific monomer used.

[0043] <Other Components> When polymerizing the specific monomer, components other than those described above (hereinafter also referred to as "other components") may be further used. A specific example of the other component is a reducing agent. The amount of the other component used is preferably 1 to 2000 ppm relative to 100 parts by mass of the specific monomer used.

[0044] <Step> In the present production method, the specific monomer is polymerized in the aqueous dispersion to produce the second fluorine-containing polymer.

[0045] The second fluorine-containing polymer obtained by the present production method contains units based on TFE (hereinafter also referred to as "TFE units") and is preferably a homopolymer of TFE (hereinafter also referred to as "PTFE"). 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 from 99.0 to 100.0 mol%, more preferably from 99.5 to 100.0 mol%, and even more preferably from 99.9 to 100.0 mol%, based on all units constituting the second fluorine-containing polymer.

[0047] The specific monomer is added to the reaction system (i.e., polymerization reaction vessel) by a conventional method. For example, the specific monomer may be added to the reaction system continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. Alternatively, the specific monomer may be dissolved in an aqueous medium, and the resulting solution may be added to the reaction system continuously or intermittently. 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. In the case of batch processing, the polymerization time is preferably 90 to 1,000 minutes, more preferably 90 to 700 minutes.

[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, such as common surfactants. The substantial absence of an emulsifier means an environment in which the content of the emulsifier is 0.03 mass ppm or less, preferably 0.02 mass ppm or less, more preferably 0 mass ppm, relative to the total mass of the aqueous medium contained in the aqueous dispersion.

[0050] As mentioned above, it is presumed that the specific monomer polymerizes within the particles of the first fluorine-containing polymer during polymerization of the specific monomer, and therefore it is thought that particles containing the first fluorine-containing polymer and the second fluorine-containing polymer are produced in this production method. That is, it is presumed 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, the production method provides 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.

[0051] [Aqueous Dispersion] The aqueous dispersion of the present invention (hereinafter also referred to as "the present aqueous dispersion") is an aqueous dispersion comprising an aqueous medium, a first fluoropolymer having a Tg of 10°C or less, and a second fluoropolymer which contains TFE units and is different from the first fluoropolymer. In the present aqueous dispersion, the content of PAVE units relative to the total of all units of the first fluoropolymer and the second fluoropolymer is 0.1 to 5.0 mol%. Furthermore, in the present aqueous dispersion, the content of the compound represented by formula (S1) described below and the content of the compound represented by formula (S2) described below are each 100 ppb by mass or less relative to the total mass of the first fluoropolymer and the second fluoropolymer.

[0052] The present aqueous dispersion can be obtained, for example, by the present production method described above.

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

[0054] The content of the first fluorine-containing polymer is preferably from 0.10 to 1.0 mass %, more preferably from 0.15 to 0.80 mass %, and even more preferably from 0.20 to 0.60 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-mentioned production method, and preferred embodiments are also the same. The second fluorine-containing polymer contained in the present aqueous dispersion contains TFE units. 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 even more preferably 99.9 to 100.0 mol%, based on all units constituting the second fluorine-containing polymer.

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

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

[0058] In the present aqueous dispersion, the content of TFE units relative to the total of all units of the first and second fluoropolymers is preferably from 90 to 99.8 mol%, more preferably from 93 to 99.5 mol%, and even more preferably from 95 to 99.0 mol%. It is sufficient that the TFE units are contained in at least the second fluoropolymer, but it is preferable that they are contained in both the first and second fluoropolymers.

[0059] In the present aqueous dispersion, the total content of the first fluorinated polymer and the second fluorinated polymer is preferably from 10 to 40 mass%, more preferably from 12 to 35 mass%, and even more preferably from 15 to 35 mass%, relative to the total mass of the present aqueous dispersion.

[0060] The first fluorine-containing polymer and the second fluorine-containing polymer may exist separately in the aqueous dispersion, but preferably exist in the form of particles containing the first fluorine-containing polymer and the second fluorine-containing polymer described above.In this case, from the viewpoint of dispersion stability, the average particle size of the particles is preferably 500 μm or less, more preferably 450 μm or less, and even more preferably 400 μm or less.Furthermore, from the viewpoint of aggregation, the average particle size of the particles is preferably 50 nm or more, more preferably 80 nm or more, and even more preferably 100 nm or more.The average particle size of the particles is measured by a laser diffraction / scattering method, a cumulative curve is calculated with the total volume of the particle group taken as 100%, and the particle size on the cumulative curve is the particle size at the point where the cumulative volume is 50%.

[0061] <Aqueous medium> Specific examples of the aqueous medium contained in the present aqueous dispersion are the same as the specific examples of the aqueous medium used in producing the first fluoropolymer described above. The content of the aqueous medium is preferably from 50 to 99 mass%, more preferably from 60 to 99 mass%, and even more preferably from 70 to 99 mass%, based on the total mass of the present aqueous dispersion, from the viewpoint of dispersion stability of the first fluoropolymer and the second fluoropolymer.

[0062] <The compound represented by formula (S1) and the compound represented by formula (S2)> The compound represented by formula (S1) and the compound represented by formula (S2) are the components that can be generated when TFE is polymerized in the presence of polymerization initiator, chain transfer agent and emulsifier (particularly hydrocarbon-based emulsifier).Therefore, when not using emulsifier during the preparation of the second fluorine-containing polymer that is contained in this aqueous dispersion, the compound represented by formula (S1) and the compound represented by formula (S2) can be suppressed to generate the amount, so that the content of these compounds can be easily made to be within the range described below.

[0063] Formula (S1): H-(CF ２ ) ｎ―１ -COOM Formula (S2): H-(CF ２ ) ｎ -SO ３ M In formula (S1) and formula (S2), M each independently represents a hydrogen atom, Na, K, or NH ４ and n's each independently represent 8 or 10.

[0064] In the present aqueous dispersion, the content of the compound represented by formula (S1) and the content of the compound represented by formula (S2) are each 100 ppb by mass or less, preferably 50 ppb by mass or less, more preferably 25 ppb by mass or less, and even more preferably 0 ppb by mass (i.e., no compound represented by formula (S1) or no compound represented by formula (S2)) relative to the total mass of the first fluorinated polymer and the second fluorinated polymer.

[0065] <Others> The present aqueous dispersion preferably does not substantially contain an emulsifier. Examples of emulsifiers include the above-mentioned fluorine-based emulsifiers and emulsifiers other than fluorine-based emulsifiers. "The present aqueous dispersion is substantially free of emulsifiers" 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, relative to the total mass of the present aqueous dispersion.

[0066] <Uses> As described above, the present aqueous dispersion does not require an emulsifier, and therefore can be easily converted into a dispersion in an organic solvent such as N-methylpyrrolidone, acetone, etc. by solvent substitution. For example, the present aqueous dispersion can be converted into a dispersion in an organic solvent by mixing the present aqueous dispersion with an organic solvent and dehydrating it by evaporation or using anhydrous sodium sulfate, etc.

[0067] The aqueous dispersion of the present invention stably disperses the fluoropolymer even without the addition of an emulsifier, and is therefore suitable for use in coating applications, binders, etc.

[0068] Furthermore, by agglomerating 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 aqueous dispersion, powders of the first fluorine-containing polymer and the second fluorine-containing polymer can be obtained.

[0069] Aggregation methods 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 in which an acid-containing solution is added to the present aqueous dispersion is preferred. Examples of acids to be added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, and hydrofluoric acid, with hydrochloric acid being preferred. The acid concentration in the acid-containing solution is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. In the case of base aggregation, a method in which a base-containing solution is added to the present aqueous dispersion is preferred. Examples of bases to be added include sodium hydroxide, potassium hydroxide, and ammonium carbonate, with sodium hydroxide being preferred. The base concentration in the base-containing solution is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. For aggregation using a coagulant, known coagulants can be used. Known coagulants include aluminum salts, calcium salts, and magnesium salts. Specific examples include 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. Alum is preferred, and potassium alum, where M is potassium, is more preferred. Base coagulation is preferred as a coagulation method, as it is particularly easy to proceed with coagulation.

[0070] [Solid composition] The solid composition of the present invention (hereinafter also referred to as "the present solid composition") is a solid composition comprising a first fluoropolymer having a glass transition temperature of 10°C or lower, and a second fluoropolymer which contains TFE units and is different from the first fluoropolymer. In the present solid composition, the content of PAVE units relative to the total of all units of the first fluoropolymer and the second fluoropolymer is 0.1 to 5.0 mol %. Furthermore, 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 ppb by mass or less relative to the total mass of the first fluoropolymer and the second fluoropolymer.

[0071] In this specification, a solid composition means a composition having a solid content of 99% by mass or more. Here, the solid content 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 is calculated by the following formula: Solid content (mass%) = 100 x (mass of residue) / (mass of solid composition)

[0072] The present solid composition is preferably obtained by an aggregation method using the present aqueous dispersion described above. Preferred embodiments of the present solid composition are the same as the preferred embodiments of the first fluorine-containing polymer and the second fluorine-containing polymer contained in the present aqueous dispersion described above, and therefore description thereof will be omitted. The first fluorine-containing polymer and the second fluorine-containing polymer may be present separately in the present solid composition, but are preferably present in the form of particles containing the first fluorine-containing polymer and the above-mentioned 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 even more preferably 0.3 to 3% by mass, relative to 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 even more preferably 97 to 99.7% by mass, relative to 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 even more preferably 99.8 to 100% by mass, relative to the total mass of the solid composition.

[0074] <Temperature T> The solid composition obtained by aggregating the aqueous dispersion of the present invention or the solid composition of the present invention preferably has a temperature T of 19°C or lower, at which the temperature T shows the maximum endothermic amount in the range of 10 to 35°C, measured by the method described below. The temperature T is more preferably 18°C ​​or lower, and even more preferably 17.5°C or lower. The lower limit of the temperature T is 10°C. By containing the first fluoropolymer and the second fluoropolymer (preferably particles containing the first fluoropolymer and the second fluoropolymer) in the aqueous dispersion, the temperature T can be adjusted to within the above range.

[0075] The present invention will be described in detail below with reference to examples. Examples 1, 2, 5, and 6 are working examples, and Examples 3, 4, and 7 are comparative examples. However, the present invention is not limited to these examples. The blending amounts of each component in the tables below are based on mass.

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

[0077] <Glass transition temperature (Tg)> Tg was measured using a NEXTA DSC600 manufactured by Hitachi High-Technologies Corporation. Specifically, 5 mg of a 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. Thereafter, the sample was cooled to -60°C at a rate of 10°C / min. Once the predetermined temperature was reached, the temperature was again raised to 100°C at 10°C / min. Tg was estimated from the inflection point observed in this second heating operation.

[0078] <Average Particle Diameter of Particles in Liquid> The raw material liquid was degassed for 5 minutes at room temperature (25°C), pressurized with nitrogen to 0.2 MPaG, and then purged to atmospheric pressure to obtain a sample for measurement. The particle size of the obtained sample was measured using a laser diffraction / scattering particle size analyzer (Otsuka Electronics Co., Ltd., ELSZ) with an accumulation number set to 100, and measurement was initiated. D50 was calculated from particle diameters measured in the range of 1 to 300 nm, and this was used as the average particle diameter of the particles in the raw material liquid. When the average particle diameter of particles in an aqueous dispersion corresponding to the raw material liquid was measured using the same method as for the raw material liquid, it was found to be identical to the average particle diameter of the particles in the raw material liquid. Here, the aqueous dispersion corresponding to the raw material liquid refers to aqueous dispersion B corresponding to raw material liquid B in the case of Example 1 described below. The average particle diameter (D50) of particles in each aqueous dispersion obtained using an aqueous dispersion corresponding to the raw material liquid was measured using a laser diffraction / scattering particle size analyzer (Otsuka Electronics Co., Ltd., ELSZ). However, the range of particle diameters to be measured was not limited, unlike the method for measuring the average particle diameter of particles in a raw material liquid. Here, the aqueous dispersion of each example obtained using an aqueous dispersion corresponding to the raw material liquid means aqueous dispersion 1 obtained using aqueous dispersion B in the case of Example 1 described below.

[0079] <Average particle size of particles after drying> The particles obtained in each example were dried and aggregated, and then photographed using a scanning electron microscope (for example, JSM-IT700HR InTouchScope, manufactured by JEOL Ltd.) The particle sizes of five different particles measured from the obtained SEM image were determined, and the arithmetic average was calculated.

[0080] <Proportion of each unit in the polymer> The proportion of each unit in the polymer is １９ It was determined by F-NMR analysis and infrared absorption spectrum analysis.

[0081] <Content of the compound represented by formula (S1)> The content of the compound represented by formula (S1) relative to the total mass of particles in the aqueous dispersion obtained in each example described below was calculated by a method using an aqueous dispersion, among the measurement methods using a liquid chromatograph mass spectrometer described in paragraphs

[0710] to

[0720] 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.

[0082] <Content of the compound represented by formula (S2)> The content of the compound represented by formula (S2) relative to the total mass of particles in the aqueous dispersion obtained in each example described below was calculated by a method using an aqueous dispersion, among the measurement methods using a 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 Fluorine-Based Emulsifier in Raw Material Liquid> The concentration of the fluorine-based emulsifier in the raw material liquid relative to the total mass of the fluoropolymer was calculated from the charged amount.

[0084] <Crystallization Energy> The melting point and crystallization energy were measured using a DSC8500 manufactured by Perkin-Elmer. Specifically, 5 mg of a sample for measurement was weighed into an aluminum sample pan, and the sample was heated to 200°C at a heating rate of 10°C / min in an air atmosphere and held for 1 minute. The sample was then heated to 380°C at a heating 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 resulting from thermal melting of the sample observed during the heating operation from 200°C to 380°C was taken as the melting point, and the crystallization energy was calculated from the peak area observed during the cooling operation from 380°C to 200°C. Note that a smaller absolute value of crystallization energy indicates a higher molecular weight.

[0085] <Temperature T> The temperature T was measured using a DSC8500 differential scanning calorimeter manufactured by Perkin Elmer. Specifically, 10 mg of a sample for measurement was weighed out and placed in an aluminum sample pan, and the temperature was increased from −20° C. to 370° C. at a rate of 10° C. / min in an air atmosphere. The temperature at which the maximum endothermic heat was observed in the range of 10 to 35° C. was taken as the temperature T.

[0086] [Production of Raw Material Liquid A] Ultrapure water (717 g), PMVE (50 g), and TFE (8 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 mass%, 5 cc) was added to initiate polymerization. As the polymerization started, the pressure in the reactor decreased, so TFE was added to maintain the pressure constant. When 2 g of TFE had been injected, the reactor was cooled to terminate the polymerization reaction. The gas remaining in the reactor was recovered, and the liquid was then withdrawn. This liquid was used as raw material liquid A. Raw material liquid A was freeze-coagulated and then filtered. The resulting fluoropolymer 1A was analyzed by NMR, and the ratio of TFE units to PMVE units was 52 / 48 (molar ratio), and the Tg was -5.9°C.

[0087] [Production of Raw Material Solution B] Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 20 g) was added to the above raw material solution A (490 g). 60 minutes after the start of stirring, the raw material solution was separated from the ion exchange resin by filtration. To the filtered raw material solution, Purolite A300 (manufactured by Purolite, anion exchange resin, 20 g) was added. 60 minutes after the start of stirring, the raw material solution was separated from the ion exchange resin by filtration to obtain raw material solution B. Raw material solution B contained particles of fluoropolymer 1A (average particle size 87 nm) dispersed in an aqueous medium, and the content of fluoropolymer 1A was 0.6 mass% based on the total mass of raw material solution B.

[0088] [Production of Raw Material Solution C] Ultrapure water (717 g), PMVE (55 g), TFE (9 g), and an aqueous ammonia solution (30% by mass, 1 drop) 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 maintain the pressure constant. When 2 g of TFE had been injected, the reactor was cooled to terminate the polymerization reaction. The gas remaining in the reactor was recovered, and the liquid was then withdrawn. This liquid was used as raw material solution C. Raw material solution C was freeze-coagulated and then filtered. The resulting fluoropolymer 1C was analyzed by NMR, and the ratio of TFE units to PMVE units was 52.4 / 47.6 (molar ratio), and the Tg was -5.3°C.

[0089] [Production of Raw Material Solution D] Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 20 g) was added to the above raw material solution C (490 g). 60 minutes after the start of stirring, the raw material solution was separated from the ion exchange resin by filtration. To the filtered raw material solution, Purolite A300 (manufactured by Purolite, anion exchange resin, 20 g) was added. 60 minutes after the start of stirring, the raw material solution was separated from the ion exchange resin by filtration to obtain raw material solution D. In raw material solution D, particles of fluoropolymer 1C (average particle size 23 nm) were dispersed in an aqueous medium, and the content of fluoropolymer 1C was 0.7% by mass based on the total mass of raw material solution D.

[0090] [Production of Raw Material Solution E] Ultrapure 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 mass%, 5 cc) was added to initiate polymerization. As the polymerization started, the pressure in the reactor decreased, so TFE was added to maintain the pressure constant. When 2 g of TFE had been injected, the reactor was cooled to terminate the polymerization reaction. After recovering the gas remaining in the reactor, the liquid was extracted. This liquid was used as raw material solution E. Raw material solution E was freeze-coagulated and then filtered to obtain fluoropolymer 1E. The Tg of fluoropolymer 1E was 110°C.

[0091] [Production of Raw Material Solution F] Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 20 g) was added to the above raw material solution E (490 g). 60 minutes after the start of stirring, the raw material solution was separated from the ion exchange resin by filtration. To the filtered raw material solution, Purolite A300 (manufactured by Purolite, anion exchange resin, 20 g) was added. 60 minutes after the start of stirring, the raw material solution was separated from the ion exchange resin by filtration to obtain raw material solution F. Raw material solution F contained particles of fluoropolymer 1E (average particle size 80 nm) dispersed in an aqueous medium, and the content of fluoropolymer 1E was 0.48 mass% based on the total mass of raw material solution F.

[0092] [Production of Raw Material Solution G] Ultrapure water (740 g), sodium sulfite (88 mg), n-BMA (n-butyl methacrylate, 330 mg), iron(II) sulfate heptahydrate (11 mg), and Chelest 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 mass%, 3.8 cc) was added, and polymerization was carried out for 60 minutes. After completion of the polymerization reaction, the liquid was withdrawn. This liquid was designated as Raw Material Solution G. Raw Material Solution G was heated to remove water, and the residue was then dried by heating to obtain a hydrocarbon polymer 1G (poly(n-BMA)). The Tg of the hydrocarbon polymer 1G was 20°C.

[0093] [Production of Raw Material Solution H] To the raw material solution G (490 g) was added Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 20 g). 60 minutes after the start of stirring, the raw material solution and the ion exchange resin were separated by filtration. To the filtered raw material solution, Purolite A300 (manufactured by Purolite, anion exchange resin, 20 g) was added. 60 minutes after the start of stirring, the raw material solution and the ion exchange resin were separated by filtration to obtain raw material solution H. Raw material solution H contained particles of hydrocarbon polymer 1G (average particle size 89 nm) dispersed in an aqueous medium, and based on the amount of n-BMA charged, the content of hydrocarbon polymer 1G was 0.044 mass% relative to the total mass of raw material solution H.

[0094] [Production of Raw Material Solution I] Ultrapure water (717 g), PMVE (55 g), TFE (9 g), and an aqueous ammonia solution (30% by mass, 1 drop) 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. As the polymerization began, the pressure in the reactor decreased, so TFE was added to maintain the pressure constant. When 1 g of TFE was injected, the reactor was cooled to 20 ° C., and the polymerization reaction was terminated. After recovering the gas remaining in the reactor, nitrogen was injected to 0.2 MPaG, and the temperature was raised to 90 ° C. The reactor was heated for 3 hours, cooled, and the liquid was extracted. This liquid was designated raw material solution I. After freeze-coagulating the raw material liquid I, it was filtered off, and the resulting fluoropolymer 1I was analyzed by NMR, and as a result, it was found that the TFE unit / PMVE unit ratio was 52 / 48 (molar ratio) and the Tg was -5.5°C.

[0095] [Production of Raw Material Solution J] Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 20 g) was added to the above raw material solution I (490 g). 60 minutes after the start of stirring, the raw material solution was separated from the ion exchange resin by filtration. To the filtered raw material solution, Purolite A300 (manufactured by Purolite, anion exchange resin, 20 g) was added. 60 minutes after the start of stirring, the raw material solution was separated from the ion exchange resin by filtration to obtain raw material J. Raw material solution J contained particles of fluoropolymer 1I (average particle size 28 nm) dispersed in an aqueous medium, and the content of fluoropolymer 1I was 0.36 mass% based on the total mass of raw material solution J.

[0096] [Production of Raw Material Solution K] Ultrapure water (45.4 kg) and PMVE (1.1 kg) were charged into a 60.5 L stainless steel pressure reactor equipped with a baffle and a stirrer, 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. As the polymerization started, the pressure inside the reactor decreased, so TFE was added to maintain the pressure constant. When 165 g of TFE had been injected, the reactor was cooled and the polymerization reaction was terminated. This liquid was used as raw material solution K. Raw material solution K contained fluoropolymer 1K. Raw material solution K was freeze-coagulated and then filtered. The resulting fluoropolymer 1K was analyzed by NMR, and the ratio of TFE units to PMVE units was 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. Raw material liquid L contains particles of fluoropolymer 1K (average particle size 50 nm) dispersed in an aqueous medium, and the content of fluoropolymer 1K was 0.77 mass% based on the total mass of raw material liquid L.

[0098] [Example 1] Ultrapure water (121 g), raw material solution B (475 g), and wax (28 g) were charged into a 1.0 L stainless steel pressure reactor to obtain aqueous dispersion B. Aqueous dispersion B was heated to 70°C while stirring at 260 rpm. TFE was injected into the reactor until the pressure reached 1.4 MPaG, and an aqueous solution of APS (ammonium persulfate) (0.2 mass%, 5 ml) was added to initiate polymerization. As the polymerization began, the pressure in the reactor decreased, so TFE was added to maintain the pressure constant. When 110 g of TFE had been injected, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 220 minutes. The content of fluoropolymer 1A was 0.48 mass% relative to the total mass of aqueous dispersion B. The content (solids concentration) of fluoropolymer 1A in aqueous dispersion B was determined by heating 2.0 g of aqueous dispersion B at 170°C for 20 minutes, weighing the mass of the residue, and then calculating the solids concentration using the following formula. The solids concentration was calculated. For each example described below, calculations were performed in the same manner, except that the type of aqueous dispersion used in that example was changed. "Solids concentration (mass%) = 100 × heating residue of aqueous dispersion B (g) / mass of aqueous dispersion B (2 g)" The concentration of the fluorine-containing emulsifier was 0 ppm by mass relative to the total mass of fluoropolymer 1A in aqueous dispersion B. When the amount of aqueous medium used in aqueous dispersion B used in the polymerization was taken as 100 parts by mass, the amount of the monomer (TFE) used in the polymerization was 18.5 parts by mass. After recovering the gas remaining in the reactor, the liquid was withdrawn. This liquid was designated aqueous dispersion 1. Aqueous dispersion 1 was a dispersion in which particles (average particle size 228 nm) containing fluorine-containing polymer 1A and fluorine-containing polymer 2A were dispersed in an aqueous medium, and had a solids concentration of 16.0% by mass. PTFE was obtained by agglomerating the particles in the obtained aqueous dispersion 1 and filtering them out. The melting point of 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 the result was that TFE unit / PMVE unit = 99.1 / 0.9 (molar ratio). Furthermore, in aqueous dispersion 1, the contents of the compound represented by the above formula (S1) and the compound represented by the above formula (S2) relative to the total mass of the particles in aqueous dispersion 1 were both 100 ppb by mass or less.

[0099] [Example 2] Ultrapure water (121 g), raw material solution D (475 g), and wax (28 g) were charged into a 1.0 L stainless steel pressure reactor to obtain aqueous dispersion D. Aqueous dispersion D was heated to 70°C while stirring at 260 rpm. TFE was injected 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. As the polymerization began, the pressure in the reactor decreased, so TFE was added to maintain the pressure constant. When 170 g of TFE had been injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 282 minutes. The content of fluoropolymer 1C was 0.56 mass% relative to the total mass of aqueous dispersion D. The concentration of the fluorine-containing emulsifier was 0 ppm by mass relative to the total mass of fluoropolymer 1C in aqueous dispersion D. Furthermore, when the amount of the aqueous medium used in aqueous dispersion D used in the polymerization was taken as 100 parts by mass, the amount of the monomer (TFE) used in the polymerization was 28.5 parts by mass. After recovering the gas remaining in the reactor, the liquid was extracted. This liquid was designated aqueous dispersion 2. Aqueous dispersion 2 was a dispersion in which particles (average particle size 258 nm) containing fluorinated polymer 1C and fluorinated polymer 2C were dispersed in an aqueous medium, and had a solids concentration of 22.3% by mass. PTFE was obtained by agglomerating the particles in the obtained aqueous dispersion 2 and filtering it off. The melting point of 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, TFE unit / PMVE unit = 99.3 / 0.7 (molar ratio). In addition, in aqueous dispersion 2, the contents of the compound represented by formula (S1) and the compound represented by formula (S2) relative to the total mass of the particles in aqueous dispersion 2 were both 100 mass ppb or less.

[0100] [Example 3] Ultrapure water (121 g), raw material liquid F (475 g), and wax (28 g) were charged into a 1.0 L stainless steel pressure reactor to obtain aqueous dispersion F. Aqueous dispersion F was heated to 70°C while stirring at 260 rpm. TFE was injected 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. As the polymerization began, the pressure in the reactor decreased, so TFE was added to maintain the pressure constant. When 70 g of TFE had been injected, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 185 minutes. After recovering the gas remaining in the reactor, the liquid was withdrawn, but the entire amount had aggregated, and it was not possible to obtain an aqueous dispersion in which fluoropolymer particles were dispersed in an aqueous medium.

[0101] [Example 4] A 1.0 L stainless steel pressure reactor was charged with raw material liquid H (596 g) and wax (28 g), and the temperature was raised 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 solution (0.2 mass%, 5 ml) was added to initiate polymerization. As the polymerization began, the pressure in the reactor decreased, so TFE was added to maintain the pressure constant. When 70 g of TFE had been injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 470 minutes. The gas remaining in the reactor was recovered, and the liquid was extracted. This liquid was designated as aqueous dispersion 4. Aqueous dispersion 4 was a dispersion in which particles (average particle size 278 nm) containing hydrocarbon polymer 1G and fluoropolymer 2G were dispersed in an aqueous medium, and had a solids concentration of 10.2 mass%. Since aqueous dispersion 4 had a low solids concentration, it can be said that the fluoropolymer was not efficiently produced. The particles in the obtained aqueous dispersion 4 were agglomerated 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. In addition, in aqueous dispersion 4, the contents of the compound represented by formula (S1) and the compound represented by formula (S2) relative to the total mass of the particles in aqueous dispersion 4 were both 100 mass ppb or less.

[0102] [Example 5] Ultrapure water (121 g), raw material solution J (475 g), and wax (28 g) were charged into a 1.0 L stainless steel pressure reactor to obtain aqueous dispersion J. Aqueous dispersion J was heated to 70°C while stirring at 260 rpm. TFE was injected into the reactor until the pressure reached 1.4 MPaG, and an aqueous DSAP (disuccinic acid peroxide) solution (0.45 mass%, 3 ml) was added to initiate polymerization. As the polymerization began, the pressure inside the reactor decreased, so TFE was added to maintain the pressure constant. When 170 g of TFE had been injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 426 minutes. The content of fluoropolymer 1I was 0.29 mass% relative to the total mass of aqueous dispersion J. The concentration of the fluorine-containing emulsifier was 0 ppm by mass relative to the total mass of fluoropolymer 1I in aqueous dispersion J. Furthermore, when the amount of the aqueous medium used in the aqueous dispersion J used in the polymerization was taken as 100 parts by mass, the amount of the monomer (TFE) used in the polymerization was 28.5 parts by mass. After recovering the gas remaining in the reactor, the liquid was extracted. This liquid was designated as aqueous dispersion 5. Aqueous dispersion 5 was a dispersion in which particles (average particle size 262 nm) containing fluorine-containing polymer 1I and fluorine-containing polymer 2I were dispersed in an aqueous medium, and had a solids concentration of 21.3% by mass. PTFE was obtained by agglomerating the particles in the obtained aqueous dispersion 5 and filtering them out. The melting point of 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 the ratio of TFE units to PMVE units was 99.6 / 0.4 (molar ratio). In addition, in aqueous dispersion 5, the contents of the compound represented by formula (S1) and the compound represented by formula (S2) relative to the total mass of the particles in aqueous dispersion 5 were both 100 mass ppb or less.

[0103] [Example 6] Ultrapure water (9.64 kg), raw material liquid L (42.0 kg), and wax (1,324 g) were charged into a 100 L stainless steel pressure reactor to obtain aqueous dispersion L. The aqueous dispersion L was heated to 70°C, and stirring was initiated. TFE was injected until the reactor pressure reached 1.76 MPaG, and an aqueous DSAP solution (0.2 mass%, 1 L) was added to initiate polymerization. As the polymerization began, the pressure in the reactor decreased, so TFE was added to maintain the pressure constant. When 14.0 kg of TFE had been injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 154 minutes. The content of fluoropolymer 1K was 0.62 mass% relative to the total mass of aqueous dispersion L. The concentration of the fluorine-containing emulsifier was 0 ppm by mass relative to the total mass of fluoropolymer 1K in aqueous dispersion L. Furthermore, when the amount of the aqueous medium used in the aqueous dispersion L used in the polymerization was taken as 100 parts by mass, the amount of the monomer (TFE) used in the polymerization was 27.1 parts by mass. After recovering the gas remaining in the reactor, the liquid was extracted. This liquid was designated as aqueous dispersion 6. Aqueous dispersion 6 was a dispersion in which particles (average particle size 200 nm) containing fluorinated polymer 1K and fluorinated polymer 2K were dispersed in an aqueous medium, and the solids concentration was 21% by mass. PTFE was obtained by agglomerating the particles in the obtained aqueous dispersion 6 and filtering them out. The melting point of PTFE dried at 150°C was 344°C and the crystallization energy was -16 J / g. The temperature T was 17°C. After drying, the composition was calculated using NMR, and the result was that TFE units / PMVE units = 99.1 / 0.9 (molar ratio). In addition, in aqueous dispersion 7, the contents of the compound represented by formula (S1) and the compound represented by formula (S2) relative to the total mass of the particles in aqueous dispersion 2 were both 100 mass ppb or less.

[0104] [Example 7] Raw material liquid B was freeze-coagulated and then filtered, and the resulting fluoropolymer 1B (0.2 g) was mixed with PTFE powder (manufactured by AGC, Fluon (registered trademark) PTFE CD145E, 9.8 g) to obtain solid composition 7. The temperature T was 22.1°C.

[0105] [Evaluation] <Colorability> 12 g of the dried particles obtained in each example was weighed out and pressed at a pressure of 0.78 MPaG for 2 minutes to form a cylindrical 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). Thereafter, the number of black foreign particles on the pellet surface was visually counted, and the colorability was evaluated according to the following criteria. The results are shown in Table 1. In the table, "-" indicates that the colorability was not evaluated. A: 0 to 4 black foreign particles B: 5 or more black foreign particles

[0106]

[0107] According to the method for producing a fluoropolymer of the present invention, it was shown that a fluoropolymer can be efficiently produced using an aqueous medium with a small environmental load and without requiring an emulsifier (Examples 1, 2, 5, and 6). Furthermore, a comparison of Examples 1, 2, and 5 showed that if a heating step of heating the aqueous medium in which the first fluoropolymer is dispersed is performed after obtaining the first fluoropolymer, a high molecular weight PTFE can be obtained (Example 5). In contrast, in Examples 3 and 4, a fluoropolymer 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 incorporated herein by reference as 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. An aqueous dispersion comprising an aqueous medium, 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 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; The content of the first fluorine-containing polymer is 0.1 to 5 mass % based on the total mass of the solid composition. 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 a unit 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; A solid composition, wherein the content of the first fluorine-containing polymer is 0.1 to 5 mass% based on the total mass of the solid composition. 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 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, The aqueous dispersion according to claim 6, wherein 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 fluorinated polymer and the second fluorinated 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 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, The solid composition according to claim 7, wherein 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 fluorinated polymer and the second fluorinated 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.