Method for producing fluorine-containing copolymers

Abstract

To provide a method for producing a fluorine-containing copolymer capable of efficiently producing a fluorine-containing copolymer in which coloration and foaming are suppressed during heating.　A method for producing a fluorine-containing copolymer having a step for polymerizing tetrafluoroethylene and another monomer other than tetrafluoroethylene in the presence of a hydroperoxide, at least one selected from the group consisting of sulfites, bisulfites, dithionites, and metabisulfites, at least one selected from the group consisting of acidic substances and substances that generate an acid upon hydrolysis, and an aqueous medium to produce a fluorine-containing copolymer.

Description

[Technical Field]

[0001] This invention relates to a method for producing fluorine-containing copolymers. [Background technology]

[0002] Tetrafluoroethylene (hereinafter also referred to as "TFE")-based fluorine copolymers, such as ethylene / tetrafluoroethylene copolymers and tetrafluoroethylene / perfluoroalkyl vinyl ether copolymers, are used in various industrial fields because they have excellent heat resistance, chemical resistance, flame retardancy, and weather resistance.

[0003] Patent Document 1 discloses a method for producing a vinylidene fluoride-based fluorine-containing copolymer using a hydroperoxide such as tert-butyl hydroperoxide and a reducing agent such as the trade name Bruggolite® as an initiator system. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Special Publication No. 2020-525581 [Overview of the project] [Problems that the invention aims to solve]

[0005] When a fluorine-containing copolymer based on TFE was prepared using the initiator system described in Patent Document 1, the resulting fluorine-containing copolymer exhibited poor thermal stability, resulting in discoloration and foaming when heated for purposes such as high-temperature molding.

[0006] The object of this invention is to provide a method for producing fluorine-containing copolymers that can efficiently produce fluorine-containing copolymers in which discoloration and foaming are suppressed during heating. [Means for solving the problem]

[0007] As a result of diligent research, the inventors have found that the above problem can be solved by the following configuration. [1] In the presence of a hydroperoxide, at least one selected from the group consisting of sulfites, bisulfites, dithionites and metabisulfites, at least one selected from the group consisting of acidic substances and substances that generate acid by hydrolysis, and an aqueous medium, A method for producing a fluorine-containing copolymer, comprising the step of polymerizing tetrafluoroethylene and other monomers other than the tetrafluoroethylene to produce a fluorine-containing copolymer. [2] The method for producing a fluorine-containing copolymer according to [1], wherein the above-mentioned hydroperoxide is a compound represented by the following formula (X). [ka] In formula (X), R x1 ~R x3 Each of these independently represents an alkyl group having 1 to 10 carbon atoms. [3] The method for producing a fluorine-containing copolymer according to [1] or [2], wherein the other monomer is at least one selected from the group consisting of ethylene, propylene, perfluoroalkyl vinyl ether, fluoroalkylethylene, and hexafluoropropylene. [4] A method for producing a fluorine-containing copolymer according to any one of [1] to [3], wherein the above-mentioned acidic substance and the substance that generates acid by hydrolysis are selected from the group consisting of compounds represented by formulas (A) to (E). [ka] In formula (A), R a1 ~R a6 Each of these independently represents either a hydrogen atom or an alkyl group. In formula (B), R b1 ~R b3 Each of these independently represents either a hydrogen atom or an alkyl group. In formula (C), R c1 represents a hydrogen atom or an alkyl group. In formula (D), R d1 ~Rd3 Each independently represents a hydrogen atom or an alkyl group. In formula (E), R e1 ~R e6 Each independently represents a hydrogen atom or an alkyl group. [5] The method for producing a fluorine-containing copolymer according to any one of [1] to [4], wherein the amount of the hydroperoxide used is 0.0001 to 1.0% by mass based on the total mass of the aqueous medium. [6] The method for producing a fluorine-containing copolymer according to any one of [1] to [5], wherein the amount of the sulfite, the bisulfite, the dithionite or the metabisulfite used is 0.0001 to 1.0% by mass based on the total mass of the aqueous medium. [7] The method for producing a fluorine-containing copolymer according to any one of [1] to [6], wherein the amount of the acidic substance or the substance that generates an acid upon hydrolysis used is 0.0005 to 20.0% by mass based on the total mass of the aqueous medium. [8] The method for producing a fluorine-containing copolymer according to any one of [1] to [7], wherein the sulfite is sodium sulfite, potassium sulfite or ammonium sulfite, the bisulfite is sodium bisulfite, potassium bisulfite or ammonium bisulfite, the dithionite is sodium dithionite, potassium dithionite or ammonium dithionite, and the metabisulfite is sodium metabisulfite, potassium metabisulfite or ammonium metabisulfite. [9] The method for producing a fluorine-containing copolymer according to any one of [1] to [8], wherein a polyalkylene oxide compound further exists in the step.

[10] The method for producing a fluorine-containing copolymer according to any one of [1] to [8], wherein an emulsifier further exists in the step. [Effects of the Invention]

[0008] According to the present invention, a fluorine-containing copolymer in which coloring and foaming are suppressed during heating can be efficiently produced. [Embodiments for Carrying Out the Invention]

[0009] The meanings of the terms used in this invention are as follows: A "unit" is a general term for an atomic group derived from a single monomer molecule, which is directly formed by the polymerization of monomers. A numerical range represented using "~" means a range that includes the numbers written before and after "~" as the lower and upper limits, respectively.

[0010] The present invention's method for producing a fluorine-containing copolymer (hereinafter also referred to as "this production method") comprises a step (hereinafter also referred to as "step 1") in which TFE and other monomers other than TFE (hereinafter simply referred to as "other monomers") are polymerized in the presence of a hydroperoxide, at least one selected from the group consisting of sulfites, bisulfites, dithionites, and metabisulfites (hereinafter also referred to as "specific reducing agent"), at least one selected from the group consisting of acidic substances and substances that generate acid by hydrolysis (hereinafter also referred to as "specific acidic substance"), and an aqueous medium to produce a fluorine-containing copolymer. The following details Step 1.

[0011] <Materials used in process 1>

[0012] (Hydroperoxide) A hydroperoxide refers to a compound containing a group represented as *-O-OH. Preferably, a hydrogen atom or an alkyl group is bonded to the * position.

[0013] In step 1, the hydroperoxide decomposes in the presence of a specific acid and a specific reducing agent, acting as a radical initiator. Unlike persulfates such as potassium persulfate, which are known radical initiators, hydroperoxide does not have ionic functional groups, thus improving the thermal stability of the fluorine-containing copolymer obtained by this manufacturing method. As a result, a fluorine-containing copolymer is obtained in which discoloration and foaming are suppressed when heated. Under conditions where specific reducing agents or specific acidic substances are absent, hydroperoxides do not decompose and therefore do not act as radical initiators. The action of hydroperoxide as a radical initiator through decomposition can be determined by the pH of the aqueous dispersion after polymerization is complete. The pH of the aqueous dispersion after polymerization is preferably 3.0 to 8.0, more preferably 4.0 to 7.0, and even more preferably 4.4 to 7.0. In this specification, pH is the value measured at 25°C and can be measured using the Horiba Compact pH Meter LAQUAtwin pH-11B.

[0014] In step 1, the hydroperoxide is preferably water-soluble. In this specification, water solubility is defined as a hydroperoxide that dissolves at least 0.01 g in 1 L of water.

[0015] Specific examples of hydroperoxides include hydrogen peroxide and compounds represented by the following formula (X). [ka] In formula (X), R x1 ~R x3 Each of these independently represents an alkyl group having 1 to 10 carbon atoms. The number of carbon atoms in the alkyl group is preferably 1 to 5, more preferably 1 to 3, and even more preferably 1.

[0016] As the hydroperoxide, the compound represented by the above formula (X) is preferred.

[0017] Specific examples of compounds represented by formula (X) include tert-butyl hydroperoxide (hereinafter also referred to as "TBHP"), 1,1,3,3-tetramethylbutyl hydroperoxide, cumene hydroperoxide, and p-menthane hydroperoxide. Among these, TBHP and 1,1,3,3-tetramethylbutyl hydroperoxide are preferred, and TBHP is more preferred.

[0018] The amount of hydroperoxide used is preferably 0.0001 to 1.0% by mass, more preferably 0.0005 to 0.5% by mass, and even more preferably 0.001 to 0.1% by mass, relative to the total mass of the aqueous medium.

[0019] Furthermore, the amount of hydroperoxide used is preferably 0.001 to 5.0% by mass, more preferably 0.005 to 2.5% by mass, and even more preferably 0.01 to 0.1% by mass, relative to the total amount (total mass) of TFE and other monomers used. The total amount of TFE and other monomers used mentioned above refers to the total mass of TFE and other monomers consumed in the reaction when producing the fluorine-containing copolymer.

[0020] (Sulfites, bisulfites, dithionites, metabisulfites) Sulfites, bisulfites, dithionites, and metabisulfites can function as reducing agents in the presence of certain acidic substances and can decompose hydroperoxides.

[0021] Examples of sulfites include sodium sulfite, potassium sulfite, and ammonium sulfite. Examples of bisulfites include sodium bisulfite, potassium bisulfite, and ammonium bisulfite. Examples of dithionite salts include sodium dithionite, potassium dithionite, and ammonium dithionite. Examples of metabisulfites include sodium metabisulfite, potassium metabisulfite, and ammonium metabisulfite. Furthermore, any one of the above-mentioned sulfites, bisulfites, dithionites, and metabisulfites may be used, or two or more may be used.

[0022] When reducing agents such as the product name Bruggolite (registered trademark) are used, chain transfer occurs during polymerization. As a result, unstable groups are present at the end of the molecule. Consequently, the resulting fluorine-containing copolymer has poor thermal stability, and discoloration and foaming occur when the copolymer is heated. In contrast, using a specific reducing agent prevents chain transfer during polymerization. Therefore, there are no unstable end groups, improving the thermal stability of the resulting fluorine-containing copolymer. As a result, discoloration and foaming are suppressed when the fluorine-containing copolymer is heated.

[0023] Of these, sulfites or bisulfites are preferred, sodium sulfites or sodium bisulfites are more preferred, and sodium sulfites are even more preferred.

[0024] The amount of specific reducing agent used is preferably 0.0001 to 1.0% by mass, more preferably 0.0005 to 0.5% by mass, and even more preferably 0.010 to 0.20% by mass, relative to the total mass of the aqueous medium. When using two or more types of sulfites, bisulfites, dithionites, and metabisulfites, it is preferable that the total content meets the above range.

[0025] (Acidic substances, substances that produce acid through hydrolysis) The specific acidic substance has the function of creating acidic conditions in the reaction system, and by using this specific acidic substance, the specific reducing agent can function as a reducing agent that decomposes hydroperoxide, as described above.

[0026] Acidic substances are substances that, when dissolved or dispersed in an aqueous medium, result in an aqueous solution or dispersion that exhibits acidity. Examples include organic acids and inorganic acids. Examples of organic acids include carboxylic acid compounds such as acetic acid, propionic acid, formic acid, and oxalic acid, and sulfonic acid compounds such as methanesulfonic acid and sodium trifluoromethanesulfonate. Examples of inorganic acids include sulfuric acid, nitric acid, hydrofluoric acid, sodium bisulfite, and phosphoric acid.

[0027] Substances that generate acid through hydrolysis are substances that, when dissolved or dispersed in an aqueous medium, undergo hydrolysis, resulting in an aqueous solution or dispersion that exhibits acidity. Substances that generate acid through hydrolysis include methyl acetate, ethyl acetate, ethylene carbonate, and dimethyl carbonate. Furthermore, any one of the acidic substances and substances that generate acid through hydrolysis may be used, or two or more may be used.

[0028] As specific acidic substances, compounds represented by formulas (A) to (E) are preferred. Compounds represented by formulas (A) to (B) and (D) to (E) are substances that generate acid by hydrolysis, and the compound represented by formula (C) is an acidic substance.

[0029] [ka]

[0030] In formula (A), R a1 ~R a6 Each of these independently represents either a hydrogen atom or an alkyl group. In formula (B), R b1 ~R b3 Each of these independently represents either a hydrogen atom or an alkyl group. In formula (C), R c1 represents a hydrogen atom or an alkyl group. In formula (D), R d1 ~R d3 Each of these independently represents either a hydrogen atom or an alkyl group. In formula (E), R e1 ~R e6 Each of these independently represents either a hydrogen atom or an alkyl group. R a1 ~R a6 , R b1 ~R b3 , R c1 , R d1 ~R d3 , and, R e1 ~R e6 The number of carbon atoms in the alkyl group represented is preferably 1 to 10, more preferably 1 to 5, and even more preferably 1 to 2.

[0031] The amount of specific acidic substance used is preferably 0.0005 to 20.0% by mass, more preferably 0.001 to 10.0% by mass, and even more preferably 0.05 to 3.0% by mass, relative to the total mass of the aqueous medium. When using two or more acidic substances and substances that generate acid through hydrolysis, it is preferable that the total content meets the above range.

[0032] (aqueous medium) Examples of aqueous media include water and mixtures of water and water-soluble organic solvents. Specific examples of water-soluble organic solvents include tert-butanol, propylene glycol, and dipropylene glycol. In the case of a mixture of water and a water-soluble organic solvent, the concentration of the water-soluble organic solvent is preferably 10% by mass or less. Water alone is preferred as the aqueous medium.

[0033] (Other monomers) Other monomers can be any monomer that can copolymerize with TFE. Other specific examples of monomers include ethylene, propylene, perfluoroalkyl vinyl ether (hereinafter also referred to as "PAVE"), fluoroalkylethylene (hereinafter also referred to as "FAE"), and hexafluoropropylene. Specific examples of PAVE include CF2=CFOCF3 (hereinafter also referred to as "PMVE"), CF2=CFOCF2CF3, CF2=CFOCF2CF2CF3 (hereinafter also referred to as "PPVE"), CF2=CFOCF2CF2CF2CF3, and CF2=CFO(CF2)8F, with PMVE and PPVE being preferred. Specific examples of FAE include CH2=CH(CF2)2F (hereinafter also referred to as "PFEE"), CH2=CH(CF2)3F, CH2=CH(CF2)4F (hereinafter also referred to as "PFBE"), CH2=CF(CF2)3H, and CH2=CF(CF2)4H, with PFEE and PFBE being preferred.

[0034] Other monomers include vinyl chloride, vinylidene chloride, and vinyl fluoride. Other monomers include monomers having an oxygen-containing polar group. Preferred oxygen-containing polar groups are acid anhydride residues, hydroxyl groups, carbonyl group-containing groups, acetal groups, and oxycycloalkane groups, with acid anhydride residues being more preferred. Among monomers having an acid anhydride residues, monomers having a cyclic acid anhydride residue are preferred, with itaconic anhydride, citraconic anhydride, 5-norbornene-2,3-dicarboxylic acid anhydride, and maleic anhydride being more preferred.

[0035] It is preferable that the proportion of TFE to the total amount of other monomers is 40 to 99.5 mol%. Within this range, the fluorine-containing copolymer becomes easier to melt-mold.

[0036] The fluorine-containing copolymer obtained by this manufacturing method has units based on tetrafluoroethylene (TFE) (hereinafter also referred to as "TFE units") and units based on other monomers (hereinafter also referred to as "other monomer units").

[0037] When other monomer units are units derived from ethylene (hereinafter also referred to as "E units"), the fluorine-containing copolymer preferably contains 40 to 70 mol% of TFE units, and more preferably 45 to 65 mol% of TFE units, relative to the total of TFE units and E units. When other monomer units are units derived from propylene (hereinafter also referred to as "P units"), the fluorine-containing copolymer preferably contains 30 to 70 mol% of TFE units, and more preferably 45 to 65 mol% of TFE units, relative to the total of TFE units and P units. When other monomer units are units derived from PAVE (hereinafter also referred to as "PAVE units"), the fluorine-containing copolymer preferably contains 90 to 99.9 mol% of TFE units, and more preferably 95 to 99.5 mol% of TFE units, relative to the total of TFE units and PAVE units. When other monomer units are units derived from FAE (hereinafter also referred to as "FAE units"), the fluorine-containing copolymer preferably contains 60 to 90 mol% of TFE units, and more preferably 70 to 80 mol% of TFE units, relative to the total of TFE units and FAE units. When other monomer units are units derived from hexafluoropropylene (hereinafter also referred to as "6F units"), the fluorine-containing copolymer preferably contains 85 to 96 mol% of TFE units, and more preferably 87 to 95 mol% of TFE units, relative to the total of TFE units and 6F units. When other monomer units include both E units and FAE units, the fluorine-containing copolymer preferably contains 40 to 70 mol% TFE units, and more preferably 45 to 65 mol% TFE units, relative to the total of TFE units, E units, and FAE units. The proportion of each unit in a fluorine-containing copolymer can be adjusted by controlling the amount of each monomer added during polymerization. Furthermore, it can be measured by NMR analysis such as nuclear magnetic resonance (NMR) analysis, fluorine content analysis, infrared absorption spectroscopy, etc.

[0038] (Other ingredients) In step 1, other components besides hydroperoxide, specific reducing agents, specific acidic substances, and aqueous media may be present during polymerization, to the extent that the effects of the present invention are not impaired.

[0039] Other components include specific polymers, polyalkylene oxide compounds, and emulsifiers, which will be described in detail later.

[0040] <Step 1 Procedure> TFE and other monomers are introduced into the reaction system (i.e., polymerization reaction vessel) by conventional methods. For example, TFE is introduced into the reaction system continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. Alternatively, for example, other monomers are dissolved in an aqueous medium, and the resulting solution is introduced into the reaction system continuously or intermittently. The hydroperoxide, specific reducing agent, and specific acid substance may be added to the reaction system all at once or in separate additions.

[0041] The polymerization temperature is preferably 10 to 95°C, and more preferably 15 to 90°C. The polymerization pressure is preferably 0.5 to 4.0 MPaG, and more preferably 0.6 to 3.5 MPaG. The polymerization time, in the case of batch processing, is preferably 90 to 1000 minutes, and more preferably 90 to 700 minutes.

[0042] In this manufacturing method, step 1 may be carried out without using an emulsifier, or it may be carried out with an emulsifier.

[0043] Preferred embodiments of Step 1 include the first to third embodiments described later. Each embodiment will be described in detail below.

[0044] (First embodiment) In the first embodiment, it is preferable to carry out step 1 under conditions in which a specific polymer further contains a unit selected from a unit based on the compound represented by formula (1) below (hereinafter also referred to as "compound (1)"), a compound represented by formula (2) below (hereinafter also referred to as "compound (2)"), and a unit based on the compound represented by formula (3) below (hereinafter also referred to as "compound (3)"). In other words, in the first embodiment, polymerization of the TFE and other monomers is carried out in the presence of a hydroperoxide, a specific reducing agent, a specific acidic substance, an aqueous medium, and a specific polymer.

[0045] In the first embodiment, it is preferable to carry out the process in a state where the emulsifier is substantially absent. Examples of emulsifiers include well-known emulsifiers and common surfactants. "Substantially free of emulsifiers" means an environment in which the emulsifier content is 0.03 ppm by mass or less relative to the total mass of the aqueous medium, preferably 0.02 ppm by mass or less, and more preferably 0 ppm by mass.

[0046] It is hypothesized that in step 1, when the specific polymer polymerizes TFE and other monomers, it adsorbs and incorporates TFE and other monomers in its hydrophobic region, thereby solubilizing TFE and other monomers. The presence of a hydroperoxide, a specific reducing agent, and a specific acidic substance in this region allows the polymerization of TFE and other monomers to proceed efficiently. Formula (1) CXY=CR 1 -L 1 -R 2 Formula (2) CXY=CR 1 -COO-(L 2 -O) n -R 3 Formula (3) CXY=CR 4 -(O) m -CH2-ZR 5

[0047] In formula (1), X and Y each independently represent a hydrogen atom, a halogen atom, or a methyl group. Preferably, X and Y are each independently a hydrogen atom, a fluorine atom, or a chlorine atom, and more preferably both are hydrogen atoms.

[0048] In formula (1), R 1 R represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 3 carbon atoms. 1 Preferably, the alkyl group has 1 to 3 carbon atoms, and a methyl group is more preferable.

[0049] In formula (1), L 1 This represents -CO-O-*, -O-CO-*, or -O-. However, * is R 2 This indicates the connection position with L. 1 -CO-O-* or -O-CO-* are preferred, and -CO-O-* is more preferred.

[0050] In formula (1), R 2 R represents a cyclic alkyl group, a monovalent aromatic hydrocarbon group, or a chain alkyl group having 1 to 6 carbon atoms. 2 The chain alkyl group having 1 to 6 carbon atoms may have an etheric oxygen atom between the carbon-carbon bonds, R2 The hydrogen atoms in the cyclic alkyl group, monovalent aromatic hydrocarbon group, and chain alkyl group having 1 to 6 carbon atoms may be substituted with halogen atoms. R 2 Preferably, the group is a cyclohexyl group, a phenyl group, a chain alkyl group having 1 to 4 carbon atoms, a chain fluoroalkyl group having 1 to 4 carbon atoms, or a chain alkyl group having 2 to 5 carbon atoms with an etheric oxygen atom between the carbon-carbon bonds, with a chain alkyl group having 1 to 4 carbon atoms or a chain fluoroalkyl group having 1 to 4 carbon atoms being more preferred.

[0051] Compound (1) is preferably the compound represented by formula (1-1). Formula (1-1) CH2=C(CH3)-CO-OR 21 In formula (1-1), R 21 This includes a cyclohexyl group, a phenyl group, a chain alkyl group having 1 to 4 carbon atoms, a chain fluoroalkyl group having 1 to 4 carbon atoms, or a chain alkyl group having 2 to 3 carbon atoms with an etheric oxygen atom between the carbon-carbon bonds. R 21 Preferably, the element is a chain-like alkyl group having 1 to 4 carbon atoms or a chain-like fluoroalkyl group having 1 to 4 carbon atoms.

[0052] In equation (2), X, Y and R 1 These are X, Y, and R in equation (1), respectively. 1 The definition is the same as that of [the specified entity], and the preferred embodiment is also the same.

[0053] In formula (2), L 2 L represents an alkylene group. 2 Preferably, an alkylene group having 1 to 6 carbon atoms is preferred, an alkylene group having 1 to 3 carbon atoms is more preferred, and an ethylene group is even more preferred. 2 The alkylene group may be linear or branched.

[0054] In formula (2), R 3This represents an alkyl group, an alkyl group in which at least one -CH2- in the alkyl group is replaced with -CO- (hereinafter also referred to as a "substituted alkyl group"), or a group represented by formula (4). Formula (4) -CO-CR 1 =CXY In equation (4), X, Y and R 1 These are X, Y, and R in equation (1), respectively. 1 The definition is the same as that of [the specified entity], and the preferred embodiment is also the same.

[0055] In formula (2), R 3 The alkyl group is preferably an alkyl group having 1 to 3 carbon atoms, and more preferably a methyl group. R 3 The number of -CO- groups in the substituted alkyl group is preferably 1 to 3, and more preferably 2. The position of the -CO- in the substituted alkyl group may be at the end of the substituted alkyl group, or it may be between -CH2- and -CH2-. 3 A preferred substituted alkyl group is -CO-CH2-CO-CH3.

[0056] In equation (2), n represents 1 or greater. n is preferably between 1 and 100, and more preferably between 1 and 50.

[0057] As compound (2), the compound represented by formula (2-1), the compound represented by formula (2-2), or the compound represented by formula (2-3) is preferred. Formula (2-1) CXY=CR 1 -COO-(L 2 -O) n -R 2a Formula (2-2) CXY=CR 1 -COO-(L 2 -O) n -CO-CR 1 =CXY Formula (2-3) CXY=CR 1 -COO-L 2 -OR 2b In equations (2-1), (2-2), and (2-3), X, Y and R 1are the same as the definitions of X, Y, and R in formula (1) respectively. 1 respectively. In formulas (2-1), (2-2), and (2-3), L 2 and n are the same as the definitions of L 2 and n in formula (2) respectively. In formula (2-1), R 2a represents an alkyl group. In formula (2-3), R 2b represents a substituted alkyl group.

[0058] In formula (3), X and Y are the same as the definitions of X and Y in formula (1) respectively, and the preferred embodiments are also the same.

[0059] In formula (3), R 4 represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 3 carbon atoms, or -CO-OCH3. R 4 is preferably an alkyl group having 1 to 3 carbon atoms or -CO-OCH3.

[0060] In formula (3), Z represents -CO-O-* or -O-CO-*. However, * represents the bonding position with R 4 respectively. Z is preferably -O-CO-*.

[0061] In formula (3), R 5 represents an alkyl group. R 5 is preferably an alkyl group having 1 to 3 carbon atoms, more preferably a methyl group.

[0062] In formula (3), m represents 0 or 1. m is preferably 0. T

[0063] As the compound (3), the compound represented by formula (3-1) is preferred. Formula (3-1) CXY=CR 4a -CH2-O-CO-R 5 C In formula (3-1), X and Y are the same as the definitions of X and Y in formula (1) respectively. In formula (3-1), R 5R in equation (3) is 5 This is the same as the definition of [the same thing]. R 4a This represents an alkyl group with 1 to 3 carbon atoms.

[0064] The specific polymer is obtained by step 0, in which compounds (1) to (3) are polymerized in the aqueous medium described above. In step 0, two or more compounds (1) to (3) may be used in combination.

[0065] Step 0 is preferably carried out in the presence of the hydroperoxide described in Step 1 and a specific reducing agent as polymerization initiators. By using the hydroperoxide described in Step 1 and a specific reducing agent as polymerization initiators, the specific polymer can be polymerized in an aqueous medium in Step 0, and then Step 1 can be carried out in the same polymerization system to produce a fluorine-containing copolymer. Polymerizing in the same polymerization system means using the aqueous medium that was used to produce the specific polymer and into which the specific polymer is present, and polymerizing TFE and other monomers in the aqueous medium in which the specific polymer is present. In Step 1, a specific polymer obtained by polymerization separately may be used, and a commercially available product may be used as the specific polymer obtained by polymerization separately.

[0066] Even when a specific polymer polymerized separately is used in step 1, it is preferable to carry out step 0 in the presence of a polymerization initiator. A water-soluble polymerization initiator is preferred as the polymerization initiator. A water-soluble radical initiator or a water-soluble redox catalyst is preferred as the water-soluble polymerization initiator. However, the specific polymer obtained in step 0 is used in step 1 after the polymerization initiator has been removed from the aqueous medium.

[0067] Preferred water-soluble radical initiators 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.

[0068] As a water-soluble redox catalyst, a combination of an oxidizing agent such as bromate or its salt, chloric acid or its salt, persulfate or its salt, permanganate or its salt, or hydrogen peroxide, and a reducing agent such as sulfurous acid or its salt, bisulfite or its salt, thiosulfate or its salt, organic acids, or inorganic salts is preferred. Potassium persulfate and ammonium persulfate are preferred as persulfates. Sodium sulfite is preferred as a sulfite. Examples of inorganic salts include a combination of a sulfate anion, sulfite anion, or chloride anion and a metal ion. Transition metals are preferred as metal ions, 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.

[0069] As a water-soluble polymerization initiator, a water-soluble redox catalyst is preferred, and among these, a combination of potassium persulfate and sodium sulfite, a combination of potassium persulfate, sodium sulfite and an inorganic salt is preferred, and a combination of potassium persulfate and sodium sulfite, and a combination of potassium persulfate, sodium sulfite and iron(II) sulfate are more preferred.

[0070] In step 0, polymerization of compounds (1) to (3) proceeds easily, so it is preferable to set the pH of the reaction system to 3 to 10, and more preferably to 6 to 8. Sulfites such as sodium sulfite, ammonia, sodium hydroxide, hydrochloric acid, etc., may be added as needed to adjust the pH.

[0071] Water-soluble polymerization initiators may be used in combination of two or more types. Regarding the method of preparing the water-soluble polymerization initiator, the entire amount may be added to the reaction system before the polymerization reaction begins, or it may be added to the reaction system continuously or intermittently.

[0072] The amount of compounds (1) to (3) used in step 0 is preferably 0.0001 to 1.0 parts by mass, and more preferably 0.001 to 0.5 parts by mass, per 100 parts by mass of aqueous medium. Within this range, a decrease in the polymerization rate can be prevented, and the amount of specific polymers mixed in the fluorine-containing copolymer when the fluorine-containing copolymer is produced in step 1 can be reduced. As for the method of adding compounds (1) to (3), it is preferable to add the entire amount to the reaction system at the beginning of the polymerization reaction.

[0073] When a specific polymer is polymerized separately, the amount of water-soluble polymerization initiator used in step 0 is preferably 0.1 to 5.0 moles, more preferably 0.1 to 2.0 moles, even more preferably 0.1 to 1.5 moles, and particularly preferably 0.2 to 1.0 moles, per mole of compound (1) to (3).

[0074] In step 0, the polymerization temperature of compounds (1) to (3) is preferably 10 to 95°C, and more preferably 50 to 90°C. The polymerization time is preferably 5 to 400 minutes, and more preferably 5 to 300 minutes, in the case of batch processing. The pressure conditions during polymerization are preferably reduced pressure or atmospheric pressure.

[0075] In step 0, an aqueous dispersion containing a specific polymer is obtained. The specific polymer is in particulate form and uniformly dispersed in the aqueous medium. The aqueous dispersion is colloidal.

[0076] The D50 of the particulate specific polymer (hereinafter also referred to as "specific particles") is preferably 10 to 1000 nm, more preferably 10 to 300 nm, even more preferably 10 to 200 nm, and particularly preferably 10 to 150 nm.

[0077] The specific particles are composed of polymers containing units based on compounds (1) to (3). The content of units based on compounds (1) to (3) in the polymer is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, relative to the total units of the polymer. The upper limit is 100% by mass.

[0078] In step 0, it is easy to obtain an aqueous dispersion containing 0.0001 to 1.0 parts by mass of specific particles with a D50 of 10 to 1000 nm per 100 parts by mass of aqueous medium. Preferably, the specific particles are contained in 0.005 to 0.5 parts by mass, and more preferably in 0.002 to 0.1 parts by mass per 100 parts by mass of aqueous medium.

[0079] (Second embodiment) In the second embodiment, step 1 is carried out in the presence of a polyalkylene oxide compound and substantially without an emulsifier. That is, in the second embodiment, polymerization of the TFE and other monomers is carried out in the presence of a hydroperoxide, a specific reducing agent, a specific acidic substance, an aqueous medium, and a polyalkylene oxide compound, and substantially without an emulsifier. As mentioned above, the product is essentially free of emulsifiers. In the first embodiment described above, step 1 was carried out in the presence of a specific polymer, whereas in the second embodiment, step 1 was carried out in the presence of a polyalkylene oxide compound and substantially without an emulsifier. In other words, the first embodiment uses a specific polymer, while the second embodiment uses a polyalkylene oxide compound. Therefore, the following will mainly describe the differences between the second embodiment and the first embodiment.

[0080] Polyalkylene oxide compounds are compounds that form nuclei (seeds) during the polymerization of TFE with other monomers. In other words, they are nucleating additives. Polyalkylene oxide compounds are compounds containing polyalkylene oxide chains. Examples of polyalkylene oxide chains include polymethylene oxide chains, polyethylene oxide chains, polypropylene oxide chains, and polytetramethylene oxide chains.

[0081] The polyalkylene oxide compound preferably has a surface tension in water exceeding about 40 dynes / cm at a concentration of 1000 ppm. The above surface tension is more preferably exceeding about 42 dynes / cm, and even more preferably exceeding about 45 dynes / cm. The above surface tension is preferably about 73 dynes / cm or less.

[0082] The number average molecular weight of the polyalkylene oxide compound is preferably from 50 to 2000, more preferably from 100 to 1500, and even more preferably from 150 to 1300.

[0083] As the polyalkylene oxide compound, the compound represented by formula (5) is preferred. Formula (5) R a -(O-R c ) p -O-R b In formula (5), R a and R b each independently represents a hydrogen atom, an alkyl group, an acryloyl group or a methacryloyl group. R c represents an alkylene group having 1 to 4 carbon atoms, which may be linear or branched. p represents from 1 to 50.

[0084] Specific examples of the polyalkylene oxide compound include polyethylene glycol, polyethylene glycol acrylate, polyethylene glycol methacrylate, polyethylene glycol methyl ether, polyethylene glycol dimethyl ether, polyethylene glycol butyl ether, polypropylene glycol, polypropylene glycol acrylate, polypropylene glycol methacrylate, polypropylene glycol dimethacrylate, polypropylene glycol methyl ether, polypropylene glycol dimethyl ether, polypropylene glycol butyl ether, polypropylene glycol dimethacrylate, and polytetramethylene glycol.

[0085] Polyalkylene oxide compounds may be used individually or in combination of two or more. The amount of polyalkylene oxide compound used is preferably 0.1 to 10 ppm by mass, and more preferably 1 to 10 ppm by mass, relative to the total mass of the aqueous medium.

[0086] In the second embodiment, it is preferable to obtain a dispersion by mixing a polyalkylene oxide compound and an oxidizing agent in an aqueous medium, and then polymerize TFE and other monomers in the obtained dispersion to produce a fluorine-containing copolymer.

[0087] Specific examples of oxidizing agents include hydrogen peroxide and polymerization initiators. Specific examples of polymerization initiators include the compounds exemplified in the water-soluble polymerization initiators described in the first embodiment above. Persulfates are preferred as polymerization initiators, and ammonium persulfate and potassium persulfate are more preferred.

[0088] When a polyalkylene oxide compound and an oxidizing agent are mixed in an aqueous medium, a dispersion is obtained in which lipophilic nucleation sites are dispersed in the aqueous medium. More specifically, when a polyalkylene oxide compound and an oxidizing agent are mixed, the hydrophilic portion of the polyalkylene oxide compound is decomposed, and the hydrophobic portion of the polyalkylene oxide compound becomes the lipophilic nucleation sites. These lipophilic nucleation sites are dispersed in the aqueous medium, and it becomes possible to finely disperse fluorine-containing copolymers at these sites. Because lipophilic nucleating sites have excellent affinity for TFE and other monomers, polymerization of TFE and other monomers proceeds easily in dispersions containing lipophilic nucleating sites. In other words, lipophilic nucleating sites can serve as a hydrophobic environment for polymerization of TFE and other monomers.

[0089] The amount of oxidizing agent used is preferably 0.01 to 1.00% by mass, and more preferably 0.05 to 0.5% by mass, relative to the total mass of the aqueous medium. The temperature at which the polyalkylene oxide compound and the oxidizing agent are mixed is preferably 20 to 120°C, and more preferably 40 to 120°C. The mixing time when mixing the polyalkylene oxide compound with the oxidizing agent is preferably 0.05 to 1.00 hours.

[0090] It is preferable to add the water-soluble inorganic salt to the aqueous medium before or during the mixing of the polyalkylene oxide compound and the oxidizing agent. The amount of water-soluble inorganic salt used is preferably 1 to 1000 ppm by mass, and more preferably 10 to 1000 ppm by mass, relative to the total mass of the aqueous medium. Specific examples of water-soluble inorganic salts include sodium sulfite, sodium bisulfite, sodium chloride, potassium sulfite, potassium bisulfite, potassium carbonate, ammonium oxalate, sodium tetraborate, sodium acetate, ammonium carbonate, ammonium dihydrogen phosphate, and diammonium phosphate. Sulfites are preferred, with sodium sulfite and ammonium sulfite being more preferred.

[0091] (Third embodiment) In the third embodiment, step 1 is carried out in the presence of an emulsifier. That is, in the third embodiment, polymerization of the TFE and other monomers is carried out in the presence of a hydroperoxide, a specific reducing agent, a specific acidic substance, an aqueous medium, and an emulsifier. Various surfactants can be used as emulsifiers. To improve the yield of the fluorine-containing copolymer, it is preferable to pre-emulsify the mixture consisting of monomer components TFE and other monomers, a surfactant, and an aqueous medium before carrying out step 1. For example, the mixture consisting of TFE, other monomers, a surfactant, and an aqueous medium is mixed and dispersed using a homomixer or a high-pressure emulsifier. The aqueous emulsion preferably contains 1.0 to 50.0 parts by mass of fluorine-containing copolymer per 100 parts by mass of aqueous medium, and more preferably 3 to 40 parts by mass.

[0092] By carrying out step 1, a fluorine-containing copolymer having TFE units and other monomer units is formed. The above-mentioned fluorine-containing copolymer is in particulate form and uniformly dispersed in an aqueous medium. The average primary particle size of particulate fluorine-containing copolymers is not particularly limited, but is often 20 to 3000 nm, and preferably 20 to 1000 nm.

[0093] In the aqueous solution in which the fluorine-containing copolymer obtained by step 1 is dispersed (hereinafter also referred to as "fluorine-containing copolymer aqueous dispersion"), it is preferable that the fluorine-containing copolymer particles are contained in 1.0 to 50.0 parts by mass, and more preferably in 2.0 to 40.0 parts by mass, per 100 parts by mass of the aqueous medium.

[0094] By agglomerating particles containing a fluorine-containing copolymer from an aqueous dispersion of the fluorine-containing copolymer, a powder containing particles of the fluorine-containing copolymer can be obtained. Methods of coagulation include, but are not limited to, freeze coagulation, acid coagulation, base coagulation, and coagulation using coagulants. In the case of freeze-coagulation, the coagulation temperature is preferably 0 to 5°C. The coagulation time is preferably 1 hour or more, and more preferably 2 hours or more. In the case of acid agglutination, it is preferable to add an acid-containing solution to an aqueous dispersion of a fluorine copolymer. Examples of acids to be added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, hydrofluoric acid, etc., with hydrochloric acid being preferred. The concentration of the acid 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. For base aggregation, a method of adding a solution containing a base to an aqueous dispersion of a fluorine-containing copolymer is preferred. Examples of bases to be added include sodium hydroxide, potassium hydroxide, and ammonium carbonate, with sodium hydroxide being 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 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. Specifically, these 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. As for the aggregation method, base aggregation is preferred because it is particularly easy to achieve. [Examples]

[0095] The present invention will be described in more detail below with reference to various examples, but the present invention is not limited to these. Examples 1, 7, and 8 are comparative examples, and Examples 2 to 6 are examples.

[0096] The various measurement and evaluation methods are as follows. Average primary particle size (nm) of fluorine-containing copolymer particles in aqueous dispersion: An aqueous dispersion of fluorine-containing copolymer particles was used as a sample, and the particle size distribution was measured using a laser diffraction / scattering particle size analyzer (Otsuka Electronics Co., Ltd., ELSZ).

[0097] Q(mm 3 Measurement of / s: The Q-value (also known as volumetric flow velocity) was measured at 297°C with a load of 7 kg using a flow tester (manufactured by Shimadzu Corporation). If the Q-value could not be measured with a load of 7 kg, it was measured with a load of 50 kg.

[0098] The proportion of each unit in fluorine-containing copolymers: The proportion of each unit in a fluorine-containing copolymer is: 19 The results were obtained from 1F-NMR analysis, fluorine content analysis, and infrared absorption spectroscopy.

[0099] (Example 1) [Process 0] After purging a 1.3L stainless steel polymerization tank with nitrogen, the pressure was reduced to -0.1 MPaG, and ultrapure water (740g), sodium sulfite (88mg), and 2-methoxyethyl methacrylate (hereinafter also referred to as "MEM") (40mg) were added. Next, the solution in the polymerization tank was heated to 60°C while stirring, and 4 ml of a solution of potassium persulfate (hereinafter also referred to as "KPS") dissolved in deionized water (KPS concentration: 5% by mass) was poured into the polymerization tank to polymerize the MEM.

[0100] [Process 1] Next, a mixed monomer with a TFE / ethylene (hereinafter also referred to as "E") ratio of 86 / 14 molars was injected into a polymerization tank containing an aqueous solution of poly-2-methoxyethyl methacrylate, the specific polymer obtained in step 0. The polymerization tank was pressurized to 2.6 MPaG, and ethyl acetate (2 ml), 12 ml of a solution of KPS dissolved in deionized water (KPS concentration: 5% by mass), and PFBE (0.73 g) were injected into the polymerization tank. Note that the aqueous solution contained in the polymerization tank still contained sodium sulfite used in step 0. The amount of ethyl acetate used was 0.24% by mass relative to the total mass of the aqueous medium. When the pressure inside the polymerization tank began to drop, a mixed monomer with a TFE / E ratio of 54 / 46 molars was added to maintain the internal pressure inside the polymerization tank at 2.6 MPaG, and polymerization proceeded. PFBE (0.73 g) was added to the polymerization tank each time 20 g of mixed monomer was injected under pressure. When the continuous loading of the mixed monomer reached 60g, the polymerization tank was cooled to room temperature, and the gas inside the polymerization tank was released into the atmosphere. The polymerization time was 491 minutes. The pH of the resulting aqueous dispersion of the fluorine-containing copolymer was 4.4, and the solid content concentration was approximately 6.6% by mass. The average primary particle size of the fluorine-containing copolymer in the aqueous dispersion was 166 nm. The aqueous dispersion was cooled to agglomerate the fluorine-containing copolymer particles and obtain a powder. Next, this fluorine-containing copolymer powder was dried at 150°C. The Q value of the obtained fluorine-containing copolymer powder at a 7 kg load was 0.2 mm. 3 The molar ratio of TFE units / E units / PFBE units in the fluorine-containing copolymer was 52.7 / 45.7 / 1.6.

[0101] (Example 2) [Process 0] After purging a 1.2L stainless steel polymerization tank with nitrogen, the pressure was reduced to -0.1 MPaG, and ultrapure water (713g), sodium sulfite (120mg), and methyl methacrylate (MMA) (10mg) were added. Next, the solution in the polymerization tank was heated to 50°C while stirring, and 1 ml of a solution of TBHP dissolved in deionized water as a hydroperoxide (TBHP concentration: 0.195% by mass) was injected into the polymerization tank to polymerize the MMA.

[0102] [Process 1] Next, a mixed monomer with a TFE / E ratio of 86 / 14 molar ratio was injected into a polymerization tank containing an aqueous solution of polymethyl methacrylate, the specific polymer obtained in step 0. The polymerization tank was pressurized to 2.6 MPaG, and methyl acetate (5 ml) and t-butyl alcohol (t-BuOH) (21 g) were injected. 8 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.195 mass%) and PFBE (0.73 g) were injected into the polymerization tank. Note that sodium sulfite used in step 0 remained in the aqueous solution contained in the polymerization tank. The amount of methyl acetate used was 0.63 mass% of the total mass of the aqueous medium. When the pressure inside the polymerization tank began to drop, a mixed monomer with a TFE / E ratio of 54 / 46 molar ratio was added to maintain the internal pressure inside the polymerization tank at 2.6 MPaG, and polymerization proceeded. 1 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.195 mass%) was added every 10 minutes from the start of polymerization. A sodium sulfite aqueous solution (sodium sulfite concentration: 0.92% by mass, 2 ml) was added to the polymerization tank each time 12 g of mixed monomer was injected under pressure. PFBE (0.73 g) was added to the polymerization tank each time 20 g of mixed monomer was injected under pressure. When the continuous charge of mixed monomer reached 100 g, the polymerization tank was cooled to room temperature and the gas inside the polymerization tank was released into the atmosphere. The polymerization time was 377 minutes. The resulting aqueous dispersion of the fluorine-containing copolymer had a pH of 4.4 and a solid content concentration of approximately 12% by mass. The average primary particle size of the fluorine-containing copolymer in the aqueous dispersion was 240 nm. The aqueous dispersion was cooled to agglomerate the fluorine-containing copolymer particles and obtain a powder. Next, this fluorine-containing copolymer powder was dried at 150°C. The Q value of the obtained fluorine-containing copolymer powder at a 7 kg load could not be measured. Therefore, the Q value of the obtained fluorine-containing copolymer powder at a 50 kg load was measured and found to be 100 mm. 3 The value was / s. The molar ratio of TFE units / E units / PFBE units in the fluorine-containing copolymer was 54.5 / 44.6 / 0.9.

[0103] (Example 3) [Process 0] After purging a 1.2L stainless steel polymerization tank with nitrogen, the pressure was reduced to -0.1 MPaG, and ultrapure water (740g), sodium sulfite (150mg), and MEM (10mg) were added. Next, the temperature of the solution in the polymerization tank was raised to 50°C while stirring, and 1 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.195 mass%) was injected into the polymerization tank to polymerize the MEM.

[0104] [Process 1] Next, a polymerization tank containing an aqueous solution of poly-2-methoxyethyl methacrylate, the specific polymer obtained in step 0, was injected with a mixed monomer in a TFE / E ratio of 86 / 14 molar ratio. The tank was pressurized to 2.6 MPaG, and methyl acetate (2 ml) and ethyl acetate (2 ml) were added. 8 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.195% by mass) and PFBE (0.73 g) were added to the polymerization tank. Note that the aqueous solution contained in the polymerization tank still contained sodium sulfite used in step 0. The amount of methyl acetate used was 0.25% by mass relative to the total mass of the aqueous medium. The amount of ethyl acetate used was 0.24% by mass relative to the total mass of the aqueous medium. When the pressure inside the polymerization tank began to drop, a mixed monomer in a TFE / E ratio of 54 / 46 molar ratio was added to maintain the internal pressure inside the polymerization tank at 2.6 MPaG, and polymerization proceeded. Every 10 minutes from the start of polymerization, 1 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.087% by mass) was added. After every 10 g of mixed monomer was added, 2 ml of an aqueous sodium sulfite solution (sodium sulfite concentration: 0.92% by mass) was added to the polymerization vessel. After every 20 g of mixed monomer was added, 0.73 g of PFBE was added to the polymerization vessel. When the continuous addition of mixed monomer reached 80 g, the polymerization vessel was cooled to room temperature and the gas inside the vessel was released into the atmosphere. The polymerization time was 592 minutes. The pH of the resulting aqueous dispersion of the fluorine-containing copolymer was 4.4, and the solid content concentration was approximately 9.7% by mass. The average primary particle size of the fluorine-containing copolymer in the aqueous dispersion was 258 nm. The aqueous dispersion was cooled to agglomerate the fluorine-containing copolymer particles and obtain a powder. Next, this fluorine-containing copolymer powder was dried at 150°C. The Q value of the obtained fluorine-containing copolymer powder at a 7 kg load was 1.6 mm. 3 The molar ratio of TFE units / E units / PFBE units in the fluorine-containing copolymer was 54.4 / 44.8 / 0.8.

[0105] (Example 4) [Process 0] After purging a 1.3L stainless steel polymerization tank with nitrogen, the pressure was reduced to -0.1 MPaG, and ultrapure water (740g), sodium sulfite (150mg), and MMA (10mg) were added. Next, the solution in the polymerization tank was heated to 50°C while stirring, and 1 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.195 mass%) was injected into the polymerization tank to polymerize the MMA.

[0106] [Process 1] Next, a mixed monomer with a TFE / E ratio of 86 / 14 molar ratio was injected into a polymerization tank containing an aqueous solution of polymethyl methacrylate, the specific polymer obtained in step 0. The polymerization tank was pressurized to 2.6 MPaG, and methyl acetate (2 ml) and t-BuOH (28 g) were injected. 8 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.195 mass%) and PFBE (0.73 g) were injected into the polymerization tank. Note that sodium sulfite used in step 0 remained in the aqueous solution contained in the polymerization tank. The amount of methyl acetate used was 0.24 mass% of the total mass of the aqueous medium. When the pressure inside the polymerization tank began to drop, a mixed monomer with a TFE / E ratio of 54 / 46 molar ratio was added to maintain the internal pressure inside the polymerization tank at 2.6 MPaG, and polymerization proceeded. Every 10 minutes from the start of polymerization, 1 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.087 mass%) was added to the polymerization tank. A sodium sulfite aqueous solution (sodium sulfite concentration: 0.92% by mass, 2 ml) was added to the polymerization vessel each time 15 g of mixed monomer was injected under pressure. PFBE (0.73 g) was added to the polymerization vessel each time 20 g of mixed monomer was injected under pressure. When the continuous charge of mixed monomer reached 100 g, the polymerization vessel was cooled to room temperature and the gas inside the polymerization vessel was released into the atmosphere. The polymerization time was 468 minutes. The pH of the resulting aqueous dispersion of the fluorine-containing copolymer was 4.0, and the solid content concentration was approximately 12.2% by mass. The average primary particle size of the fluorine-containing copolymer in the aqueous dispersion was 212 nm. The aqueous dispersion was cooled to agglomerate the fluorine-containing copolymer particles and obtain a powder. Next, this fluorine-containing copolymer powder was dried at 150°C. The Q value of the obtained fluorine-containing copolymer powder at a 7 kg load could not be measured. Therefore, the Q value of the obtained fluorine-containing copolymer powder at a 50 kg load was measured and found to be 20 mm. 3 The value was / s. The molar ratio of TFE units / E units / PFBE units in the fluorine-containing copolymer was 54.8 / 44.2 / 1.0.

[0107] (Example 5) [Process 0] After purging a 1.3L stainless steel polymerization tank with nitrogen, the pressure was reduced to -0.1 MPaG, and ultrapure water (740g), sodium sulfite (150mg), and vinyl acetate (VA) (10mg) were added. Next, the solution in the polymerization tank was heated to 50°C while stirring, and 1 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.195 mass%) was injected into the polymerization tank to polymerize the VA.

[0108] [Process 1] Next, a mixed monomer with a TFE / E ratio of 86 / 14 molar ratio was injected into a polymerization tank containing an aqueous solution of polyvinyl acetate, the specific polymer obtained in step 0. The polymerization tank was pressurized to 2.6 MPaG, and methyl acetate (5 ml) and t-BuOH (21 g) were injected. 8 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.195 mass%) and PFBE (0.73 g) were injected into the polymerization tank. Note that the aqueous solution contained in the polymerization tank still contained sodium sulfite used in step 0. The amount of methyl acetate used was 0.61 mass% of the total mass of the aqueous medium. When the pressure inside the polymerization tank began to drop, a mixed monomer with a TFE / E ratio of 54 / 46 molar ratio was added to maintain the internal pressure inside the polymerization tank at 2.6 MPaG, and polymerization proceeded. Every 10 minutes from the start of polymerization, 1 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.087 mass%) was added to the polymerization tank. A sodium sulfite aqueous solution (sodium sulfite concentration: 0.92% by mass, 2 ml) was added to the polymerization tank every 10 g of mixed monomers. PFBE (0.73 g) was added to the polymerization tank every 20 g of mixed monomers. When the continuous loading of mixed monomers reached 120 g, the polymerization tank was cooled to room temperature and the gas inside the tank was released into the atmosphere. The polymerization time was 435 minutes. The resulting aqueous dispersion of the fluorine-containing copolymer had a pH of 3.9 and a solid content concentration of approximately 13.7% by mass. The average primary particle size of the fluorine-containing copolymer in the aqueous dispersion was 240 nm. The aqueous dispersion was cooled to agglomerate the fluorine-containing copolymer particles and obtain a powder. Next, this fluorine-containing copolymer powder was dried at 150°C. The Q value of the obtained fluorine-containing copolymer powder at a 7 kg load could not be measured. Therefore, the Q value of the obtained fluorine-containing copolymer powder at a 50 kg load was measured and was found to be 56 mmHg. 3 The value was / s. The molar ratio of TFE units / E units / PFBE units in the fluorine-containing copolymer was 55.4 / 44.1 / 0.5.

[0109] (Example 6) [Process 0] After purging a 1.3L stainless steel polymerization tank with nitrogen, the pressure was reduced to -0.1 MPaG, and ultrapure water (713g), sodium sulfite (120mg), and MMA (10mg) were added. Next, the temperature of the solution in the polymerization tank was raised to 50°C while stirring, and 1 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.195 mass%) was injected into the polymerization tank to polymerize the MMA.

[0110] [Process 1] Next, a mixed monomer with a TFE / E ratio of 86 / 14 molar ratio was injected into a polymerization tank containing an aqueous solution of polymethyl methacrylate, the specific polymer obtained in step 0. The polymerization tank was pressurized to 2.6 MPaG, and methyl acetate (5 ml) and t-BuOH (21 g) were injected. 8 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.195 mass%) and PFBE (0.73 g) were injected into the polymerization tank. Note that sodium sulfite used in step 0 remained in the aqueous solution contained in the polymerization tank. The amount of methyl acetate used was 0.63 mass% of the total mass of the aqueous medium. When the pressure inside the polymerization tank began to drop, a mixed monomer with a TFE / E ratio of 52 / 48 molar ratio was added to maintain the internal pressure inside the polymerization tank at 2.6 MPaG, and polymerization proceeded. Every 10 minutes from the start of polymerization, 1 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.195 mass%) was added to the polymerization tank. A sodium sulfite aqueous solution (sodium sulfite concentration: 0.92% by mass, 1 ml) was added to the polymerization tank every time 6 g of mixed monomer was injected under pressure. PFBE (0.73 g) was added to the polymerization tank every time 20 g of mixed monomer was injected under pressure. When the continuous charge of mixed monomer reached 140 g, the polymerization tank was cooled to room temperature and the gas inside the polymerization tank was released into the atmosphere. The polymerization time was 508 minutes. The pH of the resulting aqueous dispersion of the fluorine-containing copolymer was 3.9, and the solid content concentration was approximately 16% by mass. The average primary particle size of the fluorine-containing copolymer in the aqueous dispersion was 250 nm. The aqueous dispersion was cooled to agglomerate the fluorine-containing copolymer particles and obtain a powder. Next, this fluorine-containing copolymer powder was dried at 150°C. The Q value of the obtained fluorine-containing copolymer powder at a 7 kg load could not be measured. Therefore, the Q value of the obtained fluorine-containing copolymer powder at a 50 kg load was measured and was found to be 85.8 mm. 3 The value was / s. The molar ratio of TFE units / E units / PFBE units in the fluorine-containing copolymer was 54.3 / 44.8 / 0.9.

[0111] (Example 7) [Process 0] After purging a 1.2L stainless steel polymerization tank with nitrogen, the pressure was reduced to -0.1 MPaG, and ultrapure water (740g), sodium sulfite (120mg), and MEM (10mg) were added. Next, the temperature of the solution in the polymerization tank was raised to 50°C while stirring, and 1 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.195 mass%) was injected into the polymerization tank to polymerize the MEM.

[0112] [Process 1] Next, a mixed monomer mixture with a TFE / E ratio of 86 / 14 molar ratio was injected into a polymerization tank containing an aqueous solution of poly-2-methoxyethyl methacrylate, the specific polymer obtained in step 0. The polymerization tank was pressurized to 2.6 MPaG, and 8 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.195% by mass) was injected into the polymerization tank. Note that the aqueous solution contained in the polymerization tank still contained sodium sulfite used in step 0. Polymerization was stopped after 150 minutes because it had not progressed. The pH of the resulting aqueous dispersion was 8.5.

[0113] (Example 8) [Process 0] After purging a 1.2L stainless steel polymerization tank with nitrogen, the pressure was reduced to -0.1 MPaG, and ultrapure water (704g), Bruggolite® FF6M (formula below) (150mg), and MMA (10mg) were added. [ka] Next, the temperature of the solution in the polymerization tank was raised to 50°C while stirring, and 1 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.195% by mass) was poured into the polymerization tank to polymerize MMA.

[0114] [Process 1] Next, a mixed monomer with a TFE / E ratio of 86 / 14 molar ratio was injected into a polymerization tank containing an aqueous solution of polymethyl methacrylate, the specific polymer obtained in step 0. The polymerization tank was pressurized to 2.6 MPaG, and methyl acetate (2 ml) and t-BuOH (28 g) were injected. Note that Bruggolite® FF6M, used in step 0, remained in the aqueous solution contained in the polymerization tank. 8 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.195 mass%) and PFBE (0.73 g) were injected into the polymerization tank. The amount of methyl acetate used was 0.25 mass% of the total mass of the aqueous medium. When the pressure inside the polymerization tank began to drop, a mixed monomer with a TFE / E ratio of 54 / 46 molar ratio was added to maintain the internal pressure at 2.6 MPaG, and polymerization proceeded. 1 ml of a solution of TBHP dissolved in deionized water (0.195 mass%) was added to the polymerization tank every 10 minutes from the start of polymerization. PFBE (0.73g) was added to the polymerization vessel each time 20g of mixed monomer was injected under pressure. When the continuous charge of mixed monomer reached 40g, the polymerization vessel was cooled to room temperature and the gas inside the polymerization vessel was released into the atmosphere. The polymerization time was 250 minutes. The pH of the resulting aqueous dispersion of fluorine-containing copolymer was 3.8, and the solid content concentration was approximately 5.6% by mass. The average primary particle size of the fluorine-containing copolymer in the aqueous dispersion was 164 nm. The aqueous dispersion was cooled to agglomerate the fluorine-containing copolymer particles and obtain a powder. Next, this fluorine-containing copolymer powder was dried at 150°C. The Q value of the obtained fluorine-containing copolymer powder at a 7 kg load could not be measured. Therefore, the Q value of the obtained fluorine-containing copolymer powder at a 50 kg load was measured and was found to be 32 mmHg. 3 The value was / s. The molar ratio of TFE units / E units / PFBE units in the fluorine-containing copolymer was 53.9 / 44.9 / 1.2.

[0115] (evaluation) The fluorine-containing copolymer powders obtained in each example were heated at 300°C for 2 hours, and the presence or absence of foaming and discoloration was checked. They were then evaluated according to the following criteria. The results are shown in the table below. Foaming evaluation ◎: None, ○: Slightly present, △: Present, ×: The entire resin is foamed. Color evaluation ◎: No change before and after heating, ○: Turned yellow, △: Turned from yellow to brown, ×: Completely black

[0116] In Table 1, the "Hydroperoxide Usage (1)" column represents the amount of hydroperoxide used (mass %) relative to the total mass of the aqueous medium in step 1. In Table 1, the "Hydroperoxide Usage (2)" column represents the amount of hydroperoxide used (mass %) relative to the total amount of TFE, E, and PFBE used in process 1 (total mass). In Table 1, the "Amount of Specific Reducing Agent Used" column represents the amount of specific reducing agent used (mass %) relative to the total mass of the aqueous medium in step 1. In Table 1, the "Amount of Specific Acid Substance Used" column represents the amount (mass %) of the specific reducing agent used relative to the total mass of the aqueous medium in step 1.

[0117] [Table 1]

[0118] As shown in Table 1, the fluorine-containing copolymers of Examples 2-6, obtained by polymerizing TFE and other monomers in the presence of hydroperoxide, a specific reducing agent, a specific acidic substance, and an aqueous medium, exhibited foaming and coloring of ○ or higher when heated at 300°C. The pH of the aqueous dispersions of Examples 2-6 after polymerization was 3.0-8.0. The fluorine-containing copolymers of Examples 2-4, whose aqueous dispersion pH after polymerization was 4.0-7.0, exhibited foaming of ◎ when heated at 300°C. The fluorine-containing copolymers of Examples 2 and 3, whose aqueous dispersion pH after polymerization was 4.4-7.0, exhibited coloring of ◎ when heated at 300°C. The fluorine-containing copolymer of Example 1, which used KPS as a radical initiator, exhibited foaming and coloring of × when heated at 300°C. In Example 7, which did not use a specific acidic substance, polymerization did not proceed. The fluorine-containing copolymer in Example 8, which used Bruggolite® FF6M, a specified reducing agent, exhibited foaming and discoloration (△) when heated at 300°C. Furthermore, the entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2021-101448, filed on June 18, 2021, are incorporated herein by reference as disclosure of the present invention.

Claims

1. In the presence of a hydroperoxide, at least one selected from the group consisting of sulfites, bisulfites, dithionites, and metabisulfites, at least one selected from the group consisting of acidic substances and substances that generate acid by hydrolysis, and an aqueous medium, The process includes a step of polymerizing tetrafluoroethylene and other monomers other than tetrafluoroethylene to produce a fluorine-containing copolymer, The aforementioned hydroperoxide is a compound represented by the following formula (X), The acidic substance and the substance that generates acid by hydrolysis are selected from the group consisting of compounds represented by formulas (A) to (E). The amount of hydroperoxide used is 0.0001 to 1.0% by mass relative to the total mass of the aqueous medium. The amount used of the aforementioned sulfite, bisulfite, dithionite, or metabisulfite is 0.0001 to 1.0% by mass relative to the total mass of the aqueous medium. A method for producing a fluorine-containing copolymer, wherein the total amount of the acidic substance or the substance that generates acid by hydrolysis used is 0.0005 to 20.0% by mass of the total mass of the aqueous medium. 【Chemistry 1】 In formula (X), R ｘ１ ~R ｘ３ Each of these independently represents an alkyl group having 1 to 10 carbon atoms. 【Chemistry 2】 In formula (A), R ａ１ ~R ａ６ Each of these independently represents either a hydrogen atom or an alkyl group. In formula (B), R ｂ１ ~R ｂ３ Each of these independently represents either a hydrogen atom or an alkyl group. In formula (C), R ｃ１ represents a hydrogen atom or an alkyl group. In formula (D), R ｄ１ ~R ｄ３ each independently represents a hydrogen atom or an alkyl group. In formula (E), R ｅ１ ~R ｅ６ Each of these independently represents either a hydrogen atom or an alkyl group.

2. The method for producing a fluorine-containing copolymer according to claim 1, wherein the other monomer is at least one selected from the group consisting of ethylene, propylene, perfluoroalkyl vinyl ether, fluoroalkylethylene, and hexafluoropropylene.

3. The sulfite is sodium sulfite, potassium sulfite, or ammonium sulfite. The bisulfite is sodium bisulfite, potassium bisulfite, or ammonium bisulfite. The dithionite salt is sodium dithionite, potassium dithionite, or ammonium dithionite. The aforementioned metabisulfite is sodium metabisulfite, potassium metabisulfite, or ammonium metabisulfite. A method for producing a fluorine-containing copolymer according to claim 1 or 2.

4. A method for producing a fluorine-containing copolymer according to claim 1 or 2, wherein a polyalkylene oxide compound is further present in the above step.

5. A method for producing a fluorine-containing copolymer according to claim 1 or 2, wherein an emulsifier is further present in the above step.

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