Process for producing fluorine-containing copolymer

Abstract

Provided is a method for producing a fluorine-containing copolymer, which can efficiently produce a fluorine-containing copolymer in which coloring and foaming are suppressed upon heating. A method for producing a fluorine-containing copolymer, which has the step of producing a fluorine-containing copolymer by polymerizing tetrafluoroethylene and another monomer other than the above tetrafluoroethylene in the presence of a hydroperoxide, at least one selected from the group consisting of a sulfite, a bisulfite, a dithionite, and a pyrosulfite, at least one selected from the group consisting of an acidic substance and a substance that generates an acid by hydrolysis, and an aqueous medium.

Description

Technical Field

[0001] This invention relates to a method for manufacturing fluorinated copolymers. Background Technology

[0002] Fluorinated copolymers based on tetrafluoroethylene (hereinafter also referred to as "TFE"), such as ethylene / tetrafluoroethylene copolymers or tetrafluoroethylene / perfluoroalkyl vinyl ether copolymers, are used in various industrial fields due to their excellent heat resistance, chemical resistance, flame retardancy, and weather resistance.

[0003] Patent document 1 discloses a method for preparing a fluorinated copolymer, which uses a hydroperoxide such as tert-butyl hydroperoxide and a reducing agent such as Bruggolite (a registered trademark) as an initiator system to obtain a fluorinated copolymer based on vinylidene fluoride. Existing technical documents Patent documents

[0004] Patent Document 1: Japanese Patent Publication No. 2020-525581 Summary of the Invention The technical problem that the invention aims to solve

[0005] When using the initiator system described in Patent Document 1 to manufacture TFE-based fluorinated copolymers, the resulting fluorinated copolymers have poor thermal stability and may cause coloring or foaming when heated for purposes such as high-temperature molding.

[0006] The technical problem to be solved by the present invention is to provide a method for manufacturing fluorinated copolymers, which can efficiently manufacture fluorinated copolymers in which coloring and foaming are suppressed during heating. means of solving technical problems

[0007] The inventors conducted in-depth research and found that the above-mentioned problems can be solved by the following configuration. [1] A method for manufacturing a fluorinated copolymer, comprising the following steps: in the presence of hydroperoxide, at least one selected from sulfites, bisulfites, dithionites and metabisulfites, at least one selected from acidic substances and substances that generate acid by hydrolysis, and an aqueous medium, polymerizing tetrafluoroethylene and other monomers other than tetrafluoroethylene to manufacture a fluorinated copolymer. [2] The method for manufacturing the fluorinated copolymer as described in [1], wherein the hydroperoxide is a compound represented by the following formula (X):

Chemical Formula 1

[10] A method for manufacturing a fluorinated copolymer as described in any one of [1] to [8], wherein an emulsifier is also present in the process. Invention Effects

[0008] According to the present invention, fluorinated copolymers in which coloring and foaming are suppressed during heating can be manufactured efficiently. Detailed Implementation

[0009] The meanings of the terms used in this invention are as follows. A "unit" is a group of atoms formed directly from the polymerization of monomers, and is a collective term for a single molecule of a monomer. The range of values ​​represented by “~” is the range that includes the values ​​before and after “~” as the lower and upper limits.

[0010] The method for manufacturing the fluorinated copolymer of the present invention (hereinafter also referred to as "the manufacturing method") comprises the following steps: in the presence of hydroperoxide, at least one selected from sulfite, bisulfite, dithionite and metabisulfite (hereinafter also referred to as "specific reducing agent"), at least one selected from acidic substances and substances that generate acid by hydrolysis (hereinafter also referred to as "specific acid substances"), and an aqueous medium, TFE and other monomers other than TFE are polymerized to manufacture the fluorinated copolymer (hereinafter also referred to as "step 1"). The following is a detailed description of process 1.

[0011] <Materials used in process 1>

[0012] (hydroperoxide) Hydroperoxides are compounds containing groups represented by *-O-OH. The * position preferably has a hydrogen atom or an alkyl group bonded to it.

[0013] In step 1, hydroperoxides decompose in the presence of a specific acid and under the action of a specific reducing agent, thus acting as free radical initiators. Unlike persulfates such as potassium persulfate, which are known as free radical initiators, hydroperoxides do not possess ionic functional groups, thereby improving the thermal stability of the fluorinated copolymers obtained by this manufacturing method. As a result, fluorinated copolymers in which coloring and foaming are suppressed upon heating can be obtained. In the absence of specific reducing agents or specific acidic substances, hydroperoxides will not decompose and thus cannot function as free radical initiators. The effect of hydroperoxide decomposition as a free radical initiator can be determined by the pH value of the aqueous dispersion after polymerization. The pH value of the aqueous dispersion after polymerization is preferably 3.0–8.0, more preferably 4.0–7.0, and even more preferably 4.4–7.0. Additionally, the pH value in this instruction manual is a value measured at 25°C, and can be measured using the Horiba mini pH meter LAQUAtwinpH-11B.

[0014] The hydroperoxide in step 1 is preferably water-soluble. In this application specification, if more than 0.01 g of hydroperoxide dissolves in 1 L of water, it is considered water-soluble.

[0015] Specific examples of hydroperoxides include hydrogen peroxide and compounds represented by the following formula (X).

Chemical Formula 3

[0016] As a 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 terpene hydroperoxide. Among these, TBHP and 1,1,3,3-tetramethylbutyl hydroperoxide are preferred, and TBHP is more preferred.

[0018] The amount of hydroperoxide used relative to the total mass of the aqueous medium 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.

[0019] Furthermore, the amount of hydroperoxide used relative to the total amount (total mass) of TFE and other monomers 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. In addition, 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 during the manufacture of fluorinated copolymers.

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

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

[0022] If a reducing agent such as Bruggolite (a registered trademark) is used, chain transfer occurs during polymerization. This results in an unstable state with terminal groups present. Consequently, the resulting fluorinated copolymer exhibits poor thermal stability and may discolor or foam upon heating. In contrast, if a specific reducing agent is used, chain transfer does not occur during polymerization. Therefore, there are no unstable groups acting as terminal groups, resulting in improved thermal stability of the resulting fluorinated copolymer. Consequently, coloring and foaming are suppressed when the fluorinated copolymer is heated.

[0023] Among them, sulfite or bisulfite is preferred, sodium sulfite or sodium bisulfite is more preferred, and sodium sulfite is even more preferred.

[0024] The amount of the specific reducing agent used relative to the total mass of the aqueous medium 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. 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) A specific acidic substance has the function of making the reaction system acidic. By using this specific acidic substance, as described above, a specific reducing agent can function as a reducing agent for decomposing hydrogen peroxide.

[0026] Acidic substances are substances whose aqueous solutions or dispersions are acidic when dissolved or dispersed in an aqueous medium. 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 produce acid through hydrolysis are those that hydrolyze when dissolved or dispersed in an aqueous medium, making the aqueous solution or dispersion acidic. Examples of substances that produce acids through hydrolysis include methyl acetate, ethyl acetate, ethylene carbonate, and dimethyl carbonate. Alternatively, one or more of the following can be used: an acidic substance and a substance that produces acid through hydrolysis.

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

[0029] [Chemical Formula 4]

[0030] In formula (A), R a1 ~R a6 Each can be used independently to represent a hydrogen atom or an alkyl group. In equation (B), R b1 ~R b3 Each can be used independently to represent a hydrogen atom or an alkyl group. In equation (C), R c1 It represents a hydrogen atom or an alkyl group. In equation (D), R d1 ~R d3 Each can be used independently to represent a hydrogen atom or an alkyl group. In equation (E), R e1 ~R e6 Each can be used independently to represent a hydrogen atom or an alkyl group. By R a1 ~R a6 R b1 ~R b3 R c1 R d1 ~R d3 and R e1 ~R e6 The alkyl group represented preferably has 1 to 10 carbon atoms, more preferably 1 to 5, and even more preferably 1 to 2.

[0031] The amount of the specific acidic substance used relative to the total mass of the aqueous medium 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. When using two or more acidic substances and substances that produce 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. As an aqueous medium, water alone is preferred.

[0033] (Other monomers) As for other monomers, any monomer that can copolymerize with TFE will suffice. Other specific examples of monomers include ethylene, propylene, perfluoroalkyl vinyl ethers (hereinafter also referred to as "PAVE"), fluoroalkyl vinyls (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 FAEs 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. In addition, monomers having oxygen-containing polar groups can be cited as other monomers. Preferably, the oxygen-containing polar group consists of anhydride residues, hydroxyl groups, carbonyl groups, acetal groups, or oxycycloalkyl groups; more preferably, itaconic anhydride residues. Among monomers having anhydride residues, monomers having cyclic anhydride residues are preferred; more preferably, itaconic anhydride, citraconic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, and maleic anhydride.

[0035] The proportion of TFE relative to the total of TFE and other monomers is preferably 40 to 99.5 mol%. Within this range, the fluorinated copolymer is easy to melt-form.

[0036] The fluorinated copolymers obtained by this manufacturing method contain tetrafluoroethylene (TFE)-based units (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 fluorinated copolymer contains preferably 40 to 70 mol% of TFE units, 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 fluorinated copolymer contains preferably 30 to 70 mol% of TFE units, more preferably 45 to 65 mol% of TFE units in total with respect to TFE units and P units. When other monomer units are units derived from PAVE (hereinafter also referred to as "PAVE units"), the fluorinated copolymer contains preferably 90 to 99.9 mol% 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 from FAE (hereinafter also referred to as "FAE units"), the fluorinated copolymer contains preferably 60 to 90 mol% 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 fluorinated copolymer contains preferably 85 to 96 mol% of TFE units, more preferably 87 to 95 mol% of TFE units relative to the total of TFE units and 6F units. In cases where other monomer units include both E units and FAE units, the fluorinated copolymer preferably contains 40 to 70 mol% of TFE units, more preferably 45 to 65 mol% of TFE units relative to the total of TFE units, E units and FAE units. The proportions of each unit in a fluorinated copolymer can be adjusted by the amount of each monomer added during polymerization. Furthermore, it can be determined using NMR analysis (such as nuclear magnetic resonance (NMR) analysis), fluorine content analysis, and infrared absorption spectroscopy.

[0038] (Other ingredients) In step 1, without compromising the effectiveness of the present invention, other components besides hydroperoxide, specific reducing agent, specific acidic substance, and aqueous medium may also be present during polymerization.

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

[0040] <Steps of Process 1> TFE and other monomers are added to the reaction system (i.e., the polymerization reactor) using conventional methods. For example, TFE is added to the reaction system continuously or intermittently until the polymerization pressure reaches the specified pressure. Alternatively, other monomers may be dissolved in an aqueous medium, and the resulting solution is added to the reaction system continuously or intermittently. Hydroperoxides, specific reducing agents, and specific acidic substances can be added together or separately to the reaction system.

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

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

[0043] As a preferred embodiment of step 1, the first to third embodiments described below can be cited. Each embodiment will be described in detail below.

[0044] (First Implementation) In the first embodiment, step 1 is preferably carried out in the presence of a specific polymer containing at least one unit selected from the compounds represented by formula (1) (hereinafter also referred to as "compound (1)"), the compounds represented by formula (2) (hereinafter also referred to as "compound (2)"), and the compounds represented by formula (3) (hereinafter also referred to as "compound (3)"). That is, in the first embodiment, the polymerization of the above-mentioned TFE with other monomers is carried out in the presence of hydroperoxide, a specific reducing agent, a specific acid, an aqueous medium, and the specific polymer.

[0045] Furthermore, in the first embodiment, it is preferable to carry out the work under conditions where there is virtually no emulsifier. As emulsifiers, well-known emulsifiers and conventional surfactants can be cited as examples. The condition of the absence of emulsifiers refers to an environment in which the emulsifier content relative to the total mass of the aqueous medium is less than 0.03 ppm by mass, preferably less than 0.02 ppm by mass, and more preferably 0 ppm by mass.

[0046] In step 1, when TFE is polymerized with other monomers, a specific polymer makes TFE and other monomers soluble by adsorbing and drawing in TFE and other monomers through the hydrophobic part. It is speculated that the coexistence of hydroperoxide, a specific reducing agent and a specific acid substance at this point enables the efficient polymerization of TFE and other monomers. Equation (1) CXY=CR 1 -L 1 -R 2 Equation (2) CXY=CR 1 -COO-(L 2 -O) n -R 3 Equation (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. X and Y are preferably each hydrogen atom, a fluorine atom, or a chlorine atom, and more preferably both are hydrogen atoms.

[0048] In equation (1), R 1 Represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 3 carbon atoms. As R 1 Preferably, it is an alkyl group with 1 to 3 carbon atoms, and more preferably a methyl group.

[0049] In equation (1), L 1 This represents -CO-O-*, -O-CO-*, or -O-. Where * indicates a similarity to R. 2 The bonding position. As L 1 Preferably -CO-O-* or -O-CO-*, more preferably -CO-O-*.

[0050] In equation (1), R 2 This indicates a cyclic alkyl group, a monovalent aromatic hydrocarbon group, or a chain alkyl group having 1 to 6 carbon atoms. Wherein, R... 2 The carbon-carbon bonds of alkyl chains with 1 to 6 carbon atoms may contain ether-like oxygen atoms, R 2 Hydrogen atoms in cyclic alkyl groups, monovalent aromatic hydrocarbon groups, and chain alkyl groups with 1 to 6 carbon atoms can also be replaced by halogen atoms. As R 2 Preferably, cyclohexyl, phenyl, alkyl chain with 1 to 4 carbons, fluoroalkyl chain with 1 to 4 carbons, or alkyl chain with 2 to 5 carbons having ether oxygen atoms between carbon-carbon bonds, more preferably alkyl chain with 1 to 4 carbons or fluoroalkyl chain with 1 to 4 carbons.

[0051] As compound (1), the preferred compound is the one represented by formula (1-1). Equation (1-1) CH2=C(CH3)-CO-OR 21 In equation (1-1), R 21 It is cyclohexyl, phenyl, 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 ether-like oxygen atoms between carbon-carbon bonds. As R 21 Preferably, it is a chain alkyl group having 1 to 4 carbon atoms or a chain fluoroalkyl group having 1 to 4 carbon atoms.

[0052] In equation (2), X, Y and R 1 respectively with X, Y and R in equation (1) 1 The definitions are the same, and the preferred methods are also the same.

[0053] In equation (2), L 2 Indicates alkylene. As L 2 Preferably, it is an alkylene group having 1 to 6 carbon atoms, more preferably an alkylene group having 1 to 3 carbon atoms, and even more preferably a vinyl group. 2 The alkylene groups can be linear or branched.

[0054] In equation (2), R 3 It represents an alkyl group, at least one of the alkyl groups whose -CH2- is substituted with -CO- (hereinafter also referred to as "substituted alkyl group"), or a group represented by formula (4). Equation (4) -CO-CR 1 =CXY In equation (4), X, Y and R 1 respectively with X, Y and R in equation (1) 1 The definitions are the same, and the preferred methods are also the same.

[0055] In equation (2), R is used as 3 Alkyl groups, preferably alkyl groups having 1 to 3 carbon atoms, and more preferably methyl groups. R 3 The number of groups represented by -CO- in the substituted alkyl group is preferably 1 to 3, more preferably 2. The -CO- position in the substituted alkyl group can be at the end of the substituted alkyl group or between -CH2- and -CH2-. As R 3 The substituted alkyl group is preferably -CO-CH2-CO-CH3.

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

[0057] As compound (2), the preferred compounds are those represented by formula (2-1), formula (2-2), or formula (2-3). Equation (2-1) CXY=CR 1 -COO-(L 2 -O) n -R 2a Equation (2-2) CXY=CR 1 -COO-(L 2 -O) n -CO-CR 1 =CXY Equation (2-3) CXY=CR 1 -COO-L 2 -OR 2b In equations (2-1), (2-2), and (2-3), X, Y, and R 1respectively with X, Y and R in equation (1) 1 The definitions are the same. In equations (2-1), (2-2), and (2-3), L 2 and n are respectively related to L in equation (2) 2 The definition of n is the same. In equation (2-1), R2 a Indicates alkyl group. In equation (2-3), R 2b Indicates a substituted alkyl group.

[0058] In equation (3), X and Y are defined in the same way as X and Y in equation (1), and the preferred method is also the same.

[0059] In equation (3), R 4 Represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 3 carbon atoms, or -CO-OCH3. As R 4 Preferably, it is an alkyl group with 1 to 3 carbon atoms or -CO-OCH3.

[0060] In equation (3), Z represents -CO-O-* or -O-CO-*. Where * indicates that it is related to R 4 The bonding position. For Z, -O-CO-* is preferred.

[0061] In equation (3), R 5 Indicates alkyl group. As R 5 Preferably, it is an alkyl group with 1 to 3 carbon atoms, and more preferably a methyl group.

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

[0063] As compound (3), the compound represented by formula (3-1) is preferred. Equation (3-1) CXY=CR 4a -CH2-O-CO-R 5 In equation (3-1), X and Y are defined in the same way as X and Y in equation (1). In equation (3-1), R 5 R in equation (3) 5 The definitions are the same. As R 4a , indicating an alkyl group having 1 to 3 carbon atoms.

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

[0065] Step 0 is preferably carried out in the presence of the hydroperoxide and the specific reducing agent described in Step 1, which serve as polymerization initiators. If the hydroperoxide and the specific reducing agent described in Step 1 are used as polymerization initiators, the specific polymer can be polymerized in an aqueous medium in Step 0, and Step 1 can be continued in the same polymerization system to produce a fluorinated copolymer. Continuing polymerization in the same polymerization system means using the aqueous medium used in the manufacture of the specific polymer up to the presence of the specific polymer, and polymerizing TFE with other monomers in the aqueous medium in which the specific polymer is present. In Step 1, a separately polymerized specific polymer can also be used; commercially available products can be used as the separately polymerized specific polymer.

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

[0067] As water-soluble free radical initiators, persulfates such as ammonium persulfate and potassium persulfate, and water-soluble organic peroxides such as disuccinic acid peroxide, peroxydiglutaric acid, and tert-butyl hydroperoxide are preferred.

[0068] As a water-soluble redox catalyst, combinations of the following oxidants and reductants are preferred: bromic acid or its salts, chloric acid or its salts, persulfate or its salts, permanganate or its salts, hydrogen peroxide, etc.; sulfites or their salts, bisulfite or its salts, thiosulfate or its salts, organic acids, inorganic salts, etc., are preferred reductants. Potassium persulfate and ammonium persulfate are preferred persulfates. Sodium sulfite is preferred as a sulfite. Combinations of the following anions and metal ions can be used as inorganic salts: sulfate anion, sulfite anion, or chloride anion. Transition metals are preferred as metal ions, including manganese, iron, cobalt, nickel, copper, zinc, cerium, and silver ions, with iron ions being preferred. Ferric(II) sulfate is preferred as an inorganic salt.

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

[0070] In addition, in step 0, to facilitate the polymerization of compounds (1) to (3), the pH value of the reaction system is preferably 3 to 10, more preferably 6 to 8. Sulfites such as sodium sulfite, ammonia, sodium hydroxide, hydrochloric acid, etc., can be added as needed for adjustment.

[0071] Two or more water-soluble polymerization initiators can be used in combination. In addition, as a method of feeding water-soluble polymerization initiators, the total amount can be added to the reaction system before the polymerization reaction begins, or it can be added to the reaction system continuously or intermittently.

[0072] In step 0, the amount of compounds (1) to (3) used is preferably 0.0001 to 1.0 parts by mass relative to 100 parts by mass of aqueous medium, more preferably 0.001 to 0.5 parts by mass. Within this range, a decrease in polymerization rate can be prevented, and the amount of specific polymers mixed in the fluorinated copolymer can be reduced when manufacturing the fluorinated copolymer in step 1. In addition, as a method of feeding compounds (1) to (3), it is preferable to add their total amount into the reaction system in the initial one-time addition before starting the polymerization reaction.

[0073] In the case of polymerizing a particular polymer, the amount of water-soluble polymerization initiator used in step 0 is preferably 0.1 to 5.0 moles relative to 1 mole of compounds (1) to (3), 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.

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

[0076] The D50 of the specific polymer particles (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 more preferably 90% by mass or more, relative to all units of the polymer. As an upper limit, 100% by mass can be cited as an example.

[0078] In step 0, an aqueous dispersion containing specific particles with a D50 of 10 to 1000 nm in an amount of 0.0001 to 1.0 parts by mass relative to 100 parts by mass of the aqueous medium is readily obtained. It is preferable that the dispersion contains 0.005 to 0.5 parts by mass of the specific particles relative to 100 parts by mass of the aqueous medium, and more preferably 0.002 to 0.1 parts by mass of the specific particles.

[0079] (Second Implementation) In the second embodiment, step 1 is carried out in the presence of the polyepoxide compound and in the absence of a substantially non-emulsifier. That is, in the second embodiment, the polymerization of the above-mentioned TFE with other monomers is carried out in the presence of hydroperoxide, a specific reducing agent, a specific acid, an aqueous medium, and the polyepoxide compound, and in the absence of a substantially non-emulsifier. The conditions under which emulsifiers are essentially absent are as described above. In the first embodiment described above, step 1 is performed in the presence of a specific polymer, while in the second embodiment, step 1 is performed in the presence of a polyepoxide compound and in the absence of a substantially non-emulsifier. That is, the second embodiment differs from the first embodiment in that it uses a polyepoxide compound, whereas the first embodiment uses a specific polymer. Therefore, the differences between the second and first embodiments will be mainly explained below.

[0080] Polyepoxide compounds are compounds used to form nuclei (seeds) during the polymerization of TFE with other monomers. In other words, they are equivalent to nucleating additives. Polyepoxide compounds refer to compounds that contain polyepoxide chains. Examples of polyepoxide chains include polyoxymethylene chains, polyoxyethylene chains, polyoxypropylene chains, and polyoxytetramethylene chains.

[0081] The polyepoxide compound preferably has a surface tension in water greater than about 40 dynes / cm at a concentration of 1000 ppm. More preferably, the surface tension is greater than about 42 dynes / cm, and even more preferably greater than about 45 dynes / cm. The surface tension is preferably less than about 73 dynes / cm.

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

[0083] As a polyepoxide compound, the compound represented by formula (5) is preferred. Equation (5)R a -(OR c ) p -OR b In equation (5), R a and R bEach can independently represent a hydrogen atom, alkyl group, acryloyl group, or methacryloyl group. R c This refers to alkylene groups with 1 to 4 carbon atoms, which can be either straight-chain or branched. p represents 1 to 50.

[0084] Specific examples of polyepoxide compounds 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] Polyepoxide compounds can be used alone or in combination of two or more. The amount of polyepoxide compound used relative to the total mass of the aqueous medium is preferably 0.1 to 10 ppm by mass, more preferably 1 to 10 ppm by mass.

[0086] In the second embodiment, it is preferable to mix a polyoxyalkylene compound and an oxidant in an aqueous medium to obtain a dispersion, and then polymerize TFE and other monomers in the obtained dispersion to produce a fluorinated copolymer.

[0087] Specific examples of oxidants 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] Mixing a polyepoxide compound and an oxidant in an aqueous medium yields a dispersion in which lipophilic nucleation sites are dispersed. More specifically, when a polyepoxide compound and an oxidant are mixed, the hydrophilic portion of the polyepoxide compound decomposes, and the hydrophobic portion becomes the lipophilic nucleation sites. These lipophilic nucleation sites are dispersed in the aqueous medium, allowing for the fine dispersion of fluorinated copolymers. The lipophilic nucleation sites exhibit excellent affinity for TFE and other monomers, thus facilitating the polymerization of TFE with other monomers in dispersions containing these sites. In other words, the lipophilic nucleation sites can serve as hydrophobic environmental sites for the polymerization of TFE with other monomers.

[0089] The amount of oxidant used relative to the total mass of the aqueous medium is preferably 0.01 to 1.00% by mass, more preferably 0.05 to 0.5% by mass. The preferred temperature for mixing the polyepoxide compound with the oxidant is 20–120°C, more preferably 40–120°C. The mixing time when mixing polyepoxide compounds with oxidants 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 mixing the polyepoxide compound with the oxidant. The amount of water-soluble inorganic salt used relative to the total mass of the aqueous medium is preferably 1 to 1000 ppm by mass, more preferably 10 to 1000 ppm by mass. 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, with sulfites being preferred, and sodium sulfite and ammonium sulfite being more preferred.

[0091] (Third Implementation) In the third embodiment, step 1 is carried out in the presence of an emulsifier. That is, in the third embodiment, the polymerization of the above-mentioned TFE with other monomers is carried out in the presence of hydroperoxide, a specific reducing agent, a specific acid, an aqueous medium, and an emulsifier. Emulsifiers can use a variety of surfactants. From the viewpoint of improving the yield of fluorinated copolymers, it is preferable to pre-emulsify the mixture consisting of the monomeric component TFE and other monomers, surfactants, and an aqueous medium before performing step 1. For example, the mixture consisting of TFE, other monomers, surfactants, and an aqueous medium is mixed and dispersed in a homogenizer or a high-pressure emulsifier. The aqueous emulsion contains, preferably, 1.0 to 50.0 parts by weight, more preferably 3 to 40 parts by weight, of a fluorinated copolymer relative to 100 parts by weight of an aqueous medium.

[0092] By implementing step 1, a fluorinated copolymer containing TFE units and other monomer units is formed. The aforementioned fluorinated copolymer is uniformly dispersed in an aqueous medium in the form of particles. There is no particular limitation on the average primary particle size of the particulate fluorinated copolymer, which is mostly 20 to 3000 nm, and preferably 20 to 1000 nm.

[0093] The aqueous solution containing the fluorinated copolymer obtained in step 1 (hereinafter also referred to as "fluorinated copolymer aqueous dispersion") contains particles containing the fluorinated copolymer, preferably 1.0 to 50.0 parts by mass, more preferably 2.0 to 40.0 parts by mass, relative to 100 parts by mass of the aqueous medium.

[0094] Powder containing fluorinated copolymer particles can be obtained by agglomerating particles containing fluorinated copolymer from an aqueous dispersion of fluorinated copolymer. Examples of coagulation methods include, but are not limited to, cryocoagulation, acid coagulation, alkali coagulation, and coagulation using coagulants. In the case of freeze-coagulation, the coagulation temperature is preferably 0–5°C. The coagulation time is preferably 1 hour or more, more preferably 2 hours or more. In the case of acid coagulation, it is preferable to add an acid-containing solution to the aqueous dispersion of the fluorinated copolymer. Examples of acids added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, and hydrofluoric acid, 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. As a method of alkaline coagulation, it is preferable to add an alkaline solution to an aqueous dispersion of the fluorinated copolymer. Examples of the added alkaline include sodium hydroxide, potassium hydroxide, and ammonium carbonate, with sodium hydroxide being preferred. The concentration of the alkaline solution is preferably 0.1–50% by mass, more preferably 1–30% by mass, and even more preferably 1–10% by mass. For coagulation using a coagulant, known coagulants can be used. Examples of known coagulants include aluminum salts, calcium salts, and magnesium salts. Specifically, aluminum sulfate, alum represented by the general formula M'Al(SO4)2·12H2O [where M' is a monovalent cation other than lithium], calcium nitrate, and magnesium sulfate are preferred, and potassium alum, in which M is potassium, is more preferred. As a coagulation method, alkaline coagulation is preferred because coagulation is particularly easy to perform. Example

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

[0096] The various measurement and evaluation methods are as follows. Average primary particle size (nm) of fluorinated copolymer particles in aqueous dispersion: The particle size distribution was measured using an aqueous dispersion of fluorinated copolymer particles as a sample and 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 rate) was determined using a Flow Tester (manufactured by Shimadzu Corporation) at 297°C with a 7 kg load. If the Q value could not be determined with a 7 kg load, it was determined with a 50 kg load.

[0098] The proportions of each unit in the fluorinated copolymer: The proportion of each unit in the fluorinated copolymer is determined by 19 The results were obtained through F-NMR analysis, fluorine content analysis, and infrared absorption spectroscopy analysis.

[0099] (Example 1) [Process 0] After purging the 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 referred to as "MEM") (40mg) were added. Next, the solution in the polymerization tank was heated to 60°C while stirring. A solution of 4ml of potassium persulfate (hereinafter referred to as "KPS") dissolved in deionized water (KPS concentration: 5% by mass) was injected into the polymerization tank to polymerize the MEM.

[0100] [Process 1] Next, in a polymerization tank containing an aqueous solution of the specific polymer obtained in step 0, namely poly(2-methoxyethyl methacrylate), a mixed monomer with a TFE / ethylene (hereinafter also referred to as "E") molar ratio of 86 / 14 is injected to pressurize the polymerization tank to 2.6 MPaG. Ethyl acetate (2 ml), a solution of 12 ml of KPS dissolved in deionized water (KPS concentration: 5% by mass), and PFBE (0.73 g) are then injected into the polymerization tank. Additionally, sodium sulfite used in step 0 remains in the aqueous solution contained in the polymerization tank. The amount of ethyl acetate used is 0.24% by mass relative to the total mass of the aqueous medium. When the pressure inside the polymerization tank begins to decrease, a mixed monomer with a TFE / E molar ratio of 54 / 46 is added to maintain the internal pressure of the polymerization tank at 2.6 MPaG, allowing polymerization to proceed. PFBE (0.73 g) is added to the polymerization tank for every 20 g of mixed monomer injected. When the continuous feeding of the mixed monomer reaches 60 g, the polymerization tank is cooled to room temperature, and the gas inside the polymerization tank is released to the atmosphere. The polymerization time was 491 minutes. The resulting aqueous dispersion of the fluorinated copolymer had a pH of 4.4 and a solids concentration of approximately 6.6% by mass. Furthermore, the average primary particle size of the fluorinated copolymer in the aqueous dispersion was 166 nm. The aqueous dispersion was cooled to agglomerate the fluorinated copolymer particles, yielding a powder. This fluorinated copolymer powder was then dried at 150°C. The resulting fluorinated copolymer powder had a Q value of 0.2 mm under a 7 kg load. 3 / s, the molar ratio of TFE units / E units / PFBE units in the fluorinated copolymer is 52.7 / 45.7 / 1.6.

[0101] (Example 2) [Process 0] After purging the 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. Then, while stirring the solution in the polymerization tank, the temperature was raised to 50°C, and 1ml of a solution of TBHP (a hydroperoxide) dissolved in deionized water (TBHP concentration: 0.195% by mass) was injected into the polymerization tank to polymerize the MMA.

[0102] [Process 1] Next, in a polymerization tank containing an aqueous solution of the specific polymer obtained in step 0, namely polymethyl methacrylate, a mixed monomer with a TFE / E molar ratio of 86 / 14 was injected to pressurize the polymerization tank to 2.6 MPaG. Methyl acetate (5 ml) and tert-butanol (t-BuOH) (21 g) were injected into the polymerization tank. A solution of 8 ml of TBHP dissolved in deionized water (TBHP concentration: 0.195 wt%) and PFBE (0.73 g) were injected into the polymerization tank. Additionally, 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 wt% relative to the total mass of the aqueous medium. When the pressure inside the polymerization tank began to decrease, a mixed monomer with a TFE / E molar ratio of 54 / 46 was added to maintain the internal pressure of the polymerization tank at 2.6 MPaG, allowing polymerization to proceed. From the start of polymerization, 1 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.195 wt%) was added every 10 minutes. For every 12g of mixed monomers added, an aqueous solution of sodium sulfite (0.92% by mass, 2ml) was added to the polymerization tank. For every 20g of mixed monomers added, 0.73g of PFBE was added to the polymerization tank. When the continuous feeding of mixed monomers reached 100g, 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 fluorinated copolymer had a pH of 4.4 and a solids concentration of approximately 12% by mass. Furthermore, the average primary particle size of the fluorinated copolymer in the aqueous dispersion was 240nm. The aqueous dispersion was cooled to agglomerate the fluorinated copolymer particles, yielding a powder. This fluorinated copolymer powder was then dried at 150°C. The resulting fluorinated copolymer powder had a Q value of 100 mm under a 7 kg load. 3 / s, the molar ratio of TFE units / E units / PFBE units in the fluorinated copolymer is 54.5 / 44.6 / 0.9.

[0103] (Example 3) [Process 0] After purging the 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. Then, while stirring the solution in the polymerization tank, the temperature was raised to 50°C, and a solution of 1ml of TBHP dissolved in deionized water (TBHP concentration: 0.195% by mass) was injected into the polymerization tank to polymerize the MEM.

[0104] [Process 1] Next, in a polymerization tank containing an aqueous solution of the specific polymer obtained in step 0, namely poly(2-methoxyethyl methacrylate), a mixed monomer with a TFE / E molar ratio of 86 / 14 is injected to pressurize the polymerization tank to 2.6 MPaG. Then, methyl acetate (2 ml) and ethyl acetate (2 ml) are injected. A solution of 8 ml of TBHP dissolved in deionized water (TBHP concentration: 0.195% by mass) and PFBE (0.73 g) are injected into the polymerization tank. Additionally, sodium sulfite used in step 0 remains in the aqueous solution contained in the polymerization tank. The amount of methyl acetate used is 0.25% by mass relative to the total mass of the aqueous medium. The amount of ethyl acetate used is 0.24% by mass relative to the total mass of the aqueous medium. When the pressure inside the polymerization tank begins to decrease, a mixed monomer with a TFE / E molar ratio of 54 / 46 is added to maintain the internal pressure of the polymerization tank at 2.6 MPaG, allowing polymerization to proceed. 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. For every 10 g of mixed monomer added, 2 ml of a sodium sulfite aqueous solution (sodium sulfite concentration: 0.92% by mass) was added to the polymerization tank. For every 20 g of mixed monomer added, 0.73 g of PFBE was added to the polymerization tank. When the continuous feeding of mixed monomer reached 80 g, the polymerization tank was cooled to room temperature, and the gas inside the tank was released into the atmosphere. The polymerization time was 592 minutes. The resulting aqueous dispersion of the fluorinated copolymer had a pH of 4.4 and a solids concentration of approximately 9.7% by mass. Furthermore, the average primary particle size of the fluorinated copolymer in the aqueous dispersion was 258 nm. The aqueous dispersion was cooled to agglomerate the fluorinated copolymer particles, yielding a powder. This fluorinated copolymer powder was then dried at 150°C. The resulting fluorinated copolymer powder had a Q value of 1.6 mm under a 7 kg load. 3 / s, the molar ratio of TFE units / E units / PFBE units in the fluorinated copolymer is 54.5 / 44.8 / 0.8.

[0105] (Example 4) [Process 0] After purging the 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. Then, while stirring the solution in the polymerization tank, the temperature was raised to 50°C, and a solution of 1ml of TBHP dissolved in deionized water (TBHP concentration: 0.195% by mass) was injected into the polymerization tank to polymerize the MMA.

[0106] [Process 1] Next, in a polymerization tank containing an aqueous solution of the specific polymer obtained in step 0, namely polymethyl methacrylate, a mixed monomer with a TFE / E molar ratio of 86 / 14 was injected to pressurize the polymerization tank to 2.6 MPaG. Then, methyl acetate (2 ml) and t-BuOH (10 mg) were injected. A solution of 8 ml of TBHP dissolved in deionized water (TBHP concentration: 0.195 wt%) and PFBE (0.73 g) were injected into the polymerization tank. Additionally, 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 wt% relative to the total mass of the aqueous medium. When the pressure inside the polymerization tank began to decrease, a mixed monomer with a TFE / E molar ratio of 54 / 46 was added to maintain the internal pressure of the polymerization tank at 2.6 MPaG, allowing polymerization to proceed. From the start of polymerization, 1 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.087 wt%) was added every 10 minutes. For every 15g of mixed monomer added, an aqueous solution of sodium sulfite (0.92% by mass, 2ml) was added to the polymerization tank. For every 20g of mixed monomer added, 0.73g of PFBE was added to the polymerization tank. When the continuous feeding of mixed monomer reached 100g, the polymerization tank was cooled to room temperature, and the gas inside the polymerization tank was released into the atmosphere. The polymerization time was 468 minutes. The resulting aqueous dispersion of the fluorinated copolymer had a pH of 4.0 and a solids concentration of approximately 12.2% by mass. Furthermore, the average primary particle size of the fluorinated copolymer in the aqueous dispersion was 212nm. The aqueous dispersion was cooled to agglomerate the fluorinated copolymer particles, resulting in a powder. This fluorinated copolymer powder was then dried at 150°C. The Q-value of the obtained fluorinated copolymer powder under a 7 kg load could not be determined. Therefore, the Q-value of the obtained fluorinated copolymer powder under a 50 kg load was determined, and it was 20 mm. 3 / s. The molar ratio of TFE units / E units / PFBE units in the fluorinated copolymer is 54.5 / 44.2 / 1.0.

[0107] (Example 5) [Process 0] After purging the 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. Then, while stirring the solution in the polymerization tank, the temperature was raised to 50°C, and a solution of 1ml of TBHP dissolved in deionized water (TBHP concentration: 0.195% by mass) was injected into the polymerization tank to polymerize the VA.

[0108] [Process 1] Next, in a polymerization tank containing an aqueous solution of the specific polymer obtained in step 0, namely polyvinyl acetate, a mixed monomer with a TFE / E molar ratio of 86 / 14 is injected to pressurize the polymerization tank to 2.6 MPaG. Then, methyl acetate (5 ml) and t-BuOH (21 mg) are injected. A solution of 8 ml of TBHP dissolved in deionized water (TBHP concentration: 0.195 wt%) and PFBE (0.73 g) are injected into the polymerization tank. Additionally, sodium sulfite used in step 0 remains in the aqueous solution contained in the polymerization tank. The amount of methyl acetate used is 0.61 wt% relative to the total mass of the aqueous medium. When the pressure inside the polymerization tank begins to decrease, a mixed monomer with a TFE / E molar ratio of 54 / 46 is added to maintain the internal pressure of the polymerization tank at 2.6 MPaG, allowing polymerization to proceed. From the start of polymerization, 1 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.087 wt%) is added every 10 minutes. For every 10g of mixed monomer added, an aqueous solution of sodium sulfite (sodium sulfite concentration: 0.92% by mass, 2ml) was added to the polymerization tank. For every 20g of mixed monomer added, 0.73g of PFBE was added to the polymerization tank. When the continuous feeding of mixed monomer reached 120g, the polymerization tank was cooled to room temperature, and the gas inside the polymerization tank was released into the atmosphere. The polymerization time was 435 minutes. The resulting aqueous dispersion of the fluorinated copolymer had a pH of 3.9 and a solids concentration of approximately 13.7% by mass. Furthermore, the average primary particle size of the fluorinated copolymer in the aqueous dispersion was 240nm. The aqueous dispersion was cooled to agglomerate the fluorinated copolymer particles, yielding a powder. This fluorinated copolymer powder was then dried at 150°C. The Q-value of the obtained fluorinated copolymer powder under a 7 kg load could not be determined. Therefore, the Q-value of the obtained fluorinated copolymer powder under a 50 kg load was determined, and it was 56 mm. 3 / s. The molar ratio of TFE units / E units / PFBE units in the fluorinated copolymer is 55.4 / 44.1 / 0.5.

[0109] (Example 6) [Process 0] After purging the 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. Then, while stirring the solution in the polymerization tank, the temperature was raised to 50°C, and a solution of 1ml of TBHP dissolved in deionized water (TBHP concentration: 0.195% by mass) was injected into the polymerization tank to polymerize the MMA.

[0110] [Process 1] Next, in a polymerization tank containing an aqueous solution of the specific polymer obtained in step 0, namely polymethyl methacrylate, a mixed monomer with a TFE / E molar ratio of 86 / 14 was injected to pressurize the polymerization tank to 2.6 MPaG. Then, methyl acetate (5 ml) and t-BuOH (21 mg) were injected. A solution of 8 ml of TBHP dissolved in deionized water (TBHP concentration: 0.195 wt%) and PFBE (0.73 g) were injected into the polymerization tank. Additionally, 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 wt% relative to the total mass of the aqueous medium. When the pressure inside the polymerization tank began to decrease, a mixed monomer with a TFE / E molar ratio of 52 / 48 was added to maintain the internal pressure of the polymerization tank at 2.6 MPaG, allowing polymerization to proceed. From the start of polymerization, 1 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.195 wt%) was added every 10 minutes. Sodium sulfite aqueous solution (sodium sulfite concentration: 0.92% by mass, 1 ml) was added to the polymerization tank for every 6 g of mixed monomers injected. PFBE (0.73 g) was added to the polymerization tank for every 20 g of mixed monomers injected. When the continuous feeding of mixed monomers 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 resulting aqueous dispersion of the fluorinated copolymer had a pH of 3.9 and a solids concentration of approximately 16% by mass. Furthermore, the average primary particle size of the fluorinated copolymer in the aqueous dispersion was 250 nm. The aqueous dispersion was cooled to agglomerate the fluorinated copolymer particles, resulting in a powder. This fluorinated copolymer powder was then dried at 150°C. The Q-value of the obtained fluorinated copolymer powder under a 7 kg load could not be determined. Therefore, the Q-value of the obtained fluorinated copolymer powder under a 50 kg load was determined to be 85.8 mm. 3 / s. The molar ratio of TFE units / E units / PFBE units in the fluorinated copolymer is 54.3 / 44.8 / 0.9.

[0111] (Example 7) [Process 0] After purging the 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. Then, while stirring the solution in the polymerization tank, the temperature was raised to 50°C, and a solution of 1ml of TBHP dissolved in deionized water (TBHP concentration: 0.195% by mass) was injected into the polymerization tank to polymerize the MEM.

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

[0113] (Example 8) [Process 0] After purging the 1.2L stainless steel polymerization tank with nitrogen, reduce the pressure to -0.1MPaG, and add ultrapure water (704g), Bruggolite (registered trademark) FF6M (150mg), and MMA (10mg).

Transformation 5

[0114] [Process 1] Next, in a polymerization tank containing an aqueous solution of the specific polymer obtained in step 0, namely polymethyl methacrylate, a mixed monomer with a TFE / E molar ratio of 86 / 14 was injected to pressurize the polymerization tank to 2.6 MPaG, followed by the injection of methyl acetate (2 ml) and t-BuOH (28 mg). Additionally, Bruggolite (registered trademark) FF6M, used in step 0, remained in the aqueous solution contained in the polymerization tank. A solution of 8 ml of TBHP dissolved in deionized water (TBHP concentration: 0.195 wt%) and PFBE (0.73 g) was injected into the polymerization tank. The amount of methyl acetate used was 0.25 wt% relative to the total mass of the aqueous medium. When the pressure inside the polymerization tank began to decrease, a mixed monomer with a TFE / E molar ratio of 54 / 46 was added to maintain the internal pressure of the polymerization tank at 2.6 MPaG, allowing polymerization to proceed. From the start of polymerization, 1 ml of a solution of TBHP dissolved in deionized water (TBHP concentration: 0.195 wt%) was added every 10 minutes. PFBE (0.73g) was added to the polymerization tank for every 20g of mixed monomers added. When the continuous feeding of mixed monomers reached 40g, the polymerization tank was cooled to room temperature, and the gas inside the tank was released into the atmosphere. The polymerization time was 250 minutes. The resulting aqueous dispersion of the fluorinated copolymer had a pH of 3.8 and a solids concentration of approximately 5.6% by mass. Furthermore, the average primary particle size of the fluorinated copolymer in the aqueous dispersion was 164nm. The aqueous dispersion was cooled to agglomerate the fluorinated copolymer particles, yielding a powder. This fluorinated copolymer powder was then dried at 150°C. The Q-value of the obtained fluorinated copolymer powder under a 7 kg load could not be determined. Therefore, the Q-value of the obtained fluorinated copolymer powder under a 50 kg load was determined, and it was 32 mm. 3 / s. The molar ratio of TFE units / E units / PFBE units in the fluorinated copolymer is 53.9 / 44.9 / 1.2.

[0115] (evaluate) The fluorinated copolymer powders obtained in each example were heated at 300°C for 2 hours to check for foaming and coloring, and evaluated according to the following criteria. The results are shown in the table below. Foaming evaluation ◎: None, 〇: Slightly, △: Yes, ×: Resin foaming Coloring Evaluation ◎: No change before and after heating; 〇: Colored yellow; △: Colored yellow to brown; ×: Jet black.

[0116] In Table 1, the column “Use of hydroperoxide (1)” indicates the amount of hydroperoxide used (mass%) relative to the total mass of the aqueous medium in step 1. In Table 1, the column “Use of hydroperoxide (2)” indicates the amount of hydroperoxide used (mass%) relative to the total amount of TFE, E and PFBE used in step 1 (total mass). In Table 1, the "Amount of a Specific Reducing Agent Used" column indicates the amount of a specific reducing agent used (mass%) relative to the total mass of the aqueous medium in step 1. In Table 1, the column “Use of a specific acid substance” indicates the amount (by mass%) of a specific reducing agent used relative to the total mass of the aqueous medium in process 1.

[0117] Table 1

[0118] As shown in Table 1, the fluorinated copolymers of Examples 2-6, obtained by polymerizing TFE and other monomers in the presence of hydroperoxide, a specific reducing agent, a specific acid, and an aqueous medium, exhibited foaming and coloring of ○ or higher upon heating at 300°C. Furthermore, the pH of the aqueous dispersions of Examples 2-6 after polymerization was 3.0-8.0. The fluorinated copolymers of Examples 2-4, with an aqueous dispersion pH of 4.0-7.0 after polymerization, exhibited foaming of ◎ upon heating at 300°C. The fluorinated copolymers of Examples 2 and 3, with an aqueous dispersion pH of 4.4-7.0 after polymerization, exhibited coloring of ◎ upon heating at 300°C. The fluorinated copolymer of Example 1, using KPS as a free radical initiator, exhibited foaming and coloring of × upon heating at 300°C. Example 7, which did not use a specific acid, did not undergo polymerization. The fluorinated copolymer of Example 8, using Bruggolite (registered trademark) FF6M, which is not a specific reducing agent, exhibited foaming and coloring of △ upon heating 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 as a disclosure of this invention.

Claims

1. A method for manufacturing a fluorinated copolymer, comprising the following steps: polymerizing tetrafluoroethylene and monomers other than tetrafluoroethylene to produce a fluorinated copolymer in the presence of hydroperoxide, at least one specific reducing agent selected from sulfites, bisulfites, dithionites, and metabisulfites, at least one specific acid selected from substances that produce acid by hydrolysis, and an aqueous medium. The amount of hydroperoxide used relative to the total mass of the aqueous medium is 0.0001–1.0% by mass, the amount of the specific reducing agent used is 0.0001–1.0% by mass, and the amount of the specific acidic substance used is 0.0005–20.0% by mass. The hydroperoxide is a compound represented by the following formula (X): 【Chemical Formula 1】 In equation (X), R x1 ~R x3 Each can be independently represented as an alkyl group having 1 to 10 carbon atoms. The substance that produces acid through hydrolysis is selected from the compounds represented by formulas (A) and (B): 【Chemical Formula 2】 In formula (A), R a1 ~R a6 Each can independently represent a hydrogen atom or an alkyl group. In equation (B), R b1 ~R b3 Each can be used independently to represent a hydrogen atom or an alkyl group.

2. The method for manufacturing the fluorinated copolymer as described in claim 1, wherein, The other monomers are at least one selected from ethylene, propylene, perfluoroalkyl vinyl ethers, fluoroalkyl vinyls, and hexafluoropropylene.

3. The method for manufacturing the fluorinated copolymer as described in claim 1 or 2, wherein, The amount of hydroperoxide used is 0.0005 to 0.5% of the total mass of the aqueous medium.

4. The method for manufacturing the fluorinated copolymer as described in claim 1 or 2, wherein, The amount of the specific reducing agent used is 0.0005 to 0.5% of the total mass of the aqueous medium.

5. The method for manufacturing the fluorinated copolymer as described in claim 1 or 2, wherein, The amount of the specific acidic substance used is 0.001 to 10.0% of the total mass of the aqueous medium.

6. The method for manufacturing the fluorinated copolymer as described in claim 1 or 2, 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. The metabisulfite is sodium metabisulfite, potassium metabisulfite, or ammonium metabisulfite.

7. The method for manufacturing the fluorinated copolymer as described in claim 1 or 2, wherein, Polyepoxide compounds are also present in the process described above.

8. The method for manufacturing the fluorinated copolymer as described in claim 1 or 2, wherein, An emulsifier is also present in the process described.

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