Fluorine-containing polymer, method for producing fluorine-containing polymer, and sheet

Abstract

The present invention addresses the problem of providing a fluorine-containing polymer having a high decomposition temperature and having excellent roll winding properties, and providing a method for producing the fluorine-containing polymer having a high decomposition temperature and having excellent roll winding properties. The present invention further addresses the problem of providing a sheet containing the fluorine-containing polymer. The fluorine-containing polymer satisfies requirements 1 and 2. Requirement 1: The 2% weight reduction temperature of the fluorine-containing polymer is 300°C or more, but less than 420° C. Requirement 2: The difference between the 5% weight reduction temperature of the fluorine-containing polymer and the 2% weight reduction temperature of the fluorine-containing polymer is 20°C or higher.

Description

Fluorine-containing polymer, method for producing fluorine-containing polymer, and sheet

[0001] The present invention relates to a fluorine-containing polymer, a method for producing a fluorine-containing polymer, and a sheet thereof.

[0002] Crosslinked rubber articles obtained by crosslinking a composition containing a fluorine-containing polymer are used in various industrial fields due to their excellent heat resistance, chemical resistance, flame retardancy, weather resistance, etc. Patent Document 1 describes a fluorine-containing copolymer that contains iodine atoms and also has units a based on tetrafluoroethylene, units b based on a monomer (excluding tetrafluoroethylene) having one polymerizable unsaturated bond, and units c based on a fluorine-containing monomer having two or more polymerizable unsaturated bonds, and has a metal content within a predetermined range (see claim 1). Patent Document 1 also describes a method for producing a fluorine-containing copolymer, which comprises emulsion polymerizing tetrafluoroethylene, a monomer (excluding tetrafluoroethylene) having one polymerizable unsaturated bond, and a fluorine-containing monomer having two or more polymerizable unsaturated bonds in the presence of a radical polymerization initiator and a predetermined iodine-containing compound to obtain a latex containing a fluorine-containing elastic copolymer, and then coagulating the fluorine-containing copolymer in the latex using a metal-free acid (see claim 8).

[0003] Patent No. 7140118

[0004]

[0003] Further improvements in the performance of compositions containing fluoropolymers are required. From the viewpoint of production efficiency when producing crosslinked rubber articles and the like using fluoropolymers, there is a demand for fluoropolymers that are excellent in processability, in particular in wrapability around rolls when kneading the fluoropolymer or raw materials containing the fluoropolymer using a roll kneader (hereinafter also referred to as "roll wrapability"). On the other hand, the present inventors have found that fluoropolymers that are excellent in wrapability around rolls tend to have low decomposition temperatures. Since a low decomposition temperature causes the problem of reduced plasma resistance of crosslinked rubbers, there is also a demand for fluoropolymers that have high decomposition temperatures. In other words, there is a demand for fluoropolymers that have both high decomposition temperatures and excellent roll wrapability. In response to such demands, the present inventors have studied fluoropolymers and production methods thereof with reference to Patent Document 1, and have found that there is room for further improvement in terms of achieving both high decomposition temperature and roll wrapability.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a fluoropolymer having a high decomposition temperature and excellent roll-winding properties, and to provide a method for producing a fluoropolymer having a high decomposition temperature and excellent roll-winding properties. Another object of the present invention is to provide a sheet containing the above fluoropolymer.

[0006] The present inventors have intensively studied the above-mentioned problems and found that when the 2% weight loss temperature and 5% weight loss temperature obtained by thermogravimetric analysis of a fluoropolymer are within predetermined ranges, the decomposition temperature of the fluoropolymer is high and the roll winding property is improved, thereby arriving at the present invention. Furthermore, the present inventors have intensively studied the above-mentioned problems and found that a fluoropolymer having a high decomposition temperature and excellent roll winding property can be produced by a method for producing a fluoropolymer which comprises polymerizing monomers in an aqueous dispersion which is substantially free of an emulsifier and contains a first fluoropolymer of a predetermined composition, and then carrying out a predetermined stirring treatment, thereby arriving at the present invention.

[0007] That is, the inventors have found that the above problems can be solved by the following configurations. [1] A fluoropolymer satisfying requirements 1 and 2 described below. [2] The fluoropolymer according to [1], which has units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether). [3] The fluoropolymer according to [1] or [2], which has a storage modulus G' of 300 kPa or more at 100°C and a frequency of 50 cpm. [4] The fluoropolymer according to any of [1] to [3], in which a thermogravimetric curve obtained by thermogravimetric analysis of the fluoropolymer shows an inflection point in a temperature range lower than the 5% weight loss temperature. [5] The fluoropolymer according to [2], in which the content of the units based on tetrafluoroethylene is 20 to 80 mol % based on the total content of all units in the fluoropolymer, and the content of the units based on perfluoro(alkyl vinyl ether) is 20 to 80 mol % based on the total content of all units in the fluoropolymer. [6] The fluorine-containing polymer according to any one of [1] to [5], which contains at least one selected from the group consisting of a polymerizable unsaturated bond, a chlorine atom, a bromine atom, an iodine atom, and a nitrile group.[7] A method for producing a fluoropolymer, comprising polymerizing a monomer containing tetrafluoroethylene and perfluoro(alkyl vinyl ether) in an aqueous dispersion containing a first fluoropolymer which is substantially free of a water-soluble emulsifier and contains units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), and an aqueous medium, to produce a second fluoropolymer having units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), wherein the content of the units based on perfluoro(alkyl vinyl ether) relative to the total content of the units based on tetrafluoroethylene and the units based on perfluoro(alkyl vinyl ether) in the first fluoropolymer is a method for producing a fluoropolymer, wherein the amount of the perfluoro(alkyl vinyl ether)-based units in the second fluoropolymer is 20 to 80 mol %, the content of the perfluoro(alkyl vinyl ether)-based units relative to the total content of the tetrafluoroethylene-based units and the perfluoro(alkyl vinyl ether)-based units in the second fluoropolymer is 20 to 80 mol %, the content of the first fluoropolymer is 0.01 to 4.0 mass % based on the total mass of the aqueous dispersion before initiating polymerization of the monomers, and after polymerizing the monomers in the aqueous dispersion, the aqueous dispersion is stirred at a rotational speed of 1000 rpm or more using a stirring device rotating a stirring shaft equipped with stirring blades to coagulate the second fluoropolymer, and the coagulated second fluoropolymer is recovered. [8] A method for producing a fluoropolymer according to [7], wherein the recovered second fluoropolymer is washed with ultrapure water. [9] A sheet comprising the fluoropolymer according to any of [1] to [6] or the fluoropolymer produced by the production method according to [7] or [8].

[0008] According to the present invention, there are provided a fluoropolymer having a high decomposition temperature and excellent roll-winding property, a method for producing a fluoropolymer having a high decomposition temperature and excellent roll-winding property, and a sheet containing the above fluoropolymer.

[0009] The meanings of terms used in the present invention are as follows. A numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the upper and lower limits. In the numerical ranges described in this specification in stages, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another staged numerical range. Furthermore, in the numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the Examples. In this specification, each component may be used alone or in combination with two or more substances corresponding to the component. Herein, when two or more substances are used in combination for each component, the content of that component refers to the total content of the substances used in combination, unless otherwise specified. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment. A "unit" is a collective term for an atomic group derived from one molecule of the above-mentioned monomer, formed directly by polymerization of the monomer, and an atomic group obtained by chemically converting a portion of the above-mentioned atomic group. Hereinafter, a "unit based on a monomer" will also be simply referred to as a "unit." The content (mass % or mol %) of each unit relative to all units contained in the polymer is determined by analyzing the polymer by solid-state nuclear magnetic resonance spectroscopy (NMR), and usually, the content of each unit calculated from the amount of each monomer charged substantially coincides with the actual content of each unit.

[0010] A first embodiment of the present invention is a fluoropolymer that satisfies requirements 1 and 2. Requirement 1: The 2% weight loss temperature of the fluoropolymer is 300° C. or higher and lower than 420° C. Requirement 2: The difference between the 5% weight loss temperature of the fluoropolymer and the 2% weight loss temperature of the fluoropolymer (hereinafter also referred to as "ΔTd") is 20° C. or higher.

[0011] A second embodiment of the present invention is a method for producing a fluoropolymer by polymerizing a monomer containing tetrafluoroethylene and perfluoro(alkyl vinyl ether) in an aqueous dispersion containing a first fluoropolymer which is substantially free of a water-soluble emulsifier and contains units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), and an aqueous medium, wherein the content of units based on perfluoro(alkyl vinyl ether) in the first fluoropolymer is 20 to 80 mol% relative to the total of units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), the content of units based on perfluoro(alkyl vinyl ether) in the fluoropolymer is 20 to 80 mol% relative to the total of units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), before starting polymerization of the monomers, the content of the first fluoropolymer is 0.01 to 4.0 mass% relative to the total mass of the aqueous dispersion, This is a method for producing a fluoropolymer, which comprises polymerizing a monomer in an aqueous dispersion, stirring the aqueous dispersion with a disc turbine blade at a rotation speed of 1000 rpm or more to aggregate the fluoropolymer, and recovering the aggregated fluoropolymer.

[0012] [First Embodiment] First, a fluoropolymer according to a first embodiment of the present invention will be described. The 2% weight loss temperature of the fluoropolymer according to this embodiment (hereinafter also referred to as "the polymer") is 300°C or higher and lower than 420°C (Requirement 1). Furthermore, the difference ΔTd between the 5% weight loss temperature and the 2% weight loss temperature of the polymer is 20°C or higher (Requirement 2). The fluoropolymer according to this embodiment has a high decomposition temperature and excellent roll winding properties. The details of why the above properties are improved when a fluoropolymer satisfies both Requirements 1 and 2 are unclear, but satisfying Requirement 1 indicates that the fluoropolymer contains a certain amount of low-molecular-weight components, and the presence of low-molecular-weight components makes the fluoropolymer more susceptible to plasticization and reduces the viscosity, resulting in improved roll winding properties of the fluoropolymer. Furthermore, satisfying Requirement 2 indicates that the fluoropolymer contains high-molecular-weight components, and it is presumed that the presence of high-molecular-weight components increases the decomposition temperature of the fluoropolymer.

[0013] In this specification, the "2% weight loss temperature" and "5% weight loss temperature" are measured by thermogravimetric analysis of the fluoropolymer to be measured. Specifically, a fluoropolymer sample that has not been heated to a temperature of 100°C or higher is subjected to thermogravimetric analysis in which the change in weight of the sample is measured while the temperature is increased from 30°C to 550°C at a heating rate of 10°C / min in an air atmosphere. As a result of the thermogravimetric analysis, the temperature at which the mass of the sample is 98% by mass of the mass of the sample before heating is the 2% mass loss temperature, and the temperature at which the mass of the sample is 95% by mass of the mass of the sample before heating is the 5% mass loss temperature. ΔTd in requirement 2 is calculated from the 5% weight loss temperature and the 2% weight loss temperature. An example of an apparatus used for thermogravimetric analysis is a differential thermal thermogravimetric analyzer "NEXTA STA series STA200" (manufactured by Hitachi High-Tech Corporation). More specific methods for thermogravimetric analysis to measure each weight loss temperature and to create the thermogravimetric curve described later are as described in the Examples described later.

[0014] The 2% weight loss temperature of the present polymer is 300° C. or higher and lower than 420° C., and from the viewpoint of better roll winding properties of the fluoropolymer, it is preferably 350 to 415° C., and more preferably 370 to 410° C. The 5% weight loss temperature of the present polymer is, for example, 320 to 500° C., and from the viewpoint of better decomposition temperature of the fluoropolymer, it is preferably 380 to 480° C., and more preferably 420 to 460° C.

[0015] The ΔTd of the present polymer is preferably from 20 to 100°C, more preferably from 25 to 70°C, since this provides a better decomposition temperature for the fluoropolymer.

[0016] The above-mentioned thermogravimetric analysis is performed on the fluoropolymer, and the temperature T and weight M of the fluoropolymer are plotted to obtain a thermogravimetric curve (TGA curve) showing the relationship between temperature T and weight M. It is preferable that the TGA curve obtained by thermogravimetric analysis of the present polymer has multiple inflection points. Inflection points in the TGA curve are confirmed by the following method. The TGA curve is further differentiated with respect to temperature T to obtain a differential TGA curve with "dM / dT" on the vertical axis and "T" on the horizontal axis. When a minimum peak where dM / dT changes from a decrease to an increase, or a maximum peak where dM / dT changes from an increase to a decrease, appears in this differential TGA curve, the TGA curve will have an inflection point at the peak temperature of each peak. Hereinafter, in this specification, the temperature at which an inflection point appears in the TGA curve of the fluoropolymer will be simply referred to as the "inflection point temperature". Furthermore, the temperature at which the lowest inflection point appears among the multiple inflection points is defined as the “inflection point temperature.” Typically, among the minimum peaks at which dM / dT changes from decreasing to increasing in a differential TGA curve, the first minimum peak appearing from the low temperature side corresponds to the inflection point appearing on the lowest temperature side in the TGA curve.

[0017] In order to obtain better roll wrapping properties, it is preferred that the TGA curve obtained by thermogravimetric analysis of the present polymer have an inflection point in a temperature range lower than the 5% weight loss temperature of the present polymer. The details of why the roll wrapping properties are better when an inflection point appears in a temperature range lower than the 5% weight loss temperature in the TGA curve are unclear, but in this case, it is thought that the fluoropolymer contains a certain amount of low-molecular-weight components, and the presence of a certain amount of low-molecular-weight components makes the polymer more susceptible to plasticization and reduces the viscosity, thereby improving the roll wrapping properties of the fluoropolymer.

[0018] In view of superior roll wrapping properties, the present polymer more preferably has an inflection point in the TGA curve in a temperature range 50 to 200° C. lower than the 5% weight loss temperature, and even more preferably has an inflection point in the temperature range 100 to 150° C. lower than the 5% weight loss temperature. In view of superior roll wrapping properties, the present polymer more preferably has an inflection point in the TGA curve in a range 200 to 450° C., and even more preferably has an inflection point in the range 250 to 350° C.

[0019] The storage modulus G' of the solid composition at 100°C and a frequency of 50 cpm is preferably 300 kPa or more, more preferably 350 kPa or more. From the viewpoint of moldability of crosslinked rubber articles, the storage modulus G' is preferably 730 kPa or less, more preferably 500 kPa or less. The storage modulus G' is a value measured in accordance with ASTM D6204, and detailed measurement conditions are as shown in the Examples. One example of a method for adjusting the storage modulus is a method of adjusting the amount and order of use of each of the above-mentioned monomers.

[0020] [Composition] The composition of the present polymer will be described below. The present polymer may be a polymer that contains fluorine atoms and exhibits rubber properties through crosslinking. It preferably has units based on a monomer containing fluorine atoms (hereinafter also referred to as a "fluorine-containing monomer"), and is preferably a perfluorinated polymer. Here, "perfluorinated polymer" refers to a polymer that is substantially free of hydrogen atoms bonded to carbon atoms, has fluorine atoms in place of those hydrogen atoms, and has a main chain consisting of a chain of carbon atoms. The side chain of the perfluorinated polymer may contain a polyvalent atom other than carbon atoms, and the polyvalent atom is preferably an oxygen atom. Here, "substantially free of hydrogen atoms" means that the content of hydrogen atoms in the perfluorinated polymer is 0.5% by mass or less, preferably 0.1% by mass or less, more preferably 0.07% by mass or less, and even more preferably 0.05% by mass or less. The lower limit can be 0% by mass. When the hydrogen atom content is within the above range, good heat resistance or chemical resistance is likely to be obtained. The hydrogen atom content in the perfluorinated polymer can be determined by solid-state nuclear magnetic resonance spectroscopy (NMR) analysis.

[0021] The polymer preferably contains units based on tetrafluoroethylene (hereinafter also referred to as "TFE") and units based on perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE"). Hereinafter, the units based on TFE will also be referred to as "TFE units," and the units based on PAVE will also be referred to as "PAVE units."

[0022] The PAVE from which the PAVE units are derived is preferably a monomer represented by formula (1) from the viewpoints of excellent polymerization reactivity in producing the first fluoropolymer described below and of enabling the fluoropolymer to be produced more efficiently. ２ =CF-O-R ｆ１ (1) In formula (1), R ｆ１ represents a perfluoroalkyl group having 1 to 10 carbon atoms. ｆ１ From the viewpoint of better polymerization reactivity, the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 8, more preferably 1 to 6, still more preferably 1 to 5, and particularly preferably 1 to 3. The perfluoroalkyl group may be linear or branched.

[0023] Specific examples of PAVE include perfluoro(methyl vinyl ether) (hereinafter also referred to as "PMVE"), perfluoro(ethyl vinyl ether) (hereinafter also referred to as "PEVE"), and perfluoro(propyl vinyl ether) (hereinafter also referred to as "PPVE"), and PMVE or PPVE are preferred, with PMVE being more preferred, from the viewpoint of enabling more efficient production of the fluorinated polymer.

[0024] The content of TFE units in the present polymer is preferably 5 to 90 mol%, more preferably 20 to 80 mol%, even more preferably 30 to 80 mol%, and particularly preferably 40 to 75 mol%, based on the total content of TFE units and PAVE units. The content of TFE units is also more preferably 5 to 80 mol%, based on the total content of TFE units and PAVE units. The content of PAVE units in the present polymer is also preferably 10 to 95 mol%, more preferably 20 to 80 mol%, even more preferably 20 to 70 mol%, and particularly preferably 25 to 60 mol%, based on the total content of TFE units and PAVE units. The content of PAVE units is also more preferably 20 to 95 mol%, based on the total content of TFE units and PAVE units. The preferred amounts are similar when PMVE or PPVE is used as PAVE. The total content of TFE units and PAVE units in the present polymer is preferably 80 to 100 mol %, more preferably 90 to 100 mol %, and even more preferably 95 to 100 mol %, based on the total content of all units in the present polymer.

[0025] The content of TFE units in the present polymer is preferably 5 to 90 mol%, more preferably 20 to 80 mol%, even more preferably 30 to 80 mol%, and particularly preferably 40 to 75 mol%, based on the total content of all units in the present polymer. The content of TFE units is also more preferably 5 to 80 mol%, based on the total content of all units in the present polymer. The content of PAVE units in the present polymer is also more preferably 10 to 95 mol%, more preferably 20 to 80 mol%, even more preferably 20 to 70 mol%, and particularly preferably 25 to 60 mol%, based on the total content of all units in the present polymer. The content of PAVE units is also more preferably 20 to 95 mol%, based on the total content of all units in the present polymer. The preferred amounts are similar when PMVE or PPVE is used as PAVE.

[0026] The present polymer may contain units based on monomers other than TFE units and PAVE units (hereinafter also referred to as "other monomers"), and preferably contains units based on other monomers. Specific examples of other monomers include a monomer having two or more polymerizable unsaturated bonds (hereinafter also referred to as "BO"), a monomer having one or more atoms of at least one kind selected from the group consisting of a chlorine atom, a bromine atom, and an iodine atom (hereinafter also referred to as "R Ｈａｌ "), a monomer having a nitrile group (hereinafter referred to as "R ＣＮ "), and a compound represented by formula (6) described below (hereinafter also referred to as "POAVE").

[0027] BO is a monomer having two or more polymerizable unsaturated bonds. Examples of the polymerizable unsaturated bond include a carbon atom-carbon atom double bond (C═C) and a carbon atom-carbon atom triple bond (C≡C). The number of polymerizable unsaturated bonds that BO has is preferably 2 to 6, more preferably 2 or 3, and even more preferably 2, in terms of better polymerization reactivity. BO preferably contains a fluorine atom in terms of reducing the compression set of a crosslinked rubber article at high temperatures.

[0028] BO is preferably a monomer represented by formula (2) in view of better releasability of the crosslinked rubber article.２１ R ２２ =CR ２３ -) ａ１ R ２４ (2) In formula (2), R ２１ , R ２２ , and R ２３ each independently represents a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group; a1 represents an integer of 2 to 6; R ２４ represents an a1-valent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of an a1-valent perfluorohydrocarbon group having 1 to 10 carbon atoms. ２１ , multiple R ２２ and multiple R ２３ may be the same or different, and are particularly preferably the same. a1 is preferably 2 or 3, and particularly preferably 2. In view of better polymerization reactivity of BO, R ２１ , R ２２ , and R ２３ is preferably a fluorine atom or a hydrogen atom, and R ２１ , R ２２ , and R ２３ are more preferably all fluorine atoms or all hydrogen atoms, and in view of better mold releasability of the crosslinked rubber article, R ２１ , R ２２ , and R ２３ It is particularly preferred that all of R are fluorine atoms. ２４ R may be linear, branched, or cyclic, preferably linear or branched, and particularly preferably linear. ２４ The number of carbon atoms in R is preferably 2 to 8, more preferably 3 to 7, still more preferably 3 to 6, and particularly preferably 3 to 5. ２４ Although R may or may not have an etheric oxygen atom, it is preferable that R has an etheric oxygen atom in view of better crosslinking reactivity and rubber physical properties. ２４ The number of etheric oxygen atoms in R is preferably 1 to 6, more preferably 1 to 3, and even more preferably 1 or 2. ２４ The etheric oxygen atom in R ２４It is preferred that the nucleotide sequence is located at the end of the nucleotide sequence.

[0029] Of the monomers represented by formula (2), specific examples of suitable monomers include the monomers represented by formula (3) and the monomers represented by formula (4).

[0030] (CF ２ =CF-) ２ R ３１ (3) In formula (3), R ３１ represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms.

[0031] (CH ２ =CH-) ２ R ４１ (4) In formula (4), R ４１ represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms.

[0032] Specific examples of the monomer represented by formula (3) include CF ２ = CFO (CF ２ ) ２ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ３ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ４ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ６ OCF = CF ２、 CF ２ = CFO (CF ２ ) ８ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ２ OCF (CF ３ )CF ２ OCF = CF ２ , C.F. ２= CFO (CF ２ ) ２ O(CF(CF ３ )CF ２ O) ２ CF = CF ２ , C.F. ２ = CFOCF ２ O (CF ２ CF ２ O) ２ CF = CF ２ , C.F. ２ = CFO (CF ２ O) ３ O(CF(CF ３ )CF ２ O) ２ CF = CF ２ , C.F. ２ = CFOCF ２ CF (CF ３ ) O(CF ２ ) ２ OCF (CF ３ )CF ２ OCF = CF ２ , and CF ２ = CFOCF ２ CF ２ O (CF ２ O) ２ CF ２ CF ２ OCF = CF ２ Among the monomers represented by formula (3), a more preferred specific example of the monomer is CF ２ = CFO (CF ２ ) ３ OCF = CF ２ (hereinafter also referred to as "C3DVE"), and CF ２ = CFO (CF ２ ) ４ OCF = CF ２ (hereinafter also referred to as "C4DVE").

[0033] Specific examples of the monomer represented by formula (4) include CH ２ =CH(CF ２ ) ２ CH=CH ２ , C.H. ２ =CH(CF ２ ) ４ CH=CH ２, and C.H. ２ =CH(CF ２ ) ６ CH=CH ２ Among the monomers represented by formula (4), specific examples of more preferred monomers include CH ２ =CH(CF ２ ) ６ CH=CH ２ (hereinafter also referred to as "C6DV"). Among them, C3DVE or C4DVE is preferable for BO.

[0034] R Ｈａｌ Examples of the monomer having a bromine atom include a monomer having a bromine atom and a monomer having an iodine atom. Specific examples of the monomer having a bromine atom include CF ２ = CFOCF ２ CF ２ CF ２ OCF ２ CF ２ Br, bromotrifluoroethylene, 4-bromo-3,3,4,4-tetrafluorobutene-1 (BTFB), vinyl bromide, 1-bromo-2,2-difluoroethylene, perfluoroallyl bromide, 4-bromo-1,1,2-trifluorobutene-1, 4-bromo-1,1,3,3,4,4-hexafluorobutene, 4-bromo-3-chloro-1,1,3,4,4-pentafluorobutene, 6-bromo-5,5,6,6-tetrafluorohexene, and 4-bromoperfluorobutene-1,3,3-difluoroallyl bromide. Also included are 2-bromo-perfluoroethyl perfluorovinyl ether and CF ２ Br-R ｆ -O-CF=CF ２ (R ｆ is a perfluoroalkylene group), for example, CF ２ BrCF ２ O-CF=CF ２ , ROCF = CFBr, and ROCBr = CF ２ (wherein R is a lower alkyl group or a fluoroalkyl group), more specifically fluorovinyl ethers such as CH ３ OCF = CFBr and CF ３ CH ２Specific examples of the monomer having an iodine atom include the monomer represented by the formula: CHR=CH-Z-CH ２ CHR-I (wherein R is —H or —CH ３ wherein R may be the same or different; Z is a linear or branched C alkyl group optionally containing one or more ethereal oxygen atoms; １ ~C １８ iodinated olefins of the formula I(CH) as disclosed in U.S. Pat. No. 5,717,036, which are (per)fluoroalkylene groups or (per)fluoropolyoxyalkylene groups as disclosed in U.S. Pat. No. 5,674,959. ２ CF ２ CF ２ ) ｎ OCF = CF ２ and ICH ２ CF ２ O[CF(CF ３ )CF ２ O] ｎ CF = CF ２ (wherein n = 1 to 3) and the like. Also included are iodoethylene, 4-iodo-3,3,4,4-tetrafluorobutene-1 (ITFB), 3-chloro-4-iodo-3,4,4-trifluorobutene, 2-iodo-1,1,2,2-tetrafluoro-1-(vinyloxy)ethane, 2-iodo-1-(perfluorovinyloxy)-1,1,-2,2-tetrafluoroethylene, 1,1,2,3,3,3-hexafluoro-2-iodo-1-(perfluorovinyloxy)propane, 2-iodoethyl vinyl ether, 3,3,4,5,5,5-hexafluoro-4-iodopentene, and iodotrifluoroethylene, as disclosed in U.S. Pat. No. 4,694,045. Also included are allyl iodide and 2-iodo-perfluoroethyl perfluorovinyl ether.

[0035] R ＣＮFrom the viewpoint of polymerization reactivity, it is preferable that the copolymer has a polymerizable unsaturated bond, and more preferably has one polymerizable unsaturated bond. Specific examples of the polymerizable unsaturated bond include a carbon-carbon double bond (C═C) and a carbon-carbon triple bond (C≡C).

[0036] R ＣＮ is preferably a monomer represented by the following formula (5) in view of better mold releasability and heat resistance of the crosslinked rubber article: ５１ R ５２ =CR ５３ -R ５４ -CN (5) In formula (5), R ５１ , R ５２ , and R ５３ each independently represents a hydrogen atom, a fluorine atom, or a methyl group; R ５４ represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms. ＣＮ From the viewpoint of excellent polymerization reactivity of R ５１ , R ５２ , and R ５３ is preferably a fluorine atom or a hydrogen atom, and R ５１ , R ５２ , and R ５３ It is more preferred that all of R are fluorine atoms or all of R are hydrogen atoms, and in view of the superior mold releasability and heat resistance of the crosslinked rubber article, ５１ , R ５２ , and R ５３ It is particularly preferred that all of R are fluorine atoms. ５４ R may be linear, branched, or cyclic, and is preferably linear or branched. ５４ The number of carbon atoms in R is preferably 2 to 8, more preferably 3 to 7, still more preferably 3 to 6, and particularly preferably 3 to 5. ５４ R may or may not have an etheric oxygen atom, but preferably has an etheric oxygen atom in order to obtain better rubber properties. ５４The number of etheric oxygen atoms in the formula (5) is preferably 1 to 3, and particularly preferably 1 or 2. Specific examples of the monomer represented by formula (5) include CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ CN (hereinafter also referred to as "8CNVE"), CF ２ = CFO (CF ２ ) ５ CN (hereinafter also referred to as "MV5CN"), CF ２ = CFOCF ２ CF ２ CF ２ OCF (CF ３ ) CN and CF ２ = CFO (CF ２ ) ３ CN is exemplified, and 8CNVE or MV5CN is preferred in that the crosslinked rubber article has better mold releasability and heat resistance.

[0037] POAVE is a compound represented by formula (6): CF ２ =CF(OCF ２ CF ２ ) ｎ -(OCF ２ ) ｍ -OR ｆ２ (6) In formula (6), R ｆ２ represents a perfluoroalkyl group having 1 to 4 carbon atoms, n represents an integer of 0 to 3, m represents an integer of 0 to 4, and n+m represents an integer of 1 to 7.

[0038] R ｆ２ In the formula, the perfluoroalkyl group may be linear or branched. ｆ２ The number of carbon atoms in is preferably 1 to 3. When n is 0, m is preferably 1 or 2. When n is 1, m is preferably an integer of 2 to 4. When n is 2 or 3, m is preferably 0. n is preferably an integer of 1 to 3. R ｆ２ When the number of carbon atoms, n, and m are within the above ranges, the low-temperature properties of the crosslinked rubber article are excellent, and the productivity of the crosslinked rubber article is improved.

[0039] Specific examples of POAVE include the following. The abbreviation for the compound is given in parentheses after the formula. CF ２ =CF-OCF ２ CF ２ -(OCF ２ ) ４ -OCF ３ (C9PEVE), CF ２ =CF-OCF ２ CF ２ -(OCF ２ ) ２ -OCF ３ (C7PEVE), CF ２ =CF-(OCF ２ CF ２ ) ２ -OCF ２ CF ３ (EEAVE), CF ２ =CF-(OCF ２ CF ２ ) ３ -OCF ２ CF ３ (EEEAVE), CF ２ =CF-OCF ２ -OCF ３ , C.F. ２ =CF-OCF ２ -OCF ２ -OCF ３ As the POAVE, C9PEVE, C7PEVE, EEAVE, or EEEAVE is preferred in terms of superior low-temperature properties and productivity of crosslinked rubber articles. These compounds can be produced from the corresponding alcohols by the method described in WO 00 / 056694.

[0040] The content of units based on other monomers in the present polymer is preferably 0.01 to 20 mol %, more preferably 0.01 to 10 mol %, and still more preferably 0.01 to 5 mol %, based on the total content of all units in the present polymer.

[0041] In view of superior crosslinkability, the present polymer preferably contains at least one selected from the group consisting of a polymerizable unsaturated bond, a chlorine atom, a bromine atom, an iodine atom, and a nitrile group, and more preferably contains at least one selected from the group consisting of a polymerizable unsaturated bond, a bromine atom, an iodine atom, and a nitrile group. Among these, it is preferable that the present polymer has the above-mentioned atom or group at at least one of the terminal and the side chain. When producing a fluorine-containing polymer, by using the above-mentioned other monomer in addition to TFE and PAVE, any one of a polymerizable unsaturated bond, a chlorine atom, a bromine atom, an iodine atom, and a nitrile group can be introduced into the side chain or terminal of the fluorine-containing polymer. Furthermore, by polymerizing a monomer using a chain transfer agent having an iodine atom, an iodine atom can be introduced into the terminal of the fluorine-containing polymer. When the present polymer contains iodine atoms, the content of iodine atoms is preferably 0.01 to 5.00 mass %, more preferably 0.01 to 2.00 mass %, and even more preferably 0.01 to 1.00 mass %, relative to the total mass of the present polymer.

[0042] [Method for producing fluorine-containing polymer] As the method for producing fluorine-containing polymer, for example, in the presence of polymerization initiator, there can be mentioned a method of copolymerizing monomers such as TFE and PAVE, and other monomers that are optionally used.As the polymerization method, there can be mentioned, for example, emulsion polymerization, solution polymerization, suspension polymerization, and emulsion polymerization is preferred from the viewpoint of excellent productivity and adjustment of molecular weight and copolymerization composition.When producing fluorine-containing polymer by emulsion polymerization, for example, it can be carried out by heating the above-mentioned monomers in the presence of aqueous medium, polymerization initiator, and optionally used emulsifier.

[0043]

[0023] A preferred embodiment of the method for producing the present polymer is a method for producing a fluoropolymer by polymerizing a monomer containing TFE and PAVE (hereinafter also referred to as a "specific monomer") in an aqueous dispersion (hereinafter also referred to as a "first aqueous dispersion") containing a first fluoropolymer substantially free of a water-soluble emulsifier and containing TFE units and PAVE units, and an aqueous medium, to produce a polymer (hereinafter also referred to as a "second fluoropolymer"), and then subjecting the resulting aqueous dispersion (hereinafter also referred to as a "second aqueous dispersion") containing the second fluoropolymer to agitation to coagulate the second fluoropolymer, and recovering the coagulated second fluoropolymer. In this embodiment, the step of polymerizing the specific monomer in the first aqueous dispersion to obtain a second aqueous dispersion containing the second fluoropolymer is also referred to as "step 1", and the step of subjecting the second aqueous dispersion to agitation to coagulate the second fluoropolymer and recovering the coagulated second fluoropolymer is also referred to as "step 2". Each step will be described below.

[0044] <Step 1> In step 1, specific monomers containing TFE and PAVE are polymerized in a first aqueous dispersion which is substantially free of a water-soluble emulsifier and contains a first fluorinated polymer and an aqueous medium.

[0045] The first aqueous dispersion is substantially free of a water-soluble emulsifier. "Substantially free of a water-soluble emulsifier" means that the content of the water-soluble emulsifier in the first aqueous dispersion is 10 mass ppm or less, preferably 100 mass ppb or less, and more preferably 50 mass ppb or less, relative to the total mass of the first aqueous dispersion. It is also preferable that the content is below the quantitation limit of the measurement method in the examples. An example of a lower limit is 1 mass ppb. The content of the water-soluble emulsifier can be measured using a liquid chromatograph mass spectrometer. Specifically, the measurement methods described in paragraphs 0721 to 0732 of WO 2018 / 181904 can be mentioned, and the measurement method shown in the examples is preferred.

[0046] The water-soluble emulsifier means an emulsifier having a solubility of 100 mg or more in 1000 g of water at 25°C. Examples of the water-soluble emulsifier include emulsifiers having fluorine atoms and water-soluble emulsifiers not having fluorine atoms. Note that neither the first fluorine-containing polymer nor the second fluorine-containing polymer described below falls under the category of emulsifiers. The water-soluble emulsifier may be either ionic or nonionic.

[0047] Examples of the emulsifier having fluorine atoms include anionic fluorine-containing emulsifiers, such as emulsifiers containing fluorine atoms whose total carbon number excluding the anionic group is 20 or less, and fluorine-containing emulsifiers whose anionic moiety has a molecular weight of 800 or less.

[0048] The fluorine-free emulsifier does not have a fluorine atom but has a hydrocarbon group such as an alkyl group. The hydrogen atom of the hydrocarbon group of the fluorine-free emulsifier may be substituted with a halogen atom other than a fluorine atom. Examples of the fluorine-free emulsifier include ionic hydrocarbon emulsifiers and nonionic hydrocarbon emulsifiers.

[0049] Ionic hydrocarbon emulsifiers include anionic hydrocarbon emulsifiers. Anionic hydrocarbon emulsifiers refer to hydrocarbon emulsifiers having a negatively charged hydrophilic moiety, such as a carboxylic acid group, a sulfonic acid group, a sulfate group, a phosphonic acid group, or a phosphate group, and a hydrocarbon moiety, such as an alkyl group, as a hydrophobic moiety. Examples of anionic hydrocarbon emulsifiers include the highly branched C10 tertiary carboxylic acid supplied by Resolution Performance Products as Versatic® 10, linear alkyl polyethersulfonate sodium supplied by BASF as the Avanel® S series, sodium dodecyl sulfate, and the sulfosuccinate emulsifier Lankropol® K8300 available from AkzoNobelSurfaceChemistry LLC.

[0050] Nonionic hydrocarbon emulsifiers are emulsifiers that exhibit surface activity in water without dissociating into ions and have hydrocarbon groups such as alkyl groups as their hydrophobic moieties. The hydrophilic moieties of nonionic hydrocarbon emulsifiers include water-soluble functional groups such as polyethylene oxide chains obtained from the polymerization of ethylene oxide. Nonionic hydrocarbon emulsifiers include polyalkylene oxide block copolymers, such as block copolymers having polyethylene oxide and polypropylene oxide.

[0051] Examples of nonionic hydrocarbon emulsifiers include the emulsifiers described in paragraphs

[0043] to

[0052] of JP-A No. 2016-537499.

[0052] The emulsifier with fluorine atom and the emulsifier without fluorine atom can contain silicon atom.The emulsifier containing silicon atom can include siloxane emulsifier.The siloxane emulsifier can include the emulsifier described in U.S. Patent No. 6,841,616 (Wille et al.) and U.S. Patent No. 7,977,438 (Brothers et al.).

[0053] The emulsifier having a fluorine atom and the emulsifier not having a fluorine atom may be a polymer emulsifier. Examples of the polymer emulsifier include a water-soluble polymer having a hydrophilic group in a side chain. Examples of such a polymer emulsifier include a polymer containing a unit based on a compound having a site capable of reacting by polymerization and a hydrophilic group. Further examples include polymers obtained by subjecting a polymer based on a compound having a group that can become a hydrophilic group, even if it does not have hydrophilicity during polymerization, to post-treatment such as hydrolysis.

[0054] It is preferable that the first aqueous dispersion is substantially free of an emulsifier represented by any of formulae (S1) to (S4). When no emulsifier is used in producing the first fluoropolymer contained in the first aqueous dispersion, the amount of the compound represented by any of formulae (S1) to (S4) generated can be suppressed, making it easier to adjust the content of these compounds.

[0055] H-(CF ２ ) ｎ１ -COOM (S1) F-(CF ２ )ｎ１ -COOM (S2) H-(CF ２ ) ｎ２ -SO ３ M (S3) F-(CF ２ ) ｎ２ -SO ３ M (S4) In formulas (S1) to (S4), n1 is an integer of 3 to 19, n2 is an integer of 4 to 20, and each M is independently a hydrogen atom, Na, K, or NH ４ is.

[0056] The first fluorine-containing polymer is a fluorine-containing polymer that comprises TFE units and PAVE units.It is presumed that the first fluorine-containing polymer adsorbs and incorporates the specific monomer at the hydrophobic part during the polymerization of the specific monomer described below, and solubilizes the specific monomer even when the first aqueous dispersion does not contain an emulsifier, making the polymerization of the specific monomer easier to proceed.It is also presumed that the first fluorine-containing polymer contributes to the dispersion stabilization in the first aqueous dispersion.

[0057] The details of PAVE are the same as those of the PAVE from which the PAVE units of the present polymer are derived, and the preferred embodiments are also the same.

[0058] The content of TFE units in the first fluoropolymer relative to the total content of TFE units and PAVE units is preferably 40 to 85 mol%, more preferably 50 to 75 mol%, and even more preferably 60 to 70 mol%, from the viewpoint of more efficient production of the fluoropolymer. The content of PAVE units in the first fluoropolymer relative to the total content of TFE units and PAVE units is preferably 15 to 60 mol%, more preferably 25 to 55 mol%, and even more preferably 30 to 40 mol%, from the viewpoint of more efficient production of the fluoropolymer. When PMVE or PPVE is used as PAVE, the suitable amount used is similar. The total content of TFE units and PAVE units in the first fluoropolymer is preferably 99.0 to 100.0 mol%, more preferably 99.5 to 100.0 mol%, and even more preferably 99.9 to 100.0 mol%, relative to the total content of all units in the first fluoropolymer.

[0059] The first fluorine-containing polymer may contain units based on monomers other than TFE and PAVE, and from the viewpoint of more efficient production of the fluorine-containing polymer, it is also preferable that it is substantially free of units based on other monomers. "Substantially free of units based on other monomers" means that the content of units based on other monomers is 0.01 mol% or less, and preferably 0 mol%, based on the total content of all units in the first fluorine-containing polymer.

[0060] The content of the first fluorine-containing polymer before the start of polymerization of the specific monomer is preferably 0.01 to 4.0% by mass, more preferably 0.1 to 1.0% by mass, and even more preferably 0.3 to 0.7% by mass, relative to the total mass of the first aqueous dispersion, from the viewpoint of more efficiently producing a fluorine-containing polymer. In this specification, "before the start of polymerization of the specific monomer" means immediately before the start of polymerization. Here, examples of "start of polymerization" include the time when the specific monomer (or, when a polymerization initiator is used, the polymerization initiator and the specific monomer) is made to coexist in the reactor after the reactor is heated to a polymerization temperature or higher, and the time when the reactor is heated to a polymerization temperature or higher after the specific monomer (or, when a polymerization initiator is used, the polymerization initiator and the specific monomer) is made to coexist in the reactor.

[0061] The content (solids concentration) of the first fluoropolymer in the first aqueous dispersion can be measured, for example, by the following method. 2.0 g of the first aqueous dispersion is heated at 170°C for 20 minutes, and then the mass of the residue is weighed and the solids concentration is calculated by the following formula: "Solids concentration (mass%) = 100 × mass (g) of heated residue of first aqueous dispersion / mass (2.0 g) of first aqueous dispersion"

[0062] A preferred embodiment of step 1 is an embodiment in which the content of PAVE units in the first fluoropolymer is 20 to 80 mol % relative to the total content of TFE units and PAVE units, and the content of the first fluoropolymer before the start of polymerization of the monomers is 0.01 to 4.0 mass % relative to the total mass of the first aqueous dispersion.

[0063] As a method for producing the first fluorine-containing polymer, a method of polymerizing monomers containing TFE and PAVE in an aqueous medium in the presence of a polymerization initiator is preferred. This gives the first fluorine-containing polymer dispersed in the aqueous medium in the form of particles. The aqueous medium thus obtained in which the particles of the first fluorine-containing polymer are dispersed may be used as is as the first aqueous dispersion. Alternatively, the solvent may be replaced, and the first fluorine-containing polymer may be dispersed in another aqueous medium, which may be used as the first aqueous dispersion.

[0064] The polymerization initiator used for polymerizing the first fluorine-containing polymer is preferably a water-soluble polymerization initiator. Among water-soluble polymerization initiators, persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate, or organic polymerization initiators such as disuccinic acid peroxide and azobisisobutylamidine dihydrochloride are more preferred, persulfates are still more preferred, and among persulfates, ammonium persulfate is particularly preferred.

[0065] The aqueous medium used in producing the first fluorinated polymer includes water and a mixed solvent of water and a water-soluble organic solvent. Specific examples of the water-soluble organic solvent include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol.

[0066] In producing the first fluorine-containing polymer, the aqueous medium containing the monomers preferably does not contain an emulsifier. The emulsifier (type and the like) is as described above.

[0067] The first aqueous dispersion containing the first fluorine-containing polymer is preferably used for polymerization of a specific monomer after being subjected to a purification treatment to reduce or inactivate the polymerization initiator and its decomposition products. By removing the polymerization initiator and its decomposition products that may be contained in the first aqueous dispersion containing the first fluorine-containing polymer through the purification treatment, a fluorine-containing polymer having desired physical properties is easily obtained. Examples of the purification treatment method include a method of performing a heat treatment and a method of passing the dispersion through an ion exchange resin (preferably an anion exchange resin). The purification treatment may be performed multiple times.

[0068] The anion exchange resin is preferably spherical. The average particle diameter of the anion exchange resin is preferably 0.1 to 5 mm, more preferably 0.2 to 2 mm, and even more preferably 0.3 to 1.5 mm. When the average particle diameter of the anion exchange resin is within the above range, clogging is less likely to occur when the anion exchange resin is packed. The average particle diameter of the anion exchange resin is a value determined by a sieving method. Specifically, first, the anion exchange resin is placed in a sieve shaker and the particle size distribution is measured by sieving. Then, the diameter of the sieve opening corresponding to a cumulative residual of 50% by mass is determined, and this is taken as the average particle diameter. The anion exchange resin may be of a gel type or a macroporous type. The matrix structure of the resin may be acrylic or styrene-based. Furthermore, the functional group in the anion exchange resin may be either strongly basic or weakly basic, but strongly basic is preferred from the viewpoint of impurity adsorption efficiency. The counter anion of the anion exchange resin may be a chloride ion or a hydroxide ion, but is preferably a hydroxide ion from the viewpoint of further reducing the impurity concentration in the aqueous dispersion.

[0069] Specific examples of the aqueous medium contained in the first aqueous dispersion include the aqueous medium used in the production of the first fluorine-containing polymer described above. Before the start of polymerization of the specific monomer, the content of the aqueous medium is preferably from 60 to 99.9 mass%, more preferably from 96 to 99.9 mass%, and even more preferably from 98 to 99.9 mass%, based on the total mass of the first aqueous dispersion.

[0070] The first aqueous dispersion may contain other components in addition to the first fluorinated polymer and the aqueous medium. Specific examples of the other components include a reducing agent, a pH adjuster, and a chain transfer agent, which will be described later. Specific examples of the pH adjuster include inorganic salts and ammonia. Specific examples of the inorganic salts include phosphates such as disodium hydrogen phosphate and sodium dihydrogen phosphate, and carbonates such as sodium hydrogen carbonate and sodium carbonate. More preferred specific examples of phosphates include disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate. When the first aqueous dispersion contains a pH adjuster, the content of the pH adjuster is preferably 0.004 to 3.0 parts by mass per 100 parts by mass of the aqueous medium.

[0071] (Specific Monomer) The specific monomer is a monomer containing TFE and PAVE. Preferred embodiments of TFE and PAVE as the specific monomer are the same as the preferred embodiments of TFE and PAVE in the first fluorine-containing polymer described above. The total amount of TFE and PAVE used is preferably 80 to 100 mol%, more preferably 90 to 100 mol%, and even more preferably 95 to 100 mol%, based on the amount of the specific monomer used.

[0072] The specific monomer may contain a monomer other than TFE and PAVE (hereinafter also referred to as "other monomer"). Specific examples of the other monomer include the above-mentioned BO, R Ｈａｌ , R ＣＮ and POAVE. Preferred embodiments of these other monomers are the same as the preferred embodiments of other monomers in the description of units based on other monomers that may be contained in the present polymer.

[0073] The amount of the other monomer used is preferably 0 to 20 mol %, more preferably 0 to 10 mol %, and even more preferably 0 to 5 mol %, based on the amount of the specific monomer used.

[0074] The specific monomer consists of only TFE and PAVE, or contains TFE and PAVE and BO, R Ｈａｌ and R ＣＮ It is preferable that the polymer contains at least one monomer selected from the group consisting of:

[0075] In step 1, the specific monomer is preferably polymerized in the presence of a polymerization initiator. The polymerization initiator is preferably an oil-soluble radical initiator, a water-soluble radical initiator, or a water-soluble redox catalyst. Specific examples of oil-soluble radical initiators include oil-soluble organic peroxides such as tert-butyl peroxypivalate (hereinafter also referred to as "PBPV") and diisopropyl peroxydicarbonate (hereinafter also referred to as "IPP"). Specific examples of water-soluble radical initiators include persulfates such as ammonium persulfate and potassium persulfate, disuccinic acid peroxide, bisglutaric acid peroxide, and water-soluble organic peroxides such as tert-butyl hydroperoxide (hereinafter also referred to as "TBHP"). The water-soluble redox catalyst is preferably a combination of an oxidizing agent such as bromic acid or a salt thereof, chloric acid or a salt thereof, persulfuric acid or a salt thereof, permanganic acid or a salt thereof, or hydrogen peroxide, and a reducing agent such as sulfurous acid or a salt thereof, hydrogen sulfite or a salt thereof, thiosulfuric acid or a salt thereof, organic acid, or inorganic salt. The persulfate is preferably potassium persulfate or ammonium persulfate. The sulfite is preferably sodium sulfite. The inorganic salt may be a combination of a sulfate anion, a sulfite anion, or a chloride anion with a metal ion. The metal ion is preferably a transition metal, such as manganese, iron, cobalt, nickel, copper, zinc, cerium, or silver ion, with iron ion being preferred. The inorganic salt is preferably iron(II) sulfate. The polymerization initiator is preferably an oil-soluble radical initiator or a water-soluble radical initiator. From the viewpoint of more efficient production of a fluorine-containing polymer, a water-soluble radical initiator is more preferred, and a persulfate or a water-soluble organic peroxide is even more preferred. Two or more polymerization initiators may be used in combination.

[0076] The amount of the polymerization initiator used is preferably 0.01 to 5 parts by mass, more preferably 0.01 to 3 parts by mass, and even more preferably 0.01 to 2 parts by mass, per 100 parts by mass of the specific monomer used.

[0077] (Chain Transfer Agent) In step 1, it is also preferable that the specific monomer is polymerized in the presence of a chain transfer agent. Specific examples of the chain transfer agent include chain transfer agents having an iodine atom, ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane, and chain transfer agents having an iodine atom are preferred. By polymerizing the specific monomer using a chain transfer agent having an iodine atom, a second fluorine-containing polymer having an iodine atom at its terminal can be produced.

[0078] The chain transfer agent having an iodine atom is preferably a compound represented by formula (I): (R ｆ )-(X) ２ (I) In formula (I), R ｆ is a fluoroalkylene group having 1 to 16 carbon atoms or an aromatic ring group, and X is an iodine atom or a bromine atom, and at least one of X is an iodine atom. ｆ The fluoroalkylene group of R may be linear or branched. ｆ Preferably, X is a perfluoroalkylene group. Preferably, all of X are iodine atoms.

[0079] Specific examples of the compound represented by formula (I) include 1,2-diiodoperfluoroethane, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane (hereinafter also referred to as "C4DI"), 1,5-diiodoperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, 1,3-diiodo-2-chloroperfluoropropane, 1,5-diiodo-2,4-dichloroperfluoropentane, 1,12-diiodoperfluorododecane, 1,16-diiodoperfluorohexadecane, diiodomethane, 1,2-diiodoperfluoropropane, 1,3-diiodoper ...4-diiodoperfluorobutane (hereinafter also referred to as "C4DI"), 1,5-diiodoperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, 1,3-diiodoperfluoropropane, 1,5-diiodo-2,4-dichloroperfluoropentane, 1,12-diiodoperfluorododecane, 1,16-diiodoperfluorohexadecane, diiodomethane, 1,2-diiodoperfluoropropane, 1,4-diiodoperfluorobutane, 1,5-diiodoperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorobutane, 1,5-diiodoperfluoropentane, 1,12-diiodoperfluorododecane, 1,16 Examples of the compound represented by formula (I) include iodoethane, 1,3-diiodo-n-propane, (2-iodoethyl)-substituted benzene, 1-iodo-4-bromoperfluorobutane, 1-iodo-6-bromoperfluorohexane, 1-iodo-8-bromoperfluoroctane, 1-bromo-2-iodoperfluoroethane, 1-bromo-3-iodoperfluoropropane, 2-bromo-3-iodoperfluorobutane, 3-bromo-4-iodoperfluorobutene-1, 2-bromo-4-iodoperfluorobutene-1, monoiodomonobromo-substituted benzene, and diiodomonobromo-substituted benzene. C4DI is preferred as the compound represented by formula (I).

[0080] The amount of the chain transfer agent used is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, and even more preferably 1 to 3 parts by mass, per 100 parts by mass of the specific monomer used.

[0081] In view of the superior crosslinkability of the fluoropolymer to be produced, in the method for producing a fluoropolymer according to this embodiment, the specific monomer is preferably the above-mentioned BO, R Ｈａｌ and R ＣＮ or the first aqueous dispersion preferably contains a chain transfer agent containing an iodine atom.

[0082] Step 1 is a step of polymerizing the specific monomer in the first aqueous dispersion to obtain a second aqueous dispersion containing a second fluorine-containing polymer. The specific monomer is added to the reaction system (i.e., polymerization reaction vessel) by a conventional method. For example, the specific monomer may be continuously or intermittently added to the reaction system so that the polymerization pressure reaches a predetermined pressure. Alternatively, the specific monomer may be dissolved in an aqueous medium, and the resulting solution may be continuously or intermittently added to the reaction system. When a polymerization initiator is used, the polymerization initiator may be added to the reaction system all at once or in portions. When other components (e.g., chain transfer agents) other than those mentioned above are used, the other components may be added to the reaction system all at once or in portions.

[0083] The polymerization temperature is preferably 10 to 95° C., more preferably 15 to 90° C. The polymerization pressure is preferably 0.5 to 4.0 MPaG, more preferably 0.6 to 3.5 MPaG. In the case of batch processing, the polymerization time is preferably 90 to 1,000 minutes, more preferably 90 to 700 minutes.

[0084] The polymerization of the specific monomer is preferably carried out in a reaction system substantially free of an emulsifier. Examples of the emulsifier include the emulsifiers described above. The absence of an emulsifier means an environment in which the content of the emulsifier is 0.03 ppm by mass or less, preferably 0.02 ppm by mass or less, and more preferably 0 ppm by mass, relative to the total mass of the aqueous medium contained in the first aqueous dispersion.

[0085] In step 1, the second fluoropolymer according to this embodiment is produced, and a second aqueous dispersion in which particles containing the second fluoropolymer are dispersed in an aqueous medium is obtained.

[0086] (Second aqueous dispersion) The second aqueous dispersion is an aqueous dispersion containing the second fluorine-containing polymer obtained in step 1. In other words, the second aqueous dispersion is an aqueous dispersion in which particles containing the second fluorine-containing polymer (hereinafter also referred to as "specific particles") are dispersed in an aqueous medium. The specific particles may or may not contain the first fluorine-containing polymer. The second aqueous dispersion may contain the first fluorine-containing polymer dispersed in the form of particles.

[0087] The preferred embodiment of the second fluorine-containing polymer contained in the second aqueous dispersion is as described above. The content of the specific particles containing the second fluorine-containing polymer is preferably 1 to 50 mass%, more preferably 1 to 40 mass%, and even more preferably 1 to 30 mass%, based on the total mass of the second aqueous dispersion, from the viewpoint of dispersion stability of the specific particles.

[0088] The average particle size of the specific particles is preferably 1 μm or less, and from the viewpoint of dispersion stability of the specific particles, it is more preferably 500 nm or less, and even more preferably 400 nm or less. From the viewpoint of recovery efficiency in step 2 described below, the average particle size of the specific particles is preferably 50 nm or more, more preferably 70 nm or more, and even more preferably 100 nm or more. The average particle size of the specific particles is a particle size calculated by analyzing an autocorrelation function obtained by dynamic light scattering using a monodisperse cumulant method.

[0089] Specific examples and preferred embodiments of the aqueous medium contained in the second aqueous dispersion are the same as those of the aqueous medium contained in the first aqueous dispersion. The content of the aqueous medium is preferably 50 to 99 mass%, more preferably 60 to 99 mass%, and even more preferably 70 to 99 mass%, based on the total mass of the second aqueous dispersion, from the viewpoint of dispersion stability of the specific particles.

[0090] The content of the emulsifier in the second aqueous dispersion is preferably 100 mass ppm or less, more preferably 75 mass ppm or less, even more preferably 50 mass ppm or less, and particularly preferably 1 mass ppm or less, relative to the total mass of the second aqueous dispersion. It is also preferably below the quantitation limit of the above-mentioned method for measuring the content of the emulsifier. An example of a lower limit is 1 mass ppb. The content of the emulsifier can be measured by the same method as that for the first aqueous dispersion described above. Specific examples of the emulsifier are as described above. The emulsifier in the second aqueous dispersion may or may not be water-soluble.

[0091] <Step 2> Step 2 is a step of subjecting the second aqueous dispersion obtained in step 1 to agitation treatment to coagulate the second fluoropolymer and obtain an coagulated second fluoropolymer.

[0092] (Stirring Treatment) As the stirring treatment, known stirring treatments that impart shear force to the second aqueous dispersion can be applied, and among these, stirring treatments using a stirring device that rotates a stirring shaft equipped with stirring blades are preferred. Specific examples of the shape of the stirring blades include paddle blades, propeller blades, disk blades, Pfaudle blades, anchor blades, turbine blades, and disk turbine blades. Disk turbine blades are preferred because they facilitate the production of the present polymer and provide excellent stirring efficiency. The number of stirring blades is preferably 1 to 10, more preferably 2 to 4. Specific examples of the shape of the vessel used in the stirring treatment include cylindrical, conical, elliptical, rectangular, and pyramidal shapes. Cylindrical shapes are preferred because of their mixability and fluidity. The stirring device may be provided with a baffle.

[0093] The stirring time is preferably 0.1 to 24 hours, more preferably 0.1 to 12 hours, and even more preferably 0.1 to 6 hours. The stirring rotation speed is preferably 500 rpm or more, and more preferably 1000 rpm or more. The stirring rotation speed is also preferably 5000 rpm or less. The stirring rotation speed may be constant during stirring or may change during stirring. It is also preferable that the stirring rotation speed is faster than the peripheral speed in step 1. The temperature of the aqueous dispersion during the stirring treatment is preferably 10 to 90°C, more preferably 10 to 80°C, and even more preferably 15 to 70°C.

[0094] By the stirring treatment, a solid material containing the aggregated second fluorine-containing polymer is obtained. In this specification, the term "solid material" refers to a solid that is not stably dispersed in an aqueous medium, and a dispersoid stably dispersed in an aqueous medium is considered not to be a solid material even if it is a solid that is insoluble in the aqueous medium. For example, among the insoluble components (e.g., specific particles) contained in the second aqueous dispersion after stirring, the dispersoid stably dispersed in the aqueous medium is not included in the solid material, and the precipitates and floating matter that are not stably dispersed in the aqueous medium are included in the solid material. An example of the solid material is an aggregate of the second fluorine-containing polymer. An example of the stably dispersed dispersoid is a dispersoid that passes through a type 5A filter paper specified in JIS P 3801 [filter paper (for chemical analysis)]. The particle size of the solid material is, for example, 500 μm or more, preferably 1000 μm or more.

[0095] The agglomerates of the second fluorine-containing polymer separated by the stirring treatment are recovered to give a fluorine-containing polymer containing TFE units and PAVE units. Specific examples of the method for recovering the agglomerates of the second fluorine-containing polymer include filtration and centrifugation, with filtration being preferred.

[0096] <Washing Step> The method for producing a fluoropolymer preferably further comprises a step of washing the recovered second fluoropolymer (hereinafter also referred to as "Step 3"). Step 3 makes it possible to remove other components (e.g., emulsifier, monomer, polymerization initiator, and reaction products thereof) adhered to the second fluoropolymer, making it easier to obtain a crosslinked rubber article with desired physical properties. The washing liquid in the washing step includes the above-mentioned aqueous media, with water being preferred and ultrapure water being more preferred. Specific examples of the washing method include a method of immersing the recovered second fluoropolymer in a washing liquid and a method of showering the recovered second fluoropolymer with a washing liquid. The amount of washing liquid in the washing step is preferably 1 to 50 times, more preferably 3 to 30 times, and even more preferably 5 to 15 times the total mass of the second fluoropolymer. The temperature of the washing liquid in the washing step is preferably 5 to 50°C, more preferably 10 to 40°C, and more preferably 15 to 30°C.

[0097] [Solid composition] The fluoropolymer obtained by the above-mentioned production method may be in the form of a solid composition. In this specification, a solid composition means a composition having a solid content mass of 99 mass% or more. The solid content mass is calculated by the following method based on the masses before and after heating. 2.0 g of the solid composition is heated at 170°C for 20 minutes, and then the mass of the residue is weighed and the solid content mass is calculated by the following formula: Solid content mass (mass%) = 100 × (mass of residue) / (mass of solid composition) The content of the fluoropolymer in the solid composition is preferably 99.0 to 100 mass%, more preferably 99.5 to 100 mass%, and even more preferably 99.8 to 100 mass%, based on the total mass of the solid composition.

[0098] The solid composition containing a fluoropolymer is preferably substantially free of an emulsifier. "The solid composition is substantially free of an emulsifier" means that the content of the emulsifier is 10 ppm by mass or less, preferably 150 ppb by mass or less, more preferably 50 ppb by mass or less, based on the total mass of the solid composition. The lower limit of the emulsifier content is 0 ppb by mass.

[0099] The solid composition preferably contains the compound represented by formula (S1) in an amount of 10 ppm by mass or less, more preferably 150 ppb by mass or less, and even more preferably 50 ppm by mass or less. The lower limit of the content of formula (S1) is 0 ppb by mass. The method for measuring the content of the emulsifier and the emulsifier that may be contained in the solid composition are as described above.

[0100] The metal content of the solid composition is preferably 50 ppm by mass or less, more preferably 20 ppm by mass or less, and even more preferably 10 ppm by mass or less, relative to the total mass of the solid composition. It is also preferably below the measurement limit of the following measurement method. The lower limit can be 1 ppb by mass. The metal content is the total content of 29 metal elements (Fe, Na, K, Li, Be, Mg, Al, Ca, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Rb, Sr, Zr, Mo, Ag, Cd, In, Sn, Cs, Ba, Pb, and Bi) measured by the absolute calibration curve method using an inductively coupled plasma mass spectrometer. The metal content of the solid composition can be measured by ashing the solid composition, dissolving the resulting ash in acid, and measuring the resulting solution using an inductively coupled plasma mass spectrometer. In the process for producing a fluoropolymer according to this embodiment, by using a stirring device equipped with the above-mentioned stirring blades, the energy required for flocculation can be applied without the use of a flocculant, and therefore there is no need to use a flocculant containing a metal when recovering the fluoropolymer, and the metal content of the solid composition can be easily adjusted to be within the above-mentioned range.

[0101] The solid composition is also preferably a fluorine-containing elastomer. A "fluorine-containing elastomer" is an elastic fluorine-containing polymer having no melting point and exhibiting a storage modulus G' of 80 kPa or more at 100°C and a frequency of 50 cpm, as measured in accordance with ASTM D6204, and is distinguished from a fluororesin.

[0102] <Shape> The solid composition containing the fluoropolymer according to this embodiment can be transformed into an appropriate shape depending on the manufacturing method and application of the crosslinked rubber article. The solid composition may be, for example, a sheet, granules, a tube, or a fiber, or may be in an amorphous form.

[0103] [Use] The fluoropolymer according to this embodiment is preferably used for producing crosslinked rubber articles.

[0104] Crosslinked rubber articles can be produced by crosslinking the present polymer or the solid composition. Examples of crosslinking methods include adding a crosslinking agent and kneading or molding the resulting mixture. Specific examples of crosslinking agents include organic peroxides, polyols, amines, and triazines. Organic peroxides are preferred because they provide excellent productivity, heat resistance, and chemical resistance to crosslinked rubber articles. Specific examples of organic peroxides include dialkyl peroxides, α,α'-bis(tert-butylperoxy)-p-diisopropylbenzene, α,α'-bis(tert-butylperoxy)-m-diisopropylbenzene, benzoyl peroxide, tert-butylperoxybenzene, and 2,5-dimethyl-2,5-di(benzoylperoxy)hexane. Specific examples of dialkyl peroxides include 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethylhexane-2,5-dihydroxyperoxide, tert-butylcumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)-3-hexyne, tert-butylperoxymaleic acid, and tert-butylperoxyisopropyl carbonate.

[0105] In producing crosslinked rubber articles, components other than the crosslinking agent may be used. Examples of other components include catalysts, crosslinking aids, acid acceptors, fillers and reinforcing materials, scorch retarders, crown ethers, and mold release agents. Examples of molding methods include injection molding, extrusion molding, coextrusion molding, blow molding, compression molding, inflation molding, transfer molding, and calender molding.

[0106] The crosslinked rubber article is suitably used as a material for O-rings, sheets, gaskets, oil seals, diaphragms, V-rings, and the like. Furthermore, the crosslinked rubber articles can be used for heat-resistant and chemical-resistant sealing materials, heat-resistant and oil-resistant sealing materials, wire coating materials, sealing materials for semiconductor devices, sealing materials for liquid crystal display panel manufacturing equipment, sealing materials for light-emitting diode manufacturing equipment, corrosion-resistant rubber coating materials, sealing materials for urea-resistant grease, etc., rubber coating materials, adhesive rubbers, hoses, tubes, calendered sheets (rolls), sponges, rubber rolls, oil drilling components, heat-dissipating sheets, solution-crosslinked products, rubber sponges, bearing seals (urea-resistant grease, etc.), linings (chemical-resistant), insulating sheets for automobiles, insulating sheets for electronic devices, rubber bands for watches, endoscope packings (amine-resistant), bellows hoses (processed from calendered sheets), water heater packings / valves, fenders (marine civil engineering, ships), fibers / nonwoven fabrics (protective clothing, etc.), board sealing materials, rubber gloves, stators for uniaxial eccentric screw pumps, parts for urea SCR systems, vibration isolators, vibration-damping agents, sealants, additives for other materials, and toys.

[0107] [Second Embodiment] A method for producing a fluoropolymer according to a second embodiment of the present invention (hereinafter also referred to as the "production method according to the present embodiment") will be described. The production method according to the present embodiment is a method for producing a fluoropolymer by polymerizing a monomer (specific monomer) containing TFE and PAVE in an aqueous dispersion (first aqueous dispersion) containing a first fluoropolymer that is substantially free of a water-soluble emulsifier and contains TFE units and PAVE units, and an aqueous medium, to produce a second fluoropolymer. In this embodiment, the content of PAVE units relative to the total content of TFE units and PAVE units in the first fluoropolymer is 20 to 80 mol %, the content of PAVE units relative to the total content of TFE units and PAVE units in the second fluoropolymer is 20 to 80 mol %, and the content of the first fluoropolymer relative to the total content of TFE units and PAVE units in the second fluoropolymer is 0.01 to 4.0 mass % based on the total mass of the first aqueous dispersion before the start of monomer polymerization. Moreover, in this embodiment, after polymerizing the monomers in the aqueous dispersion, the aqueous dispersion containing the second fluoropolymer (second aqueous dispersion) is stirred with a disc turbine blade at a rotational speed of 1000 rpm or more to aggregate the second fluoropolymer, and the aggregated second fluoropolymer is recovered.

[0108] According to the production method of this embodiment, a fluoropolymer having a high decomposition temperature and excellent roll winding properties can be produced. The details of the reason for this are unknown, but the following reasons are presumed. By polymerizing in a first aqueous dispersion containing a predetermined amount of a predetermined first fluoropolymer, the first fluoropolymer functions as a polymerization site, allowing the monomer to polymerize without the use of an emulsifier. Furthermore, by stirring the aqueous dispersion containing the obtained polymer using a disc turbine blade at a predetermined rotation speed, fluoropolymer aggregates can be recovered without the use of a flocculant. Flocculants and emulsifiers that have a different structure from the fluoropolymer have low decomposition temperatures and can serve as starting points for thermal decomposition. Furthermore, by suppressing the residue of these components and suppressing their bleed-out to the material surface, roll winding properties can be improved. It is presumed that the high decomposition temperature and improved roll winding properties result from the absence of an emulsifier or flocculant in the production process, since no emulsifier or flocculant remains in the fluoropolymer. Each step in the production method of this embodiment will now be described.

[0109] <Step 1> In the production method according to this embodiment, in step 1, the specific monomer described above is polymerized in a first aqueous dispersion.

[0110] The first aqueous dispersion used in step 1 of this embodiment is the same as the first aqueous dispersion used in step 1 of the first embodiment. In addition, the specific method and preferred aspects of step 1 of this embodiment are the same as the specific method and preferred aspects of step 1 described in the first embodiment.

[0111] A second aqueous dispersion containing a second fluorine-containing polymer is obtained in step 1 of this embodiment. The second fluorine-containing polymer and second aqueous dispersion obtained in step 1 of this embodiment are the same as the second fluorine-containing polymer and second aqueous dispersion in the first embodiment, including their preferred embodiments.

[0112] <Step 2> Step 2 is a step of subjecting the second aqueous dispersion containing the second fluoropolymer obtained in step 1 to a stirring treatment of stirring at a rotational speed of 1000 rpm or more using a disc turbine impeller to agglomerate the second fluoropolymer and obtain an agglomerated second fluoropolymer. The stirring treatment in step 2 of this embodiment is the same as the stirring treatment in step 2 of the first embodiment, including its preferred embodiments, except that a stirring device equipped with a disc turbine impeller is used and the rotational speed of stirring using the disc turbine impeller is 1000 rpm or more.

[0113] By the stirring treatment, the second aqueous dispersion is separated into a solid material containing the aggregated second fluorine-containing polymer and a liquid material. The liquid material is, for example, a dispersion in which dispersoids are stably dispersed in an aqueous medium. Of the insoluble components (e.g., specific particles) contained in the second aqueous dispersion, dispersoids that remain stably dispersed in the aqueous medium even after stirring are included in the liquid material. Furthermore, the solid material includes sediments and floating materials that are not dispersed in the aqueous medium after stirring. The solid material is, for example, an aggregate of the second fluorine-containing polymer.

[0114] The solid matter containing the second fluorine-containing polymer separated by the stirring treatment is recovered to give a fluorine-containing polymer containing TFE units and PAVE units. Specific examples of the method for recovering the solid matter containing the second fluorine-containing polymer include filtration and centrifugation, with filtration being preferred.

[0115] <Washing step> The production method according to this embodiment preferably further comprises step 3 of washing the recovered solid matter containing the second fluoropolymer. Step 3 makes it possible to remove other components (e.g., emulsifier, monomer, polymerization initiator, and reaction products thereof) that have adhered to the second fluoropolymer, making it easier to obtain a crosslinked rubber article with desired physical properties. Step 3 of this embodiment is the same as step 3 of the first embodiment, including its preferred embodiments.

[0116] The above production method can provide a fluoropolymer having a high decomposition temperature and excellent roll-winding property, in which the content of PAVE units is 20 to 80 mol% relative to the total content of TFE units and PAVE units. Examples of the fluoropolymer obtainable by the production method according to this embodiment and a preferred embodiment thereof, and the second fluoropolymer contained in the second aqueous dispersion and a preferred embodiment thereof, include the fluoropolymer according to the first embodiment, in which the content of PAVE units is 20 to 80 mol% relative to the total content of TFE units and PAVE units, and a preferred embodiment thereof.

[0117] Use of the fluoropolymer obtained by the production method according to this embodiment is preferred because it facilitates adjustment so as to satisfy the above-mentioned Requirement 1 relating to the 2% weight loss temperature of the fluoropolymer and Requirement 2 relating to the difference ΔTd between the 5% weight loss temperature and the 2% weight loss temperature of the fluoropolymer. More specifically, in the production method of the present composition, for example, by adjusting the content of the first fluoropolymer in the first aqueous dispersion, it is possible to adjust the content of low-molecular-weight components in the entire fluoropolymer and the content of high-molecular-weight components in the entire fluoropolymer, and the above-mentioned Requirement 1 and Requirement 2 can be set within preferred ranges.

[0118] The fluoropolymer obtained by the production method according to this embodiment may be in the form of a solid composition. The fluoropolymer obtained by the production method according to this embodiment may also be a fluoroelastomer. The above-mentioned solid composition and fluoroelastomer, including preferred embodiments thereof, are the same as those of the solid composition and fluoroelastomer described in the first embodiment.

[0119] The fluoropolymer obtained by the production method according to this embodiment is preferably used for producing a crosslinked rubber article. The production method and uses of the crosslinked rubber article, including preferred embodiments thereof, are the same as those of the production method and uses of the crosslinked rubber article described in the first embodiment.

[0120] The present invention will be described in detail below with reference to examples. Examples 1 to 3 are working examples, and Examples 4 and 5 are comparative examples. However, the present invention is not limited to these examples.

[0121] The average particle size of the particles in the aqueous dispersion was measured using a dynamic light scattering particle size measuring device (ELSZ, manufactured by Otsuka Electronics Co., Ltd.) with the aqueous dispersion of each example described below as a sample.

[0122] <Method for measuring iodine content> A solid composition comprising a fluoropolymer was hot-pressed to form a 300 μm sheet. The obtained sheet-like composition was subjected to X-ray fluorescence analysis using a ZSX Primus II (manufactured by RIGAKU Corporation), and the iodine content in the solid composition (fluoropolymer) was calculated by the fundamental parameter method.

[0123] <Method for Quantifying Emulsifier Contained in Solid Composition> (Preparation of Measurement Sample) The solid compositions obtained in each example described below were freeze-pulverized using a freeze-pulverizer Freezer Mill 6775 (manufactured by SPEX) under the following conditions. Before freeze-pulverization, 10% by mass of dibutylhydroxytoluene (BHT) was added to the solid composition in advance, based on the total mass of the solid composition, to obtain a pulverized powder. The freeze-pulverization conditions were: solid composition: 3 g, BHT: 0.3 g, run time: 5 minutes, rate: 15 cps, cycle: 3. 5 mL of methanol was added to 0.25 g of the obtained pulverized powder, and the mixture was subjected to ultrasonic treatment at 50°C for 2 hours and centrifuged (5000 rpm, 5 minutes) to precipitate each fluoropolymer. The supernatant was used as an extract. The obtained extract was subjected to LC / MS / MS analysis. The fluorine-containing emulsifier and hydrocarbon emulsifier in the extract were measured using a liquid chromatograph mass spectrometer. The measurement equipment configuration and LC-MS measurement conditions are shown in Table 1. Using aqueous solutions of fluorine-containing emulsifier and hydrocarbon emulsifier with known concentrations, aqueous solutions with five or more levels of content were prepared, and LC / MS analysis was performed on the aqueous solutions with each content. The relationship between the content and the area relative to the content was plotted to draw a calibration curve. Using the calibration curve, the area of ​​the LC / MS chromatogram of the fluorine-containing emulsifier and hydrocarbon emulsifier in the extract was converted into the content of the fluorine-containing emulsifier and hydrocarbon emulsifier.

[0124]

[0125] The MRM measurement parameters are selected appropriately depending on the structures of the fluorine-containing emulsifier and hydrocarbon emulsifier to be measured. Literature values ​​can be used for the MRM parameters, or they can be calculated using an LC-MS instrument. The specific procedure for determining MRM parameters using an LC-MS instrument is as follows: Using an LC / MS instrument (Shimadzu Corporation, LCMS-8060NX), select product ion search, input the molecular weights of the fluorine-containing emulsifier and hydrocarbon emulsifier to be measured, and then perform precursor ion, precursor adjustment, voltage optimization, and product m / z optimization. The calculated MRM measurement parameters are used. As an example, the MRM measurement parameters for compounds (S2) and (S4), which are fluorine-containing emulsifiers, are shown in the table below. In formulas (S2) and (S4), MS represents a hydrogen atom, a metal atom, NR4 (wherein R may be the same or different and represents a hydrogen atom or an organic group having 1 to 10 carbon atoms), an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent. F-(CF2)n1-COOMS (S2) F-(CF2)n2-SO3MS (S4) where n1 is an integer from 3 to 17 and n2 is an integer from 4 to 12.

[0126]

[0127]

[0128] (Quantitative Analysis of Fluorine-Containing Emulsifier and Hydrocarbon Emulsifier Contained in Solid Composition) Specifically, five levels of methanol standard solutions of fluorine-containing emulsifier and hydrocarbon emulsifier with known concentrations of 1 to 180 ng / g were prepared, and a was calculated from the sample concentration and peak integral value of each emulsifier using a first-order approximation according to formula (A1-1): A = a × X (A1-1), where A is the peak area of ​​each emulsifier and X is the concentration (ng / g) of each emulsifier.

[0129] Next, the amount of emulsifier contained in the extract was calculated using formula (A1-2). Note that a in formula (A1-2) means a obtained by the above formula (A1-1). XCm = ACm / a (A1-2) XCm: content (ng / g) of emulsifier in each extract ACm: peak area of ​​emulsifier in each extract The quantitation limit in this measurement is 1 ng / g.

[0130] The content of the emulsifier in the solid composition relative to the total mass of the solid composition (ZCm) was calculated using the following formula (A1-3): ZCm = XCm × ρ1 × La / W1 (A1-3) ZCm: content of the emulsifier contained in the solid composition ρ1: density of the extraction solvent (methanol in each example) La: volume of the extraction solvent (5 mL in each example) W1: mass of the sample used for extraction (2.5 g of solid composition in each example)

[0131] <Method for Quantifying Formula (S1) and Formula (S3) Contained in Solid Composition> The solid compositions obtained in each example described below were freeze-pulverized using a freeze-pulverizer Freezer Mill 6775 (manufactured by SPEX) under the following conditions. Before freeze-pulverization, 10% by mass of dibutylhydroxytoluene (BHT) was added to the solid composition in advance, based on the total mass of the solid composition, to obtain a pulverized powder. The freeze-pulverization conditions were: solid composition: 3 g, BHT: 0.3 g, run time: 5 minutes, rate: 15 cps, cycle: 3. 5 mL of methanol was added to 2.5 g of the obtained pulverized powder, and the mixture was subjected to ultrasonic treatment at 50°C for 2 hours and centrifuged (5000 rpm, 5 minutes) to precipitate each fluoropolymer. The supernatant was used as the extract. The obtained extract was subjected to LC / MS / MS analysis. The fluorine-containing emulsifier in the extract was measured using a liquid chromatograph mass spectrometer. The measurement equipment configuration and LC-MS measurement conditions were as described above. Using aqueous solutions of emulsifiers containing fluorine atoms with known concentrations, methanol solutions with five or more different concentrations were prepared. LC / MS analysis of the methanol solutions with each concentration was performed, and the relationship between the content and the area relative to the content was plotted to draw a calibration curve. Using the calibration curve, the area of ​​the LC / MS chromatogram of the emulsifier containing fluorine atoms in the extract was converted to the content of the emulsifier containing fluorine atoms. The content of the compound represented by formula (S1) contained in each extract was determined by converting each compound in formula (S1) where n1 = 3 to 13 into a perfluorocarboxylic acid (formula (S2)) with the same carbon number. Furthermore, the content of the compound represented by formula (S3) contained in each extract was determined by converting each compound in formula (S3) where n2 = 4 to 10 into a perfluorosulfonic acid (formula (S4)) with the same carbon number. The MRM parameters for formulas (S1) and (S3) are shown in Tables 4 and 5. Specifically, five levels of methanol standard solutions of perfluorocarboxylic acid and perfluorosulfonic acid with known concentrations ranging from 1 to 180 ng / g were first prepared, and a and a' were calculated from the respective sample concentrations and peak integral values ​​using linear approximation according to formulas (A2-1) and (A2-1').A = a × X (A2-1) A: peak area of ​​perfluorocarboxylic acid, X: concentration of perfluorocarboxylic acid (ng / g) A' = a' × X' (A2-1') A': peak area of ​​perfluorosulfonic acid, X': concentration of perfluorosulfonic acid (ng / g).

[0132]

[0133]

[0134] Specifically, first, the peak areas of the compounds represented by formula (S1) and formula (S3) contained in each of the extracts were determined using the liquid chromatograph mass spectrometer.

[0135] Next, the contents of the compound represented by formula (S1) and the compound represented by formula (S3) were calculated using formulas (A2-2) and (A2-2'), respectively. Note that a in formula (A2-2) means a calculated using formula (A2-1) above, and a' in formula (A2-2') means a' calculated using formula (A2-1') above. XCm ​​= ACm / a (A2-2) XCm: content (ng / g) of the compound represented by formula (S1) and having carbon number (n+1) in each extract ACm: peak area of ​​the compound represented by formula (S1) and having carbon number (n+1) in each extract XCm' = ACm' / a' (A2-2') XCm': content (ng / g) of the compound represented by formula (S3) and having carbon number n in each extract ACm': peak area of ​​the compound represented by formula (S3) and having carbon number n in each extract The quantitation limit in this measurement is 1 ng / g.

[0136] The content (ZCm) of the compound represented by formula (S1) in the solid relative to the total mass of the solid was calculated using the following formula (A2-3): ZCm = XCm × ρ1 × La / W1 (A2-3) ZCm: content of the compound represented by formula (S1) with carbon number (n+1) contained in the solid ρ1: density of the extraction solvent (methanol in each example) La: volume of the extraction solvent (5 mL in each example) W1: mass of the sample used for extraction (2.5 g of solid in each example)

[0137] The content (ZCm') of the compound represented by formula (S3) in the solid relative to the total mass of the solid was calculated using the following formula (A2-4): ZCm' = XCm' × ρ1 × La / W1 (A2-4) ZCm': content of the compound represented by formula (S3) with carbon number n contained in the solid ρ1: density of the extraction solvent (methanol in each example) La: volume of the extraction solvent (5 mL in each example) W1: mass of the sample used for extraction (2.5 g of solid in each example)

[0138] <Production of Raw Material Liquid A> Ultrapure water (1130 g), 30 mass% aqueous ammonia solution (30 mg), PMVE (72 g), and TFE (14 g) were charged into a 2.2 L stainless steel pressure reactor equipped with an anchor impeller, and the temperature was raised to 90°C while stirring at 600 rpm. Next, an aqueous ammonium persulfate solution (5.0 mass%, 30 mL) was added to initiate polymerization. Since the pressure in the reactor decreased with the start of polymerization, TFE was added to maintain the pressure constant. When 4 g of TFE had been injected, the reactor was cooled to terminate the polymerization reaction. The gas remaining in the reactor was recovered, and the liquid was then withdrawn. This liquid was used as raw material liquid A. Raw material liquid A was freeze-coagulated and then filtered. The resulting fluoropolymer 1-1 (first fluoropolymer) was analyzed by NMR, and the ratio of PMVE units to TFE units was 34 / 66 (molar ratio).

[0139] <Production of Raw Material Solution B> To the above raw material solution A, HPR4002Cl (anion exchange resin, manufactured by DuPont, 200 g) was added. 150 minutes after the start of stirring, the raw material solution was separated from the ion exchange resin by filtration. Next, AmberLite (registered trademark) HPR650H (cation exchange resin, manufactured by DuPont, 50 g) was added to the filtrate. 60 minutes after the start of stirring, the raw material solution was separated from the ion exchange resin by filtration to obtain raw material solution B. In raw material solution B, particles of fluoropolymer 1-1 were dispersed in an aqueous medium, and the content of fluoropolymer 1-1 was 0.6% by mass based on the total mass of raw material solution B.

[0140] Example 1 A stainless steel pressure reactor with an internal volume of 2.2 L equipped with an anchor blade was charged with raw material solution B (1000 g) and ultrapure water (175 g), to obtain aqueous dispersion B (first aqueous dispersion). The content of fluorine-containing polymer 1-1 was 0.5% by mass relative to the total mass of aqueous dispersion B. Perfluoro-1,4-diiodobutane (2.0 g), PMVE (72 g), and TFE (14 g) were charged to aqueous dispersion B, and the temperature was raised to 80 ° C. while stirring at 600 rpm. TFE and PMVE were injected at a molar ratio of 25 / 75 until the pressure in the reactor reached 1.2 MPa [gauge], and an aqueous ammonium persulfate solution (APS aqueous solution, 1.0 mass %, 20 mL, ammonium persulfate 0.2 g) was added to initiate polymerization. As the pressure in the reactor decreased with the initiation of polymerization, TFE was added to maintain the pressure constant. When 160 g of TFE and 133 g of PMVE had been injected, the reactor was cooled to terminate the polymerization reaction, thereby obtaining a fluoropolymer 1-2 (second fluoropolymer). The polymerization time was 300 minutes.

[0141] Aqueous dispersion B contained substantially no water-soluble emulsifier. Specifically, the contents of emulsifier A and the compounds represented by formulae (S1) to (S4), which will be described later, were measured by the following method. Note that, in the production of aqueous dispersion B, emulsifiers other than emulsifier A and the compounds represented by formulae (S1) to (S4) were not produced from the components used in the production of aqueous dispersion B, nor were any emulsifiers used, and therefore are not contained in aqueous dispersion B. The solids content of aqueous dispersion B was measured, and an amount of aqueous dispersion B corresponding to 0.05 g of solids was weighed into a 100 mL screw tube. Subsequently, 40 g of water and methanol were added to the weighed aqueous dispersion B so that the water / methanol ratio was 50 / 50 by volume. The mixture was then shaken vigorously until coagulation occurred. The solids were removed, and the liquid phase was centrifuged at 4,000 rpm for 1 hour, and the supernatant was extracted. The measurement was carried out in the same manner as the above-mentioned method for measuring the content of the emulsifier, except for the method for preparing the sample. As a result, the content of the compound represented by any one of Formulas (S1) to (S4) was also below the quantitation limit for aqueous dispersion B.

[0142] After the polymerization reaction was completed, the gas remaining in the reactor was recovered, and then the liquid was withdrawn from the reactor. This liquid was designated as aqueous dispersion 1. Aqueous dispersion 1 was a dispersion in which particles (average particle size 92.7 nm) containing fluoropolymer 1-2 were dispersed in an aqueous medium, and had a solids concentration of 20.5% by mass. The aqueous dispersion 1 was stirred with a disc turbine blade for 150 minutes at 1000 rpm, and then the aggregates were collected by filtration. The collected aggregates were washed with 2000 g of ultrapure water at 40°C and dried to obtain a rubbery fluoropolymer 1.

[0143] The obtained fluoropolymer 1 was analyzed by NMR, and as a result, the content of TFE units was 66 mol % based on the total content of all units in fluoropolymer 1, and the content of PAVE units (PMVE units) was 34 mol % based on the total content of all units in fluoropolymer 1. The iodine content of fluoropolymer 1 was measured by the above-mentioned measurement method, and was found to be 0.2 mass %.

[0144] <Production of Raw Material Liquid C> A fluoropolymer 2-1 (first fluoropolymer) was polymerized in the same procedure as in the production of raw material liquid A, except that the amount of each monomer component was appropriately changed, and this liquid was designated as raw material liquid C. Raw material liquid C was freeze-coagulated and then filtered off, and the resulting fluoropolymer 2-1 was analyzed by NMR, revealing that the ratio of PMVE units to TFE units was 32 / 68 (molar ratio).

[0145] <Production of Raw Material Liquid D> Raw material liquid D was produced in the same procedure as in the production method of raw material liquid B, except that raw material liquid C was used instead of raw material liquid A. Raw material liquid D contained particles of fluoropolymer 2-1 dispersed in an aqueous medium, and the content of fluoropolymer 2-1 was 0.6% by mass relative to the total mass of raw material liquid D.

[0146] Example 2 A stainless steel pressure reactor with an internal volume of 2.2 L equipped with an anchor blade was charged with raw material solution D (1000 g) and ultrapure water (175 g), to obtain aqueous dispersion D (first aqueous dispersion). The content of fluorine-containing polymer 2-1 was 0.5% by mass relative to the total mass of aqueous dispersion D. PMVE (90 g), perfluoro-1,4-diiodobutane (2.0 g), and TFE (18 g) were charged into aqueous dispersion D, and the temperature was raised to 80°C while stirring at 600 rpm. When the internal temperature reached 80°C, the pressure was 1.5 MPa [Gauge]. An aqueous APS solution (0.5% by mass, 16 mL, ammonium persulfate 0.08 g) was added to initiate polymerization. As the pressure in the reactor decreased with the initiation of polymerization, TFE and PMVE were injected at a molar ratio of 65 / 35 to maintain the pressure constant. When 256 g of TFE and 217 g of PMVE had been added, the reactor was cooled to terminate the polymerization reaction, thereby obtaining a fluoropolymer 2-2 (second fluoropolymer). The polymerization time was 290 minutes. Aqueous dispersion D contained substantially no water-soluble emulsifier. The content of the emulsifier was confirmed by the same method as for aqueous dispersion B described above.

[0147] The gas remaining in the reactor was recovered, and then the liquid was withdrawn. This liquid was designated as aqueous dispersion 2. Aqueous dispersion 2 was a dispersion in which particles (average particle size 140.3 nm) containing fluoropolymer 2-2 were dispersed in an aqueous medium, and had a solids concentration of 28.6% by mass. The above aqueous dispersion 2 was stirred with a disc turbine blade at 1000 rpm for 150 minutes, and then the aggregates were collected by filtration. The collected aggregates were washed with 2000 g of ultrapure water at 25°C and dried, yielding a rubber-like fluoropolymer 2.

[0148] The obtained fluoropolymer 2 was analyzed by NMR, and as a result, the content of TFE units was 68 mol % based on the total content of all units in fluoropolymer 2, and the content of PAVE units (PMVE units) was 32 mol % based on the total content of all units in fluoropolymer 2. The iodine content of fluoropolymer 2 was measured by the above-mentioned measurement method, and was found to be 0.05 mass %.

[0149] Example 3 A stainless steel pressure reactor having an internal volume of 2.2 L equipped with an anchor blade was charged with raw material liquid D (1000 g) and ultrapure water (175 g) to obtain aqueous dispersion D (first aqueous dispersion). The content of fluoropolymer 3-2 was 0.5% by mass relative to the total mass of aqueous dispersion D. PMVE (72 g) and TFE (14 g) were charged into aqueous dispersion D, and the temperature was raised to 80°C while stirring at 600 rpm. TFE and PMVE were injected until the pressure in the reactor reached 1.5 MPa [gauge], and an aqueous APS solution (0.5% by mass, 16 mL, 0.08 g of ammonium persulfate) was added to initiate polymerization. As the pressure in the reactor decreased with the initiation of polymerization, TFE was added to maintain the pressure constant. When 6 g of TFE had been added, perfluoro-1,4-diiodobutane (2.0 g) was injected. When 256 g of TFE and 217 g of PMVE had been added, the reactor was cooled and the polymerization reaction was terminated to obtain a fluoropolymer 3-2 (second fluoropolymer). The polymerization time was 290 minutes. Aqueous dispersion D contained substantially no water-soluble emulsifier. The emulsifier content was confirmed by the same method as for aqueous dispersion B described above.

[0150] The gas remaining in the reactor was recovered, and then the liquid was withdrawn. This liquid was designated as aqueous dispersion 3. Aqueous dispersion 3 was a dispersion in which particles (average particle size 96 nm) containing fluoropolymer 3-2 were dispersed in an aqueous medium, and had a solids concentration of 27.6% by mass. The above aqueous dispersion 3 was stirred with a disc turbine blade at 1000 rpm for 150 minutes, and then the aggregates were collected by filtration. The collected aggregates were washed with 2000 g of ultrapure water at 40°C and dried, yielding a rubbery fluoropolymer 3.

[0151] The obtained fluoropolymer 3 was analyzed by NMR, and as a result, the content of TFE units was 65 mol % based on the total content of all units in fluoropolymer 3, and the content of PAVE units (PMVE units) was 35 mol % based on the total content of all units in fluoropolymer 3. The iodine content of fluoropolymer 3 was measured by the above-mentioned measurement method, and was found to be 0.05 mass %.

[0152] <Example 4> A stainless steel pressure reactor with an internal volume of 2.2 L and equipped with anchor blades was degassed, and then ultrapure water (980 g), emulsifier C ２ F ５ OCF ２ CF ２ OCF ２ COONH ４ A 30% by mass solution (201.7 g) of (emulsifier A) and a 5% by mass aqueous solution (2.3 g) of disodium hydrogen phosphate dodecahydrate were charged, and the gas phase was replaced with nitrogen. While stirring at a speed of 600 rpm using an anchor blade, PMVE (72 g) and TFE (14 g) were injected into the vessel, and the internal temperature was then raised to 80 ° C. Next, an aqueous APS solution (0.5% by mass, 16 mL, ammonium persulfate 0.08 g) was added to initiate polymerization. Since the pressure in the reactor decreased with the start of polymerization, TFE and PMVE were injected at a molar ratio of 65 / 35, and the pressure was kept constant at 1.2 MPa [gauge]. When 160 g of TFE and 133 g of PMVE were injected, the reactor was cooled, the polymerization reaction was terminated, and a fluoropolymer 4a was obtained. The polymerization time was 262 minutes. After recovering the gas remaining in the reactor, the liquid was extracted. This liquid was designated as aqueous dispersion 4. Aqueous dispersion 4 was a dispersion in which particles (average particle diameter 80 nm) containing fluoropolymer 4a were dispersed in an aqueous medium, and had a solids concentration of 23.2 mass%. While stirring the aqueous dispersion 4, an aqueous aluminum sulfate solution (5%, 2000 g) was added, and the aggregates were collected by filtration. The collected aggregates were washed with 2000 g of ultrapure water at 40°C and dried to obtain a rubber-like fluoropolymer 4.

[0153] The obtained fluoropolymer 4 was analyzed by NMR, and as a result, the content of TFE units was 65 mol % based on the total content of all units in fluoropolymer 4, and the content of PAVE units (PMVE units) was 35 mol % based on the total content of all units in fluoropolymer 4. The iodine content of fluoropolymer 4 was measured by the above-mentioned measurement method, and was found to be 0.05 mass %.

[0154] <Example 5> A stainless steel pressure reactor with an internal volume of 2.2 L and equipped with an anchor blade was degassed, and then ultrapure water (980 g), emulsifier C ２ F ５OCF ２ CF ２ OCF ２ COONH ４ A 30% by mass solution (201.7 g) of (emulsifier A) and a 5% by mass aqueous solution (2.3 g) of disodium hydrogen phosphate dodecahydrate were charged, and the gas phase was replaced with nitrogen. While stirring at a speed of 600 rpm using an anchor blade, PMVE (54 g) and TFE (11 g) were injected into the vessel, and the internal temperature was then raised to 80 ° C. Next, an aqueous APS solution (0.5% by mass, 13 mL, 0.06 g of ammonium persulfate) was added, and polymerization was initiated. Since the pressure inside the reactor decreased with the start of polymerization, TFE and PMVE were injected at a molar ratio of 65 / 35, and the pressure was kept constant at 0.9 MPa [gauge]. When 6 g of TFE had been injected, perfluoro-1,4-diiodobutane (2.0 g) was injected. When 410 g of TFE and 280 g of PMVE were injected, the reactor was cooled to terminate the polymerization reaction, and a fluoropolymer 5a was obtained. The polymerization time was 500 minutes. After recovering the gas remaining in the reactor, the liquid was extracted. This liquid was designated as aqueous dispersion 5. Aqueous dispersion 5 was a dispersion in which particles (average particle size 80 nm) containing fluoropolymer 5a were dispersed in an aqueous medium, and the solids concentration was 38.8% by mass. The aqueous dispersion 5 was added to 2500 g of a 3% by mass aqueous nitric acid solution, and the mixture was stirred, and the coagulate was collected by filtration. The collected coagulate was washed with 2000 g of ultrapure water at 23 ° C. and dried to obtain a rubber-like fluoropolymer 5.

[0155] The obtained fluoropolymer 5 was analyzed by NMR, and as a result, the content of TFE units was 65 mol % based on the total content of all units in fluoropolymer 5, and the content of PAVE units (PMVE units) was 35 mol % based on the total content of all units in fluoropolymer 5. The iodine content of fluoropolymer 5 was measured by the above-mentioned measurement method, and was found to be 0.03 mass %.

[0156] [Measurement and Evaluation Methods] Various measurement and evaluation methods are as follows.

[0157] <2% Weight Loss Temperature and 5% Weight Loss Temperature> A 10 mg sample was weighed out from the fluoropolymer obtained in each example and transferred to an aluminum pan. The sample was heated from 30°C to 550°C at a heating rate of 10°C / min in an air atmosphere, while measuring the change in mass of the sample. The temperature at which the sample mass became 98% by mass, assuming that the sample mass before heating was 100% by mass, was defined as the 2% mass loss temperature. Similarly, the temperature at which the sample mass became 95% by mass was defined as the 5% mass loss temperature. The above thermogravimetric analysis was carried out using a differential thermal thermogravimetric analyzer "NEXTA STA series STA200" (manufactured by Hitachi High-Technologies Corporation).

[0158] From the results of thermogravimetric analysis, a thermogravimetric curve (TGA curve) showing the relationship between temperature and sample weight (mass) was created, and the TGA curve was further differentiated with respect to temperature to obtain a differential TGA curve. The inflection point temperature (°C) at which an inflection point appeared in the TGA curve of each sample was determined from the peak temperature of the peak appearing in the differential TGA curve. Table 6, described below, shows the 2% weight loss temperature, 5% weight loss temperature, and inflection point temperature of each example sample. Note that, when multiple peaks appear in the differential TGA curve and multiple inflection points appear in the TGA curve, Table 6 shows only the inflection point temperature appearing on the lowest temperature side.

[0159] <Storage modulus> A rubber processability analyzer "PREMIER RPA (manufactured by Alpha Technologies, die shape: D0380)" was used as the measuring device. The fluoropolymer obtained in each example was kneaded for 10 minutes at room temperature using two rolls to produce a sheet with a thickness of 3 mm. The thickness of the sheet was adjusted by adjusting the gap between the two rolls. The obtained sheet was cut to a weight of approximately 10 g to obtain a cut sheet. The cut sheet was sandwiched between two polyester films (ALFA Technologies PART#F0311-S, 130 mm x 130 mm x 24 μm) to obtain a sample for measurement. The sample was placed on the die of the measuring device. The die temperature was previously set to 100°C. Next, the sample was held at 100°C for 2 minutes under conditions of 30 cpm frequency and 0.2°C amplitude angle, and then the amplitude angle was set to 0.5° and the frequency was increased to 10 cpm, 20 cpm, and 50 cpm to measure the storage modulus. The storage modulus at 50 cpm and 100°C was taken as the storage modulus G' (unit: kPa) of the sample.

[0160] <Thermal decomposition temperature> The thermal decomposition temperature of the fluoropolymer was measured using the same apparatus as in the thermogravimetric analysis described above. 10 mg of a sample was weighed out from the fluoropolymer obtained in each example and transferred to an aluminum pan. While the sample was heated from 30°C to 550°C at a heating rate of 10°C / min in an air atmosphere, the temperature difference ΔT from a reference material was detected as a DTA signal, and the temperature at which the DTA signal was maximum was taken as the decomposition temperature DTA (unit: °C). An empty aluminum pan was used as the reference material.

[0161] <Roll Wrapping Property> The fluoropolymer obtained in each example was kneaded using a roll kneader (a test roll machine manufactured by Yamatetsu Corporation) to produce a sheet, and the roll wrapping property was confirmed. The roll kneader was equipped with two rolls (roll diameter 8 inches, roll length 18 inches) and two guide members arranged on the gap between the rolls and near both ends of the rolls. The guide members maintain the width of the workpiece, which spreads in the axial direction of the rolls after passing through the rolls, at a predetermined width. 200 g of fluoropolymer was weighed out and placed in a dryer to heat to 50°C, and then the fluoropolymer was introduced between the guide members of the roll kneader set under the following conditions. The time (also referred to as the "winding time") from the introduction of the fluoropolymer until the fluoropolymer accumulated on the roll gap between the guide members disappeared and the fluoropolymer was completely wrapped around the roll was measured. Roll temperature: 40° C. Roll gap: 4.2 mm Front roll rotation speed: 22 rpm Rear roll rotation speed: 20 rpm Width between guide members: 150 mm The roll temperature was adjusted using a water heater (WTC40, manufactured by Nakamura Scientific Industrial Co., Ltd.).

[0162] The roll wrapping property of the fluoropolymer was evaluated from the measurement time based on the following evaluation criteria: (Evaluation criteria for roll wrapping property) ◯: The wrapping time was 3 minutes or less. Δ: The wrapping time was more than 3 minutes but not more than 5 minutes. ×: None of the fluoropolymer was wrapped around the roll, or the wrapping time was more than 5 minutes.

[0163]

[0164] From the evaluation results of Examples 1 to 3, it was confirmed that the fluoropolymers of the present invention, which have a 2% weight loss temperature of 300°C or higher and lower than 420°C (Requirement 1) and a difference of 20°C or higher between the 5% weight loss temperature and the 2% weight loss temperature (Requirement 2), have a high decomposition temperature and excellent roll winding properties. In contrast, it was confirmed that the fluoropolymers of Examples 4 and 5, which do not satisfy Requirements 1 and 2, have poor roll winding properties. The entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2023-222267, filed on December 28, 2023, are hereby incorporated by reference as the disclosure of the present specification.

Claims

1. A fluorine-containing polymer satisfying Requirement 1 and Requirement 2. Requirement 1: The 2% weight loss temperature of the fluorine-containing polymer is 300 °C or higher and less than 420 °C. Requirement 2: The difference between the 5% weight loss temperature of the fluorine-containing polymer and the 2% weight loss temperature of the fluorine-containing polymer is 20 °C or higher.

2. The fluorine-containing polymer according to claim 1, having units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether).

3. The fluorine-containing polymer according to claim 1 or 2, wherein the storage elastic modulus G' at 100 °C and a frequency of 50 cpm is 300 kPa or higher.

4. The fluorine-containing polymer according to claim 1 or 2, wherein an inflection point appears in a temperature range lower than the 5% weight loss temperature in the thermogravimetric curve obtained by thermogravimetric analysis of the fluorine-containing polymer.

5. The content of the units based on tetrafluoroethylene is 20 to 80 mol% with respect to the total content of all the units of the fluorine-containing polymer, and the content of the units based on perfluoro(alkyl vinyl ether) is 20 to 80 mol% with respect to the total content of all the units of the fluorine-containing polymer. The fluorine-containing polymer according to claim 2.

6. The fluorine-containing polymer according to claim 1 or 2, wherein the fluorine-containing polymer contains at least one selected from the group consisting of a polymerizable unsaturated bond, a chlorine atom, a bromine atom, an iodine atom, and a nitrile group.

7. A method for producing a fluorine-containing polymer, which substantially does not contain a water-soluble emulsifier, includes a first fluorine-containing polymer containing units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), and an aqueous medium. In the aqueous dispersion, a monomer containing tetrafluoroethylene and perfluoro(alkyl vinyl ether) is polymerized to produce a second fluorine-containing polymer having units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether). In the first fluorine-containing polymer, the content of the units based on perfluoro(alkyl vinyl ether) relative to the total content of the units based on tetrafluoroethylene and the units based on perfluoro(alkyl vinyl ether) is 20 to 80 mol%. In the second fluorine-containing polymer, the content of the units based on perfluoro(alkyl vinyl ether) relative to the total content of the units based on tetrafluoroethylene and the units based on perfluoro(alkyl vinyl ether) is 20 to 80 mol%. Before starting the polymerization of the monomer, the content of the first fluorine-containing polymer is 0.01 to 4.0% by mass based on the total mass of the aqueous dispersion. After polymerizing the monomer in the aqueous dispersion, the aqueous dispersion is stirred at a rotation speed of 1000 rpm or more using a stirring device that rotates a stirring shaft equipped with a stirring blade to aggregate the second fluorine-containing polymer, and the aggregated second fluorine-containing polymer is recovered.

8. The method for producing a fluorine-containing polymer according to claim 7, wherein the recovered second fluorine-containing polymer is washed with ultrapure water.

9. A sheet containing the fluorine-containing polymer according to claim 1 or 2.

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