Fluoroelastomer production method, composition, solid composition, and crosslinked rubber article

Abstract

A fluoroelastomer production method including a step in which monomers A comprising a compound represented by CX1X2=CX3-L-Z, a cyano-group-containing monomer, and at least one compound selected from the group consisting of tetrafluoroethylene, fluorine-containing vinyl ethers, and fluorine-containing allyl ethers are polymerized in an aqueous medium under conditions that substantially no fluorine-atom-containing emulsifier is present.

Description

Method for producing fluorine-containing elastomer, composition, solid composition, and crosslinked rubber article

[0001] The present invention relates to a method for producing a fluorine-containing elastomer, a composition, a solid composition, and a crosslinked rubber article.

[0002] Crosslinked products obtained by crosslinking compositions containing fluorine-containing elastomers are used in various industrial fields because they have excellent heat resistance, chemical resistance, flame retardancy, weather resistance, etc.

[0003] For example, Patent Document 1 describes a method for producing a fluorine-containing elastomer by polymerizing a fluorine-containing monomer in the presence of a fluorine-free compound (1), a polymerization initiator and an aqueous medium, in which the fluorine-containing elastomer has a Mooney viscosity (ML1+10(100°C)) of 10 to 130 and the amount of the fluorine-free compound (1) is 3 to 5,000 ppm by mass relative to the aqueous medium.

[0004] Patent No. 7041378

[0005] In crosslinked rubber articles containing crosslinked products obtained by crosslinking fluorine-containing elastomers, there have been cases where both small compression set and surface smoothness are required.

[0006] The present disclosure has been made in view of the above circumstances, and a problem to be solved by one embodiment of the present disclosure is to provide a method for producing a fluorine-containing elastomer, a composition, and a solid composition that can provide crosslinked rubber articles having small compression set and excellent surface smoothness. Another problem to be solved by another embodiment of the present disclosure is to provide crosslinked rubber articles having small compression set and excellent surface smoothness.

[0007] The present disclosure includes the following aspects: <1> A method for producing a fluorine-containing elastomer, comprising a step of polymerizing a cyano group-containing monomer and at least one monomer selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride, a fluorine-containing vinyl ether, and a fluorine-containing allyl ether in the presence of a compound represented by the following formula (X) and an aqueous medium, and in the substantial absence of an emulsifier having a fluorine atom: CX １ X ２ =CX ３ -L-Z...(X) In formula (X), １ and X ２ are each independently a hydrogen atom, a chlorine atom, or an alkyl group; ３ <2> The method for producing a fluorine-containing elastomer according to <1>, wherein the cyano group-containing monomer is represented by the following formula (Y): １１ R １２ =CR １３ -R １４ -CN...(Y) In formula (Y), R １１ , R １２ , and R １３ each independently represents a hydrogen atom, a fluorine atom, or a methyl group; R １４represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the terminal or between a carbon-carbon bond of a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms. <3> The method for producing a fluorine-containing elastomer according to <1> or <2>, wherein the content of the cyano group-containing monomer is 0.5 to 20 mol % based on the total amount of the monomers used in polymerization of the fluorine-containing elastomer. <4> The method for producing a fluorine-containing elastomer according to any one of <1> to <3>, wherein the content of the compound represented by formula (X) is 0.1 to 5,000 ppm by mass based on the total amount of the aqueous medium. <5> A method for producing a fluorine-containing elastomer, comprising the steps of: polymerizing a first monomer containing a cyano group-containing monomer and at least one selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride, fluorinated vinyl ethers, and fluorinated allyl ethers in a first aqueous medium in the substantial absence of an emulsifier having a fluorine atom to produce a first fluorine-containing polymer, thereby obtaining an aqueous dispersion containing the first fluorine-containing polymer; and polymerizing a second monomer containing tetrafluoroethylene in the aqueous dispersion containing the first fluorine-containing polymer to obtain a second fluorine-containing polymer, thereby obtaining a fluorine-containing elastomer containing the first fluorine-containing polymer and the second fluorine-containing polymer. <6> The method for producing a fluorine-containing elastomer according to <5>, wherein the cyano group-containing monomer is represented by the following formula (Y): １１ R １２ =CR １３ -R １４ -CN...(Y) In formula (Y), R １１ , R １２ , and R １３ each independently represents a hydrogen atom, a fluorine atom, or a methyl group; R １４ 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. <7> The method for producing a fluorine-containing elastomer according to <5> or <6>, wherein the first aqueous medium further contains a compound represented by the following formula (X): CX １ X ２ =CX３ -L-Z...(X) In formula (X), １ and X ２ are each independently a hydrogen atom, a chlorine atom, or an alkyl group; ３ represents a hydrogen atom or an alkyl group, L represents a single bond or a divalent linking group, and Z represents an anionic group or a salt of an anionic group. <8> The method for producing a fluorine-containing elastomer according to <7>, wherein the content of the compound represented by formula (X) is 0.1 to 5000 ppm by mass based on the total amount of the first aqueous medium. <9> The method for producing a fluorine-containing elastomer according to any one of <5> to <8>, wherein the content of the cyano group-containing monomer is 0.5 to 20 mol % based on the total amount of the first monomer. <10> A composition comprising: a compound represented by the following formula (X): a first fluorine-containing polymer comprising structural units based on a cyano group-containing monomer and structural units based on at least one selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride, fluorinated vinyl ether, and fluorinated allyl ether; and a second fluorine-containing polymer comprising structural units based on tetrafluoroethylene, wherein the composition is substantially free of an emulsifier having a fluorine atom. １ X ２ =CX ３ -L-Z...(X) In formula (X), １ and X ２ are each independently a hydrogen atom, a chlorine atom, or an alkyl group; ３represents a hydrogen atom or an alkyl group, L represents a single bond or a divalent linking group, and Z represents an anionic group or a salt of an anionic group. <11> The composition according to <10>, wherein the metal content is 50 ppm by mass or less based on the total solid content of the composition. <12> The composition according to <10> or <11>, wherein the content of the structural units based on the cyano group-containing monomer is 0.1 to 10 mol % based on the total amount of the first fluorinated polymer and the second fluorinated polymer. <13> A solid composition comprising a fluorinated elastomer including structural units based on a cyano group-containing monomer, structural units based on tetrafluoroethylene, and structural units based on at least one selected from the group consisting of fluorinated vinyl ethers and fluorinated allyl ethers, wherein when heated in a nitrogen atmosphere under the following condition 1, the weight loss rate at 1,000 minutes after the start of heating is 2.0% or less, and the solid composition is substantially free of an emulsifier having a fluorine atom. (Condition 1) The temperature is increased from 40°C to 90°C at a rate of 20°C / min, and maintained at 90°C for 120 minutes. The temperature is increased from 90°C to 200°C at a rate of 20°C / min, and maintained at 200°C for 240 minutes. The temperature is increased from 200°C to 305°C at a rate of 20°C / min, and maintained at 305°C for 720 minutes. <14> The solid composition according to <13>, wherein the metal content is 50 ppm by mass or less based on the total amount of the solid composition. <15> The solid composition according to <13> or <14>, wherein the content of the structural units based on the cyano group-containing monomer is 0.1 to 10 mol% based on the total amount of the fluorine-containing elastomer. <16> The solid composition according to any one of <13> to <15>, wherein the storage modulus is 200 to 600 kPa. <17> A crosslinked rubber article comprising a crosslinked product obtained by crosslinking a fluorine-containing elastomer comprising structural units based on a cyano group-containing monomer, structural units based on tetrafluoroethylene, and structural units based on at least one selected from the group consisting of fluorine-containing vinyl ethers and fluorine-containing allyl ethers, wherein the weight loss rate after immersion in 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane for 12 hours and drying is 0.5% or less, and the crosslinked rubber article is substantially free of an emulsifier having a fluorine atom.<18> The crosslinked rubber article according to <17>, wherein the crosslinked product has a heterocyclic structure. <19> The crosslinked rubber article according to <17>, wherein the crosslinked product has at least one structure selected from the group consisting of an oxazole structure and a triazine structure.

[0008] According to one embodiment of the present invention, there are provided a method for producing a fluorine-containing elastomer, a composition, and a solid composition, which are capable of producing crosslinked rubber articles having small compression set and excellent surface smoothness. Another embodiment of the present invention aims to solve the problem of providing a crosslinked rubber article having small compression set and excellent surface smoothness.

[0009] In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in the present disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another staged numerical range. Furthermore, in numerical ranges described in the present disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In the present disclosure, each component may contain multiple corresponding substances. When multiple substances corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, multiple types of particles corresponding to each component may be contained. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified. In the present disclosure, an "elastomer" refers to an elastic fluorine-containing polymer that has no melting point and exhibits 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.

[0010] [Method for producing a fluorine-containing elastomer] A first embodiment of the method for producing a fluorine-containing elastomer according to the present disclosure (hereinafter also referred to as "the present production method A") comprises a step of polymerizing a cyano group-containing monomer and at least one monomer selected from the group consisting of tetrafluoroethylene (hereinafter also referred to as "TFE"), hexafluoropropylene (hereinafter also referred to as "HFP"), vinylidene fluoride (hereinafter also referred to as "VdF"), fluorine-containing vinyl ethers, and fluorine-containing allyl ethers in the presence of a compound represented by the following formula (X) (hereinafter also referred to as "compound (X)") and an aqueous medium, in the substantial absence of an emulsifier having a fluorine atom: CX １ X ２ =CX ３ -L-Z...(X) In formula (X), １ and X ２ are each independently a hydrogen atom, a chlorine atom, or an alkyl group; ３ is a hydrogen atom or an alkyl group; L is a single bond or a divalent linking group; and Z is an anionic group or a salt of an anionic group.

[0011] According to this production method A, a fluorine-containing elastomer that can be used to obtain crosslinked rubber articles having small compression set and excellent surface smoothness can be obtained by polymerizing a monomer containing a cyano group-containing monomer and at least one selected from the group consisting of TFE, HFP, VdF, fluorinated vinyl ethers, and fluorinated allyl ethers in the presence of compound (X) and an aqueous medium. In contrast, Patent Document 1 does not describe anything that focuses on the cyano group-containing monomer.

[0012] <Emulsifier> The present production method A is carried out under conditions in which an emulsifier having a fluorine atom is substantially absent. "Substantially absent" means that in the production of the fluorine-containing elastomer, the content of the emulsifier having a fluorine atom 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 amount of the aqueous medium. The lower limit of the content of the emulsifier having a fluorine atom is 0 ppb by mass.

[0013]

[0033] It is preferable that Production Method A be carried out under conditions in which emulsifiers having fluorine atoms and emulsifiers not having fluorine atoms are substantially absent, in order to prevent a decrease in the molecular weight of the fluorine-containing elastomer produced. The absence of emulsifiers having fluorine atoms and emulsifiers not having fluorine atoms (hereinafter collectively referred to as "emulsifiers") means that in the production of the fluorine-containing elastomer, 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 amount of the aqueous medium. The lower limit of the emulsifier content is 0 ppb by mass. The content of various emulsifiers can be measured using a liquid chromatograph mass spectrometer. Specific details are as described in the Examples.

[0014] Examples of emulsifiers include water-soluble emulsifiers. A water-soluble emulsifier means an emulsifier having a solubility of 100 mg or more in 1000 g of water at 25°C, and a water-insoluble emulsifier means an emulsifier other than the above-mentioned water-soluble emulsifiers. The water-soluble emulsifier may be either ionic or nonionic. Examples of emulsifiers include those that do not have a carbon-carbon double bond. None of the components contained in the monomer A used in the polymerization of this production method A are considered to be emulsifiers.

[0015] Examples of emulsifiers having fluorine atoms include anionic fluorine-containing emulsifiers. Examples of anionic fluorine-containing emulsifiers include emulsifiers containing fluorine atoms whose total carbon number excluding anionic groups is 20 or less, and emulsifiers containing fluorine atoms whose anionic moiety has a molecular weight of 800 or less. The above-mentioned "anionic moiety" means the moiety excluding the cation of the fluorine-containing emulsifier.

[0016] The fluorine-free emulsifier is an emulsifier that does not contain fluorine atoms and has a hydrocarbon group such as an alkyl group as a hydrophobic moiety. It is also possible to replace the hydrogen atom of the hydrocarbon group of the fluorine-free emulsifier with a halogen atom other than a fluorine atom.

[0017] The emulsifiers having no fluorine atoms include anionic hydrocarbon emulsifiers and nonionic hydrocarbon emulsifiers.

[0018] Anionic hydrocarbon emulsifiers refer to 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 group, such as an alkyl group, as a hydrophobic moiety. Specific examples of anionic hydrocarbon emulsifiers include sodium dodecyl sulfate, 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, and sulfosuccinate emulsifier Lankropol® K8300 available from AkzoNobelSurfaceChemistry LLC.

[0019] Nonionic hydrocarbon emulsifiers are emulsifiers that exhibit surface activity in water without dissociating into ions and have hydrocarbon groups such as alkyl groups as the hydrophobic moiety. The hydrophilic moiety of nonionic hydrocarbon emulsifiers includes water-soluble functional groups such as polyethylene oxide chains obtained by polymerization of ethylene oxide. Examples of nonionic hydrocarbon emulsifiers include polyalkylene oxide block copolymers, such as block copolymers having polyethylene oxide and polypropylene oxide.

[0020] Further, other nonionic hydrocarbon emulsifiers include those described in paragraphs

[0043] to

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

[0021] The emulsifier with fluorine atom and the emulsifier without fluorine atom can contain silicon atom.The emulsifier with silicon atom can include siloxane emulsifier.Siloxane emulsifier is a hydrocarbon-containing emulsifier with siloxane skeleton.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.).

[0022] 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 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 polymerization reaction and a hydrophilic group. Further, even if the polymer does not originally have a hydrophilic group, a polymer containing a unit based on a compound having a group that can become a hydrophilic group and subjected to post-treatment such as hydrolysis may also be used.

[0023] When the monomer A is polymerized in the presence of an emulsifier having no fluorine atoms, the emulsifier having no fluorine atoms is usually used in an amount of 0.1 to 15 parts by mass per 100 parts by mass of the aqueous medium.

[0024] <Aqueous Medium> Production Method A is carried out in the presence of an aqueous medium. Specific examples of the aqueous medium include 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.

[0025] <Compound (X)> The present production method A is carried out in the presence of compound (X).

[0026] CX １ X ２ =CX ３ -L-Z...(X) In formula (X), １ and X ２ are each independently a hydrogen atom, a chlorine atom, or an alkyl group; ３ is a hydrogen atom or an alkyl group; L is a single bond or a divalent linking group; and Z is an anionic group or a salt of an anionic group.

[0027] In formula (X), １ and X ２ are each independently a hydrogen atom or an alkyl group. The alkyl group may be linear, branched, or cyclic. The alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 3 carbon atoms, and even more preferably 1. X １and X ２ In terms of increasing the number of particles of the first polymer, it is preferable that each of X is a hydrogen atom. ３ is a hydrogen atom, a fluorine atom, or an alkyl group. Specific examples and preferred embodiments of the alkyl group are １ and X ２ The specific examples and preferred embodiments of the alkyl group in X are the same as those in X. ３ is preferably a fluorine atom or a hydrogen atom, more preferably a hydrogen atom, from the viewpoint of increasing the number of particles of the first polymer.

[0028] In formula (X), L is a single bond or a divalent linking group. Examples of the divalent linking group include an alkylene group, a carbonyl group, an ether bond, a thioether bond, a sulfonyl group, —NH—, and —SiH ２ -, phenylene group, -CF ２ -, and groups combining two or more of these. Examples of the above groups combining two or more of these include an ester bond, a thioester bond, an amide bond, a sulfonamide bond, a combination of an alkylene group and an ether bond, a combination of an alkylene group and an ester bond, and a combination of an alkylene group and an amide bond. The alkylene group may be linear, branched, or cyclic, and is preferably linear or branched, and more preferably branched. The number of carbon atoms in the alkylene group may be, for example, 1 to 6, and preferably 1 to 4.

[0029] Specific examples of L include a single bond, an alkylene group, an ether bond, an ester bond, * Ｃ -CO-NH-R-* Ｚ and the like, and examples thereof include a single bond, an alkylene group having 1 to 6 carbon atoms, and * Ｃ -CO-NH-R-* Ｚ are preferred, and particularly preferred are a single bond, an alkylene group having 1 to 2 carbon atoms, and * Ｃ -CO-NH-R-* Ｚ is more preferable. Ｃ is the bonding site to the carbon atom in formula (X), and * Ｚis a bonding site to Z in formula (X), and R is an alkylene group having 1 to 6 carbon atoms. The alkylene group represented by R may be a linear alkylene group or a branched alkylene group.

[0030] In formula (X), Z is an anionic group or a salt of an anionic group.

[0031] Examples of the anionic group include —SO ３ H, -OSO ３ H, -P(=O)(OH) ２ , -OP(=O)(OH) ２ Examples of salts of anionic groups include groups in which the hydrogen ion of the above anionic groups is replaced with a cation other than a hydrogen ion.

[0032] Examples of the cation include metal ions, ammonium ions, imidazolium cations, pyrrolidinium cations, pyridinium cations, piperidinium cations, and phosphonium cations. Examples of the metal ions include alkali metal ions such as sodium ions, potassium ions, and lithium ions; and alkaline earth metal ions such as calcium ions and magnesium ions.

[0033] Z is -SO ３ M, -OSO ３ M, -P (=O) (OM) ２ , -OP(=O)(OM) ２ From the viewpoint of productivity, Z is preferably —SO ３ M and -COOM are preferred, and -SO ３ Na and —COONa are more preferred, and —SO ３ Na is more preferred.

[0034] M is a hydrogen atom, a metal atom, N(R Ｍ１ ) ４ or P(R Ｍ２ ) ４ and R Ｍ１ and R Ｍ２are each independently a hydrogen atom or a substituent. The metal atom represented by M is preferably a metal atom of Group 1, more preferably Li, Na, or K. Ｍ１ and R Ｍ２ The substituent represented by the formula (I) is preferably a monovalent organic group, more preferably a monovalent hydrocarbon group, and even more preferably an alkyl group or an aromatic hydrocarbon group. The substituent preferably has 1 to 10 carbon atoms. The alkyl group may be linear, branched, or cyclic. The aromatic hydrocarbon group may be monocyclic or polycyclic. The aromatic hydrocarbon group is preferably a phenyl group.

[0035] The molecular weight of the compound (X) is, for example, 70 to 500, and from the viewpoint of dispersion stability, it is preferably 70 to 450, and more preferably 100 to 300.

[0036] Specific examples of compound (X) include vinyl sulfonic acid, vinyl phosphonic acid, (meth)acrylic acid, allyl sulfonic acid, allyl phosphonic acid, butenoic acid, crotonic acid, vinyl acetic acid, 2-sulfoethyl methacrylic acid, 4-vinyl benzene sulfonic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid, N-tigloylglycine, 6-acrylamidohexanoic acid, 1,1-difluoro-2-methyl-2-[(1-oxo-2-propen-1-yl)amino]-1-propanesulfonic acid, 3-methyl-3-[(2-methyl-1-oxo-2-propen-1-yl)amino]-2-butanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, 2,3-dimethyl-3-[(1-oxo-2-propen-1-yl)amino]-2-butanesulfonic acid, and salts thereof. The metal salts include salts of metal atoms represented by M.

[0037] As compound (X), vinyl compounds having a sulfonic acid group, phosphonic acid group, or carboxy group, allyl compounds having a sulfonic acid group, phosphonic acid group, or carboxy group, (meth)acrylic acid, (meth)acrylamides having a sulfonic acid group, phosphonic acid group, or carboxy group, and metal salts thereof are preferred, and vinyl sulfonic acid, sodium vinyl sulfonate, allyl sulfonic acid, sodium allyl sulfonate, 2-acrylamido-2-methyl-1-propanesulfonic acid, sodium 2-acrylamido-2-methyl-1-propanesulfonate, 2-methacrylamido-2-methyl-1-propanesulfonic acid, or sodium 2-methacrylamido-2-methyl-1-propanesulfonate are preferred. Note that the term "(meth)acrylic acid" encompasses both acrylic acid and methacrylic acid, and the term "(meth)acrylamide" encompasses both acrylamide and methacrylamide.

[0038] The content of compound (X) is preferably from 0.1 to 5000 ppm by mass, more preferably from 0.2 to 1000 ppm by mass, still more preferably from 0.3 to 500 ppm by mass, and particularly preferably from 0.5 to 100 ppm by mass, relative to the total amount of the aqueous medium.

[0039] <Monomers used in polymerization of fluorine-containing elastomer> In this production method A, a monomer containing a cyano group-containing monomer and at least one selected from the group consisting of TFE, HFP, VdF, fluorine-containing vinyl ethers, and fluorine-containing allyl ethers is polymerized. Hereinafter, the monomer used in polymerization of the fluorine-containing elastomer will also be referred to as "monomer A." Monomer A may contain other monomers in addition to the cyano group-containing monomer and at least one selected from the group consisting of TFE, HFP, VdF, fluorine-containing vinyl ethers, and fluorine-containing allyl ethers.

[0040] (Cyano Group-Containing Monomer) Monomer A includes a cyano group-containing monomer.

[0041] The cyano group-containing monomer is not particularly limited as long as it is a compound having a cyano group and a polymerizable group.

[0042] The cyano group-containing monomer is preferably a monomer represented by the following formula (Y) in that the crosslinked rubber article has better releasability and heat resistance: １１ R １２ =CR １３ -R １４ -CN...(Y) In formula (Y), R １１ , R １２ , and R １３ each independently represents a hydrogen atom, a fluorine atom, or a methyl group; R １４ 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.

[0043] From the viewpoint of excellent polymerization reactivity, R １１ , R １２ , and R １３ is preferably a fluorine atom or a hydrogen atom, and R １１ , R １２ , and R １３ 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, １１ , R １２ , and R １３ It is particularly preferred that all of are fluorine atoms.

[0044] R １４ R may be linear, branched, or cyclic, and is preferably linear or branched. １４ The number of carbon atoms is preferably 2 to 8, more preferably 3 to 7, still more preferably 3 to 6, and particularly preferably 3 to 5.

[0045] R １４ may or may not have an etheric oxygen atom, but preferably has an etheric oxygen atom in view of better rubber properties.

[0046] R １４ The number of etheric oxygen atoms in the formula (I) is preferably 1 to 3, and particularly preferably 1 or 2.

[0047] Specific examples of the monomer represented by formula (Y) include CF２ = 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.

[0048] From the viewpoint of obtaining better mold releasability and physical properties of the crosslinked rubber article, the content of the cyano group-containing monomer is preferably 0.5 to 20 mol %, more preferably 0.5 to 15 mol %, even more preferably 0.5 to 10 mol %, and particularly preferably 0.5 to 5 mol %, based on the total amount of monomer A.

[0049] (TFE, HFP, VdF, Fluorinated Vinyl Ether, Fluorinated Allyl Ether) Monomer A contains at least one member selected from the group consisting of TFE, HFP, VdF, fluorinated vinyl ethers, and fluorinated allyl ethers.

[0050] The fluorine-containing vinyl ether is preferably a compound represented by the following formula (1) because of its excellent polymerization reactivity.

[0051] CX １１ X １２ =CX １３ -O-(CX １４ X １５ ) ｍ１ -L １ - (CX １６ X １７ ) ｎ１ -A １ …(1)

[0052] In formula (1), X １１ , X １２ , X １３ , X１４ , X １５ , X １６ , and X １７ are each independently a hydrogen atom, a fluorine atom, or a fluoroalkyl group, and X １１ ~X １７ At least one of m is a fluorine atom or a fluoroalkyl group; １ is an integer from 1 to 10, and n １ is an integer from 0 to 10, and L １ is a single bond or a divalent linking group, １ is an ionic group, a salt of an ionic group, a hydrogen atom, or a fluorine atom.

[0053] In addition, when a compound having an anionic group or a salt of an anionic group corresponds to both formula (X) and formula (1), if the compound has a vinyl ether structure, it is considered to belong to formula (1).

[0054] X １１ , X １２ , X １３ , X １４ , X １５ , X １６ , and X １７ is preferably a fluorine atom.

[0055] m １ is preferably 1 to 6, more preferably 1 to 3. １ is preferably 0.

[0056] L １ The divalent linking group represented by the following formula (I) is an alkylene group, —CH═CH—, —C≡C—, —O—, —S—, —CO—, —COO—, —OCO—, —CONR ３１ -, -NR ３２ CO- and combinations thereof are preferred. ３１ and R ３２ are each independently a hydrogen atom or an alkyl group.

[0057] L １ is preferably a single bond.

[0058] A １The ionic group represented by the formula (X) may be an anionic group or a cationic group. Examples of the anionic group include the same anionic groups as those included in the formula (X). Examples of the cationic group include an ammonium group, a pyridinium group, a pyrrolidinium group, and an amino group.

[0059] A １ is preferably a hydrogen atom or a fluorine atom.

[0060] Among them, the fluorine-containing vinyl ether is preferably a compound represented by the following formula (1A): CF ２ =CF-O-R ｆ１ ...(1A) In formula (1A), R ｆ１ represents a fluoroalkyl group having 1 to 10 carbon atoms. ｆ１ From the viewpoint of superior polymerization reactivity, the number of carbon atoms is preferably 1 to 8, more preferably 1 to 6, still more preferably 1 to 5, and particularly preferably 1 to 3. The fluoroalkyl group may be linear or branched. The fluoroalkyl group is preferably a perfluoroalkyl group.

[0061] The fluorine-containing vinyl ether is preferably a perfluoroalkyl vinyl ether (hereinafter also referred to as "PAVE").

[0062] Specific examples of PAVE include perfluoro(methyl vinyl ether) (hereinafter also referred to as "PMVE"), perfluoro(ethyl vinyl ether) (hereinafter also referred to as "PEVE"), and perfluoro(propyl vinyl ether) (hereinafter also referred to as "PPVE"). Among these, from the viewpoint of excellent polymerization reactivity, PMVE or PPVE is preferred as PAVE, and PMVE is more preferred.

[0063] The fluorine-containing allyl ether is preferably a compound represented by the following formula (2) because of its excellent polymerization reactivity.

[0064] CX ２１ X ２２ =CX ２３ (CX ２４ X ２５ )-O-(CX ２６ X ２７ )ｍ２ -L ２ - (CX ２８ X ２９ ) ｎ２ -A ２ …(2)

[0065] In formula (2), X ２１ , X ２２ , X ２３ , X ２４ , X ２５ , X ２６ , X ２７ , X ２８ , and X ２９ are each independently a hydrogen atom, a fluorine atom, or a fluoroalkyl group, and X ２１ ~X ２９ At least one of m is a fluorine atom or a fluoroalkyl group; ２ is an integer from 1 to 10, and n ２ is an integer from 0 to 10, and L ２ is a single bond or a divalent linking group, ２ is an ionic group, a salt of an ionic group, a hydrogen atom, or a fluorine atom.

[0066] In addition, when a compound having an anionic group or a salt of an anionic group corresponds to both formula (X) and formula (2), if the compound has an allyl ether structure, it is considered to belong to formula (2).

[0067] X ２１ , X ２２ , X ２３ , X ２４ , X ２５ , X ２６ , X ２７ , X ２８ , and X ２９ is preferably a fluorine atom.

[0068] m ２ is preferably 1 to 6, more preferably 1 to 3. ２ is preferably 0.

[0069] L ２ The divalent linking group represented by the following formula (I) is an alkylene group, —CH═CH—, —C≡C—, —O—, —S—, —CO—, —COO—, —OCO—, —CONR ３１-, -NR ３２ CO- and combinations thereof are preferred. ３１ and R ３２ are each independently a hydrogen atom or an alkyl group.

[0070] L ２ is preferably a single bond.

[0071] A ２ The ionic group represented by the formula (X) may be an anionic group or a cationic group. Examples of the anionic group include the same anionic groups as those included in the formula (X). Examples of the cationic group include an ammonium group, a pyridinium group, a pyrrolidinium group, and an amino group.

[0072] A ２ is preferably a hydrogen atom or a fluorine atom.

[0073] Among these, the fluorine-containing allyl ether is preferably a compound represented by the following formula (2A): CF ２ =CF-CF ２ O-R ｆ２ ...(2A) In formula (2A), R ｆ２ represents a fluoroalkyl group having 1 to 10 carbon atoms. ｆ１ From the viewpoint of superior polymerization reactivity, the number of carbon atoms is preferably 1 to 8, more preferably 1 to 6, still more preferably 1 to 5, and particularly preferably 1 to 3. The fluoroalkyl group may be linear or branched. The fluoroalkyl group is preferably a perfluoroalkyl group.

[0074] The fluorine-containing allyl ether is preferably a perfluoroalkyl allyl ether (hereinafter also referred to as "PAAE").

[0075] Specific examples of PAAE include perfluoro(methyl allyl ether) (hereinafter also referred to as "PMAE"), perfluoro(ethyl allyl ether) (hereinafter also referred to as "PEAE"), and perfluoro(propyl allyl ether) (hereinafter also referred to as "PPAE"). Among them, from the viewpoint of excellent polymerization reactivity, PMAE or PPAE is preferred as PAAE, and PMAE is more preferred.

[0076] Among these, from the viewpoint of excellent polymerization reactivity, it is preferable that the at least one selected from the group consisting of TFE, HFP, VdF, fluorinated vinyl ethers, and fluorinated allyl ethers includes at least one selected from the group consisting of TFE, fluorinated vinyl ethers, and fluorinated allyl ethers.

[0077] That is, the monomer A preferably contains a cyano group-containing monomer and at least one selected from the group consisting of TFE, a fluorinated vinyl ether, and a fluorinated allyl ether.

[0078] From the viewpoint of polymerization stability, the monomer A preferably contains a cyano group-containing monomer, TFE, and a fluorine-containing vinyl ether, and more preferably contains a cyano group-containing monomer, TFE, and PAVE.

[0079] When the monomer A contains TFE, the content of TFE is preferably 10 to 90 mol%, more preferably 30 to 80 mol%, still more preferably 40 to 80 mol%, particularly preferably 40 to 70 mol%, based on the total amount of the monomer A.

[0080] When the monomer A contains a fluorinated vinyl ether, the content of the fluorinated vinyl ether is preferably from 10 to 90 mol %, more preferably from 20 to 70 mol %, still more preferably from 20 to 60 mol %, particularly preferably from 30 to 60 mol %, based on the total amount of the monomer A.

[0081] When the monomer A contains a fluorinated allyl ether, the content of the fluorinated allyl ether is preferably from 10 to 90 mol%, more preferably from 20 to 70 mol%, still more preferably from 20 to 60 mol%, particularly preferably from 30 to 60 mol%, based on the total amount of the monomer A.

[0082] Examples of other monomers include ethylene, propylene, vinyl chloride, vinylidene chloride, chlorotrifluoroethylene, fluoroalkylethylene, and monomers having two or more polymerizable unsaturated bonds (hereinafter also referred to as "BO").

[0083] BO is a monomer having two or more polymerizable unsaturated bonds. Specific 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). A carbon atom-carbon atom double bond (C═C) is more preferred as the polymerizable unsaturated bond. The number of polymerizable unsaturated bonds in BO is preferably 2 to 6, more preferably 2 or 3, and even more preferably 2, in terms of superior polymerization reactivity. BO preferably further contains a fluorine atom in terms of reducing the compression set of a crosslinked rubber article at high temperatures.

[0084] BO is preferably a monomer represented by formula (B1) in view of better releasability of the crosslinked rubber article. ２１ R ２２ =CR ２３ -) ａ１ R ２４ (B1) In formula (B1), R ２１ , R ２２ and R ２３ are each independently a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group, a1 is an integer of 2 to 6, and R ２４ is a monovalent 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 the perfluorohydrocarbon group, ２１ , multiple R ２２ and multiple R ２３ may be the same or different, and are preferably the same. a1 is preferably 2 or 3, and more preferably 2. In terms 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 , R２２ and R ２３ It is more preferred that all of R are fluorine atoms or all of R are hydrogen atoms, and in view of better mold releasability of the crosslinked rubber article, ２１ , R ２２ and R ２３ It is more preferable that all of R are fluorine atoms. ２４ R may be any of linear, branched, and cyclic, preferably linear or branched, and more 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 R may or may not have an etheric oxygen atom, but preferably 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 ２４ It is preferred that the nucleotide sequence is located at the end of the nucleotide sequence.

[0085] Of the monomers represented by formula (B1), specific examples of suitable monomers include the monomers represented by formula (B2) and the monomers represented by formula (B3).

[0086] (CF ２ =CF-) ２ R ３１ (B2) In formula (B2), R ３１ is 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 the perfluorohydrocarbon group.

[0087] (CH ２ =CH-) ２ R ４１ (B3) In formula (B3), R ４１ is 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 the perfluorohydrocarbon group.

[0088] Specific examples of the monomer represented by the formula (B2) include CF ２ =CFO(CF ２ ) ２ OCF=C F ２ 、CF ２ =CFO(CF ２ ) ３ OCF=C F ２ 、CF ２ =CFO(CF ２ ) ４ OCF=C F ２ 、CF ２ =CFO(CF ２ ) ６ OCF=C F ２、 CF ２ =CFO(CF ２ ) ８ OCF=C F ２ 、CF ２ =CFO(CF ２ ) ２ OCF(CF ３ )CF ２ OCF=C F ２ 、CF ２ =CFO(CF ２ ) ２ O(CF(CF ３ )CF ２ O) ２ CF=C F ２ 、CF ２ =CFO C F ２ O(CF ２ )CF ２ O)[[ID=7�]] ２ CF=C F ２ 、CF ２ =CFO(CF ２ O) ３ O(CF(CF ３ )CF ２ O) ２ CF=C F ２ 、CF ２ =CFO C F ２ CF(CF ３ )O(CF ２ ) ２ OCF(CF ３ )CF ２ OCF=C F ２ 、及び、CF ２ =CFO C F ２ CF ２O (CF ２ O) ２ CF ２ CF ２ OCF = CF ２ Examples include:

[0089] Among the monomers represented by formula (B2), 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").

[0090] Specific examples of the monomer represented by formula (B3) 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 Examples include:

[0091] Among the monomers represented by formula (B3), a more preferred specific example of the monomer is CH ２ =CH(CF ２ ) ６ CH=CH ２ (hereinafter also referred to as "C6DV").

[0092] Among these, BO is preferably C3DVE or C4DVE.

[0093] In particular, the following aspects of the monomer A are preferred: Aspect 1: The monomer A contains a cyano group-containing monomer, TFE, and PAVE. Aspect 2: The monomer A contains a cyano group-containing monomer, TFE, and propylene. Aspect 3: The monomer A contains a cyano group-containing monomer, HFP, and VdF.

[0094] In the case of Aspect 1, the amount of PAVE used is preferably 20 to 95 mol%, more preferably 25 to 80 mol%, and even more preferably 30 to 60 mol%, based on the total amount of TFE and PAVE used. The same applies to the case where PMVE or PPVE is used as PAVE. In the case of Aspect 1, the same applies to the case where TFE and PAVE used in total is preferably 80 to 99.9 mol%, more preferably 90 to 99.5 mol%, and even more preferably 95 to 99 mol%, based on the amount of monomer A used. The same applies to the case where PMVE or PPVE is used as PAVE.

[0095] In the case of Aspect 2, the amount of propylene used is preferably 5 to 90 mol%, more preferably 8 to 70 mol%, and still more preferably 10 to 60 mol%, based on the total amount of TFE and propylene used. In the case of Aspect 2, the total amount of TFE and propylene used is preferably 60 to 99.9 mol%, more preferably 70 to 99.5 mol%, and still more preferably 80 to 99 mol%, based on the amount of monomer A used.

[0096] In the case of Aspect 3, the amount of VdF used is preferably 5 to 90 mol %, more preferably 8 to 80 mol %, and even more preferably 10 to 70 mol %, based on the total amount of HFP and VdF used. In the case of Aspect 3, the amount of HFP and VdF used is preferably 40 to 100 mol %, more preferably 50 to 100 mol %, and even more preferably 60 to 100 mol %, based on the amount of Monomer A used.

[0097] From the viewpoint of polymerization reactivity, it is preferable that the monomer A is substantially free of other monomers. "Substantially free of other monomers" means that the content of the other monomers is 10 mol % or less, more preferably 0 mol %, based on the total amount of the monomer A.

[0098] <Polymerization initiator> A polymerization initiator may be used in Production Method A. The polymerization initiator used in Production Method A is preferably a water-soluble polymerization initiator, more preferably a persulfate such as ammonium persulfate, sodium persulfate, or potassium persulfate, or an organic polymerization initiator such as disuccinic acid peroxide or azobisisobutylamidine dihydrochloride, still more preferably a persulfate, and particularly preferably ammonium persulfate.

[0099] 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, relative to 100 parts by mass of the amount of the monomer A used.

[0100] When a polymerization initiator is used, the polymerization initiator may be added to the reactor all at once or in divided portions. When the polymerization initiator is added in divided portions, the polymerization initiator may be added in multiple stages or continuously.

[0101] The polymerization temperature is preferably 10 to 95° C., more preferably 15 to 90° C. The polymerization pressure is preferably 0.5 to 4.0 MPaG, more preferably 0.6 to 3.5 MPaG. The polymerization time is preferably 90 to 1,000 minutes, more preferably 90 to 800 minutes.

[0102] <Fluorine-containing elastomer> In the present production method A, for example, an aqueous dispersion A containing fluorine-containing elastomer particles is obtained by carrying out a step of polymerizing a monomer A. The fluorine-containing elastomer obtained by the present production method A does not fall under the category of an emulsifier having a fluorine atom.

[0103] The average particle size of the fluorine-containing elastomer particles is preferably 500 nm or less, and from the viewpoint of particle dispersion stability, more preferably 300 nm or less, even more preferably 200 nm or less, and particularly preferably 150 nm or less. The lower limit is preferably 2 nm or more, more preferably 5 nm or more, and even more preferably 10 nm or more. The average particle size of the fluorine-containing elastomer particles can be calculated by analyzing the autocorrelation function obtained by dynamic light scattering using the monodisperse cumulant method, or D50 (median diameter). The D50 is the particle size at the point on the cumulative curve where the cumulative volume is 50% when the particle size distribution is measured by laser diffraction / scattering and the total volume of the particle population is taken as 100%. Specific methods for measuring the average particle size include the methods described in the Examples below.

[0104] The fluorine-containing elastomer preferably does not have a melting point. Specific methods for measuring the melting point include the methods shown in the Examples section.

[0105] The fluorine-containing elastomer obtained by Production Method A is obtained by polymerizing monomer A. The compound (X) used in Production Method A may or may not be copolymerized with monomer A. The fluorine-containing elastomer may or may not contain a structural unit based on compound (X).

[0106] The content of the structural units based on the cyano group-containing monomer is preferably 0.1 to 15 mol %, more preferably 0.3 to 10 mol %, based on the total amount of the fluorine-containing elastomer. The content of the structural units based on at least one selected from the group consisting of TFE, HFP, VdF, fluorine-containing vinyl ethers and fluorine-containing allyl ethers is preferably 80 to 99.5 mol %, more preferably 90 to 99.7 mol %, based on the total amount of the fluorine-containing elastomer.

[0107] The fluorine-containing elastomer preferably has the following embodiments: Embodiment 1: The fluorine-containing elastomer contains a structural unit based on a cyano group-containing monomer, a structural unit based on TFE, and a structural unit based on PAVE. Embodiment 2: The fluorine-containing elastomer contains a structural unit based on a cyano group-containing monomer, a structural unit based on TFE, and a structural unit based on propylene. Embodiment 3: The fluorine-containing elastomer contains a structural unit based on a cyano group-containing monomer, a structural unit based on HFP, and a structural unit based on VdF.

[0108] In the case of Aspect 1, the content of the structural units based on TFE is preferably 25 to 85 mol%, more preferably 35 to 75 mol%, based on the total amount of the fluorine-containing elastomer. In the case of Aspect 1, the content of the structural units based on PAVE is preferably 10 to 70 mol%, more preferably 20 to 60 mol%, based on the total amount of the fluorine-containing elastomer. The suitable content is similar when PMVE or PPVE is used as the PAVE.

[0109] In the case of Aspect 2, the content of the structural units based on TFE is preferably 15 to 75 mol %, more preferably 25 to 65 mol %, based on the total amount of the fluoroelastomer. In the case of Aspect 2, the content of the structural units based on propylene is preferably 20 to 80 mol %, more preferably 30 to 70 mol %, based on the total amount of the fluoroelastomer.

[0110] In the case of Aspect 3, the content of the structural units based on HFP is preferably 5 to 40 mol %, more preferably 10 to 30 mol %, based on the total amount of the fluorine-containing elastomer. In the case of Aspect 3, the content of the structural units based on VdF is preferably 5 to 85 mol %, more preferably 15 to 75 mol %, based on the total amount of the fluorine-containing elastomer.

[0111] The fluorine-containing elastomer obtained by Production Method A preferably exhibits a weight loss rate of 2.0% or less 1,000 minutes after the start of heating when heated in a nitrogen atmosphere under the following condition 1: (Condition 1) Heat from 40°C to 90°C at a heating rate of 20°C / min, hold at 90°C for 120 minutes, heat from 90°C to 200°C at a heating rate of 20°C / min, hold at 200°C for 240 minutes, heat from 200°C to 305°C at a heating rate of 20°C / min, and hold at 305°C for 720 minutes.

[0112] The method for calculating the weight loss rate will be described in detail later.

[0113] From the viewpoint of achieving excellent compression set of the crosslinked rubber article, the weight loss rate is preferably 1.5% by mass or less, and more preferably 1.3% by mass or less. The lower limit is 0% by mass, and may be 0.1% by mass or more.

[0114] <Other Steps> The present production method A may include steps other than the step of polymerizing the monomer A.

[0115] Other steps include, for example, a step of aggregating the aqueous dispersion A and filtering the agglomerated aqueous dispersion A to obtain particles of the fluorine-containing elastomer.

[0116] Examples of aggregation methods include, but are not limited to, freeze aggregation, acid aggregation, base aggregation, mechanical aggregation, and aggregation using a coagulant. A specific example of mechanical aggregation is a method in which aqueous dispersion A is vigorously stirred to apply shear force to aggregate the primary particles of the fluorine-containing elastomer. If necessary, the pH of aqueous dispersion A may be adjusted, or an aggregation aid such as an electrolyte or a water-soluble organic solvent may be added. The aqueous dispersion A may also be diluted with water in advance so that the fluorine-containing elastomer concentration in the aqueous dispersion A is 8 to 20% by mass. Examples of pH adjusters include sodium carbonate and sodium bicarbonate. Mechanical aggregation can also be performed in the presence of one or more compounds selected from the group consisting of ammonia, ammonium salts, and urea. Examples of electrolytes include inorganic salts such as potassium nitrate, sodium nitrate, sodium carbonate, and sodium bicarbonate. Examples of water-soluble organic solvents include alcohols and acetone. In the case of freeze aggregation, the aggregation temperature is preferably −20 to 0°C. The aggregation time is preferably 1 hour or more, more preferably 2 hours or more. In the case of acid aggregation, a method in which an acid-containing solution is added to aqueous dispersion A is preferred. Examples of the acid to be added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, and hydrofluoric acid, with nitric acid being preferred. The concentration of the acid in the acid-containing solution is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 20% by mass. A method of adding a solution containing a base to aqueous dispersion A is preferred for base coagulation. Examples of the base to be added include sodium hydroxide, potassium hydroxide, and ammonium carbonate, with sodium hydroxide being preferred. The concentration of the base in the base-containing solution is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. For coagulation using a coagulant, known coagulants can be used. Known coagulants include aluminum salts, calcium salts, magnesium salts, and ammonium salts. Specifically, ammonium carbonate, aluminum sulfate, and compounds of the general formula M'Al(SO ４ ) ２ ・12H ２0 (wherein M' is a monovalent cation other than lithium), calcium nitrate, and magnesium sulfate are exemplified, with alum being preferred, and potassium alum, where M is potassium, being more preferred.

[0117] [Method for producing fluorine-containing elastomer] A second aspect of the method for producing a fluorine-containing elastomer of the present disclosure (hereinafter also referred to as "the present production method B") comprises the steps of: polymerizing a first monomer comprising a cyano group-containing monomer and at least one selected from the group consisting of TFE, HFP, VdF, fluorine-containing vinyl ether, and fluorine-containing allyl ether in a first aqueous medium in the substantial absence of an emulsifier having a fluorine atom to produce a first fluorine-containing polymer and obtaining an aqueous dispersion containing the first fluorine-containing polymer (hereinafter also referred to as "the first polymerization step"); and polymerizing a second monomer comprising TFE in the aqueous dispersion containing the first fluorine-containing polymer to obtain a second fluorine-containing polymer, thereby obtaining a fluorine-containing elastomer comprising the first fluorine-containing polymer and the second fluorine-containing polymer (hereinafter also referred to as "the second polymerization step").

[0118] According to this production method B, by including two steps, namely, a step of polymerizing a first monomer containing a cyano group-containing monomer and a step of polymerizing a second monomer containing TFE, a fluorine-containing elastomer can be obtained that can give crosslinked rubber articles having small compression set and excellent surface smoothness. In contrast, Patent Document 1 does not describe anything that focuses on the above two steps.

[0119] The present production method B may include other steps as needed. Examples of other steps include a purification step in which the dispersion containing the first fluorine-containing polymer obtained through the first polymerization step is purified, and a concentration adjustment step in which the solids concentration of the dispersion containing the first fluorine-containing polymer is adjusted. In the present production method B, for example, after the first polymerization step, a purification step and a concentration adjustment step are continuously carried out as needed, and then the second polymerization step is carried out. In the present production method B, for example, the first polymerization step, the purification step, the concentration adjustment step, and the second polymerization step are continuously carried out.

[0120] The present production method B may include other steps as necessary, such as a purification step of subjecting the dispersion containing the first fluoropolymer obtained through the first polymerization step to a purification treatment, and a concentration adjustment step of adjusting the solids concentration of the dispersion containing the first fluoropolymer.

[0121] [First Polymerization Step] <Emulsifier> The first polymerization step of Production Method B is carried out in the substantial absence of an emulsifier having a fluorine atom.

[0122] The first polymerization step is preferably carried out in the substantial absence of an emulsifier, in order to prevent a decrease in the molecular weight of the fluorine-containing elastomer to be produced.

[0123] Examples of the emulsifier include the emulsifiers described above.

[0124] The phrase "substantially free of an emulsifier having a fluorine atom" means that in the first polymerization step, the content of the emulsifier having a fluorine atom is 10 ppm by mass or less, preferably 150 ppb by mass or less, and more preferably 50 ppb by mass or less, relative to the total amount of the first aqueous medium. The lower limit is 0 ppb by mass.

[0125] The term "substantially free of emulsifier" means that the content of the emulsifier in the first polymerization step is 10 ppm by mass or less, preferably 150 ppb by mass or less, and more preferably 50 ppb by mass or less, based on the total amount of the first aqueous medium. The lower limit is 0 ppb by mass.

[0126] <First aqueous medium> The first polymerization step of Production Method B is carried out in the presence of a first aqueous medium. Specific examples of the first aqueous medium are the same as those of the aqueous medium described above.

[0127] Before starting polymerization of the first monomer used in polymerization of the first fluoropolymer, the content of the aqueous medium is preferably 20 to 80% by volume, more preferably 40 to 70% by volume, relative to the volume of the reactor. In the present disclosure, "before starting polymerization of the first monomer used in polymerization of the first fluoropolymer" means immediately before the start of polymerization. Here, examples of "start of polymerization" include the time when the first monomer is introduced into the reactor after the temperature inside the reactor has been raised to a polymerization temperature or higher, and the time when the temperature inside the reactor has been raised to a polymerization temperature or higher after the first monomer has been introduced into the reactor.

[0128] It is preferable that the first aqueous medium further contains a compound (X). Preferred aspects of the compound (X) are as described above. When the first aqueous medium contains the compound (X), the dispersibility of the first fluoropolymer produced is improved, polymerization proceeds more easily, and a first fluoropolymer having a high molecular weight and a large number of particles is obtained. Then, in the second polymerization step carried out continuously after the first polymerization step, the large number of particles of the first fluoropolymer, which serves as a polymerization site for the second monomer, improves the dispersion stability of the second fluoropolymer.

[0129] The amount of compound (X) added is preferably 0.1 to 5000 ppm by mass, more preferably 0.2 to 1000 ppm by mass, still more preferably 0.3 to 500 ppm by mass, and particularly preferably 0.5 to 100 ppm by mass, relative to the total amount of the first aqueous medium.

[0130] <First Monomer> In the first polymerization step of Production Method B, a first monomer including a cyano group-containing monomer and at least one selected from the group consisting of TFE, HFP, VdF, a fluorinated vinyl ether, and a fluorinated allyl ether is polymerized.

[0131] Preferred embodiments of the cyano group-containing monomer, the fluorine-containing vinyl ether, and the fluorine-containing allyl ether are as described above.

[0132] From the viewpoint of obtaining excellent physical properties of the crosslinked rubber article, the content of the cyano group-containing monomer is preferably 0.5 to 20 mol %, more preferably 0.2 to 20 mol %, still more preferably 0.3 to 15 mol %, and particularly preferably 0.5 to 10 mol %, based on the total amount of the first monomer.

[0133] From the viewpoint of polymerization reactivity, the first monomer preferably contains a cyano group-containing monomer, TFE, and a fluorinated vinyl ether, and more preferably contains a cyano group-containing monomer, TFE, and PAVE.

[0134] When the first monomer contains TFE, the content of TFE is preferably 10 to 90 mol%, more preferably 20 to 80 mol%, still more preferably 30 to 70 mol%, particularly preferably 40 to 60 mol%, based on the total amount of the first monomer.

[0135] When the first monomer contains a fluorinated vinyl ether, the content of the fluorinated vinyl ether is preferably 10 to 90 mol %, more preferably 20 to 80 mol %, still more preferably 30 to 70 mol %, particularly preferably 40 to 60 mol %, based on the total amount of the first monomer.

[0136] When the first monomer contains a fluorinated allyl ether, the content of the fluorinated allyl ether is preferably 10 to 90 mol%, more preferably 20 to 80 mol%, still more preferably 30 to 70 mol%, particularly preferably 40 to 60 mol%, based on the total amount of the first monomer.

[0137] The first monomer may contain at least one other monomer selected from the group consisting of the cyano group-containing monomer, TFE, HFP, VdF, fluorinated vinyl ether, and fluorinated allyl ether, such as ethylene, propylene, vinyl chloride, vinylidene chloride, chlorotrifluoroethylene, fluoroalkylethylene, and BO.

[0138] The preferred embodiments of BO that may be contained as another monomer are as described above.

[0139] From the viewpoint of polymerization reactivity, it is preferable that the first monomer is substantially free of other monomers. "Substantially free of other monomers" means that the content of the other monomers is 10 mol % or less, more preferably 0 mol %, based on the total amount of the first monomer.

[0140] <Polymerization initiator> A polymerization initiator may be used in the first polymerization step of the present production method B. Preferred embodiments of the polymerization initiator are as described above.

[0141] 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 first monomer used.

[0142] When a polymerization initiator is used, the polymerization initiator may be added to the reactor all at once or in divided portions. When the polymerization initiator is added in divided portions, the polymerization initiator may be added in multiple stages or continuously.

[0143] The polymerization temperature is preferably 10 to 95° C., more preferably 15 to 90° C. The polymerization pressure is preferably 0.5 to 4.0 MPaG, more preferably 0.6 to 3.5 MPaG. The polymerization time is preferably 10 to 300 minutes, more preferably 30 to 200 minutes.

[0144] In the first polymerization step of the present production method B, for example, an aqueous dispersion B1 containing a first fluorine-containing polymer is obtained by carrying out a step of polymerizing a first monomer.

[0145] <First Fluorine-Containing Polymer> The first fluorine-containing polymer contains a structural unit based on a first monomer. That is, the first fluorine-containing polymer contains a structural unit based on a cyano group-containing monomer and a structural unit based on at least one selected from the group consisting of TFE, HFP, VdF, a fluorine-containing vinyl ether, and a fluorine-containing allyl ether. The compound (X) contained in the first aqueous medium may or may not be copolymerized with the first monomer. The first fluorine-containing polymer may contain a structural unit based on the compound (X), or may not contain a structural unit based on the compound (X). The first fluorine-containing polymer does not fall under the category of an emulsifier having a fluorine atom.

[0146] The content of the structural units based on the cyano group-containing monomer is preferably 0.1 to 10 mol %, more preferably 0.5 to 5 mol %, relative to the total amount of the first fluorine-containing polymer. The content of the structural units based on the fluorine-containing monomer is preferably 90 to 99.9 mol %, more preferably 95 to 99.5 mol %, relative to the total amount of the first fluorine-containing polymer.

[0147] The first fluorine-containing polymer preferably contains a structural unit based on a cyano group-containing monomer, a structural unit based on TFE, and a structural unit based on a fluorine-containing vinyl ether, and more preferably contains a structural unit based on a cyano group-containing monomer, a structural unit based on TFE, and a structural unit based on PAVE.

[0148] When the first fluorine-containing polymer contains structural units based on TFE, the content of the structural units based on TFE is preferably from 10 to 90 mol %, more preferably from 20 to 80 mol %, based on the total amount of the first fluorine-containing polymer.

[0149] When the first fluorine-containing polymer contains constituent units based on PAVE, the content of the constituent units based on PAVE is preferably from 10 to 90 mol %, more preferably from 20 to 80 mol %, based on the total amount of the first fluorine-containing polymer. The suitable content is similar when PMVE or PPVE is used as PAVE.

[0150] The first fluorine-containing polymer preferably has the following embodiments: Embodiment 1: The first fluorine-containing polymer contains structural units based on a cyano group-containing monomer, structural units based on TFE, and structural units based on PAVE. Embodiment 2: The first fluorine-containing polymer contains structural units based on a cyano group-containing monomer, structural units based on TFE, and structural units based on propylene. Embodiment 3: The first fluorine-containing polymer contains structural units based on a cyano group-containing monomer, structural units based on HFP, and structural units based on VdF.

[0151] In the case of Aspect 1, the content of structural units based on TFE is preferably 25 to 85 mol%, more preferably 35 to 75 mol%, based on the total amount of the first fluoropolymer. In the case of Aspect 1, the content of structural units based on PAVE is preferably 10 to 70 mol%, more preferably 20 to 60 mol%, based on the total amount of the first fluoropolymer. The suitable content is similar when PMVE or PPVE is used as PAVE.

[0152] In the case of Aspect 2, the content of the structural units based on TFE is preferably from 15 to 75 mol %, more preferably from 25 to 65 mol %, based on the total amount of the first fluoropolymer. In the case of Aspect 2, the content of the structural units based on propylene is preferably from 20 to 80 mol %, more preferably from 30 to 70 mol %, based on the total amount of the first fluoropolymer.

[0153] In the case of Aspect 3, the content of the structural units based on HFP is preferably from 5 to 40 mol %, and more preferably from 10 to 30 mol %, relative to the total amount of the first fluorinated polymer. In the case of Aspect 3, the content of the structural units based on VdF is preferably from 5 to 85 mol %, and more preferably from 15 to 75 mol %, relative to the total amount of the first fluorinated polymer.

[0154] The first fluorine-containing polymer preferably does not have a melting point. "Doing not have a melting point" means that when the melting point of the first fluorine-containing polymer is measured using a differential scanning calorimeter, no melting peak is observed, specifically, no melting peak is observed in a temperature range of 150°C or higher (preferably a temperature range of 150 to 330°C). Note that a glass transition peak does not fall under the category of the above-mentioned melting peak. Specific methods for measuring the melting point include the measurement methods shown in the Examples section.

[0155] [Purification Step] In the purification step, which is optionally included in Production Method B, the dispersion containing the first fluoropolymer obtained through the first polymerization step is subjected to a purification treatment. In the purification step, the dispersion obtained through the first polymerization step may be directly subjected to the purification treatment, or the purification treatment may be performed after adjusting the solids concentration of the dispersion through a concentration adjustment step described below. Production Method B preferably includes a purification step in that a second fluoropolymer having desired physical properties can be easily obtained. In other words, it is preferable to polymerize the second monomer in the second polymerization step using the aqueous dispersion after purification treatment in the purification step. By passing through the purification step, impurities such as the polymerization initiator and its decomposition products can be removed, making it easier to obtain a fluoroelastomer with desired physical properties. Purification methods include heat treatment and a method of removal using an ion exchange resin, and a method of contacting the dispersion to be purified with an ion exchange resin is preferred.

[0156] The ion exchange resin is preferably a cation exchange resin or an anion exchange resin. The amount of the ion exchange resin used is preferably 1 to 100 parts by mass, more preferably 1 to 50 parts by mass, per 100 parts by mass of the dispersion to be purified. Specific examples of methods for contacting the dispersion to be purified with the ion exchange resin include a method of mixing the dispersion to be purified with the ion exchange resin and a method of passing the dispersion to be purified through a column packed with an ion exchange resin. The purification treatment may be carried out multiple times.

[0157] [Concentration Adjustment Step] In the concentration adjustment step, which is optionally included in Production Method B, the solids concentration of the dispersion containing the first fluorine-containing polymer may be adjusted. In the concentration adjustment step, for example, at least one of removal of the aqueous medium and addition of an aqueous medium is performed on the dispersion obtained in the first polymerization step or the dispersion that has been subjected to the purification step. In the concentration adjustment step, the solids concentration may be adjusted by removing only a portion of the aqueous medium contained in the dispersion, or solvent substitution may be performed in which the aqueous medium contained in the dispersion is removed and another aqueous medium is added. When an aqueous medium is added in the concentration adjustment step, the aqueous medium added may be the same type of aqueous medium as the first aqueous medium, or may be a different type of aqueous medium.

[0158] [Second polymerization step] In the second polymerization step of present production method B, a second monomer containing TFE is polymerized in an aqueous dispersion containing the first fluoropolymer to give a fluorine-containing elastomer containing the first fluoropolymer and the second fluoropolymer.

[0159] <Aqueous Dispersion> The aqueous dispersion used in the second polymerization step may be the dispersion after the first polymerization step used as is, or the dispersion after the first polymerization step which has been subjected to at least one of a purification step and a concentration adjustment step. In terms of facilitating the production of a second fluoropolymer having desired physical properties, it is preferred to use the dispersion after the first polymerization step which has been subjected to at least a purification step as the aqueous dispersion.

[0160] The content of the first fluoropolymer is preferably 0.01 to 10.0% by mass, and more preferably 0.01 to 5.0% by mass, relative to the total amount of the aqueous dispersion, from the viewpoint of more efficiently producing the second fluoropolymer. In particular, it is preferable that the above range is satisfied before the start of polymerization of the second monomer.

[0161] The aqueous medium contained in the aqueous dispersion used in the second polymerization step is referred to as the second aqueous medium. Specific examples of the second aqueous medium include those similar to those of the first aqueous medium. The type of the second aqueous medium may be the same as or different from the type of the first aqueous medium.

[0162] Before the polymerization of the second monomer is initiated, the aqueous dispersion may contain components other than the various components described above. Specific examples of other components that the aqueous dispersion may contain include a chain transfer agent, a reducing agent, and a pH adjuster. Specific examples of chain transfer agents include ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, 1,4-diiodoperfluorobutane, and propane. Specific examples of pH adjusters include inorganic salts and ammonia. Specific examples of inorganic salts include phosphates such as disodium hydrogen phosphate and sodium dihydrogen phosphate, and carbonates such as sodium bicarbonate and sodium carbonate. Specific examples of more preferred phosphates include disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate.

[0163] When the aqueous dispersion contains a chain transfer agent, the content of the chain transfer agent is preferably 0.1 to 5 parts by mass relative to 100 parts by mass of the second aqueous medium. When the aqueous dispersion contains a pH adjuster, the content of the pH adjuster is preferably 0.01 to 3.0 parts by mass relative to 100 parts by mass of the second aqueous medium.

[0164] <Second Monomer> The second monomer includes TFE.

[0165] The second monomer may include a monomer other than TFE.

[0166] Examples of the monomer other than TFE include ethylene, propylene, vinyl chloride, vinylidene chloride, chlorotrifluoroethylene, fluoroalkylethylene, VdF, HFP, fluorine-containing vinyl ether, fluorine-containing allyl ether, and BO.

[0167] The preferred embodiments of BO that may be contained as another monomer are as described above.

[0168] From the viewpoint of providing excellent physical properties of the crosslinked rubber article, the second monomer preferably includes at least one selected from the group consisting of fluorinated vinyl ethers and fluorinated allyl ethers, and from the viewpoint of providing excellent physical properties of the crosslinked rubber article, the second monomer preferably includes a cyano group-containing monomer.

[0169] Preferred embodiments of the fluorine-containing vinyl ether, the fluorine-containing allyl ether, and the cyano group-containing monomer are as described above.

[0170] The content of TFE is preferably from 10 to 90 mol %, more preferably from 20 to 80 mol %, and even more preferably from 30 to 70 mol %, based on the content of the second monomer.

[0171] Among these, the second monomer preferably contains TFE and a fluorinated vinyl ether, more preferably contains TFE, a fluorinated vinyl ether, and a cyano group-containing monomer, and even more preferably contains TFE, PAVE, and a cyano group-containing monomer.

[0172] When the second monomer contains a constituent unit based on PAVE, the content of PAVE is preferably 10 to 90 mol %, more preferably 20 to 80 mol %, based on the total amount of the second monomer. The same suitable content applies when PMVE or PPVE is used as PAVE.

[0173] When the second monomer contains a cyano group-containing monomer, the content of the cyano group-containing monomer is preferably 0.1 to 10 mol %, more preferably 0.5 to 5 mol %, based on the total amount of the second monomer.

[0174] The amount of the second monomer used is preferably 1 to 60 parts by mass, more preferably 5 to 50 parts by mass, and even more preferably 10 to 40 parts by mass, per 100 parts by mass of the second aqueous medium used.

[0175] <Polymerization initiator> A polymerization initiator may be used in the second polymerization step of the present production method B. Preferred embodiments of the polymerization initiator are as described above.

[0176] 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 second monomer used.

[0177] When a polymerization initiator is used, the polymerization initiator may be added to the reactor all at once or in divided portions. When the polymerization initiator is added in divided portions, the polymerization initiator may be added in multiple stages or continuously.

[0178] The polymerization temperature is preferably 10 to 95° C., more preferably 15 to 90° C. The polymerization pressure is preferably 0.5 to 4.0 MPaG, more preferably 0.6 to 3.5 MPaG. The polymerization time is preferably 90 to 1,000 minutes, more preferably 90 to 800 minutes.

[0179] <Steps> The second polymerization step of Production Method B is preferably carried out under conditions substantially free of an emulsifier having a fluorine atom, and more preferably under conditions substantially free of an emulsifier.

[0180] Examples of the emulsifier include the emulsifiers described above.

[0181] The phrase "substantially free of an emulsifier having a fluorine atom" means that in the second polymerization step, the content of the emulsifier having a fluorine atom is 10 ppm by mass or less, preferably 150 ppb by mass or less, and more preferably 50 ppb by mass or less, relative to the total amount of the first aqueous medium. The lower limit is 0 ppb by mass.

[0182] The term "substantially free of emulsifier" means that the content of the emulsifier in the second polymerization step is 10 ppm by mass or less, preferably 150 ppb by mass or less, and more preferably 50 ppb by mass or less, based on the total amount of the second aqueous medium. The lower limit is 0 ppb by mass.

[0183] Particles of the second fluorine-containing polymer are produced in the second polymerization step of present production method B. Specifically, by the method for producing the second fluorine-containing polymer, an aqueous dispersion in which particles of the second fluorine-containing polymer are dispersed in the above aqueous medium is obtained.

[0184] <Second Fluorine-Containing Polymer> The second fluorine-containing polymer contains structural units based on a second monomer. That is, the second fluorine-containing polymer contains structural units based on TFE. The second fluorine-containing polymer does not fall under the category of an emulsifier having a fluorine atom.

[0185] Among these, the second fluorine-containing polymer preferably contains a structural unit based on TFE and a structural unit based on a fluorine-containing vinyl ether, more preferably a structural unit based on TFE, a structural unit based on a fluorine-containing vinyl ether and a structural unit based on a cyano group-containing monomer, and still more preferably a structural unit based on TFE, a structural unit based on PAVE and a structural unit based on a cyano group-containing monomer.

[0186] <Fluorine-containing elastomer> A fluorine-containing elastomer containing the first fluorine-containing polymer and the second fluorine-containing polymer is obtained by carrying out the second polymerization step of Production Method B. The fluorine-containing elastomer obtained by Production Method B does not fall under the category of an emulsifier having a fluorine atom.

[0187] The content of the structural units based on the cyano group-containing monomer is preferably 0.1 to 10 mol %, more preferably 0.3 to 5 mol %, based on the total amount of the fluorine-containing elastomer. The content of the structural units based on TFE is preferably 10 to 90 mol %, more preferably 20 to 80 mol %, based on the total amount of the fluorine-containing elastomer.

[0188] The fluorine-containing elastomer preferably contains a structural unit based on a cyano group-containing monomer, a structural unit based on TFE, and a structural unit based on a fluorine-containing vinyl ether, and more preferably contains a structural unit based on a cyano group-containing monomer, a structural unit based on TFE, and a structural unit based on PAVE.

[0189] When the fluorine-containing elastomer contains a constituent unit based on PAVE, the content of the constituent unit based on PAVE is preferably 10 to 90 mol %, more preferably 20 to 80 mol %, based on the total amount of the fluorine-containing elastomer. The suitable content is similar when PMVE or PPVE is used as the PAVE.

[0190] The fluorine-containing elastomer preferably has the following embodiments: Embodiment 1: The fluorine-containing elastomer contains a structural unit based on a cyano group-containing monomer, a structural unit based on TFE, and a structural unit based on PAVE. Embodiment 2: The fluorine-containing elastomer contains a structural unit based on a cyano group-containing monomer, a structural unit based on TFE, and a structural unit based on propylene. Embodiment 3: The fluorine-containing elastomer contains a structural unit based on a cyano group-containing monomer, a structural unit based on HFP, and a structural unit based on VdF.

[0191] In the case of Aspect 1, the content of the structural units based on TFE is preferably 25 to 85 mol%, more preferably 35 to 75 mol%, based on the total amount of the fluorine-containing elastomer. In the case of Aspect 1, the content of the structural units based on PAVE is preferably 10 to 70 mol%, more preferably 20 to 60 mol%, based on the total amount of the fluorine-containing elastomer. The suitable content is similar when PMVE or PPVE is used as the PAVE.

[0192] In the case of Aspect 2, the content of the structural units based on TFE is preferably 15 to 75 mol %, more preferably 25 to 65 mol %, based on the total amount of the fluoroelastomer. In the case of Aspect 2, the content of the structural units based on propylene is preferably 20 to 80 mol %, more preferably 30 to 70 mol %, based on the total amount of the fluoroelastomer.

[0193] In the case of Aspect 3, the content of the structural units based on HFP is preferably 5 to 40 mol %, more preferably 10 to 30 mol %, based on the total amount of the fluorine-containing elastomer. In the case of Aspect 3, the content of the structural units based on VdF is preferably 5 to 85 mol %, more preferably 15 to 75 mol %, based on the total amount of the fluorine-containing elastomer.

[0194] After the second polymerization step of Production Method B, for example, a dispersion in which a fluorine-containing elastomer containing the first fluorine-containing polymer and the second fluorine-containing polymer is dispersed in the second aqueous medium is obtained.

[0195] In the dispersion, the first fluorine-containing polymer and the second fluorine-containing polymer are preferably present in the form of particles. The first fluorine-containing polymer and the second fluorine-containing polymer may be present separately in the dispersion, but are preferably present in the form of particles containing the first fluorine-containing polymer and the second fluorine-containing polymer, and more preferably present in the form of particles consisting of the first fluorine-containing polymer and the second fluorine-containing polymer (i.e., particles of a fluorine-containing elastomer).

[0196] In this case, the average particle size of the fluorine-containing elastomer particles is more preferably 400 nm or less, even more preferably 350 nm or less, and particularly preferably 300 nm or less. The lower limit is preferably 10 nm or more, more preferably 30 nm or more, and even more preferably 50 nm or more. The method for measuring the average particle size of the particles is as described above.

[0197] The fluorine-containing elastomer preferably does not have a melting point. Specific methods for measuring the melting point include the methods shown in the Examples section.

[0198] The fluorine-containing elastomer obtained by Production Method B preferably exhibits a weight loss rate of 2.0% or less 1,000 minutes after the start of heating when heated in a nitrogen atmosphere under the following condition 1: (Condition 1) Heat from 40°C to 90°C at a heating rate of 20°C / min, hold at 90°C for 120 minutes, heat from 90°C to 200°C at a heating rate of 20°C / min, hold at 200°C for 240 minutes, heat from 200°C to 305°C at a heating rate of 20°C / min, and hold at 305°C for 720 minutes.

[0199] The method for calculating the weight loss rate will be described in detail later.

[0200] From the viewpoint of achieving excellent physical properties and surface smoothness of the crosslinked rubber article, the weight loss rate is preferably 1.5% by mass or less, and more preferably 1.3% by mass or less. The lower limit is 0% by mass, and may be 0.1% by mass or more.

[0201] [Composition] The composition of the present disclosure (hereinafter also referred to as "the composition") comprises compound (X), a first fluorine-containing polymer comprising structural units based on a cyano group-containing monomer and structural units based on at least one selected from the group consisting of TFE, HFP, VdF, fluorinated vinyl ethers, and fluorinated allyl ethers, and a second fluorine-containing polymer comprising structural units based on TFE, and is substantially free of an emulsifier having a fluorine atom.

[0202] The composition provides crosslinked rubber articles with small compression set and excellent surface smoothness.

[0203] The composition may be a liquid or a solid at 25°C. The composition is, for example, an aqueous dispersion. The composition can be produced, for example, by polymerizing a first monomer containing compound (X), a cyano group-containing monomer, and at least one selected from the group consisting of TFE, HFP, VdF, a fluorinated vinyl ether, and a fluorinated allyl ether in the first polymerization step of the production method B, and then performing the second polymerization step of the production method B.

[0204] <Emulsifier> The present composition is substantially free of an emulsifier having a fluorine atom. "Substantially free of an emulsifier having a fluorine atom" means that the content of the emulsifier having a fluorine atom is 10 mass ppm or less, preferably 150 mass ppb or less, and more preferably 50 mass ppb or less, based on the total amount of the composition. The lower limit of the content of the emulsifier having a fluorine atom is 0 mass ppb.

[0205] The present composition is preferably substantially free of emulsifiers. "Substantially free of emulsifiers" means that the content of emulsifiers is 10 mass ppm or less, preferably 150 mass ppb or less, and more preferably 50 mass ppb or less, based on the total amount of the composition. The lower limit of the emulsifier content is 0 mass ppb.

[0206] <Compound (X)> The present composition contains compound (X). Preferred aspects of compound (X) are as described above. Compound (X) may or may not be present as a structural unit in the first fluorinated polymer described below. That is, the first fluorinated polymer described below may contain a structural unit based on compound (X), or may not contain a structural unit based on compound (X). The content of compound (X) is preferably 0.1 to 5000 ppm by mass, more preferably 0.2 to 1000 ppm by mass, still more preferably 0.3 to 500 ppm by mass, and particularly preferably 0.5 to 100 ppm by mass, relative to the total amount of the present composition.

[0207] <First Fluorine-Containing Polymer> The first fluorine-containing polymer contained in the composition contains a structural unit based on a cyano group-containing monomer and a structural unit based on at least one selected from the group consisting of TFE, HFP, VdF, a fluorine-containing vinyl ether, and a fluorine-containing allyl ether. Preferred embodiments of the cyano group-containing monomer, the fluorine-containing vinyl ether, and the fluorine-containing allyl ether are as described above.

[0208] The first fluorine-containing polymer preferably contains a structural unit based on a cyano group-containing monomer, a structural unit based on TFE, and a structural unit based on a fluorine-containing vinyl ether, and more preferably contains a structural unit based on a cyano group-containing monomer, a structural unit based on TFE, and a structural unit based on PAVE.

[0209] When the first fluorine-containing polymer contains structural units based on TFE, the content of the structural units based on TFE is preferably from 10 to 90 mol %, more preferably from 20 to 80 mol %, based on the total amount of the first fluorine-containing polymer.

[0210] When the first fluorine-containing polymer contains constituent units based on PAVE, the content of the constituent units based on PAVE is preferably from 10 to 90 mol %, more preferably from 20 to 80 mol %, based on the total amount of the first fluorine-containing polymer. The suitable content is similar when PMVE or PPVE is used as PAVE.

[0211] The first fluorine-containing polymer preferably has the following embodiments: Embodiment 1: The first fluorine-containing polymer contains structural units based on a cyano group-containing monomer, structural units based on TFE, and structural units based on PAVE. Embodiment 2: The first fluorine-containing polymer contains structural units based on a cyano group-containing monomer, structural units based on TFE, and structural units based on propylene. Embodiment 3: The first fluorine-containing polymer contains structural units based on a cyano group-containing monomer, structural units based on HFP, and structural units based on VdF.

[0212] In the case of Aspect 1, the content of structural units based on TFE is preferably 25 to 85 mol%, more preferably 35 to 75 mol%, based on the total amount of the first fluoropolymer. In the case of Aspect 1, the content of structural units based on PAVE is preferably 10 to 70 mol%, more preferably 20 to 60 mol%, based on the total amount of the first fluoropolymer. The suitable content is similar when PMVE or PPVE is used as PAVE.

[0213] In the case of Aspect 2, the content of the structural units based on TFE is preferably from 15 to 75 mol %, more preferably from 25 to 65 mol %, based on the total amount of the first fluoropolymer. In the case of Aspect 2, the content of the structural units based on propylene is preferably from 20 to 80 mol %, more preferably from 30 to 70 mol %, based on the total amount of the first fluoropolymer.

[0214] In the case of Aspect 3, the content of the structural units based on HFP is preferably from 5 to 40 mol %, and more preferably from 10 to 30 mol %, relative to the total amount of the first fluorinated polymer. In the case of Aspect 3, the content of the structural units based on VdF is preferably from 5 to 85 mol %, and more preferably from 15 to 75 mol %, relative to the total amount of the first fluorinated polymer.

[0215] The first fluorine-containing polymer preferably does not have a melting point. "Doing not have a melting point" means that when the melting point of the first fluorine-containing polymer is measured using a differential scanning calorimeter, no melting peak is observed, specifically, no melting peak is observed in a temperature range of 150°C or higher (preferably a temperature range of 150 to 330°C). Note that a glass transition peak does not fall under the category of the above-mentioned melting peak. Specific methods for measuring the melting point include the measurement methods shown in the Examples section.

[0216] <Second Fluorine-Containing Polymer> The second fluorine-containing polymer contains structural units based on TFE.

[0217] Among these, the second fluorine-containing polymer preferably contains a structural unit based on TFE and a structural unit based on a fluorine-containing vinyl ether, more preferably a structural unit based on TFE, a structural unit based on a fluorine-containing vinyl ether and a structural unit based on a cyano group-containing monomer, and still more preferably a structural unit based on TFE, a structural unit based on PAVE and a structural unit based on a cyano group-containing monomer.

[0218] In the composition, the first fluorine-containing polymer and the second fluorine-containing polymer are preferably present in the form of particles. The first fluorine-containing polymer and the second fluorine-containing polymer may be present separately in the composition, but are preferably present in the form of particles containing the first fluorine-containing polymer and the second fluorine-containing polymer, and more preferably present in the form of particles consisting of the first fluorine-containing polymer and the second fluorine-containing polymer (i.e., particles of a fluorine-containing elastomer).

[0219] In this case, the average particle size of the fluorine-containing elastomer particles is more preferably 400 nm or less, even more preferably 350 nm or less, and particularly preferably 300 nm or less. The lower limit is preferably 10 nm or more, more preferably 30 nm or more, and even more preferably 50 nm or more. The method for measuring the average particle size of the particles is as described above.

[0220] The fluorine-containing elastomer preferably does not have a melting point. Specific methods for measuring the melting point include the methods shown in the Examples section.

[0221] The content of the structural units based on the cyano group-containing monomer is preferably 0.1 to 10 mol %, more preferably 0.3 to 5 mol %, based on the total amount of the first fluorine-containing polymer and the second fluorine-containing polymer. The content of the structural units based on TFE is preferably 10 to 90 mol %, more preferably 20 to 80 mol %, based on the total amount of the first fluorine-containing polymer and the second fluorine-containing polymer.

[0222] The first fluorine-containing polymer and the second fluorine-containing polymer preferably contain a structural unit based on a cyano group-containing monomer, a structural unit based on TFE, and a structural unit based on a fluorine-containing vinyl ether, and more preferably contain a structural unit based on a cyano group-containing monomer, a structural unit based on TFE, and a structural unit based on PAVE.

[0223] When at least one of the first fluorine-containing polymer and the second fluorine-containing polymer contains a structural unit based on PAVE, the content of the structural unit based on PAVE is preferably from 10 to 90 mol %, more preferably from 20 to 80 mol %, based on the total amount of the first fluorine-containing polymer and the second fluorine-containing polymer.

[0224] The fluorine-containing elastomer comprising the first fluorine-containing polymer and the second fluorine-containing polymer preferably has the following embodiments: Embodiment 1: The fluorine-containing elastomer comprises a structural unit based on a cyano group-containing monomer, a structural unit based on TFE, and a structural unit based on PAVE. Embodiment 2: The fluorine-containing elastomer comprises a structural unit based on a cyano group-containing monomer, a structural unit based on TFE, and a structural unit based on propylene. Embodiment 3: The fluorine-containing elastomer comprises a structural unit based on a cyano group-containing monomer, a structural unit based on HFP, and a structural unit based on VdF.

[0225] In the case of Aspect 1, the content of the structural units based on TFE is preferably 25 to 85 mol%, more preferably 35 to 75 mol%, based on the total amount of the fluorine-containing elastomer. In the case of Aspect 1, the content of the structural units based on PAVE is preferably 10 to 70 mol%, more preferably 20 to 60 mol%, based on the total amount of the fluorine-containing elastomer. The suitable content is similar when PMVE or PPVE is used as the PAVE.

[0226] In the case of Aspect 2, the content of the structural units based on TFE is preferably 15 to 75 mol %, more preferably 25 to 65 mol %, based on the total amount of the fluoroelastomer. In the case of Aspect 2, the content of the structural units based on propylene is preferably 20 to 80 mol %, more preferably 30 to 70 mol %, based on the total amount of the fluoroelastomer.

[0227] In the case of Aspect 3, the content of the structural units based on HFP is preferably 5 to 40 mol %, more preferably 10 to 30 mol %, based on the total amount of the fluorine-containing elastomer. In the case of Aspect 3, the content of the structural units based on VdF is preferably 5 to 85 mol %, more preferably 15 to 75 mol %, based on the total amount of the fluorine-containing elastomer.

[0228] The composition preferably has a metal content of 50 ppm by mass or less, more preferably 30 ppm by mass or less, based on the total solid content of the composition. The lower limit is 0 ppm by mass. A metal content of 50 ppm by mass or less further improves the surface smoothness of crosslinked rubber articles.

[0229] The metal content is measured using an inductively coupled plasma mass spectrometer.

[0230] [Solid Composition] The solid composition of the present disclosure (hereinafter also referred to as "the present solid composition") contains a fluorine-containing elastomer including structural units based on a cyano group-containing monomer, structural units based on TFE, and structural units based on at least one selected from the group consisting of fluorinated vinyl ethers and fluorinated allyl ethers. Furthermore, when the present solid composition is heated under a nitrogen atmosphere under the following condition 1, the weight loss rate after 1000 minutes from the start of heating is 2.0% or less, and the composition is substantially free of an emulsifier having a fluorine atom. (Condition 1) The composition is heated from 40°C to 90°C at a heating rate of 20°C / min, held at 90°C for 120 minutes, heated from 90°C to 200°C at a heating rate of 20°C / min, held at 200°C for 240 minutes, heated from 200°C to 305°C at a heating rate of 20°C / min, and held at 305°C for 720 minutes.

[0231] This solid composition makes it possible to obtain crosslinked rubber articles with small compression set and excellent surface smoothness.

[0232] The solid composition is solid at 25°C.

[0233] The fluorine-containing elastomer contained in the present solid composition is preferably obtained by polymerization in the presence of compound (X). The fluorine-containing elastomer contained in the present solid composition can be produced, for example, in the present production method A, by polymerizing a monomer A containing a cyano group-containing monomer, TFE, and at least one selected from the group consisting of fluorine-containing vinyl ethers and fluorine-containing allyl ethers.

[0234] The fluorine-containing elastomer contained in the present solid composition can be produced, for example, by polymerizing a first monomer containing a cyano group-containing monomer and at least one selected from the group consisting of TFE, a fluorine-containing vinyl ether, and a fluorine-containing allyl ether in the first polymerization step of the present production method B, carrying out the second polymerization step of the present production method B, and removing the liquid component.

[0235] <Emulsifier> The present solid composition is substantially free of emulsifiers having fluorine atoms. "Substantially free of emulsifiers having fluorine atoms" means that the content of emulsifiers having fluorine atoms is 10 ppm by mass or less, preferably 500 ppb by mass or less, and more preferably 250 ppb by mass or less, based on the total amount of the solid composition. The lower limit of the content of emulsifiers having fluorine atoms is 0 ppb by mass.

[0236] The present solid composition is preferably substantially free of emulsifiers. "Substantially free of emulsifiers" means that the content of emulsifiers is 10 mass ppm or less, preferably 500 mass ppb or less, and more preferably 250 mass ppb or less, based on the total amount of the solid composition. The lower limit of the emulsifier content is 0 mass ppb.

[0237] <Fluorine-containing elastomer> The fluorine-containing elastomer contained in the present solid composition contains a structural unit based on a cyano group-containing monomer, a structural unit based on TFE, and a structural unit based on at least one selected from the group consisting of a fluorine-containing vinyl ether and a fluorine-containing allyl ether. The fluorine-containing elastomer contained in the present solid composition may further contain a structural unit based on compound (X), or may not further contain a structural unit based on compound (X). Preferred aspects of compound (X), the cyano group-containing monomer, the fluorine-containing vinyl ether, and the fluorine-containing allyl ether are as described above.

[0238] The content of the structural units based on the cyano group-containing monomer is preferably 0.1 to 10 mol %, more preferably 0.3 to 5 mol %, based on the total amount of the fluorine-containing elastomer. The content of the structural units based on TFE is preferably 10 to 90 mol %, more preferably 20 to 80 mol %, based on the total amount of the fluorine-containing elastomer.

[0239] The fluorine-containing elastomer preferably contains a structural unit based on a cyano group-containing monomer, a structural unit based on TFE, and a structural unit based on a fluorine-containing vinyl ether, and more preferably contains a structural unit based on a cyano group-containing monomer, a structural unit based on TFE, and a structural unit based on PAVE.

[0240] When the fluorine-containing elastomer contains a constituent unit based on PAVE, the content of the constituent unit based on PAVE is preferably 10 to 90 mol %, more preferably 20 to 80 mol %, based on the total amount of the fluorine-containing elastomer. The suitable content is similar when PMVE or PPVE is used as the PAVE.

[0241] When heated in a nitrogen atmosphere under the following condition 1, the solid composition exhibits a weight loss rate of 2.0% or less 1,000 minutes after the start of heating: (Condition 1) The composition is heated from 40°C to 90°C at a heating rate of 20°C / min, held at 90°C for 120 minutes, heated from 90°C to 200°C at a heating rate of 20°C / min, held at 200°C for 240 minutes, heated from 200°C to 305°C at a heating rate of 20°C / min, and held at 305°C for 720 minutes.

[0242] That is, the weight loss rate after successively carrying out the heating steps 1 to 6 below is 2.0% by mass or less. Starting temperature: 40°C Atmosphere: Nitrogen atmosphere Step 1: Heat from 40°C to 90°C at a heating rate of 20°C / min Step 2: Hold at 90°C for 120 minutes Step 3: Heat from 90°C to 200°C at a heating rate of 20°C / min Step 4: Hold at 200°C for 240 minutes Step 5: Heat from 200°C to 305°C at a heating rate of 20°C / min Step 6: Hold at 305°C for 720 minutes

[0243] The weight loss rate is measured by thermogravimetric analysis using the profile described above. Specifically, a sample of the solid composition is heated at 40°C using the profile described above, and the change in the sample's weight is measured. The weight loss rate is calculated from the weight of the sample before heating (immediately before step 1) and after heating (after step 6). Examples of devices used for thermogravimetric analysis include the NEXTA STA Series STA200 differential thermal thermogravimetric analyzer (manufactured by Hitachi High-Tech Corporation). A solid composition having a moisture content of 0.5% by mass or less is used as the sample. The moisture content of the sample is preferably 0.3% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0% by mass. The moisture content of the solid composition can be adjusted by drying. Drying methods include heating, reduced pressure, and a combination thereof. When drying the solid composition by heating, the heating temperature is preferably 250°C or less, more preferably 200°C or less, and even more preferably 150°C or less. The heating temperature is preferably 60°C or higher in terms of drying efficiency. The heating time can be adjusted appropriately depending on the moisture content of the sample, and is preferably 480 to 900 minutes. The moisture content of the sample can be measured using a moisture meter (e.g., a halogen moisture meter). A more specific method for measuring the weight loss rate is as described in the Examples below.

[0244] From the viewpoint of obtaining excellent physical properties and surface smoothness of the crosslinked rubber article, the weight loss rate is preferably 1.5% by mass or less, more preferably 1.3% by mass or less. The lower limit is 0% by mass, and may be 0.1% by mass or more. Methods for suppressing the weight loss rate include, for example, adjusting the amount of polymerization initiator used during polymerization and the polymerization pressure. This can suppress the generation of substances that cause weight loss. Emulsifier remaining in the fluorine-containing elastomer can cause weight loss. In order to reduce the amount of emulsifier, it is preferable to polymerize the monomer under conditions in which the emulsifier is substantially absent.

[0245] The solid composition preferably has a metal content of 50 ppm by mass or less, more preferably 30 ppm by mass or less, based on the total amount of the solid composition. The lower limit is 0 ppm by mass. A metal content of 50 ppm by mass or less further improves the surface smoothness of the crosslinked rubber article.

[0246] The solid composition preferably has a storage modulus of 200 to 600 kPa, more preferably 250 to 550 kPa. If the storage modulus is 600 kPa or more, the fluidity of the fluorine-containing elastomer during the crosslinking reaction decreases, resulting in a decrease in moldability. If the storage modulus is 200 kPa or less, the mold releasability after hot press molding decreases, resulting in a decrease in moldability.

[0247] The storage modulus is a measure of the average molecular weight, and a higher value indicates a higher molecular weight, while a lower value indicates a lower molecular weight. In the present disclosure, the storage modulus is defined as the storage modulus at a frequency of 50 cpm and 100°C.

[0248] [Crosslinked Rubber Article] The crosslinked rubber article of the present disclosure (hereinafter also referred to as the "present crosslinked rubber article") contains a crosslinked product obtained by crosslinking a fluorine-containing elastomer comprising structural units based on a cyano group-containing monomer, structural units based on TFE, and structural units based on at least one selected from the group consisting of fluorinated vinyl ethers and fluorinated allyl ethers. The present crosslinked rubber article has a weight loss of 0.5% or less after immersion in 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane for 12 hours and then drying, and is substantially free of an emulsifier having a fluorine atom.

[0249] The present crosslinked rubber article has small compression set and excellent surface smoothness. In general, increasing the number of crosslinking groups in a polymer before crosslinking is considered to reduce compression set, but increasing the number of crosslinking groups tends to decrease surface smoothness. It has been difficult to achieve both a reduction in compression set and surface smoothness. In contrast, the present crosslinked rubber article contains a crosslinked product of a fluorine-containing elastomer containing specific structural units, and has a weight loss rate of 0.5% or less after immersion in 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane for 12 hours and drying. It is also substantially free of an emulsifier having a fluorine atom, and therefore has small compression set and excellent surface smoothness.

[0250] The crosslinked product contained in the present crosslinked rubber article is produced, for example, by crosslinking a fluorine-containing elastomer containing a constituent unit based on a cyano group-containing monomer, a constituent unit based on TFE, and a constituent unit based on at least one selected from the group consisting of a fluorine-containing vinyl ether and a fluorine-containing allyl ether.

[0251] The fluorine-containing elastomer to be crosslinked is preferably obtained by polymerization in the presence of compound (X). The fluorine-containing elastomer to be crosslinked can be produced, for example, by polymerizing a monomer A containing a cyano group-containing monomer, TFE, and at least one selected from the group consisting of a fluorine-containing vinyl ether and a fluorine-containing allyl ether in the present production method A.

[0252] The fluorine-containing elastomer to be crosslinked can be produced, for example, by polymerizing a first monomer containing a cyano group-containing monomer and at least one selected from the group consisting of TFE, a fluorine-containing vinyl ether, and a fluorine-containing allyl ether in the first polymerization step of the present production method B, and then carrying out the second polymerization step of the present production method B.

[0253] <Weight Loss Rate> The crosslinked rubber article has a weight loss rate of 0.5% or less after being immersed in 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane for 12 hours and then dried.

[0254] The weight loss rate is calculated as follows.

[0255] A crosslinked rubber article is immersed in 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane for 12 hours and then vacuum dried at 100°C until drying is complete. The mass is measured every 12 hours, and drying is judged to be complete when the rate of change from the previous measurement is 0.01% by mass or less. Specifically, drying is judged to be complete when the following formula (M) is satisfied: {X(n) - X(n-1)} / X(n-1) x 100 ≤ 0.01 ... (M) X0: Mass of the crosslinked rubber article X1: Mass of the crosslinked rubber article when drying is judged to be complete X(n): Mass of the crosslinked rubber article (12 x n) hours after the start of drying (n is an integer of 1 or more) X(n-1): Mass of the crosslinked rubber article (12(n-1)) hours after the start of drying (n is an integer of 1 or more)

[0256] The weight loss rate is calculated using the following formula: Weight loss rate (%) = {X1 / X0} x 100

[0257] In order to obtain excellent surface smoothness, the weight loss rate is preferably equal to or less than 0.5%, and more preferably equal to or less than 0.3%. The lower limit is, for example, 0%.

[0258] <Emulsifier> The present crosslinked rubber article is substantially free of emulsifiers having fluorine atoms. "Substantially free of emulsifiers having fluorine atoms" means that the content of emulsifiers having fluorine atoms is 10 ppm by mass or less, preferably 500 ppb by mass or less, and more preferably 250 ppb by mass or less, based on the total amount of the crosslinked rubber article. The lower limit of the content of emulsifiers having fluorine atoms is 0 ppb by mass.

[0259] The crosslinked rubber article is preferably substantially free of emulsifiers. "Substantially free of emulsifiers" means that the emulsifier content is 10 ppm by mass or less, preferably 150 ppb by mass or less, and more preferably 50 ppb by mass or less, based on the total weight of the crosslinked rubber article. The lower limit of the emulsifier content is 0 ppb by mass.

[0260] <Crosslinked product of fluorine-containing elastomer> The crosslinked product contained in the present crosslinked rubber article is a crosslinked product obtained by crosslinking a fluorine-containing elastomer containing structural units based on a cyano group-containing monomer, structural units based on TFE, and structural units based on at least one selected from the group consisting of fluorine-containing vinyl ethers and fluorine-containing allyl ethers. Preferred embodiments of the cyano group-containing monomer, fluorine-containing vinyl ether, and fluorine-containing allyl ether are as described above.

[0261] The content of the structural units based on the cyano group-containing monomer is preferably 0.1 to 10 mol %, more preferably 0.3 to 5 mol %, based on the total amount of the fluorine-containing elastomer. The content of the structural units based on TFE is preferably 10 to 90 mol %, more preferably 20 to 80 mol %, based on the total amount of the fluorine-containing elastomer.

[0262] The crosslinked product preferably contains a structural unit based on a cyano group-containing monomer, a structural unit based on TFE, and a structural unit based on a fluorinated vinyl ether, and more preferably is a crosslinked product of a fluorinated elastomer containing a structural unit based on a cyano group-containing monomer, a structural unit based on TFE, and a structural unit based on PAVE.

[0263] When the fluorine-containing elastomer contains a constituent unit based on PAVE, the content of the constituent unit based on PAVE is preferably 10 to 90 mol %, more preferably 20 to 80 mol %, based on the total amount of the fluorine-containing elastomer. The suitable content is similar when PMVE or PPVE is used as the PAVE.

[0264] <Crosslinking> The method for crosslinking the fluorine-containing elastomer is not particularly limited, but a heating method is preferred. Specific examples of crosslinking methods by heating include hot press crosslinking, steam crosslinking, injection molding crosslinking, hot air crosslinking, molten salt crosslinking, fluidized bed crosslinking, and funnel crosslinking. The heating conditions are preferably 100 to 400°C for 1 second to 24 hours.

[0265] The crosslinked product obtained by heating the fluorine-containing elastomer (first crosslinking) may be further heated to cause second crosslinking. By performing second crosslinking, the mechanical properties, compression set, and other properties of the crosslinked product can be stabilized or improved. The heating conditions for performing second crosslinking are preferably 80 to 350°C for 30 minutes to 48 hours.

[0266] As a crosslinking method other than heating, a method of irradiating the fluorine-containing elastomer with radiation can be mentioned, and specific examples of the radiation to be irradiated include electron beams and ultraviolet rays.

[0267] <Structure> The crosslinked material preferably has a heterocyclic structure, and more preferably has at least one of an oxazole structure and a triazine structure.

[0268] In the crosslinked product, the fluorine-containing elastomer before crosslinking contains structural units based on a cyano group-containing monomer, and therefore, a heterocyclic structure (preferably, an oxazole ring) can be formed by reacting the cyano groups with the crosslinking agent. Furthermore, in the crosslinked product, the fluorine-containing elastomer before crosslinking contains structural units based on a cyano group-containing monomer, and therefore, a heterocyclic structure (preferably, a triazine structure) can be formed by reacting the cyano groups with each other. Specific examples of crosslinking agents include compounds having two or more amino groups (hereinafter also referred to as "polyamine compounds"), organic peroxides, organic ammonia-generating compounds, i.e., compounds that can generate ammonia when heated, and organic tin compounds such as allenyl-tin curing agents. In terms of excellent crosslinkability of the fluorine-containing elastomer and the production of crosslinked rubber articles with smaller compression set, the crosslinking agent is preferably a polyamine compound, and more preferably a compound having two amino groups.

[0269] The polyamine compound may be a compound in which a hydrogen atom of an aliphatic hydrocarbon is substituted with an amino group, or a compound in which a hydrogen atom of an aromatic hydrocarbon is substituted with an amino group, but from the viewpoint of achieving better effects of the present invention, a compound in which a hydrogen atom of an aromatic hydrocarbon is substituted with an amino group is preferred. The polyamine compound preferably contains a fluorine atom. This improves compatibility with the fluorine-containing copolymer, thereby allowing a crosslinked rubber article to be obtained with a smaller compression set at high temperatures.

[0270] Specific examples of the polyamine compound include hexamethylenediamine, hexamethylenediamine carbamate, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis(3-amino-4-hydroxyphenyl)propane, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (hereinafter also referred to as "BOAP", also known as bisaminophenol AF), 2,2-bis(3,4-diaminophenyl)propane, 2,2-bis(3,4-diaminophenyl)hexafluoropropane, 2,2-bis(3-amino-4-(N-phenylamino)phenyl)hexafluoropropane, 4,4'-methylenedianiline, m-phenylenediamine, adipic acid dihydrazide, and the compound represented by formula (XII) of Japanese Patent No. 5,833,657, with BOAP being preferred.

[0271] The present crosslinked rubber article has a small compression set and excellent surface smoothness, and therefore can be used in the following applications, for example.

[0272] The crosslinked rubber article is suitable for use as a material for O-rings, sheets, gaskets, oil seals, diaphragms, V-rings, and the like. The crosslinked rubber article can also be used in heat-resistant and chemical-resistant sealing materials, heat-resistant and oil-resistant sealing materials, wire coating materials, sealing materials for semiconductor manufacturing equipment, 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 (offshore civil engineering, ships), fibers and nonwoven fabrics (protective clothing, etc.), circuit board sealing materials, rubber gloves, stators for uniaxial eccentric screw pumps, parts for urea SCR systems, vibration isolators, vibration dampers, sealants, additives for other materials, and toys.

[0273] The present invention will be described in detail below with reference to examples. Examples 1 to 7 and 11 are working examples, and Examples 8 to 10 are comparative examples. However, the present invention is not limited to these examples.

[0274] [Methods for measuring and evaluating fluorine-containing polymer or fluorine-containing elastomer] Various measuring and evaluation methods are as follows.

[0275] <Average particle size of particles> The aqueous dispersion of each example described below was degassed at 25°C for 5 minutes, pressurized with nitrogen gas to 0.2 MPaG, purged, and returned to atmospheric pressure to obtain a measurement sample. The average particle size of the obtained measurement sample was measured using a dynamic light scattering particle size distribution measurement device (Otsuka Electronics Co., Ltd., ELSZ) with an accumulation number set to 100, and this was defined as the average particle size of the particles in each aqueous dispersion.

[0276] <Solid Content Concentration> After heating 2.0 g of the aqueous dispersion of each example described below at 170°C for 20 minutes, the mass (g) of the residue was weighed and the solid content concentration was calculated using the following formula: Solid Content Concentration (mass%) = 100 × (mass of residue) / (mass of aqueous dispersion (2.0 g))

[0277] <Proportion of Each Structural Unit> The proportion of each structural unit in the fluorine-containing polymer or fluorine-containing elastomer is as follows: １９ It was determined by F-NMR analysis and infrared absorption spectrum analysis.

[0278] <Melting point> The aqueous dispersion of each example described below was freeze-aggregated and then filtered to obtain a fluoropolymer. A 5 mg sample of the obtained fluoropolymer was weighed out and placed in an aluminum pan, and heated from 20°C to 360°C at a temperature increase rate of 10°C / min in an air atmosphere using a Hitachi DSC600, and the presence or absence of a melting point peak was confirmed.

[0279] <Water Content> Using the fluorine-containing elastomer obtained in each example, the water content was measured with a halogen moisture meter.

[0280] <Metal Content> The fluorine-containing elastomer was placed in a platinum crucible and ashed in a high-temperature electric heating furnace, followed by a sulfuric acid white smoke treatment. The resulting solution was then dissolved in dilute nitric acid. 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) was determined using an inductively coupled plasma mass spectrometer (ICP-MS 7500cs, manufactured by Agilent Technologies) and the absolute calibration curve method.

[0281] <Weight Loss Rate> A 10 mg sample of the fluorine-containing elastomer obtained in each example was weighed into an aluminum pan and placed in a Hitachi STA200. The starting temperature was set to 40°C, and once the sample temperature stabilized, the sample was continuously heated in a nitrogen atmosphere (nitrogen gas flow rate: 100 mL / min) according to the following profile of steps 1 to 6, while measuring the change in mass. The weight loss rate 1000 minutes after the start of heating was calculated based on the mass of the sample before heating from 40°C. The above thermogravimetric analysis was carried out using a differential thermal thermogravimetric analyzer "NEXTA STA series STA200" (Hitachi High-Tech Corporation). Step 1: Heat from 40°C to 90°C at a rate of 20°C / min. Step 2: Hold at 90°C for 120 minutes. Step 3: Heat from 90°C to 200°C at a rate of 20°C / min. Step 4: Hold at 200°C for 240 minutes. Step 5: Heat from 200°C to 305°C at a rate of 20°C / min. Step 6: Hold at 305°C for 720 minutes.

[0282] <Storage Modulus> A rubber processability analyzer "PREMIER RPA (manufactured by Alpha Technologies, die shape: D0380)" was used as the measuring device. The solid composition obtained in each example was kneaded for 10 minutes at room temperature (25°C) 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 measurement sample. 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, a frequency of 30 cpm, and an amplitude angle of 0.2°C for 2 minutes, and then the amplitude angle was changed to 0.5°C and the frequency was increased to 10 cpm, 20 cpm, 50 cpm, 100 cpm, 200 cpm, 500 cpm, 1000 cpm, and 2000 cpm to measure the storage modulus. The storage modulus at 50 cpm and 100°C was defined as the storage modulus G' (unit: kPa) of the sample.

[0283] <Method for measuring 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) based on the total mass of the solid composition was added 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 configuration of the measuring equipment and the LC-MS measurement conditions are shown in Table 1. Aqueous solutions of fluorine-containing emulsifier and hydrocarbon emulsifier with known concentrations 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.

[0284]

[0285] The MRM measurement parameters are appropriately selected depending on the structures of the fluorine 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 device. The specific procedure for determining the MRM parameters using an LC-MS device is as follows. Using an LC / MS device (Shimadzu Corporation, LCMS-8060NX), a search for product ions is selected, the molecular weights of the fluorine emulsifier and hydrocarbon emulsifier to be measured are input, and precursor ions, precursor adjustment, voltage optimization, and product m / z optimization are performed. The calculated MRM measurement parameters are used. As an example, the MRM measurement parameters for compounds (S1) and (S2), which are emulsifiers having fluorine atoms, are shown in the table below. Note that in formulas (S1) and (S2), MＳ represents a hydrogen atom, a metal atom, or NR ４ (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-(CF ２ ) ｎ１ -COOM Ｓ (S1) F-(CF ２ ) ｎ２ -SO ３ M Ｓ (S2) where n1 is an integer from 3 to 17, and n2 is an integer from 4 to 12.

[0286]

[0287]

[0288] (Quantitative Determination of Fluorine Emulsifier and Hydrocarbon Emulsifier in Solid Sample) Specifically, five levels of methanol standard solutions of fluorine 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 sample using a first-order approximation according to formula (A1): A = a × X (A1), where A is the peak area of ​​each emulsifier, and X is the concentration (ng / g) of each emulsifier.

[0289] Next, the amount of emulsifier contained in the extract was calculated using formula (A2). Note that a in formula (A2) means a calculated using formula (A1) above. XCm = ACm / a (A2) 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.

[0290] The content of the emulsifier in the solid composition relative to the total mass of the solid composition (ZCm) was calculated by the following formula (A3): ZCm = XCm × ρ1 × La / W1 (A3), where ZCm is the content of the emulsifier contained in the solid composition, ρ1 is the density of the extraction solvent (methanol in each example), La is the volume of the extraction solvent (5 mL in each example), and W1 is the mass of the sample used for extraction (2.5 g of solid composition in each example).

[0291] [Example 1] Ultrapure water (1206 L), a 50 mass% aqueous solution (30 μL) of sodium 2-acrylamido-2-methyl-1-propanesulfonate (NaAAMPS, corresponding to "compound (X)"), PMVE (81 g), TFE (17 g), and CF were placed in a 2.2 L stainless steel pressure reactor. ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ 3.4 g of CN (8CNVE) was added and the temperature was raised to 80 ° C. The pressure inside the reactor at 80 ° C. was 1.4 MPaG. Next, an aqueous ammonium persulfate solution (2.5 mass%, 7 g) was added to initiate polymerization. Since the pressure inside the reactor decreased with the start of polymerization, TFE was added to maintain the pressure constant. While intermittently adding the aqueous ammonium persulfate solution, 12 g of PMVE and 1.26 g of 8CNVE were injected every time 16 g of TFE was injected. When the amount of TFE added after the start of polymerization reached 160 g, the addition of TFE and PMVE injected after the start of polymerization was stopped, the reactor temperature was cooled to 10 ° C., the polymerization reaction was stopped, the gas remaining in the reactor was recovered, and the liquid was withdrawn to obtain aqueous dispersion A1. The total amount of TFE added before the start of polymerization was 17 g, and the total amount of PMVE added was 82 g. The total amount of TFE added after the start of polymerization was 160 g, and the total amount of PMVE added was 108 g. The total amount of TFE added was 177 g, the total amount of PMVE added was 190 g, and the total amount of 8CNVE added was 16.0 g. The average particle size of the polymer particles in aqueous dispersion A1 was 70.2 nm. Aqueous dispersion A1 was coagulated with a 5% by mass aqueous nitric acid solution, filtered, and the resulting solid was washed with ultrapure water. It was then vacuum dried at 100°C for 12 hours to obtain fluorine-containing elastomer A1. NMR analysis of the obtained fluorine-containing elastomer A1 revealed that the composition was PMVE / TFE / 8CNVE = 31.0 / 68.4 / 0.6 (molar ratio). Furthermore, fluorine-containing elastomer A1 did not have a melting point. The water content of fluorine-containing elastomer A1 was 0.0% by mass.

[0292] [Example 2] Aqueous dispersion A2 was obtained in the same manner as in Example 1, except that the total amount of TFE added after the initiation of polymerization was 150 g and the total amount of PMVE added was 126 g. The total amount of TFE added was 167 g, the total amount of PMVE added was 207 g, and the total amount of 8CNVE added was 16.0 g. The average particle size of the polymer particles in aqueous dispersion A2 was 72.7 nm. Aqueous dispersion A2 was coagulated with a 5% by mass aqueous nitric acid solution, filtered, and the resulting solid was washed with ultrapure water. It was then vacuum dried at 100°C for 12 hours to obtain fluorine-containing elastomer A2. NMR analysis of the obtained fluorine-containing elastomer A2 revealed that its composition was PMVE / TFE / 8CNVE = 33.5 / 65.8 / 0.7 (molar ratio). Furthermore, fluorine-containing elastomer A2 did not have a melting point. The water content of the fluorine-containing elastomer A2 was 0.0% by mass.

[0293] [Example 3] Aqueous dispersion A3 was obtained in the same manner as in Example 1, except that the total amount of TFE added after the start of polymerization was 400 g and the total amount of PMVE added was 288 g. The total amount of TFE added was 417 g, the total amount of PMVE added was 369 g, and the total amount of 8CNVE added was 33.6 g. The average particle size of the polymer particles in aqueous dispersion A3 was 97.1 nm. Aqueous dispersion A3 was coagulated with a 5% by mass aqueous nitric acid solution, filtered, and the resulting solid was washed with ultrapure water. It was then vacuum dried at 100°C for 12 hours to obtain fluorine-containing elastomer A3. NMR analysis of the obtained fluorine-containing elastomer A3 revealed that its composition was PMVE / TFE / 8CNVE = 30.1 / 69.5 / 0.4 (molar ratio). Furthermore, fluorine-containing elastomer A3 did not have a melting point. The water content of the fluorine-containing elastomer A3 was 0.0% by mass.

[0294] [Example 4] <First polymerization step> Ultrapure water (1206 g), a 50% by mass aqueous solution of NaAAMPS (20 μL, 10 mg of NaAAMPS), PMVE (72 g), 8CNVE (3.4 g), and TFE (15 g) were added to a 2.2 L stainless steel pressure reactor, and the temperature was raised to 90 ° C. with stirring. The pressure inside the reactor at 90 ° C. was 1.4 MPaG. Next, an aqueous solution of ammonium persulfate (2.5% by mass, 7 g) was added to initiate polymerization. Since the pressure inside the reactor decreased with the start of polymerization, TFE was added to maintain the pressure constant. This was repeated, and when the amount of TFE added after the start of polymerization reached 25 g, the addition of TFE injected after the start of polymerization was stopped, the temperature inside the reactor was cooled to 10 ° C., and the polymerization reaction was stopped. The gas remaining in the reactor was recovered, and the liquid was then extracted to obtain raw material solution B1. The total amount of TFE added before the start of polymerization was 15 g, and the total amount of PMVE was 72 g. The total amount of TFE added after the start of polymerization was 25 g, and the total amount of PMVE was 0 g. The total amount of TFE added was 40 g, and the total amount of PMVE added was 72 g. The average particle size of the particles of the first fluorinated polymer B1-1 in the raw material liquid B1 was 43.5 nm. The solids concentration of the raw material liquid B1 was 3.3 mass%. The raw material liquid B1 was freeze-coagulated and then filtered, and the obtained first fluorinated polymer B1-1 was washed with ultrapure water. Thereafter, it was vacuum-dried at 100°C. The obtained first fluorinated polymer B1-1 was analyzed by NMR, and the result was that the molar ratio was PMVE / TFE / 8CNVE = 30.269.1 / 0.9. The first fluorinated polymer B1-1 did not have a melting point.

[0295] <Purification step> HPR4002Cl (manufactured by DuPont, anion exchange resin, 40 g) was added to raw material solution B1 (1000 g). After 60 minutes from the start of stirring, the raw material solution and the anion exchange resin were separated by filtration. To the separated raw material solution, Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 40 g) was added. After 60 minutes from the start of stirring, the cation exchange resin was separated by filtration to obtain raw material solution B2.

[0296] <Second polymerization step> Raw material solution B2 (850 g), ultrapure water (332 g), 8CNVE (3.4 g), PMVE (81 g), and TFE (17 g) were added to a 2.2 L stainless steel pressure reactor, and the temperature was raised to 80 ° C. with stirring. The pressure inside the reactor was 1.4 MPaG when the temperature reached 0 ° C. Next, an aqueous ammonium persulfate solution (2.5 mass%, 7 g) was added to initiate polymerization. As the pressure inside the reactor decreased with the start of polymerization, TFE was added to maintain the pressure constant. Thereafter, while intermittently adding the aqueous ammonium persulfate solution, 12 g of PMVE and 1.3 g of 8CNVE were injected every time 16 g of TFE was injected. When the amount of TFE added after the initiation of polymerization reached 408 g, the addition of TFE and PMVE that had been injected after the initiation of polymerization was stopped, the temperature inside the reactor was cooled to 10°C, the polymerization reaction was stopped, the gas remaining in the reactor was recovered, and then the liquid was withdrawn to obtain a second aqueous dispersion B2-1.

[0297] The total amount of 8CNVE added was 16.0 g. The total amounts of monomers added before the start of polymerization were 17 g of TFE and 81 g of PMVE. The total amount of TFE added after the start of polymerization was 168 g and 108 g of PMVE. The total amount of TFE added was 185 g and the total amount of PMVE added was 189 g.

[0298] The second aqueous dispersion B2-1 was a dispersion in which particles containing a first fluoropolymer B1-1 and a second fluoropolymer B1-2 were dispersed in an aqueous medium. The average particle size of the particles in the aqueous dispersion B2-1 was 100 nm. The second aqueous dispersion B2-1 was coagulated with a 5% by mass aqueous nitric acid solution, filtered, and the resulting solid was washed with ultrapure water. It was then vacuum dried at 100°C for 12 hours to obtain a fluoroelastomer B1 containing a first fluoropolymer B1-1 and a second fluoropolymer B1-2. NMR analysis of the resulting fluoroelastomer B1 revealed that it had a composition of PMVE / TFE / 8CNVE=31.2 / 68.3 / 0.5 (molar ratio). Furthermore, the fluoroelastomer B1 did not have a melting point. The water content of the fluoroelastomer B1 was 0.2% by mass.

[0299] [Example 5] <First polymerization step> Ultrapure water (1206 g), a 50% by mass aqueous solution of NaAAMPS (20 μL, 10 mg of NaAAMPS), PMVE (72 g), PMAE (2 g), 8CNVE (3.4 g), and TFE (15 g) were added to a 2.2 L stainless steel pressure reactor, and the temperature was raised to 90 ° C. with stirring. The pressure inside the reactor at 90 ° C. was 1.4 MPaG. Next, an aqueous solution of ammonium persulfate (2.5% by mass, 7 g) was added to initiate polymerization. Since the pressure inside the reactor decreased with the start of polymerization, TFE was added to maintain the pressure constant. This was repeated, and when the amount of TFE added after the start of polymerization reached 25 g, the addition of TFE injected after the start of polymerization was stopped, the temperature inside the reactor was cooled to 10 ° C., and the polymerization reaction was stopped. The gas remaining in the reactor was recovered, and the liquid was then extracted to obtain raw material liquid B3. The total amount of TFE added before the start of polymerization was 15 g, and the total amount of PMVE was 72 g. The total amount of TFE added after the start of polymerization was 25 g, and the total amount of PMVE was 0 g. The total amount of TFE added was 40 g, and the total amount of PMVE added was 72 g. The average particle size of the particles of the first fluorine-containing polymer B2-1 in raw material liquid B3 was 43.5 nm. The solids concentration of raw material liquid B3 was 3.3 mass %. Raw material liquid B3 was freeze-coagulated and then filtered, and the obtained first fluorine-containing polymer B2-1 was washed with ultrapure water. Thereafter, it was vacuum-dried at 100°C. The obtained first fluorine-containing polymer B2-1 was analyzed by NMR, and as a result, the molar ratio was PMVE / PMAE / TFE / 8CNVE = 33.2 / 0.5 / 65.1 / 0.7. The first fluorine-containing polymer B2-1 did not have a melting point.

[0300] <Purification Step> The purification step was carried out in the same manner as in Example 4 to obtain raw material solution B4.

[0301] <Second Polymerization Step> The second polymerization step was carried out in the same manner as in Example 4 to obtain a second aqueous dispersion B2-2.

[0302] The second aqueous dispersion B2-2 was a dispersion in which particles containing a first fluoropolymer B2-1 and a second fluoropolymer B2-2 were dispersed in an aqueous medium. The average particle size of the particles in aqueous dispersion B2-2 was 96 nm. The second aqueous dispersion B2-2 was coagulated with a 5% by mass aqueous nitric acid solution, filtered, and the resulting solid was washed with ultrapure water. It was then vacuum dried at 100°C for 12 hours to obtain a fluoroelastomer B2 containing a first fluoropolymer B2-1 and a second fluoropolymer B2-2. NMR analysis of the resulting fluoroelastomer B2 revealed that it had a composition of PMVE / PMAE / TFE / 8CNVE=30.1 / 0.1 / 69.3 / 0.5 (molar ratio). Furthermore, the fluoroelastomer B2 did not have a melting point. The water content of the fluoroelastomer B2 was 0.2% by mass.

[0303] [Example 6] Ultrapure water (1206 L), a 0.25 mass% aqueous solution of sodium vinyl sulfonate (NaVSA, 20 g, NaVSA content: 50 mg), PMVE (81 g), TFE (17 g), PMAE (2 g), and 8CNVE (3.4 g) were added to a 2.2 L stainless steel pressure reactor, and the temperature was raised to 80 ° C. with stirring. The pressure inside the reactor at 80 ° C. was 1.4 MPaG. Next, an aqueous ammonium persulfate solution (2.5 mass%, 7 g) was added to initiate polymerization. As the pressure inside the reactor decreased with the start of polymerization, TFE was added to maintain the pressure constant. While intermittently adding the aqueous ammonium persulfate solution, 12 g of PMVE and 1.26 g of 8CNVE were injected every 16 g of TFE. When the amount of TFE added after the start of polymerization reached 160 g, the addition of TFE and PMVE, which had been injected after the start of polymerization, was stopped, the temperature inside the reactor was cooled to 10 ° C., the polymerization reaction was stopped, the gas remaining in the reactor was recovered, and the liquid was extracted to obtain aqueous dispersion A4. The average particle size of the polymer particles in aqueous dispersion A4 was 200 nm. The total amount of TFE added before the start of polymerization was 17 g, and the total amount of PMVE was 82 g. The total amount of TFE added after the start of polymerization was 160 g, and the total amount of PMVE was 108 g. The total amount of TFE added was 177 g, the total amount of PMVE added was 190 g, and the total amount of 8CNVE added was 16.0 g. Aqueous dispersion A4 was coagulated with a 5% by mass aqueous nitric acid solution, filtered, and the resulting solid was washed with ultrapure water. It was then vacuum dried at 100 ° C. for 12 hours to obtain fluorine-containing elastomer A4. The resulting fluorine-containing elastomer A4 was analyzed by NMR and found to have a composition of PMVE / PMAE / TFE / 8CNVE=31.6 / 0.1 / 67.7 / 0.6 ​​(molar ratio). The fluorine-containing elastomer A4 had no melting point. The water content of the fluorine-containing elastomer A4 was 0.0% by mass.

[0304] [Example 7] <First polymerization step> Ultrapure water (1196 g), PMVE (93 g), TFE (15 g), 8CNVE (3.4 g), and a 0.25 mass% aqueous solution of NaVSA (20 g, 50 mg of NaVSA) were charged into a 2.2 L stainless steel pressure reactor, and the temperature was raised to 90 ° C. with stirring. From the point when the pressure reached 1.4 MPaG, an aqueous solution of ammonium persulfate (15 mass%, total amount 20 g) was added 8 times every 5 minutes to proceed with polymerization. As the pressure in the reactor decreased with the initiation of polymerization, TFE was added to maintain the pressure constant. This was repeated, and when the amount of TFE added after the initiation of polymerization reached 40 g, the addition of TFE injected after the initiation of polymerization was stopped, the temperature inside the reactor was cooled to 10 ° C., the polymerization reaction was stopped, and the gas remaining in the reactor was recovered, followed by drawing out the liquid to obtain raw material solution B5. The average particle size of the particles of the first fluoropolymer B3-1 in raw material liquid B5 was 70 nm. The solids concentration of raw material liquid B5 was 3.3% by mass. Raw material liquid B5 was freeze-coagulated and then filtered, and the obtained first fluoropolymer B3-1 was washed with ultrapure water. Thereafter, it was vacuum-dried at 100°C. The obtained first fluoropolymer B3-1 was analyzed by NMR, and the result was that the molar ratio of PMVE / TFE / 8CNVE was 29.1 / 69.9 / 1.0. The first fluoropolymer B3-1 did not have a melting point.

[0305] <Purification Step> The purification step was carried out in the same manner as in Example 4 to obtain raw material solution B6.

[0306] <Second Polymerization Step> The second polymerization step was carried out in the same manner as in Example 4 to obtain a second aqueous dispersion B3-2.

[0307] The second aqueous dispersion B3-2 was a dispersion in which particles containing a first fluoropolymer B3-1 and a second fluoropolymer B3-2 were dispersed in an aqueous medium. The average particle size of the particles in aqueous dispersion B3-2 was 120 nm. The second aqueous dispersion B3-2 was coagulated with a 5% by mass aqueous nitric acid solution, filtered, and the resulting solid was washed with ultrapure water. It was then vacuum dried at 100°C for 12 hours to obtain a fluoroelastomer B3 containing a first fluoropolymer B3-1 and a second fluoropolymer B3-2. NMR analysis of the resulting fluoroelastomer B3 revealed that it had a composition of PMVE / PMAE / TFE / 8CNVE=30.6 / 0.1 / 68.6 / 0.7 (molar ratio). Furthermore, the fluoroelastomer B3 did not have a melting point. The water content of the fluoroelastomer B3 was 0.2% by mass.

[0308] [Example 8] <First polymerization step> Raw material solution B7 was obtained in the same manner as in Example 4, except that 8CNVE was not added. The average particle size of the particles of the first fluoropolymer B4-1 in raw material solution B7 was 43.5 nm. The solids concentration of raw material solution B7 was 2.3 mass%. Raw material solution B7 was freeze-coagulated and then filtered, and the obtained first fluoropolymer B4-1 was washed with ultrapure water. Thereafter, it was vacuum-dried at 100°C. The obtained first fluoropolymer B4-1 was analyzed by NMR, and the result was that the ratio of PMVE / TFE was 33 / 67 (molar ratio). The first fluoropolymer B4-1 had no melting point.

[0309] <Purification Step> The purification step was carried out in the same manner as in Example 4 to obtain raw material solution B8.

[0310] <Second Polymerization Step> The second polymerization step was carried out in the same manner as in Example 4 to obtain a second aqueous dispersion B4-2.

[0311] The second aqueous dispersion B4-2 was a dispersion in which particles containing a first fluoropolymer B4-1 and a second fluoropolymer B4-2 were dispersed in an aqueous medium. The average particle size of the particles in aqueous dispersion B4-2 was 140 nm. The second aqueous dispersion B4-2 was coagulated with a 5% by mass aqueous nitric acid solution, filtered, and the resulting solid was washed with ultrapure water. It was then vacuum dried at 100°C for 12 hours to obtain a fluoroelastomer B4 containing a first fluoropolymer B4-1 and a second fluoropolymer B4-2. NMR analysis of the resulting fluoroelastomer B4 revealed that it had a composition of PMVE / PMAE / TFE / 8CNVE=30.4 / 68.1 / 0.5 (molar ratio). Furthermore, the fluoroelastomer B4 did not have a melting point. The water content of the fluoroelastomer B4 was 0.2% by mass.

[0312] [Example 9] A 2.1 L stainless steel pressure reactor was charged with ultrapure water (1004 g), C ２ F ５ OCF ２ CF ２ OCF ２ COONH ４A 30% by mass aqueous solution (80.1 g) of ammonium persulfate, a 5% by mass aqueous solution (10.49 g) of disodium hydrogen phosphate dodecahydrate, PMVE (55 g), and TFE (11 g) were added, and the temperature was raised to 80°C with stirring. The internal pressure of the reactor was 0.974 MPaG when the temperature reached 0°C. Next, an aqueous solution of ammonium persulfate (3.0% by mass, 18 g) was added to initiate polymerization. When the internal pressure of the reactor dropped to 0.89 MPaG, TFE and PMVE were injected, and the internal pressure of the reactor was increased to 0.90 MPaG. 16 g of TFE and 12 g of PMVE were added, followed by the addition of 1.26 g of 8CNVE. This was repeated every time the internal pressure of the reactor dropped to 0.89 MPaG. When the polymerization rate began to slow down, a 3% by mass aqueous solution of APS was appropriately added. When the amount of TFE added after the start of polymerization reached 408 g, the addition of TFE and PMVE injected after the start of polymerization was stopped, the temperature inside the reactor was cooled to 10 ° C., the polymerization reaction was stopped, the gas remaining in the reactor was recovered, and the liquid was extracted to obtain aqueous dispersion C1. The total amount of 8CNVE added was 16.0 g. The total amount of TFE added before the start of polymerization was 17 g, and the total amount of PMVE was 81 g. The total amount of TFE added after the start of polymerization was 408 g, and the total amount of PMVE was 294 g. The total amount of TFE added was 425 g, the total amount of PMVE added was 375 g, and the total amount of 8CNVE added was 16.0 g. The average particle size of the polymer particles in aqueous dispersion C1 was 20.9 nm. Aqueous dispersion C1 was coagulated with a 5% by mass aqueous nitric acid solution and then filtered, and the resulting solid was washed with ultrapure water. Thereafter, the mixture was vacuum-dried at 100°C for 12 hours to obtain a fluorine-containing elastomer C1. NMR analysis of the obtained fluorine-containing elastomer C1 revealed that its composition was PMVE / TFE / 8CNVE = 30.1 / 69.5 / 0.4 (molar ratio). The fluorine-containing elastomer C1 did not have a melting point. The water content of the fluorine-containing elastomer C1 was 0.0% by mass.

[0313] Example 10 Aqueous dispersion C2 was obtained in the same manner as in Example 1, except that 8CNVE (3.4 g) was added to the reactor before adding the aqueous ammonium persulfate solution to start polymerization. Aqueous dispersion C2 was coagulated with a 20% by mass aqueous potassium aluminum sulfate solution, filtered, and the resulting solid was washed with ultrapure water. It was then vacuum dried at 100°C for 12 hours to obtain fluoroelastomer C2. The resulting fluoroelastomer C2 was analyzed by NMR, and its composition was PMVE / TFE / 8CNVE = 31.4 / 68.0 / 0.6 (molar ratio). Furthermore, fluoroelastomer C2 did not have a melting point. The water content of fluoroelastomer C2 was 0.0% by mass.

[0314] [Example 11] Aqueous dispersion A5 was obtained in the same manner as in Example 1, except that 3.2 g of C3DVE was added before the start of polymerization. The total amount of TFE added was 177 g, the total amount of PMVE added was 190 g, the total amount of 8CNVE added was 16.0 g, and the total amount of C3DVE added was 3.2 g. The average particle size of the polymer particles in aqueous dispersion A5 was 80.0 nm. Aqueous dispersion A5 was coagulated with a 5% by mass aqueous nitric acid solution, filtered, and the resulting solid was washed with ultrapure water. It was then vacuum dried at 100°C for 12 hours to obtain fluorine-containing elastomer A5. NMR analysis of the obtained fluorine-containing elastomer A5 revealed that its composition was PMVE / TFE / 8CNVE = 30.6 / 68.8 / 0.6 (molar ratio). Furthermore, fluorine-containing elastomer A5 did not have a melting point. The water content of the fluorine-containing elastomer A2 was 0.0% by mass.

[0315] Next, the following components were mixed in the amounts shown below: Fluorine-containing elastomer: 100 parts by mass, MT-C: 5 parts by mass, BOAP: 0.8 parts by mass

[0316] Details of the components other than the fluorine-containing elastomer are as follows: MT-C: MT Carbon N990, manufactured by Vanderbilt, carbon black BOAP: 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, crosslinking agent

[0317] The mixture was kneaded using a twin roll mill at room temperature (25°C) for 10 minutes to obtain a mixture. The gap between the twin rolls was adjusted, and the resulting mixture was processed into a 3 mm-thick sheet to obtain the fluorine-containing elastomer composition of Example 1. Next, the fluorine-containing elastomer composition obtained in each example was hot-pressed at 180°C for 20 minutes using a hydraulic press (model: SA-301 50T type, manufactured by Tester Sangyo Co., Ltd., ram diameter: 180 mm) to perform primary crosslinking, thereby obtaining an O-ring 1 (P-26 (JIS B2401:2012 standard)). The obtained O-ring 1 was heated in a nitrogen atmosphere in an oven (DN411I, manufactured by Yamato Scientific Co., Ltd.) at 90°C for 2 hours, then heated to 200°C over 2 hours, heated at 200°C for 4 hours, and further heated to 305°C over 2 hours, and heated at 305°C for 12 hours to perform secondary crosslinking. Thereafter, the O-ring was cooled to 23° C. to obtain an O-ring that was a crosslinked rubber article. All of the crosslinked bodies contained in the crosslinked rubber article had a heterocyclic structure.

[0318] <Weight Loss Rate> An O-ring was immersed in 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane for 12 hours and then vacuum dried at 100°C until drying was complete. The mass was measured every 12 hours, and drying was judged to be complete when the rate of change from the previous measurement was 0.01% by mass or less. Specifically, drying was judged to be complete when the following formula (M) was satisfied: {X(n) - X(n-1)} / X(n-1) x 100 ≤ 0.01 ... (M) X0: Mass of the crosslinked rubber article X1: Mass of the crosslinked rubber article when drying was judged to be complete X(n): Mass of the crosslinked rubber article (12 x n) hours after the start of drying (n is an integer of 1 or more) X(n-1): Mass of the crosslinked rubber article (12(n-1)) hours after the start of drying (n is an integer of 1 or more)

[0319] The weight loss rate was calculated using the following formula: Weight loss rate (%) = {X1 / X0} x 100

[0320] <Surface Roughness (Sa)> The O-ring was cut along the thickness direction to a length of 5 to 10 mm, and then further cut along the length direction (i.e., the direction perpendicular to the thickness direction) to obtain a test piece (length 5 to 10 mm, thickness 1.0 to 3.5 mm). The test piece was placed on the sample stage of the laser microscope equipped with a white light interferometer described below, and the surface of the test piece other than the cut surface was observed. The field of view was autofocused at 10x magnification (objective lens), and image data of the entire observation range (1062 μm × 1416 μm) was obtained. The obtained image data was subjected to surface shape correction (waviness correction: correction strength 5) using an analysis tool attached to the laser microscope equipped with a white light interferometer, and the arithmetic mean roughness Sa of the entire observation range was determined. The value obtained in this manner was taken as the arithmetic mean roughness Sa. Laser microscope equipped with a white light interferometer: controller unit model VK-X3000, measurement unit model VK-X3100, manufactured by Keyence Corporation

[0321] <Measurement of Compression Set> The compression set was measured according to the method described in ASTM D395 or JIS K6262 (2013). The O-rings (original thickness (wire diameter) = 3.5 mm) prepared in each example were compressed to a compression rate of 18% using a compression device. Next, the compression device with the compressed O-ring fixed thereto was placed in an electric furnace and left at 300 ° C for 70 hours, after which the compression device was removed from the electric furnace, the O-ring was immediately removed from the compression device, and the removed O-ring was left in a constant temperature room at 23 ° C for 30 minutes, and the thickness of the O-ring (thickness after compression treatment) was measured. The test was performed using two O-rings, and the arithmetic average of the measured values ​​of the two O-rings was used. The compression set was calculated using the following formula. The closer the compression set is to 0%, the smaller the compression set is, and the more preferable it is. Compression set (%) = {original thickness of O-ring (wire diameter) - thickness of O-ring 30 minutes after removal from compression device (thickness after compression treatment)} ÷ {original thickness of O-ring (wire diameter) - thickness of spacer} × 100

[0322] Table 1 shows the evaluation results of crosslinked rubber articles. In Table 1, in the type of manufacturing method, manufacturing method A means a manufacturing method in which polymerization is carried out in one stage, and manufacturing method B means a manufacturing method in which polymerization is carried out in two stages. "Amount of F-containing emulsifier" means the content of an emulsifier having a fluorine atom. "Content of TFE" means the content of structural units based on TFE. "Content of CN monomer" means the content of structural units based on a cyano group-containing monomer.

[0323]

[0324] As shown in Table 3, in Examples 1 to 7 and 11, crosslinked rubber articles having smaller compression set and superior surface smoothness were obtained compared to Examples 8 to 10.

[0325] The disclosures of Japanese Patent Application No. 2023-205993 filed on December 6, 2023, and Japanese Patent Application No. 2024-177486 filed on October 9, 2024 are incorporated herein by reference in their entirety. In addition, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually indicated to be incorporated by reference.

Claims

1. A method for producing a fluorine-containing elastomer, comprising a step of polymerizing a cyano group-containing monomer and at least one monomer selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride, fluorine-containing vinyl ethers, and fluorine-containing allyl ethers in the presence of a compound represented by the following formula (X) and an aqueous medium, and in the substantial absence of an emulsifier having a fluorine atom: CX １ X ２ = C.X. ３ -L-Z...(X) In formula (X), １ and X ２ are each independently a hydrogen atom, a chlorine atom, or an alkyl group; ３ is a hydrogen atom or an alkyl group, L is a single bond or a divalent linking group, and Z is an anionic group or a salt of an anionic group.

2. The method for producing a fluorine-containing elastomer according to claim 1, wherein the cyano group-containing monomer is represented by the following formula (Y): １１ R １２ =CR １３ -R １４ -CN...(Y) In formula (Y), R １１ , R １２ , and R １３ each independently represents a hydrogen atom, a fluorine atom, or a methyl group; R １４ 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.

3. The method for producing a fluorine-containing elastomer according to claim 1, wherein the content of the cyano group-containing monomer is 0.5 to 20 mol % based on the total amount of the monomers used in the polymerization of the fluorine-containing elastomer.

4. The method for producing a fluorine-containing elastomer according to claim 1, wherein the content of the compound represented by formula (X) is 0.1 to 5,000 ppm by mass based on the total amount of the aqueous medium.

5. A method for producing a fluorine-containing elastomer, comprising: a step of polymerizing a first monomer containing a cyano group-containing monomer and at least one selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride, fluorinated vinyl ether and fluorinated allyl ether in a first aqueous medium in the substantial absence of an emulsifier having a fluorine atom, to produce a first fluorine-containing polymer and obtain an aqueous dispersion containing the first fluorine-containing polymer; and a step of polymerizing a second monomer containing tetrafluoroethylene in the aqueous dispersion containing the first fluorine-containing polymer to obtain a second fluorine-containing polymer, thereby obtaining a fluorine-containing elastomer containing the first fluorine-containing polymer and the second fluorine-containing polymer.

6. The method for producing a fluorine-containing elastomer according to claim 5, wherein the cyano group-containing monomer is represented by the following formula (Y): １１ R １２ =CR １３ -R １４ -CN...(Y) In formula (Y), R １１ , R １２ , and R １３ each independently represents a hydrogen atom, a fluorine atom, or a methyl group; R １４ 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.

7. The method for producing a fluorine-containing elastomer according to claim 5, wherein the first aqueous medium further contains a compound represented by the following formula (X): CX １ X ２ = C.X. ３ -L-Z...(X) In formula (X), １ and X ２ are each independently a hydrogen atom, a chlorine atom, or an alkyl group; ３ is a hydrogen atom or an alkyl group, L is a single bond or a divalent linking group, and Z is an anionic group or a salt of an anionic group.

8. The method for producing a fluorine-containing elastomer according to claim 7, wherein the content of the compound represented by formula (X) is 0.1 to 5,000 ppm by mass based on the total amount of the first aqueous medium.

9. The method for producing a fluorine-containing elastomer according to claim 5, wherein the content of said cyano group-containing monomer is 0.5 to 20 mol % based on the total amount of said first monomer.

10. A composition comprising a compound represented by the following formula (X), a first fluorine-containing polymer comprising a constituent unit based on a cyano group-containing monomer and a constituent unit based on at least one selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride, fluorinated vinyl ether, and fluorinated allyl ether, and a second fluorine-containing polymer comprising a constituent unit based on tetrafluoroethylene, and substantially free of an emulsifier having a fluorine atom. CX １ X ２ = C.X. ３ -L-Z...(X) In formula (X), １ and X ２ are each independently a hydrogen atom, a chlorine atom, or an alkyl group; ３ is a hydrogen atom or an alkyl group, L is a single bond or a divalent linking group, and Z is an anionic group or a salt of an anionic group.

11. The composition according to claim 10, wherein the metal content is 50 ppm by mass or less based on the total solid content of the composition.

12. The composition according to claim 10 or 11, wherein the content of constitutional units based on the cyano group-containing monomer is 0.1 to 10 mol % based on the total amount of the first fluorine-containing polymer and the second fluorine-containing polymer.

13. A solid composition comprising a fluorine-containing elastomer including a constituent unit based on a cyano group-containing monomer, a constituent unit based on tetrafluoroethylene, and a constituent unit based on at least one selected from the group consisting of a fluorine-containing vinyl ether and a fluorine-containing allyl ether, wherein when heated under a nitrogen atmosphere under the following condition 1, the weight loss rate 1000 minutes after the start of heating is 2.0% or less, and wherein the composition is substantially free of an emulsifier having a fluorine atom: (Condition 1) The composition is heated from 40°C to 90°C at a heating rate of 20°C / min, held at 90°C for 120 minutes, heated from 90°C to 200°C at a heating rate of 20°C / min, held at 200°C for 240 minutes, heated from 200°C to 305°C at a heating rate of 20°C / min, and held at 305°C for 720 minutes.

14. The solid composition according to claim 13, wherein the metal content is 50 ppm by mass or less based on the total amount of the solid composition.

15. The solid composition according to claim 13 or 14, wherein the content of the constitutional units based on the cyano group-containing monomer is 0.1 to 10 mol % based on the total amount of the fluorine-containing elastomer.

16. The solid composition according to claim 13 or 14, having a storage modulus of 200 to 600 kPa.

17. A crosslinked rubber article comprising a crosslinked product obtained by crosslinking a fluorine-containing elastomer comprising a constituent unit based on a cyano group-containing monomer, a constituent unit based on tetrafluoroethylene, and a constituent unit based on at least one selected from the group consisting of a fluorine-containing vinyl ether and a fluorine-containing allyl ether, the weight loss rate of which after immersion in 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane for 12 hours and drying is 0.5% or less, and which is substantially free of an emulsifier having a fluorine atom.

18. The crosslinked rubber article according to claim 17, wherein the crosslinked product has a heterocyclic structure.

19. The crosslinked rubber article according to claim 17, wherein the crosslinked product has at least one structure selected from the group consisting of an oxazole structure and a triazine structure.

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