Method for producing composition, and crosslinked rubber article

Abstract

Provided are: a method for producing a composition that can form a crosslinked rubber article that exhibits an excellent plasma resistance and can resist cracking at high temperatures and high compressions; and a crosslinked rubber article that exhibits an excellent plasma resistance. The method for producing a composition comprises a kneading step for kneading a mixture comprising a fluorocopolymer (A) and a fluorocopolymer (B) wherein the kneading is performed at or above the glass-transition temperature of the fluorocopolymer (B). The fluorocopolymer (A) has a unit based on tetrafluoroethylene and a unit based on perfluoro(alkyl vinyl ether). The fluorocopolymer (B) is a copolymer different from the fluorocopolymer (A) and has the following: a unit based on a monomer having at least one functional group selected from the group consisting of the carboxy group and groups represented by formula (X); a unit based on tetrafluoroethylene; and a unit based on perfluoro(alkyl vinyl ether).

Description

Method for producing composition, crosslinked rubber article

[0001] The present invention relates to a method for making a composition and a crosslinked rubber article.

[0002] Crosslinked rubber articles obtained by crosslinking a fluorine-containing copolymer are widely used as sealing materials (e.g., O-rings, packings, oil seals, and gaskets) and cushioning materials in the fields of vehicles, ships, aircraft, general machinery, construction, etc. Patent Document 1 discloses a method for producing a composition containing a specific fluorine-containing copolymer as a method for producing a composition used in such crosslinked rubber articles.

[0003] International Publication No. 2021 / 210502

[0004] In recent years, there has been a demand in various fields for improved performance of crosslinked rubber articles, specifically for crosslinked rubber articles that are less susceptible to cracking under high-temperature, high-compression conditions and have excellent plasma resistance. In response to such demands, the present inventors evaluated crosslinked rubber articles formed using compositions obtained by the method for producing a composition as described in Patent Document 1, and found that the articles were prone to cracking when subjected to a compression set test under high-temperature, high-compression conditions, and that there was room for improvement in plasma resistance.

[0005] An object of the present invention is to provide a method for producing a composition that can suppress cracking under high temperature and high compression and that can form a crosslinked rubber article that has excellent plasma resistance, and to provide such a crosslinked rubber article.

[0006] As a result of intensive studies, the present inventors have found that the above-mentioned problems can be solved by the following configuration. [1] A method for producing a composition, comprising a kneading step of kneading a mixture containing a fluorinated copolymer (A) and a fluorinated copolymer (B) at a temperature equal to or higher than the glass transition temperature of the fluorinated copolymer (B), wherein the fluorinated copolymer (A) has units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), and the fluorinated copolymer (B) is a copolymer different from the fluorinated copolymer (A) and has units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether). [2] A method for producing the composition according to [1], wherein the fluorinated copolymer (A) has units having a nitrile group. [3] A method for producing the composition according to [1] or [2], wherein the kneading step is a step of kneading the mixture at a temperature equal to or higher than the melting point of the fluorinated copolymer (B). [4] The method for producing a composition according to any one of [1] to [3], wherein the content of the fluorine-containing copolymer (B) in the mixture is 50 parts by mass or less per 100 parts by mass of the fluorine-containing copolymer (A). [5] The method for producing a composition according to any one of [1] to [4], wherein the fluorine-containing copolymer (A) is a fully fluorinated fluorine-containing copolymer. [6] A crosslinked rubber article obtained by crosslinking the fluorine-containing copolymer (A) in the composition produced by the method for producing a composition according to any one of [1] to [5], using a crosslinking agent. [7] The crosslinked rubber article according to [6], which is a sealing material for semiconductor device.

[0007] According to the present invention, it is possible to provide a method for producing a composition that can suppress cracking under high temperature and high compression and that can form a crosslinked rubber article that has excellent plasma resistance, and a crosslinked rubber article.

[0008] The meanings of terms used in the present invention are as follows. A numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. A "unit" is a collective term for an atomic group derived from one molecule of the monomer that is formed directly by polymerizing the monomer, and an atomic group obtained by chemically converting a part of the atomic group. A "unit based on a monomer" will hereinafter also be simply referred to as a "unit." A "rubber" means a rubber that exhibits properties defined by JIS K 6200:2008, and is distinguished from a "resin."

[0009] [Method for producing composition] The method for producing a composition of the present invention (hereinafter also referred to as "the present production method") comprises a kneading step of kneading a mixture containing a fluorine-containing copolymer (A) and a fluorine-containing copolymer (B) at a temperature not lower than the glass transition temperature of the fluorine-containing copolymer (B), wherein the fluorine-containing copolymer (A) has units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), and the fluorine-containing copolymer (B) is a copolymer different from the fluorine-containing copolymer (A) and has units based on a monomer having at least one functional group selected from the group consisting of a carboxy group and a group represented by the formula (X) described below, units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether).

[0010] Crosslinked rubber articles made from the composition obtained using this production method are able to suppress cracking under high temperature and high compression and have excellent plasma resistance. The details of the reasons for this are not clear, but are presumed to be due to the following reasons. By kneading the above mixture at a temperature equal to or higher than the glass transition temperature of the fluorocopolymer (B), the fluorocopolymer (B) can be uniformly dispersed in the fluorocopolymer (A), and it is presumed that as a result, the obtained crosslinked rubber article is able to suppress cracking under high temperature and high compression and has excellent plasma resistance. Hereinafter, at least one of the effects of being able to suppress cracking under high temperature and high compression and having excellent plasma resistance will also be referred to as the "effect of the present invention."

[0011] <Mixture> The mixture used in the present production method contains a fluorine-containing copolymer (A) and a fluorine-containing copolymer (B). The mixture preferably does not contain a crosslinking agent described below. The mixture preferably consists of only the fluorine-containing copolymer (A) and the fluorine-containing copolymer (B). Specifically, the total content of the fluorine-containing copolymer (A) and the fluorine-containing copolymer (B) is preferably 90 to 100% by mass, more preferably 95 to 100% by mass, and even more preferably 99 to 100% by mass, based on the total mass of the mixture.

[0012] (Fluorine-containing copolymer (A)) The fluorine-containing copolymer (A) has units based on tetrafluoroethylene (hereinafter also referred to as "TFE") and units based on perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE"). The fluorine-containing copolymer (A) itself does not completely return to its original shape when stretched, but exhibits a property in which the ability to return to its original shape is strengthened by crosslinking, that is, it exhibits rubber properties.

[0013] The content of TFE units is preferably from 60.0 to 80.0 mol %, more preferably from 63.0 to 75.0 mol %, and even more preferably from 66.0 to 72.0 mol %, based on all units in the fluorine-containing copolymer (A).

[0014] The PAVE unit is a unit based on perfluoro(alkyl vinyl ether). From the viewpoint of excellent polymerization reactivity and rubber physical properties, the PAVE is preferably a monomer represented by formula (1): CF ２ =CF-O-R ｆ２ (1) In formula (1), R ｆ２ represents a perfluoroalkyl group having 1 to 10 carbon atoms. ｆ２ From the viewpoint of better polymerization reactivity, the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 8, more preferably 1 to 6, even more preferably 1 to 5, and particularly preferably 1 to 3. The perfluoroalkyl group may be linear or branched.

[0015] 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"), with PMVE or PPVE being preferred.

[0016] In order to obtain crosslinked rubber articles with better elasticity, the content of PAVE units is preferably from 20.0 to 40.0 mol%, more preferably from 24.0 to 36.0 mol%, and even more preferably from 27.0 to 33.0 mol%, based on all units of the fluorocopolymer (A). The suitable content is similar when PMVE or PPVE is used as PAVE.

[0017] The fluorine-containing copolymer (A) contains a monomer having a nitrile group (hereinafter referred to as "R ＣＮ It is preferable that the unit is based on R ＣＮ In order to obtain a more excellent effect of the present invention, it is preferable that the monomer further contains a fluorine atom, and the monomer represented by formula (2) is more preferable. １１ R １２ =CR １３ -R １４ -CN (2) In formula (2), R １１ , R １２ and R １３ R each independently represents a hydrogen atom, a fluorine atom, or a methyl group. 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 the perfluorohydrocarbon group.

[0018] R ＣＮ From the viewpoint of excellent polymerization reactivity of R １１ , R １２ and R １３ is preferably a fluorine atom or a hydrogen atom, and R １１ , R １２ and R １３ are more preferably fluorine atoms or hydrogen atoms, and in view of the superior mold releasability and heat resistance of the crosslinked rubber article, R １１, R １２ and R １３ More preferably, all of R are fluorine atoms. １４ R may be linear, branched, or cyclic, and is preferably linear or branched. １４ The number of carbon atoms in R is preferably 2 to 8, more preferably 3 to 7, still more preferably 4 to 7, and particularly preferably 4 to 6. １４ R may have an etheric oxygen atom, and preferably has an etheric oxygen atom in order to provide crosslinked rubber articles with better rubber physical properties. １４ The number of etheric oxygen atoms in is preferably 1 to 3, and more preferably 1 or 2.

[0019] Specific examples of the monomer represented by formula (2) include CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ CN (hereinafter 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.

[0020] R ＣＮ The content of the units is preferably from 0.05 to 5 mol %, more preferably from 0.1 to 3 mol %, and even more preferably from 0.2 to 1.5 mol %, based on the total units of the fluorine-containing copolymer (A), since the effects of the present invention are more excellent.

[0021] The fluorine-containing copolymer (A) may have units based on monomers other than those mentioned above (hereinafter also referred to as "other monomers"). Specific examples of other monomers include vinylidene fluoride (hereinafter also referred to as "VdF"), hexafluoropropylene (hereinafter also referred to as "HFP"), chlorotrifluoroethylene, a monomer having two or more polymerizable unsaturated bonds (hereinafter also referred to as "BO"), a monomer represented by formula (6), ethylene, propylene, and a monomer having a halogen atom (hereinafter also referred to as "monomer having another halogen atom"). Specific examples of monomers having another halogen atom include bromotrifluoroethylene and iodotrifluoroethylene.

[0022] The BO unit is a unit based on 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). 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 the crosslinked rubber article at high temperatures.

[0023] The BO is preferably a monomer represented by formula (3) in that the compression set under high temperature and high compression conditions is smaller. ３１ R ３２ =CR ３３ ) ａ３ R ３４ (3) In formula (3), R ３１ , R ３２ and R ３３ each independently represents a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group. a3 represents an integer of 2 to 6. R ３４ represents a trivalent 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. ３１ , multiple R ３２ and multiple R ３３a3 is preferably 2 or 3, and more preferably 2.

[0024] Since the polymerization reactivity of BO is superior, R ３１ , R ３２ and R ３３ is preferably a fluorine atom or a hydrogen atom, and R ３１ , R ３２ and R ３３ In terms of the heat resistance and chemical resistance of the crosslinked rubber article, R ３１ , R ３２ and R ３３ More preferably, all of R are fluorine atoms. ３４ R may be linear, branched, or cyclic, preferably linear or branched, and more preferably linear. ３４ The number of carbon atoms in R is preferably 2 to 10, more preferably 3 to 8, even more preferably 3 to 6, and particularly preferably 3 to 5. ３４ R may have an etheric oxygen atom, and preferably has an etheric oxygen atom in order to provide crosslinked rubber articles with better rubber physical properties. ３４ 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. ３４ The etheric oxygen atom in R ３４ It is preferred that the nucleotide sequence is located at the end of the nucleotide sequence.

[0025] Of the monomers represented by formula (3), specific examples of suitable monomers include a monomer represented by formula (4) and a monomer represented by formula (5).

[0026] (CF ２ =CF) ２ R ４１ (4) In formula (4), R ４１ represents a divalent perfluorohydrocarbon group having 2 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.

[0027] 40. 10. 4. 4. 4. 4. 4 ２ SHY(S ２ ) ２ THIS IS THE ２ 、S9 ２ SHY(S ２ ) ３ THIS IS THE ２ 、S9 ２ SHY(S ２ ) ４ THIS IS THE ２ 、S9 ２ SHY(S ２ ) ６ THIS IS THE ２、 9. The ２ SHY(S ２ ) ８ THIS IS THE ２ 、S9 ２ SHY(S ２ ) ２ 10(5) ３ 49 ２ THIS IS THE ２ 、S9 ２ SHY(S ２ ) ２ 10(S) ３ 49 ２ 9) ２ EXPERIENCE ２ 、S9 ２ THIS IS THE THING ２ 10(10) ２ 9. The ２ 9) ２ EXPERIENCE ２ 、S9 ２ SHY(S ２ 9) ３ 10(S) ３ 49 ２ 9) ２ EXPERIENCE ２ 、S9 ２ THIS IS THE THING ２ 10(40) ３ 10(40) ２ ) ２ 10(5) ３ 49 ２ THIS IS THE ２ 、および、9 ２ THIS IS THE THING ２ 9. The ２O (CF ２ O) ２ CF ２ CF ２ OCF = CF ２ CF ２ = CFO (CF ２ ) ３ OCF = CF ２ , or CF ２ = CFO (CF ２ ) ４ OCF = CF ２ is preferred.

[0028] (CH ２ =CH) ２ R ５１ (5) In formula (5), R ５１ represents a divalent perfluorohydrocarbon group having 2 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.

[0029] Specific examples of the monomer represented by formula (5) 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 and CH ２ =CH(CF ２ ) ６ CH=CH ２ is preferred.

[0030] When BO is copolymerized, the polymerizable double bond at the end of BO reacts during the polymerization to give a fluorine-containing copolymer (A) having a branched chain.

[0031] CF ２ =CF-O-R ｆ６ (6) In formula (6), R ｆ６ represents a perfluoroalkyl group having 1 to 8 carbon atoms and containing 1 to 5 etheric oxygen atoms. ｆ６The number of carbon atoms is preferably 1 to 6, and more preferably 1 to 5.

[0032] Specific examples of the monomer represented by formula (6) include perfluoro(3,6-dioxa-1-heptene), perfluoro(3,6-dioxa-1-octene), and perfluoro(5-methyl-3,6-dioxa-1-nonene).

[0033] When the fluorine-containing copolymer (A) contains other monomer units, the content of the other monomer units is preferably from 0.01 to 20 mol %, more preferably from 0.5 to 10 mol %, and even more preferably from 1 to 5 mol %, based on the total units of the fluorine-containing copolymer (A), from the viewpoint of excellent rubber physical properties of the crosslinked rubber article.

[0034] The fluorine-containing copolymer (A) is preferably a fully fluorinated fluorine-containing copolymer, since the effects of the present invention are more excellent. "Fully fluorinated fluorine-containing copolymer" refers to a fluorine-containing copolymer that does not substantially contain hydrogen atoms bonded to carbon atoms, has fluorine atoms in place of those hydrogen atoms, and has a main chain consisting of a chain of carbon atoms. The side chain of the fully fluorinated fluorine-containing copolymer may have a polyvalent atom other than carbon atoms, and the polyvalent atom is preferably an oxygen atom. "Substantially not containing hydrogen atoms" means that the content of hydrogen atoms in the fully fluorinated fluorine-containing copolymer is 0.5% by mass or less, preferably 0.1% by mass or less, more preferably 0.07% by mass or less, and even more preferably 0.05% by mass or less. When the content of hydrogen atoms is within the above range, good heat resistance or chemical resistance is likely to be obtained.

[0035] The fluorine-containing copolymer (A) may contain iodine atoms. In this case, it is preferable that the fluorine-containing copolymer (A) has an iodine atom at the end of the polymer chain. Examples of the iodine atom include iodine atoms derived from an iodine compound that functions as a chain transfer agent, as described below, and iodine atoms in units based on a monomer having an iodine atom among other halogen-containing monomers such as iodotrifluoroethylene, as described above. Iodine atoms derived from an iodine compound that functions as a chain transfer agent are preferred. When the fluorine-containing copolymer (A) contains iodine atoms, the content of the iodine atoms is preferably 0.01 to 5.0% by mass, more preferably 0.05 to 2.0% by mass, and even more preferably 0.05 to 1.0% by mass, relative to the total mass of the fluorine-containing copolymer (A). When the iodine atom content is within the above range, the crosslinking reactivity of the fluorine-containing copolymer (A) is improved, and the mechanical properties of the crosslinked rubber article are excellent.

[0036] The glass transition temperature of the fluorine-containing copolymer (A) is preferably -20 to 20°C, more preferably -10 to 10°C, and even more preferably -5 to 5°C. The glass transition temperature of the fluorine-containing copolymer (A) can be measured using a differential scanning calorimeter (DSC). Specifically, it is measured by the method described in the Examples section below. The glass transition temperature of the fluorine-containing copolymer (A) can be adjusted by the types of units constituting the fluorine-containing copolymer (A), the content ratio of those units, the molecular weight, etc. For example, the glass transition temperature of the fluorine-containing copolymer (A) tends to increase as the content ratio of TFE units increases.

[0037] The content of the fluorine-containing copolymer (A) is preferably from 60 to 99 mass %, more preferably from 70 to 99 mass %, and even more preferably from 80 to 99 mass %, based on the total mass of the mixture.

[0038] An example of the method for producing the fluorine-containing copolymer (A) is a method in which the above-mentioned monomers are copolymerized in the presence of a radical polymerization initiator.

[0039] The radical polymerization initiator is preferably a water-soluble polymerization initiator or a redox polymerization initiator. Specific examples of water-soluble polymerization initiators include persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate, and organic polymerization initiators such as disuccinic acid peroxide and azobisisobutylamidine dihydrochloride. Persulfates are preferred, and ammonium persulfate is more preferred. Examples of redox polymerization initiators include polymerization initiators that combine persulfates with a reducing agent. Polymerization initiators that can polymerize each monomer at a polymerization temperature in the range of 0 to 85°C are preferred. Specific examples of persulfates that constitute redox polymerization initiators include alkali metal salts of persulfate such as ammonium persulfate, sodium persulfate, and potassium persulfate, with ammonium persulfate being preferred. Specific examples of reducing agents to be combined with persulfates include thiosulfates, sulfites, hydrogen sulfites, pyrosulfites, and hydroxymethanesulfinates. Hydroxymethanesulfinates are preferred, and sodium hydroxymethanesulfinate is more preferred.

[0040] In the method for producing the fluorine-containing copolymer (A), the above-mentioned monomers may be copolymerized together with a radical polymerization initiator in the presence of a chain transfer agent. The chain transfer agent is preferably an iodine compound, and is represented by the formula RI ２ In the above formula, R represents an alkylene group or a perfluoroalkylene group having 3 or more carbon atoms (preferably 3 to 8 carbon atoms). ２ Specific examples of the iodo compound represented by the formula (I) include 1,3-diiodopropane, 1,4-diiodobutane, 1,6-diiodohexane, 1,8-diiodooctane, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane, 1,6-diiodoperfluorohexane, and 1,8-diiodoperfluorooctane. As the iodine compound, an iodine compound having a perfluoroalkylene group is preferred, and 1,4-diiodoperfluorobutane is more preferred. When the above-mentioned monomers are copolymerized in the presence of these iodine compounds, iodine atoms can be introduced into the fluorine-containing copolymer (A).

[0041] For details of the components other than those mentioned above used in producing the fluorine-containing copolymer (A) and the production method, reference can be made to the method described in paragraphs 0019 to 0034 of WO 2010 / 082633.

[0042] (Fluorine-containing copolymer (B)) The fluorine-containing copolymer (B) is a copolymer different from the fluorine-containing copolymer (A), and has units having at least one functional group selected from the group consisting of a carboxy group and a group represented by formula (X) (hereinafter also referred to as "specific functional group"), TFE units, and PAVE units. In other words, the fluorine-containing copolymer (B) has units having a specific functional group, TFE units, and PAVE units.

[0043] The specific functional group may be either or both of a carboxy group and a group represented by formula (X): Formula (X) *-CO-O-CO-* In formula (X), * represents a bonding position. The unit having a specific functional group is a monomer having a specific functional group (hereinafter referred to as "R Ｘ It is preferable that the unit is based on R. Ｘ R may have a plurality of specific functional groups. Ｘ When R has a plurality of specific functional groups, the types of the specific functional groups may be the same or different. Ｘ Since R is used as a monomer, it has a polymerizable unsaturated bond. Specific examples of the polymerizable unsaturated bond are as described above. Ｘ is preferably a compound having one specific functional group and one polymerizable unsaturated bond.

[0044] Examples of monomers having a carboxy group include acid anhydrides of unsaturated dicarboxylic acids such as itaconic anhydride (hereinafter also referred to as "IAH"), citraconic anhydride (hereinafter also referred to as "CAH"), 5-norbornene-2,3-dicarboxylic anhydride (also known as himic anhydride, hereinafter also referred to as "NAH"), and maleic anhydride. As the group containing the group represented by formula (X), a group formed by removing one hydrogen atom from an acid anhydride is preferred. Examples of monomers having a group represented by formula (X) include acid anhydrides of unsaturated dicarboxylic acids such as itaconic anhydride (hereinafter also referred to as "IAH"), citraconic anhydride (hereinafter also referred to as "CAH"), 5-norbornene-2,3-dicarboxylic anhydride (also known as himic anhydride, hereinafter also referred to as "NAH"), and maleic anhydride.

[0045] From the viewpoint of reactivity with the nitrile group that the fluorine-containing copolymer (A) may have, R Ｘ preferably contains a monomer having a group represented by formula (X), and from the viewpoint of facilitating the production of the fluorinated copolymer (B), more preferably contains at least one selected from the group consisting of IAH, CAH and NAH, further preferably contains NAH, and particularly preferably NAH. Ｘ may be used alone or in combination of two or more.

[0046] The TFE units and PAVE units contained in the fluorocopolymer (B) are the same as the TFE units and PAVE units contained in the fluorocopolymer (A), respectively.

[0047] The fluorine-containing copolymer (B) may have units based on monomers other than those mentioned above (hereinafter also referred to as "other monomers"). Specific examples and preferred embodiments of the other monomers are the same as those of the other monomers in the fluorine-containing copolymer (A).

[0048] The fluorine-containing copolymer (B) may further have a specific functional group as a main chain terminal group. The specific functional group as a main chain terminal group can be introduced by a radical polymerization initiator, a chain transfer agent, etc. used in the production of the fluorine-containing copolymer (B).

[0049] The content of the unit having a specific functional group is preferably 0.01 to 3 mol%, more preferably 0.03 to 2 mol%, and even more preferably 0.05 to 1 mol%, based on all units of the fluorine-containing copolymer (B), from the viewpoint of more excellent effects of the present invention. The content of the TFE unit is preferably 90 to 99.89 mol%, more preferably 95 to 99.47 mol%, and even more preferably 96 to 98.95 mol%, based on all units of the fluorine-containing copolymer (B), from the viewpoint of more excellent effects of the present invention. The content of the PAVE unit is preferably 0.1 to 9.99 mol%, more preferably 0.5 to 4.97 mol%, and even more preferably 1 to 3.95 mol%, based on all units of the fluorine-containing copolymer (B), from the viewpoint of more excellent effects of the present invention.

[0050] The glass transition temperature of the fluorine-containing copolymer (B) is preferably 40°C or higher, more preferably 50°C or higher, even more preferably 60°C or higher, and particularly preferably 70°C or higher. The upper limit is preferably 150°C or lower, more preferably 120°C or lower, even more preferably 100°C or lower, and particularly preferably 90°C or lower. The glass transition temperature of the fluorine-containing copolymer (B) can be measured using a differential scanning calorimeter (DSC). Specifically, it is measured by the method described in the Examples section below.

[0051] The melting point of the fluorine-containing copolymer (B) is preferably 250°C or higher, more preferably 270°C or higher, even more preferably 290°C or higher, and particularly preferably 295°C or higher. The upper limit is preferably 330°C or lower, more preferably 325°C or lower, even more preferably 315°C or lower, even more preferably 312°C or lower, and particularly preferably 310°C or lower. When the melting point of the fluorine-containing copolymer (B) is equal to or higher than the lower limit of the above range, crosslinked rubber articles made from a mixture containing the fluorine-containing copolymer (B) have excellent heat resistance. Furthermore, when it is equal to or lower than the upper limit of the above range, processability is excellent, and crosslinked rubber articles made from a composition containing the fluorine-containing copolymer (B) have excellent surface smoothness. The melting point of the fluorine-containing copolymer (B) can be measured using a differential scanning calorimeter (DSC). Specifically, it is measured by the method described in the Examples section below. The glass transition temperature and melting point of the fluorine-containing copolymer (B) can be adjusted by the type of units constituting the fluorine-containing copolymer (B), the content ratio of those units, the molecular weight, etc. For example, the melting point of the fluorocopolymer (B) tends to increase as the content of TFE units increases.

[0052] The melt flow rate (hereinafter also referred to as "MFR") of the fluorine-containing copolymer (B) is preferably 1 to 1000 g / 10 min, more preferably 10 to 35 g / 10 min. However, the above MFR is a value measured at a temperature 20°C or more higher than the melting point of the fluorine-containing copolymer (B) (usually 372°C). When the MFR is at least the lower limit of the above range, the fluorine-containing copolymer (B) has excellent processability, and crosslinked rubber articles made from a mixture containing the fluorine-containing copolymer (B) have excellent surface smoothness. When the MFR is at most the upper limit of the above range, the fluorine-containing copolymer (B) has excellent mechanical strength, and crosslinked rubber articles made from a mixture containing the fluorine-containing copolymer (B) have excellent mechanical strength. MFR is a measure of the molecular weight of the fluorine-containing copolymer (B); a higher MFR indicates a lower molecular weight, and a lower MFR indicates a higher molecular weight. The MFR can be adjusted by the molecular weight of the fluorocopolymer (B) and the production conditions of the fluorocopolymer (B). For example, when the polymerization time during polymerization of the monomers is shortened, the MFR tends to increase.

[0053] The content of the fluorine-containing copolymer (B) is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less, per 100 parts by mass of the fluorine-containing copolymer (A), from the viewpoint of better effects of the present invention. The content of the fluorine-containing copolymer (B) is preferably 2 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 7 parts by mass or more, per 100 parts by mass of the fluorine-containing copolymer (A). The content of the fluorine-containing copolymer (B) is preferably 1 to 40% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 20% by mass, per the total mass of the mixture.

[0054] An example of the method for producing the fluorine-containing copolymer (B) is a method in which the above-mentioned monomers are copolymerized in the presence of a radical polymerization initiator, the details of which are as described in WO 2016 / 017801.

[0055] The fluorine-containing copolymer (B) is preferably in the form of particles. That is, the fluorine-containing copolymer (B) is preferably in the form of copolymer particles containing the fluorine-containing copolymer (B). The copolymer particles may contain a polymer other than the fluorine-containing copolymer (A) and the fluorine-containing copolymer (B) (hereinafter also referred to as "other polymer"). Examples of the other polymer include fluorine-containing polymers other than the fluorine-containing copolymer (A) and the fluorine-containing copolymer (B) (for example, tetrafluoroethylene-fluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and ethylene-tetrafluoroethylene copolymer), polytetrafluoroethylene, aromatic polyester, polyamideimide, and thermoplastic polyimide. The content of the fluorine-containing copolymer (B) in the copolymer particles is preferably 80 to 100% by mass, more preferably 85 to 100% by mass, still more preferably 90 to 100% by mass, and particularly preferably 99.99 to 100% by mass, based on the total mass of the polymer particles.

[0056] The particle diameter D50 of the copolymer particles is preferably 0.02 to 50 μm, more preferably 0.02 to 35 μm, and even more preferably 0.02 to 10 μm, in order to obtain better effects of the present invention. The particle diameter D50 of the copolymer particles is the volume-based cumulative 50% diameter (D50) determined by a laser diffraction / scattering method. That is, the particle size distribution is measured by the laser diffraction / scattering method, a cumulative curve is determined with the total volume of the particle population set to 100%, and the particle diameter D50 is the point on the cumulative curve where the cumulative volume is 50%.

[0057] The copolymer particles can be produced, for example, by the method for producing resin particles and resin powder described in WO 2016 / 017801.

[0058] <Steps> (Kneading Step) The present production method includes a kneading step of kneading the above-mentioned mixture at a temperature equal to or higher than the glass transition temperature of the fluorocopolymer (B).

[0059] By carrying out the above-mentioned kneading step, the fluorine-containing copolymer (A) and the fluorine-containing copolymer are easily mixed uniformly, thereby achieving the effects of the present invention. Examples of the kneading method include known kneading methods, and a method of kneading using a kneader is preferred. Specific examples of the kneader include a roll kneader, a kneader kneader, a Banbury mixer, and an extruder. From the viewpoints of kneading ability, temperature control, and production stability, an extruder is preferred. Examples of the extruder include a device having a heating device and a cylinder with a vent, and for example, a single-screw extruder, a twin-screw extruder, or a multi-screw extruder can be used. An extruder may be used alone, or a plurality of extruders of the same or different types may be connected in series. When a twin-screw extruder is used, examples of the twin-screw extruder include a non-intermeshing co-rotating type, an intermeshing co-rotating type, a non-intermeshing counter-rotating type, and an intermeshing counter-rotating type. Specific examples of the extruder include Labo Plastomill (manufactured by Toyo Seiki Seisakusho Co., Ltd.) and Plasticoda Labostation (manufactured by Brabender).

[0060] The kneading temperature is equal to or higher than the glass transition temperature of the fluorine-containing copolymer (B), and preferably equal to or higher than the melting point of the fluorine-containing copolymer (B). The glass transition temperature and melting point of the fluorine-containing copolymer (B) are as described above. The kneading temperature is also preferably equal to or higher than the glass transition temperature of the fluorine-containing copolymer (A), and more preferably equal to or higher than the melting point of the fluorine-containing copolymer (A). Specifically, the kneading temperature is preferably 80°C or higher, more preferably 200°C or higher, even more preferably 240°C or higher, and particularly preferably 270°C or higher. The upper limit is preferably 350°C or lower, more preferably 340°C or lower, even more preferably 330°C or lower, and particularly preferably 320°C or lower. The kneading time is preferably 0.1 to 60 minutes, more preferably 1 to 30 minutes, and even more preferably 1.5 to 15 minutes. The rotation speed of the rotor (for example, blades and rotary shaft) is preferably 1 to 500 rpm, more preferably 10 to 250 rpm, and even more preferably 50 to 150 rpm.

[0061] The method of feeding the fluorine-containing copolymer (A) and the fluorine-containing copolymer (B) to the kneader is not particularly limited.Specifically, the fluorine-containing copolymer (A) and the fluorine-containing copolymer (B) may be kneaded in advance to obtain a mixture, and the mixture may be fed to the kneader, or the fluorine-containing copolymer (A) and the fluorine-containing copolymer (B) may be fed separately to the kneader.From the viewpoint of excellent effects of the present invention, the method of feeding the mixture to the kneader is preferred, and the pre-kneading step described below is more preferred.

[0062] The kneading step may be carried out once or twice or more.

[0063] (Pre-mixing step) The present production method preferably includes a pre-mixing step. The pre-mixing step is a step carried out before the above-mentioned kneading step. The pre-mixing step makes it easier to achieve the effects of the present invention.

[0064] The pre-kneading step is a step in which the fluorine-containing copolymer (A) and the fluorine-containing copolymer (B) are kneaded at a temperature below the glass transition temperature of the fluorine-containing copolymer (B) to obtain a mixture (hereinafter also referred to as the "pre-mixture"). Examples of the kneading method include the methods used in the kneading step described above, with a kneading method using a kneader being preferred and a kneading method using a roll kneader being more preferred. The kneading temperature is lower than the glass transition temperature of the fluorine-containing copolymer (B). The glass transition temperature of the fluorine-containing copolymer (B) is as described above. The kneading temperature is also preferably lower than the glass transition temperature of the fluorine-containing copolymer (A). Specifically, the kneading temperature is preferably 20 to 60°C, more preferably 22 to 55°C. The kneading time is preferably 1 to 30 minutes, more preferably 5 to 15 minutes. The rotation speed of the rotating body (e.g., blades and rotating shafts) is preferably 100 to 2000 rpm, more preferably 500 to 1500 rpm.

[0065] The pre-mixing step may be carried out once or twice or more.

[0066] The premix may contain other components in addition to those described above, provided that the effects of the present invention are not impaired. Examples of such other components include additives that do not cause the vulcanization reaction of the fluorine-containing copolymer (A) and the fluorine-containing copolymer (B) to proceed depending on the temperature, such as imide-based additives having an imide structure, such as polyimide, polyamideimide, and polyetherimide; organic additives for engineering plastics, such as polyarylate, polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyetherketone, polyoxybenzoate, and liquid crystal polymer; phosphorus-based additives, such as trioctylphosphine; metal oxide additives, such as aluminum oxide, silicon oxide, and yttrium oxide; metal carbides, such as silicon carbide and aluminum carbide; metal nitride additives, such as silicon nitride and aluminum nitride; and inorganic additives, such as aluminum fluoride, carbon fluoride, and carbon black.

[0067] [Fluorocopolymer Composition] The fluorocopolymer composition of the present invention comprises a composition obtained by the above-described method for producing a composition, and a crosslinking agent.

[0068] The composition is not particularly limited as long as it is a composition obtainable by the above-described method for producing a composition.

[0069] <Crosslinking Agent> The fluorocopolymer composition contains a crosslinking agent. Specific examples of the crosslinking agent include organic peroxides and compounds having two or more amino groups (hereinafter also referred to as "polyamine compounds"). Polyamine compounds are preferred because they are excellent in crosslinkability of the fluorocopolymer (A) and can give crosslinked rubber articles with smaller compression set under high temperature and high compression.

[0070] 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 (A), thereby enabling a crosslinked rubber article to be obtained that has a smaller compression set under high temperature and high compression.

[0071] Specific examples of polyamine compounds 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. BOAP is preferred because it provides better effects for the present invention.

[0072] The content of the crosslinking agent is preferably from 0.3 to 10 parts by mass, more preferably from 0.3 to 5 parts by mass, and even more preferably from 0.5 to 3 parts by mass, per 100 parts by mass of the fluorine-containing copolymer (A). When the content of the crosslinking agent is within the above range, the effects of the present invention are more excellent.

[0073] <Other Components> The fluorocopolymer composition may contain other components in addition to those described above, provided that the effects of the present invention are not impaired. Specific examples of other components include acid acceptors (for example, fatty acid esters, fatty acid metal salts, and oxides of divalent metals (such as magnesium oxide, calcium oxide, zinc oxide, and lead oxide)), fillers and reinforcing materials (for example, carbon black, barium sulfate, calcium metasilicate, calcium carbonate, titanium oxide, silicon dioxide, fluorine-containing copolymers other than the fluorine-containing copolymer (A) and the fluorine-containing copolymer (B) (for example, tetrafluoroethylene-fluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and ethylene-tetrafluoroethylene copolymer), polytetrafluoroethylene (PTFE), aromatic polyesters, polyamideimides and thermoplastic polyimides, clay, and talc), scorch retarders (for example, phenolic hydroxyl group-containing compounds such as bisphenol A, quinones such as hydroquinone, and α-methylstyrene dimers such as 2,4-di(3-isopropylphenyl)-4-methyl-1-pentene), crown ethers (for example, 18-crown-6), and release agents (for example, sodium stearate).

[0074] When the fluorine-containing copolymer composition contains other components, the total content of the other components is preferably from 0.1 to 30 parts by mass, more preferably from 1 to 15 parts by mass, and even more preferably from 3 to 5 parts by mass, per 100 parts by mass of the fluorine-containing copolymer (A).

[0075] Examples of methods for producing the fluorine-containing copolymer composition include a method of kneading the above-mentioned composition with a crosslinking agent (post-kneading step). The kneading temperature in the post-kneading step is preferably lower than the glass transition temperature of the fluorine-containing copolymer (B), and the glass transition temperature of the fluorine-containing copolymer (B) is as described above. The kneading temperature is also preferably lower than the glass transition temperature of the fluorine-containing copolymer (A). The kneading temperature is preferably 20 to 60°C, more preferably 22 to 55°C. The kneading time is preferably 1 to 30 minutes, more preferably 5 to 15 minutes. The rotation speed of the rotating body (for example, blades and rotating shafts) is preferably 1 to 500 rpm, more preferably 5 to 50 rpm.

[0076] The following method is preferred as a method for producing the fluorine-containing copolymer composition: A method for producing a fluorine-containing copolymer composition comprising: a pre-kneading step of kneading a fluorine-containing copolymer (A) and a fluorine-containing copolymer (B) at a temperature below the glass transition temperature of the fluorine-containing copolymer (B) to obtain a mixture; a kneading step of kneading the resulting mixture at a temperature equal to or higher than the glass transition temperature of the fluorine-containing copolymer (B) to obtain a composition; and a post-kneading step of mixing the resulting composition with a crosslinking agent to obtain a fluorine-containing copolymer composition, wherein in the mixture, the fluorine-containing copolymer (A) has units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), and the fluorine-containing copolymer (B) in the mixture is a copolymer different from the fluorine-containing copolymer (A) and has units based on a monomer having at least one functional group selected from the group consisting of a carboxy group and a group represented by formula (X), units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether). The components and steps in the above production method are as described above.

[0077] Alternatively, after obtaining a fluorine-containing copolymer composition by mixing the above-mentioned components, the fluorine-containing copolymer composition may be molded. Specific examples of methods for molding the fluorine-containing copolymer composition include compression molding, injection molding, extrusion molding, calendar molding, and methods in which the composition is dissolved in a solvent and then dipped or coated onto a substrate or the like to be molded.

[0078] [Crosslinked Rubber Article] The crosslinked rubber article of the present invention is a rubber article obtained by crosslinking the fluorocopolymer (A) in the present fluorocopolymer composition described above. As a method for crosslinking the fluorocopolymer (A) in the present fluorocopolymer composition, a method in which the present fluorocopolymer composition is heated 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.

[0079] The crosslinked rubber obtained by heating the present fluorocopolymer composition (by primary crosslinking) may be further heated to cause secondary crosslinking. By carrying out secondary crosslinking, the mechanical properties, compression set, and other properties of the crosslinked rubber can be stabilized or improved. The heating conditions for carrying out secondary crosslinking are preferably 80 to 350°C for 30 minutes to 48 hours.

[0080] As a crosslinking method other than crosslinking the fluorine-containing copolymer (A) by heating, there can be mentioned a method in which the present fluorine-containing copolymer composition is irradiated with radiation to crosslink the fluorine-containing copolymer (A). Specific examples of the radiation to be irradiated include electron beams and ultraviolet rays.

[0081] <Physical Properties> The compression set of the crosslinked rubber article under high temperature and high compression is preferably 70% or less, and more preferably 50% or less, in view of the fact that the fluorocopolymer (A) is well crosslinked and the crosslinked rubber article has better shape recovery after pressure application. The compression set of the crosslinked rubber article under high temperature and high compression is measured by the method described in the Examples section below.

[0082] <Applications> Crosslinked rubber articles are suitable for materials such as O-rings, sheets, gaskets, oil seals, diaphragms, and V-rings. The present invention can also be applied to heat-resistant and chemical-resistant sealing materials, heat-resistant and oil-resistant sealing materials, wire coating materials, sealing materials for semiconductor devices, sealing materials for liquid crystal display panel manufacturing equipment, sealing materials for light-emitting diode manufacturing equipment, corrosion-resistant rubber coating materials, sealing materials for urea-resistant greases, and the like, 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 greases, 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.), board sealing materials, rubber gloves, stators for uniaxial eccentric screw pumps, parts for urea SCR systems, vibration isolators, vibration-damping agents, sealants, additives for other materials, and toys.

[0083] The present invention will be described in detail below with reference to examples. Examples 1 to 3 are working examples, and Examples 4 to 6 are comparative examples. However, the present invention is not limited to these examples.

[0084] [Measurement of Composition of Fluorine-Containing Copolymer] The content (mol %) of each unit in the fluorine-containing copolymer (A-1) described below was １９ The content (mol %) of each unit in the fluorine-containing copolymers (B-1) and (B-2) described below was calculated by melt NMR analysis and fluorine content analysis. However, the content of NAH units was calculated by the following infrared absorption spectroscopy.

[0085] [Infrared absorption spectrum analysis] The fluorine-containing copolymer (B-1) described below was press-molded to obtain a 200 μm film. In the infrared absorption spectrum, the absorption peaks of the units based on NAH in the fluorine-containing copolymer (B-1) were all at 1778 cm －１ The absorbance of the absorption peak was measured, and the molar extinction coefficient of NAH was 20810 mol －１ ・l・cm －１The proportion of units based on NAH in the fluorine-containing copolymer (B-1) was determined using the formula:

[0086] [Glass Transition Temperature of Fluorine-Containing Copolymer] The glass transition temperature of each fluorine-containing copolymer was measured by the following method. 10 mg of a measurement sample was weighed out, and the measurement sample was cooled from room temperature (25°C) to -30°C at a heating rate of 10°C / min, and then heated at a heating rate of 10°C / min up to 350°C (1 ｓｔ Heat flux (mW) was plotted on the vertical axis and temperature (°C) on the horizontal axis to obtain a profile. ｓｔ The T at which the minimum mW at which a baseline shift was confirmed during heating was taken as the glass transition temperature of the fluorine-containing copolymer.

[0087] <Measurement conditions> Apparatus: DSC 7020, manufactured by Hitachi High-Tech Science Corporation Temperature program mode: Lamp Cooling unit: Electric cooling Gas: Air 50 mL / min, Pressure: 0.1 MPa Pan: Aluminum Sample mass: 10 mg Reference: Empty pan

[0088] [Melting Point of Fluorine-Containing Copolymer] At the glass transition temperature of the fluorocopolymer, the temperature was raised to 350°C and then lowered at a heating rate of 10°C / min, and the temperature at the minimum heat flux (mW) when an endothermic peak was observed was taken as the melting point (°C).

[0089] [MFR of Fluorine-Containing Copolymer] Using a melt indexer manufactured by Techno Seven Co., Ltd., the mass (g) of each fluorocopolymer flowing out of a nozzle having a diameter of 2 mm and a length of 8 cm in 10 minutes (unit time) at 372°C under a load of 49 N was measured.

[0090] [Compression set under high temperature and high compression] The compression set rate was measured according to the method described in ASTM D395 or JIS K6262. The O-rings (original thickness (wire diameter) = 3.5 mm) prepared in each example were compressed to a compression rate of 25% using a compression device. Next, the compression device with the compressed O-rings 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-rings were immediately removed from the compression device, and the removed O-rings were left in a constant temperature room at 23°C for 30 minutes, and the thickness of the O-rings (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 rate was calculated using the following formula. The closer the compression set rate is to 0%, the better. Compression set rate (%) = (original thickness (wire diameter) - thickness 30 minutes after removing the O-ring from the compression device (thickness after compression treatment) ÷ (original thickness of O-ring - thickness of spacer) x 100

[0091] [Cracks under High Temperature and High Compression] After the above-mentioned compression set test under high temperature and high compression, the O-rings were visually inspected for cracks.

[0092] [Plasma Resistance] The O-rings produced in each example were cut at three locations along the thickness direction so as to divide the outer periphery into three equal parts to prepare measurement samples. ２ / NF ３ (NF ３ The treatment was carried out under the conditions of a mixing ratio of 20%, a power of 300 W, a pressure of 26 Pa, and an irradiation time of 3 hours. The weight of the measurement sample was measured before and after the treatment, and the weight loss rate (mass%) was calculated. The weight was measured to the nearest 0.1 mg using an Azpro electronic balance (device name: BCA64I-1SJP, manufactured by Sartorius).

[0093] [Production of Fluorocopolymer (A-1)] A stainless steel pressure reactor having an internal volume of 20 L and equipped with an anchor blade was degassed, and then 7.2 L of ultrapure water and an emulsifier C were added. ２ F ５ OCF ２ CF ２ OCF ２ COONH ４880 g of a 30% by mass solution of 8CNVE, 7.3 g of 8CNVE, and 15.9 g of a 5% by mass aqueous solution of disodium hydrogen phosphate dodecahydrate were charged, and the gas phase was replaced with nitrogen. While stirring at a speed of 375 rpm using an anchor blade, 137 g of TFE and 635 g of PMVE were injected into the vessel, and the internal temperature was then raised to 80 ° C. The pressure inside the reactor was 0.90 MPa [gauge]. 28 mL of a 3% by mass aqueous solution of ammonium persulfate (APS) was added to initiate polymerization. The molar ratio of the monomers injected before the start of polymerization (hereinafter also referred to as "initial added monomer") was TFE:PMVE:8CNVE = 26.3:73.3:0.4.

[0094] After the initiation of polymerization, as the polymerization progressed, the monomer was injected as follows. Hereinafter, injecting a monomer after the initiation of polymerization will be referred to as "post-addition," and a monomer injected after the initiation of polymerization will be referred to as "post-added monomer." When the pressure inside the reactor dropped to 0.89 MPa [gauge], TFE was injected, and the pressure inside the reactor was increased to 0.90 MPa [gauge]. This was repeated, and every time 119.3 g of TFE was injected, 3.7 g of 8CNVE, 74 g of PMVE, and 3.7 g of 8CNVE were injected in this order. When the polymerization rate began to slow down, a 3% by mass aqueous solution of APS was appropriately added. The total amount of the 3% by mass aqueous solution of APS added after the initiation of polymerization was 35 mL. When the cycle was completed, in which the total added mass of TFE reached 1073.7 g, 119.3 g of TFE was injected. When the total added mass of the post-added TFE reached 1193 g, the addition of the post-added monomer was stopped, the internal temperature of the reactor was cooled to 10 ° C., and the polymerization reaction was stopped to obtain a latex containing a fluorine-containing copolymer. The polymerization time was 375 minutes. The total added mass of each post-added monomer was 1193 g of TFE, 666 g of PMVE, and 66.6 g of 8CNVE, which was converted to a molar ratio of TFE:PMVE:8CNVE = 74.0:25.0:1.0. The latex was added to a 5 mass% aqueous solution of aluminum potassium sulfate, and the fluorine-containing copolymer was coagulated and separated. The fluorine-containing copolymer was filtered, washed with ultrapure water, and dried under vacuum at 50 ° C. to obtain a white fluorine-containing copolymer (A-1). The content (molar ratio) of each unit in the obtained fluorocopolymer (A-1) was TFE unit:PMVE unit:8CNVE unit=70.9:28.6:0.5, and the glass transition temperature of the fluoropolymer (A-1) was −3° C.

[0095] [Fluorine-containing copolymer (B-1)] "Fluorine-containing copolymer (X1-1)" in the Examples section of WO 2016 / 017801 was pulverized with a jet mill and used as fluorine-containing copolymer (B-1). The molar ratio of each unit in fluorine-containing copolymer (B-1) was NAH unit:TFE unit:PPVE unit = 0.1:97.9:2.0. The particle size D50 of fluorine-containing copolymer (B-1) was 2 to 3 μm. The glass transition temperature of fluorine-containing copolymer (B-1) was 80 ° C., the melting point was 310 ° C., and the MFR was 17.6 g / 10 min (measurement temperature: 372 ° C.).

[0096] [Fluorocopolymer (B-2)] MJ-310 (manufactured by Mitsui-Chemours Fluoroproducts) was used as the fluorine-containing copolymer (B-2). The molar ratio of each unit in the fluorine-containing copolymer (B-2) was TFE unit:PPVE unit=98.7:1.3. The glass transition temperature of the fluorine-containing copolymer (B-2) was 90°C, the melting point was 310°C, and the MFR was 15g / 10min (measurement temperature: 372°C).

[0097] Example 1 Fluorine-containing copolymer (A-1) (100 parts by mass) and fluorine-containing copolymer (B-1) (20 parts by mass) were mixed using a roll mixer (φ8 inch × 18 inch test roll machine, manufactured by Yamatetsu Corporation) with the rotation speed of the F roll (the roll on the operator's side of the two rolls of the roll mixer) set to 9 rpm and the rotation speed of the R roll (the roll on the opposite side of the operator of the two rolls of the roll mixer) set to 13 rpm, and mixed for 10 minutes at 23 ° C. to obtain a sheet-like mixture 1 having a thickness of 1.5 mm (pre-mixing step). Immediately after the pre-mixing step, the surface temperature of the obtained mixture 1 was measured with a radiation thermometer (IT-545S, manufactured by Horiba, Ltd.) and found to be below the glass transition temperature of the fluorine-containing copolymer (B) at 50 ° C. Next, the obtained mixture 1 was cut into a size of 80 mm length × 10 mm width × 1.5 mm thickness, with the longitudinal direction parallel to the roll rotation direction. Furthermore, using a Labo Plastomill (Model 4C150, manufactured by Toyo Seiki Seisaku-sho, Ltd.), the kneading temperature was set to 250° C., and the cut mixture 1 (50 g) was charged into the mixer. Thereafter, the rotation speed was set to 100 rpm and the processing time was set to 2 minutes, and kneading was performed to obtain composition 1 (kneading step).

[0098] BOAP (2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 1 part by mass) was added to composition 1, and the mixture was kneaded using the roll kneader at 23°C for 10 minutes to obtain fluorine-containing copolymer composition 1 (post-kneading step). The obtained fluorine-containing copolymer composition 1 was hot-pressed at 180°C for 10 minutes using a hydraulic press (model: SA-301 50T type, manufactured by Tester Sangyo Co., Ltd., ram diameter: 180 mm) to obtain an O-ring (size: P-26) (primary crosslinking). Next, the obtained O-ring was heated in an oven (DN411I, manufactured by Yamato Scientific Co., Ltd.) under a nitrogen atmosphere 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, thereby performing secondary crosslinking. Thereafter, the O-ring was cooled to 23°C to obtain the O-ring of Example 1.

[0099] Examples 2 to 5 The O-rings of Examples 2 to 5 were obtained using Compositions 2 to 5 and fluorocopolymer Compositions 2 to 5 in the same procedure as in Example 1, except that the fluorocopolymers and kneading conditions were changed as shown in the table. In the production process of Compositions 2 to 5, the surface temperature of each mixture immediately after the pre-kneading step was measured with a radiation thermometer (IT-545S, manufactured by HORIBA, Ltd.) and was found to be below the glass transition temperature of the fluorocopolymer (B) at 50°C.

[0100] Example 6 Fluorine-containing copolymer (A-1) (100 parts by mass) and fluorine-containing copolymer (B-1) (20 parts by mass) were kneaded for 10 minutes at 23°C using the roll kneader described above, to obtain mixture 6. Immediately after kneading, the surface temperature of composition 6 was measured with a radiation thermometer (IT-545S, manufactured by HORIBA, Ltd.) and found to be 50°C. Next, without carrying out the kneading step, BOAP (2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 1 part by mass) was added to mixture 6, and a post-kneading step was carried out in the same manner as in Example 1, after which an O-ring of Example 6 was obtained.

[0101] In Table 1, the "-" in the "Compression set under high temperature and high compression" column for Examples 4 to 6 indicates that the O-ring cracked after the compression set test under high temperature and high compression, making it impossible to measure.

[0102]

[0103] As shown in Table 1, it was confirmed that the use of the composition obtained by this production method can suppress cracking under high temperature and high compression and form crosslinked rubber articles with excellent plasma resistance. From a comparison of Examples 1 to 3, it was confirmed that when the content of the fluorine-containing copolymer (B) in the mixture is 30 parts by mass or less per 100 parts by mass of the fluorine-containing copolymer (A), the compression set under high temperature and high compression is better. The entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2023-220825, filed on December 27, 2023, are hereby incorporated by reference.

Claims

1. A method for producing a composition, comprising a kneading step of kneading a mixture containing a fluorine-containing copolymer (A) and a fluorine-containing copolymer (B) at a temperature equal to or higher than the glass transition temperature of the fluorine-containing copolymer (B), wherein the fluorine-containing copolymer (A) has units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), and the fluorine-containing copolymer (B) is a copolymer different from the fluorine-containing copolymer (A) and has units based on a monomer having at least one functional group selected from the group consisting of a carboxy group and a group represented by formula (X), units based on tetrafluoroethylene, and units based on perfluoro(alkyl vinyl ether). Formula (X): *-CO-O-CO-*, where * represents the bonding position in the formula.

2. The method for producing a composition according to claim 1, wherein the fluorine-containing copolymer (A) has units having a nitrile group.

3. The method for producing a composition according to claim 1 or 2, wherein the kneading step is a step of kneading the mixture at a temperature equal to or higher than the melting point of the fluorine-containing copolymer (B).

4. The method for producing a composition according to claim 1 or 2, wherein in the mixture, the content of the fluorine-containing copolymer (B) is 50 parts by mass or less with respect to 100 parts by mass of the fluorine-containing copolymer (A).

5. The method for producing a composition according to claim 1 or 2, wherein the fluorine-containing copolymer (A) is a fully fluorinated fluorine-containing copolymer.

6. A crosslinked rubber article obtained by crosslinking the fluorine-containing copolymer (A) in the composition produced by the method for producing a composition according to claim 1 or 2 using a crosslinking agent.

7. The crosslinked rubber article according to claim 6, which is a sealing material for a semiconductor device.

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