Fluorinated copolymer composition and crosslinked rubber article

Abstract

To provide a crosslinked rubber article, and a fluorinated copolymer composition capable of forming a crosslinked rubber article having a low compression set at high temperature.SOLUTION: A fluorinated copolymer composition of the present invention comprises a fluorinated copolymer, an organic peroxide, a compound having two or more polymerizable unsaturated bonds and a phosphorus compound having a melting point of 60°C or lower.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a fluorocopolymer composition and a crosslinked rubber article. [Background technology]

[0002] Crosslinked rubber articles obtained by crosslinking fluorine-containing copolymers have excellent heat resistance, chemical resistance, oil resistance, weather resistance, etc., and are therefore widely used as sealing materials (e.g., O-rings, packings, oil seals, gaskets) and cushioning materials in the fields of vehicles, ships, aircraft, general machinery, construction, etc. As a fluorine-containing copolymer composition used to obtain such crosslinked rubber articles, Patent Document 1 discloses a fluorine-containing rubber composition containing a fluorine-containing rubber obtained by copolymerizing vinylidene fluoride and at least one other ethylenically unsaturated monomer copolymerizable therewith, an organic peroxide, at least one selected from a divalent metal hydroxide and a divalent metal oxide, and an organic phosphorus compound. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 06-306236 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, there has been a demand in various fields for improved performance of crosslinked rubber articles, specifically crosslinked rubber articles with small compression set at high temperatures. In response to such demands, the present inventors evaluated the crosslinked rubber article described in Patent Document 1 and found that there was room for improvement in the compression set rate when a compression set test was carried out at high temperatures (hereinafter also referred to as "compression set at high temperatures").

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a fluorocopolymer composition capable of forming a crosslinked rubber article having small compression set at high temperatures, and such a crosslinked rubber article. [Means for solving the problem]

[0006] Means for Solving the Problems The present inventors have intensively investigated the above-mentioned problems and have found that a crosslinked rubber article having small compression set at high temperatures can be obtained by using a fluorocopolymer composition comprising a fluorocopolymer, an organic peroxide, a compound having two or more polymerizable unsaturated bonds, and a phosphorus compound having a melting point of 60°C or less, thereby completing the present invention.

[0007] That is, the inventors discovered that the above problems can be solved by the following configuration. [1] A fluorine-containing copolymer composition comprising a fluorine-containing copolymer, an organic peroxide, a compound having two or more polymerizable unsaturated bonds, and a phosphorus compound having a melting point of 60°C or lower. [2] The fluorine-containing copolymer composition according to [1], wherein the melting point of the phosphorus compound is 35° C. or lower. [3] The fluorine-containing copolymer composition according to [1] or [2], wherein the phosphorus compound is a phosphine having an alkyl group. [4] The fluorine-containing copolymer composition according to any one of [1] to [3], wherein the fluorine-containing copolymer is a perfluoropolymer. [5] The fluorine-containing copolymer composition according to any of [1] to [4], wherein the fluorine-containing copolymer has units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether). [6] The fluorine-containing copolymer composition according to [5], wherein the fluorine-containing copolymer further has units based on a monomer having two or more polymerizable unsaturated bonds. [7] The fluorine-containing copolymer composition according to any of [1] to [6], wherein the compound having two or more polymerizable unsaturated bonds is a compound having two or more vinyl groups or allyl groups. [8] The fluorine-containing copolymer composition according to any of [1] to [7], wherein the compound having two or more polymerizable unsaturated bonds is a compound represented by the following formula (6): (CR 61 R 62 =CR 63 )2R 64 Formula (6) In formula (6), R 61 , R 62 and R 63 each independently represents a hydrogen atom, a fluorine atom, an alkyl group having 1 to 5 carbon atoms, or a fluoroalkyl group having 1 to 5 carbon atoms; R 64 represents a divalent fluorohydrocarbon group having 1 to 18 carbon atoms or a group having an etheric oxygen atom at the terminal or between the carbon-carbon bonds of the fluorohydrocarbon group. 61 , multiple R 62 and multiple R 63 may be the same or different from each other. [9] The fluorine-containing copolymer composition of any of [1] to [8], wherein the phosphorus compound is a trialkylphosphine.

[10] The fluorine-containing copolymer composition of any of [1] to [9], wherein the phosphorus compound is a compound represented by the following formula (7): P(R 71 )3 formula (7) In formula (7), R 71 represents a linear or branched alkyl group having 2 to 9 carbon atoms. 71 may be the same or different from each other.

[11] In the above formula (7), the three R 71 each independently represents a linear alkyl group having 2 to 9 carbon atoms.

[12] In the above formula (7), the three R 71 The fluorine-containing copolymer composition according to

[10] or

[11] , wherein

[13] A crosslinked rubber article obtained from the fluorocopolymer composition of any one of [1] to

[12] , wherein the fluorocopolymer in the fluorocopolymer composition is crosslinked.

[14] A method for producing a crosslinked rubber article, comprising heating the fluorocopolymer composition of any of [1] to

[12] at 100 to 400°C to crosslink the fluorocopolymer in the fluorocopolymer composition. Effect of the Invention

[0008] According to the present invention, there can be provided a fluorocopolymer composition capable of forming a crosslinked rubber article having a small compression set at high temperatures, and the crosslinked rubber article. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The terms used in the present invention have the following meanings. The term "unit" refers collectively to an atomic group derived from one molecule of a monomer that is formed directly by polymerization of the monomer, and an atomic group obtained by chemically converting a part of the atomic group. Hereinafter, a "unit based on a monomer" will also be simply referred to as a "unit". "Rubber" means rubber exhibiting properties defined by JIS K 6200 (2008), and is to be distinguished from "resin". "Melting point" means the temperature corresponding to the maximum value of the melting peak measured by differential scanning calorimetry (DSC). Unless otherwise specified, boiling point refers to the boiling point at atmospheric pressure (1013 hPa).

[0010] [Fluorine-containing copolymer composition] The fluorine-containing copolymer composition of the present invention (hereinafter also referred to as "the composition") contains a fluorine-containing copolymer, an organic peroxide, a compound having two or more polymerizable unsaturated bonds (hereinafter also referred to as "specific polymerizable compound"), and a phosphorus compound having a melting point of 60° C. or less (hereinafter also referred to as "specific phosphorus compound"). The specific phosphorus compound is a crosslinking accelerator. The crosslinked rubber article obtained using this composition has a small compression set at high temperatures (for example, the compression set rate when the crosslinked rubber article is stored at 250°C for 168 hours and then a compression set test is performed). Although the details of the reason for this are not clear, it is presumed to be due to the following reasons. One of the reasons why the compression set at high temperature becomes large is thought to be that the bond of the crosslinked part breaks when the crosslinked rubber article is heated and compressed.Here, since the specific phosphorus compound contained in this composition has a low melting point, when the fluorocopolymer contained in this composition is crosslinked while being heated, the specific phosphorus compound is in a liquid state in this composition.This allows the specific phosphorus compound to be well dispersed in this composition, and the crosslinking of the fluorocopolymer proceeds well, so that the crosslinking density is improved.As a result, the compression set at high temperature is thought to be small. In addition, it is believed that the use of the specific polymerizable compound in the present composition suppresses cleavage of crosslinks, making crosslinked rubber articles less susceptible to distortion even at high temperatures. It is presumed that the function of the specific phosphorus compound and the function of the specific polymerizable compound act synergistically to obtain a crosslinked rubber article having a small compression set at high temperatures.

[0011] <Fluorine-containing copolymer> The fluorine-containing copolymer is not particularly limited as long as it is a polymer that contains fluorine atoms and exhibits rubber properties through crosslinking, but it is preferably one having a monomer unit containing fluorine atoms (hereinafter referred to as "fluorine-containing monomer"), and is particularly preferably a perfluoropolymer, since it can reduce the compression set when a crosslinked rubber article is stored at high temperatures for a long period of time (for example, the compression set rate when a compression set test is carried out after storing a crosslinked rubber article at 250°C for 336 hours. Hereinafter, it is also referred to as "compression set after long-term heating"). Here, the term "perfluoropolymer" refers to a polymer that does not substantially contain hydrogen atoms bonded to carbon atoms, has fluorine atoms instead of hydrogen atoms, and has a main chain consisting of a chain of carbon atoms. The side chain of the perfluoropolymer may have a polyvalent atom other than carbon atoms, and the polyvalent atom is preferably an oxygen atom. Here, "substantially free of hydrogen atoms" means that the content of hydrogen atoms in the perfluoropolymer is 0.5 mass% or less, preferably 0.1 mass% or less, more preferably 0.07 mass% or less, and particularly preferably 0.05 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.

[0012] Specific examples of fluorine-containing monomers include tetrafluoroethylene (hereinafter also referred to as "TFE"), perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE"), vinylidene fluoride (hereinafter also referred to as "VdF"), hexafluoropropylene (hereinafter also referred to as "HFP"), and chlorotrifluoroethylene (hereinafter also referred to as "CTFE").

[0013] The PAVE units are perfluoro(alkyl vinyl ether) based units. As the PAVE, a monomer represented by the formula (1) is preferred from the viewpoint of excellent polymerization reactivity and rubber physical properties. CF2=CF-OR f1 (1) In formula (1), R f1 R represents a perfluoroalkyl group having 1 to 10 carbon atoms. f1 The number of carbon atoms in the alkyl group is preferably 1 to 8, more preferably 1 to 6, further preferably 1 to 5, and particularly preferably 1 to 3, in terms of superior polymerization reactivity. The perfluoroalkyl group may be linear or branched.

[0014] Specific examples of PAVE include perfluoro(methyl vinyl ether) (hereinafter also referred to as "PMVE"), perfluoro(ethyl vinyl ether) (hereinafter also referred to as "PEVE"), and perfluoro(propyl vinyl ether) (hereinafter also referred to as "PPVE"), and among these, PMVE and PPVE are preferred.

[0015] The fluorine-containing copolymer may have units based on monomers other than those mentioned above (hereinafter also referred to as "other monomers"). Specific examples of other monomers include a monomer having two or more polymerizable unsaturated bonds (hereinafter also referred to as "DV"), a monomer represented by the following formula (5), ethylene, and propylene. In addition, monomers having halogen atoms other than the above-mentioned fluorine-containing monomers, DV, and the monomer represented by formula (5) (hereinafter also referred to as monomers having other halogen atoms) (e.g., bromotrifluoroethylene, iodotrifluoroethylene) are also included.

[0016] The DV 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 DV is preferably from 2 to 6, more preferably 2 or 3, and particularly preferably 2, in terms of superior polymerization reactivity. It is preferred that DV further contains fluorine atoms since this leads to a smaller compression set of the crosslinked rubber article at high temperatures.

[0017] DV is preferably a monomer represented by formula (2) since the crosslinked rubber article will have a smaller compression set at high temperatures. (CR 21 R 22 =CR 23 ) a2 R 24 (2) In formula (2), R 21 , R 22 and R 23 each independently represents a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group; a2 represents an integer of 2 to 6; R 24 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. 21 , multiple R 22 and multiple R 23may be the same or different from each other, and are particularly preferably the same as each other. a2 is preferably 2 or 3, and particularly preferably 2.

[0018] Due to the superior polymerization reactivity of DV, 21 , R 22 , R 23 is preferably a fluorine atom or a hydrogen atom, and R 21 , R 22 , R 23 It is more preferable that all of R are fluorine atoms or hydrogen atoms. From the viewpoint of heat resistance and chemical resistance of the crosslinked rubber article, 21 , R 22 , R 23 It is particularly preferable that all of are fluorine atoms. R 24 R may be linear, branched, or cyclic, is preferably linear or branched, and is particularly preferably linear. 24 The number of carbon atoms is preferably 2 to 8, more preferably 3 to 7, further preferably 3 to 6, and particularly preferably 3 to 5. R 24 may or may not have an ether type oxygen atom, but preferably has an ether type oxygen atom in terms of superior crosslinking reactivity and rubber physical properties. R 24 The number of ether oxygen atoms in R is preferably 1 to 6, more preferably 1 to 3, and particularly 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.

[0019] Of the monomers represented by formula (2), specific examples of suitable monomers include those represented by formula (3) and those represented by formula (4).

[0020] (CF2=CF)2R 31 (3) In formula (3), R 31represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms or a group having an etheric oxygen atom at the terminal or between the carbon-carbon bonds of the perfluorohydrocarbon group.

[0021] Specific examples of the monomer represented by formula (3) include CF2=CFO(CF2)2OCF=CF2, CF2=CFO(CF2)3OCF=CF2, CF2=CFO(CF2)4OCF=CF2, and CF2=CFO(CF2)6OCF=CF 2、 CF2=CFO(CF2)8OCF=CF2, CF2=CFO(CF2)2OCF(CF3)CF2OCF=CF2, CF2=CFO(CF2)2O(CF(CF3)CF2O)2CF=CF2, CF2=CFOCF2O(CF2CF2O)2CF=CF2, CF Examples include 2=CFO(CF2O)3O(CF(CF3)CF2O)2CF=CF2, CF2=CFOCF2CF(CF3)O(CF2)2OCF(CF3)CF2OCF=CF2, and CF2=CFOCF2CF2O(CF2O)2CF2CF2OCF=CF2. Among the monomers represented by formula (3), specific examples of more suitable monomers include CF2=CFO(CF2)3OCF=CF2 (hereinafter also referred to as "C3DVE") and CF2=CFO(CF2)4OCF=CF2 (hereinafter also referred to as "C4DVE" or "PBDVE").

[0022] (CH2=CH)2R 41 (4) In formula (4), R 41 represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms or a group having an etheric oxygen atom at the terminal or between the carbon-carbon bonds of the perfluorohydrocarbon group.

[0023] Specific examples of the monomer represented by formula (4) include CH2=CH(CF2)2CH=CH2, CH2=CH(CF2)4CH=CH2, and CH2=CH(CF2)6CH=CH2. Among the monomers represented by formula (4), a more preferred specific example of the monomer is CH2=CH(CF2)6CH=CH2 (hereinafter, also referred to as "C6DV").

[0024] When DV is copolymerized, the polymerizable double bonds at the ends of the DV react during polymerization to give a fluorine-containing copolymer having branched chains.

[0025] Equation (5) is as follows. CF2=CF-OR f2 (5) In formula (5), R f2 R represents a perfluoroalkyl group having 1 to 8 carbon atoms and containing 1 to 5 etheric oxygen atoms. f2 The number of carbon atoms is preferably 1 to 6, and particularly preferably 1 to 5.

[0026] Specific examples of the monomer represented by formula (5) include perfluoro(3,6-dioxa-1-heptene), perfluoro(3,6-dioxa-1-octene), and perfluoro(5-methyl-3,6-dioxa-1-nonene).

[0027] Preferred combinations of the units contained in the fluorine-containing copolymer are shown below. Combination 1: TFE unit and PAVE unit combination Combination 2: TFE unit, PAVE unit, and DV unit combination Combination 3: VdF unit and HFP unit Combination 4: Combination of VdF, HFP, and TFE units Among these, combination 1 and combination 2 are preferred, with combination 2 being particularly preferred, from the standpoint of heat resistance and chemical resistance of the crosslinked rubber article.

[0028] The copolymerization compositions in the combinations 1 to 4 preferably have the following molar ratios: When the molar ratios are as follows, the crosslinked rubber articles have excellent heat resistance and chemical resistance. Combination 1: TFE unit / PAVE unit=60-80 / 20-40 (molar ratio) Combination 2: TFE unit / PAVE unit / DV unit = 60-80 / 20-40 / 0.01-1 (molar ratio) Combination 3: VdF unit / HFP unit=60-95 / 5-40 (molar ratio) Combination 4: VdF unit / HFP unit / TFE unit=30-50 / 5-45 / 5-65 (molar ratio)

[0029] The fluorine-containing copolymer may have an iodine atom. In this case, it is preferable that the fluorine-containing copolymer (polymer chain) has an iodine atom at its end. It is considered that the iodine atom present in the fluorine-containing copolymer is eliminated from the fluorine-containing copolymer during crosslinking and is captured by the specific phosphorus compound. Examples of the iodine atom include an iodine atom derived from an iodine compound that functions as a chain transfer agent described below, and an iodine atom in a unit based on a monomer having an iodine atom among monomers having other halogen atoms, such as the above-mentioned iodotrifluoroethylene, and the like. An iodine atom derived from an iodine compound that functions as a chain transfer agent is preferable. When the fluorine-containing copolymer has iodine atoms, the content thereof is preferably 0.01 to 5.0 mass%, more preferably 0.05 to 2.0 mass%, particularly preferably 0.05 to 1.0 mass%, based on the total mass of the fluorine-containing copolymer. When the iodine atom content is within the above range, the crosslinking reactivity of the fluorine-containing copolymer is improved, and the mechanical properties of the crosslinked rubber article are excellent. The fluorine-containing copolymer contained in the fluorine-containing copolymer composition of the present invention is most preferably a perfluoropolymer having iodine atom.When the fluorine-containing copolymer is a perfluoropolymer having iodine atom, it is considered that crosslinking reaction proceeds relatively quickly, and more iodine atoms are eliminated from the fluorine-containing copolymer.When the above-mentioned fluorine-containing copolymer is crosslinked in the presence of specific phosphorus compound, it is considered that the specific phosphorus compound can capture many iodine atoms and accelerate the crosslinking reaction.

[0030] The content of the fluorine-containing copolymer is preferably from 60 to 99 mass %, more preferably from 70 to 99 mass %, particularly preferably from 80 to 99 mass %, based on the total mass of the composition.

[0031] (Production method of fluorine-containing copolymer) An example of the method for producing the fluorine-containing copolymer is a method in which the above-mentioned monomers are copolymerized in the presence of a radical polymerization initiator.

[0032] As the radical polymerization initiator, a water-soluble polymerization initiator or a redox polymerization initiator is preferable. Specific examples of the water-soluble polymerization initiator include persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate, and organic polymerization initiators such as disuccinic acid peroxide and azobisisobutylamidine dihydrochloride. Among these, persulfates are preferred, and ammonium persulfate is more preferred. The redox polymerization initiator may be a polymerization initiator that combines persulfates and a reducing agent. Among these, a polymerization initiator that can polymerize each monomer at a polymerization temperature in the range of 0 to 60°C is preferred. Specific examples of persulfates that constitute the redox polymerization initiator 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 that can be combined with persulfates include thiosulfates, sulfites, hydrogen sulfites, pyrosulfites, and hydroxymethanesulfinates, with hydroxymethanesulfinates being preferred, and sodium hydroxymethanesulfinate being particularly preferred.

[0033] In the process for producing the fluorine-containing copolymer, the above-mentioned monomers may be copolymerized in the presence of a chain transfer agent together with a radical polymerization initiator. As the chain transfer agent, an iodine compound is preferred, and an iodine compound represented by formula RI2 is particularly preferred. In the above formula, R represents an alkylene group having 3 or more carbon atoms (preferably, 3 to 8 carbon atoms) or a perfluoroalkylene group. Specific examples of the iodine compound represented by formula RI2 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 preferable, and 1,4-diiodoperfluorobutane is particularly preferable. When the above-mentioned monomers are copolymerized in the presence of these iodine compounds, iodine atoms can be introduced into the fluorine-containing copolymer.

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

[0035] <Organic peroxide> The organic peroxide is used as a crosslinking agent. Specific examples of organic peroxides include dialkyl peroxides, α,α'-bis(tert-butylperoxy)-p-diisopropylbenzene, α,α'-bis(tert-butylperoxy)-m-diisopropylbenzene, benzoyl peroxide, tert-butylperoxybenzene, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, tert-butylcumyl peroxide, and dicumyl peroxide. Specific examples of dialkyl peroxides include 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethylhexane-2,5-dihydroxyperoxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)-3-hexyne, tert-butylperoxymaleic acid, and tert-butylperoxypropyl carbonate.

[0036] The content of the organic peroxide is preferably 0.3 to 10 parts by mass, more preferably 0.3 to 5 parts by mass, and particularly preferably 0.5 to 3 parts by mass, relative to 100 parts by mass of the fluorocopolymer. When the content of the organic peroxide is within the above range, the crosslinked rubber article has an excellent balance between strength and elongation.

[0037] <Specific polymerizable compound> The specific polymerizable compound is a compound having two or more polymerizable unsaturated bonds, and is used as a crosslinking auxiliary for improving the crosslinking reactivity of the fluorine-containing copolymer. Specific examples of the polymerizable unsaturated bond include a carbon-carbon double bond (C=C) and a carbon-carbon triple bond (C≡C), and from the viewpoint of superior crosslinking reactivity, a carbon-carbon double bond (C=C) is preferred. The number of polymerizable unsaturated bonds in the specific polymerizable compound is 2 or more, preferably 2 to 6, more preferably 2 or 3, and particularly preferably 2. The specific polymerizable compound is preferably a compound having two or more vinyl groups or allyl groups, since it has better crosslinking reactivity and smaller compression set at high temperatures. The specific polymerizable compound preferably contains a fluorine atom in order to provide a crosslinked rubber article with excellent weather resistance and chemical resistance.

[0038] Specific examples of the specific polymerizable compound include the compound represented by the following formula (6), triallyl cyanurate, triallyl isocyanurate, and trimethallyl isocyanurate. From the viewpoint of superior crosslinking reactivity, the compound represented by the following formula (6) and triallyl isocyanurate are preferred. From the viewpoint of smaller compression set after long-term heating of the crosslinked rubber article, the compound represented by the following formula (6) is particularly preferred.

[0039] Equation (6) is as follows. (CR 61 R 62 =CR 63 )2R 64 Formula (6) In formula (6), R 61 , R 62 and R 63 each independently represents a hydrogen atom, a fluorine atom, an alkyl group having 1 to 5 carbon atoms, or a fluoroalkyl group having 1 to 5 carbon atoms; R 64 represents a divalent fluorohydrocarbon group having 1 to 18 carbon atoms or a group having an etheric oxygen atom at the terminal or between the carbon-carbon bonds of the fluorohydrocarbon group. 61, multiple R 62 and multiple R 63 may be the same or different from each other.

[0040] R 61 , R 62 and R 63 The alkyl group or fluoroalkyl group in the formula (I) may be linear or branched, but is preferably linear. R 61 , R 62 and R 63 The alkyl group or fluoroalkyl group in the above formula has 1 to 5 carbon atoms, more preferably 1 to 3 carbon atoms, and particularly preferably 1 or 2 carbon atoms. Due to its superior crosslinking reactivity, R 61 , R 62 and R 63 It is preferable that all of are hydrogen atoms.

[0041] R 64 The fluorohydrocarbon group in is preferably a perfluorohydrocarbon group, since the crosslinked rubber article will have better heat resistance. R 64 R may be linear, branched, or cyclic, is preferably linear or branched, and is particularly preferably linear. 64 has 1 to 18 carbon atoms, preferably 2 to 8 carbon atoms, and particularly preferably 3 to 7 carbon atoms. R 64 When R has an ether oxygen atom, 64 The number of ether oxygen atoms in R is preferably 1 to 6, more preferably 1 to 3, and particularly preferably 1 or 2. 64 has an ether oxygen atom, the ether oxygen atom is 64 It is preferred that the nucleotide sequence is located at the end of the nucleotide sequence. As the compound represented by formula (6), the compound represented by formula (2) above is preferred, and the compounds represented by formulas (3) and (4) are more preferred. Among the compounds represented by formulas (3) and (4), C3DVE, C4DVE, CH2=CH(CF2)2CH=CH2, CH2=CH(CF2)4CH=CH2, and C6DV are preferred, and C6DV is particularly preferred because it reduces the compression set of the crosslinked rubber article after long-term heating.

[0042] The content of the specific polymerizable compound is preferably 0.03 to 5 parts by mass, more preferably 0.1 to 4 parts by mass, and particularly preferably 0.3 to 3 parts by mass, relative to 100 parts by mass of the fluorocopolymer. When the content is equal to or more than the lower limit of the above range, the compression set of the crosslinked rubber article becomes smaller, and when the content is equal to or less than the upper limit of the above range, the crosslinking reactivity becomes superior.

[0043] <Specific phosphorus compounds> The specific phosphorus compound is a phosphorus compound having a melting point of 60° C. or less, and is used as a crosslinking accelerator. The melting point of the specific phosphorus compound is 60°C or lower, and is preferably 35°C or lower, and particularly preferably 20°C or lower, in order to improve the dispersibility of the specific phosphorus compound and reduce the compression set of the crosslinked rubber article at high temperatures. The above compounds having melting points below a specific temperature include compounds that are liquid at 20°C.

[0044] The specific phosphorus compound is preferably a phosphine having an alkyl group, more preferably a trialkylphosphine, and particularly preferably a compound represented by the following formula (7), in order to further improve the dispersibility of the specific phosphorus compound and reduce the compression set of the crosslinked rubber article at high temperatures. P(R 71 )3 formula (7) In formula (7), R 71 represents a linear or branched alkyl group having 2 to 9 carbon atoms. 71may be the same or different, but are preferably the same from the viewpoint of reducing the compression set of the crosslinked rubber article at high temperatures.

[0045] R 71 The carbon number of is 2 to 9, preferably 4 to 9, and particularly preferably 6 to 8, in that the crosslinked rubber article has a smaller compression set at high temperatures. The three Rs are chosen because crosslinked rubber articles have a smaller compression set at high temperatures. 71 are each preferably independently a linear alkyl group having 2 to 9 carbon atoms.

[0046] Specific examples of the specific phosphorus compound include triethylphosphine (melting point -86°C, liquid at 20°C), tri-n-propylphosphine (melting point unknown, liquid at 20°C), tri-n-butylphosphine (melting point -65°C, liquid at 20°C), tri-n-pentylphosphine (melting point unknown, liquid at 20°C), tri-n-hexylphosphine (melting point unknown, liquid at 20°C), and tri-n-octylphosphine (melting point unknown, liquid at 20°C). Among the specific phosphorus compounds, tri-n-octylphosphine is preferred because it reduces the compression set of crosslinked rubber articles at high temperatures.

[0047] The content of the specific phosphorus compound is preferably 0.01 to 5 parts by mass, more preferably 0.05 to 2 parts by mass, and particularly preferably 0.1 to 1 part by mass, relative to 100 parts by mass of the fluorocopolymer. When the content is equal to or more than the lower limit of the above range, the compression set of the crosslinked rubber article becomes smaller, and when the content is equal to or less than the upper limit of the above range, the compression set of the crosslinked rubber article at high temperatures becomes smaller.

[0048] <Other ingredients> The composition may contain other components other than those described above, as long as the effect of the present invention is not impaired. Examples of other components include acid acceptors (e.g., fatty acid esters, fatty acid metal salts, oxides of divalent metals (magnesium oxide, calcium oxide, zinc oxide, lead oxide, etc.)), fillers and reinforcing materials (e.g., carbon black, barium sulfate, calcium metasilicate, calcium carbonate, titanium oxide, silicon dioxide, polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymers (PFA), clay, talc), scorch retarders (e.g., phenolic hydroxyl group-containing compounds such as bisphenol A, quinones such as hydroquinone, α-methylstyrene dimers such as 2,4-di(3-isopropylphenyl)-4-methyl-1-pentene), crown ethers (e.g., 18-crown-6), and release agents (e.g., sodium stearate).

[0049] When the composition contains silicon dioxide powder among the other components, the crosslinked rubber article obtained by using the composition has improved resistance to oxygen plasma irradiation. Such crosslinked rubber article is suitable for, for example, a part of a semiconductor manufacturing device that uses oxygen plasma. When the composition contains at least one of PTFE powder and PFA powder among the above-mentioned other components, the crosslinked rubber article obtained by using the composition has improved resistance to plasma irradiation using fluorine-based gas.Such crosslinked rubber article is suitable for, for example, parts of semiconductor manufacturing equipment that uses plasma using fluorine-based gas.

[0050] When the present composition contains other components, the total content of the other components is preferably more than 0.1 part by mass and not more than 30 parts by mass, more preferably 1 to 25 parts by mass, and particularly preferably 5 to 15 parts by mass, per 100 parts by mass of the fluorocopolymer.

[0051] The composition can be prepared by mixing the above-mentioned components using a rubber mixer such as a roll, a kneader, a Banbury mixer, or an extruder. Alternatively, the mixture may be molded after the components are mixed together to obtain a mixture. Specific examples of the method for molding the mixture include compression molding, injection molding, extrusion molding, calendar molding, or a method in which the mixture is dissolved in a solvent and dipped or coated on a substrate or the like to form the mixture.

[0052] [Crosslinked rubber article] The crosslinked rubber article of the present invention is a rubber article obtained from the above-mentioned fluorocopolymer composition, in which the fluorocopolymer in the fluorocopolymer composition is crosslinked. As a method for crosslinking the fluorocopolymer in the fluorocopolymer composition, a method in which the fluorocopolymer composition is crosslinked by heating it is preferred. Specific examples of the crosslinking method by heating include heat press crosslinking, steam crosslinking and hot air crosslinking, from which an appropriate method may be selected taking into consideration the shape and application of the fluorocopolymer composition. The heating conditions are preferably 100 to 400° C. for 1 second to 24 hours.

[0053] The crosslinked rubber obtained by heating the fluorocopolymer composition (first crosslinking) may be further heated to cause second crosslinking. By carrying out the second crosslinking, the mechanical properties, compression set and other properties of the crosslinked rubber can be stabilized or improved. When primary crosslinking and secondary crosslinking are performed, the heating temperature for the primary crosslinking is preferably 100 to 400°C, more preferably 120 to 200°C, and still more preferably 140 to 180°C. When primary crosslinking and secondary crosslinking are performed, the heating temperature for the secondary crosslinking is preferably 80 to 350°C, more preferably 140 to 300°C, and even more preferably 220 to 260°C. When primary crosslinking and secondary crosslinking are performed, the heating time for the primary crosslinking is preferably from 1 second to 60 minutes, more preferably from 1 minute to 40 minutes, and even more preferably from 5 minutes to 30 minutes. When primary crosslinking and secondary crosslinking are performed, the heating time for secondary crosslinking is preferably 30 minutes to 48 hours, more preferably 2 hours to 32 hours, and even more preferably 3 hours to 25 hours. The heating conditions for the secondary crosslinking are preferably 80 to 350° C. for 30 minutes to 48 hours.

[0054] As a crosslinking method other than crosslinking the fluorocopolymer by heating, there can be mentioned a method of crosslinking the fluorocopolymer by irradiating the fluorocopolymer composition with radiation. Specific examples of the radiation to be irradiated include electron beams and ultraviolet rays.

[0055] <Physical Properties> The compression set of the crosslinked rubber article at 250°C for 168 hours is preferably 95% or less, and from the viewpoints that the fluorocopolymer is well crosslinked and the crosslinked rubber article has better shape recovery after pressure application, it is more preferably 70% or less, and particularly preferably 50% or less. The compression set of the crosslinked rubber article at 250° C. for 168 hours is measured by the method described in the Examples section below.

[0056] <Application> The crosslinked rubber articles are suitable for use as materials for O-rings, sheets, gaskets, oil seals, diaphragms, V-rings, and the like. In addition, it can also be used for heat-resistant and chemical-resistant sealants, heat-resistant and oil-resistant sealants, electric wire coating materials, sealants for semiconductor manufacturing equipment, sealants for liquid crystal display panel manufacturing equipment, sealants for light-emitting diode manufacturing equipment, corrosion-resistant rubber paints, sealants for urea-resistant greases, etc., rubber paints, adhesive rubbers, hoses, tubes, calendar sheets (rolls), sponges, rubber rolls, oil drilling parts, heat dissipation sheets, solution crosslinked bodies, rubber sponges, bearing seals (urea-resistant grease, etc.), linings (chemical resistance), insulating sheets for automobiles, insulating sheets for electronic devices, rubber bands for watches, endoscope packings (amine-resistant), bellows hoses (processed from calendar sheets), water heater packings / valves, fenders (marine civil engineering, ships), fibers and nonwoven fabrics (protective clothing, etc.), board sealants, rubber gloves, stators for uniaxial eccentric screw pumps, parts for urea SCR systems, vibration-proofing agents, vibration-damping agents, sealants, additives for other materials, and toys. EXAMPLES

[0057] The present invention will be described in detail below with reference to examples. Examples 1 and 2 are working examples, and Examples 3 and 4 are comparative examples. However, the present invention is not limited to these examples. The blending amount of each component in the tables below is based on mass.

[0058] [Measurement of Fluorine-Containing Copolymer Composition] 19 The content (mol%) of each unit in the fluorocopolymer was calculated by F-nuclear magnetic resonance (NMR) analysis. However, the content of the propylene unit was calculated as follows: 13 Calculated from C-nuclear magnetic resonance (NMR) analysis. In addition, the content of iodine atoms in the fluorine-containing copolymer was calculated using an apparatus combining an automatic sample combustion apparatus, a pretreatment apparatus for ion chromatography (manufactured by Mitsubishi Chemical Analytech Co., Ltd., AQF-100 model) and an ion chromatograph.

[0059] [Compression set at high temperatures] In accordance with JIS K 6262:2013, the compression set rate (%) of a test piece of a crosslinked rubber article was measured when the test piece was held at 250°C for 168 hours. Note that, as the test piece, a P26 O-ring test piece in accordance with JIS B 2401-1:2012 was used. The test was performed using three test pieces, and the arithmetic average of the measured values ​​of the three test pieces was used. The compression set rate was calculated using the following formula, and the compression set rate at high temperatures was evaluated according to the following criteria. The closer the compression set rate is to 0%, the better the result is. Compression set rate (%) = (original thickness of test piece - thickness of test piece 30 minutes after removal from compression device) ÷ (original thickness of test piece - thickness of spacer) x 100 <Evaluation criteria> A: The compression set is 0% or more and 50% or less. B: The compression set rate is more than 50% and 70% or less. C: The compression set rate is more than 70% and 95% or less. D: Compression set is more than 95%.

[0060] [Compression set after long-term heating] The compression set after long-term heating was evaluated using the same procedures and evaluation criteria as in the above "Compression set at high temperatures," except that the time for which the test pieces of the crosslinked rubber articles were held at 250°C was changed from 168 hours to 336 hours.

[0061] [Production of Fluorine-Containing Copolymer 1] After degassing a 20L stainless steel pressure reactor equipped with an anchor blade, 8.2L of ultrapure water, 733g of a 30% solution of C2F5OCF2CF2OCF2COONH4, 10.0g of C3DVE, and 15.9g of a 5% aqueous solution of disodium hydrogen phosphate 12-hydrate were charged and the gas phase was replaced with nitrogen. While stirring at a speed of 375 rpm using the anchor blade, 198g of TFE and 454g of PMVE were pressed into the vessel after the internal temperature reached 80°C. The pressure inside the reactor was 0.90MPa [gauge]. 40mL of a 1% aqueous solution of ammonium persulfate was added to start the polymerization. The molar ratio of the monomers to be pressed in before the start of polymerization (hereinafter referred to as the initial monomer) was TFE:PMVE:C3DVE=41.74:57.64:0.61.

[0062] As the polymerization progressed, when the pressure inside the reactor dropped to 0.89 MPa [gauge], TFE was injected and the pressure inside the reactor was raised to 0.90 MPa [gauge]. This process was repeated, and 62 g of PMVE was also injected every time 80 g of TFE was injected. In addition, 7.0 g of 1,4-diiodoperfluorobutane was injected into the reactor from the ampoule together with 50 mL of ultrapure water when 60 g of TFE was injected. When the total added mass of TFE reached 1200 g, the addition of the monomer to be injected after the start of polymerization (hereinafter referred to as "post-added monomer") was stopped, the temperature inside the reactor was cooled to 10°C, the polymerization reaction was stopped, and a latex containing a fluorine-containing copolymer was obtained. The polymerization time was 360 minutes. The total added masses of the post-added monomers were 1200 g for TFE and 868 g for PMVE, which was converted to a molar ratio of TFE:PMVE=68:32.

[0063] Nitric acid (special grade, manufactured by Kanto Chemical Co., Ltd.) was dissolved in ultrapure water to prepare a 3% by mass aqueous solution of nitric acid. The latex was added to the aqueous nitric acid solution in a TFE-perfluoro(alkyl vinyl ether) copolymer (PFA) container to coagulate the fluorine-containing copolymer. The amount of the aqueous nitric acid solution was 150 parts by mass per 100 parts by mass of the fluorine-containing copolymer in the latex.

[0064] The aggregated fluorocopolymer was collected by filtration, and then placed in ultrapure water in a PFA container and washed by stirring at 200 rpm for 30 minutes. The amount of ultrapure water was 100 parts by mass per 100 parts by mass of the fluorocopolymer. The above washing was repeated 10 times.

[0065] The washed fluorocopolymer was recovered by filtration and dried at 50°C under reduced pressure of 10 kPa to obtain fluorocopolymer 1. The molar ratio of each unit in fluorocopolymer 1 was TFE unit:PMVE unit:C3DVE unit=71.40:28.43:0.17, and the iodine atom content was 0.10% by mass.

[0066] [Fluorine-containing copolymer 2] Fluororubber-1 in the Examples section of JP-A-06-306236 was used as fluorine-containing copolymer 2. The molar ratio of each unit in fluorine-containing copolymer 2 was VdF unit:TFE unit:propylene unit=35:40:25. No iodine atoms were contained.

[0067] [Examples 1 to 4] The components and amounts shown in Table 1 were mixed and kneaded with a two-roll mill at room temperature for 10 minutes to obtain a mixed fluorine-containing copolymer composition. The obtained fluorocopolymer composition was hot-pressed under the primary crosslinking conditions shown in Table 1 to obtain a crosslinked rubber sheet having a thickness of 1 mm (primary crosslinking). Then, in a nitrogen atmosphere, the crosslinked rubber sheet was heated in an oven under the secondary crosslinking conditions shown in Table 1 (secondary crosslinking). Thereafter, the crosslinked rubber sheet was cooled to room temperature to obtain the crosslinked rubber sheets of Examples 1 to 4. The above-mentioned physical properties were measured using the obtained crosslinked rubber sheet. The measurement results are shown in Table 1.

[0068] The components listed in Table 1, excluding the fluorine-containing copolymer, are outlined below. Perhexa 25B: Trade name, manufactured by Nippon Oil & Fats Co., Ltd., 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, organic peroxide Perkadox 14: Trade name, manufactured by Kayaku Akzo Co., Ltd., α,α'-bis(tert-butylperoxy)-p-diisopropylbenzene, organic peroxide TAIC: Trade name, manufactured by Mitsubishi Chemical Corporation, triallyl isocyanurate, specific polymerizable compound C6DV: Tosoh Finechem Corporation, CH2=CH(CF2)6CH=CH2, specific polymerizable compound TOCP: Tri-n-octylphosphine (liquid at 20°C), specific phosphorus compound, manufactured by Hokko Chemical Industry Co., Ltd.

[0069] [Table 1]

[0070] As shown in Table 1, it was confirmed that the use of a fluorine-containing copolymer composition containing a fluorine-containing copolymer, an organic peroxide, a specific polymerizable compound, and a specific phosphorus compound (Examples 1 and 2) made it possible to reduce compression set at high temperatures. The entire contents of the specification, claims and abstract of Japanese Patent Application No. 2019-192839, filed on October 23, 2019, are hereby incorporated by reference as the disclosure of the specification of the present invention.

Claims

1. A fluorine-containing copolymer composition comprising a fluorine-containing copolymer, an organic peroxide, a compound having two or more polymerizable unsaturated bonds, and a phosphorus compound having a melting point of 60° C. or lower.

2. The fluorine-containing copolymer composition according to claim 1, wherein the melting point of the phosphorus compound is 35° C. or lower.

3. The fluorine-containing copolymer composition according to claim 1 or 2, wherein the phosphorus compound is a phosphine having an alkyl group.

4. The fluorine-containing copolymer composition according to any one of claims 1 to 3, wherein the fluorine-containing copolymer is a perfluoropolymer.

5. The fluorine-containing copolymer composition according to any one of claims 1 to 4, wherein the fluorine-containing copolymer has units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether).

6. The fluorine-containing copolymer composition according to claim 5, wherein the fluorine-containing copolymer further has units based on a monomer having two or more polymerizable unsaturated bonds.

7. The fluorine-containing copolymer composition according to any one of claims 1 to 6, wherein the compound having two or more polymerizable unsaturated bonds is a compound having two or more vinyl groups or allyl groups.

8. The fluorine-containing copolymer composition according to any one of claims 1 to 7, wherein the compound having two or more polymerizable unsaturated bonds is a compound represented by the following formula (6): (CR ６１ R ６２ =CR ６３ ) ２ R ６４ Formula (6) In formula (6), R ６１ , R ６２ and R ６３ each independently represents a hydrogen atom, a fluorine atom, an alkyl group having 1 to 5 carbon atoms, or a fluoroalkyl group having 1 to 5 carbon atoms; R ６４ represents a divalent fluorohydrocarbon group having 1 to 18 carbon atoms or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of the fluorohydrocarbon group. ６１ , multiple R ６２ and multiple R ６３ may be the same or different from each other.

9. The fluorine-containing copolymer composition according to any one of claims 1 to 8, wherein the phosphorus compound is a trialkylphosphine.

10. The fluorine-containing copolymer composition according to any one of claims 1 to 9, wherein the phosphorus compound is a compound represented by the following formula (7): P(R ７１ ) ３ Formula (7) In formula (7), R ７１ represents a linear or branched alkyl group having 2 to 9 carbon atoms. ７１ may be the same or different from each other.

11. In the formula (7), three R ７１ Each independently represents a linear alkyl group having 2 to 9 carbon atoms.

12. In the formula (7), three R ７１ The fluorine-containing copolymer composition according to claim 10 or 11, wherein are the same.

13. A crosslinked rubber article obtained from the fluorocopolymer composition according to any one of claims 1 to 12, wherein the fluorocopolymer in the fluorocopolymer composition is crosslinked.

14. A method for producing a crosslinked rubber article, comprising heating the fluorocopolymer composition according to any one of claims 1 to 12 at 100 to 400°C to crosslink the fluorocopolymer in the fluorocopolymer composition.

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