Fluorine-containing copolymer composition and crosslinked rubber article

Abstract

Provided are: a fluorocopolymer composition capable of forming crosslinked rubber articles which have reduced compression set at high temperatures and do not crack after compression; and a crosslinked rubber article.　This fluorocopolymer composition comprises a fluorocopolymer having a nitrile group, a phosphorus compound having a melting point of 60°C or lower, and a crosslinking agent.

Description

[Technical Field]

[0001] The present invention relates to a fluorine-containing copolymer 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 for crosslinked rubber articles with small compression set at high temperatures. In response to such demands, the present inventors evaluated crosslinked rubber articles such as those 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"). Another property required of crosslinked rubber articles is that they do not crack after being compressed.

[0005] An object of the present invention is to provide a fluorocopolymer composition which can form a crosslinked rubber article which has a small compression set at high temperatures and does not crack after compression, and to provide such a crosslinked rubber article. [Means for solving the problem]

[0006] As a result of intensive investigations into the above-mentioned problems, the present inventors have found that the desired effects can be obtained by using a fluorinated copolymer composition containing a fluorinated copolymer having nitrile groups, a phosphorus compound having a melting point of 60°C or lower, and a crosslinking agent, and have arrived at the present invention.

[0007] That is, the inventors have found that the above problems can be solved by the following configuration. [1] A fluorine-containing copolymer composition comprising a fluorine-containing copolymer having nitrile groups, a phosphorus compound having a melting point of 60°C or less, and a crosslinking agent. [2] The fluorine-containing copolymer composition according to [1], wherein the fluorine-containing copolymer has units based on perfluoro(alkyl vinyl ether). [3] The fluorine-containing copolymer composition according to [1] or [2], wherein the fluorine-containing copolymer has units based on tetrafluoroethylene. [4] The fluorine-containing copolymer composition according to any one of [1] to [3], wherein the fluorine-containing copolymer has units based on a monomer having a nitrile group.

[0008] [5] The fluorine-containing copolymer composition according to [4], wherein the monomer having a nitrile group is a monomer represented by formula (1): CR 11 R 12 =CR 13 -R 14 -CN (1) In formula (1), R 11 , R 12 and R 13 each independently represents a hydrogen atom, a fluorine atom, or a methyl group; R 14 represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of the perfluorohydrocarbon group. [6] The fluorine-containing copolymer composition according to any one of [1] to [5], wherein the fluorine-containing copolymer is a perfluoropolymer. [7] The fluorine-containing copolymer composition of any of [1] to [6], wherein the melting point of the phosphorus compound is 35°C or lower. [8] The fluorine-containing copolymer composition of any one of [1] to [7], wherein the phosphorus compound is a phosphine or phosphine oxide having an alkyl group. [9] The fluorine-containing copolymer composition of any of [1] to [8], wherein the phosphorus compound is a trialkylphosphine or a trialkylphosphine oxide.

[0009]

[10] The fluorine-containing copolymer composition according to any one of [1] to [9], wherein the content of the phosphorus compound is 0.20 parts by mass or more per 100 parts by mass of the fluorine-containing copolymer.

[11] The fluorine-containing copolymer composition of any of [1] to

[10] , wherein the content of the phosphorus compound is 5 parts by mass or less per 100 parts by mass of the fluorine-containing copolymer.

[12] The fluorine-containing copolymer composition according to any one of [1] to

[11] , wherein the crosslinking agent is a compound having two or more amino groups.

[13] The fluorine-containing copolymer composition according to any one of [1] to

[12] , wherein the content of the crosslinking agent is 0.3 to 10 parts by mass per 100 parts by mass of the fluorine-containing copolymer.

[14] A crosslinked rubber article obtained by crosslinking the fluorocopolymer in the fluorocopolymer composition of any one of [1] to

[13] above. [Effects of the Invention]

[0010] According to the present invention, there can be provided a fluorocopolymer composition which can form a crosslinked rubber article which has a small compression set at high temperatures and does not crack after compression, and a crosslinked rubber article. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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 the monomer 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 distinguished from "resin." "Melting point" means the temperature corresponding to the maximum value of the melting peak measured by differential scanning calorimetry (DSC). "Boiling point" refers to the value measured according to the equilibrium reflux boiling point test method, specifically, JIS K2233:2017, 8.1. When a pressure is listed after the boiling point, the boiling point is the value measured under that pressure. Unless otherwise specified, the value measured according to the above-mentioned JIS K2233:2017, 8.1 method is the boiling point at 760 mmHg.

[0012] [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 having nitrile groups (hereinafter also referred to as "copolymer (A)"), a phosphorus compound having a melting point of 60°C or lower (hereinafter also referred to as "specific phosphorus compound"), and a crosslinking agent. Crosslinked rubber articles obtained using this composition have small compression set at high temperatures (for example, the compression set rate when a crosslinked rubber article is stored at 300°C for 70 hours and then subjected to a compression set test), and do not crack after compression. The details of the reason for this are not clear, but it is speculated to be due to the following reasons. The specific phosphorus compound is thought to function like an acid acceptor when crosslinking copolymer (A). Since the specific phosphorus compound contained in the composition has a low melting point, when crosslinking copolymer (A) contained in the composition while heating, the specific phosphorus compound remains liquid in the composition. This allows the specific phosphorus compound to disperse well in the composition, allowing crosslinking of copolymer (A) to proceed uniformly, improving crosslink density. As a result, compression set at high temperatures is thought to be reduced. Furthermore, since the specific phosphorus compound is uniformly dispersed in the crosslinked rubber article, it is believed that the specific phosphorus compound can be prevented from becoming a breaking point during compression, and as a result, cracks do not occur after compression.

[0013] <Copolymer (A)> Copolymer (A) is a polymer containing nitrile groups and fluorine atoms. When stretched, copolymer (A) itself does not completely return to its original shape, but crosslinking enhances its ability to return to its original shape, i.e., it exhibits rubber properties. Copolymer (A) preferably has a unit having a nitrile group and a unit based on perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE"), and particularly preferably has a unit having a nitrile group, a PAVE unit, and a unit based on tetrafluoroethylene (hereinafter also referred to as "TFE"), in order to obtain better effects of the present invention.

[0014] The unit having a nitrile group is a monomer having a nitrile group (hereinafter referred to as "R CN It is also called ". ) It is a unit based on R CN In terms of achieving better effects of the present invention, it is preferable that the monomer contains a fluorine atom, and it is particularly preferable that the monomer is a monomer represented by formula (1). CR 11 R 12 =CR 13 -R 14 -CN (1) In formula (1), R 11 , R 12 and R 13 each independently represents a hydrogen atom, a fluorine atom, or a methyl group; R 14 represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of the perfluorohydrocarbon group.

[0015] R CN Because of its excellent polymerization reactivity, 11 , R 12 , R 13 is preferably a fluorine atom or a hydrogen atom, and R 11, R 12 , R 13 It is more preferable that all of R are fluorine atoms or all of R are hydrogen atoms, and in view of the superior mold releasability and heat resistance of the crosslinked rubber article, 11 , R 12 , R 13 It is particularly preferred that all of are fluorine atoms. R 14 R may be linear, branched, or cyclic, and is preferably linear or branched. 14 The number of carbon atoms is preferably 2 to 8, more preferably 3 to 7, further preferably 3 to 6, and particularly preferably 3 to 5. R 14 may or may not have an etheric oxygen atom, but preferably has an etheric oxygen atom in view of better rubber properties. R 14 The number of etheric oxygen atoms in is preferably 1 to 3, and particularly preferably 1 or 2.

[0016] A specific example of the monomer represented by formula (1) is CF2=CFOCF2CF(CF3)OCF2CF2CN (hereinafter also referred to as "8CNVE"). 、 Examples include CF2=CFO(CF2)5CN (hereinafter also referred to as "MV5CN"), CF2=CFOCF2CF2CF2OCF(CF3)CN, and CF2=CFO(CF2)3CN, of which 8CNVE and MV5CN are preferred because they provide crosslinked rubber articles with better releasability and heat resistance.

[0017] PAVE units are perfluoro(alkyl vinyl ether) based units. The PAVE is preferably a monomer represented by formula (2) because it has excellent polymerization reactivity and rubber physical properties. CF2=CF-OR f2 (2) In formula (2), R f2 represents a perfluoroalkyl group having 1 to 10 carbon atoms. f2The number of carbon atoms is preferably 1 to 8, more preferably 1 to 6, further preferably 1 to 5, and particularly preferably 1 to 3, in terms of better polymerization reactivity. The perfluoroalkyl group may be linear or branched.

[0018] 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.

[0019] Copolymer (A) may contain 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, chlorotrifluoroethylene, a monomer having two or more polymerizable unsaturated bonds (hereinafter also referred to as "DV"), a monomer represented by the following formula (6), ethylene, and propylene. Also included are monomers other than those mentioned above that have a halogen atom (hereinafter also referred to as "monomers having another halogen atom") (e.g., bromotrifluoroethylene, iodotrifluoroethylene).

[0020] 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 2 to 6, more preferably 2 or 3, and particularly preferably 2, which provides better polymerization reactivity. It is preferred that DV further contains fluorine atoms, since this will result in a smaller compression set of the crosslinked rubber article at high temperatures.

[0021] DV is preferably a monomer represented by formula (3) since the crosslinked rubber article will have a smaller compression set at high temperatures. (CR 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 33 may be the same or different from each other, and are particularly preferably the same from each other. a3 is preferably 2 or 3, and 2 is particularly preferred.

[0022] Due to the superior polymerization reactivity of DV, 31 , R 32 , R 33 is preferably a fluorine atom or a hydrogen atom, and R 31 , R 32 , R 33 It is more preferable that all of R are fluorine atoms or hydrogen atoms, and from the viewpoint of the heat resistance and chemical resistance of the crosslinked rubber article, 31 , R 32 , R 33 It is particularly preferred that all of are fluorine atoms. R 34 R may be linear, branched, or cyclic, preferably linear or branched, and particularly preferably linear. 34 The number of carbon atoms is preferably 2 to 10, more preferably 3 to 8, further preferably 3 to 6, and particularly preferably 3 to 5. R 34 may or may not have an etheric oxygen atom, but preferably has an etheric oxygen atom in view of better crosslinking reactivity and rubber physical properties. R 34The number of etheric oxygen atoms in R is preferably 1 to 6, more preferably 1 to 3, and particularly 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.

[0023] Of the monomers represented by formula (3), specific examples of suitable monomers include the monomers represented by formula (4) and the monomers represented by formula (5).

[0024] (CF2=CF)2R 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.

[0025] Specific examples of the monomer represented by formula (4) 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. Of the monomers represented by formula (4), specific examples of more suitable monomers include CF2=CFO(CF2)3OCF=CF2 and CF2=CFO(CF2)4OCF=CF2.

[0026] (CH2=CH)2R 51 (5) In formula (5), R 51represents 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] Specific examples of the monomer represented by formula (5) include CH2=CH(CF2)2CH=CH2, CH2=CH(CF2)4CH=CH2, and CH2=CH(CF2)6CH=CH2. Among the monomers represented by formula (5), a more preferred specific example of the monomer is CH2=CH(CF2)6CH=CH2.

[0028] When DV is copolymerized, the polymerizable double bonds at the ends of the DV react during polymerization to give a copolymer (A) having a branched chain.

[0029] Equation (6) is as follows: CF2=CF-OR f6 (6) In formula (6), R f6 R represents a perfluoroalkyl group having 1 to 8 carbon atoms and containing 1 to 5 etheric oxygen atoms. f6 The number of carbon atoms is preferably 1 to 6, and particularly preferably 1 to 5.

[0030] 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).

[0031] Copolymer (A) is R CN When the unit is contained, the content thereof is preferably 0.05 to 5 mol %, more preferably 0.1 to 3 mol %, particularly preferably 0.2 to 1.5 mol %, based on the total units of the copolymer (A), in terms of better effects of the present invention. When the copolymer (A) contains TFE units, the content thereof is preferably 60 to 80 mol %, more preferably 63 to 75 mol %, and particularly preferably 66 to 72 mol %, based on the total units of the copolymer (A), in terms of better effects of the present invention. When copolymer (A) contains PAVE units, the content is preferably 20 to 40 mol %, more preferably 24 to 36 mol %, and particularly preferably 27 to 33 mol %, based on the total units of copolymer (A), in order to obtain better elasticity of the crosslinked rubber article. When copolymer (A) contains other monomer units, the content thereof is preferably 0.01 to 10 mol %, more preferably 0.5 to 10 mol %, and particularly preferably 1 to 5 mol %, based on the total units of copolymer (A), in order to obtain excellent rubber physical properties of the crosslinked rubber article.

[0032] The copolymer (A) is preferably a perfluoropolymer, as this will provide better effects of the present invention. Here, "perfluoropolymer" refers to a polymer that does not substantially contain hydrogen atoms bonded to carbon atoms, but has fluorine atoms in place of those hydrogen atoms, and whose main chain is 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% by mass or less, preferably 0.1% by mass or less, more preferably 0.07% by mass or less, and particularly 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.

[0033] The copolymer (A) may contain an iodine atom, and in this case, the copolymer (A) preferably has the iodine atom at the end of the polymer chain. Examples of the iodine atom include an iodine atom derived from an iodine compound that functions as a chain transfer agent, which will be described later, and an iodine atom in a unit based on a monomer that has an iodine atom among other halogen-containing monomers 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 preferred. When copolymer (A) contains iodine atoms, the content thereof is preferably 0.01 to 5.0 mass%, more preferably 0.05 to 2.0 mass%, and particularly preferably 0.05 to 1.0 mass%, based on the total mass of copolymer (A). When the content of iodine atoms is within the above range, the crosslinking reactivity of copolymer (A) is improved, and the mechanical properties of the crosslinked rubber article are excellent.

[0034] The content of the copolymer (A) 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.

[0035] (Method for producing copolymer (A)) An example of a method for producing the copolymer (A) is a method in which the above-mentioned monomers are copolymerized in the presence of a radical polymerization initiator.

[0036] As the radical polymerization initiator, a water-soluble polymerization initiator or a redox polymerization initiator is preferred. 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. Examples of redox polymerization initiators include polymerization initiators that combine persulfates and reducing agents. Among these, 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 the redox polymerization initiator include alkali metal salts of persulfates 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.

[0037] In the method for producing the copolymer (A), the above-mentioned monomers may be copolymerized in the presence of a chain transfer agent together with a radical polymerization initiator. The chain transfer agent is preferably an iodine compound, and particularly preferably an iodine compound represented by formula RI2: In the above formula, R represents an alkylene group or perfluoroalkylene group having 3 or more carbon atoms (preferably 3 to 8 carbon atoms). 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 preferred, and 1,4-diiodoperfluorobutane is particularly preferred. When the above-mentioned monomers are copolymerized in the presence of these iodine compounds, iodine atoms can be introduced into the copolymer (A).

[0038] For details of the components other than those mentioned above used in producing the copolymer (A) and the production method, reference can be made to the method described in paragraphs 0019 to 0034 of WO 2010 / 082633.

[0039] <Specific phosphorus compounds> The specific phosphorus compound is a phosphorus compound having a melting point of 60°C or less. The melting point of the specific phosphorus compound is 60° C. or lower, preferably 35° C. or lower, particularly preferably 20° C. or lower, since this improves the dispersibility of the specific phosphorus compound and provides better effects of the present invention. The above compounds having melting points below a specific temperature also include compounds that are liquid at 20°C. The boiling point of the specific phosphorus compound is preferably 50° C. or higher, more preferably 100° C. or higher, from the viewpoint of ease of handling.

[0040] The specific phosphorus compound is preferably a phosphine or phosphine oxide having an alkyl group, more preferably a trialkylphosphine or trialkylphosphine oxide, further preferably a compound represented by the following formula (7) or (8), 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. 71 may be the same or different, but are preferably the same in order to reduce the compression set of the crosslinked rubber article at high temperatures. PO(R 81 )3 formula (8) In formula (8), R 81 represents a linear or branched alkyl group having 2 to 9 carbon atoms. 81 may be the same or different, but are preferably the same in order to reduce the compression set of the crosslinked rubber article at high temperatures.

[0041] R 71 The number of carbon atoms is 2 to 9, preferably 4 to 9, and particularly preferably 6 to 8, since the compression set of the crosslinked rubber article at high temperatures will be smaller. The three R's 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. R 81 The carbon number of is 2 to 9, preferably 4 to 9, and particularly preferably 6 to 8, since the compression set of the crosslinked rubber article at high temperatures will be smaller. The three R's are chosen because crosslinked rubber articles have a smaller compression set at high temperatures. 81 are each preferably independently a linear alkyl group having 2 to 9 carbon atoms.

[0042] Specific examples of the compound represented by formula (7) include triethylphosphine (melting point -86°C, liquid at 20°C, boiling point 127 to 128°C), tri-n-propylphosphine (melting point unknown, liquid at 20°C, boiling point 72 to 74°C / 12mmHg), tri-n-butylphosphine (melting point -65°C, liquid at 20°C, boiling point 150°C / 50mmHg), tri-tert-butylphosphine (melting point 30 to 35°C, liquid or solid at 20°C, boiling point 102°C / 13mmHg), tri-n-pentylphosphine (melting point unknown, liquid at 20°C, boiling point unknown), tri-n-hexylphosphine (melting point unknown, liquid at 20°C, boiling point 227°C / 50mmHg), and tri-n-octylphosphine (melting point unknown, liquid at 20°C, boiling point 175°C / 0.3mmHg). Specific examples of the compound represented by formula (8) include triethylphosphine oxide (melting point 52°C, solid at 20°C), tri-n-propylphosphine oxide (melting point 39°C, solid at 20°C), tri-n-hexylphosphine oxide (melting point 34°C, solid at 20°C), and tri-n-octylphosphine oxide (melting point 52°C, solid at 20°C). Among the specific phosphorus compounds, tri-n-octylphosphine is preferred because it reduces the compression set of the crosslinked rubber article at high temperatures.

[0043] The content of the specific phosphorus compound is preferably 0.01 part by mass or more, more preferably 0.10 part by mass or more, and particularly preferably 0.20 part by mass or more, per 100 parts by mass of copolymer (A), from the viewpoint of further suppressing the occurrence of cracks in the crosslinked rubber article, and is even more preferably 0.20 part by mass or more, and particularly preferably 0.25 part by mass or more, from the viewpoint of excellent releasability of the crosslinked rubber article. The content of the specific phosphorus compound is preferably 5 parts by mass or less, more preferably 2 parts by mass or less, and particularly preferably 1.0 part by mass or less, per 100 parts by mass of copolymer (A), in order to reduce the compression set of the crosslinked rubber article at high temperatures.

[0044] <Crosslinking agent> Specific examples of crosslinking agents include organic peroxides and compounds having two or more amino groups (hereinafter also referred to as "polyamine compounds"). Polyamine compounds are preferred because they provide excellent crosslinking properties for the copolymer (A) and allow crosslinked rubber articles to be obtained that have smaller compression set at high temperatures.

[0045] 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. However, in terms 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, which improves compatibility with the copolymer (A) and allows a crosslinked rubber article to be obtained that has a smaller compression set at high temperatures.

[0046] 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. Among these, BOAP is preferred because it provides superior effects for the present invention.

[0047] The content of the crosslinking agent 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 copolymer (A). When the content of the crosslinking agent is within the above range, the effects of the present invention are more excellent.

[0048] <Other ingredients> The composition may contain other components in addition to those described above, provided that the effects of the present invention are not impaired. Examples of other components include acid acceptors (e.g., fatty acid esters, fatty acid metal salts, and divalent metal oxides (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, and talc), scorch retarders (e.g., 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 (e.g., 18-crown-6), and mold release agents (e.g., sodium stearate).

[0049] When the present composition contains other components, the total content of the other components is preferably more than 0.1 parts by mass and not more than 30 parts by mass, more preferably 1 to 15 parts by mass, and particularly preferably 3 to 5 parts by mass, per 100 parts by mass of copolymer (A).

[0050] The composition can be prepared by mixing the above components using a rubber mixing device such as a roll, kneader, Banbury mixer, or extruder. Alternatively, the mixture obtained by mixing the above components may be molded by compression molding, injection molding, extrusion molding, calendar molding, or by dissolving the mixture in a solvent and dipping or coating it onto a substrate or the like.

[0051] [Crosslinked rubber article] The crosslinked rubber article of the present invention is a rubber article obtained by crosslinking the copolymer (A) in the present composition described above. The copolymer (A) in the present composition is preferably crosslinked by heating the present composition. Specific examples of the crosslinking method by heating include heat press crosslinking, steam crosslinking, and hot air crosslinking, and an appropriate method may be selected from these methods taking into consideration the shape and application of the present composition. The heating conditions are preferably 100 to 400° C. for 1 second to 24 hours.

[0052] The crosslinked rubber obtained by heating the composition (first crosslinking) may be further heated to cause second crosslinking. By performing second crosslinking, the mechanical properties, compression set, and other properties of the crosslinked rubber can be stabilized or improved. The heating conditions for the secondary crosslinking are preferably 80 to 350° C. for 30 minutes to 48 hours. When heating, the temperature may be increased or decreased stepwise.

[0053] As a crosslinking method other than crosslinking the copolymer (A) by heating, there is a method of crosslinking the copolymer (A) by irradiating the present composition with radiation. Specific examples of the radiation to be irradiated include electron beams and ultraviolet rays.

[0054] <Physical properties> The compression set of the crosslinked rubber article at 300°C for 70 hours is preferably 70% or less, more preferably 50% or less, particularly preferably 30% or less, and most preferably 15% or less, because the copolymer (A) is well crosslinked and the crosslinked rubber article has better shape recovery after pressure application. The compression set of the crosslinked rubber article at 300° C. for 70 hours is measured by the method described in the Examples section below.

[0055] The tensile strength (tensile strength at break) of the crosslinked rubber article is preferably 10 to 50 MPa, particularly preferably 15 to 40 MPa, in terms of excellent rubber properties. The tensile elongation (elongation at break) of the crosslinked rubber article is preferably 100 to 500%, particularly preferably 150 to 400%, in terms of excellent rubber properties. The tensile strength and tensile elongation of the crosslinked rubber article are values measured by a method conforming to JIS K 6251:2010 (corresponding international standard ISO 37:2005).

[0056] The hardness (Shore-A) of the crosslinked rubber article is preferably 55 to 90, more preferably 60 to 85, in view of excellent rubber properties. The hardness (Shore-A) of the crosslinked rubber article is a value measured using a type A durometer in accordance with JIS K6253-1:2012 using a plate-shaped molded product (thickness 1 mm) of the crosslinked rubber article.

[0057] <Application> The crosslinked rubber articles are suitable for use as materials for O-rings, sheets, gaskets, oil seals, diaphragms, V-rings, and the like. It can also be used in heat-resistant and chemical-resistant sealants, heat-resistant and oil-resistant sealants, 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, rubber paints, adhesive rubbers, hoses, tubes, calendered sheets (rolls), sponges, rubber rolls, oil drilling components, heat-dissipating sheets, solution-crosslinked bodies, rubber sponges, bearing seals (urea-resistant grease, etc.), linings (chemical-resistant), insulating sheets for automobiles, insulating sheets for electronic devices, rubber bands for watches, endoscope packings (amine-resistant), corrugated hoses (processed from calendered sheets), water heater packings / valves, fenders (offshore civil engineering, ships), fibers and nonwoven fabrics (protective clothing, etc.), circuit board sealants, rubber gloves, stators for uniaxial eccentric screw pumps, parts for urea SCR systems, vibration-damping agents, vibration-damping agents, sealants, additives for other materials, and toys. [Example]

[0058] The present invention will be described in detail below with reference to examples. Examples 1 and 4 are working examples, and Examples 2 and 3 are comparative examples. However, the present invention is not limited to these examples. The blending amounts of each component in the tables below are based on mass.

[0059] [Measurement of Fluorine-Containing Copolymer Composition] 19 The content (mol %) of each unit in the fluorine-containing copolymer was calculated by F-nuclear magnetic resonance (NMR) analysis. However, the content of propylene units was calculated as follows: 1 H and 13Calculated from C-nuclear magnetic resonance (NMR) analysis.

[0060] 〔hardness〕 Using test pieces of the crosslinked rubber articles, hardness (Shore-A) was measured using a Type A durometer in accordance with JIS K6253-3:2012. The measurement device used was an automatic rubber hardness tester (Digitest Shore A, manufactured by H. Burleith Testing Instruments). The test was carried out using three test pieces, and the arithmetic mean of the measured values of the three test pieces was recorded.

[0061] [Tensile strength, tensile elongation] Test specimens were punched out of plate-shaped crosslinked rubber articles (thickness 1 mm) with a No. 4 dumbbell, and the tensile strength and tensile elongation were measured in accordance with JIS K6251:2010 (corresponding international standard ISO 37:2005). The measurement was performed using a tensile tester with data processing (Quick Reader TS-2530, manufactured by Ueshima Seisakusho Co., Ltd.). Each test was carried out using three test pieces, and the arithmetic mean of the measured values of the three test pieces was recorded.

[0062] [Compression set at high temperatures] According to JIS K 6262:2013, the compression set (%) of a test piece of a crosslinked rubber article was measured after holding it at 300°C for 70 hours. The test piece used was a P26 O-ring test piece according to JIS B 2401-1:2012. The test was performed using two test pieces, and the arithmetic average of the measured values of the two test pieces was used. The compression set was calculated using the following formula: The closer the compression set is to 0%, the better the product is. Compression set rate (%) = (original thickness of test specimen - thickness of test specimen 30 minutes after removal from compression device) ÷ (original thickness of test specimen - thickness of spacer) × 100

[0063] [Cracking after compression] After the above-mentioned "compression set under high temperature" test, the two test pieces were visually inspected for the occurrence of cracks. For the two test pieces in each example, if no cracks were found in either piece, it was marked "none," if cracks were found in only one piece, it was marked "1 / 2 failure," and if cracks were found in both pieces, it was marked "2 / 2 failure," as shown in Table 1 below.

[0064] [Mold Releasability Test] A fluorocopolymer composition was introduced into a sheet-like mold, and the fluorocopolymer composition was crosslinked at 180°C for 20 minutes to obtain a crosslinked rubber article (100mm long x 60mm wide x 1mm thick) attached to the mold. Immediately after the crosslinking reaction was completed, air was sprayed onto the interface between the crosslinked rubber article and the mold using an air gun (product name: Cyclone Duster, manufactured by Chuo Kuuki Co., Ltd.), and the mold releasability was evaluated according to the following evaluation criteria. It should be noted that, since air was injected immediately after the crosslinking reaction was completed, the temperature of the crosslinked article at the time of air injection is thought to be close to 180°C. <Air gun air injection conditions> Pressure: 0.5 MPa Air injection time: 3 seconds <Evaluation criteria> ◯: The crosslinked rubber article was released from the mold. Δ: A part of the crosslinked rubber article did not come off the mold. ×: Most of the crosslinked rubber articles did not come off the mold.

[0065] [Production of Copolymer (A-1)] A 20 L stainless steel pressure reactor equipped with an anchor impeller was degassed and then charged with 7.2 L of ultrapure water, 880 g of a 30 wt% solution of the emulsifier C2F5OCF2CF2OCF2COONH4, 7.3 g of 8CNVE, and 15.9 g of a 5 wt% aqueous solution of disodium hydrogen phosphate dodecahydrate. The gas phase was then purged with nitrogen. While stirring at 375 rpm using an anchor impeller, 137 g of TFE and 635 g of PMVE were pressurized into the reactor, and the internal temperature was raised to 80 °C. The internal pressure of the reactor was 0.90 MPa [gauge]. 28 mL of a 3 wt% 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 monomers") was TFE:PMVE:8CNVE=26.3:73.3:0.4.

[0066] After the initiation of polymerization, as the polymerization progressed, monomers were injected as follows. Hereinafter, injection of a monomer after the initiation of polymerization will also be referred to as "post-addition," and a monomer injected after the initiation of polymerization will also 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 process 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 decrease, 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 start of polymerization was 35 mL. When the cycle was completed and the total added mass of TFE reached 1073.7 g, 119.3 g of TFE was injected. When the total added mass of post-added TFE reached 1193 g, the addition of the post-added monomer was stopped, the reactor internal temperature was cooled to 10°C, and the polymerization reaction was terminated to obtain a latex containing a fluorinated copolymer. The polymerization time was 375 minutes. The total added masses of the post-added monomers were 1193 g of TFE, 666 g of PMVE, and 66.6 g of 8CNVE, which converted to a molar ratio of TFE:PMVE:8CNVE=74.0:25.0:1.0. The latex was added to a 5% by mass aqueous solution of aluminum potassium sulfate to coagulate and separate the fluorocopolymer. The fluorocopolymer was filtered, washed with ultrapure water, and vacuum dried at 50°C to obtain a white fluorocopolymer (hereinafter referred to as "copolymer (A-1)"). The content (molar ratio) of each unit in the obtained copolymer (A-1) was TFE unit / PMVE unit / 8CNVE unit = 69.1 / 30.3 / 0.6.

[0067] [Copolymer (H-1)] The copolymer (H-1) was "Fluororubber-1" described in the Examples section of JP-A-06-306236. The molar ratio of each unit in the copolymer (H-1) was VdF unit:TFE unit:propylene unit = 35:40:25.

[0068] [Examples 1 to 4] The ingredients 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 fluorine-containing copolymer composition was hot-pressed under the following primary crosslinking conditions to obtain a crosslinked rubber sheet having a thickness of 1 mm (primary crosslinking). The primary crosslinking in Examples 1, 2, and 4 was carried out by hot-pressing at 180°C for 20 minutes. The primary crosslinking in Example 3 was carried out by hot-pressing at 170°C for 10 minutes. The crosslinked rubber sheet was then heated in an oven under a nitrogen atmosphere under the following conditions (secondary crosslinking): In Examples 1, 2, and 4, the secondary crosslinking was carried out by heating at 90°C for 3 hours, then increasing the temperature to 305°C over 5 hours, and then further heating at 305°C for 13 hours. In Example 3, the secondary crosslinking was carried out by heating at 230°C for 24 hours. Thereafter, the crosslinked rubber sheet was cooled to room temperature to obtain 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.

[0069] The components listed in Table 1, excluding the fluorine-containing copolymer, are outlined below. BOAP: 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, a polyamine compound (crosslinking agent) Perhexa 25B: Trade name, manufactured by NOF Corporation, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, organic peroxide (crosslinking agent) Perkadox 14: Trade name, manufactured by Kayaku Akzo Co., Ltd., α,α'-bis(tert-butylperoxy)-p-diisopropylbenzene, organic peroxide (crosslinking agent) TOCP: Tri-n-octylphosphine (liquid at 20°C), specific phosphorus compound, manufactured by Hokko Chemical Industry Co., Ltd.

[0070] [Table 1]

[0071] In Table 1, ">100" in the column for compression set at high temperature means a value greater than 100%. As shown in Table 1, it was confirmed that by using this composition containing copolymer (A), a crosslinking agent, and a specific phosphorus compound (Examples 1 and 4), it is possible to form crosslinked rubber articles that have small compression set at high temperatures and do not crack after compression. The entire contents of the specification, claims and abstract of Japanese Patent Application No. 2020-071583, filed on April 13, 2020, are hereby incorporated by reference as part of the disclosure of the specification of the present invention.

Claims

1. a fluorine-containing copolymer having a nitrile group, a phosphorus compound having a melting point of 60°C or less, and a crosslinking agent; the fluorine-containing copolymer has units based on perfluoro(alkyl vinyl ether), units based on tetrafluoroethylene, and units based on a monomer having a nitrile group, The fluorine-containing copolymer composition, wherein the phosphorus compound is a phosphine having an alkyl group.

2. 2. The fluorine-containing copolymer composition according to claim 1, wherein the monomer having a nitrile group is a monomer represented by formula (1): CR １１ R １２ =CR １３ -R １４ -C-N (1) In formula (1), R １１ , R １２ and R １３ each independently represents a hydrogen atom, a fluorine atom, or a methyl group; R １４ represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of the perfluorohydrocarbon group.

3. The fluorine-containing copolymer composition according to claim 1 or 2, wherein the fluorine-containing copolymer is a perfluoropolymer.

4. The fluorine-containing copolymer composition according to any one of claims 1 to 3, wherein the melting point of the phosphorus compound is 35°C or lower.

5. The fluorine-containing copolymer composition according to any one of claims 1 to 4, wherein the phosphorus compound is a trialkylphosphine.

6. The fluorine-containing copolymer composition according to any one of claims 1 to 5, wherein the content of said phosphorus compound is 0.20 parts by mass or more per 100 parts by mass of said fluorine-containing copolymer.

7. The fluorine-containing copolymer composition according to any one of claims 1 to 6, wherein the content of said phosphorus compound is 5 parts by mass or less per 100 parts by mass of said fluorine-containing copolymer.

8. The fluorine-containing copolymer composition according to any one of claims 1 to 7, wherein said crosslinking agent is a compound having two or more amino groups.

9. The fluorine-containing copolymer composition according to any one of claims 1 to 8, wherein the content of said crosslinking agent is 0.3 to 10 parts by mass per 100 parts by mass of said fluorine-containing copolymer.

10. A crosslinked rubber article obtained by crosslinking the fluorocopolymer in the fluorocopolymer composition according to any one of claims 1 to 9.

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