Fluorine-containing copolymer composition, method for producing the same, and fluororubber article

Abstract

The present invention provides: a fluorine-containing copolymer composition from which it is possible to obtain a fluororubber article which exhibits excellent heat resistance; a method for producing the same; and a fluororubber article. A fluorine-containing copolymer composition according to the present invention contains: a fluorine-containing copolymer having a unit based on a monomer having a nitrile group and a unit based on tetrafluoroethylene; and a crosslinking agent that is a polyamine compound. The crosslinking agent is a solid particle having a volume-based median diameter of 40μm or less.

Description

Fluorine-containing copolymer composition, its production method, and fluororubber article

[0001] The present invention relates to a fluorine-containing copolymer composition, a method for producing the same, and a fluororubber article obtained by crosslinking the fluorine-containing copolymer composition.

[0002] Fluororubber 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 such as O-rings, packings, oil seals, gaskets, cushioning materials, etc. in the fields of semiconductor manufacturing, vehicles, aircraft, general machinery, construction, chemical plants, etc.

[0003] As a mode of crosslinking of a fluorocopolymer, for example, from the viewpoint of improving the heat resistance of a fluororubber article, it is known to introduce units based on a monomer having a nitrile group (cyano group) into the fluorocopolymer, and form a crosslinked structure containing an oxazole ring with a bisaminophenol-based crosslinking agent using the nitrile group as a crosslinking site (see Patent Documents 1 to 3).

[0004] Japanese Patent Publication No. 2-59177 International Publication No. 2007 / 013997 International Publication No. 2021 / 210503

[0005] The above-mentioned crosslinking agent is generally solid, and exists as aggregated particles in the uncrosslinked fluorocopolymer composition containing the fluorocopolymer and the crosslinking agent. Therefore, there are cases where relatively coarse particles (for example, having a volume-based median diameter of 50 μm or more) of the crosslinking agent are dispersed in the fluorocopolymer composition.

[0006] However, the particle size of the crosslinking agent is not mentioned in prior art documents such as Patent Documents 1 to 3. Therefore, the present inventors investigated the effect of the particle size of the crosslinking agent on the properties of the fluororubber, which is a crosslinked product of a fluorocopolymer, and found the conditions under which a fluororubber having excellent heat resistance at high temperatures of about 300°C can be obtained.

[0007] The present invention has been made under these circumstances, and an object of the present invention is to provide a fluorocopolymer composition from which fluororubber articles having excellent heat resistance can be obtained, a method for producing the same, and the fluororubber article.

[0008] The present invention is based on the discovery that the heat resistance of fluororubber articles can be improved by using solid crosslinking agent particles of a specific size.

[0009] The present invention provides the following means. [1] A fluorine-containing copolymer composition comprising a fluorine-containing copolymer having units based on a monomer having a nitrile group and units based on tetrafluoroethylene, and a crosslinking agent which is a polyamine compound, wherein the crosslinking agent is in the form of solid particles having a volume-based median diameter of 40 μm or less. [2] The fluorine-containing copolymer composition of [1], wherein the fluorine-containing copolymer further has units based on a perfluoroalkyl vinyl ether. [3] The fluorine-containing copolymer composition of [1] or [2], wherein the fluorine-containing copolymer is a perfluoropolymer. [4] The fluorine-containing copolymer composition of any of [1] to [3], wherein the content of the crosslinking agent is 0.1 to 10.0 parts by mass per 100 parts by mass of the fluorine-containing copolymer. [5] The fluorine-containing copolymer composition of any of [1] to [4], wherein the crosslinking agent is a bisaminophenol compound.

[0010] [6] A method for producing a fluorine-containing copolymer composition comprising a fluorine-containing copolymer having units based on a monomer having a nitrile group and units based on tetrafluoroethylene, and a solid crosslinking agent which is a polyamine compound, the method comprising a step of pulverizing the crosslinking agent by kneading the fluorine-containing copolymer and the crosslinking agent with a kneading energy of 10 J / g or more. [7] A method for producing the fluorine-containing copolymer composition of [6], comprising pulverizing the crosslinking agent into solid particles having a volume-based median diameter of 40 μm or less. [8] A method for producing the fluorine-containing copolymer composition of any of [1] to [5], comprising kneading the fluorine-containing copolymer and the crosslinking agent with a kneading energy of 10 J / g or more to pulverize the crosslinking agent to obtain the fluorine-containing copolymer composition. [9] A fluororubber article obtained by crosslinking the fluorine-containing copolymer composition of any of [1] to [5].

[0011] According to the present invention, it is possible to provide a fluorocopolymer composition from which fluororubber articles having excellent heat resistance can be obtained, a method for producing the same, and the fluororubber article.

[0012] The definitions and meanings of terms and notations used in this specification are as follows. The notation "X to Y" (X and Y are numerical values) means a numerical range with X as the lower limit and Y as the upper limit. In a numerical range (for example, a range of content, etc.), the lower limit and upper limit values ​​described in stages may be combined independently. The lower limit and upper limit values ​​of a numerical range may be replaced with numerical values ​​described in the Examples. A "unit" is a chemical structure derived from one molecule of a monomer that constitutes a polymer, and includes those that have been partially chemically converted. The molar ratio of units based on the monomer in a fluorine-containing copolymer is １９ The values ​​are calculated from F-nuclear magnetic resonance (NMR) spectra. "Rubber" means rubber exhibiting properties defined by JIS K 6200:2008, and is distinguished from "resin." The melting point refers to the temperature at the maximum value of the melting peak measured by differential scanning calorimetry (DSC).

[0013] [Fluorocopolymer composition] The fluorine-containing copolymer composition of an embodiment of the present invention (hereinafter referred to as the present embodiment) comprises a fluorine-containing copolymer having units based on a monomer having a nitrile group and units based on tetrafluoroethylene (TFE), and a crosslinking agent which is a polyamine compound, wherein the crosslinking agent is in the form of solid particles having a volume-based median diameter (hereinafter also referred to as D50) of 40 μm or less. According to the fluorine-containing copolymer composition of the present embodiment, a fluororubber article having excellent heat resistance and small compression set, particularly at high temperatures (e.g., 300°C), can be obtained.

[0014] (Fluorine-containing copolymer) The fluorine-containing copolymer of the present embodiment is a copolymer having units based on a monomer having a nitrile group and units based on TFE. The fluorine-containing copolymer does not have rubber elasticity by itself, but becomes rubber elastic by crosslinking.

[0015] The content of the fluorine-containing copolymer in the fluorine-containing copolymer composition is preferably from 60.0 to 99.9 mass%, more preferably from 70.0 to 99.9 mass%, and still more preferably from 80.0 to 99.9 mass%, from the viewpoint of good heat resistance of the fluororubber obtained by crosslinking the fluorine-containing copolymer.

[0016] The unit based on the monomer having a nitrile group preferably has a fluorine atom, from the viewpoint of good heat resistance of the fluororubber obtained by crosslinking the fluorine-containing copolymer, and is more preferably a monomer represented by the following formula (1): CR １１ R １２ =CR １３ R １４ CN (1) In formula (1), R １１ ~R １３ are each independently a hydrogen atom, a fluorine atom, or a methyl group. １４ is a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms or a group having an etheric oxygen atom at the terminal or between carbon atoms of the perfluorohydrocarbon group.

[0017] R １１ ~R １３From the viewpoint of good polymerization reactivity, R is preferably a fluorine atom or a hydrogen atom, and it is preferable that all of them are fluorine atoms or hydrogen atoms, and from the viewpoint of good heat resistance of the fluororubber obtained by crosslinking the fluorine-containing copolymer, it is particularly preferable that all of them are fluorine atoms. １４ R may be any of linear, branched, and cyclic, and is preferably linear or branched from the viewpoint of good polymerization reactivity. １４ The number of carbon atoms in R is preferably 2 to 8, more preferably 3 to 7, even more preferably 3 to 6, and even more preferably 3 to 5. １４ Preferably, R has an etheric oxygen atom from the viewpoint of good rubber elasticity of the fluororubber obtained by crosslinking the fluorine-containing copolymer. １４ The number of etheric oxygen atoms in the formula (I) is preferably 1 to 3, and more preferably 1 or 2.

[0018] Specific examples of the monomer having a nitrile group include CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ CN (abbreviated as 8CNVE), CF ２ = CFO (CF ２ ) ５ CN (abbreviated as MV5CN), CF ２ = CFOCF ２ CF ２ CF ２ OCF (CF ３ ) CN, CF ２ = CFO (CF ２ ) ３ CN, etc. The monomer having a nitrile group may be used alone or in combination of two or more. Among these, from the viewpoint of good heat resistance of the fluororubber obtained by crosslinking the fluorine-containing copolymer, 8CNVE and MV5CN are preferred, and 8CNVE is more preferred.

[0019] It is preferable that the fluorine-containing copolymer further has units based on perfluoroalkyl vinyl ether (PAVE) in addition to units based on a monomer having a nitrile group and units based on TFE, from the viewpoint of good rubber elasticity and heat resistance of the fluororubber obtained by crosslinking the fluorine-containing copolymer.

[0020] From the viewpoints of good polymerization reactivity and good heat resistance of the fluororubber obtained by crosslinking the fluorine-containing copolymer, the PAVE is preferably a monomer represented by the following formula (2): CF ２ =CF-O-R ｆ２ (2) In formula (2), R ｆ２ is a perfluoroalkyl group having 1 to 10 carbon atoms. The perfluoroalkyl group may be linear or branched. ｆ２ From the viewpoint of good polymerization reactivity, the number of carbon atoms is preferably 1 to 8, more preferably 1 to 6, even more preferably 1 to 5, and still more preferably 1 to 3.

[0021] Specific examples of PAVE include perfluoromethyl vinyl ether (PMVE), perfluoroethyl vinyl ether (PEVE), and perfluoropropyl vinyl ether (PPVE). PAVE may be used alone or in combination of two or more. Among these, PMVE and PPVE are preferred, with PMVE being more preferred, from the viewpoints of good polymerization reactivity and easy availability.

[0022] From the viewpoint of the good rubber elasticity and heat resistance of the fluororubber obtained by crosslinking, the fluorine-containing copolymer may further have units based on other monomers, in addition to the units based on the monomer having a nitrile group and the units based on TFE, from the viewpoint of the good rubber elasticity and heat resistance of the fluororubber obtained by crosslinking.As other monomers, for example, vinylidene fluoride (VdF), hexafluoropropylene, chlorotrifluoroethylene, monomers (DV) having two or more polymerizable unsaturated bonds, monomers represented by the following formula (6), ethylene, propylene, etc.In addition, as monomers other than those mentioned above, monomers having halogen atoms (for example, bromotrifluoroethylene, iodotrifluoroethylene) can also be mentioned.

[0023] Examples of the polymerizable unsaturated bond in DV include a carbon-carbon double bond (C═C) and a carbon-carbon triple bond (C≡C). From the viewpoint of good polymerization reactivity, the number of polymerizable unsaturated bonds in DV is preferably 2 to 6, more preferably 2 or 3, and particularly preferably 2. From the viewpoint of good heat resistance of the fluororubber obtained by crosslinking the fluorine-containing copolymer, DV preferably contains a fluorine atom.

[0024] From the viewpoint of good heat resistance of the fluororubber obtained by crosslinking the fluorine-containing copolymer, DV is preferably a monomer represented by the following formula (3): (CR ３１ R ３２ =CR ３３ ) ａ３ R ３４ (3) In formula (3), R ３１ ~R ３３ are each independently a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group. a3 is an integer of 2 to 6. R ３４ a is a trivalent perfluorohydrocarbon group having 1 to 10 carbon atoms or a group having an etheric oxygen atom at the terminal or between carbon atoms of the perfluorohydrocarbon group.

[0025] Multiple R ３１ ~R ３３ may be the same or different, and are particularly preferably the same. ３１ ~R ３３ is preferably a fluorine atom or a hydrogen atom from the viewpoint of good polymerization reactivity, and it is preferable that all of them are fluorine atoms or hydrogen atoms, and it is particularly preferable that all of them are fluorine atoms from the viewpoint of good heat resistance of the fluororubber obtained by crosslinking the fluorine-containing copolymer. a3 is preferably 2 or 3, and particularly preferably 2. ３４ R may be any of linear, branched, and cyclic, and is preferably linear or branched, more preferably linear, from the viewpoint of good polymerization reactivity. ３４ The number of carbon atoms in R is preferably 2 to 10, more preferably 3 to 8, even more preferably 3 to 6, and even more preferably 3 to 5. ３４Preferably, R has an etheric oxygen atom from the viewpoint of good rubber elasticity of the fluororubber obtained by crosslinking the fluorine-containing copolymer. ３４ The number of etheric oxygen atoms in R is preferably 1 to 3, and more preferably 1 or 2. ３４ The etheric oxygen atom in R ３４ It is preferred that the carbon atom is bonded to the terminal carbon atom of the formula (I).

[0026] Among the monomers represented by formula (3), DV is more preferably a monomer represented by the following formula (4) or (5): (CF ２ =CF) ２ R ４１ (4) (CH ２ =CH) ２ R ５１ (5) In formula (4) or (5), R ４１ and R ５１ is a divalent perfluorohydrocarbon group having 2 to 10 carbon atoms or a group having an etheric oxygen atom at the terminal or between carbon atoms of the perfluorohydrocarbon group.

[0027] Specific examples of DV include CF among the monomers represented by formula (4). ２ = CFO (CF ２ ) ２ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ３ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ４ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ６ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ８ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ２ OCF (CF ３ )CF ２ OCF = CF ２ , C.F. ２= CFO (CF ２ ) ２ O[CF(CF ３ )CF ２ O] ２ CF = CF ２ , C.F. ２ = CFOCF ２ O (CF ２ CF ２ O) ２ CF = CF ２ , C.F. ２ = CFO (CF ２ O) ３ O[CF(CF ３ )CF ２ O] ２ CF = CF ２ , C.F. ２ = CFOCF ２ CF (CF ３ ) O(CF ２ ) ２ OCF (CF ３ )CF ２ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ２ O (CF ２ O) ２ (CF ２ ) ２ OCF = CF ２ , and among the monomers represented by formula (5), CH ２ =CH(CF ２ ) ２ CH=CH ２ , C.H. ２ =CH(CF ２ ) ４ CH=CH ２ , C.H. ２ =CH(CF ２ ) ６ CH=CH ２ The DV may be used alone or in combination of two or more. ２ = CFO (CF ２ ) ３ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ４ OCF = CF ２ , C.H.２ =CH(CF ２ ) ６ CH=CH ２ is preferred.

[0028] Equation (6) is shown below: CF ２ =CF-O-R ｆ６ (6) In formula (6), R ｆ６ is 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, more preferably 1 to 5.

[0029] 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).

[0030] The content of units based on a monomer having a nitrile group in all units of the fluorine-containing copolymer is preferably 0.05 to 5 mol%, more preferably 0.1 to 3 mol%, and even more preferably 0.2 to 1.5 mol%, from the viewpoint of good heat resistance of the fluororubber obtained by crosslinking the fluorine-containing copolymer. The content of TFE units in all units of the fluorine-containing copolymer is preferably 60 to 80 mol%, more preferably 63 to 75 mol%, and even more preferably 66 to 72 mol%, from the viewpoint of good heat resistance of the fluororubber obtained by crosslinking the fluorine-containing copolymer.

[0031] When the fluorocopolymer contains PAVE units, the content of PAVE units in all units is preferably 19 to 39 mol%, more preferably 24 to 36 mol%, and even more preferably 27 to 33 mol%, from the viewpoint of good rubber elasticity and heat resistance of the fluororubber obtained by crosslinking the fluorocopolymer. When PAVE is PMVE, PEVE or PPVE, or a mixture of two or more of these, the suitable content is the same.

[0032] When the fluorine-containing copolymer contains units based on other monomers in addition to units based on a monomer having a nitrile group, units based on TFE and units based on PAVE, the content of the units based on other monomers is preferably 0.01 to 10 mol%, more preferably 0.05 to 10 mol%, and even more preferably 0.1 to 5 mol% of all units, from the viewpoint of good heat resistance of the fluororubber obtained by crosslinking the fluorine-containing copolymer. From the viewpoint of good heat resistance of the fluororubber obtained by crosslinking the fluorine-containing copolymer, the fluorine-containing copolymer is preferably a perfluoropolymer.

[0033] The glass transition temperature of the fluorine-containing copolymer is preferably -20 to 20°C, more preferably -10 to 10°C, and even more preferably -5 to 5°C. The glass transition temperature of the fluorine-containing copolymer varies depending on the type of monomer constituting the fluorine-containing copolymer, the unit composition based on the monomer, the molecular weight, etc. For example, the glass transition temperature of the fluorine-containing copolymer tends to increase as the content ratio of units based on TFE increases. The glass transition temperature can be measured by a differential scanning calorimeter (DSC). Specifically, it can be measured by the method described in the examples.

[0034] (Method for producing fluorine-containing copolymer) The method for producing the fluorine-containing copolymer is not particularly limited, and known methods can be applied. For example, the fluorine-containing copolymer can be obtained by copolymerizing monomers constituting the units of the fluorine-containing copolymer by emulsion polymerization, solution polymerization, suspension polymerization, or the like in the presence of a radical polymerization initiator. Any radical polymerization initiator known in the production of fluorine-containing copolymers can be used, and is selected appropriately depending on the polymerization method. For emulsion polymerization in an aqueous medium such as water, a water-soluble radical polymerization initiator is preferred, and examples include persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate, disuccinic acid peroxide, azobisisobutylamidine dihydrochloride, tert-butyl hydroperoxide, peroxydicarbonates, and the like. Of these, persulfates are preferred, and ammonium persulfate is more preferred. In addition, redox polymerization initiators can be used that are combinations of persulfates or hydrogen peroxide with reducing agents such as sodium hydrogensulfite and sodium thiosulfate, or the redox polymerization initiators can be used in combination with a small amount of a metal or metal compound such as iron, ferrous salts, or silver sulfate. As the radical polymerization initiator for solution polymerization using a solvent such as 1H-perfluorohexane, for example, organic peroxides such as bis(pentafluoropropionyl) peroxide, pivaloyl-tert-butyl peroxide, and diisopropyl peroxydicarbonate can be used. The radical polymerization initiator may be added all at once or gradually. The amount of the radical polymerization initiator used is preferably 0.0001 to 3 parts by mass, more preferably 0.001 to 2 parts by mass, and even more preferably 0.01 to 1 part by mass, per 100 parts by mass of the total of all monomers to be polymerized.

[0035] A pH buffer may be added to the reaction system. Examples of the pH buffer include disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium hydrogen carbonate, sodium carbonate, and hydrates thereof.

[0036] Examples of emulsifiers used in emulsion polymerization include hydrocarbon emulsifiers such as sodium lauryl sulfate and sodium dodecylbenzenesulfonate; ammonium perfluorooctanoate, sodium perfluorooctanoate, ammonium perfluorohexanoate, CF ３ (CF ２ ) ２ O(CF(CF ３ )CF ２ O) ２ CF (CF ３ ) COONH ４ , C.F. ３ (CF ２ ) ２ OCF (CF ３ )CF ２ OCF (CF ３ ) COONH ４ , C.F. ３ (CF ２ ) ２ O (CF ２ ) ２ OCF ２ COONH ４ , C.F. ３ (CF ２ ) ２ O (CF ２ CF ２ O) ２ CF ２ COONH ４ , C.F. ３ (CF ２ ) ３ OCF ２ CF ２ OCF ２ COONH ４ , C.F. ３ (CF ２ ) ３ O (CF ２ CF ２ O) ２ CF ２ COONH ４ , C.F. ３ (CF ２ ) ２ O (CF ２ ) ２ OCF ２ COONa, CF ３ (CF ２ ) ２ O (CF２ CF ２ O) ２ CF ２ CFCOONa, CF ３ (CF ２ ) ３ OCF ２ CF ２ OCF ２ CFCOONa, CF ３ (CF ２ ) ３ O(CF ２ CF ２ O) ２ CF ２ CFCOONa, C ２ F ５ O(CF ２ ) ２ OCF ２ CFCOONH ４ (abbreviation EEA-NH4), C ２ F ５ O(CF ２ CF ２ O) ２ CF ２ CFCOONH ４ , C ２ F ５ O(CF ２ ) ２ OCF ２ CFCOONa, C ２ F ５ O(CF ２ CF ２ O) ２ CF ２ CFCOONa, CF ３ O(CF ２ ) ３ OCF ２ CFCOONH ４ , CF ３ O(CF ２ ) ３ OCF(CF ３ )CFCOONH ４ , CF ３ O(CF ２ ) ３ OCF ２ CFCOONa, CF ３ O(CF ２ ) ３ OCF(CF ３ )CFCOONa, CF ３ O(CF ２O) ３ CF ２ COONH ４ , C.F. ３ O (CF ２ O) ３ CF ２ COONa, CF ３ OCF (CF ３ )CF ２ OCF (CF ３ ) COONH ４ , C.F. ３ OCF (CF ３ )CF ２ OCF (CF ３ ) COONa, CF ３ O (CF ２ CF ２ O) ２ CF ２ COONH ４ , C.F. ３ O (CF ２ CF ２ O) ２ CF ２ Fluorine-containing emulsifiers such as COONa may be used alone or in combination of two or more. Among these, ammonium perfluorooctanoate, CF ３ (CF ２ ) ３ O (CF ２ ) ２ OCF ２ COONH ４ , C.F. ３ (CF ２ ) ２ O (CF ２ ) ２ OCF ２ COONH ４ , EEA-NH4, CF ３ O (CF ２ ) ３ OCF ２ COONH ４is preferred. The emulsifier may be added all at once or gradually. The amount of emulsifier used is preferably 0.01 to 20 parts by mass, more preferably 0.05 to 15 parts by mass, and even more preferably 0.1 to 10 parts by mass, relative to 100 parts by mass of the aqueous medium. The raw material mixture may be substantially free of a water-soluble emulsifier. "Substantially free of an emulsifier" means that the content of the emulsifier in the raw material mixture is 0.03 ppm by mass or less, preferably 0.02 ppm by mass or less, and more preferably 0 ppm by mass.

[0037] The polymerization reaction conditions, such as pressure and temperature, are appropriately set depending on the monomer composition, the decomposition temperature of the radical polymerization initiator, etc. Usually, the pressure is preferably 0.1 to 20 MPaG, more preferably 0.3 to 10 MPaG, and even more preferably 0.3 to 5 MPaG. The temperature is preferably 0 to 100°C, more preferably 10 to 90°C, and even more preferably 20 to 85°C.

[0038] In emulsion polymerization, the fluorine-containing copolymer is obtained as a latex, which can be purified by appropriate coagulation, whereas in solution polymerization, it can be purified by washing with an aqueous medium such as methanol.

[0039] The method for aggregating the fluorine-containing copolymer is not particularly limited, and examples thereof include freeze agglomeration, acid agglomeration, base agglomeration, mechanical agglomeration, and agglomeration using a coagulant. In the case of freeze agglomeration, the agglomeration temperature is preferably -20 to 0°C. The agglomeration time is preferably 1 hour or more, more preferably 2 hours or more. In the case of acid agglomeration, examples of the acid to be added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, hydrofluoric acid, etc., with nitric acid being preferred. The concentration of the acid added is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. In the case of base agglomeration, examples of the base to be added include sodium hydroxide, potassium hydroxide, ammonium carbonate, etc., with sodium hydroxide being preferred. The concentration of the base added is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. In the case of agglomeration using a coagulant, known coagulants can be used, and examples thereof include aluminum salts, calcium salts, and magnesium salts. Specific examples include aluminum sulfate, salts of the general formula M'Al(SO ４ ) ２ ・12H ２ 0 (wherein M' is a monovalent cation other than lithium), calcium nitrate, and magnesium sulfate are exemplified, with alum being preferred, and potassium alum, where M' is potassium, being more preferred.

[0040] (Crosslinking Agent) The crosslinking agent in the fluorocopolymer composition of this embodiment is a polyamine compound in the form of solid particles having a D50 of 40 μm or less. By crosslinking the fluorocopolymer with such a crosslinking agent, a fluororubber article with excellent heat resistance can be obtained. Here, the term "solid particles" means that the particles are solid in the fluorocopolymer composition in an uncrosslinked state. From the viewpoint of ease of control of the crosslinking reaction, the melting point of the crosslinking agent is preferably 80 to 400°C, more preferably 100 to 350°C, and even more preferably 120 to 300°C.

[0041] The polyamine compound is a compound having two or more amino groups in one molecule, and the amino groups can form a crosslinked structure with the nitrile groups of the fluorine-containing copolymer. From the viewpoint of obtaining a fluororubber article having excellent heat resistance, the crosslinking agent is preferably one that can form a crosslinked structure containing an oxazole ring or an imidazole ring. From the viewpoint of heat resistance and crosslink density, it is more preferable to use one that can form a crosslinked structure containing an oxazole ring. As a crosslinking agent that can form a crosslinked structure containing an oxazole ring, for example, a bisaminophenol compound is preferred. From the viewpoint of good heat resistance of the fluororubber obtained by crosslinking the fluorine-containing copolymer, the polyamine compound preferably contains a fluorine atom.

[0042] Specific examples of the crosslinking agent include 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (abbreviated as BOAP, also known as bisaminophenol AF; melting point 243°C), 2,2-bis(3-amino-4-anilinophenyl)hexafluoropropane (abbreviated as NPh-AF; melting point 177-178°C), 3,3'-diaminobenzidine (melting point 179°C), the compound obtained in Synthesis Example 1 (melting point 179°C), the compound obtained in Synthesis Example 2 (melting point 134°C), and the compound obtained in Synthesis Example 3 (melting point 249°C) of WO 2022 / 230706, 4,4'-methylenedianiline (melting point 92°C), m-phenylenediamine (melting point 64-66°C), adipic acid dihydrazide (melting point 182°C), (CF ２ ) ６ [C(NH ２ )=NC(=NH)(CF ２ ) ５ CF ３ ] ２ Among these, BOAP and NPh-AF are preferred, and BOAP is more preferred, from the viewpoint of good heat resistance of the fluororubber obtained by crosslinking the fluorine-containing copolymer.

[0043] The crosslinking agent is present in the fluorocopolymer composition as solid particles having a D50 of 40 μm or less. Here, the D50 of the crosslinking agent of this embodiment is the D50 in the volume-based particle size distribution when 200 aggregate particles identified by optical microscope observation are extracted from a predetermined sheet-like sample of the fluorocopolymer composition in an uncrosslinked state, and the aggregate particles are assumed to be spheres with the longest diameter of the aggregate particles as their diameter. Specifically, it can be determined by the method described in the Examples.

[0044] When the D50 of the crosslinking agent in the fluorocopolymer composition is 40 μm or less, the specific surface area of ​​the solid particles of the crosslinking agent is large, and the crosslinking reaction of the fluorocopolymer tends to proceed uniformly and at an appropriate rate. As a result, it is presumed that the crosslink density is improved and fluororubber articles with excellent heat resistance can be obtained. From the viewpoint of appropriate progression of the crosslinking reaction of the fluorocopolymer to obtain fluororubber articles with excellent heat resistance, the D50 of the crosslinking agent is preferably 2.0 to 35 μm, more preferably 5.0 to 30 μm, and even more preferably 6.0 to 28 μm.

[0045] The content of the crosslinking agent in the fluorocopolymer composition is preferably from 0.1 to 10 parts by mass, more preferably from 0.3 to 5 parts by mass, still more preferably from 0.5 to 3 parts by mass, per 100 parts by mass of the fluorocopolymer, from the viewpoint of sufficient crosslink density and good heat resistance of the fluororubber obtained by crosslinking the fluorocopolymer.

[0046] (Other Components) The fluorine-containing copolymer composition may contain other components in addition to the fluorine-containing copolymer and crosslinking agent, as long as the effects of the present invention are not impaired. Examples of other components include fillers and reinforcing materials (e.g., carbon black, barium sulfate, calcium metasilicate, calcium carbonate, titanium oxide, silicon dioxide, clay, talc, etc.), 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, etc.), crown ethers (e.g., 18-crown-6, etc.), release agents (e.g., sodium stearate, etc.), pigments, etc. The other components may be used alone or in combination of two or more.

[0047] When the fluorocopolymer composition contains other components, the total content of the other components is preferably more than 0 part by mass and not more than 30 parts by mass, more preferably not more than 25 parts by mass, and still more preferably not more than 20 parts by mass, per 100 parts by mass of the fluorocopolymer.

[0048] [Method for producing a fluorine-containing copolymer composition] The method for producing a fluorine-containing copolymer composition of this embodiment is a method for producing a fluorine-containing copolymer composition containing a fluorine-containing copolymer having units based on a monomer having a nitrile group and units based on TFE, and a solid crosslinking agent which is a polyamine compound, and comprises a step of pulverizing the crosslinking agent by kneading the fluorine-containing copolymer and the crosslinking agent with a kneading energy of 10 J / g or more. By going through this kneading step, a fluorine-containing copolymer composition in which the solid crosslinking agent is sufficiently pulverized and dispersed can be obtained, and a fluororubber article excellent in heat resistance can be obtained.

[0049] The fluorine-containing copolymer and crosslinking agent in the production method of this embodiment are preferably the same as the fluorine-containing copolymer and crosslinking agent in the fluorine-containing copolymer composition described above. Further, other components that may be contained in the fluorine-containing copolymer composition are also the same as the other components described above. The production method of the fluorine-containing copolymer composition of this embodiment may be a method of kneading the above-mentioned fluorine-containing copolymer of this embodiment and the crosslinking agent of this embodiment with a kneading energy of 10 J / g or more to pulverize the crosslinking agent, thereby obtaining the fluorine-containing copolymer composition of this embodiment.

[0050] The solid crosslinking agent may be pre-pulverized, but from the viewpoint of uniform mixing with the fluorocopolymer and production efficiency of the fluorocopolymer composition, it is preferably pulverized in the step of kneading with the fluorocopolymer. The crosslinking agent is pulverized to solid particles having a D50 of preferably 40 μm or less, more preferably 2.0 to 35 μm, even more preferably 5.0 to 30 μm, and still more preferably 6.0 to 30 μm.

[0051] The D50 of the solid crosslinking agent before being kneaded with the fluorocopolymer and pulverized is preferably 1000 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less, from the viewpoint of ease of handling.

[0052] From the viewpoint of pulverizing the crosslinking agent in the step of kneading it with the fluorocopolymer as described above and uniformly dispersing it in the fluorocopolymer composition, the kneading energy when kneading the fluorocopolymer and the crosslinking agent is 10 J / g or more, preferably 100 to 15,000 J / g, more preferably 500 to 10,000 J / g, still more preferably 1,000 to 7,500 J / g, and particularly preferably 1,500 to 6,500 J / g.

[0053] The kneading step may be carried out once or twice or more times. The kneading energy is the sum of the kneading energies in each step.

[0054] As a means for kneading the fluorine-containing copolymer and the crosslinking agent, known rubber kneading devices can be applied, and examples thereof include a roll, a kneader, a Banbury mixer, and a single-screw or twin-screw extrusion kneader. The extrusion kneader may be used alone, or a plurality of extrusion kneaders of the same or different types may be connected in series. Of these, a twin-screw extrusion kneader is preferred from the viewpoint of providing sufficient kneading energy. Examples of twin-screw extrusion kneaders include non-intermeshing co-rotating types, intermeshing co-rotating types, non-intermeshing counter-rotating types, and intermeshing counter-rotating types. Specific examples of extrusion kneaders include "HAAKE Minilab II" (manufactured by Thermo Fisher Scientific), "Labo Plastomill (registered trademark)" (manufactured by Toyo Seiki Seisakusho, Ltd.), and "Plasticorder Labostation (registered trademark)" (manufactured by Brabender).

[0055] The kneading temperature (chamber temperature) is set to be lower than the melting point of the crosslinking agent in order to obtain a fluorocopolymer containing a solid crosslinking agent. The melting point of the crosslinking agent is as described above. The kneading temperature is preferably equal to or higher than the glass transition temperature of the fluorocopolymer. The kneading temperature is preferably 20 to 100°C, more preferably 30 to 85°C. The kneading time (residence time in the kneading device) is preferably 1 to 120 minutes, more preferably 20 to 60 minutes, from the viewpoint of sufficient kneading and pulverization of the crosslinking agent. When the residence time in the kneading device is 1 to 120 minutes, the screw rotation speed is preferably 50 to 2000 rpm, more preferably 500 to 1500 rpm.

[0056] [Fluororubber Article] The fluororubber article of this embodiment is obtained by crosslinking the fluorocopolymer composition of this embodiment described above. The fluororubber article of this embodiment has particularly small high-temperature compression set and excellent heat resistance. Specifically, the high-temperature compression set under conditions of 300°C, a compression ratio of 16.7%, and holding for 70 hours is preferably 48% or less, more preferably 45% or less, and even more preferably 40% or less. More specifically, the high-temperature compression set is measured by the method described in the examples.

[0057] The crosslinking method of the fluorocopolymer composition includes methods using heating, radiation irradiation, etc., and preferably crosslinking by heating. Examples of heating means include heat pressing, steam, hot air, etc. Examples of radiation used in radiation irradiation include electron beams and ultraviolet rays. The crosslinking method is appropriately selected depending on the form and use of the fluororubber article, etc.

[0058] In crosslinking by heating, for example, heating is performed at 80 to 300°C for 0.1 to 24 hours. After heating once to perform primary crosslinking, secondary crosslinking may be performed by further heating at a different temperature. From the viewpoint of appropriate progression of the crosslinking reaction, it is preferable to perform primary crosslinking at 80 to 200°C for 0.1 to 6 hours, and then secondary crosslinking at 200 to 300°C for 1 to 24 hours. By performing secondary crosslinking, the high-temperature compression set and other rubber physical properties of the fluororubber article can be stabilized or improved. Temperature control may be performed by increasing or decreasing the temperature in stages.

[0059] During the primary crosslinking, the fluorine-containing copolymer composition may be appropriately molded by, for example, compression molding, injection molding, extrusion molding, calendar molding, or a method of dissolving the composition in a solvent and dipping or coating the composition onto a substrate or the like to mold the composition.

[0060] The fluororubber article of this embodiment is suitable as a sealing material or cushioning material, for example, an O-ring, a V-ring, a packing, an oil seal, a gasket, a diaphragm, a sheet, etc. The fluororubber article can also be suitably used in a variety of applications, such as a heat-resistant and chemical-resistant sealing material, a heat-resistant and oil-resistant sealing material, an electric wire coating material, a sealing material for semiconductor devices, a corrosion-resistant rubber coating material, a sealing material for urea-based grease, a rubber coating material, an adhesive rubber, a hose, a tube, a calender sheet (roll), a sponge, a rubber roll, an oil drilling component, a heat-dissipating sheet, a solution-crosslinked product, a rubber sponge, a bearing seal, a lining, an insulating sheet for automobiles, an insulating sheet for electronic devices, a rubber band for a watch, a gasket for an endoscope, a bellows hose, a gasket / valve for a water heater, a fender, a fiber / nonwoven fabric (protective clothing, etc.), a board sealant, a rubber glove, a stator for a uniaxial eccentric screw pump, a part for a urea SCR system, an anti-vibration agent, a vibration damper, a sealant, an additive for other materials, and a toy.

[0061] The present invention will be specifically described below based on examples, but the present invention is not limited to the following examples, and various modifications are possible within the scope of the gist of the present invention.

[0062] [Compounds Used] The abbreviations for the various compounds used are explained below: EEA-NH4: perfluoro(2-ethoxy-ethoxy)ammonium acetate (C ２ F ５ O (CF ２ ) ２ OCF ２ COONH ４ ), emulsifier 8CNVE: perfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene) (CF ２ =CFCF ２ CF (CF ３ ) OCF ２ CF ２CN) TFE: tetrafluoroethylene PMVE: perfluoromethyl vinyl ether APS: ammonium persulfate BOAP: 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, manufactured by Tokyo Chemical Industry Co., Ltd.; crosslinking agent, D50: 50 μm

[0063] [Synthesis of Fluorine-Containing Copolymer] After degassing a 20 L stainless steel pressure reactor equipped with an anchor impeller, 7.2 L of ultrapure water, 880 g of a 30% by mass aqueous solution of EEA-NH4, 7.3 g of 8CNVE, and 15.9 g of a 5% by mass aqueous solution of disodium hydrogen phosphate dodecahydrate were charged. After replacing the atmosphere in the reactor with nitrogen, 137 g of TFE and 635 g of PMVE were pressure-charged while stirring with an anchor impeller (375 rpm), and the temperature inside the reactor was raised to 80 ° C. The pressure inside the reactor was 0.90 MPaG. 28 mL of a 3% by mass aqueous solution of APS was added to the reactor to initiate polymerization (the molar ratio of each monomer before the start of polymerization was TFE / PMVE / 8CNVE = 26.3 / 73.3 / 0.4).

[0064] As the polymerization progressed, when the pressure in the reactor reached 0.89 MPaG, TFE was injected and the pressure was increased to 0.90 MPaG. This operation was repeated, and every time the total amount of injected TFE reached 119.3 g, 3.7 g of 8CNVE, 74 g of PMVE, and 3.7 g of 8CNVE were additionally injected in this order. In addition, when the polymerization rate decreased, a 3% by mass aqueous solution of APS was appropriately additionally added (total additional amount 35 mL). After the additional injection of each monomer was completed when the total amount of injected TFE reached 1073.7 g, 119.3 g of TFE was injected, and the additional injection of the monomer was completed (total additional amount of each monomer: TFE 1193 g, PMVE 666 g, 8CNVE 66.6 g). The internal temperature of the reactor was lowered to 10°C to terminate the polymerization reaction, thereby obtaining a latex containing a fluorine-containing copolymer (polymerization time: 6.25 hours; molar ratio of additional monomers: TFE / PMVE / 8CNVE=74.0:25.0:1.0).

[0065] The obtained latex was added to a 5% by mass aqueous solution of aluminum potassium sulfate to coagulate the fluorocopolymer. The fluorocopolymer was separated by filtration, washed with ultrapure water, and then vacuum dried at 50°C to obtain a white fluorocopolymer (composition molar ratio of units based on each monomer: TFE unit / PMVE unit / 8CNVE unit=69.1:30.3:0.6, glass transition temperature: -3°C).

[0066] The glass transition temperature was measured by DSC as follows: 10 mg of a measurement sample of the fluorocopolymer was cooled from room temperature (25°C) to -30°C at a temperature decrease rate of -10°C / min, and then heated to 350°C at a temperature increase rate of 10°C / min. Based on a profile plotted with heat flow [mW] on the vertical axis and temperature [°C] on the horizontal axis, the temperature at the minimum heat flow at which a shift in the baseline during heating was confirmed was taken as the glass transition temperature of the fluorocopolymer.

[0067] [Example 1] 100 parts by mass of the fluorocopolymer obtained above and 1.0 part by mass of BOAP (total 20.2 g) were charged into a twin-screw extruder kneader ("HAAKE Minilab II", manufactured by Thermo Fisher Scientific K.K.) and kneaded under conditions of a chamber temperature of 40°C, a screw rotation speed of 100 rpm, and a residence time of 48 minutes, to prepare a fluorocopolymer composition.

[0068] The obtained fluorine-containing copolymer composition was charged into a mold, and while the mold was degassed with a diaphragm pump, it was heated and compressed at 180°C for 20 minutes in a hydraulic press ("SA-301 50T type", manufactured by Tester Sangyo Co., Ltd., ram diameter 180 mm; the same applies hereinafter) to produce an O-ring (P-12) (primary crosslinked product). This O-ring was heated at 90°C for 2 hours in an inert oven ("DN411I", manufactured by Yamato Scientific Co., Ltd.) under a nitrogen atmosphere, and then heated to 200°C over 2 hours and maintained there for 4 hours. Further, the temperature was raised to 305°C over 2 hours and maintained there for 12 hours to produce a fluororubber O-ring test piece (secondary crosslinked product).

[0069] Examples 2 to 4 Fluorine-containing copolymer compositions were prepared in the same manner as in Example 1 except for the kneading conditions shown in Table 1, and fluororubber O-ring test pieces were prepared.

[0070] [Measurement and Evaluation] The torque value and kneading energy in the kneading operation of each example, the D50 of the crosslinking agent in the fluorocopolymer composition, and the high-temperature compression set of the O-ring test piece were measured. The measurement methods are as follows. The measurement results are shown in Table 1. In Table 1, Examples 1 to 3 are working examples, and Example 4 is a comparative example.

[0071] (Kneading Energy) The kneading energy was defined as the work load (W [J / g]) per unit mass of the fluorocopolymer composition calculated from the kneading conditions (mass (m [g]) of the fluorocopolymer composition, screw rotation speed (r [rpm]), residence time (t [min])) and torque value (T [N m]) during kneading of the fluorocopolymer in the twin-screw extrusion kneader, using the following formula (I): W = 2π × r × T × t / m (I) The torque value T was defined as the torque output value when the filling of the fluorocopolymer composition into the chamber of the twin-screw extrusion kneader was completed. The residence time t was defined as the time measured with a timer from the end of filling the chamber with the fluorocopolymer and crosslinking agent to the end of the kneading operation.

[0072] (Volume-Based Median Diameter (D50) of Crosslinking Agent) 0.5 g of the fluorine-containing copolymer composition was heated and compressed for 5 minutes using a hydraulic press at a temperature of 60°C and a pressure of 0.4 MPa. The resulting uncrosslinked sheet-like sample (thickness 0.125 mm) was observed perpendicular to the sheet plane under coaxial epi-illumination using an optical microscope ("VHX-8000", lens "VHX-E100", manufactured by Keyence Corporation; magnification 500x). Agglomerated particles identified in the observed image were considered to be crosslinking agents, and 200 agglomerated particles were extracted. When fewer than 200 agglomerated particles were identified, an additional uncrosslinked sheet-like sample was prepared, and a total of 200 agglomerated particles were extracted. D50 was calculated assuming that the agglomerated particles were spheres with the longest diameter in the observed image as their diameter. Regarding BOAP before use in the preparation of the fluorine-containing copolymer composition, D50 was determined in the same manner as above from an observation image of the BOAP spread out as it was on the stage of an optical microscope.

[0073] (High-Temperature Compression Set) The high-temperature compression set of an O-ring test piece (designation number P12; conforming to JIS B 2401-1:2012) was measured by a method referring to JIS K 6262:2013. ０ (wire diameter) 2.4 mm) was compressed by a compression device (spacer thickness h ｓ The specimen was compressed to a thickness of 2.0 mm and held at 300°C, a compression ratio of 16.7%, and for 70 hours. The specimen was then removed from the compression device and allowed to stand at room temperature (23°C) for 30 minutes. １ The arithmetic mean value of the measured values ​​of two test pieces was used to calculate the high temperature compression set (CS [%]) according to the following formula (II): CS = (h ０ -h １ ) / (h ０ -h ｓ ) x 100 = (2.4-h １ ) × 250 (II) The smaller the high-temperature compression set, the more excellent the heat resistance.

[0074]

[0075] As shown in Table 1, it was confirmed that when the D50 of the crosslinking agent in the fluorocopolymer composition is 40 μm or less, the high-temperature compression set of the obtained fluororubber article is small (Examples 1 to 3). It was also confirmed that when the fluorocopolymer composition is kneaded with a kneading energy of 10 J / g or more, the crosslinking agent in the fluorocopolymer composition can be pulverized to a D50 of 40 μm or less.

Claims

1. A fluorine-containing copolymer composition comprising a fluorine-containing copolymer having units based on a monomer having a nitrile group and units based on tetrafluoroethylene, and a crosslinking agent which is a polyamine compound, wherein the crosslinking agent is in the form of solid particles having a volume-based median diameter of 40 μm or less.

2. The fluorine-containing copolymer composition according to claim 1, wherein said fluorine-containing copolymer further has units based on perfluoroalkyl vinyl ether.

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

4. The fluorine-containing copolymer composition according to claim 1, wherein the content of said crosslinking agent is 0.1 to 10.0 parts by mass per 100 parts by mass of said fluorine-containing copolymer.

5. The fluorine-containing copolymer composition according to claim 1, wherein the crosslinking agent is a bisaminophenol compound.

6. A method for producing a fluorine-containing copolymer composition comprising a fluorine-containing copolymer having units based on a monomer having a nitrile group and units based on tetrafluoroethylene, and a solid crosslinking agent which is a polyamine compound, the method comprising the step of kneading the fluorine-containing copolymer and the crosslinking agent with a kneading energy of 10 J / g or more to pulverize the crosslinking agent.

7. The method for producing a fluorine-containing copolymer composition according to claim 6, wherein the crosslinking agent is pulverized into solid particles having a volume-based median diameter of 40 μm or less.

8. A method for producing a fluorine-containing copolymer composition according to any one of claims 1 to 5, comprising kneading said fluorine-containing copolymer and said crosslinking agent with a kneading energy of 10 J / g or more to pulverize said crosslinking agent, thereby obtaining said fluorine-containing copolymer composition.

9. A fluororubber article obtained by crosslinking the fluorine-containing copolymer composition according to any one of claims 1 to 5.

Images