WO2012073977A1 - Crosslinkable fluororubber composition and crosslinked rubber article - Google Patents

Abstract

The purpose of the present invention is to provide: a crosslinkable fluororubber composition which enables the production of a crosslinked rubber article having both excellent chemical resistance and excellent heat resistance; and a crosslinked rubber article produced using the crosslinkable fluororubber composition. A crosslinkable fluororubber composition which comprises a fluororubber and a fluoropolymer (P) that has a repeating unit derived from a fluorodiene (b) having unsaturated side chain residual performance and also has multiple polymerizable double bonds; and a crosslinked rubber article produced by crosslinking the crosslinkable fluororubber composition.

Description

Crosslinkable fluororubber composition and crosslinked rubber article

The present invention relates to a crosslinkable fluororubber composition and a crosslinked rubber article.

As a method of obtaining a crosslinked rubber article by cross-linking fluororubber, (1) a method of generating radicals by heating using an organic peroxide and (2) a method of crosslinking radicals by irradiating fluororubber with radiation. There are known methods of forming and crosslinking, and (3) methods of crosslinking using a crosslinking agent such as a polyol crosslinking system and a polyamine crosslinking system.

In the methods (1) and (2), a crosslinkable fluororubber composition containing a polyfunctional compound is used as a crosslinking aid in order to improve the crosslinking characteristics of the fluororubber and the characteristics of the resulting crosslinked rubber article. Is done. For example, a crosslinkable fluororubber composition containing triallyl isocyanurate (TAIC) as a crosslinking aid (see Non-Patent Document 1 and Patent Document 1) is known.
By using TAIC as a crosslinking aid, the crosslinking rate of the fluororubber is improved. The crosslinked rubber article produced by the methods (1) and (2) using the crosslinkable fluororubber composition is more resistant to chemicals (particularly amine resistant) than the crosslinked rubber article produced by the method (3). Excellent). However, with the crosslinkable fluororubber composition, it has been difficult to obtain a crosslinked rubber article that is remarkably excellent in heat resistance.

Japanese Unexamined Patent Publication No. 7-179705

An object of the present invention is to provide a crosslinkable fluororubber composition that provides a crosslinkable rubber article having both excellent chemical resistance and heat resistance, and a crosslinked rubber article obtained from the crosslinkable fluororubber composition.

The present invention employs the following configuration in order to solve the above problems.
[1] A crosslinkable fluororubber composition containing fluororubber and the following fluoropolymer (P) having a plurality of polymerizable double bonds.
Fluoropolymer (P): a fluoropolymer having repeating units derived from unsaturated side chain remaining fluorodiene (b).
[2] The fluoropolymer (P) is a fluoropolymer having a repeating unit derived from the fluoromonoene (a) and a repeating unit derived from the unsaturated side chain residual fluorodiene (b). The crosslinkable fluororubber composition as described.
[3] The fluoromonoene (a) is tetrafluoroethylene, chlorotrifluoroethylene, and CF ₂ ═CFO—R ^f1 (wherein R ^f1 is a fluoroalkyl group having 1 to 6 carbon atoms, or carbon atom-carbon) The crosslinkable fluororubber composition according to [2], which is at least one selected from the group consisting of a C2-C6 fluoroalkyl group having at least one etheric oxygen atom between atoms.
[4] The crosslinkable fluororubber composition according to any one of [1] to [3], wherein the fluorodiene (b) is at least one selected from the group consisting of the following fluorodienes (b1) to (b3): object.
(B1) CF ₂ = CFO-Q ^f1 -OCF = CF ₂
(B2) CH ₂ ═CFCF ₂ O—Q ^f2 —OCF ₂ CF═CH ₂
(B3) CH ₂ ═CFCF ₂ O—Q ^f3 —OCF═CF ₂
( ^Wherein Q ^f1 and Q ^f2 each independently represents a fluoroalkylene group having 3 to 8 carbon atoms, or a fluoroalkylene group having 3 to 8 carbon atoms having one or more etheric oxygen atoms between carbon atoms and carbon atoms) It is.
Q ^f3 is a fluoroalkylene group having 1 to 6 carbon atoms or a fluoroalkylene group having 2 to 6 carbon atoms having at least one etheric oxygen atom between carbon atoms. )
[5] The crosslinkable fluororubber composition according to any one of [1] to [4], wherein the fluoropolymer (P) has a weight average molecular weight of 3,000 to 50,000.
[6] The crosslinkable fluororubber composition according to any one of [1] to [5], wherein the content of polymerizable double bonds in the fluoropolymer (P) is 0.2 to 2 mmol / g.
[7] The crosslinkable fluororubber composition according to any one of [1] to [6], which contains 1 to 50 parts by mass of the fluoropolymer (P) with respect to 100 parts by mass of the fluororubber.
[8] The fluororubber is selected from the group consisting of a tetrafluoroethylene / propylene copolymer, a vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer, and a tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer. The crosslinkable fluororubber composition according to any one of [1] to [7], which is one or more selected.
[9] The crosslinkable fluororubber composition according to any one of [1] to [8], further containing an organic peroxide.
[10] A crosslinked rubber article obtained by crosslinking the crosslinkable fluororubber composition according to [1] or [2].
[11] The crosslinked rubber article according to [10], which is a sealing material.

The crosslinkable fluororubber composition of the present invention can produce a crosslinked rubber article having excellent chemical resistance and heat resistance.
Moreover, since the crosslinked rubber article of the present invention is produced by crosslinking the crosslinkable fluororubber composition of the present invention, it has excellent chemical resistance and heat resistance.

<Crosslinkable fluororubber composition>
The crosslinkable fluororubber composition of the present invention is a composition containing fluororubber and a fluoropolymer (P) described later having a plurality of polymerizable double bonds as essential components.
[Fluoropolymer (P)]
The fluoropolymer (P) functions as a crosslinking aid in the crosslinkable fluororubber composition of the present invention. That is, the fluoropolymer (P) is bonded to the fluororubber by radicals induced by light or heat to give a crosslinked rubber article that is a three-dimensional crosslinked product.
The fluoropolymer (P) is a fluoropolymer having a repeating unit derived from the unsaturated side chain residual fluorodiene (b), and has a plurality of polymerizable double bonds (carbon-carbon double bonds) in the molecule. . The fluoropolymer (P) is preferably a fluoropolymer having a repeating unit derived from the fluoromonoene (a) and a repeating unit derived from the unsaturated side chain remaining fluorodiene (b).

(Fluoromonoene (a))
Fluoromonoene (a) is a fluorine-containing compound having one polymerizable double bond in the molecule.
Examples of the fluoromonoene (a) include fluoroethylenes such as tetrafluoroethylene (TFE), trifluoroethylene, chlorotrifluoroethylene (CTFE), and vinylidene fluoride; hexafluoropropylene, CF ₂ ═CFO—R ^f1 ( In the formula, R ^f1 is a fluoroalkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 2 to 6 carbon atoms having at least one etheric oxygen atom between carbon atoms. Fluorovinyl ether (hereinafter referred to as “fluoromonoene (a1)”) and the like.
In the present invention, the fluoroalkyl group is a group in which one or more hydrogen atoms of the alkyl group are substituted with fluorine atoms. In addition, a fluoroalkyl group having one or more etheric oxygen atoms between carbon atoms and carbon atoms means one or more hydrogen atoms of an alkyl group having one or more etheric oxygen atoms between carbon atoms and carbon atoms. A group substituted by a fluorine atom. The perfluoroalkyl group is a group in which all hydrogen atoms of the alkyl group are substituted with fluorine atoms.

As fluoromonoene (a), 1 or more types chosen from the group which consists of TFE, CTFE, and fluoromonoene (a1) are preferable.
If TFE is used as the fluoromonoene (a), the flowability of the fluoropolymer (P) is improved, and a crosslinked rubber article having particularly excellent heat resistance is obtained.
When CTFE is used as the fluoromonoene (a), the cross-linking efficiency is improved because the compatibility is good particularly when a vinylidene fluoride copolymer fluororubber is used as the fluororubber.
When the fluoromonoene (a1) is used as the fluoromonoene (a), the viscosity of the fluoropolymer (P) becomes lower and the production of the crosslinkable fluororubber composition becomes easier.

The carbon number of R ^{f1 in} the fluoromonoene (a1) is preferably 1 to 5, and more preferably 1 to 3. If the carbon number of R ^f1 is in this range, it can act as a crosslinking aid for fluororubber without reducing the fluidity and heat resistance of the fluoropolymer (P). The fluoroalkylene group for R ^f1 may be linear or branched.
In R ^f1 of the fluoromonoene (a1), from the viewpoint of heat resistance of the crosslinked rubber article, it is preferable that all hydrogen atoms of the alkyl group are substituted with fluorine atoms. That is, as the fluoromonoene (a1), CF ₂ ═CFO—R ^F1 (wherein R ^F1 is a perfluoroalkyl group having 1 to 6 carbon atoms, or one or more etheric oxygen atoms between carbon atoms and carbon atoms) And a perfluorovinyl ether (hereinafter referred to as “fluoromonoene (a11)”) represented by a C 2-6 perfluoroalkyl group.

The combined use of TFE and fluoromonoene (a1) is preferable in that the fluidity of the fluoropolymer (P) is further improved as compared with the case where they are used alone.
The fluoromonoene (a) is preferably a perfluoromonomer from the viewpoint of the fluidity of the fluoropolymer (P) and the heat resistance of the crosslinked rubber article, more preferably TFE or fluoromonoene (a11), single use of TFE, or TFE. And fluoromonoene (a11) are more preferred.
Fluoromonoene (a) may be used alone or in combination of two or more.

(Fluorodiene (b))
Fluorodiene (b) is an unsaturated side chain-remaining fluorine-containing compound having two polymerizable double bonds in the molecule. That is, in the polymerization for producing the fluoropolymer (P), at least a part of the two polymerizable double bonds does not contribute to the polymerization reaction, and the fluorodiene (b) remains a double bond after the polymerization. It is a remaining compound. Specifically, two carbon atoms in one polymerizable double bond of fluorodiene (b) form a main chain after polymerization. At least a part of the other polymerizable double bond does not contribute to the polymerization reaction and remains as an unsaturated side chain in the fluoropolymer (P).
By using the fluorodiene (b), unsaturated side chains remain in the fluoropolymer (P), and a crosslinked rubber article is obtained by a crosslinking reaction using the unsaturated side chains.

Examples of the fluorodiene (b) include perfluorodiene composed of carbon atoms and fluorine atoms, or perfluorodiene composed of carbon atoms, fluorine atoms and oxygen atoms. Moreover, the fluorodiene by which one or more of the fluorine atoms of the said perfluorodiene was substituted by the hydrogen atom is mentioned. As the fluorodiene (b), perfluorodiene is preferable from the viewpoint of heat resistance of the crosslinked rubber article, and from the viewpoint of fluidity of the fluoropolymer (P) and chemical resistance and heat resistance of the resulting crosslinked rubber article. More preferred is a perfluorodiene composed of an atom, a fluorine atom and an oxygen atom.

The number of atoms of a linking chain (total of carbon atoms and oxygen atoms) that connects two polymerizable double bonds in the fluorodiene (b) is preferably 5 to 10, and more preferably 5 to 8.
If the number of atoms in the linking chain is equal to or greater than the lower limit, it is possible to suppress intramolecular cyclization by reacting these two polymerizable double bonds in the molecule during the polymerization reaction in the production of the fluoropolymer (P). Then, the polymerizable double bond tends to remain as an unsaturated side chain in the fluoropolymer (P). If the number of atoms of the linking chain is not more than the upper limit, the polymerizable double bond remaining in the side chain of the fluoropolymer (P) causes a crosslinking reaction during storage of the crosslinkable fluororubber composition of the present invention. It is difficult to cause high molecular weight and gelation of the fluoropolymer (P). Thereby, when knead | mixing with fluororubber, it becomes easy to suppress that the fluidity | liquidity of fluoropolymer (P) falls remarkably. In addition, the fluorodiene (b) having a linking chain atom number of not more than the upper limit can be easily synthesized and purified to high purity.

The fluorodiene (b) is preferably a compound having no ring structure from the viewpoint of preventing the fluidity of the fluoropolymer (P) from being excessively lowered. As the fluorodiene (b), the following fluorodienes (b1) to (b3) are more preferable.
(B1) CF ₂ = CFO-Q ^f1 -OCF = CF ₂
(B2) CH ₂ ═CFCF ₂ O—Q ^f2 —OCF ₂ CF═CH ₂
(B3) CH ₂ ═CFCF ₂ O—Q ^f3 —OCF═CF ₂
In the formula, Q ^f1 and Q ^f2 each independently represent a fluoroalkylene group having 3 to 8 carbon atoms, or a fluoroalkylene group having 3 to 8 carbon atoms having one or more etheric oxygen atoms between carbon atoms. It is a group.
Q ^f3 is a fluoroalkylene group having 1 to 6 carbon atoms or a fluoroalkylene group having 2 to 6 carbon atoms having at least one etheric oxygen atom between carbon atoms.
In the present invention, the fluoroalkylene group is a group in which one or more hydrogen atoms of the alkylene group are substituted with fluorine atoms. In addition, the fluoroalkylene group having one or more etheric oxygen atoms between carbon atoms and carbon atoms means one or more hydrogen atoms of an alkylene group having one or more etheric oxygen atoms between carbon atoms and carbon atoms. A group substituted by a fluorine atom. The perfluoroalkylene group is a group in which all hydrogen atoms of the alkylene group are substituted with fluorine atoms.

The fluoroalkylene groups of Q ^f1 , Q ^f2 , and Q ^{f3 in} the fluorodienes (b1) to (b3) may have a branched structure.
The number of carbon atoms of the fluoroalkylene group of Q ^f1 is preferably 3-6.
The number of carbon atoms in the fluoroalkylene group of Q ^f2 is preferably 3-6.
The number of carbon atoms in the fluoroalkylene group of Q ^f3 is preferably 2-5.

As the fluorodiene (b1), the following fluorodienes (b11) and (b12) are preferable.
(B11) CF ₂ = CFO-Q ^F11 -OCF = CF _{2
^{(B12) CF 2 = CFOCH 2}} -Q F12 -CH 2 OCF = CF 2
In the formula, Q ^F11 is a ^{C 3-8} perfluoroalkylene group or a C 3-8 perfluoroalkylene group having one or more etheric oxygen atoms between carbon atoms.
Q ^F12 is a ^{C 2-6} perfluoroalkylene group or a C 2-6 perfluoroalkylene group having one or more etheric oxygen atoms between carbon atoms.

Specific examples of the fluorodiene (b11) include the following compounds.
_{CF 2 = CFO (CF 2)} 4 OCF = CF 2,
_{CF 2 = CFO (CF 2)} 5 OCF = CF 2,
_{CF 2 = CFO (CF 2)} 6 OCF = CF 2,
_{CF 2 = CFO (CF 2)} 4 OCF (CF 3) CF 2 OCF = CF 2 and so on.
Specific examples of the fluorodiene (b12) include the following compounds.
_{CF 2 = CFOCH 2 (CF 2} ) 2 CH 2 OCF = CF 2,
_{CF 2 = CFOCH 2 (CF 2} ) 4 CH 2 OCF = CF 2 and so on.

As the fluorodiene (b2), the following fluorodiene (b21) is preferable.
(B21) CH ₂ ═CFCF ₂ O—Q ^F21 —OCF ₂ CF═CH ₂
In the formula, Q ^F21 is a ^{C 3-8} perfluoroalkylene group or a C 3-8 perfluoroalkylene group having one or more etheric oxygen atoms between carbon atoms.
Specific examples of the fluorodiene (b21) include the following compounds.
_{CH 2 = CFCF 2 O (CF} 2) 2 OCF 2 CF = CH 2,
_{CH 2 = CFCF 2 O (CF} 2) 3 OCF 2 CF = CH 2,
_{CH 2 = CFCF 2 O (CF} 2) 4 OCF 2 CF = CH 2,
_{CH 2 = CFCF 2 O (CF} 2) 2 OCF (CF 3) CF 2 OCF 2 CF = CH 2 and the like.

As the fluorodiene (b3), the following fluorodiene (b31) is preferable.
(B31) CH ₂ ═CFCF ₂ O—Q ^F31 —OCF═CF ₂
In the formula, Q ^F31 is a ^C 1-6 perfluoroalkylene group or a C 2-6 perfluoroalkylene group having one or more etheric oxygen atoms between carbon atoms.
Specific examples of the fluorodiene (b31) include the following compounds.
_{CH 2 = CFCF 2 OCF (CF} 3) CF 2 OCF = CF 2,
CH ₂ = CFCF ₂ OCF (CF ₃ ) CF ₂ OCF (CF ₃ ) CF ₂ OCF = CF _{2 and the} like.

The fluorodiene (b) has a suitable degree of polymerizability in which a polymerizable double bond is likely to remain in the side chain during the synthesis of the fluoropolymer (P), and a cross-linked rubber article having more excellent heat resistance can be obtained. Therefore, fluorodiene (b1) is more preferable, and fluorodiene (b11) is more preferable.
Fluorodiene (b) may be used alone or in combination of two or more.

The fluoropolymer (P) has a repeating unit based on the fluorodiene (b), and at least a part of the repeating unit derived from the fluorodiene (b) has an unsaturated side chain having a polymerizable double bond. Remains. For example, when CF ₂ ═CF—O— (CF ₂ ) ₄ —O—CF═CF ₂ is used as the fluorodiene (b), the resulting fluoropolymer (P) has a non-polymerizable double bond. It has at least a repeating unit represented by the following formula in which a saturated side chain remains.

The weight average molecular weight (hereinafter referred to as “Mw”) of the fluoropolymer (P) is preferably 3,000 to 50,000, and more preferably 10,000 to 30,000. If Mw of fluoropolymer (P) is more than a lower limit, the heat resistance of the crosslinked fluororubber article obtained by curing the crosslinkable fluororubber composition will be better. Moreover, if Mw of fluoropolymer (P) is below an upper limit, when manufacturing a crosslinkable fluororubber composition, mixing and dispersion to fluororubber are easy. Thereby, it becomes easy to mold into a desired shape, and it becomes easy to suppress the occurrence of unevenness in characteristics of the crosslinked rubber article due to non-uniform flow. Moreover, it becomes easy to obtain the crosslinked rubber article which has higher thermal stability by setting Mw of fluoropolymer (P) high in the said range.
The Mw and the number average molecular weight (hereinafter referred to as “Mn”) in the present invention are those of Asahi Clin AK-225SEC Grade 1 (mixed solvent of dichloropentafluoropropane and hexafluoroisopropyl alcohol (dichloropentafluoro), manufactured by Asahi Glass Co., Ltd. Propane / hexafluoroisopropyl alcohol = 99/1 (volume ratio))) as a solvent, and a molecular weight calculated as PMMA (polymethyl methacrylate) equivalent molecular weight by gel permeation chromatography (GPC).

The content of the polymerizable double bond remaining in the side chain in the fluoropolymer (P) is preferably 0.2 to 2 mmol / g, more preferably 0.5 to 1.5 mmol / g. The content of the polymerizable double bond can be calculated by measurement by F ¹⁹ -NMR.
If the content of the polymerizable double bond is at least the lower limit, it is easy to sufficiently crosslink when the crosslinkable fluororubber composition is cured, and it becomes easy to obtain a crosslinked rubber article having excellent heat resistance. Moreover, if the content of the polymerizable double bond is not more than the upper limit, it is easy to suppress a decrease in heat resistance due to decomposition of unreacted polymerizable double bonds remaining in the crosslinked rubber article after curing, It is easy to prevent a decrease in fluidity due to gelation or high molecular weight due to a crosslinking reaction during production of the fluoropolymer (P).

(Synthesis of fluoropolymer (P))
The fluoropolymer (P) is obtained by homopolymerizing the fluorodiene (b) or by copolymerizing the fluoromonoene (a) and the fluorodiene (b). A part of the polymerizable double bond of diene (b) remains as a side chain without contributing to the reaction.
The polymerization method for homopolymerizing fluorodiene (b) or copolymerizing fluoromonoene (a) and fluorodiene (b) is not particularly limited, and known methods such as suspension polymerization, solution polymerization, emulsion polymerization and bulk polymerization The polymerization method can be employed. Among these, solution polymerization is particularly preferable because it can be polymerized in a state diluted with a solvent and can suppress a cross-linking reaction between molecules due to a polymerizable double bond remaining in a side chain.
Solution polymerization is a polymerization method in which fluorodiene (b) alone or fluoromonoene (a) and fluorodiene (b) are added to a polymerization initiator in a polymerization solvent to polymerize.

As a polymerization solvent in solution polymerization, a fluorine-containing solvent capable of dissolving the generated fluoropolymer (P) is preferable. Examples of the fluorine-containing solvent include dichloropentafluoropropane (HCFC-225), CF ₃ CH ₂ CF ₂ H (HFC-245fa), CF ₃ CF ₂ CH ₂ CF ₂ H (HFC-365mfc), perfluorohexane, perfluoro octane, perfluoro (2-butyl tetrahydrofuran), perfluoro _{(tributylamine), CF 3 CF 2 CF 2} CF 2 CF 2 CF 2 H, CF 3 CH 2 OCF 2 CF 2 H, CF 3 CH 2 OCH 2 CF 3, CF _{3 CF 2 OCF 2 CF 2 OCF} 2 CF 3 and the like.

In the synthesis of the fluoropolymer (P), the fluorodiene (b) or the total amount of fluoromonoene (a) and the fluorodiene (b) are not reacted at once, but a part of the total amount used. In particular, a method is preferred in which the polymerization reaction is started by previously charging the reaction mixture into the reaction vessel and the polymerization is performed while the remaining fluoromonoene (a) and fluorodiene (b) are sequentially added while the polymerization reaction proceeds.
Thereby, the molecular weight distribution and composition distribution of the resulting fluoropolymer (P) can be narrowed, the content of low molecular weight components having a molecular weight of less than 1,000 in the fluoropolymer (P) can be easily reduced, and the fluoropolymer (P The yield of P) is improved. The low molecular weight component has a lower content of polymerizable double bonds per molecule than a component having a molecular weight of 1000 or more. When a polymerizable double bond is used in a curing reaction, it generally involves volume shrinkage, so reducing the content of the low molecular weight component facilitates the uniform progress of the curing reaction, resulting in thermal stability and dimensional stability. It is easy to obtain a crosslinked rubber article excellent in the above. The content of the low molecular weight component in the fluoropolymer (P) is preferably less than 10% by mass, and more preferably less than 1% by mass.
In addition, in the copolymerization of fluoromonoene (a) and fluorodiene (b), in addition to the low molecular weight component, the content of repeating units derived from fluorodiene (b) is particularly small, Ingredients can be produced. However, the method of sequentially adding the fluoromonoene (a) and the fluorodiene (b) described above makes it easy to reduce the formation of such a compound.

Needless to say, in the homopolymerization of fluorodiene (b), 100 mol% of fluorodiene (b) is used. On the other hand, in the copolymerization of fluoromonoene (a) and fluorodiene (b), the molar ratio of fluoromonoene (a) to fluorodiene (b) is preferably 1:99 to 95: 5. When fluoroethylenes are used as the fluoromonoene (a), the molar ratio of the fluoroethylenes to the fluorodiene (b) is more preferably 5:95 to 80:20, and particularly preferably 30:70 to 70:30. If the charging ratio of fluoroethylenes is less than or equal to the above upper limit value, it is easy to suppress a decrease in fluidity due to an excessive increase in the molecular weight of the fluoropolymer (P). Moreover, the elongation of the resulting crosslinked rubber article is improved.

As a polymerization initiator used for the synthesis of the fluoropolymer (P), an organic peroxide having a 10-hour half-life temperature of 20 to 120 ° C. can be used, and a decrease in reaction rate due to a hydrogen atom extraction reaction in the polymerization initiator is prevented. From the viewpoint, fluorine-containing peroxides such as fluorine-containing diacyl peroxide are preferable.
The concentration of the polymerization initiator in the reaction solution is preferably from 0.1 to 5% by mass, more preferably from 0.5 to 2% by mass.
The polymerization temperature is preferably 20 to 120 ° C., more preferably 40 to 90 ° C., although it varies depending on the 10-hour half-life temperature of the polymerization initiator and the polymerization rate of the monomer.

In the synthesis of the fluoropolymer (P), it is preferable to use a chain transfer agent in order to adjust the molecular weight.
Examples of the chain transfer agent include chlorine compounds such as CCl ₄ , CH ₃ Cl, SO ₂ Cl ₂ and CHFCl ₂ ; iodine compounds such as fluoroalkyl iodide and fluoroalkylene diiodide; methanol, ethanol, isopropanol, hexane, Examples thereof include hydrocarbon solvents such as diethyl ether. Among these, SO ₂ Cl ₂ , I— (CF ₂ ) _n —I (n is 4 or 6) is preferable from the viewpoint of high chain transfer efficiency and high yield of the fluoropolymer (P). .
The amount of chain transfer agent used varies depending on the chain transfer constant, but when SO ₂ Cl ₂ is used, the amount of fluorodiene (b) used in fluorodiene (b) homopolymerization or the amount of fluoromonoene (a) In the copolymerization of fluorodiene (b), the molar ratio is preferably 0.001 to 0.1, preferably 0.001 to 0.05, based on the total amount of fluoromonoene (a) and fluorodiene (b). It is more preferable that If the molar ratio is at least the lower limit, it is easy to prevent the molecular weight of the fluoropolymer (P) from becoming too high. Moreover, if the said molar ratio is below an upper limit, it will be easy to prevent that the molecular weight of fluoropolymer (P) falls too much.

(Purification of fluoropolymer (P))
In the obtained fluoropolymer (P), it is preferable to remove by purification the low molecular weight component having a molecular weight of less than 1,000 after polymerization. Since the low molecular weight component in the fluoropolymer (P) can be reduced by purification, the obtained fluoropolymer (P) has a smaller molecular weight distribution expressed by Mw / Mn measured by GPC and a narrow dispersion. It becomes. Thereby, it becomes easy to obtain a crosslinked rubber article excellent in thermal stability and dimensional stability.
However, the fluoropolymer (P) may not be purified after polymerization.

As a method for removing low molecular weight components having a molecular weight of less than 1,000, (α) a method of removing the low molecular weight components by heating the fluoropolymer (P) under reduced pressure, and (β) an extraction solvent in a supercritical state. Method of extracting low molecular weight components from fluoropolymer (P), (γ) A solution of fluoropolymer (P) is put into a poor solvent, and fluoropolymer (P) having a molecular weight of 1,000 or more is precipitated and does not precipitate Examples thereof include a method for removing a low molecular weight component and (δ) a method for removing a low molecular weight component using gel permeation chromatography. Among these, the method (α) is preferable from the viewpoint of simplicity of the operation method and ease of scale-up, and it is more preferable to carry out the method (β) after the method (α).

The reduced pressure condition in the method (α) is preferably 1 to 100 hPa, more preferably 1 to 20 hPa, and most preferably 1 to 10 hPa. If the pressure is equal to or higher than the lower limit, the pressure can be reduced easily even if the apparatus size is increased. If the pressure is not more than the upper limit value, the removal efficiency of the low molecular weight component is improved.
The heating temperature in the method (α) is preferably from 100 to 150 ° C, more preferably from 120 to 150 ° C. When the temperature is at least the lower limit, the low molecular weight component can be removed in a shorter time, and the removal efficiency is improved. If temperature is below an upper limit, it will be easy to suppress that gelation reaction arises partially during heating.

In the method (β), the fluoropolymer (P) is brought into contact with the extraction solvent in a supercritical state, and then the fluoropolymer (P) and the extraction solvent are separated, whereby the low content contained in the fluoropolymer (P) is obtained. This is a method for removing molecular weight components.
The extraction solvent is a medium that can dissolve the low molecular weight component and separate the low molecular weight component from the fluoropolymer (P). The extraction solvent is not particularly limited as long as it can extract a low molecular weight component in a temperature range of not less than the critical temperature of the extraction solvent to be used and less than 130 ° C. and under a pressure of not less than the critical pressure of the extraction solvent. .
Examples of the extraction solvent include carbon atoms; fluorocarbons having 1 to 3 carbon atoms such as fluoroform (CF ₃ H; R23) and perfluoroethane (C ₂ F ₆ ; R116). Among these, carbon dioxide, fluoroform, and perfluoroethane are preferable, and carbon dioxide is more preferable in that it can be easily brought into a supercritical state and is excellent in extraction efficiency.
Only one type of extraction solvent may be used alone, or two or more types may be used in combination.

The temperature of the extraction solvent in the method (β) is preferably not less than the critical temperature of the extraction solvent to be used and less than 130 ° C. Further, the pressure of the extraction solvent is not less than the critical pressure of the extraction solvent. That is, the method (β) is preferably a method in which an extraction solvent made into a supercritical fluid of less than 130 ° C. is brought into contact with the fluoropolymer (P).
If it is in the said range, the temperature of an extraction solvent can be suitably set according to the extraction solvent to be used. The lower limit of the temperature of the extraction solvent is more preferably 0.1 ° C. higher than the critical temperature. The upper limit of the temperature of the extraction solvent is more preferably 100 ° C, and further preferably 80 ° C.
If the pressure of an extraction solvent is in the said range, it can set suitably according to the extraction solvent to be used. The lower limit of the extraction solvent pressure is preferably 10,000 Pa higher than the critical pressure, and more preferably 70 MPa higher than the critical pressure.

In the method (β), the extraction efficiency of the low molecular weight component is improved by increasing the density of the extraction solvent. This is considered to be because the solubility of the low molecular weight component in the extraction solvent increases as the density of the extraction solvent increases.
The density of the extraction solvent at the time of extraction, that is, the density of the extraction solvent in the supercritical state is preferably 0.2 g / cm ³ or more and 1.3 g / cm ³ or less.

In the method (β), a halogenated hydrocarbon solvent or a hydrocarbon solvent (hereinafter referred to as “entrainer”) may be used in combination with the extraction solvent as a cosolvent. The entrainer is preferably a halogenated hydrocarbon solvent from the viewpoint of solubility.
Examples of halogenated hydrocarbon solvents include CF ₃ CF ₂ CHCl ₂ , CF ₂ ClCF ₂ CHClF, CF ₃ CF ₂ CHCl ₂ , CFC 1 ₂ CF ₂ Cl, CCl ₄ , CF ₃ CHFCHFCF ₂ CF ₃ , CF ₃ CH ₂ OCF ₂ CF ₂ H and the like.
Examples of the hydrocarbon solvent include methanol, ethanol, propanol, isopropanol, dimethyl ether and the like.
An entrainer may be used individually by 1 type and may use 2 or more types together.
In the method (β), since extraction is performed using an extraction solvent in a supercritical state, low molecular weight substances can be efficiently reduced, and the molecular weight distribution of the resulting fluoropolymer (P) becomes narrowly dispersed.

The method (γ) is a method for removing low molecular weight components contained in the fluoropolymer (P) by adding a soot solvent to the fluoropolymer (P) and then separating the supernatant.
Examples of the poor solvent used in the method (γ) include methanol, hexane, diethyl ether and the like.

The content of the fluoropolymer (P) in the crosslinkable fluororubber composition of the present invention is 1 with respect to 100 parts by mass of the fluororubber because it is easy to obtain a crosslinked rubber article excellent in heat resistance and chemical resistance. Is preferably 50 parts by mass, more preferably 2 to 45 parts by mass, and still more preferably 3 to 40 parts by mass. If content of a fluoropolymer (P) is more than a lower limit, it will become easy to form bridge | crosslinking sufficiently and it will become easy to obtain the crosslinked rubber article excellent in heat resistance. If the content of the fluoropolymer (P) is not more than the upper limit, even if unstable terminal groups (carboxyl groups, etc.) derived from the fluoropolymer (P) in the crosslinked rubber article are present, the thermal stability due to the groups It is easy to suppress the decrease.

[Fluoro rubber]
The fluororubber can be cross-linked by (1) a method in which an organic peroxide is used to generate radicals by heating and cross-linking, or (2) a method in which a radical is generated by irradiation with radiation to cross-link. Hereinafter, the crosslinking by the method (1) may be referred to as organic peroxide crosslinking, and the crosslinking by the method (2) may be referred to as radiation crosslinking.
The fluorine content of the fluororubber is preferably 40% by mass or more, more preferably 50% by mass or more, and further preferably 55% by mass or more. If the fluorine content is at least the lower limit, a crosslinked rubber article excellent in heat resistance, chemical resistance, electrical insulation and steam resistance can be easily obtained. The fluorine content of fluororubber is the ratio of the total mass of all fluorine atoms to the total mass of fluororubber.

Fluororubber includes vinylidene fluoride / hexafluoropropylene copolymer, vinylidene fluoride / TFE / hexafluoropropylene copolymer, vinylidene fluoride / CTFE copolymer, TFE / propylene copolymer, TFE. / Propylene / vinylidene fluoride copolymer, hexafluoropropylene / ethylene copolymer, TFE / perfluoroalkyl vinyl ether copolymer, vinylidene fluoride / TFE / perfluoroalkyl vinyl ether copolymer, and the like. These may be used alone or in combination of two or more.
The fluororubber is selected from the group consisting of a TFE / propylene copolymer, a vinylidene fluoride / TFE / hexafluoropropylene copolymer, and a TFE / perfluoroalkyl vinyl ether copolymer because of its excellent chemical resistance. One or more selected from the above are preferred.

From the viewpoint of excellent heat resistance, the fluororubber is particularly preferably a perfluoroelastomer obtained by polymerizing a perfluoromonomer in which all of the hydrogen atoms of the monomer are substituted with fluorine atoms.
The perfluoroelastomer includes a repeating unit derived from TFE and CF ₂ ═CF—O—R ^F2 (wherein R ^F2 is a perfluoroalkyl group having 1 to 20 carbon atoms, or an ether between carbon atoms and carbon atoms). An elastomer having a repeating unit derived from a perfluoroalkyl group having 1 or more carbon atoms and having 1 or more carbon atoms and having 1 to 20 carbon atoms (hereinafter referred to as “perfluoromonomer (x)”) (hereinafter referred to as “elastomer (X)”). Is preferred).
In elastomer (X), the repeating unit derived from perfluoromonomer (x) may be only 1 type, and 2 or more types may be sufficient as it.

The carbon number of the perfluoroalkyl group of R ^{F2 in} the perfluoromonomer (x) is preferably 1-8. The perfluoroalkyl group for R ^F2 may be linear or branched.
As the perfluoromonomer (x), CF ₂ ═CF—O—CF ₃ , CF ₂ ═CF—O—CF ₂ CF ₃ , CF ₂ ═CF—O—CF ₂ CF ₂ CF ₃ , CF ₂ ═CF—O —CF ₂ CF (CF ₃ ) OCF ₂ CF ₂ CF ₃ , CF ₂ ═CF—O—CF ₂ CF ₂ —O—CF ₂ CF ₃ is preferred, and CF ₂ ═CF—O—CF ₃ is more preferred.

The copolymerization ratio in the elastomer (X) is preferably a repeating unit derived from TFE / repeating unit based on perfluoromonomer (x) = 30/70 to 80/20 (molar ratio) from the viewpoint of excellent rubber properties.

The fluororubber is not limited to a perfluoroelastomer, and an elastomer obtained by using a chain transfer agent or comonomer containing a small amount of hydrogen atoms may be used when polymerizing a perfluoromonomer.
Examples of the chain transfer agent containing a hydrogen atom include chain or cyclic saturated hydrocarbons such as methane, ethane, propane, butane, pentane, hexane, and cyclohexane; alcohols such as methanol, ethanol, and propanol; t-dodecyl mercaptan, and mercaptans such as n-dodecyl mercaptan and n-octadecyl mercaptan. These chain transfer agents may be used individually by 1 type, and may use 2 or more types together.
As a comonomer containing a hydrogen atom, CF ₂ ═CF—O—CH ₂ CF ₃ , CF ₂ ═CF—O—CH ₂ CF ₂ CF ₂ CF ₃ , CF ₂ ═CF—O—CH ₂ (CF ₂ CF ₂ ) ₂ H, CF ₂ ═CF—O—CF ₂ CF ₂ CH ₂ —I, CF ₂ ═CF—O—CF ₂ CF ₂ CH ₂ —Br, CF ₂ ═CF—O—CF ₂ CF ₂ (CF ₃ ) —O—CF ₂ CF ₂ CH ₂ —I, CF ₂ ═CF—O—CF ₂ CF ₂ (CF ₃ ) —O—CF ₂ CF ₂ CH ₂ —Br, and the like. These comonomers may be used individually by 1 type, and may use 2 or more types together.
When at least one of the chain transfer agent and the comonomer is used, the content of hydrogen atoms in the elastomer is preferably 0.5% by mass or less from the viewpoint of characteristics such as heat resistance and chemical resistance of the crosslinked rubber article, 0.3 mass% or less is more preferable, and 0.1 mass% or less is especially preferable.

The fluororubber is preferably a perfluoroelastomer having at least one of an iodine atom and a bromine atom (hereinafter sometimes referred to as “elastomer (Y)”), particularly in the case of organic peroxide crosslinking, and has an iodine atom. Perfluoroelastomers are more preferred. The perfluoroelastomer having at least one of an iodine atom and a bromine atom is an elastomer in which one or more fluorine atoms of the perfluoroelastomer are substituted with iodine atoms or bromine atoms. The perfluoroelastomer having iodine atoms is an elastomer in which one or more fluorine atoms of the perfluoroelastomer are substituted with iodine atoms.

Examples of the elastomer (Y) include elastomers described in JP-A-53-125491, JP-B-53-4115, and JP-A-59-20310. Specifically, in addition to at least one perfluoromonomer selected from the group consisting of TFE and perfluoromonomer (x), a monomer having at least one of an iodine atom and a bromine atom (hereinafter referred to as “monomer (y)”). I—R ^F3 —I (wherein R ^F3 is a perfluoroalkylene group having 1 to 8 carbon atoms, or has at least one etheric oxygen atom between carbon atoms and carbon atoms). And an elastomer obtained by copolymerizing the monomer in the presence of a compound represented by the formula (1).

As the monomer (y), CF ₂ ═CF—Br, CH ₂ ═CHCF ₂ CF ₂ —Br, CF ₂ ═CF—O—CF ₂ CF ₂ —I, CF ₂ ═CF—O—CF ₂ CF ₂ — Br, CF ₂ ═CF—O—CF ₂ CF ₂ CH ₂ —I, CF ₂ ═CF—O—CF ₂ CF ₂ CH ₂ —Br, CF ₂ ═CF—O—CF ₂ CF ₂ (CF ₃ ) — O—CF ₂ CF ₂ CH ₂ —I, CF ₂ ═CF—O—CF ₂ CF ₂ (CF ₃ ) —O—CF ₂ CF ₂ CH ₂ —Br, and the like can be given.

Specific examples of IR ^F3- I include diiododifluoromethane, 1,2-diiodoperfluoroethane, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane, 1,5-diiodo. Examples include perfluoropentane, 1,6-diiodoperfluorohexane, 1,7-diiodoperfluoroheptane, 1,8-diiodoperfluorooctane, and the like. Of these, 1,4-diiodoperfluorobutane and 1,6-diiodoperfluorohexane are preferred, and 1,4-diiodoperfluorobutane is particularly preferred.
The iodine atom and bromine atom in the elastomer (Y) are preferably bonded to the polymer terminal.

The total content of iodine atoms and bromine atoms in the elastomer (Y) is preferably 0.1 to 1.5% by mass from the viewpoint of easily obtaining a crosslinked rubber article excellent in rubber physical properties and compression set. More preferably, the content is 0.2 to 1.0% by mass, and particularly preferably 0.25 to 1.0% by mass.

Among the commercially available fluoro rubbers, preferred are the trade name “AFLAS PFE-1100” (manufactured by Asahi Glass Co., Ltd., TFE / perfluoroalkyl vinyl ether copolymer), and the trade name “AFLAS 100S” (manufactured by Asahi Glass Co., Ltd., TFE / propylene). Copolymer) and trade name “AFLAS 200P” (Asahi Glass Co., Ltd., TFE / propylene / vinylidene fluoride copolymer) and the like, which can be crosslinked with organic peroxides.

[Organic peroxide]
When the crosslinkable fluororubber composition of the present invention is cured by organic peroxide crosslinking, the crosslinkable fluororubber composition of the present invention preferably contains an organic peroxide. When the crosslinkable fluororubber composition is cured by radiation crosslinking, it is not necessary to contain an organic peroxide.
The organic peroxide is not particularly limited as long as it can easily generate radicals by heating, and preferably has a half-life of 1 minute at 130 to 220 ° C. Specifically, 1,1-di (t-hexylperoxy) -3,5,5-trimethylcyclohexane, 2,5-dimethylhexane-2,5-dihydroperoxide, di-t-butyl Peroxide, t-butylcumyl peroxide, dicumyl peroxide, α, α'-bis (t-butylperoxy) -p-diisopropylbenzene, 2,5-dimethyl-2,5-di (t-butylperoxide Oxy) -hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) -hexyne-3, dibenzoyl peroxide, t-butylperoxybenzene, 2,5-dimethyl-2, Examples include 5-di (benzoylperoxy) hexane, t-butylperoxymaleic acid, t-hexylperoxyisopropyl monocarbonate, and the like. Of these, α, α′-bis (t-butylperoxy) -p-diisopropylbenzene is particularly preferable.
An organic peroxide may be used individually by 1 type, and may use 2 or more types together.

When the crosslinkable fluororubber composition of the present invention contains an organic peroxide, the content of the organic peroxide is preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the fluororubber, 0.2 -4 parts by mass is more preferable, and 0.5-3 parts by mass is more preferable. If content of an organic peroxide is more than a lower limit, crosslinking efficiency will improve. If the content of the organic peroxide is not more than the upper limit value, it is easy to suppress the amount of inactive decomposition products that do not contribute to the radical reaction.

[Other ingredients]
The crosslinkable fluororubber composition of the present invention preferably contains an acid acceptor from the viewpoint of promoting the crosslinking reaction.
Examples of the acid acceptor include magnesium oxide, zinc oxide, calcium hydroxide, calcium oxide, lead oxide, dibasic lead phosphite, and hydrotalcite. Of these, magnesium oxide and zinc oxide are preferable. An acid acceptor may be used individually by 1 type, and may use 2 or more types together.
When the crosslinkable rubber composition of the present invention contains an acid acceptor, the content of the acid acceptor is preferably 0.1 to 20 parts by mass, and 0.2 to 10 parts by mass with respect to 100 parts by mass of the fluororubber. Part is more preferred. If content of an acid acceptor is more than a lower limit, the effect by an acid acceptor will be easy to be acquired. If content of an acid acceptor is below an upper limit, it will be easy to suppress that the rubber physical property of a crosslinked rubber article is impaired.

The crosslinkable fluororubber composition of the present invention preferably contains a filler from the viewpoint of improving the strength of the resulting crosslinked rubber article. As the filler, carbon black is preferable.
Carbon black is not particularly limited as long as it is used for blending rubber. Specific examples include furnace black, acetylene black, thermal black, channel black, and graphite. Of these, furnace black is more preferable.
As the grade of carbon black, HAF-LS, HAF, HAF-HS, FEF, GPF, APF, SRF-LM, SRF-HM and MT are preferable, and MT is particularly preferable.

When the crosslinkable fluororubber composition of the present invention contains a filler, the content of the filler is preferably 5 to 100 parts by mass and more preferably 10 to 50 parts by mass with respect to 100 parts by mass of the fluororubber. If the content of the filler is equal to or higher than the lower limit value, the effect of the filler is easily obtained. If content of a filler is below an upper limit, it will be easy to suppress that the elongation characteristic of crosslinked rubber articles falls. Moreover, if content of a filler exists in the said range, the balance of the intensity | strength and elongation of the crosslinked rubber article obtained will become more favorable.

Moreover, the crosslinkable fluororubber composition of the present invention may contain additives such as a reinforcing material, a processing aid, a lubricant, a lubricant, a flame retardant, an antistatic agent, a colorant, and an ultraviolet absorber.
Examples of the reinforcing material include fluororesins such as polytetrafluoroethylene and ethylene / TFE copolymer, glass fibers, carbon fibers, and white carbon.
When the crosslinkable fluororubber composition of the present invention contains a reinforcing material, the content of the reinforcing material is preferably 5 to 200 parts by mass and more preferably 10 to 100 parts by mass with respect to 100 parts by mass of the fluororubber.

Examples of the processing aid include alkali metal salts of higher fatty acids. Of these, stearates and laurates are preferable.
When the crosslinkable fluororubber composition of the present invention contains a processing aid, the content of the processing aid is preferably 0.1 to 20 parts by mass, and 0.2 to 10 parts per 100 parts by mass of the fluororubber. Mass parts are more preferred, and 1 to 5 parts by mass are even more preferred. If the processing aid is at least the lower limit value, it is easy to suppress the tensile strength of the crosslinked rubber article from being significantly lowered, or to increase the elongation and the change in tensile strength after heat aging. If the content of the processing aid is not more than the upper limit, bloom may occur on the surface of the crosslinked rubber article, the hardness of the crosslinked rubber article may be too high, or chemical resistance and steam resistance may be reduced. Easy to suppress.

[Method for producing crosslinkable fluororubber composition]
The method for producing the crosslinkable fluororubber composition of the present invention is not particularly limited, and a conventionally known method can be adopted. Among them, a kneading machine such as a two-roll, a Banbury mixer, a kneader or the like containing fluororubber, fluoropolymer (P), and organic peroxide, carbon black, acid acceptor, and other additives used as necessary. A method of kneading with the use of is preferred. Moreover, the method of knead | mixing in the state which melt | dissolved and disperse | distributed each said component in the solvent is also employable.

As the mixing order of the respective components, first, a component that is unlikely to react or decompose due to heat generation is sufficiently kneaded with fluororubber, and then a component that easily reacts or a component that easily decomposes is mixed and kneaded. preferable.
For example, when an organic peroxide is used, it is preferable to mix and knead the organic peroxide later. In this case, at the time of kneading, it is preferable to keep the kneader in a temperature range of 20 to 120 ° C. by cooling with water in order to prevent the crosslinking reaction from proceeding.

The crosslinkable fluororubber composition of the present invention described above uses a fluororubber having excellent chemical resistance. Moreover, since radicals are used for crosslinking by organic peroxide crosslinking or radiation crosslinking, the chemical resistance of fluororubber is not lowered, and a crosslinked rubber article having excellent chemical resistance can be obtained. Moreover, since sufficient crosslinking can be formed by using the fluoropolymer (P) as a crosslinking aid, excellent heat resistance is also achieved. Therefore, if the crosslinkable fluororubber composition of the present invention is used, a crosslinked rubber article having excellent chemical resistance and heat resistance can be obtained.

<Crosslinked rubber article>
The crosslinked rubber article of the present invention is an article formed by crosslinking the aforementioned crosslinkable fluororubber composition of the present invention.
The crosslinked rubber article of the present invention can be used in a wide range of transport machines such as automobiles, general equipment, electrical equipment, chemical equipment industry, semiconductors, O-rings, seats, gaskets, oil seals, bearing seals and other sealing materials, diaphragms, It can be suitably used as each member such as a cushioning material, an anti-vibration material, a wire coating material, an industrial belt, a tube / hose, a sheet and the like. Among them, a sealing material is preferable because it is excellent in chemical resistance at high temperatures and also has excellent basic properties such as strength, hardness, modulus, and heat aging resistance. More preferably.

[Method for producing crosslinked rubber article]
The crosslinked rubber article of the present invention is obtained by using the crosslinkable fluororubber composition of the present invention and curing and molding by organic peroxide crosslinking or radiation crosslinking.
For the molding of the crosslinkable fluororubber composition of the present invention, a conventionally known molding method such as extrusion molding, injection molding, transfer molding, press molding or the like can be adopted for both organic peroxide crosslinking and radiation crosslinking.

As a specific example of a method for obtaining a crosslinked rubber article by organic peroxide crosslinking, for example, a mold having a cavity complementary to the shape of one or several crosslinked rubber articles is used, and the cavity is provided in the cavity. Examples thereof include a method of filling a crosslinkable fluororubber composition containing an organic peroxide and curing the mold by heating.
The heating temperature is preferably 130 to 220 ° C, more preferably 140 to 200 ° C, and particularly preferably 150 to 200 ° C.

Further, the crosslinked rubber article (primary crosslinked product) heated and crosslinked under the above-described conditions is further heated in an oven or the like using electricity, hot air, steam or the like as a heat source as necessary to allow the crosslinking to proceed (hereinafter referred to as “2” It is also preferred to be referred to as “secondary crosslinking”. By performing secondary crosslinking, the residue of the organic peroxide contained in the crosslinked rubber article is decomposed and volatilized, and the amount thereof is reduced.
The heating temperature during secondary crosslinking is preferably 150 to 280 ° C, more preferably 180 ° C to 260 ° C, and further preferably 200 to 250 ° C.
The heating time in the secondary crosslinking is preferably 1 to 48 hours, more preferably 2 to 24 hours.

As a specific example of a method for obtaining a crosslinked rubber article by radiation crosslinking, for example, the crosslinkable fluororubber composition of the present invention is dissolved and dispersed in an appropriate solvent to form a suspension solution, which is formed by coating or the like, A method of curing by irradiating with radiation after drying is mentioned.
Examples of the radiation include ionizing radiation such as electron beams and γ rays.
The dose of ionizing radiation is preferably 1 to 300 kGy, more preferably 10 to 200 kGy.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by the following description.
[GPC analysis]
Mn and Mw of the fluoropolymer (P) obtained in this example were measured by GPC according to the method described in Japanese Patent Application Laid-Open No. 2001-208736 under the following conditions.
Mobile phase: Asahi Clin AK-225 SEC Grade 1 (mixed solvent of dichloropentafluoropropane and hexafluoroisopropyl alcohol (dichloropentafluoropropane / hexafluoroisopropyl alcohol = 99/1 (volume ratio)) manufactured by Asahi Glass Co., Ltd.).
Analytical column: Two PLgel MIXED-E columns (manufactured by Polymer Laboratories) connected in series.
Standard sample for molecular weight measurement: PMMA (polymethyl methacrylate).
Mobile phase flow rate: 1.0 mL / min.
Column temperature: 37 ° C.
Detector: Evaporative light scattering detector.

[Raw materials]
The components used in this example are as follows.
(1) Fluoro rubber Fluoro rubber (Y1): TFE / perfluoroalkyl vinyl ether copolymer elastomer (peroxide crosslinking type), trade name “AFLAS PFE-1100” (Asahi Glass Co., Ltd., fluorine content: 72 mass) %).

(2) Crosslinking aid Fluoropolymer (P1):
After degassing a stainless steel autoclave with a stirrer with an internal volume of 1 L (liter), 17 g of TFE as fluoromonoene (a) and perfluorobutylene divinyl ether (hereinafter referred to as “fluorodiene (b)”) were added to the autoclave. Of AK225cb solution containing 76 g of C4DVE), 3.0 g of SO ₂ Cl ₂ , 725 g of AK225cb (Asahi Glass Co., Ltd.) and 6.8 g of (C ₃ F ₇ COO) ₂ which is a polymerization initiator. 227 g was injected, and the temperature inside the autoclave was raised to 40 ° C. while stirring. Thereafter, TFE and C4DVE were successively added while performing the polymerization reaction for 4 hours while maintaining the pressure at 0.2 MPa so that the additional amount of TFE was 29 g and the additional amount of C4DVE was 44 g. Then, after cooling to room temperature and purging unreacted TFE, the contents were taken out into a glass beaker having an internal volume of 2 L.
Next, 500 g of methanol was added while stirring to precipitate the produced fluoropolymer, the low molecular weight component was removed by removing the supernatant, and redissolved in AK225cb to obtain a fluoropolymer solution 1. Next, the fluoropolymer solution 1 was washed with water, the lower layer was separated, and filtered using a PTFE (polytetrafluoroethylene) membrane filter having a pore diameter of 1 μm, thereby obtaining a substantially transparent fluoropolymer solution 2. Next, after distilling off the solvent from the fluoropolymer solution 2 using an evaporator, it was vacuum-dried at 100 ° C. for 2 hours to obtain 52 g of a colorless and transparent highly viscous liquid fluoropolymer (P1).
When the average molecular weight of the obtained fluoropolymer (P1) was measured by GPC, Mw was 22,800 and Mn was 7,300.
Further, when the composition of the fluoropolymer (P1) and the content of the polymerizable double bond were measured by ¹⁹ F-NMR, the molar ratio of the repeating unit derived from TFE to the repeating unit derived from C4DVE was 69/31. The content of the polymerizable double bond was 1.18 mmol / g.
Fluoropolymer (P2):
In a glass flask equipped with a stirrer and a condenser having an internal volume of 500 mL, 497 g of C4DVE, 2.5 g of I (CF ₂ ) ₆ I, and V-601 (manufactured by Wako Pure Chemical Industries) as a polymerization initiator 0.7 g of the solution was added, the solution was bubbled with nitrogen for 10 minutes, and the temperature in the flask was increased to 70 ° C. with stirring. The polymerization reaction was carried out for 25 hours while maintaining the internal temperature at 70 ° C. After cooling to room temperature, the internal volume was taken out into a glass beaker 2L by dissolving contents in C _{6 F} 13 _H.
Next, 374 g of methanol was added while stirring to precipitate the generated fluoropolymer, and the low molecular weight component was removed by removing the supernatant. By vacuum drying at 50 ° C. for 12 hours, 124 g of a colorless transparent high-viscosity liquid fluoropolymer (P2) was obtained.
When the average molecular weight of the obtained fluoropolymer (P2) was measured by GPC, Mw was 25,700 and Mn was 6,800.
Further, the content of the polymerizable double bond of the fluoropolymer (P2) was measured by ¹⁹ F-NMR, whereby the content of the polymerizable double bond was 2.68 mmol / g.

TAIC: triallyl isocyanurate.

(3) Organic peroxide Perbutyl P: α, α′-bis (t-butylperoxy) -p-diisopropylbenzene (trade name “Perkadox 14”, manufactured by NOF Corporation).

(4) Acid acceptor Kyowamag # 150: Magnesium oxide (manufactured by Kyowa Chemical Industry Co., Ltd.).
(5) Filler MT carbon: carbon black (grade: MT carbon, manufactured by CANCARB). (6) Processing aid Nonsal SN-1: Sodium stearate (manufactured by NOF Corporation).

[Example 1]
100 parts by mass of fluorine-containing rubber (Y1), 1 part by mass of Perhexa 25B (manufactured by NOF Corporation), 33.8 parts by mass of fluoropolymer (P1), 10 parts by mass of MT carbon, 3 parts by mass of Kyowamag # 150 Were kneaded with a biaxial roll to obtain a crosslinkable fluororubber composition (i). The obtained crosslinkable fluororubber composition (i) was molded into a sheet shape having a length of 100 mm × width of 100 mm × thickness of 2 mm in a hot press at 170 ° C. for 20 minutes (primary crosslinking). The obtained sheet was further placed in a gear oven at 250 ° C. for 2 hours and subjected to secondary crosslinking to obtain a sheet material.
A sample was punched out from the obtained sheet material with a No. 3 dumbbell, and the physical properties were evaluated by measuring hardness (HS), tensile strength (TB), elongation (EB), and 100% tensile stress (M100). Further, the heat aging resistance was evaluated by measuring the hardness (HS), tensile strength (TB), and elongation (EB) after heat treatment in a gear oven at 250 ° C. for 70 hours.

[Example 2]
A sheet material was prepared in the same manner as in Example 1 except that 5 parts by mass of TAIC was used instead of 33.8 parts by mass of fluoropolymer (P1) as a crosslinking aid, and Kyowamag # 150 was not used. Was measured.

[Example 3]
A sheet material was prepared in the same manner as in Example 1 except that 5 parts by mass of TAIC was used instead of 33.8 parts by mass of the fluoropolymer (P1) as a crosslinking aid, and the characteristics were measured.
[Example 4]
A sheet material was prepared in the same manner as in Example 1 except that 21.3 parts by mass of the fluoropolymer (P2) was used instead of 33.8 parts by mass of the fluoropolymer (P1) as a crosslinking aid. Was measured.
[Example 5]
A sheet material was prepared in the same manner as in Example 1 except that 14.2 parts by mass of the fluoropolymer (P2) was used instead of 33.8 parts by mass of the fluoropolymer (P1) as a crosslinking aid. Was measured.
Examples [1], [4] and [5] are examples, and examples [2] and [3] are comparative examples.

[Measuring method]
(1) Hardness (HS)
In accordance with JIS K6253-1997, the hardness (HS) was measured by a durometer type A hardness test at 23 ° C.
The hardness of the sealing material is preferably 60 to 95 °.
(2) Tensile strength (TB)
In accordance with JIS K6251-2004, the tensile strength (TB) was measured at 23 ° C.
As the tensile strength (TB) of the sealing material, 10 MPa or more is suitable.
(3) Elongation (EB)
The elongation (EB) was measured at 23 ° C. according to JIS K6251-2004.
As the elongation (EB) of the sealing material, 130% or more is suitable.
(4) 100% tensile stress (modulus)
In accordance with JIS K6251-2004, 100% tensile stress (M100) was measured at 23 ° C.
As the 100% tensile stress (M100) of the sealing material, 3 to 17 MPa is suitable.
(5) Air heating aging test (hardness change rate)
After heat treatment in gear oven at 250 ° C for 70 hours, according to JIS K6253-1997, the hardness (HS) was measured by durometer type A hardness test at 23 ° C, and the rate of change compared with the hardness of (1) Asked.
(6) Air heating aging test (rate of change in tensile strength)
After heat treatment at 250 ° C. for 70 hours in a gear oven, the tensile strength (TB) was measured at 23 ° C. according to JIS K6251-2004, and the rate of change was determined by comparison with the tensile strength of (2).
(7) Air heat aging test (elongation change rate)
After heat treatment in a gear oven at 250 ° C. for 70 hours, the elongation (EB) was measured at 23 ° C. in accordance with JIS K6251-2004, and the rate of change was determined by comparison with the elongation in (3).
Table 1 shows the compositions (parts by mass) of the respective materials used for sheet production in Examples [1] to [5], and the evaluation measurement results of the above characteristics.

As shown in Table 1, the sheet materials of Examples 1, 4 and 5 using fluoropolymers (P1 and P2) as crosslinking aids are the sheets of Example 2 and Example 3 using TAIC as the crosslinking aid. Compared to the material, the rate of change in tensile strength in the air heat aging test could be kept small, and the heat resistance was excellent.

By using the crosslinkable fluororubber composition of the present invention, a crosslinked rubber article having excellent chemical resistance (particularly amine resistance) and heat resistance can be obtained. O-ring, sheet, gasket, oil seal, bearing seal And is particularly useful as a sealing material for oil drilling.
The entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2010-266864 filed on November 30, 2010 are incorporated herein as the disclosure of the specification of the present invention. Is.

Claims (11)

1. A crosslinkable fluororubber composition comprising a fluororubber and the following fluoropolymer (P) having a plurality of polymerizable double bonds.
   Fluoropolymer (P): a fluoropolymer having repeating units derived from unsaturated side chain remaining fluorodiene (b).
2. The crosslinking according to claim 1, wherein the fluoropolymer (P) is a fluoropolymer having a repeating unit derived from the fluoromonoene (a) and a repeating unit derived from the unsaturated side chain remaining fluorodiene (b). Fluororubber composition.
3. The fluoromonoene (a) is tetrafluoroethylene, chlorotrifluoroethylene, and CF ₂ ═CFO—R ^f1 (wherein R ^f1 is a fluoroalkyl group having 1 to 6 carbon atoms, or a carbon atom-carbon atom) 3. The crosslinkable fluororubber composition according to claim 2, which is at least one selected from the group consisting of a C2-C6 fluoroalkyl group having at least one etheric oxygen atom.
4. The crosslinkable fluororubber composition according to any one of claims 1 to 3, wherein the fluorodiene (b) is at least one selected from the group consisting of the following fluorodienes (b1) to (b3).
   (B1) CF ₂ = CFO-Q ^f1 -OCF = CF ₂
   (B2) CH ₂ ═CFCF ₂ O—Q ^f2 —OCF ₂ CF═CH ₂
   (B3) CH ₂ ═CFCF ₂ O—Q ^f3 —OCF═CF ₂
   ( ^Wherein Q ^f1 and Q ^f2 each independently represents a fluoroalkylene group having 3 to 8 carbon atoms, or a fluoroalkylene group having 3 to 8 carbon atoms having one or more etheric oxygen atoms between carbon atoms and carbon atoms) It is.
   Q ^f3 is a fluoroalkylene group having 1 to 6 carbon atoms or a fluoroalkylene group having 2 to 6 carbon atoms having at least one etheric oxygen atom between carbon atoms. )
5. The crosslinkable fluororubber composition according to any one of claims 1 to 4, wherein the fluoropolymer (P) has a weight average molecular weight of 3,000 to 50,000.
6. The crosslinkable fluororubber composition according to any one of claims 1 to 5, wherein the content of the polymerizable double bond in the fluoropolymer (P) is 0.2 to 2 mmol / g.
7. The crosslinkable fluororubber composition according to any one of claims 1 to 6, comprising 1 to 50 parts by mass of the fluoropolymer (P) with respect to 100 parts by mass of the fluororubber.
8. The fluororubber is selected from the group consisting of a tetrafluoroethylene / propylene copolymer, a vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer, and a tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer. The crosslinkable fluororubber composition according to any one of claims 1 to 7, wherein the composition is at least one species.
9. The crosslinkable fluororubber composition according to any one of claims 1 to 8, further comprising an organic peroxide.
10. A crosslinked rubber article obtained by crosslinking the crosslinkable fluororubber composition according to claim 1 or 2.
11. The crosslinked rubber article according to claim 10, which is a sealing material.