WO2024090557A1

WO2024090557A1 - Fluoro rubber crosslinking composition and molded article

Info

Publication number: WO2024090557A1
Application number: PCT/JP2023/038892
Authority: WO
Inventors: 一良川崎
Original assignee: ダイキン工業株式会社
Priority date: 2022-10-27
Filing date: 2023-10-27
Publication date: 2024-05-02
Also published as: JP2024064171A

Abstract

Provided is a fluoro rubber crosslinking composition containing a fluoro rubber (a), a cross-linking agent (b), a hydrogen fluoride scavenger (c), and an organic peroxide (d). The cross-linking agent (b) is a compound having, in the molecule, 1) at least one aromatic ring, 2) a group having a carbon-carbon double bond (but excluding one forming the aromatic ring), and 3) an alkylcarbonyloxy group that is directly bound to a carbon atom forming the aromatic ring.

Description

Fluororubber crosslinking composition and molded product

This disclosure relates to a composition for crosslinking fluororubber and a molded article.

Patent document 1 describes a graftable fluoroelastomer composition that includes a polyhydroxy-curable fluoroelastomer that is substantially free of nucleophilic end groups; a monophenolic grafting agent; an accelerator; and an acid acceptor, and is characterized in that the composition has a Mooney viscosity of ML(1+18) of less than 160 at 135°C.

Patent Document 2 describes a curable partially fluorinated polymer composition that includes: (i) a partially fluorinated amorphous fluoropolymer that includes a carbon-carbon double bond or that can form a carbon-carbon double bond within the partially fluorinated amorphous fluoropolymer chain, the partially fluorinated amorphous fluoropolymer being substantially free of bromine, iodine, and nitrile; and (ii) a curing agent that includes a terminal olefin having at least one olefinic hydrogen.

JP 2008-502789 A JP 2017-538023 A

The objective of this disclosure is to provide a composition for cross-linking fluororubber that can produce molded products with high cross-linking density and excellent tensile strength.

According to the present disclosure, there is provided a composition for crosslinking fluororubber, which contains a fluororubber (a), a crosslinking agent (b), a dehydrofluorination agent (c), and an organic peroxide (d), and the crosslinking agent (b) is a compound having within its molecule 1) at least one aromatic ring, 2) a group having a carbon-carbon double bond (excluding those constituting the aromatic ring), and 3) an alkylcarbonyloxy group directly bonded to a carbon atom constituting the aromatic ring.

The present disclosure provides a fluororubber cross-linking composition that can produce molded products with high cross-linking density and excellent tensile strength.

Specific embodiments of the present disclosure are described in detail below, but the present disclosure is not limited to the following embodiments.

The disclosed composition for cross-linking fluororubber contains fluororubber (a), a cross-linking agent (b), a dehydrofluorination agent (c), and an organic peroxide (d).

In US Pat. No. 5,399,636, the above-mentioned compositions are proposed as compositions for making grafted fluoroelastomers, such as eugenol-grafted fluoroelastomers. A monophenol grafting agent, such as eugenol (2-methoxy-4-allylphenol), is used not as a crosslinking agent, but to make grafted fluoroelastomers that are resistant to premature vulcanization.

However, there is no known technology that uses a compound that has a group with a carbon-carbon double bond in the molecule and also has an aromatic ring to which an alkylcarbonyloxy group is bonded as a crosslinking agent for fluororubber.

By using a compound that has a group with a carbon-carbon double bond in the molecule and also has an aromatic ring to which an alkylcarbonyloxy group is bonded as a cross-linking agent for fluororubber, the cross-linking reaction of the fluororubber proceeds smoothly, the cross-linking density of the resulting molded product is surprisingly high, and the mechanical properties of the molded product, such as the tensile strength, are also improved.

The components of the disclosed fluororubber cross-linking composition are explained below.

(a) Fluororubber The fluororubber crosslinking composition of the present disclosure contains fluororubber. In the present disclosure, fluororubber is an amorphous fluoropolymer. "Amorphous" means that the magnitude of the melting peak (ΔH) that appears in differential scanning calorimetry [DSC] (heating rate 10°C/min) or differential thermal analysis [DTA] (heating rate 10°C/min) of the fluoropolymer is 4.5 J/g or less. Fluororubber exhibits elastomeric properties by crosslinking. Elastomeric properties refer to the property that the polymer can be stretched and can retain its original length when the force required to stretch the polymer is no longer applied.

The fluororubber may be partially fluorinated rubber or perfluororubber, but is preferably partially fluorinated rubber. Partially fluorinated rubber is a fluoropolymer that contains fluoromonomer units and has a perfluoromonomer unit content of less than 90 mol% relative to the total polymerized units, has a glass transition temperature of 20°C or less, and has a melting peak (ΔH) of 4.5 J/g or less.

A perfluoromonomer is a monomer that does not contain a carbon atom-hydrogen atom bond in the molecule. The above perfluoromonomer may be a monomer in which some of the fluorine atoms bonded to the carbon atoms are replaced with chlorine atoms, in addition to carbon atoms and fluorine atoms, and may also have nitrogen atoms, oxygen atoms, sulfur atoms, phosphorus atoms, boron atoms, or silicon atoms in addition to carbon atoms. The above perfluoromonomer is preferably a monomer in which all hydrogen atoms are replaced with fluorine atoms. The above perfluoromonomer does not include monomers that provide crosslinking sites.

The monomer that provides the crosslinking site is a monomer (cure site monomer) that has a crosslinkable group that provides the fluoropolymer with a crosslinking site for forming a crosslink with a crosslinking agent.

The fluororubber used in the present disclosure is not particularly limited, and examples thereof include fluororubber known as peroxide-crosslinkable fluororubber, fluororubber known as polyol-crosslinkable fluororubber, and the like. In addition, the fluororubber may be a fluororubber that can be crosslinked using a pyridinium-type salt as described in JP-T-2018-514627.

　Peroxide-crosslinkable fluororubber is a fluororubber having a peroxide-crosslinkable site. The peroxide-crosslinkable site is not particularly limited, and examples include iodine atoms, bromine atoms, and CN groups that the fluororubber has; and carbon-carbon unsaturated bonds that exist in the main chain or side chain of the fluororubber. In the present disclosure, a peroxide-crosslinkable fluororubber may be used as the fluororubber, but this does not mean that the crosslinking reaction of the fluororubber crosslinking composition of the present disclosure proceeds in the same manner as the crosslinking reaction of a conventionally known peroxide-crosslinkable fluororubber.

The polyol-crosslinkable fluororubber is a fluororubber having a polyol-crosslinkable site. As the polyol-crosslinkable fluororubber, polyol-crosslinkable partially fluorinated rubber is preferable. As the polyol-crosslinkable fluororubber, there is no particular limitation, and examples thereof include vinylidene fluoride (VdF)-based fluororubber. In the present disclosure, a polyol-crosslinkable fluororubber may be used as the fluororubber, but this does not mean that the crosslinking reaction of the fluororubber crosslinking composition of the present disclosure proceeds in the same manner as the crosslinking reaction of a conventionally known polyol-crosslinkable fluororubber.

Examples of fluororubbers that have sites that can be crosslinked with polyols include VdF-based fluororubbers and rubbers that have functional sites in the side chains and/or main chains that can be crosslinked with polyols.

The fluororubber used in this disclosure is preferably a fluororubber containing vinylidene fluoride (VdF) units (VdF-based fluororubber).

Examples of VdF-based fluororubbers include tetrafluoroethylene (TFE)/propylene/VdF-based fluororubbers, ethylene/hexafluoropropylene (HFP)/VdF-based fluororubbers, VdF/HFP-based fluororubbers, and VdF/TFE/HFP-based fluororubbers. These fluororubbers having polyol-crosslinkable sites can be used alone or in any combination within the scope that does not impair the effects of the present disclosure.

Among these, the fluororubber is preferably a fluororubber made of VdF and at least one other fluorine-containing monomer, and in particular at least one rubber selected from the group consisting of VdF/HFP-based fluororubber, VdF/TFE/HFP-based fluororubber, and VdF/TFE/PAVE-based fluororubber, and more preferably at least one rubber selected from the group consisting of VdF/HFP-based fluororubber and VdF/TFE/HFP-based fluororubber.

The fluororubber preferably has a Mooney viscosity at 100°C (ML1+10(100°C)) of 2 or more, more preferably 10 or more, even more preferably 20 or more, and particularly preferably 30 or more. It is also preferably 200 or less, more preferably 150 or less, even more preferably 120 or less, and particularly preferably 100 or less. Mooney viscosity is measured in accordance with ASTM D1646-15 and JIS K6300-1:2013.

The fluorine content of the fluororubber is preferably 50 to 75% by mass. More preferably, it is 60 to 73% by mass, and even more preferably, it is 63 to 72% by mass. The fluorine content is calculated from the composition ratio of the monomer units that make up the fluororubber.

The fluororubber preferably has a glass transition temperature of -50 to 0°C. The glass transition temperature can be determined by obtaining a DSC curve using a differential scanning calorimeter by heating 10 mg of a sample at 20°C/min, and finding the temperature at the intersection of an extension of the baseline before and after the secondary transition of the DSC curve and a tangent to the inflection point of the DSC curve.

The fluororubber may have at least one of iodine atoms and bromine atoms, or may have iodine atoms. The total content of iodine atoms and bromine atoms in the fluororubber is preferably 0.001 to 10 mass%, more preferably 5.0 mass% or less, even more preferably 1.0 mass% or less, particularly preferably 0.7 mass% or less, most preferably 0.5 mass% or less, more preferably 0.01 mass% or more, even more preferably 0.05 mass% or more, particularly preferably 0.08 mass% or more, and most preferably 0.10 mass% or more. The bonding positions of the iodine atoms and bromine atoms in the fluororubber may be the terminals of the main chain or the terminals of the side chain of the fluororubber, or of course both.

The iodine content can be measured by the following method: Na ₂ CO ₃ and K ₂ CO ₃ are mixed in a 1:1 (weight ratio), and the resulting mixture is dissolved in 20 ml of pure water to prepare an absorption liquid, and 5 mg of Na ₂ SO ₃ is mixed with 12 mg of a sample (fluoropolymer) to prepare a mixture, which is burned in oxygen in a quartz flask, and the generated combustion gas is introduced into the absorption liquid, and the resulting absorption liquid is left to stand for 30 minutes, after which the concentration of iodine ions in the absorption liquid is measured using a Shimadzu 20A ion chromatograph, and the iodine ion content can be determined from the measured value using a calibration curve prepared using a KI standard solution containing 0.5 ppm iodine ions and a KI standard solution containing 1.0 ppm iodine ions.

Fluororubber containing at least one of iodine and bromine atoms can be produced, for example, by a method of polymerizing iodine- or bromine-containing monomers, or by a method of polymerizing using a bromine compound or an iodine compound as a polymerization initiator or chain transfer agent.

Examples of the polymerization method using a bromine compound or an iodine compound as a chain transfer agent include a method in which emulsion polymerization is carried out in an aqueous medium under pressure in the presence of a bromine compound or an iodine compound in a substantially oxygen-free state (iodine transfer polymerization method).
General formula _: ^R8IxBr _y
(wherein x and y are each an integer of 0 to 2 and satisfy 1≦x+y≦2; and ^R8 is a saturated or unsaturated fluorohydrocarbon group or chlorofluorohydrocarbon group having 1 to 16 carbon atoms, or a hydrocarbon group having 1 to 3 carbon atoms, which may contain an oxygen atom).

Examples of the bromine compound and the iodine compound include 1,3-diiodoperfluoropropane, 2-iodoperfluoropropane, 1,3-diiodo-2-chloroperfluoropropane, 1,4-diiodoperfluorobutane, 1,5-diiodo-2,4-dichloroperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, 1,12-diiodoperfluorododecane, 1,16-diiodoperfluorohexadecane, diiodomethane, 1,2-diiodoethane, 1,3-diiodo-n-propane, CF ₂ Br ₂ , BrCF ₂ CF ₂ Br, CF ₃ CFBrCF ₂ Br, CFClBr ₂ , BrCF ₂ CFClBr, CFBrClCFClBr, BrCF ₂ CF ₂ Examples of such compounds include CF ₂ Br, BrCF ₂ CFBrOCF ₃ , 1-bromo-2-iodoperfluoroethane, 1-bromo-3-iodoperfluoropropane, 1-bromo-4-iodoperfluorobutane, 2-bromo-3-iodoperfluorobutane, 3-bromo-4-iodoperfluorobutene-1, 2-bromo-4-iodoperfluorobutene-1, monoiodomonobromo-substituted benzene, diiodomonobromo-substituted benzene, and (2-iodoethyl) and (2-bromoethyl)-substituted benzene. These compounds may be used alone or in combination with each other.

Among these, it is preferable to use 1,4-diiodoperfluorobutane, 1,6-diiodoperfluorohexane, and 2-iodoperfluoropropane in terms of polymerization reactivity, crosslinking reactivity, and ease of availability.

(b) Crosslinking Agent The fluororubber crosslinking composition of the present disclosure contains a crosslinking agent.

In one embodiment, the first crosslinker is:
1) at least one aromatic ring;
2) a group having a carbon-carbon double bond (excluding those constituting the aromatic ring), and
3) A compound having an alkylcarbonyloxy group in the molecule directly bonded to a carbon atom constituting the aromatic ring is used.

The aromatic ring may be either a monocyclic or polycyclic ring. The aromatic ring may be a so-called heterocyclic ring composed not only of carbon atoms but also of carbon atoms and heteroatoms such as oxygen atoms, sulfur atoms, and nitrogen atoms. In the aromatic ring, the carbon atom of the carbonyl group may form a ring structure.

Examples of monocyclic aromatic rings include monocyclic 5- to 7-membered aromatic rings, and specifically, preferred are a benzene ring and a monocyclic 5- to 7-membered aromatic heterocycle (including a 7-membered ring with a tropone structure), more preferred are a benzene ring, a furan ring, and a thiophene ring, and even more preferred is a benzene ring.

The number of aromatic rings in the polycyclic aromatic ring is 2 or more, preferably 2 to 8, more preferably 2 to 4, even more preferably 2 or 3, and most preferably 2.

As the polycyclic aromatic ring, a polycyclic aromatic hydrocarbon ring or a polycyclic aromatic heterocycle is preferred, and a polycyclic aromatic hydrocarbon ring is more preferred. The polycyclic aromatic hydrocarbon ring may be a polycycle in which two rings are linked via a bond, a condensed ring, or a spiro ring.

The number of carbon atoms in the polycyclic aromatic hydrocarbon ring is preferably 3 to 30, more preferably 5 or more, even more preferably 6 or more, more preferably 20 or less, even more preferably 14 or less.

The number of rings in the polycyclic aromatic hydrocarbon ring is preferably 2 to 4, more preferably 2 or 3, and even more preferably 2.

Polycyclic aromatic hydrocarbon rings include:
Polycyclic aromatic hydrocarbon rings in which two rings are linked via a bond, such as a biphenyl ring, a diphenylmethane ring, a diphenyl ether ring, a diphenyl sulfone ring, or a diphenyl ketone ring;
condensed polycyclic hydrocarbon rings such as a naphthalene ring, a phenanthrene ring, an anthracene ring, a fluorene ring, a tetracene ring, a chrysene ring, a pyrene ring, a pentacene ring, a benzopyrene ring, a triphenylene ring, and an azulene ring;
etc.

Among the polycyclic aromatic hydrocarbon rings, a naphthalene ring or a biphenyl ring is preferred.

In polycyclic aromatic heterocycles, the carbonyl group may form part of the aromatic ring. Polycyclic aromatic heterocycles also include rings that are composed only of carbon atoms and oxygen atoms of carbonyl groups.

As a polycyclic aromatic heterocycle, a ring formed by carbon atoms and atoms other than carbon atoms is preferable. As the atom other than carbon atoms, a nitrogen atom, an oxygen atom, or a sulfur atom is preferable, and an oxygen atom or a sulfur atom is more preferable. That is, as a heterocycle, a nitrogen-containing heterocycle, an oxygen-containing heterocycle, or a sulfur-containing heterocycle is preferable, and an oxygen-containing heterocycle or a sulfur-containing heterocycle is more preferable. The number of atoms other than carbon atoms in the ring is preferably 1 to 3.

The number of rings in the polycyclic aromatic heterocycle is preferably 2 to 4, more preferably 2 or 3, and even more preferably 2.

As the polycyclic aromatic heterocycle, oxygen-containing polycyclic aromatic heterocycles are preferred, such as a xanthene ring, a 1-benzopyran ring, a 2-benzopyran ring, a 1-benzofuran ring, and a 2-benzofuran ring.

The aromatic ring is preferably a benzene ring, a naphthalene ring, or a biphenyl ring, since this allows for a molded product with a higher crosslink density and superior tensile strength to be obtained.

The first crosslinking agent has a group having a carbon-carbon double bond in addition to an aromatic ring. The group having a carbon-carbon double bond includes a vinyl group as well as a group that contains a carbon-carbon double bond as part of its structure, such as an allyl group. The number of groups having a carbon-carbon double bond is preferably 1 or more, more preferably 1 or 2, and even more preferably 1.

The group having a carbon-carbon double bond may be directly bonded to a carbon atom constituting the aromatic ring, or may be bonded to a carbon atom constituting the aromatic ring via another bond. It is preferable that the group having a carbon-carbon double bond is directly bonded to a carbon atom constituting the aromatic ring, since this allows for the production of molded products with a higher crosslink density and superior tensile strength.

As the group having a carbon-carbon double bond, at least one selected from the group consisting of vinyl groups, allyl groups, and vinyloxy groups is preferred, as this allows for the production of molded products with higher crosslink density and superior tensile strength, and at least one selected from the group consisting of vinyl groups and allyl groups is more preferred.

As the alkylcarbonyloxy group, a group represented by the general formula:
R-C(=O)-O-
(wherein R is a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a fluorinated alkyl group having 1 to 5 carbon atoms) is preferred. The number of carbon atoms in the alkyl group and the fluorinated alkyl group is preferably 1 to 3, and more preferably 1. R is preferably a methyl group.

Hydrogen atoms bonded to carbon atoms constituting the aromatic ring may be substituted with a substituent other than a group having a carbon-carbon double bond and an alkylcarbonyloxy group. As such a substituent, a substituent (γ) (excluding substituents containing a hydroxyl group and alkylcarbonyloxy groups) in which at least one of the values of Hammett's substituent constants σm and σp is 0.03 or more is preferable. By directly bonding the substituent (γ) to the carbon atom constituting the aromatic ring, the electron density of the alkylcarbonyloxy group bonded directly to the carbon atom constituting the aromatic ring can be appropriately adjusted, thereby improving the properties of the molded article obtained from the fluororubber crosslinking composition.

Substituents (γ) do not include substituents containing a hydroxy group or alkylcarbonyloxy groups. Substituents containing a hydroxy group include hydroxy groups and groups that have a hydroxy group as part of their structure.

The number of substituents (γ) is preferably 0 to 4, more preferably 0 to 2, and even more preferably 0 or 1.

The substituent (γ) is a monovalent substituent in which at least one of the Hammett substituent constants σm and σp is in the range of 0.03 or more.

At least one of the substituent constants σm and σp of the substituent (γ) is 0.03 or more, preferably 0.05 or more, more preferably 0.10 or more, preferably 1.40 or less, more preferably 1.00 or less, and even more preferably 0.80 or less.

In one embodiment, the value of the substituent constant σm of the substituent (γ) is 0.03 or more, preferably 0.05 or more, more preferably 0.10 or more, preferably 1.40 or less, more preferably 1.00 or less, and even more preferably 0.80 or less.

In one embodiment, the value of the substituent constant σp of the substituent (γ) is 0.03 or more, preferably 0.05 or more, more preferably 0.10 or more, preferably 1.40 or less, more preferably 1.00 or less, and even more preferably 0.80 or less.

Hammett's rule is an empirical rule proposed by L. P. Hammett in 1935 to quantitatively discuss the effect of substituents on the reaction or equilibrium of benzene derivatives, and is widely recognized as valid today. The substituent constants determined by Hammett's rule include σp and σm values, and these values can be found in many general textbooks, but in this invention, the values described in "TABLE 1 Hammett and Modified Swain-Lupton Constants" in Chem. Rev., 1991, Vol. 91, pp. 165-195 are used. For substituents not described in the above literature, values calculated according to the calculation method described in the literature "The Effect of Structure upon the Reactions of Organic Compounds. Benzene Derivatives" (J. Am. Chem. Soc. 1937, 59, 1, 96-103) are used.

The first crosslinking agent also includes those that are not benzene derivatives, but the σm value and σp value are used as a measure of the electronic effect of the substituent, regardless of the substitution position. In this disclosure, the σm value and σp value are used in this sense.

Specific examples of the substituent (γ) include partially fluorinated alkyl groups having 1 to 5 carbon atoms, perfluoroalkyl groups having 1 to 5 carbon atoms, fluorine atoms, chlorine atoms, alkoxycarbonyl groups having 1 to 5 carbon atoms (excluding the number of carbon atoms constituting the carbonyl group), partially fluorinated alkoxycarbonyl groups having 1 to 5 carbon atoms (excluding the number of carbon atoms constituting the carbonyl group), perfluoroalkoxycarbonyl groups having 1 to 5 carbon atoms (excluding the number of carbon atoms constituting the carbonyl group), alkoxy groups having 1 to 5 carbon atoms, partially fluorinated alkoxy groups having 1 to 5 carbon atoms, perfluoroalkoxy groups having 1 to 5 carbon atoms, and the number of carbon atoms (excluding the number of carbon atoms constituting the carbonyl group). Examples of such groups include acyloxy groups with 1 to 5 carbon atoms (excluding the number of carbon atoms that make up the carbonyl group) in which a portion is fluorinated, perfluoroacyloxy groups with 1 to 5 carbon atoms (excluding the number of carbon atoms that make up the carbonyl group), acyl groups with 0 to 5 carbon atoms (excluding the number of carbon atoms that make up the carbonyl group), acyl groups with 0 to 5 carbon atoms (excluding the number of carbon atoms that make up the carbonyl group) in which a portion is fluorinated, perfluoroacyl groups with 0 to 5 carbon atoms (excluding the number of carbon atoms that make up the carbonyl group), alkylsulfonyl groups with 1 to 5 carbon atoms, alkylsulfonyl groups with 1 to 5 carbon atoms in which a portion is fluorinated, perfluoroalkylsulfonyl groups with 1 to 5 carbon atoms, and trimethoxysilyl groups.

As the substituent (γ), at least one selected from the group consisting of a partially fluorinated alkyl group having 1 to 5 carbon atoms, a perfluoroalkyl group having 1 to 5 carbon atoms, a fluorine atom, a chlorine atom, an alkoxy group having 1 to 5 carbon atoms, an alkoxycarbonyl group having 0 to 5 carbon atoms (excluding the number of carbon atoms constituting the carbonyl group), and an acyl group having 0 to 5 carbon atoms (excluding the number of carbon atoms constituting the carbonyl group) is preferred, and a perfluoroalkyl group having 1 to 5 carbon atoms, a fluorine atom, a chlorine atom, an alkoxy group having 1 to 5 carbon atoms, an alkoxycarbonyl group having 0 to 5 carbon atoms (excluding the number of carbon atoms constituting the carbonyl group), And, it is more preferable that it is at least one type selected from the group consisting of acyl groups having 0 to 5 carbon atoms (excluding the number of carbon atoms constituting the carbonyl group), and even more preferable that it is at least one type selected from the group consisting of perfluoroalkyl groups having 1 to 5 carbon atoms, fluorine atoms, chlorine atoms, and acyl groups having 0 to 5 carbon atoms (excluding the number of carbon atoms constituting the carbonyl group), and even more preferable that it is at least one type selected from the group consisting of chlorine atoms, fluorine atoms, acetyl groups, methoxycarbonyl groups, and methoxy groups, and particularly preferable that it is at least one type selected from the group consisting of acetyl groups and methoxycarbonyl groups.

The hydrogen atoms bonded to the carbon atoms constituting the aromatic ring of the first crosslinking agent may or may not be substituted with any substituent other than the substituent (γ), but it is preferable that they are not substituted with any substituent other than the substituent (γ) so as not to impair the function of the substituent (γ) that gives the hydroxy group an appropriate electron density. In one embodiment, the aromatic ring of the crosslinking agent is not substituted with any substituent other than a group having a carbon-carbon double bond and an alkylcarbonyloxy group.

As the first crosslinking agent, at least one selected from the group consisting of compounds represented by general formulas (b1) to (b3) is preferred, at least one selected from the group consisting of compounds represented by general formulas (b1) to (b2) is more preferred, a compound represented by general formula (b1) is even more preferred, and at least one selected from the group consisting of 4-vinylphenyl acetate and 4-allylphenol is particularly preferred, since this allows for the production of molded products with a higher crosslinking density and superior tensile strength.

General formula (b1):

(In the formula, R is a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a fluorinated alkyl group having 1 to 5 carbon atoms; X is a vinyl group, an allyl group, or a vinyloxy group; Y is H, or a substituent (γ) having at least one of the Hammett substituent constants σm and σp of 0.03 or more (excluding substituents containing a hydroxy group and alkylcarbonyloxy groups).)

General formula (b2):

(In the formula, R represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a fluorinated alkyl group having 1 to 5 carbon atoms; X represents a vinyl group, an allyl group, or a vinyloxy group; Y and Z each independently represent H or a substituent (γ) having at least one of the Hammett substituent constants σm and σp of 0.03 or more (excluding substituents containing a hydroxy group and alkylcarbonyloxy groups).

General formula (b3):

(wherein R is a hydrogen atom, an alkyl group having 1 to 5 carbon atoms or a fluorinated alkyl group having 1 to 5 carbon atoms; X is a vinyl group, an allyl group or a vinyloxy group; Y and Z are each independently H or a substituent (γ) having at least one value of Hammett's substituent constants σm and σp of 0.03 or more (excluding substituents containing a hydroxyl group and alkylcarbonyloxy groups); A is a bond, an alkylene group having 1 to 13 carbon atoms, an arylene group having 6 to 13 carbon atoms, a thiocarbonyl group, an oxygen atom, a carbonyl group, a sulfinyl group or a sulfonyl group; in the alkylene group and arylene group of A, some or all of the hydrogen atoms bonded to carbon atoms may be substituted with chlorine atoms or fluorine atoms; and ring B and ring C are each independently a monocyclic or polycyclic aromatic ring.)

In the same formula, Y and Z may be the same or different. Furthermore, in general formulas (b1) to (b3), R, X, Y and Z are each independent, and therefore R, X, Y and Z in the three general formulas may be different for each general formula.

In general formulas (b1) to (b3), R is a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a fluorinated alkyl group having 1 to 5 carbon atoms. The number of carbon atoms in the alkyl group and fluorinated alkyl group of R is preferably 1 to 3, and more preferably 1. R is preferably a methyl group.

In general formulas (b1) to (b3), X is a vinyl group, an allyl group, or a vinyloxy group. X is preferably a vinyl group or an allyl group.

In general formulas (b1) to (b3), Y is H or a substituent (γ) in which at least one of the Hammett substituent constants σm and σp is 0.03 or more (excluding substituents containing a hydroxyl group and alkylcarbonyloxy groups). The substituent (γ) is as described above.

Y is preferably at least one selected from the group consisting of a hydrogen atom, a chlorine atom, a fluorine atom, an acetyl group, a methoxycarbonyl group, and a methoxy group, more preferably at least one selected from the group consisting of a hydrogen atom, an acetyl group, and a methoxycarbonyl group, even more preferably at least one selected from the group consisting of a hydrogen atom, an acetyl group, and a methoxycarbonyl group, and particularly preferably a hydrogen atom.

In general formulas (b2) to (b3), Z is H or a substituent (γ) in which at least one of the Hammett substituent constants σm and σp is 0.03 or greater (excluding substituents containing a hydroxyl group and alkylcarbonyloxy groups). The substituent (γ) is as described above.

Z is preferably at least one selected from the group consisting of a hydrogen atom, a chlorine atom, a fluorine atom, an acetyl group, a methoxycarbonyl group, and a methoxy group, more preferably at least one selected from the group consisting of a hydrogen atom, an acetyl group, and a methoxycarbonyl group, even more preferably at least one selected from the group consisting of a hydrogen atom, an acetyl group, and a methoxycarbonyl group, and particularly preferably a hydrogen atom.

In general formula (b3), A represents the type of bond connecting the two aromatic rings, and is a bond, an alkylene group having 1 to 13 carbon atoms, an arylene group having 6 to 13 carbon atoms, a thiocarbonyl group, an oxygen atom, a carbonyl group, a sulfinyl group, or a sulfonyl group. In the alkylene group and arylene group of A, some or all of the hydrogen atoms bonded to the carbon atoms may be replaced by chlorine atoms or fluorine atoms.

A is preferably a bond or an alkylene group having 1 to 13 carbon atoms, more preferably a bond.

Ring B and ring C are each independently a monocyclic or polycyclic aromatic ring. The aromatic ring may be a so-called heterocyclic ring composed not only of carbon atoms but also of carbon atoms and heteroatoms such as oxygen atoms, sulfur atoms, and nitrogen atoms. The carbon atom of the carbonyl group may also constitute a ring structure.

As ring B and ring C, a monocyclic ring is preferred, since it allows the production of a molded product with a higher crosslink density and superior tensile strength, a monocyclic 5- to 7-membered aromatic ring is more preferred, a benzene ring and a monocyclic 5- to 7-membered aromatic heterocycle (including a 7-membered ring with a tropone structure) are even more preferred, a benzene ring, a furan ring and a thiophene ring are even more preferred, and a benzene ring is particularly preferred.

In general formula (b3), it is preferable that rings B and C are both benzene rings, since this allows for a molded product to be obtained that has a higher crosslink density and is more excellent in tensile strength. In other words, the compound (b3) represented by general formula (b3) is preferably a compound represented by general formula (b3-1).

General formula (b3-1):

(In the formula, R, X, Y, Z and A are as defined above.)

In one embodiment, at least one selected from the group consisting of compounds represented by formulae (b4) to (b7) is used as the second crosslinking agent.

(In each formula, R is a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a fluorinated alkyl group having 1 to 5 carbon atoms.)

The compounds represented by formulas (b4) to (b7) do not have any other substituents than hydroxyl groups, groups having a carbon-carbon double bond (excluding those constituting an aromatic ring), and alkylcarbonyloxy groups represented by -OC(=O)R.

The compounds represented by formulae (b4) and (b5) are not compounds that have a double bond and an aromatic ring to which an alkylcarbonyloxy group is bonded, but when used as a crosslinking agent, they smoothly promote the crosslinking reaction of the fluororubber, just like the compounds represented by formulae (b6) and (b7), and give molded products with high crosslink density and excellent tensile strength.

As the second crosslinking agent, at least one selected from the group consisting of compounds represented by formula (b5) and formula (b6) is preferred.

The content of the crosslinking agent is preferably 0.1 to 10 parts by mass, more preferably 0.5 parts by mass or more, even more preferably 0.7 parts by mass or more, more preferably 7 parts by mass or less, and even more preferably 5 parts by mass or less, so that the crosslinking reaction in the crosslinking step proceeds at an appropriate speed and a molded product can be obtained that has sufficient tensile strength, elongation at break, and compression set properties at high temperatures, as well as appropriate hardness.

(c) Dehydrofluorination Agent The fluororubber crosslinking composition of the present disclosure contains a dehydrofluorination agent. The use of the dehydrofluorination agent can promote the formation of an intramolecular double bond in the dehydrofluorination reaction of the fluororubber main chain, thereby promoting the crosslinking reaction.

Onium compounds are generally used as dehydrofluorination agents. There are no particular limitations on the onium compounds, and examples include ammonium salts such as quaternary ammonium salts, phosphonium salts such as quaternary phosphonium salts, and sulfonium salts, with quaternary ammonium salts and quaternary phosphonium salts being preferred.

The quaternary ammonium salt is not particularly limited, and examples thereof include 8-methyl-1,8-diazabicyclo[5,4,0]-7-undecenium chloride, 8-methyl-1,8-diazabicyclo[5,4,0]-7-undecenium iodide, 8-methyl-1,8-diazabicyclo[5,4,0]-7-undecenium hydroxide, and 8-methyl-1,8-diazabicyclo[5,4,0]-7-undecenium methylsulfate. ester, 8-ethyl-1,8-diazabicyclo[5,4,0]-7-undecenium bromide, 8-propyl-1,8-diazabicyclo[5,4,0]-7-undecenium bromide, 8-dodecyl-1,8-diazabicyclo[5,4,0]-7-undecenium chloride, 8-dodecyl-1,8-diazabicyclo[5,4,0]-7-undecenium hydroxide, 8-eicosyl-1,8-diazabicyclo[5,4,0]- 7-undecenium chloride, 8-tetracosyl-1,8-diazabicyclo[5,4,0]-7-undecenium chloride, 8-benzyl-1,8-diazabicyclo[5,4,0]-7-undecenium chloride (hereinafter referred to as DBU-B), 8-benzyl-1,8-diazabicyclo[5,4,0]-7-undecenium hydroxide, 8-phenethyl-1,8-diazabicyclo[5,4,0]-7-undecenium chloride, 8-(3-phenylpropyl)-1,8-diazabicyclo[5,4,0]-7-undecenium chloride, benzyldimethyloctadecylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride, benzyltributylammonium chloride, benzyltriethylammonium chloride, tetrabutylammonium hydrogen sulfate, and tetrabutylammonium hydroxide. Among these, DBU-B or benzyldimethyloctadecylammonium chloride are preferred in terms of crosslinking properties and physical properties of the crosslinked product.

Furthermore, the quaternary phosphonium salt is not particularly limited, and examples thereof include tetrabutylphosphonium chloride, benzyltriphenylphosphonium chloride (hereinafter referred to as BTPPC), benzyltrimethylphosphonium chloride, benzyltributylphosphonium chloride, tributylallylphosphonium chloride, tributyl-2-methoxypropylphosphonium chloride, and benzylphenyl(dimethylamino)phosphonium chloride. Among these, benzyltriphenylphosphonium chloride (BTPPC) is preferred in terms of crosslinkability and the physical properties of the crosslinked product.

The content of the dehydrofluorination agent is preferably 0.1 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, even more preferably 0.1 to 3 parts by mass, and particularly preferably 0.1 to 1.5 parts by mass, per 100 parts by mass of fluororubber, because this allows the crosslinking reaction to proceed at an appropriate speed and allows for the production of even better molded products due to the compression set properties at high temperatures.

(d) Organic Peroxide The fluororubber crosslinking composition of the present disclosure contains an organic peroxide.

As organic peroxides, those which easily generate peroxy radicals in the presence of heat or an oxidation-reduction system are preferred. Specific examples include 1,1-bis(t-butylperoxy)-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-bis(t-butylperoxy)hexane, 2,5-dimethyl-2,5-bis(t-butylperoxy)-hexyne-3, benzoyl peroxide, t-butylperoxybenzene, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butylperoxymaleic acid, t-butylperoxyisopropylcarbonate, and t-butylperoxybenzoate. Among these, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane and 2,5-dimethyl-2,5-bis(t-butylperoxy)-hexyne-3 are preferred.

The content of organic peroxide is preferably 0.05 to 10 parts by mass, more preferably 0.1 part by mass or more, more preferably 5 parts by mass or less, and even more preferably 1 part by mass or less, per 100 parts by mass of fluororubber, since this allows for a molded product with a higher crosslink density and superior tensile strength to be obtained.

(e) Acid Acceptor The fluororubber crosslinking composition of the present disclosure may further contain an acid acceptor. By containing an acid acceptor, the crosslinking reaction of the fluororubber crosslinking composition proceeds more smoothly, and the compression set properties at high temperatures are further improved.

Examples of acid acceptors include metal oxides such as magnesium oxide, calcium oxide, bismuth oxide, and zinc oxide; metal hydroxides such as calcium hydroxide; alkali metal silicates such as hydrotalcite and sodium metasilicate, which are described in JP-T-2011-522921; and metal salts of weak acids such as those described in JP-A-2003-277563. Examples of metal salts of weak acids include carbonates, benzoates, oxalates, and phosphites of Ca, Sr, Ba, Na, and K.

As the acid acceptor, at least one selected from the group consisting of metal oxides, metal hydroxides, alkali metal silicates, metal salts of weak acids, and hydrotalcite is preferred, since it allows the production of molded articles with even better compression set properties at high temperatures, and at least one selected from the group consisting of sodium metasilicate hydrate, calcium hydroxide, magnesium oxide, bismuth oxide, and hydrotalcite is more preferred. Furthermore, when the resulting molded article requires good water resistance, acid resistance, or resistance to organic acid esters, including biodiesel, the acid acceptor is preferably at least one selected from the group consisting of bismuth oxide and hydrotalcite.

In the fluororubber crosslinking composition, the content of the acid acceptor is preferably 0.1 to 100 parts by mass, more preferably 1 to 50 parts by mass, even more preferably 1 to 30 parts by mass, and particularly preferably 1 to 20 parts by mass, per 100 parts by mass of the fluororubber, since this allows for the production of molded products with better compression set properties at high temperatures.

If the content of the acid acceptor is high, the water resistance, acid resistance, and resistance to organic acid esters, including biodiesel, of the resulting molded product tend to decrease, while if the content of the acid acceptor is low, the crosslinking speed decreases and the mechanical properties tend to decrease due to the decrease in crosslink density. Therefore, the content of the acid acceptor can be selected according to the application of the resulting molded product. In addition, if an acid acceptor other than calcium hydroxide is contained, the content of calcium hydroxide can be reduced to 0 to 1.5 parts by mass, and the content of the other acid acceptor can be adjusted to adjust the crosslink density, thereby obtaining a molded product with better compression set properties at high temperatures.

(f) Other Components The fluororubber crosslinking composition may be blended with various additives as necessary, such as usual additives blended in fluororubber crosslinking compositions, for example, fillers (carbon black, bituminous coal, barium sulfate, diatomaceous earth, calcined clay, talc, wollastonite, carbon nanotubes, etc.), processing aids (waxes, etc.), plasticizers, colorants, stabilizers, tackifiers (coumarone resins, coumarone-indene resins, etc.), release agents, electrical conductivity imparting agents, thermal conductivity imparting agents, surface non-tackifiers, flexibility imparting agents, heat resistance improving agents, flame retardants, foaming agents, and antioxidants described in WO 2012/023485, and may also be blended with one or more usual crosslinking agents and dehydrofluorination agents different from the above.

Among these, the preferred carbon blacks are thermal carbon black and furnace carbon black, with MT carbon black, FT carbon black and SRF carbon black being more preferred. When carbon black or carbon black with a relatively large particle size such as FT carbon black is blended, molded products with excellent compression set properties are obtained, while when carbon black with a fine particle size is blended, molded products with excellent strength and elongation are obtained. By blending different grades together, the above properties can be balanced.

Other than carbon black, preferred fillers include barium sulfate and wollastonite.

Processing aids are not particularly limited, but may include, for example, aliphatic amines such as stearylamine, fatty acid esters such as stearic acid esters and sebacic acid esters, fatty acid amides such as stearic acid amide, long-chain alkyl alcohols, natural waxes, polyethylene waxes, phosphate esters such as tricresyl phosphate, silicone-based processing aids, etc., and blending two or more types in appropriate amounts as necessary can improve the balance between mold releasability during molding and the physical properties of the molded product.

The content of the filler such as carbon black is not particularly limited, but is preferably 0 to 300 parts by mass, more preferably 1 to 150 parts by mass, even more preferably 2 to 100 parts by mass, and particularly preferably 2 to 75 parts by mass, per 100 parts by mass of the fluororubber.

The content of processing aids such as wax is preferably 0 to 10 parts by mass, more preferably 0 to 5 parts by mass, and particularly preferably 0 to 2 parts by mass, per 100 parts by mass of fluororubber. The use of processing aids, plasticizers, and release agents tends to reduce the mechanical properties and sealing properties of the resulting molded product, so it is necessary to adjust the content of these agents within a range that allows for the desired properties of the resulting molded product.

The fluororubber cross-linking composition may contain a dialkyl sulfone compound. By containing a dialkyl sulfone compound, the cross-linking efficiency of the fluororubber cross-linking composition is increased, the cross-linking speed is increased, the compression set property is further improved, and the fluidity of the rubber material is improved. Examples of dialkyl sulfone compounds include dimethyl sulfone, diethyl sulfone, dibutyl sulfone, methyl ethyl sulfone, diphenyl sulfone, and sulfolane. Among them, sulfolane is preferred from the viewpoint of cross-linking efficiency and compression set property, as well as because it has an appropriate boiling point. The content of the dialkyl sulfone compound is preferably 0 to 10 parts by mass, more preferably 0 to 5 parts by mass, and particularly preferably 0 to 3 parts by mass, per 100 parts by mass of the fluororubber. When the fluororubber cross-linking composition of the present disclosure contains a dialkyl sulfone compound, the lower limit of the content of the dialkyl sulfone compound may be, for example, 0.1 parts by mass or more per 100 parts by mass of the fluororubber.

The dialkyl sulfone compound and the processing aid may be blended together, as this provides a good balance between the crosslinking rate, the fluidity of the rubber material during molding, the mold releasability during molding, and the mechanical properties of the molded product.

The fluororubber crosslinking composition is obtained by kneading the fluororubber (a), the crosslinking agent (b), the dehydrofluorination agent (c), the organic peroxide (d), etc., using a commonly used rubber kneading device. Examples of the rubber kneading device that can be used include a roll, a kneader, a Banbury mixer, an internal mixer, and a twin-screw extruder.

In order to disperse each component uniformly in the rubber, some of the components may be kneaded while melting them at a high temperature of 100 to 200°C using a closed kneading device such as a kneader, and then the remaining components may be kneaded at a relatively low temperature below this temperature.

Furthermore, the dispersibility can be further improved by mixing the fluororubber (a), crosslinking agent (b), dehydrofluorination agent (c), organic peroxide (d), etc., leaving the mixture at room temperature for 12 hours or more, and then mixing again.

<Molded products>
The molded article of the present disclosure can be obtained by crosslinking the fluororubber crosslinking composition. The molded article of the present disclosure can also be obtained by molding and crosslinking the fluororubber crosslinking composition. The fluororubber crosslinking composition can be molded by a conventionally known method. The molding and crosslinking methods and conditions may be within the range of known methods and conditions for the molding and crosslinking to be adopted. The order of molding and crosslinking is not limited, and molding may be followed by crosslinking, crosslinking may be followed by molding, or molding and crosslinking may be performed simultaneously.

Examples of molding methods include, but are not limited to, compression molding, casting, injection molding, extrusion molding, and roto-cure molding. Examples of crosslinking methods that can be used include steam crosslinking, heat crosslinking, and radiation crosslinking, with steam crosslinking and heat crosslinking being preferred. Specific crosslinking conditions that are not limited to these are usually within a temperature range of 140 to 250°C and a crosslinking time of 1 minute to 24 hours, and can be determined appropriately depending on the types of crosslinking agent (b), dehydrofluorination agent (c), organic peroxide (d), acid acceptor (e), etc.

Furthermore, by heating the obtained molded product in an oven or the like, it is possible to improve mechanical properties such as tensile strength, heat resistance, and compression set properties at high temperatures. Specific crosslinking conditions, which are not limited, are usually in the temperature range of 140 to 300°C, in the range of 30 minutes to 72 hours, and can be appropriately determined depending on the types of crosslinking agent (b), dehydrofluorination agent (c), organic peroxide (d), etc.

Although the embodiments have been described above, it will be understood that various changes in form and details are possible without departing from the spirit and scope of the claims.

<1> According to a first aspect of the present disclosure,
The composition contains a fluororubber (a), a crosslinking agent (b), a dehydrofluorination agent (c), and an organic peroxide (d),
The crosslinking agent (b) is
1) at least one aromatic ring;
2) a group having a carbon-carbon double bond (excluding those constituting the aromatic ring), and
3) There is provided a composition for crosslinking fluororubber, which is a compound having, in the molecule, an alkylcarbonyloxy group directly bonded to a carbon atom constituting the aromatic ring.
<2> According to a second aspect of the present disclosure,
There is provided a composition for crosslinking fluororubber according to a first aspect, in which the crosslinking agent (b) is at least one selected from the group consisting of compounds represented by general formulas (b1) to (b3).

(wherein R is a hydrogen atom, an alkyl group having 1 to 5 carbon atoms or a fluorinated alkyl group having 1 to 5 carbon atoms; X is a vinyl group, an allyl group or a vinyloxy group; Y and Z are each independently H or a substituent (γ) having at least one value of Hammett's substituent constants σm and σp of 0.03 or more (excluding substituents containing a hydroxyl group and alkylcarbonyloxy groups); A is a bond, an alkylene group having 1 to 13 carbon atoms, an arylene group having 6 to 13 carbon atoms, a thiocarbonyl group, an oxygen atom, a carbonyl group, a sulfinyl group or a sulfonyl group; in the alkylene group and arylene group of A, some or all of the hydrogen atoms bonded to carbon atoms may be substituted with chlorine atoms or fluorine atoms; and ring B and ring C are each independently a monocyclic or polycyclic aromatic ring.)
<3> According to a third aspect of the present disclosure,
The present invention provides a composition for crosslinking a fluororubber, comprising a fluororubber (a), a crosslinking agent (b), a dehydrofluorination agent (c), and an organic peroxide (d), in which the crosslinking agent (b) is at least one selected from the group consisting of compounds represented by the formulas (b4) to (b7).

(In each formula, R is a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a fluorinated alkyl group having 1 to 5 carbon atoms.)
<4> According to a fourth aspect of the present disclosure,
There is provided a composition for crosslinking fluororubber according to a third aspect, in which the crosslinking agent (b) is at least one selected from the group consisting of compounds represented by formula (b5) and formula (b6).
<5> According to a fifth aspect of the present disclosure,
There is provided a composition for crosslinking fluororubber according to any one of the first to fourth aspects, in which the fluororubber (a) contains vinylidene fluoride units.
<6> According to a sixth aspect of the present disclosure,
There is provided a composition for crosslinking fluororubber according to any one of the first to fifth aspects, in which the content of the crosslinking agent (b) is 0.1 to 10 parts by mass per 100 parts by mass of the fluororubber (a).
<7> According to a seventh aspect of the present disclosure,
There is provided a composition for crosslinking a fluororubber according to any one of the first to sixth aspects, in which the content of the organic peroxide (d) is 0.05 to 10 parts by mass per 100 parts by mass of the fluororubber (a).
<8> According to an eighth aspect of the present disclosure,
There is provided a composition for crosslinking a fluororubber according to any of the first to seventh aspects, further comprising an acid acceptor (e), the content of the acid acceptor (e) being 0.1 to 50 parts by mass per 100 parts by mass of the fluororubber (a).
<9> According to a ninth aspect of the present disclosure,
There is provided a molded article obtained from the fluororubber crosslinking composition according to any one of the first to eighth aspects.

Next, we will explain the embodiments of the present disclosure by giving examples, but the present disclosure is not limited to these examples.

The numerical values in the examples were measured using the following methods.

<Monomer composition of fluororubber>
The measurements were carried out using a ¹⁹ F-NMR (AC300P model, manufactured by Bruker).

<Fluorine content>
The content was calculated from the composition of the fluororubber measured by ¹⁹ F-NMR.

<Mooney Viscosity>
Measurement was performed in accordance with ASTM D1646-15 and JIS K6300-1:2013. The measurement temperature was 100°C.

<Glass transition temperature (Tg)>
A DSC curve was obtained by heating 10 mg of a sample at 20° C./min using a differential scanning calorimeter (DSC822e, manufactured by Mettler Toledo, or X-DSC7000, manufactured by Hitachi High-Tech Science). The glass transition temperature was determined as the temperature indicating the intersection between an extension of the baseline before and after the second-order transition of the DSC curve and a tangent to the inflection point of the DSC curve.

<Heat of fusion>
A differential scanning calorimeter (DSC822e, manufactured by Mettler Toledo, or X-DSC7000, manufactured by Hitachi High-Tech Science) was used to obtain a DSC curve by heating 10 mg of a sample at a rate of 20° C./min, and the heat of fusion was calculated from the magnitude of the melting peak (ΔH) that appeared in the DSC curve.

<Iodine content>
An absorbing solution was prepared by mixing _Na2CO3 and _K2CO3 in a 1:1 ratio (by weight) and dissolving _the resulting mixture in 20 _ml of pure water. A mixture was prepared by mixing 12 mg of a sample ( _fluororubber ) with 5 mg of _Na2SO3 , and burning the mixture in oxygen in a quartz flask, and introducing the generated combustion gas into the absorbing solution. The resulting absorbing solution was left for 30 minutes, and then the concentration of iodine ions in the absorbing solution was measured using a Shimadzu 20A ion chromatograph. The content of iodine ions was determined using a calibration curve prepared using a KI standard solution containing 0.5 ppm iodine ions and a KI standard solution containing 1.0 ppm iodine ions.

<Cross-linking characteristics (maximum torque (MH), optimal cross-linking time (T90))>
For the fluororubber crosslinking composition, a vulcanization tester (MDR H2030 manufactured by M&K Co., Ltd.) was used during primary crosslinking to obtain crosslinking curves at the temperatures listed in each table, and the maximum torque (MH) and optimal crosslinking time (T90) were obtained from the change in torque. A higher maximum torque (MH) means a higher crosslink density.

<Tensile strength and elongation at break>
A test piece in the shape of a dumbbell No. 6 was prepared using a crosslinked sheet having a thickness of 2 mm. Using the obtained test piece and a tensile tester (Tensilon RTG-1310 manufactured by A&D Co., Ltd.), the tensile strength and elongation at break were measured at 23°C under the condition of 500 mm/min in accordance with JIS K6251:2010.

<Hardness>
Three crosslinked sheets having a thickness of 2 mm were stacked, and the durometer hardness (type A, peak value) was measured in accordance with JIS K6251-3:2012.

<Compression set>
Using a small test piece for measuring compression set, the measurement was performed in accordance with JIS K6262:2013, Method A, at a compression ratio of 25%, a test temperature of 200°C, and a test time of 72 hours.

In the examples and comparative examples, the following materials were used.
Fluorine rubber A:
Vinylidene fluoride/hexafluoropropylene molar ratio: 78/22
Fluorine content: 66%
Mooney viscosity (ML1+10 (100°C)): 60
Glass transition temperature: -18°C
Heat of fusion: None observed in the second run Iodine content: 0.17% by mass
Fluorine Rubber B
Vinylidene fluoride/hexafluoropropylene molar ratio: 78/22
Fluorine content: 66%
Mooney viscosity (ML1+10 (100°C)): 70
Glass transition temperature: -18°C
Heat of fusion: Not observed in the second run Does not contain iodine atoms

MT Carbon ( _N2SA : ^8m2 /g, DBP: 43ml/100g)
Crosslinker A: 4-vinylphenyl acetate Crosslinker B: 4-allylphenol Crosslinker C: eugenol Dehydrofluorination agent A: A mixture of 91% by weight of benzyldimethyloctadecylammonium chloride and 9% by weight of isopropyl alcohol Organic peroxide A: 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane Calcium hydroxide Magnesium oxide

Example 1
100 parts by mass of fluororubber A, 20 parts by mass of MT carbon, 4 parts by mass of crosslinking agent A, 0.7 parts by mass of dehydrofluorination agent A, 0.5 parts by mass of organic peroxide A, 6 parts by mass of calcium hydroxide, and 3 parts by mass of magnesium oxide were blended and kneaded on an open roll to prepare a fluororubber crosslinking composition. The maximum torque (MH) and optimal crosslinking time (T90) of the obtained fluororubber crosslinking composition are shown in Table 1. Next, the fluororubber crosslinking composition was crosslinked by primary crosslinking (press crosslinking) under the conditions shown in Table 1 and secondary crosslinking (oven crosslinking) under the conditions shown in Table 1 to obtain a crosslinked sheet (thickness 2 mm) and a small test piece for measuring compression set. The evaluation results of the obtained crosslinked sheet and the results of the compression set test are shown in Table 1.

Example 2
A fluororubber crosslinking composition was prepared in the same manner as in Example 1, except that the crosslinking agent A was changed to the crosslinking agent B, and a crosslinked sheet (thickness 2 mm) and a small test piece for measuring compression set were obtained. The results are shown in Table 1.

Comparative Example 1
A fluororubber crosslinking composition was prepared in the same manner as in Example 1, except that the crosslinking agent A was changed to the crosslinking agent C, and a crosslinked sheet (thickness 2 mm) and a small test piece for measuring compression set were obtained. The results are shown in Table 1.

Example 3
A fluororubber crosslinking composition was prepared in the same manner as in Example 1, except that the amount of crosslinking agent A was changed to 2 parts by mass, and a crosslinked sheet (thickness 2 mm) and a small test piece for measuring compression set were obtained. The results are shown in Table 1.

Comparative Example 2
A fluororubber crosslinking composition was prepared in the same manner as in Comparative Example 1, except that the amount of crosslinking agent C was changed to 2 parts by mass, and a crosslinked sheet (thickness 2 mm) and a small test piece for measuring compression set were obtained. The results are shown in Table 1.

Comparative Example 3
A fluororubber cross-linking composition was prepared in the same manner as in Example 1, except that no cross-linking agent A was added. The results are shown in Table 1.

Example 4
100 parts by mass of fluororubber B, 20 parts by mass of MT carbon, 4 parts by mass of crosslinking agent A, 0.7 parts by mass of dehydrofluorination agent A, 0.5 parts by mass of organic peroxide A, 6 parts by mass of calcium hydroxide, and 3 parts by mass of magnesium oxide were blended and kneaded on an open roll to prepare a fluororubber crosslinking composition. The maximum torque (MH) and optimal crosslinking time (T90) of the obtained fluororubber crosslinking composition are shown in Table 2. Next, the fluororubber crosslinking composition was crosslinked by primary crosslinking (press crosslinking) under the conditions shown in Table 2 and secondary crosslinking (oven crosslinking) under the conditions shown in Table 2 to obtain a crosslinked sheet (thickness 2 mm) and a small test piece for measuring compression set. The evaluation results of the obtained crosslinked sheet and the results of the compression set test are shown in Table 2.

Comparative Example 4
A fluororubber crosslinking composition was prepared in the same manner as in Example 4, except that the crosslinking agent A was changed to the crosslinking agent C, and a crosslinked sheet (thickness 2 mm) and a small test piece for measuring compression set were obtained. The results are shown in Table 2.

Example 5
A fluororubber crosslinking composition was prepared in the same manner as in Example 4, except that the amount of crosslinking agent A was changed to 2 parts by mass, and a crosslinked sheet (thickness 2 mm) and a small test piece for measuring compression set were obtained. The results are shown in Table 2.

Claims

The composition contains a fluororubber (a), a crosslinking agent (b), a dehydrofluorination agent (c), and an organic peroxide (d),
The crosslinking agent (b) is
1) at least one aromatic ring;
2) a group having a carbon-carbon double bond (excluding those constituting the aromatic ring), and
3) A composition for crosslinking fluororubber, which is a compound having, in the molecule, an alkylcarbonyloxy group directly bonded to a carbon atom constituting the aromatic ring.
The fluororubber crosslinking composition according to claim 1, wherein the crosslinking agent (b) is at least one selected from the group consisting of compounds represented by general formulas (b1) to (b3):

(In the formula, R is a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a fluorinated alkyl group having 1 to 5 carbon atoms; X is a vinyl group, an allyl group, or a vinyloxy group; Y is H, or a substituent (γ) having at least one of the Hammett substituent constants σm and σp of 0.03 or more (excluding substituents containing a hydroxy group and alkylcarbonyloxy groups).)

(In the formula, R represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a fluorinated alkyl group having 1 to 5 carbon atoms; X represents a vinyl group, an allyl group, or a vinyloxy group; Y and Z each independently represent H or a substituent (γ) having at least one of the Hammett substituent constants σm and σp of 0.03 or more (excluding substituents containing a hydroxy group and alkylcarbonyloxy groups).

(wherein R is a hydrogen atom, an alkyl group having 1 to 5 carbon atoms or a fluorinated alkyl group having 1 to 5 carbon atoms; X is a vinyl group, an allyl group or a vinyloxy group; Y and Z are each independently H or a substituent (γ) having at least one value of Hammett's substituent constants σm and σp of 0.03 or more (excluding substituents containing a hydroxyl group and alkylcarbonyloxy groups); A is a bond, an alkylene group having 1 to 13 carbon atoms, an arylene group having 6 to 13 carbon atoms, a thiocarbonyl group, an oxygen atom, a carbonyl group, a sulfinyl group or a sulfonyl group; in the alkylene group and arylene group of A, some or all of the hydrogen atoms bonded to carbon atoms may be substituted with chlorine atoms or fluorine atoms; and ring B and ring C are each independently a monocyclic or polycyclic aromatic ring.)
A composition for crosslinking a fluororubber, comprising a fluororubber (a), a crosslinking agent (b), a dehydrofluorination agent (c), and an organic peroxide (d), wherein the crosslinking agent (b) is at least one selected from the group consisting of compounds represented by formulas (b4) to (b7).

(In each formula, R is a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a fluorinated alkyl group having 1 to 5 carbon atoms.)
The fluororubber crosslinking composition according to claim 3, wherein the crosslinking agent (b) is at least one selected from the group consisting of compounds represented by formula (b5) and formula (b6).
The fluororubber crosslinking composition according to any one of claims 1 to 4, wherein the fluororubber (a) contains vinylidene fluoride units.
The fluororubber cross-linking composition according to any one of claims 1 to 5, wherein the content of the cross-linking agent (b) is 0.1 to 10 parts by mass per 100 parts by mass of the fluororubber (a).
The fluororubber cross-linking composition according to any one of claims 1 to 6, wherein the content of the organic peroxide (d) is 0.05 to 10 parts by mass per 100 parts by mass of the fluororubber (a).
The fluororubber crosslinking composition according to any one of claims 1 to 7, further comprising an acid acceptor (e), the content of the acid acceptor (e) being 0.1 to 50 parts by mass per 100 parts by mass of the fluororubber (a).
A molded article obtained from the fluororubber crosslinking composition according to any one of claims 1 to 8.