Fluororubber composition and molded article

Abstract

Provided is a fluororubber composition containing (a) a fluororubber and (b) a crosslinking agent, wherein the crosslinking agent (b) has, in the molecule thereof, two or more hydroxy groups, two or more carbon atoms, and at least one linking group selected from the group consisting of monosulfide bonds, disulfide bonds, and polysulfide bonds, the linking group linking a carbon atom with a carbon atom; and the crosslinking agent contains no fluorine atom.

Description

Fluororubber composition and molded article

[0001] The present disclosure relates to a fluororubber composition and a molded article.

[0002] U.S. Patent No. 5,999,623 describes aromatic polyhydroxy compounds that can act as crosslinkers or co-curing agents for fluorinated elastomers as essential components in the final curable composition. One of the most useful aromatic polyphenols is the bisphenol compound hexafluoroisopropylidene-bis(4-hydroxybenzene), known as bisphenol AF.

[0003] Special Publication No. 64-418

[0004] An object of the present disclosure is to provide a fluororubber composition containing a crosslinking agent that does not have a fluorine atom.

[0005] According to the present disclosure, there is provided a fluororubber composition containing a fluororubber (a) and a crosslinking agent (b), wherein the crosslinking agent (b) has, in the molecule, two or more hydroxy groups, two or more carbon atoms, and at least one linking group connecting carbon atoms and selected from the group consisting of a monosulfide bond, a disulfide bond, and a polysulfide bond, and the crosslinking agent (b) has no fluorine atoms.

[0006] According to the present disclosure, it is possible to provide a fluororubber composition containing a crosslinking agent that does not have a fluorine atom.

[0007] Specific embodiments of the present disclosure will be described in detail below, but the present disclosure is not limited to the following embodiments.

[0008] The fluororubber composition of the present disclosure contains a fluororubber (a) and a crosslinking agent (b).

[0009] By using a crosslinkable composition containing bisphenol AF as a crosslinking agent, molded articles with sufficient physical properties can be obtained. On the other hand, if bisphenol AF adheres to equipment used for measuring or preparing the composition, since bisphenol AF is a compound containing fluorine atoms, a dedicated incineration device is required to treat the waste generated by washing the bisphenol AF adhered to the equipment, which results in a significant cost burden. Therefore, there is a demand for a compound that does not contain fluorine atoms to be used as a polyol crosslinking agent.

[0010] The fluororubber composition of the present disclosure contains a compound having the structure described below as a crosslinking agent. This compound is easy to handle because it does not contain fluorine atoms.

[0011] Each component of the fluororubber composition of the present disclosure will be described below.

[0012] (a) Fluororubber The fluororubber used in the present disclosure is preferably a polyol-crosslinkable fluororubber. The polyol-crosslinkable fluororubber is a fluororubber having a polyol-crosslinkable site. In the present disclosure, the fluororubber is an amorphous fluoropolymer. "Amorphous" means that the magnitude of the melting peak (ΔH) appearing in differential scanning calorimetry (DSC) (heating rate 20°C / min) or differential thermal analysis (DTA) (heating rate 20°C / min) of the fluoropolymer is 4.5 J / g or less. The fluororubber exhibits elastomeric properties by crosslinking. Elastomeric properties refer to the ability of a polymer to be stretched and to retain its original length when the force required to stretch the polymer is no longer applied.

[0013] Examples of the polyol-crosslinkable moiety include a moiety having a vinylidene fluoride (VdF) unit. Among these, a fluororubber containing a VdF unit is preferred because the effect of using the crosslinking agent (b) is easily exhibited.

[0014] Examples of fluororubbers having a polyol-crosslinkable moiety include VdF-based fluororubbers, rubbers having polyol-crosslinkable functional moieties in the side chain and / or main chain, etc. Examples of VdF-based fluororubbers include tetrafluoroethylene (TFE) / propylene / VdF-based fluororubbers, ethylene / hexafluoropropylene (HFP) / VdF-based fluororubbers, VdF / HFP-based fluororubbers, VdF / TFE / HFP-based fluororubbers, etc. These fluororubbers having a polyol-crosslinkable moiety can be used alone or in any combination within the scope that does not impair the effects of the present disclosure.

[0015] Among these, the fluororubber is preferably a fluororubber composed of VdF and at least one other fluorine-containing monomer, and particularly preferably at least one rubber selected from the group consisting of VdF / HFP-based fluororubbers, VdF / TFE / HFP-based fluororubbers, and VdF / TFE / PAVE-based fluororubbers, and more preferably at least one rubber selected from the group consisting of VdF / HFP-based fluororubbers and VdF / TFE / HFP-based fluororubbers.

[0016] 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. The Mooney viscosity is preferably 200 or less, more preferably 150 or less, even more preferably 120 or less, and particularly preferably 100 or less. The Mooney viscosity is measured in accordance with ASTM D1646-15 and JIS K6300-1:2013.

[0017] The fluorine content of the fluororubber is preferably 62 to 72% by mass, more preferably 64 to 71% by mass, and even more preferably 65 to 71% by mass. The fluorine content can be calculated from the composition ratio of the monomer units constituting the fluororubber.

[0018] 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 a rate of 20° C. / min, and determining the glass transition temperature as the temperature at 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.

[0019] (b) Crosslinking Agent The fluororubber composition of the present disclosure contains a crosslinking agent, which is a compound having, in its molecule, two or more hydroxy groups, two or more carbon atoms, and at least one linking group connecting carbon atoms selected from the group consisting of a monosulfide bond, a disulfide bond, and a polysulfide bond, but which does not contain a fluorine atom.

[0020] The crosslinking agent used in the present disclosure does not have a fluorine atom in the molecule, unlike 2,2-bis(4-hydroxyphenyl)perfluoropropane (bisphenol AF), which has been used as a crosslinking agent conventionally.

[0021] The crosslinking agent used in the present disclosure does not contain fluorine atoms in its molecule, as conventional crosslinking agents do, and has a structure in which carbon atoms are linked by monosulfide bonds, disulfide bonds, or polysulfide bonds. Due to its excellent heat resistance, fluororubbers are sometimes used in higher temperature environments than non-fluorinated rubbers. Because bonds between carbon atoms and sulfur atoms (C-S bonds) are more easily dissociated by heat than bonds between carbon atoms and carbon atoms (C-C bonds), it was predicted that the heat resistance of the resulting crosslinked product would be inferior if a compound having a carbon atom and a sulfur atom (C-S bond) was used as a crosslinking agent for crosslinking fluororubber. Surprisingly, it was discovered that even when a crosslinking agent that does not contain fluorine atoms in its molecule and has a structure in which carbon atoms are linked by monosulfide bonds, disulfide bonds, or polysulfide bonds is used, a crosslinked product exhibiting normal state physical properties, high-temperature compression set, and weight loss temperature equivalent to those obtained when conventional crosslinking agents are used can be obtained.

[0022] The number of hydroxy groups possessed by the crosslinking agent is 2 or more, preferably 2 to 4, more preferably 2 to 3, and even more preferably 2.

[0023] The number of carbon atoms contained in the crosslinking agent is 2 or more, preferably 3 or more, more preferably 6 or more, even more preferably 9 or more, still more preferably 12 or more, and preferably 22 or less.

[0024] The crosslinking agent preferably has two or more benzene rings. The two or more benzene rings include, for example, at least a first benzene ring and a second benzene ring. The number of benzene rings contained in the crosslinking agent is two or more, preferably 2 to 4, more preferably 2 to 3, and even more preferably 2.

[0025] The crosslinking agent has a linking group connecting two carbon atoms. When the crosslinking agent has two or more benzene rings, the crosslinking agent may have at least a first benzene ring and a second benzene ring. When the crosslinking agent has two or more benzene rings, the carbon atom constituting the first benzene ring and the carbon atom constituting the second benzene ring can be connected by a linking group.

[0026] The linking group may be a monosulfide bond (-S-), a disulfide bond (-S-S-), or a polysulfide bond (-(S) ｘ１ -(X1 is an integer of 3 or more). The linking group is preferably at least one selected from the group consisting of a monosulfide bond and a disulfide bond. X1 is preferably an integer of 3 to 10, and more preferably 3.

[0027] The crosslinking agent is preferably a compound represented by general formula (b1): (In the formula, x is an integer of 1 or more, R is a substituent not having a fluorine atom, and y and z are independently integers of 0 to 4.)

[0028] In general formula (b1), x represents the number of sulfur atoms connected. For example, when x is 2, the crosslinking agent has a disulfide bond (-S-S-) as a linking group connecting the carbon atom constituting the first benzene ring and the carbon atom constituting the second benzene ring. x is an integer of 1 or more, preferably an integer of 1 to 10, more preferably an integer of 1 to 3, and even more preferably 1 or 2.

[0029] R represents a substituent bonded to the first benzene ring or the second benzene ring. R is a substituent not having a fluorine atom, and therefore the compound represented by general formula (b1) does not have a fluorine atom.

[0030] The compound represented by general formula (b1) may or may not have a substituent represented by R. R is not limited as long as it is a fluorine atom or a monovalent group other than a group having a fluorine atom, and examples of R include, independently in each occurrence, a chlorine atom, a hydroxy group, an amino group, a cyano group, a thiol group, an alkyl group having 1 to 5 carbon atoms, and an alkoxy group having 1 to 5 carbon atoms, and independently in each occurrence, an alkyl group having 1 to 5 carbon atoms is preferred.

[0031] y and z each represent the number of substituents (R) bonded to the first benzene ring or the second benzene ring, and are independently 0 to 4, preferably 0 or 1.

[0032] The crosslinking agent (b) is preferably at least one selected from the group consisting of 4,4'-thiodiphenol, 4,4'-dithiodiphenol, and 4,4'-thiodi(o-cresol).

[0033] The content of the crosslinking agent is preferably 0.1 to 50 parts by mass, more preferably 0.3 part by mass or more, even more preferably 0.5 part by mass or more, more preferably 5.0 parts by mass or less, even more preferably 3.0 parts by mass or less, and still more preferably 2.0 parts by mass or less, relative to 100 parts by mass of the fluororubber, so that the crosslinking reaction in the crosslinking step proceeds at an appropriate rate and a molded product having sufficient tensile strength, elongation at break, and compression set properties at high temperatures, and appropriate hardness can be obtained.

[0034] (c) Crosslinking Accelerator The fluororubber composition of the present disclosure preferably further contains a crosslinking accelerator. Use of the crosslinking accelerator can accelerate the crosslinking reaction by accelerating the formation of intramolecular double bonds in the dehydrofluorination reaction of the fluororubber main chain.

[0035] An onium compound is generally used as a crosslinking accelerator for a polyol crosslinking system. The onium compound is not particularly limited, and examples thereof 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.

[0036] 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. , 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, tetrabutylammonium hydroxide, and the like. Among these, DBU-B or benzyldimethyloctadecylammonium chloride is preferred from the viewpoint of crosslinkability and physical properties of the crosslinked product.

[0037] 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 from the viewpoints of crosslinkability and the physical properties of the crosslinked product.

[0038] The content of the crosslinking accelerator is preferably 0.1 to 10 parts by mass, more preferably 0.2 parts by mass or more, even more preferably 0.3 parts by mass or more, more preferably 3.0 parts by mass or less, even more preferably 1.5 parts by mass or less, and still more preferably 1.0 part by mass or less, relative to 100 parts by mass of the fluororubber, because the crosslinking reaction proceeds at an appropriate rate and a more excellent molded product can be obtained due to the compression set properties at high temperatures.

[0039] (d) Acid Acceptor The fluororubber composition of the present disclosure may further contain an acid acceptor. By containing an acid acceptor, the crosslinking reaction of the fluororubber composition proceeds more smoothly, and the compression set properties at high temperatures are further improved.

[0040] Examples of the acid acceptor 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 described in JP-T-2011-522921A, and metal salts of weak acids described in JP-A-2003-277563A. Examples of the metal salts of weak acids include carbonates, benzoates, oxalates, and phosphites of Ca, Sr, Ba, Na, and K.

[0041] 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 this allows for the production of molded articles with better compression set properties at high temperatures, and sodium metasilicate hydrate, calcium hydroxide, magnesium oxide, bismuth oxide, and hydrotalcite are more preferred. Furthermore, when the molded articles to be produced require 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.

[0042] In the fluororubber 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 a molded product with even better compression set properties at high temperatures can be obtained.

[0043] Increasing the content of the acid acceptor tends to decrease the water resistance, acid resistance, and resistance to organic acid esters, including biodiesel, of the resulting molded article. Conversely, decreasing the content of the acid acceptor tends to decrease the crosslinking rate and the mechanical properties due to a decrease in crosslink density. Therefore, the content of the acid acceptor can be selected depending on the intended use of the resulting molded article. Furthermore, when an acid acceptor other than calcium hydroxide is contained, reducing the content of calcium hydroxide to 0 to 1.5 parts by mass, for example, and then adjusting the content of the other acid acceptor to adjust the crosslink density can result in a molded article with even better compression set properties at high temperatures.

[0044] (e) Other Components The fluororubber composition may be blended with various additives as needed, such as usual additives blended into fluororubber compositions, for example, fillers (carbon black, bituminous coal, barium sulfate, diatomaceous earth, calcined clay, talc, wollastonite, carbon nanotubes, silica, titanium oxide, alumina, etc.), processing aids (wax, etc.), plasticizers, colorants, stabilizers, tackifiers (coumarone resin, coumarone-indene resin, etc.), release agents, electrical conductivity imparting agents, thermal conductivity imparting agents, surface non-tackifying agents, flexibility imparting agents, heat resistance improvers, flame retardants, foaming agents, and antioxidants described in WO 2012 / 023485 , and may also be blended with one or more usual crosslinking agents and crosslinking accelerators different from the above.

[0045] Of these, thermal carbon black and furnace carbon black are preferred as carbon black, with MT carbon black, FT carbon black, and SRF carbon black being more preferred. By blending carbon black with a relatively large particle size, such as MT carbon black or FT carbon black, molded articles with excellent compression set properties can be obtained, while by blending carbon black with a fine particle size, molded articles with excellent strength and elongation can be obtained. By blending different grades in combination, the above properties can be balanced.

[0046] As fillers other than carbon black, barium sulfate and wollastonite are preferred.

[0047] The processing aid is not particularly limited, but examples thereof include aliphatic amines such as stearylamine, fatty acid esters such as stearic acid esters and sebacate esters, fatty acid amides such as stearic acid amide, long-chain alkyl alcohols, natural waxes, polyethylene waxes, phosphate esters such as tricresyl phosphate, and silicone-based processing aids. If necessary, blending two or more types in appropriate amounts can improve the balance between mold releasability during molding and the physical properties of the molded product.

[0048] 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, relative to 100 parts by mass of the fluororubber.

[0049] 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, relative to 100 parts by mass of the fluororubber. When processing aids, plasticizers, or release agents are used, the mechanical properties and sealing properties of the resulting molded article tend to decrease, so it is necessary to adjust the content of these agents within a range that allows the desired properties of the resulting molded article.

[0050] The fluororubber composition may contain a dialkyl sulfone compound. The inclusion of a dialkyl sulfone compound increases the crosslinking efficiency of the fluororubber composition, accelerates the crosslinking rate, further improves compression set properties, and improves the fluidity of the rubber material. Examples of dialkyl sulfone compounds include dimethyl sulfone, diethyl sulfone, dibutyl sulfone, methyl ethyl sulfone, diphenyl sulfone, and sulfolane. Among these, sulfolane is preferred from the viewpoints of crosslinking efficiency and compression set properties, as well as its suitable 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 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.

[0051] The dialkyl sulfone compound and the processing aid may be blended together, as this provides a good balance of crosslinking rate, flowability of the rubber material during molding, mold releasability during molding, and mechanical properties of the molded product.

[0052] The fluororubber composition can be obtained by kneading the fluororubber (a), the crosslinking agent (b), the crosslinking accelerator (c), the acid acceptor (d), and other components (e) using a commonly used rubber kneading device, such as a roll, kneader, Banbury mixer, internal mixer, or twin-screw extruder.

[0053] In order to uniformly disperse each component in the rubber, a method may also be used in which the fluororubber (a), the crosslinking agent (b) and the crosslinking accelerator (c) are kneaded while being melted at a high temperature of 100 to 200°C using a closed kneading device such as a kneader, and then the acid acceptor (d) and other components (e) are kneaded at a relatively low temperature below this temperature.

[0054] Furthermore, the dispersibility can be further improved by mixing the fluororubber (a), the crosslinking agent (b), the crosslinking accelerator (c), the acid acceptor (d), the other components (e), and the like, leaving the mixture at room temperature for 12 hours or more, and then mixing again.

[0055] <Molded Article> The molded article of the present disclosure can be obtained by crosslinking the fluororubber composition. Alternatively, the molded article of the present disclosure can be obtained by molding and crosslinking the fluororubber composition. The fluororubber 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 employed. 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.

[0056] Examples of molding methods include, but are not limited to, compression molding, casting, injection molding, extrusion molding, and rotocure 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, which are not limited to, are typically a temperature range of 140 to 250°C, a crosslinking time of 1 minute to 24 hours, and can be determined appropriately depending on the types of crosslinking agent (b), crosslinking accelerator (c), acid acceptor (d), and the like.

[0057] Furthermore, by heating the obtained molded article in an oven or the like, it is possible to improve mechanical properties such as tensile strength, heat resistance, and high-temperature compression set properties. Specific crosslinking conditions, which are not limited, are typically a temperature range of 140 to 300°C, a time range of 30 minutes to 72 hours, and can be determined appropriately depending on the types of crosslinking agent (b), crosslinking accelerator (c), and acid acceptor (d). The fluororubber composition can be suitably used as a molding material for obtaining molded articles. The molded articles may be sealing materials, tubes, hoses, etc.

[0058] Although the embodiments have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the claims.

[0059] <1> According to a first aspect of the present disclosure, there is provided a fluororubber composition containing a fluororubber (a) and a crosslinking agent (b), wherein the crosslinking agent (b) has, in the molecule, two or more hydroxy groups, two or more carbon atoms, and at least one linking group selected from the group consisting of a monosulfide bond, a disulfide bond, and a polysulfide bond, which links carbon atoms to carbon atoms, and wherein the crosslinking agent (b) has no fluorine atoms. <2> According to a second aspect of the present disclosure, there is provided a fluororubber composition according to the first aspect, wherein the crosslinking agent (b) has, in the molecule, two or more hydroxy groups, two or more benzene rings, and at least one linking group selected from the group consisting of a monosulfide bond, a disulfide bond, and a polysulfide bond, which links a carbon atom constituting a first benzene ring to a carbon atom constituting a second benzene ring, and ... <3> According to a third aspect of the present disclosure, there is provided a fluororubber composition according to the first or second aspect, in which the crosslinking agent (b) is a compound represented by general formula (b1): (wherein x is an integer of 1 or more, R is a substituent not having a fluorine atom, and y and z are independently integers of 0 to 4.) <4> According to a fourth aspect of the present disclosure, there is provided a fluororubber composition according to the third aspect, wherein x is 1 or 2. <5> According to a fifth aspect of the present disclosure, there is provided a fluororubber composition according to any one of the first to fourth aspects, wherein the fluororubber (a) contains a vinylidene fluoride unit. <6> According to a sixth aspect of the present disclosure, there is provided a fluororubber composition according to any one of the first to fifth aspects, wherein the content of the crosslinking agent (b) is 0.1 to 50 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 fluororubber composition according to any one of the first to sixth aspects, further containing a crosslinking accelerator (c). <8> According to an eighth aspect of the present disclosure, there is provided a fluororubber composition according to any one of the first to seventh aspects, further containing an acid acceptor (d). <9> According to a ninth aspect of the present disclosure, there is provided a molded article obtained from the fluororubber composition according to any one of the first to eighth aspects.

[0060] Next, embodiments of the present disclosure will be described with reference to examples, but the present disclosure is not limited to these examples.

[0061] The values ​​in the examples were measured by the following methods.

[0062] <Monomer composition of fluororubber> １９ Measurement was carried out using F-NMR (Bruker AC300P model).

[0063] <Fluorine content> １９ The content was calculated from the composition of the fluororubber measured by F-NMR.

[0064] <Mooney Viscosity> Measured in accordance with ASTM D1646-15 and JIS K6300-1:2013 at a measurement temperature of 100°C.

[0065] <Glass Transition Temperature (Tg)> A DSC curve was obtained by heating 10 mg of a sample at a rate of 20°C / min using a differential scanning calorimeter (DSC822e manufactured by Mettler Toledo or X-DSC7000 manufactured by Hitachi High-Tech Science Corporation), and the glass transition temperature was determined as the temperature at the intersection of 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.

[0066] <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.

[0067] <Crosslinking characteristics> For the fluororubber compositions, a crosslinking curve was determined at the temperature shown in each table using a vulcanization tester (MDR H2030 manufactured by M&K Co., Ltd.) during primary crosslinking, and the minimum torque (ML), maximum torque (MH), induction time (T10), intermediate crosslinking time (T50) and optimum crosslinking time (T90) were determined from the change in torque.

[0068] <100% Modulus, Tensile Strength, and Elongation at Break> A 2 mm thick crosslinked sheet was used to prepare a No. 6 dumbbell shaped test piece. Using the obtained test piece and a tensile tester (Tensilon RTG-1310 manufactured by A&D Co., Ltd.), the 100% modulus (M100), tensile strength, and elongation at break were measured at 23°C under conditions of 500 mm / min in accordance with JIS K6251:2010.

[0069] <Hardness> Three crosslinked sheets each 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.

[0070] <Compression Set> Compression set was measured using a small test piece for measuring compression set (O-ring of P-24 size) in accordance with Method A of JIS K6262:2013, at a compression rate of 25%, a test temperature of 200°C or 150°C, and a test time of 72 hours.

[0071] <Weight Loss Temperature> A sample of approximately 10 mg was prepared by shaving off a crosslinked sheet having a thickness of 2 mm, and the sample was heated in an air atmosphere using a TG / DTA (thermogravimetric / differential thermal analyzer) to increase the temperature from 25°C to 600°C at a rate of 10°C / min, and the temperature at which the weight of the sample had decreased by 1.0 wt % or 5.0 wt % was measured.

[0072] The following materials were used in the examples and comparative examples: Fluorine rubber A: vinylidene fluoride / hexafluoropropylene copolymer Molar ratio of vinylidene fluoride / hexafluoropropylene: 78 / 22 Fluorine content: 66 mass % Mooney viscosity (ML1+10 (100°C)): 69 Glass transition temperature: -18°C Heat of fusion: not observed in second run

[0073] Fluorine rubber B: vinylidene fluoride / hexafluoropropylene / tetrafluoroethylene copolymer Molar ratio of vinylidene fluoride / hexafluoropropylene / tetrafluoroethylene: 58 / 22 / 20 Fluorine content: 69 mass% Mooney viscosity (ML1+10 (100°C)): 42 Glass transition temperature: -13°C Heat of fusion: not observed in second run

[0074] Crosslinking agent A: 4,4'-thiodiphenol Crosslinking agent B: 4,4'-dithiodiphenol Crosslinking agent C: 4,4'-thiodi(o-cresol) Crosslinking agent D: 2,2-bis(4-hydroxyphenyl)perfluoropropane (bisphenol AF)

[0075] Crosslinking accelerator: 8-benzyl-1,8-diazabicyclo[5,4,0]-7-undecenium chloride (DBU-B) Carbon black: MT carbon (N ２ SA: 8m ２ / g, DBP: 43 ml / 100 g) Magnesium oxide: MA150 (Kyowa Chemical Industry Co., Ltd.) Calcium hydroxide: NICC5000 (Inoue Lime Industry Co., Ltd.)

[0076] Examples 1 to 10 and Comparative Examples 1 to 2 Fluororubber compositions were prepared by blending the components according to the formulations in Tables 1 and 2 and kneading them on an open roll. The crosslinking properties of the resulting fluororubber compositions are shown in Tables 1 and 2. The fluororubber compositions were then crosslinked by primary crosslinking (press crosslinking) at 170°C for 10 minutes and secondary crosslinking (oven crosslinking) at 230°C for 24 hours to obtain crosslinked sheets (2 mm thick), small test pieces for measuring compression set, and test pieces for measuring weight loss temperature. The evaluation results are shown in Tables 1 and 2.

[0077]

[0078]

Claims

1. A fluororubber composition comprising a fluororubber (a) and a crosslinking agent (b), wherein the crosslinking agent (b) has, in its molecule, two or more hydroxy groups, two or more carbon atoms, and at least one linking group connecting carbon atoms and selected from the group consisting of a monosulfide bond, a disulfide bond, and a polysulfide bond, and the crosslinking agent (b) does not have any fluorine atoms.

2. The fluororubber composition according to claim 1, wherein the crosslinking agent (b) has in its molecule two or more hydroxy groups, two or more benzene rings, and at least one linking group selected from the group consisting of a monosulfide bond, a disulfide bond and a polysulfide bond, which links a carbon atom constituting a first benzene ring with a carbon atom constituting a second benzene ring, and does not have any fluorine atoms.

3. The fluororubber composition according to claim 1 or 2, wherein the crosslinking agent (b) is a compound represented by general formula (b1): General formula (b1): (In the formula, x is an integer of 1 or more, R is a substituent not having a fluorine atom, and y and z are independently integers of 0 to 4.) 4. The fluororubber composition according to claim 3, wherein x is 1 or 2.

5. A fluororubber composition according to any one of claims 1 to 4, wherein the fluororubber (a) contains vinylidene fluoride units.

6. The fluororubber composition according to any one of claims 1 to 5, wherein the content of the crosslinking agent (b) is 0.1 to 50 parts by mass per 100 parts by mass of the fluororubber (a).

7. The fluororubber composition according to any one of claims 1 to 6, further comprising a crosslinking accelerator (c).

8. The fluororubber composition according to any one of claims 1 to 7, further comprising an acid acceptor (d).

9. A molded article obtained from the fluororubber composition according to any one of claims 1 to 8.

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