Rubber composition

Abstract

To provide a rubber composition which can obtain good breaking physical properties when formed into a cured product and contains a boron-containing silane coupling agent.SOLUTION: The rubber composition contains a diene rubber, silica, and a boron-containing silane coupling agent having a structure represented by formula (I). The content of the silica is 5-200 pts.mass based on 100 pts.mass of the diene rubber. The content of the boron-containing silane coupling agent is 0.2-20 mass% based on the content of the silica.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a rubber composition. [Background technology]

[0002] 2. Description of the Related Art Conventionally, rubber compositions containing a diene rubber, carbon black and / or a white filler, and a boron-containing silane coupling agent have been known (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6459201 Summary of the Invention [Problem to be solved by the invention]

[0004] On the other hand, there is a demand for a novel boron-containing silane coupling agent that can be applied to a rubber composition containing a diene rubber and a white filler (particularly silica). Furthermore, the rubber (cured product) obtained from the rubber composition containing the diene rubber, silica, and a boron-containing silane coupling agent is required to have, for example, good breaking properties.

[0005] Therefore, an object of the present invention is to provide a rubber composition containing a boron-containing silane coupling agent, which provides good break physical properties when cured. [Means for solving the problem]

[0006] As a result of intensive research aimed at solving the above problems, the inventors have discovered that the above problems can be solved by further containing a boron-containing silane coupling agent having a specific structure in a rubber composition containing a diene rubber and silica, thereby arriving at the present invention. That is, the present inventors have found that the above problems can be solved by the following configuration.

[0007] [1] The present invention relates to a rubber composition comprising a diene rubber, silica, and a boron-containing silane coupling agent having a structure represented by the following formula (I): the content of the silica is 5 to 200 parts by mass relative to 100 parts by mass of the diene rubber, The rubber composition has a content of the boron-containing silane coupling agent of 0.2 to 20 mass % relative to the content of the silica. [ka] In formula (I), each A independently represents a divalent saturated aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a combination thereof, which may have a heteroatom, B represents boron, X represents hydrogen or a substituent, H represents hydrogen, m is 1 or 2, n is 0 or 1, m+n is 2 or 3, and R1, R2, and R3 independently represent a substituent, provided that at least one of R1, R2, and R3 is an alkoxy group. [2] The rubber composition according to [1], wherein the boron-containing silane coupling agent contains a compound represented by the following formula (II): [ka] In formula (II), each A independently represents a divalent saturated aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a combination thereof, which may have a heteroatom, B represents boron, H represents hydrogen, and R1, R2, and R3 independently represent a substituent, provided that in each group represented by -SiR1R2R3, at least one of R1, R2, and R3 is an alkoxy group. [3] The rubber composition according to [1] or [2], wherein each A independently has a cyclohexane ring. [4] The diene rubber contains natural rubber, The rubber composition according to any one of [1] to [3], wherein the content of the natural rubber in the diene rubber is 20% by mass or more. Effect of the Invention

[0008] According to the present invention, it is possible to provide a rubber composition containing a boron-containing silane coupling agent, which provides good break physical properties when cured. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The present invention will be described in detail below. In this specification, a numerical range expressed using "to" means a range including the numerical values ​​written before and after "to". In addition, each component may be used alone or in combination of two or more. When two or more components are used in combination, the content of the components refers to the total content unless otherwise specified. In this specification, superior fracture properties of the resulting cured product may be referred to as superior effects of the present invention. In this specification, a compound represented by formula (*) may be referred to as "compound (*)".

[0010] [Rubber composition] The rubber composition of the present invention (hereinafter also referred to as "the composition of the present invention") is The composition contains a diene rubber, silica, and a boron-containing silane coupling agent having a structure represented by formula (I) described below (hereinafter, this is also referred to as a "specific silane coupling agent"); the content of the silica is 5 to 200 parts by mass relative to 100 parts by mass of the diene rubber, In the rubber composition, the content of the boron-containing silane coupling agent is 0.2 to 20 mass % relative to the content of the silica.

[0011] The composition of the present invention has such a structure, and therefore it is believed that the above-mentioned effects can be obtained. Although the reason is not clear, it is presumed that the specific silane coupling agent contained in the composition of the present invention has extremely high reactivity of the boron contained in the specific silane coupling agent with diene rubber, and as a result, the composition of the present invention has good breaking properties of the cured product obtained.

[0012] Each component contained in the composition of the present invention will be described below.

[0013] [1] Diene rubber The diene rubber contained in the composition of the present invention is not particularly limited. The compositions of the present invention may contain one or more diene rubbers.

[0014] [Specific example] Specific examples of the diene rubber include natural rubber (NR), butadiene rubber (BR), aromatic vinyl-conjugated diene copolymer rubber, isoprene rubber (IR), acrylonitrile-butadiene copolymer rubber (NBR), butyl rubber (IIR), halogenated butyl rubber (Br-IIR, Cl-IIR), chloroprene rubber (CR), etc. Examples of the aromatic vinyl-conjugated diene copolymer rubber include styrene-butadiene rubber (SBR), styrene-isoprene copolymer rubber, etc.

[0015] [Molecular weight] The weight average molecular weight (Mw) of the diene rubber is not particularly limited, but in order to obtain better effects of the present invention, it is preferably 100,000 to 5,000,000, more preferably 200,000 to 3,000,000, and even more preferably 300,000 to 2,000,000.

[0016] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are values ​​calculated as standard polystyrene by gel permeation chromatography (GPC).

[0017] [Preferred embodiment] The diene rubber preferably contains natural rubber. When the diene rubber contains natural rubber, the content of natural rubber in the diene rubber is preferably 20% by mass or more, more preferably 50% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass or more, and most preferably 100% by mass, for reasons of better effects of the present invention.

[0018] The content of the diene rubber other than natural rubber in the diene rubber is not particularly limited, but in order to obtain better effects of the present invention, it is preferably 0 to 30 mass%, more preferably 0 to 20 mass%, and even more preferably 0 to 10 mass%.

[0019] [2] Silica The silica contained in the composition of the present invention is not particularly limited, and any conventionally known silica that is compounded in rubber compositions for tires and the like can be used.

[0020] [Specific example] Specific examples of the silica include wet silica, dry silica, fumed silica, diatomaceous earth, etc. Among them, wet silica is preferred because it has better effects of the present invention. The silica may be used alone or in combination of two or more kinds. The CTAB (cetyltrimethylammonium bromide) adsorption specific surface area of ​​the silica is not particularly limited, but is preferably 100 to 300 m because the effect of the present invention is more excellent. 2 / g, and 150 to 200m 2 In this specification, the CTAB adsorption specific surface area is a value obtained by measuring the amount of CTAB adsorbed on the silica surface according to JIS K6217-3:2001 "Part 3: Determination of specific surface area - CTAB adsorption method."

[0021] [Content] In the composition of the present invention, the content of the silica is 5 to 200 parts by mass relative to 100 parts by mass of the diene rubber. In particular, the content of the silica is preferably 10 to 150 parts by mass, more preferably 20 to 100 parts by mass, and even more preferably 30 to 70 parts by mass relative to 100 parts by mass of the diene rubber, because the effect of the present invention is more excellent.

[0022] [3] A boron-containing silane coupling agent having a structure represented by formula (I): The boron-containing silane coupling agent contained in the composition of the present invention is not particularly limited as long as it is a boron-containing silane coupling agent (specific silane coupling agent) having a structure represented by formula (I). [ka]

[0023] In formula (I), each A independently represents a divalent saturated aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a combination thereof, which may have a heteroatom, B represents boron, X represents hydrogen or a substituent, H represents hydrogen, m is 1 or 2, n is 0 or 1, m+n is 2 or 3, and R1, R2, and R3 independently represent a substituent, provided that at least one of R1, R2, and R3 is an alkoxy group.

[0024] [A] As described above, in formula (I), each A independently represents a divalent saturated aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a combination thereof, which may have a heteroatom. The saturated aliphatic hydrocarbon group may be linear, branched, cyclic, or a combination thereof. The number of carbon atoms in the saturated aliphatic hydrocarbon group, aromatic hydrocarbon group, or combination thereof can be at least 1, and preferably at least 2. The upper limit of the number of carbon atoms can be, for example, 30 or less.

[0025] For reasons such as better effects of the present invention, A is preferably a single bond, a cycloalkylene group, or a group represented by -CH2CH2-Z-, where Z represents a single bond, or a divalent saturated aliphatic hydrocarbon group or aromatic hydrocarbon group having 1 to 28 carbon atoms, which may have a heteroatom, or a combination thereof. The saturated aliphatic hydrocarbon group may be linear, branched, or cyclic. The above Z is preferably a single bond, a cycloalkylene group, an alkylene group having 1 to 5 carbon atoms, or a phenylene group, more preferably a cycloalkylene group or an alkylene group having 1 to 5 carbon atoms, and even more preferably an alkylene group having 1 to 5 carbon atoms, for reasons such as better effects of the present invention.

[0026] [B, H] In formula (I), B represents boron and H represents hydrogen.

[0027] [R1, R2 and R3] As described above, in formula (I), R1, R2, and R3 each independently represent a substituent, provided that at least one of R1, R2, and R3 is an alkoxy group.

[0028] The number of carbon atoms in the alkoxy group is not particularly limited, but is preferably 1 to 5 because the effects of the present invention are superior.

[0029] Specific examples of the above-mentioned substituent other than an alkoxy group include an aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a combination thereof, and a hydrolyzable group other than an alkoxy group, such as a phenoxy group, a carboxyl group, or an alkenyloxy group. The aliphatic hydrocarbon group may be linear, branched or cyclic. Specific examples of the aliphatic hydrocarbon group include linear or branched alkyl groups (particularly having 1 to 30 carbon atoms), linear or branched alkenyl groups (particularly having 2 to 30 carbon atoms), linear or branched alkynyl groups (particularly having 2 to 30 carbon atoms), etc. Examples of the aromatic hydrocarbon group include aromatic hydrocarbon groups having 6 to 18 carbon atoms, such as a phenyl group, a tolyl group, a xylyl group, and a naphthyl group. When the above-mentioned substituent is other than an alkoxy group, the substituent other than an alkoxy group is preferably an aliphatic hydrocarbon group, more preferably an alkyl group (particularly having 1 to 5 carbon atoms), because the effects of the present invention are more excellent.

[0030] When compound (I) has a plurality of groups represented by -SiR1R2R3, in each group represented by -SiR1R2R3, at least one of R1, R2, and R3 may be an alkoxy group. The number of carbon atoms of the alkoxy group may be 1 to 30. Hereinafter, the group represented by -SiR1R2R3 in formula (I) may be referred to as a "silyl group". In one preferred embodiment of the silyl group in compound (I), all of R1, R2, and R3 bonded to one silicon atom are alkoxy groups. The alkoxy group may have 1 to 30 carbon atoms. In the compound (I), it is preferable that R1, R2 and R3 are all alkoxy groups, because the effects of the present invention are superior. The number of carbon atoms in the alkoxy group can be 1 to 30.

[0031] [m, n] In formula (I), m is 1 or 2, n is 0 or 1, and m+n is 2 or 3. For reasons such as better effects of the present invention, m is preferably 2.

[0032] [X] In formula (I), X represents hydrogen or a substituent. In formula (I), when m is 1, n is 1 and m+n is 2, X may represent hydrogen or a substituent. In formula (I), when m is 2, n is 0 and m+n is 2, X may represent hydrogen or a substituent. In formula (I), when m is 2, n is 1, and m+n is 3, X can represent a substituent. In addition, in formula (I), when m is 2, n is 1, m+n is 3, and X represents a substituent, the specific silane coupling agent can be, for example, a compound represented by formula (II) described later. In formula (I), examples of the substituent represented by X include groups other than the silyl group in formula (I). In one preferred embodiment, the substituent as X is a compound having the same structure as the structure represented by (I).When the substituent as X is a compound having the same structure as the structure represented by (I), such a specific silane coupling agent can at least include a specific silane coupling agent having a plurality of structures represented by formula (I).The specific silane coupling agent having a plurality of structures represented by formula (I) will be described later. The specific silane coupling agent may contain a compound having at least one structure represented by the above formula (I).

[0033] (Specific silane coupling agent having a plurality of structures represented by formula (I)) The specific silane coupling agent may include at least a specific silane coupling agent having a plurality of structures represented by the above formula (I). When the specific silane coupling agent includes a specific silane coupling agent having a plurality of structures represented by formula (I), in the structures represented by the above-mentioned plurality of formulas (I), -BH- in each formula (I) can be bonded to form "*-(BH)n-**". In the above-mentioned "*-(BH)n-**", the "*" and "**" at both ends are bonded to form a cyclic structure, and n is 2 or more. In the above-mentioned "*-(BH)n-**", n is preferably 2 because the effects of the present invention are more excellent.

[0034] The specific silane coupling agent may, for example, be a compound having the following structure. Silane coupling agent (S1) containing one boron atom and one silyl group Examples of the silane coupling agent (S1) having one boron atom and one silyl group include compounds represented by the following formulae (I-1) to (I-3). [ka] JPEG2025005881000005.jpg759JPEG2025005881000006.jpg2054(I-3)

[0035] · Silane coupling agent with one boron and two silyl groups (S2) Examples of the silane coupling agent (S2) having one boron atom and two silyl groups include compounds represented by the following formulae (S2-1) to (S2-2). [ka] (S2-1) In formula (S2-1), each R is independently a methyl group or an ethyl group. [ka] (S2-2)

[0036] ·Silane coupling agent (S3) As the specific silane coupling agent (S3) having a plurality of structures represented by formula (I), there can be mentioned, for example, compounds represented by the following formulae (S3-1) to (S3-3). [ka] (S3-1) In formula (S3-1), each R is independently a methyl group or an ethyl group. [ka] (S3-2) [ka] (S3-3) In formula (S3-3), each R is independently a methyl group or an ethyl group. The compound represented by the above formula (3-3) is given as an example of a trimer of the compound represented by the above formula (S2-1), but a trimer of the compound represented by the above formula (S2-2) can also be given as an example in the same manner as formula (S3-3).

[0037] The above-mentioned boron-containing silane coupling agent (specific silane coupling agent) preferably contains a compound represented by the following formula (II) for the reason that the effects of the present invention are more excellent. [ka] In formula (II), each A independently represents a divalent saturated aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a combination thereof, which may have a heteroatom, B represents boron, H represents hydrogen, and R1, R2, and R3 independently represent a substituent, provided that in each group represented by -SiR1R2R3, at least one of R1, R2, and R3 is an alkoxy group. A, R1, R2 and R3 in formula (II) are the same as A, R1, R2 and R3 in formula (I), respectively. Examples of the compound represented by formula (II) include the compounds represented by the above formulae (S3-1) to (S3-2).

[0038] The specific silane coupling agent may be a single compound having the structure represented by the above formula (I), or may be a mixture of two or more kinds.

[0039] [Method of manufacturing specific silane coupling agent] The method for producing the specific silane coupling agent is not particularly limited. For example, the specific silane coupling agent can be formed from a vinyl group-containing silane coupling agent and a boron compound. A specific example of the method for producing the specific silane coupling agent is a method for producing the specific silane coupling agent by reacting a vinyl group-containing silane coupling agent with a boron compound (IV) described below.

[0040] (Vinyl-containing silane coupling agent) The vinyl group-containing silane coupling agent that can be used in producing the specific silane coupling agent is not particularly limited as long as it is a compound having a vinyl group or a vinylene group and a silyl group (similar to the silyl group in formula (I)). In the vinyl group-containing silane coupling agent, the linking group between the vinyl group or vinylene group and the silyl group is not particularly limited as long as it is a saturated aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a combination thereof. Examples of vinyl group-containing silane coupling agents include vinyltrialkoxysilane, vinyldialkoxysilane, vinylmonoalkoxysilane, trialkoxystyrylsilane, dialkoxystyrylsilane, monoalkoxystyrylsilane, trialkoxysilylcyclohexene, dialkoxysilylcyclohexene, and monoalkoxysilylcyclohexene.

[0041] (Boron compounds (IV)) The boron compound (IV) that can be used in producing the specific silane coupling agent is a boron compound represented by the formula: H3BY. In the formula: H3BY, Y represents a ligand having an atom having an unshared electron pair (for example, a sulfur atom, a nitrogen atom, a phosphorus atom, an oxygen atom). Examples of Y include dialkyl monosulfides such as dimethyl sulfide, trialkylamines, tetrahydrofuran (THF), morpholines, nitrogen-containing heterocycles, and triphenylphosphine. Examples of morpholines include N-alkylsilyl-morpholines. Examples of the boron compound (IV) include BH3THF and compounds represented by the following structure. [ka]

[0042] The reaction between the vinyl group-containing silane coupling agent and the boron compound can be carried out, for example, in the absence of a solvent, while stirring the mixture under cooled conditions. The amount of the vinyl group-containing silane coupling agent used can be, for example, 1 to 10 molar equivalents relative to 1 molar equivalent of the boron compound.

[0043] [Content] In the composition of the present invention, the content of the boron-containing silane coupling agent (specific silane coupling agent) represented by formula (I) is 0.2 to 20 mass% relative to the content of the silica described above. In particular, the content of the specific silane coupling agent is preferably 1.0 to 15.0 mass%, more preferably 4.0 to 12.0 mass%, relative to the content of the silica described above.

[0044] When the diene rubber contains a natural rubber, the content of the specific silane coupling agent in the composition of the present invention is preferably 1.0 to 10.0 parts by mass, and more preferably 4.0 to 8.0 parts by mass, per 100 parts by mass of the natural rubber, because the effects of the present invention are more excellent.

[0045] In the composition of the present invention, the specific silane coupling agent may be reacted with the diene rubber. In this case, the content of the specific silane coupling agent refers to the content of the specific silane coupling agent at the time of compounding.

[0046] [4] Optional component The composition of the present invention may further contain other components (optional components) as necessary, provided that the effects and objects of the composition are not impaired. Examples of the optional components include various additives commonly used in rubber compositions, such as carbon black, silane coupling agents other than the specific silane coupling agents described above, terpene resins (e.g., aromatic modified terpene resins), thermally expandable microcapsules, zinc oxide (zinc white), stearic acid, antioxidants, waxes, processing aids, oils, liquid polymers, thermosetting resins, vulcanizing agents (e.g., sulfur), and vulcanization accelerators.

[0047] [5] Method for producing the composition of the present invention The method for producing the composition of the present invention is not particularly limited, and specific examples thereof include a method of mixing the above-mentioned components using a known method or device (e.g., a Banbury mixer, a kneader, a roll, etc.) When the composition of the present invention contains sulfur or a vulcanization accelerator, it is preferable to first mix the components other than the sulfur and the vulcanization accelerator at a high temperature, cool the mixture, and then mix the sulfur or the vulcanization accelerator. In addition, the composition of the present invention can be vulcanized or crosslinked under conventionally known vulcanization or crosslinking conditions. After vulcanization or crosslinking of the composition of the present invention, the composition of the present invention can become a cured product (vulcanized rubber or crosslinked rubber).

[0048] [6]Applications The composition of the present invention is preferably used as a rubber material. For example, it is preferably used for tires (particularly pneumatic tires), conveyor belts, hoses, vibration-proof materials, rubber rolls, outer covers of railway vehicles, etc. Among them, it is preferably used for tires (particularly treads). EXAMPLES

[0049] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these.

[0050] [Preparation of specific silane coupling agent 1] Vinyltriethoxysilane (5 mL, 23.9 mmol. TCI) and BH3THF (277.4 mg, 5 equiv. Sugma-Aldrich. The same applies below) were mixed in THF (5 mL) at -78°C, and then the mixture was stirred while being allowed to naturally warm to room temperature and reacted for 15 hours. The solvent was distilled off under reduced pressure to obtain 5.3 g of an oily compound. The oily compound is a mixture containing at least two compounds represented by the following structural formulas, in which R is an ethyl group. [ka] [ka] The oily compound obtained as described above was used as specific silane coupling agent 1. Of the above two types of compounds contained in specific silane coupling agent 1, the latter compound (having two boron atoms in one molecule) is also referred to as the "dimmer in specific silane coupling agent 1."

[0051] [Preparation of specific silane coupling agent 2] Preparation of 2-triethoxysilylcyclohexene (NKH253) [PdCl(η 3-C3H5)] (7.6 mg, 0.02 mmol, Fujifilm Wako Co., Ltd.), PPh3 (11.8 mg, 0.04 mmol, Sigma-Aldrich Co., Ltd.), and 1,3-cyclohexadiene (0.8 mL, 8.4 mmol, Sigma-Aldrich Co., Ltd.) were mixed under a nitrogen atmosphere and cooled in an ice bath, after which trichlorohydrosilane (1 mL, 9.9 mmol, TCI Co., Ltd.) was added dropwise. The ice bath was removed and the mixture was stirred at room temperature for 3 days. The solution was cooled again in an ice bath, and a mixed solution consisting of triethylamine (8 mL, 57.4 mmol, Sigma-Aldrich Co., Ltd.) and ethanol (24 mL, 425 mmol, Fujifilm Wako Co., Ltd.) was added dropwise, followed by stirring at room temperature for 2 hours. The reaction solution was added to a solution consisting of ethyl acetate (30 mL, Kishida Chemical Co., Ltd.) and distilled water (50 mL), followed by celite filtration (Fujifilm Wako Co., Ltd.). The ethyl acetate solution was then separated by a separation operation, washed with water and saturated saline, dried over magnesium sulfate (manufactured by Fuji Film Wako Co., Ltd.), filtered, and the solvent was removed by distillation. The mixture was then purified using a silica column (eluent: ethyl acetate / hexane = 1:5 vol / vol) to obtain 2-triethoxysilylcyclohexene (1.4 g, 5.7 mmol, 70%). The above reaction sequence for preparing 2-triethoxysilylcyclohexene is as follows: [ka]

[0052] Preparation of N-borane-N-trimethylsilylmorpholine (NKH256) N-trimethylsilylmorpholine (2 mL, 11.3 mmol, TCI) and borane dimethyl sulfide (1.1 mL, 11.6 mL, TCI) were mixed in a diethyl ether solution (11 mL) and stirred at room temperature for 2 hours. The solvent was then removed under reduced pressure to obtain N-borane-N-trimethylsilylmorpholine (1.7 g, 9.8 mmol, structure shown below). [ka]

[0053] The results of the 1H NMR analysis of N-borane-N-trimethylsilylmorpholine are as follows: 1H NMR (C6D6, RT)0.08(s,9H),2.16(m,2H),2.34(m,2H),3.23(m,2H),4.44(m,2H). 11B{1H} NMR (C6D6, RT)-17.5 (q) Bruker AVANCE 600 spectrometer equipped with CryoProbe

[0054] Preparation of specific silane coupling agent 2 (NK255) 2-Triethoxysilylcyclohexene (1.3 g, 5.3 mmol) and N-borane-N-trimethylsilylmorpholine (455.7 mg, 2.6 mmol) were mixed in a diethyl ether solution (10 mL) and stirred at room temperature for 2 days under a nitrogen atmosphere. The solvent was distilled off under reduced pressure to obtain an oily compound (1.4 g). The oily compound is a mixture containing at least two compounds represented by the following structural formulas. [ka] [ka] The oily compound obtained as described above was used as the specific silane coupling agent 2. Of the above two types of compounds contained in the specific silane coupling agent 2, the latter compound (having two boron atoms in one molecule) is also referred to as the "dimers in the specific silane coupling agent 2."

[0055] [Preparation of Rubber Composition] The components shown in Table 1 below were mixed in the ratios (parts by mass) shown in the table. Specifically, the components shown in Table 1 below, except for sulfur and vulcanization accelerator, were heated to about 140°C using a 1.7-liter closed Banbury mixer, mixed for 5 minutes, and then discharged and cooled to room temperature to obtain a master batch. Furthermore, sulfur and a vulcanization accelerator were mixed into the obtained master batch using the Banbury mixer to obtain each rubber composition.

[0056] The molar equivalent of the triethoxysilyl group contained in 4 parts by mass of the silane coupling agent (TESPT) used in Comparative Example 1 was 0.0148 molar equivalent. In this embodiment 1, for comparison with Comparative Example 1, the molar equivalent of the silyl group of the specific silane coupling agent 1 was set to 0.0148 molar equivalent, the same as Comparative Example 1. The amount of the specific silane coupling agent 1 used, 2.9 parts by mass, shown in Table 1 was calculated using the dimer in the specific silane coupling agent 1 (its molecular weight and the number of silyl groups). In this Example 2, the specific silane coupling agent 1 was used in an amount (5.8 parts by mass) twice as much as that of the specific silane coupling agent 1 used in Example 1. In this embodiment 3, for comparison with Comparative Example 1, the molar equivalent of the silyl group of the specific silane coupling agent 2 was set to 0.0148 molar equivalent, the same as Comparative Example 1. The amount of the specific silane coupling agent 2 used, 3.7 parts by mass, shown in Table 1 was calculated using the dimer in the specific silane coupling agent 2 (its molecular weight and the number of silyl groups).

[0057] 〔evaluation〕 The resulting rubber compositions were evaluated as follows.

[0058] <Break properties> Each of the obtained rubber compositions (unvulcanized) was press-vulcanized in a mold (15 cm × 15 cm × 0.2 cm) at 150°C for 30 minutes to produce a vulcanized rubber sheet as a cured product. Next, JIS No. 3 dumbbell-shaped test pieces (thickness 2 mm) were punched out of the obtained vulcanized rubber sheets in accordance with JIS K6251:2010, and the tensile strength (strength at break) and elongation at break were evaluated as breaking properties under conditions of a temperature of 20°C and a pulling speed of 500 mm / min. The results of the fracture properties (tensile strength and elongation at break) are shown in Table 1. The results are expressed as an index with the conventional example being 100. In the present invention, the rupture properties of the obtained cured product were evaluated as good when both the tensile strength and elongation at break indexes were greater than 100. The rupture properties of the obtained cured product were evaluated as being better the greater the tensile strength and / or elongation at break index was 100. On the other hand, when either the tensile strength or elongation at break index was less than 100, the resulting cured product was evaluated as having poor breaking properties.

[0059] <Bound rubber amount> 0.3 g of the obtained composition (unvulcanized) was placed in a wire mesh basket and immersed in 300 mL of toluene at room temperature for 48 hours, then removed and dried. The mass of the sample was measured and the amount of bound rubber was calculated from the following formula. Bound rubber mass = [(mass of sample after immersion in toluene and drying) - (mass of silica)] / (mass of rubber component) The results of the bound rubber amount are shown in Table 1. The results are expressed as an index with the conventional example being 100. In the present invention, it is preferred that the bound rubber amount index is more than 100. A larger bound rubber amount index means that there is more bound rubber (rubber reacted with silica via the specific silane coupling agent) and that the reactivity between the diene rubber and the specific silane coupling agent is higher.

[0060] [Table 1]

[0061] Details of each component shown in Table 1 are as follows. ·NR: Natural rubber ·Silica: ZEOSIL 1165MP (CTAB adsorption specific surface area: 159m 2 / g, manufactured by Rhodia) Zinc oxide: 3 types of zinc oxide, manufactured by Seido Chemical Industry Co., Ltd. Vulcanization accelerator: Noccela CZ-G, manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Sulfur: Kinkaji oil-filled fine sulfur, manufactured by Tsurumi Chemical Industry Co., Ltd. Silane coupling agent (TESPT): Bis(3-(triethoxysilyl)propyl)tetrasulfide. Molecular weight 539. There are two triethoxysilyl groups per molecule. Specific silane coupling agents 1 to 2: Specific silane coupling agents 1 to 2 prepared as described above

[0062] From the results shown in Table 1, Comparative Example 1, which did not contain the specific silane coupling agent but contained TESPT instead, had poor breaking properties. On the other hand, the cured product obtained from the composition of the present invention had good breaking properties. Furthermore, compared with the conventional examples, the rubber obtained from the composition of the present invention had a larger amount of bound rubber, which demonstrated that the specific silane coupling agent has good reactivity with diene rubber.

Claims

1. The present invention relates to a rubber composition comprising a diene rubber, silica, and a boron-containing silane coupling agent having a structure represented by the following formula (I): the content of the silica is 5 to 200 parts by mass based on 100 parts by mass of the diene rubber, The rubber composition has a content of the boron-containing silane coupling agent of 0.2 to 20 mass % based on the content of the silica. 【Chemistry 1】 In formula (I), A's each independently represent a divalent saturated aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a combination thereof, which may have a heteroatom; B represents boron; X represents hydrogen or a substituent; H represents hydrogen; m is 1 or 2; n is 0 or 1; m+n is 2 or 3; R １ , R ２ and R ３ Each independently represents a substituent. １ , R ２ and R ３ At least one of the groups is an alkoxy group.

2. The rubber composition according to claim 1 , wherein the boron-containing silane coupling agent comprises a compound represented by the following formula (II): 【Chemistry 2】 In formula (II), A's each independently represent a divalent saturated aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a combination thereof, which may have a heteroatom; B represents boron; H represents hydrogen; R １ , R ２ and R ３ Each independently represents a substituent. １ R ２ R ３ In the group represented by the formula: １ , R ２ and R ３ At least one of the groups is an alkoxy group.

3. The rubber composition according to claim 1 or 2, wherein each A independently has a cyclohexane ring.

4. The diene rubber contains natural rubber, The rubber composition according to claim 1 or 2, wherein the diene rubber has a content of the natural rubber of 20% by mass or more.

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