Boron-containing silane coupling agent and rubber composition

Abstract

To provide a new boron-containing silane coupling agent that enables excellent fracture properties in a cured rubber composition, and to provide a rubber composition that delivers excellent fracture properties after curing.SOLUTION: Provided are a boron-containing silane coupling agent having a cyclic structure including a coordinating hetero element, a B-O bond, and a silyl group, and a rubber composition containing a diene rubber, silica, and the boron-containing silane coupling agent.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a boron-containing silane coupling agent and a rubber composition. [Background technology]

[0002] BACKGROUND ART Conventionally, rubber compositions containing 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, rubber (cured product) obtained from a rubber composition containing a 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 novel boron-containing silane coupling agent that can improve the breaking properties of a cured product of a rubber composition. Another object of the present invention is to provide a rubber composition that provides good break properties when cured. [Means for solving the problem]

[0006] As a result of intensive research to solve the above problems, the present inventors have found that the above problems can be solved by adding a boron-containing silane coupling agent having a specific structure (a cyclic structure containing a coordinating heteroatom, a B-O bond, and a silyl group) to a rubber composition containing a diene rubber and silica, and have arrived at the present invention. That is, the present inventors have found that the above problems can be solved by the following configuration.

[0007] [1] A boron-containing silane coupling agent having a cyclic structure containing a coordinating heteroatom, a B-O bond, and a silyl group. [2] The boron-containing silane coupling agent according to [1], which is represented by the following formula (I): [ka] In formula (I), A1 and A2 each independently represent a divalent saturated aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a combination thereof, which may have a heteroatom, and R1, R2, and R3 each independently represent a substituent, provided that at least one of R1, R2, and R3 is an alkoxy group. [3] A rubber composition containing a diene rubber, silica, and the boron-containing silane coupling agent according to [1] or [2]. [4] The rubber composition according to [3], wherein the content of the silica is 5 to 200 parts by mass per 100 parts by mass of the diene rubber, and the content of the boron-containing silane coupling agent is 0.2 to 20% by mass of the content of the silica. [5] The diene rubber contains natural rubber, The rubber composition according to [3] or [4], wherein the content of the natural rubber is 20% by mass or more of the total amount of the diene rubber. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a novel boron-containing silane coupling agent that can improve the break properties of a cured product of a rubber composition. The present invention also provides a rubber composition that exhibits good break properties when cured. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a 1H-NMR spectrum of the boron-containing silane coupling agent represented by formula (6). DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in detail below. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In this specification, unless otherwise specified, 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, unless otherwise specified, the production method of each component is not limited, and examples thereof include conventionally known methods. In this specification, a compound represented by formula (*) may be referred to as "compound *." For example, a compound represented by formula (1) may be referred to as "compound 1."

[0011] [Boron-containing silane coupling agent] The boron-containing silane coupling agent of the present invention (the silane coupling agent of the present invention) is a boron-containing silane coupling agent having a cyclic structure containing a coordinating heteroatom, a BO bond, and a silyl group.

[0012] The silane coupling agent of the present invention has such a structure, and it is believed that the above-mentioned effects are obtained. Although the reason for this is not clear, it is presumed that the reactivity of the boron contained in the silane coupling agent of the present invention with diene rubber is extremely high, and as a result, the rubber composition containing the silane coupling agent of the present invention has good break properties in the cured product.

[0013] [Ring structures containing coordinating heteroatoms] The silane coupling agent of the present invention has a cyclic structure containing a coordinating heteroatom.

[0014] [Coordinating Heteroatoms] The coordinating heteroatom can be coordinated to B (boron) of the BO bond described below. Examples of the coordinating heteroelement include nitrogen, sulfur, oxygen, and phosphorus. The coordinating heteroelement may be, for example, a coordinating heteroatom such as a nitrogen atom, a sulfur atom, an oxygen atom, or a phosphorus atom. The coordinating hetero element is preferably a nitrogen atom, from the viewpoint of improving the breaking properties of the cured product of the rubber composition.

[0015] Preferred embodiments of the cyclic structure containing a coordinating heteroatom include, for example, a five-membered ring and a six-membered ring. Examples of the cyclic structure containing a coordinating heteroatom include unsaturated nitrogen-containing heterocycles such as a pyrrole ring and a pyridine ring; and unsaturated sulfur-containing heterocycles such as a thiophene ring. From the viewpoint of improving the breaking properties of the cured product of the rubber composition, the cyclic structure containing a coordinating heteroatom is preferably an unsaturated heterocycle, more preferably an unsaturated nitrogen-containing heterocycle, and even more preferably a pyridine ring. The silane coupling agent of the present invention may have at least one cyclic structure containing a coordinating heteroatom per molecule. The cyclic structure containing a coordinating heteroatom preferably has one bonding position with a B-O bond and one bonding position with a silyl group. In other words, in the above case, the cyclic structure containing a coordinating heteroatom is divalent.

[0016] [BO join] The silane coupling agent of the present invention has a B (boron)-O (oxygen) bond. An example of the B-O bond is a group represented by the formula: B-R-O-*, where each of the two Rs independently represents a hydrogen atom or a hydrocarbon group, and * represents the bonding position. The hydrocarbon group represented by R is not particularly limited. The BO bond is preferably a group represented by the formula: BH2-O-*, from the viewpoint of improving the breaking properties of the cured product of the rubber composition. The silane coupling agent of the present invention may have at least one BO bond per molecule.

[0017] [Silyl group] The silane coupling agent of the present invention has a silyl group. The silyl group is a group containing a silicon atom, and is preferably a hydrolyzable silyl group. An example of a silyl group is a group (-SiR1R2R3) in which R1, R2, and R3 are bonded to one silicon atom as substituents. R1, R2, and R3 each independently represent a substituent. However, it is preferable that at least one of R1, R2, and R3 is an alkoxy group.

[0018] The number of carbon atoms in the alkoxy group is not particularly limited, and may be, for example, 1 to 30. From the viewpoint of improving the break properties of the cured product of the rubber composition, the number of carbon atoms is preferably 1 to 5.

[0019] Specific examples of the substituent other than an alkoxy group include an aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a group combining these, as well as 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), and linear or branched alkynyl groups (particularly having 2 to 30 carbon atoms). 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), from the viewpoint of improving the break properties of the cured product of the rubber composition.

[0020] In order to improve the breaking properties of the cured product of the rubber composition, it is preferable that at least one of R1, R2, and R3 bonded to one silicon atom is an alkoxy group, and it is more preferable that two or all of R1, R2, and R3 are alkoxy groups. The alkoxy group may have 1 to 30 carbon atoms. The silane coupling agent of the present invention may have at least one silyl group per molecule. Each silyl group may have one silicon atom.

[0021] (Linking group 1 via a cyclic structure containing a coordinating heteroatom and a BO bond) The cyclic structure containing a coordinating heteroatom and the B-O bond can be bonded directly or via a linking group. In a preferred embodiment, the cyclic structure containing a coordinating heteroatom and the B-O bond are bonded via a linking group. In this specification, the linking group connecting the cyclic structure containing a coordinating heteroatom and the B-O bond is also referred to as linking group 1. The linking group 1 can be, for example, a divalent linking group. Examples of the linking group 1 include a divalent saturated aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a combination thereof, which may have a hetero atom. 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 1 or more, and preferably 2 or more. The upper limit of the number of carbon atoms can be, for example, 30 or less. The linking group 1 between the cyclic structure containing a coordinating heteroatom and the B-O bond is preferably a divalent saturated aliphatic hydrocarbon group having 2 to 10 carbon atoms, from the viewpoint of improving the break properties of the cured product of the rubber composition. Examples of the heteroatom that the linking group 1 may have include an oxygen atom, a sulfur atom, a nitrogen atom, and a phosphorus atom. Preferred embodiments of the linking group 1 include, for example, a divalent saturated aliphatic hydrocarbon group or aromatic hydrocarbon group containing no heteroatom, or a combination thereof. There are no particular limitations on which atom constituting the cyclic structure the B-O bond or linking group 1 is bonded to. When the cyclic structure is a pyridine ring, a preferred embodiment is one in which the B-O bond is bonded to the 2- or 6-position of the pyridine ring (the carbon atom adjacent to the nitrogen atom of the pyridine ring) via linking group 1.

[0022] (Linking group 2 via a cyclic structure containing a coordinating heteroatom and a silyl group) The cyclic structure containing a coordinating heteroatom and the silyl group can be bonded directly or via a linking group. In a preferred embodiment, the cyclic structure containing a coordinating heteroatom and the silyl group are bonded via a linking group. In this specification, the linking group connecting the cyclic structure containing a coordinating heteroatom and the silyl group is also referred to as linking group 2. The linking group 2 can be, for example, a divalent linking group. Examples of the linking group 2 include a divalent saturated aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a combination thereof, which may have a hetero atom. 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 1 or more, and preferably 2 or more. The upper limit of the number of carbon atoms can be, for example, 30 or less. From the viewpoint of improving the break properties of the cured product of the rubber composition, the linking group 2 between the cyclic structure containing a coordinating heteroatom and the silyl group is preferably a combination of a divalent saturated aliphatic hydrocarbon group having 2 to 10 carbon atoms and a divalent aromatic hydrocarbon group, and more preferably a combination of an ethylene group and a phenylene group. Examples of the heteroatom that the linking group 2 may have include an oxygen atom, a sulfur atom, a nitrogen atom, and a phosphorus atom. Preferred embodiments of the linking group 2 include, for example, a divalent saturated aliphatic hydrocarbon group or aromatic hydrocarbon group containing no heteroatom, or a combination thereof. There are no particular limitations on which atom constituting the cyclic structure the silyl group or linking group 2 is bonded to. When the cyclic structure is a pyridine ring, a preferred embodiment is one in which the silyl group is bonded to the 2-position or 6-position of the pyridine ring (the carbon atom adjacent to the nitrogen atom of the pyridine ring) via linking group 2.

[0023] (Boron-containing silane coupling agent represented by formula (I)) From the viewpoint of improving the break properties of the cured product of the rubber composition, the silane coupling agent of the present invention is preferably a boron-containing silane coupling agent represented by the following formula (I), and more preferably a boron-containing silane coupling agent represented by the following formula (II): [ka] In formula (I), A1 and A2 each independently represent a divalent saturated aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a combination thereof, which may have a heteroatom, and R1, R2, and R3 each independently represent a substituent, provided that at least one of R1, R2, and R3 is an alkoxy group. In formula (I), the nitrogen atom of the pyridine ring may be coordinated to the boron atom of the BH2-O- group.

[0024] The pyridine ring in formula (I) corresponds to the above-mentioned cyclic structure containing a coordinating heteroatom. BH2-O- in formula (I) corresponds to the above-mentioned BO bond. In formula (I), -SiR1R2R3 corresponds to the silyl group described above. In formula (I), -SiR1R2R3 is the same as the silyl group described above, where R1, R2, and R3 are bonded to one silicon atom as substituents (-SiR1R2R3). However, in formula (I), at least one of R1, R2, and R3 is an alkoxy group. A1 in formula (I) is the same as the above-mentioned "(linking group 1 via a cyclic structure containing a coordinating heteroatom and a BO bond)". A2 in formula (I) is the same as the above-mentioned "(linking group 2 via a cyclic structure containing a coordinating heteroatom and a silyl group)."

[0025] (Boron-containing silane coupling agent represented by formula (II)) The boron-containing silane coupling agent represented by formula (II) is as follows: [ka]

[0026] In the boron-containing silane coupling agent represented by formula (II), the nitrogen atom of the pyridine ring may be coordinated to boron, as shown in the following formula (6). [ka]

[0027] (Method of manufacturing a specific silane coupling agent) As a method for producing the specific silane coupling agent, for example, a method of reacting a raw material compound and a raw material boron compound in a solvent by cooling the mixture to, for example, −50° C. or less at the start of the reaction and then raising the temperature to room temperature can be mentioned. (Raw material compound) Examples of the raw material compounds that can be used in producing the specific silane coupling agent include raw material compounds in which a monovalent hydrocarbon group, such as a saturated aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a combination thereof, is bonded to any carbon atom constituting a cyclic structure (e.g., a pyridine ring) containing a coordinating heteroatom (provided that any carbon atom constituting the monovalent hydrocarbon group is substituted with a carbonyl group, and the monovalent hydrocarbon group may have a heteroatom other than the carbonyl group. Examples of the monovalent hydrocarbon group include acyl groups), and a silyl group is bonded to any carbon atom constituting the cyclic structure (excluding the carbon atom to which the monovalent hydrocarbon group is bonded) directly or via the above-mentioned linking group 2 (linking group 2 between the cyclic structure containing a coordinating heteroatom and the silyl group, such as a phenylene group bonded to an ethylene group). Specific examples of raw material compounds include Compound 4, which will be described later.

[0028] (Raw boron compound) Examples of the raw material boron compound that can be used when producing the specific silane coupling agent include a boron compound represented by the formula: H3BY. Y in the formula: H3BY represents a ligand having an atom having an unshared electron pair (for example, a sulfur atom, a nitrogen atom, a phosphorus atom, or an oxygen atom). Examples of Y include dialkylmonosulfides such as dimethyl sulfide, trialkylamines, tetrahydrofuran (THF), morpholines, nitrogen-containing heterocycles, and triphenylphosphine. Examples of morpholines include N-alkylsilylmorpholines. Examples of the starting boron compound include BH3SMe2, BH3THF, and compounds represented by the following structures: [ka]

[0029] (solvent) Examples of solvents that can be used in the reaction of the raw material compound with the raw material boron compound include tetrahydrofuran, methylene chloride, and toluene. (Amount of raw material compound used) The amount of the raw material compound used can be, for example, 1 to 10 molar equivalents relative to 1 molar equivalent of the raw material boron compound.

[0030] [Rubber composition] The rubber composition of the present invention (the composition of the present invention) is The rubber composition contains a diene rubber, silica, and the boron-containing silane coupling agent of the present invention (hereinafter, also referred to as the "specific silane coupling agent"). Each component contained in the composition of the present invention will be described below.

[0031] [Diene rubber] The diene rubber contained in the composition of the present invention is not particularly limited. The composition of the present invention may contain one diene rubber or two or more diene rubbers.

[0032] (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.

[0033] (molecular weight) The weight average molecular weight (Mw) of the diene rubber is not particularly limited, but from the viewpoint of improving the break properties of the resulting cured product, 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.

[0034] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are values ​​calculated as standard polystyrene obtained by gel permeation chromatography (GPC) measurement.

[0035] (natural rubber) The diene rubber preferably contains natural rubber. The natural rubber is not particularly limited, and examples thereof include conventionally known natural rubbers. (Natural rubber content) When the diene rubber contains natural rubber, the content of the natural rubber is preferably from 20% to 100% by mass of the total amount of the diene rubber, from the viewpoint of improving the break properties of the resulting cured product, more preferably from 50% to 100% by mass, even more preferably from 80% to 100% by mass, particularly preferably from 90% to 100% by mass, and most preferably 100% by mass.

[0036] The content of the diene rubber other than natural rubber is not particularly limited, but from the viewpoint of improving the break properties of the resulting cured product, it is preferably 0 to 30 mass % of the total amount of the diene rubber, more preferably 0 to 20 mass %, and even more preferably 0 to 10 mass %.

[0037] [silica] The composition of the present invention contains silica. The silica contained in the composition of the present invention is not particularly limited, and any conventionally known silica compounded in rubber compositions for tires and the like can be used.

[0038] (Example) Specific examples of the silica include wet silica, dry silica, fumed silica, diatomaceous earth, etc. Furthermore, silica derived from biomass such as rice husks may also be used. Among these, it is preferable to use wet silica, since this can improve the fracture properties of the resulting cured product. The silica may be used alone or in combination of two or more types. (CTAB adsorption specific surface area of ​​silica) The CTAB (cetyltrimethylammonium bromide) adsorption specific surface area of ​​the silica is not particularly limited, but from the viewpoint of improving the fracture properties of the obtained cured product, it is preferably 100 to 300 m 2 / g, and 150 to 200m 2 / g. In this specification, the CTAB adsorption specific surface area can be determined in accordance with JIS K6430:2008, Appendix G (Rubber compounding ingredients - Silica - Test method, Determination of specific surface area by CTAB adsorption method (quantitative determination)).

[0039] (Silica content) From the viewpoint of improving the break properties of the resulting cured product, the content of the silica is preferably 5 to 200 parts by mass, more preferably 10 to 150 parts by mass, even more preferably 20 to 100 parts by mass, and even more preferably 30 to 70 parts by mass, per 100 parts by mass of the diene rubber.

[0040] [Boron-containing silane coupling agent] The rubber composition of the present invention contains the silane coupling agent of the present invention (specific silane coupling agent). The silane coupling agent contained in the rubber composition of the present invention is not particularly limited as long as it is the silane coupling agent of the present invention. The silane coupling agent of the present invention is as described above. From the viewpoint of improving the fracture properties of the resulting cured product, the specific silane coupling agent preferably contains a boron-containing silane coupling agent represented by the above formula (I), and more preferably contains a boron-containing silane coupling agent represented by the above formula (II).

[0041] (Content of boron-containing silane coupling agent) From the viewpoint of improving the fracture properties of the resulting cured product, the content of the specific silane coupling agent is preferably 0.2 to 20 mass % of the above-mentioned silica content, more preferably 1.0 to 15.0 mass %, and even more preferably 4.0 to 12.0 mass %.

[0042] Furthermore, when the diene rubber contains natural rubber, the content of the specific silane coupling agent is preferably 1.0 to 20.0 parts by mass, more preferably 2.0 to 15.0 parts by mass, per 100 parts by mass of the diene rubber containing natural rubber, from the viewpoint of improving the break properties of the resulting cured product.

[0043] 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 amount of the specific silane coupling agent used when the specific silane coupling agent is blended with the diene rubber.

[0044] (optional ingredient) The composition of the present invention may further contain other components (optional components) as needed, provided that the effects and purposes of the composition are not impaired. Examples of the optional components include 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), vulcanization accelerators, and various other additives commonly used in rubber compositions. The types and contents of the optional components can be selected as appropriate.

[0045] (Method of 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 apparatus (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. The composition of the present invention can be vulcanized or crosslinked under conventionally known vulcanization or crosslinking conditions. After vulcanization or crosslinking, the composition of the present invention can become a cured product (vulcanized rubber or crosslinked rubber).

[0046] (Application) The composition of the present invention can be suitably used as a rubber material. For example, it can be suitably used for tires (particularly pneumatic tires and tire treads), conveyor belts, hoses, vibration-proof materials, rubber rolls, outer covers of railway vehicles, etc. In particular, it can be suitably used for tires (particularly treads). [Example]

[0047] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0048] [Preparation of specific silane coupling agent 1] (Reaction Scheme 1: Preparation of Compound 3) As shown in the following reaction formula 1, compound 1 and compound 2 were reacted for 15 hours under heating at reflux in n-propanol (31 mL, Fujifilm Wako Pure Chemical Industries, Ltd.) as a solvent in the presence of palladium acetate (11.4 mg, Fujifilm Wako Pure Chemical Industries, Ltd.), triphenylphosphine (40 mg, Sigma-Aldrich), and potassium carbonate (2.6 g, Fujifilm Wako Pure Chemical Industries, Ltd.). After the reaction, the reaction solution was separated into water and ethyl acetate and then purified using a column to obtain compound 3 (88% isolated yield). The amounts of palladium acetate and other components used in the following reaction formula 1 are based on compound 1.

[0049] [ka]

[0050] (Reaction Scheme 2: Preparation of Compound 4) As shown in Reaction Scheme 2 below, compound 3 was reacted in the presence of HSiMe(OEt) (1.1 mL, manufactured by TCI) and PtO (40.7 mg, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in toluene (7.5 mL, manufactured by Kanto Chemical Co., Ltd.) as a solvent at 80°C for 15 hours to obtain a mixture of compounds 4 and 5. The mixture was purified by silica gel column chromatography to isolate compound 4 (67% isolated yield). The amounts of HSiMe(OEt) and other compounds used in Reaction Scheme 2 below are based on compound 3.

[0051] [ka]

[0052] (Reaction Scheme 3: Production of Specific Silane Coupling Agent 1) As shown in the following reaction formula 3, compound 4 and BHSMe (0.43 mL, manufactured by Sigma-Aldrich) were mixed in tetrahydrofuran (15 mL, manufactured by Kanto Chemical Co.) as a solvent at -78°C, and then the mixture was stirred while being naturally warmed to room temperature and reacted for 1 hour. After the reaction, the solvent and other components were distilled off from the reaction solution under reduced pressure to obtain 1.1 g of a solid compound.

[0053] [ka]

[0054] The compound obtained in reaction formula 3 is dissolved in a solvent (benzene-d6:C6D6) 1 H-NMR was measured for the compound obtained in Reaction Scheme 3. 1 The H-NMR spectrum is shown in Figure 1. In Figure 1, a quartet at 4.95 ppm and a doublet at 1.55 ppm indicate that BH3 has been added to C=O in compound 4. 1As a result of H-NMR spectrum, it was found that the compound obtained in the above reaction formula 3 was compound 6 (a boron-containing silane coupling agent represented by formula (6)) shown in reaction formula 3.

[0055] [Production of rubber composition] The components shown in Table 1 below were compounded in the proportions (parts by mass) shown in the table. Specifically, the components shown in Table 1 below, excluding sulfur and the vulcanization accelerator, were first heated to around 140°C using a 1.7-liter internal Banbury mixer, mixed for 5 minutes, then discharged and cooled to room temperature to obtain a masterbatch. Furthermore, sulfur and the vulcanization accelerator were mixed into the obtained masterbatch 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 Example 1, the molar equivalent of the silyl group in the specific silane coupling agent 1 was set to half the molar equivalent of the silyl group in TESPT in Comparative Example 1. In this Example 2, for comparison with Comparative Example 1, the molar equivalent of the silyl group in Specific Silane Coupling Agent 1 was set to 0.0148 molar equivalent, the same as the molar equivalent of the silyl group in TESPT in Comparative Example 1.

[0057] [evaluation] The rubber compositions thus obtained were evaluated as follows.

[0058] (Fracture properties) Each of the resulting unvulcanized rubber compositions 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 specimens (thickness: 2 mm) were punched out of the resulting vulcanized rubber sheets in accordance with JIS K6251:2010, and the tensile strength (strength at break) and elongation at break were evaluated as fracture properties at a temperature of 20°C and a pulling rate 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 breaking properties of the obtained cured product were evaluated as good when the tensile strength and elongation at break indexes were both greater than 100. The greater the tensile strength and / or elongation at break index was, the better the breaking properties of the obtained cured product were evaluated as.

[0059] [Table 1]

[0060] Details of each component shown in Table 1 are as follows: NR: Natural rubber (RSS#3) ·Silica: ZEOSIL 1165MP (CTAB adsorption specific surface area: 159m 2 / g, manufactured by Rhodia) Zinc oxide: Zinc oxide type 3, manufactured by Seido Chemical Industry Co., Ltd. Vulcanization accelerator: Noccela CZ-G, manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Sulfur: Kinka brand oil-filled fine sulfur, manufactured by Tsurumi Chemical Industry Co., Ltd. Silane coupling agent (TESPT): Bis(3-(triethoxysilyl)propyl)tetrasulfide. Molecular weight: 539. Contains two triethoxysilyl groups (silyl groups) per molecule. Specific silane coupling agent 1: Specific silane coupling agent 1 prepared as described above. The molecular weight of specific silane coupling agent 1 is 371. The number of diethoxymethylsilyl groups (silyl groups) per molecule is one.

[0061] The results shown in Table 1 indicate that the cured products obtained from the compositions of the present invention had good breaking properties. On the other hand, the conventional example that did not contain the specific silane coupling agent and Comparative Example 1 that did not contain the specific silane coupling agent but contained TESPT instead had insufficient breaking properties.

Claims

1. A boron-containing silane coupling agent having a cyclic structure containing a coordinating heteroatom, a B—O bond, and a silyl group.

2. 2. The boron-containing silane coupling agent according to claim 1, which is represented by the following formula (I): 【Chemistry 1】 In formula (I), A １ , A ２ each independently represents a divalent saturated aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a combination thereof, which may have a heteroatom; 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.

3. A rubber composition comprising a diene rubber, silica, and the boron-containing silane coupling agent according to claim 1 or 2.

4. 4. The rubber composition according to claim 3, wherein the content of the silica is 5 to 200 parts by mass per 100 parts by mass of the diene rubber, and the content of the boron-containing silane coupling agent is 0.2 to 20% by mass of the content of the silica.

5. The diene rubber contains natural rubber, The rubber composition according to claim 3 , wherein the content of the natural rubber is 20% by mass or more of the total amount of the diene rubber.

Images