Rubber composition and pneumatic tire

Abstract

To provide a rubber composition which serves as a raw material of a vulcanized rubber for tires improved in three properties of WET performance, fuel economy, and wear resistance in a well-balanced manner, and to provide a pneumatic tire comprising a vulcanized rubber of the rubber composition.SOLUTION: The rubber composition contains a diene rubber, silica, and an organic silane. The organic silane is a compound having a terpene skeleton with a molecular weight of 200-1,000. The rubber composition further contains a sulfur-containing silane coupling agent other than the organic silane. The organic silane is preferably an ene-thiol reaction product of a silicon-containing thiol compound and a compound having a terpene skeleton with a molecular weight of 200-1,000.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Pneumatic tires are expected to be driven in a variety of environments, and improving tire performance on wet roads (hereinafter also referred to as "wet performance") is essential. In addition, in response to recent demands for resource conservation, pneumatic tires are required to have low fuel consumption, and therefore, improved heat generation, which contributes to low fuel consumption, is also required. Additionally, from the perspective of improving durability, pneumatic tires are also required to have high wear resistance.

[0003] Patent Document 1 listed below describes a rubber composition for tires that contains a diene rubber, silica, a sulfur-containing silane coupling agent, and a specific alkyltriethoxysilane, in which 50% by mass or more of the diene rubber is a styrene-butadiene copolymer rubber, the sulfur-containing silane coupling agent has a mercapto group, the silica content is 5 to 150 parts by mass per 100 parts by mass of the diene rubber, the sulfur-containing silane coupling agent content is 3 to 15% by mass relative to the silica content, and the alkyltriethoxysilane content is 0.1 to 20% by mass relative to the silica content.

[0004] Patent Document 2 listed below describes a rubber composition obtained by compounding 100 parts by mass of diene rubber, 20 to 150 parts by mass of silica, and 2 to 20% by mass of an organic silane having a monosulfide bond (-CSC-) relative to the mass of the silica.

[0005] Patent Document 3 listed below describes a rubber composition obtained by compounding 100 parts by mass of a diene rubber containing a modified diene rubber modified with at least one functional group selected from the group consisting of an alkoxy group, a carbonyl group, a hydroxyl group, an amino group, and an epoxy group with 30 to 120 parts by mass of silica and 2 to 20% by mass of an organic silane having a low molecular weight terpene skeleton relative to the mass of the silica. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4930661 [Patent Document 2] Patent No. 6018001 [Patent Document 3] Patent No. 6377476 Summary of the Invention [Problem to be solved by the invention]

[0007] The technologies described in Patent Documents 1 and 2 both address the issue of achieving both wet performance and fuel economy in a pneumatic tire. However, as a result of extensive research by the present inventors, it has been found that there is a trade-off between wet performance and fuel economy, and therefore there is room for further improvement.

[0008] In the technology described in Patent Document 3, an organic silane having a low molecular weight terpene skeleton is compounded into the rubber composition. However, as a result of extensive research by the present inventors, it has been found that there is room for further improvement, as described below.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a rubber composition that serves as a raw material for vulcanized rubber for tires, which has a well-balanced improvement in wet performance, fuel economy, and abrasion resistance, and a pneumatic tire equipped with vulcanized rubber of the rubber composition. [Means for solving the problem]

[0010] The above-mentioned problems can be solved by the following configuration: That is, the present invention relates to a rubber composition (1) containing a diene rubber, silica, and an organosilane, wherein the organosilane is a compound having a terpene skeleton and a molecular weight of 200 to 1000, and further containing a sulfur-containing silane coupling agent other than the organosilane.

[0011] In the rubber composition (1), the organic silane is represented by the following general formula (1): [ka] (In the above formula (1), R 1 , R 2 and R 3 are each independently an alkyl group having 1 to 3 carbon atoms or an alkoxy group having 1 to 3 carbon atoms, and R 1 , R 2 and R 3 At least one of them is an alkoxy group. n is an integer of 2 to 4. X is a group having a terpene skeleton and a molecular weight of 200 to 1000, and the carbon-carbon double bond in the molecule of X may be saturated or unsaturated, and X may contain a hetero element.

[0012] In the rubber composition (1) or (2), the organic silane is represented by the following general formula (2): [ka] (In the above formula (2), R 1 , R 2 , R 3 and n are the same as in the above formula (1).) and a compound represented by the following general formula (3a): [ka] A compound represented by the following general formula (3b): [ka] and a compound represented by the following general formula (3c): [ka] A rubber composition (3) which is an ene-thiol reaction product with at least one compound selected from the group consisting of compounds represented by the following formula (1) is preferred.

[0013] In any of the rubber compositions (1) to (3), when the total amount of the diene rubber is taken as 100 parts by mass, a rubber composition (4) is preferred in which the silica is contained in an amount of 30 to 150 parts by mass, the sulfur-containing silane coupling agent is contained in an amount of 1 to 15% by mass of the silica, and the content of the organic silane is 10 to 300% by mass of the sulfur-containing silane coupling agent.

[0014] The present invention also relates to a pneumatic tire (5) comprising at least a vulcanized rubber of any one of the rubber compositions (1) to (4) above. [Effects of the Invention]

[0015] When silica is compounded as a reinforcing material in a rubber composition, especially when the amount of silica compounded is large, the dispersibility of the silica in the rubber tends to deteriorate, resulting in insufficient filling effect of the silica. Therefore, various organic silanes (silane coupling agents) have been compounded to improve the dispersibility of silica in the rubber. However, as a result of extensive research by the present inventors, it has been found that the organic silanes that have been compounded so far, even when compounded with silica in the rubber, do not sufficiently soften the interface between the rubber and the silica, making it difficult to achieve a balanced improvement in the wet performance and fuel economy of the final vulcanized rubber.

[0016] On the other hand, the rubber composition according to the present invention contains, as an organosilane, a compound having a terpene skeleton with a molecular weight of 200 to 1000, in addition to the diene rubber and silica. The terpene skeleton of the organosilane with a molecular weight of 200 to 1000 has a high affinity with the diene rubber, and when present at the interface between the diene rubber and silica, it can highly soften the interface. Additionally, the terpene skeleton with a molecular weight of 200 to 1000 can highly hydrophobize the silica surface, thereby improving the dispersibility of silica in the diene rubber. As a result, the vulcanized rubber of the rubber composition according to the present invention exhibits excellent silica dispersibility in the rubber, while the interface between the diene rubber and silica is highly flexible, resulting in a well-balanced improvement in wet performance and fuel economy. Furthermore, the rubber composition according to the present invention further contains, in addition to the organosilane with a terpene skeleton with a molecular weight of 200 to 1000, a sulfur-containing silane coupling agent other than the organosilane. This results in a well-balanced improvement in wet performance, fuel economy, and abrasion resistance.

[0017] In addition, the technology described in Patent Document 3, in which an organic silane having a low molecular weight terpene skeleton is compounded in a rubber composition, contributes to improving the dispersibility of silica in the rubber to some extent, but does not sufficiently soften the interface between the diene rubber and silica. As far as the present inventors know, this is the first research that focuses on the flexibility of the interface between the diene rubber and silica, and of course, Patent Document 3 does not describe or suggest this.

[0018] The vulcanized rubber of the rubber composition according to the present invention has a well-balanced improvement in wet performance, fuel economy, and abrasion resistance, and is therefore particularly useful for the tread application of pneumatic tires. DETAILED DESCRIPTION OF THE INVENTION

[0019] The rubber composition according to the present invention contains a diene rubber, silica, an organic silane, and a sulfur-containing silane coupling agent other than the organic silane.

[0020] The diene rubber contained in the rubber composition according to the present invention is not particularly limited, and examples thereof include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer, styrene-isoprene-butadiene copolymer rubber, etc. These may be used alone or in combination of two or more.

[0021] As the silica, wet silica, dry silica, sol-gel silica, surface-treated silica, etc., which are commonly used for rubber reinforcement, are used. Among them, wet silica is preferred. From the viewpoint of improving the wet performance and fuel economy of the vulcanized rubber in a well-balanced manner, the amount of silica blended is preferably 30 to 150 parts by mass, more preferably 50 to 120 parts by mass, when the total amount of diene rubber in the rubber composition is taken as 100 parts by mass.

[0022] The rubber composition according to the present invention is characterized in that it contains, as the organosilane, a compound having a terpene skeleton with a molecular weight of 200 to 1,000. If the molecular weight of the terpene skeleton of the organosilane is less than 200 or more than 1,000, the interface between the diene rubber and the silica will not be softened sufficiently, and the improvement in wet performance and fuel economy will tend to be insufficient. In the present invention, the amount of the organosilane in the rubber composition is preferably 10 to 300% by mass of the sulfur-containing silane coupling agent used in combination, and more preferably 10 to 100% by mass of the sulfur-containing silane coupling agent used in combination.

[0023] In the present invention, the organosilane having a terpene skeleton and a molecular weight of 200 to 1000 is preferably an organosilane represented by the following general formula (1): [ka] (In the above formula (1), R 1 , R 2 and R 3are each independently an alkyl group having 1 to 3 carbon atoms or an alkoxy group having 1 to 3 carbon atoms, and R 1 , R 2 and R 3 at least one of them is an alkoxy group. n is an integer of 2 to 4. X is a group having a terpene skeleton and a molecular weight of 200 to 1000, and the carbon-carbon double bond in the molecule of X may be saturated or unsaturated, and X may contain a hetero element.

[0024] The organosilane used in the present invention is not particularly limited as long as it is a compound having a terpene skeleton and a molecular weight of 200 to 1000, but more preferably, an ene-thiol reaction product of a silicon-containing thiol compound and a compound having a terpene skeleton and a molecular weight of 200 to 1000 can be used. Examples of silicon-containing thiol compounds include those represented by the following general formula (2):

[0025] [ka] (In the above formula (2), R 1 , R 2 , R 3 and n are the same as in the above formula (1). Examples of the silicon-containing thiol compound having a mercapto group represented by the general formula (2) include a silicon-containing thiol compound having a mercapto group represented by the general formula (2). The silicon-containing thiol compound having a mercapto group can be converted into a desired organosilane by an ene-thiol reaction between the mercapto group and a carbon-carbon double bond (C=C) in a compound having a terpene skeleton and a molecular weight of 200 to 1000. Specific examples of the compound of the general formula (2) include (3-mercaptopropyl)triethoxysilane, (3-mercaptopropyl)trimethoxysilane, (3-mercaptopropyl)methyldimethoxysilane, (3-mercaptopropyl)dimethylmethoxysilane, and mercaptoethyltriethoxysilane.

[0026] The compound having a terpene skeleton and a molecular weight of 200 to 1000 is not particularly limited, but is preferably a compound represented by the following general formula (3a): [ka] A compound represented by the following general formula (3b): [ka] and a compound represented by the following general formula (3c): [ka] The general formula (3a), the general formula (3b), and the general formula (3c) may be each independently subjected to an ene-thiol reaction with a silicon-containing thiol compound having a mercapto group to produce an organosilanes, or at least two or all three of these may be mixed and subjected to an ene-thiol reaction with a silicon-containing thiol compound having a mercapto group to produce an organosilanes.

[0027] In the ene-thiol reaction, it is preferable to use a radical generator as a reaction catalyst. Radical reactions can also be carried out by irradiation with ultraviolet (UV) light. Examples of radical generators include azo compounds and organic peroxides, including those that generate radicals by heat or light irradiation. Examples of azo compounds include azobisisobutyronitrile (AIBN) and 1,1'-azobis(cyclohexanecarbonitrile) (ABCN). Examples of organic peroxides include di-tert-butyl peroxide, tert-butyl hydroperoxide, benzoyl peroxide, and methyl ethyl ketone peroxide.

[0028] The ene-thiol reaction can be carried out by mixing, for example, a compound represented by general formula (2), a compound having a terpene skeleton and a molecular weight of 200 to 1000, and a radical generator together with an organic solvent such as toluene, and maintaining the mixture under conditions that generate radicals. The reaction temperature is preferably 50 to 120°C.

[0029] The organic silane having a terpene skeleton with a molecular weight of 200 to 1000 has a monosulfide bond (-CSC-) to improve its affinity with diene rubber. Furthermore, because the organic silane having a terpene skeleton with a molecular weight of 200 to 1000 has a high affinity between the terpene skeleton with a molecular weight of 200 to 1000 and diene rubber, when present at the interface between the diene rubber and silica, it can soften the interface to a high degree. Therefore, in the vulcanized rubber of the rubber composition according to the present invention, the dispersibility of silica in the rubber is excellent, and the interface between the two is very soft, resulting in a balanced improvement in wet performance and fuel economy.

[0030] In the present invention, it is preferable to use a compound represented by the general formula (1) as the organosilane having a terpene skeleton and a molecular weight of 200 to 1000, and a compound represented by the following general formula (4a): [ka] A compound represented by the following general formula (4b): [ka] or a compound represented by the following general formula (4c): [ka] Compounds represented by the following formula are particularly preferred.

[0031] The rubber composition according to the present invention further contains a sulfur-containing silane coupling agent other than the organic silane, in addition to the organic silane having a terpene skeleton and a molecular weight of 200 to 1000. This improves the wet performance, fuel economy, and abrasion resistance in a well-balanced manner. Examples of the sulfur-containing silane coupling agent other than the organic silane, which is a compound having a terpene skeleton and a molecular weight of 200 to 1000, include bis(3-triethoxysilylpropyl)tetrasulfide (e.g., "Si69" manufactured by Evonik Japan Co., Ltd.), bis(3-triethoxysilylpropyl)disulfide (e.g., "Si75" manufactured by Evonik Japan Co., Ltd.), bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl) mercaptosilanes such as γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, mercaptopropylmethyldimethoxysilane, mercaptopropyldimethylmethoxysilane, and mercaptoethyltriethoxysilane; and protected mercaptosilanes such as 3-octanoylthio-1-propyltriethoxysilane and 3-propionylthiopropyltrimethoxysilane.

[0032] In the present invention, the content of the sulfur-containing silane coupling agent in the rubber composition is preferably 1 to 15 mass %, more preferably 1 to 10 mass %, of the compounded amount of silica.

[0033] The rubber composition according to the present invention may contain, in addition to the diene rubber, silica, an organosilane which is a compound having a terpene skeleton and a molecular weight of 200 to 1000, and a silane coupling agent other than the organosilane, carbon black, a vulcanizing agent, a vulcanization accelerator, an antioxidant, stearic acid, a softener such as wax or oil, a processing aid, etc.

[0034] As the carbon black, for example, carbon blacks commonly used in the rubber industry such as SAF, ISAF, HAF, FEF, and GPF, as well as conductive carbon blacks such as acetylene black and ketjen black can be used.

[0035] As the vulcanizing agent, sulfur can be suitably used. The sulfur may be any ordinary sulfur for rubber, such as powdered sulfur, precipitated sulfur, insoluble sulfur, or highly dispersible sulfur. In the rubber composition for tires according to the present invention, the content of the vulcanizing agent is preferably 0.5 to 3.5 parts by mass when the total amount of the diene rubber is taken as 100 parts by mass.

[0036] As the vulcanization accelerator, vulcanization accelerators commonly used for rubber vulcanization, such as sulfenamide-based vulcanization accelerators, thiuram-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiourea-based vulcanization accelerators, guanidine-based vulcanization accelerators and dithiocarbamate-based vulcanization accelerators, may be used alone or in appropriate mixtures.

[0037] As the antiaging agent, antiaging agents commonly used for rubber, such as aromatic amine antiaging agents, amine-ketone antiaging agents, monophenol antiaging agents, bisphenol antiaging agents, polyphenol antiaging agents, dithiocarbamate antiaging agents, and thiourea antiaging agents, may be used alone or in appropriate mixtures.

[0038] The rubber composition according to the present invention can be obtained by kneading diene rubber, silica, an organosilane which is a compound having a terpene skeleton and a molecular weight of 200 to 1000, a silane coupling agent other than the organosilane, carbon black, a vulcanizing agent, a vulcanization accelerator, an antioxidant, stearic acid, a softener such as wax or oil, a processing aid, and the like, using a kneading machine typically used in the rubber industry, such as a Banbury mixer, a kneader, or a roll.

[0039] The method for compounding the above-mentioned components is not particularly limited, and any of the following may be used: a method in which the compounding components other than the vulcanization-based compounding agents, such as the vulcanizing agent and vulcanization accelerator, are pre-mixed to form a master batch, and the remaining components are then added and further kneaded; a method in which the components are added in any order and kneaded; or a method in which all the components are added simultaneously and kneaded.

[0040] The vulcanized rubber of the rubber composition according to the present invention has a well-balanced improvement in wet performance, fuel economy, and abrasion resistance, and is therefore particularly useful for the tread application of pneumatic tires. [Example]

[0041] The present invention will be explained in more detail below by way of examples.

[0042] [Preparation of Rubber Composition and Vulcanized Rubber] According to the formulation (parts by mass) listed in Tables 1 to 9, diene rubber was masticated for 30 seconds using a Daihan lab mixer (300 cc). Then, silica, an organic silane or silane coupling agent, zinc oxide, stearic acid, and oil were added and kneaded for 240 seconds, after which the mixture was discharged. The discharged rubber composition was then added to the lab mixer, kneaded for 180 seconds, and then discharged. Furthermore, the discharged rubber composition, sulfur, and vulcanization accelerator were added to the lab mixer, kneaded for 60 seconds, and then discharged. The resulting unvulcanized rubber composition was sheeted using a two-roll mill to a thickness of 2 mm, and then subjected to a vulcanization press at 160°C for 20 minutes to obtain a vulcanized rubber sample. The compounding ingredients listed in Tables 1 to 9 are listed below.

[0043] (Diene rubber) SBR: ENEOS Materials "HPR350", terminal amine-modified S-SBR (silica) Tosoh Corporation's "Nip Seal AQ" (Silane coupling agent (sulfur-containing silane coupling agent)) Evonik Japan "Si75"

[0044] (organosilane) Organic silane (1) (a compound without a terpene skeleton): "Octyltriethoxysilane" manufactured by Tokyo Chemical Industry Co., Ltd.

[0045] Organic silane (2) (a compound having a terpene skeleton and a molecular weight of 200 to 1000): produced by the following synthesis method 1 (Synthesis method 1) 46.6 g of nerolidol (Tokyo Chemical Industry Co., Ltd.) represented by the general formula (3a) above, 50.0 g of (3-mercaptopropyl)triethoxysilane (Tokyo Chemical Industry Co., Ltd.), 3.4 g of 2,2'-azobis(isobutylnitrile) (Wako Pure Chemical Industries, Ltd.), and 100 mL of toluene were mixed in a recovery flask, and after bubbling with nitrogen gas for 30 minutes, the mixture was reacted at 70°C for 24 hours. The reaction solution was then concentrated, yielding 94.8 g of a pale yellow liquid (yield: 98% by mass). NMR analysis confirmed that the product was nerolidolsilane represented by the general formula (4a) above. This product was designated "organosilane (2)."

[0046] Organosilane (3) (a compound having a terpene skeleton and a molecular weight of 200 to 1000): produced by the following synthesis method 2 (Synthesis method 2) 60.9 g of geranylinalool (Tokyo Chemical Industry Co., Ltd.) represented by the general formula (3b), 50.0 g of (3-mercaptopropyl)triethoxysilane (Tokyo Chemical Industry Co., Ltd.), 3.4 g of 2,2'-azobis(isobutylnitrile) (Wako Pure Chemical Industries, Ltd.), and 100 mL of toluene were mixed in a recovery flask, and after bubbling with nitrogen gas for 30 minutes, the mixture was reacted at 70 ° C for 24 hours. The reaction solution was then concentrated, yielding 109.2 g of a pale yellow liquid (yield: 98% by mass). NMR analysis confirmed that the product was geranylinaloolsilane represented by the general formula (4b). This product was designated "organic silane (3)."

[0047] Organosilane (4) (a compound having a terpene skeleton and a molecular weight of 200 to 1000): produced by the following synthesis method 3 (Synthesis method 3) 62.2 g of isophytol (Tokyo Chemical Industry Co., Ltd.) represented by the general formula (3c), 50.0 g of (3-mercaptopropyl)triethoxysilane (Tokyo Chemical Industry Co., Ltd.), 3.4 g of 2,2'-azobis(isobutylnitrile) (Wako Pure Chemical Industries, Ltd.), and 100 mL of toluene were mixed in a recovery flask, and after bubbling with nitrogen gas for 30 minutes, the mixture was reacted at 70°C for 24 hours. The reaction solution was then concentrated to obtain 111.0 g of a pale yellow liquid (yield: 99% by mass). NMR analysis confirmed that the product was isophytolsilane represented by the general formula (4c). This product was designated "organosilane (4)."

[0048] (Other compounding agents) Zinc oxide: "Zinc Oxide No. 3" manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Kao Corporation's "Lunac S-20" Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator (1): Sumitomo Chemical's "Soxinol CZ" Vulcanization accelerator (2): "Noccela D" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0049] The obtained vulcanized rubber samples were evaluated under the following evaluation conditions. [WET performance (wet grip performance)] Using a viscoelasticity tester manufactured by Ueshima Seisakusho Co., Ltd., the loss factor tan δ was measured at a frequency of 10 Hz, static strain of 10%, dynamic strain of 1%, and temperature of 0°C. The value of Comparative Example 2 in Table 1, the value of Comparative Example 3 in Table 2, the value of Comparative Example 4 in Table 3, the value of Comparative Example 5 in Table 4, the value of Comparative Example 6 in Table 5, the value of Comparative Example 8 in Table 6, the value of Comparative Example 9 in Table 7, the value of Comparative Example 10 in Table 8, and the value of Comparative Example 11 in Table 9 are all expressed as an index, with 100 as the index. A larger index indicates a larger tan δ, which indicates better wet grip performance when made into a tire.

[0050] [Low fuel consumption (heat generation)] Using a viscoelasticity tester manufactured by Ueshima Seisakusho Co., Ltd., the loss factor tan δ was measured at a frequency of 10 Hz, static strain of 10%, dynamic strain of 1%, and a temperature of 60°C. The value for Comparative Example 2 in Table 1, the value for Comparative Example 3 in Table 2, the value for Comparative Example 4 in Table 3, the value for Comparative Example 5 in Table 4, the value for Comparative Example 6 in Table 5, the value for Comparative Example 8 in Table 6, the value for Comparative Example 9 in Table 7, the value for Comparative Example 10 in Table 8, and the value for Comparative Example 11 in Table 9 are all expressed as an index, with 100 as the index. The smaller the index, the smaller the tan δ, indicating excellent heat buildup when made into a tire.

[0051] [Wear resistance] In accordance with JIS K6264, a Lambourn abrasion tester manufactured by Iwamoto Seisakusho Co., Ltd. was used to measure the abrasion loss under conditions of a load of 40 N and a slip ratio of 30%, and the reciprocal of the measured value was expressed as an index, with the value for Comparative Example 2 in Table 1, the value for Comparative Example 3 in Table 2, the value for Comparative Example 4 in Table 3, the value for Comparative Example 5 in Table 4, the value for Comparative Example 6 in Table 5, the value for Comparative Example 8 in Table 6, the value for Comparative Example 9 in Table 7, the value for Comparative Example 10 in Table 8, and the value for Comparative Example 11 in Table 9 each being set to 100. A larger index indicates better abrasion resistance.

[0052] [Table 1]

[0053] The results in Table 1 show that compared to Comparative Example 1, which contained only a sulfur-containing silane coupling agent, and Comparative Example 2, which used a sulfur-containing silane coupling agent in combination with octyltriethoxysilane not having a terpene skeleton, Examples 1 to 3, which contained a sulfur-containing silane coupling agent and organic silanes (2) to (4) having a terpene skeleton and a molecular weight of 200 to 1000, showed a balanced improvement in wet performance, fuel economy, and wear resistance.

[0054] [Table 2]

[0055] In the blending systems in Table 2, the content of the organic silane was set to 10 mass % or more of the sulfur-containing silane coupling agent. The results in Table 2 show that compared to Comparative Example 3, in which a sulfur-containing silane coupling agent was used in combination with octyltriethoxysilane having no terpene skeleton, Examples 4 to 6, in which a sulfur-containing silane coupling agent was blended with organic silanes (2) to (4) having a terpene skeleton and a molecular weight of 200 to 1000, showed well-balanced improvements in wet performance, fuel economy, and wear resistance.

[0056] [Table 3]

[0057] In the blending systems in Table 3, the content of the organic silane was 100% by mass of the sulfur-containing silane coupling agent. The results in Table 3 show that, compared to Comparative Example 4, in which a sulfur-containing silane coupling agent was used in combination with octyltriethoxysilane having no terpene skeleton, Examples 7 to 9, in which a sulfur-containing silane coupling agent was blended with organic silanes (2) to (4) having a terpene skeleton and a molecular weight of 200 to 1000, showed well-balanced improvements in wet performance, fuel economy, and wear resistance.

[0058] [Table 4]

[0059] In the blending systems of Table 4, the content of the organic silane was 200% by mass of the sulfur-containing silane coupling agent. The results in Table 4 show that compared to Comparative Example 5, in which a sulfur-containing silane coupling agent was used in combination with octyltriethoxysilane having no terpene skeleton, Example 10, in which a sulfur-containing silane coupling agent was blended with organic silane (4) having a terpene skeleton and a molecular weight of 200 to 1000, showed a well-balanced improvement in the three aspects of wet performance, fuel economy, and wear resistance.

[0060] [Table 5]

[0061] In the blending systems of Table 5, the content of the organic silane was 300% by mass of the sulfur-containing silane coupling agent. The results in Table 5 show that compared to Comparative Example 6, in which a sulfur-containing silane coupling agent was used in combination with octyltriethoxysilane having no terpene skeleton, Example 10, in which a sulfur-containing silane coupling agent was blended with organic silane (4) having a terpene skeleton and a molecular weight of 200 to 1000, showed well-balanced improvements in the three aspects of wet performance, fuel economy, and wear resistance.

[0062] [Table 6]

[0063] The results in Table 6 show that compared to Comparative Example 7, which contained only a sulfur-containing silane coupling agent, and Comparative Example 8, which used a sulfur-containing silane coupling agent in combination with octyltriethoxysilane not having a terpene skeleton, Examples 14 and 15, which contained a sulfur-containing silane coupling agent and organic silanes (3) and (4) having a terpene skeleton and a molecular weight of 200 to 1000, showed a balanced improvement in the three aspects of wet performance, fuel economy, and wear resistance.

[0064] [Table 7]

[0065] In the blending systems of Table 7, the content of the organic silane was set to 10 mass% or more of the sulfur-containing silane coupling agent. The results in Table 7 show that compared to Comparative Example 9, in which a sulfur-containing silane coupling agent was used in combination with octyltriethoxysilane having no terpene skeleton, Examples 14 and 15, in which a sulfur-containing silane coupling agent was blended with organic silanes (3) and (4) having a terpene skeleton and a molecular weight of 200 to 1000, showed well-balanced improvements in the three aspects of wet performance, fuel economy, and wear resistance.

[0066] [Table 8]

[0067] In the blending systems of Table 8, the content of the organic silane was 100% by mass of the sulfur-containing silane coupling agent. The results in Table 8 show that, compared to Comparative Example 10, in which a sulfur-containing silane coupling agent was used in combination with octyltriethoxysilane having no terpene skeleton, Examples 16 and 17, in which a sulfur-containing silane coupling agent was blended with organic silanes (3) and (4) having a terpene skeleton and a molecular weight of 200 to 1000, showed well-balanced improvements in the three aspects of wet performance, fuel economy, and wear resistance.

[0068] [Table 9]

[0069] In the blending systems of Table 9, the content of the organic silane was 200% by mass of the sulfur-containing silane coupling agent. The results in Table 9 show that compared to Comparative Example 11, in which a sulfur-containing silane coupling agent was used in combination with octyltriethoxysilane having no terpene skeleton, Example 18, in which a sulfur-containing silane coupling agent was blended with organic silane (4) having a terpene skeleton and a molecular weight of 200 to 1000, showed well-balanced improvements in the three aspects of wet performance, fuel economy, and wear resistance.

Claims

1. A rubber composition containing a diene rubber, silica, and an organic silane, The organosilane is a compound having a terpene skeleton and a molecular weight of 200 to 1000, The rubber composition further comprises a sulfur-containing silane coupling agent other than the organic silane.

2. The organosilane is represented by the following general formula (1): 【Chemical 1】 (In the above formula (1), R １ , R ２ and R ３ are each independently an alkyl group having 1 to 3 carbon atoms or an alkoxy group having 1 to 3 carbon atoms, and R １ , R ２ and R ３ wherein at least one of them is an alkoxy group. n is an integer of 2 to 4. X is a group having a terpene skeleton and a molecular weight of 200 to 1000, and the carbon-carbon double bond in the molecule of X may be saturated or unsaturated, and X may contain a hetero element.

3. The organosilane is represented by the following general formula (2): 【Chemistry 2】 (In the above formula (2), R １ , R ２ , R ３ and n are the same as in the above formula (1).) and a compound represented by the following general formula (3a): 【Chemistry 3】 a compound represented by the following general formula (3b): 【Chemistry 4】 and a compound represented by the following general formula (3c): 【Chemistry 5】 2. The rubber composition according to claim 1, wherein the rubber composition is an ene-thiol reaction product with at least one compound selected from the group consisting of compounds represented by the formula:

4. The rubber composition according to claim 1, wherein the silica is contained in an amount of 30 to 150 parts by mass, and the sulfur-containing silane coupling agent is contained in an amount of 1 to 15% by mass of the silica, and the content of the organic silane is 10 to 300% by mass of the sulfur-containing silane coupling agent, when the total amount of the diene rubber is 100 parts by mass.

5. A pneumatic tire comprising at least a vulcanized rubber of the rubber composition according to claim 1.

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