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 WET performance and fuel economy 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. When the elastic modulus of a rubber at a silica interface is Ei and the elastic modulus of a matrix rubber is Em, Ei / Em<1.5 is satisfied. The diene rubber is preferably a modified styrene-butadiene rubber. The organic silane is preferably 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 used 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, improvement in heat generation, which contributes to low fuel consumption, is also required.

[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. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4930661 [Patent Document 2] Patent No. 6018001 Summary of the Invention [Problem to be solved by the invention]

[0006] 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.

[0007] The present invention has been made in view of the above-mentioned 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 and fuel economy, and a pneumatic tire equipped with vulcanized rubber of the rubber composition. [Means for solving the problem]

[0008] 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, characterized in that, when the elastic modulus of the rubber at the silica interface is Ei and the elastic modulus of the matrix rubber is Em, Ei / Em<1.5.

[0009] In the rubber composition (1), a rubber composition (2) is preferred in which the diene rubber is a modified styrene-butadiene rubber.

[0010] In the rubber composition (1) or (2), the organosilane is preferably a rubber composition (3) having a terpene skeleton and a molecular weight of 200 to 1,000.

[0011] In any one of the rubber compositions (1) to (3), 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 , R2 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 any one of the rubber compositions (1) to (4), 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 (5) 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 (5), a rubber composition (6) is preferred, which contains 30 to 150 parts by mass of the silica and 3 to 30% by mass of the organic silane relative to the silica, when the total amount of the diene rubber is 100 parts by mass.

[0014] The present invention also relates to a pneumatic tire (7) comprising at least a vulcanized rubber of any one of the rubber compositions (1) to (6) 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 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 of the present invention is formulated with an organic silane in addition to a diene rubber and silica, and is designed so that, where Ei is the elastic modulus of the rubber at the silica interface and Em is the elastic modulus of the matrix rubber, Ei / Em<1.5 is satisfied. As a result, flexibility is ensured at the interface between the rubber and silica, and the silica exerts a sufficient reinforcing effect, resulting in a well-balanced improvement in the wet performance and fuel economy of the final vulcanized rubber.

[0017] In particular, in the present invention, when a modified styrene-butadiene rubber is blended as the diene rubber and a compound having a terpene skeleton with a molecular weight of 200 to 1000 is blended as the organosilane, the wet performance and fuel economy of the final vulcanized rubber are improved in a particularly balanced manner. The reason for this effect is unclear, but the following reason can be assumed. The terpene skeleton with a molecular weight of 200 to 1000 of the organosilane is flexible, so when present at the interface between the diene rubber and silica, it can soften the interface to a high degree. In addition, the terpene skeleton with a molecular weight of 200 to 1000 can hydrophobize the silica surface to a high degree, thereby improving the dispersibility of silica in the diene rubber. Furthermore, when a modified styrene-butadiene rubber is used as the diene rubber, this effect is further enhanced. As a result, the wet performance and fuel economy of the final vulcanized rubber are improved in a particularly balanced manner due to the excellent dispersibility of silica in the rubber and the extremely flexible interface between the two.

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

[0019] The rubber composition according to the present invention contains a diene rubber, silica, and an 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] However, in the present invention, the use of modified styrene-butadiene rubber as the diene rubber is preferred because it provides a particularly well-balanced improvement in the wet performance and fuel economy of the final vulcanized rubber. In the present invention, "modified styrene-butadiene rubber" refers to a styrene-butadiene rubber having a functional group reactive with silica. Examples of the functional group reactive with silica include a hydroxyl group, an amino group, a carboxyl group, an alkoxy group, an alkoxysilyl group, and an epoxy group. The functional group may be introduced at the molecular end or in the molecular chain. From the viewpoint of achieving a particularly well-balanced improvement in the wet performance and fuel economy of the final vulcanized rubber, the amount of modified styrene-butadiene rubber is preferably 30 parts by mass or more, more preferably 50 parts by mass or more, and particularly preferably 100 parts by mass, based on 100 parts by mass of the total amount of rubber components.

[0022] 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.

[0023] The rubber composition according to the present invention preferably 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, which tends to result in insufficient improvements in wet performance and fuel economy. In the present invention, the amount of organosilane contained in the rubber composition is preferably 3 to 30 mass % of the amount of silica, and more preferably 3 to 15 mass % of the amount of silica.

[0024] 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 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.

[0025] 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):

[0026] [ka] (In the above formula (2), R 1 , R 2 , R 3and 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] Organosilanes having a terpene skeleton with a molecular weight of 200 to 1000 have a monosulfide bond (-CSC-) in the molecule, which is cleaved by heat to react with diene rubber, or the presence of at least a monosulfide bond improves affinity with diene rubber. Furthermore, because the terpene skeleton with a molecular weight of 200 to 1000 is flexible, organosilanes having a terpene skeleton with a molecular weight of 200 to 1000 can highly soften the interface between the diene rubber and silica when present at the interface. Therefore, the vulcanized rubber of the rubber composition according to the present invention exhibits excellent silica dispersibility in the rubber, and the interface between the two is very flexible, resulting in a balanced improvement in wet performance and fuel economy.

[0031] 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.

[0032] The rubber composition according to the present invention is a rubber composition containing the diene rubber, silica, and organic silane described above, characterized in that, when the elastic modulus of the rubber at the silica interface is Ei and the elastic modulus of the matrix rubber is Em, Ei / Em<1.5. In the rubber composition according to the present invention, the silica reacts with the organic silane, and the organic silane reacts with the diene rubber to form rubber at the silica interface (bound rubber). When Ei / Em<1.5, the flexibility of the rubber at the silica interface (bound rubber) is ensured, resulting in a balanced improvement in the wet performance and fuel economy of the final vulcanized rubber.

[0033] In the present invention, the elastic modulus Ei of the rubber (bound rubber) at the silica interface in the rubber composition can be determined, for example, by measuring the force curve using an atomic force microscope. An atomic force microscope (AFM) is a type of scanning probe microscope that detects the force acting between the atoms of a sample and a probe. The probe is attached to the tip of a cantilever (cantilever spring). The force (deflection) acting on the cantilever is measured while changing the distance between the sample and the probe, and a force curve is obtained, which is a curve plotting the relationship between the two. The elastic modulus (hardness) of the sample surface can be determined by analyzing this force curve. Determining the elastic modulus of a sample surface by force curve measurement is itself well known, and this can be done using such a well-known method.

[0034] By scanning a specified area on the sample surface, force curves are obtained at multiple points within the specified area, and a histogram is created from the elastic modulus obtained from each force curve. This histogram is then peak-separated to separate the silica component, diene rubber component, and a component with a higher elastic modulus than the matrix rubber component but a lower elastic modulus than the silica component (rubber (bound rubber) component at the silica interface). This allows the volume fraction of bound rubber in the rubber composition to be determined.

[0035] In addition, when the amount of silica blended as a filler is known, the volume fraction of silica can be calculated from the blended amount, and when peak separation of the histogram is performed, the volume fraction of silica calculated from this blended amount can be subtracted in advance, and the remainder can be divided into a matrix rubber component and a bound rubber component to determine the volume fraction of bound rubber in the rubber composition.

[0036] For details, please refer to the method described in "Nakajima Ken et al., 'An Approach to Analyzing the Structure and Physical Properties of Filler / Polymer Interfaces in the Nanoscale Using Atomic Force Microscopy,' Journal of Adhesion Technology, Vol. 35, No. 3, pp. 13-17, 2015, published by the Japan Adhesion Society." Specifically, the volume fraction of the high-modulus component, corresponding to silica, is subtracted from the elastic modulus histogram. Next, the peak on the low-modulus side of the histogram is fitted as a normal distribution using a lognormal function. The area enclosed by this fitting curve is considered to be the matrix rubber component. The components outside the histogram's fitting curve are considered to be the bound rubber component, and the volume fraction of the bound rubber component can be calculated. Furthermore, the elastic modulus of the bound rubber component (the elastic modulus of rubber at the silica interface, Ei) can be calculated from the average value of the elastic modulus histogram for the bound rubber component.

[0037] In the present invention, the elastic modulus Em of the matrix rubber in the rubber composition can be calculated as a weighted average of the elastic moduli of the force curve obtained using an atomic force microscope (AFM) excluding the filler component and bound rubber component.

[0038] In addition to the diene rubber, silica, and organic silane, the rubber composition according to the present invention may contain a silane coupling agent other than the organic silane, 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.

[0039] Suitable examples of the silane coupling agent other than organic silane, which is a compound having a terpene skeleton and a molecular weight of 200 to 1000, include sulfur-containing silane coupling agents. Examples of sulfur-containing silane coupling agents include sulfide silanes such as 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)tetrasulfide, and bis(2-trimethoxysilylethyl)disulfide; mercaptosilanes such as γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, mercaptopropylmethyldimethoxysilane, mercaptopropyldimethylmethoxysilane, and mercaptoethyltriethoxysilane; and protected mercaptosilanes such as 3-octanoylthio-1-propyltriethoxysilane and 3-propionylthiopropyltrimethoxysilane.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] The rubber composition according to the present invention can be obtained by kneading diene rubber, silica, an organic silane, a silane coupling agent other than the organic silane, 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.

[0045] 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.

[0046] The vulcanized rubber of the rubber composition according to the present invention has a well-balanced improvement in wet performance and fuel economy, and is therefore particularly useful for use as a tread for pneumatic tires. [Example]

[0047] The present invention will be explained in more detail below by way of examples.

[0048] [Method for measuring elastic modulus Ei of rubber at silica interface and elastic modulus Em of matrix rubber in rubber composition] A Bruker "Dimension Icon" atomic force microscope was used, and an Olympus "OMCL-AC240TS-R3" cantilever was used. Using this atomic force microscope, a force curve was measured at 128 x 128 points (3 μm x 3 μm), and the elastic modulus and adhesive force were calculated from each force curve to create a distribution curve. Because the filler in the rubber composition has low adhesive force, the elastic modulus of the force curve corresponding to the filler content (18 vol% in this example) at which adhesive force was low was used as the filler's elastic modulus. Next, the unvulcanized rubber was extracted from toluene, and the amount of bound rubber was determined from the remaining gel. Based on this value, the weighted average of the elastic modulus of the force curve corresponding to the amount of bound rubber at which adhesive force was low, minus the filler component, was used as the interfacial elastic modulus (Ei). Finally, the weighted average of the elastic moduli of the 128 x 128 point force curve excluding the filler and bound rubber components was taken as the elastic modulus of the matrix rubber (Em).

[0049] [Preparation of Rubber Composition and Vulcanized Rubber] According to the formulation (parts by mass) listed in Tables 1 and 2, diene rubber was masticated for 30 seconds using a Daihan lab mixer (300 cc), followed by the addition of silica, an organic silane or silane coupling agent, zinc oxide, and stearic acid. The mixture was then kneaded for 240 seconds and discharged. The discharged rubber composition was then added to the lab mixer, kneaded for 180 seconds, and discharged. The discharged rubber composition, sulfur, and vulcanization accelerator were then added to the lab mixer, kneaded for 60 seconds, and 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 and 2 are listed below.

[0050] (Diene rubber) SBR(1): ENEOS Materials "SBR1502" SBR (2): Asahi Kasei "Tufden 2000R" SBR(3): ENEOS Materials "SL563" SBR (4): ENEOS Materials Corporation "HPR350", terminal amine-modified S-SBR (silica) Tosoh Corporation's "Nip Seal AQ" (Silane coupling agent (sulfur-containing silane coupling agent)) Evonik Japan "Si75"

[0051] (organosilane) Organic silane (1) (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), 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). This product was designated "organosilane (1)."

[0052] Organic silane (2) (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 (2)."

[0053] Organic silane (3) (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 (manufactured by Tokyo Chemical Industry Co., Ltd.) represented by the general formula (3c), 50.0 g of (3-mercaptopropyl)triethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.), 3.4 g of 2,2'-azobis(isobutylnitrile) (manufactured by 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 (3)."

[0054] (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.

[0055] 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. In Table 1, the value of Comparative Example 1 for Comparative Example 2, the value of Comparative Example 3 for Comparative Example 4, the value of Comparative Example 5 for Comparative Example 6, and the value of Comparative Example 7 for Example 1 are all expressed as an index, with each being set to 100. In Table 2, the value of Comparative Example 8 for Examples 2 and 3 are all expressed as an index, with each being set to 100. In each case, the larger the index, the larger the tan δ, indicating better wet grip performance when made into a tire.

[0056] [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. In Table 1, the value of Comparative Example 1 for Comparative Example 2, the value of Comparative Example 3 for Comparative Example 4, the value of Comparative Example 5 for Comparative Example 6, and the value of Comparative Example 7 for Example 1 are all expressed as an index, with each being set to 100. In Table 2, the value of Comparative Example 8 for Examples 2 and 3 are all expressed as an index, with each being set to 100. In each case, the smaller the index, the smaller the tan δ, indicating excellent heat buildup when made into a tire.

[0057] [Table 1]

[0058] From the comparison results of Comparative Example 2 and Comparative Example 1, Comparative Example 4 and Comparative Example 3, and Comparative Example 6 and Comparative Example 5 in Table 1, it can be seen that in Comparative Examples 2, 4, and 6, in which an organic silane having a terpene skeleton with a molecular weight of 200 to 1000 was blended instead of a silane coupling agent, none of them satisfied Ei / Em<1.5, and therefore, the wet performance of some of the vulcanized rubbers improved, but the heat buildup generally deteriorated. On the other hand, from the comparison results of Example 1 and Comparative Example 7 in Table 1, it can be seen that in Example 1, in which an organic silane (3) having a terpene skeleton with a molecular weight of 200 to 1000 was blended instead of a silane coupling agent, Ei / Em<1.5 was satisfied (Ei / Em=1.0), and therefore, the vulcanized rubber exhibited significantly improved wet performance and heat buildup.

[0059] [Table 2]

[0060] From the comparison results of Examples 3 and 4 with Comparative Example 8 in Table 2, it can be seen that Example 2, in which organic silane (1) having a terpene skeleton and a molecular weight of 200 to 1000 was blended instead of a silane coupling agent, and Example 3, in which organic silane (2) having a terpene skeleton and a molecular weight of 200 to 1000 was blended, satisfy Ei / Em<1.5 (Ei / Em=1.4 for Example 2, Ei / Em=1.1 for Example 3), and therefore the vulcanized rubbers have significantly improved WET performance and heat buildup.

Claims

1. A rubber composition containing a diene rubber, silica, and an organic silane, A rubber composition characterized in that, when the elastic modulus of the rubber at the silica interface is Ei and the elastic modulus of the matrix rubber is Em, Ei / Em<1.

5.

2. 2. The rubber composition according to claim 1, wherein the diene rubber is a modified styrene-butadiene rubber.

3. 2. The rubber composition according to claim 1, wherein the organic silane is a compound having a terpene skeleton and a molecular weight of 200 to 1,000.

4. 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.

5. 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:

6. 2. The rubber composition according to claim 1, wherein the silica is contained in an amount of 30 to 150 parts by mass and the organic silane is contained in an amount of 3 to 30% by mass of the silica, when the total amount of the diene rubber is taken as 100 parts by mass.

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

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