Rubber composition and pneumatic tire

Abstract

To provide a rubber composition to be a raw material of a vulcanized rubber excellent in steering stability and wet grip performance when used as a rubber part of a pneumatic tire, especially a pneumatic tire for motor sports.SOLUTION: A rubber composition comprising: 100 parts by mass of a rubber ingredient containing at least a diene rubber; 0.1 to 10 parts by mass of a compound having an XLogP of 0.5 or more and 10 or less; and 40 to 140 parts by mass of carbon black having a nitrogen-adsorption specific surface area of 140 to 250m2 / g.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition and a pneumatic tire having a rubber portion made of a vulcanized rubber of the rubber composition. [Background technology]

[0002] Pneumatic tires, particularly those for motorsports, are required to have excellent handling stability and grip performance on wet road surfaces (hereinafter also referred to as "wet grip performance"). One method for improving the former is to increase the rigidity of the vulcanized rubber even at high temperatures (increasing hardness), and one method for improving the latter is to increase the tan δ of the vulcanized rubber, particularly tan δ at 0°C (tan δ(0°C)).

[0003] Incidentally, Patent Document 1 listed below describes a rubber composition in which a specific compound is blended in a predetermined amount when the total amount of rubber components is taken as 100 parts by mass, with the aim of improving the heat aging resistance of vulcanized rubber. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-089553 Summary of the Invention [Problem to be solved by the invention]

[0005] The vulcanized rubber of the rubber composition described in Patent Document 1 has excellent heat aging resistance. However, as a result of extensive research by the present inventors, it has been found that there is room for further improvement in terms of steering stability and wet grip performance in order to use the vulcanized rubber as the rubber portion of pneumatic tires, particularly pneumatic tires for motorsports.

[0006] 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 can be used as a raw material for vulcanized rubber that has excellent handling stability and wet grip performance when used as the rubber portion of a pneumatic tire, particularly a pneumatic tire for motorsports.

[0007] Another object of the present invention is to provide a pneumatic tire and a pneumatic tire for motorsports that are excellent in steering stability and wet grip performance. [Means for solving the problem]

[0008] The above object can be achieved by the present invention as described below. That is, the present invention relates to a rubber composition comprising 100 parts by mass of a rubber component containing at least a diene rubber, 0.1 to 10 parts by mass of a compound having an XLogP of 0.5 or more and 10 or less, and a rubber component having a nitrogen adsorption specific surface area of ​​140 to 250 m 2 The present invention relates to a rubber composition (1) characterized by containing 40 to 140 parts by mass of carbon black having a viscosity of 1 / g.

[0009] In the rubber composition (1), a rubber composition (2) containing 10 to 80 parts by mass of petroleum resin per 100 parts by mass of the rubber component is preferred.

[0010] In the rubber composition (1) or (2), the compound having an XLogP of 0.5 or more and 10 or less is preferably a rubber composition (3) of natural origin.

[0011] In any one of the rubber compositions (1) to (3), a rubber composition (4) is preferred in which the compound having an XLogP of 0.5 or more and 10 or less is at least one of 3,4-dihydroxycinnamic acid and 3,4-dimethoxycinnamic acid.

[0012] The present invention also relates to a pneumatic tire (5) having a rubber part made of a vulcanized rubber of any one of the rubber compositions (1) to (4), and further relates to a pneumatic tire (6) for motorsports having a rubber part made of a vulcanized rubber of any one of the rubber compositions (1) to (4). [Effects of the Invention]

[0013] The rubber composition of the present invention contains a compound having an XLogP of 0.5 or more and 10 or less and small particle size carbon black with a specific nitrogen adsorption specific surface area. This dramatically improves the handling stability and wet grip performance of the final vulcanized rubber. The following are thought to be the reasons for this effect.

[0014] Compounds with an XLogP of 0.5 or more and 10 or less have a moderate hydrophilicity and tend to aggregate in the rubber composition, which increases the viscosity of the rubber composition. 2 When small particle size carbon black having a particle size of 1 / g is present in a rubber composition, the increase in viscosity of the rubber composition due to the small particle size carbon black and the increase in viscosity of the rubber composition due to the compound having an XLogP of 0.5 or more and 10 or less have a synergistic effect, suppressing excessive temperature rise during rubber mixing and maintaining a high shear state of the rubber composition. As a result, the reinforcing effect of the small particle size carbon black is fully exerted, and the reaction between the compound having an XLogP of 0.5 or more and 10 or less and the rubber component proceeds at a high level. This increases the rubber hardness of the final vulcanized rubber and increases tan δ, particularly tan δ at 0°C (tan δ(0°C)). As a result, it is believed that the handling stability and wet grip performance of the vulcanized rubber are improved. In the present invention, when a compound having an XLogP of less than 0.5 is used, such a compound is thought to be too hydrophilic, resulting in poor filler dispersion. On the other hand, when a compound having an XLogP of more than 10 is used, such a compound's hydrophilicity decreases, resulting in good compatibility with the rubber, making it difficult to maintain a high shear state.

[0015] The vulcanized rubber of the rubber composition according to the present invention is excellent in handling stability and wet grip performance, and is therefore useful as a raw material for pneumatic tires, particularly pneumatic tires for motorsports. DETAILED DESCRIPTION OF THE INVENTION

[0016] The rubber composition according to the present invention contains, per 100 parts by mass of a rubber component containing at least a diene rubber, 0.1 to 10 parts by mass of a compound having an XLogP of 0.5 or more and 10 or less. The compounding amount of the compound having an XLogP of 0.5 or more and 10 or less is more preferably 0.5 to 5 parts by mass when the total amount of the rubber component is taken as 100 parts by mass.

[0017] XLogP in the present invention will be described below. The lipid solubility of a compound significantly influences its solubility as well as its pharmacokinetics, including absorption and metabolism. A typical descriptor of a compound's lipid solubility is the octanol / water partition coefficient (LogP). The P in LogP is the ratio of the molecule's concentration at equilibrium in the organic layer (octanol layer) and the aqueous layer, and LogP is its common logarithm. A larger value indicates a higher concentration in the organic layer, indicating higher lipid solubility. However, LogP has practical limitations. For example, while LogP values ​​can be determined experimentally for individual compounds, this is not very practical due to time and cost considerations, and only a limited number of compounds have been reported. Another drawback is that LogP values ​​cannot be obtained experimentally for compounds that have not yet been synthesized.

[0018] To solve the problems with LogP mentioned above, there is an approach that estimates LogP by breaking down the molecule into individual atoms and calculating the sum of each contribution, and the XLogP algorithm is the only atom-based approach that adds a correction term, with the latest model in the XLogP series being described in the paper "Computation of Octanol-Water Partition Coefficients by Guiding an Additive Model with Knowledge."XLogP is based on the LogP values ​​contained in PubChem, a chemical molecule database maintained by the National Center for Biotechnology Information (NCBI), a division of the National Library of Medicine (NLM) under the National Institutes of Health (NIH).

[0019] In the present invention, it is more preferable from the viewpoint of environmental protection if the compound having an X Log P of 0.5 or more and 10 or less is a naturally occurring compound. Examples of naturally occurring compounds include 3,4-dihydroxycinnamic acid (caffeic acid) (X Log P = 1.2), 3,4-dimethoxycinnamic acid (X Log P = 1.8), curcumin (X Log P = 3.2), sesamol (X Log P = 1.2), coumaric acid (X Log P = 1.5), cinnamic acid (X Log P = 2.1), rosmarinic acid (X Log P = 2.4), ferulic acid (X Log P = 1.5), sinapic acid (X Log P = 1.5), and 4-(4-hydroxy-3-methoxyphenyl)-2-butanone (X Log P = 0.8). Among these compounds, in the present invention, it is more preferable to use at least one of 3,4-dihydroxycinnamic acid (caffeic acid) and 3,4-dimethoxycinnamic acid, from the viewpoint of improving the handling stability and wet grip performance of the vulcanized rubber. The reason why the handling stability and wet grip performance of the vulcanized rubber are improved when at least one of 3,4-dihydroxycinnamic acid and 3,4-dimethoxycinnamic acid is used is not clear, but the following reasons (1) to (3) are thought to be the cause.

[0020] (1) When compounded with zinc compounds such as zinc oxide in a rubber composition as a raw material, two or more molecules of 3,4-dihydroxycinnamic acid or 3,4-dimethoxycinnamic acid coordinate to zinc through the hydroxyl or methoxy groups at the R2 and R3 positions in the rubber composition, forming a complex that increases the molecular weight. (2) Two or more molecules of 3,4-dihydroxycinnamic acid or 3,4-dimethoxycinnamic acid form a complex, which increases the tendency of the complex to aggregate in the rubber composition, thereby more effectively increasing the viscosity of the rubber composition. (3) The presence of small-particle-size carbon black with a specific nitrogen adsorption specific surface area in this state results in a synergistic effect between the increase in viscosity of the rubber composition due to the small-particle-size carbon black and the increase in viscosity due to the complex formation of two or more molecules of 3,4-dihydroxycinnamic acid or 3,4-dimethoxycinnamic acid. This effectively suppresses excessive temperature rise during rubber mixing, while more effectively maintaining the high shear state of the rubber composition. This enhances the reinforcing effect of the small-particle-size carbon black and further promotes the reaction between the compound with an XLogP of 0.5 or more and 10 or less and the rubber component. This further increases the rubber hardness of the final vulcanized rubber and further increases tan δ, particularly tan δ at 0°C (tan δ(0°C)). This is believed to result in further improvements in the handling stability and wet grip performance of the vulcanized rubber.

[0021] In addition, compounds that are not naturally occurring can also be used as compounds with an X Log P of 0.5 or more and 10 or less. Examples of non-naturally occurring compounds include 2,3-dimethoxycinnamic acid (X Log P = 1.8), 2,4-dimethoxycinnamic acid (X Log P = 1.8), 2,5-dimethoxycinnamic acid (X Log P = 1.8), 2,3,4-trimethoxycinnamic acid (X Log P = 1.7), 3,4,5-triethoxycinnamic acid (X Log P = 1.4), and protocatechuic acid (X Log P = 1.1). , catechol (XLogP=0.9), 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiindane (XLogP=5.1), carvacrol (XLogP=3.1), 3,4-dimethoxyhydrocinnamic acid (XLogP=1.2), and 5,6-dimethoxy-1-indanone (XLogP=1.6).

[0022] The rubber composition according to the present invention comprises a compound having an XLogP of 0.5 or more and 10 or less, and a rubber composition having a nitrogen adsorption specific surface area (hereinafter also referred to as "N2SA") of 140 to 250 m per 100 parts by mass of the rubber component. 2The rubber composition contains 40 to 140 parts by mass of carbon black with a carbon black content of 140 to 250 m / g. The synergistic effect of both improves the handling stability and wet grip performance of the finally obtained vulcanized rubber. When the handling stability and wet grip performance of the finally obtained vulcanized rubber are taken into consideration, the rubber composition contains 40 to 140 parts by mass of N2SA with respect to 100 parts by mass of the rubber component. 2 It is more preferable that the carbon black having an N2SA of 140 to 250 m / g is contained in an amount of 60 to 100 parts by mass. 2 Carbon black having a molecular weight of 1 / g is, for example, "SEAST 9" (N2SA142m) manufactured by Tokai Carbon Co., Ltd. 2 / g), Mitsubishi Chemical Corporation's product name "Diablack-UX10" (N2SA190m 2 / g).

[0023] As the rubber component, for example, a diene rubber can be suitably used. The diene rubber 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, and styrene-isoprene-butadiene copolymer rubber. These can be used alone or in combination of two or more. Preferred diene rubbers are natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, or a blend of two or more of these.

[0024] The rubber composition according to the present invention preferably contains 10 to 80 parts by mass of petroleum resin per 100 parts by mass of the rubber component, since this improves the wet grip performance of the resulting vulcanized rubber. Examples of petroleum resins include aliphatic petroleum resins, aromatic petroleum resins, and aliphatic / aromatic copolymer petroleum resins. Aliphatic petroleum resins are resins obtained by cationic polymerization of unsaturated monomers such as isoprene and cyclopentadiene, which are petroleum fractions having 4 to 5 carbon atoms (C5 fractions) (also referred to as C5 petroleum resins), and may be hydrogenated. Aromatic petroleum resins are resins obtained by cationic polymerization of monomers such as vinyltoluene, alkylstyrene, and indene, which are petroleum fractions having 8 to 10 carbon atoms (C9 fractions) (also referred to as C9 petroleum resins), and may be hydrogenated. Aliphatic / aromatic copolymer petroleum resins are resins obtained by copolymerizing the C5 fraction and the C9 fraction (also referred to as C5 / C9 petroleum resins), and may be hydrogenated. When the wet grip performance of the finally obtained vulcanized rubber is taken into consideration, it is more preferable that the petroleum resin is contained in an amount of 40 to 60 parts by mass per 100 parts by mass of the rubber component.

[0025] The rubber composition according to the present invention preferably contains silica as a filler. As the silica, wet silica, dry silica, sol-gel silica, surface-treated silica, etc., which are commonly used for rubber reinforcement, are used. Among these, wet silica is preferred.

[0026] When silica is contained as a filler, it is also preferable to contain a silane coupling agent. The silane coupling agent is not particularly limited as long as it contains sulfur in the molecule, and various silane coupling agents that are compounded together with silica in rubber compositions can be used. Examples of the silane include sulfide silanes such as bis(3-triethoxysilylpropyl)tetrasulfide (e.g., "Si69" manufactured by Degussa), bis(3-triethoxysilylpropyl)disulfide (e.g., "Si75" manufactured by Degussa), 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.

[0027] The rubber composition according to the present invention contains a filler having an N2SA of 140 to 250 m 2 Carbon black other than carbon black having an N2SA of 140 to 250 m / g may be contained. 2 Carbon black other than the carbon black having a viscosity of 1 / g may be, for example, carbon black commonly used in the rubber industry, such as ISAF, HAF, FEF, and GPF, as well as conductive carbon black such as acetylene black and ketjen black.

[0028] The rubber composition according to the present invention comprises a rubber component, a compound having an XLogP of 0.5 or more and 10 or less, and an N2SA of 140 to 250 m 2 In addition to the carbon black, filler, and petroleum resin (which are 1 / g each), vulcanizing agents, vulcanization accelerators, antioxidants, stearic acid, softeners such as wax and oil, processing aids, etc. may be blended.

[0029] 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. The amount of sulfur in the rubber composition according to the present invention is preferably 0.5 to 5 parts by mass per 100 parts by mass of the rubber component.

[0030] 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.

[0031] The rubber composition according to the present invention may use, as the antioxidant, antioxidants commonly used for rubber, such as aromatic amine-based antioxidants, amine-ketone-based antioxidants, monophenol-based antioxidants, bisphenol-based antioxidants, polyphenol-based antioxidants, dithiocarbamate-based antioxidants, and thiourea-based antioxidants, either alone or in appropriate mixtures.

[0032] The rubber composition according to the present invention comprises a rubber component, a compound having an XLogP of 0.5 or more and 10 or less, and an N2SA of 140 to 250 m 2 The rubber composition can be obtained by kneading together carbon black (weight: 1 / g), a filler, and a petroleum resin, as well as a vulcanizing agent, a vulcanization accelerator, an antioxidant, stearic acid, a softener such as wax or oil, and a processing aid, using a kneading machine typically used in the rubber industry, such as a Banbury mixer, a kneader, or a roll.

[0033] 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.

[0034] The vulcanized rubber of the rubber composition according to the present invention has excellent steering stability and wet grip performance. Therefore, the rubber composition according to the present invention is useful as a raw material for pneumatic tires, and is particularly useful as a raw material for pneumatic tires for motorsports, which require high steering stability and wet grip performance. Furthermore, when used as a raw material for the rubber portion constituting the tread portion of a pneumatic tire for motorsports, the finally manufactured pneumatic tire for motorsports exhibits extremely effective steering stability and wet grip performance, making it the most preferable. [Example]

[0035] Examples that specifically illustrate the configuration and effects of the present invention will be described below.

[0036] (Preparation of Rubber Composition) Rubber compositions were prepared by compounding the rubber compositions of Examples 1 to 12 and Comparative Examples 1 to 4 according to the compounding recipes in Tables 1 and 2 and kneading them using a conventional Banbury mixer. The compounding ingredients listed in Tables 1 and 2 are shown below (in Tables 1 and 2, the compounding amount of each compounding ingredient is shown in parts by mass per 100 parts by mass of the rubber component). Styrene-butadiene rubber: JSR Corporation, product name "JSR0202" Carbon black 1: Mitsubishi Chemical Corporation, product name "Diablack-UX10" (N2SA: 190m 2 / g) Carbon black 2: Tokai Carbon Co., Ltd., product name "Seast 9" (N2SA: 142m 2 / g) Carbon black 3: Mitsubishi Chemical Corporation, product name "Diablack N339" (N2SA: 91m 2 / g) Silica: Tosoh Silica Corporation, product name "Nipsil AQ" Silane coupling agent: bis(3-triethoxysilylpropyl)tetrasulfide, Evonik "Si69" Petroleum resin (aliphatic petroleum resin); Zeon Corporation, product name "Quinton M100" (softening point: 95°C) Oil: JX Nippon Oil & Energy Corporation, product name "Process NC140" Zinc oxide: manufactured by Mitsui Mining & Smelting Co., Ltd., product name "Zinc Oxide No. 3" Stearic acid: Kao Corporation, product name "Lunac S-20" Anti-aging agent: Sumitomo Chemical Co., Ltd., product name "Antigen 6C" 3,4-Dimethoxycinnamic acid (XLogP=1.8) 3,4-Dihydroxycinnamic acid (XLogP=1.2) Catechol (XLogP=0.9) Cinnamic acid (XLogP=2.1) 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiindane (XLogP=5.1) Acetamidocinnamic acid (XLogP=0) Tocopherol (XLogP=10.7) Sulfur: Powdered sulfur, manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator: Ouchi Shinko Chemical Industry Co., Ltd., product name "Noccela CZ"

[0037] For the vulcanized rubbers of the rubber compositions of Examples 1 to 11 and Comparative Examples 1 to 3, the rubber hardness (Hs.) and tan δ (0° C.) were evaluated by the following methods.

[0038] <Rubber hardness of vulcanized rubber (Hs.)> The rubber hardness was evaluated by measuring the hardness of sample rubber test pieces obtained by heating and vulcanizing the rubber compositions of Examples 1 to 12 and Comparative Examples 1 to 4 in a predetermined mold at 160°C for 30 minutes using a type A durometer in accordance with JIS K6253 at a temperature of 23°C, and expressing the hardness as an index with the value of Comparative Example 1 set to 100. The larger the index, the higher the rubber hardness at room temperature, indicating excellent steering stability when used in the tread portion of a pneumatic tire.

[0039] <tan δ(0℃) of vulcanized rubber> The rubber compositions of Examples 1 to 12 and Comparative Examples 1 to 4 were heated and vulcanized at 160°C for 30 minutes using a predetermined mold to obtain sample rubbers for measurement. For each sample, the storage modulus (E') and loss modulus (E") were measured using a dynamic viscoelasticity measuring device (product name: "Fully Automatic Viscoelasticity Analyzer VR-7110", manufactured by Ueshima Seisakusho Co., Ltd.), and tan δ (0°C) was measured. In Tables 1 and 2, the values ​​are expressed as an index, with the tan δ (0°C) value of Comparative Example 1 set to 100. The higher the index, the better the wet grip performance when used in the tread of a pneumatic tire. The measurement conditions are as follows: Measurement sample size: length 40 mm, width 3 mm, thickness 2 mm Measurement mode: Tensile mode Measurement temperature: 0℃ Frequency: 100Hz Dynamic distortion: 0.15%

[0040] [Table 1]

[0041] From the results in Table 1, it can be seen that the vulcanized rubber of the rubber composition of Comparative Example 2 does not improve wet grip performance when used in the tread portion of a pneumatic tire because the XLogP of the compounded acetamidocinnamic acid is 0. The vulcanized rubber of the rubber composition of Comparative Example 3 does not improve steering stability or wet grip performance when used in the tread portion of a pneumatic tire because the XLogP of the compounded tocopherol is 10.7. Furthermore, the vulcanized rubber of the rubber composition of Comparative Example 4 has an N2SA of 91mJ / s. 2It can be seen that when the rubber composition of Examples 1 to 3 is compounded with a low X Log P of 0.5 to 10, carbon black 3 (X Log P = 1.8) and carbon black 1 (N2SA), the vulcanized rubber exhibits a balanced improvement in both steering stability and wet grip performance when used in the tread of a pneumatic tire. Furthermore, the results of Examples 4 to 7 show that similar effects can be obtained with vulcanized rubbers of rubber compositions compounded with 3,4-dihydroxycinnamic acid (X Log P = 1.2), catechol (X Log P = 0.9), cinnamic acid (X Log P = 2.1), and 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiindane (X Log P = 5.1).

[0042] [Table 2]

[0043] The results in Table 2 show that the vulcanized rubbers of the rubber compositions of Examples 8 to 11, even when the amount of carbon black 1 blended is varied within the specified range, exhibit a balanced improvement in both steering stability and wet grip performance when used in the tread portion of a pneumatic tire due to the synergistic effect of 3,4-dimethoxycinnamic acid (XLogP=1.8), which has an XLogP of 0.5 or more and 10 or less, and carbon black 1, which has the specified N2SA. Furthermore, the results of Example 12 show that similar effects can be obtained with vulcanized rubbers of rubber compositions blended with carbon black 2, which has the specified N2SA.

Claims

1. Based on 100 parts by mass of the rubber component containing at least a diene rubber, 0.1 to 10 parts by mass of a compound having an XLogP of 0.5 or more and 10 or less, and 40 to 140 parts by mass of carbon black having a nitrogen adsorption specific surface area of 140 to 250 m ２ / g, a rubber composition characterized by containing the same.

2. The rubber composition according to claim 1, comprising 10 to 80 parts by mass of petroleum resin per 100 parts by mass of the rubber component.

3. 2. The rubber composition according to claim 1, wherein the compound having an XLogP of 0.5 or more and 10 or less is a naturally occurring compound.

4. 2. The rubber composition according to claim 1, wherein the compound having an XLogP of 0.5 or more and 10 or less is at least one of 3,4-dihydroxycinnamic acid and 3,4-dimethoxycinnamic acid.

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

6. A pneumatic tire for motor sports having a tread portion comprising a vulcanized rubber of the rubber composition according to claim 1.

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