Rubber compositions and pneumatic tires

Abstract

To provide a rubber composition that serves as a raw material for vulcanized rubber for tires, and a pneumatic tire equipped with vulcanized rubber of the rubber composition, which provides a balanced improvement in wet grip performance, low-temperature performance, and reduction of rolling resistance of pneumatic tires. [Solution] A rubber composition containing a diene rubber and a vegetable oil, wherein the vegetable oil is a fatty acid ester triglyceride in which a fatty acid containing at least a saturated fatty acid and an unsaturated fatty acid is ester-bonded to glycerol, and the ratio of unsaturated fatty acids in the fatty acid is 50% by mass or more, and the rubber composition contains at least modified butadiene rubber as the diene rubber. Preferably, the ratio of polyunsaturated fatty acids in the fatty acid of the vegetable oil is 15% by mass or more.

Description

Technical Field

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

Background Art

[0002] Pneumatic tires are required to have running performance in various scenarios. In particular, all-season pneumatic tires are required to have wet grip performance on wet road surfaces and low-temperature performance on frozen road surfaces, for example. In addition, due to the recent demand for resource conservation, pneumatic tires are required to have low fuel consumption regardless of the road surface, so reduction of the rolling resistance of pneumatic tires (hereinafter, also simply referred to as "rolling performance") is required.

[0003] In Patent Document 1 below, a rubber composition for a tire tread is described, which includes a raw rubber containing 20 to 50 parts by weight of a first styrene-butadiene rubber, 20 to 50 parts by weight of a second styrene-butadiene rubber, and 10 to 40 parts by weight of a butadiene rubber (BR), and, based on 100 parts by weight of the raw rubber, 80 to 180 parts by weight of a reinforcing filler, 2 to 50 parts by weight of a natural oil, and 2 to 30 parts by weight of a hydrocarbon resin.

[0004] In Patent Document 2 below, it includes 100 parts by weight of a raw rubber, 70 to 120 parts by weight of a reinforcing filler, and 10 to 60 parts by weight of a natural oil in which the ratio of linoleic acid to oleic acid is 1:0.5 to 1:5. The raw rubber includes 5 to 10 parts by weight of natural rubber, 40 to 70 parts by weight of a solution-polymerized styrene-butadiene rubber, and 20 to 50 parts by weight of a neodymium butadiene rubber. The solution-polymerized styrene-butadiene rubber has a styrene content of 20 to 50% by weight, a vinyl content of 10 to 40% by weight, a Tg of -50 to -20°C, and contains 20 to 40 parts by weight of SRAE oil. The reinforcing filler includes 65 to 100 parts by weight of silica and 5 to 20 parts by weight of carbon black. The silica has a nitrogen adsorption value of 160 to 180 m 2 / g and a CTAB adsorption value of 150 to 170 m 2A rubber composition for tire treads is described, which has a DBP oil absorption rate of 180-200cc / 100g.

[0005] Patent Document 3 below describes a crosslinkable or crosslinked rubber composition that can be used to constitute a tire tread, wherein the composition comprises at least a large-component diene elastomer of 50 phr to 100 phr selected from the group consisting of styrene-butadiene copolymer prepared in solution, styrene-butadiene copolymer prepared in emulsion, natural polyisoprene, synthetic polyisoprene having a cis-1,4 bond content of more than 95%, and mixtures thereof, and a small-component diene elastomer of 0 phr to 50 phr which is polybutadiene having a cis-1,4 bond content of more than 90%. The rubber composition described is based on a diene elastomer of type 1 or more and a plasticizer containing a vegetable oil containing at least one glycerol oleic acid triester, wherein the plasticizer contains sunflower oil as the vegetable oil, in which oleic acid accounts for 70% or more of the total fatty acids, in a mass fraction of 45% to 100%, and contains one or more paraffinic, aromatic, or naphthenic plasticizing oils extracted from petroleum in a mass fraction of 55% to 0%, and the amount of sunflower oil is in the range of 10 to 40 phr, and the amount of optionally included petroleum-extracted plasticizing oils is in the range of 0 to 30 phr. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2019-172957 [Patent Document 2] Patent No. 6522716 [Patent Document 3] Patent No. 4209200 [Overview of the project] [Problems that the invention aims to solve]

[0007] Through diligent research, the inventors of this invention found that the technologies described in the above-mentioned Patent Documents 1 to 3 are insufficient to adequately address the three issues of wet grip performance, low-temperature performance, and rolling performance.

[0008] The present invention has been made in view of the above circumstances, and its purpose is to provide a rubber composition that serves as a raw material for vulcanized rubber for tires, and a pneumatic tire equipped with vulcanized rubber of the rubber composition, which improves the wet grip performance, low-temperature performance, and reduction of rolling resistance of pneumatic tires in a balanced manner. [Means for solving the problem]

[0009] The above problems can be solved by the following configuration. That is, the present invention relates to a rubber composition (1) containing a diene rubber and a vegetable oil, wherein the vegetable oil is a fatty acid ester triglyceride in which a fatty acid containing at least a saturated fatty acid and an unsaturated fatty acid is ester-bonded to glycerol, the ratio of the unsaturated fatty acid in the fatty acid is 50% by mass or more, and the diene rubber contains at least modified butadiene rubber.

[0010] In the above rubber composition (1), the rubber composition (2) is preferable, wherein the vegetable oil has a ratio of polyunsaturated fatty acids in the unsaturated fatty acids of 15% by mass or more.

[0011] In the above rubber composition (1) or (2), rubber composition (3) is preferred in which the amount of vegetable oil is 5 to 30 parts by mass when the total amount of diene rubber is 100 parts by mass.

[0012] Of the above rubber compositions (1) to (3), rubber composition (4) is preferred in which, when the total amount of diene rubber is 100 parts by mass, the amount of modified butadiene rubber is 20 to 80 parts by mass.

[0013] Of the above rubber compositions (1) to (4), a rubber composition (5) is preferred, which further contains silica, and when the total amount of diene rubber is 100 parts by mass, the amount of silica added is 80 to 180 parts by mass.

[0014] The present invention also relates to a pneumatic tire (6) comprising at least the vulcanized rubber of the above rubber compositions (1) to (5), and more particularly to a pneumatic tire (7) comprising at least the vulcanized rubber of the above rubber compositions (1) to (5) on the surface of the tread portion. [Effects of the Invention]

[0015] The rubber composition according to the present invention contains at least modified butadiene rubber and a vegetable oil with a specific ratio of unsaturated fatty acids. More specifically, the rubber composition according to the present invention is a diene rubber containing at least modified butadiene rubber, into which a vegetable oil is blended, which is a fatty acid ester triglyceride in which a fatty acid containing at least saturated and unsaturated fatty acids is ester-bonded to glycerin, and in which the ratio of unsaturated fatty acids in the fatty acid is 50% by mass or more. The vulcanized rubber of the rubber composition having such a configuration can improve wet grip performance, low-temperature performance, and rolling performance in a well-balanced manner. In particular, when the rubber composition according to the present invention further contains a high amount of silica, the reinforcing effect of silica is more effectively exhibited due to the dispersive effect of silica by the specific vegetable oil and the interaction of silica with the modified butadiene rubber. As a result, the final vulcanized rubber can further improve wet grip performance, low-temperature performance, and rolling performance in a more well-balanced manner.

[0016] The vulcanized rubber of the rubber composition according to the present invention exhibits a well-balanced improvement in wet grip performance, low-temperature performance, and rolling performance. For this reason, the vulcanized rubber of the rubber composition according to the present invention is suitably usable in pneumatic tire applications, and is particularly useful as a vulcanized rubber for use in the tread surface portion of the tread, known as the cap tread, in pneumatic tire tread applications. [Modes for carrying out the invention]

[0017] The rubber composition according to the present invention contains diene rubber and vegetable oil.

[0018] The rubber composition according to the present invention contains at least modified butadiene rubber as a diene rubber. The modified butadiene rubber contains a functional group containing a heteroatom. The functional group containing a heteroatom may be introduced at the end of the polymer chain or introduced within the polymer chain, but is preferably introduced at the end. Examples of functional groups containing a heteroatom include amino groups, alkoxy groups, hydroxyl groups, epoxy groups, carboxyl groups, cyano groups, halogen groups, and tin functional groups. Examples of amino groups include primary amino groups, secondary amino groups, and tertiary amino groups. Examples of alkoxy groups include methoxy groups, ethoxy groups, propoxy groups, and butoxy groups. Examples of halogen groups include chlorine and bromine. The exemplified functional groups interact with various functional groups of fillers, particularly carbon black, and with the silanol groups (Si-OH) of silica. Here, interaction means, for example, in the case of silica, chemical bonding or hydrogen bonding through chemical reactions with the silanol groups of silica.

[0019] In order to improve the wet grip performance, low-temperature performance, and rolling performance of vulcanized rubber in a balanced manner, it is preferable that the amount of modified butadiene rubber blended in the rubber composition be 20 to 80 parts by mass, and more preferably 30 to 60 parts by mass, when the total amount of diene-based rubber in the rubber composition is 100 parts by mass.

[0020] The rubber composition according to the present invention may contain diene rubbers other than modified butadiene rubber. The diene rubbers are not particularly limited and include, for example, natural rubber (NR), isoprene rubber (IR), butadiene rubber without a modifying group (functional group) (BR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, and styrene-isoprene-butadiene copolymer rubber. These can be used individually or in combination of two or more.

[0021] The rubber composition according to the present invention is a fatty acid ester triglyceride in which a specific vegetable oil, specifically a fatty acid containing at least a saturated fatty acid and an unsaturated fatty acid, and glycerin are ester-bonded, and contains a vegetable oil in which the ratio of the unsaturated fatty acid in the fatty acid is 50% by mass or more. In the present invention, the vegetable oil is represented by the following formula (1).

[0022]

Chemical formula

[0023] In the above formula (1), R1, R2, and R3 are residues of either a saturated fatty acid or an unsaturated fatty acid. Examples of the saturated fatty acid include palmitic acid (C16:0), stearic acid (C18:0), etc. Examples of the unsaturated fatty acid include oleic acid (C18:1), linoleic acid (C18:2), linolenic acid (C18:3). The rubber composition according to the present invention contains a fatty acid ester triglyceride (vegetable oil) in which the ratio of the unsaturated fatty acid in the fatty acid is 50% by mass or more. In order to further improve the wet grip performance, low-temperature performance, and rolling performance of the vulcanized rubber more balancedly, it is preferable to use a fatty acid ester triglyceride in which the ratio of the unsaturated fatty acid in the fatty acid is 50% by mass or more, and more preferably to use a fatty acid ester triglyceride in which the ratio is 70% by mass or more.

[0024] From the viewpoint of solving the problem, when the total amount of the diene rubber is 100 parts by mass, the compounding amount of the fatty acid ester triglyceride (vegetable oil) in the rubber composition according to the present invention is preferably 5 to 30 parts by mass, and more preferably 10 to 25 parts by mass.

[0025] Among fatty acid ester triglycerides (vegetable oils), fatty acid ester triglycerides (vegetable oils) with a high proportion of linoleic acid or linolenic acid, which are polyunsaturated fatty acids (hereinafter also referred to as "PUFAs") having two or more unsaturated bonds, are preferred because they can improve the wet grip performance, low-temperature performance, and rolling performance of the final vulcanized rubber in a particularly well-balanced manner. In particular, in the present invention, from the viewpoint of solving the problem, it is preferable to use fatty acid ester triglycerides (vegetable oils) in which the proportion of polyunsaturated fatty acids (PUFAs) in the unsaturated fatty acids is 15% by mass or more, it is preferable to use fatty acid ester triglycerides in which the proportion is 20% by mass or more, and it is more preferable to use fatty acid ester triglycerides in which the proportion is 70% by mass or more.

[0026] In the present invention, rapeseed oil, soybean oil, safflower oil, and sunflower oil can be suitably used as fatty acid ester triglycerides (vegetable oils). Table 1 shows the fatty acid composition of each vegetable oil.

[0027] [Table 1]

[0028] As shown in Table 1, rapeseed oil (with a polyunsaturated fatty acid (PUFA) ratio of 30.8% by mass) and soybean oil (with a polyunsaturated fatty acid (PUFA) ratio of 72.3% by mass) have high PUFA ratios. Therefore, when the rubber composition according to the present invention contains rapeseed oil or soybean oil as the fatty acid ester triglyceride (vegetable oil), it is preferable because it can improve the wet grip performance, low-temperature performance, and rolling performance of the final vulcanized rubber in a particularly well-balanced manner.

[0029] Among fatty acid ester triglycerides (vegetable oils), using those with an iodine value of 100 or higher is preferable because it increases the amount of double bonds in the fatty acid ester triglycerides (vegetable oils), which in turn improves the wet grip performance, low-temperature performance, and rolling performance of the resulting vulcanized rubber in a particularly well-balanced manner.

[0030] When the rubber composition according to the present invention contains silica as a filler, and moreover, when it contains a high amount of silica, the reinforcing effect of silica is more effectively exhibited due to the dispersion effect of silica by a specific vegetable oil and the interaction of silica with modified butadiene rubber. As a result, the final vulcanized rubber can have its wet grip performance, low-temperature performance, and rolling performance improved in a more balanced manner. As silica, wet silica, dry silica, sol-gel silica, and surface-treated silica, which are normally used for rubber reinforcement, can be used. Among these, wet silica is preferred. From the viewpoint of solving the problem, when the total amount of diene rubber in the rubber composition according to the present invention is 100 parts by mass, the amount of silica is preferably 80 to 180 parts by mass, and more preferably 100 to 150 parts by mass. In particular, in the present invention, when modified butadiene rubber, a high amount of silica, and rapeseed oil or soybean oil with a high ratio of polyunsaturated fatty acids (PUFAs) in the unsaturated fatty acids are used in combination, the final vulcanized rubber can have its wet grip performance, low-temperature performance, and rolling performance improved in a more balanced manner, which is therefore preferred.

[0031] When silica is included as a filler, it is also preferable to include a silane coupling agent. The silane coupling agent is not particularly limited as long as it contains sulfur in its molecule, and various silane coupling agents that are compounded together with silica in rubber compositions can be used. Examples include sulfidosilanes such as bis(3-triethoxysilylpropyl)tetrasulfide (e.g., "Si69" manufactured by Evonik Japan), bis(3-triethoxysilylpropyl) disulfide (e.g., "Si75" manufactured by Evonik Japan), bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triecethoxysilylbutyl) 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. The amount of silane coupling agent is preferably 5 to 20% by mass, when the total amount of silica is considered to be 100% by mass.

[0032] The rubber composition according to the present invention contains diene rubber and fatty acid ester triglycerides (vegetable oil), and preferably further contains silica and a silane coupling agent. In addition to these, the rubber composition according to the present invention may also contain carbon black, vulcanizing agents, vulcanization accelerators, antioxidants, stearic acid, softeners such as waxes and oils, processing aids, etc.

[0033] The rubber composition according to the present invention may contain carbon black as a filler. In addition to carbon black commonly used in the rubber industry, such as SAF, ISAF, HAF, FEF, and GPF, conductive carbon black such as acetylene black or Ketjen black can be used. The pneumatic tire rubber composition according to the present invention preferably contains 1 to 30 parts by mass of carbon black when the total amount of diene rubber is 100 parts by mass.

[0034] Preferably, sulfur can be used as the vulcanizing agent. Any ordinary sulfur for rubber can be used, such as powdered sulfur, precipitated sulfur, insoluble sulfur, or highly dispersible sulfur. In the tire rubber composition according to the present invention, the content of the vulcanizing agent is preferably 0.1 to 10 parts by mass when the total amount of diene rubber is 100 parts by mass.

[0035] As a vulcanization accelerator, vulcanization accelerators commonly used for rubber vulcanization, such as sulfenamide-based vulcanization accelerators, thiram-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiourea-based vulcanization accelerators, guanidine-based vulcanization accelerators, and dithiocarbamate-based vulcanization accelerators, may be used individually or in appropriate mixtures.

[0036] As an anti-aging agent, you may use, individually or in appropriate combinations, any anti-aging agent commonly used for rubber, such as aromatic amine-based anti-aging agents, amine-ketone-based anti-aging agents, monophenol-based anti-aging agents, bisphenol-based anti-aging agents, polyphenol-based anti-aging agents, dithiocarbamate-based anti-aging agents, or thiourea-based anti-aging agents.

[0037] The rubber composition according to the present invention contains diene rubber and fatty acid ester triglycerides (vegetable oil), and preferably further contains silica and a silane coupling agent, as well as carbon black, a vulcanizing agent, a vulcanization accelerator, zinc oxide, an antioxidant, stearic acid, a softening agent such as wax, and processing aids, which are obtained by kneading using a kneader commonly used in the rubber industry, such as a Banbury mixer, kneader, and roll.

[0038] Furthermore, the method of blending each of the above components is not particularly limited. It may be a method in which the components other than vulcanizing agents such as vulcanizing agents and vulcanization accelerators are kneaded in advance to form a masterbatch, and the remaining components are added and kneaded further; a method in which each component is added and kneaded in any order; or a method in which all components are added and kneaded simultaneously.

[0039] The vulcanized rubber of the rubber composition according to the present invention exhibits a well-balanced improvement in wet grip performance, low-temperature performance, and rolling performance. For this reason, the vulcanized rubber of the rubber composition according to the present invention is suitably usable in pneumatic tire applications, and is particularly useful as a vulcanized rubber for use in the tread of pneumatic tires, specifically for use on the surface portion of the tread known as the cap tread. [Examples]

[0040] The present invention will be described in more detail below by illustrating some embodiments.

[0041] (Preparation of rubber composition for tires) To 100 parts by mass of rubber components, the rubber compositions of Examples 1-7 and Comparative Examples 1-3 were blended according to the formulations shown in Tables 2-3, and the mixture was kneaded using a standard Banbury mixer to prepare a rubber composition for tires. The compounding agents listed in Tables 2-3 are shown below.

[0042] (Diene-based rubber) • Butadiene rubber: Product name "D.NF35", manufactured by Asahi Kasei Corporation. • End-modified butadiene rubber: Product name "Nipol BR1261", manufactured by Nippon Zeon Co., Ltd. • Styrene-butadiene rubber: Product name "SBR1502", manufactured by ENEOS Material Co., Ltd. (vegetable oil) • Rapeseed oil: Product name "Rapeseed White Pressed Oil", manufactured by Nisshin Oillio Co., Ltd. • Soybean oil: Product name "Soybean Salad Oil (S)", manufactured by Nisshin Oillio Co., Ltd. • Palm oil: Product name "Refined Palm Oil (S)", manufactured by Nisshin Oillio Co., Ltd. • Safflower oil: Product name "Benibana Oil (High Ole)", manufactured by Nisshin Oillio Co., Ltd. • Sunflower oil: Product name "Sunflower Oil (S)", manufactured by Nisshin Oillio Co., Ltd. (Filler) • Carbon Black: Product name "N234 Seast 7HM", manufactured by Tokai Carbon Co., Ltd. • Silica: Product name "NipSeal A", manufactured by Tosoh Corporation (Other combination drugs) • Silane coupling agent: Product name "NXT", manufactured by Momentive Corporation • Oil: Product name "Process NC-140", manufactured by ENEOS Corporation • Styrene resin: Product name "SYLVATRAX4401", manufactured by Kraton. • Terpene resin: Product name "SYLVATRAX4150", manufactured by Kraton. • Wax: Product name "OZOACE0355", manufactured by Nippon Seiro Co., Ltd. • Stearic acid: Product name "Lunaq S-20", manufactured by Kao Corporation. • Anti-aging agent: Product name "Nocrac 6C", manufactured by Ouchi Shinko Chemical Industry Co., Ltd. • Zinc oxide: Product name "Zinc Oxide Type 2", manufactured by Mitsui Mining & Smelting Co., Ltd. • Vulcanization accelerator 1: Product name "Noxellar D", manufactured by Ouchi Shinko Chemical Industry Co., Ltd. • Vulcanization accelerator 2: Product name "Soxinol CZ", manufactured by Sumitomo Chemical Co., Ltd. • Sulfur: Product name "Powdered Sulfur", manufactured by Tsurumi Chemical Industry Co., Ltd.

[0043] After preparing unvulcanized samples of the rubber compositions obtained in Examples 1-7 and Comparative Examples 1-3 above, the wet grip performance, low-temperature performance, and rolling resistance were evaluated under the following conditions.

[0044] (Wet grip performance of vulcanized rubber) Four pneumatic tires (tire size: 215 / 45ZR17) were fitted to the vehicle. Under ambient temperature conditions of 25°C, the vehicle was driven on a road surface with a water depth of 2-3 mm, and the braking distance was measured when decelerating from 90 km / h to 20 km / h with ABS activated (average value of n=10). The evaluation was expressed as an index, which is the reciprocal of the braking distance, with the value of Comparative Example 1 set to 100. A larger index indicates a shorter braking distance and superior wet grip performance.

[0045] (Low-temperature performance of vulcanized rubber) Storage modulus at -5°C (E'(-5°C)): The storage modulus was measured using a viscoelasticity measuring instrument manufactured by GABO Corporation under the conditions of -5°C, frequency of 10 Hz, dynamic strain of 0.2%, and static strain of 10%. The evaluation is expressed as an index with the value of Comparative Example 1 set to 100. A smaller index indicates a lower modulus at low temperatures and superior low-temperature performance.

[0046] (Rolling resistance of vulcanized rubber) A test pneumatic tire (tire size: 215 / 45ZR17) was prepared by using a rubber composition as the tread rubber and vulcanizing it according to a conventional method. The rolling resistance of the obtained test tire was measured using a rolling resistance measuring drum tester under the conditions of air pressure of 230 kPa, load of 450 kgf (4.4 kN), temperature of 23°C, and speed of 80 km / h. The reciprocal of the rolling resistance was evaluated as an index with the value of Comparative Example 1 set to 100. A smaller index indicates lower rolling resistance and superior low rolling resistance performance (low fuel consumption performance).

[0047] [Table 2]

[0048] Rapeseed oil has a high ratio of unsaturated fatty acids (91.8% by mass) and polyunsaturated fatty acids (30.8% by mass) within its fatty acids. Soybean oil also has a high ratio of unsaturated fatty acids (84.2% by mass) and polyunsaturated fatty acids (72.3% by mass) within its fatty acids. From the results in Table 2, it can be seen that the vulcanized rubber of the rubber composition according to Example 1 using rapeseed oil, and the vulcanized rubber of the rubber composition according to Example 2 using soybean oil, showed particularly well-balanced improvements in wet grip performance, low-temperature performance, and rolling performance. Furthermore, it can be seen that the vulcanized rubber of the rubber composition according to Example 3 using safflower oil, and the vulcanized rubber of the rubber composition according to Example 4 using sunflower oil, also showed well-balanced improvements in wet grip performance, low-temperature performance, and rolling performance. However, since safflower oil and sunflower oil both have a low ratio of polyunsaturated fatty acids within their unsaturated fatty acids, their effects are inferior to those of rapeseed oil and soybean oil. On the other hand, it can be seen that the vulcanized rubber of the rubber composition according to Comparative Example 3, which uses palm oil with a low ratio of unsaturated fatty acids in the fatty acids (49.8% by mass), exhibits particularly poor low-temperature performance.

[0049] [Table 3]

[0050] The results in Table 3 show that even in the vulcanized rubbers of the rubber compositions according to Examples 5 to 7, in which the amount of rapeseed oil was varied in various ways, the wet grip performance, low-temperature performance, and rolling performance were improved in a well-balanced manner.

Claims

1. A rubber composition containing diene rubber and vegetable oil, The aforementioned vegetable oil is a fatty acid ester triglyceride in which a fatty acid containing at least saturated fatty acids and unsaturated fatty acids is esterified with glycerol, wherein the ratio of the unsaturated fatty acid in the fatty acid is 50% by mass or more. A rubber composition characterized in that the diene rubber contains at least modified butadiene rubber.

2. The rubber composition according to claim 1, wherein the vegetable oil has a ratio of polyunsaturated fatty acids in the unsaturated fatty acids of 15% by mass or more.

3. The rubber composition according to claim 1, wherein the amount of vegetable oil added is 5 to 30 parts by mass when the total amount of diene rubber is 100 parts by mass.

4. The rubber composition according to claim 1, wherein the amount of modified butadiene rubber is 20 to 80 parts by mass when the total amount of diene rubber is 100 parts by mass.

5. The rubber composition according to claim 1, further containing silica, wherein the amount of silica added is 80 to 180 parts by mass when the total amount of diene rubber is 100 parts by mass.

6. A pneumatic tire comprising vulcanized rubber of the rubber composition described in claim 1.

7. A pneumatic tire comprising vulcanized rubber of the rubber composition described in claim 1 on at least the surface of the tread portion.

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