JP2011148898A - Rubber composition for tire tread - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for tire tread which has excellent wet grip performance and abrasion resistance and suppresses hardening due to aging with time. <P>SOLUTION: The rubber composition for tire tread is obtained by blending 1-30 pts.wt. microcapsule in which vegetable oil and fat containing polyphenol originating in natural material is encapsulated and 5-120 pts.wt. carbon black having 70-160 m<SP>2</SP>/g nitrogen adsorption specific surface area (N<SB>2</SB>SA) in diene based rubber 100 pts.wt. containing ≥10 pts.wt. aromatic vinyle conjugated diene copolymer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a rubber composition for a tire tread, and more particularly, to a rubber composition for a tire tread that is excellent in grip performance and wear resistance and suppresses curing due to aging.

  A pneumatic tire for a passenger car is required to have excellent grip performance and wear resistance and to maintain excellent ride comfort performance. For this reason, the pneumatic tire for passenger cars is designed so that the pattern and hardness of the tire tread portion are optimized. However, even when the rubber hardness is optimal at the start of use of the tire, the rubber is cured by aging over a long period of time, so that there is a problem that it becomes easy to pick up unevenness on the road surface and ride comfort performance is lowered. Also, grip performance and wear resistance may change.

  As a countermeasure against such aging of the tread portion, it is conceivable to increase the amount of the anti-aging agent compounded in the tire tread rubber composition. However, even if the amount of the anti-aging agent is increased, the rubber curing due to aging cannot be sufficiently suppressed, or the anti-aging agent is transferred to the tire surface so that the tire surface is turned brown and the appearance is damaged. There was a problem to do.

  As a countermeasure against this, Patent Document 1 proposes a tire rubber composition in which a thermally expandable microcapsule containing a thermally expandable substance and a nonpolar oil is blended. However, in this rubber composition, although the oil contained in the capsule gradually migrates into the rubber, an increase in rubber hardness can be suppressed. There was room for improvement. Therefore, it has not been achieved that the grip performance and the wear resistance required for the pneumatic tire for passenger cars are secured at a high level and that the excellent ride comfort performance is maintained for a long time by suppressing the curing of rubber.

JP 2009-138181 A

  An object of the present invention is to provide a rubber composition for a tire tread which is excellent in grip performance and wear resistance and which is reduced in curing due to aging.

The rubber composition for a tire tread of the present invention that achieves the above-described object is a microcomposition in which vegetable oil containing natural polyphenol is encapsulated in 100 parts by weight of a diene rubber containing 10% by weight or more of an aromatic vinyl conjugated diene copolymer. 1 to 30 parts by weight of capsules and 5 to 120 parts by weight of carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 70 to 160 m ² / g are blended.

In addition, silica having a BET specific surface area of 70 to 300 m ² / g is blended, and the total of the carbon black and silica is preferably 40 to 120 parts by weight with respect to 100 parts by weight of the diene rubber. The vegetable oil / fat preferably contains 0.9 × 10 ⁻³ wt% or more of polyphenol, more preferably grape seed oil.

  The rubber composition for a tire tread of the present invention can be suitably used for a pneumatic tire for passenger cars, particularly a summer tire.

The rubber composition for a tire tread of the present invention includes 1 to 30 microcapsules in which a vegetable oil containing natural polyphenol is encapsulated in 100 parts by weight of a diene rubber containing 10% by weight or more of an aromatic vinyl conjugated diene copolymer. Since 5 parts by weight and 5 to 120 parts by weight of carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 70 to 160 m ² / g are blended, when used in a tread part of a pneumatic tire, wear resistance and The grip performance, particularly wet grip performance, can be improved. In addition, since the vegetable oil containing polyphenol is encapsulated in the microcapsule, it suppresses the consumption of polyphenol during molding and vulcanization of the rubber composition and acts selectively on the prevention of aging of the rubber component. In addition, the vegetable oils and fats containing polyphenols are gradually released from the microcapsules dispersed in the rubber product, and the anti-oxidation action of the polyphenols prevents the rubber components from aging. Can do. For this reason, excellent riding comfort can be sustained for a long time.

  In the rubber composition for a tire tread of the present invention, the rubber component is a diene rubber. This diene rubber necessarily contains an aromatic vinyl conjugated diene copolymer. By including the aromatic vinyl conjugated diene copolymer, the tan δ at 0 ° C. can be increased and the wet grip performance can be improved. Examples of the aromatic vinyl conjugated diene copolymer include styrene-butadiene rubber (SBR). The type of SBR may be either solution polymerization SBR or emulsion polymerization SBR.

  The glass transition temperature of the aromatic vinyl conjugated diene copolymer is preferably −25 ° C. or lower, more preferably −25 ° C. to −70 ° C., still more preferably −25 ° C. to −65 ° C. In addition, if the glass transition temperature of the aromatic vinyl conjugated diene copolymer is too low, the wear resistance performance is excellent, but tan δ in the low temperature region, particularly near 0 ° C., becomes small and the wet grip performance deteriorates. It is impossible to achieve both wear performance and grip performance. As for the glass transition temperature, a thermogram is measured by differential scanning calorimetry (DSC) under a heating rate condition of 10 ° C./min, and the temperature is set to the midpoint temperature of the transition region. In addition, when an aromatic vinyl conjugated diene copolymer contains oil extended oil, it is set as the glass transition temperature of the state except oil extended oil.

  The blending amount of the aromatic vinyl conjugated diene copolymer in the diene rubber is 10% by weight or more, preferably 10 to 95% by weight, more preferably 15 to 90% by weight. When the blending amount of the aromatic vinyl conjugated diene copolymer is less than 10% by weight, it becomes difficult to ensure excellent wet grip performance.

  In the present invention, examples of the diene rubber other than the aromatic vinyl conjugated diene copolymer include natural rubber, isoprene rubber, butadiene rubber, acrylonitrile-butadiene rubber, and butyl rubber. Of these, natural rubber, isoprene rubber, and butadiene rubber are preferable. These other diene rubbers can be used alone or as any blend.

In the present invention, by adding carbon black, the strength of the tire tread rubber composition is increased and the wear resistance is improved. The carbon black to be used has a nitrogen adsorption specific surface area (N ₂ SA) of 70 to 160 m ² / g, preferably 70 to 150 m ² / g. When the nitrogen adsorption specific surface area (N ₂ SA) of carbon black is less than 70 m ² / g, the wear resistance and rubber strength cannot be sufficiently increased. When the nitrogen adsorption specific surface area exceeds 160 m ² / g, the rolling resistance is deteriorated, the rubber viscosity is increased, and the extrusion moldability is deteriorated. The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is determined according to JIS K6217-2.

  The compounding quantity of carbon black is 5-120 weight part with respect to 100 weight part of diene rubbers, Preferably it is 10-110 weight part. When the blending amount of carbon black is less than 5 parts by weight, the rubber composition cannot be sufficiently reinforced and hardened and wear resistance is insufficient. On the other hand, when the blending amount of carbon black exceeds 120 parts by weight, the viscosity of the rubber composition is increased and the molding processability is deteriorated, and the rolling resistance is increased when the tire is formed.

  In the present invention, by adding silica, the wet grip performance (tan δ at 0 ° C.) can be increased, and the exothermic property (tan δ at 60 ° C.) of the rubber composition can be reduced to reduce the rolling resistance of the tire. .

Silica having a BET specific surface area of 70 to 300 m ² / g, preferably 90 to 280 m ² / g is used. When the BET specific surface area of silica is less than 70 m ² / g, sufficient reinforcement to the rubber composition cannot be obtained. Further, if the BET specific surface area of silica exceeds 300 m ² / g, the dispersibility of silica is deteriorated and the processability of rubber is deteriorated, which is not preferable. In addition, the BET specific surface area of a silica shall be measured based on ASTM-D-4820-93. The silica may be any silica that is usually blended in a tire rubber composition. For example, wet method silica, dry method silica, or surface-treated silica can be used.

  The amount of silica blended may be 40 to 120 parts by weight, preferably 40 to 110 parts by weight, based on 100 parts by weight of the diene rubber. If the total of carbon black and silica is less than 40 parts by weight, it will be difficult to achieve both wear resistance and grip performance. On the other hand, when the total of carbon black and silica exceeds 120 parts by weight, the viscosity of the rubber composition for a tire tread increases and molding processability deteriorates.

  In the present invention, it is preferable to add a silane coupling agent together with silica because the dispersibility of the silica with respect to the diene rubber can be improved. The amount of the silane coupling agent is preferably 1 to 12% by weight, more preferably 3 to 10% by weight, based on the amount of silica. When the amount of the silane coupling agent is less than 1% by weight, the dispersibility of silica cannot be sufficiently improved. Moreover, when the compounding quantity of a silane coupling agent exceeds 12 weight%, silane coupling agents will aggregate and condense, and it will become impossible to acquire a desired effect.

  Although it does not restrict | limit especially as a kind of silane coupling agent, A sulfur containing silane coupling agent is preferable. Examples of the sulfur-containing silane coupling agent include bis- (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, and γ-mercaptopropyl. Examples thereof include triethoxysilane and 3-octanoylthiopropyltriethoxysilane.

  In addition to silica and carbon black, other inorganic fillers can be blended in the rubber composition for a tire tread of the present invention. As other inorganic fillers, for example, clay, calcium carbonate, talc, mica, aluminum hydroxide, magnesium carbonate and the like can be blended as necessary.

  The rubber composition for tire treads of the present invention is dispersed in a rubber composition by blending microcapsules enclosing vegetable oils and fats containing polyphenols as components derived from nature (hereinafter referred to as “plant oil and fat-containing microcapsules”). The vegetable oil and fat are gradually released from the vegetable oil and fat-containing microcapsules and the rubber component is prevented from aging due to the antioxidant action of the polyphenol contained in the vegetable oil and fat. In addition, since vegetable oils and fats containing polyphenols are encapsulated in microcapsules, it is possible to prevent polyphenols from being thermally decomposed or consumed in contact with oxygen during molding and vulcanization of tire tread rubber compositions. . For this reason, polyphenol can be made to selectively act to prevent aging of the rubber component. Therefore, when the blending amount of the vegetable oil and fat containing polyphenols to the diene rubber is the same, the effect of preventing aging is better when the vegetable oil and fat is encapsulated in the microcapsule than when the vegetable oil and fat is blended as it is. However, it is possible to further reduce rubber curing.

  In the present invention, since vegetable oils and fats containing naturally derived polyphenols are encapsulated in microcapsules, they are characterized by excellent safety and hygiene. That is, the vegetable fats and oils used in the present invention do not contain natural polyphenols and / or chemically synthesized polyphenol antioxidants by artificial manipulation.

The naturally-derived polyphenol content in the vegetable oil is preferably 0.03 × 10 ⁻³ wt% or more, more preferably 0.9 × 10 ⁻³ wt% or more, and even more preferably 1.1 × 10 ⁻³ wt. % Or more. When the content of polyphenol in the vegetable oil is less than 0.03 × 10 ⁻³ wt%, the antioxidant action cannot be sufficiently obtained and the rubber component cannot be inhibited from curing. The polyphenol content in the vegetable oil was determined by the foreign-thiocult method. The foreign-thiocult method uses a foreign-thiocult reagent that develops a blue color under strong alkali against a reducing substance. Polyphenols in a sample (vegetable oil) are collectively collected by a colorimetric method (660 nm). It was measured as the amount of polyphenol. In addition, (+)-catechin was used as a standard sample, and the amount of polyphenol was determined from the calibration curve.

  Examples of vegetable oils and fats containing naturally derived polyphenols include grape seed oil, olive oil, safflower oil, sunflower oil, canola oil, walnut seed oil, sesame oil, and the like. These vegetable fats and oils can be used alone. A plurality of types may be blended and used.

As vegetable oils and fats, grape seed oil and olive oil are particularly preferable. Grape seed oil is produced all over the world, but chilean grape seed oil is particularly preferable because it has an extremely high polyphenol content of 1.1 × 10 ⁻³ wt% or more. However, in addition to Chilean grape seed oil, the same effect can be expected if it is a vegetable oil containing 0.9 × 10 ⁻³ wt% or more of polyphenol due to variety improvement or the like. Grape seed oil contains a large amount of naturally occurring polyphenols and also contains a lot of vitamin E. Vitamin E has an antioxidant action, and therefore, with polyphenol, it prevents aging of the rubber composition for tire treads and suppresses hardening.

  The shell material of the vegetable oil-and-fat-containing microcapsules prevents the vegetable oil and fat containing polyphenol from coming into contact with oxygen during the molding process and vulcanization of the tire tread rubber composition, and prevents the polyphenol from being consumed by oxidation. In addition, after vulcanization, vegetable oil and fat containing polyphenol is gradually released into a rubber product such as a pneumatic tire so that the rubber component can be prevented from being cured by aging.

  Such shell material of vegetable oil-containing microcapsules can be formed of a thermoplastic resin useful as a normal microencapsulating agent. The thermoplastic resin is formed by polymerizing a polymerizable component in the presence of a polymerization initiator. The polymerizable component generally includes a monomer component called a (radical) polymerizable monomer having at least one polymerizable double bond. The monomer component is not particularly limited. For example, nitrile monomers such as acrylonitrile; carboxyl group-containing monomers such as acrylic acid and methacrylic acid; vinylidene chloride; vinyl halide monomers such as vinyl chloride Monomer; vinyl ester monomer such as vinyl acetate; (meth) acrylic acid ester monomer such as methyl (meth) acrylate and ethyl (meth) acrylate; styrene monomer such as styrene and α-methylstyrene Acrylamide monomers such as acrylamide; ethylenically unsaturated monoolefin monomers such as ethylene and propylene. These monomer components may be used alone or in combination of two or more.

  The polymerizable component may contain a polymerizable monomer (crosslinking agent) having two or more polymerizable double bonds in addition to the monomer component. Polymerization using a crosslinking agent improves the heat resistance and solvent resistance of the microcapsule shell material, and can control the release speed of vegetable oils and fats in rubber products.

  The crosslinking agent is not particularly limited. For example, aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene; allyl methacrylate, triacryl formal, triallyl isocyanate, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate , Triethylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, 1,10-decanediol di (meth) acrylate, PEG # 200 di (Meth) acrylate, PEG # 400 di (meth) acrylate, PEG # 600 di (meth) acrylate, neopentyl glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, trimethylol Lopantrimethacrylate, glycerin dimethacrylate, dimethylol-tricyclodecane diacrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, neopentyl glycol acrylate benzoate, trimethylol propane benzoate Acid esters, 2-hydroxy-3-acryloyloxypropyl methacrylate, hydroxypivalate neopentyl glycol diacrylate, ditrimethylolpropane tetraacrylate, 2-butyl-2-ethyl-1,3-propanediol diacrylate and the like ( Mention may be made of (meth) acrylate compounds. These crosslinking agents may be used alone or in combination of two or more. In the above, a series of compounds described as “PEG # OOXX di (meth) acrylate” means polyethylene glycol di (meth) acrylate.

  The method for producing vegetable oil-containing microcapsules of the present invention always includes a polymerizable component, vegetable oil and fat, an aqueous dispersion medium containing water as an essential component, and a polymerization aid such as an electrolyte and a water-soluble additive as necessary. It is carried out by mixing the components such as the dispersion stabilizer and the dispersion auxiliary stabilizer and polymerizing the polymerizable component. The order of blending these components is not particularly limited, and components that can be dissolved or dispersed in the aqueous dispersion medium may be blended in advance and blended with other components.

  In the method for producing vegetable oil-containing microcapsules, an oily mixture such as a polymerizable component and vegetable oil is emulsified and dispersed in an aqueous dispersion medium so that spherical oil droplets having a predetermined particle diameter are prepared. Examples of the method for emulsifying and dispersing the oily mixture include, for example, a method of stirring with a homomixer (for example, manufactured by Special Machine Engineering Co., Ltd.), a homodisper (for example, manufactured by Special Machine Engineering Co., Ltd.), or the like, or a static mixer (for example, manufactured by Noritake Engineering Co., Ltd.). General dispersion methods such as a method using a static dispersion device such as a membrane emulsification method, an ultrasonic dispersion method, and a microchannel method can be given.

  Next, suspension polymerization is started by heating the dispersion in which the oily mixture is dispersed as spherical oil droplets in the aqueous dispersion medium. Although superposition | polymerization temperature is freely set by the kind of polymerization initiator, Preferably it is 30-100 degreeC, More preferably, it is 40-90 degreeC, More preferably, it controls in the range of 50-85 degreeC. The time for maintaining the reaction temperature is preferably about 0.1 to 20 hours.

  After completion of the polymerization reaction, the dispersion stabilizer is decomposed with hydrochloric acid or the like, if desired, and the resulting product (microcapsule) is isolated from the dispersion by an operation such as suction filtration, centrifugation, or centrifugal filtration. Furthermore, the water-containing cake of the obtained microcapsules can be washed with water and dried to obtain vegetable oil-containing microcapsules.

  The content of vegetable oil in the vegetable oil-containing microcapsule is preferably 10 to 70% by weight, more preferably 20 to 50% by weight. When the content of the vegetable oil / fat in the vegetable oil / fat-containing microcapsule is less than 10% by weight, the period for suppressing the aging of the rubber composition for a tire tread is shortened. On the other hand, if the content of vegetable oil exceeds 70% by weight, it becomes difficult to produce microcapsules, and it becomes fragile during molding and vulcanization.

  In the present invention, the size of the vegetable oil-and-fat-containing microcapsules is not particularly limited, but is preferably 1 to 100 μm in diameter, more preferably 5 to 50 μm in diameter. When the diameter of the microcapsule is less than 1 μm, the amount of the vegetable fat / oil is reduced. Moreover, when the diameter of a microcapsule exceeds 100 micrometers, it will become difficult to include vegetable fats and oils, and it will become easy to break during rubber molding or vulcanization.

  The amount of the vegetable oil-and-fat-containing microcapsules containing polyphenol is 1 to 30 parts by weight, preferably 2 to 25 parts by weight, per 100 parts by weight of the diene rubber. When the blending amount of the vegetable oil-and-fat-containing microcapsules is less than 1 part by weight, the antioxidant effect of polyphenol cannot be sufficiently obtained, and the rubber component cannot be inhibited from curing due to aging. Moreover, when the compounding quantity of a vegetable oil containing microcapsule exceeds 30 weight part, abrasion resistance will fall.

  The tire tread rubber composition includes various additives generally used in tire rubber compositions such as a vulcanization or crosslinking agent, a vulcanization accelerator, a processing aid, an anti-aging agent, an oil, and a plasticizer. These additives can be compounded and kneaded by a general method to obtain a rubber composition for a tire tread, which can be used for vulcanization or crosslinking. As long as the amount of these additives is not contrary to the object of the present invention, a conventional general amount can be used. The rubber composition for a tire tread can be produced by mixing the above-described components using a normal rubber kneading machine such as a Banbury mixer, a kneader, or a roll.

  The rubber composition for a tire tread of the present invention is suitable for constituting a tread portion of a pneumatic tire, particularly a summer tire for a passenger car. The pneumatic tire composed of this rubber composition for tire tread has excellent grip performance and wear resistance, and also prevents aging of the tread part and suppresses curing so as to maintain excellent riding comfort performance for a long time. Can do.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, the scope of the present invention is not limited to these Examples.

Production of microcapsules (microcapsule 1) encapsulating grape seed oil As an aqueous system, 40 g of colloidal silica with a solid content of 40%, 0.5 g of diethanolamine-adipic acid condensate, 150 g of sodium chloride and 500 g of ion-exchanged water are added and mixed. Thereafter, the pH was adjusted to 3.5 to prepare an aqueous dispersion medium. As an oil system, 100 g of acrylonitrile, 50 g of methacrylonitrile, 50 g of methacrylic acid, 1 g of ethylene glycol dimethacrylate, 3 g of azobis (2,4-dimethylvaleronitrile) are mixed, and grape seed oil (Grape Seed Oil from Chile, Catac 90 g of planner's edible grape oil) was further added to prepare an oily mixture.

  The aqueous dispersion medium and the oily mixture were mixed, and the resulting mixture was dispersed with a homomixer (TK homomixer manufactured by Tokushu Kika Kogyo Co., Ltd.) at a rotation speed of 9000 rpm for 5 minutes to prepare a suspension. This suspension was charged into an autoclave, purged with nitrogen, and reacted at a reaction temperature of 60 ° C. and a reaction pressure of 0.5 MPa for 8 hours to obtain vegetable oil-containing microcapsules (microcapsule 1). The obtained vegetable oil-and-fat-containing microcapsules contained 30% by weight of grape seed oil, and the average particle size was 19 μm.

Manufacture of microcapsules (microcapsule 2) encapsulating naphthenic oil In the manufacture of the above-mentioned vegetable oil-and-fat microcapsules (microcapsule 1), oil-containing microcapsules (microcapsules) were prepared in the same manner except that grape seed oil was changed to naphthenic oil. Capsule 2) was produced. The obtained oil-containing microcapsules contained 30% by weight of naphthenic oil and had an average particle size of 22 μm.

Preparation and Evaluation of Tire Tread Rubber Composition Fourteen types of tire tread rubber compositions (Examples 1 to 5 and Comparative Examples 1 to 9) having the compositions shown in Tables 1 to 3 were respectively used as a vulcanization accelerator and sulfur. , Weigh the ingredients except vegetable oil-containing microcapsule (microcapsule 1) and oil-containing microcapsule (microcapsule 2), knead for 5 minutes in a 1.7L closed Banbury mixer, and release the masterbatch at 150 ° C And cooled to room temperature. Then, this master batch is subjected to a 1.7 L hermetic banbury mixer, and a vulcanization accelerator, sulfur, and if necessary, vegetable oil-containing microcapsules (microcapsule 1) and oil-containing microcapsules (microcapsule 2) are added and mixed for 2 minutes. A rubber composition for tire treads was prepared.

  Using the obtained 14 types of rubber compositions for tire treads, a test sample was prepared by vulcanization molding at 160 ° C. for 30 minutes using a mold having a predetermined shape, and before and after the heat aging test by the method described below. The rubber hardness increase rate (aging hardness increase rate), wear resistance and wet grip performance were evaluated. In addition, pneumatic tires using the obtained rubber composition in the tread portion were manufactured, and the riding comfort performance after the initial stage and after running was evaluated by the following method.

Aging hardness increase rate As a test sample, a Rupke sample (thickness 12.5 mm, columnar shape having a diameter of 29 mm) was used. Each Rupke sample was divided into two groups, and one of them was subjected to air heat aging treatment at 80 ° C. for 120 hours. Using the test specimens before and after the aging treatment, the rubber hardness at a temperature of 20 ° C. was measured by a durometer type A in accordance with JIS K6253, and each (rubber hardness after aging treatment / rubber hardness before aging treatment × 100) Was used to calculate the rate of increase in rubber hardness (%) accompanying heat aging. The obtained results are shown in Tables 1 to 2 as “aging hardness increase rate” with the values of Comparative Example 1 being 100 in Tables 1 and 2 and the value of Comparative Example 9 being 100 in Table 3. A smaller index means that the curing of the rubber composition for tire tread accompanying heat aging is suppressed.

Wear resistance Based on JIS K6264, the wear amount of the obtained test sample was measured at a load of 39 N and a slip rate of 30% using a Lambourn wear tester (manufactured by Iwamoto Seisakusho). did. In Tables 1 and 2, the results are shown in Tables 1 and 2 as “wear resistance” in which the reciprocal of the wear amount in Comparative Example 1 is 100 and the reciprocal of the wear amount in Comparative Example 9 is 100 in Table 3. Indicated. Higher index means better wear resistance.

Wet Grip Performance Tan δ at a temperature of 0 ° C. of the obtained test sample was measured using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho under the conditions of an initial strain of 10%, an amplitude of ± 2%, and a frequency of 20 Hz. The obtained results are shown in Tables 1 to 3 as “wet grip performance” with Tables 1 and 2 as indices with the value of Comparative Example 1 being 100 and in Table 3 the value of Comparative Example 9 being 100. The larger the index, the larger the tan δ at 0 ° C., and the better the wet grip performance.

Riding comfort performance Tires with treads made of the 14 types of rubber compositions obtained were mounted on a domestic 2.5 liter class test vehicle, and a straight running test course with irregularities was actually driven at 50 km / h. The ride performance after traveling 7000km was sensitively evaluated by three specialized panelists. The evaluation results are shown in Tables 1 and 2, with the comparative tire 1 as 100 and the comparative example 9 as 100, respectively, in the columns of “Initial Ride Performance” and “Ride Comfort Performance After Running” in Tables 1-3. Respectively. The larger the index value, the better the ride comfort performance at the initial stage and after traveling 7000 km.

In addition, the kind of raw material used in Tables 1-3 is shown below.
NR: natural rubber, RSS # 3
SBR: styrene-butadiene rubber, Nipol 1502 manufactured by Nippon Zeon Co., Ltd., glass transition temperature -55 ° C
BR: butadiene rubber, Nipol BR1220 manufactured by Nippon Zeon
Carbon Black 1: Toast Carbon Co., Ltd. Seest 6, Nitrogen adsorption specific surface area of 119 m ² / g
Carbon black 2: Seast 116 manufactured by Tokai Carbon Co., Nitrogen adsorption specific surface area 49 m ² / g
Carbon black 3: CD2019 produced by Colombian Chemicals Company, nitrogen adsorption specific surface area of 390 m ² / g
Silica 1: Nipsil AQ manufactured by Tosoh Silica Co., BET specific surface area 200 m ² / g
Silica 2: ZEOSIL Z1115MP manufactured by Rhodia, BET specific surface area 104 m ² / g
Silane coupling agent: bis- (3-triethoxysilylpropyl) tetrasulfide, Si69 manufactured by Dexa Corporation
Zinc oxide: 3 types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd. Stearic acid: Beads manufactured by NOF Co., Ltd. Bead stearic acid anti-aging agent: SANTOFLEX 6PPD manufactured by Flexis
Wax: Paraffin wax process oil manufactured by Ouchi Shinsei Chemical Co., Ltd .: Extract No. 4 S manufactured by Showa Shell Sekiyu KK
Grapeseed oil: Chilean grapeseed oil, edible grape oil manufactured by Catac Planners, natural polyphenol content 1.3 x 10 ^-3 wt% (polyphenol content measured by the method described above)
Microcapsule 1: Microcapsule encapsulating grape seed oil, manufactured by the above-described method Microcapsule 2: Microcapsule encapsulating naphthenic oil, manufactured by the above-described method Sulfur: Fine powder with Jinhua seal oil manufactured by Tsurumi Chemical Co., Ltd. Sulfur vulcanization accelerator: Nouchira CZ-G manufactured by Ouchi Shinsei Chemical Co., Ltd.

Claims (5)

100 parts by weight of a diene rubber containing 10% by weight or more of an aromatic vinyl conjugated diene copolymer, 1 to 30 parts by weight of microcapsules containing vegetable oils and fats containing naturally derived polyphenols, nitrogen adsorption specific surface area (N ₂ SA ) Is a rubber composition for tire treads in which 5 to 120 parts by weight of carbon black having 70 to 160 m ² / g is blended. ^2. The tire tread according to claim 1, wherein silica having a BET specific surface area of 70 to 300 m ² / g is blended, and the total of the carbon black and silica is 40 to 120 parts by weight with respect to 100 parts by weight of the diene rubber. Rubber composition. The rubber composition for a tire tread according to claim 1 or 2, wherein the vegetable oil contains 0.9 x 10 ^-3 wt% or more of the polyphenol.   The rubber composition for tire treads according to claim 1, wherein the vegetable oil is grape seed oil.   The pneumatic tire for passenger cars which used the rubber composition for tire treads in any one of Claims 1-4 for the tread part.