JP2006063094A - Rubber composition for tire tread, and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for tire treads exhibiting improved braking performances particularly on a frozen road surface without deteriorating essential properties thereof such as hardness or abrasion resistance, a manufacturing method of the rubber composition for tire treads, and a pneumatic tire obtained using the rubber composition for tire treads. <P>SOLUTION: The rubber composition for tire treads comprises 100 pts.mass of a rubber component and, incorporated therewith, 10-60 pts.mass of carbon black and 5-40 pts.mass of a paraffinic oil, and further contains 0.1-50 mass% of aluminum 2-ethylhexanoate and at least 0.1 mass% of a fatty acid, each based on the paraffinic oil. The rubber composition may contain 5-50 pts.mass of silica based on 100 pts.mass of the rubber component. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a rubber composition for a tire tread that can maintain braking performance in the front-rear direction on an icing road surface for a long period of time, and a pneumatic tire using the rubber composition, particularly a studless pneumatic tire.

  In recent years, the prohibition of the use of spike tires has been legalized to prevent dust pollution caused by spike tires, and studless tires have been used instead of spike tires in cold regions. Studless tires have developed braking performance close to that of spike tires due to technological developments in recent years. Factors affecting the braking performance of studless tires include the frictional force between the tire tread rubber and the road surface. Here, there are adhesive friction, digging friction, and hysteresis friction as frictional forces.

  Therefore, in order to improve the braking performance, it is necessary to increase the adhesive frictional force of the rubber composition for a tire tread. For example, the rubber composition is softened to increase the road surface and contact area. For this purpose, the blending amount of the filler is reduced, a rubber component that is hard to cure even at a low temperature, such as polybutadiene rubber or polyisoprene rubber, or a softening agent is further blended. However, if the rubber composition is softened, the steering stability and wear resistance of the tire are lowered, so there is a limit to making the rubber composition soft.

  Moreover, the hardness of the tread rubber tends to increase with time, resulting in a decrease in tire performance. Therefore, in order to reduce the change over time in the tread rubber hardness of the tire, a method of crosslinking the rubber with a crosslinking agent that is more thermally stable than sulfur and a softening agent having a functional group that interacts with the rubber are added to the tread rubber. A method of suppressing the softening agent from transferring to adjacent tire members such as belt layer rubber is also employed.

  Also, the tread part is composed of two layers, a cap rubber layer and a base rubber layer, and the base rubber is worn out at a relatively early stage of wear by using a rubber composition in which the latter is softer than the former. By exposing, the reduction in performance was reduced.

  However, the former method requires the use of a special material, and there are problems such as difficulty in performance tuning and increased costs associated with the use of the material. On the other hand, the latter method is not sufficient in reducing the performance deterioration after the base rubber is exposed.

  Another method has been proposed in which carbon black in the rubber composition is partially replaced with silica and a silane coupling agent to lower the modulus at low temperatures and improve the adhesive frictional force. With this method, wet braking performance and icing road surface braking performance are greatly improved, but wear resistance tends to decrease.

On the other hand, a technology for blending a softener in an elastomer composition (Patent Literature 1), a technology for blending an oil gelling agent in a thermoplastic elastomer (Patent Literature 2), and a technology for gelling paraffins (Patent Literature 3) are already available. Are known.
JP 2000-53808 A JP 2004-149614 A JP 2000-109787 A

  The present invention is for solving the above-mentioned problems, and for tire treads that have improved braking performance particularly on icy road surfaces without impairing basic characteristics such as hardness and wear resistance of the tire rubber composition. The present invention provides a rubber composition, a method for producing the tire tread rubber composition, and a pneumatic tire using the tire rubber composition.

  In the present invention, 10 to 60 parts by mass of carbon black and 5 to 40 parts by mass of paraffinic oil are blended with 100 parts by mass of the rubber component, and aluminum 2-ethylhexanoate is added to the paraffinic oil. A tire tread rubber composition comprising 0.1 to 50 mass% and 0.1 mass% or more of a fatty acid.

  Here, the tire tread rubber composition may contain 5 to 50 parts by mass of silica with respect to 100 parts by mass of the rubber component. The rubber component is preferably natural rubber and / or butadiene rubber.

  In another embodiment of the present invention, 10 to 60 parts by mass of carbon black and 5 to 40 parts by mass of paraffinic oil are mixed with 100 parts by mass of the rubber component, and then the paraffinic system is prepared. A method for producing a rubber composition for a tire tread, wherein 0.1 to 50% by mass of aluminum 2-ethylhexanoate and 0.1% by mass or more of a fatty acid are mixed and dispersed with respect to oil.

  The present invention is a pneumatic tire having a tread portion of the rubber composition for a tire tread. In particular, the pneumatic tire of the present invention has a tread portion composed of two layers of a cap rubber and a base rubber, and the cap rubber contains 10 to 60 parts by mass of carbon black with respect to 100 parts by mass of the rubber component, and While blending 5 to 40 parts by mass of paraffinic oil, 0.1 to 50% by mass of aluminum 2-ethylhexanoate and 0.1% by mass or more of fatty acid are added to the paraffinic oil. .

  In the present invention, paraffinic oil is stably dispersed in the rubber composition by adding aluminum 2-ethylhexanoate and fatty acid together with paraffinic oil to the rubber component. Oil is less likely to flow out over time, and the tendency to increase hardness can be suppressed. As a result, it is possible to obtain a rubber composition for a tire tread having improved braking performance particularly on an icy road surface without lowering the basic properties such as hardness and wear resistance of the rubber composition for a tire tread.

  In the present invention, 10 to 60 parts by mass of carbon black and 5 to 40 parts by mass of paraffinic oil are blended with 100 parts by mass of the rubber component, and aluminum 2-ethylhexanoate is added to the paraffinic oil. A tire tread rubber composition comprising 0.1 to 50 mass% and 0.1 mass% or more of a fatty acid.

<Rubber component>
The type of rubber component is not particularly limited, but diene synthetic rubber, particularly natural rubber (NR) and / or polybutadiene rubber is preferably used. Diene-based synthetic rubbers include styrene-butadiene rubber (SBR), polybutadiene rubber (BR), polyisoprene rubber (IR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR). Butyl rubber (IIR) or the like can be used, and one or more kinds can be used in the rubber component used in the present invention.

  The ethylene-propylene-diene rubber (EPDM) contains a third diene component in the ethylene-propylene rubber (EPM), and the third diene component is a non-conjugated diene having 5 to 20 carbon atoms. 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, 2,5-dimethyl-1,5-hexadiene and 1,4-octadiene, for example 1,4-cyclohexadiene, cyclooctadiene And cyclic dienes such as dicyclopentadiene, for example, alkenyl norbornene such as 5-ethylidene-2-norbornene, 5-butylidene-2-norbornene, 2-methallyl-5-norbornene and 2-isopropenyl-5-norbornene. In particular, among diene, dicyclopentadiene, 5-ethylide -2-norbornene can be preferably used.

<Carbon black>
The tread rubber composition of the present invention contains carbon black as a filler. Here, the carbon black is 10 parts by mass or more and 60 parts by mass or less, preferably 20 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the rubber component. Here, the physical properties of carbon black are those having a nitrogen adsorption specific surface area (BET method) in the range of 40 to 160 m ² / g, DBP oil absorption in the range of 70 to 130 ml / 100 g, and iodine adsorption in the range of 70 to 150 mg / g. Can be used to retain paraffinic oil in the rubber composition for a long period of time. In addition, when using together with a silica, it mix | blends in the range of 0.1-10.0 times with respect to a silica compounding quantity, Preferably it is 0.5-2 times.

<Paraffin oil>
Examples of the paraffinic oil used in the present invention include normal paraffins composed of linear saturated hydrocarbons, isoparaffins containing a large amount of branched saturated hydrocarbons, liquid paraffins composed of alkyl naphthenes, and linear chains having about 25 to 35 carbon atoms. A hydrocarbon mixture paraffin wax or the like can be used. Moreover, what contains an olefin in a compound like the hydrocarbon which has a double bond at the terminals, such as polybutene, can also be made into object. Moreover, the thing which modified | denatured olefins to alkane and modified | denatured aromatic species to the saturated cyclic hydrocarbon by carrying out a hydrogenation process is also object.

  Specific examples of the paraffinic oil include normal pentane, normal hexane, normal decane, normal tridecane, normal tetradecane, normal hexadecane, isooctane, isododecane, cyclopentane, and cyclohexane.

<Aluminum 2-ethylhexanoate>
In this invention, 0.1-50 mass% of 2-ethylhexanoic acid aluminum is mix | blended with respect to paraffinic oil, More preferably, 0.5-30 mass% is mix | blended.
Here, aluminum 2-ethylhexanoate plays a role in which paraffinic oil forms a gel in the rubber composition and is stably held for a long period of time.

<Fatty acid>
In the present invention, the fatty acid is added in an amount of 0.1% by mass or more, preferably 0.5% by mass or more, based on the paraffinic oil. The fatty acid has an action of promoting the cross-linking reaction of aluminum 2-ethylhexanoate, and is usually added in a range of 20% by mass or less.

  The fatty acid that can be used in the method of the present invention is a saturated and / or unsaturated fatty acid having 8 to 24 carbon atoms. Examples include, but are not limited to, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, behenic acid, undecylenic acid, oleic acid, linoleic acid, and linolenic acid. Moreover, these can be used by 1 type and / or multiple types.

<Gelling agent>
In the present invention, aluminum salt of various fatty acids, for example, aluminum stearate, aluminum laurate, aluminum oleate, aluminum behenate, aluminum palmitate, as a gelling agent for paraffinic oil together with aluminum 2-ethylhexanoate and fatty acid Etc. can be mixed in the rubber composition.

  These gelling agents may be mixed separately from aluminum 2-ethylhexanoate, or when 2-ethylhexanoic acid aluminum is produced, a part of 2-ethylhexanoic acid is replaced with another fatty acid. Alternatively, for example, another fatty acid aluminum may be mixed in a fatty acid aluminum salt of 2-ethylhexanoic acid as a main component produced by replacing part of 2-ethylhexanoic acid with another fatty acid. Of course, one type and / or two or more types of fatty acids can be used.

  Here, the gelling agent is preferably in the range of 0.1 to 20% by mass, preferably in the range of 5 to 15% by mass, and does not exceed the blending amount of aluminum 2-ethylhexanoate with respect to the paraffinic oil. Is desirable.

<Silica>
In the present invention, 10 parts by mass or more and 50 parts by mass or less of silica is blended with respect to 100 parts by mass of the rubber component. As the silica used in the present invention, those generally used for general-purpose rubber can be used. For example, dry method white carbon, wet method white carbon, colloidal silica and the like used as a reinforcing agent. Among these, wet method white carbon mainly containing hydrous silicic acid is preferable.

  When the compounding amount of silica is less than 10 parts by mass, the properties such as wear resistance cannot be sufficiently improved due to inferior reinforcement, while when it exceeds 50 parts by mass, the viscosity of the unvulcanized rubber composition increases and the workability is increased. To lose. A more preferable blending amount of silica is 15 parts by mass or more and 40 parts by mass or less.

Then, the nitrogen adsorption specific surface area of the silica to improve the properties (BET method) is usually 50~350m ² / g, preferably 100~280m ² / g, more preferably in the range of 110~250m ² / g is there. When the specific surface area of silica is smaller than 50 m ² / g, the reinforcing property is inferior and the wear resistance is lowered. On the other hand, when the specific surface area exceeds 350 m ² / g, the workability of the rubber composition is inferior and the braking performance is further deteriorated. Here, the nitrogen adsorption specific surface area is a value measured by the BET method according to ASTM D3037-81.

  Such silicas are commercially available, for example, Nipsil VN3, Nipsil AQ manufactured by Nippon Silica Co., Ltd., Z1165MP, Z1652Gr manufactured by Rhône-Poulenc, and Ultrasil VN3 manufactured by Degussa.

<Silane coupling agent>
In the rubber composition of the present invention, a silane coupling agent, preferably a sulfur-containing silane coupling agent is blended in an amount of 0.1 to 10 parts by mass, preferably 0.5 to 5 parts by mass. . Sulfur-containing silane coupling agents include 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl-tetrasulfide, trimethoxysilylpropyl-mercaptobenzothiazole tetrasulfide, tri-ethoxysilylpropyl-methacrylate-monosulfide, dimethoxy Methylsilylpropyl-N, N-dimethylthiocarbamoyl-tetrasulfide, bis- [3- (triethoxysilyl) -propyl] tetrasulfide, 3-mercaptopropyltrimethoxysilane and the like.

  Other silane coupling agents include vinyltrichlorosilane, vinyltris (2-methoxyethoxy) silane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ- (2-aminoethyl) amino Propyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and the like can be used.

  Abrasion resistance and braking performance are further improved by blending a silane coupling agent. When the amount of the silane coupling agent is less than 0.5 parts by mass, the above effect cannot be expected. On the other hand, when the amount exceeds 10 parts by mass, scorching is likely to occur in the rubber kneading and extruding steps.

<Filler>
In the present invention, the rubber composition can contain a white filler other than silica. Examples of the white filler include clay, alumina, talc, calcium carbonate, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, magnesium oxide, and titanium oxide. These can be used alone or in combination of two or more. .

<Method for producing rubber composition>
In order to produce the tread rubber composition of the present invention, 10 to 60 parts by mass of carbon black and 5 to 40 parts by mass of paraffinic oil are mixed with 100 parts by mass of the rubber component to obtain a uniform paraffinic oil. A rubber composition dispersed in is prepared. Thereafter, 0.1 to 50% by mass of aluminum 2-ethylhexanoate and 0.1% by mass or more of fatty acid are mixed and dispersed with respect to the paraffinic oil, whereby aluminum 2-ethylhexanoate and fatty acid are mixed and dispersed. However, it can exist stably in the rubber composition for a long period of time with the paraffinic oil. The rubber component, carbon black, paraffinic oil, aluminum 2-ethylhexanoate and fatty acid can be mixed at the same time. In this case, the paraffinic oil tends to aggregate in the rubber composition, which is not preferable from the viewpoint of uniform dispersion.

<Plasticizer>
In the present invention, plasticizers such as DMP (dimethyl phthalate), DEP (diethyl phthalate), DBP (dibutyl phthalate), DHP (diheptyl phthalate), DOP (dioctyl phthalate), and DINP (phthalate) are optionally used. Acid diisononyl), DIDP (diisodecyl phthalate), BBP (butyl benzyl phthalate), DLP (dilauryl phthalate), DCHP (dicyclohexyl phthalate), hydrophthalic anhydride ester, DOZ (di-2-ethylhexyl azelate), DBS (Dibutyl sebacate), DOS (dioctyl sebacate), acetyl triethyl citrate, acetyl tributyl citrate, DBM (dibutyl maleate), DOM (2-ethylhexyl maleate), DBF (dibutyl fumarate), etc. are used. It is possible .

<Other ingredients>
In addition to the above compounding agents, a vulcanizing agent, a vulcanization accelerator, an anti-aging agent, an anti-scorch agent, and the like can be added to the rubber composition for tires of the present invention.

  As the vulcanizing agent, an organic peroxide or a sulfur vulcanizing agent can be used. Examples of organic peroxides include benzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide, and sulfur-based vulcanizing agents. For example, sulfur, morpholine disulfide, etc. can be used.

  Vulcanization accelerators include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine, aldehyde-ammonia, imidazoline, or xanthate vulcanization accelerators. Those containing at least one of them can be used. Preferably sulfenamide systems such as CBS (N-cyclohexyl-2-benzothiazylsulfenamide), TBBS (N-ter-butyl-2-benzothiazylsulfenamide), N, N-dicyclohexyl-2- Sulfenamide compounds such as benzothiazylsulfenamide, N-oxydiethylene-2-benzothiazylsulfenamide, and N, N-diisopropyl-2-benzothiazolesulfenamide can be used.

  As the anti-aging agent (deterioration preventing agent), amine-based, phenol-based, imidazole-based, carbamic acid metal salt, wax and the like can be appropriately selected and used. Furthermore, as a scorch inhibitor, for example, organic acids such as phthalic anhydride, salicylic acid and benzoic acid, nitroso compounds such as N-nitrosodiphenylamine, N-cyclohexylthiophthalimide and the like can be used.

<Hardness of rubber composition>
In the present invention, the rubber composition for a tire tread preferably has a Shore A hardness of 43 to 48. When the Shore A hardness is less than 43, the steering stability and the wear resistance tend to decrease. On the other hand, when the Shore A hardness exceeds 48, the braking performance tends to decrease.

<Pneumatic tire>
The rubber composition of the present invention is applied to a tire tread portion. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 illustrates the left half of a sectional view of a pneumatic tire according to the present invention. The tire 1 includes a tread portion 2, a pair of sidewall portions 3 extending inward in the tire radial direction from both ends thereof, and a bead portion 4 positioned at an inner end of each sidewall portion 3. Further, a carcass 6 is bridged between one bead portion 4 and the other bead portion, and a belt layer 7 having a tagging effect is disposed outside the carcass 6 in the radial direction.

  The carcass 6 is formed of one or a plurality of carcass plies in which the carcass cord is arranged at an angle of 70 to 90 ° with respect to the tire circumferential direction. The carcass 6 is folded back from the inner side in the tire axial direction to the outer side around the bead core 5 of the bead part 4 through the sidewall part 3 from the tread part 2 and locked.

  The belt layer 7 includes two or more belt plies 7a and 7b in which belt cords are arranged at an angle of, for example, 35 ° or less with respect to the tire circumferential direction, and the belt cords are arranged so that each belt cord intersects between the plies. Yes. A band layer (not shown) may be provided outside the belt layer 7. At this time, the band layer is formed by a continuous ply in which a low modulus organic fiber cord is spirally wound substantially parallel to the tire circumferential direction.

  A bead apex rubber 8 extending radially outward from the bead core 5 is disposed in the bead portion 4, and an inner liner rubber 9 that forms a tire lumen surface is adjacent to the inside of the carcass 6. The outside of 6 is protected by chafer rubber 4G and side wall rubber 3G. Although not shown, it is also possible to configure the tread portion as two layers of a base rubber adjacent to the belt layer 7 and a cap rubber on the ground surface side, and apply the tread rubber composition to the base rubber.

Examples 1 to 3 and Comparative Examples 1 to 4
(1) Rubber compounding The rubber compositions shown in Table 1 were used in Examples and Comparative Examples.

The details of the rubber component and the compounding agent used here are as follows.

  (Note 1) RSS # 3 was used as the natural rubber.

  (Note 2) Polybutadiene rubber is UBEPOL-BR150B manufactured by Ube Industries, Ltd. (cis 1,4 bond content: 96%).

(Note 3) As the carbon black, Seast 9 manufactured by Tokai Carbon Co., Ltd. was used.
The nitrogen adsorption specific surface area is 142 m ² / g, the DBP oil absorption is 115 ml / 100 g, and the iodine adsorption is 139 m ² / g.

(Note 4) Ultrasil VN3 manufactured by Degussa Co., Ltd. was used as the silica.
Nitrogen adsorption specific surface area (BET method) is 172 m ² / g (Note 5) Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa Co., Ltd. was used as the silane coupling agent.

  (Note 6) As paraffinic oil, Dyna Process Oil PW32 manufactured by Idemitsu Kosan Co., Ltd. was used.

  (Note 7) Octo-Puamyl A manufactured by Hope Pharmaceutical Co., Ltd. was used as aluminum 2-ethylhexanoate.

  (Note 8) As the wax (WAX), Sannox wax manufactured by Ouchi Shinsei Chemical Co., Ltd. was used.

  (Note 9) Norac 6C (N-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine) manufactured by Ouchi Shinsei Chemical Co., Ltd. was used as an antioxidant.

  (Note 10) Paulownia made by Nippon Oil & Fats Co., Ltd. was used as stearic acid.

  (Note 11) Zinc flower No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. was used as the zinc oxide.

  (Note 12) Sulfur produced by Tsurumi Chemical Co., Ltd. was used as sulfur.

  (Note 13) Noxeller CZ (N-cyclohexyl-2-benzothiazyl-sulfenamide) manufactured by Ouchi Shinsei Chemical Co., Ltd. was used as the vulcanization accelerator.

(2) Preparation of rubber composition Predetermined carbon black, silica, silane coupling agent and paraffinic oil were added to and mixed with the rubber component in the above basic composition. Thereafter, predetermined amounts of aluminum 2-ethylhexanoate and stearic acid (fatty acid) were added and mixed uniformly to prepare various rubber compositions.

  After mixing the compounding components excluding sulfur and the vulcanization accelerator in the compounding of Table 1, kneading was performed for 5 minutes under a temperature condition of about 150 ° C. in a Banbury. Thereafter, sulfur and a vulcanization accelerator were added to the rubber composition and kneaded for 5 minutes at a temperature of about 80 ° C. using a biaxial open roll.

(3) Physical property evaluation method <Shore-A hardness>
Using the resulting rubber composition, a sheet having a gauge of about 2 mm was prepared, and vulcanized at about 175 ° C. for 14 minutes at 25 kgf to prepare a test piece. The hardness of the rubber was measured using a test piece at a temperature of 25 ° C. according to JIS-K6253.

  Hardness was determined by measuring the hardness of the tread rubber immediately after vulcanizing the tire and after storing the tire at room temperature for 2 years.

<Braking performance (actual vehicle performance on frozen road surface)>
Using the rubber compositions of Examples and Comparative Examples, a radial tire for a passenger car (tire size 195 / 65R15) having the basic structure shown in FIG. 1 is manufactured and mounted on a 2000 cc domestic FF vehicle under the following conditions. A real car was run. The test place was Hokkaido Nayoro Test Course, and the performance on ice was -1 to -6 ° C, and the performance on snow was -2 to -10 ° C.

  The braking performance (on-ice braking stop distance) was determined by measuring the stop distance on ice required to depress and stop the lock brake at a speed of 30 km / h. The distance of Comparative Example 1 is shown as an index with the distance being 100. The larger the number, the better the braking performance.

(4) Evaluation results Comparative Example 1 does not contain aluminum 2-ethylhexanoate. In Comparative Example 2, the amount of aluminum 2-ethylhexanoate is less than 0.1% by mass.
In Comparative Example 3, the amount of aluminum 2-ethylhexanoate exceeds 50% by mass. In Comparative Example 4, the blending amount of stearic acid (fatty acid) is less than 0.1% by mass. None of these examples are satisfactory in the change in rubber hardness over time or the braking performance. On the other hand, in Examples 1 to 3 of the present invention, it is recognized that the change in rubber hardness with time and the braking performance are improved in a well-balanced manner.

  ADVANTAGE OF THE INVENTION According to this invention, the rubber composition for tires which improved the braking performance of the front-back direction on a snowy road surface and an icing road surface over a long period of time, and a pneumatic tire using the rubber composition can be provided. .

It is the left half of sectional drawing of the pneumatic tire which concerns on this invention.

Explanation of symbols

  1 tire, 2 tread part, 3 side wall part, 4 bead part, 5 bead core, 6 carcass, 7 belt layer, 8 bead apex rubber, 9 inner liner rubber.

Claims (6)

  While blending 10 to 60 parts by mass of carbon black and 5 to 40 parts by mass of paraffinic oil with respect to 100 parts by mass of the rubber component, 0.1 to 2 parts of aluminum 2-ethylhexanoate is added to the paraffinic oil. A rubber composition for a tire tread, wherein 50% by mass and 0.1% by mass or more of a fatty acid are added.   The rubber composition for a tire tread according to claim 1, wherein 5 to 50 parts by mass of silica is blended with 100 parts by mass of the rubber component.   The rubber composition for a tire tread according to claim 1, wherein the rubber component is natural rubber and / or butadiene rubber.   After producing a rubber composition by mixing 10 to 60 parts by mass of carbon black and 5 to 40 parts by mass of paraffinic oil with respect to 100 parts by mass of the rubber component, 2-ethyl is added to the paraffinic oil. A method for producing a rubber composition for a tire tread, comprising mixing and dispersing 0.1 to 50% by mass of aluminum hexanoate and 0.1% by mass or more of fatty acid.   A pneumatic tire having a tread portion of the rubber composition for a tire tread according to claim 1.   It has a tread part consisting of two layers of a cap rubber and a base rubber. The cap rubber contains 10 to 60 parts by mass of carbon black and 5 to 40 parts by mass of paraffinic oil with respect to 100 parts by mass of the rubber component. In addition, a pneumatic tire characterized by adding 0.1 to 50% by mass of aluminum 2-ethylhexanoate and 0.1% by mass or more of fatty acid to the paraffinic oil.

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