JP5129454B2 - Rubber composition for tire tread and pneumatic tire using the same - Google Patents

Description

  The present invention relates to a tire tread rubber composition containing a butyl rubber and a pneumatic tire using the same.

Conventionally, in pneumatic tires that emphasize low temperature characteristics, for example, pneumatic tires such as studless tires for passenger cars and all-season tires, a blend of natural rubber and polybutadiene rubber is used as a rubber component of the tread rubber composition. It is used for awards.
In addition, in order to improve the low temperature flexibility of the tire tread and improve the performance on ice in wet-on-ice, it has been conventionally performed to use foamed rubber having closed cells for the tread rubber (for example, Patent Documents). 1).
However, since the glass transition temperature (Tg) of rubber is low, it cannot be said that the wet performance is sufficient, and when the foaming rate is excessively high, the fracture resistance is also lowered.
In order to solve such a problem, for example, in Patent Document 2, as a part of the rubber component, a low molecular weight styrene / butadiene copolymer having a specific weight average molecular weight, a bound styrene amount, and a vinyl bond amount is used. However, it has been insufficient to satisfy the wet performance while ensuring low temperature properties, particularly low temperature flexibility and fracture resistance.
By the way, Patent Document 3 discloses that in a tread rubber using foamed rubber having closed cells, the generated gas is prevented from escaping at the time of foaming and the foaming efficiency is improved with respect to 100 parts by weight of butyl rubber. A butyl rubber masterbatch compound containing 50 to 100 parts by weight of a functional material is proposed as a blowing agent masterbatch, and 5 to 30 parts by weight is added to 100 parts by weight of a diene rubber.
Butyl rubber in this foaming agent masterbatch is blended at the same time as the vulcanizing compound (zinc white, sulfur, vulcanization accelerator), etc., at the so-called pro-kneading stage, so it does not function as a rubber component reinforced with fillers. Even if it can contribute to the increase in the foaming rate, it cannot contribute to the improvement of the wet performance, and there is a problem that the fracture resistance is lowered.
Therefore, there is a demand for a technique for further improving wet performance while ensuring low temperature properties, particularly low temperature flexibility and fracture resistance.

JP-A-63-90403 JP-A-9-194640 JP 2005-171092 A

  Under such circumstances, the present invention provides a rubber composition for a tire tread excellent in wet performance while ensuring low-temperature flexibility and fracture resistance, and a pneumatic tire having the tread disposed thereon. It is intended.

As a result of intensive studies to achieve the above object, the present inventors have found that the object can be achieved by blending butyl rubber as a part of the rubber component. The present invention has been completed based on such findings.
That is, the gist of the present invention is as follows.
1. 20-100 mass% of polybutadiene rubber, 2-80 mass% of butyl rubber, and 20-100 mass% of filler relative to 100 mass parts of rubber component comprising 0-80 mass% of natural rubber and / or polyisoprene rubber. A rubber composition for a tire tread, comprising a part.
2. 2. The rubber composition for a tire tread according to 1 above, wherein the rubber component comprises 20 to 78% by mass of polybutadiene rubber, 2 to 60% by mass of butyl rubber, and 20 to 78% by mass of natural rubber and / or polyisoprene rubber.
3. 2. The rubber composition for a tire tread according to 1 above, wherein the rubber component comprises 20 to 98% by mass of polybutadiene rubber and 2 to 80% by mass of butyl rubber.
4). 4. The rubber composition for a tire tread according to any one of the above 1 to 3, wherein the butyl rubber is a halogenated butyl rubber.
5. 5. The rubber composition for a tire tread according to 4 above, wherein the halogen content of the halogenated butyl rubber is 0.5 to 5% by mass.
6). 5. The rubber composition for a tire tread according to any one of 1 to 4 above, wherein the butyl rubber has a weight average molecular weight of 110,000 to 1,000,000.
7). 7. The tire tread rubber composition according to any one of 1 to 6, wherein the filler is carbon black and / or silica.
8). 8. The rubber composition for a tire tread as described in 7 above, wherein the carbon black has a nitrogen adsorption specific surface area of 70 to 160 m ² / g.
9. 9. The rubber composition for a tire tread according to any one of 1 to 8 above, which contains bubbles derived from a foaming agent.
10. 10. The tire tread rubber composition as described in 9 above, wherein the foaming rate of the bubbles is 5 to 40%.
11. 11. The rubber composition for a tire tread according to any one of 1 to 10 above, wherein the rubber component and the filler are kneaded in the kneading step A and then the foaming agent is kneaded in the kneading step B.
12 A pneumatic tire obtained by disposing the rubber composition according to any one of 1 to 11 on a tread.

  ADVANTAGE OF THE INVENTION By this invention, the rubber composition for tire treads which was excellent in wet performance, ensuring a low temperature softness | flexibility and fracture resistance, and a pneumatic tire formed by arrange | positioning it in a tread can be provided.

In the rubber composition for a tire tread of the present invention, the rubber component comprises 20 to 98% by mass of polybutadiene rubber, 2 to 80% by mass of butyl rubber, and 0 to 78% by mass of natural rubber and / or polyisoprene rubber. Is. This is because when the content of the polybutadiene rubber is less than 20% by mass, there is no effect of improving the low temperature flexibility, and when it exceeds 98% by mass, the fracture resistance is lowered. Moreover, when the content of butyl rubber is less than 2% by mass, there is no effect of improving the wet performance, and when it exceeds 80% by mass, the fracture resistance decreases. Furthermore, if the content of natural rubber and / or polyisoprene rubber exceeds 78% by mass, the low-temperature flexibility decreases.
Here, only one type of polybutadiene rubber or butyl rubber may be used, or two or more types may be used.

  Moreover, the rubber composition for tire treads of this invention needs to contain 20-100 mass parts of fillers with respect to 100 mass parts of said rubber components. When the filler is less than 20 parts by mass, the fracture resistance decreases, and when it exceeds 100 parts by mass, the processability of the rubber composition decreases.

  In the rubber composition for a tire tread of the present invention, when the rubber component is a three-component blend of polybutadiene rubber, butyl rubber, natural rubber and / or polyisoprene rubber, the rubber component is polybutadiene rubber 20 It is preferable that it consists of -78 mass%, butyl rubber 2-60 mass%, and natural rubber and / or polyisoprene rubber 20-78 mass%. If the polybutadiene rubber is 20% by mass or more, the low-temperature flexibility is good, and if it is 78% by mass or less, the fracture resistance is suitably secured. Moreover, when the butyl rubber is 2% by mass or more, the wet performance is good, and when it is 60% by mass or less, the fracture resistance is suitably ensured. Furthermore, natural rubber and / or polyisoprene rubber has good fracture resistance at 20% by mass or more, and low temperature flexibility is suitably ensured at 78% by mass or less.

  In the rubber composition for a tire tread of the present invention, when the rubber component is a two-component blend of a polybutadiene rubber and a butyl rubber, the rubber component includes 20 to 98% by mass of the polybutadiene rubber and butyl rubber. It is preferable to consist of 2-80 mass%. If the polybutadiene rubber is 20% by mass or more, the low temperature flexibility is good, and if it is 98% by mass or less, the wet performance is suitably secured. Moreover, when the butyl rubber is 2% by mass or more, the wet performance is good, and when it is 80% by mass or less, the low temperature flexibility is suitably secured.

The polybutadiene rubber used in the rubber composition for a tire tread according to the present invention is obtained by polymerization using a catalyst mainly composed of a cobalt-based catalyst, a nickel-based catalyst, a titanium-based catalyst, or a lanthanum-based rare earth element-containing compound. High cis-1,4 polybutadiene and polybutadiene having a relatively low cis-1,4 bond content obtained by polymerization using an organolithium catalyst are preferably used, but lanthanum series having excellent fracture resistance High cis-1,4 polybutadiene obtained by polymerization using a catalyst containing a catalyst containing a rare earth element-containing compound as a main component is particularly preferred.
The polybutadiene rubber preferably has a cis-1,4 bond content of 85% or more and a vinyl bond content of preferably 5% or less. The weight average molecular weight is preferably 100,000 to 1,000,000, and the molecular weight distribution is preferably 5 or less.
Here, the measurement of cis-1,4 bond content and vinyl bond content is based on Fourier transform infrared spectroscopy (FT-IR). The measurement of the weight average molecular weight (Mw) and the molecular weight distribution (Mw / Mn) is based on the GPC method based on polystyrene conversion using monodisperse polystyrene as a standard.

Examples of the butyl rubber used in the rubber composition for a tire tread of the present invention include halogenated butyl rubber and butyl rubber which are chlorinated butyl rubber or brominated butyl rubber, and halogenated butyl rubber is preferable. The halogen content of the halogenated butyl rubber is preferably 0.5 to 5% by mass. This is because the fracture resistance is good when the content is 0.5% by mass or more, and the workability is suitably ensured when the content is 5% by mass or less.
The weight average molecular weight of the butyl rubber is preferably 110,000 to 1,000,000. This is because the fracture resistance is good if it is 110,000 or more, and the workability is suitably secured if it is 1,000,000 or less.
Here, the measurement of the weight average molecular weight of butyl rubber is based on the GPC method based on polystyrene conversion using monodisperse polystyrene as a standard.
The above butyl rubber may be used alone or in combination of two or more.

  As the polyisoprene rubber used in the rubber composition for a tire tread of the present invention, for example, high cis-1,4 polyisoprene such as IR2200 manufactured by JSR Corporation is preferable.

As the filler used in the rubber composition for a tire tread of the present invention, carbon black and silica are preferable. The nitrogen adsorption specific surface area of carbon black (N ₂ SA, conforming to JIS K 6217-2: 2001) is preferably 70 to 160 m ² / g. This is because if 70 m ² / g or more, the wear resistance is good, and if it is 160 m ² / g or less, the workability is good. Suitable carbon blacks include furnace carbon blacks such as HAF, IISAF, ISAF, and SAF. Examples of silica include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, and the like. The most prominent wet silica is preferred. Then, the nitrogen adsorption specific surface area of the silica (N ₂ SA, conforms to the BET method) is preferably 50 to 400 m ² / g. This is because the wear resistance is good if it is 50 m ² / g or more, and the workability is good if it is 400 m ² / g or less. Suitable wet silica includes AQ, VN3, LP, NA, etc. manufactured by Tosoh Silica Co., Ltd., Ultrazil VN3 (N ₂ SA: 210 m ² / g) manufactured by Degussa, and the like.

As fillers other than those described above, an inorganic filler represented by the following general formula (I) may be blended as desired.
mM ¹ · xSiOy · zH ₂ O (I)
In the general formula (I), M ¹ is a metal selected from aluminum, magnesium, titanium, calcium, and zirconium, an oxide or hydroxide of these metals, and a hydrate thereof, or these metals. And m, x, y and z are an integer of 1 to 5, an integer of 0 to 10, an integer of 2 to 5, and an integer of 0 to 10, respectively. In the above formula, when both x and z are 0, the inorganic compound is at least one metal, metal oxide or metal hydroxide selected from aluminum, magnesium, titanium, calcium and zirconium.
As the inorganic filler represented by the general formula (I), .gamma.-alumina, alumina (Al ₂ O ₃₎ such as α- alumina, boehmite, alumina monohydrate such as diaspore (Al ₂ O ₃ · H ₂ O), Gibbsite, Bayerite, etc. Aluminum hydroxide [Al (OH) ₃ ], Aluminum carbonate [Al ₂ (CO ₃ ) ₂ ], Magnesium hydroxide [Mg (OH) ₂ ], Magnesium oxide (MgO), Carbonic acid Magnesium (MgCO ₃ ), talc (3MgO · 4SiO ₂ · H ₂ O), attapulgite (5MgO · 8SiO ₂ · 9H ₂ O), titanium white (TiO ₂ ), titanium black (TiO _2n-1 ), calcium oxide (CaO ), calcium hydroxide [Ca (OH) _2], magnesium aluminum oxide _{(MgO · Al 2 O 3)} , clay _{(Al 2 O 3 · 2SiO 2} ), kaolin ( _{l 2 O 3 · 2SiO 2 ·} 2H 2 O), pyrophyllite _{(Al 2 O 3 · 4SiO 2} · H 2 O), bentonite _{(Al 2 O 3 · 4SiO 2} · 2H 2 O), aluminum silicate (Al ₂ SiO ₅ , Al ₄ · 3SiO ₄ · 5H ₂ O, etc.), magnesium silicate (Mg ₂ SiO ₄ , MgSiO ₃ etc.), calcium silicate (Ca ₂ · SiO ₄ etc.), aluminum calcium silicate (Al ₂ O ₃ · CaO · 2SiO ₂ etc.), magnesium calcium silicate (CaMgSiO ₄ ), calcium carbonate (CaCO ₃ ), zirconium oxide (ZrO ₂ ), zirconium hydroxide [ZrO (OH) ₂ · nH ₂ O], zirconium carbonate [ Zr (CO _{3) 2],} hydrogen to correct the charge as various zeolites, such as crystalline aluminosilicates including alkali metal or alkaline earth metal is used It can be. Further, it is preferable that M ¹ in the general formula (I) is at least one selected from aluminum metal, aluminum oxide or hydroxide, hydrates thereof, and aluminum carbonate. Aluminum hydroxide is particularly preferable.

  In the rubber composition for a tire tread of the present invention, when silica is used as a filler, a silane coupling agent can be blended for the purpose of further improving the reinforcing property. Examples of the silane coupling agent include bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, and bis (2-triethoxy). Silylethyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyl Trimethoxysilane, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N, N-dimethylthioca Bamoylchitrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxy Silylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis (3-diethoxymethylsilylpropyl) tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N, N-dimethylthiocarbamoyltetra Sulfide, dimethoxymethylsilylpropyl benzothiazole tetrasulfide, etc. are mentioned, but from these points, such as reinforcing effect improvement effect, Scan (3-triethoxysilylpropyl) tetrasulfide and 3-trimethoxysilylpropyl benzothiazolyl tetrasulfide are preferable. These silane coupling agents may be used singly or in combination of two or more.

  In the rubber composition for a tire tread of the present invention, the blending amount of a preferable silane coupling agent varies depending on the type of the silane coupling agent and the like, but preferably in the range of 1 to 20% by mass based on the blending amount of silica. Selected. When this amount is in the above range, the effect as a coupling agent is sufficiently exhibited and the rubber component is hardly gelled. From the viewpoint of the effect as a coupling agent and prevention of gelation, the preferable amount of the silane coupling agent is 3 to 20% by mass, particularly preferably 5 to 15% by mass based on the amount of silica. .

  The rubber composition for a tire tread of the present invention includes various chemicals usually used in the rubber industry, for example, a vulcanizing agent, a vulcanization accelerator, a process oil, and an aging, as long as the object of the present invention is not impaired. An inhibitor, a scorch inhibitor, zinc white, stearic acid and the like can be contained.

  The rubber composition for a tire tread of the present invention is usually sulfur crosslinkable, and sulfur or the like is preferably used as a vulcanizing agent. The amount used is preferably 0.1 to 10.0 parts by weight, more preferably 1.0 to 5.0 parts by weight, as the sulfur content, per 100 parts by weight of the rubber component. When it is 0.1 parts by mass or more, the vulcanized rubber has good low heat buildup and fracture resistance, and when it is 10.0 parts by mass or less, rubber elasticity is also good.

The vulcanization accelerator that can be used in the present invention is not particularly limited, but examples thereof include thiazoles such as M (2-mercaptobenzothiazole) and DM (dibenzothiazyl disulfide), CZ (N-cyclohexyl-2). -Sulfenamides such as benzothiazylsulfenamide) or guanidine-based vulcanization accelerators such as DPG (diphenylguanidine) can be mentioned, and the amount used thereof is 100 parts by mass of the rubber component. 0.1-5.0 mass parts is preferable, More preferably, it is 0.2-3.0 mass parts.
Moreover, as a softening agent which can be used with the rubber composition for tire treads of this invention, a paraffin type and a naphthenic process oil are preferable from a viewpoint which attaches importance to a low temperature characteristic. The amount used is preferably 0 to 100 parts by mass with respect to 100 parts by mass of the rubber component, and if it is 100 parts by mass or less, the tensile strength and low heat build-up of the vulcanized rubber can be suppressed. When the low temperature property of the rubber composition is further emphasized, a plasticizer such as dibutyl phthalate (DBP), dioctyl phthalate (DOP), dioctyl adipate (DOA) or the like is used.
Furthermore, examples of the anti-aging agent that can be used in the rubber composition for a tire tread of the present invention include 3C (N-isopropyl-N′-phenyl-p-phenylenediamine, 6C [N- (1,3-dimethylbutyl)- N'-phenyl-p-phenylenediamine], AW (6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline), high-temperature condensate of diphenylamine and acetone, and the like. Is preferably 0.1 to 5.0 parts by weight, more preferably 0.3 to 3.0 parts by weight, with respect to 100 parts by weight of the rubber component.

The rubber composition for a tire tread of the present invention preferably contains bubbles derived from a foaming agent, particularly closed cells. The bubble expansion rate (Vs) is preferably 5 to 40%. Vs is calculated by the following equation.
Vs = {(ρ ₀ / ρ ₁ ) −1} × 100 (%)
Here, ρ ₁ is the density (g / cm ³ ) of the vulcanized rubber (foamed rubber), and ρ ₀ is the density (g / cm ³ ) of the solid phase part in the vulcanized rubber (foamed rubber). .
This is because if the expansion ratio (Vs) is 5% or more, the low-temperature flexibility is improved, and if it is 40% or less, the fracture resistance is suitably secured.
As the foaming agent, N, N′-dinitrosopentamethylenetetramine (DPT), azodicarbonamide (ADCA), 4,4′-oxybis (benzenesulfonylhydrazide) (OBSH) and the like are preferable. As the foaming aid, urea or a urea compound is preferable.

The rubber composition for a tire tread of the present invention can be obtained by kneading using a kneading machine such as a Banbury mixer, a roll, an internal mixer or the like according to the above compounding prescription. It is preferable that the foaming agent is kneaded in the kneading step B after the filler is kneaded. In particular, by kneading butyl rubber and filler in kneading stage A, the butyl rubber functions as a rubber component reinforced with filler, contributing to improvement in wet performance and improving fracture resistance. it can.
Usually, after kneading the rubber component and the filler in the kneading stage A (also referred to as non-pro kneading stage), the rubber composition is cooled to room temperature and allowed to stand for a certain period of time, and then kneading stage B (also called the professional kneading stage). Say).
Further, a kneading stage C (also referred to as a second non-pro kneading stage) or a kneading stage D (also referred to as an X-mill) may be provided between the kneading stage A and the kneading stage B. The kneading stage C is mainly performed when the filler is dividedly charged. In the kneading step D, kneading is performed for the purpose of lowering the viscosity of the rubber composition obtained in the kneading step A or the kneading step C and for improving the dispersibility of the filler. Usually, in the kneading stage B, a foaming agent, a foaming aid, a vulcanizing compounding agent (zinc white, sulfur, vulcanization accelerator) and the like are blended with the rubber composition obtained by the kneading in the previous stage. However, the foaming agent and foaming aid and the vulcanizing compound may be kneaded in separate kneading steps.
The tire tread rubber composition thus obtained is extruded into the shape of a titer tread, molded into a green tire, and then vulcanized to form a tire.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
The measurement of the foaming rate (Vs), fracture resistance (breaking strength), low temperature flexibility (0 ° C. storage elastic modulus E ′) and wet property (0 ° C. tan δ) of the vulcanized rubber was according to the following method. .
<Foaming rate of vulcanized rubber (Vs)>
The above method was used.
<Destruction resistance (breaking strength) of vulcanized rubber>
This was performed according to JIS K 6251: 2004. The index was displayed with the breaking strength of Comparative Example 1 as 100. The larger the index value, the greater the fracture strength and the better the fracture resistance.
<Low temperature flexibility (0 ° C. storage elastic modulus E ′) and wet property (0 ° C. tan δ) of vulcanized rubber>
Using a viscoelasticity measuring device (manufactured by Rheometrics), E ′ and tan δ were measured at a temperature of 0 ° C., a strain of 3% and a frequency of 15 Hz. The index was displayed with the reciprocal of E ′ in Comparative Example 1 being 100. The larger the index value, the lower E ′ and the better the low temperature flexibility. In addition, the tan δ of Comparative Example 1 was set to 100 and displayed as an index. The larger the index value, the larger the tan δ and the better the wettability.

Examples 1 to 3 and Comparative Example 1
Based on the formulation shown in Table 1, four types of rubber compositions of Examples 1 to 3 and Comparative Example 1 were prepared by the formulation of rubber components shown in Table 2. After vulcanizing these four types of rubber compositions, fracture resistance (fracture strength), low temperature flexibility (0 ° C. storage elastic modulus E ′) and wet properties (0 ° C. tan δ) were evaluated. These results are shown in Table 2.

  As can be seen from Table 2, by adding brominated butyl rubber, it was possible to significantly improve the wettability while ensuring fracture resistance and low temperature flexibility.

Examples 4 to 6 and Comparative Example 2
Based on the formulation shown in Table 1, four types of rubber compositions of Examples 4 to 6 and Comparative Example 2 were prepared according to the formulation of rubber components shown in Table 3. After vulcanizing these four types of rubber compositions, fracture resistance (fracture strength), low temperature flexibility (0 ° C. storage elastic modulus E ′) and wet properties (0 ° C. tan δ) were evaluated. These results are shown in Table 3.

  As is apparent from Table 3, by adding a brominated butyl rubber and making a tread rubber composition having closed cells derived from a foaming agent, the wettability is further greatly improved while ensuring fracture resistance and low temperature flexibility. I was able to improve.

  Eight kinds of tread rubber compositions of Examples 1 to 6 and Comparative Examples 1 and 2 were respectively arranged as treads of 195 / 60R14 to produce eight kinds of pneumatic tires for passenger cars, and wet on at 0 ° C. When the wet property was actually tested under ice conditions, the tires of Examples 1 to 3 had better wet properties than the tire of Comparative Example 1, and the tires of Examples 4 to 6 were Comparative Example 2. The wettability was good in all tires.

The rubber composition for a tire tread of the present invention is suitably used as a tread for various pneumatic tires for passenger cars, light vehicles, light trucks and trucks and buses, particularly as a tread for studless tires or all-season tires. .

Claims (10)

20-100 parts by mass of filler relative to 100 parts by mass of a rubber component comprising 20-98% by mass of polybutadiene rubber, 2-80% by mass of butyl rubber, and 0-78% by mass of natural rubber and / or polyisoprene rubber. and also it contains, containing bubbles from the foaming agent, foaming rate of the bubbles Ri 5-40% der, and blowing agent is N, rubber for tire tread is N'- dinitrosopentamethylenetetramine object.   The rubber composition for a tire tread according to claim 1, wherein the rubber component comprises 20 to 78% by mass of polybutadiene rubber, 2 to 60% by mass of butyl rubber, and 20 to 78% by mass of natural rubber and / or polyisoprene rubber.   The rubber composition for a tire tread according to claim 1, wherein the rubber component comprises 20 to 98% by mass of polybutadiene rubber and 2 to 80% by mass of butyl rubber.   The rubber composition for a tire tread according to any one of claims 1 to 3, wherein the butyl rubber is a halogenated butyl rubber.   The rubber composition for a tire tread according to claim 4, wherein the halogen content of the halogenated butyl rubber is 0.5 to 5% by mass.   The rubber composition for a tire tread according to any one of claims 1 to 4, wherein the butyl rubber has a weight average molecular weight of 110,000 to 1,000,000.   The rubber composition for a tire tread according to any one of claims 1 to 6, wherein the filler is carbon black and / or silica. The rubber composition for a tire tread according to claim 7, wherein the nitrogen adsorption specific surface area of carbon black is 70 to 160 m ² / g. The rubber composition for a tire tread according to any one of claims 1 to 8 , wherein the rubber component and the filler are kneaded in the kneading step A and then the foaming agent is kneaded in the kneading step B. A pneumatic tire formed by disposing a rubber composition according to the tread to claim 1-9.