JP5060686B2 - Rubber composition for tire and pneumatic tire - Google Patents

Description

表１において、比較例１は通常の発泡剤を含まないゴム組成物である。表１の結果に示されるように、本発明によるタイヤ用ゴム組成物では所定の気泡含有率と連続気泡を有す加硫ゴムを得ることができ、ゴム比重が低減され、空気入りタイヤの軽量化を実現し、また、それをキャップトレッドに用いた空気入りタイヤはノイズ性能が大幅に向上しながら、ウェットスキッド性能や耐摩耗性などの諸性能をバランスよく（表中のＡ＊Ｂ／１００の値はウェットスキッド性能と耐摩耗性のバランスを示す指標であり、１００以上を可とする）維持することが分かる。
【００７１】
発泡剤の配合量が少なく気泡含有率の少ない比較例２は軽量化効果がなく、逆に配合量が多く気泡含有率及び連続気泡の多い比較例３は軽量化及びノイズ性能は向上するが、耐摩耗性が著しく低下する。
【００７２】
最終ムーニー粘度が８０を越える比較例４，加硫速度の速い加硫促進剤Ｂを用いた比較例５，硫黄量の多い比較例６は加硫特性が適正でなく、所望の気泡含有率と連続気泡を得ることができず、軽量化効果およびノイズ性能が満足できない。また、従来の中空フィラーを用いた比較例７は、ゴム比重は低下するが、ノイズ性能の向上が期待できず、またバランスのよいタイヤ性能が得られない。
【００７３】
【発明の効果】
以上説明したように、本発明のタイヤ用ゴム組成物及びそれを用いた空気入りタイヤは、スチレン含有率が２０〜４０重量％のスチレンブタジエンゴムを７０重量部以上含むジエン系ゴムをゴム成分とするタイヤ用ゴム組成物であって、前記タイヤ用ゴム組成物の加硫ゴムは気泡含有率３〜２０％の気泡を有し、かつ前記気泡は２０％以上の連続気泡を含む発泡ゴムであることから、ゴム比重を低減して空気入りタイヤの軽量化を実現し、タイヤのノイズ性能を大幅に向上することができる。しかも、タイヤに必要な耐摩耗性やウェットスキッド性能などの諸特性はバランスよく維持する、という優れた効果を有する。
【図面の簡単な説明】
【図１】 実施例の空気入りタイヤの左半断面図である。
【符号の説明】
Ｔ……空気入りタイヤ
１……トレッド
２……キャップトレッド
３……ベーストレッド
４……サイドウォール
５……スチールベルト
６……カーカス
７……インナーライナー
８……ビードフィラー
９……ビードワイヤ
１０……フリッパー[0001]
BACKGROUND OF THE INVENTION
The present invention is a foamed rubber having a specific form capable of reducing the weight of the tire and reducing noise during running while maintaining various characteristics such as wear resistance and wet skid performance of the pneumatic tire in a well-balanced manner. The present invention relates to a rubber composition for tires that forms a tire and a pneumatic tire using the same.
[0002]
[Prior art]
Due to demands for reducing fuel consumption of automobiles, weight reduction of automobiles is required, and weight reduction of tires that are parts thereof is indispensable. In addition, reduction of noise outside the vehicle and quietness inside the vehicle are also strongly desired. For this reason, it is necessary to reduce noise as tire performance.
[0003]
In order to reduce the weight of the tire, the thickness of the rubber of the tread or the sidewall is reduced, or the steel cord of the belt layer is replaced with an organic fiber cord such as an aromatic polyamide fiber.
[0004]
However, the former has the harmful effect of reducing the ride comfort and wear resistance, and it is difficult to reduce the rubber thickness excessively. In the latter case, the specific gravity of the cord can be reduced by changing the material of the reinforcing material. However, since the weight ratio of the belt layer to the entire tire is small, a satisfactory weight reduction of the tire cannot be achieved.
[0005]
Tire noise reduction measures include tread groove and sipe placement, improved shape, improved tread and sidewall rubber hardness, and improved tire structure and belt layer modulus. However, it has not been fully satisfactory.
[0006]
[Problems to be solved by the invention]
As a technique for reducing the weight and reducing noise, a technique is known in which a foaming agent or a gas-encapsulated thermoplastic elastomer that generates gas by heat is added to a rubber composition to form foam in the rubber composition. However, it was impossible to control the foamed shape to a desired shape.
[0007]
The present invention solves the above problems, and reduces the weight and noise of a tire while maintaining a good balance of various characteristics such as wear resistance, wet skid performance, and steering stability of a pneumatic tire. An object of the present invention is to provide a tire rubber composition for forming a foamed rubber having a specific form, and a pneumatic tire using the same.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, a tire rubber composition according to the invention of claim 1 is a tire rubber composition comprising a diene rubber containing 70 parts by weight or more of a styrene butadiene rubber having a styrene content of 20 to 40% by weight as a rubber component. A rubber composition, characterized in that the vulcanized rubber of the tire rubber composition has bubbles with a bubble content of 3 to 20%, and the bubbles are foamed rubber containing 20% or more of open cells. And
[0009]
According to the present invention, while maintaining various properties such as wear resistance and wet skid performance of the tire rubber composition in a well-balanced manner, rubber properties that reduce the specific gravity of the rubber and improve the sound absorption and damping performance are obtained. It is done.
[0010]
In the invention of claim 2, the final Mooney viscosity of the rubber composition is 80 or less, the rheometer vulcanization rate (t30) at 160 ° C. is 4 minutes or more, and the maximum torque (MH) is 15 dNm or less. It is the rubber composition for tires of Claim 1 characterized by the above-mentioned.
[0011]
According to the present invention, it is possible to easily control the bubble content in the vulcanized rubber of the tire rubber composition and the formation of open cells and obtain a desired foamed rubber.
[0012]
According to a third aspect of the present invention, 40 to 100 parts by weight of carbon black and 0 to 100 parts by weight of silica are blended with 100 parts by weight of the rubber component, and the total amount of the carbon black and the silica is 40 to 100 parts by weight. The tire rubber composition according to claim 1, wherein the rubber composition for tires is a part.
[0013]
According to the present invention, it is possible to obtain a foamed rubber that maintains various properties such as wear resistance and wet skid performance necessary for a tire rubber composition.
[0014]
Invention of Claim 4 is a pneumatic tire using the rubber composition for tires of any one of Claims 1-3.
[0015]
The invention according to claim 5 is a pneumatic tire characterized by using the rubber composition for tire according to claim 4 for at least a part of a tread portion.
[0016]
Since the pneumatic tire of the present invention uses foamed rubber having a bubble content in a predetermined range and open cells, the rubber volume is maintained, the influence on the tire strength is extremely reduced, and durability is maintained. While maintaining various properties necessary for the tires in a well-balanced manner, the weight reduction by reducing the specific gravity of the foam rubber and the noise reduction by the sound absorption effect are realized.
[0017]
The rubber composition for tires of the present invention is optimally applied to tire treads, particularly so-called cap treads on the outer side in the tire radial direction, and can improve the above effects more effectively. Furthermore, it may be used as a base rubber inside the cap tread, and can also be used for other parts of the tire such as a sidewall.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0019]
The rubber composition for tires of the present invention uses a diene rubber containing 70 parts by weight or more of styrene butadiene rubber having a styrene content of 20 to 40% by weight as a rubber component.
[0020]
When the styrene content exceeds 40% by weight, the glass transition temperature rises, and when the blending amount of the styrene butadiene rubber is less than 70 parts by weight of the rubber component, rolling resistance, wear resistance, wet skid performance, etc. It becomes difficult to achieve both.
[0021]
Examples of the diene rubber include styrene butadiene rubber having the above styrene content, other solution polymerization and emulsion polymerization styrene butadiene rubber (SBR), natural rubber (NR), various butadiene rubbers (BR), and isoprene rubber (IR). A diene rubber such as butyl rubber (IIR) or a blend thereof can be used alone.
[0022]
The vulcanized rubber of the tire rubber composition of the present invention has a bubble content of 3 to 20%, and the foam is almost uniformly dispersed in the rubber by a normal vulcanization process using a foaming agent. It is formed.
[0023]
If the bubble content of the foamed rubber is less than 3%, the desired rubber specific gravity and noise reduction effect for achieving weight reduction cannot be obtained, and if it exceeds 20%, the rigidity and modulus of the foamed rubber are excessively lowered, resulting in wear resistance. This is not preferable because the performance and steering stability deteriorate.
[0024]
Here, the bubble content (V) is a value calculated by the following equation.
V (%) = (ρ0 / ρ1-1) × 100
ρ0 is the density (g / cm ³ ) of the matrix portion of the foam rubber, and ρ1 is the density (g / cm ³ ) of the foam rubber.
[0025]
The bubble diameter of the bubbles is not particularly limited, but the average diameter is preferably 10 to 1000 μm, more preferably 20 to 500 μm, and more preferably 20 to 300 μm. If the bubble diameter is small, the specific gravity of the rubber cannot be reduced. If the bubble diameter is too large, the rubber strength and wear resistance are lowered, and it becomes difficult to form stable bubbles during production.
[0026]
Therefore, the foamed rubber having a foam content of 3 to 20% can reduce the specific gravity of the rubber by 5 to 20% compared to the unfoamed rubber having the same composition.
[0027]
Examples of foaming agents include organic foaming agents such as azodicarbonamide, azo compounds such as azobisisobutyronitrile, nitroso compounds such as dinitrosopentamethylenetetramine, sulfonyl hydrazide compounds such as benzenesulfonyl hydrazide and toluenesulfonyl hydrazide, and the like. Derivatives thereof, inorganic foaming agents such as sodium bicarbonate, ammonium carbonate, ammonium nitrite and the like. Of these, oxybis-benzenesulfonylhydrazide or azodicarbonamide, which is an organic foaming agent, is particularly preferred from the viewpoint of controlling the foaming rate.
[0028]
Moreover, in order to adjust a foaming rate, you may add foaming adjuvants, such as urea, an organic acid, a metal oxide, and a metal fatty acid, as needed.
[0029]
The blending amount of the foaming agent is preferably in the range of 1 to 10 parts by weight with respect to 100 parts by weight of the rubber component. An appropriate amount can be selected by adjusting as appropriate.
[0030]
In the tire rubber composition of the present invention, the bubbles of the vulcanized foamed rubber need to contain 20% or more of open cells at random in order to effectively exhibit the noise reduction effect.
[0031]
When the open cell ratio is less than 20%, the function of absorbing the impact sound caused by the collision between the road surface unevenness and the tread surface and the noise caused by the vibration propagating from the collision is insufficient, and the noise reduction improvement effect is not exhibited. The upper limit of the open cell ratio is not particularly limited, but if it exceeds 50%, the rigidity and modulus of the rubber are insufficient, and the wear resistance and wet skid performance are deteriorated.
[0032]
This open cell is a continuous space in which two or more of approximately spherical bubbles form a void through a film that wraps each bubble, and has excellent performance in flexibility, water absorption, and sound absorption characteristics. is doing.
[0033]
Here, the open cell rate (%) represents the ratio of the number of open cells per unit volume of the rubber, and is a value obtained from the water absorption rate based on JIS K7209.
[0034]
In the rubber composition for tires of the present invention, the vulcanization characteristics are such that the final Mooney viscosity is 80 or less, the rheometer vulcanization rate (t30) at 160 ° C. is 4 minutes or more, and the maximum torque ( MH) is 15 dNm or less, which is a preferred form for forming the predetermined foamed rubber.
[0035]
In the present invention, by obtaining an appropriate combination of the above-mentioned foaming agent and vulcanization accelerator and further vulcanizing characteristics of the rubber composition suitable for foaming, the vulcanized rubber has a bubble content of 3-20. %, It becomes easier to control the ratio of the open cells to 20% or more.
[0036]
As specific vulcanization characteristics, if the rheometer vulcanization rate (t30) measured at 160 ° C. of the rubber composition is 4 minutes or more, it becomes easy to control within the bubble content, and measured at 100 ° C. If the final Mooney viscosity is 80 or less and the maximum torque (MH) of the rheometer vulcanization rate measured at 160 ° C. is 15 dNm or less, it is easy to form 20% or more of the bubbles into open cells. Become.
[0037]
If t30 is less than 4 minutes, the vulcanization reaction proceeds too fast and foam formation is suppressed, and if the final Mooney viscosity is 80 and MH exceeds 15 dNm, the rubber viscosity during vulcanization becomes too high, resulting in open cells. The bubble communication part to be formed is crushed, and it becomes difficult to control the formation of continuous bubbles.
[0038]
The Mooney viscosity and the rheometer vulcanization rate are measured according to JIS K6300.
[0039]
The use of a vulcanization accelerator that controls the above vulcanization characteristics is an important factor for properly controlling both the vulcanization reaction and the foaming reaction and obtaining stable foaming. It is necessary to select according to the use conditions such as the vulcanization temperature.
[0040]
As the vulcanization accelerator, various vulcanization accelerators such as thiazole, sulfenamide, and thiuram can be used. It is easy to obtain and is preferable.
[0041]
Further, in the tire rubber composition of the present invention, as a rubber reinforcing agent, 40 to 100 parts by weight of carbon black and 0 to 100 parts by weight of silica are blended with respect to 100 parts by weight of the rubber component, and the carbon black and the silica are mixed. The total amount is 40 to 100 parts by weight, and maintains general performances necessary for a tire such as wear resistance, low rolling resistance, wet skid performance and the like.
[0042]
If the blending amount of carbon black is less than 40 parts by weight, the effect of improving wear resistance and dispersibility when silica is blended is small, and if it exceeds 100 parts by weight, rolling resistance and wear resistance are reduced. Absent.
[0043]
The carbon black is not particularly limited, but carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 40 to 150 m ² / g and a dibutyl phthalate oil absorption (DBP) of 70 to 160 ml / 100 g is preferable.
[0044]
When the N ₂ SA of the carbon black is less than 40 m ² / g, the wear resistance is deteriorated, and when it exceeds 150 m ² / g, the rolling resistance increases, which is not preferable. On the other hand, if the DBP is less than 70 ml / 100 g, the dispersibility of the silica compound is not improved, and if it exceeds 160 ml / 100 g, the mixing processability of the rubber is deteriorated.
[0045]
Also, the silica compounding amount can be 0 parts by weight to obtain a carbon black compounding rubber composition. If the compounding amount exceeds 100 parts by weight, the wear resistance and fracture strength decrease. It is preferable to select within the range of parts.
[0046]
The said silica can use arbitrary silica currently used as a rubber compounding agent, for example, wet silica is mentioned.
[0047]
Furthermore, the total amount of both the carbon black and silica is preferably in the range of 40 to 100 parts by weight. When the total amount is less than 40 parts by weight, a sufficient reinforcing effect and wet skid performance cannot be obtained, and when it exceeds 150 parts by weight, wear resistance and rolling resistance are lowered, which is not preferable.
[0048]
Here, when silica is used in combination, it is preferable to add a silane coupling agent in order to reinforce the bond between silica and rubber, and the amount is preferably in the range of 2 to 20% by weight of the silica amount. It is. If the amount is less than 2% by weight, the reinforcing effect by the coupling cannot be obtained sufficiently. If the amount exceeds 20% by weight, the reinforcing property is lowered, and the rubber composition is easily scorched in the rubber processing step, which further increases the cost. It is not preferable.
[0049]
As the silane coupling agent, a normal silane coupling agent used as a rubber compounding agent can be used. For example, bis- [3- (triethoxysilyl) -propyl] tetrasulfide, bis- [3- (Triethoxysilyl) -propyl] disulfide, bis- [2- (triethoxysilyl) -ethyl] tetrasulfide, bis- [3- (trimethoxysilyl) -propyl] tetrasulfide, bis- [2- (trimethoxy Silyl) -ethyl] tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane and the like can be exemplified, and one or a mixture thereof can be used.
[0050]
Furthermore, the rubber composition for tire treads according to the present invention includes various rubbers such as a vulcanizing agent, a vulcanization accelerator, an anti-aging agent, a softening agent, a filler, and a plasticizer as necessary in addition to the above compounding agents. The compounding agent can be blended in the range of the usual blending amount, and the rubber composition can be prepared using a mixer usually used in the rubber industry such as a Banbury mixer and a kneader.
[0051]
The above rubber composition for tires is made of unvulcanized rubber members such as treads, sidewalls, and various liners using an extruder, roll, calender device or the like that is usually used in the rubber industry, and each pneumatic tire according to a conventional method. Pneumatic tires can be vulcanized and manufactured by applying to parts.
[0052]
In this vulcanization step, the pneumatic tire of the present invention can be manufactured by forming a foamed rubber having a desired bubble content and open cells in a predetermined part, and the specific gravity is maintained while maintaining the rubber volume of the pneumatic tire. Therefore, it is possible to reduce the weight of the tire by several to 10 to several percent of the tire weight while ensuring the tire strength and maintaining necessary tire characteristics.
[0053]
In addition, this foamed rubber has excellent sound absorption and vibration control performance, so it can be applied to treads, sidewalls and tire inner layers of pneumatic tires, resulting in pattern noise, road squeak noise and low frequency range. Noise inside and outside the car, such as a go sound, can be reduced.
[0054]
In particular, when applied to the cap tread part of pneumatic tires, it exhibits the effect of absorbing and mitigating shock noise and vibration caused by collisions between road surface irregularities and tread surfaces, greatly reducing pneumatic tire noise. can do.
[0055]
Of course, it can also be used as a so-called base rubber inside the cap tread portion, and noise can be reduced.
[0056]
Therefore, the pneumatic tire of the present invention can reduce the weight and noise of the tire while maintaining various characteristics such as wear resistance, wet skid performance, and steering stability in a well-balanced manner.
[0057]
(Example)
EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.
[0058]
The rubber component used in the examples and comparative examples shown in Table 1 is the following styrene butadiene rubber, and the various compounding agents are as follows. Each rubber composition for a tire was compounded in each compounding amount (parts by weight) shown in Table 1.
[0059]
Rubber component Styrene butadiene rubber (SBR): Emulsion polymerization styrene butadiene rubber Styrene content 35% by weight, vinyl content 18% by weight
Compounding agent, carbon black (CB): ASTM regulation N220 product Diamond Black I manufactured by Mitsubishi Kasei Co., Ltd.
・ Silica: Nippon Silica Co., Ltd. Nipsil AQ
-Foaming agent: Oxybis-benzenesulfonyl hydrazide-Hollow filler: Nippon Ferrite Co., Ltd. EXPANSEL 091DE-80
・ Vulcanization accelerator A: Nt-butyl-2-benzothiazolsulfenamide Nouchira NS manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
・ Vulcanization accelerator B: Dibenzothiazyl sulfide Ouchi Shinsei Chemical Co., Ltd. Noxeller DM
In addition, the common compounding agent and compounding quantity of each rubber composition are as follows.
[0060]
・ Zinc flower: No. 1 zinc flower 2 parts by weight ・ Stearic acid: Industrial stearic acid 2 parts by weight ・ Silane coupling agent: Degussa Si-69
Part by weight equivalent to 8% by weight with respect to silica content: 50 parts by weight of aroma-based process oil: Anti-aging agent: 1 part by weight of N-phenyl-N ′-(1,3-dimethylbutyl) -p-phenylenediamine -Paraffin wax: 2 parts by weight-Sulfur: 5% oil-treated powdered sulfur 1.5 parts by weight Each formulation shown in Tables 1 and 2 is mixed using a sealed Banbury mixer with a capacity of 20 liters according to a conventional method. And the rubber composition for tires of a comparative example was created.
[0061]
The final Mooney viscosity and rheometer vulcanization rate of each tire rubber composition were measured by the following methods and are shown in Table 1.
[0062]
Mooney viscosity: Measured at a temperature of 100 ° C. using a Mooney viscometer manufactured by Shimadzu Corporation in accordance with JIS K6300.
[0063]
Rheometer vulcanization rate: Measured at a temperature of 160 ° C. using MDR2000 manufactured by Flexis Co. in accordance with JIS K6300. MH represents the maximum torque value (dNm), and t30 represents the time (minutes) required to obtain 30% of the maximum torque value.
[0064]
Further, the bubble content (%), open cell ratio (%) and specific gravity of the vulcanized rubber of each rubber composition were measured by preparing a predetermined sample by press vulcanization at 160 ° C. for 20 minutes. And in Table 2.
[0065]
The bubble content rate (%) and the open cell rate (%) are values measured according to the method described above, and the specific gravity is an index based on the value measured according to the “floating and sinking method” described in JIS K6350, with Comparative Example 1 being 100. The results are shown in Tables 1 and 2. In addition, specific gravity is so light that a numerical value is small.
[0066]
Furthermore, a tire tread portion was prepared by a conventional method using the above rubber composition using an extruder. Next, each pneumatic tire is applied to a cap tread 2 of a test radial tire (T) having a size of 185 / 70R14 having the tread 1 of the normal cap / base structure shown in the half sectional view of the pneumatic tire of FIG. Was produced according to a conventional method. Each tire performance was evaluated by the following method, and the results are shown in Table 1.
[0067]
Noise performance: In accordance with JASO C 606, each test tire was mounted on a test vehicle, an actual vehicle ellipse test was performed, and external noise was measured. Using Comparative Example 1 as a reference value, each test tire was represented by a difference in sound pressure level (dB) from the reference value. The smaller the value, the smaller the noise and the better.
[0068]
Wet skid performance: Mounted on a test trailer using a specified rim, traveled on a wet asphalt road surface, locked the tire at a speed of 64.4 Km / h, measured braking force, and evaluated wet skid performance. Comparative example 1 is shown as an index, and the larger the value, the better.
[0069]
Abrasion resistance: The test tire was adjusted to an air pressure of 180 KPa using a specified rim, mounted on a taxi, rotated every 5,000 Km, and the tread rubber was worn from the remaining groove depth after 20,000 Km. The amount was determined and the wear resistance was evaluated.
Comparative example 1 is shown as an index, and the larger the value, the better.
[0070]
[Table 1]

In Table 1, Comparative Example 1 is a rubber composition containing no ordinary foaming agent. As shown in the results of Table 1, with the tire rubber composition according to the present invention, a vulcanized rubber having a predetermined bubble content and open cells can be obtained, the rubber specific gravity is reduced, and the weight of the pneumatic tire is reduced. Pneumatic tires with cap treads have improved noise performance, while maintaining a good balance of wet skid performance and wear resistance (A * B / 100 in the table) The value of is an index indicating the balance between wet skid performance and wear resistance, and it can be seen that 100 or more is maintained.
[0071]
Comparative Example 2 with a small amount of foaming agent and a low bubble content does not have a lightening effect, whereas Comparative Example 3 with a large amount of blending and a large amount of bubbles and open cells improves weight reduction and noise performance. Abrasion resistance is significantly reduced.
[0072]
Comparative Example 4 in which the final Mooney viscosity exceeds 80, Comparative Example 5 using the vulcanization accelerator B having a high vulcanization rate, and Comparative Example 6 having a large amount of sulfur are not suitable for vulcanization characteristics, and the desired bubble content Open cells cannot be obtained, and the weight reduction effect and noise performance cannot be satisfied. In Comparative Example 7 using the conventional hollow filler, although the specific gravity of the rubber is lowered, improvement in noise performance cannot be expected, and a well-balanced tire performance cannot be obtained.
[0073]
【Effect of the invention】
As described above, the tire rubber composition of the present invention and the pneumatic tire using the rubber composition include a diene rubber containing 70 parts by weight or more of a styrene butadiene rubber having a styrene content of 20 to 40% by weight as a rubber component. A rubber composition for a tire, wherein the vulcanized rubber of the tire rubber composition has a bubble content of 3 to 20%, and the bubble is a foamed rubber containing 20% or more of open cells. As a result, the specific gravity of the rubber can be reduced to reduce the weight of the pneumatic tire, and the noise performance of the tire can be greatly improved. In addition, it has an excellent effect of maintaining various properties such as wear resistance and wet skid performance necessary for the tire in a well-balanced manner.
[Brief description of the drawings]
FIG. 1 is a left half sectional view of a pneumatic tire of an example.
[Explanation of symbols]
T ... Pneumatic tire 1 ... Tread 2 ... Cap tread 3 ... Base tread 4 ... Side wall 5 ... Steel belt 6 ... Carcass 7 ... Inner liner 8 ... Bead filler 9 ... Bead wire 10 ... ... Flipper

Claims (5)

A tire rubber composition comprising a diene rubber containing 70% by weight or more of a styrene butadiene rubber having a styrene content of 20 to 40% by weight as a rubber component, wherein the foaming agent is 1 to 10 per 100 parts by weight of the rubber component. Containing parts by weight,
The vulcanized rubber obtained by vulcanizing at 160 ° C. for 20 minutes has bubbles with a bubble content of 3 to 20% and a bubble diameter of 20 to 500 μm, and the bubbles are continuously 20% to 50%. Ri foam rubber der containing air bubbles,
The tire rubber composition has a final Mooney viscosity measured at 100 ° C. of 80 or less, a rheometer vulcanization rate (t30) at 160 ° C. of 4 minutes or more, and a maximum torque (MH) thereof. the tire rubber composition characterized der Rukoto following 15DNm. 40-100 parts by weight of carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 40 to 150 m ² / g and a dibutyl phthalate oil absorption (DBP) of 70 to 160 ml / 100 g with respect to 100 parts by weight of the rubber component and silica The tire rubber composition according to claim 1 , wherein 0 to 100 parts by weight are blended, and the total amount of the carbon black and the silica is 40 to 100 parts by weight. The tire rubber composition according to claim 1 or 2, wherein the foaming agent is contained in an amount of 4 to 7 parts by weight with respect to 100 parts by weight of the rubber component. The tire rubber composition according to any one of claims 1 to 3, comprising Nt-butyl-2-benzothiazol sulfenamide or another sulfenamide compound as a vulcanization accelerator. . A pneumatic tire characterized by using the rubber composition for tires according to all or at least the cap tread portion of the tread portion to one of claims 1 to 4.

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