JP2012251017A - Rubber composition for tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for a tire, in which the rolling resistance is made low by blending carbon black having a large particle diameter, and the steering stability is more improved than conventionally.SOLUTION: Based on 100 pts.wt of a diene rubber, 1 to 50 pts.wt of the total of a novolac phenol resin and a methylene donor and 30 to 100 pts.wt of carbon black having a nitrogen adsorption specific surface area NSA of 55 to 95 m/g and a DBP absorption of 110 to 160 ml/100-g are blended, wherein the coefficient α is ≥1,979 when the mode diameter Dst (nm) in a mass distribution curve of Stokes diameter of the aggregate of the carbon black and the NSA are represented by the relational expression: Dst=α(NSA).

Description

  TECHNICAL FIELD The present invention relates to a rubber composition for tires that contains carbon black with controlled colloidal characteristics to reduce heat buildup and improve handling stability to a level higher than that of the prior art.

  In recent years, as a required performance for pneumatic tires, it is required to have excellent steering stability and excellent fuel efficiency. In particular, improving fuel efficiency is becoming more and more important with increasing interest in global environmental issues. In order to improve the fuel efficiency, it is necessary to reduce the rolling resistance of the tire, and the heat generation of the rubber composition constituting the tire is suppressed. Generally, 60 ° C. tan δ by dynamic viscoelasticity measurement is used as an index of exothermic property of the rubber composition.

  As a method for reducing the tan δ (60 ° C.) of the rubber composition, for example, the amount of carbon black is decreased or the particle size of the carbon black is increased. However, such a method has a problem that the rubber hardness and the elastic modulus are lowered, and the steering stability is lowered when the tire is formed.

  On the other hand, Patent Document 1 proposes blending a cashew-modified phenolic resin and a methylene donor with a diene rubber to reduce the temperature dependency of the rubber elastic modulus and suppress the change in steering stability performance. However, although this rubber composition is effective in suppressing changes in steering stability performance when used as a tire, the effect of reducing rolling resistance is not always sufficient, and further improvement has been demanded.

Japanese Patent No. 4458186

  An object of the present invention is to provide a rubber composition for a tire which is improved in steering stability to a level higher than that of a conventional one while blending carbon black with controlled colloidal characteristics to reduce rolling resistance.

In the tire rubber composition of the present invention that achieves the above object, a novolac type phenol resin and a methylene donor are blended with 100 parts by weight of a diene rubber, and the total amount is 1 to 50 parts by weight, and the nitrogen adsorption specific surface area N _2. 30 to 100 parts by weight of carbon black having SA of 55 to 95 m ² / g and DBP absorption of 110 to 160 ml / 100 g is blended, and the mode diameter Dst (nm) in the Stokes diameter mass distribution curve of the carbon black aggregate ) And the N ₂ SA, the following formula (1)
Dst = α (N ₂ SA) ^−0.61 (1)
(However, Dst is the mode diameter (nm) in the mass distribution curve of the Stokes diameter of the aggregate, N ₂ SA is the nitrogen adsorption specific surface area (m ² / g), and α is a coefficient.)
The coefficient α is 1979 or more.

The tire rubber composition of the present invention contains 1 to 50 parts by weight of the total amount of a novolac type phenol resin and a methylene donor per 100 parts by weight of the diene rubber, and a nitrogen adsorption specific surface area N ₂ SA of 55 to 55 parts. Since 30 to 100 parts by weight of carbon black having 95 m ² / g, DBP absorption of 110 to 160 ml / 100 g, and a coefficient α when expressed by the relationship of the above formula (1) is 1979 or more, Since the rubber hardness and the elastic modulus are ensured while reducing the tan δ (60 ° C.) of the rubber composition, the steering stability can be improved to a level higher than the conventional level while reducing the rolling resistance when the tire is formed.

  The coefficient α is preferably in the range of 1979 ≦ α ≦ 2450, and production costs can be suppressed while ensuring the above-described excellent characteristics.

  As the novolac type phenol resin, a resin modified with cashew oil is preferable, and the reinforcing property of the rubber composition can be further enhanced.

  The pneumatic tire in which the bead filler is constituted by the tire rubber composition of the present invention can improve steering stability to a level higher than the conventional level while reducing rolling resistance and improving fuel efficiency.

  A pneumatic tire comprising a rubber reinforcing layer having a crescent-shaped cross section of the left and right sidewall portions of a run-flat tire with the rubber composition for tires of the present invention, while reducing rolling resistance during normal running and improving fuel economy performance, Steering stability can be improved beyond the conventional level. Further, during run flat running, the run flat running performance is excellent and the durability of the rubber reinforcing layer having a crescent-shaped cross section in the sidewall portion is suppressed.

It is sectional drawing of the tire meridian direction which shows an example of embodiment of the pneumatic tire using the rubber composition for tires of this invention. It is a graph showing the relationship between Dst and N ₂ SA of the carbon black used in the rubber composition for a tire of the present invention.

  The tire to which the rubber composition for a tire of the present invention is applied is not particularly limited as long as it is a pneumatic tire. For example, a pneumatic tire for passenger cars, a pneumatic tire for trucks and buses, a pneumatic run flat tire, etc. Can be used. Examples of the pneumatic run-flat tire include a side-reinforced run-flat tire in which a crescent-shaped rubber reinforcement layer in the left and right sidewall portions is formed. FIG. 1 is a half cross-sectional view in the tire meridian direction showing an example of a side reinforcing type run-flat tire.

  In FIG. 1, the run flat tire has a tread portion 1, a sidewall portion 2, and a bead portion 3, and a two-ply carcass 6 is interposed between a pair of left and right bead cores 4 and 4, and a bead core 4 and a bead filler 5. A radial structure in which a belt layer 7 composed of a plurality of plies (2 plies in the figure) is disposed over the circumference of the tire on the outer peripheral side of the carcass 6 of the tread portion 1 so as to be folded back from the inside to wrap the tire It has become. An inner liner layer 9 is disposed on the innermost peripheral side of the tire. In addition, rubber reinforcing layers 8 and 8 having a crescent cross section are inserted inside the carcass 6 in the left and right sidewall portions 2 and 2, respectively. The position where the rubber reinforcing layer having a crescent-shaped cross section is inserted is not limited to the illustrated example, and may be inserted between the two carcass 6.

  The rubber composition for tires of the present invention can be suitably used for the bead filler 5 and / or the rubber reinforcing layer 8 having a crescent cross section. In addition, it can use suitably also for the bead filler of pneumatic tires other than a run flat tire.

  In the rubber composition for tires of the present invention, examples of the diene rubber include natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber and the like that are usually used in tire rubber compositions. Of these, natural rubber, isoprene rubber, butadiene rubber, and styrene-butadiene rubber are preferable. These diene rubbers can be used alone or as any blend.

  The rubber composition for tires of the present invention necessarily contains a novolac type phenol resin and a methylene donor. By including the novolac type phenol resin and the methylene donor, the rubber hardness and elastic modulus of the rubber composition can be increased, and the steering stability when the tire is formed can be maintained and improved.

  In the present invention, as the novolac type phenolic resin, those usually compounded in a tire rubber composition can be used. Examples thereof include those produced by a condensation reaction of phenol, cresol, resorcin, tert-butylphenol phenols or a mixture thereof with formaldehyde in the presence of an acid catalyst such as hydrochloric acid or oxalic acid. In addition, novolak-type modified phenol resins obtained by modifying novolak-type phenol resins with oils can be mentioned. Examples of the oils used for the modification of novolak-type phenol resins include rosin oil, tall oil, cashew oil, and linol. Examples include acids, oleic acid, and linolenic acid. Of these, phenol resins and cashew-modified phenol resins are preferable. These novolac-type phenol resins can be used alone or in any mixture.

  A commercial item can be used for these novolak type phenol resins. Examples of the phenol resin include Sumikalol 620 manufactured by Sumitomo Chemical Co., Ltd. Examples of cashew-modified phenolic resins include Sumitomo Resin PR-YR-170 and PR-150 manufactured by Sumitomo Bakelite Co., Ltd., Phenolite A4-1419 manufactured by Dainippon Ink & Chemicals, Inc., and the like.

  In the present invention, a methylene donor is used as a curing agent for the above-described novolak type phenol resin. Examples of methylene donors include hexamethylenetetramine and methylolated melamine derivatives. Examples of methylolated melamine derivatives include hexamethoxymethylol melamine, pentamethoxymethylol melamine, hexamethoxymethyl melamine, pentamethoxymethyl melamine, hexaethoxymethyl melamine, hexakis- (methoxymethyl) melamine, N, N ', N "-trimethyl- N, N ', N "-trimethylolmelamine, N, N', N" -trimethylolmelamine, N-methylolmelamine N, N '-(methoxymethyl) melamine, N, N', N "-tributyl-N , N ′, N ″ -trimethylol melamine, etc. Among them, hexamethylenetetramine, hexamethoxymethylol melamine, pentamethoxymethylol melamine, hexamethoxymethyl melamine and pentamethoxymethyl melamine are preferable. These can be used alone or in combination.

  Examples of hexamethylenetetramine include Sunseller HT-PO manufactured by Sanshin Chemical Industry Co., Ltd. Examples of hexamethoxymethylmelamine (HMMM) include CYREZ 964RPC manufactured by CYTEC INDUSTRIES. Examples of pentamethoxymethylmelamine (PMMM) include BARA CHEMICAL Co. , LTD. An example is Sumikanol 507A manufactured by the company.

  In the present invention, the compounding amount of the novolac phenol resin and the methylene donor is 1 to 50 parts by weight, preferably 3 to 35 parts by weight, based on 100 parts by weight of the diene rubber. To. When the total amount of the novolak type phenol resin and the methylene donor is less than 1 part by weight, the rubber hardness and elastic modulus of the rubber composition cannot be sufficiently increased. On the other hand, when the total amount of the novolak type phenolic resin and the methylene donor exceeds 50 parts by weight, the exothermic property of the rubber composition increases, and the rolling resistance when the tire is formed deteriorates.

  The weight ratio of the novolak type phenolic resin and the methylene donor used in the present invention is preferably 3/1 to 30/1, more preferably 5/1 to 20/1, for the novolak type phenolic resin / methylene donor. Good. If the weight ratio of novolak type phenol resin / methylene donor is less than 3/1, the amount of methylene donor is too much than the amount of phenol resin, so that the methylene donor remains and the crosslink density of the phenol resin becomes too high and brittle. Destruction is likely to occur. On the other hand, if the weight ratio of novolak type phenol resin / methylene donor is larger than 30/1, the amount of methylene donor is insufficient, and the crosslinking density of the resin is too low to be effective.

The tire rubber composition of the present invention has a specific nitrogen adsorption specific surface area N ₂ SA and DBP absorption, and limits the relationship between the N ₂ SA and the mode diameter Dst in the mass distribution curve of the Stokes diameter of the aggregate. By blending the new carbon black, mechanical properties such as tensile strength, tensile elongation at break, rubber hardness, and abrasion resistance are not deteriorated while reducing tan δ (60 ° C.) of the rubber composition. The compounding amount of the carbon black is 30 to 100 parts by weight, preferably 50 to 100 parts by weight with respect to 100 parts by weight of the diene rubber. When the blending amount of carbon black is less than 30 parts by weight, the rubber hardness and elastic modulus of the rubber composition are deteriorated. If the blending amount of carbon black exceeds 100 parts by weight, tan δ (60 ° C.) increases and tensile elongation at break decreases.

The carbon black used in the present invention has a nitrogen adsorption specific surface area N ₂ SA of 55 to 95 m ² / g, preferably 55 to 85 m ² / g. When N ₂ SA is less than 55 m ² / g, mechanical properties such as rubber hardness and dynamic elastic modulus of the rubber composition are lowered. When N ₂ SA exceeds 95 m ² / g, tan δ (60 ° C.) increases. N ₂ SA shall be measured according to JIS K6217-2.

  The DBP absorption amount of carbon black is 110 to 160 ml / 100 g, preferably 120 to 150 ml / 100 g. If the DBP absorption is less than 110 ml / 100 g, the rubber composition cannot be sufficiently reinforced, resulting in low hardness and reduced rigidity when used as a tire. Further, since the molding processability of the rubber composition is lowered and the dispersibility of the carbon black is deteriorated, the reinforcing performance of the carbon black cannot be sufficiently obtained. When the DBP absorption amount exceeds 160 ml / 100 g, the rubber becomes too hard and the riding comfort as tires deteriorates. In addition, workability deteriorates due to an increase in viscosity. The DBP absorption amount shall be measured according to JIS K6217-4 oil absorption amount A method.

The carbon black used in the present invention has the above-mentioned colloidal characteristics, and the mode diameter Dst and the nitrogen adsorption specific surface area N ₂ SA in the mass distribution curve of the Stokes diameter of the aggregate are expressed by the following equation (1). When expressed, the coefficient α is 1979 or more, preferably 1979 to 2450.
Dst = α (N ₂ SA) ^−0.61 (1)
(However, Dst is the mode diameter (nm) in the mass distribution curve of the Stokes diameter of the aggregate, N ₂ SA is the nitrogen adsorption specific surface area (m ² / g), and α is a coefficient.)

Carbon black has the N ₂ SA and DBP absorption amounts described above, and the coefficient α is set to 1979 or more, so that the tan δ (60 ° C.) of the rubber composition is reduced and the rubber hardness, the dynamic elastic modulus, etc. It can be maintained and improved. The upper limit of the coefficient α is not particularly limited, but is preferably 2450 or less from the viewpoint of productivity such as the yield and cost of carbon black. In the present invention, the mode diameter Dst in the mass distribution curve of the Stokes diameter of the aggregate refers to the mode diameter of the maximum frequency in the mass distribution curve of the Stokes diameter of the aggregate obtained by centrifugal sedimentation of carbon black. In the present invention, Dst is measured according to the method for obtaining the aggregate distribution by JIS K6217-6 disc centrifugal light sedimentation method.

FIG. 2 is a graph showing the relationship between Dst and N ₂ SA of the carbon black used in the present invention. In FIG. 2, the horizontal axis represents N ₂ SA (m ² / g), and the vertical axis represents Dst (nm). Representative carbon black having the ASTM standard number was plotted with square marks, and carbon black obtained by trial production was plotted with circle marks and triangle marks. Here, numbers 1 to 13 that refer to carbon blacks CB1 to CB13 used in Examples and Comparative Examples described later are attached to the plots, respectively. As shown in FIG. 2, Dst and N ₂ SA of the conventional standardized carbon black black generally satisfy the relationship of the following formula (2).
Dst = 1650 × (N ₂ SA) ^−0.61 (2)
(However, Dst represents the mode diameter (nm) in the mass distribution curve of the Stokes diameter of the aggregate, and N ₂ SA represents the nitrogen adsorption specific surface area (m ² / g).)
In FIG. 2, the relationship of the above formula (2) is represented by a dotted curve.

On the other hand, in the carbon black used in the present invention, Dst and N ₂ SA are plotted on the upper right from the curve (solid line) of the following formula (3).
Dst = 1979 × (N ₂ SA) ^−0.61 (3)
(However, Dst represents the mode diameter (nm) in the mass distribution curve of the Stokes diameter of the aggregate, and N ₂ SA represents the nitrogen adsorption specific surface area (m ² / g).)

That is, in the present invention, a new carbon black in which Dst is larger than Dst of conventional carbon black is used in the range of N ₂ SA of 55 to 95 m ² / g. Such carbon black means that the Stokes diameter of the aggregate is large and the form of the aggregate is close to a sphere even when N ₂ SA is at the same level as conventional carbon black. Thereby, in order to raise the reinforcement performance with respect to rubber | gum, mechanical characteristics, such as rubber hardness of a rubber composition and a dynamic elastic modulus, can be improved more than the conventional level.

  Carbon black having the colloidal characteristics described above is, for example, feedstock introduction conditions, fuel oil and feedstock supply rate, fuel oil combustion rate, reaction time (combustion from the last feedstock introduction position to reaction stoppage) in the carbon black production furnace. The production conditions such as gas residence time) can be adjusted.

  In the present invention, as the carbon black, the carbon black having the specific colloidal characteristics described above and other carbon blacks can be used together. At this time, the proportion of carbon black having specific colloidal characteristics exceeds 50% by weight, and the total amount of carbon black is 30 to 120 parts by weight with respect to 100 parts by weight of the diene rubber. Thus, the balance between tan δ and mechanical properties of the rubber composition can be adjusted by blending together other carbon blacks.

  Rubber compositions for tires include vulcanization or crosslinking agents, vulcanization accelerators, various inorganic fillers (dry silica, wet silica, aluminum oxide, clay, calcium carbonate, etc.), various oils, anti-aging agents, plasticizers, etc. Various additives generally used in rubber compositions for tires can be blended, and these additives are kneaded by a general method to form a rubber composition and used for vulcanization or crosslinking. Can do. 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 tires of the present invention can be produced by mixing the above components using a normal rubber kneading machine such as a Banbury mixer, a kneader, or a roll.

  The rubber composition for a tire of the present invention can be suitably used for a bead filler of a pneumatic tire and a side reinforcing rubber layer having a crescent cross section in a run flat tire. Since the pneumatic tire using the rubber composition of the present invention for these members has low heat generation during running, it can reduce rolling resistance and improve fuel efficiency. At the same time, by improving the rubber hardness and elastic modulus of the rubber composition, the handling stability when the tire is made can be improved to a level higher than the conventional level. In addition, when used in a crescent-shaped rubber reinforcement layer on the left and right sidewalls of run-flat tires, the driving stability can be improved to a level higher than conventional levels while reducing rolling resistance and improving fuel efficiency during normal driving. it can. Further, during run flat running, the run flat running performance is excellent and the durability of the rubber reinforcing layer having a crescent-shaped cross section in the sidewall portion is suppressed.

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

Fifteen types of rubber compositions (Examples 1 to 6, Comparative Examples 1 to 9) were prepared using 13 types of carbon black (CB1 to CB13). Of these, eight types of carbon black (CB1, CB2, CB8 to CB13) are commercially available grades, and five types of carbon black (CB3 to CB7) are prototypes. Tables 1 and 2 show their colloidal characteristics. In FIG. 2, the relationship between Dst and N ₂ SA of each carbon black CB1 to CB13 is plotted, and numbers for referring to the respective carbon blacks are attached.

In Tables 1 and 2, each abbreviation represents the following colloidal characteristics.
N ₂ SA: Nitrogen adsorption specific surface area measured based on JIS K6217-2 IA: Iodine adsorption amount measured based on JIS K6217-1 CTAB: CTAB measured based on JIS K6217-3 Adsorption specific surface area DBP: DBP absorption measured based on JIS K6217-4 (uncompressed sample) 24M4: 24M4-DBP absorption measured based on JIS K6217-4 (compressed sample) TINT: JIS Specific tinting strength measured based on K6217-5, Dst: Mode diameter, ΔD50, which is the maximum value of the mass distribution curve of the Stokes diameter of the aggregate by the disc centrifugal light sedimentation method measured based on JIS K6217-6 : Mass fraction of the Stokes diameter of the aggregate measured by the disc centrifugal light sedimentation method measured based on JIS K6217-6 In curves, the width of the distribution when its mass frequency is half height of the maximum point (half-width)
· Alpha: coefficient when the Dst and N ₂ SA fit to the relationship of the formula (1) described above alpha

In Tables 1 and 2, carbon blacks CB1, CB2, and CB8 to CB13 represent the following commercial grades, respectively.
・ CB1: Seest KHP made by Tokai Carbon
・ CB2: Toast Carbon Co., Ltd. Seast KH
・ CB8: Tokai Carbon Co., Ltd. Seest 300
・ CB9: Show Black 330T manufactured by Cabot Japan
-CB10: Niteron # 10N manufactured by Nippon Kayaku Carbon
・ CB11: Tokai Carbon Co., Ltd. Seest 3
・ CB12: Tokai Carbon Co., Ltd. Seest NH
CB13: Tokai Carbon Co. Seast 6

Production of carbon blacks CB3 to CB7 Using a cylindrical reactor, carbon black CB3 was changed by changing the total air supply amount, fuel oil introduction amount, fuel oil combustion rate, feedstock oil introduction amount, reaction time as shown in Table 3. -CB7 was produced.

Preparation and Evaluation of Rubber Composition for Tire 15 types of rubber compositions (Examples 1 to 6, Comparative Example 1) comprising the combinations shown in Tables 4 and 5 using the 13 types of carbon blacks (CB1 to CB13) described above. In preparing ~ 9), the components excluding sulfur and vulcanization accelerator were weighed and kneaded for 15 minutes with a 55 L kneader, and then the master batch was discharged and cooled at room temperature. This master batch was subjected to a 55 L kneader, and sulfur and a vulcanization accelerator were added and mixed to obtain a tire rubber composition.

  A pneumatic tire having a tire size of 195 / 65R15 was vulcanized and molded so as to constitute a bead filler of a pneumatic tire using the obtained 15 types of rubber compositions. The rolling resistance and steering stability of the obtained 15 types of pneumatic tires were evaluated by the methods shown below.

Rolling resistance The obtained tire is assembled to a standard rim (size 15 × 6J wheel) and attached to an indoor drum tester (drum diameter 1707 mm) in accordance with JIS D4230. A high-speed durability test was carried out in accordance with the described high-speed durability test, and the resistance force at a test load of 2.94 kN and a speed of 50 km / hour was measured to obtain a rolling resistance. The obtained results are shown in the “Rolling resistance” column of Tables 4 and 5 as an index with the reciprocal of the value of Comparative Example 1 as 100. The larger this index, the smaller the rolling resistance and the better the fuel efficiency.

Steering stability The tires obtained were assembled on a standard rim (size 15 x 6J wheel) and mounted on a domestic 2.0 liter class test vehicle. The course was run on a real vehicle, and the handling stability at that time was scored by a sensitive evaluation by three expert panelists. The obtained results are shown in the “Steering stability” column of Tables 4 and 5 as an index with the value of Comparative Example 1 as 100. The larger this index, the better the steering stability performance.

The types of raw materials used in Tables 4 and 5 are shown below.
NR: natural rubber, RSS # 3
SBR: styrene-butadiene rubber, Nipol 1502 manufactured by Nippon Zeon
Phenol resin 1: Cashew modified novolak type phenol resin, Sumitomo Bakelite Co., Ltd. Sumilite resin PR-YR-170
Phenol resin 2: Unmodified novolak-type phenol resin, PR7031A manufactured by Sumitomo Bakelite Co., Ltd.
Methylene donor: Hexamethylenetetramine, Nouchira H-PO manufactured by Ouchi Shinsei Chemical Co., Ltd.
CB1 to CB13: Carbon black aroma oils shown in Tables 1 and 2 above: Process X-140 manufactured by Japan Energy
Zinc Hana: Zinc Oxide Type 3 manufactured by Shodo Chemical Industry Co., Ltd. Stearic Acid: Beads manufactured by NOF Corporation
Vulcanization accelerator: Nouchira NS-P manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Sulfur: Shikoku Kasei Co., Ltd. Mukuron OT-20 (80% by weight of sulfur)

  As is apparent from Table 4, it was confirmed that the pneumatic tires of Examples 1 to 6 were improved in the low rolling resistance and the steering stability to the conventional level or more.

  As is apparent from Table 4, the pneumatic tire of Comparative Example 1 has a DBP absorption amount of carbon black CB9 of less than 110 ml / 100 g and a coefficient α of the formula (1) of less than 1979. Lower rolling resistance and steering stability than pneumatic tires. The pneumatic tire of Comparative Example 2 has poor steering stability because the DBP absorption amount of carbon black CB3 exceeds 160 ml / 100 g and the coefficient α is less than 1979.

  As is clear from Table 5, the pneumatic tires of Comparative Examples 3, 4, and 8 have a coefficient α of the formula (1) of carbon black CB1, CB2, and CB12 of less than 1979. Cannot be improved at the same time.

  In the pneumatic tires of Comparative Examples 5 and 7, since the DBP absorption amount of carbon black CB8 and CB11 is less than 110 ml / 100 g and the coefficient α is less than 1979, the low rolling resistance cannot be reduced and the steering stability performance is further improved. It cannot be improved.

Since the N ₂ SA of the carbon black CB10 is less than 55 m ² / g and the coefficient α is less than 1979, the pneumatic tire of Comparative Example 6 has good low rolling property but poor steering stability performance.

In the pneumatic tire of Comparative Example 9, the N ₂ SA of the carbon black CB13 exceeds 95 m ² / g and the coefficient α is less than 1979, so the low rolling resistance cannot be reduced.

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Bead core 5 Bead filler 6 Carcass 7 Belt layer 8 Rubber reinforcement layer 9 Inner liner

Claims (5)

A novolak type phenolic resin and a methylene donor are added to 100 parts by weight of the diene rubber, the total is 1 to 50 parts by weight, the nitrogen adsorption specific surface area N ₂ SA is 55 to 95 m ² / g, and the DBP absorption is 110 to 110 parts by weight. While blending 30 to 100 parts by weight of 160 ml / 100 g of carbon black, the relationship between the mode diameter Dst (nm) in the Stokes diameter mass distribution curve of the carbon black aggregate and the N ₂ SA is expressed by the following formula ( 1)
Dst = α (N ₂ SA) ^−0.61 (1)
(However, Dst is the mode diameter (nm) in the mass distribution curve of the Stokes diameter of the aggregate, N ₂ SA is the nitrogen adsorption specific surface area (m ² / g), and α is a coefficient.)
A rubber composition for tires, wherein the coefficient α is 1979 or more.   The tire rubber composition according to claim 1, wherein the coefficient α satisfies 1979 ≦ α ≦ 2450.   The rubber composition for tire according to claim 1 or 2, wherein the novolac type phenol resin is a resin modified with cashew oil.   A pneumatic tire comprising a bead filler made of the tire rubber composition according to claim 1, 2 or 3.   A pneumatic tire comprising a rubber reinforcing layer having a crescent-shaped cross section in left and right sidewall portions of a run-flat tire, using the tire rubber composition according to claim 1, 2 or 3.

Images