JP2012158660A - Rubber composition for tire tread - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for a tire tread improved in grip performance, its sustainability, and wear resistance more than in conventional levels.SOLUTION: The rubber composition is obtained by blending 100 pts.wt. of a dienec rubber containing ≥70 wt.% of a syrene-butadiene rubber having a glass transition temperature of ≥-35°C and 60 to 150 pts.wt. of carbon black A, wherein the CTAB adsorption specific surface area of the carbon black A is 150 to 250 m/g; and the DBP absorption amount is 100 to 150 ml/100-g, and wherein with dimensionless numbers X, Y and Z determined from a maximum length L, a width W, a peripheral length P, a projection area A and an enveloping area S determined by an image analysis of two-dimensional projection images of aggregates of the carbon black A, the total of a number fraction (r1%) of the aggregate satisfying the condition (1): at least one of X>1.7 and Y>110, and Z>1.6, and a number fraction (r2%) satisfying the condition (2): Y>110 and 1.6≥Z>1.3 is ≥70% and <80%, and the r2% is larger than the r1%.

Description

  The present invention relates to a rubber composition for a tire tread in which grip performance, its durability and wear resistance are improved to a level higher than conventional levels.

  A pneumatic tire for competition is required to have excellent grip performance during high-speed running, to maintain the excellent grip performance, and to have excellent wear resistance.

  Conventionally, a rubber composition constituting a tread portion of a racing tire is blended with a carbon black having a small particle diameter, an amount of the carbon black is increased, or a styrene-butadiene rubber having a high glass transition temperature. The exothermic property is increased by blending (for example, see Patent Document 1). However, when such a rubber composition is used in the tread portion, there is a problem that grip performance is gradually lowered or wear resistance is lowered when traveling at a high speed for a long time.

  Therefore, there is a problem of improving the grip performance without deteriorating the sustainability and wear resistance of the grip performance.

JP 2000-273245 A

  An object of the present invention is to provide a rubber composition for a tire tread in which the grip performance, the durability of the grip performance, and the wear resistance are improved to the conventional level or more.

The rubber composition for a tire tread of the present invention that achieves the above-mentioned object is obtained by adding 60 to 60 parts of carbon black A to 100 parts by weight of a diene rubber containing 70% by weight or more of styrene-butadiene rubber having a glass transition temperature of −35 ° C. or higher. 150 parts by weight, and the carbon black A belongs to a hard carbon black region having a CTAB adsorption specific surface area of 150 to 250 m ² / g and a DBP absorption of 100 to 150 ml / 100 g, and the carbon black A is transmissive The dimensionless numbers X, Y, and Z are calculated from the maximum length L, width W, perimeter length P, projection area A, and envelope area S obtained from image analysis of the two-dimensional projection image of the aggregate when observed with an electron microscope. The number fraction (r1%) of aggregates that satisfy the following condition (1) and the number fraction (r2%) of aggregates that satisfy the following condition (2): The total of the number fraction (r1%) and the number fraction (r2%) is 70% or more and less than 80%, and the number fraction (r2%) is larger than the number fraction (r1%). It is characterized by.
Condition (1) satisfies at least one of X> 1.7, Y> 110, and Z> 1.6.
Condition (2) Y> 110 and 1.6 ≧ Z> 1.3
(However, dimensionless numbers X, Y, and Z are obtained from the following equations.
X = L / W
Y = (P ² / A) × (100 / 4π)
Z = S / A
Here, L is the maximum length (nm) obtained from the image analysis of the two-dimensional projection image of the aggregate, W is the width (nm), P is the peripheral length (nm), A is the projected area (nm ² ), S Is the envelope area (nm ² ). )

The rubber composition for a tire tread of the present invention has a CTAB adsorption specific surface area of 150 to 250 m ² / g with respect to 100 parts by weight of a diene rubber containing 70% by weight or more of a styrene-butadiene rubber having a glass transition temperature of −35 ° C. or more. , And the aggregate number fraction (r1%) satisfying the condition (1) and the aggregate number satisfying the condition (2) belonging to the hard carbon black region having a DBP absorption of 100 to 150 ml / 100 g ( The total amount of (r2%) is 70% or more and less than 80%, and carbon black A having a number fraction (r2%) larger than the number fraction (r1%) is blended in an amount of 60 to 150 parts by weight. Performance, durability of grip performance and wear resistance can be improved to a level higher than conventional levels.

Here, 60 to 110 parts by weight of carbon black A and 10 to 50 parts by weight of carbon black B are blended with 100 parts by weight of diene rubber, and the total of carbon black A and carbon black B is 90 to 150 parts by weight. The carbon black B preferably has a CTAB adsorption specific surface area of 100 to 145 m ² / g and a DBP absorption of 100 to 150 ml / 100 g. At this time, 5 to 60 parts by weight of a copolymer having a weight average molecular weight of 2000 to 20000 may be blended with 100 parts by weight of the diene rubber.

  A pneumatic tire using the rubber composition for a tire tread can improve grip performance, durability of grip performance and abrasion resistance to a level higher than that of the conventional tire, and is particularly suitable for a pneumatic tire for competition.

  In the rubber composition for a tire tread of the present invention, the diene rubber necessarily includes a styrene-butadiene rubber having a glass transition temperature of −35 ° C. or higher. Further, other diene rubbers other than styrene-butadiene rubber having a glass transition temperature of −35 ° C. or more can be included. Examples of other diene rubbers include natural rubber, isoprene rubber, butadiene rubber, acrylonitrile-butadiene rubber, and styrene-butadiene rubber having a glass transition temperature of less than -35 ° C. Of these, natural rubber, isoprene rubber, butadiene rubber, and styrene-butadiene rubber having a glass transition temperature of less than -35 ° C are preferable. These other diene rubbers can be used alone or as any blend.

  When the diene rubber contains a styrene-butadiene rubber having a glass transition temperature of −35 ° C. or higher, preferably −30 ° C. to 0 ° C., grip performance when this rubber composition is used for a tread portion of a pneumatic tire. Can be improved. In the present specification, the glass transition temperature of the styrene-butadiene rubber is measured by a differential scanning calorimetry (DSC) under a temperature increase rate condition of 10 ° C./min, and is set as a temperature at the midpoint of the transition region. When the styrene-butadiene rubber is an oil-extended product, the glass transition temperature of the raw rubber excluding the oil is used.

  The content of styrene-butadiene rubber having a glass transition temperature of −35 ° C. or higher is 70% by weight or more, preferably 80 to 100% by weight in the diene rubber. When the content of the styrene-butadiene rubber having a glass transition temperature of −35 ° C. or higher is less than 70% by weight, the grip performance cannot be improved. When a plurality of styrene-butadiene rubbers are used in combination, the glass transition temperature of at least one styrene-butadiene rubber is −35 ° C. or higher, and the content in the diene rubber is 70% by weight. That's enough.

  In the rubber composition for tire treads of the present invention, by incorporating a new carbon black A having the shape characteristics of an aggregate, which will be described later, the wear resistance and the durability of grip performance are reduced while reducing the particle diameter of the carbon black. Can be suppressed as compared with the conventional small particle size carbon black. The compounding amount of the carbon black A is 60 to 150 parts by weight, preferably 90 to 140 parts by weight with respect to 100 parts by weight of the diene rubber. In addition, when using with the carbon black B mentioned later, the compounding quantity of the carbon black A is preferably 60 to 110 parts by weight. When the blending amount of the carbon black A is less than 60 parts by weight, sufficient grip performance cannot be obtained and the wear resistance cannot be increased. On the other hand, when the blending amount A of carbon black exceeds 150 parts by weight, the durability of the grip performance deteriorates and the wear resistance deteriorates.

Carbon black A used in the present invention, CTAB adsorption specific surface area of 150 to 250 ² / g, preferably belonging to the hard carbon black region of 160~210m ² / g. If the CTAB adsorption specific surface area of carbon black A is less than 150 m ² / g, the effect of increasing the modulus and heat build-up of the rubber composition and improving the grip performance cannot be obtained. In addition, wear resistance is reduced. When the CTAB adsorption specific surface area exceeds 250 m ² / g, the durability of the grip performance deteriorates. The CTAB adsorption specific surface area is measured according to JIS K6217-3.

  Carbon DB A has a DBP absorption of 100 to 150 ml / 100 g, preferably 120 to 140 ml / 100 g. When the DBP absorption amount of carbon black A is less than 100 ml / 100 g, grip performance and wear resistance are insufficient. Further, since the molding processability of the rubber composition is lowered and the dispersibility of the carbon black A is deteriorated, sufficient reinforcement performance for the rubber composition cannot be obtained. When the DBP absorption amount exceeds 150 ml / 100 g, the flexibility of the rubber composition is impaired and the grip performance when the tire is made deteriorates. The DBP absorption amount shall be measured according to JIS K6217-4 oil absorption amount A method.

In the present invention, carbon black A has the colloidal characteristics described above, and its aggregate has the following characteristics. First, the carbon black A is observed with a transmission electron microscope, and the maximum length L (nm), the width W (nm), the perimeter length P (nm), and the projection area A are analyzed by image analysis of the two-dimensional projection image of the aggregate. (Nm ² ) and envelope area S (nm ² ) are obtained, and dimensionless numbers X, Y, and Z are calculated for each aggregate. Based on the values of these dimensionless numbers X, Y, and Z, the number fraction (r1%) of aggregates that satisfy the following condition (1) and the number fraction (r2%) of aggregates that satisfy the condition (2) are obtained. When obtained, the total of the number fraction (r1%) and the number fraction (r2%) is 70% or more and less than 80%, preferably 70 to 79%, and the number fraction (r2%) is the number fraction. It should be larger than the rate (r1%).
Condition (1) satisfies at least one of X> 1.7, Y> 110, and Z> 1.6.
Condition (2) Y> 110 and 1.6 ≧ Z> 1.3
However, the dimensionless numbers X, Y, and Z are obtained from the following equations.
X = L / W
Y = (P ² / A) × (100 / 4π)
Z = S / A
Here, L is the maximum length (nm) obtained from the image analysis of the two-dimensional projection image of the aggregate, W is the width (nm), P is the peripheral length (nm), A is the projected area (nm ² ), S Is the envelope area (nm ² ).

The two-dimensional projection image of the carbon black aggregate was observed by the following method. First, 1 mg of the dried carbon black sample was put in a test tube, 2 ml of chloroform was added, and the mixture was dispersed with ultrasound for 3 minutes. The dispersed sample was fixed to a carbon black support film and photographed with a transmission electron microscope (direct magnification 60000 times). The obtained two-dimensional projection image is applied to an image analysis apparatus (LUZEX-F manufactured by NIRECO), and a maximum length L (nm), a width W (nm), a perimeter length P (nm), and projection for 1000 or more aggregates. Area A (nm ² ) and envelope area S (nm ² ) were determined, and dimensionless numbers X, Y, and Z were calculated for each aggregate.

The maximum length L is the maximum value (nm) of the distance between parallel lines when a parallel line circumscribing the two-dimensional projection image of the aggregate is drawn. The width W is a value (nm) of the distance between parallel lines of parallel lines circumscribing in the direction orthogonal to the direction of the maximum length L in the two-dimensional projection image of the aggregate. The perimeter P is the perimeter (nm) of the aggregate two-dimensional projection image. The projection area A is the projection area (nm ² ) of the two-dimensional projection image of the aggregate. The envelope area S is a polygonal area (nm ² ) connecting the vertices of the branched portions of the aggregate in the two-dimensional projection image of the aggregate.

  The dimensionless number X is the ratio of the maximum length L to the width W (X = L / W) and corresponds to the aspect ratio of the two-dimensional projection image of the aggregate. When it is larger than 1.7, it means that the aggregate has high anisotropy. The upper limit of X is preferably 5.0 or less, more preferably 3.0 or less. If X is greater than 5.0, the elongation at break of the rubber composition may be reduced.

The dimensionless number Y is obtained from the relationship between the perimeter length P and the projection area A by the relational expression Y = (P ² / A) × (100 / 4π). Here, (P ² / 4π) means the area of a circle whose circumferential length is P. Therefore, the dimensionless number Y is a value representing the ratio of the area (P ² / 4π) to the projected area A as a percentage, and represents the ratio of the branched portion. When Y is larger than 110, it means that the ratio of the branched portion in the aggregate is increased. The upper limit of Y is preferably 1200 or less. If Y exceeds 1200, the proportion of the branched portion becomes excessive, and the elongation at break of the rubber composition may be reduced.

  The dimensionless number Z is the ratio of the envelope area S to the projected area A (Z = S / A) and represents the degree of the length of the branched portion. In condition (1), when Z is larger than 1.6, it means that the length of the branched portion is long. At this time, the upper limit of Z is preferably 2.0. By suppressing the length of the branched portion of the aggregate from becoming excessively fragile, it is possible to stably obtain the characteristics of an excellent rubber composition. To be able to. In condition (2), when Z is greater than 1.3 and less than or equal to 1.6, it means that the length of the branched portion is controlled.

  The dimensionless numbers X, Y, and Z are calculated for each aggregate by image analysis of the above-described two-dimensional projection image of carbon black, and the number fraction (r1%) of aggregates that satisfy the condition (1) and the condition (2) The number fraction (r2%) of aggregates satisfying the above is obtained.

  Condition (1) satisfies at least one of X> 1.7 and Y> 110, and Z> 1.6, the aggregate is developed, the number of branched portions is large, and the length of the branched portions is long. Means long. Thereby, the characteristics of the rubber composition become highly reinforcing.

  Condition (2) means that Y> 110 and 1.6 ≧ Z> 1.3, the number of branched portions is large, and the length of the branched portions is controlled. Thereby, the characteristics of the rubber composition enhance the heat generation of the rubber.

  In the present invention, the total number of aggregates satisfying the condition (1) (r1%) and the number of aggregates satisfying the condition (2) (r2%) is 70% or more and less than 80%, preferably 70%. -79%. If the sum of the number fraction (r1%) and the number fraction (r2%) is less than 70%, the heat buildup of the rubber becomes insufficient. Further, if the total of the number fraction (r1%) and the number fraction (r2%) is 80% or more, the elongation at break of the rubber may be lowered.

  In addition, the number fraction (r2%) of the aggregates that satisfy the condition (2) needs to be larger than the number fraction (r1%) of the aggregates that satisfy the condition (1). By making the number fraction (r2%) larger than the number fraction (r1%), the reinforcement and heat generation properties of the rubber are balanced in a high order.

  The carbon black having the colloidal characteristics described above is obtained by using a normal carbon black production apparatus, a raw material supply location, a raw material supply amount, a raw material supply temperature, a fuel oil supply amount, a fuel atomized air supply amount, and a combustion air supply amount. It can be produced by adjusting the production conditions such as the combustion air temperature and the reaction stop point.

In the rubber composition for a tire tread of the present invention, it is preferable to mix carbon black B having a CTAB adsorption specific surface area of 100 to 145 m ² / g and a DBP absorption of 100 to 150 ml / 100 g together with the carbon black A described above. . By blending carbon blacks A and B together, the durability of the grip performance and the wear resistance can be further improved.

The carbon black B preferably has a CTAB adsorption specific surface area of 100 to 145 m ² / g, more preferably 120 to 140 m ² / g. By setting the CTAB adsorption specific surface area of the carbon black B within this range, the durability of the grip performance and the wear resistance can be further improved.

  The DBP absorption amount of carbon black B is preferably 100 to 150 ml / 100 g, more preferably 110 to 140 ml / 100 g. By making the DBP absorption amount of the carbon black B within this range, it is possible to further improve the durability of the grip performance and the wear resistance.

  In the present invention, the amount of carbon black B is preferably 10 to 50 parts by weight, more preferably 20 to 40 parts by weight, based on 100 parts by weight of the diene rubber. When the blending amount of carbon black B is 10 parts by weight or more, the durability of the grip performance and the wear resistance can be further improved. Moreover, it can suppress that grip performance falls by making the compounding quantity of carbon black B into 50 weight part or less.

  The total amount of carbon black A and carbon black B is preferably 90 to 150 parts by weight, more preferably 100 to 140 parts by weight, per 100 parts by weight of the diene rubber. By making the total amount of carbon black A and B 90 parts by weight or more, grip performance and wear resistance can be enhanced. Further, by maintaining the total amount of carbon blacks A and B to 150 parts by weight or less, the grip performance can be maintained and the wear resistance can be ensured.

  In the present invention, when carbon blacks A and B are blended together, it is preferable to blend a low molecular weight copolymer, and the grip performance can be improved. The weight average molecular weight of this copolymer is preferably 2000 to 20000, more preferably 2500 to 15000. When the weight average molecular weight is less than 2000, the wear resistance is deteriorated. On the other hand, when the weight average molecular weight exceeds 20000, the grip performance deteriorates. The weight average molecular weight of a copolymer shall be measured by gel permeation chromatography (GPC) by standard polystyrene conversion.

  Examples of the low molecular weight copolymer include a copolymer of two or more conjugated diene monomers and a copolymer of a conjugated diene monomer and an aromatic vinyl monomer. Examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, 1,3-pentadiene, and the like. . Examples of the aromatic vinyl monomer include styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, α-methylstyrene, 2,4-dimethylstyrene, 2,4-diisopropylstyrene, and 4-tert. -Butylstyrene, divinylbenzene, tert-butoxystyrene, vinylbenzyldimethylamine, (4-vinylbenzyl) dimethylaminoethyl ether, N, N-dimethylaminoethylstyrene, vinylpyridine and the like. Preferred examples of the low molecular weight copolymer include a liquid styrene butadiene copolymer, a liquid isoprene copolymer, and a liquid butadiene copolymer.

  The tire tread rubber composition includes various vulcanization or crosslinking agents, vulcanization accelerators, various inorganic fillers, various oils, anti-aging agents, plasticizers and the like that are generally used in tire tread rubber compositions. Additives can be blended, and such additives can be kneaded by a general method to form a rubber composition, which can be used for vulcanization or crosslinking. As long as the amount of these additives is not contrary to the object of the present invention, a conventional general amount can be used. The rubber composition for a tire tread 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 pneumatic tire using the rubber composition for a tire tread of the present invention can improve grip performance, sustainability of grip performance, and wear resistance to the conventional level or more. For this reason, it is suitable as a pneumatic tire for competition with excellent high-speed running performance. However, the pneumatic tire of the present invention is not limited to a racing tire, and can be suitably used as a pneumatic tire for a normal passenger car.

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

Production and properties of carbon black A Following a combustion chamber (inner diameter: 900 mm, length: 2100 mm) having an air inlet for supplying combustion air from the periphery of a fuel burner mounted in the axial direction of the furnace, a taper angle of 15 ° was formed. A reduced taper part, a cylindrical straight pipe part (inner diameter 530 mm, length 400 mm), a first raw material supply part (inner diameter 370 mm, length 3670 mm) provided with a raw material supply port capable of supplying a raw material in a direction perpendicular to the furnace axis, Manufactured by adjusting a raw material supply location, a raw material supply amount, a fuel oil supply amount, a combustion air supply amount, and a reaction stop location using a furnace having a second raw material supply section (inner diameter 254 mm, length 420 mm). . In addition, the raw material supply port has four locations (FNo. 1 to FNo. 4) in the first raw material supply portion, one location in the second raw material supply portion (FNo. 5), and three locations in the enlarged taper third raw material supply portion ( FNo. 6 to FNo. 8) are installed. In addition, the reaction residence time was adjusted by supplying the raw material from one of the above-described raw material supply ports and spraying cooling water at a predetermined reaction stop point (QW No. 1, 2, 6).

  A coal-based feedstock having a specific gravity of 1.05 (100/4 ° C.), BMCI 150, Engler viscosity (70/20 ° C.) of 1.32 and toluene insoluble content of 0.02% is used as the raw material, and a specific gravity of 0.96 (15 / 4 ° C), ash content 0.001%, Engler viscosity (40/20 ° C) 1.11, toluene insoluble content 0.007 using hydrocarbon oil, raw material supply location, raw material supply amount, fuel oil supply amount, combustion Four types of carbon black A, CB1 to CB4, were produced by adjusting the air supply amount and the reaction stop point. Further, the colloidal characteristics of the obtained carbon black A and the characteristic values obtained by image analysis of the two-dimensional projection image of the aggregate are measured by the method described above, and the number fraction of aggregates (r1%) satisfying the condition (1), The number fraction (r2%) of aggregates satisfying the condition (2) was determined. For reference, the number average value of dimensionless numbers X, Y, and Z was obtained. The obtained results are shown in Table 1.

Preparation and Evaluation of Rubber Composition for Tire Tread 20 types of rubber compositions (Examples 1 to 11) comprising the combinations shown in Tables 2 to 4 using the four types of carbon black A (CB1 to CB4) shown in Table 1. In preparing Comparative Examples 1 to 9), components excluding sulfur and a vulcanization accelerator were weighed, kneaded for 15 minutes with a 55 L kneader, the master batch was discharged at a temperature of 160 ° C., and cooled to 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 rubber composition for a tire tread. Twenty kinds of obtained rubber compositions (Examples 1 to 11 and Comparative Examples 1 to 9) were each vulcanized in a predetermined mold at 150 ° C. for 30 minutes to prepare test pieces. The abrasion resistance was evaluated by the method shown.

Abrasion resistance According to JIS K6264, the pico abrasion of the obtained test piece was measured according to FERRY MACHINE CO. It measured using the Pico abrasion tester by a company. The measurement conditions were a load 44N, a turntable rotation speed of 60 ± 2 times per minute, and a total turntable rotation speed of 80 times (20 forward rotations and 20 reverse rotations were alternately performed twice each). The obtained results are shown in Tables 2 to 4 as indexes in which Comparative Example 1 is 100 in Tables 2 and 3, and Comparative Example 8 is 100 in Table 4. The larger this index, the better the wear resistance.

  In addition, pneumatic tires having a tire size of 225 / 50R17 were manufactured using the 20 types of rubber compositions obtained in the tread portion. The resulting pneumatic tires are assembled on rims of size 17 x JJ, mounted on a domestic vehicle (displacement of 3000 cc) with an air pressure of 230 kPa, and the test driver runs 10 laps on a dry circuit course (1 lap 2 km). The lap time for each lap was measured, and the grip performance (grip performance in the first half of the run) and the sustainability of the grip performance (grip performance in the second half of the run) were evaluated using the following judgment methods. The results obtained are shown in Table 2. Shown in ~ 4.

Grip performance (Grip performance in the first half of the run)
The lap time for the second lap when the circuit course under dry conditions is continuously run for 10 laps, Tables 2 and 3 are the lap times of the pneumatic tires of Comparative Example 1, and Table 4 is the lap time of the pneumatic tires of Comparative Example 8 And evaluated according to the following criteria. The higher the score, the better the grip performance.
5: Lap time is 0.5 seconds or more faster than the reference time.
4: The lap time is 0.2 seconds or more and less than 0.5 seconds faster than the reference time.
3: The difference between the lap time and the reference time is within a range of less than 0.2 seconds.
2: Lap time is 0.2 seconds or more and less than 0.5 seconds later than the reference time.
1: Lap time is more than 0.5 seconds later than the reference time.

Persistence of grip performance (grip performance in the latter half of driving)
The lap time of the 10th lap when the circuit course under dry conditions is continuously run for 10 laps, Tables 2 and 3 are the lap times of the pneumatic tires of Comparative Example 1, and Table 4 is the lap time of the pneumatic tires of Comparative Example 8 And evaluated according to the following criteria. The higher the score, the better the grip performance.
5: Lap time is 0.5 seconds or more faster than the reference time.
4: The lap time is 0.2 seconds or more and less than 0.5 seconds faster than the reference time.
3: The difference between the lap time and the reference time is within a range of less than 0.2 seconds.
2: Lap time is 0.2 seconds or more and less than 0.5 seconds later than the reference time.
1: Lap time is more than 0.5 seconds later than the reference time.

In addition, the kind of raw material used in Tables 2-4 is shown below.
SBR1: Styrene-butadiene rubber, NIPOL 9549 manufactured by Nippon Zeon Co., Ltd., glass transition temperature = −24 ° C., oil-extended product in which 50 parts by weight of oil is blended with 100 parts by weight of rubber component.
SBR2: Styrene-butadiene rubber, Nippon Zeon NIPOL 1723, glass transition temperature = −53 ° C., oil-extended product in which 37.5 parts by weight of oil is blended with 100 parts by weight of rubber component.
CB1 to CB4: Prototype carbon black A shown in Table 1 obtained by the above-described production
CB5: Carbon Black B, Dia Black A manufactured by Mitsubishi Chemical Corporation, SAF grade carbon black copolymer having a CTAB adsorption specific surface area of 125 m ² / g and DBP absorption of 116 ml / 100 g: Liquid styrene butazine copolymer, Sartomer RICON100 made, weight average molecular weight 4500
Zinc oxide: 3 types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd. Stearic acid: Beads manufactured by NOF Co., Ltd. Beadstearic acid anti-aging agent: SANTOFLEX 6PPD manufactured by Flexis
Aroma oil: Showa Shell Sekiyu Extract 4 S
Sulfur: Fine powder sulfur vulcanization accelerator with Jinhua seal oil manufactured by Tsurumi Chemical Co., Ltd .: Noxeller CZ-G manufactured by Ouchi Shinsei Chemical Co., Ltd.

  The rubber compositions for tire treads of Examples 1 to 7 in Table 2 and Examples 8 to 11 in Table 4 were confirmed to have improved grip performance, durability of grip performance and wear resistance over conventional levels. .

  As is apparent from Tables 3 and 4, the rubber composition of Comparative Example 2 has a grip performance durability and wear resistance because the properties of the two-dimensional projection image of the carbon black CB4 aggregate are outside the scope of the present invention. Sex worsens. In the rubber compositions of Comparative Examples 3 and 4, since the glass transition temperature of the styrene-butadiene rubber was less than -35 ° C, the grip performance and its durability deteriorated. In the rubber composition of Comparative Example 5, since the blending amount of carbon black CB3 was increased with respect to Comparative Example 1, the grip performance was improved but the wear resistance was deteriorated. In the rubber composition of Comparative Example 6, since the blending amount of carbon black CB1 is less than 60 parts by weight, the grip performance and the durability of the grip performance are lowered, and the effect of improving the wear resistance cannot be obtained. In the rubber composition of Comparative Example 7, since the blending amount of carbon black CB1 exceeds 150 parts by weight, the durability of the grip performance is lowered and the wear resistance is deteriorated. In the rubber composition of Comparative Example 9, since the characteristics of the two-dimensional projection image of the aggregate of carbon black CB4 are outside the scope of the present invention, the durability of the grip performance and the wear resistance are deteriorated.

Claims (4)

60 to 150 parts by weight of carbon black A is blended with 100 parts by weight of diene rubber containing 70% by weight or more of styrene-butadiene rubber having a glass transition temperature of −35 ° C. or higher, and the carbon black A has a CTAB adsorption ratio. An image of a two-dimensional projection image of an aggregate when belonging to a hard carbon black region having a surface area of 150 to 250 m ² / g and a DBP absorption of 100 to 150 ml / 100 g, and the carbon black A is observed with a transmission electron microscope Dimensionless numbers X, Y, and Z are calculated from the maximum length L, width W, perimeter length P, projected area A, and envelope area S obtained from the analysis, and the number fraction of aggregates satisfying the following condition (1) (r1 %) And the number fraction (r2%) of the aggregate satisfying the following condition (2), the sum of the number fraction (r1%) and the number fraction (r2%) Less than 80% 70% or more and the number fraction (r2%) is the number fraction (r1%) for a tire tread rubber composition characterized by greater than.
Condition (1) satisfies at least one of X> 1.7, Y> 110, and Z> 1.6.
Condition (2) Y> 110 and 1.6 ≧ Z> 1.3
(However, dimensionless numbers X, Y, and Z are obtained from the following equations.
X = L / W
Y = (P ² / A) × (100 / 4π)
Z = S / A
Here, L is the maximum length (nm) obtained from the image analysis of the two-dimensional projection image of the aggregate, W is the width (nm), P is the peripheral length (nm), A is the projected area (nm ² ), S Is the envelope area (nm ² ). ) 60 to 110 parts by weight of the carbon black A and 10 to 50 parts by weight of the carbon black B are blended with 100 parts by weight of the diene rubber, and the total of the carbon black A and the carbon black B is 90 to 150 parts by weight. ^2. The tire tread rubber composition according to claim 1, wherein the carbon black B has a CTAB adsorption specific surface area of 100 to 145 m ² / g and a DBP absorption of 100 to 150 ml / 100 g.   The rubber composition for a tire tread according to claim 2, wherein 5 to 60 parts by weight of a copolymer having a weight average molecular weight of 2000 to 20000 is blended with 100 parts by weight of the diene rubber.   A pneumatic tire using the rubber composition for a tire tread according to claim 1, 2 or 3.