JP2013185090A - Rubber composition for tire tread - Google Patents

Abstract

Provided is a rubber composition for a tire tread which ensures excellent dry grip performance and wear resistance in a wide temperature range.
SOLUTION: 100 parts by weight of styrene butadiene rubber comprising 20 to 60% by weight of solution-polymerized styrene butadiene rubber S-SBR and 80 to 40% by weight of emulsion polymerized styrene butadiene rubber E-SBR has a nitrogen adsorption specific surface area of 100. A rubber composition containing 50 to 120 parts by weight of carbon black of ˜200 m ² / g, wherein the S-SBR has a styrene content of 30 to 38% by weight, a vinyl content of 60 to 80% by weight, and a glass transition temperature. -20--5 degreeC, a weight average molecular weight is 1 million-1,800,000, The styrene amount of said E-SBR is 40 weight% or more, It is characterized by the above-mentioned.
[Selection figure] None

Description

  The present invention relates to a rubber composition for tire treads, and relates to a rubber composition for tire treads that ensures excellent dry grip performance and wear resistance in a wide temperature range.

  It is known that the grip performance of a pneumatic tire is greatly affected by the tire temperature, and that a sufficient grip performance cannot be obtained at a low temperature, and that the wear resistance decreases at a high temperature. In particular, racing tires for rally driving are required to have high heat generation (tan δ) and excellent wear resistance in a wide temperature range so that it can cope with changing road surface conditions and speed ranges.

For this reason, a rubber composition in which a large amount of carbon black is blended with an emulsion-polymerized styrene butadiene rubber (E-SBR) having a high glass transition temperature (Tg) has been proposed (for example, see Patent Document 1). However, the demanded performance demanded by customers for racing tires will be higher, and the heat generation (tan δ) in a wide temperature range will be further increased to improve dry grip performance, and the wear resistance at high temperatures will be improved. There is a need for a rubber composition for a tread for a rally traveling tire that is made excellent.
JP-A-63-191844

  An object of the present invention is to provide a rubber composition for a tire tread that ensures excellent dry grip performance and wear resistance in a wide temperature range.

The rubber composition for a tire tread of the present invention that achieves the above object comprises a styrene butadiene comprising 20 to 60% by weight of a solution polymerized styrene butadiene rubber S-SBR and 80 to 40% by weight of an emulsion polymerized styrene butadiene rubber E-SBR. A rubber composition comprising 100 parts by weight of rubber and 50 to 120 parts by weight of carbon black having a nitrogen adsorption specific surface area of 100 to 200 m ² / g, wherein the S-SBR has a styrene content of 30 to 38% by weight, vinyl The amount is 60 to 80% by weight, the glass transition temperature is −20 to −5 ° C., the weight average molecular weight is 1 million to 1.8 million, and the styrene content of the E-SBR is 40% by weight or more. .

The rubber composition for a tire tread of the present invention has a styrene content of 30 to 38% by weight, a vinyl content of 60 to 80% by weight, a glass transition temperature of −20 to −5 ° C., and a weight average molecular weight of 1,000,000 to 1,800,000. 100 parts by weight of styrene butadiene rubber comprising 20 to 60% by weight of S-SBR and 80 to 40% by weight of E-SBR having a styrene amount of 40% by weight or more, and a nitrogen adsorption specific surface area of 100 to 200 m ² / g By blending 50 to 120 parts by weight of carbon black, heat resistance (tan δ) and rubber hardness are further improved over a wide temperature range to improve dry grip performance and excellent wear resistance at high temperatures Can be.

  It is preferable to blend 2 to 20 parts by weight of an aromatic modified terpene resin with respect to 100 parts by weight of the styrene butadiene rubber.

  The rubber composition of the present invention preferably contains 0.2 to 5 parts by weight of a cyclic polysulfide represented by the following formula (I) with respect to 100 parts by weight of the styrene butadiene rubber. By blending the cyclic polysulfide, the dry grip performance in a wide temperature range can be improved, and the rubber hardness and rigidity can be increased to further improve the wear resistance of the rubber composition.

（式（Ｉ）中、Ｒは置換もしくは非置換の炭素数４〜８のアルキレン基、置換もしくは非置換の炭素数４〜８のオキシアルキレン基、ｘは平均３〜５の数、ｎは１〜５の整数である。）

(In the formula (I), R is a substituted or unsubstituted alkylene group having 4 to 8 carbon atoms, a substituted or unsubstituted oxyalkylene group having 4 to 8 carbon atoms, x is an average number of 3 to 5, and n is 1) It is an integer of ~ 5.)

  A pneumatic tire using this rubber composition in the tread portion can ensure excellent dry grip performance and wear resistance in a wide temperature range.

  In the rubber composition for a tire tread of the present invention, the rubber component is a solution-polymerized styrene butadiene rubber (hereinafter referred to as “S-SBR”) having a high molecular weight and a high glass transition temperature, and emulsion polymerization in which the styrene amount is 40% by weight or more. It is a styrene butadiene rubber composed of styrene butadiene rubber (hereinafter referred to as “E-SBR”). That is, the total of 20 to 60% by weight of S-SBR and 80 to 40% by weight of E-SBR is made 100% by weight of styrene butadiene rubber.

  S-SBR has a styrene content of 30 to 38% by weight, a vinyl content of 60 to 80% by weight, a glass transition temperature (hereinafter referred to as “Tg”) of −20 to −5 ° C., and a weight average molecular weight (hereinafter referred to as “Mw”). ) Is a solution polymerized styrene butadiene rubber of 1 million to 1.8 million.

  The amount of styrene in S-SBR is 30 to 38% by weight, preferably 32 to 37% by weight. When the amount of styrene in S-SBR is less than 30% by weight, rubber hardness and elastic modulus are lowered, and grip performance is also lowered. On the other hand, if the amount of styrene in S-SBR exceeds 38% by weight, the wear resistance deteriorates. The amount of styrene in S-SBR is measured by infrared spectroscopic analysis (Hampton method).

  The vinyl content of S-SBR is 60 to 80% by weight, preferably 62 to 70% by weight. When the vinyl content of S-SBR is less than 60% by weight, grip performance is lowered. On the other hand, if the vinyl content of S-SBR exceeds 80% by weight, it becomes too hard and the grip performance deteriorates. The vinyl content of S-SBR is measured by infrared spectroscopic analysis (Hampton method).

  The Tg of S-SBR is -20 to -5 ° C, preferably -18 to -7 ° C. When Tg of S-SBR is lower than −20 ° C., grip performance is deteriorated. Further, when the Tg of S-SBR is higher than -5 ° C, the wear resistance is deteriorated. In the present specification, the Tg of S-SBR is a temperature at the midpoint of the transition zone by measuring a thermogram by differential scanning calorimetry (DSC) under a heating rate condition of 20 ° C./min. Moreover, when S-SBR is an oil-extended product, it is set as the glass transition temperature of S-SBR in a state not containing an oil-extended component (oil).

  The Mw of S-SBR is 1 million to 1.8 million, preferably 1.2 million to 1.6 million. When the Mw of S-SBR is less than 1 million, rubber hardness and elastic modulus are lowered. Moreover, when Mw exceeds 1.8 million, the workability of a rubber composition will deteriorate. In this specification, Mw of S-SBR and E-SBR is measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

  The content of S-SBR in 100% by weight of styrene butadiene rubber is 20 to 60% by weight, preferably 30 to 50% by weight. When the content of S-SBR is less than 20% by weight, the rubber hardness and the elastic modulus are lowered, and the grip performance is deteriorated. On the other hand, if the S-SBR content exceeds 60% by weight, the rubber hardness and elastic modulus at high temperatures are lowered, and the handling stability and the sustainability of the grip performance are deteriorated. In addition, wear resistance deteriorates.

  E-SBR is an emulsion-polymerized styrene butadiene rubber having a styrene content of 40% by weight or more. The amount of styrene in E-SBR is 40% by weight or more, preferably 40 to 45% by weight. When the amount of styrene in E-SBR is less than 40% by weight, grip performance deteriorates. The amount of styrene in E-SBR is measured by infrared spectroscopic analysis (Hampton method).

  The content of E-SBR in 100% by weight of styrene-butadiene rubber is 80 to 40% by weight, preferably 70 to 50% by weight. When the content of E-SBR is less than 40% by weight, the wear resistance is deteriorated. On the other hand, when the content of E-SBR exceeds 80% by weight, grip performance deteriorates.

The rubber composition for a tire tread of the present invention contains 50 to 120 parts by weight of carbon black having a nitrogen adsorption specific surface area of 100 to 200 m ² / g with respect to 100 parts by weight of styrene butadiene rubber.

The carbon black used in the rubber composition of the present invention, the nitrogen adsorption specific surface area _(N 2 SA) of 100 to 200 m ² / g, preferably from 120~195m ² / g. When N ₂ SA of carbon black is less than 100 m ² / g, grip performance is deteriorated. The _N 2 SA of the carbon black is more than 200m ² / g, the wear resistance is deteriorated. The N ₂ SA of carbon black is determined according to JIS K6217-2.

  The compounding amount of carbon black is 50 to 120 parts by weight, preferably 60 to 110 parts by weight with respect to 100 parts by weight of styrene butadiene rubber. When the blending amount of carbon black is less than 50 parts by weight, rubber hardness, elastic modulus, rubber strength and heat build-up are deteriorated. Moreover, the abrasion resistance in which the compounding amount of carbon black exceeds 120 parts by weight is deteriorated.

  The rubber composition for a tire tread of the present invention can contain other fillers other than carbon black. Examples of other fillers include silica, clay, mica, talc, calcium carbonate, aluminum hydroxide, aluminum oxide, and titanium oxide.

  The rubber composition for a tire tread of the present invention improves grip performance by blending an aromatic modified terpene resin. The compounding amount of the aromatic modified terpene resin is 2 to 20 parts by weight, preferably 4 to 18 parts by weight based on 100 parts by weight of the styrene butadiene rubber. If the blending amount of the aromatic modified terpene resin is less than 2 parts by weight, the grip performance cannot be sufficiently increased. When the blending amount of the aromatic modified terpene resin exceeds 20 parts by weight, the tackiness of the rubber composition increases and the molding processability and handling properties deteriorate, for example, the rubber composition adheres to the molding roll.

  The aromatic modified terpene resin is obtained by polymerizing a terpene and an aromatic compound. Examples of terpenes include α-pinene, β-pinene, dipentene, and limonene. Examples of the aromatic compound include styrene, α-methylstyrene, vinyl toluene, indene and the like. Of these, a styrene-modified terpene resin is preferable as the aromatic-modified terpene resin.

  As the aromatic modified terpene resin, one having a softening point of 80 to 160 ° C, more preferably 85 to 140 ° C is preferably used. If the softening point of the aromatic modified terpene resin is less than 80 ° C., the effect of improving the grip performance cannot be sufficiently obtained. Moreover, when the softening point of aromatic modified terpene resin exceeds 160 degreeC, there exists a tendency for abrasion resistance to deteriorate. In addition, the softening point of aromatic modified terpene resin shall be measured based on JISK6220-1 (ring ball method).

  The rubber composition for a tire tread of the present invention preferably improves the grip performance in a wide temperature range and increases the rubber hardness and rigidity by blending a cyclic polysulfide represented by the following formula (I). The wear resistance of the rubber composition can be further improved.

（式（Ｉ）中、Ｒは置換もしくは非置換の炭素数４〜８のアルキレン基、置換もしくは非置換の炭素数４〜８のオキシアルキレン基、ｘは平均３〜５の数、ｎは１〜５の整数である。）

(In the formula (I), R is a substituted or unsubstituted alkylene group having 4 to 8 carbon atoms, a substituted or unsubstituted oxyalkylene group having 4 to 8 carbon atoms, x is an average number of 3 to 5, and n is 1) It is an integer of ~ 5.)

  In the cyclic polysulfide of the above formula (I), R is an alkylene group or an oxyalkylene group, and the carbon number thereof is preferably 4 to 8, more preferably 4 to 7. Moreover, as a substituent with respect to an alkylene group and an oxyalkylene group, a phenyl group, a benzyl group, a methyl group, an epoxy group, an isocyanate group, a vinyl group, a silyl group etc. can be illustrated, for example. S is sulfur. x is preferably 3 to 5 on average, more preferably 3.5 to 4.5 on average. N is preferably an integer of 1 to 5, more preferably 1 to 4. Such a cyclic polysulfide can be produced by an ordinary method, for example, a production method described in JP-A-2007-92086 can be exemplified.

  In the present invention, the compounding amount of the cyclic polysulfide is 0.2 to 5 parts by weight, preferably 1 to 4 parts by weight, based on 100 parts by weight of the diene rubber. When the blending amount of the cyclic polysulfide is less than 0.2 parts by weight, the effect of maintaining the grip performance for a long time at a high level and the effect of improving the blowout resistance cannot be obtained. Moreover, it cannot fully suppress that the abrasion resistance of a rubber composition falls. In addition, when the compounding quantity of cyclic polysulfide exceeds 5 weight part, workability will deteriorate.

  In the rubber composition for a tire tread of the present invention, the cyclic polysulfide of the above formula (I) acts as a vulcanizing agent. The vulcanizing agent may be a cyclic polysulfide alone, or other vulcanizing agents may be used together. As another vulcanizing agent, sulfur is preferable. The amount of sulfur is 0.1 to 5 parts by weight, preferably 0.5 to 4 parts by weight, based on 100 parts by weight of the diene rubber. When sulfur is added, the weight ratio of cyclic polysulfide to sulfur (cyclic polysulfide / sulfur) is preferably 1/5 to 10/1, more preferably 1/4 to 4/1. By making the weight ratio of (cyclic polysulfide / sulfur) within such a range, the effect of maintaining the grip performance for a long time at a high level and the blowout resistance are improved, and the wear resistance is improved.

  The tire tread rubber composition generally includes a vulcanization or crosslinking agent, a vulcanization accelerator, an anti-aging agent, a plasticizer, a processing aid, a liquid polymer, a thermosetting resin, and the like. Various compounding agents used can be blended. Such a compounding agent can be kneaded by a general method to form a rubber composition, which can be used for vulcanization or crosslinking. The compounding amounts of these compounding agents can be the conventional general compounding amounts as long as they do not contradict the purpose of the present invention. The rubber composition for a tire tread can be produced by mixing each of the above components using a known rubber kneading machine such as a Banbury mixer, a kneader, or a roll.

  The rubber composition for a tire tread of the present invention can be suitably used for a pneumatic tire. The pneumatic tire using the rubber composition in the tread portion can improve the grip performance in a wide temperature range and increase the rubber hardness and rigidity to further improve the wear resistance of the rubber composition.

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

  20 kinds of rubber compositions for tire treads (Examples 1 to 8, Comparative Examples 1 to 12) having the compositions shown in Tables 1 and 2 were added to 1.8 L of components excluding sulfur, a vulcanization accelerator and a cyclic polysulfide. Was prepared by adding sulfur, a vulcanization accelerator and a cyclic polysulfide to a master batch which was kneaded and discharged for 160 minutes using a closed type mixer, and kneaded with an open roll. In Tables 1 to 3, the net compounding amount of each rubber component is shown in parentheses for SBR containing oil-extended oil.

  Twenty kinds of obtained rubber compositions for tire treads were press vulcanized for 160, 20 minutes in a mold having a predetermined shape to prepare a vulcanized rubber sample, and rubber hardness (20 ° C., 100 ° C.), 300% modulus (100 ° C.), dynamic viscoelastic modulus (tan δ at 20 ° C. and 100 ° C.) and wear resistance.

Rubber Hardness The rubber hardness of the obtained test piece was measured at 20 ° C. and 100 ° C. with a durometer type A in accordance with JIS K6253. The obtained results are shown in the columns of “Rubber Hardness (20 ° C.) Hs20” and “Rubber Hardness (100 ° C.) Hs100” in Tables 1 and 2 as indices with the value of Comparative Example 1 as 100, respectively. Further, the ratio of the rubber hardness (100 ° C.) to the rubber hardness (20 ° C.) was calculated and shown in the column of “Hardness ratio Hs100 / Hs20” in Tables 1 to 3 as an index with the value of Comparative Example 1 being 100.

  The larger the rubber hardness (20 ° C.) index, the higher the rubber hardness at 20 ° C., the better the mechanical properties, and the better the steering stability. The larger the index of rubber hardness (100 ° C.), the higher the rubber hardness at 100 ° C., the better the mechanical properties, and the better the steering stability even when the tire is in a high temperature state. Further, the larger the index of the hardness ratio Hs100 / Hs20, the smaller the change in rubber hardness at 20 ° C. and 100 ° C., which means that steering stability can be ensured in a wide temperature range.

300% modulus (100 ° C)
From the obtained test piece, a JIS No. 3 dumbbell-type test piece (thickness 2 mm) was punched out in accordance with JIS K6251 and tested at a temperature of 100 ° C. and a pulling rate of 500 mm / min. 300% modulus (300% deformation stress) ) Was measured. The obtained results are shown in the column of “300% Mod (100 ° C.)” in Tables 1 and 2 as an index with the value of Comparative Example 1 as 100. The larger the index, the greater the rigidity at high temperatures and the better the mechanical characteristics, and the better the steering stability when the pneumatic tire runs at a high speed for a long time.

Dynamic viscoelastic modulus (tan δ at 20 ° C and 100 ° C)
The exothermic property and dry grip performance of the obtained vulcanized rubber samples were evaluated by loss tangent tan δ (20 ° C.) and tan δ (100 ° C.), which are known to be these indicators. Tanδ was measured using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho under the conditions of an initial strain of 10%, an amplitude of ± 2%, a frequency of 20 Hz, a temperature of 20 ° C., and a temperature of 100 ° C. The obtained results are shown in the columns of “tan δ (20 ° C.)” and “tan δ (100 ° C.)” in Tables 1 and 2 as an index with the value of Comparative Example 1 being 100. It means that the larger the index of tan δ (20 ° C.) and tan δ (100 ° C.), the greater the heat generation in both the low temperature range and the high temperature range, and the better the dry grip performance from the low temperature range to the high temperature range.

Abrasion resistance Lambone wear of the obtained vulcanized rubber sample was measured according to JIS K6264-2 using a lambone wear tester manufactured by Iwamoto Seisakusho under the conditions of a temperature of 20 ° C., a load of 15 N, and a slip ratio of 50%. It was measured. The obtained results are shown in the “Abrasion resistance” column of Tables 1 and 2 as an index with Comparative Example 1 as 100. It means that abrasion resistance is excellent, so that this index | exponent is large.

The types of raw materials used in Tables 1 and 2 are shown below.
S-SBR1: Solution-polymerized styrene butadiene rubber, styrene content is 36% by weight, vinyl content is 64% by weight, Mw is 1,470,000, Tg is -13 ° C., oil component is 37.5 parts by weight with respect to 100 parts by weight of rubber component Oil exhibition products including Toughden E680 manufactured by Asahi Kasei Chemicals
S-SBR2: solution polymerized styrene butadiene rubber, styrene content 47% by weight, vinyl content 52% by weight, Mw 660,000, Tg -6 ° C., rubber component 100 parts by weight, oil component 37.5 parts by weight NS462 made by Nippon Zeon Co., Ltd.
S-SBR3: solution polymerized styrene butadiene rubber, styrene content is 37% by weight, vinyl content is 42% by weight, Mw is 1.26 million, Tg is -27 ° C., and the oil content is 37.5 parts by weight with respect to 100 parts by weight of the rubber component. Oil exhibition products including Toughden E581 manufactured by Asahi Kasei Chemicals
S-SBR4: solution polymerized styrene butadiene rubber, styrene content is 41% by weight, vinyl content is 41% by weight, Mw is 1.16 million, Tg is -19 ° C., oil component is 37.5 parts by weight with respect to 100 parts by weight of rubber component Oil exhibition including JHP HP755B
E-SBR1: emulsion-polymerized styrene butadiene rubber, an oil-extended product containing 40% by weight of styrene and 37.5 parts by weight of oil with respect to 100 parts by weight of rubber component, Nipol 1739 manufactured by Nippon Zeon Co., Ltd.
E-SBR2: Emulsion-polymerized styrene butadiene rubber, 23.5% by weight of styrene, an oil exhibition containing 37.5 parts by weight of oil with respect to 100 parts by weight of rubber component, Nipol 1723 manufactured by Nippon Zeon Co., Ltd.
Carbon black 1: Toast carbon company's seast 9, N ₂ SA = 142 m ² / g
Carbon black 2: Dia Black UX10 manufactured by Mitsubishi Chemical Corporation, N ₂ SA = 182 m ² / g
Carbon black 3: Colombian carbon CD2019, N ₂ SA = 340 m ² / g
・ Oil: Extract No. 4 S manufactured by Showa Shell Sekiyu KK
Terpene resin 1: aromatic modified terpene resin having a softening point of 125 ° C., YS resin TO-125 manufactured by Yashara Chemical Co., Ltd.
-Terpene resin 2: Aromatic modified terpene resin having a softening point of 85 ° C, YS resin TO-85 manufactured by Yashara Chemical Co., Ltd.

Cyclic polysulfide 1: In the above formula (I), R = (CH ₂ ) ₂ O (CH ₂ ) ₂ , X (average) = 4, n = 2 to 3 cyclic polysulfide, and preparation of cyclic polysulfide 1 are as follows: I went there.
After adding 1.98 g (0.02 mol) of 1,2-dichloroethane and 1197 g (2 mol) of 30% sodium polysulfide (Na ₂ S ₄ ) aqueous solution to toluene (500 g), further 0.64 g (0 0.1 mol) was added and reacted at 50 ° C. for 2 hours. Subsequently, the reaction temperature was raised to 90 ° C., and a solution prepared by dissolving 311 g (1.8 mol) of dichloroethyl formal in 300 g of toluene was dropped over 1 hour, and the reaction was further continued for 5 hours. After the reaction, the organic layer was separated and concentrated at 90 ° C. under reduced pressure to obtain 405 g of the above-mentioned returned polysulfide (yield 96.9%).

- cyclic polysulfide 2: In the above formula _{(I), R = (CH} 2) 6, X ( average) = 4, n = 1~4 of cyclic polysulfide, preparation of cyclic polysulfide 2 was carried out as follows.
In a three-necked flask equipped with a condenser and a thermometer, 8 g (0.102 mol) of sodium sulfide anhydride, 9.8 g (0.306 mol) of sulfur and 50 g of tetrahydrofuran (THF) were placed in a nitrogen atmosphere at 80 ° C. for 1 hour. Then, a solution of 15.5 g (0.10 mol) of 1,6-dichlorohexane in 20 g of THF was added dropwise at a temperature of 80 ° C. for 2 hours, and further reacted at the same temperature for 2 hours. After completion of the reaction, the salt of the organic phase was filtered off, and the organic phase was concentrated at 90 ° C. under reduced pressure to obtain 20.2 g (yield 95%) as the cyclic polysulfide 2 having the above-described configuration.

・ Stearic acid: NOF beads stearic acid YR
-Zinc flower: Zinc oxide manufactured by Shodo Chemical Industry Co., Ltd.-Sulfur: Fine powdered sulfur with gold flower seal oil manufactured by Tsurumi Chemical Industry Co., Ltd.-Vulcanization accelerator: Vulcanization accelerator CBS, Nouchira CZ-G manufactured by Ouchi Shinsei Chemical Co., Ltd.

  As is clear from Table 2, the rubber compositions for tire treads of Examples 1 to 8 have steering stability in a wide temperature range (rubber hardness (20 ° C.), rubber hardness (100 ° C.), hardness ratio Hs100 / Hs20, and 300% modulus (100 ° C.)), improved dry grip performance (20 ° C. tan δ and 100 ° C. tan δ) in a wide temperature range, and improved wear resistance. Pneumatic tires using this rubber composition in the tread part improve dry grip performance and steering stability in a wide range of temperatures, and further increase the rubber hardness and rigidity to further improve the wear resistance of the rubber composition. can do.

  As is clear from Table 1, the rubber compositions of Comparative Examples 1 and 2 do not contain S-SBR used in the present invention, so that the low temperature range is the same as the rubber compositions described in Examples 1 and 2. To a high temperature range, an excellent balance of rubber hardness, elastic modulus and tan δ cannot be obtained, and wear resistance is not sufficient. In the rubber composition of Comparative Example 3, the S-SBR2 has a styrene content of more than 38% by weight, a vinyl content of less than 60% by weight, and an Mw of less than 1 million. Hs20, 300% modulus (100 ° C.) and wear resistance deteriorate. In the rubber composition of Comparative Example 4, since the vinyl content of S-SBR3 is less than 60% by weight and Tg is lower than −20 ° C., rubber hardness (100 ° C.), hardness ratio Hs100 / Hs20, tan δ (100 ° C.) and resistance Abrasion deteriorates. Since the rubber composition of Comparative Example 5 does not contain the E-SBR used in the present invention, the rubber hardness (100 ° C.), the hardness ratio Hs100 / Hs20, the 300% modulus (100 ° C.), and the wear resistance are deteriorated. To do.

  The rubber composition of Comparative Example 6 has a rubber hardness (100 ° C.), a hardness ratio of Hs100 / Hs20, and tan δ (100 ° C.) because the styrene content of S-SBR4 exceeds 38 wt% and the vinyl content is less than 60 wt%. ) And wear resistance deteriorate. The rubber composition of Comparative Example 7 was blended with S-SBR2 having a styrene content of 40% by weight or more instead of E-SBR used in the present invention, so that the rubber hardness (100 ° C.), the hardness ratio Hs100 / Hs20, 300% modulus (100 ° C.) and wear resistance deteriorate. In the rubber composition of Comparative Example 8, the tan δ (20 ° C. and 100 ° C.) deteriorates because the styrene content of E-SBR2 is less than 40% by weight. In the rubber composition of Comparative Example 9, since the S-SBR content is less than 20% by weight and the E-SBR content is more than 80% by weight, the modulus is deteriorated by 300%. The rubber composition of Comparative Example 10 has an S-SBR content of more than 60% by weight and an E-SBR content of less than 40% by weight. Therefore, the rubber hardness (100 ° C.), the hardness ratio Hs100 / Hs20, and Abrasion resistance deteriorates.

As apparent from Table 2, the N ₂ SA of the carbon black 3 in the rubber composition of Comparative Example 11 exceeds 200 m ² / g, so that the hardness ratio Hs100 / Hs20 and the wear resistance are deteriorated. In the rubber composition of Comparative Example 12, since the compounding amount of the carbon black 1 exceeds 120 parts by weight, the hardness ratio Hs100 / Hs20 and the wear resistance are deteriorated.

Claims (4)

Solution polymerization styrene-butadiene rubber S-SBR and 20 to 60 wt% and emulsion-polymerized styrene-butadiene rubber E-SBR in 100 parts by weight of styrene-butadiene rubber consisting of 80 to 40 wt%, a nitrogen adsorption specific surface area of 100 to 200 m ² / g-carbon black in an amount of 50 to 120 parts by weight, the S-SBR having a styrene content of 30 to 38% by weight, a vinyl content of 60 to 80% by weight, and a glass transition temperature of -20 to- A rubber composition for a tire tread, wherein the rubber composition for tire tread is 5 ° C., has a weight average molecular weight of 1,000,000 to 1,800,000, and the styrene content of the E-SBR is 40% by weight or more.   The rubber composition for a tire tread according to claim 1, wherein 2 to 20 parts by weight of an aromatic modified terpene resin is blended with 100 parts by weight of the styrene butadiene rubber. The rubber composition for a tire tread according to claim 1 or 2, wherein 0.2 to 5 parts by weight of a cyclic polysulfide represented by the following formula (I) is blended with 100 parts by weight of the styrene butadiene rubber.

(In the formula (I), R is a substituted or unsubstituted alkylene group having 4 to 8 carbon atoms, a substituted or unsubstituted oxyalkylene group having 4 to 8 carbon atoms, x is an average number of 3 to 5, and n is 1) It is an integer of ~ 5.)   The pneumatic tire which uses the rubber composition for tire treads in any one of Claims 1-3.