JPH0629284B2 - Rubber composition for tires - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a copolymer having a styrene unit having a specific styrene chain distribution and a specific styrene composition distribution. TECHNICAL FIELD The present invention relates to a rubber composition for a tire, which uses a random styrene-butadiene copolymer as a raw material rubber, which has an excellent balance of the properties (slip resistance on wet road surface) and abrasion resistance.

[Prior Art] Random styrene-butadiene copolymers have been widely used as rubber for tires in recent years, but in recent years, due to social demands for resource saving and energy saving, there is a demand for low fuel consumption of automobiles and safety during traveling. Higher resilience and running safety as rubber for tires in response to the demand for improved tire durability, especially the demand for improved front wheel durability against increasing load on the front wheels due to the front wheel drive of automobiles. It is required to have high wet skid resistance to improve durability and excellent wear resistance to improve durability.

However, since impact resilience and wet skid resistance are contradictory properties, and abrasion resistance and wet skid resistance are also contradictory properties, in order to balance these contradictory properties, conventionally, different types of rubber have been used. Blended compositions have been used. For example, blended compositions of styrene-butadiene copolymer rubber and polybutadiene such as high-cis polybutadiene and low-cis polybutadiene have been mainly used for passenger car tires. However, these blend compositions have not yet achieved high levels of impact resilience, wet skid resistance, and abrasion resistance.

Recently, various methods have been proposed which are intended to improve impact resilience, wet skid resistance and abrasion resistance by controlling the distribution of styrene in the styrene-butadiene copolymer chain. For example, a method of greatly increasing the styrene distribution width at the terminal end in the copolymer chain (Japanese Patent Laid-Open No. 143209/56).
No.), a method for highly homogenizing styrene units in the copolymer chain (JP-A-57-100112, JP-A-57-179212, JP-A-57-179212).
59-140211), a method of blocking two kinds of copolymers having different styrene contents in the same copolymer chain (Japanese Patent Laid-Open No. Sho 57-57).
No. 165445, JP-A-57-200413), and a method for specifying the styrene reaction composition distribution width and the glass transition point peak temperature width in the copolymer (JP-A-58-154711).

[Problems to be Solved by the Invention] However, although these copolymers have some improvement effects, they have not reached a high level of impact resilience, wet skid resistance and abrasion resistance.

The present invention has been made in view of the above points, and a tire rubber composition using a branched random styrene-butadiene copolymer with improved balance of impact resilience, wet skid resistance and abrasion resistance as a raw material rubber. The purpose is to provide.

[Means and Actions for Solving Problems] As a result of extensive studies on the chain distribution and composition distribution of styrene units in the styrene-butadiene copolymer chain, the present invention has revealed that the styrene unit in the copolymer chain is specific. It was made based on the finding that a branched random styrene-butadiene copolymer having a styrene chain distribution and having a specific styrene composition distribution has an excellent balance of impact resilience, wet skid resistance and abrasion resistance. It is a thing.

That is, the present invention copolymerizes styrene and butadiene with an organolithium compound as a polymerization initiator in a hydrocarbon solvent containing at least one Lewis base, and then a polyfunctional cup having at least three reactive sites. A Mooney viscosity (ML _{1 + 4} , 100 ° C.) having a branched structure of three or more branches, which is obtained by adding a ring agent, is 30 to 150, and the ratio _W / of the weight average molecular weight ( _W ) and the number average molecular weight ( _N ) is _W / _N
Is 1.3 to 3.0 and the content of vinyl bond in the butadiene part is 16
Wt% to 48 wt%, bound styrene 10 wt% to
A styrene-butadiene copolymer having 45% by weight and 40% by weight or more of a branched component bonded with a polyfunctional coupling agent, wherein a styrene single chain having one styrene monomer is a fully bonded styrene. A long chain of styrene composed of 8% by weight or more of styrene monomer is a fully bonded styrene.
It is 5.0% by weight or less, and the temperature difference between the inflection points in the glass transition temperature region of the endothermic curve analyzed by the differential scanning calorimeter (DSC) is 15 ° C or more, and the branched random. At least styrene-butadiene copolymer
The present invention relates to a rubber composition for tires, which is obtained by blending 30% by weight of raw material rubber with 5 to 60 parts by weight of process oil for rubber and 30 to 100 parts by weight of carbon black based on 100 parts by weight of the raw material rubber.

The branched random styrene-butadiene copolymer of the present invention and the rubber composition using the copolymer as a raw material rubber exhibit excellent properties and are used for various rubber applications, but are useful for tire tread applications.

The present invention will be described in detail below.

The Mooney viscosity (ML _{1 + 4} , 100 ° C.) of the copolymer of the present invention is 30.
To 150, preferably 50 to 100. If the Mooney viscosity is less than 30, the effects of improving impact resilience and wear resistance are not sufficient. When the Mooney viscosity exceeds 150, problems remain in the processability such as calendering processability and extrusion processability of the compound.

The ratio _W / _N of the weight average molecular weight ( _W ) to the number average molecular weight ( _N ) of the copolymer of the present invention is 1.3 to 3.0, preferably 1.5 to 2.5. _{When W} / _N exceeds 3.0, the workability is improved, but the impact resilience is lowered, which is not preferable. On the other hand, if it is less than 1.3, the workability is deteriorated, which is not preferable. Generally, the styrene-butadiene copolymer obtained by emulsion polymerization has _W / _N of 3.5 or more, and is unsatisfactory in terms of impact resilience. The copolymer of the present invention is an improvement over the drawbacks of the above copolymer.

The vinyl bond content of the butadiene part of the copolymer of the present invention is
16% to 48% by weight, preferably 16% by weight or more and less than 35% by weight. When the vinyl bond content is less than 16% by weight, the abrasion resistance is improved, but the wet skid resistance is lowered, which is not preferable. On the other hand, when the vinyl bond content exceeds 48% by weight, impact resilience and abrasion resistance are deteriorated, which is not preferable.

The bound styrene of the copolymer of the present invention is 10% to 45% by weight, preferably 15% to 40% by weight. If the bound styrene content is less than 10% by weight, wet skid resistance is lowered, which is not preferable. On the other hand, bound styrene is 45% by weight
If it exceeds the range, impact resilience and wear resistance decrease, which is not preferable.

The branched component of the copolymer of the present invention is 40% by weight or more, preferably 50% by weight or more. When the amount of the branched component is less than 40% by weight, the impact resilience is lowered and the workability is further deteriorated, which is not preferable.

The styrene single chain having one styrene unit (hereinafter referred to as S ₁ ) of the copolymer of the present invention is 65% by weight or more, preferably 75% by weight or more of all bonded styrene, and styrene in which 8 or more styrene units are connected. long chain (hereinafter S ₈ referred to as _-) is more than 5.0 wt% of the total bound styrene, preferably should be 2.5 wt% or less. Even if S ₁ is less than 65% by weight of the total bound styrene or S ₈ is more than 5.0% by weight, impact resilience, abrasion resistance and wet skid resistance are deteriorated, which is not preferable.

The temperature difference (hereinafter referred to as ΔT) between the inflection points in the glass transition temperature range of the copolymer of the present invention is 15 ° C or higher, preferably 25 ° C or higher, and particularly preferably 30 to 70 ° C. When ΔT is less than 15 ° C, the distribution width of styrene composition in the copolymer chain is small, and wet skid resistance and abrasion resistance are not sufficiently improved. On the other hand, ΔT has a wider styrene composition distribution width in the copolymer chain as ΔT is higher at 15 ° C. or higher, and has excellent properties and excellent blendability with other rubbers.
When T becomes extremely large, the number of styrene single chains decreases, and the impact resilience decreases, which is not preferable. As described above, the copolymer of the present invention satisfies the specific styrene chain distribution and has a ΔT of
It is necessary to satisfy at least 15 degrees. The temperature difference (△ T) between the inflection points in the glass transition temperature range here is the first change point near the glass transition temperature in the endothermic curve obtained by measurement using a differential scanning calorimeter (DSC). To the final change point. The DSC measurement was carried out by the method shown in ASTM-D3418-82. FIG. 1 shows endothermic curves by DSC of the styrene-butadiene copolymers obtained in Examples and Comparative Examples. As shown in FIG. 1, the present invention includes a copolymer having two or more glass transition temperatures. For example, as shown in (b) of FIG. 1, a copolymer in which two kinds of copolymers having different styrene contents are present in a block in the same copolymer has two glass transition temperatures and ΔT Is relatively large,
Has desirable characteristics.

The copolymer of the present invention is produced by the method described below. One method is to copolymerize styrene and butadiene with an organolithium compound in a hydrocarbon solvent containing at least one Lewis base, as described in JP-A-59-140211. By continuously supplying butadiene so that the Stilley monomer content in the ratio falls within a specific concentration range, a block copolymer having a certain monomer composition ratio is obtained, and then the above copolymer is prepared by the same polymerization method. Two kinds of random block copolymers having different monomer composition ratios in the same copolymer chain by obtaining a block copolymer or a butadiene polymer having different monomer composition ratios and then adding a polyfunctional coupling agent Is a method for obtaining a branched random styrene-butadiene copolymer having Another method is to copolymerize styrene and butadiene with an organolithium compound in a hydrocarbon solvent containing at least one Lewis base so that the styrene monomer content in the monomer composition ratio in the polymerization system falls within a specific concentration range. Is continuously supplied to the polymerization system under specific conditions, and after completion of the copolymerization, a coupling agent having at least 3 reactive sites is added to obtain a branched random styrene-butadiene copolymer. Is. The styrene monomer content in the monomer composition ratio in the polymerization system exceeds the double amount of the bound styrene of the copolymer finally prepared, which is prepared by the total amount of styrene and a part of butadiene before the start of the copolymerization, The content is 92% by weight or less, which is lower than the content of the styrene monomer after the start of the copolymerization until the end of the supply of the remaining butadiene, and at the end of the end of the supply of the remaining butadiene, the content of the bound styrene or less of the copolymer. The balance butadiene is preferably supplied at the same time when the copolymerization starts, and the supply must be completed after the polymerization conversion rate of the copolymer reaches 92% by weight. The balance butadiene is preferably supplied so that the styrene monomer content in the monomer composition ratio in the polymerization system decreases as the copolymerization progresses.

Examples of the organolithium compound used in the present invention include n-
Monoorganolithium compounds such as propyllithium, isopropyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium, dilithiomethane, 1,4
-Dilithiobutane, 1,4-dilithio-2-ethylcyclohexane, 1,2-dilithio-1,2-diphenylmethane, 1,3,5
-A polyfunctional organolithium compound such as trilithiobenzene, which is used alone or as a mixture of two or more kinds.

Further, as the polyfunctional organolithium compound used in the present invention, a compound which can be substantially a polyfunctional organolithium compound by reacting the above monoorganolithium compound with another compound is also used. For example, a reaction product of a monoorganolithium compound and a polyvinylaromatic compound (Japanese Patent Publication No. 55-6652), a monoorganolithium compound and a conjugated diene, and / or a monovinylaromatic compound are reacted, and then a polyvinylaromatic compound Or a reaction product obtained by simultaneously reacting a monoorganolithium compound, a conjugated diene, and / or a monovinylaromatic compound, and a polyvinyl compound (West German Patent 2003384).

Aliphatic, alicyclic, and aromatic hydrocarbons can be used as the hydrocarbon solvent used in the present invention. For example, hydrocarbon solvents include propane, isobutane,
Examples of the solvent include n-hexane, isooctane, cyclopentane, cyclohexane, benzene, and toluene, and particularly preferable solvents are n-hexane, cyclohexane, and benzene. These may be used alone or as a mixture of two or more.

As the Lewis base used in the present invention, diethyl ether, ethylene glycol dimethyl ether,
Ethylene glycol di-n-butyl ether, ethylene glycol n-butyl tert-butyl ether, ethylene glycol di-tert-butyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetrahydrofuran, α-
Methoxymethyltetrahydrofuran, dioxane, 1,2
-Dimethoxybenzene, triethylamine, N, N, N ',
N ',-tetramethylethylenediamine, potassium-t
Examples include ert-amyl oxide and the like. These compounds are used alone or as a mixture of two or more kinds.

The polyfunctional coupling agent used in the present invention, epoxidized soybean oil, epoxidized linseed oil, epoxidized liquid polybutadiene, dimethyl terephthalate, diethyl terephthalate, dimethyl phthalate, dimethyl isophthalate, diethyl adipate, Terephthalic acid dichloride, phthalic acid dichloride, isophthalic acid dichloride, adipic acid dichloride, phthalic anhydride, maleic anhydride, silicon tetrachloride, methyltrichlorosilane,
Hexachlorosilane, tetramethoxysilane, carbon tetrachloride, stannic chloride, methyltrichlorotin, stannic bromide, dodecyltrichlorotin and the like can be mentioned. Of these, particularly preferred are silicon tetrachloride and stannic chloride. When the stannic chloride-coupled copolymer is kneaded with carbon black, process oil, etc., the amount of carbon gel increases, and the vulcanized product exhibits excellent impact resilience. On the other hand, copolymers coupled with silicon tetrachloride show excellent processability, especially excellent extrusion properties. Therefore, in order to obtain a copolymer having more excellent processability, it is preferable to use silicon tetrachloride as the coupling agent.

The method of adding these polyfunctional coupling agents is not particularly limited, but the polyfunctional coupling agents are usually added after the copolymerization of styrene and butadiene is completed.
Alternatively, after the copolymerization is completed, a small amount of butadiene may be added and then the polyfunctional coupling agent may be added.

The polymerization temperature in the present invention is in the range of 20 to 130 ° C. In the batch polymerization method, it is recommended to start the polymerization at 36 to 87 ° C, and to perform the polymerization at an elevated temperature so that the maximum temperature reaches 90 to 125 ° C.

The copolymer of the present invention may be used as an oil-extended rubber by mixing it with a process oil in a solution state, removing the solvent after mixing.

The copolymer of the present invention is used alone or blended with other synthetic rubbers or natural rubbers, and as a raw material rubber for various rubber applications, 5 to 60 parts by weight of process oil is added to 100 parts by weight of the raw material rubber.
It can be used by blending 30 to 100 parts by weight of carbon black. In this case, at least 30% by weight of the raw rubber needs to be the copolymer of the present invention in order to exhibit the excellent properties of the present invention. Further, other synthetic rubber or natural rubber used as a blend is preferably emulsion-polymerized styrene-butadiene copolymer, cis-1,4 polybutadiene, 1,2 syndiopolybutadiene, 1,2 vinyl bond content of 10% to 90%. % Polybutadiene rubber, polyisoprene or natural rubber, and one or more of them can be used.

Process oils used for rubber compounding consist of high boiling point components of petroleum fractions and are usually classified into three types according to the chemical structure of the hydrocarbon molecules of the oil. The criteria for classification are the viscosity specific gravity constant (abbreviated as VGC). Depending on the size. VGC is generally 0.790 to 0.849
Those of 0.850 to 0.899 are classified as paraffinic, those of 0.850 to 0.899 are classified as naphthenic, and those of 0.900 or more are classified as aromatic. Among them, since the copolymer of the present invention is used by blending carbon black, an aromatic type is generally used as a process oil, and an aromatic type having VGC of 0.930 or more is particularly preferable.

The amount of the process oil used in the present invention is 100
It is 5 to 60 parts by weight, preferably 5 to 35 parts by weight, based on parts by weight. If the process oil is less than 5 parts by weight, the dispersion of other compounding agents such as carbon black and a vulcanization accelerator is not good, and conversely
If it exceeds 60 parts by weight, the physical properties of the obtained vulcanizate will be poor.

Carbon black used in the present invention is FEF, HAF, ISAF
Etc., which are usually used,
30 to 100 parts by weight, preferably 100 parts by weight of the raw rubber,
40 to 75 parts by weight. If it is less than 30 parts by weight, the reinforcing effect is not sufficient, while if it exceeds 100 parts by weight, impact resilience, breaking strength and the like decrease.

The copolymer of the present invention, in addition to the above-mentioned carbon black and process oil for rubber, may further contain other reinforcing agents and fillers such as white carbon, calcium carbonate and magnesium carbonate, and zinc oxide, Stearic acid, antioxidants, antiozonants, vulcanization accelerators, vulcanizing agents, waxes and the like can be selected and blended as necessary.

The mixing of any of the above-mentioned compounding agents is carried out by a usual means such as Banbury, kneader or open roll.

The rubber composition of the present invention thus obtained can be used for many useful applications, for example, tire applications such as tire treads, carcasses, sidewalls, etc., after the vulcanization step.

[Examples] The present invention is described below with reference to examples, but these examples do not limit the present invention. The various properties were measured by the following methods.

The styrene chain distribution of the styrene-butadiene copolymer is
It is analyzed by the method recently developed by Tanaka et al. Specifically, the styrene chain distribution is analyzed by gel permeation chromatogram (GPC) of the decomposition product obtained by ozone cleavage of all double bonds of butadiene unit (Proceedings of the Polymer Society of Japan, Vol. 29, No. 9, No. 2055). ).

Temperature difference between inflection points in the glass transition temperature range of the copolymer (△
T) is a DSC (trade name: SSC58) manufactured by Seiko Instruments Inc.
The temperature range from the first change point near the glass transition temperature to the final change point in the endothermic curve obtained by measurement using (0). The measurement conditions were in accordance with ASTM-D3418-82.
Ratio of weight average molecular weight ( _W ) and number average molecular weight ( _N )
_W / _N is GPC (trade name: 204 compact type) manufactured by Water Co., and the weight average molecular weight ( _W ) and the number average molecular weight ( _N ) in terms of polystyrene are calculated from the GPC curve obtained by using tetrahydrofuran as a mobile phase. Calculated by asking. For the styrene monomer content and the polymerization conversion rate in the monomer composition in the weight system, the monomer conversion rate obtained by analyzing the sample extracted from the polymerization vessel using Shimadzu gas chromatography (trade name: GC7A) is used. Calculated. The branched component was obtained from the area ratio on the GPC chart.

The Mooney viscosity is 10 using the L rotor in the usual way.
It was measured at 0 ° C. The bound styrene was calculated from the absorption based on the phenyl group at 262 nm by the ultraviolet absorption spectrum method. The microstructure of the butadiene part was calculated by the Hampton method using an infrared spectrophotometer. The hardness, tensile strength, 300% modulus and elongation of the vulcanizate were measured according to JIS K6301. The impact resilience was measured using a Dunlop trypsometer at a test temperature of 70 ° C. Abrasion resistance was measured using a pico abrasion tester. Wet skid resistance was measured with a British Road Research Laboratory apparatus.

Examples 1, Comparative Examples 1 and 2 In a nitrogen atmosphere, in a polymerization vessel with a stirrer made of stainless steel and having an internal volume of about 10, a predetermined amount of cyclohexane, tetrahydrofuran, styrene (hereinafter referred to as first styrene) was used. 1,3-butadiene (hereinafter referred to as the first butadiene) was charged, and the temperature of the mixture was adjusted to about 74 ° C. while vigorously stirring the mixture in the polymerization vessel. Then, after the copolymerization was started by adding a predetermined amount of n-butyllithium, as shown in Table 1, 1,3-butadiene (hereinafter, referred to as first-additionally added) was continuously added to the polymerization system by a metering pump. Feeding was started at a constant rate. After the supply of the additionally added first butadiene was completed and the polymerization temperature reached the maximum temperature and the copolymerization was completed, a predetermined amount of stannic chloride was added and the reaction was carried out for about 10 minutes. To the copolymer solution thus obtained, 5 g of 2,6-di-tert-butyl-4-methylphenol was added as a stabilizer, and the solvent was removed by heating to obtain a copolymer. However, in Comparative Example 2, 0.17 g of 1,2-butadiene was added to the polymerization system. The content of styrene monomer in the monomer composition in the polymerization system was always about 66% by weight or less, and was about 18% by weight at the end of the supply of the additional primary butadiene. The polymerization conversion rate at the end of supply was about 95% by weight. Polymerization conditions and basic properties of the obtained copolymer are shown in Tables 1 and 3. The DSC of the copolymer obtained in Example 1 was measured by DSC, and the temperature difference between the inflection points in the glass transition temperature range and the DSC.
The endothermic curve is shown as (a) in FIG. Further, the unvulcanized rubber composition obtained by kneading and mixing these copolymers with a small pressure kneader according to the compounding method of Table 2 was vulcanized at 145 ° C. and physical properties were evaluated. The measurement results are shown in Table-3.

Example 2 In the same manner as in Example 1, except that 0.38 of primary butadiene was used.
to 0.30 kg of the first butadiene added additionally, and the start time of the addition of the first butadiene added was defined as the time when the polymerization conversion of the finally obtained copolymer reached about 50% by weight. The feed rate of the additional primary butadiene added is 0.03
Copolymerization was carried out under the polymerization conditions shown in Table 1 while changing to 75 kg / min. The polymerization conditions, basic properties and vulcanizate properties of the obtained copolymer are shown in Tables 1 and 3.

Examples 3 and 4 In the polymerization vessel used in Example 1, as shown in Table 1, a predetermined amount of cyclohexane, tetrahydrofuran, primary styrene,
Primary butadiene was charged and the temperature of this mixture was adjusted to about 79 ° C. while vigorously stirring the mixture in the polymerization vessel. Then, after the copolymerization was started by adding a predetermined amount of n-butyllithium, a predetermined amount of the additionally added first butadiene was continuously supplied to the polymerization system at a constant rate by a metering pump. After the supply of the additionally added first butadiene is completed and the copolymerization is completed, a predetermined amount of styrene (hereinafter referred to as second styrene) and 1,3-butadiene (hereinafter referred to as second butadiene) are added, and then a predetermined amount of styrene is added. 1,3-Butadiene (hereinafter referred to as additional secondary butadiene) was continuously fed to the polymerization system at a constant rate by a metering pump. After the supply of the additional secondary butadiene was completed and the copolymerization was completed, a predetermined amount of stannic chloride was added to the mixture to give about 10
Let react for minutes. As a stabilizer to the copolymer solution thus obtained, 5 g of 2,6-di-tert-butyl-4-methylphenol was added, and the solvent was removed by heating to obtain a branched random block copolymer. . However, in Example 4, the secondary styrene and the additional secondary butadiene were not added, and the total amount of styrene was added to the polymerization vessel before the addition of n-butyllithium. The polymerization conditions, basic properties and vulcanizate properties of the obtained copolymer are shown in Tables 1 and 3. The temperature difference between the inflection points in the glass transition temperature region and the DSC endothermic curve of the copolymer obtained in Example 4 by DSC measurement are shown as (b) in FIG.

Comparative Example 3 In the same manner as in Example 3, but without the additional addition of the first and second butadienes, and potassium-tert-
Butyl alkoxide (KTB) 0.056 g was newly added to the polymerization system and copolymerization was carried out under the polymerization conditions shown in Table 1 to obtain a branched random block copolymer. The polymerization conditions, basic properties and vulcanizate properties of the obtained copolymer are shown in Table-1 and Table-3.
Shown in.

Comparative Example 4 In the same manner as in Example 1, except that 0.38 of primary butadiene was used.
In addition to 0.30 kg, the addition of the first butadiene added was changed to 0.30 kg, and the addition of the first added butadiene was started at the time when the polymerization conversion of the finally obtained copolymer reached about 15% by weight. Supply rate of primary butadiene is 0.042kg
/ Min, and copolymerization was carried out under the polymerization conditions shown in Table-1. The polymerization conditions, basic properties and vulcanizate properties of the obtained copolymer are shown in Tables 1 and 3. The temperature difference between the inflection points in the glass transition temperature range and the DSC endothermic curve are shown as (c) in FIG.

Comparative Example 5 In the polymerization vessel used in Example 1, as shown in Table 1, a predetermined amount of cyclohexane, tetrahydrofuran, styrene, 1,3
-Butadiene was charged, the temperature in this mixture was adjusted to about 73 ° C while vigorously stirring the mixture in the polymerization vessel, and then a predetermined amount of n-butylithium was added to initiate copolymerization.
After the polymerization temperature reached the maximum temperature and the copolymerization was completed, a predetermined amount of stannic chloride was added and reacted for about 10 minutes, and the copolymer solution thus obtained was treated with di-tert.
5 g of -butyl-4-methylphenol was added and the solvent was removed by heating to obtain a copolymer. The polymerization conditions, basic properties and vulcanizate properties of the obtained copolymer are shown in Tables 1 and 3.

As can be seen from Table-3, Examples 1 to 4 have an excellent balance of impact resilience, wet skid resistance and abrasion resistance.

Examples 5 to 9 and Comparative Examples 6 to 9 In the same manner as in Example 1, except that the stannic chloride was changed to tetrachlorosilane, the copolymerization was carried out under the polymerization conditions shown in Table 4 to obtain a te copolymer. Got The styrene monomer content in the monomer composition ratio in each polymerization system in the above-mentioned various copolymerization systems is lower than the styrene monomer content before the start of the polymerization during the additional addition of the first butadiene, and the final styrene monomer content at the end of the supply. It was below the bound styrene of the copolymer obtained. The polymerization conversion rate at the end of the supply of the additionally added first butadiene was 92% by weight or more. Polymerization conditions, basic properties and vulcanizate properties of the copolymer obtained in the above manner are shown in Table-4 and Table-5.

As can be seen from Table-5, Examples 5 to 9 have an excellent balance of impact resilience, wet skid resistance and abrasion resistance. On the other hand, Comparative Examples 6 and 8 are excellent in impact resilience and wear resistance, but inferior in wet skid resistance. Comparative Example 7,
No. 9 is excellent in wet skid, but inferior in abrasion resistance.

[Effects of the Invention] The branched random styrene-butadiene copolymer according to the present invention has a styrene unit in the copolymer chain having a specific styrene chain unit and has a specific styrene composition distribution. The rubber composition containing a copolymer has excellent balance of impact resilience, wet skid resistance and abrasion resistance, and can be used for tire applications such as tire tread, carcass, and sidewall, and its industrial significance is large.

[Brief description of drawings]

FIG. 1 shows endothermic curves by DSC measurement of the copolymers obtained in each Example and Comparative Example. ΔT in FIG. 1 represents the temperature difference between the inflection points in the glass transition temperature range, (a) in Example 1, (b) in Example 4, and (c) in Comparative Example 4. The DSC endothermic curve of the obtained copolymer is shown.

Claims (1)

[Claims] 1. A multifunctional cup having styrene and butadiene copolymerized with an organolithium compound as a polymerization initiator in a hydrocarbon solvent containing at least one Lewis base, and then having at least three reactive sites. A Mooney viscosity (ML _{1 + 4} , 100 ° C.) having a branched structure of three or more branches, which is obtained by adding a ring agent, is 30 to 150, and the ratio _W / of the weight average molecular weight ( _W ) and the number average molecular weight ( _N ) is _W / _N is 1.
3 to 3.0, the content of vinyl bond in the butadiene part is 16% by weight
A styrene-butadiene copolymer having a content of styrene monomer of 1 to 48% by weight, bound styrene of 10% to 45% by weight, and a branched component bonded by a multifunctional coupling agent of 40% by weight or more. Single styrene single chain is 65% by weight or more of total bound styrene, long chain of styrene composed of 8 or more styrene monomers is 5.0% by weight or less of fully bound styrene, and is analyzed by differential scanning calorimeter (DSC). A raw material rubber containing at least 30% by weight of a branched random styrene-butadiene copolymer, characterized in that the temperature difference between the inflection points in the glass transition temperature region of the endothermic curve is 15 ° C. or more. 5 to 60 parts by weight of process oil for rubber, 30 to carbon black for 100 parts by weight
A tire rubber composition containing 100 parts by weight.