JPH0676516B2 - Rubber composition for tire tread - Google Patents

Description

TECHNICAL FIELD The present invention relates to a composition of a styrene-butadiene copolymer produced by using an organolithium catalyst, which is suitable for a tread of a fuel-efficient tire.

[Conventional technology]

In recent years, due to the soaring price of crude oil, energy conservation has been advocated in various fields of industry, and many attempts have been made to reduce gasoline consumption in automobiles as well, improvements in engines, weight reduction of car bodies and tires, Air resistance of vehicle bodies and rolling resistance of tires have been reduced.

Among the energy-saving efforts associated with these cars,
Various attempts have been made to reduce the rolling resistance of automobile tires, including, for example, a method of improving the tire structure and an improvement of vulcanized rubber used in the tire tread.

Among the attempts to reduce the rolling resistance of these tires, as a method for improving the vulcanized rubber, that is, a method for reducing the energy loss of the vulcanized rubber to improve the impact resilience or heat generation, Methods for improving the raw rubber generated in rubber, changing the type of carbon black, and reducing the amount of carbon black or oil used in vulcanized rubber to achieve high impact resilience have been studied.

Among the above-mentioned methods of improvement, as a method for improving the raw material rubber, from the knowledge about the physical properties of the raw material rubber and the physical properties of the vulcanized rubber up to now, by using a polymer having a higher molecular weight than before, the impact resilience is improved. Although the above-mentioned improvement can be made, it cannot be greatly improved because the Mooney viscosity of the rubber and the compound increases and the processability decreases. On the other hand, change the recipe
Even in the method of reducing the blending amount of oil and carbon black, the Mooney viscosity of the blend is increased, and in this case, the processability is deteriorated. In any method, it is difficult to improve without sacrificing the processability. .

By the way, in recent years, it has been found that a random styrene-butadiene copolymer rubber having a large number of vinyl bonds and having a branched structure can be suitably used for tire applications, rubbers having various structures have been studied, and various proposals have been made. For example, when a styrene-butadiene copolymer rubber with a high vinyl content is tin-coupled to form a branched styrene-butadiene copolymer rubber, rolling resistance is improved by adding butadiene immediately before the coupling reaction and polymerizing. Method has been proposed (JP-A-57-87407, JP-A-58-16260).
Five). However, even with this method, the rolling resistance cannot be said to be sufficiently improved, and there is a problem that the manufacturing method becomes complicated.

Further, a completely random styrene produced by continuously introducing a monomer into a polymerization zone having a high stirring efficiency controlled at a temperature of 80 ° C. or higher by a catalyst composed of an organolithium compound and a Lewis base, and allowing the polymerization to proceed. A butadiene copolymer rubber has been proposed (JP-A-57-100112).
This polymer exhibited excellent properties such as tensile strength, impact resilience, low heat buildup, abrasion resistance, and wet skid resistance.
However, the impact resilience and the low heat buildup have to be further improved.

In addition to this, various methods for introducing functional groups into the ends of the living polymer have been proposed as methods for improving the raw material rubber. For example, there is a method in which a living polymer is produced using a bifunctional anion initiator, and then organic sulfenyl chloride is allowed to act to introduce active groups into both ends of the molecule (Japanese Patent Publication No. 44-855). However, in this method, there is a problem in industrial use that a polymer having a high molecular weight and living ends at both ends is difficult to obtain, and organic sulfenyl chloride is difficult to handle, and the obtained polymer also has tensile strength and modulus. It was inadequate. There is also a method of introducing an amino group at the terminal (JP-A-59-38209, JP-A-58-162604, JP-A-60-137913, JP-A-60-137914) impact resilience, low heat buildup, wear resistance Improvement in wettability and wet skid properties was insufficient.

[Problems to be solved by the invention]

Therefore, the present inventors have proposed a styrene-butadiene copolymer rubber composition having excellent performances such as wet skid property, workability and the like, tensile strength, impact resilience, low heat buildup, and abrasion resistance. As a result of intensive studies for development, a specific styrene-butadiene copolymer rubber composition was invented.

[Means and Actions for Solving Problems]

That is, the present invention, styrene and butadiene are copolymerized in a hydrocarbon solvent using an organolithium catalyst, the amount of bound styrene is 5 to 45% by weight, the vinyl bond of the butadiene portion is 10 to 70%, and the weight average by GPC. The molecular weight distribution (Mw / Mn) represented by the ratio of molecular weight (Mw) and number average molecular weight (Mn) is
Raw rubber containing at least 10% by weight of a polymer having a Mooney viscosity of 20 to 150 in which a C = S bond is introduced into the molecule by reacting a living polymer of 1.2 to 3 with carbon disulfide, a xanthogen compound, and a dithioacid compound. It is a rubber composition suitable for a tire tread obtained by blending 10 to 100 parts by weight of carbon black, 0.3 to 5 parts by weight of sulfur and a vulcanization accelerator with respect to 100 parts by weight.

Hereinafter, the present invention will be described in detail.

The organolithium catalyst used in the present invention is a hydrocarbon having at least one or more lithium atoms bonded thereto, such as ethyllithium, propyllithium and n-.
There are butyllithium, sec-butyllithium, tert-bityllithium, phenyllithium, propenyllithium, hexyllithium, 1,4-dilithio-n-butane, etc., and n-butyllithium and sec-butyllithium are particularly preferable. This organolithium catalyst can be used not only as one kind but also as a mixture of two or more kinds. The amount of the organolithium catalyst used depends on the Mooney viscosity of the produced polymer,
Normally, 0.3 to 3 millimoles per 100 g of monomer, 0.5 as a rule
~ 1.5 mmol.

As the hydrocarbon solvent used in the present invention, n-butane, n-pentane, iso-pentane, n-hexane,
It is n-heptane, iso-octane, cyclohexane, methylcyclopentane, benzene, toluene and the like, and particularly preferable solvents are n-hexane, n-heptane and cyclohexane. This hydrocarbon solvent may be used alone or in combination of two or more kinds, and it is usually used in an amount of 1 to 20 parts by weight per 1 part by weight of the monomer.

The bound styrene content of the styrene-butadiene copolymer rubber of the present invention is 5 to 45% by weight. If it is less than 5% by weight, the tensile strength of the vulcanized rubber is inferior, and if it exceeds 45% by weight, heat generation increases and the performance deteriorates. A particularly preferred range is 10 to 35% by weight.

The vinyl bond of the butadiene portion of the styrene-butadiene copolymer rubber of the present invention is 10 to 70%, preferably 15 to 50%. Small vinyl bonds have low wet skid resistance, while high vinyl bonds have low abrasion resistance. It is particularly preferably in the range of 20-40%.

The molecular weight distribution of the styrene-butadiene copolymer rubber of the present invention is calculated by using a calibration curve of standard polystyrene using GPC, and the molecular weight distribution is represented by the ratio of the weight average molecular weight (Mw) and the number average molecular weight (Mn). Size (Mw / Mn) is 1.2 to 3
And preferably 1.5 to 2.5. If the molecular weight distribution is small, the processability is poor, and if the molecular weight distribution is large, the impact resilience and low heat buildup are poor. The molecular weight distribution by GPC may be one or two. Usually, a linear or branched coupling polymer is prepared by using a coupling agent such as silicon tetrachloride, alkyl trichloride, dialkyl silicon chloride or tin chloride, which is used for improving processability. Any method may be used.

The styrene-butadiene copolymer rubber of the present invention is preferably a random copolymer. The styrene chain distribution of styrene-butadiene copolymer rubber is
Analyzed by GPC. This method was developed by Tanaka et al., And the styrene chain distribution is the GPC obtained by decomposing all butadiene double bonds by ozone cleavage.
Analyzed by (Macromolecules, 1983,16,192
Five). The copolymer rubber of the present invention is an isolated styrene analyzed by this method, that is, styrene having a chain of 1 styrene unit is preferably 40% by weight or more, more preferably 50% by weight or more of the total bound styrene, and long chain block. Styrene, that is, styrene having a chain of 8 or more styrene units, is preferably 5% by weight or less, more preferably 2.5% by weight or less, of the total bound styrene. Whether the isolated styrene is less than 40% by weight or the long-chain block styrene is more than 5% by weight, excellent properties of the copolymer rubber of the present invention are high impact resilience, low heat buildup and high wettability. The skid resistance balance is unfavorably lowered.

The reactive compound to react with the living polymer of the styrene-butadiene copolymer of the present invention, carbon dioxide,
A xanthogen compound and a dithio acid compound. Here, the xanthogen compound has the general formula A compound having, xanthogenic acid, ethylxanthogenic acid, n-propylxanthogenic acid, isopropylxanthogenic acid, n-butylxanthogenic acid, se
Alkylxanthogenic acids such as c-butylxanthogenic acid, n-hexylxanthogenic acid and n-octylxanthogenic acid, phenylxanthogenic acid, allylxanthogenic acids such as p-tolylxanthic acid and lithium, sodium, potassium salts of these xanthogenic acids and Dimethyl xanthogen disulfide, diethyl xanthogen disulfide, di-n-propyl xanthogen disulfide, diisopropyl xanthogen disulfide, di-n-butyl xanthogen disulfide, di-se
Xanthogen disulfides such as c-butylxanthogen disulfide, di-n-hexylxanthogen disulfide, diphenylxanthogen disulfide and di-p-tolylxanthogen disulfide are preferably used. Of these, xanthogen disulfides such as dimethylxanthogen disulfide, diisopropylxanthogen disulfide, di-n-hexylxanthogen disulfide, and diphenylxanthogen disulfide are particularly preferable. The dithio acid compound has a general formula And a carbothioic acid such as dithioformic acid, dithioacetic acid, ethanecarbodithioic acid, isobutanecarbodithioic acid, and isopentanecarbodithioic acid, and their lithium, sodium, potassium salts, and thioacyl sulfide derived from these. Also, dithioesters such as methyl dithioacetate, ethyl dithioacetate, and butyl ethanecarbodithioate are preferably used. Of these, particularly preferable are dithioesters such as methyl dithioacetate, ethyl dithioacetate and butyl ethanecarbodithioate.

These compounds are based on 1 mol of the living polymer,
It is fed at a rate of 0.3 to 10 mol, preferably 0.5 to 5
It is a molar ratio. The ratio is more preferably 1 to 3 mol. When the feed amount is small, it acts only as a coupling agent for the living polymer, resulting in an abnormal increase in viscosity and a decrease in processability. On the other hand, if the feed amount is large, it is unreacted and unfavorable because of the influence of generation of odor and shortening of vulcanization time. The reaction between living polymers and these compounds is very rapid, and the reaction temperature is generally room temperature to 120 ° C.
The reaction time is from 0 ° C to several seconds to several hours.

An antioxidant is usually added to a polymer obtained by reacting these compounds with a living polymer to introduce a C = S bond in the molecule, and if necessary, oil-extended, and the solvent is removed by a usual method.

The Mooney viscosity of the styrene-butadiene copolymer rubber having C = S bond introduced in the molecule used in the present invention is It is 20 to 150, preferably 25 to 130. If the Mooney viscosity is lower than this, the tensile strength, abrasion resistance, impact resilience and low heat buildup of the vulcanized rubber will be inferior. The vulcanized rubber is inferior in performance due to the occurrence of carbon particles or poor carbon dispersion.

The styrene-butadiene copolymer rubber having C = S bond introduced into the molecule used in the present invention is used as a raw material rubber alone or blended with other synthetic rubber or natural rubber. In this case, in order to exhibit the excellent characteristics of the present invention, at least 10% by weight of the raw rubber must be a styrene-butadiene copolymer rubber having C = S bonds introduced into the molecule of the present invention. It is preferably 30% by weight or more.

Other synthetic rubbers or natural rubbers used as a blend include emulsion-polymerized styrene-butadiene copolymer rubber, 1,2 vinyl 35% or less solution-polymerized styrene-butadiene copolymer rubber, cis-1,4 polybutadiene rubber, Examples thereof include 1,2 syndiopolybutadiene rubber, 1,2-vinyl 10 to 90% polybutadiene rubber, synthetic polyisoprene rubber, and natural rubber, and one or more of these can be used.

The amount of carbon black used in the present invention depends on the raw rubber.
Carbon black is used in an amount of 10 to 100 parts by weight based on 100 parts by weight. If it is less than 10 parts by weight, tensile strength, abrasion resistance, etc. are not sufficient, and if it exceeds 100 parts by weight, the rubber elasticity is remarkably lowered, which is not preferable. It is preferably 20 to 80 parts by weight.

The types of carbon black used in the present invention are
Preferably, carbon black having an iodine adsorption amount (IA) of 60 mg / g or more and a dibutyl phthalate oil absorption amount (DBP) of 80 ml / 100 g or more is used. Such a carbon black is a small particle size, high structure carbon black,
Other than that, the high tensile strength, high impact resilience, and high wear resistance of the present invention may not be obtained.
A carbon black having an IA of 80 mg / g or more and a DBP of 100 ml / 100 g or more is preferable. Examples of these carbon blacks include those called HAF, ISAF, and SAF.

In the present invention, 0.3 to 5 parts by weight of sulfur is used as a vulcanizing agent with respect to 100 parts by weight of raw material rubber. When the amount of sulfur is small, tensile strength, impact resilience, and belt wear resistance are insufficient, and when it is too large, rubber elasticity is reduced. It is preferably 0.5 to 2.5 parts by weight.

In the present invention, various conventionally known vulcanization accelerators are used as the vulcanization accelerator, but thiazole vulcanization accelerators are preferably used. What is a thiazole vulcanization accelerator? It is a vulcanization accelerator having a basic structure of (R = alkyl, arylene) group. While these vulcanization accelerators provide the excellent tensile strength, impact resilience, and abrasion resistance of the present invention, other vulcanization accelerators may not provide adequate vulcanization. As these accelerators, a vulcanization accelerator M (2-mercaptobenzothiazole), a vulcanization accelerator DM (dibenzothiazyl disulfide), and a vulcanization accelerator CZ (N-cyclohexyl-2-benzo) are preferable. Thiazyl sulfenamide).

The amount of vulcanization accelerator used is preferably 0.2 to 3 parts by weight per 100 parts by weight of rubber.

In the composition of the present invention, those commonly used as a process oil for compounding rubber are used depending on the purpose and application. Depending on its chemical structure, it is classified into paraffinic, naphthenic and aromatic types. Aromatic type is used for applications where tensile strength and wear resistance are important, and naphthene to paraffin type is used for applications where emphasis is placed on impact resilience and low temperature properties. Is preferably used. The amount is 100
5 to 100 parts by weight is preferable with respect to parts by weight. If it is less than 5 parts by weight, the workability is poor and the dispersion of carbon black is poor, so that the performance such as tensile strength and elongation is not expressed.
If it exceeds the weight part, the tensile strength, the impact resilience and the hardness are remarkably lowered, which is not preferable.

The composition of the copolymer rubber of the present invention, when used, further
Other fillers than carbon black, zinc oxide, stearic acid, antioxidants, antiozonants, if necessary,
Wax or the like can be added.

As fillers other than carbon black, silicic acid,
Silicate, calcium carbonate, titanium oxide, various clays, etc. are used.

The composition of the copolymerized rubber of the present invention is obtained by kneading the above-mentioned components by various known methods using a known mixer for the rubber industry, such as an open roll and an internal mixer. The rubber product obtained through the vulcanization process exhibits excellent performance as compared with the rubber products obtained from conventionally known rubber compositions. Above all, it exhibits particularly high impact resilience, low heat build-up, tensile strength, and wet skid properties. Therefore, it is used for applications in which ordinary styrene-butadiene copolymer rubber compositions are used, and is particularly preferably used for tire treads.

〔Example〕

The present invention will be specifically described below with reference to some examples, but the present invention is not limited to these examples. In the following Examples and Comparative Examples, "parts" means "parts by weight" unless otherwise specified.

Example 1 A stainless steel stirrer with an internal volume of 10 and two reactors with jackets were connected in series, 1,3-butadiene and styrene (75/25 weight ratio) as monomers, and n-hexane as a solvent. , N-butyllithium as a catalyst per 100 g of monomer
Ethylene glycol dibutyl ether as a vinylating agent at a rate of 0.06 g (phm) at 0.60 phm, as an allene compound
Continuous copolymerization was carried out using 0.03 mol of 1,2-butadiene per mol of the catalyst. The internal temperature of the first unit was controlled so as to be 100 ° C., and the monomers and the like were supplied by a metering pump so that the average residence time was 45 minutes. The polymerization rate at the outlet of the first unit was measured by gas chromatography,
A butadiene polymerization rate of 97% and a styrene polymerization rate of 95% were obtained. Measure the Mooney viscosity with a Mooney viscometer, Got 41.

Further, the polymer solution was continuously introduced into the second group, and carbon disulfide was continuously added at 0.143 phm in the second group, and the internal temperature was adjusted to 100
The temperature was controlled so that the temperature became ° C.

After the addition of 2,6-ditertiarybutyl-p-cresol as an antioxidant at the outlet of the second unit, the solvent was removed by steam stripping and the product was dried on a hot roll at 110 ° C to bond C = S in the molecule. A styrene-butadiene copolymer rubber in which was introduced was obtained. This is designated as Evaluation Sample A.

The Mooney viscosity of the obtained rubber is measured with a Mooney viscometer, Got 83. In addition, 1,2-
The vinyl content was measured by the method of Hampton using an infrared spectrophotometer, and 25% by weight of bound styrene, 1, of the butadiene part
A 2-vinyl content of 29% was obtained. The molecular weight distribution was calculated using GPC using a standard polystyrene polymer calibration curve to obtain Mw / Mn: 2.4. Further, the GPC curve showed that the molecular weight distribution was one peak. Also, GP of ozone decomposition products
65 Wt% of isolated styrene calculated from C
And long-chain block styrene was 0.8 wt%.

Next, the evaluation sample A was used as a raw material rubber (IA): 90 mg / g,
(DBP): 19 ml / 100 g of N339 carbon black with the formulation shown in Table 1 using a test Banbury mixer with an internal capacity of 1.7, according to ASTM-D-3403-75 standard formulation mixing procedure, Method B. , The compound was obtained, these were vulcanized, and each physical property was measured. The measurement was performed by the method described below.

(1) Hardness, tensile strength; in accordance with JIS-K-6301.

(2) Impact resilience; Re-Yupke method according to JIS-K-6301, but
The impact resilience at 70 ℃ is measured by taking out the sample in the open at 70 ℃ for 1 hour and then taking it out quickly.

(3) Goodrich heat generation Using a Goodrich flexometer, a test was conducted under the conditions of a load of 48 pounds, a displacement of 0.225 inch, a start of 50 ° C and a rotation speed of 1800 rpm, and the difference in temperature rise after 20 minutes was expressed.

(4) Wet skid resistance A Skidley London portable skid tester was used, and a safety walk (made by 3M) was used as the road surface, and the resistance was measured according to the method of ASTM-E-808-74. S
It was displayed as an index with the measured value of BR1502 as 100.

The physical properties are shown in Table 3.

Examples 2 to 5 and Comparative Examples 1 to 2 The evaluation rubbers were produced in the same manner as in Example 1 except that the method shown in Table 2 was used. The obtained rubbers are referred to as evaluation samples B to G. Using Evaluation Samples B to G, compounds were obtained in the same manner as in Example 1 except that the methods shown in Table 3 were used, and these were vulcanized and the physical properties were measured. The physical properties are shown in Table 3.

Example 6 As carbon black (IA): 44 mg / g, (DBP): 114 ml
A compound was obtained in the same manner as in Example 1 except that / 100 g of N550 carbon black was used, and the compound was vulcanized and each physical property was measured. The physical properties are shown in Table 3.

Examples 7 to 8 and Comparative Example 3 A method was used in the same manner as in Example 1 except that the rubbers shown in Table 3 were blended and used as the rubber component. Table 3 shows each physical property.
It was shown to.

Comparative Example 4 Using SBR1502 as a raw material rubber, a compound was obtained in the same manner as in Example 1, and the compound was vulcanized to measure each physical property. The physical properties are shown in Table 3.

Table 1 Formulation No. Raw rubber 100 parts by weight Aromatic oil ^{* 1} 10 parts by weight Carbon black 50 parts by weight Stearic acid 2 parts by weight Zinc white 3.5 parts by weight Accelerator CZ ^{* 2} 1.3 parts by weight Sulfur 2 parts by weight * 1 Joint Petroleum X -140 * 2 N-cyclohexyl-2-benzothiazyl sulfenamide Vulcanization condition: 160 ° C x 20 minutes From the results shown in Table 3, the characteristics of the rubber composition of the present invention are clear as follows.

Examples 1 to 6 are all compositions of the present invention in which a polymer having a C = S group introduced into the molecule is used as a rubber component.

From the comparison between Example 1 and Comparative Example 1, the composition of the present invention was
The tensile strength, impact resilience, and heat generation are all significantly improved as compared with the composition using a polymer having no = S group.

Each of Examples 1 to 4 is a composition of the present invention in which a polymer in which isolated styrene of ozonolysis-GPC is 40% or more and a long chain block styrene is extremely small and a C = S bond is introduced into the polymer is used. . All of these have extremely excellent performance. In Example 5, ozonolysis-isolated styrene of GPC was as low as 36%, and long-chain block styrene was 4.5%.
The composition of the present invention was a composition using a polymer having a C = S bond introduced therein, and the performance thereof was slightly inferior to that of Example 1, but was extremely superior to that of Comparative Example 1.

Comparative Example 2 is a composition using polybutadiene introduced with C = S groups as a rubber component, and the tensile strength is remarkably inferior to that of Example 1.

Example 6 uses a C═S group-introduced polymer as a rubber component and N550 carbon black as a carbon black, and is significantly superior to Comparative Example 1 in impact resilience and heat generation.

Both Examples 7 and 8 are compositions in which a polymer having a C = S group introduced into the molecule was used as a part of the rubber component, while Comparative Example 3 similarly used a polymer having no C = S group. As for the composition, Examples 7 and 8 are superior to Comparative Example 3 in tensile strength, impact resilience, and heat generation.

Example 9 A reactor with an internal volume of 10 equipped with a stirrer and a jacket,
Cyclohexane 4200g, Purified butadiene 850g, Purified styrene 150g, Tetrahydrofuran 40g as polar compound
After maintaining the temperature at 60 ° C., 0.6 g of n-butyllithium was added as a catalyst to start polymerization, and then
The polymerization temperature is maintained at 60-90 ° C and the polymerization reaction is performed for 40 minutes.
To the obtained living polymer solution, first, 0.244 g of tin tetrachloride (equivalent ratio to n-butyllithium: 0.4) was added, and immediately thereafter, 3.04 g of diisopropylxanthogen disulfide was added, and the coupling reaction and C = S-bond introduction was subsequently performed.

Further, 10 g of di-tert-butylhydroxytoluene was added to the polymer solution as an antioxidant, and then the solvent was evaporated to recover the polymer.

The polymer obtained has a Mooney viscosity. 60, styrene content 15% by weight, microstructure is 1,4-
The trans bond was 34%, the 1,4-cis bond was 22%, and the 1,2-vinyl bond was 44%.

The molecular weight distribution was Mw / Mn: 1.66 from GPC, and the curve of GPC showed that the molecular weight distribution had two peaks.

The Mooney viscosity of the polymer before coupling is 13
And Mw / Mn was 1.10.

In addition, the isolated styrene determined by GPC of the ozone decomposition product was 55% by weight based on the total styrene, and the long-chain block styrene was 3.8% by weight.

Next, using this polymer as a raw rubber, N339 carbon black was used to obtain a compound having the composition shown in Table 1 in the same manner as in Example 1, vulcanized, and each physical property was measured. The measurement results are shown in Table 4.

Example 10 A reactor with an internal volume of 10 equipped with a stirrer and a jacket,
Cyclohexane 4200g, Purified butadiene 850g, Purified styrene 150g, Tetrahydrofuran 40g as polar compound
After maintaining the temperature at 40 ° C, 0.6 g of n-butyllithium was added as a catalyst to start the polymerization, and then the polymerization was performed adiabatically. After reaching the maximum temperature of 105 ° C, 10 minutes were further added. After the reaction, first, 0.244 g of tin tetrachloride (equivalent ratio to n-butyllithium: 0.4) was added, and immediately thereafter, 3.04 g of diisopropylxanthogendisulfide was added to perform coupling reaction and C = S bond. Introduction was carried out subsequently.

Further, 10 g of di-tert-butylhydroxytoluene was added to the polymer solution as an antioxidant, and then the solvent was evaporated to recover the polymer. The polymer obtained has a Mooney viscosity. 55, styrene content 15% by weight, microstructure is 1,4-
The trans bond was 34%, the 1,4-cis bond was 23%, and the 1,2-vinyl bond was 43%.

The molecular weight distribution was Mw / Mn: 1.63 from GPC, and the curve of PGC showed that the molecular weight distribution had two peaks.

The Mooney viscosity of the polymer before coupling is 15
And Mw / Mn was 1.10.

Further, the isolated styrene determined by GPC of the ozone decomposed product was 48% by weight and the long-chain block styrene was 6.8% by weight based on the total styrene.

Next, using this polymer as a raw rubber, N339 carbon black was used to obtain a compound having the composition shown in Table 1 in the same manner as in Example 1, vulcanized, and each physical property was measured. The measurement results are shown in Table 4.

Comparative Example 5 The procedure of Example 9 was repeated, except that diisopropylxanthogen disulfide was not added.

The polymer obtained has a Mooney viscosity. Was 55.

Vulcanization physical properties were measured in the same manner as in Example 9. Table 4 shows the measurement results
Shown in.

Example 9 is a composition of a polymer having a C = S bond of the present invention in which the isolated styrene determined by GPC of an ozone decomposing product is 55% and the long-chain block styrene is 5% or less, and compared with Comparative Example 5. The tensile strength, impact resilience, and heat generation are significantly improved.

Example 10 is a composition of a polymer having a C = S bond of the present invention in which isolated styrene exceeds 48% and long-chain block styrene exceeds 5%, and the performance thereof is slightly inferior to that of Example 9, but a comparative example. Compared to 5, it has been greatly improved.

〔The invention's effect〕

The rubber composition according to the present invention, as described above, tensile strength,
Very good impact resilience and heat generation. The rubber composition of the present invention is particularly suitable for tire applications centered on tire treads and has great industrial significance.

Claims (1)

[Claims] 1. Styrene and butadiene are copolymerized in a hydrocarbon solvent using an organolithium catalyst, and the amount of bound styrene is 5 to 45% by weight and the vinyl bond of the butadiene portion is 10 to 70.
%, GPC weight average molecular weight (Mw) and number average molecular weight (M
n), a living polymer having a molecular weight distribution (Mw / Mn) of 1.2 to 3 is reacted with carbon disulfide, a xanthogen compound, and a dithioic acid compound to introduce a C = S bond into the molecule. Suitable for a tire tread in which 10 to 100 parts by weight of carbon black, 0.3 to 5 parts by weight of sulfur and a vulcanization accelerator are mixed with 100 parts by weight of a raw rubber containing at least 10% by weight of a polymer having a viscosity of 20 to 150. Rubber composition.