JPH0781033B2 - Rubber composition for tire - Google Patents

Description

TECHNICAL FIELD The present invention relates to a rubber composition for a tire having improved processability and physical properties of a vulcanized product, and more specifically, to a branched polymer molecule and a specific functional group. The present invention relates to a rubber composition particularly suitable for tire tread applications, which contains a polybutadiene or a styrene-butadiene copolymer having a modified polymer molecule and a natural rubber or a synthetic polyisoprene rubber as main raw material rubber components.

[Conventional technology]

In recent years, there has been a demand for reduction of rolling resistance from the viewpoint of fuel efficiency for automobile tires, and improvement of steering stability and wet skid characteristics (braking performance on wet roads) from the viewpoint of automobile safety. On the other hand, in the production of automobile tires, it has been desired to improve quality uniformity by improving workability and productivity by improving workability.

Conventionally, as a method for reducing rolling resistance while maintaining the wet skid characteristics of a tire, for example, weight reduction of a tire, optimization of a tire structure, improvement of a tire tread pattern, rubber compound used for a tire tread. Have been tried. Among these, as a method of improving the rubber compound used for the tire tread and reducing the rolling resistance, a method of using a rubber having less hysteresis loss as a raw material rubber, a carbon black having a larger particle size is used. There are ways to change it, and reduce the amount of carbon black and oil used in vulcanized rubber.

For example, as a method for improving rolling resistance and wet skid characteristics of a polymer used for a tread, there is disclosed in
54-62248 has a glass transition temperature (T _g ) of -50 ° C or higher,
A method using a styrene-butadiene copolymer having a styrene content of 20 to 40% and a vinyl bond content of the butadiene portion of 50 to 80% is shown. However, when such a polymer is used, the rolling resistance of the tire and the balance between wet skid characteristics are improved to some extent, but the processability of the rubber compound is not preferable because the polymer has a relatively high molecular weight. Become a trend.

Further, a conjugated diene polymer obtained by adding benzophenones to the end of the polymer chain as shown in JP-A-59-117514 also shows an improvement in rolling resistance, but a polymer without addition of benzophenones. Compared with, the Mooney viscosity of the compound is higher and the processability is unfavorable.

Further, as an attempt to solve the above-mentioned problems in the processability of the polymer while maintaining the rolling resistance performance, a branched polymer disclosed in JP-B-49-36957 and a similar polymer to that of JP-A-57-36957 are disclosed. There is a method of using a branched polymer having a specific structure disclosed in JP-A-55912 and JP-A-58-168611.

However, even in a rubber composition using a polymer having these branching components, JP-A-60-9443 discloses that styrene-
When the butadiene copolymer alone is used, there is a problem that the surface of the extruded product becomes rough during extrusion processing at a high speed. Therefore, an improved method of blending natural rubber or synthetic polyisoprene rubber has been proposed.

When such a branched styrene-butadiene copolymer is used as a blend with a natural rubber rubber, the processability is improved while maintaining the performance characteristics of the branched polymer. Is desirable. However, when the branched polymer contains a polymer molecule branched by a tin compound, when the composition is blended with a natural rubber-based rubber, the composition at 50 to 70 ° C. corresponding to rolling resistance performance is obtained. The impact resilience tends to be worse than that of the rubber composition of the branched polymer alone, and this tendency is large when a large amount of the branched component is contained, and the performance of the branched polymer improved by tin is not always expressed. There was a situation.

Furthermore, as the demand for all-season tires has recently increased, the rubber used in tire treads has the same rolling resistance and wet skid characteristics as conventional rubber, but also snow and ice road surfaces in cold regions in winter. With the demand for control performance in tires, rubber compositions for tire treads are required to have higher performance balance than ever before.

In order to improve the low-temperature performance, blending natural rubber-based rubber, using oils or plasticizers with better low-temperature performance, and carbon black Attempts have been made to use such fillers. However, when such various compounding agents are used, there is a problem that the compounding agent lowers the mechanical strength and the like, and therefore the type of rubber used must be limited to those with less deterioration. The degree of freedom in composition is not necessarily high.

[Problems to be solved by the invention]

As described above, in the composition using the conventional polymer, when the processability and the low temperature performance were improved, the excellent rolling resistance performance of the polymer could not always be sufficiently exhibited. Is.

The present invention has been made in view of these points, and by using a polybutadiene or a styrene-butadiene copolymer and a natural rubber or a synthetic polyisoprene rubber in a blended state, rolling resistance, wet skid characteristics, mechanical properties The purpose of the present invention is to provide a rubber composition for a tire in which the mechanical strength, low temperature performance and processability are balanced.

[Means and Actions for Solving Problems]

The present invention is a rubber composition for a tire, which contains a blend of a polybutadiene or a styrene-butadiene copolymer and a natural rubber or a synthetic polyisoprene rubber as a raw material rubber component, and a rubber composition in a blended state. In order to improve the performance, as a result of extensive studies on the polymer structure of the polybutadiene or styrene-butadiene copolymer used, it has a specific amount of a branched polymer molecule and a linear polymer molecule, and by carbodiimides The present invention has been achieved by finding that the above object is satisfied by using a polybutadiene or a styrene-butadiene copolymer containing a modified polymer molecule.

That is, in the present invention, (A) 30 to 90 parts by weight of the raw rubber component having a total amount of 100 parts by weight, (1) 10 to 50% by weight of the molecules constituting the polymer are trifunctional or higher branching agents. (2) at least 20% by weight of molecules constituting the polymer is a linear polymer to which carbodiimides are added, and (3) the styrene content of the polymer is 0. It is a polybutadiene or a styrene-butadiene copolymer having a branched polymer molecule and a linear polymer molecule, wherein (B) 10 to 70 parts by weight of the raw rubber component is a natural rubber or a synthetic polymer. Isoprene rubber, (C) 0 to 30 parts by weight of the raw material rubber component is another conjugated diene rubbery polymer, and additionally, reinforcing carbon black, extender oil for rubber, sulfur,
A rubber composition for a tire, which contains a vulcanization accelerator.

Hereinafter, the present invention will be described in detail.

30 ~ raw material rubber composition of the rubber composition for a tire of the present invention
90 parts by weight is a specific structure of polybutadiene or styrene-butadiene copolymer having a branched polymer molecule and a linear polymer molecule. These polymers use organolithium compounds such as ethyllithium, n-propyllithium, n-butyllithium, sec-butyllithium and the like as a polymerization catalyst, and hydrocarbons such as n-pentane, n-hexane, cyclohexane and benzene. By polymerizing butadiene or copolymerizing styrene and butadiene in a solvent mainly containing, and reacting the obtained living polymer having an active end with a trifunctional or higher functional branching agent and carbodiimides in combination. can get.

The trifunctional or higher-functionality branching agent used to form the branched polymer molecule includes three or more halogen-tin bonds in one molecule,
It is a compound containing a halogen-silicon bond, an alkoxy-tin bond, an aryl-tin bond, a dicarboxylic acid diester, 3 or more epoxy groups, 3 or more isocyanate groups, and the like. Among these, compounds having 3 or more halogen-tin bonds and halogen-silicon bonds in the molecule, dicarboxylic acid esters and the like are preferable, and specific compounds include tin tetrachloride, monobutyl tin trichloride and silicon tetrachloride. , Ethylene bistrichlorosilane,
Diethyl adipate or the like is preferably used, and tin tetrachloride or monobutyl tin trichloride is particularly preferable for achieving the object of the present invention.

On the other hand, the compound used for obtaining the linear polymer molecule to which the carbodiimides are added in the present invention is a disubstituted carbodiimide compound having a general formula -N = C = N- bond in the molecule or a general formula -N- A 2-substituted cyanamide compound having a C≡N bond, and includes dialkylcarbodiimide, alkylarylcarbodiimide, diarylcarbodiimide, dialkylcyanamide, alkylarylcyanamide, diarylcyanamide, and the like.
These are used alone or as a mixture of two or more.

For example, dimethylcarbodiimide, diethylcarbodiimide, dipropylcarbodiimide, dibutylcarbodiimide, dihexylcarbodiimide, dicyclohexylcarbodiimide, dibenzylcarbodiimide, diphenylcarbodiimide, methylpropylcarbodiimide, butylcyclohexylcarbodiimide, ethylbenzylcarbodiimide, propylphenylcarbodiimide, phenylbenzylcarbodiimide, dimethylcyanamide. , Diethylcyanamide, dipropylcyanamide, dibutylcyanamide, dihexylcyanamide, dicyclohexylcyanamide, dibenzylcyanamide, diphenylcyanamide,
Examples include methylpropyl cyanamide, butylcyclohexyl cyanamide, ethylbenzyl cyanamide, propylphenyl cyanamide, and phenylbenzyl cyanamide.
Of these, particularly preferred are dicyclohexylcarbodiimide, diphenylcarbodiimide and diphenylcyanamide.

Carbodiimides are used to introduce an active functional group into the polymer terminal, and the polymer obtained by the reaction becomes a polymer containing an amino group.

In the case of introducing such an active functional group, the use of carbodiimides tends to be preferable because the Mooney viscosity after the reaction with the living polymer does not increase so much and the processing decreases little.

The branched polymer molecule bonded to the trifunctional or higher functional branching agent used in the present invention is 10 to 50% by weight of the molecule constituting the polymer, while the linear polymer molecule bonded to the carbodiimides is , At least 20% by weight of the molecules constituting the polymer.

Further, when the trifunctional or higher functional branching agent is an active tin compound, the total amount of the molecules branched by the trifunctional or higher functional tin compound and the linear polymer molecules bonded to the carbodiimides is a polymer. At least 30% by weight of the constituent molecules
When the trifunctional or higher functional branching agent is a compound other than the active tin compound, the amount of the linear polymer molecule bonded to the carbodiimides is at least 30% of the molecules constituting the polymer. It is preferably in the weight%.

In the present invention, the above-mentioned limitations regarding the branched polymer and the linear polymer are the processability of the blend, the mechanical strength of the vulcanizate, and the impact resilience when the blend is blended with the natural rubber component and the like. It is necessary for good heat resistance and low temperature performance. 10% by weight of branched polymer molecules
If it is less than the above range, there is a problem in processability even when blended with a natural rubber component and the like, and the polymer is liable to cold flow, which is not preferable for storage. On the other hand, in the case where the amount of the branched polymer is more than 50% by weight, the impact resilience when blended with the natural rubber component is largely reduced as compared with the case of the single compound.

The branched polymer molecule is particularly preferably in the range of 15 to 40% by weight of the molecule constituting the polymer in view of the balance of processability, impact resilience and heat resistance.

When the amount of the linear polymer bound to the carbodiimide is less than 20% by weight, the effect of improving the impact resilience and heat resistance is slight.

Furthermore, the total amount of the branched polymer molecule bound to the active tin compound and the amount of the linear polymer molecule bound to the carbodiimide should be 50% by weight or more of the molecules constituting the polymer. It is particularly preferable in terms of improving heat resistance.

The amounts of the branched polymer molecule and the linear polymer molecule are the equivalent ratios of active lithium and these reactive compounds because the reaction of the living polymer with the branching agent and the carbodiimides is almost quantitative. It is possible by controlling.

The amount of each component in the above polymer can be determined by separating each component by GPC (gel permeation chromatography) or by further reacting the active end with a reagent that reacts with the active end. It can be measured by comparing the GPC analysis results before and after the reaction.

Further, the styrene content of the polybutadiene or styrene-butadiene copolymer having a specific structure of the present invention is such that the rubber composition blended with the natural rubber component or the like has good tensile strength, abrasion resistance, impact resilience, and heat resistance. In order to maintain the content, it is 0 to 30% by weight, and particularly in the application requiring a high performance balance such as all season tires, the range of 5 to 20% by weight is preferable. When the styrene content exceeds 30% by weight, impact resilience, heat resistance and low temperature performance are deteriorated when blended.

On the other hand, the vinyl bond content of the butadiene portion of the polymer is 10 to
It is in the range of 80%. When the vinyl bond content is in the range of 30 to 80%, the compatibility with the natural rubber component is good, and the impact resilience and the heat resistance are less likely to deteriorate.

The specific Mooney viscosity (ML _{1 +} 4,10
(0 ° C) is 25 to 150, and a range of 35 to 100 is preferable in terms of the balance between the processability of the blend blended with the natural rubber component and others and the physical properties of the vulcanizate. When the amount exceeds 20 parts by weight of the raw rubber component, the Mooney viscosity of the specific polymer is particularly preferably in the range of 50 to 100.

When the Mooney viscosity is less than 25, abrasion resistance is lowered, and when it exceeds 150, workability becomes a problem, which is not preferable.

The styrene-butadiene copolymer rubber of the present invention is preferably a random copolymer. The styrene chain distribution of the styrene-butadiene copolymer rubber is analyzed by GPC of low temperature ozonolysis product of the copolymer rubber. This method was developed by Tanaka et al., And the chain distribution of styrene is GP of the decomposition product obtained by ozone cleavage of all double bonds of butadiene.
Analyzed by C (Macromolecules, 1983,16,192
Five). The copolymer rubber of the present invention has 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 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, based on 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 ratio (▲ ▼ / ▲ ▼) of the weight average molecular weight (▲ ▼) of the polymer measured by GPC and the number average molecular weight (▲ ▼) is in the range of 1.3 to 3.0, particularly 1.
The range of 3 to 2.0 is preferable in terms of impact resilience and heat generation of the obtained rubber composition.

Further, in the present invention, the specific polybutadiene or styrene-butadiene copolymer is obtained by reacting a precursor polymer having an active lithium terminal with a branching agent and carbodiimides, and the Mooney viscosity of this precursor polymer is obtained. (ML _{1 + 4} , 100 ° C.) is preferably in the range of 10 to 60, particularly 20 to 50 in terms of the balance of physical properties and processability of the resulting composition.

Next, 10 to 70 parts by weight of the raw rubber component of the present invention is natural rubber or synthetic polyisoprene rubber. Synthetic polyisoprene rubber has 90% or more cis-1.4 bonds. The natural rubber component not only improves the processability of the rubber composition of the present invention, but also the rubber composition together with the specific polybutadiene or styrene-butadiene copolymer described above,
It is a rubber component necessary for giving sufficient mechanical strength, heat resistance, and good low-temperature performance.

In the present invention, the specific polybutadiene and styrene-butadiene copolymer is 30 to 90 parts by weight of the raw rubber component, preferably 40 to 85 parts by weight, the natural rubber or synthetic polyisoprene rubber is 10 ~ of the raw rubber component. 70 parts by weight, preferably 20-60 parts by weight. Outside the above range, it is difficult to highly balance workability, impact resilience, heat resistance, mechanical strength, wear resistance, and low temperature performance.

Further, other conjugated diene-based rubbery polymers such as high cis-polybutadiene, low cis-polybutadiene, emulsion-polymerized styrene-butadiene copolymer, etc., as long as they do not impair the performance of the rubber composition as a raw rubber component. Can be used. The amount thereof is 0 to 30 parts by weight of the raw rubber component.

Next, in the rubber composition using each of the rubbery polymers as a raw material rubber, in addition, a reinforcing carbon black, an extender oil for rubber, an aliphatic carboxylic acid, sulfur, and a vulcanization accelerator are contained as necessary components. Further, if necessary, a compounding agent for rubber such as a vulcanization accelerator, an antioxidant, an ozone deterioration inhibitor, and a processing aid is contained.

In the present invention, the reinforcing carbon black is 35 to 100 parts by weight, preferably 40 to 80 parts by weight per 100 parts by weight of the raw rubber component.
Used in parts by weight.

As carbon black, various ones with different particle size, particle size distribution, structure, tint, etc. are used, but SAF, IS is mainly used for automobile tires.
Carbon black of each class AF, HAF or FEF is used. In the present invention, it is preferable to use furnace carbon black having a particle size of 15 to 50 mμ, an iodine adsorption amount of 40 to 160 mg / g, and a DBP oil absorption amount of 70 to 150 ml / 100 g.

In the present invention, the extender oil for rubber is used in an amount of 5 to 80 parts by weight, preferably 5 to 50 parts by weight, per 100 parts by weight of the raw rubber component.

As extender oil for rubber, aromatic type, naphthene type,
Paraffin-based extender oils are used according to the application of the rubber composition of the present invention, and especially for all-season tires and studless tires where low temperature performance is important, and for carcass applications where heat resistance is important, naphthenes are used. Type and paraffinic extender oils are preferred. Aromatic extension oils are preferred for applications where importance is attached to tensile strength and abrasion resistance. If the amount of the extending oil for rubber is less than 5 parts by weight, the workability is poor and the dispersion of carbon black is poor, and the properties such as tensile strength and elongation are not exhibited. On the other hand, if it exceeds 80 parts by weight, the tensile strength and heat resistance will be poor. It causes a decrease and is not preferable.

Further, an aliphatic carboxylic acid typified by stearic acid is used as a vulcanization aid or a processing aid in the vulcanized rubber composition, but in the rubber composition of the present invention, such a fat is used. The group carboxylic acid is necessary for cutting the bond between tin and the polymer molecule of the polybutadiene or styrene-butadiene copolymer containing the polymer molecule bonded to tin used as the raw material rubber component in the rubber kneading step. is there. The presence of the bond between the polymer and tin increases the interaction between the polymer and the reinforcing carbon black to form a so-called carbon gel, and as a result, the impact resilience, heat resistance, tensile strength, etc. The properties are improved. The aliphatic carboxylic acid is used in an amount of 0.5 to 5 parts by weight per 100 parts by weight of the raw rubber component.

Further, in the composition of the present invention, per 100 parts by weight of the raw rubber component, sulfur is used as a vulcanizing agent, 0.1 to 3.0 parts by weight, preferably 1.0 to 2.5 parts by weight, and as a vulcanization accelerator, sulfene. Vulcanization accelerators such as amide-based, guanidine-based, and thiuram-based are 0.05-
2 parts by weight, 1 type, or 2 or more types are used in combination.

The compounding agent for rubber, which is contained in the rubber composition of the present invention as necessary, is used in an amount according to the purpose of use.

The rubber composition of the present invention is kneaded by a rubber kneading roll, an internal mixer, an extruder or other rubber kneading machine, then molded, and vulcanized at a temperature of 130 to 200 ° C. according to a conventional method.

The rubber composition of the present invention is suitable for a tread of a tire as described above, and is particularly used for a fuel-efficient tire, an all-season tire, a cap tread of a high-performance tire, an undertread, and the like, making good use of other excellent performances. Needless to say, it can also be used in tire parts such as tire sidewalls, carcass and cushion rubber, and in applications such as anti-vibration rubber and industrial products.

〔Example〕

Examples will be shown below, but these show the present invention more specifically, and do not limit the scope of the present invention.

Preparation of polymer In a reactor with an internal volume of 10 equipped with a stirrer and a jacket,
Cyclohexane 4200g, Purified butadiene 640g, Purified styrene 160g, Tetrahydrofuran 60g as polar compound
After maintaining the temperature at 50 ° C., 0.34 g of n-butyllithium as a catalyst was added to start polymerization, and thereafter,
The polymerization temperature is kept at 40-85 ° C and the polymerization reaction is performed for 60 minutes.
First, 0.104 g of tin tetrachloride (equivalent ratio to n-butyllithium: 0.3) was added to the obtained living polymer,
Then 0.62 g of dicyclohexylcarbodiimide (n-
A branching reaction and an addition reaction were carried out by adding an equivalent ratio to butyllithium of 0.6). Furthermore, 8 g of di-tert-butylhydroxytoluene was added to this polymer solution as an antioxidant, and then the solvent was evaporated to recover the polymer.

The obtained polymer (Sample A) had a Mooney viscosity (ML _{1 +} 4,10
68 ° C, styrene content 20% by weight, microstructure of butadiene part is 1,4 trans bond 26%, 1,4-cis bond
19% and 1,2-vinyl bond 55%. The GPC analysis of this polymer showed that the amount of branched polymer molecules was 30%,
▲ ▼ / ▲ ▼ is 1.7 and GPC of ozone decomposition products
The obtained isolated styrene was 62% based on the total styrene, and the long-chain block styrene was 0%. Further, it was confirmed from the analysis of the amount of tin in the obtained polymer and the analysis of the reaction amount of dicyclohexylcarbodiimide that the reaction was carried out almost as intended.

The Mooney viscosity of the precursor polymer before the branching reaction is 32, GP
▲ ▼ / ▲ ▼ by C was 1.15.

Further, various polymers having different styrene contents, microstructure of butadiene portion, branching agent, ratio of branched polymer molecules, etc. were prepared in the same manner as in the case of obtaining the sample A. These were used as polymers within the scope of the invention and for comparison. Their polymer structures are shown in Table 1.

The styrene content and the microstructure of the butadiene portion were obtained by measuring the spectrum using an infrared spectrophotometer and calculating by the Hampton method.

▲ ▼ / ▲ ▼ are GPC (Shimadzu Corporation, LC-3
A, column: 10 ⁴ , 10 ⁵ , 10 ⁶ each, solvent: tetrahydrofuran, detector: differential refractometer), and a method using a calibration curve with polystyrene as a standard substance.

Among the polymers shown in Table 1, sample A to sample G are polymers falling within the scope of the present invention, and sample H to sample M are polymers for comparison.

Further, as the natural rubber and other rubber-like polymers, the rubbers shown in Table 2 were prepared and used for the preparation of the rubber compound.

Example 1 and Comparative Example 1 Using the polymers shown in Table 1 and the other raw material rubbers shown in Table 2 and using the raw material rubber components having the compositions of evaluation formulation No. 1 and Table 4 shown in Table 3, the internal content was 1.7 Using the test Banbury mixer of 1., rubber compounds were obtained by the method B of the standard compounding mixing procedure of ASTM-D-3403-75, which were vulcanized at 160 ° C. for 20 minutes, and the physical properties and The workability was evaluated.

(1) Tensile strength: According to JIS-K-6301.

(2) Impact resilience; Ripke method according to JIS-K-6301, 70 ° C
The impact resilience was measured by preheating the sample in a 70 ° C oven for 1 hour and then quickly taking it out.

(3) Goodrich heat generation Using a grid-rich 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.
It was displayed as an index with the measured value of Comparative Example 1-7 as 100.

(5) Ice skid resistance: Use the same measuring machine as the wet skid resistance. Indoors set at -8 ° C, ice with a surface temperature of -8 ° C is used as the road surface.

It was displayed as an index with the measured value of Comparative Example 1-7 as 100.

(6) Roll processability; using a 6-inch roll for testing,
The operability of the rubber compound on the roll and the winding state were observed, and the good one was not wound on the four rolls and the bagging was set to 1.

(7) Extrudability: A Carvey die was attached to a Brabender plastograph, and the extrusion amount, surface skin and edge conditions were observed. The best value was 4, and the worst value was 1.

As is clear from the results of the processability and vulcanized physical properties shown in Table 4, from the polybutadiene or styrene-butadiene copolymer (Samples A to F) having a specific structure limited in the present invention and the natural rubber. The rubber composition is
In addition to excellent workability, tensile strength, impact resilience, heat generation, wet skid characteristics, and ice skid characteristics are excellent, while Samples H to M that do not satisfy the range of limitation of the present invention. A rubber composition composed of natural rubber has poor impact resilience and heat generation when it has good processability, while a composition having good impact resilience and heat generation has a problem in processability.

Example 2 and Comparative Example 2 Using a specific polymer limited in the present invention shown in Table 5, a rubber composition was prepared in the same composition as shown in Table 3 as in Example 1, and the processability and vulcanization physical properties were measured.

As is clear from the results shown in Table 5, Examples 2-1 and 2-2 using the specific polymer of the present invention as a raw material rubber component by blending the natural rubber component and the composition limited in the present invention
The rubber composition of No. 9 has good processability and physical properties of vulcanized products, while Comparative Examples 2-1 to 2-1 have compositions outside the scope of the present invention.
The rubber composition of No. 2-4 has an inferior balance of processability and physical properties of vulcanized products.

[Advantages of the Invention] As described above, the rubber composition for a tire of the present invention has good processability of the compound such as roll processability and extrusion processability, and also has impact resilience or heat generation which is a measure of rolling resistance performance. The balance between the properties and wet skid properties is good, and the balance between the wet skid properties and ice skid properties is also good, and the strength of the vulcanizates is also high, indicating excellent vulcanizate physical properties. Such a rubber composition is particularly suitable for a tread of various tires including low fuel consumption tires and passenger car tires centering on all-season tires, and the present invention has great industrial significance.

Claims (1)

[Claims] 1. A branching agent in which 30 to 90 parts by weight of (A) a raw rubber component whose total amount is 100 parts by weight, and (1) 10 to 50% by weight of molecules constituting a polymer are trifunctional or more. (2) at least 20% by weight of molecules constituting the polymer is a linear polymer to which carbodiimides are added, and (3) the styrene content of the polymer is 0. It is a polybutadiene or a styrene-butadiene copolymer having a branched polymer molecule and a linear polymer molecule, wherein (B) 10 to 70 parts by weight of the raw rubber component is a natural rubber or a synthetic polymer. Isoprene rubber, 0 to 30 parts by weight of the raw rubber component (C) is another conjugated diene rubbery polymer, and additionally contains reinforcing carbon black, extender oil for rubber, sulfur, and vulcanization accelerator. A rubber composition for a tire.