JPH1053671A - Rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition useful for a tire tread, etc., capable of manifesting grip on ice or snow, processability and low shrink properties, comprising specific conjugated diene (co)polymers different in molecular weight in a prescribed ratio. SOLUTION: This rubber composition comprises (A) a conjugated diene polymer (P1 ) or (P2 ) a vinyl aromatic hydrocarbon-conjugated diene copolymer having >=30×10<4> weight-average molecular weight (Mw) converted to that of polystyrene and <=30wt.% of bonded styrene amount (S) and (B) the polymer P1 or the copolymer P2 having 0.2×10<4> to 8×10<4> Mw and <=30wt.% of bonded styrene amount S. The components A and B satisfy the relation of the formula S+(V/2)<25 [V is a vinyl content (%)] and the composition is composed of 30-120 pts.wt. of the component B based on 100 pts.wt. of the component A. The composition is regulated to have >=15% extract content with chloroform after the vulcanization of the composition based on the weight of the component B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition suitably used for various rubber products such as tires and industrial articles, and more particularly, to a rubber tread excellent in flexibility and grip at low temperatures. It relates to the rubber composition used.

[0002]

2. Description of the Related Art In recent years, automobiles are required to have low fuel consumption and safety, and a rubber composition used for a tread portion of a tire is required to improve wet and dry grip performance. ing.

Conventionally, butadiene rubber or styrene-butadiene copolymer rubber having a low styrene content and a low vinyl content, which is widely used for a tread portion of a tire, has a lower glass transition temperature (Tg) than other synthetic rubbers. Therefore, it is known that it has excellent flexibility at low temperatures. For this reason, it is widely used for treads of studless tires and all season tires.

However, butadiene rubber or
When a styrene-butadiene copolymer rubber having a low styrene and a low vinyl content is used for the tread, there is a problem that it is difficult to obtain a sufficient grip performance because tan δ of these rubber compositions is low.

Conventionally, in order to achieve flexibility at low temperatures, the glass transition temperature (T
g) must be lowered. On the other hand, to improve grip performance, it is required to increase Tg and increase tan δ, so that it is difficult to simultaneously satisfy these two performances. Was.

[0006] Further, butadiene rubber or styrene-butadiene copolymer rubber having low styrene and low vinyl content has a drawback that when the compounding amount is increased, processability such as roll winding property is reduced. Further, there is a disadvantage that the shrinkage is increased and the dimensional accuracy of the product is deteriorated.

[0007]

In view of the above facts, the present invention is excellent in flexibility at low temperatures, has good grip properties on ice and snow, as well as on ordinary conditions, and has a good workability such as roll winding property. It is an object of the present invention to provide a rubber composition having good properties and improved shrinkage.

[0008]

Means for Solving the Problems As a result of intensive studies and studies to achieve the above object, the present inventor has completed the present invention which is excellent in flexibility, grip and workability at low temperatures.

That is, the rubber composition according to claim 1 is selected from a conjugated diene polymer and a vinyl aromatic hydrocarbon-conjugated diene copolymer, and has a weight average molecular weight of 3 in terms of polystyrene.
0 × 10 ⁴ or more, and a high molecular weight polymer component having a bound styrene content of 30% by weight or less, a conjugated diene polymer and a vinyl aromatic hydrocarbon-conjugated diene copolymer,
Polystyrene-equivalent weight average molecular weight of 0.2 × 10 ⁴ -8
× 10 ^4, and includes a low molecular weight polymer component bonded styrene content is 30 wt% or less, a, to the high molecular weight polymer component 100 parts by weight, 30 to 120 weight the low molecular weight polymer component In the high molecular weight polymer component and the low molecular weight polymer component, when the amount of bound styrene (% by weight) is S and the content of vinyl (% by weight) is V, S + (V / 2) <25, and a rubber composition obtained by vulcanizing the polymer blend is extracted with chloroform to obtain an extract obtained by blending the low-molecular-weight polymer component with a low-molecular-weight polymer component. The molecular weight is 15% by weight or more based on the molecular weight polymer component.

Hereinafter, the present invention will be described in detail. The rubber composition of the present invention is selected from a conjugated diene polymer and a vinyl aromatic hydrocarbon-conjugated diene copolymer as a rubber raw material,
Selected from a high molecular weight polymer component having a polystyrene equivalent weight average molecular weight of 30 × 10 ⁴ or more and a bound styrene amount of 30% by weight or less, a conjugated diene polymer and a vinyl aromatic hydrocarbon-conjugated diene copolymer. Has a polystyrene equivalent weight average molecular weight of 0.2 × 10 ⁴ to 8 × 10 ⁴ ,
A low molecular weight polymer component having an amount of bound styrene of 30% by weight or less, and a high molecular weight polymer component (hereinafter, referred to as a high molecular weight component) having a weight average molecular weight of 30 ×
When it is less than 10 ⁴ , when a low molecular weight polymer component (hereinafter, referred to as a low molecular weight component) is blended, the Mooney viscosity decreases, and not only the fracture property and wear resistance decrease, but also the viscosity decreases. It is not preferable because the processability is significantly deteriorated. More preferred weight average molecular weight of the high molecular weight component,
The range is from 50 × 10 ^{4 to} 150 × 10 ⁴ .

On the other hand, if the weight average molecular weight of the low molecular weight component is less than 0.2 × 10 ⁴ , no improvement in gripping power is observed, and if it exceeds 8 × 10 ⁴ , no improvement in gripping power is observed. Further, any of these is not preferable because the workability is deteriorated. The weight average molecular weight of the low molecular weight component is 0.5 × 10 ⁴
It is more preferably in the range of 4 × 10 ⁴ from the viewpoint of improving the grip properties in a wide temperature range from a low temperature to a high temperature.

If the amount of the low molecular weight component is less than 30 parts by weight based on 100 parts by weight of the high molecular weight component, a sufficient effect of improving grip properties cannot be obtained, which is not preferable. If the low molecular weight component exceeds 120 parts by weight with respect to 100 parts by weight of the high molecular weight component, the Mooney viscosity of the blend decreases, the fracture property and abrasion resistance decrease, and the viscosity decreases and the processability becomes remarkable. It is not preferable because it deteriorates.

Further, paying attention to the microstructure of the high molecular weight component and the low molecular weight component to be blended, if the amount of bound styrene contained in each exceeds 30% by weight, the molecules of the low molecular weight component are less likely to be entangled. As a result, the effect of improving grip properties becomes insufficient, and the flexibility at low temperatures is reduced. When the bound styrene amount (% by weight) is S and the vinyl content (% by weight) is V, both the high molecular weight component and the low molecular weight component need to satisfy the following formula. This equation is the Tg (glass transition temperature) of the S and V contents.
Index correlated to Tg, taking into account the contribution to
Is shown.

S + (V / 2) <25 If this value is 25 or more, the flexibility at low temperatures is undesirably reduced.

The rubber composition obtained by vulcanizing the polymer blend of the present invention, which satisfies the above conditions, is extracted with chloroform in an amount of 15% by weight or more based on the amount of the low molecular weight component. It is necessary. The more this extract is, the better, but preferably 30 to 98% by weight. If the amount of chloroform extract is less than 15% by weight, the improvement in gripping properties becomes insufficient.

The polymer contained in the rubber raw material of the present invention contains a low molecular weight component and a high molecular weight component selected from a conjugated diene polymer and a vinyl aromatic hydrocarbon-conjugated diene copolymer.

The conjugated diene polymer has a content of 4 per molecule.
It is obtained by polymerizing a conjugated diene hydrocarbon containing from 4 to 12, preferably from 4 to 8 carbon atoms as a monomer. Examples of the conjugated diene hydrocarbon monomer used include 1,3-butadiene, Isoprene, a few
-Dimethyl-1,3-butadiene, 1,3-pentadiene, octadiene and the like are listed, and 1,3-butadiene is particularly preferred. These may be used alone or as a mixture of two or more. As the conjugated diene polymer, polybutadiene is preferable from an industrial viewpoint.

The vinyl aromatic hydrocarbon-conjugated diene copolymer is obtained by copolymerizing the above-mentioned conjugated diene hydrocarbon monomer with a vinyl aromatic hydrocarbon monomer. Examples of the hydrogen monomer include styrene, α-methylstyrene, p-methylstyrene, o-methylstyrene, p-butylstyrene, and vinylnaphthalene, and styrene is particularly preferable. These may be used alone or as a mixture of two or more. As the vinyl aromatic hydrocarbon-conjugated diene copolymer, a styrene-butadiene copolymer is preferable from an industrial viewpoint.

The method for producing the polymer component used here is not particularly limited, provided that it satisfies the above conditions.
Any polymerization method may be used. From an industrial point of view,
Anionic solution polymerization, coordination polymerization using a lithium initiator, or emulsion polymerization using dodecyl mercapton or the like is used.

In the case of synthesizing by anionic solution polymerization using a lithium-based initiator, it is preferable to use a lithium compound as an initiator. Examples of the lithium compound used include ethyl lithium, propyl lithium, and n.
-Butyllithium, sec-butyllithium, tert-butyllithium, alkyllithium such as hexyllithium,
Other hydrocarbon lithiums such as alkylenedilithium, phenyllithium, stilbenedilithium, a reaction product of butyllithium and divinylbenzene such as 1,4-dilithiobutane, or organometallic lithiums such as tributyltinlithium, lithium diethylamide, lithiumdiisopropylamide And lithium amides such as lithium piperidide. Preferably, it is n-butyllithium or sec-butyllithium. These lithium compounds may be used alone or in combination of two or more. These lithium compounds can be used in the range of 0.2 to 30 mmol per 100 g of the monomer, and the molecular weight of the polymer can be easily adjusted by adjusting the concentration of the lithium compound. In this polymerization, a randomizer is preferably used, and ethers such as THF (tetrahydrofuran) and the like which are generally well known and used; amines; hydrides of alkali metals and alkaline earth metals; Alcohol salts of alkali metals and alkaline earth metals such as potassium t-amylate;
Randomizers such as alkali metal and alkaline earth metal carboxylate, sulfonate and amine salts can be used alone or in combination as needed. When using a randomizer, it is preferable to use THF, potassium t-amylate, or the like. As the polymer synthesized by solution polymerization, a styrene-butadiene copolymer is preferable.

Examples of polymers polymerized by coordination polymerization include nickel, cobalt, neodymium and the like, for example, TiC
_{l 4 I 2 -AlR 3 (R} :. an alkyl group hereinafter referred to as the same), organic carboxylic acid cobalt -AlR ₂ Cl @ -
H ₂ O, nickel organic carboxylate-BF _3. (C ₂ H
₅ ) High cis-1,4-polybutadiene obtained using a coordination catalyst such as ₂ O—AlR ₃ as a catalyst, magnesium,
High transformer obtained using lithium and barium as catalysts
1,4-polybutadiene, high trans styrene-butadiene rubber; and the like.

Preferably, the conjugated diene polymer and vinyl aromatic hydrocarbon-conjugated diene copolymer are butadiene rubber and butadiene / styrene copolymer rubber, and both the high molecular weight component and the low molecular weight component are used. Butadiene rubber is preferred from the viewpoint of the balance between low-temperature properties and grip properties.

When a low molecular weight component and a high molecular weight component are blended to obtain a polymer contained in a rubber raw material, the low molecular weight component and the high molecular weight component may be dry-blended or may be preliminarily polymerized. The subsequent cements may be blended with each other, and when performing cement blending, cold flow of low molecular weight components can be prevented.

In the rubber raw material of the present invention, a natural rubber and / or another synthetic rubber can be blended with the above-mentioned polymer. In the case of blending, the polymer is used as a rubber raw material 100
It is necessary to add 20 parts by weight or more per part by weight, and preferably 30 parts by weight or more. For example, in a blend with natural rubber, if the amount of the polymer is less than 20 parts by weight, the flexibility and grip at low temperatures are insufficiently improved, which is not preferable.

The synthetic rubber used as a blend includes cis-1,4-polyisoprene, low cis-1,4
Polybutadiene, high cis-1,4-polybutadiene,
Examples thereof include an ethylene-propylene diene copolymer, chloroprene, halogenated butyl rubber, acrylonitrile-butadiene rubber (NBR), and the like.

In the present invention, in addition to the above rubber raw materials, vulcanizing agents such as sulfur commonly used in the rubber industry, vulcanization accelerators such as DM (dibenzothiazyl disulfide) and DPG (diphenylguanidine), BHT An anti-aging agent such as (2,6-di-t-butyl-p-cresol), a filler, and additives such as zinc oxide, stearic acid, and an ozone deterioration inhibitor can also be blended.

Typical examples of the filler used in the present invention include carbon black and white filler. Examples of the carbon black include HAF, ISAF, and SAF.
AF and the like. Preferably, carbon black having an iodine adsorption amount (IA) of 60 mg / g or more and a dibutyl phthalate oil absorption (DBP) of 80 ml / 100 g or more is used. Also, as a white filler,
For example, silica (hydrous silicic acid), silicic anhydride, calcium silicate, aluminum silicate, clay, talc, calcium carbonate, basic magnesium carbonate, alumina hydrate,
Diatomaceous earth, barium sulfate, mica, alumina sulfate, titanium oxide and the like can be mentioned, among which silica is preferable. These fillers may be used in combination, and by using them together, the effect of improving various physical properties can be increased.

The rubber composition of the present invention is obtained by kneading using a kneading machine such as a roll or an internal mixer, etc., and after molding, vulcanization is performed to obtain a tire tread, an undertread, a carcass, It can be used not only for tire applications such as sidewalls and bead portions, but also for applications such as anti-vibration rubber, belts, hoses, and other industrial products, but is particularly suitably used as a rubber for tire treads.

[0029]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the scope of the present invention. In the examples, parts and% mean parts by weight and% by weight, respectively, unless otherwise specified.

Various measurements were made by the following methods. The weight average molecular weight and molecular weight distribution of the polymer were measured by gel permeation chromatography (GPC), the differential refractive index (RI), and tetrahydrofuran (TH
Using F), the measurement was performed in terms of polystyrene using monodisperse polystyrene as a standard.

The microstructure of the butadiene portion of the styrene-butadiene copolymer was determined by the infrared method (D. Moreroe).
t al. Chem. Ind. , 41, 758 (19
59)). The bound styrene content is 6
It was determined from a calibration curve by the infrared method based on the absorption of the phenyl group at 99 cm ^-1 .

The amount of chloroform extract was obtained by extracting a vulcanized rubber sample with a Soxhlet extractor using chloroform as a solvent for 48 hours, and calculating the amount of extraction from the residual amount of vulcanized rubber.

As an index of hysteresis loss and grip performance of the vulcanized rubber composition, tan δ was used. tan
It is evaluated that the larger δ, the better the hysteresis loss property and the grip property. As an indicator of flexibility at low temperatures,
A -20 ° C storage modulus was used. The tan δ and the storage elastic modulus at −20 ° C. were measured using a viscoelasticity measuring device (manufactured by Rheometrics), where tan δ was 0 ° C. and the storage elastic modulus was −
At 20 ° C., strain 0.1% and frequency 10
Hz.

The tensile strength was measured according to JIS K6301. Also, the shrinkage rate is RHEOGRAPH 2
000 (Rheograph 2000: trade name, GOTTFE
RT Co., Ltd.). Using an isosceles triangular 2 mm thick die with a base 8 mm and a height 2 mm,
The extrudate was extruded at 10 mm / sec, and the shrinkage was calculated from the ratio of the length of the extrudate immediately after extrusion and after standing for 24 hours.

As for the shrinkage, a level having no practical problem was evaluated as good (○), a slightly poor level was evaluated as Δ, and a level causing practical problems was evaluated as poor (x).

In the following examples, the processability was evaluated by observing the processability at the time of preparing the vulcanized rubber composition, and evaluated as ○ for good, Δ for slightly poor, and × for poor.

[Synthesis Example 1] A dried and degassed 5-liter reactor was thoroughly washed with a dried and degassed cyclohexane and n-butyllithium solution, and then 15.5.
G of 1,3-butadiene in hexane solution
Is injected under nitrogen pressure, and while stirring, the temperature in the
After the temperature was adjusted to 0 ° C, 0.96 ml of a 1.6N n-butyllithium solution was added to carry out polymerization. After polymerization is complete,
About 30 ml of isopropyl alcohol containing 1 part by weight of 2,6-di-t-butyl-p-cresol (BHT) was added as an antioxidant, and the polymerization was completely stopped. The weight average molecular weight of the obtained polymer was 85 × 10 ⁴ , and the vinyl content was 10%. This is referred to as a high molecular weight polymer component.

Next, a polymer was obtained in the same manner as in the polymer except that this method was changed to 25 ml of a 1.6N n-butyllithium solution. The weight average molecular weight of the obtained polymer was 2.0 × 10 ⁴ , and the vinyl content was 10%. This is referred to as a low molecular weight polymer component.

The high molecular weight polymer component and the low molecular weight polymer component are cement blended at a predetermined blend ratio, then steam trapped, and then dried in a hot air drying oven at 60 ° C. for at least 5 hours to obtain a polymer. A blend was obtained.

[Examples 1 to 11 and Comparative Examples 1 to 8] The low molecular weight components having the molecular weights and microstructures as shown in Table 1 were adjusted by adjusting the amount of n-butyllithium and the amount of styrene / butadiene monomer, or , THF, tertiary amine, etc., by adjusting the type and amount of randomizer. This low-molecular-weight component was obtained by mixing the weight average molecular weight of 85 × obtained in Synthesis Example 1 above.
Cement was blended with 10 ⁴ , a high molecular weight component having a vinyl content of 10%, and a predetermined blend ratio shown in Table 1 to obtain a polymer blend as a sample.

The obtained polymer blend was kneaded with a 250 ml plastmill (manufactured by Toyo Seiki Co., Ltd.) in accordance with the formulation shown in Table 2, and the obtained composition was vulcanized at 145 ° C. for 33 minutes to obtain a vulcanized rubber. A composition was obtained.

Further, the viscoelasticity and tensile strength of this vulcanized rubber composition were measured, and the amount of chloroform extract was measured. The results are shown in Table 3.

[Comparative Examples 9 to 10] As Comparative Examples 9 and 10, the following commercially available rubbers were evaluated in the same manner as in Example 1. Table 3 shows the results. BR made by Nippon Synthetic Rubber
01 (weight average molecular weight: 46 × 10 ⁴ , vinyl content 3
%) And SBR # 1500 (weight average molecular weight: 45 × 10 ⁴ , styrene content: 23.5, manufactured by Nippon Synthetic Rubber Co., Ltd.)
%, Vinyl content 18%).

Comparative Example 11 100 parts by weight of polybutadiene having a weight average molecular weight of 25 × 10 ⁴ and a vinyl content of 10% as a high molecular weight component, and a low molecular weight component having a weight average molecular weight of 2.0 × 10 ⁴ and vinyl A polymer blend was obtained by cement blending 100 parts by weight of polybutadiene having a content of 10%.

This blend was prepared in the same manner as in Example 1,
A rubber composition was obtained. Evaluation was performed in the same manner as in Example 1. Table 3 shows the results.

Comparative Example 12 A styrene / butadiene copolymer having a weight average molecular weight of 90 × 10 ⁴ , a styrene content of 23.5% and a vinyl content of 17% was used as a high molecular weight component.
100 parts by weight of polybutadiene having a weight average molecular weight of 2.0 × 10 ⁴ and a vinyl content of 10% as a low molecular weight component was cement blended with 100 parts by weight to obtain a polymer blend.

This blend was prepared in the same manner as in Example 1,
A rubber composition was obtained. Evaluation was performed in the same manner as in Example 1. Table 3 shows the results.

Comparative Example 13 100 parts by weight of polybutadiene having a weight average molecular weight of 85 × 10 ⁴ and a vinyl content of 10% as a high molecular weight component, and a low molecular weight component having a weight average molecular weight of 2.0 × 10 ⁴ and vinyl A polymer blend was obtained by cement blending 100 parts by weight of polybutadiene having a content of 10%.

This blend was prepared by adding 1.5 parts of sulfur to 2.5 parts of the vulcanization accelerator DPG in the formulation shown in Table 2.
A rubber composition was obtained in the same manner as in Example 1 except that 0.6 part was added as 1.0 part. Evaluation was performed in the same manner as in Example 1. Table 3 shows the results.

[Synthesis Example 2] A solution prepared by dissolving 224 g of 1,3-butadiene in 576 g of dehydrated benzene was placed in a 2-liter autoclave which had been dried and purged with nitrogen, and 2.2 mmol of water was further added thereto for 30 minutes. Stirring was performed. The temperature of this solution was adjusted to 50 ° C., 2.9 mmol of diethylaluminum chloride, 0.008 mmol of cobalt octoate and 1.5 mmol of 1,5-cyclooctadiene were added, and the mixture was stirred for 30 minutes to remove polybutadiene. Obtained.

The polymerization was stopped by adding 5 ml of a methanol / benzene mixture (50:50) containing 0.5 g of BHT.

The weight average molecular weight of the obtained polymer (polybutadiene) was 105 × 10 ⁴ , and the microstructure of the butadiene portion was 96.6% of cis, 2.1% of vinyl / 1.3% of trans. This is referred to as a high molecular weight polymer component.

Examples 12 and 13 and Comparative Example 14 Low molecular weight components having a molecular weight and a microstructure as shown in Table 4 were added to n-butyllithium, the amount of styrene / butadiene monomer was adjusted, or THF was added. And a randomizer such as a tertiary amine and the amount of addition were adjusted. This low-molecular-weight component was combined with the weight-average molecular weight of 105 obtained in Synthesis Example 2 above.
A high molecular weight component of × 10 ⁴ and a cement blend at a predetermined blend ratio described in Table 4, steam trapping, and then drying in a hot air drying oven at 60 ° C. for at least 5 hours to obtain a polymer blend as a sample I got something.

The obtained polymer blend was kneaded with a 250 ml plastmill (manufactured by Toyo Seiki Co., Ltd.) according to the formulation shown in Table 2, and the resulting composition was vulcanized at 145 ° C. for 33 minutes to obtain a vulcanized rubber. A composition was obtained.

Further, the viscoelasticity and tensile strength of this vulcanized rubber composition were measured, and the amount of chloroform extract was measured. The results are shown in Table 5.

Comparative Example 15 A polymer was obtained in the same manner as in Synthesis Example 2 except that 1,5-cyclooctadiene was changed to 120 mmol. The weight average molecular weight of the obtained polymer was 8.5 × 10 ⁴ , and the microstructure of the butadiene portion was 96.6% of cis and 2.1% of vinyl.
/, Trans 1.3%. This was used as a low molecular weight polymer component.

Using this low molecular weight component, cement was blended in the same manner as in Example 12 at a predetermined blending ratio shown in Table 4 to obtain a vulcanized rubber composition.

Further, the viscoelasticity, tensile strength, storage modulus at -20 ° C., and the amount of chloroform extract of this vulcanized rubber composition were measured in the same manner as in Example 1, and the results are shown in Table 5.

[0059]

[Table 1]

[0060]

[Table 2]

[0061]

[Table 3]

[0062]

[Table 4]

[0063]

[Table 5]

As shown in Tables 3 and 5, the rubber composition of this example has excellent vulcanizate properties such as excellent tensile strength, high hysteresis loss, and excellent flexibility at low temperatures. It was found to be a composition. These effects are as follows: 100 parts by weight of a high molecular weight component having a weight average molecular weight of 30 × 10 ⁴ or more has a weight average molecular weight of 0.2.
30 to 120 parts by weight of a low molecular weight component of × 10 ⁴ to 8 × 10 ⁴ , which is recognized when each component has a specific microstructure (Examples 1 to 11), whereas the molecular weight of the low molecular weight component is When the amount added is out of the range of the present invention, good shrinkage and processability cannot be obtained, and in most cases, high grip properties are not observed (Comparative Examples 1 to 4).
4), high molecular weight component and / or low molecular weight component S + (V
When (2) is out of the range of the present invention, the flexibility at low temperature is significantly impaired and the effect of the present invention is not observed (Comparative Examples 5 to 8 and 12). When the molecular weight of the low molecular weight component was small (Comparative Example 11), it was shown that although the flexibility at low temperature was excellent, the tensile strength was significantly reduced, and the shrinkage and processability were poor. In addition, when the amount of chloroform extracted was small (Comparative Example 13), it was found that even if the amounts of the vulcanizing agent and the vulcanization accelerator were increased, no improvement in the grip properties was observed.

Further, it was revealed that all of the commercially available rubber compositions were inferior in either grip property or flexibility at low temperature (Comparative Examples 9 and 10). (Examples 12 and 13), the effect of the present invention was recognized even when the molecular weight was high. Even in this case, when the molecular weight of the low molecular weight component was large and when the low molecular weight component was small (Comparative Examples 14 and 15). No high grip properties were observed, and it was clarified that shrinkage and workability were poor.

[0066]

As described above, the rubber composition of the present invention is excellent in flexibility at low temperatures, has good grip on ice and snow, not only under ordinary conditions, but also has good processing properties such as roll winding property. It has an excellent effect that the properties are good and the shrinkage ratio is improved.

Claims (4)

[Claims] 1. A conjugated diene polymer and a vinyl aromatic hydrocarbon-conjugated diene copolymer having a weight average molecular weight in terms of polystyrene of 30 × 10 ⁴ or more and a bound styrene content of 30% by weight or less. Selected from a conjugated diene polymer and a vinyl aromatic hydrocarbon-conjugated diene copolymer, having a polystyrene equivalent weight average molecular weight of 0.2 × 10 ⁴ to 8 × 10 ⁴ and a bound styrene amount of A low-molecular-weight polymer component that is 30% by weight or less, and the high-molecular-weight polymer component contains 30 to 120 parts by weight of the low-molecular-weight polymer component with respect to 100 parts by weight of the high-molecular-weight polymer component. And when the amount of bound styrene (% by weight) is S and the vinyl content (% by weight) is V in the low molecular weight polymer component, the high molecular weight polymer component and the low molecular weight S + (V / 2) <25, and the rubber component obtained by vulcanizing the polymer blend is extracted with chloroform to extract the low molecular weight molecular weight polymer component. The rubber composition is 15% by weight or more with respect to the rubber composition. 2. The rubber composition according to claim 1, wherein the low molecular weight polymer component has a weight average molecular weight in terms of polystyrene of 0.5 × 10 ⁴ to 4 × 10 ⁴ . 3. The rubber composition according to claim 1, wherein the conjugated diene polymer and vinyl aromatic hydrocarbon-conjugated diene copolymer are butadiene rubber and butadiene / styrene copolymer rubber. 4. The rubber composition according to claim 1, wherein the high molecular weight polymer component and the low molecular weight polymer component are both butadiene rubbers.