JPH09268238A - Rubber composition for tire tread - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition having remarkably improved low hysteresis loss while keeping good wet-skid performance by compounding silica to a polymer produced by using an organic lithium compound as a polymerization initiator. SOLUTION: This rubber composition is produced by compounding (A) 100 pts.wt. of a rubber component consisting of (i) >=30wt.% of at least one kind of polymer selected from isoprene polymers and isoprene-styrene copolymers produced by using an organic lithium compound as a polymerization initiator and (ii) the remaining part of a diene rubber with (B) 20-120 pts.wt. of silica, (C) <=100 pts.wt. of carbon black and (D) 0.2-10 pts.wt. of at least one kind of silane coupling agent expressed by Y3 -Si-Cn H2n A [Y is a 1-4C alkyl, an alkoxyl or Cl; (n) is 1-6; A is Sm Cn H2n Si-Y3 , X or Sm Z (X is nitroso, mercapto, etc.; Z is a group of formula I to formula III; (m) is 1-6)].

Description

Detailed Description of the Invention

[0001]

[0001] The present invention relates to a rubber composition for a tire tread. In particular, the present invention relates to a rubber composition which can be suitably used for a tread of a pneumatic tire in which rolling resistance is significantly reduced without lowering wet skid resistance and fracture resistance.

[0002]

2. Description of the Related Art In recent years, due to social demands for resource saving and energy saving, research on reducing rolling resistance of tires has become important in order to save fuel consumption of automobiles. It is generally known that if the rolling resistance of the tire is reduced, the fuel consumption of the automobile is reduced, and it becomes a so-called low fuel consumption tire.To reduce the rolling resistance of the tire,
It is general to use a material having a small hysteresis loss for the tread rubber of the tire. On the other hand, from the requirement of running stability, friction resistance on wet road surface (wet skid resistance)
There is a strong demand for large rubber materials. However, these low rolling resistance and frictional resistance on a wet road surface have a trade-off relationship, and it has been very difficult to satisfy both characteristics.

Recently, the correspondence between the rolling resistance and wet skid resistance of a tire and the viscoelastic properties of a rubber composition has been theoretically shown. According to this, in order to reduce the rolling resistance when the tire is running, the hysteresis loss of the tread rubber is made small, that is, in terms of viscoelasticity, the loss tangent (tan
It has been shown that lowering δ) is effective for fuel economy. On the other hand, wet skid resistance is 10 to 2
It is known to correlate well with the loss tangent in the vicinity of 0 ° C. under the frequency of 0 Hz. Therefore, in order to improve the grip performance of the tire, it is necessary to increase the loss tangent in the vicinity of 0 ° C.

As a method of reducing the hysteresis loss, that is, a method of lowering tan δ at a temperature of 50 to 70 ° C., a material having a low glass transition temperature such as high cis polybutadiene rubber or a material having a high impact resilience like natural rubber is used. It is common to use materials. However, with these rubbers, the wet skid resistance is extremely lowered, and it has been extremely difficult to achieve both running stability and low rolling resistance in the related art.

On the other hand, according to Japanese Examined Patent Publication No. 40-20262, a tire having a tread in which silica is blended with a rubber composition containing butadiene rubber, oil and carbon black has improved slip resistance. Is disclosed. However, in this case, it is expected that the wear resistance is poor due to the low modulus. Further, Japanese Patent Publication No. 38-26765 proposes a method of obtaining a rubber having a modulus higher than that of a usual kneading method by mixing silica sol with rubber latex and then spray-drying. However, at present, even this method does not reach the reinforcing effect of carbon black.

Further, JP-A-50-88150 proposes a tread rubber for winter tires which is excellent in slip resistance by using an alkoxysilane compound containing silica and a sulfur atom, but obtains preferable tread physical properties. Therefore, a large amount of alkoxysilane compound is required.

Further, in Japanese Patent Publication No. 49-36957, a lithium terminal polymer obtained by using an organolithium compound as a catalyst is reacted with silicon tetrahalide, trichloromethylsilane or the like for the purpose of improving processability. Therefore, a method for producing a branched polymer centered on the alkoxysilane compound has been proposed, but since the functional group having reactivity with silica does not remain in the obtained polymer, silica was used as the filler. The tensile strength of the vulcanized product is insufficient. Further, the rubber in which silica is blended with this polymer increases the viscosity and the green strength in the unvulcanized state, so that the rolling and extrudability can be improved, but there is a drawback that permanent elongation and dynamic heat generation are large. are doing.

Further, in recent years, many inventions have been made to solve the above-mentioned antinomy problem by utilizing anionic polymerization. For example, JP-A-55-12133 and JP-A-56-127.
In each publication of 650, high vinyl polybutadiene rubber is disclosed in JP-A-57-55204 and JP-A-57-7303.
In Japanese Patent No. 0, it is proposed that a high vinyl styrene butadiene copolymer rubber is effective in improving the antithetic problem. Also, JP-A-59-117514 and JP-A-61-161
103902, JP 61-14214, JP 6
Japanese Patent Publication No. 1-141741 discloses that heat generation is reduced by using a modified polymer in which a functional group such as benzophenone or isocyanate is introduced into the molecular chain of the polymer. However, none of the above methods sufficiently satisfy the recent required values for low rolling resistance.

Further, in JP-A-3-252431, polybutadiene or styrene-butadiene rubber is blended with silica and a silane coupling agent to improve various properties. However, when these polymers are used, further loss reduction can be achieved. difficult.

Further, in JP-A-3-252431, polybutadiene or styrene-butadiene rubber is blended with silica and a silane coupling agent to improve various properties, and in Patent Application Publication No. WO88 / 05448, alkoxysilane is disclosed. A system in which silica is compounded into a compound-modified rubber-like polymer, tensile strength is sufficiently high without using a large amount of reinforcing aid such as a silane coupling agent, wet skid characteristics are not deteriorated, and rolling resistance is further improved. Although it was reduced, it is difficult to satisfy the requirement for further loss reduction when S-SBR (solution polymerization SBR) is used.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to overcome the above-mentioned drawbacks of the prior art and to reduce wet skid resistance and fracture characteristics without significantly reducing rolling resistance. To provide a rubber composition that can be suitably used for the tread.

[0012]

In order to solve the above problems, the present invention has the following constitution. [I] The first rubber composition for a tire tread of the present invention comprises (1) (a) an organic lithium compound as an initiator,
(A) 100 parts by weight of a rubber component having 30% by weight or more of at least one polymer selected from the group consisting of isoprene polymers and isoprene-styrene copolymers, and (2) the balance being a diene rubber. relative, (3) silica 20 to 120 parts by weight, (4) less than 100 parts by weight of carbon black, and (5) general formula _{Y 3 -Si-C n H 2n} a (I) ( wherein , Y is an alkyl group having 1 to 4 carbon atoms, an alkoxyl group or a chlorine atom, and three Ys may be the same or different, and n is an integer of 1, 2, 3, 4, 5 or 6, and A
Is _{-S m C n H 2n Si-} Y 3 group, X group, or -S _m Z group, wherein X is a nitroso group, a mercapto group, an amino group, an epoxy group, a vinyl group, a chlorine atom or an imide group,
Z is

Embedded image Is any one of the groups represented by, m and n each represent an integer of 1, 2, 3, 4, 5 or 6, and Y is as described above. ). At least one kind of the silane coupling agent represented by (4) is mixed in an amount of 0.2 to 10 parts by weight. [II] The amount of bound styrene in the isoprene polymer and the isoprene-styrene copolymer is 40% by weight or less, and the total amount of 1,2 bonds and 3,4 bonds in the isoprene portion is 5%.
˜60% by weight. [III] Furthermore, the weight average molecular weight of the isoprene polymer and the isoprene-styrene copolymer is 2 × 10 ⁵ to 2
It is characterized by being 5 × 10 ⁵ . [IV] Furthermore, the second rubber composition for a tire tread of the present invention has (1) (a) the amount of bound styrene is 40% by weight or less,
(A) The total amount of 1,2 bonds and 3,4 bonds in the bound isoprene part is 5 to 60% by weight, and (c) an isoprene polymer and / or an isoprene-styrene copolymer obtained by anionic polymerization is used. 30% by weight or more, and the active end of the polymer is represented by the following general formula X _n Si (OR) _m R _4-mn (II) (wherein X is a chlorine atom, a bromine atom or an iodine atom, etc.). Is a halogen atom, R is an alkyl group having 1 to 20 carbon atoms, an aryl group, a vinyl group or a halogenated alkyl group, m is 1, 2, 3 or 4, n is 0, 1 or 2, and the sum of m and n is 2, 3 or 4) is added to 100 parts by weight of a rubber component containing 30% by weight or more of a modified polymer modified with at least one alkoxysilane compound selected from the group represented by (2) 20 to 120 weight of silica , And (3) of carbon black 100 parts by weight or less, and wherein the blending. [V] Further, the weight average molecular weight of the polymer is 2 × 10 ^5.
It is characterized in that it is ˜25 × 10 ⁵ .

[0013]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail. Examples of the silane coupling agent blended in the first rubber composition include bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (3-trimethoxysilylpropyl). Tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane,
2-mercaptoethyltriethoxysilane, 3-nitropropyltrimethoxysilane, 3-nitropropyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 2-chloroethyltrimethoxysilane, 2- Chloroethyltriethoxysilane, 3-trimethoxysilylpropyl-N,
N-dimethylthiocarbamoyl tetrasulfide, 3-
Triethoxysilylpropyl-N, N-dimethylthiocarbamoyltetrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyltetrasulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropylbenzo Thiazole tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-
Examples thereof include trimethoxysilylpropyl methacrylate monosulfide, and bis (3-triethoxysilylpropyl) tetrasulfide, 3-trimethoxysilylpropyl benzothiazole tetrasulfide, and the like are preferable.
Further, in the formula (2), three Ys may not be the same,
For example, as examples thereof, bis (3-diethoxymethylsilylpropyl) tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, 3-nitropropyldimethoxymethylsilane, 3-chloropropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N, N- Examples thereof include dimethylthiocarbamoyl tetrasulfide and dimethoxymethylsilylpropyl benzothiazole tetrasulfide.

The amount of silane coupling agent added is 0.2.
It is -10 parts by weight, preferably 0.5-5 parts by weight, and is adjusted by the amount of silica compounded. If the addition amount of the silane coupling agent is less than 0.2 parts by weight, the coupling effect is extremely small, and therefore the rolling resistance and abrasion resistance are not improved, and if it exceeds 10 parts by weight, the reinforcing property decreases and Abrasion resistance and cut resistance deteriorate.

The polymer according to the first rubber composition of the present invention may be modified with the alkoxysilane compound represented by the general formula (II) according to the present invention.

Examples of the inert organic solvent used in the production of the alkoxysilane compound-modified polymer of the second rubber composition include pentane, hexane, cyclohexane, heptane, benzene, xylene, toluene, tetrahydrofuran, diethyl ether. And so on.

The alkoxysilane compound to be reacted with the living polymer of the present invention is represented by the general formula (II) and R
Of these, as the alkyl group, a methyl group, an ethyl group, n-
Examples thereof include propyl group and t-butyl group, examples of aryl group include phenyl group, toluyl group and naphthyl group, and examples of halogenated alkyl group include chloromethyl group, bromomethyl group, iodomethyl group, chloroethyl group and the like.

In the general formula (II), n is 0 and m
Is 2 is a dialkyl dialkoxy silane, n is 0 and m is 3 is a monoalkyl trialkoxy silane, n
Is 0 and m is 4, tetraalkoxysilane, n is 1
Where m is 1, a monohalogenated dialkylmonoalkoxysilane, when n is 1 and m is 2, a monohalogenated monoalkyldialkoxysilane, and when n is 1 and m is 3, a monohalogenated trialkoxysilane. , N is 2 and m is 1, a dihalogenated monoalkyl monoalkoxysilane, and n is 2 and m is a dihalogenated dialkoxysilane, both of which are reactive with the active end of the living polymer. Is.

Particularly, a monoalkyltrialkoxysilane in which n is 0 and m is 3, a tetraalkoxysilane in which n is 0 and m is 4, and a monohalogenated monoalkyldialkoxysilane in which n is 1 and m is 2. Is preferred from the viewpoint of improving the processability by coupling the living polymer and further imparting to the polymer a functional group having a high affinity for silica and the like.

Specific examples of the alkoxysilane compound represented by the general formula (II) used in the present invention include, for example, tetrakis (2-ethylhexyloxy) silane,
Tetraphenoxysilane, methyltris (2-ethylhexyloxy) silane, ethyltris (2-ethylhexyloxy) silane, ethyltriphenoxysilane, vinyltris (2-ethylhexyloxy) silane, vinyltriphenoxysilane, methylvinylbis (2-ethylhexyloxy) Silane, ethylvinyldiphenoxysilane, tri-t-butoxymonochlorosilane, triphenoxymonochlorosilane, monochloromethyldiphenoxysilane, monochloromethylbis (2-ethylhexyloxy) silane, monobromoethyldiphenoxysilane, monobromovinyldiphenoxysilane Silane, monobromoisopropenylbis (2-ethylhexyloxy) silane, dichloro-di-t-butoxysilane, ditolyldichlorosilane, di- -Butoxydiiodosilane, diphenoxydiiodosilane, methyltris (2-methylbutoxy) silane, vinyltris (2-methylbutoxy) silane, monochloromethylbis (2-methylbutoxy) silane, vinyltris (3-methylbutoxy) silane, etc. Can be mentioned.

Of these alkoxysilane compounds,
Alkoxysilane compounds in which n is 0 or 1 are preferred, of which monochloromethyldiphenoxysilane, vinyltris (2-ethylhexyloxy) silane, and monochlorovinylbis (2-ethylhexyloxy) silane are particularly preferred. These alkoxysilane compounds may be used alone or in combination of two or more.

The alkoxysilane compound-modified rubber-like polymer of the present invention is obtained by reacting the active end of the living polymer with the alkoxysilane compound represented by the above general formula. The amount of the alkoxysilane compound used at this time is Is obtained by reacting preferably 0.7 molecules or more, more preferably 0.7 to 5.0, and still more preferably 0.7 to 2.0 molecules per active end of the living polymer, If it is less than 0.7 mol, a large amount of branched polymer is produced, the fluctuation of the molecular weight distribution is large, and it becomes difficult to control the molecular weight and the molecular weight distribution. Not preferable.

At this time, at the active end of the living polymer,
It is also possible to add the alkoxysilane compound in two steps, such as first adding a small amount of the alkoxysilane compound to form a polymer having a branched structure, and then modifying the remaining active terminal with another alkoxysilane compound. In the present invention, the reaction between the active end of the living polymer and the alkoxysilane compound having a functional group is carried out by adding the alkoxysilane compound to the solution of the living polymer, or living in an organic solution containing the alkoxysilane compound. It is carried out by adding a solution of the polymer.

The reaction temperature is -120 to + 150 ° C, preferably -80 to + 120 ° C, and the reaction time is 1 minute to 5 minutes.
The time is preferably 5 minutes to 2 hours. After the reaction,
Steam is blown into the polymer solution to remove the solvent, or a negative solvent such as methanol is added to solidify the alkoxysilane compound-modified rubbery polymer, which is then dried on a hot roll or under reduced pressure to obtain an alkoxysilane compound-modified rubber. Polymers can be obtained. It is also possible to directly remove the solvent from the polymer solution under reduced pressure to obtain an alkoxysilane compound-modified rubbery polymer.

The isoprene polymer and the styrene-isoprene copolymer of the first and second rubber compositions are
It is obtained by anionically polymerizing an isoprene monomer or an isoprene monomer and a styrene monomer. The polymerization initiator for the first rubber composition is an organolithium-based compound, but a lithium-based initiator is preferable for the polymerization of the polymer for the second rubber composition,
Examples thereof include methyllithium, ethyllithium, propyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium, hexyllithium, octyllithium, phenyllithium, cyclohexyllithium, and 1,4-dilithiobutane. Preferred are n-butyllithium and sec-butyllithium.

These organolithium compounds may be used alone or in combination of two or more. Moreover, these organolithium compounds can be used within a range of 0.2 to 20 mmol per 100 g of the monomer. The polymerization is usually performed in the range of -20 ° C to 150 ° C, preferably 20 ° C to 120 ° C. Further, the polymerization reaction may be carried out at an elevated temperature or at an isothermal temperature.

The hydrocarbon solvent used in both inventions is selected from aliphatic hydrocarbons, alicyclic hydrocarbons and aromatic hydrocarbons, preferably propane, n-butane, i-butane, n-pentane, i. -Pentane, cis-2-butene,
Trans-2-butene, i-butene, 1-butene, n-
Hexane, n-heptane, n-octane, i-octane, methylcyclopentane, cyclopentane, cyclohexane, 1-hexene, 2-hexene, 1-pentene,
One or two selected from 2-pentene, benzene, toluene, xylene, ethylbenzene and the like are used.

The monomer concentration in the solvent is usually 5 to 50% by weight, preferably 10 to 35% by weight. The polymer is characterized in that the amount of bound styrene is 40% by weight or less, and the total amount of 1,2 bonds and 3,4 bonds in the isoprene portion is 5 to 60% by weight. When the amount of bound styrene exceeds 40% by weight, hysteresis loss is large and low rolling resistance is lowered. When the total amount of 1,2 bonds and 3,4 bonds in the isoprene part is less than 5% by weight, it is difficult to produce, and when it exceeds 60% by weight, it becomes difficult to obtain a rubber-like product, and the hysteresis loss is large and the rolling property is low. Is reduced. Further, the polymers of both inventions may be block copolymers or random copolymers according to the structure of the living polymer.

The molecular weights of the isoprene polymer and the isoprene-styrene copolymer of both inventions can be varied over a wide range, but the weight average molecular weight is preferably 2 × 10 ^{5 to} 25 × 10 ⁵ . 2 x 10 ⁵
When it is less than 1, the hysteresis loss becomes large, the low rolling resistance is inferior, and the polymer exceeding 25 × 10 ⁵ tends to be difficult in production and the processability tends to be deteriorated.

The polymer obtained by using an organolithium compound as an initiator can be used alone as a rubber component, but if necessary, it is less than 70% by weight, preferably 50 parts by weight or less based on 100 parts by weight of the rubber. Other diene rubbers, such as natural rubber or other synthetic rubbers, namely emulsion and solution polymerized styrene-butadiene copolymers, polybutadiene, polyisoprene, acrylonitrile-butadiene copolymer (NBR), butyl rubber, ethylene-propylene- A diene terpolymer, a halogenated butyl rubber or the like can be blended and used. Further, the polymer is required to be 30% by weight or more in the rubber component, but if it is less than 30% by weight, low rolling resistance and wet skid resistance cannot be achieved at the same time.

The silica compounded in the rubber component in the present invention is used as a filler and is 20 to 120 parts by weight per 100 parts by weight of the rubber component. If it is less than 20 parts by weight, the effect of filling and reinforcing is small, so that the wear resistance is poor.
If it exceeds 120 parts by weight, the workability and the fracture properties are poor. It should be noted that 100 parts by weight or less of carbon black as a filler may be used in combination with silica, whereby the workability, abrasion resistance and cut resistance can be improved as compared with the case of using silica alone. In this case, the weight ratio of carbon black / silica is preferably in the range of 95/5 to 10 to 90 in terms of the balance between wet skid resistance, rolling resistance and abrasion resistance.

The rubber composition used in the present invention may further contain powdered fillers such as magnesium carbonate, calcium carbonate and clay, and fibrous fillers such as glass fibers and whiskers, if necessary. Of course, vulcanized rubber compounding agents such as zinc white, an antioxidant, a vulcanization accelerator, and a vulcanizing agent can be added.

[0033]

EXAMPLES First, the first rubber composition will be described based on examples. (1) Preparation of Polymers A to L (see Table 1) A reactor having an internal volume of 5 liters was charged with 2250 g of cyclohexane, 440 g of isoprene and 1.1 g of tetrahydrofuran under a nitrogen atmosphere. After adjusting the starting temperature to 30 ° C., 0.30 g of n-butyllithium was added, and under adiabatic condition,
Polymerization was performed at an elevated temperature to obtain a polymer A.

Hereinafter, copolymers B, C and G were obtained by charging a styrene monomer in addition to the isoprene monomer and changing the ratio thereof. Further, the amounts of n-butyllithium in copolymer B were changed to obtain copolymers E, F and H. Further, a polymer D was obtained by changing the amount of tetrahydrofuran added to the polymer A.

Next, 9.38 ml of a cyclohexane solution of monochloromethyldiphenoxysilane was added to the polymer solution of the copolymer B after polymerization (concentration: 0.50 mol / liter, n
The molar ratio of monochloromethyldiphenoxysilane to butyllithium corresponds to 1.00), the yellow anion of the living anion disappeared and the solution viscosity increased. Furthermore, the reaction was carried out at 50 ° C. for 30 minutes. After a predetermined time, 2,6-di-t-butylphenol (BH
T) was added in an amount of 0.7 g per 100 g of the polymer, steam-dissolved, and dried on a hot roll at 100 ° C. to obtain a copolymer I.

Further, in the copolymer I, vinyltris (2-) was used instead of monochloromethyldiphenoxysilane.
Each copolymer was obtained using ethylhexyloxy) silane (copolymer J), tetraphenoxysilane (copolymer K), and methyltriethoxysilane (copolymer L).

[0037]

[Table 1]

(2) Silane coupling agent The silane coupling agent shown in Table 2 is used.

[0039]

[Table 2]

(3) Blending and kneading According to the blending recipe shown in Table 3, kneading and blending is performed with a 250 ml Labo Plastomill and a 3 inch roll.

[0041]

[Table 3]

(4) Vulcanization The compounded rubber is vulcanized at 145 ° C. for 30 minutes. (5) Evaluation of Physical Properties of Polymers A to L (Result: See Table 4) The microstructure of the polymer was determined by proton NMR.

(6) Evaluation of Physical Properties of Vulcanized Rubber (Result: See Table 4) Measurement of Breaking Strength Based on JIS K-6301, the value in Comparative Example 1 was set to 100 and displayed as an index. Measurement of tan δ (50 ° C) Dynamic shear strain (amplitude 1.0%, at 50 ° C) using a dynamic spectrometer manufactured by Rheometrics Co., USA
Tan δ was measured by applying a frequency of 15 Hz), and the reciprocal of this was expressed as an index with the value in Comparative Example 1 being 100. Therefore, the larger the value, the smaller the hysteresis loss and the better. Wet skid resistance measurement The measurement temperature is 0 ° C., tan δ is measured in the same manner as above,
The value in Comparative Example 1 was set to 100 and displayed as an index. The larger the value, the larger the wet skid resistance and the better.

[0044]

[Table 4]

Comparative Example 2 is IR2200 manufactured by Japan Synthetic Rubber Co., Ltd. as a rubber component, and Comparative Example 3 is E-SB manufactured by the same company.
R (# 1500), Comparative Example 4 is S-SBR (SL
552) was used.

Next, the second rubber composition will be described based on examples. (1) Preparation of Polymers M, N, O, P, Q, R, S (Table 5
Reference) A reactor having an internal capacity of 5 liters is charged with 2250 g of cyclohexane, 440 g of isoprene and 1.1 g of tetrahydrofuran under a nitrogen atmosphere. After adjusting the starting temperature to 30 ° C., 0.30 g of n-butyllithium was added, and under adiabatic condition,
Polymerization was carried out at elevated temperature.

Next, a cyclohexane solution of monochloromethyldiphenoxysilane (9.38 m) was added to the polymer solution.
1 (concentration 0.50 mol / l, the molar ratio of monochloromethyldiphenoxysilane to n-butyllithium corresponds to 1.00) was added, the yellow anion of the living anion disappeared and the solution viscosity was high. became. Furthermore, the reaction was carried out at 50 ° C. for 30 minutes. After a certain time, 2, 6
-Di-t-butylphenol (BHT) polymer 100
0.7 g per g was added, the solution was melted with steam, and then dried with a hot roll at 100 ° C. to obtain a polymer M. Further, a polymer O was obtained by changing the amount of tetrahydrofuran added to the polymer M.

Hereinafter, styrene monomer was charged in addition to isoprene monomer, and the ratio thereof was changed to obtain copolymers N and S. Further, the amount of n-butyllithium in copolymer I was changed to obtain copolymers P, Q and R. In Comparative Example 24, alkoxysilane-modified SBR was used.
20% by weight of bound styrene, 60% of vinyl bond
% By weight.

[0049]

[Table 5]

(2) Blending and kneading According to the blending recipe shown in Table 6, kneading and blending is performed with a 250 ml Labo Plastomill and a 3 inch roll.

[0051]

[Table 6]

(3) Vulcanization The compounded rubber is vulcanized at 145 ° C. for 30 minutes. (4) Evaluation of Physical Properties of Polymer (Result: See Table 7) The microstructure of the polymer was determined by proton NMR.

(5) Evaluation of Physical Properties of Vulcanized Rubber (Result: See Table 7) Measurement of Breaking Strength Based on JIS K-6301, the value in Comparative Example 21 was set to 100 and displayed as an index. Measurement of tan δ (50 ° C) Dynamic shear strain (amplitude 1.0%, at 50 ° C) using a dynamic spectrometer manufactured by Rheometrics Co., USA
The frequency was set to 15 Hz) and tan δ was measured, and the reciprocal of this was expressed as an index with the value in Comparative Example 21 being 100. Therefore, the larger the value, the smaller the hysteresis loss and the better. Wet skid resistance measurement tan δ was measured in the same manner as above except that the measurement temperature was 0 ° C., and the value in Comparative Example 21 was set to 100 and displayed as an index. The higher the number, the greater the wet skid resistance,
It is good.

[0054]

[Table 7]

[0055]

As described above, according to the first rubber composition of the present invention, the following effects can be obtained. By blending silica into the polymer obtained using an organolithium compound as an initiator and using a silane coupling agent, while maintaining the wet skid performance, the low loss property of isoprene is utilized, and the low hysteresis loss property is obtained. It is possible to provide a significantly improved rubber composition. That is, it can be suitably used for a tire tread excellent in low hysteresis loss property without losing wet skid resistance and breaking properties.

Further, according to the second rubber composition of the present invention, the following effects can be obtained. The alkoxysilane compound-modified polymer in the present invention is a polymer in which the low hysteresis loss property is remarkably improved by the effect of the low loss property and modification of isoprene while maintaining the wet skid performance by incorporating silica. . Therefore, the rubber composition of the present invention can be suitably used for a tire tread excellent in low hysteresis loss without losing wet skid resistance and fracture characteristics.

Claims (5)

[Claims] 1. A weight of at least one polymer selected from the group consisting of (1) (a) an organolithium compound as an initiator and (a) an isoprene polymer and an isoprene-styrene copolymer. % Or more, and (2) the balance is a diene rubber, 100 parts by weight of a rubber component, (3) 20 to 120 parts by weight of silica, (4) 100 parts by weight or less of carbon black, and (5) ) general formula Y ₃ in _{-Si-C n H 2n a (} I) ( the following formula, Y is an alkyl group having 1 to 4 carbon atoms and the three Y alkoxyl group or a chlorine atom may be the same or different , N represents an integer of 1, 2, 3, 4, 5 or 6, and A
Is _{-S m C n H 2n Si-} Y 3 group, X group, or -S _m Z group, wherein X is a nitroso group, a mercapto group, an amino group, an epoxy group, a vinyl group, a chlorine atom or an imide group,
Z is Is any one of the groups represented by, m and n each represent an integer of 1, 2, 3, 4, 5 or 6, and Y is as described above. ) At least one of the silane coupling agents represented by (4) is mixed in an amount of 0.2 to 10 parts by weight, and the rubber composition for a tire tread is characterized. 2. The amount of bound styrene in the isoprene polymer and the isoprene-styrene copolymer is 40% by weight or less, and the total amount of 1,2 bonds and 3,4 bonds in the isoprene part is 5 to 60% by weight. The rubber composition for a tire tread according to claim 1, wherein 3. The weight average molecular weight of the isoprene polymer and the isoprene-styrene copolymer is 2 × 10 ^{5 to} 25 ×.
The rubber composition for a tire tread according to claim 1 or 2, wherein the rubber composition is 10 ⁵ . 4. (1) The amount of (a) bound styrene is 40% by weight or less, and (i) the total amount of 1,2 bonds and 3,4 bonds in the bound isoprene part is 5 to 60% by weight, (C)
An isoprene polymer and / or isoprene-styrene copolymer obtained by anionic polymerization is contained in an amount of 30% by weight or more, and the active end of the polymer is represented by the following general formula X _n Si (OR) _m R _{4- mn} (II) (wherein X is a chlorine atom, a bromine atom or an iodine atom, R is
Is an alkyl group having 1 to 20 carbon atoms, an aryl group, a vinyl group or a halogenated alkyl group, m is 1, 2, 3 or 4, n is 0, 1 or 2, and the sum of m and n is 2, 3 or 4.
Is shown. ) A modified polymer modified with at least one alkoxysilane compound selected from the group represented by
A rubber composition for a tire tread, characterized in that (2) 20 to 120 parts by weight of silica and (3) 100 parts by weight or less of carbon black are compounded with respect to 100 parts by weight of a rubber component contained by weight% or more. . 5. The weight average molecular weight of the polymer is 2 × 10.
^The rubber composition for a tire tread according to claim 4, wherein the rubber composition is ^{5 to} 25 × 10 ⁵ .