JPH07188462A - Rubber composition for tire tread - Google Patents

Abstract

PURPOSE:To obtain a rubber compsn. which has an improved rolling resistance without detriment to wet skid resistance and is suitable for a low-fuel- consumption tire tread. CONSTITUTION:A rubber compsn. contains, as the rubber component, 90-50wt.% at least one rubber selected from the group consisting of natural rubbers and synthetic polyisoprene rubbers and 10-50wt.% styrene-butadiene copolymer which is obtd. by soln. polymn. and has a microstructure satisfying the relations: 15<=Vi<=70, ST<=50, Vi+2ST>100, and Vi-2ST<10 [wherein ST is the styrene content (%) in the copolymer; and Vi is the content of 1,2-bond (%) in the combined butadiene units].

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a rubber composition for a tire tread. More specifically, the present invention relates to a rubber composition that can be suitably used for a tread of a pneumatic tire that has significantly reduced rolling resistance and good wear resistance without deteriorating wet skid resistance and fracture resistance.

[0002]

2. Description of the Related Art In recent years, due to social demands for energy saving and resource saving, research into 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, use a material with small hysteresis loss as the tread rubber. Is common. Further, due to the requirement of running stability, a rubber material having a large frictional resistance (wet skid resistance) on a wet road surface has been strongly desired. However, these low rolling resistance and frictional resistance on a wet road surface have an antinomy relationship, and it is very difficult to satisfy both characteristics. Recently, the correspondence between the wet skid resistance and rolling resistance of a tire and the viscoelastic characteristics of a rubber composition is theoretically shown, and the hysteresis loss of the tread rubber is reduced to reduce the rolling resistance during tire running, that is, Tires are used when driving in terms of viscoelasticity
It has been shown that lowering the loss tangent (tan δ) at a temperature of 50 to 70 ° C. is effective for fuel economy. On the other hand, wet skid resistance is known to correlate well with the loss tangent (tan δ) near 0 ° C under a frequency of 10 to 20 Hz. Therefore, in order to improve the grip performance of a tire, a temperature near 0 ° C is known. It is necessary to increase the loss tangent of. How to reduce hysteresis loss, ie
As a method for lowering the loss tangent (tan δ) at a temperature of 50 to 70 ° C., it is common to use a material having a low glass transition temperature such as high cis polyptadienene rubber or a material having a high impact resilience such as natural rubber. is there. However, with these rubbers, the wet skid resistance was extremely lowered, and it was extremely difficult to achieve both running stability and low rolling resistance.

[0003]

SUMMARY OF THE INVENTION In view of the above-mentioned technical circumstances, an object of the present invention is to provide a pneumatic cylinder with significantly reduced rolling resistance without deterioration of wet skid resistance, abrasion resistance and fracture resistance. It is an object of the present invention to provide a rubber composition that can be suitably used for a tread of a tire.

[0004]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventors have found that at least one rubber selected from the group consisting of natural rubber and synthetic polyisoprene has a styrene-butadiene random content specific thereto. The present inventors have found that a rubber composition containing a rubber component blended with a copolymer achieves the above object, and completed the present invention.

That is, the rubber composition for a tire tread of the present invention has the following formulas: 15 ≤ Vi ≤ 70 (1) ST ≤ 50 (2) Vi + 2ST> 100 (3) Vi-2ST <10 (4) (however, , ST represents styrene% in the copolymer, and Vi represents 1 or 2 bond% in the bound butadiene.) 10 to 50 weight of the styrene-butadiene copolymer obtained by solution polymerization having a microstructure represented by %, And 90 to 50% by weight of at least one rubber selected from the group consisting of natural rubber and synthetic polyisoprene. The styrene-butadiene copolymer is an end-modified polymer obtained by anionically polymerizing butadiene and styrene, the active end of which is coupled with a modifying agent, and has a styrene content of 30 to 50% by weight. A copolymer having a 1,2-bond content of 30 to 70% can be mentioned. Further, the synthetic polyisoprene is an end-modified polymer obtained by coupling a polymer having an active end obtained by polymerization with a lithium-based initiator with a modifier, and having a cis content of 90% or more. be able to.

The styrene-butadiene copolymer of the present invention (hereinafter abbreviated as s-SBR) has the following formula: 15 ≤ Vi ≤ 70 (1) ST ≤ 50 (2) Vi + 2ST> 100 (3) Vi-2ST < 10 (4) (wherein ST represents styrene% in the copolymer, and Vi represents 1,2 bond% in the bound butadiene), which is characterized by being obtained by solution polymerization. . If Vi of the formula (1) is less than 15, polymerization is impossible and 70
If it exceeds, the fracture resistance and wear resistance are deteriorated. If ST of the formula (2) exceeds 50, the fracture resistance and wear resistance deteriorate. If the expressions (3) and (4) are not satisfied, tan δ
(0 ° C) is lowered, and good wet skid resistance cannot be obtained. The content of s-SBR in the rubber component is 10 to 10.
50% by weight, and if less than 10% by weight, tan δ (0
C.) decreases, and if it exceeds 50% by weight, fracture resistance and wear resistance decrease.

The s-SBR used in the composition of the present invention is obtained by copolymerizing a styrene monomer and a butadiene monomer in an organic solvent using a lithium-based initiator to obtain a polymer having an active terminal. From a tin halide compound, a dialkylamino-substituted aromatic compound, at least one terminal tin halide compound, an isocyanate compound, a dialkylamino-substituted aromatic compound, a cyclic urea compound and a thioether-containing compound. The end-modified polymer is obtained by a coupling treatment with at least one end-modifying agent selected from the group consisting of:

On the other hand, the synthetic polyisoprene used in the composition of the present invention is obtained by polymerizing an isoprene monomer in an organic solvent using a lithium-based initiator to obtain a polymer having an active terminal, and the active terminal is halogenated. At least one terminal selected from the group consisting of tin compounds and dialkylamino-substituted aromatic compounds has a terminal halogenated tin compound, an isocyanate compound, a dialkylamino-substituted aromatic compound,
A terminal modified polymer is obtained by a coupling treatment with at least one terminal modifying agent selected from the group consisting of cyclic urea compounds and thioether-containing compounds.

Examples of the lithium-based initiator include n-butyllithium, sec-butyllithium, alkyllithium such as 1,4-dilithiobutane, and organic lithium amides such as N-methylbenzyllithium amide and dioctyllithium amide. To be This lithium-based initiator is used within the range of 0.1 to 100 milligram equivalent as lithium atom per 100 grams of monomer.

Examples of the modifying agent for modifying the active terminal include tin tetrachloride, tin tetrachloride, diphenyl tin trichloride, diphenyl tin dichloride and tin tetrabromide.

As the isocyanate compound, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, tolidine diisocyanate, triphenylmethane triisocyanate, p -Phenylene diisocyanate, tris (isocyanatophenyl) thiophosphate, xylylene diisocyanate, benzene-1,
2,4-triisocyanate, naphthalene-1,2,5,7-tetraisocyanate, naphthalene-1,3,7-triisocyanate, phenyl isocyanate, hexamethylene diisocyanate, methylcyclohexane diisocyanate, etc. To be Preferably, a diisocyanate or triisocyanate or a dimer or trimer of various aromatic isocyanate compounds and an aromatic isocyanate compound such as an adduct body obtained by reacting the aromatic isocyanate with a polyol or a polyamine are used. . More preferably, aromatic polyisocyanate compounds such as 2,4-tolylene diisocyanate, diphenylmethane diisocyanate and naphthalene diisocyanate are used.

Examples of the dialkylamino-substituted aromatic compound include N, N'-dimethylaminobenzophenone, N, N'-diethylaminobenzophenone, N-dimethylaminobenzaldehyde, N-dimethylaminobenzoyl chloride,
Methyl ester of N-dimethylaminobenzoic acid, p-diethylaminostyrene, p-dimethylaminostyrene,
Examples include p-dimethylaminomethylstyrene and 1- (N-dimethylamino) -4-chlorobenzene. As the aromatic heterocyclic nitrogen-containing compound, 4-vinylpyridine,
Examples include 2-vinylpyridine, bis (2-pyridyl) ketone, and bis (4-pyridyl) ketone. Examples of the cyclic urea compound include 1,3, -diethyl-2-imidazolidinone, 1,3, -dimethyl-2-imidazolidinone and the like. Examples of the thioether-containing compound include methylthioacetone, 2-laurylthioethylphenylketone, thiodipropionic acid ester, and methylthioglycolic acid anhydride. These modifiers have a reactive group of 0.1 to 10 per mol of lithium atom.
Use within the equivalent range.

The organic solvent used in the (co) polymerization reaction is not particularly limited, and examples thereof include n-pentane and n.
Hydrocarbon solvents such as -hexane, n-heptane, cyclohexane, benzene, and toluene are included. You may use these in mixture of 2 or more types. Preferred solvents are n
-Hexane and cyclohexane.

After the (co) polymerization reaction with the lithium-based initiator and the coupling reaction between the active terminal and the modifying agent after the (co) polymerization reaction, the reaction is carried out in the range of 0 ° C. to 150 ° C., and the rising conditions are maintained even under isothermal conditions. It can be below. The polymerization method may be either a batch polymerization method or a continuous polymerization method.
The monomer concentration in the solvent is usually 5 to 50% by weight, preferably 10 to 35% by weight. The amount of the initiator used is usually in the range of 0.2 to 20 mmol per 100 g of the monomer.

As a regulator of the microstructure of the butadiene-unit in s-SBR, a Lewis base can be used at the same time as a randomizing agent, if necessary. For example, tetrahydrofuran, diethyl ether, dimethoxybenzene, dimethoxyethane, diethylene glycol dibutyl ether, diethylene glycol dimethyl ether, triethylamine, pyridine, N-methylmorpholine,
N, N, N ', N'-theoramethylethylenediamine,
Ethers such as 1,2-diperidinoethane and third
Examples thereof include primary amines.

Carbon black can be used in the composition of the present invention. The carbon black used is
There is no particular limitation, and conventionally known ones can be widely used. In the present invention, the numerical value DBP of dibutyl phthalate oil absorption (cm ³ ) per 100 g of carbon black determined according to ASTM D2414 and ASTM D3765.
It is preferable to use carbon black obtained from the oil absorption of cetyltrimethylammonium bromide in accordance with the above, and specific examples thereof include ISAF, HAF, and FEF. The amount of carbon black used is 100 rubber components.
20 to 150 parts by weight is preferable with respect to parts by weight.

The rubber composition of the present invention contains, in addition to the above-mentioned carbon black and silica, process oil, other fillers, antioxidants, antiozonants, zinc white, stearic acid,
It is used by blending a vulcanization accelerator and a vulcanizing agent.

The present invention has the conventional disadvantage that natural rubber and / or synthetic polyisoprene cannot obtain tan δ at 0 ° C., that is, wet skid resistance cannot be obtained.
By mixing -SBR, it was possible to prevent the tan δ at 0 ° C from decreasing so much. Therefore, the composition of the present invention does not deteriorate wet skid resistance, and since tan δ at 60 ° C. is significantly decreased by this specific s-SBR, rolling resistance is improved and a fuel-efficient tire tread is obtained. It will be suitable.

[0019]

EXAMPLES The present invention will be described below with reference to examples, but the scope of the present invention is not limited by the examples. In the present invention, various measurements were performed by the following methods.

Microstructure of bound butadiene part of s-SBR: Determined by infrared absorption spectrum method (Morero). Styrene content in bound s-SBR: It was measured using a calibration curve previously obtained by absorption of a phenyl group at 699 cm ^-1 by an infrared absorption spectroscopy. Internal loss (tan δ): Dynamic shear strain amplitude using a mechanical spectrometer manufactured by Rheometrics
It was measured at 1.0%, vibration 15 Hz, and each measurement temperature.

Lambourn abrasion index, which is an abrasion resistance test: Measured by the Lambourn abrasion method. The measurement conditions are a load of 4.5 kg, a wheel surface speed of 100 m / sec, and a test speed of 13
0 m / sec, the slip ratio was 30%, the amount of falling sand was 20 g / min, and the measurement temperature was room temperature. In the table, the value of Comparative Example 6 was set to 100 and displayed as an index. Rolling resistance index: The tire was brought into contact with a drum having an outer diameter of 1.7 m, the drum was rotated, the drum was rotated to a certain speed, and then the drum was coasted to be evaluated from the value calculated from the moment of inertia at a predetermined speed by the following formula (value Is larger, the rolling resistance is smaller). In the table, the value of Comparative Example 6 was set to 100 and indexed.

[Equation 1] Skid resistance (wet skid resistance) index of wet road surface: 80k on wet concrete road surface with water depth of 3 mm
Sudden braking from a speed of m / h, the distance from the wheel being locked until the wheel was stopped was measured, and the wet skid resistance of the test tire was evaluated by the following formula (the larger the value, the better). In the table, the value of Comparative Example 6 was set to 100 and indexed.

[Equation 2]

Production of s-SBR (A) An autoclave with an internal volume of 50 liter equipped with a stirrer and a jacket was dried and replaced with nitrogen. Into this autoclave, pre-purified and dried cyclohexane 25
Kilogram, 2 kg of styrene, 4 kg of 1,3-butadiene and 0.2 of tetrahydrofuran
Introduced 5 kilograms. Then, after the temperature inside the autoclave was set to 10 ° C, cooling water was stopped while stirring at 2 revolutions per minute, 3.2 g of n-butyllithium was added, and the polymerization reaction was performed at 30 to 90 ° C under adiabatic condition. went. After the polymerization conversion rate reached 100%, 2,4-tolylene diisocyanate was added as a modifying agent in an amount of 1.5 equivalents per 1 mol of a lithium atom to react, and di-tert-butyl was added as an antioxidant. p-cresol rubber 1
0.7 g was added to 00 g, and the mixture was dissolved and dried by a conventional method. S-SBR (A) having a microstructure with ST of 35% and Vi of 60% was obtained.

Production of s-SBR (B to F) s having the microstructure shown in Table 1 by changing the above conditions.
-SBR was obtained.

Preparation of Synthetic Polyisoprene: Cyclohexane 20 k in a reactor with an internal volume of 50 liters, which was purged with nitrogen.
After charging g and 5 kg of isoprene, 2.6 g of n-butyllithium was added and a polymerization reaction was carried out at a temperature of 40 to 90 ° C. After the polymerization conversion rate reached 100%, Sn
Cl ₄ was added in an equivalent amount to the lithium atom. As an anti-aging agent, 0.7 g of di-tert-butyl-p-cresol was added to 100 g of rubber, and the mixture was dissolved and dried by a conventional method. Cis 90% polyisoprene was obtained.

[0025]

[Table 1]

Example 1 30 parts by weight of s-SBR (A), 70 parts by weight of cis 98% polyisoprene [manufactured by Japan Synthetic Rubber Co., Ltd., "IR2200"], 50 parts by weight of HAF carbon black, aromatic oil 10 parts by weight, 2 parts by weight of stearic acid, N-
1 part by weight of phenyl-N'-isopropyl-p-phenylenediamine, 3 parts by weight of zinc white, 0.5 part by weight of N-oxydiethylene-2-benzothiazolesulfenamide, 0 of di-2-benzotidyl disulfide. 0.8 parts by weight and 1.5 parts by weight of sulfur were kneaded to obtain a rubber composition for a tire tread. Predetermined physical property tests were performed using this.
Using this rubber composition as a tread, a tire of 165SR13 was prototyped and a tire test was conducted. The results are shown in Table 2.

Examples 2 to 3 and Comparative Examples 1 to 3 Example 1 except that the s-SBR was changed as shown in Table 2.
I went the same way.

Examples 4 to 5 The procedure of Example 1 was repeated except that the polyisoprene (cis 98%) was replaced with synthetic polyisoprene [cis 90% (SnCl ₄ coupling)]. The results are shown in Table 3.

Comparative Examples 4 to 6 The same procedure as in Example 1 was carried out except that the compounding ratio of s-SBR and polyisoprene was changed. The results are shown in Table 3.

[0030]

[Table 2]

[0031]

[Table 3]

[0032]

INDUSTRIAL APPLICABILITY The present invention has the conventional drawback that natural rubber and / or synthetic polyisoprene has a decrease in tan δ at 0 ° C., that is, wet skid resistance cannot be obtained.
It was possible to prevent the tan δ at 0 ° C. from being lowered so much by incorporating a specific s-SBR into natural rubber or / and synthetic polyisoprene. for that reason,
Wet skid resistance does not deteriorate, and ta at 60 ° C
Since nδ is significantly lowered by this specific s-SBR, rolling resistance is improved, and a rubber composition suitable for a fuel tread with a low fuel consumption can be provided.

Claims (3)

[Claims] 1. The following formula 15 ≤ Vi ≤ 70 (1) ST ≤ 50 (2) Vi + 2ST> 100 (3) Vi-2ST <10 (4) (where ST is styrene% in the copolymer, (Vi represents 1 or 2 bond% in bonded butadiene) 10 to 50% by weight of a styrene-butadiene copolymer obtained by solution polymerization having a microstructure represented by natural rubber and synthetic polyisoprene. A rubber composition for a tire tread, which comprises a rubber component containing 90 to 50% by weight of at least one rubber selected from the group. 2. A styrene-butadiene copolymer is an end-modified polymer obtained by anionically polymerizing butadiene and styrene, the active end of which is coupled with a modifying agent, and the styrene content is 30 to 50% by weight. The rubber composition for a tire tread according to claim 1, wherein the content of 1,2 bonds in the bound butadiene is 30 to 70%. 3. A synthetic polyisoprene is an end-modified polymer obtained by coupling a polymer having an active terminal obtained by polymerization with a lithium-based initiator with a modifier, and having a cis content of 90% or more. The rubber composition for a tire tread according to claim 1.