JP3325683B2 - Rubber composition for tire tread - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a rubber composition for a tire tread. More specifically, reduction of rolling resistance,
The present invention relates to a rubber composition that can be suitably used for a tread of a pneumatic tire, which has satisfactory wet skid resistance in all seasons.

[0002]

2. Description of the Related Art In recent years, research on reducing the rolling resistance of tires has been important in order to save fuel consumption of automobiles in accordance with social demands for energy saving and resource saving. It is generally known that if the rolling resistance of the tire is reduced, the fuel consumption of the vehicle is reduced, and a so-called low fuel consumption tire is generally known.To reduce the rolling resistance of the tire, a material having a small hysteresis loss is used as a tread rubber. That is common. Further, from the demand of running stability, a rubber material having a large friction resistance (wet skid resistance) on a wet road surface has been strongly desired. However, these low rolling resistance and friction resistance on a wet road surface have a trade-off relationship, and it is very difficult to satisfy both characteristics. Recently, the correspondence between the wet skid resistance and rolling resistance of the tire and the viscoelastic properties of the rubber composition has been theoretically shown, and the rolling resistance during tire running is reduced by reducing the hysteresis loss of the tread rubber. Viscoelastically used when running tires
It has been shown that lowering the loss factor (tan δ) at a temperature of 50 to 70 ° C. is effective for low fuel consumption. On the other hand, it is known that the wet skid resistance correlates well with the loss factor (tan δ) around 0 ° C. under a frequency of 10 to 20 Hz. It is necessary to increase the loss coefficient of the As a method of reducing the hysteresis loss, it is common to use a material having a low glass transition temperature such as polybutadiene rubber or a material having a high rebound resilience such as natural rubber. However, with these rubbers, the wet skid resistance is extremely reduced, and it is extremely difficult to achieve both running stability and low rolling resistance.

However, in recent years, wet skid resistance has been improved by mixing high styrene-butadiene rubber with polybutadiene rubber. However, there is a problem with the properties at low temperatures, the elastic modulus at low temperatures is poor, the rubber becomes hard, and the wet skid resistance, low rolling resistance, abrasion resistance and fracture resistance in winter are reduced,
Rubber compositions for use in treads of pneumatic tires satisfactory in all seasons could not be obtained.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic tire having low rolling resistance and wet skid resistance which can be satisfied in all seasons (hereinafter referred to as all-seasonability) in view of the above technical circumstances. An object of the present invention is to provide a rubber composition for a tire tread that can be suitably used.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies on the above-mentioned problems, and have found that a styrene-butadiene copolymer obtained by solution polymerization having a specific microstructure is blended with cis-1,4-polybutadiene. By mixing a specific amount of silica into the rubber composition, a rubber composition for a tire tread having all-season properties was successfully obtained, and the present invention was completed. That is,

[0006] The rubber composition for a tire tread of the present invention comprises:
The following formula Vi ≧ ST (1) Vi + 2ST ≧ 80 (2) Vi ≦ 70 (3) ST ≦ 50 (4) (where ST is styrene% in the copolymer, and Vi is 1,1 in the bound butadiene of Styrene-butadiene copolymer (hereinafter referred to as s-SBR) obtained by solution polymerization having a microstructure represented by the following formula:
80 to 100 parts by weight of a rubber component consisting of 80 to 20 parts by weight of 80 to 20 parts by weight of cis-1,4 polybutadiene having a cis-1,4 structure of 92% or more, and 20 to 100 parts by weight of silica. I do.

[0007] The rubber component used in the rubber composition of the present invention s
-SBR is represented by the following formula: Vi ≧ ST (1) Vi + 2ST ≧ 80 (2) Vi ≦ 70 (3) ST ≦ 50 (4) (where ST is styrene% in the copolymer, and Vi is bound butadiene of (Representing 1, 2 bond% in the above). If the formula (1) is not satisfied, SBR and BR become incompatible, the storage elastic modulus (G ') at low temperature is high, and wet skid resistance at low temperature cannot be obtained. If expression (2) is not satisfied, tan δ
(0 ° C.) is too low to obtain wet skid resistance. If the expressions (3) and (4) are not satisfied,
Degradation resistance and wear resistance are reduced. The content of s-SBR is 20 to 80 parts by weight based on 100 parts by weight of the rubber component. If the amount is less than 20 parts by weight, tan δ (0 ° C.) decreases, and wet skid resistance cannot be obtained. 80
If the amount is more than 10 parts by weight, the storage elastic modulus (G ') at low temperature becomes high, and the wet skid resistance in winter cannot be obtained.

This s-SBR is obtained by solution copolymerization of styrene and butadiene using an organic alkali metal such as butyllithium as an initiator. In the polymerization method, the inert organic solvent, the monomers, that is, 1,3-butadiene and styrene and an initiator, a randomizing agent, and, if necessary, a batch charge, are placed in a reactor in which the polymerization system is replaced with nitrogen.
Polymerization is carried out by intermittent or continuous addition. For example,
Styrene as a monomer in n-pentane or benzene,
1,3 polybutadiene is impregnated, and polymerization is carried out using tetrahydrofuran as a randomizing agent and an agent for controlling the amount of 1,2 bonds in the butadiene portion, and n-butyllithium as a polymerization initiator. The polymerization temperature is usually from -120 to +150
° C, preferably -80 to + 120 ° C, and the polymerization time is usually 5
Minutes to 24 hours, preferably 10 minutes to 10 hours. The polymerization may be performed at a constant temperature within the above-mentioned temperature range.
Further, the polymerization reaction may be a patch type or a continuous type. The concentration of the monomer 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.

The following are examples of initiators and solvents used in the polymerization. The alkali metal based catalyst is lithium, sodium, potassium, rubidium, cesium metal or a complex thereof with a hydrocarbon compound or a polar compound. Preferably, it is a lithium compound having 2 to 20 carbon atoms. For example, ethyl lithium, n-
Propyl lithium, i-propyl lithium, n-butyl lithium, sec-butyl lithium, t-octyl lithium, n-decyl lithium, phenyl lithium, 2-naphthyl lithium, 2-butyl-phenyl lithium, 4-phenyl-butyl Lithium, cyclohexyllithium, 4
-Cyclopentyllithium and the like.

The preparation of the s-SBR is carried out in a hydrocarbon solvent or a solvent which does not destroy organic alkali metal initiators such as tetrahydrofuran, tetrahydropyran and dioxane. Suitable hydrocarbon solvents are selected from aliphatic hydrocarbons, aromatic hydrocarbons and alicyclic hydrocarbons, especially propane having 2 to 12 carbon atoms, n-butane, i
-Butane, n-pentane, i-pentane, n-hexane, cyclohexane, propene, 1-butene, i-butene, trans-2-butene, cis-2-butene, 1-pentene, 2-pentene, 1-hexene , 2-hexene,
Benzene, toluene, xylene, ethylbenzene and the like are preferred. These solvents can be used as a mixture of two or more kinds.

If necessary, a Lewis base can be used as a regulator of the microstructure of the butadiene unit in the polymer together with the randomizing agent. These include, for example, dimethoxybenzene, tetrahydrofuran, dimexiethane, diethylene glycol dibutyl ether,
Diethylene glycol dimethyl ether, triethylamine, pyridine, N-methylmorpholine, N, N, N '
Examples thereof include ethers such as N'-terolamethylethylenediamine and 1,2-dipiperidinoethane, and tertiary amines.

The cis-1,1 in the rubber component of the composition of the present invention
4 The content of polybutadiene is 80 to 20 parts by weight. If it is less than 20, tan δ (0 ° C.) decreases, and wet skid resistance decreases. When it exceeds 80, G ′ becomes high, and wet skid resistance in winter cannot be obtained.

The silica used in the composition of the present invention includes:
There is no particular limitation, and conventionally known ones can be widely used, for example, silicic anhydride by a dry method, hydrated silicic acid by a wet method,
And synthetic silicates. Silica modified with a silane coupling agent can be used.

In the composition of the present invention, carbon black can be used together with silica. The carbon black to be used is not particularly limited, and conventionally known carbon blacks can be widely used. In the present invention, the numerical value DBP of dibutyl phthalate oil absorption per 100 g of carbon black (cm ³ ) determined according to ASTM D2414 and ASTM
It is desirable to use carbon black determined from the oil absorption of cetyltrimethylammonium bromide according to D3765, and specifically, ISAF, HAF, F
EF etc. can be illustrated. Silica content is rubber component 100
20 to 100 parts by weight with respect to parts by weight. If the amount is less than 20 parts by weight, good wet skid resistance cannot be obtained. If it exceeds 100 parts by weight, the fracture resistance and the wear resistance are reduced.

The rubber composition of the present invention is used by blending process oil, carbon black, other fillers, antioxidants, antiozonants, zinc white, stearic acid, vulcanization accelerators, vulcanizing agents and the like. Is done.

The vulcanizate of the rubber composition of the present invention is suitable for use in tires such as tread rubber because of its low rolling resistance and wet skid resistance being satisfied in all seasons and low heat generation. Is done.

According to the composition of the present invention, tan δ at 0 ° C. does not decrease so much due to specific s-SBR, so that wet skid resistance does not decrease. The feature is that the rubber sometimes does not become hard, so that it is possible to obtain all-seasonability which has not been obtained conventionally.

[0018]

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 spectroscopy (Morello). Bound styrene content of s-SBR: Measured using a calibration curve previously determined from the absorption of a phenyl group at 699 cm ^-1 by infrared absorption spectroscopy. Internal loss (tan δ): Dynamic shear strain amplitude is measured using a mechanical spectrometer manufactured by Rheometrics.
It measured at 1.0%, vibration 15Hz, and each measurement temperature. Lambourn abrasion index, which is a wear resistance test: measured by the Lambourn abrasion method. The measurement conditions are as follows:
The surface speed of the grindstone was 100 m / sec, the test speed was 130 m / sec, the slip ratio was 30%, the amount of sand falling was 20 g / min, and the measurement temperature was room temperature. In the table, the value of Comparative Example 9 was set to 100 and indexed. Rolling resistance index: The tire was brought into contact with a drum having an outer diameter of 1.7 m, and the drum was rotated. After ascending to a certain speed, the drum was coasted, and the value calculated from the moment of inertia at a predetermined speed was evaluated by the following equation (value The larger is the smaller the rolling resistance is). In the table, the value of Comparative Example 9 was set to 100 and indexed.

(Equation 1) Index of wet skid resistance (wet skid resistance) index: 80 k on a wet concrete road surface having a depth of 3 mm
The brake was suddenly braked at a speed of m / h, the distance from when the wheel was locked to when it 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 9 was set to 100 and indexed.

(Equation 2)

Production of s-SBR (A) An autoclave equipped with a stirrer and a jacket and having a capacity of 50 liters was dried and replaced with nitrogen. In this autoclave, 25% of previously purified and dried cyclohexane was added.
Kilogram, 1 kilogram of styrene, 4 kilograms of 1,3-butadiene and 0.2 kilogram of tetrahydrofuran.
Five kilograms were introduced. Then, after the temperature in the autoclave was set to 10 ° C., the cooling water was stopped while stirring at two revolutions per minute, 3.0 g of n-butyllithium was added, and polymerization was carried out for 30 minutes. Vi is 62% of s
-SBR was obtained.

Production of s-SBR (BE) In the same manner as in the production of s-SBR (A), the amount and temperature of tetrahydrofuran were changed to produce s-SBR having ST% and Vi% shown in Table 1. Obtained.

[0021]

[Table 1]

Example 1 60 parts by weight of s-SBR (A), cis-1, 4 having a structure of 9
2% of cis-1,4-polybutadiene [Japan Synthetic Rubber Co., Ltd., "BR01"] 40 parts by weight, 5 parts by weight of carbon black, silica Nippon Silica Co., Ltd., "Nipsil VN _3"] 45 parts by weight , 10 parts by weight of aroma oil,
2 parts by weight of stearic acid, 1 part by weight of N-phenyl-N'-isopropyl-p-phenylenediamine, 3 parts by weight of zinc white, 0.5 part by weight of N-oxydiethylene-2-benzothiazolesulfenamide , 0.8 parts by weight of di-2-benzothidyl disulfide and 1.5 parts by weight of sulfur were kneaded to obtain a rubber composition for a tire tread. A predetermined physical property test was performed using this. A tire of 165SR13 using this rubber composition for a tread was prototyped and subjected to a tire test. Table 2 shows the results.

Examples 2 to 4, Comparative Example 1 Example 1 was repeated except that s-SBR was changed as shown in Table 1.
The same was done.

Comparative Examples 2 to 6 The same procedure as in Example 1 was carried out except that s-SBR and polybutadiene were changed.

Comparative Example 7 cis-1,4 structure of cis-1,4 polybutadiene 92%
Was carried out in the same manner as in Example 1, except that was changed to 36%.

Comparative Examples 8 to 10 The same procedures as in Example 1 were carried out except that the composition of the composition was changed as shown in Table 4.

[0027]

[Table 2]

[0028]

[Table 3]

[0029]

[Table 4]

[0030]

According to the present invention, there has been provided a rubber composition for a tire tread which can be preferably used for a pneumatic tire having low rolling resistance and wet skid resistance which can be satisfied in all seasons (hereinafter referred to as all season properties). .

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-140240 (JP, A) JP-A-57-125228 (JP, A) JP-A-60-240746 (JP, A) JP-A 61-140 60738 (JP, A) JP-A-3-239737 (JP, A) JP-A-2-160846 (JP, A) JP-A-7-133377 (JP, A) JP-A-3-258841 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C08L 9/00-9/10 C08K 3/36

Claims (1)

(57) [Claims] 1. The following formula: Vi ≧ ST (1) Vi + 2ST ≧ 80 (2) Vi ≦ 70 (3) ST ≦ 50 (4) (where ST is the styrene% in the copolymer and Vi is the bond of 20 to 80 parts by weight of a styrene butadiene copolymer obtained by solution polymerization having a microstructure represented by 1,2 bond% in butadiene) and a cis-1,4 structure having 92% or more. 8 of 1,4 polybutadiene
A rubber composition for a tire tread containing 20 to 100 parts by weight of silica with respect to 100 parts by weight of a rubber component consisting of 0 to 20 parts by weight.