JPH10273560A - Rubber composition for tire tread - Google Patents

Abstract

(57) [Problem] To provide a rubber composition for a tire tread which has sufficient abrasion resistance and is used for manufacturing a tire having excellent wet grip properties. SOLUTION: The rubber composition for a tire tread comprises at least 50 parts by weight or more of a styrene-butadiene rubber;
A rubber composition comprising 5 to 30 parts by weight of isoprene rubber and 100 to 250 parts by weight of a filler and 15 to 50 parts by weight of a low freezing point plasticizer per 100 parts by weight of a rubber component Wherein the styrene-butadiene rubber contains 30% by weight or more of a styrene structural unit and 30% or more of a double bond is a butadiene structural unit having a vinyl group, and is obtained by solution polymerization. In the isoprene rubber, 70% or more of the double bond is an isopropenyl group and / or a vinyl group, and the filler contains 50 to 150 parts by weight of silica as an essential component,
The low freezing point plasticizer is a plasticizer comprising at least one selected from adipic acid derivatives, sebacic acid derivatives and phosphoric acid derivatives.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition for a tire tread, and more particularly to a rubber composition used for producing a tire tread for a race and having excellent wet grip properties.

[0002]

2. Description of the Related Art Generally, when a road surface is wet due to rain or the like when driving a car, water is interposed between the tire and the road surface, so that grip performance (wet grip performance) is reduced. This phenomenon is noticeable in racing tires that run at high speed on rough roads. Conventionally, to increase wet grip, (1) increase hysteresis loss,
(2) Enhancing the adhesive frictional force, (3) Enlarging the excavating frictional force, and the like have been considered.

[0003] Therefore, by increasing the amount of carbon black used as a filler, the hysteresis loss is increased, the wet grip property is enhanced, and a sufficient abrasion resistance is also obtained. However, there is a limit to improving wet grip properties by increasing the amount of carbon black. In view of this point, in recent years, attempts have been made to increase the adhesive frictional force and improve the wet gripping property by replacing part or all of the carbon black with silica.

[0004]

However, when the carbon black is replaced with silica, there is a problem that the hysteresis loss is reduced, the wet grip property is not improved as much as expected, and the abrasion resistance is slightly reduced. The problem to be solved by the present invention is to provide a rubber composition for a tire tread which has sufficient abrasion resistance and is used for producing a tire having excellent wet grip properties.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, have used silica and, as rubber components, styrene-butadiene rubber and isoprene rubber having a specific molecular structure. Use a rubber component with a high glass transition temperature, including
It has been found that the use of a low freezing point plasticizer can improve wet grip properties without causing the above-mentioned problems, and the present invention has been achieved.

That is, the rubber composition for a tire tread of the present invention contains at least 50 parts by weight or more of styrene-butadiene rubber and 5 to 30 parts by weight of isoprene rubber, based on 100 parts by weight of a rubber component. , 100-2
A rubber composition comprising 50 parts by weight of a filler and 15 to 50 parts by weight of a low freezing point plasticizer, wherein the styrene-butadiene rubber contains 30% by weight or more of a styrene structural unit, A butadiene structural unit in which 30% or more of the bond is a vinyl group, which is obtained by solution polymerization, wherein the isoprene rubber has an isopropenyl group and / or a vinyl group in which 70% or more of the double bond is Wherein the filler contains 50 to 150 parts by weight of silica as an essential component, and the low freezing point plasticizer comprises at least one plasticizer selected from adipic acid derivatives, sebacic acid derivatives and phosphoric acid derivatives It is characterized by the following.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, each component constituting the rubber composition for a tire tread of the present invention will be described in detail. [Rubber Component] The rubber component used in the present invention contains at least styrene-butadiene rubber and isoprene rubber, and may further contain other rubbers. Both styrene-butadiene rubber and isoprene rubber have a high glass transition temperature, and by adding a low freezing point plasticizer described below to these rubber components, increase hysteresis loss and impart excellent wet grip properties. Can be.

[0008] Styrene-butadiene rubber is a rubber containing a styrene structural unit derived from styrene and a butadiene structural unit derived from butadiene. The styrene-butadiene rubber includes those obtained by solution polymerization (solution-polymerized styrene-butadiene rubber) and those obtained by emulsion polymerization (emulsion-polymerized styrene-butadiene rubber), depending on the production method. Is a solution polymerized styrene-butadiene rubber. Solution polymerized styrene-butadiene rubber is, for example,
It is obtained by copolymerizing styrene and butadiene in the presence of an organic alkali metal compound in a solution such as a hydrocarbon solvent. Solution polymerized styrene-butadiene rubber is
For example, it is classified into a random type, a block type, a symmetric block type and the like.

The proportion of the styrene structural unit contained in the styrene-butadiene rubber is at least 30% by weight, preferably at least 35% by weight, more preferably at least 40% by weight. If the proportion of the styrene structural unit is less than 30% by weight, the glass transition temperature of the styrene-butadiene rubber will be low, the hysteresis loss will be small, and the wet grip property will be reduced.

Each of the butadiene structural units contained in the styrene-butadiene rubber has one double bond. The double bond in the butadiene structural unit has a 1,2-addition to butadiene to form a vinyl group,
It is conceivable that 1,4-addition to butadiene is included in the main chain of the styrene-butadiene rubber to form a cis or trans structure.

In the styrene-butadiene rubber used in the present invention, at least 30% of the double bonds of the butadiene structural unit are vinyl groups (that is, 1,2-addition structure), preferably at least 35%, more preferably at least 35%. It is preferably at least 40%. When the vinyl group content is less than 30%, the glass transition temperature of the solution-polymerized styrene-butadiene rubber decreases,
Hysteresis loss is small and wet grip performance is reduced.

The compounding ratio of the styrene-butadiene rubber is as follows:
It is 50 parts by weight or more, preferably 60 parts by weight or more, and more preferably 70 parts by weight or more in 100 parts by weight of the rubber component. The compounding ratio of styrene-butadiene rubber is 50
If the amount is less than the weight part, the hysteresis loss becomes small, and the wet grip property is reduced. Next, isoprene rubber is a rubber obtained by polymerizing isoprene and containing isoprene structural units derived from isoprene. The double bond in the isoprene rubber may be 1,2-addition to isoprene to form a vinyl group, 3,4-addition to isoprene to form an isopropenyl group, or isoprene. To 1,4-addition to the main chain of the isoprene rubber to form a cis or trans structure.

In the isoprene rubber used in the present invention,
More than 70% of the double bonds are isopropenyl groups (ie, 3,
4-addition structure) and / or vinyl group (that is, 1,2
-Additional structure), preferably at least 75%, more preferably at least 80%. Isopropenyl group and / or
Alternatively, when the vinyl group content is less than 70%, the glass transition temperature of the isoprene rubber is low, the hysteresis loss is small, and the wet grip property is low.

The mixing ratio of isoprene rubber is as follows.
5 to 30 parts by weight, preferably 10 to 100 parts by weight.
To 25 parts by weight, more preferably 10 to 20 parts by weight. If the compounding ratio of the isoprene rubber is less than 5 parts by weight, the hysteresis loss is small and the wet grip property is reduced. On the other hand, when the compounding ratio of the isoprene rubber exceeds 30 parts by weight, the abrasion resistance decreases.

The rubber component contains at least the styrene-
As long as it contains butadiene rubber and isoprene rubber, other rubber components, that is, styrene-butadiene rubber and isoprene rubber, have different structures from those described above, natural rubber, butadiene rubber (BR) , Isoprene-isobutylene rubber (IIR),
It may further contain another rubber such as halogenated butyl rubber (X-IIR). [Filler] The filler used in the present invention is compounded to obtain a sufficient hardness when a rubber composition is molded to produce a tire tread for racing or the like. The filler is not particularly limited as long as it contains silica as an essential component. By blending silica in the rubber composition, the adhesive frictional force increases, and wet grip properties are improved.

As the filler other than silica, for example,
Carbon black, clay, talc, calcium carbonate,
Inorganic fillers such as basic magnesium carbonate, alumina, mica, graphite, glass powder and the like, and organic fillers such as high styrene resin, coumarone indene resin, phenol resin, modified melamine resin, petroleum resin, etc. At least one of them can be used in combination with silica. Among them, it is preferable to use carbon black in combination. This is because the abrasion resistance is improved, the hysteresis loss is increased, and the wet grip performance is further improved.

The compounding ratio of the filler (including silica) in the rubber composition for a tire tread is 100 to 250 parts by weight, preferably 15 to 100 parts by weight, per 100 parts by weight of the rubber component.
0 to 250 parts by weight, more preferably 200 to 250 parts by weight. If the compounding amount of the filler is less than 100 parts by weight, the hysteresis loss is small, sufficient adhesive frictional force cannot be obtained, and the wet grip property is reduced. On the other hand, when the compounding amount of the filler exceeds 250 parts by weight, a large load is generated in a tire manufacturing process such as kneading or extrusion, and the tire may not be manufactured.

The mixing ratio of silica, which is an essential component of the filler, is 50 to 150 parts by weight, preferably 80 to 150 parts by weight, more preferably 100 to 150 parts by weight, per 100 parts by weight of the rubber component. . If the mixing ratio of silica is less than 50 parts by weight, a sufficient adhesive friction force cannot be obtained, and the wet grip property is reduced. On the other hand, when the compounding ratio of silica exceeds 150 parts by weight, a large load is generated in a tire manufacturing process such as kneading or extrusion, so that a tire may not be manufactured. [Low Freezing Point Plasticizer] The low freezing point plasticizer used in the present invention is a plasticizer composed of at least one selected from adipic acid derivatives, sebacic acid derivatives and phosphoric acid derivatives, together with the styrene-butadiene rubber and isoprene rubber. By blending, the rubber composition for a tire tread has excellent wet grip properties. It should be noted that such excellent wet grip properties are achieved by blending a low freezing point plasticizer to be flexible at low temperatures, and by softening the high frequency (low temperature) side involved in wet grip properties, the real contact area is increased. It is considered that the adhesive frictional force is increased.

Examples of the low freezing point plasticizer include adipic acid derivatives such as di (2-ethylhexyl) adipate (DOA), diisooctyl adipate (DIOA) and dibutoxyethyl adipate (DBEA);
Ethylhexyl) sebacate (DOS), dibutyl sebacate (DBS), diisooctyl sebacate (DIO)
S) and other phosphoric acid derivatives such as tri (2-ethylhexyl) phosphate (TOP) and tributyl phosphate (TBP).
Only the species may be used, or two or more species may be used in combination.

The mixing ratio of the low freezing point plasticizer in the rubber composition for tire tread is 1 to 100 parts by weight of the rubber component.
5 to 50 parts by weight, preferably 15 to 40 parts by weight,
More preferably, it is 20 to 30 parts by weight. If the blending amount of the low freezing point plasticizer is less than 15 parts by weight, a sufficient adhesive frictional force cannot be obtained, and wet grip properties are reduced. On the other hand, if the blending amount of the low freezing point plasticizer exceeds 50 parts by weight,
Hysteresis loss is not increased, and wet grip performance is reduced, and wear resistance is reduced. [Other components] In the rubber composition for tire tread, if necessary, a softening agent such as a naphthenic process oil or an aroma oil; a vulcanizing agent such as sulfur, insoluble sulfur or a sulfur compound; zinc oxide, stearic acid or the like Vulcanization aids: mercaptobenzothiazole (MBT), benzothiazyldisulfide (MBTS), N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazylsulfen Amide (CBS)
Thiazole compounds such as diphenylguanidine (D
A vulcanization accelerator comprising a guanidine compound such as PG);
Additives such as organic fibers, foaming agents, antioxidants, and waxes can be added. The mixing ratio of these additives in the tread rubber composition is not particularly limited, and can be appropriately selected.

Above all, it is preferable to add a softening agent as an additive to the rubber composition for a tread, since the hysteresis loss increases and the wet grip property is improved. As a method for producing the rubber composition for a tire tread, a known method can be applied. It is obtained by kneading each of the above components using a kneader such as a kneader or a Banbury mixer under ordinary methods and conditions. The kneading temperature is preferably from 120 to 180 ° C.

By molding and vulcanizing the above-described rubber composition for a tire tread, a tire tread is obtained, which can be used for a racing tire.

[0023]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples. However, the present invention is not limited to the following Examples. (Examples 1 to 6 and Comparative Examples 1 to 6) The following Tables 1 and 2 were prepared using a Banbury type mixer having a capacity of 50 liters.
In the formulation (unit: parts by weight) shown in (1), each component was divided into three parts as shown below and kneaded at a 70% filling rate for four minutes each to prepare a rubber composition for a tire tread.

First time: the total amount of the rubber component, the coupling agent and the low-temperature plasticizer, and half the amount of silica, carbon black and aroma oil. 2nd time: 1st kneaded product, total amount of stearic acid and zinc oxide, half amount of silica, carbon black and aroma oil. Third time: The total amount of the second kneaded material, sulfur and the vulcanization accelerator.

A cart tire was prepared using the obtained tread rubber composition, and the performance was evaluated by the following evaluation methods. The results are shown in Tables 1 and 2. <Evaluation method> 1. Hardness (Hs) According to the method specified in JIS K-6301,
Rubber strength Hs (JIS-A) at 25 ° C. was measured.

2. Lap time during running (evaluation of wet grip property) Cart tire (size: Front 1) obtained above
0x4.50-5, Rear 11x7.10-5), the race car was run 10 laps on a wet circuit of about 700 m per lap, and the top 3 cars with the fastest running time per lap were run. The average of the data was calculated.

3. Abrasion Resistance After the measurement of the lap time during running, the abrasion pitch appearing on the tire surface was measured, and the average value was obtained and evaluated according to the following evaluation criteria. Among the four tires mounted on the automobile, only the tire on the right front wheel, which was severely worn, was evaluated for its wear resistance.

A: The abrasion pitch is 3 mm or less. ：: Ablation pitch is more than 3 mm and 5 mm or less. ×: Ablation pitch exceeds 5 mm.

[0029]

[Table 1]

[0030]

[Table 2]

* 1 Obtained by solution polymerization, manufactured by Sumitomo Chemical Co., Ltd., containing 40% by weight of a styrene structural unit, and in a butadiene structural unit, 50% of double bonds are vinyl groups. In addition,
Of the 137.5 parts by weight, 100 parts by weight are styrene-butadiene rubber and the remaining 37.5 parts by weight are oil-extended oil. * 2 Toughden 2330, manufactured by Asahi Kasei Corporation, obtained by solution polymerization. Styrene structural unit is 25% by weight, and 30% of double bonds in butadiene structural unit are vinyl groups.
Of the 137.5 parts by weight, 100 parts by weight was styrene-
Butadiene rubber, the remaining 37.5 parts by weight is oil extended oil.

* 3 NIPOL9520, manufactured by Nippon Zeon Co., Ltd., obtained by emulsion polymerization. Styrene structural units are 35% by weight, and 18% of double bonds in butadiene structural units are vinyl groups. In addition, in 137.5 parts by weight, 100
The parts by weight are styrene-butadiene rubber, and the remaining 37.5 parts by weight is oil extended oil. * 4 ISOGRIP, manufactured by KARBO CHEM, the total amount of isopropenyl groups and vinyl groups is 75
%, 1,4-addition structure is 25 of double bonds.
%.

* 5 N110, manufactured by Mitsubishi Chemical. * 6 VN3, manufactured by Degussa. * 7 Tri (2-ethylhexyl) phosphate, manufactured by Daihachi Chemical. * 8 Di (2-ethylhexyl) sebacate, manufactured by Sanken Kako. * 9 Di (2-ethylhexyl) adipate, manufactured by Sanken Kako.

* 10 Process X-260, manufactured by Japan Energy. In Examples and Comparative Examples, in addition to the components shown in Tables 1 and 2, stearin 2 parts by weight (Tungsten, manufactured by Nippon Oil & Fats), zinc white 3 parts by weight (made by Mitsui Kinzoku), and a coupling agent of silica were used. (X-50S, manufactured by Degussa), 1.5 parts by weight of sulfur (powder sulfur, manufactured by Karuizawa Seisakusho), 2 parts by weight of vulcanization accelerator (CBS) (Suncellar CM-G, manufactured by Sanshin Chemical Co., Ltd.) ) And 2 parts by weight of a vulcanization accelerator (DPG) (Vaxinol D, manufactured by Sumitomo Chemical Co., Ltd.).

<Evaluation Results> In Examples 1 to 6, the lap time when traveling on a circuit on a wet road surface is fast, and the wet grip property is excellent. Also, the abrasion resistance is good. In Comparative Example 1, the abrasion resistance was low because the amount of the isoprene rubber was large. Comparative Example 2 does not contain isoprene rubber, and thus has poor wet grip properties.

In Comparative Examples 3 and 4, since the amount of the solution-polymerized styrene-butadiene rubber was small, the wet grip property was low. In Comparative Example 5, since the blending amount of the low freezing point plasticizer was large, the hysteresis loss was not increased, and the wet gripping property was reduced and the abrasion resistance was reduced. In Comparative Example 6, since the blending amount of the low freezing point plasticizer was small, a sufficient adhesive frictional force was not obtained, and the wet grip property was reduced and the abrasion resistance was reduced.

[0037]

Industrial Applicability The rubber composition for a tire tread of the present invention has sufficient abrasion resistance and can be used for producing a tire having excellent wet grip properties. Therefore, this composition is particularly excellent for the production of racing tires.

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Claims (1)

[Claims] (1) at least 50 parts by weight of styrene
100 to 250 parts by weight of a filler and 15 to 50 parts by weight of a low freezing point plasticizer are blended with 100 parts by weight of a rubber component containing butadiene rubber and 5 to 30 parts by weight of isoprene rubber. The styrene-butadiene rubber contains 30% by weight or more of a styrene structural unit and 30% or more of a double bond is a vinyl group butadiene structural unit, and is obtained by solution polymerization. The isoprene rubber is obtained, wherein 70% or more of the double bond is an isopropenyl group and / or a vinyl group, and the filler contains 50 to 150 parts by weight of silica as an essential component, Wherein the low freezing point plasticizer is a plasticizer comprising at least one selected from adipic acid derivatives, sebacic acid derivatives and phosphoric acid derivatives. Head for the rubber composition.