JP2000119445A - Tire tread rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide tires which reconcile low rolling resistance with high gripping performance. SOLUTION: Treads are formed by using a tire tread rubber composition comprising 100 pts.wt. rubber component composed of a solution polymerization styrene/butadiene rubber alone which has a hydrogenation ratio of the butadiene unit of 10-60% and a ratio of hydrogenated 1, 2-butadiene units to the hydrogenated entire butadiene units of 0.6 to 1.0 or a blend of a diene rubber with this styrene/butadiene rubber; 40-100 pts.wt. silica; and 0-20 pts.wt. carbon black.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a rubber composition for a tire tread. More specifically, the solution polymerized styrene-butadiene rubber (hereinafter, also referred to as S-SBR) 1,
SBR alone or hydrogenated selectively with a vinyl group contained in a 2-butadiene unit (the same meaning as a 1,2-butadiene binding unit, hereinafter the same description means the same content) or a diene rubber The present invention relates to a rubber composition for a tire tread for achieving both low rolling resistance and high grip performance by blending silica as a reinforcing agent in a blend.

[0002]

2. Description of the Related Art In recent years, there has been an increasing social demand for low fuel consumption due to environmental problems such as global warming, and low fuel consumption tires having low rolling resistance in response to low fuel consumption of automobiles. Has been actively developed.

In order to reduce the rolling resistance of a tire, the amount and type of carbon black, which is a reinforcing agent for a rubber composition for a tire tread, is changed, or the hysteresis loss is reduced by replacing carbon black with silica. (For example, Japanese Patent Application Laid-Open No. 9-71687).

[0004] However, in general, reducing the rolling resistance of a tire often impairs other performances, particularly performances related to safety such as dry grip performance and wet grip performance, and it is difficult to achieve both.

For example, as described in JP-A-7-76635 and JP-A-9-227723,
The rubber composition comprising carbon black and S-SBR in which the vinyl group of 1,2-butadiene unit of S-SBR is selectively hydrogenated is lower than the rubber composition comprising general-purpose S-SBR and carbon black. Although fuel efficiency and wet grip performance have been improved, carbon black is used as a reinforcing agent, and the effect has not yet reached a satisfactory level.

Further, for example, when silica is used as a reinforcing agent instead of carbon black, attempts have been made to achieve both high wet grip performance and low rolling resistance, but they have still reached a sufficiently satisfactory level. Absent.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and has a hydrogenation rate of butadiene units of 10 to 60%, and hydrogenation of all butadiene units is carried out. 100 parts by weight (hereinafter referred to as "parts") of a rubber component composed of S-SBR alone having a 1,2-butadiene unit ratio of 0.6 to 1.0 or a blend thereof with a diene rubber, and 40 to 100 parts of silica And a rubber composition for a tire tread containing 0 to 20 parts of carbon black.

The butadiene unit is a unit in which butadiene is cis-1,4-bonded, trans-1,4.
There are linked units and 1,2-linked units. These are cis-1,4-butadiene bond, trans-1,4-butadiene bond and 1,2
-Sometimes referred to as a butadiene bond. In addition, the vinyl group contained in the 1,2-bonded unit may be referred to as a vinyl moiety.

[0009]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, the hydrogenation rate of butadiene units is from 10 to 60%, and the ratio of hydrogenated 1,2-butadiene units to all hydrogenated butadiene units is from 0.6 to 0.6%. A rubber component consisting of S-SBR of 1.0 (hereinafter also referred to as hydrogenated S-SBR) alone or a blend thereof with a diene rubber is used. Since the rubber component is used in combination with silica, it is possible to achieve both low rolling resistance and high grip performance.

The S-SBR is obtained by using styrene and butadiene in a hydrocarbon solvent (eg, hexane, cyclohexane, etc.), using an organic lithium compound (eg, n-butyllithium) as a catalyst, and optionally using a co-catalyst (eg, Alkoxides such as potassium butoxide,
Using an organic acid salt such as sodium stearate) and emulsion polymerization SBR obtained by redox polymerization in an aqueous emulsifier solution.
(E-SBR) with different characteristics, higher performance tires,
Suitable for improving characteristics such as fuel efficiency. The ratio of styrene / butadiene in S-SBR used in the present invention is preferably 5/95 to 40/60 by weight. If the butadiene content is too low, the composition of the present invention will have reduced rubber elasticity, high hardness, and low fuel economy and abrasion resistance. If the styrene content is too low, the composition of the present invention tends to have low rebound resilience. The rebound resilience is better when styrene units are randomly copolymerized than when block or partially block copolymerized.

The hydrogenation rate of the butadiene unit of the hydrogenated S-SBR is from 10 to 60%, preferably from 23 to 55%. Differences from SBR are reduced, and conversely 6
If it is higher than 0%, the rubber elasticity becomes insufficient.

The 1,2-butadiene units are selected such that the ratio of hydrogenated 1,2-butadiene units to the total hydrogenated butadiene units of the hydrogenated S-SBR is 0.6 to 1.0. Hydrogenated. When the ratio is less than 0.6, hydrogenated S
-SBR, and in this case, the rolling resistance characteristics of the manufactured tire deteriorate, and the effect of the present invention cannot be sufficiently obtained.

In order to increase the ratio of hydrogenated 1,2-butadiene units to the total hydrogenated butadiene units to 0.6 to 1.0, usually 0.8 to 1.0, 1 It is necessary to selectively hydrogenate the vinyl moieties in the 1,2-butadiene unit without or without hydrogenation of the CＣC bond in the 1,4-butadiene unit. As this method, a method in which hydrogenation is carried out under a mild condition at a low pressure and a low temperature using a uniform organometallic compound of titanium or an organometallic compound of lithium, magnesium, and aluminum alone is preferable. Specifically, a method of hydrogenation in an inert organic solvent in the presence of a catalyst comprising bis (cyclopentadienyl) titanium dichloride and an alkyllithium compound (Japanese Patent Publication No.
No. 3-4841), a method of hydrogenating a di-allyl-substituted phenylbis (η-cyclopentadienyl) titanium compound such as di-p-tolylbis (η-cyclopentadienyl) titanium as a hydrogenation catalyst (particularly, Fairness 1-3
No. 7970). These catalyst systems have selective hydrogenation properties necessary for obtaining the hydrogenated S-SBR used in the present invention. Furthermore, hydrogenation is possible with a small amount, and the catalyst residue after the reaction may be used as it is without decalcification.

When the hydrogenated S-SBR has a molecular chain structure which is coupled with a tin compound, this catalyst system allows a hydrogenation reaction to be performed while completely maintaining the tin-carbon bond formed before hydrogenation. Is possible. That is, hydrogenation can be performed without causing a decomposition reaction of a coupling polymer molecule which may be caused by another catalyst system. Further, selective hydrogenation is possible by using this catalyst system, and the Mooney viscosity of the selected partially hydrogenated polymer can be reduced as compared with a normal hydrogenated polymer. That is, it is possible to obtain a partially hydrogenated polymer having significantly improved processability as compared with before hydrogenation. When the hydrogenation selectivity of 1,2-bond is low, hydrogenation-
The 1,4-bond content increases, the Mooney viscosity of the partially hydrogenated polymer increases, and the processability also decreases. On the other hand, a hydrogenation method using another catalyst can be used as long as the hydrogenation can be performed.

The hydrogenated S-SBR has a hydrogenation ratio of butadiene units of 10 to 60%,
-There is no particular limitation except that the ratio of butadiene units is 0.6 to 1.0, but the weight average molecular weight is 10,000 to 500.
Those having a molecular weight distribution (weight average molecular weight / number average molecular weight, the same applies hereinafter) of 1.1 to 5 and a Tg of about −50 to 0 ° C. have good workability and high strength of the produced tread, It is preferable because it has high grip performance and low rolling resistance and has a good balance.

Specific examples of the hydrogenated S-SBR include, for example, those used in the present embodiment, which have a styrene unit ratio of 36% and a Tg of -38 ° C., and a styrene unit ratio of 39%. Those having a Tg of -30 ° C are exemplified.

The rubber component used in the present invention comprises the hydrogenated S
-SBR may be used alone, or a blend of the hydrogenated S-SBR and a diene rubber may be used.

The diene-based rubber is a component used to improve the performance of the hydrogenated S-SBR. In order to form a blend with the diene-based rubber, the processability, the low-temperature characteristics, and the abrasion resistance are improved. The effect of improvement is obtained.

The diene rubber contains natural rubber or a diene monomer such as butadiene or isoprene, preferably butadiene, in an amount of 20 to 100% by weight (hereinafter referred to as%).
And a monomer copolymerizable therewith, for example, styrene, isoprene, isobutylene, acrylonitrile, or the like, is not particularly limited as long as it is a (co) polymer obtained by (co) polymerizing 0 to 80%. Average molecular weight is 1
10,000-5,000,000, molecular weight distribution 1.1-5, Tg -50
Approximately 0 ° C. to 0 ° C. is preferred because of good compatibility with hydrogenated S-SBR, good workability, and good performance balance.

Specific examples of the synthetic rubber among the diene rubbers include butadiene rubber, SBR, isoprene rubber, chloroprene rubber, nitrile rubber, butyl rubber and the like.

When a blend of the hydrogenated S-SBR and the diene rubber is used, the blend ratio is 10
The hydrogenated S-SBR is preferably blended in an amount of 60 parts or more, more preferably 70 parts or more so that the amount becomes 0 part. The upper limit of the blended amount of hydrogenated S-SBR can be approached to 100 parts as long as it can be used alone, but from the viewpoint that a clear effect obtained by blending the diene rubber can be obtained, Parts are preferred.

The silica used in the present invention is a component used as a reinforcing agent. Among the various reinforcing agents, silica is particularly used because it has a low rolling resistance and a high wet grip performance when used as a tire, and has a low rolling resistance and a high wetness which each of the rubber component and the reinforcing agent has. This is because a balance between low rolling resistance and high wet grip performance, which could not be achieved conventionally, can be realized by a synergistic effect without impairing the grip performance. Such a remarkable effect has been found for the first time by the present inventors.

The silica has, for example, a CTAB adsorption specific surface area (hereinafter referred to as CTAB) of 100 to 200.
m ² / g, BET nitrogen adsorption specific surface area (hereinafter, referred to as BET) is used. For 100 to 250 m ² / g.

Specific examples of the silica include, for example, Nipsil VN3 (manufactured by Nippon Silica Co., Ltd., CTAB 144).
m ² / g, BET 210 m ² / g), Nipsil AQ (manufactured by Nippon Silica Co., Ltd., CTAB 150 m ² / g, BET
227 m ² / g).

The amount of the silica used depends on the rubber component 10
The amount is 40 to 100 parts, preferably 45 to 95 parts with respect to 0 parts. If the amount is too small, the reinforcing properties are insufficient, and the abrasion resistance and strength are reduced. If the amount is too large, the viscosity of the composition becomes too high, and workability becomes difficult.

The composition comprising the rubber component and silica may be combined with carbon black as a reinforcing agent in order to improve processability. Interaction is diminished, and low rolling resistance and high grip performance are impaired. Therefore, the addition of carbon black is preferably 20 parts or less, more preferably 15 parts or less, and particularly preferably 10 parts or less. In order to obtain a clear effect by using carbon black, it is preferable to use 5 parts or more.

The composition of the present invention comprises the above-mentioned rubber component, silica and optionally used carbon black. If necessary, additives generally used as additives for rubber compositions for tire treads are generally used. You may add in the range.

Specific examples of the additives include process oils (paraffinic process oils, naphthenic process oils, aromatic process oils), vulcanizing agents (sulfur, sulfur chloride compounds, organic sulfur compounds, etc.), vulcanizing agents, and the like. Sulfur accelerators (guadinine-based, aldehyde-amine-based, aldehyde-ammonia-based, thiazole-based, sulfenamide-based, thiourea-based, thiuram-based, dithiocarbamate-based, xanthate-based compounds, etc.), crosslinking agents (organic peroxide compounds) , Radical generators such as azo compounds, oxime compounds, nitroso compounds, polyamine compounds, etc.), reinforcing agents (high styrene resin, phenol-
Formaldehyde resin), antioxidants or antioxidants (diphenylamine-based, p-phenylenediamine-based amine derivatives, quinoline derivatives, hydroquinone derivatives, monophenols, diphenols, thiobisphenols, hindered phenols, Phosphate esters and the like).

The method for producing the composition of the present invention is not particularly limited, and the composition may be produced by a conventional method using a rubber component having predetermined characteristics.

The rubber composition produced is used to form the tread portion of a tire, and the produced tire has an unexpected effect due to having a tread from a composition comprising a specific rubber component and silica. It has low rolling resistance and high grip performance.

[0031]

EXAMPLES Next, the composition of the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

The raw materials used in the examples and comparative examples and the evaluation methods are summarized below.

Hydrogenated S-SBR styrene / butadiene = 22/78 (weight ratio), weight average molecular weight 800,000, 1,4-butadiene unit / 1,
Hydrogenated S-SBR having 2-butadiene units = 67/33, having a hydrogenation ratio of 28% and a ratio of hydrogenated 1,2-butadiene units to all hydrogenated butadiene units of 0.82. NR # 3 grade of commonly used RSS SBR SBR 1502: Sumitomo Chemical Co., Ltd. SBR SL574: Nippon Synthetic Rubber Co., Ltd. Silica Nipsil VN3: Nippon Silica Co., Ltd., CTAB 144m ² /
g, BET 210 m ² / g Carbon black N351: Silane coupling agent manufactured by Mitsubishi Chemical Corporation Si69: Process oil Diana Process PS32 manufactured by Degussa Co., Ltd. Stearic acid paulownia manufactured by Idemitsu Kosan Co., Ltd. Zinc flower manufactured by NOF Corporation Two types of zinc oxide: Wax manufactured by Mitsui Kinzoku Co., Ltd. Sunnock wax: Antioxidant manufactured by Ouchi Shinko Chemical Co., Ltd. Ozonone 6C: Vulcanization accelerator accelerator manufactured by Seiko Chemical Co., Ltd. Accelerator CBS: Noxeller CZ, Ouchi Shinko Accelerator DPG manufactured by Chemical Co., Ltd .: Succinol D, manufactured by Sumitomo Chemical Co., Ltd.

(Grip Performance) A tire having a size of 185 / 65R14 was manufactured by using a predetermined rubber composition for a tire tread in a tread.

Using the vehicle equipped with the obtained tires, the performance of dry grip and wet grip on the asphalt surface of the test course and the road surface sprayed with water and the steering stability were evaluated and compared. The evaluation was a sensory evaluation by a test driver, which was indicated by an index. The higher the index, the better the performance.

(Rolling Resistance) Using a tire manufactured in the same manner as in the case of grip performance, the tire was run at a load of 345 kg, an internal pressure of 200 kPa, and a speed of 80 km / h by a testing machine manufactured by Kobe Steel, Ltd. to reduce the rolling resistance. It was measured. The larger the index, the lower the rolling resistance and the better the rolling resistance.

(Abrasion resistance) A car equipped with tires manufactured in the same manner as in the case of the grip performance was used so that the ratio of the highway to the ordinary road was about 1: 3, and the total was 30,000 k.
After running m, the remaining grooves of the tread were examined to evaluate the degree of wear. A larger index indicates better wear resistance.

Examples 1-2 and Comparative Examples 1-10 Compositions containing the components shown in Table 1 (excluding sulfur and the vulcanization accelerator) in the proportions shown in Table 1 were manufactured by Kobe Steel Ltd. The mixture was kneaded with a 1.7 L Banbury for 4 minutes. The composition obtained by adding sulfur and a vulcanization accelerator in the proportions shown in Table 1 to the obtained kneaded product and kneading the mixture at 80 ° C. for about 4 minutes with a biaxial roller is vulcanized at 170 ° C. for 10 minutes to obtain a tire tread A green rubber composition was prepared.

Using the composition obtained, 185 / 65R1
4 were manufactured and evaluated. Table 1 shows the results.

The tire performance of Examples 1 and 2 and Comparative Examples 1 to 4 is indicated by an index with Comparative Example 2 being 100, and the tire performance of Comparative Examples 5 to 10 is indicated by an index with Comparative Example 6 being 100. Indicated by

[0041]

[Table 1]

The influence of the filler was examined in Comparative Examples 1 and 2, and in Comparative Example 2 using silica, grip performance and rolling resistance performance were improved compared to Comparative Example 1 using carbon black. On the other hand, in Comparative Examples 5 to 7, when the performance difference caused by changing the rubber was investigated, hydrogenated S-
In Comparative Example 7 using SBR, improvement in grip performance and rolling resistance performance was observed.

In Examples 1 and 2 in which hydrogenated S-SBR and silica were used in combination, the rolling resistance and the grip performance were improved more than expected from rubber and filler. This tendency was observed in blends with natural rubber (Comparative Examples 3, 4 and 8).
-10).

[0044]

By using the rubber composition for a tire tread of the present invention, it is possible to achieve both low rolling resistance and high grip performance.

Claims (1)

[Claims] 1. The hydrogenation rate of a butadiene unit is from 10 to 6.
At 0%, the ratio of hydrogenated 1,2-butadiene units to total hydrogenated butadiene units is 0.6-0.6%.
Rubber component 1 consisting of a solution-polymerized styrene-butadiene rubber alone or a blend of the same and a diene rubber
A rubber composition for a tire tread, comprising 00 parts by weight, 40 to 100 parts by weight of silica, and 0 to 20 parts by weight of carbon black.