JPS6335668B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a new rubber composition, particularly a rubber composition suitable for tire tread. In recent years, particular importance has been placed on the performance of rubber for automobile tire leads, such as good wet skid properties, heat generation properties, and durability, which are related to running stability, and low rolling friction resistance, which is related to fuel efficiency. Ta. Conventionally, there is no single rubber that can satisfy these properties, and blend compositions of different rubbers have been used to balance the properties. For example, compositions consisting of styrene-butadiene copolymer rubber/polybutadiene rubber have been widely used as tread rubber for passenger cars. However, these compositions do not necessarily have sufficient wet skid properties, and improvements have been desired. Conventionally, it has been known to add a resin with a high glass transition temperature as a means of improving wet skid properties, but this has the problem of significantly lowering dynamic properties, especially heat generation properties, making it difficult to improve wet skid properties. It was hot. An object of the present invention is to provide a new rubber composition with improved wet skid properties and heat generation properties. According to the invention, 3 to 30% by weight of bound styrene and 60% by weight of 1,2 bonds in the butadiene moiety.
Random styrene-butadiene copolymer rubber polymerized under organic alkali metal catalyst from 10% to 95%
Natural rubber, polyisoprene rubber, styrene with a glass transition temperature of -40°C or less, ranging from 90% by weight
90% by weight of one or more rubbers selected from butadiene copolymer rubber and polybutadiene rubber
A rubber composition comprising 10% by weight is provided. The random styrene-butadiene copolymer rubber of the present invention is produced by IM Kolthoff et al. J. Polymer Sci. vol. 1 p429
(1946) and other oxidative decomposition methods,
It means a styrene-butadiene copolymer rubber containing 10% by weight or less of blocked styrene in the bound styrene. The rubber composition according to the invention has significantly improved wet skid properties compared to conventional tire tread rubber compositions, despite having approximately the same heat build-up. Also, compared to rubber compositions that have the same wet skid properties by adding polymers with high glass transition temperatures such as resins and high styrene rubber,
Significant improvement in heat generation. It is also excellent in terms of compatibility between blended rubbers and processability. These characteristics of the present invention include 3 to 30% by weight of bound styrene, preferably 5 to 20% by weight, and 60 to 95% of 1,2 bonds in the butadiene moiety, preferably 70 to 95% by weight.
%, more preferably 80-95% Mooney viscosity (ML ₁₊₄ 100
C) 20-150 by using random styrene-butadiene copolymer rubber as part of the rubber component. If the bound styrene content of the copolymer rubber is less than 3% by weight, the tensile strength will be low, while if it is more than 30% by weight, the heat generating properties will be reduced. Furthermore, if the 1,2 bonds in the butadiene moiety are less than 60%, the wet skid properties will deteriorate. Further, if the Mooney viscosity is less than 20, it is unfavorable in terms of tensile strength and heat generation properties, and if the Mooney viscosity exceeds 150, it is unfavorable in terms of processability. What is the organic alkali metal catalyst used in the present invention?
It is an organic compound of an alkali metal such as Li, Na, or K, and an organic lithium compound is particularly preferably used. The random styrene-butadiene copolymer rubber polymerized with the organolithium compound catalyst is produced by mixing styrene and butadiene monomers with ether or tertiary in a hydrocarbon solvent, as described in, for example, Japanese Patent Publication No. 36-15386 and Japanese Patent Publication No. 48-41038. It is obtained by polymerization using an organolithium compound as an initiator in the presence of an additive such as an amine. Furthermore, the styrene-butadiene copolymer rubber which is the object of the present invention can also be obtained, for example, by the method described in JP-A-52-101287. In the composition of the present invention, the random styrene-butadiene copolymer rubber is used in a proportion of 10 to 90% by weight, preferably 20% to 80% by weight, and if the proportion is less than 10% by weight, wet skid properties may be impaired. If the content is not improved, and if it exceeds 90% by weight, the fracture properties will deteriorate, which is not preferable. The rubber to be blended with the above random styrene-butadiene copolymer rubber is a diene-based rubber with a glass transition temperature of -40°C or lower, preferably -50°C or lower, and is polymerized with natural rubber, a Ziegler type catalyst, or an organolithium catalyst. high cis 1,4 polyisoprene rubber, emulsion polymerized styrene butadiene copolymer rubber,
Styrene-butadiene copolymer rubber polymerized with an organolithium catalyst, high cis 1,4 polybutadiene polymerized with a Ziegler type catalyst, low cis polybutadiene polymerized with an organolithium catalyst, etc. are used. By using a rubber having a Tg of -40°C or less, a rubber composition with excellent wear resistance and durability can be obtained. On the other hand, if a rubber with a high Tg is used in combination, the wet skid resistance will improve, but the heat generation temperature will become high, which is not preferable. These natural rubbers and synthetic rubbers are used alone or in combination of two or more in an amount of 10% to 90% by weight in the composition. 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, and vulcanizing agents. The vulcanized product of the rubber composition of the present invention has excellent wet skid properties and low heat generation, and is therefore suitable for use in tire applications including tread rubber. Furthermore, in addition to tire applications, the rubber composition of the present invention can also be used as an industrial rubber that takes advantage of its characteristics, such as industrial belts with good heat resistance and traction. The present invention will be explained below with reference to Examples, but the scope of the present invention is not limited by these Examples. Examples 1 to 4, Comparative Examples 1 to 3 Styrene and 1,3-butadiene were added as monomers to cyclohexane 8, and potassium dodecylbenzenesulfonate and diethylene glycol dimethyl ether were used as a randomizing agent and a 1,2 bond amount regulator in the butadiene moiety. The polymerization was carried out using n-butyllithium as a polymerization initiator. The polymer was prepared by adding 1.0 parts by weight of 2,6-ditertiarybutyl p-cresol per 100 parts by weight of the polymer to the polymer solution, removing the solvent by steam stripping, and drying with a roll at 100°C. I got it. The polymerization conditions and main properties of the polymer are shown in Table 1. Next, the obtained styrene-butadiene copolymer rubber or polybutadiene rubber was mixed and compounded with natural rubber using a Banbury mixer and a roll according to the formulation shown in Table 2, and vulcanization was performed at 145°C for 45 minutes. The properties of the vulcanizate are shown in Table 3. The compositions of Examples 1 to 4 have high tensile strength, elongation, and wet skid resistance, and low exothermic temperatures. Comparative Example 1 is inferior in tensile strength and elongation. Comparative Example 2 is inferior in wet skid resistance. Comparative Example 3 is inferior in terms of heat generation characteristics.

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[Table] Examples 5 to 7, Comparative Examples 4 to 5 Using the random styrene-butadiene copolymer of Example 1, the vulcanized physical properties were evaluated by changing the blending ratio with cis-1,4 polybutadiene. The compounding recipe and vulcanization conditions are shown in Table 4. The properties of the vulcanizate are the fifth
Shown in the table. Examples 5 to 7 have high wet skid resistance and are also excellent in modulus, tensile strength, tear strength, and flex crack growth resistance, and are well balanced.

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Claims (1)

[Scope of Claims] 1 (A) A random styrene-butadiene copolymer rubber polymerized under an organic alkali metal catalyst containing 3.0 to 30% by weight of bound styrene and 60% to 95% of 1,2 bonds in the butadiene moiety. 10% to 90% by weight and (B) natural rubber with a glass transition temperature of -40°C or lower;
A rubber composition comprising 90% to 10% by weight of one or more rubbers selected from polyisoprene rubber, styrene-butadiene copolymer rubber, and polybutadiene rubber. 2. The composition according to claim 1, wherein the random styrene-butadiene copolymer rubber contains 5 to 20% by weight of bound styrene and 70 to 95% of 1,2 bonds in the butadiene moiety.