KR0177639B1 - Rubber composition for pneumatic tire treads - Google Patents

Abstract

The present invention relates to a rubber composition for tread of pneumatic tire, which synthesizes a polybutadiene polymer having a low molecular weight cis-1, 4 content of 90% or more, and polystyrene equivalent weight average molecular weight measured by GPC in hydrocarbon solvent. In a hydrocarbon solvent, a solution of a styrene-butadiene copolymer rubber having a Mooney viscosity range of 40-130 made by copolymerizing 1,3-butadiene and styrene using an organolithium-based polymerization initiator was sprayed with respect to 100 parts by weight of this copolymer rubber. 3-30 parts by weight of the polybutadiene polymer, and finally prepare a solid rubber and apply it to the tread rubber composition of pneumatic tires for automobiles to maintain a high level of road surface abrasion resistance while improving abrasion resistance and productivity It provides a rubber composition that does not.

Description

Rubber composition for tread of pneumatic tire

The present invention relates to a tread rubber composition of pneumatic tires for automobiles that improves wear resistance while maintaining road surface grading power. More specifically, a low molecular weight liquid polybutadiene polymer is mixed with a styrene-butadiene copolymer rubber in a polymerization step. By manufacturing and applying it to the tread rubber composition of pneumatic tires, the tread rubber of pneumatic tires for automobiles can not only significantly improve abrasion resistance while maintaining the road surface grasping power, but also prevent productivity degradation. To a composition.

Recently, as the highway network is expanded, various proposals have been repeated due to the acceleration of automobiles and the examination of high-speed driving tires. In addition, the tread rubber composition has been examined in this regard. In order to increase the frictional force between the tread and the road surface of the pneumatic tire, that is, the road grasping force, it is necessary to use a tread rubber having a large hysteresis loss (tanδ) during deformation. Styrene-butadiene copolymer rubber (SBR) having a high styrene content or vinyl content is used to increase the tan δ of the tread rubber, or carbon black or a process oil is blended in a large amount. However, if the road grasping power is increased in this way, the wear resistance of the styrene-butadiene rubber is inevitable. Therefore, it is difficult to obtain a tread rubber having both of these methods because the improvement of the wear resistance while maintaining high road surface grasping power is a phenomenon of opposite performance.

In order to improve the wear resistance, a method of applying polybutadiene rubber having a high content of cis-1 and 4-polybutadiene may be adopted. This polybutadiene rubber is not blended well with other rubbers, and especially blended with other rubbers. When the carbon dispersion is slowed down, there is a problem in that excellent physical properties cannot be exhibited to the maximum. In addition, in order to improve the carbon dispersibility in the blended rubber composition, the time required for the refining processing time becomes long, which inevitably lowers the productivity.

In addition, as a method for improving wear resistance in terms of carbon black, there is a method of blending a large amount of high reinforcing carbon black having a high specific surface area and reducing the amount of process oil added. However, when the amount of process oil is reduced, the amount of power required for refining increases, and the viscosity increases, resulting in deterioration of refining processability.

Therefore, low-molecular weight diene-based rubbers such as polyisoprene are expected to be applied to rubber compositions for treads, which act as process oils to lower the viscosity of rubber compositions in refining and extrusion processes, and vulcanizates added together during vulcanization of molded tires. Attempts have been made to contribute to the improvement of mechanical properties such as tensile strength by allowing the low molecular weight liquid rubber to participate in crosslinking by the system.

This approach is equally applicable to cis-1, polybutadiene with high content of 4-polybutadiene, i.e. low molecular weight liquid polybutadiene is added to the styrene-butadiene copolymer rubber to act as a kind of oil component during processing. It is possible to improve the refining processability and to improve wear resistance without impairing the excellent road surface grasping power of styrene-butadiene rubber composition by effectively utilizing the excellent properties of polybutadiene rubber with high cis-1 and 4-polybutadiene content after vulcanization. .

However, in the conventional refining method of applying a liquid polybutadiene rubber to a rubber composition to which carbon black is added, the rubber is generally applied for a certain period of time after being used for a certain period of time. Not only does not mix uniformly with styrene-butadiene rubber, but also the penetration time of carbon black is different so that there is a problem that the physical effects of butadiene rubber cannot be fully exhibited, resulting in unsatisfactory in terms of productivity and physical properties. .

Therefore, it is an object of the present invention to solve the problems described above to provide a rubber composition for tire treads that improves wear resistance and does not deteriorate productivity while maintaining road surface grasping power.

As a result of intensive studies to solve the above problems, the present inventors have to increase the tanδ value of the tread rubber in order to obtain high road grasping force, but even in a tread having such a large tanδ value, the softener is a liquid low molecular weight polybutadiene. By changing to a polymer and not injecting it in the refining stage of compounded rubber, in particular, by mixing and drying and solidifying in the manufacturing stage of styrene-butadiene rubber, it is possible to maintain a high road surface grasping power and greatly change abrasion resistance without lowering productivity. The present invention has been completed. That is, a part of the process oil that has been applied to the styrene-butadiene copolymer rubber that has been used in the past is replaced by a low molecular weight liquid cis-1 and 4-polybutadiene rubber in the polymerization production step of the styrene-butadiene copolymer. The present invention has been found that when applied to the rubber composition can greatly improve the wear resistance without lowering productivity while maintaining the high road surface grasping power.

The present invention synthesizes a liquid polybutadiene polymer having a low molecular weight cis-1, 4-polybutadiene content of 90% or more in the range of 2,000-50,000 polystyrene equivalent weight average molecular weight measured by gel permeation chromatography (GPC) in a hydrocarbon solvent. In a liquid of a styrene-butadiene copolymer rubber having a Mooney viscosity range of 40-130 made by copolymerizing 1,3-butadiene and styrene using an organic lithium-based polymerization initiator in a hydrocarbon solvent, 3-30 parts by weight of the polybutadiene polymer is mixed, and the process of removing the hydrocarbon solvent and the unreacted monomer and the like to finally prepare a solid rubber and apply it to the tread rubber composition of pneumatic tires for automobiles.

The rubber composition for tread of the present invention is a diene system comprising at least one styrene-butadiene copolymer rubber having a content of 45% by weight or more, more preferably 50% by weight or more, of the vinyl units of styrene units and butadiene as rubber components. Use rubber.

If the total amount of the styrene units of the styrene-butadiene copolymer rubber and the vinyl units of butadiene is 45% by weight or less, sufficient road surface grasping power cannot be obtained.

In addition, when the blended rubber of the styrene-butadiene copolymer rubber and other rubber is used as the diene rubber, the other rubber compounded is one or two or more of polybutadiene rubber, natural rubber, polyisoprene rubber, butyl rubber and butyl halide rubber. Is preferably used, and the blend ratio of styrene-butadiene rubber and the other rubber is preferably 70-100% by weight of styrene-butadiene rubber and 30-0% by weight of other rubber. If the blend ratio of other rubber is 30% by weight or more, sufficient road grasp cannot be obtained.

50-130 parts by weight of carbon black, more preferably 60-100 parts by weight, is applied to the rubber composition for tread of the present invention based on 100 parts by weight of the styrene-butadiene copolymer, and the process oil is 100 parts by weight of this styrene-butadiene rubber. It is good to apply 50-0 parts by weight. The amount and molecular weight range of the liquid polybutadiene can be determined according to the Mooney viscosity or molecular weight level of the styrene-butadiene rubber itself.

If the amount of carbon black exceeds 130 parts by weight, it is not good because high speed durability is lowered, and the type of carbon black can be selected according to the level of desired road grasping power.

If the blending ratio of liquid polybutadiene is less than 3 parts by weight with respect to 100 parts by weight of styrene-butadiene rubber, the improvement of wear resistance and low temperature characteristics is not sufficient. Therefore, the blending ratio of the liquid polybutadiene is preferably 3-30 parts by weight based on 100 parts by weight of styrene-butadiene rubber. In addition, if the cis-1 and 4-polybutadiene content of the liquid polybutadiene is 90% or less, it is not good because it impairs the excellent wear resistance of the polybutadiene rubber, and more preferably, the cis-1 and 4-polybutadiene content is 95% or more. Good to do.

The polystyrene reduced weight average molecular weight measured by GPC of liquid polybutadiene is preferably 2,000-50,000, and more suitable weight average molecular weight range is 5,000-40,000. If the molecular weight is 2,000 or less, mechanical properties such as tensile strength are not remarkably good. If the molecular weight is 50,000 or more, the viscosity rises excessively, making it difficult to expect the role of the liquid softener.

The styrene-butadiene rubber and liquid polybutadiene mixture may be prepared by mixing a liquid polybutadiene in an organic solution of styrene-butadiene copolymerization or by mixing an organic solution of an undried liquid polybutadiene, followed by drying and solidification. It can also solidify.

In addition, the tread rubber composition of the present invention is prepared by adding sulfur, vulcanization accelerator, anti-aging agent, zincation, stearic acid and the like as a compounding agent.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated concretely based on an Example.

EXAMPLE

The rubber compositions of Examples, Comparative Examples 1 and 2 were prepared in the formulation shown in Table 1 below. A styrene-butadiene rubber having a styrene content of 36% and a vinyl content of 55% in the butadiene unit is polymerized, and a low molecular weight liquid butadiene rubber having a cis-1 and 4-polybutadiene bond content of 96% and a weight average molecular weight of 12,000 is polymerized. The mixed, coagulated, and dried products were added at the time of compounding or added separately at the compounding stage to evaluate their properties. The mixing ratio of the liquid butadiene rubber was 10 parts by weight based on 100 parts by weight of styrene-butadiene rubber.

In the styrene-butadiene copolymer rubber, the vinyl content was determined by infrared spectroscopy (morero method), and the styrene content was measured from a calibration curve previously obtained by infrared spectroscopy based on absorption of phenyl group of 699 / cm.

On the other hand, the weight average molecular weight of liquid polystyrene was calculated | required from the measurement result about the polymerization sample using the GPC apparatus, the calibration curve was created using the polystyrene of constant molecular weight. Tetrahydrofuran was used as a solvent.

In the rubber composition of Examples and Comparative Examples, a solid rubber was added in a BR Banbari mixer, followed by Soviet Union for 30 seconds, followed by adding liquid polybutadiene rubber, oil, and carbon black, followed by additional mixing for 3 minutes, and discharging the carbon black master batch. After leaving, the master batch and the vulcanizing agent were added, followed by mixing for 2 minutes to obtain a final unvulcanized rubber composition. This blending procedure and blending time were the same for all examples and comparative examples.

Finally, the obtained unvulcanized rubber composition was press-vulcanized at 160 ° C. for 15 minutes to obtain a vulcanized rubber specimen for physical property evaluation.

The road grasping force was determined by using a Rheovibron tester, and the tanδ values at 60 ° C. under 11 Hz frequency and 1.25% dynamic strain were compared. The larger tan δ value, the better the surface grasping force.

Wear resistance is non. F. Using the Pico wear tester manufactured by Goodrich (B.F.Goodrich), the amount of specimens was obtained, and the value of Comparative Example 1 was expressed as an index by 100. The larger the index value, the better the wear resistance.

As can be seen from Table 1, the present invention is prepared by mixing a low molecular weight liquid polybutadiene copolymer in the styrene-butadiene copolymer rubber in the polymerization step and applying it to a rubber composition for tread while maintaining the high road surface abrasion resistance It is effective because it can greatly improve the efficiency and prevent productivity loss.

Claims (4)

A rubber composition for tread of pneumatic tires containing 3-30 parts by weight of liquid polybutadiene polymer rubber, 50-130 parts by weight of carbon black and 50-0 parts by weight of process oil, based on 100 parts by weight of styrene-butadiene copolymer rubber. The rubber composition according to claim 1, wherein the styrene-butadiene copolymer rubber has a Mooney viscosity of 40-130 made by copolymerizing 1,3-butadiene and styrene using an organolithium-based polymerization initiator in a hydrocarbon solvent. The rubber composition according to claim 1 or 2, wherein the styrene-butadiene copolymer rubber has a total amount of styrene units and butadiene vinyl units of 45% by weight or more. The rubber according to claim 1, wherein the liquid polybutadiene polymer rubber has a low molecular weight cis-1,4-polybutadiene content of at least 2,000-50,000 in terms of polystyrene equivalent weight average molecular weight measured by GPC in a hydrocarbon solvent. Composition.