JPH0120651B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a rubber composition for tire treads, and more specifically, it uses styrene-butadiene copolymer rubber and polybutadiene rubber, both of which have specific properties, as raw material rubbers to improve both abrasion resistance and wet grip properties. The present invention relates to a rubber composition for tire tread. The main characteristic required of tires is wear resistance, which determines their lifespan. Furthermore, running stability, especially road grip performance on wet road surfaces (wet grip performance), is also an important factor. Attempts have been made for a long time to improve both of the characteristics required for tires in rubber compounding.
Conventionally, these two properties were considered to be contradictory rubber material properties. That is, when BR with a low glass transition temperature (Tg) is blended, wet grip properties deteriorate. Additionally, if high styrene SBR or halogenated butyl rubber with a high Tg is blended to improve wet grip properties, wear resistance will decrease. The object of the present invention is to provide a rubber composition for tire tread which improves the wear resistance of the tire and also improves running stability in rainy weather and running stability at high speed. used. As mentioned above, to improve wet grip.
Rubber with high Tg, e.g. high amount of bound styrene
SBR can be used, but this results in reduced wear resistance. If a rubber with a low Tg, such as BR with a high cis bond in the butadiene moiety, is used to improve wear resistance, the wet grip property will be significantly reduced. Next, it is possible to change the level of both physical properties, that is, wet grip properties and abrasion resistance, by blending the two, but in these blend systems, both physical properties only change according to the blend ratio. Determining the level of either physical property will also determine the level of the other. Therefore, it is impossible to improve both physical properties at the same time. Therefore, it is conceivable to improve both physical properties by changing the blending amount and type of carbon black. It is known that increasing the amount of carbon black not only improves abrasion resistance but also improves wet grip properties. Furthermore, wear resistance improves as the particle size of carbon black becomes smaller or as the amount of dibutyl phthalate (DBP) oil absorption increases. Therefore, it is possible to improve wet grip and abrasion resistance by blending a larger amount of carbon black with finer particle size and/or carbon black with higher DBP oil absorption, but it is possible to improve wet grip properties and abrasion resistance. makes it difficult to process the rubber composition. Wet grip, which is an important property required of this tire, can be evaluated in the laboratory by measuring the wet skid resistance value on a wet road surface using a portable skid tester (according to ASTM E303-74). Can be done. Similarly, wear resistance, which is an important characteristic required of tires, is evaluated in the laboratory by Akron A wear amount, etc. Recognizing the above facts, the inventors of the present invention conducted extensive studies on how to improve both physical properties at the same carbon black blending level, and as a result, they blended SBR and BR, which have specific properties, in a specific ratio and used it as a raw material rubber. The inventors have discovered that a rubber composition achieves the above object, leading to the present invention. In addition, it has specific properties.
When SBR and BR are used alone as raw material rubber, wet grip properties and abrasion resistance are not at a satisfactory level, but by blending both rubber components within a specific range, both properties can be improved in a well-balanced manner. Can be done. That is, in the present invention, the amount of bound styrene is 30 to 60
Polybutadiene rubber having 25 to 75% by weight of styrene-butadiene copolymer rubber (SBR), at least 60% by weight of trans-1,4 bonds, and having a glass transition temperature of -100°C to -50°C A rubber composition for a tire tread, characterized in that the raw rubber contains 75 to 25% by weight of (BR), and the styrene content in the raw rubber is 11% by weight or more. The amount of bound styrene in the SBR used in the present invention must be in the range of 30 to 60% by weight; if the amount of bound styrene is less than 30% by weight, wet grip properties will decrease, and if it exceeds 60% by weight, the wear resistance will decrease. It tends to reduce sex. In addition, the BR used in the present invention has a trans 1,4 bond amount of 60% by weight or more and a Tg of -100%.
The temperature must be between ℃ and -50℃, and transformers 1 and 4
If the amount of bonding is less than 60% by weight, wet grip properties will deteriorate, if Tg is higher than -50°C, rolling resistance will deteriorate, and if Tg is lower than -100°C, wet grip properties will be extremely reduced, which are not preferred. In the present invention, the styrene content in the raw rubber is 11
It is necessary that the content is at least 11% by weight; if it is less than 11% by weight, wet grip properties and breaking strength will decrease. In addition, the blending ratio in the raw rubber is SBR25 to 75% by weight, BR75 to 25% by weight, and SBR is 25% by weight.
If it is less than 75%, the wet grip properties will be poor, and if it exceeds 75%, the wear resistance will be poor. The present invention requires SBR with a high styrene content and BR with a high trans 1,4 bond content, and the vulcanized rubber sheet of a rubber composition using a blend of these as raw rubber can be prepared by observing the blended state of the rubber using an electron microscope. When looked at, it looks very similar to a rubber composition containing SBR1502 or SBR1712 alone, giving the impression that they are compatible. However, when BR with a trans-1,4 bond content of less than 60% by weight was blended with SBR, it was observed that it was separated into an SBR portion and a BR portion. In other words, it was considered to be an incompatible rubber compound. When the Tg of these rubber compositions is measured using a differential scanning calorimeter (DSC), two inflection points due to endotherm are observed near the Tg of the original rubber in the blend system, and one inflection point in the single system. is,
It was suggested that the size that can be detected by DSC is separated into two phases (microphase separation). This suggests that the blended state of the rubber differs due to the difference in the properties of BR. It is thought that the BR with a high amount of trans bonds used in the present invention has a considerably smaller dispersion unit during blending than the BR with a high amount of cis bonds. The reason why the rubber composition of the present invention simultaneously satisfies the contradictory properties of abrasion resistance and wet grip properties is not clear, but considering the above phenomenon, it is inferred that the reason is that the rubber composition is unique in its dispersion state. In the rubber composition for tire treads of the present invention, commonly used carbon black, fillers, softeners, process oils, etc. may be added as appropriate, and as a vulcanizing agent, other than sulfur may be added. A vulcanizing agent containing sulfur may be appropriately added in combination with sulfur. It is desirable that carbon black be blended in an amount of 20 to 200 parts by weight per 100 parts by weight of raw rubber. If the amount of carbon black is less than 20 parts by weight, the breaking strength and abrasion resistance will decrease, and if it exceeds 200 parts by weight, the Mooney viscosity of the rubber composition will become extremely high.
Each of these is undesirable because it becomes difficult to process the rubber composition. The present invention will be specifically described below based on Examples and Comparative Examples. Examples 1 to 9 and Comparative Examples 1 to 11 Various SBRs and BRs having structures shown in Table 1
is used as the raw material rubber, and the compounding agents shown in Table 2 are added to it,
And the blending ratio of raw rubber is as shown in Table 3,
A rubber composition was prepared by mixing in a small internal mixer. The rubber composition thus obtained was heated at 160°C.
Vulcanized rubber was obtained by vulcanization for 20 minutes, and the impact resilience, wet skid resistance, abrasion resistance, 300% tensile stress, hardness, tensile strength, and elongation of the vulcanized rubber were measured. In addition, 300% tensile stress, tensile strength, and elongation are JIS
In accordance with K6301, hardness was determined using a dumbbell punching machine in accordance with JIS K6301, and rebound resilience was determined by the Riupke rebound test at 70°C in accordance with JIS K6301. In addition, wet skid resistance was measured using a British portable skid tester, and the road surface was measured using a 3M Outdoor Type B Safety Walk in an atmosphere of 25°C after being moistened with distilled water. was measured by Akron A wear amount. The results are shown in Table 3, and the relationship between Akron A wear amount and wet skid resistance value is shown in FIG. Note that all formulation values in Tables 2 and 3 are parts by weight.

【table】

【table】

[Table] Rusulfenamide

【table】

[Table] As shown in Table 1, compared to Comparative Example 1, which is a conventional basic formulation, Comparative Example 2, which is a single formulation of SBR-C, is inferior in wear resistance. Also, BR-A, BR-
In Comparative Examples 3 and 4 containing only B, the wet skid resistance is reduced. On the other hand, Examples 1 and 2 in which SBR-A, SBR-B, and BR-A were blended, respectively, have improved wear resistance and wet skid resistance compared to Comparative Example 1, and other properties are also within the desired range. However, SBR−
In Comparative Examples 5 and 6, in which A, SBR-B and BR-B, which has a small amount of trans bond in the butadiene moiety and a low glass transition temperature, are blended, the wet skid resistance is low. Also SBR-C, SBR-D and BR-
Examples 3 to 4 in which A and BR-B were blended, respectively,
Also in Comparative Examples 7-8, Examples 1-2 and Comparative Example 5
-6 results were obtained. In Example 5 and Comparative Examples 9 to 10, in which SBR-A, BR-A, and BR-B were mixed in varying amounts, Example 5 showed preferable wear resistance and wet skid resistance, but Comparative Examples 9 to 10 showed preferable wear resistance and wet skid resistance. Due to the low styrene content in the raw rubber, wet skidding properties are poor. especially
In Comparative Example 10 using BR-B, the tensile strength also decreased rapidly. Examples 6 to 9, in which the type of SBR was changed and a variable amount was mixed with BR-A, had wear resistance and wet skid resistance equal to or higher than Comparative Example 1. Comparative Example 11, in which SBR-E with a low amount of bound styrene was blended alone, had significantly poor wear resistance. As explained above, SBR with specific properties
By using the rubber composition for tire tread of the present invention, which is a raw material rubber containing a specific proportion of It has the advantage of improved running stability and longer life compared to the previous model.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between Akron A wear amount and wet skid resistance value of Comparative Examples 1 to 11 and Examples 1 to 9.

Claims (1)

[Claims] 1 Styrene with a bound styrene content of 30 to 60% by weight
25 to 75% by weight of butadiene copolymer rubber and 75 to 25% by weight of polybutadiene rubber having at least 60% by weight of trans-1,4 bonds and having a glass transition temperature of -100°C to -50°C. 1. A rubber composition for tire tread, characterized in that the raw material rubber has a styrene content of 11% by weight or more.