JPH0420019B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a rubber composition for tire tread suitable for running on snow-covered roads or frozen roads, in particular, in the temperature dispersion of dynamic viscoelasticity, the value of the complex modulus of elasticity and the integral value of the loss coefficient are adjusted to a specific range. This invention relates to a rubber composition for tire tread which has excellent starting, acceleration, hill-climbing, and turning braking properties on road surfaces and frozen roads, as well as wet grip performance on ordinary road surfaces. In order to drive safely and reliably on fresh snow roads, compressed snow roads, frozen roads, icy roads, etc. in snowy areas during winter,
A method of attaching a chain to a summer tire, a method of using a tire for snowy roads with finely divided blocks and deep tread grooves, and a method of using a tire for snowy and icy roads with spikes in which spikes are driven into a tire for snowy roads. There is. However, the method of attaching chains to summer tires requires time and effort, such as having to temporarily stop the car when attaching them, and depending on the type of chain, although longitudinal driving force can be obtained, , the stability in the lateral direction is poor, and it also has an adverse effect such as damage to the tread rubber. In addition, with the method of using tires specifically designed for snowy roads, acceleration and braking performance can be obtained on fresh snow and compacted snow roads, but in general, on frozen snow and roads at very low temperatures, the tread rubber hardens and becomes difficult to drive. However, if a compound containing a large amount of natural rubber or synthetic butadiene rubber, which has a low glass transition point, is used in the tread rubber, the low-temperature properties will improve. It has the disadvantage of poor wet grip performance, poor steering stability, etc. on general roads. Furthermore, tires for snowy and icy roads with spikes, which are tires specifically designed for snowy roads with spikes, have superior performance on frozen roads compared to the first two, but when driving on regular roads, they There are problems such as damage. Therefore, attaching accessories such as chains or spikes to tires to improve snow running performance comes at the expense of general road running performance, and the snow-specific tires also do not provide sufficient snow running performance. Since it is not possible to achieve both performance and road performance, there was an urgent need to research treaded rubber suitable for driving on snowy roads and general roads. Therefore, the inventors of the present invention have conducted extensive research to determine the friction of treaded rubber on snowy and icy roads, and have found that a rubber with the following properties has excellent starting acceleration, hill climbing, braking performance, etc., and has excellent performance on general roads. It has been found that the vehicle exhibits good wet braking performance and steering stability performance even when driving. In other words, when the frequency is 10Hz, the heating rate is 1℃/min, and the dynamic strain and dynamic stress are set to specific conditions, the complex modulus of elasticity at a temperature of -30℃ or higher is 400Kgf/cm in the temperature dispersion of dynamic viscoelasticity. ² or less and -30℃～
This is a tread rubber composition for tires on snowy and icy roads, which has an integral value of loss coefficient of 5 or more in the temperature range of -15°C. Here, the specific conditions for dynamic strain and dynamic stress settings are: if the dynamic stress exceeds 2Kgf/cm ² when the dynamic strain is 1%, the dynamic stress is constant at 2Kgf/cm ² ;
If it does not exceed f/cm ² , the dynamic strain is constant at 1%. Generally, the friction of rubber on snowy/icy roads, etc.
Internal friction, i.e., hysteresis loss inside the tread rubber due to deformation, and external friction, i.e., cohesive force due to contact with the road surface. External wear is also caused by affinity with water and ice, and water between the snow/ice surface and the tread surface. This can be divided into the lubricating effect of the film and the hardness of the tread rubber, ie, the ease with which it adheres to the snow/ice surface, and the latter two are important factors that determine the contact area with the road surface. From the viewpoint of formulation, it is preferable that the rubber component has a low Tg and the rubber hardness does not increase even at low temperatures. Select natural rubber or butadiene rubber.Styrene-butadiene rubber, which has a relatively high Tg and hardens at low temperatures, is not preferred, but the second-party rubber has good properties in low-temperature snow and ice, but does not work well on ordinary roads from room temperature. There were safety issues due to poor handling stability at the operating temperature (approximately 70 degrees Celsius) and poor braking performance, especially on wet roads. Among the factors related to the friction of treaded rubber, the inventors focused on the hysteresis loss, or loss coefficient, of the rubber, and the elastic modulus, which represents the hardness of the treaded rubber, and as a result of repeated studies, they came to the following conclusion. Ivy. In other words, in order to have good snow running performance, the complex modulus of elasticity is determined by the road surface temperature of snowy and icy roads, that is, from 0°C to -
It has been found that a lower temperature at 30°C is preferable, and in particular, a lower temperature of 400 Kgf/cm ² at -30°C or higher improves running performance on snowy and icy roads. Furthermore, patent application No. 56-157927 (Japanese Patent Application No. 58-59239)
As shown in issue), wet grip performance and -
It is known that there is a high correlation between the integral value of the loss coefficient in the dynamic viscoelasticity between 30°C and -15°C, and in order to have high wet grip performance on general roads, it is necessary to reduce the loss between -30°C and -15°C. It has been found that it is necessary for the integral value of the coefficient to be 5 or more in order to improve the wet grip performance. However, none of the styrene-butadiene rubber, natural rubber, butadiene rubber, etc. currently used for Toledo products satisfies both of the above characteristics, and two of the above rubbers are It has been used by a blend of three people. According to the present invention, snow removal, which has been considered difficult in the past,
It is possible to achieve both starting, acceleration, hill climbing, and braking performance on icy roads, and wet grip and steering performance on regular roads. In the present invention, it is necessary that the complex modulus of elasticity measured at a frequency of 10 Hz is 400 kgf/cm ² or less in the range of -30°C or higher, so that the road surface is in a low temperature state (-30°C to 0°C). ) Even if the grip is frozen, the hardening of the tread rubber can be effectively prevented and the grip performance can be maintained. Further, in the present invention, it is necessary that the integral value of the loss coefficient measured at a frequency of 10 Hz in the range of -30°C to -15°C is 5 or more. This is because if the integral value is less than 5, the wet grip performance on ordinary road surfaces will deteriorate. In addition, as a rubber composition that satisfies the above conditions,
20 to 80% by weight of synthetic isoprene rubber containing at least 15 mol% of 1,2 bonds and/or 3,4 bonds in the molecular chain based on 100 parts by weight of the rubber component.
Including, especially 80 of the above synthetic isoprene
It is a mixture of ~20 parts by weight of natural rubber and/or cis 1,4 synthetic isoprene rubber of 80 to 20 parts by weight that is the integral value of the complex modulus at cryogenic temperatures and the loss coefficient from -15°C to -30°C. desirable from the perspective of balance. The reason why synthetic isoprene rubber with a high content of 1, 2 bonds or 3, 4 bonds is used here is that those having such a microstructure have particularly excellent wet grip performance. The tread rubber composition of the present invention can be suitably employed not only in tires for general passenger cars, but also in tires for motorcycles, tires for trucks and buses, tires for light trucks, and the like. The present invention will be explained in the following examples. Example 1 Various performances were evaluated using the basic formulations shown in Table 1 and the polymer species shown in Table 2 in the formulations shown in Table 3.

【table】

[Table] Azyl sulfenamide

【table】

【table】

[Table] The viscoelastic property values in the table are measured using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd., using a sample with a length of 30 mm, width of 4 mm, and thickness of 2 mm at a frequency of 10 Hz and a heating rate of 1°C/min.
This is the value measured at Here, if the dynamic stress exceeds 2Kgf/cm ² at 1% dynamic response, the dynamic stress is 2Kgf/cm ²
Measurements were made under constant conditions, and when the dynamic strain did not exceed 2 Kgf/cm ² , the dynamic strain was constant at 1%. In addition, the skid resistance index was measured using a portable skid resistance tester manufactured by Stanley, UK, on road surfaces at 40°C, 20°C, 0°C, -
The skid resistance on frozen road surfaces was measured in a low-temperature test chamber at 10°C, -20°C, and -30°C, and the higher the value, the better. As shown in Table 3, in Examples 1 to 4, the integral value of the loss coefficient at -30°C to -15°C is all extremely high compared to the comparative example, and the wet skid resistance index at 20°C and 40°C is also extremely high. expensive. In addition, natural rubbers such as Comparative Examples 1 and 3, which were conventionally considered to have the best complex modulus at 0°C to -30°C, were 400 Kgf/cm ² or less,
It can be seen that it is superior to butadiene rubber-based rubber, and shows extremely excellent performance in both wet grip performance and driving performance on snowy and icy roads. From the above, the tires with the tread rubber adjusted according to the present invention can simultaneously satisfy the starting acceleration, turning, and braking performance on snow and ice, as well as the wet braking performance on ordinary roads, which has been considered completely difficult in the past. It is something to do.

Claims (1)

[Claims] 1. At least 1, 2 bonds and/or 3, 4 bonds in the molecular chain per 100 parts by weight of the rubber component.
20 to 80 parts by weight of synthetic isoprene rubber containing 25 mol% or more and less than 35 mol%, and 80 to 20 parts by weight of natural rubber and/or cis 1,4 synthetic isoprene rubber.
It is a mixture of parts by weight and has a complex modulus of elasticity of 400Kg/ ^cm2 or less at temperatures of -30℃ or higher, and -30℃ to -15℃.
A rubber composition for tire tread, which has an integral value of loss coefficient of 5 or more in a temperature range of .