JPS58196245A - Rubber composition for tire tread - Google Patents

Abstract

PURPOSE:A rubber composition for tire tread that has a specific complex elastic modulus and a specific dissipation loss, thus showing good start, acceleration, slope climbing and turning control on snow-covered or frozen road surfaces as well as high wet-gripping properties on usual road surfaces. CONSTITUTION:The objective composition contains 20-80wt%, based on the 100pts.wt. of the rubber components, of a synthetic isoprene rubber containing more than 15mol% of 1,2- and/or 3,4-bonds in the molecule, having a complex elastic modulus of less than 400kgf/cm<2> at a temperature higher than -30 deg.C and an integrated dissipation loss of more than 5 in a temperature range -30- -15 deg.C. The above rubber composition preferably consists of 20-80pts.wt. of the above synthetic isoprene rubber and 80-20pts.wt. of natural rubber and/or cis- 1,4-polyisoprene synthetic rubber.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a rubber composition for a tire tread suitable for running on snow-covered roads or frozen roads, in particular a rubber composition for a tire tread that is suitable for running on snow-covered roads or frozen roads.
Here, the value of the complex modulus of elasticity and the integral value of the loss coefficient are adjusted to a specific range, and the starting, acceleration,
Pitching! The present invention relates to a rubber composition for a tire tread that has excellent turning and turning performance as well as wet grip performance on a single-stage road surface.

In order to drive safely and reliably on fresh snow roads, compacted snow roads, frozen roads, icy roads, etc. in winter and snowy areas, there is a method for attaching chains to summer tires, and if blocks are standard (divided and A method using tires specifically designed for snowy roads with deep tread grooves;
There is also a method of using spikes or tires for icy roads, which are tires specifically designed for snowy roads with spikes.

However, the method of attaching a chain to a summer tire requires time and effort, such as having to temporarily stop the east wheel when attaching it, and although it is possible to obtain driving force in the acid direction depending on how the chain is inserted. , 1 The stability in the reed direction is poor,
Additionally, there are signs of damage to Tolerado rubber.

In addition, with the method of using tires exclusively for snowy roads, good braking performance can be obtained on fresh snow and compacted snow, but the -1 effect is
On frozen snow or icy roads at very low temperatures, the tread rubber hardens, reducing running performance at the tooth edges, causing slips and other problems in terms of running safety. On the other hand, in order to suppress the increase in rubber hardness at low temperatures, natural rubber with a low glass transition point,
If the tread rubber is made of Jugo, which uses a large amount of synthetic butadiene rubber, the low-temperature properties will improve, but the wet grip performance on ordinary roads will be poor.

It has the disadvantage of poor handling stability.

In addition, tires for 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, ['i There are problems such as adding iJM.

Therefore, attaching accessories such as chains or spikes to tires to improve driving performance sacrifices various performances such as general road driving performance, and the above-mentioned snow-specific tires also have sufficient snow driving performance. Since it is not possible to achieve both performance and road performance, research into tread rubber suitable for driving on snowy roads and general roads has been carried out.

Therefore, the inventors of the present invention conducted extensive research to confirm that the friction of tread rubber on snowy and icy roads is such that rubber with the following properties has excellent starting acceleration, pitching, braking performance, etc. It has been discovered that the vehicle exhibits good wet braking performance and four-way longitudinal stability even when driving on general roads.

That is, when a frequency of 101 (z, a heating rate of 1°C/min, and dynamic strain and dynamic stress are set to specific conditions, the complex modulus of elasticity at a temperature of -30°C or higher in the temperature dispersion of dynamic viscoelasticity is 4.
00 ktf/d or less and -30'C to -15
This is a tread rubber composition for tires on snowy and icy roads, in which the integral term of the loss coefficient is 5 or more in the temperature range of °C. Here @stone, @the specific conditions for stress setting are dynamic strain 11
If the stress exceeds 211f/d at g, the dynamic stress is 2k.
If t2f/d is constant and 2k4f/d cannot be achieved, the condition is that dynamic strain 1 is constant.

In general, the friction of rubber on icy roads, etc. can be divided into 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. The tread rubber hardness, i.e., the ease of adhesion to the ice surface, the lubricating effect of water dripping between the snow/water surface and the tread surface, and the latter two are the contact area with the road surface. This is an important factor that determines the

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. Natural rubber and butadiene rubber are selected; styrene/butadiene rubber, which has a relatively high Tg and hardens at low temperatures, is not preferred; There were safety problems due to poor handling stability at running temperatures (approximately 70'C'J) and poor braking performance, especially on wet roads.

The inventors focused on the hysteresis loss, or loss coefficient, of the rubber and the elastic modulus, which indicates the hardness of the tread rubber, among the factors related to the friction of the tread rubber, and as a result of conducting inspections, the following conclusions were reached. I came to the conclusion that

That is, in order to have good running performance on snow, the complex modulus of elasticity is preferably low at the road surface temperature of snowy/icy roads, that is, 0°C to -30°C, and especially -3Q't: 400°C or higher.
It has been found that driving performance on snowy and icy roads is improved when the vehicle speed is 4 f/d or less.

Furthermore, as shown in Japanese Patent Application No. 56-157927, it is known that there is a high correlation between wet grip performance and the integral value of the loss coefficient of dynamic viscoelasticity between 0°C and -15'Ct. It was found that in order to have high wet grip performance on general roads, it is necessary for the integral of the loss coefficient to be 5 or more at -30°C to -15°C in order to improve wet grip performance. .

However, none of the styrene-butadiene rubber, natural rubber, butadiene rubber, etc. currently used for treads satisfies both of the above-mentioned properties. It has been used by many blends.

According to the present invention, it is possible to achieve both starting, acceleration, pitching, and braking performance on snowy and icy roads, and wet grip and steering performance on ordinary roads, which has been considered difficult in the past.

In the invention, it is necessary that the complex modulus of elasticity measured at a frequency of 10H2 is 400 cut f/cA or less in a range of 130'e or more, so that the road surface is kept in a low temperature state (-S
Even if the tread rubber is frozen at O'CI (~0°C), hardening of the tread rubber can be effectively prevented and grip performance etc. can be maintained.

Further, in the present invention, it is necessary that the integral value of the loss coefficient measured at a frequency of 10H2 in the range of -30tEN-15°C be 5 or more. This is because if the integral value is less than 5, the wet grip performance on ordinary road surfaces will deteriorate.

A rubber composition satisfying the above conditions must have at least 15 m of 1.2 bonds and/or 5,4 bonds in the molecular chain.
A synthetic imprene rubber containing 20 to 80 parts by weight of Sl based on 100 parts by weight of the rubber component, especially one containing 80 to 20 parts by weight of the above synthetic isogrene and natural rubber and/or A mixture of 80 to 20 quadrants of cis 1,4 synthetic isoprene rubber is desirable from the viewpoint of the balance between the complex modulus at extremely low temperatures and the integral value of the loss coefficient at -15°C to -30°C.

The reason why a synthetic in-brane rubber having a large amount of 1,2 bonds or 3,4 bonds is used here is that rubber having such a microstructure has particularly excellent wet grip performance.

The tread rubber composition according to 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 Example 3 below.

Example 1 The basic formulations shown in Table 1 were used, and the polymers listed in Table 2 were used in the formulations shown in Table 3 to evaluate the performance of each material.

2 Attention RSS 5 Note 2) 5RR-1500 Sumitomo Chemical Co., Ltd. 5) BR
-150 manufactured by Ube Koryu ■ 2 The viscoelastic property values in the table are measured using a viscoelastic spectrometer manufactured by Karamoto Seisakusho ■, using a sample with a length of 30 m, 4 lengths, and a thickness of 2 fins, at a frequency of 10 Hgs heating rate. This is a value measured at 1°C min. Here, if the @ stress exceeds 2 Jf/d at the time of dynamic response 14, the dynamic stress 2 Jf/d is constant, and 2
When the slope f/d was not exceeded, measurements were made under constant conditions.

In addition, the skid resistance index was measured using a portable skid resistance tester made by British company Snonray on road surfaces at 40'C and 20°C, and at 0°C and -100 and -20°C.
7. The skid resistance on an untied road surface at -30°C is a value measured in a low-temperature test chamber, and the higher the value, the better. It can be seen that it shows extremely excellent performance in both snow and waterway driving performance.

From the above, it can be seen that the ability of the present invention is adjusted according to the following:
It simultaneously satisfies wet braking performance on ordinary roads.

Patent applicant: Sumitomo Rubber Industries, Ltd. Agent: Patent Attorney Yoshihira Nakamura 4 Mr. Kazuo Wakasugi, Commissioner of the Patent Office 4. Agent Corrected to "composition".

Claims (1)

[Claims] (The elastic modulus at a temperature of 11-30"C or higher is 400 f/d or less, and the integral value of the loss coefficient is 5 or more in the temperature range of -30C to -15C. A certain rubber composition for a tire tread. Synthetic isoprene rubber containing at least 15 m○14 +211.2 bonds and/or 6.4 bonds in the molecular chain in an amount of 20 to 80.dt per 100 parts by weight of the -rubber component.
! 4. The composition of claim 1. (20 to 80 parts of synthetic bosoderene rubber containing at least 15 mol'1 of 311,2 bonds and/or 3,4 bonds in the molecular chain, and natural rubber and/or hasis 1.4 parts of synthetic isoprene rubber) The composition of claim 1, which is a mixture of 80 to 20 vit parts.