JPH0445136A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To obtain the title tire excellent in wear resistance and the drivability and brakeability on ice-and-snow-covered roads by providing its tread with a composition prepared by incorporating a diene rubber-predominant rubber with an internally crosslinked styrene-based thermoplastic elastomer. CONSTITUTION:The objective tire can be obtained by providing its tread with a composition prepared by incorporating (A) 100pts.wt. of a rubber component consisting mainly of a diene rubber (e.g. natural rubber, polybutadiene rubber) with (B) 1 - 50 (pref. 5 - 40)pts.wt. of a styrene-based thermoplastic elastomer (pref. styrene-butadient-styrene type block copolymer elastomer) internally crosslinked, using a sulfur- or radiation- crosslinking technique, to such an extent as to be 10 - 1,000% in the increase rate of the tensile stress at its 100% extension. In the above composition, the component B is dispersed in the matrix in the form of particles with a mean domain diameter of 1 - 1,000mum.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention provides a pneumatic tire that improves driving performance, braking performance, and maneuverability on icy and snowy roads without impairing maneuverability, durability, and wear resistance, especially in summer. This invention relates to a pneumatic tire with significantly improved properties.

(Prior Art) In conventional pneumatic tires, spiked tires with spike pins driven into the tread surface have been frequently used to ensure driving performance, braking performance, and maneuverability when driving on icy and snowy roads. However, such tires generate dust due to wear of the spike pins themselves and wear and tear on the road, which has become a major social problem. In order to deal with this, regulations on the protrusion amount and number of spike pins and the material of the spike pins have been studied, but this has not provided a fundamental solution to the social problem.

On the other hand, in recent years, studless tires that have driving, braking, and maneuverability on icy and snowy roads without the use of spikes or chains have been studied and are rapidly becoming popular, but they still do not have sufficient performance on icy and snowy roads compared to spiked tires. It is difficult to say that he is demonstrating his full potential.

Conventionally, the tread rubber of studded female tires has been formulated using a polymer with a low glass transition point in order to ensure rubber elasticity at low temperatures. However, depending on the hysteresis properties of such polymers,
Even if it exhibits a certain level of performance in the ice and snow temperature range, there is a problem in that braking and maneuverability on wet and dry roads are insufficient.

Also, JP-A-55-135149, JP-A-58-19
9203, JP-A-60-137945, etc., it is also known to similarly improve low-temperature properties by using a rubber composition in which a large amount of a softener or plasticizer is blended into tread rubber. However, despite the degree of improvement in performance on ice and snow, these methods have major problems such as a decrease in wear resistance when running on a ship route and separation of tread rubber.

Furthermore, no matter which technology is used, performance on ice and snow is good in a relatively low temperature region below -5°C (so-called dry-on-ice), but performance in wet conditions around 0°C (
On ice and snow (so-called wet-on-ice), a sufficient coefficient of friction cannot be obtained, and it cannot be said that driving performance, braking performance, and maneuverability are generally improved.

(Problems to be Solved by the Invention) An object of the present invention is to provide a pneumatic tire that has improved driving performance, braking performance, and maneuverability on icy and snowy roads without impairing maneuverability and durability in summer. The object of the present invention is to provide a tire that has improved driving performance, braking performance, and maneuverability on wet, icy and snowy road surfaces without particularly reducing wear resistance.

(Means for Solving the Problems) The present inventors have provided a styrene-based thermoplastic elastomer with an internal crosslinking structure in advance so that when the styrene-based thermoplastic elastomer is filled into a tread rubber, it forms domains without melting and flowing. In order to improve the coefficient of friction of the tread rubber on ice and snow, and because the styrenic thermoplastic elastomer causes a co-crosslinking reaction with the matrix rubber, the tread rubber composition can be used with or without filling with this thermoplastic elastomer. The present invention was completed by confirming that the same level of wear resistance was maintained.

In other words, this invention provides a rubber component mainly composed of diene rubber with an increase rate of tensile stress of 1 at 100% elongation.
This is a pneumatic tire in which the tread is provided with a rubber composition containing a styrene-based thermoplastic elastomer that is internally crosslinked to within a range of 0 to 1000%.

(Function) The internally crosslinked styrenic thermoplastic elastomer used in the present invention can be used in various crosslinking systems conventionally applied to styrenic thermoplastic elastomers, such as sulfur crosslinking, peroxide crosslinking, and radiation crosslinking. Any method may be applied, and the crosslinking method and crosslinking structure are not particularly limited.

The styrenic thermoplastic elastomer that is the target of the crosslinking reaction contains at least one, preferably 1 to 2, non-rubber polymer block segments (hereinafter referred to as polystyrene blocks) mainly composed of styrene, and rubber-like polymer block segments ( (hereinafter referred to as rubber block) at least 1
It contains Such styrene-based thermoplastic elastomers have, for example, a molecular structure with polystyrene blocks at both ends and a rubber block in the middle, a structure with only one polystyrene block and a rubber block on the other, and a structure with three or more polystyrene ends. There is a structure in which these are connected by rubber blocks, and a structure in which polystyrene blocks and rubber blocks are further introduced alternately in the above structure. The rubber block may be any polyolefin-based elastomer block such as a polybutadiene block or a polyisoprene block, and is not particularly limited. Among these, styrene-butadiene-styrene (S
-B-3) type block copolymer elastomer or styrene-butadiene (S-B) type block copolymer elastomer is preferred.

The manufacturing method of these styrenic thermoplastic elastomers is as follows:
It is well known, for example, in JP-A-60-243109 and JP-B-48-2423, a 5-B-3 type block copolymer elastomer catalyzed by an organic Li compound is described in JP-B-36-19286. The publication describes the production of S-B type and 5-B-8 type block copolymer elastomers using similar catalysts.

The necessary degree of internal crosslinking of the styrenic thermoplastic elastomer can be determined by the rate of increase in tensile stress at 100% elongation measured according to ASTM D 638, which is within the range of 10-1000%. By applying internal crosslinking to this degree or higher, when this internally crosslinked styrenic thermoplastic elastomer is filled into a tread rubber, it can be dispersed in the matrix as particles having an average domain diameter of 1 μm or more. If the average domain diameter of the particles is less than 1 μm, the performance of the tire on ice and snow will not be sufficient. However, if the internal crosslinking reaction is carried out excessively, the average domain diameter will exceed 1,000 μm, which is not good because the wear resistance of the tread will decrease.

The internally crosslinked styrene thermoplastic elastomer is preferably blended in an amount of 1 to 50 parts by weight, more preferably 5 to 40 parts by weight, per 100 parts by weight of the rubber component. If the amount is less than 1 part by weight, the effect of improving driveability, braking performance, and maneuverability on icy and snowy roads will be small, and if it is more than 50 parts by weight, the kneading workability of the rubber composition will be reduced.

Rubber components include natural rubber, polyisoprene rubber, polybutadiene rubber, styrene-butadiene copolymer rubber, styrene-isoprene-butadiene terpolymer rubber, styrene-isoprene copolymer rubber, and isoprene-butadiene copolymer rubber. Combined rubber etc. account for the main part. The main part means that one or more of these rubbers accounts for 50 to 50% of the total rubber components.
It means occupying 100%.

In addition to the diene rubber and the internally crosslinked styrene thermoplastic elastomer, the composition disposed in the tread of the pneumatic tire of the present invention may contain other rubbers and compounding agents commonly used in tread rubber, such as fillers. , an anti-aging agent, a vulcanizing agent, and a vulcanization accelerator, and the types and amounts thereof are within the range normally used for tread rubber and are not particularly limited.

(Examples) Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples.

Tests of tread rubber properties and tire performance using test tires shown below were conducted in the following manner.

(1) Average domain diameter of internally crosslinked styrene thermoplastic elastomer in tread rubber
A lot of samples were selected, the diameters of 20 domains of the internally crosslinked styrene thermoplastic elastomer were measured within the field of view of an optical microscope, the average domain diameter was calculated for each lot, and the average domain diameter of the 10 lots was calculated. Calculated.

(2) Coefficient of friction on ice Rubber's coefficient of friction on ice, especially in a wet state around 0°C, is determined by measuring a sample (sample dimensions: length 10 mm, width 10 mm, thickness 5 mm) on ice with a surface temperature of -0,500. )
Contact the ice with the surface of the
Static friction coefficient was measured using a needle. Load 2 as measurement condition
kg/cm2, sliding speed 1101n/5eC1, ambient temperature -2°C, and surface condition approximated to a mirror surface.

(3) Ice braking performance test tires, radial tires for passenger cars PSR (165S
R13) was built, and after a 50 km normal run as a break-in run, it was used for testing. (The same applies to the next wear test.) Each of the four test tires was mounted on a passenger car with a displacement of 1500 cc, and the braking distance was measured on ice at an outside temperature of -5°C. The tire of Comparative Example 1 was set as 100 and expressed as an index.

The larger the value, the better the braking performance.

(4) Wear test Two tires for each test were attached to the drive shaft of a passenger car with a displacement of 1500 cc, and the tires were run on the concrete road surface of a test course at a predetermined speed. The amount of change in groove depth was measured and expressed as an index with the tire of Comparative Example 1 set as 100. The larger the value, the better the wear resistance performance.

Examples 1 to 5, Comparative Examples 1 to 4 S-B-8 type and S-B type styrenic thermoplastic elastomers were subjected to an internal crosslinking reaction with the formulation content or radiation dose shown in Table 1, and sulfur crosslinking or radiation A crosslinked structure was formed.

Samples A-D were prepared by kneading with the formulation shown in Table 1,
This was carried out by pressure vulcanization at 145° C. for 40 minutes to introduce sulfur crosslinks.

A rubber composition containing the internally crosslinked styrene thermoplastic elastomer and a rubber composition without it for comparison were prepared with the formulations shown in Table 2, and the coefficient of friction on ice and average domain diameter of the vulcanizates were measured. . Furthermore, the braking performance on ice and the wear resistance performance of tires whose treads were provided with these rubber compositions were measured. The results are shown in Table 2.

As is clear from Table 2, by applying internal crosslinking,
Example 1 in which the average domain diameter in the rubber composition of styrene thermoplastic elastomer was within the range of 1 to 1000 μm
The compositions of ~5 improve the coefficient of friction on ice compared to the normal tread rubber composition shown in Comparative Example), and the tires using these in the tread also have the same wear resistance performance as the tire of Comparative Example 1. Above all, in both cases, the braking performance on ice has been significantly improved.

On the other hand, as seen in Comparative Examples 2 and 3, when the internal crosslinking of the styrenic thermoplastic elastomer is insufficient and the average domain diameter in the rubber composition is less than 1 μm, the rubber composition is Almost no improvement was observed in either the friction coefficient or the tire's braking performance on ice. In comparative example 4,
Because the styrenic thermoplastic elastomer was subjected to an excessive internal crosslinking reaction, the average domain diameter in the rubber composition was 10.
It can be seen that the diameter exceeds 0.00 μm, which significantly reduces the wear resistance.

(Effect of the invention) As is clear from the Examples and Comparative Examples, a styrene-based rubber component containing diene rubber as a main component is internally crosslinked until the increase rate of tensile stress at 100% elongation is at least 10%. Pneumatic tires whose tread is made of a rubber composition containing a thermoplastic elastomer improve driveability, braking performance, and maneuverability on wet and dry icy and snowy roads without reducing wear resistance. can be significantly improved.

Claims (1)

[Claims] 1. A styrene-based thermoplastic elastomer that is internally crosslinked to a rubber component mainly composed of diene rubber until the increase rate of tensile stress at 100% elongation is within the range of 10 to 1000%. A pneumatic tire characterized by having a tread provided with a compounded rubber composition. 2. Styrenic thermoplastic elastomer is 1 to 1000μ
The pneumatic tire according to claim 1, having an average domain diameter within the range of m.