JPH04362403A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To obtain a pneumatic tire, as an all-season tire in reality, which secures sufficient control stability, durability and low fuel consumption in summer and provides sufficient drivability and brakability on dry-on-ice roads as well as wet-on-ice roads. CONSTITUTION:Rubber composition that 100 pts.wt. rubber and 5-6 pts.wt. syndiotactic-1,2-polybutadiene resin, which has an average grain size ranging within 10-500mum and a crystal melting point of 110 deg.C or higher, are mixed together is arranged on a tread.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pneumatic tire,
Specifically, the present invention relates to a so-called all-season pneumatic tire that has significantly improved driving performance, braking performance, and maneuverability on icy and snowy roads without impairing steering stability performance and durability performance in summer. BACKGROUND OF THE INVENTION In recent years, there has been an increasing demand for so-called all-season tires that can be used in the winter without having to change tires in the same way as in the summer. Such tires must have the same dry grip, wet grip, steering stability, durability, and fuel efficiency in winter as they do in summer, and also have sufficient driving and braking performance on ice and snow. is required. Conventionally, the tread rubber used for such tires has been required to have low hardness at low temperatures for summer tread rubber, and therefore a polymer with a low glass transition point has been used, or a polymer with a low glass transition temperature has been used. A method using a softener or plasticizer that can maintain an appropriate elastic modulus is known. However, the former method has the problem that, due to the hysteresis characteristics of the polymer, although it exhibits reasonable performance in the freezing and snow temperature range, braking performance and maneuverability on wet and dry road surfaces are insufficient. The latter method is also disclosed in Japanese Patent Application Laid-open Nos. 135149-1982 and 1983-
No. 199203, Japanese Unexamined Patent Publication No. 1992-137945, etc., but in both methods, the abrasion resistance and durability when driving on ordinary roads are low, considering the degree of improvement in performance on ice and snow. Problems have been pointed out, such as the large negative impact it has on people. [0005] Problems to be Solved by the Invention [0005] No matter which of the above-mentioned techniques is used, it is true that the performance on ice and snow in the so-called dry-on-ice in a relatively low-temperature region of -5°C or lower is good. However, in wet conditions around 0℃, so-called wet-on-ice performance on ice and snow, a sufficient coefficient of friction cannot be obtained, and it is difficult to say that driving performance, braking performance, and maneuverability have been sufficiently improved. . Therefore, an object of the present invention is to sufficiently ensure steering stability, durability, and fuel efficiency in the summer, and to provide a vehicle not only for dry-on-ice driving but also for wet-on-ice driving.
The objective is to provide a true all-season tire that has sufficient driving and braking performance even on ice. Means for Solving the Problems The present inventors have conducted intensive studies on the performance of the tread rubber of such all-season or studless tires on ice and snow, particularly on the performance on ice and snow road surfaces in wet conditions. syndiotactic rubber composition with a specific structure
By using a rubber composition blended with particles of 1,2-polybutadiene resin, the performance on ice and snow can be significantly improved, and performance such as steering stability and durability required in summer or when driving on normal roads is not impaired. The inventors discovered that there is no such thing and completed the present invention. Furthermore, it was confirmed that when the rubber constituting the matrix portion other than the above-mentioned particles is a foamed rubber composition, further improvement in performance on ice and snow can be obtained. That is, the pneumatic tire of the present invention uses syndiotactic-1,2-polybutadiene resin, which is granular with an average particle size within the range of 10 to 500 μm and whose crystalline melting point is 110° C. or higher, as a rubber. The rubber composition is characterized in that the tread is provided with a rubber composition in an amount of 5 to 60 parts by weight per 100 parts by weight. Syndiotactic used in the present invention
The particle size of 1,2-polybutadiene resin is 10 to 500 μm
The reason for this is that if the particle size is smaller than 10 μm, the performance on ice and snow that is the objective of the present invention will not be sufficient, while if it is larger than 500 μm,
This is because although a certain degree of effect is recognized in terms of performance on ice and snow, it degrades other performances required of a tire such as wear resistance, so it is not preferable. In addition, here "
"Grain" refers to tread in both the tire equatorial plane cross section and the tire radial cross section perpendicular to the tire equatorial plane.
It means that the average value of the ratio M of the longest diameter to the shortest diameter of syndiotactic-1,2-polybutadiene resin particles is 6 or less, preferably 4 or less. That is, in order to improve driveability and braking performance on ice and snow, syndiotactic-1,2-polybutadiene resin is dispersed in the tread rubber composition in the form of granules rather than microorganic short fibers. It requires that. [0010] Also, such syndiotactic-1,
2-polybutadiene resin generally has crystallinity, but the melting point of the crystal part is required to be 110°C or higher. The reason for this is that if the melting point is less than 110°C, the resin may soften and deform when it is added and kneaded during compounding.
This is because if some or all of the particles melt, the desired particle size cannot be maintained, and the desired improvement in performance on ice and snow cannot be achieved. The rubber composition for a tread of a pneumatic tire of the present invention requires 5 to 60 parts by weight of the above-mentioned syndiotactic-1,2-polybutadiene resin per 100 parts by weight of rubber. The reason for this is that if the amount is less than 5 parts by weight, the desired performance on ice and snow will hardly be improved, whereas if it is more than 60 parts by weight, other tire performance such as wear resistance will be significantly impaired. This is because not only is the tire damaged, but also the workability during tire manufacture is significantly deteriorated, making it impossible to put it to practical use. In the present invention, the type of rubber forming the rubber composition into which the syndiotactic-1,2-polybutadiene resin is blended, the type of filler to be blended, and other chemicals are determined according to those commonly used. Any one can be used, and there are no particular limitations. For example, as a rubber component, natural rubber, polyisoprene rubber,
Polybutadiene rubber, styrene-butadiene copolymer rubber, styrene-isoprene-butadiene terpolymer rubber, styrene-isoprene copolymer rubber, isoprene-
Examples include butadiene copolymer rubber. In addition, the composition disposed in the tread can include, for example, fillers, anti-aging agents, vulcanizing agents, and vulcanization accelerators, and the types and amounts of these are also within the range normally used for tread rubber. However, it is not particularly limited. [0013] In the present invention, the tread rubber is 3 to 3
It is preferable to have closed cells with an expansion ratio of 5%. 0
This is because such closed cells are useful for increasing the microscopic water absorption and drainage effect by the pores and exhibiting excellent performance on ice and snow when there is a lot of melted water on the ice surface at temperatures around .degree. Foaming may be performed using either a foaming agent or high-pressure mixing of gases. Note that if the foaming ratio is less than 3%, the foaming effect will not be sufficient;
If it exceeds 5%, the tread rigidity will be insufficient, leading to a decrease in wear resistance and the occurrence of groove bottom cracks, which is not preferable. Here, the foaming rate Vs of the foamed rubber is determined by the following formula: Vs = {(ρ0-ρ9)/(ρ1-ρ9)-1}×1
00 (%) ... (1) where ρ1 is the density of foamed rubber (g/cm3), ρ
0 is the density of the solid phase part of the foam rubber (g/cm3), ρ9
is the density (g/cm3) of the gas part within the foamed rubber cells. Foamed rubber is composed of a solid phase portion and a cavity (closed cell) formed by the solid phase portion, that is, a gas portion within the cell. Since the density ρ9 of the gas part is extremely small, close to zero, and extremely small compared to the density ρ1 of the solid phase part, equation (1) can be expressed as the following equation Vs = {(ρ0-ρ1)-1
}×100(%) ... (2) It is almost equivalent to. Furthermore, in the pneumatic tire of the present invention,
A composition of ordinary rubber or foam rubber blended with the above-mentioned syndiotactic-1,2-polybutadiene resin,
It may be provided only in the cap portion of the tread portion having a cap-base structure. [Examples] The present invention will be explained in more detail below with reference to Examples and Comparative Examples. First, the methods for measuring each physical property value performed in this example will be described. 1) Melting point of resin crystals Using a differential thermal analyzer DSC200 manufactured by Seiko Electronics Co., Ltd., the temperature was raised in the temperature range from 30 °C to 250 °C at a heating rate of 10 °C/min, and the endothermic peak obtained was The melting point temperature was measured. 2) Measurement of coefficient of friction on ice The coefficient of friction on ice of rubber, especially in the wet state around 0°C, is as follows:
The sample surface obtained from a slab sheet obtained by the usual vulcanization method on ice with a surface temperature of -0.5 °C (sample dimensions, length 1
(0 mm, width 10 mm, thickness 5 mm) was brought into contact with ice and measured using a dynamic/static friction coefficient meter manufactured by Kyowa Kaimen Kagaku Co., Ltd. The measurement conditions were a load of 2 kg/cm2 for radial tires for passenger cars, a load of 5 kg/cm2 for radial tires for trucks and buses, and a sliding speed of 1.
The test was carried out at a speed of 0 mm/sec, an ambient temperature of -2° C., and a surface condition approximated to a mirror surface. 3) Small tire performance test 3-1) Braking performance test on ice A tire PSR (165SR13) was prepared, and after running normally for 50 km as a break-in run, it was subjected to a test. The same applies to the wear resistance performance test and the wet skid resistance performance test. Each of the four test tires had a displacement of 1500cc.
The braking distance was measured on ice at an outside temperature of -5°C. The control tire of Comparative Example 1 was set as 100 and expressed as an index. The larger the value, the better the braking. 3-2) 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 a concrete road surface of a test course at a predetermined speed. Measure the amount of change in groove depth,
The control tire of Comparative Example 1 was set as 100 and expressed as an index. The larger the value, the better the wear resistance performance. 3-3) Wet skid resistance The skid resistance on wet road surfaces (wet skid resistance) is as follows:
80km/on a wet concrete road with a water depth of 3mm
The wet skid resistance of the test tire was evaluated using the following formula by suddenly braking from a speed of h and measuring the distance from when the wheels were locked to when the wheels came to a stop. The larger the value, the better the wet skid resistance. 4) Large tire performance test test tire TBR
(1000R20) was created and run for 150 km on an 8 ton, 2D type truck under 100% loading condition with a test tire mounted on the drive shaft. 4-1) Braking performance on ice: 8 tons, under 100% loading conditions on a 2D type truck,
Test tires were installed on all wheels, and the braking distance was measured when full lock brakes were applied from a speed of 20 km/h. The ice temperature is -5°C. The results are expressed as an index relative to the control tire of Comparative Example 7. The larger the number, the better the braking performance on ice. 4-2) Wear test under 100% loading condition on 8 tons, 2D type truck,
Attach test tires to all wheels and perform normal driving.5
The groove depth after running for 10,000 km was expressed as an index, with the control tire of Comparative Example 7 set as 100. The larger the value, the better the wear resistance. Table 1 below shows various syndiotactic-1,
The average particle size and crystal melting point of 2-polybutadiene resin are shown. The particle size was measured using an Air Jet Sheep particle size analyzer model 200LS manufactured by ALPINE, and the cumulative
The particle size of 0% was taken as the average particle size. [0021] Tables 2 and 3 show the compounding formulations (
(parts by weight), the vulcanized physical properties of the obtained particle-containing rubber, and the tire performance when the rubber is applied to a tire tread. Specifically, Table 2 examines radial tires for passenger cars (PSR), and Table 3 examines radial tires for trucks and buses (TBR). [Table 2] [Table 3] [0024] From Table 2 showing the performance evaluation test results for radial tires for passenger cars, the following was confirmed. In Examples 1 to 4, 20 parts by weight of syndiotactic-1,2-polybutadiene resin species B, C, D and E, which satisfy the conditions of the present invention in average particle size and crystal melting point, were blended into the tread rubber. Comparative Examples 2 to 5 in which resin types A, F, G, and H that do not meet the conditions are blended
Compared to the control tire of Comparative Example 1, the braking performance on ice was significantly improved, and the wet skid resistance and abrasion resistance were hardly impaired. Furthermore, in Examples 5 and 6, in which syndiotactic-1,2-polybutadiene resin type D satisfying the conditions of the present invention was blended into the tread rubber, and the matrix rubber was foamed rubber, most of the other tire performances were improved. We were able to further improve braking performance on ice without any loss. In addition, in Comparative Example 6 in which only foamed rubber was used without blending resin, although the braking performance on ice was improved, there was a problem in terms of wear resistance. Next, from Table 3 showing the performance evaluation test results for radial tires for trucks and buses, the following was confirmed. Examples 7 to 1 in which syndiotactic-1,2-polybutadiene resin type D satisfying the conditions of the present invention was blended into tread rubber within the blending amount specified by the present invention
0, compared to Comparative Examples 8 to 10 in which the blending amount of resin type D deviates from the range of the present invention, the braking performance on ice compared to the control tire of Comparative Example 7 was significantly improved, and the wear resistance was improved. There was almost no damage. In addition, in Example 11, syndiotactic-1,2-polybutadiene resin type D satisfying the conditions of the present invention was blended into the tread rubber within the blending amount specified by the present invention, and this matrix rubber was foamed rubber. , it was possible to further improve the braking performance on ice without compromising the performance of other tires. In addition, in Comparative Examples 11 and 12 in which the resin was blended in an amount deviating from the amount specified in the present invention and foamed rubber was used, although the braking performance on ice was improved, there was a problem in terms of wear resistance. [0026] As explained above, in the pneumatic tire of the present invention, the rubber composition of the tread portion contains syndiotactic-1,2-
By using a rubber composition containing a predetermined amount of polybutadiene resin particles, it exhibits sufficient drive and braking performance not only on dry ice but also on wet ice, significantly improving performance on ice and snow, and even in summer. Alternatively, it is possible to obtain the effect that the performance of steering stability, durability, and fuel efficiency required when driving on a normal road surface is hardly impaired. Therefore, the pneumatic tire of the present invention can be said to be an all-season tire in the true sense.

Claims (3)

[Claims] Claim 1: Syndiotactic-1,2-polybutadiene resin, which is granular with an average particle size within the range of 10 to 500 μm and whose crystalline melting point is 110° C. or higher, is added in an amount of 5 to 100 parts by weight of rubber. A pneumatic tire characterized in that a tread is provided with a rubber composition containing up to 60 parts by weight of a rubber composition. 2. The pneumatic tire according to claim 1, wherein the rubber constituting the matrix portion other than the particles comprises a foamed rubber composition. 3. A pneumatic tire characterized in that the tread portion has a cap-base structure, and the rubber composition used for the cap portion is comprised of the rubber composition according to claim 1 or 2.