JPH06157829A - Pneumatic radial tire for truck and bus - Google Patents

Abstract

PURPOSE:To obtain a tire excellent in durability in high speed sunning because of reduced heat build-up and having abrasion resistance comparable to that of the conventional tires by forming the tread having a two-layer structure consisting of a cap rubber and a base rubber in such a manner that it has a new constitution. CONSTITUTION:This title tire has a two-layer structure of treated rubber consisting of a cap rubber and a base rubber, wherein the cap rubber (C) and the base rubber (B) satisfy the relations of the formulas E'C>E'B>=8.5MPa and tan deltaC>0.12>=tan deltaB (wherein E'C and E'B respectively are the dynamic moduli of the rubbers C and B measured at 80 deg.C; and tan deltaC and tan deltaB respectively are the loss tangents of the rubbers C and B at the temperature) and wherein the ratio (TB/TA) of the base rubber thickness (TB) to the total thickness (TA) of tread rubber at the tire shoulder part is (0.25:1) to (0.70:1).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radial tire for trucks and buses, and particularly to a radial tire for heavy loads, which has low tire heat generation during running, excellent high-speed durability, and wear resistance comparable to conventional tires. It concerns tires.

[0002]

2. Description of the Related Art Conventional pneumatic radial tires for trucks and buses are 10 to 20% of the thickness of the cap tread.
The heat generation temperature of the entire tire was reduced by providing a low-heat-generation base tread with a small thickness.

For the cap tread of this type of tire, a wear-resistant rubber composition having a high elastic modulus and a high loss tangent, which is generally blended with carbon black having a fine particle size and a relatively high structure, is used. An example of the dynamic elastic modulus and loss tangent measured at a temperature of 80 ° C. when using carbon black is about 12 MPa and 0.
15, the low exothermic base tread is blended with carbon black having a larger particle size than the cap tread, the dynamic elastic modulus and the loss tangent are smaller than those of the cap tread, the low exothermic property and the normal dynamic elastic modulus are A rubber composition having a range of 4 to 8 MPa and a loss tangent of 0.07 to 0.1 was used.

[0004]

[Problems to be Solved by the Invention] In recent years, with the development of high-speed and mass-transportation, the use conditions of tires mounted on vehicles such as trucks and buses, which are the protagonists, have become more severe (high speed-high horsepower). As a result, there has been a strong demand for improvement in wear resistance of radial tires for high loads and improvement in high-speed durability due to a decrease in heat generation temperature.

Therefore, in order to improve the wear resistance of the conventional structure tire, the carbon black having a smaller particle diameter is used, or the reinforcing amount of the cap tread is increased by increasing the blending amount, so that the above-mentioned rigidity can be obtained. Loss tangent corresponding to dynamic elastic modulus and heat generation becomes high, wear resistance is improved, but tire heat generation becomes large and deterioration of adhesive strength between steel cord and rubber used for belt is promoted, There is a drawback that it causes a decrease in belt durability, and instead of increasing the reinforcing property of the cap tread as described above,
Even if you try to reduce the heat generation of the entire tire by increasing the relative thickness ratio (T _B / T _C ) of the conventional base tread as it is, the tire temperature hardly changes, and the belt durability due to the decrease in heat generation It was difficult to expect an improvement in.

As described above, the loss tangent of the base tread is
It is smaller than that of cap tread and has low heat generation,
It is considered that the strain of the entire tread is concentrated on the base due to the increase in the thickness of the base rubber having a small dynamic elastic modulus and a low rigidity, which causes such a result.

As described above, various types and thicknesses of rubber have been studied for the tread structure of the cap / base structure, but no satisfactory solution has been found yet. In view of the above circumstances, the present invention finds that the above problems can be overcome by increasing the rigidity of the base rubber of the two-layer tread of the cap rubber and the base rubber to reduce the movement of the base. SUMMARY OF THE INVENTION It is an object of the present invention to provide a pneumatic radial tire for trucks and buses, which has improved high-speed durability while maintaining at least the current level of wear resistance.

[0008]

In order to achieve the above object, the inventors of the present invention have conducted extensive studies and found that the difference between the dynamic elastic modulus and the thickness ratio of the upper and lower two layers of the tread rubber composed of the cap / base can be determined. It has been found that the proper purpose can be achieved by an appropriate combination, and the present invention has been completed. That is, the present invention relates to a pneumatic radial tire for trucks / buses in which the tread rubber has a two-layer structure of a cap rubber and a base rubber, and each of the cap rubber (C) and the base rubber (B) measured at a temperature of 80 ° C. When the dynamic elastic moduli are E ′ _C and E ′ _B, and the respective loss tangents of the rubbers at the same temperature are tan δ _C and tan δ _B , the dynamic elastic moduli and the loss tangents are E ′. _{C> E 'B ≧ 8.5MPa (} 1) tan δ C> has a 0.12 ≧ tan [delta] relationship _B (2), and the tread rubber thickness of the base rubber in the tire shoulder portion (T _{B) A} pneumatic radial tire for trucks and buses, characterized in that the ratio (T _B / T _A ) to the total thickness (T _A ) is in the range of 0.25 <T _B / T _A <0.70. is there.

In the present invention, the dynamic elastic modulus (E ' _B ) and loss tangent (tan δ _B ) of the base rubber are respectively lower than those of the cap rubber but higher than those of the conventional base rubber,
The ratio of the thickness of the base rubber to the total tread thickness (T _B / T _A ) is made larger than that of the conventional one to form a cap / base two-layer structure tread. As a result, the heat generation of the entire tire becomes lower than that predicted from the loss tangent of the cap rubber and the base rubber for the reason described below, and the high speed durability is improved accordingly.

When the dynamic elastic modulus of the base rubber is increased to increase the rigidity, the strain applied to the base tread is relaxed, so that heat generation based on hysteresis can be suppressed to a small level as compared with the case of using the conventional base rubber. It is considered that the heat generation temperature of the entire tire is lowered. In this case, if the loss tangent of the base rubber is too large, the above-described heat generation lowering effect is canceled out, so the value of tan δ _B must be 0.12 or less.

The rubber component used in the cap rubber and the base rubber according to the present invention is, in addition to natural rubber, a rubber component comprising at least one diene-based synthetic rubber such as isoprene rubber, butadiene rubber and styrene-butadiene rubber. However, the present invention is not limited to this.

The carbon black compounded in the cap rubber is preferably a wear resistant carbon black of SAF grade (eg N110), ISAF grade (eg N220),
It is also possible to use an improved carbon black having a finer particle size. Carbon black compounded in the base rubber includes ISAF grade (eg N220), HAF grade (eg
Although any conventional carbon black for base such as N330) can be used, ISAF grade carbon black is preferable in consideration of abrasion resistance after the middle running period.

In carrying out the present invention, various compounding prescriptions can be considered in order to set the dynamic elastic modulus and loss tangent of the cap rubber and the base rubber to predetermined values. For example, carbon in the rubber composition can be considered. It can be achieved relatively easily by increasing or decreasing the amount of black compounded or adjusting the colloidal characteristics of carbon black.

Further, in the present invention, as the ratio (T _B / T _A ) of the thickness of the base rubber to the total thickness of the tread rubber in the tire shoulder portion where the belt end is located increases, the heat generation temperature of the tire decreases. However, this ratio is 0.7
If it exceeds 0, the surface exposure of the base rubber is accelerated, the wear resistance after the middle of running is deteriorated, and the wear life of the entire tire is impaired, which is not preferable. On the contrary, when it is as small as 0.25 or less, the heat generation reducing effect of the base rubber becomes small, and the intended purpose is not achieved. Therefore, the T _B / T _A ratio is 0.25 to
It must be in the range of 0.70.

The tire tread is usually provided with a wear indicator, and if this is considered to be the wear limit, the thickness of the base tread is set to the height to the surface of the indicator. Is also possible,
With this configuration, the durability can be surely improved without impairing the wear resistance, which is safe and practical.

[0016]

In the present invention, the dynamic elastic modulus (E ' _B ) of the base rubber is set higher than that of the conventional base rubber within the range where the loss tangent (tan δ _B ) does not exceed 0.12. Even when the thickness of the base is increased, the heat generation temperature of the tire is lowered and the high speed durability is improved. Further, by setting the ratio of the thickness of the base to the tread (T _B / T _A ) within a specific range, it becomes possible to improve the high-speed durability at least without impairing the wear resistance.

[0017]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples. The term “parts” simply means “parts by weight”.

Table 1 shows the composition of the rubber composition used for the cap tread and the base tread. For the blending amount of carbon black, see Table 2
As shown in, the predetermined viscoelastic characteristics (E '
And a rubber composition for a base having tan δ). The characteristic values of these rubber compositions are as shown in Table 2.

Using the rubber compositions for caps and bases thus obtained, tires of 1000 R 20 14PR having the thickness composition ratio (T _B / T _A ) of the tread described in Table 2 were manufactured by a conventional method. The tire was run in a bench endurance test (step speed method), and the temperature on the edge of the outermost belt (here, the No. 3 belt) was measured at a step speed of 80 km / h to evaluate the durability. It was used as an index. The results are summarized in Table 2. In this table, the temperature difference between each tire and the tire having the conventional structure (Comparative Example 1) is also shown for reference. The wear life is obtained by measuring the total life (generally indicated by the mileage per mm of the tire that has run to the wear limit) when the above tires are run on a general transportation route including a highway under almost the same conditions. evaluated. The values shown in Table 2 are indexed with the tire of Comparative Example 1 being 100, and the larger the value, the better the abrasion resistance.

[0020]

[Table 1]

[Table 2] As can be seen from Table 2, in the present invention, the heat generation temperature of the tire is lowered and the high-speed durability is improved, and at the same time, the reduction in wear resistance due to the low heat generation, which has been conventionally recognized, is suppressed to the minimum. It is possible to obtain a tire that can exhibit wear resistance that is substantially equal to or higher than the current level.

[0021] In more detail, the first embodiment and the carbon black amount bulking 5 parts of the base rubber compositions of the prior structure tire (Comparative Example 1), E _'B and tan [delta] _B, respectively 9.0MPa It is a tire having a two-layer structure tread in which the base thickness is increased to a T _B / T _A ratio of 0.30 and the base layer thickness is increased to 0.11. Abrasion resistance is equivalent. Example 2 is the same as Example 1 except that the thickness of the base is further increased to obtain T
A tire constructed by setting the _B / T _A ratio 0.50. The heat generation temperature of this tire was lower than that of the tire of Example 1, but the wear life was also reduced by 4 points. However, as compared with Comparative Example 3 having the same tread thickness configuration and using the conventional type base rubber, the wear life was 4 points better, and the wear resistance was reduced with respect to the decrease in heat generation at -8 ° C. It can be said that there is no example that could be suppressed to such a minimum.
Example 3 respectively 13.8 MPa E _'C and tan [delta] _C and was increased 5 parts of carbon black of the cap rubber composition
While increasing to 0.19, the thickness of the base is T _B / T _A ratio 0.
The tire has a thickness of 60, which is lower in heat generation and improved in wear resistance as compared with the tire of Comparative Example 1.

Comparative Examples 2 and 3 are tires in which the thickness of the base in Comparative Example 1 is increased to T _B / T _A ratios of 0.30 and 0.50, respectively. Thus, simply by increasing the thickness of the conventional base tread, the tires are The exothermic temperature of does not decrease. Comparative Example 4 is a tire having the same T _B / T _A ratio (0.15) as the conventional one, using the same composition for base as in the above Example, so that the heat generation increases as much as tan δB as compared with Comparative Example 1. . In Comparative Example 5, since the T _B / T _A ratio is too large, heat generation is reduced, but wear resistance is significantly deteriorated. Comparative Example 6 has too much carbon black in the base rubber, so ta
n δ _B becomes higher, the exothermic temperature rises as compared with Comparative Example 1,
Inferior high speed durability. Comparative Example 7 is a tire in which all the treads are made of the rubber composition for caps for reference, and the tire temperature increased to 126 ° C. and showed the maximum value without the low heat-generating base tread.

[0023]

As can be seen from the above results, in the present invention, a rubber composition having a specific range of dynamic viscoelasticity and loss tangent is used for the base tread, and By setting the thickness ratio to a specific range that is higher than before, it became clear that the heat generation temperature during running can be effectively reduced, and based on this, wear resistance almost equal to or higher than the current level can be obtained. Provided are radial tires for trucks and buses which are equipped with the tires and have improved high-speed durability.

Claims (1)

[Claims] 1. A pneumatic radial tire for trucks and buses comprising a two-layer structure of a cap rubber and a base rubber, wherein each of the cap rubber (C) and the base rubber (B) measured at a temperature of 80 ° C. When the dynamic elastic moduli are E ′ _C and E ′ _B, and the respective loss tangents of the rubbers at the same temperature are tan δ _C and tan δ _B , the dynamic elastic moduli and the loss tangents are E ′. _{C> E 'B ≧ 8.5MPa (} 1) tan δ C> has a 0.12 ≧ tan [delta] relationship _B (2), and the tread rubber thickness of the base rubber in the tire shoulder portion (T _B) Total thickness (T _A )
The ratio (T _B / T _A ) to 0.25 <T _B / T _A <0.70 (3) is a pneumatic radial tire for trucks and buses.