JPS588407A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To heighten the durability of a tire for a truck or a bus, by blending base rubber with a predetermined amount of prescribed polybutadiene. CONSTITUTION:Composite rubber, which is provided as base rubber 2, comprises 5-50wt% of substantially amorphous polybutadiene including 65-90mol% of 1,2- links, and 95-50wt% of natural rubber and/or polyisoprene rubber. The presence of said amount of the polybutadiene suppresses the splitting of the base rubber 2 and the separation of the tread and heightens the resistance to fatigue.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pneumatic tire, and more specifically to a base rubber (
The present invention relates to a pneumatic tire, particularly for track-pass vehicles, using a rubber composition using a specific polybutanoene rubber with significantly improved fatigue resistance (undertread rubber), natural rubber, and/or polyethylene rubber as raw material rubber.

In general, for truck and pass tires, there is a high demand for durability, including tread separation resistance, as the load capacity increases and speeds increase. This is extremely important for tires.

These demands for improved durability have arisen in parallel with efforts to extend the life of cap tread rubber by increasing its wear resistance and cut chipping resistance.

In other words, in conventional tires, increasing the abrasion resistance and cut chipping resistance of the cap tread rubber generally tends to increase the level of heat generation of the rubber; There is a need to significantly improve gender.

In order to fully demonstrate the durability function of this base rubber, the compounding is more car-like than before. It is necessary to add less black, use more zinc oxide to increase blowout resistance, optimize the amount of various compounding agents such as vulcanization accelerators and sulfur, and use general-purpose high-cis polybutadiene. Attempts have been made to improve durability by blending a specific amount of rubber (BR), but this has not been sufficient. Attempts have been made to improve durability by making changes, but these lead to new problems such as group cracks, spot tears, and exposure of the pace rubber at the end of wear.

By the way, in order to improve the durability of carab treads and base rubber treads for pneumatic tires, the microstructure of polybutadiene in the tread, especially its relationship with the 1,2-vinyl content, has been attracting attention. tic-
Polybutadiene (Japanese Unexamined Patent Publication No. 152612/1983) having a 1,2-structure with a 6-20 weight microstructure
- The fatigue durability and heat resistance of large pneumatic tires or aircraft tires have been improved by using vinyl polybutadiene (%KAI No. 54-122506) whose structure is 30 to 550 to 55 parts by weight.

However, in order to keep up with the current severe usage conditions, it is increasingly necessary to improve the fatigue resistance of tires.

As described above, there is a need to improve the durability of pneumatic tires, particularly by improving the fatigue resistance of the tire's pace rubber.

The present invention enables high-loading and high-speed running without impairing the heat generation characteristics during running.

The aim is to provide pneumatic tires that suppress the occurrence of de-separation and sugerite phenomena and improve durability.
It is widely used in automobile tires such as bus tires, and is particularly suitable as truck and pass tires that require high durability.

As a result of intensive research in accordance with the above-mentioned objective, the present inventors have discovered that the durability of tires can be significantly improved by using a rubber composition with improved fatigue resistance as a pace rubber, and have arrived at the present invention.

That is, the present invention uses 5 to 505 to 50 parts by weight of essentially amorphous I-liptadiene (hereinafter referred to as V-BR) having 65 to 90 moles of 1.2 bonding units and/or polyisolune. A pneumatic tire characterized in that a rubber composition containing 95 to 505 to 50 parts by weight of rubber is disposed as a pace rubber.

In the present invention, the blending ratio of V-BR in the raw rubber in the rubber composition disposed as a pace rubber is 5 to 50% by weight, preferably 20 to 400% by weight, as described above.
If the proportion of 40 parts by weight of V-BH is less than 5 parts by weight, blowout failure occurs in the indoor durability test and no durability improvement effect is observed. Further, if the V-BR exceeds 500 parts by weight, the sgelit phenomenon will occur in the base rubber portion at an early stage, which is undesirable.

Generally, when the amount of polysitatsuene rubber blended in the raw rubber increases, the fracture phenomenon after dynamic or thermal fatigue changes from a blowout phenomenon to a sugerite phenomenon, and the fatigue life itself decreases, but when V-BR is blended, fracture occurs. Although the phenomenon itself was the same, the fatigue life was significantly longer than that of polybutanoene rubber with a high-strength bond, and an improvement in durability was observed.

Note that the V-B R used in the present invention, that is, 1.
Polybutadiene rubbers having 65 to 90 moles of two bonding units can be made, for example, by the method described in U.S. Pat. No. 3,301,840.

The rubber composition used in the present invention also contains appropriate amounts of compounding agents commonly used for base rubbers, such as carpin black, vulcanization accelerators, vulcanizing agents, vulcanization aids, and anti-aging agents. .

Hereinafter, the present invention will be specifically explained based on Examples, Comparative Examples, and Standard Examples. The amounts in Table 1 are parts by weight.

Examples 1 to 4, Comparative Examples 1 to 2, and Standard Example 1 The raw rubber shown in Table 1, the vulcanization accelerator, and the compounding agents excluding sulfur were mixed into 1
After kneading for 4 minutes using a 81 Banbury mixer, a vulcanization accelerator and sulfur were added thereto, and the mixture was kneaded for 4 minutes using an 8-inch roll to obtain a rubber composition for base rubber.

This rubber composition was press-vulcanized at 140° C. for 30 minutes, and the properties of the vulcanized product were evaluated. The results are shown in Table 1. Note that the characteristics of the vulcanizate were evaluated by the following method.

Breaking strength, elongation at break, 300% monolaminosis, hardness and tear strength were determined in accordance with JIS K 6301, and test piece B was used for tear strength. The heat resistance and fatigue life were measured using a Gutdrich flexmeter using a cylindrical test piece with a diameter of 1/2 inch and a height of 1 inch under a load of 1800 rpm (50 lbs) and a dynamic strain (22,
5%) stimulus was applied, the degree of heat generation was measured using a thermocouple inserted at the bottom of the test piece, and the fatigue life was determined by measuring the number of cycles until failure occurred. The heat resistance and fatigue life of these are expressed as an index, with the value of Standard Example 1 being 100, and the higher the index value, the better the heat resistance and fatigue resistance.

In Table 1, Standard Example 1 is a normal base rubber rubber composition using raw rubber NR, and Comparative Example 1 is a rubber composition in which part of NR is replaced with normal BH in order to improve fatigue resistance. However, fatigue resistance is not significantly improved. On the other hand, in Examples 1 to 4, a part of the NR used in Standard Example 1 was replaced with V-BH, but the fatigue resistance was significantly improved and the heat resistance was not significantly impaired. .

However, as in Comparative Example 2 (when a large amount of V-BR is blended, the heat resistance becomes poor, which is not preferable).

Example 5, Comparative Example 3 and Standard Example 2 Bias tire for trucks and buses 1000-20 14
The rubber compositions of Example 2, Comparative Example 1, and Standard Example 1 were used as base rubbers for PR, and the heat generation resistance and fatigue resistance of the tires were evaluated and confirmed in an indoor drum durability test. Note that a tire using the rubber composition of Example 2 as a base rubber is called Example 5, and a tire using the rubber composition of Comparative Example 1 as a base rubber is called Comparative Example 3 and a rubber composition of Standard Example 1. Standard example 2 is a tire using as the base rubber
And so.

The base rubber thickness at of the tires used in this test had a profile of a:b=1:1, which is typical for track/pass bias tires. Line AA' connects a portion of the tire shoulder and the center of the tire (see FIG. 2).

This indoor drum durability test was conducted by running at a constant speed of 57 km/hr and increasing the load at the time steps shown in Table 2 (FMV-SS Al 19 (US tire safety standard)). The durability was evaluated based on the mileage traveled up to the point where the tire was running, and the rate of change in the physical properties of the base rubber after taking out the base rubber from the tire after running.In addition, the heat generation property was evaluated in advance by checking the X section in Figure 2 (tire running A drill hole with a diameter of 40% and a depth that reaches the bottom of the base rubber is drilled in the area where the heat generation level is high for special grade rubber, and the temperature is measured with a thermocouple in the 6th step, and the heat resistance is determined at that temperature level. was evaluated.

The results are shown in Table 3.

Table 2 (FMV-8S 4119 conditions) Furthermore, high-speed users (A
car) and a pavement ratio of 80 or less and a loading capacity of at least 20
An actual vehicle durability test was conducted by running 4 vehicles each (B vehicles) on rough roads with a load of 0 or higher.

The running period of car A is 1 year (approximately 10,000km), and car B
The car was driven for 3 months (approximately 20,000 km), and the base rubber was removed from the tire after driving, and the durability was evaluated based on the rate of change in the physical properties of the base rubber compared to that of a new tire. Third
The table shows the average value of the rate of change for car A and the rate of change for car B.

Note that when the tires were cut after running, signs of tread separation were observed in all but Example 5.

Table 3 As is clear from Table 3, in the indoor drum durability test, Example 5 increased the running distance by 10 to 20% compared to Standard Example 2 and Comparative Example 3, and the degree of change in physical properties also improved in durability. It can be seen that the durability has been greatly improved because the related decrease rate of elongation at break and tear strength is small. It does not lose its heat-generating properties.

In the actual vehicle durability test, the degree of change in the physical properties of the base rubber was similar to the indoor drum durability test.

υAs explained above, a rubber composition containing a specific amount of V-BH was found to be effective in improving both heat resistance and fatigue resistance.
The pneumatic tire of the present invention using the rubber composition as a base rubber has significantly improved durability without impairing wear resistance or other properties.

[Brief explanation of drawings]

Figure 1 is an example of a cross-sectional view of a truck/pass tire.
2 is an enlarged sectional view of a portion of the tire shoulder shown in FIG. 1, in which a thermocouple insertion hole for temperature measurement is provided to evaluate heat resistance. 1... Carab tread rubber, 2... Base comb (under tread rubber), 3... Side tread rubber, 4... Carcass, 5... Bead portion, X...
Thermocouple insertion hole, A-A'... A line connecting part of the tire shoulder and the center of the tire, a... Thickness of the side tread part on the A-A' thin line, b... A-A' Thin line Thickness of the cap tread part on the line. Patent Applicant Yokohama Rubber Co., Ltd. Agent Patent Attorney Tatsuo Ito Agent Patent Attorney Tetsuya Ito Figure 1 Figure 2

Claims (1)

[Claims] 1.2 A rubber composition comprising essentially amorphous polybutanoene having 65 to 90 moles of bonding units, 95 to 50% by weight of thermal rubber and/or polyisozolene comb of 5 to 50% by weight, and a raw material rubber. A pneumatic tire characterized by having the following as a base rubber.