JPS644921B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention protects the belt layer by providing a polyisoprene-based high elastic rubber layer on the belt layer to improve durability, more specifically, resistance to tread separation and cut resistance, and ) Regarding a high-load pneumatic radial tire with improved performance. Conventionally, high-load pneumatic radial tires have been used for trucks, buses, etc., and these tires have one or more radial ply carcass layers and a belt layer formed of two or more metal cord plies. ing. The properties required for high-load pneumatic tires include abrasion resistance, cut resistance, high-speed durability, and retreadability.In order to satisfy each of these properties, radial tires are being used instead of conventional bias tires. Tires began to be used. Steel cords are used in the belt layer of this type of radial tire to provide rigidity.
If you step on a rock while driving on rough terrain, damage may occur that reaches or penetrates the belt layer. In this case, moisture entering through such scratches causes rust on the steel cord, causing separation between the tread and the belt layer, or making it impossible to retread, significantly shortening the life of the tire. As a method to prevent damage to the belt layer due to such cuts, etc., there is a method of arranging a helical metal cord on the belt layer (Japanese Patent Application Laid-Open No. 116503/1983), and a method that prevents rust from occurring due to the twisted structure and plating composition of the steel cord. How to suppress the
-131201) etc. are publicly known. However, the former has disadvantages such as rust occurring on the spiral metal cord itself if a scratch occurs that reaches the spiral metal cord, and the latter also has insufficient effectiveness during rehabilitation. be. Furthermore, as a technique for improving the cut resistance of tires, there is a technique in which granular vulcanized rubber is blended into the cap tread rubber of tires (Japanese Patent Laid-Open No. 50-150755).
(No.), and one in which recycled rubber is blended into the cap lead rubber (Japanese Patent Application Laid-open No. 10534/1983).
However, although these techniques improve cut resistance, they have the disadvantage of being inferior in crack growth resistance and increasing tire heat generation. In addition, although there are conventional technologies for blending natural rubber into the undertread portion, all of them are aimed at low heat generation, and carbon black is made by mixing up to 45 parts by weight of soft carbon with respect to the rubber.
The hardness is also 55 or less. Therefore, it is not possible to prevent scratches on the tire from reaching the cord layer, leading to problems such as rusting of the steel cord and a reduction in the retreading rate. Furthermore, what is undertread?
This refers to the rubber layer inserted between the line connecting the groove bottoms of the tire tread and the outermost edge of the breaker, and a rubber that generates less heat than the tread rubber is used for this in order to reduce the heat generated by the tire tread. In other words, GPF, FEF, etc., which are called soft carbons, are usually used as carbon blacks, which have a small loss modulus E'' or loss tangent tanδ in terms of viscoelasticity, are composed of soft rubber compositions, and are the thickest and most carbon blacks. The present invention has been made in view of the above circumstances, and is a radial tire having a steel cord in the belt layer. By placing a rubber composition with high modulus and less deterioration of physical properties at high temperatures between the tires, cut scratches on the tire are prevented from reaching the steel cord layer, and tread separation is prevented to improve retreadability. The purpose of the present invention is to provide a high-load pneumatic radial tire with a high load capacity.For this purpose, in a radial tire having a steel cord in the belt layer, polyisoprene rubber is used.
For every 100 parts by weight of raw rubber containing 60 parts by weight or more, 40 parts by weight of hard carbon is added as carbon black.
~65 parts by weight, 100% elongation stress is smaller than belt wire coating rubber, and
A rubber composition with a 300% elongation stress greater than that of the cap tread rubber was measured at the groove bottom of the tire tread portion and the outermost layer of the belt layer at a width of 75% or more of the width of the outermost layer of the belt layer and at the slip sign position. The cap lead rubber layer is disposed between the cap lead rubber layer and the belt layer, and has a thickness of 25% or more of the thickness between the cap lead rubber layer and the belt layer. Hereinafter, the configuration of the present invention will be explained in detail. The rubber composition used in the present invention to be disposed between the captread rubber layer and the belt layer is as follows:
Polyisoprene rubber (natural rubber, isoprene rubber, etc.) accounts for 60 parts by weight or more, preferably 70 parts by weight or more in 100 parts by weight of raw material rubber, and hard carbon as carbon black is added to 100 parts by weight of raw material rubber. (HAF, EPC and finer particles, specifically iodine adsorption amount
40 to 65 parts by weight, preferably 42.5 to 60 parts by weight of carbon black (60 mg/g or more),
More preferably ISAF or finer carbon black, i.e. iodine adsorption capacity 110
It is preferable to use 15 parts by weight or more of carbon black of mg/g or more, thereby further reducing the deterioration of rubber physical properties at high temperatures.
That is, the above rubber composition constitutes the so-called undertread rubber layer provided between the cap tread rubber layer and the belt layer constituting the radial tire that is the object of the present invention. When the amount of hard carbon contained in the rubber composition constituting the undertread rubber layer is less than 40 parts by weight, the high-temperature properties of the rubber composition, that is, the undertread rubber layer, which is the effect of the hard carbon formulation, will decrease. In particular, the heat deterioration resistance is not sufficiently improved or improved, and the significance of incorporating hard carbon becomes small, and it is also difficult to use in the present invention.
When the amount of hard carbon such as ISAF and HAF exceeds 65 parts by weight, these hard carbons
Compared to soft carbon such as FEF, the particle size is smaller and the surface area is larger.Compared to soft carbon, it has greater adhesion to rubber and has a greater reinforcing effect, and exhibits the function of suppressing heat generation when the tire is running. do. However, if the amount added to the rubber is too large, carbon will come into contact with each other.
65 because it promotes fever rather than suppressing it.
It is not preferable to add more than % of hard carbon. In general, rubber with excellent cut resistance has high elasticity and hardness to disperse stress, and has a large viscoelastic E″ or tanδ to absorb energy. In some cases, it has been difficult to put the rubber into practical use because the heat generated by running is large and the physical properties of the rubber deteriorate due to high temperatures, making the tire more likely to break. By blending hard carbon, rather than soft carbon, into polyisoprene rubber in an amount ranging from 40 to 65% by weight, they were able to overcome the above drawbacks. The rubber composition of the invention not only has a 100% elongation stress lower than that of belt wire coating rubber and a 300% elongation stress greater than that of captread rubber, but also has a JIS hardness.
A rubber layer is formed that satisfies the properties of 58 or more, preferably 60 or more. If the 100% elongation stress is greater than that of the belt wire coating rubber, separation will easily occur between the belt layer and the belt layer, and if the 300% elongation stress is less than that of the cap tread rubber, or if the JIS hardness is less than 58, the cut resistance will be poor. This is because it is insufficient. In the present invention, as shown in FIG.
The above rubber composition 1 is applied to the captread rubber layer 2.
and the belt layer 3. Note that 4 represents a radial carcass, and 5 represents a bead wire. When arranging in this way, as shown in FIG. 2, 75% of the width D of the outermost layer of the belt layer 3
Thickness B between the groove bottom of the tire tread portion and the outermost layer of the belt layer 3 when the width C is above (C≧0.75D), preferably 100% or more, and at the slip sign position. With a thickness A of 25% or more (A≧
0.25B), preferably 33% or more. This is because the belt layer 3 cannot be sufficiently protected unless it has such a width and thickness. The radial tire thus obtained has excellent tread separation resistance and cut resistance, and is particularly suitable as a tire for trucks, buses, etc. that run on rough or partially rough terrain. Between the cap tread rubber layer and the belt layer constituting the radial tire, the above 100% elongation stress specified in the present invention is smaller than that of the belt wire coating rubber, and the 300% elongation stress is smaller than that of the cap tread rubber. The existence of a rubber composition that satisfies the characteristic of large size gives the tire so-called continuity of rigidity, and in addition to characteristics such as separate durability, it also has retreadability, that is, the ability to remove the cap tread layer of a used tire. This has the advantage that the cap tread layer can be renewed with new rubber and the tire can be recycled and reused over and over again. Examples are illustrated below. Example 1 Rubber composition 1 with the formulation shown in Table 1 below
The elongation at break (%) of each of the samples 1 to 12 was measured. The results are shown in Table 1 below. Furthermore, Table 1
The numbers inside represent parts by weight.

【table】

[Table] As is clear from Table 1 above, from the relationship between the particle size and blending amount of carbon black and the elongation at break,
It can be seen that when the carbon black content is 40 parts by weight or more and hard carbon is used, the retention rate of elongation at break at high temperatures is high. Of the raw rubber,
If the amount of polyisoprene rubber (natural rubber or isoprene rubber) is less than 60 parts by weight, the elongation at break at high temperatures will decrease significantly even if hard carbon is used in carbon black and 40 parts by weight or more is added. Furthermore, Fig. 3 is a diagram showing the relationship between the F/E value, that is, the fracture elongation retention rate at high temperature, and the blending amount of carbon black. In either case, when the amount of carbon black added to the rubber reaches about 40 parts by weight, the F/E value increases rapidly, but the increase is significantly larger for hard carbon than for soft carbon. In the case of soft carbon, the blending amount is approximately
When it exceeds 40 parts by weight and reaches about 50 parts by weight, F/E
In contrast, in the case of hard carbon, the F/E value does not decrease and tends to reach saturation as it is. Example 2 Test tires were prepared using compounds A to C having the formulations shown in Table 2 below. This tire has a 1000R20 14PR side lug design and a belt wire compound with a 100% tensile stress of 67Kg/
cm ² , standard specification (standard example),
There were three types: one with the specifications of the present invention (inventive example) and one with the specification using a normal undertread for the belt protective layer (comparative example) for comparison. The results of running tests using these tires are shown in Table 3 below.
Shown below.

【table】

[Table] Quinoline polymer

[Table] * Traveling speed at the time of tread separation failure in indoor rotation test. standard example
Index set to 100.
** Reciprocal of the number of scratches reaching the belt layer after the rough road test.
As is clear from Table 3 above, the examples of the present invention have superior damage resistance compared to the standard examples and comparative examples, and therefore have good retreadability and tread separation resistance. It turns out to be excellent. In addition, as shown in Table 4 below, if the thickness of the belt protective layer is 25% or more of the thickness between the groove bottom and the outermost layer of the belt layer measured at the slip sign position, damage resistance The effects of improvement are significant. In addition, 95% of the scratches reaching the belt layer after the rough road running test of the standard example.
is concentrated in the center 75% of the width of the outermost belt, so the belt protective layer needs to cover at least 75% of the width of the outermost belt.

【table】 [Brief explanation of drawings]

FIG. 1 is an explanatory cross-sectional view of an example of a high-load pneumatic radial tire of the present invention, FIG. 2 is an enlarged explanatory view of the right half thereof, and FIG. 3 is an explanatory view of the elongation at break of a rubber composition at high temperatures. FIG. 2 is an explanatory diagram showing the relationship between retention rate and carbon black blending amount in a graph. DESCRIPTION OF SYMBOLS 1...Rubber composition, 2...Captread rubber layer, 3...Belt layer.

Claims (1)

[Claims] 1 In a radial tire having a steel cord in the belt layer, 100% elongation stress is obtained by blending 40 to 65 parts by weight of hard carbon as carbon black to 100 parts by weight of raw rubber containing 60 parts by weight or more of polyisoprene rubber. A rubber composition whose 300% elongation stress is smaller than that of the belt wire coating rubber and whose 300% elongation stress is larger than that of the cap tread rubber was measured at a width of 75% or more of the width of the outermost layer of the belt layer and at the slip sign position. A high-load pneumatic pump characterized by having a thickness of 25% or more of the thickness between the groove bottom of the tire tread and the outermost layer of the belt layer, and disposed between the cap tread rubber layer and the belt layer. tire.