JPH09226318A - Pneumatic radial tire for bad road running - Google Patents

Abstract

PROBLEM TO BE SOLVED: To heighten the durability of a belt cord by forming an outermost layer cord of a belt disposed between a carcass and a tread as a plural-stranded structure with a comparatively large elongation, setting the filament diameter of the cord within a specified range, and setting the rubber permeability into the strand. SOLUTION: A high elongation cord of a plural stranded structure of n×m, the breaking elongation being 5-8%, is used in a belt outermost layer, and in the case where the motion of a tread during rolling of a tire is large like a lug pattern, the cord 2 can follow up the motion. By setting the filament diameter of the cord 2 of the belt outermost layer within the range of 0.30-0.44mm, the speed of abrasion of the cord 2 caused by gravel or the like entering through a tire cut part is decreased. Further, by setting the rubber permeability into a strand 3 of the belt outermost layer cord, that is, the rubber penetration rate to 50-85%, the adhesion breakage between the cord and the rubber caused from the tire cut part can be restrained so as to lengthen the running life.

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 running on rough roads, which has an extended running life due to an improved belt cord.

[0002]

2. Description of the Related Art Tires for running on rough roads often have a lug pattern as shown in FIG. 1, that is, a tread pattern in which a groove is formed in a radial direction in order to increase traction. In such a tire, when the tire rolls, as shown in FIG. 2, the movement of the tread becomes large especially at the groove portion, so that the cord used for the outermost belt of the tire has a large tension input and compression input. Will receive. Therefore, as such a belt cord, a so-called high elongation cord having a double twist with excellent elasticity has been used. Normal steel cord has a cut elongation (breaking elongation) of about 2 to 3% of the sample length, but in the case of such a high elongation cord, it has a cut elongation of 5 to 8% and is extremely stretchable. It's a rich code. A comparison of the SS curves showing the relationship between the elongation and the stress of the high elongation cord and the ordinary steel cord is shown in FIG.

Further, in tires for running on rough roads, in order to prevent moisture from being propagated inside the cord from the cut portion, the permeability of rubber into the cord (hereinafter abbreviated as "rubber penetrability"). ) High code has been applied as a belt code.

[0004]

The above-mentioned high elongation cord, which has been mainly used in the belt of tires for running on bad roads, is usually 0.175 to 0.28 m.
A tire having a filament diameter of m, but using such a cord for a belt had the following problems when cut by a protrusion or the like. That is, there is a problem that gravel or the like enters the cut portion, the cord is worn away by the gravel, the protective layer is lost, and a puncture is likely to occur when the protrusion is next stepped on. In addition, such a problem also occurs when the belt cord is broken when the protrusion is stepped on due to insufficient cord elasticity.

When a cord having a high rubber penetrability is used for the outermost layer of the tire belt, the rubber impregnated inside the cord hinders the elasticity of the cord, so that the belt cord cannot follow the movement of the tread and the belt cord is easily broken. There was a problem that it became easier to get a flat tire.

Therefore, an object of the present invention is to increase the durability of the belt cord of a pneumatic radial tire for running on rough roads such as off-road and extend the running life of the tire.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that in a pneumatic radial tire for running on rough roads, the filament diameter of the outermost belt of the high elongation cord is set to the conventional value. By making the cord thicker and controlling the rubber penetrability of the cord within an appropriate range, it was found that the cord-rubber bond failure caused from the tire cut portion can be suppressed, and the present invention has been completed.

That is, the present invention provides a pneumatic radial tire for traveling on rough roads, which comprises a carcass straddling a pair of bead cores in a toroidal shape, and a tread arranged on the outer peripheral side of the carcass. The outermost cord of the belt arranged between the carcass and the tread has a double twist structure of n × m in which the cut and stretch is 5 to 8%, and the filament diameter of the cord is 0.30 to 0. Within the range of 44 mm, the rubber penetration rate into the strand is 50 to 8
It is characterized by being in the range of 5%.

The pneumatic radial tire for traveling on rough roads according to the present invention works particularly advantageously when the tread has a lug pattern.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the pneumatic radial tire of the present invention, the outermost belt layer is a rug by using an n × m multi-twist structure high elongation cord having an elongation of 5 to 8%. Even when the movement of the tread during tire rolling is large like a pattern, the cord can follow the movement. If the cut length is less than 5%, the cord cannot sufficiently follow the movement of the tread, while if it exceeds 8%, the broom effect of the belt cannot be sufficiently exerted. Here, the n × m double twist structure is not limited to a specific structure as long as the cut elongation is maintained in the range of 5 to 8%, and various known double twist structures are available. Can be adopted.

In the present invention, the cord outermost layer has a filament diameter of 0.30 mm or more, so that the abrasion rate of the cord due to gravel entering from the tire cut portion can be delayed. However, if it is made too thick, the tensile surface strain on the outside of the filament becomes large and the breaking life is shortened, so it is made 0.44 mm or less.

Further, in the present invention, it is necessary that the rubber permeation rate into the strand of the belt outermost cord, that is, the rubber penetration rate is 50 to 85%. Rubber penetration rate is 50
If it is less than%, it is not possible to sufficiently prevent moisture transmission inside the cord from the tire cut portion, and the adhesive fracture between the cord and rubber progresses from the cut portion, leading to separation failure. On the other hand, when the content exceeds 85%, the rubber is excessively impregnated inside the cord, so that the cord cannot be sufficiently expanded and contracted, and the belt cord is easily broken at the groove bottom of the lug pattern. Note that the rubber penetrating rate is 6 when the cord has a 3 × 6 structure shown in FIG.
Take out the strand consisting of the filament of the book (Fig. 4
(A)), the core filament of the strand and the two adjacent filaments are removed ((c) in FIG. 4), and the amount of rubber remaining inside the remaining three filaments is then 10 cm. It was obtained by measuring the hits.

[0013]

[Example] 15 cords / number of cords shown in Table 1 below
Size 1800R2 applied to the outermost layer of the belt at 5 cm
No. 7 off-road tire was manufactured. The average running life (time) of 10 tires to which each code is applied when the tire is mounted on an actual vehicle and is run on a rough road is shown in Comparative Example 1.
Was compared with an index of 100. The larger the value, the longer the running life. Table 1 also shows the obtained results.

[0014]

[Table 1]

[0015]

EFFECTS OF THE INVENTION In the pneumatic radial tire for running on bad roads according to the present invention, the filament diameter of the belt outermost layer cord is increased even if a cut that reaches the belt code is made during running on bad roads. Sufficient rubber penetrability to prevent abrasion of water while ensuring the elasticity of the cord while ensuring the abrasion time of the filament, thereby suppressing the adhesive fracture between the cord and the rubber from the cut portion. Therefore, the running life of the tire can be significantly extended.

[Brief description of drawings]

FIG. 1 is a perspective view of an example of a pneumatic radial tire for traveling on rough roads of the present invention.

FIG. 2 is an explanatory view showing a tread state during tire rolling.

FIG. 3 is a graph showing the relationship between elongation of steel cord and stress.

FIGS. 4A to 4C are explanatory views showing a method for measuring a rubber penetration rate, respectively.

[Explanation of symbols]

 1 outermost belt 2 cord 3 strand

Claims (2)

[Claims] 1. A pneumatic radial tire for traveling on rough roads, comprising a carcass straddling a pair of bead cores in a toroidal shape, and a tread arranged on the outer peripheral side of the carcass, wherein the carcass and the tread are provided. The outermost cord of the belt disposed between the cord and the cord has a multi-twist structure of n × m whose cut and stretch is 5 to 8%, and the filament diameter of the cord is 0.30.
A pneumatic radial tire for running on rough roads, which has a rubber penetration rate within a range of 50 to 85% within a range of 0.44 mm to 0.44 mm. 2. The radial tire for traveling on rough roads according to claim 1, wherein the tread has a lug pattern.