JPH07251605A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To prevent a steel belt end from being damaged because of fatigue crack without any restriction of a degree of freedom in material design by providing end part layer rubber between layers in the belt width direction both end parts of a belt layer and setting dynamic moduli of elasticity of the end part layer rubber and steel cord coating rubber to the predetermined relation and to the predetermined values. CONSTITUTION:Steel cords of belt layers 2, 3 adjacent to each other vertically are formed into crossed layers crossing with each other, while the end part layer rubber 4 which is different from the steel cord coating rubber 5 is arranged between layers in the belt width direction end parts. When a dynamic modulus of elasticity of the end part layer rubber 4 is set to E' and a dynamic modulus of elasticity of the steel cord coating rubber 5 is set to E'0, the relation between them is expressed as 0.1XE'0<=E'<=0.6XE'0, and 1.0X10<8>dyn/cm<2=E '0<=4.0X10<8>-dyn/cm<2>. Therefore, the anti peel-off performance of a tire can be improved without unnecessarily restricting the degree of freedom in design of the cord coating rubber 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the durability of a belt structure in a pneumatic radial tire having a belt structure composed of a steel cord.

[0002]

2. Description of the Related Art A carcass layer in which a plurality of cords are arranged in a direction substantially perpendicular to the meridian direction of a tire and a plurality of steel cords are arranged in a tire radial direction outer side of the carcass layer. In a radial tire having a belt structure in which several belt layers are laminated, severe local stress and strain occur between layers of so-called intersecting belt layers in which the cord directions of adjacent belt layers intersect with each other during running of the tire, resulting in belt width direction. Fatigue crack damage occurs in the rubber around the steel cord starting from the end of the, and if it grows, it may eventually lead to peeling failure between the belt layers. In particular, when the tire is used as a retreaded tire for a long time such as when the tire is used for a long time, or when a heavy load is applied, such crack damage of the rubber around the steel cord and delamination of the belt are caused. It is necessary to give sufficient consideration to prevent the occurrence of failures. For this reason, in the past, many improvements have been made by focusing on the rubber around the steel cord, particularly the rubber coated with the steel cord. For example, in order to reduce the stress strain of the belt layer during tire running, the elastic modulus of the coated rubber is increased to increase the rigidity of the belt layer, or the creep property of the coated rubber is reduced to suppress the deformation of the belt layer. And to suppress the growth of the tire shape during tire pressure filling and reduce the stress strain of the belt layer end, and also for the aging resistance of the coated rubber, fatigue resistance, cracking resistance of the related coated rubber, etc. Attempts have been made to improve the breaking limit, for example, Japanese Patent Application Laid-Open No. 50-60904.
Then, in order to improve the peeling failure resistance of the cord coated rubber,
It has been proposed that the filler mixed in the coated rubber is optimally selected to improve the fracture characteristics and fatigue resistance of the coated rubber.

[0003]

However, since the coated rubber of the steel belt is required to maintain a large number of high-performance properties in a well-balanced manner, an improvement focused on only the improvement of the coated rubber quality as in the past. With the plan, it was difficult to obtain sufficient results. For example, in the above-mentioned Japanese Patent Laid-Open No. 50-60904, there is no mention of the creep resistance although the effect of improving the anti-destructive property of the coated rubber can be expected, and the current rubber compounding technique generally suppresses the creep property. Since there is a trade-off relationship between the improvement of the anti-destructive property and the improvement of the anti-destructive property, there is a limit to the improvement of the properties of the coated rubber. Further, as one of the solutions for improving the balance of such various types of coated rubber properties, Japanese Patent Laid-Open No. 52-14041
In No. 03, the central portion of the belt and the both end portions of the belt are made to share the functions, and the central portion of the belt is covered with rubber to improve the creep resistance so as to suppress the outer diameter growth of the tire. It has been proposed to use a coated rubber that concentrates on improving the properties. However, in steel cord belts, on the other hand, it is necessary to give due consideration to the compounding conditions for maintaining the adhesion between the cord and the rubber, and as mentioned above, there is a limit to the improvement effect of the rubber that is focused on specific performance. And that it is necessary to change the coated rubber type in three places within the width of the belt, which causes problems such as the number of work steps in the calendering process and the complexity of equipment in manufacturing the belt member. Yes, it has not been put to practical use. Therefore, an object of the present invention is to prevent the development of fatigue crack damage at the end of a steel belt due to tire running without restricting the degree of freedom in designing the material of the coated rubber material, and to improve the peeling resistance of the belt layer. .

[0004]

In order to achieve the above object, in the tire of the present invention, as described in claim 1, a plurality of staples are arranged on the radial radial portion of the radial arcus layer in the tire radial direction. -In a belt structure in which at least two belt layers in which the cords are arranged in parallel and covered with a covering rubber are laminated, the belt width direction end portions of the intersecting layers in which the cord directions of vertically adjacent belt layers intersect each other An end layer rubber different from the steel cord-covered rubber is interposed between the layers, and the dynamic elastic modulus E ′ of the end layer rubber and the steel cord are different from each other.
The relationship with the dynamic elastic modulus E ₀ `of the coated rubber is 0.1 × E <sub>0`</sub> ≦ E` ≦ 0.6 × E <sub>0</sub> `... (1), and the steel cord The dynamic elastic modulus E ₀ `of the coated rubber is 1.0 × 10 <sup>8</sup> dyn / cm <sup>2</sup> ≦ E <sub>0`</sub> ≦ 4.0 × 10 ⁸ dyn / cm ² (2) It is a pneumatic radial tire.

In the production of the end-layer inter-layer rubber and the steel cord-coated rubber satisfying the above relationships, the compounding composition of these rubbers includes natural rubber as an elastomer or natural rubber and a synthetic diene rubber. It may be composed of various rubber chemicals that are generally used such as a blending agent with carbon black, which is usually used as a reinforcing material, and a vulcanizing agent.

The dynamic modulus of elasticity E ₀ `and E` are measured by using a spectrometer manufactured by Iwamoto Seisakusho Co., Ltd.
In the condition of ℃, vibration frequency 52Hz, strain amplitude 2%,
The rubber piece cut out from the belt part of the tire has a thickness of 0.3-
The sample was uniformly buffed to 1.0 mm, punched into a size of width 4.7 mm, length 3 cm (measurement distance between chucks 2 cm) to obtain a measurement sample.

[0007]

The present inventor dissected many tires after an indoor drum endurance test, and observed and examined in detail the state of crack generation and growth at the belt layer end, which resulted in tire peeling failure in conventional tires. As shown in FIG. 2, a microcrack is generated at the end of the belt cord of the belt crossing layer due to running fatigue, and the microcrack is formed inside the belt width along the longitudinal direction of each cord. Growth progresses toward a certain distance, and then cracks progressing in the longitudinal direction of the cords are connected between adjacent cords to form microdelamination between the belt layers. It has been found that the belt peels between the belt layers and spreads inward in the tire circumferential direction or in the belt width direction, resulting in a tire peeling failure. The degree of slowness of the process from the occurrence of a small crack at the end of the belt cord to the progress of this crack for a certain distance in the longitudinal direction of the cord governs the speed of occurrence of tire peeling failure. It has been found that after the temperature reaches, the peeling rapidly spreads between the belt layers, resulting in a tire peeling failure. That is, the belt cord
The process from the generation of a small crack at the end of the cord to the propagation of this crack for a certain distance in the longitudinal direction of the cord is the rate-determining step that determines the occurrence speed of the peeling failure of the tire. The inventors of the present invention focused on this rate-determining step, and as a result of various devising experiments, by adjusting the relationship between the elastic modulus of the cord-coated rubber and the end-layer interlayer rubber of the belt, the microcracks at the end of the belt cord were adjusted. The traveling direction can be changed to the direction of the adjacent belt layers, that is, the direction in the rubber layer between the end rubber layers of the belt, without advancing along the longitudinal direction of the cord. It was found that it is possible to significantly slow down the crack progress rate along the conventional cord longitudinal direction by the selective combination of both elastic moduli of the rubber.

In the present invention, based on the above findings,
The relationship between the dynamic elastic modulus of the coating rubber and the belt-end interlayer rubber is shown in the above equation (1). E'is E ₀ `60
If it is larger than%, it is not possible to change the progressing direction of the crack from the direction along the longitudinal direction of the cord to the direction inside the belt-end rubber layer, and it is not possible to slow down the crack rate in the rate-determining step. On the other hand, if E ′ is less than 10% of E <sub>0</sub> `, the cracks will proceed without following the code, but the deterioration of the anti-destructive property of the belt-end inter-layer rubber itself will become large, so that in the end-layer inter-layer rubber. The crack progresses extremely fast. In the process leading to the above-mentioned tire peeling failure, the upper and lower limit values are slightly different depending on the tire size and the tire structure. Therefore, 0.2 × E ₀ `≦ E` ≦ 0.5 is preferable. It is desirable to set in the range of × E ₀ `,.

Further, as described above, the relationship between the dynamic elastic moduli of both rubbers is limited, and at the same time, the dynamic elastic modulus E of the cord-coated rubber is limited.
Let ₀ `be the range of equation (2) above. E <sub>0</sub> `is 1.0 × 10 ⁸
When the value is smaller than dyn / cm ² , the outer diameter growth of the tire is increased, the stress strain is increased at the belt end portion, and the breaking speed of the rubber at the belt end portion is increased irrespective of the crack progressing direction.
Also, if E ₀ `is a value larger than 4.0 × 10 ⁸ dyn / cm ² , if the tire receives a constant strain input when driving on a bad road, it will exceed the limit of rubber elongation. -There is an increased concern that the coated rubber will break.

[0010]

EXAMPLE As shown in FIG. 1, the tire size is 11R22.5, 14PR, the number of belt layers is 4, and the second belt 2 is 2.
The third belt 3 is used as an intersecting layer, and an end layer rubber 4 is provided between the intersecting layers.
As for the tire having the belt structure 1 in which the above-mentioned is inserted, as shown in Table 1, various cord-coated rubbers 5 having different main compounding compositions and the end portion interlayer rubber 4 were combined with each other to obtain Examples 1, 2, 3,
A predetermined number of 9 types of tires of 4 and Comparative Examples 1, 2, 3, 4, and 5 were prototyped. Further, the dynamic elastic moduli (E ₀ `and E`) of the cord-coated rubber and the end-layer interlayer rubber of the tires of the above various Examples and Comparative Examples are shown in Table 1 according to the difference in the main compounding of each rubber. The combinations are as shown. In setting the main composition, in order to change the dynamic elastic moduli of both rubbers, the basic polymer is a natural rubber (NR) or a blend of natural rubber and butyl rubber (BR), and carbon (HAF) is used. Alternatively, the amount of LS-HAF) mixed is adjusted. Next, various tires thus prototyped were mounted on a drive shaft of a 10-ton truck, and a peeling durability test of an actual vehicle running on a good road and a bad road was conducted. In the good road test, 100% of the JIS standard load was applied to the tires and after running 100,000 km on the highway-mainly paved road, and in the bad road test, the load of 150% of the JIS standard load was applied and mainly the gravel road The rough road of 40,000k
After running for m, the tire was removed from the car and the belt was dissected to confirm the growth state of the crack 6 at the end of the belt crossing layer. The larger the index in the table, the smaller the growth of the crack 6 at the end of the belt crossing layer and the better the peeling durability. Comparative Example 1
The crack growth state is indexed as 100
I am trying.

A detailed examination of the test results shows that in Comparative Example 2, the durability on a good road is poor because the dynamic elastic modulus E ₀ `of the cord-coated rubber is too low. On the contrary, in Comparative Example 5 in which the dynamic elastic modulus E <sub>0</sub> `is too high, the durability on rough roads is significantly reduced. Comparative Examples 3 and 4 are examples in which the dynamic elastic modulus E ′ of the end interlayer rubber is out of the relational expression (1) with the dynamic elastic modulus E ₀ ′ of the cord-coated rubber, and good road and bad road. The durability is lower than that of the conventional standard product of Comparative Example 1. On the other hand, in the tires of Examples 1, 2, 3, and 4 which satisfy the limited range of the dynamic elastic modulus proposed by the present invention, the peeling durability is greatly improved on both the good road and the bad road. Is recognized.

In particular, in the case of Examples 2 and 3, the same cord-coated rubber as the standard product of Comparative Example 1 was used, and only the dynamic elastic modulus of the end-layer interlayer rubber was changed, so that the peeling durability was improved. Has been obtained. This requires a high degree of balance of properties as a belt material, and is relatively less restricted by changing the code-coated rubber, which is highly restricted in terms of productivity and manufacturing cost during tire production. It is shown that a great improvement in peeling durability can be easily obtained only by changing the rubber between the end layers. Of course, the peeling durability can be improved by changing the code-coated rubber itself, and the tire can be made to specialize in the peeling resistance improvement for each use condition of running on a good road or running on a bad road. It can be designed for each application.

[0012]

[Table 1]

[0013]

According to the present invention, while the dynamic elastic modulus of the code-coated rubber is kept within a predetermined range, the dynamic elastic modulus of the belt crossing layer end layer interlayer rubber and that of the code-coated rubber are reduced. A cord-coated rubber that requires a material design that extremely balances many properties such as adhesion, heat generation, and processability by adjusting the ratio with the dynamic elastic modulus to be within a certain range. The peeling resistance of the tire can be significantly improved without unduly narrowing the degree of freedom in design, and from the viewpoint of tire manufacturing, the workability of the belt material is not deteriorated and the manufacturing cost is low. The peel resistance of the tire can be improved without increasing Furthermore, by properly selecting the dynamic elastic modulus of the belt crossing layer end layer interlayer rubber and the dynamic elastic modulus of the cord-coated rubber within the above-mentioned ratio, it is possible to withstand various uses such as good roads and bad roads. It is possible to easily make a so-called application-specific tire that specializes in peelability.

[Brief description of drawings]

FIG. 1 is a diagram showing a crack growth process at a belt end portion of a tire of the present invention.

FIG. 2 is a diagram showing a crack growth process at a belt end portion of a conventional tire.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Belt structure 2 2nd belt 3 3rd belt 4 End part inter-layer rubber 5 Code coating rubber 6 Belt crossing layer end part crack

Claims (1)

[Claims] 1. A belt structure in which at least two or more belt layers, which are arranged on an upper side in a tire radial direction of a radial arcuate layer and have a plurality of steel cords arranged in parallel and covered with a covering rubber, are laminated, An inter-layer rubber different from the steel cord-covered rubber is interposed between the layers at both ends in the belt width direction of the intersecting layer in which the cord directions of the adjacent belt layers intersect with each other, and the movement of the end-layer rubber is The relation between the dynamic elastic modulus E ′ and the dynamic elastic modulus E ₀ ′ of the steel cord-coated rubber is 0.1 × E ₀ ≦≦ E ′ ≦ 0.6 × E _{0 ′} , and The value of the dynamic elastic modulus E ₀ `of the steel cord coated rubber is 1.0 × 10 <sup>8</sup> dyn / cm <sup>2</sup> ≦ E <sub>0`</sub> ≦ 4.0 × 10 ⁸ dyn / cm ^2. Pneumatic radial tire.