JPS63134309A - Pneumatic radial tire for heavy load - Google Patents

Abstract

PURPOSE:To improve the durability of a belt by installing a buffer layer in the separation part of the first belt layer and arranging the specific rubber compound which is prepared by compounding the cobalt salt of organic acid into natural rubber, as buffer layer. CONSTITUTION:In a tire 1, at least three layers of belt layers 41-43 are arranged between a tread 2 and a carcass layer 3. The cords of the second and third belt layers 42 and 43 are inclined with respect to the tire peripheral direction and cross each other. The first belt layer 41 is divided in the direction of width, and arranged in the both shoulder parts. In this case, in the separation part of the first belt layer 41, a buffer layer 45 is formed. The rubber compound which is prepared by compounding 4.5-8 wt. parts sulfur, 0.4-1.0 wt. parts accelerator, and cobalt salt of organic acid in 0-0.4 wt. part into 100 parts of raw material rubber containing natural rubber, etc., in 20 wt% or less is arranged as the buffer layer 45.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to improving the durability of a belt portion of a heavy-duty pneumatic radial tire reinforced with a steel belt.

[Prior art]

Conventionally, heavy-duty pneumatic radial tires for trucks, buses, small trucks, etc. that use steel cord as a belt layer have been used, for example, as shown in FIG.
between the tread 2 and the carcass layer 3, a heald layer (hereinafter abbreviated as No. 1 belt) 41 having a cord angle of 40' to 75 degrees with respect to the tire circumferential direction, which is arranged adjacent to the carcass layer 3. Two belt layers (hereinafter abbreviated as No. 2 belt and No. 3 belt) 4 are laminated on the top surface of this No. 1 belt 4I and each cord has an angle of 10° to 30° with respect to the tire circumferential direction and each cord intersects with each other. It is constructed by laminating and arranging belt layers 4 consisting of □, 43. The carcass N3 in this case is made of one layer of steel cord, and the carcass cord forms an angle of approximately 90° (substantially in the radial direction) with respect to the tire circumferential direction. 44
is the number 4 belt. However, in the radial tire shown in FIG. 2, by arranging the No. 1 belt 41 over almost the entire area of the crown part a, reinforcement against the tire filling air pressure is achieved.
By increasing the cross-sectional bending rigidity in the tire radial direction (tire width direction) over the entire tread contact area, this tire has an excellent effect on uneven wear. It is difficult for the tread surface to follow the changes, and the tread in the central region of the crown is easily damaged due to stress concentration due to these irregularities.In addition, heat generation in the central region of the crown increases, causing separation between the belt layers. It had the disadvantage of being easy.

Therefore, in order to improve these shortcomings, belt No. 4
A so-called split belt structure (hereinafter abbreviated as split belt structure) in which the belt 1 is separated from the central region of the crown and placed in both shoulder parts, and a buffer layer 45 made of soft low heat generation rubber is inserted between them. A tire having the structure shown in FIG. 1, which aims to relieve stress by lowering the radial cross-sectional bending rigidity of the central region of the crown, which is easily susceptible to stress concentration, to provide flexibility, is mainly used for use on rough roads. However, tires with this belt structure show good performance when used on rough roads with a short running life. However, due to the lack of rigidity, the adhesion between the steel cord and the cord covering rubber tends to deteriorate in both the No. 2 belt 4□ placed above and below this buffer layer and the carcass cord layer due to heat accumulation, which tends to induce separation. There was a drawback.

This split belt structure has a long running life and improves belt durability when used on highways. A method of interposing an insert ply between the belt 4 and No. 2 belt 4
No. 54305) is known, but although this method tends to improve belt durability when used on good roads and highways, the stress relaxation effect when running on rough roads is reduced. It is difficult to achieve belt durability under both conditions of rough road driving and good road high speed driving.

The present inventors conducted various studies on the above-mentioned reduction in adhesion due to heat accumulation during high-speed driving on good roads, and as a result, obtained the following interesting findings.

Conventionally, a soft low heat generation rubber is used as the rubber stock disposed in the buffer layer 45, but in this case, the rubber composition contains a small amount of sulfur in order to obtain soft properties, and in order to obtain low heat production properties, the rubber composition contains a small amount of sulfur. Generally, a large amount of accelerator is added.

On the other hand, No. 2 belt 4□ placed above and below this buffer layer 45
The steel cord coating rubber composition for the carcass layer generally contains a large amount of sulfur and a small amount of accelerator for adhesion to the steel cord. As a result, tires that are used on rough roads, etc. often do not have their treads retread, and the running period is short, so this is not a problem. It has been found that when running for a long period of time, migration of the compounding ingredients of the rubber composition occurs between the steel cord covering rubber and the rubber of the buffer layer due to the heat generated during running of the tire. That is, since a concentration gradient of sulfur and accelerator occurs between the steel cord coating rubber and the buffer layer rubber, a so-called migration occurs in which the compounding ingredients move in a direction where the concentration gradient disappears. This migration is accelerated by the heat generated while the tire is running, resulting in a decrease in the amount of sulfur compounded and an increase in the amount of accelerator in the steel cord coated rubber. For this reason, it was found that the adhesion to the steel cord was reduced and separation between the belt plies was likely to occur. It has been found that an effective method for improving the migration of sulfur and accelerator is to reduce the concentration gradient of sulfur and accelerator between the steel cord coating rubber and the buffer layer rubber. However, simply increasing the amount of sulfur in the buffer layer rubber to about the same amount as the amount of sulfur in the steel cord coating rubber usually slows down the vulcanization rate, and when the tread gauge is thick such as in heavy-duty pneumatic radial tires. , strong vulcanization is not carried out and heat generation is disadvantageous. For this reason, if the tire vulcanization conditions are set according to the vulcanization speed of this buffer layer rubber, the heat generation properties of the buffer layer rubber will be improved, but other trends, sidewalls, etc. will be over-vulcanized, and the tread and This is undesirable because it causes deterioration in physical properties of side walls and the like.

As described above, in the rubber composition for the buffer layer, it is necessary to improve migration by limiting the amount of sulfur and accelerator blended, as well as to optimize the vulcanization rate and provide physical properties such as low heat generation.

In order to simultaneously satisfy these requirements, the present inventors investigated the usefulness of a specific rubber composition.

[Purpose of the invention]

The present invention was conceived in view of these circumstances, and by specifying the composition and physical properties of the rubber composition used for the buffer layer in a split belt structure, it is possible to improve the performance of the split belt structure under rough road running and good road high speed running. The purpose of the present invention is to provide a heavy-duty pneumatic radial tire with improved belt durability.

[Structure of the invention]

Therefore, in the present invention, at least three belt layers made of steel cords are arranged between the carcass layer and the tread, and the cords of the second and third belt layers counting from the carcass layer in the tread direction are arranged. The first belt layer is divided in the width direction and placed on both shoulder parts, and the distance between them in the center area of the crown is determined by the width of the tread contact width. 25 to 45%, and furthermore, in a radial tire in which the cord of the first belt layer is inclined with respect to the tire circumferential direction, a buffer layer is provided in the spaced part of this first belt layer, and as this buffer layer. , 4.5 to 8 parts by weight of sulfur and 0 parts by weight of accelerator per 100 parts by weight of raw rubber containing 20% by weight or less of natural rubber and/or diene-based synthetic rubber.
．． 4 to 1.0 parts by weight and 0 as cobalt element content
The gist of the present invention is a heavy-duty pneumatic radial tire characterized by disposing a rubber composition containing ~0.4 parts by weight of an organic acid cobalt salt.

Hereinafter, the configuration of the present invention will be explained in detail.

In the present invention, in the sprint belt structure shown in FIG. 1, the cords of the second belt 4 41 are arranged to be spaced apart from each other in the crown central region, and the cord angle of the No. 1 belt 4I with respect to the tire circumferential direction is set to 40' to 75°.Also, the interval at which the No. 1 belt 4I is separated from each other in the crown central region is It should be in the range of 25 to 45% of the tread contact width.If it is less than 25%, the effect of relieving the stress concentration in the crown center region, which is the separation effect of the No. 1 belt 4, will be unsatisfactory, and if it exceeds 45%, the crown center On the other hand, the carcass layer 3 consists of one layer, and the carcass cord is at an angle of approximately 90° (substantially in the radial direction) with respect to the tire circumferential direction. All of these cords are made of steel cords, and the twisting structure of these cords is in accordance with conventional practice.

In the present invention, a rubber composition consisting of the following (11 to (4)) is arranged as the buffer layer 45 in FIG.

(1) Raw rubber.

Rubber containing 20% by weight or less of natural rubber and/or diene-based synthetic rubber.

Natural rubber is preferred, but it is also possible to replace 20% by weight or less of the raw material rubber with diene-based synthetic rubber such as styrene-butadiene rubber or polybutadiene rubber. Note that if the diene synthetic rubber is substituted in an amount of 20% by weight or more, the hardness and exothermic property will not be balanced, which is not preferable.

(2) Sulfur.

The amount of sulfur added to 100 parts by weight of raw rubber is 4.5 to 8.
Parts by weight are required, but if it is less than 4.5 parts by weight, there will be a large concentration gradient with the amount of sulfur compounded in the rubber covering the belt cord and carcass cord, which will inhibit the adhesion between the belt cord and carcass cord and the rubber covering the cord. do. In addition, if it exceeds 8 parts by weight, although the adhesion between the belt cord and carcass cord and the cord covering rubber is satisfactory, the vulcanization speed is delayed, the hardness increases, and the low heat generation property as the buffer layer 45 is lost, resulting in a practical use. Not on point.

(3) Accelerator.

The amount of accelerator added is 0.4 to 100 parts by weight of raw rubber.
The amount is 1.0 parts by weight, but preferably 0.6 to 0.8 parts by weight. If it is less than 0.4 parts by weight, heat generation will increase, which is undesirable, and if it exceeds 1.0 parts by weight, it will cause migration of the coating rubber of the belt cord and carcass cord, which will impair adhesion, which is not preferred. The accelerator used here is preferably a thiazole type. Specifically, for example, N, N'-
Dicyclo-N,N'-dicyclo-hexyl-2-benzothiazylsulfenamide and N-oxydiethylene-2-
It is benzothiazyl sulfenamide.

(4) Organic acid cobalt salt.

The organic acid cobalt salt is blended with a cobalt element content of 0 to 0.4 parts by weight based on 100 parts by weight of the raw rubber. 0.
If it exceeds 4 parts by weight, although the vulcanization rate is satisfactory, the heat resistance properties are disadvantageous, which is not preferable. The organic acid cobalt salts used here include cobalt naphthenate, cobalt octylate,
Cobalt stearate and the like are not particularly limited.

As other compounding agents, compounding agents commonly used in the rubber industry can be added in appropriate amounts.

In buffer N45, it is necessary to knead the rubber composition, and after rolling or extrusion molding and vulcanization, complete the required rubber physical properties. As for the physical properties of the rubber after vulcanization, the hardness is 72.
It is more preferable to set the Lübcke repulsion to 50 to 60%.

If the hardness is less than 72, it is possible to reduce the Lübcke rebound, but the contribution to the cross-sectional bending rigidity is reduced, and on the contrary, the amount of deformation becomes large, which substantially increases heat generation, which is not preferable. If it exceeds 80, it is not possible to provide flexibility to the buffer layer 45 and the strength decreases, which is not preferable.

By using the buffer layer 45 made of such a rubber composition, it is well adapted to the split belt structure and is advantageous against distortion in the central region of the crown, and also prevents belt cords and carcass due to migration of compounding agents promoted by heat generation during running. This makes it possible to suppress deterioration in adhesion to the cord.

Furthermore, in tires used under high-speed running conditions, the above-mentioned buffer layer 4. If one or more organic fiber cord layers are inserted into the belt, the durability of the belt can be improved. In this case, by using the above-mentioned rubber composition also for the organic fiber cord coating rubber, the belt durability can be further improved. As the organic fiber cord used here, for example, nylon cord, aramid fiber cord, polyester cord, etc. can be used. The cord angle of this organic fiber cord layer is 0° to 10° with respect to the tire circumferential direction.
Good.

Examples and comparative examples are shown below.

Examples and Comparative Examples A test tire having a tire size of 1000 R20 and a structure shown in FIG. 1 was manufactured with the specifications shown in Table 1 below.

(Margins below this page) The rubber composition of the buffer layer of this test tire, the physical properties of the vulcanized rubber, and the results of the indoor drum test are shown in Table 2 below.

All formulations in Table 2 are parts by weight. Vulcanized rubber physical properties are 1
Physical property values after vulcanization at 60°C for 20 minutes, JIS K
100% modulus, tensile strength, according to 6301
Hardness JIS A) was measured. The Lübke rebound modulus is measured at 25°C using the JIS K 6301 rebound test method.
It was calculated using the value measured in In the indoor drum durability test, the prototype tire was left in a constant temperature chamber at 60°C for one month, and then the load was J using an air pressure of 7.25 kgf/c + J and a rim of 750 V.
Measurements were performed at 130% of the IS standard load and at a speed of 50 km/h. Durability life (drum durability) was determined by the running time until the tire broke and expressed as an index. The rubber attachment of the No. 1 belt was evaluated by disassembling the tire after running it under the above conditions for 60 hours.

(Margins below this page) As is clear from the performance comparison in Table 2, when the amount of sulfur in the rubber composition of the buffer layer is low, the adhesion between the No. 1 belt, carcass cord, and coating rubber decreases during tire running. However, the durability was poor (Comparative Example 1, Comparative Example 10). Further, even if cobalt naphthenate is added, no improvement in adhesion can be expected, which is not preferable (Comparative Example 4). If the amount of sulfur added is 4.5 parts by weight or more, the adhesion is improved, but if too much is added, the hardness increases and the tensile strength decreases, resulting in poor durability (Comparative Example 6). When a small amount of accelerator is blended (Comparative Example 7), the adhesion is good, but the rebound is poor, and the heat generation increases, resulting in a disadvantage in durability.When a large amount is blended (Comparative Example 12), the adhesion is poor. Significantly decreased.

When an organic fiber cord is inserted into the buffer layer (Comparative Example 10, Example 11), durability is improved compared to a rubber layer alone.

However, the durability also differs depending on the composition of the organic fiber cord covering rubber. That is, the durability can be further improved by specifying the organic fiber cord-coated rubber composition in the same manner as the evaluation results for the rubber composition alone.

〔Effect of the invention〕

As explained above, according to the present invention, in the sprint belt structure of a heavy-duty pneumatic radial tire, the drawback that conventional belt durability under good road and high-speed driving conditions could not be satisfied can be resolved under bad road driving conditions. Since it is possible to improve the characteristics of the filter while maintaining its characteristics, it is possible to meet the demands for improved durability under today's wide variety of harsh driving conditions.

[Brief explanation of the drawing]

FIG. 1 is an explanatory half-section diagram in the tire meridian direction showing a split belt structure, and FIG. 2 is an explanatory half-section diagram in the tire meridian direction showing an example of the belt structure. 1... Tire, 2... Tread, 3... Carcass layer, 4I... No. 1 belt, 4□... No. 2 belt, 4
3...3rd belt, 44...4th belt, 45...
- Buffer layer, a...crown part.

Claims (1)

[Claims] At least three belt layers made of steel cords are arranged between the carcass layer and the tread, and the cords of the second and third belt layers are arranged in the circumferential direction of the tire, counting from the carcass layer in the tread direction. The first belt layer is divided in the width direction and arranged at both shoulder portions, and the distance between them in the central region of the crown is set to 25 to 45% of the tread contact width. , in a radial tire in which the cords of the first belt layer are inclined with respect to the tire circumferential direction, a buffer layer is provided in the spaced apart part of the first belt layer, and the buffer layer is made of natural rubber and/or diene. 2 types of synthetic rubber
4.5 to 8 parts by weight of sulfur, 0.4 to 1.0 parts by weight of accelerator, and 0 to 0.4 parts by weight of organic acid as cobalt element content per 100 parts by weight of raw rubber containing 0% by weight or less. A pneumatic radial tire for heavy loads characterized by disposing a rubber composition containing cobalt salt.