JPH079813A - Pneumatic tire for heavy load - Google Patents

Abstract

PURPOSE:To provide a pneumatic tire for heavy load, which improves the fault of exfoliation of steel cords, by covering a plurality of steel cords coaxially with a composition constituted of matrix rubber, sulfur, lead oxide, and organic cobalt salt, thereby coupling these with each other by the composition, so as to form a sheet-shaped reinforcing layer. CONSTITUTION:A steel cords c constituting a curcus 4 is covered coaxially with a first cover composition d, and a plurality of steel cords c covered with rubber d are coupled with each other by a second cover rubber composition e, whereby it is in sheet shape. The thickness t of the first cover rubber composition d is at least 0.35mm or over, and for the composition, sulfur, by 4.5-8 pts.wt., lead oxide, by 7-10 pts.wt., and organic cobalt salt, by 0.10-0.50 pts.wt. by cobalt equivalent, are mixed to the 100 pts.wt. of matrix rubber. For the composition of the second rubber composition e, sulfur, by 3-3.5 pts.wt. and lead oxide, by 4-8 pts.wt., are mixed to the 100 pts.wt. of matrix rubber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy-duty pneumatic tire with improved peeling failure of steel cord.

[0002]

2. Description of the Related Art As a reinforcing cord for a carcass, a belt or the like of a heavy duty pneumatic tire, a steel cord is used which has remarkably excellent strength and elastic modulus as compared with other cords. This heavy duty pneumatic tire undergoes repeated market running, storage, and rehabilitation over a long period of time under harsh conditions, and due to the effects of fatigue and moisture due to repeated mechanical stretching and compression, it causes adhesion between the steel cord and the coated rubber. There are many cases where defects occur.

In order to prevent the above-mentioned peeling failure, sulfur is blended in the coated rubber, and this sulfur is used at the time of laminating or vulcanizing after tire molding and during long-term tire use. In addition, since it gradually shifts to adjacent members with a small amount of sulfur compounded, the sulfur concentration near the steel cord decreases compared to the initial composition, and peeling failure of the steel cord occurs when the above fatigue and humidity are applied. Come to do.

As a measure against the above-mentioned sulfur migration, Japanese Patent Laid-Open No. 145104/1988 discloses a rubber composition in which the surface of the coated rubber of the steel cord contains 1.2 times or more of the sulfur contained in the coated rubber. It is proposed to provide things. However, the provision of such a rubber composition has a problem that air may remain at the interface in some cases, which promotes peeling failure of the steel cord.

There is also a proposal to prevent migration of sulfur by increasing the gauge of the rubber composition coating the steel cord. However, there is a defect that an increase in gauge thickness increases a tire weight and a material cost increases.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heavy-duty pneumatic tire in which peeling failure of a steel cord is improved without causing the above-mentioned conventional problems.

[0007]

According to the present invention for achieving the above object, a first coated rubber composition is concentrically coated around a steel cord in a thickness of at least 0.35 mm, and a plurality of these are coated. The reinforcing layer has a sheet-like reinforcing layer which is formed by connecting the two coated rubber compositions to each other, and the first coated rubber composition contains sulfur in an amount of 4.5 to 8 with respect to 100 parts by weight of the matrix rubber. Parts by weight, 7 to 10 parts by weight of zinc oxide,
Organic acid cobalt salt in the cobalt equivalent of 0.10 to 0.50
The composition is such that the second coated rubber composition is added to the matrix rubber in an amount of 3 to 3 parts by weight.
It is characterized in that 5.5 parts by weight and 4 to 8 parts by weight of zinc oxide are mixed.

As described above, the coating rubber composition is made into two types, one that directly surrounds the steel cords and one that connects the steel cords to each other, so that the thickness of the rubber coating each steel cord is always secured. At the same time, since the decrease of the sulfur concentration near the steel cord is suppressed, the adhesive force between the steel cord and the coated rubber can be maintained for a long time. Therefore, the peeling failure of the steel cord does not easily occur even under the influence of fatigue and moisture during long-term traveling.

Further, since the sulfur compounding amount of the adjoining member is not unnecessarily increased, physical properties such as aging are not deteriorated, and further, it is not necessary to make the gauge of the coated rubber composition thick, and therefore the weight of The increase can be suppressed. FIG. 1 shows an example of a heavy duty pneumatic tire of the present invention. Reference numeral 1 is a tread portion, 2 is a bead portion, and 3 is a sidewall portion. A carcass 4 is provided inside the tire, and both end portions of the carcass 4 are folded back from the inside of the tire to the outside of the left and right bead cores 5, and a bead filler 6 is provided on the outer periphery of the bead core 5. A chafer 7 is arranged outside the folded portion of the carcass 4. Further, in the tread portion 1, a plurality of layers of belts 8 made of steel cords are provided on the outer peripheral side of the carcass 4.

As shown in FIG. 2, the steel cord c constituting the carcass 4 has the first coated rubber composition d coated concentrically around the steel cord c. The plurality of steel cords c coated with the coating rubber d are further connected to each other by the second coating rubber composition e to form a sheet. The thickness t of the first coated rubber composition d is at least 0.35 mm or more, and the composition is 4.5 to 8 parts by weight of sulfur and 7 to 10 parts by weight of zinc oxide with respect to 100 parts by weight of the matrix rubber. By weight, 0.10 to 0.50 parts by weight of cobalt salt of an organic acid cobalt salt is mixed. On the other hand, the composition of the second coated rubber composition e is
Sulfur is 3 to 5.5 with respect to 100 parts by weight of the matrix rubber.
By weight, 4 to 8 parts by weight of zinc oxide are mixed.

In the carcass 4 having the above-described structure, first, as a first step, one steel cord c is passed through a die having a constant diameter to coat the first coated rubber d, and then a plurality of the obtained cords are obtained. It can be manufactured by aligning the two and coating the second coated rubber e with a known calendar. Since each steel cord c is concentrically coated with the first coated rubber composition d in a thickness of 0.35 mm or more, as shown in FIGS. 3 (a) and 3 (b), Even when the second coated rubber composition e is stretched or wavy during vulcanization and the first coated rubber composition d is exposed on the surface of the second coated rubber composition e, the steel is still steel. Since the first coated rubber composition d having a predetermined thickness or more can be secured around the cord c, the adhesiveness between the steel cord c and the coated rubber can be always stabilized. Further, by limiting the composition of the first and second coated rubber compositions as described above, it is possible to suppress a decrease in the sulfur concentration in the vicinity of the steel cord due to the migration of sulfur, and to prevent the steel cord c and the first coated rubber. It is possible to increase the adhesive strength with. Therefore, the peeling failure of the steel cord is not easily caused even by the influence of fatigue and moisture during long-term traveling.

In the above-mentioned embodiment, the reinforcing material used in the present invention has been described by taking the carcass 4 as an example, but the present invention can be applied to any reinforcing material in which a steel cord is coated with a rubber composition, It can also be applied to a belt 8 and a chafer 7 using a steel cord. Further, the above-mentioned coated rubber composition, if necessary, a reinforcing agent such as carbon black to be blended with a rubber composition for a general tire, a fatty acid containing stearic acid, an antioxidant, a softening agent, a vulcanization accelerator, A vulcanization retarder, various resins and the like can be added.

[0013]

EXAMPLES Tires of the present invention having the same tire size of 11R22.5 14 and the structure shown in FIG. 1 (Examples)
And a comparative tire (comparative example) that deviates from the limit value defined by the present invention, with the configuration contents of Table 1, respectively. After these tires were left under conditions of 80 ° C. and 95% relative humidity for 30 days, the rubber around the carcass was visually checked according to the following criteria and evaluated by scoring, and the results are shown in Table 1. I got the result.

The scores 0 to 5 used for evaluation have the following meanings. 5 ... The surface of the member is completely covered with rubber. 4 ... 80% of the member surface is covered with rubber. 3: 60% of the member surface is covered with rubber. 2 ... 40% of the member surface is covered with rubber. 1 ... 20% of the member surface is covered with rubber. 0 ... There is no rubber on the surface of the member, and the wire is exposed.

[0015]

[Table 1] As is clear from Table 1, the tire of the present invention has a rubber evaluation around the carcass of 4.5 or more, which is extremely good, and it is understood that the peeling failure of the steel cord is improved.

[0016]

As described above, according to the present invention, by restricting the constitution of the reinforcing material as described above, the thickness of the rubber covering the steel cord is always ensured and the sulfur concentration near the steel cord is reduced. Because it can be suppressed
It is possible to increase the adhesive force between the steel cord and the coated rubber. As a result, it is possible to prevent the peeling failure of the steel cord due to the influence of fatigue and moisture during long-term traveling. Further, since it is not necessary to increase the amount of sulfur blended in the adjacent member, physical properties such as aging are not deteriorated,
Further, since it is not necessary to make the gauge of the second coated rubber composition thick, an increase in weight can be suppressed.

[Brief description of drawings]

FIG. 1 is a half cross-sectional view of a heavy duty pneumatic tire of the present invention.

FIG. 2 is a partially enlarged sectional view showing a carcass structure used in the tire of the present invention.

3A is an explanatory diagram when the carcass of FIG. 2 is inflated, and FIG. 3B is an explanatory diagram when an internal pressure is applied to the vulcanized tire of the carcass of FIG.

[Explanation of symbols]

4 Carcass (Reinforcement Material) c Steel Cord d First Covered Rubber Composition e Second Covered Rubber Composition t Thickness of First Covered Rubber

Claims (1)

[Claims] 1. A steel cord is concentrically coated with a first coated rubber composition to a thickness of at least 0.35 mm, and a plurality of these are connected to each other by a second coated rubber composition. It has a sheet-like reinforcing layer as a reinforcing material, and the first coated rubber composition contains 4.5 to 8 parts by weight of sulfur and 7 to 10 parts by weight of zinc oxide with respect to 100 parts by weight of the matrix rubber.
By weight, the organic acid cobalt salt is 0.10 in terms of cobalt equivalent.
0.50 parts by weight of the second coated rubber composition, and 100 parts by weight of the matrix rubber, 3 to 5.5 parts by weight of sulfur and 4 to 8 parts by weight of zinc oxide. Heavy duty pneumatic tires.