JPH061108A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To provide a pneumatic radial tire of ameliorated durability and lightened in weight by improving corrosion resistance and fretting resistance of a steel cord of bunch ply composition. CONSTITUTION:A steel cord 4 is made by means of twisting N (N>=8) number of strands 6 in the identical direction and in the identical pitch and making at least N-1 number of spiral sprands flat in the identical direction while keeping its flatness ratio Di/Ds of the major diameter Di and the minor diameter Ds of the cord outside contour shape within the range of 1.2 to 2.0. The flatness line of the steel cord 4 is so arranged as to be along the surface line of the steel cord ply.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire using a steel cord as a reinforcing cord, and particularly to a pneumatic cord for improving the durability of the steel cord when used for vehicles such as trucks and buses. Concerned radial tires.

[0002]

2. Description of the Related Art In a pneumatic radial tire, a steel cord layer obtained by rubberizing a plurality of steel cords oriented in parallel is used for a belt layer, a carcass layer and the like. There are various proposals for the twisted structure of the steel cord used for the steel cord layer, but especially for pneumatic radial tires for heavy loads such as trucks and buses, as reinforcement cords, eight or more strands are arranged in the same direction. There is one that uses a bunched cord that is twisted together. This bunched cord is, for example, 1 × 12, 1 × 1
As shown in FIGS. 5 to 7, each of which has a twisted structure of 9, 1 × 27, and has 12, 19, and 27 element wires 16 closely contacting each other in the cord cross section, in the same direction and at the same pitch. Are twisted together.

However, the bunched cord having the above-mentioned twisted structure has poor rubber permeability between the strands, so that when water enters, corrosion occurs from that portion as a starting point.
The durability of the steel cord was reduced. Also, since there is no rubber between the strands, the cords repeatedly deform while the tire is running, causing the strands to rub against each other and wear away easily, resulting in so-called fretting, which improves the durability of the tire. There was a problem of being damaged.

Therefore, for example, the strand diameter of the side portion is smaller than the strand diameter of the core portion of the bunched cord, the number of strands of the side portion is reduced, or the spiral of the strand of the side portion is reduced. It has been attempted to improve the rubber permeability by forming a gap between the strands by making the outer shape formed by the elliptical shape. However, in these steel cords, since the core wire and the side wire of the cords have different configurations of strands, tension or friction with the roller in the rubber coating process for processing the steel cord into the steel cord layer, bending deformation, etc. Since the strands on the side are easily moved and deformed to reduce the gap, rubber permeability is likely to decrease, and since the mechanism of rubber permeation into the core has not been devised, corrosion resistance and corrosion resistance still remain. Improvement of fretting property is insufficient,
It was not possible to improve the durability of the pneumatic radial tire.

On the other hand, the steel cord has a very large specific gravity as compared with the organic fiber cord, so that it has an excellent mechanical property but increases the tire weight. Therefore, reducing the weight of the tire has become an issue imposed on the steel cord layer in view of recent global environmental measures.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to improve the corrosion resistance and fretting resistance of a steel cord having a bunched twist structure so as to improve the durability, and to enable the weight reduction. It is to provide a pneumatic radial tire.

[0007]

A pneumatic radial tire according to the present invention is a pneumatic radial tire having a steel cord layer rubberized on a plurality of steel cords oriented in parallel. N
≧ 8) Twist the wires in the same direction and at the same pitch,
The helical shape of at least N-1 strands is flattened in the same direction, and the major axis D _i and the minor axis D of the outer shape of the cord are flattened.
The flatness ratio D _i / D _s and _s with a range of 1.2 to 2.0, and is characterized in that the flat direction is arranged so as to extend along the surface direction of the steel cord layer .

When the steel cord is a bunched cord composed of N strands as described above, the spiral shape of almost all the strands constituting the cord is flattened in the same direction, and the major axis of the outer shape of the cord. By setting the flatness ratio D _i / D _s between D _i and the minor axis D _{s in} the range of 1.2 to 2.0, not only the outer layer but also the wires to the core form a gap between the wires. Therefore, the rubber can be sufficiently permeated into the core portion of the steel cord through the gap. Therefore, the corrosion resistance and fretting resistance of the steel cord can be improved more than before, and the durability of the pneumatic radial tire can be improved.

Further, by arranging the flat direction (longer diameter side) of the steel cord along the surface direction of the steel cord layer, the gauge (thickness) of the steel cord layer can be made thin, so that the tire is lightweight. Can be converted. In particular, when such a steel cord layer is used for a belt layer, a carcass layer, etc., the in-plane bending rigidity thereof is increased and the traction performance is improved.

In the present invention, it is preferable to flatten the spiral shape of all the strands of the cord. For example, in a bunched cord having a twist structure of 1 × 19, one strand placed on the central axis is used. Since the line does not have a spiral shape,
In such a case, the spiral shape of N-1 strands is flattened. Hereinafter, the structure of the pneumatic radial tire of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a pneumatic radial tire for heavy load, 1 is a tread portion, 2 is a carcass layer, 3 is a belt layer,
5 is a bead core. The carcass layer 2 is composed of a steel cord layer in which a plurality of steel cords 4 are rubberized, and an end portion of the carcass layer 2 is folded back from the inside of the tire to the outside of the bead core 5, so that the carcass layer 2 is mounted between the left and right bead cores 5. The belt layer 3 is composed of a plurality of steel cord layers in which a plurality of steel cords 4 are rubberized, and four layers are arranged between the carcass layer 2 and the tread portion 1.

In the present invention, the steel cord 4 used for the carcass layer 2 has eight or more strands in the same direction,
The strands are twisted at the same pitch, and almost all of the strands are formed by flattening each spiral shape in one direction with a flatness ratio substantially the same as the outer shape of the entire cord. For example,
In the case of a 1 × 12, 1 × 19, 1 × 27 twist structure, as shown in FIGS. 2 to 4, when 12, 19 and 27 strands 6 are twisted in the same direction, Each strand 6
Is flattened so that the projection of the spiral shape on the plane orthogonal to the axial direction of the cord is substantially elliptical. Moreover, when the major axis of the outer shape of the steel cord 4 is D _i and the minor axis is D _s , the flatness ratio D _i /
D _s is 1.2 to 2.0. The steel cords 4 are arranged so that the flat direction is along the plane direction of the carcass layer 2.

As can be seen from FIGS. 2 to 4, in the steel cord 4, since the spiral shape of each wire 6 is flattened, there is a gap between the wires of the outer layer portion and the core 6 as well. It is formed so that the rubber sufficiently penetrates into the core of the steel cord 4 through this gap. Therefore, the corrosion resistance and fretting resistance of the steel cord can be improved, and the durability of the pneumatic radial tire can be improved.

Further, by disposing the long diameter side of the steel cord 4 along the plane direction of the carcass layer 2,
The gauge (thickness) of the belt layer 3 can be reduced to reduce the weight, and the in-plane bending rigidity of the belt layer 3 is increased,
The traction performance is improved. In the present invention, when the flatness ratio D _i / D _s of the steel cord 4 is less than 1.2, the rubber permeability between the strands is lowered, and the effect of improving the corrosion resistance and the fretting resistance cannot be obtained. . Further, if it exceeds 2.0, the rubber permeability is improved, but since the strain applied to the surface of the strand during the production of the cord must be increased, the cord is likely to be broken, and the strand contact pressure increases. Fretting tends to occur, and fatigue durability decreases.

As the cord structure of the steel cord 4,
1 x 9 x 0.22 mm, 1 x 12 x 0.22 mm, 1 x
19 × 0.175 mm, 1 × 27 × 0.22 mm, etc. can be used. Further, it is possible to make specifications in which only the wire diameter is different in these twisted structures. For example, 1x
In the twisted structure of 12, the core wire diameter is 0.22 m
It is also possible to use a combination structure of different-diameter strands such that the strand has a diameter m of 0.20 mm and the side portion has a strand diameter of 0.20 mm.

In addition, the number of cords to be driven into the steel cord layer must be set so that the cord / cord interval becomes a certain value or more due to the limitation in calendering (rubbering) work, but the tensile strength is large. If a high strength steel cord is used, the cord diameter can be reduced, so that a cord having a larger flatness ratio can be used even if the number of driven cords is large. Such a high strength steel cord has a carbon content of 0.80 to 1.0.
5% by weight, preferably 0.82% by weight, 0.92% by weight
It is desirable to use the same one.

Although the steel cord layer used for the carcass layer has been described in the above embodiments, the present invention can be used as a steel cord layer for other portions such as a belt layer and a reinforcing layer around beads. Is. Next, a method for manufacturing the flattened steel cord as described above will be described. In order to flatten the steel cords, almost all the strands arranged in the core and sides are bent excessively and twisted in the same direction and at the same pitch. An open structure 1 × N bunched cord is formed, each having an appropriate gap. Then, this cord is lightly rolled in one direction by a straightening roller or the like to be flattened to have a flat cross-sectional shape with a flatness ratio of 1.2 to 2.0. In the present invention, since the spiral shape of almost all of the strands is flattened in one direction, the cord structure is stable against tension in the rubber coating process, friction with the roller, bending deformation, etc. The gap between them can be maintained at almost the initial size.

[0018]

【Example】Experiment A As shown in Fig. 2, the cord structure is 1 x 12 x 0.22 mm.
And its flatness ratio D_i/ D _s8 as shown in Table 1
Manufacture steel cords of various types and use the following method to make rubber
The degree of penetration was evaluated.

The tire size is 11R22.5 and the carcass layer (cord driving density: 27/50 m).
m, a cord angle with respect to the tire circumferential direction: about 90 °) is arranged as shown in FIG. 1, and a tire partially incorporating all of the above eight types of steel cords as a cord to be used in this carcass layer is manufactured as a trial product. Corrosion resistance and fretting resistance were evaluated by the method. The results are also shown in Table 1.

In Table 1, the wire spacing is the wire spacing of the cord outermost layer, and the ply weight is the ply weight of the carcass layer itself as 100 in the conventional example. Rubber penetration: A steel cord was embedded in rubber and vulcanized to form a sample with a cross-sectional diameter of 3 mm and a length of 50 cm, which was disassembled to visually observe the rubber penetration state of the core, The ratio of the length of complete penetration between the lines is shown as a percentage. Corrosion resistance: 30m from the sidewall of the test tire
A carcass cord layer having a size of m and a length of 100 mm, which is still covered with rubber, is cut out, the side portion thereof is sealed with an epoxy resin adhesive, and immersed in a 20% NaCl aqueous solution for 3 days, and then a single cord is peeled off. Then, the corrosion length was measured. The evaluation result is shown by an index with the conventional example being 100. The smaller this value, the better the corrosion resistance. Anti-fretting resistance: After mounting a test tire on a test car and running on a pavement for 150,000 km, the cord was taken out from the tire and disassembled. The score was calculated by scoring 5 points when the shaving was not scraped and 0 score when the shaving was cut to half. The evaluation result is shown by an index with the conventional example being 100. The larger this value, the better the fretting resistance.

[0021] As is clear from Table 1, Examples 1 to 5 of the present invention
In each of these, since the rubber penetration between the strands is high, the corrosion resistance and fretting resistance are superior to those of Conventional Example 1 and the weight can be reduced.

On the other hand, the flatness ratio D_i/ D_sIs 1.1
In Comparative Example 1, the rubber penetration into the cord was low.
Therefore, the effect of improving corrosion resistance and fretting resistance is insufficient.
It was a minute. Also, the flatness ratio D_i/ D_sIs as large as 2.1
In Comparative Example 2, the strain applied to the surface of the strand during the production of the cord is
On the contrary, since it was large, the fretting resistance was low. Experiment B The cord structure is 1 × 19 × 0.175 mm as shown in FIG.
And its flatness ratio D_i/ D_s8 as shown in Table 2
Produce different types of steel cords and use the same method as Experiment A
The rubber penetration was evaluated more.

The tire size is 11R22.5 and the carcass layer (cord driving density: 27/50 m).
m, a cord angle with respect to the tire circumferential direction: about 90 °) are arranged as shown in FIG. 1, and the flatness ratio is 2. as a cord used for this carcass layer among the above eight types of steel cords.
A tire in which seven types of steel cords except for the steel cord of No. 3 were partially built was produced as a prototype, and corrosion resistance and fretting resistance were evaluated by the same method as in Experiment A. The results are also shown in Table 2.

[0024] As is clear from Table 2, Examples 6 to 9 of the present invention
Since each of them had a high rubber penetration between the strands, it was superior to the conventional example 2 in corrosion resistance and fretting resistance, and it was possible to reduce the weight.

On the other hand, the flatness ratio D_i/ D_sIs 1.1
In Comparative Example 3, which has a small value, the rubber penetration into the cord is low.
Therefore, the effect of improving corrosion resistance and fretting resistance is insufficient.
It was a minute. Also, the flatness ratio D_i/ D_sIs as large as 2.1
In Comparative Example 4, the strain applied to the surface of the strand during the production of the cord is large.
Fretting resistance is low due to
Flatness D on top_i/ D_sComparative example 5 has a large diameter
Becomes too large and the specified number of shots cannot be obtained.
I couldn't get the data as an ear. Experiment C The code structure is 1 × 27 × 0.22 mm as shown in FIG.
And its flatness ratio D_i/ D _s8 as shown in Table 3
Produce different types of steel cords and use the same method as Experiment A
The rubber penetration was evaluated more.

The tire size is 385 / 65R2.
2.5 out of the four belt layers, the second and third belt layers (cord driving density: 19/50 m)
m, a cord angle with respect to the tire circumferential direction: ± 20 °) are arranged as shown in FIG. 1, and as a cord to be used in this belt layer, a tire partially incorporating all of the above eight types of steel cords is trial-produced. The corrosion resistance was evaluated by the method, and the belt cord was taken out by the same method as in Experiment A to evaluate the fretting resistance. The results are shown in Table 3.
Are also shown. Corrosion resistance: A belt cord layer with a width of 200 mm was cut out from the belt portion of the test tire while the rubber was still coated, and the side portion was sealed with an epoxy resin adhesive, and the 20% NaCl aqueous solution was used. After soaking for 3 days, the single cord was peeled off and the corrosion length was measured. The evaluation result is shown by an index with the conventional example being 100. The smaller this value, the better the corrosion resistance.

[0027] As is clear from Table 3, Examples 10 to 14 of the present invention
In each case, since the rubber penetration between the strands is high, the corrosion resistance and fretting resistance are superior to those of Conventional Example 3 and the weight can be reduced.

On the other hand, the flatness ratio D _i / D _s is 1.1.
In Comparative Example 3, in which the rubber composition has a small value, the rubber penetration into the cord was low, and therefore the effect of improving the corrosion resistance and fretting resistance was insufficient. Further, in Comparative Example 7 in which the flatness ratio D _i / D _s was as large as 2.1, the fretting resistance was low.

[0029]

As described above, according to the present invention, the steel cord used in the steel cord layer of the pneumatic radial tire is formed by twisting N (N ≧ 8) strands of wire in the same direction and at the same pitch. Further, the spiral shape of at least N-1 strands is flattened in the same direction, and the flatness ratio D _i / D _s of the major axis D _i and the minor axis D _s of the outer shape of the cord is 1.2 to. Since the range is set to 2.0, a gap can be formed between almost all the strands of the cord, and the rubber can be sufficiently permeated to the core of the steel cord through the gap. Therefore, the corrosion resistance and fretting resistance of the steel cord are improved, and the durability of the pneumatic radial tire can be improved. Further, since the flat direction of the steel cord is arranged along the surface direction of the steel cord layer, the gauge of the steel cord layer can be thinned to reduce the weight of the tire.

[Brief description of drawings]

FIG. 1 is a half cross-sectional view showing a pneumatic radial tire according to the present invention.

FIG. 2 is a cross-sectional view showing a steel cord having a twist structure of 1 × 12 used in the steel cord layer of the pneumatic radial tire according to the present invention.

FIG. 3 is a cross-sectional view showing a steel cord having a twist structure of 1 × 19 used for the steel cord layer of the pneumatic radial tire according to the present invention.

FIG. 4 is a cross-sectional view showing a steel cord having a twist structure of 1 × 27 used for the steel cord layer of the pneumatic radial tire according to the present invention.

FIG. 5 is a cross-sectional view showing a steel cord having a twist structure of 1 × 12 used for a steel cord layer of a conventional pneumatic radial tire.

FIG. 6 is a cross-sectional view showing a steel cord having a twist structure of 1 × 19 used for a steel cord layer of a conventional pneumatic radial tire.

FIG. 7 is a cross-sectional view showing a steel cord having a twist structure of 1 × 27 used for a steel cord layer of a conventional pneumatic radial tire.

[Explanation of sign]

 1 tread part 2 carcass layer 3 belt layer 4 steel cord 5 bead core 6 steel cord wire

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display area D07B 1/06 A

Claims (1)

[Claims] 1. A pneumatic radial tire having a steel cord layer rubberized on a plurality of steel cords oriented in parallel, wherein the steel cords are N (N ≧ N).
8) Twist the two strands of wire in the same direction and at the same pitch, and flatten the spiral shape of at least N-1 strands of wire in the same direction, and the major diameter D _i and the minor diameter D _s of the outer shape of the cord.
And a flatness ratio D _i / D _s in the range of 1.2 to 2.0, and a pneumatic radial tire arranged such that the flattening direction is along the plane direction of the steel cord layer.