JPH11278012A - Radial tire containing air for heavy load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simultaneously provide rust resistance and edge-separation resistance of a belt layer serving as a tension-resistant layer, by providing two steel element lines of a core with two-dimensional waving structure represented by a specific equation and specifying an oblate ratio of a steel cord. SOLUTION: Two steel element lines f1 of a core fA are arranged right and left in parallel, and respectively have waving structures formed in two-dimensional wave shapes upwards and downward. The waving height H, the waving pitch L, and the diameter (d) of the steel element lines f1 satisfy the relation ship represented by the equations: 1.2<=H/d<=1.9, 8<=L/d, H/d>=0.048 L/d+0.536. A steel cord (f) is formed in a flat structure whose longitudinal axis is in the belt width direction, and an oblate ratio, represented by long diameter/short diameter, is set in the range of 1.05-1.25. Thus, while a strength of the steel cord (f) is kept, rubber can be satisfactorily permeate up to the inside of the core fA of the steel cord (f). Therefore, rust resistance can be greatly improved.

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 radial tire, and more particularly to a heavy-duty pneumatic radial tire having improved edge separation resistance while greatly improving rust resistance of a belt layer. Regarding tires.

[0002]

2. Description of the Related Art A belt layer of a pneumatic radial tire for heavy loads used for large vehicles such as trucks and buses includes:
For example, a steel cord having a twist structure such as 3 + 9 + 15 is used. Since these steel cords have a closed structure in which the strands are in close contact with each other,
The rubber permeability inside the steel cord during tire vulcanization is extremely poor. For this reason, if the tread portion receives an external injury such as a cut, and moisture enters the gap inside the steel cord from the external injury, rust is generated. When the rust grows by passing through the internal voids, the adhesiveness is reduced, resulting in a problem that tire durability is significantly deteriorated.

In order to improve this, for example, a 3 + 8 structure in which a gap is provided between wires is used.
No rubber entered the inside of × 3, which was still insufficient for improvement of rust resistance.

In order to further improve rust resistance, a steel cord core is formed by bundling two to four wires in parallel, and at least one of the wires has a corrugated structure.
By arranging a twisted sheath around the wire in an open structure with a gap between the wires,
There has been proposed a technique for greatly improving the rubber permeability inside the steel cord (Japanese Patent Application Laid-Open No. 6-108387). However, even if a steel cord having a corrugated wire is used for such a core, the corrugated height of the corrugated wire, the size of the corrugated pitch, and their balance are not optimized. Then, there is a problem that the rubber penetration is insufficient. Also, instead of the 3 + 9 + 15 or 3 + 8 structure, 2
When the +8 structure is used, there is a problem that the edge separation resistance is deteriorated because the rigidity of the belt is reduced.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic radial tire for heavy loads capable of achieving both rust resistance and edge separation resistance of a belt layer serving as a tension-resistant layer. .

[0006]

According to the present invention, which achieves the above-mentioned object, at least one of a plurality of belt layers provided on the outer periphery of a carcass layer of a tread portion has a steel cord of at least two belt layers serving as a tension-resistant layer. A core in which a steel strand is made untwisted, and a sheath in which six to eight steel strands arranged on the outer periphery of the core have a twisted structure having a gap between the strands, and two of the cores Of the steel strand of the present invention has a two-dimensional corrugated structure that satisfies the following formulas, respectively.
1.25 is a flat structure in which the major axis is in the belt width direction.

1.2 ≦ H / d ≦ 1.98 ≦ L / d H / d ≧ 0.048 L / d + 0.536, where H: height of corrugated steel wire d: diameter of steel wire L : Corrugation pitch of steel strand

[0008] As described above, the steel cord of the belt layer serving as a tension-resistant layer has a twisted structure having a core in which two steel strands are non-twisted and six to eight steel strands on the outer periphery thereof having a gap. In order to form a two-dimensional corrugated structure with the two core strands specified above as described above, without impairing the strength of the steel cord as a belt layer, the steel cord is not vulcanized at the time of tire vulcanization. The rubber can be sufficiently penetrated into the core. As a result, rust resistance can be significantly improved.

Further, the flatness ratio of the steel cord is set to 1.05.
If the above, and the long axis is arranged in the belt width direction, and further, the rubber thickness of the belt layer is reduced by the amount that the cord diameter in the belt thickness direction of the steel cord is reduced,
The in-plane rigidity of the belt layer is effectively increased by a synergistic effect with the improvement of the rigidity of the steel cord in the belt width direction,
The edge separation resistance can be improved. Moreover, by defining the flatness ratio of the steel cord as described above, the problem that the flattening prevents the rubber penetration from occurring does not occur.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 shows an example of a pneumatic radial tire for heavy loads according to the present invention, wherein 1 is a tread portion, 2 is a sidewall portion, and 3 is a bead portion. On the inner side of the tire, a carcass layer 4 in which reinforcing cords extending along the tire width direction are arranged between right and left bead portions 3 is mounted. It is folded from the inside to the outside. On the outer periphery of the carcass layer 4 of the tread portion 1, there are provided four belt layers 7 in which arranged steel cords are embedded in a rubber layer.

In the four belt layers 7, the carcass layer 4
The steel cords of the first and second belt layers 7a and 7b counted from the side are inclined in the same direction with respect to the tire circumferential direction. On the other hand, in the third third belt layer 7c and the fourth fourth belt layer 7d, the steel cord is inclined in the opposite direction to the first and second belt layers 7a and 7b with respect to the tire circumferential direction. The third belt layers 7b and 7c function as tension-resistant layers.

As shown in FIG. 2, each of the steel cords f of the belt layers 7b and 7c serving as a tension-resistant layer is arranged around a core fA in which two steel strands f1 are non-twisted and an outer periphery of the core. And a sheath fB formed by twisting six to eight steel strands f2. The two steel strands f1 of the core fA are arranged side by side on the left and right, and each have a corrugated structure formed in a two-dimensional wave shape in the vertical direction as shown in FIG. Also, the same corrugated pitch L (m
m) and the corrugated height H (mm) such that the two lines overlap in a substantially parallel right and left waveform with the same phase without displacement. The relationship between the corrugated height H and the corrugated pitch L and the diameter d (mm) of the steel strand f1 satisfies the following equations.

1.2 ≦ H / d ≦ 1.98 ≦ L / d H / d ≧ 0.048 L / d + 0.536 On the other hand, 6 to 8 steel wires f forming the sheath fB
2 has an open structure arranged so that a gap is formed between the strands f2.

Further, the steel cord f is formed in a flat structure in which the major axis is in the belt width direction, and the flat ratio represented by the long diameter / short diameter is in the range of 1.05 to 1.25. As described above, in the present invention, the steel cord f of the belt layers 7b and 7c functioning as a tension-resistant layer is made up of the core fA composed of two non-twisted corrugated steel strands f1 and the six to eight steel strands f2. And a sheath fB having a twisted structure with a gap interposed, and a steel strand f1 of the core fA.
By specifying the corrugated structure as described above, the rubber can be sufficiently penetrated into the core fA of the steel cord f while ensuring the strength of the steel cord f. Therefore, rust resistance can be greatly improved.

Further, by setting the flatness ratio of the steel cord f to 1.05 or more as described above and setting the long axis to the belt width direction, the diameter of the steel cord f in the belt thickness direction can be reduced. It is possible to reduce the thickness T of the rubber of the belt layer by the required amount while securing the required cord / cord thickness T1. As a result, the in-plane bending stiffness of the belt layer can be increased by a synergistic effect with the improvement of the rigidity of the steel cord in the belt width direction, so that the edge separation resistance of the belt layer can be improved. If the rubber thickness T1 is too thin, the edge separation resistance deteriorates. By setting the upper limit of the flatness ratio of the steel cord f to 1.25, the flattening does not hinder rubber penetration.

If the number of core wires of the core fA is one, it is difficult to secure the strength as a belt layer. Conversely, if the number of wires is three or more, rubber cannot be sufficiently penetrated into the core fA. If the number of wires of the sheath f is less than 6,
It is difficult to secure the required strength. Conversely, if the number of wires exceeds 8, sufficient clearance cannot be secured between the strands.

Even if H / d is smaller than 1.2,
Even in the region below 0.048 L / d + 0.536, the gap between the strands f1 of the core fA is too small, so that the rubber penetration into the core is poor. On the other hand, if it is larger than 1.9, the wire f1 is excessively habitually formed, resulting in a decrease in the wire strength. Further, even if L / d is less than 8, the strength of the wire is greatly reduced due to excessive curling of the wire f1.

If the flatness ratio of the steel cord f is less than 1.05, the effect of improving the rigidity of the steel cord in the belt width direction is poor, the in-plane bending rigidity cannot be effectively increased, and the belt layer has an edge resistance. It becomes difficult to improve the separation property. Conversely, if it is greater than 1.25,
Since the wires are excessively flattened, it is not possible to secure a sufficient gap between the wires, and the rubber permeability deteriorates.

FIG. 4 is a graph showing the relationship between L / d and H / d. Each square mark plotted is obtained by actual measurement. In FIG. 4, the equation of a straight line connecting the points (rubber permeability 75) is 0.048 L /
d + 0.536, and the higher range is rubber permeability 7
A preferred range is 5 or more. In FIG. 4, the shaded portion is a range that simultaneously satisfies the above-described formula. In addition, the numerical value attached next to each mark is the rubber permeability represented by an index value, where the value when the rubber completely penetrates into the core is 100.

FIG. 5 is a graph showing the relationship between the flatness ratio and the rubber permeability as an index value with the rubber penetration at a flatness ratio of 1 being 100. When the aspect ratio exceeds 1.25, the rubber permeation decreases rapidly, and it is understood that the aspect ratio is preferably set to 1.25 or less.

In the present invention, the above-mentioned steel cord f is simultaneously formed by arranging left and right steel strands drawn from the left and right unwinding reels and passing between a pair of upper and lower wheels having teeth arranged at a predetermined pitch. It can be easily obtained by shaping into a corrugated form, spirally winding a steel wire of a sheath around the outer periphery thereof, twisting them, and crushing them flat.

The two steel strands f1 of the core fA have the same corrugated pitch L and corrugated height H as described above.
It is preferable to arrange the books on the left and right so that they are overlapped with the same-phase waveform without shifting, from the viewpoint of easy manufacture as described above. However, the present invention is not limited thereto.
May be different as long as the above-mentioned range is satisfied, or the two may be shifted from each other.

The steel cords of the first and fourth belt layers 7a and 7d are not particularly limited as long as they have a conventionally known structure. However, since the fourth belt layer 7d is located on the outermost side, the rubber is formed inside the steel cord. It is preferable to use one that penetrates up to In the above embodiment, the second and third belt layers 7b, 7
c is composed of the steel cord f shown in FIG.
The first and fourth belt layers 7a and 7d are also the second and third belt layers 7b,
7c may be formed using the same steel cord f. In the present invention, at least the belt layer serving as a tension-resistant layer may be formed from the steel cord f.

Further, in the above-described embodiment, the pneumatic radial tire for heavy load provided with four belt layers having two tensile strength layers has been described. However, the present invention relates to a plurality of pneumatic radial tires having at least two tensile strength layers. , Especially a pneumatic radial tire for heavy load using at least three belt layers 7a to 7c.

[0025]

[Example] The tire size is made common to 1200R24,
In the tire having the configuration shown in FIG. 1, the steel cords of the second and third belt layers have a core element having a corrugated structure,
The tires 1 and 2 of the present invention and the comparative tires 1 and 2 having the flatness ratio of the steel cord and the rubber thickness T of the belt layer as shown in Table 1.
2 and a conventional tire.

Each of the test tires has a steel cord structure of 2 + 8 × 0.35, H = 0.55 mm, L = 5.5 mm, and is common to H / d = 1.57 and L / d = 15.7. is there. Each of these test tires has a rim size of 24 × 8.50V
The rim was mounted on the rim, and an evaluation test for rubber penetration and belt edge separation resistance was performed under the following measurement conditions. The results shown in Table 1 were obtained.

Rubber Permeability Each test tire is vulcanized after being vulcanized and then decomposed. The state of the rubber permeated into the core of the steel cord is observed, and the result is defined as 100% of the state where the rubber has completely permeated the core. It was evaluated in percentage. The smaller the value, the lower the rubber permeability. Belt edge separation resistance (edge separation resistance)

Each test tire was mounted on a vehicle at an air pressure of 760 kPa, and after traveling 150,000 km on a general paved road, each test tire was disassembled, and the peeling amount at the edge of the third belt layer was measured over the entire circumference. , The maximum peeling amount at that time (m
m). The smaller this value is, the more excellent the edge separation resistance of the belt is.

[0029]

[Table 1]

As is evident from Table 1, the tire of the present invention has a high rubber permeability and an extremely small maximum amount of peeling, and it can be seen that both the rust resistance and the edge separation resistance of the belt layer can be satisfied. Also, comparative tire 1
This shows that even if the rubber thickness of the belt layer is reduced as in the case of the tire 1 of the present invention without using the flat structure, the edge separation resistance is not improved, but rather deteriorates.

[0031]

As described above, according to the present invention, a steel cord of a belt layer serving as a tension-resistant layer has a core formed by twisting two steel strands and 6 to 8 cores arranged around the core.
A steel wire having a twisted structure having a gap between the wires, and the two steel wires of the core have the corrugated structure specified as described above, while the steel cord is flattened. Since the ratio has the flat structure in which the major axis is in the belt width direction in the above range, the rubber can be sufficiently penetrated into the steel cord, and the belt layer can be made thin to improve in-plane bending rigidity. Therefore, both rust resistance and edge separation resistance can be achieved.

[Brief description of the drawings]

FIG. 1 is a tire meridian sectional view showing an example of a heavy-duty pneumatic radial tire of the present invention.

FIG. 2 is an enlarged sectional view showing an example of a steel cord of a second and third belt layers in FIG.

FIG. 3 is a main part arrow view of a steel strand constituting a core of the steel cord of FIG.

FIG. 4 is a graph showing the relationship between L / d and H / d.

FIG. 5 is a graph showing a relationship between an aspect ratio and rubber permeability.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 7a 1st belt layer 7b 2nd belt layer 7c 3rd belt layer 7d 4th belt layer f Steel cord fA core fB sheath f1, f2 steel strand

Claims (5)

[Claims] 1. A core in which at least a steel cord of a belt layer serving as a tension-resistant layer among a plurality of belt layers provided on the outer periphery of a carcass layer of a tread portion has two steel wires non-twisted, and the core And a sheath having a twisted structure in which six to eight steel wires arranged on the outer periphery of the core have a gap between the wires, and the two steel wires of the core are two-dimensional, each satisfying the following expression. On the other hand,
A heavy duty pneumatic radial tire having a flat structure in which the steel cord has a flat ratio represented by a major axis / a minor axis of 1.05 to 1.25 and a major axis in a belt width direction. 1.2 ≦ H / d ≦ 1.9 8 ≦ L / d H / d ≧ 0.048 L / d + 0.536 where H: Corrugated height of steel strand d: Diameter of steel strand L: Steel strand Line corrugated pitch 2. The pneumatic radial tire for heavy loads according to claim 1, wherein the two steel strands of the core are arranged side by side and corrugated in a vertical direction. 3. The two steel strands of the core are in phase with the same corrugation pitch and corrugation height.
The pneumatic radial tire for heavy loads according to 1. 4. The heavy-duty load according to claim 1, wherein the tension-resistant layer is at least two belt layers in which steel cords are arranged so as to intersect with each other with a slant in a tire circumferential direction. Pneumatic radial tire. 5. The heavy load device according to claim 4, wherein the plurality of belt layers are at least three layers, and the belt layer serving as the tension-resistant layer is a second or third belt layer counted from the carcass layer side. Pneumatic radial tire.