JPH07109684A - Steel cord for reinforcing rubber product and pneumatic radial tire - Google Patents

Abstract

PURPOSE:To provide a steel cord useful as a carcass-reinforcing material, dramatically improved in durability, esp. fretting resistance and resistance to filament rupture, thus significantly improving the service life of radial tires. CONSTITUTION:Using virtually same filaments each <=0.23mm in diameter (hereafter, referred to be Fy), 6 to 9 Fys are coaxially stranded around 1 to 3 Fys-stranded core to form into a 1st sheath, and 12 to 15 Fys are coaxially stranded around the 1st sheath to form into a 2nd sheath. In this case, the core and the 1st and 2nd sheaths are stranded in the same direction, respectively, with the stranding pitch of the 2nd sheath shorter than that of the 1st sheath, to form a three layer-stranded steel cord. This steel cord is suitable as a reinforcing material for the carcass of radial tires and also can be applied to reinforcing the belt and bead parts of radial tires.

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, a conveyor belt, a steel cord used as a reinforcing material for rubber articles such as rubber crawlers, and a pneumatic radial tire to which the steel cord is applied. More specifically, it is used as a carcass reinforcing material for radial tires, particularly radial tires for trucks / buses, radial tires for light trucks or radial tires for off-the-road, and its durability, especially fretting resistance and filament breakage resistance. Relates to a steel cord and a pneumatic radial tire thereof, which dramatically improve the durability life of the radial tire.

[0002]

2. Description of the Related Art Tires, particularly steel cords for reinforcing radial tires such as truck / bus tires, light / truck tires, off-the-road tires, etc., especially carcass reinforcing steel cords, have a two-layer or three-layer twist. Code is usually used. Also, as the two-layer twisted cord, twisted structures such as 3 + 8 and 3 + 9 are known, and as the three-layer twisted cord, 1 + 6 +
Twisted structures such as 12, 3 + 9 + 15 are known.

Such a two-layer twisted or three-layer twisted cord is used as a carcass reinforcing material for tires, and one of the main causes of fatigue during use with severe input and deformation such as running of tires is one of the main causes. It is also well known that it is based on abrasion (fretting) caused by rubbing between filaments. That is, the filaments forming the steel cord rub against each other and fretting, the cross-sectional area of the filament decreases, and as a result, stress concentrates on this fretting portion, leading to fracture at that portion. (Fretting property). If even one of the filaments twisted as a steel cord breaks, the input carried by the other filaments in the cord increases by that amount, and the breakage of the filament propagates rapidly to the surrounding filaments. Therefore, the cord will be broken.

In the running of a tire in which a two-layer twisted cord or a three-layer twisted cord is applied as a carcass ply, the strength of the outermost layer filament is extremely decreased, and the main cause of this decrease in strength is the wrap filament. It has also been proposed to remove the wrap filaments from the cord to prevent fretting of the outermost layer filaments, as they are based on fretting of the outermost layer filaments. Certainly, with this proposal, the fretting caused by the wrap filament will not occur, and the strength reduction of the cord can be suppressed, but since the wrap filament is removed, the filament converging property deteriorates, and the cord will not be greatly affected by running at low internal pressure. It is also known that when a bending input is applied, the filaments are separated, an abnormal compression input is locally applied to the filament, and the filament buckles and breaks (filament breakability). It is also known that the breaking life of the cord in this case is much shorter than that due to fretting.

That is, in order to prevent the shortening of the life of the cord due to an extreme bending input, it is necessary that the filaments of the cord are bundled in some form. As a measure to reduce fretting of the wrap filament and the outermost layer filament while suppressing abnormal input,
A proposal has also been made (Japanese Patent Laid-Open No. 4-202869) that a core, a sheath and a wrap filament of a two-layer twisted or three-layer twisted steel cord are twisted in the same direction.

[0006]

By the way, the steel cord is required to have long-term durability as a reinforcing material for a tire, which bears internal pressure, load, and the like, withstands severe deformation and distortion due to running. That is, the carcass of the tire holds the internal pressure, and the carcass strength required to bear a constant load is not only required when the tire is new, but is required not only during the entire period the tire is used, Recently, due to the development of long-distance truck transportation network, its durability performance is required to have a higher level.

[0007] The present invention is to provide a steel cord having a new twisted structure that satisfies the demand for improved durability performance of tires that are becoming more and more sophisticated. That is, it is to provide a steel cord having excellent fretting resistance and filament breakage resistance.

To explain this problem more specifically, the carcass of a tire is constructed by arranging steel cords in parallel and embedding it in rubber. The number of cords that can be arranged in the rubber is , Depends on the diameter of the cord. That is, a large number of cords can be arranged in a carcass having a constant width with a thin diameter steel cord, but a large number cannot be arranged with a thick diameter cord. The carcass strength is expressed as the product of the number of cords embedded in rubber and its strength.

However, in order to densely arrange and embed cords having a small cord diameter in rubber, there are problems in manufacturing technology, and it is actually quite difficult. Therefore, as a steel cord actually used for tire production, a cord having a cord diameter of a certain value or more, that is, a cord strength of a certain value or more is used.

On the other hand, it is obvious that it is preferable to use a filament having a small diameter in order to alleviate an abnormal input to the filament and improve the filament breakage resistance.

However, since the strength of the filament is proportional to the cross-sectional area of the filament, it is necessary to increase the number of filaments to be twisted in order to twist a filament having a small diameter to construct a cord having a cord strength of a certain level or more. is there. That is, a cord obtained by twisting many thin filaments together is preferable as a carcass cord.

As a twisted structure in which a large number of filaments are twisted together, a three-layer twisted cord is generally more advantageous than a two-layer twisted cord.

In this way, the inventors have reached the conclusion that it is preferable from the standpoint of tire durability to use a three-layer twisted steel cord composed of thin filaments as a carcass reinforcing material, and prototyped a tire. However, we came to a new technical problem.

That is, it is generally known that when a filament having a small diameter is subjected to fretting, the influence of a decrease in the filament cross-sectional area is more serious than that of a filament having a large diameter. As a result of the study by the inventors, when the fretting form of a cord having a normal twist structure in which the wrap filament is twisted in the different direction from the second sheath in the 3 + 9 + 15 structure (Comparative Example 1) is observed well, Since the two sheaths intersect in different directions, the filaments come into point contact with each other and rub against each other in that state, resulting in deeply engraved fretting, and the remaining strength of the filament is also significantly reduced.

That is, in the case of a three-layer twisted steel cord composed of filaments having a small diameter, when deep fretting such as fretting with a wrap filament is made, the strength of the filament is severely reduced, and the effect thereof is that of a thick filament. It was observed to be more serious than in the case.

In order to improve the fretting resistance of the cord composed of filaments having such a small diameter, it is possible to prevent the footings from being deeply gouged locally by the wrap filaments and to make the fretting not too deep. It turns out that changing is more important than ever before. In addition, a structure in which the wrap filament is twisted in the same direction as conventionally proposed, or a wrap filament is twisted in the same direction as the second sheath filament (Japanese Patent Laid-Open No. 4-202869).
However, it was found that the effect was not yet sufficient.

That is, a more specific problem to be solved by the present invention is superior to the conventional proposals so that it can be applied to a three-layer twisted steel cord composed of filaments having a small diameter. Cause uniform fretting,
Further, it is to provide a new twisted structure in which filament breakage due to buckling of the filament hardly occurs even under a large bending input.

[0018]

A steel cord for reinforcing a rubber article according to claim 1 has a core formed by twisting 1 to 3 filaments, and 6 to 6 arranged around the core.
A first sheath formed by coaxially twisting nine filaments, and a second sheath formed by coaxially twisting 12 to 15 filaments arranged around the first sheath,
In a three-layer twisted steel cord formed by twisting the periphery of the second sheath with one wrap filament, the core, the first sheath, the second sheath and the wrap filament are twisted in the same direction, and the twist pitch of the second sheath Is twisted shorter than the twist pitch of the first sheath.

A steel cord for reinforcing rubber articles according to a second aspect is the steel cord according to the first aspect, wherein the filament diameters of the core, the first sheath and the second sheath are 0.23 mm or less and are substantially the same. It is characterized by being.

The pneumatic radial tire according to claim 3 is characterized in that the steel cord according to claim 1 or 2 is used in the belt layer.

A pneumatic radial tire according to a fourth aspect is provided with the steel cord according to the first aspect or the second aspect.
It is characterized in that it is applied to a carcass composed of a ply of radial array cords extending in a toroidal shape between a pair of bead portions.

As a steel cord for reinforcing the carcass of a radial tire, the inventors of the present invention have conducted intensive studies focusing on the twisted structure of a three-layer twisted cord. As a result, the core, the first sheath, the second sheath and the wrap filament are Steel cords with a twisted structure that are twisted in the same direction and the twist pitch of the second sheath is shorter than the twist pitch of the first sheath, and the fretting of the second sheath based on the wrap filament is too deep. However, the inventors have found that the fretting is excellent in uniformity, and that the filament is less likely to be broken due to the buckling of the filament under a large bending input, and the present invention has been completed.

The present invention will be described in detail below. Figure 1 shows the components of a typical three-ply stranded steel cord. 1 to 3 cores of the present invention, 6 to 9 first sheath,
The second sheath is composed of 12 to 15 filaments. From the basic technical idea of the present invention, that is, a three-layer twist structure composed of as many filaments as possible, the number of filaments of the core is preferably 2 to 3, and the first sheath filament is 7
-9 are preferred, and the second sheath filament is 13
-15 are preferable. When the number of filaments is more than this, the stability of twisting when the steel cord is twisted is disturbed.

The wrap filament of the present invention has a length of 2 to 6 m.
Wrap around the second sheath at a pitch of m. The wrap filament has a filament diameter of usually 0.1 to 0.2 mm, preferably 0.15 mm.

The core filament, the first sheath, the second sheath, and the wrap filament of the present invention have the same twisting direction, and the twisting pitch of the second sheath is shorter than that of the first sheath. This is one feature. Furthermore, the relationship of the twist pitch will be described in detail by expressing it in terms of the twist angle. Usually, as shown in FIG. 9, the twist angle of the steel cord is the twist angle P1 of the core, the twist angle P2 of the first sheath, and the second twist angle. Represented by the twist angle P3 of the sheath, P
1, P2 and P3 are usually within 80 °. On the other hand, the twist angle P4 of the wrap filament is usually within 40 ° in many cases. In the present invention, the twist pitch of the second sheath is set smaller than that of the first sheath. Expressed in terms of twist angle, the twist angle P3 of the second sheath is 80 °.
It is almost applicable to the following.

Further, in the present invention, the twist angle of the second sheath is preferably 75 ° or less. If the twisting angle of the second sheath exceeds 75 °, even if the second sheath and the wrap filament are twisted in the same direction, the mutual angle difference becomes large, and the angle at which the filaments intersect with each other becomes large. Since it approaches the contact, the contact pressure at the contact point becomes high, which is not preferable for fretting.

As an example of the three-layer twist structure of the present invention, 1+
6 + 11, 1 + 6 + 12, 2 + 6 + 11, 2 + 7 + 1
2, 3 + 8 + 13, 3 + 9 + 15, etc.
It is not limited to these.

2, 3 and 4, the cross section of the steel cord for reinforcing rubber articles according to the present invention has a twist structure 3 + 9.
+ 15 + 1, 2 + 7 + 12 + 1, 1 + 6 + 12 + 1 are shown as typical examples. The three, two, and one filaments indicated by diagonal lines in each figure are the core 1, and the filaments arranged adjacent to each other around the core 1 are the first sheath, and in the example of FIG. The first sheath 2 is provided, the example of FIG. 3 is provided with seven first sheaths 2, and the example of FIG. 4 is provided with six first sheaths 2. The filaments arranged adjacent to each other around the first sheath are the second sheaths, which have 15 second sheaths 3 in the example of FIG. 2 and 12 second sheaths 3 in the example of FIG. , Fig. 4
In this example, 12 second sheaths 3 are provided. The state in which one wrap filament 4 is arranged around the second sheath is as shown in FIGS.

Further, FIGS. 5, 6 and 7 are sectional views of a steel cord for reinforcing a rubber article according to the present invention, showing twisted structures 3 + 8 + 13 + 1, 2 + 6 + 11 + 1, and 1+.
6 + 11 + 1 is shown as a representative example. The core 1 is composed of three filaments, two filaments, and one filament, respectively, and the first sheath 2 arranged around the core 1 has eight filaments,
6 and 6 spaced apart filaments, the second sheath 3 being disposed outside the first sheath 2 thereof comprises 13, 11 and 11 spaced apart filaments, respectively. This is an example in which a wrap filament 4 is provided on the outside thereof.

That is, in this example, since a gap is formed between the filaments of the first sheath 2 and a gap is also formed between the filaments of the second sheath 3, when the tire is reinforced, for example, It is a structure in which rubber easily enters between the filaments. Therefore, even when a large bending input is applied, especially when the tire is used at a low internal pressure, the rubber filled between the filaments restricts the movement of the filaments, and the buckling and breaking characteristics of the filaments are reduced. Be improved.

As described above, in order to allow rubber to enter the cord, in the case of a core made of one filament,
The core may be shaped in a wave shape or a spiral shape and used to form a gap between filaments.

The filament diameter applicable to the present invention is not particularly limited, but a thin filament diameter is preferable from the viewpoint of preventing the buckling of the filament at the time of large bending input, and specifically, it is 0.23 mm or less. A filament diameter is preferred.

The filament diameter applied to the present invention does not necessarily have to be the same, and different filament diameters can be applied to the core, the first sheath and the second sheath, and a gap can be formed between the filaments. In some cases, the filament diameter may be intentionally made different in order to allow the rubber to penetrate, but from the viewpoint of improving the productivity of steel cord production, it is preferable to use substantially the same filament diameter.

The steel cord of the present invention can be applied as a rubber reinforcing material to other portions such as a belt of a radial tire, a carcass, or a reinforcing material of a bead portion of a radial tire, a conveyor belt, a rubber crawler. Although it can be applied to the reinforcement of rubber articles such as the above, it is preferably applied as a carcass reinforcing material for radial tires from the viewpoint of steel cord having excellent fatigue resistance.

[0035]

Since the fretting property of the filament of the second sheath of the three-layer twisted cord is abrasion between the wrap filament and the second sheath filament, it depends on the contact state between both filaments and the momentum in the contact state. Will be decided. That is, it depends on the angle at which both filaments cross each other (intersection angle) and the relative momentum of both. For example, the smaller the crossing angle, the more the contact areas that contact each other and wear each other increase, the contact pressure per unit area at a constant input decreases, the fretting becomes shallow, and the fretting becomes uniform overall. Will tend to be. Therefore, by twisting the second sheath and the wrap filament in the same direction, this crossing angle can be reduced.

However, the twist angle P3 of the second sheath is usually within 80 °, and the twist angle P4 of the wrap filament is
Is usually 40 ° or less, so even if the second sheath and the wrap filament are twisted in the same direction, the crossing angle remains about 40 °. Therefore, by making the twist pitch of the second sheath shorter than that of the first sheath, that is, by setting the twist angle P3 of the second sheath to be 80 ° or less, this crossing angle can be made smaller and the fretting resistance can be improved. Improved sex. Further, preferably, when the twisting angle P3 of the second sheath is set to 75 ° or less, the crossing angle is further reduced, and the effect of improving the fretting resistance is remarkable.

When the tire rolls, the carcass ply cord of the tire grounding portion is twisted in the axial direction. Then, the relative momentum of the second sheath and the wrap filament due to this twist input influences the fretting amount. Therefore, by twisting the wrap filament and the second sheath in the same direction and reducing the overall momentum between the filaments generated when this twist input acts in the direction in which the cord is tightened or when the cord is twisted in the direction in which the cord loosens, The fretting property is improved.

However, when the twisting input is applied in the direction opposite to the twisting direction, since the wrap filament is twisted in the same direction as the second sheath, the wrap filament has a low filament focusing property, The twisting of the second sheath, the first sheath, and the core filament which are twisted in the direction is likely to be loosened. Particularly, since the first sheath is twisted at the same twist angle as that of the second sheath, the first sheath is likely to come apart. Therefore, when the tire travels at a low internal pressure, a large bending input is applied at the same time as the torsional input, and the filaments thus loosened buckle, and the filament breakage is likely to occur especially around the first sheath. . As described above, in the structure using the wrap filament twisted in the same direction as the core and the sheath, the filament breaking resistance is improved as compared with that of the cord not using the wrap filament, but it is still practically not perfect. Not a level.

Therefore, the core, the first sheath, the second sheath and the wrap filament are twisted in the same direction.
By making the twist pitch of the sheath shorter than that of the first sheath, it was possible to particularly improve the filament breakage resistance of the first sheath. That is, in terms of twist angle, the twist angle P4 of the wrap filament is within 40 °,
Since the twist angle P2 of the first sheath is within 80 °, the twist angle of the second sheath is within the normal 80 °, preferably 7 °.
By making the angle smaller than 5 °, it becomes possible to sufficiently prevent the untwisting of the first sheath and the core filament.

Further, since the twist angle becomes smaller,
Untwisting of the second sheath itself can also be prevented, and filament breakage resistance can be improved.

By adopting the twisted structure of the steel cord of the present invention, uniform fretting property is achieved,
At the same time, even when a large bending input is applied, filament buckling breakage does not occur, and a high degree of improvement in the durability of the steel cord is achieved.

[0042]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples as long as the gist of the present invention is not exceeded. Various evaluation methods were as follows. (1) Fretting depth The filament used for the sample was a rib tire for 1000R20 trucks / buses as a trial tire, and after running 100,000 km on a general road with 100% load and an internal pressure of 8 kg / cm ² , Ten ply cords were pulled out with a length reaching from the bead to the bead and cut at a portion corresponding to the center of the tread. The rubber cord is impregnated with toluene to remove the wrap filament along with the rubber.
The sheath filament was taken out and used as a sample.

The fretting depth was determined by breaking the second sheath filament for two cords by a tensile test,
The cross section was observed under a microscope, and the cross section of the original filament was used as a circle, and the average value of h measured in FIG. 8 was expressed as the fretting depth of the cord.
Based on this fretting depth, it was shown as a fretting index by the following formula.

[0044]

[Equation 1]

(2) Filament breakage rate at the time of large bending input With the inner pressure of the running tire set to zero, the tire was mounted on the drive shaft of a car and run for 1000 km on a test course. The presence or absence of breakage was examined. That is, in the case of the 3 + 9 + 15 twist structure, the ratio of the number of broken filaments in the filament 27X10X2 was calculated. Using the ratio of the number of broken filaments, the filament breakage index was determined by the following formula.

[0046]

[Equation 2]

(3) Method of measuring twist angle The definition of the twist angle is explained in FIG. In FIG. 9, (A1), (A2), (A3) and (A4) are
Each of the steel cord cores shown in (A), first
The sheath, the second sheath and the wrap filament l ₁ ,
l ₂ , l ₃ and l ₄ and r ₁ , r ₂ , r ₃ and r ₄ are shown.

Further, in (B1), (B2), (B3) and (B4), with l ₁ , l ₂ , l ₃ and l ₄ as one side, 2πr ₁ , 2πr ₂ , 2πr ₃ and 2πr, respectively.
_In a triangle with ₄ as another piece, l ₁ , l ₂ , l ₃
And the diagonal angle of l _{4 is shown} as the twist angles P ₁ , P ₂ , P ₃ and P ₄ of the core, the first sheath, the second sheath and the wrap filament, respectively.

P ₁ , P ₂ , P ₃ , and P ₄ are r ₁ , r ₂ , r ₃ , and r ₄ and l ₁ , l ₂ , l, respectively.
The values of ₃ and l ₄ were measured, and the following formula:

[0050]

[Equation 3]

Calculated from Here, l ₁ , l ₂ ,
l ₃ and l ₄ represent the twist pitch lengths of the core, the first sheath, the second sheath and the wrap filament, respectively.

Examples 1 to 4 The steel cords shown in Table 1 were applied to a carcass ply, and a trial tire having a tire size of 1000R20 (radial tire for trucks and buses) and a driving number of 22.0 / 5 cm was manufactured and tested. I went to The results are summarized in Table 1.

Comparative Examples 1 to 3 The steel cords shown in Table 2 were applied to the carcass ply in the same manner, and trial tires were manufactured in the same manner as in the examples and subjected to the tests. The results are summarized in Table 2.

[0054]

[Table 1]

[0055]

[Table 2]

With the fretting index and filament breakage index of Comparative Example 1 in Table 2 set to 100, in the case where the wrap filament was removed as previously proposed (Comparative Example 2), the fretting was improved, but the filament was improved. It can be seen that the rupture property of is worse. Further, in the example of the steel cord in which the wrap filament is twisted in the same direction as the second sheath filament (Comparative Example 3), both fretting property and filament breakability are improved. However, it can be seen that the twisted structures of the present invention shown in Examples 1 to 3 have a very remarkable improvement effect in terms of both fretting resistance and filament rupture resistance.

[0057]

As described above, in the three-layer twist structure in which the core, the first sheath, the second sheath and the wrap filament are twisted in the same direction, the twist pitch of the second sheath is shorter than that of the first sheath. By using the twisted steel cord as a carcass reinforcing material for a radial tire, the fretting resistance and the filament breaking resistance are particularly improved, and the durability performance of the radial tire can be remarkably improved.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating components of a typical three-layer twist structure steel cord.

FIG. 2 is a cross-sectional view of a twist structure 3 + 9 + 15 + 1 according to the present invention.

FIG. 3 is a cross-sectional view of a twisted structure 2 + 7 + 12 + 1 according to the present invention.

FIG. 4 is a cross-sectional view of a twisted structure 1 + 6 + 12 + 1 according to the present invention.

FIG. 5 is a cross-sectional view of a twisted structure 3 + 8 + 13 + 1 according to the present invention.

FIG. 6 is a cross-sectional view of a twisted structure 2 + 6 + 11 + 1 according to the present invention.

FIG. 7 is a cross-sectional view of a twisted structure 1 + 6 + 11 + 1 according to the present invention.

FIG. 8 is a schematic diagram showing a fretting depth h.

FIG. 9 is a schematic diagram illustrating a method for measuring a twist angle.

[Explanation of symbols]

 1 core 2 first sheath 3 second sheath 4 wrap filament

Claims (4)

[Claims] 1. A core formed by twisting 1 to 3 filaments, a first sheath formed by twisting 6 to 9 filaments arranged around the core coaxially, and a periphery of the first sheath. The second sheath formed by coaxially twisting 12 to 15 filaments arranged in the above, and the three-layer twisted steel cord formed by twisting the periphery of the second sheath with a single wrap filament. 1
A steel cord for reinforcing rubber articles, wherein the sheath, the second sheath and the wrap filament are twisted in the same direction, and the twist pitch of the second sheath is twisted shorter than the twist pitch of the first sheath. 2. The steel cord for reinforcing rubber articles according to claim 1, wherein the filament diameters of the core, the first sheath, and the second sheath are 0.23 mm or less and are substantially the same. . 3. A pneumatic radial tire comprising the steel cord according to claim 1 or 2 as a belt layer. 4. A pneumatic radial tire, wherein the steel cord according to claim 1 or 2 is applied to a carcass composed of a ply of radial array cords extending in a toroidal shape between a pair of bead portions.