JPH08176978A - Rubber article-reinforcing steel cord and pneumatic radial tire - Google Patents

Abstract

PURPOSE: To produce a steel cord capable of markedly improving the durability of a radial tire through reinforcing its carcass therewith, esp. markedly improving the rupture resistance of the constituent filaments, and to produce the radial tire reinforced with this steel cord. CONSTITUTION: This steel cord has two-layer structure of (3+n) or (3+n+1) ((n) is 7-10) with the respective tensile strengths of the core and sheath filaments of >=360kg/mm<2> . In this case, the preforming/postforming rate of the sheath filament is set at 90-150%, while that rate of the core filament is set at the rate of the 1st sheath filament ±3%. The radial tire is obtained by reinforcing the carcass with this steel cord.

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 the filament breaking resistance of the steel cords used as the carcass cords. The present invention relates to an ultra-high-strength steel cord, which dramatically improves the durability of a radial tire, and a pneumatic radial tire to which the steel cord is applied.

[0002]

2. Description of the Related Art Steel cords for reinforcing tires, in particular, radial tires such as truck / bus tires, light / truck tires, off-the-road tires, etc., especially carcass reinforcing steel cords, are 2-layer or 3-layer twisted cords. Is usually used. And
A two-layer twisted cord is preferable to a three-layer twisted cord in view of social demands such as productivity of steel cords, weight reduction of tires, and low fuel consumption.

However, since the conventional steel filament has a tensile strength of about 280 kg / mm ² , a conventional two-layer twisted cord using a steel ultrafine wire may be insufficient in maintaining the strength of the carcass as an internal pressure container of a tire. In many cases, a three-layer twist structure was unavoidable.

Therefore, it has been earnestly researched and developed in this industrial field to improve the tensile strength of steel ultrafine wires, and the results have been achieved.

However, as the tensile strength of the steel ultrafine wire increases, the corrosion fatigue resistance, which is the most important characteristic relating to the running input and environmental conditions of the tire, decreases. For this reason, if steel filament having a super high tensile strength, for example, a tensile strength of 360 Kg / mm ² or more, is applied as a reinforcing material for a tire, it meets the social requirements such as weight saving and fuel efficiency of the tire, but corrosion resistance performance. In order to solve the problem, the conventional technology for controlling the cord structure when the cord is twisted using steel filament of high tensile strength starts with filament breakage. It became clear that it caused a code break.

Therefore, it is important to design a cord using a new technology to suppress filament breakage and cord breakage more than ever before in cords using ultra-high strength steel with a tensile strength of 360 kg / mm ² or more. Has become.

In addition, as a conventional two-layer twisted cord, 3+
A twisted structure of 8, 3 + 9, etc. is known. 2 like this
Layered 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 abrasion due to rubbing between filaments (fretting). It is also well known to be based on.

That is, the filaments constituting the steel cord rub against each other and fretting, the cross-sectional area of the filament decreases (fretting property), and as a result, the fretting part corrodes and stresses. Are concentrated, leading to breakage (filament breakage).

When even one of the filaments twisted as a steel cord is broken, the input carried by the other filaments in the cord is increased accordingly, and the filament breakage is rapidly propagated to the surrounding filaments. As a result, the cord will be broken.

As the tire rolls, the filaments in the cord move relative to each other, which creates scratches called fretting between the filaments, which fretting between the sheath filaments. It occurs both between the sheath / core filament and between the core / core filament.

As described above, the corrosion starting from the fretting scratch progresses and the filament breaks to the cord break under the influence of the voids in the cord and the moisture environment existing in the rubber. is there.

[0012]

SUMMARY OF THE INVENTION The problem to be solved by the present invention is to provide a two-layer twisted cord composed of an ultra-high-strength steel material as a filament, which has some problems in corrosion fatigue resistance. It is an object of the present invention to provide a new structure of a steel cord capable of suppressing breakage and cord breakage. Further, it is to provide a radial tire having excellent durability by applying such a steel cord as a reinforcing material for a carcass.

[0013]

DISCLOSURE OF THE INVENTION The inventor of the present invention has developed 3 + n and 3 + n + 1 (n = n) using an ultra-high strength steel material, particularly a steel filament having a tensile strength of 360 kg / mm ² or more.
7-10) In a steel cord with a twisted structure, fretting scratches occur in any of wrap / sheath, sheath / sheath, sheath / core, core / core, and fretting between wrap / sheath is generally Is the deepest.

This is because the wrap filament may be thin, but the wrap twisted around the first sheath also has a large amount of relative movement with the sheath due to bending.

It is true that the fretting damage governs the total strength of the cord itself after fatigue, but in the process of diligently examining the filament breakage and the cord breakage to be solved here, these filament breakage and cord breakage will not occur. Fretting not directly controlled by the depth of the wound,
The fact that the fatigue of the fretting end is controlled by corrosion fatigue has become clear from the observation of the tire part of the filament that breaks first (preceding break), the position in the cord, and the fracture surface.

Focusing on the fact that the filaments that break ahead progress from the fretting wound end portion mainly based on the interaction between the sheath and the sheath or between the sheath and the core, the mutual relationship between the sheath type ratio and the core type ratio is determined. It was found that the filament breakage rate could be suppressed to a minimum only when the balance of the above was within a certain range, and the present invention was reached.

The present invention is described in detail below.

That is, the steel cord for reinforcing a rubber article according to claim 1 has a core formed by twisting three filaments, and a core having a diameter of 7 to 7 which is substantially the same as the core diameter around the core. In a two-layer twisted steel cord consisting of a first sheath formed by twisting 10 filaments together, the tensile strength of the filaments of the core and the first sheath is 36
0 kg / mm ² or more, and 0.15-0.25 mm
And the first sheath filament has a molding ratio of 90 to 105.
%, And the mold ratio of the core filament is within ± 3% of the mold ratio of the sheath filament.

The steel cord for reinforcing rubber articles according to a second aspect is the steel cord according to the first aspect, wherein the filament diameter of the core filament is larger than the filament diameter of the first sheath.

The steel cord for reinforcing a rubber article according to claim 3 is the steel cord according to claim 1 or 2, wherein the twist direction of the wrap filament that bundles the first sheath filament is the twist direction of the first sheath filament. It is characterized by being the same as.

A steel cord for reinforcing a rubber article according to a fourth aspect is the steel cord according to the first aspect, the second aspect or the third aspect, wherein the first sheath constitutes seven filaments. I am trying.

The steel cord for reinforcing rubber articles according to claim 5 is the steel cord according to claim 1, claim 2 or claim 3, wherein the first sheath comprises eight filaments. I am trying.

The steel cord for reinforcing rubber articles according to claim 6 is the steel cord according to claim 1, claim 2 or claim 3, wherein the first sheath comprises nine filaments. I am trying.

The steel cord for reinforcing rubber articles according to claim 7 is the steel cord according to claim 1, claim 2 or claim 3, wherein the core and the first sheath have the same twist direction. Is characterized by.

A steel cord for reinforcing a rubber article according to claim 8 is the steel cord according to claim 1, claim 2 or claim 3, wherein the core and the first sheath have the same twist direction. The twist pitch is almost the same.

The steel cord for reinforcing rubber articles according to claim 9 is the steel cord according to any one of claims 1 to 8, wherein the surface of the filament is coated with brass plating, and the average thereof is obtained. The target plating thickness is 0.15 μm or more.

A pneumatic radial tire according to a tenth aspect is the same as the steel cord according to any one of the first to ninth aspects, in which a radial array cord extending in a toroidal shape between a pair of bead portions is formed. It is characterized by being applied to a carcass made of ply.

[0028]

The ultra-high strength filament having a tensile strength of 360 Kg / mm ² or more has a property of being inferior in corrosion fatigue resistance.
Corrosion from the fretting between filaments easily leads to filament breakage, which causes a problem in tire durability.

3 + n or 3 + n + 1 (n = 7-1)
It has been found that in a 0) structured steel cord, reducing the fretting between the filaments can be achieved by balancing their sheath and core imprinting rates to optimal ranges.

That is, with respect to the molding rate of the sheath,
The outer diameter of an ideally twisted steel cord, that is, the cord diameter when the three twisted first sheaths on the circumference of the core are circumscribed at equal intervals in an ideal shape is D (see FIG. 1), When the amplitude of the wire that bends in a wavy shape when the sheath filament of the cord is unraveled to the wire is H, and when D and H are almost in the same range, the interaction between the sheath and the sheath is suppressed to the minimum. H / DX100 is 90 ~
It has been found necessary to be in the range of 105%. Further, regarding the mold ratio of the core, the outer diameter of the core, that is, the diameter of the circle circumscribing between the three core filaments is D
As c, when Hc is the amplitude of the filament curved in a wavy shape when the core is loosened, in order to minimize the interaction between the cores and the core, the same molding ratio as the sheath, that is, Hc / DcX100 Has been found to be in the range of 90-105%.

The most recent finding of the present invention is that in order to minimize the interaction between the sheath and the core, Hc
It is an invention that it is ideal to control the core molding ratio of / DcX100 (%) to be the same as the molding ratio of the sheath circumscribing the core.

In practice, the core molding rate is controlled within a range of ± 3% around the core molding rate of the sheath circumscribing the core to minimize the sheath / core interaction. It turned out to be possible.

Sensitivity of the molding ratio of the sheath and core to such filament breakage and cord breakage is 360 Kg.
This is particularly noticeable in a twist structure composed of ultra-high strength filaments having a tensile strength of / mm ² or more, and is not necessarily an effect observed in the case of a twist structure composed of ordinary tensile strength filaments.

When the sheath type ratio is 90% or less, the core is tightly tightened by the sheath and the core pre-breakage becomes remarkable, and when it is 105% or more, the interaction between the sheath filaments becomes large and the sheath pre-breakage occurs. It occurs with priority.

A typical two-layer twisted steel cord 1 shown in FIG.
The constituent elements of are shown below. Three cores 2 and first sheath 3
Consists of 9 filaments, which are fastened with a wrap filament 4 to bundle the filaments.

From the point of view of the present invention of improving corrosion fatigue resistance as much as possible, a gap is provided between the sheath filaments so that the rubber easily enters between the filaments of the steel cord, so that moisture that causes corrosion can be prevented. From the viewpoint of preventing diffusion, the 3 + 7 structure (A in FIG. 2) or the 3 + 8 structure (B or E in FIG. 2) is preferable.

If the core filament diameter is larger than the sheath filament diameter, a gap between the sheath filaments can be easily formed, which is generally preferable (FIG. 2).
See E).

However, the present invention is a 3 + 9 structure or a 3 + 10 structure.
The present invention can be applied to a structure, or a structure called 1 × 12 compact structure, in which rubber is not intended to enter between filaments.

One of the essences of the present invention is that the sheath shaping ratio is in the range of 90 to 105%. If the sheath shaping ratio is 90% or less, the core is tightly tightened by the sheath. Preceding breakage becomes remarkable, 105%
In the above case, the interaction between the sheath filaments becomes large, and the sheath leading breakage occurs preferentially.

This tendency is emphasized and synergized by the imbalance of the core molding rate, resulting in remarkable core pre-break and sheath pre-break.

In the steel cord of the present invention, the first sheath filament may be bundled with the wrap filament, or the wrap filament may not be used.

Without the wrap filament, there is no fretting between the first sheath filament and the wrap filament, which is preferred for corrosion fatigue. Also,
Since there is no tightening of the steel cord with the wrap filament, a gap between the filaments can be easily formed, which is also preferable for invading rubber between the filaments.

However, the use of a wrap filament does not impair the essence of the present invention, in which case the wrap filament does not necessarily have to be an ultra-high strength steel material, and a pitch of 2 to 6 mm for the first sheath. It is preferable to wrap it around.

The filament diameter of the wrap filament is
Usually 0.1 to 0.2 mm, preferably 0.15 mm is used.

Further, the twisting directions of the core filament and the first sheath filament of the present invention are preferably the same, and / or the twisting pitches are also preferably the same. The reason is that the contact area between the core / sheath filaments can be increased by adopting a twist structure having the same twist direction or / and the same twist pitch, which is preferable because fretting is reduced.

It is preferable that the twist direction of the wrap filament is the same as that of the first sheath filament because fretting between the wrap filament and the first sheath filament can be suppressed, but even if the twist direction is different, it is still essential to the essence of the present invention. It's not different.

FIG. 2 shows a cross section of a steel cord for reinforcing rubber articles according to the present invention, which has a twisted structure 3 + 7 (A in FIG. 2), 3
+8 (B and E in FIG. 2), 3 + 9 (C in FIG. 2) 3 + 9 +
1 (FIG. 1) and 3 + 10 (D in FIG. 2) are shown as typical examples. Each of the three illustrated filaments is a core 2, the filaments arranged adjacent to each other around the core 2 are the first sheath 3, and one wrap filament 4 is arranged around the first sheath 3. There is.

The filament diameter applicable to the present invention is not particularly limited, but from the viewpoint of preventing the buckling of the filament at the time of large bending input, a thin filament diameter is preferable, and specifically, it is 0.25 mm or less. A filament diameter is preferred.

Further, the filament diameters applied to the present invention do not necessarily have to be the same, and different filament diameters may be applied to the core and the first sheath, and a gap may be formed between the filaments to form a rubber. In some cases, the filament diameters may be intentionally made different for the purpose of penetration, 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 a belt of a radial tire, a carcass, or a reinforcing material of a bead portion of a radial tire, and the like, and can also be applied to a reinforcing belt, 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.

[0051]

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) Fracture Rate of Filament The steel cord to be evaluated is filled with 300 ml of water inside the tire, and the load is 30,000 Km under normal load and normal internal pressure.
After running on a drum, take out the carcass cord, and from the rate of broken filaments and the state of the broken filaments, from which fretting is broken, and the broken filaments are It was also observed whether it was a core filament or a sheath filament.

(2) Measurement of Surface Residual Stress Index Surface residual stress is already known as one of the material factors that greatly affects the corrosion fatigue resistance. Here, the effects are compared in the same state. This surface residual stress (index) is calculated by mechanical calculation from the bending direction and size of the filament that occurs when the other surface is dissolved in nitric acid solution after coating a polymer such as nail polish on one side of the filament. It was

(3) Measurement of Filament Tensile Strength A measurement filament sample is fixed to the upper and lower chucks and measured with a tensile tester under the following conditions.

* Sample length 200 ± 1 mm * Pulling speed 20 ± 2 mm / min * Capacity 0 to 980 N load cell or switchable one. (4) Measurement of cord strength The cord strength was measured according to JIS G3510.

(5) Measurement of cord diameter It was carried out in accordance with JIS G3510.

In Examples 1 and 2, steel filaments having a filament diameter of 0.23 mm (tensile strength 360K) were brass-plated with an average plating thickness of 0.21 μm.
g / mm ² or more), a steel cord wrapped with a 0.15 mm wrap filament is added to a two-layer twist structure consisting of three core filaments and nine first sheath filaments as shown in FIG. Manufactured.

Regarding the twist pitch, the core was 6.0 mm in the S direction, the first sheath was 12.0 mm in the S direction, and the wrap filament was 3.5 mm in the Z direction.

The cords shown in Table 1 were used as the scoring ratios, and rubber treats arranged so that the number of cords to be corded in per 5 cm was 30 were used as a carcass of tires, radial tires for trucks and buses, Size 11 /
70R22.5 was prototyped.

In Comparative Example 1, a tire was similarly trial-produced by using a steel cord in which only the molding rate was changed from those in Examples 1 and 2.

In Comparative Example 2, a tire was similarly trial-produced using a steel filament having a regular level of tensile strength.

The tires thus prototyped were tested,
The results are shown in Table 1.

[0064]

[Table 1]

In Examples 1 and 2, the mold ratio of the first sheath filament was in the range of 90 to 105%, and the mold ratio of the core filament was ± 3% of the mold ratio of the first sheath filament. Since it is within the range, as a result of the drum test of the tire, it is found that the filament is not broken and the tire has excellent durability.

The remarkable improvement of the filament breaking resistance of this steel cord can be clearly understood by comparing with Comparative Examples 1 and 2.

In other words, the mold ratio of the first sheath filament of the steel cord used in Comparative Example 1 was 94%, but the mold ratio of the core filament was as low as 84%.
It can be seen that filament breakage is 40%, which is very easy to occur. This indicates that the balance between the sizing rate of the first sheath filament and the sizing rate of the core filament is very important.

In Comparative Example 2, a cord having a mold rate close to that of Comparative Example 1 is used, but the applied steel material is 280 kg / mm.
^Since it is ² and the regular steel material, its corrosion fatigue resistance is good, and therefore, even in the tire after the drum test, the filament is not broken.

As described above, in the case of a regular steel material having a margin in corrosion fatigue resistance, the balance between the mold ratios of the core and the first sheath filament is not of decisive importance, It can be seen that this is of fatal importance in the ultra-high strength steel having a tensile strength of 360 kg / mm ² or more.

In Example 3 and Comparative Example 3, tires were prototyped by changing the structural factors of the steel cord by the method according to Example 1, and the results of testing the tires are shown in Table 2.
It was shown to.

[0071]

[Table 2]

The structure of the steel cord is (3 + 8) X0.
21 + 1, and as a result of comparative examination of the balance between the mold ratio of the first sheath filament and the mold ratio of the core filament in Example 3 and Comparative Example 3, the cord structure of the first sheath filament was also modified. It was found that the filament breakage resistance of the tire of Example 3 in which the die-casting rate of the core filament did not greatly differ from the rate was significantly improved compared to that in Comparative Example 3.

In Example 4 and Comparative Example 4, tires were manufactured as prototypes by changing the structural factors of the steel cord by the method according to Example 1, and the results of testing the tires are shown in Table 3.
It was shown to.

[0074]

[Table 3]

The steel cord structure is 3 × 0.24 + 9
X0.225 + 1 was changed, and the balance between the mold ratio of the first sheath filament and the mold ratio of the core filament was compared and examined in Example 4 and Comparative Example 4. As a result, even in this cord structure, It has been found that the filament breakage resistance of the tire of Example 4 in which the core filament molding ratio does not greatly differ from the molding ratio is significantly improved as compared with that of Comparative Example 4.

In Example 5 and Comparative Example 5, tires were experimentally manufactured by changing the structural factors of the steel cord by the method according to Example 1, and the results of testing the tires are shown in Table 4.
It was shown to.

[0077]

[Table 4]

The structure of the steel cord is 3 × 0.23 + 1
Change to 0X0.215 + 1, and balance the sizing rate of the first sheath filament and the sizing rate of the core filament.
As a result of comparison and examination between Example 5 and Comparative Example 5, even with this cord structure, the filament breaking resistance of the tire of Example 5 in which the molding ratio of the core filament is not significantly different from the molding ratio of the first sheath filament is It was found that, compared with that of Comparative Example 5, it was significantly improved.

[0079]

As described above, 3 + n or 3
In a two-layer steel cord having a + n + 1 (n is 7 to 10) structure and a tensile strength of its core and sheath filaments of 360 Kg / mm ² or more, the first sheath filament has a mold ratio of 90 to 105%. Set to range,
Durability of the tire when the steel cord is used in a carcass of a radial tire by setting the sizing rate of the core filament within the range of ± 3% around the sizing rate of the first sheath filament. In particular, it has been found that the steel cords used as the reinforcing carcass cord can greatly improve the filament breakage resistance.

[Brief description of drawings]

1 is a cross-sectional view of a twisted structure 3 + 9 + 1 and a spiral development of a filament according to the present invention.

2 a twisted structure 3 + 7, 3 + 8, 3+ according to the invention, FIG.
It is sectional drawing of 9, 3 + 10.

[Explanation of symbols]

 1 Steel cord 2 Core 3 First sheath 4 Wrap filament

Claims (10)

[Claims] 1. A core formed by twisting three filaments together with 7 to 10 filaments having a wire diameter substantially the same as the core wire diameter, which are wound around the core.
In a two-layer twisted steel cord consisting of a sheath, the tensile strength of the filaments of the core and the first sheath is 360 kg /
mm ² or more, and is composed of filaments having a wire diameter of 0.15 to 0.25 mm, the mold ratio of the first sheath filament is 90 to 105%, and the core filament mold A steel cord for reinforcing rubber articles, characterized in that the coverage is within ± 3% of the sheath filament mold coverage. 2. The core wire of the core filament is thicker than the filament diameter of the first sheath.
A steel cord for reinforcing rubber articles according to. 3. The steel cord for reinforcing a rubber article according to claim 1, wherein the twisting direction of the wrap filament that bundles the first sheath filaments is the same as the twisting direction of the first sheath filaments. 4. The filament constituting the first sheath is 7
A steel cord for reinforcing rubber articles according to claim 1, 2 or 3, which is a book. 5. The filament constituting the first sheath is 8
A steel cord for reinforcing rubber articles according to claim 1, 2 or 3, which is a book. 6. The filament constituting the first sheath is 9
A steel cord for reinforcing rubber articles according to claim 1, 2 or 3, which is a book. 7. The twisting direction of the core and the first sheath are the same, claim 1, claim 2 or claim 3
A steel cord for reinforcing rubber articles according to. 8. The rubber article reinforcing material according to claim 1, wherein the core and the first sheath have the same twisting direction and substantially the same twisting pitch. Steel cord. 9. The surface of the filament is coated with brass plating, and the average plating thickness is 0.15 μm.
The steel cord for reinforcing rubber articles according to any one of claims 1 to 9, wherein the steel cord is m or more. 10. The steel cord according to any one of claims 1 to 10 is applied to a carcass including a ply of a radial arrangement cord extending in a toroidal shape between a pair of bead portions. Pneumatic radial tire to be.