KR20050014371A - Steel cord for use in pneumatic radial tire - Google Patents

Abstract

PURPOSE: A steel cord of a pneumatic radial tire is provided to keep technical advantage of the existing core-parallel 2+5 structure and to improve the durability of the tire by removing stress concentration on a core filament by two-dimensionally deforming the core filament. CONSTITUTION: A steel cord applied for a belt or a carcass comprising a pneumatic radial tire has a 2+5 structure composed of two core filaments arranged in parallel to each other and five sheath filaments for covering the core filaments. Two core filaments are deformed two-dimensionally. The diameter of the core filament is 0.15¯0.30 mm. The diameter of the sheath filament is 0.22¯0.40 mm. The diameter ratio(Dc/Ds) of the core filament and the sheath filament is 0.5 <= Dc/Ds <= 0.85. The twist length(Ls) of the sheath filament is 10.0 <= Ls <= 20.0 mm.

Description

Steel cord for pneumatic radial tires {Steel cord for use in pneumatic radial tire}

The present invention relates to a steel cord for a pneumatic radial tire, and more particularly, in a steel cord having a 2 + 5 structure consisting of two core filaments arranged in parallel and five sheath filaments surrounding the core filaments. A steel cord for pneumatic radial tires, characterized in that two core filaments are two-dimensionally deformed.

A steel cord used for the belt layer of pneumatic radial tires for small trucks or buses, which is conventionally comprised of six filaments with a diameter larger than the core filaments around a core with three filaments as shown in FIG. Steel cords of 1 × 3 + 6 structure with sheath) layers have been commonly used. On the other hand, in recent years, it is possible to manufacture the steel cord in a one-step process by twisting the core filament and the sheath filament in the same direction and the same pitch in the twisted pair process at the time of steel cord manufacturing, as shown in Figure 2 Compact cords of steel cords, denoted as 1 × 12 structures, have begun to be used.

However, the steel cord of the 1 × 3 + 6 structure cannot avoid the formation of a closed space in the center because the three filaments of the core are in compact contact with each other, and as a result, the belt rubber on the finished tire reaches the center of the core. It is impossible to penetrate enough. Therefore, the moisture generated in the tire during the tire manufacturing process or the moisture penetrated from the outside through cracks caused by a trauma worn on the road, etc., causes corrosion on the metal surface of the steel cord. Belt layer failure due to degradation, and separation of the belt layer due to deterioration of the adhesion of rubber and steel cord in the belt layer due to corrosion will occur. In addition, even in a twisted structure having the same twisting direction and twisting length of the filaments of the core and the sheath as in the 1 × 12 structure, the belt rubber penetrates sufficiently to the center of the core on the finished tire because each filament is arranged in closest packing. It is impossible to do so, as in the 1 × 3 + 6 structure, belt layer breakage and belt layer separation occur. Furthermore, in the case of 1 × 12 structures, the sheath filament's binding force to the core is weak, causing a so-called core migration phenomenon in which the core filament deviates between the cut portions of the cord by repeated compression or bending of the tire while driving. easy to do.

In addition, each of the above-described conventional steel cords cannot be made thin in the rubber thickness of the belt layer because the cross-section is close to the round, so that the tire weight is somewhat difficult. Further, in the tire to which each steel cord is applied, the rigidity in the belt width direction is not sufficiently exhibited, and there is a limit in improving steering stability in cornering of the tire and the like.

As an alternative, a 2 + 5 (or 2/5) structure as shown in FIG. 3 for the purpose of reducing the number of sheath filaments and shortening the stranded process to improve rubber permeability to the core, as shown in FIG. Has been proposed (see Republic of Korea Patent Publication No. 2000-19281). However, in the case of the 2 + 5 structure, since the core and the sheath filaments are stranded in a one-step process, the core is easily stranded in a 1 + 6 form as shown in FIG. 4, which is structurally more stable than the 2 + 5 form. Therefore, it is difficult to penetrate rubber into one of the two core filaments, as a result of which the core movement phenomenon occurs.

In order to prevent structural variation from the 2 + 5 form to the 1 + 6 form, a method of manufacturing an elliptical cross section of the cord by pressing the cord after the twisted pair has been proposed. In the case of a steel cord having a 2 + 5 structure having an elliptical cross section manufactured in this way, it is easy to penetrate rubber up to two filaments of the core, and furthermore, by introducing a cord having an elliptical cross section into the belt layer in the tire, The thickness can be reduced to obtain a lightening effect of the tire, thus making it possible to provide a tire that can reduce rolling resistance.

However, the pressing applied to form an elliptical cross section causes fretting between the core filament or between the core and the sheath filament, resulting in defects on the surface of the filament, resulting in a decrease in the durability of the cord, i.e. fatigue resistance. . In addition, since the cross section of the core rotates 360 ° within the twist length of one pitch, it is virtually impossible to produce a constant elliptical shape in the longitudinal axis direction by pressing, thus reducing the weight of the tire using a cord having an elliptical cross section. And thereby the reduction of the rolling resistance becomes difficult.

Recently, the technique of Fig. 5 has been developed in which core 2 strands of 2 + 5 structure are arranged in parallel without being twisted with each other, thereby improving the structural stability of twisting and imparting anisotropy of steel cords. (See Korean Patent Publication No. 2003-41072) In the case of core parallel 2 + 5 structure, the stranded wire is very simple and easy to reduce the unit cost of the steel cord, and the twisting is stable, so the rubber permeability is excellent and the tire durability is improved. The advantage is that the top gauge can be lowered without reducing the bending stiffness, making the tire lighter. However, in the case of the core parallel 2 + 5 structure, when the tensile or compressive stress is applied to the steel cord, the stress is concentrated first on the straight core filament without deformation rather than the sheath filament with the twist for twisting, and then the core filament is destroyed first. Stress is concentrated in the sheath filament and secondary fracture after core filament failure. Therefore, the steel cord breakage of the 2 + 5 structure occurs under a stress lower than the theoretical tensile strength of the steel cord (the tensile strength inherent in each filament). As a result, steel cords having a core parallel 2 + 5 structure require an additional steel cord as much as the difference between theoretical tensile strength and actual fracture strength, which leads to an increase in tire weight and consequent reduction in fuel efficiency. .

The present invention is to solve the problems of the prior art as described above, the present inventors in the conventional core parallel 2 + 5 structure, when the two-dimensional deformation of the core filament, the structural elongation due to the deformation is added to the core The present invention was found to be able to prevent the phenomenon of stress concentration into filaments.

That is, the present invention is a steel cord applied to the belt or carcass constituting the pneumatic radial tire, a steel cord of a 2 + 5 structure consisting of two core filaments arranged in parallel and five sheath filaments surrounding the core filament A steel cord for pneumatic radial tires, characterized in that the two core filaments are deformed two-dimensionally.

1 is a cross-sectional view of a conventional 1 × 3 (0.20) +6 (0.35) structural steel cord;

2 is a cross sectional view of a conventional 1 × 12 (0.25) structural steel cord;

3 is a partial perspective view of a conventional 2 (0.20) + 5 (0.35) structural steel cord;

4 is a cross-sectional view of a conventional 2 (0.20) +5 (0.35) structural steel cord that has been transformed into a 1 + 6 structure;

5 is a partial perspective view of a conventional core parallel 2 (0.20) +5 (0.35) structural steel cord;

6 is a partial perspective view of a 2 (0.18) +5 (0.35) structural steel cord of the present invention; And

7 is a cross sectional view of a 2 (0.18) +5 (0.35) structural steel cord of the present invention.

Hereinafter, the present invention will be described in more detail.

In the present invention, a 0.3 to 0.5 μm thick brass layer is plated on the surface of a steel wire made of carbon steel having a carbon content of 0.70 to 0.96 wt% as a filament to improve adhesion with rubber, and is 260 kg / mm 2 to 385 kg / Use the one with tensile strength of 2mm2.

The present invention is characterized in that two core filaments are arranged in parallel, and five sheath filaments are stranded around the core filaments, wherein two-dimensional deformation is applied to the core filaments.

In the steel cord of the present invention, the diameter (Dc) of the core filament is in the range of 0.15 to 0.30 mm, the diameter (Ds) of the sheath filament is in the range of 0.22 to 0.40 mm, and the ratio of Dc and Ds is 0.50≤Dc / Ds≤0.85 The twist length Ls of the sheath filament is adjusted to be 10.0≤Ls≤20.0mm.

Meanwhile, the two-dimensional deformation applied to the core filament is such that the waveforms given to each core filament are arranged side by side to be parallel to each other to have a two-dimensional shape. The deformation preferably has the form of a sine function in which the amplitude Hc is 0.05 Dc to 1/0 Dc and the period Ac is in the range of 0.2 Ls to 1.0 Ls.

6 and 7 are views showing the structure of a steel cord according to the present invention. As shown, the amplitude direction of the two-dimensional waveform of the core filament is a short axis direction, and the waveforms of the two core filaments are arranged side by side parallel to each other.

In the steel cord of the present invention, when the core filament is deformed in two dimensions, when the steel cord is stressed, structural elongation due to the deformation of the core filament is generated in response to the structural elongation due to the sheath filament twisting to concentrate the stress on the core filament. The phenomenon can be prevented. Therefore, the tensile failure of the steel cord can be closer to the theoretical tensile strength (sum of tensile strength of each filament), thereby improving the durability of the tire.

Hereinafter, the present invention will be described in more detail with reference to examples, but these examples are for illustrative purposes only and should not be construed as limiting the present invention.

Examples and Comparative Examples

The physical properties of the steel cord of the present invention and the conventional core parallel 2 + 5 structure, 1 × 3 + 6 structure and 1 × 12 structure of steel cords are shown in Table 1 below.

Example Comparative Example 1 Comparative Example 2 Comparative Example 3 standard rescue 2 (0.18) +5 (0.35) 2 (0.20) + 5 (0.35) 1 x 3 (0.20) + 6 (0.35) 1 × 12 (0.25) Properties Core Strain Amplitude (Unit: mm) 0.1 - - - Core deflection cycle (unit: mm) 4.5 - - - Twist Length (core / sheath) (Unit: mm) -/ 18.0 -/ 18.0 10.0 / 18.0 18.0 Twisting direction (core / sheath) -/ S -/ S S / Z S Cord Diameter (Long Diameter / Short Diameter) (Unit: mm) 0.57 0.57 0.57 1.00 Cord Diameter (Long Diameter / Short Diameter) 1.09 / 0.98 1.13 / 0.93 1.13 / 1.13 1.02 / 1.02 Rigidity ratio (long diameter / short diameter) 110 110 100 100 Cutting strength (kgf) 169 165 205 145 Rubber penetration (Unit:%) 100 100 70 60 Rubber Adhesion Retention Rate Domestic Aging (Unit:%) 95 95 85 70 Retention rate Salt water aging (unit:%) 95 90 75 40

[Property evaluation method]

1) Stiffness ratio (long diameter / short diameter): The rigidity against 15 ° bending was measured for each of the long and short diameter directions using a Taber stiffness tester.

2) Rubber Penetration: After measuring the rubber adhesive force as described above, the steel cord was dismantled and expressed as the ratio of the rubber covering the core filament.

3) Rubber Adhesion Retention Ratio: The adhesion strength after aging under water (70 ° C. deionized water × 3 weeks) and brine (20% NaCl aqueous solution × 3 weeks) conditions compared to the adhesion before the aging test was determined as the adhesive strength in ASTM D2229-99. It measured based on.

As shown in Table 1, the steel cord of the present invention has improved rubber permeability, and excellent retention of adhesion in water and salt water. It is also possible to reduce the thickness of the belt layer due to the smaller cord diameter, and the stiffness of the cord is also improved compared to the parallel core 2 + 5 structure.

Steel cord of the present invention can improve the durability of the tire by solving the stress concentration problem to the core filament by two-dimensional deformation of the core filament while maintaining the technical benefits of the conventional core parallel 2 + 5 structure.

Claims (3)

A steel cord applied to a belt or a carcass constituting a pneumatic radial tire, the steel cord having a 2 + 5 structure consisting of two core filaments arranged in parallel and five sheath filaments surrounding the core filaments, wherein Steel cord for a pneumatic radial tire, characterized in that two core filaments are deformed in two dimensions. The diameter (Dc) of the core filament is 0.15 to 0.30 mm, the diameter (Ds) of the sheath filament is 0.22 to 0.40 mm, the ratio of Dc and Ds is 0.50≤Dc / Ds≤0.85, Steel cord for pneumatic radial tires, characterized in that the twist length (Ls) of the sheath filament is 10.0≤Ls≤20.0 mm. 2. The pneumatic radial tire according to claim 1, wherein the deformation applied to the core filament is in the form of a sinusoidal function having an amplitude Hc of 0.05 Dc to 1.0 Dc and a period Ac of 0.2 Ls to 1.0 Ls. Steel cord.