JP2006328557A - Steel cord for reinforcing rubber product and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel cord for reinforcing rubber products satisfying lightening, durability and steering stability at the same time by applying it as a reinforcing material for tire belts, and a pneumatic tire. <P>SOLUTION: The steel cord for reinforcing rubber products is constituted of a core in which two untwisted core strands having different diameters are arranged in a longitudinal direction and a sheath of one layer in which 3-5 strands are twisted around the core, and has a flat shape of cord profile at the cross section orthogonal to the cord axis. Inclination of the core strands viewed from the cord side face is ≤3° to the cord direction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a steel cord for reinforcing rubber articles and a pneumatic tire, and more specifically, a steel cord used as a reinforcing material for rubber articles such as a pneumatic tire and an industrial belt, and the steel cord as a reinforcing material for a belt. Related to pneumatic tires. In the present invention, weight reduction is achieved without impairing the durability of a rubber article, particularly a pneumatic tire, which is to be reinforced with a steel cord.

  In pneumatic tires, which are typical examples of rubber articles, as a factor that reduces the durability of the tires, moisture entering the inner belt from the outside of the tire via cut flaws corrodes the belt cord, and this corroded area There is a known separation that occurs when the cord and rubber are peeled off due to the expansion of.

  In order to avoid the separation, a so-called rubber penetrating structure in which rubber is sufficiently infiltrated into the cord so that a gap for transmitting moisture between the filaments of the cord is not effective. This rubber penet structure realizes the penetration of rubber by increasing the gap between filaments by loosely twisting the cord, and is particularly suitable for a single twist cord having a 1 × 3 or 1 × 5 structure.

  However, in recent years, a steel cord with higher rigidity has been demanded in terms of performance such as riding comfort and handling stability of a pneumatic tire. Although it is possible to ensure the tensile rigidity of the belt by increasing the number of cords driven in the tire belt, it causes an increase in the weight of the tire, and because the adjacent cord interval in the belt is narrowed, The rubber peeling starting from the cord end of the belt width direction end portion easily propagates between the adjacent cords, and so-called belt edge separation is easily caused.

As a steel cord having high rigidity, Patent Document 1 proposes a steel cord having a 2 + 4 twist structure. This steel cord has a relatively high rigidity as compared with a steel cord having a 1 × N structure in which flexibility is obtained by twisting.
JP 2002-227081 A (Claims etc.)

  However, in the steel cord described in Patent Document 1, since the corrugated spiral brazing is applied to the bundle of the two steel strands constituting the core, when the tension is applied to the cord applied during tire manufacture, There is no gap between the sheath strands, and sufficient rubber penetration into the cord cannot be obtained. For this reason, there was a problem that a separation phenomenon occurred.

  Accordingly, an object of the present invention is to increase the tensile rigidity of a rubber article reinforced with a steel cord without causing a decrease in durability due to the occurrence of separation around the cord, and 1 × An object of the present invention is to provide a steel cord based on a 2 + n (n = 3 to 5) structure capable of improving the code productivity as compared with an N structure cord.

  Another object of the present invention is to provide a pneumatic tire that satisfies the weight reduction, durability, and steering stability by applying the steel cord as a belt reinforcing material.

  In order to solve the above-mentioned problems, a steel cord for reinforcing rubber articles according to the present invention includes a core formed by arranging two untwisted core strands having different diameters in parallel in the longitudinal direction, and three to five. A steel cord for reinforcing rubber articles, comprising a sheath of one layer formed by twisting a sheath wire around the core and having a flat cord contour shape in a cross section perpendicular to the cord axis, The inclination of the core wire viewed from the side is 3 ° or less with respect to the cord axis direction.

  The pneumatic tire of the present invention is characterized in that the steel cord for reinforcing rubber articles is used as a belt reinforcing material.

  According to the steel cord of the present invention, the tensile rigidity of the rubber article can be increased without causing a decrease in durability due to the occurrence of separation around the cord in the rubber article. By doing so, it becomes possible to satisfy the weight reduction, durability and steering stability of the tire at the same time.

Hereinafter, embodiments of the present invention will be specifically described.
The steel cord for reinforcing rubber articles of the present invention comprises a core formed by arranging two untwisted core strands in parallel in the longitudinal direction, and three to five sheath strands twisted around the core. The cord contour shape in a cross section perpendicular to the cord axis is flat. By adopting such a configuration, the rigidity is relatively higher than that of the steel cord having the 1 × N structure, and the code productivity is improved as compared with the cord having the 1 × N structure.

  Here, in the present invention, it is important that the inclination of the core wire viewed from the side of the cord is 3 ° or less, preferably substantially 0 ° with respect to the cord axis direction. The reason for this is that the core strands are arranged side by side and are almost straight, so that the cord elongation when applying tension to the cord applied during tire manufacture is suppressed, and no closed space is formed between the core and the sheath. It is. As a result, rubber easily penetrates between the core strand and the sheath strand, so moisture that has entered the inner belt from the outside of the tire via cut flaws corrodes the belt cord, and this corrosion Separation in which separation occurs between the cord and the rubber due to the expansion of the area can be avoided.

  In the steel cord for reinforcing rubber articles of the present invention, it is necessary to use two core wires having different diameters. The diameter ratio of these two core wires (thin wire diameter / thick wire diameter) is preferably 0.85 to 0.95, and the diameter ratio is within this range. When a tension is applied to the cord during manufacturing, even if the cord is stretched by tension, a space in which rubber can enter is surely secured between the core wire having a small diameter and the sheath wire. Become. If the diameter ratio exceeds 0.95, the space cannot be secured. On the other hand, if the diameter ratio is less than 0.85, the parallelism of the two cores deteriorates because the diameters of the two core wires are too different, and the twist property Becomes unstable.

  Furthermore, in the steel cord for reinforcing rubber articles according to the present invention, it is preferable that the sheath wires are not uniformly distributed around the core but are arranged in a biased manner (see FIG. 1 in an embodiment described later). With this arrangement, the thickness in the vertical direction of the cord can be reduced, and further, the thickness of the belt layer can be reduced, so that the weight of the tire can be reduced. Further, the flexibility and buckling property of the belt against buckling deformation occurring outside the tread surface during cornering is improved.

Furthermore, the tensile strength of the core wire and the sheath wire of the steel cord for reinforcing rubber articles of the present invention is preferably 2.9 kN / mm ² (300 kg / mm ² ) or more from the viewpoint of weight reduction. The diameters of the core wire and the sheath wire are preferably in the range of 0.21 mm to 0.24 mm. If the diameter is less than 0.21 mm, it is difficult to ensure the strength of the belt. If it exceeds .24 mm, the bending rigidity in the out-of-plane direction of the belt becomes too large, and the steering stability is lowered.

  In the pneumatic tire of the present invention, a ply formed by embedding a plurality of the steel cords of the present invention in parallel with each other and embedded in a rubber sheet is applied as a belt, and the tire structure other than the belt should be particularly limited Instead, it can be appropriately employed in accordance with common usage.

  Here, in applying the steel cord of the present invention as a reinforcing material for a belt, it is important that the side-by-side direction of the core wires is arranged substantially along the belt width direction. With such an arrangement, the rigidity against in-plane bending deformation that occurs in the direction along the belt surface is increased, and the steering stability of the tire is improved. That is, in the steel cord of the present invention, two core strands are arranged side by side, and the core strands are in contact with each other side by side. This is because the cord bending rigidity in the lateral direction increases and the tire belt in which the side-by-side direction of the cords is substantially aligned in the belt width direction has high in-plane bending rigidity. In addition, since the steel cord of the present invention is thinner in the vertical direction than the conventional steel cord having a circular cross section, the thickness of a rubber article, for example, a belt is also reduced, and the weight can be reduced.

Hereinafter, the present invention will be described in detail based on examples and comparative examples.
Example 1
FIG. 1 shows a steel cord having a 2 + 4 twist structure. In the figure, (a) is a partial side view as seen from above, (b) is a code shaft at each of positions aa, bb, cc, dd, and ee in (a). It is sectional drawing of the cross section orthogonal to. (C) is a partial side view seen from the side, and (d) is orthogonal to the code axis at positions aa, bb, cc, dd, and ee in (c). It is sectional drawing of the cross section to do. In the figure, 1 is a core wire, 2 is a sheath wire, and two core strands 1 having different diameters are substantially straight in the cord axis direction and are held in parallel with each other. On the other hand, the four sheath strands 2 are twisted on the outer layer of the core strand 1 with a pitch P of 14 mm.

  In producing such a steel cord, in order to reduce the inclination of the core in the cord axis direction, the core unwinding tension at the time of stranded wire was made larger than the unwinding tension of the sheath, and the after-forming amount after twisting was optimized.

  FIG. 2 shows an enlarged cross section of the steel cord perpendicular to the cord axis. In addition, the specifications of this steel cord (wire diameter (core and sheath), strand tensile strength, core strand inclination viewed from the side of the cord (core inclination in the major axis direction and core inclination in the minor axis direction, here The “major axis direction” is the maximum diameter direction of the cord cross section per sheath pitch, and the “minor axis direction” is the direction perpendicular to the major axis direction)).

  The produced steel cord was applied to a belt composed of the first and second belt layers with the number of drivings shown in Table 1 below, and a tire of size 185 / 70R14 was prototyped. The belt has an inner first belt layer disposed on the carcass in a direction in which the steel cord is inclined at an angle of 22 ° to the left with respect to the equator plane of the tire, and further on the equator plane of the tire. The second belt layer was arranged with the steel cord inclined at an angle of 22 ° to the right.

  After mounting the prototype tire on a standard rim defined in the JATMA standard, the tire was filled with an internal pressure corresponding to the maximum load capacity in the JATMA YEAR BOOK and mounted on a passenger car. After running on the paved road for 50000 km, the tire was dissected to investigate the corrosion length of the cord from the cut flaw and the crack length at the belt end. Here, there is no problem in durability if the corrosion length is 10 mm or less and the crack length is 20 mm or less. As for steering stability, each tire was mounted on a specific test road in the same driving mode, and a feeling evaluation was performed by three drivers. This feeling evaluation was performed on a 10-point scale, and the average value of the three drivers was calculated. If the numerical value is 6.5 or more, there is no practical problem. These evaluations and survey results are also shown in Table 1 below.

Examples 2 to 4 and Comparative Examples Steel cords having the specifications shown in Table 1 below were produced as Examples 2 to 4 and Comparative Examples. One cross section orthogonal to the cord axis of the steel cord of Example 2 is shown in an enlarged manner in FIG. As can be seen from FIG. 3, in this steel cord, the sheath wire 2 is distributed almost uniformly around the core. The enlarged view of one section orthogonal to the cord axis of the steel cords of Examples 3 and 4 is the same as FIG. FIG. 4 is an enlarged view of a cross section orthogonal to the cord axis of the steel cord of the comparative example.

  Using these steel cords, tires were manufactured in the same manner as in Example 1 and evaluated in the same manner. Further, the belt weight of the tire was expressed as an index when Example 1 was taken as 100. A smaller value indicates a lighter weight. Furthermore, the overall evaluation is the result of adding the evaluation results of lightness (belt weight) and steering stability to the value obtained by multiplying the average values of corrosion length and crack length, which are evaluation items related to durability. Shown on a 10-point scale. These evaluation results are also shown in Table 1.

It is explanatory drawing of the steel cord of Example 1. FIG. It is an expanded sectional view of the steel cord of Examples 1, 3, and 4. 3 is an enlarged sectional view of a steel cord of Example 2. FIG. It is an expanded sectional view of the steel cord of a comparative example.

Explanation of symbols

1 Core wire 2 Sheath wire P Pitch

Claims (7)

  A core formed by arranging two untwisted core strands having different diameters in parallel in the longitudinal direction, and a one-layer sheath obtained by twisting three to five sheath strands around the core A steel cord for reinforcing rubber articles in which a cord outline shape in a cross section perpendicular to the cord axis is flat, and the inclination of the core wire viewed from the side of the cord is 3 ° or less with respect to the cord axis direction A steel cord for reinforcing rubber articles, characterized by being   The steel cord for reinforcing rubber articles according to claim 1, wherein a diameter ratio of the two core wires is 0.85 to 0.95.   The steel cord for reinforcing rubber articles according to claim 1 or 2, wherein the sheath wires are not uniformly distributed around the core but are arranged in a biased manner. The steel cord for reinforcing rubber articles according to any one of claims 1 to 3, wherein a tensile strength of the core wire and the sheath wire is 2.9 kN / mm ² (300 kg / mm ² ) or more.   The steel cord for reinforcing rubber articles according to any one of claims 1 to 4, wherein the core strand and the sheath strand have a diameter of 0.21 mm to 0.24 mm.   A pneumatic tire, wherein the steel cord for reinforcing rubber articles according to any one of claims 1 to 5 is used as a reinforcing material for a belt.   The pneumatic tire according to claim 6, wherein the steel cord for reinforcing rubber articles is arranged such that a side-by-side direction of core wires of the core is substantially along a belt width direction.

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