JP2007063725A - Steel cord for reinforcing rubber article and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel cord for reinforcing a rubber article satisfying light weight, durability and steering stability simultaneously without causing the reduction of uniformity of a tire by applying it as the reinforcing material of the tire belt, and a pneumatic tire. <P>SOLUTION: This steel cord for reinforcing the rubber article consists of a core arranging 2 pieces of core wires 1 in parallel without stranding them in longitudinal direction and one layer sheath obtained by stranding 3-5 pieces of sheath wires 2 around the core, and the cord outline shape at the cross section crossing at right angle to the cord axis is flat. The diameter of the core wire 1 is smaller than that of the sheath wire 2. <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 uniformity and 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 this separation, a so-called rubber penetrating structure in which rubber is sufficiently infiltrated into the cord so as not to form a gap through which moisture propagates between the filaments of the cord is effective. This rubber penet structure is a structure in which the gap between the filaments is increased by twisting the cord loosely to achieve the penetration of the rubber, and is particularly suitable for a single twist cord of 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 was no gap between the sheath strands, and sufficient rubber penetration into the inside of the cord was not obtained, which was not always sufficient in terms of separation phenomenon. In addition, since the core strand and the sheath strand have the same diameter, there is a problem that it is difficult to control the torsion when the cord is manufactured.

  Steel cords used as tire reinforcements are drawn in parallel in the calendering process at the time of tire manufacture, and this is covered with a sheet of rubber to form a composite with rubber (hereinafter referred to as a treat). In the cutting process, the treat is cut obliquely with respect to the longitudinal direction of the cord at regular intervals to obtain a treat member, the side surfaces of the cut treat member are joined together, and steel is formed obliquely with respect to the length direction of the treat. It is used for the belt part of a tire as a strip-shaped treating material in which cords are arranged. At this time, if the steel cord has a torsion, a force for rotating in the circumferential direction of the cord cross section is generated at the end of the treat when cutting, and as a result, the end of the treat member jumps up. The treating member having such a shape in which the end portion is raised has a problem in that the side surfaces cannot be joined in the next joining step. In addition, when the degree of the bounce is not large, the bounce can be manually corrected and joined. However, manual correction is troublesome and avoids disturbing the cord driving of the junction (correction part). However, there was a problem that the tire uniformity was lowered and the durability of the belt portion was lowered due to this.

  Therefore, an object of the present invention is to improve 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 × Steel cords based on a 2 + n (n = 3-5) structure that can improve cord productivity over N-structured cords, reducing weight without compromising the uniformity and durability of rubber articles to be reinforced It is to provide a steel cord that can be realized.

  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-described problems, a steel cord for reinforcing rubber articles according to the present invention includes a core in which two untwisted core strands are arranged in parallel in the longitudinal direction, and three to five sheaths. A steel cord for reinforcing rubber articles, which is constituted by a single-layer sheath formed by twisting strands around the core and has a flat cord contour shape in a cross section perpendicular to the cord axis, The diameter is smaller than the diameter of the sheath wire.

  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 has a core in which two untwisted core strands are arranged in parallel in the longitudinal direction and three to five sheath strands are twisted around the core. The cord contour shape is flat in a cross section that is configured by a single layer sheath and is orthogonal to the cord axis. 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 to use a core wire thinner than the sheath wire. The ratio ds / dc between the diameter dc of the core wire and the diameter ds of the sheath wire is preferably 1.05 to 1.10. It is possible to satisfactorily balance the stabilization of the torsion and the tire performance during production. When the diameter ratio is less than 1.05, the rotational torque of the sheath with respect to the core is insufficient, which is not sufficient in terms of stabilization of torsion. On the other hand, when the diameter ratio exceeds 1.10, the sheath wire becomes thick, the bending rigidity in the out-of-plane direction of the belt becomes too large, and the handling stability is not sufficient.

  In the steel cord for reinforcing rubber articles of the present invention, the inclination of the core wire viewed from the side of the cord is preferably 5 ° or less, more preferably 3 ° or less, and still more preferably substantially, with respect to the cord axis direction. Therefore, it is 0 °. The reason for this is that the core strands are arranged side by side and substantially straight, so that the cord elongation during tension application to the cord during tire manufacture is suppressed, and a closed space is formed between the core and the sheath. This is because there is not. As a result, the rubber easily infiltrates between the core strand and the sheath strand, and the cord of the belt corrodes due to moisture that has entered the inner belt from the outside of the tire through cut flaws, etc. Separation in which separation occurs between the cord and the rubber due to the expansion of the area can be avoided.

  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 of the cord in the vertical direction can be reduced, and further, the thickness of the belt layer can be reduced when applied to the tire, 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 N / mm ² (300 kg / mm ² ) or more from the viewpoint of weight reduction. Moreover, it is preferable that the diameter of a core strand and a sheath strand exists in the range of 0.20 mm-0.24 mm. If the diameter is less than 0.20 mm, it is difficult to ensure the strength of the belt. On the other hand, if the diameter exceeds 0.24 mm, the bending rigidity in the out-of-plane direction of the belt becomes too large, and the steering stability is lowered. Become.

  In the pneumatic tire of the present invention, a ply formed by aligning 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 is not particularly limited. However, it can be appropriately employed according to common usage.

  Here, when the steel cord of the present invention is applied as a belt reinforcing material, 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 belt of the tire in which the cord side-by-side direction 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 conventional steel cords 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 FIG. 1, (a) is a side view of a portion viewed from above, (b) is a position at a-a, bb, cc, dd, ee in (a). It is sectional drawing of the cross section orthogonal to a code axis. Moreover, (c) is a partial side view seen from the side orthogonal to (a), (d) is each position of aa, bb, cc, dd, ee in (c). It is sectional drawing of the cross section orthogonal to a code axis | shaft. In the figure, reference numeral 1 is a core strand, and reference numeral 2 is a sheath strand. The two core strands 1 are held in parallel with each other in a straight line in the cord axis direction. 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 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 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 cord torsion was evaluated by measuring the cord rotation when the cord was taken out from the cord take-up reel by 5 m in a state where the cord was restrained and then the cord was released from the cord. The total number was measured in the width direction of the treat member. If all the torsion of each cord was within 3 times, the end of the treat member did not jump up, and if it was larger, the jump of the end of the treat member occurred, and x.

  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. At this time, the horizontal arrangement direction of the core wires of the steel cord was arranged substantially along the belt width direction.

  The belt has an inner first belt layer disposed on the carcass in such a direction that the steel cord is inclined at an angle of 22 ° to the left with respect to the tire equatorial plane. The second belt layer was placed with the cord tilted 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 JATMA YEARBOOK and mounted on a passenger car. After running on the paved road for 50000 km, the tire was dissected and the corroded length of the cord from the cut wound and the length of the crack at the belt end were investigated. 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. Regarding steering stability, each tire was mounted on a specific test road in the same driving mode, and feeling evaluation was performed by three drivers. This feeling evaluation was performed on a 10-point scale, and was calculated as the average value of 3 drivers. 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 5, Comparative Examples Examples 2 to 5 and steel cords having specifications shown in Table 1 below were produced as comparative examples. A cross section perpendicular to the cord axis of the steel cord of Example 2 is shown enlarged in FIG. As can be seen from FIG. 4, the core strands are wrinkled. FIG. 3 is an enlarged view showing a cross section orthogonal to the cord axis of the steel cord of the third embodiment. As can be seen from FIG. 3, in this steel cord, the sheath wire 2 is distributed almost uniformly around the core. Is arranged. The figure which expands and shows the cross section orthogonal to the cord axis of the steel cord of Example 4 and 5 is the same as FIG. FIG. 5 is an enlarged view of one cross section orthogonal to the cord axis of the steel cord of the comparative example. As can be seen from FIG. 5, the core wire 1 and the sheath wire 2 have the same diameter.

  Tires were prototyped using these steel cords in the same manner as in Example 1, and the same evaluation was performed. 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 result of adding the evaluation results of lightness (belt weight) and handling stability to the value obtained by multiplying the average values of corrosion length and crack length, which are evaluation items related to code torsion and durability, It was shown as a 10-point scale as a comprehensive evaluation. These evaluation results are also shown in Evaluation 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, 4, and 5. 6 is an enlarged sectional view of a steel cord of Example 3. FIG. 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 (9)

  Consists of a core formed by arranging two untwisted core strands in parallel in the longitudinal direction, and a one-layer sheath formed by twisting three to five sheath strands around the core A rubber article reinforcing steel cord having a flat cord contour shape in a cross section perpendicular to the cord axis, wherein the diameter of the core strand is smaller than the diameter of the sheath strand. Steel cord for reinforcement.   The steel cord for reinforcing rubber articles according to claim 1, wherein a ratio ds / dc between a diameter dc of the core wire and a diameter ds of the sheath wire is 1.05 to 1.10.   The steel cord for reinforcing rubber articles according to claim 1 or 2, wherein an inclination of the core wire viewed from the side of the cord is 5 ° or less with respect to a cord axis direction.   The steel cord for reinforcing rubber articles according to claim 3, wherein the inclination of the core wire as viewed from the side of the cord is 3 ° or less with respect to the cord axis direction.   The steel cord for reinforcing rubber articles according to any one of claims 1 to 4, wherein the sheath wire is not uniformly distributed around the core but is biased. The steel cord for reinforcing rubber articles according to any one of claims 1 to 5, wherein the core strand and the sheath strand have a tensile strength of 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 6, wherein the core strand and the sheath strand have a diameter of 0.20 mm to 0.24 mm.   A pneumatic tire, wherein the steel cord for reinforcing rubber articles according to any one of claims 1 to 7 is used as a reinforcing material for a belt.   The pneumatic tire according to claim 8, 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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