JP2009062655A - Steel cord for reinforcing rubber article and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an open structure steel cord that has an intended elliptical shape which has a uniform ratio of the minor axis to the major axis in the longitudinal direction of the cord. <P>SOLUTION: The steel cord is a single-layer open-structure steel cord formed of seven or more steel filaments and has a cross-section of an elliptical shape extending continuously in the longitudinal direction of the cord wherein the ratio A/B of the minor axis A to the major axis B in the elliptical shape is 0.4-0.8; the diameter d of the steel filament is 0.12-0.26 mm; and the ratio a/d of the twist pitch (a) of the cord to the diameter d of the steel filament is 30-80. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a steel cord having excellent flexibility and high durability, and a pneumatic tire with improved handling stability, durability, and weight reduction.

  Conventionally, pneumatic tires, particularly passenger car tires, have a carcass extending in a toroidal shape between a pair of bead portions as a skeleton, and a belt composed of at least two layers of rubber sheets is disposed outside the carcass in the tire radial direction. A structure in which a tread is arranged on the outside is common.

  Particularly, a structure in which a belt portion of a pneumatic tire is disposed at a predetermined inclination angle with respect to the equator plane of the tire, and at least two rubber sheets mainly covered with rubber are laminated so as to intersect each other between layers. Thus, a pneumatic tire having a maneuverability and durability that matches the vehicle performance is known.

  The higher the tensile strength of the cord used for reinforcing the belt of such a pneumatic tire, the more the deformation in the belt surface is suppressed during cornering of the tire. Further, the smaller the bending rigidity of the cord, the smaller the belt buckling and the larger the ground contact surface. Furthermore, since the impact received when getting over a protrusion etc. is absorbed, riding comfort improves. As a cord having such a small bending rigidity, a cord that uses organic fibers to suppress the rigidity to 9.8 MPa or less has been proposed (see Patent Document 1).

  However, cords using organic fibers are not practical because their durability against adhesion to rubber is inferior to steel cords during heat generation. Further, since the twisted structure becomes complicated, there is a concern that the durability of the rubber product becomes a problem because the rubber does not sufficiently penetrate into the inside of the cord when applied to a tire.

  With regard to this durability, in steel cords, it is necessary to suppress the deterioration of the durability caused by this corrosion due to corrosion of the steel cord by moisture that has entered the inside of the tire from the damage of the tire. That is, when moisture enters the inside of the tire due to the damage of the tire and the moisture reaches the cord, the cord is corroded by the moisture. If there is a gap inside the cord, moisture propagates through the gap in the longitudinal direction of the cord, and the corroded area expands along the cord. As a result, the durability of the steel cord is reduced due to this corrosion.

  As the steel cord for suppressing the decrease in durability, there is proposed a steel cord having an open structure in which the strands are arranged apart from each other in a cross section perpendicular to the longitudinal direction of the cord (Patent Document 2 and Patent Document). 3). Since such a steel cord has a gap between the strands, rubber can be easily infiltrated from the outside to the inside of the cord at the time of vulcanization molding, and the gap inside the cord can be filled with the rubber. For this reason, for example, there is no gap in which moisture that has entered the tire through the tire damage propagates through the inside of the cord. As a result, expansion of the corroded area is suppressed, and it is possible to suppress a decrease in the durability of the steel cord.

  On the other hand, in recent years, there has been an increasing demand for improvement in vehicle handling stability and low fuel consumption of automobiles, which started with global environmental problems. In addition, a steel cord having an elliptical cross-sectional shape perpendicular to the cord longitudinal direction has been proposed (see Patent Document 4).

That is, since the in-plane bending rigidity of the belt used for reinforcing the pneumatic tire is increased by flattening the cord with the cross-sectional shape orthogonal to the longitudinal direction of the cord being an ellipse, the handling stability of the vehicle is improved. Further, since the thickness of the belt can be reduced, the weight of the pneumatic tire can be reduced, and the reduction in fuel consumption of the vehicle is promoted.
JP-A-10-203110 Japanese Patent Laid-Open No. 9-158066 Japanese Patent Laid-Open No. 11-81168 JP-A-6-1108

  However, since the steel cord is formed by twisting a plurality of strands at the same pitch, the ratio between the short axis and the long axis in the elliptical shape is not stable in the longitudinal direction of the steel cord. This is because when a plurality of strands are twisted together, the strands constituting the outer shape of the cord and the strands constituting the inner portion of the cord occur, and an appropriate cord outer shape cannot be obtained.

  If the ratio between the short axis and the long axis of the steel cord is not uniform in the longitudinal direction, when the steel cord is applied to the tire belt, there is a portion where a gap between adjacent steel cords arranged in parallel cannot be secured. This causes a disadvantage that causes the belt to break down.

  Further, it is effective to advance the flattening of the cord for the improvement of the steering stability and the reduction in fuel consumption as described above. However, any of the above-described cords has a core portion having a strand in the axial center portion of the cord. Due to the structure, it is difficult to promote flattening. In particular, when the number of strands constituting the cord is 7 or more and flattening is promoted by assuming an open structure with a gap between the strands, a hollow portion in which no strands are arranged in the axial center portion of the cord However, even a steel cord having a structure continuous in the longitudinal direction of the cord, that is, a steel cord having a so-called single-layer open structure, has a problem that it is difficult to obtain a desired flattening.

  This is because such a steel cord has N wires (N ≧ 7) when the number of strands constituting the steel cord is N (N ≧ 7). Since a hollow portion larger than the diameter of the cord is formed, some of the strands constituting the cord enter the hollow portion inside the cord toward the inside in the cord radial direction. As a result, a cross section perpendicular to the cord axis direction becomes a steel cord that is not uniform in the cord longitudinal direction.

  Accordingly, the present invention has an object to provide a steel cord having a desired elliptical shape, in which the ratio between the short axis and the long axis in the elliptical shape is uniform in the longitudinal direction of the cord, in particular, a single-layer open structure. And

  The inventor has earnestly studied how to give a desired oval shape in a steel cord having a single-layer open structure in which seven or more strands are twisted, and has completed the present invention.

That is, the gist configuration of the present invention is as follows.
(1) A steel cord having a single-layer open structure composed of seven or more strands, having an elliptical cross-sectional shape continuous in the longitudinal direction of the cord, and the ratio of the short axis A to the long axis B in the ellipse A / B is 0.4 to 0.8, the wire diameter d is 0.12 to 0.26 mm, and the ratio a / d between the cord twist pitch a and the wire diameter d is 30 to 80. Steel cord characterized by that.

(2) The said strand is a steel cord as described in said (1) whose tensile strength is 2924-3922.66 MPa.

(3) The steel cord according to (1) or (2), wherein the steel cord is formed by elliptically shaping a steel cord having a circular cross-sectional shape perpendicular to the cord axis direction.

(4) The steel cord according to any one of (1) to (3), wherein the steel cord has a corrugated shaping shape in which an amplitude λ in the cord radial direction is λ ≦ 0.8 × long axis B.

(5) A pneumatic tire having a steel cord layer formed by coating a plurality of steel cords arranged in parallel with rubber, the steel cord layer comprising the steel cord according to (1) to (4) A pneumatic tire characterized in that its long axis is arranged in a direction along the direction of the rotation axis of the tire.

(6) A pneumatic tire having a carcass extending in a toroidal shape between a pair of bead portions and having at least one layer of belt on the outer side in the tire radial direction of the carcass. A pneumatic tire obtained by applying the steel cord according to (4).

  According to the present invention, a steel cord having a single-layer open structure composed of seven or more strands has a desired elliptical shape, thereby providing a steel cord excellent in flexibility and durability. Is possible. Furthermore, by using this steel cord for the reinforcement of a pneumatic tire, it becomes possible to provide a pneumatic tire excellent in handling stability and weight reduction.

First, a cross section perpendicular to the longitudinal direction of the cord of the steel cord according to the present invention is shown in FIG.
That is, the steel cord 1 shown in FIG. 1 has a single-layer open structure in which seven strands 2 are distributed and arranged with a gap S between the strands 2 along the cord outline. The cross-sectional shape orthogonal to the direction is an ellipse. In addition, the steel cord 1 shown in FIG. 2 has a single-layer open structure in which eight strands 2 are distributed and arranged between the strands 2 with a gap S along the cord outline, as in FIG. And the shape of the cross section perpendicular to the cord axis direction is an ellipse.

  Here, the steel cord 1 of the present invention is intended for one made of seven or more strands. This is because, in the steel cord 1 in which the number of the strands 2 is 7 or more, a part of the strands 2 constituting the steel cord 1 can enter the cavity inside the cord toward the inside in the cord radial direction. This is because it is possible to make the cord cross-sectional shape an expected ellipse while maintaining the single-layer open structure. Therefore, the steel cord 1 targeted by the present invention limits the number of constituent wires to 7 or more.

  In the present invention, the upper limit of the number of strands constituting the steel cord 1 is not particularly defined, but preferably 10. In other words, if the number exceeds 10, the amount of wire for maintaining the outer shape of the cord increases, and as a result, the cord shape may become unstable.

  As described above, the steel cord 1 of the present invention has a single-layer open structure, and it is essential that the steel cord 1 has a predetermined elliptical cross-sectional shape that will be described later, which is continuous in the longitudinal direction of the cord. That is, if the single-layer open structure is used, the axial center portion of the steel cord 1 becomes a hollow without a strand, so that a desired flat elliptical shape can be obtained. Further, since a gap is secured between the strands 2 constituting the steel cord 1, rubber can be sufficiently infiltrated from the outside of the cord to the inside of the cord during vulcanization molding. As a result, the corrosion resistance of the steel cord 1 is improved, and it is possible to suppress fretting wear that occurs due to friction between the strands.

  Furthermore, in the steel cord 1 of the present invention, a part of the strands constituting the cord 1 does not enter the hollow portion of the axial center portion of the cord 1 toward the inside in the cord radial direction. It becomes possible to maintain a predetermined elliptical shape in the cross-sectional shape orthogonal to the longitudinal direction of the cord. Therefore, when this steel cord 1 is used to reinforce the belt of a pneumatic tire, such a steel cord is arranged so that its long axis is oriented along the direction of the tire's rotational axis to reduce the thickness of the belt. Therefore, it is possible to reduce the amount of the covering rubber necessary for the belt, and it is possible to reduce the weight of the belt.

In addition, the steel cord 1 of the present invention has an intended flat elliptical shape,
Since the rigidity in the belt in-plane direction is improved under the above cord arrangement, the rigidity of the belt can be ensured.

  Here, it is important that the ratio A / B of the minor axis A and the major axis B of the elliptical shape given to the cord cross section is 0.4 to 0.8. First, when the ratio A / B is less than 0.4, the rubber permeability from the outside of the cord to the inside of the cord is improved at the time of vulcanization molding, but the long axis B becomes larger than necessary and becomes a problem. . In other words, when the steel cord 1 with the long axis B larger than necessary is used to reinforce the belt of the pneumatic tire, the number of steel cords 1 required per unit width is secured for the basic performance of the tire. I can't.

  On the other hand, if the ratio A / B exceeds 0.8, the thickness of the belt in which the cord is embedded increases, and the amount of the cord-covered rubber increases more than necessary, so the weight of the belt cannot be expected.

  Moreover, it is important that the diameter d of the strand 2 is 0.12 to 0.26 mm. That is, when the diameter d of the strand 2 is less than 0.12 mm, it becomes difficult to secure the necessary strength with respect to the basic performance of the tire, particularly the strength.

  On the other hand, when the diameter d of the strand 2 exceeds 0.26 mm, the out-of-plane bending rigidity of the belt increases, and the steering performance decreases.

  The steel cord 1 of the present invention is a steel cord in which strands having different diameters are combined, for example, a strand having a diameter d of 0.175 mm or 0.15 mm, as long as the strand diameter d is within the above-described range. Even if the steel cord is combined, the advantageous effects of the present invention can be obtained.

  And it is important that ratio a / d of the twist pitch a of the steel cord 1 and the diameter d of the strand is 30-80. That is, if the ratio a / d is less than 30, the productivity deteriorates and the cost increases.

  On the other hand, if the ratio a / d exceeds 80, the outer shape of the cord is not stable, and the strands constituting the cord are easily replaced when twisted.

  And in order for the strand 2 to ensure the strength required for a tire, it is preferable that tensile strength is 2924-3922.66 MPa.

  The steel cord 1 satisfying the above requirements is preferably produced by molding a steel cord having a circular cross-sectional shape perpendicular to the longitudinal direction of the cord into the above-mentioned predetermined elliptical shape.

  Further, in performing the above-described typing, it is preferable to perform wave-type typing in which the amplitude λ in the cord radial direction is λ ≦ 0.8 × long axis B. Here, the corrugated molding means a shape with waviness in the longitudinal direction of the cord as shown in FIG. If the amplitude λ exceeds 0.8 × the value of the long axis B, the thickness of the belt in which the cord is embedded increases and the amount of the cord covering rubber increases more than necessary. Absent.

  Incidentally, it is preferable to adjust the amplitude λ in the code molding in a molding apparatus having a gear. This apparatus can adjust the amplitude λ of the steel cord and process a circular steel cord into a predetermined ellipse. In general, the steel cord is processed into an elliptical shape through a cord between flat rolls arranged in a staggered pattern as shown in FIG. 4, but in the present invention, the gear pair 4 including the gears 4a and 4b shown in FIG. It can also be processed into an oval shape.

  That is, when a steel cord is passed between the gear pair 4 shown in FIG. 5, this steel cord is wave-shaped in the longitudinal direction of the cord and processed into an ellipse. At that time, the pitch P of each gear in the gear pair 4 is preferably 0.2a ≦ P ≦ 1.5a (a: cord twist pitch). This is because if the gear pitch is less than 0.2a, it is difficult to process the steel cord into an elliptical cross section, and it becomes difficult to obtain a desired elliptical cross section. On the other hand, if the gear pitch exceeds 1.5a, the cord properties after processing deteriorate, which is not preferable.

  Incidentally, when the cord is given a type of λ ≦ 0.8 × long axis B, when the steel cord is shaped into a wave shape and an ellipse shape with a gear, the amplitude λ is enlarged when passing through the gear. The adjustment can be made by reducing the amplitude λ through the flat roll shown in FIG.

  The above steel cords are used for reinforcing tires by applying a steel cord layer in which a plurality of steel cords are arranged in parallel to each other at predetermined intervals and embedded in a rubber sheet to a tire belt and a carcass. However, the structure of the tire may conform to a conventional tire. For example, the tire structure shown in FIG. In the figure, reference numeral 5 denotes a bead core, a carcass 6 wound around the bead core 5 from the inside to the outside of the tire, a belt 7 having at least a two-layer structure disposed on the carcass 6, and at least disposed on the belt 7 A two-layer belt reinforcing layer 8 and a pair of belt reinforcing layers 9 and 10 disposed from the end portion of the belt reinforcing layer 8 to the shoulder portion are treads disposed on the crown portion of the carcass 6.

  And it is important that said steel cord layer arrange | positions the steel cord 1 of this invention in the direction where the major axis in the elliptical cross section follows the rotating shaft direction of a tire. That is, if the steel cord 1 is arranged in a direction in which the major axis is along the tire rotation axis direction, the thickness of the belt is reduced, so that the amount of cord covering rubber can be reduced. As a result, the weight of the belt can be reduced and the weight of the tire can be reduced.

  Further, the steel cord layer according to the present invention is a steel cord having a long axis arranged in a direction along the rotation axis direction of the tire. Therefore, by applying this steel cord layer to the belt, the surface of the belt The inner bending stiffness (ability to resist deformation in the direction along the surface of each layer of the belt) increases, and the out-of-plane bending stiffness (ability to resist deformation in the direction perpendicular to the surface of the belt) decreases, and the tire As a result, the traction performance is improved and buckling is suppressed.

  Furthermore, since the bending spring constant and rebound resilience of the steel cord are small, it becomes a gentle and smooth behavior even under high speed running. As a result, the handling stability feeling felt by the driver at the time of handling operation under high speed running becomes a significant difference. The tire belt of the present invention also has high water absorption and dispersibility of external force received from the road surface, which is effective in reducing noise.

  Under the specifications of Table 1-1 and Table 1-2, various steel cords based on a flat steel cord having a single-layer open structure shown in FIG. 1 were produced. And this steel cord was used for the reinforcement of the belt, and the pneumatic tire of size 225 / 45R17 was produced. Thereafter, the pneumatic tire was used to investigate handling stability, corrosion durability, belt weight, and rubber permeability. The results are shown in Table 1-1 and Table 1-2.

  The belt structure of the pneumatic tire described above is the same structure as the tire structure shown in FIG. 6, and at least two belt reinforcing layers on the outer side in the tire radial direction of the belt in the cross section in the tire width direction shown in FIG. 8 and a pair of belt reinforcement layers 9 disposed from the end of the belt reinforcement layer 8 to the shoulder portion on the outer side in the tire radial direction of the belt reinforcement layer 8.

Steering stability is determined by attaching the pneumatic tire with the air pressure of 210 kPa to a four-wheeled passenger car as a test vehicle, and running the test vehicle on the test course by the test driver at that time. The driving stability including ride comfort was evaluated. The result was compared with the feeling result of the pneumatic tire in the prior art example 1, and it displayed on Table 1-1 and Table 1-2. The reference points for evaluation are as follows.
+3: Good +2: Somewhat good +1: Somewhat good ± 0: No change -1: Somewhat bad -2: Somewhat bad -3: Bad

  For corrosion durability, the prototype pneumatic tire was mounted on a standard rim defined in JATMA standards, filled with air pressure corresponding to the maximum load capacity in JATMA YEAR BOOK, and mounted on a passenger car. Then, after the passenger car traveled 50000 km on the paved road, it was evaluated by dissecting the pneumatic tire and investigating the corrosion length of the steel cord from the cut flaw. Here, if the corrosion length is 10 mm or less, there is no problem in durability.

The belt weight is obtained by laminating two pieces of a ply obtained by rubberizing a plurality of various cords shown in Table 1-1 and Table 1-2 under the arrangement in which the long axis of each cord is along the width direction of the belt. Thus, a steel cord ply was prepared, and its weight was measured and evaluated. At this time, the steel cord amount of all plies is made the same, and the distance between the tangent parallel to the long axis of the cord and the surface of the steel cord ply through the outer portion of the steel cord is made the same for all the steel cord plies. Thus, each steel cord ply was produced. In addition, the measurement result was displayed as an index with the weight of the ply when the steel cord of Conventional Example 1 was used as 100.

It is a figure which shows the cross section orthogonal to the cord longitudinal direction in the steel cord according to this invention. It is a figure which shows the cross section orthogonal to the cord longitudinal direction in the steel cord according to this invention. It is a figure which shows the corrugated shaping | molding shape in the steel cord according to this invention. It is a figure which shows the flat roll according to this invention. FIG. 3 shows a gear according to the invention. 1 is a cross-sectional view showing a tire structure suitable for applying a steel cord according to the present invention.

Explanation of symbols

1 steel cord 2 strand 4 gear pair 5 bead core 6 carcass 7 belt 8 belt reinforcement layer 9 belt reinforcement layer 10 tread S gap

Claims (6)

  A steel cord having a single-layer open structure composed of seven or more strands, having an elliptical cross-sectional shape continuous in the longitudinal direction of the cord, and a ratio A / B of the minor axis A and the major axis B in the ellipse 0.4 to 0.8, the wire diameter d is 0.12 to 0.26 mm, and the ratio a / d of the cord twist pitch a to the wire diameter d is 30 to 80. Steel cord.   The steel cord according to claim 1, wherein the strand has a tensile strength of 2924 to 3922.66 MPa.   The steel cord according to claim 1 or 2, wherein the steel cord is formed by elliptically shaping a steel cord having a circular cross-sectional shape orthogonal to the cord axis direction.   4. The steel cord according to claim 1, wherein the steel cord has a corrugated shaped shape in which an amplitude λ in a cord radial direction is λ ≦ 0.8 × long axis B. 5.   A pneumatic tire having a steel cord layer formed by covering a plurality of steel cords arranged in parallel with rubber, the steel cord layer comprising the steel cord according to any one of claims 1 to 4, A pneumatic tire characterized by being arranged in a direction along a rotation axis direction of the tire.   5. A pneumatic tire having a carcass extending in a toroidal shape between a pair of bead portions, and having at least one layer of belt on the outer side in the tire radial direction of the carcass, wherein the belt is provided in any one of claims 1 to 4. A pneumatic tire characterized by applying a steel cord.

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