JP2007023402A - Steel cord and pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel cord having improved corrosion resistance durability and uniform cord form in axial direction and satisfying the requirements of tire such as light weight and low cost and provide a pneumatic radial tire produced by using the cord. <P>SOLUTION: The steel cord 1 has a 2+1 structure composed of a single filament 13 spirally wound around two filaments 11, 12 paralleled in non-twisted state. These filaments 11, 12, 13 are arranged in a manner to position the center O1 of the circumscribing circle S in the cord axis direction of the steel cord constantly on a nearly straight line L in the cord axis direction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a steel cord and a pneumatic radial tire, and more specifically, a steel cord excellent in weight reduction effect and fatigue resistance while improving rubber penetration, which is mainly used as a reinforcing material for belts and sidewalls of radial tires, Further, the present invention relates to a pneumatic radial tire that is lighter and more durable using the steel cord.

  A pneumatic radial tire generally has a belt in which a plurality of belt plies made of steel cord are crossed and laminated with a tread rubber on a carcass outer peripheral side of a tread portion.

  Conventionally, steel cords used for belt plies of passenger car tires are generally 1 × n structure (n = 3 to 5), but from tread damage and cracks in 1 × n structure steel cords. In order to prevent belt failure due to moisture intrusion, 1 × n structure (Patent Document 1) in which the filament is excessively typed and twisted loosely, and the filament is wound spirally around the aligned filament bundle Many steel cords having improved rubber penetration such as m + n structure, for example, 2 + 2, 2 + 1 structure (Patent Document 2) have been disclosed to improve tire durability.

However, in recent years, pneumatic radial tires, especially passenger car tires, have strong market demands such as further weight reduction, improved ride quality, and lower prices in addition to the above-mentioned improvement in durability. There is an urgent need to develop a steel cord that can handle the above.
JP-A-6-330486 Japanese Examined Patent Publication No. 2-29408

  However, if the filament is over-typed, the twisting of the cord becomes loose and the elongation in the low-load region increases, so that the cord tension in the topping process can be managed and the unevenness on the surface of the topping sheet As a result, the workability in the tire manufacturing process is adversely affected, and the topping sheet becomes thicker against the weight reduction.

  In addition, the steel cord of the m + n structure has a large cord diameter as a result of the cord cross-sectional shape becoming asymmetric because the n filaments are wound around the M untwisted aligned filament bundle and the cord surface is uneven in the cord axial direction. The rubber penetration is good and the elongation characteristics in the constant load range are good, but the rubber coating thickness increases due to the increase in the amount of rubber used, which is disadvantageous in terms of weight reduction and cost of the tire, and the cross section is asymmetrical. It has the disadvantage of being inferior in fatigue, and none of them has fully satisfied the above required performance.

  The present invention has been made in view of such a situation, and by making the steel cord rubber penetrated, the durability of the tire, in particular, the corrosion resistance durability due to the damage of the belt portion is improved, and the shape in the cord axis direction is made uniform. Accordingly, it is an object of the present invention to provide a steel cord capable of satisfying demands for weight reduction and price reduction of a tire, and a pneumatic radial tire using the steel cord as a reinforcing material.

  The steel cord of the present invention is a steel cord having a 2 + n structure (1 ≦ n ≦ 7) in which n filaments are spirally wound around two filaments arranged in a non-twisted manner. Each filament is arranged so that the center of the circumscribed circle in the cord axis direction is always positioned substantially in a straight line in the cord axis direction.

  In the steel cord of the present invention, the two untwisted filaments are spirally shaped around the cord axis while being in contact with each other in parallel, and the shaping rate of the helical amplitude is 150 ± 5%. As a result, the surface shape in the cord axis direction can be made uniform and the cord diameter can be reduced.

  The pneumatic radial tire of the present invention is characterized by using the steel cord as a reinforcing material.

  According to the steel cord of the present invention, by adopting a 2 + n structure, rubber penetration into the cord is ensured and the corrosion resistance durability of the tire is improved, and a spiral swell is imparted to two parallel filaments to thereby provide a cord surface. The surface of the cord in the direction of the cord axis is made uniform by reducing the unevenness of the cord, improving the fatigue fatigue and reducing the cord diameter and reducing the thickness of the coated rubber (the amount of rubber used). And cost reduction.

  FIG. 1 shows a side view of a steel cord 1 according to an embodiment of the present invention, and a cross-sectional view of a cord taken along lines A, B, C, D, and A for each 1/4 pitch P.

  The steel cord 1 is a steel cord having a 2 + 1 structure in which a single filament 13 is spirally wound around two filaments 11 and 12 that are arranged without twisting.

  As shown in the figure, the steel cord 1 is provided with a spiral type with a pitch P and a predetermined amplitude while keeping two filaments 11 and 12 arranged in a non-twisted manner in parallel with each other. A single filament 13 is wound around the parallel filaments 11 and 12 at a pitch P along the spiral undulation.

  The steel cord according to the present invention employs a steel cord generally represented by a 2 + n structure such as a 2 + 2, 2 + 3 to 2 + 7 structure in addition to the 2 + 1 structure, thereby ensuring rubber penetration. Here, n is 1 ≦ n ≦ 7, and when n = 8 or more, since many filaments are wound around two parallel filaments, rubber penetration into the cord becomes difficult. In order to ensure penetration, it is preferably 6 or less. In addition, the core of the cord is made of two filaments. With one filament, the load on the filament becomes large and the fatigue resistance is lowered. This is because corrosion resistance cannot be ensured. In general, filaments having the same diameter are preferably used.

  Thereby, in the steel cord 1, the filaments 11 and 12 are substantially vertical in the A and C lines, as shown in the figure, as the cross-sectional shape of the cords in the A, B, C, D, and A lines every 1/4 pitch with respect to the pitch P. The filaments 13 are arranged in a substantially horizontal position, and the three filaments 11, 12, 13 are arranged in a substantially vertical direction on the B and D lines, and this filament arrangement is arranged at every pitch. It will be repeated periodically. As a result, an open portion is formed between the two parallel filaments 11 and 12 and the surrounding filament 13 so that the rubber sufficiently penetrates in the direction of the cord axis. Prevents penetration in the direction and improves corrosion resistance.

  Here, as shown in the enlarged cross-sectional view of the steel cord 1 in FIG. 2, the cord 1 is arranged such that the center O1 of the circumscribed circle S in the cord axis direction is always located substantially on the straight line L in the cord axis direction. Yes. That is, the center O1 of the circumscribed circle of the steel cord 1 and the axial center (= L) of the cord 1 substantially coincide.

  In this case, when the untwisted two parallel filaments 11 and 12 are spirally shaped around the center O1 (= cord axis L) of the circumscribed circle of the cord, the amplitude shaping rate is 150 ± 5%. The center O1 and the cord axis L can be accurately matched within an allowable range of ± 5% to ensure uniform surface shape in the cord axis direction and reduce the cord diameter D1.

  Further, the steel cord 1 can obtain the symmetry of the cross-sectional shape of the cord with respect to the cord axis by the above configuration, and can particularly improve the fatigue resistance against bending. Furthermore, by providing spiral undulations to the parallel filaments 11 and 12, it is possible to relax compression and tensile stress and improve fatigue resistance. It can absorb the impact of time and prevent the cord from breaking.

  Here, as shown in FIG. 4, the mold rate is the ratio of the maximum amplitude Hr, Wr and the filament diameter d in the vertical and horizontal directions of the amplitude of the filament whose spiral cross section is molded into an elliptical shape R, Hr Expressed as a percentage of / d and Wr / d.

  On the other hand, in the steel cord 2 having the conventional 2 + 1 structure shown in FIG. 3, the two filaments 21 and 22 aligned without twisting are molded at a molding rate of about 100 to 120%. When the molding rate shown in the figure is 100%, the contact point X of the two filaments 21 and 22 is arranged on the substantially same straight line L, that is, the center O2 of the circumscribed circle of the steel cord 2 and the cord axis The center (L in this case) matches and does not match in the longitudinal direction. For this reason, the degree of irregularities of the filament on the cord surface is increased, and as a result, the cord diameter D2 is increased, and the thickness (use amount) of the topping rubber at the time of rubber coating is increased, resulting in an increase in tire weight and cost. Become.

  Therefore, according to the steel cord 1 of the present invention, when the steel cord is covered with rubber, the rubber can be thinned by the difference ΔD (= D2−D1) between the cord diameters D1 and D2, that is, the amount of rubber used. This makes it possible to reduce tire weight and cost.

  In addition, the conventional 2 + 1-structured cord 2 has a shape that is asymmetric in cross section with respect to the cord axis L (B and D line portions), and therefore, the tendency to be inferior in bending fatigue resistance is unavoidable. The two aligned filaments 21 and 22 are almost linear, which is disadvantageous for fatigue resistance.

  In practicing the present invention, the diameter of the filament used in the steel cord is preferably 0.20 to 0.38 mm, and if the filament diameter is less than 0.20 mm, the cord strength and belt rigidity are insufficient and the steering is performed. Stability and rolling resistance become insufficient, and if it exceeds 0.38 mm, it becomes too rigid and ride comfort and fatigue resistance are lowered. The filament diameter and the number of n can be appropriately selected and used according to the tire size, application, and use site in the tire.

  Further, the pitch of the spiral type forming of the two untwisted filaments, that is, the twist pitch P of the cord is preferably about 30 to 60 times the filament diameter, and if the pitch P is less than 30 times, the spiral shape Molding becomes difficult and code productivity decreases, and if it exceeds 60 times, fatigue resistance is impaired, which is not preferable.

Furthermore, by using a high-strength steel cord with a filament strength of 2800 to 3400 N / mm ² , the amount of cord used corresponding to the increase in strength can be reduced compared to the conventional 2500 to 2600 N / mm ² grade steel cord. This will further promote weight reduction of the tire. If the strength is less than 2800 N / mm ² , the effect of reducing the weight is not sufficiently obtained, and if it exceeds 3400 N / mm ² , fatigue resistance is impaired due to deterioration of filament drawing workability and brittleness reduction due to strong working, Even if such a problem does not occur, if the cord usage is reduced too much, the rigidity of the steel belt will be reduced, which will affect the tire characteristics such as steering stability and rolling resistance. There is a risk of deviating from the object of the present invention. Of course, a conventional steel cord of 2500 to 2600 N / mm ² grade can be used.

  The steel cord 1 of the present invention can be manufactured using, for example, a buncher type twisted wire machine 20 shown in FIG. In the twisting machine 20, guide rollers 22, 23, 24, and 25 are provided on the center axis of rotation of the twisting machine main body 21, and a disk roller that rotates in the same manner as the guide roller outside the rotation axis. Arcuate loops 26, 27 with 26a, 26b and 27a, 27b are provided. A filament supply bobbin 28 that keeps a fixed position regardless of the rotation of the main body is disposed in the main body 21 of the twisted wire machine, and molding devices 29 and 30 that give the filaments a mold are provided. Two filament supply bobbins 31 a and 31 b and a winding bobbin 32 for winding a cord are provided outside the stranded wire main body 21.

  When the steel cord 1 is manufactured, the two filaments 11 and 12 that form a non-twisted and aligned bundle are drawn out from the bobbins 31a and 31b and introduced into the main body 21 of the twisted wire, and the guide roller 22 → the disk roller 26a → the disk roller. 26 b → guide roller 23 → molding device 29 → guide roller 24 → disk roller 27a → disk roller 27b → guide roller 25 and then wound around the winding bobbin 32.

  On the other hand, the winding filament 13 is pulled out from the bobbin 28, passes through the shaping device 30 → the guide roller 24 → the disk roller 27 a → the disk roller 27 b → the guide roller 25, and is wound around the winding bobbin 32.

  The winding bobbin 32 rotates with the disk rollers 26a, 26b, 27a, 27b rotating on the loop while the two loops 26, 27 rotate at the same time as the main body 21 rotates. 1 is continuously wound up.

  In the above process, the filaments 11 and 12 drawn from the bobbins 31 a and 31 b are twisted in one direction before passing through the guide roller 22, the disk rollers 26 a and 26 b, and the guide roller 23. When passing through, the molding is performed in a spiral shape with a molding rate of 150%.

  On the other hand, when the filament 13 drawn out from the bobbin 28 passes through the shaping apparatus 30, the filament 13 is shaped at the same pitch as that of the spiral and is drawn to the filaments 11 and 12. Since the two filaments 11 and 12 are twisted back in the opposite direction while passing through the guide rollers 24 and 25, the filaments 11 and 12 are in a non-twisted state in which only a dampening by the shaping device 29 remains. The filament 13 is wound around the two parallel filaments 11 and 12 while passing through the guide rollers 24 and 25, and is wound around the bobbin 32 as a steel cord 1 having a 2 + 1 structure. The steel cord 1 of the present invention can be manufactured not only with a buncher type twisting machine but also with a tubular type twisting machine.

  The pneumatic radial tire of the present invention uses the steel cord as a reinforcing material, and includes various belt belts for passenger car tires, side reinforcing layers, belts for large tires such as trucks and buses, and chafers. It can be used as a reinforcing member for a part, and can improve fatigue resistance while ensuring rubber penetration, contributing to weight reduction and cost reduction of the tire.

  Hereinafter, the present invention will be specifically described by way of examples.

Use three filaments with a strength of 3000 N / mm ² and a diameter of 0.27 mm. It was made using. The production conditions and cord diameter are shown in Table 1. The cord diameter is measured according to JIS G3510.

  Next, toppings were produced using a calender device with a steel cord of 19 pieces / 25 mm driven, a rubber coating thickness above and below the cord being constant, and a counter width of 1 m. This topping is applied to the belt ply (cutting angle 21 °, 2 ply), and the carcass ply is a polyester cord 1670 dtex / 2, and the number of drivings 24/25 mm is one ply and the size is 215 / 60R16 passenger car. Tires were manufactured and evaluated as follows. The results are shown in Table 1.

[Topping anti-weight]
A sample was taken from the center in the width direction of the topping, and the weight was measured to determine the weight per unit area. Each of the conventional examples is indicated by an index of 100. The smaller the index, the lighter the weight.

[Tire weight]
Ten tires each using the topping anti-belt as a belt ply were randomly selected, their weights were measured, and the average value was taken as the tire weight. Each of the conventional examples is indicated by an index of 100. The smaller the index, the lighter the weight.

[Tire durability]
Each tire is adjusted to an air pressure of 100 kPa using a specified rim, and is run for 5000 km with a drum tester at a load of 400 kg and a speed of 60 km / h. did. The total number of ruptures for each of the two tires was obtained and indicated by an index with the conventional example being 100. The smaller the value, the better the durability.

[Rough road durability]
Drill holes of 5mmφ reaching the belt ply at four places on the circumference of each tire, adjust the air pressure to 200kPa using a specified rim, and install it on a domestic FF vehicle (displacement 2000cc), including gravel roads and muddy water paths After traveling 5000 km on the road test course, the tread portion was disassembled and examined for the occurrence of belt separation around the drill hole.

  As shown in Table 1, the steel cords of the examples can reduce the amount of rubber used by making the cord surface shape uniform and reducing the cord diameter, and can reduce tire weight and rubber material costs. . Further, the durability of a tire using the steel cord can be improved by improving the fatigue resistance of the steel cord. On the other hand, in Comparative Examples 1 and 2 in which the molding rate deviates from 150 ± 5%, the reduction in the cord diameter is small and the effect of reducing the weight is insufficient. In addition, the bad road durability of each tire is excellent due to the effect of rubber penetration into the cord by the 2 + 1 structure.

  As described above, the steel cord according to the present invention is suitably used as a reinforcing material for a pneumatic radial tire, such as a belt and a sidewall, and enables weight reduction, cost reduction, and improvement in durability. Of course, it can also be used as a reinforcing material for various rubber products such as crawlers other than tires, conveyor belts, high-pressure hoses, and anti-vibration rubbers.

It is the side view of the steel cord of an Example, and sectional drawing for every 1/4 pitch. It is sectional drawing for every 1/4 pitch which the steel cord same as the above expanded. It is sectional drawing for every 1/4 pitch which the conventional example steel cord expanded. It is explanatory drawing explaining a typing rate. It is explanatory drawing which shows an example of the manufacturing apparatus of an Example steel cord.

Explanation of symbols

1 …… Steel cord 11,12 …… Parallel filament 13 …… Wound filament L …… Straight line O1 …… Center of circumscribed circle S …… Circle circumscribed circle

Claims (3)

In a steel cord having a 2 + n structure (1 ≦ n ≦ 7) in which n filaments are spirally wound around two filaments arranged in an untwisted manner,
The steel cord is characterized in that each filament is arranged so that the center of a circumscribed circle in the cord axis direction of the steel cord is always in a substantially straight line in the cord axis direction. The untwisted two filaments are spirally molded around the cord axis while contacting in parallel with each other, and the rate of spiral amplitude molding is 150 ± 5%. The steel cord according to 1. A pneumatic radial tire using the steel cord according to claim 1 or 2 as a reinforcing material.

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