JP2012219389A - Steel cord and pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel cord which meets a requirement for light weight tire while improving durability and to provide a pneumatic radial tire using the same.SOLUTION: A steel cord comprises two first filaments 11, 12 with the same diameter that are bundled without twist and n second filaments 13 spirally wound by the second filament 13 around the circumference of the first filaments so as to form 2+n structure (1≤n≤5), in which the first filaments 11, 12 are preformed in a spiral shape with the same pitch P as the spiral winding of the second filaments 13 so that a preforming rate, which is represented by the percentage of a ratio Hr/d, is set to 200±25% where d represents a diameter of the first filament and Hr represents a maximum width in a cross section of the spiral width. Each filament 11,12,13 is arranged so that the centers O1 of the circumscription circle S are always aligned approximately in a straight line L in a cord axis direction and a cord diameter is 0.75 mm or less.

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 formed by laminating a plurality of belt plies made of steel cords with the cords crossed between the tread rubber on the outer side of the carcass of the tread portion. . In recent years, pneumatic radial tires, especially passenger car tires, have strong market demands such as lighter weight, improved ride comfort, and lower prices. In response, the trend of simplifying steel cords used for belt layers has accelerated. is doing.

  Conventionally, a steel cord used for a belt ply of a tire for a passenger car is generally a 1 × n structure (n = 3 to 5), but the 1 × n structure steel cord constitutes the cord. Since the distance between the strands, that is, the filaments is narrow, the permeability of the rubber is deteriorated, and the progress of the corrosion of the steel cord due to the penetration of moisture is unavoidable, resulting in a problem that the durability is lowered. For this reason, a steel cord having an m + n structure, for example, a 2 + n structure, in which filaments are spirally wound around the aligned filament bundle is used for the belt ply.

  However, in the conventional 2 + n structure, the center of the cord circumscribing circle is not arranged in a straight line in the cord axis direction, so that the cord diameter becomes large and the topping sheet when the rubber is coated becomes thick, which reduces the weight. It was difficult to reduce the price.

  Specifically, in the conventional steel cord 2 having a 2 + 1 structure shown in FIG. 6, two filaments 21 and 22 aligned without twisting are molded at a molding rate of about 100 to 120%. In this case, the contact point X of the two filaments 21 and 22 is arranged on the substantially same straight line L, so that the center O2 of the circumscribed circle of the steel cord 2 and the cord axis L are matched or mismatched in the longitudinal direction. Will repeat. For this reason, the degree of unevenness of the filament on the cord surface is increased, and as a result, the outer diameter D2 of the cord is increased and the rubber thickness (amount of use) at the time of rubber coating is increased. It will be a thing. In addition, the conventional 2 + 1-structured cord 2 has a shape that is asymmetric in cross section with respect to the cord core L (B and D line portions), and therefore tends to be inferior in bending fatigue resistance. The two filaments 21 and 22 aligned in the above are almost linear, which is disadvantageous for fatigue resistance.

  In order to solve such a problem, Patent Document 1 below discloses that an untwisted first wire bundle is spiraled in the longitudinal direction in an N (N = 2 to 5) + M (M = 1 to 3, N ≧ M) structure. A steel cord is disclosed in which a second wire bundle is wound around the bundle and the center of the circumscribed circle of the cord lies on a substantially straight line. However, in this document, the first wire bundle serving as the core is configured by three or four filaments as a specific example, and in that case, a gap through which rubber cannot enter the center of the first wire bundle This causes a problem if the corrosion resistance cannot be ensured. Further, the cord diameter is large, and the recent demand for further weight reduction has not been fully satisfied.

  On the other hand, in the following Patent Document 2, in the steel cord having a 2 + n structure in which n filaments are spirally wound around two filaments arranged in a non-twisted manner, the center of a circumscribed circle in the cord axis direction is There is disclosed a structure in which each filament is arranged so as to be always in a substantially straight line in the cord axis direction. However, in this document, the rate of forming the helical amplitude in the two untwisted filaments is set to 150 ± 5%, and it cannot be said that the diameter of the cord is sufficiently small. It is as large as 83 mm, and has not fully satisfied the recent demand for further weight reduction.

JP 2001-098480 A JP 2007-023402 A

  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, an object of the present invention is to provide a steel cord that can satisfy the demand for reducing the weight of a tire, and a pneumatic radial tire using the steel cord as a reinforcing material.

  The steel cord according to the present invention has a 2 + n structure (1 ≦ n ≦ 5) in which n second filaments are spirally wound around two first filaments of the same diameter that are aligned without twisting. In the steel cord, the two untwisted first filaments are spirally shaped at the same pitch as the spiral winding of the n second filaments, and the first filament with respect to the diameter of the first filament The mold rate expressed as a percentage of the maximum width ratio in the cross section of the spiral amplitude of one filament is 200 ± 25%, and the center of the circumscribed circle in the cord axis direction of the steel cord is always almost in the cord axis direction. The first filament and the second filament are arranged so as to be positioned on a straight line, and the cord diameter is 0.75 mm or less.

  The pneumatic radial tire according to 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 the 2 + n structure, it is possible to ensure rubber intrusion into the cord and improve the corrosion resistance durability of the tire. In addition, by providing spiral undulations by the above-mentioned specific shaping to the two untwisted first filaments, it is possible to reduce the irregularities on the cord surface and to make the surface shape uniform in the cord axis direction. Fatigue can be improved. Furthermore, by making the cord diameter smaller than before, the thickness of the covering rubber (the amount of rubber used) can be reduced, and the weight and cost of the tire can be reduced.

It is a side view of the steel cord concerning one embodiment of the present invention. It is sectional drawing for every 1/4 pitch of the steel cord. It is explanatory drawing for demonstrating a typing rate. It is explanatory drawing which shows typically an example of the manufacturing apparatus of the steel cord. It is sectional drawing for every 1/4 pitch of the steel cord concerning other embodiments. It is sectional drawing for every 1/4 pitch of the steel cord of a prior art example.

  Embodiments of the present invention will be described below with reference to the drawings.

  As shown in FIGS. 1 and 2, the steel cord 1 according to the embodiment spirals one second filament 13 around the two first filaments 11 and 12 arranged in a non-twisted manner. It is a 2 + 1 structure steel cord that is wound.

  Here, in the steel cord according to the present invention, a steel cord structure represented by a 2 + n structure (1 ≦ n ≦ 5) such as a 2 + 2, 2 + 3, 2 + 4, and 2 + 5 structure is adopted in addition to the 2 + 1 structure. Also good. By constituting the first filament as the core in this way, the rubber penetration into the cord is excellent. That is, when there are three or more first filaments that serve as the core, a gap that does not allow rubber to enter the central portion of the core occurs, and the corrosion resistance is impaired. On the other hand, when the number of the first filaments as the core is one, the load applied to the core filament is increased and the fatigue resistance is lowered. Therefore, the number of the first filaments can be improved by using two. In addition, with respect to the second filament wound around the first filament, when n = 6 or more, many filaments are wound around the two first filaments, so that the rubber penetration into the cord becomes difficult. . The number of second filaments is preferably 4 or less, more preferably 1 or 2.

  In the steel cord 1 according to the present embodiment, the two first filaments 11 and 12 having the same diameter, that is, having the same filament diameter d are used. Also for the second filament 13, those having the same diameter as that of the first filaments 11 and 12 are usually used. That is, the steel cord 1 is preferably composed of filaments 11, 12 and 13 having the same diameter.

  The two first filaments 11 and 12 aligned without twisting are spirally molded at the same pitch P as the spiral winding of the single second filament 13. Specifically, the two first filaments 11 and 12 are spirally shaped with a predetermined pitch P and amplitude while being in contact with each other in parallel and maintaining the contact state. A second filament 13 is wound around the two first filaments 11 and 12 at the same pitch P as described above.

  The two first filaments 11 and 12 aligned in parallel are spirally shaped around the cord axis L. In this example, the first filaments 11 and 12 are molded so that the spiral cross-sections thereof are elliptical (ellipsoidal), and the helical amplitude has a molding rate of 200 ± 25% (that is, 175). ˜225%).

  Accordingly, as shown in FIG. 2, the steel 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. That is, the first and second filaments 11, 12, and 13 are arranged so that the center O1 of the circumscribed circle S of the steel cord 1 and the axis L of the steel cord 1 substantially coincide.

  In this example, the steel cord 1 has the first filament in the A and C lines, as shown in FIG. 11 and 12 are arranged in a substantially vertical direction, and a second filament 13 is arranged at a side (that is, a horizontal position) at an intermediate position in the vertical direction, and the three filaments 11, 12, and 13 are mutually connected. It arrange | positions in the triangle shape which contacts two other filaments. In the B and D lines, three filaments 11, 12, and 13 are arranged in a line in a substantially vertical direction. And such a filament arrangement is configured to be repeated periodically for each pitch P. As a result, an open portion is formed between the two first filaments 11 and 12 and the surrounding second filament 13 so that the rubber sufficiently penetrates in the direction of the cord axis. Can be prevented from penetrating in the direction of the cord axis and corrosion fatigue resistance can be improved.

  Here, the molding rate is a percentage of the ratio of the maximum width in the cross section of the spiral amplitude of the first filament to the diameter of the first filaments 11 and 12. As described above, when the spiral cross section of each of the first filaments 11 and 12 is elliptical, as shown in FIG. 3, the vertical direction of the filament F in the helical cross section forming the elliptical R (that is, Of the amplitude Hr in the vertical direction and the amplitude Wr in the left-right direction (that is, in the horizontal direction), the larger amplitude is set as the maximum width (Hr in the illustrated example), and the ratio between this and the filament diameter d, that is, Hr / Expressed as a percentage of d.

  In the steel cord 1 of the present embodiment, the mold rate of the first filaments 11 and 12 is 200 ± 25% as described above, and the center O1 of the circumscribed circle S in the cord axis direction is along the cord axis L. As shown in FIG. 2, the apparent outer diameter D1, which is the maximum diameter in the spiral cross section of the second filament 13, is reduced by arranging the steel cord 1 on a substantially straight line. Therefore, the diameter of the steel cord 1 can be reduced. it can. In addition, it is preferable that the molding rate of the first filaments 11 and 12 is 200 ± 15% in order to reduce the tire weight by further reducing the diameter and to improve the durability.

  In the present embodiment, the cord diameter of the steel cord 1 is set to 0.75 mm or less by the above-described filament arrangement including the setting of the molding rate, and the diameter is further reduced as compared with the conventional case. When the cord diameter exceeds 0.75 mm, the effect of reducing the weight of the tire is insufficient. The cord diameter is more preferably less than 0.70 mm. The lower limit of the cord diameter is not particularly limited, but is usually 0.50 mm or more. Here, the cord diameter is measured according to JIS G3510 (micrometer method), and the diameter at two points in the vicinity of the center excluding the end in the cord axis direction is measured in two directions at right angles. The average value of the values obtained is taken as the cord diameter.

  Therefore, in the case of the steel cord 1 according to the present embodiment, when the rubber cord is applied and used, the thickness of the coated rubber can be reduced by the small cord diameter, thereby reducing the amount of the coated rubber used. This makes it possible to reduce the weight and cost of the tire.

  Further, in the steel cord 1 according to the present embodiment, as shown in FIG. 2, the two untwisted first filaments 11 and 12 are provided with spiral swells by the above-described specific shaping, as shown in FIG. The unevenness on the surface can be reduced, and the surface shape in the cord axis direction can be made uniform. That is, the symmetry of the cord cross-sectional shape with respect to the cord axis line can be obtained, and in particular, the fatigue resistance against bending can be improved. Further, the spiral swell is imparted to the first filaments 11 and 12 serving as the core, so that the compression and tensile stress can be relieved and the fatigue resistance can be improved. It can absorb the impact when stepping on the object and prevent the cord from breaking.

  The diameter of the filament used in the steel cord 1 according to this embodiment, that is, the filament diameter d is preferably 0.20 to 0.32 mm. When the filament diameter d is less than 0.20 mm, the cord strength and belt rigidity are insufficient, and the steering stability and rolling resistance may be insufficient. On the other hand, if it exceeds 0.32 mm, it is difficult to reduce the cord diameter, and the steel cord becomes too rigid, which may reduce ride comfort and fatigue resistance. The filament diameter d is more preferably 0.23 to 0.30 mm.

  Moreover, it is preferable that the pitch P of the spiral type | molding of two untwisted 1st filaments, ie, the twist pitch P of a cord, is about 30 to 80 times the filament diameter d. If the pitch P is less than 30 times the filament diameter, it is difficult to form a spiral shape and the cord productivity may be reduced, and if it exceeds 80 times, fatigue resistance may be impaired. More preferably, it is about 30 to 60 times the filament diameter.

Further, the filament used in the steel cord 1 is preferably a high strength steel cord having a strength (ie, tensile strength) of 2800 to 3400 N / mm ² , so that the conventional steel of 2500 to 2600 N / mm ² is used. The cord usage corresponding to the increase in strength can be reduced with respect to the cord, and the weight reduction of the tire can be further promoted. 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 the wire drawing workability of the filament and brittleness reduction due to strong working, which is not preferable. Even if such a problem does not occur, if the cord usage is reduced too much, the rigidity of the steel belt may be reduced, which may affect the tire characteristics such as steering stability and rolling resistance. Of course, a conventional steel cord of about 2500 to 2600 N / mm ² can also be used.

  The steel cord 1 of the present embodiment can be manufactured using, for example, a buncher type twisting 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 single filament supply bobbin 28 for supplying the second filament 13 is disposed in the stranding machine main body 21 regardless of the rotation of the main body, and the first and second filaments 11, Molding devices 29 and 30 are provided to give the molds 12 and 13 a typing. Further, two filament supply bobbins 31 a and 31 b for supplying the first filaments 11 and 12 and a winding bobbin 32 for winding the cord are provided on the outside of the main body 21 of the strand wire machine.

  When the steel cord 1 is manufactured, the two first filaments 11 and 12 that are untwisted and aligned bundles are drawn out from the bobbins 31a and 31b and introduced into the main body 21 of the stranding machine, and the guide roller 22 → the disk roller 26a → The disk passes through the disk roller 26b → guide roller 23 → molding device 29 → guide roller 24 → disk roller 27a → disk roller 27b → guide roller 25 and is wound on the winding bobbin 32.

  On the other hand, the second filament 13 for winding 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 first filaments 11 and 12 drawn out from the bobbins 31a and 31b are twisted in one direction before passing through the guide roller 22, the disk rollers 26a and 26b, and the guide roller 23. When passing through the device 29, the mold is formed in a spiral shape with a mold rate of 200 ± 25%.

  On the other hand, when the second filament 13 drawn out from the bobbin 28 passes through the shaping apparatus 30, the second filament 13 is shaped at the same pitch as that of the spiral and is drawn to the first filaments 11 and 12. Since the two first filaments 11, 12 are twisted back in the opposite direction while passing through the guide rollers 24, 25, the first filaments 11, 12 are non-twisted so that the molding device 29 remains with a mold. It becomes a state. The second filament 13 is wound around the two first 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 can of course be manufactured not only with a buncher type twisting machine but also with a tubular type twisting machine.

  FIG. 5 shows a steel cord 15 according to another embodiment. In this example, a 2 + 2 structure is formed in which two second filaments 13 and 14 are spirally wound around two first filaments 11 and 12 that are aligned without twisting.

  The two first filaments 11, 12 that are aligned in a non-twisted manner are spirally molded at the same pitch P as the spiral winding of the two second filaments 13, 14, and are the same as in the above embodiment. The mold rate of the helical amplitude of each of the first filaments 11 and 12 is set to 200 ± 25%, so that the center O1 of the circumscribed circle S in the cord axis direction is always almost on the straight line L in the cord axis direction. The cord diameter of the steel cord 15 is 0.75 mm or less.

  Specifically, in this example, the steel cord 15 has a cross-sectional shape of the cords at lines A, B, C, D, and A for each quarter pitch with respect to one pitch P as shown in FIG. The first filaments 11 and 12 are arranged in a substantially vertical direction, and are adjacent to the side thereof (that is, adjacent to the horizontal position of each of the first filaments 11 and 12). , 14 are arranged in a substantially vertical direction, and four filaments 11, 12, 13, 14 are arranged in a square shape. In the B and D lines, the two first filaments 11 and 12 are arranged in a substantially vertical direction, and the two second filaments 13 and 14 are arranged in a substantially horizontal direction on either one of the upper and lower sides thereof. Has been. And such a filament arrangement is configured to be repeated periodically for each pitch P.

  In this example, the two untwisted first filaments 11 and 12 spirally molded around the cord axis L have a perfect circular shape whose cross section is not an ellipse, The mold rate of the helical amplitude is set to 200 ± 25% (that is, 175 to 225%). In this case, since the spiral cross-sectional shape of the first filaments 11 and 12 is a circular shape, the maximum width in the cross-section of the helical amplitude when obtaining the above-described shaping rate is the diameter of the circular shape.

  Since the other configurations and functions and effects of the other embodiment shown in FIG. 5 are the same as those of the above-described embodiment shown in FIGS.

  The pneumatic radial tire of the present embodiment uses the steel cord 1 as a reinforcing material, such as a belt for passenger car tires, a side reinforcing layer, a belt for large tires for trucks and buses, and a chacher. It can be used as a reinforcing member for various applications and parts, 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.

Steel cords of Examples, Comparative Examples, and Conventional Examples are manufactured according to the conditions shown in Table 1 below using a filament having a strength of 3000 N / mm ² and a diameter of 0.27 mm, or a filament having a strength of 3100 N / mm ² and a diameter of 0.25 mm. did.

  Specifically, in Examples 1 to 3, Comparative Examples 1 and 2 and the conventional example, three filaments having a diameter of 0.27 mm were used, and the molding rate of two untwisted filaments was changed to be 2 + 1 × 0. Each steel cord having a .27 structure was produced using a buncher type twisted wire machine. In Examples 4 and 5 and Comparative Examples 3 and 4, four filaments having a diameter of 0.25 mm were used, and each steel cord having a structure of 2 + 2 × 0.25 was changed by changing the molding rate of two untwisted filaments. Was produced using a buncher type twisted wire machine. In Comparative Example 5, three filaments having a diameter of 0.27 mm were collectively twisted by a buncher type twisting machine to produce a steel cord having a 1 × 3 structure.

  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 was applied to a belt ply (cutting angle 25 °, 2 plies) to produce a passenger car pneumatic radial tire of size 215 / 65R16. As a common configuration of each tire, the carcass ply has a polyester cord of 1670 dtex / 2, a driving number of 24/25 mm and two plies, and as a belt reinforcing layer, nylon 66 fiber 940 dtex / 2, a driving number of 34/25 mm, A driving angle of 0 ° was provided.

  The steel cord and tire test evaluation method is as follows.

[Filament diameter, cord diameter]
It is an average value of values obtained by measuring the diameters at two arbitrary points near the center of the sample in two directions at right angles according to JIS G3510. The difference in cord diameter is the difference in cord diameter with respect to the conventional example.

[Moulding height (maximum diameter Hr in the section of spiral amplitude of the first filament)]
It is an average value obtained by measuring the height of one pitch crest and valley using a metal projector and measuring five pitches.

[pitch]
Measured according to JIS G3510 (trace method).

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

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

[Tire durability]
Each tire was adjusted to an air pressure of 100 kPa using a specified rim, and was run for 5000 km with a drum tester at a load of 3.92 kN and a speed of 60 km / h, and then the belt portion of the tire was X-rayed to determine the number of belt cord breaks. It was measured. 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]
Drilled 5mmφ drill holes reaching the belt ply at four locations on the circumference of each tire, adjusted to an air pressure of 200kPa using a specified rim and mounted on a domestic FF vehicle (displacement of 2000cc), and tested for bad roads including gravel roads After traveling 5000 km on the course, the tread part was disassembled and examined for the occurrence of belt separation around the drill hole.

  The results are shown in Table 1, and 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, reducing the weight of the tire and saving rubber material costs. We were able to. Moreover, the durability of the tire could be improved while reducing the weight by improving the fatigue resistance of the steel cord. Furthermore, the rough road durability was excellent due to the effect of rubber penetration into the cord by the 2 + 1 structure or the 2 + 2 structure.

  On the other hand, in Comparative Examples 1 to 4 in which the molding rate deviated from 200 ± 25%, the effect of reducing the cord diameter was not obtained, and the weight reduction of the tire was insufficient. In Comparative Example 5 having a 1 × 3 structure, although the weight was reduced, the effect of improving the durability was small and the poor road durability was poor.

  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 rollers other than tires, conveyor belts, high-pressure hoses, and anti-vibration rubber.

1, 15 ... Steel cords 11, 12 ... First filaments 13, 14 ... Second filament L ... Straight line (cord axis)
O1 …… Center of circumscribed circle S …… circumscribed circle of code

Claims (2)

In a steel cord having a 2 + n structure (1 ≦ n ≦ 5) in which n second filaments are spirally wound around two first filaments having the same diameter arranged in a non-twisted manner,
The two untwisted first filaments are spirally shaped at the same pitch as the spiral winding of the n second filaments, and the first filament spirals with respect to the diameter of the first filament. The molding rate expressed as a percentage of the ratio of the maximum width in the cross section of the amplitude is 200 ± 25%, and the center of the circumscribed circle in the cord axis direction of the steel cord is always positioned substantially in a straight line in the cord axis direction. The steel cord is characterized in that the first filament and the second filament are arranged, and the cord diameter is 0.75 mm or less. A pneumatic radial tire using the steel cord according to claim 1 as a reinforcing material.

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