JP2013001274A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic radial tire capable of improving tire durability performance when providing a belt layer formed by arranging a plurality of single-line steel wires in an aligned manner and embedding them in a rubber.SOLUTION: In the pneumatic radial tire, the belt layer 8, which is formed by arranging the plurality of single-line steel wires 10 in an aligned manner and embedding them into the rubber, is provided on the outer peripheral side of a carcass layer 4 of a tread part 1, and the tread part 1 is provided with a circumferential groove 1A which is elongated in the circumferential direction of the tire. A wire diameter d of the single-line steel wire 10 is chosen to be in the range of 0.28-0.38 mm; torsion is applied around the axis of each of the single-line steel wires 10; an average interval between the single-line steel wires 10 is set at 0.10 mm or more; and out-of-plane bending stiffness per inch of the circumferential length of the tread part 1 when setting a position of the circumferential groove 1A as a point of effort is set at 6,000 N mmor more.

Description

  The present invention relates to a pneumatic radial tire provided with a belt layer in which a plurality of single wire steel wires are aligned and embedded in rubber, and more particularly, a pneumatic radial tire that can improve tire durability performance. Regarding tires.

  Conventionally, a steel cord formed by twisting a plurality of filaments is used as a reinforcing cord for a belt layer of a pneumatic radial tire. However, a steel cord formed by twisting a plurality of filaments has a large cord diameter due to an internal gap formed between the filaments, and accordingly, a large amount of coat rubber is required. Therefore, the rolling resistance of a pneumatic radial tire is reduced. Easy to grow.

  Accordingly, in order to reduce the rolling resistance of the pneumatic radial tire by reducing the coating rubber of the belt layer, it has been proposed to use a single wire steel wire as a reinforcement cord of the belt layer (for example, refer to Patent Documents 1 and 2). . Here, in order to sufficiently secure the reinforcing effect of the single wire steel wire, it is necessary to sufficiently increase the strength of the single wire steel wire by wire drawing. However, in a drawn single-wire steel wire, since the metal structure is excessively oriented toward the wire surface closer to the drawing die, if the single-wire steel wire is used as a reinforcing cord for the belt layer as it is, the single-wire steel There exists a problem that the fatigue resistance of a wire is bad and tire durability performance falls.

JP 2006-218988 A JP 2010-89727 A

  An object of the present invention is to provide a pneumatic radial tire capable of improving tire durability performance when providing a belt layer in which a plurality of single wire steel wires are arranged and embedded in rubber. .

In order to achieve the above object, a pneumatic radial tire of the present invention comprises a belt layer formed by aligning a plurality of single wire steel wires and embedding them in rubber on the outer peripheral side of a carcass layer in a tread portion. In a pneumatic radial tire provided with a circumferential groove extending in the tire circumferential direction at the portion, the wire diameter of the single wire steel wire is 0.28 mm to 0.38 mm, and each single wire steel wire is twisted around its axis. The out-of-plane bending rigidity per inch of the circumferential length of the tread portion when the average distance between the single wire steel wires is 0.10 mm or more and the position of the circumferential groove is a power point is 6000 N · mm ² or more. It is characterized by that.

  As a result of earnest research on a pneumatic radial tire having a belt layer in which a plurality of single wire steel wires are aligned and embedded in rubber, the present inventors have found that the wire diameter of the twisted single wire steel wire In addition to optimizing the average distance, the tire durability performance is remarkably improved by sufficiently securing the out-of-plane bending rigidity of the tread portion including the belt layer and suppressing the buckling of the tread portion. That is what led to the present invention.

  That is, in the present invention, when a single wire steel wire is used as a reinforcing cord for the belt layer, the single wire steel wire is twisted to alleviate the excessive orientation of the metal structure caused by the wire drawing in the single wire steel wire. Therefore, the fatigue resistance of the single wire steel wire can be improved. In addition, it is possible to prevent breakage of the single wire steel wire by making the wire diameter of the single wire steel wire relatively small, and to prevent a separation failure of the belt layer by securing a sufficient average distance between the single wire steel wires. Can do. Furthermore, by setting the out-of-plane bending rigidity of the tread portion to a relatively large value, buckling of the tread portion with the circumferential groove as a bending point can be suppressed, and breakage of the single wire steel wire can be prevented. As a result, even when a belt layer formed by arranging a plurality of single wire steel wires and embedding them in rubber is provided, the tire durability performance can be improved.

  In order to improve the fatigue resistance of the single-wire steel wire, it is desirable to increase the wire surface twist angle. However, if it is excessive, the productivity of the single-wire steel wire is lowered and the manufacture becomes difficult. Therefore, the wire surface twist angle with respect to the axial direction of the single wire steel wire is preferably 1 ° to 15 °.

  Further, it is preferable that the belt cover layer is wound around the outer peripheral side of the belt layer at least in a region corresponding to the circumferential groove located on the outer side in the tire width direction. As a result, the thickness of the tread portion at the position of the circumferential groove on the outer side in the tire width direction is made larger than usual to increase the out-of-plane bending rigidity of the tread portion, and the circumferential groove on the outer side in the tire width direction is used as a bending point. Buckling of the tread portion can be effectively suppressed. In particular, in order to effectively suppress buckling of the tread portion, the ratio of the minimum value to the maximum value of the thickness of the tread portion is preferably 38% or more.

In the present invention, the out-of-plane bending rigidity of the tread portion is measured as follows in accordance with JIS Z2248. First, a cut sample having a circumferential length of 1 inch (25.4 mm) is cut out from the pneumatic radial tire. Then, the tread surface of the cut sample is supported so that the distance L (mm) between the fulcrums is 20 mm around the center position in the width direction of the circumferential groove, and the tread portion is pushed out from the back side with the position of the circumferential groove as a power point. At that time, the extrusion rate is set to 10 mm / min, and the distortion amount Y (mm) in the extrusion direction of the tread portion when the load W (N) reaches 100 N is measured. Such distortion Y is measured at three locations on the tire circumference, and the average value is obtained. Based on the distance L between fulcrums L (L = 20 mm), the load W (W = 100 N) and the amount of strain Y, the out-of-plane bending stiffness R (N · mm ² ) of the tread portion is calculated from the following equation (1).
R = (L ³ × W) / (48 × Y) (1)

In the present invention, the wire surface twist angle θ is measured as follows. First, a single wire steel wire is taken out from a pneumatic radial tire, the wire is immersed in an organic solvent to swell the rubber adhering to the surface, and then the rubber is removed. Then, the single wire steel wire is observed with an optical microscope, the strand diameter d (mm) of the single wire steel wire is measured, and the twist pitch P (mm) is ½ of the drawn trace formed on the wire surface. Measure the value and double it to determine the twist pitch P. The twist pitch P is an average value of the measured values at at least 10 locations. Based on the wire diameter d and the twist pitch P, the wire surface twist angle θ is calculated from the following equation (2).
θ = ATAN (π × d / P) × 180 / π (2)

1 is a meridian half cross-sectional view showing a pneumatic radial tire according to an embodiment of the present invention. FIG. 2 is an enlarged sectional view showing a part of a belt layer in the pneumatic radial tire of FIG. 1. It is a side view which shows the single wire steel wire used for a belt layer by this invention. It is a side view which expands and shows a part of FIG. It is explanatory drawing which shows the measuring method of the out-of-plane bending rigidity of a tread part.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a pneumatic radial tire according to an embodiment of the present invention, FIG. 2 shows its belt layer, and FIGS. 3 and 4 show a single wire steel wire used for the belt layer in the present invention.

  In FIG. 1, 1 is a tread portion, 2 is a sidewall portion, and 3 is a bead portion. A carcass layer 4 is mounted between the pair of left and right bead portions 3 and 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded from the tire inner side to the outer side around the bead core 5 disposed in each bead portion 3. As a reinforcing cord for the carcass layer 4, an organic fiber cord is generally used, but a steel cord may be used. A bead filler 6 is disposed on the outer periphery of the bead core 5, and the bead filler 6 is wrapped by the main body portion and the folded portion of the carcass layer 4.

  On the other hand, a plurality of belt layers 8 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. These belt layers 8 include a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and are arranged so that the reinforcing cords cross each other between the layers. In the belt layer 8, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set, for example, in a range of 10 ° to 40 °.

  On the outer peripheral side of the belt layer 8, at least one belt cover layer 9 formed by arranging reinforcing cords at an angle of 5 ° or less with respect to the tire circumferential direction is arranged for the purpose of improving high-speed durability. . The belt cover layer 9 preferably has a jointless structure in which a strip material formed by aligning at least one reinforcing cord and covering with rubber is continuously wound in the tire circumferential direction. Further, the belt cover layer 9 may be disposed so as to cover the entire width direction of the belt layer 8 as illustrated, or may be disposed so as to cover only the outer edge portion of the belt layer 8 in the width direction. good. As the reinforcing cord of the belt cover layer 9, a cord using organic fibers such as nylon, PET, and aramid alone or in combination may be used.

  The tread portion 1 is formed with a plurality of circumferential grooves 1A extending straight along the tire circumferential direction, and a plurality of rows of land portions 1B are defined by the circumferential grooves 1A. Therefore, the thickness of the tread portion 1 has a minimum value at a portion where the circumferential groove 1A exists, and has a maximum value at a portion where the land portion 1B exists. In addition to the circumferential groove 1A, the tread portion 1 can be provided with various grooves including lateral grooves and sipes extending in the tire width direction as needed.

  In the pneumatic radial tire, a single wire steel wire 10 (see FIGS. 3 and 4) in which a twist is applied around the shaft is used as a reinforcing cord constituting the belt layer 8. 3 and 4, a wire trace 11 caused by wire drawing is formed on the surface of the single wire steel wire 10, and the axial direction of the single wire steel wire 10 determined based on the wire trace 11 is shown. The wire surface twist angle θ with respect to is in the range of 1 ° or more, more preferably in the range of 1 ° to 15 °.

  In the pneumatic radial tire provided with the belt layer 8 in which a plurality of single wire steel wires 10 are aligned and embedded in rubber as described above, each single wire steel wire 10 is twisted about its axis, and the single wire By defining the wire surface twist angle θ with respect to the axial direction of the steel wire 10, the excessive orientation of the metal structure caused by the wire drawing in the single wire steel wire 10 is alleviated, so that the fatigue resistance of the single wire steel wire 10 is reduced. Can improve tire durability performance. And the rolling resistance of a pneumatic radial tire can be reduced by reducing the coating rubber of the belt layer 8 based on the use of the single wire steel wire 10.

  Here, if the wire surface twist angle θ is less than 1 °, the effect of improving the fatigue resistance of the single-wire steel wire 10 becomes insufficient. Further, if the wire surface twist angle θ exceeds 15 °, the productivity of the single-wire steel wire 10 is lowered, and the manufacture becomes difficult.

  In the pneumatic radial tire described above, the wire diameter d of the single wire steel wire 10 is 0.28 mm to 0.38 mm. If the strand diameter d is less than 0.28 mm, the mutual spacing of the single-wire steel wires 10 becomes narrow in order to secure the total strength of the belt layer 8, and the tire durability performance deteriorates. On the other hand, when the wire diameter d exceeds 0.38 mm, the fatigue resistance of the single wire steel wire 10 is lowered, and the tire durability is deteriorated.

  As shown in FIG. 2, in the belt layer 8, the average interval G of the single wire steel wires 10 is 0.10 mm or more, more preferably 0.10 mm to 0.30 mm. If the average distance G is less than 0.10 mm, a separation failure of the belt layer 8 is likely to occur. On the other hand, if the average distance G exceeds 0.30 mm, it is difficult to ensure the total strength of the belt layer 8.

In the pneumatic radial tire described above, the out-of-plane bending rigidity per inch of the circumferential length of the tread portion 1 when the position of the circumferential groove 1A is a power point is 6000 N · mm ² or more, more preferably 6000 N · mm ^2. It is set to 10000 N · mm ² .

  That is, as shown in FIG. 5, a cut sample having a circumferential length of 1 inch is cut out from the pneumatic radial tire so that the distance L between the fulcrums is 20 mm with the center position in the width direction of the circumferential groove 1A as the center. The tread surface of the cut sample is supported by a pair of supports S, the tread portion 1 is pushed out from the back side with the position of the circumferential groove 1A as a power point, and the distortion amount Y of the tread portion 1 when the load W reaches 100 N is calculated. The out-of-plane bending rigidity R of the tread portion 1 measured and calculated from the above equation (1) based on the distance L between the fulcrums, the load W, and the strain amount Y is set in the above range. The out-of-plane bending rigidity of the tread portion 1 is, for example, the wire diameter d and average distance G of the single wire steel wire 10 used for the belt layer 6, the structure and arrangement of the belt cover layer 9, the thickness of the tread portion 1, and , And can be appropriately controlled based on the depth of the circumferential groove 1A.

  In this way, by setting the out-of-plane bending rigidity of the tread portion 1 to a relatively large value, buckling of the tread portion 1 with the circumferential groove 1A as a bending point is suppressed, and breakage of the single wire steel wire 10 is prevented. be able to. As a result, even when the belt layer 8 is formed by arranging a plurality of single-wire steel wires 10 and embedding them in rubber, the tire durability performance can be improved.

  In the pneumatic radial tire, as shown in FIG. 1, the belt cover layer 9 may be disposed on the outer peripheral side of the belt layer 8 in a region corresponding to the circumferential groove 1 </ b> A located at the outer side in the tire width direction. More preferably, the number of layers of the belt cover layer 9 in the region corresponding to the circumferential groove 1A located on the outer side in the tire width direction is preferably larger than the number of layers of the belt cover layer 9 in the region closer to the center. . Accordingly, the thickness of the tread portion 1 at the position of the circumferential groove 1A on the outer side in the tire width direction is made larger than usual to increase the out-of-plane bending rigidity of the tread portion 1, and the circumferential groove 1A on the outer side in the tire width direction is increased. Buckling of the tread portion 1 as a bending point can be effectively suppressed.

  The ratio of the minimum value to the maximum value of the thickness of the tread portion 1 is preferably 38% or more. As a result, the out-of-plane bending rigidity of the portion of the circumferential groove 1A where the thickness of the tread portion 1 becomes the minimum value and the out-of-plane bending rigidity of the portion of the land portion 1B where the thickness of the tread portion 1 becomes the maximum value are reduced. The buckling of the tread portion 1 can be effectively suppressed by reducing the size. The effect which suppresses the buckling of the tread part 1 falls that the said ratio is less than 38%.

  The tire size is 195 / 65R15, and two belt layers are formed by arranging a plurality of single-wire steel wires on the outer circumference side of the carcass layer in the tread portion and embedded in rubber. In a pneumatic radial tire provided with a layer, the tread portion when the wire diameter d of the single wire steel wire of the belt layer, the wire surface twist angle θ, the driving density E and the average interval G, and the position of the circumferential groove are the power points Example 1 in which the out-of-plane bending stiffness per inch in the circumferential direction and the thickness of the tread part, the minimum value, and the ratio of the minimum value to the maximum value (%) are set as shown in Table 1. 4 and Comparative Examples 1 to 4 were manufactured.

  In Examples 1 to 4 and Comparative Examples 1 to 4, the tire radial inner belt layer has a width of 155 mm and a cord angle of 21 degrees, and the tire radial outer belt layer has a width of 145 mm and a cord angle of 21 degrees. It is. The belt cover layer is formed by continuously winding a strip material having a thickness of 0.80 mm, in which nylon fiber cords (940 dtex / 2) are uniformly coated at a driving density of 70 pieces / 50 mm and covered with rubber, in the tire circumferential direction. Therefore, the thickness of the tread portion was adjusted by adjusting the winding amount according to the position in the tire width direction.

  About these test tires, the tire durability performance was evaluated by the following evaluation method, and the results are also shown in Table 1.

Tire durability:
Each test tire was assembled into a rim, the air pressure was set to 170 kPa, and a running test was performed on a drum having a diameter of 1707 mm at a speed of 25 km / h while changing the load and slip angle in a rectangular wave. The load was 3.2 ± 2.1 kN, the slip angle was 0 ± 5 °, and the fluctuation frequency was 0.067 Hz. Then, the tire was disassembled after traveling 300 km, the presence or absence of breakage of the single wire steel wire constituting the belt layer was examined, and the length of separation (maximum value) generated in the belt layer was measured. It is good if the separation length is 5 mm or less.

  As can be seen from Table 1, the tires of Examples 1 to 4 were not broken in the single wire steel wire constituting the belt layer after the durability performance test under severe conditions, and the belt layer There was also little separation.

  In contrast, the tires of Comparative Examples 1 to 4 had insufficient tire durability performance. In particular, in the tire of Comparative Example 1, since the out-of-plane bending rigidity of the tread portion is too low, the single wire steel wire constituting the belt layer is broken, and the separation of the belt layer is expanded due to an increase in movement of the tread portion. . In the tire of Comparative Example 2, the separation between the belt layers was increased because the average distance G between the single-wire steel wires was too small. In the tire of Comparative Example 3, since the wire diameter d of the single wire steel wire is too small and the out-of-plane bending rigidity of the tread portion is too low, the single wire steel wire constituting the belt layer is broken and the movement of the tread portion is increased. As a result, the separation of the belt layer was expanded. In the tire of Comparative Example 4, since the wire diameter d of the single wire steel wire was too thick, the single wire steel wire constituting the belt layer was broken.

DESCRIPTION OF SYMBOLS 1 Tread part 1A Circumferential groove 1B Land part 2 Side wall part 3 Bead part 4 Carcass layer 5 Bead core 6 Bead filler 8 Belt layer 9 Belt cover layer 10 Single wire steel wire 11 Wire trace

Claims (4)

A pneumatic radial having a belt layer formed by aligning a plurality of single-wire steel wires and embedding them in rubber on the outer peripheral side of the carcass layer in the tread portion, and providing a circumferential groove extending in the tire circumferential direction in the tread portion In the tire, the wire diameter of the single wire steel wire is 0.28 mm to 0.38 mm, each single wire steel wire is twisted about its axis, and the average interval between the single wire steel wires is 0.10 mm or more, A pneumatic radial tire characterized in that an out-of-plane bending rigidity per inch in the circumferential length of the tread portion when the circumferential groove position is a power point is 6000 N · mm ² or more.   The pneumatic radial tire according to claim 1, wherein a wire surface twist angle with respect to an axial direction of the single wire steel wire is set to 1 ° to 15 °.   3. The pneumatic radial tire according to claim 1, wherein a belt cover layer is wound around the outer peripheral side of the belt layer at least in a region corresponding to a circumferential groove positioned on the outer side in the tire width direction.   The pneumatic radial tire according to any one of claims 1 to 3, wherein a ratio of a minimum value to a maximum value of the thickness of the tread portion is set to 38% or more.

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