JP5227826B2 - Pneumatic radial tire - Google Patents

Description

  The present invention relates to a pneumatic radial tire (hereinafter, also simply referred to as “tire”), and more specifically, has a circumferential rigidity necessary for a product while ensuring extensibility at the time of tire manufacture, and durability and limit performance. The present invention relates to a pneumatic radial tire with improved performance.

  The circumferential reinforcing layer of the tire functions to improve the durability of the tire by preventing the crown portion of the tire from protruding by centrifugal force generated when the tire rotates at a high speed. Further, also in cornering, the circumferential rigidity contributes to the in-plane rigidity of the belt and contributes to the lateral force.

  Conventionally, an organic fiber such as Kevlar or nylon is used as a reinforcing member for such a circumferential reinforcing layer, but the circumferential rigidity can be further increased by applying a steel cord. In particular, strong in-plane rigidity may be required as a tire for motor sports, which is effective in such a case. However, since the steel cord has high rigidity, it has problems such as poor yield due to lack of stretchability in processes such as tire molding and vulcanization.

  As a technique for solving such a problem, a highly twisted cord with high twist (HE cord) or a cord obtained by spirally winding a cord typed into a waveform in the circumferential direction has been proposed. That is, in the tire manufacturing process, a cord that has stretchability and exhibits high rigidity at the time of product can be said to be ideal. For example, Patent Document 1 discloses a flexible steel cord having a 1 × N structure, 6 to 12 steel strands, and a steel strand diameter of 0.08 to 0.21 mm. Further, Patent Document 2 discloses the difference between the initial elongation strain of the steel cord at the end portion in the tire width direction and the initial elongation strain of the steel cord at the center portion in the tire width direction. A steel cord having elasticity that is within ± 2% of the initial elongation strain of the steel cord at the center is disclosed.

JP 2007-162163 A JP 2008-155733 A

  On the other hand, in high-performance tires applied to passenger cars and tires for racing, the tires may be flattened in order to increase cornering limit performance. In such a case, since a flat tire applies a relatively large tension to the center of the tread during internal pressure, if the rigidity of the center of the tread is lower than that of the shoulder, the radius of curvature of the crown decreases, and the ground contact of the shoulder is reduced. There is a problem that the limit performance deteriorates.

  Further, in the tire manufacturing process, the shoulder portion needs to be sufficiently pressure-bonded to the carcass portion in order to prevent poor air entry in the molding process. As described above, since the load applied in the manufacturing process is different between the tread center portion and the shoulder portion, it is difficult to say that the technique described in the above document is sufficient, and in order to exhibit the same physical properties at the time of product, further improvement Was necessary.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic radial tire that has a circumferential rigidity necessary for a product and has improved durability and limit performance while ensuring extensibility during manufacture of the tire.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that the above-mentioned problems can be solved by setting the steel cord to the following configuration, and has completed the present invention.

That is, the pneumatic radial tire of the present invention is a pneumatic radial tire having a circumferential belt layer using a steel cord as a reinforcing material.
The steel cord has an open twist structure of 1 × N, the number of steel strands is 7 or more, and
The elongation H when the second derivative of the elongation-tensile load curve of the steel cord is maximum is 4.5% or more, and the expansion rate of the steel cord is expressed by the following formula:
Expansion rate (%) = [(steel cord length at tire product) − (steel cord length before tire molding)] / (steel cord length before tire molding) × 100
Then, the expansion rate A of the steel cord at the central portion of the circumferential belt layer and the expansion rate B of the steel cord at a position 20 mm from the end of the circumferential belt layer are represented by the following formulas (I) and (II). ,
(H-4) ≦ A ≦ (H−0.1) (I)
(H-1.5) ≦ B ≦ (H-0.1) (II)
It is characterized by satisfying the relationship represented by

  In this invention, it is preferable that the diameter of the steel strand which comprises the said steel cord is 0.15-0.45 mm, and it is preferable that the said number of steel strands is 9-15.

  ADVANTAGE OF THE INVENTION According to this invention, the pneumatic radial tire which has the circumferential rigidity required at the time of a product, and improved durability and limit performance, ensuring the extensibility at the time of tire manufacture can be provided.

1 is a cross-sectional view in the width direction of a preferred example of a pneumatic radial tire of the present invention. It is sectional drawing of one suitable example of the steel cord which concerns on this invention. It is a graph which shows the elongation-tensile load curve in an Example.

DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional view of a preferred example of the pneumatic radial tire of the present invention. The illustrated tire has a skeleton of a carcass 2 extending in a toroidal shape across at least a pair of bead cores 1, and has at least two crossing belt layers 3a on the outer periphery of which the cord directions cross each other between the layers. 3b and circumferential belt layers 4a and 2b are sequentially arranged. In the figure, reference numeral 11 denotes a tread portion, reference numeral 12 denotes a sidewall portion, and reference numeral 13 denotes a bead portion.

  In the pneumatic radial tire of the present invention, it is important that the steel cord constituting the circumferential belt layer 4 has a 1 × N open twist structure and the number of steel strands is 7 or more. FIG. 2 shows a preferred example of a cross-sectional view of a steel cord according to the present invention. The steel cord 10 according to the present invention is composed of seven or more steel strands 5 in the illustrated example, and nine steel strands 5 in the illustrated example, and has a brazed open twist structure. By adopting such a structure, elasticity in the manufacturing process can be obtained, and at the time of product, the rubber that penetrates the inside of the cord is vulcanized and has uncompressed physical properties, so the high rigidity inherent in steel cord Will be demonstrated. If the number of steel strands is less than 7, the stretchability before vulcanization and the rigidity after vulcanization cannot be compatible. Preferably it is 9-15.

  It is also important that the steel cord according to the present invention has an elongation percentage H of 4.5% or more when the second derivative of the elongation-tensile load curve is maximized. By setting the elongation H when the second order differential is maximum to 4.5% or more and using an open twisted structure that is excessively brazed, it is possible to follow the expansion and contraction at the time of tire molding, and to eliminate air entry defects. . In FIG. 3, the elongation-tensile load curve (SS curve) and its secondary differential curve of the steel cord which concerns on Example 1 of this invention mentioned later are shown as an example.

Furthermore, the steel cord according to the present invention represents the expansion rate of the steel cord by the following formula:
Expansion rate (%) = [(steel cord length at tire product) − (steel cord length before tire molding)] / (steel cord length before tire molding) × 100
The steel cord expansion rate A at the center portion of the circumferential belt layer, and the steel cord expansion rate B at a position 20 mm from the end of the circumferential belt layer are represented by the following formulas (I) and (II):
(H-4) ≦ A ≦ (H−0.1) (I)
(H-1.5) ≦ B ≦ (H-0.1) (II)
It is also important to satisfy the relationship expressed by

  By adjusting the expansion ratio of the steel cords at the center and the end of the circumferential belt layer within the above range, it is possible to maintain the tire shoulder part contrast and the rigidity of the tire center part and improve the limit performance.

  If the expansion ratio A is less than (H-4)%, the gap between the steel strands is large even when the product is used, the rubber is not confined inside the cord, and deforms like a spring, so that the sufficient circumferential direction Stiffness is not demonstrated. On the other hand, when the expansion rate A is greater than (H-0.1)%, the rubber does not sufficiently penetrate into the cord, and the corrosion when the tire is damaged by nail catches spreads.

  Moreover, even when the expansion rate B is less than (H-1.5)%, the gap between the steel strands is large, the rubber is not trapped inside the cord, and deforms like a spring, Sufficient circumferential rigidity is not exhibited. On the other hand, when the expansion rate A is greater than (H-0.1)%, the rubber does not sufficiently penetrate into the cord, and the corrosion when the tire is damaged by nail catches spreads.

  Moreover, in this invention, it is preferable that the diameter of the steel strand which comprises a steel cord is 0.15-0.45 mm. If the diameter of the steel strand is less than 0.15 mm, the strength of the resulting cord is low, so it is necessary to greatly increase the number of cords driven to secure the circumferential rigidity as a belt layer. And code separation. Alternatively, high-speed durability may be impaired due to diameter growth during high-speed running. On the other hand, since the steel strand having a diameter exceeding 0.45 mm has too high bending rigidity, it is difficult to ensure sufficiently low out-of-plane bending rigidity when used as a belt reinforcing material for high-performance radial tires.

  In the tire of the present invention, any steel belt may be applied to the circumferential belt layer, and the desired effect of the present invention can be obtained thereby. The number of reinforcements to be struck and specific tire structures and materials other than the circumferential reinforcing layer can be appropriately set according to a conventional method and are not particularly limited.

  Steel cords of Examples 1 to 3 and Comparative Examples 1 to 3 were produced according to the conditions shown in Tables 1 and 2 below. The obtained steel cord was applied to the circumferential belt layers 4a and 4b, and each test tire of tire size 225 / 45ZR17 having the tire structure of FIG. 1 was produced. For Comparative Example 2, a nylon cord having the conditions shown in Table 1 below was used. In each test tire, the cross belt 3 is composed of a plurality of steel cords, and a circumferential belt layer 4a in which a reinforcing cord is spirally wound at substantially 0 ° with respect to the tire equatorial plane on the outer circumferential side thereof. 4b is provided. The tires thus obtained were evaluated for high-speed durability, cornering limit feeling, poor air entry, and corrosion propagation. The results are shown in Tables 1 and 2.

(High speed durability)
Each test tire was mounted on a rim having a rim size of 7.5 J × 17 at an air pressure of 300 kPa, and the step speed method was performed in accordance with the test method of JATMA standard. As a result, the case where it is equal to or higher than that on the basis of the speed at the time of failure of the test tire of Conventional Example 1 was evaluated as ◯, and the case where it was inferior was evaluated as ×.

(Cornering limit feeling)
Each test tire is mounted on four wheels of a passenger car at an air pressure of 205.8 kPa (2.1 kgf / cm ² ), and the test driver runs the test course in this test vehicle, and the feeling result about the cornering by the test driver is shown. Evaluation was based on a 10-point scale.

(Defective air entering)
In each of the test tire manufacturing processes, the case where an air-filling defect occurred was rated as x, and the case where it did not occur was marked as ◯.

(Corrosion propagation)
Each test tire was mounted on a standard rim defined in the JATMA standard, filled with an internal pressure corresponding to the maximum load capacity in JATMA YEAR BOOK, and mounted on a passenger car. After traveling 10,000 km on the paved road, the tire was dissected to investigate the corrosion length of the cord from the cut wound. Based on Comparative Example 1, the results were evaluated as “good” when equal or better, and “poor” when inferior.

※１：伸び率−引張荷重曲線の２次微分が最大となるときの伸び率
※２：周方向ベルト層中央部分のスチールコードの拡張率Ａ
※３：周方向ベルト層の端部より２０ｍｍの位置のスチールコードの拡張率Ｂ

* 1: Elongation rate when the second derivative of the elongation-tensile load curve is maximum * 2: Steel cord expansion rate A at the center of the circumferential belt layer
* 3: Steel cord expansion rate B 20mm from the end of the circumferential belt layer

※１：伸び率−引張荷重曲線の２次微分が最大となるときの伸び率
※２：周方向ベルト層中央部分のスチールコードの拡張率Ａ
※３：周方向ベルト層の端部より２０ｍｍの位置のスチールコードの拡張率Ｂ

* 1: Elongation rate when the second derivative of the elongation-tensile load curve is maximum * 2: Steel cord expansion rate A at the center of the circumferential belt layer
* 3: Steel cord expansion rate B 20mm from the end of the circumferential belt layer

  From Tables 1 and 2 above, it is confirmed that the pneumatic radial tire of the present invention has the circumferential rigidity necessary for the product while ensuring the extensibility during the manufacture of the tire, and has improved durability and limit performance. It was. It can also be seen that sufficient corrosion propagation properties can be maintained.

DESCRIPTION OF SYMBOLS 1 Bead core 2 Carcass 3a, 3b Crossing belt layer 4a, 4b Circumferential belt layer 5 Steel strand 10 Steel cord 11 Tread part 12 Side part 13 Bead part

Claims (3)

In a pneumatic radial tire having a circumferential belt layer using a steel cord as a reinforcing material,
The steel cord has an open twist structure of 1 × N, the number of steel strands is 7 or more, and
The elongation H when the second derivative of the elongation-tensile load curve of the steel cord is maximum is 4.5% or more, and the expansion rate of the steel cord is expressed by the following formula:
Expansion rate (%) = [(steel cord length at tire product) − (steel cord length before tire molding)] / (steel cord length before tire molding) × 100
Then, the expansion rate A of the steel cord at the central portion of the circumferential belt layer and the expansion rate B of the steel cord at a position 20 mm from the end of the circumferential belt layer are represented by the following formulas (I) and (II). ,
(H-4) ≦ A ≦ (H−0.1) (I)
(H-1.5) ≦ B ≦ (H-0.1) (II)
A pneumatic radial tire characterized by satisfying the relationship expressed by:   The pneumatic radial tire according to claim 1, wherein a diameter of a steel wire constituting the steel cord is 0.15 to 0.45 mm.   The pneumatic radial tire according to claim 1 or 2, wherein the number of steel strands is 9 to 15.

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