JP2010179774A - Heavy duty tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heavy duty tire which is increased in peripheral rigidity required in the form of product while securing a tension during manufacturing and which has an excellent wear performance. <P>SOLUTION: This heavy duty tire includes a belt having a peripheral belt layer in which a steel cord is used as a reinforcement. The steel cord has a 1×N open strand structure and is formed of nine or more steel wires, and the elongation percentage H of the steel cord when the secondary differentiation of the elongation percentage-tension curve of the steel cord in maximum is 1.5% or larger. When the extension rate of the steel cord is represented by the expression: Extension rate (%)=[(length of steel cord when tire is in the form of product)-(length of steel cord before tire is molded)]/(length of steel cord before tire is molded)×100, the extension rate A of the steel cord at the center of the belt layer in the peripheral direction and the extension rate B of the steel cord at a position 20 mm away from the end of the peripheral belt layer 20 satisfy the requirements represented by the expression: B-A≥0.2(%). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a heavy-duty tire (hereinafter, also simply referred to as “tire”), and more specifically, it improves the circumferential rigidity necessary for a product while ensuring the extensibility during manufacture of the tire, and has excellent wear performance. The present invention relates to a heavy duty tire.

  Tires have a circular shape and mostly curved surfaces. In the manufacturing process, flexibility is required, and in a vulcanization process, the tire is usually expanded in a hook to fit the mold. On the other hand, after it becomes a product, high strength, rigidity, and dimensional stability are required to withstand severe use for a long period of time and to exhibit stable performance.

  In particular, the crown part of the tire always receives a tensile input in the circumferential direction due to internal pressure during use, and creeps and extends the circumference due to use, resulting in distortion and deterioration in durability, and changes in the tire cross-sectional shape and wear. It is known to deteriorate characteristics.

  To deal with such a problem, for example, Patent Document 1 discloses that a plurality of cords having a two-layer crossing belt in a tread portion around a carcass and at least one layer of a waveform (or zigzag shape) in a lower layer thereof. The purpose of effectively preventing separation without increasing the weight of the tire by arranging a strip-shaped crown reinforcing layer made of a large number of cords (or filaments) oriented along the equator. Is stated. It is also stated that the use of strips in which corrugated or zigzag cords or filaments are oriented along the equator makes it easy to produce because the elongation during vulcanization is easily obtained. Patent Document 2 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. It is disclosed.

Japanese Patent No. 2783826 JP 2007-162163 A

  However, when the method of Patent Document 1 is applied, in order for this steel cord to exhibit sufficient rigidity after becoming a product, the above-described corrugation or zigzag is stretched with internal pressure applied to the product. It needs to be almost eliminated. For this reason, high accuracy is required in the process of molding in order to match the physical properties of the product to the target value. Further, when the circumferential rigidity of the belt end portion is low in such a tire, there is a problem that the wear of the shoulder portion is likely to proceed and uneven wear is likely to occur.

  To solve this problem, there is a method of adding a new reinforcing material to the end of the circumferential belt. However, this increases the product weight, complicates the manufacturing process, and uses the step as a core. New problems arise, such as making it easier to cause failure. Moreover, it is difficult to apply the method of Patent Document 2 to a heavy duty tire as it is.

  Accordingly, an object of the present invention is to provide a heavy-duty tire that improves the circumferential rigidity required for a product and has excellent wear performance while ensuring extensibility during manufacture of the tire.

  As a result of intensive studies to solve the above problems, the present inventor has found that the above problems can be solved by making the steel cord have the following structure, and the present invention has been completed.

That is, the heavy load tire of the present invention is a heavy load tire provided with a belt 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 N of steel strands is 9 or more, and
The elongation H when the second derivative of the elongation-tensile stress curve of the steel cord is maximized is 1.5% 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 expressed by the following formula:
B−A ≧ 0.2 (%)
It is characterized by satisfying the relationship represented by

  In the present invention, the diameter of the steel wire constituting the steel cord is preferably 0.30 mm to 0.50 mm, and the circumferential belt layer is disposed as the innermost belt layer of the belt. It is preferable that

  According to the present invention, it is possible to provide a heavy-duty tire that improves the circumferential rigidity required for a product and has excellent wear performance while ensuring stretchability during tire manufacture.

It is a width direction sectional view of one suitable example of a tread part of a heavy load 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 in the width direction of a preferred example of the tread portion of the heavy duty tire of the present invention. The illustrated tire has a skeleton of a carcass 1 extending in a toroid shape across at least a pair of bead cores (not shown), and circumferential belt layers 2a and 2b on the outer periphery thereof, and the cord direction is an interlayer. And a belt structure in which at least two crossing belt layers 3a and 3b crossing each other are sequentially arranged.

  In the heavy duty tire of the present invention, it is important that the steel cord constituting the circumferential belt layer has an open twist structure of 1 × N, and the number N of steel strands is 9 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 has an open structure including nine or more steel strands 4 in the illustrated example, and nine steel strands 4 in the illustrated example. 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.

  Also, if the number of steel strands N is less than 9, the strength required for the tire cannot be obtained, and when the plunger test is performed, not only the portion where the pin is pressed, but also the fracture propagates in the width direction. Resulting in. In the present invention, the number N of steel strands is preferably 9 to 15.

  In addition, the circumferential belt reinforcing layer is preferably the innermost layer of the belt layer, and this arrangement reduces the possibility of reaching the circumferential belt layer even when cut from the outside. The rigidity in the circumferential direction of the tire can be maintained.

  It is also important that the steel cord according to the present invention has an elongation H of 1.5% or more when the second derivative of the elongation-tensile stress curve is maximized. By setting the elongation H when the second order differential is maximum to 1.5% or more, it is possible to follow the expansion and contraction at the time of tire molding, and it is possible to eliminate poor air entry. FIG. 3 shows, as an example, an elongation-tensile stress curve (SS curve) and a secondary differential curve of a steel cord according to Example 1 of the present invention described later.

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
Then, the expansion rate A of the steel cord at the center 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 expressed by the following formula:
B−A ≧ 0.2 (%)
It is also important to satisfy the relationship expressed by By satisfying the above relationship, the circumferential rigidity of the tread center portion contrast shoulder portion is increased, and uneven wear can be improved.
However, if (BA) is too large, tire performances other than uneven wear are adversely affected.
(BA) ≦ 1.0
It is.

  Moreover, in this invention, it is preferable that the diameter of the steel strand which comprises a steel cord is 0.30 mm-0.50 mm from the point of manufacturing cost and product weight.

  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 and 2 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 a circumferential belt to produce a pneumatic radial tire for a truck having a tire size shown in FIG. 1 and having a tire size of 265 / 60R22.5. The obtained tire was evaluated with respect to the fracture mode during the plunger test, poor inner member contact, insufficient vulcanization of the tread portion, and uneven wear. The results are shown in Tables 1 and 2.

(Fracture mode during plunger test)
The plunger test was performed according to the test method described in JIS-D4230 with a plunger diameter of 38 mm. At that time, the case where the ruptured portion by the plunger expanded to the periphery was evaluated as x, and the case where no ruptured portion was observed was evaluated as ◯.

(Inside member contact failure)
Each of the obtained test tires was dissected and the contact state of the members inside the tire was confirmed. The case where the steel cord of the circumferential belt layer was in contact with the steel cord of the inner layer was rated as x, and the case where there was no contact as ◯.

(Insufficient tread vulcanization)
In the tire vulcanization process of each test tire, the case where poor vulcanization occurred in the tread portion was evaluated as x, and the case where it did not occur was evaluated as ◯.

(Uneven wear)
Each tire was assembled on a commercial truck with a rim width of 8.25 and filled with an internal pressure of 900 kPa. Then, with a load of 25480 N (2600 kgf) on average applied, run 100 km on a 30% pavement highway and 70% pavement general road, center groove depth and shoulder groove depth at the end of the run. Were measured, and the amount of wear from a new article was compared.

※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, a difference of 2 mm or more occurred in the tire of the comparative example, but it was within 1 mm in the tire of each example, and it was confirmed that uneven wear was improved in the examples.

DESCRIPTION OF SYMBOLS 1 Carcass 2a, 2b Circumferential belt layer 3a, 3b Crossing belt layer 4 Steel strand 10 Steel cord

Claims (3)

In a heavy duty tire provided with a belt 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 N of steel strands is 9 or more, and
The elongation H when the second derivative of the elongation-tensile stress curve of the steel cord is maximized is 1.5% 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 expressed by the following formula:
B−A ≧ 0.2 (%)
A heavy-duty tire characterized by satisfying the relationship represented by:   The heavy duty tire according to claim 1, wherein a diameter of a steel wire constituting the steel cord is 0.3 mm to 0.50 mm.   The heavy-duty tire according to claim 1 or 2, wherein the circumferential belt layer is an innermost belt layer of the belt.

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