JP2000273778A - Steel cord for tire reinforcement and steel radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a steel cord with good rubber penetration thereinto, capable of raising the rigidity of the direction rectangular to that of tire rotation while reducing the rigidity in the direction of tire rotation, good in fatigue resistance to both compression and bending, and excellent in productivity and handling operability as well, and to obtain a tire using the above steel cords. SOLUTION: This steel cord for tire reinforcement is so designed that, two core wires 1 are stranded together nearly in contact with each other, part of five side wires 2 adjacent to one another are stranded together spacedly; when the two core wires 1 are arranged nearly in one row in the direction of the major axis W of the cross section of this cord, they exist inside so as to be enclosed by the five side wires 2, whereas when the two core wires 1 are arranged nearly perpendicularly to the direction of the major axis W of the cross section of this cord, one of the core wires is in contact with the inner side of one of the side wires, the other being arranged so as to be forced into between other two of the side wires, and the flatness (T/W:%) of the nearly elliptical shape of this cord is 65-88% (T: minor axis).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel cord used as a reinforcing material for automobile tires and a steel radial tire using the same.

[0002] In general, steel cords of this type are used as automobile tires in a state where a large number of steel cords are coated in parallel with a rubber material. The steel cord is required to have not only excellent mechanical strength, but also good chemical and physical adhesion to rubber material, and good steel cord. And good rubber infiltration into the metal. That is, in order for the steel cord to sufficiently fulfill the role of a tire reinforcing material, it is necessary to form a complete composite with a rubber material having excellent mechanical strength.

[0003]

2. Description of the Related Art Conventionally, as a typical example of this type of steel code, there is a steel code having a two-layer twist (3 + 6) structure. In this (3 + 6) steel cord, as shown in FIG. 5, three core strands are twisted to form a core, and six side strands are twisted around the core to form a steel cord. Has formed. Since this steel code requires two twisting steps, the productivity is low and the production cost is high. Also,
In the (3 + 6) steel cord, rubber hardly penetrates to the center of the three-stranded core, and a void is easily generated in the center of the core. As a result, internal corrosion and fretting wear easily occur from that portion, and the life of the steel cord is considerably shortened. Further, since the cross section of the steel cord is substantially circular, the thickness of the rubber sheet is increased in the tire design, the weight of the tire is increased, and the riding comfort is deteriorated.

[0004] Because of these disadvantages, a steel code having a 2/5 structure has recently been proposed as disclosed in Japanese Patent Application Laid-Open No. 9-31876 (and a procedure amendment filed subsequently). ing. This steel code is shown in FIG.
(A) As shown in (b), two wires are used as core wires,
A stitch made by twisting five wires together as a side strand
The steel cord is a steel cord in which the shaping rate of the core strand is larger than the shaping rate of the side strands and the cross section is flat. According to the specification, the following effects are described. Since there are two core strands, there is no void in the core, and it has excellent rubber penetration and
The cross section is flat, so it is possible to secure a sufficient pitch interval in the calendering process.
You can lay a lot of books on the table. In the tire, fretting does not occur, code integrity is enhanced, and twisting of the wire is less likely to occur. Therefore, warpage of the rubber sheet does not substantially occur.

[0005] However, according to the results of trial production of this steel code and confirmation of its effects, the following problems became apparent. Because the core wire has a large molding rate,
When the steel cord is pulled under a low load, the low load elongation is too large, which hinders the calendering process in tire manufacturing. For example, when this steel cord is used, it is necessary to pull the steel cord with an extremely low load in the calendar process, and it is difficult to control the tension. In a calendering process in which the tension is excessive, if the sheet is cut thereafter, the steel code shrinks and the length of the steel code becomes shorter than the length of the rubber sheet. Further, since the core element wire has a large molding rate, the flatness (short diameter T / long diameter W) of the steel cord cannot be reduced, so that the thickness of the rubber sheet cannot be reduced. Since the position of the core element wire is not stable, the twist of the cord is unstable and is inferior to twisting and buckling.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a steel code which eliminates the various disadvantages of the conventional steel code as described above and a tire using the steel code. The purpose of the present invention is to improve the safety, driving stability, riding comfort, cornering, economy, and the like of automobiles.

[0007]

In order to achieve the above-mentioned object, a steel cord for reinforcing a tire according to the present invention has a diameter of 0.15.
The two strands having a wire diameter of 0.25 mm to 0.25 mm are used as core strands, and 5 strands having a wire diameter of 0.34 mm to 0.40 mm
This is a steel cord in which two strands are twisted in the same direction at the same time as a side strand, and its cross section is substantially the same direction in the longitudinal direction and has a substantially elliptical shape (major axis W, minor axis T). In a tire reinforcing steel cord, two core strands are substantially in contact with each other and twisted together, and a part of the five side strands adjacent to each other are partially twisted with a space. When the books are arranged substantially in a line in the major axis direction of the cross section of the code, they are inherently surrounded by five side strands, and two core strands are substantially arranged in the major axis direction of the cross section of the code. When they are arranged vertically, one of them
One core strand is in contact with the inside of one side strand, and the other core strand is arranged so as to be interrupted between the other two side strands. The flattening rate (percentage of T / W) is 65% to 88%.

[0008] The steel radial tire of the present invention comprises:
A steel radial tire reinforced with a steel cord in which a plurality of strands are twisted, and the steel radial tire is provided.
In the same manner, two strands having a wire diameter of 0.15 mm to 0.25 mm are defined as core strands, and five strands having a wire diameter of 0.34 mm to 0.40 mm are defined as side strands. A steel cord which is twisted in one direction at a time, and whose cross section is substantially the same direction in the longitudinal direction and has a substantially elliptical shape (long diameter W, short diameter T). The two core strands are twisted substantially in contact with each other, and a part of the adjacent side strands of the five side strands are twisted together with a space, and the two core strands are formed in a longitudinal direction of the cross section of the cord. When the two core wires are substantially perpendicular to the longitudinal direction of the cross section of the cord, one of the core wires is one of them. The core strand is in contact with the inside of one side strand, and the other core strand is arranged so as to be interrupted between the other two side strands. And which, moreover aspect ratio of the substantially elliptical shape (percentage of T / W) is characterized in that 65% to 88%.

The twist pitch of the steel cord is preferably about 5 to 20 mm for the reasons described below. It is preferable that the core element wire and the side element wire have the same diameter.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIGS. 1A and 1B are schematic views showing an example of the steel code of the present invention and its cross section. In this steel cord, two core wires 1 having a wire diameter of 0.175 mm or 0.20 mm are substantially in contact with each other and twisted, and five side wires 2 having a wire diameter of 0.370 mm are adjacent to each other. A part of the wire is twisted with a gap. It is composed of two core strands 1 having a so-called molding rate of about 100%, and five side strands 2 having a molding rate of more than 100%. Since the two core wires are twisted by being substantially in contact with each other at a molding rate of about 100%, the low load elongation when the steel cord 3 is pulled with a low load is low. 5 side strands 2
Is easy to infiltrate the rubber into the steel cord because there is a gap between them.

The wire diameter of the core element wire 1 is 0.15 mm to 0.1 mm.
It is desirable to set the range to 25 mm. If the thickness is smaller than 0.15 mm, sufficient strength cannot be obtained, and this is disadvantageous in cost. If the thickness is larger than 0.25 mm, the flexibility is inferior, and the cord diameter becomes large, and the rubber sheet becomes thick. The wire diameter of the side strand 2 is 0.34 mm or more.
A range of 0.40 mm is desirable. If the thickness is smaller than 0.34 mm, the strength is weak, and it is necessary to increase the number of strands in order to obtain sufficient strength. If the thickness is larger than 0.40 mm, the flexibility is poor, the fatigue value is low, the gap between the wires is small, and the rubber penetration is poor.

Further, the core wires 1 are twisted so as to be substantially in contact with each other, and the cord has a substantially elliptical cross-section with a substantially same cross-section in the longitudinal direction. -The record may be arranged in the same direction or in the perpendicular direction with respect to the major axis direction of the transverse section. When arranged in the same direction, two core strands 1 are inherently surrounded by five side strands 2. When arranged in the vertical direction, one core strand is arranged so as to be in contact with one side strand, and the other core strand is interposed between two opposite side strands. ing.

Therefore, the twisted shape is stable, and
It is possible to reduce the oblateness (short diameter T / long diameter W) in the transverse section of the metal. Here, the case where the core strand is interrupted between the side strands means, as shown in FIG. 2, a core strand extending beyond a so-called center line A connecting the centers of the cross sections of the two side strands 2. It means that 1 invades in the meantime. When the flattening ratio (minor axis T / major axis W) decreases, the rubber sheet becomes
The tire can be made thinner, and the weight of the tire can be reduced.

The flattening ratio (short diameter T / long diameter W) of the substantially elliptical shape in the transverse section of the steel code is set to 65% to 88%. In the configuration, the twisting becomes unstable, and at the same time, each wire is hardly bent at the end of the long diameter, and the handling workability is poor and the fatigue resistance is poor. If it exceeds 88%, the effect of the present invention cannot be expected because the cross section approaches a perfect circle. In addition, 65% to 88
In the range of%, when the core strands are arranged in a direction perpendicular to the major axis of the cross-section, the core strands are interrupted between the two side strands. I do.

The steel cord has a twist pitch of 6 mm.
~ 28 mm is preferred. This is because, if it is less than 6 mm, the amount of bending becomes extremely large, so that disconnection is likely to occur, and the number of twists per length of the steel cord increases, and the productivity decreases. On the other hand, when the twist pitch of the steel cord exceeds 28 mm, the steel cord is twisted.
This is because the flexibility of the metal is lost, so that the fatigue value becomes low, the twist becomes unstable, and flare tends to occur, which is not practical.

According to the steel cord of the present invention, two core strands and five side strands are twisted at a time, but a preset habit is applied to each of the core strands and the side strands. Twisted by making the tension of the side strands weaker than the tension of the core strands and twisting them out a little longer, then passing between rollers with flat surfaces and applying a fairly strong compression process It is possible.

Although the steel cord of the present invention can be manufactured by a tuber type twisting machine, it is more efficient and practical to manufacture it by a buncher type twisting machine. If a buncher-type twisting machine is used, the strands will be twisted.
It is necessary to take that point into consideration because the habit of the country is different.

When the tire steel cord of the above construction is pressed and vulcanized by sandwiching it between two rubber sheets, the steel cord can be applied even if a little strong tension is applied to the steel cord. This eliminates the phenomenon that the gap between the strands is elongated due to the extension of the cord and the rubber penetration becomes worse, and the steel cord after the calendar contracts. Then, the rubber completely penetrates into the steel code to form a complete composite of the steel code and the rubber having a stable shape. At this time, the steel cords are buried in a direction in which the long side of the steel cords extends in the left-right direction with respect to the sheet horizontal plane, and the steel cords are arranged substantially in a line in the longitudinal direction. The cross section of the steel cord has a stable shape and a low flatness, so that the thickness of the rubber sheet can be reduced, which contributes to the weight reduction of the tire. Furthermore, the bending stiffness is higher in the horizontal direction than in the vertical direction, and the rigidity in the width direction of the belt increases,
The lateral rigidity of the tire is increased, and the cornering characteristics and steering stability are improved.

[0019]

Embodiments of the present invention will be described below. FIG. 1 is a schematic view showing a cross section of a steel code of the present invention. FIG. 1 (a) shows a case where two core wires are arranged substantially perpendicularly to the major axis direction of the cross section of the cord, and FIG. 1 (b) shows a case where the core strands are arranged substantially in a line in the major axis direction.

In order to evaluate the properties of the steel cord of the present invention, the number of core strands M, the number of side strands N, the twist pitch P (mm), the molding rate of the core strands are shown in Table 1 below. ,
Example 1 of a steel cord in which the shaping rate of the side strand, the minor axis T (mm) and the major axis W (mm) of the elliptical cross section of the steel cord were varied within the scope of the present invention. And 2, FIG.
Conventional example 1 of steel code of 3 + 6 configuration as shown in FIG.
2 / having a cross-sectional shape as shown in FIGS.
Conventional example 2 of steel code having 5 constitutions was manufactured. For each of these steel cords, the rubber penetration rate, fatigue resistance, cord shrinkage allowance, rigidity ratio, workability during tire manufacturing, workability during cord manufacture were evaluated. The results as shown in Table 2 were obtained. Test conditions and evaluation methods for each item shown in Table 2 are as follows.

Rubber penetration rate: Each steel cord was embedded in rubber while applying a 4 kg tensile load, and after vulcanization, the steel cord was taken out of the rubber and the steel cord was removed.
The cord was disassembled to observe a certain length of the strand, and the ratio of the observed length to the length of the trace in contact with the rubber was expressed in%. In the table, the larger the value, the better the rubber penetration rate.

Fatigue resistance: A three-point pulley using a composite sheet in which a plurality of steel cords are embedded in a rubber sheet.
The number of repetitions until the embedded steel cord breaks through fretting wear, buckling, etc. is determined by testing using a bending fatigue tester, and the twisted steel of the conventional example 1 is obtained.
The index was expressed as an index with the value of the record being 100. In the table, the larger the value, the better the fatigue resistance.

Code shrinkage allowance: Approximately 100 steel cords are arranged in parallel at 2 mm intervals and embedded in a rubber sheet to form a composite sheet having a width of 20 cm and a length of 2 m. The steel cord is cut at both ends. If the steel cord is greatly elongated, the length of the steel cord is greatly reduced after cutting. In this case, the percentage of the length of the steel cord contracted to the length of the rubber sheet was defined as the shrinkage of the cord.

Stiffness ratio: As shown in FIG. 3 (a), "5 steel cords having a 100% modulus of 35 kg /
The test piece 12 was embedded in a row so that the major axis of the steel cord cross section was horizontal with respect to the rubber sheet 11 having a size of ² cm ² , and as shown in FIG. The steel cord was embedded in the rubber sheet 11 in parallel so that the major axis of the steel cord had a vertical cross-section. "A test piece 13 was manufactured and shown in FIG. As described above, the test piece 12 or 13 is mounted on a three-point bending test machine having a span Sp = 20 mm, and “the weight G when the test piece 12 is held down by 5 mm” / “test piece 1”.
The weight G when 3 was held down by 5 mm "was defined as the rigidity ratio.

That is, the rigidity ratio was defined as "the bending rigidity of the steel cord in the minor axis direction" / the bending rigidity of the steel cord in the major axis direction. In the table, a smaller value indicates a difference in bending stiffness. In addition, the stainless steel of the conventional example 1
In the record, there is no major axis and minor axis, so the rigidity ratio was set to 1.00. The thickness of the test piece 12 or 13 is 4 mm, the width is 15 mm, and the length is 100 mm.

Handling operability at the time of cord production: Good operability and productivity in unwinding, twisting and winding operations in the stranding process of steel cord production, Was evaluated as x, and an intermediate level was evaluated as Δ. Handling workability during tire manufacturing: Good workability and productivity in each of the following operations: handling of steel cord, calendaring, calendar cutting, tire molding, and vulcanization in the handling work in the tire manufacturing process. 〇, の も の indicates a defective one, and △ indicates an intermediate one.

[0027]

[Table 1]

[0028]

[Table 2]

The following points are apparent from Tables 1 and 2. In Conventional Example 1, three core strands having a wire diameter of 0.20 mm were twisted into a Z twist at a twist pitch of 10.0 mm, and six side strands having a wire diameter of 0.35 mm were twisted around the core. 0m
Steel cord twisted in S twist at m. Z /
It is a steel cord with a perfect circular cross section twisted into S twist and closed twist, and has excellent shrinkage of cord and excellent handling workability during tire manufacturing, but rubber infiltration. Poor performance, poor fatigue resistance and poor rigidity ratio.
Twisting and S-twisting work are required, resulting in poor productivity.

In Conventional Example 2, two core strands having a wire diameter of 0.175 mm and five side strands having a wire diameter of 0.35 mm were twisted at a time at a twist pitch of 18.0 mm into an S twist at a time. The shaping rate of the wire is 133%, the shaping rate of the side strand is 115%,
The oblateness was set to 80%. This steel code is excellent in rubber penetration, fatigue resistance and rigidity ratio,
The shrinkage of the cord is large, and the handling workability during tire production and cord production is poor.

The steel cords of Examples 1 and 2 do not have the above-mentioned disadvantages and are excellent in any of the characteristics. When used in tires, the steel cords are deformed according to the force from the road surface and ride. Comfortable and good cornering characteristics,
The tire is not easily deformed during cornering.

[0032]

The steel cord for reinforcing a tire and the steel radial tire according to the present invention are constituted as described above and have the following effects. Since the two core strands have a molding rate of about 100% and are almost in contact with each other and twisted, and the steel cord has a small elongation under a low load, the winding reel on which the steel cord is wound is used. Less deformation and damage, good workability. In the calendering process in tire manufacturing, steel
Even when the steel cord is slightly tensioned and pulled, the steel cord is less elongated and the steel cord is not deformed or shrunk, so that the tire is excellent in quality and workability in manufacturing. Compared with the conventional steel cord, the flattening ratio (short diameter T / long diameter W) of the code cross section can be reduced, and the rubber sheet thickness when embedded in rubber to form a sheet can be further increased. By making it thinner, the weight of the tire can be kept small, the cost of the tire can be reduced, and the fuel efficiency of the automobile can be improved. Since the core strands have a structure in which the core strands are interposed between the side strands at a 1/2 pitch interval, the core strands do not come off. By reducing the oblateness and decreasing the rigidity in the tire rotation direction, the riding comfort is improved, while the rigidity in the direction perpendicular to the tire rotation direction can be increased, so that the cornering performance can be improved. it can. The arrangement of the two core strands and the five side strands is very stable, so that the penetration of rubber into the inside becomes very good and the fatigue resistance is also improved. Both conventional tuber type and buncher type stranded wire machines can be manufactured, and troubles such as poor twisting are reduced.
Excellent handling workability.

[Brief description of the drawings]

FIG. 1 shows an embodiment of a tire reinforcing steel cord of the present invention. It is the schematic which shows the cross section of a 2/5 structure.
(A) is when the two core strands are arranged substantially perpendicular to the major axis direction of the cross section of the code, and (b) is when the core strands are arranged substantially in a line in the major axis direction.

FIG. 2 is an explanatory diagram illustrating a case where a core element wire 1 is interrupted between side element wires 2;

3A and 3B are diagrams showing test pieces used for a three-point bending test, wherein FIG. 3A is a schematic view of a test piece for measuring bending stiffness in a short diameter direction, and FIG. FIG. 3 is a schematic view of the test piece of FIG.

FIG. 4 is an explanatory view showing a three-point bending test method.

FIG. 5 is a sectional view of a conventional steel cord having a 3 + 6 structure of a close twist.

FIG. 6 is a sectional view of a conventional steel code having a 2/5 structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Core strand 2 ... Side strand 3 ... Steel cord 11 ... Rubber sheet 12, 13 ... Test piece W ... Steel cord cross section Major axis T: minor axis of steel code cross section A: center line

Claims (2)

[Claims] 1. A core wire comprising two wires having a wire diameter of 0.15 mm to 0.25 mm and a core wire of 0.34 mm to 0.4 mm.
A steel cord obtained by twisting five strands having a wire diameter of 0 mm as side strands at a time in the same direction, and having a substantially elliptical cross section with a substantially same cross-section in the longitudinal direction (major axis). W, minor diameter T), two core strands are substantially in contact with each other and twisted together, and a part of the five side strands adjacent to each other has a space. Twisted,
When the two core strands are arranged substantially in a line in the major axis direction of the cross section of the cord, the two core strands are embedded so as to be surrounded by the five side strands, and the two core strands have the cross section of the code. When arranged substantially vertically in the major axis direction, one of the core strands is in contact with the inside of one side strand, and the other core strand is interrupted between the other two side strands. And the flattening rate (percentage of T / W) of the substantially elliptical shape is 65% to 88%.
A steel cord for reinforcing a tire, characterized in that: 2. A steel radial tire reinforced with a steel cord in which a plurality of strands are twisted, the steel cord having a wire diameter of 0.15 mm to 0.25 mm. Are used as core wires, and 0.34 mm to
A steel cord in which five strands each having a wire diameter of 0.40 mm are twisted at a time in the same direction with side strands having a substantially elliptical cross section having substantially the same longitudinal direction. In the tire reinforcing steel cord having a (long diameter W, short diameter T), two core strands are substantially in contact with each other and twisted, and a part of the five side strands adjacent to each other has a space. When two core strands are arranged in a line in the major axis direction of the cross section of the cord, the core strands are inherently surrounded by the five side strands, and the two core strands are When they are arranged substantially perpendicular to the major axis direction of the cross-section of the core, one of the core strands is in contact with the inside of one side strand, and the other core strand is the other two side strands. The flattening rate (percentage of T / W) of the substantially elliptical shape is 65% to 8
Steel radial tire characterized in that it is 8%.