JP2000008281A - Steel cord for reinforcing rubber article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide steel cords for reinforcing rubber articles that hardly have the parts at which the core wires intersect each other with small residual internal torsion and shows excellent efficiency of strength development and excellent durability in the steel cords of the M parallel + N structure. SOLUTION: In a rubber article-reinforcing steel cord that is composed of the core in which two core straight wires having the same diameter dc are arranged in parallel without twisting and the one-layer sheath in which seven sheath wires having the same diameter ds are twisted around the core and has a flat cross section contour, the diameter dc of the core wire is 0.3-0.38 mm, while the diameter ds of the sheath wire is in the range from dc+0.03 to dc-0.03 mm, and the twisting pitch P of the sheath wire is > 50-fold the diameter dc of the core wire and < 120-fold the diameter ds of the sheath wire.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a steel cord for reinforcing rubber articles, and more particularly to a steel cord suitable as a reinforcing material for a belt layer of a radial tire (TBR) for trucks and buses.

[0002]

2. Description of the Related Art Conventionally, as a steel cord for reinforcing a belt layer of a TBR, a core formed by twisting a plurality of strands, a two-layer sheath formed by twisting strands around the core into two layers, or the like is used. A steel cord having a three-layer structure was used. However, recently, a steel cord having a two-layer structure including a core and a single-layer sheath has been widely used in order to reduce the weight and simplify the structure.

[0003] Among these two-layer steel cords,
It is known that a steel cord having a core in which a plurality of core wires are arranged in parallel without being twisted has the following advantages. (1) It is economical because it can be manufactured by one-step twisting. (2) By arranging the steel cords so that the parallel direction of the core strands is along the width direction of the belt layer of the tire, a tire having excellent steering stability can be obtained without impairing riding comfort. Further, since the thickness of the belt layer can be reduced, the weight of the tire can be reduced.

A plurality of (M) core strands are arranged in parallel without being twisted, and a single-layer sheath formed by twisting a plurality (N) of sheath strands around the core. 2
Regarding a steel cord for reinforcing a rubber article having a layer structure (hereinafter, referred to as “M parallel + N structure”), for example, the following technology is disclosed.

Japanese Patent Application Laid-Open No. 9-1580065 discloses a core in which a plurality of core strands are non-twisted and a plurality of the core strands are arranged in a side-by-side row, and a plurality of sheath strands are used as a core strand. A steel cord having an M-parallel + N structure, which is made of a sheath circumscribed and twisted around a core and having an elliptical cross-sectional shape, is disclosed.

Japanese Unexamined Patent Publication No. 9-156314 discloses a core in which two core wires having the same diameter are arranged in parallel without twisting, and has a diameter 0.8 to 1.2 times the core wire. A cross section comprising 5 to 8 sheath wires having the same diameter, which are spirally wound at a pitch of 40 to 60 times the sheath wire diameter in close contact with the core while providing a gap between the wires. A steel cord having a two-parallel + N structure (N = 5 to 8) having a substantially elliptical contour is disclosed.

[0007]

However, the conventional M-parallel + N steel cord has the following problems. (1) Since the load difference between the core element wire and the sheath element wire is large, the strength display efficiency and durability are poor. (2) A portion where core strands intersect easily exists. (3) Since internal torsion remains between the core and the sheath, when the rubber sheet in which a plurality of the steel cords are buried in parallel is breached, the sheet ends are likely to be warped. For this reason, handleability during tire production is poor.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems, and in a steel cord having an M-parallel + N structure, a portion where core wires intersect hardly exists, the residual internal torsion is small, and the strength exhibiting efficiency and An object of the present invention is to provide a steel cord for reinforcing rubber articles having excellent durability.

[0009]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that in a steel cord for reinforcing rubber articles having a two-parallel +7 structure, the wire diameter and the twist pitch ratio are optimized. As a result, the present inventors have found that the above object can be achieved, and have completed the present invention.

That is, the steel cord for reinforcing a rubber article of the present invention comprises a core formed by arranging two straight core strands having the same diameter dc in parallel in the longitudinal direction without twisting them.
A steel cord for reinforcing a rubber article having a flat cross-sectional profile, comprising a single-layer sheath formed by twisting seven sheath strands having the same diameter ds around the core. 0.30m in diameter dc
m or more and 0.38 mm or less, the diameter d of the sheath element wire
s is not more than dc + 0.03 mm and not less than dc−0.03 mm, and the twist pitch P of the sheath wire is not less than 50 times the diameter dc of the core wire and not more than 120 times the diameter ds of the sheath wire. It is assumed that.

[0011] In the steel cord for reinforcing rubber articles of the present invention, particularly preferably, the diameter dc of the core strand is 0.3.
2 mm or more and 0.36 mm or less, diameter d of sheath wire
This is a steel cord in which s is dc + 0.03 mm or less and dc-0.01 mm or more, and the twist pitch P is 60 times or more the core element diameter dc and 90 times or less the sheath element diameter ds.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A steel cord for reinforcing a rubber article according to the present invention will be described with reference to FIG. FIG. 1 is a diagram showing a cross section of a steel cord for reinforcing a rubber article according to an example of the present invention. The steel cord 1 shown is a core 2
And a single-layer sheath 3. Core 2 is
Two core strands 2a and 2b are arranged in parallel without twisting. The core strands 2a and 2b have substantially the same diameter dc, where dc is at least 0.30 mm and 0.3
8 mm or less.

The sheath 3 comprises seven sheath wires 4 twisted around the core 2. All seven sheath wires 4 have substantially the same diameter ds, and ds is the core wire diameter d.
c + 0.03 mm or less and dc−0.03 mm or more. Further, the twist pitch P of the sheath wire 4 is the core wire diameter d.
It is in the range of 50 times or more of c and 120 times or less of the sheath wire diameter ds. As shown in FIG. 1, seven sheath wires 4
Is wound substantially in contact with the core strands 2a and 2b, whereby the profile of the cross section of the steel cord 1 becomes substantially elliptical. The core strands 2a and 2b and the sheath strand 4 preferably have a tensile strength of 2800 MPa or more,
More preferably, a brass-plated steel wire having a pressure of 3000 MPa or more is used.

As a basic structure of the steel cord for reinforcing rubber articles of the present invention, the sheath element wire diameter ds is dc + 0.03 m.
The reason why the 2-parallel +7 structure that is less than m is adopted is as follows. First, the reason why the number of core strands is set to two is that if the number of core strands is three or more, a portion in which the core strands are not arranged in a line in a cord cross section is likely to be generated. This is because the effect of reducing the thickness of the belt layer when used is impaired. In addition, sheath wire diameter ds
Is set to dc + 0.03 mm or less, and the number of sheath strands is set to seven because it is easy to form a gap between sheath strands large enough to allow rubber to penetrate without extreme bias.

Next, the reasons for the limitations on the core wire diameter dc, sheath wire diameter ds and twist pitch P, which are the characteristics of the steel cord of the present invention, will be described.

The lower limit of the diameter dc of the core strand is 0.30 mm.
The reason for this is to secure sufficient strength and rigidity as a TBR belt layer reinforcing cord under the above basic structure. On the other hand, the upper limit is set to 0.38 mm because dc
Exceeds 0.38 mm, when wound on a spool,
This is because straightness is impaired due to the winding habit of the parallel core wires. A particularly preferred range of dc is 0.32 mm
It is not less than 0.36 mm.

Further, the sheath wire diameter ds is set to dc + 0.03
mm or less, but the lower limit is set to dc−0.03 mm, and the twist pitch P is set to 50 times or more of the core element diameter dc by adding such a limitation that the core elements intersect each other. This is because it has been found that it becomes difficult to form a portion where the code is formed, and that residual torsion inside the code can be suppressed. This will be described in detail below.

FIG. 2 is a diagram showing an example of a method of manufacturing a steel cord having a two-parallel + 7 structure. Core strands 2a and 2
b is supplied from the outside of the tubular type twisting wire machine 10,
After passing through the rotating barrel 11, at the twisting die 12, the seven sheath wires 4 supplied from inside the barrel 11 are used.
Are twisted to form a 2-parallel +7 structure. In this process, the direction connecting the centers of the core strands 2a and 2b (hereinafter referred to as "core parallel direction") should be theoretically constant, but in actuality, it is twisted due to the passage resistance in the barrel 11, and the like. Is generated. Twisting of the sheath wire 4 in the twisting die 12 has a correcting action for this twist. However, if the twist is excessive, a portion where the core wires cross each other or a large torsion is generated inside the cord. May occur.

One method for reducing the twist in the core parallel direction when passing through the barrel 11 is to increase the passing speed of the core strands 2a and 2b with respect to the rotation speed of the barrel 11, that is, to reduce the twist pitch P. It is to make it big. Specifically, when a normal twisting machine is used, the twist in the core parallel direction is sufficiently reduced by setting the twist pitch P to 50 times or more, preferably 60 times or more the diameter dc of the core strand. In addition, when the sheath wires 4 are repaired by twisting, the intersection of the core wires and the occurrence of large internal torsion can be significantly suppressed. However, if the twist pitch P is too large, the shape retention of the sheath after twisting deteriorates.
The twist pitch P is 120 times or less, preferably 90 times or less the sheath wire diameter ds.

On the other hand, the sheath wire diameter ds is dc−0.03
When the diameter is less than mm, the rigidity of the sheath wire is small. Therefore, in order to sufficiently correct the twist in the core parallel direction, it is necessary to twist the sheath so as to have a large latent torsion against the twist of the core. The thus twisted steel cord has a large amount of sheath rotation at the cut end, and when the rubber sheet in which a plurality of the steel cords are laid in parallel is breached, the sheet end is easily warped greatly. Therefore, the sheath wire diameter ds is set to dc−0.03 mm or more, preferably dc−0.01 mm or more.

Further, the sheath wire diameter ds and the core wire diameter d
Since the difference from c is as small as 0.03 mm or less, the correction device 1
In 3, the difference in bending strain between the core strand and the sheath strand when repeated bending by a roller or the like is applied is small, and straightness, twist, and the like can be effectively corrected.

The above limitation on the sheath wire diameter ds and the twist pitch P in the present invention also has the effect of alleviating the load-bearing difference between the core wire and the sheath wire in the M-parallel + N structure. A steel cord having excellent properties can be obtained.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. A steel wire having brass plating on the surface and containing about 0.82% by weight of carbon is used as a strand, and according to the production method shown in FIG. 2, the steel cords of Examples 1 to 7 shown in Table 1 below and Steel cords of Comparative Examples 1 to 5 shown in Table 2 were produced, respectively.

In the table, Examples 1 to 7 are examples of a steel cord having a two-parallel +7 structure according to the present invention.

Comparative Example 1 is an example of a steel cord having a two-parallel + 7 structure in which the twist pitch P is excessive and deviates from the scope of the present invention.

Comparative Example 2 is an example of a steel cord having a two-parallel + 7 structure in which the twist pitch P is too small and deviates from the scope of the present invention.

Comparative Example 3 is an example of a steel cord having a two-parallel + 7 structure in which the sheath wire diameter ds is too small relative to the core wire diameter dc and deviates from the scope of the present invention.

Comparative Example 4 is an example of a steel cord having a two-parallel + 7 structure in which the sheath wire diameter ds is excessively large relative to the core wire diameter dc and deviates from the scope of the present invention.

Comparative Example 5 is an example of a steel cord having a two-parallel + 7 structure in which the core strand diameter dc is excessively large and deviates from the scope of the present invention.

With respect to the steel cords of these examples and comparative examples, the evaluation methods for the following items are as follows. (1) Breaking strength Measured according to the cutting load measuring method of JIS G3510. (2) Sheath rotation amount at cut end The evaluation was made based on the rotation amount of the cut end of the sheath when the steel cord was cut with a blade. (3) Rubber penetration Steel cord is buried in unvulcanized rubber,
An evaluation sample was prepared by performing a vulcanization treatment for 5 minutes, and the state of rubber penetration was evaluated by observing the cross section of the steel cord in the sample. (4) Winding habit Winding tension of about 25 cm on a spool with a winding drum diameter of 12 cm
The steel cord was wound in N and evaluated for the presence or absence of a curl after being left for 2 weeks.

The results obtained are shown in Tables 1 and 2 below.

[0032]

[Table 1]

[0033]

[Table 2]

As shown in Tables 1 and 2, Examples 1 to
Steel cord No. 7 showed good results for all evaluation items.

On the other hand, the steel cord of Comparative Example 1 in which the twist pitch P was too large was poor in shape retention and insufficient in rubber penetration.

The steel cord of Comparative Example 2 in which the twist pitch P is too small has a large amount of sheath rotation at the cut end,
Intersections between core strands also occurred frequently. In addition, compared to the steel cord of Example 3 using the same element wire, the efficiency of the strength was lower and the breaking strength was slightly lower.

In the steel cord of Comparative Example 3 in which the sheath wire diameter ds was too small with respect to the core wire diameter dc, the amount of rotation of the sheath at the cut end was large, and residual twist in the core parallel direction was also observed.

The steel cord of Comparative Example 4 in which the sheath strand diameter ds was excessively large with respect to the core strand dc was insufficient in rubber penetration.

The steel cord of Comparative Example 5 in which the core strand diameter dc was excessively had a curl.

[0040]

As described above, the steel cord for reinforcing rubber articles according to the present invention has advantages such as twisting in the core parallel direction, residual internal torsion, and an increase in the load bearing difference between the core wire and the sheath wire. The problem of the conventional steel cord having the M parallel + N structure can be improved.

The steel cord for reinforcing a rubber article of the present invention is particularly suitable as a reinforcing material for a belt layer of a TBR, and the steel cord is arranged such that the core-parallel direction with little twist is along the width direction of the belt layer of the tire. By arranging the tires, the original characteristics of the M-parallel + N structure can be sufficiently exhibited, and a tire with excellent steering stability and reduced weight can be obtained without impairing riding comfort.

[Brief description of the drawings]

FIG. 1 is a sectional view of a steel cord according to the present invention.

FIG. 2 is a view showing a method of manufacturing a steel cord having a two-parallel + 7 structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel cord 2 Core 2a Core strand 2b Core strand 3 Sheath 4 Sheath strand 10 Twisting machine 11 Barrel 12 Twisting die 13 Straightening device

Claims (2)

[Claims] 1. A core formed by arranging two straight core wires having the same diameter dc in parallel in the longitudinal direction without twisting them, and seven sheath wires having the same diameter ds. A steel cord for reinforcing a rubber article having a flat cross-sectional profile constituted by a single-layered sheath twisted around the core wire, wherein the core element wire has a diameter dc of 0.30 mm or more and 0.3 mm or more.
8 mm or less, the diameter ds of the sheath wire is dc + 0.0
Rubber article having a length of 3 mm or less and dc-0.03 mm or more, and a twist pitch P of the sheath wire is 50 times or more of the diameter dc of the core wire and 120 times or less of the diameter ds of the sheath wire. Steel cord for reinforcement. 2. The diameter dc of the core strand is 0.32 mm.
Not less than 0.36 mm, the diameter ds of the sheath wire
Is not more than dc + 0.03 mm and not less than dc-0.01 mm, and the twist pitch P is not less than 60 times the core wire diameter dc and not more than 90 times the sheath wire diameter ds. Steel cord.