JPH1193087A - Steel cord for reinforcing rubber article and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cord structure capable of suppressing the occurrence of cord breakage for a compression input. SOLUTION: This steel cord for reinforcing a rubber article is obtained by reducing the lay pitch of a steel filament constituting the outermost layer of a core strand 1 from that of a steel filament constituting the outermost layer of sheath strands 4, in the steel cord comprising the sheath strands 4, prepared by laying plural filaments and arranged around the core strand 1 obtained by laying plural steel filaments.

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 rubber articles such as pneumatic tires and industrial belts, and a pneumatic tire in which the steel cord is applied to a carcass, particularly a pneumatic tire for construction vehicles. It is about tires.

[0002]

2. Description of the Related Art Rubber articles and pneumatic tires, which are typical examples thereof, have a carcass reinforced with a steel cord as a skeleton, and various inputs are repeated on the steel cord as the tire rolls. It is. In particular, since pneumatic tires for construction vehicles are mainly used in rough terrain, they are susceptible to input from the width direction of the tire, so-called lateral force, and when this lateral force is applied, the tire is formed on the carcass, especially on the tread surface layer. The compression input concentrates on the carcass portion corresponding to the region where the rubber is thin on the radially inner side of the groove, and the cord of the carcass ply is broken. As a result, the strength of the carcass ply is reduced.

[0003]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to suppress the occurrence of code breakage in a compressed input.
The aim is to improve the durability of the carcass of the tire, in particular, by providing a new cord structure.

[0004]

Conventionally, cords for reinforcing a carcass ply of a construction vehicle tire include, for example, (1+
6) + 6 × (1 + 6) structure, (3 + 9) + 6 × (3+
9) Structures and multi-twisted cords such as (3 + 9 + 15) + 6 × (3 + 9 + 15) structures are mainly used. After elaborately studying a technique for avoiding cord breakage due to compression input in these cords, firstly, the core strand It has been found that it is essential to improve the foldability, and that it is effective to regulate the twist pitch in the strands of the cord. That is, in the above-mentioned conventional cord, it was found that it is extremely effective to break the cord by changing the twist pitch, which was the same in all strands, especially between the core strand and the sheath strand. The invention has been completed.

That is, the present invention relates to a steel cord in which a sheath strand in which a plurality of steel filaments are twisted is arranged around a core strand in which a plurality of steel filaments are twisted, wherein the outermost layer of the core strand is formed. A steel cord for reinforcing rubber articles, wherein the twist pitch of the constituent steel filaments is smaller than the twist pitch of the steel filaments forming the outermost layer of the sheath strand.

Here, the ratio of the twist pitch of the steel filament constituting the outermost layer of the sheath strand to the twist pitch of the steel filament constituting the outermost layer of the core strand is more preferably set to 1.2 or more.

In the case where the core strand and the sheath strand have the same structure in which one or more layers of a sheath made of a plurality of steel filaments are twisted around a core made of a plurality of steel filaments, In the strand and the sheath strand, the respective twist pitches of the core and the sheath each layer are:
Advantageously, the core strand is smaller than the sheath strand.

Also in this case, the ratio of the twist pitch of the core of the sheath strand and each layer of the sheath to the twist pitch of the core and each layer of the sheath is 1.
More preferably, it is 2 or more.

Further, the present invention is a pneumatic tire in which the above-mentioned steel cord is applied to a carcass extending in a toroidal shape between a pair of bead portions.

[0010]

1 to 4 show a cross section of a steel cord for reinforcing a rubber article according to the present invention.
First, in FIG. 1, reference numeral 1 denotes a core strand, and the core strand 1 is a 1 + 6 structure strand in which a sheath 3 of six steel filaments is twisted around a core 2 of one steel filament,
Furthermore, around this core strand 1, similarly, the core 2
(1 + 6) + 6 ×, in which six sheath strands 4 having a 1 + 6 structure in which a sheath 3 is twisted around the wire are twisted.
It is a multi-twist cord having a (1 + 6) structure. L is a wrapping filament.

Here, the structure of the core strand 1 and the sheath strand 4 is not particularly limited as long as a plurality of steel filaments are twisted, that is, in addition to the 1 + 6 layer twisted structure shown in FIG. Twisted structure or multiple twisted structure is suitable.

However, the twisting pitch of the sheath 3 by the steel filaments constituting the outermost layer of each strand, in the illustrated example, six steel filaments, that is, the twisting pitch _Pc of the core strand 1 and the twisting pitch of the sheath strand 4 P _s is, it is essential to satisfy the relationship of P _c <P _s. When the strand has a single twist structure or a multiple twist structure, the twist pitch of the steel filament forming the outermost layer is nothing less than the twist pitch at the time of producing each strand.

[0013] That is, between the core strand 1 and the sheath strands 4 and smaller than the pitch P _s twisting the twisting pitch P _c, increasing the angle for the code axis direction of the outermost layer filaments of the core strand located in the center of the code Since the outermost filament of the sheath strand can be made closer to the angle with respect to the axial direction of the cord, the burden of compressing the core strand when the cord has a compressive input in the axial direction can be reduced. Premature breaks of the core strand with respect to the sheath strand are advantageously avoided. As a result, the durability against breakage of the cord, that is, the so-called compression fatigue resistance is improved. On the other hand, in the conventional multi-twisted cord, since the compression input in the cord axial direction is concentrated on the core strand, the core strand breaks prior to the sheath strand, and the cord is easily broken. That is, in the conventional multi-twisted cord, since each sheath strand itself has a twist pitch and is twisted around the core strand, if the core strand and the sheath strand have the same pitch, the above-described cord shaft Since the angle of the outermost filament to the direction is smaller on the core strand than on the sea strand, the compression input is concentrated on the core strand.

Therefore, since the cord of the present invention suppresses the breakage of the cord in response to the compression input, when this cord is used for a carcass, it is possible to prevent the tire from being broken due to the breakage of the carcass ply.

Next, the code shown in FIG. 2 is based on a strand having a 3 + 9 structure. That is, a sheath 3 composed of nine steel filaments is twisted around a core 2 in which three steel filaments are twisted.
Around core strand 1 having a +9 structure, 3 + 9
Six sheath strands 4 of the structure were twisted, (3
+9) + 6 × (3 + 9) structure. In this code, the twisting pitch P _c and twist pitch P _s of the sheath 3 of the sheath strands 4 of the sheath 3 of the core strand 1, it is essential to satisfy the relationship of P _c <P _s.

The cord shown in FIG. 3 has a core strand 1 and a substrand 5 in which five steel filaments are twisted around one steel filament.
Is adopted, and around the core strand 1, 6 of the 3 + 9-structured sheath strands 4 are twisted.
Twisted books, {4 × (1 + 5)} + 6 × (3+
9) A multi-twist cord having a structure. In this code,
The twist pitch of the steel filament constituting the outermost layer of the core strand 1 corresponds to the twist pitch when four of the sub-strands 5 are simultaneously twisted, and the twist pitch P _c and the twist of the sheath 3 of the sheath strand 4. pitch P _s is, it is essential to satisfy the relationship of P _c <P _s.

[0017] Here, the twisting pitch P _c and P _s, the ratio P _s / P _c of the pitch P _s twisting for the twisting pitch P _c is 1.2
It is preferable that it is in the above range. Because the ratio P
_{If s} / _Pc is less than 1.2, the effect of reducing the compression input in the code axis direction cannot be expected. On the other hand, the ratio P _s /
If P _c exceeds 6.0, the angle of the outermost filament of the core strand with respect to the cord axis direction becomes too large, and the balance of the compression input load may be lost.

Further, in the cord shown in FIG. 4, a first sheath 3a of nine steel filaments is twisted around a core 2 in which three steel filaments are twisted, and further, around a first sheath 3a. 3 + 9 + 15 twisted second sheath 3b of 15 steel filaments
Around core strand 1 of structure, also 3 + 9 + 15
Six sheath strands 4 of the structure were twisted, (3
+ 9 + 15) + 6 × (3 + 9 + 15) structure. In this code, the twisting pitch P _s of the second sheath 3b of the outermost layer of the pitch P _c and the sheath strands 4 twists second sheath 3b of the outermost layer of the core strand 1, P _c
<Is possible to satisfy the relationship of P _s, it is important.

Here, as shown in the cord structure of FIG. 4, the core strand 1 and the sheath strand 4 are formed by twisting two or more layers of a sheath made of a plurality of steel filaments around a core 2 made of a plurality of steel filaments. In the case of the same structure, in addition to regulating the twisting pitch of the outermost second sheath 3b, the twisting pitch of the inner first sheath 3a and the core 2 is also smaller than that of the sheath strand. It is advantageous for the strand to be small. The regulation of the twist pitch of the core 2 is the same in the cord shown in FIG. The reason for this is the same as the reason for restricting the twist pitch in the outermost layer of the strand. Further, specific ratio of the twist pitch is the same as the above ratio P _s / P _c.

Each of the above-mentioned cords is an example in which six sheath strands are arranged around one core strand. However, the present invention relates to, for example, nine sheath strands around three core strands. It can also be applied to cords in the case where strands are arranged. In short, the above-mentioned twist pitch P _c in the core strand located near the center of the cord is
It is smaller than the twist pitch P _s of the sheath strands disposed thereabout.

As shown in FIG. 3, a steel filament constituting the core strand has a diameter different from that of the steel filament constituting the sheath strand, and has the same strand diameter except for the strand structure. It is also possible to Note that the twist direction of the strand does not need to be particularly limited.

[0022]

EXAMPLES Steel cords having various structures according to FIGS. 1 to 4 were prototyped under the specifications shown in Table 1. Next, each of the produced steel cords was applied to a carcass of a construction vehicle radial tire having a size of 29.5R25 whose structure is shown in FIG. In addition,
The application of each steel cord to the carcass was performed by adjusting the number of shots so that the carcass strength was the same between all the test tires. In FIG. 5, reference numeral 6 denotes a pair of bead cores, a carcass 7 extending in a toroidal shape is arranged between the bead cores 6, and a belt 8 and a tread 9 are arranged radially outside the crown portion. Become.

Each of the tires thus obtained was subjected to 25.00 / 3.5
After assembling into the rim, internal pressure 7kgf / cm ^TwoAfter filling
Attached to the car, with repeated sharp turns on a zigzag path
After running 5,000 km, dissect the tires and
Pull out 10 steel cords in the carcass below
Then, the number of broken filaments was measured. And
10 teal cords broken in total filaments
The ratio of the number of filaments is expressed as a percentage as the breaking rate.
Was. Table 1 shows the results of these surveys.

[0024]

[Table 1]

From the same table, it can be seen that in the same cord structure in which the twist pitch is regulated between the core strand and the sheath strand according to the present invention, the breaking rate of the filament is greatly reduced.

[0026]

As described above, according to the cord of the present invention, since the occurrence of cord breakage in response to a compression input is suppressed, the durability of the carcass to which the cord is applied, and hence the durability of the tire, are improved. be able to. Therefore, it is possible to provide a reinforcing material suitable for a tire for a construction vehicle particularly on the premise of traveling on a rough terrain.

[Brief description of the drawings]

FIG. 1 is a diagram showing a code structure of the present invention.

FIG. 2 is a diagram showing a code structure of the present invention.

FIG. 3 is a diagram showing a code structure of the present invention.

FIG. 4 is a diagram showing a code structure of the present invention.

FIG. 5 is a diagram showing a cross section of the tire in the width direction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Core strand 2 Core 3 Sheath 4 Sheath strand 5 Substrand 6 Bead core 7 Carcass 8 Belt 9 Tread

Claims (5)

[Claims] Claims: 1. A steel cord comprising a plurality of steel filaments twisted around a core strand and a plurality of steel filaments twisted around a sheath strand, the steel cord comprising an outermost layer of the core strand. The steel cord for reinforcing rubber articles, characterized in that the twist pitch is smaller than the twist pitch of the steel filament constituting the outermost layer of the sheath strand. 2. The method according to claim 1, wherein the ratio of the twist pitch of the steel filament constituting the outermost layer of the sheath strand to the twist pitch of the steel filament constituting the outermost layer of the core strand is 1.2 or more. Steel cord for reinforcing rubber articles. 3. The same structure according to claim 1, wherein the core strand and the sheath strand are formed by twisting one or more layers of a sheath of a plurality of steel filaments around a core of a plurality of steel filaments. A steel cord for reinforcing rubber articles, wherein the core strand and the sheath strand have a smaller twist pitch in each of the core and sheath layers in the core strand than in the sheath strand. 4. The ratio of the twist pitch of the core of the sheath strand and each layer of the sheath to the twist pitch of the core of the core strand and each layer of the sheath according to claim 3.
A steel cord for reinforcing rubber articles, characterized in that the number is 2 or more. 5. A pneumatic tire obtained by applying the steel cord according to any one of claims 1 to 4 to a carcass extending in a toroidal shape between a pair of bead portions.