JP6865095B2 - Steel cords and tires for reinforcing rubber articles - Google Patents

Description

The present invention relates to a steel cord and a tire for reinforcing a rubber article having a double twist structure and high strength.

Double-twisted steel cords are used to reinforce rubber articles such as tires for construction and mining vehicles. In recent years, studies have been made to reduce the weight of rubber articles such as tires by simplifying the cord structure and reducing the cord diameter to reduce the thickness of the reinforcing layer including the steel cord. Various researches and developments have been carried out on increasing the strength of double-twisted steel cords in order to reduce the weight while having the strength required for reinforcement.

However, with the double-twisted steel cord, it is difficult to obtain the cord strength commensurate with the strength of the individual filaments constituting the cord. Therefore, there has been a demand for a steel cord in which the decrease in cord strength is smaller than the total strength of the filaments constituting the cord.

Regarding the double-twisted steel cord, there is a steel cord for reinforcing a rubber article in which the twisting direction of the sheath filament of the outermost layer constituting the strand and the twisting direction of the sheath strand are the same (Patent Document 1).

Japanese Unexamined Patent Publication No. 8-170283

The steel cord for reinforcing a rubber article of Patent Document 1 improves the strength of the cord by specifying the twisting direction of the filament and the strand. However, the demand for strengthening the steel cord has not stopped, and in particular, it has been required that the decrease in cord strength with respect to the total strength of the filaments constituting the cord is small.

Therefore, an object of the present invention is to provide a steel cord for reinforcing a rubber article and a tire using the steel cord, which has a small decrease in cord strength with respect to the total strength of the filaments constituting the cord for a double-twisted steel cord.

As a result of intensive research on double-twisted steel cords, the present inventors adjusted the lamella orientation angle of the surface layer of the filaments of the steel cord to reduce the cord strength with respect to the total strength of the filaments constituting the cord. We have found that a steel cord for reinforcing a rubber article with a small size can be obtained, and have completed the present invention.

That is, the steel cord for reinforcing a rubber article of the present invention has a double-twisted structure in which a plurality of strands formed by twisting two or more layers of filaments are twisted together, and at least a part of the filaments has a tensile strength of 3000 MPa or more. And
The lamella orientation angle of the surface layer portion of at least a part of the filament is 0.0 ° or more and 6.0 ° or less, or 12.5 ° or more and 18.5 ° or less.

The steel cord for reinforcing a rubber article of the present invention preferably has a filament space factor of 48% or more and less than 54%.
The cord twist angle is preferably 78 ° or more and less than 84 °.
The average value of the crossing angles of adjacent filaments excluding the wrapping filament is preferably less than 17 °.
The gap between adjacent sheath filaments constituting the strand is preferably 0.065 mm or more.
The double-twisted structure is preferably a 1 + n (n = 6 to 7) structure in which 6 to 7 sheath strands are twisted around one core strand.
It is preferable that the twisting direction of the sheath filament of the core strand and the twisting direction of the sheath filament of the sheath strand are opposite to each other.
It is preferable that the twisting direction of the sheath filaments of the sheath strands is opposite to that of the sheath filaments of the adjacent sheath strands.
Further, the tire of the present invention uses the above-mentioned steel cord for reinforcing a rubber article for reinforcement.

According to the present invention, with respect to a double-twisted steel cord, it is possible to provide a steel cord for reinforcing a rubber article and a tire using the steel cord, in which the decrease in cord strength with respect to the total strength of the filaments constituting the cord is small.

It is sectional drawing of the steel cord for reinforcing a rubber article of one Embodiment of this invention. It is the schematic of the filament cross section for demonstrating the surface layer part. It is a schematic diagram of the metal structure of the filament cross section. It is explanatory drawing of the change of the lamella direction before and after the final drawing. It is explanatory drawing of the cord twist angle. It is explanatory drawing of the crossing angle, FIG. 6A shows the crossing angle of the adjacent filament, and FIG. 6B shows the crossing angle of the sheath filament of the adjacent strand, respectively. It is explanatory drawing of the gap between adjacent sheath filaments.

Hereinafter, the steel cord for reinforcing the rubber article of the present invention and the tire using the steel cord will be described more specifically with reference to the drawings.

FIG. 1 shows a steel cord for reinforcing a rubber article (hereinafter, simply referred to as “steel cord”) according to an embodiment of the present invention, in a cross section perpendicular to the longitudinal direction of the steel cord. The steel cord 10 shown in FIG. 1 is a cord having a double-twisted structure in which one core strand 11 and six sheath strands 12 are twisted together, and has a cord structure of (3 + 9) + 6 × (3 + 9) + 1. There is. A wrapping filament 13 is wound around the outermost layer of the sheath strand 12. The core strand 11 has a two-layer twist structure in which nine sheath filaments 112 are twisted around three core filaments 111, and the sheath strand 12 has nine sheath filaments around three core filaments 121. It has a two-layer twisted structure in which 122 are twisted together.

The steel cord of the present invention is not limited to the cord structure shown in FIG. Preferably, it can have a code structure of 1 + n (n = 6 to 7).
Since the features of the steel cord of the present invention described below are the same not only for the steel cord 10 of FIG. 1 but also for other steel cords of the present invention, the steel cord 10 shown in FIG. 1 is represented in the following description. As an example, an embodiment of the present invention will be described with respect to the case where the steel cord 10 is used for reinforcing the tire.

In the steel cord 10 of the present embodiment, at least a part of the filament has a tensile strength of 3000 MPa or more. When a part of the filament of the steel cord 10 has a tensile strength of 3000 MPa or more, the steel cord 10 of the present embodiment can be made highly strong. From the viewpoint of increasing the strength of the steel cord 10, it is preferable that all the filaments constituting the steel cord 10 have a tensile strength of 3000 MPa or more.

In the steel cord 10 of the present embodiment, at least a part of the filament has a lamella orientation angle of the surface layer portion of 0.0 ° or more and 6.0 ° or less, or 12.5 ° or more and 18.5 ° or less. The surface layer portion refers to a region d from the outermost surface of the filament to a range of 20% volume fraction, as shown in FIG. 2 as a schematic view of a filament cross section. Among the filaments constituting the steel cord 10, some filaments satisfy the above-mentioned lamella orientation angle, so that the cord strong exertion rate is improved. It is more preferable that all filaments satisfy the above lamella orientation angle.

The effect of adjusting the lamella orientation angle and the lamella orientation angle will be described. FIG. 3 shows a schematic view of the metal structure of the filament cross section in FIG. 3A as an overall view and in FIG. 3B as a partially enlarged view thereof. The filament used for the steel cord is composed of a block in which colonies having a lamellar structure in which ferrite F and cementite C are arranged in layers are aggregated. As shown in FIG. 4 showing the change in the lamella orientation before and after the final drawing, the lamella orientation of the colony is aligned with the drawing direction, in other words, the longitudinal direction of the filament, by the final drawing during the production of the filament. As it is oriented, the lamella spacing becomes narrower. The angle formed by the longitudinal direction of the filament and the orientation direction of the lamella tissue is called the lamella orientation angle, and the average value of the lamella orientation angles in the surface layer portion of the filament is the value of the lamella orientation angle. For example, when the lamella orientation is the longitudinal direction of the filament, the lamella orientation angle is 0 °.
The lamella orientation angle of the surface layer portion can be adjusted to the above range by, for example, adjusting the die angle at the time of final wire drawing. The lamella orientation angle can be measured by observing the metallographic structure of the filament.

According to the research by the present inventors, it was found that the lamella orientation angle of the surface layer portion affects the resistance of the filament to the lateral pressure applied from the adjacent filament. When the lamella orientation angle of the surface layer is 0.0 ° or more and 6.0 ° or less, or 12.5 ° or more and 18.5 ° or less, the resistance to the lateral pressure applied to the filament increases, and the cord strength exertion rate improves. , Twisting loss is reduced. When the lamella orientation angle of the surface layer portion exceeds 6.0 ° and is less than 12.5 °, the shear stress generated between the cementite layer and the ferrite layer at the time of lateral pressure input increases, and the cord strength decreases. When the lamella orientation angle of the surface layer portion exceeds 18.5 °, the tensile strength of the filament itself becomes low, and it is difficult to increase the cord strength.

Further, the steel cord 10 of the present embodiment preferably has a filament space factor of 48% or more and less than 54%. The filament space factor is a value expressed as a percentage by multiplying the total cross-sectional area of the filaments constituting the steel cord by the area of the circumscribed circle of the steel cord by 100. That is, the Philamen space factor (%) = (total cross-sectional area of the filaments constituting the steel cord) / (area of the circumscribed circle of the steel cord) × 100.

When the filament space factor is in the range of 48% or more and less than 54%, the steel cord can be made highly strong with high filament filling efficiency, and high rubber permeability can be obtained. If the filament space factor is less than 48%, the filament filling efficiency is low, so the diameter of the steel cord 10 becomes large in order to obtain the required strength required for the steel cord 10, and the steel cord 10 is used to reinforce the tire. Since the thickness of the rubber reinforcing layer becomes thicker when used in, it is disadvantageous in terms of reducing the weight of the tire. When the filament space factor is 54% or more, the gap between adjacent filaments, which will be described later, becomes small, so that the rubber permeability is inferior. The preferred filament space factor is 48% or more and less than 50%.

The steel cord 10 of the present embodiment preferably has a cord twist angle of 78 ° or more and less than 84 °. As shown in the explanatory view in FIG. 5, the cord twist angle α is in the direction perpendicular to the longitudinal direction of the steel cord and in the longitudinal direction of the strand (in the case of the steel cord 10 in FIG. 1, it refers to the sheath strand 12). The angle formed by the direction along the line. The cord twist angle can be measured from the steel cord, or can be calculated from the cord diameter, strand diameter, and strand twist pitch of the steel cord.

When the cord twist angle is in the range of 78 ° or more and less than 84 °, a steel cord having a small twist loss and stable twist properties can be obtained. If the twist angle of the cord is less than 78 °, the twist is strong and the twist loss becomes too large, so that the steel cord cannot obtain the predetermined strength. Here, the twist loss is a value obtained by subtracting the value of the percentage of the cord strong exertion rate from 100. That is, twist loss (%) = 100-cord strong exertion rate. The cord strength exertion rate is a value expressed as a percentage by multiplying the value obtained by dividing the strength of the steel cord by the total strength of the filaments constituting the steel cord by 100. That is, the cord strength exertion rate (%) = (strength of the steel cord) / (total strength of the filaments constituting the steel cord) × 100. The code strength exertion rate is preferably 90% or more. It can be said that the larger the cord strength exertion rate and the smaller the twist loss, the smaller the decrease in cord strength compared to the total strength of the filaments constituting the cord. When the cord twist angle is 84 ° or more, the twist is weak and the twist property becomes unstable. The preferred cord twist angle is 80 ° or more and less than 84 °.

In the steel cord 10 of the present embodiment, the average value of the crossing angles of the adjacent filaments is less than 17 °, except for the wrapping filament. Since the average value of the crossing angles of the adjacent filaments is less than 17 °, the twist loss can be reduced. The crossing angle refers to the angle formed by the longitudinal direction of one filament and the longitudinal direction of filaments adjacent to the filament, as shown in FIGS. 6 (a) and 6 (b). The average value of the crossing angles of the steel cord 10 is the crossing angle between the adjacent core filaments 111 of the core strand 11, the crossing angle between the adjacent sheath filaments 112, the crossing angle between the core filament 111 and the sheath filament 112, and the sheath strand 12. The crossing angle between the adjacent core filaments 121, the crossing angle between the adjacent sheath filaments 122, the crossing angle between the core filament 121 and the sheath filament 122, the sheath filament 112 of the core strand 11, and the sheath filament 122 of the sheath strand 12 The average value of the crossing angles of all adjacent filaments, such as the crossing angle of the sheath strands 12 and the crossing angles of the sheath filaments 122 of the adjacent sheath strands 12. However, the crossing angle between the wrapping filament 13 and the other filament is excluded from the average value.

When the average value of the crossing angles of the adjacent filaments is 17 ° or more, the contact pressure between the adjacent filaments becomes high when the steel cord is pulled, and the twist loss becomes large. The average value of the crossing angles of adjacent filaments is preferably less than 14 °. Twisting loss can be further reduced below 14 °.

In the steel cord 10 of the present embodiment, the gap between the adjacent sheath filaments of the sheath filaments constituting the strand is 0.065 mm or more. More specifically, as shown in the explanatory view in FIG. 7, the gap between the adjacent sheath filaments is between the adjacent sheath filaments in both the sheath filament 212 constituting the core strand 21 and the sheath filament 222 constituting the sheath strand 22. The gap g of is 0.065 mm or more. When the gap between the adjacent sheath filaments is 0.065 mm or more, the rubber permeability of the steel cord can be improved. If the gap between the adjacent sheath filaments is less than 0.065 mm, the rubber permeability is inferior. The preferred gap is 0.065 mm or more and 0.100 mm or less.

In the steel cord 10 of the present embodiment, it is preferable that the twisting direction of the sheath filament 112 of the core strand 11 and the twisting direction of the sheath filament 122 of the sheath strand 12 are opposite to each other. Since the twisting direction of the sheath filament 112 of the core strand 11 and the twisting direction of the sheath filament 122 of the sheath strand 12 are opposite to each other, the average value of the crossing angles of the adjacent filaments described above can be made lower.

In the steel cord 10 of the present embodiment, it is preferable that the twisting direction of the sheath filament 122 of the sheath strand 12 is opposite to the twisting direction of the sheath filament 122 of the adjacent sheath strand 12. Since the twisting directions of the sheath filaments 122 of the adjacent sheath strands 12 are opposite to each other, the average value of the crossing angles of the adjacent filaments described above can be made lower.

Next, a method of manufacturing the steel cord 10 of the present embodiment will be described. As the filament constituting each strand, a filament having a predetermined wire diameter is obtained through heat treatment, plating treatment and final wire drawing after drawing the raw material of the steel wire. In consideration of the lamella orientation angle of the surface layer portion of the filament described above, it is preferable to adjust the wire drawing conditions at the time of final wire drawing.
After this final wire drawing, strain removal annealing can be performed. It is preferable that the strain removing annealing temperature is 250 ° C. or higher and lower than 300 ° C. A steel cord having high strength and low twist loss can be easily obtained by strain-removing annealing at 250 ° C. or higher and lower than 300 ° C. If the strain-removing annealing temperature is less than 250 ° C., the strain-removing annealing effect is weak and the twist loss is large. When the strain removing annealing temperature is 300 ° C. or higher, the strain removing annealing causes annealing more than necessary, and the strength of the filament decreases.

Before the strain-removing annealing, it is preferable that the filament after the final wire drawing is not straightened. The straightening process is, for example, a process of repeatedly bending the filament through a staggered roll to improve the residual stress and straightness of the filament. However, when the filament is repeatedly bent by straightening, the processing strain inside the filament becomes large and the twist loss becomes large. Therefore, in order to reduce the twist loss, the straightening process should not be performed.

The steel cord 10 of this embodiment is suitable for use in reinforcing a tire. The use of the steel cord 10 of this embodiment is not limited to tires.

(Examples 1 to 5, conventional examples, comparative examples 1 to 6)
The cord strength and the cord strength exertion rate of the steel cords of Examples, Conventional Examples and Comparative Examples shown in Table 1 were investigated. For the steel cords of each example, the conventional example, and each comparative example, the cord structure, the filament diameter constituting the steel cord, the tensile strength of the filament, and the lamella orientation angle of the filament surface layer portion are described together in the table. The code strength is represented by an index when the conventional example is 100.
In Table 1, the cord diameter is a value excluding the wrapping filament. Further, it can be said that the cord strong exertion rate for evaluating the twist loss is a good characteristic if it is 90% or more.

As can be seen from Table 1, the steel cords of Examples 1 to 5 have a lamella orientation angle of 0.0 ° or more and 6.0 ° or less, or 12.5 ° or more and 18.5 ° or less of the filament surface layer portion. Therefore, the code strength performance rate has improved compared to the conventional example.

Looking more specifically at Examples 1 to 6, in Example 1, the lamella orientation angle of the filament surface layer portion is in the range of 0.0 ° or more and 6.0 ° or less, and the code strength exertion rate is higher than that of the conventional example. Has improved.
In Example 2, the lamella orientation angle of the filament surface layer portion was in the range of 12.5 ° or more and 18.5 ° or less, and the cord strong exertion rate was improved as compared with the conventional example.
Example 3 is an example in which the lamella orientation angle of the filament surface layer portion is 0 °, Example 4 is an example in which the lamella orientation angle of the filament surface layer portion is 6 °, and Example 5 is an example in which the lamella orientation angle of the filament surface layer portion is 0 °. In each case, the orientation angle was 12.5 °, and the code strength exertion rate was improved as compared with the conventional example.

In Comparative Example 1, all the filaments constituting the strand had a tensile strength of less than 3000 MPa, the cord strength was inferior to that of Example 1, and the lamella orientation angle of the filament surface layer portion was 30 °.
In Comparative Example 2, all the filaments constituting the strand had a tensile strength of less than 3000 MPa, and the cord strength was inferior to that of Example 1.
In Comparative Example 3, the lamella orientation angle of the filament surface layer portion exceeded 18.5 °, and the code strong exertion rate was inferior to that of Example 1.
Comparative Example 4 was an example in which the lamella orientation angle of the filament surface layer portion was 7 °, and the code strong exertion rate was inferior to that of Example 1.
In Comparative Example 5, the lamella orientation angle of the filament surface layer portion was 12 °, and the code strong volatility was inferior to that of Example 1.

(Example 1, Examples 6 to 9)
For the steel cords of each example shown in Table 2, the cord strength and the cord strength exertion rate and the rubber penetration coverage rate on the core filament surface of the core strand were investigated. The cord structure of the steel cord, the filament space factor, the twist angle, the average crossing angle, the filament diameter constituting the steel cord, the tensile strength of the filament, the twist direction of the filament, and the gap between the adjacent sheath filaments are also shown in the table. did.
In Table 2, the cord diameter is a value excluding the wrapping filament. Further, it can be said that the cord strong exertion rate for evaluating the twist loss is a good characteristic if it is 90% or more. Further, it can be said that the rubber penetration coverage of the core filament surface of the core strand for which the rubber penetration rate has been evaluated is good if it is 30% or more.

Example 1 was the same steel cord as in Example 1 in Table 1, and a good cord strength exertion rate was obtained.
In Example 6, since the filament space factor was 48% or more and less than 54%, the rubber penetration rate was improved as compared with Example 1.
In Example 7, the cord twist angle was 78 ° or more and less than 84 °, and the average value of the crossing angles of the adjacent filaments was less than 17 °. Therefore, the cord strength exertion rate was improved as compared with Example 1.
In Example 8, the filament space factor is 48% or more and less than 54%, the cord twist angle is 78 ° or more and less than 84 °, and the average value of the crossing angles of adjacent filaments is less than 17 °. Compared to 1, both the cord strength exertion rate and the rubber penetration rate were improved.
Example 9 is an example in which the filament space factor is 48% or more and less than 54%, the cord twist angle is 78 ° or more and less than 84 °, and the gap between adjacent sheath filaments is 0.065 mm or more, which is good. A steel cord with a strong cord exertion rate and a good rubber penetration rate was obtained.
In Example 10, the filament space factor is 48% or more and less than 54%, the cord twist angle is 78 ° or more and less than 84 °, the average value of the crossing angles of adjacent filaments is less than 17 °, and between adjacent sheath filaments. This is an example in which the gap between the two is 0.065 mm or more, and a steel cord having a better cord strength exertion rate and a better rubber penetration rate than in Example 9 was obtained.

Separately from Examples 1 to 10, a steel cord in which the twisting direction of the sheath filament of the core strand and the twisting direction of the sheath filament of the sheath strand are opposite is prepared, and the cord strength exertion rate and the core filament surface of the core strand are prepared. When the rubber penetration coverage was examined, it was confirmed that the cord strength exertion rate was improved.
Further, apart from Examples 1 to 10, a steel cord in which the twisting direction of the sheath filament of the sheath strand is opposite to that of the sheath filament of the adjacent sheath strand is prepared, and the cord strength exertion rate and the core filament surface of the core strand are prepared. When the rubber penetration coverage was examined, it was confirmed that the cord strength exertion rate was improved.

10 Steel cord 11 Core strand 12 Sheath strand 13 Wrapping filament 111 Core filament 112 Sheath filament 121 Core filament 122 Sheath filament

Claims (9)

It has a double-twisted structure in which a plurality of strands formed by twisting two or more layers of a plurality of filaments are twisted, and at least a part of the filaments has a tensile strength of 3000 MPa or more.
A steel cord for reinforcing a rubber article, wherein the lamella orientation angle of the surface layer portion of at least a part of the filament is 0.0 ° or more and 6.0 ° or less, or 12.5 ° or more and 18.5 ° or less. The steel cord for reinforcing a rubber article according to claim 1, wherein the filament space factor is 48% or more and less than 54%. The steel cord for reinforcing a rubber article according to claim 1 or 2, wherein the cord twist angle is 78 ° or more and less than 84 °. The steel cord for reinforcing a rubber article according to any one of claims 1 to 3, wherein the average value of the crossing angles of adjacent filaments excluding the wrapping filament is less than 17 °. The steel cord for reinforcing a rubber article according to any one of claims 1 to 4, wherein the gap between adjacent sheath filaments constituting the strand is 0.065 mm or more. The invention according to any one of claims 1 to 5, wherein the double-twisted structure is a 1 + n (n = 6 to 7) structure in which 6 to 7 sheath strands are twisted around one core strand. Steel cord for reinforcing rubber articles. The steel cord for reinforcing a rubber article according to claim 6, wherein the twisting direction of the sheath filament of the core strand and the twisting direction of the sheath filament of the sheath strand are opposite to each other. The steel cord for reinforcing a rubber article according to claim 6, wherein the twisting direction of the sheath filaments of the sheath strands is opposite to that of the sheath filaments of the adjacent sheath strands. A tire using the steel cord for reinforcing a rubber article according to any one of claims 1 to 8 for reinforcement.

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