JP2995709B2 - Steel cord for belt reinforcement of pneumatic tires for heavy loads - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a twisted steel cord used as a belt reinforcing member for heavy duty pneumatic tires such as trucks and buses, and to promote penetration of rubber material into the cord. For the steel cord of open twist for the same, it is possible to increase the lateral rigidity while securing the radial flexibility of the tire,
As a result, the running performance of the pneumatic tire for heavy loads can be significantly improved.

[0002]

2. Description of the Related Art Generally, a steel cord of this kind is used as a reinforcing material for a rubber product of an automobile tire, in which a large number of steel cords are coated in parallel with a rubber material. Therefore, the indispensable conditions for a steel cord are, of course, good mechanical strength, good chemical adhesion to rubber, and good penetration of rubber into the steel cord. That is.
That is, in order for the steel cord to sufficiently fulfill the role of a reinforcing material for a rubber product, it must be a complete composite material with a rubber material.

Conventionally, as a steel cord for reinforcing a belt portion of a heavy-duty pneumatic tire in a truck, a bus, or the like, as shown in FIG. 6, nine steel wires are provided around three strands arranged substantially at the center. Is a steel cord having a polygonal cross section in which twelve wires 10 having the same wire diameter are densely twisted in the same direction at the same pitch, a so-called 1 × 12 steel cord.
A structured steel cord 11 is known.

As shown in FIG. 7, a strand 13 composed of three strands 12 tightly twisted is used as a steel cord having the same number of strands as the steel cord 11.
A steel cord 15 having a so-called 3 + 9 structure in which nine wires 14 are densely twisted in a direction or a pitch different from the above-mentioned twisting around the wire.

The steel cord 11 having the 1 × 12 structure described above.
Is that the steel cord 15 having the 3 + 9 structure requires two twisting steps, but can be produced in one twisting step, without having many expensive twisting facilities.
It has the advantage that the production time can be shortened and the production cost can be reduced.

However, in the steel cord 11 having the 1 × 12 structure, since the adjacent wires 10 are closely or extremely close to each other, the rubber material can penetrate from the space between the wires at the time of forming the tire. However, a complete composite with a rubber material could not be formed merely by coating the outer peripheral portion of the cord. Accordingly, in the tire using the steel cord 11, the cord and the rubber material are not sufficiently adhered to each other, so that the cord and the rubber material are peeled off when the automobile is running, that is, a so-called separates phenomenon occurs, or the adjacent wires are not separated from each other. A part of the cord is broken by the fretting phenomenon due to the contact of the tire, and the function of the tire is significantly impaired. Further, the water in the rubber material or the water entering from the cuts of the tires reaches the gap E inside the cord, propagates in the longitudinal direction of the cord, corrodes the steel cord, and greatly reduces the mechanical strength. Become. Also, in the steel cord 15 having the 3 + 9 structure, as in the case of the steel cord 11, since the wires 14 are closely or extremely close to each other, the rubber material has poor penetration.

In recent years, in view of the above circumstances, various steel cords of this kind having a twisted structure in which a rubber material sufficiently penetrates into the cord have been proposed.

For example, as shown in FIG. 8, a steel cord 16 has a wire diameter slightly larger than that of the above-mentioned strand 18 around a strand 18 composed of three densely twisted strands 17 arranged substantially at the center. 6 small strands 19
Are twisted in a different twisting direction or a different twisting pitch from the twisting of the strand 18. The steel cord 16 has a gap C between the wires 19 arranged around the steel cord 16.
And a rubber material is sufficiently penetrated into the cord through the gap C, and is known as a so-called 3 + 6 steel cord. As shown in FIG. 9, nine strands having the same wire diameter are used, and two strands 20 of the strands are densely twisted to form a strand 21 and a strand 21 is formed around the strand 21.
The two strands 22 are twisted in a different twisting direction or a different twisting pitch from the twisting of the strand 21, so-called 2
A steel cord 23 having a +7 structure is also known.

[0009]

However, since the steel cords 16 and 23 have the structure of the strand 18,
21 is processed first, and then the strands 18 and 21 are processed.
Around the two strands 19 or seven strands 22 are twisted in a different twisting direction or a different twisting pitch than the strands 18 and 21 in a twisting step of two steps, and the twisting cost is reduced. There was a problem of being expensive.

Further, in the steel cord 16,
In order to improve the penetration of the rubber material, the diameter of the six strands 19 is reduced (for example, from 0.38 mm to 0.35 mm).
Attempts have been made to provide a large gap C between the strands. However, even in this case, the rubber material does not penetrate into the contact portion between the strands of the strand 18 composed of the three strands 17 at the center of the cord or the gap E surrounded by the three strands 17, and therefore, Various adverse effects as described above.

Further, the steel cords 16, 23
Since the cord has a low elongation property, when used in a tire, it is necessary to use a steel cord with a high elongation property of the cord in the outermost layer of the tire belt in order to obtain the flexibility of the tire. A complicated reinforcement structure that would increase the cost had to be adopted.

Incidentally, a heavy-duty pneumatic tire requires in-plane bending strength of a belt layer in order to obtain stable running performance, so that a steel cord has excellent lateral rigidity and a good riding comfort. Excellent flexibility) is also required.

Therefore, the present invention is used as a belt portion reinforcing member of a pneumatic tire for heavy load,
For steel cords with an open twist structure to promote the penetration of rubber material into the cords, the in-plane bending strength of the belt layer has been improved, the lateral rigidity has been increased, and the running performance of the tire has been improved. Another object is to devise the configuration and structure of the steel cord.

[0014]

Means taken to solve the above problem is a single-layer twisting method in which a plurality of strands are twisted so that a circumscribed circle of a steel cord has the same substantially elliptical shape in the longitudinal direction of the cord. An open structure steel cord,
Number of strands n = 6 to 8, strand diameter d = 0.23 to 0.38m
m, twist pitch P = 40d-80dmm, oval flattening ratio (elliptical major axis B / elliptical minor axis A) = 1.2-2.
Assuming the steel cord for reinforcing the belt portion of the pneumatic tire for heavy load, which is No. 5, the following components (a) to (c) are provided. (A) The minor axis A of the elliptical shape is 2d to 3dmm, and (b) the rigidity ratio according to the bending direction (bending rigidity in the major axis direction of the elliptical shape / bending rigidity in the minor axis direction of the elliptical shape) = 1. 05 to 1.20,
(C) Load of 1734Kg (40K) of Charpy impact test
g-cm) of 10 to 40 kg-cm
That.

By the way, the above-mentioned various numerical limitations are determined based on the results obtained by a number of experiments, and the outline thereof is as follows.

If the number n of the wires is less than 6, there is also a relationship with the wire diameter d, so that it must be larger than the range of the wire diameter d in order to satisfy the mechanical strength. Inferior in flexibility, and when it exceeds 8, the twisted state is not stable, the arrangement of the strands is disturbed and the penetration of the rubber material is deteriorated, and the flexibility is inferior. Range.

If the wire diameter d is smaller than 0.23 mm, the mechanical strength is inferior. If it exceeds 0.38 mm, the minor and major diameters of the elliptical cord are increased and the flexibility is inferior. Therefore, the range was set to 0.23 to 0.38 mm.

If the twist pitch P is less than 40 dmm, the cord elongation characteristics increase, the tire is deformed by air pressure, and the "hatch effect" as a reinforcing material is inferior. Was reduced, the flexibility was inferior, and the riding comfort of the automobile was lowered, so the range was 40 to 80 dmm.

The reason why the minor axis A of the ellipse is set to 3 dmm or less is that if the minor axis A is larger than 3 dmm, it becomes close to a circle, the flexibility in the minor axis direction is inferior, and the bending rigidity in the major axis direction is inferior. .

When the rigidity ratio (elliptical long-axis bending rigidity / short-axis bending rigidity) is less than 1.05, the in-plane bending rigidity of the tire belt layer is inferior, and the running stability of the tire is improved. If it cannot be expected, and if it exceeds 1.20, the in-plane bending stiffness of the belt layer becomes too large, which rather degrades the riding comfort of the vehicle, so the range was 1.05 to 1.20.

If the elliptical aspect ratio (the major axis B of the ellipse / the minor axis A of the ellipse) is less than 1.2, the strands are easily moved by an external force, and the rubber generated at the time of rubber vulcanization is vulnerable. The gap between the strands is reduced by the pressure due to the flow, so that not only the infiltration of the rubber material is inferior, but also the rigidity ratio is reduced. Also 2.
If it exceeds 5, the major axis B of the elliptical shape becomes too large, and when arranged in parallel on the belt layer of the tire, the cords are too close to contact with each other, or when arranged in parallel with a gap between the cords, the use of cords The number is reduced, and the durability of the tire is reduced. Therefore, the elliptical flatness ratio is in the range of 1.2 to 2.5.

Charpy impact test load of 1734Kg
(40Kg-cm), the impact absorption is 10Kg-
If it is less than 10 cm, the toughness is inferior. If the tire steps on a stone or a curb, the cord itself is cut and the life of the tire is shortened. Envelope effect that embraces is not sufficient and running stability is inferior.
The range was 40 Kg-cm.

In the above construction, if the distance C between adjacent strands located on the minor diameter side is less than 0.04 mm, the penetration of rubber is inferior, and if it exceeds 0.25 mm, the major diameter increases and The range of 0.04 to 0.25 mm is appropriate because the elongation characteristics of the steel cord increase and the "hatch effect" as a tire reinforcing material is inferior.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a steel cord for reinforcing a belt portion of a heavy-duty pneumatic tire according to the present invention will be specifically described below with reference to the drawings.

Example 1 As shown in FIG. 1, six wires 1 having a wire diameter d of 0.38 mm and the surface of which is subjected to brass plating are twisted such that the twist direction is the S direction. A cord having a circular cross section of an open structure is formed by a single layer twist of a 1 × 6 structure, and the cord is pressed to form a circumcircle of the cord having a substantially elliptical shape in the same direction in the longitudinal direction of the cord. The gap C between adjacent strands located on the minor axis side is 0.12 to 0.20 mm, the twist pitch P is 16 mm, and the elliptical minor axis A is 0.1 mm.
The steel cord 2 was 79 mm, the major axis B of the ellipse was 1.66 mm, the elliptical flatness ratio was 2.10, and the shock absorption was 33 Kg-cm. The hard steel wire used for the steel cord 2 was C: 0.82% by weight, Si:
0.20% by weight, Mn: 0.54% by weight, P: 0.00
7% by weight, S: 0.005% by weight or less, with the balance being Fe and chemical components of unavoidable impurities.

Example 2 As shown in FIG. 2, eight wires 3 having a wire diameter d of 0.28 mm and the surface of which is subjected to brass plating are twisted so that the twist direction is the S direction. A cord having a circular cross section of an open structure is formed by single-layer twisting of a 1 × 8 structure, and the cord is pressed to form a circumcircle of the cord having a substantially elliptical shape in the same direction in the longitudinal direction of the cord. The gap C between adjacent strands located on the minor axis side is 0.09 to 0.20 mm, the twist pitch P is 14 mm, and the elliptical minor axis A is 0.1 mm.
The steel cord 4 was 82 mm, the major axis B of the ellipse was 1.41 mm, the flatness ratio of the ellipse was 1.72, and the shock absorption was 22 kg-cm. The hard steel wire used for the steel cord 4 had substantially the same chemical composition as that of the first embodiment.

Embodiment 3 As shown in FIG. 3, seven strands 5 each having a strand diameter d of 0.30 mm and having a surface plated with brass are twisted so that the twist direction is the S direction. A single-layer twisted 1 × 7 structure is used to form an open-structured circular cord having a circular cross section, and the cord is pressed to form a circumcircle of the cord having a substantially elliptical shape in the same direction in the longitudinal direction of the cord. The gap C between adjacent strands located on the minor axis side is 0.15 to 0.20 mm, the twist pitch P is 16 mm, and the minor axis A of the elliptical shape is 0.1 mm.
The steel cord 6 was 80 mm, the major axis B of the ellipse was 1.56 mm, the flatness ratio of the ellipse was 1.95, and the shock absorption was 28 kg-cm. The hard steel wire used for the steel cord 6 also had substantially the same chemical composition as in each of the above examples.

Embodiment 4 Although the illustration is omitted because its outline is very similar to that of FIG. 1, six strands having a strand diameter d of 0.25 mm and a brass plated surface are twisted in the direction S. Twisted in the direction
Forming a cord having a circular cross section of an open structure with a single layer twist of a × 6 structure, and pressing the cord, the circumcircle of the cord has a substantially elliptical shape in the same direction in the longitudinal direction of the cord, The gap C between adjacent strands located on the minor diameter side is 0.
04 to 0.10 mm, twist pitch P is 12 mm
The major axis A of the ellipse is 0.68 mm and the major axis B of the ellipse
Was 0.95 mm, the elliptical flatness ratio was 1.40, and the shock absorption was 16 kg-cm.
The steel cord of this embodiment has C: 0.85
Wt%, Si: 0.68 wt%, Mn: 0.54 wt%, P: 0.004 wt%, S: 0.005 wt% or less, Ni: 0.19 wt%, balance Fe and inevitable impurities A hard steel wire composed of the following chemical components was used.

Next, in order to confirm the performance characteristics of the steel cord of the present invention, steel cords as shown in Table 1 were prepared, the amount of impact absorption by Charpy impact test, the penetration of rubber material, the major axis and the minor axis. The rigidity in the direction and its rigidity ratio, fatigue properties, twist cost, and breaking strength were evaluated.
Test No. 1 to 3 are conventional examples, and test Nos. 4 to 11 are Examples and Test Nos. 12 to 16 are comparative examples. Table 2 shows the results.

[0030]

[Table 1]

[0031]

[Table 2]

In this evaluation, the following test conditions and evaluation method were used.

The amount of impact absorption (Kg-cm) is the amount of impact absorption according to the Charpy impact test.
(40 Kg-cm), the lifting angle = 150 degrees, and the supporting distance = 90 mm.

The penetration of rubber material (%) is 5K for each cord.
g under a tensile load of 100% modulus of 3
After embedding in a 5 kg / cm ² rubber material and vulcanizing, take out the steel cord, disassemble the cord, observe a certain length between each strand, and contact the rubber material with the observed length. The ratio of the lengths of the traces obtained was determined as a percentage, and the average value was displayed.

As shown in FIG. 4, a load G at the time of pressing down the test piece 7 by 5 mm at a span (L) = 20 mm by a three-point bending test is calculated as shown in FIG. It is calculated from (load G) / bending rigidity (load G) in the minor axis direction of the ellipse. As shown in FIG. 5, the test piece 7 includes five test cords 8 arranged in a row and having a 100% modulus of 35 kg / cm.
² was embedded in a rubber sheet 9 of required dimensions. The dimensions of the rubber sheet 9 are 4 mm thick and 15 m wide.
m and length 100 mm. The bending stiffness in the short diameter direction is measured by embedding the test cord 8 sideways as shown in FIG.
As shown in (b), the code 8 was erected and embedded.

The fatigue property was measured by embedding a plurality of cords in a rubber sheet made of a rubber material having a 100% modulus of 35 kg / cm ² and using this sheet by a three-point pulley bending fatigue tester to evaluate fretting wear and buckling. The number of repetitions until the cord breaks after passing through the test is determined. 4 was set to 100 and indicated by an index.

The twisting cost is evaluated by the number of twisting steps, and is represented by an index with the conventional 3 + 6 structure being 100.

Next, as apparent from Table 2, the test N
o. The steel cords of the present invention of Test Nos. 4 to 11 were tested.
Compared with the conventional examples 1, 2, and 3, the rubber material was excellent in the infiltration property, the fatigue property, and the twisting cost, and in particular, the twisting cost was reduced by half. In addition, the steel cord of the present invention exhibited a relatively high level of shock absorption even though the strength was slightly lower than that of the conventional example, and was excellent in shock absorption. Further, in Test No. In 15, 16
When the number of strands was increased to 9 and the twisted state was checked, there was a phenomenon in which the strand arrangement was partially disturbed, which was not seen in the present invention, and a portion where the gap between the strands hardly existed was found. As a result, the penetration of the rubber material was deteriorated, and the fatigue property was reduced. Test No. In the comparative example of No. 12, the flatness ratio was reduced, so that the gap between the strands was reduced during rubber vulcanization, and the infiltration of the rubber material was deteriorated, and the fatigue property was reduced.

The test No. The steel cords of the present invention having a rigidity ratio of 4 to 11 (rigidity in the major axis direction / rigidity in the minor axis direction) exhibit a value of 1.06 to 1.19, and have high rigidity in the major axis direction, It was found that the minor axis direction had flexibility.

In the steel cord of the present invention, since the cord has an elliptical cross-section, the minor axis of the ellipse is smaller than the circular diameter of the conventional example. By arranging the direction so that the direction of the minor axis of the ellipse coincides, the thickness of the belt layer can be reduced, and the weight of the tire can be reduced. Further, as a material of the steel cord, a steel wire for high strength in which chemical components such as C and Si are used as used in Example 4 (for example, C: 0.85% by weight, Si: 0.68% by weight) , M
n: 0.54% by weight, P: 0.004% by weight, S: 0.
005% by weight or less, Ni: 0.19% by weight), the strength of the strands can be increased and the diameter can be reduced, the weight of the cord can be reduced, and the weight of the tire can be reduced. .

Further, since the steel cord of the present invention is excellent in flexibility in the direction of the minor axis of the ellipse, the arrangement of the cords is excellent in the envelope effect on the unevenness of the tire contact surface, and further, in the direction of the major axis of the cord. Are oriented in the in-plane bending direction of the belt portion, so that the in-plane bending stiffness of the belt layer important as a belt portion reinforcing material can be increased. Further, since the steel of the present invention has an elongation of 4 to 7% as a result of a tensile test when measuring the breaking strength, a steel cord having a large elongation characteristic of the cord is used for the outermost layer of the belt portion as in the prior art. Without this, the flexibility of the tire can be ensured. In order to minimize the number of reinforcing cords, the higher the numerical value, the better,
Usually, a cord having a cord breaking strength of 60 to 120 kgf is used as a belt portion reinforcing cord of a heavy-duty pneumatic tire, so if it is used for reinforcing a belt portion of a heavy-duty pneumatic tire, 80 kgf or more is sufficient. It is.

[0042]

The steel cord for reinforcing the belt portion of the heavy-duty pneumatic tire according to the present invention has a single-layer twisted structure, so that the twisting cost is low, and the reinforcing properties required for the belt portion are flexibility and shock absorption. When used for heavy duty pneumatic tires such as trucks and buses,
Compared to the conventional 3 + 6 and 2 + 7 steel cords, the tires have excellent characteristics in terms of tire durability and running stability, and are particularly advantageous in that the twisting cost is extremely low and the economic effect is large. It has an effect.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a steel cord according to a first embodiment.

FIG. 2 is a sectional view showing a steel cord according to a second embodiment.

FIG. 3 is a sectional view showing a steel cord according to a third embodiment.

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

FIG. 5 shows a test piece used for a three-point bending test;
(A) is a schematic diagram of a test piece used for bending stiffness in the short diameter direction, and (B) is a schematic diagram of a test piece used for bending stiffness in the long diameter direction.

FIG. 6 is a sectional view showing a conventional steel cord having a 1 × 12 structure.

FIG. 7 is a sectional view showing a conventional steel cord having a 3 + 9 structure.

FIG. 8 is a sectional view showing a conventional steel cord having a 3 + 6 structure.

FIG. 9 is a sectional view showing a conventional steel cord having a 2 + 7 structure.

[Explanation of symbols]

 1, 3, 5 ... strand 2, 4, 6 ... steel cord 7 ... test piece 8 ... test cord 9 ... rubber material A ... short diameter B ... long diameter c ... Gap E ... Space (gap) G ... Load L ... Span

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI B60C 9/00 B60C 9/18 G 9/18 C08J 5/04 C08J 5/04 B29C 67/14 Z // B29K 105: 06

Claims (1)

(57) [Claims] 1. A steel cord having a single-layer twisted open structure in which a plurality of strands are twisted so that a circumscribed circle of the cord has the same substantially elliptical shape in the longitudinal direction of the cord, and the number of strands is n = 6 to 8, strand diameter d = 0.23 to 0.38 mm, twist pitch P = 40d to 80 dmm, oval flattening ratio (elliptical major axis B / elliptical minor axis A) = 1.2 to 2.5 In a steel cord for reinforcing a belt portion of a heavy-duty pneumatic tire, the minor axis A of the ellipse is 2d to 3dmm, and the rigidity ratio according to the bending direction (bending rigidity in the major axis direction of the ellipse / short of the ellipse) Bending rigidity in the radial axis direction) = 1.05 to 1.2
0, and the load of the Charpy impact test was 1,734 kg (40 kg-c).
A steel cord for reinforcing a belt portion of a heavy-duty pneumatic tire having a shock absorption of 10 to 40 kg-cm in m).