JP2000280708A - Tire reinforcing steel cord - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve fatigue resistance, and improve manufacturing and handleability by setting a core wire diameter to specific times a side wire diameter in a specific wire diameter, setting a core wire to a biased pitch of an expression I, forming a cord short diameter and a biased outside diameter so as to satisfy an expression II, and setting the aspect ratio of an almost elliptic shape to a specific value. SOLUTION: A diameter d1 of a side wire 3 is 0.15 to 0.22 mm, and a diameter d2 of a core wire 2 is 1.1 times to 2.0 times of the diameter d1 of the side stranded wire 3. Here, the diameter d2 of the core wire 2 is not less than 0.22 mm. In a steel cord 1, a short diameter T and an almost spirally biased outside diameter D applied to the core stranded wire 2 satisfy the relationship of an expression II:T-D=0.03 to 0.30. A spirally biased pitch P1 applied to the core wire 2 is set to a twist pitch P, an expression I:P1=0.1 P to 0.5 P is realized, and at this habit pitch interval, the core wire 2 appears between the side wires 3 positioned on both sides for sandwiching the long diameter axis. The aspect ratio T/W is 38 to 60%. Thus, a rubber permeating rate, fatigue resistance, the rigidity ratio and handleadility can be improved.

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 an automobile tire, and more particularly to a steel cord used for a steel cord.
The present invention relates to a steel code in which a total of 13 to 13 strands are twisted and the cross section of the code is substantially elliptical.

[0002]

2. Description of the Related Art In general, steel cords of this kind are used as reinforcing materials for automobile tires by being covered with a rubber material in a state where many steel cords are aligned in parallel. And
The conditions required for steel code include not only excellent mechanical strength, but also good chemical and physical adhesion to rubber materials, and the inside of steel code. And good rubber penetration. 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.

[0003] In particular, for tires used for heavy vehicles such as trucks and buses, steel cords having high strength and flexibility are required. One of them is a steel having a 1 + n structure. -Records have been used.

However, the conventional 1 + n steel condenser
As shown in FIG. 6, the cross-sectional structure of the cord is a close-twisted structure, and the individual wires 9 are completely adhered to each other so that there is no gap, so that the cavities S are scattered inside the cord. . Therefore, when the composite sheet is formed by sandwiching the steel code 8 between two rubber sheets, the rubber material does not penetrate into the cavity S, and a complete composite with the rubber material is formed. Cannot be formed.

[0005] Therefore, when this rubber sheet is used for a tire, if the rubber coating is partially broken by a foreign substance such as a nail, moisture that has entered from the outside propagates into the cavity S, and the steel sheet is removed. Is oxidized over the entire surface. When this happens, the adhesion between the rubber and steel cord becomes weaker,
Both will peel off, and the effect of the steel cord as a reinforcing material will be very weak.

[0006] In order to solve this problem, a steel cord 10 in which a core element wire 11 is hampered as shown in FIG. 7 has been proposed.

[0007]

[0007] As shown in FIG.
The steel cord 10 of 1 + n configuration in which a spiral shape is applied to 1 has a substantially perfect circular cross-section, so that the rigidity of the steel cord is not limited in any direction. Is the same. Therefore, if the rigidity is increased in order to improve the cornering performance of the tire, there is a problem that the ride quality is deteriorated. Further, the steel code of FIG.
The cord diameter becomes thicker than that of the cord with a close twist, and the rubber sheet after the calendar (rubber coating step) becomes thicker. In addition, the cord diameter becomes larger. Rubber sheet
A predetermined number of steel codes cannot be embedded in the sheet, and the strength of the sheet decreases. Therefore, when this rubber sheet is used for a tire, it is necessary to increase the number of stacked sheets, and as a result, there is a problem that the weight of the tire increases. Further, from the viewpoint of steel code production, FIG.
The steel cord in which the side strands 12 are arranged neatly in the space as described above is impossible and the twist is extremely unstable.

[0008] The present invention relates to the above-mentioned various conventional steel coils.
It was made in order to solve various problems of the tire, the problem is that when used in tires as reinforcement,
Good rubber penetration into steel code, high rigidity in the direction perpendicular to the tire rotation direction while reducing rigidity in the tire rotation direction, good fatigue resistance to compression and bending, and manufacturing. Another object of the present invention is to provide a steel code excellent in handling workability.

[0009]

In order to achieve the above object, the steel cord for reinforcing a tire according to the present invention has four to one steel cords.
The three strands are a core cord, one of which is a core strand, the remaining strands are side strands, and are twisted at a time at a twist pitch P in the same direction, and have a longitudinal cross section. substantially elliptical shape (major axis W, minor T) in substantially the same orientation in the direction the tire reinforcing steel is - Turkey - in de, side wire diameter d ₁ is 0.15
0.22 mm, the side wire diameter d ₂ is 1.1d ₁ ~2.0d ₁
mm (provided that d ₂ ≧ 0.22 mm) and the core wire has a habit pitch P ₁ and a core pitch satisfying the following equations (1) and (2).
Has a habit de substantially spiral minor axis of the habit outer diameter D, also appeared at substantially the pitch P ₁ spacing between the side strands located on both sides of the core element wire sandwich the major axis axis of the generally elliptical And the flattening rate (percentage of T / W) of the substantially elliptical shape is 38.
% To 60%. P ₁ = 0.1 P to 0.5 P (1) T−D = 0.03 to 0.30 (2) P ₁ : habit pitch (mm) P: twist pitch (mm) T: core Short diameter (mm) D: Habit outside diameter of core strand in the short diameter direction of code (mm)

Since the steel cord of the present invention has a substantially elliptical cross-section with a substantially uniform longitudinal direction and a large flatness, the steel cord has a large rigidity in the minor axis direction and the major axis direction. different. Further, the steel cords after calendering are arranged substantially parallel to the longitudinal direction with the long diameter portion left and right in the rubber sheet, so that the bending rigidity is low in the vertical direction and high in the horizontal direction. Therefore, when a tire is formed using this rubber sheet, the riding comfort is good because the rigidity in the tire rotation direction is low, and the cornering performance is enhanced because the rigidity in the direction perpendicular to the tire rotation direction is high. Can be done.

Further, since the steel cord of the present invention has a substantially elliptical cross section, almost all the steel cords are substantially parallel to the longitudinal direction with the major axis portion left and right at the time of calendaring. Therefore, the thickness of the rubber sheet corresponds to the short diameter portion of the steel cord, and the sheet can be made thin. And the number of inserted steel codes can be reduced. As a result, the weight of the tire has been reduced, and it has become possible to reduce the cost of the tire and to improve the fuel efficiency of the automobile. Furthermore, in terms of twist stability, the twist is stable and almost the same shape even after being embedded in a rubber sheet, as compared with the steel cord as shown in FIG. Excellent in work.

By the way, steel of the present invention - Turkey - in de, 0.15～0.22Mm side wire diameter d _1, a core wire diameter d ₂ of 1.1d ₁ ~2.0d ₁ mm (provided that d ₂ ≧
0.22 mm) because the side strand diameter d ₁ is 0.15 m.
If it is less than m, sufficient strength cannot be obtained, and if it exceeds 0.22 mm, the flexibility of steel code is reduced and the fatigue value is reduced. The core element diameter d ₂ is equal to the side element diameter d.
The reason why the ratio is 1.1 to 2.0 times ₁ and 0.22 mm or more is that if it is less than 0.22 mm, the low-load elongation of the steel cord becomes large, and after rubber vulcanization for the following reasons. This is because the flattening rate decreases and the effect of the present invention cannot be expected.
If it exceeds 2.0 times the side wire diameter d ₁ steel - Turkey -
Loss of flexibility and lower fatigue values. The steel code of the present invention is a steel code which is rich in flexibility, has low elongation under low load, and has almost the same flatness even when embedded in rubber as before the embedding.

Here, a steel with a large low load elongation is used.
The reason why the flatness decreases after vulcanization (the cross-sectional shape becomes round) will be described. In the calendar process,
When sandwiching the record between the rubber sheets,
A steel cord having a low tension of about kg, but having a large low load elongation, is sandwiched in a state where its shape is deformed so as to be expanded by this tension and the cross-sectional area is reduced. In the subsequent vulcanization treatment, the rubber material is heated and becomes fluid, so that the shape returns to the original shape in the rubber (spring back). Since the amount of springback at this time is large on the minor diameter side, it is considered that the shape changes so that the cross-sectional shape becomes round. On the other hand, steel cords having a low low load elongation have a high strength against tension, and are sandwiched between sheets without being deformed. Therefore, even if this sheet is vulcanized, no springback occurs, and it is considered that the shape before vulcanization remains as it is. The steel cord of the present invention is a cord in which the core element wire diameter is increased and the low load elongation is suppressed, so that even if it is embedded in rubber, the flatness does not change from that before embedding.

The twist pitch of the steel cord is from 6 mm to 2 mm.
8 mm is preferred. Because if it is less than 6 mm,
This is because the bending amount is extremely increased, so that disconnection is liable to occur, and the number of twists per length of the steel cord is increased, thereby lowering productivity. Furthermore, in the present invention, since the habit pitch of the core element wire is even smaller than the twist pitch, a twist pitch of less than 6 mm is not appropriate. On the other hand, if the twist pitch of the steel cord exceeds 28 mm, the flexibility of the steel cord is lost, so that the fatigue value decreases, the twist becomes unstable, and flare is liable to occur. Not.

Assuming that the twist pitch of the steel cord is P, the habit pitch P ₁ of the core wire having a habit is 0.1.
Was a 1P~0.5P, when P ₁ is less than 0.1P, strands undergo extreme plastic deformation, breakage productivity is deteriorated as well as multiple, whereas, if it exceeds 0.5P However, the effect of the core element wire cannot be achieved, and the gap between the element wires decreases due to the tensile force due to the flow of the rubber at the time of molding the rubber sheet or the ironing force applied to the cord. This is because a sufficient gap does not occur between the wires. On the other hand, if it exceeds 0.5P, the steel code cannot be rolled sufficiently, the short diameter (T) of the steel code cross section becomes large, and the rubber sheet thickness cannot be reduced.

Assuming that the short diameter of the substantially elliptical cross section of the steel cord is T, the outside diameter D in the short diameter direction of the hard core wire is TD = 0.03- The reason why the expression of 0.30 is satisfied is that processing smaller than 0.03 is practically difficult, and 0.03 or more is better in order to sufficiently penetrate the rubber between the strands. is there. On the other hand, if it exceeds 0.30, the effect of flattening is reduced and the thickness of the rubber sheet cannot be reduced. Therefore, this range is most suitable in terms of production and operation and effect.

The flatness of a substantially elliptical shape in the transverse section of the steel cord (ratio of minor axis T to major axis W, percentage of T / W)
Is set to 38% to 60%. If it is less than 38%, twisting becomes unstable, and at the same time, each wire becomes hardly bent at the long diameter end portion, and handling workability is poor and fatigue resistance is poor. It depends. Further, even if the shape exceeds 60%, the twist becomes unstable and the shape becomes close to a perfect circle, so that the effect of the steel code of the present invention cannot be expected.

In the present invention, a structure is not adopted in which a core wire having a habit is not made to appear at both ends of the substantially elliptical shape and the core wire is completely disposed inside the side wire. in the both sides of the major axis shaft, until the structure as a core element wire to arrange to appear at substantially the pitch P ₁ spacing between the side strands, resulting almost monolayer at first glance to twist, steel -
The steel code of the present invention could be completed by flattening the record. Therefore, the twist is more stable than before, and a suitable gap is maintained between the strands, and a steel cord having a large flatness is obtained.

The steel cord according to the present invention is characterized in that a single strand is given a predetermined habit to form a core strand, and a side strand is twisted around the core strand, and then a roller having a flat surface is formed. -It can be manufactured by passing through and applying a rather strong compression process. Conventionally, in such a method, it was thought that the twist of the steel cord was broken and the cord was defective. It was also found that it was easy to manufacture by applying tension and applying strong compression.

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. When a buncher-type twisting machine is used, the strands are twisted, so that the habit of attaching in advance and the habit of the steel cord are different, so that it is necessary to consider this point.

When the steel cord having the above structure is pressed and vulcanized by sandwiching it between two rubber sheets, the rubber easily penetrates between the individual wires, and the rubber thickness can be reduced. The bending rigidity is extremely higher in the left-right direction than in the up-down direction. At this time, the steel code is buried in the steel plane with respect to the sheet horizontal plane.
The major axis portion of the record is in the left-right direction, and each steel code is arranged substantially parallel to the longitudinal direction.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 to 3 are schematic views showing a cross section of a steel cord according to various embodiments of the present invention. The steel cord 1 shown in FIG. 1 has a substantially spiral shape. Have one
The core wire 2 is composed of four core wires 2 and four side wires 3 having a smaller diameter than the core wire 2. The steel code 1 shown in FIG. 2 is also composed of one core element wire 2 and eight side element wires 3, and the steel code 1 shown in FIG. It is composed of a strand 2 and 12 side strands 3.

[0024] Figures 1-3 all steel shown in - Turkey - at de 1, the diameter d ₁ of the Side Element Wire 3 is in 0.15～0.22Mm,
Diameter d ₂ of the core wire 2, is 2.0 times 1.1 times the diameter d ₁ of the Side Element Wire 3. However, the diameter d ₂ of the core element wire 2 is equal to 0.
It is 22 mm or more. Then, the minor axis T of the steel cord 1 and the minor outer diameter D of the substantially spiral small habit applied to the core wire 2 in the minor axis direction are TD = 0.03 to 0.3.
0 is satisfied. Further, the pitch of the spiral habit applied to the core wire 2 is 0.1 to 0.5 times the twist pitch, and the pitch of the spiral habit is such that the core wire 2 is positioned on both sides of the major axis. Appear between the side strands 3 to be formed. Further, the flattening rate (T / W) is 38-60%
It is.

[0025]

EXAMPLES steel of the present invention - Turkey - To evaluate the characteristics of the soil, the number of the wires N, twist pitch P, the side wire diameter d _1, a core wire diameter d _2, the pitch of the habit of the core wire Steel cords in which P ₁ , outer diameter D, steel cord cross-sectional elliptical minor axis T, and major axis W were varied within the scope of the present invention are referred to as Examples 1 to 5, respectively. Steel codes in which the numerical values of any one of the constituents are out of the range of the present invention were used in Comparative Examples 1 to 3.
5, a steel code having a cross-sectional shape as shown in FIG. 6 is referred to as Conventional Example 1, and a steel code having a cross-sectional shape as shown in FIG. Lucco-
Changes in flatness after rubber vulcanization, rubber penetration rate,
When the fatigue resistance, rigidity ratio and handling workability were evaluated, the results shown in Table 1 were obtained.

[0026]

[Table 1]

The test conditions and evaluation methods for each item shown in Table 1 are as follows.

Change in flattening rate: calendar-step before process
The flatness A of the raw code (raw code) and the flatness B after rubber vulcanization were compared by B / A. If this value is larger than 1, it indicates that the cross-sectional shape has changed to be close to a circle after rubber vulcanization. The flatness B after vulcanization was determined by embedding a sample taken from rubber into a resin and using a projector to obtain a long diameter w.
-It was determined by measuring the minor axis t.

Rubber penetration rate: Each steel cord was embedded in rubber with a tensile load of 5 kg applied thereto, and after vulcanization, the steel cord was taken out of the rubber and the steel cord was taken out.
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., was determined by testing with a bending fatigue tester, and the twisted steel of the conventional example 2 was 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.

Rigidity ratio: As shown in FIG. 4 (a), five steel cords 4 were prepared with a 100% modulus of 35 kg /.
A test piece 6 embedded in a row so that the longitudinal direction of the cross section of the steel cord is horizontal with respect to the rubber sheet 5 of cm ² , and five test pieces as shown in FIG. No
The rubber sheet 5 is applied to the rubber sheet 5 by a steel cord.
A test piece 7 was prepared by embedding the test piece 7 in parallel so that the major axis direction of the cross-section was vertical, and as shown in FIG. 5, a three-point bending test with the test piece 6 or 7 having a span Sp = 20 mm The weight was set when the test piece 6 was held down by 5 mm and the weight G when the test piece 7 was held down by 5 mm. 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. The test piece 6 or 7 had a thickness of 4 mm, a width of 15 mm, and a length of 100 mm.

Handling workability: Good workability was evaluated as 〇, poor workability as ×, and intermediate workability as △.

The following points are clear from Table 1.

In Comparative Example 1, the steel cord diameter d ₂ is smaller than the lower limit of the present invention, and the other steel codes are within the scope of the present invention. This steel cord has low rigidity of the core strand,
After vulcanization of rubber, the steel cord cross section becomes close to a circle (B
/ A), the rigidity ratio is inferior.

Comparative Example 2 is a steel code in which the core element diameter d ₂ is larger than the upper limit of the present invention, contrary to Comparative Example 1. In this steel cord, the rigidity of the core strand is too large and the flexibility is inferior, so that the fatigue resistance is low. In addition, handling workability is slightly inferior.

Comparative Example 3 is a steel code in which the core element diameter d ₂ is as small as Comparative Example 1, and the habit pitch P _{1 of the} core is out of the range of the present invention. This steel code has a small gap, is inferior in rubber penetration, and has a cross section close to a circle after vulcanization of rubber (B / A), and has a low rigidity ratio.

In Comparative Example 4, although the core wire diameter d ₂ falls within the range of the present invention, the habit pitches P ₁ and T
-D is a steel code in which the value of -D is larger than the upper limit of the present invention, and the flattening ratio A of the substantially elliptical shape of the code cross section is larger than the upper limit of the present invention. This steel cord has a small gap between the strands, is inferior in rubber penetration and inferior in rigidity.

In Comparative Example 5, both the core wire diameter d ₂ and the habit pitch P _{1 of the} core are within the scope of the present invention.
Is larger than that of Comparative Example 4 and is outside the upper limit of the present invention, and the aspect ratio A is still larger than the upper limit.
Is. This steel code is further inferior in rubber penetration than Comparative Example 4, and all of the fatigue resistance, rigidity ratio and handling workability are not good.

The steel cord of Conventional Example 1 has hardly any rubber penetrated.

The steel cord of Conventional Example 2 has a substantially circular cross section instead of an elliptical cross section. For this reason, rubber
When the steel cord is sandwiched between the rubber sheets, the thickness of the rubber sheet cannot be reduced. Further, rubber penetration, fatigue resistance, rigidity ratio and handling workability are inferior to the steel cords of Examples 1 to 5.

The steel codes of Examples 1 to 5 do not have the above-mentioned disadvantages and are all excellent steel codes.

[0042]

The steel cord for reinforcing a tire according to the present invention is constituted as described above and has the following effects. Since there is no hollow portion in almost the entire length of the steel cord in the longitudinal direction and the minor axis of the cross-sectional shape is extremely small (so-called thin), it is preferable that the rubber enters the inside of the steel cord. Since the low load elongation is small, the flatness does not change even when embedded in rubber. Since the thickness of the rubber sheet can be extremely reduced, the weight of the tire can be reduced, and the cost of the tire can be reduced and the fuel efficiency of the vehicle can be improved. The rigidity in the tire rotation direction can be reduced, so that the riding comfort can be improved. On the other hand, the rigidity in the direction orthogonal to the tire rotation direction can be increased, so that the cornering performance can be enhanced. A core wire having a small habit does not appear at both ends of the major axis of a substantially elliptical cross section, and is located substantially at the center, and has a substantially pitch P ₁ between the side wires located on both sides of the major axis. Since they appear at intervals, the shape as a steel code is very stable, and the penetration of rubber into the inside becomes very good. Since there is no wire in a state like a core wire and all wires have a structure like a single-layer twist, fatigue resistance is improved. Both conventional tuber type and buncher type twisting machines can be manufactured, and there is no trouble such as poor twisting, so that handling efficiency is excellent.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a steel code according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view showing another embodiment of the steel code of the present invention.

FIG. 3 is a schematic sectional view showing still another embodiment of the steel code of the present invention.

FIG. 4 shows test pieces used in a three-point bending test;
(A) is a schematic diagram of a test piece for measuring bending stiffness in the minor axis direction, and (b) is a test piece for measuring bending stiffness in the major axis direction.
FIG.

FIG. 5 is an explanatory view showing a three-point bending test method.

FIG. 6 is a schematic sectional view showing an example of a conventional steel code.

FIG. 7 is a schematic sectional view showing another example of a conventional steel cord.

[Explanation of symbols]

1, 4, 8 Steel cord 2, 11 Core strand 3, 9, 12 Side strand 5 Rubber sheet 6, 7 Test piece d ₁ Side strand diameter d ₂ Core strand diameter D Outside of core strand Diameter W Length of steel cord cross section T Minor diameter of steel code cross section S Cavity

Claims (1)

[Claims] 1. Four to thirteen strands, one strand being a core strand and the remaining strands being side strands, having a twist pitch P in the same direction.
In the steel cord for tire reinforcement, which has a substantially elliptical shape (major axis W and minor axis T), the transverse sections of which are substantially the same in the longitudinal direction and are twisted at once. Wire diameter d ₁ is 0.15 to 0.22 mm, core wire diameter d ₂
Is 1.1 d _{1 to} 2.0 d ₁ mm (however, d ₂ ≧ 0.2
2 mm), and the core element has a substantially spiral shape having a habit pitch P ₁ and a habit outer diameter D in the code minor diameter direction satisfying the following formulas (1) and (2). line appeared at substantially the pitch P ₁ spacing between the side strands positioned on both sides of the major axis axis of the substantially elliptical, moreover (percentage of T / W) aspect ratio of the substantially elliptical 38% to 60% A steel cord for reinforcing a tire, characterized in that: P ₁ = 0.1 P to 0.5 P (1) T−D = 0.03 to 0.30 (2) P ₁ : habit pitch (mm) P: twist pitch (mm) T: core Short diameter (mm) D: Habit outside diameter of core strand in the short diameter direction of code (mm)