JP2000096466A - Steel cord for reinforcing tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel cord capable of improving the penetrability of a rubber into the steel cord, lowering the stiffness of the steel cord in the rotation direction of a tire, enhancing the stiffness of the steel cord in the direction orthogonal to the rotation direction of the tire, and improving the fatigue resistance of the steel cord against compression and bending, and having excellent productivity and handling workability. SOLUTION: This steel cord for reinforcing a tire has the following characteristics. The core element wire 1 has an approximately spiral small curl at a curl pitch P1 of 0.1P to 0.5P. The core element wire 1 appears from the insides of side element wires 2 for each distance of constant element wires or variable element wires. The side element wires 2 are arranged and disposed on both the sides of an approximately oval shape through its major axis. The flatness degree of the approximately oval shape is 38-60%.

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 automobile tires, and more particularly to a steel cord used for reinforcing a steel cord.
The present invention relates to a steel cord in which a total of 13 to 13 strands are twisted at a time, and the cord has a substantially elliptical cross section.

[0002]

2. Description of the Related Art Generally, a steel cord of this kind is used as a reinforcing material for automobile tires by being covered with a rubber material in a state where many cords are aligned in parallel. And
The conditions required for steel cord include not only excellent mechanical strength, but also good chemical and physical adhesion to rubber materials, and rubber penetration into the steel cord. And the like. 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, and as one of them, a steel cord having a 1 + n configuration has been conventionally used. It has been.

However, as shown in FIG. 7, the conventional 1 + n steel cord has a cross-sectional structure of a close-twisted structure, and the wires 7 are completely adhered to each other with no gap. S are scattered inside the code. Therefore, when a composite sheet is formed by sandwiching the steel cord between two rubber sheets, the rubber material does not penetrate to the cavity S, and a complete composite with the rubber material 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, the moisture penetrating from the outside propagates into the cavity S, and the steel cord extends over the entire surface. Causes oxidation. When this happens, the adhesion between the rubber and the steel cord becomes weaker,
Both will peel off, and the effect of the steel cord as a reinforcing material will be very weak.

In order to solve this problem, a core wire 8 having a larger diameter than the side wire 8a as shown in FIG.
As shown in (1), a steel cord in which the core element wire 9 is formed is proposed.

[0007]

Since the steel cord shown in FIG. 8 has no hollow portion between the side strand and the core strand, moisture does not propagate inside the steel cord.
The cord diameter increases to increase the core strand diameter, and the rubber sheath
G thickens. For this reason, the weight of the tire increases, and when it is used in an automobile, the fuel efficiency deteriorates, which is not preferable. In addition, since the core strand 8 and the side strand 8a are always in contact, the fatigue value due to fretting wear is poor. Furthermore, since the core element wire diameter is large, the rigidity of the steel cord is increased, and there is a problem that the riding comfort is deteriorated when used for a tire.

Further, as shown in FIG. 9, a steel cord having a 1 + n configuration in which the core element wire 9 is spirally formed on the core element wire 9 at one time so that the core element wire 9 and the side element wire 9a are always in contact with each other. The fatigue properties are improved because nothing is done, but the rigidity of the steel cord is the same in any direction because the cross-sectional shape is a substantially circular shape. Therefore, if the rigidity is increased in order to improve the cornering performance of the tire, there is a problem that the riding comfort is deteriorated. further,
The steel cord of FIG. 9 has a larger cord diameter than the closed twist cord as shown in FIG. 7, and the rubber sheet after calendering (rubber coating step) becomes thicker. A predetermined number of steel cords 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 the production of the steel cord, it is impossible to arrange the steel wire neatly in the space as shown in FIG. 9, and the twist becomes extremely unstable.

The present invention has been made to solve the various problems of the above-mentioned various conventional steel cords.
Good penetration of rubber into steel cord, 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 and handling work It is an object of the present invention to provide a thrill code having excellent characteristics.

[0010]

[MEANS FOR SOLVING THE PROBLEMS] To achieve the above object
The steel cord for reinforcing a tire according to the present invention has a diameter of 0.15.
6 to 13 strands with a wire diameter of mm to 0.40 mm
One core wire and the remaining wires side wires
Steel cord twisted at a time with twist pitch P
A cross section of which is substantially elliptical in a substantially same direction in a longitudinal direction.
Steel core for tire reinforcement with shape (long diameter W, short diameter T)
The core wire has a habit pitch P ₁ = 0.1P ~
It has a small spiral shape of approximately 0.5P, and
Core wires are almost aligned on both sides of the major axis of the above-mentioned ellipse
A fixed number of gaps or indefinite numbers between side strands
Appears to interrupt from the inside at several intervals, and
Flatness of elliptical shape (percentage of T / W) is 38% to 60%
The first invention is characterized by the fact that the first invention
In the invention of the above, the core element wire sandwiches the major axis of the substantially elliptic.
Interrupted from the inside between the side strands aligned on both sides
The frequency of occurrence is so long that the side strands are two to five wires apart.
This is the second invention. In addition,
The twist pitch of the cord is 6 to 28 m for the reason described below.
m is preferable. Also, the wire diameter of the core strand and side strand is
All may be the same, but the wire diameter of the core strand and the side strand
The wire diameter may be slightly changed.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The steel cord of the present invention has a structure similar to a single-layer twist, despite the fact that the core strands enter between the side strands, although the strands are multi-strands. Is a substantially elliptical shape with a large degree of flatness (the flatness ratio T / W is small). For this reason, the rigidity of the steel cord differs greatly in the minor axis direction and the major axis direction. Further, the steel cords after calendering are arranged substantially parallel to the longitudinal direction of the rubber sheet with the long diameter portion left and right, 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 tire has a low rigidity in the rotational direction and thus has a good ride comfort, and the rigidity in a direction perpendicular to the tire rotational direction is high and the cornering performance can be enhanced. On the other hand, since the core strands appear to intervene from the inside between the side strands, the rubber sufficiently penetrates into the inside from the gap between the strands formed due to the relationship.

Further, since the steel cord of the present invention has a substantially elliptical cross section, almost all the steel cords are arranged substantially parallel to the longitudinal direction with the long diameter portion left and right during calendering. Has a thickness corresponding to the short diameter portion of the steel cord, and the sheet can be made thinner. And the number of steel cords inserted 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 embedding in a rubber sheet, as compared to a steel cord as shown in FIG. 9, which is excellent in manufacturing and handling work. ing.

It is more preferable that the frequency at which the core strands appear to be inserted from the inside between the side strands on both sides of the major axis of the substantially elliptical cross section of the steel cord is two to five intervals. It is. In order to make the spacing between the single strands, the habit of the core strands becomes small and the wire is likely to be broken. The result is that the degree does not increase. If the spacing is six or more, the twist is likely to be disturbed, and the infiltration of rubber is not sufficient.

The twist pitch of the steel cord is from 6 mm to 2
8 mm is preferred. Because if it is less than 6 mm,
This is because the amount of bending is extremely increased, so that disconnection is likely 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, when the twist pitch of the steel cord exceeds 28 mm, the flexibility of the steel cord is lost, so that the fatigue value is lowered, the twist becomes unstable, and flare is easily generated, which is not practical.

The wire diameter of the strand is 0.15 mm to 0.40 mm
The reason for this is that if it is too thin, sufficient strength cannot be obtained, and if it is too thick, the steel cord diameter will increase. Also, when the strands are made thicker, the flexibility of the steel cord is lost, and the fatigue value becomes lower. This tendency is more remarkable in the present invention in which a strand having a small habit exists, and when the strand diameter exceeds 0.4 mm, it becomes a practical obstacle.

When the twist pitch of the steel cord is P, the habit pitch P ₁ of the core wire having a habit is 0.1 mm.
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 as a core element wire cannot be achieved, and the gap between the element wires decreases due to the tensile force due to the flow of rubber during molding of the rubber sheet or the ironing force applied to the cord, and a sufficient gap for rubber penetration This is because it does not occur between the strands. On the other hand, if it exceeds 0.5P, the steel cord cannot be sufficiently rolled, and the minor diameter T of the steel cord cross section increases,
Rubber sheet thickness cannot be reduced.

Flatness of 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. . 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 cord of the present invention cannot be expected.

In the present invention, the core wire is not disposed completely inside the side wire, but the core wire is disposed between the side wires from the inside on both sides of the major axis. As a result, the steel cord of the present invention was finally completed by flattening to a structure such as an almost single-layer twist having no core wires at a glance. As a result, a steel cord with more stable twisting than before and with an appropriate gap maintained between the strands, and having an extremely large flatness (small flatness T / W) was obtained.

[0019] The steel cord of the present invention is obtained by giving a preset twist to one strand to form a core strand, twisting side strands around the core strand, and then passing between rollers having a flat surface. It can be manufactured by applying a considerably strong compression process. Conventionally, in such a method, the twist of the steel cord was broken, and it was thought that the cord was defective.However, appropriate tension was applied to each of the wires constituting the steel cord, and the steel cord was applied to the steel cord. It was also found that manufacturing could be easily performed by applying a strong compression process from one direction. In this case, the habit to be given to the core strand in advance depends on the number of strands to be twisted, but the pitch of the steel cord when twisted is 0.1P or more.
If it is set to 0.5 P and the habit outer diameter is set to be about 2 to 2.8 times the diameter of the side strand, it can be manufactured more easily.

Although the steel cord of the present invention can be manufactured with a tubular type twisting machine, it is more efficient and practical to manufacture with a buncher type twisting machine. In any case, twisting can be performed in one step. When using a buncher-type twisting machine, it is necessary to take into account that the twisting of the strands causes the difference between the habit of attaching in advance and the habit of using a steel cord.

When the steel cord for a tire having the above structure is pressed and vulcanized while being sandwiched between two rubber sheets, the rubber easily penetrates between the individual wires, the rubber thickness can be reduced, and the bending rigidity can be reduced. Also, the horizontal direction is extremely higher than the vertical direction. At this time, the steel cord is buried in a direction in which the long diameter portion of the steel cord is in the left-right direction with respect to the horizontal plane of the sheet, and the steel cords are arranged substantially parallel to the longitudinal direction.

[0022]

Embodiments of the present invention will be described below. FIG. 1 is a schematic view showing a cross section of the steel cord of the present invention. This steel cord has a substantially spiral shape.
It comprises a core wire 1 and nine side wires 2 having the same wire diameter. In the drawing, D ₁ is a habit outer diameter of the core wire.

FIG. 2 is a schematic view showing a cross section of a steel cord according to the present invention similarly constituted by one core strand and eight side strands.

FIG. 3 shows a single core wire and a side wire 12 similarly.
It is the schematic which shows the cross section of the steel cord of this invention comprised from the book.

FIG. 4 is an external view in the longitudinal direction showing one embodiment of the steel cord of the present invention comprising one core strand and six side strands. FIG. 4A is a schematic plan view. (B)
It is a schematic front view.

In order to evaluate the characteristics of the steel cord of the present invention, the number N of strands, the twist pitch P, the pitch P ₁ of the habit of the core strand, the minor axis T and the major axis W of the elliptical cross section of the steel cord are used. Steel cords changed within the scope of the present invention are referred to as Examples 1 to 4, and steel cords in which the numerical values of any of the components are out of the scope of the present invention are referred to as Comparative Examples 1 to 3. A steel cord having a cross-sectional shape as shown in FIG. 9 is referred to as Conventional Example 1, and a steel cord having a cross-sectional shape as shown in FIG. 9 is referred to as Conventional Example 2, and for each steel cord, a rubber penetration rate, fatigue resistance, and rigidity are shown. When the ratio and handling workability were evaluated,
The results as shown in Table 1 below were obtained. Test conditions and evaluation methods for each item shown in Table 1 are as follows.

Rubber penetration rate: Each steel cord is embedded in rubber while being subjected to a tensile load of 5 kg, and after vulcanization, the steel cord is taken out of the rubber, and the steel cord is disassembled to a certain length of the strand. The length was observed, and the ratio of the length having a trace of contact with the rubber to the observed length was expressed as a percentage. In the table, the larger the value, the better the rubber penetration rate.

Fatigue resistance: A composite sheet in which a plurality of steel cords are embedded in a rubber sheet is tested by a three-point pulley bending fatigue tester. The embedded steel cord breaks through fretting wear, buckling, etc. The number of repetitions up to this point was calculated, and the value of the twisted steel cord of Conventional Example 2 was set to 100 and indicated as an index. In the table, the larger the value, the better the fatigue resistance.

Stiffness ratio: As shown in FIG. 5 (a), "the five steel cords 3 have a 100% modulus of 35 kg.
The steel cord was embedded in a single row so that the longitudinal direction of the cross section of the steel cord was horizontal with respect to the rubber sheet 4 having a thickness of / cm ^2. "
As shown in FIG. 5 (b), the test piece 5 and “five steel cords 3 were embedded in the rubber sheet 4 in parallel with each other so that the longitudinal direction of the cross section of the steel cord was vertical. The test piece 6 was manufactured, and as shown in FIG. 6, the test piece 5 or 6 was made to have a span Sp = 20 mm.
On the three-point bending tester that was set as above, and “the weight G when the test piece 5 was held down by 5 mm” / “the test piece 6
The weight G when 5 mm is held down was defined as the rigidity ratio.

That is, the rigidity ratio was defined as “bending rigidity of steel cord in the minor axis direction” / “bending rigidity of steel cord in the major axis direction”. In the table, a smaller value indicates a difference in bending stiffness. The test piece 5 or 6 had a thickness of 4 mm, a width of 15 mm, and a length of 100 m.
m.

Handling operability: A sample with good workability was rated as “〇”, a sample with poor workability was rated as “x”, and a sample with intermediate workability was rated as “△”.

[0032]

[Table 1]

The following points are evident from Table 1. Comparative Example 1 is larger than the upper limit of the present invention P ₁ of the core strands, flattening of the substantially elliptical shape of the cord cross section is larger than the upper limit of the present invention, moreover from the inside between the core element wire of the side strand This is a case where the intervals appearing so as to interrupt are 5 to 7 lines. That is, the steel cord has a large habit pitch of the core strand and a flatness greater than the upper limit of the present invention. This steel cord has a small gap between the wires, is inferior to rubber penetration,
Stiffness ratio is slightly inferior.

Comparative Example 2 is a case where P ₁ of the core element wire is within the range of the present invention, but the flatness is larger than the upper limit. In this steel cord, the phenomenon that the core strands appear to be inserted from the inside between the side strands cannot be clearly confirmed. And this steel cord is further inferior to rubber intrusion than Comparative Example 1, and all are not good in fatigue resistance, rigidity ratio, and handling workability.

[0035] Comparative Example 3 is P ₁ of the core wire is far outside the scope of the present invention is comparable to Comparative Example 2 is also a flat rate. Further, as in Comparative Example 2, a phenomenon in which the core strands appear to be interrupted from the inside between the side strands cannot be clearly confirmed. This steel cord had even worse results than Comparative Example 2.

The steel cord of Conventional Example 1 has problems such as insufficient rubber penetration rate, lack of flexibility due to thick core strands, poor fatigue resistance, and thick rubber cord due to large cord diameter. occured.

The steel cord of Conventional Example 2 has a substantially circular cross section rather than an elliptical cross section. Therefore, when the steel cord is sandwiched between rubber sheets, the thickness of the rubber sheet cannot be reduced. Further, as compared with the steel cords of Examples 1 to 4, rubber intrusion, fatigue resistance, rigidity ratio, and handling workability were inferior.

The steel cords of Examples 1 to 4 do not have the above-mentioned disadvantages, have a low rigidity ratio, and when used in tires, are deformed in response to the force from the road surface and have good ride comfort. Moreover, it is difficult to deform during cornering. However, in the third embodiment, the interval is 1 to 6 lines, and varies from 1 to 6 lines. For this reason, the results were slightly inferior to the other examples in rubber penetration and fatigue resistance.

[0039]

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 closed cavity inside the cord over almost the entire area in the longitudinal direction of the steel cord, and the minor axis of the cross-sectional shape is extremely small (so-called thin), the rubber penetrates into the inside of the steel cord is good. Since the thickness of the rubber sheet when it is embedded in rubber to form a 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 automobile can be improved. Since the rigidity in the tire rotation direction can be reduced, the riding comfort can be improved. On the other hand, the rigidity in the direction perpendicular to the tire rotation direction can be increased, so that the cornering performance can be improved. Since the core strand with a small habit does not appear at both ends of the major axis of the substantially elliptical cross section, it is located almost at the center, so the shape as a steel cord is very stable, and into the inside Rubber penetration 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 tubular 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 shows an embodiment of a steel cord for reinforcing a tire according to the present invention. It is the schematic which shows the cross section of the steel cord of this invention comprised from one core strand of a 1 + 9 structure, and nine side strands.

FIG. 2 shows an embodiment of a steel cord for reinforcing a tire according to the present invention. It is the schematic which shows the cross section of the steel cord of this invention comprised from one core strand of a 1 + 8 structure, and eight side strands.

FIG. 3 shows an embodiment of a steel cord for reinforcing a tire according to the present invention. It is the schematic which shows the cross section of the steel cord of this invention comprised from 1 core wire of 12 structure, and 1 side wire.

FIG. 4 shows an embodiment of a steel cord for reinforcing a tire according to the present invention. It is an external appearance explanatory view in the longitudinal direction of the steel cord of the present invention composed of one core element wire having a 1 + 6 structure and six side element wires, (a) is a schematic plan view, and (b) is a schematic front view. .

5A and 5B are diagrams showing test pieces used for a three-point bending test, wherein FIG. 5A is a schematic view of a test piece for measuring bending stiffness in a short diameter direction, and FIG. 5B is a test for measuring bending stiffness in a long diameter direction. It is the schematic of a piece.

FIG. 6 is an explanatory view showing a three-point bending test method.

FIG. 7 is a sectional view of a conventional steel cord having a 1 + 6 structure of a closed twist.

FIG. 8: Conventional closed-twisted 1+ with a large core strand diameter
It is sectional drawing of the steel cord of 6 structures.

FIG. 9 is a sectional view of a conventional 1 + 6 steel cord in which a core wire is provided with a small spiral in a substantially spiral shape.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Core strand 2 ... Side strand 3 ... Steel cord 4 ... Rubber sheet 5,6 ... Test piece d ... Strand diameter D ₁ ... Core strand Habit outside diameter W: long diameter of steel cord cross section T: short diameter of steel cord cross section S: hollow part

Claims (2)

[Claims] 1. Twist to 13 strands having a wire diameter of 0.15 mm to 0.40 mm, one as a core strand, the other strands as side strands, and a twist pitch P in the same direction. In a steel cord for tire reinforcement, which is twisted at one time and has a substantially elliptical cross-section in a direction substantially the same in the longitudinal direction, the core element wire has a habit pitch P ₁ = 0.1
It has a substantially spiral small habit of P to 0.5P, and its core strands are spaced by a certain number or indefinite between side strands that are arranged substantially on both sides sandwiching the major axis of the ellipse. A steel cord for reinforcing a tire, wherein the steel cord appears so as to be interrupted from the inside at intervals of a number, and the oblateness of the substantially elliptical shape is 38% to 60%. 2. The side wire 2 according to claim 1, wherein the frequency at which the core wire appears so as to be inserted from the inside between side wires arranged side by side on both sides of the major axis of the substantially ellipse. A steel cord for reinforcing a tire, wherein the cords are spaced from one to five wires.