JPH08325962A - Steel cord for tire reinforcement - Google Patents

Abstract

PURPOSE: To obtain a steel cord having high penetrability of rubber into the cord, low rigidity in the rotational direction of tire, high rigidity in the direction perpendicular to the rotational direction of tire, good fatigue resistance and excellent handling workability. CONSTITUTION: A core element wire 1 is placed at the center and a plurality of side element wires 2 are placed around the core wire in twisted state to form a circumscribing circle of the cord having nearly an elliptic form directed nearly the same longitudinal directions. The core element wire 1 has a flat spiral form in a direction same as the flat direction of the side element wires 2, the form pitch of the core element wire 1 is 0.2P to 0.7P (P is twist pitch of the side element wire 2), the ratio of the major diameter (dL) to the minor diameter (dS) of the outer diameter of the spiral form of the core element wire 1 (dL/dS) is >=1.10, the ratio of the major diameter (dL) to the diameter (d) of the element wire (dL/d) is 1.40 to 1.75, the major diameter (dL) of the core element wire, the major diameter DL of the circumscribing circle and the diameter (d) of the element wire satisfy the formula (DL-2d)/dL=1.05 to 1.60 and the ratio of the major diameter DL to the minor diameter DS of the circumscribing circle of the cord (DL/DS) is >=1.10.

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 of 1 + n multi-layer twist having one core wire and a plurality of side wires. It is about.

[0002]

2. Description of the Related Art In general, a large number of steel cords of this kind are covered with a rubber material in a state where they are aligned in parallel and used as a reinforcing material for an automobile tire. And
The conditions required for steel cords are not only good mechanical strength, but also good chemical and physical adhesion to the rubber material, and rubber penetration into the steel cord. It is good. That is, it is necessary for the steel cord to be a complete composite with the rubber material in order to fully fulfill the role of the tire reinforcing material.

In particular, for tires used in heavy vehicles such as trucks and buses, a steel cord having high strength and flexibility is required, and one of them is a steel cord having a structure of 1 + n conventionally. It has been.

However, the cross-sectional structure of the conventional 1 + n steel cord is a closed twist structure as shown in FIG.
And since each wire 7 is completely adhered to each other and there is no gap,
The cavities D are scattered inside the cord. Therefore, when this steel cord is sandwiched between two rubber sheets to form a composite sheet, the rubber material does not penetrate to the cavity D,
Cannot form a complete complex with rubber material.

Therefore, when this rubber sheet is used for a tire, even if a part of the rubber coating is broken by foreign matter such as nails, the water infiltrated from the outside propagates into the cavity D and the steel cord is entirely covered. Causes oxidation. When this happens, the adhesive strength between the rubber and steel cord becomes weaker,
Both will peel off, and the effect of the steel cord as a reinforcing material will become very weak.

In order to solve this problem, a core wire 8 having a large diameter as shown in FIG. 5 and a steel cord having a core wire 9 shaped as shown in FIG. 6 have been proposed. .

[0007]

In the steel cord shown in FIG. 5, since there is no cavity between the side wire and the core wire, water does not propagate inside the steel cord.
Since the core wire diameter is increased, the cord diameter is increased and the thickness of the rubber sheet is increased. Therefore, the weight of the tire is increased, and the fuel consumption is deteriorated when the tire is used in an automobile, which is not preferable. Further, since the core wire 8 and the side wire 8a are always in contact with each other, the fatigue value due to fretting wear is poor. Furthermore, since the core wire diameter is large, the rigidity of the steel cord is increased, and when used in a tire, there is a problem that the riding comfort becomes poor.

Further, as shown in FIG. 6, in the steel cord having a 1 + n structure in which the core wire 9 is provided with a spiral shape, the core wire 9 and the side wire 9a are not always in contact with each other. Therefore, the fatigue resistance is improved, 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. 6 has a thicker cord diameter than the cord of the closed twist as shown in FIG. 4, and the rubber sheet after the calendar (rubber coating step) becomes thicker. Since a predetermined number of steel cords cannot be embedded in the rubber sheet, the strength of the sheet becomes weak. Therefore, when this rubber sheet is used for a tire, it is necessary to increase the number of stacked sheets, resulting in a problem that the weight of the tire increases.

The present invention has been made in order to solve various problems of the above-mentioned various conventional steel cords, and its object is to use it as a reinforcing material for a tire,
It has good rubber penetration into the steel cord and can increase the rigidity in the direction orthogonal to the tire rotation direction while lowering the rigidity in the tire rotation direction. It has good fatigue resistance against compression and bending, and it is easy to handle. To provide excellent steel cord.

[0010]

In order to achieve the above object, the steel cord for tire reinforcement of the present invention has a thickness of 0.2 mm.
One core wire composed of the same wire diameter of ~ 0.4mm is arranged in the center with three to eight side wires twisted on the outside, and the circumscribed circle of the cord is in the longitudinal direction. In a steel cord that is approximately oval in the same direction, the core wire has a flat spiral habit in the same direction as the flat direction of the side wire, and the habit of the core wire is the twist pitch of the side wire. Let P be
Has a habit pitch 0.2P～0.7P, the ratio of the major diameter d _L to the minor axis d _S of the outer diameter of the habit of Shinmotosen "d _L / d _S" is 1.10 or more, the major axis The ratio of d _L to the wire diameter d “d _L
/ D ”is 1.40 to 1.75, and the relationship between the major axis d _L and the major axis D _L of the circumscribed circle of the cord and the strand diameter d is“ (D _L
-2d) / d _L = 1.05~1.60 in ", the ratio of the long diameter D _L and the minor axis D _S code circumscribed circle" D _L / D _S "is 1.1
It is characterized by being 0 or more. In addition, the twist pitch of the side wire of the steel cord is 6 to 20 mm for the reason described below.
The degree is preferred.

[0011]

In the steel cord of the present invention, since the circumscribed circles of the core wire and the side wires are both substantially elliptical, the steel cord has different rigidity in the major axis direction and the minor axis direction. In addition, since the steel cords after calendering are arranged substantially parallel to each other in the longitudinal direction with the major axis portion left and right in the rubber sheet, the bending rigidity is low in the vertical direction and high in the lateral direction. Therefore, when this rubber sheet is used to form a tire, the rigidity in the tire rotation direction is low and the ride comfort is good, and the rigidity in the direction orthogonal to the tire rotation direction is high, and the cornering performance can be improved.

Further, since the steel cord of the present invention has a substantially elliptical shape, almost all cords are arranged substantially parallel to each other in the longitudinal direction with the major axis portion left and right at the time of calendaring. The thickness corresponds to the amount, and the sheet can be made thin.

The twist pitch of the steel cord side wires is 6
mm to 20 mm is preferable. The reason for this is that if the length is less than 6 mm, the amount of processing becomes extremely large, so that wire breakage is likely to occur, and the number of twists per length of the steel cord increases, resulting in reduced productivity. Further, in the present invention, since the peculiar pitch of the core wire is smaller than the twist pitch of the side wire, it is not suitable to be less than 6 mm. On the other hand, if the twist pitch of the side strands of the steel cord exceeds 20 mm, the flexibility of the steel cord is lost, the fatigue value becomes low, and flare easily occurs, which is not practical.

The reason why the core wire has a diameter of 0.2 mm to 0.4 mm is that if it is too thin, sufficient strength cannot be obtained, and conversely if it is too thick, the steel cord diameter becomes large. Also, the thicker the core wire, the lower the fatigue value.
This tendency becomes more prominent in the present invention in which the circumscribed circle of the core wire has a substantially elliptical shape, and becomes a practical obstacle when the wire diameter exceeds 0.4 mm.

The peculiar pitch P ₁ of the core wire to the twist pitch P of the side wire is set to 0.2P to 0.7P because the wire is extremely plastically deformed when P ₁ is less than 0.2P. Received,
Productivity deteriorates with frequent disconnection, while P ₁
When the value exceeds 0.7P, the gap between the strands decreases due to the tensile force caused by the flow of rubber during rubber sheet molding or the ironing force applied to the cord, and there is a sufficient gap for rubber penetration to the side strands. Because it will not occur in.

The major axis d _L and the minor axis d _S of the outer diameter of the eccentricity of the core wire
The ratio was defined as "d _L / d _S" or the ratio "D _L / D _S" of the major axis to D _L to the minor axis D _S code circumcircle 1.10 or more and, flat ratio is less than 1.10 Is close to a circle, and the difference in rigidity in the vertical and horizontal directions due to the substantially elliptical shape, which is a feature of the present invention, does not sufficiently appear.

The ratio "d _L / d" of the major axis d _{L of the} outside diameter of the core wire to the wire diameter d is set to 1.40 to 1.75 because the ratio is smaller than 1.40. This is because there is no sufficient gap between the side strands for rubber penetration. However, if the ratio exceeds 1.75, the processing of the core wire becomes strong, the strength decreases, and the stability of twisting is impaired.

The steel cord of the present invention is manufactured by forming a small substantially spiral shape on a core wire, twisting side wires around the core wire, and then passing the rollers through a certain amount of compression processing. It is possible. Since the present invention can be manufactured by a double twist type twisting machine (buncher type), it is particularly excellent in practical use.

When a certain amount of compression is applied, a gap S is formed between the circumscribed circle 1'of the core wire 1 and the inscribed circle 2'of the side wire group 2 as shown in FIG. , Core wire 1 is side wire 2
Since some parts do not come into contact with, the fretting becomes smaller and the fatigue resistance improves.

If the gap S is too small, the contact between the core element wire 1 and the side element wire 2 increases, and if the gap S is too large, the twisted shape becomes unstable. relationship between d _L and diameter code circumscribed circle D _L and wire diameter d is, (D
_It is preferable that _L -2d) / dL is between 1.05 and 1.60.

The steel cord of the present invention can be manufactured by either a tubular type twisting machine that does not twist the strand or a buncher type twisting machine that twists the strand.

When a tubular type twisting machine is used, the steel cord of the present invention is a method of twisting the side strands after performing a substantially elliptical habit on the core strand in advance, or It can be produced by any of the methods of imparting a spiral habit, twisting the side wires, and then compressing.

However, when a buncher type twisting machine is used, if the core wire is preliminarily provided with a substantially elliptical habit,
When twisting the side wire, it may be twisted and may not be manufactured well. Therefore, in the buncher type twisting machine, it is preferable that the steel cord as shown in FIG. 6 is subjected to the compression step after being manufactured.

When using a buncher type twisting machine,
Since Shinmotosen and the side strands are twisted at the same time, (D _L -2d)
When the range of / d _L is 1.10 to 1.50, the production is easy. Even when using a stranded wire machine tubular type, when compressed into a substantially elliptical shape at the same time Shinmotosen and side strands, the range of _{(D L -2d) / d L} 1.10~1.
The number 50 is easier to manufacture.

When the steel cord for a tire having the above structure is sandwiched between two rubber sheets and pressure-vulcanized, the rubber easily penetrates between the core wire and the side wires, and the rubber thickness is also increased. In addition to being thin, the bending rigidity in the horizontal direction is higher than in the vertical direction. The steel cord burying direction at this time is such that the long diameter portion of the cord is the left-right direction with respect to the horizontal plane of the seat, and the steel cords are arranged substantially parallel to the longitudinal direction.

[0026]

Embodiments of the present invention will be described below. FIG. 1 is a sectional view showing a steel cord of the present invention. This steel cord is composed of a single core wire 1 having a substantially spiral small habit and having a wire diameter d = 0.34 mm, and a wire diameter d = 0.0.2 mm twisted around the core wire 1 at a twist pitch P = 18.0 mm. 34 mm
And six side wires 2 of

[0027] To evaluate the characteristics of the steel cord of the present invention, the long diameter D _L and the minor axis D _S and Side Element Wire major axis d _L to the minor axis d _S and Code circumscribed circle of the outer diameter of the habit of Shinmotosen Examples 1 to 3 are steel cords in which the peculiar pitch of the core wire with respect to the twist pitch is changed within the scope of the present invention, and the cross-sectional shape is the same as that shown in FIG. Steel cords whose numerical values are out of the range of the present invention are Comparative Examples 1 to 3, steel cords having a cross-sectional shape as shown in FIG. 5 are conventional examples 1, and steel cords having a cross-sectional shape as shown in FIG. Conventional example 2,
When each steel cord was evaluated for rubber penetration rate, fatigue resistance, rigidity ratio and handling workability, the results shown in Table 1 below were obtained. The test conditions and evaluation methods for each item shown in Table 1 are as follows.

Rubber infiltration rate = Each steel cord was embedded in rubber under a tensile load of 5 kg and vulcanized, and then the steel cord was taken out of the rubber, and the steel cord was disassembled to obtain a certain length of wire. The length was observed, and the ratio of the length with the trace in contact with the rubber to the observed length was expressed in%.

Fatigue resistance = Tested by a 3-point pulley bending fatigue tester using a composite sheet in which a plurality of steel cords are embedded in a rubber sheet, and the embedded steel cords are fractured after fretting wear, buckling, etc. The number of repetitions up to the above was calculated and indexed with the value of the steel cord of the twisted structure of Conventional Example 2 as 100.

Rigidity ratio = As shown in FIG. 2 (a), "5 steel cords 3 have 100% modulus of 35 kg /
The rubber sheet 4 having a size of cm ² was embedded in a row so that the cross sectional major axis direction of the steel cord was horizontal. ”As shown in FIG. 2B,“ 5 steel cords 3 Embedded in parallel to the rubber sheet 4 so that the longitudinal direction of the steel cord becomes vertical. ”A test piece 6 was prepared, and the test piece 5 or 6 was spanned as shown in FIG. It was mounted on a three-point bending tester with S _P = 20 mm, and the rigidity ratio was defined as “load G when the test piece 5 is pressed by 5 mm” / “load G when the test piece 6 is pressed by 5 mm”.

That is, the rigidity ratio of "the bending rigidity of the steel cord in the minor axis direction" / "the bending rigidity of the steel cord in the major axis direction" was defined as the rigidity ratio. The thickness T of the test piece 5 or 6 is 4 mm, the width W is 15 mm, and the length L is 100 mm.

Handling workability = good workability is indicated by ◯, workability is poor by x, and intermediate workability is indicated by Δ.

[0033]

[Table 1]

The following points are clear from Table 1. Comparative Example 1 is a case (D _L -2d) / d _L is larger than the upper limit of the present invention, and d _L / d is smaller than the lower limit of the present invention. That is, the steel cord has a large gap S between the inner trace drawn by the side wire and the trace drawn by the core wire, and a small peculiar pitch of the core wire. This steel cord is
Since the gap S was too large, the twisted shape became unstable, and the handling workability was very poor. Further, since the elongation of the core wire is small, the balance with the side wire is lost, and the strength of the cord is deteriorated.

Comparative Example 2 is a case where d _L / d and D _L / D _S are smaller than the lower limit of the present invention. Since the gap S between the strands of this steel cord is not sufficient, rubber penetration is extremely poor, Fatigue resistance was also not good.

[0036] Comparative Example 3 is the (D _L -2d) / d a case _L and d _L / d is larger than the upper limit of the present invention, a steel cord having an increased imprint both Shinmotosen and Side Element Wire . This steel cord does not have good fatigue resistance due to the large amount of core wire processed. Further, D _L (major axis of the circumscribed circle of the cord) is large, and the number of embedded rubber sheets 4 becomes small as shown in FIG.
Book), the strength of the rubber sheet was insufficient. Furthermore, the twist stability was poor and the handling workability was also poor.

In the steel cord of Conventional Example 1, the rubber penetration rate was not sufficient, the core wire was thick, so that it lacked flexibility, and the diameter of the cord was large, so the rubber sheet also became thick.

The steel cord of Conventional Example 2 has a larger D _S than the steel cords of Examples 1 to 3. Therefore, when such a steel cord is used, the rubber sheet cannot be thinned. Note that d _L / d _S and D
_{The fact that L} / D _S is not 1.00 is due to manufacturing variations.

Since the steel cords of Examples 1 to 3 do not have the above-mentioned drawbacks and the rigidity ratio is small, when they are used for tires, they are deformed in response to the force from the road surface, and moreover, they are cornered. Sometimes it becomes difficult to deform.

[0040]

EFFECTS OF THE INVENTION Since the steel cord for tire reinforcement of the present invention is constructed as described above, it has the following effects. Since there is no cavity inside the cord over almost the entire area in the longitudinal direction of the cord, rubber penetration is good. Since the thickness of the rubber sheet when it is embedded in rubber to form a sheet can be reduced, the weight of the tire can be reduced and fuel consumption can be improved. Since the rigidity of the tire in the rotating direction can be lowered, the riding comfort can be improved, while the rigidity in the direction orthogonal to the rotating direction of the tire can be increased, so that the cornering performance can be improved. Since the contact surface between the core wire and the side wire is small, fatigue resistance is improved. Since it can be manufactured with both conventional buncher type and tubular type twisting machines, there is no trouble such as twisting failure,
Excellent workability.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a 1 + 6 structure showing an embodiment of a steel cord for tire reinforcement of the present invention.

FIG. 2 is a diagram showing a test piece used in a three-point bending test, FIG. 2 (a) is a schematic diagram of a test piece for measuring bending rigidity in a minor axis direction, and FIG. 2 (b) is a bending rigidity in a major axis direction. It is a schematic diagram of a test piece for measurement.

FIG. 3 is an explanatory diagram showing a three-point bending test method.

FIG. 4 is a cross-sectional view of a conventional closed-twisted steel cord having a 1 + 6 structure.

[Fig. 5] 1+ of conventional closed twist with thick core wire diameter
It is sectional drawing of the steel cord of 6 structure.

FIG. 6 is a sectional view of a conventional steel cord having a 1 + 6 structure in which a core wire is provided with a substantially spiral habit.

[Explanation of symbols]

1 ... Shinmotosen 2 ... Side Element Wire 3 ... steel cord 4 ... rubber sheets 5,6 ... habit of minor d _L ... Shinmotosen of habit outer diameter of the test piece d ... wire diameter d _S ... Shinmotosen Outer diameter major axis D _S … Cord circumscribing circle minor axis D _L … Cord circumscribing circle major axis S… Gap

Claims (1)

[Claims] 1. A core wire composed of the same wire diameter of 0.2 mm to 0.4 mm is arranged in the center with 3 to 8 side wires twisted on the outside thereof. Moreover, in the steel cord whose circumscribed circles are substantially elliptical with the same direction in the longitudinal direction, the core wire has a flat spiral-like habit in the same direction as the flat direction of the side wire, and the eccentricity of the core wire , when the twisting pitch of the Side Element Wire is P, have a habit pitch 0.2P～0.7P, the ratio "d _L of the major axis to d _L to the minor axis d _S of the outer diameter of the habit of Shinmotosen / D _S ”is 1.10 or more, the ratio“ d _L / d ”of the major axis d _L to the strand diameter d is 1.40 to 1.75, and the major axis d _L and the circumscribed circle of the cord are relationship between the long diameter D _L and the wire diameter d is _{"(D L -2d) / d L} = 1.05~1.6
"0", the ratio of the major diameter D _{L of the} circumscribed circle of the cord to the minor diameter D _S of "D"
_L / D _S "tire reinforcing steel cord, characterized in that at 1.10 or more.