JPH0617385A - Steel cord for reinforcing rubber products - Google Patents

Abstract

(57) [Summary] [Purpose] To maximize the strength of each wire in tension, fatigue limit, etc. so that each wire acts as a cord. [Structure] An element wire having straightness, P ₁ = 0.1P to 0.7P when the peculiarity pitch P ₁ is the twist pitch, and the apparent outer diameter d ₁ is the element wire diameter d. Then, d ₁ = (d +
Steel cord having a 1 × n (n = 2 to 6) structure obtained by twisting together a wire having a small spiral-shaped habit such as 2/100 mm) to (d + 2/10 mm) and having a small spiral shape. The cord is configured such that the apparent circumscribed circle of a strand having a habit and the strand having straightness are included inside and substantially inscribed in one circle, and the center of this one circle, that is, the circumscribed circle A steel cord for reinforcing rubber products, which is formed by twisting together with the center of the cord twist.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel cord for reinforcing rubber products used as a rubber reinforcing material for automobile tires, conveyor belts and the like.

[0002]

2. Description of the Related Art In general, this type of steel cord has a so-called closed twist structure in which a plurality of element wires as shown in FIGS. There is. A plurality of the steel cords 7 are covered in parallel with each other and covered with a rubber material to be used as a rubber product reinforcing material for automobile tires, conveyor belts and the like.

By the way, when steel cords are used as a reinforcing material for rubber products, the essential requirements are:
First, in addition to being excellent in strength, it is also possible to chemically adhere well to the rubber material and to cause the rubber material to often penetrate into the steel cord. That is, in order for the steel cord to sufficiently fulfill the role of the rubber reinforcing material, it is necessary that the steel cord is completely in a composite with the rubber material.

However, in the conventional steel cord 7 shown in FIGS. 7 (b) to 7 (c), since the individual wires 8 constituting the steel cord are closely contacted and twisted together,
At the time of molding a composite sheet of a steel cord and a rubber sheet, the rubber material does not penetrate into the hollow portion D formed in the central portion of the steel cord, and the hollow portion D continuously exists in the longitudinal direction of the cord. .

Therefore, in the tire using the conventional steel cord 7, moisture generated in the hollow portion D as a result of the condensation of the gas generated from the rubber material, or when the tire is damaged, Moisture that has entered the cavity D propagates in the cavity D in the longitudinal direction of the cord, corrodes the steel cord, reduces the adhesion between the steel cord and the rubber material, and separates the steel cord and the rubber material. That is, the so-called separation phenomenon was caused, and the life of the tire was significantly shortened.

The steel cord 7 shown in FIG.
However, since the rubber E is not coated on the contact portion E between the wires 8, there is a problem that when bending and compression are repeated, fretting wear occurs and fatigue resistance deteriorates.

In view of the above circumstances, various steel cords having a structure capable of improving the adhesion between the steel cord and the rubber material have been proposed in recent years.

For example, in Japanese Unexamined Patent Publication No. 3-193983 and Japanese Unexamined Patent Publication No. 55-90692, FIGS.
As shown in (C), a steel cord 9 called a so-called open twisted cord, which is twisted with a gap C between the individual wires 10 and has a loose twist, is also disclosed in JP-A-57-57.
Japanese Laid-Open Patent Publication No. 193253 discloses two strands 11 having parallel or nearly parallel twist pitches as shown in FIG.
And a steel cord 13 having a 2 + 2 twist structure, which includes two strands 12 twisted in the same direction and at the same pitch as the twist of the steel cord.

[0009]

In the former steel cord 9 having an open twist structure, in order to allow the rubber material to adhere to the entire circumference of each wire and to sufficiently infiltrate the rubber material into the inside, It is necessary to make the gap C between the wires 10 sufficient to allow the rubber material to penetrate, that is, 0.01 mm or more.

However, if the clearance C is sufficiently large, the free space in which each wire 10 can move becomes large, and the twisted structure tends to become unstable during the manufacture of the steel cord.
As shown in (a) and (b), the strands 10 are offset, and the twist becomes non-uniform in the longitudinal direction of the cord.

Further, since the steel cord 9 has a large elongation under an extremely low load, not only the handleability and workability at the time of rubber molding are poor, but also the above-mentioned gap C is reduced by the low load tension applied at the time of rubber molding. However, after all, it becomes the same as the steel cord of the closed twist structure as shown in FIG. 7, and there is a problem that the rubber material does not sufficiently penetrate into the cord and it is difficult to improve the adhesiveness with the rubber material. .

Further, in the latter steel cord 13, since the rubber material can well infiltrate in the portions other than the contact portion of the wire and the elongation due to the tension of the low load is small, the disadvantage of the former steel cord 9 is solved. However, the twisted form is very unstable in the longitudinal direction of the cord. Therefore, when bending stress is repeatedly applied to the steel cord 13, buckling is likely to occur, and stress concentration occurs at this time, so that the individual wires forming the steel cord do not exert the effect as a cord integrally, and fatigue occurs. This causes breakage, has poor fatigue resistance, and has a problem that fretting wear is likely to occur at the contact portion of the wire.

In view of the above-mentioned problems, the inventor of the present invention provides a small spiral-shaped habit in addition to the twist habit of some of the plurality of wires forming the cord. By twisting the wire with a straight wire, the rubber material penetrates inside the steel cord, making the adhesion between the rubber material and the steel cord good, while suppressing the elongation under low load. We have proposed a steel cord that stabilizes the twist in the direction and is less likely to buckle due to repeated bending stress and has excellent fatigue resistance.

The present invention is a further improvement of this steel cord.

In the subsequent tensile test and the like, the steel cord has a breaking load (breaking strength) slightly lower than that of the conventional cord, and either the strand having straightness or the strand having a small spiral habit at the time of breaking. In some cases, the wire breaks extremely quickly, and even in a particularly severe fatigue test, one of the strands is extremely inferior in fatigue resistance.

[0016] Therefore, as a result of earnestly investigating the cause of this by a large number of experiments, the inventor of the present invention, in the steel cord formed by twisting the strand having straightness and the strand having a small spiral habit as described above, The spiral habit of the cord twist of the wire was not constant, the shape of the cord cross section was unstable, and the center of the cord twist was fluctuated in the longitudinal direction of the cord. Therefore, we found that the forces acting between the individual strands were not uniform, so that at the time of fracture, all individual strands could not function together as a cord.
The present invention has been completed.

The center of the cord twist is the center of the spiral for constituting the cord in the cord twist of each element wire constituting the cord. This can be judged from the measurement of the cord diameter over the pitch and the sectional structure.

Explaining these with reference to the drawings, the above-mentioned cord ("0013") having a cross-sectional structure in which the cross-sectional shape of the cord is unstable as shown in FIGS. It is considered that each of the strands is a cord having a spiral habit having a shape as shown in (a) and (c) of FIG. In general, a strand having a small spiral habit has a spiral habit due to a cord twist, and a strand having straightness has a spiral habit due to a cord twist.

A cord whose center of twist of the cord fluctuates is a cord in which cross-sectional structures as shown in FIGS. 5 and 1 and 2 appear in the longitudinal direction of the cord, and the respective strands of the cord are respectively drawn. (A), (b) or (b) shown in 6
It is considered to be a cord having a spiral habit with a shape such as (C) or (C) or (D). In FIG. 5, E
Indicates the outer diameter of the cord, and B indicates the center of cord twist.

The present invention is intended to solve such a new problem, and in a cord formed by twisting a wire having straightness and a wire having a small spiral habit, those wires are twisted together. By setting the spiral habit in the cord twist of each strand to be approximately the same and configuring the cord so that those strands are inscribed in a single circle and keeping the center of the cord twist in a substantially constant position, tension and fatigue It is an object of the present invention to provide a steel cord having excellent characteristics such that the strength of each strand at the limit and the like is maximized and each strand acts as a cord in an integrated manner.

[0021]

In order to achieve the above-mentioned object, the steel cord for rubber reinforcement of the present invention has a straight wire and a habit pitch P ₁ where P ₁ = 0 when the twist pitch is P. 1P to 0.7P, and the apparent outer diameter d ₁ is the wire diameter d ₁ = (d + 2/100 mm)
1 × n (n = n = n = n = n), which is formed by twisting together a wire having a small spiral habit such that (d + 2/10 mm)
2-6) A steel cord having a structure, which includes an apparent circumscribed circle of a wire having a small spiral-like habit and a wire having straightness inside so that they are substantially inscribed in one circle. And the center of this one circle, that is, the circumscribed circle, is twisted with the center of the cord twist being approximately the center.

In the above structure, the number of the strands having the small spiral habit is one or two, which is 1/2 of the constituent strands.
A number of 2 or less is suitable, and if too many,
The elongation under a low load increases, which may hinder the rubber material from penetrating into the cord, and the twisting tends to be unstable. If there is even a gap in the rubber material, it will penetrate from there and fully penetrate into the interior.

Further, in the above structure, a small spiral-shaped habit is d ₁ = (d + 2/100 mm) to (d + 2).
/ 10 mm) is limited to less than d + 2/100 mm, even if a rubber material having good fluidity is used, the rubber material does not sufficiently penetrate into the steel cord during pressure vulcanization, and d + 2/100 If it is larger than 10 mm, the stability of the twist will be deteriorated, the fatigue resistance will be lowered, and the elongation under an extremely low load will be large.

The wire diameter d of the wire used for the steel cord of the present invention is preferably in the range of 0.15 to 0.40 mm. And each strand does not necessarily need to have the same strand diameter. Further, the small spiral peculiar peculiar pitch P _{1 is set} to P ₁ = 0.1P to 0.7P, because if it is smaller than 0.1P, the strand is forced to be plastically deformed at the time of peculiarity, so that the strand is If it is more than 0.7P, the gap between the strands will decrease due to the tensile force due to the flow of the rubber material when molding the rubber product or the ironing force applied to the cord surface, and the rubber material will not penetrate. This is because it will not be enough.

Here, the apparent outer diameter d ₁ is as shown in FIG.
(B), as shown in FIG. 2 (b), it is the apparent outer diameter of the strand that has been curled into a small spiral shape, and the curbed pitch P ₁ is the curled as shown in FIG. It is the habit pitch of the wire.

The small spiral-like habit does not need to be exactly spiral-shaped, and even if it is simply wavy, it has the same effect as the spiral-shape, and therefore includes such a shape. . Moreover, the direction of this spiral habit may be the same as the twist direction, or may be the opposite direction. In the case of the same, the small spiral habit and the spiral habit in the cord twist are in the same direction, and a double spiral strand is formed.

Next, an example of a method for measuring the shape of the small spiral and the center of cord twist will be described. First, for a small spiral shape, the cord to be measured is embedded in a resin or the like, and an enlarged photograph of the cord cross section of the end face is taken while cutting in the longitudinal direction (the concept is shown in FIGS. 4 (a) to (i)). It can be easily measured.

Further, the center of the cord twist is determined by measuring the cord diameter in the longitudinal direction (at least twice the twist pitch, preferably 3 to 5 times). For this purpose, a universal projector or a micrometer with a wide anvil is used to reduce the pressure and perform measurement.

There is also a method in which the twisted strands can be unraveled and can be determined from the shape of the spiral habit of each strand. However, in this case, each strand may be slightly different between the spiral habit in the form of a cord and the spiral habit after being unraveled, which is not necessarily an appropriate measurement method.

From the results of a number of experiments, it can be judged that the steel cord of the present invention has the same cross-section as the structure shown in FIGS. When the center position of the twist changes to any other position, the cord outer diameter E greatly differs from the value that can be measured in the cross-sectional structure (the value of the diameter of the one circle, that is, the circumscribed circle). Further, when each strand is not substantially inscribed in one circle, it can be clearly identified in its cross-sectional shape. In addition, reference numerals 1 and 4 are steel cords,
2, 5 are wires with a small spiral habit, 3,
6 is an element wire having straightness.

[0031]

EXAMPLES Examples of the present invention will now be specifically described in comparison with conventional examples and comparative examples. Table 1 shows the test results of steel cords having various configurations in which a plurality of brass-coated wires are twisted together. The number of strands of steel cord, strand diameter, twist pitch, small spiral peculiar shape, and the center of cord twist are changed. In the table, CD is the cord diameter, FS is the breaking strength, SL
Is cord elongation under load of 5 kg, RP is rubber penetration rate, RF
Indicates compression tensile bending fatigue resistance, RS indicates residual strength, and HW indicates handling workability.

[0032]

[Table 1]

Experiment No. 1, 5 and 11 are shown in FIG.
Experiment N of the closed twist structure shown in (b) and (c)
O.2, 6, and 12 are steel cords of the conventional example having the open twist structure shown in FIGS. 8 (a), 8 (b), and 8 (c), respectively. Experiment Nos. 4, 8, 9, 10, 14, 15 Is a steel cord for reinforcing a rubber product of the present invention shown in FIGS. 1 (a), (b), (c) and FIG. 2 (c). Also, experiment N
O. Reference numerals 3, 7, and 13 are steel cords of comparative examples shown in FIGS. 5 (a), 5 (b), and 5 (e).

As a means for imparting a small spiral-like habit to the wire, as shown in Japanese Patent Publication No. 63-63293, a shaving device that rotates with the supplied wire as a shaft core is used. There is a method to give a certain straitness in advance before it is supplied to the twisting and twisting wire machine, or a method to make a single wire bite into a gear etc. and twist the strand to give a certain straitness .

A buncher machine was used as a twisting machine for manufacturing the steel cord for reinforcing rubber products in this experiment. Conventional steel cord (Experiment No. 1, 2, 5,
6, 11 and 12) were twisted in a spiral shape by passing them between three pins of a curling cone provided before the twist gathering point.

Comparative Examples and Steel Cords of the Present Invention (Experiment Nos. 3, 4, 7, 8, 9, 10, 13, 14, 1)
In 5), as a means for imparting a small spiral-like habit to an element wire, the element wire is passed between a plurality of pins provided on the object attachment device, and the element wire is used as a shaft core for the object attachment device. It was rotated at a high speed, a small spiral-like habit was applied to the passing wire, and then a spiral-like habit for twisting was carried out by passing it between the three habit cone pins provided immediately before the twist gathering point. . Here, the adjustment of the disposition of each strand of the twist center and the cord cross section is determined by variously selecting the diameter and interval of the cone pin, the pushing degree, the tension of the strand, and the like for each strand.

Then, these steel cords are shown in FIG.
As shown in (a), the composite sheet 12 was prepared by covering the upper and lower sides with the rubber sheet 11. Also, this composite sheet 12
11B, the belt portion 13 of the tire 14 is
Used for.

The breaking strength FS of various steel cords, the elongation SL under a load of 5 kg, the rubber penetration ratio RP between the strands when rubber is vulcanized, the compression tensile bending fatigue resistance RF as a composite with rubber. The residual strength RS after the fatigue test and the handling workability HW during rubber product processing were evaluated as follows.

Breaking strength FS This is the breaking load of only the steel cord before being embedded in the rubber sheet.

Residual Strength After Fatigue Test RS steel cords were embedded in a composite rubber sheet, and three-point pulley bending fatigue was repeated with this sheet for a certain number of times, after which the cords were taken out from the rubber sheet and the breaking strength was measured. It was compared with the breaking strength before the test and expressed as an index.

Rubber infiltration rate RP After embedding in rubber with a tensile load of 5 kg applied to each cord and vulcanizing, the steel cord was taken out and the strand was peeled off. The area ratio of contact was displayed.

Compressive Tensile Bending Fatigue Property A plurality of RF steel cords were embedded in a rubber sheet, and this sheet was evaluated by a 3-point pulley bending fatigue tester. The results are shown as an index with Experiment Nos. 1, 5, and 11 set to 100. Eventually, fretting wear, buckling, etc. lead to breakage, but the number of repetitions until this state is evaluated.

Handling workability HW: The handling workability of steel cords in the production of steel cords, embedding in a rubber sheet, and in the molding process of tires, etc. means the flareability of steel cords, low load elongation, steel cords. Entanglement and straightness are related to each other. When compared with the conventional product, the product was evaluated as × when it was extremely inferior, as Δ when slightly inferior, and as ◯ when there was no difference.

In Experiment Nos. 1, 5, and 11, since all the strands were in contact with each other, almost no infiltration of the rubber material was observed.

Experiments Nos. 2, 6 and 12 all have an average shaping ratio [(cord diameter when twisted with a gap between each strand / cord when each strand is tightly twisted) (Diameter) × 100] 116 to 120% open twist cord, which is excellent in rubber material penetration rate PR and fatigue property RF, but has large elongation SL at initial load and handling workability H
Inferior to W.

Experiments Nos. 3, 7, and 13 were 1 × 2, 1 × 3, and 1 using a wire having a small spiral habit.
Although it is a steel cord with a twisted structure of × 5, since the center of the cord twist is offset and the placement of each wire in the cord cross section is not appropriate, compression tensile bending fatigue resistance RF, residual strength RS and breaking strength FS Inferior.

Experiment Nos. 4, 8, 9, 10, 14, 15
Is a steel cord having a structure of 1 × 2, 1 × 3, and 1 × 5, which is an embodiment of the present invention, and an apparent circumscribed circle of a wire having a small spiral habit and a wire having straightness are inside , The cords are arranged so that they are substantially inscribed in one circle, and the center of this one circle, that is, the circumscribed circle is
As shown in (a), (b), (c), and FIG. 2 (c), it is a steel cord in which the cord twist is substantially centered.

From the above comparison test results, the steel cord of the present invention has a breaking strength FS, an elongation SL at an initial load, a rubber penetration rate RP, a compression tensile bending fatigue resistance RF, a residual strength RS,
All of the handling workability HW can be satisfied.

[0049]

Since the steel cord for reinforcing a rubber product of the present invention has the above-mentioned constitution, when the rubber cord is covered with the rubber cord, the rubber cord easily penetrates into the inside of the steel cord through the gap formed between the wires 2 and 3. Therefore, it is possible to surely cover each of the wires 2 and 3 forming the cord with the rubber material, and the rubber material and the steel cord can be reliably bonded.

Further, since the elongation under a very low load is small, the workability is greatly improved. For example, when winding a steel cord on a reel or when calendering on a rubber sheet, if the elongation at an extremely low load is large, the reel may flatten or the rubber sheet may wrinkle. In the invention, this is solved.

Further, although the twist in the longitudinal direction of the steel cord is stabilized and a small spiral-like harshness is imparted to the wire, there is no significant decrease in breaking strength, compressive tensile bending fatigue resistance and residual strength. It has an excellent effect.

[Brief description of drawings]

1A to 1F are schematic sectional views of a steel cord according to an embodiment of the present invention.

2A to 2D are schematic sectional views of a steel cord according to another embodiment of the present invention.

FIG. 3 is a schematic side view of the steel cord shown in FIG.

4 (a) to (i) are schematic views showing changes in the cross-sectional shape of the steel cord of FIG. 1 (b) at one pitch in the longitudinal direction.

5A to 5F are schematic sectional views of a steel cord showing a comparative example.

6 (a) to (d) are schematic diagrams showing different cord twist spiral eccentric shapes of each wire.

7A to 7C are schematic cross-sectional views of a steel cord having a closed twist structure showing a conventional example.

8A to 8C are schematic cross-sectional views of a conventional steel cord having a sweet twist structure.

9A and 9B are schematic cross-sectional views showing a state where the strands in FIG. 7C are offset.

10A and 10B are schematic sectional views of a steel cord having a 2 + 2 structure of a conventional example.

FIG. 11A is a cross-sectional view of a rubber sheet in which a steel cord is embedded, and FIG. 11B is a cross-sectional view of a main part of a tire using the sheet as a belt portion.

[Explanation of symbols]

1, 4, 7, 9, 13 ... Steel cords 2, 5 ... Small spiral-shaped strands 3, 6, 8, 10 ... Straight strands 11, 12, ...・ A group of strands A, B ... Center of twist C ... Gap D ... Cavity d ... Diameter of strand d ₁ ... Apparent outer diameter E ... Cord diameter

Claims (1)

[Claims] 1. An element wire having straightness and a peculiarity pitch P ₁ where P is a twist pitch, P ₁ = 0.1P to 0.7P
And when the apparent outer diameter d ₁ is the wire diameter d ₁ =
A steel cord having a 1 × n (n = 2 to 6) structure formed by twisting together a wire having a small spiral-like habit of (d + 2/100 mm) to (d + 2/10 mm), which is a small spiral. The cord is configured such that the apparent circumscribed circle of a strand having a shape habit and the strand having straightness are included inside and substantially inscribed in one circle, and this one circle, that is, the circumscribed circle A steel cord for reinforcing rubber products that is twisted around the center of the cord.