JPH07279071A - Metal cord and composite material of the cord and rubber - Google Patents

Abstract

PURPOSE:To produce a metal cord for the reinforcement of a rubber article having excellent oblique shear strength characteristics and produce a composite material such as tire, conveyor belt or high-pressure hose produced by embedding the metal cord as a reinforcing material in a rubber. CONSTITUTION:This metal cord is composed of a core produced by twisting 2-3 metal filaments 1 having metal-plated surface and 6-8 metal filaments 2 having metal-plated surface and arranged on the outer surface of the core. The twisting pitch P of the single-layered sheath is >=20mm and the core and the single-layered sheath have same twisting directions and different twisting pitches and twisting angles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal cord for reinforcing a rubber article which is excellent in diagonal shear strength resistance, and a tire, a conveyor belt, a high pressure hose, etc. made by embedding the metal cord in a rubber as a reinforcing material. Regarding the complex of.

[0002]

2. Description of the Related Art Reinforcing materials used to reinforce rubber articles are usually made of high carbon steel wire (JIS G 3502 piano wire) and have brass (brass) on the surface to provide adhesion with rubber. Metal, such as copper or zinc, is drawn and drawn to a diameter of 0.1 to 0.5 mm, and is single-stranded, double-stranded, or multi-layered, and is used to reinforce tires, conveyor belts, high-pressure hoses, etc. Widely used as a material.

For example, a metal cord having a 3 + 6 double-layer twist structure is used as a belt portion reinforcing material for radial tires for trucks / buses.

Quality characteristics required for this kind of rubber reinforcing material include adhesiveness with rubber, corrosion resistance and various other mechanical characteristics (diagonal shear strength, cutting strength, rigidity, etc.).

Among these, regarding the corrosion resistance, when a rubber-uncovered portion is present in the reinforcing material embedded in the rubber, the tire is stepped on stones, nails and the like while running, and the scratches reach the reinforcing material. When it reaches, the water propagates and the corrosion is promoted to lower the cutting strength and corrosion resistance of the reinforcing material.

Further, the adhesiveness between the reinforcing material and the rubber is lowered,
There is a risk of peeling and causing quality problems such as tire cut separation.

Therefore, in order to prevent such cut separation due to corrosion propagation, a cord structure has been proposed in which rubber sufficiently penetrates into the metal cord. For example, JP-A-63-235587 and JP-A-2-1540.
No. 86 and Japanese Unexamined Patent Publication No. 5-44184 have three to two cores to eliminate a closed space, while the number of strands is set to 7 to 8 in order to facilitate rubber infiltration. It is disclosed that the filaments have a sizing rate of more than 100%.

Further, in Japanese Patent Laid-Open No. 4-327278, in order to maintain cord cutting strength and facilitate rubber penetration,
A metal cord having a single twist structure of × N (N ≧ 6) has been proposed.

[0009]

All of the above-mentioned conventional examples are aimed at facilitating the permeation of rubber into the inside of the cord and suppressing the corrosion propagation to suppress the strength reduction due to the corrosion of the cord.

However, this type of cord is subjected to a diagonal shear stress locally when the tire is stepped on a stone having sharp corners, and the tread surface of the tire is cut and damaged. In some cases, the metal cord itself is subjected to oblique shear stress, and the filaments forming the metal cord are broken.

Therefore, for the purpose of preventing the filaments from breaking due to diagonal shear stress, a tire using a high extension cord having a 4 × 4 or 3 × 7 structure having a double twist structure and a small twist pitch immediately below the tire tread is also used. Seen (JP-A-62-96104).

However, it is difficult to maintain a high elongation even after being embedded in rubber, and in reality, a sufficient effect has not been obtained. Therefore, the present invention relates to a 3 + 6 two-layer structure cord that is commonly used as a reinforcing member for a belt portion of a tire, and a metal cord with improved diagonal shear strength, which has been a problem in the past, and a durable durability using this metal cord as a reinforcing member. An object of the present invention is to provide a composite material such as a tire, a conveyor belt, and a high pressure hose having improved properties.

[0013]

The present invention, which was developed to solve the above-mentioned problems, has a metal plated surface.
~ A metal cord with a two-layer structure in which 6 to 8 metal filaments with metal plating on the surface are twisted with a twist pitch of 20 mm or more around the circumference of a core formed by twisting ~ 3 metal filaments Yes, it is characterized by twisting at a significantly larger twist pitch than conventional metal cords of this type, and the twist pitch and twist angle of the core and single sheath are different. For application to at least a single sheath, it is preferable to use a steel wire having a carbon content in the range of 0.65 to 0.78% by weight. Moreover, it is desirable that the twisting directions of the core and the single sheath are the same, the relationship between the twisting pitch pc of the core and the twisting pitch P of the sheath is pc <P, and the twisting angle αc of the core and the sheath twisting angle αc are the same. The relationship with the twist angle α

[0014]

[Equation 2]

It is preferable that

Further, the diameter of the metal filament adapted to the core and the single sheath is preferably in the range of 0.15 to 0.35 mm. Made by embedding such a metal cord as a reinforcing material in rubber mainly composed of natural rubber or synthetic rubber,
Tires, conveyor belts, high-pressure hoses, and the like are the rubber composites of the present invention, and the composites have excellent durability as compared with the conventional ones.

The metal plating applied to the surface of the metal filament is made of brass, in order to improve adhesion with rubber.
It is desirable to coat copper, zinc, or brass with a plating such as a ternary alloy in which an element such as Co, Ni, or Sn is added.

[0018]

In order to improve the diagonal shear strength of the metal cord or the metal filament alone, it is conceivable to make the diameter of the metal filament as small as possible and suppress the strength reduction caused by the plastic deformation due to the twist during the twisting process. Further, in the same composite, that is, in the metal cord or the metal filament embedded in the tire or the like, it is possible to maintain the elongation as high as possible, and to obtain the blue heat brittleness (or age hardening phenomenon) due to the vulcanization molding temperature (140 to 170 ° C.) of the rubber. It is important that the impact is small.

Considering the twist structure of the cord for improving the diagonal shear strength from these points, a metal cord having a twist pitch significantly larger than the twist pitch (20 mm or less) of the conventional 3 + 6 cord (two-layer structure) is used. By doing so, it is considered that the structure that reduces the plastic deformation due to the twist during the twisting process is good, and that it is advantageous to make the metal filament as thin as possible.

However, the smaller the diameter of the metal filament, the larger the number of cords in order to maintain the strength of the cord, and the larger the number of metal filament supply devices of the twisting machine, which easily leads to the enlargement of the equipment. , There is a risk that investment will become excessive.

As a result of repeated examinations from the above viewpoints, in the present invention, in addition to the metal filament having a twist pitch larger than that of the conventional 3 + 6 cord, the twisting is stabilized and the strength of the wire contact surface of both metal filaments is increased. In order to improve, the twisting directions of the core and single sheath are the same,
A metal cord was used in which the twist pitch and twist angle were appropriately made different, and the metal filament was made as thin as possible.

The reasons for limiting the numerical values will be described below. The number of metal filaments that are twisted together to form a core is set to 2 to 3 because the minimum number of twisted wires is 2 and the maximum number is the cross-sectional area of the cavity inside the core. As the number of tires increases, the corrosion propagation due to water from the tire tread cut becomes faster, so four or more are not considered, and the maximum was three. Further, the number of single sheaths composed of metal filaments surrounding this core is set to 6 to 8, and if the number is less than 6, it is thicker than the conventional 3 + 6 cord metal filaments from the viewpoint of maintaining strength. Therefore, there is a possibility that the diagonal shear strength may decrease, and the maximum number is the result of examination including the optimization of the number of core twists and the gap between single sheaths (preferably 0.025 to 0.075 mm), 1 from the theoretical number calculated from the design side of the twist structure when the filament diameter is the same
The number was reduced to eight.

The twisting pitch of the single sheath composed of the metal filaments surrounding the core is set to 20 mm or more. If the twisting pitch is less than 20 mm, the plastic deformation due to twisting during twisting is much different from the conventional 3 + 6 cord. It is because there is no such thing, and the effect of suppressing the decrease in strength cannot be obtained.

Next, numerical limitation of both twist pitches and twist angles will be described. If the twist pitch is the same, the contact resistance of both filaments in the longitudinal direction of the cord is small, and the core is easily pulled out. Therefore, it is necessary to reduce (or increase) one of the twist pitches, but it is effective to reduce the twist pitch of the core in consideration of the contribution rate for increasing the diagonal shear strength.

Further, if the twist angles are the same, there is a portion where the circumscribing circle of the core and the metal filament forming the single sheath come into contact with each other, and a portion where the twist does not exist, so that the cord diameter changes in the cord longitudinal direction, which is preferable. On the other hand, if the twisting angles of the two are greatly different, the contact state of the two metal filaments shifts from a line to a point, which is not preferable from the viewpoint of maintaining strength, and the difference between the twisting angles of the two is an absolute value in the optimum range.
It was set to 0 ° or less. On the other hand, the carbon content of at least m of the twisted metal filaments is 0.65 to 0.78.
The range of wt% is less than 0.65%, since it is necessary to make the metal filament a large diameter in order to maintain the strength as a reinforcing material, the diagonal shear strength is reduced, and 0.78 wt% If it exceeds the range, in the compound with rubber, the influence of blue heat brittleness due to the temperature at the time of vulcanization molding becomes large and the cutting strength becomes large, but the diagonal shear strength decreases conversely, so this range is preferable.

As described above, the smaller the diameter of both metal filaments is, the smaller the decrease in diagonal shear strength is, but on the other hand, the cost is increased and the number of twists is increased to secure the required cutting strength. It is easy to become.

Therefore, it is not preferable that the diameter is too thin. Considering the number of twisted metal filaments and the cutting strength, the appropriate range of the diameter is 0.15 to 0.35 mm (more preferably,
0.20 to 0.32 mm).

[0028]

[Example] Diameter 0.20 mm with positive plating on the surface
3 of the metal filaments 1 are twisted in the S direction with a pitch 26
A metal filament 2 with a diameter of 0.35 mm around a core formed by twisting together with a diameter of 13 mm (13 mm in the cord state)
We obtained a metal cord with a cross-sectional structure shown in Fig. 1 (a), which was constructed by twisting a single sheath composed of 6 pieces in the same direction as the core with a twist pitch of 26 mm. Examples 1 to 3 were obtained because the ratio was in the range of 0.65 to 0.78% by weight.

On the other hand, the cord having the same twist structure and the same twist direction, in which only the twist pitch of the core and the single sheath has a small pitch similar to the conventional one, and the carbon content of the steel wire used is only 0.82 weight. %, And metal cords in which only the twisting direction was reversed and the difference in twist angle exceeded 3.0 ° were also obtained (Comparative Examples 1 to 3).

Next, using a metal filament obtained by subjecting a steel wire having a carbon content of 0.72% by weight to a plus plating, the twisting structure, the twisting direction, the twisting pitch, and the diameter of the metal filament are changed to cut load. Figure 1 with the same level
Metal cords (Examples 4, 5, 7, 8 and Comparative Examples 4 to 7) having a cross-sectional structure shown in (b) and FIG. 1 (c) were produced.

Further, in the 3 + 6 structure, the twisting directions are the same, the twisting pitch is further increased to reduce the twisting (twisting) reduction rate and the cutting load is improved (Example 6), and further the steel material. Conventional 3 + 6 double-layer twisted metal cords (conventional examples 1 to 4) in which the carbon content of the wire was changed and the twist directions were different and the pitch was small were also made. With respect to each of the above samples, the cutting load was measured, and the diagonal shear strength retention rate, which is a substitute characteristic of the tire tread surface with respect to the cutting performance, was examined based on the measured cutting load. In addition, the test machine shown in FIG. 3 was used for the diagonal shear strength measurement. This tester uses sample 3
Both ends of the (metal cord) are received by the cylindrical fixing pin 4 and grasped by the chuck 6, and the intermediate portion of the sample is bent by the moving pin 5 whose position can be adjusted by the handle 7, and the bending angle θ is constant. Pull one of the chucks below to obtain the tensile force at the time of cutting.

Here, the test condition is that the tip R of the moving pin 5 is R =
The test was conducted at 0.2 mm and a bending angle θ = 40 °.

The results are shown in Table 1.

[0034]

[Table 1]

[0035]

As described above, in the metal cord of the present invention, since the plastic deformation due to the twist during the twisting of the metal filament is reduced, the diagonal shear strength is less decreased, and the twist directions are the same. Since the difference in the twist angle is small, the metal filaments are in line contact with each other and the cutting load can be improved.

Therefore, the durability of a rubber compound such as a tire, a conveyor belt, a high pressure hose, etc. made of this as a reinforcing material is improved.

Further, since the twist pitch is large and the number of twists can be reduced, productivity can be improved and cost can be reduced in terms of manufacturing.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view of Examples (a), (b) and (c).

FIG. 2 is a partially cutaway side view of the embodiment.

FIG. 3 is a side view of a testing machine used for measuring diagonal shear strength.

[Explanation of symbols]

 1 Metal Filament for Core 2 Metal Filament for Single Sheath 3 Sample 4 Fixed Pin 5 Moving Pin 6 Chuck 7 Handle P Twist Pitch of Metal Filament for Single Sheath pc Twist Pitch of Metal Filament for Core α α of Metal Filament for Single Sheath Twisting angle αc Twisting angle of metal filament for core θ Bending angle R Bending radius of moving pin tip

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Claims (6)

[Claims] 1. A core formed by twisting two or three metal filaments having metal plating on the surface and 6 to 8 metal filaments having metal plating on the surface surrounding the core. In a two-layer metal cord with a single sheath, the twist pitch of the single sheath is 2
A metal cord having a twist pitch and twist angle of 0 mm or more and the core and the single sheath being different. 2. The carbon filament of at least one of the metal filaments applied to a single sheath has a carbon content of 0.65.
Use of steel wire in the range of ~ 0.78% by weight.
The described metal cord. 3. The metal cord according to claim 1, wherein the core and the single sheath are twisted in the same direction in the metal cord. 4. In the metal cord, the relationship between the twist pitch pc of the core and the twist pitch P of the sheath is pc <P.
And the relationship between the twist angle αc of the core and the twist angle α of the sheath is The metal cord according to any one of claims 1 to 3, wherein 5. The diameter of both metal filaments is 0.1.
The metal cord according to any one of claims 1 to 4, which is in a range of 5 to 0.35 mm. 6. A tire, a conveyor belt, a high pressure hose, etc. made by embedding the metal cord according to any one of claims 1 to 5 in a rubber mainly composed of natural rubber or synthetic rubber as a reinforcing material. Rubber compound.