JPH0660470B2 - Metal cord - Google Patents

Description

TECHNICAL FIELD The present invention relates to a metal cord having a novel twist structure using a filament made of high carbon steel. Especially when this metal cord is used for a belt reinforcing layer of a radial tire, its high strength is utilized to exhibit excellent corrosion resistance, so that a radial tire having a long service life, a light weight and a low rolling resistance can be obtained.

[Conventional technology]

A steel cord having a so-called 1 × 4 or 1 × 5 structure in which 4 or 5 filaments are twisted together has been widely used for a belt reinforcing layer of a steel radial tire. In recent years, in radial tires, the demand for reduction of rolling resistance has been highlighted, and the steel cord of the belt reinforcing layer has a high strength per unit area in order to reduce the weight of the tire without increasing the number of driving, The application of so-called high-strength yarn cords is considered for the twisted structure. As a means of increasing the strength per unit area from the steel cord surface, increasing the carbon content of the metal composition is considered, and is actually a category of known technology. However, the inventors of the present invention have found that the steel cord of the above-mentioned high carbon steel has a serious defect when it is applied to commercialization in order to obtain a lightweight radial tire having a low rolling resistance.

In other words, when the steel cord as described above is used for the belt reinforcement layer, when the tire receives trauma that reaches the metal cord by pebbles, nails, etc. while traveling on the road surface, the water that invades from the wound will come to the center of the cord. The metal cord easily penetrates into the cavity, and as a result, the fatigue property of the metal cord during corrosion is significantly reduced, and the adhesion between the cord and rubber is also reduced, which is a phenomenon called separation between the cord and rubber. There was a drawback that caused.

Various studies have been made to date to improve such drawbacks. Among them, as disclosed in JP-A-55-90692, voids are formed between filaments as shown in FIG. Compared to conventional cords, which have the most compact cord diameter at all, by twisting the cord diameters slightly larger, a gap is created between the filaments without allowing the filaments to contact each other, and the cord cross section is circular. A cord as shown in Fig. 2 having a uniform cross-section that touches is proposed. When such a cord is embedded in rubber and then in a hot vulcanization step, when the rubber is in a fluid state in the initial stage of vulcanization. Since the rubber penetrates through the voids between filaments into the cavity in the center of the cord, the water invading from the wound does not diffuse inside the cord, improving the corrosion resistance of the metal cord. It has to be.

[Problems to be Solved by the Invention]

However, according to the experience of the present inventors, the cord described in the above publication usually has a hot vulcanization step of 4 to 40 kg.
Since this is done under a pressure of / cm ^2, the pressure causes the bulge of the cord to be crushed, and the voids between filaments are almost lost, and as a result, the rubber in the fluidized state almost penetrates into the cavity at the center of the cord. Even if it penetrates, the rubber slightly penetrates even if it penetrates, so if the product using such a cord is damaged, the moisture that has penetrated from the damage will cause the rubber and the cord to partially penetrate. The interface is corroded in a short time, and the moisture further diffuses in the gap in the length direction of the cord, resulting in the separation between the cord and the rubber. it is obvious.

In view of the present situation, an object of the present invention is to provide a metal cord having a completely new concept that can solve the above-mentioned drawbacks when used as a belt reinforcing material for radial tires, for example.

[Means for Solving the Problems]

As a result of intensive studies by the present inventors to solve the above-mentioned drawbacks,
By taking advantage of the high strength of the high-carbon steel metal cord, it was possible to obtain a steel cord having excellent corrosion fatigue resistance and sufficient practicality.

That is, the present invention, for example, simultaneously satisfies the reduction of rolling resistance from the steam cord surface and the corrosion fatigue resistance of the cord as a lightweight tire without impairing the steering stability when used as a belt reinforcing material of a radial tire. The present invention relates to a metal cord that can be used, and more specifically, a high carbon steel having a carbon amount (C%) of the cord of 0.78 to 0.85% is
A cord formed by twisting together five metal filaments, which has the drawback of lowering corrosion fatigue resistance due to the higher strength of the steel cord, so that the twisted structure of the cord is devised so that rubber penetrates as much as possible on the cord surface. The present invention provides a metal cord for a belt reinforcing material. The twisted structure devised here means that the elongation (P ₁ ) when a load of 5.0 kg is applied to each cord is in the range of 0.2 to 1.2%, and the elongation is 2.0 kg. Elongation (P ₂ ) when a load is applied is P
₂ (%) ≦ 0.947P ₁ −0.083 The twisted structure is a metal cord in the range.

The metal cord according to the present invention is, for example, a cord in which various cross-sectional shapes shown in FIG. 3 are mixed in at least three kinds in the length direction of the cord, and the elongation when a load of 5.0 kg is applied. P ₁ is in the range of 0.2 to 1.2%, and 2.0 kg
Elongation P ₂ (%) when applying a load of 0.947P ₁ −
0.083 or less, preferably 0.947P ₁ -0.02
It must be 04 or less. The reason for this is that when P ₁ is less than 0.2%, it is not much different from the conventional compact cord, and the object of the present invention cannot be achieved.
This is because if it exceeds%, the ends of the chopped cord are likely to be twisted and disturbed, which causes a problem in workability, which is not preferable. Of these, P ₁ is more preferably in the range of 0.2 to 0.7% if workability is important. Also, P ₂ is 0.947P ₁ -0.0
If it exceeds 83, the cross-sectional shape of the cord, which is easily crushed by the vulcanization pressure in the step of being embedded in rubber and then vulcanized by heating, becomes large, and as a result, it becomes difficult for the rubber to permeate, which is not preferable.

The relationship between P ₂ and the permeability of rubber to the cord will be described in more detail below.

Generally, in an open twist cord, when a tensile stress is applied to the cord, each constituent filament tends to compress toward the center of the cord. Here, even if the elongation P ₁ is constant, the elongation P ₂ may be large or small.

The former is the case where the cross-sectional shape of the cord is uniform in the length direction (the filament interval is uniform) as shown in FIG.
Since each constituent filament freely tries to move toward the center, the elongation as a cord becomes relatively large under a load of 2 kg. In contrast, the latter is shown in Fig. 3 (1 x
As shown in B) to E) of 5), the cross-sectional shape of the cord is non-uniform and the filaments are in contact with each other. Since the contact pressures (repulsive forces) work on each other, the elongation of the cord becomes small under the load of 2 kg.

In the cross-sectional shape, if the number of contact points between filaments is the number of contact points, then the non-uniformity of the cross-sectional shape of the cord is represented by the number of contact points. The cross section is more uneven as the number of contacts increases.

In the single twist structure, the number of contacts is 4 when the filament configuration is 1 × 5 (E of 1 × 5 in FIG. 3) and the number of contacts is 3 when 1 × 4 (D of 1 × 4 in FIG. 3). In the case of 1), the non-uniformity of the cross-sectional shape is maximized.

In the metal cord of the present invention, the twist pitch is preferably 6 to 14 mm. The reason for this is that if the twist pitch is less than 6 mm, the productivity at the time of manufacturing the cord will be significantly reduced, and it will not be practically applicable to commercial bases. If it exceeds 14 mm, the cord bending resistance due to bending fatigue of the cord will be greatly reduced. This is because the case is not preferable.

Further, the filament constituting the metal cord of the present invention, which is particularly suitable for the belt reinforcing material, needs to have a diameter of 0.20 mm or more and a C% of 0.78 to 0.85%. . This has a filament diameter of 0.
If it is less than 2 mm, the strength as a radial belt material is too small and the fatigue resistance is inferior, and if it is less than 0.78% as C%, it is also low in rigidity as a belt reinforcing material for a lightweight radial tire and of a radial tire. This is because the steering stability is significantly lowered, and if it exceeds 0.85%, the corrosion fatigue resistance of the cord is lowered, which causes the belt cord to break, and the wire drawing workability is also lowered, which is not preferable. If the diameter of the filament exceeds 0.30 mm, the weight of the cord is increased and the merit of weight reduction is lost, which is not preferable, and the diameter of the filament is more preferably 0.20 to 3.0 mm. The filament has Cu, Sn, Zn or the like or Ni on these in order to improve the adhesiveness with the surface of the filament.
It may be coated with an alloy containing Co or Co.

Furthermore, the metal cord of the present invention can be manufactured as follows. That is, it can be produced by compressing a filament that has previously been excessively crushed in the radial direction of the cord so as to have a predetermined P ₁ (elongation under a load of 5 kg).

Finally, the rubber for embedding the metal cord of the present invention is natural rubber or synthetic rubber. When the metal cord of the present invention is used for the belt reinforcing layer of a radial tire, 50% of the embedded rubber is used.
The modulus is preferably 10-40 kg / cm ² . The reason for this is that when the 50% modulus is less than 10 kg / cm ^2, the distortion of the metal cord end portion becomes large and the belt end separation resistance (which means crack growth of the belt coating rubber from the belt cord end) resistance decreases, while 40%
This is because if it exceeds kg / cm ² , the durability of the belt cord, that is, the cord is likely to be broken, and at the same time, the workability is significantly deteriorated, which is not preferable in any case.

In the radial tire using the metal cord of the present invention having the above-described structure, since the rubber has sufficiently penetrated in the longitudinal direction and the cross-sectional direction of the cord, rust on the surface of the metal cord due to the intrusion of water due to external damage. Is prevented from spreading. Therefore, the separation phenomenon due to the decrease in the adhesive force between the cord and the rubber due to the corrosion of the metal cord is significantly improved, and the durability of the radial tire using the metal cord of the present invention is significantly improved. Further, the metal cord of the present invention is not only effective as a belt reinforcing material for lightweight tires, but can also be used in a wide range of fields such as agricultural tillers and lightweight products for industrial products such as belts.

Although the radial tire using the metal cord of the present invention as a belt reinforcing material has been described, the metal cord can also be applied as a carcass ply reinforcing material.

Example 1 18 kinds of metal cords shown in Table 1 were prepared by twisting steel filaments plated with brass. These metal cords are embedded in 50% modulus 25 kg / cm ² rubber used as a tire belt coating rubber, vulcanized, and then the metal cords are sampled so that the rubber penetrates almost completely in the center of the cord. The length of the portion was measured, and the rubber penetration degree was evaluated with an index as a ratio to the entire length of the cord. For comparison, a conventional metal cord as shown in FIG. 1 was also evaluated in the same manner. The results are shown together in Table 1. Here, P ₁ and P ₂ have a total length of 20 to
Elongation (%) when a load of 5.0 kg and 2.0 kg is applied to a 50 cm metal cord, and the cross-sectional shape is the cross-sectional shape of the cord at 5 mm intervals in the length direction of the cord. It is observed with a magnifying glass and displayed with the symbols shown in FIG.

Regarding the codes of Experiment Nos. 1 to 7 in Table 1 above, P ₁ is taken on the horizontal axis and P ₂ is taken on the vertical axis, and the degree of rubber penetration is 80 to 10
0 is ○, 60 to 79 is ◇, 40 to 59 is □, and 29 to 39
Are plotted as Δ and 0 to 19 are plotted as ▽ in FIG.

As is clear from Table 1 and FIG. 4, P ₂ ≦ 0.94
7P ₁ -0.083 (preferably P ₂ ≦ 0.947P ₁
The metal cords of Experiment Nos. 1 to 4 (preferably Experiment Nos. 1 and 2) in the range of -0.204) have a rubber penetration degree of 6
It is 0 or more (preferably 80 or more), and rubber penetrates well into the metal cord, while P ₂ > 0.947P
The metal cords of Experiment Nos. _{5 to} 7 in the range of _{1 to} 0.083 are close to cords of uniform cross section in which the filaments do not contact each other, and it is understood that the penetration degree of rubber is inferior.

Next, the metal cords of Experiment No. 1 to No. 18 in Table 1 were used as the belt reinforcing layer (50% modulus of the embedded rubber 25 kg / cm ² ).
A radial tire, size 175SR14, which was also used for some carcass ply reinforcements, was prepared.
The characteristic values of the test tires with respect to the contents of various metal codes in the table were measured, and the results are shown in Table 2. The tire numbers in Table 2 are
Corresponds to the metal code No. Regarding the measuring method, etc., a hole with a diameter of 3 mm reaching the metal cord of the belt is made in the ground contact portion of the tire, the tire is actually driven for 1,000 km, and then the tire is placed in a water tank of 5% NaCl aqueous solution. The tires were dissected for 1 day and then run on a general road for a total of 40,000 km, then the internal pressure was reduced to 1.3 kg / cm ² and a constant mountain slope road was run for 20,000 km, after which the tires were dissected.

1. Corrosion resistance: A metal cord corresponding to the position of the hole of the tire is taken, and the length of the adhesive interface with the embedded rubber is evaluated as the corrosion length of the cord. The corrosion length of the tire metal cord of Tire No. 8 was expressed as an index by the formula with the corrosion length as 100.

The smaller the value, the better.

2. Cord breakage resistance The number of breakages of the metal cords collected in the above corrosion resistance test was calculated and expressed as an index by the following formula.

The larger the index, the smaller the number of folds and the better.

3. Steering stability (cornering power) A lateral slip angle is given to the tire to generate a lateral force (cornering force) caused by frictional resistance with the road surface. At this time, the component force acting at a right angle to the traveling direction of the vehicle is plotted on the vertical axis. The slope (cornering power) of the linear region when the sideslip angle was plotted on the abscissa was obtained and expressed as an index by the following formula.

4. Rolling resistance Measured by the conventional method, the measurement conditions are diameter 1707.6mm, width 35
JIS 100% on 0mm steel drum
A tire having an internal pressure of 1.7 kg / cm ² was applied with a load, the drum was rotated by a motor drive, and after running for 30 minutes at a speed of 80 m / h, the speed was increased to 200 km / h. Then, the motor-driven couch was cut and coasted, and the rolling resistance of the tire and the drum at a speed of 50 km / h was calculated based on the drum deceleration and the time change. The net tire rolling resistance was obtained by subtracting the previously calculated drum resistance from this value. The rolling resistance index was expressed by the following formula.

Examples of the present invention No. 1 to No. 4, No. 9, No. 16 to N
As can be seen from the tire of o.18, when the metal cord of the present invention is used, both corrosion fatigue resistance and rolling resistance can be achieved without impairing the steering stability of the tire.

Although it seems that the rolling resistance improvement effect is less than the corrosion fatigue resistance effect, increasing the rolling resistance by 5% compared to the current one is a very difficult task for tire technology. In that respect, it can be sufficiently judged that the metal cord of the present invention has a remarkable effect.

Example 2 Next, as in Example 1, brass-plated steel filaments were twisted together to prepare four types of metal cords shown in Table 3. All of these metal cords have a steel filament diameter of 0.25 mm, a twist pitch of 9.5 mm, and a carbon content of the filament composition of 0.82%. These metal cords are applied to the belt ply layer of radial tires for passenger cars with a tire size of 175 / 70R13, and after vulcanization, the metal cords are collected from the tire, and the rubber is almost completely penetrated into the central portion of the cord. Was measured, and the degree of rubber penetration was evaluated by an index as a ratio to the total length of the cord. The results are shown in Table 3 and illustrated in FIG. Experiment No. 19 and 20
Is indicated by ●, and Experiment Nos. 21 and 22 are indicated by ■.

It can be understood from Example 2 that when the tire of the present invention is embedded in the belt ply layer, the degree of rubber penetration is significantly improved.

[Brief description of drawings]

FIG. 1 is a sectional view of a conventional compact type metal cord, FIG. 2 is a sectional view of the metal cord disclosed in Japanese Patent Laid-Open No. 55-98692, and FIG. 3 is a sectional view of the metal cord of the present invention. , FIG. 4 is a diagram showing the relationship between the penetration degree of rubber and P ₁ and P ₂ . 1 ... Cord, 2 ... Filament, 3 ... Contact point

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-52-82621 (JP, A) JP-A-56-43008 (JP, A) JP-A-57-43866 (JP, A) JP-B-54- 31733 (JP, B1)

Claims (1)

[Claims] 1. A cord comprising 4 to 5 steel filaments having a wire diameter of at least 0.2 mm and having a carbon content of the filament composition in the range of 0.78 to 0.85%. The elongation (P ₁ ) when a load of 5.0 kg is applied is 0.2 to 1.2%, and the elongation (P ₂ ) when a load of 2.0 kg is applied per piece P
_A metal cord in the range represented by ₂ (%) ≦ 0.947P ₁ -0.083.