JP2517844B2 - Belt ply for radial tire - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a belt ply for a radial tire using a metal cord having a novel twist structure of filaments made of high carbon steel. When used in radial tire belt plies (hereinafter sometimes referred to as belt reinforcement layers), this metal cord exerts its high strength and exhibits excellent corrosion resistance, which improves its service life, reduces weight, and reduces rolling resistance. Radial tires with less

[0002]

2. Description of the Related Art A steel cord having a so-called 1 × 4 or 1 × 5 structure in which four or five filaments are twisted together has been widely used for a belt reinforcing layer of a steel radial tire. In recent years, the demand for rolling resistance reduction in radial tires has been highlighted.
It has been considered that the above twisted structure is applied to the steel cord of the belt reinforcing layer in order to reduce the weight of the tire without increasing the number of driving, so that a so-called high-strength yarn cord having a high strength per unit area is applied. 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, resulting in a significant decrease in the fatigue resistance of the metal cord when corroded, and further a reduction in the adhesion between the cord and rubber, which is a phenomenon called separation between the cord and rubber. There was a drawback that caused.

Various investigations have been made to date to improve such drawbacks, among which, Japanese Patent Laid-Open No. 55-906.
As disclosed in Japanese Patent Publication No. 92, No. 92, each filament is formed by twisting the cord diameter slightly larger than the conventional cord having the most compact cord diameter without any voids between the filaments as shown in FIG. There is proposed a cord as shown in Fig. 3 which has a uniform cross section such that the cord cross section is inscribed in a circle by providing voids between filaments without contacting each other. In the hot vulcanization process after embedding, when the rubber is in the fluidized state at the initial stage of vulcanization, the rubber penetrates from the voids between the filaments into the cavity at the center of the cord, so that the water invading from the wound damages the cord. Since it does not diffuse inside, it is said that the corrosion resistance of the metal cord is improved.

[0004]

However, according to the experience of the present inventors, the code described in the above publication is
Since the hot vulcanization process is usually carried out under a pressure of 4 to 40 kg / cm ² , the bulge of the cord is crushed by this pressure, and the voids between the filaments are almost lost, and as a result, the rubber in a fluidized state is lost. Can hardly penetrate into the cavity in the center of the cord, and even if it penetrates, a small amount of rubber penetrates, so when a product using such a cord is injured, due to the moisture infiltrated from the injury, The interface between the partially penetrated rubber and the cord is corroded in a short time, and moisture further diffuses in the gap in the length direction of the cord, resulting in separation between the cord and the rubber. It is obvious that it has the drawback of being lost.

In view of the present situation, an object of the present invention is to provide a belt ply for a radial tire using a metal cord of a completely new concept which can solve the above-mentioned drawbacks.

[0006]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned drawbacks, the inventors of the present invention have taken advantage of the high strength of the high carbon steel metal cord, and have sufficient practicality of excellent corrosion fatigue resistance. It was possible to obtain a durable steel cord and bury it in rubber to make a belt ply for radial tires. That is, the present invention simultaneously satisfies the reduction of rolling resistance from the steel 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 belt ply using a metal cord that can be used. More specifically, the carbon amount (C%) of the cord is 0.
A cord formed by twisting 78 to 0.85% of high carbon steel as 4 to 5 metal filaments, which has a drawback of deterioration in corrosion fatigue resistance due to high strength of the steel cord. A belt ply is devised so that rubber can penetrate as much as possible into the cord surface. The twisted structure devised here means that the elongation (P ₁ ) when a load of 5.0 kg per cord is in the range of 0.2 to 1.2%, Elongation (P ₂ ) under load is P ₂ (%) ≦ 0.947P
A twisted structure comprising a metal cord in the range represented by ₁ -0.083.

The metal cord according to the present invention is, for example, a cord in which at least three kinds of various cross-sectional shapes shown in FIG. 1 are mixed in the length direction of the cord, and when a load of 5.0 kg is applied. The elongation P ₁ is in the range of 0.2 to 1.2%,
And the elongation P ₂ (%) when a load of 2.0 kg is applied is 0.947 P ₁ -0.083 or less, preferably 0.94.
It is necessary to be 7P ₁ -0.0204 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, and when it exceeds 1.2%, the ends of the cutting cord are twisted and disordered. This is because it is not preferable because it is liable to occur and there is a problem in workability. Of these, P ₁ is 0.2 if workability is important.
The range of up to 1.7% is more preferable. Also, P ₂ is 0.94
If it exceeds 7P ₁ -0.083, the cord is apt to be crushed by the vulcanizing pressure in the step of being hot-vulcanized after being embedded in the rubber, so that the cross-sectional shape is increased, and as a result, it becomes difficult for the rubber to penetrate, which is preferable. Because there is no.

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. Even if the elongation P ₁ is constant, the elongation P ₂ may be large or small. In the former case, as shown in FIG. 3, when the cross-sectional shape of the cord is uniform in the length direction (the filament spacing is uniform), each constituent filament tries to move freely toward the center, and a load of 2 kg is applied. Then, the growth as a cord becomes relatively large. On the other hand, the latter is the case where the cross-sectional shape of the cord is non-uniform and the filaments are in contact with each other, as shown in B to E of FIG. 1 (1 × 5), and each filament moves toward the center. However, since the contact pressure (repulsive force) acts on each of the two filaments that have come into contact with 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,
The non-uniformity of the cross-sectional shape of the cord is represented by the number of contacts. The cross section is more uneven as the number of contacts increases.

In the single twist structure, when the filament configuration is 1 × 5, the number of contacts is 4 (1 × 5 E in FIG. 1), 1 ×
When the number of contacts is 4, when the number of contacts is 3 (1 × 4 D in FIG. 1), the nonuniformity of the cross-sectional shape becomes maximum.

In the metal cord according to the present invention, the twist pitch is 6
It is preferably ˜14 mm. The reason for this is that if the twist pitch is less than 6 mm, the productivity during production of the cord will be significantly reduced, and it will not be practically applicable on a commercial basis. 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 suitable for the belt ply of the present invention has a diameter of 0.20 m.
It is necessary that the content be at least m and that the C% be 0.78 to 0.85%. This is because if the filament diameter is less than 0.2 mm, the strength as a radial belt material is too small and the fatigue resistance is poor, and the C% is 0.
Similarly, if it is less than 78%, the rigidity is low as a belt reinforcing material for a lightweight radial tire, and the steering stability of the radial tire is significantly lowered, and if it exceeds 0.85%, the corrosion fatigue resistance of the cord is lowered, and the belt is deteriorated. This is because the cord breakage is caused and the wire drawing workability is also deteriorated. In addition, if the diameter of the filament exceeds 0.30 mm, the weight of the cord will be reduced and the merit of weight reduction will not be achieved unless the driving amount of the cord is reduced. Therefore, the diameter of the filament is 0.20 to 0.30 mm. Is more preferable. Further, the above filament has Cu, Sn, Zn, etc. or N
It may be covered with an alloy containing i or Co.

Further, the metal cord according to the present invention can be manufactured as follows. That is, it can be manufactured by compressing a filament which has previously been excessively crushed in the radial direction of the cord so as to have a predetermined P ₁ (elongation under load of 5 kg). Finally, the rubber used in the belt ply of the present invention is natural rubber or synthetic rubber, but 50% of the embedded rubber is used.
The modulus is preferably 10 to 40 kg / cm ² . The reason is that 50% modulus is 10 kg / cm ²
If less than 40%, the strain at the end of the metal cord becomes large and the belt end separation resistance (which means crack growth of the belt coating rubber from the end of the belt cord) decreases, while if it exceeds 40 kg / cm ² , durability of the belt cord This is because the cord is easily broken, and the workability is significantly lowered at the same time, which is not preferable in any case.

[0013]

EXAMPLES Example 1 Eighteen kinds of metal cords shown in Table 1 were prepared by twisting steel filaments plated with brass. These metal cords are embedded in a rubber having a 50% modulus of 25 kg / cm ^{2 which} is used as a belt coating rubber for tires, and after vulcanization, the metal cords are sampled and the rubber is almost completely penetrated into 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. 2 was similarly evaluated. The results are shown together in Table 1. Here, P ₁ and P ₂ have a total length of 20 to 5
Elongation (%) when a load of 5.0 kg and 2.0 kg is applied to a 0 cm metal cord, and the cross-sectional shape is
The cross-sectional shape of the cord at a position at intervals of 5 mm in the length direction of the cord is observed with a magnifying glass and is represented by the symbol shown in FIG.

[0014]

[Table 1]

Experiment No. 1 in Table 1 above. With respect to the codes of ₁ to 7, the horizontal axis is P ₁ and the vertical axis is P ₂ , and the rubber penetration degree is 80 to 100, ◯, 60 to 79 is ◇, 40 to 59 is □, 29 to 39 is Δ and 0. 19 is plotted in FIG. 4 as ▽. As is clear from Table 1 and FIG. 4, P ₂ ≦
0.947P ₁ -0.083 (preferably P ₂ ≦ 0.9
No. 47P ₁ -0.204). 1-4
The metal cords (preferably Experiment Nos. 1 and 2) have a rubber penetration of 60 or more (preferably 80 or more),
Rubber penetrates the metal cord well, while P ₂ >
Experiment No. in the range of 0.947P ₁ -0.083. 5
It can be seen that the metal cords of Nos. 7 to 7 are close to cords having a uniform cross-sectional shape in which the filaments do not come into contact with each other, and the degree of rubber penetration is poor.

Next, the experiment No. 1 to No. Radial tire, size 175SR14, in which 18 metal cords were used for the belt reinforcing layer (50% modulus of embedded rubber 25 kg / cm ² ) and also for some carcass ply reinforcing materials.
Was prepared, the characteristic values of the test tires for various metal cord contents in Table 1 were measured, and the results are shown in Table 2. Tire No. of Table 2 Is a metal code No. Corresponding to. Regarding the measuring method, etc., a hole with a diameter of 3 mm that reaches the metal cord of the belt portion is made in the ground contact portion of the tire and the tire is
After running the vehicle for 000 km, the tire was 5% NaC.
l Immerse in a water bath for 1 day, and then on a general road for a total of 4
The tire was dissected after running the vehicle for 10,000 km, then lowering the internal pressure to 1.3 kg / cm ² and running on a constant mountain slope for 20,000 km.

1. Corrosion resistance: A metal cord corresponding to the position of the hole of the tire is sampled, and the length of the adhesive interface with the embedded rubber is evaluated as the corrosion length of the cord. Tire No. The corrosion length of the tire metal cord of No. 8 was expressed as an index with 100 as the corrosion length. {(Corrosion length of metal cord of test tire) / (corrosion length of tire metal cord of tire No. 8)} × 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. {(Number of bent metal cords of tire No. 8 tire)
/ (Number of bent metal cords of the test tire)}
The larger the x100 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 right angles 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. {(Cornering power of test tire) / (Tire N
o. 8 tire cornering power)} × 100

4. Rolling resistance Measured by the conventional method, measurement conditions are diameter 1707.6mm, width 3
JIS 10 on a 50 mm steel drum
With a 0% load on a tire with an internal pressure of 1.7 kg / cm ² ,
The drum was rotated by a motor drive, and after running in for 30 minutes at a speed of 80 m / h, a speed of 200 km / h
raised to h. Then, the motor drive clutch is disengaged to coast, and the speed is reduced to 50 based on the drum deceleration and the time change.
The rolling resistance of the tire and the drum at km / h was calculated. 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. {(Rolling resistance of tire No. 8 tire) / (Rolling resistance of test tire)} × 100

[0021]

[Table 2]

Example No. 2 of the present invention 1 to No. 4, N
o. 9, No. 16-No. As can be seen from No. 18 tire, when the belt ply of the present invention was used, both corrosion fatigue resistance and rolling resistance could 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 belt ply of the present invention has a remarkable effect.

Example 2 Next, four kinds of metal cords shown in Table 3 were prepared by twisting brass-plated steel filaments in the same manner as in Example 1. Each of these metal cords has a steel filament diameter of 0.25 mm,
The twist pitch is 9.5 mm, and the amount of carbon in the filament composition is 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 shown in FIG. Experiment No. 19 and 20 are indicated by ●, and the experiment No. 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.

[0024]

[Table 3]

[0025]

In the radial tire using the belt ply of the present invention having the above-mentioned structure, the rubber has sufficiently penetrated in the longitudinal direction and the cross-sectional direction of the cord, which results from the infiltration of water due to external damage. Diffusion of rust on the metal cord surface is prevented. 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 belt ply of the present invention is significantly improved. Further, the belt ply of the present invention not only exhibits the effect as a belt ply of a lightweight tire, but can also be used in a wide range of fields such as agricultural tillers and lightweight products for industrial products such as belts.

[Brief description of drawings]

FIG. 1 is a sectional view of a metal cord used in the belt ply of the present invention,

FIG. 2 is a sectional view of a conventional compact type metal cord,

FIG. 3 is a cross-sectional view of a metal cord described in JP-A-55-98692.

FIG. 4 is a diagram showing the relationship between P ₁ and P ₂ and the degree of rubber penetration.

[Explanation of symbols]

 1: Cord 2: Filament 3: Contact point

Claims (2)

(57) [Claims] 1. A wire diameter of 4-5 having a wire diameter of at least 0.2 mm.
Cord consisting of two steel filaments, the carbon content of the filament composition is in the range of 0.78 to 0.85%, and the elongation at the time of applying a load of 5.0 kg per cord (P ₁ ) Is in the range of 0.2 to 1.2%, and the elongation (P ₂ ) when a load of 2.0 kg is applied is represented by P ₂ (%) ≦ 0.947P ₁ -0.083. A belt ply for a radial tire, in which a metal cord within the range is embedded in rubber made of natural rubber and / or synthetic rubber. 2. The radial tire according to claim 1, wherein a rubber having a 50% modulus of 10 to 40 kg / cm ² is used as the rubber in which the steel cord is embedded.