JPH0126882B2 - - Google Patents

Description

[Detailed description of the invention]

By combining a novel twisted structure with a high carbon steel metal cord, the present invention takes advantage of the high strength of the metal cord and at the same time improves its corrosion resistance, thereby significantly extending its service life and This relates to a radial tire that is lightweight and has low rolling resistance. 4 in the belt reinforcement layer of steel radial tires
Steel cords having a so-called 1×4 or 1×5 structure in which one to five filaments are twisted together have been widely used. In recent years, there has been a growing demand for reduced rolling resistance in radial tires, and in order to reduce the weight of the tire without increasing the number of steel cords in the belt reinforcing layer, we have developed high-strength steel cords per unit area. It has been considered to apply a so-called high-strength yarn cord to the above-mentioned twisted structure. As a means to increase the strength per unit area compared to the steel cord surface, it has been considered to increase the carbon content of the metal composition, and this is currently a known technology. However, the present inventors have discovered that the above-mentioned high carbon steel cord has a serious defect when it is applied to a commercial product to obtain a lightweight radial tire with low rolling resistance. In other words, when a steel cord like the one described above is used for the belt reinforcement layer, if the tire receives trauma from a pebble or nail that reaches the metal cord while running on the road surface, moisture that has entered through the wound will be absorbed into the center of the cord. It easily penetrates into the cavity of the body,
As a result, the fatigue resistance of the metal cord when corroded is significantly reduced, and furthermore, the adhesion between the cord and the rubber is reduced, resulting in a phenomenon called separation between the cord and the rubber. To date, various studies have been made to improve these drawbacks, but among them, Japanese Patent Application Laid-Open No. 55-90692
As stated in the above publication, compared to the conventional cord, which has no gaps between each filament as shown in Fig. 1 and has a compact cord diameter,
By twisting the cord with a slightly larger diameter, a gap is created between each filament without making the filaments contact each other, and the cord has a uniform cross section inscribed in a circle, as shown in Figure 2. A cord like this has been proposed, and in the heat vulcanization process after being embedded in rubber, when the rubber is in a fluid state at the beginning of vulcanization, the rubber will flow through the gaps between the filaments into the center of the cord. By penetrating into the cavities of the metal cord, the corrosion resistance of the metal cord is improved because water that has entered from an external wound does not diffuse into the cord. However, according to the experience of the present inventors, the code described in the above-mentioned publication does not work because the hot vulcanization process is usually carried out under a pressure of 4 to 40 kg/ ^cm2 .
This pressure crushes the bulge in the cord, almost eliminating the air gap between the filaments, and as a result, the fluidized rubber can hardly penetrate into the cavity in the center of the cord, and even if it does, it can only partially penetrate. If a product using such a cord is subjected to trauma even though only a small amount of rubber has penetrated, the interface between the partially penetrated rubber and the cord will corrode in a short period of time due to the moisture that has penetrated from the trauma. It is clear that this method has a drawback in that moisture further diffuses in the length direction of the cord through the gaps, resulting in separation between the cord and the rubber. In view of the current situation, the inventors of the present invention conducted extensive research to solve the above-mentioned drawbacks, and as a result, they developed a steel that takes advantage of the high strength of high carbon steel metal cords, has excellent corrosion fatigue resistance, and is sufficiently practical. I was able to get the code. That is, the present invention provides a radial tire that uses such a steel cord as a belt reinforcing material and satisfies both the reduction in rolling resistance from the steel cord surface as a lightweight tire and the corrosion resistance and fatigue properties of the cord without impairing handling stability. More specifically, it is a cord made of high carbon steel with a carbon content (C%) of 0.78 to 0.85% twisted together as at least three metal filaments, the steel cord having high strength. The present invention provides a radial tire using a cord as a belt reinforcing material, which solves the problem of reduced corrosion fatigue resistance due to corrosion by devising a cord twisting structure and penetrating the cord surface with rubber as much as possible. In addition, the devised twisted structure referred to here means that the elongation P ₁ is in the range of 0.2 to 1.2% when a load of 5.0 kg is applied to each cord, and the elongation is 2.0 kg.
The elongation P ₂ when a load is applied is P ₂ (%)≦0.947P ₁ −
It has a twisted structure that results in a metal cord within the range expressed by 0.083. The metal cord used in the present invention is, for example, a cord in which at least three different cross-sectional shapes as shown in FIG. _P1 is 0.2-1.2%
and the elongation P ₂ (%) when applying a load of 2.0 kg is 0.947P ₁ −0.083 or less, preferably
It must be less than 0.947P ₁ −0.204. The reason for this is that if P ₁ is less than 0.2%, it is not much different from the conventional compact cord, and the purpose of the present invention cannot be achieved, and if it exceeds 1.2%, the ends of the cut cord tend to become disordered, making it difficult to work. This is because it is undesirable due to sexual problems. Among these, if workability is considered as important, _P1 is more preferably in the range of 0.2 to 0.7%. Furthermore, if P ₂ exceeds 0.947P ₁ −0.083, the cord will have a cross-sectional shape that is likely to be crushed by the vulcanization pressure during the heat vulcanization process after being embedded in rubber, making it difficult for the rubber to penetrate. This is because it is not desirable. The relationship between P ₂ and the permeability of rubber into the cord will be discussed in more detail below. Generally, in open-strand cords, 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. In the former case, as shown in Figure 2, the cross-sectional shape of the cord is uniform in the length direction (the filament gap is uniform).
In this case, each constituent filament tries to move freely toward the center, so when a load of 2 kg is applied, the elongation of the cord becomes relatively large. On the other hand, the latter is B to E in Figure 3 (1 x 5).
As shown in , the cross-sectional shape of the cord is uneven,
This is a case where the filaments are in contact with each other, and even if each filament tries to move toward the center, contact pressure (repulsive force) acts on each of the two contacting filaments, so when a load of 2 kg is applied, the cord will not elongate. It becomes smaller. In the cross-sectional shape, if the number of contact points between filaments is the number of contacts, then the non-uniformity of the cross-sectional shape of the cord is expressed by the number of contacts. The cord with more contacts has a more uneven cross section. In the single-strand structure, the filament configuration is 1×
5, the number of contacts is 4 (E in Figure 3 1x5), 1x
When the number of contacts is 3 (D in 1×4 in FIG. 3), the non-uniformity of the cross-sectional shape becomes maximum. The metal cord used in the present invention preferably has a twist pitch of 6 to 14 mm. The reason for this is that if the twist pitch is less than 6 mm, the productivity during cord manufacturing will be significantly reduced, and it will not be practical for commercial use.
This is because if it exceeds 14 mm, the cord breakage resistance due to cord bending fatigue will be greatly reduced, which is not preferable in either case. Further, the filament constituting the metal cord used in the belt reinforcing material of the present invention has a diameter of 0.20~
It needs to be 0.30 mm and have a C% of 0.78 to 0.85%. This is because if the diameter of the filament is less than 0.2, the strength as a radial belt material is too small and the fatigue resistance is also poor;
If the C% exceeds 0.78%, the cord weight increases and there is no benefit in weight reduction, and if the C% is less than 0.78%, the cord is lowered as a belt reinforcement material for lightweight radial tires, resulting in low rigidity and poor handling stability of radial tires. If it exceeds 0.85%, the corrosion and fatigue resistance of the cord will decrease, leading to belt cord breakage, and wire drawability will also decrease, which is undesirable. In addition, the surface of the above filament has Cu, Sn, and
It may be coated with Zn or an alloy containing Ni or Co. Further, the metal cord used in the present invention can be manufactured as follows. In other words, the filament, which has been excessively curled in advance, _is
It can be manufactured by compressing the cord in the radial direction so that it has (elongation under a load of 5 kg). Finally, in the present invention, the rubber in which the metal cord is embedded is natural rubber or synthetic rubber, but when the metal cord of the present invention is used in the belt reinforcing layer of a radial tire, the 50% modulus of the embedded rubber is 10 to 40.
Preferably, it is Kg/cm ² . The reason for this is that if the 50% modulus is less than 10 kg/ ^cm2 , the distortion at the end of the metal cord will increase and the resistance to belt end separation (referring to the growth of cracks in the belt coating rubber from the end of the belt cord) will decrease. 40Kg/
This is because if it exceeds cm ² , the durability of the belt cord, that is, the cord is likely to break, and at the same time, the workability is also significantly reduced, which is not preferable in either case. In the radial tire using the metal cord of the present invention having the above-described structure, the rubber is sufficiently permeated in the longitudinal direction and the cross-sectional direction of the cord, so that the surface of the metal cord is not affected by moisture intrusion due to external injury. The spread of rust is prevented. Therefore, the separation phenomenon caused by a decrease in the adhesion between the cord and rubber due to corrosion of the metal cord is greatly improved, and the durability of the radial tire using the metal cord of the present invention is significantly improved. Furthermore, the metal cord used in 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 applications such as agricultural tillers and lightweight industrial products such as belts. Although the present invention has been described with respect to a radial tire using a specific metal cord as a belt reinforcing material,
The metal cord can also be applied as carcass ply reinforcement. Example 1 Nineteen types of metal cords shown in Table 1 were made by twisting brass-plated steel filaments. After embedding and vulcanizing these metal cords in rubber with a 50% modulus of 25 kg/cm ² used as tire belt coating rubber,
A metal cord was sampled and the length of the central part of the cord where the rubber had almost completely penetrated was measured, and the degree of rubber penetration was evaluated using an index as a ratio to the total 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 in Table 1. Here, P ₁ and P ₂ are the elongation (%) when a load of 5.0 kg and 2.0 kg is applied to a metal cord with a total length of 20 to 50 cm, respectively, and the cross-sectional shape is 5 mm in the length direction of the cord. The cross-sectional shape of the cord at the position of the interval was observed with a magnifying glass and indicated by the symbols shown in FIG.

[Table] Regarding the codes of experiments No. 1 to 12 in Table 1 above,
The degree of rubber penetration is measured by taking P ₁ on the horizontal axis and P ₂ on the vertical axis.
80-100 is 〇, 60-79 is ◇, 49-59 is □, 29-39
Figure 4 shows the blots as △ and 0 to 19 as ▽. However, from Table 1, metal code No. 14,
P ₁ and P 2 of 16, 17, 18, _{and 19} are the same values as No. 2,
P ₁ and P ₂ of metal code No. 15 are the same values as No. 6,
Also, the P ₁ and P ₂ values of No. 13 are off the graph and cannot be plotted, so they are plotted for 12 metal codes on the drawing. As is clear from Table 1 and Figure 4, P ₂
≦0.947P ₁ −0.083 (preferably P ₂ ≦0.947P ₁ −
The metal cords of Experiment Nos. 1 to 5 (preferably Experiments Nos. 1, 2, and 5) in the range of 0.204) have a rubber penetration degree of 60 or more (preferably 80 or more), and the metal cord has a Although it has penetrated well, P ₂ >
It can be seen that the metal cords of Experiment Nos. 9 to 12 in the range of 0.947P ₁ -0.043 are close to cords with a uniform cross-sectional shape in which the filaments do not touch each other, and the degree of rubber penetration is poor. Next, the metal cords of experiments No. 1 to No. 19 in Table 1 were added to the belt reinforcement layer (50% modulus of embedded rubber 25 kg/
A radial tire, size 175SR14, was prepared using a radial tire (cm ² ) and also partially used as a carcass ply reinforcing material, and the characteristic values of the test tire corresponding to the various metal code contents in Table 1 below were measured, and the results are summarized in Table 1. It is shown in Table 2. The tire numbers in Table 2 correspond to the metal code numbers. The measurement method is as follows: A diameter of 3 mm that reaches the metal cord of the belt at the ground contact part of the tire.
After drilling the hole and running the tire for 1000km, the tire was immersed in a water tank containing 5% NaCl solution for one day, and then run for a total of 40,000km on public roads, and then the internal pressure was set to 1.3Kg/ ^cm2 . 20,000km on a constant downward slope
After driving, the tires were dissected. 1 Corrosion resistance: A metal cord corresponding to the position of the hole in the tire was taken, and the corrosion length of the cord was evaluated as the length of the adhesive interface with the buried rubber where the adhesion decreased. The corrosion length of the tire metal cord of tire No. 13 was set as 100 and expressed as an index using the following formula. Corrosion length of metal cord of test tire/Corrosion length of metal cord of tire No. 13 x 100 The smaller the value, the better. 2 Belt Cord Folding Resistance The number of bent metal cords sampled in the above corrosion resistance test was determined and expressed as an index using the following formula. Number of broken metal cords of tire No. 13/number of broken metal cords of test tire x 100 The larger the index, the fewer the number of broken cords, which is better. 3 Steering stability (cornering power) A side slip angle is given to the tires to generate a lateral force (cornering force) due to frictional resistance with the road surface, and the component force acting at right angles to the direction of travel of the vehicle is expressed on the vertical axis. Then, when the sideslip angle is plotted on the horizontal axis, the slope of the straight line area (cornering power) was determined and expressed as an index using the following formula. Cornering power of test tire / cornering power of tire No. 13 × 100 4. Rolling resistance Measured by coasting method, measurement conditions are diameter 1707.6 mm, width
JIS100 on a 350mm steel drum
% load on a tire with an internal pressure of 1.7Kg/ ^cm2 , the drum was rotated by a motor, and the speed was 80Km/cm2.
After running for 30 minutes at
The speed was increased to 200km/h. Next, the motor drive clutch was disengaged to coast, and the rolling resistance of the tire and drum at a speed of 50 km/h was calculated based on the drum deceleration and time change. The drum resistance calculated in advance was subtracted from this value to determine the net rolling resistance of the tire. The rolling resistance was expressed as an index using the following formula. Rolling resistance of tire No. 13 / Rolling resistance of test tire x 100

【table】

[Table] This shows that it becomes easier to fall.
As can be seen from Examples No. 1 to No. 5, No. 14, and No. 19 tires of the present invention, the objective of the present invention is to improve corrosion resistance, fatigue resistance, and rolling resistance without impairing the handling stability of the tire. I was able to balance resistance. Although the effect of improving rolling resistance seems to be small compared to the effect of corrosion and fatigue resistance, increasing rolling resistance by 5% compared to the current level is almost an extremely difficult feat for tire technology. In this respect, it can be concluded that the present invention has achieved remarkable effects.

[Brief explanation of drawings]

Figure 1 is a sectional view of a compact conventional metal cord, Figure 2 is a sectional view of a metal cord described in Japanese Patent Application Laid-Open No. 55-90692, and Figure 3 is a sectional view of a metal cord used in the present invention. FIG. 4 is a diagram showing the relationship between P ₁ and P ₂ and the degree of rubber penetration. 1...cord, 2...filament, 3...contact point.

Claims (1)

[Scope of Claims] 1. A belt embedded inside the tread portion, comprising a tread portion, a pair of side portions connected at both shoulders of the tread portion, and a pair of bead portions formed on the inner periphery of the side portion, respectively. In a radial tire having a carcass reinforced with
A cord consisting of 3 to 5 steel filaments with a diameter of 0.20 to 0.30 mm, the carbon content of the filament composition is in the range of 0.78 to 0.85%, and each cord weighs 5.0 kg before being embedded in rubber. The elongation P ₁ when a load is applied 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 _{P 2 (} %)
A radial tire comprising a metal cord within the range of ≦0.947P ₁ −0.083. 2. The radial tire according to claim 1, wherein rubber having a 50% modulus of 10 to 40 kg/cm ² is used as the rubber in which the belt steel cord is embedded.