JP2000185509A - Pneumatic radial tire for passenger car - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve mainly durability by using simplified cord of 2+5 structure as a belt for passenger car tires. SOLUTION: A double layer belt on a carcass 2 is made of steel cord of layer twist structure in which a sheath is formed by twisting five strands of steel filaments around a core filament 1 which is made of two strands of steel filaments. The steel cord before making the tire is cut into 10 cm in length, then plating on each filament surface is removed by ammonium persulfate solution. After a semi-circumferential portion of each filament is covered with lacquer in a longitudinal direction, etching is performed in nitric acid solution. If bending of the filament to the etched side is considered to be negative and bending in the lacquer covered side is considered to be positive, the bending amount at which the filament is in a maximum bent state is +10 mm or less by the average of all filaments constituting the steel cord.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire for a passenger car, particularly having improved durability.

[0002]

2. Description of the Related Art Vehicles mainly traveling on paved roads, especially passenger cars, have been improved year by year, have been used under good maintenance, and the road network has been further expanded. Tires used in passenger cars are required to further improve their running performance, especially steering stability. here,
Since the belt stability of a tire has a great effect on the steering stability of a tire, various proposals have been made for rubber and cord used for the belt.

On the other hand, in response to recent demands for energy saving and resource saving, reduction in weight of tires which contributes to improvement of fuel efficiency of automobiles has been promoted. Specifically, reduction of various materials constituting tires and reduction of manufacturing cost have been promoted. Due to the practice, it has become extremely difficult to achieve desired performance with low cost and a small amount of material.

Under these circumstances, Japanese Patent Application Laid-Open No. 9-31876 discloses a technique for cords used for tires, which aims at achieving both simplification of the structure, improvement of productivity and characteristics required for cords. A steel cord with a 2 + 5 structure is disclosed.

[0005]

However, the above publication only discloses that the steel cord is used for a belt for truck and bus tires, and the steel cord is used especially for a belt for tires for passenger cars. It is difficult to satisfy the characteristics required for the above. Because the steel cords disclosed in these publications are premised on application to truck and bus tires, the cord diameter, particularly the sheath filament diameter of the cord is large, and when the cord is applied to the belt of passenger car tires, This is because cord breakage is likely to occur and durability is reduced, and the thickness of the belt ply is increased, which hinders weight reduction of the tire.

[0006] In view of the above, the present invention intends to provide a method for improving durability mainly when a simplified cord having a 2 + 5 structure is applied to a belt of a passenger car tire.

[0007]

DISCLOSURE OF THE INVENTION The present inventors have made intensive studies on cords suitable for use in belts for passenger car tires and have found that cord breaks in 2 + 5 structural cords are related to the surface residual stress of the filament. Was. In other words, in the case of a tire belt under extremely severe operating conditions such as repeatedly turning the vehicle repeatedly, tensile deformation and compression deformation are repeatedly applied to the cord, but this deformation causes the filament to crack from the outermost surface The inventors have found that cord breakage occurs, and particularly that cord breakage is likely to occur if there is an excessive tensile residual stress on the filament surface, and the present invention has been completed.

The gist configuration of the present invention is as follows. (1) A pneumatic radial tire having a carcass composed of at least one ply of organic fiber cords extending radially in a toroidal shape between a pair of bead portions and having at least two layers of belts on the carcass The belt is composed of a steel cord having a layered structure in which two steel filaments are used as a core, and five steel filaments are twisted around the core to form a sheath. After cutting the steel cord before production to a length of 10 cm, loosening the twist, the plating on the surface of each filament is removed with an aqueous solution of ammonium persulfate, and then a half-circumferential portion of each filament is covered with a lacquer in its longitudinal direction,
Etching is performed in a nitric acid aqueous solution, and the amount of bending when the bending of the filament is maximized after the etching is defined as a negative value when the filament is bent on the etched side and a positive value when the filament is bent on the lacquer coating side. The pneumatic radial tire for a passenger car, wherein when bent, the amount of bending is +10 mm or less as an average value of all filaments constituting the steel cord.

(2) The pneumatic radial tire for a passenger car according to the above (1), wherein the diameter of the steel filament constituting the sheath is 0.2 to 0.3 mm.

(3) The pneumatic radial tire for a passenger car according to the above (1) or (2), wherein the bending amount of the steel filament is -10 mm or less.

[0011]

FIG. 1 illustrates a specific example of a radial tire for a passenger car according to the present invention. This tire is 1
A carcass 2 composed of at least one ply of organic fiber cords extending in a toroidal shape in the radial direction between a pair of bead cores 1, a belt 3 composed of at least two layers disposed outside a crown portion of the carcass 2 in a tire radial direction, and The belt 3 is composed of a tread 4 disposed radially outward of the belt 3. In the illustrated example, the belt 3 and the tread 4
A belt reinforcing layer 5 formed by winding an organic fiber cord in the circumferential direction is disposed between the belt 3 and the entire width of the belt 3.

The belt 3 has a laminated structure of a first belt layer 3a and a second belt layer 3b in order from the side of the carcass 2 in the illustrated example, and is inclined with respect to the ply cord of the carcass 2, preferably 22 to 26. It has a structure in which a plurality of rubber coating layers made of a number of steel cords arranged at an inclination angle of ° are overlapped in an arrangement in which the steel cords cross each other between the layers.

As the steel cord forming the belt 3, for example, a steel cord shown in FIG. 2 as a typical example is applied. That is, a core 6 in which two steel filaments 6a and 6b are twisted or simply aligned.
Is a layer twisted steel cord in which five steel filaments 7a to 7e are twisted around to form a sheath 7. When the core 6 is twisted with filaments, using a cord in which the sheath 7 is twisted in the same direction and at the same pitch as the core 6 is advantageous for improving durability.

Now, in the tire of the present invention, in which the organic fiber cord is applied to the carcass 2, the tire may be used in a case where continuous slalom running or running at a low internal pressure significantly different from a standard internal pressure is performed. Buckling deformation easily occurs. When this buckling deformation occurs, the belt portion receives a large amount of compression input, and as a result, the durability against cord breakage deteriorates. In a tire having such a structure, it is effective to minimize the surface distortion applied to the filament constituting the belt cord, particularly the sheath filament, in order to prevent the cord from being broken. This buckling deformation occurs particularly frequently when at least one belt reinforcing layer in which organic fiber cords are arranged in the circumferential direction on the outer peripheral side of the belt is arranged. Therefore, the present invention is particularly effective for a tire having a belt reinforcing layer.

Here, the surface strain generated at the time of bending deformation of the sheath filament is represented by d / 2r, where d is the filament diameter and r is the radius of curvature of the bending deformation. Is smaller, the surface distortion is smaller. Therefore, the diameter of the sheath filament was determined to be relatively small, 0.3 mm or less. However, when the diameter of the sheath filament is less than 0.2 mm, the steering rigidity of the tire is reduced due to a decrease in the rigidity of the cord, so that the diameter of the sheath filament is 0.2 to 0.3.
Limit to mm.

The diameter of the core filaments 6a and 6b constituting the core 6 is preferably 0.1 to 0.2 mm. That is, when the diameter of the core filament is 0.
If it is less than 1 mm, the gap between the core 6 and the sheath filament becomes too small, so that the rubber permeability required as a belt cord for a passenger car tire is deteriorated. In addition, the rigidity of the cord is reduced, and the steering stability is reduced as the tire performance, which is not preferable. Also, if it exceeds 0.2 mm,
It is not preferable because the filament surface distortion increases.

Further, in the present invention, the surface residual stress of the filament constituting the belt cord is adjusted to a predetermined range. That is, if there is an excessive tensile residual stress on the surface of the filament, especially when the outermost surface of the filament is subjected to tensile deformation, tensile strain is applied and fatigue fracture easily proceeds. For example, under extremely severe conditions of use, such as repeatedly turning a vehicle sharply, the belt of the tire is deformed, tensile and compressive deformation is repeatedly applied to the cord, and this deformation causes plastic deformation from the outermost surface of the filament. Cracks are generated, and particularly, the cracks on the outermost surface of the filaments grow faster when the residual stress of the filaments is on the tensile side than on the compressive side, resulting in cord breakage. Therefore, the resistance to breakage of the cord, that is, the breakage resistance of the belt cord, is significantly improved by forming the cord with a filament having no excessive tensile stress remaining on the surface.

In the present invention, the surface residual stress of the filament is quantified by the following method. That is, a steel cord before tire production was cut at a length of 10 cm, and after untwisting, the plating on the surface of each filament was removed with an aqueous solution of ammonium persulfate. Then, as shown in FIG. After coating with a lacquer in the longitudinal direction, nitric acid aqueous solution at 50 ° C (concentration: 50
vol%), and the amount of bending when the bending of the filament becomes maximum after this etching is defined as the amount of surface residual stress. In the case where the filament is bent before etching, the difference in the amount of bending before and after etching is determined as the surface residual stress amount. As shown in FIG. 3, the determination of whether the surface residual stress is tensile or compressive is made by compressing the filament bent on the etched side and tension by bending the filament on the lacquer-coated side. And
The amount of bending determined as described above was measured for all the filaments constituting the steel cord, and the average of the measured values was defined as the amount of surface residual stress. When the amount of bending of the filament thus determined is less than +10 mm, the above surface residual stress is not on the excessive tensile side, and the desired cord breakage resistance can be obtained.

FIG. 4 shows the result of investigation on the relationship between the amount of bending of the filament and the resistance to cord breakage. As shown in FIG. 4, when the amount of bending of the filament becomes +10 mm or less, the resistance to cord breakage is improved. You can see that In particular, when the amount of bending is −10 mm or less on the compression side, the cord breakage resistance is sharply improved. Therefore, the bending amount of the filament is +10 mm or less, more preferably -10 mm.
It is specified below. The cord breaking resistance was measured according to a tire durability test described later.

Incidentally, the residual stress on the surface of the filament can be excessively increased, for example, by passing the filament after the die drawing or the cord after twisting the filament through a plurality of rollers to appropriately apply tensile and bending strains. From the tension side to the compression side.

The organic fiber cords constituting the carcass 2 and the belt reinforcing layer 5 can be made of polyester, nylon, rayon or the like.

[0022]

EXAMPLE A steel cord having the specifications shown in Tables 1 and 2 was applied to a belt 3 of a radial tire for a passenger car having the structure shown in FIG. 1, and a tire of size 235 / 80R16 was vulcanized at 180 ° C. for 15 minutes. And post-curing inflation conditions: Prototypes were produced at an internal pressure of 2.5 kgf / mm ² for 30 min. The belt 3 has a first belt layer 3a disposed on the carcass 2 in a direction in which a steel cord is inclined at an angle of 22 degrees to the left with respect to the equatorial plane of the tire. A second belt layer 3b is disposed in a direction in which the cord is inclined at an angle of 22 ° to the right, and a belt reinforcing layer made of a nylon cord extending substantially along the equatorial plane of the tire so as to further cover the belt end. 5 are arranged. The number of cords driven on the belt 3 was 25/50 mm.

Here, the belt cord was subjected to the following treatment to adjust the surface residual stress of the filament so as to have various bending amounts. That is, after the filament was passed between nine rollers (diameter: 15 mm) arranged in a staggered manner, a roller axis was arranged in a direction orthogonal to the roller axes of these roller groups, and the rollers were similarly arranged in a staggered manner. In the process of passing the filament between the nine rollers, the amount of pushing of each roller into the filament was appropriately adjusted to obtain a desired surface residual stress.

The organic fiber cord of the carcass 2 includes:
PE obtained by twisting 1500 denier PET fiber yarn twice
T fiber cord was used. Then, the PET fiber cord is driven 5 times in a direction orthogonal to the equatorial plane of the tire.
Carcass 2 was formed by arranging 1.7 pieces / 50 mm.

Incidentally, the PET fiber cord can be manufactured according to the following steps. First, a PET solid-phase polymerized polymer (IV: 0.90) was spun with a spinneret 10-70.
The mixture was quenched in a gas atmosphere at ℃ to produce a raw yarn. On this occasion,
Spinning speed 300 ~ 1500m / min and draw ratio 1.40 ~
Perform by selecting the optimal conditions within the range of 2.80. Next, a PET fiber cord is obtained by subjecting the raw yarn to predetermined twisting. Further, the PET fiber cord is subjected to, for example, a dipping treatment in order to improve the adhesion with the rubber.

Next, regarding the tire thus obtained,
After adjusting to the air pressure corresponding to the maximum load capacity built into the rim of size 6J-16, it is attached to the actual vehicle, and 60 to 200 km /
After traveling 50,000 km on the test course at a speed of h, the feeling of driving stability was evaluated by two drivers.
That is, the steering stability was evaluated by two drivers on items such as straight running stability, turning stability, rigidity, handling, etc., on a 10-point scale, and all items and the scores of the two drivers were averaged. The obtained score was indicated by an index when the score of the tire of Comparative Example 3 was set to 100. The higher the index, the better the steering stability.

Further, with respect to the durability of the tire, the tire was incorporated into a standard rim, adjusted to an air pressure corresponding to the maximum added capacity, mounted on an actual vehicle, and traveled 20,000 km on a zigzag path having a constant curvature at 60 km / h. Thereafter, the tire is dissected, cords are collected from the belt, the number of broken cords is measured, and the result is expressed as an index by the following equation. The smaller the index, the smaller the number of cord breaks and the better the belt cord break resistance. (Break resistance index of belt cord) = (number of folds in test tire) / (number of folds in tire of Comparative Example 3) × 100 The evaluation results and measurement results described above are shown in Tables 1 and 2.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

According to the present invention, durability is improved without sacrificing steering stability in a tire for a passenger car in which a simplified cord having a 2 + 5 structure is applied to a belt to achieve a reduction in weight. Can be.

[Brief description of the drawings]

FIG. 1 is a diagram showing a tire structure of the present invention.

FIG. 2 is a schematic diagram showing a procedure for measuring the surface residual stress of a filament.

FIG. 3 is a schematic view showing a procedure for measuring the surface residual stress of a filament.

FIG. 4 is a graph showing the relationship between the amount of bending of a filament and the cord breaking resistance.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bead core 2 Carcass 3 Belt 3a 1st belt layer 3b 1st belt layer 4 Tread 5 Belt reinforcement layer 6 Core 6a, 6b Core filament 7 Sheath 7a-7e Sheath filament

Claims (3)

[Claims] 1. A pneumatic radial having a carcass comprising at least one ply of organic fiber cords extending radially in a toroidal manner between a pair of bead portions and having at least two layers of belts on the carcass. A tire, wherein the belt is composed of a steel cord having a layered structure in which two steel filaments are used as a core, and five steel filaments are twisted around the core to form a sheath. After cutting the steel cord before tire production with a length of 10 cm, loosening the twist, the plating on the surface of each filament was removed with an aqueous solution of ammonium persulfate, and then half the circumference of each filament was covered with lacquer in the longitudinal direction. After that, etching is performed in an aqueous nitric acid solution, and after this etching, The bending amount in the state where the bending of the steel cord is the maximum is defined as a negative value when the filament is bent on the etched side and a positive value when the filament is bent on the lacquer-coated side. A pneumatic radial tire for passenger cars, characterized in that the average value of all filaments constituting the tire is +10 mm or less. 2. The pneumatic radial tire for a passenger car according to claim 1, wherein the diameter of the steel filament constituting the sheath is 0.2 to 0.3 mm. 3. The pneumatic radial tire for a passenger car according to claim 1, wherein a bending amount of the steel filament is −10 mm or less.