JP2531771B2 - Radial tires for heavy loads - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heavy load such as a radial tire for trucks and buses, a radial tire for light trucks, etc., in which a metal cord applied to a carcass ply of a radial tire has been improved and a durability life thereof has been significantly improved. The present invention relates to a technology for providing a radial tire.

BACKGROUND ART In recent years, in order to respond to the increasing social needs such as resource saving and energy saving, the weight of radial tires has been reduced, rolling resistance has been reduced, and the life of the product has been extended by improving the rehabilitation life.
The demand for flattening is also occurring in radial tires for heavy loads. When developing tires that meet such requirements, it is important to solve the problems of fracture resistance, corrosion fatigue resistance, and fretting resistance at the carcass ply end of the metal cord as a carcass ply material. Become.

Therefore, from the viewpoint of input to the carcass ply cord, as a method of reducing the contact pressure between the cord filaments, a 3 + 9 two-layer twist structure of the steel cord is provided (Japanese Patent Laid-Open No. 59-59).
-124404) or a compact cord twist structure that is a closest packing structure such as 1 × 12 (Japanese Patent Application No. 60-35215).
In order to improve the corrosion fatigue resistance and fretting resistance, the twisting property of these cords has been examined (Japanese Patent Laid-Open No. 59-124404).

On the other hand, as a belt outermost layer cord of a large radial tire for rough roads, a 1 × 4 twist or 1 × 5 twist single layer twist structure obtained by twisting a pre-shaped filament or 1
A tire using a twisted cord having a two-layer twist structure in which two filaments are cored is disclosed in JP-A-60-116504.

The inventors of the present invention have made diligent studies to develop a radial tire for heavy load that can significantly improve the durability life. As a result, a carcass ply with a conventional 3 + 9 two-layer twist structure or a 1 × 12 compact cord twist structure is obtained. Since rubber did not penetrate into the cord at both ends of the cord, stress concentration at the cord end was remarkable, and the fracture resistance at both ends of the carcass ply was not sufficient. Further, it is difficult for rubber to embed the cord into the cord, and it is surrounded by holes inside the cord, that is, surrounded by steel filaments, and the holes inside the cord opened in the axial direction of the cord are hardly blocked by the rubber penetrating. Therefore, it has been found that it is impossible to prevent the moisture invading from the cut generated in the tread from moving to a long distance through the pores inside the cord, and the corrosion fatigue resistance is not sufficiently improved.

Regarding the occurrence of fretting (a phenomenon in which the filaments of the cord are scraped off by scraping), the contact pressure between filaments is high in the conventional 3 + 9 two-layer twist structure and the 1 × 12 compact twist structure, which is why When a carcass ply cord such as a radial tire for truck bus (TBR) or a radial tire for light truck (LSR) is applied, it causes fretting due to severe input, induces a decrease in strength, and durability of the heavy tire radial case There was a problem that it drastically decreased.

On the other hand, the technique described in JP-A-60-116504 relates to a technique for improving the belt layer of a large radial tire for bad roads, and cannot meet recent social demands such as weight reduction of radial tires. Moreover, it is impossible to directly apply such a technique to the carcass ply because of problems in bead durability and case strength.

Further, in Japanese Patent Laid-Open No. 57-51502, most of the filaments that make up the steel cord contain 0.75 to 0.85 carbon.
A pneumatic tire is disclosed in which a steel cord having a twisted structure of 7 × 4 and having a high tensile strength is used as a reinforcing material for a carcass ply, the steel tire being made of a steel material that is contained in a weight percentage. However, since this steel cord has a double-twisted structure of 7 × 4, fretting between strands is very large, and rubber permeability into the cord is poor, so that the technical problem to be solved by the present invention is to be solved. The solution could not be matched.

Therefore, the object of the present invention is to significantly reduce the tire weight, the carcass ply end of the fracture resistance of the problem,
Improves corrosion fatigue resistance and fretting resistance, and at the same time, side tire resistance to radial tires (cord resistance)
To provide an improved technique of a heavy duty radial tire capable of significantly improving the performance of the above.

DISCLOSURE OF THE INVENTION To achieve the above object, the present invention comprises at least one layer of carcass plies arranged in a tire equatorial plane at an angle of substantially 90 ° and wound around the bead core from inside to outside. In a heavy duty radial tire, a filament diameter of 0.13 to 0.32 mm is used as a reinforcing material for the carcass ply.
The carcass has a single twist structure in which 3 to 5 metal filaments are twisted, and the elongation P ₁ is 0.35 to 1.0% as an arithmetic mean value during a load of 0.25 to 5 kgf / wire. The cord clearance at the end of the ply is 0.25 mm or more, and the tire has a road index (Lo 4) according to ISO 4209/1.
ad Index) is 100 or more and 121 or less, the tensile strength TS (kgf / mm ² ) of the metal filament and the filament diameter d
(Mm) has the following relationships 1) to 3), 1) When the number of metal filaments is 5 (In the formula, d = 0.13 to 0.25.) 2) When the number of metal filaments is 4 (In the formula, d = 0.14 to 0.25.) 3) When the number of metal filaments is 3 (In the formula, d = 0.15 to 0.25.) And if the tire has a load index of 122 or more according to ISO 4209/1, the tensile strength TS (kgf / mm ² ) of the metal filament is And the filament diameter d (mm) have the following relationships 1) to 3): 1) When the number of metal filaments is 5 (In the formula, d = 0.15 to 0.32.) 2) When the number of metal filaments is 4 (In the formula, d = 0.16 to 0.32.) 3) When the number of metal filaments is 3 (In the formula, d = 0.17 to 0.32.) Is satisfied.

The single twist structure of a metal cord formed by twisting 3 to 5 metal filaments is specifically 1 × 3,
Notated as 1 × 4 and 1 × 5.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a 1 × 5 open twist structure metal filament diameter d at a load index of 100 to 121.
2 is a graph showing the relationship between the tensile strength TS of the filament and the tensile strength TS of the filament, and FIG.
Fig. 3 is a graph showing the relationship between the tensile strength TS of the filament and the tensile strength TS of the filament, and Fig. 3 is a metal filament diameter d of 1 × 3 open twist structure at a load index of 100 or more and 121 or less.
Fig. 4 is a graph showing the relation between the tensile strength TS of the filament and the tensile strength TS of the filament.
A graph showing the relationship between the diameter d of a metal filament having an open twist structure of × 5 and the tensile strength TS of the filament, and FIG.
A graph showing the relationship between the diameter d of a metal filament having an open twist structure of × 4 and the tensile strength TS of the filament, FIG. 6 shows 1 at a load index of 122 or more.
The graph which shows the relationship between the metal filament diameter d of the open twist structure of x3, and the tensile strength TS of this filament, FIG. 7 is an explanatory view of a mold attachment, FIG. 8 is an explanatory view of a fretting resistance test, FIG. [Fig. 4] is an explanatory view of a corrosion fatigue resistance test.

BEST MODE FOR CARRYING OUT THE INVENTION In order to explain the present invention in more detail, it will be described below with reference to the accompanying drawings.

The present invention, in the heavy duty radial tire, IS
The load index according to O 4209/1 is
When it is 100 or more and 121 or less, the tensile strength TS (kgf / mm ² ) of the metal filament and the filament diameter d (mm) have the following relationship 1) to 3): 1) The number of metal filaments is 5
In the case of a book (A in Fig. 1) (In the formula, d = 0.13 to 0.25.) 2) When the number of metal filaments is 4 (A in FIG. 2) (In the formula, d = 0.14 to 0.25.) 3) When the number of metal filaments is 3 (A in FIG. 3) (In the formula, d = 0.15 to 0.25) is preferably satisfied.

More preferably, in the heavy duty radial tire, when the load index is 100 or more and 121 or less, the tensile strength TS (kgf / mm ² ) of the metal filament is
And the filament diameter d (mm) have the following relationships 1) to 3): 1) When the number of metal filaments is 5 (B in FIG. 1) (In the formula, d = 0.18 to 0.25.) 2) When the number of metal filaments is 4 (B in FIG. 2) (In the formula, d = 0.18 to 0.25.) 3) When the number of metal filaments is 3 (B in FIG. 3) (In the formula, d = 0.21 to 0.25.) Is satisfied.

That is, FIGS. 1 to 3 (and FIGS. 4 to 6 described later).
Shows the conditions for obtaining the case strength necessary for improving side trauma resistance. By setting the relationship between filament diameter and tensile strength in the area indicated by the arrow in each figure, excellent side resistance Traumaticity can be secured. If it deviates from this region, it is necessary to increase the number of driving in order to obtain the required case strength, and the fracture resistance of the end portion of the carcass ply is significantly lowered, so that the intended purpose cannot be achieved.

Further, in the heavy duty radial tire according to the present invention, when the load index is 122 or more, the tensile strength TS (kgf / mm ² ) and the filament diameter d (mm) of the metal filament are as follows 1) to Relationship of 3), 1) When the number of metal filaments is 5 (A in FIG. 4) (In the formula, d = 0.15 to 0.32.) 2) When the number of metal filaments is 4 (A in FIG. 5) (In the formula, d = 0.16 to 0.32.) 3) When the number of metal filaments is 3 (A in FIG. 6) (In the formula, d = 0.17 to 0.32) is preferably satisfied.

More preferably, in the heavy duty radial tire, when the load index is 122 or more, the tensile strength TS (kgf / mm ² ) of the metal filament and the filament diameter d (mm) are the following 1) to 3 1) When the number of metal filaments is 5 (B in FIG. 4) (In the formula, d = 0.21 to 0.32.) 2) When the number of metal filaments is 4 (B in FIG. 5) (In the formula, d = 0.23 to 0.32.) 3) When the number of metal filaments is 3 (B in FIG. 6) (In the formula, d = 0.27 to 0.32.) Is satisfied.

On the other hand, the twist pitch of the metal cord in the present invention is 5 to
Select appropriately within the range of 20 mm.

In addition, the metal cord of the present invention may be formed by, for example, forming a metal filament in advance before twisting the cord, performing plastic working, and then twisting. Here, as shown in FIGS. 7 (a) and 7 (b), the molding rate means that the maximum diameter in the twisted cord state is A, and the maximum amplitude when the filaments forming the cord are loosened is B. Rate is It is represented by. In the present invention, it is preferable that the patterning rate is 93% or more. There is no particular upper limit to the molding rate, but it is preferably 120% in terms of production.

In the present invention, in order to improve the durability of the carcass ply end portion of the heavy duty radial tire, the elongation P ₁ between the load 0.25 to 5 kgf / piece of the metal cord taken out from the tire is 0.35% as an arithmetic mean value. A metal cord with a so-called single twist open structure, which is ~ 1.0%, is used as a reinforcing material for the carcass ply.This structure can significantly reduce the stress concentration at the end of the carcass ply. At the same time, it was found that the breaking resistance at the end of the carcass ply can be synergistically improved by setting the cord gap at the end of the carcass ply at 0.25 mm or more.

Here, Shore A is used as a coating rubber for the metal cord.
It is preferable to use a rubber composition having a hardness of 60 to 80 because the durability of the end portion of the carcass ply is further improved.

In the present invention, when the metal cord having the elongation P ₁ within the above range is used, the coated rubber sufficiently penetrates into the metal cord, so that it is possible to prevent corrosion of the metal cord due to intrusion of water into the cord. Moreover, since the filaments of the metal cord do not come into contact with each other, the fretting resistance is significantly improved. However, when the elongation P ₁ is less than 0.35%, the coated rubber hardly penetrates into the cord, and it becomes 1.0
If it exceeds%, the tension tends to become non-uniform during the calendering work for wrapping the metal cord with the coated rubber, and the uniformity of the tire and the carcass durability are likely to deteriorate due to the cord disorder of the tire, which is not preferable in any case.

Further, when the metal filament is 1 × 2 twist, the cord strength is small, and it is impossible to maintain the case strength capable of withstanding the external damage of the side portion. In this case, in order to maintain the strength of the case that can withstand the external damage on the side, 1x3 twists, 1
It is necessary to increase the number of shots or to make the filament diameter thicker than in the case of × 4 twist and 1 × 5 twist, but the former is difficult due to problems in tire manufacturing technology and the problem of reduced bead part durability, and the latter is filament. There is a problem that the cord is detached from the bead due to a significant increase in bending rigidity that is proportional to the fourth power of the diameter, or the corrosion fatigue resistance is deteriorated due to an increase in input. On the other hand, when the number of twists is 1 × 6 or more, at least one of the filaments inevitably falls into the interior, resulting in a substantially two-layer structure, thus making it difficult for rubber to penetrate into the cord having a core structure as described above. I have a problem. Therefore, in order to satisfy necessary case strength, manufacturing suitability, etc., and to secure corrosion fatigue resistance and fretting resistance, it is necessary to use a single layer twist of 1 × 3 twist, 1 × 4 twist or 1 × 5 twist. However, it is preferably 1 × 4 twist or 1 × 5 twist.

Regarding the diameter of such filaments, the lower limit is related to the maintenance of necessary case strength and the reduction of the durability of the end of the carcass ply, and the upper limit is related to the reduction of the bead floating and the corrosion fatigue resistance with the increase of the bending rigidity. Therefore, in the present invention, the filament diameter is set to 10 as described above, respectively.
In the heavy load radial tire having 0 or more and 121 or less, in the case of 1 × 5 twist, it is limited to 0.13 to 0.25 mm. Preferably, it is within the range of 0.18 to 0.25 mm. Also, 1 × 4
In the case of twisting, it is limited to 0.14 to 0.25 mm, preferably 0.19
Within 0.25 mm. Furthermore, in the case of 1 × 3 twist,
It is limited to 0.15 to 0.25 mm, preferably 0.21 to 0.25 mm.

Similarly, in a heavy duty radial tire having a road index of 122 or more, in the case of 1 × 5 twist,
It is limited to 0.15 to 0.32 mm, preferably 0.21 to 0.32 mm. Further, in the case of 1 × 4 twist, it is limited to 0.16 to 0.32 mm, preferably 0.23 to 0.32 mm. Further, in the case of 1 × 3 twist, it is limited to 0.17 to 0.32 mm, preferably 0.27 to 0.32 mm.

In the present invention, if the relationship between the tensile strength (TS) and the filament diameter (d) is satisfied, the cord diameter of the metal cord can be suppressed, and the durability of the carcass ply end can be further improved. Not only can the case strength be improved, but also the breakage of the metal cord due to the cutting of the sidewall portion can be improved.

Among the metal filaments of the present invention, those having a high tensile strength have, for example, a surface reduction ratio of 97.5% and a lubricant having a good wire drawability, and the number of drawing times is increased by 3 to 4 times as compared with normal wire drawing. It can be made by performing multi-stage wire drawing. The carbon content of the metal filament is preferably 0.72 to 0.95%, and more preferably 0.82 to 0.95% because a higher tensile strength can be obtained. However, if it exceeds 0.95%, the metal filament becomes brittle, which is not preferable. The area reduction rate is preferably 96% or more.

Further, the metal filament according to the present invention is preferably a steel filament, and usually, a metal simple substance of Cu, Zn, Ni or Co, or one coated with an alloy such as a Cu—Zn alloy (brass) is used.

Next, the present invention will be specifically described with reference to Examples and Comparative Examples.

TBR 11R24.5 having a road index of 140 (Examples 1 to 7 and Comparative Examples 1 to 10) and LSR 750R16 having a road index of 108 (Example 8) were used as tires for evaluation.
-11, Comparative Examples 11-17) were used respectively.

In the case of 11R24.5, the carcass ply structure is 3 + 9 in the control tire of Comparative Example 1 as shown in Table 1.
× 0.23mm + 1 steel cord in the tire circumferential direction
Arranged at an angle of 90 ° with a implantation density of 26 pieces / 50 mm,
In the tires of other comparative examples and examples, the steel cords applied to each carcass ply shown in Table 1 were determined at the same angle with respect to the circumferential direction and so as to match the case strength of the control tire of comparative example 1. Arranged by the number of implants.

Further, in the case of 750 R16, in the control tire of Comparative Example 11 as shown in Table 2, steel cords of 3 + 9 × 0.19 mm + 1 were arranged at an angle of 90 ° with respect to the tire circumferential direction and a driving density of 30 pieces / 50 mm, In the tires of other comparative examples and examples, the steel cords applied to each carcass ply shown in Table 2 were determined at the same angle with respect to the circumferential direction and to match the case strength of the control tire of comparative example 11. Arranged by the number of implants.

As the coated rubber, a rubber composition containing 100 parts by weight of natural rubber having a Shea A hardness of 68 and 50 parts by weight of carbon black HAF was used.

The following performance evaluations were performed on the prototype tire.

Anti-fretting resistance From the prototype tire (the same method for running tires and new tires), pull out the cord of the rubber carcass cord layer from one bead to the other bead and cut it in half at the crown center. Next, the rubber is dissolved with a solvent and the filaments are loosened one by one. For each loosened filament, insert the end of the crown center side and the end of the bead side with a chuck and measure the strength with a tensile tester.Set the broken surface of the filament on the microscope so that you can see it from directly above, and enlarge it. Take a photograph, cover the magnified photograph with a piece of graph paper, and draw a circle in line with the edge of the part where no fretting is occurring. The fretting amount is the value obtained by measuring the area S, dividing the value by the cross-sectional area of a new steel filament for 10 steel cords, and averaging the values.

In the case of TBR 11R24.5 tires, this value is Comparative Example 1
In the case of LSR 750R16, Comparative Example 11 was set as 100 as the control tire, respectively, and Tables 1 and 2 were indexed such that the smaller the fretting amount, the larger.
Table is fretting resistance.

Corrosion fatigue resistance (degree of decrease) The test method is as shown in Fig. 9, where the rubber cord 3 taken out from the tire is hung on three pulleys 4 with a diameter of 40 mm as shown in the figure, and a new one is attached via the fixed pulley 5. Tensile load is applied to the weight 6 equivalent to 10% of the cord breaking load, and the 3 pulleys are moved 20 cm repeatedly to the left and right to repeatedly bend the cord to cause the cord to fatigue fracture and the number of repetitions until the cord breaks is 10 cords. The value obtained by deciding the degree of deterioration of the new tire cord is 100, which is the degree of decrease in corrosion fatigue resistance.
Corrosion fatigue resistance shown in Table 1 and Table 2 is the above value.
In the case of TBR 11R24.5 tires, comparative example 1 is used, and LSR 7
In the case of 50R16, each of Comparative Example 11 was set as 100 as a control tire and is shown by an index value. The larger the value, the better the corrosion fatigue resistance.

Side trauma resistance Steel cord used in the prototype tire was vertically embedded in rubber in a lengthwise direction of 3 mm in thickness, 50 mm in width, and 300 mm in length. Split tension is applied, the blade die with a weight of 20 kg is dropped from above at right angles to the cord direction, and the side damage resistance is compared by the height at the time of cutting. Tables 1 and 2 show this property with the values of the control tires of Comparative Examples 1 and 11 as 100, and the larger the value, the better the side damage resistance.

Carcass ply end fracture resistance Buffing the tread rubber of the prototype tire, the carcass ply end fracture resistance is evaluated in a state where the belt layer is not heated and the belt layer is not damaged. Specifically, load each prototype tire
JIS 200%, speed 60kg / hr, internal pressure 8.25kg / for 11R24.5
In the case of cm ² and 750R16, it is rotated on the drum under the condition of the internal pressure of 8.0 kg / cm ² , and when the vibration increases due to the separation at the tip of the carcass ply cord, the drum travel distance is used as a comparison example. 1 and the control tires of Comparative Example 11 were compared with those of the control tire, and indicated by an index. The larger the value, the better the bead durability.

Adhesion resistance (decrease in adhesion) 300cc of water is enclosed in a trial tire, load JIS 200%, speed
60 km / hr, turning in on the drum internal pressure 7.25kg / cm ^2, 750R16 condition of the internal pressure 8.0 kg / cm ² in the case of the case of 11R24.5, stopped after 20,000 km running, low temperature (-60 ° C. ), The four cords were peeled from the rubber, and the amount of rubber remaining on the cord was measured for each cord with an image analyzer at the portion where the decrease in the amount of rubber was the largest, and Comparative Example 1 and Comparative Example It is shown as an index in comparison with those of 11 control tires. The larger the value, the better the adhesion resistance.

Confirm the effect of the tread with trauma.From the inside of the tire, make a hole in the center of the tread, cut only the ply cord, and then enclose 300cc of water, and use the same conditions and the same method as above for corrosion fatigue resistance, fretting resistance and resistance. The adhesiveness was evaluated.

Weight reduction effect The steel cord used for the prototype tire is filled with carcass coating rubber to form a ply treat composite,
In order to obtain the same strength as the ply treat of the control tire of Comparative Example 1 as a composite, the weight reduction effect by reducing the number of impacts when the number of impacts of each trial treat is changed is a steel cord used per tire. The weight used is shown in Comparative Example 1 and Comparative Example 11 as a control tire contrast index. The smaller the value, the better the weight reduction effect.

Method of measuring elongation P ₁ After removing the rubber from the steel cord sample taken out from the tire, the length between chucks was 200 mm and the pulling speed was 5 mm.
/ min, full scale 10kg at Instron type tensile tester load-elongation test to calculate the elongation between load 0.25 ~ 5kgf / book, and the result of 50 tests is arithmetically averaged and elongation P ₁ did.

The performance evaluation results of the prototype tires described above are based on the TBR 11R2
For 4.5 tires, see Table 1 below, and also LSR 750R1
The six tires are shown in Table 2 below.

From the test results shown in Tables 1 and 2, the following was confirmed.

First, the case of the TBR11R24.5 tire shown in Table 1 will be described.

The twist structures of Examples 1 and 5 to 7 are all 1 × 5, but in Example 5, the tensile strength is slightly deviated from the optimum range in relation to the filament diameter, so that the case strength is set due to the constraint of the driving limit. It is slightly lower than in Example 1. For this reason, the side damage resistance is slightly lower than in Example 1, and the carcass ply edge end fracture resistance is also slightly deteriorated because the number of driving is large. However, compared with the control of Comparative Example 1, all the performances are significantly improved.

In Example 6, since the filament diameter is at the lower limit of the optimum range in relation to the tensile strength, the case strength is lower than the driving limit constraint. Therefore, the side trauma resistance is Example 1
The carcass ply edge fracture resistance is somewhat worse because the number of driving is higher than that of the carcass ply. However, the comparison with the control of Comparative Example 1 is sufficiently good, and all other performances are significantly improved.

Example 7 is an example in which the filaments have different diameters and have two types of filament diameters. In this example, all the performances of the control are good.

Example 4 is an example of a structure in which a spiral of 1 × 5 + 1 is wound, and it is considered that buckling does not easily occur due to winding the spiral. However, due to the spiral, no matter how loosely it is wound, the rubber does not sufficiently penetrate into that portion, and the rubber permeability is poor, and the durability is slightly reduced as compared with Example 1, but the control No problem compared to.

Examples 2 and 3 are examples of 1 × 3 and 1 × 4 twisted structures, respectively, and the number of filaments is smaller than that of Example 1.
Therefore, it is necessary to maintain the case strength at a certain level or higher in order to maintain the side damage resistance. Therefore, in these examples, the filament diameter is increased and the number of implants is increased. For this reason, the corrosion fatigue resistance and carcass ply edge fracture resistance are slightly worse than in Example 1, but they are significantly improved in comparison with the control.

On the other hand, Comparative Example 2 is an example in which P ₁ is too small, which results in poor rubber permeability, and particularly when the tread is cut, the corrosion fatigue resistance, fretting resistance and adhesion resistance are both controlled. At almost the same level, there was almost no improvement effect, and the adhesion resistance was rather poor.

Comparative Example 3 is an example in which the tensile strength is too low, the case strength is significantly reduced, and the side damage resistance is significantly reduced. It is necessary to increase the number of driving in order to secure the fracture resistance of the end of the carcass ply.

Comparative Example 4 is an example in which the number of driving is increased in order to enhance the side damage resistance, but conversely, the carcass ply end edge fracture resistance is significantly reduced.

Comparative Example 5 is an example in which P ₁ is too large. Therefore, the movement of the filament is violent, the adhesion resistance is deteriorated, and the factors of driving disorder are also added, and the corrosion fatigue resistance and fretting resistance are also improved so much. Absent.

Comparative Example 6 is an example in which the filament diameter is too small. In this example, the case strength is insufficient even when the filament is driven up to the impact limit, the side scratch resistance is not improved, and the carcass ply end edge fracture resistance is significantly reduced. . Further, when the tire side is collided with a curb, the cord is bent due to buckling.

Comparative Example 7 is an example in which the filament diameter is too large. In this example, since the filament diameter is too large, the corrosion fatigue resistance is lower than that in Comparative Example 1.

Comparative Examples 8 and 9 are 1 × 2 and 1 × 6 twisted structure examples, respectively. In the case of 1 × 2, the filament diameter is increased so that the corrosion fatigue resistance is not deteriorated because the number of filaments is too small. Even so, the side trauma resistance may decrease. For this reason, when the number of drives was increased close to the drive limit, the cord spacing became narrower, and the carcass ply end fracture resistance was significantly reduced compared to the control. Further, since the rubber permeability is low, the cushioning effect of the rubber is small, which affects the reduction of the case strength and deteriorates the side damage resistance.

On the other hand, in the case of 1 × 6, since the twisted structure is unstable, one filament is dropped and the rubber permeability is deteriorated.
In particular, since one filament is entangled with each other, corrosion resistance against control is poor, and adhesion resistance during tread cutting is also poor.

Further, Comparative Example 10 is an example in which P ₁ is too small as 0.25, rubber penetration is not sufficient in this example, and corrosion fatigue resistance and adhesion resistance are significantly reduced especially when external damage is caused on the tread. Absent.

Next, the case of the tire of LSR750R16 shown in Table 2 will be described.

Example 8 has a 1 × 5 twist structure and a filament diameter of 0.21 m.
This is an example of m and tensile strength of 380 kg / mm ^{2. In} this example, the performances such as corrosion fatigue resistance and fretting resistance are significantly better than the control of Comparative Example 11.

Examples 9 and 10 are examples of 1 × 3 and 1 × 4 twisted structures, respectively, and the filament diameter is increased or the number of implants is increased in order to keep the case strength above a certain value. In these examples, the various performances are slightly worse than in Example 8, but the overall performance is significantly improved in comparison with the control of Comparative Example 11.

Example 11 is a case where there is a spiral. When the spiral is present, the rubber permeability to the cord tends to be inferior, and the durability is lower than that of Example 8, but it is good in comparison with the control of Comparative Example 11.

Comparative Example 12 is an example of a 1 × 2 twist structure. in this case,
As in Comparative Example 8, the rubber has a small cushioning effect,
When the number of driving was increased to maintain the strength of the case, the carcass ply end fracture resistance deteriorated. Further, even if such a measure is taken, the side damage resistance is worse than that of the control because the case strength is still low.

Comparative Example 13 is an example of a 1 × 6 twisted structure, but in this example as well, as in Comparative Example 9, one cord dropped,
Since it has a two-layer twist structure, rubber permeability is poor. In particular, the adhesiveness at the shoulder portion during tread cutting is poor.

Industrial Applicability As is clear from the tire performance evaluation results shown in Tables 1 and 2 above, all the performances of the prototype tire of the present invention have been significantly improved.
The durability life of heavy-duty radial tires such as radial tires for buses and radial tires for light trucks can be significantly improved.

Claims (4)

(57) [Claims] 1. A carcass ply having at least one layer of carcass ply wound around the bead core from the inside to the outside arranged at an angle of substantially 90 ° on the equatorial plane of the tire and having a road index of 100 according to ISO 4209/1. In the heavy load radial tire having the above 121 or less, the reinforcing material of the carcass ply has a filament diameter of
Metal cord with a single twist structure consisting of 3 to 5 metal filaments of 0.13 to 0.32 mm, and an elongation P ₁ of 0.35 to 1.0% as an arithmetic mean value under a load of 0.25 to 5 kgf / fiber Is arranged such that the cord gap at the end of the carcass ply is 0.25 mm or more, and the tensile strength TS (kgf / mm ² ) of the metal filament and the filament diameter d (mm) are the following 1) to 3). , 1) When the number of metal filaments is 5 (In the formula, d = 0.13 to 0.25) 2) When the number of metal filaments is 4 (In the formula, d = 0.14 to 0.25) 3) When the number of metal filaments is 3 (In the formula, d = 0.15 to 0.25) The radial tire for heavy load is characterized by being satisfied. 2. The tensile strength TS (kgf / mm ² ) of the metal filament
And the filament diameter d (mm) are further 1) to
Relationship 3), 1) When the number of metal filaments is 5 (In the formula, d = 0.18 to 0.25) 2) When the number of metal filaments is 4 (In the formula, d = 0.19 to 0.25) 3) When the number of metal filaments is 3 The radial tire for heavy loads according to claim 1, which satisfies the formula (d = 0.21 to 0.25). 3. At least one layer of carcass ply wound around the bead core from the inside to the outside arranged at an angle of substantially 90 ° on the equatorial plane of the tire and having a load index of 122 according to ISO 4209/1. In the heavy duty radial tire as described above, the filament diameter as the reinforcing material of the carcass ply is
Metal cord with a single twist structure consisting of 3 to 5 metal filaments of 0.13 to 0.32 mm, and an elongation P ₁ of 0.35 to 1.0% as an arithmetic mean value under a load of 0.25 to 5 kgf / fiber Are arranged such that the cord gap at the end of the carcass ply is 0.25 mm or more, and the tensile strength TS (kgf / mm ² ) of the metal filament and the filament diameter d (mm) have the following relations 1) to 3). , 1) When the number of metal filaments is 5 (In the formula, d = 0.15 to 0.32) 2) When the number of metal filaments is 4 (In the formula, d = 0.16 to 0.32) 3) When the number of metal filaments is 3 (In the formula, d = 0.17 to 0.32) Radial tire for heavy load characterized by satisfying the following. 4. Tensile strength TS (kgf / mm ² ) of metal filament
And the filament diameter d (mm) are further 1) to
Relationship 3), 1) When the number of metal filaments is 5 (In the formula, d = 0.21 to 0.32) 2) When the number of metal filaments is 4 (In the formula, d = 0.23 to 0.32) 3) When the number of metal filaments is 3 The radial tire for heavy load according to claim 3, wherein d = 0.27 to 0.32 is satisfied.