JPH059881A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To obtain pneumatic radial tires having increased high-speed performances, improved flex fatigue resistance and maneuvering stability by using organic yarn as a belt material. CONSTITUTION:Pneumatic tires using an elliptic or rectangular cord which is prepared by impregnating and coating a cord-like yarn bundle comprising a great number of filaments having >=15g/d tensile strength and 1-15 denier fineness of filament with 30-70 % resin having <=150kg/mm<2> elastic modulus in tension having a flatness ratio of cross sectional shape of major axis (b)/ minor axis (a) of 1.5-5 as cord for belt reinforcing of at least one layer.

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, and more particularly to a pneumatic radial tire having improved high-speed performance, flex fatigue resistance and steering stability.

[0002]

2. Description of the Related Art The popularization of pneumatic radial tires today is due to the fact that the radial structure provides superior steering stability, high speed resistance and wear resistance as compared with conventional bias tires. Generally, a radial tire has a structure in which a carcass formed by arranging cords in the radial direction of the tire is supported by a pair of beads, and a belt layer surrounds the carcass. This belt layer is generally composed of two or more cord layers in which cords are arranged at an angle of 10 to 30 with respect to the tire circumferential direction, and the carcass has carcass cords arranged at approximately 90 ° with respect to the circumferential direction. It is formed from one or two plies.

The carcass portion and the belt layer play an important role in maintaining the strength of the radial tire together with the bead portion. The first feature of radial tires is
Located in this belt layer and carcass. The carcass portion gives the tire flexibility, while the belt layer restrains the carcass portion, which acts like a trough of a trough.

By the way, recently, with the development of highways, tires having higher high-speed performance have been required, and the development of new materials for belt layers has become an urgent task. Steel cords are mainly used in the belt layers of conventional radial tires, but this steel belt has a problem of being heavy, that is, a big problem for tires that require high speed due to the development of highways, automobiles, etc. Have Heavy steel cords increase growth to the outside of the tire due to centrifugal force during high-speed rotation, which increases movement inside the tire and increases rolling loss. Further, this loss causes heat generation, which leads to tire destruction. Therefore,
Steel cord belts are not suitable for tires that require higher speed performance.

On the other hand, recent research on organic fibers has been remarkable, and in particular, a lightweight, high-strength, high-modulus fiber material that has the potential to replace steel cords by liquid crystal spinning, super-drawing, gel spinning, etc. It has appeared. For example, aramid fiber, carbon fiber, ultra high strength polyethylene fiber, high strength PVA fiber, polyoxymethylene fiber, wholly aromatic polyester fiber and the like. These fibers are about one-fifth the weight of steel cords, have strengths comparable to those of steel cords, and elastic characteristics comparable to steel cords.

[0006]

However, since these organic fibers are composed of a large number of thin filaments, the method of adding and twisting them in the same manner as in the conventional organic fiber tire cord is Since the flexural and compression rigidity is low due to the decrease in the tensile elastic modulus and the flexibility of the thin filament, there arises a problem that the belt rigidity as a radial tire decreases. For this reason, sufficient belt rigidity like that of steel cords cannot be obtained, and the steering stability, high-speed durability, wear resistance, etc. of the tire are deteriorated.

Therefore, an object of the present invention is to solve the above problems and to provide a pneumatic radial tire in which organic fibers are used as a belt material to enhance high-speed performance and to improve bending fatigue resistance and steering stability. Especially.

[0008]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that when using an organic fiber cord composed of a large number of filaments as a belt material, the tensile elastic modulus of the cord is As a binding method that does not lower the compression modulus and increases the compression modulus, it has been found that a method of binding by impregnating and adhering a resin to the organic fiber bundle without twisting the organic fiber bundle is effective. However, the fiber cord without twist has a drawback in fatigue resistance. Therefore, as a result of further diligent research to find out this solution, by flattening the cross-sectional shape of such a cord (elliptical or rectangular),
It was found that a fiber cord having a high elastic modulus and excellent bending fatigue resistance can be obtained, and the present invention has been completed.

That is, the present invention has a tensile strength of 15 g /
Cord-like fiber bundles consisting of a large number of filaments of d or more and filament fineness of 1 to 15 denier, preferably 1 to 5 denier are impregnated with 30 to 70% of resin having a tensile elastic modulus of 150 kg / mm ² or less. At least, the elliptic or rectangular cord having the flatness of its cross-sectional shape within the range of 1.5 to 5 in the ratio of major axis (b) / minor axis (a) is used as at least one belt reinforcing cord. The present invention relates to a pneumatic radial tire that does.

The cord-shaped fiber bundle used in the present invention is required to have a tensile strength of 15 g / d or more. If it is less than 15 g / d, the strength of the belt will be insufficient, resulting in an increase in the amount of belt cords used to supplement the strength, which is not preferable. That is, if the number of cords used is increased, the number of belt layers is increased or the number of layers is not increased, the interval between cords is narrowed, the strain of the rubber between cords increases, and the loss due to this causes heat generation, which reduces high-speed durability. I will let you.

Since the cord-like fiber bundle composed of a large number of filaments is used without twisting, the filament surface strain during bending is large, and when the fineness of the single fiber is larger than 15 denier, the fatigue resistance is deteriorated. When it is thinner than 1 denier, the filament has irregularities, dust inside the filament,
Since stress concentrates on defects due to micro-bubbles and the like, the strength is weakened, so the range is 1 to 15 denier, preferably 1 to 5 denier.

In the present invention, as a method for binding the above filaments, a method of impregnating and adhering a resin between the filaments is adopted. Examples of such resins include thermosetting resins such as epoxy resins, unsaturated polyester resins, phenol resins, melamine resins, vinyl ester resins, polyimide resins, bismaleimide resins, Friedel Crafts resins, furan resins, silicone resins, and allyl resins. Is mentioned. Also, as the thermoplastic resin, 6,6-nylon,
6-nylon, polyester, polyether ether ketone, polycarbonate, polyacetal and the like can be mentioned. These resins may be two or more types of thermosetting resins, two or more types of thermoplastic resins, or an appropriately selected blend of a thermosetting resin and a thermoplastic resin.

If the resin is too rigid and too brittle as a cured product, it is possible to impart toughness by using a resin modified with an elastomer such as acid-terminated liquid rubber. The tensile elastic modulus of the impregnated resin in the present invention needs to be 150 kgf / mm ² or less. If it exceeds 150 kgf / mm ² , it will be broken locally because it is not flexible, and the deformation will concentrate on the broken part and cause belt breakage.

The amount of these resins impregnated and deposited is 30.
It must be ~ 70%. If it is less than 30%, the resin is not uniformly impregnated and adhered between the filaments, while if it exceeds 70%, the amount of the impregnated resin becomes too large and the strength as a belt cord,
Tensile rigidity decreases. The cord-shaped fiber bundle thus produced has a problem in bending fatigue resistance because it is almost untwisted. Therefore, in the present invention, in order to improve the bending fatigue resistance, the cross-sectional shape of the resin-impregnated cord is flattened,
It was decided to alleviate the filament surface strain during bending. The flatness ratio needs to be within the range of 1.5 to 5 in terms of major axis (b) / minor axis (a). If the flattening ratio is less than 1.5 for the same cross-sectional area, the filament strain in the cord is not so relaxed, and the bending fatigue resistance cannot be improved. Also, considering the strength due to the number of shots, if the flatness ratio is 5 or more, the cord interval becomes narrow, and during the molding process (work before vulcanization), the cord and rubber are easily separated, resulting in poor workability. Productivity drops. More preferably, the flattening rate is 1.
It is within the range of 5 to 3.

Depending on the type of matrix resin, RFL
Before the adhesive treatment, the cord may be pretreated with an aqueous epoxy solution or the like, or surface adhesion activity may be imparted by plasma treatment, corona discharge treatment, acid treatment or the like. Further, as an adhesive system, a dry bonding system in which a resorcin, etc., and a formaldehyde generator such as hexamethylenetetramine, silica, etc. are compounded in a rubber compound for coating a cord may be used. On the other hand, the cord adhesive treatment step can be omitted.

[0016]

EXAMPLES Example 1, Comparative Examples 1 and 2, In order to investigate the relationship between the rigidity of the resin and the local flexural fracture of the cord, a Kevlar fiber bundle of 3,000 denier manufactured by Dupont Co. was thermoset with bisphenol A type epoxy as the main component. We made a prototype cord for radial tire belts by impregnating and adhering a functional resin. The content (parts by weight) of the thermosetting resin and the curing conditions are as shown in Table 1 below.

[0017]

[Table 1]

Examples 2-4 and Comparative Example 3 In Examples 2-4, the same resin as that of Example 1 was used, and the flatness of the cross-sectional shape was changed by changing the die shape. The relationship between the cross-sectional shape and the fatigue resistance of the resin-impregnated fiber bundle was investigated. The size of the prototype tire was 195/70 HR 14, the belt had a two-layer structure, and the number of cords was changed as shown in Table 2 depending on the flattening ratio of the cord.
They were placed so that they intersect each other. In addition, the carcass part
It has a two-layer structure using 1000 d / 2 polyester cord.

In the test, the trial tire was run on a drum with an internal pressure of 1.0 kg / cm ² and a load of 600 kg for 10,000 km (speed 60 km / hr), and then the belt cord was dissected and taken out for strong measurement. The strength retention was calculated by dividing by the strength of the running tire belt cord and used as a guideline for fatigue resistance.

[0020]

[Table 2]

From Table 2, as for the belt cord of the resin-impregnated fiber bundle, the flattened cord shape has higher strength retention and better fatigue resistance than the circular shape b / a = 1. I understand. As a result, the cord cross-sectional shape b / a is
The range of 1.5 to 5 is considered to be a practical range. Examples 6 to 8 and Comparative Examples 4 to 6 The aramid untwisted fiber bundle cords made by impregnating and adhering the resins shown in Table 1 above were set to have a cross-sectional shape and belt strength shown in Table 3 below. The belt cord was applied to tires of tire size 195/70 HR 14. The belts of these tires had a two-layer structure, and were arranged so that they crossed each other at 20 ° in the tire circumferential direction with 34 driving numbers per 5 cm width. The carcass had a two-layer structure using 1000 d / 2 polyester cord.

The conditions and detailed contents of the performance evaluation items of the above-mentioned test tire are as follows. Tire rolling resistance index A test tire adjusted to an internal pressure of 1.70 km / cm ² was installed on a drum with an outer diameter of 1708 mm, and after applying a JIS 100% load, 80
Preliminarily run for 30 minutes at km / hr and readjust the air pressure to 200 km
After the drum rotation speed was increased to a speed of / hr, the drum was coasted and calculated from the moment of inertia until the drum rotation speed decreased from 185 km / hr to 20 km / hr.

Tire rolling resistance = ds / dt (ID / RD ² + It / Rt ² ) -resistance of drum alone Formula ID: moment of inertia of drum It: moment of inertia of tire RD: radius of drum Rt: tire radius The rolling resistance value at 50 km / hr obtained in step 1 was obtained as a representative value. The environment was measured in a room controlled at 24 ± 2 °. Test tire index = 100 +
It was expressed as 100 x (representative value of control tire-representative value of test tire / representative value of control tire). As a result, the smaller the rolling resistance value, the larger the index, and therefore the better the fuel economy.

The control tire was the tire of Comparative Example 4. Steering stability index test In a driver's feeling test, the control tire (Comparative Example 4) was evaluated as an index with 100 points. The larger the index, the better the result. 8-shaped turning test In the 8-shaped turning test, an 8-shaped curve was drawn by using an automatic driving device, and after this was lapped 300 times, the tire was dissected and the number of broken belt layer cords was examined.

The number of breaks of the belt layer cord of the control tire (Comparative Example 4) was examined, and the number of breaks of the tires of Examples 7 to 9 and the tires of Comparative Examples 5 and 6 were obtained. An index is displayed according to the number of test tire breakage × 100. The larger the index, the better the result.

The results obtained are also shown in Table 3.

[0027]

[Table 3]

From the test results shown in Table 3, the following was confirmed. In the case of the belt cord according to the present invention, steering stability tended to be better when the shape (b / a) was increased, similar to steel cord. This is because the resin-impregnated cord is unlikely to deform with respect to the side force. With respect to rolling resistance, in the case of the belt cord according to the present invention, when the shape (b / a) is increased, which is similar to that of a steel cord, the amount of the covering rubber used is reduced, which is in a good direction.

It was also found that when the cord shape (b / a) is increased, the high-speed durability also decreases the amount of the covering rubber used, reduces the deformation due to centrifugal force, and improves the level.
The breakage of the cord by the figure-8 turning test was better than that of the steel cord belt layer in each of the examples, and the cord surface strain was eased as the flatness (b / a) of the cord shape increased, but it was difficult to break. 15 cord impregnated resin
When it was 0 kg / mm ² or more, many breaks occurred.

[0030]

As described above, in the pneumatic tire of the present invention, when an organic fiber cord composed of a large number of filaments is used as a belt material, the organic fiber bundle is impregnated with a resin without twisting. It is possible to improve the high-speed performance and improve the bending fatigue resistance and the steering stability by sticking and flattening the cord cross section.

Claims (1)

Claims: 1. A cord-shaped fiber bundle composed of a large number of filaments having a tensile strength of 15 g / d or more and a filament fineness of 1 to 15 denier, and a tensile elastic modulus of 150 kg / mm ^2.
The following resin is impregnated with 30 to 70% and the flatness of the cross-sectional shape is set at a ratio of major axis (b) / minor axis (a) within the range of 1.5 to 5 and elliptical or rectangular cord is at least one belt A pneumatic radial tire characterized by being used as a reinforcing cord.