JPH0399904A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To improve the break resistance of a belt cord at the rapid turning of a car by forming a steel cord used for a belt layer by twisting a few filaments specified in their diameter into single twist structure having a specified twist pitch, and setting their twisting angle within a specified angular range. CONSTITUTION:A pneumatic radial tire is provided with a belt layer which is formed of a steel cord arranged outside a crown part of a carcass body composed of a ply cord having actually radial arrangement and further inside a tread. In such a tire, the steel cord is formed by twisting 2-4 filaments being 0.28-0.50mm in their diameter into 1Xn single twist structure having a twist pitch of 18-28mm. A twist angle of the steel cord taken out of the tire is established within a range of 84-87.5 deg.. Thus the break resistance of a belt cord at the rapid turning of a car can be sharply improved without the deterioration of various performances of the tire.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a pneumatic radial tire that has significantly improved belt cord bending resistance during fast turns without deteriorating various tire performances. It is something.

(Prior art) As a technology for improving the cord breakage resistance of pneumatic tires using steel cord belts, for example, as seen in Japanese Patent Application Laid-Open No. 64-36502, three filaments are twisted together. By adopting a special belt structure made by coating this with soft belt coating rubber, it is known that the technology significantly improves the belt cord breakage resistance, and at the same time improves the ride comfort and heat resistance of the tire. .

Furthermore, in Japanese Patent Application Laid-Open No. 134308/1983, three metal filaments are formed as a belt reinforcing cord with a predetermined filament arrangement in the same direction, and the twist pitch is 6.5 to 20 mm, and one cord is 5.0k per hit
When a cord with an elongation of 0.2 to 1.24% is placed under a load of
．． Arrange the belt width (B) so that it is 5 to 1.3 mm.
By configuring the ratio (B/H) between the contact width (H) and the ground contact width (H) of the tread to be 1.2 or less, it is possible to achieve both cord bending resistance and weight reduction of the metal cord, and also to improve rolling resistance. Techniques have been disclosed that significantly improve durability. In addition, in the same publication, the steel filament for belt reinforcement has a strand content of 0.75 to 0.85% by weight and a tensile strength of 280 kg/
It is said that the thickness is preferably 2 mm or more.

Similarly, in WO88105624 related to an international patent application, in a 3×8 twisted structure, the wire diameter (δ) is set to 0.
．． 27~0.35mm, twist pitch 14mm, P
, L, E, (elongation under partial load) are set to 0.2 to 0.45% to significantly improve the rubber permeability into the cord and the fatigue resistance.

(Problem to be solved by the invention) Single-strand structure of steel cord for reinforcing radial tires 1
×n (n=2 to 6) is preferable because it has a simple structure and can be manufactured at low cost, and many documents regarding this are known.

When transitioning from the currently widely known 1×5 single-stranded cord to a more simplified cord, the strength of each cord decreases, so the tensile strength of the filament steel must be increased or the filament diameter must be increased. Furthermore, it is necessary to increase the number of strikes to maintain appropriate belt strength. However, when the filament diameter is increased, when the cord is embedded in the belt of a radial tire, dynamic deformation during running causes the filament to break, making it unusable.

Therefore, an object of the present invention is to solve the above-mentioned problems with a cord that is simpler than conventional cords, and to significantly improve the bending resistance of the belt cord during rapid turns without deteriorating various tire performances. An object of the present invention is to provide an improved pneumatic radial tire.

(Means for Solving the Problems) The inventors of the present invention have conducted extensive studies on the folding resistance of the belt cord during rapid turning, which is the problem in question, and have found that it is possible to As a result of setting the twist pitch and twist angle of the filaments, which are involved in the bending rigidity as a body and the fatigue resistance of the cord, to an appropriate range, there is a certain range in which the bending resistance of the belt cord can be significantly improved. They discovered this and completed the present invention.

That is, the present invention provides a bell consisting of a steel cord disposed outside the crown portion of a carcass body consisting of substantially radially arranged ply cords and inside the tread.
71, wherein the steel cord has a filament diameter of 0.28 to 0.50 m.
A steel cord made by twisting 2 to 4 m filaments of wood into a 1×n single-strand structure at a pitch of 18 to 28, and the twist angle (θ) of the steel cord taken out from the tire is 84 to 87. .5@ range.

A major factor in increasing bending rigidity is the filament diameter, and the thicker the filament, the more the tire input is suppressed during rapid turns. Therefore, in the present invention, the filament diameter is set to 0.28 mm or more in order to obtain sufficient bending rigidity as a belt layer composite. However, if the filament diameter exceeds 0.50 mm, the weight of the cord exceeds the practical range, so the upper limit is set to 0.50 mm.

Preferably, the filament diameter is within the range of 0.32 to 0.42 mm. For example, in a medium-sized tire of PSR185SR14 size, cord bending can be effectively avoided when the filament diameter is 0.32 mm or more.

Another factor that increases bending stiffness is the twist pitch of the cord. The shorter the pitch, the better the fatigue resistance of the cord. If the pitch is 18 mm or more, it is advantageous in terms of rigidity, but if the pitch is 28 mm or less, the fatigue resistance of the cord is not significantly reduced. Therefore, in the present invention, the twisting pitch of the cord is defined within the range of 18 to 28 twists below the filament diameter. Preferably, it is within the range of 19 to 26 digits.

In addition, in the present invention, the twist angle (θ) of the cord is 1×n
It is specified as 84 to 87.50 under twisting (n = 2 to 4), but this is because if the twist angle (θ) is less than 84°, the belt will not have adequate bending rigidity as a rubber-cord composite. ,
This is because the folding resistance of the belt cord decreases, and on the other hand, if the angle exceeds 87.5°, the fatigue resistance of the cord itself decreases significantly, which is also disadvantageous to the folding resistance of the belt cord.

P, LJ, (elongation under partial load) of such a cord is 1
×4 or 1×3 short twisted structure 0.30 to 0.
A range of 85% is preferred. P, L, E are 0.
If it is less than 30%, the rubber permeability is insufficient and belt cord folding occurs, and if it exceeds 0.85%, the twisting property tends to be disordered, which is disadvantageous in terms of mechanical fatigue resistance.

In the present invention, the single-strand structure 1×n can be applied to any of n=2 to 4, and the twist angle (θ) determined by the cord twist pitch and the cord diameter, which is controlled by the filament diameter. Also shows good belt cord folding resistance in the above range. In particular, for cords with 1×2, iX3 and 1×4 twist structures, 85.5 to 8
Significant performance improvements are possible in the regions of 7.5', 85-87° and 84-86.5°.

(Example) Next, the present invention will be explained based on examples.

Various steel cords for reinforcing belts shown in Table 1 below were manufactured, and various radial tires of tire size PSR185SR14 were prototyped using these steel cords for belt reinforcement. Such a radial tire has two belt layers of predetermined steel cords, each having two belt layers in the circumferential direction of the tire.
They are arranged so that they intersect at an angle of 2 degrees. Further, as the carcass, one ply having a polyester fiber cord was used.

These prototype tires were subjected to tire performance evaluation tests as shown below.

At least 5 belt cords dissected and extracted from the belt layer of the tire are dissolved in nitrobenzene, and for each cord, the average cord radius (R) is determined from the length of 5 inches or more in the longitudinal direction of the cord using the projection method. , from this cord radius (R) and twist pitch (S), the following formula is obtained: P, L, lE of the steel cord.

At an initial load of 100 g, elongation (%) between a load of 0.25 kg and 5 kg was measured using an Instron.

The vehicle equipped with the test tire was rotated approximately 2 times with a lateral gravity of 0.7G.
After making 300 figure-8 turns at 5 kg/hour, take out the belt layer of the tire 1. Measure the number of folds in the belt cord around the entire circumference using I asked for

The evaluation results in Table 1 are expressed as an index with Comparative Example 1 as a control and expressed as 100. The larger the number, the better the result.

The results obtained are shown in Table 1 below.

The twist angle (θ) was determined and the average value for each cord was taken as the final twist angle.

(Effect of the invention) As can be seen from the test results shown in Table 1, the pneumatic radial tire of the present invention has a 1×n structure (n=2 to
By optimizing the combination of filament diameter, twisting pitch, and twisting angle in the steel cord for reinforcing the belt (4), the bending resistance of the belt cord during rapid turning has been improved without deteriorating various performances in the winding and winding motions. I was able to improve it significantly.

Claims (1)

[Scope of Claims] 1. A pneumatic radial tire comprising a belt layer made of steel cords arranged on the outside of the crown portion of the carcass body and inside the tread and made of ply cords in a substantially radial arrangement, comprising: The cord is a steel cord made of 2 to 4 filaments with a filament diameter of 0.28 to 0.50 mm twisted together in a 1×n single-strand structure with a twisting pitch of 18 to 28 mm, and the steel cord is taken out from a tire. A pneumatic radial tire having a twist angle (θ) in the range of 84 to 87.5°. 2. The pneumatic radial tire according to claim 1, wherein the filament diameter is 0.32 mm or more. 3. P. of the steel cord before being embedded in the tire. L. E
．． The pneumatic radial tire according to claim 1, which has an elongation under partial load of 0.30 to 0.85%. 4. The pneumatic radial tire according to claim 1, wherein the steel cord has a 1×4 single-strand structure, and the twist angle (θ) of the cord is in the range of 84 to 86.5 degrees. 5. The pneumatic radial tire according to claim 1, wherein the steel cord has a 1×3 single-strand structure, and the twist angle (θ) of the cord is in the range of 85 to 87 degrees. 6. The pneumatic radial tire according to claim 1, wherein the steel cord has a 1×2 single-strand structure, and the twist angle (θ) of the cord is in the range of 85.5 to 87.5 degrees.