JPH05279975A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To prolong the life of a tire by preventing the lowering of strength of an outer sheath wire filament of a compact cord having 1X12 structure and constituting a carcass ply of a radial tire and improving the durability of the tire cord. CONSTITUTION:The inner sheath wire filament of a compact cord having 1X12 structure has a diameter equal to or larger than the diameter of a wire filament of the core. The diameter of the outer sheath wire is made to be smaller than those of the core and the inner sheath wire filaments. A wrapping wire filament is wound around the coaxial layer sheath composed of the above filaments to form a spirally wound wire. The interior angle facing the outer sheath of the circumscribed nonagon of the cross-sectional contour of the coaxial layer is made to be >=124 deg. and <180 deg. and the interior angle facing the inner sheath is made to be <180 deg. by selecting the filament diameters. A metal cord having the above construction is used as a reinforcing element of a carcass ply of the objective pneumatic radial tire.

Description

Detailed Description of the Invention

[0001]

[Industrial application] Metal cords are useful for strong carcass reinforcement of pneumatic radial tires, and are widely used in this type of usage in accordance with recent demands for performance improvement in pneumatic radial tires. Has been done. This specification will be described below in connection with the results of the development research aiming to further increase the utilization efficiency of the metal cord for reinforcing the carcass, and particularly to improve the fatigue resistance and the strength retention.

[0002]

2. Description of the Related Art In order to improve the corrosion fatigue resistance of a two-layer twisted or at most three-layer twisted metal cord, a so-called compact structure in which the twist pitch of each layer is equal is used.
It is effective to increase the contact area between both wire filaments of the inner layer (that is, the central basic structure: hereinafter abbreviated as the core) and the outer layer (that is, the sheath).

However, at that time, in a normal compact cord (hereinafter abbreviated as NCC) in which wire filaments having the same wire diameter are used for the core and the sheath, a large contact pressure is generated between the adjacent wire filaments in the sheath under the action of cord tension. However, a phenomenon in which the wire filament breaks early due to the fretting of that portion as a core is observed, and as a result, the breaking life of the metal cord is rather shorter than that of a normal layer twisted cord having a different twist pitch.

In order to reduce the contact pressure between adjacent wire filaments in a layer in NCC, a part or all of the wire filament wire diameter may be made slightly thinner than the wire filament used for the core. -The reason why the effect of increasing the area adjacent to the sheath is properly exhibited and the corrosion fatigue resistance is improved is that Japanese Patent Application No. 60-35215 (Japanese Patent Application Laid-Open No. 61-201091) and Japanese Patent Application No. 60-35216 (Japanese Patent Application No. Kaisho 61
-201092 publication).

[0005]

Generally, when a metal cord is used for a tire cord, for example, during the load running due to the operation of the tire, the fretting wear reduces the cross-sectional area of the wire filament and the cord strength decreases. However, if the reduction of the cross-sectional area of only some of the wire filaments in the cord is severe at that time, the wire filaments are likely to be subjected to impact tension and breakage under repeated bending.

Once the wire filament breaks,
The tensile stress of other wire filaments is increased, which promotes fatigue fracture of the cord. Therefore, in order to increase the durability of the cord, it is necessary to prevent some wire filaments in the cord from prematurely breaking. It is desirable, if unavoidable, that the reduction in wire filament strength in the cord is almost uniform throughout each wire filament.

[0007] Actually, according to the result of a follow-up investigation of the deterioration of the strength of the wire filament in the tire after use, for example, the deterioration of the strength of the wire filament of 1 × 12 structure NCC is not uniform, and compared with the core and the inner sheath. It was found that the strength reduction in the wire filaments that make up the outer sheath was extremely large, and in particular, the main cause of this strength reduction was fretting wear with the wrapping wire filaments, which are usually called spiral windings. The weakening of the sheath is much more pronounced than that which occurs with normal 3 + 9 structural twisted cords. In the case of NCC where the wire filament diameters that make up the cord are all the same, this phenomenon is improved by making the wire filament of the outer layer, that is, part or all of the sheath, slightly smaller than the core basic structure (internal) wire filament. Almost the same occurs in the compact code.

Therefore, it is an object of the present invention to effectively prevent a decrease in strength that occurs first in the wire filament of the outer sheath, improve the durability of the tire cord, and extend the service life of the pneumatic radial tire.

[0009]

SUMMARY OF THE INVENTION The present invention has a central basic structure consisting of three wire filaments of the same diameter. Nine wire filaments adjacent to each other around this central basic structure are In the inner sheath of three wire filaments each having the same diameter as or larger than the wire filament of the central basic structure, and each one of the two wire filaments in the central basic structure, For the remaining 6 filaments facing each of the two filaments, the outer sheath consisting of a wire filament having a diameter smaller than that of the core filament of the central basic structure is appropriate and twisted in the same pitch and in the same direction as the central filament. And a single wrapping wire filament around this coaxial layer An inner angle α facing the wire filament of the outer sheath in a hypothetical 9-sided polygon circumscribing the cross-sectional contour of the coaxial layer, which has a spiral winding wound around it, is 124 ° or more and less than 180 °. It is a pneumatic radial tire in which a metal cord having an inner angle β of less than 180 ° and a wire diameter distribution satisfying a relation of α <β is used as a reinforcing element of a carcass ply.

Here, in a compact structure cord in which the twist pitch of the core and the sheath is the same, when the wire filaments of two or more kinds of wire diameters are combined, the outline of the cord cross section is made closer to a circle, so that the outer sheath wire filament and the spiral wire are particularly effective. It becomes possible to guide the contact pressure equalization with the wrapping wire filament used for the winding and suppress the local fretting in the outer sheath.

Now, FIG. 1 shows a cross section of a compact structure cord according to the present invention. In FIG. 1, reference numeral 1 designates a core consisting of three wire filaments of the same diameter, that is, a central basic structure.
2 is an inner sheath, 3 is an outer sheath, and 4 is a spiral winding, and the inner sheath 2 and the outer sheath 3 form a coaxial layer. The central basic structure 1 and a sheath or coaxial layer composed of nine wire filaments arranged adjacent to each other around the central basic structure 1 are arranged in the same direction,
When twisted to the same pitch, the inner sheath 2 is a coaxial layer made up of three wire filaments, each of which is in contact with both adjacent filaments of the wire filaments of the central basic structure 1 formed of wire filaments of the same diameter. The remaining six coaxial layers are the outer sheath 3.

By the way, for comparison, in the 3 + 9 structure twisted cord shown in FIG. 2 (a), the distance from the cord center to the sheath wire filament center is always arranged at equal intervals, and the cord cross section and circumscribed polygon Is a regular hexagon and all interior angles are 140 °, while in NCC, the polygon circumscribed in the code cross section is hexagonal as shown in Fig. 2 (b), and its interior angle is 120 °.

Further, in a compact structure cord composed of wire filaments of two or three kinds of wire diameters, the polygon circumscribing the cord is a hexagon and the size of the inner angle varies depending on the combination of the wire diameters. As described in.

[0014]

As already apparent, the nonuniformity of the reduction in strength of the wire filament of the compact cord is due to its unique geometric structure. That is, the cause of local fretting in the outer sheath is that the contact pressure between the wire filament of the outer sheath and the wrapping wire filament along the outer sheath becomes closer as the cord cross-sectional contour shape becomes closer to a triangle. This is not equal to that on the filament, but is higher in the outer sheath portion and lower in the inner sheath portion.

Contrary to this, in the usual 3 + 9 structure twisted cord, the cross-sectional contour shape is originally close to a circle, so that local fretting hardly occurs. Therefore, the above problems to be solved by the present invention are peculiar to the compact structure code.

Assuming an inner angle α on the outer sheath 3 or an inner angle β on the inner sheath in the hexagon 5 circumscribing the cross-sectional profile of the cord shown in FIG.
Is smaller and the difference from β is larger, the local contact force between the spiral winding 4 and each wire filament of the outer sheath 3 increases when tension is applied to the metal cord, and conversely, the spiral winding 4 and the inner sheath 3 The contact force between each wire filament of 3 is reduced because the radius of curvature of the wrapping wire filament of the spiral winding 4 is small facing the wire filament of the outer sheath 3, whereas that of the inner sheath 2 is smaller. This is because the face becomes larger.

Here, the internal angles α and β are 1 × 12 obtained by twisting wire filaments having different wire diameters in the same twist pitch in the same direction.
In the structural twisted cord, when the core wire diameter is d _c , the inner sheath wire diameter is d _i , and the outer sheath wire diameter is d ₀ , the cord cross section is drawn under the following conditions and the angle is measured. The wire filament cross-sectional contour is approximated by a circle. Each wire filament of the core abuts each other. Each wire filament of the inner sheath contacts two wire filaments of the core. Each wire filament of the outer sheath is in contact with the wire filaments of the core and the inner sheath, but there is a gap between the wire filaments of the outer sheath. A hexagon that circumscribes the cord cross section is drawn, and an intersection angle between adjacent sides of the outer sheath 3 that contact the filament is an internal angle α, and an intersection angle of adjacent sides that contact the filament of the inner sheath 2 is an internal angle β.

Therefore, cords having different combinations of wire filament diameters of the core, the inner sheath and the outer sheath were produced as trials and used as tire cords, and the inner angles α and β of the respective 9-angles circumscribing the cross-sectional contours of the metal cords were used. Then, the relationship between the strength reduction amount generated in the wire filament of the sheath after the test running of the tire was examined.

The results are shown in Table 1, and all values of α and β are
It is effective when a gap is formed between the wire filaments of the outer sheath by forming a hexagon that is smaller than 180 ° and satisfies the relationship of α <β, and especially regarding the value of α
It was found that when it is larger than 124 °, preferably 130 ° to 140 °, fretting wear due to contact between the wire filament of the outer sheath 3 and the spiral winding 4 is suppressed, and the strength retention is remarkably improved. ..

[0020]

[Table 1]

[0021]

[Example] The size of the test tire was 10.00R2014PR, and the tire cord made into 15.2 pieces / 2.5 cm carcass ply was the same as the tire cord of Comparative Example 1 with 3 + 9 + 1 structure cord, with a twist pitch of 6 mm per core, and a sheath. About S twist with a twist pitch of 12 mm, and the spiral has a Z direction wrapping with a pitch of 3.5 mm and a wire diameter of 0.15 mm. Comparative Examples 2 and 3 and Examples 1 to 5 have a twist pitch of 12 mm for both the core and the sheath.
The S-twist and spiral of Z direction wrapping with a pitch of 3.5 mm and wire diameter of 0.15 mm. As an evaluation method, tires are 100,000 km
After running the drum for up to, the cord was taken out from the tire and the strength of the filament was measured by the following formula.

[Outer 1] The average value of 9 sheaths for the 3 + 9 + 1 structure cord of Comparative Example 1 and the average value of 6 outer sheaths and 3 inner sheaths for the 1 × 12 + 1 compact cord of Comparative Example 1 were listed.

[0022]

EFFECTS OF THE INVENTION In a cord for a tire having a 1 × 12 + 1 compact structure, by reducing fretting wear due to the spiral winding of the wire filament of the outer sheath, the uniformity of the reduction in the filament strength in the cord is improved and the cord durability is improved. Since the durability is improved, the service life of the pneumatic radial tire can be extended.

[Brief description of drawings]

FIG. 1 is a sectional view of a cord according to the present invention,

FIG. 2 is a cross-sectional view of a comparative code shown in FIG. 2 (a), (b), (c),

3 (a) to 3 (e) are cross-sectional views of cords of an embodiment.

Claims (1)

[Claims] 1. A central basic structure composed of three wire filaments of the same diameter, and nine wire filaments adjacent to each other around this central basic structure, of which two in each of the central basic structures.
Three wire filaments, one for each wire filament, having the same diameter or a larger diameter than the wire filament of the central basic structure, and one wire filament for the central basic structure. The remaining 6 wires facing each other, totaling 6 wires, are suitable for the outer sheath made of wire filaments having a diameter smaller than that of the central basic structure, and are coaxial layers formed by twisting them in the same pitch and in the same direction as the central basic structure. And a spiral winding in which one wrapping wire filament is wound around the coaxial layer, and the coaxial layer faces the wire filament of the outer sheath in a hypothetical 9-sided shape circumscribing its cross-sectional contour. Interior angle α is greater than 124 ° and less than 180 °, similar interior angle for inner sheath A pneumatic radial tire in which a metal cord having β of less than 180 ° and having a wire diameter distribution satisfying α <β is used as a reinforcing element of a carcass ply.