LU100826A1 - Nylon top tablecloth 6.6 - Google Patents

Abstract

A strip or fabric of tows for a tire, made from 6,6 / nylon 6,6 cords, alternately arranged with different lengths of web twist is disclosed. Such a web or cable fabric for a tire improves high-speed durability, tread separation resistance, and impact resistance when used in the form of a crown ply spirally wound at zero degree angle on the belt package in radial-ply type pneumatic tires.

Description

The present invention relates to a new strip or a new cord fabric for a pneumatic tire comprising alternately arranged nylon 6,6 cables having different twists. A new strip or cable fabric of this type for a pneumatic tire improves durability at high speed, resistance to separation of the tread and impact resistance when used in the form of a crown ply wound in a spiral at an angle equal to zero degrees on a pack of belts in pneumatic tires of the radial ply type.

FOUNDATION OF THE INVENTION

In high speed conditions, the external diameter of the tire increases under the influence of the centrifugal forces generated by the tread and the bundle of belts formed by steel cords. Such an increase in diameter or such an expansion of the pneumatic tire increases the pantographic movements of the cables at the edges of the belts, which gives rise to crack initiations, to propagation of the cracks and to separations from the terminal edges to the belts.

Furthermore, the rise in temperature at the edges of the belts under high speed conditions can trigger a deterioration in the local adhesion of the textile top ply band and gives rise to local separations between the tread and the top plies, which can ultimately result in separation of the edges of the belts in a very short period of time on the basis of non-uniform stress distributions.

The crown ply layer which wraps in a circumferential direction around the belt pack prevents excessive expansion of the tire under high speed conditions by exerting compressive forces (restraining forces) on a thick belt pack consisting of layers of steel cables of the diagonal ply type. In order to increase the restriction force, it is usual to use top ply strips having cords of the type with a high number of cords ends (high epdm value) (such as nylon, 1400x2, 110 epdm or nylon 1400x1, 140 epdm, etc.).

At present, the most widely used materials for crown plies represent nylon 6,6 cords and hybrid aramid / nylon cords which are wound in a spiral on a bundle of belts forming angles of 0 to 5 degrees from the equatorial plane of the tire.

Nylon cords have excellent resistance to fatigue when subjected to bending and axial compression, as well as bielastic characteristics of tensile strength, which makes it possible to have an easy treatment during the making of the pneumatic tire. In addition, the generation of a thermal shrinkage force following an increase in the operating temperature under high speed conditions improves the resistance to separation at the edges of the belts, as well as durability at high speed.

It is well known that hybrid cables comprising high modulus and low modulus wires having a bielastic behavior of tensile strength are also used to act as crown plies in pneumatic tires intended for high speeds. The low modulus component of the hybrid cable allows easy lifting of the belt pack in the absence of excessive formation of tight tight cords due to its high extensibility and the high modulus component is effective under service conditions. When hybrid cables are used as the crown ply, the total thickness of the crown ply layer and the rubber content can be reduced, and the high modulus component of the hybrid cable increases the restrictive force and improve durability at high speed.

U.S. Patent 4,284,117 describes a nylon top web which is formed from individual yarns, rather than from cords. The crown ply is thinner than conventional crown plies in that it has characteristics of superior flexibility and superior heat dissipation. However, the limited fatigue resistance exhibited by cables of individual plies represents the major drawback of said request. The increase in torsion to improve the resistance to fatigue gives rise to a dramatic fall in the modulus and the restraining force.

In US Patent 5,115,853, a radial ply type tire is described having a crown ply structure which is disposed in the radial direction outside of the belt reinforcement structure. The top ply structure comprises nylon cords of the 420x2 type laid side by side having a cordset twist of not more than 280 rpm. The limited torsion, in this case the low torsion (slightly marked helical angle), has negative effects on the resistance to fatigue and on impact resistance.

In US Patent No. 2006/0237113, a belt reinforcing layer is described forming an angle of zero degrees, consisting of at least one first elongated element which represents a hybrid cord including at least one filament with high elastic modulus and at least one filament with low elastic modulus, twisted to one another and which are arranged alternately. The elastic modulus of said at least one second elongated element is less than the elastic modulus of said at least one first elongated element.

Such reinforcement of the crown ply is not sufficiently effective at the edge of the belts given the limited restriction force and the limited value of the thermal shrinkage of hybrid cables compared to those of nylon.

In U.S. Patent 6,799,618, a textile top ply structure is described which overlaps in a radial direction outside the belt assembly and which is reinforced with cords which are made of materials, including nylon and aramid. At the initial elongation of the cables, the wires which support the primary load are nylon wires and after appreciable elongation, the wires which support the primary load are aramid wires. It is a conventional hybrid cable that is used for a crown ply, with reduced impact resistance.

In US Patent No. 2013/0025758, a high performance type radial ply tire for passenger vehicles is described, in which a hybrid cable is used which consists of two wires. aramid and a single ply nylon thread having different coefficients of twist for the first twist and different coefficients of twist for the second twist, as the top ply, the cable in question having better durability at high speed and better driving stability. It is also a conventional hybrid cable that is used for a crown ply, having reduced impact resistance.

SUMMARY OF THE INVENTION

The present invention relates to a new strip or a new cord fabric for a pneumatic tire comprising parallel nylon cables 6,6 alternately arranged having different twists. A new strip or cable fabric for a pneumatic tire improves durability at high speed, resistance to separation of the tread and impact resistance when used in the form of a crown ply which is wound in a spiral forming an angle of zero degrees in pneumatic tires of the radial ply type.

As is well known, nylon 6,6 has an excellent resistance to fatigue and a bielastic behavior of tensile strength, which makes possible the lifting process in the absence of a formation of tightly tight cords and this which provides a sufficient restrictive force under high speed conditions. However, because of the low initial modulus of nylon 6,6 cords, it is necessary to use bands or fabrics having a high epdm value (number of ends of cords high per decimeter) in order to obtain the restriction force. sufficient with regard to the belt package (as can be seen in Figure 1).

On the other hand, the distance from cord to cord (rivet) in strips or in fabrics of this type is too narrow, which makes it difficult for the rubber to penetrate between the cables, without premature vulcanization. In addition, cracks in the rubber can easily occur between cables having a narrow rivet under dynamic conditions on the basis of high shear stresses.

According to the invention, the nylon 6,6 cables having different twists in the top ply strips have different modules (or different LASE values) and different thermal shrinkage values. During uplift (during expansion) during the vulcanization process, nylon 6,6 cords of the low twist type (high modulus, cords with little stretch) are subjected to a load far greater than that of cords of the high torsion type (low module, highly extensible cables).

In addition to superior tensile strength of the cable, low-twist type nylon cables subjected to higher loads generate a higher thermal shrinkage value (greater contraction force) at the vulcanization temperature. On the basis of a higher cable load and a higher thermal shrinkage value, nylon cables of the low twist type penetrate better than cables of the high torsion type through the compound acting as a gumming layer.

Due to the different penetration levels of nylon 6,6 cables of the low twist type and the high twist type in the compound acting as an exfoliation layer, the top layer layer of monolayer type is transformed into a strip of partially bilayered (wavy) top (as can be seen in Figure 2).

DEFINITIONS

Wired: reinforcing element which is obtained by reciprocal twisting of wires of the type with two or more plies.

Denier: the weight in grams of a thread having a length of 9000 m.

Dtex: the weight in grams of a wire having a length of 10,000 m.

LASE: the load at a specified elongation.

LASE 7%: the load at an elongation of 7% in the curve 30 load / elongation.

Linear density ; the weight per unit of length expressed in g / dtex or in g / d (denier).

Restrictive force; the force exerted by the crown ply on the pack 5 of belts when driving to prevent the expansion of the tire.

Total linear density; the sum of the nominal linear densities of the ply wires of the cable.

Two-ply type cable: cable that is prepared by reciprocal twisting of two-ply type wires.

Three-ply type cable: cable that is prepared by reciprocal twisting of three-ply type wires.

Twist: the number of turns per meter (rpm or rpm).

Warp: the group of threads or cords in all the woven fabrics, which extend in a longitudinal direction and parallel to the selvedge and which come to intertwine with the filling material.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a cross-sectional view of a conventional nylon crown ply (from the prior art) over a packet of belts formed by steel cords of the diagonal ply type, after the vulcanization process.

a represents a pack of belts constituted by steel cables of the diagonal ply type;

b represents a conventional crown ply on a pack of belts;

c represents a tread.

FIG. 2 is a cross-sectional view of a nylon top ply according to the invention on a pack of belts formed by steel cords of the diagonal ply type, after the vulcanization process.

a represents a pack of belts constituted by steel cables of the diagonal ply type;

b represents a crown ply on a pack of belts according to the invention;

c represents a tread.

FIG. 3a is a cross-sectional view of arrangements of nylon top ply cords according to the invention on a pack of belts constituted by steel cords of the diagonal ply type, (1) before the vulcanization process ; (2) after the vulcanization process.

A: represents a nylon 6,6 cord having a high torsion or a high coefficient of torsion, having a low modulus;

B: represents a nylon 6.6 cord having a low twist or a low coefficient of twist, having a high modulus;

H: represents the difference in penetration of cables A and B in a rubber matrix.

FIG. 3b is a top view of a strip of nylon top ply formed by cables A (high twist, low modulus, low tensile strength) and B (low twist, high modulus, high tensile strength ).

FIG. 4a is a cross-sectional view of a nylon top ply comprising cables arranged in pairs side by side in accordance with the invention on a pack of steel cable belts of the diagonal ply type, (3) before the vulcanization process; (4) after the vulcanization process.

FIG. 4b is a top view of cables A (high twist, low modulus, low tensile strength) and B (low twist, high modulus, high tensile strength) in a strip of top ply

Figure 5 shows the changes in the distance between a cable and another cable (rivet area, spacing) after the vulcanization process.

: distance from wired to wired between A and B before the expansion and vulcanization process;

: distance from wired to wired between A and B after the expansion and vulcanization process;

: distance from wired to wired between A and A after the expansion and vulcanization process;

S4: distance from wired to wired between B and B after the expansion and vulcanization process;

FIG. 6 represents 1 + 2 + 1 arrangements of cords of crown plies.

(1) arrangement of cables A + B + B + A + B + B + A + ... before the expansion and vulcanization process;

(2) arrangement of cables A + B + B + A + B + B + A + ... after the expansion and vulcanization process.

Figure 7 shows 2 + 1 + 2 cable arrangements.

(1) arrangement of cables A + A + B + A + A + B + A + A + ... before the expansion and vulcanization process;

(2) arrangement of cables A + A + B + A + A + B + A + A + ... after the expansion and vulcanization process.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention, strips of crown plies or fabrics of crown plies wound in a spiral on packages of pneumatic bandage belts with radial plies in the circumferential direction, having parallel nylon 6,6 warp cords arranged in alternation, with different torsion coefficients:

improve durability at high speed on the basis of the high modulus of 10 nylon cables of the low twist type and on the basis of the greater distances from cable to cable (by reducing the shear stresses) between the cables (offset of cables in vertical direction, formation of two layers or zigzag configuration) (as can be seen in Figures 3a, 3b and 5); improve the impact resistance manifested by the belt pack on the basis of superior energy absorption by high-twist, highly stretchy nylon cords; and also improve the resistance to separation between the tread and the crown plies thanks to the corrugated surface structure of the crown ply. The zigzag configuration of the surface also improves the mechanical connection between the compound serving as the crown ply and the compound serving as the tread.

The first nylon cords (high twist type cords, A) and the second nylon cords (low twist type cords, B) in a top ply band represent two plies and / or three-ply type.

The angle formed by the strips of crown plies wound in a spiral with respect to the circumferential midline (or with respect to the equatorial plane of the tire) rises from 0 to 5 °.

In order to obtain the advantages mentioned above, the minimum twist difference between the alternating nylon cords having the same total dtex value of the cords must be 50, preferably 100 tprn (for example a first cable, 1400x2, Z / S, 350/350 rpm, and a second cable 1400x2, Z / S, 250/250 tprn). However, the minimum cable (cable) twist cannot be less than 150 rpm.

When the difference in cable twist is less than 50 rpm between the first and second cables, the LASE value, the module or the difference in extensibility between the first and second cables becomes insignificant. Under these conditions, the undulating surface of the crown ply cannot be obtained on the pack of belts of the tire.

Furthermore, the difference in twist between the first and second cables cannot exceed 50% of the twist of the first cable (cable of the high torsion type, A), for example 350 rpm compared to 175 rpm.

The total linear density of the cables is at least 500 dtex and maximum at 6000 dtex. The cables of top plies which have a value lower than 500 dtex are too fine and the LASE values are too low and do not allow to confer a sufficient restriction force, even with very high numbers of cable ends (high epdm value ). Apart from this drawback, during the lifting and vulcanization process, they can cause cuts in the compound acting as a gumming layer for the belt layer and come into contact with the steel cords. The cables of crown plies which have a value greater than 6000 dtex are too thick and require too much rubber for the coating. The potential drawback associated with such cords in pneumatic tires is the increase in rolling resistance and greater heat buildup in the crown area.

The difference in total linear density between the first and second cables is less than 15%. Preferably, the total linear densities of the first and second cables will be identical.

According to the invention, the sequence of nylon cables of the high twist type and of the low twist type, which are parallel to each other in a strip of crown ply, represents an alternating shape as indicated below: A + B + A + B + A + B + ... etc., in which A represents the first cable having a high twist and B represents the second cable whose twist is less than that of A. Such a strip of ply crown allows to obtain a uniform wavy surface after the vulcanization process, which binds strongly to the compound acting as a tread, improving the resistance to separation of the tread under high speed conditions.

According to the invention, the sequence of nylon cables of the high twist type and of the low twist type, which are parallel to each other in a strip of crown ply, represents an alternating shape as indicated below: AB + AB + AB + ... etc., in the form of cables arranged in pairs, in which A represents the first cable having a high twist and B represents the second cable whose twist is less than that of A.

According to the invention, the sequence of high twist type and low twist type nylon cords, which are parallel to each other in a strip of crown ply, represents an alternating shape as indicated below; A + B + B + A + B + B + A + B + B + ... etc., in which A represents the first cable with high twist and B represents the second cable with less twist than that of AT.

According to the invention, the sequence of nylon cables of the high twist type and of the low twist type, which are parallel to each other in a strip of crown ply, represents an alternating shape as indicated below: A + A + B + A + A + B + A + A + B + ... etc., in which A represents the first cable having a high twist and B represents the second cable whose twist is lower compared to that of A .

In accordance with the invention, the number of cable ends in the strip amounts to a minimum of 70 epdm (ends per decimeter). In the case of numbers of ends of cables whose value is less than 70 epdm, the efficiency of the surface ripple is not sufficient to obtain a mechanical connection to the tread.

In accordance with the invention, the difference between the LASE values at 7% of the first and second nylon cords is at least 15% and preferably 25% (l_ASE values at 7% determined in accordance with the standard

ASTM D885-16).

According to the invention, the width of the strips of crown plies is between 8 and 25 mm, preferably between 10 and 15 mm.

Claims (16)

1. Strip of crown ply made from first and second parallel nylon 6.6 cables, arranged alternately, which 5 is wound in a circumferential direction around a pack of belts of a pneumatic tire with a radial ply, characterized in that the difference between the coefficients of twist of the first and second cords in the strip of crown ply s' student at 10 at least 50 rpm; and the coefficient of torsion of the second cables (cables of the low twist type, B) does not represent less than 50% of the torsion coefficient of the first cables (cables of the high torsion type, AT). 2. A top ply strip according to claim 1, in which the first and second nylon 6,6 cords are cords of the two-ply type. 20 3. crown ply strip according to claim 1, in which the first and second nylon 6,6 cords are cords of the three ply type. 4. top ply strip according to claim 1, in which the The difference between the twist coefficients of the first and second nylon 6,6 cables amounts to a minimum of 100 rpm. 5. The top ply strip according to claim 1, in which the linear density of said nylon 6,6 cords amounts to a minimum of 30,500 dtex and a maximum of 6000 dtex. The top ply strip of claim 1, wherein the difference between the linear densities of the first and second nylon 6,6 cords is less than 15%. 5 7. top ply strip according to claim 1, in which the linear densities of the first and second nylon 6,6 cords are identical. 8. The top ply strip of claim 1, wherein 10 the arrangement of the first and second nylon 6,6 cables in said strip is as indicated below A + B + A + B + A + B etc. 9. The top ply strip of claim 1, wherein the arrangement of the first and second nylon 6.6 cords in Said strip is as indicated below AB + AB + AB etc., in the form of cables arranged in pairs. 10. The top ply strip according to claim 1, in which the arrangement of the first and second nylon 6,6 cables in Said band is as indicated below A + B + B + A + B + B + A + B + B + A etc. 11. top ply strip according to claim 1, in which the arrangement of the first and second nylon 6,6 cords in said strip is as indicated below A + A + B + A + A + B + A + A + B etc. 12. strip of crown ply according to claim 1, in which the number of ends of cables in said strip amounts to a minimum of 70 epdm (ends per decimeter). 13. crown ply strip according to claim 1, in which the difference of the LASE values at 7% (determined in accordance with standard ASTM D885-16) between the first and second nylon 6,6 cords is at least at 15%. 14. top ply strip according to claim 1, in which the 5 difference of the LASE values at 7% (determined in accordance with standard ASTM D885-16) between the first and the second nylon 6,6 cables amounts to at least 25%. 15. strip of crown ply according to claim 1, in which the 10 width of said top web strip is at least 8 mm and a maximum of 25 mm. 16. The top ply strip according to claim 1, wherein the width of said top ply strip is a minimum of 10 mm and a maximum of 15 mm.