LU100827A1 - Polyester Summit Tablecloth - Google Patents

Abstract

A strip or fabric of tows for a tire comprising parallel, alternately arranged polyethylene terephthalate (PET) cords having different lengths of 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 spiral wound at zero degree angle in radial-ply type pneumatic tires.

Description

DESCRIPTION

FIELD OF THE INVENTION

The present invention relates to a new strip or fabric of cords for a pneumatic tire comprising parallel polyester cords arranged alternately 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 bands having cables of the type with a high number of cable ends (high epdm value) (such as for example PET, 1100 × 2, 110 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.

PET (polyethylene terephthalate) cords have a higher modulus and higher tensions between the cords inside the tire as compared to reinforcements in the form of nylon 6.6 crown plies. Due to a lower number of active sites (functional groups) on the surface of the fibers compared to nylon 6,6, PET is more sensitive to thermal degradation as regards adhesion with rubber to high temperatures. This is why the resistance to separation between the tread and the crown plies, manifested by PET is lower than that of nylon 6,6.

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.

US Patent 7,584,774 describes a polyethylene terephthalate (PET) cord as a belt reinforcement layer (crown ply) which spirally wraps around the belt pack in the circumferential direction. Said PET cable has a modulus of elasticity which is not less than 2.5 mN / dtex.% Under a load of

29.4 N at 160 ° C.

The major drawback with conventional PET crown plies in pneumatic radial ply tires intended for high speeds concerns the need to obtain a robust dynamic adhesion to delay the formation of cracks between cables (due to shear forces ). In high speed conditions, the temperature at the edges of the belts also becomes higher and the cable modulus of the PET top plies decreases. This is the reason why it is preferred to use, to act as a monolayer top ply, strips having a high number of cable ends. However, crown plies with a high number of cable ends show a greater tendency to form cracks, which can lead to separation of the plies.

SUMMARY OF THE INVENTION

The present invention relates to a new strip or fabric of cords for a pneumatic tire made from alternately arranged cords (woven) 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.

Due to the lower dynamic adhesion manifested by polyester (PET), it is preferable to use it in the form of a monolayer type top ply having a high number of cable ends and a narrow rivet on packages. belts in pneumatic tires with radial ply intended for high speeds (as can be seen in Figure 1).

On the other hand, the distance from cord to cord (rivet area) 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, in the top ply strips, the PET cords having different twists have different modules or different LASE values and different thermal shrinkage values.

During uplift (during expansion) during the vulcanization process, PET cables of the low twist type (high modulus, low stretch cables) are subjected to a load far greater than that of the twist type cables. high (low module, highly extensible cables). In addition to a higher resistance of the cable to tensions, nylon cables of the low-twist type subjected to higher loads generate a value of thermal shrinkage greater (a force of contraction greater) 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.

Given the different penetration levels of low twist type and high twist type PET cords, the top band layer of the single ply type turns into a bilayer type top band (as can be see 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.

Equatorial plane: the plane passing through the circumferential midline in the tire.

LASE: the load at a specified elongation.

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

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

PET: polyethylene terephthalate.

Restriction force: the force exerted by the crown ply on the belt pack while driving to prevent 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 polyester (PET) crown ply (prior art) on 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;

Ί c represents a tread.

FIG. 2 is a cross-sectional view of a polyester (PET) crown 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 a nylon top ply in accordance with the invention on a pack of belts formed by steel cords of the diagonal ply type, (1) before the vulcanization process; (2) after the vulcanization process.

A: represents a first polyester (PET) cord having a high twist or a high coefficient of twist, having a lower modulus than that of cord B;

B: represents a second polyester (PET) cord having a low twist or a low coefficient of twist, having a modulus greater than that of cord A;

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

FIG. 3b is a top view of a strip of PET top ply constituted by 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 PET top ply comprising cords arranged in pairs side by side according to the invention on a pack of steel cord belts of the diagonal ply type, (1) before the vulcanization process; (2) after the vulcanization process.

Figure 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 top ply strip.

Figure 5 shows the changes in wired-to-wired distance after the vulcanization process; (1) before the vulcanization process; (2) after the vulcanization process: distance from cable to cable 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;

S3: wired to wired distance 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;

Figure 6 shows 1 + 2 + 1 cable arrangements.

(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 packets of pneumatic bandage belts with radial plies in circumferential direction, having alternating polyester (PET) warp cords , having different coefficients of torsion;

improve durability at high speed on the basis of the high modulus of 10 cables in PET 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 (shifting 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 a higher energy absorption by high twist and highly extensible type PET 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 PET cords (A) and the second PET cords (B) in a top ply strip represent cords of the two-ply type and / or the 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 be able to obtain the advantages which have been mentioned above, the twist coefficient of a PET cable (A) having a high twist coefficient, which is determined in accordance with the formula (1) indicated above. below is at least 13,000 and less than 17,000. The

Torsion coefficient = cable twist (rpm) x (total linear cable density 5 expressed in dtex) ^1/2 (1)

According to the invention, the twist coefficient of the second PET cable (B) (of the low twist type) represents at least 15% and preferably 25% less than the twist coefficient of the first PET cable (A ) (of the high torsion type).

When the twist coefficient of the second PET cord (B) (of the low twist type) represents less than 15% of the twist coefficient of the first PET cord (A) (of the high twist type), the LASE value, the module or the difference in extensibility between the first and second cables becomes insignificant. Under these conditions, the corrugated surface of the crown ply cannot be obtained in the tire.

The total linear density of the cables is a minimum of 1,000 dtex and a maximum of 5,000 dtex. The cables of top plies which have a value lower than 1.000 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 5,000 dtex are too thick and require too much rubber for the coating. The potential drawback of such cables 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 PET cable (A) and the second PET cable (B) is less than 15%. Preferably, the total linear densities of the first PET cable (A) and the second PET cable will be identical.

According to the invention, the sequence of the first PET cable (A) and the second PET cable (B), 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 lower than that of A. Such a band of the crown ply makes it possible to obtain a uniform corrugated surface after the vulcanization process, which comes to bind strongly to the compound acting as a tread by improving the resistance to separation of the tread under high speed conditions ( as can be seen in Figure 3a).

According to the invention, the sequence of the first PET cable (A) and the second PET cable (B), 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 ( as can be seen in Figure 4a).

According to the invention, the sequence of the first PET cable (A) and the second PET cable (B), which are parallel to one another 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 having a high twist and B represents the second cable whose twist is lower compared to that of A (as can be seen in Figure 6).

According to the invention, the sequence of the first PET cable (A) and the second PET cable (B), which are parallel to each other in a strip of crown ply, represents an alternate form as indicated below; A + A + B + A + A + B + A + A + B + ..., etc., in which A represents the first cable with high twist and B represents the second cable with less twist than that of A (as can be seen in Figure 7).

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.

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 (12)

1. Strip of top ply produced from first and second cords in parallel woven polyethylene terephthalate (PET) 5 alternately, having the same linear densities, which is wound in a circumferential direction around a pack of belts of a pneumatic tire with radial ply, characterized in that the coefficient of torsion of the first cable made of PET (A) , which is determined in accordance with the formula given below 10 twist coefficient = twist of the cable (rpm) x (total linear density of the cable expressed in dtex) ^1/2 ; is at least 13,000 and less than 17,000; and the twist coefficient of the second PET cable (B) is at least 15% and preferably 25% less than the coefficient of 15 twist of the first PET cable (A). 2. crown ply strip according to claim 1, in which the first and second PET cords are cords of the two-ply type. 3. crown ply strip according to claim 1, in which the first and second PET cords are cords of the three-ply type. 25 4. The top ply strip according to claim 1, in which the linear density of said PET cords amounts to a minimum of 1,000 dtex and a maximum of 5,000 dtex. 5. top ply strip according to claim 1, in which the 30 difference between the linear densities of the first and second PET cables is less than 15%. The top ply strip according to claim 1, in which the arrangement of the first and second PET cables in said strip is as indicated below A + B + A + B + A + B, etc. 5 7. crown ply band according to claim 1, in which the arrangement of the first and second PET cords in said band is as indicated below AB + AB + AB, etc., in the form of cords arranged in pairs. 10 8. top ply strip according to claim 1, in which the arrangement of the first and second PET cables in said strip is as indicated below A + B + B + A + B + B + A + B + B + A, etc. 9. The top ply strip of claim 1, wherein The arrangement of the first and second PET cables in said strip is as indicated below A + A + B + A + A + B + A + A + B, etc. 10. strip of crown ply according to claim 1, in which the number of ends of cables in said strip is at least 70 20 epdm (tips per decimeter). 11. top ply strip according to claim 1, in which the width of said top ply strip amounts to a minimum of 8 mm and a maximum of 25 mm. 12. top ply strip according to claim 1, in which the width of said top ply strip amounts to a minimum of 10 mm and a maximum of 15 mm.