LU100713A1 - Novel bielastic aramid tire cord as cap ply - Google Patents

Abstract

The present invention relates to a novel tire cord reinforcement made of ultra high modulus aramid fibers which has bi-elastic tensile properties. Such a novel bi-elastic tire cord improves high speed durability and eliminates flatspotting when used as cap ply in pneumatic radial tires.

Description

NEW BIELASTIC ARAMID CABLE FOR BANDAGE

TIRE AS SUMMIT TABLECLOTH

FIELD OF THE INVENTION

The present invention relates to a new tire reinforcement for pneumatic tires made from aramid fibers with ultrahigh modulus, which has bielastic properties of tensile strength. A new bielastic pneumatic tire of this type improves durability at high speed and eliminates leveling, when used as a crown ply in pneumatic tires of the radial ply type.

DESCRIPTION OF THE PRIOR ART

In high speed conditions, the outside diameter of the tire increases due to the centrifugal forces generated by the pack of steel cable belts and the tread. Such an increase in diameter or such widening of the pneumatic tire increases the pantographic movements of the cables from the edge of the belt, giving rise to crack initiation, propagation of cracks and ultimately separation of the edges of belts.

The top ply layer wound in a spiral over the belt pack prevents excessive expansion of the tire under high speed conditions by exerting compressive forces (restraining force) on a thick belt pack made from layers of steel cables with diagonal structure.

Currently the most widely used materials for crown plies are multi-ply nylon 6.6 layers or single-layer hybrid cords which are spirally wound on the belt pack at an angle of 0 to 5 degrees from the equatorial plane of the tire.

Nylon cords have excellent resistance to fatigue under conditions of bending and axial compression and a bielastic characteristic of tensile strength allowing easy treatment during the making of the tire. In addition, the generation of a shrinking or shrinking force proportional to the rise in operating temperature under high speed conditions improves the resistance to separation of the edges of belts, as well as durability at high speed. However, the low glass transition temperature of nylon poses problems of flattening in the tire when parking after traveling at high speed. Another potential drawback associated with a multilayer type nylon crown ply assembly relates to its high rubber content which results in an increase in the rolling resistance of the tire by hysteresis (heat accumulation).

It is well known that hybrid cables comprising high modulus wires and low modulus wires having a bielastic behavior of tensile strength are also used as crown ply in pneumatic tires of the high speed type. The low module component of the hybrid cable allows easy lifting of the belt pack in the absence of tight cable formation due to its high extension capacity and the high module component becomes effective under service conditions. By using hybrid cords 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 cord increases the retaining force and improves durability at high speed. But the presence of nylon also leads to a certain leveling out.

Furthermore, cables made from wires with an ultra-high module having a high torsion are also used as reinforcement of a pneumatic tire in order to eliminate leveling and improve performance at high speed, but a high twist rate of the cable gives rise to drastic losses of the module and of the breaking strength.

In United States patent US-A 4,893,665, a hybrid cord is described comprising at least two wires, each of which consists only of aramid filaments, and a single central wire which is constituted only by filaments chosen from the group consisting of polyamides whose structure is at least partially oriented and by polyesters whose structure is at least partially oriented.

US Patent 5,558,144 describes a hybrid cable having high modulus aramid and low modulus nylon wound spirally and continuously on a bundle of belts in the circumferential direction of the tire by forming an angle of 0 to 3 degrees relative to the equatorial plane.

In US Patent US-A 6,799,618, a textile top ply structure is described which is superimposed radially outward on the belt assembly, which is reinforced with cords. made from materials that include nylon and aramid. During the initial elongation of the cables, the wires supporting the main load are nylon wires and after appreciable elongation, the wires carrying the main load are the aramid wires.

In U.S. Patent No. 2013/0025758, a high performance radial ply tire for passenger vehicles is described, which uses a hybrid cable that consists of a two-type aramid wire plies and a single ply type nylon thread having different coefficients of twist for the first twist and different coefficients of twist for the second twist, as the top ply, and thus having better durability at great speed and better directional stability.

SUMMARY OF THE INVENTION

The invention relates to a cable reinforcement of the type with two or more plies, produced from an aramid yarn having bielastic properties of tensile strength. More precisely, a low initial modulus and a high modulus after the initial elongation. In order to prevent excessive losses in terms of modulus and breaking strength, a high twist rate of the cord has been avoided

The principle of production of the transformation of the linear behavior of tensile strength of the cable into aramid into a bielastic characteristic is based on the opening of the cable layers and on the insertion of an RFL adhesive in said opening. The aramid cable which contains RFL between its open plies exhibits a bielastic behavior of tensile strength under tension.

Definitions

Wired: the product that is obtained by twisting two or more layers of type of wire together.

Cable layer: single ply type wires within the cable.

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

Flattening: cables in a pneumatic tire with a low Tg value and a high thermal shrinkage force are subjected to imprint shrinkage. When cooled to this position, the cable maintains flattening until it regains its Tg value during use.

Wired unbleached: wired twisted before immersion and heat curing.

Heat curing: the process of imparting resistance to deformation and heat resistance to wires, cables or fabrics using either moisture or heat.

Wired after heat curing: Wired exposed to high temperature (for example from 120 ° C to 260 ° C under voltage).

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

Spacing (s): reciprocal distance from ply to ply within a twisted cable of the multiple ply type.

TASE at 2% elongation: deformation at 2% elongation expressed in cN / dtex.

Tenacity: breaking strength (N) divided by the linear density (dtex).

Tg: glass transition temperature of a polymer.

Total nominal dtex of a cable: sum of the nominal linear densities of a wire (3340 dtex for a cable 1670x2).

Twist: number of turns around its axis per meter of a wire or cable (t / m or rpm).

Ultra-high modulus wire: tensile elastic modulus greater than 100 GPa.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1 and 2 are cross-sectional views of conventional cables (prior art) of aramid of the two-ply and three-ply type, respectively.

Figure 3 is a cross-sectional view of a conventional hybrid cable (prior art) of the two-ply type, in which

A represents a tablecloth (a thread) of aramid, B represents a tablecloth (a thread) of nylon.

Figure 4 is a cross-sectional view of a conventional hybrid cable (prior art) of the three-ply type, in which

A represents a tablecloth (a thread) of aramid, and B represents a tablecloth (a thread) of nylon.

Figures 5 and 6 are cross-sectional views of conventional (prior art) nylon cords (nylon 6 or nylon 6.6) of the two-ply and three-ply type, respectively.

FIG. 7 shows the opening of the cross sections of the cable and the subsequent penetration of the immersion solution between the cable layers for aramid cables of the two-layer and three-layer type, in which

A represents a cross-sectional view of aramid cords of the two-ply and three-ply type, in the form of closed plies,

B represents a cross-sectional view of aramid cords of the two-ply and three-ply type, in the form of open plies,

C represents a cross-sectional view of aramid cords of the two-ply and three-ply type, in a form impregnated by immersion in accordance with the invention,

D represents the immersion solution containing an adhesive (RFL) filling the openings between the sheets and covering the surface of the cables.

Figure 8a is a side view in cross section of a conventional aramid cable of the two-ply type.

FIG. 8b is a side view in cross section of an aramid cable of the two-ply type in the open form according to the invention (before the immersion step).

Figure 9a is a side view in cross section of a conventional aramid cable of the three-ply type.

FIG. 9b is a side view in cross section of an aramid cord of the three-ply type in the open form according to the invention (before the immersion step).

Figures 10a, 10b, 10c and 10d show cross-sectional views of closed and open forms of cable plies. D represents the diameter of the cable and s represents the spacing (the opening) between the cable layers.

FIG. 11 represents the stress-elongation curves of aramid cables, in which represents a 1670 dtex / 3 cable in aramid after immersion having a Z / S twist, 320/320 rpm (prior art) having a linear characteristic of resistance to tensile, represents a 1670 dtex / 3 aramid cable having a Z / S twist, 320/280 rpm (subjected to a backward twist of 40 rpm in the Z direction) and after immersion, having a bielastic characteristic of resistance to traction according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Aramid with its ultra-high modulus and high resistance represents a material which resists deformation very well. Thanks to its highly crystalline microstructure, it does not show any significant thermal shrinkage when exposed to a high temperature. In its twisted form as a two-ply or three-ply type cable, it can be used as a reinforcement in pneumatic tires and in mechanical rubber articles such as V-belts (as can be seen in the figures 1 and 2).

The twisting of the cord improves the fatigue resistance of the aramid in flexion and under compression, but at the same time reduces the modulus as well as the resistance.

In applications involving zero degree crown plies in radial ply pneumatic tires, the high modulus is required for the holding force in order to prevent separation of the edges of the belts under high speed conditions, but there is also a need for an initial capacity for extension with low forces (low initial modulus) for the capacity for treatment during the lifting of the pack of belts in the processes of making and vulcanizing the pneumatic tire in order to avoid cable cuts through the rubber compound of the belt.

Aramid / nylon hybrid cables solve this problem, but the presence of nylon creates problems of flattening and asymmetrical cable structures (as can be seen in Figures 3 and 4).

Nylon 6 or nylon 6.6 cords of the two-ply or three-ply type (as can be seen in Figures 5 and 6) represent well-known reinforcements as a crown ply in pneumatic ply-type tires radial designed for passenger vehicles and vans, but flattening and a low level of modulus are their major drawbacks.

According to the present invention, aramid cords of the type with two or more plies can be obtained in the absence of any ply acting as a low-modulus component, such as nylon, with bielastic properties of tensile strength. (as can be seen in Figure 7). New aramid bielastic cords of this type can be used as a zero degree crown ply in pneumatic radial ply tires to improve durability at high speed and do not show any leveling off.

In accordance with the invention, the basic production principle of the bielastic aramid cable consists of opening the cable layers and inserting the immersion solution containing an adhesive between the layers. Aramid cord containing a high percentage of adhesive such that the RFL between its plies becomes stretchable with low forces, and during this extension, the plies of aramid cords exert compressive forces on the adhesive material (RFL) and compress it. During this compression process, the cord undergoes elongation with low forces. Once the aramid cable plies have moved closer to one another, the aramid cable resists elongation and it becomes again a cable with an ultra-high module (as can be seen in FIG. 11).

To be able to obtain a bielastic tensile strength characteristic, the aramid cable plies can be opened using different methods:

a) unbleached aramid cables of the type with two or more plies are heat-cured at a temperature between 120 ° C and 260 ° C and after cooling, they are subjected to a partial twist back in the direction opposite to the twist hardwired. During this backward twisting process, the cable plies are opened (as can be seen in Figures 8a, 8b, 9a, 9b, 10a, 10b, 10c and 10d). Aramid cords with their open plies are again subjected to immersion and heat curing and, during these processes, the voids between the cords of cords are filled with the immersion solution and the outer surface of the Cable layers are also covered by the immersion solution.

b) unbleached aramid cords of the type with two or more plies are subjected to immersion and heat curing at a temperature between 120 ° C and 260 ° C and after cooling, they are subjected to partial back twist in the opposite direction to the twisted cable. During this backward twisting process, the cable plies are opened. Aramid cords with their open plies are again subjected to immersion and heat curing and, during these processes, the voids between the cords of cords are filled with the immersion solution and the outer surface of the Cable layers are also covered with an additional amount of the immersion solution.

c) aramid cables of the type with two or more plies are subjected to axial compression during the immersion process and the cable with its open plies under compression absorbs the immersion solution between the open cable plies. After the immersion process, the aramid cable, in which the immersion solution has entered between the sheets, is dried and heat-cured between 120 ° and 260 ° C.

The characteristic of bielasticity of tensile strength of the aramid cord can be modified with the degree (s) of opening of the sheets (as can be seen in Figures 10b and 10d), with the type of solution d immersion, with the content of immersion solution between the layers and with the degree of hardening of the immersion solution at high temperatures (hardness of the immersion solution).

According to the invention, the aramid cable of the type with two or more plies has a TASE value of less than 2.0 cN / dtex at an elongation of 2%, determined in accordance with standard ASTM D885-16 and the spacing ( the gaps) between the cable layers, which is (are) filled (s) with the immersion solution containing an adhesive is (are) greater than 0.1 xD and less than 0.8xD.

A 2% TASE value greater than 2.0 cN / dtex results in tight cords when applied as a crown ply during the tire lifting process.

Preferably, s is greater than 0.2xD and less than 0.5xD.

According to the invention, the absorption of the immersion solution containing an adhesive (DPU) of the cable after immersion is greater than 10% and less than 50%, preferably greater than 15% and less than 35%, by weight .

A DPU less than 10% does not completely fill the openings between the cable layers and a DPU greater than 50% gives rise to excessively thick cable diameters.

According to the invention, the twist coefficient of the cable is greater than 10,000 and less than 25,000, as determined on the basis of the following formula:

Torsion coefficient = twist of the cable (rpm) x square root of the total nominal dtex value of the cable (1).

Cables with a torsional coefficient of less than 10,000 have insufficient resistance to bending fatigue and cables with a torsional coefficient of more than 25,000 have significant module reductions.

According to the invention, the total nominal linear density of the cable is greater than 200 dtex and less than 6,000 dtex. Cables with a value less than 200 dtex are not efficient enough and cables with a value greater than 6,000 dtex are too thick.

Claims (8)

1. Wired in aramid after immersion and heat curing having at least two layers and having a distance (s) between said layers of cables, the TASE value of which is less than 2.0 cN / dtex at an elongation of 2.0%, characterized in that the spacing (s) between the layers of cables represents (s) more than 10% and less than 80% of the diameter (D) of the cable. 2. Aramid cabled after immersion and heat curing according to claim 1, the spacing (s) spacing (s) between the layers of cords of said cabled preferably represent (s) more than 20% and less than 50% the diameter (D) of the cable. 3. Aramid cord after immersion and heat curing according to claim 1, the absorption value of the immersion solution containing an adhesive (DPU) of said cord is greater than 10% and less than 50%, by weight. . 4. Aramid cabled after immersion and heat curing according to claim 1, the absorption value of the immersion solution containing an adhesive of said cabled is greater than 15% and less than 35%, by weight. 5. Wired in aramid after immersion and heat curing according to claim 1, the torsion coefficient of which is between 10,000 and 25,000, which is calculated by referring to formula (1). 6. Wired in aramid after immersion and heat curing according to claim 1, whose total nominal linear density is between 200 dtex and 6,000 dtex. 7. Wired in aramid after immersion and heat curing according to claim 1, which is used as a crown ply wound in a circumferential direction on the pack of belts in pneumatic tires of the radial ply type. 8. Wired in aramid after immersion and heat curing according to claim 1, which is used as a reinforcement of mechanical rubber articles.