LU100709A1 - Novel bielastic carbon fiber cord as cap ply - Google Patents

Abstract

The present invention relates to a novel tire cord reinforcement made of ultra high modulus carbon fibers which has bi-elastic tensile propertires. 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 CABLE IN CARBON FIBERS AS

SUMMIT TABLECLOTH

FIELD OF THE INVENTION

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

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 an expansion of the pneumatic tire increases the pantographic movements of the cables from the edge of the belt, giving rise to crack initiations, propagation of cracks and ultimately separation of the edges of belts.

The top ply layer which wraps around the belt pack in a circumferential direction 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 a 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 force proportional to the rise in the operating temperature under high speed conditions improves the resistance to separation of the belt edges, 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 multi-ply type nylon crown ply assembly relates to its high rubber content which results in increased rolling resistance of the tire by hysteresis (heat build-up).

It is well known that hybrid cables comprising wires with high modules and wires with low modules having a bielastic behavior of tensile strength are also widely 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 cables as the top ply, the total thickness of the top ply layer and the rubber content can be reduced, and the high modulus component of the hybrid cable improves the holding force and durability. great speed. But the presence of nylon also leads to a certain leveling out.

In addition, cables made from wires with an ultra-high module having a high torsion are also used as reinforcement of the pneumatic tire in order to eliminate leveling and improve performance at high speed, but a high rate of twisting 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 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 carrying 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 hybrid cable composed of a two ply aramid yarn and d '' a single ply nylon yarn with different coefficients of twist for the first twist and different coefficients of twist for the second twist, as the top ply, and thus has better durability at high speed and better stability directional.

SUMMARY OF THE INVENTION

The invention provides a cable reinforcement of the type with two or more plies, produced from a carbon fiber 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 on the module and the breaking strength, a high twist rate of the cord was avoided.

The principle of production of the transformation of the linear behavior of tensile strength of the cord in carbon fibers into bielastic characteristics is based on the opening of the layers of cables and on the insertion of an RFL adhesive in said opening. The carbon fiber 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 fingerprint 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.

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 carbon fibers 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 ply (wire) of aramid or carbon fibers, B represents a ply (wire) 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 fibers, B represents a tablecloth (a thread) of nylon.

Figures 5 and 6 are cross-sectional views of conventional (prior art) nylon cords 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 by immersion between the layers of cables for carbon fiber cables of the two-ply and three-ply type, in which

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

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

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

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

Figure 8a is a side and cross-sectional view of a conventional carbon fiber cable of the two-ply type.

FIG. 8b is a side and cross-sectional view of a carbon fiber cable of the two-ply type in the open form according to the invention (before the immersion step).

Figure 9a is a side and cross-sectional view of a conventional carbon fiber cable of the three-ply type.

FIG. 9b is a side view in cross section of a carbon fiber cable 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 carbon fiber cables, in which represents a 2000 dtex / 2 carbon fiber cable after immersion having a Z / S twist, 200/200 rpm (prior art) having a characteristic linear tensile strength, represents a 2000 dtex / 2 carbon fiber cable having a Z / S twist, 200/160 rpm (subjected to a backward twist of 40 rpm in the Z direction) and after immersion, having a bielastic tensile strength characteristic according to the invention, represents a 2000 dtex / 2 carbon fiber cable having a Z / S twist, 200/200 rpm, compressed in the axial direction and the cable layers being open during the immersion process, having a bielastic tensile strength characteristic according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Carbon fiber with its ultra-high modulus and high resistance represents a material that 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 cable of the two-ply or three-ply type, it can be used as reinforcement in pneumatic tires and in mechanical rubber articles such as V-belts (as can be seen in the figures 1 and 2). In applications targeting V-belts, in order to prevent friction between the fibers and to improve the resistance to bending fatigue, the fibers are completely impregnated (full penetration) with adhesive elastomers.

The twisting of the wire improves the fatigue strength of the carbon fiber in bending and under compression, but at the same time reduces the modulus as well as the resistance.

In applications of crown plies of the zero degree type in pneumatic tires with radial ply, the high modulus is required for the retaining force in order to prevent separation of the edges of the belts under conditions of high speed, but also needs initial stretch ability with low forces (low initial modulus) for processability during lifting of the belt pack in the tire making and vulcanization processes in order to avoid cable cuts through the rubber compound of the belt.

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

Nylon 6 and 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 the crown ply in pneumatic tires of the radial ply type for passenger vehicles and vans, but flattening and a low level of modulus are their major drawbacks.

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

According to the invention, the basic production principle of bielastic carbon fiber cable consists of opening the cable layers and inserting the immersion solution in an adhesive between the layers. Carbon fiber cable containing a high percentage of immersion solution in an adhesive such that the RFL between its sheets becomes stretchable with low forces, and during this extension, the sheets of carbon fiber cables exert forces compression on the adhesive material (RFL) and compress it. During this compression process, the cord undergoes elongation with low forces. Once the layers of carbon fiber cables have moved closer to each other, the carbon fiber cable resists elongation and it becomes again a cable with an ultra-high module (as can be seen in FIG. 11).

In order to be able to obtain a bielastic tensile strength characteristic, the sheets of carbon fiber cords can be opened using various methods:

a) unbleached carbon fiber 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 opposite direction to twisting the cable. 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). Carbon fiber cords with their plies open are again subjected to immersion and heat curing and, during these processes, the gaps between the plies of cords are filled with the immersion solution and the surface The outer layers of cables are also covered by the immersion solution.

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

c) carbon fiber 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 carbon fiber cable, in which the immersion solution has entered between the sheets, is dried and heat-cured between 120 ° and 260 ° C.

The bielasticity characteristic of tensile strength of the carbon fiber cable can be modified with the degree (s) of opening of the plies (as can be seen in FIGS. 10b and 10c), with the type of immersion solution, 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 carbon fiber 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 spacings) between the cable layers, which is (are) filled (s) with the immersion solution in an adhesive is (are) greater than 0.15xD 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 in an adhesive (DPU) of the cable after immersion is greater than 20% and less than 50%, preferably greater than 25% 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 12,000 and less than 20,000, 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 torsion coefficient of less than 12,000 have insufficient resistance to bending fatigue and cables with a torsion coefficient of more than 20,000 have significant module reductions.

In accordance with the invention, the total nominal linear density of the cable is greater than 200 dtex and less than 5,000 dtex.

Cables with a value below 200 dtex are not efficient enough and cables with a value above 5,000 dtex are too thick.

Claims (8)

1. Wired in carbon fibers after immersion and heat curing having at least two layers and having a spacing (s) between said layers of cords, the TASE value of which is less than 2.0 cN / dtex at one elongation of 2.0%, characterized in that the spacing (s) spacing (s) between said layers of cables represents (s) more than 15% and less than 80% of the diameter (D) of the cable. 2. Cabled in carbon fibers after immersion and heat curing according to claim 1, the spacing (s) spacing (s) between the layers of cords preferably represent (s) more than 20% and less than 50% the diameter (D) of the cable. 3. Cabled in carbon fibers after immersion and heat curing according to claim 1, the absorption value of the immersion solution in an adhesive (DPU) of said cabled is greater than 20% and less than 50%, in weight. 4. Carbon fiber cord after immersion and heat curing according to claim 1, the absorption value of the immersion solution in an adhesive (DPU) of said cord is preferably greater than 25% and less than 35 %, in weight. 5. Wired in carbon fibers after immersion and heat curing according to claim 1, the torsion coefficient of which is between 12,000 and 20,000, which is calculated by referring to formula (1). 6. Wired in carbon fibers after immersion and heat curing according to claim 1, whose total nominal linear density is between 200 dtex and 5,000 dtex. 7. Wired in carbon fibers 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. Cabled in carbon fibers after immersion and heat curing according to claim 1, which is used as a reinforcement of mechanical rubber articles.