FIELD OF INVENTION
The present invention relates to a novel two or more ply aramid tire cord reinforcement which contain adhesive dip not only on the cord surface, but also between their plies. Such a novel inter-ply dip penetrated bi-elastic tire cord improves high speed durability and eliminates flatspotting when used as carcass reinforcement (body ply) in pneumatic radial and bias tires.
DESCRIPTION OF THE RELATED ART
It is well known that the conventional textile tire reinforcements are two or three- ply cords having closed plies, which means, each individual ply has interface contact with each other. Such textile cords, for example, can be rayon, polyester, nylon and aramid/nylon hybrid cords in pneumatic radial and bias tires.
The aramid/nylon hybrid cords having bi-elasic tensile properties comprising high modulus aramid and low modulus nylon yarns have improved bending fatigue resistance compared to the aramid cord with comparable constructional parameters like total dtex, and twist multiplier. The cushion effect of the low modulus nylon(less abrasion between the cord plies) improves the fatigue resistance of aramid/nylon hybrid cords.
 US Patent No. 4,155,394
describes a composite (hybrid) cord suitable for tire reinforcement comprised of a plurality of plies of yarns selectively cabled in a manner so that, upon application of longitudinal stress, at the initial elongation of the cable, the primary load bearing ply is a polyester or a nylon yarn and so that after appreciable elongation of the cable, the primary load bearing yarn is an aramid yarn. The invention further relates to a pneumatic tire, industrial belt or hose having a carcass containing a fabric of such a cord as a reinforcing member.
 US Patent No. 7,484,545
describes heavy dtex hybrid cords having high modulus aramid and low modulus nylon as carcass and crown reinforcement in radial aircraft tires. The breaking strength of such hybrid cords are higher than 1050N and elongation at break values are higher than 12 and less than 20% .
 US Patent No. 2014/0360648
describes a carcass cord consisting of one single aramid first yarn twisted helically about one single polyester second yarn. The first yarn and second yarn have different moduli of elasticity. The first yarn has a modulus greater than the modulus of the second yarn.
 US Patent No. 2014/0223879
describes an aramid fiber cord which has high strength as well as good disk fatigue property such that, when it is used as a tire reinforcement, the degradation of its physical properties and the degradation of its adhesion strength with respect to a rubber after long and high speed driving can be minimized, and to a method for manufacturing the same. The aramid fiber cord of the present invention comprises an aramid cabled yarn; and an adhesive coated on an outer surface of the aramid cabled yarn, wherein penetration rate of the adhesive into the aramid cabled yarn is 3.5 to 9%.
SUMMARY OF INVENTION
The invention according to claim 1, relates to a two or more ply cord reinforcement made of aramid yarn having bielastic tensile properties. Namely, low initial modulus and high modulus after initial elongation. In order to prevent excessive modulus and breaking strength loss, high level of cord twisting has been avoided.
The production principle of the transformation of linear tensile behaviour of the aramid cord to bielastic characteristic is based on the opening the cord plies and insertion of RFL adhesive in it. The aramid cord having RFL between its opened plies shows bielastic tensile behaviour under tension.
Cord: The product formed by twisting together two or more plied yarns
Cord ply: Plied single yarns within cord.
Dtex: The gram weight of yarn having 10.000 meter length.
Flatspotting: Cords in tire having low Tg and high thermal shrink force is subjected to shrinkage at footprint. When cooled in this position, the cord maintains flatspot until it again reaches its Tg in use.
Greige cord: Twisted cord before dipping and heat-setting
Heat-setting: The process of conferring dimensional stability and heat resistance to the yarns, cords or fabrics by means of either moist or heat.
Heat-set cord: Cord exposed to high temperature (e.g. 120°C to 260°C under tension)
Linear density: Weight per unit length as g/dtex or g/d (denier)
Spacing(s): Mutual ply-to-ply distance within a multi-ply twisted cord
TASE at 1.0% elongation: Stress at 1.0% elongation as cN/dtex
Tenacity: Breaking force (N) divided by linear density (dtex)
Tg: Glass transition point of polymer
Total nominal cord dtex: Sum of nominal yarn linear densities (3340 dtex for 1670x2 cord)
Twist: Number of turns about its axis per meter of a yarn or cord (t/m or tpm)
Ultra high modulus yarn: Tensile modulus higher than 100GPa
BRIEF DESCRIPTION OF THE DRAWINGS
Figure-1 and 2 are cross-sectional views of conventional (prior art) two and three-ply aramid cords respectively.
Figure-3 is a cross-sectional view of a conventional (prior art) two-ply hybrid cord in which,
A is aramid ply (yarn), B is nylon ply(yarn)
Figure-4 is a cross-sectional view of a conventional (prior art) three-ply hybrid cord in which,
A is aramid ply (yarn) and, B is nylon ply(yarn)
Figure-5 and 6 are cross-sectional views of conventional (prior art) two and three-ply nylon cords respectively.
Figure-7 describes the opening of the cord cross-sections and subsequent dip penetration between the cord plies for two and three-ply aramid cords, in which
A is cross-sectional view of two and three-ply aramid cords in closed-plies form,
B is cross-sectional view of two and three-ply aramid cords in opened-plies form,
C is cross-sectional view of two and three-ply aramid cords in dip impregnated form according to invention.
D is adhesive dip (RFL) filling the openings between the plies and covering the cord surface.
Figure-8a is lateral and cross-sectional view of conventional two-ply aramid cord.
Figure-8b is lateral and cross-sectional view of two-ply aramid cord in opened form according to invention (before dipping step).
Figure-9a is lateral and cross-sectional view of conventional three-ply aramid cord
Figure-9b is lateral and cross-sectional view of three-ply aramid cord in opened form according to invention (before dipping step).
Figure-10a, 10b, 10c and 10d are cross-sectional views of closed and opened forms of cord plies. D is cord diameter and s is spacing (opening) between cord plies.
Figure-11 is load-elongation curves of aramid cords in which,
- 1 is 1670dtex/3 dipped aramid cord having Z/S, 320/320tpm twist (prior art) having linear tensile characteristic,
- 2 is 1670dtex/3 aramid cord having Z/S, 320/280 tpm (40tpm back-twisted in Z direction) and dipped having bielastic tensile characteristic according to invention.
DETAILED DESCRIPTION OF THE INVENTION
Aramid with its ultra high modulus and high strength is very dimensionally stable material. Due to its highly crystalline microstructure, it does not show any significant thermal shrinkage when exposed to high temperature. In twisted form as two or three-ply cord, it can be used as reinforcement in tires and mechanical rubber goods like V-belts (figures 1 and 2).
The cord twisting improves bending and compression fatigue resistance of the aramid, but at the same time reduces the modulus and strength too.
Aramid/Nylon hybrid cords can be used as carcass reinforcement in radial aircraft tires and bias truck tires to reduce the number of plies and rubber (Figures-3 and 4). By reducing number of of carcass layers (plies), the total gauge at sidewall becomes thinner and flexible. On the other hand, tire with less rubber becomes lighter and cooler under dynamic conditions due to less rubber hysteresis.
Two or three-ply nylon 6 and 6.6 cords(Figures-5 and 6) are well known reinforcements as carcass in radial aircraft tires and bias truck tires, but due to lower breaking strength(tenacity) of nylon cords, it is necessary to use several carcass layers in such tires. Interlaminar shear strains between such carcass layers cause heat build up and temperature rise resulting in early ply separations and tire failures.
According to the present invention, two or more ply aramid cords without any low modulus component ply like nylon, can be produced with bielastic tensile properties (Figure-7). Such novel bi-elastic aramid cords can be used as carcass reinforcement in radial and bias tires with improved high speed durability and without any flatspotting.
According to invention, the basic production principle of the bielastic aramid cord is to open the cord plies and insertion of the adhesive between the plies. The aramid cord containing high content of adhesive like RFL between its plies becomes extensible with low forces and during this extension the aramid cord plies applies compressive forces to the adhesive material (RFL) and squeeze it. During this squeezing process cord elongates with low forces. After aramid cord plies having been approached to each other, aramid cord resist to elongation and it becomes ultra high modulus cord again (Figure-11).
In order to obtain a bi-elastic tensile characteristics, the aramid cord plies can be opened with different methods:
- a- The two or more ply greige aramid cords are heat-set at a temperature between 120°C and 260°C and after cooling down they are partially back-twisted in opposite direction of cord twist. During this back-twisting process, the cord plies are opened(Figures-8a, 8b, 9a, 9b, 10a, 10b, 10c and 10d) The aramid cords with its opened plies are dipped and heat set again, and during this process the voids between cord plies are filled with dip solution and the external surface of the cord plies are also covered dip solution.
- b- The two or more ply greige aramid cords are dipped and heat-set at a temperature between 120°C and 260°C and after cooling down they are partially back-twisted in opposite direction of cord twist. During this back-twisting process, the cord plies are opened. The aramid cords with their opened plies are dipped and heat set again, and during this process the voids between cord plies are filled with dip solution and the external surface of the cord plies are also covered additional dip solution.
- c- The two or more ply aramid cords are subjected to axial compression during dipping process, and the cords with opened plies under compression absorbs dip solution between the open cord plies. After dipping process, the aramid cord with penetrated dip solution between the plies are dried and heat set between 120° and 260°C.
The tensile bi-elasticity characteristic of the aramid cord can changed with the ply opening degree(s) in figure-10b and 10d), dip type, dip content between the plies and the curing degree of the dip at high temperature (dip hardness).
According to invention, two or more ply aramid cord has less than 2.0cN/dtex TASE value at 1.0% elongation determined in accordance with ASTM D885-16 and the spacing(s) between the cord plies which is filled with adhesive dip, is higher than 0.1xD and less than 0.5xD.
The aramid cords with 1.0% TASE higher than 2.0cN/dtex have not enough extensibility and bending (flexural) fatigue resistance.
Preferably, s is higher than 0.2xD and less than 0.4xD.
According to invention, the dip pick up (DPU) in the dipped cord is higher than 10% and less than 50%, preferably, higher than 15% and less than 35%, by weight.
Less than 10% DPU can not totally fill the the openings between the cord plies, and higher than 50% DPU leads to too thick cord diameters.
According to invention, the twist factor of the cord is higher than 10,000 and less than 25,000 which is determined based on the following formula;
The cords with lower than 10,000 twist factor have insufficient fatigue resistance under bending and the cords with higher than 25,000 twist factor have significant modulus reductions.
According to invention, the total nominal cord linear density is higher than 600dtex and less than 6000dtex.
The cords having less than 600dtex are not effective enough, and the cords having higher than 6000dtex are too thick.
1. A dipped and heat-set aramid cord has at least two plies and has spacing(s) between the said cord plies which has less than 2.0cN/dtex TASE at 1.0% elongation (in accordance with ASTM D885-16) is characterized in that,
the spacing(s) between the said cord plies is longer than 10% and shorter than 50% of the cord diameter (D).
2. A dipped and heat-set aramid cord according to claim 1 wherein the spacing(s) between the cord plies of the said cord is preferably longer than is preferably longer than 20% and shorter than 40% of the cord diameter (D).
3. A dipped and heat-set aramid cord according to claim 1 wherein the adhesive dip pick up (DPU) of the said cord is higher than 10% and less than 50%, by weight.
4. A dipped and heat-set aramid cord according to claim 1 wherein the adhesive dip pick up (DPU) of the said cord is preferably higher than 15% and lower than 35%, by weight.
A dipped and heat-set aramid cord according to claim 1 has a twist factor in between 10,000 and 25,000 which is calculated according to formula (1).
6. A dipped and heat-set aramid cord according to claim 1 has a total nominal linear density in between 600 dtex and 6,000 dtex.
1. Getauchte und thermofixierte Aramidschnur weist mindestens zwei Lagen undeinen Abstand (Abstände) zwischen den genannten Schnurlagen auf, der (die) weniger als 2.0 cN/dtex TASE bei einer Dehnung von 1.0% (gemäß ASTM D885-16) aufweist (aufweisen), ist dadurch gekennzeichnet, dass ein Abstand (die Abstände) zwischen den genannten Schnurlagen länger als 10% und kürzer als 50% des Schnurdurchmessers (D) ist (sind).
2. Getauchte und thermofixierte Aramidschnur nach Anspruch 1, wobei der Abstand (Abstände) zwischen den Schnurlagen der genannten Schnur vorzugsweise länger als 20% und kürzer als 40% des Schnurdurchmessers (D) ist (sind).
3. Getauchte und thermofixierte Aramidschnur nach Anspruch 1, wobei der Klebstoff-Tauchaufnehmer (DPU) der genannten Schnur nach Gewicht mehr als 10% und weniger als 50% ist.
4. Getauchte und thermofixierte Aramidschnur nach Anspruch 1, wobei der Klebstoff-Tauchaufnehmer (DPU) der genannten Schnur nach Gewicht vorzugsweise höher als 15% und niedriger als 35% ist.
Getauchte und thermofixierte Aramidschnur nach Anspruch 1 weist einen Verdrillungsfaktor zwischen 10,000 und 25,000 auf, der gemäß Formel (1) berechnet wird.
6. Getauchte und thermofixierte Aramidschnur nach Anspruch 1 weist eine nominelle lineare Gesamtdichte zwischen 600 dtex und 6,000 dtex auf.
1. Corde en aramide trempée et thermofixée a au moins deux plis et a un (des) espacement(s) entre lesdits plis qui a moins de 2.0cN/dtex TASE à un allongement de 1.0% (conformément à la norme ASTM D885-16) est caractérisée en ce que l'espacement (les espacements) entre lesdits plis de corde est (sont) supérieur à 10% et inférieur à 50% du diamètre (D) de la corde.
2. Corde en aramide trempée et thermofixée selon la revendication 1 dans laquelle l'espacement (les espacements) entre les plis de ladite corde est (sont) de préférence plus long que 20% et plus courte que 40% du diamètre (D) de la corde.
3. Corde en aramide trempée et thermofixée selon la revendication 1 dans laquelle le ramassage de l'adhésif par trempage (DPU) de ladite corde est supérieur à 10% et inférieur à 50%, en poids.
4. Corde en aramide trempée et thermofixée selon la revendication 1 dans laquelle le ramassage de l'adhésif par trempage (DPU) de ladite corde est de préférence supérieur à 15% et inférieur à 35%, en poids.
Corde en aramide trempée et thermofixée selon la revendication 1 a un facteur de torsion compris entre 10,000 et 25,000 qui est calculé selon la formule (1).
6. Corde en aramide trempée et thermofixée selon la revendication 1 a une densité linéaire nominale totale comprise entre 600 dtex et 6,000 dtex.