Bielastic polyester tire cord as cap ply

Abstract

The present invention relates to a novel polyester tire cord reinforcement which has bi-elastic tensile properties. The tire cord includes at least two cord plies, and there is a spacing between the cord plies. Such a novel bi-elastic polyester tire cord improves high speed durability and significantly eliminates flatspotting when used as a cap ply in pneumatic radial tires.

Claims

1. A dipped and heat-set polyester cord, comprising a plurality of cord plies having a spacing between the plurality of cord plies, wherein a TASE at 2.0% elongation of the dipped and heat-set polyester cord is less than 2.0 cN/dtex; wherein the spacing between the plurality of cord plies is longer than 10% and shorter than 60% of a cord diameter of the cord plies.

2. The dipped and heat-set polyester cord according to claim 1, wherein the spacing between the plurality of cord plies of the dipped and heat-set polyester cord is preferably longer than 20% and shorter than 50% of the cord diameter.

3. The dipped and heat-set polyester cord according to claim 1, wherein an adhesive dip pick-up (DPU) of the cord is higher than 8% and less than 30% by weight.

4. The dipped and heat-set polyester cord according to claim 1, wherein the adhesive dip pick-up (DPU) of the dipped and heat-set polyester cord is preferably higher than 10% and lower than 20% by weight.

5. The dipped and heat-set polyester cord according to claim 1, wherein the dipped and heat-set polyester cord has a twist factor in between 10,000-22,000; wherein the twist factor is calculated according to the following formula (1):
twist factor =cord twist (tpm) square root of total nominal cord dtex (1).

6. The dipped and heat-set polyester cord according to claim 1, wherein the dipped and heat-set polyester cord has a total nominal linear density in between 800 dtex-6,000 dtex.

7. The dipped and heat-set polyester cord according to claim 1, wherein the dipped and heat-set polyester cord is a polyethylene terephthalate cord.

8. The dipped and heat-set polyester cord according to claim 1, wherein the dipped and heat-set polyester cord is a polyethylene naphthalate cord.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross-sectional view of a conventional (prior art) two-ply polyester cord.

(2) FIG. 2 is a cross-sectional view of a conventional (prior art) three-ply polyester cord.

(3) FIG. 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).

(4) FIG. 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).

(5) FIG. 5 is a cross-sectional view of a conventional (prior art) two-ply nylon cord.

(6) FIG. 6 is a cross-sectional view of a conventional (prior art) three-ply nylon cord.

(7) FIG. 7A-7D describes the opening of the cord cross sections and subsequent dip penetration between the cord plies for two and three-ply polyester cords, in which

(8) FIG. 7A are cross-sectional views of two and three-ply polyester cords in closed-plies form,

(9) FIG. 7B are cross-sectional views of two and three-ply polyester cords in opened-plies form,

(10) FIG. 7C are cross-sectional views of two and three-ply polyester cords in dip impregnated form according to invention,

(11) FIG. 7D is adhesive dip (RFL) filling the openings between the plies and covering the cord surface.

(12) FIG. 8A are respectively lateral and cross-sectional views of a conventional two-ply polyester cord.

(13) FIG. 8B are respectively lateral and cross-sectional views of two-ply polyester cord in opened form according to invention (before dipping step).

(14) FIG. 9A are respectively lateral and cross-sectional view of a conventional three-ply polyester cord.

(15) FIG. 9B are respectively lateral and cross-sectional views of a three-ply polyester cord in opened form according to invention (before dipping step).

(16) FIG. 10 are cross-sectional views of closed and opened forms of cord plies. D is cord diameter and s is spacing (opening) between cord plies.

(17) FIG. 11 shows load-elongation curves of a polyester (PET) cords in which,

(18) curve 1 is 1670 dtex/2 dipped PET cord having Z/S, 350/350 tpm twist (prior art) having linear tensile characteristic,

(19) curve 2 is 1670 dtex/2 aramid cord having Z/S, 350/300 tpm (50 tpm back-twisted in Z direction) and dipped having bielastic tensile characteristic according to invention.

DETAILED DESCRIPTION OF THE INVENTION

(20) PET with its high modulus and low thermal shrinkage is a dimensionally stable material. In twisted form as two or three-ply cord, it can be used as carcass and cap ply reinforcement in radial passanger and light truck tires (FIG. 1 and FIG. 2).

(21) The cord twisting improves bending and compression fatigue resistance of the PET, but at the same time reduces the modulus and strength too.

(22) In zero degree cap ply applications in pneumatic radial tires, the high modulus is needed for restraining force to prevent belt edge separations under high speed conditions, but initial extensibility with low forces (initial low modulus) is also needed for processability during lifting of belt package in tire building and curing processes to avoid cord cuttings through the belt skim compound.

(23) Aramid/Nylon hybrid cords solve this issue, but existence of nylon creates flatspot problem and asymmetric cord structure (FIG. 3 and FIG. 4)

(24) Two or three-ply nylon 6 and 6.6 cords (FIG. 5 and FIG. 6) are well known reinforcements as cap ply in radial passenger car and light truck tires, but flatspot and low level of modulus are their major drawbacks.

(25) According to the present invention, two or more ply polyester cords without any low modulus component ply like nylon, can be produced with bielastic tensile properties (FIG. 7A-7D). Such a novel bi-elastic polyester cords can be used as zero degree cap ply in radial tires to improve high speed durability and do not show any significant flatspotting.

(26) According to invention, the basic production principle of the bielastic polyester cord is to open the cord plies and insertion of the adhesive between the plies. The polyester cord containing high percentage of adhesive like RFL between its plies becomes extensible with low forces and during this extension the polyester cord plies applies compressive forces to the adhesive material (RFL) and squeeze it. During this squeezing process cord elongates with low forces. After polyester cord plies having been approached to each other (closed), polyester cord resist to elongation and it becomes high modulus cord again (FIG. 11).

(27) In order to obtain a bielastic tensile characteristics, the polyester cord plies can be opened with different methods: aThe two or more ply greige polyester cords are heat-set at a temperature between 120 C. and 250 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 (FIGS. 8-10) The polyester 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. bThe two or more ply greige polyester cords are dipped and heat-set at a temperature between 120 C. and 250 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 polyester 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 additional dip solution. cThe two or more ply polyester cords are subjected to axial compression during dipping process, and the cord with opened plies under compression absorbs dip solution between the open cord plies. After dipping process, the polyester cord with penetrated dip solution between its plies are dried and heat set between 120 and 250 C.

(28) The tensile bielasticity characteristic of the polyester cord can be changed with the ply opening degree(s) in FIG. 10B and FIG. 10D), dip type, dip content between the plies and the curing degree of the dip at high temperature (dip hardness).

(29) According to invention, two or more ply polyester cord has less than 2.0 cN/dtex TASE value at 2% 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 0.1 xD and less than 0.6 xD.

(30) 2% TASE higher than 2.0 cN/dtex cause tight cords when applied as cap ply during process lifting of the tire.

(31) Preferably, s is higher than 0.2 xD and less than 0.5 xD.

(32) According to invention, the dip pick up (DPU) in the dipped cord is higher than 8% and less than 30%, preferably, higher than 10% and less than 20%, by weight.

(33) Less than 8% DPU can not totally fill the the openings between the cord plies, and higher than 30% DPU leads to too thick cord diameters.

(34) According to invention, the twist factor of the cord is higher than 10,000 and less than 22,000 which is determined based on the following formula;
Twist factor=cord twist (tpm)square root of total nominal cord dtex (1)

(35) The cords with lower than 10,000 twist factor have insufficient fatigue resistance under bending and the cords with higher than 22,000 twist factor have significant modulus reductions.

(36) According to invention, the total nominal cord linear density is higher than 800 dtex and less than 6000 dtex.

(37) The cords having less than 800 dtex are not effective enough, and the cords having higher than 6000 dtex are too thick.

(38) The preferable polyester polymer types are polyethylene terephthlate and polyethylene naphthlate.