Cap ply strip with alternate nylon 6,6 and PET cords

Abstract

The present invention relates to a novel tire cord fabric or strip made of alternating PET and nylon 6.6 warp cords which is used as tire reinforcement. Such a novel tire cord fabric or strips improve high speed durability, tread separation resistance and impact resistance when used as zero degree spirally wound cap ply in pneumatic radial tires.

Claims

1. A cap ply strip comprising: alternately woven parallel nylon 6,6 and PET cords circumferentially wound on a belt package of a pneumatic radial tire; wherein a cable twist factor of the PET cord, determined according to the following formula
Twist factor=cord cable twist(total cord linear density).sup.1/2, is at least 15% higher than a cable twist factor of the nylon 6,6 cord; wherein the nylon 6,6 and the PET cords in the cap ply strip are arranged in a repeated pattern where two nylon 6,6 cords are followed by one PET cord.

2. The cap ply strip according to claim 1, wherein the cable twist factor of the nylon 6,6 cord is minimum 10,000 and maximum 15,000.

3. The cap ply strip according to claim 1, wherein the cable twist factor of the PET cords is less than 20,000.

4. The cap ply strip according to claim 1, wherein the nylon 6,6 cords and the PET cords are two-ply cords.

5. The cap ply strip according to claim 1, wherein the nylon 6,6 cords and the PET cords are three-ply cords.

6. The cap ply strip according to claim 1, wherein a-linear density of the nylon 6,6 cords and the PET cords is minimum 500 dtex and maximum 5,000 dtex.

7. The cap ply strip according to claim 1, wherein a difference of the linear densities between the nylon 6,6 and the PET cords is less than 15%.

8. A cap ply strip comprising: alternately woven parallel nylon 6,6 and PET cords circumferentially wound on a belt package of a pneumatic radial tire; wherein a cable twist factor of the PET cord, determined according to the following formula
Twist factor=cord cable twist(total cord linear density).sup.1/2, is at least 15% higher than a cable twist factor of the nylon 6,6 cord; wherein the nylon 6,6 and the PET cords in said cap ply strip are arranged in a repeated pattern where one nylon 6,6 cord is followed by two PET cords.

9. The cap ply strip according to claim 1, wherein a-cord count in the strip is minimum 70 epdm (ends per decimeter).

10. The cap ply strip according to claim 1, wherein a difference of the 7% LASE values (determined according to ASTM D885-16) between the PET cords and the nylon 6,6 cords is minimum 25%.

11. The cap ply strip according to claim 1, wherein a difference of the 7% LASE values between the PET cords and the nylon 6,6 cords is minimum 35%.

12. The cap ply strip according to claim 1, wherein a-width of the cap ply strip is minimum 8 mm and maximum 25 mm.

13. The cap ply strip according to claim 1, wherein a-width of the cap ply strip is minimum 10 mm and maximum 15 mm.

14. The cap ply strip according to claim 8, wherein the cable twist factor of the nylon 6,6 cord is minimum 10,000 and maximum 15,000.

15. The cap ply strip according to claim 8, wherein the cable twist factor of the PET cords is less than 20,000.

16. The cap ply strip according to claim 8, wherein the nylon 6,6 cords and the PET cords are two-ply cords.

17. The cap ply strip according to claim 8, wherein the nylon 6,6 cords and the PET cords are three-ply cords.

18. The cap ply strip according to claim 8, wherein a-linear density of the nylon 6,6 cords and the PET cords is minimum 500 dtex and maximum 5,000 dtex.

19. The cap ply strip according to claim 8, wherein a-difference of the linear densities between the nylon 6,6 and the PET cords is less than 15%.

20. The cap ply strip according to claim 8, wherein a-cord count in the strip is minimum 70 epdm (ends per decimeter).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross-sectional view of conventional (prior art) nylon cap ply on cross-ply steel cord belt package after curing process.

(2) a is cross ply steel cord belt package

(3) b is conventional cap ply on belt package

(4) c is tread

(5) FIG. 2 is a cross-sectional view of cap ply according to invention comprising alternately arranged nylon 6.6 and PET cords on cross-ply steel cord belt package after curing process.

(6) a is cross ply steel cord belt package

(7) b is cap ply on belt package according to invention

(8) c is tread

(9) FIG. 3A is a cross-sectional view of the cap ply according to invention on cross-ply steel cord belt package, (1) before curing process, (2) after curing process

(10) A: Nylon 6.6 cord having lower initial modulus

(11) B: PET cord having higher initial modulus

(12) H: Cord penetration difference in rubber matrix

(13) FIG. 3B is a top view of the cap ply strip made of A (nylon 6.6, lower modulus, lower tension) and B (PET, higher modulus, higher tension) cords

(14) FIG. 4A is a cross-sectional view of the cap ply with side-by-side (nylon 6.6/PET) paired cords according to invention on cross-ply steel cord belt package, (1) before curing process, (2) after curing process

(15) FIG. 4B is a top view of side-by-side (paired) A (nylon 6.6, lower modulus, lower tension) and B (PET, higher modulus, higher tension) cords in cap ply strip

(16) FIG. 5 shows the cord-to-cord distance changes after curing process.

(17) (1) before curing process, (2) after curing process

(18) S1: Cord-to-cord distance between A and B before process expansion and curing.

(19) S2: Cord-to-cord distance between A and B after process expansion and curing

(20) S3: Cord-to-cord distance between A and A after process expansion and curing

(21) S4: Cord-to-cord distance between B and B after process expansion and curing

(22) FIG. 6 shows 1+2+1 cord arrangements.

(23) (1) before curing process, (2) after curing process

(24) (1)A+B+B+A+B+B+A+ . . . cord arrangement before process expansion and curing

(25) (2)A+B+B+A+B+B+A+ . . . cord arrangement after process expansion and curing

(26) FIG. 7 shows 2+1+2 cord arrangements.

(27) (1)A+A+B+A+A+B+A+A+ . . . cord arrangement before process expansion and curing

(28) (2)A+A+B+A+A+B+A+A+ . . . cord arrangement after process expansion and curing

DETAILED DESCRIPTION OF THE INVENTION

(29) According to the invention, the spirally wound cap ply fabrics or cap ply strips on belt package of the pneumatic radial tires in circumferential direction, having alternate nylon 6,6 and PET cords as warp; improve the high speed durability due to high modulus of PET cords, high thermal shrink force of nylon 6.6 cords, and increased cord-to-cord distances (less shear stresses) between the cords (cord shiftings in vertical direction, two layer or zig-zag formation, FIGS. 3A, 3B and 5) improve the impact resistance of belt package due to higher energy absorption of nylon 6,6 and higher twist PET cords improves the tread-cap ply separation resistance due to the wavy surface structure of the cap ply. The zig-zag surface enhances also mechanical bonding between cap ply and tread compound and reduces flatspot problem due to less content of nylon 6,6 and higher T.sub.g of PET cord

(30) The nylon 6,6 and PET cords in cap ply strip are two or three-ply cords.

(31) The angle of spirally wound cap ply strips to circumferential center line (or equatorial plane of the tire) is 0 to 5.

(32) In order to have effective nylon 6.6 modulus and fatigue resistance combination, the cable twist factor of the nylon 6.6 cord is minimum 10,000 and maximum 15,000 according to the following formula:
Twist factor=cord cable twist(total cord linear density).sup.1/2(1)

(33) Twist as tpm

(34) Linear density as dtex

(35) In order to obtain the advantages mentioned above, the cable twist of the PET cord is at least 50 tpm higher than that of nylon 6,6 cord (e.g. nylon 6.6 cord, 14002, Z/S, 250/250 tpm, and PET cord, 14402, Z/S, 300/300 tpm or 350/350 tpm).

(36) If the cord twist difference is less than 50 tpm between the first and the second cords, the LASE, modulus or extensibility difference between the first and the second cords becomes insignificant. Under those conditions, the wavy cap ply surface can not be created in tire.

(37) The total linear densities of the cords are minimum 500 dtex and maximum 5,000 dtex. The cap ply cords having less than 500 dtex are too thin and LASE values are too low which can not provide enough restraining force even with very high cord counts (epdm). Besides this drawback, during process lifting and curing, they can cut the skim compound of the belt layer and contact to steel cords. The cap ply cords having higher than 5,000 dtex are too thick and requires too much rubber for coating. The potential drawback for such cords in tire is increased rolling resistance and heat build-up in crown area.

(38) The total linear density difference between the first and the second cords is less than 15%. Preferably, the total linear densities of first and second cords should be same.

(39) According to the invention, the sequence of the nylon 6,6 and PET cords parallel to each other in a cap ply strip is in an alternating form as A+B+A+B+A+B+ . . . and so on, wherein A is the nylon 6,6 cord with lower twist, and B is the PET cord with higher twist compared to A. Such a cap ply strip creates a uniform wavy surface after curing process, which bonds to tread compound strongly improving tread separation resistance under high speed conditions.

(40) According to the invention, the sequence of the nylon 6,6 and PET cords parallel to each other in a cap ply strip is in an alternating form as AB+AB+AB+ . . . and so on, as paired cords, wherein A is the nylon 6,6 cord with lower twist, and B is the PET cord with higher twist compared to A.

(41) According to the invention, the sequence of the nylon 6,6 and PET cords parallel to each other in a cap ply strip is in an alternating form as A+B+B+A+B+B+A+B+B+ . . . and so on, wherein A is the nylon 6,6 cord with lower twist, and B is the PET cord with higher twist compared to A.

(42) According to the invention, the sequence of the nylon 6,6 and PET cords parallel to each other in a cap ply strip is in an alternating form as A+A+B+A+A+B+A+A+B+ . . . and so on, wherein A is the nylon 6,6 cord with lower twist, and B is the PET cord with higher twist compared to A.

(43) According to the invention, the cord count in strip is minimum 70 epdm (ends per decimeter). In case of cord counts lower than 70 epdm, the effectiveness of surface waviness is not enough for mechanical bonding to tread.

(44) According to the invention, the difference between the 7% LASE values of the first and second nylon cords is minimum 15%, and preferably 25% (7% LASE values are determined according to ASTM D885-16).

(45) According to the invention, the width of the cap ply strips is 8 to 25 mm, preferably 10 to 15 mm.