HYBRID CORD AS CARCASS REINFORCEMENT IN BIAS TIRES

Abstract

A bias tire carcass reinforced with hybrid cords consisting one ply aramide yarns (1) and one ply nylon yarns (2), and nylon content within cord is between 45 to 65%; the nylon yarn content within those range improves fatigue resistance and reduces sidewall gauge with respect to reference bias tire having nylon carcass; in one embodiment of the present invention, a bias tire carcass for pneumatic tires which have reinforcing layers comprising hybrid cords consist of one ply is made of aramide yarns and one ply is made of nylon yarns with 45-65% nylon content by weight, are balanced twisted cords.

Claims

1. A bias carcass for pneumatic tires comprising plurality of two ply hybrid cords, wherein the two ply hybrid cords consist of a first ply of aramide yarns and a second ply of nylon yarns; the two ply hybrid cords have 45-65% nylon content by weight and a total linear density value between 6000-9000 dtex and twisting levels of 150-400 turns/meter.

2. The bias carcass for pneumatic tires according to claim 1, wherein the two ply hybrid cords have 50-60% nylon content by weight.

3. The bias carcass for pneumatic tires according to claim 1, wherein the two ply hybrid cords are balanced twisted cords.

4. The bias carcass for pneumatic tires according to claim 1, wherein the second ply of nylon yarns is polyamide 66.

5. The bias carcass for pneumatic tires according to claim 1, wherein the second ply of nylon yarns is polyamide 6.

6. The bias carcass for pneumatic tires according to claim 1, wherein the first ply of aramide yarns has up to 3% overfeed.

7. The bias carcass for pneumatic tires according to claim 2, wherein the two ply hybrid cords are balanced twisted cords.

8. The bias carcass for pneumatic tires according to claim 2, wherein the second ply of nylon yarns is polyamide 66.

9. The bias carcass for pneumatic tires according to claim 3, wherein the second ply of nylon yarns is polyamide 66.

10. The bias carcass for pneumatic tires according to claim 7, wherein the second ply of nylon yarns is polyamide 66.

11. The bias carcass for pneumatic tires according to claim 2, wherein the second ply of nylon yarns is polyamide 6.

12. The bias carcass for pneumatic tires according to claim 3, wherein the second ply of nylon yarns is polyamide 6.

13. The bias carcass for pneumatic tires according to claim 7, wherein the second ply of nylon yarns is polyamide 6.

14. The bias carcass for pneumatic tires according to claim 2, wherein the first ply of aramide yarns has up to 3% overfeed.

15. The bias carcass for pneumatic tires according to claim 3, wherein the first ply of aramide yarns has up to 3% overfeed.

16. The bias carcass for pneumatic tires according to claim 4, wherein the first ply of aramide yarns has up to 3% overfeed.

17. The bias carcass for pneumatic tires according to claim 5, wherein the first ply of aramide yarns has up to 3% overfeed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The characteristics and other advantages of the invention will be better understood with reference to the description of a non-limitative example, with which are associated in the drawings;

[0018] FIG. 1a. is a Radial cross-section view of two ply hybrid cord in which, [0019] 1. aramide ply (semi-circular) [0020] 2. nylon ply (semi-circular) [0021] 3. contact surface of aramide and nylon plies (interface)

[0022] FIG. 1b. is a Radial cross-section view of three-ply hybrid cord in which, [0023] 4. aramide ply (triangular) [0024] 5. nylon ply (triangular) [0025] 6. contact surface of aramide and nylon plies (interface)

DETAILED DESCRIPTION

[0026] According to the present invention, two ply aramid/nylon hybrid cords which have one ply is made of aramide yarns and the other ply is made of nylon yarns, these yarns having a twist in one direction prior to plying (may also called as cabling), and the plurality of yarns being plied together with a twist in the opposite direction to form cord, the yarn twist being at least equal to the plying (cabling) twist, said yarn and plying (cabling) twists being such as to give a balanced twisted cord with optimum nylon content, improves bias tire endurance and enables to eliminate post-cure inflation process. In two-ply hybrid cord constructions, aramide and nylon plies (yarns within cord) have smooth contact surface with each other at interface. In case of three or higher number of plies, semi-circular ply cross-sections become triangular which gives rise to increased contact surface and higher degree of friction at the interface under dynamic conditions. On the other hand, interface filaments of the each ply yarn are much more deformed due to triangular cross-sections. Therefore, two-ply hybrid cord constructions are proposed in our invention.

[0027] Disc fatigue lab results are given below. According to the lab results two-ply hybrid cord having the same helix angle and even the same nylon content gives better fatigue resistance results (strength retention after fatigue) than three-ply hybrid cord.

TABLE-US-00001 TABLE 1 Disc fatigue analysis results AR3340 + AR1670/2 + Cord construction NY2800 NY2800/1 AR1670/2 + 1400 Number of plies 2 3 3 Nylon content (%) 45.6 45.6 29.5 Cord twist 335 335 380 Helix angle 46? 46? 46? Retained strength after 85 81 74 disc fatigue* *3.6 million cycle(2.0% extension and 14% compression)

[0028] Tire results confirm the lab results. Reference is a bias truck tire 10.00-20 with 8 ply 1400/2 nylon carcass. Based on equal carcass strength, by using AR/NY hybrid cords, number of carcass plies has been reduced from 8 to 4. By using AR3340+NY2800 as carcass reinforcement, overload endurance has been improved approximately 40% compared to AR1670/2+NY1400/1 (4-ply carcass) and nylon 6, 1400/2 (8-ply carcass).

[0029] Nylon has two-fold function, namely it works as lubricant or cushion together with aramide yarn improving dynamic fatigue resistance, and other function is to enhance overall hybrid cord (aramide+nylon) adhesion. As well known, non-active surface of aramide filaments gives poor adhesion retention under flexing. Nylon filaments having more active sites (functional groups) on their surface gives superior adhesion even with conventional RFL adhesives.

[0030] Optimum nylon content of the said hybrid cord is preferably between 45 and 65%, more preferably between 50 and 60%. If the nylon content of said hybrid cord less than 45%, flex fatigue resistance and adhesion retention after flexing becomes poorer, and if the nylon content of said hybrid cord is higher than 65%, effective modulus and tenacity becomes lower. With higher nylon contents, cord diameters becomes larger which leads to higher rubber gauge and lower cord-to-cord distance (rivet area) between parallel cords within the carcass layer. Lower rivet area between cords can easily initiate the crack between the cords under flexing conditions.

[0031] High nylon surface on hybrid cords improves cord-rubber separation resistance under dynamic conditions, namely against inter-laminar stresses between carcass plies due to pantographing movements.

[0032] In the present invention, total linear density value of the said hybrid cord is preferably between 4000-12000 dtex, more preferably between 6000-9000 dtex. The total hybrid cord linear density value can be obtained by adding the nominal linear density values of aramid and nylon yarns used in hybrid cord (e.g. the total linear density value for AR3340+NY2800 is 6140 dtex).

[0033] The invention in its preferred form, twist level of the hybrid cord changes between 150 and 400 turns per meter (tpm).

[0034] In most preferred embodiment of the present invention, a bias tire carcass for pneumatic tires which have reinforcing layers comprising hybrid cords consist of one ply is made of aramide yarns and one ply is made of nylon yarns with 50-60% nylon content by weight, are balanced twisted cords and total linear density value of said hybrid cord is between 6000-9000 dtex.

[0035] In order to increase the breaking strength (simultaneous breaking of nylon and aramid plies in hybrid cord), up to 3% overfeed of aramid ply can be applied during twisting process (the length of aramid yarn in untwisted hybrid cord can be up to 3% longer than nylon yarn).