Tire cord fabric

Abstract

The present invention relates to a reinforcement ply of a pneumatic tire wherein the paired cords are used instead of single cords as warp.

Description

[0001] TIRE CORD FABRIC

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a reinforcement ply of a pneumatic tire wherein the paired cords are used instead of single cords as warp.

[0004] BACKGROUND OF INVENTION

[0005] In pneumatic tires, the cord reinforcements used as the carcass and the cap ply have twisted structures and circular cross-sections as it is shown in Figure 1 . The twist directions of yams and cords are expressed with letters S and Z. When the twisted yam or cord is in vertical position, if the spiral bendings around the central axis is parallel to the middle portion of the letter S, it is defined as S twisted (S-like twist); if it is parallel to the middle portion of the letter Z, it is defined as Z twisted (Z-like twist).

[0006] In a rubberized (calendered) tire cord fabric, there are additional mbber layers on the top and bottom sides of the cords in order to provide required tire performance. On the other hand, mbber matrix causes heat buildup and rolling resistance under dynamic conditions because of its viscoelastic behavior.

[0007] The ply thickness is calculated according to a cord diameter having required breaking strength for a given ply strength and optimized number of cords per unit length (epdm). In order to decrease the mbber and tire weight, the ply thickness should be decreased. With this purpose, the cord diameter can be reduced by increasing the epdm (cord count) without changing the unit ply strength. But the increase in epdm also means a reduction in spacing between the cords which may cause poor bending and compression fatigue resistance in tire. For this reason, it is a very limited possibility to increase epdm without sacrificing tire durability.

[0008] According to U.S. Pat. No. 6,959,534, to reduce twisting cost, the tire cords having lower ply twists than that of cable twists have already been used in tire industry as reinforcement. According to the said patent, the dipped / heat-set and calendered cords are difficult to process due to their residual torques, caused by the unbalanced ply and cable twists. The residual torques result in the tip rise and curling in the dipped, and rubberized cord fabrics. For this reason, the cords having S and Z twists are placed alternately in the fabric, in the said patent application, instead of conventional tire cord fabric made of fully S twisted cords. In the application, it is stated, when the cords having unbalanced S and Z twists used alternately in the cord fabric, the torques formed in dipped and calendered cord fabric in S and Z direction would neutralize each other and eliminate the process problems. However, the said patent does not mention the potential superiority of mutual Z and S twisted cords with respect to reduced shear strain between them. Besides the technical advantage, which was not mentioned, the unbalanced twisted cords disclosed in the patent have lower breaking strength and modulus compared to the corresponding balanced twisted cords.

[0009] Patent document numbered GB243705 present in the state of the art related with tire reinforcement fabric having side by side cords (warps) having opposite twist directions. The possible goal could be balancing residual cord torques which may result in tip rise or curling in fabric during processing. Nevertheless, it does not mention the potential advantage of side-by-side cords with opposite twisting direction in tire performance, especially bending and compression fatigue resistance. The other drawback of this document is the lack of the spacing (rivet) between the paired strips. Such fabrics without any rivet do not function in bias or radial tires and results in cord breaks under bending and compression.

[0010] BRIEF DESCRIPTION OF THE DRAWINGS

[0011] “A tire cord fabric” developed to fulfill the objectives of the present invention is illustrated in the accompanying figures, in which:

[0012] FIG. 1 side view and top sectional view of prior art

[0013] FIG. 2 (a) side view and top sectional view of the tire cord fabric having paired cords with similar twists (b) side view and top sectional view of the single paired cord having similar twists.

[0014] FIG. 3 (a) side view and top sectional view of the tire cord fabric having paired cords with opposite twists (b) side view and top sectional view of the single paired cord having opposite twists.

[0015] FIG. 4 (a) view of the angular movements of the similar twisted cords under compression (b) view of the angular movements of the opposite twisted cords under compression.

[0016] FIG. 5 (a) view of the surface strain directions of the similar twisted cords under compression (b) view of the surface strain directions of the opposite twisted cords under compression.

[0017] FIG. 6 (a) view of the angular movements of the similar twisted cords under tension (b) view of the angular movements of the opposite twisted cords under compression.

[0018] FIG. 7 (a) view of the surface strain directions of the similar twisted cords under tension (b) view of the surface strain directions of the opposite twisted cords under compression.

[0019] FIG. 8 (a) view of the cord structure having Z yam twist / S cord twist (b) view of the cord structure having S yam twist / Z cord twist. The components given in the figures are numbered and the numbers refer to the following:

[0020] 1. Tire cord fabric

[0021] 2. Paired cord

[0022] 3. S twisted cord

[0023] 4. Z twisted cord

[0024] 5. Similar twisted cord pair

[0025] 6. Opposite twisted cord pair

[0026] 7. RFL adhesive

[0027] 8. S twisted yam

[0028] 9. Z twisted yam

[0029] A. Weft yams

[0030] O. Prior art

[0031] P. Tensile or compressive force

[0032] R. Angular movement direction of the cords

[0033] D. Cord surface movement direction

[0034] BRIEF DESCRIPTION OF THE INVENTION

[0035] The objective of the present invention is to provide afire cord fabric having opposite twisted paired cords, namely S and Z twisted cords as pairs. The invention is providing a tire cord fabric with reduced shear strain within and between the paired cords under dynamic conditions. Further objective of the present invention is to provide a tire cord fabric which enables to use less rubber and higher content of cords in a given cord-rubber composite volume (thinner cords) resulting lighter pneumatic tire.

[0036] DETAILED DESCRIPTION OF THE INVENTION

[0037] The tire cord fabric (1) according to the invention enables using less mbber and higher cord content in a given cord-mbber composite volume, and it can be used in vehicle tires as reinforcement by using the paired cords (2) connected to each other as warps.

[0038] The tire cord fabric (1) according to the invention is made of paired cords (2) to be used as reinforcement in pneumatic tires. The paired cords (2) may have similar cord twists (5) such as S- S or Z-Z as shown in Figure 2 (a) and 2 (b). In paired cords (2) which are preferably used, opposite cord twists (6) such as S-Z or Z-S are used. This is shown in Figure 3(a) and 3(b).

[0039] In the preferred embodiment of the invention, the paired cord (2) structure is made of two cords (6) having opposite cord twists, namely S-Z or Z-S. The shear strain between the mutual faces of the cords (6) having opposite cord twists (SZ or ZS) is less than the conventional SS or ZZ cords (5). View of the angular movements of the similar or opposite twisted cords under compression is shown in Figure 4. View of surface strain directions of the similar or opposite twisted cords under compression are shown in Figure 5. View of the angular movements of the similar or opposite twisted cords under tension is shown in Figure 6. View ofthe surface strain directions ofthe similar or opposite twisted cords under tension is shown in Figure 7.

[0040] In the preferred embodiment of the invention, the adhesive (7) fdling the spacing between the cords (3, 4) in paired cord (2) is the RFL (Resorcinol Formaldehyde Latex) film layer formed because of dipping the paired cord fabric (2) into RFL solution. In fabrics (1), having paired cords (2), each paired cord (two cords) (2) is interconnected to each other with a suitable RFL film. In said paired cord fabric (2) structure, there is a desired spacing between the paired cord (2) strips for rubber penetration to provide sufficient rubber adhesion and tire durability.

[0041] The ply stiffness is an important parameter controlling the tire performance. In case of cap ply, the ply stiffness controls the tire growth and belt-edge separation resistance(durability) under highspeed conditions.

[0042] Compared to the regular tire cord fabric with parallel single cords as reference, strips containing paired cords comprises higher number of cords with the same rivet area(spacing) between paired cords of the reference strip.

[0043] Higher number of cords means higher ply stiffness. If ply stiffness increase higher than 12% of the reference, the tire performance improvement becomes significant. Higher ply stiffness means higher contractional force of the cap ply preventing tire growth and belt edge separation of the belt package under high-speed conditions.

[0044] Another potential advantage of the cap ply strips with paired cords can be gauge(thickness) reduction by using thinner cords but by keeping ply stiffness constant.

[0045] In cases of tension, compression and bending, the angular shear strain between the faces of SZ or ZS opposite twisted cord (6) type paired cords (3, 4) is less than the conventional applications. The single cords having different twist directions (SZ or ZS) within pairs do not create any shear strains at contact interface within the pairs leading to the improved paired-cords stability. Therefore, the suitable cord spacing between the paired cords (2) can be narrower than that of the current tire cord reinforcements (O) having all cords the similar twisting direction (for example S-S twisted cord pairs (5). Besides, in case of mutual contact, SZ or ZS opposite twist cord pairs (6) have surface contact (parallel contact) between the mutual paired cords (2), whereas SS cord (3) or ZZ cord pairs (5) have point contact (cross contact).

[0046] In one embodiment of the invention, the paired cords (2) have same balanced twists, but they are arranged in opposite directions.

[0047] In one embodiment of the invention, the paired cord strips (2) (S-S, Z-Z (5) or S-Z (6) cord twist combinations) contain unbalanced twisted cords applying residual torque to each other. The twists towards each other within the paired cord (2) increase separation resistance and stability in paired cords (2).

[0048] If there is an unbalanced twist in a cord, yam (ply) and cord twists are different from each other, the cords try to rotate. The reason for this is the residual torque caused by the difference between the twists. When the difference between the twists increases, the residual torque also increases. If there is no difference between the twists, no residual torque is seen.

[0049] In one embodiment of the invention, one of the cords within the paired cord (2) has unbalanced twist applying residual torque towards the other cord, whereas the other cord (the one which does not have residual torque anymore) has balanced twist.

[0050] In the preferred embodiment of the invention, the cords used in the paired cord (2) strip is made from a polymeric material selected from a group comprising Polyethylene terephthalate (PET), aramid, rayon, Polyethylene naphthalate (PEN), Nylon 66, Nylon 46 or PET / nylon and aramid / nylon blends.

[0051] The linear density of the cords (3, 4) used in the paired cord (2) is between 200 and 10.000 dtex. Preferably, the said value may be specifically between 1000 and 5.000 dtex, and more specifically 1500 and 4000.

[0052] The tire cord fabric (1) according to invention can be used as carcass reinforcement in passenger vehicle and light truck tires.

[0053] In the preferred embodiment of the invention, the number of the paired cords (2) in 10 cm changes between 25 to 110 (50 to 220 cords / 10 cm).

[0054] Within the framework of these basic concepts, it is possible to develop a wide variety of embodiments of the tire cord fabrics (1) according to invention. The invention cannot be limited to the examples described herein and it is essentially as defined in the claims.

[0055] The invention is a tire cord fabric of polymeric reinforcement for a pneumatic radial tire as spirally wound strips having a width of 5 to 25mm with 0 to 10 degrees to the circumferential plane of the tire, comprising paired cords used as warps, in which the single cords are connected to each other as pairs by adhesive dip. The number of the paired cords in the said tire cord fabric in 10cm is minimum 25 and maximum 110(50 to 220 single cords / 10cm). The twist of each cord in each pair is in opposite direction like SZ or ZS. The ply strength and ply stiffness of the paired cord fabric is at least 12% higher than that of the conventional cord fabric comprising the same single cords with the same cord-to-cord distance. Paired cords are prepared from at least one polymeric material selected from the group comprising nylon 66, nylon 46, PET, PEN, or aramid. Paired cords have a total linear density between 200 and lO.OOOdtex.

[0056] Comparative experiments are given below table. comparative experiment is given below table.

[0057] „ , 100-(epdm x thickness)

[0058] Rivet= - - - epdm-1 - In example 1, ply strength of fabric with paired cord is 124X where ply strength of regular fabric with single cord is 104X. ply strength of fabric with paired cord is %19 higher. The total ply strength of the paired cord fabric at the same dtex and the same rivet area is min 12% higher than the regular designed fabric.

[0059] Tire cord fabric of the invention is preferably manufactured from a totally or partially recycled polymer or totally or partially bio-based polymer.

Claims

CLAIMS1. Tire cord fabric (1) for pneumatic radial tire where spirally wound strips having a width of 5 to 25mm with 0 to 10 degrees to the circumferential plane of the tire characterized in comprising paired cords (2) used as warps, in which the single cords are connected to each other as pairs and number of the paired cords (2) in the said tire cord fabric (1) in 10cm is minimum 25 and maximum 110 and twist of each cord in each pair is in opposite direction as SZ or ZS and ply strength and ply stiffness of the paired cord fabric is at least 12% higher than that of cord fabric comprising the same single cords with the same cord-to-cord distance.

2. Tire cord fabric according to Claim 1, characterized in that said single cords are connected to each other as pairs by adhesive (7) dip.

3. Tire cord fabric according to Claim 2, characterized in that said adhesive (7) is Resorcinol Formaldehyde Latex (RFL).

4. Tire cord fabric according to Claim 1, characterized in that material of paired cords (2) is selected from group comprising nylon 66, nylon 46, Polyethylene terephthalate, Polyethylene naphthalate, aramid or blends thereof.

5. Tire cord fabric according to Claim 1, characterized in that said paired cords (2) have a total linear density between 200 and 10.000 dtex.

6. Tire cord fabric according to Claim 5, characterized in that paired cords (2) have a total linear density between 1000 and 5000 dtex.

7. Tire cord fabric according to Claim 6, characterized in that paired cords (2) have a total linear density between 1500 and 4000 dtex.

8. Tire cord fabric according to Claim 1 characterized in that, at least one cord of paired cords (2) has unbalanced twist.

9. Tire cord fabric according to any one of Claim 1-8 is manufactured from a totally or partially recycled polymer.

10. Tire cord fabric according to any one of Claim 1-8 is manufactured from a totally or partially bio-based polymer.

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