WIRE COAT COMPOSITION AND A TIRE COMPRISING A WIRE COAT COMPOSITION

Abstract

The invention relates to a wire coat rubber composition for coating metal wires in a tire, the rubber composition comprising from 60 to 100 phr of natural rubber, from 0 to 40 phr of synthetic polyisoprene, from 40 to 70 phr of oxidized carbon black, up to 5 phr of a resin and up to 8 phr of oil. The present invention also relates to a tire comprising such a wire coat composition.

Claims

1. A wire coat rubber composition comprising from 60 phr to 100 phr of natural rubber, up to 40 phr of synthetic polyisoprene, and from 40 phr to 100 phr of a filler, wherein the filler includes at least 40 phr of a surface oxidized carbon black, wherein the wire coat rubber composition contains no more than 5 phr of resins, and wherein the wire coat rubber composition contains no more than 8 phr of oils.

2. The wire coat rubber composition of claim 1 wherein the filler is present at a level which is within the range of 40 phr to 70 phr, wherein said filler comprises from 45 to 65 phr of the surface oxidized carbon black.

3. The wire coat rubber composition of claim 2, wherein the surface oxidized carbon black is present at a level which is within the range of 50 phr to 60 phr.

4. The wire coat rubber composition of claim 1, wherein the filler is further comprised of silica, wherein the ratio of the surface oxidized carbon black to the silica is at least 2:1.

5. The wire coat rubber composition of claim 4, wherein the ratio of the surface oxidized carbon black to the silica is at least 3:1.

6. The wire coat rubber composition of claim 1, wherein the surface oxidized carbon black is hydrogen peroxide treated carbon black.

7. The wire coat rubber composition of claim 1, wherein the surface oxidized carbon black is ozone treated carbon black.

8. The wire coat rubber composition of claim 1, wherein the pH of the surface oxidized carbon black is below 6.

9. The wire coat rubber composition of claim 1, wherein the pH of the surface oxidized carbon black is below 4.

10. The wire coat rubber composition of claim 1, wherein the pH of the surface oxidized carbon black is within the range of 1 to 3.

11. The wire coat rubber composition of claim 1, wherein said surface oxidized carbon black includes on its surface at least one of carboxyl groups and at least one hydroxyl groups.

12. The wire coat rubber composition of claim 1, wherein the surface oxidized carbon black is a surface oxidized N234 carbon black.

13. The wire coat rubber composition of claim 1, further comprising from 0.1 phr to 5 phr of a cobalt salt.

14. The wire coat rubber composition of claim 13 wherein the cobalt salt is present at a level which is within the range of 0.2 phr to 2 phr.

15. The wire coat rubber composition of claim 1, further comprising from 1 phr to 20 phr of zinc oxide.

16. The wire coat rubber composition of claim 1 wherein the zinc oxide is present at a level which is within the range of 5 phr to 15 phr.

17. The wire coat rubber composition of claim 1 which is further comprised of 4 phr to 10 phr of sulfur.

18. The wire coat rubber composition of claim 1, wherein the rubber composition is essentially resin free.

19. The wire coat rubber composition of claim 1, wherein the composition contains less than 2 phr of the resin and less than 5 phr of oil.

20. A pneumatic tire which is comprised of a generally toroidal-shaped carcass with an outer circumferential tread, two spaced beads, at least one textile reinforced ply extending from bead to bead, and sidewalls extending radially from and connecting said tread to said beads, wherein said tread is adapted to be ground-contacting, and wherein the tire further includes metal reinforcing wires which are embedded in the wire coat rubber composition of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The structure, operation and advantages of the invention will become more apparent upon contemplation of the following description taken in conjunction with the accompanying drawings, wherein:

[0049] FIG. 1 represents a schematic cross-section of a tire in accordance with an embodiment of the invention.

[0050] FIG. 2 represents a schematic cross-section of a ply (e.g. a belt, carcass or overlay ply) comprising wires or cords coated with the rubber composition in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] FIG. 1 is a schematic cross-section of a tire 1. The tire 1 has a tread 10, an inner liner 13, a belt structure comprising four belt plies 11, a carcass ply 9, two sidewalls 2, and two bead regions 3 comprising bead filler apexes 5 and beads 4. The example tire 1 is suitable, for example, for mounting on a rim of a vehicle, e.g. a truck or a passenger car. As shown in FIG. 1, the belt plies 11 may be covered by an overlay ply 12. The carcass ply 9 includes a pair of axially opposite end portions 6, each of which is associated with a respective one of the beads 4. Each axial end portion 6 of the carcass ply 9 may be turned up and around the respective bead 4 to a position to anchor each axial end portion 6. One or more of the carcass ply 9, belt plies 11 and overlay ply 12 comprise a rubber composition in accordance with the invention and may have a plurality of substantially parallel reinforcing members made of metal wire. The turned-up portions 6 of the carcass ply 9 may engage the axial outer surfaces of two flippers 8 and axial inner surfaces of two chippers 7. As shown in FIG. 1, the example tread 10 may have four circumferential grooves, each groove essentially defining a U-shaped opening in the tread 10. The main portion of the tread 10 may be formed of one or more tread compounds, which may be any suitable tread compound or compounds.

[0052] While the embodiment of FIG. 1 suggests a plurality of tire components including for instance apexes 5, chippers 7, flippers 8 and overlay 12, such components are not mandatory for the invention. Also, the turned-up end of the carcass ply 9 is not necessary for the invention or may pass on the opposite side of the bead area 3 and end on the axially inner side of the bead 4 instead of the axially outer side of the bead 4. The tire could also have for instance more or less than four grooves.

[0053] The schematic cross-section of FIG. 2 shows a ply, e.g. a carcass, belt or overlay ply 9 which comprises a plurality of metal, for instance steel, wires 15 reinforcing the rubber composition material 20. Typically, such a ply is made in a wire calendar in which a plurality of essentially parallel metal wires is coated from both sides with a layer or sheet of rubber composition 20. Such methods are well known to the person skilled in the art of tire building. After curing, the wires 15 are embedded in the rubber composition 20, reinforcing the same.

[0054] Metal wires 15 may be coated with brass for better adhesion properties with regards to connection of the wires 15 to the cured rubber composition 20. The wires 15 may also be dipped in dipping solutions or emulsions for better adhesion properties as known in the art. Neither a dip nor a metal coating is shown here in FIG. 2. For the sake of better adhesion of the compound 20 to the metal wire 15, the compound 20 may comprise cobalt salt. Moreover, the compound 20 can comprise zinc oxide which may also improve the adhesion between the metal wire 15 and the cured compound 20.

[0055] While the schematic drawing of FIG. 2 indicates nine wires, the number of parallel wires per ply could be different, for instance at least 5 or 10. The invention could also be used in a ply strip comprising the rubber composition, with the strip comprising only between 3 and 6 metal wires.

[0056] Examples of rubber compositions in accordance with the invention are shown in below Table 1 in comparison with a control sample. The control sample comprises highly dispersed silica (HDS) whereas the compounds according to the invention comprise oxidized carbon black. Moreover, Inventive Example 1 is a full natural rubber composition whereas Example 2 comprises a blend of natural rubber and synthetic polyisoprene. Apart from said main difference in the rubber material, Example 1 has a slightly higher amount of oil than Example 2 whereas Example 2 has a higher amount of sulfur than Example 1.

[0057] While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention.

TABLE-US-00001 TABLE 1 Parts by weight (phr) Inventive Inventive Material Control Example 1 Example 2 Natural Rubber 100 100 75 Synthetic Polyisoprene 0 0 25 Oil.sup.1 3.5 3.5 2 Zinc Oxide 9 9 9 Precipitated HDS Silica.sup.2 55 0 0 Silica Coupler.sup.3 6 0 0 Carbon Black 6 0 0 Oxidized Carbon Black.sup.4 0 55 55 Cobalt Salt 0.5 0.5 0.5 Antidegradants 4.5 4.5 4.5 Stearic acid 1 1 1 Accelerator.sup.5 2 2 2 Sulfur 5 5 6 .sup.1Rubber process oil comprised of TDAE oil .sup.2Precipitated silica as Zeosil 1165MP from Solvay .sup.3Silica coupler as X50S from Evonik .sup.4Oxidized carbon black as an oxidized N234 .sup.5Sulfur cure accelerators as a sulfenamide

[0058] Below Table 2 discloses mechanical test results for the Control composition and Example compositions in accordance with the invention. Shore A hardness is slightly lower in the Examples according to the invention than in the Control Sample. Rebound properties are the same or better than of the Control Sample which is remarkable as no silica is used. The low strain values for G follow the behavior of the Shore A hardness such that they are below the Control Sample values. The tangent delta values are also almost unchanged when comparing the Control and Invention Examples. Elongation at break is roughly about 10% worse for Example 1 than for the Control Sample and for Example 2 about 20% lower than for the Control Sample. Modulus at 100% strain values are about 10% lower for Example 1 than for the Control while they are about 5% higher for Example 2. Modulus 300% values have increased by more than 10% over the Control Sample. While the tensile strength has slightly increased for Example 1, it has slightly decreased for Example 2 in comparison with the Control Sample. For the SWAT adhesion test, the pulling force has decreased more significantly compared to the Control, i.e. roughly in the order of 20%.

[0059] Remarkably, the volume resistivity of the compound has significantly decreased from 10.sup.11 Ohm cm to 810.sup.7 Ohm cm in Example 1 and to 310.sup.7 Ohm cm in Example 2 which is more than a 3 order of magnitude decrease in volume resistivity. In other words, the conductivity was significantly increased.

[0060] In summary, many differences in the properties as listed in Table 2 are relatively small whereas the change in the resistivity between the Control Sample and the Examples according to the invention is very significant, making these compounds sufficiently electrically conducting. This reduced resistivity may allow to replace silica in wire coat compounds with oxidized carbon black, while essentially maintaining (or in some cases even improving) the level of properties compared to the silica sample. This can be of special interest when electrical conductivity is required for the specific application of the compound.