Ply coat rubber composition and a tire comprising a ply coat rubber composition

Abstract

In accordance with the invention, a ply coat rubber composition for a tire ply comprises from 60 phr to 90 phr of natural rubber, from 10 phr to 40 phr of synthetic polyisoprene, from 30 phr to 80 phr of pre-silanized and precipitated silica, from 0.1 phr to 5 phr of a cobalt salt, up to 15 phr of carbon black, up to 5 phr of resin, and up to 8 phr of oil. Moreover, the invention is directed to a tire comprising such a rubber composition.

Claims

1. A ply coat rubber composition, the rubber composition comprising: 60 phr to 100 phr of natural rubber, up to 40 phr of synthetic polyisoprene, 30 phr to 80 phr of pre-silanized precipitated silica, 0.1 phr to 5 phr of a cobalt salt, 0 to 15 phr of carbon black, 0 to 5 phr of a resin, a silica coupling agent, wherein the phr ratio of said pre-silanized precipitated silica to the silica coupling agent is between 5:1 and 30:1, and 0 to 8 phr of oil.

2. The ply rubber composition of claim 1 wherein the natural rubber is present at a level which is within the range of 70 phr to 80 phr, wherein the synthetic polyisoprene is present at a level which is within the range of 20 phr to 30 phr, wherein the pre-silanized precipitated silica is present at a level which is within the range of 50 phr to 60 phr, and wherein the carbon black is present at a level which is within the range of 2 phr to 10 phr.

3. The ply rubber composition of claim 1, wherein the cobalt salt is present at a level which is within the range of 0.2 phr to 2 phr.

4. The ply rubber composition of claim 1 wherein the ply rubber composition is further comprised of 1 phr to 20 phr of zinc oxide and/or 1 phr to 15 phr of sulfur.

5. The ply rubber composition of claim 1 wherein the pre-silanized precipitated silica has a CTAB adsorption surface area which is within the range of 130 m.sup.2/g to 210 m.sup.2/g.

6. The ply rubber composition of claim 1 wherein said pre-silanized precipitated silica is precipitated silica pre-reacted with a sulfur-containing silane which is comprised of bis(3-triethoxysilylpropyl)polysulfide containing an average of from 2 to 5 connecting sulfur atoms in its polysulfidic bridge, or an alkoxyorganomercaptosilane.

7. The ply rubber composition of claim 1, wherein the surface of said pre-silanized precipitated silica is pre-hydrophobated with a hydrocarbon chain material having at least 4 carbon atoms along its chain.

8. The ply rubber composition of claim 1, wherein the pre-silanized precipitated silica has a hydrocarbon chain material on its surface, and wherein the carbon on the surface of the pre-silanized precipitated silica is present at a level which is within the range of 3 weight percent to 8 weight percent.

9. The ply rubber composition of claim 1 wherein the ply rubber composition contains less than 5 phr of oil and wherein the ply rubber composition is essentially free of polyethylene glycol.

10. A ply rubber composition, the rubber composition comprising: 60 phr to 100 phr of natural rubber, up to 40 phr of synthetic polyisoprene, 30 phr to 80 phr of pre-silanized precipitated silica, 0 to 15 phr of carbon black, 0 to 5 phr of a resin, a silica coupling agent, wherein the phr ratio of said pre-silanized precipitated silica to the silica coupling agent is between 5:1 and 30:1, and 0 to 8 phr of oil.

11. The ply rubber composition of claim 10 wherein the natural rubber is present at a level which is within the range of 70 phr to 80 phr, wherein the synthetic polyisoprene is present at a level which is within the range of 20 phr to 30 phr, wherein the pre-silanized precipitated silica is present at a level which is within the range of 50 phr to 60 phr, and wherein the carbon black is present at a level which is within the range of 2 phr to 10 phr.

12. The ply rubber composition of claim 10 wherein the ply rubber composition is further comprised of 1 phr to 20 phr of zinc oxide and/or 1 phr to 15 phr of sulfur.

13. The ply rubber composition of claim 10 wherein the pre-silanized precipitated silica has a CTAB adsorption surface area which is within the range of 130 m.sup.2/g to 210 m.sup.2/g.

14. The ply rubber composition of claim 10 wherein said pre-silanized precipitated silica is precipitated silica pre-reacted with a sulfur-containing silane which is comprised of bis(3-triethoxysilylpropyl)polysulfide containing an average of from 2 to 5 connecting sulfur atoms in its polysulfidic bridge, or an alkoxyorganomercaptosilane.

15. The ply rubber composition of claim 10 wherein the surface of said pre-silanized precipitated silica is pre-hydrophobated with a hydrocarbon chain material having at least 4 carbon atoms along its chain.

16. The ply rubber composition of claim 10 wherein the pre-silanized precipitated silica has a hydrocarbon chain material on its surface, and wherein the carbon on the surface of the pre-silanized precipitated silica is present at a level which is within the range of 3 weight percent to 8 weight percent.

17. The ply rubber composition of claim 10 wherein the ply rubber composition contains less than 5 phr of oil and wherein the ply rubber composition is essentially free of polyethylene glycol.

18. A tire having at least one ply selected from the group consisting of a belt ply, a carcass ply, an overlay ply, and a ply strip, wherein at least one of the plies or the ply strip of the tire comprises a rubber composition comprising: from 60 phr to 100 phr of natural rubber, from 0 phr to 40 phr of synthetic polyisoprene, from 30 phr to 80 phr of pre-silanized precipitated silica, optionally from 0.1 to 5 phr of a cobalt salt, from 0 phr to 15 phr of carbon black, from 0 phr to 5 phr of resin, a silica coupling agent, wherein the phr ratio of said pre-silanized precipitated silica to the silica coupling agent is between 5:1 and 30:1, and from 0 phr to 8 phr of oil.

19. The tire of claim 18 wherein the ply or the ply strip comprises a textile which is calendered on both sides with the rubber composition.

20. The tire of claim 18 wherein the ply or the ply strip is comprised of a plurality of essentially parallelly extending metal wires which are coated with the rubber composition, and wherein optionally the plurality of parallelly extending metal wires define a plane of parallelly extending metal wires which are calendered on both sides with the rubber composition.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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:

(2) FIG. 1 represents a schematic cross-section of a tire in accordance with an embodiment of the invention.

(3) 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

(4) 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 a fabric material such as polyester, rayon, or similar suitable organic polymeric compounds or 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.

(5) 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.

(6) 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.

(7) 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.

(8) 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 cords or wires.

(9) A preferred example of a ply coat rubber composition in accordance with the invention is shown in Table 1 in comparison with a Control Sample. The Control Sample comprises highly dispersed silica (HDS) whereas the compound according to the invention comprises pre-silanized precipitated silica. The pre-silanized precipitated silica in the Example has been pre-hydrophobated by the addition of hydrocarbon chains to the surface of the silica and has further been pre-silanized with mercaptosilanes, thereby adding mercaptogroups to the surface of the pre-silanized precipitated silica. However, the present invention shall not be limited to exactly this combination. Further possibilities in accordance with the invention are set out in the appended claims as well as in the summary of the invention.

(10) The Example composition comprises a blend of natural rubber and synthetic polyisoprene rubber and less oil than the Control Sample. The amounts of zinc oxide, cobalt salt and antidegradants are not changed. The amounts of carbon black and (separate) silica coupler are reduced in the Example of the invention while the amount of pre-silanized precipitated silica is significant with 55 phr.

(11) Carbon black is blended in relatively small amounts, basically for providing the tire material with a black color.

(12) TABLE-US-00001 TABLE 1 Parts by weight (phr) Invention Material Control Example Natural Rubber 100 75 Synthetic Polyisoprene 0 25 Oil.sup.1 3.5 1 Zinc Oxide 9 9 Precipitated HDS Silica.sup.2 55 0 Pre-Silanized Precipitated Silica.sup.3 0 55 Silica Coupler.sup.4 6 3 Carbon Black 6 3 Cobalt Salt 0.5 0.5 Antidegradants 4.5 4.5 Stearic acid 1 0 Accelerator.sup.5 2 2 Sulfur 5 6 .sup.1Rubber process oil comprised of an TDAE oil .sup.2Precipitated silica such as Zeosil 1165MP ™ from Solvay .sup.3Pre-silanized precipitated silica (CTS) such as Agilon 400 ™ from PPG Industries as precipitated silica chemically treated with an alkoxyorganomercaptosilane .sup.4Silica coupler such as Si266 ™ and Si69 ™ from Evonik comprised of bis(3-triethoxysilylpropyl) polysulfide having an average of from about 2 to about 2.6 and from about 3.4 to about 3.8, respectively, connecting sulfur atoms in its polysulfidic bridge .sup.5Sulfur cure accelerators such as sulfenamide

(13) Table 2 discloses mechanical test results for the Control composition and the Example composition disclosed in Table 1. While the Shore A hardness has decreased at an acceptable degree versus the Control Sample, the Example composition shows a significant improvement in rebound values tested at 23° C. and 100° C. which may likely result in practice in smaller hysteresis and thus reduced rolling resistance. The same is indicated by a significant improvement in the tangent delta measurement. In particular, rebound at 23° C. has improved by about 20% and rebound at 100° C. has improved by about 15%. The tangent delta (tan δ) shows an improvement by more than 30%.

(14) TABLE-US-00002 TABLE 2 Invention Test/Property Units Control Example Shore A hardness(23° C.).sup.a — 78.3 71 Rebound (23° C.).sup.b % 50.4 61.5 Rebound (100° C.).sup.b % 69 79.8 G′ (1%).sup.c MPa 3.8 1.9 G′ (10%).sup.c MPa 2.2 1.4 G′ (15%).sup.c MPa 1.8 1.2 G′ (50%).sup.c MPa 1.0 0.8 Tan delta (10%).sup.c — 0.15 0.10 .sup.aShore A hardness measured according to ASTM D2240. .sup.bRebound measured on a Zwick Roell 5109 rebound resilience tester according to DIN 53512/ASTM D1054 at given temperature. .sup.cData obtained with an RPA 2000 ™ Rubber Process Analyzer of Alpha Technologies based on ASTM D5289.

(15) The combination in this example using a significant amount of pre-silanized precipitated silica has resulted in a significant change in the physical properties of the composition, especially with regards to rolling resistance predictors such as tangent delta and rebound values.

(16) If not otherwise indicated herein, amounts of materials are usually expressed in parts of material per 100 parts of rubber by weight (phr).

(17) Variations in the present invention are possible in light of the provided description. While certain representative embodiments, examples 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 invention. It is, therefore, to be understood that changes may be made in the particular example embodiments described which will be within scope of the invention as defined by the following appended claims.

(18) In any case the above described embodiments and examples shall not be understood in a limiting sense. In particular, the features of the above embodiments may also be replaced or combined with one another.