Wire coat rubber composition for a tire and a tire comprising a wire coat rubber composition

Abstract

In accordance with the invention a wire coat rubber composition for a tire comprises from 70 phr to 100 phr of cis 1,4-polyisoprene rubber, from 0 phr to 30 phr of solution styrene butadiene rubber, from 65 phr to 95 phr pre-silanized precipitated silica, from 0.1 phr to 5 phr of a cobalt salt, up to 15 phr carbon black, up to 10 phr of a resin, and up to 10 phr oil. Further the present invention is directed to a tire comprising such a wire coat composition.

Claims

1. A wire coat rubber composition for a tire, the rubber composition comprising: 75 phr to 90 phr of cis 1,4-polyisoprene rubber, from 10 phr to 25 phr of solution-polymerized styrene-butadiene rubber, from 65 phr to 95 phr of pre-silanized precipitated silica, from 0.1 phr to 5 phr of a cobalt salt, from 0 phr to 15 phr carbon black, from 0 phr to 10 phr of a resin, and from 0 phr to 10 phr oil, 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, wherein the solution-polymerized styrene-butadiene rubber has a glass transition temperature which is within the range of −30° C. and −90° C., and wherein the solution-polymerized styrene-butadiene rubber is tin-coupled or thio-functionalized.

2. The wire coat rubber composition of claim 1, wherein the solution-polymerized styrene-butadiene rubber has a bound styrene content which is within the range of 10% to 20%, and a vinyl content which is within the range of 20% to 40%.

3. The wire coat rubber composition of claim 1, wherein the solution-polymerized styrene-butadiene rubber has a glass transition temperature which is within the range of −50° C. and −70° C. and wherein the solution-polymerized styrene-butadiene rubber is tin-coupled.

4. The wire coat rubber composition of claim 1, wherein the solution-polymerized styrene-butadiene rubber is functionalized for improved compatibility with silica, and wherein the solution-polymerized styrene-butadiene rubber is thio-functionalized.

5. The wire coat rubber composition of claim 1 wherein the pre-silanized precipitated silica is present at a level which is within the range of from 70 phr to 90 phr.

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

7. The wire coat rubber composition of claim 1, wherein said pre-silanized precipitated silica is pre-hydrophobated by treating silica with both an organomercaptosilane and an alkylsilane at a weight ratio of said organomercaptosilane to said alkylsilane which is within the range of from 10/90 to 90/10; wherein said alkylsilane is of the general Formula):X.sub.n—Si—R.sub.4-n, wherein R is an alkyl radical having from 1 to 8, carbon atoms, wherein n is a numeral from 1 to 3, and X is a halogens or an alkoxy radical of the formula: R.sup.1O—, wherein R.sup.1 is an alkyl radical having from 1 to 3 carbon atoms; and where said organomercaptosilane is of the general formula: (X).sub.n(R.sup.2O).sub.3-n—Si—R.sup.3—SH), wherein X is a halogen, wherein R.sup.2 is an alkyl radical containing from 1 to 4 carbon atoms, and R.sup.3 is an alkylene radical containing from 1 to 4 carbon atoms, and wherein n represents an integer from 0 to 3.

8. The wire coat 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.

9. The wire coat rubber composition of claim 1, wherein the carbon black is present at a level of less than 3 phr.

10. The wire coat rubber composition of claim 1, wherein the level of resin in the composition is less than 5 phr.

11. The wire coat rubber composition of claim 1, wherein the wire coat rubber composition contains less than 5 phr oil.

12. The wire coat rubber composition of claim 1 further comprising from 1 to 15 phr of sulfur.

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

14. A tire comprising a ply or a ply strip, wherein the ply or the ply strip is comprised of wires which are coated with the wire coat rubber composition according to claim 1.

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 is a schematic cross section of a tire comprising amongst others belt plies and carcass plies comprising the rubber composition in accordance with an embodiment of the invention.

(3) FIG. 2 is a schematic cross section of a ply comprising wires and a wire coat material 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 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/wire coat 20. Typically, such a ply is made in a wire calendar in which a plurality of essentially parallel metal and spaced apart 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) Preferred examples of the rubber composition are shown in Table 1 in comparison with a Control sample. The control sample comprises carbon black as a filler material whereas the compounds according to the invention comprise pre-silanized precipitated silica. Moreover, the first example comprises a significant amount of an SSBR whereas the control and the second example each comprise 100 phr natural rubber. Moreover, the first and second examples comprise also a resin system of reactive resins and higher amounts of accelerators and antidegradants than the control sample.

(10) TABLE-US-00001 TABLE 1 Parts by weight (phr) Inventive Inventive Material Control Example 1 Example 2 Natural rubber 100 83 100 Carbon Black 60 0 0 SSBR.sup.1 0 17 0 Pre-silanized Precipitated Silica.sup.2 0 80 80 Zinc Oxide 10 8 8 Resin.sup.3 0 2.5 2.5 0i1.sup.4 1 1 1 Antidegradants 2 3 3 Stearic Acid 0 1 1 Cobalt Salt 0.5 0.5 0.5 Accelerator.sup.5 1 1.5 1.5 Sulfur 5 5 5 .sup.1SSBR as Sprintan ™ SLR 3402 of the company Trinseo ™ having a T.sub.g of about −62° C. .sup.2Pre-silanized (pre-hydrophobated) precipitated silica as Agilon 400 ™ from PPG Industries as precipitated silica chemically treated with an alkoxyorganomercaptosilane .sup.3Resin system comprising a phenol formaldehyde reactive type resin and a hexamethoxymethylmelamine .sup.4Naphthenic oil .sup.5Sulfur cure accelerators as sulfenamide

(11) Table 2 discloses mechanical test results for the control composition and the example compositions disclosed in Table 1. Shore A hardness of both inventive examples has increased over the control sample. Rebound values have also increased significantly by more than 5% over the control sample. Rebound can be a good indicator for stiffness/hysteresis ratio. G′ at 1% and G′ at 15% have also increased significantly in the order of 50% for both inventive examples. While tangent delta values have increased for Example 1, it remains flat for example 2 in comparison with the control sample. Modulus values at 100% and 200% keep roughly the level of the control. Elongation at break values have increased. Tensile strength has also increased when comparing the inventive examples with the control sample. The improvement in the rebound test values as well as the improvement in the G′ and shore A hardness values, indicating a high compound stiffness, predict together also an improvement of the component's hysteresis behavior which has also a positive influence on rolling resistance.

(12) TABLE-US-00002 TABLE 2 Inventive Inventive Test/Property Units Control Example 1 Example 2 Shore A hardness(23° C.) .sup.a — 70.1 72.6 71.5 Rebound(23° C.) .sup.b % 48.38 52.1 50.27 G′ (1%) .sup.c MPa 2.78 4.41 4.6 G′ (15%) .sup.c MPa 1.48 2.25 2.08 Tan delta (10%) .sup.c — 0.15 1.3 0.15 Modulus (100%) .sup.d MPa 3.7 3.1 3.7 Modulus (200%) .sup.d MPa 9.6 9.4 7.7 Elongation at break .sup.d % 316 365 490 Tensile strength .sup.d MPa 16.0 17.0 20.0 .sup.a Shore A hardness measured according to ASTM D2240. .sup.b Rebound measured on a Zwick Roell 5109 rebound resilience tester according to DIN 53512/ASTM D1054 at given temperature. .sup.c Data obtained with an RPA 2000 ™ Rubber Process Analyzer of Alpha Technologies based on ASTM D5289. .sup.d Ring sample test based on ASTM D412 and DIN 53504, percentages are percentages of elongation, respectively strain; tensile strength is stress at break; elongation is elongation at break in %.

(13) The amounts of materials are usually expressed in parts of material per 100 parts of rubber by weight (phr).

(14) If an amount of ingredient is mentioned with “up to” herein, this shall include also the option of 0 (zero) phr of that ingredient or “from 0 to”.

(15) 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.

(16) 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.