Rubber composition and a tire

Abstract

The present invention is directed to a non-vulcanized rubber composition which is comprised of (1) 90 phr to 100 phr cis 1,4-polyisoprene; (2) 10 phr to 40 phr of pre-silanized precipitated silica; (3) 10 phr to 40 phr of carbon black, (4) 0.1 phr to 5 phr of a cobalt salt, and (5) 1 phr to 15 phr of a resinous reaction product of a methylene donor composition and a methylene acceptor composition. Moreover, the present invention is directed to a tire or tire component comprising the cured rubber composition.

Claims

1. A non-vulcanized rubber composition which comprises: (1) 90 phr to 100 phr of cis 1,4-polyisoprene; (2) 10 phr to 40 phr of pre-silanized precipitated silica; (3) 10 phr to 40 phr of carbon black, (4) 0.1 phr to 5 phr of a cobalt salt, and (5) 1 phr to 15 phr of a resinous reaction product of a methylene donor composition and a methylene acceptor composition, 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.

2. The non-vulcanized rubber composition as specified in claim 1 wherein the resinous reaction product of the methylene donor composition and the methylene acceptor composition is formed in situ within the rubber composition.

3. The non-vulcanized rubber composition as specified in claim 2 wherein the methylene donor composition is comprised of hexamethoxymethylmelamine.

4. The non-vulcanized rubber composition as specified in claim 3 wherein the hexamethoxymethylmelamine is present in the methylene donor composition at a level of at least 80 weight percent.

5. The non-vulcanized rubber composition as specified in claim 2 wherein the methylene donor composition is comprised of hexamethoxymethylmelamine and up to 50 weight percent of one or more methylene donor compounds selected from the group consisting of hexamethylenetetramine, methoxymethylmelamaine, N,N′N″-trimethyl N,N′N″-trimethylolmelamine, hexamethyolmelanime, N,N′N″-dimethylolmelamine, N-methylolmelamine, N,N′-dimethylolmelamine, N,N′N″-tris(methoxymethyl)melamine, N,N′N″-tributyl-N,N′N″-trimethylol-melamine and hexaethoxymethylmelamine.

6. The non-vulcanized rubber composition as specified in claim 2 wherein the methylene acceptor composition is comprised of at least one member selected from the group consisting of resorcinol, resorcinol derivatives, monohydric phenols and their derivatives, dihydric phenols and their derivatives, polyhydric phenols and their derivatives, unmodified phenol novolak resins, modified phenol novolak resin, and rescorcinol novolak resins.

7. The non-vulcanized rubber composition as specified in claim 1 wherein the non-vulcanized rubber composition further comprises 5 phr to 15 phr of zinc oxide.

8. The non-vulcanized rubber composition as specified in claim 1 wherein the non-vulcanized rubber composition comprises 15 phr to 30 phr of the pre-silanized precipitated silica and 15 phr to 30 phr of the carbon black.

9. The non-vulcanized rubber composition as specified in claim 1 wherein the non-vulcanized rubber composition comprises from 90 phr to 100 phr of natural rubber.

10. The non-vulcanized rubber composition as specified in claim 1 wherein a ratio of the pre-silanized precipitated silica to the carbon black ranges between 1.20 to 1 and 1 to 1.2.

11. The non-vulcanized rubber composition as specified in claim 1 wherein the non-vulcanized rubber composition comprises less than 10 phr oil.

12. The non-vulcanized rubber composition as specified in claim 1 wherein said pre-silanized precipitated silica is precipitated silica which is pre-reacted with a sulfur-containing silane.

13. The non-vulcanized rubber composition as specified in claim 12 wherein the sulfur-containing silane is comprised of bis(3-triethoxysilylpropyl)polysulfide containing an average of from 2 to 5 connecting sulfur atoms in its polysulfidic bridge.

14. The non-vulcanized rubber composition as specified in claim 12 wherein the sulfur-containing silane is an alkoxyorganomercaptosilane.

15. A reinforced rubber component which is comprised of a metal reinforcing element which is embedded in a cured rubber composition which is made by curing the metal reinforcing element in the non-vulcanized rubber composition specified in claim 1.

16. The reinforced rubber component as specified in claim 15 wherein the reinforced rubber component is a tire ply or a tire ply strip.

17. The reinforced rubber component as specified in claim 16 wherein the metal reinforcing element is a brass coated steel wire.

18. A tire having a rubber ply or rubber ply strip which is comprised of a cured rubber which is made by curing the non-vulcanized rubber composition specified in claim 1.

19. The non-vulcanized rubber composition as specified in 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 150 m.sup.2/g.

20. The non-vulcanized rubber composition as specified in claim 1 wherein the pre-silanized precipitated silica has a CTAB adsorption surface area which is within the range of 195 m.sup.2/g to 205 m.sup.2/g.

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 having the rubber composition in accordance with an embodiment of the invention; and

(3) FIG. 2 is a schematic cross section of a ply comprising wires and a wire coat material rubber composition in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(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 and/or may include one or more breaker plies. 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/breaker 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 (in particular breaker ply) or overlay ply 9′ which comprises a plurality of metal, for instance steel, wires 15 reinforcing the rubber composition/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. However, in another embodiment, the rubber composition could also be provided in a rubber ply or rubber ply strip which is not reinforced by (metal) wires.

(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 a 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) Table 1 shows examples of a rubber composition in accordance with examples of the present invention. Control Sample 1 and Control Sample 2 constitute wire coat rubber compositions in the absence of a resin and utilizing carbon black in relatively high quantities of 60 phr. Control Sample 1 is comprised of 100 phr natural rubber, while Control Sample 2 comprises a blend of natural rubber and synthetic cis-1,4 polyisoprene. Control Sample 3 comprises a reactive resin system and precipitated silica together with 100 phr natural rubber. Control Sample 4 is also a full natural rubber examples comprising the same reactive resin system but comprise 24 phr carbon black together with 23 phr silica as filler material. In Control Samples 3 and 4 appropriate amounts of silane have been added to the composition. In contrast to all control samples, the Inventive Examples 1 and 2 comprise a combination of a pre-silanized silica in combination with carbon black. In these non-limiting examples, equal parts of silica and carbon black (23 phr) have been added to the composition. Inventive Example 2 differs over Inventive Example 1 in that it comprises a blend of natural rubber and synthetic polyisoprene, while Inventive Example 1 is a full natural rubber compound.

(10) TABLE-US-00001 TABLE 1 Parts by weight (phr) Control Control Control Control Inventive Inventive Sample Sample Sample Sample Example Example Material 1 2 3 4 1 2 Natural Rubber 100 60 100 100 100 60 Synthetic cis 1,4- 0 40 0 0 0 40 polyisoprene Pre-Silanized Silica.sup.1 0 0 0 0 23 23 Carbon Black 60 60 4 24 23 23 Precipitated silica.sup.2 0 0 43 23 0 0 Silane.sup.3 0 0 5.2 2.8 0 0 Cobalt Salt 1 1 0.5 0.5 0.5 0.5 Antidegradants 2 2 2.5 2.5 2.5 2.5 Methylene donor.sup.4 0 0 4.1 4.1 4.1 4.1 Methylene acceptor.sup.5 0 0 1.5 1.5 1.5 1.5 Accelerators 1 1.2 1.8 1.8 1.8 2.0 ZnO 10 10 10 10 10 10 Sulfur 6.3 6.3 6.3 6.3 6.9 6.9 .sup.1Pre-silanized (pre-hydrophobated) precipitated silica as Agilon 400 ™ from PPG Industries as precipitated silica chemically treated with an alkoxyorganomercaptosilane .sup.2Precipitated silica as Zeosil ™ 1165 MP from the company Solvay .sup.3Bis-triethyoxysilylpropyl tetrasulfideas SI 69 ™ from the company Evonik .sup.4Hexamethoxymethylmelamine .sup.5100% phenol formaldehyde reactive type resin

(11) Table 2 shows test data for the compositions listed above in Table 1.

(12) Shore A hardness is on a similar level for all tested samples. G′ levels, which may be considered as stiffness indicators, are significantly higher for the Inventive Examples. Such an increased stiffness could amongst others help to improve steering performance. Most remarkable are the differences in tangent delta which are an indicator for improved hysteresis and thus also for improved rolling resistance. In particular, the Inventive Examples show a decrease in tangent delta which range roughly between −20% and −40% with respect to the control samples. While tensile strength and elongation at break have decreased for the inventive examples as well, those are still deemed to be at an appropriate level. Modulus measurements are at a comparable level with the exception of the almost full silica example of Control Sample 3 which is less favorable. In summary, the combination of a pre-silanized silica, carbon black and a resin, as exemplarily shown in the below Inventive Examples, results in a considerably advanced hysteresis behavior and thus in improved rolling resistance.

(13) TABLE-US-00002 TABLE 2 Control Control Control Control Inventive Inventive Test/ Sample Sample Sample Sample Example Example Property Units 1 2 3 4 1 2 Shore A — 66 68 67 71 67 70 hardness (23° C.).sup.a G′ (1%).sup.b MPa 1849 2237 1981 1942 2613 2989 G′ (15%).sup.b MPa 1072 1159 1177 1112 1585 1695 Tan delta — 0.17 0.18 0.16 0.18 0.11 0.12 (10%).sup.b Modulus MPa 3.1 3.2 2.3 3.4 3.3 3.3 (100%).sup.c Modulus MPa 8.1 7.9 5.5 8.3 8.2 7.6 (200%).sup.c Elongation at % 316 374 506 435 277 297 break.sup.c Tensile MPa 13.3 15.8 17.6 20.6 11.3 11.4 strength.sup.c .sup.aShore A hardness measured according to ASTM D2240 or equivalent. .sup.bData obtained with an RPA 2000 ™ Rubber Process Analyzer of Alpha Technologies based on ASTM D5289; percentages are percentages of strain; Tan delta has been determined at 100° C.. .sup.cRing sample test based on ASTM D412 or equivalent, percentages are percentages of elongation, respectively strain; tensile strength is stress at break; elongation is elongation at break in %.

(14) 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.