RUBBER COMPOSITION AND A TIRE

Abstract

In a first aspect, the present invention is directed to a rubber composition comprising 70 phr to 100 phr of styrene butadiene rubber including a first styrene butadiene rubber having a glass transition temperature within a range of −49° C. to −15° C. and a second styrene butadiene rubber having a glass transition temperature within a range of −50° C. to −89° C. Moreover, the rubber composition comprises 10 phr to 30 phr of one or more of natural rubber and synthetic polyisoprene rubber, 40 phr to 70 phr of silica, and 10 phr to 40 phr of at least one hydrocarbon resin selected from one or more of C5 resins, CPD resins, DCPD resins, C9 modified C5 resins, C9 modified CPD resins, and C9 modified DCPD resins. In another aspect, the present invention is directed to a tire comprising a tire tread with the aforementioned rubber composition.

Claims

1. A rubber composition comprising: 70 phr to 90 phr of styrene butadiene rubber, comprising a first styrene butadiene rubber having a glass transition temperature within a range of −49° C. to −15° C. and a second styrene butadiene rubber having a glass transition temperature within a range of −50° C. to −89° C.; 10 phr to 30 phr of one or more members selected from the group consisting of natural rubber and synthetic polyisoprene rubber; 40 phr to 70 phr of silica; and 10 phr to 40 phr of at least one hydrocarbon resin selected from one or more of C5 resins, CPD resins, DCPD resins, C9 modified C5 resins, C9 modified CPD resins, C9 modified DCPD resins.

2. The rubber composition according to claim 1 wherein the resin has a softening point within a range of 80° C. to 150° C. and a weight average molecular weight within a range of 500 g/mol to 1000 g/mol.

3. The rubber composition according to claim 2 wherein the resin has a softening point within a range of 90° C. to 110° C.

4. The rubber composition according to claim 2 wherein the resin has a weight average molecular weight Mw within a range of 500 g/mol to 800 g/mol.

5. The rubber composition according to claim 1 wherein the resin has a glass transition temperature within a range of 30° C. to 60° C.

6. The rubber composition according to claim 1 wherein the resin is selected from one or more of C9 modified CPD and C9 modified DCPD resins.

7. The rubber composition according to claim 6 wherein the resin has an aromatic proton content within a range of 5% to 15%.

8. The rubber composition according to claim 6 wherein said resin is at least partially hydrogenated.

9. The rubber composition according to claim 1 wherein the rubber composition comprises from 50 phr to 65 phr of the silica.

10. The rubber composition according to claim 1 wherein the silica is a reinforcing silica having a BET surface area which is within the range of 190 m.sup.2/g to 260 m.sup.2/g.

11. The rubber composition according to claim 10 wherein the reinforcing silica has a BET surface area within a range of 205 m.sup.2/g to 260 m.sup.2/g.

12. The rubber composition according to claim 1 further comprising one or more of: from 0.1 phr to 10 phr of carbon black; from 4 phr to 8 phr of reinforcing silane; from 4 phr to 7 phr of a blocked mercapto silane; from 0 phr to 10 phr of liquid plasticizers.

13. The rubber composition according to claim 1 comprising 40 phr to 60 phr of the first styrene butadiene rubber and 30 phr to 50 phr of the second styrene butadiene rubber.

14. The rubber composition according to claim 1 wherein at least one of the first and the second styrene butadiene comprises at least one functional group configured for the coupling to the silica.

15. The rubber composition according to claim 1 wherein at least one of the first and the second styrene butadiene comprises at least one functional group configured for the coupling to the silica, and wherein said functional group is selected from one or more of polysiloxy, alkylsiloxy, amino alkylsiloxy, tin amino, amino siloxane, and amino silane groups.

16. The rubber composition according to claim 14 wherein each styrene butadiene rubber comprises at least one functional group configured for the coupling to silica.

17. The rubber composition of claim 14 wherein one styrene butadiene rubber of the first and the second styrene butadiene rubbers is functionalized with an amino silane group and another one of the first and the second styrene butadiene rubbers is functionalized with an amino siloxane group.

18. The rubber composition of claim 1 wherein the first styrene butadiene rubber has a glass transition temperature within a range of −20° C. to −35° C. and the second styrene butadiene rubber has a glass transition temperature within a range of −55° C. to −69° C.

19. The rubber composition of claim 1 comprising from 15 phr to 30 phr of the resin.

20. A tire which is comprised of a generally toroidal-shaped carcass with an outer circumferential tread, two sidewalls, two spaced beads, at least one 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 outer circumferential tread is comprised of the rubber composition as specified in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The structure, operation, and advantages of the invention will become more apparent upon contemplation of the following description taken in conjunction with the accompanying drawing, wherein:

[0057] FIG. 1 is a schematic cross section of a tire comprising a tread and further rubber components.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0058] FIG. 1 is a schematic cross-section of a pneumatic 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. 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 tread 10 comprises one or more tread compounds as described herein in accordance with embodiments of the invention.

[0059] While the embodiment of FIG. 1 suggests a plurality of tire components including for instance apexes 5, chippers 7, flippers 8 and an 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. The present invention shall not be limited to the example of the tire 1 depicted and described in accordance with FIG. 1.

[0060] Preferred examples of rubber compositions in accordance with embodiments of the present invention, i.e. Inventive Examples 1 to 4 (which are particularly suitable for a tire tread 10), are shown in TABLE 1 in comparison with two Comparative Examples 1 and 2 which are not in accordance with the present invention. All Examples comprise a combination of natural rubber (polyisoprene) and styrene butadiene rubber. In particular, the presence of polyisoprene rubber is deemed beneficial for the present composition types with regard to well-balanced tensile properties. Moreover, all examples are based on a combination of a high Tg styrene butadiene rubber with a low Tg styrene butadiene rubber as listed in TABLE 1.

[0061] All compositions (apart from Comparative Example 1) rely on moderate amounts of high surface area silica wherein Inventive Examples 2 and 5 have an even higher surface area silica type. The Inventive Examples further comprise a blocked mercapto silane, whereas the Comparative Examples rely mainly on a bis-triethoxysilylpropyl disulfide type silane. With regard to resins, the Comparative Examples have a terpene resin whereas the Inventive Examples include a DCPD resin type. Furthermore, all examples comprise 1,6-bis(N,N-dibenzylthiocarbamoyldithio)hexane (BDBzTH) which has essentially been utilized to support the abrasion resistance of the composition, which is also an important property for many tread rubber compositions.

TABLE-US-00001 TABLE 1 Comparative Comparative Inventive Inventive Inventive Inventive Example 1 Example 2 Example 1 Example 2 Example 3 Example 4 Ingredients phr Natural rubber 20 20 20 20 20 20 SSBR 1.sup.1 45 35 0 0 0 0 SSBR 2.sup.2 35 45 45 45 60.95 60.95 SSBR 3.sup.3 0 0 36.75 36.75 20 20 Silica 1.sup.4 70 57 57 0 57 0 Silica 2.sup.5 0 0 0 50 0 50 Silane 1.sup.6 0 0 4.6 5 4.6 5 Silane 2.sup.7 7 5.7 0 0 0 0 Stearic Acid 2 2 2 2 2 2 Resin 1.sup.8 26.5 21 0 0 0 0 Resin 2.sup.9 0 0 21 21 21 21 Silane 3.sup.10 2 2 2 2 2 2 Waxes 3 3 3 3 3 3 Antidegradants.sup.11 3 3 3 3 3 3 Zinc Oxide 1.1 1.1 1.1 1.1 1.1 1.1 Sulfur 0.6 0.6 0.75 0.9 0.75 0.9 BDBzTH.sup.12 2.2 2.2 2.2 2.2 2.2 2.2 Accelerators.sup.13 3.1 2.9 2.9 3 2.9 3 .sup.1Thio-functionalized, solution-polymerized styrene butadiene rubber as SLR3402 from Trinseo, having a Tg of −62° C. .sup.2Amino silane-functionalized solution-polymerized styrene butadiene rubber as HPR355H from JSR having a Tg of −27° C. .sup.3Amino siloxane-functionalized solution-polymerized styrene butadiene rubber as F1038 from LG Chem having a Tg of −62° C., with 5% oil extension by weight .sup.4Precipitated silica as Zeosil ™ Premium 200 MP with a BET surface area of about 215 m.sup.2/g .sup.5Precipitated silica with a BET surface area of about 250 m.sup.2/g .sup.63-Octanoylthio-1-propyltriethoxysilane as NXT ™ from Momentive .sup.7Bis-triethoxysilylpropyl disulfide as SI 266 from Evonik .sup.8Alpha pinene terpene resin as Dercolyte ™ A115 from DRT .sup.9C9 modified and hydrogenated DCPD resin as Oppera ™ 383 from Exxon Mobil .sup.1050% bis-triethoxysilylpropyl tetrasulfide on 50% N330 carbon black carrier, as X50S from Evonik .sup.11Mixed p-phenylene diamine types .sup.121,6-bis(N,N-dibenzylthiocarbamoyldithio)hexane as Vulcuren ™ from Lanxess .sup.13Sulfenamide and guanidine types

[0062] The rubber compositions listed above in TABLE 1 have been tested in tire treads of passenger car tires of same construction. Results of these tests for rolling resistance and wet braking are shown in TABLE 2 below. Moreover, these compositions have been tested with regards to their stiffness and abrasion properties as also shown in TABLE 2.

[0063] Comparative Example 1 (not in accordance with the present invention) comprises considerably more silica than the other tested compositions which may be a reason for the larger stiffness observed for Comparative Example 1 compared to the other tested Examples. However rolling resistance of Comparative Example 1 is significantly worse compared to the other Examples in this comparison. Comparative Example 2 (also not in accordance with the present invention) has the same filler composition as the Inventive Examples 1 and 3, which may be one reason for the improved rolling resistance performance but potentially also for a decreased wet braking performance. At the same time, compound stiffness is reduced for Comparative Example 2 and the Inventive Examples 1 to 4 compared to Comparative Example 1 which may have an impact on the ride and handling properties of the tire. In addition, Comparative Example 2 has a significantly increased abrasion over the abrasion observed for Comparative Example 1.

[0064] The Inventive Examples have all a significantly improved rolling resistance over Comparative Example 1. While Comparative Example 2 may have a slightly better rolling resistance performance than Inventive Examples 3 and 4, the overall balance between rolling resistance, wet braking and abrasion is improved for the Inventive Examples. Inventive Examples 1 and 2 have particular strengths in rolling resistance and abrasion. Remarkably, Inventive Example 1 shows a significant improvement in rolling resistance with very limited tradeoff in wet performance and abrasion. Inventive Example 3 shows improved rolling resistance and wet braking performance at the same time. In particular, the wet braking performance of Inventive Examples 1, 3 and 5 is considerably better than the same performance of Comparative Example 2. Moreover, in view of the considerably improved rolling resistance, it is also of advantage to use one or more of the Inventive Examples in a bottom tread cap layer of a tire tread. In such case, the slightly increased abrasion of some of the Examples is not very relevant, the same applies to the wet braking performance. However, the preferred application of the Inventive Examples would be in a radially outermost tread cap layer of a tire tread.

TABLE-US-00002 TABLE 2 Performances/ Comparative Comparative Inventive Inventive Inventive Inventive Properties Example 1 Example 2 Example 1 Example 2 Example 3 Example 4 Rolling 100 103.6 110.9 106.8 102.7 102.7 Resistance.sup.a Wet Braking.sup.b 100 96.7 99.1 95.7 103.8 99.4 Compound 1.4 1.2 1.2 1.2 1.1 1.2 stiffness.sup.c Abrasion.sup.d 128 136 129 126 136 132 .sup.aRelative tire test results, normalized to Comparative Example 1 (higher is better) .sup.bRelative tire test results, normalized to Comparative Example 1 (higher is better) .sup.cCompound test results showing G′ at 1% strain, obtained with an RPA 2000 ™ Rubber Process Analyzer of the company Alpha Technologies, based on ASTM D5289. .sup.dRotary drum abrasion test according to ASTM D5963 or equivalent.

[0065] 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. In any case, the above described embodiments and examples shall not be understood in a limiting sense.