RUBBER COMPOSITION AND A TIRE

Abstract

The present invention is directed to a sulfur vulcanizable rubber composition comprising 50 phr to 100 phr of at least one styrene butadiene rubber functionalized for the coupling to silica, 0 phr to 50 phr of a diene based elastomer, 40 phr to 200 phr of filler, wherein said filler predominantly comprises a pre-silanized silica. Furthermore, the rubber composition comprises at least 0.5 phr of a sulfur-containing compound having the structure

##STR00001##

with n being an integer from 1 to 15, and with R1, R2, R3, R4 being each independently an organic group comprising 1 to 20 carbon atoms. Moreover, the present invention is directed to a rubber component and/or a tire comprising such a rubber composition.

Claims

1. A sulfur vulcanizable rubber composition comprising: 50 phr to 100 phr of at least one styrene butadiene rubber functionalized for the coupling to silica; 0 phr to 50 phr of a diene based elastomer; 40 phr to 200 phr of a filler, wherein said filler comprises predominantly a silanized or pre-silanized silica; and at least 0.5 phr of a sulfur-containing compound having the structure ##STR00007## with n being an integer from 1 to 15 and with R1, R2, R3, R4 each being independently an organic group comprising 1 to 20 carbon atoms.

2. The rubber composition according to claim 1, wherein the silanized or pre-silanized silica has a BET surface area smaller than 120 g/m.sup.2.

3. The rubber composition according to claim 1, wherein said silanized or pre-silanized silica is a silica which is pre-reacted with a sulfur-containing silane.

4. The rubber composition according to claim 3, wherein the sulfur-containing silane is one or more of i) a bis(3-triethoxysilylpropyl)polysulfide containing an average of from 2 to 5 connecting sulfur atoms in its polysulfidic bridge, and ii) an alkoxyorganomercaptosilane.

5. The rubber composition according to claim 1, wherein the filler comprises from 50 phr to 150 phr of the silanized or pre-silanized silica.

6. The rubber composition according to claim 1, wherein said filler comprises less than 10 phr of carbon black.

7. The rubber composition according to claim 1, wherein the rubber composition comprises from 1 phr to 5 phr of the sulfur-containing compound.

8. The rubber composition according to claim 1, wherein one or more of R1, R2, R3, R4 comprise a benzyl group.

9. The rubber composition according to claim 1, wherein said sulfur-containing compound has the following structure: ##STR00008##

10. The rubber composition according to claim 1, further comprising at least 5 phr of a hydrocarbon resin.

11. The rubber composition according to claim 10, wherein said hydrocarbon resin is selected from the list of coumarone-indene-resins, petroleum resins, C5 resins, C9 resins, C5/C9 resins, DCPD resins, CPD resins, MCPD resins, terpene resins, alphamethyl styrene resins, and combinations of those.

12. The rubber composition according to claim 1, comprising less than 10 phr of liquid plasticizer.

13. The rubber composition according to claim 1, wherein the styrene butadiene rubber has one or more of: i) a styrene content of less than 40%, and ii) a vinyl content within a range of 30% to 60%, and iii) a glass transition temperature within a range of −10° C. to −40° C.

14. The rubber composition according to claim 1, comprising less than 0.9 phr of sulfur.

15. The rubber composition according to claim 1, wherein the styrene butadiene rubber has a weight average molecular weight (Mw) within a range of 200,000 g/mol to 500,000 g/mol.

16. The rubber composition according to claim 1, wherein the styrene butadiene rubber functionalized for the coupling to silica has one or more groups selected from an amino group, an amino siloxane group, and an amino silane group.

17. The rubber composition according to claim 1, comprising 70 phr to 100 phr of the styrene butadiene rubber, and 0 phr to 30 phr of one or more of polybutadiene rubber, polyisoprene, and natural rubber.

18. A rubber component for a tire comprising the rubber composition according to claim 1.

19. A tire comprising a rubber component with the rubber composition according to claim 1 in a vulcanized form.

20. The tire of claim 19, wherein the rubber component is a tread of the tire.

Description

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

[0092] Below Table 1 shows two Comparative rubber compositions which are not in accordance with the present invention. Comparative Example 1 shows a rubber composition which comprises the same diene-based rubber matrix as Comparative Example 2. Most ingredients of both compositions are the same. However, Comparative Example 1 has 80 phr of conventional silica together with 7 phr of added Silane 1, whereas Comparative Example 2 has 90 phr of pre-silanized silica. Moreover, Comparative Example 1 comprises 10 phr of oil whereas Comparative Example 2 comprises 5 phr of oil. For example, these two Comparative Examples show that typically the use of pre-silanized silica instead of comparable amounts of conventional, i.e. non-pre-silanized silica decreases the compound stiffness as further shown herein in below Table 2.

TABLE-US-00001 TABLE 1 Amounts in phr Comparative Comparative Ingredient Example 1 Example 2 SSBR 1.sup.1 80 80 PBD 1.sup.2 20 20 Resin 1.sup.3 7 7 Waxes 1.5 1.5 Oil.sup.4 10 5 Processing aids.sup.5 3 3 Stearic Acid 3 3 Silica.sup.6 80 0 Pre-silanized silica.sup.7 0 90 Silane 1.sup.8 7 0 Zinc Oxide 2.5 2.5 Sulfur 1.3 1.3 Antidegradants.sup.9 3 3 DPG.sup.10 2.9 0 CBS.sup.11 2.3 2.3 Silane 2 on carbon black carrier.sup.12 2 2 .sup.1Solution polymerized styrene butadiene rubber as SLR-4602 from Trinseo .sup.2Polybutadiene rubber as Budene ™ 1223 from Goodyear .sup.3Polyterpene resin as Sylvatraxx ™ 4150 from Arizona Chemical .sup.4TDAE oil .sup.5including glycerine monoesters of stearic acid and zinc soaps of fatty acids .sup.6Precipitated silica as Zeosil ™ Premium 200MP from Solvay .sup.7Pre-silanized, precipitated silica as Agilon ™ 400 from PPG Industries .sup.8Bis-triethoxysilylpropyl disulfide as SI266 ™ from Evonik .sup.9based on phenylenediamines .sup.10Diphenylguanidine (accelerator) .sup.11N-cyclohexyl-2-benzothiazolesulfenamide (accelerator) .sup.1250% bis-triethoxysilylpropyl tetrasulfide on 50% N330 carbon black carrier, as X50S from Evonik

TABLE-US-00002 TABLE 2 Comparative Comparative Property Example 1 Example 2 G′(1%), 1 Hz [MPa] .sup.a 2.2 1.5 Tangent Delta (6%), 30° C. .sup.b 0.22 0.19 .sup.a G′ has been obtained with an RPA 2000 ™ Rubber Process Analyzer of the company Alpha Technologies, based on ASTM D5289, at a strain of 1% and 100° C., a frequency of 1 Hz .sup.b Tangent Delta has been obtained by a Metravib ™ instrument at 6% strain and 7.8 Hz based on ISO 4664, DIN 53513, or equivalent at a temperature of 30° C.

[0093] It is observed that the stiffness of Comparative Example 2 is considerably smaller than the stiffness of Comparative Example 1 as shown by the about 35% drop in stiffness. That drop is even more remarkable as the composition of Comparative Example 2 has already an increased content of silica, wherein more filler typically also increases the stiffness of the composition. Even more, Comparative Example 2 has 5 phr less oil than Comparative Example 1 which typically also increases the compound stiffness. According to a non-binding theory of the inventors, the pre-silanized silica may disperse better in the rubber composition which could result in a reduced stiffness.

[0094] Furthermore, Tangent Delta is improved by the use of the pre-silanized silica by about 14%. Tangent Delta can be considered as a hysteresis indicator so that its reduction indicates a reduced hysteresis and thus rolling resistance if the rubber composition is used in a tire. While the above-described improvement in Tangent Delta is desirable, the significant drop in stiffness may for instance be undesirable from many performance oriented tire applications.

[0095] Table 3 comprises further Comparative Examples, which are not in accordance with the present invention, as well as Inventive Examples 1 and 2, which are embodiments in accordance with the present invention. All Examples of Table 3 comprise solution-polymerized styrene-butadiene rubbers which are functionalized for the coupling to silica together with a polybutadiene rubber. Moreover, Comparative Example 4, Inventive Example 1 and Inventive Example 2 comprise pre-silanized silica, whereas Comparative Example 3 comprises conventional silica. Both Inventive Examples comprise further a sulfur-containing compound of the structure

##STR00006##

[0096] wherein Inventive Example 1 comprises a smaller amount of the compound and Inventive Example 2 comprises a larger amount. All Examples of Table 3 comprise a plasticizing resin.

TABLE-US-00003 TABLE 3 Amounts in phr Compar- Compar- ative ative Inventive Inventive Ingredient Example 3 Example 4 Example 1 Example 2 SSBR 2.sup.13 or SSBR 3.sup.14 80 80 80 80 PBD 1.sup.2 20 20 20 20 Resin 1.sup.3 7 7 7 7 Waxes 1.5 1.5 1.5 1.5 Oil.sup.4 10 5 5 5 Stearic Acid 3 3 1 1 Silica.sup.6 80 0 0 0 Pre-silanized silica.sup.7 0 90 90 90 Silane 1.sup.8 7 0 0 0 Zinc Oxide 2.5 2.5 1 1 Processing aids.sup.5 3 3 2 3 Sulfur 1.2 1.2 0.55 0.55 Antidegradants.sup.9 3 5.2 5.2 5.2 DPG.sup.10 2.9 0 0 0 CBS.sup.11 2.3 2.3 1.3 1.5 Sulfur-containing 0 0 1.4 1.7 compound.sup.15 Silane 2 on carbon black 2 2 2 2 carrier.sup.12 .sup.13Solution polymerized styrene butadiene rubber functionalized for the coupling to silica having a glass transition temperature of −25° C., a bound styrene content of 28% and a vinyl content of 42% (RHC) .sup.14Solution polymerized styrene butadiene rubber functionalized for the coupling to silica having a glass transition temperature of −25° C., a bound styrene content of 21% and a vinyl content of 50% (RHC) .sup.15BDBzTH as Vulcuren ™ from Rhein Chemie/Lanxess

[0097] As shown in Table 4 below, stiffness, Tangent Delta and abrasion have been determined for the compositions with SSBR 2 as listed in Table 1.

TABLE-US-00004 TABLE 4 Compar- Compar- ative ative Inventive Inventive Properties with SSBR 2 Example 3 Example 4 Example 1 Example 2 G′(1%), 1 Hz [MPa] .sup.a 1.76 1.38 1.86 1.83 Tangent Delta (6%), 0.18 0.16 0.15 0.14 30° C. .sup.b Abrasion [mm.sup.3] .sup.c 112 101 79 94 .sup.a G′ has been obtained with an RPA 2000 ™ Rubber Process Analyzer of the company Alpha Technologies, based on ASTM D5289, at a strain of 1%, a temperature of 100° C., a frequency of 1 Hz .sup.b Tangent Delta has been obtained by a Metravib ™ instrument at 6% strain and 7.8 Hz based on ISO 4664, DIN 53513, or equivalent at a temperature of 30° C. .sup.c DIN 53516 abrasion resistance test using a Zwick drum abrasion unit, model 6102 with 2.5 Newtons force, relative loss in mm.sup.3

[0098] As shown in Table 4, Tangent Delta is improved by the provision of the pre-silanized silica when comparing Comparative Example 4, Inventive Example 1 and Inventive Example 2 with Comparative Example 3. The improvement in Tangent Delta indicates a low hysteresis and thus improved rolling resistance. However, at the same time, Comparative Example 4 (with pre-silanized silica) has a significantly lower stiffness indicator (G′) than Comparative Example 3 (with conventional silica). Inventive Examples 1 and 2, comprising the sulfur-containing compound according to an embodiment of the present invention, have unexpectedly a higher stiffness than Comparative Example 4. In this context it is also emphasized that the stiffnesses of Inventive Examples 1 and 2 is even higher than the stiffness of Comparative Example 3, despite the use of pre-silanized silica in Inventive Examples 1 and 2.

[0099] Below Table 5 shows similar measurements as Table 4 but considering SSBR 3 instead of the same compositions with SSBR 2.

TABLE-US-00005 TABLE 5 Compar- Compar- ative ative Inventive Inventive Property with SSBR 3 Example 3 Example 4 Example 1 Example 2 G′(1%), 1 Hz [MPa] .sup.a 1.87 1.54 1.68 1.76 Tangent Delta (6%), 0.19 0.15 0.13 0.14 30° C. .sup.b Abrasion [mm.sup.3] .sup.c 113 119 86 87

[0100] Also with a different SSBR, the results obtained according to Table 5 are similar to those observed already in Table 4. Thus, the use of pre-silanized silica improves Tangent Delta as shown by the comparison of Comparative Example 4 with Comparative Example 3. However, a drawback is the loss in stiffness and even the abrasion is negatively impacted by the use of the pre-silanized silica according to Comparative Example 4, when compared with Comparative Example 3. The additional use of the sulfur-containing compound in accordance with the embodiment of the invention results, in comparison with Comparative Example 4, surprisingly in an improvement of stiffness (as indicated by G′), hysteresis (as indicated by Tangent Delta) and abrasion. While the stiffness indicator of Inventive Examples 1 and 2 is not higher than the respective value of Comparative Example 3, Tangent Delta and abrasion have been significantly improved over Comparative Example 3.

[0101] Variations in the present invention are possible in light of the description of it provided herein. 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. It is, therefore, to be understood that changes can be made in the particular embodiments described which will be within the full intended scope of the invention as defined by the following appended claims.