RUBBER COMPOSITION FOR TYRES WITH LOW ROLLING RESISTANCE AND GOOD WINTER PROPERTIES

Abstract

Rubber composition for tyres with low rolling resistance and good winter properties The present invention relates to a cross-linkable rubber composition, a cross-linked rubber composition obtained by cross-linking such a rubber composition, a method of preparing a tyre and a tyre. In a cross-linkable rubber composition, the cross-linkable rubber composition comprises, per hundred parts by weight of rubber (phr): ≥91 to ≤99 phr of natural rubber or isoprene rubber or combination thereof, a syndiotactic 1,2 polybutadiene, and ≥1 to ≤100 phr of a filler comprising carbon black, wherein the ratio of the syndiotactic 1,2 polybutadiene to the carbon black is in the range of 1:8 to 1:3 and in that the ratio of the syndiotactic 1,2 polybutadiene to the carbon black is in the range of ≥1:8 to ≤1:3.

Claims

1. A cross-linkable rubber composition, the cross-linkable rubber composition comprising, per hundred parts by weight of rubber (phr): ≥91 phr to ≤99 phr of natural rubber or isoprene rubber or a combination thereof, a syndiotactic 1,2 polybutadiene, and ≥1 phr to ≤100 phr of a filler comprising carbon black, characterized in that the syndiotactic 1,2 polybutadiene is present in an amount of ≥1 phr to ≤9 phr and in that the ratio of the syndiotactic 1,2 polybutadiene to the carbon black is in the range of ≥1:8 to ≤1:3.

2. The rubber composition according to claim 1, wherein the syndiotactic 1,2 polybutadiene contains at least 90 percent of its repeating units in a 1,2-configuration and has a melting point of between 100° C. to 130° C.

3. The rubber composition according to claim 1, wherein the filler comprises or is a carbon black having a tint strength in the range of 126% to 136% (determined by ASTM D3265) and an iodine adsorption number in the range of 134 g/kg to 150 g/kg (determined by ASTM D1510).

4. The rubber composition according to claim 1, wherein the filler is or comprises a blend of a first and a second carbon black.

5. The rubber composition according to claim 4 wherein the second carbon black has a tint strength in the range of 101% to 116% (determined by ASTM D3265) and an iodine adsorption number in the range of 80 g/kg to 95 g/kg (determined by ASTM D1510).

6. The rubber composition according to claim 1, wherein the filler further comprises silica in an amount of ≥1 phr to ≤15 phr.

7. The rubber composition according to claim 6, wherein the total amount of the filler is in a range of ≥20 phr to ≤100 phr.

8. A cross-linked rubber composition, characterized in that it is obtained by cross-linking a rubber composition according to claim 1.

9. The cross-linked rubber composition according to claim 8 with a G′0.56 at 100° C. (measured by RPA strain sweep ISO 6502) ranging from ≥0.30 MPa to ≤0.40 MPa.

10. The cross-linked rubber composition according to claim 8 with a rebound value at 70° C. (as per ISO 4662) ranging from ≥60% to ≤67%.

11. The cross-linked rubber composition according to claim 8 with a tan delta value at 70° C. (as per DMA double shear −80° C. to 25° C. at 0.1%) ranging from ≥0.09 to ≤0.16.

12. The cross-linked rubber composition according to claim 8 with a tear strength (as per delft 20′ at 160° C.) ranging from ≥16 MPa to ≤20 MPa.

13. A method of preparing a tyre, comprising the steps of: providing a tyre assembly comprising a cross-linkable rubber composition according to claim 1; and cross-linking at least the cross-linkable rubber composition in the tyre assembly.

14. A tyre for a light truck, bus or truck comprising a tread, characterized in that the tread comprises a cross-linked rubber composition according to claim 8.

Description

EXAMPLE 1

[0040] In accordance with the preceding, cross-linkable rubber compositions were prepared according to the following table 1. In a first step, the rubber components were added and mixed, followed by a second step wherein the fillers, oil and additives were added and mixed and a last step wherein the curing package was added. Composition Ref1 is a comparative example and composition E1 is the composition according to the invention. Amounts for the components are given in PHR. Unless stated otherwise, glass transition temperatures given were determined by DSC according to ISO 22768.

TABLE-US-00001 TABLE 1 Composition of Examples: Ref1 E1 Component (phr) (phr) NR 100 95 Syndiotactic 1,2-polybutadiene 5 Carbon black 48 36.2 Silica 8 8 Oil 2 2

[0041] Natural rubber (NR) was TSR 20, with a Mooney Viscosity 80 and a Tg of −70° C.

[0042] Syndiotactic 1,2-polybutadiene rubber was AT 400 supplied by JSR corporation.

[0043] Carbon black for the reference composition was N220 supplied by Columbian Carbon and for the composition E1 of the present invention was N134 supplied by Orion Engineered Carbons.

[0044] Silica was supplied by PPG

[0045] Oil was RAE processing oil supplied by Repsol.

[0046] Rebound at 70° C. and Tan delta (70° C.) were measured to check (relate) for rolling resistance (RR) of the compounds. G′ (storage modulus) at −20° C. was measured for indication of snow performance and Tan delta (0° C.) was measured to check wet grip. Payne effect was measured using a rubber process analyzer to evaluate rolling resistance (RR). The following table 2 shows the results obtained from the cured compositions.

TABLE-US-00002 TABLE 2 Test results: Component Ref1 E1 Rebound (70° C.) [%] 54.00 64.00 Tan δ 70° C. 0.25 0.14 (RR indicator) Tan δ 0 ° C. 0.12 0.12 (Wet grip indicator) Elongation at break % 560.23 549.78 M 300% MPa 9.79 9.74 Tensile strength MPa 23.12 23.02 Tear strength (delft) 20′ at MPa 15.41 17.62 160° C. G′ (−20° C.) MPa 15.48 6.08 G′ 100.02 (100° C.) MPa 0.05 0.07 G′ 0.56 (100° C.) MPa 0.54 0.34

[0047] The results show for the composition E1 an increase of rebound at 70° C. from 54.00 to 64.00 and a decrease in Tan delta at 70° C. from 0.25 to 0.14. Rebound testing at 70° C. (ISO 4662) is believed to be an indicator for rolling resistance (RR). A higher rebound value at 70° C. relates to a lower rolling resistance for a tyre whose tread comprises such a cured rubber. In a similar fashion, a lower tan δ at 70° C. is an indicator for improved rolling resistance.

[0048] Tan delta at 0° C. did not change and was measured as 0.12 for both the compositions. This was an indicator that the wet grip of the compound did not change. Further it can be seen for the elongation at break, modulas at 300%, tensile strength and tear strength (delft) 20′ at 160° C. that remain unchanged which shows that the durability was same.

[0049] Further, the results show for the composition E1 a decrease of G′ at −20° C. from 15.48 to 6.08 which is an indicator of better snow performance. The results also show for the composition E1 the Payne value decreasing from 0.54 to 0.34, which also is an indicator for better rolling resistance.

[0050] In summary, this shows a surprising improvement of the rolling resistance indicators and the snow performance while maintaining the wet grip and durability. Without being bound to a specific theory, it is believed that the replacement of carbon black with syndiotactic polybutadiene led to this change.

[0051] These results illustrate an improvement in the rolling resistance and snow performance of the tyres due to the rubber composition of the invention.