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

Abstract

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): ≤50 phr of a first rubber, the first rubber being a solution polymerized styrene-butadiene rubber (SSBR) comprising an alkoxysilane group and a primary amino group; ≥20 phr of a second rubber; and a coupling agent, a filler, and a resin, wherein the rubber composition comprises >15 phr of a third rubber; and ≥10 phr of a fourth rubber; and wherein the composition comprises ≥1 phr to ≤20 phr of at least two coupling agents wherein one of the coupling agents is or comprises a mercapto based silane and wherein the ratio of the mercapto based silane to the second coupling agent is in a range of ≥2:1 to ≤10:1.

Claims

1. A cross-linkable rubber composition, the cross-linkable rubber composition comprising, per hundred parts by weight of rubber (phr): ≤50 phr of a first rubber, the first rubber being a solution polymerized styrene-butadiene rubber (SSBR) comprising an alkoxysilane group and a primary amino group; ≥20 phr of a second rubber; and a coupling agent, a filler, and a resin, wherein the rubber composition comprises ≥15 phr of a third rubber; and ≥10 phr of a fourth rubber; and wherein the composition comprises ≥1 phr to ≤20 phr of at least two coupling agents wherein one of the coupling agents is or comprises a mercapto based silane and wherein the ratio of the mercapto based silane to the second coupling agent is in a range of ≥2:1 to ≤10:1.

2. The rubber composition according to claim 1, wherein the second, the third and the fourth rubber are selected from the group of solution polymerized styrene-butadiene rubber (SSBR), polybutadiene rubber (BR), and natural rubber (NR), and wherein the second, the third and the fourth rubber have a glass transition temperature Tg of ≥−120° C. to ≤−40° C., the glass transition temperature Tg being measured by differential scanning calorimetry (DSC) according to ISO 22768.

3. The rubber composition according to claim 1, wherein the second rubber is a butadiene rubber (BR) with a cis group content, as determined by infrared spectroscopy (IR), of ≥90%.

4. The rubber composition according to claim 1, wherein the third rubber is a solution polymerized styrene-butadiene rubber (SSBR) having a glass transition temperature Tg of ≥−120° C. to ≤−40° C., the glass transition temperature Tg being measured by differential scanning calorimetry (DSC) according to ISO 22768.

5. The rubber composition according to claim 1, wherein the fourth rubber is a natural rubber.

6. The rubber composition according to claim 1, wherein the composition comprises: ≥10 phr ≤40 phr of the first rubber; ≥20 phr ≤40 phr of the second rubber; ≥10 phr ≤30 phr of the third rubber; and ≥10 phr ≤20 phr of the fourth rubber.

7. The rubber composition according to claim 1, wherein the second coupling agent is selected from disulfide silanes, tetrasulfide silanes or a combination thereof.

8. The rubber composition according claim 1, wherein the composition comprises ≥1 phr of an aliphatic or aromatic resin.

9. The rubber composition according to claim 1, wherein the composition comprises ≥60 phr ≤130 phr of silica.

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

11. The cross-linked rubber composition according to claim 10, with a tan delta at 0° C. of ≥0.2 to ≤0.5 (determined from dynamic mechanical analysis (DMA) measurements according to ISO 4664-1, frequency 10 Hz, 0.1% dynamic strain) and a tan delta at 70° C. of ≥0.05 to ≤0.15 (determined from DMA measurements according to ISO 4664-1, frequency 10 Hz, 6% dynamic strain).

12. The cross-linked rubber composition according to claim 10, wherein the G′ at −20° C. (determined from DMA measurements according to ISO 4664-1) is in a range from 15 MPa to 25 MPa.

13. The cross-linked rubber composition according to claim 10, having a rebound at 70° C., determined according to ISO 4662, of ≥60% to ≤75%.

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

15. A tyre comprising a tyre tread, characterised in that the tyre tread comprises a cross-linked rubber composition according to claim 10.

Description

EXAMPLE 1

[0051] 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 additives were added and mixed and a last step wherein the curing package was added. Composition Ref1 is a comparative example and compositions E1 and E2 are the compositions according to the invention. Amounts for the components are given in PHR. Unless stated otherwise, glass temperatures given were determined by DSC according to ISO 22768.

TABLE-US-00001 TABLE 1 Composition of Examples: Ref1 E1 E2 Component (phr) (phr) (phr) NR 10 15 10 BR 55 35 30 SSBR I — 35 35 SSBR II 40 15 25 SSBR III 10 — — Fillers 130 120 120 Coupling agent 1 — 9 9 Coupling agent 2 10 1 2 Resin 30 25 25 Processing aids 34 33 33 Anti-degradation agents 6 5 5 Curing agents 11 9.5 9.5

[0052] The reference composition used a standard recipe without resin for a reference tread compound based on NR, NiBR, SSBR polymer, Ni-catalysed BR and reinforcing or inert filler content between 60-130 phr. The experimental tread compounds E1 and E2 comprised a resin and substituted the Ni-catalysed BR completely by Nd-catalysed BR. Further a functionalized non oil extended SSBR was substituted by a blend of a fourth generation SSBR and a low Tg SSBR.

[0053] NR rubber was TSR 20, with a Mooney Viscosity 80 and a Tg of −70° C.

[0054] BR rubber used for E1 and E2 was Nd catalyzed butadiene rubber with a cis content of 95% and a T.sub.g of −102° C.

[0055] SSBR I was HPR850 manufactured by JSR Corporation, a solution polymerized styrene-butadiene rubber (SSBR) comprising an alkoxysilane group and a primary amino group with a styrene content of 27 wt. % and vinyl content of 58.8% and a T.sub.g of −25° C., non-oil extended product was used.

[0056] SSBR II was a functionalised SSBR and had a styrene content of 15%, a vinyl content of 30% and a T.sub.g of −65° C.

[0057] SSBR III was a non oil extended SSBR with a styrene content of 21%, a vinyl content of 63% and a T.sub.g of −24° C.

[0058] Fillers used in the above examples were Carbon black N339 and High Dispersion Micro-Pearl Silica (HDS, MP) supplied by PPG Industries

[0059] Coupling agent 1 was Silaan VP Si 363 Degussa supplied by Evonik Industries.

[0060] Coupling agent 2 was TESPD (disulphide silane) supplied by Evonik Industries. The reference example “Ref1” had TESPD and thiocarboxylate (NXT) as the silane component.

[0061] The Resin used was Sylvatraxx 4202 with a molecular weight of 565 g/mol supplied by Kraton Corporation.

[0062] Rebound at 70° C. and Tan delta (70° C.) were measured to check (relate) for rolling resistance (RR) of the compounds. Rebound at 23° C. and Tan delta (0° C.) were measured to check wet grip. Further, a DMA shear strain sweep (<65%) was performed at 40° C. to evaluate rolling resistance (RR). Payne effect was measured using a rubber process analyzer. The following table 2 shows the results obtained from the cured compositions.

TABLE-US-00002 TABLE 2 Test results: Component Ref1 E1 E2 Rebound 23° C. [%] 25.20 21.90 25.00 Rebound (70° C.) [%] 48.30 54.00 58.30 Tan δ 70° C. 0.18 0.13 0.11 (RR indicator) Tan δ 0° C. 0.219 0.283 0.316 (Wet grip indicator)

[0063] The results show for the compositions E1 and E2 an increase of rebound at 70° C. from 48.30 to 54.00 and 58.30 respectively and a decrease in Tan delta at 70° C. from 0.18 to 0.13 and 0.11 respectively. 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.

[0064] Tan delta at 0° C. increased from 0.219 to 0.283 and 0.316 respectively. The reduction in rebound (ISO 4662) is a well-known indicator of an increase in the wet grip in the tyre industry. Lower rebound value at −23° C. relates to an improvement in wet grip. In a similar fashion, a higher tan δ at 0° C. is related to better wet grip.

[0065] Further, strain sweep measurements showed an almost independent Tan delta behavior under strain.

[0066] In summary, this shows a surprising improvement of the rolling resistance indicators and the wet grip indicators. Without being bound to a specific theory, it is believed that the coupling agents lower hysteresis.

EXAMPLE 2

[0067] 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 additives were added and mixed and a last step wherein the curing package was added. Composition Ref2 is a comparative example and composition E3 is the composition according to the invention. Amounts for the components are given in PHR. Unless stated otherwise, glass temperatures given were determined by DSC according to ISO 22768.

TABLE-US-00003 TABLE 3 Composition of Examples: Ref2 E3 Component (phr) (phr) NR 20 15 BR 30 35 SSBR I — 30 SSBR II — 20 SSBR III 50 — Fillers 87 77 Coupling agent 1 — 7 Coupling agent 2 6.65 2 Resin — 17 Processing aids 30 10.5 Anti-degradation agents 6 5 Curing agents 9 9

[0068] The reference composition used a standard recipe without resin for a reference tread compound based on NR, NiBR, SSBR polymer, Ni-catalysed BR and reinforcing or inert filler content between 60-100 phr. The experimental tread compound E3 comprised a resin and substituted the Ni-catalysed BR completely by Nd-catalysed BR. Further a functionalized non oil extended SSBR was substituted by a blend of a fourth generation SSBR and a low Tg SSBR.

[0069] NR rubber was TSR 20, with a Mooney Viscosity 80 and a Tg of −70° C.

[0070] BR rubber used for E3 was Nd catalyzed butadiene rubber with a cis content of 95% and a T.sub.g of −102° C.

[0071] SSBR I was HPR850 manufactured by JSR Corporation, a solution polymerized styrene-butadiene rubber (SSBR) comprising an alkoxysilane group and a primary amino group and with a styrene content of 27 wt. % and vinyl content of 58.8% and a T.sub.g of −25° C., non-oil extended product was used.

[0072] SSBR II was a functionalised SSBR and had a styrene content of 15%, a vinyl content of 30% and a T.sub.g of −65° C.

[0073] SSBR III was a functionalised non oil extended SSBR with a styrene content of 21%, a vinyl content of 63% and a T.sub.g of −24° C.

[0074] Fillers used in the above examples were Carbon black N339 and High Dispersion Micro-Pearl Silica (HDS, MP) supplied by PPG Industries

[0075] Coupling agent 1 was Silaan VP Si 363 Degussa supplied by Evonik Industries.

[0076] Coupling agent 2 was TESPD (disulphide silane) supplied by Evonik Industries. The reference example “Ref2” had TESPD as the only silane component.

[0077] The Resin used was Sylvatraxx 4202 with a molecular weight of 565 g/mol supplied by Kraton Corporation.

[0078] 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 indicate wet grip. Further, a DMA shear strain sweep (<65%) was performed at 40° C. to evaluate rolling resistance (RR). Payne effect was measured using a rubber process analyzer. The following table 4 shows the results obtained from the cured compositions.

TABLE-US-00004 TABLE 4 Test results: Component Ref2 E3 Rebound 23° C. [%] 36.20 40.40 Rebound (70° C.) [%] 58.3 67.6 Tan δ 70° C. 0.16 0.09 (RR indicator) G′ (−20° C.) [MPa] 29.18 18.41 Tan δ 0° C. 0.1832 0.312 (Wet grip indicator)

[0079] The results show for the composition E3 an increase of rebound at 70° C. from 58.30 to 67.60 and a decrease in Tan delta at 70° C. from 0.16 to 0.09. 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.

[0080] G′at −20° C. decreased from 29.18 to 18.41 which is an indicator of better snow grip.

[0081] Tan delta at 0° C. increased from 0.1832 to 0.312. The reduction in rebound (ISO 4662) is a well-known indicator of an increase in the wet grip in the tyre industry. Lower rebound value at −23° C. relates to an improvement in wet grip. In a similar fashion, a higher tan δ at 0° C. is related to better wet grip.

[0082] Further, strain sweep measurements showed an almost independent Tan delta behavior under strain.

[0083] In summary, this shows a surprising improvement of the rolling resistance indicators and the wet grip indicators. Without being bound to a specific theory, it is believed that this was achieved by substituting the functionalized non-oil extended SSBR by a blend of a SSBR comprising alkoxysilane primary amino groups and a low Tg SSBR, while the coupling agents are believed to lower hysteresis.

EXAMPLE 3

[0084] Two sets of two 205/55R16 All Season tyres were fabricated using the rubber compositions of the reference composition Ref2 and the composition according to the invention E3 and were tested for rolling resistance on a drum following procedure ECE R117. The following table 5 shows the results obtained from the tyre testing.

TABLE-US-00005 TABLE 5 Test results of tyres: Ref2 E3 Rolling resistance ECE R117 [%] 100 112

[0085] The results of the reference tyres were normalized to 100% and the rolling resistance as measured in KG/Ton is shown as a percentage change in the table 5. The results show that the rolling resistance was improved for the for the tyres fabricated from composition E3 from a baseline of 100% to 112%. This result illustrates a significant reduction in the rolling resistance of a tyre due to the rubber composition of the invention.

EXAMPLE 4

[0086] Two sets of four 205/55R16 All Season tyres were fabricated using the reference composition Ref and the composition according to the invention E3 and were tested for snow breaking and snow handling on a car in a snow testing ground. The following table 6 summarizes the results obtained from the snow testing of tyres.

TABLE-US-00006 TABLE 6 snow testing results of tyres: Ref2 E3 Deceleration snow ABS [%] 100 102.6 Acceleration snow [%] 100 101.8 Handling Snow [%] 100 104.6

[0087] The results of the reference tyres were normalized to 100% and acceleration and deceleration on snow is shown as a percentage from a baseline for the reference of 100% in the table 6. The results show that acceleration, deceleration and snow handling was improved for the tyres fabricated from composition E3.

[0088] These results illustrate an improvement in the snow performance of the tyres due to the rubber composition of the invention.