Rubber composition for tyres with good wet grip and winter properties by tailoring phase morphology

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): ≥1 phr to ≤99 phr of a rubber component selected from the group of styrene-butadiene rubber (SBR), polybutadiene rubber (BR), natural rubber (NR) or a mixture thereof; and ≥1 phr to ≤120 phr of an aliphatic resin component. The composition further comprises ≥1 phr to ≤50 phr of a polyisoprene rubber (IR) having ≥mol-%, as determined by NMR spectroscopy, of 3,4-linked units derived from isoprene. It has surprisingly been found that such a polyisoprene rubber having 3,4-linked units derived from isoprene in combination with aliphatic resin worked very well in broadening the tan delta curve of the compound, indicating the compound can perform well in wide range of conditions when cured and used as a rubber for a tyre tread.

Claims

1. A cross-linked rubber composition obtained by cross-linking a rubber composition comprising, per hundred parts by weight of rubber (phr): ≥1 phr to ≤99 phr of a rubber component selected from the group of styrene-butadiene rubber (SBR), polybutadiene rubber (BR), natural rubber (NR) or a mixture thereof; and ≥1 phr to ≤120 phr of an aliphatic resin component; wherein the composition further comprises ≥1 phr to ≤50 phr of a polyisoprene rubber (IR) having ≥10 mol-%, as determined by NMR spectroscopy, of 3,4-linked units derived from isoprene; and wherein the cross-linked rubber composition has a tan delta at 0° C. of ≥0.3 to ≤0.4 (determined from DMA measurements according to ISO 4664-1, frequency 10 Hz, 0.1% dynamic strain) and a tan delta at 70° C. of ≥0.10 to ≤0.25 (determined from DMA measurements according to ISO 4664-1, frequency 10 Hz, 6% dynamic strain).

2. The cross-linked rubber composition according to claim 1, wherein its tan delta curve (determined from DMA measurements according to ISO 4664-1, frequency 10 Hz, 0.1% dynamic strain) has a full width at half maximum of ≥65° C.

3. The cross-linked rubber composition according to claim 1, wherein the polyisoprene rubber has a glass transition temperature of ≥−15° C. to ≤−5° C. (measured by DSC, according to ISO 22768).

4. The cross-linked rubber composition according to claim 1, wherein the polyisoprene rubber has a Mooney viscosity (ML 1+4, ASTM D1646-15) of ≥60 to ≤75 M. U.

5. The cross-linked rubber composition according to claim 1 wherein the composition comprises ≥5 phr to ≤40 phr of the polyisoprene rubber.

6. The cross-linked rubber composition according to claim 1, wherein the composition comprises ≥5 phr to ≤60 phr of the aliphatic resin component.

7. The cross-linked rubber composition according to claim 1, wherein the composition comprises ≥70 phr of rubbers with a glass transition temperature of ≥−120° C. to ≤−50° C. (measured by DSC, according to ISO 22768).

8. The cross-linked rubber composition according to claim 1, wherein the composition comprises: ≥45 phr to ≤65 phr of styrene-butadiene rubber (SBR); ≥15 phr to ≤35 phr of polybutadiene rubber (BR); ≥0 phr to ≤20 phr of natural rubber (NR).

9. The cross-linked rubber composition according to claim 1, wherein the aliphatic resin component has a molecular weight Mw of ≥800 to ≤2500 g/mol.

10. The cross-linked rubber composition according to claim 1, wherein the aliphatic resin component comprises a polyterpene resin, C5 resin or DCPD resin.

11. The cross-linked rubber composition according to claim 1, wherein the styrene-butadiene rubber component comprises a first styrene-butadiene rubber and a second styrene-butadiene rubber which is different from the first styrene-butadiene rubber.

12. A tyre comprising a tyre tread, wherein the tyre tread comprises a cross-linked rubber composition according to claim 1.

Description

(1) The present invention will be further described with reference to the following figures and examples without wishing to be limited by them.

(2) FIG. 1 shows temperature-dependent tan delta curves for examples C1, C2, C3, I1 and I2

(3) FIG. 2 shows temperature-dependent tan delta curves for examples C1, C4, C5 and C6

(4) To develop a tread compound with improved winter performance and wet grip, the compound is expected to perform well in wide range of temperatures. In this case, a compound which exhibits a broad tan delta curve (dynamic mechanical properties) is of great interest. Such a broad tan delta curve implies heterogeneity of the polymer network or polymer chains with wide distribution of segmental motions at different temperatures. As a measure for the broadness of the tan delta curve, the full width at half maximum (FWHM) of the tan delta curves was determined.

(5) In order to develop a compound which can exhibit broad tan delta curve, a polyisoprene rubber with 3,4-linked isoprene units having a Tg of −10° C. has been added to the polymer blend to intentionally create immiscibility. As a result of this, dual tan delta peaks were obtained which resulted in slight broadening of the tan delta curve but there was no significant improvement in wet grip (tan delta at 0° C.).

(6) In the next iteration, three different types of resin were added to the immiscible polymer blend in place of processing oil. Surprisingly, the aliphatic resins, polyterpene and C5, worked particularly well and broadened the tan delta curve. This is believed to be due to their preference to the phase comprising polyisoprene rubber. On the other hand, AMS resin did not help in broadening the tan delta curve indicating no preference to the phase comprising polyisoprene rubber.

(7) Another approach of creating immiscible polymer blend has been attempted by introducing high styrene SSBR (SSBR III) possessing a Tg of −36° C. (40% styrene and 24% vinyl) to the polymer blend. In this case, dual tan delta peaks were obtained but there is no improvement in wet grip (tan delta at 0° C.). In a similar manner as for the other immiscible polymer blend, AMS and polyterpene resin were added. The addition of resins resulted only in the Tg shift but there was no observation of a broadening of the tan delta curve.

(8) In accordance with the preceding, cross-linkable rubber compositions were prepared as described in the tables below. Compositions C1 to C6 are comparative examples and composition I1 and I2 are compositions according to the invention.

(9) The polyisoprene rubber used was Isogrip of Karbochem, a solution-polymerised 3,4 addition polyisoprene with a T.sub.g of −10° C., a 3,4-addition product content of 60% and a viscosity (ML 1+4): of 65-70 M. U. according to its data sheet.

(10) The polyterpene resin used was Sylvatraxx TR 7125 of Arizona Chemical, having a Mw of 1090 g/mol.

(11) The C5 resin used was Piccotac 1098 of Eastman Chemical Company, having a Mw of 2150 g/mol.

(12) The AMS (alpha methyl styrene) resin used was Sylvatraxx 4401 of Arizona Chemical, having a Mw of 1300 g/mol.

(13) The SSBR I used was Sprintan SLR 4602 of Trinseo having a 21% styrene 50% vinyl content and a Tg of −25° C.

(14) The SSBR II used was Sprintan SLR 3402 of Trinseo having a 15% styrene 30% vinyl content and a Tg of −62° C.

(15) The SSBR III used was Sprintan SLR 6430 of Trinseo, an oil extended SSBR (27.27% of oil) with 40% styrene and 24% vinyl.

(16) The butadiene rubber used was BUNA cis-132 of Trinseo having a Tg of −102° C.

(17) The table below shows the compositions C1-6 and I1, I2:

(18) TABLE-US-00001 C1 C2 C3 C4 C5 C6 I1 I2 NR 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 Butadiene 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 Rubber SSBR I 25.00 15.00 15.00 10.00 10.00 10.00 15.00 15.00 SSBR II 40.00 40.00 40.00 30.00 30.00 30.00 40.00 40.00 polyisoprene 10.00 10.00 10.00 10.00 rubber SSBR III 34.40 34.40 34.40 TDAE 39.00 39.00 20.00 30.00 10.00 10.00 20.00 20.00 (processing oil) AMS resin 20.00 20.00 Polyterpene 20.00 20.00 resin C5 resin 20.00

(19) All Amounts in Phr

(20) In addition, all cross-linkable rubber compositions contained 2.00 phr ZnO, 1.00 phr stearic acid, 6 phr antioxidant and antiozonant, 8 phr processing promotor, 1.75 phr sulphur, 3.25 phr accelerator, 5.00 phr N 375 carbon black, 100.00 phr silica and 6.50 phr TESPD.

(21) The cured rubbers derived from the aforementioned compositions had the mechanical properties outlined in the following table. DMA according to ISO 4664-1 tests were performed at −80° C. to 25° C. (dynamic strain 0.1% and frequency 10 Hz) and at 25° C. to 80° C. (dynamic strain 6% and frequency 10 Hz). Without wishing to be bound by theory it is believed that a higher tan delta value at 0° C. corresponds to better wet grip. Rebound testing at 70° C. (ISO 4662) is believed to be an indicator for rolling resistance. A higher rebound value at 70° C. relates to a lower rolling resistance for a tyre whose tread comprises such a cured rubber. Tensile testing was performed according to ISO 37.

(22) Full width at half maximum was determined from the tan delta curve and taken as a measure for the broadness of the curve, and hence the ability of the compound to perform well at a high temperature interval.

(23) TABLE-US-00002 C1 C2 C3 C4 C5 C6 I1 I2 Hardness (Sh A) 62.20 62.5 63.8 64.2 64.8 64.8 62.3 63 Elongation at break (%) 478.1 519.6 520.6 526 527.6 561.7 541.7 501.3 M300% (MPa) 8.87 8.29 9.22 8.96 8.54 7.89 8.72 8.59 M300%/M100% 4.27 3.66 4.03 4.11 3.97 4.00 3.78 3.84 Tensile strength (MPa) 16.47 16.23 17.64 18.05 17.67 18.23 17.23 16.23 Tear strength (MPa) 9.31 8.84 10.2 11.23 9.41 10.49 10.15 8.68 Rebound 70° C. (%) 55.1 53.5 51.8 52.6 50.2 49.3 50.7 50.7 Dynamic mechanical properties Tan delta at 0° C. 0.18 0.2 0.25 0.17 0.23 0.22 0.32 0.32 Tan delta at 70° C. 0.16 0.18 0.18 0.18 0.19 0.19 0.18 0.18 Full width at half −55 to −14 −60 to 1 −50 to 4 −57 to −4 −51 to 11 −47 to 3 −52 to 19 −56 to 25 maximum range (° C.) Full width at half 41 61 54 53 62 50 71 81 maximum (FWHM) (° C.)

(24) With respect to compositions C1 to C3 and I1 and I2, as shown in FIG. 1, the comparative example C2 displays two peaks indicating incompatibility, the first peak at −42° C. and the second peak at −10° C. being representative of 3,4 isoprene. It can be easily understood that the presence of 3,4 isoprene possessing Tg of −10° C. is incompatible to the other polymers in the recipe (NR, BR and SSBR). As a result of incompatibility, the tan delta curve is broadened compared to C1 and there is only a slight increase in the wet grip indicator (tan delta at 0° C.). Comparing C2 against C3, the comparative example C3 contains AMS resin which resulted only in shifting of the tan delta curve and there is no peak broadening effect.

(25) The inventive example I1 which contains both polyisoprene rubber and polyterpene resin reveals a broad tan delta curve. Adding polyterpene resin in an incompatible polymer composition containing polyisoprene rubber leads to an extremely broad tan delta curve. Without being bound to theory it is believed that this is because of the enrichment of polyterpene resin in the polyisoprene rubber phase. As a result of this, tan delta at 0° C. is enormously increased indicating an increase in wet grip. In addition to that the FWHM is increased to 71, covering a temperature range of −52 to 19° C. A similar effect is observed for inventive example I2 with contains both polyisoprene rubber and C5 resin. Therefore, the inventive example offers an improvement in wet grip without losing on winter performance. Thus the trade-off between winter and wet is eliminated by creating a broad tan delta curve.

(26) With respect to compositions C1 and C4 to C6, as shown in FIG. 2, the graphs for C4, C5 and C6 also display two peaks indicating incompatibility. In this case, incompatibility is achieved by using high styrene/low vinyl SSBR as seen in C4. Incorporating high Tg resins, both AMS and polyterpene caused only a shift in tan delta curve. There is no peak broadening effect.

(27) Without being bound to theory, it is believed that the aliphatic resins (I1 and I2) have a good miscibility and a greater preference to the incompatible isoprene rubber than other polymers which is evident from the increased peak height in the temperature range of −10 to 10° C. compared to C2. The high preference of the aliphatic resins with the polyisoprene rubber might be related to the comparative chemical structure of the aliphatic resin and polyisoprene rubber. This resulted in broadening of the tan delta curve overall in the first set of inventive examples (I1 and I2). In the second set of examples (C5 and C6), the resin's preference and miscibility are most likely lacking with the incompatible SSBR rubber III, hence not resulting in a broadening of the tan delta curve.

(28) Overall, among the comparative examples (C1 to C6), the inventive examples demonstrate improvement in wet grip without compromising on winter performance.