Rubber composition for tires with improved winter performance and abrasion resistance

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 tire and a tire. A cross-linkable rubber composition comprises, per hundred parts by weight of rubber (phr): 100 phr of a diene-based elastomer component with an average molecular weight Mn in a range of 100000 to 5000000 g/mol and a homopolymer of polybutadiene, wherein the homopolymer of polybutadiene has an average molecular weight Mn in a range of 10000 to 45000 g/mol and a glass transition temperature Tg in a range of 110 C. to 60 C.

Claims

1. A cross-linkable rubber composition, the cross-linkable rubber composition comprising, per hundred parts by weight of solid rubber (phr): 100 phr of a diene-based elastomer component with an average molecular weight Mn in a range of 100000 to 5000000 g/mol and a homopolymer of polybutadiene, wherein the homopolymer of polybutadiene has an average molecular weight Mn in a range of 10000 to 45000 g/mol and a glass transition temperature Tg in a range of 110 C. to 60 C., wherein the rubber composition comprises 5 to 15 phr of the homopolymer of polybutadiene, and wherein the diene-based elastomer component comprises 40 phr to 90 phr of a styrene-butadiene rubber component comprising a first styrene-butadiene and a second butadiene rubber that is different from the first styrene-butadiene rubber and 10 phr to 60 phr of a combination of a natural rubber and a butadiene rubber.

2. The rubber composition according to claim 1, wherein the homopolymer of polybutadiene has a vinyl (1,2-) content in a range of 0 to 40 wt %.

3. The rubber composition according to claim 1, wherein the homopolymer of polybutadiene has a melt viscosity of range of 15 to 500 Pa s at 38 C.

4. A cross-linked rubber composition obtained by cross-linking the cross-linkable rubber composition according to claim 1.

5. The cross-linked rubber composition according to claim 4 with a tan at 0 C. of 0.16 to 0.35.

6. The cross-linked rubber composition according to claim 4 with a glass transition temperature Tg of 50 C. to 35 C.

7. The cross-linked rubber composition according to claim 4 with an abrasion resistance of 75 mm.sup.3.

8. The cross-linked rubber composition according to claim 4 with an elastic modulus G at 20 C. of 25 to 40 MPa.

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

10. A tire comprising a tire tread, characterised in that the tire tread comprises a cross-linked rubber composition according to claim 4.

Description

EXAMPLE

(1) Homopolymers of polybutadienes with several molecular weights and Tg's were mixed with a standard recipe as given in table 1 and vulcanised to study the DMA curve according to ISO 4664-1, with a frequency of 10 Hz, a dynamic strain of 0.1% and a temperature range from 80 to +25 C. The abrasion resistance (wear test) was measured according to ISO 4649.

(2) The properties of the ingredients can be obtained by methods commonly used in the art. For example the average molecular weight Mn can be measured by GPC according to ASTM D6579-11. Melt Viscosity can be measured at 38 C. with a Brookfield viscometer. Vinyl content can be measured by 1H-NMR or FTIR and determined from the obtained spectrum. Glass transition temperatures (Tg) of the homopolymers of polybutadiene can be obtained with differential scanning calorimetry (DSC) according to ISO 22768. Glass transition temperatures (Tg) of the cross-linked rubber mixture were determined from the DMA measurement, corresponding to the temperature at the maximum of the tan curve (the FIGURE).

(3) TABLE-US-00001 TABLE 1 NR 25 phr BR 31 phr SSBR (50% vinyl 21% styrene) 12 phr SSBR (50% vinyl 21% styrene, oil extended (27.3%)) 44 phr (32 phr SSBR) Homopolymer of polybutadiene or oil 10 phr Carbon Black (N375) 5 phr Silica 100 phr Silane (TESPD, bis-triethoxysilylpropyldisulfidosilane) 6.5 phr Process oil 17 phr Zinc Oxide 2 phr Stearic Acid 1 phr Antioxidant/Antiozonant 6 phr Processing promoter 8 phr Sulphur 1.75 phr TBBS (N-tert-butyl-2-benzothiazyl sulfenamide) 1.75 phr DPG (diphenyl guanidine) 2.5 phr

(4) The variation of homopolymers of polybutadiene and the properties of the compound are given in Table 2. The corresponding graph is shown in the FIGURE.

(5) It is apparent from the results that the rubber composition according to the invention (I1), with a liquid homopolymer of polybutadiene with a high average molecular weight offers a well-balanced combination of good abrasion resistance, good winter performance and good wet grip compared to the references.

(6) The inventive example (I1) has a much better abrasion resistance compared to comparative example 2 (C2) and 3 (C3), and is only slightly less compared to comparative example 1 (C1). In terms of winter performance, the examples with liquid homopolymer of polybutadiene all show a Tg shift to lower temperature and a G (20 C.) compared to comparative example 3 (C3), with oil. However, the inventive example (I1) also displays an improvement in Tan (0 C.) compared to the other examples, corresponding to enhanced wet grip.

(7) In summary, the rubber composition according to the invention not only decreases Tg to lower temperatures, e.g. compared to comparative example 3 (C3) lacking liquid polybutadiene, but also broadens the peak in the DMA curve (the FIGURE), thereby gaining on wet grip compared to comparative example 1 and 2 with liquid homopolymer of polybutadiene according to the prior art. Without being wished to be bound by theory it is believed that this is related to the reduced miscibility of a relative high molecular weight liquid homopolymer of polybutadiene with the diene-based elastomer compound of the cross-linked rubber compositions. In addition, a good abrasion resistance is maintained with respect to the comparative examples.

(8) TABLE-US-00002 TABLE 2 I1.sup.[1] C1.sup.[2] C2.sup.[3] C3.sup.[4] wear (DIN) 69.17 58.63 86.67 87.65 Tg 41.80 42.12 40.49 37.54 G (20 C.) 32.85 36.68 30.4 42.57 Tan (0 C.) 0.174 0.154 0.168 0.167 .sup.[1]Homopolymer of polybutadiene: LBR 305 of Kuraray, Mn: 26000 g/mol, Tg: 95 C., melt viscosity (38 C.): 40 Pa S, vinyl content: 16.7% .sup.[2]Homopolymer of polybutadiene: LBR 307 of Kuraray, Mn: 8000 g/mol, Tg: 95 C., melt viscosity (38 C.): 1.5, vinyl content: 5.9% .sup.[3]Homopolymer of polybutadiene: Ricon 130 of Cray Valley, Mn: 2500 g/mol, Tg: 85 C., vinyl content: 28% .sup.[4]Oil: TDAE oil

(9) Therefore, a rubber mixture comprising, per hundred parts by weight of rubber (phr), 100 phr of a diene-based elastomer component with an average molecular weight Mn in a range of 100000 to 5000000 g/mol and a homopolymer of polybutadiene, wherein the homopolymer of polybutadiene has an average molecular weight Mn in a range of 10000 to 45000 g/mol and a Tg in a range of 110 C. to 60 C. results in an excellent balance of good abrasion resistance, good winter performance and good wet grip.