Rubber composition for tyres

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. The cross-linkable rubber composition comprises, per hundred parts by weight of rubber (phr): 100 phr of a blend of a natural rubber (NR), a polybutadiene rubber (BR), and first and second solution polymerized styrene -butadiene rubbers (SSBR); a silica filler, and a resin, wherein the rubber composition comprises: ≥ 5 phr to ≤ 40 phr of NR; ≥ 20 phr to ≤ 80 phr of BR; ≥ 5 phr to ≤ 40 phr of the first SSBR having a glass hansition temperature Tg, determined by differential scanning calorimetry (DSC) according to ISO 22768, in a range of ≥ -30°C to ≤ 0°C; ≥ 10 phr to ≤ 50 phr of the second SSBR having a glass transition temperature Tg, determined by differential scanning calorimetry (DSC) according to ISO 22768, in a range of ≥ -120°C to ≤ -40°C; ≥ 5 phr to ≤ 50 phr of a first silica filler having a BET surface area in a range of ≥ 190 m2 / g to ≤ 320 m2 / g, determined according to ASTM DI 993, and ≥ 50 phr to ≤ 120 phr of a second silica filler having a BET surface area in a range of ≥ 150 m2 / g to ≤ 185 m2 / g, determined according to ASTM DI 993.

Description

[0001] Rubber for tyres

[0002] The present invention relates to a cross-linkable rubber composition, a cross-linked rubber composition obtained by cross-linking the rubber composition, a method of preparing a tyre and a tyre.

[0003] Tread rubber is one of the important portions of a pneumatic tyre which contributes enormously to the overall performance of a tyre. A tyre must perform well in severe weather conditions, and it has to exhibit a variety of performances, while particularly winter and all-season tyres have to observe a balance of various properties such as rolling resistance and grip on snow. In addition, further requirements for all-season and winter tyres are required, such as wear and mechanical properties. A tread compound can be optimized to exhibit improvements in winter performance or in rolling resistance; but optimizing the tread compound for winter performance normally results in trade-off in rolling resistance and vice versa.

[0004] Good rolling resistance of tyre treads can be achieved using silica-based compounds. Silica offers tyre compounds with lower rolling resistance and higher wet grip, so less fuel consumption and better safety. When compared to carbon black, the interaction between silica and hydrocarbon rubber is weaker. A successful use of silica in rubber compounds requires sufficient bonding and / or interaction between silica and rubber interphases. Sulfur containing silane coupling agents such as bis-(3-triethoxysilylpropyl) tetrasulfide (TESPT) are commonly applied in such compounds cured with a sulfur system to provide a chemical reaction denoted silanization, which generally improves the interaction between silica and rubber interphases.

[0005] WO 2021069514 Al discloses a rubber composition for an all season-tread with a balanced property of snow and wet grip. The rubber composition comprises a blend of four rubbers selected from a natural rubber (NR), a polybutadiene rubber (BR), and first and second solution polymerized styrene -butadiene rubbers (SSBRs), a silica filler, a resin, and > 1 phr to < 20 phr of at least two coupling agents wherein one of the coupling agents is a mercaptosilane and wherein the ratio of the mercapto based silane to the second coupling agent is in a range of > 2: 1 to < 10: 1. The second coupling agent may be selected from a disulfide silane, a tetrasulfide silane, or a combination thereof.

[0006] CN 114230884 A is directed to a cross-linkable rubber composition for a summer tyre comprising two styrene -butadiene rubbers and optionally a natural rubber. The rolling resistance is reduced by a system of combining two silicas with different specific surface areas and two silane coupling agents to respectively modify the silica and the rubber to reduce the rolling resistance. However, summer tyres provide no snow performance.

[0007] The present invention has the object to overcome the drawbacks at least partially and to provide a composition for a tyre tread for a winter or an all season-tread which provides improved rolling resistance in balance with snow and wear performance.

[0008] This object is achieved by a cross-linkable rubber composition according to claim 1, a cross-linked rubber composition according to claim 10, a method according to claim 14 and a tyre according to claim 15. Advantageous embodiments are the subject of dependent claims. They may be combined freely unless the context clearly indicates otherwise.

[0009] Hence, a cross-linkable rubber composition is provided, the cross-linkable rubber composition comprising, per hundred parts by weight of rubber (phr):

[0010] 100 phr of a blend of a natural rubber (NR), a polybutadiene rubber (BR), and first and second solution polymerized styrene -butadiene rubbers (SSBR); a silica filler, and a resin, wherein the rubber composition comprises:

[0011] > 5 phr to < 40 phr of NR;

[0012] > 20 phr to < 80 phr of BR;

[0013] > 5 phr to < 40 phr of the first SSBR having a glass transition temperature Tg, determined by differential scanning calorimetry (DSC) according to ISO 22768, in a range of > -30°C to < 0°C; > 10 phr to < 50 phr of the second SSBR having a glass transition temperature Tg, determined by differential scanning calorimetry (DSC) according to ISO 22768, in a range of > -120°C to < -40°C;

[0014] > 5 phr to < 50 phr of a first silica filler having a BET surface area in a range of > 190 m2 / g to < 320 m2 / g, determined according to ASTM DI 993, and

[0015] > 50 phr to < 120 phr of a second silica filler having a BET surface area in a range of > 150 m2 / g to < 185 m2 / g, determined according to ASTM DI 993.

[0016] It has surprisingly been found that such a rubber composition comprising a blend of four rubbers and two silicas of different BET surface area provides for an improved rolling resistance, snow and wear performance. A balanced combination of rolling resistance, snow performance, referring to handling and braking performance on snow, and wear performance provides a notable advantage, as this is difficult to balance.

[0017] As used herein, the term “handling” refers to how well a vehicle handles the road and how well the vehicle responds to steering input. Tyre handling is a measurement of what a driver can perform with a car such as steering, stability during lane change and cornering, lap time, accelerating and braking.

[0018] It will be understood that in formulations discussed in connection with the present invention the phr amount of all rubber components adds up to 100 phr. To differentiate between the two different solution polymerized styrene -butadiene rubbers (SSBRs), terms like first SSBR and second SSBR are used. In embodiments where two different silica fillers are present, the terms first silica filler and second silica filler are used likewise to differentiate between the respective silicas. The crosslinkable rubber composition according to the invention comprises cross-linkable groups in the individual rubber components. They may be cross-linked (cured, vulcanised) by methods known to a skilled person in the rubber technology field.

[0019] The rubber composition comprises two silica fillers of different BET surface area. The BET (Brunauer, Emmett and Teller) theory is commonly used to evaluate gas adsorption data and generate a specific surface area result expressed in units of area per mass of sample (m2 / g). The technique is referenced by several standard organizations such as ASTM. The rubber composition comprises a first silica filler having a high BET surface area and a second silica filler having a low BET surface area.

[0020] In embodiments, the first silica filler has a BET surface area in a range of > 190 m2 / g to < 300 m2 / g, determined according to ASTM D1993. In embodiments, the first silica filler has a BET surface area in a range of > 190 m2 / g to < 220 m2 / g, preferably in a range of > 200 m2 / g to < 220 m2 / g, or in a range of > 250 m2 / g to < 290 m2 / g. It was found that both ranges of BET surface area in combination with a low surface area silica and the rubber blend provided advantageous test results regarding a balance of wear performance with rolling resistance and snow handling. Silica which meets a BET surface area of 190 to 320 m2 / g includes highly dispersible silica (HDS) and super high surface area (SHSA) silica. Highly dispersible silica may be precipitated from a silicate solution, for example, by hydrolysis and / or high temperature oxidation conversion. Examples of commercial silica having a BET surface area of 190 to 320 m2 / g are Zeosil HRS 1200MP (BET: 200 m2 / g) manufactured by Solvay AG and Z Premium SW (BET: 275 m2 / g) manufactured by Solvay AG.

[0021] In embodiments, the second silica silica filler has a BET surface area in a range of > 150 m2 / g to < 170 m2 / g, determined according to ASTM D1993. Silica which meets a BET surface area of 150 to 170 m2 / g (according to ASTM D1993) includes highly dispersible silica (HDS) and semi HDS. Highly dispersible silica may be precipitated from a silicate solution, for example, by hydrolysis and / or high temperature oxidation conversion. Examples of commercial silica having a BET surface area of 150 to 170 m2 / g are Ultrasil® 7000GR (Evonik Industries AG), Zeosil 1165MP (Solvay AG), and HiSil IZ 160GD (PPG Industries).

[0022] In embodiments, the rubber composition comprises the first silica filler in an amount in a range of > 5 phr to < 45 phr, preferably in a range of > 7 phr to < 35 phr. In embodiments, the rubber composition comprises the second silica filler in an amount in a range of > 55 phr to < 110 phr, preferably in a range of > 55 phr to < 105 phr. It is assumed that such amounts of first and second silica facilitates balancing improved rolling resistance with good snow handling and wear properties.

[0023] The rubber composition comprises the first silica filler in an amount in a range of > 5 phr to < 50 phr and the second silica filler in a range of > 50 phr to < 120 phr. In embodiments, the rubber composition comprises first and second silica filler in an amount in a range of > 55 phr to < 170 phr, preferably in a range of > 60 phr to < 155 phr or in a range of > 60 phr to < 140 phr.

[0024] The rubber composition may comprise carbon black. The rubber composition may comprise carbon black in an amount in a range of > 2 phr to < 15 phr, preferably in a range of > 4 phr to < 10 phr.

[0025] The composition comprises a blend of four rubbers, a natural rubber (NR), a polybutadiene rubber (BR), and first and second solution polymerized styrene -butadiene rubbers (SSBRs) of different glass transition temperature. Without being bound to a specific theory it is assumed that the polymer blend contributes to the good snow performance and rolling resistance of the cured composition that is necessary for winter and all-season tyres.

[0026] In embodiments, the butadiene rubber (BR) has a cis group content, as determined by infrared spectroscopy (IR), of > 95%, preferably of > 96%. Abutadiene rubber (BR) with a high cis group content is obtainable under neodymium catalysis (Nd BR). The cis content of the polybutadiene rubber is usually provided by the supplier and may be determined with FTIR (Fourier-transform infrared spectroscopy). The method is based on the calculation of the ratio between the intensity of the bands attributable to the 1 ,4-trans and 1 ,2-vinyl isomers and a reference band (internal standard) falling at 1312 cm1(E. J. Bellamy, The Infrared Spectra of Complex Molecules, Vol. 1 Third Edition, Chapman and Hall). The 1,4-cis content is determined by the difference from 100. Butadiene rubber obtained under neodymium catalysis may be denoted a cis 1 ,4-polybutadine.

[0027] The natural rubber may be a sheet processed natural rubber such as a Ribbed Smoked Sheets (RSS) rubber or may be a Technically Specified Rubber (TSR). TSR grades such as TSR10, TSR20 are preferred for a tyre tread compound. The first SSBR has a glass transition temperature Tgof > -30 °C to < 0 °C. The glass transition temperatures Tgof the rubber compounds as referred herein are measured by differential scanning calorimetry (DSC) according to ISO 22768. This norm specifies a heating rate of 20 °C / min. Preferably the first SSBR has a glass transition temperature Tgof > -28 °C to < -20 °C. The first SSBR thus is a rubber with comparatively high Tg.

[0028] Such a SSBR preferably comprises alkoxysilane groups such as -Si(OR)3 with each R independently being an alkyl rest. Preferred are trimethoxysilane groups and triethoxysilane groups. Furthermore, this SSBR also comprises primary amino groups -NH2. Such dualfunctionalised SSBRs are commercially available and may be synthesised from non-functionalised SSBRs by methods known in the art such as hydrosilylation with H-Si(OR)3 compounds, thiol-ene- coupling using aminothiol compounds and hydrosilylation with H-Si(OR)2-Linker-NH2 compounds. For example, and as taught in US 7,342,070, the first rubber may be of the formula (I) or (II):

[0029] (R1- NH2)n

[0030] Pk - Si - (OR2)m wherein P is a (co)polymer chain of a conjugated diolefin or a conjugated diolefin and an aromatic vinyl compound, R1is an alkylene group having 1 to 12 carbon atoms, R2and R3are each independently an alkyl group having 1 to 20 carbon atoms, an allyl group or an aryl group, n is an integer of 1 or 2, m is an integer of 1 or 2, and k is an integer of 1 or 2, with the proviso that n+m+k is an integer of 3 or 4, wherein P, R1, R2and R3have the same definitions as give for the above-mentioned formula I, j is an integer of 1 to 3, and h is an integer of 1 to 3, with the provision that j+h is an integer of 2 to 4. The first SSBR may comprise > 25% to < 35%, preferably > 27 to < 29%, as determined by nuclear magnetic resonance (NMR) spectroscopy, of styrenic groups. In the first SSBR > 75 mol-%, preferably > 90 mol-% to < 100 mol-%, as determined by nuclear magnetic resonance (NMR) spectroscopy, of the alkoxysilane groups and the primary amino groups are located at the chain ends of the rubber polymer chains. A specific example for a commercial SSBR having a Tgof > -30 °C to < 0 °C is HPR850 manufactured by JSR Corporation.

[0031] The first SSBR is combined with a second low TgSSBR. The second solution polymerized styrenebutadiene rubber (SSBR) has a glass transition temperature Tg(measured by differential scanning calorimetry (DSC) according to ISO 22768) of > - 120 °C to < - 40 °C. Preferably, the second SSBR has a glass transition temperature Tgof > -90 °C to < -50 °C, more preferably of > -80 °C to < -60 °C. Using a low TgSSBR in combination with a first high TgSSBR can improve snow and rolling resistance performance in balance with wet grip. Preferably, the second SSBR is a functionalised styrene -butadiene rubber. A specific example for a commercial SSBR having a Tgof > - 120 °C to < - 40 °C is SPRINTAN™ SLR 3402, with Tgof -65 °C.

[0032] In embodiments, the composition comprises:

[0033] > 10 phr to < 40 phr, preferably > 10 phr to < 30 phr, of NR; and / or

[0034] > 30 phr to < 60 phr, preferably > 35 phr to < 55 phr, of BR; and / or

[0035] > 5 phr to < 30 phr, preferably > 10 phr to < 25 phr, of the first SSBR; and / or

[0036] > 10 phr to < 40 phr, preferably > 15 phr to < 30 phr, of the second SSBR.

[0037] It is understood that the phr amount of all rubber components in the composition adds up to 100 phr. In these ranges improved snow handling of the cured tread rubber could be combined with favourable rolling resistance properties.

[0038] In embodiments, the composition comprises a resin. A variety of aliphatic or aromatic resins may be used. Important base monomers are indene, methyindenes, dicyclopentadiene, styrene, alphamethylstyrene and various vinyl toluenes. Examples of the poly terpene resins include terpene homopolymer or copolymer resins polymerised from terpene compounds such as a-pinene, P- pinene, limonene, dipentene, or -pinene / limonene, as well as hydrogenated terpene resins prepared by hydrogenating any of the terpene resins.

[0039] In embodiments, the composition comprises a resin selected from the group of alpha-methyl styrene (AMS) resin, terpene resin, polyterpene resin, terpene phenolic resin, a C5 resin, C9 resin, coumarone indene resin, dicyclopentadiene (DCPD) resin or a combination thereof. The term “C5 resin” refers to hydrocarbon resins obtained from the polymerization of C5 aliphatic olefin and diolefin. The term “C9 resin” refers to aromatic hydrocarbon resins made from C9, or more generally from a C8 to CIO fraction, aromatic hydrocarbons. Further examples for aromatic resins are coumarone-indene resins The term “alpha-methyl styrene resin” refers to copolymer resins of styrene and alpha-methyl styrene. In embodiments, the composition comprises an alpha-methyl styrene resin. In embodiments, the composition comprises in a range of > 10 phr to < 30 phr, preferably > 15 phr to < 25 phr, of the resin, preferably of an alpha-methyl styrene resin. Such embodiments provide particularly balanced properties of rolling resistance and snow performance.

[0040] The cross -linkable rubber composition also comprises at least one coupling agent. The crosslinkable rubber composition may comprise in a range of > 1 phr to < 15 phr of at least one coupling agent, preferably of first and second coupling agents. The at least one coupling agent may be selected from a disulfide silane, a tetrasulfide silane, or a combination thereof. In embodiments, the rubber composition comprises first and second coupling agents, wherein the first coupling agent is a mercaptosilane and the second coupling agent is selected from a disulfide silane, a tetrasulfide silane, or a combination thereof. The use of a mercaptosilane in combination with a silane selected from a disulfide silane, a tetrasulfide silane, or a combination thereof is assumed to improve the hysteresis of the composition comprising a rubber blend. The ratio of the mercaptosilane to the silane may be in a range of > 2: 1 to < 10:1, preferably in a range of > 2: 1 to < 4: 1. In the context of this invention a “mercaptosilane” denotes a silane coupling agent containing one or more mercapto group(s) (-SH group, also denoted thiol group, sulfanyl group or sulfhydryl group) or other sulfur- containing groups that function as protected mercapto groups or react to form a mercapto group. Examples for mercaptosilanes are 3-mercaptopropylmethyldimethoxysilane, 3- mercaptopropyltrimethoxysilane (MTMO), (3-mercaptopropyl)triethoxysilane (MPTES), 3- mercaptopropyl-di(tridecan-l-oxy-13-penta(ethyleneoxide)) ethoxysilane (VP Si363), 3- octanoylthio-l-propyltriethoxysilane (NXT), thiocyanatosilane (TCPTEO), trimethoxy(3- thiocyanatopropyl) silane, triethoxy (3- thiocyanatopropyl) silane and 3- isocyanatopropyltriethoxysilane. Commercial examples for mercaptosilane are Silaan VP Si 363 Degussa available from Evonik Industries and NXT available from Momentive. A specific example for a disulphide silane is bis-(3-triethoxysilylpropyl)disulfide (TESPD) available from Evonik Industries. A specific example for a tetrasulphide silane is bis-(3-triethoxysilylpropyl)tetrasulfide (TESPT) available from Evonik Industries.

[0041] Further silane coupling agents that are usable as single coupling agent or as first coupling agent together with a second coupling agent selected from a disulfide silane, a tetrasulfide silane, or a combination thereof may be selected from the group comprising ethoxy and / or methoxy groups selected from the group of vinyltriethoxysilane(VTEO), Vinyltris(2-methoxyethoxy)silane (VTMOEO), 3 -chloropropyltrimethoxy silane (CPTEO), 3 -methacryloxypropyl-trimethoxy silane (MEMO), 3-aminopropyltriethoxysilane (AMEO), propyltriethoxysilane (PTEO), octyltriethoxysilane (OCTEO).

[0042] The cross-linkable rubber compositions may be sulfur- vulcanizable and / or peroxide-vulcanizable.

[0043] If desired, additives can be added. Examples of usual additives are stabilizers, antioxidants, lubricants, fillers, dyes, pigments, flame retardants, conductive fibres and reinforcing fibres.

[0044] Another aspect of the present invention relates to a cross-linked rubber composition that is obtained by cross-linking a rubber composition according to the invention.

[0045] In an embodiment, the cross-linked rubber composition has an abrasion, determined according to ISO 4649, in a range from > 40 mm3to < 80 mm3, preferably in a range from > 40 mm3to < 70 mm3. A lower loss of compound of the cured tyre during a wear test is indicative for better wear properties.

[0046] In embodiments, the cross-linked rubber composition has a tan delta at 60 °C, determined from DMA measurements according to ISO 4664-1, in a range from > 0.08 to < 0.16, preferably in a range from > 0.09 to < 0.13. Such ranges are indicative for good rolling resistance.

[0047] In embodiments, the cross-linked rubber composition has a rebound at 70 °C, determined according to ISO 4662, in a range of > 50 % to < 70 %, preferably in a range of > 55 % to < 65 %. Such ranges are indicative for good rolling resistance.

[0048] In other embodiments of the cross-linked rubber composition, a storage modulus (dynamic stiffness) E' at -20 °C, determined from DMA measurements according to ISO 4664-1, may be in a range from > 35 MPa to < 75 MPa, preferably in a range from > 40 MPa to < 70 MPa. Such ranges are indicative for good handling properties of the cured tyre on snow.

[0049] The present invention also relates to a method of preparing a tyre, comprising the steps of:

[0050] - providing a tyre assembly comprising a rubber composition according to the invention, and

[0051] - cross-linking at least the rubber composition according to the invention in the tyre assembly.

[0052] The present invention also encompasses a tyre comprising a tyre tread, characterised in that the tyre tread comprises a cross-linked rubber composition according to the invention.

[0053] The present invention will be further described with reference to the following examples without wishing to be limited by them.

[0054] Methods:

[0055] Hardness Test: A hardness test was performed on a durometer with scale A as per ISO 48-4:2018 to determin the indentation hardness (Shore hardness, given in Shore A) of the vulcanized rubber. Tensile strength: Tensile strength analysis was performed for cured samples on a Zwick Z005 apparatus with a speed of 500 mm / min speed. Samples were cured at 160°C for 20 minutes and standard tensile specimens were cut from rubber sheet according to ISO 37 standard. Measuring tensile strength and force elongation properties via tensile method also determines modulus at various elongations such as 300% which indicates static stiffness.

[0056] Rebound: Rebound measurements were performed for cured samples on a Zwick / Roell 5109 Rebound Resilience Tester according to the standardised ISO4662 method at 23°C and 70°C.

[0057] Temperature sweep by DMA: Dynamic mechanical analysis (DMA) analysis was performed for cured samples by Metravib DMA+450 according to ISO 4664-1. DMA was performed by temperature sweep at constant frequency 10 Hz with 6 % strain in a temperature range of 25 °C to 80°C. DMA was also performed by temperature sweep at constant frequency 10 Hz with 0.1 % strain in a temperature range of -80°C to 25°C. For determination of tan delta DMA analysis was performed in tensile mode. For determination of storage modulus (dynamic stiffness) E' DMA analysis was performed in tensile mode.

[0058] Wear test: This method describes the determination of the resistance of rubber to abrasion by means of a rotating cylindrical drum device. Measurements were performed as per ISO 4649:2017. Abrasion is expressed as volume loss in cubic millimeters, for instance, 100 mm3.

[0059] Example 1

[0060] 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. Compositions “Ref’ are comparative compositions and compositions “Exp” 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 1: Composition of Examples:

[0061] Natural rubber (NR) was TSR 20, with a Mooney Viscosity 80 and a Tg of -70 °C supplied by Nam Hua Rubber Company Limited.

[0062] BR rubber was Buna CB 29 with 37.5 phr oil extended, a Nd catalyzed 1,4 butadiene rubber with a cis content of 96%, supplied by Arlanxeo.

[0063] SSBR 1 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 27.5 wt.% and vinyl content of 59% and a Tgof -25 °C. Non-oil extended product was used.

[0064] SSBR 2 was SPRINTAN™ SLR 3402, a functionalised SSBR and had a styrene content of 15%, a vinyl content of 30% and a Tgof -65 °C from Synthos.

[0065] Silica 1 was Zeosil HRS 1200MP with a BET surface of 200 m2 / g from Solvay AG.

[0066] Silica 2 was High Dispersible Silica (medium HDS) with a BET surface of 150-180 m2 / g supplied by PPG Industries.

[0067] Carbon black was N339 (HAF-HS) supplied by Orion Engineered Carbons.

[0068] Mercaptosilane was Silaan VP Si 363 Degussa supplied by Evonik Industries.

[0069] Silane coupling agent was TESPD (disulphide silane) supplied by Evonik Industries.

[0070] The hydrocarbon resin was Impera™ Pl 504 Hydrocarbon Resin supplied by Eastman Chemical Company.

[0071] Durometer hardness (shore A) was measured to relate to physical properties.

[0072] Tan delta (60°C) was measured relating to rolling resistance (RR).

[0073] Rebound at 70°C was measured relating to rolling resistance.

[0074] Storage modulus E' (-20°C) was measured relating to snow performance.

[0075] T tan_max was measured relating to snow performance. Storage modulus E' (70°C) was measured relating to handling on dry surface.

[0076] Tan delta (70°C) was measured relating to rolling resistance (RR).

[0077] Table 2: Test results:

[0078] The results show for the compositions Expl to Exp3 compared to the reference compositions a decrease in tan delta at 70°C and an increase in rebound at 70°C, which are considered an indicator of better rolling resistance (RR). Further, all compositions Expl to Exp3 showed a decrease of storage modulus E' (-20°C) which is considered an indicator of better snow handling. Also, T tan_max, relating to the glass transition temperature of the cured rubber composition tan delta at 70°C, illustrated good behavior on snow. Further, wear properties and mechanical properties of hardness and tear strength remained similar compared to the reference compositions.

[0079] Example 2

[0080] In accordance with the preceding, cross-linkable rubber compositions were prepared according to the following table 3. 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 composition and compositions “Exp4”, “Exp 5” and “Exp 6” are 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 3: Composition of Examples:

[0081] Natural rubber (NR) was TSR 20, with a Mooney Viscosity 80 and a Tg of -70 °C supplied by Nam Hua Rubber Company Limited.

[0082] BR rubber was Buna CB 29 with 37.5 phr oil extended, a Nd catalyzed 1,4 butadiene rubber with a cis content of 96%, supplied by Arlanxeo.

[0083] SSBR 1 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 27.5 wt.% and vinyl content of 59% and a Tgof -25 °C. Non-oil extended product was used.

[0084] SSBR 2 was SPRINTAN™ SLR 3402, a functionalised SSBR and had a styrene content of 15%, a vinyl content of 30% and a Tgof -65 °C from Synthos.

[0085] Silica 1 was Zeosil Premium SW (BET: 275 m2 / g) manufactured by Solvay AG.

[0086] Silica 2 was Highly Dispersible Silica (P type) with a BET surface of 150-180 m2 / g supplied by PPG Industries.

[0087] Carbon black was N339 (HAF-HS) supplied by Orion Engineered Carbons.

[0088] Mercaptosilane was Silaan VP Si 363 Degussa supplied by Evonik Industries.

[0089] Silane coupling agent was TESPD (disulphide silane) supplied by Evonik Industries.

[0090] The hydrocarbon resin was Impera™ Pl 504 Hydrocarbon Resin supplied by Eastman Chemical Company.

[0091] Durometer hardness (shore A) was measured to relate to physical properties.

[0092] Tan delta (70°C) was measured relating to rolling resistance (RR).

[0093] Storage modulus E' (-20°C) was measured relating to snow performance.

[0094] Storage modulus E' (70°C) was measured relating to handling.

[0095] T tan_max was measured relating to snow performance (Tg- glass transition temperature). Tan delta (70°C) was measured relating to rolling resistance (RR). Table 4: Test results:

[0096] The results show for the compositions Exp4 to Exp6 compared to the reference composition a decrease in tan delta at 70°C and an increase in rebound at 70°C, which are considered an indicator of better rolling resistance (RR). Further, all compositions Exp4 to Exp6 showed a decrease of E’ (-20°C) which is considered an indicator of better snow handling. Also, T tan_max, relating to the glass transition temperature of the cured rubber composition tan delta at 70°C, illustrated good behavior on snow. Further, wear properties and mechanical properties of hardness and tear strength remained similar compared to the reference compositions.

[0097] In summary, the results illustrate a balanced property of an improvement in rolling resistance without compromising snow performance and wear suitable with advantage particularly for winter tyres and high performance all season-tyres. Without being bound to a specific theory, it is believed that this results from a combination of silica fillers of differing BET surface area in a blend of natural rubber, polybutadiene rubber, and two solution polymerized styrene -butadiene rubbers having different Tg.

Claims

Patent claims1. A cross -linkable rubber composition, the cross -linkable rubber composition comprising, per hundred parts by weight of rubber (phr):100 phr of a blend of a natural rubber (NR), a polybutadiene rubber (BR), and first and second solution polymerized styrene -butadiene rubbers (SSBR); a silica filler, and a resin, wherein the rubber composition comprises:> 5 phr to < 40 phr of NR;> 20 phr to < 80 phr of BR;> 5 phr to < 40 phr of the first SSBR having a glass transition temperature Tg, determined by differential scanning calorimetry (DSC) according to ISO 22768, in a range of > -30°C to < 0°C;> 10 phr to < 50 phr of the second SSBR having a glass transition temperature Tg, determined by differential scanning calorimetry (DSC) according to ISO 22768, in a range of > -120°C to < -40°C;> 5 phr to < 50 phr of a first silica filler having a BET surface area in a range of > 190 m2 / g to < 320 m2 / g, determined according to ASTM DI 993, and> 50 phr to < 120 phr of a second silica filler having a BET surface area in a range of > 150 m2 / g to < 185 m2 / g, determined according to ASTM DI 993.

2. The rubber composition according to claim 1, wherein the first silica filler has a BET surface area in a range of > 190 m2 / g to < 300 m2 / g, preferably in a range of > 200 m2 / g to < 220 m2 / g or in a range of > 250 m2 / g to < 290 m2 / g, determined according to ASTM DI 993.

3. The rubber composition according to claim 1 or 2, wherein the second silica filler has a BET surface area in a range of > 150 m2 / g to < 170 m2 / g, determined according to ASTM D1993.

4. The rubber composition according to any one of the preceding claims, wherein the rubber composition comprises the first silica filler in an amount in a range of > 5 phr to < 45 phr, preferably in a range of phr to < 35 phr.

5. The rubber composition according to any one of the preceding claims, wherein the rubber composition comprises the second silica filler in an amount in a range of > 55 phr to < 110 phr, preferably in a range of > 55 phr to < 105 phr.

6. The rubber composition according to any one of the preceding claims, wherein the rubbercomposition comprises first and second silica filler in an amount in a range of > 80 phr to < 150 phr, preferably in a range of > 85 phr to < 120 phr.

7. The rubber composition according to any one of the preceding claims, wherein the composition comprises:> 10 phr to < 40 phr, preferably > 10 phr to < 30 phr, of NR; and / or> 30 phr to < 60 phr, preferably > 35 phr to < 55 phr, of BR; and / or> 5 phr to < 30 phr, preferably > 10 phr to < 25 phr, of the first SSBR; and / or> 10 phr to < 40 phr, preferably > 15 phr to < 30 phr, of the second SSBR.

8. The rubber composition according to any one of the preceding claims, wherein the composition comprises a resin selected from the group of alpha-methyl styrene resin, terpene resin, polyterpene resin, terpene phenolic resin, a C5 resin, C9 resin, coumarone indene resin, dicyclopentadiene (DCPD) resin or a combination thereof.

9. The rubber composition according to claim 8, wherein the composition comprises > 10 phr to < 35 phr, preferably > 10 phr to < 30 phr, of the resin.

10. A cross-linked rubber composition, characterised in that it is obtained by cross-linking a rubber composition according to any one of claims 1 to 9.

11. The cross-linked rubber composition according to claim 10, having an abrasion, determined according to ISO 4649 in a range from > 40 mm3to < 70 mm3.

12. The cross-linked rubber composition according to any one of claims 10 or 11, having a tan delta at 60 °C, determined from DMA measurements according to ISO 4664-1, in a range from > 0.08 to < 0.16, preferably in a range from > 0.09 to < 0.13.

13. The cross-linked rubber composition according to any one of claims 10 to 12, having a rebound at 70 °C, determined according to ISO 4662, in a range of > 50 % to < 70 %, preferably in a range of > 55 % to < 65 %.

14. A method of preparing a tyre, comprising the steps of:- providing a tyre assembly comprising a rubber composition according to any one of claims 1 to 9, and- cross-linking at least the rubber composition according to any one of claims 1 to 9 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 any one of claims 10 to 13.

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