BACKGROUND OF THE INVENTION

Field of the Invention

[0001] This invention relates generally to rubber compositions useful for rubber articles such as tires and more particularly, to rubber compositions having low Tg functionalized SBR.

Description of the Related Art

[0002] It is known in the industry that tire designers must often compromise on certain characteristics of the tires they are designing. Changing a tire design to improve one characteristic of the tire will often result in a compromise; i.e., an offsetting decline in another tire characteristic. One such comprise exists between tire rolling resistance and traction. It is known by those skilled in the art that lowering the amount of reinforcing filler in a rubber composition for a tread will improve the rolling resistance of a tire. However a reduction of the reinforcing filler in the tread’s rubber composition typically results in a loss of the braking performance (both wet and dry) that is known to be improved, for example, by increasing the amount of reinforcing filler in a rubber composition for a tread.

[0003] Tire designers and those conducting research in the tire industry search for materials and tire structures that can break some of the known compromises. It would be desirable to provide new tire designs that break the compromise between wear and wet braking.

SUMMARY OF THE INVENTION

[0004] Particular embodiments of the present invention include rubber compositions useful for a tire tread. Such rubber compositions may be based upon a cross-linkable rubber composition, the cross-linkable rubber composition having greater than 80 phr of a modified styrene-butadiene rubber (SBR) component having within its polymer chain an alkoxysilane moiety bearing an amine functional group. Optionally such rubber compositions may include up to 20 phr of an additional highly unsaturated diene elastomer. [0005] Particular embodiments of such rubber compositions may further include an effective amount of a plasticizing system having a plasticizing resin with a glass transition temperature Tg of at least 25 °C and a plasticizing liquid, wherein the effective amount of the plasticizing system provides a shear modulus G* for the rubber composition as measured at 60 °C of between 0.7 MPa and 1.1 MPa. An inorganic reinforcing filler is also included in an amount of between 80 phr and 150 phr in some embodiments.

[0006] The foregoing and other objects, features and advantages of the invention will be apparent from the following more detailed descriptions of particular embodiments of the invention.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0007] Particular embodiments of the present invention include tires and tread for vehicles that surprisingly break a compromise faced by tire designers; i.e., an improvement in rolling resistance results in a decrease in wet and dry braking performance. This compromise may be broken by forming unique tire treads from a rubber composition that includes a rubber component that is a modified styrene -butadiene rubber (SBR) having a functional moiety located within the polymer chain (i.e., not at its end) that is capable of reacting with the silica filler material. The rubber composition, which is a low-rigidity composition, further includes a plasticizing system that may include a high Tg plasticizing resin, a liquid plasticizing liquid or combinations thereof.

[0008] Surprisingly it has been found that when treads are formed from a rubber composition having, inter alia, the modified SBR that has been modified within the polymer chain with an alkoxysilane moiety bearing an amine functional group, then the tread performance has improved rolling resistance without a significant decrease in either wet or dry braking performance.

[0009] As used herein, "phr" is“parts per hundred parts of rubber by weight” and is a common measurement in the art wherein components of a rubber composition are measured relative to the total weight of rubber in the composition, i.e., parts by weight of the component per 100 parts by weight of the total rubber(s) in the composition.

[0010] As used herein, elastomer and rubber are synonymous terms. [0011] As used herein,“based upon” is a term recognizing that embodiments of the present invention are made of vulcanized or cured rubber compositions that were, at the time of their assembly, uncured. The cured rubber composition is therefore“based upon” the uncured rubber composition. In other words, the cross-linked rubber composition is based upon or comprises the constituents of the cross -linkable rubber composition.

[0012] As is known generally, a tire tread is the road-contacting portion of a vehicle tire that extends circumferentially about the tire. It is designed to provide the handling characteristics required by the vehicle; e.g., traction, dry braking, wet braking, cornering and so forth - all being preferably provided with a minimum amount of noise being generated and at a low rolling resistance.

[0013] Treads of the type that are disclosed herein include tread elements that are the structural features of the tread that contact the ground. Such structural features may be of any type or shape, examples of which include tread blocks and tread ribs. Tread blocks have a perimeter defined by one or more grooves that create an isolated structure in the tread while a rib runs substantially in the longitudinal (circumferential) direction and is not interrupted by any grooves that run in the substantially lateral direction or any other grooves that are oblique thereto.

[0014] The radially outermost faces of these tread elements make up the contact surface of the tire tread - the actual surface area of the tire tread that is adapted for making contact with the road as the tire rotates. The total contact surface of the tire tread is therefore the total surface area of all the radially outermost faces of the tread elements that are adapted for making contact with the road. As used herein, the tread is that portion of the tire that contacts the road surface and is formed of the rubber compositions that are disclosed herein.

[0015] As noted above, particular embodiments of the rubber compositions for treads disclosed herein include a modified styrene-butadiene rubber (SBR) component having within its polymer chain ( i.e ., not at its end) an alkoxy silane moiety bearing an amine functional group. In particular embodiments the amine is a tertiary or secondary amine functional group. It is recognized that the modified SBR component is an elastomer mixture resulting from the modification of a diene elastomer by a coupling agent that introduces, into the elastomer chain, an aminoalkoxy silane group. It is understood that this means the aminoalkoxysilane group within its polymer chain, especially in the middle of the chain, and that the silicon atom of this aminoalkoxysilane group bonds the two pieces of the chain of the diene elastomer. This mixture includes, relative to the total weight of the mixture resulting from this modification, more than 50% by weight of a diene elastomer coupled by the aminoalkoxysilane group. Indeed, during such a modification of a diene elastomer, several elastomer species are recovered (chain-end functionalized elastomer, nonfunctionalized elastomer, coupled elastomer, etc.) that form the elastomer mixture. Preferably, this diene elastomer coupled by an aminoalkoxysilane group is present in this mixture in an amount of at least 65% by weight, more preferably still 75% by weight, relative to the total weight of the elastomer mixture.

[0016] Useful modified SBR components for particular embodiments of the rubber compositions disclosed herein may further be characterized as having a polydispersity index (the ratio of the weight average molecular weight to the number average molecular weight, i.e., polydispersity index = M _w /M _n ) of between 1.25 and 1.75 or alternatively between 1.4 and 1.6.

[0017] Useful modified SBR components for the rubber compositions disclosed herein have a styrene content of between 10 wt% and 35 wt% or alternatively between 10 wt% and 25 wt%, between 10 wt% and 20 wt% or between 12 wt% and 20 wt%. Additionally such components may have a content (mol %) of 1, 2-units of the butadiene part of between 10% and 30% or alternatively between 20% and 30% and a glass transition temperature (Tg), measured in accordance with ASTM D3418, of between -40 °C and -80 °C or alternatively between -60 °C and -80 °C, between -62 °C and -80 °C, between -60 °C and - 75 °C or between -62 °C and -75 °C. Such useful modified SBR components are fully disclosed in US9175124 patent, which is fully incorporated herein by reference.

[0018] In addition to the modified SBR component described above, the rubber compositions disclosed herein may further include an additional highly unsaturated diene elastomer. The diene elastomers or rubbers that are useful for such rubber compositions are understood to be those elastomers resulting at least in part, i.e., a homopolymer or a copolymer, from diene monomers, i.e., monomers having two double carbon-carbon bonds, whether conjugated or not. [0019] Diene elastomers may be classified as either“essentially unsaturated” diene elastomers or“essentially saturated” diene elastomers. As used herein, essentially unsaturated diene elastomers are diene elastomers resulting at least in part from conjugated diene monomers, the essentially unsaturated diene elastomers having a content of such members or units of diene origin (conjugated dienes) that is at least 15 mol. %. Within the category of essentially unsaturated diene elastomers are highly unsaturated diene elastomers, which are diene elastomers having a content of units of diene origin (conjugated diene) that is greater than 50 mol. %.

[0020] Those diene elastomers that do not fall into the definition of being essentially unsaturated are, therefore, the essentially saturated diene elastomers. Such elastomers include, for example, butyl rubbers and copolymers of dienes and of alpha-olefins of the EPDM type. These diene elastomers have low or very low content of units of diene origin (conjugated dienes), such content being less than 15 mol. %.

[0021] Particular embodiments of the rubber compositions disclosed herein include no diene elastomers other than the modified SBR and the highly unsaturated diene elastomers. Examples of suitable highly unsaturated diene elastomers may include polybutadienes, particularly those having a content of 1,2- units of between 4 mol. % and 80 mol. % or those having a cA-l,4 content of more than 80 mol. %. Also included are polyisoprenes and butadiene/isoprene copolymers, particularly those having an isoprene content of between 5 wt. % and 90 wt. % and a glass transition temperature (Tg, measured in accordance with ASTM D3418) of -40° C to -80° C. Natural rubber is also a suitable highly unsaturated diene elastomer as would be other styrene-butadiene rubbers (SBR).

[0022] In summary, suitable additional highly unsaturated diene elastomers for particular embodiments of the rubber compositions disclosed herein may include, for example, polybutadienes (BR), polyisoprenes (IR), natural rubber (NR), butadiene copolymers, isoprene copolymers and mixtures of these elastomers. Such copolymers include butadiene/styrene copolymers (SBR), isoprene/butadiene copolymers (BIR), isoprene/styrene copolymers (SIR) and isoprene/butadiene/styrene copolymers (SBIR). [0023] In particular embodiments the additional highly unsaturated diene elastomers may include just one of or one or more of a styrene -butadiene rubber, a polybutadiene rubber, a natural rubber and/or a synthetic polyisoprene rubber.

[0024] The additional highly unsaturated diene elastomer included in particular embodiments of the rubber compositions may be only one such elastomer or alternatively, a mixture of several such elastomers.

[0025] The rubber compositions disclosed herein may include greater than 80 phr of the modified SBR component disclosed above or alternatively, between 80 phr and 100 phr of the modified SBR component, between 85 phr and 100 phr, between 90 phr and 100 phr, between 95 phr and 100 phr, between 90 phr and 95 phr, or 100 phr of the modified SBR component.

[0026] The rubber compositions disclosed herein may further include between 0 phr and less than 20 phr of the additional highly unsaturated diene elastomer or alternatively, between 0 phr and 20 phr, between 0 phr and 15 phr, between 0 phr and 10 phr, between 0 phr and 5 phr, between 5 phr and 10 phr, or none of the additional highly unsaturated diene elastomer.

[0027] Particular embodiments of the rubber compositions disclosed herein include no other rubber component other than the modified SBR and optionally an amount of the additional highly unsaturated diene elastomer.

[0028] In addition to the modified SBR component and the additional highly unsaturated diene elastomer, the rubber compositions disclosed herein may further include an inorganic reinforcing filler. Reinforcing fillers are added to rubber compositions to, inter alia, improve their tensile strength and wear resistance. Inorganic reinforcing fillers include any inorganic or mineral fillers, whatever its color or origin (natural or synthetic), that are capable without any other means, other than an intermediate coupling agent, of reinforcing a rubber composition intended for the manufacture of tires. Typically such fillers may be characterized as having the presence of hydroxyl (-OH) groups on its surface.

[0029] It is noted that particular embodiments may further include an amount of carbon black as may be typically included to color the rubber composition black. Such amounts may range up to about 10 phr or alternatively up to about 6 phr. Carbon black may also be added in the form of a marketed version as a carrier for the silane coupling agent as is known to those having ordinary skill in the art that also can be used to color the rubber composition black.

[0030] Inorganic reinforcing fillers may take many useful forms including, for example, as powder, microbeads, granules, balls and/or any other suitable form as well as mixtures thereof. Examples of suitable inorganic reinforcing fillers include mineral fillers of the siliceous type, such as silica (Si0 ₂ ), of the aluminous type, such as alumina (Al0 ₃ ) or combinations thereof.

[0031] Useful silica reinforcing fillers known in the art include fumed, precipitated and/or highly dispersible silica (known as“HD” silica). Examples of highly dispersible silicas include Ultrasil 7000 and Ultrasil 7005 from Degussa, the silicas Zeosil 1165MP, 1135MP and 1115MP from Rhodia, the silica Hi-Sil EZ150G from PPG and the silicas Zeopol 8715, 8745 and 8755 from Huber. In particular embodiments, the silica may have a BET surface area, for example, of between 60 m /g and 250 m /g or alternatively between 80 m ² /g and 230 m ² /g.

[0032] Examples of useful reinforcing aluminas are the aluminas Baikalox A125 or CR125 from Baikowski, APA-100RDX from Condea, Aluminoxid C from Degussa or AKP- G015 from Sumitomo Chemicals.

[0033] For coupling the inorganic reinforcing filler to the diene elastomer, a coupling agent that is at least bifunctional provides a sufficient chemical and/or physical connection between the inorganic reinforcement filler and the diene elastomer. Examples of such coupling agents include bifunctional organosilanes or polyorganosiloxanes. Such coupling agents and their use are well known in the art. The coupling agent may optionally be grafted beforehand onto the diene elastomer or onto the inorganic reinforcing filler as is known. Otherwise it may be mixed into the rubber composition in its free or non-grafted state. One useful coupling agent is X 50-S, a 50-50 blend by weight of Si69 (the active ingredient) and N330 carbon black, available from Evonik Degussa.

[0034] In the rubber compositions according to the invention, the coupling agent may be included at any suitable amount for the given application, examples of which are between 2 phr and 15 phr or alternatively, between 2 phr and 12 phr. It is generally desirable to minimize its use. In particular embodiments, the amount of coupling agent may represent between 0.5 and 15 wt. % relative to the total weight of the silica filler. In the case for example of tire treads for passenger vehicles, the coupling agent may be less than 12 wt. % or even less than 8 wt. % relative to the total weight of the silica filler.

[0035] In particular embodiments, the amount of total reinforcing filler may be between 80 phr and 150 phr of the reinforcing filler or alternatively between 90 phr and 140 phr, between 90 phr and 135 phr or between 100 phr and 130 phr.

[0036] In addition to the elastomers and reinforcing filler, particular embodiments of the rubber compositions disclosed herein may further include a plasticizing system. The plasticizing system may provide both an improvement to the processability of the rubber mix and/or a means for adjusting the rubber composition’s glass transition temperature and/or its rigidity. Suitable plasticizing systems may include a plasticizing liquid, a plasticizing resin or combinations thereof.

[0037] Suitable plasticizing liquids may include any liquid known for its plasticizing properties with diene elastomers. At room temperature (23 °C), these liquid plasticizers or these oils of varying viscosity are liquid as opposed to the resins that are solid. Examples include those derived from petroleum stocks, those having a vegetable base and combinations thereof. Examples of oils that are petroleum based include aromatic oils, paraffinic oils, naphthenic oils, MES oils, TDAE oils and so forth as known in the industry. Also known are liquid diene polymers, the polyolefin oils, ether plasticizers, ester plasticizers, phosphate plasticizers, sulfonate plasticizers and combinations of liquid plasticizers.

[0038] Examples of suitable vegetable oils include sunflower oil, soybean oil, safflower oil, com oil, linseed oil and cotton seed oil. These oils and other such vegetable oils may be used singularly or in combination. In some embodiments, sunflower oil having a high oleic acid content (at least 70 weight percent or alternatively, at least 80 weight percent) is useful, an example being AGRTPETRE 80, available from Cargill with offices in Minneapolis, MN. In particular embodiments of the present invention, the selection of a suitable plasticizing oil is limited to a vegetable oil having a high oleic acid content.

[0039] The amount of plasticizing liquid useful in any particular embodiment of the present invention depends upon the particular circumstances and the desired result. In general, for example, the plasticizing liquid may be present in the rubber composition in an amount of between 0 or 10 phr and 60 phr or alternatively, between 0 or 10 phr and 55 phr, between 0 or 10 phr and 50 phr, between 0 or 5 phr and 40 phr or between 0 or 10 phr and 35 phr. In particular embodiments, there may be no plasticizing liquid utilized.

[0040] A plasticizing hydrocarbon resin is a hydrocarbon compound that is solid at ambient temperature ( e.g ., 23 °C) as opposed to a liquid plasticizing compound, such as a plasticizing oil. Additionally a plasticizing hydrocarbon resin is compatible, i.e., miscible, with the rubber composition with which the resin is mixed at a concentration that allows the resin to act as a true plasticizing agent, e.g., at a concentration that is typically at least 5 phr (parts per hundred parts rubber by weight).

[0041] Plasticizing hydrocarbon resins are polymers that can be aliphatic, aromatic or combinations of these types, meaning that the polymeric base of the resin may be formed from aliphatic and/or aromatic monomers. These resins can be natural or synthetic materials and can be petroleum based, in which case the resins may be called petroleum plasticizing resins, or based on plant materials. In particular embodiments, although not limiting the invention, these resins may contain essentially only hydrogen and carbon atoms.

[0042] The plasticizing hydrocarbon resins useful in particular embodiment of the present invention include those that are homopolymers or copolymers of cyclopentadiene (CPD) or dicyclopentadiene (DCPD), homopolymers or copolymers of terpene, homopolymers or copolymers of C5 cut and mixtures thereof.

[0043] Such copolymer plasticizing hydrocarbon resins as discussed generally above may include, for example, resins made up of copolymers of (D)CPD/ vinyl- aromatic, of (D)CPD/ terpene, of (D)CPD/ C5 cut, of terpene/ vinyl- aromatic, of C5 cut/ vinyl- aromatic and of combinations thereof.

[0044] Terpene monomers useful for the terpene homopolymer and copolymer resins include alpha-pinene, beta-pinene and limonene. Particular embodiments include polymers of the limonene monomers that include three isomers: the L- limonene (laevorotatory enantiomer), the D-limonene (dextrorotatory enantiomer), or even the dipentene, a racemic mixture of the dextrorotatory and laevorotatory enantiomers. [0045] Examples of vinyl aromatic monomers include styrene, alpha- methylstyrene, ortho-, meta-, para-methylstyrene, vinyl-toluene, para-tertiobutylstyrene, methoxy styrenes, chloro- styrenes, vinyl-mesitylene, divinylbenzene, vinylnaphthalene, any vinyl-aromatic monomer coming from the Cg cut (or, more generally, from a C ₈ to C _l0 cut). Particular embodiments that include a vinyl- aromatic copolymer include the vinyl-aromatic in the minority monomer, expressed in molar fraction, in the copolymer.

[0046] Particular embodiments of the present invention include as the plasticizing hydrocarbon resin the (D)CPD homopolymer resins, the (D)CPD/ styrene copolymer resins, the polylimonene resins, the limonene/ styrene copolymer resins, the limonene/ D(CPD) copolymer resins, C5 cut/ styrene copolymer resins, C5 cut/ C9 cut copolymer resins, and mixtures thereof.

[0047] Commercially available plasticizing resins that include terpene resins suitable for use in the present invention include a polyalphapinene resin marketed under the name Resin R2495 by Hercules Inc. of Wilmington, DE. Resin R2495 has a molecular weight of about 932, a softening point of about l35°C and a glass transition temperature of about 9l°C. Another commercially available product that may be used in the present invention includes DERCOLYTE L120 sold by the company DRT of France. DERCOLYTE L120 polyterpene- limonene resin has a number average molecular weight of about 625, a weight average molecular weight of about 1010, an Ip of about 1.6, a softening point of about H9°C and has a glass transition temperature of about 72° C. Still another commercially available terpene resin that may be used in the present invention includes SYLVARES TR 7125 and/or SYLVARES TR 5147 polylimonene resin sold by the Arizona Chemical Company of Jacksonville, FL. SYLVARES 7125 polylimonene resin has a molecular weight of about 1090, has a softening point of about 125° C, and has a glass transition temperature of about 73°C while the SYLVARES TR 5147 has a molecular weight of about 945, a softening point of about 120 °C and has a glass transition temperature of about 71° C.

[0048] Other suitable plasticizing hydrocarbon resins that are commercially available include C5 cut/ vinyl- aromatic styrene copolymer, notably C5 cut / styrene or C5 cut / Cg cut from Neville Chemical Company under the names SETPER NEVTAC 78, SUPER NEVTAC 85 and SUPER NEVTAC 99; from Goodyear Chemicals under the name WINGTACK EXTRA; from Kolon under names HIKOREZ T1095 and HIKOREZ T1100; and from Exxon under names ESCOREZ 2101 and ECR 373.

[0049] Yet other suitable plasticizing hydrocarbon resins that are limonene/styrene copolymer resins that are commercially available include DERCOLYTE TS 105 from DRT of France; and from Arizona Chemical Company under the name ZT115LT and ZT5100.

[0050] It may be noted that the glass transition temperatures of plasticizing resins may be measured by Differential Scanning Calorimetry (DCS) in accordance with ASTM D3418 (1999). In particular embodiments, useful resins may be have a glass transition temperature that is at least 25° C or alternatively, at least 40° C or at least 60° C or between 25° C and 95° C, between 40° C and 85° C or between 60° C and 80° C.

[0051] The amount of plasticizing hydrocarbon resin useful in any particular embodiment of the present invention depends upon the particular circumstances and the desired result. The plasticizing hydrocarbon resin may be present in the rubber composition in an amount of, for example, between 30 phr and 80 phr or alternatively, between 35 phr and 75 phr, 40 phr and 70 phr or between 35 phr and 70 phr.

[0052] The amount of the plasticizing system, i.e., the amount of the resin and plasticizing liquid included in the rubber compositions disclosed herein, is the amount that is effective in providing a low rigidity rubber composition with a shear modulus G* measured in accordance with ASTM D5992-96 at 60 °C of between 0.7 MPa and 1.1 MPa or alternatively between 0.8 MPa and 1.0 MPa. The ratio of the oil to resin, by weight, may in particular embodiments be adjusted to achieve the desired shear modulus, such ratios ranging between 0.2 and 0.7 or alternatively between 0.4 and 0.6.

[0053] The glass transition temperature of the rubber compositions disclosed herein is adjusted in known way with the plasticizing system to provide the tread with a glass transition temperature of between -35 °C and -15 °C or alternatively between -30 °C and -15 °C or between -25 °C and -15 °C.

[0054] The rubber compositions disclosed herein may be cured with any suitable curing system including a peroxide curing system or a sulfur curing system. Particular embodiments are cured with a sulfur curing system that includes free sulfur and may further include, for example, one or more of accelerators, stearic acid and zinc oxide. Suitable free sulfur includes, for example, pulverized sulfur, rubber maker’s sulfur, commercial sulfur, and insoluble sulfur. The amount of free sulfur included in the rubber composition is not limited and may range, for example, between 0.5 phr and 10 phr or alternatively between 0.5 phr and 5 phr or between 0.5 phr and 3 phr. Particular embodiments may include no free sulfur added in the curing system but instead include sulfur donors.

[0055] Accelerators are used to control the time and/or temperature required for vulcanization and to improve the properties of the cured rubber composition. Particular embodiments of the present invention include one or more accelerators. One example of a suitable primary accelerator useful in the present invention is a sulfenamide. Examples of suitable sulfenamide accelerators include n-cyclohexyl -2-benzothiazole sulfenamide (CBS), N-tert-butyl-2-benzothiazole Sulfenamide (TBBS), N-Oxydiethyl-2-benzthiazolsulfenamid (MBS) and N'-dicyclohexyl-2-benzothiazolesulfenamide (DCBS). Combinations of accelerators are often useful to improve the properties of the cured rubber composition and the particular embodiments include the addition of secondary accelerators.

[0056] Particular embodiments may include as a secondary accelerant the use of a moderately fast accelerator such as, for example, diphenylguanidine (DPG), triphenyl guanidine (TPG), diorthotolyl guanidine (DOTG), o-tolylbigaunide (OTBG) or hexamethylene tetramine (HMTA). Such accelerators may be added in an amount of up to 4 phr, between 0.5 and 3 phr, between 0.5 and 2.5 phr or between 1 and 2 phr. Particular embodiments may exclude the use of fast accelerators and/or ultra-fast accelerators such as, for example, the fast accelerators: disulfides and benzothiazoles; and the ultra- accelerators: thiurams, xanthates, dithiocarbamates and dithiophosphates.

[0057] Other additives can be added to the rubber compositions disclosed herein as known in the art. Such additives may include, for example, some or all of the following: antidegradants, antioxidants, fatty acids, waxes, stearic acid and zinc oxide. Examples of antidegradants and antioxidants include 6PPD, 77PD, IPPD and TMQ and may be added to rubber compositions in an amount, for example, of from 0.5 phr and 5 phr. Zinc oxide may be added in an amount, for example, of between 1 phr and 6 phr or alternatively, of between 1.5 phr and 4 phr. Waxes may be added in an amount, for example, of between 1 phr and 5 phr. [0058] The rubber compositions that are embodiments of the present invention may be produced in suitable mixers, in a manner known to those having ordinary skill in the art, typically using two successive preparation phases, a first phase of thermo-mechanical working at high temperature, followed by a second phase of mechanical working at lower temperature.

[0059] The first phase of thermo-mechanical working (sometimes referred to as "non-productive" phase) is intended to mix thoroughly, by kneading, the various ingredients of the composition, with the exception of the vulcanization system. It is carried out in a suitable kneading device, such as an internal mixer or an extruder, until, under the action of the mechanical working and the high shearing imposed on the mixture, a maximum temperature generally between 120° C and 190° C, more narrowly between 130° C and 170° C, is reached.

[0060] After cooling of the mixture, a second phase of mechanical working is implemented at a lower temperature. Sometimes referred to as "productive" phase, this finishing phase consists of incorporating by mixing the vulcanization (or cross-linking) system (sulfur or other vulcanizing agent and accelerator(s)), in a suitable device, for example an open mill. It is performed for an appropriate time (typically between 1 and 30 minutes, for example between 2 and 10 minutes) and at a sufficiently low temperature lower than the vulcanization temperature of the mixture, so as to protect against premature vulcanization.

[0061] The rubber composition can be formed into useful articles, including treads for use on vehicle tires. The treads may be formed as tread bands and then later made a part of a tire or they be formed directly onto a tire carcass by, for example, extrusion and then cured in a mold. As such, tread bands may be cured before being disposed on a tire carcass or they may be cured after being disposed on the tire carcass. Typically a tire tread is cured in a known manner in a mold that molds the tread elements into the tread, including, e.g., the sipes molded into the tread blocks.

[0062] The invention is further illustrated by the following examples, which are to be regarded only as illustrations and not delimitative of the invention in any way. The properties of the compositions disclosed in the examples were evaluated as described below and these utilized methods are suitable for measurement of the claimed properties of the present invention.

[0063] Modulus of elongation (MPa) was measured at 100% (MA100) at a temperature of 23 °C based on ASTM Standard D412 on dumb bell test pieces. The measurements were taken in the second elongation; i.e., after an accommodation cycle. These measurements are secant moduli in MPa, based on the original cross section of the test piece.

[0064] Wet braking for a tire mounted on an automobile fitted with an ABS braking system was determined by measuring the distance necessary to go from 50 MPH to 0 MPH upon sudden braking on wetted ground (asphalt concrete). A value greater than that of the control, which is arbitrarily set to 100, indicates an improved result, that is to say a shorter braking distance.

[0065] Dry braking for a tire mounted on an automobile fitted with an ABS braking system was determined by measuring the distance necessary to go from 60 MPH to 0 MPH upon sudden braking on a dry asphalt surface. A value greater than that of the control, which is arbitrarily set to 100, indicates an improved result, that is to say a shorter braking distance.

[0066] The rolling resistance of each of the tires tested was measured by running on a test drum, at an ambient temperature of 25 °C, under a load of 530 kg and at a speed of 80 km/h, the internal pressure of the tire being 2.6 bar.

[0067] The maximum tan delta dynamic properties for the rubber compositions were measured at 23° C on a Metravib Model VA400 ViscoAnalyzer Test System in accordance with ASTM D5992-96. The response of a sample of vulcanized material (double shear geometry with each of the two 10 mm diameter cylindrical samples being 2 mm thick) was recorded as it was being subjected to an alternating single sinusoidal shearing stress at a frequency of 10 Hz under a controlled temperature of 23° C. Scanning was effected at an amplitude of deformation of 0.05 to 50 % (outward cycle) and then of 50 % to 0.05% (return cycle). The maximum value of the tangent of the loss angle tan delta (max tan d) was determined during the return cycle.

[0068] Dynamic properties (Tg and G*) for the rubber compositions were measured on a Metravib Model VA400 ViscoAnalyzer Test System in accordance with ASTM D5992- 96. The response of a sample of vulcanized material (double shear geometry with each of the two 10 mm diameter cylindrical samples being 2 mm thick) was recorded as it was being subjected to an alternating single sinusoidal shearing stress of a constant 0.7 MPa and at a frequency of 10 Hz over a temperature sweep from -60° C to 100° C with the temperature increasing at a rate of 1.5° C/min. The shear modulus G* at 60° C was captured and the temperature at which the max tan delta occurred was recorded as the glass transition temperature, Tg.

Example 1

[0069] Rubber compositions were prepared using the components shown in Table 1. The amounts of each component making up the rubber composition shown in Table 1 are provided in parts per hundred parts of rubber by weight (phr). The location of the functional moiety in the modified SBR is shown as either end-of-chain or mid-chain. The polydispersity index (the ratio of the weight average molecular weight to the number average molecular weight, i.e., polydispersity index = M _w /M _n ) is also shown for the elastomers. The mid functional moiety is an alkoxysilane moiety bearing a secondary amine functional group while the end-chain functional moiety is SiOH.

Table 1 - Rubber Formulations

[0070] The silica was ZEOSIL 160, a highly dispersible silica available from Rhodia having a BET of 160 m2/g. The plasticizing oil was AGRTPETRE 80. The silane coupling agent was liquid silane 69 from Evonik Degussa. The curative package included sulfur, accelerators, zinc oxide and stearic acid. The resin for Wl and Fl was Oppera 383N, a DCPD-C9 resin available from Exxon-Mobil having a glass transition temperature of 54 °C and the resin for the remaining compositions was Wingtack STS, a modified C5 resin available from Cray Valley having a glass transition temperature of 44 °C.

[0071] Table 2 shows the physical properties of the rubber compositions and the tire test results.

Table 2 - Physical Properties and Tire Tests

[0072] The terms“comprising,”“including,” and“having,” as used in the claims and specification herein, shall be considered as indicating an open group that may include other elements not specified. The term“consisting essentially of,” as used in the claims and specification herein, shall be considered as indicating a partially open group that may include other elements not specified, so long as those other elements do not materially alter the basic and novel characteristics of the claimed invention. The terms“a,”“an,” and the singular forms of words shall be taken to include the plural form of the same words, such that the terms mean that one or more of something is provided. The terms“at least one” and“one or more” are used interchangeably. The term“one” or“single” shall be used to indicate that one and only one of something is intended. Similarly, other specific integer values, such as“two,” are used when a specific number of things is intended. The terms“preferably,”“preferred,” “prefer,”“optionally,”“may,” and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention. Ranges that are described as being“between a and b” are inclusive of the values for“a” and“b.”

[0073] It should be understood from the foregoing description that various modifications and changes may be made to the embodiments of the present invention without departing from its true spirit. The foregoing description is provided for the purpose of illustration only and should not be construed in a limiting sense Only the language of the following claims should limit the scope of this invention.