Rubber compound providing improved dynamic properties and wear

Abstract

A vulcanizable composition comprising: (i) a base rubber component; (ii) a low molecular weight polydiene additive having a Mn of less than 100 kg / mol, a Mw of less than 110 kg / mol, a Tg above -30 °C, and a vinyl content of more than 35 mol% based on the diene monomer units; (iii) a filler; and (iv) a curing agent.

Description

Technical Field

[0001] Embodiments of the present invention provide rubber compounds and vulcanizates having improved abrasion characteristics and / or improved viscoelastic properties, particularly those useful as tire treads.

Background Art

[0002] In the technical field of manufacturing tires, oil has historically been included in rubber compounds to provide processing advantages. That is, by introducing oil into the rubber composition, the overall viscosity of the compound can be reduced, thereby promoting, inter alia, the ability to mix the rubber compound and disperse various additives such as reinforcing fillers and curing agents throughout the rubber composition. It is also known that certain oils can provide other advantages including improvement of one or more viscoelastic properties of the resulting vulcanizate.

[0003] Although the inclusion of oil can provide several advantages to rubber compounds and the resulting vulcanizates, those skilled in the art also understand that the low molecular weight nature of the oil can provide trade - offs and disadvantages. For example, those skilled in the art understand that oil can have a detrimental effect on rolling resistance and tread wear.

Summary of the Invention

[0004] One or more embodiments of the present invention provide a vulcanizable composition comprising: (i) a base rubber component; (ii) a low - molecular - weight polydiene additive having an Mn of less than 100 kg / mol, an Mw of less than 110 kg / mol, a Tg above - 30°C, and a vinyl content of more than 35 mol% based on the diene monomer units; (iii) a filler; and (iv) a curing agent.

[0005] Yet other embodiments of the present invention provide a vulcanizate prepared by subjecting the vulcanizable composition according to any one of the preceding claims to curing conditions.

[0006] Another embodiment of the present invention provides a method for preparing a vulcanizate, the method comprising subjecting a vulcanizable composition according to any one of the preceding claims to curing conditions.

Embodiments for Carrying Out the Invention

[0007] Embodiments of the present invention are based at least in part on the discovery of rubber formulations containing low molecular weight polydiene additives. Rubber formulations useful in the manufacture of tires, particularly tire treads, provide rubber vulcanizates characterized by improvements in at least one of viscoelastic properties and wear. For example, improved viscoelastic properties may include an increased tan δ at 0° C., which is thought to indicate improved wet traction, and a decreased tan δ at 65° C., which is thought to indicate improved rolling resistance, compared to a comparative vulcanizate prepared in the absence of a low molecular weight polydiene polymer additive. According to embodiments of the present invention, the low molecular weight polydiene additive is a polymer characterized by a relatively low molecular weight and a relatively high glass transition temperature. In certain embodiments, the low molecular weight polydiene additive can advantageously act as a substitute for at least a portion of the oil that would otherwise be required to enable processing of the rubber formulation, so the rubber formulation contains less than a threshold amount of oil.

[0008] Rubber formulation The rubber formulation of the present invention, which may also be referred to as a vulcanizable composition, comprises a base rubber component, a low molecular weight polydiene additive, a filler, and a curing agent. The composition may also optionally include other components including, but not limited to, waxes, anti-degradants, oils, solid resins, liquid resins, and curing accelerators.

[0009] Low molecular weight polydiene additive According to embodiments of the present invention, a low molecular weight additive or LMW polydiene additive, or a low molecular weight polydiene additive that may also simply be referred to as an additive, is a polydiene homopolymer or polydiene copolymer. As will be understood by those skilled in the art, the term polydiene refers to a synthetic polymer or copolymer prepared by polymerizing one or more conjugated diene monomers, optionally together with one or more vinyl aromatic monomers. Exemplary conjugated diene monomers can include, but are not limited to, 1,3-butadiene, isoprene, 1,3-pentadiene, 1,3-hexadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene, 4-methyl-1,3-pentadiene, and 2,4-hexadiene. Exemplary vinyl aromatic monomers can include, but are not limited to, styrene, p-methylstyrene, α-methylstyrene, and vinylnaphthalene. Exemplary low molecular weight polydiene additives can include, but are not limited to, polybutadiene, polyisoprene, poly(butadiene-co-isoprene), poly(styrene-co-butadiene), poly(styrene-co-isoprene), poly(styrene-co-butadiene-isoprene).

[0010] As described above, the LMW polydiene additive is characterized by a relatively low molecular weight, including a relatively low number average molecular weight (Mn) and a relatively low weight average molecular weight (Mw). According to embodiments of the present invention, the molecular weight moments (e.g., Mn and Mw) can be determined by gel permeation chromatography (GPC) using a polystyrene standard. In one or more embodiments, the LMW polydiene additive has an Mn of less than 100 kg / mol, in other embodiments less than 90 kg / mol, in other embodiments less than 80 kg / mol, and in other embodiments less than 70 kg / mol. In these or other embodiments, the LMW polydiene additive has an Mn of greater than 10 kg / mol, in other embodiments greater than 20 kg / mol, in other embodiments greater than 30 kg / mol, in other embodiments greater than 40 kg / mol, in other embodiments greater than 50 kg / mol, in other embodiments greater than 60 kg / mol, and in other embodiments greater than 70 kg / mol. In one or more embodiments, the LMW polydiene additive has an Mn of about 10 to about 100, in other embodiments about 20 to about 90, in other embodiments about 30 to about 80, in other embodiments about 50 to about 95, in other embodiments about 60 to about 90, and in other embodiments about 40 to about 70 kg / mol.

[0011] In one or more embodiments, the LMW polydiene additive has an Mw of less than 110 kg / mol, in other embodiments less than 100 kg / mol, in other embodiments less than 90 kg / mol, and in other embodiments less than 80 kg / mol. In these or other embodiments, the LMW polydiene additive has an Mw of greater than 10 kg / mol, in other embodiments greater than 20 kg / mol, in other embodiments greater than 30 kg / mol, and in other embodiments greater than 40 kg / mol. In one or more embodiments, the LMW polydiene additive has an Mw of about 10 to about 110, in other embodiments about 20 to about 100, in other embodiments about 30 to about 90, and in other embodiments about 40 to about 80 kg / mol.

[0012] In one or more embodiments, the LMW polyene additive can be characterized by a molecular weight distribution (Mw / Mn) of less than 3, in other embodiments less than 2.5, in other embodiments less than 2, and in other embodiments less than 1.5.

[0013] As described above, the LMW polyene additive is characterized by a relatively high glass transition temperature (Tg). According to embodiments of the present invention, Tg can be determined by using differential scanning calorimetry (DSC) at 10 °C / min. In one or more embodiments, the LMW polyene additive has a Tg greater than -30 °C, in other embodiments greater than -25 °C, in other embodiments greater than -20 °C, and in other embodiments greater than -15 °C. In these or other embodiments, the LMW polyene additive has a Tg less than 30 °C, in other embodiments less than 20 °C, in other embodiments less than 10 °C, and in other embodiments less than 0 °C. In one or more embodiments, the LMW polyene additive has a Tg of about -30 to about 30, in other embodiments about -25 to about 25, in other embodiments about -20 to about 20, and in other embodiments about -15 to about 5 °C.

[0014] The LMW polydiene additive used in the present invention can be further characterized by the vinyl content of the diene mer units of the copolymer. According to an embodiment of the present invention, the vinyl content can be determined by FTIR including FTIR coupled to GPC. As will be understood by those skilled in the art, the vinyl content of the LMW polydiene is expressed as a mole percent relative to the moles of butadiene mer units in the copolymer. In one or more embodiments, the LMW polydiene additive has a vinyl content of greater than 35 mol%, in other embodiments greater than 40 mol%, in other embodiments greater than 45 mol%, and in other embodiments greater than 50 mol%. In these or other embodiments, the LMW polydiene additive has a vinyl content of less than 75 mol%, in other embodiments less than 70 mol%, in other embodiments less than 65 mol%, and in other embodiments less than 60 mol%. In one or more embodiments, the LMW polydiene additive has a vinyl content of from about 35 to about 75 mol%, in other embodiments from about 40 to about 70 mol%, in other embodiments from about 45 to about 65 mol%, and in other embodiments from about 50 to about 60 mol%.

[0015] In embodiments where the LMW polydiene additive comprises mer units derived from a polymer of a vinyl aromatic monomer, the LMW polydiene additive can be further characterized by the bound styrene content of the copolymer. According to embodiments of the present invention, the bound styrene can be determined by FTIR including FTIR coupled to GPC. As will be understood by those skilled in the art, the bound styrene (i.e., bound vinyl aromatic monomer) content is expressed as a weight percent relative to the total weight of the copolymer. In one or more embodiments, the LMW polydiene additive has a bound styrene content of greater than 20 wt%, in other embodiments greater than 25 wt%, in other embodiments greater than 30 wt%, and in other embodiments greater than 35 wt%. In these or other embodiments, the LMW polydiene additive has a bound styrene content of less than 65 wt%, in other embodiments less than 60 wt%, in other embodiments less than 55 wt%, and in other embodiments less than 50 wt%. In one or more embodiments, the LMW polydiene additive has a bound styrene content of from about 20 to about 65 wt%, in other embodiments from about 25 to about 60 wt%, in other embodiments from about 30 to about 55 wt%, and in other embodiments from about 35 to about 50 wt%.

[0016] Base rubber As described above, the rubber composition of the present invention includes a base rubber, which may also be referred to as a base rubber component. The base rubber component can generally include a vulcanizable rubber, a rubber polymer, an elastomer, or an elastomer polymer that can simply be referred to as rubber. The elastomer polymer includes polymers that can be vulcanizable. The elastomer polymer may be synthetic and / or natural. Synthetic elastomer polymers, which may be referred to as synthetic polymers or synthetic elastomers, can include polydienes and polydiene copolymers. Specific examples of these synthetic polymers include, but are not limited to, polybutadiene, poly(styrene-co-butadiene), polyisoprene, poly(styrene-co-isoprene), poly(styrene-co-isoprene-butadiene), and their functionalized derivatives. Other polymers that can be included in the base rubber include neoprene, poly(ethylene-co-propylene), poly(styrene-co-butadiene), poly(ethylene-co-propylene-co-diene), polysulfide rubber, acrylic rubber, urethane rubber, silicone rubber, epichlorohydrin rubber, syndiotactic polybutadiene, and mixtures thereof or mixtures with polydienes and polydiene copolymers. These synthetic polymers can have countless macromolecular structures including linear, branched, and star-shaped structures. These synthetic polymers can also typically include one or more functional units containing heteroatoms attached to the polymer backbone. A blend of natural rubber and one synthetic rubber may be used. In other embodiments, a blend of natural rubber and two or more synthetic rubbers may be used. In other embodiments, a blend of two or more synthetic rubbers can be used in the absence of natural rubber.

[0017] In one or more embodiments, the synthetic polymer that constitutes the base polymer component of the rubber composition of the present invention includes relatively high molecular weight polymers, which are elastomeric polymers characterized by a relatively high molecular weight relative to the LMW polydiene additive. Those skilled in the art will understand that the molecular weight can be quantified by the number average molecular weight (Mn) and the weight average molecular weight (Mw). According to embodiments of the present invention, the molecular weight moments (e.g., Mn and Mw) can be determined by gel permeation chromatography (GPC) using polystyrene standards.

[0018] In one or more embodiments, the base polymer (e.g., synthetic polymer) has an Mn of greater than 110 kg / mol, in other embodiments greater than 130 kg / mol, in other embodiments greater than 150 kg / mol, and in other embodiments greater than 170 kg / mol. In these or other embodiments, the base polymer has an Mn of about 110 to greater than about 1,000 kg / mol, in other embodiments about 130 to greater than about 800 kg / mol, in other embodiments about 150 to about 600 kg / mol, and in other embodiments about 170 to about 400 kg / mol.

[0019] In one or more embodiments, the base polymer (e.g., synthetic polymer) has an Mw of greater than 120 kg / mol, in other embodiments greater than 160 kg / mol, in other embodiments greater than 200 kg / mol, and in other embodiments greater than 240 kg / mol. In these or other embodiments, the base polymer has an Mw of about 120 to greater than about 1,000 kg / mol, in other embodiments about 160 to greater than about 950 kg / mol, in other embodiments about 200 to about 800 kg / mol, and in other embodiments about 240 to about 700 kg / mol.

[0020] In one or more embodiments, the base polymer (e.g., synthetic polymer) can be characterized by a molecular weight distribution (Mw / Mn) of less than 5, in other embodiments less than 4, in other embodiments less than 3, and in other embodiments less than 2.

[0021] In one or more embodiments, the base polymer (e.g., a synthetic polymer) is characterized by its glass transition temperature (Tg). According to embodiments of the present invention, the Tg can be determined by using differential scanning calorimetry (DSC) at 10 °C / min. In one or more embodiments, the base polymer has a Tg greater than -110 °C, in other embodiments greater than -80 °C, in other embodiments greater than -70 °C, and in other embodiments greater than -60 °C. In these or other embodiments, the base polymer has a Tg less than -20 °C, in other embodiments less than -30 °C, in other embodiments less than -35 °C, and in other embodiments less than -40 °C. In one or more embodiments, the base polymer has a Tg of about -110 to about 20 °C, in other embodiments about -80 to about 30 °C, in other embodiments about -70 to about 35 °C, and in other embodiments about -60 to about -40 °C.

[0022] Filler As suggested above, the vulcanizable composition can include a filler such as a reinforcing filler. Examples of the filler include, but are not limited to, carbon black and silica.

[0023] In one or more embodiments, useful carbon blacks include furnace black, channel black, and lamp black. More specific examples of carbon black include super abrasion furnace black, intermediate super abrasion furnace black, high abrasion furnace black, high speed extrusion furnace black, fine furnace black, semi-reinforcing furnace black, medium processing channel black, hard processing channel black, conductive channel black, and acetylene black.

[0024] In one or more embodiments, examples of suitable silica fillers include precipitated amorphous silica, wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), fumed silica, calcium silicate, aluminum silicate, calcium aluminum silicate, magnesium silicate, and the like.

[0025] In one or more embodiments, the surface area of the silica, when measured by the BET method, is about 32 to about 400 m 2 / g (including 32 m 2 / g to 400 m 2 / g), may be, preferably in the range of about 100 m 2 / g to about 300 m 2 / g (including 100 m 2 / g to 300 m 2 / g), and more preferably in the range of about 150 m 2 / g to about 220 m 2 / g (including 150 m 2 / g to 220 m 2 / g). In one or more embodiments, the silica may be characterized by a pH of about 5.5 to about 7, or slightly above 7, or in other embodiments about 5.5 to about 6.8. Some commercially available silica fillers that can be used include those sold under the Hi-Sil trade names such as 190, 210, 215, 233, and 243 by PPG Industries, as well as those available from Degussa Corporation (e.g., VN2, VN3), Rhone Poulenc (e.g., Zeosil™ 1165 MP), and J.M.Huber Corporation, but are not limited thereto.

[0026] In one or more embodiments, a silica coupling agent is included in the vulcanizable composition. As will be understood by those skilled in the art, these compounds include a hydrolyzable silicon moiety (often called a silane) and a moiety that can react with the vulcanizable polymer.

[0027] Suitable silica coupling agents include, for example, those containing groups such as alkylalkoxy, mercapto, blocked mercapto, sulfide-containing (e.g., monosulfide-based alkoxy-containing, disulfide-based alkoxy-containing, tetradisulfide-based alkoxy-containing), amino, vinyl, epoxy, and combinations thereof. In certain embodiments, the silica coupling agent may be added to the rubber composition in the form of pretreated silica. The pretreated silica has been surface-treated with silane prior to being added to the rubber composition.

[0028] Non-limiting examples of alkylalkoxysilanes suitable for use in certain embodiments of the fourth embodiment disclosed herein include octyltriethoxysilane, octyltrimethoxysilane, trimethylethoxysilane, cyclohexyltriethoxysilane, isobutyltriethoxysilane, ethyltrimethoxysilane, cyclohexyltributoxysilane, dimethyldiethoxysilane, methyltriethoxysilane, propyltriethoxysilane, hexyltriethoxysilane, heptyltriethoxysilane, nonyltriethoxysilane, decyltriethoxysilane, dodecyltriethoxysilane, tetradecyltriethoxysilane, octadecyltriethoxysilane, methyloctyldiethoxysilane, dimethyldimethoxysilane, methyltrimethoxysilane, propyltrimethoxysilane, hexyltrimethoxysilane, heptyltrimethoxysilane, nonyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, tetradecyltrimethoxysilane, octadecyltrimethoxysilane, methyloctyldimethoxysilane, and mixtures thereof, but are not limited thereto.

[0029] Non-limiting examples of bis(trialkoxysilylorgano)polysulfides suitable for use in a particular embodiment of the fourth embodiment disclosed herein include bis(trialkoxysilylorgano)disulfides and bis(trialkoxysilylorgano)tetrasulfides. Particular non-limiting examples of bis(trialkoxysilylorgano)disulfides suitable for use in a particular exemplary embodiment of the fourth embodiment disclosed herein include 3,3'-bis(triethoxysilylpropyl)disulfide, 3,3'-bis(trimethoxysilylpropyl)disulfide, 3,3'-bis(tributoxysilylpropyl)disulfide, 3,3'-bis(tri-t-butoxysilylpropyl)disulfide, 3,3'-bis(trihexyloxysilylpropyl)disulfide, 2,2'-bis(dimethylmethoxysilylethyl)disulfide, 3,3'-bis(diphenylcyclohexyloxysilylpropyl)disulfide, 3,3'-bis(ethyl-di-sec-butoxysilylpropyl)disulfide, 3,3'-bis(propyldiethoxysilylpropyl)disulfide, 12,12'-bis(triisopropoxysilylpropyl)disulfide, 3,3'-bis(dimethoxyphenylsilyl-2-methylpropyl)disulfide, and mixtures thereof, but are not limited thereto. Non-limiting examples of bis(trialkoxysilylorgano)tetrasulfide silica coupling agents suitable for use in a particular embodiment of the fourth embodiment disclosed herein include bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl-benzothiazole tetrasulfide, 3-triethoxysilylpropylbenzothiazole tetrasulfide, and mixtures thereof, but are not limited thereto.Bis(3-triethoxysilylpropyl)tetrasulfide is sold under the trade name Si69 by Evonik Degussa Corporation.

[0030] Non-limiting examples of mercaptosilanes suitable for use in certain embodiments of the fourth embodiment disclosed herein include 1-mercaptomethyltriethoxysilane, 2-mercaptoethyltriethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldiethoxysilane, 2-mercaptoethyltripropoxysilane, 18-mercaptooctadecyldiethoxychlorosilane, and mixtures thereof, but are not limited thereto.

[0031] Non-limiting examples of blocked mercaptosilanes suitable for use in certain embodiments of the fourth embodiment disclosed herein include those described in U.S. Patent Nos. 6,127,468, 6,204,339, 6,528,673, 6,635,700, 6,649,684, and 6,683,135 (the disclosures of which are incorporated herein by reference), but are not limited thereto. Representative examples of blocked mercaptosilanes used herein in certain exemplary embodiments disclosed herein include 2-triethoxysilyl-1-ethylthioacetate, 2-trimethoxysilyl-1-ethylthioacetate, 2-(methyldimethoxysilyl)-1-ethylthioacetate, 3-trimethoxysilyl-1-propylthioacetate, triethoxysilylmethyl-thioacetate, trimethoxysilylmethylthioacetate, triisopropoxysilylmethylthioacetate, methyldiethoxysilylmethylthioacetate, methyldimethoxysilylmethylthioacetate, methyldiisopropoxysilylmethylthioacetate, dimethylethoxysilylmethylthioacetate, dimethylmethoxysilylmethylthioacetate, dimethylisopropoxysilylmethylthioacetate, 2-triisopropoxysilyl-1-ethylthioacetate, 2-(methyldiethoxysilyl)-1-ethylthioacetate, 2-(methyldiisopropoxysilyl)-1-ethylthioacetate, 2-(dimethylethoxysilyl-1-ethylthioacetate, 2-(dimethylmethoxysilyl)-1-ethylthioacetate, 2-(dimethylisopropoxysilyl)-1-ethylthioacetate, 3-triethoxysilyl-1-propylthioacetate, 3-triisopropoxysilyl-1-propylthioacetate, 3-methyldiethoxysilyl-1-propyl-thioacetate, 3-methyldimethoxysilyl-1-propylthioacetate, 3-methyldiisopropoxysilyl-1-propylthioacetate, 1-(2-triethoxysilyl-1-ethyl)-4-thioacetylcyclohexane, 1-(2-triethoxysilyl-1-ethyl)-3-thioacetylcyclohexane, 2-triethoxysilyl-5-thioacetylnorbornene,2-Triethoxysilyl-4-thioacetylnorbornene, 2-(2-triethoxysilyl-1-ethyl)-5-thioacetylnorbornene, 2-(2-triethoxy-silyl-1-ethyl)-4-thioacetylnorbornene, 1-(1-oxo-2-thia-5-triethoxysilylphenyl)benzoic acid, 6-triethoxysilyl-1-hexylthioacetate, 1-triethoxysilyl-5-hexylthioacetate, 8-triethoxysilyl-1-octylthioacetate, 1-triethoxysilyl-7-octylthioacetate, 6-triethoxysilyl-1-hexylthioacetate, 1-triethoxysilyl-5-octylthioacetate, 8-trimethoxysilyl-1-octylthioacetate, 1-trimethoxysilyl-7-octylthioacetate, 10-triethoxysilyl-1-decylthioacetate, 1-triethoxysilyl-9-decylthioacetate, 1-triethoxysilyl-2-butylthioacetate, 1-triethoxysilyl-3-butylthioacetate, 1-triethoxysilyl-3-methyl-2-butylthioacetate, 1-triethoxysilyl-3-methyl-3-butylthioacetate, 3-trimethoxysilyl-1-propylthiooctanoate, 3-triethoxysilyl-1-propyl-1-propylthiopalmitate, 3-triethoxysilyl-1-propylthiooctanoate, 3-triethoxysilyl-1-propylthiobenzoate, 3-triethoxysilyl-1-propylthio-2-ethylhexanoate, 3-methyldiacetoxysilyl-1-propylthioacetate, 3-triacetoxysilyl-1-propylthioacetate, 2-methyldiacetoxysilyl-1-ethylthioacetate, 2-triacetoxysilyl-1-ethylthioacetate, 1-methyldiacetoxysilyl-1-ethylthioacetate, 1-triacetoxysilyl-1-ethyl-thioacetate, tris-(3-triethoxysilyl-1-propyl)trithiophosphate, bis-(3-triethoxysilyl-1-propyl)methyldithiophosphonate, bis-(3-triethoxysilyl-1-propyl)ethyldithiophosphonate, 3-triethoxysilyl-1-propyldimethylthiophosphinate, 3-triethoxysilyl-1-propyldiethylthiophosphinate,Tris-(3-triethoxysilyl-1-propyl)tetrathiphosphate, bis-(3-triethoxysilyl-1-propyl)methyltrithiophosphonate, bis-(3-triethoxysilyl-1-propyl)ethyltrithiophosphonate, 3-triethoxysilyl-1-propyldimethyldithiophosphinate, 3-triethoxysilyl-1-propyldiethyldithiophosphinate, tris-(3-methyldimethoxysilyl-1-propyl)trithiophosphate, bis-(3-methyldimethoxysilyl-1-propyl)-methyldithiophosphonate, bis-(3-methyldimethoxysilyl-1-propyl)-ethyldithiophosphonate, 3-methyldimethoxysilyl-1-propyldimethylthiophosphinate, 3-methyldimethoxysilyl-1-propyldiethylthiophosphinate, 3-triethoxysilyl-1-propylmethylthiosulfate, 3-triethoxysilyl-1-propylmethanethiosulfonate, 3-triethoxysilyl-1-propylethanethiosulfonate, 3-triethoxysilyl-1-propylbenzenethiosulfonate, 3-triethoxysilyl-1-propyltolueneethiosulfonate, 3-triethoxysilyl-1-propylnaphthalenethiosulfonate, 3-triethoxysilyl-1-propylxylenethiosulfonate, triethoxysilylmethylmethylthiosulfate, triethoxysilylmethylmethanethiosulfonate, triethoxysilylmethylethanethiosulfonate, triethoxysilylmethylbenzenethiosulfonate, triethoxysilylmethyltolueneethiosulfonate, triethoxysilylmethylnaphthalenethiosulfonate, triethoxysilylmethylxylenethiosulfonate are mentioned, but not limited thereto. Mixtures of various blocked mercaptosilanes can be used. Further examples of blocked mercaptosilanes suitable for use in specific exemplary embodiments are those sold under the trade name NXT silane (3-octanoylthio-1-propyltriethoxysilane) by Momentive Performance Materials Inc.,

[0032] oil As suggested above, the vulcanizable composition can optionally contain oil. In one or more embodiments, the oil comprises an organic material having an absolute viscosity of less than 10,000 cP under standard conditions of temperature and pressure, less than 5,000 cP in other embodiments, and less than 2,500 cP in other embodiments. As is generally understood in the art, oil refers to a compound having a relatively low viscosity compared to other components of the vulcanizable composition such as resin. Exemplary oils include, but are not limited to, aromatic oils, paraffinic oils, naphthenic oils, vegetable oils (other than castor oil), low PCA oils (such as MES, TDAE, and SRAE), and heavy naphthenic oils. Suitable low PCA oils also include oils of various plant origins, such as those that can be obtained from vegetables, nuts, and seeds. Non-limiting examples include soy or soybean oil, sunflower oil, safflower oil, corn oil, linseed oil, cottonseed oil, rapeseed oil, cashew oil, sesame oil, camellia oil, jojoba oil, macadamia nut oil, coconut oil, and palm oil.

[0033] Solid resin As suggested above, the vulcanizable composition can contain resin. In one or more embodiments, the resin can be a solid having a Tg above 20 °C, above 30 °C in other embodiments, above 40 °C in other embodiments, and above 50 °C in other embodiments. Resins include, but are not limited to, alicyclic resins, aliphatic resins, aromatic resins, and hydrocarbon resins such as terpene resins, and further combinations thereof. Useful resins include styrene-alkylene block copolymers, thermoplastic resins such as C5-based resins, C5-C9-based resins, C9-based resins, terpene-based resins, terpene aromatic compound-based resins, rosin-based resins, dicyclopentadiene resins, alkylphenol-based resins, and partially hydrogenated resins thereof, but are not limited thereto.

[0034] Curing agent As suggested above, the rubber composition contains a curing agent. In one or more embodiments, the vulcanizable composition of the present invention includes a curing system. The curing system includes a curing agent, which may also be referred to as a crosslinking agent, a rubber curing agent, or a vulcanizing agent. The curing agent is described in Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 20, pgs. 365-468, (3 rd Ed. 1982), particularly, Vulcanization Agents and Auxiliary Materials, pgs. 390-402, and A.Y. Coran, Vulcanization, Encyclopedia of Polymer Science and Engineering, (2 nd Ed. 1989), which are incorporated herein by reference. In one or more embodiments, useful curing systems include sulfur or sulfur-based crosslinking agents, organic peroxide-based crosslinking agents, inorganic crosslinking agents, polyamine crosslinking agents, resin crosslinking agents, oxime-based and nitrosoamine-based crosslinking agents, and the like. Examples of suitable sulfur crosslinking agents include sulfur donors such as soluble sulfur of "rubber manufacturers", amine disulfides, polymeric polysulfides, or sulfur olefin adducts, and insoluble polymeric sulfur. In other embodiments, the crosslinking agent includes sulfur and / or sulfur-containing compounds. In other embodiments, the crosslinking agent excludes sulfur and / or sulfur-containing compounds. The vulcanizing agents may be used alone or in combination.

[0035] Other Components Other components typically used in rubber compounding can also be added to the rubber composition. These include accelerators, activator accelerators, addition plasticizers, waxes, scorch inhibitors, processing aids, zinc oxide, tackifying resins, reinforcing or curing resins, fatty acids (e.g., stearic acid), peptizing agents, and anti-degradants (e.g., antioxidants and anti-ozone agents).

[0036] Component Loading LMW Polydiene Additive In one or more embodiments, the rubber composition of the present invention contains a low molecular weight polydiene additive in an amount of more than 8 parts by weight (pbw) per hundred rubber (phr), in other embodiments more than 12 pbw, in other embodiments more than 14 pbw, and in other embodiments more than 16 pbw, based on 100 parts by weight of the rubber constituent, and the rubber constituent does not contain a low molecular weight polydiene additive. In these or other embodiments, the rubber composition contains a low molecular weight polydiene additive in an amount of less than 50 parts by weight (pbw) phr, in other embodiments less than 40 pbw, in other embodiments less than 35 pbw, and in other embodiments less than 30 pbw. In one or more embodiments, the rubber composition contains a low molecular weight polydiene additive in an amount of about 8 to about 50 phr, in other embodiments about 12 to about 40 phr, in other embodiments about 14 to about 35 phr, and in other embodiments about 16 to about 30 pbw.

[0037] Base rubber In one or more embodiments, the rubber composition of the present invention contains a base rubber in an amount of more than 25% by weight, in other embodiments more than 30% by weight, and in other embodiments more than 35% by weight, based on the total weight of the composition. In these or other embodiments, the rubber composition contains a base rubber in an amount of less than 80% by weight, in other embodiments less than 70% by weight, and in other embodiments less than 60% by weight, based on the total weight of the rubber composition. In one or more embodiments, the rubber composition contains a base rubber in an amount of about 25 to about 80% by weight, in other embodiments about 30 to about 70% by weight, and in other embodiments about 35 to about 60% by weight, based on the total weight of the rubber composition. Those skilled in the art will understand that the amount of rubber (as well as other components of the vulcanizate) corresponds to the amount of rubber and rubber additives contained in the vulcanizable composition.

[0038] In one or more embodiments, the base rubber comprises more than 5 wt%, in other embodiments more than 10 wt%, and in other embodiments more than 15 wt% natural rubber, based on the total weight of the base rubber. In these or other embodiments, the rubber comprises less than 40 wt%, in other embodiments less than 35 wt%, and in other embodiments less than 25 wt% natural rubber, based on the total weight of the base rubber. In one or more embodiments, the base rubber comprises from about 5 to about 40 wt%, in other embodiments from about 10 to about 35 wt%, and in other embodiments from about 15 to about 25 wt% natural rubber, based on the total weight of the base rubber. In one or more embodiments, the base rubber may be lacking or substantially lacking in natural rubber.

[0039] Oil In one or more embodiments, the rubber composition comprises more than 0 phr, in other embodiments more than 3 phr, and in other embodiments more than 5 pbw of oil and liquid plasticizer. In these or other embodiments, the rubber composition may comprise less than 20 phr, in other embodiments less than 15 phr, in other embodiments less than 10 phr, and in other embodiments less than 8 pbw of oil. In one or more embodiments, the vulcanizable composition may comprise from 0 to about 20 phr, in other embodiments from about 3 to about 15 phr, and in other embodiments from about 5 to about 8 pbw of oil. In certain embodiments, the vulcanizable composition is lacking in oil.

[0040] Solid resin In one or more embodiments, the rubber composition comprises more than 0 phr, in other embodiments more than 3 phr, and in other embodiments more than 5 pbw of solid plasticizer. In these or other embodiments, the rubber composition generally may comprise less than 20 phr, in other embodiments less than 15 phr, in other embodiments less than 10 phr, and in other embodiments less than 8 pbw of solid plasticizer. In one or more embodiments, the vulcanizable composition may comprise from 0 to about 20 phr, in other embodiments from about 3 to about 15 phr, and in other embodiments from about 5 to about 8 pbw of solid plasticizer. In certain embodiments, the vulcanizable composition does not contain a solid plasticizer.

[0041] Filler In one or more embodiments, the rubber formulation includes a filler such as carbon black or silica. In one or more embodiments, the rubber formulation includes more than 10 parts by weight (pbw) per 100 parts by weight (phr) of the base rubber, more than 35 pbw in other embodiments, and more than 55 pbw in other embodiments of a filler (e.g., carbon black and / or silica). In these or other embodiments, the rubber formulation includes less than 140 pbw phr, less than 95 pbw in other embodiments, and less than 75 pbw in other embodiments of a filler. In one or more embodiments, the rubber formulation includes from about 10 to about 200 pbw phr, from about 10 to about 140 pbw in other embodiments, from about 35 to about 95 pbw in other embodiments, from about 40 to about 130 pbw in other embodiments, from about 50 to about 120 pbw in other embodiments, and from about 55 to about 75 pbw in other embodiments of a filler (e.g., carbon black and / or silica). Carbon black and silica can be used together at a silica to carbon black weight ratio of about 0.1:1 to about 30:1, about 0.5 to about 20:1 in other embodiments, and about 1:1 to about 10:1 in other embodiments.

[0042] In one or more embodiments where silica is used as the filler, the rubber formulation may include a silica coupling agent. In one or more embodiments, the rubber formulation may include more than 1 pbw phr, more than 2 pbw in other embodiments, and more than 3 pbw in other embodiments of a silica coupling agent. In these or other embodiments, the rubber formulation may include less than 40 pbw phr, less than 20 pbw in other embodiments, and less than 10 pbw in other embodiments of a silica coupling agent. In one or more embodiments, the rubber formulation includes from about 1 to about 40 pbw phr, from about 2 to about 20 pbw in other embodiments, from about 2.5 to about 15 pbw in other embodiments, and from about 3 to about 10 pbw in other embodiments of a silica coupling agent.

[0043] In these or other embodiments, the amount of the silica coupling agent can be defined relative to the weight of the silica. In one or more embodiments, the amount of the silica coupling agent introduced into the silica (either in situ or pre-reacted) is from about 1 to about 25 pbw, in other embodiments from about 2 to about 20 pbw, and in other embodiments from about 3 to about 15 pbw of the silica coupling agent per 100 parts by weight of the silica.

[0044] Vulcanizing agent One skilled in the art will be able to readily select the amount of the vulcanizing agent to achieve the desired level of cure. In certain embodiments, sulfur is used as the curing agent. In one or more embodiments, the vulcanizable composition may contain more than 0.5 phr, in other embodiments more than 1 phr, and in other embodiments more than 2 pbw of sulfur. In these or other embodiments, the vulcanizable composition may generally contain less than 10 phr, in other embodiments less than 7 phr, and in other embodiments less than 5 pbw of sulfur. In one or more embodiments, the vulcanizable composition may generally contain from about 0.5 to about 10 phr, in other embodiments from about 1 to about 6 phr, and in other embodiments from about 2 to about 4 pbw of sulfur.

[0045] Preparation of vulcanizate In one or more embodiments, the vulcanizate is prepared by vulcanizing a vulcanizable composition comprising an elastomeric polymer and a low molecular weight polydiene additive as defined herein. The vulcanizable composition is otherwise prepared using conventional mixing techniques. The vulcanizable composition is then formed into a green vulcanizate, which is then subjected to conditions that bring about curing (i.e., crosslinking) of the polymer network. For example, all components of the vulcanizable composition can be mixed in standard mixing equipment such as a Banbury or Brabender mixer, an extruder, a kneader, and a two-roll mill. In one or more embodiments, this may include a multi-step mixing procedure in which the components are introduced and / or mixed in two or more steps. For example, in a first step (often referred to as the masterbatch mixing step), an elastomer (including the functionalized polymer of the present invention), a filler, and any optional components are mixed. In one or more embodiments, when a silica functionalizing agent according to the present invention (i.e., including a hydrogen bonding functional group) is included in the vulcanizable composition, the silica functionalizing agent is added in one or more masterbatch steps. Similarly, when a silica coupling agent (i.e., a conventional type of silica coupling agent) is used alone or in combination with the silica functionalizing agent, it may also be added during one or more masterbatch steps. Generally speaking, the masterbatch mixing step includes the step of adding components and carrying out the mixing conditions with energy exceeding the energy that burns the composition in the presence of a curing agent (e.g., temperature and shear). Similarly, the remill mixing step is carried out with the same or similar energy, except that the components are not added during the remill mixing step. The energy imparted to the vulcanizable composition during masterbatch or remill mixing is considered sufficient to disperse the filler and cause hydrolysis and subsequent condensation of the hydrolyzable groups. For example, during one or more of these mixing steps, it is considered that the hydrolyzable groups of the silica functionalizing agent are hydrolyzed and then bound to the silica particles via a condensation reaction. For this purpose, in one or more embodiments, the masterbatch or remill mixing can be carried out in the presence of a catalyst that helps to promote the reaction between the hydrolyzable group and the silica (e.g., between the silica functionalizing agent and the silica, or between the silica coupling agent and the silica).These catalysts are generally known in the art and include, for example, strong bases such as alkali metal alkoxides such as sodium or potassium alkoxides, guanidines such as triphenylguanidine, diphenylguanidine, di-o-tolylguanidine, N,N,N',N'-tetramethylguanidine, and hindered amine bases such as 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]nona-5-ene, tertiary amine catalysts such as N,N-dimethylcyclohexylamine, triethylenediamine, triethylamine, quaternary ammonium bases such as tetrabutylammonium hydroxide, and bisaminoethers such as bis(dimethylaminoethyl)ether, but are not limited thereto.

[0046] Accordingly, the masterbatch and remill mixing are carried out in the absence of the curing agent and proceed at a temperature at which curing would occur if the curing agent were present. For example, this mixing can be carried out at a temperature above 120°C, in other embodiments above 130°C, in other embodiments above 140°C, and in other embodiments above 150°C.

[0047] In one or more embodiments, the low molecular weight additive can be introduced into the rubber formulation together with the other masterbatch components. In other embodiments, the low molecular weight additive can be introduced into the rubber formulation alone or together with the other remill components after masterbatch mixing. In other embodiments, a portion of the low molecular weight additive can be introduced into the rubber formulation together with the masterbatch components and a portion can be introduced after masterbatch mixing (e.g., as part of the remill).

[0048] Once the masterbatch is prepared, at the final mixing stage, a vulcanizing agent may be introduced into and mixed with the masterbatch. This final mixing stage is typically carried out at a relatively low temperature, thereby reducing the possibility that the vulcanization timing becomes too early. For example, this mixing may be carried out at a temperature of less than 120°C, in other embodiments less than 110°C, and in other embodiments less than 100°C. It is also possible to employ an additional mixing stage, sometimes called remill, between the masterbatch mixing stage and the final mixing stage.

[0049] During the curing process, covalent bonds are formed between polymer chains and optionally between one or more of the other components of the rubber formulation. In one or more embodiments, a sulfur-based curing system is utilized. With respect to the low molecular weight polydiene additive, covalent bonds (i.e., crosslinks) can be formed between the base polymer and the low molecular weight polydiene additive.

[0050] Industrial Applicability The vulcanizate of the present invention is useful in tire components. This can include use in tire treads, sidewalls, body plies, inner liners, bead fillers, and wear strips. This vulcanizable composition can be processed into tire parts according to conventional tire manufacturing techniques, including standard rubber forming, molding, and curing techniques.

[0051] To demonstrate the practice of the present invention, the following examples were prepared and tested. However, these examples should not be regarded as limiting the scope of the present invention. The claims define the present invention.

Examples

[0052] Experimental Section Using the rubber formulations and mixing sequences provided in Table I, a vulcanizable composition was prepared. This rubber formulation was shown to be a rubber formulation useful for the production of tire treads. As shown in Table I, the mixing procedure was a three-step mixing procedure including a masterbatch mixing step, a "remill mixing step", and a final mixing step. The various mixing steps were carried out in a Banbury mixer. During the preparation of the masterbatch, the mixer was operated at 75 rpm and the composition reached a peak temperature of 160 °C. At that point, the composition was dropped from the mixer and cooled to below about 85 °C. At this point, the composition was reintroduced into the mixer together with the components specified for the "remill stage" and mixing was continued at 75 rpm to achieve a composition peak temperature of about 160 °C. The composition was dropped from the mixer again and cooled to a temperature below about 50 °C. Next, the composition was reintroduced into the mixer again together with the components specified for the "final mixing stage".

[0053] As is apparent from Table I, the amounts of the oils and low molecular weight polydiene additives listed as variables changed in the various samples. It should also be understood that the oils and low molecular weight polydiene additives were included in at least some of the samples in both the masterbatch and remill steps. The exact amounts used in each sample are provided in Table II along with the results of the mechanical and dynamic tests performed on the rubber formulation or the resulting vulcanizates.

[0054]

Table 1

[0055] Regarding the data in Table II, rheometer measurements were performed using an MDR2000 operating at the temperatures specified in the table. The tensile mechanical properties of the vulcanizates (e.g., maximum stress, modulus of elasticity, elongation, and toughness) were measured by using the standard procedures described in ASTM-D412. The dynamic rheological properties of the vulcanizates (e.g., tan δ) were obtained from temperature sweep studies performed over a range of about -80 °C to about 80 °C and 10 Hz, and strain sweep studies performed in 0.25% increments over a range of 0.05 to about 7.5% strain.

[0056] Also, it should be understood that the base rubber constituent contained 20 parts by weight of natural rubber and 80 parts by weight of synthetic rubber. The type of synthetic rubber used was varied across the entire sample as shown in Table II. SBR I was a poly(styrene-co-butadiene) characterized by a Mn of about 545 kg / mol, a Mw of about 814 kg / mol, a Tg of about -34 °C, a vinyl content of about 60 mol%, and a bound styrene content of about 20 wt%. SBR II was a poly(styrene-co-butadiene) characterized by a Mn of about 199 kg / mol, a Mw of about 264 kg / mol, a Tg of about -40 °C, a vinyl content of about 26 mol%, and a bound styrene content of about 38 wt%. PB I was a poly(butadiene) characterized by a Mn of about 193 kg / mol, a Mw of about 204 kg / mol, a Tg of about -91 °C, and a vinyl content of about 15 mol%. PB II was a poly(butadiene) characterized by a Mn of about 206 kg / mol, a Mw of about 513 kg / mol, a Tg of about -109, and a vinyl content of about 1 mol%.

[0057] Furthermore, the LMW polyene additive used in these samples contained a poly(styrene-co-butadiene) random copolymer characterized by a Mn of 92.5 kg / mol, a Mw of 102.1 kg / mol, a bound styrene of 38.3 wt%, a vinyl content of 54.3 mol% (in the butadiene portion), and a Tg of -1.5 °C.

[0058]

Table 2

[0059] Various modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the invention. The invention is not formally limited to the exemplary embodiments described herein.

Claims

1. A vulcanizable composition comprising: (i) a base rubber component; (ii) a low molecular weight polydiene additive, wherein the low molecular weight polydiene additive has a Mn of less than 100 kg / mol, a Mw of less than 110 kg / mol, a Tg above -30 °C, and a vinyl content of more than 35 mol% based on the diene monomer units; (iii) a filler; (iv) a curing agent;

2. The vulcanizable composition according to claim 1, wherein the base rubber component contains about 5 to about 40% by weight of natural rubber based on the total weight of the base rubber component, and the balance contains a synthetic elastomer.

3. The vulcanizable composition according to claim 1 or 2, wherein the vulcanizable composition contains about 25 to about 80% by weight of a base rubber component based on the total weight of the composition.

4. The vulcanizable composition according to any one of claims 1 to 3, wherein the base rubber component contains a synthetic elastomer, and the synthetic elastomer is characterized by a Mn above 110 kg / mol.

5. The vulcanizable composition according to any one of claims 1 to 4, wherein the synthetic elastomer of the base rubber component is characterized by a Mw above 120 kg / mol.

6. The vulcanizable composition according to any one of claims 1 to 5, wherein the synthetic elastomer of the base rubber component is characterized by a Tg below -20 °C.

7. The vulcanizable composition according to any one of claims 1 to 6, wherein the synthetic elastomer of the base rubber component is selected from the group consisting of polybutadiene, poly(styrene-co-butadiene), polyisoprene, poly(styrene-co-isoprene), poly(styrene-co-isoprene-butadiene), or a functionalized derivative thereof.

8. The vulcanizable composition according to any one of claims 1 to 7, wherein the filler contains silica.

9. The vulcanizable composition according to any one of claims 1 to 8, wherein the low molecular weight polydiene additive is further characterized by a bound styrene content of more than 20% by weight.

10. The vulcanizable composition according to any one of claims 1 to 9, wherein the low molecular weight polydiene copolymer is selected from the group consisting of poly(styrene-co-butadiene), poly(styrene-co-isoprene-co-butadiene), and poly(styrene-co-isoprene).

11. The vulcanizable composition according to any one of claims 1 to 10, wherein the vulcanizable composition contains about 8 to about 50 parts by weight of the low molecular weight polydiene additive per 100 parts by weight of the base rubber.

12. The vulcanizable composition according to any one of claims 1 to 11, wherein the vulcanizable composition further contains oil.

13. The vulcanizable composition according to any one of claims 1 to 12, wherein the vulcanizable composition contains less than 20 parts by weight of oil per 100 parts by weight of the base rubber.

14. The vulcanizable composition according to any one of claims 1 to 13, wherein the vulcanizable composition contains about 10 to about 200 parts by weight of a filler per 100 parts by weight of the base rubber.

15. The vulcanizable composition according to any one of claims 1 to 14, wherein the vulcanizable composition contains a resin.

16. The vulcanizable composition according to any one of claims 1 to 15, wherein the vulcanizable composition contains less than 20 parts by weight of the resin per 100 parts by weight of the base rubber.

17. The vulcanizable composition according to any one of claims 1 to 16, wherein the curing agent contains sulfur.

18. A vulcanizate prepared by subjecting the vulcanizable composition according to any one of claims 1 to 17 to curing conditions.

19. A method for preparing a vulcanizate, the method comprising subjecting the vulcanizable composition according to any one of claims 1 to 18 to curing conditions.

20. The method according to any one of claims 1 to 19, wherein the method further comprises forming the vulcanizable composition into a green tire tread.

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