BR102024006182A2 - RUBBER COMPOSITION AND ARTICLE - Google Patents

Abstract

The present invention relates, according to one aspect of the exemplary embodiment, to a rubber composition that includes at least 20 phr of a compound material, at least 3 phr of a conjugated diene elastomer, a cure activator, and a sulfur-based curing agent. The compound material includes a reinforcing carbon black dispersed in natural rubber. The compound material and the conjugated diene elastomer together provide at least 90 phr of vulcanizable elastomers in the rubber composition. The rubber composition may further include a reinforcing filler other than carbon black. The reinforcing filler may include silica. The rubber composition may include at least 5 phr, or at least 8 phr of silica, or up to 30 phr, or up to 18 phr of silica.

Description

FUNDAMENTALS OF THE INVENTION

[001] Aspects of the exemplary embodiment relate to compositions suitable for use in a variety of tire components, such as in a tire tread, base, and in wire casings, and in particular to compositions incorporating a preformed natural rubber compound with carbon black in addition to natural rubber in conventional form.

[002] Tire treads are commonly formed from natural rubber or other elastomers that are blended with various additives, such as fillers and curing aids, prior to the addition of a sulfur-based curing agent, such as elemental sulfur. These compounding ingredients are often selected to improve performance indicators related to tread wear and tire mileage. There is often a trade-off between improvements in tread wear and mileage and other parameters, such as tear and rolling resistance.

[003] U.S. Patent No. 8,536,262B2 describes a rubber inner layer of a tire tread formed from a rubber including a minor amount of syndiotactic 1,2-polybutadiene and a major amount of at least one of a polymer or copolymer of isoprene and/or 1,3-butadiene and a copolymer of styrene and isoprene and/or 1,3-butadiene. The composition further includes a mixture of rubber-reinforced carbon black fillers having iodine absorption values (ASTM D2515) of about 20 to about 50 g/kg and 100 to about 300 g/kg, respectively. The rubber inner layer of the tread is positioned between the tire cap and the carcass and is designed to promote tire handling while substantially maintaining the hysteresis property of the rubber, reducing the tendency for internal heat to build up during tire service. While beneficial, adding an extra tread layer can increase the cost or construction time of the tire.

[004] Recently, elastomeric composite materials containing natural rubber latex and carbon black have been developed for use in tire compositions, as described, for example, in Patent Nos. 9,156,955B2 and 10,767,028B2. The compounds can be compounded with a curing agent and other additives to produce a composition suitable for forming a tire tread, for example. However, such compounds tend to provide a limited range of properties.

[005] There remains a need for rubber compositions formed from compounds that can maintain the rolling resistance and tear properties of tires formed from the cured compositions without unduly impacting tread wear.

SUMMARY OF THE INVENTION

[006] According to one aspect of the exemplary embodiment, a rubber composition includes at least 20 phr of a compound material, at least 3 phr of a conjugated diene elastomer, a cure activator, and a sulfur-based curing agent. The compound material includes a reinforcing carbon black dispersed in natural rubber. The compound material and the conjugated diene elastomer together provide at least 90 phr of vulcanizable elastomers in the rubber composition.

[007] The rubber composition may further include a reinforcing filler other than carbon black. The reinforcing filler may include silica. The rubber composition may include at least 5 phr, or at least 8 phr of silica, or up to 30 phr, or up to 18 phr of silica.

[008] The compound material may provide to the rubber composition at least 20 phr of the reinforcing carbon black, or at least 30 phr, or up to 80 phr, or up to 55 phr of the reinforcing carbon black. The compound material may provide to the rubber composition at least 50 phr of the natural rubber, or at least 70 phr, or up to 95 phr, or up to 90 phr of the natural rubber. The compound material may be a solid at 21°C and atmospheric pressure.

[009] The conjugated diene elastomer may include at least one of natural rubber and synthetic polyisoprene. The rubber composition may include at least 5 phr of the conjugated diene elastomer, or at least 10 phr, or up to 50 phr, or up to 30 phr of the conjugated diene elastomer.

[010] The cure activator may be selected from the group consisting of fatty acids, zinc oxide and mixtures thereof.

[011] The rubber composition may further include at least 0.1 phr of at least one processing aid selected from the group consisting of a resin, an oil and mixtures thereof.

[012] The rubber composition may further include at least 1 phr of at least one of an antioxidant and an antiozonant and/or at least 0.5 phr of a cure accelerator and/or at least 0.05 phr of a cure retarder.

[013] The composite material and the conjugated diene elastomer can together provide at least 98 phr of the vulcanizable elastomers in the rubber composition.

[014] In another aspect of the exemplary embodiment, an article is formed from the rubber composition in any of the aspects described above. The article may include a tire tread.

[015] In another aspect of the exemplary embodiment, a method of forming a rubber composition includes mixing a composite material with a conjugated diene elastomer at a temperature of at least 115°C to form a mixture. The composite material includes a reinforcing carbon black dispersed in natural rubber. The composite material and the conjugated diene elastomer together provide at least 90 phr of a total of 100 phr of vulcanizable elastomers. The mixture is mixed with a sulfur-based curing agent to form the rubber composition.

[016] In the method, the mixture may also include silica.

[017] The method may further include curing the rubber composition to form a molded article.

DETAILED DESCRIPTION

[018] Aspects of the exemplary embodiment relate to a rubber composition suitable for use in forming a molded or extruded article, and to an article formed from the composition, such as a tire tread. The composition includes a preformed composite material, a conjugated diene-based elastomer, a reinforcing filler such as silica, a sulfur-based curing agent, and optionally one or more of processing aids such as oils and waxes, coupling agents, antioxidants, antiozonants, other components of a sulfur-based cure package such as cure activators, cure accelerators, and cure retarders, and other additives known in the art.

[019] The exemplary composite material includes natural rubber and carbon black as the main components. The combination of the composite material and the separate conjugated diene-based rubber results in a cured rubber composition with a multiphase morphology in which the carbon black is heterogeneously dispersed in the rubber composition, which provides good rolling resistance and tire tear properties without unduly impacting tread wear.

[020] In the description of this invention, the term "phr" refers to parts of a respective material per 100 parts by weight of rubber or elastomer. The term "phf" refers to parts per hundred loads, by weight. By convention, the uncured rubber employed in the sealant composition totals 100 phr.

[021] The terms “rubber” and “elastomer” may be used interchangeably unless otherwise indicated. The terms “cure” and “vulcanize” may be used interchangeably unless otherwise indicated.

[022] As used herein, Mooney viscosity (ML 1+4) is measured in M.U. at 100°C in accordance with ASTM D1646-19a, “Standard Test Methods for Rubber—Viscosity, Stress Relaxation, and Prevulcanization (Mooney Viscometer).”

[023] The glass transition temperature (Tg) of an elastomer or elastomer composition, when referred to herein, represents the glass transition temperature(s) of the respective elastomer or elastomer composition in its uncured state or possibly a cured state in the case of an elastomer composition. The Tg values referred to herein are determined as a peak midpoint by a differential scanning calorimeter (DSC) at a temperature rise rate of 10°C per minute in accordance with ASTM D3418-21, “Standard Test Method for Transition Temperatures and Enthalpies of Melting and Crystallization of Polymers by Differential Scanning Calorimetry.”

The composite material

[024] The composite material includes natural rubber and a reinforcing carbon black, which is dispersed in the natural rubber. In one embodiment, natural rubber and carbon black together constitute at least 90 wt. %, or at least 95 wt. %, or at least 98 wt. %, or up to 100 wt. % of the composite material.

[025] In one embodiment, the composite material has a Mooney viscosity of not more than 100 M.U., or not more than 85 M.U., or at least 60 M.U. The composite material may be a solid or a liquid that is pourable at room temperature (21°C) and atmospheric pressure. In another embodiment, the composite material may be a solid material at room temperature, for example in the form of strips or crumbs.

[026] The composite material is non-vulcanized and is free of sulfur-based curing agents and organoperoxide curing agents. The composite material may also be free of reinforcing fillers other than carbon black and free of cure accelerators, cure activators and cure retarders, examples of which are mentioned below.

[027] The compound material may be used in the rubber composition in an amount of at least 20 phr, or at least 30 phr, or at least 50 phr, or at least 80 phr, or at least 100 phr, or up to 160 phr, or up to 150 phr, or up to 140 phr. The elastomer (primarily natural rubber) content in the compound material contributes to the total 100 phr of elastomers in the rubber composition. Consequently, the maximum phr of the compound material in the rubber composition depends, at least in part, on its rubber content. For example, the composite material may provide at least 10 phr, or at least 20 phr, or at least 50 phr, or at least 60 phr, or at least 70 phr, or at least 80 phr, or up to 95 phr, or up to 90 phr of the total elastomers in the rubber composition.

[028] The composite material may contribute at least 10 phr, or at least 15 phr, or at least 20 phr, or at least 30 phr, or at least 40 phr, or up to 80 phr, or up to 60 phr, or up to 50 phr of carbon black to the rubber composition.

[029] A ratio of carbon black to natural rubber in the composite material, by weight, may be at least 20:80, or at least 30:70, or up to 50:50, or up to 40:60, such as about 35:65.

[030] The carbon black in the composite material may be a single reinforcing carbon black or may include two or more different types of carbon black.

[031] Carbon blacks useful in the composite material may have a nitrogen surface area (NSA) of 15 m2/g to 300 m2/g, or at least 40 m2/g, as determined in accordance with ASTM D6556-21, “Standard Test Method for Carbon Black - Total and External Surface Area by Nitrogen Adsorption.” Exemplary carbon blacks include ASTM designations N110, N121, N134, N220, N231, N234, N242, N293, N299, N315, N326, N330, N332, N339, N343, N347, N351, N358, N375, N539, N550, N582, N630, N642, N650, N683, N754, N762, N765, N774, N787, N907, N908, N990, and N991, as specified by ASTM D1765-21, “Standard Classification System for Carbon Blacks used in Rubber Products.”

[032] Blends of two or more forms of carbon black may be employed. An example of a composite material suitable for use herein that includes two types of carbon black is described in U.S. Patent No. 10,767,028B2. Other composite materials containing different carbon blacks are described in U.S. Publication No. 20100071817 A1.

[033] In one embodiment, the carbon black is pretreated prior to formation of the composite material, for example, with silicon. An example of a silicon-treated carbon black is available from Cabot Corporation as CRX™ 2000 ECOBLACK®.

[034] Exemplary composite materials including carbon black and natural rubber are available from Cabot Corporation as Engineered Elastomer Composites (E2C™), such as E2C™ DX9620 and E2C™ DX9640. E2C™ DX9620 has a Mooney Viscosity ML(1+4) at 100°C of about 69 M.U., a 300% modulus of about 17.0 MPa, a tensile strength of about 29.8 MPa, an elongation at break of about 528%, and a tan δ at 60°C of about 0.130. E2C™ DX9640 has a Mooney viscosity of about 84 M.U., a 300% modulus of about 18.5 MPa, a tensile strength of about 30.1 MPa, an elongation at break of about 473% and a tan δ at 60°C of about 0.15.

[035] When two or more forms of carbon are used, a first of the carbon blacks in the composite may have been heat treated at a temperature between 1100°C and 1800°C to provide a more crystalline structure than the second carbon black. The partially crystallized first carbon black may have an OAN structure of 120 cm3/100 g to 200 cm3/100 g, as determined in accordance with ASTM D2414-22, “Standard Test Method for Carbon Black—Oil Absorption Number (OAN),” and a Raman microcrystalline planar size (La) of 25 A to 50 A, as determined using the method of Gruber et al., “Raman Studies of Heat-Treated Carbon Blacks,” Carbon, Vol. 32 (7), pp. 1377–1382 (1994).

[036] In a specific embodiment, the carbon black has an external surface area, as measured by STSA, of at least 95 m2/g and a dibutyl phthalate adsorption of greater than 80 mL/100 g, and the composite material includes at least 65 phr of the carbon black. In another specific embodiment, the carbon black has a surface area of at least 75 m2/g as measured by STSA and a dibutyl phthalate adsorption of greater than 60 mL/100 g, and the composite material includes at least 70 phr of the carbon black. In another specific embodiment, the carbon black is present in the composite material in an amount that meets L^- 0.26*S+94, where L is the amount of carbon black in the composite material in phr and S is the surface area of the carbon black in m2/g as measured by STSA. These and other suitable composite materials are described, for example, in U.S. Publication No. 20150105491 A1.

[037] Although the composite material may consist essentially of carbon black and natural rubber (e.g., these two materials are at least 95 wt. %, or at least 98 wt. %, or up to 100 wt. % of the composite material, in total), it is also contemplated that the composite material may include other components. For example, in one embodiment, from 2 to 25 wt. %, or up to 15 wt. %, or up to 8 wt. %, of the composite may be composed of other rubber-forming elastomers. These other elastomers may include other conjugated diene elastomers, such as synthetic cis-1,4-polyisoprene, polybutadienes, butadiene copolymers, isoprene copolymers, and blends of these elastomers. Suitable copolymers may be selected from the group consisting of butadiene/styrene copolymers, isoprene/butadiene copolymers, isoprene/styrene copolymers, and isoprene/butadiene/styrene copolymers.

[038] The composite material may be formed by mixing carbon black with natural rubber for a sufficient time at a suitable temperature (e.g., at least 100°C, or at least 120°C), to obtain a highly dispersed mixture. In one embodiment, carbon black is added to natural rubber as a paste and the mixture is coagulated using a coagulant, such as an acid. One such method is described in Patent No. 9,156,955 B2. The paste may be formed by mixing carbon black and water, which may be ground to improve dispersion, as described, for example, in Publication No. 20150105491 A1. The Conjugated Diene-Based Elastomer

[039] The conjugated diene-based elastomer (which is not part of the compound material) may be present in the rubber composition in an amount of at least 3 phr, or at least 5 phr, or at least 6 phr, or at least 8 phr, or at least 10 phr, or at least 12 phr, and/or up to 90 phr, or up to 80 phr, or up to 60 phr, or up to 40 phr, or up to 30 phr, or up to 20 phr, or up to 16 phr, such as in a range of 10 to 30 phr.

[040] In one embodiment, a weight ratio of the conjugated diene-based elastomer to the natural rubber present in the composite material is at least 5:95, or at least 6:94, or at least 10:90, or at least at least 12:88, or up to 30:70, or up to 25:75, or up to 20:80.

[041] The conjugated diene-based elastomer consists of one or more elastomers derived solely or predominantly (e.g., at least 60 wt. %, or at least 90 wt. %, or at least 95 wt. %) from a conjugated diene. For example, the conjugated diene-based elastomer may be selected from natural rubber, synthetic polyisoprene, polybutadiene, and blends and copolymers thereof. All such elastomers include a double bond in each monomer unit.

[042] Natural rubber is derived predominantly from isoprene (2-methyl-1,3-butadiene) and is therefore predominantly (e.g., at least 99% by weight) polyisoprene. As used herein, the term “natural rubber” means naturally occurring rubber, such as may be harvested from sources such as Hevea rubber trees and non-Hevea sources (e.g., guayule bushes and dandelions, such as TKS). In other words, the term “natural rubber” should be construed to exclude synthetic polyisoprene rubber. Natural rubber produced from the cuplump of the Brazilian Hevea tree is a common form of natural rubber. For example, technically specified or lump rubber (TSR), is a natural rubber available in Indonesia, where it may be referred to as Standard Indonesian Rubber (SIR), Malaysia (as SMR), and Thailand (as STR). It can be obtained in several grades, including TSR 10 and TSR 20, with TSR 10 being the purest grade.

[043] In one embodiment, the conjugated diene-based elastomer is at least 60 wt % natural rubber, or at least 80 wt %, or at least 90 wt %, or at least 95 wt %, or up to 100 wt % natural rubber.

[044] In some embodiments, synthetic polyisoprene, in particular, cis-1,4-polyisoprene having a cis content of at least 94 wt % or at least 96 wt %, can be used in the conjugated diene-based elastomer. The Tg of the synthetic polyisoprene can be in the range of -60°C to -70°C. In one embodiment, a blend of synthetic polyisoprene and natural rubber is used as the conjugated diene-based elastomer.

[045] Other conjugated diene-based elastomers that may optionally be present in lesser amounts (e.g., totaling up to 10 phr, or up to 5 phr, or up to 2 phr) may include one or more of butadiene rubber (BR), isoprene-isobutylene copolymer, and halobutyl rubber, e.g., bromobutyl rubber and chlorobutyl rubber.

Other Vulcanizable Elastomers

[046] In addition to the natural rubber present in the composite material and the conjugated diene-based elastomer, other vulcanizable elastomers may be present in the rubber composition in smaller amounts (e.g., totaling up to 10 phr, or up to 5 phr, or up to 2 phr), and may be selected from nitrile rubber, liquid rubbers, polynorbornene copolymer, ethylene-propylene-diene rubber, chloroprene rubber, acrylate rubber, fluorine rubber, silicone rubber, polysulfide rubber, epichlorohydrin rubber, styrene-isoprene-butadiene terpolymer thermopolymer rubber, hydrated acrylonitrile butadiene rubber, isoprene-butadiene copolymer, butyl rubber, hydrogenated styrene-butadiene rubber, acrylonitrile butadiene rubber, a terpolymer formed from ethylene monomers, propylene monomers and/or ethylene propylene diene monomer (EPDM), isoprene-based block copolymers, butadiene-based block copolymers, styrene block copolymers, styrene-butadiene-styrene block copolymer (SBS), styrene-ethylene/butylene-styrene block copolymer (SEBS), styrene-[ethylene-(ethylene/propylene)]-styrene block copolymer (SEEPS), styrene-isoprene-styrene block copolymer (SIS), random styrenic copolymers, hydrogenated styrene block copolymers, styrene butadiene copolymers, polyisobutylene, ethylene vinyl acetate (EVA) polymers, polyolefins, amorphous polyolefins, semicrystalline polyolefins, alpha-polyolefins, reactor-ready polyolefins, acrylates, polymers and metallocene catalyzed polyolefin elastomers, reactor-made thermoplastic polyolefin elastomers, olefin block copolymer, copolyester block copolymer, polyurethane block copolymer, polyamide block copolymer, thermoplastic polyolefins, thermoplastic vulcanizates, ethylene vinyl acetate copolymer, ethylene n-butyl acrylate copolymer, ethylene methyl acrylate copolymer, neoprene, acrylics, urethane, poly(acrylate), ethylene acrylic acid copolymer, polyether ether ketone, polyamide, atactic polypropylene, polyethylene including atactic polypropylene, ethylene-propylene polymers, propylene-hexene polymers, ethylene-butene polymers, ethylene-octene polymers, propylene-butene polymers, propylene-octene polymers, polymers metallocene-catalyzed polypropylene polymers, metallocene-catalyzed polyethylene polymers, ethylene-propylene-butylene terpolymers, copolymers made from propylene, ethylene, C4-C10 alpha-olefin monomers, polypropylene polymers, maleated polyolefins, polyester copolymers, copolyester polymers, ethylene acrylic acid copolymer, and/or polyvinyl acetate, and/or wherein the polymer optionally comprises a modification and/or functionalization selected from one or more of hydroxyl-, ethoxy-, epoxy-, siloxane-, amine-, aminosiloxane-, carboxy-, phthalocyanine-, and silane-sulfide groups, at the ends of the polymer chain or at pendant positions within the polymer, and mixtures thereof.

[047] In one embodiment, the rubber composition is free of other vulcanizable elastomers.

Reinforcement Fillers

[048] One or more reinforcing fillers, other than the carbon black found in the composite material, may be present in the rubber composition. Examples of such reinforcing fillers include silica, calcium carbonate (CaCO3), titanium dioxide, hydrated aluminum silicate clay, 2:1 layered silicate clay and organoclay formed therefrom, calcium silicate, graphite, graphene, carbon nanotubes, wollastonite, talc, diatomaceous earth, starch, lignin, alumina, other carbon black, for example, other than the carbon black present in the composite material, and mixtures thereof.

[049] The reinforcing filler(s) may be present in the rubber composition from 0 to 150 phr, such as at least 2 phr, or at least 4 phr, or at least 6 phr, or at least 8 phr, or more to 100 phr, or up to 80 phr, or up to 50 phr, or up to 20 phr, or up to 15 phr, up to 10 phr, such as 5 to 15 phr.

[050] In one embodiment, the reinforcing filler includes or consists of silica particles, such as amorphous (e.g., precipitated) silica and/or crystalline silica. The term “silica” is used herein to refer to silicon dioxide, SiO2 (which may contain small amounts of impurities, generally less than 1 wt. %, resulting from the process in which the silica is formed). The term “precipitated silica” is used to refer to synthetic amorphous silica, typically obtained by a process in which a silicate is precipitated with an acidifying agent.

[051] Silica may be present in the rubber composition in an amount of at least 2 phr, or at least 4 phr, or at least 6 phr, or at least 8 phr, or up to 100 phr, or up to 80 phr, or up to 50 phr, or up to 20 phr, or up to 18 phr, or up to 15 phr, up to 10 phr, such as from 5 to 15 phr.

[052] Silica can be prepared by several methods. Precipitated silica can be prepared by digesting amorphous silica, for example found in rice husks or other biological waste, with sodium hydroxide to form sodium silicate and precipitating the silica from the sodium silicate by reaction with an acidifying agent such as sulfuric acid or carbon dioxide. The resulting silica precipitate is washed and filtered. Methods for preparing precipitated silica are disclosed, for example, in Patent Nos. 5,587,416 A, 5,800,608 A, 5,882,617 A, and 9,359,215 B2 and Publication Nos. 20020081247 A1 and 20050032965 A1. Precipitated silica can also be formed from silica gel, as described, for example, in Patent Nos. 5,708,069, 7,550,610, and 5,789,514. Silica gels can be derived, for example, by hydrophobizing a silica hydrogel with, for example, an organo mercapto silane and alkyl silane and drying the product.

[053] Several methods are available for determining the surface area of silica. In ASTM test method D6845-20 “Standard Test Method for Silica, Precipitated, Hydrated—CTAB (Cetyltrimethylammonium Bromide) Surface Area,” the measurement of the specific surface area of silica excludes the area contained in micropores too small to admit CTAB molecules. This test method is suitable for characterizing rubbery silicas of all types.

[054] The silica used in the reinforcing filler may have a CTAB specific surface area, in accordance with ASTM D6845-20, of at least 120 m2/g, or at least 140 m2/g, or at least 220 m2/g, or at least 240 m2/g. The silica may have a CTAB specific surface area of up to 500 m2/g, or up to 400 m2/g, or up to 300 m2/g.

[055] Examples of precipitated silicas suitable for use herein include Hi-Sil™ 532, Hi-Sil™ 532 EP, and Hi-Sil™ EZ 160G from PPG Industries; Hubersil™ 4155 from J. M. Huber Company; Zeosil™ under the designations 115GR, 125GR, 165GR, 175GR, 185GR, 195GR, 1085GR, 1165MP, 1115MP, HRS 1200MP, Premium MP, Premium 200MP, Premium SW, and 195HR from Solvay; Ultrasil™ under the designations VN2, VN3, VN3GR, 5000GR, 6000GR, 7000GR, and 9000GR from Evonik; Zeopol™ under the designations 8755LS and 8745 from Evonik; Newsil™ under the designations 115GR and 2000MP from Wuxi Quechen Silicon Chemical Co., Ltd; and Tokusil™ 315 from Maruo Calcium Co., Ltd, and mixtures thereof.

[056] In one embodiment, the silica is present in the rubber composition at 1 phr or more, such as at least 2 phr, or at least 5 phr, or at least 6 phr, or at least 7 phr, or up to 20 phr, or up to 18 phr, or up to 15 phr, or up to 14 phr, or up to 12 phr, or up to 10 phr. The silica can be at least 2 phr, or at least 4 phr, or at least 8 phr, or at least 12 phr, or up to 25 phr, or up to 20 phr, or up to 18 phr of the reinforcing fillers.

[057] In one embodiment, a ratio of silica to total elastomer (e.g., natural rubber), by weight, in the rubber composition is at least 4:100, or at least 6:100, and can be up to 20:100, or up to 15:100.

[058] In one embodiment, a ratio of silica to carbon black, by weight, in the rubber composition is at least 4:100, or at least 7:100, or at least 12:100, or at least 15:100 and can be up to 3:10 or up to 2:10.

[059] In one embodiment, the silica may have been surface treated, for example, with a coupling agent and/or a polyalkylene oxide, such as polyethylene glycol, prior to incorporation of the pretreated silica into the rubber composition. The pretreatment may serve to increase the dispersion and/or adhesion of the silica to the elastomers. In another embodiment, the silica may be treated in situ within the rubber composition, generally prior to addition of the curing agent, with a coupling agent and/or polyalkylene oxide.

[060] Polyalkylene glycols that can be used for silica pretreatment or in situ in the rubber composition include polyethylene glycol, polypropylene glycol, and mixtures thereof. In one embodiment, the polyalkylene oxide is polyethylene glycol. The polyalkylene oxide can have a weight average molecular weight Mw of at least 500, such as at least 2,000, or at least 4,000, or up to 15,000, or up to 12,000, or up to 10,000, or up to 8,500. The polyalkylene oxide can be absent from the rubber composition. In cases where polyalkylene oxide, for example polyethylene glycol, is used, it may be included in an amount of at least 0.1 phr, such as at least 0.2 phr, or at least 0.3 phr, or up to 5 phr, or up to 3 phr, or up to 2 phr, or up to 1 phr, or up to 0.6 phr.

[061] Examples of commercially available polyethylene glycols include Carbowax™ PEG 3350 and Carbowax™ PEG 8000 from Dow Chemical Company where the number indicates an approximate weight average molecular weight. Other polyalkylene oxide polymers may be used, as described, for example, in U.S. Pat. Nos. 6,322,811 and 4,082,703.

[062] Suitable coupling agents generally include a first moiety, which is reactive with hydroxyl groups (e.g., silanol groups) that are present on the surface of the precipitated silica, and a second moiety capable of reacting with a diene-based elastomer, such as exemplary natural rubber. The two moieties are connected by a linking group, e.g., a hydrocarbyl or sulfide bridge, such that the precipitated silica is chemically bonded to the elastomer. Examples of silica coupling agents include those containing groups such as alkyl, alkoxy, mercapto, blocked mercapto, sulfide-containing (e.g., monosulfide-based alkoxy-containing, disulfide-based alkoxy-containing, tetrasulfide-based alkoxy-containing), amino, vinyl, epoxy, and combinations thereof. The silica coupling agent may be present in an amount sufficient to provide a ratio of the total amount of coupling agent to silica filler of at least 0.1:100 or up to 1:5 by weight, for example a ratio of at least 1:100, or at least 1:50, or up to 1:20, or up to 1:10.

[063] Additional reinforcing fillers, in addition to silica and carbon black, may be used, for example, in total amounts of up to 30 phr, or up to 20 phr, or up to 10 phr, or up to 1 phr, or may be absent. Examples of such additional reinforcing fillers include alumina, aluminum hydroxide, clay (reinforcing grades), magnesium hydroxide, boron nitride, aluminum nitride, titanium dioxide, reinforcing zinc oxide, and combinations thereof.

[064] In one embodiment, the components of the rubber composition, other than natural rubber, carbon black and silica, are present in the rubber composition in a total amount of not more than 40 phr, or not more than 30 phr, or not more than 20 phr, or not more than 15 phr.

Processing Aids

[065] Processing aids may be used in the rubber composition in a total of 1 to 20.0 phr, or up to 10 phr, or up to 5 phr, and may include one or more of a resin and a liquid plasticizer, such as an oil.

[066] Examples of resins that can be used in rubber compounding include tacky resins such as unreactive phenol formaldehyde, and stiffening resins such as reactive phenol formaldehyde and resorcinol or resorcinol and hexamethylene tetramine resins, benzoxazine resins, hydrocarbon resins such as aromatic resins, aliphatic and cycloaliphatic resins.

[067] Example hydrocarbon resin may have a Tg of at least 30°C or as high as 50°C. The Tg of the hydrocarbon resin may be determined by DSC according to the procedure discussed above for elastomer Tg measurements. The hydrocarbon resin may have a softening point of at least 70°C or as high as 100°C. The softening point of a hydrocarbon resin is generally related to its Tg. The Tg is generally lower than its softening point, and the lower the Tg, the lower the softening point.

[068] Examples of aliphatic resins include C5 fraction homopolymer and copolymer resins. Examples of cycloaliphatic resins include cyclopentadiene homopolymer or copolymer (“CPD”) resins, dicyclopentadiene homopolymer or copolymer (“DCPD”) resins, and combinations thereof.

[069] Examples of aromatic resins include aromatic homopolymer resins and aromatic copolymer resins. An aromatic copolymer resin refers to a hydrocarbon resin comprising a combination of one or more aromatic monomers in combination with one or more other (non-aromatic) monomers, the majority by weight of all monomers being generally aromatic.

[070] Specific examples of aromatic resins include coumarone-indene resins, alkylphenol resins, and vinyl aromatic homopolymer or copolymer resins. Examples of alkylphenol resins include alkylphenol-acetylene resins, such as p-tert-butylphenol-acetylene resins, alkylphenol-formaldehyde resins (such as those having a low degree of polymerization). Aromatic vinyl resins may include one or more of the following monomers: alpha-methylstyrene, styrene, ortho-methylstyrene, meta-methylstyrene, para-methylstyrene, vinyltoluene, para(tert-butyl)styrene, methoxystyrene, chlorostyrene, hydroxystyrene, vinylmesitylene, divinylbenzene, vinylnaphthalene, and the like. Examples of vinyl aromatic copolymer resins include vinyl aromatic/terpene copolymer resins (e.g., limonene/styrene copolymer resins), vinyl aromatic/C5 fraction copolymer resins (e.g., C5 fraction/styrene copolymer resin), vinyl aromatic/aliphatic copolymer resins (e.g., CPD/styrene copolymer resin and DCPD/styrene copolymer resin).

[071] In the case of an aromatic resin based on one or more of the above-mentioned vinyl aromatic monomers (e.g., styrene, alpha-methylstyrene), at least at least 80 wt.%, or at least 85 wt.%, or at least 90 wt.%, or at least 95 wt.%, or up to 100 wt.% of the monomers in the aromatic resin may be aromatic monomers.

[072] Other aromatic resins include terpene resins such as alpha-pinene resins, beta-pinene resins, limonene resins (e.g., L-limonene, D-limonene, dipentene which is a racemic mixture of L- and D-isomers), beta-phellandrene, delta-3-carene, delta-2-carene, and combinations thereof.

[073] In one embodiment, the hydrocarbon resin includes a combination of aromatic and aliphatic/cycloaliphatic hydrocarbons. In such cases, the total amount of any aliphatic and/or cycloaliphatic resin used in combination with the aromatic resin may not be greater than 5 phr, or less than 4 phr, or less than 3 phr, or greater than 20 wt %, or no more than 15%, or no more than 10 wt % of the total amount of hydrocarbon resins).

[074] The aromatic resin may have a Mw of at least 1,000 grams/mol and/or up to 4,000 grams/mol.

[075] A total amount of resin in the rubber composition may be at least 1 phr, or at least 2 phr, or up to 20 phr, or up to 10 phr, or up to 5 phr, or may be absent.

[076] The term liquid plasticizer is used to refer to plasticizer ingredients that are liquid at room temperature (i.e., liquid at 25°C and above) and includes both oils and non-oils. Hydrocarbon resins, in contrast to liquid plasticizers, are generally solid at room temperature. Generally, liquid plasticizers will have a Tg below 0°C, often well below, such as below -30°C, or below -40°C, or below -50°C, such as a Tg of 0°C to -100°C.

[077] Suitable liquid plasticizers include oils (e.g., petroleum oils as well as vegetable oils) and non-petroleum liquid plasticizers such as ether plasticizers, ester plasticizers, phosphate plasticizers, and sulfonate plasticizers. The liquid plasticizer may be added during the compounding process or later as an extender oil (which is used to extend a rubber). Petroleum-based oils may include aromatic, naphthenic, low polycyclic aromatic (PCA) oils, and mixtures thereof. Vegetable oils may include oils harvested from vegetables, nuts, seeds, and mixtures thereof, such as triglycerides. The Tg of the oil or oils used may be -40°C to -100°C.

[078] When present, the rubber composition may include at least 1 phr of liquid plasticizer, or up to 20 phr, or up to 10 phr, or up to 5 phr of liquid plasticizer. In one embodiment, no liquid plasticizer is employed.

[079] In addition to one or more of the above processing aids, the rubber composition may include a peptizer, such as pentachlorothiophenol, dibenzamidodiphenyl disulfide, or a mixture thereof. Typical amounts of peptizer, if used, may be from 0.1 phr to 1 phr.

Antidegradants (Antioxidants, Antiozonants)

[080] The rubber composition may include one or more antidegradants, such as antiozonants and/or antioxidants. These compounds aid in protecting the tire against oxidation and ozonation. Representative antidegradants include amine-based antioxidants, such as monophenols, bisphenols, thiobisphenols, polyphenols, hindered polymeric phenols, hydroquinone derivatives, phosphites, phosphate mixtures, thioesters, naphthylamines, diphenolamines, as well as other diarylamine derivatives, para-phenylenediamines (PPDs), quinolines, and mixed amines. Exemplary amine-based antioxidants include diphenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), oligomerized 2,2,4-trimethyl-quinoline (TMQ), and others. , such as those disclosed in The Vanderbilt Rubber Handbook (1978), pages 344-347. The antioxidants may be at least 0.1 phr, or at least 0.3 phr, or at least 1 phr, or at least 2 phr, or up to 10 phr, or up to 5 phr of the rubber composition.

[081] Exemplary antiozonants include physical protectants such as waxes. Suitable waxes include paraffin waxes and microcrystalline waxes, which may be of the type described in The Vanderbilt Rubber Handbook (1978), pp. 346 and 347. The wax(s) may be present at 0.1 phr or more, such as at least 0.3 phr, or at least 0.5 phr, or up to 5 phr, or up to 2 phr.

Healing Package Vulcanizing agent

[082] The exemplary cure package includes a vulcanizing (curing) agent and one or more of a cure accelerator, a cure activator, and a cure inhibitor. The cure package may be used in the rubber composition at 0.5 to 20 phr, or at least 5 phr, or up to 10 phr.

[083] Vulcanization of the rubber composition may be conducted in the presence of a sulfur-based vulcanizing agent. Examples of suitable sulfur-based vulcanizing agents include elemental sulfur (free sulfur), insoluble polymeric sulfur, soluble sulfur, and sulfur-donating vulcanizing agents, e.g., an amine disulfide, polymeric polysulfide, or sulfur olefin adduct, and mixtures thereof.

[084] Sulfur vulcanizing agents may be used in an amount of 0.1 to 10 phr, such as at least 0.3 phr, or at least 0.4 phr, or at least 0.5 phr, or at least 0.7 phr, or up to 5 phr, or up to 3 phr in the rubber composition.

Healing Accelerators, Healing Activators, Healing Retarders

[085] Cure accelerators act as catalysts for the vulcanizing agent. Suitable cure accelerators include amines, disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides, dithiocarbamates, and xanthates. Examples of thiazole cure accelerators include 2-mercaptobenzothiazole and 2,2'-dithiobis(benzothiazole) (MBTS). Examples of sulfenamide cure accelerators include benzothiazole sulfenamides such as N-cyclohexyl-2-benzothiazolesulfenamide (CBS) and N-tert-butyl-2-benzothiazolesulfenamide (TBBS). Guanidine cure accelerators include diphenyl guanidine (DPG).

[086] Curing accelerators with a rapid onset of vulcanization time, referred to as “t0”, of less than 3 minutes are referred to as ultraaccelerators. Examples of ultraaccelerators that can be used include 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane (BDBZTH), tetrabenzylthiuram disulfide (TBzTD), tetramethylthiuram monosulfide (TMTM), tetramethylthiuram disulfide (TMTD), tetraethylthiuram disulfide (TETD), tetraisobutyl thiuram disulfide (TiBTD), dipentamethylene thiuram tetrasulfide (DPTT), zinc dibutyl dithiocarbamate (ZDBC), zinc diethyl dithiocarbamate, zinc dimethyl dithiocarbamate, copper dimethyl dithiocarbamate, tellurium diethyl dithiocarbamate (TDEC), zinc dibenzyl dithiocarbamate (ZBED), zinc diisononyl dithiocarbamate, zinc pentamethylene dithiocarbamate, zinc dibenzyldithiocarbamate (ZBEC), zinc isopropyl xanthate (ZIX). ), zinc butyl xanthate (ZBX), sodium ethyl xanthate (SEX), sodium isobutyl xanthate (SIBX), sodium isopropyl xanthate (SIPX), sodium n-butyl xanthate (SNBX), sodium amyl xanthate (SAX), potassium ethyl xanthate (PEX), potassium amyl xanthate (PAX), zinc 2-ethylhexylphosphorodithioate (ZDT/S) and of the same.

[087] In some cases, a combination of accelerators is used, with one acting faster than the other.

[088] The cure accelerator may be incorporated into the rubber composition at 0.1 to 10 phr, or at least 0.5 phr, or at least 1 phr, or at least 2 phr, or up to 8 phr, or up to 5 phr. The amount of cure accelerator may be selected to provide an acceptable cure time, such as less than 90 minutes.

[089] Cure activators are additives used to support vulcanization. Cure activators include inorganic and organic cure activators. Zinc oxide is a widely used inorganic cure activator and when used may be present at 1 phr to 10 phr, e.g. at least 2 phr, or up to 5 phr.

[090] Organic cure activators include stearic acid, palmitic acid, lauric acid, mixtures thereof, zinc salts of each of the foregoing, and thiourea compounds, e.g., thiourea and dihydrocarbylthioureas, such as dialkylthioureas and diarylthioureas, and mixtures thereof. Specific thiourea compounds include N,N'-diphenylthiourea, trimethylthiourea, N,N'-diethylthiourea (DEU), N,N'-dimethylthiourea, N,N'-dibutylthiourea, ethylenethiourea, N,N'-diisopropylthiourea, N,N'-dicyclohexylthiourea, 1,3-di(o-tolyl)thiourea, 1,3-di(p-tolyl)thiourea, 1,1-diphenyl-2-thiourea, 2,5-dithiobiurea, guanylthiourea, 1-(1-naphthyl)-2-thiourea, 1-phenyl-2-thiourea, p-tolylthiourea, and o-tolylthiourea. A commonly used organic cure activator is a mixture of stearic, palmitic and oleic acid, with stearic acid being the main component of the mixture.

[091] The total amount of organic healing activator(s), when used, may be from 0.1 to 6 phr, such as at least 0.5 phr, or at least 1 phr, or up to 4 phr.

[092] Cure retarders are used to control the vulcanization process and generally slow or inhibit vulcanization until the desired time and/or temperature is reached. Examples of cure retarders include cyclohexylthiophthalimide.

[093] The amount of cure retarder, when used, may be at least 0.1 phr, or up to 3 phr, or up to 2 phr.

Composition Examples

[094] TABLE 1 illustrates examples of rubber compositions according to aspects of the exemplary embodiment. TABLE 1: Example of Rubber Compositions

Preparation of Rubber Composition

[095] Rubber compositions may be prepared by mixing the compound material, natural rubber and/or when used, other vulcanizable elastomers, silica and other rubber compounding ingredients, not including the curing agent, in at least one sequential mixing stage with at least one mechanical mixer, generally referred to as a “non-productive” mixing stage, or stage(s), at an elevated temperature under high shear rubber mixing conditions, followed by a final “productive” mixing stage in which a sulfur-based cure package, such as a sulfur-based curing agent and cure accelerators, is added to the mixture and mixed at a lower mixing temperature to avoid unnecessary pre-curing of the rubber mixture during the mixing stage.

[096] The ingredients may be mixed in the non-productive mixing stage(s) for a few minutes at a temperature of 115°C to 150°C, for example about 124°C. Once the curing package has been added, the subsequent productive mixing stage may be conducted at a temperature below the vulcanization (curing) temperature in order to avoid undesirable pre-curing of the rubber composition, for example less than 180°C, or not more than 160°C, or not more than 120°C, such as at least 40°C, or at least 60°C, for example for 2 minutes at a temperature of 100-115°C. Mixing may be carried out, for example, by kneading the ingredients together in a Banbury mixer or on a roller mill. The rubber composition may be cooled to a temperature below 40°C between each of the mixing stages. For example, the rubber compound can be poured from the mixer after each mixing step, removed from an open mill, and allowed to cool below 40°C after each mixing step.

[097] When the curing package is thoroughly mixed, the rubber composition may be extruded, molded or otherwise shaped to form an article, such as a tire tread. The temperature of the mixture may be increased to effect curing. Curing of the pneumatic tire or part thereof may be carried out at a temperature of 120°C to 200°C, for example, at least 140°C, or up to 180°C, or about 150°C. Any of the usual vulcanization processes may be used, such as heating in a press or mold, or heating with superheated steam or hot air. Such tires may be constructed, shaped, molded and cured by various methods which are known and will be readily apparent to those skilled in the art.

[098] In one embodiment, a tire is provided, the tire having a tread formed at least in part from the exemplary rubber composition. Other portions of the tire, such as tire sidewalls or wire casings, may additionally or alternatively be formed at least in part from a rubber composition as described herein. The tire may be a pneumatic tire for a road vehicle, such as an automobile or truck, or a tire for an off-road vehicle, airplane, or the like. The tread of the tire may have a tread depth of at least 20 mm, e.g., 22-28 mm, which is suitable for use on a truck.

[099] The rubber composition is not limited to use in tires, but can be applied to rubber gloves, surgical instruments and the like.

Article Properties

[0100] The use of the rubber composition in tires, such as in tire treads, can result in a tire with improved or desirable tread properties. These improved or desirable properties can include tear resistance and elongation at break. The rubber composition can also produce improvements in the properties of cord casings and base formulations.

[0101] These improvements have been demonstrated, in part, through laboratory studies, plant-scale testing, and field evaluations with a commercial composite material, Cabot Corporation's E2C™ DX9640. Replacing some of the natural rubber in rubber compositions with the natural rubber and carbon black composite material can significantly improve compound properties beneficial to improving mileage (in particular, toughness and abrasion resistance).

[0102] Without intending to limit the scope of the exemplary embodiment, the following examples illustrate the preparation of exemplary rubber compositions employing a composite material and its properties.

EXAMPLES

[0103] Table 1. Tire tread cap formulations are prepared with the goal of achieving split tread wear or better (as indicated by the Grosch Medium Radial Truck Tire (MRT) test), improved rolling resistance (as indicated using Rebound at 100°C), and metallic tear resistance or better (as indicated by original and aged Strebler adhesion at 100°C) when the compound material is employed. Tire base and wire casing formulations have also been prepared that aim to achieve rolling resistance and tear resistance.

EXAMPLE 1

[0104] Rubber compositions suitable for use in truck tire tread covers are prepared using the formulations shown in TABLE 2.

[0105] Examples A, B and C are prepared using ASTM N121 grade carbon black and natural rubber and no compounding material. Example A is formulated as a baseline composition suitable for use in medium duty radial truck tires. Example B adds silica to the baseline composition and Example C utilizes a modified cure package.

[0106] For these three examples, in a first mixing step, the natural rubber is mixed with a portion of the carbon black (30phr) until the mixture reaches 160°C. It is then removed from the mixer and allowed to cool. In a second mixing step, the remainder of the carbon black (18 phr), silica if used, waxes and antioxidants are added. In the productive mixing step, sulfur, curing accelerator and retarder are added and the mixture is removed from the mixer at a temperature below the curing temperature.

[0107] Examples D, E, and F are prepared using both natural rubber and the composite material (a material containing approximately 64.5 wt. % natural rubber and 35.5 wt. % carbon black). The amount of carbon black and natural rubber in these three compositions is approximately the same as in base formulations A, B, and C. Each of these examples utilizes silica. Example E uses a modified cure package, and Example F uses a higher surface area silica than in Examples D and E.

[0108] To prepare examples D, E and F, in a single non-productive step, the composition is mixed until the temperature reaches 124°C and removed from the mixer. In the productive step, sulfur, curing accelerator and retarder are added and the mixture composition is mixed in the mixer until it reaches 104°C and removed from the mixer. The rotor speed is kept constant at 50 rpm during this stage. Mixing at lower temperatures in the non-productive and productive steps helps to preserve the polymer filler networks in the composite material, and thus, maintains the performance indicators. In the curing stage, the rubber composition is heated to a temperature of 150°C for 32 minutes. TABLE 2: Rubber Compound Formulations (in phr) 1 masterbatch of carbon black E2C™ DX9640 from Cabot Corporation 2 Carbon black ASTM N121 from Birla Carbon 3 Amorphous precipitated silica, ULTRASIL® 6100 GR from Evonik, with a BET nitrogen surface area of about 160 m2/g. 4 Amorphous precipitated silica, obtained as Premium SW from Solvay, with a CTAB surface area of about 250 m2/g. 5 Blend of microcrystalline and paraffin waxes. 6 Primarily stearic acid (at least 90% stearic acid) as a mixture of stearic, palmitic and oleic acids. 7 Mixture of para-phenylenediamines and quinolines. 8 Elemental sulfur. 9 N-tert-Butyl-benzothiazole sulfenamide (TBBS). 10 N-tert-Butyl-benzothiazole sulfenamide (TBBS). 10 N-(cyclohexylthio) phthalimide (CTP).

[0109] Performance tests were performed on the cured samples as follows:

[0110] Specific Gravity: Determined in accordance with ASTM D297-21, “Standard Test Methods for Rubber Products - Chemical Analysis.”

[0111] Cured Stiffness: The storage modulus G' is determined with a Rubber Process Analyzer (RPA 500). Storage modulus values are measured on uncured samples at 10% strain and after curing at 10% and 50% strain (in MPa), at a temperature of 40°C. Measurements on the cured samples are indicative of the driving and handling of a tire using the rubber composition in the tread. Tan Δ values (the ratio of G'' to G') at 10% strain are also obtained.

[0112] Tensile Properties: The ring tensile modulus at 300% strain (MPa) for specimens before and after aging, the tensile strength, MPa, and the elongation at break, %, are measured with an Instron Corporation instrument.

[0113] Rolling Resistance Predictor: Percent rebound is measured on the cured sample as an indicator of the tire’s wet braking capability with a ZwickRoell 5109 Rebound Resilience Tester at a given temperature in accordance with ASTM D7121-05 (2018), “Standard Test Method for Rubber Properties – Resilience Using Schob-Type Rebound Pendulum”, with higher values being better. Rebound is a measure of the hysteresis of the compound when subjected to loading. Generally, the higher the measured rebound, the lower the rolling resistance.

[0114] Strebler Adhesion Steady State Average Load is determined at 100°C (N/mm) on cured samples, before and after aging. This is a peel test that determines interfacial adhesion by pulling one rubber composition away from another at a right angle to the untorn test sample, with the two ends of the rubber compositions being separated at an angle of 180° to each other.

[0115] Crack Growth: DeMattia shear growth (N/min) is determined at 95°C on aged specimens in accordance with ASTM D813-07(2019), “Standard Test Method for Rubber Deterioration — Crack Growth”. In Table 3, the higher the shear growth rate, the greater the tread groove resistance to surface crack growth.

[0116] Abrasion Resistance: indicative of tread wear is determined as the Grosch abrasion rate, in terms of mg/km of rubber worn. The test rubber sample is placed at a sliding angle under constant load (Newtons) as it travels a given distance on a rotating abrasive disc. Medium and high abrasion severity tests are performed. The main differences between these two tests are in relation to load and slip angle. The high severity Grosch is an average of two samples run at 70N load at a 12 degree angle, while the medium severity is an average of two tests at 70N and 40N load and angles of 12 and 6 degrees respectively.

[0117] The results are shown in TABLE 3. The results are normalized, with those from Example A being set to 100. Higher is generally better for all parameters. TABLE 3:Results

[0118] The results in Table 3 indicate that Examples D and E exhibited higher aged Strebler adhesion values and improved high gravity abrasion resistance, with reduced medium gravity abrasion resistance. This improved balance in performance indicators was achieved by utilizing the compound material to replace some of the natural rubber in the formulation. Example F showed a similar improvement in Strebler values as Examples D and E, with tradeoffs in both low and high gravity abrasion resistance.

[0119] Example E is identical to Example D except that it includes slightly less sulfur, accelerator, and cure retarder. Compared to Example A, Example E provided a 10% improvement in rolling resistance indicator, while improving the compound's tear strength indicator and Grosch abrasion resistance at high gravity, and maintaining stiffness and elongation at break values within general guidelines for inline conveyor drive applications.

[0120] An increase in the percentage of dispersion based on the higher tensile modulus ratio from 300% to 100% (i.e., better filler-polymer interaction) was observed in the samples containing the composite material. An additional non-productive mixing step could further improve the dispersion and processing indicator in this case.

EXAMPLE 2

[0121] Rubber compositions suitable for use as a tread base for truck tires are prepared using the formulations shown in TABLE 4.

[0122] Examples G, H and I are prepared using ASTM N347 grade carbon black and natural rubber and no compounding material. Example G is formulated as a tread base composition suitable for use in medium duty truck radial tires. Example H partially replaces the carbon black with silica compared to the baseline composition, and Example I utilizes a modified cure package.

[0123] For these three examples, in a first mixing step, natural rubber is mixed with a portion of carbon black (up to 17.1 phr), silica (up to 9.7 phr), oil and cure activators until the mixture reaches 155°C. It is then removed from the mixer and allowed to cool. In a second mixing step, silica (up to 5.5 phr) and silane are mixed to a temperature of 145°C. After cooling, the remainder of the carbon black (up to 5 phr), silica (up to 1.8 phr), waxes and antioxidants are mixed in a third mixing stage. In the productive mixing step, sulfur, cure accelerator and retarder are added and the mixture is removed from the mixer at a temperature below the cure temperature.

[0124] Examples J and K are prepared using both natural rubber and the composite material (a material containing approximately 64.5 wt. % natural rubber and 35.5 wt. % carbon black). The amounts of carbon black and natural rubber in these three compositions are approximately the same as in baseline formulations G, H, and I. Each of these examples utilizes silica. Example K uses the same cure package as Example I.

[0125] To prepare Examples J and K, the first non-productive stage is similar to the first non-productive stage for Examples H and I. The difference is in the smaller amount of natural rubber in the first non-productive stage for Examples J and K. The second non-productive stage for Examples J and K corresponds to that of Examples H and I. In the third non-productive stage, the compound material is added to Examples J and K, along with the remaining amount of silica (1.8 phr) and weathering agents, and mixed until the temperature reaches 124°C. In the productive stage, sulfur, curing accelerator and retarder are added and the mixture composition is mixed in the mixer until it reaches 104°C and removed from the mixer. The rotor speed is kept constant at 50 rpm during this stage. In the curing stage, the rubber composition is heated to a temperature of 150°C for 32 minutes. TABLE 4: Rubber Compound Formulations 1 Master batch of E2C™ DX9640 carbon black from Cabot Corporation 2 ASTM N347 carbon black from Orion Engineered Carbons 3 Amorphous precipitated silica, ULTRASIL® 6100GR from Evonik 4 Stearic acid primarily (at least 90% stearic acid) as a mixture of stearic, palmitic, and oleic acids. 5 Mixture of para-phenylenediamines and quinolines. 6 80% sulfur 80% oil-treated (90% insoluble) 7 N-tert-butyl-benzothiazole sulfenamide (TBBS) 8 N-(cyclohexylthio)phthalimide (CTP)

[0126] The results for these formulas are shown in TABLE 5.TABLE 5: Results

[0127] Example K provided improvements in Bose fatigue and RPA 500 tan (δ) values, while maintaining results for Strebler, DeMattia and elongation at break above the minimum acceptable values defined in the general guidelines for MTR tread base compounds. Improvements in cured stiffness (G') and tensile properties are also observed.

[0128] The results of Examples 1 and 2, and other evaluations not reported herein, demonstrate that improvements in treadwear and tire mileage can be achieved with the exemplary compositions, without significant trade-offs in other parameters such as tear resistance and rolling/hysteresis that are commonly experienced when modifying rubber compositions. This indicates that the exemplary compositions can expand the “performance triangle” of rolling resistance, tear resistance, and treadwear, thereby overcoming challenges commonly faced during the development of new compound formulations for tire programs.

[0129] Each of the documents referred to above is hereby incorporated by reference. Except in the Examples, or where otherwise explicitly indicated, all numerical quantities in this description specifying amounts of materials, reaction conditions, molecular weights, number of carbon atoms, and the like are to be understood as modified by the word "about." Unless otherwise indicated, each chemical product or composition referred to herein is to be interpreted as being a commercial quality material that may contain the isomers, by-products, derivatives, and other materials that are commonly understood to be present in commercial quality. However, the amount of each chemical component is shown exclusive of any solvent or diluent oil, which may be customarily present in commercial material, unless otherwise indicated. It is to be understood that the upper and lower limits of quantity, range, and proportion set forth herein may be combined independently. Likewise, the ranges and amounts for each element of the invention may be used in conjunction with ranges or amounts for any of the other elements.

[0130] It will be appreciated that variants of the above disclosed features and functions and others, or alternatives thereof, may be combined in many other different systems or applications. Various presently unforeseen or unexpected alternatives, modifications, variations or improvements may subsequently be made by those skilled in the art, which are also intended to be encompassed by the following claims.

Claims (10)

1. Rubber composition CHARACTERIZED by: at least 20 phr of a composite material defined by a reinforcing carbon black dispersed in natural rubber; at least 3 phr of a conjugated diene elastomer, the composite material and the conjugated diene elastomer together providing at least 90 phr of vulcanizable elastomers in the rubber composition; a cure activator, and a sulfur-based curing agent. 2. The rubber composition of claim 1, wherein the rubber composition comprises at least 5 phr of silica. 3. The rubber composition of claim 1, wherein the compound material provides the rubber composition with at least 20 phr of reinforcing carbon black. 4. The rubber composition of claim 1, wherein the compound material provides the rubber composition with at least 50 phr of natural rubber. 5. Rubber composition according to claim 1, CHARACTERIZED by the fact that the composite material is solid. 6. Rubber composition according to claim 1, CHARACTERIZED by the fact that the conjugated diene elastomer comprises at least one of natural rubber and synthetic polyisoprene. 7. Rubber composition according to claim 1, CHARACTERIZED by the fact that the rubber composition comprises at least 5 phr of the conjugated diene elastomer. 8. Rubber composition according to claim 1, further CHARACTERIZED by at least 1 phr of at least one of an antioxidant and an antiozonant. 9. Article, CHARACTERIZED by being formed from the composition as defined in claim 1. 10. The article of claim 9 featuring a tire tread.