Rubber composition based on multiphase dilution of composite blend

Abstract

To provide a rubber composition based on multiphase dilution of composite blend.SOLUTION: A method of forming a vulcanizable rubber composition includes a sequence of non-productive mixing steps. In a first of the non-productive mixing steps, a composite blend is mixed with a first elastomer to generate a first mixture. The composite blend includes a second elastomer, which may be the same as, or different from, the first elastomer, and carbon black. In a second of the non-productive mixing steps, a third elastomer, different from the first elastomer, is mixed with the first mixture, or with a mixture generated from the first mixture, to generate a second mixture. In a productive mixing step, a curing agent is mixed with the second mixture, or with a mixture generated from the second mixture, to generate the vulcanizable rubber composition, which includes the first, second, and third elastomers, carbon black from the composite blend, and an additional amount of a reinforcing filler.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001]

[0001] Described herein is a method for forming a rubber composition suitable for forming pneumatic tire components such as tire treads. The method has particular application to the formation of multiphase rubber compositions in which one or more fillers are differentially partitioned between the phases of the rubber composition. [Background technology]

[0002]

[0002] Rubber compositions suitable for use in tires often contain a mixture of elastomers along with reinforcing fillers such as carbon black and silica. To form the rubber composition, the elastomer is generally combined in a first non-productive stage along with some of the rubber composition's ingredients, such as fillers. Additional ingredients may be introduced and mixed with the elastomer in one or more additional non-productive stages. In a subsequent productive stage, a curative, such as sulfur, is added to the mixture. The introduction of the elastomer in the first non-productive stage results in an uncured rubber composition, or masterbatch, comprising a homogeneous polymer matrix in which the other ingredients are uniformly dispersed.

[0003]

[0003] In some cases, the elastomer includes a mixture of polydiene rubbers, such as a mixture of polybutadiene rubber and styrene-butadiene rubber, or two different types of styrene-butadiene rubber. For example, U.S. Patent Application Publication No. 20120077902A1 describes a tread composition including two specific styrene-butadiene rubbers and a specific cis-1,4 polybutadiene. U.S. Patent Application Publication No. 20210032442A1 describes a tread composition including a specific solution-polymerized styrene-butadiene rubber, natural rubber or synthetic polyisoprene, and optionally a specific cis-1,4 polybutadiene. U.S. Patent Application Publication No. 20200071506A1 describes a tread including specific first and second functionalized solution-polymerized styrene-butadiene rubbers and optionally a polyisoprene having a cis-1,4 content greater than 95%.

[0004]

[0004] In recent years, preformed elastomer composite blends, sometimes referred to as "masterbatches," have been developed for use in tire compositions. These typically contain a generally highly purified natural rubber latex and carbon black, as described, for example, in U.S. Patent Application Publication Nos. 20120172492 A1 and 20190040225 A1. The composite blends are formed by combining a liquid latex with an aqueous dispersion of carbon black to produce a well-dispersed coagulated mixture. The mixture can be dried to remove water to form a solid, which may be in the form of a sheet, fiber, or granules. Such composite blends can be diluted with additional natural rubber and compounded with curatives and other additives to obtain a composition suitable for forming a tire tread, as described, for example, in U.S. Patent Application No. 18 / 127,763, filed March 29, 2023, entitled "RUBBER COMPOSITION INCORPORATING A PREFORMED NATURAL RUBBER-CARBON BLACK COMPOSITE MATERIAL."

[0005]

[0005] There remains a need for rubber compositions that can utilize such composite blends to provide rubber compositions that can provide improved or different properties, such as improved heat buildup, tear performance, wear and abrasion. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent Application Publication No. 20120077902A1 [Patent Document 2] U.S. Patent Application Publication No. 20210032442A1 [Patent Document 3] U.S. Patent Application Publication No. 20200071506A1 [Patent Document 4] U.S. Patent Application Publication No. 20120172492A1 [Patent Document 5] U.S. Patent Application Publication No. 20190040225A1 [Patent Document 6] U.S. Patent Application No. 18 / 127,763 [Patent Document 7] U.S. Patent No. 6,048,923A [Patent Document 8] U.S. Patent Application Publication No. 20020086917A1 [Patent Document 9] U.S. Patent Application Publication No. 20190048150A1 [Patent Document 10] U.S. Patent No. 5,583,173A [Patent Document 11] U.S. Patent Application Publication No. 20050288393A1 [Patent Document 12] U.S. Patent Application Publication No. 20060266454A1 [Patent Document 13] U.S. Patent Application Publication No. 20080216935A1 [Patent Document 14] U.S. Patent Application Publication No. 20140171557A1 [Patent Document 15] U.S. Patent No. 4,843,120A [Patent Document 16] U.S. Patent No. 6,103,842A [Patent Document 17] U.S. Patent Application Publication No. 20020099148A1 [Patent Document 18] U.S. Patent Application Publication No. 20140135437A1 [Patent Document 19] U.S. Patent Application Publication No. 20040249020A1 [Patent Document 20] U.S. Patent Application Publication No. 20040254301A1 [Patent Document 21] U.S. Patent Application Publication No. 20080287601A1 [Patent Document 22] U.S. Patent Application Publication No. 20040122194A1 [Patent Document 23] U.S. Patent Application Publication No. 20230312780A1 [Patent Document 24] U.S. Patent Application Publication No. 20230312784A1 [Patent Document 25] U.S. Patent Application Publication No. 20230312792A1 [Patent Document 26] U.S. Patent Application Publication No. 20230312798A1 [Patent Document 27] U.S. Patent No. 5,698,643 [Patent Document 28] U.S. Patent No. 5,451,646 [Patent Document 29] U.S. Patent No. 5,587,416A [Patent Document 30] U.S. Patent Application Publication No. 20020081247A1 [Patent Document 31] U.S. Patent Application Publication No. 20050032965A1 [Patent Document 32] U.S. Patent Application Publication No. 20110178227A1 [Patent Document 33] U.S. Patent No. 5,708,069 [Patent Document 34] U.S. Patent Application Publication No. 20210355301A1 [Non-patent literature]

[0007] [Non-Patent Document 1] Ting Wang et al., “CEC and its application in off-the-road tires,” Rubber World, 277(6), pp. 33-38 (2003) [Non-patent document 2] The Vanderbilt Rubber Handbook (1978), pp. 346 and 347 [Non-patent document 3] The Vanderbilt Rubber Handbook (1978), pp. 344-347 Summary of the Invention [Means for solving the problem]

[0008] According to one embodiment, a method for forming a vulcanizable rubber composition includes, in a first non-productive mix step, mixing a composite blend with a first elastomer to produce a first mixture. The composite blend includes a second elastomer and carbon black. The second elastomer is the same as or different from the first elastomer. In a second non-productive mix step, a third elastomer different from the first elastomer is mixed with the first mixture or a mixture formed from the first mixture to produce a second mixture. In a productive mix step, a curative is mixed with the second mixture or a mixture formed from the second mixture to produce a vulcanizable rubber composition including the first, second, and third elastomers, the carbon black from the composite blend, and an additional amount of reinforcing filler.

[0009]

[0007] In various aspects of the method, alone or in combination: The first elastomer may be or include a first of natural rubber and a polydiene elastomer, and the third elastomer may be or include a second of natural rubber and a polydiene elastomer. The first elastomer may be or include natural rubber, and the third elastomer may be or include a polydiene elastomer.

[0010]

[0009] The polydiene elastomer may include a styrene-butadiene rubber. The styrene-butadiene rubber may be or include an emulsion polymerized styrene-butadiene rubber.

[0011]

[0010] The weight ratio of the first elastomer to the third elastomer in the vulcanizable rubber composition may be at least 1:10, or at least 1:5, or at least 1:2, or at least 1:1.5, or at least 1:1, or at most 10:1, or at most 5:1, or at most 3:1, or at most 2:1, or at most 1.5:1.

[0012] The first and third elastomers may be present in the vulcanizable rubber composition in a combined amount of at least 20 phr, or at least 30 phr, or at most 70 phr, or at most 60 phr, or at most 50 phr, or at most 40 phr.

[0013] The second elastomer may be or may include natural rubber.

[0014] The composite blend may include carbon black in an amount of at least 40 phr per 100 phr of the second elastomer.

[0015] The reinforcing filler may comprise carbon black in an amount of at least 10 phr, or at least 20 phr per 100 phr of the second elastomer. The reinforcing filler may further comprise silica in an amount of at least 5 phr.

[0016] The vulcanizable rubber composition may further include at least one of a processing aid, a cure activator, and a cure accelerator.

[0017] A tire tread may be formed from the vulcanizable rubber composition formed by the above-described method. The tire may include the tread.

[0018] According to another embodiment, a vulcanizable rubber composition comprises 100 phr of an elastomer. The elastomer comprises at least 5 phr of a first elastomer, at least 20 phr of a second elastomer provided in the form of a composite blend with carbon black, and at least 5 phr of a third elastomer. The third elastomer differs in chemical composition from the first elastomer. In addition to the carbon black in the composite blend, the vulcanizable rubber composition further comprises at least 5 phr of a particulate filler. The particulate filler is selected from the group consisting of carbon black, silica, and combinations thereof. The vulcanizable rubber composition further comprises a cure activator, a cure accelerator, and a sulfur-based curative.

[0019]

[0018] In one embodiment, the vulcanizable rubber composition comprises multiple phases including a first phase comprising a first elastomer, a second phase comprising a second elastomer, and a third phase comprising a third elastomer, wherein the concentration of carbon black in the third phase is lower than the concentration of carbon black in the first phase.

[0020] The vulcanizable rubber composition may further comprise a processing aid selected from the group consisting of resins, liquid processing aids, waxes, and combinations thereof.

[0021]

[0020] A tire tread may be formed from the vulcanizable rubber composition described above. A pneumatic tire may include a tread.

[0022] According to another embodiment, a method for forming a vulcanizable rubber composition includes, in a first non-productive mix step, mixing a composite blend, natural rubber, and carbon black together to form a first mixture, the composite blend including natural rubber and carbon black. In a second non-productive mix step, styrene-butadiene rubber is mixed with the first mixture, or a mixture derived from the first mixture, to form a second mixture including 100 phr of elastomer. The elastomer includes at least 45 phr of natural rubber and at least 10 phr of styrene-butadiene rubber. The second mixture further includes at least 40 phr of carbon black and at least 5 phr of silica. In a productive mix step, a curative is mixed with the second mixture, or a mixture derived from the second mixture, to form the vulcanizable rubber composition. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a flowchart illustrating a method of making a vulcanizable rubber composition and articles formed therefrom. DETAILED DESCRIPTION OF THE INVENTION

[0024] A method for forming a rubber composition is described that includes introducing an elastomer at different stages of a mixing process, thereby forming a multi-phase vulcanizable rubber composition.

[0025] The rubber composition formed by this method is a mixture of elastomers and additives suitable for forming a cured article, such as a tire or portion thereof, e.g., a tire tread. The elastomer includes a first elastomer (e.g., polyisoprene, e.g., natural rubber and / or synthetic rubber), a second elastomer (e.g., polyisoprene, e.g., natural rubber and / or synthetic rubber), and a third elastomer different from the first elastomer (e.g., a polydiene, e.g., styrene-butadiene rubber (SBR)). In one embodiment, the first elastomer is natural rubber and the third elastomer is styrene-butadiene rubber.

[0026] The polyisoprene, e.g., natural rubber, and other second elastomers are provided in the form of a composite blend, which provides at least a first portion of the carbon black in the rubber composition, and an optional second portion of the carbon black is provided separately.

[0027]

[0026] Other additives that may be incorporated into the vulcanizable rubber composition include one or more of other reinforcing fillers such as silica, liquid processing aids, resins, cure activators, cure accelerators, sulfur-based curatives, anti-degradants, and combinations thereof.

[0028] By way of example, the vulcanizable rubber composition may be derived from: A) (i) at least 5 phr of a first elastomer; (ii) at least 20 phr of a second elastomer in the form of a composite blend with carbon black; and (iii) at least 5 phr of a third elastomer whose chemical composition differs from that of the first elastomer; 100 phr of elastomers, including; B) at least 5 phr of particulate filler in addition to the carbon black in the composite, (i) Carbon black (ii) silica, and The combination a particulate filler selected from: C) Optionally, (i) resin, (ii) liquid processing aids; (iii) wax, and The combination one or more processing aids which may be selected from: D) (i) Zinc oxide (ii) a fatty acid, and The combination a cure activator which may be selected from: E) cure accelerator; F) sulfur-based curing agents; and G) Optionally, one or more additional ingredients, such as antiozonants, antioxidants, set retarders, peptizers, and the like.

[0029] In one embodiment, a method for preparing a vulcanizable rubber composition includes a series of at least two non-productive mix stages (NP), i.e., a mix stage performed before a sulfur-based vulcanizing agent is added to the mixture, followed by a productive mix stage (PR) in which the sulfur-based vulcanizing agent is added to the mixture. The non-productive mix stages may include at least a first non-productive mix stage (NP1) and a second subsequent non-productive mix stage (NP2). Additional non-productive mix stages may optionally be performed before or after NP2. In the first non-productive mix stage, the composite blend is mixed with a first elastomer, which may be one of polyisoprene and polydiene elastomers, and optionally an additional reinforcing filler, such as carbon black. In the second non-productive mix stage, the mixture formed in NP1 (or an intermediate NP stage) is mixed with a third elastomer, which is different from the first elastomer and may be the other of polyisoprene and polydiene rubber.

[0030] In the resulting vulcanizable rubber composition, the carbon black is not evenly distributed throughout the three (or more) elastomers, resulting in a multiphase mixture that provides advantageous properties to articles formed therefrom, such as tire treads for pneumatic tires. In particular, the vulcanizable rubber composition may include three phases: a first phase in which the carbon black is dispersed in a first elastomer at a first carbon black:elastomer weight ratio (CB:E ratio); a second phase in which the carbon black is dispersed in a second elastomer at a second CB:E ratio; and a third phase in which the carbon black is dispersed in a third elastomer at a third CB:E ratio. Generally, the second phase has the highest CB:E ratio, and the third phase has the lowest CB:E ratio, especially when little or no carbon black is added in NP2. As will be appreciated, the three phases are partially intermixed but sufficiently different to provide unique physical properties to the rubber composition, and articles formed therefrom, and to provide a good blend of properties indicative of tear resistance, wear, and heat generation in a tire.

[0031] definition The terms "rubber" and "elastomer" may be used interchangeably unless otherwise indicated. The terms "rubber composition" or "compounded rubber" are used interchangeably to refer to "rubber blended or mixed with various ingredients and materials," and such terms are well known to those skilled in the rubber mixing or compounding arts. The terms "cure" and "vulcanize" may be used interchangeably unless otherwise indicated.

[0032]

[0031] As used herein, unless otherwise indicated, the term "tread" refers to both that portion of the tire that comes into contact with the road under normal inflation and load, and optionally the subtread.

[0033] As used herein, the term "phr" means parts per hundred parts by weight of rubber. Generally, using this convention, a rubber composition contains 100 parts by weight of rubber / elastomer. A claimed composition may contain rubbers / elastomers other than those expressly recited in the claims, provided that the phr value of the claimed rubber / elastomer complies with the claimed phr range and the amounts of all rubbers / elastomers in the composition total 100 parts rubber. The term "phf" means parts per hundred parts by weight of filler in the rubber composition.

[0034] Unless otherwise stated, the following methods are used to determine the properties:

[0035]

[0034] Molecular weights of elastomers, rubber compositions, and resins, such as Mn (number average molecular weight), Mw (weight average molecular weight), and Mz (z average molecular weight), are determined herein using gel permeation chromatography (GPC) using polystyrene calibration standards in accordance with ASTM D5296-19, "Standard Test Method for Molecular Weight Averages and Molecular Weight Distribution of Polystyrene by High Performance Size-Exclusion Chromatography."

[0036] The glass transition temperature (Tg) of an elastomer or elastomeric composition is the glass transition temperature of the respective elastomer or elastomeric composition in its uncured state, or, in the case of elastomeric compositions, in its cured state, as the case may be.

[0037]

[0036] The Tg value of an elastomer is determined as the midpoint of the peak by differential scanning calorimetry (DSC) at a heating rate of 10°C per minute in accordance with ASTM D3418-21 "Standard Test Method for Transition Temperatures and Enthalpies of Fusion and Crystallization of Polymers by Differential Scanning Calorimetry", hereinafter ASTM D3418.

[0038]

[0037] The glass transition temperature Tg of a resin is determined as the peak midpoint by differential scanning calorimetry (DSC) at a heating rate of 10°C per minute in accordance with ASTM D6604-00(2017) "Standard Practice for Glass Transition Temperatures of Hydrocarbon Resins by Differential Scanning Calorimetry", hereinafter ASTM D6604.

[0039]

[0038] The glass transition temperature Tg of the oil is determined as the peak midpoint by differential scanning calorimetry (DSC) at a heating rate of 10°C per minute according to ASTM E1356-08(2014) "Standard Test Method for Assignment of the Glass Transition Temperatures by Differential Scanning Calorimeter".

[0040] The softening point of a resin is determined in accordance with ASTM E28-18 "Standard Test Methods for Softening Point of Resins Derived from Pine Chemicals and Hydrocarbons, by Ring-and-Ball Apparatus", hereinafter ASTM E28, and is sometimes referred to as the ring-and-ball softening point.

[0041] Mooney viscosity (ML 1+4) is measured in MU at 100°C in accordance with ASTM D1646-19a "Standard Test Methods for Rubber - Viscosity, Stress Relaxation, and Pre-Vulcanization Characteristics (Mooney Viscometer)", hereinafter ASTM D1646.

[0042] The term "alkyl" refers to straight-chain, branched, and cycloalkyl groups. The term "aryl" refers to groups containing at least one aromatic ring, and includes alkylaryl groups.

[0043]

[0042] The cis, trans, and vinyl content (%) of a polymer refers to the molar fraction of 1,4-cis, 1,4-trans, and 1,2-vinylbutadiene units in the polymer, generally totaling 100%, unless otherwise indicated. These percentages can be determined by H-NMR mass spectrometry according to ISO 21561-1:2015. Styrene content refers to the wt. % of bound styrene in a polymer, such as a styrene-butadiene polymer, and can be determined by FT-IR.

[0044] Exemplary Methods Vulcanizable rubber compositions may be prepared by mixing vulcanizable elastomers, fillers such as carbon black, and other rubber compounding ingredients, excluding curatives, to elevated temperatures under high shear rubber mixing conditions in a series of mixing stages using at least one mechanical mixer, commonly referred to as "non-productive" mix stages, after which, in a final "productive" mix stage, sulfur-based curatives and cure accelerators are added to the mixture and mixed at a lower mixing temperature so as not to unnecessarily pre-cure the rubber mixture in the productive mix stage.

[0045]

[0044] Figure 1 shows an exemplary method for forming a vulcanizable rubber composition. The method begins at S100.

[0046]

[0045] In S102, in a first non-productive mixing stage (NP1), a first elastomer is combined with a composite blend (including a second elastomer) and optionally a first portion of additives (excluding curatives) and mixed in a suitable mixing device for a period of time such as at least 1 minute to form a first mixture.

[0047]

[0046] In S104, following the first non-productive mixing stage, the first mixture may be dropped from the mixing device or otherwise cooled.

[0048] In S106, in a second non-productive mix stage (NP2), a third elastomer to be incorporated into the rubber composition is combined with the first mixture from S102 or S104, or an intermediate mixture derived therefrom, and optionally a second portion of the additives (excluding curatives), and mixed in a suitable mixing device for a period of time such as at least 1 minute. The product of this step is a second mixture comprising the first, second, and third elastomers, and at least a portion of the additives (excluding curatives).

[0049]

[0048] In S108, following the second non-productive mixing stage, the mixture may be dropped from the mixing device or otherwise cooled.

[0050] Optionally, one or more additional non-productive mix stages may be performed prior to the productive mix stage.

[0051] In S110, in a productive mix stage, a curative is combined with the mixture produced in S106 or S108 (or a subsequent non-productive mix stage, if performed) and mixed for a suitable period of time, such as at least 1 minute. The product of this step is a vulcanizable rubber composition containing the first, second, and third elastomers, additives, and curative.

[0052]

[0051] In S112, the vulcanizable rubber composition formed in S110 can be extruded, molded, and / or otherwise shaped to form a raw rubber component, such as a tire tread or portion thereof.

[0053]

[0052] In S114, the raw rubber component may optionally be cured, for example by heating, along with other components of the article, such as a tire.

[0054] The method ends at S116.

[0055]

[0054] It will be appreciated that fewer, additional, and / or different steps than those described above may be performed in the method.

[0056] In NP1 (S102), a first elastomer may be mixed with the composite blend, additional carbon black, silica, and some or all of the additives (except the curative) to form a first mixture. Mixing may be carried out to a temperature of 130°C to 200°C, for example, about 150°C to about 165°C, for about 1 to 2 minutes. This step may be carried out in the absence of a third elastomer or in the presence of a minor amount of the third elastomer, for example, 10 wt.% or less, or 5 wt.% or less of the third elastomer.

[0057] After cooling the first mixture (S104), the first mixture is combined with the third elastomer and any additives not yet added and mixed to form a second mixture (S106). Mixing may be carried out for about 2 minutes to a temperature of 130°C to 200°C, for example, from about 150°C to about 165°C. In one embodiment, the incorporation of carbon black (and optionally silica) is carried out before the second mixing step, i.e., before the entire or major amount (at least 90 wt.%, or at least 95 wt.%) of the third elastomer is added. As a result, more carbon black remains dispersed in the first and second elastomers than in the third elastomer.

[0058] After cooling the second mixture (S108), one or more further non-productive mixing steps (designated NP3, etc.) may be performed to produce a third mixture, etc., derived from the second mixture. In one embodiment, the third mixing step is performed without adding any additional components. Mixing in NP3, etc., may be performed to a temperature of 130°C to 200°C, for example, about 150°C to about 165°C, for about 2 minutes, followed by a cooling step.

[0059] In the productive mix stage (S110), the second mixture (or a third, etc. mixture derived from the second mixture, as described above) is combined with a curative. The productive mix step may be carried out at a temperature below the vulcanization (cure) temperature and / or for a short period of time, e.g., 120°C or less, e.g., at least 60°C, e.g., 110-115°C for 2 minutes, to avoid unnecessary pre-curing of the rubber composition. Mixing may be carried out, for example, by kneading the ingredients together in a Banbury mixer or on a rolling mill.

[0060] The rubber composition may be cooled between each mixing stage to a temperature of less than about 40° C. For example, the rubber composition may be discharged from the mixer after each mixing step, removed from an open mill or sheeted onto a roller die, and cooled to less than 40° C. after each mixing step.

[0061]

[0060] Once the curatives added in the productive mix step (and any cure accelerators and other ingredients not previously added to the mixture) have been thoroughly mixed into the rubber composition, the rubber composition may be molded or otherwise formed into the shape of a green tire component, such as a tire tread (S112).

[0062] In S114, the temperature of the green components may be elevated to effect curing. Curing of the pneumatic tire or portion 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, for at least 10 minutes. Any of the usual vulcanization processes may be used, such as heating in a press or mold, or by heating with superheated steam or hot air. Such tires may be built, shaped, molded, and cured by a variety of methods known and readily apparent to those skilled in the art.

[0063] Next, the rubber composition will be described in further detail. A. Elastomer For ease of explanation, the first elastomer will be described in terms of polyisoprene rubber and the third elastomer will be described in terms of polydiene rubber, although it will be understood that this could be reversed.

[0064] The weight ratio of the first elastomer to the third elastomer in the vulcanizable rubber composition may be at least 1:10, or at least 1:5, or at least 1:2, or at least 1:1.5, or at least 1:1, or at most 10:1, or at most 5:1, or at most 3:1, or at most 2:1, or at most 1.5:1. In total, the first and third elastomers may be present in the vulcanizable rubber composition in an amount of at least 20 phr, or at least 30 phr, or at most 70 phr, or at most 60 phr, or at most 50 phr, or at most 40 phr.

[0065] (i) First Elastomer The first elastomer comprises or consists of natural and / or synthetic polyisoprene, such as natural rubber. The first elastomer may be present in the rubber composition in an amount of at least 5 phr, or at least 10 phr, or at least 15 phr, or at most 70 phr, or at most 60 phr, or at most 40 phr, or at most 30 phr, for example, 22±5 phr.

[0066] As used herein, the term "natural rubber" means naturally occurring rubber such as may be harvested from sources such as the hevea tree and non-hevea sources (e.g., guayule shrub and dandelion such as TKS). In other words, the term "natural rubber" should be construed to exclude synthetic polyisoprene.

[0067] Synthetic polyisoprene refers to a polymer made from isoprene monomers and should not be construed as including naturally occurring rubber. However, the term polyisoprene should be construed as including polyisoprene made from natural sources of isoprene monomers.

[0068] Natural rubber is predominantly cis-polyisoprene. The cis-1,4-polyisoprene content of natural rubber may be at least 90%, or at least 95%. In one embodiment, the natural rubber is natural cis-1,4-polyisoprene rubber having a cis-1,4 content of at least 96% and a Tg in the range of −60° C. to −110° C., as determined according to ASTM D3418.

[0069] Several forms of natural rubber are commercially available. Natural rubber can meet the ISO TSR20 or ISO TSR10 grade specifications for purity. ISO TSR20 natural rubber has a maximum ash content of 1 wt.% as determined in accordance with ISO 247:1990, a maximum volatile matter content of 0.8 wt.% as determined in accordance with ISO 248:1991, a maximum nitrogen content of 0.6 wt.% as determined in accordance with ISO 1656:1996, a minimum initial Wallace plasticity index of 30 as determined in accordance with ISO 2007:1991, and a minimum plasticity residue index of 40 as determined in accordance with ISO 2930:1995. TSR10 specifies a maximum ash content of 0.75 wt.%, a maximum nitrogen content of 0.6 wt.%, a maximum volatile matter content of 0.8 wt.%, a minimum plasticity index of 30, and a minimum plasticity residue index of 50. In other embodiments, the natural rubber may be smoke-free sheet (RSS) rubber.

[0070] (ii) Second Elastomer (Composite Blend) The composite blend includes a mixture of a second elastomer and a particulate filler such as carbon black. Components of the composite blend other than the second elastomer and the particulate filler may be present in an amount of 20 phr or less, or 10 phr or less, or 5 phr or less. The composite blend may be free of cure accelerators, cure activators, and curing agents.

[0071] The weight ratio of the second elastomer to the carbon black in the composite blend may be at least 0.5:1, or at least 1:1, or at least 1.5:1, or at least 1.7:1, or at most 10:1, or at most 5:1, or at most 4:1, or at most 3:1, or at most 2.5:1, or at most 2:1. Expressed alternatively, the carbon black may represent at least 10 phr, or at least 20 phr, or at least 30 phr, or at least 40 phr, or at least 50 phr, or at most 90 phr, or at most 70 phr, or at most 60 phr per 100 phr of elastomer in the composite blend.

[0072] In one embodiment, the second elastomer consists of or comprises natural rubber.

[0073] The carbon black in the composite blend may be any of the ASTM grades commonly used in forming rubber compositions, as further described below. Exemplary ASTM grades include N134, N220, and N234.

[0074] The composite blend may have a storage viscosity (ML(1+4) at 100° C.) of at least 140, or at least 150, or up to 200, or up to 190.

[0075] Composite blends are formed by a wet mixing process in which a fluid elastomer latex (e.g., natural rubber) is combined with an aqueous slurry of particulate filler, such as carbon black and / or silica. Composite blends may be formed by the methods described in U.S. Patent No. 6,048,923 A and U.S. Patent Application Publication Nos. 20020086917 A1 and 20190048150 A1. These references generally disclose wet mixing processes in which separate streams of carbon black slurry and elastomer latex are combined in a mixing zone under conditions that result in coagulation of the elastomer latex without the need for added coagulants. In one embodiment, the slurry is fed into the mixing zone as a continuous, high-velocity jet of injected fluid, while the natural rubber latex fluid is fed at a relatively slow velocity, as described, for example, in U.S. Patent Application Publication No. 20190048150 A1. The high velocity, flow rate and particulate concentration of the filler slurry are sufficient to cause mixing of the latex fluid and high shear, turbulent flow of the mixture within at least the upstream portion of the mixing zone, causing substantially complete coagulation of the elastomer latex prior to the discharge end.

[0076] The coagulated mixture may be dewatered to a moisture content of about 15% to 25%. After dewatering, the resulting dehydrated coagulum may be dried, for example, by thermal drying. The dehydrated coagulum may be mechanically masticated during drying. For example, the dehydrated coagulum may be mechanically processed using one or more of a continuous mixer, an internal mixer, a twin-screw extruder, a single-screw extruder, or a roll mill. Further drying may be carried out to reduce the moisture content to less than about 1 wt.%, or less than 0.5 wt.%, or less than 0.2 wt.%. The resulting dried composite blend may be granulated or otherwise broken into small pieces for easier handling.

[0077] An exemplary composite blend is available from Cabot Corporation. 2 C (trademark) DX9730, E 2 C(trademark)FX9390, E 2C (trademark) DX9660, E 2 These are commercially available as C(trademark) EX9620, E29620, etc.

[0078]

[0078] The preparation method of such Engineered Elastomeric Composites (E2C) and their properties are further described, for example, in Ting Wang et al., "CEC and its application in off-the-road tires," Rubber World, 277(6), pp. 33-38 (2003).

[0079] (iii) a third elastomer In an exemplary embodiment, the third elastomer consists of or includes a synthetic conjugated diene-based elastomer (referred to herein as a polydiene or polydiene elastomer). The third elastomer may be present in the rubber composition in an amount of at least 5 phr, or at least 10 phr, or at least 15 phr, or up to 70 phr, or up to 60 phr, or up to 40 phr, or up to 30 phr, for example, 18±5 phr.

[0080] The polydiene elastomer comprises at least one polydiene elastomer, each of which is at least partially derived from butadiene. For example, at least 20%, or at least 30%, of the units in the polydiene rubber are formed from butadiene. In one embodiment, the polydiene rubber is a copolymer of butadiene and another monomer, such as one or more of vinyl arene monomers, such as styrene, α-methylstyrene, divinylbenzene, and vinylpyridine.

[0081]

[0081] Exemplary polydiene elastomers include styrene-butadiene rubber (SBR) and polybutadiene (PBD). The styrene-butadiene rubber may be emulsion-polymerized styrene-butadiene rubber (ESBR) and / or solution-polymerized styrene-butadiene rubber (SSBR).

[0082] In one embodiment, the polydiene elastomer comprises or consists of ESBR. The ESBR may have a bound styrene content of 5 to 50 wt.%, for example, 20 to 30 wt.%. In emulsion polymerization, styrene and 1,3-butadiene are copolymerized as an aqueous emulsion. Emulsion polymerization processes are described, for example, in U.S. Patent No. 5,583,173 A and U.S. Patent Application Publication Nos. 20050288393 A1, 20060266454 A1, 20080216935 A1, and 20140171557 A1.

[0083]

[0083] An example of an ESBR is available from Goodyear Tire & Rubber Company as PLIOFLEX 1502™, which has a styrene content of 23.5 wt. % and a Tg of -50°C, and is prepared by tin-catalyzed aqueous emulsion polymerization of styrene and 1,3-butadiene monomers.

[0084] ESBR may be oil-extended to facilitate processing. One oil-extended ESBR is BUNA™ SB 1723-Schkopau from Dow, which is produced by low-temperature polymerization using a mixed rosin acid / fatty acid soap. It is plasticized with 37.5 parts mineral oil per 100 parts rubber and has a Mooney viscosity ML1+4 of 49 at 100°C. Another example of an oil-extended ESBR has a bound styrene content of 40% styrene, a Tg of -33°C, and is extended with 37.5 phr of RAE oil, and is available from Synthos as KER™ 1789 ESBR.

[0085] In one embodiment, the polydiene elastomer comprises or consists of SSBR. The SSBR may have a bound styrene content of 5 to 50 wt.%, e.g., 9 to 36 wt.%, or 26 to 31 wt.%. SSBR can be prepared, for example, by anionic polymerization in an inert organic solvent. For example, SSBR can be synthesized by copolymerizing styrene and 1,3-butadiene monomers in a hydrocarbon solvent using an organolithium compound as an initiator. Alternatively, the SSBR can be tin-coupled. Methods for preparing SSBR are described, for example, in U.S. Patent Nos. 4,843,120A and 6,103,842A, and U.S. Patent Application Publication Nos. 20020099148A1, 20120077902A1, and 20140135437A1.

[0086]

[0086] An example of an SSBR is available from Dow as SE-SLR® 6430.

[0087]

[0087] SSBR may be oil-extended. The oil-extended SSBR may have a bound styrene content of 25 to 45 wt. % based on the weight of the rubber, a vinyl 1,2 content of 10 to 60 wt. %, and a Tg of -40°C to -5°C. One example of an oil-extended SSBR has 40 wt. % bound styrene, 14 wt. % vinyl, a Tg of -34°C, and is extended with 37.5 phr of TDAE oil, and is available from Dow Schkopau as SE SLR6430™ SSBR. Another example of an oil-extended SSBR has 34 wt. % bound styrene, 38 wt. % vinyl, a Tg of -25°C, and is extended with 37.5 phr of SRAE oil, and is available from Asahi Kasei Corporation as Tufdene™ E680.

[0088] In one embodiment, the first and / or third elastomer may be hydrogenated and / or functionalized. Hydrogenation reduces the percentage of double bonds in the elastomer. The hydrogenation of the polydiene elastomer may be partial or complete. By partial, it is meant that less than all of the double bonds present in the polydiene segments of the elastomer are hydrogenated, for example, using a hydrogenation catalyst. For example, at least 10%, or at least 20%, or at least 30%, or at least 40%, or at least 60%, or at least 80% of the double bonds present in the polydiene segments of the elastomer are saturated by hydrogenation. In some embodiments, up to 100% of the double bonds present in the polydiene segments of the elastomer are saturated by hydrogenation.

[0089]

[0089] Functionalization can incorporate various functional groups, such as alkoxysilane groups, primary amine groups, thiol groups, and combinations thereof. For example, functionalized SBR can be obtained by copolymerizing styrene and butadiene with primary amino and / or thiol groups and alkoxysilyl groups attached to the polymer chain. In one embodiment, the alkoxysilyl groups are ethoxysilyl groups. For example, styrene-butadiene rubber can be produced by anionic polymerization of styrene and butadiene in a hydrocarbon solvent using an organic alkali metal and / or organic alkaline earth metal initiator, adding a terminal capping compound having a protected primary amino group and / or a protected thiol group and an alkoxysilyl group to react with the living polymer chain ends when polymerization is substantially complete, followed by deblocking, for example, by hydrolysis or other suitable procedure.

[0090]

[0090] Methods for preparing functionalized styrene-butadiene rubbers are disclosed, for example, in U.S. Patent Application Publication Nos. 20040249020A1, 20040254301A1, and 20080287601A1. Chain-functionalized amino-functionalized SBR is described, for example, in U.S. Patent Application Publication No. 20040122194A1.

[0091] SBR functionalized with alkoxysilane and amino groups has a bound styrene content of 27%, a 1,2-vinyl content of 57%, and a Tg of −27° C. and is available from JSR Corporation as HPR355H. Tin-coupled SBR functionalized with alkoxysilane and thiol groups has a Tg of approximately −25° C. and is available from Trinseo as Sprintan® SLR4602. SSBR functionalized with alkoxysilane and thiol groups, has a bound styrene content of 15 wt.%, a 1,2-vinyl content of 30 wt.%, and a Tg of approximately −60° C. and is available from Trinseo as SPRINTAN® SLR3402. Hydroxy-functionalized SBR is available from Asahi Kasei Corporation as Tufdene® 3330. Epoxy-functionalized SBR is available from Asahi Kasei Corporation as Tufdene® E50. Amino / siloxy functionalized SBR is available from Trinseo as SLR4601™ and from JSR Corporation as T5560™.

[0092] In one embodiment, the elastomer can be both functionalized and hydrogenated. The elastomer to be hydrogenated may be functionalized at the end, as described, for example, in U.S. Patent Application Publication Nos. 20230312780A1, 20230312784A1, 20230312792A1, and 20230312798A1. Functionalization may also be performed in the middle of the end. In another embodiment, the elastomer is functionalized with an alkoxysilane group and, optionally, at least one functional group selected from the group consisting of a primary amine and a thiol. For example, a (co)polymer chain of a conjugated diene or a conjugated diene and an aromatic vinyl compound may be terminated with a terminating compound having a protected primary amino group and an alkoxysilyl group, as described, for example, in U.S. Patent Application Publication No. 20040254301A1. Another SBR functionalized with alkoxysilane groups and thiols is described in US Patent Application Publication No. 20080287601A1.

[0093] Suitable styrene-butadiene rubbers functionalized with alkoxysilane groups and primary amine groups are commercially available, for example HPR340 from Japan Synthetic Rubber Co., Ltd. (JSR Corporation).

[0094] Suitable styrene-butadiene rubbers functionalized with alkoxysilane groups and thiol groups are commercially available, for example, Sprintan SLR3402 from Trinseo.

[0095] Polybutadiene rubber, which may be utilized as the third elastomer, may be prepared, for example, by organic solution polymerization of 1,3-butadiene. The PBD may be characterized, for example, by having at least 90% cis-1,4-microstructure content ("high cis" content), or at least 95%, or at least 96% cis-1,4-microstructure. The glass transition temperature (Tg) of the PBD, determined according to ASTM D3418, may range from -95 to -112°C. The PBD may have a Mooney viscosity, determined according to ASTM D1646, of 45 to 65 M.U.

[0096] Suitable polybutadiene rubbers are commercially available, for example, The Goodyear Tire & Rubber Company's Budene® 1207, Budene® 1208, Budene® 1223, and Budene® 1280. These high cis-1,4-polybutadiene rubbers can be synthesized utilizing nickel or neodymium catalyst systems, such as those containing a mixture of (1) an organonickel compound, (2) an organoaluminum compound, and (3) a fluorine-containing compound, as described, for example, in U.S. Pat. Nos. 5,698,643 and 5,451,646. For example, nickel-catalyzed Budene® 1207 has a cis 1,4-content of at least 96%, a Mooney viscosity of 55, and a Tg of -100°C to -104°C, while neodymium-catalyzed Budene® 1223 has a cis 1,4-content of at least 96%, a Mooney viscosity of 55, and a Tg of about -104°C.

[0097]

[0097] When used, PBD may be present in the rubber composition in an amount of at least 10 phr, or at least 15 phr, or at least 20 phr, or up to 50 phr, or up to 40 phr, or up to 35 phr. In other embodiments, PBD is omitted.

[0098] (iv) Other elastomers Other vulcanizable elastomers may be present in the rubber composition (for example, a total of up to 20 phr, or up to 10 phr, or up to 5 phr, or up to 2 phr, or up to 1 phr). Examples of such other elastomers include halobutyl rubbers, such as bromobutyl rubber and chlorobutyl rubber, nitrile rubber, polynorbornene copolymers, ethylene-propylene-diene rubber, chloroprene rubber, acrylate rubber, fluororubber, silicone rubber, polysulfide rubber, epichlorohydrin rubber, butyl rubber, terpolymers formed from ethylene monomers and propylene monomers and / or ethylene propylene diene monomers (EPDM), isoprene-based block copolymers, styrenic block copolymers, styrene-ethylene / butylene-styrene block copolymers (SEBS), styrene-[ethylene-(ethylene / propylene)]-styrene block copolymers (SEEPS), styrene-isoprene-styrene block copolymers (SIS), random styrenic copolymers, hydrogenated styrenic block copolymers, polyisobutylene, ethylene vinyl acetate (EVA) polymers, polyolefins, amorphous polyolefins, semi-crystalline polyolefins, alpha-poly Olefins, reactor-ready polyolefins, acrylates, metallocene-catalyzed polyolefin polymers and elastomers, reactor-made thermoplastic polyolefin elastomers, olefin block copolymers, copolyester block copolymers, polyurethane block copolymers, polyamide block copolymers, thermoplastic polyolefins, thermoplastic vulcanizates, ethylene vinyl acetate copolymers, ethylene n-butyl acrylate copolymers, ethylene methyl acrylate copolymers, neoprene, acrylic acid, urethanes, poly(acrylates), ethylene acrylic acid copolymers, polyether ether ketone, polyamides, atactic polypropylene, polyethylene including atactic polypropylene, ethylene-propylene polymers, propylene-hexene polymers, ethylene-butene polymers, ethylene-octene polymers, propylene-butene polymers, propylene-octene polymers, metallocene-catalyzed polypropylene polymers,These polymers include metallocene-catalyzed polyethylene polymers, ethylene-propylene-butylene terpolymers, copolymers produced from propylene, ethylene, C4 to C10 alpha-olefin monomers, polypropylene polymers, maleated polyolefins, polyester copolymers, copolyester polymers, ethylene acrylic acid copolymers, and / or polyvinyl acetate. Such polymers optionally contain modifications and / or functionalizations at the polymer chain ends or pendant positions within the polymer selected from one or more of hydroxyl groups, ethoxy groups, epoxy groups, siloxane groups, amine groups, aminesiloxane groups, carboxy groups, phthalocyanine groups, and silane-sulfide groups.

[0099] B. Particulate fillers In addition to the particulate filler provided by the composite blend, additional amounts (e.g., at least 5 phr, or at least 10 phr, or at least 20 phr, or at least 40 phr, or up to 100 phr, or up to 60 phr) of one or more particulate reinforcing fillers are used in forming the rubber composition. Examples of such particulate fillers include carbon black and silica. The additional fillers may be added in an amount sufficient to provide the rubber composition with a total particulate filler of at least 40 phr, or at least 50 phr, or at least 60 phr, or up to 120 phr, or up to 100 phr, or up to 80 phr.

[0100] (i) Carbon black

[0100] Carbon black may be present in the rubber composition in a total amount of 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 at least 50 phr, or at least 60 phr, or up to 90 phr, or up to 80 phr, or up to 75 phr, or up to 70 phr. The ratio of carbon black present in the composite blend to additional carbon black added separately may be at least 1:3, or at least 1:2, or at least 1:1.5, or up to 3:1, or up to 2:1, or up to 1.5:1, or up to 1.2:1.

[0101]

[0101] Exemplary carbon blacks have a surface area of at least 8 mm, as determined in accordance with ASTM D6556-21, "Standard Test Method for Carbon Black—Total and External Surface Area by Nitrogen Adsorption." 2 / kg, or at least 20m 2 / kg, or at least 100m 2 / kg, or at least 120m 2 / kg, or up to 200m 2 / kg, or up to 132m 2 / kg. The specific (external) surface area based on the statistical thickness method (STSA) is defined as the specific surface area accessible to rubber. Examples of carbon black include furnace black, channel black, and lamp black. Specific examples of useful carbon black include super abrasion furnace (SAF) black, high abrasion furnace (HAF) black, fast extrudable furnace (FEF) black, fine furnace (FF) black, semi-super abrasion furnace (ISAF) black, semi-reinforcing furnace (SRF) black, medium processability channel black, difficult processability channel black, and conductive channel black. Other carbon blacks that can be used include acetylene black. In certain embodiments, the rubber composition comprises a mixture of two or more types of carbon black.

[0102]

[0102] Exemplary carbon blacks useful herein as additional carbon blacks include those having the 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 defined in ASTM D1765-21, "Standard Classification System for Carbon Blacks Used in Rubber Products." These carbon blacks have an iodine absorption, determined according to ASTM D1510-21, ranging from 9 to 145 g / kg, and a viscosity of 34 to 150 cm 3 / 100g. For example, the N121 grade has an iodine absorption of about 121 g / kg, an iodine absorption of about 121 m 2 / kg CATB specific surface area, approximately 132 m 2The N220 grade is a granular carbon black with a DBP absorption of 116-126 g / kg and an ash content of less than 0.5 wt.%. 2 / kg CATB specific surface area, 109-119m 2 / kg DBP absorption and an ash content of less than 0.5 wt.%.

[0103] (ii) Silica In some embodiments, the rubber composition may contain at least 2 phr of silica, or at least 4 phr, or at least 5 phr, or up to 110 phr, or up to 60 phr, or up to 40 phr, or up to 15 phr, or up to 12 phr. The silica may be at least 1 phr, or at least 5 phr, or at least 8 phr, or up to 40 phr, or up to 20 phr, or up to 12 phr of reinforcing filler. In other embodiments, silica is not present in the rubber composition.

[0104]

[0104] When used in conjunction with carbon black, silica can reduce hysteresis and increase tear resistance while minimizing the loading of the carbon black.

[0105] Silica may be 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 by which the silica is formed). The term "precipitated silica" is used to refer to synthetic amorphous silica, typically obtained by a process in which silicates are precipitated with an acidifying agent.

[0106] Silica may be prepared by various methods. Precipitated silica may be prepared, for example, by digesting amorphous silica, found in rice husks or other biological waste, with sodium hydroxide to form sodium silicate, and then precipitating silica from the sodium silicate by reacting 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 U.S. Pat. No. 5,587,416 A and U.S. Patent Application Publication Nos. 20020081247 A1, 20050032965 A1, and 20110178227 A1. Precipitated silica may also be formed from silica gel, as described, for example, in U.S. Pat. No. 5,708,069. Silica gel may be obtained, for example, by hydrophobizing silica hydrogel with, for example, organomercaptosilanes and alkylsilanes, and drying the product.

[0107]

[0107] The surface area of silica can be measured in a variety of ways. One method is by nitrogen adsorption according to ASTM D1993-18, "Standard Test Method for Precipitated Silica - Surface Area by Multipoint BET Nitrogen Adsorption," which is referred to herein as nitrogen surface area. Another method is according to ASTM D6845-20, "Standard Test Method for Silica, Precipitated, Hydrated - CTAB (Cetyltrimethylammonium Bromide) Surface Area," which is referred to herein as CTAB surface area. CTAB molecules are relatively large and therefore do not adsorb into micropores or surface irregularities. Therefore, CTAB surface area reflects only the silica surface available for interaction with rubber molecules.

[0108] In an exemplary embodiment, the silica is at least 140 m 2 / g, or at least 160m 2 / g, or at least 200m 2 / g, or at least 220m 2 / g, or up to 350m 2 / g, or up to 300m 2 / g of CTAB surface area.

[0109] An exemplary high surface area silica is available from Solvay as Zeosil™ Premium SW. This silica has a surface area of approximately 250 m 2 / g CTAB surface area. Other precipitated silicas include Hi-Sil™ 532, Hi-Sil™ 532EP, and Hi-Sil™ EZ160G from PPG Industries; Hubersil™ 4155 from JMHuber Company; Zeosil™ models 115GR, 125GR, 165GR, 175GR, 185GR, 195GR, 1085GR, 1165MP, 1115MP, HRS1200MP, Premium MP, Premium 200MP, and 195HR from Solvay; Ultrasil™ models VN2, VN3, VN3GR, 5000GR, 7000GR, and 9000GR from Evonik; Zeopol™ models 8755LS and 8745 from Evonik; and Wuxi Quechen Silicon Chemical. Co. Ltd., models 115GR and 2000MP, Newsil®; and Maruo Calcium Co., Ltd., Tokusil® 315.

[0110]

[0110] The silica may be surface treated, for example with an organosilane coupling agent and / or a polyalkylene oxide, such as polyethylene glycol, prior to incorporation of the pretreated silica into the rubber composition to enhance dispersion and / or adhesion to the elastomer. In another embodiment, the silica may be treated with the coupling agent and / or polyalkylene oxide in situ within the rubber composition, for example, prior to addition of the curative.

[0111] Coupling agents generally contain a first moiety reactive with the hydroxyl groups (e.g., silanol groups) present on the surface of the precipitated silica, and a second moiety capable of reacting with the diene-based elastomer. The two moieties are connected by a linking group, e.g., a hydrocarbyl and / or sulfide bridge, so that the precipitated silica is chemically bonded to the elastomer. Organosilanes are commonly used coupling agents.

[0112]

[0112] Other particulate reinforcing fillers which may additionally or alternatively be incorporated into the rubber composition include alumina, aluminum hydroxide, clay (reinforcing grades), magnesium hydroxide, boron nitride, aluminum nitride, titanium dioxide, and combinations thereof.

[0113] C. Processing aids

[0113] The rubber composition may also contain processing aids such as liquid plasticizers, waxes, resins, and mixtures thereof.

[0114] The term liquid plasticizer is used to refer to a plasticizer component that is liquid at room temperature (i.e., liquid at or above 25°C), as distinguished from hydrocarbon resins, which are generally solid at room temperature. Generally, liquid plasticizers have a Tg below 0°C, generally well below, for example, below -30°C, or below -40°C, or below -50°C, for example, between 0°C and -100°C.

[0115] Suitable liquid plasticizers include both oils (e.g., oils derived from petroleum and plants) and other non-oil liquid plasticizers, such as ether plasticizers, ester plasticizers, phosphate plasticizers, and sulfonic acid plasticizers. The liquid plasticizer may be added in one or more stages, such as NP1, NP2, or as an extender oil for one of the elastomers. Petroleum-based oils may include aromatic oils, naphthenic oils, low polyaromatic (PCA) oils (such as MES, TDAE, and SRAE), and mixtures thereof. Vegetable oils may include oils derived from vegetables, nuts, seeds, and mixtures thereof, such as triglycerides.

[0116]

[0116] Liquid plasticizers may be used in the rubber composition at 0 to 30 phr, or at least 0.5 phr, or at least 1 phr, or at least 2 phr, or up to 10 phr, or up to 5 phr.

[0117] Suitable waxes include paraffin waxes and microcrystalline waxes, which may be of the type described in The Vanderbilt Rubber Handbook (1978), pages 346 and 347. Such waxes can function as antiozonants.

[0118]

[0118] Waxes, when used, may be present at 0.1 phr or more, for example at least 0.2 phr, or at least 0.5 phr, or up to 5 phr, or up to 3 phr, or up to 2 phr.

[0119]

[0119] Resins may be used at 0 to 10 phr, or at least 0.1 phr, or at least 0.5 phr, or up to 5 phr. When the rubber composition includes one or more resins, the resins may be selected from hydrocarbon traction resins, natural resins such as rosin, tackifying resins such as non-reactive phenol formaldehyde resins, stiffening resins such as reactive phenol formaldehyde resins, and combinations thereof.

[0120] Examples of hydrocarbon traction resins that can be used include those having a glass transition temperature, Tg, determined in accordance with ASTM D6604, greater than 20° C., or at least 30° C., or up to 50° C. The traction resin may also have a softening point, determined in accordance with ASTM E28, of at least 30° C., or at least 70° C., or up to 100° C. The Tg is generally lower than the softening point; the lower the Tg, the lower the softening point. The hydrocarbon traction resin may be selected from terpene-phenolic resins, terpene resins, terpene-styrene resins, styrene / alpha-methylstyrene resins, coumarone-indene resins, polydicyclopentadiene (DCPD) resins, DCPD / C9 resins, hydrogenated DCPD resins (H2DCPD), H2DCPD / C9 resins, C5 resins, C9 resins, H2C5 resins, H2C9 resins, C5 / C9 resins, rosin-derived resins, and copolymers and mixtures thereof (H2 indicates that the resin is hydrogenated, and C5 and C9 indicate the number of carbon atoms in the monomers from which the resin is formed before functionalization). Such resins may be partially or fully hydrogenated and / or functionalized. Exemplary hydrocarbon-based traction resins are described in U.S. Patent Application Publication No. 20210032442A1. Resins are also described in U.S. Patent Application Publication No. 20210355301A1.

[0121] Resins may also be derived from naturally occurring rosin and its derivatives, including, for example, gum rosin, wood rosin, and tall oil rosin. Gum rosin, wood rosin, and tall oil rosin have similar compositions, although the amount of the rosin component may vary. Such resins may be dimerized, polymerized, or disproportionated. Such resins may be in the form of esters of rosin acids with polyols such as pentaerythritol or glycols. In one embodiment, the rubber composition contains 1 to 4 phr of rosin.

[0122] D. Curing activator Cure activators are additives used to aid in vulcanization. Cure activators include both (i) inorganic cure activators and (ii) organic cure activators. Zinc oxide is the most widely used inorganic cure activator and may be present in an amount of at least 1 phr, e.g., at least 2 phr, or up to 7 phr, or up to 5 phr.

[0123]

[0123] Organic cure activators include fatty acids such as stearic acid, palmitic acid, lauric acid, and mixtures thereof, calcium and zinc salts of unsaturated fatty acids, amides of unsaturated fatty acids, and thiourea compounds such as thiourea and dihydrocarbyl thioureas, 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.

[0124]

[0124] In one embodiment, a mixture of fatty acids, primarily stearic acid, is used as the organic active agent.

[0125] The total amount of organic cure activator may be at least 0.1 phr, such as at least 0.5 phr, or at least 1 phr, or at least 2 phr, or up to 6 phr, or up to 5 phr, or up to 3 phr.

[0126] E. Curing accelerator

[0126] Accelerators, like activators, act as catalysts for the vulcanization agents. Accelerators are used to control the time and / or temperature required for vulcanization and to improve the properties of the vulcanizate, such as by crosslinking, and can be used alone or in combination. The total amount of accelerators can be 0.1 to 10 phr, or at least 0.3 phr, or at least 0.5 phr, or up to 3 phr.

[0127] In one embodiment, a single accelerator system, i.e., a primary accelerator, may be used. The primary accelerator may be used in amounts ranging from 0.3 to 5 phr, or up to 2 phr. In another embodiment, a combination of two or more accelerators may be used. A secondary accelerator is generally used in a smaller amount to activate the vulcanizate and improve its properties. Such accelerator combinations have historically been known to produce a synergistic effect in the final properties of sulfur-cured rubber, often somewhat superior to those produced by the use of either accelerator alone. Additionally, delayed-action accelerators may be used, which are less affected by normal processing temperatures but produce a satisfactory cure at normal vulcanization temperatures.

[0128] Representative examples of accelerators include amines, disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides, dithiocarbamates, and xanthates. In one embodiment, the primary accelerator is a sulfenamide, such as N-cyclohexylbenzothiazole-2-sulfenamide (CBS) or N-tert-butyl-2-benzothiazole-sulfenamide (TBBS). If a secondary accelerator is used, it may be a guanidine, dithiocarbamate, or thiuram compound, such as N,N'-diphenylguanidine (DPG), although a second sulfenamide accelerator may also be used. Examples of thiazole cure accelerators include 2-mercaptobenzothiazole and 2,2'-dithiobis(benzothiazole) (MBTS).

[0129]

[0129] Cure accelerators with fast cure initiation times, usually less than 3 minutes, are called ultra-accelerators. Examples of ultra-accelerators that may be used alone or in combination with other accelerators include 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane (BDBZTH), tetrabenzylthiuram disulfide (TBzTD), tetramethylthiuram monosulfide (TMTM), tetramethylthiuram disulfide (TMTD), tetraethylthiuram disulfide (TETD), tetraisobutylthiuram disulfide (TiBTD), dipentamethylenethiuram tetrasulfide (DPTT), zinc dibutyldithiocarbamate (ZDBC), zinc dibenzyldithiocarbamate (ZBED), zinc dibenzyldithiocarbamate (ZBEC), and mixtures thereof.

[0130]

[0130] Free radical initiators that may be used in some embodiments are sometimes known as redox initiators and include combinations of chelated iron salts, sodium formaldehyde sulfoxylate, and organic hydroperoxides. Representative organic hydroperoxides include cumene hydroperoxide, p-menthane hydroperoxide, and tertiary butyl hydroperoxide. The free radical initiator may be used in combination with or as a replacement for the sulfur-based vulcanizing agent. When used, the amount of the free radical initiator may be 0.1 to 4 phr, or 0.5 to 2 phr. In other embodiments, the free radical initiator may not be included in the rubber composition.

[0131] Cure inhibitors are used to control the vulcanization process, generally delaying or inhibiting vulcanization until a desired time and / or temperature is reached. Examples of cure inhibitors include cyclohexylthiophthalimide. When used, the amount of cure inhibitor may be 0.1 to 3 phr, or 0.5 to 2 phr. In one embodiment, no cure inhibitor is used.

[0132] If used, the amount of set retarder may be 0.05 to 2 phr, or at least 0.1 phr, or up to 1 phr, or up to 0.5 phr. In one embodiment, no set retarder is used.

[0133] The rubber composition may include 0.1 to 15 phr of an organosilane coupling agent, for example, at least 1 phr, or up to 5 phr. The amount of organosilane coupling agent may be based on the amount of silica in the composition, for example, 1 to 10 phr.

[0134]

[0134] Examples of organosilane coupling agents include those containing groups such as alkylalkoxy, 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.

[0135]

[0135] Examples of alkylalkoxysilanes suitable for use include octyltriethoxysilane, octyltrimethoxysilane, trimethylethoxysilane, cyclohexyltriethoxysilane, octadecyltrimethoxysilane, methyloctyldimethoxysilane, and mixtures thereof.

[0136] Examples of bis(trialkoxysilylorgano) polysulfides suitable for use 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(trihexoxysilylpropyl) disulfide, 2,2'-bis(dimethylmethoxysilylethyl) disulfide, 3,3'-bis(diphenylcyclohexoxysilylpropyl) disulfide, 3,3'-bis(ethyl-di-sec-butoxysilylpropyl) disulfide, 3,3'-bis(propyldiethoxysilylpropyl) disulfide, 12,12'-bis(triisopropyl ... bis(3-triethoxysilylpropyl) disulfide, 3,3'-bis(dimethoxyphenylsilyl-2-methylpropyl) disulfide, 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-triethoxysilylpropyl benzothiazole tetrasulfide, and mixtures thereof. Bis(3-triethoxysilylpropyl) tetrasulfide is available from Evonik Corporation as Si69®, and bis(3-triethoxysilylpropyl) disulfide, with an average of 2.15 connecting sulfur atoms in the polysulfide bridge, is available from Evonik Corporation as Si266®. One example of a suitable blocked mercaptosilane is NXT™ silane (3-octanoylthio-1-propyltriethoxysilane), available from Momentive Performance Materials Inc., Albany, NY.

[0137] F. Sulfur-based curing agent

[0137] The vulcanization (curing) of the rubber composition is carried out in the presence of a curing (vulcanizing) agent, such as a sulfur-based curative. Examples of suitable sulfur-based curatives include elemental sulfur (free sulfur), insoluble polymeric sulfur, soluble sulfur, and sulfur-donating curatives such as amine disulfides, polymeric polysulfides, or sulfur olefin adducts, and mixtures thereof.

[0138] The sulfur-based curative may be used in an amount (expressed as pure sulfur) of at least 0.1 phr, for example at least 0.2 phr, or at least 0.4 phr, or at least 0.5 phr, or up to 2 phr, or up to 1.5 phr, or up to 1 phr. The amount of sulfur-based curative can be minimized by using a sulfur-donating accelerator.

[0139] G. Antioxidants, antidegradants, antiozonants, and other additives Various compounds that help reduce oxidation, ozone degradation, and other forms of degradation may be incorporated into the rubber composition. These compounds may be present in the rubber composition in a total amount of 1 phr or more, for example, at least 2 phr, or at least 2.5 phr, or up to 6 phr, or up to 5 phr. In other embodiments, they may be absent.

[0140]

[0140] Exemplary antidegradants suitable for use in the rubber composition include amine antioxidants, such as the paraphenylenediamines (PPD) including alkyl-aryl paraphenylenediamines, e.g., para-phenylenediamines such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), N,N'-diphenyl-1,4-phenylenediamine (DPPD), and trimethyl-dihydroquinoline (TMQ) antidegradants, such as those disclosed in, for example, The Vanderbilt Rubber Handbook (1978), pages 344-347.

[0141] In addition to the above components, the rubber composition may contain other rubber compounding ingredients, such as a peptizer, such as pentachlorothiophenol, dibenzamidodiphenyl disulfide, or mixtures thereof. If used, typical amounts of peptizers may be from 0.1 phr to 1 phr.

[0142]

[0142] In one embodiment, the components of the rubber composition other than the first, second and third elastomers, carbon black, silica, activators, accelerators, cure retarders, plasticizers, antiozonants, and sulfur-based vulcanizing agents are present in an amount of 20 phr or less, or 10 phr or less, or 5 phr or less of the rubber composition.

[0143] 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 the tire sidewalls, may additionally or alternatively be formed at least in part from the rubber compositions described herein. The tire may be a pneumatic tire for a road vehicle, such as a bus or truck, or an automobile, or may be a tire for an off-road vehicle, airplane, or the like.

[0144]

[0144] The rubber composition is not limited to use in tires, but may also be applied to rubber hoses, rubber gloves, surgical instruments, etc.

[0145] Exemplary Compositions

[0145] Table 1 shows exemplary rubber compositions according to aspects of exemplary embodiments.

[0146] [Table 1]

[0147] tire tread characteristics Use of the rubber composition in a tire, such as a tire tread, can result in a tire having improved or desirable tread properties. These improved or desirable properties may include, for example, improved mileage while retaining other properties. [Example]

[0148]

[0147] While not intended to limit the scope of the exemplary embodiments, the following examples illustrate the preparation of exemplary rubber compositions and their properties.

[0149]

[0148] Rubber compositions are prepared using the formulations shown in Table 2. Each composition is mixed in four stages, all but the last being non-productive (NP), which is productive (PR). In the first stage, the mixture is dropped when it reaches about 165°C, in the second at about 160°C, in the third at about 155°C, and in the final productive stage at about 110°C. The compounds are mixed in a laboratory mixer. The compositions are cured at a temperature of 135°C for 140 minutes.

[0150] Example A uses a mixture of natural rubber (NR) and ESBR as the elastomer in a ratio of 15:85. Examples B, C, and D all use a composite blend equivalent to 60 phr of natural rubber and 33 phr of carbon black. In Example B, the composite blend is further diluted with 21.82 phr of natural rubber and then with 18.18 phr of ESBR, resulting in an NR:ESBR ratio of 81.82:18.18. In Example C, the composite blend is diluted with natural rubber alone, and in Example D, it is diluted with ESBR alone, resulting in an NR:ESBR ratio of 60:40. The amount of carbon black used in Composition A is 60 phr, and is similar in Examples B through D (excluding that used as a carrier for the coupling agent) at 66 phr. However, the distribution of the particulate fillers, particularly carbon black, in the elastomer differs due to the sequential mixing, resulting in a multiphase mixture. For example, in Example B, mixing the composite material with natural rubber and carbon black in NP1 results in two natural rubber phases with different weight ratios of carbon black to elastomer (the CB:E ratio is higher in the natural rubber phase from the composite blend than in the natural rubber added in NP1). Subsequent addition of ESBR in NP2 results in three phases with different CB:E ratios, with the ESBR phase having the lowest CB:E ratio (lowest proportion of carbon black) and the natural rubber from the composite blend having the highest CB:E ratio. NP3 is an additional mixing step that does not involve the incorporation of additional components and may be omitted.

[0151] [Table 2] 1 Tin-catalyzed emulsion-polymerized styrene-butadiene copolymer, 23.5% bound styrene, containing some antioxidants. Contains mixed acid emulsifiers and is salt-acid coagulated. PLIOFLEX® 1502 from The Goodyear Tire & Rubber Company. 2A composite blend obtained from Cabot as E2C™ DX9730, consisting of natural rubber and 55 phr of carbon black, ie, 93 phr of composite blend is equivalent to 60 phr of natural rubber and 33 phr of carbon black. 3 Smoked rubber sheet (RSS). 4 Technically Graded Rubber (TSR). 5 Carbon black ASTM D 1765 grade N220 obtained from Tokai Carbon Co., Ltd. 6 Approximately 250m 2 Solvay's Zeosil® Premium SW, a precipitated silica with a nitrogen (BET) surface area in the range of 1 / g. 7 Petroleum-based hydrocarbon resins and mixtures of alkylated and aromatic hydrocarbon resins. 8 A modified gum rosin tackifying resin having a softening point of 97°C obtained from Resinall Corp as R-224. 9 Paraffin wax. 10 N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD). 11 Obtained as SureMix® S6, CO2 from Flow Polymers, Polymer Solutions Group. 12 A mixture of fatty acids, primarily stearic acid. 13 TBBS (n-tert-butyl-benzothiazole sulfenamide). 14 N,N'-diphenylguanidine (DPG). 15 N-(cyclohexylthio)phthalimide (optional) 16Bis-[3-(triethoxysilyl)propyl]tetrasulfide (TESPT) obtained from Evonik as Si69® supported on 50% carbon black ASTM grade N347 from Tokai Carbon Co., Ltd.

[0152] Rubber composition properties

[0150] Physical testing was performed on samples of the rubber compositions, and the results are shown in Table 3.

[0153] [Table 3]

[0154] RPA results for storage modulus G' and G'' are determined by a Rubber Process Analyzer (RPA) at 100°C and 1 Hz using a Dynamic Cure Cycle. Tan Delta is the ratio of G'' to G'. RPA Tan Delta at 10% strain indicates the degree of heat generation in the tire (lower is better).

[0155]

[0152] Tensile properties (tensile elongation at 100% modulus (TE), tensile strength, elongation at break, Instron tear, and rebound at 100°C) are determined using an automated testing system instrument from Instron Corporation after curing at 135°C for 140 minutes. TE and tensile strength tests are performed using dumbbell-shaped specimens at 23°C and a pull rate of 50 cm / min. Instron tear is determined at 95°C and a pull rate of 50.8 cm / min (higher values are better). Rebound is determined by the Zwick rebound test at 100°C and indicates rolling resistance, which is linked to tire heat buildup.

[0156]

[0153] Wear, which indicates tread wear, is determined as the Grosch wear rate converted to mg / km of worn rubber. The test rubber specimen is placed under a constant load (70 Newtons) at a given slip angle as it travels a given distance on a rotating abrasive disc. A lower wear value (mg / km) at a given slip angle indicates a higher expected mileage.

[0157]

[0154] The toughness factor is the area under the stress-strain curve.

[0158] Strebler tear is determined at 100°C after curing for 140 minutes at 135°C and aging for 7 days at 90°C. The test is conducted at a pull rate of 50 cm / min. This is a peel test, which determines interfacial adhesion by pulling one rubber composition away from the other at right angles to the unbroken specimen, with the two ends of the rubber composition pulled apart at an angle of 180°. A higher value is an indication of the robustness of the composition.

[0159] As can be seen from the data, the vulcanizable rubber composition samples of Example B (composite blends diluted with natural rubber and ESBR) performed better overall than the samples of Comparative Example A, and also performed better than the samples using all NR or all ESBR as the diluent elastomer (Examples C and D). In particular, the RPA Tan Delta at 10% strain, Instron Tear and Abrasion results indicate that Inventive Example B has a good blend of properties. The rebound properties of Examples B, C, and D are comparable.

[0160] Each of the documents referenced above is incorporated herein by reference. Except in the examples or where otherwise expressly indicated, all numerical quantities herein specifying amounts of materials, reaction conditions, molecular weights, number of carbon atoms, and the like, are understood to be modified by the word "about." Unless otherwise indicated, each chemical or composition referred to herein should be construed as a commercial-grade material, which may include isomers, by-products, derivatives, and other such substances typically understood to be present in commercial grades. However, the amount of each chemical component is given excluding solvents, diluent oils, or other carrier materials that may be customarily present in commercially available materials, unless otherwise indicated. It should be understood that the upper and lower amount limits, ranges, and ratios described herein can be independently combined. Similarly, the ranges and amounts of each element of the present invention may be used in conjunction with any ranges or amounts of the other elements.

[0161] It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements may subsequently occur to those skilled in the art, which are also intended to be encompassed by the following claims.

Claims

1. mixing the composite blend with a first elastomer in a first non-productive mixing step to produce a first mixture, the composite blend comprising a second elastomer and carbon black, the second elastomer being the same as or different from the first elastomer; mixing a third elastomer, different from the first elastomer, with the first mixture or a mixture produced from the first mixture in a second non-productive mixing step to produce a second mixture; and mixing a curative with the second mixture or a mixture produced from the second mixture in a productive mix step to produce a vulcanizable rubber composition comprising the first, second, and third elastomers, the carbon black from the composite blend, and an additional amount of reinforcing filler; 1. A method for forming a vulcanizable rubber composition comprising:

2. 10. The method of claim 1, wherein the first elastomer comprises a first one of natural rubber and a polydiene elastomer, and the third elastomer comprises a second one of natural rubber and a polydiene elastomer.

3. The method of claim 2 , wherein the first elastomer comprises natural rubber and the third elastomer comprises a polydiene elastomer.

4. The method of claim 2 wherein the polydiene elastomer comprises styrene-butadiene rubber.

5. The method of claim 4, wherein the styrene-butadiene rubber comprises an emulsion-polymerized styrene-butadiene rubber.

6. 10. The method of claim 1, wherein the weight ratio of the first elastomer to the third elastomer in the vulcanizable rubber composition is at least 1:10, or at least 1:5, or at least 1:2, or at least 1:1.5, or at least 1:1, or at most 10:1, or at most 5:1, or at most 3:1, or at most 2:1, or at most 1.5:

1.

7. 10. The method of claim 1, wherein the first and third elastomers are present in the vulcanizable rubber composition in a combined amount of at least 20 phr, or at least 30 phr, or at most 70 phr, or at most 60 phr, or at most 50 phr, or at most 40 phr.

8. The method of claim 1 , wherein the second elastomer comprises natural rubber.

9. 10. The method of claim 1, wherein the composite blend comprises carbon black in an amount of at least 40 phr per 100 phr of the second elastomer.

10. The method of claim 1 , wherein the reinforcing filler comprises carbon black in an amount of at least 10 phr, or at least 20 phr, per 100 phr of the second elastomer.

11. The method of claim 10, wherein the reinforcing filler further comprises silica in an amount of at least 5 phr.

12. The method of claim 1 , wherein the vulcanizable rubber composition further comprises at least one of a processing aid, a cure activator, and a cure accelerator.

13. A tire tread formed from the vulcanizable rubber composition formed by the method of claim 1.

14. A tire comprising the tread of claim 13.

15. at least 5 phr of a first elastomer; at least 20 phr of a second elastomer provided in a composite blend with carbon black; and at least 5 phr of a third elastomer, the third elastomer having a chemical composition different from that of the first elastomer; 100 phr of an elastomer comprising in addition to the carbon black in the composite blend, at least 5 phr of a particulate filler selected from the group consisting of carbon black, silica, and combinations thereof; a curing activator; A curing accelerator; A vulcanizable rubber composition comprising: a sulfur-based curing agent.

16. 16. The vulcanizable rubber composition of claim 15, wherein the vulcanizable rubber composition comprises multiple phases including a first phase comprising a first elastomer, a second phase comprising a second elastomer, and a third phase comprising a third elastomer, wherein the concentration of carbon black in the third phase is lower than in the first phase.

17. 16. The vulcanizable rubber composition of claim 15, further comprising a processing aid selected from the group consisting of resins, liquid processing aids, waxes, and combinations thereof.

18. A tire tread formed from the vulcanizable rubber composition of claim 15.

19. A pneumatic tire comprising a tread according to claim 18.

20. mixing together a composite blend, natural rubber, and carbon black in a first non-productive mix step to form a first mixture, the composite blend comprising natural rubber and carbon black; in a second non-productive mix step, mixing styrene-butadiene rubber with the first mixture or a mixture derived from the first mixture to produce a second mixture comprising 100 phr of an elastomer comprising at least 45 phr natural rubber and at least 10 phr styrene-butadiene rubber, at least 40 phr carbon black, and at least 5 phr silica; and mixing a curative with the second mixture or a mixture produced from the second mixture in a productive mix step to produce a vulcanizable rubber composition.

1. A method of forming a vulcanizable rubber composition, comprising:

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