Tread rubber composition of branched and linear cis-polybutadiene with polyisoprene

Abstract

A rubber composition for a heavy truck tire tread that comprises, based on 100 parts by weight of elastomer (phr), at least three diene elastomers each being a different rubber material. The elastomers include polybutadienes and a polyisoprene. The polybutadienes comprise an equal or majority portion of a first polybutadiene synthesized with a nickel or cobalt series catalyst, and an equal or minority portion of second polybutadiene synthesized with a lanthanide-based catalyst. Less than 3 phr of total plasticizer is present in the composition. The at least three elastomers are each characterized by a high cis content of greater than 90 percent.

Description

TREAD RUBBER COMPOSITION OF BRANCHED AND LINEAR CISPOLYBUTADIENE WITH POLYISOPRENEFIELD OF THE INVENTION

[0001] The subject matter of the present invention relates to a composition for rubber elastomer that uncured exhibits improved industrial characteristics and when cured exhibits improved abrasion resistance. The rubber elastomer may be used in the manufacturing of tires and specifically for the use of the tire’s treads. Particularly, the invention relates to rubbers compositions containing a majority of polybutadiene, at least one isoprene and minimal amounts of plasticizer.BACKGROUND OF THE INVENTION

[0002] The details and benefits of rubber compositions comprising nickel catalyzed polybutadiene rubber, lanthanide catalyzed polybutadiene rubber and polyisoprene are described e.g., in Pat. App. Nos. US2023 / 0323097A1; US2015 / 0031790A1; and CN111117027A.

[0003] US Patent Application US2023 / 0323097A1 describes a rubber composition comprising at least three diene elastomers each of which is different rubber material, the elastomer includes at least two polybutadienes which a majority portion of which is a first polybutadiene synthesized with a lanthanide series catalyst, the first polybutadiene having a first Mooney viscosity, and a minority portion of a second polybutadiene synthesized with a nickel-based catalyst, the second polybutadiene having a Mooney viscosity within ± 5 MU of the Mooney viscosity of the first polybutadiene; and also including a synthetic polyisoprene, where the three elastomers has a cis content of greater than 80-90%. The application claims the composition is useful for heavy load vehicles and exhibits in the green state “strong adhesion” and contains a higher level of resin compared to the conventional heavy load tire compound. The rubber composition includes greater than 2 phr vegetable triglyceride oil or soybean oil and includes greater than 4 phr in total of one or a combination of resin.

[0004] US Patent Application US2015 / 0031790A1 describes a vulcanizable rubber mixture comprises: 100 pts. wt. of an oil-free rubber matrix consisting of 15-79 phr of at least one solution styrene-butadiene rubber, 20-75 phr of at least one 1,4-cis-polybutadiene,1-37.5 phr of natural rubber (oil-free) and / or at least one synthetically produced polyisoprene; at least one polybutadiene-based microgel that contains hydroxyl groups; at least one oxide filler that contains hydroxyl groups; and at least one polysulfide-containing alkoxysilane.

[0005] Chinese patent application CN111117027A discloses a rubber composition for a tire retread which includes 10-30 pts. wt. of natural rubber, 70-90 pts. wt. of synthetic rubber, 2-5 pts. wt. anti-aging agent, 0.1-0.5 pts. wt. vulcanizing agent, 6-13 pts. wt. active agent, 50-70 pts. wt. of reinforcing agent, 1-4 pts. wt. of vulcanization accelerator, and 2-8 pts. wt. of a softener. The antioxidant is selected from phenolic antioxidants.

[0006] All of these prior examples fall short of a rubber formulation that offer improved erosion resistance and reduced hysteresis with an acceptable processability. A need exists for a rubber formulation having a higher abrasion resistance but with reduced hysteresis that still having adequate industrial processability characteristics.SUMMARY OF THE INVENTION

[0007] Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

[0008] A rubber composition for a tire comprising, based on 100 parts by weight of elastomer (phr) comprised of at least three diene elastomers each being a different rubber material, the elastomers comprising: 65 phr to 95 phr of a polybutadiene blend comprising: a first polybutadiene synthesized with a lanthanide series catalyst; a second polybutadiene synthesized with a nickel or cobalt catalyst; wherein the first polybutadiene represents 50% to 5% of the polybutadiene blend and the second polybutadiene represents 50% to 95% of the polybutadiene blend and wherein the first polybutadiene and the second polybutadiene have a cis content greater than 90%; 1 phr to 35 phr of an at least one polyisoprene; and 3 phr or less of plasticizer.

[0009] These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention provides a rubber composition having excellent abrasion resistance, reduced hysteresis and good industrial processing characteristics. In particular it discloses a novel formulation where higher loadings of polybutadiene have been achieved with reduced loadings of plasticizers in a rubber formulation that exhibits such the above improved characteristics that has not been previously described. For purposes of describing the invention, reference now will be made in detail to embodiments and / or methods of the invention, one or more examples of which are illustrated in or with the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features or steps illustrated or described as part of one embodiment, can be used with another embodiment or steps to yield a still further embodiments or methods. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

[0011] As used herein, the term “comprise” and variations of the term, such as “comprising”, “comprises”, and “comprised”, are used in a manner that means inclusive of and are not intended to exclude additional additives, components, integers, or steps.

[0012] As used herein, the terms “polymer”, “rubber”, and “elastomer” may be used interchangeably, unless otherwise prescribed. The terms “rubber composition,” “compounded rubber” and “rubber compound” are used interchangeably to refer to rubber which has been blended or mixed with various ingredients and materials and such terms are well known to those having ordinary skill in the rubber mixing or rubber compounding art.

[0013] This disclosure is directed to a rubber composition where high erosion resistance and low hysteresis is desired, such as for truck tire tread and is particularly suitable for use as a rubber composition forming a retread for a truck tire. The heavy load tire rubber composition comprises, based on 100 parts by weight of elastomer (phr), at least three diene elastomers each being a different rubber material and equal to or less than 3 phr of plasticizer. The elastomers include a first polybutadiene synthesized with a lanthanide series catalyst; a second polybutadiene synthesized with a nickel-based catalyst; and a polyisoprene, which may be a natural rubber or a synthetic polyisoprene. The first polybutadiene is characterized in that it has a low amount of molecular branching, or in other words, a linear molecular structure or a “linear BR” which is typical of a lanthanidecatalyst synthesized polybutadiene. Neodymium is a particular useful element of the lanthanide series of elements for polybutadiene synthesis and as such the first polybutadiene be a neodymium catalyzed polybutadiene. The second polybutadiene is similarly characterized, except in that it has a high degree of molecular branching, in other words, is a “highly branched BR” which is typical of a nickel catalyst synthesized polybutadiene. All three of the elastomers are characterized by a high cis content of greater than 90 percent.

[0014] Selected combinations of aspects of the disclosed technology correspond to a plurality of different embodiments of the present invention. It should be noted that each of the exemplary embodiments presented and discussed herein should not insinuate limitations of the present subject matter. Features or steps illustrated or described as part of one embodiment may be used in combination with aspects of another embodiment to yield yet further embodiments. Additionally, certain features may be interchanged with similar devices or features not expressly mentioned which perform the same or similar function.

[0015] The terms "a," "an," and the singular forms of words shall be taken to include the plural form of the same words, such that the terms mean that one or more of something is provided. The terms "at least one" and "one or more" are used interchangeably. The term “generally”, “about”, or “approximately” is defined as being within a half of a unit of measurement or within a half of a percentage. For example, “approximately 0 phr” means a de minimis amount of 0.1 phr or 0.5 phr would also be viewed as equivalent to “approximately 0 phr”, or “approximately 90%” would be inclusive of 89.5% and 90.5%. Rubber Elastomers

[0016] An aspect of the disclosed rubber compound is that it is a blend of at least three conjugated diene-based elastomers and preferably only three conjugated diene-based elastomers. Representative conjugated diene-based elastomers are, for example, comprised of at least one of cis 1,4-polyisoprene and cis 1,4-polybutadiene.

[0017] In practice, each elastomer is a different rubber polymer. Various rubber polymers may be used for the rubber composition such as, for example, polymers and copolymers of at least one of isoprene and 1,3-butadiene copolymerized with at least one of isoprene and 1,3-buta-diene, and mixtures thereof. In one embodiment, the blend is formed from all synthetic polymers. In another embodiment, the blend if formed from natural and synthetic polymers.

[0018] Representative synthetic polymers are the homopolymerization products of butadiene and its homologues and derivatives, for example, methylbutadiene,dimethylbutadiene and pentadiene as well as copolymers such as those formed from butadiene or its homologues or derivatives with other unsaturated monomers. Among the latter are acetylenes, for example, vinyl acetylene; olefins, for example, isobutylene, which copolymerizes with isoprene to form butyl rubber; vinyl compounds, for example, acrylic acid, acrylonitrile, which polymerize with butadiene to form NBR, methacrylic acid and styrene, the latter compound polymerizing with butadiene to form SBR, as well as vinyl esters and various unsaturated aldehydes, ketones and ethers, e.g., acrolein, methyl isopropenyl ketone and vinylethyl ether.

[0019] Examples of synthetic rubbers include neoprene (polychloroprene), polybutadiene (including cis- 1,4-polybutadiene), polyisoprene (including cis-l,4polyiso- prene), butyl rubber, halobutyl rubber such as chlorobutyl rubber or bromobutyl rubber, styrene / isoprene / butadiene rubber, copolymers of 1,3-butadiene or isoprene with monomers such as styrene, acrylonitrile and methyl methacrylate, as well as ethyl ene / propylene terpolymers, also known as ethyl ene / propylene / diene monomer (EPDM), and in particular, ethyl ene / propyl ene / dicyclopentadiene terpolymers. Additional examples of rubbers which may be used include alkoxy-silyl end functionalized solution polymerized polymers (SBR, PBR, IBR and SIBR), silicon-coupled and tin-coupled star- branched polymers.

[0020] The preferred elastomers are polyisoprene and polybutadiene. Cis 1,4- polyisoprene and cis 1,4-polyisoprene natural rubber are well known to those having skill in the rubber art. In many embodiments tread rubber composition contains natural rubber. Synthetic polyisoprene may also be used in addition to the natural rubber or, alternatively, in place of natural rubber.

[0021] In at least one embodiment, the cis-1,4 polyisoprene is characterized by a high cis content of greater than about 90%, as measured by QA5114-01 (IR). In such an embodiment, the rubber composition comprises from about 1 to about 35 phr and, or alternatively from about 1 to about 30phr, or alternatively, from about 1 to about 9 phr.

[0022] The disclosed rubber composition comprises the polyisoprene in a minority amount relative to total content of elastomer. The majority elastomer comprises a different synthetic polymer.

[0023] In practice, the rubber composition comprises at least two high cis polybutadiene rubbers each, preferably, having a cis 1,4 content of at least about 90%, and preferably more than about 95%, as measured by QA 5114-01 (IR). In the inventiondisclosed herein, one polybutadiene is highly branched, while the other polybutadiene is possesses a more linear structure.

[0024] At least one of the cis 1,4-polybutadiene elastomers may be prepared, for example, by polymerization of 1,3-polybutadiene monomer in an organic solvent solution in the presence of a lanthanide-based polymerization catalyst. Suitable catalyst may include lanthanide catalysts based on cerium, praseodymium, neodymium, or gadolinium. In one embodiment, the lanthanide-based polymerization catalyst is neodymium catalyst system. Such a polybutadiene is characterized in that it possesses a generally linear structure.

[0025] At least one of the cis 1,4-polybutadiene elastomers may be prepared, for example, by polymerization of 1,3-polybutadiene monomer in an organic solvent solution in the presence of a Nickel based polymerization catalyst. Suitable catalyst may be based on a nickel compound, an organoaluminium compound, and a halogen compound.

[0026] The rubber composition can comprise two cis 1,4-polybutadienes each prepared by a different catalyst. In one embodiment, the rubber composition can comprise a first cis 1,4-polybutadiene prepared by lanthanide-based catalyst and a second cis 1,4- polybutadiene prepared by a catalyst that is not lanthanide- based. In one embodiment, the rubber composition can comprise a first cis 1,4-polybutadiene prepared by lanthanide- based catalyst and a second cis 1,4-polybutadiene prepared by a nickel -based catalyst or alternatively a cobalt-based catalyst..

[0027] In the contemplated embodiment, the polybutadiene rubber composition comprises from about 65 to about 95 phr and, more preferably, from about 65 to about 90 phr, and even more preferably from about 65 to about 85 phr of polybutadienes. In one embodiment, the polybutadiene rubbers can be present at equal levels, but the preferred embodiment contemplates a first and at least a second polybutadiene at different levels. Particularly the nickel or cobalt catalyzed polybutadiene is present in a greater amount by weight than the lanthanide series catalyzed polybutadiene. In one embodiment, the polybutadiene portion of rubber composition comprises from 50% to about 95% phr of polybutadiene formed using a nickel based or cobalt based catalyst and from 50% to about 5% of a polybutadiene formed using a lanthanide based catalyst. Preferably the lanthanide based catalyst is a neodymium based catalyst.

[0028] It is discovered that having an equal or greater portion of the polybutadiene being a polybutadiene formed using a nickel-based or cobalt-based catalyst, and an equal or lesser portion of the polybutadiene is formed using a lanthanide-series catalyst and where both polybutadienes have a high-cis content, that a low loading of plasticizer, or about 3phr of plasticizer or lower, is possible and still achieve good industrial handling characteristics. This results in a rubber mix that is able to achieve good erosion characteristics, and low hysteresis. In other words, the rubber mixture is able to form treads for tires having greater wear durability and better rolling efficiency.Plasticizer

[0029] As used herein, “plasticizer” refers to a processing aid such as AMO 110, AMO 70, AMO 40, structols, oils, resins, tac resins, or TG resins, etc. The invention described here has low plasticizer loading of 3 phr or less of total plasticizer content. As used herein, “plasticizer” does not include vulcanizations systems such as TBBS, MBTS, DBTPG, CBS, accelerators or protections systems such as 6PPD, TMQ, 77PD, DAPD, IPPD, etc.

[0030] The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.Curing Agent:

[0031] A critical aspect of the present disclosure is the cure package. Accelerators are used to control the time and / or temperature required for vulcanization and to improve the properties of the vulcanizate. Typically, the rubber compositions truck tires and truck tire retreads use primary and secondary accelerators. Combinations of these accelerators might be expected to produce a synergistic effect on the final properties of a conventional compound and are somewhat better than those produced by use of either accelerator alone. Example primary accelerators are amines, disulfides, thioureas, thiazoles, sulfenamides (e.g., N-cyclo- hexyl-2-benzothiazolesulphenamide (CBS), and N-Tert- butyl-2- Benzothiazolesulfenamide (TBBS)) and xanthates. Specific examples of secondary accelerators are a guanidine (e.g., diphenylguanidine (DPG)), dithiocarbamate or thiuram compound.

[0032] Embodiments are contemplated in which a single accelerator system may be used, i.e., primary accelerator. The primary accelerator s) may be used in total amounts ranging from about 0.5 to about 6, preferably about 1 to about 4, phr. Preferably, the primary accelerator is a sulfena- mide. One non-limiting example of a sulfenamide is N- Ter- tbutyl-2-Benzothiazolesulfenamide (TBBS).

[0033] In addition, delayed action accelerators may be used which are not affected by normal processing temperatures but produce a satisfactory cure at ordinary vulcanization temperatures. Vulcanization retarders might also be used. A nonlimiting example of a retarder can be N-cyclo- hexylthiophthalimide (CTP).Reinforcement Network

[0034] The present compound also comprises a filler system or reinforcement network. The filler system comprises at least carbon black and silica in combination. In one embodiment, the majority filler is carbon black. In one embodiment, the minority filler portion belongs to silica.

[0035] Representative examples of carbon blacks include N110, N121, N134, N220, N231, N234, N242, N293, N299, S315, N326, N330, M332, N339, N343, N347, N351, N358, N375, N539, N55O, N582, N630, N642, N650, N683, N754, N762, N765, N774, N787, N907, N908, N990 and N991. These carbon blacks have iodine absorptions ranging from 9 to 145 g / kg and DBP number ranging from 34 to 150 cm3 / 100 g.

[0036] The silica filler may be any suitable silica or a combination of any such silica. Commonly used siliceous pigments that are used in rubber compounding applications include pyrogenic and precipitated siliceous pigments (silica), as well as precipitated high surface area (“EISA”) silica and highly dispersive silica (“HDS”).

[0037] The conventional siliceous pigments preferably employed in this invention are precipitated silicas such as, for example, those obtained by the acidification of a soluble silicate, e.g., sodium silicate.

[0038] The precipitated silicas can be characterized, for example, by having a BET surface area, as measured using nitrogen gas, preferably in the range of about 40 to about 600, and more usually in a range of about 50 to about 300 square meters per gram. The BET method of measuring surface area is described in the Journal of the American Chemical Society, Volume 60, page 304 (1930). The conventional silica may also be typically characterized by having a dibutylphthalate (DBP) absorption value in a range of about 100 to about 400, and more usually about 150 to about 300. The conventional silica might be expected to have an average ultimate particle size, for example, in the range of 0.01 to 0.05 micron as determined by the electron microscope, although the silica particles may be even smaller, or possibly larger, in size.

[0039] When precipitated silica is a pre-hydrophobated precipitated silica, additional precipitated silica (non-pre- hydrophobated silica) and / or a coupling agent may optionally be added to the rubber composition.

[0040] In one embodiment, the rubber composition may also include a (e.g., silane) coupling, such as bis(a>-tri- alkoxy alkyl silyl) polysulfide, w-mercaptoalkyl-trialkoxysi- lane, or combination thereof. In one example, the bis-fo)- trialkoxysilylalkyl) polysulfide has an average of from about 2 to about 4 connecting sulfur atoms in its polysulfidic bridge. In another example, the bis-(co-trialkoxysilylalkyl) polysulfide has an average of from about 2 to about 2.6 connecting sulfur atoms in its polysuflidic bridge. In yet another example, the bis-(ro-trialkoxysilylalkyl)polysulfide has an average of from about 3.3 to about 3.8 connecting sulfur atoms in its polysulfidic bridge. The alkyl group of the silylalkyl moiety of the bis-(<B-trialkoxysilylalkyl)polysul- fide may be a saturated C2-C6 alkyl group, e.g., a propyl group. In addition, at least one of the alkyl groups of the trialkoxy moiety of the bis-(<B-trialkoxysilylalkyl)polysul- fide can be an ethyl group and the remaining alkyl groups of the trialkoxy moiety can be independently saturated C2-C18 alkyls. In another example, at least two of the alkyl groups of the trialkoxy moiety of the bis-(ro-trialkoxysilylalkyl) polysulfide are ethyl groups and the remaining alkyl group of the trialkoxy moiety is independently a saturated C3-C18 alkyl. In one example, the bis- (ro-trialkoxysilylalkyl) polysulfide coupling agent is bis-3 -(tri ethoxy silylpropyl) tetrasulfide (“TESPD”). In another example, the bis-(<B-trialkox- y silylalkyl) Polysulfide coupling agent is bis-3- (triethoxysilylpropyl) tetrasulfide (“TESPT”). The co- mercaptoalkyltrialkoxysilane may have its mercapto moiety blocked from pre-reacting with hydroxyl groups (e.g., silanol groups) contained on the precipitated silica aggregates prior to unblocking the blocked mercapto moiety at an elevated temperature.

[0041] The silane coupling agent is present in the rubber compound in an amount no less than 10% by weight of silica. In another example, the silane coupling agent is present in an amount no more than about 20% by weight of silica.

[0042] The silane coupling agent may be present in an amount between from about 0 to about 10 phr and, more specifically, from about 0.5 to about 5 phr. The silane coupling agent may be present in the rubber compound in an amount no greater than 5 phr and, more specifically, 4 phr in some embodiments. In another example, the silane coupling agent may be present in an amount no less than about 2 phr and, in certain embodiments, 3 phr. Sulfur Curative

[0043] It may be preferred to have the rubber composition for use in the tire component to additionally contain a conventional sulfur containing organosilicon compound.

[0044] Specific examples of sulfur containing oiganosili- con compounds which may be used in accordance with the present invention include: 3,3'-bis(trimethoxysilylpropyl)disulfide, 3,3'-bis (triethoxysilylpropyl) disulfide, 3,3'-bis (triethoxysilylpropyl) tetrasulfide, 3,3'-bis(triethoxysilylpro- pyl) octasulfide, 3,3'-bis(trimethoxysilylpropyl) tetrasulfide, 2,2'-bis(tri ethoxy silyl ethyl) tetrasulfide, 3 ,3 '-bis (trimethoxysilylpropyl) trisulfide, 3,3'-bis(triethoxysilylpro- pyl) trisulfide, 3,3'-bis(tributoxysilylpropyl) disulfide, 3,3'-bis(trimethoxysilylpropyl) (trimethoxysilylpropyl) (trioctoxysilylpropyl) (trihexoxysilylpropyl) ethylhexoxysilylpropyl) (triisooctoxysilylpropyl) hexasulfide, 3,3'- bis octasulfide, 3, 3'-bis tetrasulfide, 3,3'-bis disulfide, 3,3'-bis(tri-2"- trisulfide, 3,3'-bis tetrasulfide, 3 ,3'-bis(tri-t- butoxysilylpropyl) disulfide, 2,2'-bis(methoxy diethoxy silyl ethyl) tetrasulfide, 2,2'-bis(tripropoxysilylethyl) pentasulfide, 3,3'- bis(tricyclonexoxysilylpropyl) tetrasulfide, 3 ,3 '-bis (tricyclopentoxysilylpropyl) trisulfide, 2,2'-bis(tri-2"-meth-ylcyclohexoxysilylethyl) tetrasulfide, bis (trimethoxysilylmethyl) tetrasulfide, 3 -methoxy ethoxy propoxy silyl 3'-diethoxybutoxy-silylpropyltetrasulfide, 2,2'- bis(dimethyl methoxysilylethyl) disulfide, 2,2'-bis(dimethyl sec .butoxy silylethyl) trisulfide, 3,3'-bis(methyl butyl ethoxy silyl propyl) tetrasulfide, 3 ,3'-bis(di t- butylmethoxysilylpro- pyl) tetrasulfide, 2,2'-bis(phenyl methyl methoxysilylethyl) trisulfide, 3,3'-bis(diphenyl isopropoxysilylpropyl) tetrasulfide, 3,3'-bis(diphenyl cyclohexoxysilylpropyl) disulfide, 3,3'-bis(dimethyl ethylmercaptosilylpropyl) tetrasulfide, 2,2'-bis(methyl dim ethoxy silyl ethyl) trisulfide, 2,2'-bis (methyl ethoxyprop oxy silyl ethyl) tetrasulfide, 3 ,3 '-bis (diethyl methoxysilylpropyl) tetrasulfide, 3 ,3'-bis(ethyl disec. butoxysilylpropyl) disulfide, 3,3'-bis(propyl diethoxysilylpropyl) disulfide, 3,3'-bis(butyl dimethoxysilylpropyl) trisulfide, 3,3'-bis(phenyl dimethoxysilylpropyl) tetrasulfide, 3- phenyl ethoxybutoxy silyl 3 '-trimethoxy silyl- propyl tetrasulfide, 4,4'- bis(trimethoxysilylbutyl) tetrasulfide, 6,6'-bis(triethoxysilylhexyl) tetrasulfide, 12,12'- bis(tri- isopropoxysilyl dodecyl) disulfide, 18,18'-bis(trimethoxysilyloctadecyl) tetrasulfide, 18,18'-bis(tripropoxysilyloctadecenyl) tetrasulfide, 4,4'-bis(trimethoxysilyl- buten-2-yl) tetrasulfide, 4,4'-bis(trimethoxysilylcyclohexylene) tetrasulfide, 5,5'-bis (dimethoxymethyl silylpentyl) trisulfide, 3,3'-bis(trimethoxysilyl-2-methylpropyl) tetrasulfide, 3,3'-bis(dimethoxyphenyl silyl-2-methyl propyl) disulfide.Additives

[0045] It is readily understood by a person of ordinary skill in the art that the rubber composition would be compounded by methods generally known in the rubber compounding art, such as mixing the various sulfur-vulcanizable constituent rubbers with various commonly used additive materials such as, for example, sulfur donors, curing aids, such as activators, accelerators and retarders and processing additives, fillers, pigments,fatty acid, zinc oxide, waxes, antioxidants and antiozonants and peptizing agents. As known to those skilled in the art, depending on the intended use of the sulfur vulcanizable and sulfur-vulcanized material (rubbers), the additives mentioned above are selected and commonly used in conventional amounts. Representative examples of sulfur donors include elemental sulfur (free sulfur), an amine disulfide, polymeric poly sulfide and sulfur olefin adducts. Preferably, the sulfur-vulcanizing agent is elemental sulfur. The sulfur- vulcanizing agent may be used in an amount ranging from 0.5 to 8 phr, with a range of from 1 to 6 phr being preferred. Typical amounts of antioxidants comprise about 0.5 to about 5 phr. Representative antioxidants may be, for example, polymerized trimethyl dihydroquinoline, mixture of aryl-p-phenylene diamines, and others, such as, for example, those disclosed in The Vanderbilt Rubber Handbook (1978), pages 344 through 346. Typical amounts of antiozonants comprise about 1 to 5 phr. A non-limiting representative antiozonant can be, for example, N-(l,3 dimethyl butyl)-n'-phenyl-p-phenylenediamine. Typical amounts of fatty acids, if used, which can include stearic acid as an example. A wax may be used. Often microcrystalline waxes are used, but refined paraffin waxes or combinations of both can be used. Typical amounts of peptizers comprise about 0.1 to about 1 phr. Typical peptizers may be, for example, pentachlorothiophenol and dibenzamidodiphenyl disulfide.

[0046] The mixing of the rubber composition can be accomplished by methods known to those having skill in the rubber mixing art. For example, the ingredients are typically mixed in at least two stages, namely, at least one nonproductive stage followed by a productive mix stage. The final curatives including sulfur-vulcanizing agents are typically mixed in the final stage which is conventionally called the “productive” mix stage in which the mixing typically occurs at a temperature, or ultimate temperature, lower than the mix temperature(s) of the preceding non-productive mix stage(s). The terms “non-productive” and “productive” mix stages are well known to those having skill in the rubber mixing art. The rubber composition may be subjected to a thermomechanical mixing step. The thermomechanical mixing step generally comprises a mechanical working in a mixer or extruder for a period of time suitable in order to produce a rubber temperature between 140° C. and 190° C. The appropriate duration of the thermomechanical working varies as a function of the operating conditions, and the volume and nature of the components. For example, the thermomechanical working may be from 1 to 20 minutes.

[0047] Vulcanization of a pneumatic tire of the present invention is generally carried out at conventional temperatures ranging from about 100° C. to 200° C. Preferably, thevulcanization is conducted at temperatures ranging from about 110° C. to 180° C. Any of the usual vulcanization processes may be used such as heating in a press or mold, heating with superheated steam or hot air. Such tires can be built, shaped, molded and cured by various methods which are known and will be readily apparent to those having skill in such art.

[0048] The disclosure contemplates a heavy load tire component formed from such method. The tire component can be ground contacting or non-ground contacting. The tire can be pneumatic or non-pneumatic. In one embodiment, the tire component can be a tread.

[0049] The tire of the present disclosure may be a race tire, passenger tire, aircraft tire, agricultural, earthmover, off-the- road, truck (commercial or passenger) tire, and the like. Preferably, the tire is for a heavy load or heavy-duty vehicle, such as a bus, garbage truck, and the like. The tire may also be a radial or bias, with a radial being preferred.

[0050] The rubber composition itself may also be useful as a tire sidewall or other tire components or in rubber tracks, conveyor belts or other industrial product applications. Particularly, improved abrasion resistance offers advantages in a wide variety of rubber products, such as windshield wiper blades, brake diaphragms, washers, seals, gaskets, hoses, conveyor belts, power transmission belts, shoe soles, shoe foxing and floor mats for buildings or automotive applications.

[0051] The following examples are presented for the purposes of illustrating and not limiting the present invention. All parts are parts by weight unless specifically identified otherwise.

Claims

WHAT IS CLAIMED IS:

1. A rubber composition for a tire comprising, based on 100 parts by weight of elastomer (phr): at least three diene elastomers each being a different rubber material, the elastomers comprising:65 phr to 95 phr of a polybutadiene blend comprising: a first polybutadiene synthesized with a lanthanide series catalyst; a second polybutadiene synthesized with a nickel or cobalt catalyst; wherein the first polybutadiene represents 50% to 5% of the polybutadiene blend and the second polybutadiene represents 50% to 95% of the polybutadiene blend and wherein the first polybutadiene and the second polybutadiene have a cis content greater than 90%;1 phr to 35 phr of an at least one polyisoprene; and3 phr or less of plasticizer.

2. The rubber composition of claim 1 wherein the polybutadiene blend is present in the amount greater than 65 phr and less than 90 phr.

3. The rubber composition of claim 1 wherein the polybutadiene blend is present in the amount greater than 65 phr and equal to or less than 85 phr.

4. The rubber composition of any one of the above claims wherein the polyisoprene has a cis content of above 90 %.5 The rubber composition of any one of the above claims wherein the first polybutadiene and the second polybutadiene have a cis content greater than 95%.

6. The rubber composition of any one of the above claims wherein the at least one polyisoprene is natural rubber.

7. The rubber composition of any one of the above claims wherein the first polybutadiene is synthesized with a neodymium catalyst.

8. The rubber composition of any one of the above claims wherein the second polybutadiene is more highly branched than the first polybutadiene.

9. The rubber composition of any one of the above claims wherein the first polybutadiene has a linear molecular structure.