High-range rubber composition for radial medium-sized truck (RMT) tire tread

Abstract

A tire tread of a drive tire suitable for long-distance freight trucks is composed of a vulcanizable rubber composition comprising 100 phr of an elastomeric component comprising natural rubber and polydiene rubber; at least 40 phr of carbon black; and a curing system comprising a combination of a sulfur-based curing agent, a zinc-based curing activator, an organic curing activator, and a curing accelerator. The curing accelerator includes (i) a sulfenamide accelerator, (ii) a metal dithiocarbamate accelerator, and (iii) at least one of a thiazole polysulfide accelerator and a thiuram polysulfide accelerator.

Description

Technical Field

[0001] A rubber composition suitable for forming a component of a pneumatic tire, such as a tire tread, is described herein. The composition is particularly useful for providing a road tire having high mileage and low rolling resistance. Background Art

[0002] Rubber compositions suitable for tires generally include elastomers and reinforcing fillers such as carbon black and silica. For example, for radial medium truck (RMT) tires for regional transportation and urban applications, lower rolling resistance is desirable, which contributes to the low CO2 emissions of vehicles. Tire treads are important contributors to overall tire performance. The friction energy dissipated under deformation when rolling depends on factors such as the material properties of the rubber composition used.

[0003] In order to reduce rolling resistance, rubber compositions including various types of synthetic and natural rubbers have traditionally been used in the manufacture of tire treads. However, lower rolling resistance often results in tread wear damage.

[0004] Rubber compositions have been developed for improving tread wear without significantly increasing rolling resistance. For example, U.S. Pat. No. 11,118,036 B2 describes a vulcanizable rubber composition comprising solution-polymerized styrene-butadiene rubber, polybutadiene, silica, coumarone-indene resin, and hydrocarbon resins derived from styrene and α-methylstyrene. U.S. Pat. No. 11,214,667 B2 describes a tire tread rubber composition comprising solution-polymerized styrene-butadiene rubber, natural rubber or synthetic polyisoprene; cis-1,4 polybutadiene, processing oil, hydrocarbon resin, and silica.

[0005] Such compositions are typically cured with a sulfur-based curing agent such as elemental sulfur. High levels of sulfur can improve the cure level but can make the cured composition more susceptible to age hardening. There remains a need for a rubber composition that can provide a tire tread having high wear resistance and good aging properties for high mileage applications. Summary of the invention

[0006] According to one embodiment, a tire tread formed from a vulcanizable rubber composition is provided. The rubber composition includes, expressed in parts by weight per hundred parts of elastomer (phr), 100 phr of an elastomeric component, the elastomeric component comprising natural rubber and polydiene rubber; at least 40 phr of carbon black; optionally, one or more processing aids, the one or more processing aids selected from liquid plasticizers, waxes, and mixtures thereof; a curing system comprising a sulfur-based curing agent, a zinc-based curing activator, an organic curing activator, and a combination of curing accelerators. The combination of curing accelerators includes (i) a sulfonamide accelerator, (ii) a metal dithiocarbamate accelerator, and (iii) at least one of a thiazole polysulfide accelerator and a thiuram polysulfide accelerator.

[0007] Among the various aspects of this embodiment that may be combined:

[0008] The elastomeric component may include 45-65 phr of natural rubber and 30-55 phr of polydiene rubber.

[0009] The polydiene rubber may include polybutadiene rubber and styrene butadiene rubber in a weight ratio of at least 1:1, or at least 1.5:1, or at least 2:1, or at most 5:1, or at most 4:1, or at most 3:1, or at most 2.5:1.

[0010] Carbon black may be present in the rubber composition in an amount of at least 45 phr or at most 65 phr.

[0011] The rubber composition may include not greater than 2 phr of silica.

[0012] The rubber composition may include no greater than 1 phr of resin.

[0013] The combination of curing accelerators may include (i) 0.5 to 2 phr of a sulfenamide accelerator, (ii) 0.3 to 1.2 phr of a metal dithiocarbamate accelerator, and (iii) 0.05 to 0.4 phr of at least one of a thiazole polysulfide accelerator and a thiuram polysulfide accelerator.

[0014] The combination of curing accelerators may include (i) 0.8 to 1.5 phr of a sulfenamide accelerator, (ii) 0.4 to 0.9 phr of a metal dithiocarbamate accelerator, and (iii) 0.07 to 0.2 phr of at least one of a thiazole polysulfide accelerator and a thiuram polysulfide accelerator.

[0015] The sulfenamide accelerator may be selected from N-cyclohexyl-2-benzothiazole sulfenamide (CBS), N-tert-butyl-2-benzothiazole-sulfenamide (TBBS), and mixtures thereof.

[0016] The metal dithiocarbamate accelerator may include zinc dibenzyldithiocarbamate (ZBEC).

[0017] The at least one of the thiazole polysulfide accelerator and the thiuram polysulfide accelerator may include mercaptobenzothiazole disulfide (MBTS).

[0018] The rubber composition may include 2.5 phr to 8 phr of a processing aid.

[0019] The sulfur-based curing agent may provide 0.3 phr to 1.2 phr of active sulfur to the rubber composition.

[0020] The zinc-based cure activator may consist of no more than 5 phr of zinc oxide of the rubber composition.

[0021] The rubber composition may further include at least one of an antioxidant and an antiozonant.

[0022] A pneumatic truck tire may include a tread as described in any of the above aspects.

[0023] According to another embodiment, a method of forming a high mileage tire includes forming a rubber composition comprising combining: 100 phr of an elastomeric component comprising natural rubber and polydiene rubber; at least 40 phr of carbon black; optionally, one or more processing aids selected from liquid plasticizers, waxes, and mixtures thereof; and a cure system comprising a sulfur-based curing agent, a zinc-based cure activator, an organic cure activator, and a combination of cure accelerators. The combination of cure accelerators includes: a sulfenamide accelerator, a metal dithiocarbamate accelerator, and at least one of a thiazole polysulfide accelerator and a thiuram polysulfide accelerator. The method further includes vulcanizing the rubber composition to form at least a portion of a tire.

[0024] A tire formed by the method may be provided.

[0025] According to another embodiment, a tire tread formed from a vulcanizable rubber composition is provided. The rubber composition includes, expressed in parts by weight per hundred parts of elastomer (phr): 100 phr of an elastomeric component, the elastomeric component comprising natural rubber, polybutadiene rubber, and styrene-butadiene rubber, the weight ratio of natural rubber to polybutadiene rubber being 50:40 to 60:30, and the weight ratio of polybutadiene rubber to styrene-butadiene rubber being 30:20 to 40:10; 40 to 70 phr of carbon black; not more than 1 phr of resin; not more than 2 phr of silica; and a curing system. The curing system includes (i) 0.5 to 2.0 phr of a sulfonamide accelerator, (ii) 0.3 to 1.2 phr of a metal dithiocarbamate accelerator, and (iii) 0.05 to 0.4 phr of a thiazole polysulfide accelerator.

[0026] The present invention discloses the following scheme

[0027] Embodiment 1. A tire tread formed from a vulcanizable rubber composition comprising, expressed in parts by weight per hundred parts of elastomer (phr):

[0028] 100 phr of an elastomeric component, the elastomeric component comprising natural rubber and polydiene rubber;

[0029] At least 40 phr of carbon black;

[0030] Optionally, one or more processing aids selected from liquid plasticizers, waxes, and mixtures thereof;

[0031] A sulfur curing system comprising a sulfur-based curing agent, a zinc-based curing activator, an organic curing activator, and a combination of curing accelerators, wherein the combination of curing accelerators comprises:

[0032] (i) sulfenamide accelerator,

[0033] (ii) a metal dithiocarbamate accelerator, and

[0034] (iii) at least one of a thiazole polysulfide accelerator and a thiuram polysulfide accelerator.

[0035] Option 2. The tire tread according to Option 1, wherein the elastomeric component comprises 45-65 phr of natural rubber and 30-55 phr of polydiene rubber.

[0036] Option 3. The tire tread according to Option 1, wherein the polydiene rubber comprises polybutadiene rubber and styrene butadiene rubber in a weight ratio of at least 1.5:1.

[0037] Option 4. The tire tread of Option 1, wherein the rubber composition comprises at least 45 phr of carbon black.

[0038] Option 5. The tire tread according to Option 1, wherein the rubber composition comprises no greater than 2 phr of silica.

[0039] Aspect 6. The tire tread according to aspect 1, wherein the rubber composition comprises no more than 1 phr of the resin.

[0040] Option 7. The tire tread according to Option 1, wherein the combination of curing accelerators comprises:

[0041] (i) 0.5 to 2 phr of a sulfenamide accelerator,

[0042] (ii) 0.3 phr to 1.2 phr of a metal dithiocarbamate accelerator, and

[0043] (iii) 0.05 to 0.4 phr of the at least one of a thiazole polysulfide accelerator and a thiuram polysulfide accelerator.

[0044] Option 8. The tire tread according to Option 1, wherein the combination of curing accelerators comprises:

[0045] (i) 0.8 to 1.5 phr of a sulfenamide accelerator,

[0046] (ii) 0.4 to 0.9 phr of a metal dithiocarbamate accelerator, and

[0047] (iii) 0.07 to 0.2 phr of the at least one of a thiazole polysulfide accelerator and a thiuram polysulfide accelerator.

[0048] Option 9. The tire tread according to Option 1, wherein the sulfenamide accelerator is selected from N-cyclohexyl-2-benzothiazole sulfenamide (CBS); N-tert-butyl-2-benzothiazole-sulfenamide (TBBS); and mixtures thereof.

[0049] Embodiment 10. The tire tread of embodiment 1, wherein the metal dithiocarbamate accelerator comprises zinc dibenzyl dithiocarbamate (ZBEC).

[0050] Embodiment 11. The tire tread of embodiment 1, wherein the at least one of the thiazole polysulfide accelerator and the thiuram polysulfide accelerator comprises mercaptobenzothiazole disulfide (MBTS).

[0051] Embodiment 12. The tire tread according to embodiment 1, wherein the rubber composition comprises 2.5 phr to 8 phr of a processing aid.

[0052] Embodiment 13. The tire tread of embodiment 1, wherein the sulfur-based curing agent provides 0.3 phr to 1.2 phr of active sulfur to the rubber composition.

[0053] Embodiment 14. The tire tread of embodiment 1, wherein the zinc-based cure activator consists of no greater than 5 phr of zinc oxide based on the rubber composition.

[0054] Aspect 15. The tire tread according to aspect 1, wherein the rubber composition further comprises at least one of an antioxidant and an antiozonant.

[0055] Embodiment 16. A pneumatic truck tire comprising the tread according to embodiment 1.

[0056] Embodiment 17. A method of forming a high mileage tire, comprising:

[0057] a) forming a rubber composition comprising combining:

[0058] 100 phr of an elastomeric component, the elastomeric component comprising natural rubber and polydiene rubber;

[0059] At least 40 phr of carbon black;

[0060] Optionally, one or more processing aids selected from liquid plasticizers, waxes, and mixtures thereof;

[0061] A sulfur-curing system comprising a combination of a sulfur-based curing agent, a zinc-based curing activator, an organic curing activator, and a curing accelerator, wherein the combination of curing accelerators comprises:

[0062] (i) sulfenamide accelerator,

[0063] (ii) a metal dithiocarbamate accelerator, and

[0064] (iii) at least one of a thiazole polysulfide accelerator and a thiuram polysulfide accelerator; and

[0065] b) curing the rubber composition to form at least a portion of a tire.

[0066] Embodiment 18. A tire formed by the method according to Embodiment 17.

[0067] 19. A tire tread formed from a vulcanizable rubber composition comprising, expressed in parts by weight per hundred parts of elastomer (phr):

[0068] 100 phr of an elastomer component, the elastomer component comprising natural rubber, polybutadiene rubber and styrene-butadiene rubber, the weight ratio of natural rubber to polybutadiene rubber being 50:40 to 60:30, and the weight ratio of polybutadiene rubber to styrene-butadiene rubber being 30:20 to 40:10;

[0069] 40 to 70 phr of carbon black;

[0070] Not more than 1phr of resin;

[0071] No more than 2 phr of silicon dioxide; and

[0072] A sulfur curing system comprising:

[0073] (i) 0.5 to 2.0 phr of a sulfenamide accelerator,

[0074] (ii) 0.3 to 1.2 phr of a metal dithiocarbamate accelerator, and

[0075] (iii) 0.05 to 0.4 phr of a thiazole polysulfide accelerator.

[0076] Embodiment 20. A pneumatic tire comprising the tire tread according to Embodiment 19. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Figure 1 is a graph of wear versus friction energy density for three rubber compositions. DETAILED DESCRIPTION

[0078] A rubber composition is described herein, which is suitable for the tread of a radial medium truck (RMT) tire, particularly for high mileage applications, such as tires for long-distance transport applications, but it can also be applied to buses and regional transport trucks. For example, the tire can be used on the drive wheel of a truck cab for tractor trailers to transport goods. The rubber composition provides improvements in tire wear resistance and aging resistance to bring generally higher mileage. The rubber composition benefits from the use of an optimized curing system to provide high mileage, while other properties are not significantly lost.

[0079] The curing system includes a mixture of accelerators, including a primary accelerator, and a combination of auxiliary (faster acting) accelerators, which may be referred to as super accelerators, at least one of which may also serve as an anti-reversion agent. This helps to limit aging and heat accumulation in the tire. The super accelerator is dispersed in a polymer matrix with a high natural rubber content and a carbon black filler together with the one or more slower acting primary accelerators, which may be free of or substantially free of resin. The combination of the primary accelerator and the super accelerator brings improvements in tread wear and rolling resistance.

[0080] In one embodiment, a rubber composition includes a polymer matrix of natural rubber (NR) and at least one synthetic conjugated diene-based elastomer (referred to herein as polydiene rubber), such as polybutadiene (PBD) and / or styrene-butadiene rubber (SBR), and carbon black, and a cure system including a sulfur-based curative, a fatty acid, zinc oxide, and an accelerator mixture, the accelerator mixture including a primary accelerator such as a sulfenamide accelerator, a first ultra accelerator such as a dithiocarbamate, and a second ultra accelerator, which may contain a thiazole / thiuram functionality.

[0081] definition

[0082] Unless otherwise specified, the terms "rubber" and "elastomer" are used interchangeably. The terms "rubber composition" or "compounded rubber" are used interchangeably to mean "rubber that has been blended or mixed with various ingredients and materials," and these terms are well known to those skilled in the art of rubber mixing or rubber compounding. Unless otherwise specified, the terms "cure" and "vulcanize" are used interchangeably.

[0083] As used herein, and unless otherwise indicated, the term "tread" means that portion of the tire that comes into contact with the road when normally inflated and loaded, optionally also referring to any subtread.

[0084] As used herein, the term "phr" refers to parts per hundred parts of rubber by weight. Typically, using this convention, a rubber composition includes 100 parts by weight of rubber / elastomer. The claimed composition may include other rubbers / elastomers beyond those explicitly mentioned in the claims, as long as the phr value of the claimed rubber / elastomer meets the claimed phr range and the amount of all rubbers / elastomers in the composition totals 100 parts of rubber.

[0085] Unless otherwise stated, the following methods were used to determine properties:

[0086] The molecular weight of elastomers, rubber compositions and resins, such as M n (number average molecular weight), M w (weight average molecular weight) and M z(z-average molecular weight) is determined herein using gel permeation chromatography (GPC) according to ASTM D5296-19, "Standard Test Method for Molecular Weight Averages and Molecular Weight Distribution of Poly Polystyrene by High Performance Size-Exclusion Chromatography," using polystyrene calibration standards.

[0087] The glass transition temperature (Tg) of an elastomer or an elastomeric composition is the glass transition temperature of the respective elastomer or elastomeric composition in its uncured state or, in the case of an elastomeric composition, possibly in the cured state.

[0088] The Tg value of the elastomer is measured as the peak midpoint by differential scanning calorimetry (DSC) at a heating rate of 10° C. / min 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 referred to as ASTM D3418).

[0089] The glass transition temperature Tg of the resin is measured as the peak midpoint by differential scanning calorimetry (DSC) at a heating rate of 10°C / min according to ASTM D6604-00 (2017), “Standard Practice for Glass Transition Temperatures of Hydrocarbon Resins by Differential Scanning Calorimetry” (hereinafter referred to as ASTM D6604).

[0090] The glass transition temperature Tg of the oil is measured as the peak midpoint by a differential scanning calorimeter (DSC) at a heating rate of 10°C / min in accordance with ASTM E1356-08 (2014), “Standard Test Method for Assignment of the Glass Transition Temperatures by Differential Scanning Calorimeter”.

[0091] The softening point of a resin is measured according to ASTM E28-18, “Standard Test Methods for Softening Point of Resins Derived from Pine Chemicals and Hydrocarbons, by Ring-and-Ball Apparatus” (hereinafter referred to as ASTM E28), which is sometimes referred to as the ring and ball softening point.

[0092] The Mooney viscosity (ML 1+4) is measured in units of MU at 100° C. according to ASTM D1646-19a, “Standard Test Methods for Rubber—Viscosity, Stress Relaxation, and Pre-Vulcanization Characteristics (Mooney Viscometer)” (hereinafter referred to as ASTM D1646).

[0093] The term "alkyl" refers to straight chain, branched chain and cyclic alkyl groups. The term "aryl" refers to a group including at least one aromatic ring and includes alkaryl groups.

[0094] Rubber composition

[0095] An exemplary tire tread is formed from a vulcanizable rubber composition comprising, expressed in parts by weight per hundred parts of elastomer (phr):

[0096] 1) 100 phr of an elastomeric component, the elastomeric component comprising a) natural rubber (NR); and b) a polydiene rubber;

[0097] 2) at least 40 phr of a filler component comprising carbon black;

[0098] 3) optionally, one or more processing aids selected from a) liquid plasticizers, such as oils; b) waxes; c) resins and mixtures thereof;

[0099] 4) a cure system comprising a) a sulfur-based curing agent; b) a cure activator comprising (i) zinc oxide, and (ii) one or more organic activators, such as fatty acids, alkaline earth metal salts of fatty acids, and combinations thereof; d) a mixture of cure accelerators comprising (i) a sulfenamide accelerator, (ii) a metal dithiocarbamate super accelerator; (iii) a thiazole polysulfide and / or thiuram polysulfide super accelerator; and optionally, e) a cure retarder; and

[0100] 5) Optionally, additional rubber compounding materials, such as antioxidants, antiozonants, antidegradants, etc. may be included in the rubber composition.

[0101] Examples of these components are described below.

[0102] 1) Elastomer

[0103] One or more vulcanizable elastomers can be used in the rubber composition. In one embodiment, the elastomer includes natural rubber (NR) and polydiene rubber. The term "polydiene rubber" refers to a synthetic rubber formed by at least one conjugated diene and optionally one or more other monomers.

[0104] The weight ratio of natural rubber to polydiene rubber may be at least 45:55, or at least 50:50, or at most 70:30, or at most 65:35.

[0105] One or more of the elastomers may be at least partially hydrogenated and / or functionalized.

[0106] a) Natural rubber

[0107] Natural rubber is primarily cis-polyisoprene. The cis-1,4-polyisoprene content in the natural rubber may be at least 90% by weight or at least 95% by weight. In one embodiment, the natural rubber is a natural cis-1,4-polyisoprene rubber having a cis-1,4-content of at least 96% and a Tg of about -65°C as measured according to ASTM D3418.

[0108] Several forms of natural rubber are available. The purity of the natural rubber may meet the ISO TSR 20 grade specification or the ISO TSR 10 grade specification. ISO TSR 20 natural rubber has a maximum ash content of 1 wt % as determined according to ISO 247:1990, a maximum volatile matter of 0.8 wt % as determined according to ISO 248:1991, a maximum nitrogen content of 0.6 wt % as determined according to ISO 1656:1996, a minimum initial Wallace plasticity of 30 as determined according to ISO 2007:1991, and a minimum plasticity retention index of 40 as determined according to ISO 2930:1995. For TSR 10, a maximum ash content of 0.75 wt %, a maximum nitrogen of 0.6 wt %, a maximum volatile matter of 0.8 wt %, a minimum plasticity of 30, and a minimum plasticity retention of 50 are specified. In other embodiments, the natural rubber may be a ribbedsmoked sheet (RSS) rubber.

[0109] Natural rubber may be used in the rubber composition in an amount of at least 45 phr, or at least 50 phr, or at most 70 phr, or at most 65 phr.

[0110] b) Polydiene rubber

[0111] The polydiene rubber may include at least one polydiene rubber, which may be a homopolymer, a copolymer, or a mixture thereof. In one embodiment, the polydiene rubber includes one or more polydiene rubbers at least partially derived from butadiene. For example, at least 20% or at least 30% of the units in the polydiene rubber are formed by butadiene.

[0112] A kind of suitable polydiene rubber is synthetic polybutadiene rubber (PBD), which is the homopolymerization product of single monomer butadiene. In one embodiment, cis-1,4-polybutadiene rubber is used. Another suitable polydiene rubber is a conjugated diene monomer such as butadiene and at least one other monomer such as vinyl aromatic monomer, for example, a copolymer of styrene, which together form for example styrene / butadiene rubber (SBR). PBD and / or SBR can be hydrogenated and / or functionalized. If functionalized, it can be selected from one or more of hydroxyl, ethoxy, epoxy, siloxane group, amine group, amine siloxane group, carboxyl, phthalocyanine group and silane-sulfide group at the side chain position in the polymer chain end or polymer.

[0113] In one embodiment, the polydiene rubber includes PBD and SBR, which may be present in the rubber composition in a weight ratio of PBD to SBR of at least 1:1, or at least 1.5:1, or at least 2:1, or at most 5:1, or at most 4:1, or at most 3:1, or at most 2.5:1.

[0114] In another embodiment, SBR is omitted from the rubber composition.

[0115] Suitable polybutadiene rubbers can be prepared, for example, by organic solution polymerization of 1,3-butadiene. The PBD may be characterized, for example, by having a cis-1,4-microstructure content of at least 90% by weight ("high cis" content), or at least 95% by weight or at least 96% by weight of a cis-1,4-microstructure. The glass transition temperature (Tg) of the PBD measured according to ASTM D3418 may be -95°C to -112°C. The PBD may have a Mooney viscosity measured according to ASTM D1646 of 45-65 M.U.

[0116] Suitable polybutadiene rubbers are available commercially, such as from The Goodyear Tire & Rubber Company. and These high cis-1,4-polybutadiene rubbers can be treated with nickel or neodymium

[0117] Catalyst systems are synthesized, such as those comprising 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 Having a cis-1,4-content of at least 96 wt%, a Mooney viscosity of 55 and a Tg of -100°C to -104°C, while the neodymium-catalyzed It has a cis 1,4-content of at least 96 wt%, a Mooney viscosity of 55, and a Tg of about -104°C.

[0118] When using PBD, it can 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 at most 50 phr, or at most 40 phr, or at most 35 phr, such as 35 ± 5 phr. In other embodiments, PBD is omitted (and at least partially replaced by SBR).

[0119] Styrene / butadiene copolymer rubbers can be formed by the polymerization of styrene and 1,3-butadiene monomers. Such copolymers can help improve tire handling and wet (wet traction) performance of the tire tread, but tend to have a negative impact on mileage.

[0120] In one embodiment, SBR includes or is composed of styrene-butadiene (ESBR) derived from emulsion polymerization. ESBR can have a combined styrene content of 5 to 50% by weight, such as 20 to 28% by weight of combined styrene, or for some applications, 30 to 45% by weight. In emulsion polymerization, styrene and 1,3-butadiene are copolymerized into an aqueous emulsion. Emulsion polymerization methods are described in, for example, U.S. Patent Nos. 5,583,173A, 7,244,783B2 and 7,594,528B2 and U.S. Publication Nos. 20060266454A1 and 20140171557A1.

[0121] In another embodiment, SBR includes or is composed of SBR (SSBR) derived from solution polymerization. SSBR may have a combined styrene content of 5 to 50% by weight, such as 9 to 36% by weight or 26 to 31% by weight. 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 organic lithium compound as an initiator. Alternatively, SSBR is tin coupled. Other methods for preparing SSBR are described in U.S. Patent No. 8,312,905B2 and U.S. Publication No. 20140135437A1.

[0122] Methods of preparing functionalized styrene-butadiene rubbers are disclosed, for example, in US Pat. Nos. 7,137,423 B2 and 7,342,070 B2 and US Publication No. 20080287601 A1. In one embodiment, the SSBR is thiofunctionalized to improve stiffness and / or good hysteresis behavior of the rubber composition.

[0123] An exemplary ESBR is available as Plioflex 1502NN TM Available from The Goodyear Tire & Rubber Company. It has a styrene content of 23.5 wt% and a Tg of -50°C and is prepared by aqueous emulsion polymerization of styrene and 1,3-butadiene monomers. ESBR can be oil-extended for ease of processing. One oil-extended ESBR is BUNA available from Dow TM SB 1723-Schkopau, which is made by cold polymerization using mixed rosin acid / fatty acid soaps. It is plasticized with 37.5 parts of mineral oil / 100 parts of rubber and has a Mooney viscosity ML1+4@100°C of 49.

[0124] An exemplary polydiene rubber blend may include (a) 15 to 40 phr of a cis-1,4-polybutadiene rubber having a cis-1,4-content of at least 96 wt. % and a Tg of -90°C to -110°C, and (b) 5 to 20 phr of a styrene / butadiene copolymer rubber having a styrene content of 20 to 25 wt. % and a Tg of -40°C to -60°C, wherein the sum of a) and b) is at least 35 phr.

[0125] Other polydiene rubbers that can be used in the rubber composition include polyisoprene, styrene-isoprene-butadiene terpolymer rubber, butadiene acrylonitrile rubber, hydrated acrylonitrile / butadiene rubber, isoprene / butadiene copolymer, isoprene-isobutylene copolymer, butadiene-based block copolymers, such as styrene-butadiene-styrene block copolymers (SBS) and hydrogenated and functionalized derivatives thereof. In one embodiment, these other polydiene rubbers are used in an amount not greater than 10 phr in total.

[0126] c) Other elastomers

[0127] Other vulcanizable elastomers may be present in the rubber composition in minor amounts (e.g., up to 10 phr, or up to 5 phr, or up to 2 phr, or up to 1 phr in total) and may be selected from synthetic polyisoprenes, halogenated butyl 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, propylene monomers and / or ethylene propylene diene monomer (EPDM), isoprene-based block copolymers, styrene block copolymers, styrene-ethylene / butylene-styrene block copolymers (SEBS), styrene-[ethylene-(ethylene / propylene)]-styrene block copolymers (SEEPS), styrene-isoprene-styrene block copolymers (SIS), random styrene copolymers, hydrogenated styrene block copolymers, polyisobutylene, ethylene vinyl acetate (EVA) polymers, polyolefins , amorphous polyolefins, semicrystalline polyolefins, alpha-polyolefins, 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, chloroprene rubber, acrylics, urethanes, poly(acrylates), ethylene acrylic acid copolymers, polyetheretherketones, 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, metallocene-catalyzed polyethylene polymers, ethylene-propylene-butene terpolymers, propylene, ethylene, C4-C 10 The invention relates to copolymers made from α-olefin monomers, polypropylene polymers, maleated polyolefins, polyester copolymers, copolyester polymers, ethylene acrylic acid copolymers and / or polyvinyl acetate. Such polymers are optionally modified and / or functionalized at the polymer chain ends or side chain positions within the polymer to include one or more selected from hydroxyl groups, ethoxy groups, epoxy groups, siloxane groups, amine groups, amine siloxane groups, carboxyl groups, phthalocyanine groups and silane-sulfide groups.

[0128] 2) Reinforcement filler

[0129] The rubber composition may include a total of at least 40 phr, or at least 45 phr, or at least 50 phr, or at most 80 phr, or at most 70 phr, or at most 65 phr, or at most 60 phr of one or more particulate reinforcing fillers.

[0130] In one embodiment, carbon black (CB) is the only reinforcing filler in the rubber composition.In other embodiments, additional fillers may be used.

[0131] The carbon black may have a m / z of at least 8, or at least 20, or at least 100, or at least 120, or at most 132. 2 The specific surface area of ​​1000 g / kg is determined according to ASTM D6556-21, "Standard Test Method for Carbon Black—Total and External Surface Area by Nitrogen Adsorption". The specific (external) surface area based on the statistical thickness method (STSA) is defined as the specific surface area of ​​the accessible rubber.

[0132] Exemplary carbon blacks useful herein include those having ASTM designations N110, N121, N134, N220, N231, N234, N242, N293, N299, N315, N326, N330, N332, N339, N343, N347, N351, N358, N375, N539, N550, N582, N630, N642, N650, N683, N754, N762, N765, N774, N787, N907, N908, N990, and N991 as specified in ASTM D1765-21, "Standard Classification System for Carbon Blacks Used in Rubber Products." These carbon blacks have an iodine absorption of 9 to 145 g / kg as determined according to ASTM D1510-21 and an iodine absorption of 34 to 150 cm 3 / 100g of DBP absorption as determined according to ASTM D2414. For example, N121 grade is a grade having an iodine absorption of about 121 g / kg, an iodine absorption of about 121 m / kg, and an iodine absorption of about 121 m / kg. 2 / kg of CATB specific surface area, about 132m 2 / kg DBP absorption and less than 0.5% by weight of ash content of granular carbon black. N220 grade is 116-126g / kg iodine absorption, 106-116m 2 / kg CATB specific surface area, 109-119m 2 / kg of DBP absorption and less than 0.5% by weight of ash content of granular carbon black.

[0133] Reinforcing fillers other than carbon black may be used, for example, in an amount not greater than 30 phr, or up to 20 phr, or up to 10 phr, or up to 5 phr, or up to 1 phr in total, or may be absent. Examples of such additional reinforcing fillers include silica, alumina, aluminum hydroxide, clay (reinforcing grades), magnesium hydroxide, boron nitride, aluminum nitride, titanium dioxide, and combinations thereof.

[0134] In one embodiment, rubber composition components other than the polydiene rubber, natural rubber, and carbon black (such as other elastomers, other reinforcing fillers, non-reinforcing fillers, coupling agents, resins, processing aids, antioxidants, antiozonants, antidegradants, and cure systems) are present in no more than 40 phr of the rubber composition, or no more than 30 phr, or no more than 25 phr, or no more than 20 phr of the rubber composition.

[0135] 3) Processing Aids

[0136] The exemplary rubber composition may include one or more processing aids which may be selected from a) liquid plasticizers, such as oils; b) waxes; c) resins, and mixtures thereof.

[0137] a) Liquid plasticizer

[0138] The term liquid plasticizer is used to refer to a plasticizer component that is liquid at room temperature (i.e., liquid above 25°C), and is distinguished from hydrocarbon resins that are generally solid at room temperature. Typically, liquid plasticizers have a Tg below 0°C, typically well below 0°C, such as below -30°C, or below -40°C, or below -50°C, such as a Tg of 0°C to -100°C.

[0139] Suitable liquid plasticizers include oil (e.g., petroleum oil and oil from plant sources) and other non-oil liquid plasticizers, such as ether plasticizers, ester plasticizers, phosphate plasticizers and sulfonate plasticizers. Liquid plasticizers can be added during compounding, or added later as extender oil (which is used to extend the rubber). Oil based on petroleum can include aromatic oils, naphthenic oils, low polycyclic aromatic hydrocarbons (PCA) oils such as MES, TDAE and SRAE and mixtures thereof. Vegetable oils can include oils harvested from vegetables, nuts, seeds, and mixtures thereof, such as triglycerides.

[0140] Liquid plasticizers may be used in the rubber composition at 0 to 10 phr, or at least 0.5 phr, or at least 1 phr, or at least 2 phr, or at least 4 phr, or up to 8 phr, or up to 7 phr, or up to 6 phr, or up to 3 phr. In one embodiment, a traction resin may be used to replace at least some of the oil, so that the oil can be present in only small amounts, such as 1 phr or less, or omitted entirely.

[0141] b) Wax

[0142] 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. These waxes may act as antiozonants.

[0143] The wax may be present at 0.1 phr or more, such as at least 0.3 phr, or at least 0.5 phr, or at most 5 phr, or at most 3 phr, or at most 2 phr.

[0144] c) Resin

[0145] Resins can be used to improve the wet traction of the tire, but this may come at the expense of high mileage. In one embodiment, resins are omitted from the rubber composition. In another embodiment, small amounts of resins may be used, such as up to 1 phr, or up to 0.5 phr, or up to 0.2 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 phenolic resins, rigid resins such as reactive phenolic resins, and combinations thereof.

[0146] Examples of hydrocarbon traction resins that can be used include those having a glass transition temperature, Tg, greater than 20° C., or at least 30° C., or at most 50° C., as determined according to ASTM D6604. The traction resin may have a softening point, as determined according to ASTM E28, of at least 30° C., or at least 70° C., or at most 100° C. The Tg is generally lower than its softening point, and the lower the softening point, the lower the Tg. The hydrocarbon traction resin may be selected from terpene-phenol resins, terpene resins, terpene-styrene resins, styrene / α-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 forming the resin prior to any functionalization). Such resins may be partially or fully hydrogenated and / or functionalized. Exemplary hydrocarbon traction resins are described in U.S. Pat. No. 11,214,667 B2. Exemplary resins are also described in U.S. Pat. No. 11,591,454 B2.

[0147] Resins may also be derived from naturally occurring rosins and their 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 amounts of the components of the rosin may vary. Such resins may be dimerized, polymerized, or disproportionated. Such resins may be in the form of esters of rosin acid and a polyol such as pentaerythritol or ethylene glycol.

[0148] 4. Curing system

[0149] The curing system achieves vulcanization (curing) of the rubber composition and may include a) a sulfur-based curing agent, b) a curing activator, (c) a combination of a curing accelerator, and optionally, d) a vulcanization inhibitor. The curing system may be used for the rubber composition at 0.5 to 20 phr, or at least 5 phr, or at least 7 phr, or at most 10 phr.

[0150] a) Sulfur-based curing agents

[0151] The vulcanization (curing) of the rubber composition is carried out in the presence of a curing (vulcanizing) agent, such as a sulfur-based curing agent. Examples of suitable sulfur-based curing agents include elemental sulfur (free sulfur), insoluble polymeric sulfur, soluble sulfur and sulfur-donating vulcanizing agents, such as disulfide amines, polymeric polysulfides or sulfur olefin adducts and mixtures thereof.

[0152] Sulfur-based curing agents can be used in an amount of at least 0.1 phr, such as at least 0.2 phr, or at least 0.4 phr, or at least 0.5 phr, or up to 1.2 phr, or up to 1 phr, or up to 0.7 phr (expressed as pure sulfur). The amount of sulfur-based curing agent can be minimized by using a sulfur-donating accelerator.

[0153] b) Curing Activator

[0154] Curing activators are additives for assisting vulcanization. Curing activators include (i) inorganic curing activators and (ii) organic curing activators. Zinc oxide is the most widely used inorganic curing activator and can be present in an amount of at least 1 phr, such as at least 2 phr, or at most 6 phr, or at most 5 phr, or at most 4 phr.

[0155] Organic curing 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 dialkylthioureas 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-dithiodiurea, guanylthiourea, 1-(1-naphthyl)-2-thiourea, 1-phenyl-2-thiourea, p-tolylthiourea and o-tolylthiourea.

[0156] In one embodiment, a fatty acid mixture, primarily stearic acid, is used as the organic activator.

[0157] The total amount of organic curing activator may be at least 0.1 phr, such as at least 0.5 phr, or at least 1 phr, or at least 1.5 phr, or at most 5 phr, or at most 4 phr, or at most 3 phr.

[0158] c) Curing accelerator

[0159] Curing accelerators, similar to activators, act as catalysts for vulcanizing agents. Accelerators are used to control the time and / or temperature required for vulcanization, and are also used to improve the properties of vulcanized rubber, such as by crosslinking. Super accelerators usually have a rapid vulcanization initiation time. In this case, the combination of the primary accelerator and the auxiliary accelerator can minimize the amount of sulfur curing agent, while also producing crosslinking, which has been found to provide an improvement in the mileage of the resulting tire. The super accelerator used starts the vulcanization process faster than other accelerators to produce a shorter crosslinking that is ideal for this application. In particular, super accelerators can undergo additional reactions to form stable monosulfide crosslinks outside the crosslinking formed with the sulfonamide system. This reduces the need for other compounding techniques, such as increasing the sulfur content in order to reach the desired state of vulcanization so that the rubber composition is more susceptible to aging and hardening. Super accelerators can also serve as anti-vulcanization reversion aids to protect the polymer matrix of the tire tread formed, particularly when it becomes hot. This helps to reduce fragmentation and chunking, where small fragments of the tire fall off.

[0160] Exemplary combinations of accelerators include sulfenamide accelerators, metal dithiocarbamate accelerators, and thiazole / thiuram polysulfide accelerators.

[0161] The total amount of curing accelerator may be 0.8 to 5 phr, or at least 0.9 phr, or at least 1 phr, or at least 1.2 phr, or at least 1.5 phr, or up to 4 phr, or up to 3 phr, or up to 2 phr, or up to 1.7 phr.

[0162] The ratio of the total weight of the cure accelerator to the total weight of sulfur in the sulfur-based curing agent may be at least 1:1, or at least 1.2:1, or at least 1.5:1, or at most 3:1, or at most 2:1.

[0163] (i) Sulfenamide Accelerator

[0164] Sulfonamide accelerator serves as primary accelerator. Primary accelerator provides delayed curing reaction (higher activation temperature) usually, but is more resistant to decomposition than super accelerator. Sulfonamide accelerator can be benzothiazole sulfonamide, which can be selected from N-cyclohexyl-2-benzothiazole sulfonamide (CBS), N-tert-butyl-2-benzothiazole sulfonamide (TBBS), N-dicyclohexyl-2-benzothiazole sulfonamide (DCBS), N-oxydiethylbenzothiazole-2-sulfonamide, N, N-diisopropylbenzothiazole-2-sulfonamide and mixtures thereof. Such sulfonamide accelerator does not contain any sulfur-sulfur bond (-SS-). In one embodiment, sulfonamide accelerator includes TBBS or is composed of TBBS.

[0165] Sulfenamides can be prepared by the reaction of 2-mercaptobenzothiazole with N-chloroamine or by oxidation of the amine salt of 2-mercaptobenzothiazole.

[0166] The sulfenamide accelerator may be present in the rubber composition in an amount of at least 0.5 phr, such as at least 0.8 phr, or at most 2 phr, or at most 1.5 phr, or at most 1.2 phr, or at most 1.0 phr. For example, a sulfenamide such as TBBS may be present in an amount of 0.95 ± 0.1 phr.

[0167] The weight ratio of primary accelerator to super accelerator may be at least 1.1:1, or at least 1.2:1, or at most 1.5:1, or at most 1.3:1.

[0168] (ii) Metal dithiocarbamate accelerator

[0169] Metal dithiocarbamates act as the first super promoter. The metal in the metal dithiocarbamates can be selected from zinc, sodium, copper, bismuth and tellurium, wherein zinc is common. The dithiocarbamates can be selected from dialkyl dithiocarbamates (wherein the alkyl can be selected from methyl, ethyl, butyl), diaryl dithiocarbamates (wherein the aryl can be benzyl) and mixtures thereof. The metal dithiocarbamates are characterized in that the metal is directly connected to two or more sulfur atoms in the compound (-S-Zn-S- in the case of zinc, four S-Te bonds in the case of tellurium). Examples of metal dithiocarbamate accelerators include zinc dibenzyl dithiocarbamate (ZBEC), sodium dibenzyl dithiocarbamate, zinc dibutyl dithiocarbamate (ZDBC), zinc diethyl dithiocarbamate, zinc dimethyl dithiocarbamate, copper dimethyl dithiocarbamate (CuDD), tellurium diethyl dithiocarbamate (TDEC), zinc diisononyl dithiocarbamate, zinc pentamethylene dithiocarbamate, and mixtures thereof. In one embodiment, the metal dithiocarbamate comprises or consists of zinc dibenzyl dithiocarbamate.

[0170] The metal dithiocarbamate accelerator may be present in the rubber composition in an amount of at least 0.3 phr, such as at least 0.4 phr, or at most 2 phr, or at most 1.5 phr, or at most 1.2 phr, or at most 1.0 phr. For example, a metal dithiocarbamate accelerator, such as zinc dibenzyl dithiocarbamate, may be present in an amount of 0.66 ± 0.07 phr.

[0171] The weight ratio of the sulfenamide accelerator to the metal dithiocarbamate accelerator may be at least 3:1, or at least 4:1, or at most 10:1, or at most 8:1.

[0172] (iii) Thiazole or thiuram polysulfide accelerator

[0173] The thiazole polysulfide or thiuram polysulfide accelerator acts as a second super accelerator. The polysulfide comprises two or more, such as up to 8 or up to 4 linked sulfur atoms. In the case of thiazole polysulfide, it may be mercaptobenzothiazole disulfide (MBTS).

[0174] In the case of thiuram polysulfides, they may be selected from alkylthiuram disulfides, alkylthiuram tetrasulfides, arylthiuram disulfides, arylthiuram tetrasulfides and mixtures thereof. Both thiuram polysulfides and thiazole polysulfides include a sequence of two or more sulfur atoms, which are attached at each end to a carbon, which in turn is directly attached to a sulfur atom and a nitrogen atom.

[0175] In one embodiment, the thiuram polysulfide has the general formula:

[0176]

[0177] wherein n is at least 2, such as at most 6 or at most 4,

[0178] R 1 , R 2 , R 3 and R 4 are each independently an alkyl group or an aryl group, the alkyl group or the aryl group optionally containing one or more heteroatoms selected from O, S and N, wherein R 1 and R 2 and / or R 3 and R 4 Together with the respective nitrogen to which they are attached they form a cycloalkyl or aryl ring optionally containing one or more heteroatoms selected from O, S and N.

[0179] Examples of thiuram polysulfide accelerators include tetramethylthiuram disulfide (TMTD), tetraethylthiuram disulfide (TETD), bis(N-benzylpiperazino)thiuram disulfide (BPTD), tetrabenzylthiuram disulfide (TBzTD), tetramethylthiuram disulfide (TMTD), tetraethylthiuram disulfide (TETD), tetraisobutylthiuram disulfide (TiBTD), dipentamethylenethiuram disulfide, dipentamethylenethiuram (DPTT) tetrasulfide, dipentamethylenethiuram hexasulfide, bis(4-methyl-1-piperazinylthiocarbonyl) disulfide, dimorpholinothiuram disulfide, and combinations thereof. In one embodiment, the second super accelerator includes or consists of mercaptobenzothiazole disulfide.

[0180] The thiazole polysulfide or thiuram polysulfide accelerator may be present in the rubber composition in an amount of at least 0.05 phr, such as at least 0.07 phr, or at most 0.4 phr, or at most 0.2 phr, or at most 0.15 phr, or at most 0.12 phr. For example, thiazole polysulfide, such as MBTS, may be present in 0.09 ± 0.01 phr.

[0181] d) Curing retardants

[0182] Cure retarders can be used to control the vulcanization process, and generally delay or inhibit vulcanization until the desired time and / or temperature is reached. Examples of cure retarders include N-(cyclohexylthio)phthalimide.

[0183] If used, the amount of cure retarders may be from 0.1 to 2 phr, or at least 0.2 phr, or up to 1 phr, or up to 0.5 phr. In one embodiment, no cure retarders are used.

[0184] 5) Antioxidants, antidegradants and antiozonants

[0185] Various compounds can be incorporated into the rubber composition that help reduce oxidation, ozone degradation, and other forms of degradation. These compounds can be present in the rubber composition in total at more than 1 phr, such as at least 2 phr, or at least 2.5 phr, or at most 6 phr, or at most 5 phr. In other embodiments, they may not be present.

[0186] Exemplary antidegradants suitable for use in the rubber composition include amine-based antioxidants such as p-phenylenediamine (PPD), including alkyl-aryl p-phenylenediamines, for example, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), p-phenylenediamines such as N,N'-diphenyl-1,4-phenylenediamine (DPPD) and trimethyl-dihydroquinoline (TMQ) antidegradants and others, such as those disclosed in The Vanderbilt Rubber Handbook (1978), pages 344-347.

[0187] In addition to the above ingredients, the rubber composition may also include other rubber compounding ingredients, such as a peptizer, such as pentachlorothiophenol, dibenzamidodiphenyl disulfide, or a mixture thereof. If a peptizer is used, a typical amount thereof may be 0.1 phr to 1 phr.

[0188] Preparation of rubber composition

[0189] The rubber composition can be prepared by mixing a vulcanizable elastomer, filler such as carbon black, and other rubber compounding ingredients excluding a curing agent under high shear rubber mixing conditions to an elevated temperature in at least one sequential mixing stage with at least one mechanical mixer (commonly referred to as a "non-productive" mixing stage), followed by a final "productive" mixing stage, wherein a sulfur-based curing agent and a curing accelerator are added to the mixture and mixed at a lower mixing temperature to avoid unnecessary pre-curing of the rubber mixture in the productive mixing stage. These ingredients can be mixed in the non-productive mixing stage for about 2 minutes to a temperature of 130° C. to 200° C., such as about 150° C. to about 165° C. Once the curing agent is added, the subsequent productive mixing step can be carried out at a temperature below the vulcanization (curing) temperature and / or for a short time to avoid unwanted pre-curing of the rubber composition, such as at a temperature not higher than 120° C., such as at least 60° C., such as at a temperature of 110-115° C. for 2 minutes.

[0190] The mixing can be carried out, for example, by kneading the ingredients together in a Banbury mixer or on a milled roll. The rubber composition can be cooled to a temperature below about 40° C. between each mixing stage. For example, the rubber composition can be poured out of the mixer after each mixing step, sheeted out from an open mill or on a roller die, and cooled to below 40° C. after each mixing step.

[0191] When curing agent, curing accelerator and any other ingredients added in the productive mixing step are fully mixed into the rubber composition, the rubber composition can be molded or otherwise shaped into the raw rubber component of the tire, such as the shape of the tire tread. The temperature of the raw rubber component can be raised to achieve curing. The curing of the pneumatic tire or its part can be carried out at 120 ℃ to 200 ℃, for example, at least 140 ℃ or at most 180 ℃ or about 150 ℃ for at least 10 minutes. Any conventional vulcanization method can be used, such as heating in a press or mold, or heating with superheated steam or hot air. Such a tire can be constructed, shaped, molded and cured by various known methods, and it is obvious to those skilled in the art.

[0192] In one embodiment, a tire is provided, the tire having a tread formed at least in part by an exemplary rubber composition. Other portions of the tire, such as the tire sidewall, may additionally or alternatively be formed at least in part by a rubber composition as described herein. The tire may be a pneumatic tire for a road vehicle such as a bus or truck, or a car, or a tire for an off-road vehicle, an aircraft, etc. The tire tread may have a tread depth of at least 20 mm, such as at least 22 mm, such as at most 28 mm or at most 27 mm, which is suitable for trucks.

[0193] The rubber composition is not limited to use in tires, but can be used in rubber hoses, rubber gloves, surgical instruments, and the like.

[0194] Exemplary compositions

[0195] Table 1 shows exemplary rubber compositions according to aspects of the exemplary embodiments.

[0196] Table 1: Exemplary rubber composition (phr)

[0197]

[0198]

[0199] Tire tread properties

[0200] Use of the rubber composition in a tire, such as a tire tread, can produce a tire having improved or desirable tread properties. These improved or desirable properties can include improved mileage while maintaining other properties, such as rolling resistance, the ability to maintain high speeds, and resistance to chipping and chunking.

[0201] Without intending to limit the scope of the exemplary embodiments, the following examples illustrate the preparation of exemplary rubber compositions and their properties.

[0202] Example

[0203] Example 1

[0204] The rubber composition (Example A) is prepared using the formulation shown in Table 2. The composition is mixed in four stages in a factory scale mixer, three of which are non-productive and the last stage is productive. In the first stage, the mixture is put into the mixture when it reaches 165°C, the second stage is at 160°C, the third stage is at 155°C, and the last productive stage is at 110°C. The formulation is mixed in a laboratory mixer. In the first stage, elastomers and some carbon black, naphthenic oil, zinc oxide and stearic acid are combined, and in the second stage, the remaining carbon black, as well as wax and antiozonant are added. Sulfur and accelerators are added in the last stage.

[0205] A comparative formulation (Example B) was also prepared in a manner similar to Example A. Example B had higher sulfur (1.0 vs 0.55 phr) and no zinc dibenzyldithiocarbamate accelerator.

[0206] Prototype tires were constructed using treads formed from the rubber composition to demonstrate benefits in physical properties and tire performance compared to a comparative formulation (Example B).

[0207] Table 2: Rubber composition (expressed in phr)

[0208] Components Example A Example B <![CDATA[Natural Rubber (NR) 1 > 50 50 <![CDATA[Polybutadiene (PBD) 2 > 25 <![CDATA[Polybutadiene (PBD) 2A > 35 <![CDATA[Styrene-butadiene rubber (SBR) 3 > 15 25 <![CDATA[Carbon black 4 > 55 55 <![CDATA[Processing oil 5 > 5 5 <![CDATA[wax 6 > 1.5 1.5 <![CDATA[Anti-degradant 7 > 3 3 <![CDATA[Fatty acid 8 > 2.5 2.5 ZnO 3 3 <![CDATA[Sulfur 9 > 0.55 1 <![CDATA[Secondary sulfonamide main accelerator 10 > 0.95 0.95 <![CDATA[Dithiocarbamate ultra-accelerator 11 > 0.66 - <![CDATA[Thiazole super accelerator 12 > 0.09 0.09 Total phr 172.25 172.04 proportion 1.117 1.119

[0209] 1 Technically Specified Rubber (TSR).

[0210] 2 High cis-1,4-polybutadiene rubber, solution polymerized, nickel-catalyzed butadiene homopolymer, as Available from The Goodyear Tire & Rubber Company (made by nickel catalysis of 1,3-butadiene monomer), it has an onset Tg of approximately -109°C, a cis-1,4-content of 97% and a Mooney viscosity of 55, stabilized with a non-staining antioxidant.

[0211] 2A High cis-1,4-polybutadiene rubber, solution polymerized, neodymium-catalyzed butadiene homopolymer, as Available from The Goodyear Tire & Rubber Company (made by neodymium catalysis of 1,3-butadiene monomer), it has an onset Tg of approximately -110°C, a cis-1,4-content of 97% and a Mooney viscosity of 55, stabilized with a non-staining antioxidant.

[0212] 3 Solution polymerized copolymer of butadiene and styrene (SSBR), as 18B 10 was obtained from The Goodyear Tire Rubber Company (made by sequential polymerization of butadiene and styrene, stabilized with a non-staining antioxidant) with a Tg of -70°C, a Mooney viscosity of 70, 18.5 wt% styrene.

[0213] 4 ASTM grade N121 carbon black.

[0214] 5 Naphthenic oil.

[0215] 6 Microcrystalline wax.

[0216] 7 A 2:1 weight ratio combination of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) (an antiozonant and antioxidant) and N,N'-diphenyl-1,4-phenylenediamine (DPPD) (an antioxidant).

[0217] 8 A mixture of fatty acids, primarily stearic acid.

[0218] 9 Elemental sulfur.

[0219] 10 N-tert-butyl-benzothiazole sulfenamide (TBBS) is the primary accelerator.

[0220] 11 Zinc dibenzyldithiocarbamate (first super accelerator).

[0221] 12 Mercaptobenzothiazole disulfide (MBTS) (second super accelerator).

[0222] Properties of rubber compositions

[0223] Physical tests were performed on samples of the rubber composition. The results are shown in Tables 3 and Figure 1 middle.

[0224] Table 3: Physical properties of rubber compositions

[0225]

[0226]

[0227] a The data were obtained using an Automated Testing System instrument from Instron Corporation, which can be used to determine ultimate tension, ultimate elongation, modulus, etc. The data reported in this table were generated by running a Zwick Roell ring tensile testing station.

[0228] b Rebound is measured on cured samples and is an indicator of the hysteresis of the compound when subjected to load, as measured according to ASTM D1054-02 (2007), "Standard Test Method for Rubber Property-Resilience Using a Goodyear-Healey Rebound Pendulum (Withdrawn 2010)". Higher rebound values ​​at 100°C indicate better rolling resistance.

[0229] c Self-adhesion, Strebler test. This is a peel test that measures the interfacial adhesion of one rubber composition to another pulled apart at right angles into a non-destructive specimen, where the two ends of the rubber composition are pulled apart at an angle of 180° relative to each other. Higher values ​​indicate a more robust composition.

[0230] d The storage modulus G' at 100°C after curing is determined by a Rubber Process Analyzer (RPA) at 1% strain and 10% strain. Tan Δ at 10% strain is the ratio of G" to G'. The storage modulus values ​​are measured on uncured samples and after curing at different strain values. The measurement on the uncured sample is an indicator of its processability, while the measurement on the cured sample is an indication of the ride and handling of the tire using the rubber composition in the tread and indicates the deformation of the tire blocks and therefore the wear / mileage of the tire.

[0231] e DIN abrasion is measured by moving a piece of rubber against an abrasive material mounted on a rotating drum. The amount of material scraped off during abrasion is expressed as volume loss in cubic millimeters.

[0232] The data in Table 3 show that the composition of Example A using the zinc dibenzyldithiocarbamate super accelerator in addition to the other two accelerators and a higher PBD / SBR ratio resulted in property improvements that would be expected to result in high mileage, such as lower wear.

[0233] Abrasion, an indicator of treadwear, is determined as the Grosch wear rate expressed in mg / km of rubber worn away. When the rubber sample under test travels a given distance on a rotating abrasive disc, it is placed at a slip angle under a constant load (Newtons). Figure 1 Grosch wear rates are shown at four slip angles (4°, 8°, 12° and 16°, corresponding to increasing friction energy density). Lower wear values ​​(mg / km) at a given friction energy density represent higher expected mileage, especially for 12° and 16° slip angles, which are considered more relevant for long-haul applications.

[0234] from Figure 1 As can be seen, the performance of the Example A sample is significantly better than the Comparative Example B sample, and is much better than the sample of the conventional tire formulation (Example C).

[0235] Tires with treads formed from Examples A and B were also tested. These tires exhibited comparable rolling resistance (Example A slightly better) and comparable wet grip performance, demonstrating that Exemplary Composition A is able to achieve higher mileage than Comparative Example B (e.g., Figure 1 shown), while maintaining rolling resistance and wet grip properties.

[0236] High speed performance tests also showed better performance. Specifically, the driver of the tire with the tread of Example A can maintain a higher speed than that of Comparative Example B.

[0237] Tire wear results were also obtained for two truck fleets traveling on similar roads. Based on the tire wear results, it was estimated that the expected mileage of a long-haul truck drive tire using the Example A tread would be 10% higher than a tire of similar construction but using Example B.

[0238] Example 2

[0239] Additional rubber compositions were prepared in a manner similar to Example 1 by varying the amounts of some ingredients as shown in Table 4. The samples were mixed in a laboratory scale mixer, so the physical test results (Table 5) may differ slightly from those obtained with a plant scale mixer in Example 1. All of these samples included a mixture of polybutadiene, styrene-butadiene rubber, and natural rubber as the elastomer. Example A is included for comparison.

[0240] Table 4: Rubber composition (expressed in phr)

[0241]

[0242]

[0243] Table 4 (continued)

[0244]

[0245]

[0246] Table 5 shows the results of physical testing on these compositions.

[0247] Table 5: Physical properties of rubber compositions

[0248]

[0249]

[0250] Table 5 (continued)

[0251]

[0252]

[0253]

[0254] The results show that the three accelerators used in Example A provide improved properties for the test predicting high mileage, without significant loss of other properties, compared to Example DL without MBTS. Modification of the amounts of the other two accelerators cannot compensate for the absence of MBTS.

[0255] Each document mentioned above is incorporated herein by reference.Except in the embodiments or otherwise indicated, all numerical values ​​of the amount of material, reaction conditions, molecular weight, carbon number, etc., specified in this specification should be understood to be modified by the word "about".Unless otherwise stated, each chemical or composition mentioned herein should be interpreted as a commercial grade material, which may contain isomers, by-products, derivatives and other such materials generally understood to be present in the commercial grade.But, unless otherwise stated, the amount of each chemical component stated does not include any solvent, diluent oil or other carrier material that may be conventionally present in commercial materials.It is to be understood that the upper and lower limits, scopes and ratio limits listed herein can be independently combined.Similarly, the scope and amount of each element of the present invention can be used together with the scope or amount of any other element.

[0256] It will be appreciated that variations of the features and functions disclosed above and other or their alternatives may be combined into many other different systems or applications. Those skilled in the art may subsequently make various currently unforeseeable or unexpected alternatives, modifications, changes or improvements, which are also intended to be covered by the following claims.

Claims

1. A tire tread formed from a vulcanizable rubber composition comprising, expressed in parts by weight per hundred parts of elastomer (phr): 100 phr of an elastomeric component, the elastomeric component comprising natural rubber and polydiene rubber; At least 40 phr of carbon black; Optionally, one or more processing aids selected from liquid plasticizers, waxes, and mixtures thereof; A curing system comprising a sulfur-based curing agent, a zinc-based curing activator, an organic curing activator, and a combination of curing accelerators, wherein the combination of curing accelerators comprises: (i) sulfenamide accelerator, (ii) a metal dithiocarbamate accelerator, and (iii) at least one of a thiazole polysulfide accelerator and a thiuram polysulfide accelerator.

2. The tire tread of claim 1, wherein the elastomeric component comprises 45-65 phr of natural rubber and 30-55 phr of polydiene rubber.

3. The tire tread of claim 1, wherein the polydiene rubber comprises polybutadiene rubber and styrene butadiene rubber in a weight ratio of at least 1.5:

1.

4. The tire tread of claim 1, wherein the rubber composition comprises at least 45 phr of carbon black.

5. The tire tread of claim 1, wherein the rubber composition comprises no greater than 2 phr of silica.

6. The tire tread of claim 1, wherein the rubber composition comprises no greater than 1 phr of resin.

7. The tire tread of claim 1, wherein the combination of cure accelerators comprises: (i) 0.5 to 2 phr of a sulfenamide accelerator, (ii) 0.3 phr to 1.2 phr of a metal dithiocarbamate accelerator, and (iii) 0.05 to 0.4 phr of the at least one of a thiazole polysulfide accelerator and a thiuram polysulfide accelerator.

8. The tire tread of claim 1, wherein the combination of cure accelerators comprises: (i) 0.8 to 1.5 phr of a sulfenamide accelerator, (ii) 0.4 to 0.9 phr of a metal dithiocarbamate accelerator, and (iii) 0.07 to 0.2 phr of the at least one of a thiazole polysulfide accelerator and a thiuram polysulfide accelerator.

9. The tire tread of claim 1, wherein the sulfenamide accelerator is selected from the group consisting of N-cyclohexyl-2-benzothiazole sulfenamide (CBS); N-tert-butyl-2-benzothiazole-sulfenamide (TBBS); and mixtures thereof.

10. The tire tread of claim 1, wherein the metal dithiocarbamate accelerator comprises zinc dibenzyl dithiocarbamate (ZBEC).

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