pneumatic tires

Abstract

To provide a pneumatic tire having a tread rubber composition for a tire which has wet skid resistance, low rolling resistance, good abrasion characteristics and low temperature traction force suitable for snow driving.SOLUTION: A pneumatic tire has a tread containing a vulcanizable rubber composition which contains, based on 100 pts.wt. (phr) of an elastomer, maximum 100 phr of solution polymerization styrene-butadiene rubber; 5 to 50 phr of fatty acid monoester represented by the following formula, wherein R1 is selected from straight-chain or branched alkyl having 1 to 8 carbon atoms, straight-chain or branched alkenyl having 1 to 8 carbon atoms and straight-chain or branched alkyl having 2 to 6 carbon atoms, substituted with 1 to 5 hydroxyl groups; and R2 is alkyl having 11 to 21 carbon atoms or alkenyl having 11 to 21 carbon atoms; 5-50 phr of a hydrocarbon resin having Tg of -40 to 20°C; less than 10 phr of petroleum-derived oil; and 50-130 phr of silica, optionally, approximately 1 to 50 phr of carbon black.SELECTED DRAWING: None

Description

[Technical Field]

[0001] [Background technology]

[0002] It is highly desirable for a tire to have good wet skid resistance, low rolling resistance, and good wear characteristics. It has heretofore been very difficult to improve the wear characteristics of a tire without sacrificing wet skid resistance and traction characteristics. These properties are highly dependent on the dynamic viscoelastic properties of the rubber used in manufacturing the tire.

[0003] To reduce rolling resistance and improve tire treadwear characteristics, high-resilience rubbers have traditionally been used in manufacturing tire tread rubber compounds. On the other hand, to increase the tire's wet skid resistance, rubbers that experience high energy loss have generally been used in tire treads. To balance these two viscoelastically incompatible properties, various types of synthetic and natural rubber blends are commonly used in tire treads.

[0004] It may be desirable to have a tire with a tread for improving traction on snow. Various rubber compositions can be proposed for the tire tread. The challenge here is to reduce the cured stiffness of the tread rubber composition, as indicated by having a lower storage modulus G' at -20°C, for low temperature winter conditions, especially when the tread is intended for use in snow driving of vehicles.

[0005] Providing such a tire tread rubber composition that maintains both wet traction while enhancing low temperature (e.g., winter) performance would present a significant challenge. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 7,342,070 [Patent Document 2] International Publication No. 2007 / 047943 [Patent Document 3] U.S. Patent No. 5,504,135 [Patent Document 4] U.S. Patent No. 6,103,808 [Patent Document 5] U.S. Patent No. 6,399,697 [Patent Document 6] U.S. Patent No. 6,410,816 [Patent Document 7] U.S. Patent No. 6,248,929 [Patent Document 8] U.S. Patent No. 6,146,520 [Patent Document 9] U.S. Patent Application Publication No. 2001 / 00023307 [Patent Document 10] U.S. Patent Application Publication No. 2002 / 0000280 [Patent Document 11] U.S. Patent Application Publication No. 2002 / 0045697 [Patent Document 12] U.S. Patent Application Publication No. 2001 / 0007049 [Patent Document 13] European Patent Application Publication No. 0839891 [Patent Document 14] Patent Publication No. 2002097369 [Patent Document 15] Spanish Patent No. 2122917 [Patent Document 16] U.S. Patent No. 6,242,534 [Patent Document 17] U.S. Patent No. 6,207,757 [Patent Document 18] U.S. Patent No. 6,133,364 [Patent Document 19] U.S. Patent No. 6,372,857 [Patent Document 20] U.S. Patent No. 5,395,891 [Patent Document 21] U.S. Patent No. 6,127,488 [Patent Document 22] U.S. Patent No. 5,672,639 [Patent Document 23] U.S. Patent No. 6,608,125 [Patent Document 24] U.S. Patent Application Publication No. 2006 / 0041063 [Patent Document 25] U.S. Patent Application Publication No. 2003 / 0130535 [Non-patent literature]

[0007] [Non-Patent Document 1] Standard Methods for Analysis&Testing of Petroleum and Related Products and British Standard 2000 Parts, 2003, 62nd edition, the Institute of Petroleum, United Kingdom [Non-patent document 2] Journal of the American Chemical Society, Vol. 60, p. 304 (1930) [Non-patent document 3] The Vanderbilt Rubber Handbook (1978), pp. 344-346 Summary of the Invention [Means for solving the problem]

[0008] The present invention provides a polymerizable composition comprising up to 100 parts by weight (phr) of solution polymerized styrene-butadiene rubber: formula 1

[0009] [ka]

[0010] [In the formula, R 1is selected from C1-C8 linear or branched alkyl, C1-C8 linear or branched alkenyl, and C2-C6 linear or branched alkyl substituted with 1 to 5 hydroxyl groups; R 2 5 to 50 phr of fatty acid monoesters of C11 to C21 alkyl or C11 to C21 alkenyl; 5-50 phr of hydrocarbon resin with a Tg in the range of -40°C to 20°C; Less than 10 phr of petroleum-derived oils; and Silica 50-130 phr, In some cases, carbon black about 1 to 50 phr The present invention is directed to a pneumatic tire having a tread comprising a vulcanizable rubber composition comprising: DETAILED DESCRIPTION OF THE INVENTION

[0011] Solution polymerized styrene-butadiene rubber up to 100 phr, based on 100 parts by weight (phr) of elastomer; formula 1

[0012] [ka]

[0013] [In the formula, R 1 is selected from C1-C8 linear or branched alkyl, C1-C8 linear or branched alkenyl, and C2-C6 linear or branched alkyl substituted with 1 to 5 hydroxyl groups; R 2 5 to 50 phr of fatty acid monoesters of C11 to C21 alkyl or C11 to C21 alkenyl; 5-50 phr of hydrocarbon resin with a Tg in the range of -40°C to 20°C; Less than 10 phr of petroleum-derived oils; and Silica 50-130 phr, In some cases, carbon black about 1 to 50 phr A pneumatic tire having a tread comprising a vulcanizable rubber composition comprising:

[0014] In one embodiment, the fatty acid monoester comprises at least one monoester selected from the group consisting of alkyl oleate, alkyl stearate, alkyl linoleate, and alkyl palmitate.

[0015] In one embodiment, the fatty acid monoester comprises at least 80 weight percent alkyl oleate. In one embodiment, the alkyl oleate is selected from the group consisting of methyl oleate, ethyl oleate, 2-ethylhexyl oleate, isopropyl oleate, and octyl oleate.

[0016] In one embodiment, the fatty acid monoester comprises at least 80 weight percent oleic acid monoester. In one embodiment, R 1 is a C1 to C8 linear or branched alkyl.

[0017] In one embodiment, R 1 is selected from the group consisting of methyl, ethyl, 2-ethylhexyl, isopropyl, and octyl. In one embodiment, the monoester of Formula 1 is selected from the group consisting of monoesters of ethylene glycol, glycerin, trimethylolpropane, pentaerythritol, erythritol, xylitol, sorbitol, dulcitol, mannitol, and inositol.

[0018] In one embodiment, the rubber composition comprises 40 to 55 phr of the fatty acid monoester of Formula 1. The rubber composition comprises 5 to 50 phr, alternatively 20 to 40 phr, of a hydrocarbon resin having a glass transition temperature between -40°C and +20°C. In one embodiment, the hydrocarbon resin has a Tg in the range of between -40°C and 0°C. In one embodiment, the hydrocarbon resin has a Tg in the range of between -40°C and -10°C. A suitable measure of Tg for the resin is DSC according to ASTM D6604 or equivalent. The hydrocarbon resin has a softening point between 0°C and 70°C as determined by ASTM E28, which may sometimes be referred to as the Ring and Ball softening point.

[0019] The hydrocarbon resin is selected from the group consisting of coumarone-indene resins, petroleum hydrocarbon resins, terpene polymers, styrene-alpha methyl styrene resins, terpene phenolic resins, rosin-derived resins and copolymers, and / or mixtures thereof.

[0020] In one embodiment, the resin is a coumarone-indene resin, which contains coumarone and indene as monomer components and constitutes the resin backbone (main chain). Monomer materials other than coumarone and indene that can be incorporated into the backbone include, for example, methyl coumarone, styrene, alpha-methylstyrene, methyl indene, vinyl toluene, dicyclopentadiene, cyclopentadiene, and diolefins such as isoprene and piperylene. Suitable coumarone-indene resins are commercially available, such as the Novares® C series from Rutgers Novares GmbH.

[0021] Suitable petroleum resins include aromatic and non-aromatic types. Several types of petroleum resins are available. Some resins have low unsaturation and high aromatic content, while others, despite being highly unsaturated, contain no aromatic structures. The differences in resins primarily depend on the olefin feedstock from which they are derived. Conventional derivatives of such resins include any C5 compounds (olefins and diolefins containing an average of 5 carbon atoms), such as cyclopentadiene and dicyclopentadiene; diolefins, such as isoprene and piperylene; and any C9 compounds (olefins and diolefins containing an average of 9 carbon atoms), such as vinyltoluene, alpha-methylstyrene, and indene. Such resins can be produced by any mixture formed from the above-mentioned C5 and C9 compounds.

[0022] In one embodiment, the resin may be a terpene resin comprised of polymers of at least one of limonene, alpha pinene, beta pinene, and delta-3-carene.

[0023] Styrene / alpha-methylstyrene resins are herein considered to be relatively short-chain copolymers of styrene and alpha-methylstyrene. They may have, for example, a styrene content ranging from about 10 to about 90 percent. In one embodiment, such resins may be suitably prepared by cationic copolymerization of styrene and alpha-methylstyrene, for example, in a hydrocarbon solvent. Thus, contemplated styrene / alpha-methylstyrene resins may be characterized, for example, by their chemical structure, i.e., their styrene and alpha-methylstyrene content, as well as their glass transition temperature, molecular weight, and molecular weight distribution. Suitable styrene / alpha-methylstyrene resins are commercially available, such as PURE 20 AS from Rutgers Novares GmbH.

[0024] Terpene phenolic resins may also be used, which may be derived from the copolymerization of terpene and phenolic monomers such as limonene, pinene, and delta-3-carene.

[0025] In one embodiment, the resin is derived from rosin and derivatives, such as gum rosin, wood rosin, and tall oil rosin. Gum rosin, wood rosin, and tall oil rosin have similar compositions, but the amount of rosin component may vary. Such resins may be dimerized, polymerized, or disproportionated. Such resins may be in the form of esters of rosin acid with polyols such as pentaerythritol or glycols.

[0026] In one embodiment, the resin may be partially or fully hydrogenated. The rubber composition comprises a solution-polymerized styrene-butadiene rubber. Solution-polymerized SBR (S-SBR) typically has a bound styrene content ranging from about 5 to about 50 percent, preferably from about 9 to about 26 percent. S-SBR can be conveniently prepared, for example, by organolithium catalysis in the presence of an organic hydrocarbon solvent.

[0027] References to the glass transition temperature or Tg of an elastomer or elastomeric composition, as referred to herein, refer to the glass transition temperature of the respective elastomer or elastomeric composition in the uncured state or, in the case of an elastomeric composition, possibly in the cured state. Tg may suitably be determined by differential scanning calorimetry (DSC), for example, as the peak midpoint at a heating rate of 10°C per minute according to ASTM D7426 or equivalent.

[0028] In one embodiment, the solution polymerized styrene-butadiene rubber has a glass transition temperature in the range of -85°C to 0°C. In one embodiment, the styrene-butadiene rubber has a glass transition temperature (Tg) in the range of -85°C to -50°C.

[0029] In one embodiment, the styrene-butadiene rubber has a glass transition temperature (Tg) in the range of -40°C to 0°C. In one embodiment, the styrene-butadiene rubber comprises a blend of two or more styrene-butadiene rubbers of different Tg. Such blends of styrene-butadiene rubbers may be functionalized or unfunctionalized, or may include a combination of functionalized and unfunctionalized styrene-butadiene rubbers.

[0030] The styrene-butadiene rubber may be functionalized with various functional groups, or the styrene-butadiene rubber may be unfunctionalized. In one embodiment, the styrene-butadiene rubber is a functionalized styrene-butadiene rubber. Such functionalized styrene-butadiene rubber may have one or more functional groups attached to the polymer chain, either terminally or in-chain. The functional groups can be incorporated during polymerization as functional initiators or terminators for end-addition or as functional monomers for intra-chain insertion. The functional groups may include hydroxyl, amino, alkoxy, alkoxyamine, thiol, silane, alkoxysilane, alkoxyaminosilane, etc. Such functional groups provide the functionalized styrene-butadiene rubber with the ability to react with surface-active groups, such as hydroxyl groups, on silica, facilitating dispersion and interaction between the silica and the functionalized styrene-butadiene rubber when mixed into a rubber compound.

[0031] In one embodiment, the styrene-butadiene rubber is functionalized with an alkoxysilane group and at least one of a primary amine group and a thiol group. In one embodiment, the styrene-butadiene rubber is obtained by copolymerization of styrene and butadiene, and is characterized in that the styrene-butadiene rubber has primary amino groups and / or thiol groups and alkoxysilyl groups attached to the polymer chain. In one embodiment, the alkoxysilyl groups are ethoxysilyl groups. In one embodiment, the styrene-butadiene rubber is not functionalized.

[0032] The primary amino group and / or thiol group may be bonded to any of the polymerization initiation terminal, polymerization termination terminal, main chain, and side chain of the styrene-butadiene rubber, as long as it is bonded to the styrene-butadiene rubber chain. However, the primary amino group and / or thiol group is preferably introduced to the polymerization initiation terminal or polymerization termination terminal, since this suppresses energy dissipation at the polymer terminal and improves hysteresis loss characteristics.

[0033] Furthermore, the content of alkoxysilyl groups bonded to the polymer chains of the (co)polymer rubber is preferably 0.5 to 200 mmol / kg of styrene-butadiene rubber, more preferably 1 to 100 mmol / kg of styrene-butadiene rubber, and particularly preferably 2 to 50 mmol / kg of styrene-butadiene rubber.

[0034] The alkoxysilyl group may be attached to any of the polymerization initiation end, polymerization termination end, main chain, and side chain of the (co)polymer, as long as it is attached to the (co)polymer chain. However, the alkoxysilyl group is preferably introduced to the polymerization initiation end or polymerization termination end, because energy dissipation from the (co)polymer end can be suppressed and the hysteresis loss characteristics can be improved.

[0035] Styrene-butadiene rubber can be produced by anionic polymerization of styrene and butadiene in a hydrocarbon solvent using an organic alkali metal and / or organic alkaline earth metal initiator, adding a terminator compound having a protected primary amino group and / or a protected thiol group and an alkoxysilyl group to react with the living polymer chain ends when the polymerization is substantially complete, followed by deblocking, e.g., by hydrolysis or other suitable procedure. In one embodiment, styrene-butadiene rubber can be produced as disclosed in U.S. Pat. No. 7,342,070. In another embodiment, styrene-butadiene rubber can be produced as disclosed in WO 2007 / 047943.

[0036] In one embodiment, and as taught in US Pat. No. 7,342,070, the styrene-butadiene rubber is of formula (I) or (II):

[0037] [ka]

[0038] [wherein P is a conjugated diolefin or a (co)polymer chain of a conjugated diolefin and an aromatic vinyl compound; R 1 is an alkylene group having 1 to 12 carbon atoms, and R 2 and R 3 are each independently an alkyl group, an aryl group, or an aryl group having 1 to 20 carbon atoms, n is an integer 1 or 2, m is an integer 1 or 2, and k is an integer 1 or 2, provided that n+m+k is an integer 3 or 4.

[0039] [ka]

[0040] [In the formula, P, R 1 , R 2 and R 3 has the same definition as given for formula I above, j is an integer from 1 to 3, and h is an integer from 1 to 3, provided that j+h is an integer from 2 to 4.

[0041] The terminator compound having a protected primary amino group and an alkoxysilyl group may be any of a variety of compounds known in the art. In one embodiment, the compound having a protected primary amino group and an alkoxysilyl group may be, for example, N,N-bis(trimethylsilyl)aminopropylmethyldimethoxysilane, 1-trimethylsilyl-2,2-dimethoxy-1-aza-2-silacyclopentane, N,N-bis(trimethylsilyl)aminopropyltrimethoxysilane, N,N-bis(trimethylsilyl)aminopropyltriethoxysilane, N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane, N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane, N,N-bis(trimethylsilyl)aminopropylmethyldimethoxysilane, N,N-bis(trimethylsilyl)aminopropylmethyldimethoxysilane, N,N-bis(trimethylsilyl)aminopropylmethyldimethoxysilane, N,N-bis(trimethylsilyl)aminopropylmethyldimethoxysilane, N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane, N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane, N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane, N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane, N,N-bis(trimethylsilyl)aminopropylmethyldimethoxy ... Examples of suitable silanes include N,N-bis(trimethylsilyl)aminoethyltriethoxysilane, N,N-bis(trimethylsilyl)aminoethylmethyldimethoxysilane, and N,N-bis(trimethylsilyl)aminoethylmethyldiethoxysilane, with 1-trimethylsilyl-2,2-dimethoxy-1-aza-2-silacyclopentane, N,N-bis(trimethylsilyl)aminopropylmethyldimethoxysilane, and N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane being preferred. In one embodiment, the compound having a protected primary amino group and an alkoxysilyl group is N,N-bis(trimethylsilyl)aminopropyltriethoxysilane.

[0042] In one embodiment, the compound having a protected primary amino group and an alkoxysilyl group has Formula III RN-(CH2) X Si(OR')3, III wherein R is a protected amine group that, in combination with the nitrogen (N) atom, yields a primary amine upon suitable post-treatment; R' represents a group having 1 to 18 carbon atoms selected from alkyl, cycloalkyl, allyl, or aryl; and X is an integer from 1 to 20. In one embodiment, at least one R' group is an ethyl radical. Suitable post-treatment to yield a primary amine refers to reaction of the living polymer with a compound having a protected primary amino group and an alkoxysilyl group, followed by removal of the protecting group. In the case of a bis(trialkylsilyl) protecting group, such as in N,N-bis(trimerylsilyl)aminopropyltriethoxysilane, hydrolysis is used to remove the trialkylsilyl group and leave the primary amine.

[0043] In one embodiment, the rubber composition comprises about 40 to about 60 phr of a styrene-butadiene rubber functionalized with alkoxysilane groups and primary amine or thiol groups. Suitable styrene-butadiene rubbers functionalized with alkoxysilane groups and primary amine groups are commercially available, such as HPR 340 from Japan Synthetic Rubber (JSR).

[0044] In one embodiment, the solution polymerized styrene-butadiene rubber is as disclosed in WO 2007 / 047943 and is functionalized with alkoxysilane groups and thiols, and is combined with a living anionic polymer and a polymer of formula IV (R 4 O) x R 4 y Si-R 5 -S-SiR 4 3IV where Si is silicon; S is sulfur; O is oxygen; x is an integer selected from 1, 2, and 3; y is an integer selected from 0, 1, and 2; x+y=3; and R 4 are the same or different, (C1-C 16 ) alkyl; R' is aryl and alkylaryl or (C-C16 ) alkyl. In one embodiment, R 5 (C1-C 16 ) alkyl. In one embodiment, each R 4 groups are the same or different and each is independently C1-C5 alkyl; R 5 is C1-C5 alkyl.

[0045] Suitable styrene-butadiene rubbers functionalized with alkoxysilane and thiol groups are commercially available, such as Sprintan SLR 3402 or Sprintan SLR 4602 from Trinseo.

[0046] In one embodiment, the styrene-butadiene rubber in the rubber composition is present in an amount ranging up to 100 phr. In one embodiment, the styrene-butadiene rubber is present in an amount ranging from 10 to 90 phr, together with 90 to 10 phr of at least one additional diene-based elastomer. In one embodiment, the styrene-butadiene rubber is present in an amount ranging from 30 to 70 phr, together with 70 to 30 phr of at least one additional diene-based elastomer.

[0047] The rubber composition may optionally contain one or more additional rubbers or elastomers containing olefinic unsaturation. The phrase "rubber or elastomer containing olefinic unsaturation" or "diene-based elastomer" is intended to include natural rubber and its various raw and reclaim forms, as well as various synthetic rubbers. In describing this invention, the terms "rubber" and "elastomer" can be used interchangeably unless otherwise specified. The terms "rubber composition," "compounded rubber," and "rubber compound" are used interchangeably to refer to rubber blended or mixed with various raw materials and ingredients, and such terms are familiar to those skilled in the art of rubber mixing or compounding. Specific examples of synthetic rubbers include polybutadiene (including cis-1,4 polybutadiene), polyisoprene (including cis-1,4 polyisoprene), butyl rubber, styrene / isoprene / butadiene rubber, and copolymers of 1,3 butadiene or isoprene with styrene. Additional examples of rubbers that may be used include alkoxysilyl end-functionalized solution polymerized polymers (SBR, PBR, IBR, and SIBR), silicon-coupled and tin-coupled star-branched polymers. Preferred rubbers or elastomers are polyisoprene (natural or synthetic), polybutadiene, and SBR.

[0048] In one embodiment, the at least one additional rubber is preferably at least two of diene-based rubbers, such as a combination of two or more rubbers, such as cis-1,4-isoprene rubber (natural or synthetic, but preferably natural), 3,4-isoprene rubber, styrene / isoprene / butadiene rubber, emulsion and solution polymerization derived styrene / butadiene rubber, cis-1,4-polybutadiene rubber, and emulsion polymerization prepared butadiene / acrylonitrile copolymers.

[0049] In one embodiment of the invention, emulsion polymerization-derived styrene / butadiene (E-SBR) having a relatively traditional styrene content of about 20 to about 28 percent bound styrene may be used.

[0050] By emulsion polymerization-prepared E-SBR, it is meant that styrene and 1,3-butadiene are copolymerized as an aqueous emulsion. Such are well known to those skilled in the art. The bound styrene content can vary, for example, from about 5 to about 50 percent.

[0051] Solution polymerization prepared SBR (S-SBR) typically has a bound styrene content ranging from about 5 to about 50, preferably from about 9 to about 26 percent. S-SBR can be conveniently prepared, for example, by organolithium catalysis in the presence of an organic hydrocarbon solvent.

[0052] In one embodiment, cis-1,4 butadiene rubber (BR) may be used. Such BR can be prepared, for example, by organic solution polymerization of 1,3-butadiene. The BR can be conveniently characterized, for example, as having at least a 90 percent cis-1,4-content and a glass transition temperature, Tg, in the range of about -95°C to about -110°C.

[0053] In one embodiment, natural rubber or synthetic cis-1,4 polyisoprene may be used. The rubber composition may contain up to 10 phr of processing oil. In one embodiment, the amount of processing oil ranges from 1 to 5 phr. In one embodiment, the rubber composition does not contain processing oil. Processing oil may be included in the rubber composition as an extender oil, typically used to extend elastomers. Processing oil may also be included in the rubber composition by direct addition of oil during rubber compounding. The processing oil used may be included in both the extender oil present in the elastomer and the process oil added during compounding. Suitable processing oils include various oils known in the art, including aromatic, paraffinic, naphthenic, and low PCA oils, e.g., MES, TDAE, and heavy naphthenic oils, and vegetable oils, e.g., sunflower, soybean, and safflower oils.

[0054] In one embodiment, the rubber composition comprises a low PCA oil.Suitable low PCA oils include, but are not limited to, mild extractive solvates (MES), treated distillate aromatic extracts (TDAE) and heavy naphthenic oils, which are known in the art: see, for example, U.S. Patent Nos. 5,504,135; 6,103,808; 6,399,697; 6,410,816; 6,248,929; 6,146,520; U.S. Patent Application Publication Nos. 2001 / 00023307; 2002 / 0000280; 2002 / 0045697; 2001 / 0007049; European Patent Application Publication No. 0839891; Japanese Patent Application Publication No. 2002097369; Spanish Patent No. 2122917. Generally, suitable low PCA oils include those having a glass transition temperature, Tg, in the range of about -40°C to about -80°C. MES oils generally have a Tg in the range of about -57°C to about -63°C. TDAE oils generally have a Tg in the range of about -44°C to about -50°C. Heavy naphthenic oils generally have a Tg in the range of about -42°C to about -48°C. A suitable measurement of the Tg of TDAE oils is DSC according to ASTM E1356 or equivalent.

[0055] Suitable low PCA oils include those having a polycyclic aromatic content of less than 3 weight percent as determined by the IP 346 method, which procedure can be found in Standard Methods for Analysis & Testing of Petroleum and Related Products and British Standard 2000 Parts, 2003, 62nd Edition, published by the Institute of Petroleum, United Kingdom.

[0056] Suitable TDAE oils are available as Tudalen SX500 from Klaus Dahleke KG, VivaTec 400 and VivaTec 500 from H&R Group, Enerthene 1849 from BP, and Extensoil 1996 from Repsol. The oils may be available alone as oils or together with elastomers in the form of extended elastomers.

[0057] Suitable vegetable oils include, for example, soybean oil, sunflower oil, and canola oil in the form of esters containing a certain degree of unsaturation. The vulcanizable rubber composition may contain from about 50 to about 130 phr of silica.

[0058] Commonly used siliceous pigments that may be used in rubber compounds include conventional pyrogenic and precipitated siliceous pigments (silica), with precipitated silicas being preferred. The conventional siliceous pigments preferably used in the present invention are precipitated silicas such as those obtained by the acidification of soluble silicates, e.g., sodium silicate.

[0059] Such conventional silicas can be characterized as having a BET surface area, as measured, for example, using nitrogen gas, preferably in the range of about 40 to about 600 square meters per gram, more usually in the range of about 50 to about 300 square meters per gram. The BET method for measuring surface area is described in Journal of the American Chemical Society, Vol. 60, p. 304 (1930).

[0060] Conventional silicas may also be characterized as having a dibutyl phthalate (DBP) absorption value typically ranging from about 100 to about 400, more usually from about 150 to about 300. Conventional silica can be expected to have an average ultimate particle size in the range of 0.01 to 0.05 microns as determined by, for example, electron microscopy, although the silica particles may be smaller or possibly larger in size.

[0061] Various commercially available silicas may be used, such as, by way of example only and not limitation, silicas available under the Hi-Sil trademark from PPG Industries having the designations 210, 243, 315, etc.; silicas available from Rhodia having the designations Z1165MP and Z165GR, and silicas available from Degussa AG having the designations VN2 and VN3, etc.

[0062] The vulcanizable rubber composition may optionally contain from about 1 to about 50 phr of carbon black. Commonly used carbon blacks can be used as conventional fillers. Representative examples of such carbon blacks include N110, N121, N134, N220, N231, N234, N242, N293, N299, S315, N326, N330, M332, N339, N343, N347, N351, N358, N375, N539, N550, 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 iodine concentrations ranging from 34 to 150 cm. 3 / 100g range of DBP numbers.

[0063] Other fillers may be used in the rubber composition, including, but not limited to, ultra-high molecular weight polyethylene (UHMWPE), particulate fillers including particulate polymer gels such as those disclosed in U.S. Pat. Nos. 6,242,534; 6,207,757; 6,133,364; 6,372,857; 5,395,891; or 6,127,488, and plasticized starch composite fillers such as those disclosed in U.S. Pat. No. 5,672,639.

[0064] Preferably, the rubber composition used in the tire component may further comprise a conventional sulfur-containing organosilicon compound. Examples of suitable sulfur-containing organosilicon compounds include those represented by Formula 2: Z-Alk-S n-Alk-Z 2 [Wherein Z is

[0065] [ka]

[0066] wherein R 3 is an alkyl group of 1 to 4 carbon atoms, cyclohexyl, or phenyl; R 4 is an alkoxy of 1 to 8 carbon atoms or a cycloalkoxy of 5 to 8 carbon atoms; Alk is a divalent hydrocarbon of 1 to 18 carbon atoms, and n is an integer of 2 to 8.

[0067] Specific examples of sulfur-containing organosilicon compounds that may be used in accordance with the present invention include the following: 3,3'-bis(trimethoxysilylpropyl) disulfide, 3,3'-bis(triethoxysilylpropyl) disulfide, 3,3'-bis(triethoxysilylpropyl) tetrasulfide, 3,3'-bis(triethoxysilylpropyl) octasulfide, 3,3'-bis(trimethoxysilylpropyl) tetrasulfide, 2,2'-bis(triethoxysilylethyl) tetrasulfide. sulphide, 3,3'-bis(trimethoxysilylpropyl) trisulphide, 3,3'-bis(triethoxysilylpropyl) trisulphide, 3,3'-bis(tributoxysilylpropyl) disulphide, 3,3'-bis(trimethoxysilylpropyl) hexasulphide, 3,3'-bis(trimethoxysilylpropyl) octasulphide, 3,3'-bis(trioctaoxysilylpropyl) tetrasulphide, 3,3'-bis(trihexaoxysilylpropyl) disulphide, 3,3' -Bis(tri-2''-ethylhexoxysilylpropyl) trisulfide, 3,3'-bis(triisooctaoxysilylpropyl) tetrasulfide, 3,3'-bis(tri-t-butoxysilylpropyl) disulfide, 2,2'-bis(methoxydiethoxysilylethyl) tetrasulfide, 2,2'-bis(trippropoxysilylethyl) pentasulfide, 3,3'-bis(tricyclonexoxysilylpropyl) tetrasulfide xysilylpropyl)tetrasulfide), 3,3'-bis(tricyclopentoxysilylpropyl) trisulfide, 2,2'-bis(tri-2''-methylcyclohexoxysilylethyl)tetrasulfide, bis(trimethoxysilylmethyl)tetrasulfide, 3-methoxyethoxypropoxysilyl 3'-diethoxybutoxy-silylpropyl tetrasulfide, 2,2'-bis(dimethylmethoxysilylethyl) disulfide, 2,2'-bis(dimethylsec.butoxysilylethyl) trisulfide, 3,3'-bis(methylbutylethoxysilylpropyl) tetrasulfide, 3,3'-bis(di-t-butylmethoxysilylpropyl) tetrasulfide, 2,2'-bis(phenylmethylmethoxysilylethyl) trisulfide, 3,3'-bis(diphenylisopropoxysilylpropyl) tetrasulfide, 3,3'-bis(diphenylcyclohexyloxysilylpropyl) disulfide, 3,3'-bis(dimethylethyl methyl captosilylpropyl) tetrasulfide, 2,2'-bis(methyldimethoxysilylethyl) trisulfide, 2,2'-bis(methylethoxypropoxysilylethyl) tetrasulfide, 3,3'-bis(diethylmethoxysilylpropyl) tetrasulfide, 3,3'-bis(ethyldi-sec.butoxysilylpropyl) disulfide, 3,3'-bis(propyldiethoxysilylpropyl) disulfide, 3,3'-bis(butyldimethoxysilylpropyl) trisulfide Sulfide, 3,3'-bis(phenyldimethoxysilylpropyl)tetrasulfide, 3-phenylethoxybutoxysilyl 3'-trimethoxysilylpropyl tetrasulfide, 4,4'-bis(trimethoxysilylbutyl)tetrasulfide, 6,6'-bis(triethoxysilylhexyl)tetrasulfide, 12,12'-bis(triisopropoxysilyldodecyl)disulfide, 18,18'-bis(trimethoxysilyloctadecyl)tetrasulfide, 18 ,18'-Bis(tripropoxysilyloctadecenyl)tetrasulfide, 4,4'-bis(trimethoxysilylbuten-2-yl)tetrasulfide, 4,4'-bis(trimethoxysilylcyclohexylene)tetrasulfide, 5,5'-bis(dimethoxymethylsilylpentyl)trisulfide, 3,3'-bis(trimethoxysilyl-2-methylpropyl)tetrasulfide, 3,3'-bis(dimethoxyphenylsilyl-2-methylpropyl)disulfide.

[0068] The preferred sulfur-containing organosilicon compounds are 3,3'-bis(trimethoxy or triethoxysilylpropyl) sulfides. The most preferred compounds are 3,3'-bis(triethoxysilylpropyl) disulfide and 3,3'-bis(triethoxysilylpropyl) tetrasulfide. Thus, for Formula 2, preferably, Z is:

[0069] [ka]

[0070] is [In the formula, R 4 is an alkoxy of 2 to 4 carbon atoms, with 2 carbon atoms being particularly preferred; alk is a divalent hydrocarbon of 2 to 4 carbon atoms, with 3 carbon atoms being particularly preferred; and n is an integer of 2 to 5, with 2 and 4 being particularly preferred.

[0071] In another embodiment, suitable sulfur-containing organosilicon compounds include those disclosed in U.S. Patent No. 6,608,125. In one embodiment, the sulfur-containing organosilicon compound includes 3-(octanoylthio)-1-propyltriethoxysilane, CH3(CH2)6C(=O)-S-CH2CH2CH2Si(OCH2CH3)3, commercially available as NXT™ from Momentive Performance Materials.

[0072] In another embodiment, suitable sulfur-containing organosilicon compounds include those disclosed in U.S. Patent Application Publication No. 2006 / 0041063. In one embodiment, the sulfur-containing organosilicon compound includes the reaction product of a hydrocarbon-based diol (e.g., 2-methyl-1,3-propanediol) with S-[3-(triethoxysilyl)propyl]thiooctanoate. In one embodiment, the sulfur-containing organosilicon compound is NXT-Z™ from Momentive Performance Materials.

[0073] In another embodiment, suitable sulfur-containing organosilicon compounds include those disclosed in U.S. Patent Application Publication No. 2003 / 0130535. In one embodiment, the sulfur-containing organosilicon compound is Si-363 from Degussa.

[0074] The amount of the sulfur-containing organosilicon compound of Formula 2 in a rubber composition may vary depending on the level of other additives used. Generally, the amount of the compound of Formula I ranges from 0.5 to 20 phr. Preferably, the amount ranges from 1 to 10 phr.

[0075] Those skilled in the art will readily appreciate that the rubber composition can be compounded by methods generally known in the rubber compounding art, such as blending the various components of sulfur-vulcanizable rubber with various commonly used additives, such as sulfur donors, curing aids (e.g., activators and retarders), fillers, pigments, fatty acids, zinc oxide, waxes, antioxidants, antiozonants, and peptizers. As known to those skilled in the art, the additives listed above are selected and generally used in conventional amounts depending on the intended use of the sulfur-vulcanizable and sulfur-vulcanized materials (rubbers). Representative examples of sulfur donors include elemental sulfur (free sulfur), amine disulfides, polymeric polysulfides, and sulfur olefin adducts. In one embodiment, the sulfur-vulcanizing agent is elemental sulfur. The sulfur-vulcanizing agent may be used in an amount ranging from 0.5 to 8 phr, alternatively from 1.5 to 6 phr. Typical amounts of antioxidants include from about 1 to about 5 phr. Representative antioxidants include, for example, diphenyl-p-phenylenediamine and others, such as those disclosed in The Vanderbilt Rubber Handbook (1978), pages 344-346. Typical amounts of antiozonants include about 1 to 5 phr. Typical amounts of fatty acids, which, if used, can include stearic acid, include about 0.5 to about 3 phr. Typical amounts of zinc oxide include about 2 to about 5 phr. Typical amounts of wax include 1 to 5 phr. Microcrystalline wax is often used. Typical amounts of peptizers include 0.1 to 1 phr. Typical peptizers may be, for example, pentachlorothiophenol and dibenzamidodiphenyl disulfide.

[0076] Accelerators are used to control the time and / or temperature required for vulcanization and to improve the properties of the vulcanizate. In one embodiment, a single accelerator system, i.e., a primary accelerator, may be used. The primary accelerator(s) may be used in a total amount ranging from about 0.5 to about 4 phr, alternatively from about 0.8 to about 1.5 phr. In another embodiment, a combination of primary and secondary accelerators may be used, with the secondary accelerator being used in a lower amount, such as from about 0.05 to about 3 phr, to activate and improve the properties of the vulcanizate. These accelerator combinations can be expected to produce a synergistic effect on the final properties, which are somewhat better than those produced by either accelerator used alone. Additionally, delayed-acting accelerators may be used that are not affected by normal processing temperatures but produce a satisfactory cure at normal vulcanization temperatures. Vulcanization retarders may also be used. Suitable types of accelerators that may be used in the present invention are amines, disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides, dithiocarbamates, and xanthates. In one embodiment, the primary accelerator is a sulfenamide. If a second accelerator is used, the secondary accelerator may be a guanidine, dithiocarbamate or thiuram compound.

[0077] Mixing of the rubber composition can be accomplished by methods known to those skilled in the rubber mixing art. For example, the raw materials are typically mixed in at least two stages: at least one non-productive stage followed by a productive mix stage. The final curative, including the sulfur vulcanizing agent, is typically mixed in the final stage, conventionally referred to as the "productive" mix stage, where mixing is typically performed at a temperature or final temperature lower than the mixing temperature(s) of the preceding non-productive mix stage(s). The terms "non-productive" and "productive" mix stages are well known to those skilled in the rubber mixing art. The rubber composition may be subjected to a thermodynamic mixing step. The thermodynamic mixing step generally involves mechanical operation in a mixer or extruder for a period of time suitable to produce a rubber temperature between 140°C and 190°C. The suitable duration of the thermodynamic operation varies as a function of the operating conditions and the amounts and properties of the components. For example, the thermodynamic operation may be from 1 to 20 minutes.

[0078] The rubber composition can be incorporated into various rubber components of a tire. For example, the rubber component can be a tread (including a tread cap and a tread base), a sidewall, an apex, a chafer, a sidewall insert, a wire coat, or an innerliner. In one embodiment, the component is a tread.

[0079] The pneumatic tire of the present invention may be a race tire, passenger tire, aircraft tire, farm tire, earthmoving tire, off-road tire, truck tire, etc. In one embodiment, the tire is a passenger or truck tire. The tire may also be radial or bias.

[0080] Vulcanization of the pneumatic tires of the present invention is generally carried out at conventional temperatures ranging from 100°C to 200°C. In one embodiment, vulcanization is carried out at a temperature ranging from 110°C to 180°C. Any of the conventional vulcanization methods may be used, such as heating in a press or mold, heating with superheated steam or hot air, etc. Such tires can be built, shaped, molded, and cured by a variety of methods known and readily apparent to those skilled in the art.

[0081] The present invention is illustrated by the following examples, which are illustrative only and should not be construed as limiting the scope of the invention or the manner in which it can be practiced. Parts and percentages are given by weight unless otherwise indicated. [Example]

[0082] Rubber compounds were mixed according to the formulations shown in Table 1, with amounts given in phr including standard amounts of additives and curatives. The compounds were cured and tested for physical properties shown in Table 2. Compounds C1 and C2 were controls, and compounds E1-E4 were representative of the invention.

[0083] Compound Sample C1 includes naphthenic oil to enhance rubber processing and snow grip performance of a silica-reinforced cured rubber composition containing tin-coupled solution-polymerized SBR and high-cis polybutadiene. Compound Sample E1 is prepared by modifying the Sample C1 composition, replacing the naphthenic oil with a traction-enhancing combination of hydrocarbon resin and high-oleic sunflower oil monoester. It is noted that predicted snow grip performance improves as evidenced by a decrease in G' property measured at -20°C from 13.8 MPa to 10.7 MPa. Additionally, predicted rolling resistance improves significantly as evidenced by an increase in rebound from 34 to 38 at 23°C. Predicted treadwear performance improves, from 71 to 50 mm. 3The tire exhibits a significantly reduced wear rate. This is achieved without a significant change in predicted wet traction, as the rebound at 0°C is similar to that of Sample C1. Compound Sample E2 was prepared by modifying the Sample C1 composition, replacing the naphthenic oil with a traction-enhancing combination of hydrocarbon resin and soybean oil. It is noted that similar improvements in predicted properties of snow grip, tread wear, and rolling resistance are obtained without substantially compromising the predicted properties of wet grip.

[0084] Compound Sample C2 includes naphthenic oil to enhance rubber processing and snow grip performance of a silica-reinforced, cured rubber composition containing functionalized, tin-coupled solution-polymerized SBR and high-cis polybutadiene. Compound Sample E3 is prepared by modifying the Sample C2 composition, replacing the naphthenic oil with a traction-enhancing combination of hydrocarbon resin and a monoester of high oleic sunflower oil. It is noted that predicted snow grip performance improves as evidenced by a decrease in G' property measured at -20°C from 13.9 MPa to 7.6 MPa. Additionally, predicted rolling resistance improves significantly as evidenced by an increase in rebound from 35 to 39 at 23°C. Predicted treadwear performance improves, reducing wear rates from 63 to 48 mm. 3 to 0°C. This is achieved without a significant change in predicted wet traction, as the rebound at 0°C is similar to that of Sample C2. Compound Sample E4 was prepared by modifying the Sample C2 composition, replacing the naphthenic oil with a traction-enhancing combination of hydrocarbon resin and soybean oil. It is noted that similar improvements in predicted properties of snow grip, tread wear, and rolling resistance are obtained without substantially compromising the predicted properties of wet grip.

[0085] [Table 1]

[0086] [Table 2]

[0087] While certain representative embodiments and details have been shown for the purpose of explaining the subject invention, it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the scope of the subject invention.

[0088] [Embodiments of the Invention] 1. Solution polymerized styrene-butadiene rubber up to 100 phr based on 100 parts by weight (phr) of elastomer; formula 1

[0089] [ka]

[0090] [In the formula, R 1 is selected from C1-C8 linear or branched alkyl, C1-C8 linear or branched alkenyl, and C2-C6 linear or branched alkyl substituted with 1 to 5 hydroxyl groups; R 2 5 to 50 phr of fatty acid monoesters of C11 to C21 alkyl or C11 to C21 alkenyl; 5-50 phr of hydrocarbon resin with a Tg in the range of -40°C to 20°C; Less than 10 phr of petroleum-derived oils; and Silica 50-130 phr, Optionally, about 1 to 50 phr of carbon black A pneumatic tire having a tread comprising a vulcanizable rubber composition comprising: 2. The pneumatic tire of 1, wherein the hydrocarbon resin having a Tg in the range of -40°C to 20°C is a coumarone-indene resin. 3. The pneumatic tire of 1, wherein the hydrocarbon resin having a Tg in the range of -40°C to 20°C is derived from styrene and alpha-methylstyrene. 4. The pneumatic tire of 1, wherein the styrene-butadiene rubber has a glass transition temperature (Tg) in the range of -85°C to -50°C. 5. The pneumatic tire of 1, wherein the styrene-butadiene rubber has a glass transition temperature (Tg) in the range of -40°C to 0°C. 6. A pneumatic tire according to claim 1, wherein the coumarone-indene resin having a Tg in the range of -40°C to 20°C contains residues of coumarone, indene, and at least one residue selected from the group consisting of methyl coumarone, styrene, α-methylstyrene, methyl indene, vinyl toluene, dicyclopentadiene, cyclopentadiene, and diolefins such as isoprene and piperylene. 7. The pneumatic tire of 1, wherein the monoester of Formula 1 is selected from the group consisting of monoesters of ethylene glycol, glycerin, trimethylolpropane, pentaerythritol, erythritol, xylitol, sorbitol, dulcitol, mannitol, and inositol. 8. R 1 1. A pneumatic tire according to claim 1, wherein the alkyl group is selected from the group consisting of methyl, ethyl, 2-ethylhexyl, isopropyl, and octyl. 9. R 1 1. A pneumatic tire according to 1, wherein is a C1 to C8 linear or branched alkyl. 10. The pneumatic tire of 1, wherein the fatty acid monoester comprises at least one monoester selected from the group consisting of alkyl oleate, alkyl stearate, alkyl linoleate, and alkyl palmitate. 11. The pneumatic tire of 1, wherein the fatty acid monoester comprises at least 80 weight percent alkyl oleate. 12. The pneumatic tire of 6, wherein the alkyl oleate is selected from the group consisting of methyl oleate, ethyl oleate, 2-ethylhexyl oleate, isopropyl oleate, and octyl oleate. 13. The pneumatic tire of 1, wherein the diene-based elastomer is selected from the group consisting of natural rubber, polybutadiene, synthetic polyisoprene, solution-polymerized styrene-butadiene rubber, and emulsion-polymerized styrene-butadiene rubber. 14. A pneumatic tire according to claim 1, containing 40 to 55 phr of a fatty acid monoester of formula 1. 15. The pneumatic tire of 1, wherein the fatty acid monoester comprises at least 80 weight percent oleic acid monoester. 16. The pneumatic tire of 1, wherein the styrene-butadiene rubber is functionalized. 17. The pneumatic tire of 1, wherein the rubber composition comprises 10 to 90 phr of styrene-butadiene rubber and 90 to 10 phr of at least one additional diene-based elastomer. 18. The pneumatic tire of 1, wherein the rubber composition comprises 30 to 70 phr of styrene-butadiene rubber and 70 to 30 phr of at least one additional diene-based elastomer.

Claims

1. 100 parts by weight of an elastomer consisting of 30 to 70 parts by weight of solution polymerized styrene-butadiene rubber and 70 to 30 parts by weight of polybutadiene, based on 100 parts by weight of elastomer (phr); Formula 1 【Chemical 1】 [In the formula, R １ is selected from C1 to C8 linear or branched alkyl, C1 to C8 linear or branched alkenyl, and C2 to C6 linear or branched alkyl substituted with 1 to 5 hydroxyl groups; R ２ is C11-C21 alkyl or C11-C21 alkenyl; 5 to 50 phr of coumarone-indene resin having a Tg in the range of -40°C to 20°C; less than 10 phr of petroleum-derived oils; and Silica 50 to 130 phr, optionally, 1 to 50 phr of carbon black; A pneumatic tire having a tread characterized by a vulcanizable rubber composition comprising:

2. 2. The pneumatic tire of claim 1, wherein the styrene-butadiene rubber has a glass transition temperature (Tg) in the range of -85°C to 0°C.

3. 2. The pneumatic tire of claim 1, wherein the styrene-butadiene rubber has a glass transition temperature (Tg) in the range of -40°C to 0°C.

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