pneumatic tires

Abstract

To provide a pneumatic tire having a tread containing a tire tread rubber composition which maintains wet traction while enhancing low-temperature (for example, winter season) performance.SOLUTION: A pneumatic tire has a tread containing a vulcanizable rubber composition which contains, based on 100 pts.wt. (phr) of an elastomer, (A) approximately 45 to approximately 100 phr of low cis-polybutadiene having a vinyl-1,2 percentage content of 5 to 30 percent and Tg of -95 to -70°C; (B) approximately 0 to approximately 40 phr of solution polymerization styrene-butadiene rubber having a glass transition temperature (Tg) of -85 to -50°C; (C) 0 to 30 phr of natural rubber or synthetic polyisoprene; (D) 0 to 20 phr of process oil; (E) 55 to 80 phr of a resin having an aromatic hydrogen percentage content of 3 to 30 mol% and Tg exceeding 30°C; and (F) 110 to 160 phr of silica.SELECTED DRAWING: None

Description

[Background technology]

[0001] 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.

[0002] 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.

[0003] 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.

[0004] 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]

[0005] [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. 7,214,731 [Patent Document 4] U.S. Patent No. 4,704,414 [Patent Document 5] U.S. Patent No. 6,123,762 [Patent Document 6] U.S. Patent No. 6,573,324 [Patent Document 7] U.S. Patent No. 6,608,125 [Patent Document 8] U.S. Patent Application Publication No. 2003 / 0130535 [Non-patent literature]

[0006] [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]

[0007] The present invention is based on 100 parts by weight (phr) of elastomer. (A) about 45 to about 100 phr of low-cis polybutadiene having a vinyl-1,2 content in the range of 5 to 30 percent and a Tg in the range of -95°C to -70°C; (B) about 0 to about 40 phr of solution-polymerized styrene-butadiene rubber having a glass transition temperature (Tg) in the range of -85°C to -50°C; (C) natural rubber or synthetic polyisoprene 0-30 phr; (D) Process oil 0-20 phr; (E) 55 to 80 phr of resin having an aromatic hydrogen content in the range of 3 to 30 mole percent and a Tg greater than 30°C; and (F) Silica 110~160phr The present invention is directed to a pneumatic tire having a tread comprising a vulcanizable rubber composition comprising:

[0008] The present invention is further directed to a method of manufacturing a tire. DETAILED DESCRIPTION OF THE INVENTION

[0009] Based on 100 parts by weight (phr) of elastomer, (A) about 45 to about 100 phr of low-cis polybutadiene having a vinyl-1,2 content in the range of 5 to 30 percent and a Tg in the range of -95°C to -70°C; (B) about 0 to about 40 phr of solution-polymerized styrene-butadiene rubber having a glass transition temperature (Tg) in the range of -85°C to -50°C; (C) natural rubber or synthetic polyisoprene 0-30 phr; (D) Process oil 0-20 phr; (E) 55 to 80 phr of a resin having an aromatic hydrogen content in the range of 3 to 30 mole percent and a Tg greater than 30°C; and (F) Silica 110~160phr A pneumatic tire having a tread comprising a vulcanizable rubber composition comprising:

[0010] Also disclosed is a method of manufacturing a tire. One component of the rubber composition is from about 45 to about 100 phr, alternatively from 55 to 80 phr, of polybutadiene.

[0011] In one embodiment, the polybutadiene is a low-cis polybutadiene having a vinyl-1,2 content of 5 to 30 percent and a Tg in the range of -95 to -70°C. Such low-cis polybutadienes typically consist of cis-1,4 / trans-1,4 / vinyl-1,2 monomer insertions, each up to 50 percent in the polybutadiene polymer chain, and are produced by anionic solution polymerization using a lithium catalyst. In one embodiment, the low-cis polybutadiene contains 10 to 30 percent vinyl-1,2; 15 to 45 percent cis-1,4; and the remainder trans-1,4, making up 100 percent of the polymer. In one embodiment, the low-cis polybutadiene is SE PB-5800 from Trinseo, containing approximately 11% vinyl-1,2, 39% cis-1,4, and 50% trans-1,4 insertions, and has a Tg of approximately -90°C.

[0012] In one embodiment, the low-cis polybutadiene is a functionalized low-cis polybutadiene. Such functionalized low-cis polybutadiene may have one or more functional groups attached to the polymer chain, either terminally or intrachain. The functional groups can be incorporated during polymerization as functional initiators or terminators for end-addition or as functional monomers for intrachain insertion. The functional groups may include hydroxyl, amino, alkoxy, alkoxyamine, thiol, silane, alkoxysilane, alkoxyaminosilane, etc. Such functional groups provide the functionalized low-cis polybutadiene with the ability to react with surface-active groups, such as hydroxyl groups, on silica, facilitating dispersion and interaction between the silica and the low-cis polybutadiene when mixed in a rubber compound.

[0013] The rubber composition includes 0 to 40 phr, alternatively 20 to 40 phr, of a styrene-butadiene rubber having a glass transition temperature (Tg) ranging from -85°C to -50°C. 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 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, characterized in that the styrene-butadiene rubber has primary amino 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 unfunctionalized.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] In one embodiment, and as taught in US Pat. No. 7,342,070, the styrene-butadiene rubber is of formula (I) or (II):

[0019] [ka]

[0020] [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 3are 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.

[0021] [ka]

[0022] [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.

[0023] 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.

[0024] In one embodiment, the compound having a protected primary amino group and an alkoxysilyl group has Formula III RN-(CH2) X Si(OR')3III The compound may be any of the following compounds: 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.

[0025] 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).

[0026] 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 (C1-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 a C1-C5 alkyl; R 5 is a C1-C5 alkyl.

[0027] Solution polymerized styrene-butadiene rubber has a glass transition temperature in the range of -85°C to -50°C. 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, possibly, in the case of an elastomeric composition, 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] Suitable styrene-butadiene rubbers functionalized with alkoxysilane and thiol groups are commercially available, such as Sprintan SLR 3402 from Trinseo.

[0029] Another component of the rubber composition is from about 0 to about 40 phr, alternatively from 10 to 30 phr, of natural rubber or synthetic polyisoprene. In one embodiment, the rubber composition contains from 15 to 25 phr of natural rubber or synthetic polyisoprene. In one embodiment, the rubber composition contains from 5 to 15 phr of natural rubber or synthetic polyisoprene.

[0030] The rubber composition may contain 0 to 20 phr of processing oil, alternatively 1 to 20 phr. The processing oil may be included in the rubber composition as an extender oil, typically used to extend elastomers. The 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 processing oil added during compounding. Suitable processing oils include various oils known in the art, including aromatic, paraffinic, naphthenic, and low-PCA oils, such as MES, TDAE, and heavy naphthenic oils, vegetable oils, such as sunflower, soybean, and safflower oils, and monoesters of fatty acids selected from the group consisting of alkyl oleate, alkyl stearate, alkyl linoleate, and alkyl palmitate.

[0031] 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.

[0032] 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.

[0033] 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 rubber composition further comprises from 50 to 80 phr, alternatively from 55 to 80 phr, of a resin. In one embodiment, the resin is selected from a C5 / C9 resin and a dicyclopentadiene (DCPD) / C9 resin.

[0034] In one embodiment, the resin is a C5 / C9 hydrocarbon resin comprising a C5 and a C9 hydrocarbon fraction, having a glass transition temperature greater than 30° C. A suitable measurement of Tg for a resin is DSC according to ASTM D6604 or equivalent. Hydrocarbon resins have a softening point, sometimes referred to as the ring and ball softening point, between 0° C. and 160° C. as measured by ASTM E28.

[0035] Suitable C5 / C9 resins may contain both aromatic and non-aromatic components. The distinction between C5 / C9 resins is primarily due to the olefins in the feedstock from which the hydrocarbon components are derived. C5 / C9 resins may also contain "aliphatic" hydrocarbon components, with the hydrocarbon chain formed from the C4-C6 fraction containing variable amounts of piperylene, isoprene, monoolefins, and non-polymerizable paraffinic compounds. Such C5 / C9 resins are based on pentene, butane, isoprene, and piperylene, with minor amounts of cyclopentadiene or dicyclopentadiene. C5 / C9 resins may also contain "aromatic" hydrocarbon structures, with the polymer chain formed from aromatic units such as styrene, xylene, alpha-methylstyrene, vinyltoluene, and indene.

[0036] According to the present invention, the C5 / C9 resins used in rubber compounding contain olefins such as piperylene, isoprene, amylene, and cyclic components. The C5 / C9 resins may also contain aromatic olefins such as styrene-based and indene-based components.

[0037] Piperylene is generally a distillate or synthetic mixture of C5 diolefins, including, but not limited to, cis-1,3-pentadiene, trans-1,3-pentadiene, and mixed 1,3-pentadienes. Generally, piperylene does not include branched C5 diolefins such as isoprene. In one embodiment, the C5 / C9 resin has 40-90% (by weight) piperylene, or 50-90%, more preferably 60-90%. In a particularly preferred embodiment, the C5 / C9 resin has 70-90% piperylene.

[0038] In one embodiment, the C5 / C9 resin is substantially free of isoprene. In another embodiment, the C5 / C9 resin contains up to 15% isoprene, or less than 10% isoprene. In yet another embodiment, the C5 / C9 resin contains less than 5% isoprene.

[0039] In one embodiment, the C5 / C9 resin is substantially free of amylene. In another embodiment, the C5 / C9 resin contains up to 40% amylene, or less than 30% amylene, or less than 25% amylene. In yet another embodiment, the C5 / C9 resin contains up to 10% amylene.

[0040] The cyclic compounds are generally distillates or synthetic mixtures of C5 and C6 cyclic olefins, diolefins, and dimers thereof. Cyclic compounds include, but are not limited to, cyclopentene, cyclopentadiene, dicyclopentadiene, cyclohexene, 1,3-cyclohexadiene, and 1,4-cyclohexadiene. A preferred cyclic compound is cyclopentadiene. Dicyclopentadiene may be in either the endo or exo form. Cyclic compounds may be substituted or unsubstituted. Preferred substituted cyclic compounds include cyclopentadiene and dicyclopentadiene substituted with C1-C40 linear, branched, or cyclic alkyl groups, preferably one or more methyl groups. In one embodiment, the C5 / C9 resin may contain up to 60% cyclic compounds or up to 50% cyclic compounds. Typical minimum limits are at least about 0.1%, at least about 0.5%, or about 1.0% cyclic compounds. In at least one embodiment, the C5 / C9 resin may contain up to 20% cyclic compounds, or more preferably up to 30% cyclic compounds. In particularly preferred embodiments, the C5 / C9 resin contains from about 1.0 to about 15% cyclic compounds, or from about 5 to about 15% cyclic compounds.

[0041] Preferred aromatic olefins that may be present in the C5 / C9 resin include one or more of styrene, indene, derivatives of styrene, and derivatives of indene. Particularly preferred aromatic olefins include styrene, alpha-methylstyrene, beta-methylstyrene, indene, and methylindene, and vinyltoluene. The aromatic olefin is generally present in the C5 / C9 resin at 5 to 45%, or more preferably 5 to 30%. In a particularly preferred embodiment, the C5 / C9 resin contains 10 to 20% aromatic olefin.

[0042] Styrenic components include styrene, derivatives of styrene, and substituted styrenes. Generally, styrenic components do not contain fused rings, such as indenes. In one embodiment, the C5 / C9 resin contains up to 60% styrenic components or up to 50% styrenic components. In one embodiment, the C5 / C9 resin contains 5-30% styrenic components or 5-20% styrenic components. In a preferred embodiment, the C5 / C9 resin contains 10-15% styrenic components.

[0043] The C5 / C9 resin may contain less than 15% indenic components, or less than 10% indenic components. The indenic components include indene and derivatives of indene. In one embodiment, the C5 / C9 resin contains less than 5% indenic components. In another embodiment, the C5 / C9 resin is substantially free of indenic components.

[0044] Preferred C5 / C9 resins have a melt viscosity of 300-800 centipoise (cP) at 160° C., or more preferably, 350-650 cP at 160° C. In particularly preferred embodiments, the melt viscosity of the C5 / C9 resin is 375-615 cP at 160° C. or 475-600 cP at 160° C. Melt viscosity can be measured using a Brookfield viscometer with an ASTM D6267 "J" type spindle.

[0045] Typically, C5 / C9 resins have a weight average molecular weight (Mw) greater than about 600 g / mol, or greater than about 1000 g / mol. In at least one embodiment, the C5 / C9 resin has a weight average molecular weight (Mw) of 1650 to 1950 g / mol, or 1700 to 1900 g / mol. Preferably, the C5 / C9 resin has a weight average molecular weight of 1725 to 1890 g / mol. The C5 / C9 resin may have a number average molecular weight (Mn) of 450 to 700 g / mol, or 500 to 675 g / mol, or more preferably 520 to 650 g / mol. The C5 / C9 resin may have a z-average molecular weight (Mz) of 5850 to 8150 g / mol, or more preferably 6000 to 8000 g / mol. Mw, Mn, and Mz can be measured by gel permeation chromatography (GPC).

[0046] In one embodiment, the C5 / C9 resin has a polydispersity index ("PDI", PDI=Mw / Mn) of less than or equal to 4. In a particularly preferred embodiment, the C5 / C9 resin has a PDI of 2.6 to 3.1.

[0047] Preferred C5 / C9 resins have a glass transition temperature (Tg) of about -30°C to about 100°C, or about 0°C to 80°C, or about 40-60°C, or 45-55°C, or more preferably 48-53 degrees Celsius. Differential scanning calorimetry (DSC) may be used to measure the Tg of the C5 / C9 resins.

[0048] In another embodiment, the C5 / C9 resin may be hydrogenated. In one embodiment, the C5 / C9 resin comprises 50-90% (by weight) piperylene, 0-5% isoprene, 10-30% amylene, 0-5% cyclic, 0-10% styrenic, and 0-10% indenic.

[0049] In one embodiment, the C5 / C9 resin comprises 50-90% (by weight) piperylene, 0-5% isoprene, 10-30% amylene, 2-5% cyclic, 4-10% styrenic, and 4-10% indenic.

[0050] In one embodiment, the C5 / C9 contains about 60% (by weight) piperylene, about 22% amylene, about 3% cyclics, about 6% styrene, and about 6% indene, and further has a melt viscosity of 436 cP at 160°C; Mn of 855 g / mol; Mw of 1595 g / mol; Mz of 3713 g / mol; PDI of 1.9; and Tg of 47°C.

[0051] The resins, including but not limited to C5 / C9 resins or DCPD / C9 resins, can be further characterized by their aromatic hydrogen content as determined by H NMR. In one embodiment, the resin has an aromatic hydrogen content in the range of 3 to 30 mole percent. In one embodiment, the resin has an aromatic hydrogen content of less than 25 mole percent. In one embodiment, the resin has an aromatic hydrogen content between 3 and 15 mole percent.

[0052] One example of a useful resin is the Oppera series of polymeric additives available from ExxonMobil Chemical Company, including, but not limited to, Oppera 373.

[0053] In one embodiment, the resin is a DCPD / C9 resin. A suitable DCPD / C9 resin is a hydrogenated DCPD / C9 resin available as Oppera 383, having an aromatic hydrogen content of about 10 mole percent.

[0054] The phrase "rubber or elastomer containing olefinic unsaturation" is intended to include natural rubber and both its various raw and reclaim forms as well as various synthetic rubbers. In describing this invention, the terms "rubber" and "elastomer" may 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 well known to those skilled in the rubber mixing or rubber compounding art.

[0055] The vulcanizable rubber composition may contain from about 1100 to about 160 phr of silica. 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.

[0056] 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).

[0057] 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 silica particles may be smaller or possibly larger in size.

[0058] 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.

[0059] Pre-hydrophobized precipitated silica may also be used. By pre-hydrophobized, it is meant that the silica is pretreated, i.e., the pre-hydrophobized precipitated silica is hydrophobized by treatment with at least one silane prior to its addition to the rubber composition. Suitable silanes include, but are not limited to, alkylsilanes, alkoxysilanes, organoalkoxysilyl polysulfides, and organomercaptoalkoxysilanes. Alternatively, instead of reacting the precipitated silica in situ with the silica coupling agent within the rubber, the precipitated silica may be pre-treated with a silica coupling agent, such as an alkoxyorganomercaptosilane or a combination of an alkoxysilane and an alkoxyorganomercaptosilane, before mixing the rubber with the pre-treated silica. See, for example, U.S. Pat. No. 7,214,731. For various pre-treated precipitated silicas, see, for example, U.S. Pat. Nos. 4,704,414, 6,123,762, and 6,573,324. Suitable pretreated or pre-hydrophobized silicas are commercially available, for example as Agilon 400 from PPG.

[0060] The vulcanizable rubber composition may contain from about 1 to about 20 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.

[0061] 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 the formula: Z-Alk-S n -Alk-Z V [Wherein Z is

[0062] [ka]

[0063] wherein R 6 is an alkyl group of 1 to 4 carbon atoms, cyclohexyl, or phenyl; R 7 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.

[0064] 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(tricyclohexoxysilylpropyl) tetrasulfide (3,3'-bis(tricyclonexo 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.

[0065] 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 V, preferably, Z is:

[0066] [ka]

[0067] is [In the formula, R 7 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.

[0068] 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.

[0069] In one embodiment, the sulfur-containing organosilicon compound comprises 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.

[0070] 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.

[0071] The amount of sulfur-containing organosilicon compound 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.

[0072] Those skilled in the art will readily appreciate that rubber compositions can be compounded by methods commonly known in the rubber compounding art, such as blending various components of sulfur-vulcanizable rubber with various commonly used additives, such as sulfur donors, curing aids, e.g., activators and retarders, and processing additives, 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. Preferably, the sulfur-vulcanizing agent is elemental sulfur. The sulfur-vulcanizing agent ranges from 0.5 to 8 phr, with a range of 1 to 6 phr being preferred. 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 5 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.

[0073] 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 0.5 phr to 4 phr, preferably from about 0.8 to about 2.0 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. Preferably, the primary accelerator is a sulfenamide. If a second accelerator is used, the secondary accelerator is preferably a guanidine, dithiocarbamate or thiuram compound.

[0074] 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.

[0075] The rubber composition may be incorporated into the tread of a tire. The pneumatic tire of the present invention may be a race tire, passenger tire, aircraft tire, farm tire, earthmovers tire, off-road tire, truck tire, etc. Preferably, the tire is a passenger tire or truck tire. The tire may also be radial or bias, although radial is preferred.

[0076] Vulcanization of the pneumatic tires of the present invention is generally carried out at conventional temperatures ranging from 100°C to 200°C. Preferably, vulcanization is carried out at temperatures ranging from 110°C to 180°C. Any of the usual 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.

[0077] The following examples are offered for the purpose of illustrating, but not limiting, the present invention. All parts are by weight unless otherwise specified. [Example]

[0078] This example illustrates the advantages of rubber compositions according to the present invention. Rubber compounds were mixed according to the formulations shown in Tables 1 and 3, with the amounts given in phr. The compounds were cured and tested for the physical properties shown in Tables 2 and 4.

[0079] Tables 1-4 include compound formulations using high loading levels of polybutadiene, including high aromatic hydrogen content and low aromatic hydrogen content traction resins. Inventive Examples E1-4 containing low aromatic hydrogen C5 / C9 resins have superior properties compared to Comparative Examples C1-4 containing high aromatic hydrogen traction resins in that they exhibit lower low temperature stiffness (characterized by lower G' at 1.5% strain, -20°C), indicating better tire snow traction, lower room temperature hysteresis (characterized by higher resilience at 23°C), indicating lower tire rolling resistance, and equivalent low temperature hysteresis (characterized by similar resilience at 0°C), indicating equivalent tire wet traction.

[0080] [Table 1]

[0081] [Table 2]

[0082] [Table 3]

[0083] [Table 4] [Example]

[0084] In this example, a rubber composition featuring a blend of a fully functionalized low Tg polymer, a high Tg plasticizer, and a high silica loading is described in Inventive Example E6, as shown in Tables 5 and 6. Such a composition exhibits better rolling resistance performance, indicated by rebound values ​​at 23°C, better snow performance, indicated by storage modulus (G') values ​​at -30°C, better wet performance, indicated by rebound at -10°C, Din abrasion data (relative volume loss), and sustained mileage compared to C5 and E5.

[0085] [Table 5]

[0086] [Table 6]

[0087] [Table 7]

[0088] [Table 8]

[0089] [Table 9]

[0090] [Table 10]

[0091] 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.

[0092] [Mode of the invention] 1. Based on 100 parts by weight (phr) of elastomer, (A) about 45 to about 100 phr of low-cis polybutadiene having a vinyl-1,2 content in the range of 5 to 30 percent and a Tg in the range of -95°C to -70°C; (B) about 0 to about 40 phr of solution-polymerized styrene-butadiene rubber having a glass transition temperature (Tg) in the range of -85°C to -50°C; (C) natural rubber or synthetic polyisoprene 0-30 phr; (D) Process oil 0-20 phr; (E) 55 to 80 phr of a resin having an aromatic hydrogen content in the range of 3 to 30 mole percent and a Tg greater than 30°C; and (F) Silica 110~160phr A pneumatic tire having a tread comprising a vulcanizable rubber composition comprising: 2. The pneumatic tire of 1, wherein the low-cis polybutadiene comprises a vinyl-1,2 content of 10 to 30 percent and a cis-1,4 content of 15 to 45 percent. 3. The pneumatic tire according to 1, wherein the low cis polybutadiene is a functionalized low cis polybutadiene. 4. The pneumatic tire of 1, wherein the low cis polybutadiene is a functionalized low cis polybutadiene functionalized with at least one member of the group consisting of hydroxyl, amino, alkoxy, alkoxyamine, thiol, silane, alkoxysilane, and alkoxyaminosilane. 5. The pneumatic tire of 1, wherein the resin is a C5 / C9 resin containing 50-90% (by weight) piperylene, 0-5% isoprene, 10-30% amylene, 0-5% cyclic compounds, 0-10% styrenes, and 0-10% indenes. 6. The pneumatic tire of 1, wherein the resin is a C5 / C9 resin containing 50-90% (by weight) piperylene, 0-5% isoprene, 10-30% amylene, 2-5% cyclic compounds, 4-10% styrenes, and 4-10% indenes. 7. The pneumatic tire of 1, wherein the resin has an aromatic hydrogen content of less than 25 mole percent. 8. The pneumatic tire of 1, wherein the resin has an aromatic hydrogen content between 3 and 15 mole percent. 9. The pneumatic tire of 1, wherein the solution-polymerized styrene-butadiene rubber is functionalized with an alkoxysilane group and at least one functional group selected from the group consisting of a primary amine and a thiol. 10. The pneumatic tire of 1, wherein the oil is selected from the group consisting of aromatic, paraffinic, naphthenic, MES, TDAE, heavy naphthenic oils, and vegetable oils. 11. The pneumatic tire of 1, wherein the solution-polymerized styrene-butadiene rubber is functionalized with alkoxysilane groups and primary amine groups and is represented by formula (1) or (2).

[0093] [ka]

[0094] [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, with the proviso that n+m+k is an integer 3 or 4.

[0095] [ka]

[0096] [In the formula, P, R 1 , R 2 and R 3 has the same definition as given in the above formula (1), j is an integer from 1 to 3, and h is an integer from 1 to 3, with the proviso that j+h is an integer from 2 to 4. 12. Solution-polymerized styrene-butadiene rubber was functionalized with alkoxysilane and primary amine groups to form living polymer chains and the formula RN-(CH2) X -Si-(OR ’ )3, I wherein R in combination with the nitrogen (N) atom is a protected amine group that upon suitable workup provides a primary amine; R ’ represents a group having 1 to 18 carbon atoms selected from alkyl, cycloalkyl, allyl, or aryl; and X is an integer of 1 to 20. 13. Solution-polymerized styrene-butadiene rubber was functionalized with alkoxysilane groups and thiols to give living anionic polymers and the formula (R 4 O) x R 4 y Si-R 5 -S-SiR 4 3 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 5 is aryl, alkylaryl, or (C1-C 16 2. The pneumatic tire according to claim 1, comprising a reaction product of a silane sulfide modifier represented by the formula: 14. The pneumatic tire according to 1, wherein the amount of styrene-butadiene rubber is in the range of 20 to 40 phr. 15. The pneumatic tire according to 1, wherein the amount of low-cis polybutadiene is in the range of 55 to 80 phr. 16. A pneumatic tire as described in 1, wherein the amount of oil is in the range of 1 to 20 phr. 17. A pneumatic tire according to 1, wherein the amount of resin is in the range of 55 to 80 phr.

Claims

1. (A) 45 to 100 parts by weight of a low-cis polybutadiene rubber having a cis-1,4 content in the range of 15 to 45 percent, a vinyl-1,2 content in the range of 5 to 30 percent, and a Tg in the range of -95°C to -70°C; (B) 0 to 40 parts by weight of a solution-polymerized styrene-butadiene rubber having a glass transition temperature (Tg) in the range of -85°C to -50°C; and (C) 0 to 30 parts by weight of a natural or synthetic polyisoprene rubber. 100 parts by weight of rubber consisting of Based on 100 parts by weight (phr) of the rubber (D) process oil 0 to 20 phr; (E) 55 to 80 phr of a resin having an aromatic hydrogen content in the range of 3 to 30 mole percent and a Tg greater than 30°C; and (F) Silica 110 to 160 phr A pneumatic tire having a tread characterized by a vulcanizable rubber composition comprising:

2. 2. The pneumatic tire of claim 1, wherein the low cis polybutadiene comprises a vinyl-1,2 content of 10 to 30 percent.

3. 10. The pneumatic tire of claim 1, wherein the low cis polybutadiene is a functionalized low cis polybutadiene functionalized with at least one functional group from the group consisting of hydroxyl, amino, alkoxy, alkoxyamine, thiol, silane, alkoxysilane, and alkoxyaminosilane.

4. 2. The pneumatic tire of claim 1, wherein the resin is a C5 / C9 resin containing 50-86% (by weight) piperylene, 0-5% isoprene, 10-30% amylene, 0-5% cyclic compounds, 4-10% styrenes, and 0-10% indenes.

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