Patent Description:
In view of a continuing demand for improved tire performance, new material combinations are constantly being evaluated and tested by tire manufacturers. In particular, in many tire tread elastomer compositions, it is difficult to break the hysteresis/tear tradeoff. While it may be possible to obtain good tensile and/or tear properties and to maintain rolling resistance indicators at a high level in some approaches, it has been found difficult to obtain at the same time desired stiffness properties. There is thus a need to provide new elastomer compositions for tires which provide good stiffness, tear and rolling resistance properties.

The invention relates to an elastomer composition in accordance with claim <NUM> and to a tire in accordance with claim <NUM>.

A first object of the present invention is to provide an elastomer composition having desirable rolling resistance and/or hysteresis properties.

Another object of the present invention is to provide an elastomer composition having good tensile properties.

Another object of the present invention is to provide an elastomer composition with sufficient or advanced stiffness.

Yet another object of the present invention is to provide an elastomer composition exhibiting a good balance of hysteresis properties, tensile properties and compound stiffness.

In a first aspect of the invention, the present invention is directed to a sulfur vulcanizable (or vulcanized) elastomer composition (in other words rubber composition) comprising <NUM> phr to <NUM> phr of at least one partially saturated elastomer comprising repeat units, wherein at most <NUM>% of all repeat units of the partially saturated elastomer comprise a double bond. Moreover, the elastomer composition comprises <NUM> phr to <NUM> phr of at least one diene based elastomer and <NUM> phr to <NUM> phr of at least one filler, wherein the filler predominantly comprises silanized silica, preferably pre-silanized silica. In other words, the majority (by weight) of the filler is the silianized or pre-silanized silica.

Surprisingly, the inventors have found that the combination of the partially unsaturated elastomer having a limited number of double bonds with a silanized or pre-silanized silica results in an unexpected increase in compound stiffness. Typically, the contrary has been observed when employing such silica in combination with conventional elastomers, resulting in a limited stiffness. However, in combination with the unsaturated polymer having a limited number of double bonds, unexpectedly an opposite effect has been found by the inventors.

In one embodiment, the partially saturated elastomer has a glass transition temperature within a range of -<NUM> to -<NUM>. Such a Tg range is for instance suitable for the application of the polymer in the rubber composition for passenger car and truck tread applications.

In another embodiment, the partially saturated elastomer has a weight average molecular weight Mw of <NUM>,<NUM>/mol to <NUM>,<NUM>/mol, preferably of <NUM>,<NUM>/mol to <NUM>,<NUM>/mol. Mw is determined with gel permeation chromatography (GPC) according to ASTM <NUM>-<NUM> using polystyrene calibration standards, or equivalent. Such a molecular weight range helps to obtain a suitable balance between processability and hysteresis properties.

In another embodiment, the partially saturated elastomer has a glass transition temperature within a range of -<NUM> to -<NUM>, preferably of -<NUM> to -<NUM>.

In still another embodiment, the partially saturated elastomer has a glass transition temperature within a range of -<NUM> to -<NUM>, preferably of -<NUM> to -<NUM>.

In yet another embodiment, at most <NUM>%, preferably at most <NUM>%, of all repeat units have a double bond and/or at least <NUM>% of the repeat units have a double bond. In particular, it may be less desirable that the elastomer is fully free of double bonds or completely hydrogenated. In particular, some of the double bonds (typically originating from a double bond of a monomer unit) shall remain in place for the purpose of cross linking, or in other words, the sulfur vulcanization. When counting double bonds herein, the bonds in an aromatic structure or group, such as of a styrene repeat unit, are not counted as double bond. However, a styrene unit is still counted as a repeat unit for the determination of the total number of repeat units in a polymer or elastomer.

In yet another embodiment, the partially saturated elastomer comprises repeat units formed by residues of monomers selected from ethylene, propylene, butadiene, isoprene, and styrene. These monomers are preferably used to make or obtain the partially saturated elastomer. One or more of the residues may be hydrogenated. In other words, double bonds of one or more of the residues may be hydrogenated.

In yet another embodiment, the partially saturated elastomer is a hydrogenated styrene-butadiene rubber, preferably a hydrogenated solution-polymerized styrene-butadiene rubber (SSBR). Hydrogenated SSBR and its manufacturing as such is known to the person skilled in the art and is for instance described in United States Patent Application Publications <CIT>, <CIT> and <CIT>.

In still another embodiment, the partially saturated elastomer is a styrene-butadiene rubber, such as a partially saturated solution-polymerized styrene butadiene rubber, having one or more of:.

In another preferred embodiment, the hydrogenated styrene-butadiene rubber has from <NUM>% to <NUM>% of hydrogenated double bonds. In other words, there are still double bonds remaining which have not been hydrogenated. As known to the person skilled in the art, the number of double bonds can be determined by NMR. This applies also to partially saturated elastomers which are not styrene-butadiene rubbers.

In yet another embodiment, the bound styrene content of the styrene-butadiene rubber will be within the range of <NUM>% to <NUM>% and its bound butadiene content will be within the range of <NUM>% to <NUM>%, by weight, as determined by NMR. The styrene-butadiene rubber will typically have a bound styrene content which is within the range of <NUM>% to <NUM>% and a bound butadiene content which is within the range of <NUM>% to <NUM>%.

In still another embodiment, the silica has a BET surface area smaller than <NUM>/m<NUM>, preferably smaller than <NUM>/m<NUM>, even more preferably at most <NUM>/m<NUM>.

In still another embodiment, the silica has a BET surface area within a range of <NUM>/m<NUM> to <NUM>/m<NUM>. A low surface area may help herein to provide a better silica dispersion which helps to obtain low hysteresis.

Such a BET surface area is measured herein by Nitrogen adsorption according to ASTM D6556 or equivalent. The BET method of measuring surface area is also described, for example, in the <NPL>.

In still another embodiment, the silanized or pre-silanized (and preferably precipitated) silica has a CTAB adsorption surface area of between <NUM><NUM>/g and <NUM><NUM>/g, optionally between <NUM><NUM>/g and <NUM><NUM>/g. The CTAB (cetyl trimethyl ammonium bromide) method for determination of the silica surface area according to ASTM D6845 is known to the person skilled in the art.

In another embodiment, the silanized or pre-silanized (and optionally precipitated) silica utilized is hydrophobated prior to its addition to the elastomer composition by treatment with at least one silane. Suitable silanes include but are not limited to alkylsilanes, alkoxysilanes, organoalkoxysilyl polysulfides and organomercaptoalkoxysilanes.

In still another embodiment, said pre-silanized silica is a silica which is pre-reacted with a sulfur-containing silane.

In another embodiment, the pre-silanized silica may be pre-treated with a silica coupling agent comprising, for example, an alkoxyorganomercaptoalkoxysilane or a combination of alkoxysilane and organomercaptoalkoxysilane prior to blending the pre-silanized silica with the elastomer instead of reacting the silica with the silica coupling agent in situ within the elastomer composition. For example, see <CIT>, showing further details of making such pre-silanized silica.

In another embodiment, said silanized or pre-silanized silica is an (optionally precipitated) silica pre-reacted with a silica coupler comprised of bis(<NUM>-triethoxysilylpropyl)polysulfide containing an average of from <NUM> to <NUM> connecting sulfur atoms (preferably <NUM> to <NUM>) in its polysulfidic bridge or an alkoxyorganomercaptosilane. The silane improves compatibility with the rubber material, dispersion or rubber matrix and/or supports the curing process.

The amount of mercapto groups on the surface of the silica may be in the range of between <NUM> and <NUM> weight percent, alternatively <NUM> to <NUM> weight percent or <NUM> to <NUM> weight percent, wherein <NUM>% is the (whole) weight of the silica sample. Such a determination of mercapto groups is carried out by titration.

In addition to mercapto groups coupled to the silica, the silica may comprise a compatibilizer which is typically a (hydro-)carbon chain material having multiple carbon atoms (for instance at least <NUM> carbon atoms) along its chain. Such a compatibilizer may facilitate the mixing of the composition. In an example, the weight % of carbon surface load / functionalization is between <NUM> and <NUM>, or alternatively between <NUM> and <NUM>. Again <NUM>% is the whole weight of the silica sample herein.

The silanized or pre-silanized silica may optionally be treated with a silica dispersing aid. Such silica dispersing aids may include glycols, such as fatty acids, diethylene glycols, polyethylene glycols, fatty acid esters of hydrogenated or non-hydrogenated C<NUM> or C<NUM> sugars, and polyoxyethylene derivatives of fatty acid esters of hydrogenated or non-hydrogenated C<NUM> or C<NUM> sugars. Exemplary fatty acids include stearic acid, palmitic acid and oleic acid. Exemplary fatty acid esters of hydrogenated and non-hydrogenated C<NUM> and C<NUM> sugars (e.g., sorbose, mannose, and arabinose) include, but are not limited to, the sorbitan oleates, such as sorbitan monooleate, dioleate, trioleate and sesquioleate, as well as sorbitan esters of laurate, palmitate and stearate fatty acids. Exemplary polyoxyethylene derivatives of fatty acid esters of hydrogenated and non-hydrogenated C<NUM> and C<NUM> sugars include, but are not limited to, polysorbates and polyoxyethylene sorbitan esters, which are analogous to the fatty acid esters of hydrogenated and non-hydrogenated sugars noted above except that ethylene oxide groups are placed on each of the hydroxyl groups.

The optional silica dispersing aids, if used, are present in an amount ranging from about <NUM>% to about <NUM>% by weight based on the weight of the silica, with about <NUM>% to about <NUM>% by weight being suitable, and about <NUM>% to about <NUM>% by weight based on the weight of the silica also being suitable.

In another embodiment, the pre-silanized silica is pre-hydrophobated by treating silica in an aqueous colloidal form thereof with both an organomercaptosilane and an alkylsilane in a weight ratio of said organomercaptosilane to said alkylsilane in a range of from <NUM>/<NUM> to <NUM>/<NUM>; wherein said alkylsilane is of the general Formula (I):.

wherein R is an alkyl radical having from <NUM> to <NUM> carbon atoms, preferably from <NUM> to <NUM> carbon atoms, such as methyl, ethyl, isopropyl, n-butyl and octadecyl radicals, n is a numeral from <NUM> to <NUM> and X is a radical selected from halogens, namely chlorine or bromine, preferably a chlorine radical, and alkoxy radicals, preferably an alkoxy radical as (R<NUM>O)-, wherein R<NUM> is an alkyl radical having from <NUM> to <NUM> carbon atoms, such as, methyl, ethyl and isopropyl radicals, preferably from methyl and ethyl radicals, and where said organomercaptosilane is of the general formula (II):.

(X)n(R<NUM>O)<NUM>-n-Si-R<NUM>-SH     (II),.

wherein X is a radical selected from halogens, such as chlorine or bromine, preferably a chlorine radical, and alkyl radicals having from <NUM> to <NUM> carbon atoms, preferably selected from methyl, ethyl, n-propyl, and n-butyl radicals; wherein R<NUM> is an alkyl radical having from <NUM> to <NUM> carbon atom, preferably from <NUM> to <NUM> carbon atoms, preferably selected from methyl and ethyl radicals and R<NUM> is an alkylene radical having from <NUM> to <NUM> carbon atoms, preferably from <NUM> to <NUM> carbon atoms, preferably a propylene radical; wherein n represents an integer from <NUM> to <NUM> with n preferably representing zero.

Representative alkylsilanes of Formula (I) are, for example, trichloro methyl silane, dichloro dimethyl silane, chloro trimethyl silane, trimethoxy methyl silane, dimethoxy dimethyl silane, methoxy trimethyl silane, trimethoxy propyl silane, trimethoxy octyl silane, trimethoxy hexadecyl silane, dimethoxy dipropyl silane, triethoxy methyl silane, triethoxy propyl silane, triethoxy octyl silane, and diethoxy dimethyl silane.

Representative organomercaptosilanes of Formula (II) are, for example, triethoxy mercaptopropyl silane, trimethoxy mercaptopropyl silane, methyl dimethoxy mercaptopropyl silane, methyl diethoxy mercaptopropyl silane, dimethyl methoxy mercaptopropyl silane, triethoxy mercaptoethyl silane, and tripropoxy mercaptopropyl silane.

Some examples of pre-silanized silicas which are suitable for use in the practice of this invention include, but are not limited to, Ciptane® <NUM> LD and Ciptane® LP (PPG Industries) silicas that have been pre-treated with a mercaptosilane, and Coupsil® <NUM> (Degussa) that is the product of the reaction between organosilane Bis(triethoxysilylpropyl) polysulfide (Si69) and Ultrasil® VN3 silica, and Coupsil® <NUM>, Agilon® <NUM> silica from PPG Industries, Agilon® <NUM> silica from PPG Industries, and Agilon® <NUM> silica from PPG Industries.

In an embodiment, the elastomer composition is exclusive of non-pre-silanized silica or comprises less than <NUM> phr, preferably less than <NUM> phr of non-pre-silanized silica.

In general, the pre-silanized silica is not necessarily pre-silanized precipitated silica herein but is preferably pre-silanized precipitated silica.

In an embodiment, the elastomer composition may also include (non-pre-silanized) silica which is optionally precipitated silica. Such conventional silicas might be characterized, for example, by having a BET surface area as measured using nitrogen gas. In one embodiment, the BET surface area may be in the range of <NUM> to <NUM> square meters per gram. In another embodiment, the BET surface area may be in a range of <NUM> to <NUM> square meters per gram. The conventional silica may also be characterized by having a dibutylphthalate (DBP) absorption value in a range of <NUM> to <NUM>, alternatively <NUM> to <NUM>. A conventional silica might be expected to have an average ultimate particle size, for example, in the range of <NUM> to <NUM> micron as determined by the electron microscope, although the silica particles may be even smaller, or possibly larger, in size. Various commercially available silicas may be used, such as, only for example herein, and without limitation, silicas commercially available from PPG Industries under the Hi-Sil trademark with designations <NUM>, <NUM>, EZ160G, etc; silicas available from Solvay, with, for example, designations of Z1165MP and Premium200MP, etc.; and silicas available from Evonik AG with, for example, designations VN2 and Ultrasil 6000GR, 9100GR, etc..

In one embodiment, where the elastomer composition contains added/non-pre-silanized silica (in addition to said pre-silanized silica), said elastomer composition contains added silica coupler (silica coupler added to said elastomer composition), wherein said silica coupler has a moiety reactive with hydroxyl groups (e.g. silanol groups) on said silica and said pre-silanized silica and another different moiety interactive with the elastomers of the elastomer composition. In one embodiment, said silica coupler added to said elastomer composition is comprised of bis(<NUM>-triethoxysilylpropyl) polysulfide having an average of from about <NUM> to about <NUM> connecting sulfur atoms in its polysulfidic bridge.

Representatives of the aforesaid silica coupler (or in other words silica coupling agent) having a moiety reactive with hydroxyl groups on pre-silanized silica and on silica and another moiety interactive with said elastomers, may be comprised of, for example: (A) bis(<NUM>-trialkoxysilylalkyl) polysulfide containing an average in range of from about <NUM> to about <NUM>, alternatively from about <NUM> to about <NUM> or from about <NUM> to about <NUM>, sulfur atoms in its connecting bridge, or (B) an alkoxyorganomercaptosilane, or (C) their combination. A representative of such bis(<NUM>-trialkoxysilylalkyl) polysulfide is comprised of bis(<NUM>-triethoxysilylpropyl) polysulfide. As indicated, for the pre-silanized precipitated silica, the silica coupler may be desirably an alkoxyorganomercaptosilane. For the non-pre-silanized silica, the silica coupler may be desirably comprised of the bis(<NUM>-triethoxysilylpropyl) polysulfide.

In one embodiment, the elastomer composition may contain a conventional sulfur containing organosilicon compounds or silanes. Examples of suitable sulfur containing organosilicon compounds are of the formula:.

in which Z is selected from the group consisting of
<CHM>
where R<NUM> is an alkyl group of <NUM> to <NUM> carbon atoms, cyclohexyl or phenyl; R<NUM> is an alkoxy of <NUM> to <NUM> carbon atoms, or cycloalkoxy of <NUM> to <NUM> carbon atoms; Alk is a divalent hydrocarbon of <NUM> to <NUM> carbon atoms and n is an integer of <NUM> to <NUM>. In one embodiment, the sulfur containing organosilicon compounds are the <NUM>,<NUM>'-bis(trimethoxy or triethoxy silylpropyl) polysulfides. In one embodiment, the sulfur containing organosilicon compounds are <NUM>,<NUM>'-bis(triethoxysilylpropyl) disulfide and/or <NUM>,<NUM>'-bis(triethoxysilylpropyl) tetrasulfide. Therefore, as to formula I, Z may be
<CHM>
<CHM>
where R<NUM> is an alkoxy of <NUM> to <NUM> carbon atoms, alternatively <NUM> carbon atoms; Alk is a divalent hydrocarbon of <NUM> to <NUM> carbon atoms, alternatively with <NUM> carbon atoms; and n is an integer of from <NUM> to <NUM>, alternatively <NUM> or <NUM>. In another embodiment, suitable sulfur containing organosilicon compounds include compounds disclosed in <CIT>. In one embodiment, the sulfur containing organosilicon compounds includes <NUM>-(octanoylthio)-<NUM>-propyltriethoxysilane, CH<NUM>(CH<NUM>)<NUM>C(=O)-S-CH<NUM>CH<NUM>CH<NUM>Si(OCH<NUM>CH<NUM>)<NUM>, which is available commercially as NXT™ from Momentive Performance Materials. In another embodiment, suitable sulfur containing organosilicon compounds include those disclosed in <CIT>. In one embodiment, the sulfur containing organosilicon compound is Si-<NUM> from Degussa. The amount of the sulfur containing organosilicon compound in an elastomer composition may vary depending on the level of other additives that are used. Generally speaking, the amount of the compound may range from <NUM> phr to <NUM> phr. In one embodiment, the amount will range from <NUM> phr to <NUM> phr.

In one embodiment, the elastomer composition is exclusive of a separate silica coupler, i.e., a silica coupler added separately to the rubber composition.

In still another embodiment, said filler comprises at least <NUM> phr of silica, preferably from <NUM> phr to <NUM> phr of silica, wherein the silica is predominantly pre-silanized silica (all by weight).

In still another embodiment, said filler comprises from <NUM> phr of the pre-silanized silica to <NUM> phr of the pre-silanized silica. In a preferred embodiment, said filler comprises from <NUM> phr of the pre-silanized silica to <NUM> phr of the pre-silanized silica.

In still another embodiment, said filler comprises from <NUM> phr of the pre-silanized silica to <NUM> phr of the pre-silanized silica. Such a range is of particular interest for truck tires.

In still another embodiment said filler comprises less than <NUM> phr of carbon black, preferably less than <NUM> phr of carbon black, or even more preferably less than <NUM> phr of carbon black.

In another preferred embodiment, the elastomer composition comprises at most <NUM> phr of liquid plasticizers, preferably at most <NUM> phr of oil. Liquid plasticizer means herein a plasticizer which is in a liquid state at <NUM>.

In another preferred embodiment, the elastomer composition comprises less than <NUM> phr of oil, preferably less than <NUM> phr of oil, more preferably less than <NUM> phr of oil, or even more preferably less than <NUM> phr of oil. It may also comprise less than <NUM> phr of oil or be essentially or completely free of oil.

In still another embodiment, the elastomer composition further comprises from <NUM> phr to <NUM> phr (preferably from <NUM> phr to <NUM> phr) of a polyoctenamer. Addition of a polyoctenamer helps to further improve tensile properties and also the co-curability to other diene based elastomeric compounds. Moreover, the presence of the polyoctenamer helps to improve rolling resistance indicators in combination with the partially saturated elastomer such as a hydrogenated SSBR.

In another preferred embodiment, the polyoctenamer has one or more of: a glass transition temperature within a range of -<NUM> to -<NUM>, determined under ASTM D3418 as mentioned hereinbelow; a weight average molecular weight Mw within a range of <NUM>,<NUM>/mol to <NUM>,<NUM>/mol, determined by gel permeation chromatography (GPC) using polystyrene calibration standards according to ASTM <NUM>-<NUM> or equivalent; and a melting point within a range of <NUM> to <NUM>, measured by DSC in second heating, according to ASTM D3418 or equivalent.

In yet another preferred embodiment, the polyoctenamer has between <NUM>% and <NUM>% of trans double bonds of all double bonds in the polyoctenamer.

In another embodiment, the elastomer composition comprises from <NUM> phr (preferably <NUM> phr) to <NUM> phr of the partially saturated elastomer, and/or from <NUM> phr to <NUM> phr (preferably <NUM> phr) of one or more of polybutadiene rubber, polyisoprene, and natural rubber. In particular, a high amount of the partially saturated elastomer has been found to be most desirable.

In still another embodiment, said polybutadiene rubber has a glass transition temperature within a range of -<NUM> to -<NUM> and/or is a (high) cis-polybutadiene rubber having a cis-microstructure content of at least <NUM>%.

In another embodiment, the composition may comprise one or more hydrogenated plasticizers chosen from one or more of hydrogenated liquid plasticizers and hydrogenated hydrocarbon resins. In particular, hydrogenated liquid plasticizers could include hydrogenated oils and/or hydrogenated liquid polymers, preferably hydrogenated liquid diene-based polymers. Such hydrogenated liquid and diene-based polymers have preferably an average molecular weight Mw of less than <NUM>,<NUM>/mol, wherein Mw is determined with gel permeation chromatography (GPC) using polystyrene calibration standards according to ASTM <NUM>-<NUM> or equivalent. Liquid diene-based polymers could include liquid styrene-butadiene rubbers, butadiene rubbers, isoprene rubbers, styrene isoprene rubbers, isoprene butadiene rubbers and styrene isoprene butadiene rubbers, or combinations thereof.

In an embodiment, the hydrogenated hydrocarbon resin is selected from fully or partially hydrogenated C9 resins, fully or partially hydrogenated C5 resins, fully or partially hydrogenated alpha methyl styrene resins, fully or partially hydrogenated terpene resins, fully or partially hydrogenated rosin resins, or mixtures thereof. It is also possible that the resin is modified by one or more aliphatic or aromatic groups.

In another embodiment, the hydrogenated hydrocarbon resin is selected from the group of fully or partially hydrogenated (in particular aliphatic) C5 resins, fully or partially hydrogenated cyclopentadiene resins, fully or partially hydrogenated dicyclopentadiene resins, and combinations of those. It is also possible that the resin is modified by one or more aliphatic or aromatic groups. However, the majority of the monomer residues of the resin are preferably partially or fully hydrogenated cyclopentadienes, fully or partially hydrogenated dicyclopentadienes, and combinations of those.

In still another embodiment, the hydrogenated hydrocarbon resin is free of double bonds. Such a highly hydrogenated hydrocarbon resin is even more compatible with the rubber matrix according to the present invention.

In another embodiment, the hydrogenated hydrocarbon resin is a fully or partially hydrogenated cyclopentadiene resin, fully or partially hydrogenated dicyclopentadiene, or a combination thereof.

In another embodiment, the elastomer composition may comprise at least one resin, preferably a hydrocarbon resin, even more preferably a plasticizing hydrocarbon resin (for instance the hydrogenated hydrocarbon resins as described herein above). A resin may be present at a range of <NUM> phr to <NUM> phr, preferably <NUM> phr to <NUM> phr, or even more preferably <NUM> phr to <NUM> phr.

In another embodiment, a glass transition temperature of the resin is within a range of <NUM> to <NUM>, preferably <NUM> to <NUM>, or even more preferably within a range of <NUM> to <NUM>. A glass transition temperature of a resin is determined herein as a peak midpoint by a differential scanning calorimeter (DSC) at a temperature rate of increase of <NUM> per minute, according to ASTM D6604 or equivalent.

In another embodiment, the resin has a softening point of at least <NUM> as determined according to ASTM E28, or equivalent, which might sometimes be referred to as a ring and ball softening point. Preferably, the softening point is at most <NUM> or more preferably at most <NUM>, or even more preferably at most <NUM>.

In still another embodiment, the resin has a polydispersity index within a range of <NUM> to <NUM>, preferably <NUM> to <NUM>, or even more preferably <NUM> to <NUM>.

In yet another embodiment, the resin has an average molecular weight Mw within a range of <NUM>/mol to <NUM>/mol, preferably <NUM>/mol to <NUM>/mol, or more preferably <NUM>/mol to <NUM>/mol, or even more preferably <NUM>/mol to less than <NUM>/mol. Mw is determined with gel permeation chromatography (GPC) using polystyrene calibration standards according to ASTM <NUM>-<NUM> or equivalent. In still another embodiment, the elastomer composition further comprises at least <NUM> phr of vulcanizing agents, preferably comprising elemental sulfur. For instance, the composition may comprise from <NUM> phr to <NUM> phr of vulcanizing agents which may comprise, but are not limited to, elemental sulfur or sulfur containing silanes.

In another embodiment, the elastomer composition comprises from <NUM> phr to <NUM> phr of at least one vulcanization accelerator selected from the dithiocarbamate accelerators and/or thiuram accelerators. Such accelerators are known to be fast accelerators and are herein considered as particularly beneficial in view of the utilization of the limited amounts of double bonds in the elastomer and/or hydrogenated resin. The composition may comprise further accelerators.

In still another embodiment, said vulcanization accelerator is tetrabenzylthiuramdisulfide which has turned out to be a preferred choice in combination with the partially saturated polymer.

In an embodiment, the elastomer composition may include at least one and/or one additional diene-based rubber. Representative synthetic polymers may be the homopolymerization products of butadiene and its homologues and derivatives, for example, methyl butadiene, dimethylbutadiene and pentadiene as well as copolymers such as those formed from butadiene or its homologues or derivatives with other unsaturated monomers. Among the latter may be acetylenes, for example, vinyl acetylene; olefins, for example, isobutylene, which copolymerizes with isoprene to form butyl rubber; vinyl compounds, for example, acrylic acid, acrylonitrile (which polymerize with butadiene to form NBR), methacrylic acid and styrene, the latter compound polymerizing with butadiene to form SBR, as well as vinyl esters and various unsaturated aldehydes, ketones and ethers, e.g. acrolein, methyl isopropenyl ketone and vinylethyl ether. Specific examples of synthetic rubbers include neoprene (polychloroprene), polybutadiene (including cis <NUM>,<NUM>-polybutadiene), polyisoprene (including cis <NUM>,<NUM>-polyisoprene), butyl rubber, halobutyl rubber such as chlorobutyl rubber or bromobutyl rubber, styrene/isoprene/butadiene rubber, copolymers of <NUM>,<NUM>-butadiene or isoprene with monomers such as styrene, acrylonitrile and methyl methacrylate, as well as ethylene/propylene terpolymers, also known as ethylene/propylene/diene monomer (EPDM), and in particular, ethylene/propylene/dicyclopentadiene terpolymers. Additional examples of rubbers which may be used include alkoxy-silyl end functionalized solution polymerized polymers (SBR, PBR, IBR and SIBR), silicon-coupled and tin-coupled star-branched polymers. Preferred rubber or elastomers may be in general natural rubber, synthetic polyisoprene, polybutadiene and SBR including SSBR. One or more of these rubbers may be functionalized, such as for the coupling to silica.

In another embodiment, the composition may comprise at least two diene-based rubbers. For example, a combination of two or more rubbers is preferred such as cis <NUM>,<NUM>-polyisoprene rubber (natural or synthetic, although natural is preferred), <NUM>,<NUM>-polyisoprene rubber, styrene/isoprene/butadiene rubber, emulsion and solution polymerization derived styrene/butadiene rubbers, cis <NUM>,<NUM>-polybutadiene rubbers and emulsion polymerization prepared butadiene/acrylonitrile copolymers. In some embodiments, the partially saturated elastomer may also be a diene-based polymer but it is not necessarily diene-based.

In another embodiment, an emulsion polymerization derived styrene/butadiene (ESBR) might be used having a styrene content of <NUM> to <NUM> percent bound styrene or, for some applications, an ESBR having a medium to relatively high bound styrene content, namely a bound styrene content of <NUM> to <NUM> percent. By emulsion polymerization prepared ESBR, it may be meant that styrene and <NUM>,<NUM>-butadiene are copolymerized as an aqueous emulsion. Such are well known to those skilled in such art. The bound styrene content can vary, for example, from <NUM> to <NUM> percent. In one aspect, the ESBR may also contain acrylonitrile to form a terpolymer rubber, as ESBR, in amounts, for example, of <NUM> to <NUM> weight percent bound acrylonitrile in the terpolymer. Emulsion polymerization prepared styrene/butadiene/acrylonitrile copolymer rubbers containing <NUM> to <NUM> weight percent bound acrylonitrile in the copolymer may also be contemplated as diene-based rubbers.

In another embodiment, solution polymerization prepared SBR (SSBR) may be used. Such an SSBR may for instance have a bound styrene content in a range of <NUM> to <NUM> percent, preferably <NUM> to <NUM>, percent. The SSBR can be conveniently prepared, for example, by anionic polymerization in an inert organic solvent. More specifically, the SSBR can be synthesized by copolymerizing styrene and <NUM>,<NUM>-butadiene monomer in a hydrocarbon solvent utilizing an organo lithium compound as the initiator. As noted above, such a rubber may also be functionalized for the coupling to silica.

In one embodiment, a synthetic or natural polyisoprene rubber may be used. Synthetic cis <NUM>,<NUM>-polyisoprene and cis <NUM>,<NUM>-polyisoprene natural rubber are as such well known to those having skill in the rubber art. In particular, the cis <NUM>,<NUM>-content may be at least <NUM>%, optionally at least <NUM>%.

In one embodiment, cis <NUM>,<NUM>-polybutadiene rubber (BR or PBD) is used. Suitable polybutadiene rubbers may be prepared, for example, by organic solution polymerization of <NUM>,<NUM>-butadiene. The BR may be conveniently characterized, for example, by having at least a <NUM> percent cis <NUM>,<NUM>-content ("high cis" content) and a glass transition temperature Tg in a range of from -<NUM> to -<NUM>. Suitable polybutadiene rubbers are available commercially, such as Budene® <NUM>, Budene® <NUM>, Budene® <NUM>, or Budene® <NUM> from The Goodyear Tire & Rubber Company. These high cis-<NUM>,<NUM>-polybutadiene rubbers can for instance be synthesized utilizing nickel catalyst systems which include a mixture of (<NUM>) an organonickel compound, (<NUM>) an organoaluminum compound, and (<NUM>) a fluorine containing compound as described in <CIT> and <CIT>.

A glass transition temperature, or Tg, of an elastomer or rubber represents the glass transition temperature(s) of the respective elastomer or rubber in its uncured state. A glass transition temperature, or Tg, of an elastomer composition or a rubber composition represents the glass transition temperatures of the respective elastomer composition or rubber composition in its cured state. A Tg is determined as a peak midpoint by a differential scanning calorimeter (DSC) at a temperature rate of increase of <NUM> per minute, according to ASTM D3418.

The term "phr" as used herein, and according to conventional practice, refers to "parts by weight of a respective material per <NUM> parts by weight of rubber, or elastomer". In general, using this convention, an elastomer composition is comprised of <NUM> parts by weight of rubber/elastomer. The claimed composition may comprise other rubbers / elastomers than explicitly mentioned in the claims, provided that the phr value of the claimed rubbers/elastomers is in accordance with claimed phr ranges and the amount of all rubbers/elastomers in the composition results in total in <NUM> parts of rubber. In an example, the composition may further comprise from <NUM> phr to <NUM> phr, optionally from <NUM> phr to <NUM> phr, of one or more additional diene-based rubbers, such as SBR, SSBR, ESBR, PBD/BR, NR and/or synthetic polyisoprene. In another example, the composition may include less than <NUM>, preferably less than <NUM>, phr of an additional diene-based rubber or be also essentially free of such an additional diene-based rubber. The terms "compound" and "composition" may be used herein interchangeably, unless indicated otherwise. The terms "rubber" and "elastomer" may also be used herein interchangeably, unless indicated otherwise.

In an embodiment, the elastomer composition may also include oil, in particular processing oil. Processing oil may be included in the elastomer composition as extending oil typically used to extend elastomers. Processing oil may also be included in the elastomer composition by addition of the oil directly during rubber compounding. The processing oil used may include both extending oil present in the elastomers, and process oil added during compounding. Suitable process oils may include various oils as are known in the art, including aromatic, paraffinic, naphthenic, vegetable oils, and low PCA oils, such as MES, TDAE, SRAE and heavy naphthenic oils. Suitable low PCA oils may include those having a polycyclic aromatic content of less than <NUM> percent by weight as determined by the IP346 method. Procedures for the IP346 method may be found in<NPL>.

In an embodiment, the elastomer composition may include also carbon black as one of the filler materials. Preferred amounts in this application range from <NUM> phr to <NUM> phr, preferably from <NUM> phr to <NUM> phr or from <NUM> phr to <NUM> phr. Representative examples of such carbon blacks include N110, N121, N134, N220, N231, N234, N242, N293, N299, N315, N326, N330, N332, N339, N343, N347, N351, N358, N375, N539, N550, N582, N630, N642, N650, N683, N754, N762, N765, N774, N787, N907, N908, N990 and N991 grades. These carbon blacks have iodine absorptions ranging from <NUM>/kg to <NUM>/kg and a DBP number ranging from <NUM><NUM>/<NUM> to <NUM><NUM>/<NUM>.

In another embodiment, other fillers may be used in the elastomer composition including, but not limited to, particulate fillers including ultra-high molecular weight polyethylene (UHMWPE), crosslinked particulate polymer gels including but not limited to those disclosed in <CIT>, <CIT>, <CIT>, <CIT>, <CIT> or <CIT>, and a plasticized starch composite filler including but not limited to that disclosed in <CIT>. Such other fillers may be used in an amount ranging from <NUM> phr to <NUM> phr.

It is readily understood by those having skill in the art that the elastomer composition may be compounded by methods generally known in the rubber compounding art, such as mixing the various sulfur-vulcanizable constituent rubbers with various commonly used additive materials such as, for example, sulfur donors, curing aids, such as activators and retarders, and processing additives, such as oils, resins including tackifying resins and plasticizers, fillers, pigments, fatty acid, zinc oxide, waxes, antioxidants and antiozonants and peptizing agents. As known to those skilled in the art, depending on the intended use of the sulfur vulcanizable and sulfur-vulcanized material (rubbers), the additives mentioned above are selected and commonly used in conventional amounts. Representative examples of sulfur donors include elemental sulfur (free sulfur), an amine disulfide, polymeric polysulfide and sulfur olefin adducts. In one embodiment, the sulfur-vulcanizing agent is elemental sulfur. The sulfur-vulcanizing agent may for instance be used in an amount ranging from <NUM> phr to <NUM> phr, alternatively within a range of from <NUM> phr to <NUM> phr. Typical amounts of tackifier resins, if used, comprise for example <NUM> phr to <NUM> phr, usually <NUM> phr to <NUM> phr. Typical amounts of processing aids, if used, comprise for example <NUM> phr to <NUM> phr (this may comprise in particular oil). Typical amounts of antioxidants, if used, may for example comprise <NUM> phr to <NUM> phr. Representative antioxidants may be, for example, diphenyl-p-phenylenediamine and others, such as, for example, those disclosed in <NPL>. Typical amounts of antiozonants, if used, may for instance comprise <NUM> phr to <NUM> phr. Typical amounts of fatty acids, if used, which can include stearic acid, may for instance comprise <NUM> phr to <NUM> phr. Typical amounts of waxes, if used, may for example comprise <NUM> phr to <NUM> phr. Often microcrystalline waxes are used. Typical amounts of peptizers, if used, may for instance comprise <NUM> phr to <NUM> phr. Typical peptizers may be, for example, pentachlorothiophenol and dibenzamidodiphenyl disulfide.

Accelerators may be preferably but not necessarily 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 may be used, i.e. primary accelerator. The primary accelerator(s) may be used in total amounts ranging from <NUM> phr to <NUM> phr, alternatively <NUM> phr to <NUM> phr. In another embodiment, combinations of a primary and a secondary accelerator might be used with the secondary accelerator being used in smaller amounts, such as from <NUM> phr to <NUM> phr, in order to activate and to improve the properties of the vulcanizate. Combinations of these accelerators might be expected to produce a synergistic effect on the final properties and are somewhat better than those produced by use of either accelerator alone. In addition, delayed action accelerators may be used which are not affected by normal processing temperatures but produce a satisfactory cure at ordinary vulcanization temperatures. Vulcanization retarders might also be used. Suitable types of accelerators that may be used in the present invention are for instance 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 for instance a guanidine, dithiocarbamate or thiuram compound. Suitable guanidines include dipheynylguanidine and the like. Suitable thiurams include tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetrabenzylthiuram disulfide.

The mixing of the elastomer composition can be accomplished by methods known to those having skill in the rubber mixing art. For example, the ingredients may be typically mixed in at least two stages, namely, at least one nonproductive stage followed by a productive mix stage. The final curatives including sulfur-vulcanizing agents may be typically mixed in the final stage which is conventionally called the "productive" mix stage in which the mixing typically occurs at a temperature, or ultimate temperature, lower than the mix temperature(s) of the preceding nonproductive mix stage(s). The terms "nonproductive" and "productive" mix stages are well known to those having skill in the rubber mixing art. In an embodiment, the elastomer composition may be subjected to a thermomechanical mixing step. The thermomechanical mixing step generally comprises a mechanical working in a mixer or extruder for a period of time, for example suitable to produce a rubber temperature which is within the range of <NUM> to <NUM>. The appropriate duration of the thermomechanical working varies as a function of the operating conditions, and the volume and nature of the components. For example, the thermomechanical working may be from <NUM> to <NUM> minutes.

The elastomer composition may be incorporated in a variety of rubber components, e.g., of a tire (or in other words tire components). For example, the rubber component may be a tread (including tread cap and tread base), sidewall, apex, chafer, sidewall insert, wirecoat or innerliner. Tread rubber applications are the preferred applications for the present invention.

In a second aspect of the present invention, a vulcanized elastomer composition is provided, which is based on the elastomer composition according to the first aspect of the present invention. In other words, the vulcanized elastomer composition is the vulcanization product of the sulfur vulcanizable elastomer composition according to the first aspect and/or its embodiments.

In a third aspect of the invention, a rubber component, preferably a rubber component for a tire, is provided, in particular comprising the elastomer composition in accordance with the first aspect of the invention, or in accordance with the second aspect of the invention, and/or one or more of their embodiments. Thus, the tire may be an uncured tire or cured tire, i.e. a vulcanized tire.

In a fourth aspect of the invention, a tire is provided comprising the rubber composition according to the first or second aspect of the invention, or having a rubber component according to the third aspect of the invention.

In a preferred embodiment, the tire comprises a tread, preferably a tread cap, comprising the elastomer composition. In another embodiment, the tire has a radially outer tread cap layer, intended to come into contact with the road when driving, comprising the elastomer composition.

The tire of the present invention may for example be a pneumatic tire or nonpneumatic tire, a race tire, a passenger tire, an aircraft tire, an agricultural tire, an earthmover tire, an off-the-road (OTR) tire, a truck tire or a motorcycle tire. The tire may also be a radial or bias tire.

Vulcanization of the pneumatic tire may for instance be carried out at conventional temperatures which is within the range of <NUM> to <NUM>. In one embodiment, the vulcanization is conducted at temperatures which are within the range of <NUM> to <NUM>. Any of the usual vulcanization processes may be used such as heating in a press or mold, heating with superheated steam or hot air. Such tires can be built, shaped, molded and cured by various methods which are known and will be readily apparent to those having skill in such art.

Moreover, in a fifth aspect, the present invention is directed to a method of making an elastomer composition (e.g., the elastomer composition as described in the aforementioned aspects), the method comprising one or more steps of:.

In a sixth aspect, the present invention is directed to a method of manufacturing a tire, preferably with the composition according to an aforementioned aspect and/or made with the method of making the elastomer composition according to the fifth aspect, wherein the method of manufacturing the tire comprises:.

Multiple features of the aspects and embodiments mentioned herein may be combined with one another.

Below Table <NUM> shows two Comparative elastomer compositions which are not in accordance with the present invention. Comparative Example <NUM> shows an elastomer composition which comprises the same diene-based rubber matrix as Comparative Example <NUM>. Most ingredients of both compositions are the same. However, Comparative Example <NUM> comprises <NUM> phr of conventional silica together with <NUM> phr of Silane <NUM>, whereas Comparative Example <NUM> has <NUM> phr of pre-silanized silica. Moreover, the Comparative Example <NUM> comprises <NUM> phr of oil, whereas Comparative Example <NUM> comprises <NUM> phr of oil. For example, these two Comparative Examples show that the use of pre-silanized silica instead of comparable amounts of conventional, i.e. non-pre-silanized silica, typically decreases the compound stiffness. This effect is shown herein below in Table <NUM>.

It is observed that the stiffness of Comparative Example <NUM> is considerably smaller than the stiffness of Comparative Example <NUM> as shown by the about <NUM>% drop in G'. That stiffness drop is even more remarkable as the composition of Comparative Example <NUM> has already an increased content of silica (by <NUM> phr), wherein more filler typically increases the stiffness of the composition. Even more, Comparative Example <NUM> has <NUM> phr less oil than Comparative Example <NUM> which typically also increases the compound stiffness. The pre-silanized silica disperses better in the elastomer composition which results in a reduced stiffness at low strain.

As also shown in Table <NUM>, Tangent Delta is improved by the use of the pre-silanized silica by about <NUM>%. Tangent Delta can be considered as a hysteresis indicator so that its reduction suggests also a reduced rolling resistance if the same elastomer composition is used in a tire. Tensile strength remains identical and relatively low for Comparative Example <NUM> and Comparative Example <NUM>.

While the above-described improvement in Tangent Delta is desirable, the significant drop in stiffness may for instance be undesirable for many performance oriented tire applications.

In accordance with embodiments of the present invention, the inventors have found Inventive Examples <NUM> and <NUM> as shown in Table <NUM> below. Inventive Examples <NUM> and <NUM> are listed together with Comparative Examples <NUM> and <NUM> which are not in accordance with the present invention. All Examples of Table <NUM> comprise a partially saturated elastomer in the form of hydrogenated solution-polymerized styrene-butadiene rubbers. Moreover, Inventive Examples <NUM> and <NUM> comprise pre-silanized silica, whereas Comparative Examples <NUM> and <NUM> comprise conventional silica, similar to Comparative Examples <NUM> and <NUM>. Comparative Example <NUM> and Inventive Example <NUM> comprise each a high-Tg hydrogenated solution-polymerized styrene-butadiene rubber. Comparative Example <NUM> and Inventive Example <NUM> comprise each a low-Tg hydrogenated solution-polymerized styrene-butadiene rubber.

Stiffness, Tangent Delta and Tensile strength have been determined for the Examples of Table <NUM> and are listed in Table <NUM> below.

As shown in Table <NUM>, Inventive Example <NUM> has a substantially higher stiffness than its associated Comparative Example <NUM>. This surprising and unexpected effect is completely different than what is observed for the combination of conventional diene-based rubbers with pre-silanized silica. Such a typical behavior has for example been demonstrated by Comparative Examples <NUM> and <NUM> in Table <NUM>, in which the opposite effect of a stiffness drop occurs upon replacement of a conventional silica with pre-silanized silica. However, when using the pre-silanized silica in combination with partially saturated elastomers (here in the form of a hydrogenated solution-polymerized styrene-butadiene rubber), stiffness even increases when replacing the conventional silica by the pre-silanized silica. The same behavior can be observed when comparing the stiffness values of Comparative Example <NUM> and Inventive Example <NUM>, as also shown in Table <NUM>. Moreover, the respective Tangent Delta values as hysteresis / rolling resistance indicator improve significantly upon deployment of the pre-silanized silica versus the use of conventional silica. In addition, the Comparative Examples <NUM> and <NUM> as well as Inventive Examples <NUM> and <NUM> show good tensile strength.

Claim 1:
A sulfur vulcanizable elastomer composition comprising:
<NUM> phr to <NUM> phr of at least one partially saturated elastomer comprising repeat units, wherein at most <NUM>% of all repeat units of the partially saturated elastomer comprise a double bond;
<NUM> phr to <NUM> phr of at least one diene based elastomer; and
<NUM> phr to <NUM> phr of at least one filler, wherein the filler comprises predominantly silanized silica or pre-silanized silica.