MXPA99008889A - Composed for the bearing band of a line - Google Patents

Abstract

Unexpectedly it has been determined that isoprene-butadiene rubber with a high glass transition temperature in the range of about -40 ° C to about -25 ° C (high Tg IBR) can be loaded with silica as filler and used in the manufacture of treads for tires that have outstanding performance characteristics. For example, these tire treads offer lower hysteresis at higher temperatures (better rolling resistance) and higher hysteresis at lower temperatures (better wet traction characteristics). By using the high Tg IBR in the tire tread compounds, the maximum benefits of the silica composition can be obtained without the need for styrene-butadiene rubber in solution or emulsion (SBR) in the rubber formulations for the rotation band. The tire tread rubber formulations of this invention will typically contain about 20 phr (parts per hundred parts rubber) to about 100 phr of the high Tg IBR. In other words, rubber for the tread will normally contain at least 20 phr of high Tg-IBR and may contain up to 100 phr of high Tg IBR. The tread compound will also contain 40 phr to 150 phr of a filler, provided that at least about 20 phr of silica is included in the filler. The compound for the tire bearing surface will also contain a silica coupling agent. This invention more specifically describes a rubber composition for tire tread which is composed of: (1) at least about 20 phr of an isoprene-butadiene rubber with a glass transition temperature within the range of about -40 ° C. at -25 ° C, (2) from 40 phr to 150 phr of a charge material, provided that the charge material contains at least about 20 phr of silica, and (3) a syphilitic coupling agent

Description

COMPOSITE FOR THE ROLLING BAND OF A RIM BACKGROUND OF THE INVENTION It is desirable that a rim has good traction characteristics in dry and wet pavements, and that the rim provides good wear and low rolling resistance. To reduce the rolling resistance of a tire, it is possible to use rubbers that have a high rebound in the manufacture of tire treads. The tires made with these rubbers present less energy loss during the bearing. The traditional problem associated with this approach is that the characteristics of wet traction and resistance to wet skidding of the rim are compromised. This is because the good rolling resistance that favors low energy loss and the good traction characteristics that favor high energy loss are non-consistent viscoelastic properties. To balance these two inconsistent viscoelastic properties, different types of synthetic and natural rubbers are usually used in tire treads. For example, different mixtures of styrene-butadiene rubber and polybutadiene rubber are normally used as a rubbery material for tire treads for automobiles. In addition, to improve the traction characteristics, silica is included in the rubber for the tread as a loading material. However, these mixtures are not totally satisfactory for all purposes. U.S. Patent No. 4,843,120 discloses that tires that have better performance characteristics can be prepared using rubbery polymers that have multiple vitreous transition temperatures such as rubber for the tread. These rubbery polymers having multiple vitreous transition temperatures exhibit a first glass transition temperature that is within the range of about -110 ° C to -20 ° C and have a second glass transition temperature within the range of about -50 ° C. at 0 ° C. According to U.S. Patent No. 4,843,120, these polymers are prepared by polymerizing at least one conjugated diolefin monomer in a first reaction zone at a temperature and under conditions sufficient to produce a first polymeric segment having a glass transition temperature. between -110 ° C and -20 ° C, and subsequently the polymerization is continued in a second reaction zone at a temperature and under conditions sufficient to produce a second polymeric segment having a glass transition temperature between -20 ° C and 20 ° C. ° C. These polymerizations are usually catalyzed with an organolithium catalyst and are usually carried out in an inert organic solvent. U.S. Patent 5,137,998 describes a process for preparing a rubbery terpolymer of styrene, isoprene and butadiene having multiple glass transition temperatures and with an excellent combination of properties for use in the manufacture of tire treads which consists of terpolymerize styrene, isoprene and 1,3-butadiene in an organic solvent at a temperature no greater than about 40 ° C in the presence of: (a) at least one member selected from the group consisting of tripiperidinophosphine oxide and alkali metal alkoxides, and (b) an organolithium compound. U.S. Patent 5,047,483 discloses a pneumatic tire having an outer circumferential tread, wherein the tread is a sulfur-cured rubber composition composed of, based on 100 parts by weight of rubber (phr), (A) about 10 to about 90 parts by weight of a terpolymer rubber of styrene, isoprene, butadiene (SIBR), and (B) about 70 to about 30% by weight of at least one cis 1,4, polyisoprene rubber and rubber cis 1,4-polybutadiene, wherein the SIBR rubber is composed of: (1) about 10 to about 35% by weight of bound styrene, (2) about 30 to about 50% by weight of bound isoprene, and (3) about 30 to about 40% by weight of bound butadiene, and is characterized by having a single glass transition temperature (Tg) which is in the range of about -10 ° C to about -40 ° C and, in addition, the bound butadiene structure contains about 30 to about 40% of 1,2-vinyl units, the bound isoprene structure contains about 10 to about 30% of units 3,4 and the sum of the percent of 1,2-vinyl units of bound butadiene and the percent of units 3 , 4 of the bound isoprene is in the range of about 4 to about 70%. U.S. Patent 5,272,220 discloses a styrene-isoprene-butadiene rubber which is particularly valuable for use in the manufacture of treads for truck tires which has better characteristics of rolling resistance and wear of the tread, being rubber composed of repeating units which are from about 5% to about 20% by weight of styrene, from about 7% by weight to about 35% by weight of isoprene and from about 55% by weight to about 88% by weight 1,3-butadiene weight, wherein the repeating units from styrene, isoprene and 1,3-butadiene are practically in random order, wherein from about 25% to about 40% of the repeat units from 1, 3-butadiene are of the cis microstructure, wherein from about 40% to about 60% of the repeating units from 1, 3-b utadiene are of the trans microstructure, wherein from about 5% to about 25% of the repeating units derived from 1,3-butadiene are from the vinyl microstructure, wherein from about 75% to about 90% of the repeat units from isoprene are of the microstructure 1,4, where from about 10% to about 25% of the repeating units from isoprene are of the microstructure 3,4-, where the rubber has a glass transition temperature that is within the range of about -90 ° C to about -70 ° C, wherein the rubber has a number average molecular weight in the range of about 150,000 to about 400,000, wherein the rubber has a weight average molecular weight of about 300,000 to about 800,000, and where the rubber has a non-homogeneity within the range of about 0.5 to about 1.5. U.S. Patent 5,231,153 and U.S. Patent 5,336,739 disclose that the alkyl tetrahydrofurfuryl ether compounds, with the structural formula: wherein n is an integer from 5 to about 10, can be used as modifiers in the synthesis of polydiene rubbers, such as isoprene-butadiene rubbers. These patents specifically describe the synthesis of isoprene-butadiene copolymers having high vitreous transition temperatures of -30 ° C, -32 ° C, -37 ° C and 38 ° C. Some specific examples of the alkyl tetrahydrofurfuryl ethers reported to be useful as modifiers include hexyl tetrahydrofurfuryl ether, heptyttetrahydrofurfuryl ether, octyl tetrahydrofurfuryl ether and nonyltetrahydrofurfuryl ether. The hexyl tetrahydrofurfuryl ether reported as highly preferred due to its use does not result in the creation of noxious odors and its use results in the rapid polymerization rate and high vinyl contents.

SUMMARY OF THE INVENTION Unexpectedly it has been determined that isoprene-butadiene rubber with a high vitreous transition temperature in the range of about -40 ° C to about -25 ° C (high Tg IBR) can be charged with silica as the material of load and used in the manufacture of treads for tires that have outstanding performance characteristics. For example, these tire treads offer less hysteresis at higher temperatures (better rolling resistance) and higher hysteresis at lower temperatures (better wet traction characteristics). By using the high Tg IBRs in the tire tread compounds it is possible to obtain maximum benefits of the composition with silica without the need for styrene-butadiene rubber in solution or in emulsion (SBR) in the rubber formulations for the tread. The rubber formulations for the tire rolling band of this invention will normally contain about 60 phr (parts per 100 parts rubber) to about 100 phr of high Tg IBR. In other words, the rubber for the bearing surface will normally contain at least 20 phr of high Tg IBR and can contain up to 100 phr of high Tg IBR. The tread compound will also contain 40 phr to 150 phr of a filler, provided that at least about 20 phr of silica is included in the filler. The compound for the tire tread will also contain a silica coupling agent.

This invention more specifically describes a tire tread rubber compound which is composed of (1) at least about 20 phr of an isoprene-butadiene rubber with a glass transition temperature that is within the range of about -40. ° C to -25 ° C, (2) 40 phr to 150 phr of a filler, provided that the filler material contains at least about 20 phr of silica, and (3) a silica coupling agent. The present invention also discloses a pneumatic rim with an outer circumferential tread, wherein the tread is a sulfur-cured rubber composition which is composed of: (1) at least about 20 phr of an isoprene rubber -butadiene with a vitreous transition temperature in the range of about -40 ° C to -25 ° C, (2) 40 phr to 150 phr of a filler, provided that the filler material contains at least about 20 phr of silica, and (3) a silica coupling agent.

DETAILED DESCRIPTION OF THE INVENTION The high Tg IBR of this invention is synthesized by solution polymerization. These solution polymerizations will normally be carried out in a hydrocarbon solvent which may be one or more aromatic, paraffinic or cycloparaffinic compounds. These solvents will normally contain from 4 to 10 carbon atoms per molecule and will be liquid under the conditions of polymerization. Some representative examples of suitable organic solvents include pentane, isooctane, cyclohexane, normal hexane, benzene, toluene, xylene, ethylbenzene and the like, alone or in mixtures. In the solution polymerizations of this invention there will usually be from about 5 to about 35% by weight of monomers in the polymerization medium. These polymerization media, of course, are composed of the organic solvent, 1,3-butadiene monomer and isoprene monomer. In most cases it will be preferred that the polymerization medium contains from 10 to 30% by weight of monomers. It is generally more preferred that the polymerization medium contains from 20 to 25% by weight of monomers. The monomer charge compositions used in the polymerizations of this invention will usually contain from about 20% by weight to about 80% by weight of isoprene and from about 20% by weight to about 80% by weight of monomer 1, 3. -butadiene. It is usually preferred that the composition of the monomer charge contain from about 25% by weight to about 70% by weight of isoprene and from about 30% by weight to about 75% by weight of 1,3-butadiene. The high Tg IBR used in the tread formulations of this invention can be synthesized continuously, by a semi-continuous process or by a batch process. In the continuous process, the monomers, an organolithium initiator, a modifier and an organic solvent system are continuously fed to a reaction vessel or series of reaction vessels. The pressure in the reaction vessel is usually sufficient to maintain a substantially liquid phase under the conditions of the polymerization reaction. The reaction medium will generally be maintained at a temperature in the range of about 70 ° C to about 140 ° C during copolymerization. It is generally preferred that the copolymerization be carried out in a series of reaction vessels and that the reaction temperature be increased from one reaction vessel to the other as the polymerization proceeds. For example, it is desirable to use two reactor systems, wherein the temperature in the first reactor is maintained within the range of about 70 ° C to 90 ° C, where the temperature in the second reactor remains within the range of about 90 °. C at approximately 100 ° C. The organolithium compounds that can be used as initiators in the terpolymerizations of this invention include the organomonolithium compounds and the organomonofunctional lithium compounds. The organomultifunctional lithium compounds will commonly be the organodilithium compounds or the organotrilithium compounds. Some representative examples of suitable multifunctional organolithium compounds include 1,4-dilithiobutane, 1, 10-dilithiodecane, 1, 20-dilithioeicosane, 1,4-dilithiobenzene, 1,4-dilithioaphthalene, 9,10-dilithioanthracene, 1, 2- dilithium-1, 2-diphenylethane, 1,3,5-tritylthiopentane, 1, 5, 15-trilithioeicosane, 1,3,5-tritylthiocyclohexane, 1, 3, 5, 8-tetralithiodecane, 1,5,10,20- tetralithioeicosan, 1, 2, 4, 6-tetralithiocyclohexane, 4,4'-dilithiodiphenyl and the like, the organolithium compounds which can be used are usually the organomonolithium compounds. Organolithium compounds that are preferred can be represented by the formula R-Li, wherein R represents a hydrocarbyl radical containing from 1 to 20 carbon atoms. In general, these monofunctional organolithium compounds will contain from about 1 to about 10 carbon atoms. Some representative examples of the organolithium compounds that may be employed include methillithium, ethyllithium, isopropyllithium, n-butyllithium, sec-butyllithium, n-octyllithium, tert-octyllithium, n-decyllithium, phenyllithium, 1-naphthylthio, 4-butylphenyllithium, p- tolillithium, 1-naphthylthio, 4-butyl phenyllithium, p-tolyl lithium, 4-phenyl butyl lithium, cyclohexyl thio, 4-butyl cyclohexyl thio and 4-cyclohexyl butyllithium. The amount of the organolithium initiator that is employed will depend on the molecular weight that is desired for the high Tg IBR to be synthesized. An amount of the organolithium initiator will be selected to give rise to the production of high Tg IBR with a Mooney viscosity ML1 + 4 within the range of 35 to 100. The amount of the organolithium initiator will preferably be selected to give rise to the production of High Tg IBR with a Mooney viscosity ML1 + 4 within the range of 40 to 80. The amount of the organolithium initiator most preferred will be selected to result in the production of a high Tg IBR with a Mooney viscosity ML1 + 4 within the range from approximately 45 to 65. As a general rule, in all anionic polymerizations, the molecular weight (Mooney viscosity) of the polymer produced is inversely proportional to the amount of catalyst used. As a general rule, from about 0.01 to about 1 phm (parts per hundred parts of monomer by weight) of the organolithium compound will be used. In most cases it will be preferred to use from about 0.015 to about 0.1 phm of the organolithium compound, with it being more preferred to use from about 0.025 phm to 0.07 phm of the organolithium compound. To inhibit gelation and achieve the desired high vitreous transition temperature it is important to perform the polymerizations in the presence of a polar modifier, such as N, N, N ', N' -tetramethylethylenediamine (TMEDA). For this reason, it is highly desirable to continuously feed a polar modifier into the reaction vessel used. The ethers and tertiary amines that act as the Lewis bases are representative examples of the polar modifiers that can be used. Some specific examples of common polar modifiers include diethyl ether, di-n-propyl ether, diisopropyl ether, di-n-butyl ether, tetrahydrofuran, dioxane, ethylene glycol dimethyl ether, ethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, trimethylamine, triethylamine, N, N, N ', N' -tetramethylethylenediamine, N-methylmorpholine, N-ethylmorpholine, N-phenylmorpholine and the like. The dipepyridine ethane, dipyrrolidine ethane, tetramethylethylenediamine, diethylene glycol, dimethyl ether, TMEDA and tetrahydrofuran are representative of the highly preferred modifiers. U.S. Patent 4,022,959 describes the use of tertiary ethers and amines as polar modifiers in greater detail. As an option, 1,2-butadiene can also be fed continuously into the reaction zone. 1,2-Butadiene will usually be present in the polymerization medium at a concentration in the range of 10 to about 500 ppm (parts per million). It is generally preferred that 1,2-butadiene is present at a level in the range of about 50 ppm to about 300 ppm. It is generally more preferred that 1,2-butadiene is present at a level in the range of about 100 ppm to about 200 ppm. The polar modifier will usually be present in a molar ratio of the polar modifier to the organolithium compound within the range of about 0.2: 1 to about 1: 1. The amount of the polar modifier used will be adjusted to obtain the desired vitreous transition temperature within the range of about -40 ° C to about -25 ° C. The molar ratio of the polar modifier to the organolithium initiator will preferably be adjusted to produce an isoprene-butadiene rubber with a glass transition temperature in the range of about -38 ° C to about 30 ° C. The isoprene-butadiene rubber most preferably prepared will have a glass transition temperature in the range of about -36 ° C to about -32 ° C. The polymerization is carried out for a sufficient time to allow practically complete polymerization of the monomers. In other words, the polymerization will normally be carried out until the high conversions are obtained. The copolymerization will normally be allowed to continue until an excess conversion of about 90%. It is preferred that the conversion be in excess of about 95% with virtually quantitative conversions greater than about 99% being achieved. The polymerization can then be terminated using a normal technique. The polymerization can be terminated with a conventional type of non-copulant terminator (such as water, an acid and a lower alcohol) or with a coupling agent. Then, the high Tg IBR produced is recovered from the organic solvent. The high Tg IBR can be recovered from the organic solvent by standard techniques, as it can be by decantation, filtration, centrifugation and the like. It is common to precipitate the high Tg IBR from the organic solvent by the addition of lower alcohols containing from 1 to about 4 carbon atoms in the polymer solution. Lower alcohols suitable for precipitation of high Tg IBR from the polymer cement include methanol, ethanol, isopropyl alcohol, n-propyl alcohol and t-butyl alcohol. The use of the lower alcohols to precipitate the high Tg IBR of the polymeric cement also "kills" the latent IBR chains by inactivating the lithium end groups. After the IBR is recovered from the organic solvent, steam entrainment can be used to reduce the level of volatile organic compounds in the rubber. The high Tg IBR prepared by the process of this invention is characterized by being composed of repeating units that are derived from about 20 wt.% To about 80% isoprene and from about 20 wt.% To about 80 wt.% 1, 3-butadiene, where the repeating units from isoprene and 1,3-butadiene are in practically random order. The repeating units that come from isoprene or 1,3-butadiene differ from the monomer from which they are derived in that the double bond was consumed by the polymerization reaction. The repeating units from isoprene and 1,3-butadiene are in the IBR in an almost random order. The term "random" as used herein means that the repeating units that come from isoprene are well dispersed throughout the polymer and are mixed with repeating units from 1,3-butadiene For the purposes of this patent , "randomized" means that more than 60% of isoprene in the IBR is present in blocks of 3 or less repeating units The high Tg IBR used in the tire treads of this invention can also be prepared by the process described in U.S. Patent 5,336,739, the teachings of which are incorporated herein by reference in their entirety In this process, isoprene is copolyzed with 1,3-butadiene in the presence of a catalyst system composed of: (a) an initiator selected from the group consisting of organolithium compounds, organosodium compounds, organomagnesium compounds and organo-organ compounds; and (b) a modifier such as ethyl tetrahydrofurfuryl ether, propyltetrahydrofurfuryl ether or butyltetrahydrofurfuryl ether. Modifiers of this type that can be used to synthesize the high Tg IBR are structural formulas: wherein n is an integer from 1 to 10. It is preferred that n is an integer from 5 to 9 and more preferably that n is 5. The most preferred alkyl tetrahydrofurfuryl ether modifier is hexyltetrahydrofurfuryl ether. The modifier of this type can be introduced into the polymerization zone that is being used in any way. In one embodiment, this can be reacted with the organometallic compound with the reaction mixture thereof being introduced into the polymerization zone as the initiator. In another embodiment, the modifier can be introduced into the polymerization zone directly without first reacting it with the organometallic compound that is used as the initiator. In other words, the modifiers can be introduced into the polymerization zone in the form of a reaction mixture with the organometallic initiator or they can be introduced into the polymerization zone separately. The high Tg IBR according to this invention in the manufacture of tire treads can be compounded using conventional ingredients and standard techniques. For example, the high Tg IBR containing mixtures will usually be mixed with carbon black, sulfur, fillers, accelerators, oils, waxes, overheating inhibitors and processing aids. In addition, up to about 40 phr of rubbery polymers in addition to the high Tg IBR can be included in the rubber compounds for the tread of this invention. For example, isoprene-butadiene rubbers with glass transition temperatures less than about -40 ° C (low Tg IBR), rubber with high cis-1,4-polybutadiene content, natural rubber, synthetic polyisoprene rubber, 3, 4-polyisoprene, styrene-butadiene rubber and / or styrene-isoprene-butadiene rubbers can be included in these combinations. In most cases, at least approximately 30 phr of high Tg IBR will be present in the mixture. More commonly, at least about 40 phr of high Tg IBR will be present in the mixture. For example, the mixture will contain from about 65 phr to about 90 phr of high Tg IBR and from about 10 phr to about 35 phr of high cis-1,4-polybutadiene, high Tg IBR or natural rubber. These mixtures may also contain from about 70 phr to about 85 phr of high Tg IBR and from about 15 phr to about 30 phr of high cis-1,4-polyutadiene, low Tg IBR or natural rubber. In most cases, the high Tg IBR containing rubber blends will be composed of sulfur and / or a sulfur-containing compound, at least one accelerator, at least one antidegradant, at least one processing oil, zinc oxide , optionally a thickener resin, optionally a reinforcing resin, optionally one or more fatty acids, optionally a peptizing agent and optionally one or more overheating inhibiting agents. These mixtures will normally contain from about 0.5 to 5 phr (parts per hundred parts of rubber by weight) of sulfur and / or a sulfur-containing compound, with 1 phr to 2.5 phr being preferred. It may be desirable to use insoluble sulfur in cases where efflorescence is a problem. Normally, from 40 phr to 150 phr of the filler material will be used in the mix, with 50 phr to 100 phr of the filler being preferred. In general, it is more preferred that the tread compound of the rim contains from about 70 phr to about 85 phr of the filler material. It is important that the filler material include at least approximately phr of silica. In most cases, the filler material will be composed of practically silica and will contain at least about 40 phr, and most preferably, at least 50 phr of silica. However, in most casesAt least some of the carbon black will be used in the charging material. For example, it is preferred to use about 70 phr to about 80 phr of silica and about 3 phr to about 8 phr of carbon black as the filler. Small amounts of clays and / or talc can be included in the filler material to reduce the cost. The commonly used silicon pigments that are used in the applications for the rubber composition can be used as the silica in this invention, including pyrogenic and precipitated silica pigments (silica), although precipitated silicas are preferred. The silicon pigments preferably used in this invention are precipitated silicas such as, for example, those obtained by acidification of a soluble silicate.; for example sodium silicate. These silicas can be characterized, for example, by having a BET surface area, measured using nitrogen gas, preferably in the range of about 40 to about 600, and usually in a range of about 50 to about 300 square meters per gram. The BET method for measuring surface area is described in the Journal of the American Chemical Society, volume 60, page 304 (1930). Silica can also be commonly characterized as having a dibutyl phthalate (DBP) absorption value in a range from about 100 to about 400, and more commonly from about 150 to about 300. The silica can be expected to have a final particle size average, for example in the range of 0.01 to 0.05 microns determined by the electron microscope, although the silica particles may be even smaller, or possibly larger in size. Various commercially available silicas can be considered for use in this invention such as, for example only and without limitation, the silicas available commercially from PPG Industries under the trademark Hi-Sil with the names 210, 243, etc.; available silicas of Rhone-Poulenc, with for example, designations of Z1165MP and Z165GR and silicas available from Degussa AG with, for example, designations VN2 and VN3. It is also important that the rubber compounds for the tread of this invention contain a silica coupling agent to fully obtain the overall advantages of the mixtures of this invention. The silica coupling agent will usually be an organosilicon compound containing sulfur. Examples of suitable organosilicon-containing sulfur compounds are of the formula: Z-Alk-Sn-Alk-Z (i: in which Z is selected from the group consisting of: ? r R 'R4 I If R "Yes - R" If R2 I I R1 R2 R2 where R is an alkyl group of 1 to 4 carbon atoms, cyclohexyl or phenyl; wherein R2 is alkoxy of 1 to 8 carbon atoms or cycloalkoxy of 5 to 8 carbon atoms; and wherein Alk is a divalent hydrocarbon of 1 to 18 carbon atoms and n is n of 1 to 8. Specific examples of the organosilicon compounds containing sulfur and which can be used in accordance with the present invention include: 3, 3'-bis (trimethoxysilylpropyl) disulfide, 3,3'-bis (triethoxysilylpropyl) tetrasulfide, 3'3'-bis (triethoxysilylpropyl) octasulfide, 3'3'-bis (trimethoxysilylpropyl) tetrasulfide, tetrasulfide 2, 2'-bis (triethoxysilylethyl), 3,3'-bis (trimethoxysilylpropyl) trisulfide, 3,3'-bis (triethoxysilylpropyl) trisulfide, 3,3'-bis (tributhoxysilylpropyl) disulfide, hexasulfide of 3, 3'-bis (trimethoxysilylpropyl), 3,3'-bis (trimethoxysilylpropyl) octasulfide, 3, 3'-bis (trioctoxysilylpropyl) tetrasulfide, 3, 3'-bis (trihexoxysilylpropyl) disulfide, 3, 3 'trisulfide -bis (tri-2"-ethylhexoxysilylpropyl), 3,3 '-bis (triisooctoxysilylpropyl) tetrasulfide, 3,3'-bis (tri-t-butoxysilylpropyl) disulfide, 2,2'-bis (methoxy diethoxy) tetrasulfide silyl ethyl), 2, 2'-bis (tripropoxysilylethyl) pentasulfide, 3,3'-bis (tricyclohexoxysilylpropyl) tetrasulfide, 3,3'-bis trisulfide (tricyclopentoxysilyl lpropyl), 2,2'-bis (tri-2"-methylcyclohexoxysilylethyl) tetrasulfide, bis (trimethoxysilylmethyl) tetrasulfide, 3'-methoxybutoxysilylpropyltetrasulfide of 3-methoxyethoxypropoxysilyl, 2,2'-bis (dimethylmethoxysilylethyl) disulfide , 2,2'-bis (dimethyl sec.butoxysilylethyl) trisulphide, 3,3'-bis (methylbutylethoxysilylpropyl) tetrasulfide, 3,3'-bis (di-t-butylmethoxysilylpropyl) tetrasulfide, 2,2 'trisulfide bis (phenyl methyl methoxysilylethyl), 3,3'-bis (diphenyl isopropoxysilylpropyl) tetrasulfide, 3,3'-bis (diphenyl cyclohexoxysilylpropyl) disulfide, 3, 3'-bis (dimethyl ethylmercaptosilylpropyl) tetrasulfide, trisulfide 2 , 2'-bis (methyl dimethoxysilylethyl), 2,2'-bis (methyl ethoxypropoxysilylethyl) tetrasulfide, 3,3'-bis (diethylmethoxysilylpropyl) tetrasulfide, 3,3'-bis disulfide (ethyl-di-sec) butoxysilylpropyl), 3,3'-bis (propyl diethoxysilylpropyl) disulfide, 3,3'-bis (butyl dim) trisulfide ethoxysilylpropyl), 3,3'-bis (phenyl dimethoxysilylpropyl) tetrasulfide, 3-phenyl ethoxybutoxylysilyl 3'-trimethoxysilylpropyl tetrasulfide, 4,4'-bis (trimethoxysilylbutyl) tetrasulfide, 6,6'-bis (triethoxysilylhexyl) tetrasulfide) , 12, 12'-bis (triisopropoxysilyl dodecyl) disulfide, 18,18'-bis (trimethoxysilyloctadecyl) tetrasulfide, 18, 18'-bis (tripropoxysilyloctadecenyl) tetrasulfide, 4,4'-bis tetrasulfide (trimethoxysilyl-buten) -2-yl), 4,4'-bis (trimethoxysilylcyclohexylene) tetrasulfide, 5,5'-bis (dimethoxymethylsilylpentyl) trisulfide, 3'3'-bis (trimethoxysilyl-2-methylpropyl) tetrasulfide and 3-disulphide. 3'-bis (trimethoxysilyl-2-methylpropyl).

The preferred sulfur-containing organosilicon compounds are 3, 3'-bis (trimethoxy or triethoxy silylpropyl) sulfides. The most preferred compound is tetrasulfide 3, 3 '.bis (treyetoxysilylpropyl.) Therefore, for the formula I, preferably Z is: R2 I - Si - R2 I R2 where R 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 preferred; and n is an integer of 3 to , being particularly preferred with 4. The amount of the sulfur-containing organosilicon compound of the formula I in a rubber composition will vary, depending on the level of silica used. In a general sense, the amount of the compound of formula I will be in the range of about 0.01 to about 1.0 parts by weight per parts by weight of silica. Preferably, the amount will be in the range from about 0.02 to about 0.4 parts by weight per parts by weight of the silica. More preferably, the amount of the compound of the formula I will be in the range from about 0.05 to about 0.25 parts by weight per parts by weight of the silica. It will be appreciated that the silica coupler can be used together with carbon black; namely, premixed with carbon black prior to addition to the rubber composition, and this carbon black must be included in the aforementioned amount of carbon black for the formulation of the rubber composition. Tire tread formulations will usually be mixed using thermomechanical mixing techniques. The mixing of the rubber formulation for the tread of the rim can be carried out by methods known to those skilled in the art of caubho mixing. For example, the ingredients are commonly mixed in at least two stages; namely, at least one non-productive stage followed by a stage of productive mixing. Final curatives that include vulcanizing agents for sulfur are commonly mixed in the final stage that is commonly referred to as the "productive" mixing stage in which mixing normally occurs at a temperature, or final temperature, less than the temperature (s). ) of the mixture that the stage (s) of the preceding nonproductive mixture. The rubber, silica and organosilicon containing sulfur, and carbon black if used, are mixed in one or more stages of non-productive mixing. The terms "non-productive" and "productive" mixing stages are well known to those skilled in the art of rubber mixing. The sulfur-vulcanizable rubber composition containing the sulfur-containing organosilicon compound, the vulcanizable rubber and generally at least part of the silica will be subjected to a thermomechanical mixing step. The thermomechanical mixing step generally consists of a mechanical work in a mixer or extruder for a suitable time to produce a rubber temperature between 140 ° C and 190 ° C. The proper duration of the thermomechanical work varies as a function of the operating conditions and the volume and nature of the components. For example, the thermomechanical work can be with a duration in the range of approximately 2 minutes to approximately 20 minutes. It is usually preferred that the rubber reaches a temperature in the range of about 145 ° C to about 180 ° C and is maintained at this temperature for a period in the range of about 4 minutes to about 12 minutes. It is usually more preferred that the rubber reaches a temperature in the range of about 155 ° C to about 170 ° C and is maintained at this temperature for a time in the range of about 5 minutes to about 10 minutes. Likewise, the mixture will also include from 0.1 phr to 2.5 phr of at least one accelerator, being preferred from 0.2 phr to 1.5 phr. Antidegradants, such as antioxidants and antiozonants, will generally be included in the mixture in the range from 0.25 phr to 10 phr, with amounts in the range of 1 phr to 5 phr being preferred. The processing oils will generally be included in the mixture in amounts in the range of 2 phr to 100 phr, with amounts in the range of 5 phr to 50 phr being preferred. The high Tg IBR containing mixtures of this invention will typically also contain from 0.5 phr to 10 phr of zinc oxide, with 1 phr to 5 phr being preferred. These mixtures can optionally contain from 0 to 10 phr of thickener resins, from 0 to 10 phr of reinforcing resins, from 1 to 10 phr of fatty acids, from 0 to 2.5 phr of peptizers and from 0 to 1 phr of inhibitors of overheating . The high Tg IBR-containing rubber blends of this invention can be used in tire treads together with normal tire manufacturing techniques. The tires are built using normal procedures simply by replacing the high Tg IBR with rubber compounds commonly used as tread rubber. After the tire has been built with the mixture that ~~ contains high Tg IBR, this can be vulcanized using a normal tire curing cycle. The rims manufactured in accordance with this invention can be cured over a wide range of temperatures. However, it is generally preferred that the tires of this invention be cured at a temperature in the range from about 132 ° C (270 ° F) to about 166 ° C (330 ° F). It is more common for the tires of this invention to be cured at a temperature in the range from about 143 ° C (290 ° F) to about 154 ° C (310 ° F). It is generally preferred that the curing cycle used to vulcanize the tires of this invention have a duration of about 10 to about 14 minutes, with a curing cycle of about 12 minutes being more preferred. This invention is illustrated by the following examples which are merely for the purpose of illustration and are not to be construed as limiting the scope of the invention or the manner in which it may be practiced. Unless specifically indicated otherwise, the parts and percentages are given by weight.

Examples 1-5 In this experiment, the high Tg IBR was synthesized using methyl tetrahydrofurfuryl ether as the modifier. In the procedure used, 1,500 grams of an anhydrous silica / molecular sieve / aluminum premix with a content of 19.4 percent of a 50:50 mixture of isoprene and 1,3-butadiene in hexane was charged to a one-gallon reactor ( 3.8 liters). After the level of the debugger 2. 9 ppm, as determined, pure MTE (ethyl tetrahydrofurfuryl ether, 7.2 M) and 1.65 ml of a 0.75 M solution of n-butyl lithium (in hexane, 1.3 ml for the initiation and 0.35 ml for the purification of the premix) was added to the reactor. The polymerization was allowed to continue at 70 ° C for 1 hour. The analysis of the residual monomers contained in the polymerization mixture by gas chromatography indicated that the polymerization was 96.5% complete at this time. The polymerization was continued for another 30 minutes to ensure a 100% conversion. Then 5 ml of a 1M solution of ethanol (in hexane) was added to the reactor to interrupt the polymerization and the polymer was separated from the reactor and stabilized with 1 phm of antioxidant. After evaporating the hexane, the resulting polymer was dried in a vacuum oven at 50 ° C. The Tg of the IBR produced together with the MTE / n-BuLi ratios used are shown in Table I.

Table I 50/50 isoprene-butadiene copolymers prepared by means of MTE / n-BuLi at 70 ° C Examples 6-12 In this experiment, different mixtures of high Tg IBR were prepared and compared with the rolling surface rubber with a conventional silica content (Example 6) in Examples 7-10, the high Tg IBR used contained 27 percent bound isoprene, had a Mooney viscosity ML1 + 4 of 48 and had a Tg of -33 ° C. This high Tg IBR contained 4.2 percent repeating units 1, 2-polyissephene, 5.8 percent repeating units 1, 4-polyisoprene, 17.4 percent by weight of 3, 4-polyisoprene repeat units, 46.6 percent of 1, 2-polybutadiene repeat units and 26 percent of 1,4-polybutadiene repeat units. In Examples 11 and 12, the high Tg_ IBR used contained 66 percent bound isoprene, Mooney viscosity ML1 + 4 of 62 and Tg of -36 ° C. This high Tg IBR contained 29.9 percent repeating units 1, 4-polyisoprene, 36.3 percent repeating units 3, 4-polyisoprene, 15.2 percent repeating units 1, 2-polybutadiene, and 18.6 percent units of repetition 1, 4-polybutadiene. The results of these comparisons are shown in Table II.

The low rebound levels found in Examples 7-12 at 0 ° C indicate good wet traction. The high delta values found at 0 ° C are also an indication of good traction characteristics. Examples 7-12 also show high bounce at 100 ° C which is indicative of good rolling resistance. This is consistent with the low tan delta values found in Examples 7-12 at 50 ° C, which are also indicative of low hysteresis and good rolling resistance. Although certain representative embodiments and details have been shown for the purpose of illustrating the present invention, it will be apparent to those skilled in the art that various changes and modifications may be made herein without departing from the spirit and scope of the subject matter of the invention.

Claims (10)

1. A rubber composition for the tread of tires that is characterized by being composed of: (1) at least 20 phr of an isoprene-butadiene rubber with a glass transition temperature within the range of -40 ° C to -25 ° C, (2) 40 phr to 150 phr of a filler, provided that the filler material contains at least 20 phr of silica, and (3) a silica coupling agent selected from the group consisting of: disulfide of 3, 3'-bis (trimethoxysilylpropyl), 3,3'-bis (triethoxysilylpropyl) tetrasulfide, 3'3'-bis (triethoxysilylpropyl) octasulfide, 3,3'-bis (trimethoxysilylpropyl) tetrasulfide, tetrasulfide 2 , '-bis (triethoxysilylethyl), 3,3'-bis (trimethoxysilylpropyl) trisulfide, 3,3'-bis (triethoxysilylpropyl) trisulfide, 3,3'-bis (tributoxysilylpropyl) disulfide, 3, 3' hexasulfide -bis (trimethoxysilylpropyl), 3, 3'-bis (trimethoxysilylpropyl) octasulfide, 3, 3'-bis tetrasulfide (trioctox ylpropyl), 3,3'-bis (trihexoxysilylpropyl) disulfide, 3,3'-bis (tri-2"-ethylhexoxysilylpropyl) trisulfuride, 3'3'-bis (triisooctoxysilylpropyl) tetrasulfide, 3'3'-disulfide - bis (tri-t-butoxysilylpropyl), 2,2'-bis (methoxy diethoxy silyl ethyl) tetrasulfide, 2,2'-bis (tripropoxysilylethyl) pentasulfide, 3,3'-bis (tricyclohexoxysilylpropyl) tetrasulfide, trisulfide 3, 3'-bis (tricyclopentoxysilylpropyl), 2,2'-bis (tri-2"-methylcyclohexoxysilylethyl) tetrasulfide, bis (trimethoxysilylmethyl) tetrasulfide, 3'-diethoxybutoxysilylpropyltetrasulfide of 3-methoxyethoxypropoxysilyl, 2,2-disulfide '-bis (dimethylmethoxysilylethyl), 2,2'-bis (dimethyl sec.butoxysilylethyl) trisulfide, 3,3-bis (methylbutylethoxysilylpropyl) tetrasulfide, 3,3'-bis (di-t-butylmethoxysilylpropyl) tetrasulfide) , 2,2'-bis (phenylmethylmethoxysilylethyl) trisulfide, 3,3'-bis (diphenyl isopropoxysilylpropyl) tetrasulfide) , 3, 3'-bis (diphenyl cyclohexoxysilylpropyl) disulphide, 3,3'-bis (dimethyl ethylmercaptosilylpropyl) tetrasulfide, 2,2'-bis (methyl dimethoxysilylethyl) trisulfide, 2,2'-bis (methyl) tetrasulfide ethoxypropoxysilylethyl), 3, 3'-bis (diethylmethoxysilylpropyl) tetrasulfide, 3,3'-bis (ethyl-di-sec.butoxysilylpropyl) disulfide, 3, 3'-bis (propyl diethoxysilylpropyl) disulfide, trisulfide 3, , 3'-bis (butyl dimethoxysilylpropyl), 3,3'-bis (phenyl dimethoxysilylpropyl) tetrasulfide, 3-phenyl ethoxybutoxylysilyl 3'-trimethoxysilylpropyl tetrasulfide, 4,4'-bis (trimethoxysilylbutyl) tetrasulfide, tetrasulfide 6, 6'-bis (triethoxysilylhexyl), 12, 12'-bis (triisopropoxysilyl dodecyl) disulfide, 18,18'-bis (trimethoxysilyloctadecyl) tetrasulfide, 18,18'-bis (tripropoxysilyloctadecenyl) tetrasulfide, tetrasulfide of 4,4 '-bis (trimethoxysilyl-buten-2-yl), 4,4'-bis (trimethoxysilylcyclohexylene tetrasulfide) ), 5, 5'-bis (dimethoxymethylsilylpentyl) trisulphide, 3,3'-bis (trimethoxysilyl-2-methylpropyl) tetrasulfide and 3,3'-bis (trimethoxysilyl-2-methylpropyl) disulfide.

2. The rubber composition for the tread of the rim as specified in claim 1 is characterized in that the isoprene-butadiene rubber is present at a level of at least 60 phr, where the filler material contains when minus 40 phr of silica.

3. The rubber composition for the tread of tires as specified in claim 1, characterized in that the filler material contains at least 50 phr of silica, where at least 70 phr of isoprene-butadiene rubber is present.

4. The rubber composition for the tread of tires as specified in claim 3, characterized in that the rubber composition for the tread tire is also composed of a rubber selected from the group consisting of isoprene rubbers. -butadiene with glass transition temperatures less than -40 ° C, rubber with high cis-1, 4-polybutadiene content, natural rubber, synthetic polyisoprene rubber, 3,4-polyisoprene, styrene-butadiene rubber and styrene-isoprene-butadiene rubber.

5. The rubber composition for the tire tread as specified in claim 4, characterized in that the load material is present at a level within the range of 50 phr to 100 phr and is characterized because it is present at least 75 phr of isoprene-butadiene rubber.

6. The rubber composition for the tread of tires as specified in claim 5, which is further characterized by being composed of carbon black, wherein the carbon black is present at a level within the range of 3. phr at 8 phr, and where silica is present at a level within the range of 70 phr to 80 phr.

7. The rubber composition for the tire tread as specified in claim 6, characterized in that the isoprene-butadiene rubber has a glass transition temperature within the range of -38 ° C to -30 ° C.

8. The rubber composition for the tire tread as specified in claim 7 is characterized in that the silica coupling agent is an organosilicon compound containing sulfur.

9. The rubber composition for the tire tread as specified in claim 7 is characterized in that the silica coupling agent is 3,3'-bis (triethoxysilylpropyl) tetrasulfide.

10. A pneumatic tire having an outer circumferential tread, wherein the tread is a sulfur-cured rubber composition characterized by being composed of the rubber composition for the tread of tires specified in the claim 1 SUMMARY OF THE INVENTION Unexpectedly it has been determined that isoprene-butadiene rubber with a high vitreous transition temperature in the range of about -40 ° C to about -25 ° C (high Tg IBR) can be loaded with silica as filler and used in the manufacture of treads for tires that have outstanding performance characteristics. For example, these tire treads offer lower hysteresis at higher temperatures (better rolling resistance) and superior hysteresis at low temperatures (best characteristics of wet traction). By using the high Tg IBR in the tire tread compounds, the maximum benefits of the silica composition can be obtained without the need for styrene-butadiene rubber in solution or emulsion (SBR) in the rubber formulations for the rotation band. The tire tread rubber formulations of this invention will typically contain about 20 phr (parts per hundred parts rubber) to about 100 phr of the high Tg IBR. In other words, the tread rubber will normally contain at least 20 phr of high Tg IBR and may contain up to 100 phr of high Tg IBR. The tread compound will also contain 40 phr to 150 phr of a filler, provided that at least about 20 phr of silica is included in the filler. The compound for the tire bearing surface will also contain a silica coupling agent. This invention more specifically describes a rubber composition for tire tread which is composed of: (1) at least about 20 phr of an isoprene-butadiene rubber with a glass transition temperature within the range of about -40 ° C at -25 ° C, (2) from 40 phr to 150 phr of a filler, provided that the filler material contains at least about 20 phr of silica, and (3) a silica coupling agent.