Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L9/00—Compositions of homopolymers or copolymers of conjugated diene hydrocarbons
  • C08L9/06—Copolymers with styrene
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
  • B60C1/00—Tyres characterised by the chemical composition or the physical arrangement or mixture of the composition
  • B60C1/0016—Compositions of the tread
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L21/00—Compositions of unspecified rubbers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/02—Elements
  • C08K3/04—Carbon
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/34—Silicon-containing compounds
  • C08K3/36—Silica
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/26—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers modified by chemical after-treatment
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L29/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal or ketal radical; Compositions of hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Compositions of derivatives of such polymers
  • C08L29/02—Homopolymers or copolymers of unsaturated alcohols
  • C08L29/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L31/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an acyloxy radical of a saturated carboxylic acid, of carbonic acid or of a haloformic acid; Compositions of derivatives of such polymers
  • C08L31/02—Homopolymers or copolymers of esters of monocarboxylic acids
  • C08L31/04—Homopolymers or copolymers of vinyl acetate
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L33/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides or nitriles thereof; Compositions of derivatives of such polymers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L9/00—Compositions of homopolymers or copolymers of conjugated diene hydrocarbons

Definitions

• the present invention relates to a method for improving processability and storage stability of a silica filled elastomeric composition, and to elastomeric compositions obtainable therefrom, and also to vulcanized articles, particularly tyres, including said compositions.
• silica as reinforcing filler for elastomeric compositions has several shortcomings.
• One of the most apparent drawback is a scarce processability of the unvulcanized compositions, mainly due to an excessive viscosity. Therefore, to achieve a good dispersion of silica in the rubber matrix, an intense and prolonged thermo-mechanical kneading of the composition is necessary.
• the silica particles having a strong tendency to coalesce even when finely dispersed in a rubber base, impair storage stability of the unvulcanized compositions by forming agglomerates with a remarkable increase of the compound viscosity upon time.
• the acid moieties which are present on the silica surface can cause strong interactions with basic substances commonly employed in rubber compositions, such as vulcanization accelerators, thus impairing cross-linking efficiency.
• silica is usually blended with a coupling agent, for instance a sulfur-containing organosilane product, having two different moieties: the first moiety is able to interact with the silanol groups present on the silica surface, the second moiety promotes interaction with the sulfur-curable elastomers.
• a coupling agent for instance a sulfur-containing organosilane product, having two different moieties: the first moiety is able to interact with the silanol groups present on the silica surface, the second moiety promotes interaction with the sulfur-curable elastomers.
• European Patent Application EP-801,112 discloses the use of polysiloxane compounds having alkoxysilyl and/or acyloxysilyl groups to increase storage stability of silica filled rubber compositions.
• the use of such polysiloxane compounds would avoid the problems due to generation of hydrogen gas and gelation deriving from the reaction of the Si-H residual groups commonly present in polysiloxane compounds.
• a silane coupling agent may be added.
• a silanol condensation catalyst is added to accelerate the reaction between the above polysiloxane compound and/or the silane coupling agent with the silica surface silanol groups. This should result in a sufficient coating of the silica surface even using relatively low amounts of the above compounding agents.
• European Patent Application EP-890,603 discloses the use, as processing aids to improve processability of silica filled diene elastomer compositions, of hydrogenated and non-hydrogenated fatty acid esters of C5 and C6 sugars, or polyoxyethylene derivatives thereof, preferably in the presence of a silane, such as octyltriethoxysilane.
• a silane such as octyltriethoxysilane.
• Other mineral fillers, such as talc or mica are also added to inhibit re-agglomeration of silica .
• a silica filled rubber stock of improved processability is prepared by mixing the rubber base with an amorphous silica filler, from 0 to less than about 1% by weight (based on said silica filler) of bis [ 3- (triethoxysilyl ) propyl] - tetrasulfide (Si69) , an alkylalkoxysilane and a curing agent.
• a polyol or fatty acid ester is preferred to further reduce the amount of Si ⁇ 9.
• the fibers for instance cellulose or synthetic polymer fibers, are oriented along the circumferential direction of the tyre, so as to impart anisotropic characteristics.
• Road grip on ice or snow surfaces would be improved by the presence of polyvinylalcohol particles which, when contacted with water, would dissolve, leaving in the tread cavities which increase roughness and hence road grip of the tread.
• the amount of polyvinyl alcohol powder should not exceed 15 phr, so as not to worsen wear resistance to an unacceptable extent. Besides, low amounts of polyvinylalcohol are necessary not to increase tread stiffness and therefore not to worsen the road grip on dry grounds. Polyvinylalcohol is always employed in rubber compositions containing carbon black as reinforcing filler.
• an elastomeric composition for use in tyre tread manufacture which includes modified polyvinylalcohol, in the form of powder or fibers.
• modified polyvinylalcohol has polyoxyalkylene groups along the chain, which increase water solubility of the polymer, hence promoting dissolution of the same when the tread gets in touch with a wet surface, leaving cavities in the tread itself and forming a sticky layer at the interface with the road surface which should increase the tyre road grip .
• hydrophilic polymers deriving from starch in elastomeric compositions is described in US patents Nos. 5,374,671 and 5,545,680.
• elastomeric compositions comprising from 1 to 50 phr of a hydrophilic polymer having a glass transition temperature (Tg) ranging from 150 °C to 0°C depending upon the absorbed amount of water.
• Tg glass transition temperature
• Such hydrophilic polymer is a destructured starch comprising amylose, amylopectine, or mixtures thereof.
• the presence of the destructured starch in a rubber composition for tyre treads is said to increase traction on wet grounds, while reducing at the same time rolling resistance on dry roads.
• the destructured starch may be homogeneously dispersed throughout the elastomeric matrix or, preferably, it is immiscible with the polymeric matrix so that it tends to form fibers, preferably oriented fibers, within said matrix. Since destructured starch is a hydrolyzable and biodegradable polymer, its presence in a tyre is said to increase its biodegradability .
• a grafting agent may be added to the rubber composition, in order to bind the hydrophilic polymer to the elastomeric base. No indications are given either about the grafting agent to be used, or on how to accomplish such grafting.
• Destructured starch may be compounded with silica, however no effects on processability or storage stability were reported.
• US Patent No. 5,672,639 describes an elastomeric composition reinforced with a destructured starch combined with a plasticizer compatible with the destructured starch, so as to form a starch/plasticizer composite.
• a plasticizer compatible with the destructured starch, so as to form a starch/plasticizer composite.
• the plasticizer has a softening point lower than the softening point of destructured starch.
• poly (ethylene- vinylalcohol) having a softening point lower than 160°C, preferably comprised between 90° and 130 °C, may be employed as a plasticizer.
• plasticizers include: ethylene/ vinylacetate copolymers, ethylene/glycidylacrylate copolymers and ethylene/maleic anhydride copolymers, cellulose acetate, diesters of dibasic organic acids, and the like.
• a coupling agent having a group which reacts with the hydroxyl groups of the composite and a group capable of interacting with the elastomeric matrix is suggested in order to couple the starch/plasticizer composite with the elastomeric matrix.
• the use of coupling agents normally employed in silica- containing rubber compositions, in particular an organosilane tetrasulfide is indicated.
• the destructured starch/ plasticizer composite may be compounded with silica, however no effects on processability or storage stability were reported.
• the compounding agents suggested in the prior art discussed above to improve processability of silica filled elastomeric compositions give unsatisfactory results.
• polysiloxanes are in fact scarcely reactive with the silanol groups on the silica surface, therefore they can reduce the viscosity of the rubber compositions substantially by acting as plasticizers, their interaction with silica being very poor.
• the addition of a silanol condensation catalyst, as taught in EP-801,112 gives a scarce, or even negligible, improvement.
• the low molecular weight products containing hydroxyl groups suggested, for instance, in EP-890,603 and US-5, 717 , 022 basically acts as plasticizers.
• the use of the above processing aids as plasticizers while reducing the viscosity of the rubber compound, cause a remarkable reduction of the reinforcement effect of silica, thus resulting in a worsening of tensile and elastic properties of the cross-linked articles obtained therefrom.
• the negative influence on tensile and elastic properties is clearly enhanced when the above processing aids are added in relatively high amounts to increase their effectiveness as plasticizers.
• thermoplastic polymer having a main hydrocarbon chain to which hydroxy groups are linked, said polymer containing hydroxy groups having a weight-average molecular weight of at least 8,000.
• the above thermoplastic polymer is highly effective in reducing and stabilizing viscosity of the composition, even when used in relatively low amounts, while maintaining or even enhancing the reinforcement effect of silica on the elastomeric composition.
• a remarkable improvement of processability and storage stability of the elastomeric compositions can be achieved combined with a reinforcing effect. Therefore, the polymer containing hydroxy groups is able to exert a reinforcing action on the elastomeric material, thus replacing, at least partially, the conventional reinforcing fillers, while keeping excellent, both tensile and dynamic, mechanical properties.
• the Applicant has found that the above beneficial effects on processability and storage stability can be even enhanced by adding to the silica filled composition the above thermoplastic polymer containing hydroxy groups and a polymer having groups reactive with said hydroxy groups.
• the resulting cross-linked articles have even improved tensile and elastic properties, deriving from an enhanced reinforcement of the material.
• the Applicant has found that the addition to the elastomeric composition of a destructured starch combined with poly (ethylene-vinylalcohol) having a softening point lower than 160°C as plasticizer (as disclosed in US-5, 672, 639) has a detrimental affect both on the elastic properties of the vulcanized composition and, particularly, on the abrasion resistance.
• the present invention relates to a method for improving processability and storage stability of a silica filled elastomeric composition, said method comprising mixing at least an elastomeric diene polymer with a reinforcing filler comprising silica, characterized in that said method further comprises adding to said composition a thermoplastic polymer having a main hydrocarbon chain to which hydroxy groups are linked, said polymer containing hydroxy groups having a weight-average molecular weight of at least 8,000, preferably from 10,000 to 150,000, more preferably from 12,000 to 50,000.
• said polymer containing hydroxy groups has a melting point of at least 160 °C, more preferably from 170°C to 230°C, even more preferably from 180°C to 220°C.
• the method further comprises adding to the silica filled elastomeric composition a polymer containing functional groups reactive with said hydroxy groups.
• the present invention relates to an elastomeric composition
• an elastomeric composition comprising: at least an elastomeric diene polymer; at least a reinforcing filler comprising silica; at least a thermoplastic polymer having a main hydrocarbon chain to which hydroxy groups are linked, said polymer containing hydroxy groups having a weight-average molecular weight of at least 8,000, preferably from 10,000 to 150,000, more preferably from 12,000 to 50,000; with the proviso that, when said polymer containing hydroxy groups is poly (ethylene-vinylalcohol) , the composition is substantially devoid of destructured starch.
• the present invention relates to an elastomeric article obtained by cross- linking the above elastomeric composition.
• the present invention relates to a tyre for vehicle wheels comprising at least an element including an elastomeric material, characterized in that said elastomeric material is obtained by cross-linking a composition comprising: at least an elastomeric diene polymer; at least a reinforcing filler comprising silica; at least a thermoplastic polymer having a main hydrocarbon chain to which hydroxy groups are linked, said polymer containing hydroxy groups having a weight-average molecular weight of at least 8,000, preferably from 10,000 to 150,000, more preferably from 12,000 to 50,000.
• said element including said composition is a tread belt.
• the present invention relates to a tread belt comprising the above elastomeric composition.
• thermoplastic polymer having a main hydrocarbon chain to which hydroxy groups are linked (for the sake of conciseness also “polymer containing hydroxy groups” ) it is meant a synthetic polymer wherein hydroxy groups, either directly or through side groups, are linked to the main hydrocarbon chain, said chain being either linear or branched and free from glycoside bonds.
• glycoside bonds are ether bonds, cleavable by hydrolysis, deriving from polycondensation of monosaccharides, which are typically present in polysaccharides such as starch and cellulose.
• the average molecular weight of the polymer containing hydroxy groups according to the present invention may be determined by known techniques, usually by Gel Permeation Chromatography (GPC) .
• the melting point of the polymer containing hydroxy groups may be determined by means of differential thermal analysis using a technique well known to anyone skilled in the art, such as a Differential Scanning Calorimeter (DSC) equipment.
• DSC Differential Scanning Calorimeter
• the polymer containing hydroxy groups is added to the elastomeric composition in an amount of from 0.1 to 60 phr, more preferably from 1 to 30 phr, even more preferably from 2 to 15 phr.
• phr means parts by weight per
• the polymer containing functional groups reactive with the hydroxy groups (in the following also referred to, for the sake of conciseness, " functionalized polymer” ) is added to the elastomeric composition in an amount so as to obtain a weight ratio between the polymer containing hydroxy groups and the functionalized polymer comprised between 0.5:1 and 10:1, preferably between 1:1 and 5:1.
• the polymer containing hydroxy groups according to the present invention is capable to absorb at least 0.1% by weight of water based on the polymer weight, after a 24-hour exposure in an environment having a 50% relative humidity at the temperature of 24 °C (according to standard method ASTM D570) .
• the polymer containing hydroxy groups according to the present invention may be selected in particular from: polyhydroxyalkylacrylate, polyvinylalcohol, vinylalcohol/ vinylacetate copolymers, ethylene/vinylalcohol copolymers, ethylene/vinylalcohol/vinylacetate terpolymers, and mixtures thereof.
• said polymer containing hydroxy groups comprises repeating units having the formula CH- CH (I)
• This preferred class of polymer containing hydroxy groups includes: polyvinylalcohol, ethylene/vinylalcohol copolymers, ethylene/vinylalcohol/vinylacetate terpolymers.
• Polymers may also be used wherein the groups of formula (I) have been at least partially modified, for instance by partial acetylation with aliphatic aldehydes (as described, for instance, in US patent 4,002,796). The following are particularly preferred:
• vinylalcohol polymers obtained by hydrolysis of polyvinylacetate, with a hydrolysis degree of from 50 to 100 mol %, preferably from 70 to 90 mol %;
• ethylene/vinylalcohol copolymers having a content of ethylene units generally of from 20 to 60 mol %, preferably from 25 to 50 mol %.
• Copolymers of type (i) are commercially available under the trademarks Mowiol® (Clariant) , Gohsenol® (Nippon Gohsei) , Elvanol® ( Du Pont), Airvol® (Air Products) . Copolymers of type (ii) are commercially available under the trademark Soarnol® (Atochem) .
• the functionalized polymer employable in the present invention is a thermoplastic hydrocarbon polymer containing groups selected from: carboxylic groups, anhydride groups, ester groups, silane groups, epoxy groups, or combinations thereof.
• the amount of functional groups present in the polymer is generally from 0.05 to 50 parts by weight, preferably from 0.1 to 10 parts by weight, based on 100 parts by weight of the polymer.
• the functional groups may be introduced during the production of the polymer, by co-polymerization with corresponding functionalized monomers containing at least one ethylene unsaturation, or by subsequent modification of the hydrocarbon polymer by grafting said functionalized monomers in the presence of a free radical initiator (in particular, an organic peroxide) .
• a free radical initiator in particular, an organic peroxide
• the functional groups by reacting pre-existing groups of the hydrocarbon polymer with a suitable reagent, for instance by an epoxydation reaction of a diene polymer containing double bonds along the main chain and/or as side groups with a peracid (for instance, m-chloroperbenzoic acid or peracetic acid) or with hydrogen peroxide in the presence of a carboxylic acid or a derivative thereof.
• a suitable reagent for instance by an epoxydation reaction of a diene polymer containing double bonds along the main chain and/or as side groups with a peracid (for instance, m-chloroperbenzoic acid or peracetic acid) or with hydrogen peroxide in the presence of a carboxylic acid or a derivative thereof.
• the base hydrocarbon polymer may be selected from:
• propylene or 1-octene (preferably propylene or 1-octene) , comprising in general from 35 to 97 mol % of ethylene and from 3 to 65 mol % of alpha-olefin;
• Functionalized monomers which may be used include for instance: silanes containing at least one ethylene unsaturation; epoxy compounds containing at least one ethylene unsaturation; monocarboxylic or, preferably, dicarboxylic acids containing at least one ethylene unsaturation, or derivatives thereof, in particular anhydrides or esters.
• silanes containing at least one ethylene unsaturation are: gamma-methacryloxypropyltrimethoxy- silane, allyltrimethoxy-silane, allyltriethoxy-silane, allylmethyldimethoxy-silane, allylmethyldiethoxy-silane, vinyltris (2-methoxyethoxy ) -silane, vinyltrimethoxy-silane, vinylmethyldimethoxy-silane, vinyltriethoxy-silane, and the like, or mixtures thereof.
• Examples of epoxy compounds containing at least one ethylene unsaturation are: glycidyl acrylate, glycidyl methacrylate, itaconic acid monoglycidyl ester, maleic acid glycidylester, vinylglycidyl ether, allylglycidyl ether, and the like, or mixtures thereof.
• Examples of monocarboxylic or dicarboxylic acids containing at least one ethylene unsaturation are: maleic acid, maleic anhydride, fumaric acid, citraconic acid, itaconic acid, acrylic acid, methacrylic acid, and the like, and anhydrides or esters derived therefrom, or mixtures thereof.
• Maleic anhydride is particularly preferred.
• Polyolefins grafted with maleic anhydride are available as commercial products identified for instance by the trademarks Fusabond® (Du Pont) , Orevac® (Elf Atochem) , Exxelor® (Exxon Chemical), Yparex® (DSM).
• the elastomeric diene polymers usable as polymeric base in the present invention may be selected from those commonly used in sulfur-vulcanizable elastomeric compositions, particularly suitable for tyre manufacture, i.e. among unsaturated chain elastomeric polymers or copolymers having a glass transition temperature generally lower than 20°C, preferably comprised between 0° and - 90 °C.
• Such polymers or copolymers may be of natural origin or may be obtained by solution or emulsion polymerization of one or more conjugated diolefins, possibly mixed with one or more monovinylarenes in an amount generally not higher than 50% by weight.
• the conjugated diolefins have from 4 to 12, preferably from 4 to 8, carbon atoms, and may be selected from the group comprising: 1, 3-butadiene, isoprene, 2, 3-dimethyl-l, 3-butadiene, 1, 3-pentadiene, 1,3- hexadiene, 3-butyl-l, 3-octadiene, 2-phenyl-l, 3-butadiene, and the like, or mixtures thereof. 1 , 3-butadiene and isoprene are particularly preferred.
• Monovinylarenes that may be used as comonomers generally have from 8 to 20, preferably from 8 to 12 carbon atoms, and may be selected for instance from: 1- vinylnaphthalene; 2-vinylnaphthalene; various alkyl, cycloalkyl, aryl, alkylaryl or arylalkyl styrene derivatives, such as for instance: alpha-methylstyrene, 3- methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, 4- dodecylstyrene, 2-ethyl-4-benzylstyrene, 4-p-tolylstyrene, 4- (4-phenylbutyl) styrene, and the like, or mixtures thereof. Styrene is particularly preferred.
• the elastomeric diene polymers usable as a polymeric base in the present invention may be selected from: cis-1, 4-polyisoprene (either natural or synthetic, preferably natural rubber), 3, 4-polyisoprene, poly-1,3- butadiene (in particular, high vinyl 1, 3-polybutadiene having a content of 1, 2-polymerized units comprised between 15 and 85% by weight, and cis-1, -polybutadiene) , polychloroprene, possibly halogenated isoprene/isobutene copolymers, 1, 3-butadiene/acrylonitrile copolymers, styrene/1, 3-butadiene copolymers, 1, 3-butadiene/isoprene copolymers, styrene/ isoprene/1, 3-butadiene copolymers, butadiene/acrylonitrile copolymers, and the like, or mixtures thereof
• Diene polymers functionalized by reaction with suitable terminating or coupling agents may also be employed.
• diene polymers obtained by anionic polymerization in the presence of an organometal initiator in particular, an organo-lithium initiator
• suitable terminating or coupling agents such as imines, carbodiimides, alkyltin halides, substituted benzophenones, alkoxy- or aryloxy silanes (see, for instance, European patent EP-451,604 and US patents 4,742,124 and 4,550,142) .
• the silica usable according to the present invention may generally be pyrogenic silica or, preferably, precipitated silica, having a BET surface area comprised between 50 and 500 m 2 /g, preferably between 70 and 200 m 2 /g (measured according to ISO standard 5794/1) .
• Additional reinforcing fillers may be added, such as: carbon black, alumina, aluminum silicates, calcium carbonate, kaolin and the like, or mixtures thereof. Carbon black is particularly preferred.
• the carbon black grades usable according to the present invention may be selected from those conventionally used in tyre manufacture, generally having a surface area not smaller than 20 m 2 /g (determined by CTAB absorption as described in ISO standard 6810) .
• a silica coupling agent may be advantageously incorporated, which is capable of interacting with silica and to bind the latter to the elastomeric base during vulcanization.
• Coupling agents of preferred use are those based on silane, identifiable for instance by the following structural formula:
• R 3 Si-C n H 2n -X (II) wherein: groups R, equal or different from each other, are selected from: alkyl, alkoxy, aryloxy groups or halogen atoms, with the proviso that at least one of the R groups is an alkoxy or aryloxy group; n is an integer of from 1 to 6;
• X is a group selected from: nitrous, mercapto, amino, epoxy, vinyl, imido, chloro, - (S) m -C n H 2n -Si (R) 3 , wherein m and n are integers of from 1 to 6, and the R groups are as defined above.
• silane-based coupling agent bis (3- trietoxysilylpropyl) tetrasulfide (Si69) is particularly preferred, either as such or suitably mixed with a small amount of inert filler (for instance, carbon black) to facilitate the incorporation of the same in the rubber composition.
• the method according to the present invention may further include adding to the silica filled elastomeric compositions an effective amount of a silanol condensation catalyst.
• the silanol condensation catalyst may be generally added in an amount of from 0.05 to 7% by weight, preferably from 0.1 to 5% by weight, with respect to the weight of silica.
• the silanol condensation catalyst can be selected from those known in the art for condensation reactions, and in particular: carboxylates of metals such as tin, zinc, zirconium, iron, lead, cobalt, barium, calcium, manganese and the like, for example: dibutyltin dilaurate, dibutyltin diacetate, dioctyltin dilaurate, stannous acetate, stannous caprylate, lead naphthenate, zinc caprylate, zinc naphthenate, cobalt naphthenate, ferrous octanoate, iron 2-ethyl hexanoate, and the like; - arylsulphonic acids or derivatives thereof, for example: p-dodecylbenzenesulphonic acid,
• compositions according to the present invention may be vulcanized according to known techniques, and in particular with sulfur-based vulcanizing systems commonly employed for diene elastomers.
• sulfur or a sulfur-containing vulcanizing agent is incorporated in the composition together with vulcanization activators and accelerators.
• the temperature is generally kept below 120°C, preferably below 100°C, to prevent undesired pre-cross-linking phenomena.
• the vulcanizing agent of most advantageous use is sulfur or sulfur-containing molecules (sulfur donors) with accelerators and activators known to anyone skilled in the art.
• Particularly effective activating agents are zinc compounds and in particular ZnO, ZnC0 3 , zinc salts of fatty acids, saturated or unsaturated, having from 8 to 18 carbon atoms, such as for instance zinc stearate, preferably formed in si tu in the rubber composition starting from ZnO and fatty acid, as well as BiO, PbO, Pb 3 0 4 , Pb0 2 , and mixtures thereof.
• Accelerators of common use may be selected from: dithiocarbamates, guanidines, thioureas, thiazoles, sulphenamides, tiourams, amines, xanthates, and the like, or mixtures thereof.
• compositions according to the present invention may include other additives of common use selected on the basis of each specific application they are intended for. For instance, the following may be added to said compositions: antioxidants, antiageing agents, plasticizers, adhesive agents, antiozonants, modifying resins, fibers (for instance, Kevlar® pulp), and the like.
• a plasticizer generally selected from mineral oils, vegetable oils, synthetic oils and the like, or mixtures thereof, for instance: aromatic oil, naphthene oil, phthalates, soybean oil, and the like, may be added to the cross-linking compositions of the present invention.
• the amount of the plasticizer may generally range between 2 and 100 phr, preferably between 5 and 50 phr.
• compositions according to the present invention may be carried out by mixing the polymer components with the reinforcing filler and the other additives according to techniques known in the art. Mixing may be carried out for instance by means of an open-mill type mixer, or by means of an internal mixer of the type with tangential (Banbury) or interpenetrating (Intermix) rotors, or in continuous mixers of the Ko-Kneader (Buss) type, or of twin-screw co-rotating or counter-rotating type.
• the polymer containing hydroxy groups, and the functionalized polymer as optional component may be used in the form of powder, beads or pellets.
• such polymers may be used combined with a plasticizer, such as glycerin, pentaerythrite, and the like.
• the compositions according to the present invention are produced in two steps. In a first step, the polymer containing hydroxy groups, and possibly the functionalized polymer, is mixed with a portion of the elastomeric base, thereby forming a asterbatch. In a subsequent step, the masterbatch is mixed with the remaining portion of the elastomeric base and the other components, according to conventional methods.
• the first preparation step of the masterbatch is preferably carried out in a continuous mixer, for instance a twin-screw extruder, at a temperature of more than 120°C, so as to obtain an excellent dispersion of the thermoplastic polymers in the elastomeric base.
• the continuous mixers of preferred use are characterized by an adjustable geometry of the screw and thermal profile of the cylinder.
• the masterbatch is prepared in a continuous mixer at a temperature of from 180° to 230°C, more preferably from 190° e 230°C.
• a tyre 1 conventionally comprises at least one carcass ply 2 whose opposite side edges are coupled with respective bead wires 3, each incorporated in a bead 4 along a circumferential internal edge of the tyre, at which said tyre engages on a rim 5 which makes part of a vehicle wheel.
• the coupling between the carcass ply 2 and the bead wires 3 is usually achieved by bending the carcass ply 2 around the bead wires 3, as shown in Figure 1.
• the conventional bead wires 3 may be substituted by a couple of circumferentially inestensible annular inserts in the form of elongated elements extending in concentric coils (not represented in Figure 1) (see for instance European patent applications Nos. 928,680 and 928,702).
• the carcass ply 2 is not bended around the bead wires 3, the coupling between them being provided by a second carcass ply (not represented in Figure 1) externally applied to the first one .
• a couple of sidewalls 7 is applied, each of which extends from the bead 4 up to a so-called "shoulder" zone 8 of the tyre, defined at the opposite ends of the belt strip 6.
• the tread 9 is externally provided with a rolling surface 9a, intended for getting in touch with the ground, wherein circumferential grooves 10 may be formed, intercalated with transversal slits, not shown in the attached figure, which define a plurality of blocks 11, variously distributed on said rolling surface 9a.
• the production process of the tyre according to the present invention may be carried out with techniques and apparatuses known in the art. More particularly, such process usually comprises an assembling step of the green tyre, wherein several semi-finished products, previously and separately prepared from each other and corresponding to the different parts of the tyre (carcass plies, belt strips, bead wires, fillings, sidewalls and treads) are associated with each other with a suitable assembling machine.
• Alternative processes for producing a tyre or parts thereof without using semi-finished elements are described, for instance, in the above cited patent applications EP-928,680 and EP-928,702.
• the green tyre thus obtained is transferred to the subsequent shaping and cross-linking steps.
• a vulcanization mould is used, adapted to house the tyre under working within a moulding cavity having walls counter-shaped with respect to the outer surface of the tyre once the cross-linking has been completed.
• Shaping of the green tyre may be carried out by feeding a pressurized fluid into the space defined by the tyre inner surface, in order to press the outer surface of the green tyre against the walls of the molding cavity.
• a vulcanization chamber made of elastomeric material, filled with vapor and/or other fluids, is inflated within the tyre enclosed in the molding cavity. In this way, the green tyre is pushed against the inner walls of the molding cavity, obtaining the desired shaping.
• shaping may be carried out without an inflatable vulcanization chamber, by preparing within the tyre a toroidal metal support shaped in accordance to the configuration of the inner surface of the tyre to be obtained (see for instance patent EP-242,840).
• the different coefficient of thermal expansion between the toroidal metal support and the green elastomeric material is exploited to achieve an adequate molding pressure.
• the cross-linking step of the green elastomeric material present in the tyre is carried out.
• the outer wall of the vulcanization mold is caused to get in touch with a heating fluid (generally, vapor) , so that the outer wall reaches a maximum temperature generally comprised between 100°C and 230°C.
• the inner surface of the tyre is brought to the cross-linking temperature with the same pressurized fluid employed to press the tyre against the walls of the molding cavity, heated up to a maximum temperature comprised between 100°C and 250°C.
• the time necessary to obtain a satisfactory degree of cross-linking throughout the mass of the elastomeric material may generally range between 3 min and 90 min, and mainly depends on the tyre size .
• compositions according to the present invention were prepared as follows .
• the maximum temperature reached during the extrusion was of 200°C ⁇ 5°C.
• the masterbatch was air cooled.
• SBR styrene/butadiene copolymer, obtained by emulsion polymerization, containing 40% by weight of styrene, mixed with 37.5 phr of extension oil (marketed by Enichem Elastomeri under the abbreviation SBR 1721) ;
• PVA polyvinylalcohol obtained by hydrolysis of polyvinylacetate, having hydrolysis degree of 83 mol %, viscosity (DIN 53 015) of 2.8 ⁇ 0.3 mPa-s2, melting point of 180°C, weight-average molecular weight M w of 18,000 (marketed by Clariant Italia under the trademark Mowiol® 3-83) ;
• PE-MA polyethylene grafted with 0.5% by weight of maleic anhydride, having a Melt Flow Index (at 190 °C and 2.16 kg) of 4 (marketed by Elf Atochem under the trademark Orevac® OE 330) .
• Sulfur-vulcanizable rubber compositions filled with silica were prepared. The compositions are reported in Table 2A (in phr) . The masterbatch of PVA was used as a partial replacement of silica.
• SBR styrene/butadiene copolymer, obtained by emulsion polymerization, containing 25% by weight of styrene, mixed with 37.5 phr of extension oil (marketed by Bayer under the abbreviation SBR 5025) ;
• BR cis-1, 4-polybutadiene (product Europrene Neocis® BR 40 - Eniche Elastomeri);
• DPG diphenylguanidine (product Vulkacit® D Bayer) ;
• Silane bis( 3-triethoxysilylpropyl )tetrasulfide (product X50S comprising 50% carbon black and 50% silane - Degussa) (the value reported in the table refer to the actual amount of added silane) ;
• Antioxidant phenyl-p-phenylene diamine.
• the Mooney viscosity ML (1+4) at 100°C (according to standard ISO 289/1) of the above compositions was measured after 1 day and after 8 days of storage at room temperature. The results are reported in Table 2B.
• compositions thus prepared were submitted to MDR rheometric analysis utilizing a Monsanto MDR rheometer, carrying out the tests at 151°C for 60 min with an oscillation frequency of 1.66 Hz (100 oscillations per minute) and an oscillation amplitude of +0.5°.
• the mechanical properties (according to standard ISO 37) and the hardness in IRHD degrees at 23°C and 100°C (according to ISO standard 48) were measured on samples of the aforesaid compositions cross-linked at 151°C for 30 minutes. The results are shown in Table 2B.
• Table 2B also shows the dynamic elastic properties, measured with a dynamic Instron device in the traction- compression mode according to the following method.
• the dynamic elastic properties are expressed in terms of dynamic elastic modulus (E') and tandelta (loss factor) values.
• the tandelta value is calculated as a ratio between the viscous modulus (E") and the elastic modulus (E') , both of them being determined with the above dynamic measurements .
• Sulfur-vulcanizable rubber compositions filled with silica were prepared with the same method described for Examples 4-5.
• the compositions are reported in Table 3A (in phr) .
• the masterbatch of PVA was used as an additive, maintaining the same amount of silica.
• the same compositions were prepared wherein polyethylene glycol (PEG 600) or sorbitol mono-oleate were used as silica stabilizers instead of the PVA masterbatch.
• SBR styrene/butadiene copolymer, obtained by emulsion polymerization, containing 25% by weight of styrene, mixed with 37.5 phr of extension oil (marketed by Bayer under the abbreviation SBR 5025) ;
• BR cis-1, 4-polybutadiene (product Europrene Neocis® BR 40 - Enichem Elastomeri)
• PEG 600 polyethylenglycol (product Lipoxol® 600 - Condea Chemie GmbH) ;
• SMO sorbitan mono-oleate (product Span® 80 - ICI)
• DPG diphenylguanidine (product Vulkacit® D Bayer)
• CBS N-cyclohexyl-2-benzothiazyl-sulfenamide (product Vulkacit® CZ - Bayer)
• Silane bis (3-triethoxysilylpropyl) tetrasulfide (product X50S comprising 50% carbon black and 50% silane - Degussa) (the value reported in the table refer to the actual amount of added silane) ;
• Antioxidant phenyl-p-phenylene diamine.
• Sulfur-vulcanizable rubber compositions filled with a mixture of silica and carbon black, were prepared with the same method described for Examples 4-5.
• the compositions are reported in Table 4A (in phr) .
• the masterbatch of PVA was used as a partial replacement of carbon black, while maintaining the same amount of silica.
• DBTL condensation catalyst
• SBR styrene/butadiene copolymer, obtained by emulsion polymerization, containing 40% by weight of styrene, mixed with 37.5 phr of extension oil (marketed by Bayer under the abbreviation SBR 1721);
• BR cis-1, 4-polybutadiene (product Europrene Neocis® BR 40 - Enichem Elastomeri);
• Silane bis (3-triethoxysilylpropyl) tetrasulfide (product X50S comprising 50% carbon black and 50% silane - Degussa) (the value reported in the table refer to the actual amount of added silane) ;
• Antioxidant phenyl-p-phenylene diamine.

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  • 2000-12-19 AU AU31608/01A patent/AU3160801A/en not_active Abandoned
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  • 2000-12-19 WO PCT/EP2000/012956 patent/WO2001049786A1/en not_active Application Discontinuation
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