Patent Application
20090165915
The present invention relates to a tire and to a crosslinkable elastomeric composition.
More in particular the present invention relates to a tire comprising at least one layer including a crosslinked elastomeric material having air barrier properties, said crosslinked elastomeric material being obtained by crosslinking a crosslinkable elastomeric composition comprising at least one butyl rubber, at least one reinforcing filler and at least one modified polycarboxylate.
Moreover, the present invention also relates to a crosslinkable elastomeric composition comprising at least one butyl rubber, at least one reinforcing filler and at least one modified polycarboxylate, as well as to a crosslinked manufactured article obtained by crosslinking said crosslinkable elastomeric composition.
The inner surface of tires, in particular of tubeless tires, generally includes a layer of crosslinked elastomeric material which is designed to prevent or retard air and moisture permeation and to maintain tire pressure, so ensuring a hermetic seal of the tire when the tire is installed on a rim and inflated. Said layer is often referred to as “liner” or “innerliner”.
Butyl rubbers and/or halogenated butyl rubbers are commonly used for making tire innerliners because they are relatively impermeable to air and moisture and exhibit other desirable physical properties such as, for example, flex fatigue resistance and age durability.
It is also known to use white filler in rubber compositions for tire innerliners.
For example, Japanese Patent Application 2004/204099 relates to a rubber composition comprising 100 pts. mass (in mass part) of a rubber component and 35-200 pts. mass of a white filler. As a rubber component, halogenated butyl rubbers and other diene rubbers such as, for example, natural or synthetic polyisoprene rubber, polybutadiene rubber, are disclosed. As a white fillers, titanium oxide, silica, calcium carbonate, magnesium carbonate, mica, zinc white, clay, are disclosed. The abovementioned rubber composition is said to be suitable for white and light-color innerliners. Adhesivity with other tire structural elements, durability and strength of said innerliners is said to be improved.
Furthermore, it is also known to add layered clays to crosslinkable elastomeric compositions in order to improve air barrier properties.
For example, International Patent Application WO 02/48257 relates to an elastomeric composition including an isobutylene-based copolymer such as, for example, a halogenated poly(isobutylene-co-p-methylstyrene), halogenated star branched butyl rubber, halogenated butyl rubber, or mixture thereof, at least one filler such as, for example, calcium carbonate, silica, carbon black, and a polybutene oil having a number average molecular weight greater than 400. Said elastomeric composition may also include an exfoliated clay which may be selected from natural or synthetic phyllosilicates, particularly smectite clays such as, for example, montmorillonite. The above-mentioned elastomeric composition is said to have improved air barrier properties and processing properties and to be particularly useful as an air barrier.
International Patent Application WO 02/100936 relates to a nanocomposite comprising a clay, an interpolymer, one or more exfoliating additives, wherein the exfoliating additive is an amine having the structure R2R3R4N, wherein R2, R3 and R4 are C1 to C20 alkyls or alkenes which may be identical or different. The interpolymer may be a copolymer of a C4 to C7 isomonoolefin derived units, a para-methylstyrene derived units and a para(halomethylstyrene) derived units. The clay may be selected from natural or synthetic phyllosilicates, particularly smectite clays such as, for example, montmorillonite. The abovementioned nanocomposite is said to have improved air barrier properties. A tire innerliner and a tire innertube comprising said nanocomposite are also disclosed.
International Patent Application WO 2004/005388 relates to a nanocomposite comprising a clay and an elastomer comprising C2 to C10 olefin derived units, wherein said elastomer also comprises functionalized monomer units pendant to the elastomer. Preferably, the elastomer is selected from poly(isobutylene-co-p-alkylstyrene) elastomers and poly(isobutylene-co-isoprene) elastomers, which are functionalized by reacting free radical generating agents and unsaturated carboxylic acids, unsaturated esters, unsaturated imides, and the like, with the elastomer. The abovementioned nanocomposite is said to have improved air barrier properties and to be particularly useful for tire innerliner and innertubes.
European Patent Application EP 1,408,074 relates to a rubber compound comprising at least one solid, optionally halogenated, butyl elastomer and at least one nanoclay such as natural or synthetic clays, optionally modified with organic modifiers, such as, for example, smectite clays (for example, sodium or calcium montmorillonite). The abovementioned rubber compound is said to have low die swell, less mill shrinkage, faster extrusion times and improved heat aging combined with a lower Mooney scorch. The abovementioned rubber compound is said to be particularly suitable for a number of applications such as, for example, tire treads and tire sidewalls, tire innerliners, tank linings, hoses, rollers, conveyors belts, curing bladders, gas masks, pharmaceutical enclosures and gaskets.
Japanese Patent Application 2003/335902 relates to a rubber composition formed by mixing 100 parts by weight of solid rubber and 1-150 parts by weight of an organically treated layered mineral clay, which further includes 1-50 parts by weight of liquid rubber having an ammonium salt structure produced from liquid rubber containing a maleic anhydride structure, said liquid rubber being used as a compatibilizing agent for said solid rubber and layered mineral clay. The solid rubber may be selected from diene rubber or hydrogenated diene rubber, olefin rubber, halogen containing rubber, silicone rubber, thermoplastic rubber. The organically treated layered clay may be selected from natural or synthetic clays such as smectites (for example, montmorillonite). The abovementioned rubber composition is said to be useful for pneumatic tires innerliners.
The Applicant has faced the problem of obtaining crosslinkable elastomeric compositions having improved air barrier properties.
The Applicant has now found that it is possible to obtain crosslinkable elastomeric compositions that may be advantageously used in the manufacturing of crosslinked manufactured products, in particular in the manufacturing of tires, more in particular in the manufacturing of tire innerliners, by adding to the crosslinkable elastomeric compositions at least one reinforcing filler and at least one modified polycarboxylate as defined hereinbelow.
Said crosslinkable elastomeric compositions show improved air barrier properties. Moreover, said improvements are obtained without negatively affecting mechanical properties (both static and dynamic) of the crosslinked elastomeric compositions. Furthermore, a good processability and extrudability of the same is obtained as shown by their viscosity values.
According to a first aspect, the present invention relates to a tire comprising:
For the purposes of the present description and of the claims which follow, the term “phr” means the parts by weight of a given component of the elastomeric composition per 100 parts by weight of the rubber.
For the purpose of the present description and of the claims which follow, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term “about”. Also, all ranges include any combination of the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.
According to one preferred embodiment, said at least one layer including a crosslinked elastomeric material having air barrier properties is applied in a radially inner position with respect to said carcass structure.
According to a further preferred embodiment, said at least one layer including a crosslinked elastomeric material having air barrier properties is a tire innerliner.
According to further embodiment, said at least one layer including a crosslinked elastomeric material having air barrier properties is included in said at least one carcass ply. In this case, said at least one layer including a crosslinked elastomeric material having air barrier properties may be the layer which at least partially coats the plurality of reinforcing cords arranged parallel to each other which are generally included in the carcass ply. Alternatively, in the case in which more carcass plies are present, said at least one layer including a crosslinked elastomeric material having air barrier properties may be placed between two of said carcass plies.
According to a further aspect, the present invention also relates to a crosslinkable elastomeric composition comprising:
According to one preferred embodiment, said crosslinkable elastomeric composition may further comprise (e) at least one polyoxyalkylene glycol in an amount of from 0 phr to 10 phr, preferably of from 0.5 phr to 5 phr.
According to a further preferred embodiment, said crosslinkable elastomeric composition may further comprise (f) at least one silane coupling agent in an amount of from 0 phr to 10 phr, preferably of from 0.5 phr to 5 phr.
According to a further aspect, the present invention also relates to a crosslinked manufactured article obtained by crosslinking a crosslinkable elastomeric composition above disclosed. Preferably, said crosslinked manufactured article is an inner tube to be fitted into a tire.
According to one preferred embodiment, said butyl rubber (a) may be selected from isobutyl rubbers.
Preferably, said isobutyl rubbers may be selected from homopolymers of isoolefin monomer containing from 4 to 12 carbon atoms or copolymers obtained by polymerizing a mixture comprising at least one isoolefin monomer containing from 4 to 12 carbon atoms and at least one conjugated diolefin monomer containing from 4 to 12 carbon atoms.
Preferably, said copolymers contain from 70% by weight to 99.5% by weight, preferably from 85% by weight to 95.5% by weight, based on the hydrocarbon content of the copolymer, of at least one isoolefin monomer and from 0.5% by weight to 30% by weight, preferably of from 4.5% by weight to 15% by weight, based on the hydrocarbon content of the copolymer, of at least one conjugated diolefin monomer.
Preferably, the isoolefin monomer may be selected from C4-C12 compounds such as, for example, isobutylene, isobutene, 2-methyl-1-butene, 3-methyl-1-butene, 2-methyl-2-butene, methyl vinyl ether, indene, vinyltrimethylsilane, hexene, 4-methyl-1-pentene, or mixtures thereof. Isobutylene is preferred.
Preferably, the conjugated diolefin monomer may be selected from C4-C14 compounds such as, for example, isoprene, 1,3-butadiene, 2,3-dimethyl-1,3-butadiene, myrcene, 6,6-dimethyl-fulvene, hexadiene, cyclopentadiene, piperylene, or mixtures thereof. Isoprene is preferred.
Other polymerizable monomers such as, for example, styrene, styrene optionally substituted with C1-C4-alkyl groups or halogen atoms, such as, for example, methylstyrene, dichlorostyrene, may also be present in the abovementioned isobutyl rubbers.
According to one preferred embodiment, the isobutyl rubbers may be selected from copolymers containing from 95% by weight to 99.5% by weight based on the hydrocarbon content of the copolymer of isobutylene and from 0.5% by weight to 5% by weight based on the hydrocarbon content of the copolymer of isoprene.
Further details regarding isobutyl rubbers and the methods for their preparation may be found, for example, in U.S. Pat. No. 2,356,128, U.S. Pat. No. 3,968,076, U.S. Pat. No. 4,474,924, U.S. Pat. No. 4,068,051, or U.S. Pat. No. 5,532,312.
Examples of commercially available isobutyl rubbers which may be used in the present invention are the products Exxon® butyl grade of poly(isobutylene-co-isoprene), or Vistanex® polyisobutylene rubber, from Exxon.
According to a further preferred embodiment, said butyl rubber (a) may be selected from halogenated butyl rubbers.
Halogenated butyl rubbers are derived from the butyl rubbers above disclosed by reaction with chlorine or bromine according to methods known in the art. For example, the butyl rubber may be halogenated in hexane diluent, working at a temperature of from 40° C. to 60° C., using bromine or chlorine as the halogenation agent. Preferably, the halogen contents is from 0.1% by weight to 10% by weight, preferably from 0.5% by weight to 5% by weight, based on the weight of the halogenated butyl rubber.
Halogenated butyl rubbers that are particularly preferred according to the present invention are chlorobutyl rubbers, bromobutyl rubbers, or mixtures thereof.
Further details regarding the halogenated butyl rubbers and the methods for their preparation may be found, for example, in U.S. Pat. No. 2,631,984, U.S. Pat. No. 3,099,644, U.S. Pat. No. 4,554,326, U.S. Pat. No. 4,681,921, or U.S. Pat. No. 5,681,901.
Examples of commercially available chlorobutyl and bromobutyl rubbers which may be used in the present invention are the products Chlorobutyl 1240, or Bromobutyl 2030, from Lanxess.
According to a further preferred embodiment, said butyl rubber (a) may be selected from branched or “star-branched” butyl rubbers (SBB), halogenated “star-branched” butyl rubbers (HSSB), or mixtures thereof.
Preferably, the star branched butyl rubber is a composition of a butyl rubber, either halogenated or not, and a polydiene or block copolymer, either halogenated or not. The polydiene/block copolymer or branching agents (hereinafter referred to as “polydienes”), are typically cationically reactive and are present during the polymerization of the butyl rubber, or may be blended with the butyl rubber to form the star branched butyl rubber.
More particularly, the star branched butyl rubber is typically a composition of the butyl or halogenated butyl rubber as disclosed above and a copolymer of a polydiene and a partially halogenated polydiene selected from the group comprising styrene, polybutadiene, polyisoprene, polypiperylene, natural rubber, styrene-butadiene rubber, ethylene-propylene diene rubber (EPDM), ethylene-propylene rubber (EPM), styrene-butadiene-styrene or styrene-isoprene-styrene block copolymers, or mixtures thereof. These polydienes are present, based on the monomer wt %, in an amount of from 0.3 wt % to 3 wt %, preferably of from 0.4 wt % to 2.7 wt %.
Further details regarding star branched or halogenated star branched butyl rubbers and methods for their preparation may be found, for example, in European Patent EP 678,529, or in U.S. Pat. No. 4,074,035, U.S. Pat. No. 5,071,913, U.S. Pat. No. 5,182,333, U.S. Pat. No. 5,286,804, or U.S. Pat. No. 6,228,978.
Examples of commercially available star branched butyl rubbers which may be used in the present invention are the products Chlorobutyl 1066, or Bromobutyl 2222, from Exxon Mobil.
According to a further preferred embodiment, said butyl rubber (a) may be selected from halogenated isobutylene/p-alkylstyrene copolymers.
Said halogenated isobutylene/p-alkylstyrene copolymers may be selected from copolymers of an isoolefin containing from 4 to 7 carbon atoms such as, for example, isobutylene, and of a p-alkylstyrene such as, for example, p-methylstyrene. Said copolymers are known in the prior art and are disclosed, for example, in U.S. Pat. No. 5,162,445.
Preferred products are those derived from the halogenation of a copolymer between an isoolefin containing from 4 to 7 carbon atoms such as, for example, isobutylene, and a comonomer such as p-alkylstyrene in which at least one of the substituents on the alkyl groups present in the styrene unit is a halogen, preferably chlorine or bromine.
Further details regarding the preparation of halogenated isobutylene/p-alkylstyrene copolymers that are suitable for carrying out the present invention are disclosed, for example, in U.S. Pat. No. 5,512,638.
Examples of halogenated isobutylene/p-alkylstyrene copolymers which may be used in the present invention and which are currently commercially available include the Exxpro® products from Exxon Mobil.
Mixtures of the above disclosed butyl rubbers may also be advantageously used for the aim of the present invention.
According to one preferred embodiment, said diene elastomeric polymer (b) may be selected from those commonly used in sulfur-crosslinkable elastomeric materials, that are particularly suitable for producing tires, that is to say from elastomeric polymers or copolymers with an unsaturated chain having a glass transition temperature (Tg) generally below 20° C., preferably in the range of from 0° C. to −110° C. These polymers or copolymers may be of natural origin or may be obtained by solution polymerization, emulsion polymerization or gas-phase polymerization of one or more conjugated diolefins, optionally blended with at least one comonomer selected from monovinylarenes and/or polar comonomers in an amount of not more than 60% by weight.
The conjugated diolefins generally contain from 4 to 12, preferably from 4 to 8 carbon atoms, and may be selected, for example, from the group comprising: 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, 3-butyl-1,3-octadiene, 2-phenyl-1,3-butadiene, or mixtures thereof. 1,3-butadiene or isoprene are particularly preferred.
Monovinylarenes which may optionally be used as comonomers generally contain from 8 to 20, preferably from 8 to 12 carbon atoms, and may be selected, for example, from: styrene; 1-vinylnaphthalene; 2-vinylnaphthalene; various alkyl, cycloalkyl, aryl, alkylaryl or arylalkyl derivatives of styrene such as, for example, α-methylstyrene, 3-methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2-ethyl-4-benzylstyrene, 4-p-tolylstyrene, 4-(4-phenylbutyl)styrene, or mixtures thereof. Styrene is particularly preferred.
Polar comonomers which may optionally be used may be selected, for example, from: vinylpyridine, vinylquinoline, acrylic acid and alkylacrylic acid esters, nitriles, or mixtures thereof, such as, for example, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, acrylonitrile, or mixtures thereof.
Preferably, the diene elastomeric polymers may be selected, for example, from: cis-1,4-polyisoprene (natural or synthetic, preferably natural rubber), 3,4-polyisoprene, polybutadiene (in particular polybutadiene with a high 1,4-cis content), optionally halogenated isoprene/isobutene copolymers, 1,3-butadiene/acrylonitrile copolymers, styrene/1,3-butadiene copolymers, styrene/isoprene/1,3-butadiene copolymers, styrene/1,3-butadiene/acrylonitrile copolymers, or mixtures thereof.
The above disclosed crosslinkable elastomeric composition may optionally comprise (b′) at least one elastomeric copolymer of ethylene and at least one α-olefin, optionally with a diene. The α-olefins generally contains from 3 to 12 carbon atoms, such as, for example, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, or mixtures thereof. The diene optionally present generally contains from 4 to 20 carbon atoms and is preferably selected from: 1,3-butadiene, isoprene, 1,4-hexadiene, 1,4-cyclohexadiene, 5-ethylidene-2-norbornene, 5-methylene-2-norbornene, vinylnorbornene, or mixtures thereof. Among these, the following are particularly preferred: ethylene/propylene copolymer (EPR), ethylene/propylene/diene copolymers (EPDM); or mixtures thereof.
Optionally, the diene elastomeric polymers and/or the elastomeric copolymers above disclosed may be functionalized by reaction with suitable terminating agents or coupling agents. In particular, the diene elastomeric polymers obtained by anionic polymerization in the presence of an organometallic initiator (in particular an organolithium initiator) may be functionalized by reacting the residual organometallic groups derived from the initiator with suitable terminating agents or coupling agents such as, for example, imines, carbodiimides, alkyltin halides, substituted benzophenones, alkoxysilanes or aryloxysilanes (see, for example, European Patent EP 451,604, or U.S. Pat. No. 4,742,124 or U.S. Pat. No. 4,550,142).
Optionally, the diene elastomeric polymer and/or the elastomeric copolymers above disclosed may include at least one functional group selected from carboxylic groups, carboxylate groups, anhydride groups, ester groups, epoxy groups, or mixtures thereof.
According to one preferred embodiment, said reinforcing filler (c) may be selected from: calcium carbonate, magnesium carbonate, titanium oxide, silica, mica, zinc white, clay, alumina, aluminosilicates, kaolin, carbon black, or mixtures thereof. Calcium carbonate, carbon black, or mixtures thereof are particularly preferred.
When silica is used as a reinforcing filler (c), said silica may generally be a pyrogenic silica or, preferably, a precipitated silica, with a BET surface area (measured according to ISO standard 5794/1) of from 50 m2/g to 500 m2/g, preferably of from 70 m2/g to 200 m2/g.
Moreover, when silica is used as a reinforcing filler, the crosslinkable elastomeric composition above disclosed may advantageously incorporate at least one silane coupling agent (g) capable of interacting with silica and of linking it to the elastomeric polymers during the vulcanization. Examples of silane coupling agents which may be used will be disclosed below.
When carbon black is used as a reinforcing filler (c), said carbon black reinforcing filler may be selected from those having a surface area of not less than 20 m2/g (determined by CTAB absorption as described in Standard ISO 6810:1995).
According to a further preferred embodiment, said reinforcing filler (c) may be selected from layered materials having an individual layer thickness of from 0.01 nm to 30 nm, preferably of from 0.05 nm to 15 nm, more preferably of from 0.1 nm to 2 nm.
According to one preferred embodiment, said layered material may be selected, for example, from: phyllosilicates such as: smectites, for example, montmorillonite, bentonite, nontronite, beidellite, volkonskoite, hectorite, saponite, sauconite; vermiculite; halloisite; sericite; aluminate oxides; hydrotalcite; or mixtures thereof. Montmorillonite, bentonite, or mixtures thereof, are particularly preferred. These layered materials generally contain exchangeable ions such as sodium (Na+), calcium (Ca2+), potassium (K+), magnesium (Mg2+), hydroxide (HO−), or carbonate (CO32−) present at the interlayer surfaces.
In order to render the layered materials more compatible with the rubber, said layered materials may be optionally treated with at least one compatibilizing agent. Said compatibilizing agent is capable of undergoing ion exchange reactions with the ions present at the interlayers surfaces of the layered materials.
Said compatibilizing agent may be selected, for example, from the quaternary ammonium or phosphonium salts having general formula (I):
wherein:
The treatment of the layered materials with the compatibilizing agent may be carried out according to known methods such as, for example, by an ion exchange reaction between the layered material and the compatibilizing agent: further details are described, for example, in U.S. Pat. No. 4,136,103, U.S. Pat. No. 5,747,560, or U.S. Pat. No. 5,952,093.
According to one preferred embodiment, the layered materials are untreated, i.e. they are not treated with a compatibilizing agent.
Example of layered materials which may be used according to the present invention and are available commercially are the products known by the name of Cloisite® Na+ from Southern Clays, or Bentonite® AG/3 from Dal Cin S.p.A.
According to one preferred embodiment, said copolymer of at least one ethylenically unsaturated carboxylic acid or a derivative thereof with at least one ethylenically unsaturated monomer containing at least one polyoxyalkylene side chain (d) may be selected from compounds having the following general formula (II):
wherein:
wherein:
According to one preferred embodiment, said copolymer of at least one ethylenically unsaturated carboxylic acid or a derivative thereof with at least one ethylenically unsaturated monomer containing at least one polyoxyalkylene side chain (d) has a weight-average molecular weight (Mw) of from 500 to 100,000, preferably of from 1,000 to 50,000, more preferably of from 2,000 to 30,000. Said weight average molecular weight (Mw) may be determined according to known techniques such as, for example, by gel permeation chromatography (GPC).
The copolymer of at least one ethylenically unsaturated carboxylic acid or a derivative thereof with at least one ethylenically unsaturated monomer containing at least one polyoxyalkylene side chain (d) above disclosed may be obtained by processes known in the art. For example, said copolymer may be obtained by the free-radical polymerization of about 1 wt % to 99 wt % of at least one unsaturated monocarboxylic or dicarboxylic acid or a derivative thereof (such as, for example, (meth)acrylic acid, maleic acid, maleic anhydride), with about 99 wt % to 1 wt % of at least one compound having the following general formula (VI):
wherein R and Y have the same meanings as above disclosed.
The copolymers so obtained may be further reacted with alkali metal hydroxides, alkaline-earth metal hydroxides, zinc hydroxide, or ammonium compounds.
Said copolymers may be terminated with hydrogen atoms or residues of the polymerization iniziators usually used such as, for example, peroxides, persulfates, azo-type iniziators.
Further details about the processes for producing said copolymers may be found, for example, in International Patent Application WO 03/106369, in U.S. Pat. No. 5,798,425, or U.S. Pat. No. 5,632,324, or in United States Patent Application US 2003/0144384.
Examples of copolymers of at least one ethylenically unsaturated carboxylic acid or a derivative thereof with at least one ethylenically unsaturated monomer containing at least one polyoxyalkylene side chain (d) which may be used in the present invention and which are currently commercially available are the products Melflux® from Degussa Construction Polymers (in particular, Melflux® PP100, Melflux® VP2651, Melflux® 1641), Narlex® from Alco Chemical (in particular, Narlex® D36, Narlex® D38), Peramin® Conpac S149 from Perstorp.
As disclosed above, said crosslinkable elastomeric composition may further comprise (e) at least one polyoxyalkylene glycol. Preferably, said polyoxyalkylene glycol may be selected, for example, from polyoxyethylene glycol, polyoxypropylene glycol, or mixtures thereof. Polyoxyethylene glycol is particularly preferred.
As disclosed above, said crosslinkable elastomeric composition may further comprise (f) at least one silane coupling agent.
According to one preferred embodiment, said silane coupling agent (f) may be selected from those having at least one hydrolizable silane group which may be identified, for example, by the following general formula (VII):
(R7)3Si—CnH2n—X (VII)
wherein the groups R7, which may be equal or different from each other, are selected from: alkyl, alkoxy or aryloxy groups, or from halogen atoms, on condition that at least one of the groups R7 is an alkoxy or aryloxy group; n is an integer of from 1 to 6, extremes included; X is a group selected from: nitroso, mercapto, amino, epoxy, vinyl, imido, chloro, —(S)mCnH2n—Si—(R7)3, or —S—COR7, in which m and n are integers of from 1 to 6, extremes included, and the groups R7 are defined as above.
Among the silane coupling agents that are particularly preferred are bis(3-triethoxysilylpropyl)tetrasulphide, or bis(3-triethoxysilylpropyl)disulphide. Said coupling agents may be used as such or as a suitable mixture with an inert filler (for example carbon black) so as to facilitate their incorporation into the rubber used.
The crosslinkable elastomeric composition above disclosed may be vulcanized according to known techniques, in particular with sulfur-based vulcanizing systems commonly used for elastomeric polymers. To this end, in the crosslinkable elastomeric composition, after one or more steps of thermal-mechanical processing, a sulfur-based vulcanizing agent is incorporated together with vulcanization accelerators. In the final processing step, the temperature is generally kept below 120° C. and preferably below 100° C., so as to avoid any unwanted pre-crosslinking phenomena.
The vulcanizing agent most advantageously used is sulfur, or molecules containing sulfur (sulfur donors), with accelerators and activators known to those skilled in the art.
Activators that are particularly effective are zinc compounds, and in particular ZnO, ZnCO3, zinc salts of saturated or unsaturated fatty acids containing from 8 to 18 carbon atoms, such as, for example, zinc stearate, which are preferably formed in situ in the elastomeric composition from ZnO and fatty acid, and also BiO, PbO, Pb3O4, PbO2, or mixtures thereof.
Accelerators that are commonly used may be selected from: dithiocarbamates, guanidine, thiourea, thiazoles, sulfenamides, thiurams, amines, xanthates, or mixtures thereof.
Said crosslinkable elastomeric composition may comprise other commonly used additives selected on the basis of the specific application for which the composition is intended. For example, the following may be added to said crosslinkable elastomeric composition: antioxidants, anti-ageing agents, plasticizers, adhesives, anti-ozone agents, modifying resins, fibers (for example Kevlar® pulp), or mixtures thereof.
In particular, for the purpose of further improving the processability, a plasticizer generally selected from mineral oils, vegetable oils, synthetic oils, or mixtures thereof, such as, for example, aromatic oil, naphthenic oil, phthalates, soybean oil, or mixtures thereof, may be added to said crosslinkable elastomeric composition. The amount of plasticizer generally ranges from 0 phr to 70 phr, preferably from 5 phr to 30 phr.
The above disclosed crosslinkable elastomeric composition may be prepared by mixing together the rubber components (i.e., the butyl rubber (a), the diene elastomeric polymer (b) and/or the other elastomeric polymer (b′) optionally present), the reinforcing filler (c) and the copolymer (d), with the other additives optionally present, according to techniques known in the art. The mixing may be carried out, for example, using an open mixer of open-mill type, or an internal mixer of the type with tangential rotors (Banbury) or with interlocking rotors (Intermix), or in continuous mixers of Ko-Kneader type (Buss), or of co-rotating or counter-rotating twin-screw type.
The present invention will now be illustrated in further detail by means of the attached
“a” indicates an axial direction and “r” indicates a radial direction. For simplicity,
The tire (100) comprises at least one carcass ply (101), the opposite lateral edges of which are associated with respective bead structures comprising at least one bead core (102) and at least one bead filler (104). The association between the carcass ply (101) and the bead core (102) is achieved here by folding back the opposite lateral edges of the carcass ply (101) around the bead core (102) so as to form the so-called carcass back-fold (101a) as shown in
Alternatively, the conventional bead core (102) can be replaced with at least one annular insert formed from rubberized wires arranged in concentric coils (not represented in
The carcass ply (101) generally consists of a plurality of reinforcing cords arranged parallel to each other and at least partially coated with a layer including a crosslinked elastomeric material having air barrier properties which may be made according to the present invention. These reinforcing cords are usually made of textile fibers, for example rayon, nylon or polyethylene terephthalate, or of steel wires stranded together, coated with a metal alloy (for example copper/zinc alloy, zinc/manganese alloy, zinc/molybdenum/cobalt alloy, and the like). Alternatively, in the case in which more carcass plies are present, said layer including a crosslinked elastomeric material having air barrier properties which may be made according to the present invention may be placed between two of said carcass plies (not represented in
The carcass ply (101) is usually of radial type, i.e. it incorporates reinforcing cords arranged in a substantially perpendicular direction relative to a circumferential direction. The core (102) is enclosed in a bead (103), defined along an inner circumferential edge of the tire (100), with which the tire engages on a rim (not represented in
A belt structure (106) is applied along the circumference of the carcass ply (101). In the particular embodiment in
A side wall (108) is also applied externally onto the carcass ply (101), this side wall extending, in an axially external position, from the bead (103) to the end of the belt structure (106).
A tread band (109), whose lateral edges are connected to the side walls (108), is applied circumferentially in a position radially external to the belt structure (106). Externally, the tread band (109) has a rolling surface (109a) designed to come into contact with the ground. Circumferential grooves which are connected by transverse notches (not represented in
A tread underlayer (111), is placed between the belt structure (106) and the tread band (109).
As represented in
Alternatively, the tread underlayer (111) may have a variable thickness in the transversal direction. For example, the thickness may be greater near its outer edges than at a central zone.
In
A strip made of elastomeric material (110), commonly known as a “mini-side wall”, may optionally be present in the connecting zone between the side walls (108) and the tread band (109), this mini-side wall generally being obtained by co-extrusion with the tread band and allowing an improvement in the mechanical interaction between the tread band (109) and the side walls (108). Alternatively, the end portion of the side wall (108) directly covers the lateral edge of the tread band (109).
In the case of tubeless tires, an innerliner (112), which may be made according to the present invention, which provides the necessary impermeability to the inflation air of the tire, may be provided in an inner position relative to the carcass ply (101).
In the case of a tire provided with an inner tube (not represented in
The process for producing the tire according to the present invention may be carried out according to techniques and using apparatus that are known in the art, as described, for example, in European Patent EP 199,064, or in U.S. Pat. No. 4,872,822, or U.S. Pat. No. 4,768,937, said process including at least one stage of manufacturing the crude tire and at least one stage of vulcanizing this tire.
More particularly, the process for producing the tire comprises the steps of preparing, beforehand and separately from each other, a series of semi-finished products corresponding to the various structural elements of the tire (for example, carcass plies, belt structure, bead wires, fillers, sidewalls, innerliner and tread band) which are then combined together using a suitable manufacturing machine. Next, the subsequent vulcanization step welds the abovementioned semi-finished products together to give a monolithic block, i.e., the finished tire.
The step of preparing the abovementioned semi-finished products will be preceded by a step of preparing and molding the various crosslinkable elastomeric compositions, of which said semi-finished products are made, according to conventional techniques.
The crude tire thus obtained is then passed to the subsequent steps of molding and vulcanization. To this end, a vulcanization mould is used which is designed to receive the tire being processed inside a molding cavity having walls which are countermolded to define the outer surface of the tire when the vulcanization is complete.
Alternative processes for producing a tire or parts of a tire without using semi-finished products are disclosed, for example, in the abovementioned European Patent Applications EP 928,680, or EP 928,702.
According to one preferred embodiment, said layer including a crosslinked elastomeric material (for example, said innerliner) is formed by a plurality of coils of a continuous elongated element. Said elongated element may be produced, for example, by extruding the crosslinkable elastomeric composition above disclosed. Preferably, said layer is assembled onto a support.
For the purposes of the present description and of the claims which follow, the term “support” is used to indicate the following devices:
an auxiliary drum having a cylindrical shape, said auxiliary drum preferably supporting a belt structure;
a shaping drum having a substantially toroidal configuration, said shaping drum preferably supporting at least one carcass structure with a belt structure assembled thereon;
a rigid support preferably shaped according to the inner configuration of the tire.
Further details regarding said devices and the methods of forming and/or depositing the above mentioned layer on a support are described, for example, in International Patent Application WO 01/36185, or in European Patent EP 976,536, both in the name of the Applicant, or in European Patent Applications: EP 968,814, EP 1,201,414, or EP 1,211,057.
The crude tire may be molded by introducing a pressurized fluid into the space defined by the inner surface of the tire, so as to press the outer surface of the crude tire against the walls of the molding cavity. In one of the molding methods widely practiced, a vulcanization chamber made of elastomeric material, filled with steam and/or another fluid under pressure, is inflated inside the tire closed inside the molding cavity. In this way, the crude tire is pushed against the inner walls of the molding cavity, thus obtaining the desired molding. Alternatively, the molding may be carried out without an inflatable vulcanization chamber, by providing inside the tire a toroidal metal support shaped according to the configuration of the inner surface of the tire to be obtained as described, for example, in European Patent EP 1,189,744.
At this point, the step of vulcanizing the crude tire is carried out. To this end, the outer wall of the vulcanization mould is placed in contact with a heating fluid (generally steam) such that the outer wall reaches a maximum temperature generally of from 100° C. to 230° C. Simultaneously, the inner surface of the tire is heated to the vulcanization temperature using the same pressurized fluid used to press the tire against the walls of the molding cavity, heated to a maximum temperature of from 100° C. to 250° C. The time required to obtain a satisfactory degree of vulcanization throughout the mass of the elastomeric material may vary in general from 3 min to 90 min and depends mainly on the dimensions of the tire. When the vulcanization is complete, the tire is removed from the vulcanization mould.
The present invention will be further illustrated below by means of a number of preparation examples, which are given for purely indicative purposes and without any limitation of this invention.
The elastomeric compositions given in Table 1 were prepared as follows (the amounts of the various components are given in phr).
All the components, except zinc oxide, antioxidant (6-PPD), sulfur, accelerator (MBTS 80), and retardant (PVI), were mixed together in an internal mixer (model Pomini PL 1.6) for about 4 min (1st Step). As soon as the temperature reached 120±5° C., the elastomeric material was discharged. The zinc oxide, antioxidant (6-PPD), sulfur, accelerator (MBTS 80), and retardant (PVI), were then added and mixing was carried out in an open roll mixer (2nd Step).
The Mooney viscosity ML(1+4) at 100° C. was measured, according to Standard ISO 289-1:1994, on the non-crosslinked elastomeric compositions obtained as disclosed above. The results obtained are given in Table 2.
The static mechanical properties according to Standard ISO 37:1994 as well as hardness in IRHD degrees at 23° C. according to ISO standard 48:1994, were measured on samples of the abovementioned elastomeric compositions vulcanized at 170° C. for 10 min. The results obtained are given in Table 2.
Table 2 also shows the dynamic mechanical properties, measured using an Instron dynamic device in the traction-compression mode according to the following methods. A test piece of the crosslinked elastomeric composition obtained as disclosed above (vulcanized at 170° C. for 10 min) having a cylindrical form (length=25 mm; diameter=14 mm), compression-preloaded up to a 25% longitudinal deformation with respect to the initial length, and kept at the prefixed temperature (23° C. or 70° C.) for the whole duration of the test, was submitted to a dynamic sinusoidal strain having an amplitude of ±3.5% with respect to the length under pre-load, with a 100 Hz frequency. The dynamic mechanical properties are expressed in terms of dynamic elastic modulus (E′) and Tan delta (loss factor) values. The Tan delta value is calculated as a ratio between viscous modulus (E″) and elastic modulus (E′).
The permeability was measured, at 23° C., according to ISO standard 2782:1995, on samples of the crosslinked elastomeric composition obtained as disclosed above (vulcanized at 170° C. for 10 min). To this purpose, test pieces having a diameter of 120 mm and a nominal thickness of 1 mm, were conditioned at 23° C. for 16 hours and then subjected to the permeability test: the results obtained are given in Table 2. In Table 2, the numbers relative to the air permeability are shown by taking the value of comparative Example 1 as 100: the lower the number, the better the air permeation resistance.
The elastomeric compositions given in Table 3 were prepared as follows (the amounts of the various components are given in phr).
All the components, except zinc oxide, antioxidant (6-PPD), sulfur, accelerator (MBTS 80), and retardant (PVI), were mixed together in an internal mixer (model Pomini PL 1.6) for about 4 min (1st Step). As soon as the temperature reached 120±5° C., the elastomeric material was discharged. The zinc oxide, antioxidant (6-PPD), sulfur, accelerator (MBTS 80), and retardant (PVI), were then added and mixing was carried out in an open roll mixer (2nd Step).
The Mooney viscosity ML(1+4) at 100° C. was measured, according to Standard ISO 289-1:1994, on the non-crosslinked elastomeric compositions obtained as disclosed above. The results obtained are given in Table 4.
The static mechanical properties according to Standard ISO 37:1994 as well as hardness in IRHD degrees at 23° C. according to ISO standard 48:1994, were measured on samples of the abovementioned elastomeric compositions vulcanized at 170° C. for 10 min. The results obtained are given in Table 4.
Table 4 also shows the dynamic mechanical properties, measured using an Instron dynamic device in the traction-compression mode according to the following methods. A test piece of the crosslinked elastomeric composition obtained as disclosed above (vulcanized at 170° C. for 10 min) having a cylindrical form (length=25 mm; diameter=14 mm), compression-preloaded up to a 25% longitudinal deformation with respect to the initial length, and kept at the prefixed temperature (23° C. or 70° C.) for the whole duration of the test, was submitted to a dynamic sinusoidal strain having an amplitude of ±3.5% with respect to the length under pre-load, with a 100 Hz frequency. The dynamic mechanical properties are expressed in terms of dynamic elastic modulus (E′) and Tan delta (loss factor) values. The Tan delta value is calculated as a ratio between viscous modulus (E″) and elastic modulus (E′).
The permeability was measured, at 23° C., according to ISO standard 2782:1995, on samples of the crosslinked elastomeric composition obtained as disclosed above (vulcanized at 170° C. for 10 min). To this purpose, test pieces having a diameter of 120 mm and a nominal thickness of 1 mm, were conditioned at 23° C. for 16 hours and then subjected to the permeability test: the results obtained are given in Table 4. In Table 4, the numbers relative to the air permeability are shown by taking the value of comparative Example 1 as 100: the lower the number, the better the air permeation resistance.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2005/012716 | 11/29/2005 | WO | 00 | 1/5/2009 |
