Patent Application
20080142142
Pneumatic self-supporting run-flat tires have been commercialized for several years. A self-supporting run-flat tire is a tire that does not require any components, either located inside the tire cavity or external to the tire, to enable the tire to continue to operate during under-inflated conditions. Such tires are provided with internal sidewall inserts that stiffen the tire sidewalls and support the tire load during under-inflated operations.
However, the increased stiffness of the tire sidewalls can result in reduced comfort during both normal and underinflated operation. As the tire travels over road irregularities, vibrations are transferred through the stiff sidewall inserts to the vehicle, reducing ride comfort. Attempts have been made to optimize the Shore A and other hardness properties of the sidewall inserts to maximize comfort while maintaining run-flat characteristics. However, this is still a trade-off between two tire properties.
During such under-inflated operations, stress may occur between the sidewall inserts and the carcass ply cords, leading to degradation of the inserts and/or the carcass.
The present invention is directed to a pneumatic run-flat tire, the tire comprising at least one carcass reinforcing ply, at least one pair of sidewall wedge inserts, and a belt reinforcing structure, the belt reinforcing structure comprising at least a pair of cross cord belt reinforcing plies, the tire being characterized by at least one pair of elastomeric layers each located radially inward of the at least one carcass reinforcing ply and radially outward of each of the sidewall wedge inserts; the elastomeric layers extending from axially inward of an edge of the belt reinforcing structure to at least a midpoint of a sidewall, the elastomeric layers comprising a rubber composition comprising:
The following definitions are controlled for the disclosed invention.
“Annular”; formed like a ring.
“Apex” means an elastomeric filler located radially above the bead core and between the plies and the turn-up ends of the plies. The apex is sometimes referred to as a “bead filler”.
“Aspect Ratio” (AR) means the ratio of the section height (SH) of a tire to its section width (SW). This term is also used to refer to the cross-sectional profile of the tire. A low-profile tire, for example, has a low aspect ratio.
“Axial” and “axially” are used herein to refer to lines or directions that are parallel to the axis of rotation of the tire.
“Bead” or “Bead Core” generally means that part of the tire comprising an annular tensile member of radially inner beads that are associated with holding the tire to the rim; the beads being wrapped by ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes or fillers, toe guards and chafers.
“Belt Structure” or “Reinforcement Belts” or “Belt Package” means at least two annular layers or plies of parallel cords, woven or unwoven, underlying the tread, unanchored to the bead, and having both left and right cord angles in the range from 170 to 270 relative to the equatorial plane (EP) of the tire.
“Bias ply tire” means a belted or circumferentially-restricted pneumatic tire in which at least one ply has cords which extend from bead to bead are laid at cord angles less than 65°, typically 15 to 40°, with respect to the equatorial plane (EP) of the tire. (Compare “Radial ply tire”.)
“Breaker” means the same as “Belt structure”.
“Carcass” means the tire structure apart from the belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads.
“Circumferential” most often means circular lines or directions extending along the perimeter of the surface of the annular tread of the tire, perpendicular to the axial direction. It can also refer to the direction of the sets of adjacent circular curves whose radii define the axial curvature of the tread, as viewed in cross section.
“Cord” means one of the reinforcement strands, including fibers, with which the plies and belts are reinforced.
“Crown” or “Tire crown” means the tread, tread shoulders and adjacent portions of the sidewalls.
“Equatorial Plane” (EP) means the plane perpendicular to the tire's axis of rotation and passing through the center of its tread, or the plane containing the circumferential centerline of the tread.
“EMT tire” means “extended mobility technology tire,” and can be used interchangeably with “runflat tire.”
“Inner liner” means the layer or layers of elastomer or other material that form the inside surface of a tubeless tire and that contain the inflating fluid (e.g., air) within the tire.
“Lateral” means a direction parallel to the axial direction.
“Meridional” refers to a direction parallel to the axial direction but, more specifically, to a laterally disposed curved line that lies in a plane that includes the axis of the tire.
“NRD” means nominal rim diameter, which is substantially equal to the diameter of the tire at the inner surface of the bead region. It is the outside diameter of a rim upon which the tire is intended to be mounted.
“Ply” means a cord-reinforced layer of rubber-coated radially deployed, parallel cords.
“Radial” and “radially” mean directions radially toward or away from the axis of rotation of the tire.
“Radial ply structure” means the one or more carcass plies or which at least one ply has reinforcing cords oriented at an angle of between 65 and 90 degrees with respect to the equatorial plane (EP) of the tire.
“Radial ply tire” means a belted or circumferentially-restricted pneumatic tire in which at least one ply has cords which extend from bead to bead are laid at cord angles between 65 and 90 degrees with respect to the equatorial plane (EP) of the tire.
“Runflat” or “runflat tire” is a pneumatic tire that is designed to provide limited service while uninflated or underinflated.
“Section height” (SH) means the radial distance from the nominal rim diameter (NRD) to the outer diameter of the tire at its equatorial plane (EP).
“Section width” (SW) means the maximum linear distance parallel to the axis of the tire and between the exterior of its sidewalls when and after the tire has been inflated at normal pressure for 24 hours, but unloaded, excluding elevations of the sidewalls due to labeling, decoration or protective bands.
“Shoulder” means the upper portion of sidewall just below the lateral edge of the tread.
“Tread” means the ground-contacting portion of the tire.
“Turn-up” or “turn-up end” means the end portion of a carcass reinforcing ply that extends radially outward, beyond the bead core around which the ply is wrapped (typically 180°).
“Sidewall” means that portion of a tire between the tread region and the and the bead region.
The invention will be described by way of example and with reference to the accompanying drawings in which:
The following language is of the best presently contemplated mode or modes of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. The reference numerals as depicted in the drawings are the same as those referred to in the specification. For purposes of this application, the various embodiments illustrated in the figures each sue the same reference numeral for similar components. The structures employed basically the same components with variations in location or quantity thereby giving rise to the alternative constructions in which the inventive concept can be practiced.
Located radially outward of the carcass structure is a belt structure. The belt structure has at least two cross cord reinforcing plies 22, 24. The plies 22, 24 are inclined at angles of 18° to 35° relative to the tire centerline CL, with the cords in each ply 22, 24 being oppositely inclined relative to the cords in the adjacent ply. While not illustrated in
Radially outward of the belt structure is a tread 25. The tread 25 will has a tread pattern comprised of a series of lateral and circumferential grooves, not illustrated. The tread is conventionally formed of a single elastomer, but may also be comprised of multiple elastomers, the different elastomers arranged radially in a cap/base formation or axially to create a zoned tread.
In accordance with one embodiment of the present invention, located between the carcass reinforcing ply 12 and the sidewall wedge insert 20 is an elastomeric layer 28. Formulated as a elastomeric component, the layer 28 acts as a barrier gum strip to reduce abrasion and penetration of carcass ply 12 into sidewall wedge insert 20 due to excess stress during a deflation event. The elastomer layer 28 is compounded from an elastomeric base.
To achieve the desired effect, in one embodiment as shown in
The thickness of the elastomeric layer 28 ranges from about 0.5 mm to about 2 mm. In another embodiment, the thickness of the elastomeric layer 28 ranges from about 0.8 mm to about 1.2 mm.
The tire 10 may generally be of a range of aspect ratio, as defined herein. In one embodiment, the aspect ratio is at least 0.5, or 50 percent.
The elastomer layer 28 comprises an elastomeric rubber compound. The elastomer rubber compound will have a hot rebound of at least 85, a cold rebound of at least 78, a Shore A hardness ranging from 60 to 65, and an elongation at break of at least 200 percent.
The phrase “rubber or elastomer containing olefinic unsaturation” is intended to include both natural rubber and its various raw and reclaim forms as well as various synthetic rubbers. In the description of this invention, the terms “rubber” and “elastomer” may be used interchangeably, unless otherwise prescribed. The terms “rubber composition”, “compounded rubber” and “rubber compound” are used interchangeably to refer to rubber which has been blended or mixed with various ingredients and materials and such terms are well known to those having skill in the rubber mixing or rubber compounding art. The term “phr” as used herein, and according to conventional practice, refers to “parts by weight of a respective material per 100 parts by weight of rubber, or elastomer.”
The rubber composition contains a rubber containing olefinic unsaturation. In one embodiment, the rubber is natural rubber (NR) or synthetic polyisoprene (IR, including cis 1,4-polyisoprene). The rubber may also include from about 10 to about 20 phr of polybutadiene rubber (BR) (including cis 1,4-polybutadiene). BR can be prepared, for example, by organic solution polymerization of 1,3-butadiene. The BR may be conveniently characterized, for example, by having at least a 90 percent cis 1,4-content.
In one embodiment, the rubber composition comprises a polyoctenamer. Suitable polyoctenamer may include cyclic or linear macromolecules based on cyclooctene, or a mixture of such cyclic and linear macromolecules. Suitable polyoctenamer is commercially available as Vestenamer 8012 or V6213 from Degussa AG High Performance Polymers. Vestenamer is a polyoctenamer produced in a methathesis reaction of cyclooctene. In one embodiment, the octenamer may have a weight averaged molecular weight of about 90,000 to about 110,000; a glass transition temperature of from about −65° C. to about −75° C.; a crystalline content of from about 10 to about 30 percent by weight; a melting point of from about 36° C. to about 54° C.; a thermal decomposition temperature of from about 250° C. to about 275° C.; a cis/trans ratio of double bonds of from about 20:80 to about 40:60; and Mooney viscosity ML 1+4 of less than 10.
In one embodiment, polyoctenamer is added in an amount ranging from 1 to about 20 phr. Alternatively, from about 5 phr to about 15 phr polyoctenamer is added to the rubber composition.
In addition to the polyoctenamer and rubber containing olefinic unsaturation in the rubber component of the tire, silica is present. The amount of silica may range from 15 to 40 phr. Preferably, the silica is present in an amount ranging from 20 to 35 phr.
The commonly-employed siliceous pigments which may be used in the rubber compound include conventional pyrogenic and precipitated siliceous pigments (silica), although precipitated silicas are preferred. The conventional siliceous pigments preferably employed in this invention are precipitated silicas such as, for example, those obtained by the acidification of a soluble silicate, e.g., sodium silicate.
Such conventional silicas might be characterized, for example, by having a BET surface area, as measured using nitrogen gas, preferably in the range of about 40 to about 600, and more usually in a range of about 50 to about 300 square meters per gram. The BET method of measuring surface area is described in the Journal of the American Chemical Society, Volume 60, Page 304 (1930).
The conventional silica may also be typically characterized by having a dibutylphthalate (DBP) absorption value in a range of about 100 to about 400, and more usually about 150 to about 300.
The conventional silica might be expected to have an average ultimate particle size, for example, in the range of 0.01 to 0.05 micron as determined by the electron microscope, although the silica particles may be even smaller, or possibly larger, in size.
Various commercially available silicas may be used, such as, only for example herein, and without limitation, silicas commercially available from PPG Industries under the Hi-Sil trademark with designations 210, 243, etc; silicas available from Rhone-Poulenc, with, for example, designations of Z1165MP and Z165GR and silicas available from Degussa AG with, for example, designations VN2 and VN3, etc.
The rubber composition substantially excludes carbon black as a filler. By substantially excludes, it is meant that carbon black is not included in the composition in amounts effective as a filler. However, some amount of carbon black may be present either as a contaminant or as a carrier for coupling agents such as sulfur containing organosilicon compounds. In such cases, the amount of carbon black will be less than 5 phr, and preferably less than 3 phr.
It may be preferred to have the rubber composition for use in the tire component to additionally contain a conventional sulfur containing organosilicon compound. Examples of suitable sulfur containing organosilicon compounds are of the formula:
Z-Alk-Sn-Alk-Z
in which Z is selected from the group consisting of
where R1 is an alkyl group of 1 to 4 carbon atoms, cyclohexyl or phenyl; R2 is alkoxy of 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8 carbon atoms; Alk is a divalent hydrocarbon of 1 to 18 carbon atoms and n is an integer of 2 to 8.
Specific examples of sulfur containing organosilicon compounds which may be used in accordance with the present invention include: 3,3′-bis(trimethoxysilylpropyl)disulfide, 3,3′-bis(triethoxysilylpropyl)disulfide, 3,3′-bis(triethoxysilylpropyl)tetrasulfide, 3,3′-bis(triethoxysilylpropyl)octasulfide, 3,3′-bis(trimethoxysilylpropyl)tetrasulfide, 2,2′-bis(triethoxysilylethyl)tetrasulfide, 3,3′-bis(trimethoxysilylpropyl)trisulfide, 3,3′-bis(triethoxysilylpropyl)trisulfide, 3,3′-bis(tributoxysilylpropyl)disulfide, 3,3′-bis(trimethoxysilylpropyl)hexasulfide, 3,3′-bis(trimethoxysilylpropyl)octasulfide, 3,3′-bis(trioctoxysilylpropyl) tetrasulfide, 3,3′-bis(trihexoxysilylpropyl)disulfide, 3,3-bis(tri-2″-ethylhexoxysilylpropyl)trisulfide, 3,3′-bis(triisooctoxysilylpropyl)tetrasulfide, 3,3′-bis(tri-t-butoxysilylpropyl)disulfide, 2,2′-bis(methoxy diethoxy silyl ethyl)tetrasulfide, 2,2′-bis(tripropoxysilylethyl)pentasulfide, 3,3′-bis(tricyclonexoxysilylpropyl)tetrasulfide, 3,3′-bis(tricyclopentoxysilylpropyl)trisulfide, 2,2′-bis(tri-2″-methylcyclohexoxysilylethyl)tetrasulfide, bis(trimethoxysilylmethyl)tetrasulfide, 3-methoxy ethoxy propoxysilyl 3′-diethoxybutoxy-silylpropyltetrasulfide, 2,2′-bis(dimethyl methoxysilylethyl)disulfide, 2,2′-bis(dimethyl sec.butoxysilylethyl)trisulfide, 3,3′-bis(methyl butylethoxysilylpropyl)tetrasulfide, 3,3′-bis(di t-butylmethoxysilylpropyl)tetrasulfide, 2,2′-bis(phenyl methyl methoxysilylethyl)trisulfide, 3,3′-bis(diphenyl isopropoxysilylpropyl)tetrasulfide, 3,3′-bis(diphenyl cyclohexoxysilylpropyl)disulfide, 3,3′-bis(dimethyl ethylmercaptosilylpropyl)tetrasulfide, 2,2′-bis(methyl dimethoxysilylethyl)trisulfide, 2,2′-bis(methyl ethoxypropoxysilylethyl)tetrasulfide, 3,3′-bis(diethyl methoxysilylpropyl)tetrasulfide, 3,3′-bis(ethyl di-sec. butoxysilylpropyl)disulfide, 3,3′-bis(propyl diethoxysilylpropyl)disulfide, 3,3′-bis(butyl dimethoxysilylpropyl)trisulfide, 3,3′-bis(phenyl dimethoxysilylpropyl)tetrasulfide, 3-phenyl ethoxybutoxysilyl 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(trimethoxysilyl-buten-2-yl)tetrasulfide, 4,4′-bis(trimethoxysilylcyclohexylene)tetrasulfide, 5,5′-bis(dimethoxymethylsilylpentyl)trisulfide, 3,3′-bis(trimethoxysilyl-2-methylpropyl)tetrasulfide, 3,3′-bis(dimethoxyphenylsilyl-2-methylpropyl)disulfide.
The preferred sulfur containing organosilicon compounds are the 3,3′-bis(trimethoxy or triethoxy silylpropyl)sulfides. The most preferred compounds are 3,3′-bis(triethoxysilylpropyl)disulfide and 3,3′-bis(triethoxysilylpropyl)tetrasulfide. Therefore as to the above formula, preferably Z is
where R2 is an alkoxy of 2 to 4 carbon atoms, with 2 carbon atoms being particularly preferred; alk is a divalent hydrocarbon of 2 to 4 carbon atoms with 3 carbon atoms being particularly preferred; and n is an integer of from 2 to 5 with 2 and 4 being particularly preferred.
The amount of the sulfur containing organosilicon compound of the above formula in a rubber composition will vary depending on the level of other additives that are used. Generally speaking, the amount of the compound of the above formula will range from 0.5 to 20 phr. Preferably, the amount will range from 1 to 10 phr.
It is readily understood by those having skill in the art that the rubber composition would be compounded by methods generally known in the rubber compounding art, such as mixing the various sulfur-vulcanizable constituent rubbers with various commonly used additive materials such as, for example, sulfur donors, curing aids, such as activators and retarders and processing additives, such as oils, resins including tackifying resins and plasticizers, fillers, pigments, fatty acid, zinc oxide, waxes, antioxidants and antiozonants and peptizing agents. As known to those skilled in the art, depending on the intended use of the sulfur vulcanizable and sulfur-vulcanized material (rubbers), the additives mentioned above are selected and commonly used in conventional amounts. Representative examples of sulfur donors include elemental sulfur (free sulfur), an amine disulfide, polymeric polysulfide and sulfur olefin adducts. Preferably, the sulfur-vulcanizing agent is elemental sulfur. The sulfur-vulcanizing agent may be used in an amount ranging from 0.5 to 8 phr, with a range of from 1.5 to 6 phr being preferred. Typical amounts of tackifier resins, if used, comprise about 0.5 to about 10 phr, usually about 1 to about 5 phr. Typical amounts of processing aids comprise about 1 to about 50 phr. Such processing aids can include, for example, aromatic, naphthenic, and/or paraffinic processing oils. Typical amounts of antioxidants comprise about 1 to about 5 phr. Representative antioxidants may be, for example, diphenyl-p-phenylenediamine and others, such as, for example, those disclosed in The Vanderbilt Rubber Handbook (1978), Pages 344 through 346. Typical amounts of antiozonants comprise about 1 to 5 phr. Typical amounts of fatty acids, if used, which can include stearic acid comprise about 0.5 to about 3 phr. Typical amounts of zinc oxide comprise about 2 to about 5 phr. Typical amounts of waxes comprise about 1 to about 5 phr. Often microcrystalline waxes are used. Typical amounts of peptizers comprise about 0.1 to about 1 phr. Typical peptizers may be, for example, pentachlorothiophenol and dibenzamidodiphenyl disulfide.
Accelerators are used to control the time and/or temperature required for vulcanization and to improve the properties of the vulcanizate. In one embodiment, a single accelerator system may be used, i.e., primary accelerator. The primary accelerator(s) may be used in total amounts ranging from about 0.5 to about 10, preferably about 0.8 to about 8, phr. In another embodiment, combinations of a primary and a secondary accelerator might be used with the secondary accelerator being used in smaller amounts, such as from about 0.05 to about 3 phr, in order to activate and to improve the properties of the vulcanizate. Combinations of these accelerators might be expected to produce a synergistic effect on the final properties and are somewhat better than those produced by use of either accelerator alone. In addition, delayed action accelerators may be used which are not affected by normal processing temperatures but produce a satisfactory cure at ordinary vulcanization temperatures. Vulcanization retarders might also be used. Suitable types of accelerators that may be used in the present invention are amines, disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides, dithiocarbamates and xanthates. Preferably, the primary accelerator is a sulfenamide. If a second accelerator is used, the secondary accelerator is preferably a guanidine, dithiocarbamate or thiuram compound.
Suitable antireversion agents as are known in the art may be used in an amount of 1 to 10 phr, including 1,3-bis(citraconimidomethyl)benzene and the like.
The mixing of the rubber composition can be accomplished by methods known to those having skill in the rubber mixing art. For example the ingredients are typically mixed in at least two stages, namely at least one non-productive stage followed by a productive mix stage. The final curatives including sulfur-vulcanizing agents are typically mixed in the final stage which is conventionally called the “productive” mix stage in which the mixing typically occurs at a temperature, or ultimate temperature, lower than the mix temperature(s) than the preceding non-productive mix stage(s). The rubber and compound is mixed in one or more non-productive mix stages. The terms “non-productive” and “productive” mix stages are well known to those having skill in the rubber mixing art. If the rubber composition contains a sulfur containing organosilicon compound, one may subject the rubber composition to a thermomechanical mixing step. The thermomechanical mixing step generally comprises a mechanical working in a mixer or extruder for a period of time suitable in order to produce a rubber temperature between 140° C. and 190° C. The appropriate duration of the thermomechanical working varies as a function of the operating conditions and the volume and nature of the components. For example, the thermomechanical working may be from 1 to 20 minutes.
Vulcanization of the pneumatic tire of the present invention is generally carried out at conventional temperatures ranging from about 100° C. to 200° C. Preferably, the vulcanization is conducted at temperatures ranging from about 110° C. to 180° C. Any of the usual vulcanization processes may be used such as heating in a press or mold, heating with superheated steam or hot air.
The invention is further illustrated by the following non-limiting examples.
In this Example, a rubber composition for use in the tire of the present invention is illustrated.
Rubber compositions containing the materials set out in Table 1 was prepared using multiple stages of addition (mixing); at least one non-productive mix stage and a productive mix stage. The non-productive stages were mixed for two minutes at a rubber temperature of 160° C. The drop temperature for the productive mix stage was 115° C.
The rubber compositions are identified as Sample 1 through Sample 2. The Samples were cured at about 160° C. for about 20 minutes. Table 2 illustrates the physical properties of the cured Samples 1 and 5. Samples were tested according to the following protocols:
1Budene 1207 from The Goodyear Tire & Rubber Company
2Zeosil 1165 MP from Rhone Poulenc Company
350 percent organosilicon sulfide type on carbon black carrier, X50S from Degussa
4sulfenamide and thiuram type
5p-phenylenediamine type
6Vestenamer 8012 from Degussa GmbH
The inventive tires were subjected to a runflat test to compare the tires' runflat abilities compared to the control tire. The lab runflat test, operated at 38° C., involved deflating the tires, loading the tires with an initial load equal to 55% of the tires' rated load carrying capacity, and running the tires at 88 kph. After a warm-up period of 176 km, the tire load is increased 5% every 88 km until the tires' runflat capacity is determined. The lab runflat test shows that the tires comprising the elastomeric layer were capable of achieving superior run-flat distances to the control/conventional run-flat tire. The numbers reported in Table 3 are normalized milages, where the mileage of the control tire is normalized at 100. The processing of sample 2 is also significantly improved in accordance with the increased green strength.
While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.
