Tire with optimized apex

A pneumatic tire is described having a triangular shaped apex which extends radially outward of the bead core, and wherein the apex is formed of at least two zones. Each zone is formed of a different material, wherein the first zone extends from the base of the apex to the tip of the apex, and the second zone is located adjacent the ply. The zones are preferably formed by extrusion to form one cohesive apex. The first zone is formed of a material having a G″/G′ ratio in the range of about 0.155 to about 0.183. The second zone is formed of a material having a G″/G′ ratio in the range of about 0.125 to about 0.133.

FIELD OF THE INVENTION

The invention relates in general to tire manufacturing, and more particularly to a tire component such as an apex.

BACKGROUND OF THE INVENTION

Tire manufacturers have progressed to more complicated designs due to an advance in technology as well as a highly competitive industrial environment. In particular, tire designers seek to use multiple rubber compounds in a tire in order to meet customer demands. Using multiple rubber compounds per tire can result in a huge number of compounds needed to be on hand for the various tire lines of the manufacturer. For cost and efficiency reasons, tire manufacturers seek to limit the number of compounds available due to the extensive costs associated with each compound. Each compound typically requires the use of a Banbury mixer, which involves expensive capital expenditures. Furthermore, Banbury mixers have difficulty mixing up tough or stiff rubber compounds. The compounds generated from the Banbury mixers are typically shipped to the tire building plants, thus requiring additional costs for transportation. The shelf life of the compounds is not finite, and if not used within a certain time period, is scrapped.

Thus an improved method and apparatus is desired which substantially reduces the need for the use of Banbury mixers while providing an apparatus and methodology to provide custom mixing at the tire building machine by blending of two or more compounds together, and controlling the ratio of the compounds and other additives. Both non-productive compounds and productive compounds could be blended together. It is further desired to have a system at the tire building machine which provides for the ability to manufacture customizable compounds with accelerators. Yet an additional problem to be solved is to generate the compounds continuously at the tire building machine.

One component of interest is the tire apex. The tire apex is of interest because an optimal design can lower tire rolling resistance. The tire apex is subject to varying levels of stress and strain depending upon the use. Selection of apex materials is often a compromise due to the nature of the stress-strain loading being location specific. In order to optimize the apex design, the optimal material needs to be selected. Thus an improved apex design is desired which improves rolling resistance.

DEFINITIONS

“Aspect Ratio” means the ratio of a tire's section height to its section width.

“Axial” and “axially” means the lines or directions that are parallel to the axis of rotation of the tire.

“Bead” or “Bead Core” means generally that part of the tire comprising an annular tensile member, the radially inner beads are associated with holding the tire to the rim 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 “Reinforcing Belts” 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 17° to 27° with respect to the equatorial plane of the tire.

“Bias Ply Tire” means that the reinforcing cords in the carcass ply extend diagonally across the tire from bead-to-bead at about 25-65° angle with respect to the equatorial plane of the tire, the ply cords running at opposite angles in alternate layers.

“Breakers” or “Tire Breakers” means the same as belt or belt structure or reinforcement belts.

“Carcass” means a laminate of tire ply material and other tire components cut to length suitable for splicing, or already spliced, into a cylindrical or toroidal shape. Additional components may be added to the carcass prior to its being vulcanized to create the molded tire.

“Circumferential” means lines or directions extending along the perimeter of the surface of the annular tread 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, which are used to reinforce the plies.

“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 within the tire.

“Inserts” means the reinforcement typically used to reinforce the sidewalls of runflat-type tires; it also refers to the elastomeric insert that underlies the tread.

“Ply” means a cord-reinforced layer of elastomer-coated, radially deployed or otherwise 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° with respect to the equatorial plane of the tire.

“Radial Ply Tire” means a belted or circumferentially-restricted pneumatic tire in which the ply cords which extend from bead to bead are laid at cord angles between 65° and 90° with respect to the equatorial plane of the tire.

“Sidewall” means a portion of a tire between the tread and the bead.

“Laminate structure” means an unvulcanized structure made of one or more layers of tire or elastomer components such as the innerliner, sidewalls, and optional ply layer.

“Productive compound” means a rubber compound that includes accelerators, sulfur and other materials needed to cure the rubber.

“Non-productive compound” means a rubber compound that does not have one or more of the following items: 1) accelerator; 2) sulfur; or 3) curing agent(s).

DETAILED DESCRIPTION OF THE INVENTION

I. Tire Construction

FIG. 1illustrates a bead area of a tire100of the present invention. The tire may be a passenger tire, a truck tire, a run flat tire or pneumatic tire suitable for other applications. The tire has conventional tire components such as a ground-engaging tread (not shown) that terminates in the shoulders at the lateral edges of the tread. Sidewalls160extend from the shoulders140and terminate in a pair of bead portions180, each bead portion180has an annular inextensible bead core200. The bead cores200are preferably constructed of a single or monofilament steel wire continuously wrapped and a suitable bead core construction is described in U.S. Pat. No. 5,263,526. The tire100has a carcass reinforcing structure220that extends from the first bead portion180through the first sidewall160, tread120, second sidewall portion160to the second bead portion180.

The carcass reinforcing structure220comprises at least one reinforcing ply. In the illustrated embodiment, there is a first radially inner reinforcing ply structure240, the ends of which are turned up around the bead cores200, and may further include an optional second radially outer second reinforcing ply structure260, the ends of which are turned about the bead cores200. Each ply240,260is formed from a single layer of parallel reinforcing cords. The cords may be made of any material normally used for cord reinforcement of rubber articles, for example, and not by way of limitation, rayon, nylon, polyester, and steel. Preferably, the cords are made of material having a high adhesion property with rubber and high heat resistance. While this embodiment has shown only two plies, any number of carcass plies may be used.

Located within each bead portion180and the radially inner portion of the sidewall160is an elastomeric apex280disposed between carcass plies240,260and the turnup ends of the first carcass ply240. The elastomeric apex280extends from the radially outer side of the bead cores200and up into the sidewalls160, gradually decreasing in cross-sectional width. The apex280terminates prior to the maximum section width of the tire100.

The apex280is preferably divided into at least two zones282,284. The first zone282extends from the outer surface of the bead to the tip287. The first zone282is formed of a first material designed to optimize the energy controlled deformation and is further described below. The apex further comprises and a second zone284which is located adjacent the ply turnup and at a radial location of between 1 to 4 bead diameters as measured from the center of the bead. The second zone is formed of a second material different than said first material, and designed to control or minimize the strain in the second zone. As shown inFIG. 1, the second zone is rectangular in shape and has a length oriented primarily in the radial direction and having a length of 2-3 bead diameters, and a width about ⅔ the width of the apex.

The apex280may further optionally comprise a third zone286which is the tip of the apex. The third zone may comprise the same material as the second zone.

Rolling resistance is directly related to energy loss Q of each tire component. Energy loss Q is directly proportionate to G″ or loss modulus, and also directly proportionate to G′ or storage modulus, as represented below.
Q≈G″*(G′)m-1

M is the deformation index. The deformation index can be further subdivided into three pure modes of deformationM=+1 for strain controlM=0 for energy controlM=−1 for stress control.

Thus depending upon the specific tire application, the tire apex can be subdivided into distinct energy control, stress control and strain control zones.FIG. 2illustrates finite element analysis of a radial medium truck tire wherein the apex has been analyzed. Shown inFIG. 2, the apex has two primary zones: an energy control zone282, and a strain control zone. The apex may further comprise a third zone286for strain control at the tip. In each zone, the heat generation and thus the rolling resistance can be minimized by optimizing the material properties. For the stress control zone a material is selected such that the G″/G′ ratio is minimized. For the energy control, G″/G′ or tan delta is minimized. And for strain control, G″ is minimized.

For the apex as shown inFIGS. 1 and 2, the first zone282is formed of a material having a G″/G′ ratio in the range of about 0.155 to about 0.183. The second zone284and third zone286is formed of a material having a G″/G′ ratio in the range of about 0.125 to about 0.133.

Unless otherwise noted, all G′ values are measured on a rubber sample at a sample temperature of 90° C., at a measurement frequency of 10 Hz and at a strain amplitude of 50%. The rubber sample is taken from a cured tire manufactured to the desired manufacturer specifications. For the purposes of this invention, the storage modulus property G′ is a viscoelastic property of a rubber composition and may be determined by a dynamic mechanical analyzer over a range of frequencies, temperature and strain amplitude. One example of a dynamic mechanical analyzer (DMA) suitable for measuring G′, G″ is model number DMA+450 sold by the 01-dB Metravib company. The DMA instrument uses dynamic mechanical analysis to evaluate rubber compositions. A cured sample of the respective rubber composition is subjected to a precisely controlled dynamic excitation (frequency and amplitude) at a frequency (Hertz) and temperature (° C.) and the sample stress response is observed by the instrument. The observed sample response can be separated, by the instrument, into viscous or loss modulus (G″) and elastic or storage modulus (G′) components. Unless otherwise indicated, all G″ are measured at the same conditions as G′.

In order to form the apex of multiple zones of different materials, the extruder apparati as described below may be utilized to continuously extrude an apex having the desired material zones. A computer controller may be used to divide the apex into a grid of small discrete annular subareas. For each discrete subarea, the desired material properties are selected. The extruder apparatus ofFIG. 6or7may be used to continuously extrude a strip of a first rubber compound having the desired characteristics of zone1. The extruder apparatus may also be used to extrude a second rubber compound having the desired characteristics of zone2. The apex may be divided into multiple zones, wherein each zone has a different material composition.

FIGS. 3 and 4illustrate a second embodiment of a bead area300of the present invention. The tire components are the same as described above, except for the apexes as described in detail, below. The bead area300is comprised of a first apex310and a second apex320. The first apex310is located radially inward of the second apex, and has a base312located adjacent the bead core200, and extends radially outward in a triangular shape forming a tip314. Located adjacent the first apex is the second apex320. The second apex320has a first end322located axially outward of the first apex and axially inward of the ply turnups242,262. The first end322extends radially inward in the vicinity of the bead core200. The second apex extends radially outward from the first end322and extends well past the tip314of the first apex and up into the sidewall area ending in second end324in the mid portion of the sidewall.

The first apex320is shown under a stress-strain finite element analysis inFIG. 4. The average deformation index for the first apex is 0.09, so that the apex in its entirety is under strain control. For strain control, the first apex310should be formed of a material having a G″/G′ ratio in the range of about 0.125 to about 0.133. The second apex320is shown under a stress-strain finite element analysis inFIG. 5. The average deformation index for the second apex320is 0.03, so that the apex is under energy control. For energy control, the second apex320is preferably selected from a material having a. G″/G′ ratio in the range of about 0.155-0.183.

FIG. 6illustrates a first embodiment of a method and apparatus10for a continuous mixing system suitable for use for making rubber compositions for tires or tire components. The continuous mixing system10is not limited to tire applications and may be used for example, to make other rubber components not related to tires such as conveyors, hoses, belts, etc. The continuous mixing system is particularly suited for making small tire components having a varying composition, such as inserts, apexes and treads (including those for retreaded tires). The mixing system may be provided directly at the tire or component building station for direct application of the rubber composition to a tire building drum or other component building apparatus. As shown inFIG. 6, the continuous mixing apparatus10includes a main extruder20. The main extruder20has an inlet22for receiving one or more rubber compositions as described in more detail, below. The main extruder may comprise any commercial extruder suitable for processing of rubber or elastomer compounds. The extruder may comprise a commercially available extruder commonly known by those skilled in the art as a pin type extruder, a twin screw or a single screw extruder, or a ring type of extruder. One commercially available extruder suitable for use is a multicut transfermix (MCT) extruder, sold by VMI Holland BV, The Netherlands. Preferably, the extruder has a length to diameter ratio (L/D) of about 5, but may range from about 3 to about 5. A ring type, pin type or MCT type of extruder is preferred, but is not limited to same. The main extruder20functions to warm up the compound A to the temperature in the range of about 80° C. to about 150° C., preferably about 90° C. to about 120° C., and to masticate the rubber composition as needed.

The main extruder inlet22receives a first compound A, which may be a productive or non-productive rubber composition. Examples of compound A compositions are described in more detail, below. Compound A is first extruded by a first extruder8and optionally a second pump5, preferably a gear pump. The extruder8may be a conventional pin type, ring type, dual screw or single screw type extruder. The pump5functions as a metering device and a pump and may have gears such as planetary gears, bevel gears or other gears. The extruder8and gear pump5may also be a combination unit. Preferably, the extruder8has an L/D of about 3, but may range from about 3 to about 6.

A second compound, referred to as “compound B” also enters the main extruder20at the inlet22and is mixed together with compound A as the compounds travel through the main extruder. Compound B may also comprise a productive or non-productive rubber composition. Examples of compound B compositions are described in more detail, below. Compound B is first extruded by second extruder40and optionally a second pump42, preferably a gear pump. The extruder40may be a conventional pin type, ring type, dual screw or single screw type extruder. The pump42functions as a metering device and a pump and may have gears such as planetary gears, bevel gears or other gears. The extruder40and gear pump42may also be a combination unit. Preferably, the extruder40has an L/D of about 3, but may range from about 3 to about 6.

The main extruder20blends compound A and compound B together in a precisely controlled amount. Oil may also be optionally injected into the main extruder22via an oil pump60. The oil pump may be located at any desired location, but is preferably located at the inlet22. The oil controls the viscosity of the compound mixture.

The apparatus10may further include a first additive pump70for pumping one or more additives such as a primary accelerator, which is added to the mixture at the main extruder inlet22. The apparatus may further include a second additive pumping device80for pumping one or more additives such as a secondary accelerator into the main extruder inlet22. The additive pumps70,80may be gear pumps, gear pump extruders, Venturi pumps or other pumping means known to those skilled in the art.

If more than one accelerator is used, they may be added into the mixture separately or together. For example, a primary accelerator and a secondary accelerator may both be added. Accelerators are used to control the time and/or temperature required for vulcanization and to improve the properties of the rubber. The accelerator may be in powder form or an encapsulated powder into a resin or rubber base. Examples of accelerator compositions are described in more detail, below.

Other additives include a curative agent or precursor, which may also be added to the mixer via additive pump90. One example of a curative agent is sulfur. The sulfur may be added in solid form. The additive pump90may be a gear pump, gear pump extruder combination, Venturi pump or other pumping means known to those skilled in the art.

Thus all of the constituents including compound A, compound B, sulfur, oil and any desired curative agents or precursors, or accelerators of the desired rubber composition are added to the inlet of the main extruder20. The main extruder blends all the constituents together and produces an output mixture of compound C which is a precise mixture of the A and B compound, optional oil the optional accelerant and optional additives. The output mixture of compound C exits the main extruder and enters an optional gear pump25. The optional gear pump25and main extruder20is preferably located in close proximity adjacent a tire component building station or tire building station95for direct application onto a core, mandrel, blank or tire building drum, as shown inFIG. 6. Gear pump25preferably has a special nozzle95or shaping die which applies the compound formulation output from the mixer exit directly onto the tire building machine95in strips which are wound onto a tire building drum or core.

The ratio of the volumetric flow rate of compound A to the volumetric flow rate of compound B is precisely controlled by the ratio of the speed of the gear pump5for compound A and the speed of gear pump42for compound B. For example, the compound output from the system10may comprise a ratio of 20% of compound A and 80% of compound B by volume, as shown inFIG. 3. Alternatively, the compound output from the system may comprise a mixture D having a ratio of 35% of compound B and 65% of compound A by volume. Alternatively, the compound output from the system may comprise a mixture Z having a ratio of 10% of compound B and 90% of compound A by volume. The ratio of compound A to compound B can thus range from 0:100% to 100%:0. The ratio may be adjusted instantaneously by varying the speeds of gear pumps25and42by a computer controller99. The computer controller99may additionally controls the extruder and gear pump operating parameters such as operating pressure, operating temperature, pump or screw speed.

Preferably, the computer controller99sets a pressure target value for the exit pressure of each extruder. The extruder speed is controlled by the controller, and is varied until the pressure target is met. The pressure target value affects the quality of mixing by causing backflow of the material in the extruder.

The system10of the present invention advantageously has a short residence time due to the following design features. First, all the components of compound C are added at the inlet of the main extruder. Because all the ingredients are added at the exact same location, precise formulations can be generated and controlled. Second, each extruder has a small length to diameter ratio. Third, the system is preferably located adjacent a component building station or tire building station to minimize the system line lengths in order to further reduce system residence time.

FIG. 7illustrates a second embodiment of the extruder apparatus of the present invention. Everything is the same as described above, except for the following. Compound A is fed into the inlet22of the main extruder20. Compound B passes through an extruder40in combination with a gear pump42as described above, and then is fed into the main extruder at a specific upstream location identified herein for reference purposes as “L.” A primary accelerator is pumped through a pumping device70and enters the main extruder at the same location L. An optional secondary accelerator passes through a pumping device80and then enters the main extruder20at the same location L. Other additives include a curative agent or precursor, which may also be added to the mixer at location L via additive pump90. Thus the addition of all the ingredients at the same extruder location allows for precise control of the compound constituents.

The following are compositions which may be used in conjunction with the invention.

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 4, alternatively about 0.8 to about 1.5, 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 vulcanized rubber. 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. In one embodiment, the primary accelerator is a sulfenamide. If a second accelerator is used, the secondary accelerator may be a guanidine, dithiocarbamate or thiuram compound. Suitable guanidines include dipheynylguanidine and the like. Suitable thiurams include tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetrabenzylthiuram disulfide.

Representative rubbers that may be used in the rubber compound include acrylonitrile/diene copolymers, natural rubber, halogenated butyl rubber, butyl rubber, cis-1,4-polyisoprene, styrene-butadiene copolymers, cis-1,4-polybutadiene, styrene-isoprene-butadiene terpolymers ethylene-propylene terpolymers, also known as ethylene/propylene/diene monomer (EPDM), and in particular ethylene/propylene/dicyclopentadiene terpolymers. Mixtures of the above rubbers may be used. Each rubber layer may be comprised of the same rubber composition or alternating layers may be of different rubber composition.

The rubber compound may contain a platy filler. Representative examples of platy fillers include talc, clay, mica and mixture thereof. When used, the amount of platy filler ranges from about 25 to 150 parts per 100 parts by weight of rubber (hereinafter referred to as phr). Preferably, the level of platy filler in the rubber compound ranges from about 30 to about 75 phr.

The various rubber compositions may be compounded with conventional rubber compounding ingredients. Conventional ingredients commonly used include carbon black, silica, coupling agents, tackifier resins, processing aids, antioxidants, antiozonants, stearic acid, activators, waxes, oils, sulfur vulcanizing agents and peptizing agents. As known to those skilled in the art, depending on the desired degree of abrasion resistance, and other properties, certain additives mentioned above are commonly used in conventional amounts. Typical additions of carbon black comprise from about 10 to 150 parts by weight of rubber, preferably 50 to 100 phr. Typical amounts of silica range from 10 to 250 parts by weight, preferably 30 to 80 parts by weight and blends of silica and carbon black are also included. Typical amounts of tackifier resins comprise from about 2 to 10 phr. Typical amounts of processing aids comprise 1 to 5 phr. Typical amounts of antioxidants comprise 1 to 10 phr. Typical amounts of antiozonants comprise 1 to 10 phr. Typical amounts of stearic acid comprise 0.50 to about 3 phr. Typical amounts of accelerators comprise 1 to 5 phr. Typical amounts of waxes comprise 1 to 5 phr. Typical amounts of oils comprise 2 to 30 phr. Sulfur vulcanizing agents, such as elemental sulfur, amine disulfides, polymeric polysulfides, sulfur olefin adducts, and mixtures thereof, are used in an amount ranging from about 0.2 to 8 phr. Typical amounts of peptizers comprise from about 0.1 to 1 phr.

The rubber composition may also include up to 70 phr of processing oil. Processing oil may be included in the rubber composition as extending oil typically used to extend elastomers. Processing oil may also be included in the rubber composition by addition of the oil directly during rubber compounding. The processing oil used may include both extending oil present in the elastomers, and process oil added during compounding. Suitable process oils include various oils as are known in the art, including aromatic, paraffinic, naphthenic, vegetable oils, and low PCA oils, such as MES, TDAE, SRAE and heavy naphthenic oils. Suitable low PCA oils include those having a polycyclic aromatic content of less than 3 percent by weight as determined by the IP346 method. Procedures for the IP346 method may be found in Standard Methods for Analysis & Testing of Petroleum and Related Products and British Standard 2000 Parts, 2003, 62nd edition, published by the Institute of Petroleum, United Kingdom.

Variations in the present inventions are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described which will be within the full intended scope of the invention as defined by the following appended claims.