Abstract:
The invention relates to a polymeric product (plastic or elastomeric) having domains of injected ingredients therein. A tire having precisely placed and oriented injected ingredients is described. The nature of the injected components, and their density, as well as their placement and orientation, are determined based on tire property enhancements desired. Fibers may be injected into the tread shoulder area of an uncured tire to provide abrasion resistance and traction in the cured tire. High tack rubbers or adhesives may be injected into the central tread region of a cured tire to enhance traction and grip.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to polymeric articles having domains of injected ingredients, and in an illustrated embodiment of the invention relates to tires made using elastomers that are injected with fiber reinforcement.  
         BACKGROUND OF THE INVENTION  
         [0002]    In general, the presence of short fibers in a cured rubber compound results in an increase in initial or low strain (low elongation) modulus (stiffness). Concomitantly, the presence of short fibers in rubber often times results in reduced fatigue endurance and in higher hysteretic heat build-up under periodic stresses.  
           [0003]    Various discontinuous short fibers have been used to enhance stiffness (modulus) of rubber vulcanizates. For example, discontinuous cellulose fibers have been used as dispersions in rubber as disclosed in U.S. Pat. Nos. 3,697,364; 3,802,478 and 4,236,563. Other discontinuous fibers have been suggested or used such as, for example, aromatic polyamides (aramids), aliphatic polyamides (nylon), cotton, rayon, polyester, glass, carbon and steel.  
           [0004]    Many of the polymeric fibers used in the tire art are known as fully or highly oriented short fibers. Elastomers reinforced with short fibers, for example Kevlar® pulp, demonstrate good stiffness. As the loading of Kevlar® pulp in an elastomer increases, the stiffness of the composite increases, but unfortunately, the crack growth resistance decreases.  
           [0005]    International patent application WO 90/04617 to Allied Signal Inc. teaches the preparation of partially oriented yarns (POY short fibers) and discloses that such short fibers can be used in tires.  
           [0006]    The application of these fibers to tires is described in U.S. Pat. No. 5,576,104 by The Goodyear Tire &amp; Rubber Company. Said patent is incorporated herein by reference.  
           [0007]    Although there has been interest in the use of short fibers for reinforcing plastic and polymeric products for many years, the potential for such reinforcement has not been fully developed due to limitations in extrusion and mixing. Under existing processing, fibers are typically introduced into the compound as an ingredient during the mixing stage. However, such mixes are limited to short length fibers, low fiber loading and low compound viscosity, because of the difficulties in processing due to the increase in compound viscosity caused by fiber incorporation. In addition, during compound mixing fibers tend to fracture and aggregate within the compound, producing pockets of poorly dispersed fibers within the compound matrix.  
           [0008]    After mixing, fibers in a compound are generally randomly oriented. Attempts at achieving directionally oriented fibers in rubber components have been met with some, but not complete success. During extrusion and calendering, fibers in a compound tend to align in the direction of flow, although the random fiber orientation introduced during the mixing stage can never be entirely eliminated due to the viscoelastic nature of the elastomer matrix. Thus, fiber orientation during processing can not be fully controlled, even by using highly aligning flow fields. As a consequence, complete, i.e. 100% fiber orientation cannot be achieved in the lengthwise direction of extruded or calendered components.  
           [0009]    Although some degree of lengthwise fiber orientation can be achieved via extrusion and calendering processes, and lengthwise orientation has advantages in some applications, it is hypothesized that fibers oriented perpendicular to the surface, or in the-thickness direction of a rubber component, can improve the abrasion and lateral stiffness properties of a component. However, such fiber composites cannot be produced by conventional processing operations.  
           [0010]    While very difficult to manufacture, attempts at achieving a perpendicular fiber orientation have been made by two methods. The first method is highly laborious and involves cutting small sections of calendered or extruded fiber-filled components, where some degree of lengthwise fiber orientation is obtained, then rotating the cut sections of the calendered sheet side by side to provide perpendicular fiber orientation. A second method involves extruding a short-fiber reinforced compound through an abrupt expansion die that causes the extrudate sheet to fold upon itself in an accordionlike manner, so that a lamellar-type structure is obtained with substantially perpendicularly oriented fiber reinforcement.  
           [0011]    It is an object of the invention to provide reinforced composites with precisely placed and angled ingredients.  
           [0012]    It is a further object of the invention to provide products having an elastomeric matrix having injected domains of precisely placed and oriented reinforcement.  
           [0013]    A tire made using a reinforced matrix of the invention is also disclosed.  
           [0014]    Other objects of the invention will be apparent from the following description and claims.  
         SUMMARY OF THE INVENTION  
         [0015]    The invention relates to a polymeric product having domains of injected ingredients therein. The injected ingredients are distributed in the product in a specific controlled pattern.  
           [0016]    In one embodiment, the injected ingredients may be fibers disposed in a plurality of groups, wherein all the fibers in each group have a controlled angle of orientation in the product. The fibers may be arranged in a geometric pattern.  
           [0017]    In an illustrated embodiment, the invention relates to a tire comprising at least one carcass ply, reinforcement disposed over the at least one carcass ply in a crown area of the tire, tread disposed over the reinforcement, and sidewalls disposed over the at least one carcass ply radially inward of the tread, at least one component of the tire having injected ingredients wherein the injected ingredients are distributed in the component in a specific, controlled pattern.  
           [0018]    The composite may be a tire tread, and the injected ingredients may be distributed in different zones of the tread in specific densities and specific angles of orientation. For example, the injected ingredients may be fibers having a fiber density greater in a shoulder zone of the tread than in a central zone of the tread.  
           [0019]    The angle of orientation of the fiber may vary with the curvature of the tread such that all fibers are at the same angle relative to the surface of the tread. Or, the fibers may all be parallel to one another regardless of the curvature of the tread. Alternatively, the angle of orientation of the fiber may vary with the curvature of the tread to provide maximum fiber reinforcement for the zone of the tread where the fiber is located.  
           [0020]    In an illustrated embodiment, the fibers are located in two shoulder zones and two center zones, wherein the fiber density in each shoulder zone is at least eight times the density of each center zone.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1 illustrates a tire which can be made using the composites of the invention.  
         [0022]    [0022]FIG. 2 illustrates an apparatus that can be used to inject fibers into a tire tread.  
         [0023]    [0023]FIG. 3 illustrates a top view of a pattern of fiber reinforcement in a tire tread.  
         [0024]    [0024]FIG. 4 illustrates a cross section of a tire tread with an alternative pattern of fiber reinforcement.  
         [0025]    [0025]FIG. 5 illustrates a composite comprising a second alternative pattern of fiber reinforcement. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]    In the conception of the present invention, based on the belief of the inventors that precise orientation of reinforcement fibers, in a fiber reinforced product, would significantly improve such reinforcement, the inventors proposed to precisely inject fibers into a product. By injecting fibers into a product, it is believed that the orientation (angle) of the fiber and concentration of the fiber can be controlled and optimized for most beneficial and efficient use of the fiber reinforcement. For example, the fiber reinforcement may be placed in a high density where most reinforcement is needed, and the fiber reinforcement may be precisely oriented (angled) to maximize the reinforcement.  
         [0027]    It will be apparent to those skilled in the art that the apparatus used in the invention can be used to inject a broad range of materials, e.g. reinforcing polymer blends, high tack adhesives, fillers, etc. into a polymeric substrate, e.g. plastics or elastomers. For ease of illustration, the invention will be described as it relates to the injection of fiber reinforcement into a tire or tire component. Those skilled in the art will recognize that tires can be made with other types of injected materials. In the illustrated embodiment, monofilament or yarn fibers can be used.  
         [0028]    Discrete fiber injection involves the injection of individual fibers into an uncured elastomer matrix to achieve precision fiber orientation and distribution within an elastomeric composite. The fibers are introduced into the elastomer after the mixing and shaping stages of processing, so discrete fiber injection is not limited as to fiber size, fiber loading, or compound viscosity.  
         [0029]    It is believed that the invention may be practiced with injectable fibers, or other injectable materials, at a density up to about 10 10  fibers per square inch.  
         [0030]    It is desirable to inject the reinforcing material into an uncured elastomer, especially a rubber. As the elastomer reaches curing temperature it flows, and the curing process enhances the mechanical trapping of reinforcement into the elastomer, and the curing process itself raises the possibility of cross-linking between the reinforcement and the elastomer.  
         [0031]    To fully understand the mechanisms of fiber reinforcement, it is necessary to know the structure of the fibers and how they are made, particularly in terms of orientation of the polymer chains in the fiber.  
         [0032]    Conventional fibers such as polyamides, polyesters and polyolefins have a flexible molecular chain structure and tend to crystallize into folded-chain crystalline domains. Fully oriented, or strictly speaking highly oriented, extended-chain crystalline fibers can be prepared by spinning liquid crystalline melts or solutions of stiff-chain polymers, known respectively as thermotropic and lyotropic polymers. When spinning liquid crystalline (anisotropic) melts or solutions, only the spinning process is required and drawing is not necessary to obtain highly oriented fibers.  
         [0033]    Highly oriented, extended-chain crystalline fibers are made from rigid-rod, aromatic heterocyclic polymers by a liquid crystalline solution-spinning route. The best known examples of this class of fibers are poly (p-phenylene-benzobisthiazole) or PBZT, and poly (p-phenylenebenzobisoxazole), known as PBZO.  
         [0034]    Highly oriented aramid fibers can also be prepared by conventional spinning of an isotropic solution of an aromatic copolyamide, followed by drawing of the spun fibers at very high temperatures and draw ratios. A fiber of this type, copoly (pphenylene/3,4-oxydiphenyleneterephthalamide), is made commercially by Teijin, Ltd., Japan, under the trade name Technora® and can be converted to a pulp that can be used in the hybrid reinforcement composites.  
         [0035]    Highly oriented, extended-chain crystalline fibers can also be produced from flexible chain polymers by a gel spinning technique. Examples of this type of fiber are polyvinylalcohol (PVA) fiber and some polyolefin fibers (e.g. polyethylene).  
         [0036]    It is noted that all these fibers, whether stiff or flexible chain, whether made by a liquid crystalline or a conventional solvent spinning process or via gel spinning, have one common characteristic, viz., a high degree of orientation. An ultra-high degree of orientation, and concomitant mechanical anisotropy, is the main microstructural feature responsible for the tendency of these fibers to undergo, to a greater or lesser extent, axial splitting and fibrillation under shear, yielding pulp-like products.  
         [0037]    In one embodiment of the invention, an elastomer composition employing POY (partially oriented yarn) short fibers can be used as a component in a pneumatic tire. In the illustrated embodiment, such reinforcement is used in the tread of a tire.  
         [0038]    Examples of specific fibers that can be partially oriented are nylon 6, nylon 46, nylon 66, polypropylene, polyethylene, polyethyleneterephthalate (PET) and polyethylenenaphthalate (PEN).  
         [0039]    In the tire illustrated in the present invention, where fibers are oriented in the tread of a tire for abrasion resistance and traction, it is believed that the highly oriented, stiff fibers will work best. Concept testing will employ steel fibers. Those skilled in the art will recognize that injected POY fibers and plastic reinforcement domains, as well as injectable filler materials and other reinforcement materials, may be suitable for other applications.  
         [0040]    Eastomers that can be used in a tire of the invention include, but are not limited to natural rubber, butadiene rubbers, polyisoprene rubber (IR), styrene butadiene rubber (SBR), butyl and halobutyl rubbers (IIR, BIIR, CIIR), ethylene propylene rubbers (EPM, EPDM), crosslinked polyethylene (XLPE) and chloroprene rubbers (CR), nitrile rubbers (NBR), and mixtures thereof.  
         [0041]    In an illustrated embodiment, the majority of fibers in the tread are oriented at a substantially 90° angle with respect to the surface of the tread of the tire.  
         [0042]    Any angle of orientation of the short fibers can be used.  
         [0043]    With reference now to FIG. 1, a tire ( 10 ) is illustrated which has been made with a fiber reinforced tread ( 22 ) of the invention. The crown area of the tire may be further reinforced by a belt package ( 26 ) which comprises belts or breakers ( 50 ), and an optional overlay ply ( 59 ).  
         [0044]    As is conventional in the art, the tire comprises a pair of beads ( 12 ) over which have been wrapped carcass plies ( 24 ). The turning up of carcass plies ( 24 ) over beads ( 12 ) forms apex ( 14 ) between carcass ( 24 ) and turn up ( 16 ). When a tubeless tire is made, the tire will have an inner liner ( 28 ) disposed inwardly of carcass ply ( 24 ). Tire ( 10 ) may also have optional chafer ( 36 ). The width of the tread (TW) is defined substantially as the part of the tire tread that is in contact with the ground when the tire is on the ground and is stationary. Those skilled in the art will recognize that during cornering, the shoulder portion of the tread ( 30   a ) may contact the road surface as well.  
         [0045]    Sidewalls ( 20 ) meet tread ( 12 ) at shoulder ( 30 ) to substantially complete the tire&#39;s construction. In the illustrated embodiment of FIG. 1, fiber reinforcement ( 16 ) has been injected into shoulder area ( 30   a ) at one fiber density, and into central lugs ( 34 ) at a different fiber density.  
         [0046]    The high density of fibers ( 16 ) in the shoulder region ( 30   a ) of the tread provides increased abrasion resistance where it is most needed in the tread, and may increase the tire&#39;s ability to hold the road when the tire corners, because of the potential biting effect of each individual fiber end.  
         [0047]    The use of fewer fibers ( 16 ) in lugs ( 34 ) means that the rubber in lugs ( 34 ) will have a modulus (hardness) less than that observed in the rubber seen in the shoulder area ( 30   a ) of the tread, which suggests that lugs ( 34 ) will show increased traction properties, relative to highly fiber-loaded shoulder areas ( 30   a ). The fiber ends contacting the road surface may also improve the lateral stability of the tire.  
         [0048]    The fibers may be injected into an uncured tire ( 10 ) by hand, which method is very labor intensive, or by using an automated apparatus as shown in FIG. 2. Such an automated apparatus is described in detail in copending Doc. No. (ID 1997-428), filed of even date herewith.  
         [0049]    In the automated apparatus shown in FIG. 2, a needle assembly  40  can be used to inject a fiber into a tire tread while the completed, uncured tire ( 10 ) rotates on a drum ( 42 ). The fiber may be injected at any desired angle, and may be injected at a fiber density that is appropriate for its intended purpose. In FIG. 2, a tire is illustrated with three rows of fibers injected in one shoulder ( 44 ), and six rows of fibers in opposite shoulder ( 46 ).  
         [0050]    The fibers may also be injected into product components separately, for example, into a tread, belt, apex or sidewall as they exit an extruder, wherein the fiber loaded component can be built into a tire, or other product where appropriate.  
         [0051]    [0051]FIG. 3 may be representative of a belt (conveyor belt, tire belt, or transmission belt, for example) or a tire tread or sidewall, or other elastomeric component ( 32 ). In the illustrated embodiment, the component ( 32 ) is injected with a higher concentration of injected material ( 38 ) (fibers, fillers, adhesives, high tack rubbers) at the edge ( 46 ) than in the center portion ( 48 ). Those skilled in the art will recognize the concentration of injectable material may vary as desired for a specific application.  
         [0052]    In a tire, the choice of the angle of the injection is determined based on the kind of forces encountered by, and the kind of surface the tire ( 10 ) is expected to encounter when being used. For example, with reference to FIG. 4, if the shoulder ( 52 ) of a tire tread ( 50 ) needs abrasion resistance, fibers ( 16 ) may be injected at an angle that will be normal (perpendicular) to the surface of the tread when the tire is cornering. To further illustrate, if traction on a smooth surface is desired, a high tack rubber may be injected into a central portion ( 54 ) of the tread ( 50 ) at an angle which maximizes contact between the high tack rubber in a rotating tread surface and a road surface.  
         [0053]    Alternatively, using the tire tread of FIG. 4 as an example, a higher density of fibers  16  may be incorporated in shoulder ( 52 ) of tread ( 50 ) where more reinforcement and traction is needed due to stresses on the shoulder of the tire during cornering. Lower densities of fiber ( 16 ) may be used in the center portion ( 54 ) of the tire where stresses and abrasion are less.  
         [0054]    For most applications, it is believed that orientation of the fibers perpendicular to the surface of the tread is most beneficial, although it may be speculated, for increased traction, that fibers may be oriented in the center of the tread at an acute angle that is chosen so that the fibers bite into the pavement during acceleration of the tire.  
         [0055]    Those skilled in the art will be able to determine suitable concentrations and orientations of injected reinforcement in other elastomeric components of a tire, such as apexes, sidewalls, toe guards etc., and in other products, such as conveyer belts, based on the stresses and forces that act on the component or product, using the principles described herein.  
         [0056]    With reference now to FIG. 5, in a further embodiment of the invention, the application of an injectable material may be asymmetrical, or a calculated random pattern can be used. For example, a tire tread ( 56 ) may have a higher concentration of injectable material in a shoulder area ( 60 ) of tread ( 56 ) than in shoulder area ( 58 ).  
         [0057]    Such a structure may be applicable to racing tires, for example, that are used on a circular or oval track, where the outside tire on the vehicle is subjected to higher cornering forces than the inside tire. In such an embodiment, the shoulder ( 60 ), with a high level of reinforcement, and an increased modulus, would represent the outside shoulder of the tire.  
         [0058]    While the invention has been variously illustrated and described, those skilled in the art will recognize that the invention can be variously modified and practiced without departing from the spirit of the invention.