WO2001017800A1

WO2001017800A1 - A precured non-cord reinforced carcass

Info

Publication number: WO2001017800A1
Application number: PCT/US1999/020979
Authority: WO
Inventors: Frederick Forbes Vannan, Jr.; William Allen Rex; Brian Joseph Wilson; Kevin James Pyle; Scott Richard Harshbarger
Original assignee: The Goodyear Tire & Rubber Company
Priority date: 1999-09-09
Filing date: 1999-09-09
Publication date: 2001-03-15
Also published as: AU5920699A

Abstract

A precured non-cord reinforced tire carcass (20) having a nominal rim diameter of at least 6.0 inches (15.25 cm) has a pair of bead portions (22), a pair of sidewall portions (16, 18), a central crown portion (14), all made from a single elastomeric rubber alloy material (2). The carcass (20) further can be simultaneously formed with a tread (12) all made from the same material (2), thereby making a complete tire (10).

Description

A PRECURED NON-CORD REINFORCED CARCASS Technical Field This invention relates to pneumatic tires. More particularly, the invention is directed to a tire or tire carcass that requires no cord reinforcement. Background of the Invention

Generally the pneumatic tire has been produced by forming a toroidally-shaped carcass having one or more layers of plies reinforced by cords. These cords are generally arranged in a paralleled orientation within each layer. Bias plied tires have the cords oriented in equal but opposite directions in each adjacent layer or ply. Radial ply tires have the cords oriented generally about 90° relative to the tire's centerplane.

The carcasses have a variety of other components, each designed for a specific function or task. The combination of tire components, after undergoing a procedure commonly referred to as "vulcanization", results in a composite structure recognized in the art as a pneumatic tire.

Ideally, tire engineers strive to achieve tire performance objectives while also reducing the cost. This can be accomplished by either processing improvements or material changes.

Modern tire factories are and continue to evolve into a highly capital intensive industry. The tire carcass of the present invention greatly simplifies the manufacture of tires resulting in huge opportunities to niinimize cost.

The present invention can result in a tire carcass that is a single component formed by a single material that is vulcanized as it is being formed.

The preferred embodiment invention can also include an integral tread portion such that the article of manufacture can be the complete tire requiring no other components other than the rim to which the tire is to be mounted.

The concept, as described above, is best performed by selecting a single compound calling for a unique elastomeric rubber alloy material for the carcass and by injection or compression transfer molding that compound to form the tire carcass or tire.

Unlike any of the prior art tires used in the toy industry, this tire preferably has a nominal rim diameter of about 6 inches (15 cm) or greater and is designed to meet the performance criteria of conventional tires.

The resultant tire carcass is suitable for a variety of uses in applications such as, but not limited to, passenger or light truck vehicles, lawn and garden tractors and mowers, golf cart tires and other all-terrain vehicle tires. The concept of a single compound for forming a tire is well known and common in such areas as toys wherein plastic or rubber tires are made from a single material. Unlike these small reduced scale concepts, the present application is a full scale tire carcass subject to real use conditions. Heretofore, materials to make such a tire have been unavailable. Recent developments in the field of rubber compounding technology has resulted in rubber compositions known as rubber alloys. These alloys have thermoplastic side chains grafted thereto, the thermoplastic being selected from the groups consisting of, but not limited to, nylons, polypropylene, and polyphenylene oxides. These alloys can be compounded extremely tough and having unique physical properties that enable the carcass to be manufactured from a single compound.

Prior attempts to make non-reinforced tires have been disclosed in U.S. Patent Nos. 4,061,171 and 4,230,169; both patents having Jacques Boileau of Michelin as the inventor. Both patents disclose the need for additional rubber mass in either the bead area or in the tread sidewall areas. Neither invention disclose the use of alloy type rubber materials for the forming of a tire carcass. Such materials were not known in the mid-1970's and, as a result, such tires were never commercialized.

This recent breakthrough in compounding an alloy rubber enables the process tooling and method of manufacturing to be greatly simplified. The following discloses the article and a preferred method of manufacturing the article. Disclosure of the Invention

Summary of the Invention

A precured non-cord reinforced tire carcass (20) has a pair of radially inner bead portions (22), a pair of sidewall portions (16, 18), one sidewall portion (16, 18) extending from each bead portion (22) radially outwardly, and a central crown portion (14) extending from and between each radially outer portion of the sidewall portions (16, 18).

The combination of bead portions (22), sidewall portions (16, 18) and crown portions (14) define the peripheral boundary of an internal chamber (15) of the tire when mounted on a rim (30).

The carcass (20) has the bead portions (22), sidewall portions (16, 18) and the crown portions (14) all made of the same elastomeric material (2), the elastomeric material (2) being a rubber alloy of rubber and one or more thermoplastic material having side chains grafted to the rubber. The vulcanized compound (2) has a modulus at 100% of at least 5.0 MPa and a percent elongation of at least 100% and a Shore A hardness of less than 100 at room temperature.

Preferably, the formed carcass (20) of the vulcanized compound of the rubber alloy material (2) has a percent elongation of less than 400 % . In one embodiment, the invention incorporates all of the features of the non-cord reinforced carcass (20) with a tread portion (12) disposed radially outward of the crown portion (14) of the non-cord reinforced carcass (20), thus, forming a tire (10).

Interposed between the tread (12) and the carcass (20) can be a belt reinforcing structure (36) having two or more belt reinforcing plies (50, 51). Additionally, the tire (10) may further have an overlay (59) having substantially circumferentially extending cords disposed radially outward of the belt reinforcing structure (36).

In one embodiment, the tread (12) is made from the carcass rubber alloy material (2). In that embodiment, the tread (12) is integrally attached to the carcass (20). Preferably, the tread (12) and carcass (20) are simultaneously formed by injection molding. Preferably the resultant tire (10) has a nominal rim diameter of 6.0 inches (15 cm) or more.

Brief Description of Drawings

FIGURE 1 is a cross-sectional view of the precured non-cord reinforced carcass. FIGURE 2 is a cross-sectional view of the precured non-cord reinforced carcass with a tread and belt reinforcing structure applied.

FIGURE 3 is a preferred embodiment of the invention wherein a tire is shown in cross- section, the tire has the tread and non-cord reinforced carcass simultaneously formed.

FIGURE 4 is a schematic view of the carcass being formed in an injection molding machine having a solid core mold. FIGURE 5A, 5B and 5C are schematic views of the carcass (20) being removed from the mold (60).

FIGURE 6 is a schematic view of the apparatus for molding the carcass (20). Definitions

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

"Bead core" means that part of the tire comprising an annular tensile member to fit in the bead portion of the carcass securing the carcass to the design rim. "Belt reinforcing structure" 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. "Carcass" or "Casing" means the tire structure apart from the belt structure and the tread.

"Circumferential" means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction.

"Cord" means one of the reinforcement filaments, cables or strands of which the plies in the prior art tire are comprised. "Equatorial Plane (EP)" means the plane perpendicular to the tire's axis of rotation and passing through the center of its tread.

"Innerliner and 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. "Ply" means a continuous layer of rubber-coated parallel cords. "Precure" or "Precured", as used herein, means the rubber material (2) is partially or completely vulcanized.

"Radial" and "radially" mean directions radially toward or away from the axis of rotation 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.

"Section Height" (SH) means the radial distance from the nominal rim diameter to the outer diameter of the tire at its equatorial plane.

"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 it 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 tread edge. "Sidewall" means that elastomeric portion of a tire between the tread and the bead. "Tread" means a rubber component which when integrally formed with or bonded to a tire carcass includes that portion of the tire that comes into contact with the road surface when the tire is normally inflated and under normal load. Detailed Description of the Invention

With reference to FIGURE 1, a precured non-cord reinforced tire carcass (20) is shown. As illustrated, the tire carcass (20) has a nominal rim direction of at least 6.0 inches (15 cm).

The carcass (20) has a pair of sidewall portions (16, 18) and a central crown portion (14). As shown, one sidewall portion (16, 18) extends from each bead portion (22) radially outwardly. The central crown portion (14) extends from and between each radially outer portion of the sidewall portions (16, 18).

The combination of the bead portions (22), sidewall portions (16, 18) and crown portions (14) define the peripheral boundary of an internal chamber (15) of the tire (10) when mounted on a rim (30) as illustrated in FIGURE 3.

The precured non-cord reinforced tire carcass (20) has the bead portions (22) sidewall portions (16, 18) and central crown portions (14) being of the same compound of elastomeric material (2) wherein the compound (2) contains an alloy of rubber and one or more thermoplastic materials producing a modulus at 100% of at least 5.0 MPa and a percent elongation of at least 100% but less than 400% , preferably.

As shown in FIGURE 3, the bead portion (22) has a radially inner bead seat (24) which extends generally axially outwardly. The rim (30) that the tire carcass (20) is mounted onto may have a pair of annular bead cores or rings (26) that fit radially outwardly of the bead seats (24). These bead cores or rings (26) clamp the tire carcass (20) rigidly to the rim (30). The bead core or rings (26) can be integrally formed as part of the tire carcass or, alternatively and preferably, may be separate pieces as shown in FIGURE 3. When one or both of the bead cores (26) are not part of carcass (20) as it is formed, the use of a solid core mold (60) is feasible. This greatly simplifies the tooling cost and enables the carcass (20) to be stretched over a solid mold core (62) during manufacture. With reference to FIGURES 4, 5A, 5B and 5C, the preferred method to mold the tire carcass (20) is illustrated.

The tire carcass (20) is formed by plasticizing the elastomeric alloy material or compound (2) under heat and pressure and passing the compound through a central gate (66) that feeds annularly from a first portion (64) of the tire mold (60). The central gate (66) creates a round disk (40) with a shallow annular tear ring (42) at the upper bead portion (22) as shown. The compound (2) then flows through the bead portion (22) and the sidewalls (16) through the central crown region (14) and fills the opposite sidewall (18) and bead portion (22). After a short cure time, the mold (60) is opened as shown in FIGURE 5A; wherein the first portion (64) is moved relative to the second portion (65) of the mold (60) and then the core (62) with the precured carcass (20) is moved relative to the second portion (65) and, then in FIGURE 5B air pressure is sent through the round disk (40) of the central gate (66). As the air enters the carcass (20) and the disk (40) expands, the expansion creates a release of the carcass (20) from the core (62) as shown in FIGURE 5B. The first portion (64) of the mold (60) is positioned close to the expanding carcass (20) so that as the carcass (20) expands on the gate side the carcass (20) contacts the first portion (64) of the mold (60) restraining the movement of the carcass (20). Then, the first portion (64) of the mold is further moved away from the core (62). As this further movement occurs, the first portion (64) restrains the carcass (20) as the lower side of the carcass (20) along the sidewall (18) and bead portion (22) radially expands sliding as it expands over the core (62). Once the bead portion (22) is over halfway stretched on the core (62) , the expanded bead portion (22) starts to contract as it passes over the rest of the core (62) and, accordingly, the air pressure can be cut off as the freshly-formed carcass (20) automatically releases itself from the core (62) as it contracts to an unloaded non-stretched condition as shown in FIGURE 5C. FIGURE 6 shows a partial schematic view of the apparatus for molding the carcass (20).

The apparatus (4) for forming the carcass (20), as illustrated in FIGURE 6, has a frame (6), a mold (60) attached to the frame (6) a means (80) for moving the first portion (64) of the mold, and a means (90) for injecting a volume of plasticized rubber material (2) into a carcass- forming cavity (100) of the mold (60). The mold (60) has a movable first portion (64) and a fixed second portion (65) and a core

(62). The core (62) in combination with the first portion (64) and the second portion (65) and a core (62) form a carcass-forming cavity (100).

The means (80) for moving the first portion (64) of the mold (60) preferably is one or more hydraulic cylinders (82). The means (90) for injection the volume of plasticized rubber material (2) into the carcass-forming cavity (100) preferably is an injection or compression molding press, not all of the press is illustrated as being understood what a press is in the art.

The mold (60) has one central gate (66) for forming a disk (40) and an annular tear ring (42). The annular tear ring (42) has a reduced cross-section thickness and is connected to one bead seat (24) forming portion of the carcass-forming cavity (100).

An air pressure nozzle (70) is provided which supplies air between the formed carcass (20) and the core (62) from an air supply (99). The air pressure nozzle (70) is attached to a movable plate (7) which is moved by one or more hydraulic cylinders (84). The apparatus further can have sensors (72) for determining when to stop the air flow from the nozzle (70), the sensor (72) is actuated after the first portion (64) or the second portion (65) is moved a predetermined distance.

As the FIGURE 6 illustrates, connecting rods (85) are threadingly engaged into the second mold portion (65) and, the first portion (64) has bearings (86) to allow the first portion

(64) to slide or move relative to the core (62) and second mold portion (65). The sensor (72) when the contact the grooves (88) can activate a signal to initiate air pressure and shut off air pressure as the portion (64) moves to a more open location as previously discussed.

The amount of stretch required of the bead portion (22) is at least a 100% relative to the relaxed state. The fact that the carcass material (2) is still hot generally at a temperature of 100°C to 150°C in combination with the specifically formulated alloy rubber material or compound (2) insures that the bead portion (22) can be stretched without exhibiting surface fractures. Heretofore, common rubbers employed in the manner described above had a wide range of surface fractures in the bead seat (24). To compensate for this problem, an alloy material (2) having specifically selected physical properties was compounded into the carcass (20) as described below as been developed.

This invention specifically relates to a process for manufacturing a carcass (20) which comprises (1) using a rubber composition wherein the rubber composition is comprised of (a) an alloy comprised of (i) elastomeric rubber, (ii) an elastomeric rubber having thermoplastic side chains grafted thereto, and (iii) dispersed thermoplastic wherein the thermoplastic is selected from the group consisting of, but not limited to, nylons, polypropylene, and polyphenylene oxides, (b) a rubber, (c) carbon black, (d) at least one curative, (e) zinc oxide, (f) a processing oil, (g) stearic acid, and (h) antioxidant; (2) molding the carcass into the geometric form desired for the carcass ; and (3) curing the rubber composition at a temperature within the range of 130 °C to 210 °C to produce the carcass. Preferably, the elastomeric rubber is a natural rubber.

The subject invention also discloses a process for manufacturing a carcass which comprises injection molding a rubber composition into the desired geometric form at a temperature which is within the range of 130 °C to 210 °C; wherein the rubber composition is comprised of (a) a rubber alloy comprised of (i) elastomeric rubber, (ii) elastomer rubber having thermoplastic side chains grafted thereto, and (iii) dispersed thermoplastic wherein the thermoplastic is selected from the group consisting of, but not limited to, nylons, polypropylene, polyethylene, low density polyethylene, polyethylene terephthalate, PTFE, polyurea, polyurethane, aramid, and polyphenylene oxides, (b) rubber, (c) carbon black, (d) at least one curative, (e) zinc oxide, (f) a processing oil, and (g) stearic acid, and (2) curing the rubber composition at a temperature within the range of 130° C to 210° C to produce the carcass. The rubber composition which is compression transferred or injection molded is comprised of (a) an alloy comprised of (i) natural rubber, (ii) an natural rubber having thermoplastic side chains grafted thereto, and (iii) dispersed thermoplastic, wherein the thermoplastic is selected from the group consisting of, but not limited to, nylon, polyesters, and polyphenylene oxides, (b) natural rubber, (c) carbon black, (d) at least one curative, (e) zinc oxide, (f) a processing oil, and (g) stearic acid. The total amount of thermoplastic in the alloy will be within the range of from about 2 phr to about 25 phr (parts per hundred parts of rubber). This is the total amount of thermoplastic in the natural rubber having thermoplastic side chains grafted thereto and the dispersed thermoplastic in the alloy. It is normally preferred for the amount of thermoplastic in the composition to be within the range of about 3 phr to about 20 phr. It is more preferred for the amount of thermoplastic in the rubber composition to be within the range of about 4 phr to about 13 phr, due to process considerations.

The rubber having thermoplastic side chains grafted thereto can be prepared utilizing natural rubber or, alternatively, EPDM rubber in the technique disclosed by U.S. Patent 4,996,263 or U.S. Patent 4,996,262. This technique involves reacting nylon with a functionalized rubber (maleated rubber) to produce rubber having nylon side-chains grafted thereto. As another example, the functionalized rubber can also be a carboxy lated or sulfonated EPDM. Such procedures result in the formation of alloys (blends) which contain (i) functionalized EPDM rubber (which did not react), (ii) EPDM rubber having thermoplastic side chains grafted thereto, and (iii) dispersed thermoplastic (which did not react). In the preparation of such alloys, the thermoplastic is normally molten during the period which it is mixed with the rubber. The morphology of the dispersed thermoplastic phase depends upon a variety of factors. Among these factors is the relative ratio of the viscosities of the two phases being mixed. Experience has shown that the domain size of the dispersed phase is smaller when the viscosities of the two phases are closely matched. One means of "matching" these viscosities after the thermoplastic material has melted is to reduce the viscosity of the elastomer phase by increasing, the temperature of mixing to further soften the elastomer. However, this approach is not always viable and the temperature control needed to accomplish this objective is very sensitive.

The viscosities of the two phases can also be "matched" by adding an extending oil to the alloy during mixing to reduce the viscosity of the elastomer. This brings the viscosities of the two phases closer together and results in there being a better dispersion of the thermoplastic. This oil extension approach eliminates or reduces the need to raise the mixing temperature to match the viscosities of the two phases. This saves the rubber from undesirable degradation which can occur at higher temperatures. Another benefit realized by using this approach is that much higher concentrations of the thermoplastic can be employed in the alloy without a detrimental effect on processing.

The oil extension process can be accomplished during alloy formation or the elastomer can be oil-extended prior to mixing. The only drawback to prior oil extension is that the soft nature of the elastomer will retard heat buildup during mixing and complicate processing. There may be limitations of this process from the nature of the extending oil and the two polymer phases. For example, the extending oil should extend the elastomer and not alter the thermoplastic. Also, the extending oil should be easily taken up by the base elastomer and should not be volatile relative to the alloying temperature.

Virtually any type of nylon can be utilized as the thermoplastic in preparing the rubber compositions of this invention. These nylons are polyamides which can be prepared by reacting diamines with dicarboxylic acids. The diamines and dicarboxyhc acids which are utilized in preparing such nylons will generally contain from about 3 to about 12 carbon atoms. Nylons can also be prepared by addition polymerization. Nylon which is prepared by reacting hexamethylene diamine with adipic acid (hexanedioic acid) can be utilized in the process of this invention. It is generally referred to as nylon-6,6 because it is derived from a diamine which contains 6 carbon atoms and a dicarboxylic acid which contains 6 carbon atoms. Nylon-6,6 typically has a number average molecular weight of 12,000 to 20,000, is exceptionally strong, abrasion resistant, and available from a wide variety of sources.

Polycapryllactam, which is generally referred to as nylon- 8, is generally prepared by polymerization capryllactam. This polymerization takes place readily in the melt with a small amount of amino acid initiator. Capryllactam is prepared by dimerization of butadiene to cyclooctadiene, which is hydrogenated to cyclooctane, oxidized to cyclooctanone, converted to the oxime with hydroxylamine, and subjected to the Beckmann rearrangement. Nylon-8 has a melting point of 200°C.

Poly ( -aminoundecanoic acid), known as nylon-11, can be prepared by the melt polymerization of -aminoundecanoic acid under an inert gas atmosphere at a temperature of about 215°C. Nylon-11 has a melting point of 190°C.

Nylon- 12 or poly( -dodecanolactam) is normally prepared by the polymerization of - dodecanolactam at a high temperature of at least about 300°C utilizing an acid catalyst. - dodecanolactam is prepared by trimerization of butadiene to cyclododecatriene, the subsequent hydrogenation to cyclododecane, followed by oxidation to cyclododecanone, which is converted to the oxime with hydroxylamine, with the oxime being rearranged by Beckmann rearrangement to yield the -dodecanolactam. Nylon-12 has a melting point of 179°C.

Nylon-6 or poly( -caprolactam) is normally prepared by the polymerization of - caprolactam at 250-270°C in the presence of water and an initiator such as nylon-6,6 salt or aminocaproic acid. Polymerization to ^" 90% completion can be obtained. Monomer and higher ohgomers can be extracted with hot water and the polymer then dried, -caprolactam is usually prepared by conversion of cyclohexanone to the oxime with hydroxylamine, the oxime being rearranged by Beckmann rearrangement to yield -caprolactam. Nylon-6 has a melting point of 223°C.

The nylons used in the process of this invention will typically have a number average molecular weight which is within the range of about 8,000 to about 40,000. Such nylons will more typically have number average molecular weights which are within the range of about 10,000 to about 25,000. The nylon utilized can be capped or can have free primary amine end groups. However, nylons having free amine end groups are believed to react more quickly with maleic anhydride and are accordingly preferred. The nylons which are preferred for utilization in the process of this invention have melting points which are within the range of about 150°C to about 295°C. Some representative examples of such preferred nylons include nylon-4, nylon-6, nylon-7, nylon-8, nylon-9, nylon-10, nylon-11, nylon-12, nylon-4,6, nylon-6,6, nylon-6,8, nylon-6, 9, nylon- 6,10, nylon-6, 12, and copolymers thereof. The polyesters which can be used as the thermoplastic material will generally have a melting point of less than about 240°C. In most cases it is preferable for the polyester to have a melting point of less than about 200°C. The polyester utilized to modify the rubber will typically be a polyester elastomer. Virtually any type of polyester elastomer having a melting point of less than about 240°C can be used. Such polyester elastomers are widely available commercially.

For instance, E. I. du Pont de Nemours & Company sells suitable polyester elastomers under the trademark Hytrel™. Dupont Hytrel™ 5555 has been determined to be highly suitable for use as a polyester elastomer in the high modulus rubber compositions of this invention.

The polyester elastomers used in the alloys of this invention will normally contain both polyether and polyester segments. For example, such a polyester elastomer is comprised of the reaction product of (a) terephthahc acid or a dialkyl ester thereof, (b) a dimer acid, (c) a poly(tetramethylene oxide) glycol and (d) 1 ,4-butane diol. Polyester elastomers of this general type are described in greater detail in U.S. Patent No. 4,254,001, which is hereby incorporated herein by reference in its entirety. Similar polyester elastomers which additionally contain chain branching agents and ionic compounds are described in U.S. Patent No. 4,383,106 and U.S. Patent No. 4,390,687. U.S. Patent Nos. 2,623,031, 3,023,192, 3,651 ,014, 3,763, 109, 3,766,146, 3,896,078, 4,013,624 and 4,264,761, all of which are incorporated herein by reference in their entirety, also describe polyester elastomers and techniques that can be utilized in their preparation.

In preparing the rubber composition, it is generally preferred to first prepare a nonproductive blend. Such nonproductive blends contain polymeric components of the rubber composition and certain other compounding ingredients but do not include the curatives. The rubber composition will normally contain from about 10 phr to about 150 phr of carbon black and/or silica. Typically at least about 50 phr of carbon black and/or silica is required to provide the level of stiffness desired. On the other hand, the utilization of more than about 150 phr of carbon black and/or sihca leads to compositions which are very difficult to process and extrude. It is normally preferred for the rubber composition to contain from about 40 phr to about 70 phr of carbon black and/or silica. It is most preferred for the carbon black and/or sihca to be present in the rubber composition at a level which is within the range of about 50 phr to about 60 phr. It is important to include a processing oil (an extending oil) in the rubber composition at a level which is within the range of about 5 phr to about 90 phr. It is preferred for the processing oil to be present in an amount ranging from about 5 phr to about 70 phr. It is most preferred for the processing oil to be present in the rubber composition at a level which is within the range of about 5 phr to about 50 phr. Zinc oxide is also included in the rubber composition at a level within the range of about 1 phr to about 10 phr. It is normally preferred for zinc oxide to be present in the rubber composition in an amount which is within the range of about 2 phr to about 8 phr. It is normally more preferred for the zinc oxide to be in the rubber composition at a level which is within the range of about 2 phr to about 6 phr. Stearic acid is also included in the rubber composition in an amount which is within the range of about 0.25 phr to about 5 phr. It is preferred for the stearic acid to be present in the rubber composition in an amount which is within the range of about 0.5 phr to about 4 phr. It is most preferred for the stearic acid to be present in the rubber composition at a level which is within the range of about 1 phr to about 3 phr.

The productive rubber composition is prepared by adding a curative, such as sulfur and an accelerator to the nonproductive rubber composition. Sulfur or a sulfur containing compound is typically added in an amount which is within the range of about 0.2 phr to 6 phr. It is normally preferred for sulfur to be present in the productive rubber composition in an amount which is within the range of about 0.3 phr to 4 phr. It is most preferred for sulfur to be present in the rubber composition in an amount which is within the range of 0.5 phr to 2 phr.

One or more accelerators will also be included with sulfur curatives in the productive rubber composition. Some representative examples of accelerators which can be used include: benzothiazyl disuifide, 2-mercaptobenzothiazole, N-oxydiethylene benzothiazole-2- sulfenamide, N-cyclohexyl-2-benzothiazolesulfenamide, bismuth dimethyldithiocarbamate, cadmium diethyldithiocarbamate, copper dimethyldithiocarbamate, lead dimethyldithiocarbamate, selenium diethyldithiocarbamate, selenium dimethyldithiocarbamate, tellurium diethyldithiocarbamate, zinc dimethyldithiocarbamate, zinc dibutyldithiocarbamate, tetramethylthiuram disuifide, tetraefhylthiuram disuifide, dipentamethylene thiuram hexasulfide, tetramethylthiuram monosulfide, and dimethylethyl thiourea. The productive rubber composition containing sulfur curatives will typically contain from about 1 phr to about 12 phr of accelerator. It is normally preferred for the accelerators to be present in an amount which is within the range of about 2.5 phr to about 10 phr. It is most preferred for the accelerator to be utilized at a level which is within the range of about 4 phr to about 8 phr.

Productive rubber compositions can also be made with peroxide curatives. Such peroxide curatives will normally contain at least one peroxide compound, a crosslinking agent, and zinc oxide. It should be noted that zinc oxide is also used in standard sulfur curative systems. A wide variety of peroxide compounds can be used in such peroxide curative systems. However, acidic materials, such as peroxides based on acids or esters, should be avoided. Some representative examples of peroxide compounds which can be used include: methylethyl ketone peroxide, cyclohexanone peroxide, cumene hydroperoxide, pinane hydroperoxide, p-menthane hydroperoxide, t-butyl hydroperoxide, dicumyl peroxide, 2,5- dimethylhexane-2,5-dihydroperoxide, di-t-butyl peroxide, and the like. Dicumyl peroxide and di-t-butyl peroxide are highly preferred peroxide compounds. Some representative examples of crosslinking agents which can be used include: pentaerythritol tetraacrylate, trimethylol trimethacrylate, diallyl phthalate.

In an alternative embodiment of this invention, the carcass (20) can be made by injection molding. When injection molding is used, the carcass (20) is molded directly into the desired shape. The injection molding is normally conducted at a temperature which is within the range of 130°C to 210°C which is sufficient to cure the rubber composition in the desired geometric shape. It is preferred to utilize a temperature within the range of 140°C to 200°C with temperatures within the range of 170°C to 195°C being most preferred.

This invention is illustrated by the following examples which are merely for the purpose of illustration and are not to be regarded as limiting the scope of the invention or the manner in which it can be practiced. Unless specifically indicated otherwise all parts and percentages are given by weight.

Example 1 An alloy, natural rubber with nylon side-chains grafted thereto and dispersed nylon, was prepared by mixing one part of nylon-6 with four parts of natural rubber. This mixing was carried out in a twin screw extruder wherein the extruder temperature was held between 325°F to 425°F (163°C to 218°C) and an average residence time of from 2 to 4 minutes was maintained. The extrudate temperature was typically in the 430°F to 490°F (221°C to 254°C) range.

Examples 2-4

A rubber blend containing the polymer alloy of Example 1 and a natural rubber stock was prepared in a Banbury mixer using two stages of addition. The rubber stock was one characteristic of those used in carcass (20) applications. For the purposes of comparison, rubber stocks were prepared as shown in Table I with these combinations of alloy and natural rubber being mixed in the first stage with conventional amounts of carbon black, processing oil, zinc oxide and stearic acid. The first stage mix was conducted for 2.5 minutes at 165°C and 65 rpm. Next, the second stage reactants were added to make a productive blend. The second stage reactants were sulfur, accelerators and metal dithiocarbamate. The second stage was mixed for 2.0 minutes at 120°C and 35 rpm. Test specimens from this stock were prepared by shaping according to the test requirement and curing the stock for 18 minutes at 340°F (171°C). Carcass (20) samples were made for the purpose of determining burst strength.

This nylon-6 is derived from the alloy.

Example 5

A rubber blend containing nylon-6 and a rubber stock was prepared as in Examples 2-4 wherein the nylon-6 was added directly to the stock during the first stage of mixing. The remaining ingredients were added as described in the examples. After mixing was carried out, the composition was found to have large pieces of undispersed nylon-6 throughout the sample and was found to be completely unsuitable for further mixing, since the second stage mix would not provide any further dispersion of the nylon-6. The resultant carcass (20) preferably has a Shore A hardness of less than 100, most preferably about 80 or more. The exemplary tire shown in FIGURE 3 had a Shore A of 83 where formed of an alloy having nylon as the thermoplastic.

A second critical feature of the tire carcass (20) design that inhibits the bead portion from stretching involves the thickness of the bead portion (22). In one embodiment of the invention, the bead portion (22) has an enlarged base (24) axially outwardly extending that can be easily clamped onto the rim by a separate ring or annular bead core (26).

In another embodiment, the bead portion (22) has a molded cavity (22B) to accept a bead core (26) in this apphcation. The bead portions (22) can be made appreciably thinner allowing for easier stretching without surface fracturing.

In both cases, the bead and sidewall portions (22) must have a reasonable amount of thickness to provide sufficient lateral stiffness to permit the carcass (20) to perform in a manner similar to cord reinforced pneumatic tires of the prior art. The air pressure applied to the non- cord reinforced carcass (20) expands the rubber tensioning the rubber carcass (20). This alone provides insufficient lateral stiffness when the sidewalls (16, 18) are of a thickness comparable to a cord reinforced tire. Accordingly, the sidewalls (16, 18) and bead portions (22) must have a greater thickness which is proportional to the vehicle mass V_m at cornering forces approximating 2g's. As one will easily appreciate, the thickness T_avg is increased somewhat proportional to the vehicular weight. Interestingly, the sidewall thickness (16, 18) is also related to the tire's normal inflation pressure, Accordingly, if the normal operating pressure is lower than the exemplary pressures for a given vehicle mass V_m, then the sidewall thickness T_avg should, accordingly, be increased, the objective being to keep the overall spring rate K„_pι. of the tire with the non-cord- reinforced carcass (20) for lightly-loaded vehicles in less than 600 lb. range; K^ to about 120 lb. /in. to 200 lb. /in., for heavier passenger vehicles, this spring rate is preferably in the 800 to 1,200 lb/in range. The tire engineer will select the thickness T_avg to operate within these parameters at a given operating pressure.

Satisfying both this relations has the distinct advantage of providing a good handling tire carcass (20) with a good ride performance comparable to a conventional cord reinforced tire.

While the tire carcass (20) of the present invention has many novel features, it should be appreciated that in one apphcation, the tire carcass (20) and the tread (12) can be formed simultaneously using the same rubber alloy material (2). In this apphcation, the resultant invention is a complete tire having the precured non-cord reinforced carcass (20) and the tread. As shown, this exemplary tire is an all-terrain vehicle tire designed to be operated at low inflation pressures.

The more conventional application such as passenger tires the tire carcass (20) will have a belt reinforcing structure having two or more layers of belt material and a tread all radially outward of the central crown portion.

Additionally, overlays (59) of aramid or nylon cord (70) may be placed between the belts and the tread as illustrated.

As one skilled in the art will readily appreciate, the resultant invention permits the tire to be made of minimal components in a very rapid time. A completely cured carcass (20) can be fabricated in about 7 minutes or less.

Claims

1. A precured non-cord reinforced tire carcass (20) comprising: a pair of radially inner bead portions (22); a pair of sidewall portions (16, 18) one sidewall portion (16, 18) extending from each bead portion (22) radially outwardly; a central crown portion (14) extending from and between each radially outer portions of the sidewall portions (16, 18); the combination of bead portions (22), sidewall portions (16, 18) and crown portions (14) define the peripheral boundary of an internal chamber (15) of the tire (10) when mounted on a rim (30); the tire carcass (20) characterized by: the bead portion (22), sidewall portions (16, 18) and crown portion (14) being of the same elastomeric material (2); wherein the elastomeric material (2) is a rubber alloy of elastomeric rubber and one or more thermoplastic materials, the cured compound (2) having a modulus, 100 % of at least 5.0 MPa and a percent elongation of at least 100 % .

2. The cured non-cord reinforced tire carcass (20) of claim 1 wherein the cured compound from the rubber alloy material (2) has a Shore A hardness RT of less than 100.

3. The cured non-cord reinforced carcass (20) of claim 1 wherein the rubber alloy material (20) has percent elongation is less than 400%.

4. A pneumatic tire (10) having a precured non-cord reinforced carcass (20), the carcass (20) having a pair of bead portions (22), a pair of sidewall portions (16, 18) and a central crown portion (14) radially outward of and extending between the sidewall portions (16, 18), a tread portion (12) disposed radially outward of the crown portion (14) of the non-cord reinforced carcass (20), the tire (10) characterized in that non-cord reinforced carcass (20) is made from an elastomeric rubber alloy compound material (2).

5. A pneumatic tire (10) of claim 4 wherein the tread (12) is made from the carcass material (2) and, the tire has a nominal rim diameter of 6.0 inches (15 cm).

6. The pneumatic tire (10) of claim 4 further characterized by a belt reinforcing structure (36) having two or more belt reinforcing plies (50, 51).

7. The pneumatic tire (10) of claim 4 being further characterized by an overlay (58) having substantially circumferentially extending cords (70), the overlay being radially outward of the belt reinforcing structure (36).

8. A process for manufacturing a carcass (20) which comprises injection molding a rubber composition into the desired geometric form for the carcass (20) at a temperature which is within the range of 130°C to 210°C; wherein the rubber composition is comprised of (a) an alloy comprised of (i) elastomer rubber, (ii) an elastomeric rubber having thermoplastic side chains grafted thereto, and (iii) dispersed thermoplastic wherein the thermoplastic is selected from the group consisting of, but not limited to, nylons, polyesters, and polyphenylene oxides, (b) an elastomeric rubber, (c) carbon black, (d) at least one curative, (e) zinc oxide, (f) a processing oil, and (g) stearic acid; (2) curing the rubber composition at a temperature within the range of 130°C to 210°C while the rubber composition is physically restrained in the desired geometric form to produce the carcass (20); wherein the carcass (20) does not contain fabric reinforcement.

9. A process as specified in claim 8 wherein the thermoplastic is nylon and wherein the amount of nylon in the compound having nylon side-chains is sufficient for there to be from about 2 phr to about 25 phr of nylon in the rubber composition based upon the total amount of elastomeric rubber in the composition and wherein the elastomeric rubber is a natural rubber.

10. A process as specified in claim 9 wherein the rubber composition contains from about 40 phr to about 60 phr of carbon black and/ or sihca, from about 5 phr to about 30 phr of processing oil, from about 1 phr to about 10 phr of zinc oxide, from about 0.25 phr to about 5 phr of stearic acid, from about 0.2 phr to about 6 phr of sulfur, and from about 1 phr to about 12 phr of accelerator.

11. A process as specified in claim 10 wherein the nylon is selected from the group consisting of nylon-4, nylon-6, nylon-7, nylon-8, nylon-9, nylon-10, nylon-12, nylon-4,6, nylon-6,6, nylon-6,8, nylon-6, 9, nylon-6, 10, and nylon-6, 12.

12. A process as specified in claim 9 wherein the nylon is nylon-6.

13. A process as specified in claim 12 wherein the rubber composition contains from about

3 phr to about 20 phr of nylon, from about 40 phr to about 60 phr of carbon black, from about 5 phr to about 25 phr of processing oil, from about 3 phr to about 8 phr of zinc oxide, from about 0.5 phr to about 4 phr of stearic acid, from about 0.3 phr to about 4 phr of sulfur, and from about 2.5 phr to about 10 phr of accelerators.

14. A process as specified in claim 12 wherein the rubber composition contains from about

4 phr to about 13 phr of nylon, from about 50 phr to about 60 phr of carbon black, from about 5 phr to about 15 phr of processing oil, from about 4 phr to about 6 phr of zinc oxide, from about 1 phr to about 3 phr of stearic acid, from about 0.5 phr to about 2 phr of sulfur, and from about 4 phr to about 8 phr of accelerator.

15. A process as specified in claim 1 wherein the thermoplastic is polyethylene terephthalate.

16. A process as specified in claim 1 wherein the thermoplastic is a blend of poly(phenylene oxide) and polystyrene.

17. A process as specified in claim 16 wherein the polystyrene is high impact polystyrene.

18. A process as specified in claim 1 wherein the rubber used in making the alloy was oil extended.