Pneumatic tire and a process to retread a tire

A pneumatic tire and a process to retread a tire is provided. The retreaded tire has a carcass and a crown region, wherein the crown region comprises a belt reinforcement structure located between the carcass and a tread. The retreaded tire further comprises a cementless cushion layer located radially outward of said belt reinforcement structure, and one or more reinforcement plies located radially outward of the cementless cushion layer. The one or more reinforcement plies is formed from a substantially continuous strip of reinforced elastomer which is wound from one side of the crown to the other side in a substantially continuous manner. The reinforcement ply may be formed from spirally winding the strip about the carcass, or one or more reinforcement plies may be formed from winding the strip about the carcass in a zigzag pattern.

FIELD OF THE INVENTION

This invention relates to a pneumatic tire such as an aircraft tire or truck tire and processes to manufacture or retread such a tire.

BACKGROUND OF THE INVENTION

Pneumatic tires for high speed applications experience a high degree of flexure in the crown area of the tire as the tire enters and leaves the contact patch. This problem is particularly exacerbated on aircraft tires wherein the tires can reach speed of over 200 mph at takeoff and landing. When a tire spins at very high speeds, the crown area tends to grow in dimension due to the high angular accelerations and velocity tending to pull the tread area radially outwardly. Counteracting these forces is the load of the vehicle, which is only supported in the small area of the tire known as the contact patch.

Aircraft tires typically exhibit excessive wear in the tread portion of the tire, while the carcass portion typically does not. Thus to save money, many aircraft companies choose to retread their aircraft tires in order to extend the service life of the tire. Retread tires tend to flex in the crown area.

It is known in the prior art how to retread tires. Typically, the tread is buffed or sanded down to the buff line, which is typically located in the cushion layer. Next, a precut layer of cushion gum which is sized to a particular tire is applied. Next, two or more layers of precut R/T plies are applied. Then a new tread layer is applied and then the tire is cured in a mold. One disadvantage to the prior art process is that you have to store all of the different components, because the dimensions of the components vary depending upon the tire type and size.

Thus it is desired to have a retread without the need for precut and custom tire components which must be premade and stored prior to assembly onto a tire. It is also desired to have an improved retreaded tire design that eliminates R/T cut ply endings.

SUMMARY OF THE INVENTION

A pneumatic tire is disclosed having a carcass and a crown region, the crown region comprising a crown reinforcement structure and a tread portion, with a radially inner side and a tread on its radially outer side, wherein the crown reinforcement structure is located between the tread portion and the carcass and comprises a continuous layer of a strip of cord reinforced elastomer, wherein the cords are made of a low lase cord.

In further accordance with the invention, a process to retread a pneumatic tire is disclosed, the process comprising the steps of: providing a tire to be retreaded, the tire comprising a tread portion and a carcass, separating the tread portion from the carcass along a buff-line and removing the tread portion, extruding a cushion layer directly onto the tire, and applying a continuous strip of cord reinforced elastomer over the cushion layer to cover the crown portion of the tire, applying a continuous strip of tread rubber over the crown, and then curing the tire in a mold.

DEFINITIONS

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

“Bias ply tire” or “bias tire” means a tire having a carcass with reinforcing cords in the carcass ply extending diagonally across the tire from bead core to bead core preferably at a 25°-50° angle with respect to the equatorial plane of the tire. Cords run at opposite angles in alternate layers.

“Carcass” means the tire structure apart from the tread reinforcing belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads.

“Cord” means one of the reinforcement strands of which the plies in the 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.

“Ply” means a layer of rubber-coated parallel cords.

“Radial” and “radially” mean directions radially toward or away from the axis of rotation of the tire.

“Radial-ply tire” or “radial 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 preferably between 65° and 90° with respect to the equatorial plane of the tire.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a cross-sectional view of a retreaded tire10. The tire10may be either a radial or bias tire. The tire10comprises two bead portions12each containing one or more bead cores14embedded therein. A sidewall portion24extending radially outward from each of the bead portions, and a tread portion25of substantially cylindrical shape extending between the radially outer ends of the sidewall portions24. Furthermore, the tire10comprises a carcass30toroidally extending from one of the bead portions to the other bead portion. The carcass30is comprised of at least one carcass ply32, but may comprise a plurality of carcass plies32. The carcass plies32are wound around the bead core to form turnup portions. Each of these carcass plies32preferably contains many nylon cords such as nylon-6,6 cords, for example extending substantially perpendicular to an equatorial plane E of the tire10(i.e., extending in the radial direction of the tire). A tread rubber25is arranged radially outside of the carcass30.

The tire10further comprises a belt layer40which reinforces the crown area of the tire. The belt layer40is positioned between the carcass30and the tread rubber25. The belt layer40may be comprised of a plurality of cut belt layers, zigzag belts or zero degree belts. Located radially outward of the belt layer40is a layer of cushion gum50. The buff line52is typically located on the innermost portion of the cushion gum layer50. The tire further comprises one or more layers of RT ply60located radially outward of the cushion gum layer50. The RT ply is located between the cushion gum50and the tread rubber25.

The tire retread process of the invention includes buffing a tire to be retreaded to remove the tread, RT plies, down to the buff line. Next, a layer of cushion gum is applied to the tire. Preferably, the cushion gum layer is extruded or otherwise applied directly onto the carcass. Preferably, the cushion gum layer comprises a cementless cushion such as described in U.S. Pat. No. 5,503,940 which is hereby incorporated by reference. One example of a solventless adhesive composition suitable for use in the invention includes a mixture of at least one elastomer, at least one tackifier, and at least one bisimide compound of the general formula:

where R1, R2, R3, and R4, independently are hydrogen, an alkyl group having from 1 to 5 carbon atoms, a phenyl group, an alkylphenyl group having 7 to 10 carbon atoms or a halogen substituted alkyl group having from 1 to 5 carbon atoms, a halogen substituted phenyl group, or a halogen substituted alkylphenyl group having a total of from 7 to 10 carbon atoms, and where X is an alkylene group having from 1 to 5 carbon atoms, a phenylene group, an alkylphenylene or alkylenephenyl group having 7 to 10 carbon atoms or a halogen substituted alkylene having from 1 to 5 carbon atoms, a halogen substituted phenylene group, or a halogen substituted alkylphenylene or alkylenephenyl group having a total of from 7 to 10 carbon atoms.

The cushion layer50is applied directly onto the carcass preferably using an extruder. One example of an extruder suitable for use is manufactured by A-Z Formen-und Maschinenbau GmbH, Munchen, Germany and is illustrated in U.S. Pat. No. 6,089,844. Another example of an extruder suitable for applying cushion gum to the carcass is shown in U.S. Pat. No. 5,342,473 to Steelastic. The cushion layer may be applied in strips or may be applied in a single large strip.

After the cushion gum layer50is applied to the buffed carcass, next one or more layers of RT ply60are applied. The RT ply layer is preferably comprised of a continuous strip70of reinforced elastomer, as shown inFIG. 2. Preferably the elastomer is rubber. The strip may comprise one or more cords72, typically in the range of 1 to 16 cords per strip, and the strip having a width Wo in the range of about 5 mm to about 30 mm. Preferably, the cords are made of nylon 6,6. Preferably the cords are comprised of a low lase cord which allows the cord to stretch as the rubber is cured, preventing the cords from being pulled in a radially downward direction during cure. The low lase cord properties are preferably in the range of about 15 to 50N, with a break strength preferably in the range of about 100 to about 150N. One low lase cord suitable for use with the invention is made of nylon 6,6 and has a 1260/2 denier construction. Another example of a low lase cord suitable for use with the invention is made of nylon 6,6 and has a 840/2 denier construction.

In a first embodiment of the invention, the RT ply layer60is formed of a continuous reinforced strip70that is spirally wound in a substantially circumferential direction about the tire carcass approximating a “zero degree” layer. SeeFIG. 5. The layer has no cut ends at the lateral edges44,45. The cord angle is in the range of less than 10 degrees and preferably less than 5 degrees to the tire circumferential direction. The strip may be initiated in the centerplane of the carcass, and extend to a first lateral edge45and then reversing direction to extend to a second lateral edge44, as shown inFIG. 3. Alternatively, the strip may start at one end44and progress to the other end45as shown inFIG. 4, with an overlap of the cords at the edges.

It is preferred that the strip be comprised of a low lase cord made of nylon or nylon 6,6 and have an 840/2 denier construction. The strips are located adjacent one another and may be spaced with a gap between the windings, or alternatively, the strip windings may be overlapped.

The spirally wound circumferential layer60with no cut cord endings, by resisting growth in the crown area of the tire, reduces the cut propensity due to foreign object damage. This means the tire's high-speed durability is enhanced.

In a second embodiment of the invention an RT ply layer80is formed in a zigzag configuration, as shown inFIG. 6. In the zigzag configuration, the continuous strip70is wound from lateral edge44to lateral edge45, repeating the side to side winding throughout the circumference of the tire in a zigzag manner as shown inFIG. 6. The zigzag winding is continued, shifting the strip slightly per revolution so that either the strips abut or they overlap the adjacent strip windings73. As a result, the strip windings73extend substantially zigzag in the circumferential direction while changing the bending direction at both side ends44,45. At the side edges44,45it is desired that the strip is angled slightly so that R/W (radius of curvature/strip width) is not less than 2 in order to reduce strain at the edges.

The angle of inclination θ of the zigzag strip relative to the carcass center plane, as shown inFIG. 5, varies typically in the range of about 5 to about 35 degrees, and more particularly in the range of about 10 to about 20 degrees.