Pneumatic tires and method of making

#The present invention relates to pneumatic tires and the method of making such tires. More particularly, the present invention relates to the construction of a preform tire using an inner liner formed of a plurality of overlaying plies.

#The automotive pneumatic tire is typically made using the flat band method of tire building wherein the various components, or plies, of the tire are applied, as flat stock, upon a rotating tire building drum forming a hollow, barrel shaped preform. In building the preform, the inner liner is first wrapped upon the drum followed by the carcass plies generally containing the tire reinforcement. The carcass plies are then followed by the belt plies, the side wall plies and the tread ply. The barrel shaped preform is then removed from the building drum and placed within a vulcanizing mold, having the general shape of the finished tire. The barrel shaped preform is next heated and expanded radially outward into the mold periphery typically by directing pressurized hot gas or steam into a bladder disposed within the preform. During the radial expansion of the preform within the mold, the cylindrically shaped plies must expand radially outward to radial dimensions much beyond those of the original preform. Therefore, the elastomeric material of each preform ply must stretchingly expand much like a balloon. During this expansion step the material thickness of the preform plies may be expected to decrease.

#Of particular concern, in the present invention, is the inner liner ply. Typically the inner liner ply is laid upon the building drum as a flat piece of elastomeric stock having a uniform thickness. Thus, as the inner liner ply expands radially outward during the expansion step, the thickness of the inner liner is stretchingly thinned resulting in an inner liner ply having a thickness that progressively decreases from the tire bead area to the tire crown.

#FIG. 1 presents a cross sectional view of a typical automotive tire construction, subsequent to expansion of the preform but before vulcanization has taken place, embodying the preferred embodiment of the present invention;

#FIG. 2 presents a schematic perspective illustrating the flat band method of building a tire preform and showing application of the inner liner flat stock to the tire building drum in accord with the present invention;

#FIG. 3 presents a cross sectional view taken along line 3—3 of FIG. 2 showing the inner liner, flat stock plies as laid upon the tire building drum;

#To best illustrate the present invention, FIG. 1 shows a typical automotive tire preform 10, in cross-section, as it exists after expansion of the tire preform but prior to complete vulcanization. Tire preform 10 generally comprises two bead areas 12 and 13, side walls 16 and 17, tread or crown region 20, and an inner liner 21 having two distinct plies 24 and 25, in accordance with the present invention. For clarity of the present invention, the typical carcass reinforcing, extending between bead areas 12 and 13, the belt structure in the crown area under the tread, and the bead ring structure are not shown. The preform has an inner meridional width L extending about the interior surface 23 of preform 10 from the outer edge of bead area 12 to the outer edge of bead area 13, as shown in FIG. 1.

#As illustrated in FIGS. 2 and 3, the uncured inner liner 21 comprises two separate and distinct plies 24 and 25 of flat elastomeric material each having a uniform thickness and a width less than width L but greater than one half of width L. During the tire preform building stage, the inner liner plies 24 and 25 are laid upon the tire building drum 22, as illustrated in FIGS. 2 and 3, wherein the first ply 24 extends from one edge 27 of preform width L to a predetermined position 28 on drum 22 beyond the midpoint 29 of width L. The second ply 25 is applied to the drum extending from the opposite edge 30 of preform width L to a predetermined position on drum 22 beyond the midpoint 29 of width L to overlap ply 24. Plies 24 and 25 are arranged to overlap one another by the length X. The length X will necessarily vary depending upon tire size and the desired amount of overlap X′ in the expanded tire, as shown in FIG. 1. For clarity of the invention, the additional plies typically applied to the tire preform upon the building drum 22 are not shown.

#When a flat band tire preform 10 is built with the inner liner plies 24 and 25 laid upon the tire building drum 22, as shown in FIGS. 2 and 3, and is expanded in the vulcanizing mold, plies 24 and 25, being anchored at beads 12 and 13, respectively, will stretch circumferentially in an amount proportional to the final diameter divided by the diameter of the tire preform prior to expansion. This stretch is responsible for the reduction in the gauge of the plies 24, 25. Typically, during expansion of preform tire 10, there is no substantial meridional, i.e. bead to bead, stretch of the plies. It is preferred that the amount of overlap X′, after expansion of the preform, extends across crown 20 and to the breaker or shoulder regions 14 and 15, as illustrated in FIG. 1.