Maintaining the shape and overall dimensions of the tire bead is critical for assembly and manufacture of high quality tires, however, conventional tire beads typically distort or deform during tire assembly and curing. Conventional bead insulation compositions typically have good bead wire adhesion and processability but do not maintain their shape and overall dimensions (i.e., geometry) in an uncured or green state. “Processability” is a term understood by those skilled in the art, and is typically indicated by scorch resistance, viscosity and the ability of the rubber composition to be used in bead forming equipment known to those skilled in the art.
Numerous solutions have been adopted by those skilled in the art in an attempt to overcome the problem of distortion and deformation of the shape and overall dimensions of conventional tire beads during tire manufacturing, yet each has associated disadvantages. One solution has been to precure the green tire beads so as to provide a tire bead which will maintain its bead geometry during tire manufacturing. Conventional tire beads are typically precured in an autoclave at 285° F. for 11 minutes. A disadvantage of precuring is that it raises manufacturing costs by adding an additional manufacturing step, raising energy costs and lowering tire bead manufacturing yields.
Two additional solutions, which also involve preprocessing steps, have been to wrap or staple tire beads. Wrapping the beads requires significant manpower and time, and, accordingly, significantly raises manufacturing costs. The disadvantages of stapling the bead are that special automatic equipment is required involving significant capital, increased operational complexity, lowered process yields, and, accordingly, also increased manufacturing times.
Tire manufacturing involves forcing two tire beads over the ends of a tire carcass. The tire carcass and conventional tire bead is then assembled with other tire components, such as the tread and side wall components, and then vulcanized. The tire bead must have dimensional integrity such that the tire bead can be placed over the tire carcass, and turned thereover, without distorting or deforming the tire bead.
U.S. Pat. No. 4,575,534 to Oshima et al., Pat. No. 4,540,744 to Oshima et al., Pat. No. 5,283,289 to Yamamoto et al., Pat. No. 5,098,941 to Tsuriya, and Pat. No. 3,715,266 to Winters et al. disclose conventional tire rubber compositions which contain uncrosslinked styrene butadiene rubber. In particular, the '744 patent to Oshima discloses a tire rubber composition containing a butadiene polymer with a branched polymer through a tin-carbon bond and a styrene butadiene rubber. The '289 patent to Yamamoto et al. discloses a fiber reinforced styrene butadiene containing rubber composition. The '941 patent to Tsuriya discloses a phenolic resin reinforced bead filler composition having a low amount of hexamine which reduces the amount of deterioration of the tire carcass. The '266 patent to Winters et al. discloses adding an adhesion component to conventional uncrosslinked styrene butadiene to improve the adhesion between the bead wire and the bead insulation composition. A disadvantage of these conventional tire rubber compositions is that they typically must be precured, cloth wrapped or stapled to maintain dimensional stability when used in making tire beads.
What is desired, therefore, is a bead insulation composition and tire bead that is dimensionally stable and that does not have to be preprocessed, but which provides sufficient bead wire adhesion and processability. Also desired is a method of manufacturing a tire using a dimensionally stable tire bead which exhibits sufficient bead wire adhesion and processability but which is not preprocessed, and a method of making a tire bead using a dimensionally stable bead insulation composition.