In recent years, the use of a sheet comprising a thermoplastic resin or a thermoplastic resin composition obtained by blending a thermoplastic resin and an elastomer in a pneumatic tire inner liner has been proposed and studied (Japanese Unexamined Patent Application Publication No. 2009-241855A).
When actually using a sheet comprising a thermoplastic resin or a thermoplastic resin composition obtained by blending a thermoplastic resin and an elastomer in a pneumatic tire inner liner, a manufacturing technique of winding a sheet laminate of the sheet of a thermoplastic resin or a thermoplastic resin composition obtained by blending a thermoplastic resin and an elastomer and an elastomer layer that undergoes vulcanization adhesion to the sheet of a thermoplastic resin or a thermoplastic resin composition obtained by blending a thermoplastic resin onto a tire molding drum, performing a lap splice, and then supplying the product to the tire vulcanization molding process is ordinarily used.
However, when a tire is manufactured by cutting the aforementioned laminate sheet comprising an elastomer layer and a sheet comprising a thermoplastic resin or a thermoplastic resin composition obtained by blending a thermoplastic resin and an elastomer, which is wound so as to form a roll-like winding, to a prescribed size (length) by pulling out a portion of a required length from the roll-like winding, winding the sheet onto a tire molding drum, performing a lap splice on the drum or the like, and further performing vulcanization molding, separation may occur between the sheet of the thermoplastic resin or thermoplastic resin composition constituting an inner liner and the elastomer layer 3 subjected to vulcanization adhesion to the sheet 2 of the thermoplastic resin or thermoplastic resin composition after the tire has begun moving.
When explaining this with reference to the drawings, as illustrated in FIG. 2A, a sheet laminate 1 comprising an elastomer layer 3 and a sheet 2 comprising a thermoplastic resin or a thermoplastic resin composition obtained by blending a thermoplastic resin and an elastomer is cut to a prescribed size (length) with a blade or the like. A lap splice portion S is provided at both end sections so as to form an annular shape, and the end sections are overlapped and spliced on the tire molding drum. When one sheet laminate 1 is used, both end sections are spliced and formed into an annular shape, or when a plurality of the sheet laminates 1 are used, the mutual end sections of each of the laminates are spliced and collectively formed as a single annular shape.
In addition, cutting into a prescribed size may be performed in the state of the sheet laminate 1 obtained by laminating the elastomer layer 3 with the sheet 2 comprising a thermoplastic resin or a thermoplastic resin composition obtained by blending a thermoplastic resin and an elastomer, or both the sheet 2 and the elastomer layer may be laminated after being cut separately.
Further, other parts (not illustrated) required for tire manufacturing are wound, and after being formed as a green tire, the tire undergoes vulcanization molding with a bladder.
After vulcanization molding, an inner liner layer 10 comprising the elastomer layer 3 and the sheet 2 of a thermoplastic resin or a thermoplastic resin composition obtained by blending a thermoplastic resin and an elastomer is formed, and a portion in which the sheet 2 comprising a thermoplastic resin or the aforementioned thermoplastic resin composition is exposed and a portion in which the sheet 2 is embedded in the elastomer layer 3 are formed in the vicinity of the overlapped splice portion S, as illustrated in the model diagram of FIG. 2B.
The phenomenon in which the aforementioned sheet 2 of a thermoplastic resin or a thermoplastic resin composition and the vulcanization-adhered elastomer sheet 3 are separated occurs where the sheet 2 of the thermoplastic resin composition illustrated in FIG. 2B is exposed and at a distal end vicinity 4 of the sheet 2, wherein a crack is first generated, and the crack continues to grow so as to progress into the sheet separation phenomenon.
Such a phenomenon is not limited only to cases in which the sheet laminate 1 is used as an inner liner, and it is thought to similarly occur in cases in which the laminate is used as a reinforcing member or the like inside the tire. In any case, the separation of the sheet 2 or the sheet laminate 1 due to the cracks leads to a reduction in the life of the tire, which is not preferable.
In response to problems such as those described above, attention was focused on the form at the end sections of the sheet 2 or the sheet laminate 1 which are superimposed to form the splice portion S, and it has been proposed that when the end sections are formed by cutting the sheet material, the sheet material is cut at a temperature equal to or lower than the melting point and using a blade with an edge that is not sharp (Japanese Patent No. 5146591B).
The proposal of Japanese Patent No. 5146591B specifically focuses on a form in which the end sections of the sheet 2 or the sheet laminate 1 constituting the splice portion S are sharpened by cutting at a temperature equal to or lower than the melting point and using a guillotine-type blade with an edge that is not sharp. This proposal focuses on the fact that with a form in which the end sections of the sheet 2 or the sheet laminate 1 are sharpened, the occurrence of cracks or separation of the sheet 2 or the sheet laminate 1 can be satisfactorily prevented, resulting in an excellent product which achieves an effect of preventing the occurrence of cracks and separation.
However, it has been difficult to cut the sheet end sections while maintaining an ideal end section form that is stable and uniform over the entire width of a cut section thereof. Therefore, the separation of the sheet 2 may occur at an earlier stage than other portions in some locations, and this may progress and shorten the life of the entire tire, so there have been demands for further improvements.