The present invention relates to a method for producing shoe soles by injection-molding. It is known to produce, by virtue of appropriate molds, the sole of a shoe by placing a tread in a mold. The tread is made of an adapted material, such as for example rubber, adapted to provide greater grip on the ground.
The tread has a perimetric ridge that protrudes at an angle of approximately 90.degree. with respect to the lateral surface of the sole and constitutes a confinement barrier for the subsequent injection-molding of thermoplastic materials.
A second material, such as for example polyurethane, is then injection-molded to obtain a collar that constitutes the shell for anchoring the upper to the tread.
In these conventional molds, closure occurs on a horizontal plane, so that the injection of polyurethane forms, along the ridge of the tread, flash of considerable thickness and possibly discontinuous, which protrudes laterally to the upper end of the sole that does not interact with the ground.
The presence of the flash constitutes a considerable drawback as regards the overall time and cost for producing the finished sole.
The lateral flash must in fact be removed and this requires trimming it in an optimum manner, since in order to allow the subsequent anchoring, for example of the polyurethane, the sole must then be treated by washing, chlorination, and gluing.
Difficulties have in fact been found, in the prior art, specifically as regards controlling the chlorination of the sole, especially at its lateral edge from which the flash protruded.
It has in fact been observed that perimetric separation, for example of the polyurethane injection-molded over the tread, can occur; this entails either the rejection of the product during quality control or, as an even worse drawback, perimetric separation on the first time the product is used, i.e. when the first stress is applied to the sole.
Another drawback that has been observed in the prior art consists of the fact that molding in place, for example of the polyurethane, on the rubber tread is not always easy, because the tread can shift inside the mold as there are no locator points for its position.