Method for manufacturing a shoe sole with a composite tread sole, and compound used in the method

A method for manufacturing a composite sole for shoes having a tread sole that comprises vulcanized rubber coupled to a polyurethane mid-sole, the method comprising:

• a) preparing a mix for the vulcanizable rubber, which is combined with at least one reinforcing filler and at least one vulcanization accelerator, and comprises a compound that contains:
• a1) at least one nitrile-based vulcanizable rubber, and
• a2) at least one acrylic resin;
• b) introducing a metered quantity of said mix within a first cavity of a mold for forming a tread sole, said first cavity being formed by a pseudocylindrical side wall in which a sole bottom piston is movable, the first cavity being closed in an upper region by a first replaceable dummy last;
• c) waiting for a vulcanization time, while keeping the sole bottom piston at temperatures of 100-200° C. and the dummy last at temperatures of 100-200° C., said temperatures being adjustable independently;
• d) moving the sole bottom piston with the tread sole in contact therewith, so as to generate a second cavity, and replacing the dummy last with a second dummy last or with a last with a fitted upper, and closing the second cavity with mold rings;
• e) injecting or pouring into said second cavity a metered quantity of polyurethane to form the mid-sole;
• f) waiting for a reaction time of the polyurethane to elapse, while keeping the second dummy last and the mold rings at a temperature lower than 120° C.;
• g) removing the composite sole and allowing it to rest for a stabilization time.