Methods for achieving improved bond strength between unvulcanized and vulcanized rubbers

An improved method for achieving enhanced bond strength between components of unvulcanized and at least partially vulcanized rubber the improvement comprising the steps of selecting first and second initially unvulcanized rubber components (10, 12) for the manufacture of a vulcanized rubber article (21); applying an interphase layer (11) of rubber material, essentially devoid of crosslinking agents and containing from about 0.1 to about 4 parts by weight of at least one accelerator, per 100 parts by weight of rubber, to the first component; prevulcanizing the interphase layer and the first component together until both are at least partially vulcanized, establishing a gradient crosslink density (43) primarily in the interphase layer and thereby providing a lower crosslink concentration at the surface of the interphase layer opposite the first component; applying the second rubber component to the surface of lower crosslink density; and covulcanizing the components together, wherein the first and second unvulcanized rubber components and the interphase layer comprise rubber selected from the group consisting of natural and synthetic rubber and blends thereof. A similar improved method for achieving improved bond strength between components of unvulcanized and at least partially vulcanized rubbers the improvement comprising the steps of selecting two unvulcanized rubber components (10, 12) for the manufacture of a vulcanized rubber article (25, 35); treating one of the components under conditions that will establish a gradient crosslink density with a lower crosslink concentration at the surface (43); applying the other rubber component to the surface; and covulcanizing the components together.