Process for adhering vulcanized rubbers and process for producing rubber products using said process for adhering

A process for adhering a vulcanized rubber and an unvulcanized rubber to each other, said process comprising the steps of:

• (1) laminating a sheet material to a surface of a first rubber prior to vulcanizing the first rubber to form a laminate, wherein said sheet material is a fabric having a maximum height of surface roughness (Ry) of 1 to 5000 μm, which is sufficiently durable under rubber vulcanization conditions and which is easily peelable from the first rubber after the first rubber has been vulcanized;
• (2) vulcanizing the laminate;
• (3) removing the sheet material or the sheet material having rubber vulcanizate residue from the vulcanized laminate immediately before adhesion of the first vulcanized rubber in the laminate to a second unvulcanized rubber, such that the surface of the first vulcanized rubber is rough and such that the surface is free of buffings from a buffing treatment and free of substances bleeding out from the first vulcanized rubber, which buffings and substances would inhibit adhesion;
• and
• (4) adhering the rough surface of the first vulcanized rubber and the second unvulcanized rubber to each other by vulcanization in accordance with a method of adhesion, wherein the method of adhesion is adhesion by vulcanization using a rubber composition for adhesion, the content of sulfur in the rubber composition for adhesion being greater than the content of sulfur in each of the first rubber and the second rubber, and a difference between the content of sulfur per 100 parts by weight of rubber in the rubber composition for adhesion and the content of sulfur per 100 parts by weight of rubber in each of the first rubber and the second rubber being 1 to 10 parts by weight.