Roller manufacturers use synthetic rubber, which is a complex mixture containing natural rubber and sundry chemicals that have obtained stability and elasticity through the process of vulcanization. The basic characteristics are inherited by the rubbery materials from the raw rubber present in mix. Several vulcanization agents are added for further vulcanization. One important vulcanization agent is Plasticizers (fluid oils), they along with the extenders and vulcanizing agents process the overall degree of hardness of the material. The amount of plasticizer used is directly related to softness of the vulcanized rubber.
Shore Hardness –The shore hardness of a roller is determined with the help of a shore meter, this property can be defined as the resistance of roller against penetration by a needle; the needle being in the shape of a conic section or a point, pressed with a defined force for an interval of 3 seconds against the surface of rubber. We use conic section for soft rollers while point needles for hard rollers.
Those rollers which are going to be used for inking must be oil-friendly. In any inking system that uses conventional inks; soft rollers are used in between 30 degrees and 35 degrees. Printer with UV inks, uses soft rollers with hardness of 25 degrees and the rest of the systems use between 40 degrees to 45 degrees.
Those rollers that will be used for dampening must be water–friendly. For systems that use alcohol to dampen a hardness of 25 degrees and 30 degrees is most suitable. In direct dampening hard rubber roller work the best.