In this series of blog tips, We will give you some information on the critical importance of the rollers for the quality and efficiency of your print processes. We are sure you will find this of great interest.

Shore Hardness

• In line with their task of transferring ink, inking rollers must be adjusted to be oil-friendly (or oleophilic). In an inking system with conventional inks, rollers of Shore A hardness between 30° and 35° are used. For UV inks, rollers with Shore A hardness of 25° and between 40° and 45° are used.

• Dampening rollers should be water-friendly (hydrophilic). For alcohol dampening systems, Shore A hardness of between 25° and 30° is suitable. In direct dampening systems, hard rubber rollers are used.

The Shore hardness of a roller determined with a Shore meter designates the resistance against penetration of a needle taking the form of either a conic section (Shore A) or a point (Shore D), pressed with a defined force (1 kp) for a period of three seconds against the rubber surface. Soft rollers are measured with Shore A, and hard rollers with Shore D. The general hardness tolerances according to DIN/EN are +/- 5° Shore A

Shore hardness can be easily measured and gives the printer information on the condition of the rollers. Rollers tend to become harder with use, as they are exposed to inks, dampening agents and detergents, as well as the atmosphere. Additional hardening of 5° Shore in the first months of use should be regarded as normal. Accelerated hardening in use can be a sign that the rollers are gradually shrinking. If you adjust a roller that has been subject to hardening and shrinkage to its original gap width, it may well be that its original transfer characteristics will be reproduced. At the same time, however, the gap width is closer than previously. This leads to higher pressure and higher temperatures – and thereby to higher wear on the roller.

Increased hardness can also indicate that a hard film of paper coating and dampening agents has become deposited on the roller surface. This film should be regularly removed to prevent the roller hardening and glazing with use. The clean and satin-like surface of a roller is even more important than its hardness.

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