Close and trustful cooperation with roller manufacturer Sauer goes back many years. One element of this cooperation has been work to optimise the performance of the Rapida 106 with the DuraPrint roller generation. Five test results with significant influence on daily production in the printshop stand out from the wealth of findings.

Printed image

The extremely smooth and homogeneous surface of the rollers delivers an exceptionally brilliant printed image. Comparative tests with conventional rubber rollers revealed inhomogeneous screen dots with reduced edge sharpness, whereas the dots delivered by the pore-free elastomer material of the DuraPrint rollers displayed a high level of sharpness.

Washing results

Printers are today faced with an ever-increasing number of job changes. As a consequence, they must also perform more wash-ups. Tests were conducted to determine whether the DuraPrint rollers still achieved a very good washing result in daily practice with short intervals between wash-ups. This was proven. As the DuraPrint rollers can be washed faster and significantly more thoroughly than rubber rollers, there is no cross contamination from previously printed inks. Washing intervals can be extended and both washing times and solvent consumption are reduced. That achieves an additional ecological benefit.

Dirk Winkler (l), head of print technology at Koenig & Bauer Sheetfed, and Volker Eggelmann, management board member at Sauer, have worked together closely on the project to optimise the use of DuraPrint rollers on Rapida presses

Dimensional stability

Printers who work with alternating ink systems know the problem all too well: The use of conventional inks leads to plasticisers being released from the rubber and causes rubber rollers to shrink. The other ink systems used in mixed operation (UV, HR-UV or LED-UV in combination with UV washing solvents), on the other hand, cause the rollers to swell. Long-term testing has shown that, in mixed and UV operation in particular, the DuraPrint ink rollers are dimensionally stable. The need for constant re-adjustment is practically eliminated.

Stable production

Rapida presses are characterised by their dynamic and very fast-reacting short-train inking units. The inking unit of the Rapida 106 includes eight rubber-coated rollers with enlarged diameters. Ink run-up times, makeready times and thus also reaction times are therefore extremely short. This inherent benefit is often dampened by the sluggish response of porous rubber rollers. Tests proved the DuraPrint rollers to be maximally compatible. The smooth surface provides for an optimum response during press acceleration and production.

Fast colour control

Rapida sheetfed offset presses are known for their fast, reliable and dynamic colour control. Fast-reacting inking rollers amplify this effect. Here, too, the test results were very positive, as the smooth surface of the DuraPrint rollers enables them to react much faster to ink key adjustments than rubber rollers.

On the basis of these test results, a number of Rapida presses have already been delivered with a starting complement of DuraPrint rollers. In the meantime, more than 30 medium-format presses and over a dozen large-format Rapidas in Germany are printing with DuraPrint rollers.

Roland Glin

Questions:

Dirk Winkler