Stenciling

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Schematic representation of the stenciling effect

In printing machines, stenciling is understood to mean fluctuations in the thickness of the ink layer due to the multiple unrolling of the ink application roller and the uneven removal of ink on the roller depending on the print image. The inking roller transfers part of its ink layer to the printing form elements of the printing plate as it rolls on the printing forme cylinder . This uneven (discontinuous) color removal from the inking roller is alleviated by friction rollers and the supply of new printing ink from the inking unit , but it cannot be completely eliminated. During the next revolution, the layer thickness of the ink application on the printing plate is therefore still somewhat influenced by the ink transfer of the previous revolution. This effect of the printed image on the ink layer thickness, a revolution (the inking roller) later created a kind of negative ghost images (Engl. Ghosting ) and is referred to as Schabloniereffekt.

Countermeasures

One measure to avoid the stenciling effect is to use several inking rollers running one behind the other. In typical front-heavy arrangements with four rollers, most of the paint application (> 80%) takes place via the first two rollers. The two following rollers apply relatively little ink, but have a smoothing effect on the ink layer on the printing plate. Different diameters can also prevent the stenciling effect of individual rollers from being superimposed. In order to avoid grooves in the paint layer of the paint application rollers, the distribution rollers (with a hard surface) perform a pendulum movement (traversing movement) in the direction of their axis. As a result, grooves occurring in the running direction are "blurred" transversely to the running direction.

Individual evidence

  1. ↑ a b Helmut Kipphan: Handbook of Print Media: Technologies and Production Processes . Springer, Berlin Heidelberg 2000, ISBN 3-540-66941-8 , pp. 221 ff .
  2. ↑ MAN-ROLAND Druckmaschinen AG: EP0189827 - traversing drive for the distribution rollers of at least one inking unit of a printing unit of an offset rotary printing press . European patent application, 1986. [1]