Use of anti set-off powders

In the delivery pile, the color on the printed sheets is usually not completely dry. The freshly printed ink is transferred from the surface of one printed sheet to the back of another sheet above in the stack.

To enable the sheets to dry, KSL anti set-off powder is sprayed between the sheets as spacer. This allows air and oxygen to get to the ink and enable evaporation and oxidative drying. Especially for coated paper, where drying does not occur via absorption by the substrate, the use of KSL anti set-off powders is indispensable.

Positive side effect:

The powdering increases the slidability of the sheets and promotes an even, smooth-edged pile formation. This is crucial for print finishing.

When freshly printed sheets are sticking together heavily, this is called blocking. It occurs especially for varnished sheets. No matter if it is a classic oil-based varnish or a water-based dispersion varnish, both need time to dry, just like the freshly printed ink.

By using water-based varnish, it is highly recommended to apply surface treated powder. These are hydrophobic, i.e. water-repellent, so they stay on the surface of the aqueous dispersion varnish and thus create the necessary distance between the printed sheets. Our coated powders are the KSL anti set-off powders of the S5WL-series.

Conclusion:

To prevent set-off and blocking, as well as to enable smooth print finishing, the established printer rule applies: no sheet-fed printing without KSL powder.

The glass plate effect describes the sticking together of two smooth surfaces. It occurs not only in sheet-fed printing, but in almost all common printing processes.

The glass plate effect reduces the slipperiness of the printed products and makes further processing and finishing difficult or even impossible. In contrast to set-off and blocking, not insufficient drying of ink or varnish is responsible for its occurrence, but the physical effect of adhesion.

In sheet-fed printing, the glass plate effect mainly occurs for papers with very smooth surfaces on both sides as well as on full-surface coatings. This also applies to flexographic printing, whereas the gluing of printed foils, which inherently have a smooth surface, also plays a major role here. In digital and UV printing, the glass plate effect occurs primarily at high printing speeds and high stacks.

Small amount – big effect

Already very small amounts of KSL spray powder are sufficient to guarantee a smooth printing process and easy postpress. A correctly dosed application of KSL powders can significantly increase printing speed and process reliability.