Press room problems and solutions – Series 4 – Darkening

Posted: October 1, 2012 in ISO Press standardisation, print control
Tags: , , ,

A host of factors affect the quality of your printed products: in addition to the machine itself, there are the printing stock and inks, as well as external factors such as atmospheric humidity, and room temperature. Often, when problems arise in the pressroom, the root cause is not immediately apparent. Frequently, it takes time to filter out the underlying cause from among the many possible variables.

This series of blog with Professional Tips offers advice on tips in the most common problem cases. This handy guide should not be missing from any pressroom.

Darkening

When darkening occurs, the darker colors are transferred from the blanket over the printing plate onto the succeeding inking system, where they contaminate the light colors. During wet-on-wet printing, the tackiness of the inks must be coordinated.

Nevertheless, it can happen that the darker colors from the first printing units contaminate the lighter colors (mainly yellows) in the latter printing units.

remedy

• Change to a different kind of ink

• Deposit the lighter colors more in the direction of the sheet-feeder

• Follow the rule of thumb “screen before surface” for the inking sequence

• Raise the dampening solution feed in the lighter colors, or increase the lighter colors

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