Ink set-off with light-coloured designs

When printing light-coloured designs (with a high proportion of unprinted areas; for example, black is printed only in very small areas) on substrates with reduced ink-spread behaviour (e.g. uncoated, sized cardboard or cardboard backs), ink may be deposited.

The proportion of fountain solution (used to keep the printing plates clean) is very high compared to the proportion of printing ink, and the fountain solution can therefore emulsify or break down into the printing ink.

Emulsified printing ink dries very poorly, and this can then lead to ink set-off.

Countermeasures include, first and foremost, reducing the amount of dampening solution to just before toning (the printing plate becomes clogged with ink) and, additionally, incorporating ink take-off bars into the trim.

These ink-removal bars ensure that more fresh ink is drawn from the ink fountain across the width of the press, thereby preventing emulsification.

If the printed sheet does not provide sufficient space for the additional ink-removal bars, it is advisable to add a cobalt drier (additive) to the ink. Care must be taken with the dosage.