Dampening solution film

Fountain solution film describes the specific amount of fountain solution that is applied to an offset printing plate .

The dampening solution film prevents the oily ink from inking the print-free areas. It adheres well to the moistened gum arabic that covers these areas while the machine is running. This makes them extremely hydrophilic . The ink-carrying points are covered with a thin layer of plastic, e.g. B. a photopolymer. This material must be water-repellent, i.e. hydrophobic , so that it only accepts the oily printing ink.

One or more dampening form rollers apply the dampening solution film to the plate. Usually these are the rollers that are the first to come into contact with the printing plate with each revolution of the printing plate cylinder (pre-moistening). There are exceptions, for example in newspaper printing , where there are reversible printing units in which the dampening form roller is the last one to run over the printing plate; one speaks here of "rewetting". The dampening system is responsible for tracking the fresh dampening solution mixture .

Depending on the application technique, the dampening solution film runs in waves over the rollers (lift dampening unit) or largely evenly in thickness (film dampening unit). It can be controlled more or less in the machine direction using metering devices. A zonal regulation, i.e. a different dosage across the width of the machine, is not provided.