The printing machine with an electrostatic substrate-contact unit has a corona-discharge system to prevent a sparking which might lead to igniting of an explosive air-ink solvent mixture. The current supply to the point electrodes (25) is disconnected at least for discrete sub-groups of electrodes. In each of the sub-groups the max. current flowing through one of its points is limited to a value which is smaller than the critical spark current for the particular adjacent atmosphere. The maximum flowing current is limited pref. to 15-25% of the short-circuit current which would flow without disconnection or current limitation.
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