Multicolour extrusion-based 3D print process

A 3D extrusion printer, comprising:

• a first printing head comprising a nozzle which receives a coated solid build material filament, melts the coated solid build material filament, thereafter applies the melted coated solid build material as print to a print bed;
• a filament supply stream in communication with the first printing head which supplies a fixed coated solid build material filament to the first printing head;
• a coating unit upstream to the first printing head on the filament supply stream which applies a coating to a solid build material filament;
• a coating fixing region located between the coating unit and the first printing head;
• a plurality of feed containers equipped with metering devices to supply a coating composition comprising at least one of an additive and an ink to the coating unit;
• and
• a mixing unit between and in communication with the plurality of feed containers wherein the coating composition is mixed prior to being supplied to the coating unit;
• and
• wherein the coating material applied to the filament in the coating unit is completely or incompletely fixed in the fixing region before entering the first printing head.