Selective wetting of a roller

A selective wetting apparatus comprising:

• a roller rotatable about a roller axis and comprising a wettable roller surface;
• an applicator unit having a lip which extends parallel to the roller axis and is radially spaced apart from the roller surface by a gap, wherein the applicator unit is to convey liquid agent towards the roller so that the liquid agent forms a liquid bridge over the gap to wet the wettable roller surface;
• a gas flow source comprising a plurality of blowers;
• a plurality of flow guides in fluid communication with the gas flow source, wherein the flow guide includes an elongate member extending from a gas flow reception portion away from the gap to a flow guide edge adjacent the gap to direct a gas flow from the gas flow reception portion along the flow guide to be discharged at the flow guide edge into a regulated axial portion of the gap to divert a path of the liquid agent away from the roller surface to locally prevent formation of the liquid bridge, and thereby prevent wetting of a corresponding axial portion of the roller surface, wherein individual blowers of the plurality of blowers are individually associated with a respective flow guide of the plurality of flow guides;
• and
• a controller to selectively control the individual blowers of the plurality of blowers to generate a gas flow onto the respective flow guide of the plurality of flow guides.

A selective wetting apparatus comprising:

• a roller rotatable about a roller axis and comprising a wettable roller surface;
• an applicator unit having a lip which extends parallel to the roller axis and is radially spaced apart from the roller surface by a gap, wherein the applicator unit is to convey liquid agent towards the roller so that the liquid agent forms a liquid bridge over the gap to wet the wettable roller surface;
• a gas flow source comprising an elongate nozzle to direct a planar gas jet along a jet direction normal to the roller axis;
• and
• a flow guide in fluid communication with the gas flow source, wherein the flow guide includes an elongate member extending from a gas flow reception portion away from the gap to a flow guide edge adjacent the gap to direct a gas flow from the gas flow reception portion along the flow guide to be discharged at the flow guide edge into a regulated axial portion of the gap to divert a path of the liquid agent away from the roller surface to locally prevent formation of the liquid bridge, and thereby prevent wetting of a corresponding axial portion of the roller surface, and wherein the flow guide is to direct a portion of the planar jet into the regulated axial portion of the gap.