Thermally actuated printhead unit having inert gas operating environment

1. A printing assembly that comprises

a printing unit including at least one thermally actuated ink jet printhead comprising a thermal bend actuator; and

an inert gas supply that is connected to the printing unit to provide the at least one thermal bend actuator with an inert gas during a printing operation to prevent oxidation of the thermal bend actuator.

2. A printing assembly as claimed in claim 1 , in which the thermal bend actuator comprises an active beam and a passive beam connected to the active beam, the active beam receiving an electrical heating current during a print operation, wherein the inert gas is provided to at least the active beam.

3. A printing assembly as claimed in claim 1 , in which the printing unit has at least one ink jet printhead that incorporates micro-electromechanical components for the ejection of ink.

4. A printing assembly as claimed in claim 3 , in which the micro-electromechanical components are thermally actuated, wherein the inert gas is provided to the micro-electromechanical components.

5. A printing assembly as claimed in claim 4 , in which the printing unit includes a printhead assembly that has at least one printhead chip and defines an inert gas inlet, the at least one printhead chip comprising a plurality of nozzle assemblies positioned on a wafer substrate, each nozzle assembly having nozzle chamber walls and a roof wall that define a nozzle chamber and an ink ejection port in fluid communication with the nozzle chamber and a micro-electromechanical actuator that acts on ink within the nozzle chamber to eject ink from the nozzle chamber.

6. A printing assembly as claimed in claim 5 , in which a conduit assembly is arranged within the printing unit to provide an inert gas conduit from the inlet to the at least one printhead chip, the conduit assembly being configured so that inert gas pumped into the conduit assembly provides an inert operating environment for the printhead assembly and an inert gas supply device is connected to the printing unit at the inlet to supply the conduit assembly with inert gas.

7. A printing assembly as claimed in claim 6 , in which the printing unit includes a number of printhead chips, and a number of corresponding nozzle guards that are positioned over respective printhead chips, each nozzle guard having a cover member and a support structure that supports the cover member over each printhead chip, the cover member defining a plurality of passages, each passage being aligned with a respective ink ejection port so that an ink droplet ejected from each ink ejection port can pass through the passage and onto a print medium, the support structure defining a plurality of openings so that inert gas can pass into a region between each printhead cover and its associated printhead chip and through the passages defined by the printhead cover.

8. A printing assembly as claimed in claim 1 , in which the inert gas supply is in the form of a nitrogen supply unit.

9. A printing assembly as claimed in claim 8 , in which the nitrogen supply unit is a membrane nitrogen separation unit.