Printhead assembly with ink leakage containment walls

1. A printhead assembly that comprises

a substrate defining a plurality of ink inlets;

a plurality of nozzle assemblies positioned on the substrate, each nozzle assembly defining a nozzle chamber in fluid communication with a respective ink inlet and a nozzle opening from which ink can be ejected; and

a plurality of endless containment walls extending from the substrate and each surrounding a respective nozzle assembly so that leakage ink from the nozzle assemblies can be contained within the containment walls surrounding them.

2. A printhead assembly as claimed in claim 1 , wherein each pair of adjacent containment walls comprises a common wall portion.

3. A printhead assembly as claimed in claim 2 , wherein adjacent pairs of nozzle assemblies are staggered with respect to each other.

4. A printhead assembly as claimed in claim 2 , wherein the containment walls are of substantially the same material as the substrate.

5. A printhead assembly as claimed in claim 1 , further comprising a guard member defining a plurality of passages that are aligned with respective nozzle openings and which together with the containment walls defines a plurality of containment chambers.

6. A printhead assembly as claimed in claim 5 , in which both the substrate and the guard member are substantially of silicon material.

7. A printhead assembly as claimed in claim 1 , in which the substrate incorporates drive circuitry and each nozzle assembly comprises a micro-electromechanical ink ejection mechanism that is connected to the drive circuitry to eject ink from the nozzle chamber on receipt of a signal from the drive circuitry.

8. A printhead assembly as claimed in claim 7 , in which each micro-electromechanical ink ejection mechanism comprises a thermal bend actuator that is connected to the drive circuitry to be deflected as a result of differential thermal expansion and contraction on receipt of an electrical signal from the drive circuitry, and an ink displacement member that is connected to the thermal bend actuator, the ink displacement member being operatively arranged with respect to the nozzle chamber so that deflection of the thermal bend actuator results in the ejection of ink from the nozzle chamber.

9. A printhead assembly as claimed in claim 8 , in which each ink displacement member defines part of the nozzle chamber such that movement of the ink displacement member under action of the thermal bend actuator results in a change in volume of the nozzle chamber and subsequent ejection of ink from the nozzle chamber.