Patent ID: 7118198

Claim:
An ink jet printhead comprising: a plurality of nozzles adapted for supply with an ejectable liquid; and, a heater corresponding to each of the nozzles respectively, the heater having at least one heater element configured for thermal contact with a bubble forming liquid; such that, heating the heater element to a temperature above the boiling point of the bubble forming liquid forms a gas bubble that causes the ejection of a drop of the ejectable liquid from the nozzle; wherein, the heater element is configured so that the heat energy of an ejected drop differs from the heat energy of an equivalent volume of the ejectable liquid supplied to the nozzle to replace the drop, the heat energy difference being substantially equal to the electrical energy the heater requires to eject the drop, and the nozzle and an inlet though which the ejectable liciuid is supplied to the nozzle are configured so that the outgoing heat energy due to the net effect of the ejected and replacement quantities of ejectable liquid is substantially equal to the amount of heat energy added to the ejectable liquid by the heater element; such that, after the gas bubble collapses and before the heater subsequently activates, the temperature of the bubble forming liquid is at least 10 degrees C. cooler than its boiling point.