Ink-cooled thermal ink jet printhead

An apparatus for cooling a printhead in an ink-jet printer, said printhead ejects ink by having firing resistors therein heated with electrical printing pulses, comprising:

• a) a plurality of the firing resistors located in firing chambers on a substrate in the printhead and in thermal communication with both the ink in the printhead and the substrate in the printhead, said firing resistors being subjected to a plurality of electrical printing pulses at selected firing rates, said firing resistors generate direct and residual heat from said electrical printing pulses, said direct heat being that heat directly transferred into the ink in the firing chambers from the firing resistors and said residual heat being that heat absorbed by the printhead substrate from the firing resistors;
• and
• b) a heat exchanger in thermal communication with both the printhead substrate and the ink for transferring heat from the printhead substrate to the ink flowing to the firing chambers, said heat exchanger having a flow path for the ink while in thermal communication therewith formed by two, substantially parallel, spaced apart, surfaces, at least one surface of which transfers heat absorbed by the printhead substrate to said ink, said two surfaces being spaced apart by a dimension of between about 0.010 cm and about 0.015 cm.