HP 2500C Series - Manual (Page 124)

Functional Overview 6-4
Writing System
Thermal InkJet Technology
The HP printer family uses Thermal InkJet II (TIJ II) technology. The basic principle of
TIJ II is to apply heat to a tiny amount of ink until it expands and is propelled through a
nozzle.
The first step in the process is to fill a small reservoir, known as the firing chamber, with
ink.
The next step is to heat the ink with a thin-film resistor layered above the firing chamber.
As the ink heats up, it expands to form a bubble.
The bubble continues to expand and finally "bursts". At the instant when the bubble
bursts, the ink is forced through the nozzle located below the firing chamber and out onto
the paper.