HP 400 - Manual (Page 56)

Operation and Usage 3-11
Thermal Inkjet II Technology
The HP DeskJet 400 printer uses Thermal InkJet II (TIJ II) technology. This technology is based on a
disposable print cartridge which propels ink out of 48nozzles. The basic principle of TIJ II is to apply heat
to a tiny measure 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 climactic instant
when the bubble bursts, the ink is forced through the nozzle located below the firing chamber and out
onto the paper.
This process is repeated up to 5,000 times per second and creates residual heat in the resistor. A layer of
silicon is placed above the resistor to cool it by transferring the residual heat away.
Figure 2-3. Thermal Inkjet II Technology
Cooling Layer of Silicon
Heated Thin-Film Resistor
Firing Chamber
Nozzle
Propelled Ink Droplet
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