HP Deskjet 870 HP DeskJet 870C Printer - Support Information - Page 37
Thermal Inkjet Technology
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Thermal Inkjet Technology The HP DeskJet printer family uses Thermal InkJet II (TIJ II) technology. This technology centers on a disposable print cartridge which propels ink out of 300 nozzles (192 nozzles on the color print cartridge). 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. This is achieved by first filling 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. As the bubble continues to expand and burst, it is forced through the nozzle located below the firing chamber. This process is repeated up to 12,000 times per second and creates residual heat in the resistor which must be removed. A layer of silicon placed above the resistor transfers the residual heat from the resistor.