HP Deskjet 320 Solutions Guide - Page 92

Thermal Inkjet II Technology The HP DeskJet 300 Series printers use Thermal InkJet II (TIJ II) technology. This technology is based on a disposable print cartridge which propels ink out of 50 nozzles (48 nozzles for the color print cartridge1). 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. Cooling Layer of Silicon Heated Thin-Film Resistor Firing Chamber Nozzle 2121614 Propelled Ink Droplet Figure 3-6. Thermal Inkjet II Technology 1. The HP DeskJet Portable prints black only; it cannot use the color print cartridge. 3-36 Operation and Usage