For inkjet printers, there is the continuous drop process, which works with a continuous ink jet, and the drop-on-demand process, which works with ink droplets. The latter includes the bubblejet and the piezo printer. The bubblejet process is a thermal process in which the ink, which is located behind a nozzle, is briefly heated and sprayed onto the printing paper at high pressure.
The bubblejet process is triggered by a brief heating pulse that lasts only a few microseconds. The heating pulse creates an ink bubble in the ink exit channel, which grows larger in microseconds. As the ink bubble grows larger, the pressure in the nozzle continues to increase until the bubble ejects a drop of ink through the nozzle. The ink bubble then condenses, creating a vacuum behind the nozzle, which causes ink to flow from the reservoir into the nozzle area.
Heating reaches 250°C to 350°C and, like cooling, takes only a few microseconds. The resulting spray frequencies are 10,000 drops per second and more. Print heads of bubblejet printers consist of many tiny nozzles, which can easily be several hundred in the case of high- resolution black printers. Color printers with three or four print heads work according to the CMY color model or the CMYK color model and can have several hundred nozzles that are controlled individually.
The achievable resolution is between 300 and 1,400 dpi, which corresponds to a smallest dot size of 20 µm. Top devices achieve up to 10,000 dpi. With some manufacturers, a print dot is formed from up to 30 ink droplets.
Bubblejet printheads are subject to relatively high wear. The service life of the print head is given as about 200 million characters. The print head itself is integrated into the printer cartridges.