Thermal Bubble Printing Of the several technologies used by inkjet printer manufacturers, the most popular is the bubble jet. It has been given this name because inside the bubble jet print head, tiny resistors generate heat that vaporises the ink to create a bubble. The expansion that creates the bubble causes a droplet to form and eject from the print head. The bubble jet print head typically has 64 or 128 tiny nozzles, and all of them can fire a droplet simultaneously.

                  Each nozzle is approximately 70 microns, or about the same diameter as a human hair. Dot sizes vary between 50 and 60 microns in diameter. The smallest dot size visible to the naked eye is around 30 microns. The nozzles are capable of delivering drops with a volume of around 8 - 10 picolitres. Dye-based cyan, magenta and yellow inks are normally delivered via a combined colour print-heads.

                 Several small colour ink drops - typically between four and eight - can be combined to deliver dots of varying sizes. This also achieves a bigger palette of non-halftoned colours and smoother halftones. Black ink, which is generally based on bigger pigment molecules, is delivered from a separate print-head in larger drop volumes of around 35pl. Resolution varies between 300 and 600 dots per inch, with enhanced resolutions on some printers of 1200dpi.

                 A technology that relies on heat, such as thermal, creates two limitations on performance. First, because the firing process is heat based, the ink must be resistant to heat. And second, because of the heating, there is a secondary need for a cooling process, which affects print speed. Print speed is chiefly a function of how quickly the nozzles can be made to fire ink drops and the width of the swath across the paper printed by the print-head. This typically translates into print speeds of between 4 to 8 pages per minute for monochrome text and 2 to 4ppm for colour text and graphics.