What technologies are hidden behind the name "inkjet"?

Depending on the type, inkjet printers can form ink droplets in a different way. Nowadays printer manufacturers use two main technologies. One uses heat; the other – vibration. A third technology uses continuous flow of ink and will be discussed briefly.

Thermal bubble, also known as bubble jet, is a technology used in printers made by HP (Hewlett Packard), Canon and Lexmark. It was discovered in 1977 by a Canon engineer. The name bubble jet comes from the fact that in order to push ink through the nozzles, small resistors create heat, which vaporizes and creates a bubble. While the bubble is expanding, some parts of the ink are pushed by it through the nozzle on the paper. Once the bubble pops, a vacuum is created which pulls more ink from the cartridge into the print head.
The bubble jet print head usually has 64 or 128 nozzles, which can send a droplet at the same time. The inks are dye-based or water-soluble pigment. The resolution varies between 300 and 600 dpi, sometimes up to 1200. One drawback of this technology is that the ink should be heat-resistant. The next drawback follows from the same heating techniques – the ink needs to cool down, which requires additional time. Monochrome text is printed at the speed of 4-8 pages per minute. Color and graphics – 2-4ppm. Still one advantage remains, the bubble jet print head is usually produced at less cost than other inkjet technologies.

The Epson printers function thanks to a patented technology with piezo crystals. This utilizes the fact that piezo crystals change their properties if a current is applied on them. A piezo crystal is sitting behind each nozzle. The crystal vibrates every time when it receives a small electric charge. If it vibrates inwards, it send ink through the nozzle. If it vibrates outwards, more ink is pulled from the reservoir into the printhead. The good sides of this technology is that it allows for more control on the shape and size of the droplet. The number of nozzles is 128 for black and 64 for each of the three colors CMY. The basic resolution is 720 dpi, but it can be improved to 1440dpi. In addition, there is no heating and cooling of the ink, so time is saved. The inks used for this printing technology are very quick-drying. They can be of bigger variety than the ones used in thermal inkjet technology. Once they penetrate the paper, they tend to hold their shape and not spread, which creates a very good image on different coated papers.

In 1951 Siemens introduced another printing technology – continuous inkjet. It involves a continuous stream of ink droplets. This technology has the advantage that the nozzles do not clog because the jet is always in use. However the fluid handling system is usually very complicated.