The functional principle of the laser printers is based on static electricity. With a photoelectrical coated drum, which is at first charged negatively through the charging corona or the charging rollers, it is possible that through an impinging ray of light that hits a rotating mirror, a portrayal of the page will be depicted. The charge will be maintained as long as the darkness. If the rays of light, called lasers, hit the mirror and then the drum, there will be a partial discharge at the exposed points. On these exposed and discharged areas, the toner will stick to apply graphics or texts. The toner powder is negatively charged as well and reacts magnetic if it’s a one-component toner whereas two component toners are composed of iron particles.
The printing process:
While printing the paper sweeps across the drum, and toner will be applied to the paper. On the contrary to a liquid ink cartridge, the toner needs to be liquefied first, as it’s made entirely out of dry powder. The liquefaction occurs at high temperatures above 200 degrees Celsius. Through high pressure, with help of the fuser unit, the toner powder is the melted onto the paper. Finally, a full discharge and exposing of the drum occurs. Although there are other printing methods with lower fuser temperature, which are also more environmentally friendly, they tend to be way too expensive and unsuitable for end users. This functional principle takes effect for shades of grey, which are resolved due to the half toner rasterization in the printing mechanism. With a color print the principle is the same, although the process has to be repeated multiple times because for each basic color, four thereof, a printing mechanism is needed. The lighting and the print are always made line for line, in which the laser is alternating between off and on. There is only iteration needed per page.
Advantages and disadvantages of laser printing:
The advantages of laser printing are the waterproofness, UV-resistance and speed. In comparison to ink-jet printing the price-per-page is cheaper, since there are no inks that could dry out and the page yield of one toner cartridge is generally higher than those of an ink. The maintenance costs are cheaper as well – only the acquisition cost is higher.