The process by which laser printers affix the printed image on media (paper) can be a bit fuzzy; though it clear that the machine relies on static electricity to run the entire printing cycle. Unlike inkjet printers that literally spray ink through micron size nozzles, laser printers use the negatively charged OPC drum to attract the positively charged toner particles into the image set over the drum surface by the laser scanning assembly. Simply put, charged toner particles freely jump into the rotating photoreceptor drum.
The host computer and printer work in tandem to generate and process the image on the printed document. Data is supplied by the host computer and received by the printer control board which deals with all the incoming signals and places the deciphered information on the page as directed. Since the information has been converted into a serial bit stream it is forwarded to the laser scanning assembly that emits it as multiple dots on the photoreceptor drum.
The photosensitive drum revolves as the laser scanning assembly transfers the stream of information across the surface of the drum. The process is referred to as registration. But before the action of the laser assembly commences, the drum is first exposed to a set of erase lamps that will clear the component from residual traces of the previous image. As the drum is now left with a neutral electrical charge and as high voltage is applied to the corona wire it creates a charged negative field. This conditions the drum to accept a uniform negative charge (-1000V) applied across it. As the images is being made by the laser scanning assembly, the toner cartridge works to apply toner on the negatively charged dots.
The toner cartridge is outfitted with a developer roller that turns simultaneously with the photosensitive drum, and expels a measured amount of toner through a restricting blade. A regulated AC voltage is applied to assist toner particles as it leaves the cartridge and literally jumps into the negatively charged dots on the drum surface. But toner cartridges like the Brother TN-350 are programmed to gather toner excesses from the drum and recycle it back to the cartridge. Prior to reuse, the recycled toner is first subjected to an additional positive charge before it enters the toner chamber. Once the image formed on the drum has been transferred to paper, the whole ensemble (paper and toner) moves to the fuser assembly that binds toner to paper permanently.
Toner refill kits when used in the laser printing process must be of similar formulation to the OEM toner; not only in terms of substances and grain size but also in the aspect of melting point to meet the equipment specification. Thus laser printer manufacturers insist that toner must be of high quality and similar to the original toner to avoid inconsistencies in the printouts.