Ink for computer printers is supplied in a variety of ways. An ink jet printer uses liquid ink that is applied to the paper either by spraying, by a drop-on-demand method, by a thermal method, or by a piezoelectric method. Solid ink printers ink a drum with melted wax, and the drum transfers the ink to the paper. By contrast, printer toner, the source of ink for laser printers, is a fine powder that is transferred to paper by electrostatic means.
Printer toner is supplied in a toner cartridge. The toner is mainly made of pigment and plastic, and it is supplied with an electrical charge, which is essential to how it works in the printer. When a print is requested, the printing drum starts off with a positive charge. The printer uses a laser beam to discharge certain spots on the drum surface as it revolves, creating an electrostatic image. Next, the drum is coated with the charged toner, which clings to the discharged areas of the drum only.
The paper is given a negative charge, and then as the drum rolls over the paper, the paper pulls the printer toner onto itself, picking up the image. Next, the paper passes to the fuser, which is where the role of the plastic in the toner comes in. The plastic is melted by the fuser and binds the pigment to the paper fibers, helping to prevent smudging and bleeding. In the meantime, the electrostatic image on the drum is discharged, readying it for the next image.
That description is the process for a black ink printer. For a color printer, the entire process must be repeated four times, with one pass for each of the ink colors: cyan, magenta, yellow, and black.
Printer toner is often supplied in a print cartridge, which may be printer-specific. This means that they are not interchangeable between printers. Many print cartridge suppliers offer a “regular” and a “high yield” toner cartridge, with the output being measured in typical pages. This allows customers to choose a size that fits their needs. Some organizations offer to refill toner cartridges, but care is required. Contrary to what many people believe, purchasing refill kits will not void a printer warranty, and it would be illegal for it to do so.