The black substance used in photocopiers is not ink. Instead, it is a fine dry powder known as toner.
Understanding Photocopier "Ink"
Photocopiers, particularly those that utilize the widely adopted process called xerography, operate fundamentally differently from inkjet printers. Unlike liquid inks that are sprayed onto paper, photocopiers rely on a powdered substance to create images.
The Role of Toner in Xerography
Toner is a key component in the xerographic process, which is the technology behind most photocopiers and laser printers. It is composed of tiny plastic particles, often mixed with carbon for black toner, or various pigments for color toner.
The process involves several steps to transfer this powder to paper:
- Electrostatic Image Creation: A special drum or belt within the photocopier develops an electrostatic charge. When light from the original document scans the drum, areas corresponding to the white parts of the document lose their charge, while the black (or colored) areas retain it, creating an invisible electrostatic image.
- Toner Adhesion: Fine toner particles, which are also electrically charged, are then attracted to and adhere only to the charged areas of the drum, making the invisible image visible.
- Transfer to Paper: The toner image is subsequently transferred from the drum onto a sheet of paper.
- Fusing: Finally, the paper passes through a fuser unit, where intense heat and pressure melt the plastic components of the toner, permanently bonding the image to the paper's surface. This fusion process is crucial for creating durable, smudge-proof copies.
Key Differences: Toner vs. Ink
It's important to differentiate between toner and liquid ink, as they serve similar purposes (producing images on paper) but function in distinct ways and have different properties.
Feature | Liquid Ink (Inkjet Printers) | Dry Powder Toner (Photocopiers/Laser Printers) |
---|---|---|
Composition | Liquid dye or pigment suspended in a solvent | Fine, plastic-based powder mixed with carbon (for black) or colorants |
Application | Sprayed onto paper through tiny nozzles | Transferred electrostatically to a drum, then fused onto paper with heat/pressure |
Drying/Fixing | Dries by absorption or evaporation | Fused by heat and pressure |
Common Use | Home printers, photo printing, graphic design | Photocopiers, laser printers, multifunction devices |
Understanding this distinction helps clarify why photocopiers don't use "ink" in the traditional sense, but rather a specialized dry powder designed for the xerographic process.