One of the interesting aspects of laser printers and copiers is the toner. Rather than the printer applying ink, the paper actually “grabs” the toner. The toner itself is not ink, but rather an electrically-charged powder made of plastic and pigment.
How does toner work?
The two ingredients of toner, plastic and pigment, each have a simple role in the printing process.
The pigment provides the color, while the plastic allows the pigment to stick to the paper when the plastic is heated and melts.
The melting process gives laser toner an advantage over ink, in that it binds firmly to the paper fibers, resisting smudges and bleeding.
This also provides an even, vivid tone that helps text appear sharp on paper.
Another advantage of toner is the cost. Offices usually choose laser printers because the cost of replacing the toner cartridges is less than inkjet printer cartridges, and laser printers tend to cost only slightly more than inkjet printers.
Anatomy of a toner cartridge
The design of a toner cartridge varies with different models and manufacturers, but the following components are commonly found in most toner cartridges.
Toner hopper: The small container which houses the toner
Seal: A removable strip that prevents toner from spilling before installation
Doctor blade: Helps control the precise amount of toner that is distributed to the developer
Developer: Transfers toner to the OPC drum
Waste bin: Collects residual toner wiped from the OPC drum
Wiper blade: Wipes away residual toner applied to the page
Primary charge roller (PCR): Applies a uniform negative to the OPC drum prior to laser-writing. It also erases the laser image
Organic photo-conductor (OPC) drum: holds an electrostatic image and transfers toner onto the paper
Drum shutter: protects the drum from light when outside the machine and retracts the drum into the printer
How does the cartridge work?
In most cartridges, the toner hopper, developer and drum assembly are all part of the replaceable cartridge unit.
When an image or text is being printed on paper, the printer gathers toner from the hopper with the developer.
The developer, composed of negatively-charged magnetic beads attached to a metal roller, moves through the hopper gathering toner.
The developer collects positively-charged toner particles and brushes them past the drum assembly.
The electrostatic image on the drum has a stronger negative charge than the beads on the developer, so the toner is pulled from the developer onto the drum.
Next, the drum moves over the paper. The paper has an even stronger negative charge than the drum, and pulls the toner particles off of the drum in the shape of the electrostatic image.
Next, the paper is discharged by the detac corona wire.
At this point, gravity is the only thing keeping the toner in place. In order to affix the toner, the paper needs to pass through the fuser rollers, which are heated by internal quartz tube lamps.
The heat melts the plastic in the toner particles, causing the toner to be absorbed into the paper fibers.
Although the melted plastic sticks to the paper, it does not adhere to the heated fuser rollers.
This is possible because the rollers are coated with Teflon, the same material that helps food slide out of non-stick frying pans.
Color vs. Monochrome Printing
Color toner works essentially the same way as monochrome toner, except the process is repeated for each of the toner colors.
The standard toner colors are cyan (blue), magenta (red), yellow and black. The black is needed because the three primary colors (red, yellow and blue) can be combined to form any color except black.
The reason for this is black is not technically a color, but the complete absence of color.
These four toner colors, when combined at varying levels of saturation and lightness, can produce millions of different shades and hues.
This quick guided tour of toner cartridges should help provide a basic understanding of how they work.
The current technology of toner cartridges has allowed laser printers to dominate the office printing market.
In the years to come, new designs of toner cartridges promise to provide more efficient and cost-effective solutions for office and home printing.