For those curious how a laser printer works, here’s a rundown of the process. They’re based on the principle like charges repel and opposite charges attract. A laser printer uses these static electricity charges on a drum and toner to produce an image. Some of the charges can go as high as 7000 VDC, however at micro amps. Toner will have either a positive or negative charge depending on the manufacturer or speed. Once the image is transferred it needs fused. The melting point of toner also varies according to speed. Fuser temperatures are typically around 190°. Depending on the brand the order may vary. But a laser printer works the same no matter who makes it. Here’s a breakdown of each step.
Many of the steps are happening at the same time but charge is typically considered the starting point. The laser process works by applying an electrical charge to a photoconductive drum by either a corona wire or a charge roller. The corona wire may have a charge of 7000 VDC applied, however, a scortron grid within a few millimeters of the drum will regulate the charge applied to around 600-700 VDC. A roller applies a uniform charge of 600-700 VDC with direct contact to the drum. Most high end color printers will use a corona wire. A charge roller will get contaminated quicker which will cause defects in the image.
In this step a class 1 laser will “write” an image to the photoconductor. Some faster printers will have 2 or more lasers. No matter how many, the laser is stationary and shines on a rotating mirror with 6 or more sides. The laser beam(s) write the image from top to bottom one thin line at a time. The photoconductive drum does not stop and rotates at a constant speed while the image is being written. Some printers have an LED array instead of a laser. They “write” one line at a time as the drum rotates as well.
The image written on the drum at this point is invisible electrical charges. As the drum rotates this latent image comes close to the developer roller and toner is attracted to the image area but repelled from the non-image area. The voltage difference here is very critical. Any variance can cause a light overall image because not enough toner was attracted or a dark background because too much toner was attracted.
Now that the image has been developed it will need to be transferred to the paper. This works by the paper coming into contact with the drum and a charge is applied behind the paper. The toner leaves the drum because it is attracted to the corona wire or transfer roller behind the paper. A weak charge here can cause an overall light image. After the image is transferred to the paper another charge is applied to assist the paper from separating from the drum.
During the transfer process not quite 100% of the toner is transferred from the drum. The residual toner is cleaned off with a blade or in some cases a brush. Depending on the model this small amount of toner is recycled back to the developer or sent to a waste toner container. Also, during this step the drum is discharged with light to remove the latent image.
Although the image is now on the paper, it is not permanent yet. The fuser rollers work by applying heat and pressure which melts the toner into the paper. After passing through the fuser the image is set into the paper. Because of the heat an pressure the fuser is the most strained part in any laser printer. The fusers are designed to handle the stress and last 100,000 pages or more. The heavier weight paper it can handle. the more durable the fuser.
Several of the steps are happening simultaneously to the drum as it rotates. While they can handle being charged and discharged tens of thousands of times, it only takes a few seconds of direct sunlight to ruin one. The photoreceptive drum is most commonly made from organic materials or Amorphous silicon. Years ago some were made with Cadmium Sulfide, which is toxic.
Toner is non-toxic and made from carbon. By itself it won’t hold a charge and needs a carrier. Iron filings was common but wax is quickly becoming the standard carrier. Because wax based toner is finer it can make better half-tones. More half-tones means a bigger color gamut. Wax based toner will also produce a semi-gloss appearance so fuser oil is no longer needed.
Whether it’s at 10 pages per minute or 150 pages per minute those are the basics of how a laser printer works. If you think a laser printer is right for you check out the laser printer buying guide.