Understanding How Laser Printers Work
Have you ever wondered how laser printers work? Interestingly, they’re a go-to in office environments, as opposed to inkjet printers, but less common in manufacturing settings.
Let’s see how they compare to other printing technology, like the print engines used in high-speed labelers. We’ll cover everything you need to know when it comes to how laser printers work and when they make a good choice for labeling.
Xerography: The Principle Behind Laser Printers
Most commercial printing methods, including the processes used to make product labels, are based around a printing plate. This plate is etched, creating raised or sunken areas that collect ink. The plate is coated in ink, which only collects in the etched areas, and then pressed against the paper. This ink transfer creates the desired design.
High-speed printing uses curved plates mounted to a drum. This drum picks up the ink and rolls it across the paper surface as it’s pushed past by a series of rollers.
But, what if you could make a printing plate without altering its surface? This is what xerography does. Instead of depending on physical space to hold ink, it uses an electrostatic charge to attract a powdered pigment, called toner. This toner is transferred to the paper and melted, fixing the dye to form an image. A second static charge wipes the surface of the drum clean, so it’s ready to receive a new electrostatic pattern. Laser printers get their name from the laser used to control the electrostatic charge on the printing drum.
The laser printing process can be broken down into six steps.
Cleaning
Before printing, the drum needs to be cleaned both physically and electrically. Excess toner powder is removed using a rubber blade, while an electrostatic lamp neutralizes the electrical charge on the surface of the drum.
Preparing the Drum
The drum rolls past a corona wire or a charge roller. These devices send a high-voltage current across the drum’s surface, creating a uniform negative electrostatic charge.
Exposing the Drum
The printer’s laser neutralizes the electrostatic charge on the drum. The laser is mounted in a fixed position, shining its light on a mirror that rotates back and forth. This exposes the drum line by line, much like the print head on an inkjet printer. Lenses focus the beam, accounting for the difference in distance between the laser and the paper. The laser beam is only on when it passes an area that will be printed. This process leaves the drum with an electric “etching” of the print.
Developing the Image
The surface of the drum passes by the toner cartridge, which has a negative charge. Since identical charges repel each other, the negatively charged toner only sticks to areas neutralized by the laser. Modern printers use a cartridge with a built-in developer roller and toner hopper. The roller transfers the toner to the paper surface. Any excess toner is scraped off and dropped back in the hopper. This ensures an even coat with each pass of the drum.
Toner Transfer
The piece of paper moves past a corona wire or transfer roller, which gives it a positive charge. The positively charged paper and negatively charged areas of the drum attract each other, ensuring even contact. As the sheet of paper rolls across the drum, the toner particles are transferred to the paper. A second corona wire or roller neutralizes the paper’s charge, so the paper peels off the drum without disturbing the toner.
Fusing
The main ingredient in toner is polypropylene, which melts at relatively low temperatures. The fuser is a pair of heated rollers that rapidly bring the paper surface to this temperature, melting and fixing the toner to the paper. Fusing draws more power than any other function in a laser printer, and it also has the biggest effect on printing speed.
While efforts to lower toner melting temperatures decrease power consumption, there’s no getting around the added heat needed to warm thicker paper. Most high-volume office printers, home office printers, and copiers include a way to adjust fuser temperatures to compensate for different paper stock. Since pressure-sensitive labels are thicker than normal paper due to their coatings and backing paper, they require more power than standard paper printing.
How Laser Printers Work During Color Printing
Color laser printers use the same principles as black and white printers, except the process is repeated for each pigment. That means a CMYK color printer and photocopier, which stands for Cyan, Magenta, Yellow, and Key (Black), requires four passes for each printout to use each ink cartridge.
After the final pass, a paper discharger directs the printed page away from the drum. The added passes have a major impact on printing speed, so purpose-built label printers only print in black and white.
What’s the Difference Between Laser Printers and Print Engines?
Do laser printers work the same as print engines? Not exactly.
Print engines are designed for reliable, high-speed output in industrial settings. Instead of a laser, these printers use heat. Thermal transfer printers melt ink from a ribbon onto the label, much like a laser printer. Direct thermal printers use heat to darken thermal paper.
Each printing method is suited for specific tasks, but both methods have a similar high-quality performance. Print engines and laser printers offer the same print quality, with both types of printers usually topping out at 600 dpi. It’s not as high as a photo-quality laser printer, but it’s more than adequate for printing text and monochrome barcodes.
The biggest difference between laser and thermal printing is speed. While a laser printer’s speed is measured in inches per minute, a print engine’s speed is measured in inches per second.
Our print-and-apply labelers use print engines to prevent labeling from becoming a bottleneck in a high-speed production system. By comparison, laser label printers make more sense for small-volume printing – this could be on-demand printing for labels in a warehouse or alongside a manual or small semi-automatic label applicator.
At first glance, uptime for both printing technologies seems to be nearly identical.
Toner cartridges in laser printers include most major wear items, so each cartridge replacement refreshes the printer. Fuser units are also a common failure point, and most commercial printers are designed to make this part easy to replace. The only major wear item on a print engine is the print head, which burns out over time. It’s easy to replace, minimizing downtime.
Service life is an entirely different matter. Print engines are designed to run around the clock, with occasional cleaning and maintenance. While the quoted service life for a print engine is for constant use, service life estimates for laser printers are based on using them at 10-20% maximum capacity.
Simplify Your Printing and Labeling Processes
Looking for a fast, accurate way to print and apply labels? CTM Labeling Systems can help. We make a wide range of machines to handle all types of containers. Contact us, and we’ll set you up with your local distributor. They’ll look at your current production system and help you find a solution tailored to your business.
