When you're at work in the office, you may not pay much attention to the laser printer in the corner unless it’s broken. But peel back the plastic panels of a conventional laser printer and you’ll actually find sophisticated, interesting technology with its roots in the 1960s.
It’s understandable if it’s all a bit confusing, too, because the ubiquity of laser printers has masked just how much is going on inside these clever machines.
If you’re at all curious about the inner workings of the laser printer, though, don’t worry – just read on, because we’ve got you covered!
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The history of the laser printer
Laser printers were first developed in the late 1960s. An engineer at Xerox, Gary Starkweather, created a prototype in 1969 by modifying a photocopier with a laser beam.
His big idea was simple: use the laser to “draw” an image of what needed to be copied directly onto the copier drum, and print that on the output paper.
Throughout the 1970s, Starkweather and colleagues added control systems and character generators to their early models, and the first commercial laser printer was released by IBM in 1976, and designed for data centers.
By the early 1980s, the first laser printers for office use began to appear and, by the middle of that decade, printers from HP, Brother and others followed IBM into the market, with machines like the HP LaserJet changing the game with huge advances to design and affordability.
As time has passed, technology has improved dramatically, and now laser printers are a staple in many offices.
Who uses laser printers?
Laser printers are known for their fast print speeds, high-quality text printing, and lower cost per page. Combine that with their relative lack of moving parts and their durability, and it’s easy to see why they’re popular in offices.
They’re especially useful for high-volume and high-quality document printing in businesses, universities and public sector organizations with huge print loads, and where text quality is crucial – think legal documents, reports, business letters and official paperwork.
That’s not the only area where laser printers have found success, though. Because they can print monochrome documents quickly and because they’re straightforward and reliable, they’re useful in warehouses where shipping labels need to be produced at pace, and in medical environments where you need guaranteed paperwork fast.
Specialist laser printers are often used for printing adhesive labels, barcode tabs or shipping documents, and other models can be augmented with secure print release abilities for confidential documents.
And thanks to advances in color laser printing technology, other laser printers have the quality to produce glossy marketing materials at speed – previously a task where slower and more expensive inkjet printers dominated.
Looking into the lasers
No matter how a laser printer is used, though, many of the fundamentals about its operation remain the same.
One of the most surprising things about laser printers? They don’t use ink. Instead, they use toner – a fine, dry powder made of pigments and plastics that comes in cylindrical cartridges that are placed inside the machine.
Because it’s not conventional ink, it binds to paper very quickly and easily, so it doesn’t smudge or bleed, which is a common issue with some conventional inks.
To get that toner onto your paper, the process starts with a simple command – pressing “print” on your PC, laptop or mobile device.
When that happens, your device sends the file for printing to the onboard processor on the printer. The processor converts that data into information that the printer can understand, like PCL (Printer Command Language) or PostScript.
This PCL or PostScript file is then converted to a Bitmap image – essentially a series of dots – that the printer will use as its design.
Depending on your printer, the data is sent to the device using either a wired or wireless network, or sometimes a USB connection. In an office setting, you may need to verify your identity to confirm that the information has been sent successfully.
Charging up
When the printer has the file, it’s time to charge up with static electricity. At the heart of a laser printer is the photoreceptor drum, which is a cylinder that’s coated with materials that react to light by losing their electrical charge.
To charge the drum in the first place, a primary corona wire or a charging roller applies a uniform, positive electrical charge across its entire surface. It’s this consistency that's vital for initiating the process.
This is usually the longest part of the process, because it’s important to wait for the corona wire to reach the required temperature. If you wait for a printer to “warm up” before it starts producing design, this is what’s happening.
Load up the laser
When the drum is sufficiently and consistently charged, the printer warms up the most exciting component – the laser.
And while it’s easy to be blasé about laser printers given how they’re omnipresent and often affordable office companions, the level of precision required here cannot be overstated – any distortion means a poor print, and most laser printers can produce thousands of printed dots per inch if required.
When it’s ready to go, the laser works with a movable mirror and a selection of lenses to direct its beam at the drum. It turns on and off rapidly while it moves, removing positive electric charge from specific areas of the drum.
This moving, flashing laser process creates an invisible, negative electrostatic image on the drum in the shape of the design required.
Once the design is rendered on the drum with negative electric charges, it is ready to be transferred to paper.
And while it’s true that most printers give drums a positive charge before the laser gets to work, there are some models that use a negative charge on the drum with neutralization delivered by the laser.
In both instances, though, the concept remains the same – attractive and repellent electrical charges are used to create the design.
Time to tone
In most laser printers, alongside the central drum, you’ll find the toner cartridge and a hopper. While the laser is busy creating the invisible electrostatic image on the main drum, the toner cartridge and hopper release positively-charged toner particles.
Because they’re positively charged, they’re attracted to any areas of negative charge on the drum.
And, as we’ve established, those areas of negative charge actually represent the design that needs to be printed. That means the positive toner is attached to the negative design. Because the toner and the non-printing areas of the drum are both charged positively, those parts of the drum remain untouched.
Prepping the paper
Up until now, the laser printer has concentrated on getting the design onto the drum in the form of positively charged toner.
But now it’s time for the paper to get involved.
A transfer belt rolls paper through the printer, which gives it a positive electrical charge in the process. As the positively charged paper passes the drum, there’s a natural attraction between the positive paper and the negative areas of design on the drum.
The rollers and belts press the drum and paper together. Remember that, at this point, the design is negatively charged and the paper is positively charged – so the two are drawn together, with the toner in the middle.
At this point, a hot roller called the fuser unit melts the toner onto the paper, which leaves the design on the page.
There’s some serious heat going on, too, because some fuser units and rollers apply around 200°C or 392°C of temperature to get the toner melted successfully onto the paper. And because everything is moving so fast, the paper doesn’t have a chance to burn despite the high temperatures involved in laser printing.
As we’ve mentioned before, changes in the charges applied across the various components may result in slight variations in the charges at this stage of the process. Despite that, the underlying concepts remain the same.
Doing it all again
That’s the process for printing one sheet – and while it’s quite involved, it takes fractions of a second.
But there’s a bit more work necessary to print the hundreds of pages routinely required in laser print jobs.
Once a page has been printed, a cleaning blade or an electrically charged eraser removes any leftover toner from the drum and a discharge lamp erases any charges and images from the drum. Once this is completed, the printer is ready to start the process again.
The process is a little more complex if you’re printing in color, too. Color laser printers have four toner cartridges in Cyan, Magenta, Yellow and Black – that’s the CMYK code that is often used in the print and design industries.
Some laser printers use a single-pass method where all four colors are applied in one single pass over the paper, with multiple drums and lasers working at the same time. Other printers send the paper over one drum several times, with a different color deployed on each pass.
And if you’ve got a laser printer with duplexing – a feature that allows printing on both sides of the page – internal rollers are used to flip the paper over once the first pass of printing has been completed.
Print perfection
Laser printing is a complex process, then, involving rollers, electrical charges, toners, wires and the lasers themselves – even if it often happens so quickly that it’s easy to forget what’s going on inside.
This technology is a marvel, though, even if it’s just churning out reports, documents, or letters.
So next time you send a job to the laser printer in the office, maybe stop and think about what is going on inside the grey box in the corner of the room, because you might be surprised.
For our top printers, see our guides to the best home printers and best laser printers.