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Understanding Laser Technology

From the Printware Blog on Friday 15th March 2013 in Printing Technology, Resources

A laser (or LED) printer is a very versatile machine that is suitable for both home and office use. Text is always razor sharp and images are clean. Photo quality can be an issue at the lower end of the price bracket although even the most expensive laser can not compete with a decent inkjet for photo quality printing. Laser printers generally enjoy the lowest running costs although it may be worth considering an inkjet for light use.

Technical Summary:

Static electricity is the principle behind laser printing which uses a revolving cylinder, a laser beam, fine powder toner, and heat to create images on paper. Black and white lasers (black toner) are relatively inexpensive and common in many homes and small offices. Colour lasers were once seldom found outside service bureaux and commercial printers, but falling prices have made them standard for most offices and attractive to home users for their cheap running costs.

Adobe PostScript capabilities found in many laser printers make them popular with graphic designers and desktop publishers who often utilize EPS images and PostScript files. Hewlett-Packard's PCL language is another popular command language used by laser printers.

What's the difference between LED and laser?

The main mechanical difference between the printers is that rather than using a single laser to create the image on the page, an LED array is used, which is the width of the page. That's just about it.

LED printers, of which OKI is the leading manufacturer, were the first printers to employ "single pass" technology. That is rather than having a single drum to create the images from the four colours, one drum is assigned to each colour making the process quicker. See "How it works" below for more information about this.

Traditionally, manufacturing constraints meant that LED heads were only capable of producing a 600x600 dpi image, and the impression was that they were inferior in quality to a laser. Nowadays however, improvements in technology mean that LED printers are comparable to their laser equivalents. In fact, they are virtually identical in performance and we believe they should all just be called laser printers!

How it works

The basic underlying concept behind laser printers is static electricity. On a small scale, it's what makes your woolly christmas jumper crackle when you take it off, on a larger scale, it's lightning! This charge can either be positive or negative.

Laser printers use this natural phenomenon as a kind of temporary glue, as you will see below.

First of all the drum/ OPC Belt/ Photoconductor is given a clean and then a total positive charge by traditionally a corona wire, but nowadays a charge roller.

As the drum revolves, a tiny laser beam writes the characters and images to the drum, now making the written area negatively charged. The drum is then coated with positively charged toner, however under the opposites attract theory, it only sticks to the negatively charged area written by the laser beam.

Now for the paper, this is given a stronger negative charge than the drum which allows the paper to draw the toner from the drum. As the paper is moving at the same speed as the drum, the exact image from the drum is transferred to the paper. The paper is then discharged using a discharge roller to prevent it sticking to the drum.

Finally the paper passes through the fuser, which is a pair of heated rollers that apply heat and pressure, which in turn melts the toner and fuses it into the fibres of the paper.

This is the basic process for a mono laser, and the process for colour follows the same process, except for the following subtle differences. In a 4 pass laser printer, the process is repeated 4 times using 1 drum, once for each colour (CMYK). In a single pass laser printer, the process is performed once on 4 (CMYK) drums.

If you have any more questions about print technologies please contact Andy Leighton on 023 9262 3333 or email him at andyl@printware.co.uk


by Andy Leighton

Feel free to leave a comment:

Friday 21st June 2013 - Laser Tek

That's very informative and curiosity-heightener. I didn't know that laser printers works that efficient. Well, I got use with inkjet that I didn't bother to check on the advantages of lasers. Maybe I should consider buying one sooner.

Friday 21st June 2013 - Anthony Morgan, Printware

Maybe! Thanks for the feedback.

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