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Computing & Information Services Newsletter
  Laser Printers

The use of a personal computer to perform publishing tasks that would otherwise require much more complicated equipment and human effort. Desktop publishing allows an individual to combine text, numerical data, photographs, charts, and other visual elements in a document that can be printed on a laser printer or more advanced typesetting machine. The primary advantages of desktop publishing over conventional publishing apparatus are low cost and ease of use.

"The dots make a difference"

Yes, we mean dots. It's true. Almost all printers form the images we see and read by creating a pattern of closely spaced dots. What's important is how the printers make the patterns on the paper. To pick the right printer, you need to know some fundamentals about the popular print technologies that make the dots, what their capabilities and drawbacks are, and the tradeoffs between the different technologies.

Dot size and pattern are major factors in our visual response to printed images. We tend to like images better as the dots move closer together. By the way, the spacing between the dots is called print density. But, there is far more to printing technology than patterns, print density, and dot size. It's in your interest to know a lot more - particularly, the types of printing jobs each technology can handle. In plain words, here is what these popular print technologies can do for you.

Computer printers are commonly divided into two general classes according to the way they produce images on paper: nonimpact and impact. Here we are going to deal with nonimpact printers.

Most nonimpact printers form images from a matrix of dots, but they employ different techniques for transferring images to paper. The most popular type, the laser printer, uses a beam of laser light and a system of optical components to etch images on a photoconductor drum from which they are carried via electrostatic photocopying to paper. Another type of nonimpact printer, the ink-jet printer, sprays electrically charged drops of ink onto the print surface.

"What Laser Printers are good for...

Laser printers can make very small dots and place them very close together. Typical laser printers provide dot spacing between 300 and 1200 dots per inch (dpi). Laser printers are very popular, because when the dot spacing gets up to 300 dpi or higher, the printed images look crisp and sharp to our eyes. Laser printers offer great versatility for your printing jobs. They can easily print applications ranging from bar coded labels to MIS reports.

Generally, "laser" technologies use either multiple LED's or a laser beam as the light source to help make the dots. However dot size and resolution are only part of the laser printing story. The toner used in making the dots needs to be "fused" to the paper so the dots won't rub off. Fusing the toner can be done in several ways: heat-pressure fusing, cold-pressure fusing, or flash fusing.

Heat-pressure fusing and flash fusing are the most common. Heat-pressure fusing melts and presses the toner onto the page, but the right kind of paper must be used. With heat-pressure fusing, paper is subjected to temperatures in the 300 to 400 F range and you can damage certain types of paper or encounter other problems. For example, wax-backed pressure sensitive labels can melt, causing label "float" or adhesives can melt and gum up the printer. Use of laser quality media can alleviate these problems.

Cold-pressure fusing, as the name implies, fuses the toner to the page by pressure, but without heat. The major advantage of cold-pressure fusing is its low cost. Though cold-pressure printers have fewer moving parts and longer lives than other lasers, the relatively high pressure they use in the transfixing process prints somewhat glossy images. Commonly, those images are not durable and can be rubbed off.

Flash fusing fixes the toner onto the page with high intensity lamps, whose light energy is absorbed by the toner, causing it to melt and adhere to the page. Unlike other laser fusing technologies, no heat or pressure is applied. This is an important difference because it places fewer restrictions on the types of media that can be run through the printer. You don't need to worry about glue melting or anything else. More advanced flash fusing printers are able to fuse toner onto many synthetic materials such as mylar and plastic cards in addition to a wide range of paper stocks.

There are two types of laser printers - continuous form and cut sheet. Your choice will depend upon the requirements of your print job. Continuous forms are best suited to production print runs that require laser quality output. Continuous form lasers can also provide a straight paper path with pin-feed tractors that give highly accurate paper control. Continuous forms are superior for applications that require tight forms registration. And the power stacking of continuous forms printers make them suitable for unattended production runs, where they are dedicated to specific types of print jobs. Cut sheet printing, which uses friction feed to advance the paper, is more common in desktop printers that run a variety of media, such as letterhead, envelopes, and transparencies, for print jobs shared in an office environment.

To be continued with "impact" printers...

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