Paper: The Digital Difference

Today’s toner-based electrophotographic printers have come a long way since their introduction into the commercial printing industry in the 1970s. With production-speed output and outstanding color quality, these presses have become the workhorses for commercial digital printers. Nonetheless, toner-based technology still has its own set of drawbacks and considerations when it comes to paper selection.

In any printing environment, there are three basic considerations for paper:

1. Runnability, the ability to run through the output device smoothly
2. Printability, the quality and look of the printed piece
3. Usability, the characteristics needed for proper finishing and distribution

Toner-based output devices add other demands on paper due mostly to two steps in the electrophotographic process—toner transfer and fusing.

Toner transfer is accomplished by placing a charge on the paper prior to it reaching the photoreceptor. The efficiency of the process depends on the characteristics of the paper, including thickness and moisture content. Where there are variations, toner may not adhere correctly causing toner specks or ghosting.

Once the toner image is placed on the paper it must be fused. Here again, the efficiency of toner fusing depends on the characteristics of the paper. While most toner-based digital presses such as those from Xerox, Konica Minolta, Ricoh, Kodak, Xeikon, etc. use dry toner that is fused with heat and pressure, the HP Indigo press uses Electroink, which is fused at lower temperatures and pressures. Digital papers are certified separately for dry and liquid toner use.

Paper Characteristics

Moisture level is one of the more important considerations in digital printing paper use. Too dry and there can be static and paper jams. Too moist and paper can curl and cause jams. Moisture levels not only are dependent on how the paper is milled, but also on how it has been stored.

Full-color digital printing, with heavier toner coverage and higher fuser temperatures, calls for more stringent paper quality control to prevent jams in the complex paper paths. Important characteristics are surface properties, surface strength, dimensional stability, grain direction, smoothness, and charging characteristics.

Also important is paper opacity because heavier toner coverage can lead to images showing through on two-sided digital print jobs. “The demands of color laser printers are different than those of black and white printers,” said Edmonds. “When you use color, you subject the paper to four layers of toner. With black and white printing, only one layer of toner is applied. For this reason, high-quality color printing papers have a different set of product specifications.”

According to Chris Harrold, Vice President, Business Development, Digital Media, Mohawk Fine Papers, “The same characteristics that make a great offset paper apply to digital paper: formation, smoothness, brightness, and opacity. All four of these qualities play a role in superior print results and shouldn’t be overlooked. In addition, digital papers are made to specific calipers, contain less moisture, and are precision-cut to digital sheet sizes/rolls. Digital papers may also have a product-specific surface treatment for toner and inkjet applications.”

Sources

With the growing importance of digital printing, the available variety of papers specifically formulated to meet digital printing demands is steadily increasing. Digital papers rated and approved for the various toner and inkjet digital presses are available from most paper manufacturers and distributors and from the makers of the digital output devices. For a listing of sources, see the vendors listed under Consumables & Suppliers, Paper, Digital Print Media at: www.MyPrintResource.com.