Get the Most from Your Digital Paper

TIMES ARE tough. To save money, you might be tempted to load less expensive sheets into your digital printers, rather than those developed specifically for digital printing.

But don't do it, the experts warn. Digital papers will save you money (and headaches) in the end by yielding better ink transfer and adhesion, fewer jams, increased uptime and less waste. Also, says Glatfelter's Melissa Klug, using the wrong paper could ultimately harm your equipment.

"You will end up with increased service costs with your extremely expensive and valuable digital equipment," she says. "Digital papers are specially manufactured to meet the exacting specifications of today's digital equipment; it is not the same paper in a different wrapper."

There's also the curl factor, adds Cindy Hamrick, of Hammermill Paper. Offset papers contain about 6 percent moisture, she says, while digital papers have 4.5 percent.

"In general, papers with a high moisture content (over 5 percent) show a high propensity for curl in digital equipment and produce more print mottle."

Adds Boise's Kirk Krahn, "Digital papers generally have a smoother surface to allow for better print quality [i.e. toner adhesion] in comparison to less expensive sheets."

How about using papers designed for inkjet on your toner device, or vice versa?

"There is a huge difference in inkjet and toner papers," notes Molly Rosenthal, of Mohawk Fine Papers, Inc. "Inkjet papers are designed to fix the ink and absorb moisture."

"A sheet designed for toner-based printing may not have the proper holdout necessary for the water-based, low viscosity of inkjet applications," adds Russ Leone, of Boise.

"Problems can arise with substitutions," agrees Appleton's Jason Morgan. "Inkjet papers do not contain enough resin to bind toners well, while papers that work well with toner are not absorbent enough to give good inkjet print quality."

That said, multi-purpose papers may seem like a good solution. Observers say these sheets may work well for simple black-and-white prints, but...

"In cases where there is more color applied, that is where you will see the largest differences between multi-purpose and digital-specific papers," points out Glatfelter's Klug, adding that on digital paper, moisture specifications are tighter to prevent paper jams.

"Anything involving screens, gradations, solids, color builds and process color will do dramatically better on a true digital sheet," adds Leone, of Boise.

"Running multipurpose paper may not show differences in short print runs," concludes Appleton's Jason Morgan, "but productivity will be reduced in high-volume applications."

We asked these and other experts for some tips to help in-plants with the purchasing and use of digital papers. Here are some of their suggestions.

Examine Your Paper Carefully

Mohawk: Papers with good formation (an even distribution of fibers) and a smooth finish provide the best quality on most digital equipment. Bright white paper will add to color brilliance, contrast and definition of your printed piece. Toner does not adhere well to uneven paper surfaces, so heavily embossed or highly textured papers are not recommended for traditional digital presses. Depending on your project, opacity does come into play, the higher the opacity, the less "show through."

Hammermill: Hold a sheet up to the light and look through it. If you see big fluffy "clouds," chances are solid-coverage areas will not look uniform. This can also contribute to show-through in areas where there is lower or uneven fiber distribution in the sheet. A high quality digital sheet's surface will also have a smooth, silky feel.

Boise: Depending on the graphics, formation can play a huge roll in how your print job ends up looking. Take a few competitive sheets and hold them up to the light. More even and consistent fiber formation will translate into better print quality. Print mottle can be a direct result of poor or inconstant formation.

Appleton: Attributes to look for in a good digital sheet include good stiffness for the particular paper weight, no curl in any direction either out of the ream or after printing, and uniformity front to back.

Coated vs. Uncoated

Mohawk: Check the specifications of the digital printing equipment before running coated paper. The paper's basis weight should fit within the equipment's specifications. Some machines must run 20 to 24 lb. (70 to 90 gsm) paper; while others have a much wider range. Make sure the operator uses the proper setting on your digital equipment for optimal outcome on paper.

Using Recycled Paper

Boise: Keep in mind that recycled paper may have different stiffness properties. Also, even the best recycled paper may have higher dirt counts than its virgin counterparts. It's important to set the end user expectations in advance of running on recycled paper.

Mohawk: Using high-quality recycled paper on digital equipment does not have an adverse effect on press performance. These days, recycled content is much cleaner than years ago. Keep in mind, the higher the recycled content, the higher degree of specks you may see in a sheet.

Storage Tips

Mohawk: Choose an area that's protected from extreme temperatures and humidity. Temperature and humidity are critical factors in how paper performs in your equipment. Store paper at 50 percent relative humidity, at 70°. Leave paper in its wrapper until you are ready to use. Store your paper in shelves or pallets or in cabinets, rather than right on the floor to avoid absorption. Pile cartons no more than five high, pallets no more than three high.

Wausau: Keeping paper in the same room as manufacturing is the best way to prevent moisture swings because the paper will become better acclimated to the room's temperature. Keep paper wrapped and away from outside walls. Long-term storage of paper in a non-controlled environment is acceptable, provided that adequate time is available for proper temperature acclimation prior to opening.

Boise: 70° and 50-55 percent humidity is an ideal environment to store paper. Temperature acclimation is most important. If your warehouse is colder/hotter than your pressroom, acclimating to pressroom temperature will improve feeding and running performance. All paper should be stored in a dry, temperature- and humidity-controlled environment whenever possible.

Hammermill: Paper/wood fibers (pulp) absorb water easily (that's why they're used in diapers). It's best to keep paper wrapped in its ream packaging to protect it from humidity, which leads to moisture absorption.

Paper Handling Tips

Mohawk: If you store paper in a warehouse and not in the pressroom, acclimate it 48 hours on the pressroom floor, in sealed cartons. To achieve the best results, you should leave reams sealed in their original ream wrapper, in the shipping carton. Do not open the wrapper until you are ready to load the paper into your digital device. The ream wrapper has an inner lining which guards against moisture absorption. Once the package is open, the protective barrier is gone and moisture can seep in and cause excessive curl and other problems. After you have opened the ream, reseal the package with tape, if you are going to leave overnight. Do not store paper in your digital printing device's paper trays.

Wausau: Acclimate paper prior to opening. Bring the paper to the same temperature as the air that is around it before you remove the wrap. For a full pallet, acclimation time should be 10 hours for every 10 degrees. For a carton, 24 hours is adequate. Opening the carton and taking the individual reams out to warm up is O.K. If you bring cold skids (say Mohawk: Digital printing is very sensitive to moisture in paper. High humidity causes damp edges and wavy paper. Low humidity dries out the paper edges and makes it contract and become tight.

Wausau: Keep temperatures constant. Turning up or down the temperature in a room at night or over the weekend is a bad idea. It is often done to save money, but when paper issues arise, the downtime adds up fast and the cost savings are lost. Watch the outside doors for moisture loss/gain; consider installing a second barrier between the loading docks and the production areas.

Paper Curl

Hammermill: International Paper products have a slight curl built into the side not imaged first, to help sheets release from the fuser. Curl is built in so that when the sheet curls due to the heat, it is actually correcting itself, so you end up with a flatter sheet. If you are experiencing high curl on a sheet printed on a laser printer or copier, try printing the other side first.

Boise: Most curl issues can be related to moisture levels of the air in the press room or not allowing paper that has been stored to acclimate to the pressroom environment.

Improving Runnability

Appleton: Runability can be improved by using a few techniques. First, reams should be fanned when loaded into print trays. Printers with vacuum or air-assisted feeding systems will generally feed more consistently. Finally, equilibrating stock in the pressroom can further improve runability.

Boise: Proper print testing should be done when switching papers to ensure compatibility with ink/toner, graphics and the environment.

Mohawk: Make sure you "air-up" paper prior to loading into your digital press. Adding air between the sheets can help stocks feed easier and provide less downtime for paper jams.

Cracking on Folds

Wausau: A common concern with digital printing is cracking, especially on folded areas. If basic design principles are followed, problems are less likely to arise when it is time for folding and finishing, trimming and binding. Discuss sequencing with the designer of the piece and the amount of gutter space needed for the chosen binding. Remember that folding with the grain is preferable, as opposed to against it.

Wausau: Acclimate the paper post-press. If a sheet has been excessively dried out, it will become brittle. As a result, the fibers will be crisp and tend to crack and separate. The moisture will come back eventually, even if you do not want it to. When it does, the paper will grow. So, let the paper acclimate for a couple of days (at least hours) prior to binding, folding, shrink-wrapping, etc. If paper is to be stored between processes in less-than-ideal conditions, cover the paper with plastic bags to help control the moisture pick-up or loss.IPG

Reams should be fanned when loaded into print trays. Adding air between the sheets can help stocks feed easier.