Published Article

Digital Printing from the Post Press Perspective
By: Fred Daubert, President, The Riverside Group
Published in: GATFPress

It wasn't all that long ago that digital printing was seen as something of a curiosity rather than a viable production option. Digital print quality was suspect - especially for color applications - and production times were sluggish. That combination relegated digital printing to only very short runs of the simplest applications.

My, how digital printing has changed at this point! Digital print quality now approaches that of offset printing. In fact, the differences are imperceptible to all but a trained eye. Production speed has also improved, along with the range of substrates that can be used. These improvements have made digital printing an attractive option for a broad range of products - including a few that may surprise you.

From a binding and finishing standpoint, there are plenty of differences between digital and offset printing. We'll cover some of those differences here, and offer planning tips to keep in mind when designing for digital printing.

Toner vs. Ink
One of the main differences between digital and offset printing is what's being applied to the paper. Digital toners have a different chemistry than standard offset inks. To begin with, toners are dry when they're laid on the sheet. Paper and toner are then fused using heat and "fuser oil", which helps bond the toner to the paper surface. By contrast, ink is balanced with water, which allows the ink to dry as it seeps into the sheet.

The reaction between toner and paper and ink and paper is also different. As ink dries, it seeps into the sheet, whereas toner sits on the surface of the sheet. This difference is important for a finisher to keep in mind, as it can impact the quality of certain applications. For example, many laminating films used on offset-printed pieces are not aggressive enough to properly bond to toner. The presence of fuser oil can also pose challenges later down the line. Many finishers have found that a substantial amount of fuser oil on a sheet compromises gluing and UV coating adhesion.

The choice of paper may have a bearing on whether toner will flake. Uncoated sheets are ideal, while a matte finish will also prevent flaking. On the other hand, sheets with a gloss finish will not allow the toner to fuse properly, making it more apt to flake.

It's All in the Layout
Properly-planned layouts can add to the success of any print project. In the digital printing world, layouts have an even greater impact on post press costs, in part because there's a limited range of available sheet sizes. Since most digitally-printed products are one-up, your layout should strive for the most efficient use of paper. There are other considerations, however:

Grain direction - Whenever possible, layout projects so that the grain direction of the sheet runs parallel to the spine on book projects, and parallel to any folds. Because toner sits on the surface of the sheet, it's more susceptible to cracking during folding - especially if the fold occurs cross-grain.

Location on the sheet - Many digitally-printed sheets are laid out so the image area is in the center of the sheet. This can cost you both time and money once your project reaches your post press provider. For example, a 6" x 9" image placed in the center of an 8-1/2" x 11" sheet will need to be trimmed on all four sides. Placing the image in one of the top corners allows for only two-sided trimming, reducing both cost and production time (unless there are bleeds on opposite sides of the image, in which case trimming all four sides is unavoidable).

Binding and Finishing Considerations
Proper job planning will help you design projects from the start that are compatible with any post press processes your project requires. Here are a few planning tips to keep in mind:

Folding: Because toner sits on top of the sheet, digitally-printed products are susceptible to cracking at the fold. The digital printing process involves heating the sheets to fuse the toner to the paper. That heat tends to dry the paper out, which also contributes to cracking. To combat cracking, you may want to consider scoring prior to folding, especially if your projects have dense blocks of color or are on sheets thicker than 80 lb.

Laminating: Coating digitally-printed sheets - especially those with a substantial amount of toner - will help protect them during cutting or packaging. Be careful how you protect those sheets, though. For example, single-sided laminating may not be the best solution for sheets printed on both sides. The toner on the opposite (non-laminated) side may flake off as the sheet moves through the laminating process, which is a result of the friction placed on the sheet.

Saddle stitching: Saddle stitching is a popular binding option for many digital printing applications. It's appropriate for thinner book projects such as guides, brochures and newsletters. One of the keys to the economy of stitching is its ability to be performed in-line with several ancillary functions. A post press services provider that can gather sheets, stitch, fold and face trim inline will be able to offer the tight turnaround times that digital print applications demand.

Mechanical binding: When planning a project for mechanical binding, be sure to leave ample punching margins between your copy and the spine edge. For Wire-O projects punching 3:1 (three holes per inch), leave a margin of at least 3/8". For 2:1 Wire-O books, the margin should be at least 1/2". To clarify, that's the margin from the spine edge of the sheet to the edge of the hole closest to the spine.

To help determine the proper wire size, have your finisher provide a printed sample on the exact stock to be used for the production run. This is especially important for digitally-printed products. Many computer design programs allow you to factor book bulk by calculating paper weight and the number of sheets to be bound. However, these programs don't account for the minute increase in thickness caused by the toner sitting on top of the sheet. When multiplied over dozens of pages, that extra bulk will render those computer-generated calculations useless. A printed sample on the exact production stock allows your post press services provider to take an accurate book thickness measurement and suggest an appropriate binding wire size.

Perfect Binding: As with offset-printed pieces, digitally-printed perfect-bound products should incorporate proper trim margins. In addition to a 1/8" grind-off margin at the spine, be sure to also leave at least a 1/8" trim margin on the other three sides. In addition, a ¼" glue trap at the foot of your covers will help prevent glue from seeping onto subsequent covers during binding. This may require you to print covers with bleeds on a different size stock than the text sheets.

Adhesive Case Binding: Believe it or not, adhesive case binding can be a viable option for digital printing applications. The case binding process involves gluing a book block to a hard case, forming a strong bind that's long lasting. Normally, the cost and production time associated with case binding aren't inline with the short-run applications of digital printing. However, many case-bound book applications would benefit from having digitally-printed text sheets - if the cost and turnaround time allowed it. At The Riverside Group, we have created an inventory of pre-formed cases in several colors, styles and format sizes common for digital printing applications. That allows adhesive case binding to be a realistic option for many digitally-printed products.

Under One Roof Solutions
The quality and speed of digital printing has improved a great deal in the past few years. That makes it an attractive option for a broader range of applications, most of which require some form of binding or finishing work. Keep in mind that while many post press functions are applicable to digital printing projects, not all post press providers are well suited to handle it. The key is to find a provider with the range of equipment, production capacity and experience to meet your needs and the needs of your customers.

Fred Daubert is Vice President of the Riverside Group, an "under-one-roof" bookbinding and finishing company located in Rochester, N.Y. They specialize in both soft and hard cover binding production, including perfect binding; PUR binding; notch binding; Smyth sewing; cased-in mechanical and perfect binding; and more. Additional capabilities include mechanical binding; laminating and UV coating; folding; gluing; tabbing; die cutting; foil stamping; embossing and more. For more information, contact Fred Daubert at (800)777-2463, or book@riversidegroup.com.