Printing and Design Tips: June 2010, Issue #107

Roll Sheeter

I recently saw an interesting piece of equipment at a local printer. It is called a roll sheeter, and it attaches to the main 10-unit press at the point where stacks of sheetfed stock are fed into the press.

What this does for the printer—and you—is reduce the cost of paper, because rolls of printing stock are cheaper per square-unit of measure than boxes of cut sheets, and this discount is often reflected in your printing bill.

If your printer has sheetfed presses (most have either sheetfed presses or web-fed presses but not both), the norm for paper use is to buy, store, and then use cut sheets of a particular size appropriate to the press. This may be 20” x 26” cover stock or 28” x 40” text stock (or a multitude of other sizes), but the paper usually arrives at the printer in cartons of 500 or 1,000 sheets. Prior to being sent to the printer, sheets are cut from the rolls of paper produced by the paper mill. Therefore, the cost of this interim step can elevate the final cost.

Granted, the sheeting still must be done by someone, but if the printer does this work on equipment he has already purchased, using in-house staff, the cost is reduced, because the middlemen (and their mark-ups) have been removed from the equation. Furthermore, once set up, the roll sheeter automatically cuts the sheets from the rolls and drops them into the paper hopper, ready to be fed into the press. So it's a more efficient process, as well, and this further reduces preparation and press time (i.e., yielding an additional savings).

So why doesn't this change the 10-unit sheetfed press into a web press? The main difference is that a web press would not cut the sheets at this point in the process. Rather, it would feed the paper as a continuous strip—at a high tension—through the press (and then perhaps through an oven, a folder, etc.). The sheetfed press is not set up to maintain the tension of a continuous strip of paper running through the length of the press. It is designed to use a stack of cut sheets from a feeding unit (like a hopper on a photocopy machine). And web presses are much larger and much more expensive for the same final sized press sheet and the same number of inking units. (It should also be noted that the quality of printing available on a sheetfed press is still superior to the print quality achieved on a web press--although the quality gap is closing.)

But the gist of this argument is that a roll sheeter can benefit both you and your printer. And as an additional piece of printing equipment (if it can in fact be fitted to your printer's press), it is a relatively cheap way to save you and your printer money. (The printer's cost to retrofit a printing press with a roll sheeter will vary, depending on the press in question. However, the printer can expect to save 5 to 15 percent of the cost of paper by buying rolls instead of sheets.)

FYI, the roll sheeter doesn't need to be attached to the press. It can in some cases be moved from press to press, or it can be operated off-line, chopping rolls of paper into sheets that are then stored and carried to the appropriate press.

Offsetting vs. Set-Off

“Offsetting” and “set-off” mean the same thing, and you'll not want to hear either word from your printer. On a stack of printed press sheets, when the ink from one sheet rubs off onto the sheet immediately adjacent to it within the paper stack, you have a problem called offsetting. To minimize this problem, printers spray “anti-set-off powder” between the press sheets (these minuscule granules lift one sheet slightly off the other, allowing air to circulate between the sheets and dry the ink before offsetting occurs).

Allowing one side of the sheet to dry before printing the other is crucial, and it is important to keep in mind that excessive humidity (as is usual in the summer) and certain ink colors (such as any color mixture in which Reflex blue is a component) retard drying and encourage offsetting or set-off.

This printing problem can also manifest during trimming or other post-press activities requiring clamping the press sheets together. For instance, if the operator puts a stack of printed sheets in the guillotine trimmer before the ink has completely dried, the intense pressure of the clamp that holds the sheets together for trimming can cause the not-yet-fully-dried ink to transfer from one sheet to the next. When this happens, your printer needs to stop the process and allow more ink drying time before proceeding.

So when your printer says the press sheets need extra time to dry, it's not an excuse.

Fortunately, the newer UV inks circumvent this problem. Because UV inks don't dry by oxidation or evaporation--but rather are cured through exposure to UV light—the press sheets come off the press completely dry and can therefore be immediately backed up (printed on the reverse side) or trimmed.

Not all printers have presses equipped to handle UV inks (because the press needs to be fitted with a UV-curing unit), so ask your printer about their UV capabilities early in the process to ensure a good result.

[Steven Waxman is a printing consultant. He teaches corporations how to save money buying printing, brokers printing services, and teaches prepress techniques. Steven has been in the printing industry for thirty-three years working as a writer, editor, print buyer, photographer, graphic designer, art director, and production manager.]