In most cases, you have two options for printing multi-signature publications and books. The first is sheetfed offset custom printing. In this case, sheets of printing paper are fed one at a time into a small to mid-sized press. In most cases, you print one side of the sheet (sending it through four or more ink units) and then air dry the sheets. Once the ink has dried, you re-feed the press sheets into the press to print the opposite side of the paper. (In some cases, on “perfecting” presses, you can print both sides of the sheet in one pass, but this is not always an option.)
Your other choice is the web press (cold-set and heatset). If you’re custom printing a high-quality job on coated paper, you would use a heatset web (without the “heatset” component of the press, the amount of ink on a page would slow ink drying and promote ink smudging). On a heatset web press, paper from a large roll travels quickly through a huge, multi-unit press, printing both sides of the web at once (“perfecting,” just like the perfecting sheetfed press).
The press throughput is much faster on a web press than on a sheetfed press (perhaps 20,000 cut sheets per hour rather than the approximately 12,000 or more flat sheets per hour you might get with a sheetfed press). On a heatset web press, as the paper travels through the equipment, the inked printing plates deposit ink first onto the press blankets and from there onto the printing paper. After leaving the printing units, the paper web then travels through high-heat dryers, which flash the solvent out of the ink (i.e., drying the ink by the evaporation process rather than by absorption), leaving the ink sitting on top of the coated sheet. Chill rollers then cool the ink and paper, curing and setting the ink.
At this point, the printing paper enters the finishing end of the press, where it can be folded into complete signatures. This in-line folding capability eliminates the need for folding in the bindery unit of the commercial printing plant. Press signatures can then be gathered, bound, and trimmed.
If, on the other hand, your job is printed with black ink and no photos or tint screens on uncoated book paper, it may go through a cold-set web press instead of a heatset press. This is a much simpler process. Essentially, the job is the same up to the point of drying the web of paper. Paper travels through the four (or more) ink units, but since the paper absorbs the ink (i.e., drying the ink by absorption rather than by the evaporation process), the dryer assembly and chill rollers are unnecessary. The web of paper, having been printed, can enter the folder directly.
A third option, which is closer to heatset web offset, is UV web printing, whereby special inks are not dried with heat but cured with UV light, allowing the ink to sit up on the press sheet (called hold-out) in much the same way as ink printed on a heatset web press.
Why You Need to Know This
- Custom printing longer jobs (i.e., longer press runs and/or multi-signature jobs like print books and magazines) will usually be cheaper on a web press than on a sheetfed press. It is wise, therefore, to get estimates from both sheetfed commercial printers and web printers and compare them. I have seen a 15 percent savings (or more) in choosing the right technology. For a long job I once designed and printed, this amounted to a $10,000 savings.
- Not needing to fold the job offline (but instead folding it right on press) also saves you money.
More Things You Need to Know
- On a press check, a sheetfed printer stops the press to have you check the color and registration on a press sheet. When the pressman has made your requested changes, the press starts up again. In contrast, a web press never stops. You just see periodic sheets cut off at the delivery end of the press. Since the press is traveling at a much faster speed than a sheetfed press, it is imperative that you make changes quickly and then move on. This is not just about wasting paper; it is more about using up the amount of paper allotted for the job. Price estimates are drafted and paper ordered assuming a quick make-ready and minimal changes. If you make too many changes, you could conceivably use up your paper allotment before the end of your press run.Therefore, in most cases, it would be wise to leave the press check to the printer. This is particularly true for a publication. Publication printers (magazine and newspaper printers) schedule all jobs tightly to have the presses running at all times. If you miss your place in line, your job could get bumped by several weeks.
In contrast, if you go to a commercial web printer, your schedule will be less tight. You will also have more access to a variety of printing papers and book, magazine, or catalog sizes, and there will be more flexibility with press checks. That said, web presses eat up paper quickly, so it behooves you to make all press check decisions quickly and decisively to contain costs.
- Another thing to remember when custom printing a job on a web press is that the press has a fixed printing size. Rolls for a full-web press that might be 36” wide may have a cut-off (one complete trip around a press cylinder) of 22 3/4”. So your cut press sheet would effectively be 36” x 22 3/4”. An 8.5” x 11” book page within a 16-page signature (8 pages on either side of the sheet) will not fit in this space with room for press bars and bleeds. Therefore, the page size needs to be reduced to 8 3/8” x 10 7/8”. In fact, if you have a book with these dimensions, you can assume it has been printed on a full-web press.
- A final rule of thumb is to keep an open mind when considering heatset web offset printing. The conventional wisdom had been that web offset does not provide as high quality a product as sheetfed offset. But this has been changing, particularly with closed loop color management and automated registration control on press. Color level information can travel electronically from the prepress department to the presses and be consistently and automatically maintained using equipment currently in place at heatset web printers.
If your job requires enough press impressions, keep web offset custom printing in mind as a viable alternative. Your printer can help you determine the cutoff point where sheetfed becomes pricey and web printing becomes an attractive option.
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on Monday, April 15th, 2013 at 12:56 pm and is filed under Book Printing.
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