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Q&A: Perfect Binding for Digital Print

In the finishing realm, perfect binding plays an important role in promoting efficient operations and fast turnarounds as the market moves toward digital print. As print becomes more prominent as a marketing piece, short-run perfect binding is becoming more desirable.

What are the advantages of perfect binding for digitally printed products?

Perfect or adhesive binding is a method of binding single sheets – as opposed to signatures – into a book. Many digital books are printed as stacks of single sheets. One of the most easily automated of finishing processes, perfect binding’s low cost makes it a popular choice for binding a variety of printed matter, wherein single sheets are gathered, stacked and the binding edge covered with glue. A cover is attached to the book and is held in place by the glued spine. Then, the entire product is three-side trimmed on a dedicated trimmer or guillotine cutter.

Professionally perfect-bound books have square backs, smooth spines and adequate adhesive strength to prevent the pages from being pulled from the binding. The only way to accomplish this used to be with large offline production machines, which required lengthy makereadies and resulted in expensive short-run applications. In recent years, however, a combination of factors has prompted printers to seek out small-format standalone perfect binders. Solutions answering these needs are modular, flexible, integrated, run at speeds as fast or faster than the output device and offer multiple opportunities for reductions in labor, including quality verification. They are easy to operate and quick to set-up for new jobs and, last but not least, feature connectivity and JDF. They are machines that can handle books from digital printers and offset presses and perfect bound books of one or 1,000 quickly, efficiently and profitably.

What challenges are there when using perfect binding for digital print?

Among the biggest challenges are failure to form a durable adhesive bond on digitally qualified papers, as well as the potential cracking of inks and coatings. In particular, the presence of fuser oil left on digital sheets can have a severe impact on the pull-strength of a digitally printed, perfect-bound book when hot-melt adhesives are used. Toner can have the same effect if the printing bleeds into the spine of the book.

For these reasons, the perfect binding of toner-based color sheets using conventional hot-melt adhesive has been largely supplanted by the use of polyurethane-reactive or PUR adhesives on fast-makeready binders. While PUR is more expensive than traditional hot-melt adhesives, it also lasts longer, weathers extreme temperatures, looks good and holds difficult plastic or coated stocks reliably. PUR technology ensures reliably high adhesion to the sheet edges so that finished products can be opened flat without problem, even with difficult materials such as heavily coated papers and digital print products.

While PUR provides an added measure of safety that the job will not be rejected, it also adds significant cost. Given the recent migration to inkjet and oil-less fusing of toner based products, however, hot-melt glues can provide a more cost effective solution as long as the spine preparation is sufficient to result in good book adhesion (good pull results).

What considerations are there when trimming?

Trimming is accomplished with either a dedicated three-knife trimmer or a guillotine paper cutter. The issue with three-knife trimming is that the capital cost for the machine is most often above $100,000 US, while the quality of trimming delivered by machines currently on the market often is not up to market expectations due to spine knicking.

A cost-effective alternative is to use a guillotine cutter instead, even though it adds another material-handling step to the process. Heidelberg has studied the problem and found that at quantities up to 1,000 books per hour, the cost and productivity of guillotine trimming can be advantageous. Over the very short run, the challenge is to reduce the makeready of the cutter from book to book size, so that equipment suppliers are exploring ways to add automation to the cutting process. By sending the cutting parameters to the guillotine at the point of prepress, or by using a bar code on the book to load the cutting parameters, the cutting process can be sped up substantially while reducing re-runs and waste.

This Q&A was excerpted from an article   in the Summer 2011 issue of The Binding Edge, written by Steve Calov, postpress product manager for Heidelberg USA. A leading solution provider for the print media industry, Heidelberg manufactures precision printing presses, platesetters, postpress equipment and software for integrating all printshop processes. For more information, visit www.us.heidelberg.com or call 770.419.6500.