Printers often incorporate spine perforations into the printed signature, whether folding a sheetfed form or delivering directly from a web press. The perforation provides a distinct advantage to the folding process. A spine perforation allows air to escape during the folding process, reducing the chances of wrinkling, bottling or shingling. This, in turn, results in a better looking final product.
A significant risk that is often overlooked by a folder operator or web press operator is the size of the perforation blade or wheel. If a perforation is too aggressive, i.e., lots of perf, not much paper remaining; the spine of the signature may break apart during the collation/gathering process at the bindery.
The amount of paper that is left intact on the spine provides the only strength to hold the spine together during the collation process. The mechanical gathering process in the bindery requires that the spine of a signature be pulled down into the collator grippers using vacuum suckers. If the perforation blade or wheel used at the folder or press was too aggressive, the paper will peel apart at the spine of the signature when the vacuum suckers begin to the pull the form into the grippers.
Once this happens, there is often no alternative other than to hand feed the affected signatures. Hand feeding or hand collation results in increased expense and decreased production speed on the binder. This is a phone call that the bindery does not want to make and the printer doesn’t want to receive.
A quick way to check the strength of the perforation is to flex and jog a handful of signatures at the folder or web press. If the perforations show any indication of splitting or breaking apart during the hand jogging routine, they will break and fail during the mechanical collating process. If this is noticed, it is time to change to a less aggressive perforation wheel or blade, thus helping to avoid unanticipated problems and additional charges during the binding process.