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Perfect binding: What you need to know

For many printers, perfect binding is now a key component of their business. If you have a perfect-bound job to complete, or are looking at purchasing a perfect-bind machine, you should understand the basics.

What is perfect binding?

Perfect binding is the process where either flat sheets or signatures (a sheet with multiple pages printed onit) are bound together using a flexible adhesive with a wrap-around cover thatcreates a square-shaped spine.

The equipment

The equipment can range from small tabletop machines to million-dollar systems. With the increase in on-demand book binding, dozens of affordable machines are now available that include many of the features found previously only on high-production machines.

Perfect binding machines have on ecommon element – a glue applicator. Almost all hot-melt machines use a contactroller or multiple rollers to apply the glue to the spine of book blocks. Thena cover is pinched around the spine and held in place for up to 10 seconds toallow the glue to set. The amount of glue being applied is adjustable. Moreadvanced machines will also apply a side glue to the edges of the book blockbefore adding a cover. Side gluing is important because it binds the edge ofthe cover to the side of the book block (scored hinge area), allowing the bookto open and close properly. This helps to prevent the spine lining and thebook’s end sheets from becoming partially unglued from the cover.

In order for the glue to havemaximum adhesion, most commercial-grade perfect binders have a grinding wheelthat grinds notches into the spine of the book block anywhere from 1-3 mm deep.This allows the glue to flow up into the spine to obtain maximum adhesion.Smaller perfect binders require the operator to place the covers in position,while more automated binders have integrated cover feeders that automaticallyfeed the next cover into position.

The paper and grain direction

The cover and the interior stockshould not be more than 100 GSM apart. Although it’s common to attempt tocreate a feel of quality with a heavier cover stock, this must also beaccompanied by a heavier interior book block stock. Grain direction is thefinal alignment of the paper fibres during the manufacturing process. Inperfect binding it’s essential that the grain runs in the same direction orparallel to the spine of the book. If it doesn’t, the book will not open andlay flat correctly, and the additional pressure placed on the spine willincrease the chances of warping, sheets falling out – or worse, completesections of the book block separating.

The glue

Hot-melt EVA (Ethylene VinylAcetate) glues have long been the staple of the small commercial bookbinder. They’reinexpensive and can be left in the machine and reheated at any time, makingthem the choice for almost all small-format perfect binders under six pockets.The main limitation to these hot melt glues is their inability to bind somedigitally printed and coated stocks reliably. Due to the rapid set-up speed(five to eight seconds), it’s difficult for the glue to penetrate into thefibres of these stocks because the coating or toner acts as a barrier. Withoutproper penetration into and between the sheets, a perfect-bound book will havea limited ability to stay together. A cold glue or PUR (Polyurethane ReactiveAdhesive) adhesive will solve this problem.

Although more expensive, PUR isbecoming increasingly popular in binding coated stocks and digitally producedtoner output. PUR is different from EVA glues in that it’s dispensed through anapplicator head instead of being applied through a traditional roller. Thisapplicator allows the glue to be forced up into the book block (with pressurefrom a heavy-duty pump) penetrating the spine and creating a much strongerbind. It also prevents the escape of fumes and any premature moisture curing ofthe PUR adhesive by exposing it to the atmosphere. PUR binding, however,requires up to 24 hours to completely cure.

A third type of adhesive PVA(Polyvinyl Acetate) is applied as a cold liquid with a look and viscositysimilar to ordinary white glue. Being cold, the glue has a much longer dryingtime, allowing it to absorb into the fibres of the paper, facilitating thebinding of both heavier and coated-paper stocks. PVA’s are more difficult toapply and consistent chemistry is needed for consistent results. As a result,only large binding lines currently use this adhesive.

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