Binding Basics

Perfect Binding Perfect binding refers to a binding process in which the inside pages of a publication are ground down and glued at the spine before a soft cover is attached. Afterward, the cover and pages are trimmed on the non-spine sides to produce a publication with a clean, “perfect” edge. When perfect binding is used in the case binding process, endsheets are attached and the book block is trimmed prior to casing in.

binding. The PUR glue used for the spine can be followed with a different hot-melt adhesive for the side of the spine to adhere to the cover. Hot melts are comprised of a mixture of resins and polymers that bond in high temperatures and reach a solid state when cooled. A metering roller is used during the gluing process to remove excess glue and ensure the adhesive covers the backbone fully and evenly. Once the glue is applied to the book block, its cover is fed through a separate track where a feeding mechanism scores the inner spine at the width needed for the cover to fold neatly around the book block. After hot-melt adhesive is applied, the track carrying the scored cover rises to meet the spine of the clamped book block. While the front, back and sides of the book block are held firmly in place, the cover is pressed onto the backbone and the nipping station clamps the spine on the hinge scores, holding for a moment to allow the glue to seep fully into the backbone. The untrimmed publication is then placed on a conveyor belt on its way to the trimmer. The length and speed of the conveyor belt is designed to last the exact amount of time required for the adhesive to dry enough for trimming. For traditional hot-melt adhesives, this initial dry time only lasts 45 seconds, but the adhesive takes about eight hours to dry completely. The trimming unit takes the most time per product compared to the other processes in a perfect binding system, so some binding systems deliver overflow product to a stacker for off-line trimming. For on-line trimming, the conveyor belt delivers the publications directly into a three knife trimmer, where three large

Assembly required The industrial construction of a perfect bound publication varies between machinery and binderies, but the basic process in a perfect binding line is as follows. After the inner pages of a publication are printed and folded into signatures, a gatherer sorts them in the correct sequence to create what is called a book block. The book block is then compressed in a clamp, which carries the publication spine-side down as it moves through the binder. The clamp glides the book block across a backbone saw which removes the signature folds and grinds the spine. The spine is ground down, notched and roughened with brushes or sandpaper which exposes paper fibers and increases the surface area of the backbone so the side glue can adhere more effectively. Still spine-side down, the book block is carried through the gluing station. Many perfect binders use a type of hot-melt adhesive for the spine glue called polyurethane reactive, or PUR glue. Applicator wheels roll the PUR glue from heated glue pots up onto the spine of the publication. Side glue is applied following the spine glue, as a combination of hot-melt adhesives with varying viscosities is often used for perfect

Because perfect binding is the only softcover binding method that allows for printing on the spine, it is a popular choice for publications which are likely to be stored on shelves.

Binding Basics

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