A common question asked of Allied Bindery is whether or not the spine area of a perfect bound book needs to be “knocked out”. For non-printers, this question revolves around whether a coating (varnish, aqueous, ink or UV) can be applied to the spine area of the book cover, without negatively impacting adhesion.
If the spine area of a book cover must be knocked out, the printer must cut away a portion of the printing blanket. This cut away portion will then prevent coating from being applied to the press sheet. By not applying a coating to the spine area of the book cover, the adhesive will do a better job of adhering text pages to the cover. However, the printer will be unable to use the printing blanket again, because it was customized for a specific job. This can be expensive and time consuming for the printer.
There are a couple of things to be considered when determining whether or not a “knock out” of the spine is required. When a book is to be bound with EVA adhesive, the spine area should be knocked out to achieve best results. Although EVA adhesives are a fine choice for many text sheets, they are not formulated to stick well to varnishes, aqueous coatings, heavy ink coverage, or UV Coatings that are often applied to book covers. Knocking out the spine and hinge score areas will result in the best overall adhesion.
Choosing PUR adhesive will help overcome several of the performance shortfalls of EVA adhesive. PUR will stick very well to varnish coatings, aqueous coatings and nearly all ink choices (metallic being an exception). If the printer is utilizing a UV coating on a book cover or the spine area of text sheets, it is still a good idea to knock out these areas. Although PUR may stick to a UV coating, the effectiveness of the adhesion is determined by the amount of silicone content and the resulting Dyne level of the coating. Since the silicone level in a UV coating is not controlled by the bindery, the risk of the PUR not sticking to UV coating is reasonably high. As a result, Allied Bindery recommends knocking out the spine and hinge score areas of a book cover when a UV coating is being used.
We encourage you to contact your Allied Bindery Representative to discuss project planning issues such as cover knock outs and coatings. Our experience and ideas will likely save you money or help avoid the creation of a production problem.