Binding Solutions, LLC

Advances In Gluing-Off Add Productivity
Advantages In Hard Cover Binding
Gluing off, as the first adhesive application in case bound or edition bound book production, sets the stage for all subsequent processes. The purpose of gluing off is to hold the signatures together in a unified bookblock so that subsequent operations, such as rounding and backing can take place. In the past, the majority of edition bound books were either Smythe sewn or side sewn prior to gluing off.
More recently, higher speeds have been achieved by using a high speed binder and its attached gatherer to glue off signatures, which may be burst bound or perfect bound. The high speed systems lend themselves to many different adhesive combinations, such as liquid two shot, liquid/hot melt two shot, one shot hot melt, and PUR.
When books are Smythe sewn, the signatures stay together, but the backbone is very loose. When signatures are glued off with liquid adhesives, they are held together tightly, and the loose strings from the sewing operation are either adhered to the backbone or they are burned off in the drying operation.
The choice of adhesive is critical for this operation. The product must be flexible to withstand the subsequent rounding operation without splitting, and it must be fast drying to allow for maximum line speed. The tack level must also be relatively low, as many times the bookblocks are trimmed two or three up, and the pressure of the trimmer clamp could cause them to block together.
More recently, standard perfect binders that can glue off books at two to three times the speed of the older machines have been used. These lines typically split off into two separate lining machines in order to maximize production. Drying is achieved by gas heaters or infrared heaters. In Europe and in Canada, RF (radio frequency) drying is more common. This high speed process allows the bindery to either glue off or make one-shot perfect bound books on the same machine.
The next most common gluing-off method involves a liquid primer followed by a rubber-based hot melt top coat. The advantage of this type of gluing-off is that the liquid coating is very thin and can be dried very easily. The top coat must be a rubber-based hot melt because EVA type hot melts have memory, are very hard to round, and have very poor round retention.
Most EVA hot melts have poor adhesion to liquid primers because the two materials differ in thermal expansion rates. That is, the plastic-like hot melt tends to be less flexible than the dried liquid primer and will expand less during heating. This weakens the bond between the two products. National has developed a new EVA hot melt, EZ OPEN™ 70-4341, that reacts like a rubber-based hot melt and expands and contracts like the primer, thus maintaining the bond between hot melt and primer.
New Trends
Many perfect binders have been using PUR to produce books with better heat and cold resistance, and to achieve better strength on coated papers. Since gluing off and capping (or feeding on combined end sheets) is done on many of the high speed binders, PUR would seem to be an excellent choice for gluing off. In the past, the stumbling block was the slow strength build-up of the PUR which would cause problems in the rounding and backing. The newest generation of PUR has excellent green strength and has been run in line with a Kolbus rounder and backer and then directly into the casing in machine.
Two other benefits of using PUR for gluing off would be the ease of roundability and the ultimate round retention. Even though the PUR has developed enough strength to go through the subsequent operations, it is still uncured and pliable enough to draw an excellent round. Once the round is in the book, and the PUR cures, the retention of that round is far better than any of the other methods of gluing off.
Another trend in gluing off has been the use of either the liquid system or the two shot liquid/hot melt system. The bookblock is subsequently dropped bareback onto the belts to be trimmed and then lined. Although some binderies have been doing this for years, there is still some concern over the retention of the round and the possibility of splitting without the reinforcement of the cap. This method, when done with liquids, produces books with excellent round, but care must be taken to choose the proper lining adhesive so that the bond between the dried liquid and the lining adhesive is maintained over time. Likewise, when the two shot liquid/rubber hot melt system is employed, the use of traditional EVA hot melts, as well as animal glue, needs to be reexamined. National's EASY MELT™ 34-1211 has been proven to perform satisfactorily with all of the above combinations.
Under many circumstances, the application of any of these new gluing-off techniques can provide significant productivity advantages in the production of case bound or edition bound books. Additionally, some of these technologies, such as PUR, can eliminate traditional bookbinding steps, while improving the overall quality of the book.
Binding Solutions, LLC. Copyright 2015.