There are a number of binding options, including Polyurethane Reactive (PUR), Ethylene Vinyl Acetate (EVA) hotmelt and Polyvinyl Acetate (PVA) cold emulsion adhesives, or Smythe Sewing. PUR has only been in bookbinding since about 1989. PUR binding was first adapted by midsize trade binderies for producing many trade journals and annual reports due to short lead times using highly coated and cross-grained papers without sewing. These markets will continue to be the high users of PUR, but publishers are now recognizing the benefits of PUR and are requesting the use of PUR binding to ensure quality and longevity to their products.
Why PUR?
Since its introduction, PUR use has increased dramatically. PUR is chosen over standard hotmelt adhesives for many reasons, the most important of which are its superior adhesion and the ability of a PUR-bound book to lie flat when open.
It is very important to understand the main differences of the two important binding technologies in the market today.
Advantages of PUR
1. Excellent flexibility and desired lay-flat quality.
2. Cold and heat resistance enabling books to be bound, stored and used in extremes of temperature.
3. PUR can bind coated paper.
4. PUR can bind varnished, UV-coated, carton, mylar and other stocks.
5. Impervious to print oils/ink used in the lithography or digital print process and binding quality is unaffected by ink migration into the spine.
6. 40% to 60% better page pull resistance as compared to EVA Hotmelt.
7. Can handle recycled papers.
8. Handles cross-grained stocks better.
9. Square backbone: Because only a small amount of PUR needs to be used for binding, less adhesive is squeezed out when the cover station and side clinchers attach the cover and form the back.
10. PUR is also environmentally friendly due to its low VOC (Volatile Organic Compounds) and the working temperature is set at around 120 degrees Celsius while EVA is at around 170 degrees Celsius.
Advantages of EVA
1. Fast curing (in a few seconds) & quick trunaround time as compared to PUR which needs 24 hours to cure.
2. It is cheaper when compared to PUR glue.
3. Ease of operation. Most often it is much easier to handle and maintain an EVA Hotmelt gluing system as compared to a PUR gluing system.
4. Finished book can be immediately handled. A PUR bound book cannot be handled within 24 hours of processing.
5. Cleaning process of EVA binders is very simple/easy as compared to PUR binders. Most often, it takes more time to clean PUR binders.
6. EVA Hotmelt glue still have their place in bookbinding, especially when it comes to binding thread-sewn books, as the thicker glue allows for greater penetration into the spine area of the folded sections.
In summary, both processes are still widely used within print finishing. The question 'which is better', probably needs to be replaced with the question 'which is more suitable', as the decision to use one over the other is very much job specific and would involve numerous considerations -- from substrate used and thickness of the book, to the intended use of the product and any financial constraints to produce.
Amey Alshi, Duplo International's Blog
