Polyurethane Hot Melt Offers Strong Binding
Polyurethane hot met is the strongest, most flexible binding adhesive available, offering several additional advantages over other binding adhesives. When inks, coatings or digital print toners are present in the spine area, these can often compromise the strength of a typical hot melt perfect binding. Polyurethane hot melt, however, is resistant to this and will form a super-strong bond with all weights and finishes of paper stocks. In addition, polyurethane hot melt works well with synthetic and recycled-content stocks.
So what is the difference between traditional hot melt and polyurethane hot melt? Why should you spend more money on a binding system you think you already have? Traditional perfect binding uses ethylene vinyl acetate (EVA) adhesives whereas polyurethane binding uses polyurethane reactive (PUR) adhesives. The PUR glue offers superior adhesion over EVA as exampled by the ability to lay a bound book flat without compromising the binding strength. More often than not, the EVA glue will not be able to retain all pages once heavy handling starts to take place. Nonetheless, a PUR bound publication will retain all pages and will not lose strength in either hot or cold conditions. Generally, the page pull-strength of a PUR-bound book is 2.5 times more than that of a standard EVA adhesive perfect-bound publication.
The type of paper in the book will also have an effect on the bind. The polar nature of polyurethane molecule allows it to adhere to UV-cured coatings, films, as well as to traditional uncoated and clay-coated papers. The composition of polyurethane adhesive enables it to form a strong bond with the paper even in the presence of inks, coatings and varnishes, making it the ideal way to bind digitally printed pages.
Polyurethane hot melt adhesives differ from conventional EVA hot melts in that they cure by crosslinking via a chemical reaction with moisture contained in the paper stock or surrounding air. Once cured, do leave a freshly bound book 24 hours for a full cure to take place, the adhesive's higher molecular weight provides a tough, pliable bond that is resistant to temperature extremes.
This counters another common concern with EVA bound books: their stability in extremely hot or cold temperatures. Polyurethane hot melt adhesive is impervious to temperature extremes. This means that PUR-bound books can be used almost anywhere, from the hottest summer conditions to the most harsh of winter weather.
EVA hot melt glues still have their place in book-binding, 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, but more and more perfect binding applications are being pushed towards polyurethane hot melt.
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