PUR 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. PUR is resistant to this and will form a super-strong bond with all weights and finishes of paper stocks. In addition PUR works well with synthetic and recycled-content stocks.
A Stronger Bind
So what is the difference between hot-melt and PUR? 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 PUR 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: you may recall a tired old road atlas in the trunk of your car, pages lose or already missing! That is EVA glue. A PUR bound publication will retain all pages and will not lose strength in either hot or cold conditions. The page pull-strength of a PUR-bound book is more than 2.5 times 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 PUR 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.
Survive in Heat or Cold
PUR 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 yet another common concern with EVA bound books: their stability in extremely hot or cold temperatures. PUR adhesive is impervious to temperature extremes. This means that PUR-bound books can be used almost anywhere—from the hottest summer conditions (our road map in the car again?!) to the most harsh of winter weather—without unwanted re-melting or cold cracking.
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 PUR.
Smaller, Lower Cost Units
The one drawback with the process until recently is that a large $$ investment has been required to get into this area of post-press productivity. However, UK based finishing equipment manufacturer and supplier, Morgana Systems (Booth 3561), believes that this is changing. Ray Hillhouse, UK Sales Manager at the company, said of the recently introduced DigiBook range of PUR binding systems: “Wherever we show these products they seem to generate significant interest. Affordable PUR binding is ideal for digital print companies, and we have been pleased to welcome a significant number of printers who see PUR as a real benefit to their businesses to demonstration events in the UK.”
The DigiBook range of machines are suited to both traditional and digital printers who require either short-run or production capacity PUR perfect bound books to a professional standard. This innovative range of machines is equipped with a patented closed gluing system, where the spine and side gluing is applied by a slot applicator for the utmost binding quality and accuracy.
Easy to Operate
DigiBook machines are innovative bookbinding products designed and built for the very latest market requirements. The products are also easy to use by non-specialised personnel, with a touch screen panel that uses icon graphics and is suitable for the programming of all precision operations in just a few seconds. These include both start-up and shutdown and use a new, innovative system that is covered by a number of international patents.
The adhesive applicator is direct, and is hermetically sealed, without odour or toxic fume emissions, meaning that no extractor fan is required. This solution allows for the use of polyurethane glue in cartridges of up to 3kg, all adding up to simple and waste-free binding.