Our customers regularly ask us to consider and explain the merits of PUR binding over Perfect binding. These considerations are often made against a backdrop of performance and ever increasingly, price constraints. With this in mind, let’s consider the differences between PUR and perfect binding and try to contextualise when it is appropriate to PUR bind or perfect bind.
The fundamental difference between the two types of binding is the adhesive used in the process. Perfect binding uses ethylene vinyl acetate (EVA) adhesives whereas PUR uses polyurethane reactive (PUR) adhesives. Put simply, the binding really only differs by way of the type of glue used. It is the properties of each type of adhesive, however, which is important in determining which is suitable.
Arguably the most important thing to consider is that PUR adhesive affords superior adhesion over EVA. This means it will offer increased binding strength, with page pull tests reportedly showing a 40-60% stronger result when compared against the more traditional perfect binding. This can often prove beneficial if brochures/publications are to exist within environments which will mean they may have to withstand rigorous use. Incidentally, PUR adhesive is also much more suited to withstanding temperature extremes without glue failure.
The strength that PUR adhesive offers, combined with the fact it adheres to a wide variety of substrates means it has universal appeal. It will for instance, be equally at ease adhering to ink, UV-cured coatings, aqueous coatings, coated papers and boards in a variety of weights and films as well as traditional uncoated papers.
A key reason PUR adhesive is often the preferred choice is due to its excellent flexibility and ‘lay-flat’ qualities. The benefits here are two fold. Firstly, due to PUR requiring a smaller layer of adhesive when compared to perfect binding, it allows even the thinnest of books (a minimum of 3mm is still recommended) to maintain a square and rigid spine. Secondly, when applied to standard thickness, PUR glue affords considerably more flexibility and pliability than EVA, which allows books to demonstrate lie flat characteristics. This in turn minimises any spine cracking when the finished product is ‘flattened’ out for reading.
The benefits of PUR binding outlined above should not mean that the use of EVA in perfect binding is dismissed as a viable option. EVA adhesives are still very effective and continue to produce strong, commercially sound products. EVA adhesives for the print finishing process were originally designed for lightweight uncoated papers for book binding, but perfect binding is commonly used within the magazine industry as it is also suited to lightweight coated substrates. It a cheaper option when compared against PUR, with binding houses today charging approximately 30% more for the PUR process.
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 most 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.