Thanks to their outstanding bonding performance and durability, PUR hotmelts are continuing to take the graphic arts industry by storm. They meet all of the industry's requirements in terms of perfect binding and gluing-off thread-stitched and thread-sealed books through to side gluing and end papering. With the aid of high-performance nozzle application systems, even the high speeds of modern perfect binders are no problem.

A risk with serious consequences
The only drawback so far has been their relatively long cure, which for conventional PUR adhesives depends on the moisture in the air and in the paper and can take as much as five hours. Only then can the quality be objectively and reliably evaluated with the pull test. For bookbinders, every job performed with PURmelt is therefore a leap in the dark. During the process itself, it is only possible to assess spine preparation and adhesive application. Thereafter bookbinders have to simply rely on the process's known high success rate. There is always a risk involved, however, especially with high-speed production of high-circulation soft covers, as flaws during processing can never be entirely excluded and can be extremely costly for the bookbinder.

80 percent cure in 15 minutes
Against this background, Henkel has now tailored its process for accelerated-cure PUR hotmelts, which is already proven in book production, to the requirements of the soft cover market. The system is based on modified polyurethane adhesives which, on exposure to UV light, cure by up to 80 percent in only 15 minutes. The UV lamps needed for this are integrated in the perfect binder. Several manufacturers have been certified for the production of the lamps, which are triggered either by microwaves or by electrodes. The system can be installed on any commonly used perfect binder and ideally on those with two gluing units.

Excellent results in practice
Successful pilot projects with customers in Germany, Italy and Spain have confirmed the process's maturity. Exhaustive tests have shown excellent application and cure performance even at the perfect binder's top speed. The typical problems associated with cutting, knife contamination on the trimmers, adhesive deposits on the transfer conveyer belts or with offsets in thicker publications have been dramatically reduced, and the finished print products can be shipped out rapidly. The UV technology developed by Henkel thus permits inline quality checks of soft cover production with PURmelts and enhances reliability when using high-performance binders and application systems. Major bookbinders and publishers all over the world have already shown great interest in this new development.

Henkel AG & Co. KGaA