The product Purmelt is a reactive polyurethane hotmelt. As a result of its prepolymers, it is moisture curing. PU hotmelts are used today in a broad range of industrial sectors.
Performance of various adhesives systems for perfect binding
Requirement Dispersion Hotmelt EVA-based Hotmelt PU-based Adhesion +++ ++ ++++(+) Cold resistance ++ (+) ++++(+) Heat resistance +++ + ++++(+) Curing speed + ++++ +++(+) Aging ++++ ++ ++++ Resistance to oils +++ (+) ++++ Cuttability + +++ ++ Roundability +++ +++ +++(+) Processability +++ +++ +++
The graphic arts industry also has challenging applications for this type of adhesive. Whatever the application – perfect binding, gluing off thread-stitched or thread-sealed books, side gluing or endpapering – Purmelt meets all the requirements and ensures optimum results in terms of pot life, fast curing and maximum initial tack.
This new generation of adhesives is distinguished particularly by its tremendous adhesion to a multitude of different paper types and various other materials. With a coat thickness of only 0.3 to 0.6 mm, they differ noticeably from conventional adhesives systems. Depending on air humidity and paper moisture, 50 to 80 percent of ultimate bond strength can be achieved after only about 6 hours. Final curing takes a maximum of 24 hours.
After reaction, the Purmelt film displays high flexibility at both high and low temperatures. Brochures bound with Purmelt show no loss of quality at temperatures up to 120°C and remain elastic rather than becoming brittle even down to temperatures as low as minus 40°C.
Purmelt has already made inroads into the hard cover sector as well. The adhesive is still roundable for a definable period after perfect binding/gluing off with Purmelt. Even after final curing, the book spine permanently retains the desired rounded shape thanks to Purmelt's physical properties.
After final curing, Purmelt is absolutely immune to the migration of mineral oils from the printing inks. This yields considerable benefits in the converting of papers printed in the sheet-fed offset process.
The recycling process also benefits from the extreme hardness of Purmelt, as it can be filtered with ease during paper recovery. Entrainment in the paper is excluded, thus eliminating the risk of stickies.
Purmelt Dual Cure
Henkel‘s patented Purmelt Dual Cure system allows for in-line binding of edition bound books. This revolutionary product offers a dramatic improvement upon the standard 24-36 hour crosslink and cure rate of standard Polyurethane based hot-melt. With Dual Care, when adhesives are applied to perfect bound books, and exposed to UV lamps, the crosslinking process begins immediately, and 80 % cure level is achieved in approximately 3 minutes.
Purmelt Micro Emission
Purmelt Quality + Henkel Responsible Care = MicroEmission
Although Henkel achieves high standards with its existing products and occupational health and safety instructions, Purmelt MicroEmission represents the only sustainable solution to the problem – with a massive reduction in monomeric isocyanate. No labeling as hazardous materials is required. Product quality and the resultant economy for the user remain at the high standard for which Henkel is renowned. Purmelt MicroEmission delivers full adhesive performance. Together we can push the technical standard of occupational health and environmental protection to a higher level.