Glue trolley: For easy handling of the VPN book spine nozzle.

The use of PUR in adhesive binding is continually increasingworldwide. Its good lay-flat characteristics with thin glue application and high binding quality with heavily coated papers are important arguments in favor of using PUR. Yet, handling PUR is not entirely simple. Often, glue application is inconsistent and too thick. Furthermore, the glue costs for PUR are higher than for conventional adhesives.

This is where Muller Martini offers valuable support, providing its new VPN (Volumetric PUR Nozzle) book spine nozzle. With the VPN book spine nozzle, the glue film can be applied sparingly...with constant, minimal thickness. This gives products sharp-edged book spines and ideal lay-flat characteristics. High product quality is further underscored by optimal side gluing and high pull resistance values – with the widest variety of paper types.

Complete System for PUR Production
With the VPN book spine nozzle, Muller Martini offers a complete, closed PUR application system, an improvement versus open PUR gluing stations used in the past. The Muller Martini system consists of:

• A MOD 30 block melter for nozzle application
• Heated PUR feed and return hose
• The VPN book spine nozzle, and
• A glue trolley for easy handling of the VPN nozzle.

The MOD 30 block melter is a pre-melting system, sealed from the outside air. It works according to the principle of melting-on-demand technology. Only a small amount of PUR is melted and conveyed into the level-monitored reservoir container. A processor precisely calculates the pump speed required for conveying the adhesive from the reservoir container to the application head for production, based on the glue film dimensions. Due to the fact that only a minimum of adhesive – calibrated to actual need – is melted, it is ensured that fresh adhesive always exits the nozzle first. With this principle, unnecessary temperature loads and viscosity changes in the adhesive are avoided, and the PUR bonding process does not begin until it is where you want it: on the book spine.

Simple Operating Principle
The operating principle of the new and exclusive Muller Martini system is simple: A speed controlled gear pump conveys the polyurethane out of the block heater volumetrically depending on glue film dimensions and binder speed, and through the heated feed hose directly to the nozzle applicator head (see diagram). If no product is in the clamp, the PUR flows back into the reservoir container of the block melter and mixes with freshly melted adhesive. Thus, the circulation system additionally contributes to the prevention of viscosity changes in the adhesive.

Operating Principle of the PUR Complete System 1. Book block2.VPN application nozzle 3.PUR feed hose
4.PUR return hose 5.MOD 30 block melter6.PUR container 7.Heated/cooled melting coil
8.Reservoir container (for fluid PUR) 9.Gearwheel pump 10.Throttle with non-return valve

The application head is a slot nozzle, with which the defined glue film can be applied consistently and precisely. This ensures consistently high binding quality from book to book. Uniform application with the slotted nozzle and the side guides that support the book block during glue application prevent "mushrooming” of the adhesive on the spine of the book block, which can often happen with roller application. The result is products with nicely edged spines. In contrast to roller application, all the pages – from the first to the last pages of a book – are embedded in the glue with nozzle application. This increases book strength.

Higher Productivity
Higher production speeds can be achieved with the closed PUR application system versus the open roller system. The overall capacity is no longer determined by the glue application itself, but rather much more by the product and the overall system configuration. As a result of the higher productivity, an investment in a VPN system from Muller Martini pays for itself in just a short time.

The new nozzle technology can be used in the Acoro, Bolero and Corona adhesive binders. When equipped with the new nozzle, Muller Martini adhesive binders are optimized to meet the challenges of PUR production.