UV curing in inert atmospheric conditions
The Hönle group uses its experience within the field of inert curing technology to optimise each inert installation according to customer requirements. The established product line of its UV curing equipment works at arc lengths between 60-2600mm with power control from 20-100% and is available with all standard and many non standard spectra.
The principle of the technology is based on the radical formation of photo initiators by the impact of UV irradiation. These free radicals are able to split the double bonds of the binder vehicle and start the polymerisation process. The presence of oxygen (O2) can obstruct the radical formation and the chain propagation. Instead of forming long polymer chains the radicals of the photo initiators and monomers react prematurely with the O2 molecules whereby the cross linking breaks off.
At the inertion process the O2 in the irradiated area is displaced by an inert gas, usually nitrogen (N2). Positive effects of inertisation on the production process include:
• excellent surface-curing and outstanding characteristics
• complete curing by precipitation, no postcuring
• even problematic colours including full surface white can run at high speeds
• cost saving through lower photo initiator levels within the UV inks and varnishes
• less migration because of significantly lower amounts of photo initiator and high cross-linking levels
• less UV irradiation and increased production speed
• reduced ozone production
• smell reduction
• less yellowing
N2 is fed by pipes from a tank directly into the inert chamber of the UV facility. To ensure constant process conditions and a continuous quality level, monitoring of the remaining O2 within the inert chamber is recommended.
In this case the gas filling of the inert chamber is controlled and optimised by constant gas regulation.
Automatic regulation takes into consideration the adherence of the remaining O2 limits and economic optimisation. The maximum remaining amount of O2 therefore depends on the requirements of the chemistry and can be different depending on the application.
For example, radical curing silicones for release coatings require an O2 minimum of 50ppm and make high demands on the system and also because of the extremely high process speed. With other applications the inerting level can be within a %range which keeps investment costs and N2 consumption costs under control and leads to an economic inertisation process. To supply and control the UV units electronic power supplies made by Hönle are used.
Compared to conventional ballasts, the UV output can be increased by 10% while the electrical power is the same. With improved reignition, the usable life of the UV lamps can be extended. The maximum power output of the electronic power supplies ranges from 7.2 kW (single unit) to 12 kW for the cascaded version and up to 34 kW (EPS 340).
Hönle develops and produces its own UV lamps, ensuring that those supplied are designed and adjusted as required for the specified application. Lamps are available in arc lengths from 50-3000 mm and power outputs of up to 60 kW.
Hönle
T: +49 89 85608-0