Operational principle of inert technology
The principle of UV curing 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 polymerization process. The presence of oxygen can obstruct the radical formation and the chain propagation illustrated below. Instead forming long polymer chains, the radicals of the photoinitiators and monomers react prematurely with the O2 molecules, whereby the cross linking breaks off.
At the inertization process the oxygen (O2) in the irradiated area is displaced by an inert gas, usually nitrogen (N2).
The positive effects of inertization on the production process are various:
- excellent surface curing and outstanding characteristics
- complete curing by precipitation, no post-curing
- even „ problematic colours“ like full surface white can cured at high speeds
- cost savings 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
Principle structure of inerted UV systems
System features:
- Residual oxygen control < 30 ppm possible
- Nitrogen volume control by residual oxygen measuring device
- Low nitrogen consumption
- Low temperature load
Advantages:
- Increased productivity
- Improved surface quality
- Energy savings
- Processing of temperature sensitive materials
Plant design for horizontal respectively vertical pass
Example for Siliconization: < 30 ppm remaining oxygen level,
2 x 200 W/cm, 400 m/min
Plant design on water chilled drum
Advantage: lower temperature load on the substrate
