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UV curing in atmospheric air always implies presence of oxygen in the process chamber.  But the oxygen hinders the curing (polymerization) of the coating and thus reduces significantly the efficiency of the drying process. 

 

 

When the processing chamber is purged with the inert gas nitrogen, the oxygen can be almost entirely removed (up to 0.005% / 50ppm). The nitrogen acts neutral as an inert component and does not hinder the process like oxygen does.

This procedure is called nitrogen inerting.

A hardening of the coating without inert gas is possible in principle, but the UV lamps must be operated at a higher power, which comes with a loss in surface quality.

Benefits of UV curing with inert gas :

Increased network density of the polymers:

  • Improved hardness, wear and abrasion resistance of the coating.
  • Higher gloss.
  • Increased chemical resistance.
  • Much better curing of "problem" colors like opaque white.

Savings of photoinitiator of 8-15% to <2%, which leads to:

  • Reduction of the coating costs.
  • Odor reduction.
  • Reduction of global migration, which is important for food packaging.
  • Reduce the tendency to yellowing.
  • Curing without photinitiators in combination with DirectCure lamps

Increase of productivity:

  • Increase of the production rates and/or drop of energy costs.
  • Less heating of the substrate
  • Energy saving up to 60 %
  • Ozone formation is avoided

 

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