Excimer

With Excirad 172 a completely new generation of VUV sources becomes available for surface curing and matting of UV-polymerizable materials.

IOT-GmbH offers you a full service, from the first preliminaries untill the production

• Construction, delivery, installation and commissioning of Excirad systems. On request, including conveyor belt and inerted UV dryers

• Non-binding test of the entire system in advance of the realization in our own workshop. There, we test and optimize the interaction of the coating formulation, substrate, Excirad lamp and UV dryer with the materials of the customer.

• Rental of excimer systems for testing under production conditions.

• Conception and planning of the Excirad lamp unit according to the customer’s wishes and requirements.  An integration into an existing irradiation unit is of course possible.

Applications:

Packaging, Lamination, Floors, Exterior facades, Auto parts, Decorative papers, Films

• Radiation width: 100-2500 mm selectable
• Wavelenghts: 172 nm or 222 nm
• Lamp power: 10-25 W/cm
• UV Intensity: 10-30 mW/cm2
• Production speed  up to 100m/min per lamp
• Higher speed possible with lamp arrays
• Cassette insertion technique for a quick and easy change
• Easy connection of media through quick couplings
  
• Two ways to proceed the cooling:
  • combined nitrogen / deionised water
  • pure nitrogen

The top figure shows a cross-sectional view through an excimer lamp. A cylindrical, double-walled quartz tube is filled with around 600 hPa xenon.  Electrodes, which are situated on the inner and outer wall of the quartz tube are connected to a HF high voltage generator.  When the high-frequency high voltage is applied, micro-discharges develop in the gas to produce a 172 nm radiation.  Suppose the following mechanism: electrons, which are generated and accelerated during the micro-discharge, transfer their energy to Xenon atoms. There arise Xenon ions or excited states of Xenon:

e^– + Xe → Xe^*,Xe⁺.

{gallery width=400 alignment=right crop=0} UV/Excimer/exirad172_diagram.png{/gallery}

In a second step, a Molecule of excited Xenon Xe2* is formed in a reaction between two atoms of Xenon Xe in ground state and an excited Xenon atom Xe* :

Xe^* + 2Xe → Xe₂^* + Xe.

The Xe * excimer produces a 172 nm photon. The resulting ground state is unstable and decays into two xenon atoms.

Xe₂^* → 2Xe + hν (172 nm).

Because the 172 nm Photons are strongly absorbed by Oxygen, it is necessary to do the irradiation of coatings under nitrogen.  In practice, we use a closed chamber with nitrogen supply.  IOT GmbH has in the last few years successfully implemented 172 nm Excimer lamps for physical matting to an industrial use.

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