III. What creates the UV Radiations?

emitted between 200 and 5.000 Nm :
- on one hand to get the maximum rapidity of polymerization,
- on the other hand to be able to use the same lamp and obtain the best possible reaction with different basic oligomers and monomers.

Life duration of the lamps
1.000 hours at full intensity.
2.500 hours can be reasonably expected.

b) The lamps without electrodes.
Based on a magnetron - a generator of hyperfrequencies “with cross-linked magnetic fields
The advantage of this type of lamps called “ electrode-less” is their functioning temperature lower by about 100°C and a quick “re-lighting”

c) The pulsed xenons.
Some manufacturers of screenprinting equipment have during 1993, decided to use it again under the form of “flash effect” (therefore efficient only with very transparent inks).

d) The reflectors.
Here again, a new controversy based on three tendencies:
- focalization at the surface of the substrate,
- focalization above the substrate,
- total absence of focalization.

e) The “related” problems.
- the heat produced,
- the lightning and re-lightning time of the lamps,
- the production of ozone,
- the protection of the eyes and skin against the ultraviolet radiations.

1. The heat produced.
To avoid it or limitate its effects :
- Several tests on different models of UV reactors have proven that if a “filter or dichroic dividing of the infrareds” is used, a lost of efficiency is lost.
- The passive mode of action = speed of passing through
- The active mode of action guarantees a very strong cooling of the lamp reflector, the printed substrate and sometimes the lamp itself within the limits seen earlier.

After years of contests, it seems that the cooling “all by air” took the advantage for obvious reasons of simplicity, cost, and efficiency.

2. The cooling by air only
3. The cooling by water circulation around the reflector.
4. The cooling by water circulation around the lamp.
5. These systems above with the addition of a heat pump.
“heat pump”! wrong term ! “Heat” cannot be “pumped”

6. Other active cooling procedure : the addition of a cooling unit.
It is my favorite solution :
all the UV reactors in my plant have one cooling unit added at the end of
each UV reactor on the belt.
It blows air at 5°C and 90% of humidity on a length of 2 meters.
= After the thermal shock, we have something like a refrigerant shock.

7. The lightning and re-lightning time of the lamps.

8. The production of ozone.
How to eliminate this ozone?
Two solutions :
- not to produce any (!),
- to evacuate it.
- to block the UV radiations situated between 170 and 200 Nanometers,
but a part of the efficiency is lost : from 10% to 20%, which reduces
as much the rapidity of reaction.

9. The protection of the eyes and skin.

10. The conveyor belt.
The best are in fiberglass woven in large meshes, covered with Teflon.