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Drying
 UV inks dry through a chemical poly- merisation reaction initiated by expo- sure to UV radiation. This reaction, which occurs in a fraction of a second, can be broken down into several diffe- rent steps. The fluid ink (once printed) is exposed to UV radiation (by way of passing under fitted UV lamps within the printing process). This exposure creates the chemical reaction sensiti- sing the photoinitiators in the ink. The photoinitiators generate reaction spe- cies known as free radicals, which pro- pagate the reaction. The free radicals set off a chain reaction between the oligomer and monomer binders in the formulation. The liquid ink hardens. At the end of the reaction, a solid network is formed integrating the pigment. 
Process for UV curing


Like any other form of light radiation, UV radiation may be characterised by its wavelength (λ). The UV radiation spectrum is situated in a range of wavelengths shorter than visible light, and may be broken down into 3 parts:
UV-C (200-280 nm) activate the photoinitiators and assure surface drying.
• UV-B (280-315 nm) maintain the polymerisation reaction.
• UV-A (315-380 nm) assure in-depth drying.
Electromagnetic spectrum
 
UV lamps emit in different UV ranges in order to have maximum drying efficiency.
> See « UV dryers ».
 
 Precautions
Whatever the type of dryers or inks used, it is vital to check the compatibility of the following parameters when printing:
The power rating, nature and condition of the lamps.
The printing speed.
The amount of ink deposited.

I
f the inks do not dry correctly, several actions may be taken:
Check the efficiency of each lamp and its number of hours of use (simple equipment is available for checking the condition of UV lamps).
Slow down the printing speed.
Add 1 to 3 % UV Photoinitiator to the ink.
>
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