UV Drying/Curing

Posted: September 22, 2012 in Color, Density, FOGRA, ISO Press standardisation, UV Curing, UV Drying
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UV drying of printing inks (and varnishes) is based on radical polymerizable vehicles. UV inks with appropriate UV dryers are suitable for sheet-fed printing presses and web presses. Drying between the print units – interunit drying  can be used to prevent a reversal of the ink splitting in the following inking unit. In flexographic and gravure printing, drying has to be carried out after each inking unit (e.g., straight (recto) printing and perfecting) because of the ink properties (ink trapping, etc.). Very often an overall drying becomes necessary after the last inking unit, possibly at a higher output rate.

UV inter-unit dryers for sheet offset printing press after printing unit and coating unit; UV dryer (blue) can be replaced by IR dryer (red),(IST Strahlungstechnik metz)

In case of UV drying, the ink film polymerizes and dries completely as soon as radiation occurs. Polymerization takes fractions of a second. The UV drying method, however, requires special inks  containing completely different binders (vehicles) and additional photoinitiators.  The color black prevents UV radiation from penetrating in the ink layer and the curing effect is less than with chromatic colors or varnishes. 

Conventional UV dryers work with one or several mercury vapor lamps.  The wave length range lies between 100 and 380 nm. The system is enclosed by a reflector housing. Optimum cooling and extraction of generated ozone is necessary for the complete system.The units are designed in such a way that the permissible threshold limit value of 0.ppm (parts per million = one millionth of the volume of the substance in question, e.g., air) is not exceeded and damage (e.g., irritation to the mucous membrane) to one’s health is prevented.

UV drying system.
a) Ranges of the UV spectrum and their effect;
b) UV radiator reflector system (Dr. Hönle)

 

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