Control of UV Performance

ESMA is an Association of European Manufacturers of machinery and consumables for the specialist printing industry, including screen, digital and pad printing processes.

ESMA is a non-profit organization, founded by manufacturers, for manufacturers and to the ultimate benefit of their costomers.

ESMA runs well supported seminars for giving information relevant to European users of specialist printing techniques.

ESMA has close links to the other major national and pan European trade associations in the printing industry.

For a consistent, reproducible and reliable production process with UV screen printing colours it is decisive to know, control and maintain the current UV capacity of dryers at a consistent level. This is even more decisive taking into consideration the deviations of UV radiation intensity per bulb due to age and number of bulbs, quantity of starts and total of operating hours. thus it is insufficient to only give information like two UV bulbs at 120W/cm each; the most important factors for successful varnish curing are the delivered UV energy (=UV dose) in mJ/cm², the correct focus of radiation as well as maximum output at UV peak in mW/cm², but always depending on line-speed. The unnoticed sinking of radiat flux density leads to a reduced extent of colour curing/ polymerization resulting in minor colour properties, like adhesion in overpressures, chemical stability, extent of brilliance and specific odour. Because of that reclamations are inevitable.

To prevent this latent uncertainty it is important to periodically measure (eg weekly) the dryer at standardized line-speed (eg 20m/min.) using UV integrators or UV-Tec control strips. The performance hasto be determined for every single UV bulb (measurement in the middle, left and right). Both results and number of operating hours have to be documented in the machine´s log book. By this you maintain production at a consistent level and allow a constant, complete and concise overview of UV dryer performance. Furthermore you have to record changes of UV bulbs, since in the case UV performance sharply increases. For this reason it is advisable to change only one single bulb, so that the second , odler, and thus low performance bulb will balance variations inperformance to some extent.

Generally the UV integrator is used for curing or drying plants with assembly line. UV-Tec control strips are used for plants without assembly lines, eg solid print, lable print or optical disc print. It is also important alwaysto measure the dryer with the same UV integrator as well as to not constantlychange measuring instruments. In combination with the prescribed of measuring instruments this simple and fast method clearly increases production reliability of UV dryers.