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FLEXO Magazine : October 2012
well controlled, reaching fully linear behavior under most printing conditions. Just as important, this straightforward, open technology is easy to implement and is supported by nearly all existing, popular digital plate manufacturers. It fits right into a current digital plate workflow. Second generation HD flexo technology can: • Provide detail sharpness and image contrast to entire tonal range • Offer transitions to zero • Provide smooth solids, with higher solid ink density • Generate higher lineatures defined by higher resolution dots, with no rosettes or moirés • Offer easier makereadies • Work with any plate, using any process • Require no change to normal anilox lpi • Deliver consistent and repeatable results INSIDE EXPOSURE Consistent light exposure throughout the entire plate can be a challenge. The larger the plate, the more pronounced the UV main exposure is. In certain print conditions, such as wide web flexibles and postprint corrugated, there is a need to reproduce superior highlights to zero along with a strong midtone dot structure. Unfortunately, the inconsistency of bank light UV main exposure is compromised due to the plate’s position on the frame bed and the distance from middle of the plate to its corners. UV bank lights typically do degrade over 500 hours down to their expected 5,000 -hour lifetime, but the decrease in lighting is different for each individual lamp. Compensation needs to be made at least twice a year to correct the exposure, but is very much related to the amount of hours the frame lights are used. This lack of intensity measurement and replacement control can lead to unstable plate quality. And, unfortunately, extending the exposure time will not completely compensate for the loss of mW intensity. Without enough brilliant light, the polymerization of the plate cannot be completed, resulting in poorly formed dot structure. Thus, extending the lifetime of the lamp by increasing the exposure time will not succeed. Individual lamp aging—and the quality of light emission— can also be troublesome. It results in uneven light emission between the lamps themselves. Emitted light is multi-direction- al, and not focused, so, even throughout the area of the bed, a plate does not receive even exposure. Figure 8: When UV exposure is introduced within the plate imager, there is no UV degradation over time, and the expected lifetime is at least 5,000 hours. Figure 9: Internal plate exposure delivers light through a simultaneous movement of the UV source over the plate by drum rotation, controlled by software. Each area receives exactly the same light quality and quantity. It is continuously monitored and tuned. 64 FLEXO octobEr 2012 www.flexography.org