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FLEXO Magazine : October 2012
dation over time, and the expected lifetime is at least 5,000 hours. Thus, with digital UV exposure, plate departments can expect perfectly controlled plate production. Also, because 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. Figure 9 attests to it being continuously monitored and tuned. When the diode can- not work anymore, it will warn the operator and shut down. The results are uniform dot shaping throughout the entire plate, a light source that is perpendicular to the plate surface, and cool light that does not distribute heat to the plate. With no required UV back exposure, this new system makes the plate in a one-step procedure. For applications outside of standard flexo—beverage cans, tubes, security printing, etc. , using CTP letterpress metal-backed plates (Figure 10), this technology works well. FLATTENING DOTS Until recently, HD technology at its latest incarnation generated round dots. There is increased tonal range in the highlights and drop shadows, with special screening for solids. And, while it delivers exceptional highlights, the solids, although smooth and better, for certain applications and press conditions require more ink in the shadows and solids, without loss of detail. For example, wide web flexible and postprint corrugated require smooth highlights to zero, but also require strongly built midtone dots to transfer ink at high press speeds on a wide range of substrates. Flat top dots have been a popular topic with flexo plate pro- duction. They have been known to deliver vibrant colors with very strong solid ink densities. Many companies have found ways to create flat top dots, along with HD flexo, by eliminat- ing oxygen from the UV main exposure: by introducing nitro- gen to the process; using a clear lamination layer; using high energy bursts of UV light; or introducing a film-based system. Unfortunately, there is a downside to flat top dots. The resul- tant dot gain within the highlights—common to all flat top dot systems—will always restrict the imaging of highlights down to zero, resulting in a hard edge. In Figure 11, you can see the difference between round dots and flat dots. Ultimately, a printer would like the highlights from a round dot (left side) and shadows from a flat dot (right side). Full HD Flexo (Figure 12) combines the excellent print behavior of round top dots in the highlights with the print behavior of flat top dots in the shadows. The new technology involves programmable variable control of the intensity and timing of the LED UV diode during the UV main exposure inside the imager. The digital control from the Laser Diode UV main exposure inside the imager can be used to gener- ate both dot types on a job-to-job basis: digital round top and conventional flat top plates. This is achieved by using variable power density levels of UV exposure. Flat top dots require more UV exposure of light than round top dots. This burst accelerates the polymeriza- tion reaction, so that the oxygen within the surrounding air is not capable of influencing it anymore. This creates a perfect 1:1 reproduction of the image without dot sharpening. HD technology has matured and evolved to extend the ton- al range of print. Figure 13 illustrates the progression. From a 10 percent highlight dot and 1.25 SID in 1995, it expanded to a 0 percent highlight and 1.4 SID with inline UV in 2009. Now, in 2012, with full HD Flexo using Inline UV2, it can deliver highlight dots to zero along with 1.7 SID. Because the range of tones on plates has expanded, full HD flexo can reproduce more Pantone colors very accurately. Smooth solids and full highlights extend the printable color space. Over 70 percent of all Pantones can be emulated on Figure 13: High definition technology has matured and evolved to extend the tonal range of print. From a 10 percent highlight dot and 1.25 SID in 1995, it expanded to a 0 percent highlight and 1.4 SID with inline UV in 2009. Now, in 2012, with full HD Flexo using Inline UV2, it can deliver highlight dots to zero along with 1.7 SID. Figure 11: Ultimately, a printer would like the highlights from a round dot (left side) and shadows from a flat dot (right side). Figure 12: Full HD Flexo (Figure 12) combines the excellent print behavior of round top dots in the highlights with the print behavior of flat top dots in the shadows. The new technology involves programmable variable control of the intensity and timing of the LED UV diode during the UV main exposure inside the imager. 66 FLEXO ocTobEr 2012 www.flexography.org