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FLEXO Magazine : July 2007
4 6 F L E X O J U LY 2 0 0 7 w w w . f l e x o g r a p h y . o r g gLObaL markets WCPC produces an accurate, inde- pendent measurement of both the cell volume and shape. The bar graph shown in Figure 4 clearly indicates the effect that increased anilox pressure at con- stant printing speed has on the ink release from the anilox cells. The schematic shown in Figure 5 indi- cates what effect speed has on the ink release from the anilox cells. Slumping of the ink that takes place as the anilox roller exits the inking chamber is clearly shown in the upper schematic of Figure 6. The graph of tone gain shown in the lower graph in Figure 6 indicates the effect that the press speeds have on the tone gain. The plot indicates that tone gain is significantly reduced in the midtones as press speed is increased. Inconsistent image copying can be a significant cause for color variation on press. The upper graph shown in Figure 7 indicates that different dot-copying characteristics are obtained by us- ing three different equivalent plates from three different plate manufacturers. The lower graph shown in Figure 7 indicates a difference within five plates made on different occasions from the same file by the same plate maker. The plates reproduced different dot sizes, par- ticularly in the quartertone area of the reproduction curve. These are typical examples of the type of much-needed fundamental re- search that leads to a better understanding of the process. This, in turn, allows appropriate controls to be implemented to improve the production consistency desired by brand owners. Summary It is a well-known fact in scientific circles that flexography is an inherently complex process. It was once said by an eminent pro- fessor who spent many years researching the chemistry aspects of flexography, “In theory, like the humble bumble bee, the flexo- graphic printing process should not work.” If the industry is going to remain competitive, both commercially and technically, stan- dardization is an appropriate way to proceed. The understanding and application of the appropriate science will help to improve the overall equipment effectiveness and elimi- nate uncontrolled processes—for example, color variability. This will have the beneficial effect of solving the paradox set by the buy- ers of improving quality while reducing production costs.? ABOUT THE AUTHOR: David Galton is a director of Asahi Photoproducts. He is based in London and leads the company’s U.K. flexographic printing plate business activities. Galton is an active researcher and has published numerous technical papers and articles on his research. He is a board member of the European Flexographic Technical Association (EFTA) and was recently elected to the board of Technical Association of the Graphic Arts (TAGA). He has a Master’s of Science from the Color Chemistry Department of University of Leeds. Galton’s contribution to education and training was recognized with the presentation of a gold award for his services to the U.K. flexographic industry by the EFTA in 2005. This article is an expansion of com- ments made during his presentation at FFTA’s 2007 Annual Forum in Montréal, QC, Canada. Figure 7. Different dot-copying characteristics. This can negatively affect the print quality or, at the very least, the press production speed. The series of images included in Figure 3 are produced by a technique called “white-light inter- ferometry.” The Single-Cell Analysis technique developed by the Anilox Anilox Low Speed High Speed Slumping of ink as anilox exits the chamber Figure 6. The effects of speed on the inking process. -1 -2 -3 -4 -5 Original Dot Area (%) 10 20 35 45 55 To n e G ai n D if fe re n ce 40m/min 60m/min 70m/min 90m/min 0 110m/min How does speed effect the tonal reproduction 1. Cells in chamber Ink Anilox 2. Blade wipes across cells Ink Anilox 3. Wiping action removes quantity of ink- Ink slumps to trailing edge of cell Ink Anilox 4. Ink levels as anilox leaves chamber Anilox Figure 5. Schematic of the cells filling from an ink chamber. 20 15 10 5 0 Nominal Dot Are(%) 0 20 40 60 80 100 G ai n d u e to p la te ex p os u re ( % ) Company A Company B Company C 20 15 10 5 0 Nominal Dot Are(%) 0 25 50 75 100 To n e G ai n ( % ) Plate 1 Plate 2 Plate 3 Plate 4 Plate 5 How does inconsisten plate
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