Ursachen von Missing Dots im Tiefdruck
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This work has shown that the number of local defects (craters) beyond certain limit values correlates very well with the number of missing dots, and therefore the surface topography ofthe paper has definitely the greatest impact on printability in rotogravure. The deepenings have an average depth of 2-5μm and diameters between 50-250μm. When ESA is used bigger craters as regards depth and diameter are necessary to cause missing dots. However, not all missing dots can be explained and described by means of surface topography. Non-topographic factors, such as electric properties of papers (especially when using the ESA), fibre and filler distribution, ink absorbency or microscopic compressibility can also have an influence on printability as regards missing dots. Paper independent factors (e.g. printing ink or printing machine) may also have a certain influence on missing dots. Therefore, investigations in these fields, together with the results of topography analysis, are necessary in order to draw clear and general conclusions regarding the causes of missing dots in rotogravure printing.
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