When printing with the flexographic (Flexo) printing process it is not uncommon for the 95-99% tone patches to have reported dot areas greater than 100%. While visiting a ColorMetrix customer last week I got a refresher course on why this phenomenon occurs. So, I thought I would start the year of golden nuggets off with this flexographic 101 information.
Because Flexo is a relief printing process, the actual printing surface is raised. So, a solid tone area would look like a raised rubber stamp block. A 95% tone area, however, would have small dimples covering the surface of the area. Flexo makes use of a viscous ink which is transferred to the plate by an anilox roller.
Unlike the offset process which lays down a relatively uniform ink film thickness on the entire printing plate, the combination of an anilox roller and a dimpled 95% tone area allows a Flexo plate to carry more ink in some areas. The dimples or little valleys get filled with ink by the anilox and then when the ink is transferred to the substrate the additional ink in the dimple gets piled on top of the rest of the ink laid down by the plate.
Combine this with the fact that in Flexo printing it is not uncommon for a 95% tone area to already be printing as a solid due to the pressure of the “rubber stamp” nature of the process. Before reading this far many of you probably had been questioning my math skills. By this point, however, it should be clear that if you print more density in a “planned” 95% tone area than in a “planned” solid tone area, you will end up with a calculated dot area greater than 100%.
There is some real value in understanding at what tone value this maximum density occurs. While previous releases of ColorMetrix displayed dot areas greater than 100% we seem to have fixed this “bug” at some point. We will have a new release of ColorMetrix built and ready for distribution in the coming weeks, and you will once again be able to display dot percentages greater than 100% from a set of ColorMetrix measurements.