Viscosity Standardization in Flexographic Printing: A new approach to controlling the largest variable in flexo and gravure printing In the history of our company we have applied every type of viscosity sensor: rotational, falling ball, falling piston and acoustic wave. The similarity between these sensors is that they are all calibrated with a cup, in our case the DIN cup with a 4 mm outlet. In itself this worked well and due to lack of a better alternative DIN cup 4 became the standard measurement in the flexo and gravure industry.
In December 2017, when looking for a better solution, I came in contact with the Rheonics SRV as an alternative to the sensors we had been using, which were too inaccurate and insufficiently repeatable. In January 2018 we started testing two of these sensors and in June 2018 we equipped all 8 printing stations of the CI press with Rheonics SRVs. Last year we conducted many
tests, gathering experience and new insights. We developed a formula to convert the unit centipoise, or mPaS, which is the unit delivered by the SRV, to DIN Cup 4 seconds because we were accustomed to working with these units. After a few months we decided to completely stop using the DIN Cup units, for reasons that will become clear in this article.
The current generation of printing machines are extremely accurate in terms of adjustment (in Îźm range) and have a very high degree of automation, such as a 100% inspection system, fully automatic impression setting of anilox rolls and plate cylinders, automatic register control and inline spectral colour measurement. However, the largest variable in the printing process,
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