Atif Doc04, Check-Up procedure for flexographic presses (Rev. 04-2013), suggests different levels of acceptability:
- good if ≤ 50 µm,
- sufficient if ≤ 100 µm,
- insufficient if > 100 µm.
How would you evaluate it? With a microscope, featuring sufficiently accurate measurement capabilities, the register is measured by checking some printed samples that are representative of a print run for the printing condition under examination (different substrates could produce different register values).
In any case, the register tolerance is a characteristic of the printing system that must be assessed and managed: a 100 µm register cannot be requested from a printing system that has 500 µm accuracy. The register tolerance must therefore be assessed during the system check-up and fingerprint operations and shall be shared and agreed between all parties involved in production workflow: printers can keep their production under control, prepress has precious information about necessary trap values and customer can have better and clear expectations of the final result.