The register between colors is a fundamental aspect for the quality of the printed product. But what is the correct register tolerance and how to evaluate it?
ISO 12647-6 connects the register tolerance to the print linescreen. The higher the linescreen, the greater the expected accuracy on the printed product. According to this norm, register tolerance shall be within 2÷linescreen, and it should be within 1÷linescreen. For example: at 120 lpi (48 l/cm) it shall be ≤ 420 µm and it should be ≤ 210 µm.
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.
EXAMPLE OF WRONG REGISTER:
EXAMPLE OF CORRECT REGISTER:
Article and pictures: by courtesy of Mr. Stefano d'Andrea, flexo•expert