In multi-colour screen printing, each colour is printed with its own screen, and the colours must line up. Registration is how well they do. Small shifts are a normal feature of the process, so the question is how much is acceptable and how the design copes with it, not whether it ever happens.

Why it happens

Causes include screens that are not locked in position, worn or stretched screen frames, pallets that move, fabric that shifts or stretches on the pallet while printing, and a knit that was not stabilised or was pulled differently on each print. Knit fabric is more likely to distort than woven,. Changes in humidity can also change the fabric’s size.

Design for it

Artwork can be made more tolerant. Trapping means a small overlap between adjacent colours so a shift shows as overlap and not a white gap. Thin outlines or tight fit between colours show shifts at once, so avoid them on knit unless the printer can hold tolerance. Larger shapes with some overlap or a darker colour printed over a lighter one hide misregistration better.

Set a tolerance

Write a numeric tolerance in the tech pack, in millimetres, for the maximum allowed shift between colours, and say how it is measured, for example with a ruler or a loupe at an agreed distance. Choose it with the printer after seeing a sample on your fabric, not from a guess. Also set the viewing distance, so inspectors judge a print the way a wearer sees it.

Approve and inspect

Approve a pre-production print on the actual fabric after washing, with ISO 6330, since shrinkage can alter alignment. Check fabric weight against the sample with ASTM D3776. At inspection, sample pieces under ISO 2859-1 and treat misregistration beyond the written tolerance as a defect with a defined class.

What to tell the factory

Share the tolerance and the approved sample, and ask the printer to check registration during the run and not only at the start. Print a few pieces at the start of each shift or screen change and keep them as a reference, so that drift can be seen when it begins and not found in finished cartons. If a design needs very tight registration, consider simplifying it to fewer colours or a single-colour print, which removes the problem entirely and often costs less per piece than reprinting rejects.