A repeating light and dark pattern in a screened flexographic image is easy to mistake for uneven impression, ink variation or an anilox transfer problem. If the pattern has a regular direction and spacing, changing pressure or viscosity may alter its visibility without removing the cause. Moiré is an interference pattern between regular structures. In flexo, the halftone on the plate and the engraving on the anilox are part of that review. Preserve the first printed evidence, identify every screen in the affected station and confirm the roller fitted to the press before anyone changes several settings at once.
Keep the first sample and the exact press condition
Mark a full-width sample at the first point where the pattern is visible. Record the press, station, colour, job, plate ID, anilox ID, substrate, ink, speed, impression settings and the time in the run. Keep an accepted sample from the same job or colour standard beside it where one exists. A photograph alone may miss the direction or spacing of a fine interference pattern.
Describe where the pattern appears. Note whether it is visible in one separation, a two-colour overlap, a neutral area, a vignette or a surface-screened solid. Check whether it follows the plate repeat, remains in the same cross-web position or appears only when particular colours overprint. These observations help prepress and the pressroom decide which regular structures must be compared.
Do not immediately add impression, change ink strength or replace every plate. Those actions can change dot gain, density and contrast, making the pattern look different while removing the original evidence. Hold the press at a safe approved condition and change one controlled variable only after the screening data has been collected.
Collect the plate screening data from prepress
Ask for the production separation file or plate report, not a verbal note that the job uses a standard screen. Record the plate lines per inch or lines per centimetre, screen angle for each separation, screening type, dot shape, imaging resolution and any surface pattern applied to the plate. Add the plate material, thickness and imaging or exposure workflow so that the exact production set can be traced.
The Flexographic Technical Association defines moiré as an interference pattern created by overlapping regular dots or lines and notes that the relative screens of the anilox and halftone plate can cause it in flexographic printing. That is why the complete angle set matters. Looking only at the colour where the pattern is most visible can miss an interaction created by another screened separation below or above it.
Confirm that the plates on press match the recorded revision. Check the plate IDs, colour labels, mounting form and job repeat. If a remake used a different screen set or a plate from an older revision remained in the rack, the approved prepress record will not describe the physical job. Resolve that identity before attempting a new separation or ordering an anilox.
Verify the anilox fitted to the affected station
Read and photograph the roller or sleeve identification. Obtain its engraving certificate where available and record the engraving family, angle, line count, stated volume and measurement units. Compare this with the anilox selected in the job recipe. A correct recipe cannot diagnose the pattern if a different roller was fitted during changeover.
Zecher lists Hexa 60° as its established standard engraving and also offers application-specific structures including SteppedHex, H.I.T., Diamond 45°, Trihelical and customised engravings. These names describe different cell arrangements and intended applications. Do not assume that two rollers with a similar volume or line count present the same regular structure to the plate.
Check the roller condition without turning the diagnosis into a cleaning trial. Blocked cells, wear, scoring or contamination can change ink transfer and should be recorded, but cleaning cannot correct an incompatible screen relationship. If the physical specification cannot be confirmed, arrange an inspection or measurement before using that roller as the basis for a new plate-screen decision.
Separate interference from other repeating defects
A periodic mark is not automatically moiré. Gear marks, bounce, plate-edge effects, sleeve runout, cylinder damage and contamination can also repeat. Compare the distance between marks with the plate repeat, gear pitch and circumference of the rotating components. A defect that repeats once per cylinder revolution needs a mechanical review as well as an image review.
Inspect the printed dots under suitable magnification. Record whether the interference is built from the halftone pattern, whether dots are slurred in the machine direction, whether highlights bridge or whether ink transfer changes across the web. Moiré diagnosis is stronger when the visible pattern can be related to the regular screens in the printed image, not merely to a general description of banding.
Where the plant procedure permits, make controlled pulls that isolate the affected separation or overlap while keeping substrate, ink, speed, anilox and impression unchanged. Label every pull with the condition. If the pattern appears only in a particular combination, send that evidence with the screening files to prepress and the anilox supplier.
Review the screen relationship before changing hardware
Bring the plate maker, prepress team and anilox specialist into the same review. Provide the actual separation angles and ruling together with the anilox engraving angle, count, volume and geometry. The FTA identifies screen angle as a basic screening parameter and treats moiré as a relationship between regular patterns. The answer must therefore be checked for the complete job rather than copied from a different press or colour set.
Do not select a replacement anilox only from a higher cell count, and do not change the plate screen only to move away from one angle. The roller still has to transfer the required film for the ink, substrate, speed and graphic content. Zecher's range includes different engraving geometries because transfer and print requirements differ. Compatibility with the screened image is one part of the specification, not the whole specification.
For repeat work, keep the approved plate-screen set and the exact anilox identity in the job standard. If an alternative roller is allowed, list it only after a controlled print trial. A store description such as process anilox is not enough when several rollers have different angles, geometries or measured volumes.
Prove the correction on the real production construction
Test the agreed change with the normal substrate, ink system, plate build, tape, press speed and drying or curing condition. Keep all unaffected separations and mechanical settings at the approved baseline. Print enough material to reach stable production condition, then compare the same image areas under the same light and magnification.
Check more than the disappearance of the visible pattern. Measure the normal colour and tonal controls, inspect fine type and reverses, confirm highlights and shadows, and verify register and finished-product requirements. A screen change that hides moiré but damages tonal reproduction or ink transfer has not produced an acceptable production standard.
Royal Coat represents Zecher anilox technology across India, Bangladesh, Sri Lanka, Nigeria and Kenya. For an anilox-screen review, send the press and station, plate screen ruling and angle for every separation, screening type, anilox engraving certificate, roller ID, volume and condition, ink, substrate, speed, marked samples and photographs under magnification.
Questions from production and purchasing teams
What to ask about flexographic moiré diagnosis
Can increasing impression remove flexographic moiré?
It may change the contrast or dot gain and make the pattern look different, but it does not correct an incompatible relationship between regular screens. Preserve the sample and check the plate and anilox data first.
Which anilox details are needed for a moiré review?
Record the roller ID, engraving family, angle, line count, volume, measurement units, certificate and physical condition, then confirm that the identified roller is actually fitted to the station.
Is every repeating flexo pattern a moiré pattern?
No. Gear marks, bounce, runout, plate-edge effects and contamination can also repeat. Compare the repeat distance and inspect the printed dot structure before deciding the cause.
Should the plate screen or the anilox be changed first?
Neither should be changed by guesswork. Review the complete separation-angle set, anilox geometry and transfer requirement together, then test one agreed change under controlled production conditions.
What evidence should be sent to Royal Coat?
Send the job and press details, separation rulings and angles, screening type, plate IDs, anilox certificate and ID, ink, substrate, speed, marked samples and magnified images of the pattern.