Ink can appear acceptable at the delivery and still fail tape, rub, lamination or end-use checks. On film, that complaint should not send the press crew straight to viscosity, impression or a different ink. First separate three questions: did the liquid wet the surface, did the printed layer dry or cure correctly, and does the finished construction pass its required adhesion test? A dyne result helps with the first question. It does not answer all three.
Preserve the failed sample before changing the process
Keep an unaltered section of the failed web and mark the print side, roll number, lane, repeat position and machine direction. Record the film type and construction, supplier, batch, age, storage condition, treatment specification, ink code and batch, colour, anilox, press speed, drying or curing condition and the exact test that failed. Without that record, a later passing sample cannot show which variable corrected the fault.
Describe the symptom precisely. Poor wetting can appear as pinholes, fish-eyes or a liquid film that pulls away from parts of the substrate. An ink layer that looks uniform but releases during tape, rub, heat or lamination testing may point to a different combination of surface condition, drying, cure, ink compatibility or contamination.
Confirm the film and the surface being tested
Polyethylene, polypropylene, polyester, polyamide and coated or metallised constructions do not present the same surface to the ink. Confirm the exact material and which side was supplied for printing. Mark the treated side when the roll is opened and carry that identity through slitting, printing and any off-line test. Testing the reverse side produces a valid reading for the wrong surface.
The Flexographic Technical Association notes that film substrates are non-absorbent and that low surface energy can prevent ink from wetting evenly. Its technical guidance also describes surface treatment and ink formulation as linked conditions. A substrate reading should therefore be evaluated against the approved ink, coating or adhesive system, not against an isolated number copied from another job.
Check the material at the point of use. Treatment can change with time, storage, transport, additives and contamination, and rolls sold under the same description can behave differently. Keep the receipt date, storage location, opened date and time between treatment and printing with the test result.
Use one controlled wetting-tension method
ASTM D2578-23 is the active ASTM test method for wetting tension of polyethylene and polypropylene films. ASTM also states that using the method on other polymers requires the user to establish its applicability and significance. Record the method or approved work instruction, solution or instrument identity, condition, operator, test location, room condition and result so that readings can be compared properly. Use fresh test material under the current safety data sheet and site procedure.
Test across the width when the complaint varies by lane and test around the roll when it appears after a splice or at a particular roll diameter. Retain the mapped result with the corresponding printed sample. One reading from the outer wrap does not establish the condition of the complete roll.
Do not treat the dyne result as an adhesion certificate
ASTM explains that measured wetting tension can be related to ink, coating or adhesive retention through experience, but is not by itself a complete measure of adhesion. That distinction matters. A film may show the expected wetting behaviour while the printed layer still fails because of contamination, incorrect ink chemistry, incomplete drying or cure, excessive retained solvent, additive migration or an unsuitable finished-product test condition.
Build the acceptance limit from the approved substrate, liquid system and end-use result. Keep the wetting-tension reading with the ink supplier's required surface condition and with samples that passed the defined adhesion, rub, resistance, lamination or converting test. Do not turn a generic dyne value into a universal specification for every film and ink.
If the measured surface condition is below the approved job requirement, quarantine the affected material while the treatment history and re-treatment option are reviewed. If the reading is within the established range, continue the diagnosis instead of applying more treatment without evidence. Excess treatment and repeated passes can introduce other material or handling risks and need the substrate supplier's and equipment maker's limits.
Separate wetting, drying and cure during the press trial
Run a controlled trial with the identified film, ink and anilox. Record viscosity by the approved method, ink temperature, pH for water-based systems where applicable, impression, speed and dryer or curing settings. Change one variable at a time. Adding solvent, reducer, wetting agent or another material without the ink supplier's instruction can hide the original cause and create a different compliance problem.
The FTA's film-printing guidance notes that non-absorbent film does not take solvent into the substrate, so drying occurs from the printed surface. Confirm that airflow, temperature, extraction, lamp or LED condition and web speed match the approved process. Poor adhesion after apparently good wetting can be a drying or curing problem rather than a reason to increase surface treatment.
Take samples at startup, normal speed, the planned maximum speed, stop and restart and after the line has reached stable operating condition. Allow any required conditioning time before testing. Keep the test method, tape or tool, dwell time, test direction and acceptance decision consistent with the ink supplier, customer specification and end use.
Release the roll from product evidence, not one process number
The release record should connect the film identity, test side, wetting-tension method and result, treatment setting where used, ink and press conditions, drying or cure evidence and the finished-product test. That chain shows whether the approved combination was reproduced. A dyne figure written alone on a roll label does not show that the print will survive converting or use.
For a film-adhesion review, send Royal Coat the substrate construction and batch, treated side, storage history, ink or coating, anilox, speed, drying or curing arrangement, wetting-tension method and mapped results, photographs of the symptom and the exact product test that failed. That information is more useful than a request to increase treatment or change ink without the failed sample.
Questions from production and purchasing teams
What to ask about film wetting tension and ink adhesion
Does a passing dyne test prove that flexo ink will adhere to the film?
No. It provides evidence about wetting tension under the test method. Adhesion also depends on the film surface, contamination, ink compatibility, drying or cure and the finished-product test.
Should wetting tension be checked only when the film arrives?
No. Check it at the point required by the approved process, especially after storage, a batch or roll change, a splice, a treatment adjustment or an unexplained adhesion complaint.
Can ASTM D2578 be used unchanged for every plastic film?
ASTM D2578-23 is intended for polyethylene and polypropylene films. ASTM states that applicability and significance must be established when its reagents are used with other polymers.
What should be recorded with a dyne result?
Record the film, batch, surface side, sample location, method, test material or instrument, condition, operator, date, room condition and corresponding printed-sample result.
What should be checked when wetting tension is acceptable but adhesion still fails?
Check contamination, ink compatibility, viscosity and temperature, drying or cure, web speed, retained solvent where relevant, conditioning time and the exact finished-product test.