Executive answer
Four boundaries to freeze before comparing samples
- Approve a named film, printable surface, ink system and print process together; a material name or attractive first sample is not an adhesion result.
- Test evidence follows the specimen state: a flat witness, converted overlay and installed panel may answer different questions.
- Record the separation location and the changed input before deciding whether to adjust printing, converting or the mounting adhesive.
Current guidance context
What OEM engineers and sourcing teams should decide first
An overlay can look correct at first inspection and still lose printed legends when the film, ink or process changes. The first buyer question is which interface must remain attached: ink to the designated print surface, a protective layer to the print, a spacer to the overlay, or mounting adhesive to the enclosure. These are different joints. Name the joint, its construction and the sample condition before requesting a pass or fail statement.
For an OEM RFQ, the useful deliverable is a controlled film–print pair and an acceptance plan that survives conversion into the real part. An approved color proof alone cannot answer whether print will stay on a die-cut or embossed overlay, nor whether a mounted panel will remain usable after its specified cleaning and handling. The project owner should define the exposures and decision limits; the supplier should identify which process and specimen each record represents.
Separate ink adhesion from the other overlay interfaces
A typical membrane-switch front stack may have a touch-side hardcoat, a polyester or polycarbonate film, graphics printed on the reverse side, optional protective or blocking layers, an adhesive or spacer beneath, and finally a housing surface. A failure at one boundary does not identify a failure at another. A scratched hardcoat concerns the operator-facing surface; a lifted legend concerns the printed side; an edge that peels from the enclosure concerns the mounting bond. Describe the separated surfaces and location before assigning a corrective action.
MacDermid Alpha's overview describes Autotex hardcoated polyester with an ink-receptive primer. Its Windotex page identifies the second surface as the Autotex graphic print surface. These are supplier-specific statements, not a claim that all polyester films, primers or HYR overlays use that stack. A drawing that says only polyester with hardcoat omits the surface to be printed and the ink compatibility decision.
3M's thin-bonding guidance separately gives examples of printed polycarbonate bonded to polyester within a membrane switch and printed polycarbonate bonded to an ABS substrate. Those are adhesive joints with their own surfaces and application conditions. Their presence beneath a graphic overlay does not establish how well the ink adheres to the film above. If a sample peels, inspect which material remains on each side: ink on the film, ink on the adhesive, adhesive on the housing, or a split within a layer. That observation directs the next controlled comparison; it is not a root-cause verdict by itself.
Use a supplier comparison as a question, not a transferred approval
Tekra describes membrane-switch overlay samples printed by UV inkjet on uncoated polycarbonate and on a print-receptive coated JetView polycarbonate. In the comparison Tekra reports, ink was removed from the uncoated sample during its tape-based adhesion check while the coated sample retained its print. That is direct evidence that the particular film surface changed the observed result in the supplier's evaluation. It is not evidence that one entire polymer family is unsuitable or that a coated film will pass every OEM acceptance test.
The public note identifies the film comparison and printer model, but it does not supply a complete transferable schedule for the exact ink formulation, cure window, sample count, aging, later converting operations and customer acceptance threshold. An OEM should therefore ask what was actually held constant and what will be repeated on its own artwork and production-intent material. Record any reported supplier result as source evidence and label the proposed OEM comparison as a new, unperformed plan until specimens and records exist.
A coated surface can be helpful when a specified print process needs it, but changing a film may also change finish, optical behavior, flexibility, thickness or conversion settings. The purchase decision should link the print result to the rest of the overlay requirements. If the current film and print system already meet a documented project plan, a supplier example alone is not a reason to substitute materials. If the proposed ink or printer changes, a previous passing sample should be treated as a baseline for comparison, not as blanket approval for the new combination.
Freeze the film, printable side and print process as one revision
Begin with a layer drawing that labels the operator side and the protected print side. Specify the film supplier and grade, gauge, finish, surface treatment or primer, and which side receives each ink or protective layer. A printer-facing instruction such as reverse print should still identify the actual surface and drawing view; otherwise a mirrored artwork proof can look plausible while its printed layers are on the wrong side of a window or adhesive zone.
Treat the ink as a defined system rather than a color name. The supplier should record the ink manufacturer and product family or approved equivalent, print route, surface preparation, number and sequence of passes where relevant, cure equipment and controlled settings, and any overprint or blocking layer. The OEM need not publish confidential recipes, but the quotation and approval record should identify who controls them, which revision was sampled, and what change requires a new review. Color and opacity can be accepted separately from adhesion; a visual match is not a bond measurement.
MacDermid Alpha's film range illustrates why even one broad family needs exact grade selection: its Autotex overview names an ink-receptive primer, while its Windotex page identifies the graphic print surface. Another PET, PC, finish or primer still needs its own material and print compatibility review. The same discipline applies when a printer, ink supplier or cure route changes but the artwork does not.
Record the intended converting operations beside the print process. Die cutting can bring a printed region close to an edge; embossing can strain a graphic around a key; a transparent window may need different coverage from an opaque legend; lamination can introduce pressure and handling. None of these automatically causes failure. Each becomes a reason to decide whether the flat print witness represents the delivered part or whether a converted sample must be inspected separately.
Work through a staged comparison before tooling approval
Consider an illustrative supplier-transfer case: the artwork and enclosure stay fixed, while a proposed overlay uses a different polycarbonate grade and printing route. The old approved sample is the visual and functional reference, not proof that the new film will print the same way. Stage one compares matched flat print witnesses with identified film surfaces and process records. If the print separates, stop and identify whether the new film surface, ink or preparation differs before introducing die cutting and mounting as additional variables.
Stage two inspects production-intent converted overlays. Use the actual graphic zones: a high-coverage opaque field, a fine legend, the edge of a display window and a region near any embossed key or die-cut edge. Record appearance and the agreed adhesion observation for each chosen zone. The method and acceptance limit must be approved before testing; this guide supplies neither a universal test class nor a numerical result. A flat witness may be useful for process comparison while remaining insufficient to approve a converted edge or formed key.
Stage three uses a representative assembly if the delivered scope includes spacer lamination, a mounting adhesive or an enclosure interface. Check the mounted panel after the specified installation sequence and exposures, such as the approved cleaning agent or handling cycle where applicable. If a failure appears only after assembly, preserve an unmounted companion specimen so reviewers can distinguish a print change from adhesive, housing, pressure or edge effects. A mounted sample can reveal the combined effect but cannot independently assign cause without the earlier controls.
The table below is an original hypothetical HYR editorial worksheet. It defines what evidence would make two proposals comparable; it does not say that HYR made these specimens, ran the tests or approved a film. The OEM should replace every open method and acceptance field with a controlled project requirement and document the person or organization authorized to release the comparison.
Define what a failure report must show before a retest
A report marked pass or fail is weak if it omits the specimen state. Record the film and print revisions, material lot, printed side, ink and process revision, cure record, conversion state, mounting method, conditioning and actual inspection zone. Photograph the same location before and after the agreed check where images are useful. Preserve the original observations and any deviations, including a shifted cut line, unexpected residue or cleaning solution that contacted an exposed print edge.
Describe the failure surface rather than simply saying the overlay peeled. Ink separating from a print receptive side raises a different question from adhesive leaving a painted enclosure, ink splitting within its own stack, a protective overprint lifting, or a hardcoat scratching on the operator side. Where the interface cannot be identified visually, request an agreed follow-up inspection instead of naming the cause from a photograph. Likewise, a stable appearance immediately after printing may not settle behavior after the specified conversion or use exposure.
Before testing, agree on whether the decision is process screening, prototype approval, supplier comparison or production inspection. These stages may need different representative specimens and different consequences for failure. Define the acceptance language, who may authorize a deviation, when a failed sample requires root-cause work, and which new sample must replace it. Do not quietly accept a second result after modifying cure, adhesive, film or handling; that is a new configuration whose change should be visible in the record.
Five common gaps deserve an explicit check: a report names PC but not its grade or print side; a visually attractive color proof is used as an adhesion result; the printed area tested is far from the converted edge that fails; a housing-bond peel is interpreted as ink loss; or a new supplier's material substitution is hidden under the original artwork revision. Each gap is an evidence problem first. Correcting the record helps the responsible engineer choose whether to resample the print, adjust conversion, revisit the mounting adhesive or reopen the part design.
Release one RFQ package with a change-triggered evidence rule
Send the same controlled package to each candidate supplier: overlay artwork and drawing; first- and second-surface labels; film grade, finish and print receptive treatment; intended color, opacity and window requirements; expected print process; converting steps; adhesive and housing boundary; operating and cleaning exposure; and the specimen and acceptance plan. Mark the fields still open for supplier proposal. This allows quotations to distinguish a documented film–print pair from a visually similar alternative that has not yet been qualified.
Ask the supplier to return a revision-linked construction proposal and an evidence ownership map. The overlay producer can identify the material and process it proposes, supply process or specimen records within the agreed commercial boundary, and flag substitutions. The OEM owns the equipment use conditions, critical legends, acceptance criteria and installed-system approval. A material manufacturer's published example can justify a test question, but cannot sign off either party's actual design or completed lot.
Define change triggers at the same time as first-article approval. Film supplier or grade, print receptive treatment, ink family, printer route, cure process, protective layer, emboss tool, die-cut position, adhesive or housing finish can alter different interfaces. A change does not automatically require repeating every test. It requires an impact review that names which previous evidence remains representative and which witness, converted-part or mounted check must be repeated. Retain the approved master and revisions so a later reorder can be compared to the state that was actually accepted.
For an HYR engineering review, send the controlled overlay drawing, existing sample or photos, named film and print requirements, expected changes, proposed acceptance method and any actual supplier records through the secure RFQ. Label missing data as a question. An inquiry can start before every parameter is fixed, but a production approval should rest on the agreed construction and evidence, not on an unqualified statement that the print is durable.