How to Inspect Printed Logos: Adhesion, Alignment and Colour Tests

Printed marks generate an unusual share of findings for two reasons. They are the most visible thing on the product, so any departure reads immediately. And they are applied by a process that continues changing after the units leave the printing area — which means the moment you check them matters as much as how you check them.

The consequence is that plenty of print findings are wrong rather than merely unwelcome. A mark judged too pale on the same afternoon it was applied, judged against an unapproved artwork file, or judged on a unit with release film still in place — each produces a finding that later turns out to have been about the check rather than the bag.

What Are the Print Methods, and How Do They Fail Differently?

Four methods account for nearly everything on a bag programme, and each has its own characteristic failure. Knowing which one is specified tells you what to look at first, in the same way knowing a chain type tells you where a zipper will fail.

How Is Adhesion Actually Tested?

By applying a stated tape to the cured mark, pressing it down with a stated pressure, leaving it for a stated interval and removing it at a stated angle and speed — then recording how much came away. Every one of those variables changes the answer, which is why "tape test" alone is not a method.

Published methods exist for this work and using one is better than inventing a version, because everybody understands what was done. Where the product or the substrate falls outside the published method's scope, write your own and agree it in advance rather than adapting somebody else's silently.

Timing deserves its own line. Adhesion develops over time as the ink or film bonds, and a mark tested too early can fail and then pass a day later. Test after the stated cure period, and record how long after printing the test was made.

What Does Alignment Mean on a Curved Panel?

Placement has to be measured from a stated datum on the panel, not judged against the edges of whatever tool happens to be nearby. On a flat panel that is straightforward. On a curved or gusseted surface — where most bag logos actually sit — the mark follows a surface whose apparent position changes with how the panel lies.

Two practical answers. Reference the mark to a seam, a folded edge or a constructed feature rather than to the silhouette of the panel, because features do not move when the bag is relaxed. And state the condition the panel is in when it is measured — empty, relaxed and flat where possible, or the reading will vary with whoever did the relaxing.

Where the mark spans a seam, a pocket or another feature, say how the tolerance is applied across it. A continuous mark interrupted by a seam is genuinely harder to read than a flat one, and agreed guidance is better than the inspector deciding which side of the seam governs.

How Is Print Colour Checked?

Against a colour reference from the same system the artwork specified, under the same light source used for the rest of the programme, after full cure. Everything else follows from those three conditions, and skipping any of them produces readings that cannot be defended.

Two traps catch people repeatedly. The first is comparing against a screen or a printout rather than a reference produced in the ink or film actually used. The second is ignoring the substrate: identical ink reads differently on different materials, and a mark that matches the reference on one panel may not on another.

How Does Registration Work With Multi-Colour Marks?

Registration is how well successive colours sit against each other. Poor registration shows as a fringe of one colour beside the edge of another, or as a gap between abutting colours, and the tolerable amount is a measurement rather than an impression — stated in fractions of a millimetre on the artwork sheet.

Where a mark includes fine detail or small text, agree a legibility criterion instead of a measurement. "Legible at arm's length" is not enforceable; "all characters distinct and complete when read at stated distance" gets much closer, and a reference image of both the pass and the fail condition removes what is left.

What Happens Once the Print Has Cured?

Several things continue. Films develop their final bond. Some inks continue to darken or lighten for a period. Plastisol-type deposits complete their fusion. And any release film or backing still applied must come off before anything can be judged — which sounds obvious and is routinely missed on a busy floor.

State the cure condition as a time and, where relevant, a temperature. Then state that units will not be assessed before that condition has been met. A programme that inspects immediately after printing will generate failures against itself.

Ask what happens to units printed during line stoppages or at shift change. These are the ones most likely to have been applied under different conditions from the rest of the run, and they are rarely identifiable later unless somebody recorded which they were.

What Should the Report Say About a Print Finding?

Unit number, which mark, the check that failed, the method referenced, the reading, and what was seen. "Print poor" is not a finding; "unit 17, front pocket transfer, adhesion test per agreed method, approximately 15% of the lower edge lifted at first pull" is, and it tells the production floor exactly where to look.

Ask for photographs showing the mark and the reference together in one frame, and ask for the source unit to be identifiable in the picture. A close-up with no scale reference and no unit identity cannot be traced back to anything, and it will not survive contact with a disputing party.

Where several units show the same fault, count them and say whether the fault was positionally consistent. Ten units with the same fault in the same place is one process problem; ten units with the same fault scattered randomly is a different thing entirely, and the correction differs accordingly.

How Should Print Interact With Required Markings?

Required markings — legal origin, material composition, care symbols, any warnings — are not decoration and should not be inspected as though they were. Legibility after the product's expected life matters rather than legibility on the day, so a rub or abrasion check carries more weight than placement for these.

Give them their own entries in the defect list, their own tolerance, and usually a higher class than an equivalent decorative mark would carry. Where a required marking becomes illegible, the product may be unlawful rather than merely imperfect, and no sampling plan is built to reason about that.

Store evidence for these at least as long as the goods are in market. A usable record of what was applied and what it tested like is what distinguishes a short conversation with an authority from a long one.

How Should a Print Finding Be Classed?

Ask the usual question — what does the customer do when they notice it. A mark that is illegible, incomplete, badly misplaced, or coming off, is a major, because the product cannot be sold or would be returned. A slight registration fringe inside tolerance or a minor shade shift visible only on close inspection tends to be minor.

Placement deserves a specific note because behaviour differs by product. On some programmes placement outside tolerance is cosmetic; on others — where the mark relates to a safety instruction, a required marking or a brand standard enforced by the retailer — it goes higher. Decide per programme and write it down.

What Belongs in the Print Clause?

Most of these take one line. Together they convert print from the most argued attribute on the product into one of the most straightforward — because every question that would otherwise be settled by opinion has already been settled by a number.

What Should Happen With Print on Trims and Webbing?

Print on binding, webbing and tape fails for reasons a flat panel does not. Webbing is often finished to resist water, which is a very good reason for ink not to adhere; and narrow surfaces receive uneven pressure when heat is applied. Both produce marks that look acceptable and lift later.

Treat these as separate entries rather than assuming the panel results transfer. Test adhesion on the trim material specifically, at the same place along its length where the application is weakest — usually where it crosses a seam or changes direction — and say in the clause that trim print is assessed in its own right.

Curved and heavily contoured surfaces deserve the same caution. Applying even pressure across a compound curve is difficult, and the deficiency tends to appear later at exactly the point where the surface fell away from the platen rather than across the mark as a whole.

How Does the Substrate Drive the Print Specification?

Almost entirely, and it is the variable most often left out. Coated fabrics, laminates and highly finished synthetics resist adhesion; untreated textiles absorb ink and change its apparent colour; dark substrates require an underprint that adds a layer with its own behaviour. The same ink specified on two materials is two specifications.

Approve print on the production substrate, not on a convenient equivalent. This costs almost nothing at sampling stage and it is the usual explanation for the awkward category of finding where the mark passes every test at the mill and fails in the field.

Where print crosses multiple substrates on one unit — a mark running from a coated panel onto a webbing trim is common — approve it across the transition specifically. The transition line is where adhesion fails first and the place everybody forgets to look.

What Should the Inspector Do With No Reference Unit?

Stop and ask, rather than making do. A print check without an approved reference either collapses into an opinion about whether the mark looks acceptable, or gets skipped entirely — and both outcomes are worse than a one-day delay.

Prevent it mechanically: include reference units in the list of what the production floor must have before booking can be confirmed. Two, ideally — one held on the floor and one retained by the buyer, cross-checked the way colour reference sets are.

How Do You Keep Print Consistent Across a Repeat?

Keep the same three artefacts the first order produced: an approved physical reference unit, the artwork file with its version, and the printed reference swatch showing acceptable limits. Together they answer nearly every question a repeat raises, and their absence is why so many second orders look slightly different from the first.

Where a mark must match across programmes running years apart, add an instrument reading of the approved reference to the file. Colour reference materials age and marked-up numbers do not, and the instrument reading tells you later whether the drift belongs to the reference or to the production.

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