In stamping, boilermaking and metal fabrication, identification is usually applied to the part before finishing. The part is formed, welded and labelled, and only then goes through shot blasting, pre-treatment baths, painting and the curing oven. The label travels with the part and is exposed to the same conditions. If it fails, the part comes off the line painted and unidentified, which is exactly what the label was meant to prevent.
The label goes through the entire finishing line
No two lines are the same. Some shot blast and powder coat; others degrease, phosphate and go through cataphoresis; others apply liquid paint and cure in air. But they all share one idea: what decides which label works is not the maximum temperature it withstands, but the sequence of stages that come after the point where it is applied.
The right question isn't “what temperature does the label withstand?”, but “what is going to happen to it between the point where it is applied and the end of the line?”.
Stage by stage: what happens to the label
These are values from real lines that customers in automotive, boilermaking and metal fabrication have shared with us. They give an idea of the order of magnitude; each installation has its own.
| Stage | Values seen on real lines | What attacks the label |
|---|---|---|
| Shot blasting | Steel shot by wheel or pressurised air, up to Sa 3 finish | Impact that erodes the material and the print |
| Degreasing | Alkaline immersion up to 80 °C and pH 12, around 30 min | Edges, adhesive and any print that isn't resin |
| Pickling and phosphating | Phosphoric acid at 45–60 °C, pH 2 to 4, a few minutes | The same, with acidic chemistry |
| Cataphoresis | Immersion in the paint bath at around 35 °C, with voltage applied | Full immersion of the label |
| Powder coating | Electrostatic application; curing at 170 to 200 °C, from 15 min to several hours | Paint on the label and sustained heat |
| Liquid paint | Booth up to around 50 °C, or air curing | Paint and solvents on the label |
| Cataphoresis oven | From around 200 °C to 250 °C; in one case, 250 °C for 50 min | Shrinks the film and attacks the print and adhesive |
The oven is the stage that causes the most confusion: a material may withstand the temperature for a few minutes but not for an hour. Both figures are needed: temperature and time.
The three common failures, and why more adhesive doesn't fix them
Failure 1 — The film shrinks in the oven
It's the most deceptive failure, because the label appears to have withstood the process. In a trial on an automotive cataphoresis line, a first polyester sample withstood the temperature, came out still adhered with the print intact, but a couple of millimetres smaller. A standard polyester releases internal stresses under heat and contracts: the edge lifts, adhesive is left exposed and paint gets underneath.
✓ Solution
A heat-stabilised polyester, heat-treated to minimise shrinkage at elevated temperatures. The second sample from that same trial, made of this material, went through the line with no noticeable change in size.
Failure 2 — The print lifts or the code stops reading
Pre-treatment baths and the oven attack the ink. Wax ribbon lifts off, and wax-resin isn't designed for this combination of chemistry and heat. Even resin ribbons differ: on a cataphoresis line with an oven at 250 °C, of several ribbons tested, only one withstood the full cycle of baths, paint and oven.
✓ Solution
Thermal transfer printing with resin ribbon and, when the process allows it, a transparent protective laminate that is removed after painting. Validation is done by reading the codes on exit from the line, not by visual inspection.
Failure 3 — The label comes loose from the part
The surface of a freshly stamped or welded part is rarely clean: it carries stamping oil, welding residue or a layer of oxide. Asking for “more adhesive” doesn't solve it. If the film shrinks or the surface is dirty, a stronger adhesive only delays the problem.
✓ Solution
High-adhesion permanent acrylic adhesive on a clean, dry surface, applied with firm pressure and above the material's minimum application temperature.
Shot blasting: why an adhesive label isn't the answer
Shot leaves the wheel at between 50 and 100 m/s. On a label, shot doesn't clean: it erodes. An adhesive label exposed directly to the blast isn't designed to come out intact, and in an automatic wheel blast machine with a conveyor there usually isn't a sheltered area on the part. So when the part is shot blasted, there are three options:
⚠ The first question
Can the identification be removed before shot blasting and put back on after painting? If the answer is no, the solution is to hang it or protect it, and in both cases it has to be trialled in your own blasting cabinet before deciding.
- Label after shot blasting. This is the most reliable option: the label is applied to the part once it has already been shot blasted, and only has to withstand pre-treatment, paint and the oven.
- Hang the identification, without adhesive. A hang tag fixed with wire or a cable tie, in a material that also withstands the oven afterwards, such as laminated KPK or HOT 151 polyimide. The tag also receives shot, so its position and resistance are validated in your own blasting cabinet.
- Protect the label during shot blasting. A protective tape covers the printed area and is removed afterwards. This is the option described below.
The impact-protection tape
To protect an adhesive label during shot blasting, we work with a 0.91 mm impact-protection tape. It is a sacrificial layer: its thickness absorbs the impact of the shot far better than a conventional tape, and it is removed once the part has already gone through the blast.
- One or two layers. For aggressive blasting, such as an Sa 3 finish, it's prudent to trial two. If the label is wider than the tape, two strips are applied in parallel and, on the second layer, the position is staggered to reinforce the edges.
- An extra protective film first, if needed. If the print itself also needs protecting, a transparent polyester film is applied to the label before the tape, and it stays on permanently.
- Not for the oven. The tape isn't designed for oven curing: it is removed beforehand. With paints that cure in air, in a low-temperature booth, it can stay on until the end — check this in the trial.
It doesn't work miracles: depending on the pressure, the type of abrasive, the distance and the exposure time, the shot can erode the tape or lift it at the edges. That's why validation is done with a comparative trial: unprotected labels, with one layer and with two, checking in each case code readability, the condition of the label, any adhesive residue left when removing the tape, and the effect on the paint that follows. We send you a sample of the tape so you can run the trial.
Powder coating and cataphoresis: the material that decides
If the label is applied after shot blasting, the challenge is pre-treatment, painting and, above all, the oven. When the oven is within its range, the combination that works for both powder coating and cataphoresis is a heat-stabilised polyester with permanent acrylic adhesive and resin print. This is the construction of our Ref. 81020: a 50 µm white film, heat-stabilised to minimise shrinkage, service from −40 to +150 °C, +180 °C for one hour and +220 °C under brief exposure.
The two types of paint don't treat the label the same way. In cataphoresis, paint is deposited onto the metal by electric current: the label, which doesn't conduct, comes out of the bath unpainted, even though it has been submerged and then goes through the oven. In powder coating, paint is sprayed onto the part and can also land on the label: if the code has to be readable at the end of the line, the label needs a protection that can be removed.
That's why the label we propose is normally set up with a transparent protective laminate that is removed after painting. The part goes through painting and the oven with the laminate in place; it is then removed, the paint goes with it, and the label comes out clean, with the code legible. When a line prints and applies the label in a single step, we adapt it to work the way that line operates, without that extra step, and validate it in the real process.
Between +180 and +220 °C, oven time decides, and it is validated with a sample. When the oven exceeds +220 °C, or holds above +180 °C for more than an hour, polyester falls short. That's where adhesive polyimide comes in, such as the Ref. RD-514C, which withstands 300 °C for 15 minutes, 250 °C for 90 minutes and 200 °C for 240 hours. You can see the full range in high-temperature labels.
How to specify: six questions before choosing
With these answers, the choice becomes technical and the trial quick. Without them, any recommendation is a guess.
- At what point on the line is the label applied? Above all, whether it's before or after shot blasting, and whether the workflow allows removing it and putting it back on.
- What stages come afterwards? Degreasing, pickling, phosphating, cataphoresis, powder or liquid paint, with their chemistries and temperatures.
- What temperature is the oven, and for how long? Both figures. This is the difference between a heat-stabilised polyester and a polyimide.
- What surface is it applied to? Steel with stamping oil, a freshly welded part, shot-blasted steel, galvanised steel, aluminium or existing paint.
- Can the label be painted over, or does it have to come out clean? If it has to come out clean, it carries a protective laminate that is removed after painting.
- How is it printed and how is it read? Thermal transfer printer or print-and-apply equipment, barcode or DataMatrix, and at what point it is read coming off the line.
“With the line sequence and the oven time on the table, choosing the label is a technical matter. Without that data, it's a gamble.”
Which label for each situation
| Situation | Solution | Reference |
|---|---|---|
| Powder coating or cataphoresis, oven up to +150 °C continuous, +180 °C 1 h or +220 °C brief | Adhesive heat-stabilised polyester, with removable laminate or without laminate | Ref. 81020 |
| Oven above +220 °C, or more than +180 °C for hours | High-temperature adhesive polyimide | Ref. RD-514C |
| Identification before shot blasting, unable to remove it | Hang tag without adhesive, mechanically fixed | KPK or HOT 151, to be validated |
| Identification before shot blasting, protected | Adhesive label with 0.91 mm impact-protection tape, in one or two layers, removed afterwards | Ask us; to be validated in your line |
The temperatures in the table are those from the technical data sheets. Final validation is always done with a sample on the real line.
Is your part labelled before painting? Tell us the line sequence and the oven's temperature and time.
Ask with no obligationSummary
When a part is labelled before finishing, the label is exposed to everything that comes afterwards: shot, pre-treatment baths, paint and the oven. There are three common failures: the film shrinks, the print lifts, or the label comes loose. None of them is fixed with more adhesive.
For powder coating and cataphoresis, a heat-stabilised polyester printed with resin ribbon is the starting point while the oven stays within its range; above +220 °C, or with long cures, a polyimide. Shot blasting is a different story: the reliable approach is labelling afterwards; if that's not possible, hang the identification or protect it with an impact-protection tape, and trial it in the blasting cabinet.
In every case, the test that counts is a run through the real line, reading the codes on exit.
Frequently asked questions
Which label withstands powder coating and the curing oven?
A heat-stabilised polyester with permanent acrylic adhesive and thermal transfer printing with resin ribbon. Our Ref. 81020 works from −40 to +150 °C, withstands +180 °C for one hour and +220 °C under brief exposure, and the film is heat-stabilised to minimise shrinkage. Between +180 and +220 °C, oven time decides; above that, the alternative is an adhesive polyimide.
Why does a polyester label shrink in the oven?
Because a standard polyester film releases internal stresses under heat and contracts. It can withstand the temperature and still come out a couple of millimetres smaller: the edge lifts, the adhesive is left exposed and paint gets underneath. A heat-stabilised film has been heat-treated to minimise that shrinkage.
Can an adhesive label withstand shot blasting?
Exposed directly to the blast, it is not expected to: the shot impacts at high speed and erodes the material and the print. The reliable approach is to label after shot blasting. If the part has to carry identification beforehand, it is protected with a 0.91 mm impact-protection tape, in one or two layers, or a hang tag without adhesive is used instead. In both cases, it is validated with a trial in your own blasting cabinet.
Which ribbon is used for parts that go through cataphoresis or painting?
A resin ribbon. Wax and wax-resin are not intended for chemical baths or for the oven. Even so, the combination of ribbon, bath and oven is what decides: the test that counts is reading the codes coming out of the real line.
Does the label need to be laminated?
If the label has to come out clean of paint, yes. The one we propose for paint and oven applications is normally set up with a transparent protective laminate that is removed after painting: the paint stays on the laminate and the label comes out clean. When the line prints and applies the label in a single step, it is adapted without the laminate and validated in that process.
How is the label validated before production?
With a sample in your line: real parts are labelled at the point on the line where the label will go, they go through all the stages, and adhesion, dimensions and code readability on exit are checked. We send you the sample at no cost.