Testing standard
Leather — Test for adhesion of finish
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ISO 11644 measures the adhesion of the finish to leather, or the adhesion between two adjacent layers of the finish. A strip of the finished side is bonded to a hard plate and peeled at about 90 degrees, and the force is the adhesion value.
A strip of finished leather is conditioned and its finished side bonded to a hard adherent plate with an adhesive chosen not to penetrate the finish. Once that mounting adhesive has cured, the separation is started at one end and the leather and the plate are peeled apart at about 90 degrees while the jaws separate at 100 ± 5 mm/min. The mean force over the steady portion is divided by the specimen width to give the adhesion, and where the separation actually ran — between finish and leather, between two finish layers, or into the leather itself — is identified and reported with it.
Whether the finish stays on, which is a property entirely independent of how strong the leather is and is the one a customer notices first. A hide can pass ISO 3376 for tensile strength and ISO 3377-2 for tear and still have a finish that lifts at a crease, rubs off at a seam or peels from a car seat bolster in service. Nothing in a strength test warns of it. The method also covers adhesion between two adjacent layers within a finish system, which is where multi-coat finishes usually let go.
The scope exclusions are specific and worth reading before cutting specimens.
This is the failure mode a leather tensile or tear test cannot see. A hide can be strong and its finish can still lift, and a lifting finish is what a customer notices first.
Mean separation force divided by the specimen width
Force per unit width. State the width convention, as with every peel result.
Adhesive in the finish stiffens and reinforces the layer under test
The mounting adhesive has to stay on top of the finish. Once it is inside it, the specimen is a different material.
Pneumatic vice action grips hold each arm of the T at a constant pressure through a long peel, which a screw grip does not — a peel test runs for hundreds of millimetres and a slipping grip corrupts the whole trace.
SpecificationsVery low forces and long, steady travel. Finish adhesion is commonly a few newtons per unit width, so the load cell is chosen for that rather than for the frame. Grips must hold a thin leather strip and a rigid plate without damaging either, and the plate needs supporting so the angle stays near 90 degrees as the peel front advances rather than drifting as the strip is drawn off.
The rate is a fixed jaw separation of 100 ± 5 mm/min, and it is an apparatus requirement rather than a procedural option: the machine has to be able to run that speed uniformly, not merely to reach it. On the 100 mm by 10 mm strip the method cuts, a peel of any useful length therefore takes a minute or two, so the drive has to hold the speed over that whole travel and the recorder has to produce a force-distance diagram from it — a mean over the steady portion cannot be taken from a peak reading alone.
The mounting bond failing before the finish does, which measures the wrong adhesive entirely — the direct analogue of the intermediate-strip problem in ISO 2411, and checked the same way, by confirming on every specimen that the plate bond held. Adhesive penetrating into the finish. Running the method on an excluded leather because it was the material to hand. Reporting a force without saying where the separation ran, when one of the three possible loci is not a finish adhesion result at all. And omitting the width convention, which leaves a figure that could plausibly be read at either of the two scales in common use across peel standards.
| ISO 11644 — leather | ISO 2411 — coated fabric | |
|---|---|---|
| Substrate | Finished leather | Woven base fabric |
| Question | Does the finish stay on? | Does the coating stay on? |
| Method | Bond to a plate, peel | Separate the coating and peel |
| Shared risk | The mounting bond failing first | The intermediate strip failing first |
Two industries with the same problem — a surface layer that has to stay attached — and the same trap, that the auxiliary bond used to grip the layer can fail before the layer does.
It is the ISO test for the adhesion of a finish to leather, or between two adjacent layers of a finish. A strip of the finished side is bonded to a hard plate and peeled at about 90 degrees, and the force required is the adhesion value. The current edition is ISO 11644:2022, the third, published in October 2022.
Unpigmented articles and those without a continuous coating layer — the standard names nubuck, aniline, pull-up, suede and perforated leathers. The reason is practical: the method needs a smooth surface that can be bonded to a plate without the adhesive soaking in, and none of those provides one. Running it on them produces a number that describes the mounting adhesive rather than the finish.
Because if the mounting adhesive soaks into the finish, it stiffens and reinforces the very layer being tested. The specimen is then a different material from the product, and the measured adhesion is higher than the finish would ever achieve on its own. The adhesive has to sit on top of the finish, which is why the method restricts itself to smooth, continuously coated surfaces.
The result is void — it measured the mounting adhesive rather than the finish. This is the direct analogue of the intermediate-strip problem in ISO 2411 for coated fabrics: whenever an auxiliary bond is used to get hold of a layer, that bond has to outlast the one under test, and checking it did is part of validating each specimen.
Because there are three possible ones and only two of them are finish adhesion. The separation can run between the finish and the leather, between two layers within the finish, or into the leather itself. The third means the finish was better attached than the corium beneath it — a legitimate finding, but not an adhesion value, and it should be reported as what it is.
Because they are unrelated properties and the customer sees the finish. A hide can pass ISO 3376 for tensile strength and ISO 3377-2 for tear and still have a finish that lifts at a crease, rubs off at a seam or peels from a car seat bolster. Nothing in a strength test gives any warning of it, which is why finish adhesion is specified separately.
Force per unit width, and as with every peel result the width convention has to be stated. Newtons per millimetre and force per some larger stated width are both in circulation across peel standards, and a figure quoted without saying which is a number that could be either.
Dak verifies against whichever standard the method names, and where a class applies our frames sit a class tighter than it asks.
| The method asks for | Dak supplies | |
|---|---|---|
| Capacity | Very low — finish adhesion is commonly a few newtons per unit width | Load cells from 1 kg to 60 ton on the Series 7200, and 0.5 to 100 kN on the Series 9000 |
| Force accuracy | Class 1 at the actual working load | ISO 7500-1 Class 0.5, verified to ASTM E4, DIN 51221 and BS 1610 |
| Gripping | A hard adherent plate bonded to the finished surface, peeled at about 90 degrees | Our peel and adhesion fixtures, built to the specimen |
| Environment | 23 ± 2 °C standard laboratory atmosphere | 3009 series chambers, −150 °C to +400 °C — temperature only |
This page describes the method as practised. The governing text is the current edition from the issuing body. Tell us what you are testing and we will answer with the machine, the fixture and a quotation.
