ISO 19402 Paints and Varnishes - Adhesion of Coatings

The standard “ISO 19402 Paints and varnishes - Adhesion of coatings” published by the International Organization for Standardization (ISO) describes commonly used methods for assessing the bond strength of coatings on a substrate, whether this be another coating beneath the substrate or the substrate itself.

Often, adhesive strength cannot be adequately assessed by a single method. Purely physical methods for measuring adhesive strength are those in which mechanical quantities (e.g. force or torsional moment) are directly measured. All other methods are based on the evaluation of behavior under mechanical stress according to practical conditions. For these methods, viscoelastic properties have a large influence on the assessment of adhesive strength, so they can only be tested comparatively within one method.

Each method has its own specific application. An inappropriate method can lead to incorrect information. All test methods for assessing adhesive strength require the tester to have a certain routine, especially in determining the separation line. For most test methods, the test results depend, among other things, on the film thickness of the coating to be tested. In addition, for the various methods, differences between tests on a test board and in practice can occur due to different roughness of the substrate.

The effects of delamination caused by weathering or corrosion effects are not the subject of this standard.

If cohesion failures occur frequently during an adhesive strength test, this is not a measure of the adhesive strength. However, it can provide information about the corrosion protection effect of the coating.

For the purposes of this standard, the following definitions apply in addition to the terms and definitions given in ISO 4618:

Adhesion is the retention at the interface between a solid surface and another material due to molecular forces. Adhesion is not the same as cohesion.
Cohesion is the forces that bind a film or coating together into a single entity.
Adhesion failure is the separation of a coating from a substrate due to external forces. The substrate may be another coating or work material underneath.
Cohesion failure is the loss of coherence within a coating due to external forces.
Adhesive strength is the force required to separate a coating from a substrate or another coating.
Wet adhesive strength is the adhesive strength immediately after exposure to moisture.
The separation line is the interface at which adhesive failure occurs.
The defect pattern is the total of visual coating defects caused by the adhesive strength test.
Fault pattern evaluation is the classification of a fault pattern by means of criteria or reference patterns.
Fault pattern analysis is the quantitative evaluation of a fault pattern by specifying the relative percentages of areas and dividing lines for adhesive and cohesive failure.
The main dividing line is the dividing line with the largest area.
Repeatability conditions are those conditions in which independent test results are obtained at short intervals by the same method on the same test items in the same laboratory by the same operator using the same equipment.
The limit of repeatability is the value or less that would be expected with 95 percent probability for the absolute difference between two test results obtained under repeatability conditions.
Repeatability conditions are those conditions under which independent test results are obtained by the same method on the same test items in different laboratories using different operators and different equipment.
The limit of repeatability is the value or less that would be expected with 95 percent probability for the absolute difference between two test results obtained under repeatability conditions.

When performing a tensile test, a uniformly increasing tensile force is applied to a test cylinder (metal cylinder with a diameter of 20 mm) bonded to the coating and continues until the test cylinder is pulled. The tensile strength is determined by calculating the tensile force required to pull the test cylinder and the area of the test cylinder.

When performing the bend-off test, a uniformly increasing torsional moment is applied to a test cylinder (a metal cylinder with a diameter of 12 mm or 15 mm) bonded to the coating by means of a motor-driven test fixture and held until it is bent off. The adhesive strength (shear strength) can be read directly from the test fixture as the shear stress.

In performing the peel test 1, a fabric specified by material, yarn size and pore size is placed on a freshly applied coating material. After the coating has cured, a tensile tester grasps the overlapping fabric and the coating is peeled from the substrate due to a continuous tensile force at 90 degrees. Peel strength is determined as the force required for peeling and is referenced to the width of the test specimen.

When performing peel test 2, the coating is peeled from the substrate under specified conditions by means of an electrically operated test apparatus. The force required for peeling is determined and refers to the peel width.

When performing a bending test with a wedge-shaped conical mandrel, the test panel is deformed from the direction of the substrate by pressing it into a wedge-shaped conical mandrel of specified geometry. The smallest mandrel radius at which delamination defect cannot be detected in the deformed area is determined.

Among the numerous tests, measurements, analyses and evaluation studies carried out for businesses in various sectors, our organization also provides testing services defined in the “ISO 19402 Paints and varnishes - Adhesion of coatings” standard with its trained and expert staff and advanced technological equipment.