Testing

Adhesion testing

The adhesion of the paint/ink layer to the substrate can be tested in several ways. In a scratch test (Kratzprobe), the printed/painted part or test specimen is provided with scratches in a regular pattern. The paint/ink layer will not come off near the scratches if adhesion is good. Poor adhesion on the other hand will result in paint/ink particles that separates from the substrate.

The crosshatch + tape pull-off test (Gitterschnitt) is a combined scratch and peel test.

Scratches are made in the printed/painted surface in two perpendicular directions and an adhesive tape is then stuck to the surface. The tape is pulled off and the ratio between the area of the undamaged surface and the area where the paint/ink layer has peeled off with the tape is established visually.

Depending on the specific application, additional exposure tests may be requested, like:

- Humidity exposure
- Water soak
- Heat aging
- Thermal shock
- Steam jet
- Stone chipping

Chemical resistance testing

The stress crack resistance of the substrate to a particular paint/ink system can be tested by coating tensile bars while they are subjected to a strain of up to 1%. Uncoated tensile bars and tensile bars that are coated without an applied strain are used as a reference. The tensile bars are subjected to a tensile test after the coating process and the stress-strain curves of the test bars are compared with the curve of the reference bars.

Impact testing

Impact performance after painting/printing can be tested with several impact tests, like a puncture test or a falling dart test.

Scratch resistance

The scratch resistance can be established e.g. in the Taber abrasion test, where the amount of haze is established after a number of abrasive cycles. The scratch resistance can also be determined quantitatively by measuring the weight loss after a number of sanding cycles (see DIN 53754). The pen test according ISO 1518 determines the indentation caused by a sharp pencil applied with a defined force.