Standard Practice for Estimating Critical Surface Tensions

Importancia y uso:

5.1 Knowledge of the critical surface tension of substrates, primers and other coatings is useful for explaining or predicting wettability by paints and other coatings applied to those surfaces. Surfaces with low critical surface tensions usually are prone to suffer defects such as crawling, picture framing, cratering and loss of adhesion when painted. Low or irregular values, or both, often are indicative of contamination that could reduce adhesion. Surfaces with high critical surface tensions are easy to wet and usually provide an excellent platform for painting.

5.2 The swab, marking pen and draw-down tests all simulate the application of a film

5.3 The swab and marking pen techniques are simple and rapid and are particularly useful for testing in the field or on curved, irregular or porous surfaces where contact angles cannot be measured. The drop test does not work well on such surfaces and the draw-down method requires a flat specimen that is relatively large.

5.4 The estimation of critical surface tension has been useful in characterizing surfaces before and after cleaning processes such as power washes and solvent wipes in order to evaluate the efficiency of the cleaning.

5.5 One or more of these techniques could be the basis of a go/no-go quality control test where if a certain liquid wets, the surface is acceptable for painting, but if that liquid retracts and crawls, the surface is not acceptable.

5.6 Another go/no go test is possible where the test liquid is a paint and the surface is a substrate, primer or basecoat. A form of this test has been used for coatings for plastics.

Subcomité:

D01.23

Volúmen:

06.01

Número ICS:

25.220.01 (Surface treatment and coating in general)

Palabras clave:

critical surface tension; dewetting; surface contamination; wettability; wetting;