Adhesion Properties of Polysiloxane Topcoats

摘要

This paper summarizes the results from laboratory investigations of the adhesion of polysiloxane topcoats. Low adhesion together with internal stress and lack of paint film flexibility and strength are expected to be the main reasons for the cracking and flaking of protective coatings. Internal stresses and mechanical properties were discussed in two previous papers. Topcoat flaking would occur if in-plane tensile stresses exceed the shear mode adhesive strength of the topcoat. Today's qualification test regime only covers tensile mode adhesion under dry conditions. Any reduction in adhesion from moisture is not covered. Therefore, dry and wet adhesion has been measured in a new test setup, allowing load to be applied in both tensile mode and shear mode. Two commercially available polysiloxane topcoats have been tested, both as a single coat and as part of a two-coat system. The laboratory tests have shown that the internal stresses reported in the earlier paper could not cause flaking of any of the tested products. Shear load mode adhesion was found to be insignificantly different from the tensile load mode adhesion. Water immersion reduced the adhesive strength in some tests, but not to the extent where this would indicate vulnerability to topcoat flaking. [PUBLICATION ABSTRACT]