Adhesion of waterborne acrylic and hybrid paint on wood treated with primers: Fid-Bau Portal

Adhesion of waterborne acrylic and hybrid paint on wood treated with primers

Turkulin, H. / Richter, K. / Sell, J.

Impregnation of spruce wood prior to application of water-based acrylic and hybrid finishing system for exterior wood was performed using two types of primers. Resorcinol-phenolic aequous primer (HMR-primer), and solvent-borne isocyanate (IC) primer were tested for their effectiveness in improving the adhesion of base-coat in dry and in wet condition. Both primers proved effective in improving the dry adhesion, although results did not show the best pull-off strength values. The reason rnainly lays in the properties of the substrate which greatly influence the initiation and spreading of the cracks. The direct application of the top-coat (without base-coat) on wood, and especially on primed wood, proved advantageous in terms of dry adhesion. Base-coat seems to be the weakest link in terms of wet adhesion. The water ingress into the micro-voids of the base-coat contributes to its swelling and abatement of its coherence. The application of the HMR and IC primers has improved the wet adhesion of subsequent coats because of the better spreading of the base-coat on the primed wood and better adhesion to a thin deposit of the primer. Wet adhesion of the top-coat, when applied directly on wood, was significantly better than was the case with base-coat application. FE-SEM analysis showed no indication whatsoever that any of the tested primers penetrated the cell wall, causing its physical modification. Combination of the adhesion testing and microscopic observation of the tested finishing systems proved very useful, particularly as far as SEM is concerned. Microscopic analysis of the surface topography of fractured areas could support a better interpretation of the mechanical results of the pull-off adhesion testing.