A METHOD TO MEASURE THE ADHESION OF THIN GLASS COATINGS ON POLYMER-FILMS

A simple and reliable method to measure the adhesion of thin, hard coa tings on polymer substrates is presented, based on the rupture mechani cs of brittle films on ductile substrates. The regular fragmentation p attern of the coating obtained after straining specimens under uniaxia l tension is analyzed through a classical shear-lag analysis at the co ating/substrate interface. The model links the mean crack spacing meas ured on strained specimens to the interfacial shear strength and the r eversible adhesion energy. Fragmentation tests were carried out on a P ET film coated on both sides by SiO2 layers (24 nm on the thick side, and 6 nm on the thin side). The interfacial shear strength was found t o be close to 100 MPa for both coatings and the adhesion energy of SiO 2 on PET was found to be of the order of 230 mJ/m2, both values being slightly higher for the thin coating side.