The Effect of Temperature of Test on the Adhesion of Polyethylene Coatings Applied to Metals as a Hot Melt

The adhesion of polyethylene coatings applied as a hot melt to steel, zinc and copper with various surface pretreatments has been studied over a temperature range from ambient to 70 or 80°C. Tensile properties and tear strength of the polymer itself were measured over the same temperature range. Substrates which give high adhesion at room temperature give a fall in adhesion with temperature. This can be understood in terms of a fall in fracture energy of the polymer as indicated by tensile and tear tests. Substrates which give low adhesion at room temperature show first a significant rise and then a fall in adhesion as temperature is raised. Examination of the fracture surfaces by electron microscopy shows a progressive increase in plastic deformation of the polymer as the adhesion rises. The rise in adhesion and change in failure mode are interpreted in the light of the change in mechanical properties of the polymer. The adhesion maxima are not viscoelastic in origin as time-rate equivalence was not observed.