Use of Evaporated Acrylate Coatings to Smooth the Surface Of Polyester and Polypropylene Film Substrates

It is well known that all film substrates have a characteristic surface roughness which depends on the way that it is made and the various chemical additives that it contains. In many cases this roughness is desirable since it provides the sheet material with a low coefficient of friction which prevents blocking during handling. On the other hand these additives may be undesirable since they can lower the water and oxygen barrier properties of a barrier layer applied to this film or reduce the surface reflectivity. This paper attempts to characterize the surface roughness of some common film substrates using scanning electron microscopy and the WYKO RST interferometer surface measurement system. The roughness was visually displayed and quantitative numbers are given for the peak to valley roughness, the number of peaks, and their average height. These substrates were coated by vapor deposition of a radiation curable acrylate monomer in layers of various thicknesses. The effect of these coatings in smoothing out the surface roughness was shown. This paper demonstrates the effectiveness of both evaluation methods in characterizing the roughness of plain and coated film.