Thermal modeling of vacuum web coating

The paper presents an analytical model for the prediction of the substrate temperature in vacuum web coaters. The model is based on the theory of heat transfer between a continuously moving workpiece and a stationary source, or sink, of energy. The investigation concerns the Physical Vapor Deposition (PVD) of a metal layer on a polymer film by means of thermal evaporation, but many aspects apply equally well to sputtering and electron beam evaporation. The contributions to the specific heat load on the web are quantified, and the influence of the heat exchange between the film and the cooling drum is discussed in detail. After satisfactorily comparing the predictions with available literature results, the model is used as a guideline for a series of experimental tests aimed at determining the influence of the operating conditions on the final quality of the products obtained from vacuum deposition of thick metal layers on thin polymer substrates. The experimental results demonstrate the influence of the mechanical traction of the web on the thermal conductance between the film and the cooling drum.