BRDF characterization of Al-coated thermoplastic polymer surfaces
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BRDF characterization of Al-coated thermoplastic polymer surfaces Tommaso Fontanot, Jan Audenaert, Peter Hanselaer, Ilaria Pecorari, Vanni Lughi, Erik Vesselli , Sara Paroni, Fre´de´ric B. Leloup
Ó American Coatings Association 2020 Abstract In this paper, we present a combined morphological and optical characterization of aluminum-coated thermoplastic polymer surfaces. Flat plastic substrates, obtained by means of an injection molding process starting from plastic granules, were coated with ultra-thin aluminum films evaporated in vacuo, on top of which a silicon-based protective layer was plasma deposited in order to prevent oxidation of the metal reflective surface. Different sample treatments were studied to unravel the influence of substrate chemistry, substrate thickness, aluminum and protective layer thickness, and surface roughness on the actual optical reflectance properties. Bidirectional reflectance distribution function measurements, corroborated by surface morphological information obtained by means of atomic force microscopy, correlate reflectance characteristics with the root-meanT. Fontanot, E. Vesselli (&) Department of Physics, University of Trieste, Via A. Valerio 2, 34127 Trieste, Italy e-mail: [email protected] T. Fontanot, S. Paroni Marelli Automotive Lighting Italy S.p.A., Via dell’Industria 17, 33028 Tolmezzo, Udine, Italy J. Audenaert, P. Hanselaer, F. B. Leloup (&) Light and Lighting Laboratory, Department of Electrical Engineering (ESAT), KU Leuven, Gebroeders De Smetstraat 1, 9000 Ghent, Belgium e-mail: [email protected] I. Pecorari, V. Lughi Department of Engineering and Architecture, University of Trieste, Via A. Valerio 6a, 34127 Trieste, Italy E. Vesselli Istituto Officina dei Materiali CNR-IOM TASC Laboratory, Area Science Park, S.S. 14 km 163.5, 34149 Trieste, Italy
square surface roughness, providing evidence for the role of the substrate and the thin films’ morphology. The results unravel information of interest within many applicative fields involving metal coating processes of plastic substrates as an example in the case of automotive lighting. Keywords BRDF, Aluminum coating, Thin film, AFM, Surface roughness
Introduction The deposition of metallic layers on different substrates has gained increasing attention in a large variety of industrial fields, such as electronics,1 biotechnology,2 and chemistry,3 to mention a few examples. Metallization processes are extensively used because they enable tailoring of crucial properties such as electric conductivity,4 adhesion,5 corrosion resistance,6 and thermal and optical characteristics.7,8 The automotive industry exploits metallization processes within the framework of several applicative fields, covering a large number of components and functions.9,10 In this paper, we examine the optical properties of metallized plastic reflector components of automotive rear lamps, which are used in combination with a light source to obtain the desired light intensity and intensity distribution. The purpose of the metallization proces
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