Recovering recyclable materials: Experimental analysis of CD-R laser processing

This paper examines the influence of operating parameters in diode laser processing of CD-Rs for the purpose of recovering two of the main constituents: the polycarbonate substrate and the silver reflective layer. The targets used in experimental tests were 'silver' CD-Rs. Four operating parameters were investigated during experimental tests on selected CD-Rs, namely transverse and rotating speed, output power, and focal length. CD-Rs were successfully treated by using sufficiently wide operating ranges, and in optimized process conditions. It took less than 4.7 s to treat a CD-R, that is, 0.3 s less than the fastest CD-R manufacturing time. The best process performance is expressed in terms of transparency index, and is achieved by using both higher scanning speed and best focus conditions in conjunction. Output power is not so influential, but in order to attain the most effectiveness CD-R laser processing, values that are too low must be avoided. The extent of treated, untreated, and burnt areas of CD-Rs after diode laser processing was defined and measured, from which the most appropriate processing windows were found, including the quality of the recycled materials. Experimental findings were then used to define and validate an analytical model of CD-R laser processing. Two different mechanisms operating at low and high process speeds were inferred, and lastly, several aspects concerning the industrial application of the technique are discussed at length. (C) 2006 Elsevier Ltd. All rights reserved.