Blu-Ray Disc cover layer production using spin coating technology

Abstract

ABSTRACT A spin coating technique for the 100 micron cover layer for Blu-Ray Disc production has been developed. The process includes a controlled manipulation of the viscosity of the lacquer with heat and UV light during spin coating. Stability and cost efficiency, two vital criteria for mass production, have been considered. Keywords: Optical Storage, Spin Coating, Blu-Ray Disc 1. INTRODUCTION With the Blu-Ray Disc, the 3rd generation of optical storage media is today appearing on the consumer market. While moulding and sputtering processes for substrate preparation and functional layer application are very similar to the currently used processes for CD and DVD production, the reliable and cost efficient application of a highly precise, 100 P m thick optical layer on top of the information layer is the challenging production step for this format. Since the very beginning of the Blu-Ray Disc, there have been two techniques discussed between media developers, equipment manufacturers, consumables suppliers and media producers for the 100 P m cover layer production: Spin coating of a UV curable resin is seen as one candidate, bonding a cover layer sheet stands as the alternative. Looking at the foil bonding technology one has to distinguish between PSA-sheet bonding and UV-resin bonding of a thin polycarbonate sheet. The PSA sheet bonding is a proven method which gives excellent cover layer thickness homogeneity. The PSA adhesive is supplied together with the foil and the manufacturing process of the disc is relatively simple. But due to the high cost per sheet it can only be seen as a start-up technology for the Blu-Ray Disc media family. It is not seen as an attractive solution for economic mass production because the cost per sheet cannot be reduced significantly. The foil bonding technology using UV-resin combines a spinning process and a bonding process similar to standard DVD bonding technology. A UV-curable resin is applied onto the BD substrate, spread over the disc in a spin coating process and combined with the foil, preferably in a vacuum bonding process, and finally the system is cured under UV irradiation. Like PSA-sheet bonding, foil bonding technology us ing UV-resin is a practical way to go. In both cases it is the quality of the foil which significantly de termines the quality of the cover layer. Using a spin coating process