Functional hard-coat for cartridge-free DVR-blue
ABSTRACT Optical discs with larger storage capacity and higher data recording rates are required for the coming digital network society, for example, to realize non-linear editing and long term data archiving on broadcasting tasks. We have been developing a new phase change optical disc, which has much higher data recording rate of up to 140 Mbps (T. Kato et al, Tech. Dig. ISOM2001, pp. 200-201, 2001), based on the DVR system (λ=405 nm, NA=0.85, cover layer thickness=100 μm) (Y. Kuroda et al, 1999; M.J. Dekker et al, 2000; Y. Kasami et al, 2000). As a general rule, the smaller the laser spot size on the disc surface, the more sensitive the disc becomes to scratches or fingerprints on it. In such a system, the distance between the disc surface and objective lens (i.e. working distance) is very narrow due to a high NA. Therefore it is also feared that the objective lens hits the disc surface due to an external impact. To avoid these problems when the disc is taken out of a cartridge, we have developed a new hard-coat. The cartridge-free DVR-blue disc was expected to be accomplished by the following properties: (1) abrasion resistance; (2) scratch resistance; (3) water and oil repellency (low surface free energy). Among these properties, the abrasion resistance is considered to be the most important.