| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an optical disk which eliminates a user's economical burden and the problem of environmental deterioration while taking advantage of an terminable disk. <P>SOLUTION: A protective coat 24 is formed all over the optical disk 10 except a key data area 13. The protective coat 24 has a high light transmittance, and even if kept in an atmosphere including oxygen or moisture for a long term, it is not denaturalized. A denaturalized protective coat 25 is formed only above the key data area 13. Although the denaturalized protective coat 25 has a high light transmittance during a predetermined term after a vacuum packaging of disk is opened, the light transmittance reduces due to denaturation resulting from oxidization etc. after the predetermined term passes. After the predetermined time has passed, the light transmittance of the denaturalized protective coat 24 decreases and reading of enciphered title key data Kt recorded on the key data area 13 becomes impossible. <P>COPYRIGHT: (C)2007,JPO&INPIT |
