| 摘要 |
<p>An information device comprising a substrate having applied thereto: (1) an agent which absorbs electromagnetic radiation in the infra-red to ultra-violet region of the spectrum, said agent being capable of easy removal from the substrate by physical means, and (2) a second agent which is capable of increasing the fixation of the first agent to the substrate, said second agent being applied to the substrate in a localised manner to form an invisible image which becomes detectable when the substrate is subjected to a treatment capable of selectively removing the first agent from those parts of the substrate to which the second agent has not been applied. t</p> |
