| 摘要 |
The device comprises layers (1), (3) and (4). The sheet of paper (1) carries a permanent mark (2) and is coated top and bottom in each case with a transparent synthetic-resin material film (3, 4). The temporary mark can be applied to the film (3) by means of a writing substance which contains a water-soluble dye and a solvent which evaporates at room temperature. <IMAGE> |
