| 摘要 |
PROBLEM TO BE SOLVED: To enable the recognition of an invisible or hardly visible print even when a fluorescent whitening agent is used as the fluorescent material to print on a printing medium contg. a flurescent whitening agent. SOLUTION: An absorbent material in an amount of 0.15-1.0wt.% having an absorption near at a wavelength of 700-850nm is added to a water-soluble fluorescent ink contg., as the main ingredients, water, a water-soluble resin, a hydrophilic org. solvent, and a fluorescent whitening agent excitable by ultraviolet rays from a black lamp. The ink is then used to print on a printing medium. The medium thus printed is exposed to ultraviolet rays, and the reflected light having wavelengths of 700nm or higher and light emitted by the ink are detected to check the existence of the ink, enabling the reading of print contents. |
