| 摘要 |
PCT No. PCT/CA91/00101 Sec. 371 Date Oct. 1, 1992 Sec. 102(e) Date Oct. 1, 1992 PCT Filed Mar. 28, 1991 PCT Pub. No. WO91/15805 PCT Pub. Date Oct. 17, 1991.A method and apparatus for preventing reproduction of printed matter on a substrate by photocopying, telefaxing and the like. A substrate is provided with at least one main surface and a photochromic dye is applied to the one main surface, wherein the dye changes color in response to exposure to light with a response time which is a function of the amount of light absorbed by the dye in a given time period. The one main surface is illuminated with a given amount of light and the response time is decreased to accelerate the change in color of the dye by increasing the proportion of light which is absorbed by the dye from the given amount of light.
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