| 摘要 |
PCT No. PCT/GB90/01613 Sec. 371 Date Apr. 8, 1992 Sec. 102(e) Date Apr. 8, 1992 PCT Filed Oct. 19, 1990 PCT Pub. No. WO91/06925 PCT Pub. Date May 16, 1991.An optical security device for use on a security article comprises a number of layers including an optically diffracting layer and an at least partially reflective layer which together generate a first image. A non-optically diffracting second image is provided within the device in association with the first image. |
